welding inspection handbook - 1 file download

WeldingInspectionHandbook

Copyright American Welding Society Provided by IHS under license with AWSNo reproduction or networking permitted without license from IHS

--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

550 N.W. LeJeune Road, Miami, Florida 33126

WeldingInspectionHandbook

Third Edition2000

Prepared byAWS Committee on Methods of Inspection

Under the Direction ofAWS Technical Activities Committee

Approved byAWS Board of Directors


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

ii

International Standard Book Number: 0-87171-560-0

American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126

© 2000 by American Welding Society. All rights reservedPrinted in the United States of America

T

HE

W

ELDING

I

NSPECTION

H

ANDBOOK

is a collective effort of many volunteer technical spe-cialists to provide information to assist welding inspectors and supervisors in the technologyand application of visual and nondestructive examination.

Reasonable care is taken in the compilation and publication of the

Welding Inspection Hand-book

to ensure authenticity of the contents. However, no representation is made as to the accu-racy or reliability of this information, and an independent substantiating investigation should beundertaken by any user.

The information contained in the

Welding Inspection Handbook

shall not be construed as agrant of any right of manufacture, sale, use, or reproduction in connection with any method,process, apparatus, product, composition, or system, which is covered by patent, copyright, ortrademark. Also, it shall not be construed as a defense against any liability for such infringe-ment. Whether or not use of any information in the Handbook would result in an infringementof any patent, copyright, or trademark is a determination to be made by the user.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

iii

Personnel

P. A. Grimm, Chair

Modern Welding Company

R. L. Holdren, Vice Chair

Edison Welding Institute

C. B. Pollock, Secretary

American Welding Society

*R. E. Blaisdell

The Pritchard Corporation

*W. Borges

Consultant

*C. R. Brashears

Alyeska Pipeline Service Company

R. Brosilow

Welding Design and Fabrication

W. A. Bruce

Edison Welding Institute

*E. L. Criscuolo

Consultant

*P. E. Deeds, Jr.

Consolidated Edison Company ofNew York

F. J. Gentry

Ashland Chemical Company

J. Giarrusso

North American Power Services,Incorporated

*C. J. Hellier

Hellier Associates

*D. L. Isenhour

Newport News Shipbuilding andDry Dock Company

L. A. Laime

Northeast Utilities

*C. E. Lautzenheiser

Southwest Research Institute

E. D. Levert

LTV Aerospace and Defense Company

R. D. McGuire

The National Board of Boiler andPressure Vessel Inspectors

*W. C. Minton

Southwest Research Institute

*M. N. Pfeiffer

National Aeronautics and SpaceAdministration

H. Walls, Jr.

Centerior Energy Corporation

S. J. Walmsley

Westinghouse Electric Corporation

*Advisor


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

iv

Foreword

The inspection of welds and welded assemblies requires knowledge of many factors of weld-ing quality control. This includes dimensional inspection, nondestructive examination methods,welding processes, welding metallurgy, destructive testing, and the qualification of weldingprocedures and personnel. It also includes the examination and test requirements of codes, cri-teria, and specifications; the acceptance standards to be employed; and an understanding ofdrawings, and welding and nondestructive examination symbols. Knowledge about discontinu-ities that may be associated with different welding processes, and the ability to evaluate the dif-ference between discontinuities and rejectable defects, is also an important element of weldinginspection.

This third edition of the

Welding Inspection Handbook

has been prepared by the AWSCommittee on Methods of Inspection. The objective is to provide a reliable source of usefulreference information. This is particularly relevant for the technically trained individual whomay not be directly involved with inspection but whose position requires knowledge aboutwelding inspection. This book also is intended for the inspector who needs a general refresherin the basic requirements of weld inspection.

Additional books on the subjects covered in each chapter may be found in good technicallibraries. The many specifications and codes that have been used as examples may also be con-sulted for more detailed information.

This book is an instructive reference. Codes or specifications applicable to any particularweldment always take precedence over the generalized material contained herein. The text ofthis book has, of necessity, been written in general terms and cannot include all the conditionsapplicable to a specific instance. Thus, examples given are general and are used only for thepurpose of illustration.

Every effort has been made to present this material in convenient form so that the book canbe used as a training text for inspectors, engineers, and welders. Although the information gen-erally relates to the arc welding processes, most of it applies to any weldment—fabricated byany joining process—for which the inspection methods described herein may be required.

For the inspection of brazed assemblies, refer to

The Brazing Handbook

published by theAmerican Welding Society. For the inspection of resistance welded assemblies, refer to AWS/SAE D8.7,

Recommended Practices for Automotive Weld Quality—Resistance Spot Welding

,also published by the American Welding Society.

Information on nondestructive examination methods is available in AWS B1.10,

Guide forNondestructive Examination of Welds

, and in AWS B1.11,

Guide for the Visual Examination ofWelds.

Comments and inquiries concerning this publication are welcome. They should be sent to theManaging Director, Technical Services Division, American Welding Society, 550 N.W. LeJeuneRoad, Miami, FL 33126.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

v

Contents

Chapter Page

Personnel

....................................................................................................................................iii

Foreword

.....................................................................................................................................iv

List of Tables

..............................................................................................................................vi

List of Figures

............................................................................................................................vii

1 Scope and Application .................................................................................................12 Symbols........................................................................................................................33 Requirements for the Welding Inspector....................................................................134 Welding Inspection Operations ..................................................................................195 Inspection Safety Considerations...............................................................................256 Quality Assurance ......................................................................................................297 Ferrous Welding Metallurgy ......................................................................................338 Preheating and Postweld Heat Treating .....................................................................459 Weld and Weld Related Discontinuities.....................................................................49

10 Qualification of Welding Procedure Specifications ...................................................6511 Qualification of Welders and Welding Operators.......................................................8112 Computerization of Welding Inspection and Quality.................................................9313 Destructive Testing of Welds......................................................................................9914 Proof Tests................................................................................................................12315 Nondestructive Examination Methods.....................................................................12516 Qualification of Nondestructive Examination Personnel .........................................21517 Codes and Other Standards ......................................................................................21718 Metric Practice .........................................................................................................227

Index.........................................................................................................................239


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

vi

List of Tables

Table Page

4.1 Sequence of Welding and Inspection Operations................................................................22

10.1 Welding Procedure Specification and Welder Qualification FactorsWhich May Require Requalification..........................................................................71

13.1 Typical Hardness Conversion Table (Approximate) (for Carbon and LowAlloy Steels in Accordance with ASTM E-140 and ASTM A-370) ........................107

15.1 Considerations when Selecting an NDE Method.....................................................12615.2 Radiographic Isotopes Used in Industrial Radiography...........................................13615.3 Approximate Radiographic Equivalence Factors of Several Metals........................13815.4 Resistivity and Conductivity of Some Metals and Alloys........................................195

18.1 SI Base and Supplementary Units and Symbols......................................................22718.2 SI Derived Units and Symbols .................................................................................22818.3 SI Factors, Prefixes, and Symbols............................................................................22818.4 Units Not Part of the SI System ...............................................................................22918.5 SI Unit Conversion Factors ......................................................................................23018.6 General Conversion Factors .....................................................................................23118.7 Commonly Used Metric Conversions (Inch–Millimeter Conversion) .....................23418.8 Pressure and Stress Equivalents—psi and ksi to kPa and MPa................................23518.9 Conversions for Fahrenheit–Celsius Temperature Scales ........................................236


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

vii

List of Figures

Figure Page

2.1 AWS Standard Welding Symbols.................................................................................42.2 Comparison of Welding Symbol and Written Explanation..........................................62.3 Examples of Typical Fillet Welds Showing the Corresponding Symbols

and Dimensions............................................................................................................72.4 Examples of Typical Groove Welds Showing the Corresponding

Symbols and Dimensions.............................................................................................82.5 Standard Location of Elements for NDE Symbols ......................................................92.6 Examples of Typical Nondestructive Examination Symbols .......................................92.7 Master Chart of Welding, Allied Processes, and Thermal Cutting ............................10

7.1 Iron-Carbon Phase Diagram.......................................................................................347.2 Crystal Structure of Cold Rolled Steel in Weld Area.................................................357.3 Martensite Showing Needle-Like or Acicular Structure

(500X Before Reduction)...........................................................................................357.4 Example of Delayed Cracking in HAZ......................................................................377.5 Corrosion Attack of Sensitized Stainless Steel in Acid Environment........................407.6 Microfissure in Austenitic Stainless Steel (100X) .....................................................417.7 Closeup of Lamellar Tear Under a Fillet Weld Showing Typical Stepped

Appearance (Magnification 8X).................................................................................42

9.1 Typical Distortion of Welded Joints ...........................................................................509.2 Overlap.......................................................................................................................519.3 Weld Sizes..................................................................................................................529.4 Acceptable and Unacceptable Weld Profiles per AWS D1.1 .....................................539.5 Incomplete Joint Penetration and Incomplete Fusion ...............................................559.6 Underfill .....................................................................................................................569.7 Various Types of Cracks.............................................................................................589.8 Porosity ......................................................................................................................619.9 Lamellar Tearing ........................................................................................................64

10.1 AWS Structural Welding Code Prequalified Procedures............................................6910.2 Standard for Welding Procedure Qualification ..........................................................7510.3 ASME Procedure Qualification Record.....................................................................77

11.1A Test Plate for Unlimited Thickness—Welder Qualification.......................................8311.1B Optional Test Plate for Unlimited Thickness—Horizontal Position—

Welder Qualification ..................................................................................................8311.2A Tubular Butt Joint—Welder Qualification—Without Backing ..................................8411.2B Tubular Butt Joint—Welder Qualification—With Backing .......................................8411.3A Positions of Groove Welds .........................................................................................8511.3B Positions of Fillet Welds ............................................................................................8611.4 Positions of Test Plates for Groove Welds .................................................................8711.5 Positions of Test Pipe or Tubing for Groove Welds ...................................................8811.6 Positions of Test Plate for Fillet Welds ......................................................................8911.7 Positions of Test Pipes for Fillet Welds......................................................................90


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

viii

11.8 Suggested Form for Welding Performance Qualification ..........................................91

12.1 A Welding Inspection Data Base ...............................................................................94

13.1 Typical Photomacrographs.......................................................................................10113.2 Photomicrograph Illustrating the Appearance of a Crack in the

Heat-Affected Zone (Approximately 100X)............................................................10213.3 Photomicrographs ....................................................................................................10213.4 Typical Stress-Strain Diagram Used in the Offset Method......................................10813.5 Standard Tension Specimens....................................................................................11013.6A Transverse Face- and Root-Bend Specimens...........................................................11213.6B Transverse Side-Bend Specimens ............................................................................11313.7 Fixture for Guided Bend Test...................................................................................11413.8A Transverse Rectangular Tension Test Specimen (Plate) ..........................................11613.8B Longitudinal Rectangular Tension Test Specimen (Plate) .......................................11713.9 Typical Fillet Weld Break and Macroetch Test for Fillet Welder or

Welding Operator Qualification ...............................................................................11813.10 Charpy (Simple-Beam) Impact Test Specimens ......................................................12113.11 Charpy (Simple-Beam) Impact Test.........................................................................122

15.1 Welding Engineer Data Sheet ..................................................................................12915.2 Scales and Gauges for Checking Fit-Up and Weld Dimensions..............................13015.3 Weld Bead Contours ................................................................................................13015.4 Workmanship Standard ............................................................................................13115.5 Sketches of Weld Undercut and Overlap .................................................................13215.6 Photographs of Weld Undercut and Overlap............................................................13315.7 Weld Inspection Gauges...........................................................................................13415.8 Typical “Shadow Graph” .........................................................................................13515.9 The Penumbral Shadow ...........................................................................................14015.10 Geometric Principles of Shadow Formation ............................................................14115.11 Factors Affecting Quality of Radiographic Image ...................................................14415.12 Sources of Scattered Radiation ................................................................................14515.13 Characteristic Curve For a Typical Industrial X-Ray Film ......................................14715.14 The “Tools of The Trade” for the Radiographer ......................................................14915.15 Typical Penetrameter Design ...................................................................................15015.16 Typical Radiographic Exposure Arrangements........................................................15215.17 Typical Radiographs of Weld Discontinuities..........................................................15715.18 Block Diagram, Pulse-Echo Flaw Detector .............................................................15915.19 Decibel-To-Screen Height or Voltage Nomograph ..................................................16115.20 Snell’s Law of Reflection and Refraction ................................................................16215.21 Amplitude Calibration Using Flat Bottom Holes ....................................................16415.22 Shear Wave Ultrasonic Beam...................................................................................16415.23 Amplitude Calibration..............................................................................................16615.24 Ultrasonic Ruler Application ...................................................................................17015.25 Flaw Orientation ......................................................................................................17115.26 Sound Beam Propagation Showing Sound Path Distance .......................................17115.27 Magnetic Field in a Bar Magnet ..............................................................................17415.28 Magnetic Field in a Bar Magnet That Has Been Cut in Half...................................175

Figure Page


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

ix

15.29 Magnetism Around a Notch Cut in a Bar Magnet ...................................................17515.30 Magnetic Field Around a Conductor Carrying Current ...........................................17615.31 Field of Ferromagnetic Conductor is Confined Almost Entirely to the

Conductor Itself........................................................................................................17615.32 Magnetic Particles Near a Defect are Attracted to the Local Poles .........................17615.33 In Large Parts, Local Areas Can Be Magnetized; Arrows Indicate Field ................17715.34 Part to be Inspected Can Be Magnetized by Making it the Core of a Solenoid.......17815.35 Crack in Large Plate is Indicated by Alignment of Particles Between Prods ..........17915.36 Dry Powder Magnetic-Particle Inspection of Welds with Portable

Equipment ................................................................................................................18115.37 Wet Fluorescent Magnetic-Particle Inspection to Show Fine Surface Defects........18215.38 Typical Indication of Surface Crack in a Weld ........................................................18515.39 Indication of a Subsurface Crack in a Weld (The Dry Magnetic

Particles Assume a Less Defined Pattern) ................................................................18615.40 Liquid Penetrant Comparator...................................................................................19115.41 Frequencies Used for Various Test Problems...........................................................19315.42 Cross-Sectional View of a Bar With a Small Crack, Surrounded by an

Exciting Coil and a Pickup Coil, Showing Eddy Current Distribution....................19315.43 Relative Conductivity of Metals and Alloys Related to Eddy Current

Meter Readings ........................................................................................................19415.44 Influence of Impurities on the Conductivity of Pure Copper ...................................19615.45 Typical B/H (Hysteresis) Curve ...............................................................................19715.46 Lines of Magnetic Flux Surrounding a Solenoid .....................................................19715.47A Instrumentation Readout for Electromagnetic Testing.............................................19815.47B Typical Eddy Current Readout from Strip Chart Illustrating Good and Bad

Weld Areas ...............................................................................................................19815.48 Production of Eddy Currents by an Alternating Field..............................................19915.49 Testing Coils Carrying Alternating Current .............................................................20015.50 Examples of Electromagnetic Probe Coils...............................................................20115.51 Eddy Current Strength Drops Off With Distance From Surface..............................20115.52 Eddy Current Flaw Detection Equipment ................................................................20215.53 Microstructure of Austenitic Weld Specimen ..........................................................20815.54 Schaeffler Diagram for Stainless Steel Weld Metal .................................................20915.55 DeLong Diagram for Stainless Steel Weld Metal ....................................................21015.56 Typical Flow Diagram from Contract to Approved Operations Procedures ............212

Figure Page


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

1

1.1 Scope

The scope of this handbook includes test-ing and examination methods that apply toa majority of metallic and nonmetallic weld-ments used in construction. The extent ofinspections should be clearly defined in con-tract documents or on drawings that refer toa particular weldment (unless otherwisedefined in applicable codes or specifications).Furthermore, acceptance criteria should beclearly understood and agreed upon by boththe supplier and the purchaser before any pro-duction welding begins. Acceptance criteriafor weld discontinuities are specificallyexcluded from this handbook.

1.2 Application

The information in this handbook pertainsto the general duties and responsibilities ofwelding inspectors and is intended to enhancetheir performance. This book provides spe-cific information about methods of weldmentinspection; however, much of the informationwill also generally apply to the examinationof nonwelded components, such as base metalinspection prior to fabrication. For the inspec-

tion process to be effective, the weldinginspector should be knowledgeable abouteach examination method required.

It is the responsibility of those chargedwith the administration and supervision ofinspection to make certain that the principlesand methods to be used are properly under-stood and applied uniformly. This responsi-bility may include the qualification andcertification of inspectors where such certifi-cation is required by codes, specifications, jobcontracts, civil law, or company policies.

The following documents address the qual-ification of welding inspection and nonde-structive examination personnel:

1

(1) ASNT Recommended Practice SNT-TC-1a

(2) AWS QC1,

Specification for Qualifica-tion and Certification of Welding Inspectors

Even when a particular qualification forcertification program is not mandatory, everywelding inspector should be aware of the eth-ical criteria for welding inspectors containedin documents such as AWS QC1.

1. See Chapter 17 for addresses of standards-writingorganizations.

Chapter 1Scope and Application


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

3

2.1 Communication

Communication can determine whether ajob will be a success or a failure. In industry,drawings convey the designer’s concepts tothose performing the work. Intricate detailscan be much more accurately and efficientlydescribed through graphic presentation thanthrough the written word.

In the case of welded construction, a greatdeal of information may be required in orderfor the welder to successfully provide a weldadequate for the designer’s intended purpose.Using written notes is one method for con-veying the necessary design concepts. How-ever, written descriptions can become quitecomplex and time consuming for intricatedetails. A simpler and more efficient methoduses welding symbols.

The American Welding Society has devel-oped a system of standard welding symbolsnow used and accepted worldwide. Figure 2.1depicts the various types of weld and weldingsymbols and explains the purposes and loca-tions of the basic elements. A detaileddescription of the system can be found inAWS A2.4,

Standard Symbols for Welding,Brazing, and Nondestructive Examination

.Figure 2.2 shows the advantages offeredwhen welding symbols replace the writtenexplanation. Figures 2.3 and 2.4 show otherwelding symbols and how they are used tospecify the welding requirements. The adja-cent details illustrate the significance of eachsymbol.

Just as the welding symbol is important tothe welder, equally important is the weldinginspector’s knowledge of its meaning. With-out this knowledge, the inspector would beunable to assure that the welder has compliedwith the requirements set forth by the

designer. Typical information depicted bywelding symbols that is of interest to a weld-ing inspector includes type of weld, size ofweld, weld location, joint configuration, fin-ished condition of face and root of the weld,as well as any special instructions.

Knowledge of the information provided bythe welding symbol is essential to the inspec-tor when a weld is to be visually examined(VT). Once the inspector understands whatthe engineer requires, a thorough and highlyeffective visual examination can result. Manysituations warrant a more extensive checkthan can be provided by visual examinationalone. In such cases, other forms of non-destructive examination (NDE) are oftenemployed.

The inspector can gain a great deal ofinsight from the welding symbol as to theapplicability of a particular test when nonde-structive examination is involved. In ultra-sonic testing (UT), for example, usefulinformation provided by the welding symbolmight include the joint configuration andlocation. From this information, the NDEoperator can determine whether the test canbe physically conducted as well as whattransducer angle would most readily revealany discontinuities.

The welding symbol can also provide valu-able information concerning how the test canbe applied when radiographic examination(RT) is to be used. Information such as jointconfiguration, weld location, type of weld,and size of weld can help the radiographer todetermine the types of discontinuities whichmay be present and the best method for theirdetection. Such details allow the inspector toplan his test so that the best technique andprocedure will be used.

Chapter 2Symbols


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

4/Symbols

Figure 2.1—AWS Standard Welding Symbols

Contour by Grinding


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Symbols/5

Figure 2.1 (Continued)—AWS Standard Welding Symbols


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

6/Symbols

2.2 NondestructiveExamination Symbols

With the increased use of nondestructiveexamination by construction industries, itbecomes convenient for the engineer toinclude testing requirements on the fabrica-tion drawings. Noting testing requirements onthe drawings helps to avoid many after-the-fact inconsistencies associated with the extentor type of testing. As with welding symbols, asystem has been established to communicatenondestructive examination information usingsymbols similar to those used for welding. Acomplete description of this system isincluded in AWS A2.4.

The construction of nondestructive exami-nation symbols uses the same basic elementsfound in welding symbols along with similargoverning rules. Therefore, arrow-side andother-side designations retain their same loca-tion significance. Figure 2.5 shows the basicelements of the examination symbol and theirstandard locations with respect to one another.

Figure 2.6 illustrates the shorthand nota-tions used with nondestructive examinationsymbols.

2.3 Master Chart of Welding,Allied Processes, and Thermal Cutting

Inspection personnel must be familiar withthe welding and allied processes within thescope of their work. A welding or allied pro-cess is basic to the operation to be performed,and may be subdivided into more specificprocesses.

In the hierarchy of welding, the weldingprocess stands first. Each welding processdefinition is complete so that it will standalone. Processes are defined for prescribedelements of operation. This method of organi-zation is the basis for the Master Chart shownin Figure 2.7.

The chart is a display of a hierarchy ofwelding and allied processes; the highestgeneric levels (least specific) are in the center,and the more specific are in boxes on theperimeter. The chart is intended to be compre-hensive and includes not only widely usedproduction processes, but also some that are oflimited use because they have been replacedby other processes, have only recently beenintroduced, or have limited applications.

Figure 2.2—Comparison of Welding Symbol and Written Explanation


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Symbols/7

Figure 2.3—Examples of Typical Fillet Welds Showingthe Corresponding Symbols and Dimensions


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

8/Symbols

Figure 2.4—Examples of Typical Groove Welds Showingthe Corresponding Symbols and Dimensions


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Symbols/9

Figure 2.5—Standard Location of Elements for NDE Symbols

Figure 2.6—Examples of Typical Nondestructive Examination Symbols


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

10/Symbols

Figure 2.7—Master Chart of Welding, Allied Processes, and Thermal Cutting


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Symbols/11

Figure 2.7 (Continued)—Master Chart of Welding,Allied Processes, and Thermal Cutting


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

13

It is appropriate here to consider attributesdesirable for an individual employed as awelding inspector. The nature of the jobemphasizes an individual’s physical, techni-cal, and ethical qualities. Any weaknesses inthese areas can reduce the effectiveness of theindividual’s performance.

3.1 Inspector Classifications

There are many types of welding inspec-tors, depending upon technical requirementsfor the particular fabrication process or pro-cesses. These include destructive testingspecialists, nondestructive examination spe-cialists, code inspectors, military inspectors,and owner’s representative inspectors. All ofthese may consider themselves weldinginspectors simply because they

do

inspectwelds.

The fact that welding inspectors work inmany different industries performing so manyquality-related tasks makes it difficult toclearly and concisely describe what a weldinginspector is and how that job function is spe-cifically performed.

One fundamental complication is that anindividual may perform many functions oronly a single function. For example, it is com-mon to perform numerous aspects of weldingquality control (e.g., welding procedure quali-fication, welder qualification, in-process andfinal visual examination, destructive testing,and final nondestructive examination). How-ever, it is also common for an individualinvolved in welding inspection to performonly one of those tasks (e.g., a nondestructiveexamination specialist).

Another important difference relates to theinspector’s employer. The inspector may be

directly employed by the manufacturer, thecustomer, the customer’s representative, or anindependent agency. While this should notaffect the technical application of the individ-ual’s inspection skills, it may to some degreeinfluence the logistics of that activity.

In this handbook, however, only a singleinclusive category of “inspector” is used—one that includes as many different categoriesbasic to the responsibility of the individualinspector as the particular job may require.Each specific job then would depend upon therelevant requirements, duties, and responsi-bilities of each inspector.

With this generic approach, descriptionsgiven here are not intended to specificallydefine the job function of a welding inspector.Information herein should be viewed simplyas a general overview of the numerous activi-ties that could be considered part of the weld-ing inspector’s job. There will be descriptionsof operations and activities which are beyondthe scope of certain welding inspectors. Inother cases, welding inspectors may be per-forming other functions that are not specifi-cally addressed in this book. Informationprovided here should be applied only when inagreement with an inspector’s specific jobdescription.

The following are important factors that acompany should take into consideration whenselecting a person for the job of weldinginspector.

3.2 Attributes of the Welding Inspector

The job of welding inspector carries a tre-mendous amount of responsibility. Selectionof the right person for that position should be

Chapter 3Requirements for the Welding Inspector


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

14/Requirements for the Welding Inspector

based on consideration of the following fourcritical attributes:

(1) Physical(2) Technical(3) Ethical(4) Personal

3.2.1 Physical

3.2.1.1 Physical Condition.

To performduties in the most effective manner, the weld-ing inspector should be in good physical con-dition. Since the primary job involves visualinspection, it is obvious that the weldinginspector should have good vision, whethernatural or corrected. For instance, if color orcontrast is important to the inspection processbeing employed (liquid penetrant, magneticparticle, or color coded parts) then an individ-ual should be tested for the ability to detectthose colors. The AWS Certified WeldingInspector (CWI) program requires a mini-mum 20/40 visual acuity and the ability toperceive certain colors, as determined throughactual testing.

Another aspect of physical conditioninginvolves the size of some welded structures.Since welds could be located anywhere on avery large structure, the inspector must becapable of going to the weld at any location inorder to make an evaluation. The inspectormust comply with safety regulations whenperforming these duties.

The ability of the welding inspector to getto the work may be reduced if the inspection isnot performed immediately after welding. Forexample, such aids for the welder as laddersand scaffolding may be removed, makingaccess impossible or dangerous. Within safetyguidelines, the welding inspector should notbe prevented from performing proper inspec-tion because of a physical condition.

3.2.1.2 Technical Ability.

While there maybe no specific level of education and trainingrequired for welding inspectors, the job mayinvolve interpretation of results. Therefore, anindividual must have at least some level oftechnical knowledge to perform well as aninspector. In order to perform welding inspec-

tion, the individual will continually be askedto make judgments based on visual observa-tions of physical characteristics of welds andweldments and their comparison with draw-ings or standards.

If an individual is unable to understandsome written requirement, it will be difficultto make a judgment as to a weld’s acceptabil-ity in accordance with that standard. There ismore to an evaluation than just reading thespecifications. Once read, the inspector mustinterpret its meaning. Even then, somerequirement of a code or specification mayappear very clear and straightforward wheninitially read; however, comparison of thiswritten requirement with an existing physicalcondition may still prove to be extremelydifficult.

Technical ability is also necessary in orderfor the welding inspector to effectivelyexpress ideas or inspection findings. In addi-tion, once an inspection has been performed,the inspector must be capable of describingthe methods used and subsequent results withsufficient accuracy to adequately communi-cate to others familiar with the work beingperformed.

3.2.2 Technical

3.2.2.1 Interpretation of Drawings andSpecifications.

Another quality which thewelding inspector should develop is an abilityto understand and apply the various docu-ments describing weld requirements. Theseinclude, in part: drawings, codes, and specifi-cations. These documents provide most of theinformation regarding what, when, where,and how the inspection is to be performed. Infact, these documents literally constitute therules under which the welding inspector mustperform. They also state the requirements bywhich the welding inspector will judge theweld quality. Obviously, such documentsmust be reviewed prior to the start of anywork, because the welding inspector shouldbe aware of the job requirements before anyproduction. Many times this review willreveal required “hold points” for inspections,welding procedure and welder qualification


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Requirements for the Welding Inspector/15

requirements, and special processing steps ordesign deficiencies such as weld inaccessibil-ity during fabrication.

Although the welding inspector should bethorough in reviewing documents, it is notnecessary that requirements be memorized.These are

reference

documents and should bereadily available at any time in the fabricationprocess. Generally, the inspector is the indi-vidual most familiar with all of these docu-ments. The inspector may be called upon byothers for information and interpretationregarding the welding requirements.

3.2.2.2 Inspection Experience.

Havingactual on-the-job inspection experience isvery important. Text books and classroomstudies simply do not provide all of the thingsneeded to inspect effectively. Experience willaid the welding inspector in becoming moreefficient. In time, better ways of thinking andworking will develop.

On-the-job experience will also help theinspector develop the proper attitude andpoint of view regarding job assignment. Afterworking with various codes and specifica-tions, the inspector’s effectiveness willimprove because of an improved understand-ing of welding requirements. To emphasizethe need for inspection experience, it is com-monplace to see a novice inspector pairedwith an experienced one so that proper tech-niques can be passed along. Most inspectorcertification programs require some minimumlevel of actual inspection experience.

3.2.2.3 Knowledge of Welding.

Anotherdesirable quality for a welding inspector is abasic knowledge of welding and related pro-cesses. Because of their background, weldersare sometimes chosen as welding inspectortrainees. Such a person is certainly better pre-pared as an inspector to understand manyproblems that the welder may encounter. Thisknowledge helps the inspector in gainingrespect and cooperation from the welders.Further, this understanding helps the weldinginspector predict what weld discontinuitiesmay be encountered in a specific situation.

The welding inspector can then monitor criti-cal welding variables in order to help preventthese welding problems. When the inspectoris experienced in welding processes andunderstands their advantages and limitations,possible problems can be more easily identi-fied and prevented.

3.2.2.4 Knowledge of ExaminationMethods.

Knowledge of various destructiveand nondestructive examination methodsshould be helpful to the welding inspector.Although the inspector may not perform thesetests, from time to time it may be necessary toreview test results. As with welding pro-cesses, the welding inspector is aided by abasic understanding of testing methods. It isimportant that the inspector be aware of alter-nate methods which could be applied toenhance visual inspection.

3.2.3 Ethical.

In order to safeguard publichealth and to maintain integrity and high stan-dards of skills, practice, and conduct in theoccupation of welding inspection, the inspec-tor must render decisions promptly whileremaining impartial and tolerant of the opin-ions of others. The following recommenda-tions for a welding inspector’s behavior arepatterned after the ethical requirements speci-fied in AWS QC1,

Standard for Qualificationand Certification of Welding Inspectors

.

3.2.3.1 Integrity.

The welding inspectormust act with complete integrity (honesty) inprofessional matters and be forthright andcandid with respect to matters pertaining towelding inspector qualification requirements.

3.2.3.2 Responsibility to the Public.

Thewelding inspector is obligated to preserve thehealth and well-being of the public by per-forming the duties required of weld inspec-tion in a conscientious and impartial mannerto the full extent of the inspector’s moral andcivic responsibilities and qualifications.Accordingly, the welding inspector shall:

(1) Undertake and perform assignmentsonly when qualified by training, experienceand capability,


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


(2) Present credentials upon request,(3) Neither falsely represent current status

nor seek to misrepresent certification level ormodification of certification documents orfalse verbal or written testimony of currentlevel or status,

(4) Be completely objective, thorough, andfactual in any written report, statement or tes-timony of the work and include all relevant orpertinent testimony in such communiques ortestimonials,

(5) Sign only for work that the inspectorhas inspected, or for work over which theinspector has personal knowledge throughdirect supervision, and

(6) Neither associate with nor knowinglyparticipate in a fraudulent or dishonest venture.

3.2.3.3 Public Statements.

The weldinginspector will issue no statements, criticisms,or arguments on weld inspection matters con-nected with public policy which are inspiredor paid for by an interested party, or parties,without first identifying the party, the speaker,and disclosing any possible pecuniary interest.

The welding inspector will not publiclyexpress any opinion on a weld inspection sub-ject unless it is founded upon adequateknowledge of the facts in issue, upon a back-ground of technical competence pertinent tothe subject, and upon honest conviction of theaccuracy and propriety of the statement.

3.2.3.4 Conflict of Interest.

The weldinginspector shall avoid conflict of interest withthe employer or client and will disclose anybusiness association, or circumstances thatmight be so considered.

The welding inspector shall not acceptcompensation, financial or otherwise, frommore than one party for services on the sameproject, or for services pertaining to the sameproject, unless the circumstances are fullydisclosed and agreed to by all interested par-ties or their authorized agents.

The welding inspector shall not solicit oraccept gratuities, directly or indirectly, fromany party, or parties, dealing with the client oremployer in connection with the CWI’s and

Certified Associate Welding Inspector’s(CAWI’s) work.

The welding inspector shall, while servingin the capacity of an elected, retained, oremployed public official, neither inspect,review, nor approve work in the capacity ofCWI or CAWI on projects also subject to theinspector’s administrative jurisdiction as apublic official, unless this practice isexpressly dictated by a job description, speci-fication, or both, and all affected parties to theaction are in agreement.

3.2.3.5 Solicitation of Employment.

Thewelding inspector shall neither pay, solicit, oroffer, directly or indirectly, any bribe or com-mission for professional employment with theexception of the usual commission requiredfrom licensed employment agencies.

The welding inspector shall neither falsify,exaggerate, nor indulge in the misinterpreta-tion of personal academic and professionalqualifications, past assignments, accomplish-ments, and responsibilities, or those of theinspector’s associates. Misrepresentation ofcurrent certification status at the time of, orsubsequent to, submission of requestedemployment information, or in the solicita-tion of business contracts wherein currentcertification is either required or inherentlybeneficial (advertisements for trainingcourses, consulting services, etc.) shall be aviolation of this section.

The welding inspector is cautioned againstfunctioning as an independent in fields out ofhis or her capability, without first investigat-ing for possible industry or public require-ments and additional education/experiencerequirements (e.g., industrial labs, in the con-crete and soil testing field, etc.)

3.2.4 Personal

3.2.4.1 Professional Attitude.

The first,and perhaps the most important personalquality, is a professional attitude. This is areal key to the success of the welding inspec-tor, because it will determine the degree ofrespect and cooperation the inspector willreceive from others during the performance


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Requirements for the Welding Inspector/17

of inspection duties. Included in this categoryis the ability of the welding inspector tomake decisions based on facts so that theyare fair, impartial and consistent. If aninspector’s decisions show partiality orinconsistency, they will undermine theinspector’s reliability.

In keeping with this professional attitude,the welding inspector’s decision should beconsistent with job requirements so thatdecisions are neither too critical nor toolenient. For example, it is a mistake to havepreconceived ideas as to a component’sacceptability. The inspector should reviewthe facts and make decisions based solely onthose facts.

This need for professionalism also extendsinto a person’s dress and manner, and lan-guage used when dealing with others. If thesecharacteristics become offensive to others,they may well, by themselves, reduce aninspector’s effectiveness.

The inspector should develop a positiveattitude. The goal is to assure that the weld-ing has been done properly, rather than to tryand find something wrong. Every attemptshould be made to be cooperative and help-ful. When decisions are being formulated, thewelding inspector should genuinely considerall opinions and recommendations. Onlyafter carefully listening to input from otherinvolved parties, and combining that informa-tion with all the facts and requirements, canthe welding inspector make a truly soundjudgment.

Memberships in professional and technicalorganizations offer individual inspectors up-to-date information on revised standards andnew industrial practices and requirementsaffecting their work.

The AWS CWI Program for Qualificationand Certification of welding inspectors doesnot require AWS membership, but AWSmembership does show the employer theintent and desire of the individual to improveand maintain welding technology.

3.2.4.2 Learning Potential.

Individuals areoften hired as welding inspectors primarily

because of their learning potential. Theinspector can perform the job more effec-tively after being trained extensively in a vari-ety of subjects. In fact, because the job ofwelding inspector involves so many differentaspects, it is virtually impossible to gain all ofthe necessary information through experiencealone. Personal and professional experiencemust be supplemented by additional training.

3.2.4.3 Completing and MaintainingInspection Records.

A final attribute, whichis not to be taken lightly, is the welding inspec-tor’s ability to complete and maintain inspec-tion records. The welding inspector must becapable of accurately communicating allaspects of the inspection, including the results.

The records should be legible and understand-able to anyone familiar with the work; therefore,neatness is important. The welding inspectorshould also consider these records as protectionshould questions later arise. Reports should con-tain sufficient information regarding how theinspection was performed so that similar resultscan be obtained later by someone else.

Once records have been developed, thewelding inspector should be capable of main-taining all necessary information in anorderly fashion to facilitate easy retrieval.Accordingly, there are a few “rules of eti-quette” relating to inspection records. First,records should be completed in ink; if incor-rect entries are noted, they can be lined outand corrected. This corrective action shouldthen be initialed and dated for explanation.Next, the report should accurately and com-pletely state the job name and inspectionlocation in addition to specific test informa-tion. The use of sketches and pictures mayalso help to convey information regarding theinspection results. Finally, the completedreport should then be signed and dated by theinspector who actually performed the work.

3.3 Certification of Qualification

Education, training, and experience arecrucial to the qualification of a welding


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


inspector. A potential welding inspectorshould be aware that the increasing variety ofwelding processes, materials, codes, andother standards applied to today’s producttechnologies makes the job more complicatedand difficult. This simply means that weldinginspectors have an increasingly important joband that this job must be done in a more uni-form manner throughout the United States.

Since 1976, the American Welding Societyhas been actively involved in the examination,qualification, and certification of weldinginspection personnel. The guidelines for theCertified Welding Inspector program havebeen established by the AWS QualificationCommittee and Certification Committees andapproved by the AWS Board of Directors. Theadministration of this program is the responsi-bility of the AWS Certification Department.

In order to qualify as a Certified WeldingInspector (CWI) or a Certified Associate

Welding Inspector (CAWI), an individualmust show evidence of specified minimumlevels of experience, educational training, andvision requirements which have been estab-lished by the AWS Qualification Committee.After these preliminary requirements havebeen met, the individual is required to suc-cessfully pass a three-part examination. Uponpassing of all three parts of the examination,AWS will certify, register, and document thequalification and issue an identification card.A stamp bearing the individual’s name andcertification number may be purchased foruse in identifying parts or inspection reportsapproved by the Certified Welding Inspector.Recertification is required every three years.

For information regarding the CWI pro-gram, contact the AWS Certification Depart-ment. Other publications from Chapter 17,Codes and Other Standards, should be used asreferences and guides.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

19

The last chapter outlined desirable charac-teristics and responsibilities of a weldinginspector. This chapter concentrates on themost essential operations involved in thewelding inspection process.

Welding inspectors can have a diversifiedrange of responsibilities, depending upon thespecification or code to which they are work-ing, and the particular manufacturing or fabri-cation industry in which they are employed.Welding inspection operations will, for themost part, follow the general sequence of thefabrication process. The following outline is alist of activities encountered in weldinginspection:

(1) Review of drawings, specifications, andmanufacturing instructions

(2) Review of the manufacturer’s approvedquality assurance/ quality control program

(3) Verification of welding procedures andpersonnel qualifications

(4) Verification of approved procedure forqualifying welding and inspection personnel

(5) Selection and examination of produc-tion test samples

(6) Evaluation of test results(7) Preparation of test reports and mainte-

nance of records(8) Observance and monitoring of recom-

mended safety guidelines.

4.1 Review of Drawings, Specifications, and Manufacturing Instructions

Welding inspectors should have a workingknowledge of the product being manufac-tured, especially those components or subas-semblies which they will inspect. Detailedknowledge of drawing requirements, specifi-

cation requirements, and any manufacturinginstructions is essential. It also is helpful tohave a knowledge of the material to be usedin the weldment because certain metals mayrequire special treatment for satisfactorywelding. Welding and related proceduresshould contain information that incorporatesall of the specified variables for performingthe operation. Manufacturing instructionsdetail the use of particular procedures for var-ious phases of fabrication.

The welding inspector should be alert toany changes made in these documents toassure compliance with all other proceduresand fabrication requirements. Deviationsfrom drawings, specifications, and manufac-turing instructions should be referred to theappropriate technical function for resolution.In some instances, deviations from drawingsor specifications should be referred to a regu-latory agency for approval.

It is not always possible to write a specifi-cation that contains all the detailed informa-tion needed to provide an answer for allquestions that might arise. Those parts of thespecification that are unclear should bereferred to the appropriate technical person-nel for interpretation.

4.2 Review of the Manufacturer’s Approved Quality Assurance/Quality Control Program

The welding inspector should be aware ofthe manufacturer’s quality program. A qualityprogram provides the administrative stepsneeded to inspect and control the quality ofthe completed product. Chapter 6, “QualityAssurance,” describes the elements of goodprogram.

Chapter 4Welding Inspection Operations


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

20/Welding Inspection Operations

Quality assurance includes all planned andsystematic actions necessary to provide ade-quate confidence that a structure, system, orcomponent will perform satisfactorily todesign requirements or intended service.Quality control, which may be included inquality assurance, includes those actionsrelated to the physical characteristics of amaterial, structure, component, or system.These actions provide a means to control thequality of the material, component, or systemto predetermined requirements.

A quality program may include controlover a manufacturer’s procedures. This mayinclude final approval and control of proce-dure revisions, or procedures and job orderapplicability. Other functions might includethe administration of the manufacturer’sinstrument calibration program. A qualityassurance program will document complianceto requirements of the applicable code orstandard. The inspector should have generalfamiliarity with program requirements toassure that compliance with the program isachieved.

The welding inspector should be familiarwith rules, procedures, and methods for han-dling and reporting discrepancy findings tothe manufacturer.

4.3 Verification of Welding Procedure and Personnel Qualifications

Prior to the start of fabrication, the inspec-tor should verify that the fabricator hasprepared written welding procedure specifica-tions that meet the applicable specification,standard, or code. The welding procedureshould be capable of producing weldmentswith adequate strength, ductility, and tough-ness to satisfy the applicable specification orcode. Chapter 10, “Qualification of WeldingProcedures,” describes the elements of awelding procedure specification and explainsthe reasons for its use.

Prior to the start of production welding, theinspector should review the qualifications ofwelders and welding operators that will workon the project. It may be desirable, dependingupon the contract, to review the fabricator’sprocedures for qualification of welders andwelding operators. Some contracts may requirethis, and also require that the procedure beapproved. The welding inspector should besure that (1) only approved welding proceduresare used on the applicable contract, and (2)welders and welding operators are qualified.The contract should specify the requirementsas to how this may be accomplished.

Additionally, the welding inspector shouldbe alert to changes of variables in any weld-ing procedure. Changes or deviations in theprocedural requirements should be brought tothe attention of the proper personnel. Revi-sions should be qualified by tests whererequired and distributed to welders and weld-ing operators performing the work. New per-formance qualifications may be required ifthe revised procedures exceed the welder orwelding operator’s limitations of variablesdefined in the applicable specification orcode.

The chapters on “Qualification of WeldingProcedures” and “Qualification of Weldersand Welding Operators” contain sample qual-ification requirements and examples wherewelders may not be working within the limitsof their qualifications.

The objective of a welding procedure quali-fication test is to determine the mechanicalproperties of the welded joint. The objectiveof performance qualification is to determinethe ability of an individual to deposit soundweld metal with a previously qualified weld-ing procedure.

As with welder and welding operator quali-fications, inspection personnel should also bequalified prior to the start of the inspection ofproduction welds. The fabricator shouldensure that only qualified personnel areallowed to perform inspection operations. Itmay be desirable or a requirement, dependingupon the contract, to have a procedure detail-


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Welding Inspection Operations/21

ing qualification methods. Some contractsmay require the procedure to be approved.

4.4 Verification of Approved Procedures for Qualifying Welding and Inspection Personnel

Although welding and inspection personnelare qualified in accordance with approvedprocedures, verification is nonetheless neces-sary to provide added assurance that proce-dures are applied properly and competently.To a large extent, the quality of welding andthe quality of inspection depend upon theapplication of the correct inspection proce-dures. The welding inspector should verifythat procedures specifically approved oragreed upon for the job are being used. Thewelding inspector may find it advantageous toprepare a checklist for each inspection proce-dure to use as a guide for performing therequired duties. Various recognized inspec-tion methods and tests are described in Chap-ters 13, “Destructive Testing of Welds,” 14,“Proof Tests,” and 15, “Nondestructive Exam-ination Methods.”

In general, inspection processes should beperformed in sequence with the manufactur-ing operations, as established by the fabrica-tor. There are good reasons for doing this,some of which are the following:

(1) Interference between inspection andproduction is kept to a minimum.

(2) Inspection operations required at a par-ticular stage of fabrication can be completed(such as when performance of the next manu-facturing step would make inspection of thepreceding step impossible).

(3) In-process inspection permits earlydetection and correction of deficiencies,improving economics and efficiency.

The following sequence of welding andinspection operations is offered as a generaloverall guide. It should be understood that theactual operations and the order in which theyare accomplished will depend upon the type

of weldment, the method of manufacture, andthe requirements of the governing contract.The inspector may want to establish witnessor hold points to verify one or more of theitems shown in Table 4.1.

4.5 Selection and Examination of Production Test Samples

In many types of welded assemblies, cer-tain inspections of the finished product maybe performed on samples selected by thewelding inspector from the production line.These samples may be selected at random, orin accordance with established criteria. Ineither case, the selection and the witnessingof the testing of these samples are among theimportant duties of the welding inspector. Insome cases, selection of samples is left to thejudgment and discretion of the weldinginspector, rather than prescribed by specifica-tion or code. In such cases, the number ofsamples should not be more than is needed toreasonably determine conformance to therequired standards. It is common practice formost contracts to mandate a specific samplingplan and, further, to require additional sam-pling be performed for each unsatisfactorysample until workmanship standards are con-firmed.

Certain tests or treatments may be pre-scribed for the samples selected by thewelding inspector. These may include radiog-raphy, hydrostatic tests, trepanning, metallur-gical examination, mechanical testing todestruction, or other detailed examinations.The welding inspector should determine thatsuch work, as prescribed, is properly carriedout. Various sampling, testing, and inspectingmethods are described in this handbook.

4.6 Evaluation of Test Results

It would be impractical for the weldinginspector to perform or witness all tests madein connection with some weldments. Wherethe job requires, however, the welding inspec-


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

22/Welding Inspection Operations

tor should witness or observe sufficient testprocesses to assure that the tests are beingperformed in the proper manner and that theresults are accurate. Evaluation and final dis-position of test results will usually require thewelding inspector to carefully consider theattributes of the entire process.

From time to time, the welding inspectorwill review test or inspection results that donot meet the required standards for accep-tance in every detail. The final disposition ordecision will require careful judgment byappropriate technical personnel as to whetherthe product meets the intent of the specifica-tion requirements. In such cases, the results ofthe test should be carefully evaluated. In someinstances, such as inadvertent inspection of

work not intended to be or not required to beinspected, or when the work has borderlineacceptability, an engineering judgement byappropriate technical personnel should bemade as to the acceptability of the product.Engineering judgements should be performedonly where the specification or contractallows and only when sufficient informationis available from which to exercise soundjudgment.

4.7 Preparation of Test Reports and Maintenance of Records

Any work performed under a specificationor code that requires inspection or tests willalso require records. However, whether

Table 4.1Sequence of Welding and Inspection Operations

Prior to Welding During Welding After Welding

• Material Identification— Chemical analysis— Mechanical properties

• Base Metal Conditions— Freedom from internal and

surface discontinuities— Flatness, straightness,

dimensional accuracy• Joint Condition

— Edge Shape— Dimensional accuracy— Cleanliness— Root opening— Alignment— Backing— Tack welds

• Special Assembly/Fabrication Practice— Adequacy and accuracy of

jigging, bracing, or fixturing

— Application and accuracy of pre-stressing or precambering

• Preheat and interpass temperatures— Controls— Measurement methods

• Filler Metal— Identification— Control— Handling

• Root Pass— Contour— Soundness

• Root preparation prior to welding second side

• Cleaning between passes• Appearance or passes

(sometimes in comparison with workmanship standard)

• In-process NDE as required or specified

• Conformance to approved welding procedure

• Postheat treatment requirements• Acceptance inspection• Method of cleaning for

inspection• Nondestructive examination

— Visual examination— Surface contour and finish

of welds— Conformity of welds with

drawings— Magnetic particle— Liquid penetrant examination— Radiographic examination— Ultrasonic examination— Proof testing— Other suitable methods

• Destructive testing— Chemical— Mechanical— Metallographic

• Marking for acceptance or rejection

• Repairs• Inspection after repair


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Welding Inspection Operations/23

required or not, the welding inspector shouldkeep adequate records. Records provide doc-umentation for the welding inspector shouldquestions arise at some later time.

It is also the welding inspector’s duty tocheck his/her records for completeness andaccuracy in accordance with specifiedrequirements and to make certain that they areavailable when needed.

Any records that require the fabricator’ssignature should be prepared by the fabricatorrather than by the welding inspector.

Records should contain as much detail asnecessary. It is desirable that the weldinginspector comment on the general characterof the work, how well it stayed within pre-scribed tolerances, difficulties that wereencountered, and whether any defects werenoted. All repairs should be explained. Copiesof these records should go to all persons enti-tled to receive them, and the welding inspec-tor should keep a copy on file.

4.8 Observance and Monitoring of Recommended Safety Guidelines

Another of the welding inspector’s duties isto recognize a safety hazard that could resultin injury to welding and inspection personnel.For more information, refer to Chapter 5,“Inspection Safety Considerations” or ANSIZ49.1,

Safety in Welding, Cutting, and AlliedProcesses

. Well versed welding inspectorsshould be able to recognize problems such aspoor ventilation, which could cause dizzinessand cause injury to the welder.

When welding is being performed it is agood idea to assure that all aspects of weldingsafety procedures are being followed. This istrue not only for proper welding quality, but tomake the shop a safe place to work. Thesepractices do not only show up in good weldquality, but result in money saved in the pre-vention of down time due to accidents.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

25

5.1 Scope

Safety is an important consideration in allaspects of nondestructive examination (NDE)methods. This chapter covers hazards thatmay be encountered with nondestructiveinspection equipment and processes. Theinspector should read and understand themanufacturers’ instructions and the materialsafety data sheets (MSDSs) on safety and rec-ommended practices for the inspection pro-cess, materials, and equipment, to minimizepersonal injury and property damage, andassure proper disposal of wastes.

The NDE methods used that are applicableto the inspection of weldments listed belowwill be discussed in this chapter:

(1) Visual Testing (VT)(2) Liquid Penetrant Testing (PT)(3) Magnetic Particle Testing (MT)(4) Radiographic Testing (RT)(5) Electromagnetic Testing (ET)(6) Ultrasonic Testing (UT), and(7) Acoustic Emission Testing (AET)

5.2 Visual Testing (VT)

Lighting of the weld joint should be suffi-cient for good visibility. In addition to ambi-ent light, auxiliary lighting may be needed.The inspector should be aware that improperlighting may cause eye problems. If the areato be inspected is not readily visible, theinspector may use mirrors, borescopes, flash-lights, or other aids.

5.3 Liquid Penetrant Testing (PT)

Liquid penetrant inspection material con-sists of fluorescent and visible penetrants,emulsifiers, solvent base removers, and devel-oper. These materials typically contain

trichloroethylene, trichloroethane, methylchloroform, perchloroethylene, acetone, or avolatile petroleum distillate. These materialsmay be toxic or flammable, or both. The fol-lowing safety and health inspection precau-tions are recommended per the materialsafety data sheets by the manufacturer andshould be observed:

(1) Keep flammable materials away fromheat, arcs, and flames. Do not smoke in workareas. Do not puncture, incinerate, or storepressurized containers above 120ºF (48ºC).Aerosol cans may rupture at temperaturesabove 130ºF (54ºC) and spray out flammableliquids.

(2) Use chemicals in well-ventilated areasonly. Avoid breathing vapors or spray mists.Inhalation of vapors may cause dizziness andnausea. When affected by fumes, move thevictim to fresh air.

(3) If a solvent or other chemical isingested, do not induce vomiting. In all cases,immediately call a physician.

(4) Wear appropriate eye protection at alltimes. If a chemical or foreign particle entersan eye, flush the eye promptly with water.

(5) Avoid repeated or prolonged skin con-tact with solvents and other test substances.After contact, wash the exposed areaspromptly, and apply a soothing lotion.

(6) Verify all chemical containers in thework area are clearly labeled with the con-tents. Never use a chemical from an unlabeledcontainer.

(7) Do not combine products from differentmanufacturers in the same container.

5.4 Magnetic Particle Testing (MT)

Operators should be aware of any potentialhazards and know how to prevent them. The

Chapter 5Inspection Safety Considerations


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

26/Inspection Safety Considerations

following precautions are recommended perthe Material Safety Data Sheets by the manu-facturer and should be observed.

Magnetic powders should be kept dry andprotected from moisture at all times. Oil-based suspensions may be flammable andshould be handled with care where ignition ispossible. Be aware that water-based suspen-sions may contribute to a shock hazard whenused near electrical equipment.

5.5 Radiographic Testing (RT)

Federal, state, and local governments issuelicenses for the operation of industrial radio-graphic equipment. The federal licensing pro-gram is concerned mainly with thosecompanies that use radioactive isotopes assources. To become licensed under federalprograms, a facility or operator should showthat it meets standard protection of both oper-ating personnel and the general public fromexcessive levels of radiation.

The amount of radiation that is allowed toescape from the area over which the licenseehas direct and exclusive control is limited toan amount that is safe for continuous expo-sure. In most cases, a maximum exposure of2 millirems per hour (2 mrem/h), 100 mremin seven consecutive days, or 500 mrem in a12-month period is considered to be safe.

5.5.1 Radiation Monitoring.

A radiationsafety program should ensure that both thefacility and all personnel subject to radiationexposure are monitored. Facility monitoringgenerally is accomplished by periodicallytaking readings of radiation leakage duringoperation of each source under various condi-tions. Calibrated instruments should be usedto measure radiation dose rates at variouspoints within the restricted area and at variouspoints around the perimeter of the restrictedarea.

To guard against inadvertent leakage ofradiation from a shielded work area, inter-locks disconnect power to an X-ray tubewhen an access door is opened, or preventsany door from being opened if the unit is

turned on. Alarms are connected to a separatepower source which activate audible or visi-ble signals, or both, whenever the radiationlevel exceeds a preset value.

All personnel within the restricted areashould be monitored to assure that no oneabsorbs excessive amounts of radiation.Devices such as pocket dosimeters and filmbadges are the usual means of monitoring.Often both devices are worn. Pocket dosime-ters may be direct reading or remote reading.

5.5.2 Access Control.

Permanent facilitiesare usually separated from unrestricted areasby shielded walls. Sometimes, particularlywith on-site radiographic inspection, accessbarriers may be only ropes and sawhorses, orboth. In such instances, the entire perimeteraround the work area should be under contin-ual surveillance by radiographic personnel.Signs that carry a symbol designated by theU.S. Government should be posted aroundany high-radiation area. This helps to informcasual bystanders of the potential hazard, butshould never be assumed to prevent unautho-rized entry into the danger zone. In fact, nointerlock, no radiation alarm, and no othersafety devices should be considered a substi-tute for constant vigilance on the part ofradiographic personnel.

5.6 Electromagnetic Testing (ET)

Electromagnetic testing, commonly callededdy current testing, uses alternating currentsources, therefore, normal electrical precau-tions should be observed—see Electrical Haz-ards section 5.8. Eddy current testing does notpresent unique safety hazards to personnel.

5.7 Ultrasonic Testing (UT) and Acoustic Emission Testing (AET)

With high-power ultrasonic and acousticemission equipment, high voltages arepresent in the frequency converter and thecoaxial cables connecting these components.The equipment should not be operated with


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Inspection Safety Considerations/27

the panel doors open or housing coversremoved. Door interlocks are usuallyinstalled to prevent introduction of power tothe equipment when the high voltage circuitryis exposed. The cables are fully shielded andpresent no hazard when properly connectedand maintained. All operators should bewareof electrical hazards. See Electrical Hazardssection 5.8.

5.8 Electrical Hazard

Electrical shock can kill. However, it canbe avoided. Do not touch live electrical parts.Read and understand the manufacturinginstructions and recommended safe practices.Faulty installations, improper grounding, andincorrect operation and maintenance of elec-trical equipment are all sources of danger.

Make sure all electrical connections aretight, clean, and dry. Poor connections canoverheat and even melt. Further, they can pro-duce dangerous arcs and sparks. Do not allowwater, grease, or dirt to accumulate on plugs,sockets, or electrical units. Moisture can con-duct electricity. To prevent shock, keep thework area, equipment, and clothing dry at alltimes. Wear dry gloves, rubber soled shoes, orstand on a dry board or insulated platform.

Keep cables and connectors in good condi-tion. Improper or worn electrical connectionsmay set up conditions that could cause elec-trical shock or short circuits. Do not useworn, damaged, or bare cables. Do not touchlive electrical parts.

In case of electrical shock, turn off thepower. If the rescuer must resort to pulling thevictim from the live contact, use nonconduct-

ing material. If the victim is not breathing,qualified personnel should administer car-diopulmonary resuscitation (CPR) as soon ascontact with the electrical source is broken.Call a physician and continue CPR untilbreathing has been restored, or until a physi-cian has arrived. Cover electrical or thermalburns with a clean, dry, and cold (iced)compress to prevent contamination. Call aphysician.

5.9 General Safety Information

(1) Wear proper eye and hand protection.Use face shields, safety glasses, and gogglesas appropriate. Should a foreign particle enteran eye, promptly flush the eye with water tominimize irritation.

(2) Be aware of electrical hazards—seesection 5.8.

(3) Be alert for sharp objects, pinch points,and moving objects. Avoid wearing clothingor jewelry that could be snagged by movingmachinery. Items of particular concern arerings, necklaces, bracelets, long hair, andloose clothing.

5.10 References

1.

Welding Handbook

, Volume 1. AmericanWelding Society, Miami, Fla.

2. Manufacturer’s Instructions and MaterialSafety Data Sheets (MSDSs).

3.

Training for Nondestructive Testing

.ASNT and ASM International, MetalsPark, Ohio.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

29

Chapter 6

Quality assurance (QA) includes allplanned and systematic actions necessary toprovide adequate confidence that a structure,system, or component will perform satisfacto-rily to design requirements or intended ser-vice. This includes periodic audits of the QAsystem’s operation and related controls toassure that they are being implemented andfunctioning as expected.

Quality control (QC) is the implementationpart of quality assurance through examinationof physical characteristics and comparisonwith predetermined requirements from appli-cable codes, specifications, other standards,and drawings. A quality control program maystand alone or be part of a larger QA plan. Ineither case, quality control specifications,procedures, and acceptance criteria should bewritten for all required inspection operations.If a quality program is to be implemented, thefollowing attributes may be a consideration.

6.1 Quality Assurance Program

It is the responsibility of the manufacturerto provide for the development and imple-mentation of a QA program. The programshould describe the company’s commitmentto provide products and services in accor-dance with established requirements. The fol-lowing representative areas to be included ina quality assurance program that describes theelements of a QA system are subsequentlysupported by detailed QC implementationprocedures.

6.1.1 Organization Requirements.

Adminis-tration of the quality assurance program isvested in a responsible element of the organi-zation. The QA/QC function’s authority andresponsibility should be clearly defined, inde-pendent of production, and have direct access

to upper management. The organizationshould be staffed with technically qualifiedpersonnel to make decisions with regard to:

(1) Identification of quality problems,(2) Determining compliance with specifica-

tions and procedures,(3) Providing solution(s) through func-

tional channels,(4) Determining implementation of solu-

tions, and(5) Controlling further actions until an

acceptable quality has been attained.

6.1.2 Purchasing.

The quality assurancedepartment should determine quality assur-ance and inspection requirements for theproject, the magnitude of the inspection workfor each class of material and equipment, andthe extent of the work to be performed by thedepartment prior to purchasing.

The quality assurance and inspectionrequirements for procured items should beincluded in the purchase requisition andinclude the following, as applicable:

(1) Descriptive title of item or servicedesired

(2) List of drawings and technical specifi-cations, including revision level

(3) Codes, other standards, and regulatoryrequirements

(4) Inspection acceptance criteria(5) Special process requirements(6) Customer contract requirements(7) Documentation and record requirements(8) Source inspection and audit requirementsPurchasing should maintain an approved

list of acceptable vendors that comply withthe specified QA and QC program for theproject. This list should be maintained toensure vendors are selected that have anacceptable QA/QC program. In the event aquality assurance program is not being used,

Chapter 6Quality Assurance


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

30/Quality Assurance

the quality control program should encom-pass the qualifications of the vendors.

6.1.3 Document Control.

Control of docu-ments relating to engineering, procurement,policies, procedures, and instructions shouldbe maintained. Procedures should be imple-mented to provide appropriate review ofchanges prior to revision and issuance ofthese documents. Document control measuresshould include the following:

(1) Identification of individuals responsi-ble for preparation, revision, review, approval,and distribution of documents

(2) Use of correct documents identified andverified

(3) Procedures for controlling receipt,reproduction, distribution, storage, andretrieval of contract documents.

6.1.4 Process Control.

Manufacturing pro-cesses should be controlled and implementedusing established procedures for standardcommercial processes and special manufac-turing processes. Special processes such aswelding, heat treating, nondestructive exami-nation, testing, and inspection should becontrolled and accomplished by qualified per-sonnel. Special process procedures shoulddefine process methods, personnel trainingand qualification criteria, required certifi-cation and records, as well as requirementsfrom applicable codes, other standards, andspecifications.

Welding procedures should be reviewedprior to use to ensure that the procedures meetthe specification requirements. Audits or sur-veillance should be performed during produc-tion to ascertain that the correct proceduresare being implemented. Welder performancerecords should be audited periodically todetermine that welders are properly qualifiedto procedures being used for fabrication. Ifrequired by specifications, permanent identifi-cation or records of welders’ performancequalifications should be maintained. It shouldbe noted that a decision to inspect only aftercompletion of welding is not the best way toensure quality.

6.1.5 Inspection.

The quality control person-nel who perform inspections during the vari-ous stages of fabrication should be qualifiedin accordance with a formal certification pro-gram. It is the responsibility of those chargedwith the administration and supervision ofinspection to assure that inspectors are quali-fied and certified. Quality control personnelshould perform nondestructive examinationand destructive testing in accordance withestablished procedures.

Certification of inspection personnel maybe required by contract, codes, specifications,or civil laws. In this regard, it may be benefi-cial to consider certification of weldinginspectors by the American Welding Societyunder the Certified Welding Inspector (CWI)and Certified Associate Welding Inspector(CAWI) programs. The American Society forNondestructive Testing (ASNT) and AWSprovide certification guidelines for NDE per-sonnel. Other programs may be used for certi-fication of inspection personnel.

Inspection activities may be performed byquality control personnel in accordance withwritten procedures and instructions to assurethat the product meets applicable require-ments. The welding inspector determines theaccuracy, completeness, and acceptability ofmaterials and workmanship. Inspection activ-ities also include verification that:

(1) Measuring and test equipment used forinspections are calibrated.

(2) Process hold points are observed.(3) Surveillance of manufacturing activities

is accomplished.(4) Material receiving inspection is performed.A sampling program may be used to verify

acceptability of a group of items. The sampleprocedure should be based on standard prac-tices and provide sample size and selectionprocess. For example, MIL-STD-105 providessample sizes and acceptable quality levels.

6.1.6 Identification and Control of Mate-rial.

The QA/QC procedures should specifythe requirements and control of items. Identi-fication and control may be maintained byheat number, part number, serial number, or


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Quality Assurance/31

purchase order number. The identificationshould be placed on the item. Identificationmarking should be clear and applied so as notto affect the function or identity of the itemduring processing.

6.1.7 Nonconforming Materials or Items.

The QA/QC program should establishdetailed written procedures that describe thecontrols used for the identification, documen-tation, segregation, and disposition of non-conforming items, material deficiencies, andprocedural requirements. Individuals havingthe responsibility and authority for the dispo-sition of nonconforming items or deficienciesshould be identified in the procedures. Itemsthat do not meet requirements should be soidentified to prevent inadvertent use.

6.1.8 Records.

Records should document thequality of items and should meet the require-ments of the applicable codes, other stan-dards, specifications, and contracts. Records

may include results of inspections, audits,material analyses, and process and test activi-ties. Quality procedures should describe thenecessary controls for the identification, prep-aration, legibility, maintenance, and retrievalof these records, and how they are to be pro-tected against damage, deterioration, or loss.Unless otherwise specified by the engineeringdesign, the retention of records should bebased on the requirements of the applicablestandard for the project.

6.1.9 Audits.

Audits are useful to verify com-pliance with a quality assurance program andcontract requirements and determine theeffectiveness of the program. A system shouldbe established by QA/QC procedures forinternal and external audits. The audit proce-dures should include the requirements fortraining and qualifying auditors, the planningand scheduling of audits, preparation of auditreports, and resolution of audit findings andimplementation of corrective actions.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

33

This is an introduction to metallurgicalconcepts that influence welding processes andwelding quality control. Special emphasis isplaced upon the terms often used duringinspection activities.

This chapter is intended to provide intro-ductory material. Simplified definitions andexplanations will at times be employed.

7.1 Carbon Steel

The two general types of steel are plain car-bon steels, and alloy steels.

Plain carbon steel contains iron with con-trolled amounts of carbon.

Among plain carbon steels are: low-carbontypes which contain less than 0.30% carbon(C); medium-carbon steels contain approxi-mately 0.30–0.55% C; and high-carbon steelscontain up to 1.7% C.

Alloy steel may be defined as a steel whosedistinctive properties are due to the presenceof one or more elements other than carbon.

The following are some elements which arealloyed with carbon steels:

(1)

Chromium

. Increases resistance to cor-rosion; improves hardness and toughness,improves the response to heat treatment.

(2)

Manganese

. Increases strength andresponsiveness to heat treatment.

(3)

Molybdenum

. Increases toughness andimproves strength at higher temperatures.

(4)

Nickel

. Increases strength, ductility andtoughness.

(5)

Vanadium

. Retards grain growth andimproves toughness.

Plain carbon steels contain iron plus smallquantities of other elements. The five mostcommon elements mixed with iron and theirquantitative limits in a representative grade,AISI/SAE 1020 steel, are the following:

(1) Carbon (C) 0.18–0.23%(2) Manganese (Mn) 0.30–0.60%(3) Silicon (Si) 0.30% max(4) Phosphorus (P) 0.040% max(5) Sulfur (S) 0.050% max

These are commonly called

ferritic

or

ferrite-pearlite steels

. The terms

ferrite

and

pearlite

refer to the microstructural aspects of theslowly cooled steel, but, as will be shown,other microstructures can form if the steel israpidly cooled from high temperatures.

Slowly cooled plain-carbon steels have auniform microstructure with low tensilestrength and high ductility. These propertiescan be changed by heat treating, mechanicalworking, addition of alloying elements, orcombinations thereof. The effect of heatingand cooling is of particular interest to weld-ing, since part of the metal is heated to themelting point in most welding processes.

When plain-carbon steel is heated duringwelding or heat treating, the first importantchange, a predominately mechanical one,starts at about 950

°

F (500

°

C). The changelowers the yield strength of the steel. Some ofthe residual stresses caused by cold workingor weld shrinkage are relieved, and the mate-rial is softened.

A major metallurgical change occurs whenferritic steel is heated above its lower trans-formation temperature, often referred to asthe

A

1

temperature

. The temperature thatshould be reached to complete the transfor-mation, which is referred to as

upper trans-formation temperature

, depends upon thespecific chemical composition of the steel.For plain-carbon steel (e.g., AISI 1020), thetransformation temperature is at about1560

°

F (850

°

C). Figure 7.1 shows thechanges that occur at various temperaturesduring heating and cooling.

Chapter 7Ferrous Welding Metallurgy


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

34/Ferrous Welding Metallurgy

It is important to note that metallurgicalchanges occur every time a weld bead isdeposited. Changes in the metallurgical prop-erties also occur in the base metal adjacent tothe bead that did not melt during the weldingprocess. This area is called the heat-affectedzone (HAZ). The width of the HAZ is prima-rily determined by the amount of heatapplied, and the metal’s chemistry and thick-ness. Aluminum welds, for example, exhibitlarger HAZs than welds in steel because alu-minum conducts heat faster than steel, i.e.,has a higher thermal conductivity.

As a weld cools, two major events occur:(1) Residual stresses and distortions

develop. These stresses are caused by a com-bination of expansion and shrinkage duringthe cooling and solidification of the metal.Shrinking and expansion may be due to ther-mal contraction and expansion, and they may

be complicated by metallurgical transforma-tions to other phases which have differentdensities. The resulting mechanical effects arediscussed in Chapter 9.

(2) The mechanical properties of the weldmetal and the HAZ are changed. Thesechanges depend markedly on the rate atwhich the cooling takes place through themetal’s transformation range. If slow coolingcan be achieved, the transformation cycleupon cooling will be the reverse of the trans-formation cycle upon heating. Although grainsize may be changed, as shown in Figure 7.2,the HAZ will contain a combination of eitherferrite and pearlite, or pearlite and cementite,depending on the chemical composition ofthe steel. Because these products were notquenched to produce hard martensite, thestrength will be similar to the original softbase metal.

Cooling rates can be affected by total heatinput, and preheat temperature, and themetal’s size, thickness, and thermal conduc-tivity. Since the mass melted during weldingis usually quite small compared to the adja-cent base metal, rapid cooling rates do occur.This can be observed by noting that the weldbead cools from the molten state to about1200˚F (650˚C) in just a few seconds. Whenvery-low-carbon steels (e.g., modern lower-strength steels with less than 0.10% C) arecooled rapidly, the steel remains soft and duc-tile. For this reason, many types of weldingelectrodes are designed with relatively lowcarbon content. However, conventional plaincarbon steels containing between 0.18–0.35%C are commonly used for piping, pressurevessels, and structures. The rapid cooling rateassociated with welding tends to produceharder and less-ductile metallurgical struc-tures called martensite or bainite. Both mar-tensite and bainite have a needle-like oracicular appearance, as shown for martensitein Figure 7.3.

While a certain amount of martensite andbainite is normally unavoidable, their amountand their effect can be minimized by properbase metal and electrode selection, weldingtechnique, and proper preheating and inter-

Figure 7.1—Iron-CarbonPhase Diagram


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Ferrous Welding Metallurgy/35

pass temperatures. The need for such actionsbecomes more important as material thick-ness or carbon content, or both, increase.Thicker base metal removes heat in less timefrom the weld area and thus increases the rateof cooling. A unit called

carbon equivalent

(CE)

is often employed to predict the com-bined effect of carbon and manganese uponthe tendency to form martensite. For mild-carbon steel, the carbon equivalent is mostcommonly expressed as:

(Eq. 7-1)

The higher the CE and the thicker the mate-rial, the greater the need for preheating.

As the CE, or the thickness, or bothincrease, even the use of preheating and care-fully planned welding techniques may fail tolimit the amount of residual stresses andunwanted martensite formations. This mayintroduce the need for postweld heat treatment(PWHT). In most cases, this is accomplishedby heating the weldment between 950

°

F(500

°

C) and the lower transformation temper-ature of 1333

°

F (723

°

C). Within that tempera-ture range, the yield point of the materialdrops considerably. This causes locked in orresidual stresses to be lowered; at the highertemperatures within that range, some of themartensite will be softened. Metallurgistsrefer to the second effect of this operation,which softens the steel, as

tempering

. This

CE =%C %Mn4

-------- or CE = + %C + %Mn6

--------

Figure 7.2—Crystal Structure ofCold Rolled Steel in Weld Area

Figure 7.3—Martensite ShowingNeedle-Like or Acicular Structure

(500X Before Reduction)


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


explains why the PWHT operation is oftencalled “stress relieving” by the welder and“tempering” by the metallurgist.

7.2 Low-Alloy Steels

Alloy steels contain carbon and other inten-tionally added elements, such as nickel, chro-mium, copper, molybdenum, and vanadium.Other elements may also be added for specialapplications that do not involve welding.

Weldable alloy steels are designed to permithigher strength with adequate ductility, low-temperature notch toughness, improved corro-sion resistance, or other specific properties.

The welding engineer should select elec-trodes capable of matching the mechanicalproperties and the chemical composition ofthese alloy steels in order to achieve a uni-form structure.

Although the addition of such elements aschromium, nickel, molybdenum, copper, andvanadium can significantly change the prop-erties of the steel, the basic metallurgicalconcepts are similar to those that apply toplain-carbon steel. Softening will startbetween 1000

°

F (540

°

C) and 1250

°

F(680

°

C), depending upon the specific compo-sition. The lower transformation temperatureof a given alloy steel may be above or belowthat of a carbon steel. In general, nickel alloy-ing lowers the lower transformation tempera-ture, while chromium and molybdenumalloying raises the lower transformation tem-perature. Numerous reference books, such asthe

Atlas of Isothermal Transformation Dia-grams

, published by ASM International, con-tain information about alloy steels to allowreasonable estimation of the transformationof many steels. Since this temperature variessome for each low-alloy steel classification,optimum PWHT temperatures should beestablished and documented for each. Forseveral alloy steels, it is not uncommon tostress relieve the welded component at muchhigher temperatures.

During welding, part of the alloy steel willpass through the lower and the upper transfor-mation temperatures. In this respect, there is

little difference between plain carbon andlow-alloy steel. Also, all other things beingequal, the weld cooling rate for low-alloysteels is the same as the rate for plain-carbonsteels. However, the alloy material is moresusceptible to hardening, to embrittling, andsubsequently to cracking, since martensitecan form at slower cooling rates. The abilityof the alloy steel to form martensite can againbe expressed as a carbon equivalent (CE) forwhich there are many similar formulas thatinclude many elements in addition to carbonand manganese. The following formula iscommonly used to show the effects of addingvarious elements to alloy steels, taken from

Welding Handbook

, Volume 4, 8th Edition:

(Eq. 7-2)

With a high CE, even a relatively slow cool-ing of the weldment will produce large quan-tities of martensite and bainite. Preheating,while essential for nearly all alloy-steelwelds, often fails to retard the cooling ratesufficiently; however, it can prevent crackingduring fabrication. Thus, PWHT is mandatoryfor many alloy steels to restore sufficient duc-tility prior to exposing the assemblies to ser-vice conditions.

7.3 Delayed Cracking

7.3.1 Causes of Delayed Cracking.

Delayedcracking is undoubtedly the most widespreadtype of heat-affected zone defect. The cracksmay form up to 48 hours after completion ofthe weld. The delayed cracking processdepends on the diffusion of soluble hydrogeninto the stressed sites. Common sites for thesecracks are in the toe or root of the weld, and atlocal details, which result in sharp stress con-centrations. A typical example is shown inFigure 7.4.

Buried underbead cracks may also beobserved, but these are less common. Thecracks are generally quite shallow, but can

CE = %C +%Mn

6------------- %Cr %Mo %V+ +

5----------------------------------------------+

%Ni %Cu+15

-----------------------------+


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


sometimes penetrate several millimeters intothe base metal. They are usually, but notexclusively, confined to the HAZ.

The formation of delayed cracks in theHAZ requires the presence of four indepen-dent conditions. If any one of these conditionsis missing, a delayed crack cannot form. Thefour conditions are: 1) the presence of hydro-gen; 2) a susceptible microstructure; 3) thepresence of stress; and 4) low temperature.Each of these four conditions is described indetail below.

7.3.2 Presence of Hydrogen.

All arc weldingprocesses introduce hydrogen into the weldmetal to various degrees. The hydrogen canoriginate from moisture in electrode coatings,shielding gases, and the flux. Moisture mayalso originate from oxides on the metal, fromhydrocarbons, lubricants, or other contami-nants on the plate or welding wire, and evenfrom the moisture in the room air.

The welding arc’s intense heat is sufficientto break down most compounds into their

constituent elements. Molten steel has a sub-stantial capacity for dissolving hydrogen.Immediately after solidification, the diffusionrate of hydrogen in steel is high. Thus, there isconsiderable potential for hydrogen to diffuseinto the HAZ during the welding operation.

While the steel is above the Ac tempera-ture, it has a relatively high solubility forhydrogen. However, upon cooling, it trans-forms to a phase that has a much lower solu-bility for hydrogen. As cooling continues, thesolubility decreases, as does the diffusionrate. The situation can arise where a supersat-uration of hydrogen exists that cannot diffuseaway. Under such conditions, the hydrogencan be a potent embrittling agent in the steel.

7.3.3 Susceptible Microstructure.

A widevariety of microstructure can exist in the HAZof carbon-manganese and low-alloy steels,depending on the composition of the steel andthe welding procedure. In general, only hardmicrostructures are susceptible to hydrogencracking. Such microstructures are promotedby high hardenability in the steel and by fastcooling rates (which also restrict the timeavailable for hydrogen diffusion), and aregenerally martensitic or bainitic in nature. Fastcooling rates are promoted by low-arc energylevels, low preheat/interpass temperatures andthick sections. The critical hardness level tocause cracking is a function of hydrogen con-tent of the weld, and to a lesser extent ofrestraint, but would typically be 350HV forhigh hydrogen levels and 450HV for lowhydrogen levels. There is a lot of evidence tosuggest that the critical hardness level islower in lower carbon equivalent steels.

7.3.4 Presence of Stress.

No crack of anydescription can form in the absence of stress.For hydrogen cracking, this would arise fromstresses imposed by the contraction on cooling.It should be recognized that the residual stressesdue to welding in a carbon-manganese steelcan be of yield point magnitude. The presenceof notches or sharp profile changes causesstress concentrations which can help initiatecracks.

Figure 7.4—Example ofDelayed Cracking in HAZ


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


7.3.5 Low Temperature.

The embrittlingeffect of hydrogen on steel is very dependenton temperature since the minimum notch ten-sile strength occurs at temperatures of onlyslightly above ambient. At higher tempera-tures, the cracking is less likely to form sincehydrogen can more readily diffuse away, andthe inherent toughness of the steel is alsoincreased. At lower temperatures, the hydro-gen is effectively immobilized by its low dif-fusion rate, although the toughness of thesteel will also decrease.

The mechanism of hydrogen embrittlementis complex, and is far from being totallyunderstood.

The term

delayed cracking

is sometimesused to describe hydrogen cracking. Oftencracks are not detected until some time afterthe weld has been completed and cooleddown. One school of thought suggests that itinitiates very soon after ambient temperatureshave been reached, but that the rate of growthis fairly slow, and a considerable time isrequired to allow the defect to grow to adetectable size. However, it is also notuncommon for an incubation period of crack-ing to occur, associated presumably with timerequired for hydrogen to diffuse to appropri-ate areas.

7.4 Prevention

Since delayed cracking requires four condi-tions to be present at the same time. Delayedcracking can be minimized or eliminatedcompletely by removing or controlling anyone of those conditions.

7.4.1 Controlling the Presence of Hydro-gen.

It is possible to severely limit the amountof hydrogen entering the weld metal by theuse of suitably prepared consumables, use oflow-hydrogen electrodes, and by scrupulouscleanliness. Flux shielded welding processes,including flux cored arc welding, can intro-duce hydrogen through moisture in the fluxbecause it is generally impossible to removeall the inherent moisture. In fact, moistureremoval from cellulosic coated electrodes

(EXX10 type) is undesirable because theseelectrode types require a reducing atmospherein the arc to work satisfactorily.

The manufacturer’s instructions for thecare and storage of welding consumablesshould be carefully followed.

Note that “low hydrogen” as applied toconsumables does not mean hydrogen-free.Even low-hydrogen consumables can contrib-ute the hydrogen needed to cause delayedcracking. The moisture content of fluxes andelectrodes can be reduced by drying the elec-trodes or fluxes in ovens. The electrode manu-facturer should be consulted regarding theproper oven temperature. Care should betaken to ensure that ovens are not overloaded,and that drying lasts sufficiently long toensure that

all

the contents receive the mini-mum baking time at the correct temperature.

Recently, fluxes and coatings that aresignificantly less hygroscopic have beendeveloped. However, the coatings on low-hydrogen electrodes will absorb moisture rap-idly if not stored at proper temperatures or inairtight containers.

The hydrogen level can also be reduced bythe use of gas shielded processes such as gasmetal arc welding (GMAW) and gas tungstenarc welding (GTAW). Maximum diffusiblehydrogen levels under specific test conditionsfor various types of welding electrodes andwires can be included on product purchaseorders by invoking optional supplemental dif-fusible hydrogen designators which areincluded in AWS filler metal specifications.

Cleanliness of the weld joint, wire, andwelding apparatus is also important. Paint,rust, grease, degreasing agents, and lubricantson welding wire are other potential sources ofhydrogen.

Another prevention measure is to removesome of the hydrogen that inevitably entersthe weld, such that the levels are reduced toacceptable values by the time the weld hascooled. This is achieved by increasing theduration of the weld thermal cycle, usually byapplying a preheat. This reduces the coolingrate and therefore allows more time for thehydrogen to diffuse away from the weld zone.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Maintenance of the proper interpass tempera-ture will prevent the weld from cooling intothe range of maximum embrittlement, andwill also aid hydrogen diffusion. However,the interpass temperature should be suffi-ciently low to permit the austenite decompo-sition reaction to go to completion, sinceaustenitic weld metal has a comparativelyhigh solubility for hydrogen. The use ofhigher arc energies is also beneficial since thisalso increases the duration of the thermalcycle. However, the use of high arc energiescan result in a loss of toughness in both weldmetal and heat-affected zone (HAZ). Hydro-gen levels can also be reduced by post-weldheat treatment for several hours after welding,possibly at a higher level than was used forpreheating during welding.

In severe cases where it is not possible toapply preheat, or dry electrodes satisfactorily,austenitic filler metal can be used. This tech-nique is particularly valuable when undertak-ing difficult repairs on very hardenable steels.Austenitic stainless steel weld metal has acomparatively high solubility for hydrogen,coupled with a low diffusivity. The hydrogentherefore tends to remain in the austeniticweld metal, where it is relatively harmless.While providing a method for reducing thesusceptibility for hydrogen cracking, the useof austenitic stainless steel for welding alloysteel should be considered carefully by theengineers to ensure that issues of corrosion,differences in thermal expansion, and othermetallurgical factors are considered.

7.4.2 Microstructural.

The risk of delayedcracking in the HAZ is reduced as the hard-ness decreases. The hardness level in carbon-manganese and low-alloy steels increases asthe cooling rate through the transformationtemperature ranges increases, since this leadsto the formation of lower temperature trans-formation products such as martensite andlower bainite, which have lower inherent duc-tility. The formation of these hard constitu-ents can be restricted by the following:

(1) Reducing the cooling rate by using ahigher heat input.

(2) Using a suitably developed multipassprocedure in which the hard HAZ constituentsof one pass are heated by subsequent passes.This can result in retransformation to a softermicrostructure, or tempering of the hard struc-tures without subsequent transformation.

(3) Increasing the preheat/interpass temper-ature level to reduce the cooling rate throughthe transformation temperature range.

It should be noted that items (1) and (3)will also aid hydrogen diffusion, althoughthey may conflict with other requirements,such as achieving good toughness.

7.4.3 Restraint.

The restraint of a weld isoften difficult to vary, although a certaindegree of control can be exercised by alteringthe edge preparation, strongback design, etc.In production, the restraint imposed on twoidentical joints may vary considerably. Forinstance, a weld made early in a rigid struc-ture will be lightly restrained, but identicalclosing welds that complete the structure maybe highly restrained. Since restraint is diffi-cult to predict or control in practice, it isadvisable to ensure that conditions of highrestraint are present in procedural trials by theuse of suitable strongbacks, end beams to pre-vent angular rotation and lateral contraction,or both. Restraint is also increased by poorfit-up.

7.4.4 Temperature.

Delayed cracking ismost likely to occur at temperatures below212°F (100°C). The use of high preheat andinterpass temperatures will promote hydrogendiffusion, thus reducing the risk of cracking.In some instances, such as repair welds onthick sections in confined situations, it may beimpractical to apply a stipulated preheat leveland maintain an environment in which awelder can comfortably work. In such cases,the use of the maximum feasible preheatwould be required. The temperature shouldthen be increased to 400°–475°F (200°–250°C) after completion of welding—withoutallowing the weld to cool—thereby allowingadditional time for the hydrogen to diffuse outof the metal.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


7.5 Austenitic Stainless Steel

The most common austenitic stainlesssteels contain between 18 and 25 percentchromium and between 8 and 20 percentnickel as primary alloying elements. Productforms such as plates, castings, forgings, andfiller metals are classified by a three-digitnumbering system and can be easily recog-nized since the first digit is a 3, and thedetailed chemical composition is indicated bythe last two digits. These materials are oftenreferred to as

austenitic chromium-nickelsteels

or 300-series steels.The 300-series steels have many chemical

and metallurgical characteristics that clearlydistinguish them from ferritic steels such asplain carbon or low-alloy steels. Specifically,the 300-series steels are more corrosion resis-tant in most environments and nonmagneticor only slightly magnetic, have higher tensileand creep strength at elevated temperatures,and cannot be hardened by heat treatment.

Austenitic stainless steels do not undergothe normal phase changes associated withferritic steels. While plain-carbon steel is aus-tenitic and nonmagnetic at elevated tempera-tures, it will transform into ferrite, pearlite,martensite, and other phases as it is cooledthrough the transformation range.

However, when austenitic stainless steel iscooled, all or nearly all of the material isretained as austenite at room temperature.Without phase changes, no hardening willoccur. Thus, hard areas are not found in theheat-affected zone (HAZ) of 300-series stain-less steels. This reduces the need for preheat-ing and postweld heat treating.

This chapter will not discuss the differentgrades of stainless steels and the optimumapplication of each. However, when thesematerials are welded, two forms of metallur-gical degradation can occur: sensitization andmicrofissuring.

The corrosion resistance of the 300-seriesstainless steels depends upon the addition ofvarious alloying elements, of which chro-mium is of primary importance. If the alloy isheated to the sensitization temperature range

of 800–1600

°

F (425–870

°

C), some of thechromium can combine with any carbon thatis available and form a chromium-rich precip-itate. Whenever this occurs, as it can in cer-tain zones during welding, less chromium isavailable to resist corrosion. This is especiallyserious if the corrodent is an acid (for exam-ple, see Figure 7.5).

This sensitization can be overcome by anyone of the following actions:

(1) Heat the steel after welding to about1900

°

F (1050

°

C) to dissolve the carbides, andcool rapidly through the sensitization range.This is called

solution annealing

. It is prac-ticed in steel and pipe mills, but it is not easilyadapted to shop assemblies and field erection.

(2) Use 300 series stainless steels in thefiller metal and base metal with low carboncontent. By limiting the percent carbon to amaximum of 0.03 or 0.04, these L grades(e.g., 308L, 316L, etc.) limit the amount ofcarbides that can form and thus limit theamount of chromium that may be depleted.Extra-low-carbon stainless steel filler metalare also available.

(3) Use stabilized stainless steel materials.Elements like columbium and titanium willcombine preferentially with carbon andreduce the carbon available to form chro-mium carbide. This will retain the chromiumdispersed for corrosion protection even when

Figure 7.5—Corrosion Attack ofSensitized Stainless Steel in

Acid Environment


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


reaching the sensitization range during weld-ing or other operations.

Microfissuring is another problem associ-ated with austenitic stainless steels. It wasnoted earlier that 300-series steels are pre-dominantly austenitic. Pure austenite hasexcellent mechanical and corrosion-resistantproperties. However, its ability to absorbimpurities without cracking during solidifica-tion and cooling from elevated temperaturesis limited. Low-melting point impurities maybe forced to the grain boundaries. Excessiveamounts weaken these grain boundaries, cre-ating the possibility of microscopic grain-boundary flaws called

micro-fissures

(shownon Figure 7.6). This condition is of greaterconcern when the solidification is under thehigh restraint associated with welding.

One method of reducing microfissuring isto disperse these impurities among discon-nected grain boundaries that surround islands

Figure 7.6—Microfissure inAustenitic Stainless Steel (100X)

of a second phase, delta ferrite. This isaccomplished by modifying the chemicalcomposition of the weld metal. Ferrite canabsorb many impurities, and will definitelyreduce microfissuring tendencies.

However, too much delta ferrite can cause asecond problem by transforming to sigmaphase when the metal is heated to tempera-tures associated with welding and heat treat-ing. Small amounts of sigma phase canembrittle large areas of stainless steel.

Minimum and maximum limitations on fer-rite are desirable to prevent microfissuringand sigma phase formation. Many nominallyaustenitic stainless steel electrode composi-tions can be formulated to produce depositswithin a specific Ferrite Number (FN) range,such as 4 to 10 FN or 5 to 15 FN. The FerriteNumber can be measured as a scheduledinspection operation by using a magneticgauge calibrated to AWS A4.2,

Standard Pro-cedures for Calibrating Magnetic Instrumentsto Measure the Delta Ferrite Content of Aus-tenitic and Duplex Austenitic-Ferritic Stain-less Steel Weld Metal

.

2

In addition, it ispossible to estimate the FN from the chemicalanalysis of the weld deposit using various“constitution diagrams.” Estimation by dia-gram should not be substituted for actualmeasurement.

7.6 Lamellar Tearing

Lamellar tearing occurs in rolled-steel platewhere welding imposes high through-thick-ness stress on the plate. The tear, or crack,usually occurs just outside the weld heat-affected zone (HAZ). It has a characteristicstepped appearance. Figure 7.7 shows a typi-cal lamellar tear.

The tear forms in two stages. First,through-thickness stress perpendicular tothe rolling direction separates rolled-outinclusions from the steel at their interface.Then, fractures perpendicular to the rolling

2. Available from American Welding Society, 550N.W. LeJeune Road, Miami, FL 33126.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


direction connect the inclusions to relievethrough-thickness stresses, resulting in thecharacteristic stepped appearance.

7.6.1 Causes.

Lamellar tearing results from acombination of through-thickness stress onthe plate resulting from welding and from use

Figure 7.7—Closeup of Lamellar Tear Under a Fillet Weld Showing Typical

Stepped Appearance (Magnification 8X)

of susceptible base material. Level ofthrough-thickness stress depends on jointdesign and on joint restraint.

7.6.2 Joint Design.

Corner joints impose thehighest level of through-thickness stress.Such joints are found in set-through nozzles,welded girders, and ring stiffeners in cylindri-cal structures, for example.

7.6.3 Joint Restraint.

Degree of jointrestraint is difficult to quantify. However,analysis of joint design can give a qualitativeindication of the amount of restraint to beexpected. A T-joint in a welded I-beam orgirder, for example, would produce moderatethrough-thickness restraint on the flange. Aweld of identical dimension that was acting asa stiffener or a closing weld in a rigid struc-ture would be highly restrained.

7.6.4 Material.

Susceptibility of a steel tolamellar tearing depends on its inclusion con-tent and on the shape and distribution of theinclusions (All steels contain some inclu-sions, by-products of the steel-refining pro-cess). Presence of a large number of widelyspread plate-like inclusions leads to poorthrough-thickness ductility and to high sus-ceptibility to lamellar tearing. Lamellar tear-ing rarely occurs in castings becauseinclusions in castings are not rolled flat butretain their spherical form.

A steel grade shows no correlation withsusceptibility to lamellar tearing. Neitherdoes steel composition. However, in carbon-manganese steel, measures of short-transversereduction in area (STRA) can relate to sulfurcontent and hence to inclusion content forspecific thickness ranges.

Thin plate, able to flex in response to stress,shows little susceptibility to lamellar tear-ing. Tears have been seen, however, in plate5/16 in. (8 mm) thick. The fact that materialis thin is not a guarantee that lamellar tearingwill not occur.

7.6.5 Avoidance.

Most measures to avoidlamellar tearing come at an increase in cost.However, experience indicates that added pre-ventive costs are substantially less than cost


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


of remedial action, including repair, late-delivery penalties, or subsequent litigation.

Preventive action relies on the use of non-susceptible material and avoidance of designsthat impose through-thickness stress. The fol-lowing are some approaches to minimizelamellar tearing:

(1) Change the location and design of thewelded joint to minimize through-thicknessstrains.

(2) Use a lower strength weld metal.(3) Reduce available hydrogen.(4) Use preheat and interpass temperatures

of at least 200

°

F (90˚C).

7.6.6 Material Selection.

Specification ofsuitable steels at the design stage will in mostcases avoid lamellar tearing. Where lamellartearing is a possibility, the designer shouldspecify steel of guaranteed through-thicknessductility.

7.6.7 Design to Avoid Through-ThicknessStress.

Attention to joint design in fillets, T-,and corner welds can significantly reduce riskof tearing. Where possible, design to avoidstress in the through-thickness direction. Usesuitably bevelled edge preparations on cornerjoints.

Designers should avoid use of excessivelythick material, which increases stiffness (andcost), complex node structures, unnecessarystiffeners, and other attachments. In lightlyloaded structures, cruciform joints maybe staggered to reduce risk of lamellar tear-ing, though this is generally considered poordesign practice.

7.6.8 Welding Procedures.

In general, modi-fications to welding procedures will not pre-vent lamellar tearing. The welding processhas little effect. High-heat-input processes,like submerged arc welding, reduce the riskby producing large HAZ with graduated hard-ness and strain gradients and low peak hard-ness. Electroslag and electrogas welding,sometimes cited as low-risk processes, are notnormally suited to joint designs consideredhere. High-heat-input processes deposit softweld metal, which can absorb some strain that

would otherwise go to the base plate. For sim-ilar reasons, selection of a low-strength con-sumable is advised. Some manufacturerssupply low-hydrogen electrodes specificallyformulated for avoidance of lamellar tearing.

The use of consumables that deposit weldmetal of unnecessarily high strength shouldbe avoided.

Where tearing is a risk and where base-material cannot be changed (e.g., in existingweldments). One or more layers of ductilematerial should be deposited onto the lamel-lar-tearing-susceptible substrate. Weld passesare then made on top of the buttering. Thesofter layers absorb contraction stresses, help-ing to prevent lamellar tears.

Evidence suggests that HAZ hydrogencracking can trigger lamellar tearing. If this isso, preheat and high-heat input would aid inits avoidance in steels.

7.6.9 Fabricating Techniques.

Joint designis important in avoiding lamellar tearing: atight fit raises the restraint stress on plate; alarge gap raises the volume of weld metalrequired. A gap of 0.04 to 0.12 in. (1–3 mm)is reasonable; this range is within require-ments of most welding codes. In some cases,soft steel wires can hold a root gap.

If the member being stressed through thethickness is buttered with a layer of weldmetal prior to welding the main joint, the pro-pensity for delaminating is reduced.

Peening, which introduces compressivestresses below the weld, has been suggestedas a preventive measure. However, peeningmay provide limited benefits and maydegrade toughness and lead to cracking in theweld metal.

7.7 Other Metallurgical Considerations

The soundness of a weld during fabricationand during its service life is influenced bymany metallurgical considerations. Whilemost are beyond the scope of this book and


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


the activities of an inspector, a few conceptshave been highlighted below.

Many elements are added to steel or otherbase metals to produce certain desirable prop-erties. However, certain elements mayseverely deteriorate the base and weld metalproperties by penetrating into the moltenweld metal. These include the following ele-ments that may be in contact with a metalduring welding related operations:

(1) Copper (in the form of contact tips andmagnetic particle examination prods)

(2) Lead (in the form of caulking or lining)(3) Sulfur (in the form of molecular sulfur

that has been deposited while the equipmentwas in service)

(4) Zinc when welding austenitic stainlesssteel and carbon steels (in the form of galva-nized components or cathodic protectionequipment)


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

45

Preheating and postweld heat treating maybe necessary in order to produce soundwelded assemblies for certain base metals andwelded joints. These preheat and postweldheat-treat requirements should be specified inthe applicable welding procedure specifica-tion(s) and should be followed during produc-tion welding.

8.1 Preheating

Preheating is the heating of the weld jointto attain and maintain the specified preheattemperature prior to welding. In addition toestablishing a preheat temperature, an inter-pass temperature limitation may need to beconsidered for many materials.

When preheating is specified, the entireweld joint area should be heated through themetal thickness to the desired minimum tem-perature. To obtain a uniform temperaturethrough the metal thickness, it is desirable tolocate the heating source(s) on one surfaceof the metal and to measure the metal tem-perature on the opposite surface. However,when heating and temperature measurementshould be done from the same surface, theinspector should be certain that more thanjust the surface has been heated; the heatshould have soaked through the entire mate-rial thickness.

In a multipass weld, the temperature of theweld area prior to depositing the next weldpass is called the

interpass temperature

.When specified, the interpass temperatureshould be checked prior to the next pass. Theapplicable code may specify the location atwhich interpass temperature is to be mea-sured. Welding may not continue if the mea-sured temperature is not within thetemperature range specified in applicable

welding procedures. Within the instructionsof the WPS, accelerated cooling is sometimesauthorized for certain alloys (e.g., austeniticstainless steel and high-nickel alloys). How-ever, it should be noted that for other alloys,accelerated cooling may be detrimental, andits use should be investigated carefully.

Depending on the metallurgical or mechan-ical properties of the weldment, or both, pre-heat and interpass temperature may bespecified as follows:

(1) Minimum temperature only (e.g., mildcarbon steel without special requirements)

(2) Maximum temperature only (e.g., alu-minum and nickel alloys)

(3) Minimum and maximum temperatures(e.g., low-alloy steels with impactrequirements)

In situations where a preheat temperaturehas been specified but neither range nor inter-pass temperatures have been defined, it is nor-mal to consider the preheat temperature as aminimum preheat and interpass temperature.

While furnace preheating is sometimesemployed (as for cast iron), local heatingsources are selected for most preheating oper-ations. Local heating sources include resis-tance elements, induction coils, and oxyfueltorches. The selection of a heat source is usu-ally based on the shape of the component, thenumber of welds involved, the geographiclocation of the work, the availability of equip-ment, and the cost of the operation.

The welding inspector should monitor theheating process with thermocouples, pyrom-eters, or temperature-indicating materialssuch as crayons, paints, and pellets that meltor change color at predetermined tempera-tures. Such indicators should be removedprior to depositing the next bead to avoid con-taminating the weld. When thermocouples

Chapter 8Preheating and Postweld Heat Treating


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

46/Preheating and Postweld Heat Treating

and surface pyrometers are employed, theyshould be calibrated according to the manu-facturer’s instructions.

A drying operation is desirable for mostmetals and is designed to remove surface con-densate and other forms of moisture that oth-erwise would cause porosity or weldcracking. Such a drying operation requiresonly that the surface be heated to evaporatethe surface moisture prior to starting a weld-ing operation.

8.2 Postweld Heat Treating (PWHT)

As the name implies, PWHT is any heattreatment occurring after the welding opera-tion. In a stress relieving treatment, the resid-ual stresses created by the localized heatingand cooling associated with welding arereduced by plastic and creep deformation. Allwelds can be expected to retain localizedresidual stresses equal to the room tempera-ture yield strength of the material. When theequipment designer or the applicable codeconsiders the retention of such stresses unac-ceptable, the situation can be corrected byheating the weldment to a temperature atwhich the yield strength is considerablyreduced. At such elevated temperatures, theresidual stresses will dissipate or equalizewith time to a level equal to the yield strengthof the material at that temperature. Thus, theeffectiveness or the completeness of the stressrelieving operation is increased as the holdingtemperature or holding time, or both, areincreased. To prevent the reestablishment ofhigh residual stresses, slow and uniform cool-ing is needed from the PWHT temperature.

The effectiveness of stress relievingdepends primarily on the holding temperatureselected for the PWHT operation. Somecodes permit a lowering of the stress relieftemperature with a concurrent increase intime. Other factors that may contribute to thesuccess of PWHT operations include thefollowing:

(1) Holding time should be of sufficientlength, since stress relieving does not occurinstantaneously. For carbon steels, holdingtimes of one hour per inch of thickness withina minimum of one hour has proven effectivewhen no other instructions are available.

(2) The heating area is of special concernduring localized PWHT. Since “spot” PWHTcauses high localized stresses, the heating of awide area or a circumferential band is desir-able and usually mandated by the applicablecode.

(3) The rate of heating should be uniformover and through the thickness to be treated.Some codes and other standards restrict themaximum heating rate for this purpose.

(4) Cooling rates and the uniformity of thecooling operation should be specified in detailand executed with care. Some codes restrictthe maximum cooling rate. To achieve spe-cific properties in some metals, acceleratedcooling is desirable. However, for most com-ponents, slow cooling maximizes temperingand minimizes residual stresses. Some PWHToperations have failed to meet their objectivedue to the occurrence of improper coolingrates.

Applicable codes and specifications, jobrequirements and qualification test resultsgovern the specific PWHT cycle. The ade-quacy of a PWHT operation on carbon andlow-alloy steels can often be measured byhardness testing. Such a testing is mandatedby a few specifications (e.g., ASME B31.3,

Chemical Plant and Petroleum Piping

).In addition to full furnace PWHT opera-

tions, local PWHT equipment is frequentlyemployed. The same processes used for pre-heating, mentioned earlier in this chapter,may be successfully employed for this pur-pose. However, the use of oxyfuel torch heat-ing is generally undesirable for PWHToperations since uniform temperature dis-tribution is difficult to achieve. A detailed dis-cussion of each process, including the relativeadvantages and disadvantages of each, is pre-sented in AWS D10.10,

Recommended Prac-tices for the Local Heating of Welds in Pipingand Tubing

.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Preheating and Postweld Heat Treating/47

8.2.1 Heat Treating Inspection.

Many pro-grams implemented by the manufacturer tocontrol the quality of the product utilizeinspection during various points of the fabri-cation sequence. Those inspection pointsrelated to weldment heat treating may includethe following:

(1) Verification of preheat, interpass, andpostweld heat treat temperatures

(2) Verification of surface cleanliness priorto preheating, welding, and postweld heattreating

(3) Calibration of temperature indicatingand measuring devices and monitoring oftheir correct placement

(4) Monitoring the postweld heat treatingoperation to assure that the procedure require-ments have been met

(5) Verification of the dimensional accu-racy of the weldment after the final heattreatment

(6) Verification of weld quality after finalheat treatment

8.2.2 Precautions.

In all heating operations,care is needed to assure that the heat sourcesand the temperature-indicating tools do notadversely affect the weldment.

Weld surfaces should be thoroughlycleaned prior to heat treating if they havebeen exposed to materials that may be detri-mental to the metal during heat treating. Itemsof special concern include:

(1) Copper, lead, and mercury (this appliesto most metals)

(2) Chlorides and zinc (this applies espe-cially when using stainless steels)

(3) Sulfur in small quantities (this appliesespecially when using nickel alloys)

(4) Sulfur in large quantities (this applies tomost metals)

(5) Metal cutting fluids used for coolingthat contain halogens

(6) Painted metal should have the paintremoved prior to heating operations

(7) Paint or other surface coatingsThe aforementioned contaminants can

deteriorate the properties of the weld andadjacent area or accelerate the corrosion pro-cess. The most severe deterioration will occurwhen an accidental arc strike or a scheduledwelding operation melts the contaminant.Such molten materials can attack and destroythe grain boundaries, resulting in cracks in theweld or the base metal.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

49

A weld discontinuity is an interruption ofthe typical structure of a weldment, such as aninhomogeneity in the mechanical, metallurgi-cal, or physical characteristics of the materialor weldment. A discontinuity is, by definition,not necessarily a defect.

9.1 General

A weld that does not meet any or all of thespecific requirements of a particular specifica-tion or code is considered a defective weld. Adefective weld is impossible to assess withoutreference to some particular standard or require-ment related to the intended use of the weld.

For practical reasons, the terminology usedin this chapter will be addressed withoutregard to any particular code or standard fordetermination of acceptability or rejectability.This chapter will address itself to three gen-eral classifications of discontinuities:

(1) Procedure/Process(2) Metallurgical(3) Base MetalThese classes of discontinuities may be fur-

ther subdivided as follows:(1)

Procedure/Process

(a) Geometric— Misalignment— Distortion— Final Dimension— Weld Size— Overlap— Weld Profile— Convexity— Concavity— Weld Reinforcement

(b) Weld/Structural— Incomplete Fusion— Incomplete Joint Penetration— Undercut

— Underfill— Inclusions

– Slag– Tungsten

— Cracks– Hot/Cold– Weld/Base Metal– Longitudinal/Transverse– Root– Toe– Crater– Throat– Underbead

— Delayed Cracking— Porosity

– Scattered– Cluster– Aligned– Piping

— Surface Irregularities– Weld Ripples– Spatter– Arc Strikes

(2)

Metallurgical

(a) Mechanical— Strength— Ductility— Hardness

(b) Chemical— Chemistry— Corrosion Resistance

(3)

Base Metal

— Laminations— Delaminations— Lamellar Tears— Seams and Laps

The text describes some of the precedingwelding discontinuities, limiting its scope to(1) defining the discontinuity, (2) explainingthe plausible cause of the discontinuity, and(3) outlining methods for possible corrective

Chapter 9Weld and Weld Related Discontinuities


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

50/Weld and Weld Related Discontinuities

actions. The text is based on the most com-monly used welding processes; however, theinformation will be useful for welds made bymany other welding processes, applied to (1)metals known to permit satisfactory produc-tion welds, (2) joint designs that can producesatisfactory weldments, and (3) filler metalsthat are capable of producing sound deposits.

9.2 Procedure/Process

9.2.1 Geometric.

In order for a productionweldment to be satisfactory, its final dimen-sions, as well as individual weld sizes andlengths, shall be as specified on the applicabledrawing. Dimensional data with tolerancesmay be found on drawings and in specifica-tions and codes. Assemblies not meeting therequirements should be corrected before finalacceptance. Discontinuities of this nature aredescribed in the paragraphs that follow.

9.2.1.1 Misalignment.

The term misalign-ment is often used to denote the amount ofoffset or mismatch across a butt joint betweenmembers of equal thickness. Many codes andspecifications limit the amount of allowableoffset because misalignment can result instress risers at the toe and the root. Excessivemisalignment can be a result of improper fit,fixturing, tack welding, or a combination ofthese factors.

9.2.1.2 Distortion.

The welding operationcommonly involves the application of heat toproduce fusion of the base metal. Stresses ofhigh magnitude will result from thermalexpansion and contraction and weld metalsolidification, and will remain in the weld-ment after the structure has cooled. Suchstresses tend to cause distortion when thewelding sequence is not properly controlled(see Figures 9.1 and 9.2). Rigid fixtures and

Figure 9.1—Typical Distortion of Welded Joints


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Weld and Weld Related Discontinuities/51

careful selection of welding sequence, weld-ing processes, and joint design can minimizethis condition. Peening, if permitted by speci-fication and performed under controlled con-ditions, has also been used to some extent tohelp reduce distortion. Sequencing of weldsmay balance stresses and reduce or avoid dis-tortion. Correction of distortion in a com-pleted weldment requires one or more of thefollowing procedures:

(1) A mechanical straightening operation,with or without the application of heat

(2) The removal of the weld or welds caus-ing the distortion and subsequent rewelding

(3) The addition of heat from a weldingprocess (with or without a filler metal addi-tion) in specific areas

(4) A postweld heat treatment(5) Flame straighteningThe corrective measures selected usually

depend upon the applicable specification orthe terms of an agreement between the fabri-cator and the customer.

9.2.1.3 Final Dimensions.

Weldments arefabricated to meet certain dimensions,whether specified on detailed drawings orhand-written sketches. The fabricator should

be aware of the amount of shrinkage to beexpected at each weld joint. This will affectthe final overall dimensions of the product.The effect of welding sequence on distortionand the use of postweld heat treatment to pro-vide dimensional stability of the weldmentin service should also be recognized by thefabricator.

Weldments that require rigid control offinal dimensions usually should be finishedby machining or grinding after welding orafter postweld heat treatment to stay withinlimits. Tolerances for as-welded componentsobviously will depend upon the thickness ofthe material, the alloy being welded, and theoverall size of the product. Thus, tolerances infinal dimensions might be specified in rangesfrom plus-or-minus a few thousandths of aninch to as much as plus-or-minus a quarter ofan inch or more.

The inspector should discuss weldmentdimensions and tolerances with the fabricatoror the designer, or both, so that the inspectormay closely watch those dimensions that arecritical. Discussion prior to fabrication ismost important.

9.2.1.4 Overlap.

Overlap is the conditionin which weld metal protrudes beyond theweld interface at the toe of a weld as illus-trated in Figure 9.2. The condition tends toproduce notches which can be detrimental toweldment performance.

Overlap is usually caused by the use ofeither incorrect welding technique or byimproper welding parameter settings. Overlapcan occur at the toe of either a fillet or grooveweld, as well as at the weld root of a grooveweld.

9.2.1.5 Weld Size.

The size of a normalequal-leg fillet weld is expressed as the leglength of the largest isosceles right trianglethat can be inscribed within the fillet weldcross section (shown in Figure 9.3). The sizeof a groove weld is the depth of the joint pen-etration. Welds that are not of the correct size,either too big or too small, may be detectedvisually. This examination is often aided by

Figure 9.2—Overlap

OVERLAP


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


the use of a weld gauge or by comparisonwith approved workmanship samples.

9.2.1.6 Weld Profile.

The profile of a fin-ished weld may affect the service perfor-mance of the joint. The surface profile of aninternal pass or layer of a multipass weld maycontribute to the formation of incompletefusion or slag inclusions when the next layeris deposited. Figure 9.4 illustrates varioustypes of weld profiles in fillet and groovewelds.

9.2.1.7 Convexity.

Convexity is the maxi-mum distance from the face of a convex filletweld to a line joining the weld toes. At thejunction of the weld layer and the base metal,

it forms a mechanical notch, similar to thatproduced by an overlap discontinuity, but notnearly as severe. It may effectively stiffen theweld section. Also, as convexity increases inheight, the stiffening effect may increase andthe notch effect could intensify. The angleformed by the intersection of the reinforce-ment and the base material is critical. Anglesless than 90˚ result in geometric notchesbeing formed which will increase the concen-tration of stresses. As such, the amount ofconvexity or weld reinforcement (in terms ormaximum allowable height) or the re-entrantangle is normally limited by the applicableweld specification.

The notch effected by excessive convexitycan also be detrimental when located in an

Figure 9.3—Weld Sizes

(A) INCOMPLETE JOINT PENETRATION(A) PARTIAL JOINT PENETRATION

(B) COMPLETE JOINT PENETRATION

(C) CONVEX FILLET WELD

(D) CONCAVE FILLET WELD


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 9.4—Acceptable and Unacceptable Weld Profiles per AWS D1.1


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


intermediate pass of a multipass weld. It maybe the cause for incomplete fusion or slaginclusions. Corrective action, by grinding orgouging should be performed prior to depos-iting the next weld layer.

9.2.1.8 Concavity.

Concavity is the maxi-mum distance from the face of a concave filletweld perpendicular to a line joining the weldtoes. A concave profile fillet weld size cannotcorrectly be measured by its leg size. Ifmeasured by its leg size and accepted asthe design size, the weld throat will be lessthan that required by the design. Thus, theweld strength will be less than that intendedby the design specification. Concave filletwelds should be inspected by using a filletweld gauge capable of measuring the throatdimension.

The condition of concavity tends to occurprimarily in the flat welding position or whenwelding pipe in the 5G and 6G positions. It iscaused by employing excessive welding cur-rent or arc length in arc welding, or in down-hill position welding.

9.2.1.9 Weld Reinforcement.

This condi-tion is weld metal in excess of the quantityrequired to fill a weld groove. Weld reinforce-ments may be located at either the weld faceor root surface, and may therefore be morespecifically referred to as either face rein-forcement or root reinforcement, respectively.Excessive weld reinforcement is also undesir-able. The problems associated with excessivereinforcement have been described in 9.2.1.7.This condition may result from improperwelding technique or insufficient weldingcurrent.

9.2.2 Weld/Structural Discontinuities.

Dur-ing welding, a number of types of discontinu-ities may be developed within the weld. Theseinclude porosity, cracks, incomplete jointpenetration, slag inclusions, etc. These typesof discontinuities are described as weldmentand structural-related discontinuities. Theterm is not used in the sense that there is achange in metallographic structure at thesepoints, but rather that there is an interruption

or a discontinuity in the soundness of theweld or its adjacent base material. Disconti-nuities of this nature are described in theparagraphs that follow.

9.2.2.1 Incomplete Fusion.

This is a dis-continuity in which fusion did not occurbetween the weld metal and the fusion facesor adjoining weld beads (see Figure 9.5). Inother words, deposited weld metal did notfuse with the base metal or the weld metal didnot fuse with previously deposited weldmetal. Incomplete fusion may be caused byfailure to raise the temperature of the basemetal or previously deposited weld metal tothe melting point. Incorrect welding tech-niques, improper preparation of the materialsfor welding, or incorrect joint designs pro-mote incomplete fusion in welds. The weld-ing conditions that principally contribute toincomplete fusion are insufficient weldingcurrent and lack of access to all faces of theweld joint that should be fused during weld-ing. Insufficient preweld cleaning may con-tribute to incomplete fusion, even if thewelding conditions and technique are adequate.

9.2.2.2 Incomplete Joint Penetration.

Incomplete joint penetration is a joint rootcondition in a groove weld in which weldmetal does not extend through the joint thick-ness. Figure 9.6 illustrates incomplete jointpenetration. It may be caused by the failure ofthe root face or root edge of a groove weld toreach fusion temperature for its entire depth.This would leave a void that was caused bybridging of the weld metal from one memberto the other.

Although incomplete joint penetration may,in a few cases, be due to failure to dissolvesurface oxides and impurities, reduced heattransfer at the joint is a more common sourceof this discontinuity. If the areas of base metalthat first reach fusion temperatures are abovethe root, molten metal may bridge these areasand insulate the arc from the base metal at theroot of the joint. In arc welding, the arc willestablish itself between the electrode and thenearest part of the base metal to the electrode.All other areas of the base metal will receive


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


heat principally by conduction. If the portionof the base metal closest to the electrode is aconsiderable distance from the root, conduc-tion of heat may be insufficient to attain thefusion temperature at the root.

Incomplete joint penetration may beundesirable, particularly if the root of theweld is subject to either tension or bendingstresses. The unfused area permits stress con-centrations that could cause failure without

appreciable deformation. Even though theservice stresses in the structure may notinvolve tension or bending at this point, theshrinkage stresses and consequent distortionof the parts during welding will frequentlycause a crack to initiate from the unfusedarea. Such cracks may progress, as successivebeads are deposited, until they extend throughor nearly through the entire thickness of theweld.

Figure 9.5—Incomplete Joint Penetration and Incomplete Fusion


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


The most frequent cause of this type of dis-continuity is the use of a groove design notsuitable for the welding process or the condi-tions of actual construction. When a groove iswelded from one side only, complete jointpenetration is not likely to be obtained consis-tently under certain conditions. These condi-tions are: if the root face dimension is toogreat (even though the root opening is ade-quate), the root opening is too small, or thegroove angle is too small. Any of these condi-tions will make it difficult to reproduce quali-fication test results under conditions of actualproduction. If, however, the design is knownto be satisfactory, incomplete joint penetra-tion may be caused by the use of electrodesthat are too large, electrode types that have atendency to bridge rather than to penetrate atan abnormally high rate of travel, or insuffi-cient welding current.

9.2.2.3 Undercut.

This term is used todescribe either (1) the melting away of thesidewall of a welding groove at the edge of alayer or bead, thus forming a sharp recess inthe sidewall in the area to which the nextlayer or bead should fuse, or (2) the reductionin base metal thickness at the junction of theweld reinforcement with the base metalsurface (e.g., at the toe of the weld). See Fig-ure 9.5.

Visible undercut is generally associatedwith either improper welding technique, suchas excessive arc length, or welding current, orboth. Undercut may also result where exces-sive travel speeds are used. Undercut discon-tinuities create a mechanical notch at the weldinterface. If examined carefully, many weldshave some degree of undercut. Often, theundercut may only be seen in metallographicexamination where etched weld cross sectionsare evaluated under magnification. Whenundercut is controlled within the limits of therequired specification and does not constitutea sharp or deep notch, it is not considered tobe detrimental.

Undercut in the sidewalls of a multipassweld will not affect the completed weld if thecondition is corrected before the next bead is

deposited. Correction can be accomplished bygrinding to allow access to the root of theundercut.

9.2.2.4 Underfill.

This is associated withgroove welds and is described as a depressionon the weld face or root surface extendingbelow the adjacent surface of base metal.

Underfill

is usually defined as a conditionwhere the total thickness through a weld isless than the thickness of the adjacent basemetal. It results from the failure of a welder orwelding operator to completely fill the weldjoint called for in the job specifications, as aresult, the groove weld is undersize. It israrely acceptable. Figure 9.6 illustrates theconfigurations of underfill.

9.2.2.5 Inclusions.

There are two basictypes of inclusions related to welds, slaginclusions and tungsten inclusions.

(1)

Slag Inclusions.

During deposition offiller metal and subsequent solidification ofweld metal, many chemical reactions occurbetween the weld metal and the electrodecovering materials, forming slag compoundssoluble only to a slight degree in the moltenmetal. Due to their lower specific gravity,slags rise to the surface of the molten metalunless they are restrained.

During welding with flux shielded pro-cesses, slag will be formed and forced belowthe surface of the molten metal by the stirringaction of the arc. Slag may also flow ahead ofthe arc, allowing the metal to be deposited

Figure 9.6—Underfill


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


over it. Also, with some electrode types, slagin crevices of previously deposited weldmetal will not remelt and will become trappedin that location. When slag is present in themolten metal from any cause, factors such ashigh viscosity of the weld metal, rapid solidi-fication, or too low a temperature may preventits release. Most slag inclusions can be pre-vented by proper preparation of the groovebefore each bead is deposited, using care tocorrect contours that are difficult to fully pen-etrate with the arc. The release of slag fromthe molten metal will be expedited by anyfactor that tends to make the metal less vis-cous or retard its solidification (such as high-heat input).

(2)

Tungsten Inclusions.

Tungsten inclu-sions are pieces of the electrode that have sep-arated and become trapped in weld metaldeposited with the gas tungsten arc weldingprocess, and to a lesser degree, the plasma arcwelding process. These inclusions may betrapped in a weld if the tungsten electrode isdipped into the molten weld metal, or if thewelding current is too high and causes melt-ing and transfer of tungsten droplets into themolten weld metal.

Tungsten inclusions appear as light areason a radiograph because tungsten is moredense than the surrounding metal and absorbslarger amounts of x-rays or gamma radiation.

9.2.2.6 Cracks.

Cracking of welded jointsresults from localized stresses that exceed theultimate strength of the material. Whencracks occur during or as a result of welding,little deformation is usually apparent. Figure9.7 illustrates various types of cracks.

Cracks which occur during solidificationare sometimes called

hot cracks. Cold cracks

are those that occur after the weld has cooledto ambient temperature, or once the weldmenthas been placed in service. Hot cracks willpropagate along grain boundaries while coldcracks, sometimes associated with hydrogenembrittlement, will propagate both alonggrain boundaries and through grains.

It is known that materials having low duc-tility, when stressed in a single direction, may

fail without appreciable deformation. How-ever, when stresses on a material are multi-directional, failure can occur in a more brittlemanner. Typically, shrinkage stresses fromwelding can result in the creation of thesemulti-directional stresses, especially in caseswhere welds having different orientations areconnected. Because of such stresses, a joint[or any adjacent region such as the heat-affected zone (HAZ)] may be unable to with-stand appreciable deformation without fail-ure. In that case, additional stresses set up dueto deposition of subsequent layers (or in thewelding of adjacent joints) may force thatpart to deform and fail. An unfused area at theroot of a weld may result in cracks withoutappreciable deformation if this area is sub-jected to tensile or bending stresses. Whenwelding two members together, the root of theweld is subjected to tensile stress as succes-sive layers are deposited, and, as alreadystated, a partially fused root will frequentlypermit a crack to start and progress throughpractically the entire thickness of the weld.

After a welded joint has cooled, cracking ismore likely to occur if the metal is eitherexcessively hard or brittle. A ductile material,by localized yielding, may withstand stressconcentrations that might cause a hard or brit-tle material to fail.

9.2.2.7 Weld Metal Cracking.

The abilityof the weld metal to remain intact under thestresses that are imposed during the weldingoperation depends upon the composition andstructure of the weld metal. In multi-layerwelds, cracking is most likely to occur in thefirst layer of the weld and, unless repaired,will often continue through other layers asthey are deposited. When cracking of theweld metal is encountered, improvement maybe obtained by one or more of the followingmodifications:

(1) Change the welding technique or weld-ing parameters to improve the contour orcomposition of the deposit.

(2) Decrease the travel speed. Thisincreases the thickness of the deposit and pro-vides more weld metal to resist the stresses.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


(3) Use preheat to reduce the cooling rateand to reduce thermal stresses.

(4) Use low-hydrogen electrodes.

(5) Sequence welds to balance shrinkagestresses.

(6) Avoid quenching and rapid coolingconditions.

(7) Maintain filler metals and other weldingmaterials properly.

Three different types of cracks that canoccur in weld metal are as follows:

(1)

Transverse Weld Cracks.

These cracksare perpendicular to the axis of the weld and,in some cases, extend beyond the weld intothe base metal—see Figure 9.7(B). This typeof crack is more common in joints that have ahigh degree of restraint in the weld axis direc-tion. Use of low-ductility weld metal tends topromote transverse cracking.

Figure 9.7—Various Types of Cracks


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


(2)

Longitudinal Weld Cracks.

Longitudinalweld cracks are found mostly within the weldmetal, and are usually confined to the centerof the weld—see Figure 9.7(A). In filletwelds, longitudinal weld metal cracks are alsoreferred to as throat cracks—see Figure9.7(E). Such cracks may occur as the exten-sion of crater cracks formed at the end of theweld. They may also be the extension,through successive layers, of a crack thatstarted in the first layer. A crack formed in thefirst layer and not removed or completelyremelted before the next layer is depositedtends to progress into the layer above, andthence each succeeding layer, until finally, itmay appear at the surface. The final extensionto the surface may occur during cooling afterwelding has been completed. Those jointsexhibiting a high degree of restraint perpen-dicular to the weld axis are most prone to thistype of weld metal cracking.

(3)

Crater Cracks.

Whenever the weldingoperation is interrupted, there is a tendencyfor a crack to form in the crater. These cracksare often star shaped and progress only to theedge of the crater—see Figure 9.7(C). How-ever, these may be starting points for longitu-dinal weld cracks, particularly when theyoccur in the crater formed at the end of theweld—see Figure 9.7(D). This, however, isnot always the case, and sometimes fine, star-shaped cracks are seen at various locations.Crater cracks are found most frequently inmaterials with high coefficients of thermalexpansion, for example austenitic stainlesssteel. However, the occurrence of any suchcracks can be minimized or even prevented byfilling craters to a slightly convex shape priorto extinguishing the arc.

The above discussion on cracking is anattempt to give a rudimentary knowledge ofwhat can cause cracking. However, suchknowledge cannot always be applied, sincemany designs provide no other alternativesbecause of the thicknesses involved, designcriteria, accessibility, etc.

9.2.2.8 Base Metal Cracking.

This type ofcracking occurs within the heat-affected zone

of the metal being welded and is almostalways associated with hardenable materials.High hardness and low ductility in the HAZwelded joints are metallurgical effects thatresult from the thermal cycle of welding andare among the principal factors that tend tocause cracking. While a complete metallurgi-cal discussion is beyond the scope of this sec-tion, a rudimentary knowledge of thetendency of various groups of metals toharden or become brittle will be of value tothe inspector.

In the case of low carbon, medium carbon,and low-alloy steels, hardness and the abilityto deform without rupture depend upon thealloy group to which the steel belongs andalso upon the rate of cooling from the ele-vated temperatures produced by the weldingoperation. The rate of cooling will obviouslydepend upon a number of physical factorssuch as the following:

(1) The temperatures produced by thewelding

(2) The temperatures of the base metal(3) The thickness and thermal conductivity

of the base metal(4) The heat input per unit time at a given

section of the weld(5) The ambient temperatureWith a given cooling rate, the low-carbon

steels will harden considerably less than themedium-carbon steels. Low-alloy steelsexhibit a wider variation in their hardeningcharacteristics; some of them may be similarto low-carbon steel, while others will reactlike medium-carbon steel.

High-alloy steels should be considered sep-arately since this group includes the austeniticand ferritic stainless steels, as well as the mar-tensitic steels. The latter behave similarly tothe medium carbon and low-alloy groups,except that they harden to a greater degreewith a given cooling rate. Neither the austen-itic steels (of which the common 18% chro-mium-8% nickel stainless steel is an example)nor the ferritic stainless steels (of which thelow carbon straight chromium steels contain-ing 12% or more chromium are an example)harden upon quenching from elevated


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


temperatures. However, in general, the ferriticstainless steels are rendered brittle (but nothard) by welding operations.

The metallurgical characteristics of themetals are of prime importance. Base metalcracking is associated with lack of ductility inthe HAZ. Since ductility usually decreaseswith increasing hardness, cracking oftenoccurs. This is not the complete answer, how-ever, for it has been established that differentheats of the same steel of equal hardenabilityvary appreciably in cracking tendency. Fur-thermore, recent information establishesbeyond a doubt that in shielded metal arcwelding the characteristics of the electrode asdetermined by its covering have considerableeffect upon the tendency toward HAZcracking.

Hardenable steels are usually more difficultto weld for two reasons:

(1) Variations in microstructure of theHAZ, which can occur with variations in thecooling rate, cause differences in mechanicalproperties.

(2) Due to the hardenability of the steel, areduction in ductility occurs.

When base metal cracking is encounteredwith hardenable steels, the condition can beimproved in the following ways.

(1) Use of preheat to control cooling rate(2) Use of controlled heat input(3) Use of the correct filler metal

While this subject has been treated in ageneral manner, each case usually involvesconditions peculiar to the particular weldmentin question. However, the four types of basemetal cracking that can occur as a result ofthe welding operation are as follows:

(1)

Transverse Base Metal Cracks.

Thistype of cracking is oriented perpendicular tothe axis of welding and usually associatedwith welds on steels of high hardenability.Such cracks usually cannot be detected untilthe weldment has cooled to room temperature.

(2)

Longitudinal Base Metal Cracks.

Thesecracks lie parallel to the weld and are in thebase metal. They may be extensions of weldinterface cracks. Longitudinal base metal

cracks may be divided into three types: toecracks, root cracks, and underbead cracks.

(a)

Toe Cracks

. Toe cracks are generallycold cracks that initiate approximately normalto the base material surface and then propa-gate from the toe of the weld where residualstresses are high, and the weld profile pro-duces a stress concentration—see Figure9.7(F). These cracks are generally the resultof thermal shrinkage strains acting on a weldHAZ. Toe cracks sometimes occur when thebase metal cannot accommodate the shrink-age strains that are imposed by welding.

(b)

Root Cracks.

Root cracks are longitudi-nal cracks which might progress into the basemetal.

(c)

Underbead Cracks.

Underbead cracksare cold cracks that form in the HAZ. Theyare also called delayed cracks since they maynot appear until several hours after the weld-ment has cooled to room temperature. Theymay be short and discontinuous, but may alsoextend to form a continuous crack. Under-bead cracking can occur in steels when threeelements are present:

— Hydrogen in solid solution— A crack susceptible microstructure— High residual stress

When present, these cracks are usually foundat regular intervals under the weld metal anddo not normally extend to the surface.

9.2.2.9 Porosity.

Porosity, as shown inFigure 9.8, is the result of gas beingentrapped in solidifying weld metal. The dis-continuity is generally spherical, but may beelongated.

Porosity results when contaminants ormoisture become included in the weld puddle.Sources of these impurities include: the basemetal surface, the filler metal surface, weld-ing fluxes, welding gases, and welding equip-ment (cooling systems, drive rolls, etc.)Porosity differs from inclusions in that poros-ity contains a gas rather than a solid substanceand generally are spherical in shape.

The formation of porosity can be avoidedby maintaining cleanliness for welding, byproviding protection barriers in preventing


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


the loss of gas shielding, and by keeping theequipment maintained. During welding,excessive current and excessive arc lengthshould be avoided. Either of these may resultin excessive loss of deoxidizer elements asthey transfer across the arc, leading to incom-plete deoxidation within the molten weld pooland subsequently porosity.

Porosity may be subdivided into four types:scattered, cluster, linear, and piping.

(1)

Scattered Porosity

. Scattered porosity,as shown in Figure 9.8(A), is widely distrib-uted in a single weld bead or in several beadsof a multipass weld. Whenever scatteredporosity is encountered, the cause is generallyfaulty welding technique or contaminatedmaterials or both.

(2)

Cluster Porosity

. Cluster porosity is alocalized grouping of pores occurring in clus-ters separated by considerable lengths ofporosity-free weld metal. Cluster porositymay result from improper initiation or termi-nation of the welding arc.

(3)

Aligned Porosity

. Aligned porosity is alocalized array of porosity oriented in aline—see Figure 9.8(B). It often occurs alongthe weld interface, the weld root, or an inter-bead boundary and develops by contamina-tion that causes gas to be liberated at theselocations.

(4)

Piping Porosity

. Piping porosity haslength greater than its width, and lies approxi-mately perpendicular to the weld face. In filletwelds it extends from the root toward theweld face. When a few pores are seen in theweld face, careful excavation will often showthat there are many subsurface pores that donot extend all the way to the weld face.

(5)

Elongated Porosity.

Elongated porosityhas a length greater than its width, and liesapproximately parallel to the weld axis. It issometimes seen on the weld face where gasesbecame trapped between the already solidi-fied slag and the still-molten weld metal. Thiscondition is sometimes called pock marks orworm tracks—see Figure 9.8(D). In pipelinewelding of the root bead with cellulosic elec-trodes and excessive travel speed, the result-ing porosity is called hollow bead.

9.2.2.10 Surface Irregularities.

Perfectlyacceptable welds will naturally exhibit somedegree of surface roughness, however,improper technique or equipment adjustmentcan result in surface irregularities that exceedspecification requirements. Unsatisfactoryworkmanship indicates that proper proce-

Figure 9.8—Porosity


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


dures are not being followed. Surface irregu-larities are not limited to, but generallygrouped as weld ripples, spatter, and arcstrikes.

(1)

Weld Ripples

. While depressions andvariations in the weld surface are consideredto be discontinuities, they may not affect theability of the weld to perform its intendedpurpose. The applicable standard shoulddescribe the degree of surface irregularitypermissible to prevent the presence of high-stress concentrations.

(2)

Spatter

. Spatter consists of metal parti-cles expelled during fusion welding that donot form a part of the weld. Spatter particlesthat become attached to the base metal adja-cent to the weld are the most detrimental tothe product, but spatter propelled away fromthe weld and base metal is of concern becauseof its potential to inflict burns.

Normally, spatter is not considered to be aserious flaw unless its presence interfereswith subsequent operations, especially nonde-structive examinations or serviceability of thepart.

(3)

Arc Strikes

. An arc strike is a disconti-nuity resulting from an arc consisting of anylocalized remelted metal, HAZ, or change inthe surface profile of any metal object. Arcstrikes result when the arc is initiated on thebase metal surface away from the weld joint,either intentionally or accidentally. When thisoccurs, there is a localized area of the basemetal surface which is melted and then rap-idly cooled due to the massive heat sink cre-ated by the surrounding base metal. Arcstrikes are not desirable and often are notacceptable, as they could lead to cracking andshould be removed.

9.3 Metallurgical

9.3.1 Mechanical Properties.

Metals notonly offer many useful properties and charac-teristics in their mechanical behavior, but theycan also develop a large number of combina-tions of those properties. The versatility ofmetals with respect to mechanical propertieshas encouraged the selection of the

best combination of properties to facilitatefabrication and to ensure good service per-formance. Some applications require consid-erable thought about base and filler metalselection and treatment, particularly wherefabricating properties differ from the requiredservice properties.

Mechanical properties that should bechecked against prescribed requirementsinclude tensile strength, yield strength, ductil-ity, hardness and impact strength. Also, chem-ical properties may be deficient because ofincorrect weld metal composition or unsatis-factory corrosion resistance; where required,these can be checked against the welding pro-cedure specification.

9.3.2 Base Metal Properties.

It should bepointed out that not all discontinuities are dueto improper welding conditions. Many suchdiscontinuities may be attributed to the basemetal. Base metal requirements are definedby applicable specifications or codes. Depar-ture from these requirements should be con-sidered cause for rejection.

9.3.2.1 Tensile Strength.

When materialhas reached its highest tensile load it can sus-tain before rupturing, it is said to havereached its ultimate tensile strength, which isthe value regularly listed for the strength ofmaterial.

Tensile strength values obtained for metalsare influenced by many factors. Tensilestrength is dependent upon chemistry, micro-structure, grain size and other factors.

9.3.2.2 Yield Strength.

The yield point ofmaterial is the load at which deformationincreases without any additional increase ofthe applied load. Once the yield strength hasbeen exceeded, the material exhibits perma-nent deformation, and will never return to itsoriginal size and shape. Certain metals, suchas low-carbon steel, exhibit a yield pointwhich is the stress just above the elasticlimit. The elastic limit is the upper limit ofstress where the material will return to itsoriginal dimensions when the load isreleased.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Engineers and designers are most oftenconcerned with yield strength when selectingmaterials for construction. The allowablestresses defined by most codes are calculatedas a percentage of the yield strength, depend-ing upon the desired safety factor, the type ofapplied stress, and the operating temperatureof the material.

9.3.2.3 Chemistry.

The chemical composi-tion of base metals and filler metals deter-mines a material’s relative weldability. A basemetal’s chemical composition also affect itshardness, ductility, tensile strength and corro-sion resistance. Low carbon and medium car-bon steels (up to 0.4%) are considered to havegood weldability. The higher the carbon con-tent, the more hardenable the material andhence the more difficult to weld. High-carbon(more than 0.4%) steels may require preheat,interpass temperature control, and strict atten-tion to the welding procedure.

Elements such as excess sulfur might leadto cracking or a reduction in its corrosionresistance. For these reasons, chemical ele-ments should be verified between the materialtest report and the material specification,which are established by several codes.

9.3.2.4 Corrosion Resistance.

The corro-sion properties of a metal determine its modeand rate of deterioration by chemical or elec-trochemical reaction with the surroundingenvironment. Metals and alloys differ greatlyin their corrosion resistance. Corrosion resis-tance often is an important consideration inplanning and fabricating a weldment for aparticular service. Therefore, a designershould know something about the behavior ofweld joints under corrosive conditions.

Many times, weld joints display corrosionproperties that differ from the remainder ofthe weldment. These differences may beobserved between the weld metal and the basemetal, and sometimes between the HAZ andthe unaffected base metal. Even the surfaceeffects produced by welding, like heat tintformation or oxidation, fluxing action of slag,and moisture absorption by slag particles, canbe important factors in the corrosion behavior

of the weld metal. These considerations areparticularly important in the design and fabri-cation of weldments of unpainted weatheringsteels, including the selection of filler metals.

Welds made between dissimilar metals orwith a dissimilar filler metal may be subjectto electrochemical corrosion.

9.4 Base Metal

It should be pointed out that not all discon-tinuities are due to improper welding condi-tions. Many such discontinuities may beattributed to the base metal. Base metalrequirements are defined by applicable speci-fications or codes. Departure from theserequirements should be considered cause forrejection.

Base metal properties that may not meetprescribed requirements include chemicalcomposition, cleanliness, lamination/delami-nation, mechanical properties, seams andlaps. The inspector should keep factors suchas these in mind when trying to determine thereason for welding discontinuities that haveno apparent cause (see Figure 9.9).

9.4.1 Laminations.

Laminations may exist inany rolled product to some degree. Lamina-tions normally occur near the center of thethickness of plate or pipe materials and tendto be parallel to the surface. They are usuallycaused by inclusions or blow holes in theoriginal ingot. During rolling, these disconti-nuities become elongated and appear as flat,longitudinal stringers of nonmetallics.

9.4.2 Delamination.

Delamination is the sep-aration of lamination under stress. Thestresses may be generated by welding or byexternally applied loads. Both lamination ordelamination, if extended to the edges of thematerial, may be detected by visual, magneticparticle, or liquid penetrant examination. Iflamination or delamination is a concern,ultrasonic testing should be conducted utiliz-ing the straight beam method to assure mate-rial integrity.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


9.4.3 Lamellar Tearing.

Some rolled struc-tural materials are susceptible to a crackingdefect known as

lamellar tearing

. This crackhas a characteristic morphology, which isstep-like in nature—see Figure 9.9. The mostcommonly accepted theory is that whenrestraint stresses and thermal strains imposedby welding exceed the strength of the materialin the through-thickness direction, the stressconcentration at nonmetallic inclusions (com-mon to most structural materials) initiatescracks. The cracks initiate by decohesion ofthe inclusion-metal interface and propagateby ductile rupture to the next inclusion in thatplane or by localized shear fracture to aninclusion which is in a slightly differentplane.

9.4.4 Seams and Laps.

Seams and laps arelongitudinal base-metal discontinuities some-times found in forged and rolled products.They differ from laminations in that theypropagate to the rolled surface even thoughthey may run in a lamellar direction (parallelto the rolled surfaces) for some portion oftheir length. When one of these discontinui-ties lies parallel to the principal stress, it is notgenerally considered to be a critical flaw.However, when seams and laps are perpendic-ular to the applied or residual stresses, theywill often propagate as cracks. Seams andlaps are surface-connected discontinuities.However, their presence may be masked bymanufacturing processes that have subse-quently modified the surface of the mill prod-uct. Welding over seams and laps can causecracking and should be avoided.

Figure 9.9—Lamellar Tearing


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

65

There are numerous welding process vari-ables that should be described in a weldingprocedure. It is always desirable and oftenessential that the variables associated with thewelding be described in a welding procedurewith sufficient detail to permit reproductionof the weld and to afford a clear understand-ing of the parameters for performing the pro-duction weld. These variables are stipulatedin two different documents:

(1)

Welding Procedure Specifications(WPSs)

—Detailed methods and practicesinvolved in the production of a weldment.

3

(2)

Procedure Qualification Records(PQRs)

—A record of actual welding vari-ables used to produce an acceptable test weld-ment and the results of the tests conducted onthe weldment. This document qualifies theWPS.

7

Generally, proposed welding proceduresshould be proven adequate by either proce-dure qualification tests or by sufficient prioruse and service experience to assure depend-ability. The purpose of a welding procedurespecification is, therefore, to define thosedetails that are to be carried out in weldingspecific materials or parts. To fulfill this pur-pose effectively, a welding procedure specifi-cation should be as concise and clear aspossible; it is a recipe for welding.

10.1 Description and Important Details

Industry today uses two common types ofwelding procedure specifications. One is a

3. WPS and PQR documents are available fromAmerican Welding Society, 550 N.W. LeJeune Road,Miami, FL 33126.

broad, general type that applies to all weldingprocesses of a given kind on a specific mate-rial. The other is a narrower, more definitivetype that spells out in detail the welding of asingle size and type of joint in a specificmaterial or part.

The narrower, more definitive type is mostfrequently used by manufacturers for theirown control of repetitive in-plant weldingoperations or by purchasers desiring certainspecific metallurgical, chemical, or mechani-cal properties. However, either type may berequired by a customer or agency, dependingupon the nature of the welding involved andthe judgment of those in charge. In addition,the two types are sometimes combined invarying degrees, with addenda to show theexact details for specific joints attached to thegeneral specification.

Arrangement and details of the weldingprocedure specifications as written should bein accordance with the contract or purchaserequirements and good industry practice. Theprocedure should be sufficiently detailed toensure welding that will satisfy the require-ments of the applicable code, purchase speci-fications, or both.

Welding procedure specifications are some-times required by the purchaser to govern fab-rication of a given product in a fabricator’sshop. Most often, however, the purchaser willsimply specify the properties desired in theweldment in accordance with a code or speci-fication, leaving the fabricator to use a weld-ing procedure that will produce the specifiedresults. In other cases, the purchaser will pre-scribe that the fabricator establish definitewelding procedure specifications and testthem to prove that the resulting welds willmeet requirements specified by the purchaser.

Chapter 10Qualification of Welding Procedure Specifications


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

66/Qualification of Welding Procedure Specifications

The fabricator is then required to use theseprocedures during production.

The following paragraphs list the details usu-ally covered in welding procedure specifications.

10.1.1 Scope.

The welding process(es), thematerial, and the governing specificationsshould be clearly stated.

10.1.2 Base Metals and Applicable Specifi-cations.

Base metals should be specified. Thismay be done either by giving the chemicalcomposition and mechanical properties or byreferring to the applicable material specifica-tions. In addition, if the base metal requiresspecial care before welding, this also shouldbe indicated (i.e., normalized, annealed,quenched and tempered, solution treated, coldworked, etc.). The thickness of the base metalhas an effect on the cooling rate from weldingtemperatures, and therefore, should be speci-fied. Usually a range is specified (i.e., 1/4 in.–1 in.).

In some cases, these factors are very impor-tant. A welding procedure that will provideexcellent results with one material might notprovide the same results with another, or evenwith the same material that has been pro-cessed differently. Thus, the fabricator shouldidentify material.

10.1.3 Welding Processes.

The welding pro-cess(es) that is (are) to be used should beclearly defined. Most specifications considerthe welding process an essential variable, andrequire requalification if the process ischanged.

10.1.4 Type, Classification, Composition,and Storage of Filler Metals.

Chemicalcomposition, specification, or classification ofthe filler metal should always be specified. Inaddition, sizes of filler metal or electrodesthat can be used when welding differentthicknesses of material in the different posi-tions should be designated. Filler metal mark-ing is usually sufficient for identification. Forsome applications, additional details are spec-ified. These may include manufacturer, type,heat, lot, or batch of welding consumables.

Certain types of filler metals and fluxesrequire special conditions during storage andhandling. For example, low-hydrogen elec-trodes should be stored at elevated tempera-ture to maintain the moisture content at a lowlevel. The welding procedure can state theserequirements.

10.1.5 Type of Current and CurrentRange.

Whenever welding involves the use ofelectric current, the type of current to be usedshould be specified. Some electrodes workbetter on alternating current (ac) than directcurrent (dc). If dc is specified, the polarityshould be specified, since most electrodesoperate better on a certain polarity. In addi-tion, the current ranges for the different sizesof electrodes for different positions and forwelding various thicknesses of materialshould be specified.

10.1.6 Arc Voltage and Travel Speed.

For allarc welding processes, it is common practiceto list voltage ranges. Ranges for travel speedare sometimes mandatory for automatic weld-ing processes and are desirable many timesfor semiautomatic processes. Also, whenwelding some steels where heat input is animportant consideration, it becomes impera-tive that the permissible limits for travel speedbe specified.

10.1.7 Joint Designs and Tolerances.

Per-missible joint design details should be indi-cated, as well as the designated sequence forwelding. This may be done by means ofcross-sectional sketches showing the thick-ness of material and details of the joint or byreferring to standard drawings or specifica-tions. Tolerances should be indicated for alldimensions. These tolerances are important,since, for example, increasing the root open-ing may create a condition wherein even themost expert welder may not be able to pro-duce a satisfactory weld.

10.1.8 Joint Preparation and Cleaning ofSurfaces for Welding.

The methods that maybe used to prepare joints, as well as the degreeof surface cleaning and surface roughnessrequired, should be designated in the proce-


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Qualification of Welding Procedure Specifications/67

dure specification. This may include oxygencutting, air carbon arc, or plasma cutting(with or without post-cleaning). It may alsoinvolve machining or grinding followed byvapor, ultrasonic, dip, or lint-free cloth clean-ing with any of a variety of special cleaners.The cleaning methods and practices specifiedfor the production work should be used whenqualifying the welding procedure. Thisincludes the use of weld spatter-resistingcompounds on the surfaces.

10.1.9 Tack Welding.

Whenever the tackwelding practices could affect the end results,details concerning just what is to be done inconnection with tack welds should be includedin the welding procedure specification.

10.1.10 Joint Welding Details.

All detailsthat influence weld quality, in terms of thespecification requirements, should be clearlyoutlined. Details often include the sizes ofelectrodes for the different portions of thejoints and the different positions, the arrange-ment of weld passes for filling the joints, passwidth or electrode weave limitations, currentranges, and whatever other details are impor-tant. These details help determine the sound-ness of the welds and influence the propertiesof the finished joint.

10.1.11 Positions of Welding.

A procedurespecification should always designate theposition(s) in which the welding is to be (ormay be) performed.

10.1.12 Preheat and Interpass Tempera-tures.

Whenever preheat or interpass temper-atures are significant factors in the productionof sound welds, or influence the properties ofweld joints, the temperature limits should bespecified. With heat-treated alloy steels, thepreheat and interpass temperatures should bekept within a well-defined specified range toavoid degradation of the base-metal heat-affected zone.

Preheat and interpass temperatures are gen-erally determined by touching the workpiececlose to the weld joint with temperature indi-cating materials or mechanical thermometers.These materials melt at a specified tempera-

ture or indicate the temperature by the colorof the mark. Contact pyrometers or tempera-ture-indicating paints are also used.

When chemical temperature indicatingmaterials are used on austenitic stainlesssteels, nickel alloys, and other materials, careshould be taken to ensure that these materialsdo not contain elements that are detrimental(such as sulfur, zinc, lead, mercury, andchlorine).

10.1.13 Heat Input.

Heat input during weld-ing is usually important (for example, whenwelding heat-treated steels and alloys orwhenever impact property testing is speci-fied). Whenever heat input is of concern, itshould be prescribed with the details for con-trol outlined in the procedure specification.

10.1.14 Root Preparation Prior to WeldingFrom Second Side.

When joints are to bewelded from both sides, the methods that areto be used (or may be used) to prepare thesecond side should be stated in the procedurespecification. Specifying any necessary prep-aration is of primary importance in producingsound weld joints. These may include chip-ping, grinding, air carbon arc or oxyfuelgouging, or whatever is needed to prepare theroot.

10.1.15 Peening.

Indiscriminate use of peen-ing should not be allowed. However, it issometimes used to avoid cracking or toreduce distortion of the weldment. If peeningis to be used, the details of its application andtooling should be covered in the procedurespecifications.

10.1.16 Removal of Weld Sections forRepair.

When repairs to welds are required,local section(s) or the complete weld mayhave to be removed. The methods to be usedfor removing welds or sections of welds forsuch repair may be designated in the weldingprocedure specification or in a separate proce-dure. Quite often, the metal removal methodsare the same as those used for preparing thesecond side of joints for welding.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


10.1.17 Repair Welding.

Repairs to weldsmay be performed using the same procedurespecified for the original weld or may requirea separate procedure.

10.1.18 Post Weld Heat Treatment.

Whenmaterials or structures require heat treatmentafter welding to develop required mechanicalproperties, dimensional stability, or corrosionresistance, such treatment should be stated inthe welding procedure specification and beapplied to all procedure qualification testwelds. This may include a full description ofthe heat treatment in the actual welding pro-cedure or in a separate fabrication document,such as a shopheat-treating procedure or ashop drawing.

10.1.19 Summary of Important WeldingProcedure Details.

Not all of the precedingapplies to every process or application. Thevarious items are listed only for illustration.Due to the diversity of welding methods andapplication requirements, many of the itemscould be of major consequence in one appli-cation and of minor influence if applicable atall in another. In considering or reviewingwelding procedure specifications, inspectorsshould weigh these points accordingly.

The factors which are consider critical in awelding procedure are called

variables

. Someessential variables could effect the mechani-cal properties of a weldment and wouldrequire requalification of the welding proce-dure. Changes to other variables wouldrequire that the welding procedure be rewrit-ten to recognize the change, but would notrequire requalification. The applicable codeor specification should be consulted to deter-mine which variables are essential.

10.2 Prequalified and Standard Welding Procedure Specifications (WPSs)

10.2.1 Prequalified WPSs.

The AWSD1.1,

Structural Welding Code—Steel

,employs the concept of prequalified weld

joints. By following a number of well-definedvariables, the user of this code does not haveto qualify the procedure. Instead, the valuesof the specific variables used are recorded.Qualification is required only if any of thesevariables are changed beyond their specifiedlimits. Records of such procedures are main-tained using the form shown in Figure 10.1,and the factors to be considered in qualifica-tion are listed in Table 10.1.

10.2.2 Standard WPSs.

AWS publishesStandard Welding Procedure Specifications(SWPSs). These specifications are preparedby the Welding Procedures Committee of theWelding Research Council, and are ballotedthrough the AWS standards development pro-gram as American national standards. Stan-dard WPSs may be used on work covered byAWS D1.1,


,the National Board Inspection Code, ASME

Boiler and Pressure Vessel Code

, and on othergeneral fabrication work.

10.3 Qualification of Welding Procedure Specifications

The mechanical and metallurgical proper-ties of a welded joint may be altered by thewelding procedure specifications selected forthe job. It is the responsibility of each manu-facturer or contractor to conduct the properweld metal tests required by the applicablecodes and contractual documents. It is theduty of the engineer or inspector to reviewand evaluate the results of such qualifications.These qualification activities should be com-pleted prior to any production welding toassure that the selected combination of mate-rials and methods to be used is capable ofachieving the desired results. This is accom-plished by any of the following three alterna-tives or a combination thereof:

10.3.1 Employment of Prequalified Weld-ing Procedures.

This concept is based on thereliability of certain proven procedures spelledout by the applicable code or specification.Any deviation outside specified limits voids


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 10.1—AWS Structural Welding Code Prequalified Procedures


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 10.1 (Continued)—AWS Structural Welding Code Prequalified Procedures


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Tab

le 1

0.1

Wel

ding

Pro

cedu

re S

peci

ficat

ion

and

Wel

der

Qua

lifica

tion

Fact

ors

Whi

ch M

ay R

equi

re R

equa

lifica

tion

NO

TE

: Thi

s ta

ble

is s

how

n FO

R I

LL

UST

RA

TIO

N P

UR

POSE

S O

NLY

to in

dica

te th

e ge

nera

l nat

ure

of c

ode

requ

irem

ents

gov

erni

ng r

equa

lifica

tion

of w

eld-

ing

proc

edur

es, w

elde

rs, a

nd o

pera

tors

. It c

anno

t be

used

by

an in

spec

tor

to d

eter

min

e w

heth

er r

equa

lifica

tion

is r

equi

red

in a

spe

cifi

c in

stan

ce. F

or th

at in

for-

mat

ion

refe

renc

e sh

ould

be

mad

e to

the

part

icul

ar c

ode

or s

peci

fica

tion

appl

icab

le to

the

wor

k be

ing

insp

ecte

d.

Proc

edur

e fa

ctor

Proc

edur

e re

qual

ifica

tion

may

be

requ

ired

whe

n th

e w

eldi

ng p

ract

ices

are

cha

nged

to

the

exte

nt in

dica

ted

belo

w.

Wel

der

or w

eldi

ng o

pera

tor

requ

alifi

-ca

tion

may

be

requ

ired

for

the

prac

tice

chan

ges

indi

cate

d be

low

.

Type

, com

posi

tion,

or

proc

ess

cond

ition

of

the

base

mat

eria

l

Whe

n th

e ba

se m

etal

is c

hang

ed to

one

not

con

form

ing

to th

e ty

pe, s

peci

fica

tion,

or

proc

ess

cond

ition

qua

lified

. (So

me

code

s an

d sp

ecifi

catio

ns p

rovi

de li

sts

of m

ater

ials

w

hich

are

app

roxi

mat

ely

equi

vale

nt f

rom

the

stan

dpoi

nt o

f w

elda

bilit

y an

d w

hich

m

ay b

e su

bstit

uted

with

out r

equa

lifica

tion)

.

Usu

ally

not

requ

ired

, unl

ess

a m

arke

d ch

ange

is m

ade

in th

e ty

pe o

f fille

r met

al

used

or c

over

ing

ther

eon,

e.g

., fe

rriti

c to

au

sten

itic

or n

onfe

rrou

s m

etal

; cel

lulo

sic

to

low

-hyd

roge

n ty

pe e

lect

rode

cov

erin

g, e

tc.

Thi

ckne

ss o

f ba

se

met

alW

hen

the

thic

knes

s to

be

wel

ded

is o

utsi

de th

e ra

nge

qual

ified

. (T

he v

ario

us c

odes

an

d sp

ecifi

catio

ns m

ay d

iffe

r co

nsid

erab

ly in

this

res

pect

. Mos

t pro

vide

for

qua

lifica

-tio

n on

one

thic

knes

s w

ithin

a r

easo

nabl

e ra

nge;

e.g

., 3/

16 in

. to

2T, 1

/2T

to 2

T, 1

/2T

to

1.1

T, e

tc. S

ome

may

req

uire

qua

lifica

tion

on th

e ex

act t

hick

ness

or

on th

e m

ini-

mum

and

max

imum

).

Whe

n th

e th

ickn

ess

to b

e w

elde

d is

out

-si

de th

e ra

nge

qual

ified

.

Join

t des

ign

Whe

n es

tabl

ishe

d lim

its o

f ro

ot o

peni

ngs,

roo

t fac

e, a

nd in

clud

ed a

ngle

of

groo

ve

join

ts a

re in

crea

sed

or d

ecre

ased

; i.e

., ba

sic

dim

ensi

ons

plus

tole

ranc

es. (

Som

e co

des

and

spec

ifica

tions

pre

scri

be d

efini

te u

pper

and

low

er li

mits

for

thes

e di

men

sion

s,

beyo

nd w

hich

req

ualifi

catio

n is

nec

essa

ry. O

ther

per

mit

an in

crea

se in

the

incl

uded

an

gle

and

root

ope

ning

and

a d

ecre

ase

in th

e ro

ot f

ace

with

out r

equa

lifica

tion.

Als

o,

requ

alifi

catio

n is

oft

en r

equi

red

whe

n a

back

ing

or s

pace

r st

rip

is a

dded

or

rem

oved

or

the

basi

c ty

pe o

f m

ater

ial o

f a

back

ing

or s

pace

r st

rip

is c

hang

ed).

Whe

n ch

angi

ng f

rom

a d

oubl

e-w

elde

d jo

int o

r a

join

t usi

ng b

acki

ng m

ater

ial t

o an

ope

n ro

ot o

r to

a c

onsu

mab

le in

sert

jo

int.

Pipe

dia

met

erU

sual

ly n

ot r

equi

red.

In

fact

, som

e co

des

perm

it pr

oced

ure

qual

ifica

tion

on p

late

to

satis

fy th

e re

quir

emen

ts f

or w

eldi

ng to

be

perf

orm

ed o

n pi

pe.

Whe

n th

e di

amet

er o

f pi

ping

or

tubi

ng

is r

educ

ed b

elow

spe

cifi

ed li

mits

. (It

is

gene

rally

rec

ogni

zed

that

sm

alle

r pi

pe

diam

eter

s re

quir

e m

ore

soph

istic

ated

te

chni

ques

, equ

ipm

ent,

and

skill

s).


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


(Con

tinu

ed)

Type

of

curr

ent a

nd

pola

rity

(if

dc)

Usu

ally

not

req

uire

d fo

r ch

ange

s in

volv

ing

elec

trod

es o

r w

eldi

ng m

ater

ials

ada

pted

fo

r th

e ch

ange

d el

ectr

ical

cha

ract

eris

tics,

alth

ough

som

etim

es r

equi

red

for

chan

ge

from

ac

to d

c, o

r vi

ce v

ersa

, or

from

one

pol

arity

to th

e ot

her.

Usu

ally

not

req

uire

d fo

r ch

ange

s in

volv

ing

sim

ilar

elec

trod

es o

r w

eld-

ing

mat

eria

ls a

dapt

ed f

or th

e ch

ange

d el

ectr

ical

cha

ract

eris

tics.

Ele

ctro

de c

lass

ifica

-tio

n an

d si

zeW

hen

elec

trod

e cl

assi

fica

tion

is c

hang

ed o

r w

hen

the

diam

eter

is in

crea

sed

beyo

nd

that

qua

lified

.W

hen

the

elec

trod

e cl

assi

fica

tion

grou

ping

is c

hang

ed a

nd s

omet

imes

w

hen

the

elec

trod

e di

amet

er is

in

crea

sed

beyo

nd s

peci

fied

lim

its.

Wel

ding

cur

rent

Whe

n th

e cu

rren

t is

outs

ide

of th

e ra

nge

qual

ified

.U

sual

ly n

ot r

equi

red.

Posi

tion

of w

eldi

ng

(For

defi

nitio

ns, s

ee

App

endi

x A

)

Usu

ally

not

req

uire

d, b

ut d

esir

able

.W

hen

the

chan

ge e

xcee

ds th

e lim

its o

f th

e po

sitio

n(s)

qua

lified

is o

nly

requ

ired

by

som

e co

des;

oth

ers

only

w

hen

empl

oyin

g ve

rtic

al-u

p po

sitio

n.

Dep

ositi

on o

f w

eld

met

al.

Whe

n a

mar

ked

chan

ge is

mad

e in

the

man

ner

of w

eld

depo

sitio

n; e

.g.,

from

a s

mal

l be

ad to

a la

rge

bead

or

wea

ve a

rran

gem

ent o

r fr

om a

n an

neal

ing

pass

to a

no

anne

al-

ing

pass

arr

ange

men

t, or

vic

e ve

rsa.

Usu

ally

not

req

uire

d.

Prep

arat

ion

of r

oot o

f w

eld

for

seco

nd s

ide

wel

ding

Whe

n m

etho

d or

ext

ent i

s ch

ange

d.U

sual

ly n

ot r

equi

red.

Preh

eat a

nd in

terp

ass

tem

pera

ture

sW

hen

the

preh

eat o

r in

terp

ass

tem

pera

ture

is o

utsi

de th

e ra

nge

for

whi

ch q

ualifi

ed.

Usu

ally

not

req

uire

d.

Preh

eat t

reat

men

tW

hen

addi

ng o

r de

letin

g po

sthe

atin

g or

whe

n th

e po

sthe

atin

g te

mpe

ratu

re o

r tim

e cy

cle

is o

utsi

de th

e ra

nge

for

whi

ch q

ualifi

ed.

Usu

ally

not

req

uire

d.

Use

of

spat

ter

com

-po

und,

pai

nt, o

r ot

her

mat

eria

l on

the

sur-

face

s to

be

wel

ded.

Usu

ally

not

req

uire

d, b

ut d

esir

able

whe

n em

ploy

ing

unpr

oven

mat

eria

ls.

Usu

ally

not

req

uire

d.

Tab

le 1

0.1

(Co

nti

nu

ed)

Wel

ding

Pro

cedu

re S

peci

ficat

ion

and

Wel

der

Qua

lifica

tion

Fact

ors

Whi

ch M

ay R

equi

re R

equa

lifica

tion


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


prequalifications. It should be noted that onlya few codes, such as AWS D1.1, recognize theconcept of prequalified welding procedures.

10.3.2 Employment of Standard Qualifica-tion Tests.

Such tests may or may not simu-late the actual welding condition anticipatedfor a given project. Usually, such standardtests involve conventional butt joints on pipesor plates, or fillet welds between two plates.Base metals, welding consumables, and ther-mal treatments follow production weldingplans within specific tolerances. Variablessuch as joint geometry, welding position, andaccessibility are not considered essential bySection IX of the

ASME Boiler and PressureVessel Code.

4

Thus, the variables used

toqualify the welding procedure may bear littleresemblance to production conditions andshould be changed by revision of the weldingprocedure specification. Other documents,such as API 1104,

Standard for Welding Pipe-lines and Related Facilities

, require qualifica-tion tests that resemble production conditionsclosely.

10.3.3 Employment of Mock-up Tests.

Suchtests simulate actual production conditions tothe extent necessary to ascertain that a soundplan with proper tooling and inspection hasbeen selected. While few of the conventionalwelding codes and specifications mandatesuch mock-up qualifications, contractual doc-uments or trouble-shooting activities mayrequire such tests. Especially for the latter, amock-up qualification is a valuable tool todemonstrate specific skill levels under difficultor otherwise restrictive welding conditions.

The controls used to ensure the productionof satisfactory welds are (1) qualification of awelding procedure, (2) qualification of thewelders and welding operators to determinetheir ability to deposit sound weld metalusing the qualified procedure, (3) suitablesupervision and monitoring of production

4. See Chapter 17 for addresses of standards develop-ment organizations.

welding, and (4) suitable inspection prior to,during, and following completion of welding.All four are vital elements in the quality pro-duction chain. Through these controls, it ispossible to achieve, repeatedly, welds of suit-able quality and known physical and chemicalproperties.

10.4 Description

There are five basic steps in the qualifica-tion of a welding procedure:

(1) Preparation and welding of suitablesamples

(2) Testing of representative specimens(3) Evaluation of overall preparation, weld-

ing, testing, and end results(4) Possible changes in procedure(5) Approval

10.4.1 Preparation of Procedure Qualifica-tion Test Joints.

Plate or pipe assemblieswith a representative welded joint are used forprocedure qualification testing. The size,type, and thickness are governed by the thick-ness and type of material to be welded in pro-duction and the type, size, and number ofspecimens to be removed for testing. The lat-ter are usually prescribed by the applicablecode or specification. The materials used andall details associated with the welding of thetest joints should be in accordance with theparticular welding procedure specificationthat is to be qualified.

Whether the procedure is qualified orprequalified, it has to address the essential,nonessential, and supplementary essentialvariables for that process which is to bequalified.

10.4.2 Testing of Procedure QualificationWelds.

Test specimens are usually removedfrom the test joint for examination to deter-mine strength, ductility, and soundness. Thetype and number of specimens removed andthe tests made thereto depend upon therequirements of the particular code or specifi-cation. Typically, the tests include tensile and


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


guided bend specimens to determine strength,ductility, soundness, and adequacy of fusion.If only fillet welds are tested, shear tests andbreak specimens or macroetch specimens areusually employed.

Additional tests may be specified by theapplicable codes or contract documents tomeet specific needs. These may include:

(1) Impact tests to determine notch tough-ness (resistance to brittle fracture) of the weldand the HAZ at specified temperatures. WhileCharpy-V-notch specimens are most commonlyused for such tests, many other concepts,including drop weight and crack-tip-opening-displacement (CTOD) tests, are sometimesemployed.

(2) Nick-break tests to determine weldsoundness.

(3) Free Bend tests to determine the elon-gation of deposited weld metal, and weldductility.

(4) Shear tests to determine the shearstrength of fillet welds or clad bonding.

(5) Hardness tests to determine adequacyof heat treatment and suitability for certainservice conditions. Such tests may be per-formed on surfaces or on cross sections of theweld.

(6) All-weld-metal tension tests to deter-mine the mechanical properties of the depos-ited weld metal with minimum influence dueto base metal dilution.

(7) Elevated temperature tests to determinemechanical properties at temperatures resem-bling service conditions.

(8) Restraints or “torture” tests to deter-mine crack susceptibility and the ability toachieve sound welds under highly restrainedconditions.

(9) Corrosion tests to determine the proper-ties needed to withstand aggressive environ-ments including high temperature, hydrogen,chlorides, etc.(10) Nondestructive examinations and

macro or micro samples to determine thesoundness of a weld and to evaluate theinspectability of production welds.(11) Delayed cracking tests to detect resis-

tance to hydrogen cracking in HSLA (high

strength, low-alloy) steels and some othermaterials.

Most of the detailed specimen preparationand testing procedures can be found in otherchapters.

10.4.3 Evaluation of Test Results.

Once awelding procedure has been prequalified orhas been tested in accordance with the appli-cable code and contractual documents, therelevant data should be recorded in detail.Recommended forms are offered by somespecifications and representative sampleshave been reproduced in the chapter. Figure10.2 illustrates the Procedure QualificationRecord suggested by AWS B2.1, while Figure10.3 is a copy of the ASME Section IX Proce-dure Qualification Record (PQR).

In evaluating any welding procedure or anytest results, the applicable codes provide gen-eral guidance and some specific acceptance-rejection criteria. For instance, the minimumtensile strength and the maximum number ofinclusions or other discontinuities is specifiedby many documents. In general, it is best ifthe weld matches the mechanical and metal-lurgical properties of the base metal, but thisis not always possible. In addition to the weldmetal and base metal being different productforms, they often have somewhat differentchemical compositions and mechanical prop-erties. It requires engineering judgment toselect the most important properties for eachindividual application. This is especiallyimportant for service at high or low tempera-ture, and under corrosive conditions.

10.4.4 Changes in a Qualified Procedure.

Ifa fabricator that has qualified a welding pro-cedure desires at some later date to make achange in the procedure, it may be necessaryto conduct additional qualifying tests. Thesetests establish that the revised welding proce-dure will produce satisfactory results.

Such requalification tests are not usuallyrequired when only minor details of the origi-nal procedure have been changed. Theyare required, however, if the changes mightalter the properties of the resulting welds.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 10.2—Standard for Welding Procedure Qualification


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 10.2 (Continued)—Standard for Welding Procedure Qualification


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 10.3—ASME Procedure Qualification Record


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 10.3 (Continued)—ASME Procedure Qualification Record


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Reference should always be made to the gov-erning code or specification to determinewhether a given change in the welding proce-dure requires requalification.

10.4.5 Approval of Qualification Tests andProcedure Specifications.

Often welding

procedures will be approved by the customeror the authorized inspection agency beforeany production welding is performed.

QW-483 Procedure Qualification Record(PQR) (see QW-201.2, Section IX, 1974ASME Boiler and Pressure Vessel Code).


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

81

Welder, welding operator, and tack welderperformance qualification tests are used todemonstrate the ability of those tested to pro-duce acceptably sound welds using a quali-fied Welding Procedure Specification (WPS).These tests are not intended to be used as aguide for welding during actual construction,but rather to assess whether an individual hasa certain minimum skill level. The tests do notdetermine what an individual normally will orcan do in production. For this reason, com-plete assurance should not be placed on per-formance qualification testing of individualsperforming welding. The quality of produc-tion welds should be determined by inspec-tion during and following completion of theactual welding.

Various codes (such as AWS D1.1,

Struc-tural Welding Code—Steel

) and specificationsgenerally prescribe methods or details forqualifying welders, welding operators, andtack welders. The applicable code or docu-ment should be consulted for specific detailsand requirements. A detailed description of astandard system for performance quali-fications can be found in AWS B2.1,

Standardfor Welding Procedure and PerformanceQualification

.

5

The types of performance qualificationtests that are most frequently required aredescribed in this chapter.

11.1 Performance Qualification Requirements

The qualification requirements for weldingpressure vessels, piping systems, structures,

5. AWS standards are available from American Weld-ing Society, 550 N.W. LeJeune Road, Miami, FL33126.

and sheet metal usually state that everywelder or welding operator shall make one ormore test welds using a qualified weldingprocedure. Each qualification weld is tested ina specific manner (i.e., radiography or bendtests). In addition, essential variables thatinfluence the welding are usually limited tocertain ranges, such as the thickness of mate-rial and the test positions that will qualify forwelding on different thicknesses and in differ-ent positions. Some variables pertinent to per-formance qualification testing and the extentof qualification are the groove type, whetheror not the joint has backing, and the directionof welding in depositing weld metal.

Performance qualification requirements forwelding pressure pipe differ from those forwelding plate and structural members chieflyin the type of test assemblies used. Whetherqualifying fillet welds or groove welds, con-sideration for test requirements should also beconsidered, for the qualification requirementsmay differ. The test positions may also differto some extent. As a rule, the test requires useof pipe assemblies instead of flat plate.Accessibility restrictions may also beincluded as a qualification factor if the pro-duction work involves welding in restrictedspaces.

11.1.1 Essential Variables.

Since it isimpractical to test a welder for all the possiblevariables to be met in production, most codesestablish limitations or ranges within whichthese variables are assumed not to change theresults. The variables cover such items aswelding process, base metal type and thick-ness, filler metal, shielding medium, position,and root welding technique. The followingare examples of essential variable changeswhich may require requalification of thewelder:

Chapter 11Qualification of Welders and Welding Operators


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

82/Qualification of Welders and Welding Operators

(1)

Welding Process

. For example, achange from gas tungsten arc welding(GTAW) to submerged arc welding (SAW).

(2)

Filler Metal

. Filler metals are dividedinto groups and assigned “F” numbers. Thegrouping of electrodes and welding rods isbased essentially on the usability characteris-tics that fundamentally determine the abilityof a welder to make satisfactory welds with agiven electrode.

(3)

Welding position

. Positions are classi-fied differently for plate and pipe. A change inposition may require requalification. For exam-ple with pipe welding, a change from rotated tofixed position requires requalification.

(4)

Joint detail

. For example, the omissionof backing on joints welded from one-sideonly may require requalification.

(5)

Thickness

. Test plates are generallytested at two or three thicknesses. To allowthe welder to weld the production thicknessesrequired, it may be necessary to qualify onmore than one test thickness.

(6)

Technique

. A change in the weldingtechnique may also require a welder torequalify. For example, in vertical positionwelding a change in the direction of weldingprogression normally requires requalification.Where a combination of uphill and downhillprogression is to be used in production, awelder may be qualified by a single test usingthe same combination as specified in produc-tion welding.

11.2 The Test Specimen

A typical qualification test plate from AWSD1.1,


, forunlimited thickness is shown in Figure 11.1A.The plate is 1 in. (25.4 mm) thick with a 45

°

groove angle and a 1/4 in. (6.35 mm) rootopening.

The groove weld plate for limited thickness(less than 3/4 in. [19.05 mm]) qualification isessentially the same as the plate shown inFigure 11.1A and B except for the thickness.The plate thickness is 3/8 in. (9.5 mm).

Joint detail for groove weld qualificationtests for butt joints on pipe or square or rectan-

gular tubing should be in accordance with aqualified welding procedure specification for asingle welded pipe butt joint (see Figure11.2A). As an alternative, the following jointdetails are frequently used: pipe diameter-wallthickness as required, single-V-groove weld,60 degree groove angle, and suitable rootopening with backing (see Figure 11.2B).

Codes and specifications nearly alwaysrequire that welder qualification tests be madein one or more of the most difficult positionsto be encountered in production (e.g., vertical,horizontal, or overhead) if the productionwork involves other than flat position weld-ing. In most cases, qualification in a more dif-ficult position qualifies for welding in lessdifficult positions (e.g., qualification in thevertical, horizontal, or overhead position isusually considered adequate for welding inthe flat position). Figures 11.3A and Billustrate the ranges of positions designatedfor production groove and fillet welds,respectively.

Figures 11.4 through 11.7 illustrate weld-ing positions for groove and fillet welds intest samples for both plate and tubular shapes.

11.3 Testing of Qualification Welds

All codes and specifications have definiterules for testing qualification welds to deter-mine compliance with requirements. The testsmost frequently required for groove welds aremechanical bend tests of which specimens areremoved from specific locations in the welds.Fillet welds do not readily lend themselves tomechanical bend tests. In such cases, filletweld break tests or macroetch tests, or both,may be required. For a description of thesetests, see Chapter 13.

Radiographic testing is sometimes allowedas an alternative to mechanical or other tests.Penetrant examination is frequently requiredon welds, especially those in nonferrous andother nonmagnetic materials. Some codeshave requirements and acceptance standardsfor visual examination or workmanship stan-dards in addition to destructive testing andother nondestructive examinations.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Qualification of Welders and Welding Operators/83

Figure 11.1A—Test Plate for Unlimited Thickness—Welder Qualification

Figure 11.1B—Optional Test Plate for Unlimited Thickness—Horizontal Position—Welder Qualification


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 11.2A—Tubular Butt Joint—Welder Qualification—Without Backing

Figure 11.2B—Tubular Butt Joint—Welder Qualification—With Backing

Usually, the primary requirement is that thetest welds be sound and thoroughly fused tothe base metal. Welders who make test weldsthat meet the prescribed requirements areconsidered to be qualified to apply the pro-cess and weld with filler metals and proce-dures similar to those used in testing.

11.4 Qualification Records

Records of both the tests made for the qual-ification of welders and welding operators andof their usage of the process for which theywere qualified are essential. An illustrativerecord form for welder or welding operatorqualification testing is shown in Figure 11.8.

11.5 Standardization of Tests

The objective of welder and welding opera-tor qualification tests is to determine whetherthe person has the ability to deposit soundweld metal. Examination of test specimenshelps to determine this. However, the test spec-imen welds required for performance qualifi-cation tests do not always correspond in detailto those that will be encountered in productionwelding. The reason for this is that many vari-ations exist in normal production welding, andto cover all the details would require far toomany tests. In addition, it has been found thatadditional tests add little to the informationabout the welder’s or welding operator’s abil-ity. For this reason, welder or welding operator

qualification tests have been standardized toeliminate the need for additional qualificationtests every time a procedure or productionapplication detail is slightly altered.

Separate requalification tests are requiredwhenever radically different procedures orproduction conditions are involved. In addi-tion, for some critical production weldingapplications, in-process performance tests aresometimes required.

11.6 Relation of Qualification Tests to Welder or Welding Operator Training

As previously noted, the welds required forqualification are not usually identical to thosea welder or welding operator will be requiredto make during normal production work. Forthis reason, it is not enough to train a welderor welding operator only to the extent neces-sary to pass the prescribed qualification tests.Training should be broader and more exten-sive, sufficient to cover all procedures andjoint details that will be encountered in actualproduction. This training is the responsibilityof the fabricator.

11.6.1 Welding Certification.

Written veri-fication that a welder has produced welds meet-ing a prescribed standard of welder performance.

11.6.2 Welder Performance Qualification.

The demonstration of a welder’s ability toproduce welds meeting prescribed standards.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 11.3A—Positions of Groove Welds

Tabulation of positions of groove welds

Position Diagram reference Inclination of axis Rotation of face

Flat A 0° to 15° 150° to 210°

Horizontal B 0° to 15° 080° to 150°210° to 360°

Overhead C 0° to 80° 000° to 80°0280° to 360°

Vertical D 15° to 80°80° to 90°

080° to 280°000° to 360°

Notes:1. The horizontal reference plane is always taken to lie below the weld under construction.2. The inclination of the weld axis is measured from the horizontal reference plane toward the vertical

reference point.3. The axis of rotation of the weld face is determined by a line perpendicular to the weld face at its

center which passes through the weld axis. The reference position (0 degrees) or rotation of theweld face invariably points in the direction opposite to that in which the weld axis angle increases.When looking at point “P,” the angle of rotation of the weld face is measured in a clockwise directionfrom the reference position (0 degrees).


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 11.3B—Positions of Fillet Welds

Tabulation of positions of fillet welds

Position Diagram reference Inclination of axis Rotation of face

Flat A 0° to 15° 150° to 210°

Horizontal B 0° to 15° 125° to 150°210° to 235°

Overhead C 0° to 80° 000° to 125°235° to 360°

Vertical DE

15° to 80°80° to 90°

125° to 235°000° to 360°

Notes:1. The horizontal reference plane is always taken to lie below the weld under construction.2. The inclination of the weld axis is measured from the horizontal reference plane toward the vertical

reference point.3. The axis of rotation of the weld face is determined by a line perpendicular to the weld face at its

center which passes through the weld axis. The reference position (0 degrees) or rotation of theweld face invariably points in the direction opposite to that in which the weld axis angle increases.When looking at point “P,” the angle of rotation of the weld face is measured in a clockwise directionfrom the reference position (0 degrees).


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 11.4—Positions of Test Plates for Groove Welds


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 11.5—Positions of Test Pipe or Tubing for Groove Welds


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 11.6—Positions of Test Plate for Fillet Welds


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 11.7—Positions of Test Pipes for Fillet Welds


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 11.8—Suggested Form for Welding Performance Qualification


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

93

12.1 Control Data

The widespread application of computersthroughout all industries has made a majorimpact on the way business functions are nowaccomplished. The use of computers in differ-ent work environments is prompted by agrowing business need for improved perfor-mance. Computers are used by industries in awide variety of functional areas, both foroffice and manufacturing applications. Com-puters can provide improved efficiency at rea-sonable costs in areas such as the following:

(1)

Office

(a) Correspondence and letter files(b) Payroll and financial management(c) Management planning and control

of schedules and costs(d) Marketing and sales(e) Purchasing(f) Engineering design and scientific

calculations(g) Electronic mail

(2)

Manufacturing

(a) Welding process control(b) Shop automation(c) Inventory control(d) Production scheduling(e) Quality assurance, quality control

and nondestructive examinationPersonal computer software for general use

is readily available for word processing,spreadsheet data base management applica-tions, and statistical analysis. Much of thepaperwork connected with welding inspectionand quality control can be eliminated by stor-ing information in computerized data basesthat organize it and allow the user to recall itin a useful order. Compared to hard-copyarchiving, the benefits of computerized stor-age are numerous: it speeds data recording by

substituting keypad input or bar-code readingfor handwriting; can avoid errors in datarecording and retrieval inherent with manualentry; gives easy and comprehensive access toinformation; keeps up-to-the minute records;and single entries can simultaneously updateall affected documents.

Additionally, computer programs can bene-fit the user by acting as a teaching tool. Train-ing personnel in the use of computers andsoftware is crucial to successful integration ofworkplace computerization. Such training canbe performed on-site at a central trainingfacility sponsored by software vendors, or insome cases, with computer software trainingmodules.

This chapter will highlight welding inspec-tion and quality-control improvements gainedthrough the use of computers and softwareand will provide an overview of welding andinspection data management and the use ofstatistics as a tool to control variability ofprocesses.

12.1.1 Welding Inspection Applications.

Statistics, computers, and commerciallyavailable software can provide valuable assis-tance in the welding inspection and documen-tation functions. Through the proper use ofthese tools, quality and productivity can begained with cost savings. These improve-ments can be achieved through the establish-ment of a welding inspection data base forregularly performed welding processes. Thisinspection data base can be used in controlcharts for identification of in- and out-of-control conditions, and to aid in the establish-ment of realistic and accurate process controllimits.

When welding inspection data is thus orga-nized so that it can be readily analyzed to pro-vide meaningful information, the quality of

Chapter 12Computerization of Welding Inspection and Quality


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

94/Computerization of Welding Inspection and Quality

the welding process can be improved. Thefollowing are some representative attributesfor monitoring:

(1) Classification of defects by grading oftypes

(2) Severity and number of occurrencesobserved

(3) Weld process, operator, and equipmentused

(4) Ambient environment, including tem-perature, humidity, etc.

(5) Article welded(6) Condition of joint prior to welding(7) Joint cleanliness(8) Repair and rework(9) Variables of weld processesThe use of weld reject data in the form of

bar charts, by deficiency type and frequencyof occurrences can be a powerful tool inimproving quality and reducing the number ofrejected welds by directing attention to the

greatest offenders. Such charting can be facil-itated by the computerized data base.

A welding inspection data base can be usedto store technical project information forwelding procedures, welder performance andinspection data as shown in Figure 12.1. Thisdata can include welding procedure specifica-tion and welder performance information,inspection results, accept/reject rates, processuse, NDE procedures, inspector/tester certifi-cations, and instrument calibration controlsystems.

Hands-free computer technology existswhich allows for remote accessing of thecomputer as through a headset, thus reducingtime and effort. Storage and retrieval of infor-mation can occur through a verbal dialoguebetween the inspector and the computer. Cur-rently this technology may be available athigh cost and in limited applications.

On-line computer hardware and softwareprograms are available that take data directly

File: NUCMD Record Number: 248 Change Weld Information? Yes No

PERSONAL DATA WELDING DATA

I.D. Number 37136Name JOE SMITHDate of Birth 01/23/56Initial Date 01/23/88Primary Update 01/23/88Secondary Update 01/23/88Renewal Date 01/23/88

Process GMAW Type Semi-AutomaticCurrent (AC/DCRP/DCSP/NA) DCRPJoint Type PIPE GROOVE—ONE SIDEWeld Metal Thk. (In.) 0.093Weld Filler F No. 6Base Metal Thk. (In.) 0.218Base Metal P No. 1Type of Fuel Gas N/ABacking METAL Insert NPosition 6GPipe Size (In.) 2.000Weld Progression UPArc Trans. Method SARCPart No N/ATravel Speed (ipm) N/AFil. Metal Desc. E70T 1Base Metal Desc. A106 Grade B

TEST DATA

Conducted By L. MCDUFFIE, SR.Type of Test (RT/Btr/Bln/Fil/Ten)BTRProc. No./PQT No. LHC36 Revision Number 2Test Report Number TR345

This formatted screen represents a complete welder-qualification record. All new records and modificationsshould fit this format, a sure way to keep consistent, complete records.

Figure 12.1—A Welding Inspection Data Base


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Computerization of Welding Inspection and Quality/95

from instrumentation on resistance weldingmachines and evaluates the data to determineweld quality. Some will print out images ofheat patterns within a weld nugget to give animage of the nugget and will rate the weld asacceptable or rejectable.

12.1.1.1 Quality Assurance and Inspec-tor Computer Interfaces.

Inspectors shoulduse a common means of classifying weldingand inspection data. This classification sys-tem should be based on clearly defined termsto enable the inspector to identify the specificor relative quality observed during the inspec-tion. This is necessary to achieve uniformityamong inspectors’ observations and to pro-vide the basis for data organization statisticscorrelation accuracy, or at least consistency.Nonstandard terms, adjectives, or classifica-tions would not be recognized by the database software.

Real-time computer hardware and softwarecan provide for direct analysis of nondestruc-tive examination. An example of this type ofapplication is when electronic test signals godirectly to the computer for analysis by theinspector.

12.1.1.2 Use of Computers.

QA and QCorganizations can generate essential datawhich should be accessible and can be use-fully analyzed. Computers can be used to gofrom a manual paper filing system to an elec-tronic filing system, thereby realizing costsavings by eliminating the need to microfilm.Increased productivity and improved qualitycan be realized through the use of ComputerAided Drafting (CAD), Computer AidedManufacturing (CAM), and coordinate mea-suring machines which provide automatedmeasurement of dimensions. Other potentialreasons to manage data are the following:

(1) Customer complaints(2) Field service reports(3) Weld process stability and control(4) Reliability and trend analysis(5) Quality cost dataCommercially available software and hard-

ware allow users to tailor the system to theirown application. A basic approach to incorpo-

rating computers into the inspection areaincludes:

(1) Start small—it’s easier to justify thecost, and it provides insight into what is reallyneeded.

(2) Consider computer compatibility withother office equipment.

(3) Use commercial software and hard-ware—don’t reinvent the wheel.

(4) Select a reliable vendor that has a goodreputation and provides good service and sup-port for personnel training and maintenanceof the equipment.

(5) Start with inspection areas such asincoming inspection of weld material andvendor control.

(6) Evaluate the human factor. A change inthe way people work can affect processes andorganizational relationships.

(7) Initial development of the data entryand analysis system should be performed bythe same individuals.

(8) Developed programs can be operated byproperly trained personnel.

12.1.1.3 Hardware.

A computerized qual-ity control system may be a stand alone workstation or it may be connected to other sys-tems or to a central main computer. In anycase, the QC work station will require, atminimum, a dedicated or shared processingunit (the computer); a data input device (key-board, optical reader, or other); an alphanu-meric readout device (video monitor, digitalalphanumeric display, or other); a printer toproduce hard copies for signoffs and otherpurposes; and a modem for plant-to-plant orshop-to-field communications.

12.1.1.4 Software.

Software (computerapplication programs) selection should followan analysis of the actual applications. Goodcomputer software is readily available. Thefollowing general software categories will beuseful in the quality assurance and inspectionenvironment:

12.1.1.4.1 Word Processing Pro-grams—Applications of Word ProcessingSoftware.

Word Processing software allows


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


the computer to replace the typewriter as atyping tool. Advantages of word processinginclude:

(1) Typing can be done and correctionsmade before anything is put on paper, mini-mizing typographical errors.

(2) Editing can be done simply and easily.Major changes can be made without cuttingand pasting or use of correction fluids.

(3) Using the computer the author can com-pose, edit and print letters, or reports. Thiseliminates many steps in composing on paper,having it typed, correcting errors and editing,retyping, etc.

(4) Model letters, reports, etc., can be usedas blanks and can be modified as necessaryto produce new ones. This eliminates retyp-ing everything from scratch for repetitiveoperations.

(5) Originals can be stored electronically,taking up much less space than paper copies.

Word processing can be used in almost anyway that the typewriter can. It can be used toproduce letters, reports, viewgraphs, lists,procedures, and forms.

12.1.1.4.2 Spreadsheet Programs—Applications of Spreadsheet Software.

Spreadsheets are used when forms, lists,tables, and graphs are to be prepared. Theyspecialize in areas where calculations are tobe performed on tables or lists of numbers, orwhere sorting is desired. With most softwareprograms, graphs can be produced from thetables or lists of data that are being manipu-lated. Advantages of spreadsheet softwareinclude the following:

(1) Tables of numbers can be added, multi-plied, etc., quickly by the computer, thenprinted.

(2) Data entry errors can be corrected eas-ily without spoiling the calculation as whenusing a calculator.

(3) A set of numbers can be used for manydifferent calculations without having to enterthe data more than once.

(4) Graphs based on the data can be pre-pared automatically.

(5) Data can be sorted by magnitude oralphabetized automatically by the computer.

Spreadsheet software is used when repeti-tive calculations are to be performed to com-plete forms, tables, or graphs. It is especiallyuseful when the form of the table is constant,but the data is updated periodically, andwhere several calculations are to be per-formed on the same data.

12.1.1.4.3 Database Management—Ap-plications of Database Management Soft-ware.

Database management software is usedfor the ordered storage of related pieces ofdata, and excels at maintaining files of infor-mation that have a constant form such as phonedirectories, personnel files, etc. Once the datais entered, the database can be searched to findinformation that is related in any of variousways. Advantages of this software include thefollowing:

(1) Needs less storage in much less spacethan paper.

(2) Searches of the database can be donefor needed information without poring overlarge quantities of paper; thecomputer does the searching.

(3) Information can be updated at any time,so that it is always current.

(4) Changes to the data do not require theproduction of new pieces of paper.

12.1.1.5 Special Purpose Programs.

Themarket offers dozens of quality control pro-grams. Companies may either design theirown programs or purchase software packagesthat can be customized to specific operations.Almost without exception, users of QC com-puter programs require that the software con-form to existing operations.

QC software programs commonly dupli-cate record-keeping formats used by manu-facturers. A flashing cursor signal prompts theuser through QC-record pages item by item,to enter the data. The software acts as a teach-ing and QC tool, assuring that every itemnecessary to a procedure is recorded, thusavoiding oversights and errors. The followingare examples of special purpose QC softwareprograms:


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Computerization of Welding Inspection and Quality/97

(1) Welder performance and welding pro-cedure qualification record keeping softwareincludes lists of welders who are qualified togiven procedures, and can identify and main-tain welders’ names and requalification dates.

(2) QC functions such as tracking of defectand reject rates by the welder, by the job, orby the procedure.

(3) Code specific, and user assistancesoftware.

(4) Libraries of prequalified and recom-mended welding procedures

(5) Computer-aided inspection record sys-tems which combine visual and ultrasonicinspection methods with computer aideddrafting and records management of actualrepairs and schedule priority.

12.1.1.6 Statistical Process Control.

Com-puters make possible the use of statistical pro-cess control (SPC), a technique that allowsfor collection and analysis of large amountsof data. There are numerous companies thatmake software products for statistical processcontrol. These products frequently supportstatistical analyses, quality cost analysis,gauge repeatability monitoring, data acquisi-tion, graphics, and plotting. Software prod-ucts can vary in hardware compatibility andcosts. The use of software products for SPCcan provide a valuable tool in properly inter-preting the large amounts of data that qualitydepartments generally produce. Several eval-uation criteria for selecting SPC software fora quality program are

(1) Ease of use,(2) Good documentation,(3) Comprehensiveness,(4) Service/support,(5) Reputation of supplier,(6) Price,(7) Quality of output (i.e., graphs, charts),(8) Portability of software between differ-

ent types of hardware for informationretrieval and analysis between different worklocations.

12.1.1.7 Quality Trends Identificationand Control Charts.

In-process inspection

provides important information for achievingquality and is the first point of contact withthe product or process. To assure quality,inspection cannot be the end objective, ratherit is a way of reducing waste and improvingproduct quality. Replacing the “conformance-to-specification limits” criteria with the ideaof reducing product variability, is a viableway to improve the overall quality. Theinspection function provides data gathering torecognize quality trends, analyze data andestablish achievable control limits. There aremany types of control charts.

Control charts can be used as a tool fortracking inspection information and identify-ing out-of-bounds situations or product vari-ability. Control charts allow variations to beseparated into common or system causes,which need to be brought to management’sattention, or local variations, which are theworkers’ responsibility. Control charts cantrack weld reject causes and point out whenattention or change is needed and minimizeprocess adjustment.

To set up a control chart, the followingsteps will assist in determining the informa-tion that is needed:

(1) Decide what and how frequently tomeasure.

(2) Collect a representative sample ofdata.

(3) Determine the upper and lower controllimits.

Quality is built into the product and cannotbe inspected into the product. SPC and simplecontrol charts can be used as tools to helpidentify nonconforming welding trends soappropriate attention can be applied toachieve a stable process, obtain informationon important variables, reduce manufactur-ing and inspection costs, and promote pro-cess/product understanding.

12.1.1 Summary.

The computer can providevaluable assistance to the welding inspectorin helping to carry out job functions in a moreeffective and efficient manner. Perhaps thegreatest benefits that can be realized throughthe use of computers includes improved cycle


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


time, reduced cost of performing processingoperations, greater production, and improvedquality, consistency and accuracy of informa-tion. Personnel could have improved access toappropriate information necessary to perform

their job function. Both computer softwareand hardware are increasingly user-friendlyso that the benefits mentioned above areachievable without extensive technical com-puter skills.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

99

Historically, the testing of welds in weldedstructures is as old as welding. Early testingwas directed toward detecting gross defectsand evidence of ductility. This evolved intotests designed to determine specifics such aschemical, mechanical, and metallurgicalproperties, and to locate defects such ascracks, porosity, incomplete fusion, inade-quate joint penetration, entrapped slag, etc.

Most of these tests are, of necessity,destructive in nature. They are generally per-formed on sample weldments made with pro-cedures duplicating as close as possible thoseused in the fabrication of the actual weldedstructure.

Tests are conducted for the qualification ofwelding procedures, the qualification of weld-ers and welding operators, and for qualitycontrol. These destructive tests may be chem-ical tests, metallographic tests, mechanicaltests, or any combination thereof. The testsspecified should be those that provide reason-able assurance of the required performance ofthe weldment in service.

The ideal test would, of course, be one thatexactly duplicates the service conditions.However, the difficulty and cost of applyingsuch tests is obvious; thus, certain standardtests are alternatively used. Details of destruc-tive tests of welded joints and deposited fillermetals can be found in the latest edition ofAWS B4.0,

Standard Methods for Mechani-cal Testing of Welds

.

6

The inspector has the responsibility to con-firm that specified tests are conducted prop-erly and that test results are in compliancewith required specifications. The inspector

6. Available from American Welding Society, 550N.W. LeJeune Road, Miami, FL 33126.

needs to be thoroughly familiar with the test-ing procedures, the effect of revealed defectson the test results, and the interrelation ofdefects in the test sample with the same typesof defects in the production weldment. With athorough background in these, one will beable to discuss test results with engineeringpersonnel to gain final acceptance or rejectionof production work. No matter how carefullycodes and specifications are written, much isleft to the judgment of the inspector. In fair-ness to oneself, the manufacturer, and theemployer, one should be equipped with athorough knowledge on which to base deci-sions. The inspector has the sole responsibil-ity of confirming that the weld jointproperties are in accordance with the specifi-cation. Acceptance of material that does notconform to specification requirements canonly be made by an authorized engineer.

Brief descriptions of various types of stan-dard destructive tests applied to welds andweldments follow. The effect of defects onthe results of these tests is presented briefly. Itis realized that much more could be written,but is hoped that interested inspectors willavail themselves of opportunities for furtherstudy of the technical literature.

Tests should be performed with carefulattention to specimen preparation and the testprocedure. The quality and reliability of testresults is in direct proportion to the care takenin the test. In general, the term

destructivetesting

is used to describe an evaluation pro-cess of a weld by a technique that of necessitydestroys the test specimen or destroys its abil-ity to function in its design application. Thedestructive testing technique should, there-fore, be used with some form of partial sam-pling, rather than complete sampling (seeChapter 14).

Chapter 13Destructive Testing of Welds


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

100/Destructive Testing of Welds

The destructive testing techniques can beclassified as three general types: chemical,metallographic, and mechanical.

13.1 Chemical Tests

Usually, chemical tests are conducted on aspecimen to determine its chemical composi-tion or its resistance to corrosion.

13.1.1 Chemical Composition Tests.

Testsfor chemical composition are often requiredto ascertain whether the base metal and theweld metal meet the requirements of thecodes or specifications. Special analyses ofbase metal and weld metal are used for spe-cial service requirements. Experience indi-cates what range of composition is suitablefor a particular service condition. A chemicalcomposition of the base metal and filler metalshould be selected that will perform satisfac-torily in service.

Weld defects are sometimes caused by vari-ations in chemical composition of the base orfiller metals. Variations in composition suchas high sulfur or phosphorous, or residual ele-ments such as tin, can cause weld discontinui-ties, defects, or both. Complete chemicalanalysis of the material and weld compositionshould be made and thoroughly reviewedwhen cracking persists.

In general, deposited composition of theweld metal should match as closely as possi-ble that of the base metal. However, if no heattreatment of the weldment is performed,sometimes, depending upon the servicerequirements of the joint, a weld metal of sig-nificantly different composition from that ofthe base metal is specified.

13.1.2 Corrosion Tests.

Corrosion of weldsand weldments is a great concern for the man-ufacturer and customer of numerous itemsranging from welded equipment for thechemical industry and refineries, automobilebodies, welded ship hulls, metal containers,etc., which should perform satisfactorily invarious environments, many of which are cor-rosive. Many tests have been devised to simu-late the type of corrosion anticipated in

corrosive environments. These tests canaccelerate trans- or intergranular corrosion,pitting corrosion, stress corrosion cracking,and other preferential types of attack. Testsare conducted under laboratory conditionsand can provide a reasonably accurate fore-cast of the weldment performance in service.

Welding is used for joining a wide range ofmetals, including iron, nickel, copper, alumi-num, magnesium, titanium, and their alloys.Corrosion tests are available for all alloysused in construction. No effort will be madein this text to describe any specific test.Details of test procedures for conducting cor-rosion tests can be found in ASTM standards(refer to the

Annual Index to Standards

forspecific test procedures).

13.2 Metallographic Tests

Metallographic examination is sometimesrequired in specifications for weldments. It isused to determine the following:

(1) The soundness of welds(2) The distribution of nonmetallic inclu-

sions in the weld(3) The number of weld passes(4) The metallurgical structure in the weld

and fusion zone(5) The extent and metallurgical structure

of the heat-affected zone(6) The location and depth of penetration of

the weldThese tests may involve merely visual

examination, in which case the prepared spec-imens (called

macro-specimens

) are etched tobring out the gross structure and bead config-uration and are examined by the unaided eyeor at magnifications below 10X; or they mayinvolve microscopic examination, in whichcase the specimens (called

micro-specimens

)are prepared and etched for examination atmagnifications over 10X.

Samples may be secured by sectioning testwelds or production control welds includingrun-off tabs. They can be prepared by cutting,machining, grinding, or polishing to revealthe desired surface for etching.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Destructive Testing of Welds/101

Sectioning production welds by core drill-ing or trepanning has been used for years as aquality-control tool. However, the reweldingof the cored or trepanned areas was oftenmore difficult than the original welding andfrequently produced defects in the repair area.This concern, together with the extensiveimprovements in nondestructive examina-tion, have made obsolete the sectioning ofproduction welds as a quality-control tool. Infact, many users prohibit sectioning for suchpurposes. However, sectioning remains animportant tool for failure analysis.

13.2.1 Macro Specimens.

For macroscopicexamination, different metals require differ-ent methods of preparation. As an example,for plain-carbon steel welds, the surface to beexamined may be prepared by one of the fol-lowing methods:

(1) After sectioning the weld, and prepar-ing a relatively smooth finish on the surface tobe examined, place in a 50 percent solution ofhydrochloric acid in water at 150

°

F (66

°

C)until there is a clear definition of the macrostructure of the weld. This will requireapproximately one-half hour immersion.

(2) Another type of macro specimen is pre-pared by grinding and polishing smooth spec-imens with an emery wheel or emery paper,and then etch by treating with a solution ofone part by weight ammonium persulphate(solid) and nine parts of water. The solutionshould be used at room temperature andshould be applied by swabbing the surface tobe etched with a piece of cotton that is alwayssaturated with the solution. The etching pro-cess should be continued until there is a cleardefinition of the macro structure of the weld.

After being etched, the specimens arewashed in clear water and the excess water isquickly removed. The specimens are thenwashed with propyl or ethyl alcohol anddried. The etched surface may be preservedby the application of a thin, clear lacquer. Fig-ure 13.1 shows two typical macroetched sam-ples (see also illustrations of weld flaws inChapter 9).

Macroscopic examination is used to revealthe number of weld passes, the penetration ofthe weld, the extent of weld undercut, theextent of the heat-affected zone (HAZ), andgross discontinuities. Defects shown to existby various nondestructive examinations canbe exposed for further evaluation by usingmacroscopic examination.

13.2.2 Micro Specimens.

When examiningfor exceedingly small defects or for metallur-gical structure at high magnification, speci-mens should be cut from the actual weldmentor from welded test specimen samples. Thesemicro specimens are given a highly polishedmirror-like surface and etched for examina-tion with a metallograph at an appropriatemagnification to reveal the structure of thebase metal, HAZ, fusion zone, weld metaldeposit, segregation, small discontinuities,etc.

Figure 13.2 shows a photomicrograph of acrack in the heat-affected zone. Figure 13.3illustrates the weld metal, HAZ, and the basemetal of an electroslag weld.

Figure 13.1—TypicalPhotomacrographs


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Samples such as these may be required insome codes and specifications; they are fre-quently useful in identifying problems and indetermining solutions. A qualified metallog-rapher can read a great deal from microscopicexaminations. However, the procedure iscomplicated; considerable skill is necessaryto properly polish the samples and to use theproper etchants and technique to show what isdesired. (For a detailed discussion of micro-scopic examination procedures, referencemay be made to ASTM Standards E2 and E3.)

13.3 Mechanical Tests

For any welded product, the determinationof the quality of welds depends to a largeextent on competent inspection and adequatetesting. In general, specifications and codescall out the mechanical tests for weld strengthand other weld and HAZ properties to deter-mine the quality of welds and adjacent areas.In addition, other tests (both destructive andnondestructive) may be required.

Mechanical tests for welds are similar tothe mechanical tests applied to base metals,altered as necessary to determine the proper-ties of the areas of the welds. There are other

specialized tests used to determine materialproperties; however, these are beyond thescope of this section.

This section gives suggested requirementsfor mechanical testing, and the methods ofobtaining the desired information. It is not a

Figure 13.2—Photomicrograph Illustrating the Appearance of a Crack

in the Heat-Affected Zone(Approximately 100X)

Figure 13.3(A)—Photomacrograph 1 in. Thick Electroslag Weld in ASTM A236

(B)—Photomicrograph (100X) of Heat-Affected Zone of Same Weldment

(C)—Photomicrograph (100X) of Weld Metal, Same Weldment


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


specification. Those who call for mechanicaltests as a portion of a specification for awelded product should state definitely:

(1) The one or more tests that are required(2) The AWS or other applicable standard

that covers the procedures for testing(3) The limiting numerical values of the

properties and the minimum and maximumlimits permitted, and

(4) The interpretation, if any needed, of thetest results.

Although there may be agreement amongthe design and welding engineers on proper-ties to be determined and, in general, on testprocedures, there has been of necessity a widedivergence relative to the shape and size ofthe specimens and the details of the testprocedures.

In preparing this section, no attempt hasbeen made to cover the use of new or unusedtests.

This section will describe tests that aremost frequently used for determining themechanical properties of weld metal andwelded joints, including the standard hard-ness tests, tension tests, shear tests, and someother tests that are commonly used, thoughsomewhat specialized.

7

If there are specifications for the basemetal, tests should be conducted in accor-dance with these specifications. If no suchbase metal specifications have been listed, yeta test is desired, the tests should be conductedin accordance with the standards of ASTM.

The terminology used in this section con-forms to the ASTM Standard E6,

StandardDefinitions of Terms Relating to Methods ofTesting

. The term

soundness

as used heremeans a degree of freedom from defects dis-cernible by visual inspection of any exposedsurface of weld and or adjacent metal aftertesting. In reports of tests made in accordance

7. All tests described should be carried out in accor-dance with applicable ASTM and AWS standards.Some of these are as follows: (1) Tension Testing ofMetallic Materials, (2) Notched Bar Impact Testing ofMetallic Materials, (3) Guided Bend Test for Ductilityof Welds.

with this section, nomenclature should con-form to the above standards and definitions.

13.3.1 Mechanical Properties.

The weldmetal properties most generally required byspecifications (hardness, tensile strength,yield point, yield strength, and ductility) willbe described briefly. (Reference may be madeto AWS or ASTM standards for detailed defi-nition and explanation of these properties, aswell as for others not covered.)

13.3.2 Hardness Tests.

The hardness of aweldment or a weld is determined by forcinga hardened steel ball or diamond point into aflat surface on the weldment or welded speci-men, with a predetermined load, in a cali-brated hardness testing machine, andmeasuring the size of the resultant indenta-tion. Hardness is affected by the compositionof the base metal and the weld metal, the met-allurgical effects of the welding process andcooling rate, cold working of the metal, heattreatment, and many other factors. Certaincodes, specifications, and other standards, aswell as experience has dictated that limita-tions be placed on the hardness range of oneor more of the following: the base metal,HAZ, fusion line, and weld metal of certainmetals (usually higher carbon and alloysteels). If too hard, they will not have suffi-cient ductility for the service conditions, theircorrosion resistance may be impaired, orsome other factor may dictate this limitation.

The following are the most widely usedmethods of measuring hardness, and withthem, a brief discussion of their limitationsand the factors that should be considered toobtain as accurate as possible readings. Thethree most widely used scales for hardnessmeasurement are the Brinell, the Rockwell,and the Vickers.

Equipment used for hardness testing differsin many respects, as indicated in subsequentparagraphs. For the welding inspector, themost important difference involves the size ofthe indentor, which may range from a0.394 in. (10 mm) diameter ball to a smalldiamond tip. When such tools are used, themetal indentation may range between


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


0.197 in. (5 mm) and a small fraction of amillimeter. For reasonably homogenous basemetal and weld metal, the size of the indenta-tion has little effect on the test results. How-ever, when an HAZ that may be 0.118 in.(3 mm) wide and contains several metallurgi-cally differing zones is tested, the size of theindentation is of major importance. A smallindentor may detect the hardened zone or thesoft or tempered zone, while the 0.394 in.(10 mm) ball represents an average value.Thus, any test requirement that includes HAZhardness should specify and record the size ofthe indentor employed.

13.3.2.1 Brinell.

The Brinell hardness testconsists of impressing a special hardened steelball into the specimen under test, using a defi-nite load for a definite time and accuratelymeasuring the diameter of the impression. Thespecimen should be thick enough so thatdeflection of the specimen is minimized. Sta-tionary machines employ hydraulic pressureto impress a 0.394 in. (10 mm) ball into thespecimen. The load for steel is 6615 lb(3000 kg) and for softer metals, 1100 lb(500 kg).

The diameter of the impression is measuredby the eye, using a special, high-powerBrinell microscope graduated in tenths ofmillimeters. The average of two diameters atright angles to each other is determined, andthe Brinell hardness number, obtained from achart or table of diameters of impressionrelated to hardness numbers.

An alternate portable method of Brinelltesting is available when the configuration ofthe weldment size, or both, prevents it frombeing placed on a Brinell testing machine.This test consists of impressing a 0.394 in.(10 mm) ball simultaneously into a specimenof known hardness and the test piece. Toobtain a hardness number, the tester is held insuch a way that the ball is between the bar ofknown hardness and the specimen. The anvilis struck a sharp blow with a hammer, thediameters of the indentations made in the bar,and the specimen is measured. The hardnessis calculated from tables or a special slide

rule. Brinell hardness numbers can be multi-plied by 500 to obtain the approximate tensilestrength of the material being tested. Consid-erable operator skill is required to obtain con-sistent and accurate hardness measurementswith use of this and other portable hardnesstesting instruments.

Several precautions should be taken toensure obtaining true hardness values. Thesurface to be tested should be flat and reason-ably smooth. Impressions should be takenat representative locations. The specimenshould be firmly supported in such a way thatthe load is applied at a right angle to the sur-face of the specimen. The test should not beused on specimens of soft steel that are lessthan about 1/2 in. (13 mm) thick, or on speci-mens so small as to produce flow of metal atthe edges as a result of the ball impression.Impressions should not be taken closer thanabout two indentor diameters from each other,else the cold work caused by the previousimpression will produce erroneous data.

13.3.2.2 Rockwell.

The Rockwell hardnesstester measures the depth of penetration madeby a small hardened steel ball or a diamondcone. The test is performed by applying aminor load of 10 kg which seats the penetra-tor in the surface of the specimen and holds itin position. A major load is then applied.After the pointer comes to rest, the major loadis released, leaving the minor load on. TheRockwell hardness number is read directly onthe dial.

As Rockwell hardness numbers are basedon the difference between the depths of pene-tration at major and minor loads, it will beevident that the greater this difference, theless the hardness number and the softer thematerial. This difference is automatically reg-istered when the major load is released (theminor load still being applied) by a reversedscale on the indicator dial, from which theRockwell hardness number may be readdirectly. Hardened steel balls of 1/8 in. or1/16 in. (3.2 mm or 1.6 mm) diameter areused for the softer metals, and a cone-shapeddiamond penetrator is used for hard metals.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Several precautions should be taken toensure obtaining true values. Surfaces that areridged by rough grinding or coarse machiningoffer unequal support to the penetrator. Boththe surface at the penetrator side and theunderside should be free of perceptibleridges. The specimen should seat solidly, withno rocking, and should be of such thicknessthat the underside of the specimen does notshow a perceptible impression. This thicknesswill vary greatly according to the hardness ofthe material treated. Softer material requires agreater thickness of specimen, or lighter load,or both. Results from tests on a curved sur-face may be in error and should not bereported without stating the radius of curva-ture. In testing round specimens, the effect ofcurvature may be eliminated by filing a smallflat spot on the specimen. Impressions shouldnot be made within about two penetratordiameters of the edge of the specimen, norcloser than that to each other. When changingfrom one scale to another, a standard testblock of a specified hardness in the range ofthe new scale should be used to checkwhether all the required changes have beenmade and whether the penetrator has seatedproperly. Care should be taken not to damagethe penetrator or the anvil by forcing themtogether when a specimen is not in themachine. The minor load should be appliedcarefully so as not to overshoot the mark. Theloading level should be brought back gently.The ball penetrator tends to become flattenedby use, especially in testing hardened steels,and should be checked occasionally andreplaced when necessary. In the same manner,the diamond cone penetrator should be exam-ined frequently and replaced when it is foundto be blunted or chipped.

13.3.2.3 Vickers.

The Vickers hardness testis another of the class of tests that measureresistance to penetration. It is generally usedas a laboratory tool by a technician or engi-neer to determine hardness of the room-temperature metallurgical constituents andregions of the welded joint.

The Vickers hardness test consists ofimpressing a square-based pyramid penetratorinto the surface of a specimen under a prede-termined load. The penetrator is forced intothe specimen, and the diagonals of the squareimpression are measured and averaged.

DPH

(diamond pyramid hardness) =

(Eq. 13-1)

where

P

= load in kilograms

D

= average of the measured diagonals ofthe indentation expressed in mm.

The application and removal of the loadafter a predetermined interval are controlledautomatically. Since the Vickers indentor is adiamond, it can be used in testing the hardeststeels and remains practically undeformed.The load is light, varying from 1 to 120 kg.,according to requirements. A normal loadingof 30 kg is used for homogeneous materials,and 10 kg is used for soft, thin, or surface-hardened materials. The specimen surfacepreparation is very important; it shouldapproach a metallographic polish.

Section C2 of AWS B4.0,

Standard Meth-ods for Mechanical Testing of Welds

, givesfurther information on hardness testing.

8

Portable Brinell and shore scleroscopemachines using the same or very similar prin-ciples are used on welded configurations thatcannot be placed in one of the Brinell, Rock-well, or Vickers standard instruments. How-ever, their accuracy leaves much to bedesired, and should be used only for basemetal evaluation. The inspector should beacquainted with the use and limitations of theseveral types.

13.3.2.4 Summary.

Each of the abovehardness tests supplements the others. TheBrinell impression, being large, can only be

8. Refer to footnote 6 on page 99.

1.854 P

D2

------


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


used for obtaining hardness values over a rel-atively large area such as the face of a weld orthe base metal. The Rockwell test and theVickers test, however, can be applied to sur-vey the hardness of small zones such as thecross section of a weld, the fusion line, theheat-affected zone or various individualbeads. Conversion data from the Rockwell tothe Brinell to the Vickers are available. Table13.1 shows a typical conversion chart. Inusing this chart, however, it should be remem-bered that the data were obtained from a largenumber of tests and represent average values.The scattering obtained in the actual tests wasconsiderable and depended greatly upon theanalyses of materials and their condition.

13.3.3 Tensile Strength.

Since a large pro-portion of design is based on tensile proper-ties, it is important that the tensile propertiesof the base metal, the weld metal, the bondbetween the base metal and weld metal, andthe HAZ conform to the design consider-ations of the weldment. Where butt joints areused, the weld metal should usually developthe minimum tensile properties of the basemetal. In the case of fillet welds, plug welds,and spot welds, shear strength is usually thesignificant factor. Tensile strength of weldmetal or weld joints is obtained by pulling aspecimen to failure. All-weld-metal speci-mens are usually cylindrical (0.505 in. diam.[12.7 mm]). Welded joint specimens are usu-ally rectangular, reduced cross-section speci-mens, as shown in AWS B4.0,

StandardMethods for Mechanical Testing of Welds

.Tensile strength is determined by dividing themaximum load by the cross-sectional areabefore deformation. The result will be in unitsof stress per cross-sectional area.

13.3.4 Yield Point and Yield Strength.

These properties are determined with thesame specimens that determine tensilestrength. Yield properties are usually obtainedfor individual parts of the welded joints, suchas base metal or weld deposit.

13.3.4.1 Yield Point.

Yield point is definedas the stress per square inch of the original

cross-sectional area that causes a markedincrease in extension without increase in theload. The yield point may be determined byone of the methods described in the follow-ing paragraphs.

(1)

Drop of the Beam Method.

In thismethod the load is applied to the specimen ata steady rate of increase. The operator keepsthe beam in balance by running out the poiseat an approximately steady rate. When theyield point of the material is reached, theincrease of load stops, and the beam of themachine drops for a brief but appreciableinterval of time. In a machine fitted with aself-indicating, load-measuring device, thereis a sudden halt of the load-indicating pointer.This point corresponds to the drop of thebeam. The load at the “halt in the gauge” orthe “drop of the beam” is recorded, and thecorresponding stress is taken as the yieldpoint. This method of determining yield pointrequires only one operator to conduct the test.

(2)

Total Strain Method Using Extensome-ter.

An extensometer reading to 0.0001 inchper inch of gauge length is attached to thespecimen at the gauge marks. When the spec-imen is in place and the extensometerattached, the load is increased at a uniformrate. The observer watches the elongation ofthe specimen as shown by the extensometerand notes for this determination the load atwhich the rate of elongation shows a suddenincrease.

Note: The strain method is more sensitive andmay show the start of the yield elongation at aslightly lower stress than that given by thefirst method.

13.3.4.2 Yield Strength.

Yield strengthmay be defined as the load per square inch ofcross-sectional area that caused a specific setof the specimen as determined by either theoffset method or the extension-under-loadmethod.

(1)

Offset Method.

For nearly all metals, ifat any point on the stress-strain diagram theload is released, the curve of decreasing loadwill be approximately parallel to the initialportion of the curve of increasing load (see


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Table 13.1Typical Hardness Conversion Table (Approximate) (for Carbon and

Low-Alloy Steels in Accordance with ASTM E-140 and ASTM A-370)

ApproximateTensile

Strength,psi

Rockwell

ShoreScleroscope

Number

ApproximateBrinell

Number*

Brinellmm

Impression

CDiamond

Cone

ADiamond

Cone

BHardenedSteel Ball

310 000 56 79.0 75 577 2.55301 000 55 78.5 74 560 2.59292 000 54 78.0 72 543 2.63283 000 53 77.4 71 525 2.67273 000 52 76.8 69 512 2.71264 000 51 76.3 68 496 2.75255 000 50 75.9 67 481 2.79246 000 49 75.2 66 469 2.83237 000 48 74.7 64 455 2.87229 000 47 74.1 63 443 2.91222 000 46 73.6 62 432 2.94215 000 45 73.1 60 421 2.98208 000 44 72.5 58 409 3.02201 000 43 72.0 57 400 3.06194 000 42 71.5 56 390 3.10188 000 41 70.9 55 381 3.13181 000 40 70.4 54 371 3.17176 000 39 69.9 52 362 3.21170 000 38 69.4 51 353 3.25165 000 37 68.9 50 344 3.29160 000 36 68.4 (109.0) 49 336 3.33155 000 35 67.9 (108.5) 48 327 3.37150 000 34 67.4 (108.0) 47 319 3.42147 000 33 66.8 (107.5) 46 311 3.45142 000 32 66.3 (107.0) 44 301 3.51139 000 31 65.8 (106.0) 43 294 3.55136 000 30 65.3 (105.5) 42 286 3.60132 000 29 64.7 (104.5) 279 3.64129 000 28 64.3 (104.0) 41 271 3.68126 000 27 63.8 (103.0) 40 264 3.73123 000 26 63.3 (102.5) 38 258 3.77120 000 25 62.8 (101.5) 253 3.81118 000 24 62.4 (101.0) 37 247 3.85115 000 23 62.0 100.0 36 243 3.89112 000 22 61.5 99.0 35 237 3.93110 000 21 61.0 98.5 231 3.97107 000 20 60.5 97.8 34 226 4.02103 000 18 96.7 33 219 4.10100 000 16 95.5 32 212 4.15

97 000 14 93.9 31 203 4.2593 000 12 92.3 29 194 4.3390 000 10 90.7 28 187 4.40

*A 10 mm Tungsten Carbide ball should be used on all steels over R

C 46

.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 13.4 for a typical stress-strain dia-gram). These curves may, however, be offsetafter the release of load. The value of this off-set is expressed in terms of the percentage oforiginal gauge length. Yield strength may bedetermined by the offset method as follows:

On the stress-strain diagram shown in Fig-ure 13.4, a straight line is drawn parallel tothe initial straight line portion of the diagramand at a distance to the right corresponding tothe value of the offset specified. The load cor-responding to the point where this straightline intersects the initial curve, divided by theoriginal cross-sectional area of the specimen,is the value of the “yield strength.”

In reporting values of yield strengthobtained by this method, the specified valueof offset used should be stated in parenthesesafter the term

yield strength

. Thus, “52 000

psi yield strength (0.2 percent)” indicates thatat a stress of 52 000 psi, the approximate per-manent set of the metal is 0.2 percent of theoriginal gauge length. This method is devisedfor determining a stress corresponding to awell-marked plastic deformation.

(2)

Extension Under Load Method.

Fortests to determine the acceptance or rejectionof material whose stress-strain characteristicsare well known from previous tests of similarmaterial in which stress-strain diagrams wereplotted, the total strain corresponding to thestress at which the specified permanent setoccurs will be known within acceptablelimits.

Therefore, in such tests, a specified totalstrain may be used, and the stress on the spec-imen, when this total strain is reached, is thevalue of the yield strength. To determine yieldstrength by this method, the initial reading ofthe extensometer for the initial load isrecorded, and the load increased until theextension in the specimen is that prescribed.The corresponding load divided by the origi-nal cross-sectional area of the specimen is theyield strength.

13.3.5 Ductility.

Ductility, or percentageelongation and reduction of area, may also beobtained from the tensile test. Ductility valuesare not usually used in designing a structure;nevertheless, minimum values are included inmost specifications because they indicate thequality of the weld metal.

Percentage elongation is obtained by plac-ing gauge marks on the specimen (usuallyusing a double center punch with the pointsaccurately distanced to the gauge lengthrequired) before testing. After testing, thebroken specimen is fitted tightly together andthe final distance between gauge marks mea-sured. The difference between the final andoriginal gauge lengths, divided by the originalgauge length and multiplied by 100, gives thepercentage elongation in the specified gaugelength. Sometimes, because of defectivemachining or some other factor, the specimenwill not break in the center portion of thegauge length and may even break completely

Figure 13.4—Typical Stress-Strain Diagram Used in the Offset Method


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


outside the gauge length. In such cases, thetest results are usually not acceptable,because most of the elongation has takenplace at a position other than where originallyintended.

Elongation of a specimen under tensile loadis uniform until necking occurs. Thereafter,elongation is confined almost exclusively tothe small area of the neck. This area of local-ized necking would be a greater proportion ofa short gauge length than of a long gaugelength. Other things being equal, the shorterthe gauge length, the higher the percent elon-gation obtained from any given specimen.

Reduction of area is determined by care-fully fitting together the ends of the fracturedspecimen and measuring the dimensions ofthe smallest cross section. The differencebetween this area and the original cross-sectional area, expressed as a percentage ofthe original area, is defined as the reduction ofarea.

13.3.5.1 Standard Tension Test.

The stan-dard tension test specimen should complywith the requirements of Figure 13.5. Thestandard specimen should be used unless thesize of the welded joint or deposited weld issuch that a specimen of this size cannot bemachined from it. In this case, the 0.350 in.(8.90 mm) or 0.250 in. (6.35 mm) round spec-imen with the largest test and grip may beused, choosing the specimen with the largestdiameter that can be machined from the mate-rial to be tested. The portion of the specimenincluded in the gauge length G should consistentirely of metal from the deposited zone ofthe joint. End preparation of tension speci-mens may be of any shape to fit the type jawsused in the tension testing machine.

All three specimens are geometrically simi-lar in all significant dimensions. Therefore,the properties determined from any one ofthem tend to be approximately the same asthe properties determined from the others.However, it is desirable that comparisons bemade only between specimens of the samesize. Percent elongation is particularlyaffected by the gauge length used for the test.

The apparatus, material, methods, and rateof depositing the weld metal in the test plateshould, so far as practicable, be the same asthose used in making welds with the givenfiller metal.

Note: Due to unavoidable differences in themethod of depositing the filler metal and therates of cooling, the properties of the weldmetal determined from a specimen willdepend upon the dimensions of the adjacentmetal. Therefore, it is preferred that the testspecimens be removed from a weldment geo-metrically similar to the production weld-ment. For thermit welds, a suitable refractorymaterial may be used for a trough in whichthe weld metal is allowed to solidify.

In the standard tension test procedure, thediameter of the specimen at the middle of thereduced section should be measured in inchesand the gauge length defined by a gauge markat each end. The specimen is then rupturedunder tensile load and the maximum load inpounds determined.

As a result of this type of test, the tensilestrength, yield strength, percent elongation,and reduction in area may be determined.

13.4 Tests of Welded Joints

13.4.1 Test Specimens.

Individual specifica-tions may designate which specimensdescribed in this section are to be used andthe order in which they will be cut from anyprepared pipe or plate sample. Specimensremoved from the test piece should be locatedno closer than 1 in. (25.4 mm) from the startor end of the weld being tested.

13.4.2 Bend Specimens.

Bend ductility spec-imens for pipe or plate should be in accor-dance with those shown in Figure 13.6.Soundness and ductility specimens includeface, root, side, and longitudinal guidedbends. (See AWS B4.0,

Standard Methods forMechanical Testing of Welds

, for additionalinformation.)


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Notes:1. The reduced section may have a gradual taper from the ends toward the center with the ends not

more than 1 percent larger in diameter than the center (controlling dimension).2. If desired, the length of the reduced section may be increased to accommodate an extensometer

of any convenient gauge length. Reference marks for the measurement of elongation should nev-ertheless be spaced at the indicated gauge length.

3. The gauge length and fillets shall be as shown but the ends may be of any form to fit the holders ofthe testing machine in such a way that the load shall be axial. If the ends are to be held in wedgegrips it is desirable to make the length of the grip section great enough to allow the specimen toextend into the grips a distance equal to 2/3 or more of the length of the grips.

4. The use of specimens smaller than 0.250 diameter shall be restricted to cases when the materialto be tested is of insufficient size to obtain larger specimens or when all parties agree to their usefor acceptance testing. Smaller specimens require suitable equipment and greater skill in both ma-chining and testing.

5. For transverse weld specimens, the weld shall be approximately centered between gauge marks.6. Any standard thread is permissible that provides for proper alignment and aids in assuring that the

specimen will break within the reduced section.7. On specimen 5 (see page 19), it is desirable to make the length of the grip section sufficient to

allow the specimen to extend into the grips a distance equal to 2/3 or more of the length of thegrips.

8. The use of UNF series of threads (3/4 in. by 16, 1/2 in. by 20, 3/8 in. by 24, and 1/8 in. by 28) isrecommended for high-strength, brittle materials to avoid fracture in the threaded portion.

9. Surface finish within the gauge length shall be no rougher than 63 microinches R

a

.10. On the round specimens in this figure, the gauge lengths are equal to 4 times the nominal diame-

ter. In some product specifications other specimens may be provided for but unless the 4 to 1 ratiois maintained within dimensional tolerances, the elongation values may not be comparable withthose obtained from the standard test specimen. Note that most metric based codes use a 5 to 1ratio of gauge length to diameter.

Figure 13.5—Standard Tension Specimens

Dimensions

Standard Specimen Small-size specimens proportional to standard specimen

Nominal Diameter

in.0.500

in.0.350

in.0.250

in.0.160

in.0.113

G. gauge length 2.000 ± 0.005 1.400 ± 0.005 1.000 ± 0.005 0.640 ± 0.005 0.450 ± 0.005

D. diameter 0.500 ± 0.010 0.350 ± 0.007 0.250 ± 0.005 0.160 ± 0.003 0.113 ± 0.002

R. radius of fillet, min 3/8 1/4 3/16 5/32 3/32

A. length of reduced section min

2-1/4 1-3/4 1-1/4 3/40 5/80


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 13.5 (Continued)—Standard Tensile Specimens

Dimensions

Specimen 1in.

Specimen 2in.

Specimen 3in.

Specimen 4in.

Specimen 5in.

G — gauge length 2.000± 0.005

2.000± 0.005

2.000± 0.005

2.000± 0.005

2.000± 0.005

D — diameter (Note 1) 0.500± 0.010

0.500± 0.010

0.500± 0.010

0.500± 0.010

0.500± 0.010

R — radius of fillet, min. 3/8 3/8 1/16 3/8 3/8

A — length of reduced section (Note 2) 2-1/4 min 2-1/4 min 4 approx 2-1/4 min 2-1/4 min

L — over-all length approx. 5 5-1/2 5-1/2 4-3/4 9-1/2

B — length of end section 1-3/8 approx 1 approx 3/4 approx 1/2 approx 3 min

C — diameter of end section 3/4 3/4 23/32 7/8 3/4

E — length of shoulder and fillet section, approx. — 5/8 — 3/4 5/8

F — diameter of shoulder — 5/8 — 5/8 19/32


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 13.6(A)—Transverse Face- and Root-Bend Specimens


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Face and root bends are generally used formaterials 3/8 in. (10 mm) or less in thickness.Pipe and plate specimen preparation anddimensions are shown in Figure 13.6(A). Sidebends are used for materials 3/8 in. andgreater in thickness. Specimen preparationand dimensions are shown in Figure 13.6(B).Longitudinal bends may be used for weldedjoints having differing mechanical properties.Specimens are prepared with the longitudinalaxis of the weld running parallel to the longdimension of the specimen. Specimen prepa-ration should be in accordance with dimen-sions and details shown in Figure 13.6. Toolmarks, if any, should be parallel to the longdimension of the specimen.

Note: Tests have shown that the severity of theguided bend test increases to some extent withincreasing width-to-thickness ratio of thespecimen. Results of the side bend test aretherefore not directly comparable when

obtained on specimens shown in Figure 13.6,having different widths, W. Other materialssuch as aluminum and copper alloys may besubject to different requirements.

13.4.2.1 Procedure.

Each specimen shouldbe bent in a fixture with the working contourshown in Figure 13.7, and otherwise substan-tially in accordance with that figure. How-ever, steels and other materials with a tensilestrength over 100 000 psi (690 MPa) requirethat rollers be used instead of hardened andgreased shoulders. For higher yield strengthsteels and other materials, the plunger radiusis sometimes increased to three times thethickness of the material, or more. Any conve-nient means may be used to move the plungermember with relation to the die member.

In performing this test, the specimen isplaced on the die member of the fixture withthe weld at midspan. Face-bend specimensare placed with the face of the weld directed

Figure 13.6(B)—Transverse Side-Bend Specimens


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 13.7—Fixture for Guided Bend Test

Fixture Dimensions for 20% Elongation of Weld

Specimen Thickness, Tin.

Plunger Radius, Ain.

Die Radius, Bin.

3/8 3/4 1-3/16

T 2T A + T + 1/16

Notes:1. Tapped hole of appropriate size, or other suitable means for attaching plunger to testing machine.2. Either hardened and greased shoulders or hardened rollers free to rotate shall be used in die.3. The plunger and its base shall be designed to minimize deflection and misalignment.4. The plunger shall force the specimen into the die until the specimen becomes U-shaped. The weld

and heat-affected zones shall be centered and completely within the bent portion of the specimenafter testing.

5. Weld sizes indicated are recommendations. The actual size is the responsibility of the user toensure rigidity and design adequacy.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


toward the gap. Root-bend specimens areplaced with the root of the weld directedtoward the gap. Side-bend specimens areplaced with that side showing the greaterdefects, if any, directed toward the gap.

The two members of the fixture are forcedtogether until the specimen attains a specifiedangle of bend. For steels containing less thanapproximately 2% alloying elements, the finalshape is usually a “U” and the plunger is con-tinued downward until a 1/8 in. (3.2 mm)diameter wire cannot be placed between thespecimen and any point on the curvature ofthe plunger member of the fixture. Welds withmore than this alloy content, or tensilestrengths in excess of 100 000 psi (690 MPa),seldom have sufficient ductility to make acomplete “U” bend without fracture.

Materials having yield strength over 50 000psi (345 MPa) minimum may be tested bybending the specimen to increased radii.

13.4.2.2 Results.

The convex surface ofthe specimen is examined for the appearance ofcracks or other open defects. Any specimen inwhich cracks or other open defects are presentafter the bending, in excess of a specified numberand size, is considered as having failed. Cracksthat occur on the corners of the specimens duringtesting generally are considered irrelevant.

13.4.3 Tensile Strength Specimens.

Forwelded butt joints in plate, the tension speci-men should comply with the requirements ofFigure 13.8(A) and (B). Circumferentiallywelded joints in pipe may be tested as sec-tioned specimens or a complete pipe or tube,depending on the diameter of the test piece.Pipe or tubing 2 in. (50 mm) in diameter andlarger may be tested using tension specimensas in Figure 13.8. The ends of the specimensmay be modified to accommodate the testingmachine jaws. Pipe and tubing less than 2 in.

Notes:1. It is essential to have adequate rigidity so that the bend fixture will not deflect during testing. The

specimen shall be firmly clamped on one end so that it does not slide during the bending operation.2. Test specimens shall be removed from the bend fixture when the roller has traversed 180° from the

starting point.

Figure 13.7 (Continued)—Fixture for Guided Bend Test


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


(50 mm) in diameter may be tested using thecomplete welded specimen without section-ing. Weld reinforcement may or may not beremoved depending upon the governing codeor specification.

13.4.3.1Procedure.

For reduced tensionspecimens the least width and correspondingthickness of the reduced section is measuredin inches (or millimeters). For small tubespecimens, the average outside diameter(O.D.) of the base metal, at a distance notexceeding 1/2 in. (13 mm) from the boundarybetween the base metal and the weld metal,and the average inside diameter (I.D.) of the

base metal at either end of the specimen aremeasured in inches (or millimeters). Thespecimen is ruptured under tensile loadand the maximum load in pounds (or kg) isdetermined.

13.4.4 Fillet Weld Test.

The fillet weldsoundness test is used to evaluate proceduresand welders for T-or lap joints.

13.4.4.1 Specimen.

The fillet weldbreak specimen should be prepared as shownin Figure 13.9. Material used for the test plateshould have sufficient yield strength to causefracture in the weld zone without bending. The

Notes:1. Thin base metal being tested tends to tear and break near the shoulder. In such cases, dimension C

shall be no greater than 1-1-3 times the width of the reduced section.2. Weld reinforcement and backing strip, if any, shall be removed flush with the surface of the

specimen.3. When the thickness, t, of the test weldment is such that it would not provide a specimen within the

capacity limitations of the available test equipment, the specimen shall be parted through itsthickness into as many specimens as required.

4. The length of reduced sections shall be equal to the width of the widest portion of weld, plus 1/4 in.minimum on each side.

5. All surfaces in the reduced section should be no rougher than 125 microinches R

a

.6. Narrower widths (W and C) may be used when necessary. In such cases, the width of the reduced

section should be as large as the width of the material being tested permits. If the width of thematerial is less than W, the sides may be parallel throughout the length of the specimen.

Figure 13.8(A)—Transverse Rectangular Tension Test Specimen (Plate)

¬


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 13.8(B)—Longitudinal Rectangular Tension Test Specimen (Plate)

Dimensions

Specimen 1in.

Specimen 2in.

W = width 1 ± 0.05 1-1/2 ± 0.125

B = width of weld 1/2 approx 3/4 approx

nominal C = width of grip section 1-1/2 2

Notes:1. The weld reinforcement and backing, if any, shall be removed, flush with the surface of the

specimen.2. The width of the weld may be varied to approximate 1/2 W by selecting an appropriate specimen

thickness, T, and its location within the weld.3. The width, W, may be varied within reason to accommodate the width of the weld if it is not possible

to meet the requirements of Note 2.4. The grip sections of the specimen shall be symmetrical with the center line of the reduced section,

within 1/8 in.5. All surfaces in the reduced section should be no rougher than 125 microinches R

a

.6. Narrower widths (W and C) may be used when necessary. In such cases, the width of the reduced

section should be as large as the width of the material being tested permits. If the width of thematerial is less than W, the sides may be parallel throughout the length of the specimen.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 13.9—Typical Fillet Weld Break and Macroetch Testfor Fillet Welder or Welding Operator Qualification

Notes:1. L = 8 min. (welder), 15 min. (welding operator)2. Either end may be used for the required macroetch specimen, The other end may be discarded.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


weld is deposited using the material, position,and procedure intended for production welds.

13.4.4.2 Procedure. The test plate iswelded on one side of the T joint. Specimensfor evaluation are removed for break andmacroetch tests as shown in Figure 13.9. Thefillet weld break specimen is broken byapplying pressure to cause the fracture tooccur at the welded joint. The macroetchspecimen is prepared by polishing and etch-ing the cross section with a suitable reagent.

13.4.4.3 Results. The surfaces of thefracture are examined for compliance with theapplicable code or specification. The macro-etched specimen is examined for bead config-uration and evidence of defects.

13.4.5 Fracture Toughness Tests. Fracturetoughness is a term for the resistance to theextension of a crack in metal. The most com-mon method used in the U.S. for measuring thefracture toughness of a welded joint is theCharpy V-notch Impact Test (CV). Other typesor fracture toughness tests of welds that are usedto some extent are the Dynamic Tear (DT), thePlain-Strain Compact Tension Fracture Tough-ness (Kq), and the Drop Weight Nil-DuctilityTemperature (DWNDT) tests. The procedurefor these tests of welds are given in AWS B4.0.

Impact testing of ferritic steels is necessarybecause certain types fail by brittle fracture atservice temperatures even though they exhibitnormal properties during the standard tensiletest. This failure by brittle fracture may occurwhen the material is used in the notched con-dition. Notched conditions include restraintdue to deformation in directions perpendicu-lar to the major stress, multi-axial stress, andstress concentrations. It is in this field that theimpact tests prove useful to determine suscep-tibility of the steels to notch-brittle behavior.However, test results cannot be used directlyto appraise the serviceability of a structure.

Notched impact tests, such as Charpy V-notch, bring out notched behavior by applying asingle overload of stress. The absorbed energy“values” determined are quantitative compari-sons based on a selected specimen; they cannot

be converted into energy values that wouldserve for engineering design calculations.

Whenever possible, testing should be per-formed using the standard size specimen.Increasing either the width or depth of thespecimen increases the volume of metal sub-ject to distortion and the energy absorptionwhen the specimen is broken. However, anyincrease in size, particularly in width, alsotends to increase the degree of restraint and,by increasing the tendency to induce brittlefracture, may decrease the amount of energyabsorbed. Thus, while a standard size speci-men may be on the verge of brittle fracture, adouble-width specimen may actually requireless energy to rupture than one of standardwidth. For these reasons, correlation of theenergy values obtained from specimens of dif-ferent size or shape is, in general, not feasible.

Testing conditions also affect the notchedbehavior. So pronounced is the effect of tem-perature on the behavior of notched steel, thatcomparisons are frequently made by examin-ing specimen fractures and plotting energyvalue and fracture appearance against temper-ature from tests of notched bars at a series oftemperatures. When the test temperature hasbeen carried low enough to start cleavagefracture, there may be either an extremelysharp drop in impact value or a relativelygradual falling off toward the lower tempera-tures. The transition temperature at which thisembrittling effect takes place varies consider-ably with chemical composition, welding pro-cedure, and postweld heat treatment.9

9. Some of the many definitions of transition tempera-ture currently being used are:

(1) The lowest temperature at which the specimenexhibits a fibrous structure

(2) The temperature at which the specimen fractureshows a 50 percent crystalline and a 50 percent fibrousappearance

(3) The temperature corresponding to the energyvalue that equals 50 percent of the difference betweenvalues obtained at 100 percent fibrous and zero fibrous

(4) The temperature corresponding to a specificenergy value

(5) Lateral expansion at hinge of at least 0.010 in.(0.25 mm)


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


13.4.5.1 Specimens. The Charpy speci-mens are machined as shown in Figure 13.10.It is important that the root of the notch hasthe proper radius, and is machined with sharp(preferably carbide) cutters to minimize tear-ing and other nonuniform notch contours.

The energy absorption is related to thenotch geometry. A sharp crack started in thenotch can reduce the energy absorption sig-nificantly. For example, if the notch ismachined with a flat bottom, then a crack canform at the sharp corner where the flat bottomintersects the side wall. This reduces thereported energy absorption, but the test isinvalid because the standard notch toleranceswere not present.

13.4.5.2 Procedure. Testing is per-formed on a pendulum-type apparatus. Thesupports and striking edge should be of theform and dimensions shown in Figure 13.11.Other dimensions of the pendulum and sup-port should be such as to minimize interfer-ence between pendulums, supports, andbroken specimens.

The support should be such that the centerof gravity of the test specimen is on a line tan-gent to the arc of travel of the striking point ofthe pendulum, drawn at the position ofimpact.

The machine should be furnished withscales graduated either in degrees, joules, or

foot-pounds force. Percentage of error inenergy of blow caused by variations in theweight of the pendulum, height of fall, or fric-tion should not exceed ±0.4 percent. Severalmachines of this type are made commerciallyand should be calibrated at least once a yearwith standard specimens. These may beobtained from the National Institute of Stan-dards and Technology (NIST). A completedescription of notched-bar impact testing iscontained in ASTM Standard A370.

13.4.5.3 Results. After testing all speci-mens, the complete report should contain thefollowing:

(1) the type and model of machine used,(2) the type of specimen used,(3) machine calibration date,(4) the temperature of the specimen, or the

room condition if both are the same,(5) the energy actually absorbed by the

specimen in breaking reported in total joulesor foot-pounds force,

(6) appearance of fractured surface [(per-cent shear (dull)], percent cleavage or crystal-line (shiny)],

(7) the number of specimens failing tobreak, and

(8) lateral expansion at hinge of impactspecimen.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


NOTE—Dimensional Tolerances shall be as follows:Notch length to edge 90° ± 2°Adjacent sides shall be at 90° ± 10 minutesCross section dimensions ±0.003 in.Length of specimen (L) +0, –0.100 in.Centering of notch (L/2) ±0.039 in.Angle of notch ±1°Radius of notch ±0.001 in.Notch depth ±0.001 in.Finish requirements 63 microinches Ra on notched surface and opposite face; 125 microinches

Ra on other two surfaces

Figure 13.10—Charpy (Simple-Beam) Impact Test Specimens


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 13.11—Charpy (Simple-Beam) Impact Test


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

123

A

Proof Test

is a test of an object’s ability towithstand the applicable service forces. Prooftesting can use many different methods todetermine that the object will meet the require-ments imposed. Hardness test, pressure test,chemical test, tensile test, bend test, load test,spin test, leak test, and peel test are some of themany standard tests used to determine thequality/usability (proof test) of the object. Theleak test is a specific proof test and the subjectof leak testing is covered in Chapter 15.

14.1 Nondestructive Examination

Visual inspection (see Chapter 15) mayalso be a part of the proof test. In most cases,proof tests are applied in connection with“visual” examination (or at least some formof visual examination is required). Details ofany required test or examination are usuallyspecified by the drawings, specifications, orcontract for the object.

Many welded components are proof testedduring or subsequent to fabrication. This mayinvolve overloading the component or testingfor leaks or both. The proof test may be adestructive test of one object or a series ofidentical objects, or a object may be prooftested by applying specific loads without fail-ure or permanent deformation. Such tests areusually designed to subject the parts tostresses exceeding those anticipated duringservice. However, the stresses are maintainedbelow or at the minimum specified yieldstrength of the materials.

Structural members are often proof testedby demonstrating their ability to carry loadsequal to or larger than any anticipated serviceconditions. This can be accomplished by stat-ically loading with a testing machine, sand

bags, or scrap iron, or by dynamically loadingwith special testing equipment. Acceptance isbased on freedom from cracking, or objec-tionable permanent deformation.

14.2 Hardness Test

A Hardness Test is a test (proof) to deter-mine if the material and the weld, or both,meets the specified requirements. Hardnesstesting of welds and materials is in Chapter13, Destructive Testing of Welds.

Pneumatic testing, hydrostatic testing, andvacuum box testing are testing methods usedto proof test containments such as pacemak-ers, autoclaves, cross-country pipelines, etc.A leak in a pacemaker is unacceptable, and aleak in a city water main can occur and beunacceptable to city residents impacted by theleak. The inspector is guided by Federal,National, State, and City codes and otherstandards, and project requirements whenevaluating if a leak is tolerable. See Chapter15 for the leak testing guidelines.

Open containers may be tested hydrostati-cally (by filling with water) and visually exam-ined for leakage. Examples are water or oilstorage tanks, or containers for other liquids.Watertight bodies for amphibious vehicles areusually tested by running the vehicle fullyloaded into water and examining the seams forleakage while the vehicle is floating.

Weldments associated with rotatingmachinery parts or equipment are proof testedby overspinning the component and permit-ting centrifugal force to provide the desiredstress levels, such as “150% design stress.”Visual and nondestructive examination plusdimensional measurements are employed todetermine the acceptability (function prop-erly) of the part.

Chapter 14Proof Tests


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

124/Proof Tests

Most fabrication standards and codes donot specify proof tests to obtain “Reliabilityor Quality.” The American Welding Society(AWS) standards and codes do not specifyproof tests, but rely on Nondestructive Exam-inations to maintain the standard or codequality. The American Society of MechanicalEngineers’ Boiler and Pressure Vessel codesuse proof tests to only establish the MaximumAllowable Working Pressure (MAWP).

Contract specifications generally includespecific requirements for testing, inspection,and repair in accordance with applicablecodes and specifications.

If repair welding is to be done after test-ing, reference is made to AWS F4.1,

Recom-mended Safe Practices for the Preparationfor Welding and Cutting of Containers thatHave Held Hazardous Substances

, to ensurethat hazardous environments are not present.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

125

15.1 Introduction

Nondestructive Examination (NDE) is ageneral term used in this text to identifymethods that permit evaluation of welds andrelated materials without destroying their use-fulness. Nondestructive Examination (NDE),Nondestructive Inspection (NDI), and Nonde-structive Testing (NDT) are synonymousterms also used to identify these evaluationmethods. The majority of prospective weldinspectors already know that visual examina-tion certainly meets this criterion, but thereare other NDE inspection methods. The pur-pose of this chapter is to acquaint the weldinginspector with some of the more commonlyused NDE methods and the fundamental con-ditions for their use.

The essential elements common to most allNDE methods include the following:

(1) A probing medium(2) A test specimen that is appropriate for

the medium being used so that discontinuitiesmay be detected

(3) A detector capable of measuring thedistributions or alterations in the media

(4) A technique for recording or displayinginformation received from the detector, suit-able for evaluation.

(5) The operator who should be trained tointerpret detector feedback to evaluate results.

Many types of media have been used inNDE methods; similarly, many properties ofmaterials have been the fundamental basis forselecting a particular NDE technique. Forpurposes of this text only the following basicNDE methods will be discussed:

(1) Visual examination(2) Radiographic examination(3) Ultrasonic examination(4) Magnetic particle examination

(5) Penetrant examination(6) Eddy current examination(7) Acoustic emission examination(8) Leak examination(9) Ferrite content examinationNondestructive examination methods are

not intended as a replacement for destructivetests. The welding inspector should beadvised that destructive tests frequently areused to complement nondestructive exami-nation and that each method may providesupport for the other. It is not uncommon forthe acceptance-rejection criteria of an NDEmethod to be developed by destructive testinvestigations correlated with NDE results. Itis not within the scope of this chapter to offercomparative advantages between specificNDE methods, nor to present a full handbookof information on the numerous NDE tech-niques. Table 15.1 contains a brief summaryof typical considerations generally used inselecting an NDE method for weld inspec-tion. The general knowledge presented in thischapter should be of valuable assistance to theinspector as it provides an overview of theinspection methods available without unnec-essary detail. Also contained within this chap-ter is a brief section on NDE procedures andthe highlights of those requirements that com-plement the decision to establish writtenprocedures.

15.2 Inspection by Visual Examination

For many types of welds, integrity is veri-fied principally by visual examination. Evenfor weldments with joints specified for exam-ination throughout by other nondestructiveexamination methods, visual examination isperformed. Visual examination constitutes an

Chapter 15Nondestructive Examination Methods


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

126/Nondestructive Examination Methods

Tab

le 1

5.1

Con

side

ratio

ns w

hen

Sel

ectin

g an

ND

E M

etho

d

Equ

ipm

ent N

eeds

App

licat

ions

Adv

anta

ges

Lim

itatio

ns

Vis

ual

Mag

nifi

ers,

col

or e

nhan

cem

ent,

proj

ecto

rs, o

ther

mea

sure

men

t eq

uipm

ent,

i.e.,

rule

rs, m

icro

me-

ters

, opt

ical

com

para

tors

, lig

ht

sour

ce.

Wel

d pr

epar

atio

ns a

nd w

eld

surf

aces

for

dim

ensi

onal

an

d su

rfac

e co

nditi

ons.

Eco

nom

ical

, exp

edie

nt a

nd re

lativ

ely

little

equ

ipm

ent f

or m

any

appl

ica-

tions

.

Lim

ited

to e

xter

nal o

r su

rfac

e co

nditi

ons

only

. L

imite

d to

the

visu

al a

cuity

of

the

obse

rver

/in

spec

tor.

Rad

iogr

aphy

(G

amm

a)

Gam

ma

ray

sour

ces,

gam

ma

ray

cam

era

proj

ecto

rs, fi

lm h

olde

rs,

film

s, le

ad s

cree

ns, fi

lm p

roce

ss-

ing

equi

pmen

t, fi

lm v

iew

ers,

ex

posu

re f

acili

ties,

rad

iatio

n m

onito

ring

equ

ipm

ent,

shie

ldin

g m

ater

ial.

Mos

t wel

d di

scon

tinui

ties

incl

udin

g cr

acks

, por

osity

, la

ck o

f fu

sion

, inc

ompl

ete

pene

trat

ion,

sla

g, a

s w

ell

as c

orro

sion

and

fit-

up

cond

ition

s.

Perm

anen

t rec

ord—

enab

les

revi

ew

by p

artie

s at

a la

ter

date

. Gam

ma

sour

ces

may

be

posi

tione

d in

side

of

acce

ssib

le o

bjec

ts, i

.e.,

pipe

s, e

tc.,

for

pano

ram

ic te

chni

que

radi

o-gr

aphs

. Ene

rgy

effic

ient

sou

rce

requ

ires

no

elec

tric

al e

nerg

y fo

r pr

oduc

tion

of g

amm

a ra

ys.

Rad

iatio

n is

saf

ety

haza

rd—

requ

ires

con

trol

of

faci

litie

s or

are

as w

here

radi

atio

n w

ill b

e us

ed a

nd

requ

ires

spe

cial

mon

itori

ng o

f exp

osur

e le

vels

and

do

sage

s to

per

sonn

el. S

ourc

es (

gam

ma)

dec

ay

over

thei

r ha

lf-l

ives

and

sho

uld

be p

erio

dica

lly

repl

aced

. Gam

ma

sour

ces

have

a c

onst

ant e

nerg

y of

out

put (

wav

elen

gth)

and

can

not b

e ad

just

ed.

Req

uire

s ac

cess

to o

ppos

ite s

ides

of

wel

ds.

Gam

ma

sour

ce a

nd re

late

d lic

ensi

ng re

quir

emen

ts

are

expe

nsiv

e. R

adio

grap

hy r

equi

res

high

ly

skill

ed o

pera

ting

and

inte

rpre

tive

pers

onne

l.

Rad

iogr

aphy

(X

-Ray

s)

X-r

ay s

ourc

es (

mac

hine

s), e

lec-

tric

al p

ower

sou

rce,

sam

e ge

nera

l eq

uipm

ent a

s us

ed w

ith g

amm

a so

urce

s (a

bove

).

Sam

e ap

plic

atio

ns a

s ab

ove.

Adj

usta

ble

ener

gy le

vels

, gen

eral

ly

prod

uces

hig

her

qual

ity r

adio

grap

hs

than

gam

ma

sour

ces.

Off

ers

perm

a-ne

nt r

ecor

d as

with

gam

ma

(abo

ve).

Hig

h in

itial

cos

t of

X-r

ay e

quip

men

t Not

gen

er-

ally

con

side

red

port

able

, rad

iatio

n ha

zard

as

with

ga

mm

a so

urce

s, s

kille

d op

erat

iona

l and

inte

r-pr

etiv

e pe

rson

nel r

equi

red.

(Con

tinu

ed)


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Nondestructive Examination Methods/127

Ult

raso

nic

Puls

e-ec

ho in

stru

men

t cap

able

of

exci

ting

a pi

ezoe

lect

ric

mat

eria

l an

d ge

nera

ting

ultr

ason

ic e

nerg

y w

ithin

a te

st p

iece

, and

hav

ing

a su

itabl

e ca

thod

e ra

y tu

be c

apa-

ble

of d

ispl

ayin

g th

e m

agni

tude

s an

d lo

catio

ns o

f re

ceiv

ed s

ound

en

ergy

. Cal

ibra

tion

stan

dard

s,

liqui

d co

upla

nt.

Mos

t wel

d di

scon

tinui

ties

incl

udin

g cr

acks

, sla

g, la

ck

of f

usio

n, la

ck o

f bo

nd,

accu

rate

thic

knes

s m

easu

re-

men

ts p

ossi

ble.

Poi

sson

’s

ratio

may

be

obta

ined

by

dete

rmin

ing

the

mod

ulus

of

elas

ticity

.

Mos

t sen

sitiv

e to

pla

nar t

ype

defe

cts.

Te

st r

esul

ts k

now

n im

med

iate

ly.

Port

able

. Ultr

ason

ic fl

aw d

etec

tors

do

not

req

uire

an

elec

tric

al p

ower

ou

tlet.

Hig

h ou

tlet.

Hig

h pe

netr

atio

n ca

pabi

lity.

Req

uire

s ac

cess

fro

m

only

one

sur

face

.

Surf

ace

cond

ition

sho

uld

be s

uita

ble

for c

oupl

ing

of tr

ansd

ucer

. Cou

plan

t (liq

uid)

req

uire

d. S

mal

l, th

in w

elds

may

be

diffi

cult

to in

spec

t. R

efer

ence

st

anda

rds

are

requ

ired

. Req

uire

s a

rela

tive

ly

skill

ed o

pera

tor/

insp

ecto

r, a

nd s

kille

d in

ter-

pret

ive

pers

onne

l. R

esol

utio

n of

sm

all d

efec

ts

near

sur

face

dif

ficul

t.

Mag

neti

c P

arti

cle

Prod

s, y

okes

, coi

ls s

uita

ble

for

indu

cing

mag

netis

m in

to th

e te

st

piec

e. P

ower

sou

rce

(ele

ctri

cal)

. M

agne

tic p

owde

rs, s

ome

appl

i-ca

tions

req

uire

spe

cial

fac

ilitie

s an

d ul

trav

iole

t lig

hts.

Gau

ge

met

ers

and

fiel

d in

dica

tions

.

Mos

t wel

d di

scon

tinui

ties

open

to o

r ne

ar th

e su

rfac

e.

Mos

t sui

tabl

e fo

r cra

cks

and

othe

r lin

ear

cond

ition

s.

Rel

ativ

ely

econ

omic

al a

nd e

xpe-

dien

t. In

spec

tion

equi

pmen

t is

cons

ider

ed p

orta

ble.

Unl

ike

liqui

d pe

netr

ants

, mag

netic

par

ticle

can

de

tect

som

e ne

ar s

urfa

ce d

isco

n-tin

uitie

s. C

an in

spec

t thr

ough

thin

co

atin

gs.

App

licab

le o

nly

to fe

rrom

agne

tic m

ater

ials

. Par

ts

shou

ld b

e cl

ean

befo

re a

nd a

fter

insp

ectio

n. T

hick

co

atin

gs m

ay m

ask

reje

ctab

le in

dica

tions

. Som

e ap

plic

atio

ns r

equi

re p

arts

to b

e de

mag

netiz

ed

afte

r in

spec

tion.

Mag

netic

par

ticle

insp

ectio

n re

quir

es u

se o

f el

ectr

ical

ene

rgy

for

mos

t app

lica-

tions

. Som

e po

tent

ial f

or a

rc s

trik

es o

n su

rfac

e.

Liq

uid

Pen

etra

nt

Fluo

resc

ent o

r vi

sibl

e dy

e.

Pene

tran

t, de

velo

pers

, cle

aner

s (s

olve

nts,

em

ulsi

fier

s, e

tc.)

. Su

itabl

e cl

eani

ng g

ear.

Ultr

a-vi

olet

ligh

t sou

rce

and

dark

ened

ar

ea if

fluo

resc

ent d

ye is

use

d.

Wel

d di

scon

tinui

ties

open

to

sur

face

, i.e

., cr

acks

, po

rosi

ty, s

eam

s.

May

be

used

on

all n

onpo

rous

mat

e-ri

als.

Por

tabl

e, re

lativ

ely

inex

pens

ive

equi

pmen

t. E

xped

ient

insp

ectio

n re

sults

. Res

ults

are

eas

ily in

ter-

pret

ed. R

equi

res

no e

lect

rica

l ene

rgy

exce

pt f

or li

ght s

ourc

e. I

ndic

atio

ns

may

be

furt

her

exam

ined

vis

ually

.

Surf

ace

film

s su

ch a

s co

atin

gs, s

cale

, sm

eare

d m

etal

mas

k or

hid

e re

ject

able

def

ects

. Ble

ed o

ut

from

por

ous

surf

aces

can

als

o m

ask

indi

catio

ns.

Part

s sh

ould

be

clea

ned

befo

re a

nd a

fter

insp

ectio

n.

(Con

tinu

ed)

Tab

le 1

5.1

(Co

nti

nu

ed)

Con

side

ratio

ns w

hen

Sel

ectin

g an

ND

E M

etho

d

Equ

ipm

ent N

eeds

App

licat

ions

Adv

anta

ges

Lim

itatio

ns


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Edd

y C

urre

nt

An

inst

rum

ent c

apab

le o

f in

duc-

ing

elec

trom

agne

tic fi

elds

with

in

a te

st p

iece

and

sen

sing

the

resu

lting

ele

ctri

cal c

urre

nts

(edd

y) s

o in

duce

d w

ith a

sui

tabl

e pr

obe

or d

etec

tor.

Cal

ibra

tion

stan

dard

s.

Wel

d di

scon

tinui

ties

near

th

e su

rfac

e (i

.e.,

crac

ks,

poro

sity

, fus

ion)

. Allo

y co

nten

t, he

at tr

eatm

ent v

ari-

atio

ns, w

all t

hick

ness

, and

pl

atin

g or

coa

ting

thic

knes

s.

Rel

ativ

ely

expe

dien

t, w

ith in

stan

ta-

neou

s re

sults

. Aut

omat

ion

poss

ible

fo

r sy

mm

etri

cal p

arts

. No

coup

lant

re

quir

ed. P

robe

doe

s no

t hav

e to

be

in in

timat

e co

ntac

t with

test

pie

ce.

Skill

ed in

terp

retiv

e pe

rson

nel.

Lim

ited

to c

ondu

ctiv

e m

ater

ials

. Sha

llow

dep

th

of p

enet

ratio

n. S

ome

indi

catio

ns m

ay b

e m

aske

d by

par

t geo

met

ry d

ue to

sen

sitiv

ity v

aria

tions

. R

efer

ence

sta

ndar

d re

quir

ed.

Aco

usti

c E

mis

sion

Em

issi

on s

enso

rs, a

mpl

ifyi

ng

elec

tron

ics,

sig

nal p

roce

ssin

g el

ectr

onic

s in

clud

ing

freq

uenc

y ga

tes,

filte

rs. A

sui

tabl

e ou

tput

sy

stem

for

eva

luat

ing

the

acou

stic

sig

nal (

audi

o m

onito

r,

visu

al m

onito

r, co

unte

rs, t

ape

reco

rder

s, X

-Y r

ecor

der.)

Inte

rnal

cra

ckin

g in

wel

ds

duri

ng c

oolin

g, c

rack

initi

a-tio

n an

d gr

owth

rat

es. I

n se

rvic

e m

onito

ring

of

wel

ds.

Rea

l tim

e an

d co

ntin

uous

sur

veil-

lanc

e in

spec

tion.

May

be

insp

ecte

d re

mot

ely.

Por

tabi

lity

of in

spec

tion

appa

ratu

s. C

an id

entif

y so

urce

of

emis

sion

s.

Req

uire

s th

e us

e of

tran

sduc

ers

coup

led

on th

e te

st p

art s

urfa

ce. P

art s

houl

d be

in “

use”

or

stre

ssed

. Mor

e du

ctile

mat

eria

ls y

ield

low

am

plitu

de e

mis

sion

s. N

oise

sho

uld

be fi

ltere

d ou

t of

the

insp

ectio

n sy

stem

.

Lea

k Te

st

Exa

ct e

quip

men

t dep

ends

upo

n th

e le

ak te

st m

etho

d us

ed (

see

text

). G

ener

ally

nee

ds e

quip

men

t ca

pabl

e of

indu

cing

a p

ress

ure

diff

eren

tial a

nd s

ome

form

of

dete

ctio

n de

vice

cap

able

of

sens

-in

g th

e le

ak. S

ome

appl

icat

ions

w

ill r

equi

re s

peci

al le

ak te

st

med

ium

.

Wel

ds w

hich

hav

e de

fect

s ex

tend

ing

thro

ugh

the

wel

d vo

lum

e.

Man

y co

mpo

nent

s m

ay b

e “r

eal

time”

insp

ecte

d in

con

junc

tion

with

a

proo

f te

st. S

ome

appl

icat

ions

ut

ilize

rel

ativ

ely

little

ope

rato

r tr

aini

ng. T

est r

esul

ts a

re u

sual

ly

expe

dien

t.

Som

e m

etho

ds r

equi

re s

peci

al f

acili

ties

and

are

time

cons

umin

g to

insp

ect.

App

licat

ions

re

quir

ing

high

leve

ls o

f se

nsiti

vity

are

usu

ally

un

econ

omic

al a

nd r

equi

re p

erso

nnel

ext

ensi

vely

tr

aine

d.

Tab

le 1

5.1

(Co

nti

nu

ed)

Con

side

ratio

ns w

hen

Sel

ectin

g an

ND

E M

etho

d

Equ

ipm

ent N

eeds

App

licat

ions

Adv

anta

ges

Lim

itatio

ns


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


important part of practical quality control.Therefore, visual examination is of the firstorder of importance.

The most extensively used of any methodof nondestructive examination, visual exami-nation is easy to apply, quick, relatively inex-pensive, requires good eyesight, and givesimportant information regarding the generalconformity of the weldment to specifications.

For convenience of presentation, visualexamination is discussed under five mainheadings: visual examination practice, exami-nation prior to welding, examination duringwelding, examination after welding, andmarking welds for repairs. The welding engi-neer data sheet checklist for visual inspection(see Figure 15.1) identifies points to considerduring each welding phase.

15.3 Visual Examination Practice

The inspector should be familiar with theapplicable documents, workmanship stan-dards, and all phases of good shop practice.The weld to be examined should be welllighted. Inaccessible areas can be viewed witha borescope, and, when so required by a cus-tomer, a low power magnifier may be used. Alow power magnifier should be used with cau-tion since it does accentuate the surface andcan make decisions arguable.

Welds that are inaccessible in the finishedproduct should be examined during theprogress of the work. Scales and gauges (seeFigure 15.2) are used for checking the fit-upof pieces and the dimensions of the weldbead. Although visual inspection is the sim-plest of the inspection methods, a definiteprocedure should be established in order toinsure adequate coverage.

15.3.1 Examination Prior to Welding.

Inspection starts with examination of thematerial prior to fabrication, a practice thatcan eliminate conditions that tend to causeweld defects. Scabs, seams, scale, or otherharmful surface conditions may be detectedduring visual examination. Plate laminationsmay be observed on cut edges. Plate dimen-

sions may be determined by measurement.Identification of material type and gradeshould be made.

After the parts are assembled in positionfor welding, the inspector should check rootopenings taking into account structural toler-ances, edge preparation, and other features ofjoint preparation that might affect the qualityof the welded joint. The inspector should

Before Welding

__ Review applicable documentation__ Check welding procedures__ Check individual welder qualifications__ Establish hold points__ Develop inspection plan__ Develop plan for recording inspection results

and maintaining those records__ Develop system for identification of rejects__ Check condition of welding equipment__ Check quality and condition of base and filler

materials to be used__ Check weld preparations__ Check joint fit-up__ Check adequacy of alignment devices__ Check weld joint cleanliness__ Check preheat, when required

During Welding

__ Check welding variables for compliance with welding procedure

__

Check quality of individual weld passes

__

Check interpass cleaning

__

Check interpass temperature

__

Check placement and sequencing of individual weld passes

__

Check backgouged surfaces

__

Monitor in-process NDT, if required

After Welding

__ Check finished weld appearance

__

Check weld size

__

Check weld length

__

Check dimensional accuracy of weldment

__

Monitor additional NDT, if required

__

Monitor postweld heat treatment, if required

__

Prepare inspection reports

Figure 15.1—Welding EngineerData Sheet


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


check the following conditions for conformityto the applicable specifications:

(1) Joint preparation, dimensions, and finish(2) Clearance dimensions of backing strips,

rings, or backing filler metal(3) Alignment and fit-up of the pieces

being welded(4) Verification of cleanliness(5) Approved/qualified weld procedure

specification and welders/welding operators

15.3.2 Examination During Welding.

Visualexamination checks details of the work whilefabrication is in progress, such as:

(1) Welding process and conditions(2) Filler metal(3) Flux and/or shielding gas(4) Preheat and interpass temperature(5) Distortion control(6) Interpass chipping, grinding, or gouging(7) Weld bead contours (Figure 15.3)The inspector should be thoroughly famil-

iar with all the items involved in the qualifiedwelding procedure specification. Theseshould be checked with particular care, espe-cially during the early stages of production,and compliance with all details of the proce-dure should be verified.

Examination of successive layers of theweld deposit is sometimes carried out with

the assistance of a workmanship standard.Figure 15.4 indicates how such a standardmay be prepared. This is a section of a jointsimilar to the one in production, in which por-tions of successive weld layers are shown.Each layer of the production weld may becompared with corresponding layer of theworkmanship standard. One should realizethat this workmanship sample was made

Figure 15.2 —Scales and Gauges for Checking Fit-Up and Weld Dimensions

Figure 15.3—Weld Bead Contours


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 15.4—Workmanship Standard


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


under ideal conditions and may not truly repre-sent actual job conditions; allowances shouldbe made for production tolerances.

The first layer, or root pass of a weld, is themost important one from the point of view offinal weld soundness. Because of the geome-try of the joint, the relatively large volume ofbase metal with respect to that of the root passweld metal, the fact that the plate may becold, and the possibility that the arc may notstrike into the root, the root pass freezesquickly. In so doing, it tends to trap slag orgas that resists removal during subsequentpasses. In addition, the metal melted duringthis pass is particularly susceptible to crack-ing. Such cracks may not only remain, butmay extend to subsequent layers. Examina-tion of this pass should be thorough, and aworkmanship standard can be very useful forthis inspection. As will be shown later in thissection, nondestructive examinations maygive evidence as to conditions in the rootpass, and thus serve as a verification of visualexamination.

Examination of the root pass offers anotheropportunity to inspect for plate laminations,since these discontinuities tend to get largerbecause of the affects of heat incident to thewelding operation.

In the case of double-groove welds, slagfrom the root pass on one side of the weldmay be trapped in the deposit on the otherside of the weld. Such deposits are usuallychipped, ground, or gouged out prior to weld-ing the opposite side. Where slag removal isincomplete, slag will remain in the root of thefinished weld.

The root opening should be monitored asroot pass welding progresses. Special empha-sis should be placed on the adequacy of thetack welds and clamps or braces designed tomaintain the root opening to assure penetra-tion and alignment. The importance of thisroot opening is not limited to butt joints butalso applies to branch and angle connectionsthat are more difficult to inspect after the weldhas been completed. (The inspector shouldtake advantage of opportunities for checkexaminations whenever they are offered.)

15.3.3 Inspection After Welding.

Visualinspection is useful for finished product veri-fication of such items as:

(1) Dimensional accuracy of the weldment(including distortion)

(2) Conformity to drawing requirements(involving determination of whether allrequired welding has been done, and whetherfinished welds conform to required size andcontour) (Figure 15.3)

(3) Acceptability of welds with regard toappearance includes such items as surfaceroughness, weld spatter, etc. (Figures 15.3and 15.4)

(4) The presence of unfilled craters, arcstrikes, undercuts, overlaps, and cracks (Fig-ures 15.5 and 15.6)

(5) Evidence of mishandling from centerpunch or other inspection marking or exces-sive grinding

Dimensional accuracy of weldments isdetermined by conventional measuring meth-ods and need not be commented upon in thissection.

The conformity of weld size and contourmay be determined by the use of weld gauges.The size of a fillet weld in joints whose mem-bers are at right angles, or nearly so, is gener-ally defined in terms of the length of the leg,the thickness or “throat” and the profile (con-cavity or convexity). Gauges will determine

Figure 15.5—Sketches ofWeld Undercut and Overlap

UNDERCUT

UNDERCUT

UNDERCUT

OVERLAP OVERLAP


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


whether the size is within allowable limitsand whether there is excessive concavity orconvexity.

Special gauges may be made for use wherethe surfaces are at angles of less than orgreater than 90 degrees. There are a variety ofcommercially available weld gauges, filletgauges, protractors, etc. [see Figure 15.7].

For groove welds, the width of finishedwelds will vary in accordance with therequired groove angle, root face, root open-ing, thickness of the material, and permissibletolerances. The height of reinforcementshould be consistent with specified require-ments. Requirements as to surface appearancediffer widely, and, in general, the weld sur-face should be as specified in a code or cus-tomer’s specifications. Visual standards, orsample weldments submitted by the fabricatorand agreed to by the purchaser, can be used asguides to appearance. Sometimes a smoothweld, strictly uniform in size and contour, is

required because the weld forms part of theexposed surface of the product and goodappearance is desirable.

The presence of defects that affect serviceperformance is, in most instances, moreobjectionable than those that affect appear-ance. The former are discussed in Chapter 9;however, the following are a few examples:

(1) Cracks(2) Undercuts(3) Overlap(4) Excessive weld irregularity(5) Dimensional inaccuraciesFor accurate detection of such defects, the

weld surface should be thoroughly cleanedbefore inspection.

15.3.4 Marking Welds For Repair.

One ofthe most important details of nondestructiveexamination is the proper marking of theareas to be repaired. This marking should be:

(1) Positive and clear,(2) In accordance with a method of mark-

ing established and understood, by all inspec-tors and by shop personnel involved inmaking the repair,

(3) Of a distinctive color or technique thatit is not easily confused with other markings,

(4) Permanent enough to be evident untilafter the repair has been made and inspected,

(5) Selected so that the ink, paint, etc. willnot damage the material, and

(6) Removed if not acceptable to serviceconditions.

The repair should be inspected, and theinspector should be able to find the markings;therefore, the marking medium should besuch that the marks will survive rough han-dling incident to repair. After the repair hasbeen made and inspected, it should be prop-erly marked to indicate whether or not therepair is satisfactory.

15.3.5 Summary.

Visual examination, asindicated above, is invaluable as an inspectionmethod; however, some caution should beused in drawing conclusions. For example,good surface appearance is often regarded asindicative of careful workmanship and highweld quality. However, surface appearance

Figure 15.6—Photographs ofWeld Undercut and Overlap


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


alone does not prove careful workmanshipand is not a conclusive indication of subsur-face condition. Thus, judgment of weld qual-ity should be based on evidence that is inaddition to that afforded by surface indica-tions. Such additional evidence is afforded byobservations that have been made prior to andduring welding and the implementation ofother NDE methods. For instance, if theinspector knows that the plate was free oflaminations, that the edge preparation wascorrect, that the root opening was as speci-fied, that the root pass was sound, and that thequalified welding procedure was followedcarefully, the inspector may be reasonablysafe in judging the completed weld on thebasis of visual examination.

15.4 Inspection By Radiographic Examination

Radiography is a method of nondestructiveexamination that utilizes radiation to pene-trate an object and (1) record images on avariety of recording devices such as film orphotosensitive paper, (2) be viewed on a fluo-rescent screen, or (3) be monitored by varioustypes of electronic radiation detectors. When

an object to be examined is exposed to pene-trating radiation, see Figure 15.8, some radia-tion will be absorbed, some will be scattered,and some radiation will be transmittedthrough the test object onto the recordingdevice. Radiation will be differentiallyabsorbed over various areas of the test object.

Most conventional radiographic processesused today involve exposures that record apermanent image on a photographic film.Additionally, most weldment examinationsperformed by the radiographic method useelectromagnetic radiation, such as x-rays andgamma rays. Therefore, this section will belimited to radiography of weldments withthose processes mentioned above. Only abrief introduction to the theory of radio-graphic testing as it applies to weld inspectionand a review of the general application tech-niques will be presented in this text. Manyexcellent sources of reference materials areavailable to the welding inspector, containingdetailed and specific technique consider-ations, terms and definitions in general use, aswell as advanced and highly specializedaspects of the various attributes of the com-plete radiographic examination process.Some of these sources are listed at the end ofthis article and are highly recommended.

Figure 15.7—Weld Inspection Gauges


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 15.8—Typical “Shadow Graph”


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


15.4.1 Essential Elements.

The basic processof radiographic examination involves (1) theproduction of the radiograph, and (2) theinterpretation of the radiograph. The essentialelements needed to carry out these two opera-tions consist of the following:

(1) A source of radiation (usually gammaor x-rays) and associated accessories

(2) An object to be radiographed (weld-ment)

(3) An x-ray film enclosed in a lightprooffilm holder (cassette)

(4) A trained person to produce an accept-able radiograph

(5) A means of chemically processing theexposed film

(6) A person certified to interpret the radio-graphic images using adequate viewingdevices

The following is a brief discussion abouteach of these six essential elements of theradiographic inspection process.

15.4.1.1 A Source of Radiation.

The illus-tration shown in Figure 15.8 details the basicessentials in the making of a radiograph. Radi-ation, electromagnetic radiant energy withpenetrating properties related to its energylevel wavelength, is unique in that it cannot bedetected by any of mankind’s five naturalsenses: sight, touch, taste, hearing, or smell.More important to the radiographic process

is the unique ability of radiation to ionizeelements.

The two types of radiation sources mostcommonly used in weld inspection are x-raymachines and radioactive isotopes. The radia-tion emitted by these sources has anextremely short wavelength (about 1/10 000of the wavelength or less than that of visiblelight) that enables them to penetrate materialsthat absorb or reflect light. X-rays are pro-duced by x-ray tubes; gamma rays are emittedfrom the disintegrating nuclei of radioactiveelements. Although the wavelength of radia-tion produced can be quite different, bothx-ray and gamma radiation behave similarlyfor radiographic purposes.

In the past, radium (a natural emitter ofgamma radiation) has been used extensivelyfor industrial radiography; however, with theavailability of artificially produced isotopes,its use has decreased greatly. Of the radioiso-topes, the three in common use are cobalt 60,cesium 137, and iridium 192 shown in Table15.2. These have been named in order ofdecreasing energy level (penetrating ability).Cobalt 60 and iridium 192 are more widelyused than cesium 137.

Sources of x-radiation are very diversifiedtoday and consist of smaller, portable tube-type x-ray machines of the 50 KV range up tomammoth linear accelerators and betatrons inthe 1 to 30 million electron volt range.

Table 15.2Radiographic Isotopes Used in Industrial Radiography

IsotopeHalf-Life

(years)Energy Levels

MEV

Approximate Mean Effective Energy Level

MEV

Characteristic Intensity–

Roentgens per Hour per Curie

at 1 meter

Cobalt-60 .05.3 1.17 and 1.33 1.20 1.35

Cesium-137 33 0.66 0.39

Iridium-192 75 0.137 to 0.651 0.55


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


It should be noted that each source of radia-tion has advantages and limitations and thewelding inspector should become familiar withsuch terms as

curie

,

half-life

,

half-value layer

,

specific activity

,

energy or wavelength of emis-sivity

, and

source intensity

. Although the singlemost significant aspect of a radiation source isusually its image quality producing properties,other important considerations that may neces-sitate “trade-offs” in selecting a source includeits portability and costs. Portability and costsspeak for themselves. The image-quality prop-erties will be detailed later in this section.

The welding inspector should further notethat all radiation producing sources are haz-ardous, and special precautionary measuresshall be taken when entering or approaching aradiographic area. This will also be discussedlater in this section.

15.4.1.2 An Object to be Radiographed.

The test object is an essential part of theradiographic process for rather obvious rea-sons; however, we should have a basic under-standing about radiation interaction with thetest object in order to fully appreciate theresultant film image. As was illustrated inFigure 15.8, the radiographic process isdependent upon the differential absorption ofradiation as it penetrates the test object. Thetwo key factors that determine the rates of dif-ferential absorption are (1) the amount ofmass represented by the object, and (2) thepenetrating power (defined by the energy) ofthe radiation source. The amount of mass isrelated to the density or object composition aswell as to the amount or thickness of theobject. Generally, the higher the atomic num-ber of the object material, the more radiationwill be absorbed and the less will penetratethe object to reach the film; more radiationwill pass through thin sections than will passthrough thick sections.

The penetrating power of the radiationsource is dependent upon the kilovoltageselected on the x-ray machine or the particu-lar isotope selected for gamma radiography.As the energy of the radiation source isincreased, the more easily it will penetrate

thicker or more dense materials. Table 15.3shows the approximate radiographic equiva-lence factors for several metals. It is impor-tant to remember these two variables, for it isthe differences in absorption occurring duringthe exposure process that accounts for theresultant differences in dark regions and lightregions on the radiograph, i.e., contrast. Thedark regions on the radiograph represent themore easily penetrated parts of the test object,while the lighter regions represent the moredifficult to penetrate regions of the test object.

Discontinuity dimensions parallel to thedirection of radiation are most likely to createa discernible image, while discontinuitydimensions that are normal to (planar) thedirection of radiation are least likely to createa discernible image. Thus, the weldinginspector should realize that orientation ofradiation to test object/discontinuity is animportant consideration. Radiographic expo-sure of the test object in multiple directions istherefore very common and often necessary.The inspector should realize there is a limit tothe amount of differential absorption that isradiographically discernible (sensitivity) andthat higher energy levels used for penetrationproduce lower sensitivity levels. Thus, theradiographer should select energy levels thatwill permit penetration of the object in a rea-sonable time period while still achieving ade-quate sensitivity and contrast for detectionand interpretation of defects.

15.4.1.3 An X-Ray Film Enclosed in aLightproof Film Holder (Cassette).

Film isan essential for radiography. While the gen-eral makeup of the film itself is relatively sim-ple, its behavior characteristics are muchmore complicated, and the latter are of con-cern to the radiographer, since the success andquality of the work will depend upon knowl-edge and correct use of films that are manu-factured with many different properties.

An industrial radiographic film is a thin,transparent, flexible plastic base that has beencoated with gelatin-containing microscopiccrystals of silver bromide. Some films haveone side coated and some have both sides of


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Tab

le 1

5.3

App

roxi

mat

e R

adio

grap

hic

Equ

ival

ence

Fac

tors

of S

ever

al M

etal

s

Met

al

X-R

ays

(kV

)14

-24

ME

V

Gam

ma

Ray

s

5010

015

022

040

010

0020

00Ir

idiu

m-1

92C

esiu

m-1

37C

obal

t-60

Mag

nesi

um0.

60.

60.

050.

08

Alu

min

um1.

01.

00.

120.

180.

350.

350.

35

2024

(al

umin

um

allo

y)1.

41.

20.

130.

140.

350.

350.

35

Stee

l12

.01.

001.

01.

01.

01.

01.

01.

01.

001.

00

18-8

(st

eel)

allo

y12

.01.

001.

01.

01.

01.

01.

01.

01.

001.

00

Cop

per

18.0

1.60

1.4

1.4

1.1

1.10

1.10

Zin

c18

.01.

401.

31.

31.

11.

001.

00

Bra

ss*

1.4*

1.3*

1.3*

1.2*

1.2*

1.1*

1.1*

01.

1*0

Lea

d1.

4012

.05.

02.

54.

03.

202.

30

Not

e: A

lum

inum

is ta

ken

as th

e st

anda

rd m

etal

at 5

0 kV

, and

100

kV

, and

ste

el a

t the

hig

her

volta

ges

and

gam

ma

rays

. The

thic

knes

s of

ano

ther

met

al is

mul

ti-pl

ied

by th

e co

rres

pond

ing

fact

or to

obt

ain

the

appr

oxim

ate

equi

vale

nt th

ickn

ess

of th

e st

anda

rd m

etal

. The

exp

osur

e ap

plyi

ng to

this

thic

knes

s of

the

stan

dard

met

al is

use

d. E

xam

ple:

To

radi

ogra

ph 0

.5 in

. of

copp

er a

t 200

kV

, mul

tiply

0.5

in. b

y th

e fa

ctor

1.4

, obt

aini

ng a

n eq

uiva

lent

thic

knes

s of

0.7

in. o

f st

eel.

The

re-

fore

, giv

e th

e ex

posu

re r

equi

red

for

0.7

in. o

f st

eel.

*Tin

or

lead

allo

yed

in th

e br

ass

will

incr

ease

the

fact

ors

give

n he

re.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


the base coated with a layer of silver bromidecrystals, approximately 0.001 in. (0.02 mm)thick. The silver emulsion is not only sensi-tive to x-radiation and gamma radiation but isalso sensitive to light. For this reason, the filmis enclosed in a light-tight holder loaded in aphotographic darkroom and remains in thisholder (cassette) until the exposure process iscompleted and the film is ready for develop-ment. At that time, it is unloaded in the dark-room so that the film is never “exposed to”light until the development processing iscompleted. Films will be discussed in moredetail later in this section.

15.4.1.4 A Trained Person to Produce anAcceptable Radiograph.

In addition to thebasic “material” components of the radio-graphic process, the production of successfulradiographs is highly dependent upon atrained person capable of safely making reli-able exposures. Radiography may be relatedto photography as there are some similaritiesbetween the two processes. Figure 15.9 showssome of the basic geometric principles ofpenumbral “shadow formation” or image pro-jection common to most all image recordingprocesses. Figure 15.10 shows the basic geo-metrical requirements for producing shadowimages which are not blurred, i.e., unsharp. Ingeneral, the following rules apply to exposuregeometry:

(1) The radiation source should be as smallas possible. Sharpness in a radiograph isclosely related to the physical size of thesource of radiation.

(2) The distance from the source of radi-ation to the film should be as great as ispractical.

(3) The film should be as close to the speci-men as possible. Ideally the cassette or filmholder should be in contact with the specimen.

(4) The primary source alignment axis ofthe radiation beam should be directed perpen-dicular to the film plane where possible. Thiswill minimize distortion of the specimen andflaw images.

(5) The plane of maximum interest on thespecimen should be parallel to the plane ofthe film.

The art of establishing successful radio-graphic techniques is highly dependent uponthe knowledge of all of these as well as otherprinciples. Through judgment and experience,the radiographer should develop a “feel” forthe geometry of the exposure technique.Arrangement of the position of the radiationsource, the specimen, and the film relative toone another will determine the geometric pro-jections and “sharpness” of the radiographicimages. The radiographic exposure sharpnessobtained is referred to as

definition

and expo-sures that show images resulting from poordefinition will be blurred much the same as aphotograph made with an out-of-focus lens.

To achieve maximum effectiveness, theradiographer should be capable of selectingthe proper film, intensifying screens, filters,and materials to reduce radiation scatter. Dur-ing the handling and exposure of the film, theradiographer should exercise extreme care toavoid the introduction of film artifacts such ascrimp marks, scratches, pressure marks, staticelectricity, etc. that will interfere with subse-quent interpretation of the radiographicimage. Other film “artifacts” are discussedunder film processing.

It was mentioned earlier that radiationsources can be hazardous and that special pre-cautions should be taken while working withradiation. The radiographer or qualified per-son making the exposure should be trained inthe aspects of radiation safety. In this country,the Nuclear Regulatory Commission (NRC)of the federal government has jurisdictionover certain isotopes, whereas x-ray exposuredevices are usually controlled by state gov-ernments. In either instance, exposure dos-ages to radiation are controlled by strict rulesand regulations, and one of the most—if notthe most—important responsibilities of theauthorized person making the exposure is tosee that no unwarranted radiation exposure isreceived by anyone. The welding inspectorshould be aware of the possibly harmfulaffects of radiation.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


It should also be mentioned that most fabri-cation specifications and codes in use today inthis country require that personnel engaged innondestructive examination activities, includ-ing radiographic personnel, be certified as totheir abilities and levels of technical compe-tence. In more recent developments in thiscountry, some states now require specificradiation safety training for radiographersfollowed by certification testing prior toperformance of gamma radiography. TheAmerican Society for Nondestructive Testing(ASNT) (Ref. 15.9) has published a recom-mended practice for such certifications and isan example of the increasing emphasis beingplaced on inspection personnel certifications.Inspection personnel usually should obtain

minimum levels of education, training, experi-ence, pass a written an examination, and havea tested minimum visual acuity. The weldinginspector should ensure that all necessaryrequirements have been satisfactorily met.

15.4.1.5 Processing the Film.

The radio-graphic process is only partially completedonce the exposure has been made. Properchemical processing of the film to develop thelatent image of the object is an essential ele-ment of the process. Improper processingmay make it impossible to read the film andmay render useless the most careful radio-graphic exposure work.

Processing the radiographic film convertsthe latent invisible image (produced in the

Figure 15.9—The Penumbral Shadow


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 15.10—Geometric Principles of Shadow Formation


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


film emulsions by exposure to x-ray, gammaray, or light) to a visible, permanent image.Processing, as well as the handling of radio-graphic films is carried out in a darkroomunder special lighting (safe light) of a color towhich the film is relatively insensitive. Radio-graphic films are only as good as the process-ing they receive.

The first step in processing films is immer-sion in a developer solution. This causes theexposed portions of the film to become dark;the amount of darkening of the film willdepend upon the degree of development andthe degree of exposure to radiation the filmhas received.

A second optional step is either a waterrinse or an acid stop bath to reduce or stop thedeveloping action on the film.

The third step is the fixing bath. The func-tion of the fixer is to dissolve unexposed sil-ver bromide from the areas not darkened bythe developer solution and to harden theemulsion so that it will with stand dryingtemperatures.

The fourth step is a water wash bath toremove the fixer and products of the fixingaction from the film emulsion.

The fifth step (optional) is immersion in awetting solution (soap) that allows the waterto run off the surface of the film to help pre-vent spotting.

The sixth and final step is drying.Radiographic film development techniques

are either automatic or manual (hand tanksand racks). Automatic processing cycles usu-ally do not involve a stop bath or a specificcleaning stage or applications of a wettingagent. Modern automatic film processorstransport exposed films from one chemicalsolution to the next and include a rapid dryingcycle. In all instances involving film handling,cleanliness is of utmost importance. Dust,dirt, oily residues, fingerprints, and chemicalspills, including drops of water on the filmbefore exposure and processing, could affectthe image on the finished radiograph. Indica-tions that appear on radiographic films andare irrelevant to the weld image under exami-nation are referred to as

artifacts.

15.4.1.6 A Skilled Person to Interpret theRadiograph.

The final essential element ofthe radiographic inspection process involvesevaluation of the completed radiograph and asubsequent disposition of the test objectunder examination. Evaluation of the com-pleted radiograph is usually called “film inter-pretation” and the person performing theinterpretation is a

film interpreter

or

filmreader.

If absolute perfection were the requiredlevel of quality for all materials and assem-blies, then the interpretation of radiographswould be a relatively easy task. The inter-preter would simply declare the product orassembly unacceptable if any kind or amountof discontinuity was found. However, practi-cal considerations usually allow somethingless than perfection for most products. Engi-neering design specifications will establishquality guidelines for the radiographic exami-nation of the test object. The interpreter willbe required to make judgments about theacceptability of discontinuities existing in theproduct under examination. The art of filminterpretation, therefore, is a judgment pro-cess, and the individual who performs thesejudgments will need basic understanding notonly of radiography, but also of the technol-ogy of the product being examined.

The essentials of film interpretation are dis-cussed in some detail later in this section. Thedegree of skill required of a film interpreteris acquired through long experience orextensive training, or a combination of both.Accurate interpretation requires a broadknowledge of the characteristic appearancesof weld and related discontinuities associatedwith the particular types of material or mech-anisms in which they occur. This knowledgecan only be fully gained from experience inscrutinizing a wide range of specimens radio-graphed and preferably correlated with sec-tioned or prepared workmanship samples.Secondly, it is essential that the interpreter beknowledgeable of the types of discontinuitieslikely to be encountered in a particular weld-ing process and the manner in which theirimages are likely to vary with the angle at


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


which they are projected onto the film by theradiation beam. Needless to say, the inter-preter should possess a knowledge of theradiographic techniques used.

Some specifications and codes may requirecertification that the film interpreter has metminimum levels of education, training, andexperience in conjunction with an examina-tion for technical competence.

15.4.2 Radiographic Techniques.

The radio-graphic process, though simple in concept,involves a large number of variables andrequires well-organized techniques to obtainconsistent quality.

This section presents some of those tech-nique essentials that have been proven usefuland practical in industry. For further informa-tion on radiographic techniques, see “Refer-ences and Suggested Reading Material” at theend of this chapter.

The radiographic image should provideuseful information regarding the internalsoundness of the specimen. Image quality isgoverned by two categories of variableswhich control: (1) radiographic contrast and(2) radiographic definition. Both of these gen-eral categories may be further subdivided (seeFigure 15.11) and will be briefly discussed.

15.4.2.1 Radiographic Contrast.

In theradiograph of Figure 15.8, the various intensi-ties of radiation passing through the testobject are displayed as different film densitiesin the resultant image. The difference in filmdensity from one area to another contributesto “radiographic contrast.” Any shadow ordetail within the image is visible by means ofthe contrast between it and the backgroundimages. Up to a certain degree, the greater thedegree of contrast or density differences inthe radiograph (between two or more areas ofinterest), the more readily various images willstand out. The radiographic contrast of con-cern here is the result of a combination of twocontributing contrast components of theradiographic system, i.e., subject contrast andfilm contrast.

15.4.2.2 Subject Contrast.

Subject con-trast is that contribution made to the overallradiographic contrast by the range of differ-ence in radiation absorption by the subject ortest object. As mentioned earlier, the key ele-ments in absorption are (1) the mass of thetest object, including the atomic number ofthe absorbing substance and the thickness ofthe absorber, and (2) the penetrating power ofthe radiation used (i.e., the energy or wave-length of radiation used). A flat plate ofhomogeneous material with a very smallthickness variation would have a very lowsubject contrast. Conversely, a test objectwith a large thickness variation would yield alarge difference in absorbed radiation andwould, therefore, have a high subject contrast.A given test object with a given thicknessvariation (such as Figure 15.11) can have alow subject contrast using high-energy radia-tion (short wavelength) and a high subjectcontrast using low-energy radiation (longerwavelength).

Subject contrast is also affected by scat-tered radiation. When a beam of x-rays orgamma rays strikes any object, some of theradiation will be absorbed, some will be scat-tered, and some will pass straight through.The electrons of the atoms constituting theobject scatter radiation in all directions, muchas light is dispersed by a fog. The wave-lengths of much of the scattered radiation areincreased by the scattering process and,hence, the scatter is always somewhat“softer” or less penetrating than the unscat-tered primary radiation. Figure 15.12 illus-trates two basic scattering processes withwhich the welding inspector should be famil-iar: (1) internal object scattering, and (2)external reflected scattering. In the radiogra-phy of thicker, more dense materials withlower energy x-ray sources of radiation, scat-tered radiation forms the greater percentageof the total radiation reaching the film. Forexample, in the radiography of a 3/4 in.(19 mm) thickness of steel, the scattered radi-ation from the test object is almost twice asintense as the primary radiation reaching thefilm; in the radiography of a 2 in. (50 mm)


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Subject Contrast

1. Absorption characteristics of specimen (material density, thickness variation, etc.

2. Radiation energy level (KEV–MEV)3. Control or radiation scattering processes

a. Lead screensb. Film backscatter shields (backing lead, etc.)c. Filters, masks, and diaphragmsd. Source collimation

Radiographic Contrast

Film Contrast

1. Film type2. Film processing

a. Cycle timeb. Developer temperaturec. Processing chemistry activity

3. Film density (as related to position on film characteristic curve)

4. Type of screen (lead or fluorescent)

Radiographic Image

Geometric Factors

1. Focal spot size2. Source to film distance3. Film–specimen contact4. Specimen configuration and thickness variation5. Film–screen contact6. Source–specimen–film movement

Definition

Film Graininess

1. Film type (speed, etc.)2. Screen type3. Radiation energy level4. Film processing

Figure 15.11—Factors Affecting Quality of Radiographic Image

thickness of aluminum, the scattered radiationis two and a half times as great as the primaryradiation. As may be expected, preventingscatter from reaching the film markedlyimproves the quality of the radiographicimage.

As a general rule the greater portion of thescattered radiation affecting the film is fromthe internals of the test being radiographed.

Figure 15.12(A) illustrates internal radiationscattering effects to the film. Although thisscattered radiation can never be completelyeliminated, a number of means are availableto reduce its effect. Lead foil screens (usuallyon the order of a few thousandths of an inchin thickness) are commonly employed as fil-ters and are positioned between the test objectand the film to absorb the “softer,” less


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


penetrating scattered radiation prior to itsreaching the film. In addition to improvementof the radiographic image by reduction ofscattered radiation, the screens intensify theradiographic image. Lead screens intensify byemitting secondary radiation and fluorescentscreens intensify by emitting visible light. Asa result of this intensification characteristic,intimate film–screen contact should be main-tained. Also employed are diaphragms and fil-ters of various absorbent materials placedclose to the radiation source between thesource and the test object to absorb softerradiation prior to its reaching the test object.This latter method has the effect of improvingthe “quality” of the radiation that actually

penetrates the test object and the better theradiation quality, the less problem in control-ling the unwanted internal scattered radiation.As a general rule, the same principles willapply to both gamma and x-radiation; how-ever, since gamma radiation from commonindustrial gamma ray sources is highly pene-trating, methods used for controlling internalscattered radiation from these sources willusually necessitate different applications.

Scattered radiation originating in matteroutside the test object, i.e., externally, is mostserious for test objects that have a propensityfor high radiation absorption. This is obvi-ously due to the fact that scattering fromexternal sources may be large compared to

Figure 15.12—Sources of Scattered Radiation


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


the primary image-forming radiation thatreaches the film through the test object. Fig-ure 15.12(B) illustrates the effects on a testobject from common sources of external radi-ation scattering. Most sources of externalscattering (such as walls, floors, ceilings, ornearby support apparatus) are poor absorbersof radiation and consequently reflect radiationback to the test object (back scattering) andthe film. This reflected radiation, then, causesa decrease in the fundamental image contrastin much the same way as internal scatteredradiation. Common industrial methods usedto control this type of scattered radiationinclude the use of heavy (0.01 to 0.02 in. [0.2to 0.5 mm]) lead screens in contact with theback side of the film (inside cassette). Heavybacking lead (1/4 to 1/3 in. [6 to 8 mm],depending upon the conditions) between thefilm and the floor; or sometimes specialmasks made of some highly absorbent mate-rial are placed around the test object. Dia-phragms or collimators that restrict thedirection of primary radiation intensity to thetest object have also proven to be valuableaids in controlling external scattered radiationeffects on subject contrast.

15.4.2.3 Film Contrast.

Film contrast isthat contribution made to the overall radio-graphic contrast by the film and its relatedcharacteristic variables. The recording pro-cess, depending upon the film type andrelated variables, can amplify the differencein film densities created by subject contrast.This is called

process contrast amplificationor the degree of film contrast. Film emulsionscan be manufactured to render differentdegrees of film contrast in addition to otherproperties such as speed (the exposure dura-tion required to achieve a certain film con-trast) and the level of graininess of theemulsion. Each film type detects and recordsvarying radiation exposure differences as sig-nificant film density changes on the radio-graph. The principles of film contrast are bestdescribed and understood by the film charac-teristic curve, sometimes called the H&Dcurve.

Figure 15.13 illustrates a typical character-istic curve for an industrial radiographic film.This curve relates film density (the degree ofdarkness of the radiograph) to the logarithmof radiation exposure. The radiation exposure,R, of a film is defined as the product of theradiation intensity, I, exposing the film, andthe time, t, of exposure duration. This rela-tionship may be expressed as follows:

(1) R = I × t (Eq. 15-1)

whereR = radiation exposureI = source intensityt = time of exposure duration

The exposure value is expressed as a loga-rithm (usually base 10) for two reasons: (1)for convenience in compressing an otherwiselong scale of exposure units, and (2) on a log-arithmic scale, a change in exposure (a radia-tion or exposure difference, R) has a constantspread throughout the scale, whereas thesame R would have a wider and wider spreadalong an arithmetic scale. A constant expo-sure difference is the basic “tool” that rendersa characteristic curve useful.

Film density, or optical transmission den-sity, is defined as follows:

(2) D = Log10 Io/It (Eq. 15-2)

whereD = film densityIo = intensity of light incident on filmIt = intensity of light transmitted through

the film (as seen by the eye)

The logarithmic value is used for convenienceto express the density as a small number. Afilm density of 1.0 H&D units means that 1out of 10 parts of light will reach the eye afterbeing transmitted through the film, or

D = Log10 units= 1.0 H&D density 1 unit (Eq. 15-3)

The characteristic curve shape (i.e., slope)at any particular film density is not onlydependent upon the type of film selected, butis also influenced by the degree of develop-ment and the type of intensification screens


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


used. Intensification screens are thin sheets ofmaterials placed within the film cassette inintimate contact with the film for the purposeof catalyzing the photographic action on thefilm during exposure. There are two basicconcepts used in intensification processes (1)fluorescent type screens (such as calciumtungstate) emit light when the screen isexposed to radiation, which further exposesthe film; (2) lead type screens, which mayalso serve as scatter foils, emit electronswhich expose the film. These screens are usu-ally referred to as intensification screens.They change the shape of the characteristiccurve, depending upon which type is used.

Film contrast (i.e., the difference in filmdensities resulting from the same percentagechange in radiation exposure) then is deter-

mined by (1) the shape or slope of the char-acteristic curve and (2) the film density levelof the radiograph. For a better understandingof the fundamentals, refer to the curve shownin Figure 15.13. The characteristic curveshows the resultant film densities (D1, D2, D3,and D4) occurring from exposure dosages R1and R2. The exposure differences, ∆R or (R2 –R1), could arise from different equivalentthicknesses in the exposed specimen, causedby perhaps a discontinuity. The same dosagedifference (R2 – R1), at various positionsalong the slope of the characteristic curveproduces different amounts of film contrast,∆D or (D2 – D1). The degree of film contrast,(∆D), will be lowest at the “toe” of the char-acteristic curve and highest where the curve issteepest.

Figure 15.13—Characteristic Curve For a Typical Industrial X-Ray Film

The specimen above illustrates a typical defect in terms of a thickness reduction, (T). R2'–R1' = thedosage of difference for a relative exposure (1): R2 – R1 = the dosage difference for a relative exposure(2). If these exposure differences are transferred to the logarithmic scale on the curve at left, therelative exposure dose difference ∆R has the same spread throughout the large scale. When ∆R isapplied to the gradient curve, the slope of the curve will dictate the difference in film densities(contrast) for the corresponding areas of the specimen.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Where the slope of the characteristic curveis 1.0, no contrast amplification will occur.Slopes less than 1.0 will actually reduce thecontrast. For this reason, good radiographictechniques expose the film long enough toobtain film densities along the high gradientportion of the characteristic curve. Manyradiographic specifications require a mini-mum film density of 1.5 H&D units. The opti-mum value should be sought by constructingsuch a film characteristic curve for the radio-graph processing variables that will be experi-enced. Upper limits on film densities areusually imposed by the radiographer’s view-ing illumination. Many viewing boxes canilluminate films with densities as high as 4.0H&D units.

Complex geometries, shapes, and changingthicknesses may require multiple film-exposure techniques. When castings are radio-graphed, several films with different speedsmay be used in a single simultaneous expo-sure to ensure that adequate film densities areobtained over a desired thickness range.

15.4.2.4 Radiographic Definition. Radio-graphic definition is equal in importance toradiographic contrast. Definition concerns thesharpness of the image. Sharpness means thedegree of abruptness of the transition fromone density to another. The more abrupt thistransition, the greater the ease in identifyingor defining the image. It is easier to discerndetails in a sharp radiograph than those in an“out-of-focus” one. Two components ofradiographic definition are exposure geome-try and film graininess (see Figure 15.11).

15.4.2.4.1 Exposure Geometry. Thesharpness aspect of the exposure geometry,illustrated in Figure 15.10, shows how “pen-umbral shadow” is affected by: (1) sourcesize, (2) source-to-film distance, and (3) spec-imen-to-film distance.

Every source of radiation has physicaldimensions larger than a pinpoint, casting apenumbral shadow behind any object, whichthus blurs the image. For a given x-ray orgamma ray source, the radiographer usuallyhas no way to change source size. Gamma

sources generally vary from 1/16 in. (1.6 mm)diameter to slightly less than 1/2 in. (12 mm)diameter. X-ray focal spot sizes vary fromseveral mm2 (generally 6 to 8) down to a frac-tion of a square millimeter. However, as maybe seen in Figure 15.10, the effects of penum-bral shadow may be reduced and renderedless noticeable by increasing the distancebetween source and specimen or decreasingthe distance between specimen and film.Changes in exposure conditions related togeometry (both focus and projection) areinterdependent in their effect upon imagesharpness. Excessive object thickness ampli-fies the penumbral shadow. Should the objectunder examination be moved or positionedfarther from the film for a given source-to-film distance (S.F.D.), the penumbral shadowwill noticeably increase as may be seen inFigure 15.10. The variables governing thepenumbral shadow or “geometric unsharp-ness” may be mathematically related asfollows:

(3) (Eq. 15-4)

whereUg = geometric unsharpnessF = focal spot size of the largest dimen-

sion of the sourceT = specimen thicknessD = source-to-specimen distance

Most good radiography is generally per-formed with a value of Ug less than 0.040.Most codes will give limits of Ug acceptance.

Poor definition of the radiographic imagemay also result from any movement of thespecimen or source, especially in a transversedirection normal to the axis of exposure. Ifintensifying screens are used in the cassette,they should be in as intimate contact with thefilm as possible to avoid two undesirable con-sequences: (1) the specimen could be movedunnecessarily farther from the film, and (2)electron impingement onto the film from theintensifying screen could exaggerate the sizeof the image, reducing the sharpness.

Ug

D------- FT=


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


15.4.2.4.2 Graininess of the Film. Filmgraininess is the visual appearance of irregu-larly spaced grains of black metallic silverdeposited in the finished radiograph. Theunexposed radiographic film contains anemulsion with countless grains of silverhalide. The graduation in density results fromthe number of grains developed in each area,each grain being uniformly black. Fast filmshave large grains and, thus, a coarsely struc-tured image. Slow films have finer grains anda less grainy image.

Radiographic films of all types and brandspossess some amount of graininess. The fol-lowing are some factors that will determine thedegree of graininess on a finished radiograph:

(1) Type and speed of film(2) Type of screens used(3) Energy of radiation used(4) Type and degree of development usedFluorescent intensifying screens produce

what is termed screen mottle. Screen mottlegives an appearance of graininess, consider-ably “softer” in outline than film graininess.The cause of screen mottling is a statisticalvariation in the absorption of radiation quantaby areas of the screen and the resulting fluctu-ation in intensification. In general, the smallerthe number of radiation quanta absorbed bythe screen, the more readily may screen mot-

tle be observed. It is important to keep allintensification screens clean as well as ingood condition, free from blemishes, cracks,or surface deterioration, in order to precludeadditional statistical variations in the intensi-fication process. Because of this potential for“mottling,” some codes and other standardsdo not permit the use of fluorescent screens.

The energy level of the radiation sourceused affects film graininess. Generally, high-energy radiation produces increased graini-ness. This has been attributed to electron scat-tering within the emulsion and subsequentsensitization of adjacent silver halide grains(see Ref. 15.11).

Development or processing of the exposedradiograph beyond the manufacturer’s recom-mended times and temperatures can cause anincrease in amount of grain “clumping” and,thus, an increase in the visual impression offilm graininess.

Image Quality Indicators. Due to the largenumber of variables that affect the imagequality of a radiograph (see Figure 15.11),some assurance is needed that an adequateradiographic technique has been achieved.The tool used by the radiographer to demon-strate technique is the image quality indicator(IQI) or penetrameter. Figure 15.14 illustratestypical conventional penetrameters used

Figure 15.14—The “Tools of The Trade” for the Radiographer


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


extensively in this country. Other design typesused abroad are available. The other “designtypes” refer primarily to wire gauges. Theseare now included in the ASME Code andshould no longer be considered as “foreign.”

Conventional penetrameters (ASTM, Mili-tary) consist of a strip of material of simplegeometric shape that has absorption character-istics similar to the weld metal under investi-gation (see Figure 15.15). Use of this type ofIQI provides information about (1) the radio-graphic contrast, and (2) the radiographicimage quality. Each penetrameter has specificabsorption characteristics. When a weldmentis to be radiographed, a penetrameter withthickness equal to a specified percentage (1%,2%, 4%, etc.) of the weld thickness is gener-ally selected. A lead identification number atone end of the IQI shows the thickness of thepenetrameter in millimeters or thousandths ofan inch. Conventional penetrameters usuallycontain three holes drilled in the face of theplaque, the diameters of which vary in size asmultiples of the plaque thickness. Most speci-fications and codes in use today call for an IQI

with 1T, 2T, and 4T diameter holes, where “T”is the plaque thickness. As may be seen in Fig-ure 15.15, these holes are carefully positionedon the plaque and, for each particular designof penetrameter, usually remain in the samesequence for all sizes and material groups.

Penetrameters are manufactured in stan-dard sizes or increments of thickness.Although requirements will vary from user touser, the thickness increments are generallyclose enough together so that little or no sig-nificant penalty is paid when an exact thick-ness penetrameter is not available for aparticular weld thickness. In addition, con-ventional penetrameters are usually manufac-tured in material groupings rather than incountless numbers of penetrameters for allmaterial types. Most specifications and codesorganize all major materials into a minimumof five absorption categories, ranging fromlighter metals (Group I) to heavy metal(Group V). The specimen to be examinedshould have its penetrameter made from thesame grouping as the specimen material orfrom a grouping of lighter metal.

Figure 15.15—Typical Penetrameter Design


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Most radiographic image quality require-ments are expressed in terms of penetrameterthickness and desired hole size. For example,the requirement might be a 2-2T level of sen-sitivity. The first 2 requires the penetrameterthickness to be 2 percent of the thickness ofthe specimen; the symbol 2T requires the holehaving a diameter of twice the plaque thick-ness to be visible on the radiograph. The 2-2Timage quality level is commonly specified forroutine radiography. For more sensitive radi-ography, a 1-2T or 1-1T could be required.More relaxed image quality requirementswould include 2-4T and 4-4T.

Figure 15.14 also illustrates typical place-ment relationship of penetrameter and welds.It is important that penetrameter placement becontrolled to obtain similar quality for theweld and the penetrameter. In most instancesthe penetrameter will be placed on the sourceside of the specimen, as this is the position ofleast favorable geometry. However, in somecases this will not be practical, as in the radi-ography of a circumferential weld in a longpipe section where the weld is inaccessiblefrom the inside. In this case, the penetrametermay be located on the “film side” of the weld-ment. Most specifications and codes willspecify the circumstances or conditions whena “film side” penetrameter may be used andwill also stipulate how the film side penetram-eter size shall be selected.

Note also in Figure 15.14 that the penet-rameter has been placed on another piece ofmaterial. This piece of material is called ashim and is of radiographically similar mate-rial to the weldment being examined. Thethickness of the shim will generally equal thethickness of weld reinforcement and backingso that the image of the penetrameter will beobtained by projection through the samethickness of material as the area of interest,which in this case is the welded joint.

In the hands of a skilled radiographic inter-preter, the appearance of the penetrameterimage on the radiograph will indicate thequality of the radiographic technique. Itshould be remembered that even if a certainhole in a penetrameter is visible on the radio-

graph, a void or discontinuity of the sameapproximate diameter and depth as the holesize may not be visible. Penetrameter holeshave sharp boundaries and abrupt changes indimensions, whereas voids or discontinuitiesmay have a gradual or blending-in change indimension and shape. A penetrameter, there-fore, is not an indicator or gauge to measurethe size of a discontinuity or the minimumdetectable flaw size. A penetrameter is animage quality indicator of the success of theradiographic technique.

15.4.3 Exposure Techniques. In determiningthe most proficient arrangement of the essen-tials needed to make a radiograph, a radiog-rapher should select the best locations forpositioning of the radiation source and film inconjunction with the test object. The followingare typical factors that should be considered:

(1) Which arrangement will provideoptimization of image quality and weldcoverage?

(2) Which arrangement will provide thebest view for those discontinuities most likelyto be present within the weldment?

(3) Will a multiple film exposure techniquebe required for weld coverage?

(4) Can a “panoramic” [see Figure15.16(F)] type of exposure be used?

(5) Which arrangement will require theshortest exposure duration?

(6) Can the exposure be made safely?Figure 15.16(A) through (G) shows typical

exposure arrangements for some commontypes of weldments. A flat weldment (A) isone of the simplest test objects to radiograph.Most of the essentials of good radiographycan be easily applied, i.e., good exposuregeometry and proper positioning of radio-graphic tools for the most practical set-up.

Figure 15.16(B) through (F) illustrate sometypical exposure arrangements for radiogra-phy of pipe weldments. If the pipe nominaldiameter is relatively small (1-1/2 in.[38 mm] or less), it may be practical toexpose a portion of two walls of the pipeweldment with one exposure straight throughboth walls, as shown in view C. Unfortu-


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 15.16—Typical Radiographic Exposure Arrangements


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


nately, in this case, the image of both wallswould be projected superimposed onto thesame film area. It would be difficult to deter-mine the exact location of a discontinuity ifone were present. Depending upon the wallthickness of the pipe, a better arrangementmay be to position the source “offset” fromthe plane of the weld, as shown in view D, sothat the images will be cast onto the film asan ellipse, which will improve the visibilitycharacteristics of each wall separately.Should discontinuities exist, they could beindividually located.

In some instances, trade-offs are possiblethat will influence the radiographer’s choiceof conditions. The welding inspector shouldbe cautioned that one method may be as goodas another, depending upon the variablesinvolved. The radiographer usually has reli-able information at hand when planning thesetup.

Circumferential welds in slightly largerpipe sizes (2 to 3-1/2 in. [50 to 90 mm] nomi-nal diameters), are also usually radiographedin the double-wall fashion, the radiation pene-trating both walls to make the exposure. Morethan one exposure may be required, however,to obtain good coverage of the weldment.

Nominal pipe sizes over 3-1/2 in. (90 mm)usually are exposed for single-wall film view-ing. This may be accomplished in one of threeways: (1) the radiation source may be posi-tioned on the inside of the pipe [Figure15.16(F)] with the film wrapped around theoutside; (2) the radiation source may be posi-tioned on the outside of the pipe with the filmon the inside (view E); and (3) the radiationsource may be positioned on the outside ofthe pipe with the film on the diametricallyopposite side of the pipe so that the radiationsource penetrates both walls (view B). In thislatter arrangement, the wall closest to thesource is treated as if it were not there (sourceis usually offset). In all instances, sufficientnumbers of exposures should be made toensure complete weld coverage for either sin-gle-wall or double-wall film viewing. Thepreferred arrangement would be that whichcontains the most favorable trade-off of expo-

sure and geometry variables as determined bythe radiographer for the prevailing conditionsor a radiographic procedure which the radiog-rapher should follow.

Figure 15.16(G) illustrates a technique thatmay be used to determine the depth of a dis-continuity found in a plate type of test object.A single radiograph, which is a two-dimen-sional plane surface, will not indicate thedepth location of a discontinuity. A doubleexposure provides parallax to reveal the thirddimension. Essentially, lead markers V1 andV2 are positioned on the source and film sidesof the test object as shown. Two exposures aremade, the radiation source being moved leftor right any convenient distance D for the sec-ond exposure. The position of the images ofmarker V2 will change very little as a result ofthis source shift. The shadows of the flaw Fand reference marker V1 will change positionsignificant amounts, ∆F and ∆V1, respec-tively. Depending upon the detail of the flaw,both exposures may be made on the samefilm; however, one exposure has a tendency tofog the other. If the thickness of the specimenis t, the distance of the flaw above the filmplane is (t∆F)/∆V1.

It should be noted that this calculationassumes that the image of the bottom marker(V2) remains essentially stationary withrespect to the film. This may not always betrue; for example, if the cassette or filmholder is not in contact with the bottom sur-face of the test object, or if larger sourceshifts are used.In that instance, the location ofthe flaw may be computed by the followingformula:

X = h∆F (Eq.15-5)

D + ∆F

whereX = distance of flaw above filmh = focus-to-film distance∆F = change in position of flaw imageD = distance source has shifted from L1

to L2 [see Figure 15.16(G)]

15.4.4 Interpretation of Radiographs. Sinceaccurate interpretation of radiographs allows


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


work to be judged on its merits according toapplicable standards, the welding inspectorshould strive to become proficient in readingradiographs.

The essential steps in evaluating a radio-graph of a weldment are these:

(1) Check the identification of the radio-graph against accompanying records for accu-racy.

(2) Determine the weldment design andwelding procedure used to construct the joint.

(3) Determine the radiographic setup pro-cedure used and the correctness of techniqueattributes.

(4) Review film under adequate film view-ing conditions.

(5) Identify the presence of any film arti-facts and request a re-radiograph if necessary.

(6) Identify any surface marks or irregulari-ties not associated with internal soundnessand verify their type and presence.

(7) Evaluate and propose disposition of dis-continuities revealed in the radiograph.

(8) Prepare a complete radiographic report.

15.4.4.1 Film Viewing Conditions. Toproperly interpret a radiograph, it should beexamined under conditions of best legibilityand maximum comfort for the observer. Theviewing equipment should be located in awell-ventilated room with background light-ing subdued to reduce glare. The illuminatorshould provide a cold light or should haveforced ventilation so that the films placedagainst it for viewing do not curl due to heat.

Fluorescent lamps provide satisfactory coldlight sources, and ventilated high-intensityincandescent lamps with rheostat or variaccontrols are commercially available. Forviewing radiographs of butt joints in whichthe background film density does not varysignificantly, a single-intensity viewer willusually suffice. However, variable-intensityviewers are more versatile and provide advan-tages when viewing high-density negatives.

The viewing equipment should mask offthe extraneous area beyond the film. Theradiograph should be placed at eye level sothat the interpreter may sit erect comfortably.

15.4.4.2 Film Artifacts. Certain indica-tions that appear on radiographic films andare irrelevant to the weld being inspected arereferred to by the general term artifacts.These may be caused during the exposure orby improper handling or processing of thefilm. Some of the principal causes are asfollows:

(1) Screens that are dirty, scratched, muti-lated, or have foreign material between themand the film will have these imperfectionsreproduced as part of the image.

(2) Electrostatic discharge during film han-dling will expose the film to light and causean easily-recognized pattern of sharp blacklines on the developed film.

(3) Localized pressure on or bending ofpre-processed film results in typical “pressuremarks” or “crimp marks” when the film isprocessed.

(4) Processing defects of various kinds mayoccur; such as colored stains or blisters thatresult from improper stop-bath applicationbetween developing and fixing solutions.Streaks could be the result of improper agita-tion during development. Fogging could becaused by overexposure of the film to a safe-light lamp before fixing, or by using old film.Stains can be caused by improperly mixed orexhausted solutions, and water marks canresult from handling partially dried film. Fin-gerprints are obviously caused by handlingthe film. Scratches result from rough han-dling, especially during processing (when theemulsion is soft). Chemical fog may becaused by overdeveloping.

Properly used automatic processing equip-ment, in large measure, tends to eliminatemany of these deficiencies; but it too can giverise to certain others. These may includemarks from the rollers in the equipment ifthey become scored, contaminated withchemical residue, or do not function properly.Further data on film processing may beobtained from literature published by film andprocessor manufacturers.

It is the duty of the inspector to learn to rec-ognize and evaluate film artifacts, with regard


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


to their influence on film interpretation, and torequire re-radiography when warranted.

15.4.4.3 “Pitfalls” in Interpretation. As ageneral rule radiographs fall into one of threeevaluation categories: (1) unquestionablyacceptable, (2) clearly rejectable, and (3) bor-derline. There will be many borderline casesin radiographic interpretation. This categoryarises from honest differences of opinion, andfrom cases without clear-cut evidence. Forexample, although most standards permit slaginclusions in varying degree, some reject anyincomplete fusion; yet incomplete fusion maybe similar in appearance to an inclusion innature and in appearance on the radiograph.Generally, the two are indistinguishable withtotal certainty. The inspector should decidewhether the radiograph indicates a rejectablelack of fusion or an acceptable inclusion.

The inspector may be called upon to judgerepair welds in castings or assembly welds ofcast items. Here, the inspector may be facedwith inequalities between casting standardsand welding standards (the latter are, on thewhole, more restrictive): if an indicationcould be construed as a casting discontinuity,it may be acceptable; yet, if interpreted as aweld discontinuity, it may be rejectable.

The conscientious inspector should alwaysattempt to render judgment equitably, inaccordance with the applicable standards,bearing in mind that the prime considerationis a safe and serviceable component.

15.4.4.4 Radiographic Acceptance Stan-dards in Specification, Codes, and OtherStandards. Most industrial radiography isaccomplished in accordance with some speci-fied set of rules or mutually agreed upon con-ditions.These rules and conditions maypertain to such aspects as radiographic tech-nique conditions, coverage requirements,acceptance criteria, and radiographic pro-cedure approvals. Controlling criteria areusually contained in a manufacturing specifi-cation, code, or standard for fabricating com-ponents of a particular nature. Some of theorganizations that have adopted such criteriafor weldments include:

(1) The Armed Forces (military standards)(2) American Welding Society(3) American Society of Mechanical

Engineers(4) American Society for Testing and

Materials(5) American Petroleum Institute(6) Ship Structure Committee

15.4.4.5 Technique Conditions. Mostspecifications and codes will, as a minimum,specify requirements for controlling radio-graphic image quality. These controls willnormally consist of penetrameter sizes, filmdensity requirements, source-to-film focaldistances, radiation energy range, and expo-sure technique arrangement requirements.They may also specify certain techniques forensuring weld coverage, such as the position-ing of spot or location markers on the testobject. Some specification and codes willsometimes refer to an alternate standard orpractice and will adopt such criteria asrequirements for complying with their ownrequirements.

15.4.4.6 Coverage Requirements. Specifi-cations and codes will specify what sectionsor components of an assembly will requireradiographic examination. In addition, theywill usually state conditions for which partialradiography will be allowed or whether 100percent coverage will be required. Therequired terms of samplings for initial radiog-raphy are usually stated, as well as those forfollow-up examination after a defect has beenlocated. Some specifications and codes pro-vide options for using a different NDEmethod instead of or in conjunction with radi-ography. In many instances, coverage require-ments are finally governed by the designer orengineer who works closely with the specifi-cation or code or customer. In this case, cov-erage requirements may be specified onfabrication shop or field drawings.

15.4.4.7 Acceptance Criteria. An essentialof most specifications or codes is the specify-ing of the acceptance criteria to be used forfilm evaluation. Acceptance standards may be


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


indicated as written rules, formulae, pictori-als, charts, graphs, or reference radiographs.In some cases, it will be a matter of conve-nience as to which method will be used. It isbeyond the scope of this section to discussacceptance criteria in detail, as there are manydifferent applications and rules; however, thewelding inspector should be familiar with thespecification or code being used and be ableto evaluate workmanship in accordance withthe applicable acceptance criteria.

15.4.4.8 Procedure Approvals. Somespecifications and codes require qualificationof radiographic techniques and procedures.Usually, the major emphasis is on the abilityof the procedure to detect discontinuities thatare of concern to the product service. Such aqualification for radiography may involveradiographing a test object with knowndefects, using the technique essentials con-tained in the basic specification or code. Ifthese qualification radiographs are judgedcapable of rendering a meaningful examina-tion of the test object, the technique is said tobe qualified or to have a “demonstrated profi-ciency.” Qualification of radiographic tech-niques is an added assurance feature of thecapabilities of radiographic technique.

15.4.5 Radiographs of Weld Discontinuities.Generally, defects in welds consist either of avoid in the weld metal or an inclusion thatdiffers in density from surrounding weldmetal, a valuable reference on discontinuitiesis section 2 of Reference 15.2. Radiographsmay show internal discontinuities as well assurface discontinuities (see Chapter 9). Figure15.17 provides photographs of some typicalweldments and related radiographic imagesof discontinuities.

15.4.6 Advantages and Limitations ofRadiography

15.4.6.1 Advantages. Since radiogra-phy operates on the principle of radiationabsorption, it is noteworthy that some of thephysical dilemmas that affect other NDEmethods pose little or no significant problems

for radiography. Radiography is not restrictedto ferrous materials—or any other one type ofmaterial. Since radiation is penetrating, radi-ography is good for surface as well as subsur-face discontinuities. Although there arerequirements for exposure geometry, radiog-raphy does not require precisely parallel sidesas a prerequisite for inspection. Multiple filmradiography provides a tremendous thicknessrange over which a single exposure may yieldvalid indications. Another advantage is that apermanent record is available for both thecustomer and manufacturer to review for pos-itive quality assurance, and a picture type ofimage is permanently available. Althoughconventional radiography is more of an artthan a science, it does not require extensivedevelopmental studies to adapt it to variationsin technique.

15.4.6.2 Limitations. Certainly, a majorlimitation is the hazard of radiation exposureto the radiographer and nearby personnel. Incertain industries, radiographic examinationcan be disruptive. Radiography usuallyrequires special facilities or areas where radi-ation may be used in a controlled mannerwithout endangering personnel.

Radiography can detect cracks that arealigned parallel with the radiation beam; suchcracks are usually normal to the plate sur-faces. However, radiography usually cannotdetect laminations in plate. Other NDE meth-ods are capable of detecting such conditionsand, with the proper choice of technique, canusually be relied upon to detect cracks normalto the plate surfaces. Discontinuity orienta-tion, then, is a major consideration whenspecifying radiography as an examinationmethod.

Additional limitations include the high costof x-ray machines, isotopes and their relatedlicensing, safety programs, exposure dosime-try control, and film processing equipment.Permanent exposure facilities, such as radio-graphic booths constructed of heavy concrete,are expensive and not portable.

The lengthy time cycle of film radiographicexamination is another limitation. A typical


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 15.17—Typical Radiographs of Weld Discontinuities


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


cycle involves (1) the exposure process, (2)the film processing and related handling, and(3) the film interpretation process. Due to thedegree of specialization frequently encoun-tered, the exposed radiograph usually changeshands several times before the examination iscomplete and disposition is rendered. Manyother NDE methods render more “on-the-spot” results, without such time delays. Thislimitation may sometimes be overcome by theapplication of various “real time” radio-graphic techniques.

Other limitations include the need foraccessibility to opposite sides of the testobject or clearance of several feet on severalsides of the test object for placement of radio-graphic apparatus. The radiographic process,as a whole, requires operators with broad anddiversified skills.

More information is available in the litera-ture on industrial radiography, some of whichare listed in the references and suggestedreading material at the end of this chapter.

15.5 Ultrasonic Examination of Welds and Weld Related Materials

15.5.1 General Principle. Ultrasonic exami-nation is a nondestructive method of detect-ing, locating, and evaluating internaldiscontinuities in metals and other materials.The basic principle involves directing a high-frequency sound wave into the test materialon a predictable path, which, upon reflectingback from an interruption in material continu-ity (interface), produces a signal that is ampli-fied and usually displayed as a verticaldisplacement on a cathode ray tube (CRT).

The detection, location, and evaluation ofdiscontinuities becomes possible because (1)the velocity of sound through a given materialis nearly constant, making distance measure-ment possible, and (2) the relative amplitudeof a reflected pulse is more or less propor-tional to the size of the reflector.

15.5.2 Equipment. Equipment operating inthe A scan mode of the pulse-echo method

with video presentation is most commonlyused for hand scanning of welds and materi-als (see Figure 15.18). The pulse-echo equip-ment produces repeated pulses of high-frequency sound with a rest-time intervalbetween pulses to allow for the detection ofreturn signals from sound reflectors. The timerate between pulses, called the pulse rate,usually occurs at about 500 pulses per second,depending upon the equipment in use.

In the video presentation, the time base lineis located horizontally along the bottom of theCRT screen, with a vertical initial-pulse indi-cation at the left end of the base line. The Ascan indicates that the time lapse betweenpulses is represented by the horizontal direc-tion; and the relative amplitude of signal isrepresented by the degree of vertical deflec-tion on the CRT screen. The screen is usuallygraduated in the horizontal and vertical direc-tions to facilitate measurement of pulsedisplays.

The horizontal time interval (sweep-length)is adjustable with a material and velocity con-trol knob, making it possible to translate thetime interval into material distance. The hori-zontal location of the initial pulse with asweep delay adjustment allows the whole pre-sentation to be properly positioned on theCRT screen.

In order that a sound wave might bedirected into material, a search unit should beused. The search unit consists of some kind ofholder and a transducer. The transducer ele-ment is a piezoelectric crystalline or ceramicsubstance. When excited with high-frequencyelectrical energy produced by the power sup-ply, the transducer produces a mechanicalvibration at a natural frequency of the trans-ducer element. A transducer also has the abil-ity to receive vibrations and transform theminto low-energy electrical impulses. In thepulse-echo mode, the ultrasonic unit sensesthe return impulses, amplifies them, and pre-sents them as vertical deflections (pips) on theCRT screen. The horizontal location of areflector pip on the screen is proportional tothe distance the sound has traveled in the testpiece, making it possible to determine loca-


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


tion of reflectors by using horizontal screengraduations as a distance measuring ruler.

The vertical display is adjustable with apulse energy-level gain or attenuation controlthat makes it possible to show relative heightof reflector indications.

15.5.3 Sound Behavior. The behavior ofhigh-frequency sound resembles that of visi-ble light in the following ways:

(1) The sound wave divergence can be con-trolled by focusing.

(2) The sound wave will reflect predictablyfrom surfaces of different densities.

(3) The sound wave will refract at an inter-face between materials of different density.

When a search unit is applied to the surfaceof a uniform thickness test piece, only a smallportion of the reflected sound energy isabsorbed by the transducer, while the remain-der will reflect from that surface back into thetest piece interface, reverberating between theparallel test piece surfaces and causing anadditional indication on the CRT screen upon

each return of the sound wave to the initialsurface.

Unlike audible sound, high-frequencysound is easily attenuated by air, but travelsfreely in homogeneous solids or liquids.Therefore, it is necessary to eliminate any airgap that might occur between the search unitand the test material surface, using a fluidcouplant.

15.5.4 Interpretation. There are two basicmethods of evaluating reflector amplitudes.The one offering greater range and affordinggreater evaluation accuracy uses a calibrateddecibel gain or attenuation control. The otheremploys percentile CRT screen height ratios.

The percentile method often requires thatsound attenuation patterns be drawn or over-layed on the CRT screen to compensate forsound attenuation with distance. With units soequipped, compensation for these losses canbe made with a calibrated decibel gain orattenuation control. The decibel is a unit mea-suring the relative amplitudes of two acousticor electric signals. In order to use the decibel

Figure 15.18—Block Diagram, Pulse-Echo Flaw Detector


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


system for flaw evaluation, each indication tobe evaluated is adjusted to a reference levelon the CRT with use of the calibrated gain orattenuator control; decibel ratings are mademathematically.

Some ultrasonic units are also equippedwith distance amplitude correction (DAC)features that compensate electronically foramplitude losses, but the linearity of the verti-cal scale, especially when used in conjunctionwith decibel amplitude readings.

15.5.5 Equipment Qualification. AWS D1.1,Structural Welding Code—Steel, is probablythe most restrictive code for ultrasonicinspection in that the tolerable decibel error isplus or minus one decibel over a sixty decibelrange.

The decibel, as related to ultrasonics, is afunction of voltage ratios. Usually, the per-centile and voltage graduations on the CRTscreen are linear, making the decibel ratioslogarithmic in nature. The following equationcan be applied for converting voltage changesto decibel differences:

DN = 20 Log10 V1 (Eq. 15-6)

V2

whereDN = decibel differenceV1 = voltage oneV1 = voltage two.

Screen percentages can be substituted forvoltages in the equation. The nomographshown on Figure 15.19 is a graphical solutionto the equation.

15.5.6 Ultrasonic Attenuation and WaveForm. Ultrasonic attenuation is a combina-tion of sound loss due to the divergence of thesound and the losses due to dispersion of thesound wave when encountering an interface.

High-frequency sound does not alwayspass through a material in the same manner.There are three basic modes of sound-wavepropagation that can usually be associatedwith weld or weld-related materials. The sim-plest mode is the longitudinal (straight or

compressional) wave mode that results whenhigh-frequency sound is introduced into thetest medium in a direction normal to the inter-face between the search unit and test material.In this mode, the principal direction of mate-rial particle vibration is parallel to the direc-tion of sound-wave propagation through thematerial.

Another mode is the shear (angle or trans-verse) mode in which the principal directionof material particle vibration is perpendicularto the direction of sound wave propagation.

The third mode is the surface (Rayleigh)wave, transverse in nature, that follows alongmaterial surfaces. Shear and surface wavescannot propagate in liquid media.

When a longitudinal ultrasonic beam isdirected from one medium into another of dif-ferent acoustic properties at an angle otherthan normal to the interface between the twomedia, a wave-mode transformation occurs.The resultant transformation is dependentupon the incident angle in the first mediumand on the velocity of sound in the first andsecond media.

In each transformation, there is an equalangle of reflection back into the first medium,along with at least one shear wave form ofrefracted angle in the second medium only ifthe incident wave is less than the first criticalangle.

15.5.7 Geometry. Snell’s law can be used tocalculate angle transformations based on thesound-path angles and the sound velocities ofthe two media [see Figure 15.20(A)]. Forexample, the sine of incident angle a is to thesine of d (longitudinal) or e (shear) refractedangle as the sound velocity of the incidentMedium 1 is to the sound velocity of therefracted Medium 2. This same equation canbe used for determining refracted reflectedangles that occur in wave-mode conversionswithin the same medium, using the soundvelocities of different wave modes in theequation [see Figure 15.20(B)].

For example, in views (A) and (B) of Fig-ure 15.20, the sine of incident angle a is to thesine of refracted reflected angle c as the sound


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 15.19—Decibel-To-Screen Height or Voltage Nomograph


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 15.20—Snell’s Law of Reflection and Refraction


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


velocity of incident angle sound beam is tothe sound velocity of the c angle sound beam.

These equations can be written as follows:

View A:

(Eq. 15-7)

or

(Eq. 15-8)

View B:

(Eq. 15-9)

As the incident angle a is increased fromthe normal, which results in only longitudinalwave form, the resultant longitudinal angle dalso increases until it becomes 90°, at whichtime there is no longer any longitudinal waveentering the second medium. This angle ofmedium one is called the first critical angle.

As the incident angle a is further increased,the shear angle e also increases until itbecomes 90°, at which point the total shearwave in the second medium has been trans-formed into a surface wave. This angle in theincident medium is known as the second criti-cal angle.

These calculations are based on simplegeometry, using the centerline of sound beamfor input. However, actual application ismuch more complex in that the sound beamhas breadth, divergence, and also higheramplitudes at its centerline that graduallydiminish to its outside extremities.

Figures have been developed to showeffects of angle changes on amplituderesponses; but, because of critical variables,

sin asin d-----------

velocity (Medium 1, long.)velocity (Medium 2, long.)----------------------------------------------------------------,=

sin asin e----------- velocity (Medium 1, long.)

velocity (Medium 2, shear)-----------------------------------------------------------------=

sin a (long.)sin c (shear)----------------------------- velocity (Medium 1, long.)

velocity (Medium 2, shear)-----------------------------------------------------------------=

sin a (long.)sin c (shear)----------------------------- velocity (Medium 1, short)

velocity (Medium 2, long.)----------------------------------------------------------------=

these can be used only for tendencies and notfor relative amplitude calculations.

15.5.8 Calibration. Since both the horizon-tal (time) and the vertical (amplitude) dimen-sions on the CRT screen are related todistance and size, respectively, but are not rel-ative to any zero starting point, it is necessaryto calibrate an ultrasonic unit to some basicstandard before examination can commence.

Various types of reflectors can be machinedin blocks of material similar in acoustic quali-ties to those of the material to be examined.Such reflectors can be used as calibrationmedia for standardizing equipment settings ofdistance and amplitude.

Acceptable longitudinal distance calibra-tion can usually be made with flat blocks hav-ing parallel surfaces. As a sound beam istransmitted into the block from one of theparallel surfaces, most of the sound energyreverberates back and forth between the par-allel surfaces. This reverberation will result inmultiple back wall indications on the cathoderay tube screen, which can be used for dis-tance calibration.

Flat-bottom holes of various sizes anddepths can be drilled into this block to pro-vide sound amplitude standardization andacceptability standard levels (see Figure15.21).

When a shear-wave ultrasonic beam isintroduced into material at an angle other thannormal to its parallel surfaces, the sound ispropagated away from the sound entry point,with none being reflected back to the searchunit (see Figure 15.22). For this reason, cer-tain types of reflectors should be introducedinto material to provide reflectors for calibra-tion purposes.

In addition to providing distance calibra-tion, a calibration block usually should pro-vide amplitude standardization for flaw sizeevaluation. Figure 15.23 illustrates most ofthe types of reflectors used for this purpose.Holes drilled normal to the test surface of (A),parallel to the test surface (B), or flat-bottomholes at an angle making the flat bottom nor-mal to the sound beam (C) can be used for


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


this purpose. Other types of reference reflec-tors can be in the form of square corners (D),square or beveled grooves cut normal to thesound beam (E) and (F), or radial grooves(G). Combinations of different types or sizesof indicators can be put into single blocks ifnecessary.

The cost of producing reference test platesdictates a simplicity of construction. How-ever, the initial cost may be quite insignificantwhen compared to their usefulness in attain-ing repeatable standardization.

The transducer element height-to-widthratio is an important factor in considering the

Figure 15.21—Amplitude Calibration Using Flat Bottom Holes

Figure 15.22—Shear Wave Ultrasonic Beam


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


type of reference reflector for use in attainingdesired results. The wider element will pro-duce higher amplitude response from thereflectors shown in Figure 15.23(B), (E), and(F), while an element of greater height willrespond at higher amplitude to those shown inviews (A) and (G). Hence, the square ornearly square transducer element are usuallymore desirable for indication evaluation on asound amplitude basis.

Reflectors (A), (D), and (E) depend uponcorner incidence for amplitude response,which makes surface and corner conditionsaround the intersection of the hole-to-platesurface critical in attaining repeatability fromvarious reference blocks. Significant probeangle differences also create a variable thatshould be compensated for when using thecorner incidence method of calibration, due toultrasonic wave mode conversion.

The cylindrical hole drilled parallel to thetest surface (B) is a widely used type of refer-ence reflector. The general tendency is torelate the diameter of this type of hole to aweld discontinuity size, which will not usu-ally be true since its reflectance amplitude isbased on its being a one-one reflector withnearly equal amplitude reflectance regardlessof hole diameter, especially as the sound-pathdistance is increased.

Corner incidence effects can also occur oncalibration reflectors as shown in Figure15.23 (B), (D), (E), and (F) when the soundbeam is directed slightly toward the intersec-tion between the reference reflector and theside of the reference plate, which will createhigher amplitude responses, making this typeof reflector difficult to use in attaining repeat-ability if the length of reflector is not consid-erably greater than the ultrasonic sound-beamwidth, and the sound beam is not directedtoward the center of the reflector.

The size evaluation of the lamellar type ofreflector (root of groove, E) that lies in aplane parallel to the plate test surface is ratherdifficult with shear wave, due to the acuteangle of 1 sound-beam-to-reflector surface.This type of evaluation is usually limited tostraight-beam (longitudinal) examination.

The flat-bottom hole (C) reference reflectorseems almost ideal at first glance, but unlessthe inclination angle of the flat bottom of thehole exactly matches that of the sound beam,a great deal of variation of sound amplituderesponses will occur. Most tolerance of probeangles is at least plus or minus 2 degrees.

The radial groove (G) reflector has all theadvantages of all the other types of reflectorsin that it responds equally with any angle ofprobe at a constant sound path distance anddoes not create corner incidence effects.However, the intricate machining of this typeof groove is costly and the choice of a squareor nearly square transducer element is impor-tant in attaining desirable results.

15.5.9 Determinate Variables. The soundvelocity through a given material is the dis-tance that sound energy will propagate in thatmaterial in a given amount of time and is afunction of material density, acoustic imped-ance, and temperature.

Since these sound velocities are relativelyhigh, the most common means of expressionare in meters or feet per second. The soundvelocity of a shear wave in a given material isusually about half that of a longitudinal andabout 1.1 times that of a surface wave. Forcalculations of angle transformation, specificvelocities should be used and are usuallyavailable from technical data or can be deter-mined with instrumentation.

Effects of temperature on sound velocityare not usually very significant in most metalsbut should be considered when calculatingangles in plastics for use as wedge materialfor shear wave-search units.

The frequency of the sound used for testingwelds and weld-related materials is usuallybetween 1 and 6 megahertz (MHz = millioncycles per second), with the most commonlyused frequency being about 2.25 MHz.

A transducer element will resonate at itsnatural frequency when excited electrically ormechanically. This frequency is not a singlefrequency, but a relatively narrow band of fre-quencies, with one or more specific frequen-cies responding at the highest amplitude. The


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Fig

ure

15.2

3—A

mpl

itud

e C

alib

rati

on


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Fig

ure

15.2

3 (C

onti

nued

)—A

mpl

itud

e C

alib

rati

on


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


frequency is related to the transducer-elementthickness, increasing as its thickness isreduced. The electrical pulse that excites thetransducer element should be of a frequencyin resonance with the natural frequency of theelement in order to attain maximum sound-amplitude response, although broad bandpulse generation is usually quite effective andis usually used with portable test equipment.

Wave length, usually symbolized by theGreek letter “lambda,” is a function of veloc-ity divided by the frequency. The expectedminimum size of reflector detectable withhigh-frequency sound is about one-half wavelength as measured in a direction perpendicu-lar to the direction of sound propagation.

15.5.10 Equipment Selection. A longitudinalultrasonic wave is generally limited in use todetecting inclusions and lamellar-type discon-tinuities in base material. Shear waves aremost valuable in the detection of weld discon-tinuities because of their ability to furnishthree-dimensional coordinates for discontinu-ity locations, orientations, and characteristics.The sensitivity of shear waves is also aboutdouble that of longitudinal waves for thesame frequency and search unit size.

Shear-wave angles are measured in the testmaterial from a line perpendicular to the testsurface. The three most commonly usedangles are 70°, 60°, and 45°. Search unitangle selection is usually based on expectedflaw orientation or as stated in AWS D1.1,possible orientation in a direction most detri-mental to the integrity of the weld joint(which would be normal to the materialsurface).

It is advisable to pretest the material areathrough which the shear-wave should travel intesting a weld with longitudinal wave forassurance that the base material does not con-tain discontinuities that would interfere withthe shear wave evaluation of the weld.

15.5.11 Coupling. It is not usually necessaryto remove weld reinforcement to obtain satis-factory results in testing a weld, as the soundbeam is directed under the weld bead at anangle from the base material. If a weld is to be

ground flush to satisfy contractual require-ments, final testing should be done aftergrinding is completed.

The material surface to which the searchunit is applied should be smooth and flatenough to maintain intimate coupling. It isusually not necessary to remove tight millscale or thin layers of smooth paint; however,for many reasons, it is advisable to test weldsprior to painting.

Grinding, unless very closely controlled,will usually result in an inferior work surfaceas compared to the unground surface. Weldspatter in the scanning area should beremoved for complete weld coverage; this canoften be accomplished with a hand scraper. Inthe event that sand, granulated weld flux, ordirt blows onto a test area to which couplanthas been applied, the only solution is to wipethe surface clean and apply new couplant.

Couplant materials used for testing shouldbe hydraulic in nature and have enough bodyto maintain coverage of the test surface dur-ing testing. Some common couplant materialsare water, oil, grease, glycerine, and cellulosegum powder mixed with water. Sometimes itis necessary to add a wetting agent to a cou-plant to promote wetting of the test surfaceand thus allow sound to be introduced into thetest material. Some qualities that should beconsidered in the selection of a couplantmaterial are viscosity, safety (slipping haz-ard), ease of removal, and effects of residueon future part operations, such as hydrocar-bon pick-up during weld repair. Some signifi-cant advantages of cellulose gum powdermixed with water as a couplant are low cost,variable viscosity, residue does not createslipping hazard, residue will not contaminateweld repairs, and weldment will not usuallyrequire solvent cleaning prior to painting. Anumber of proprietary couplants are availablethat combine desirable features of the cou-plant materials mentioned above.

15.5.12 Flaw Location and Interpretation.One of the most useful characteristics ofultrasonic testing is its ability to determinethe position of flaws in a weld or weld-related


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


materials. In order to attain the necessaryaccuracy of cross-sectional location with ashear wave, it is important to translate sound-path-distance displays to surface and depthmeasurements. This can be very easilyaccomplished with the use of ultrasonic rul-ers, an example of which is shown in Figure15.24.

There is a ruler for each of the commontesting angles. Each ruler contains threescales. The B scale is a common inch rulerand represents the actual dimension of thesound path. For each inch of sound path, thereis an A scale inch of surface measurement anda C scale inch of depth. These surface anddepth dimensions can be translated to com-mon inch distances by using the B scale.

It is not usually necessary to translatesurface dimensions, as the ruler can be placeddirectly on the test material and measuredwith the A scale set to the search unit indexpoint. The example shown in Figure 15.24relates a 4 in. (??? mm) sound path to a3-3/4 in. (94 mm) surface measurementand a 1-3/8 in. (35 mm) depth.

The measurements used by AWS D1.1 forthe X, Y, and Z directional location of flawsare shown in Figure 15.25.

15.5.13 Procedures. Most weld testing isdone with a transducer frequency of about2.25 MHz. This frequency is usually adequatefor weld testing in both longitudinal andshear-wave modes. With the use of miniaturesearch units (less than 1/2 in. × 1/2 in. [13 ×13 mm]), it is usually necessary to use higherfrequency transducers in order to reducesound beam divergence which is increased bythe smaller size of the element.

Most ultrasonic testing of welds is donefollowing a specific code or procedure. Somerequirements are much more straight-forwardand specific than others. An example of sucha procedure is that contained in AWS D1.1 fortesting groove welds in a thickness range of5/16 in. (8 mm) to 8 in. (200 mm) in struc-tural types of steels.

The following are several basic rulesapplied in the use of this procedure:

(1) The sound path distance is basicallylimited to 10 in. (see Figure 15.26).

(2) Three basic search unit angles are usedfor weld testing: 70°, 60°, and 45°, as mea-sured in test material from a line normal tothe test surface of the material.

(3) The weld throat thickness is dividedinto three zones described as the top quarter,middle half, and bottom quarter of throatthickness.

(4) It is assumed that any weld flaw mightbe oriented in a plane normal to the test mate-rial surface and parallel to the weld axis. Thisflaw orientation would be the most seriousdirection for flaws in most welds.

(5) The 70° search unit would providehighest amplitude response from the type offlaw described in rule 4, with second highestresponse from the 60°, and lowest responsefrom the 45° unit. Hence, the order of prefer-ence is the same.

(6) It is assumed that the relative amplituderesponse from a weld flaw is in direct propor-tion to its effect on the integrity of the weld.The generally accepted diminishing order offlaw severity in welds is as follows:

(a) Cracks(b) Incomplete fusion(c) Incomplete penetration (except near

material surface; in which case, high ampli-tude response can be expected)

(d) Slag(e) Porosity

(7) Ultrasonic indications are evaluated ona decibel amplitude basis. Each indication tobe evaluated is adjusted with the calibrateddB gain or attenuation control to a referencelevel height on the CRT, and the decibel set-ting number is recorded as indication level a.

(8) Reference level b is attained from areflector in an approved calibration block.The reflector indication is maximized withsearch unit movement and then adjusted withthe gain or attenuation control to produce areference level height indication. This decibelreading is the reference level.

(9) Decibel attenuation factor c used forstructural steel weldment testing is at the rateof two decibels per inch of sound path after


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 15.24—Ultrasonic Ruler Application


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 15.25—Flaw Orientation

Figure 15.26—Sound Beam Propagation Showing Sound Path Distance


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


the first inch. Example: a 5-in. sound pathwould produce an attenuation factor of (5–1)× 2 = 8.

(10) Decibel rating d for flaw evaluation inaccordance with the code for equipment withgain control is attained by applying the equa-tion a – b – c = d; and for equipment withattenuation control, b – a – c = d (letters takenfrom rule numbers 7, 8, 9, and 10).

(11) There are no direct provisions in thecode for testing fillet welds, some unusualgeometries, or certain material thicknesses.These omissions are based not on the inabilityof ultrasonics to detect flaws, but on the needfor specialized applications for evaluation.

By following the general format in the pre-ceding rules, special procedures can be estab-lished providing satisfactory results in thetesting of other materials that have significantacoustic differences, such as sound velocityand sound attenuation. AWS D1.1 containsprovisions for establishing special ultrasonicprocedures upon agreement between ownerand producer for testing techniques not cov-ered by the code.

Other codes and specifications for ultra-sonic testing of welds leave many factors tothe discretion of the operator, such as theselection of search unit angle and frequency.Some codes depend on the operator to iden-tify the type and size of flaw, evaluating it tothe approximate equivalent of a radiographicstandard, using the relative percentile screenheight of indication as a reject or disregardcriterion. Others require records of all dataso that an indication can be plotted as tolocation, position in a weld or adjacent mate-rial, vertical dimension, and length.

15.5.14 Reporting. In the past, a majorobjection to the use of ultrasonics in deter-mining the quality of welds was its inabilityto produce permanent records. Careful tabu-lation of information on a report form similarto that in AWS D1.1 will usually satisfy theseobjections. The welding inspector should befamiliar with the kinds of data that should berecorded and evaluated so that a complete andsatisfactory determination of acceptability

can be obtained in accordance with a code orspecification requirement for the particularproject or weld being examined.

15.6 Magnetic-Particle Examination

Magnetic-particle inspection is a nonde-structive method of detecting discontinuitiesin ferromagnetic materials. This method willdetect surface discontinuities including thosethat are too fine to be seen with the unaidedeye. It will also detect those discontinuitiesthat lie slightly below the surface, althoughsensitivity is reduced and the method shouldnot be relied on to detect these discontinuities.

Not all discontinuities in metal detract fromsatisfactory performance in service. It is nec-essary, therefore, for the inspector to be ableto interpret the indications given by the mag-netic-particles to determine which discontinu-ities are to be regarded as detrimental. Sincevariation in the evaluation of results is tobe expected, the following points should beagreed upon when examination is beingdiscussed:

(1) What weldments or sections of weld-ments are to be inspected

(2) What techniques will be used (specifiedin detail)

(3) What types and extent of discontinuitieswill be rejected or accepted

(4) Definition of rework and subsequentexamination

A great deal of information regarding thesoundness of weldments can be obtained fromproper application of magnetic particle exami-nation. This method may be used to inspectwelds and plate edges prior to welding and forthe examination of welded repairs. Among thedefects that can be detected are surface cracksof all kinds, both in the weld and in the adja-cent base metal; laminations or other defectson the prepared edge of the base metal;incomplete fusion and undercut; subsurfacecracks; and inadequate joint penetration.

This technique is not a substitute for radi-ography or ultrasonics in locating subsurfacediscontinuities, but may present advantages in


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


locating tight cracks and surface defects. Itmay often be employed to advantage in caseswhere the application of radiography or ultra-sonics is neither available nor practicalbecause of the shape of the weldment or loca-tion of the weld.

The magnetic particle method of examina-tion is applicable only to ferromagnetic mate-rials in which the deposited weld metal is alsoferromagnetic. It cannot be used to inspectnonferrous materials or austenitic steel, anddifficulties may arise in inspecting weldmentswhere the magnetic characteristics of thedeposited metal are appreciably differentfrom those of the base metal. Joints betweenmetals of dissimilar magnetic characteristicscreate magnetic discontinuities that may pro-duce irrelevant indications even though thejoints themselves are sound.

The degree of sensitivity in this methoddepends upon certain factors. Sensitivitydecreases with a decrease in size of the dis-continuity, and also with an increase in depthbelow the surface. A decrease in sensitivity isevident when discontinuities are rounded orspherical, rather than linear, or cracklike.Maximum sensitivity is obtained whendefects are essentially perpendicular to thedirection of the magnetic flux.

A discontinuity should sufficiently interruptor distort the magnetic field to cause an exter-nal magnetic flux leakage. Fine, elongated dis-continuities, such as seams, inclusions, or finecracks, will not interrupt a magnetic field thatis parallel to the direction of the discontinuity.In this case no indication of the discontinuitywill be apparent. Such discontinuities can,however, be detected by using a magnetic fieldthat is not parallel to the discontinuity.

If the general direction of possible defectsis unknown, it is necessary to perform mag-netic-particle inspection by magnetizing frommutually perpendicular directions.

The surface conditions also influence thesensitivity of the inspection process. The sur-face should be clean, dry, and free from oil,water, excessive slag, or other accumulationsthat would interfere with efficient inspection.Wire brushing, sandblasting, or other compa-

rable cleaning methods are usually satisfac-tory for most welds. Surface roughnessdecreases the sensitivity and tends to distortthe magnetic field and may cause nonrelevantindications. It also interferes mechanicallywith the formation of powder patterns andmay result in false indications.

15.6.1 Principles of Magnetic-ParticleExamination. The basic principle of mag-netic particle examination is that when a mag-netic field is established in a piece offerromagnetic material containing one ormore discontinuities in the path of the mag-netic flux, minute poles are set up at the dis-continuities. The magnetic field lines of force(flux lines) are distorted by the presence ofthe discontinuity, and if at or near the surface,the magnetic field is forced from the partresulting in a flux leakage or leakage field atthe site of the discontinuity. Applied magneticparticles will be attracted to the poles estab-lished on opposite sides of the discontinuity,thereby creating a magnetic-particle indica-tion that outlines the shape and orientation ofthe discontinuity.

The piece to be inspected is magnetized byintroducing electric current into it, or by put-ting the piece in a current-carrying coil or incontact with the poles of a strong magnet. Themagnetic field in the part is interrupted bydiscontinuities and a leakage field is producedon the surface. The areas to be inspected arecovered by finely divided magnetic particlesthat react to the magnetic leakage field pro-duced by the discontinuity. These magneticparticles form a pattern or indication on thesurface that assumes the approximate shapeof the discontinuity. The two types of magne-tization generally employed in magnetic-par-ticle testing are longitudinal magnetizationand circular magnetization.

An example of longitudinal magnetizationis the magnetic field associated with a perma-nent bar magnet having a north and south poleat opposite ends. These poles produce a flowof imaginary lines of force between them tocreate a magnetic field in the surroundingmedium (see Figure 15.27).


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


The most apparent characteristic of a mag-net is its ability to attract any magnetic mate-rials placed within its field. This property isattributed to the tendency of the lines of forceto pass through these magnetic materials,since they offer a path of lower reluctancethan a path through the surrounding atmo-sphere; hence, the lines of force tend to crowdinto the magnetic material.

If the bar magnet is cut in half, each halfbecomes an individual magnet with twopoles, and the opposite faces of the cutassume opposite polarity (see Figure 15.28).

If, instead of cutting the magnet, a notch ismade in it, the flux distribution or the flow ofthe lines of force will be markedly changedonly in the area surrounding the notch, andthe distortion diminishes as the distance fromthe notch increases (see Figure 15.29).

Each face of the notch assumes oppositepolarity and produces a flow of leakage fluxacross the air gap. It is this leakage flux thatpermits the detection of defects by the mag-netic particle method.

The other type of magnetization commonlyemployed in magnetic-particle examination,is circular magnetization, obtained with an

electric current. In general practice, it is notpractical to use a permanent magnet, so theelectromagnetic field produced by a highamperage, low-voltage current flowingthrough a conductor is used.

A different condition of flux flow is pro-duced in which the density and direction ofthe lines of force may be controlled.

A current flowing through a conductor cre-ates a magnetic field, and the lines of forcethus produced flow in concentric circles atright angles to the conductor, with their cen-ters at the center of the conductor as shown inFigure 15.30. The intensity of the field is pro-portional to the amount of current.

The flux flows within the conductor as wellas around it, and when the conductor is a fer-romagnetic material (as it is when used inmagnetic-particle examination), the field isalmost entirely confined to the conductoritself (see Figure 15.31). The field will bezero at the center of the conductor andincrease to its maximum value at the surfaceof the conductor.

Thus, if a current is made to flow through asteel section, the magnetic field produced willbe uniform if the section is uniform. If, how-

Figure 15.27—Magnetic Field in a Bar Magnet


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


ever, there is a flaw or sharp change of sec-tion, the same effect is produced as if therewere a notch in a bar magnet: local polesform and a leakage flux flows across thedefect encountered. If a finely divided mag-netic material is dusted on the surface whilethe current is flowing, the particles near thedefect will be attracted to the local poles, andtend to build up across the gap and therebyreduce the reluctance of the path of leakageflux (see Figure 15.32). If any surplus mag-netic powder is then removed, the outlines ofthe defect, with regard to dimensions anddirections, are rather well defined by the pow-der that remains.

Circular magnetization is used to detectlengthwise cracks. The part to be examined is“set up” in the inspection unit and current ispassed through the part or through an electri-cal conductor within the part. The circularmagnetic field cutting across the crackattracts and holds iron powder, to indicate theinvisible defects. Electricity is passed throughthe part parallel to the defects to be found.This is commonly referred to as a head shot.

Figure 15.28—Magnetic Field in a Bar Magnet That Has Been Cut in Half

Figure 15.29—Magnetism Around a Notch Cut in a Bar Magnet


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 15.30—Magnetic Field Around a Conductor Carrying Current

Figure 15.31—Field of Ferromagnetic Conductor is ConfinedAlmost Entirely to the Conductor Itself

Figure 15.32—Magnetic Particles Near a Defect are Attracted to the Local Poles


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


providing the defect is perpendicular to theflux path. If, however, the flux path is parallelto the defect, it is probable that no pattern (or,in the case of the larger defect, only a weak orindefinite pattern) will appear.

On large parts, such as large weldments,strong magnetic fields may be produced bypassing a high current through local areas bymeans of contact prods (prod magnetiza-tion—see Figure 15.33), which also producescircular magnetization.

15.6.2 Orientation of Magnetic Field. Themagnetic field should be in a favorable direc-tion to produce indications. When parallel toa discontinuity, the indication may be weak orlacking. The best results are obtained whenthe magnetic field is at right angles to the dis-continuity. Thus, when applying currentdirectly to the part, the best discontinuityindications are produced when the current isflowing parallel to the discontinuity, becausethe magnetic field is always at right angles tothe flow of current.

15.6.2.1 Longitudinal Magnetization.The part to be inspected can be made the coreof an electromagnet by placing it within asolenoid (see Figure 15.34). This produces afield that runs through the part in a directionparallel to the axis of the coil and producestwo or more poles, usually at the ends of thepart. This is referred to as longitudinal or bi-polar magnetization. Similar effects can beobtained by making the workpiece a link in amagnetic circuit or by placing it in a magneticfield created by a strong permanent magnet orelectromagnet. Shafts, drums, girders, and thelike may be magnetized by means of a flexi-ble electric cable coiled around the part.When a current is passed through the cable,the part is longitudinally magnetized.

15.6.2.2 Overall Circular Magnetiza-tion. Circular magnetization is normallyobtained by passing high current through thepiece itself (see Figure 15.32). This is knownas the direct method of magnetization. Themagnetic field produced is usually circular in

Figure 15.33—In Large Parts, Local Areas Can Be Magnetized;Arrows Indicate Field


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


form and is at right angles to the direction ofcurrent flow. It can be used to detect disconti-nuities that lie approximately in the directionof current flow.

Circular magnetization may also beobtained on hollow parts (such as cylinders)by passing magnetizing current through aconductor or bar placed through a centralopening in the part. When the current ispassed through the bar, the inner surface aswell as the outer surface of the cylinder ismagnetized. This is known as the indirectmethod of magnetization. The surface of thebore of a hollow part is not magnetized whencurrent is passed through the part.

When the direct method of circular magneti-zation is used, the field is normally containedwithin the contours of the part. This providesmaximum field strength and, therefore, maxi-mum sensitivity to subsurface discontinuities.

15.6.2.3 Prod Magnetization. It is gener-ally impractical to attempt to magnetize largeparts as a whole. They may be magnetized

locally by passing current through areas orsections by means of contacts or prods (seeFigure 15.35). This produces a local circularfield in the area between the contact points.The technique is generally used in the inspec-tion of large weldments where only the weldand adjacent metal are to be inspected. Theprods are applied to the surface to be testedand held firmly in position while the currentis passed through the area to be examined.

The contact prods and the areas to beexamined should be sufficiently clean to per-mit passage of high current without arcingor burning. A low open-circuit voltage (2 to16 v) is advisable for this reason and also toprevent arc flash. The usual procedure is toposition the contact prods parallel to the axisof the weld and to perform a second inspec-tion with the prods transverse to the axis ofthe weld.

It is necessary to have some convenientmethod for turning the magnetizing currenton and off to prevent arcing. This may beaccomplished by a switch connected in the

Figure 15.34—Part to be Inspected Can Be Magnetized byMaking it the Core of a Solenoid


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


circuit of the generator or in the primary cir-cuit of the stepdown transformer. The switchis usually located on the handle of one of thecontact prods.

15.6.3 Amount of Magnetizing Current.The current should be of sufficient strength toindicate all discontinuities that might affectthe performance of the weldment in service.Excessive magnetizing current should beavoided because it may produce irrelevantpatterns. Magnetizing current should bedetermined by specifications, standards, orpurchase orders. If these documents areunavailable, current requirements may bedetermined by experience or actual experi-ment. Voltage has no effect on the magneticfield and should be kept low to prevent arcingand overheating.

15.6.4 Type of Magnetizing Current. Alter-nating current, direct current, and rectifiedcurrent all may be used for magnetizing theparts to be examined. High amperage, low-voltage current is usually employed.

Portable equipment that makes use of elec-tromagnets and permanent magnets is occa-sionally used. These are generally satisfactoryfor the detection of surface cracks only.

15.6.4.1 Alternating Current. Alternatingcurrent produces a field primarily on the sur-face. The use of alternating current increasesparticle mobility. The method is effective forlocating discontinuities that extend to the sur-face, such as fatigue or service cracks. It maybe used to examine welds where subsurfaceevaluation is not required. Surface cracks will

Figure 15.35—Crack in Large Plate is Indicated byAlignment of Particles Between Prods


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


be indicated, but deeper lying discontinuitieswill not.

15.6.4.2 Direct Current. Direct currentproduces a field that penetrates deeper withinthe part and is, therefore, more sensitive thanalternating current for the detection of subsur-face discontinuities. Full-wave, three-phaserectified current produces results essentiallycomparable to direct current obtained frombatteries.

Half-wave rectified single-phase currentprovides maximum sensitivity. The pulsatingfield increases particle mobility and enablesthe particles to line up more readily in weakleakage fields. The pulse peaks also produce ahigher magnetizing force.

15.6.5 Sequence of Operations. Thesequence of operations of magnetization andapplication of the inspection medium has animportant bearing on the sensitivity of themethod. The two primary methods aredetailed below.

15.6.5.1 Continuous Method. The mag-netic particles are applied to the surface of thework while the magnetizing current is flow-ing. This method offers maximum sensitivity,since the magnetic field is at its maximumwhile the magnetic particles are beingapplied. The magnetizing current continues toflow during the entire time the particles areapplied and the excess removed. Should thecurrent be turned off before the excess parti-cles are removed, the only indicationsremaining will be those held by the residualfield.

ASTM Specification E-109 recommendsthat the air stream used to remove excess dryparticles be so controlled that it does not dis-turb or remove lightly held powder patterns.

When using a wet suspension with the con-tinuous method, it is usual to flow the mate-rial over the area being inspected andimmediately apply the magnetizing currentfor approximately one-half second. Theinspection medium should not be reappliedafter the current has ceased to flow, since this

would tend to wash away lightly heldindications.

15.6.5.2 Residual Method. This methodrelies on the residual magnetic field thatremains after the magnetizing current hasbeen switched off, since the inspectionmedium is applied at this time. Thus, sincethe accuracy and sensitivity depend upon thestrength of the residual field, this method canbe used only on materials of relatively highmagnetic retentivity (which should be deter-mined by actual experiment). Many codesand other standards prohibit the application ofthis method.

15.6.6 Inspection Media. Various forms andcolors of magnetic particles are available. Thetype of surface and the type of defect sus-pected will determine the material to beselected.

15.6.6.1 Dry Method. Additional informa-tion on the dry method is provided in ASTME709, Practice for the Magnetic ParticleExamination Method. Finely divided ferro-magnetic particles in dry powder form, coatedto afford greater particle mobility, are dusteduniformly over the work by means of a dust-ing bulb, shaker atomizer, or spray gun. Themagnetic particles are available in variouscolors. The dry method is easier to use onrough surfaces and has maximum portability.The powder should be applied in a low-velocity cloud with just enough motive forceto direct the particles to the desired location.This permits particles to line up in indicatingpatterns as they near the surface of themagnetized part. Excess powder should beremoved with a stream of air just strongenough to carry away the excess powderwithout disturbing lightly held powder pat-terns. Figure 15.36 shows the dry powdermethod in use.

When examining with dry powder, bestresults are obtained by blowing excess pow-der from around the indications and by havinga surface reasonably free from oil, moisture,and dirt.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


15.6.6.2 Wet Method. The indicating par-ticles for the wet method are smaller thanthose used in the dry method and are sus-pended in a liquid bath of light petroleum dis-tillate or water. Because of the small particlesize, the wet method is more sensitive to finesurface defects (see Figure 15.37), but it is notas sensitive as the dry method for the detec-tion of subsurface discontinuities.

The magnetic particles for liquid suspen-sion are available either in a paste or in dryconcentrate form. The formulations are usu-ally prepared for use either with oil or with awater bath and are not necessarily inter-changeable. The proportion to be used in thebath should be in accordance with the manu-facturer’s recommendations. Prepared bathsin pressurized spray cans are also available.

The bath should be continuously agitated toprevent indicating materials from settling out.The use of a water suspension has severaladvantages: its sensitivity is equal to or betterthan that of oil, and the fire hazard due to arc-ing is eliminated. There is also an economicadvantage. However, when using water, otheradditives such as rust inhibitors, wettingagents, and anti-foaming agents may be nec-essary. Also, whenever water is used in closeproximity to electrical circuits, a potentialhazard may exist. Precautions should be takento protect workers from such hazards.

The bath is either flowed onto or sprayedover the surface to be inspected, or the partcan be immersed in the suspension. Thesmaller particle size increases the sensitivity,and exceedingly fine defects are located

Figure 15.36—Dry Powder Magnetic-Particle Inspectionof Welds with Portable Equipment


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


without difficulty. Visible particles may beused in the bath and are commonly availablein colors such as black, grey, or red. As withdry powders, the color selection should bebased on that which will provide best colorcontrast with the surface being examined.

When the particles are coated with a dyethat fluoresces brilliantly under ultraviolet(black) light, the sensitivity of the method isincreased. Fluorescent inspection materialindicates very small or fine discontinuitiesand permits rapid inspection of irregular ordark surfaces. The inspection should be per-formed in a darkened area.

The fluorescent magnetic-particle methodis particularly valuable in locating discontinu-ities in corners, keyways, splines, deep holes,and similar locations. Nonrelevant indications

can generally be eliminated by reducing thecurrent below the points where these indica-tions form.

The fluorescent magnetic-particle methodis applicable only to magnetic materialsand should not be confused with fluorescentpenetrant inspection, which is describedelsewhere.

Additional information on the wet methodis provided in ASTM E709, Practice for theMagnetic Particle Examination Method.

15.6.7 Demagnetization. Demagnetization isusually necessary for engine and machineparts that have been strongly magnetized.These parts are exposed to filings, grindings,and chips (resulting from operational wear)that would be attracted by the magnetized

Figure 15.37—Wet Fluorescent Magnetic-Particle Inspectionto Show Fine Surface Defects


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


parts. In aircraft construction, all steel parts inclose proximity to the compass should bedemagnetized to eliminate any effect upon thecompass.

Most weldments do not require demagneti-zation after magnetic particle inspection. Aresidual magnetic field in a part has no appre-ciable effect on its mechanical characteristics.Demagnetization is unnecessary unless theresidual field interferes with subsequentmachining, arc-welding operations, or withstructures (such as aircraft) where sensitiveelectrical instruments might be affected.

Demagnetization may be accomplished byinserting the part in the field of an alternatingcurrent coil and gradually withdrawing itfrom the field. Larger parts may be demagne-tized by subjecting them to an alternating cur-rent field that is gradually reduced in intensityby means of a current controller. If circularresidual fields remain in cylindrical parts,they should be converted to longitudinalfields prior to demagnetization.

When large masses of iron or steel areinvolved, alternating current has insufficientpenetration to demagnetize such pieces thor-oughly; direct current should be used andgradually reduced to zero while undergoingcyclic reversals. Hammering or rotating in thefield will sometimes assist demagnetization.Heat treating or stress relief will demagnetizeweldments, and total demagnetization isalways accomplished when the workpiece isheated above the curie temperature of themetal (1414°F [768°C] for carbon steel).

15.6.8 Equipment. The basic equipment formagnetic-particle inspection is relatively sim-ple. It includes facilities for setting up fieldsof proper strengths and in correct directions.Means are provided for adjusting the current,and an ammeter, plainly visible to the inspec-tor, should be provided in the magnetizingcircuit so that the inspector will know that the56-correct magnetizing force has been cre-ated for each inspection. Many instrumentsallow for application of either ac or dccurrent.

15.6.9 Recording the Indications. It is fre-quently desirable to record not only theappearance of the indications on a part, butalso their locations on a part. One way ofaccomplishing this is by lifting the magneticparticles from the part by carefully pressingtransparent pressure-sensitive tape over theindication; the indication adheres to the tapewhen it is removed. This may be placed onwhite paper or directly on a sketch or reportto form a permanent record. In this procedure,the tape should be cut long enough not only tocover the indication, but also to extend to acorner hole, keyway, or other change of sec-tion that may be used as a reference. Whenused with the wet method, the oil should thenbe removed from around the indication to pre-vent smearing and distortion when tape isapplied. This is most easily accomplished bypermitting the part to dry in the air for 4 to 5hours or drying the part with warm air orcareful application of a volatile solvent. Adrawing or simple sketch may also be used toindicate the location at which the transfer wasmade.

A permanent record may also be made byphotographs. Other special techniques such asmagnetic rubber solutions are also available.

15.6.10 Common Applications

15.6.10.1 Inspection of Large Weld-ments. Magnetic particle inspection may beapplied to all types of large weldments aslong as the materials are magnetic. It is usu-ally used to inspect the finished welds. Onheavy, multiple-pass welds, however, it issometimes used to inspect intermediate weldpasses during welding. It is also used toinspect roots of joints that have been back-chipped in order to be certain that the weldmetal has been removed to sound metal andthat no cracks are present.

Where the weldment is to be stressrelieved, it is usual to make a final inspectionafter stress relieving. It is possible to obtaingreater sensitivity for detection of subsurfacedefects after stress relief.

The dry continuous method, using sometype of direct current and employing local


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


circular magnetization (prod technique), isusually recommended for heavy weldments.Half-wave rectified current is preferable forlocation of subsurface discontinuities. Alter-nating current may be used if inspection is tobe limited to detection of cracks that extendto the surface. The weld is magnetized with aprods by passing about 600 to 1000 A alongthe length of the weld, using a prod spacing offrom 4 to 8 in. (100 to 200 mm). Prods arepositioned both parallel and transverse to theaxis of the weld. The prod positions should beoverlapped slightly on consecutive shots.

15.6.10.2 Inspection of Light Weldments(Aircraft Type). Many steel weldments usedin aircraft are inspected by the magnetic-particle method. These parts in service aresubjected to conditions that cause fatigue fail-ure, which means that location and elimina-tion of all surface cracks are particularlyimportant. Also, since the weldments are rela-tively thin, magnetic-particle inspection mayprovide sufficient sensitivity to detect anysubsurface discontinuities that might bedetrimental.

Light, aircraft-type weldments are usuallyinspected by the wet continuous method.Direct current is usually used, although alter-nating current has been found satisfactory onthin materials. The continuous method is usu-ally recommended despite the high retentivityof many of the alloys commonly used in air-craft structures.

Small weldments that can conveniently begiven overall examination at a standard sta-tionary-type examination setup are given twoexaminations that use both longitudinal andcircular fields. Larger weldments are exam-ined by local circular magnetization. This isaccomplished by making contact with thestructure using clamps or other suitable con-tacts. A longitudinal field may be used onlarge structures by wrapping several turns ofcable around the weld area.

15.6.10.3 Plate Inspection. Magnetic-par-ticle examination is frequently used to inspectplate edges prior to welding. The purpose ofthis examination is to detect cracks, lamina-

tions, inclusions, and segregations. It willreveal only those discontinuities that are nearor extend to the edge being examined.

Not all discontinuities found on plate edgesare objectionable; however, it is necessary toeliminate those that would affect either theweldability of the plate or the ability of thematerial to assume design loads under serviceconditions.

The dry continuous method, using the prodtechnique with either alternating or direct cur-rent, is suitable for plate edge examination.When alternating current is used, the exami-nation is limited to discontinuities that extendto the edge being examined.

15.6.10.4 Repair or Rework Examina-tion. Magnetic-particle examination can beapplied with good effect in conjunction withrepair work or rework procedures, both onnew parts and on parts that may have devel-oped cracks in service. This applies not onlyto repair of weldments, but also to reworkdone by welding in the repair or salvage ofcastings and forgings.

Many objectionable discontinuities thathave been detected by magnetic particle,radiographic, visual, or other examinationmethods may be removed by chipping, goug-ing, or grinding, and the repair made by weld-ing. In this type of work, it is useful toexamine the cavity after the defect has beenremoved to make certain that the discontinu-ity has been reduced to acceptable limitsbefore proceeding with the repair weld. It isalso advisable to check the completed repairweld.

In general, the same examination proce-dures should be used in connection withrepair or rework procedures as would be usedon the original parts.

15.6.11 Interpretation of Patterns. Theshape, sharpness of outline, width, and heightto which the particles have built up are theprincipal features by which discontinuitiescan be identified and distinguished from oneanother.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


15.6.11.1 Surface Cracks. Powder pat-terns are sharply defined, tight held, and usu-ally built up heavily with powder. The deeperthe crack, the heavier the buildup of the indi-cation (see Figure 15.38).

15.6.11.2 Subsurface Discontinuity Indi-cations. Powder patterns have a fuzzy appear-ance, less sharply defined and less tightly held(see Figure 15.39).

15.6.11.3 Crater Cracks. These cracks arerecognized by their patterns, which are smalland occur at the terminal point of a weld.They may be a single line in almost any direc-tion, or possibly multiple, or star-shaped.

15.6.11.4 Incomplete Fusion. Accumula-tion of powder will generally be pronounced,and the edge of the weld will be seen. The

pattern will be sharper the closer the disconti-nuity is to the surface.

15.6.11.5 Undercut. A pattern that is heldless strongly than the indications obtained byincomplete fusion is produced at the weldedge. Undercut is usually detected by visualexamination.

15.6.11.6 Inadequate Joint Penetrationor Gap Between Plates at the Weld Root.The powder pattern may resemble that pro-duced by a subsurface crack. The require-ments for the particular weld will determinewhether such inadequate penetration consti-tutes a defect.

15.6.11.7 Subsurface Porosity. In thiscase, the powder patterns are not clearlydefined. They are neither strong nor pro-nounced, yet are readily distinguished from

Figure 15.38—Typical Indication of Surface Crack in a Weld


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


indications of surface conditions. Smallrounded porosity cannot be detected.

15.6.11.8 Slag Inclusions. A pattern simi-lar to subsurface porosity appears when astrong magnetizing field strength is used andslag inclusions are present.

15.6.11.9 Seams. The indications arestraight, sharp, fine, and often intermittent.Buildup of magnetic particles is slight.

15.6.11.10 Irrelevant Indications. Irrele-vant or false indications that do not indicatethe presence of cracks or other discontinui-ties, which have no significance concerningthe soundness of the welds, are frequentlyproduced. They occur when some examina-tion factor causes the magnetic field tochange direction suddenly. This causes flux

leakage, which irrelevant or false indicationson the surface.

Irrelevant indications are real indicationscaused by a leakage field or change in mate-rial permeability. They are real but nonrele-vant because they are to be expected. AnExample would be small radii, root of thread,press-fit parts. Also changes in permeabilitywhere “hard” and “soft” metals are joined cancause irrelevant indications.

False indications are not caused by actualleakage fields but are caused by mechanicalentrapment of magnetic particles such as inweld ripples, scratches, etc.

15.6.11.10.1 Physical Contour. A thinarea, a change in section, an oil vent, or a holedrilled in the part all will tend to produceindications that have no significance withrespect to joint performance. The magnetic

Figure 15.39—Indication of a Subsurface Crack in a Weld(The Dry Magnetic Particles Assume a Less Defined Pattern)


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


particle patterns are usually readily identifiedby their location and the shape of the part.

15.6.11.10.2 Change in MagneticCharacteristics. Abrupt changes in magneticproperties may occur at the edge of the HAZ.The pattern will be diffused and fuzzy andwill run along the base metal in a line paralleland usually quite close to the edge of theweld. This pattern resembles closely thatcaused by undercutting, but is very looselyheld. Postweld thermal treatment may restorethe magnetic characteristics, in which case,the indications will not reappear.

15.6.11.10.3 Magnetic-to-NonmagneticMetal. A similar pattern may occur when amagnetic (ferritic) base metal is welded withnonmagnetic (austenitic) filler metal. Mag-netic-particle examination is not applicable tothe inspection of welds of this type.

15.6.11.10.4 Materials with DifferingMagnetic Properties. When two materialswith widely differing magnetic properties arejoined, an indication develops at the junction.This indication is very difficult to distinguishfrom a crack. It occurs, for example, whenlow-alloy steel or carbon steel is welded orbonded to high-carbon steel.

When a magnetized steel part is struck byanother part or dragged over it, leakages mayoccur at the places that have been coldworked. Consequently, indications that arenot caused by discontinuities will appear.These conditions are liable to occur duringexamination or transportation and are calledmagnetic writing.15.6.12 Evaluation. The examination willdetermine the existence, if any, of discontinu-ities. The weld will be judged acceptable, orrejectable according to evaluation of the dis-continuities disclosed by examination. Thedecision will be governed by applicable spec-ifications, standards, or purchase orders.

Indications of subsurface discontinuities,unless clearly understood, should be investi-gated by radiographic examination or othersuitable nondestructive methods, sectioning,or chipping. It should also be determined

whether or not subsequent processing ormachining operations would expose orremove the defective area. All crack-like dis-continuities, particularly those that occur atthe surface, can be regarded as potential stressraisers. Fatigue or other service cracks maydevelop from these discontinuities, or theymay become starting points for corrosion.

15.6.13 Standards. Many standards havebeen developed in which the service condi-tions alone dictate the acceptance criteria fora part. When indications are found on a partthat has performed satisfactorily in service,the indication is either an irrelevant indicationor a discontinuity that has not affected serviceperformance.

It is not only the size of the indication butalso its location and orientation that areimportant. In all cases of doubt, acceptance orrejection should be made with a view towardsafety. In areas of high stress, the slightestdiscontinuity may be unacceptable; in lesshighly stressed regions, a relatively large dis-continuity may be acceptable with a widemargin of safety.

When unusual patterns are produced, itmay be necessary to establish identity by cor-relating the results with other examinationmethods such as observation under magnifi-cation, sectioning, etching, or metallurgicalexaminations. Once the proper interpretationhas been established for a given type of indi-cation, in many cases, this interpretation canreadily be applied to similar indications onother parts.

15.7 Penetrant Examination

The liquid penetrant examination method isbase on the ability of certain types of liquidsto enter into voids and crevices by capillaryaction and to remain there when the surfaceliquid is removed. Thus, liquid penetrantexamination, when done properly, is a reliableand revealing method for detecting disconti-nuities open to the surface. Very small andtight imperfections usually can be shown. The


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


several variations of the method each havetheir advantages and disadvantages.

15.7.1 Technique. The penetrant liquids and,therefore, the penetrant examination tech-niques are divided into two basic categories:fluorescent dye and visible dye.

The fluorescent methods offer exception-ally good resolution of indications; the visiblemethod is almost as good in this respect.

Water washable methods may be preferablefor certain classes of work in which the objectcan be transported to a routine examinationarea, whereas non-water-washable methodscan be performed on location or where wateris not available or should not be used.

Examination using fluorescent penetrantsinvolves use of a liquid that will fluoresceunder ultraviolet or “black” light. This is nearultraviolet light, 330 to 390 nm wavelength. Awavelength of about 365 nm is consideredoptimum. Lamps emitting such light are nec-essary to this technique and are marketed asstandard equipment by nondestructive exami-nation equipment suppliers. To be effective,the examination should be performed undersubdued or darkened lighting conditions.

Examination using the visible dye tech-nique is based on use of a penetrant contain-ing a vivid red dye that contrasts sharply withthe background of white developer.

The importance of following an approvedprocedure in liquid penetrant examinationcannot be overstated. The simplicity of thetest may mislead the user: there are manyvariables that influence the examinationresults. For example, inadequate cleaningmay not permit the penetrant to enter the dis-continuity, and the examination results will bemeaningless.

Regardless of the type test selected, theprocedure can be described in seven basicsteps, as follows:

(1) Clean the surface to be examined.(2) Apply penetrant.(3) Allow sufficient penetrant dwell time.(4) Remove excess penetrant.(5) Apply developer to indicate retained

penetrant.

(6) Examine part.(7) Clean, if required.

15.7.1.1 Fluorescent Penetrant Method.Fluorescent penetrants can be either waterwashable for removal of excess penetrant, ormade water washable by application of anemulsifier to the surface of the penetrant. Thedirectly water washable type has additivesthat give the penetrant this property; however,these additives may somewhat reduce its pen-etration efficiency.

Developers may be dry powder type, watersuspension type, or nonaqueous suspensiontype. The effect of each is to draw out thepenetrant from a discontinuity so that itbecomes visible under excitation of blacklight. Steps to be followed in a fluorescentpenetrant examination are as follows:

15.7.1.1.1 Precleaning. All extraneousmaterial such as scale, slag, grease, oil, paint,water, and the like should be removed. Clean-ing with chlorinated hydrocarbons, volatilepetroleum distillates, or acetone is effective. Itshould be remembered that the chlorinatedhydrocarbons are toxic if inhaled, and thepetroleum distillates are highly flammable.Proper precautions should be observed. Vapordegreasing is likewise effective, if applicable.Suitable cleaners are marketed by producersof the inspection materials. A short timeshould be allowed for the evaporation of thevolatile cleaner from discontinuities beforethe penetrant is applied.

15.7.1.1.2 Application of Penetrant.The penetrant should be applied to the dry partover the areas to be examined. This may be doneby dipping, brushing, or spraying.

15.7.1.1.3 Sufficient Dwell Time.Sufficient dwell time for the penetrant to enterdiscontinuities should be allowed. The dwelltime may vary depending upon conditions,materials, and temperatures. Approved proce-dures should be followed.

15.7.1.1 Excess Penetrant Removal.If the directly water washable type penetrant hasbeen used, the excess penetrant is rinsed from the


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


part with a spray nozzle. Special nozzles are mar-keted by equipment producers for this purpose.Since hot water may tend to wash out penetrantfrom some discontinuities, an upper limit of110∞F (43∞C) for rinse water should be main-tained. Water sprays should be directly at an angleof less than 90% to the surface and the pressurecontrolled to some maximum (e.g., 40 psi). Thepart or area should be checked by observationunder black light to assure complete removal ofexcess penetrant.

If a post-emulsifiable type penetrant hasbeen used, an emulsifier should be applied torender the excess penetrant water-removable.The emulsifier may be applied by dipping,flowing on, or spraying. The length of timenecessary for the emulsifier to work is impor-tant, and recommendations of the producershould be followed. Following emulsification,the part is water washed as detailed above.

15.7.1.1.5 Application of Developer.Wet developer, made by a water suspension ofdry powder, may be applied to the part imme-diately after rinsing away the excess penetrant.It should then be dried by circulating warm airover the part being examined. Pools of excessdeveloper should be avoided because theymight flow the penetrant out of discontinui-ties.

Nonaqueous wet developers are also avail-able. These are suspensions in volatile, non-aqueous liquids. These are always applied byspraying. Pressurized cans of developer aremarketed for spraying. The part should be dryprior to application, as with dry powderdevelopers.

Suspension-type wet developers may beapplied by brushing or by spraying from pres-surized equipment. Spraying is consideredpreferable, since it gives a smooth, even coat-ing of developer. If brushing is employed, careshould be taken to avoid a thick coating. It isnecessary to keep the suspension well agitatedin spray equipment, and coagulation of thesolid particles should be avoided. Pools ofdeveloper should be avoided as they dry to athick coating that could mask fine indications.

15.7.1.1.6 Examination. Sufficient timeshould be allowed after the developer hasbeen applied to permit it to draw or blot outthe penetrant from any discontinuities.Roughly, this developing time should beabout half the penetrant dwell time and isusually determined by code or standard. Rec-ommendations of the producer should be fol-lowed. The part should be examined underblack light in a darkened area or enclosure.Indications of discontinuities glow brilliantlywhen excited by the black light and contrastsharply with the darker background.

15.7.1.1.7 Final Cleaning. If required,the part or area may be cleaned with solventsfollowing completion of the examination.

15.7.1.2 Visible Dye Penetrant Methods,Type B. As with fluorescent penetrants, thevisible dye penetrants may be directly waterwashable as applied; may be water washableafter the addition of an emulsifier; or may notbe water washable, but removable by certainsolvents. The directly water washable typeleads to a less sensitive examination becausethe water rinse may remove penetrant fromdiscontinuities.

Developers may be dry powder, aqueoussuspensions, or nonaqueous wet developer,the latter being the one most often used. Stepsto be followed in a dye penetrant examinationare as follows:

15.7.1.2.1 Precleaning. Cleaning asstated for precleaning for fluorescent methods.

15.7.1.2.2 Application of Penetrant.The penetrant may be applied by spraying,brushing, or immersion. Immersion would bedesirable for multiple small parts. Whilespraying is often used, the dye has a certainnuisance factor because of staining, so someconsider brushing more controllable and pre-fer this method.

15.7.1.2.3 Sufficient Dwell Time. Thedwell time may vary depending on condi-tions, materials, and temperatures. Approvedprocedures should be followed. The part andthe penetrant should be between 60°F and


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


125°F (15 and 52°C) for best results. Thepenetrant should not be permitted to dry onthe surface during the dwell time. (While thisshould not normally happen, if it does, thepart should be re-cleaned and the processrepeated.)

15.7.1.2.4 Excess Penetrant Removal.If directly water-washable penetrant has beenused, the excess penetrant is rinsed off with awater spray. If a post-emulsifiable penetranthas been used, the emulsifier should be appliedover the penetrant, after which the excesspenetrant is rinsed off as a water-washableemulsion.

Methods of removing the solvent-removable excess penetrant vary. For highestexamination accuracy, and as required bymost specifications, as much of the excess aspossible is first wiped off with a clean lint-free cloth or absorbent paper, followed bywiping with a clean cloth or paper lightlydampened with solvent. This process shouldbe repeated until the dampened wiping clothor paper shows essentially no red stain. Thesurface should not be overcleaned once allexcess dye is shown to be removed.

In all instances, flushing of the surface withsolvent cleaner should be prohibited. Produc-ers of the examination material market clean-ers for their penetrant products, and their useis recommended.

15.7.1.2.5 Application of Developer.If water rinsing has been employed, the partshould be dried before application of developer,except when an aqueous suspension developer isused. In this case, drying is accomplished afterthe application of the developer. If dry powder isused, it is dusted on the part. As stated previously,the nonaqueous developer is the one most oftenemployed. The directions for the application ofsuspension-type wet developers are applicablehere. Developers should be sprayed lightly.Heavy application can give incorrect interpreta-tion or mask indications.

15.7.1.2.6 Examination. After the devel-oper has dried, a short time is allowed for thedry developer to blot or draw the red dye from

a discontinuity. The waiting time will varyand will depend on the size and type of dis-continuity; however, even the smallest andtightest may be expected to give an indicationin from five to seven minutes. Discontinuitiesare bright red indications against the whitebackground of the developer.

15.7.1.2.7 Final Cleaning. The partor area may be cleaned with solvents or othermeans following completion of examination.

15.7.2 Applications. As-welded surfaces arenormally suitable for penetrant examinationmethods if the surface contour does not con-tain sharp depressions between beads or weldripples that could interfere with completecleaning and complete excess-penetrantremoval. Any one of these could result infalse or irrelevant indications. Such weld sur-faces should be ground smooth prior to exam-ination.

In setting acceptance or rejection standardsfor dye penetrant examination, the severity ofservice of the piece should be considered. Inmost weld standards, cracks are consideredunacceptable. Cracks are shown by liquidpenetrant examination as a solid linear indica-tion or, for very tight cracks, as a series ofsmall, aligned, adjacent indications that mayjoin up upon longer development time. Fordeeper cracks, the indication may first showas a thin line and widen with longer develop-ment time as more penetrant is drawn out ofthe defect. (This is true for indications in gen-eral: the deeper ones will continue to bleedout penetrant and enlarge the indication asdevelopment time lengthens).

When examining welds in conjunction withcast materials, it should be recognized that acertain amount of casting imperfections are tobe expected in some cast metals. Because ofthe effectiveness of liquid penetrant examina-tion, these will all show on casting surfaces.This aspect should be taken into consider-ation when judging such weld assemblies.

Some specifications call for liquid pene-trant examination of nonmagnetic materials,and magnetic-particle examination for ferro-magnetic materials. Except that magnetic-


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


particle examination may show some subsur-face defects, it should be realized that liquidpenetrant inspection is just as effective asmagnetic particle for discontinuities open tothe surface.

15.7.3 Liquid Penetrant Comparator.When it is not practical to make a liquid pene-trant examination within the temperaturerange of 60 to 125F (16 to 52°C), the exami-nation procedure at the proposed temperaturerequires qualification. This may be accom-plished by producing quench cracks in an alu-minum block, which for this purpose isdesignated as a liquid penetrant comparator.One section of the block can then be exam-ined at the proposed temperature and theother section at a temperature in the range of60 to 125°F.

The liquid penetrant comparator shown inFigure 15.40 is made of aluminum, SB-211,Type 2024, 3/8 in. (10 mm) thick, withapproximate face dimensions of 2 by 3 in. (50by 75 mm). At the center of each face, an areaapproximately 1 in. (25 mm) in diameter ismarked with a 950°F (510 °C) temperatureindicating crayon or paint. The marked area isthen heated with a blow torch, a Bunsenburner, or similar device to a temperaturebetween 950 and 975°F (510 and 525°C) andthe specimen is then quenched in cold waterto produce a network of fine cracks on eachface. The block is then dried by heating toapproximately 300°F (150°C). A groove maybe machined across the center of each faceapproximately 1/16 in. (1.6 mm) deep and3/64 in. (1.2 mm) wide, or some other meansprovided to permit side-by-side comparison

Figure 15.40—Liquid Penetrant Comparator


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


without interfering cross-contaminationbetween the two sides. One half of the speci-men may be designated “A” and the other “B”for identification in subsequent procedures.Figure 15.40 illustrates the comparator afterthe grooves, have been cut.

15.7.3.1 Comparator Application. If it isdesired to qualify a liquid penetrant examina-tion procedure at a temperature less than 60°F(16°C), the proposed procedure may beapplied to area “B” after the block and allmaterials have been cooled to the proposedexamination temperature. The block is thenallowed to warm up to a temperature between60 and 125°F (16 and 52°C), and area “A”examined in a manner that has previouslybeen demonstrated as suitable for use in thistemperature range. The indication of cracks iscompared between areas “A” and “B.” If theindications obtained under the proposed con-ditions are essentially the same as obtainedunder examination at 60 to 125°F, the pro-posed procedure is considered qualified foruse.

If the proposed temperature for the exami-nation is above 125°F, then the block is held atthis temperature throughout the examinationof the “B” section (the penetrant and devel-oper are not preheated). The block is thenallowed to cool to a temperature between 60and 125°F and area “A” is examined and com-pared as described in the previous paragraph.

15.7.3.2 Evaluation of Indications. Allindications are examined in terms of theacceptance standards of the referencing code.

Discontinuities at the surface will be indi-cated by the bleeding out of the penetrant;however, localized surface irregularities, suchas from machining marks or other surface con-ditions, may produce nonrelevant indications.

Broad areas of fluorescence or pigmenta-tion that could mask indications of disconti-nuities are unacceptable, and such areasshould be cleaned and re-examined.

For further details of liquid penetrantinspection methods, reference may be madeto the latest issue of ASTM specificationE165, Liquid Penetrant Inspection, and to lit-

erature published by the various producers ofliquid penetrant examination materials.

15.8 Eddy Current (Electromagnetic) Examination

This section describes the electromagneticexamination (ET) of both ferromagnetic andnonferromagnetic metals. ET was formerlycalled eddy current testing. This method usesan alternating magnetic filed applied to ametal, and the field induces an electric current(eddy current). These eddy currents induceanother magnetic field that will be distorted,at discontinuities, and at locations where thephysical or metallurgical properties change.

15.8.1 General. Eddy current (electromag-netic) testing is a nondestructive examinationbased on the principle that an electric currentwill flow in any conductor subjected to achanging magnetic field. It is used to checkwelds in magnetic and nonmagnetic materialsand is particularly useful in testing bars, bil-lets, welded pipe, and tubes. Test frequenciesvary from 50 Hz to 1 MHz, depending on thetype and thickness of material and the appli-cation. Frequency ranges for some applica-tions are shown in Figure 15.41.

15.8.2 History. While the investigation ofelectromagnetic wave examination methodspreceded the development of practically everyother modern technique of nondestructiveexamination, the method was slow to developcommercially. Until recently, the electromag-netic method had only limited applications,because the process could not discriminatebetween responses to discontinuities, heattreatment variations, internal stresses due toforming operations, and small vibrations ofthe part or of examination coils. Thus, elec-tromagnetic examinations were limited inusefulness.

15.8.3 Theory. Nondestructive examinationby electromagnetic methods involves induc-ing electric currents (eddy or foucault cur-rents) in a test piece and measuring the


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


changes caused in those currents by disconti-nuities or other physical differences in the testpiece. Thus, such examinations can be usednot only to detect discontinuities but also tomeasure variations in test piece dimensionsand resistivity. Since resistivity is dependentupon such properties as chemical composi-tion (purity and alloying), crystal orientation,heat treatment, and hardness, these propertiescan also be determined indirectly. Electro-magnetic methods are classified as magneto-inductive and eddy current methods. Theformer pertains to examinations where themagnetic permeability of a material is the fac-tor affecting the examination results and thelatter to examinations where electrical con-ductivity is the factor involved.

One method of producing eddy currents ina test specimen is to make the specimen thecore of an alternating current (ac) inductioncoil as shown in Figure 15.42. There are twoways of measuring changes that occur in themagnitude and distribution of these currents.The first is to measure the resistive compo-nent of impedance of the exciting coil (or of asecondary test coil), and the second is to mea-sure the inductive component of impedanceof the exciting (or of a secondary) coil. Elec-tronic equipment is available to measureeither the resistive or inductive impedancecomponents singly or both simultaneously.

15.8.4 Electric and Magnetic Properties ofMetals. Electronic test equipment measuressuch properties as hardness, crack depth,coating thickness, etc., indirectly throughtheir relationship to properties that can be

measured electronically, such as conductivityand permeability. Two such characteristics ofa metal that are measured directly and are ofimportance to electromagnetic examinationare electrical conductivity and magneticinduction.

15.8.5 Electrical Conductivity. Conductivitycan be expressed mathematically as thereciprocal of the electrical resistivity of themetal.

C = L = 1 (Eq.15-10)

R × A p

Figure 15.41—Frequencies Used for Various Test Problems

Figure 15.42—Cross-Sectional View of a Bar With a Small Crack, Surroundedby an Exciting Coil and a Pickup Coil, Showing Eddy Current Distribution


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


whereC = Conductivity (ohm/unit length)p = Resistivity (ohm unit length)L = LengthR = Resistance (ohm)A = Cross-sectional area

The conductivity of various metals and alloysis shown in Figure 15.43. A convenient meansof categorizing metals is to refer to them aseither “conductors” or “nonconductors.” Theconductivity and resistivity of metals andalloys is a material property (See Table 15.4).

The addition of impurities to a pure metal willnormally reduce its conductivity sometimesmarkedly. For example, copper containing0.005 percent phosphorus exhibits a conduc-tivity of only four percent of that of pure cop-per. The effect of other alloying elements incopper on the conductivity of copper alloys isshown in Figure 15.44. Most other additionsto pure copper also affect the conductivity,although not as severely as phosphorus.

The current distribution within a test piecemay also be changed by the presence of inho-

Figure 15.43—Relative Conductivity of Metals and Alloys Related toEddy Current Meter Readings


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


mogeneities. If a sample is perfectly homoge-neous, free from discontinuities, and has aregular spaced lattice, the mean-free path ofan electron passing through it will have themaximum length. That is, the conductivitywill be maximum. A crack, slip plane, inclu-sion, high- or low-density regions, chemicalinhomogeneity, cavity or void, or other condi-tions in an otherwise homogeneous materialwill cause a back scattering of the electronand thereby shorten its mean-free path, andreduce the conductivity. When a devicedetects a change in conductivity in a work-piece, it is detecting the presence of an inho-mogeneity or a discontinuity.

If an electric wave is considered instead ofelectrons, the same factors impeding the flowof a single electron will impede the passageof a wave front, causing it to be totally or par-tially reflected, or absorbed, or both. The vari-ous relationships between conductivity andsuch factors as impurities, cracks, grain size,hardness, strength, etc., have been investi-gated and reported in detail.

15.8.4.1 Magnetic Induction. When amagnetic material is placed within an appliedfield (H), there is induced into that material aflux density (B) that may be stronger than theoriginal applied field. As H is increased fromzero, B also increases. The typical curveshown in Figure 15.45 can provide consider-able information on the magnetic propertiesof materials. Notice that the virgin curve doesnot retrace itself. The envelope curve isreferred to as the hysteresis loop.

15.8.5 Electromagnetic Properties of Coils.When a coil is energized, a magnetic field isproduced around the coil as indicated in Fig-ure 15.46. If a conductor is present in theinduced field, then the field induces eddy cur-rents into the conductor which set up a mag-netic field that acts in opposition to themagnetic field induced by the coil. Theimpedance (Z) of the exciting coil, or, for thatmatter, any coil in close proximity to the con-ductor is affected by the presence of theinduced eddy currents in the specimen. Thepath of the eddy currents in the specimen is

Table 15.4Resistivity and Conductivity of Some Metals and Alloys

MetalResistivity

p (ohm-m) × 10–8Conductivity

o (ohm/m)× 107

Temperature

˚F ˚C

Silver 000.001.629 6.140 64 18

Copper 0000.01.692 5.910 68 20

Aluminum 000.02.63 3.800 32 0

Zinc 000.05.75 1.740 32 0

Iron (99.98%) 010 1.000 68 20

Platinum 010 1.000 68 20

Aluminum Bronze 12–13 0.83–0.77 32 0

Lead 022 0.455 68 20

Titanium 00.43.1 0.232 72 22

Steel (4% Si) 062 0.161 68 20

Bismuth 119 0.084 64 18

Steel (5% V. 1.1% C) 121 0.083 68 20


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


distorted by the presence of discontinuities orother inhomogeneities. The apparent imped-ance of the coil is also altered by the presenceof discontinuities in the specimen. Thischange in impedance indicates that disconti-nuities or differences in physical, chemical,and metallurgical structure are present in theconductor. Instrumentation and circuitry read-out of the coil impedance are shown in Figure15.47.

In electromagnetic examination, theapplied magnetic field strength (H) is of greatimportance in determining the validity of an

examination procedure. The field strength ofa system is determined by the current in theprimary coil. In magnetoinductive examina-tion, the field strength and its selection are ofprime importance. Magnetoinductive exami-nation is electromagnetic examination whereeddy currents are present but are of no signifi-cance in the procedure; magnetic properties,such as permeability and related variables, arethe prime factors.

15.8.5.1 Properties of Eddy Currents.Eddy currents are induced into the conducting

Figure 15.44—Influence of Impurities on the Conductivity of Pure Copper


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 15.45—Typical B/H (Hysteresis) Curve

Figure 15.46—Lines of Magnetic Flux Surrounding a Solenoid


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


test specimen by alternating electromagneticinduction or transformer action (see Figure15.48). Eddy currents are electrical in natureand have all the properties associated withelectric currents. In generating eddy currents,the test piece, which should be a conductor, isbrought into the field of a coil carrying alter-nating current as shown in Figure 15.49. The

coil (a) may encircle the part, (b) may be inthe form of a probe, or (c) in the case of tubu-lar shapes, may be wound to fit inside a tubeor pipe. Typical coils are illustrated in Figure15.50. As stated, an eddy current in the metalspecimen also sets up its own magnetic fieldwhich opposes the original magnetic field.The impedance of the exciting coil, or of a

Figure 15.47(A)—Instrumentation Readout for Electromagnetic Testing

Figure 15.47(B)—Typical Eddy Current Readout from Strip ChartIllustrating Good and Bad Weld Areas


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


second coil magnetically coupled to the first,in close proximity to the specimen, is affectedby the presence of the induced eddy currents.This second coil is often used as a conve-nience and is called a test, sensing, or pickupcoil. The path of the eddy current is distortedby the presence of a discontinuity or otherinhomogeneity.

Subsurface discontinuities may also bedetected, but the current declines with depthas shown in Figure 15.51. Figure 15.52 showshow a crack both diverts and crowds eddycurrents. In this manner, the apparent imped-ance of the coil is changed by the presence ofthe discontinuity. This change can be mea-sured and is used to give an indication of dis-continuities or differences in physical,chemical, and metallurgical structure.

15.8.6 Alternating Current Saturation. Ahigh alternating current magnetizing forcemay be used to simultaneously saturate (mag-

netically) a test piece and create an eddy cur-rent signal. This enhances certain disturbingmagnetic variables.

All ferromagnetic materials that have beenmagnetically saturated will retain a certainamount of magnetization, called the residualfield, when the external magnetizing force hasbeen removed. The magnitude of the residualfield depends on the magnetizing forceapplied.

Demagnetization is necessary whenever theresidual field (1) affects the operation or accu-racy of instruments when placed in service,(2) interferes with inspection of the part atlow field strengths or with the proper func-tioning of the part, and (3) might cause parti-cles to be attracted and held to the surface ofmoving parts, particularly parts running in oil,thereby causing undue wear. There are manyways to demagnetize an object, the most com-mon being to pass current directly through the

Figure 15.48—Production of Eddy Currents by an Alternating Field


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 15.49—Testing Coils Carrying Alternating Current


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 15.50—Examples of Electromagnetic Probe Coils(A–B) Custom made probes for testing inside of a hole

(C) Custom shielded probe for testing inside a hole in aluminum work(D) Surface probe (note set screw for sliding coil up and down to obtain a given lift-off)

Figure 15.51—Eddy Current Strength Drops Off With Distance From Surface


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


test piece. The selected method should givethe required degree of removal of the residualfield.

15.8.7 Electromagnetic Examination. Elec-tromagnetic testing consists of observing theinteraction between electromagnetic fieldsand metals. The following are three thingsrequired for an electromagnetic examination:

(1) A coil or coils carrying an alternatingcurrent

(2) A means of measuring the electricalproperties of the coil or coils

(3) A metal part to be testedAs specialized sensing elements, the test

coils are in some ways analogous to lenses inan optical system, and their design is a funda-mental consideration depending upon thenature of the examination. Probe coils that arebrought up against the surface to be examinedare used in examining a variety of metallicshapes for physical properties, flaws ordefects, and plating or coating thicknesses.Annular coils encircle the part and are usedespecially for examining tubing, rods, bars,wires, and small parts.

Electromagnetic examination involves (1)interaction between applied and induced elec-tromagnetic fields, and (2) imparting ofenergy into the test part much like the trans-mission of x-rays, heat, or ultrasound. Uponentering the test piece, a portion of the elec-tromagnetic energy produced by the examina-tion coil is absorbed and converted into heatthrough the action of resistivity and, if theconductor is magnetic, hysteresis. The rest ofthe energy is stored in the electromagneticfield. As a result, the electrical properties ofthe examination coil are altered by the proper-ties of the part under test. Hence, the currentflowing in the coil carries information aboutthe part: its dimensions, its mechanical, met-allurgical, and chemical properties, and thepresence of discontinuities.

The character of the interaction betweenthe applied and induced electromagneticfields is determined by two basically distinctphenomena within the test part:

(1) The induction of the eddy currents inthe metal by the applied field

(2) The action of the applied field upon themagnetic domains, if any, of the part

Figure 15.52—Eddy Current Flaw Detection Equipment


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Obviously, only the first phenomenon canact in the case of nonferromagnetic metals. Inthe case of ferromagnetic metals, both phe-nomena are present; however, the second usu-ally has the stronger influence. This accountsfor the basic difference in principle betweenthe examination of ferromagnetic and nonfer-romagnetic metals.

Among the physical and metallurgical vari-ables that affect electromagnetic examinationin metals are the following:

(1) Physical shape, external dimensions,and thickness of the part

(2) Distance between the part and the elec-tromagnetic coil

(3) Plating or coating thickness(4) Chemical composition(5) Distribution of alloying or impurity

atoms (influenced by heat treatment of thepart and, hence, may be a clue to hardness,strength, phase, gain size, etc.)

(6) Lattice dislocations caused by heavyworking or radioactive bombardment

(7) Temperature(8) Discontinuities and inhomogeneities(9) In ferromagnetic metals, residual and

applied stressesIn practice, many, and sometimes all, of the

above factors may vary simultaneously. It isdifficult under such conditions to obtain ameaningful response from the magnetic fluxset-up within the test piece since several vari-ables may have affected the examination sig-nal. The resulting voltage, which is thevariable usually sensed by electromagneticexamination devices, should be very carefullyanalyzed to isolate the sought-after effectsfrom the extraneous effects.

Associated with any electromagnetic exam-ination signal are three important attributes:amplitude, phase, and frequency. The exami-nation signal may contain either a single fre-quency (that selected for the examination), ora multitude of frequencies (harmonics of theexamination signal frequency). In the lattercase, the test-signal frequency is referred to asthe fundamental frequency. In addition, thereare amplitude and phase factors associatedwith each harmonic frequency. The engineer

has available a number of techniques thatmake use of all this information, thereby per-mitting the discrimination between examina-tion variables. The important techniques usedare amplitude discrimination, phase discrimi-nation, harmonic analysis, coil design, choiceof examination frequency, and magnetic satu-ration.

Because each examination involvesstraightforward scanning of the test-part sur-face by an examination coil or coils, eithermanually or by mechanical methods, the fol-lowing section will emphasize the results ofselected standard specimens or examples.

15.8.8 Equipment Calibration and QualityAssurance Standards. In using electromag-netic examination methods for the examina-tion of metals, it is essential that adequatestandards be available (1) to make sure theequipment is functioning properly and ispicking up imperfections or discontinuities,and (2) to ascertain whether the are cause forrejection of the sample (defects). The discon-tinuities are inhomogeneities, deviations inphysical, mechanical, or geometrical proper-ties, or heat treatment effects. A discontinuityis any imperfection in a metal, which may ormay not be harmful. A defect is a discontinu-ity in a metal that is unacceptable. A defect isalways a discontinuity, but a discontinuity isnot necessarily a defect.

It is not the discontinuity that is detected bythe test equipment, but rather, the effect thatthe discontinuity has on the electromagneticproperties of the metal being examined. It isnecessary, therefore, that it be possible to cor-relate the change in electromagnetic proper-ties with the cause of the change. For thisreason, calibration standards containing natu-ral or artificial discontinuities should be used.The calibration standards should producesimilar changes in the electromagneticresponse as production product containingsimilar discontinuities. Such standards areusually considered equipment calibrationstandards; that is, they demonstrate that theequipment is, in fact, detecting the disconti-nuities for which the metal is being examined.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


These standards are not only used to facili-tate the initial adjustment or calibration of theexamination instrument, but also used to peri-odically check on the reproducibility of themeasurements.

It is not enough just to be able to locate dis-continuities in a test piece; the inspectorshould determine if the discontinuity is unac-ceptable. For this purpose, quality assurancestandards are required against which theexamination instrument can be calibrated toshow the limits of acceptability or rejectabil-ity for any type of discontinuity. Once accep-tance criteria are established, qualityassurance standards may be selected fromactual production items or from preparedsamples containing indications representingthe limits of acceptability.

A quality assurance standard performs afunction altogether different from that of anequipment calibration standard. While theequipment calibration standard shows whatthe instrument can do under a certain adjust-ment, the quality assurance standard seeks tokeep this level of performance, whatever it is,identical and reproducible at all times andunder all conditions of time and temperature.

15.8.9 Application. Research activities ofscientists and engineers, together with theconstant expansion of the knowledge of elec-tronics, have stimulated the selection and useof electromagnetic examination techniques toa greater extent than ever before. Althoughcomparatively little use was made of electro-magnetic examination techniques prior to1950, in more recent years, industry hasfound electromagnetic examination most use-ful and particularly adaptable to rapid, 100percent automatic examination of productionitems and materials. The urgent need ofindustry to examine bars and welded tubinghas led to the development of a number ofcommercial instruments and equipment capa-ble of handling many of the problemsinvolved in defect detection. This has beenparticularly true in the application of electro-magnetic methods to the critical examinationof items having high-quality requirements.

15.8.10 Advantages. There are two significantadvantages of electromagnetic examination.

(1) It can, in many cases, be completelyautomated; thus, it provides automatic inspec-tion at high speed and at relatively low cost.

(2) Under certain circumstances, the indi-cations produced are proportional to theactual size of the defect; thus, the examina-tion results can be useful for grading andclassifying.EXAMPLE: Tubing now can be electromag-netically examined for minute cracks andother discontinuities at speeds of more than300 ft/min (1.5 m/s), while a comparablevisual examination would usually proceed atmuch less than a tenth of this speed andwould fail to detect flaws that were not on thesurface.

15.9 Acoustic Emission Examination

Acoustic emission examination (AET)methods are currently considered supplemen-tary to other nondestructive examinationmethods. They have been applied, however,during proof testing, during recurrent inspec-tions, during service, and during fabrication.

AET consists of the detection of acousticsignals produced by plastic deformation orcrack formation during loading. These signalsare present in a wide frequency spectrumalong with ambient noise from many othersources. Transducers, strategically placedon a structure, are activated by arriving sig-nals. By suitable filtering methods, ambientnoise in the composite signal is significantlyreduced, and any source of significant signalsis plotted by triangulation based on the arrivaltimes of these signals at the differenttransducers.

AET methods have successfully beenapplied to welded pressure vessels and otherwelded structures during proof testing, suchas pressurization. A sound vessel stops emit-ting signals when the load is reduced, anddoes not emit further bursts until the previousload has been exceeded. A growing crackemits an increasing number of signals as it is


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


loaded. Location of suspect areas in suchstructures is a very well established AETtechnique. Locating systems have been devel-oped, some providing sophisticated analysisof the signal data collected. The informationobtainable on the nature and significance ofthe recorded “events” obtained by AET meth-ods is currently considered to be limited.Efforts are being made by many organizationsto develop and improve techniques for suchevaluation.

AET applied during recurrent inspectionshas not been fully developed due to insuffi-cient experience. These applications of AETmay be considered an extension of proof test-ing, requiring pressurization in order to com-pare a prior AET examination with a laterone.

AET surveillance of structures during oper-ation offers many potential advantages.Transducers, constructed for long-term resis-tance to thermal and nuclear environments,have been developed, and wave guides maybe used to remove the active elements fromthe most hostile regions, thus allowing eithercontinuous or triggered-mode operation. AEToffers advantages of reduced exposure to per-sonnel, early warnings of problem areas, andreduction of access problems.

Standards and code-writing organizationsare active in preparing standards for AET sothat a data base can be obtained and credenceestablished for routine, regular use. TheAmerican Society of Mechanical Engineers(ASME) has published a proposed Standardfor AE Examination During Application ofPressure. The American Society for Testingand Materials (ASTM) Committee E-7 onNDT is standardizing AE terminology, trans-ducers, methods of application, acousticwaveguides, etc., and is developing a recom-mended practice for calibrating frequencyresponses. The Committee also deals with AEinstrumentation, such as recommended prac-tices for performance of event-counting andlocating systems, and applications of AET. Itis clear that great effort is being expended toreduce AET technology to established, rou-tine practice.

AET monitoring of some structures duringthe welding operations is possible, the objectof which is to detect defects as they arise dur-ing fabrication. Such conditions as delayedcracking should be detectable.

15.9.1 Summary

(1) AET equipment development has pro-ceeded for several years and has reached ahigh state of refinement.

(2) Locating of AET sources during prooftesting is an established method, has beenapplied to welded steel structures, and anexperience base has been achieved.

(3) Evaluation of sources of AET signalsneeds further development and standardization.

(4) AET during proof testing may be ofpresent value to fabricators and user andoffers promise of wider application for thispurpose.

(5) Standardization efforts are beginning toproduce tangible results toward providingindustry with a common basis for evaluationand comparisons of AET results.

(6) AET monitoring can improve produc-tion control of welding during fabrication.

Acoustic emission is considered to be in itsearly stages of use by industry. Additional andmore extensive use is to be anticipated in thefuture. For more information on the subject ofAE, see “References and Suggested ReadingMaterial” at the end of this chapter and themore than 35 papers on the subject that havebeen published in “Materials Evaluation,” thejournal of the American Society for Nonde-structive Testing (ASNT).

15.10 Leak Examination

Leak testing is a term used to describe sev-eral methods of nondestructive examination.Common to all these methods is the fact thatleak testing is used to discover discontinuitiesthat extend from the inside to the outside of avessel.

This nondestructive examination can beused on any material as long as a pressure dif-ferential can be created across the material.The American Society for Nondestructive


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Testing recognizes four methods of leakingtesting and the ASM Metals Handbook Vol.II, 8th edition describes at least eight tech-niques of leak testing.

15.10.1 Techniques. The most commonlyused leak testing method is visual examina-tion. A vessel is pressurized using a fluid thatwill be visible to the human eye. After pres-surization, the vessel is visually examined forleaks.

Other techniques of leak testing includeacoustic methods, bubble testing, flow detec-tion, and gas detection.

15.10.1.1 Acoustic Methods. When a gasis forced through a small opening, sound isproduced at both sonic and supersonic fre-quencies. When sound is produced at sonicfrequencies it is possible to detect it with theear. Electronic instruments are needed todetect sound at supersonic frequencies. Ultra-sonic detectors can detect air leaking througha 0.010 in. diameter hole at 5 psi pressurefrom a distance of 50 feet.

15.10.1.2 Bubble Testing. One of the mostsimple techniques is this method, small ves-sels are pressurized and submerged in a liq-uid, where any leaks will show as bubbles inthe liquid. Bubble testing can also be appliedby flowing a bubble-forming solution over thesurface of the item to be tested. Care shouldbe taken that the bubbles are not formed bythe process itself.

15.10.1.3 Flow Detection. In this tech-nique, a pressurized vessel is placed inside alarger vessel and connected by a duct. A leakin the pressurized vessel will cause a flow ofgas from the pressurized vessel to the enclos-ing vessel. An instrument designed to mea-sure flow is attached to the connecting ductand measures the flow rate.

15.10.1.4 Gas Specific Detectors. A vari-ety of instruments are available that willdetect the leakage of a specific gas. Thehuman nose is the most common of thesedevices. Other instruments use chemical-reaction to detect gases or positive ion flow

that increases with an increase in the amountof gas detected. Thermal conductivity is alsoused by some instruments to detect specificgases. Each gas has a specific ability to cool aheated electrical filament, thereby controllingthe temperature of the filament which in turndetermines the filament’s electrical resistivity.

In most cases, when using leak testing, it isadvisable to first use a method that is capableof detecting gross leaks. Those methods thatare sensitive to small leaks cannot be used inthe presence of gross leaks. After determiningthe presence, or lack thereof of gross leaks,then proceed to use more sensitive methods.Leak testing should be done in at least twosteps, gross leakage detection, and small leak-age detection.

The reader should realize that hydro-testingis not leak testing. Usually, measurement ofthe leak rate is not accomplished duringhydro testing. Hydro testing is a proof test, ortesting for leaks.

15.11 Ferrite Content Examination

15.11.1 Effects of Ferrite Content. Fullyaustenitic stainless steel weld deposits have atendency to develop small fissures even underconditions of minimal restraint. These smallfissures tend to be located transverse to theweld fusion line in weld passes (and basemetal) that were reheated to near the meltingpoint of the material by subsequent weldpasses. Cracks are clearly injurious defectsand usually cannot be tolerated. On the otherhand, the effect of fissures on weldment per-formance is less clear, since these micro-fis-sures are quickly blunted by the very toughaustenitic matrix. Countless tons of fissuredweld deposits have performed satisfactorilyunder very severe conditions. However, a ten-dency to form fissures generally goes hand-in-hand with a tendency for larger cracking,so that it is often desirable to avoid fissure-sensitive weld metals.

Since the 1940s, at least, it has been recog-nized that the presence of a small fraction ofthe magnetic delta ferrite phase in an other-


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


wise austenitic (nonmagnetic) weld deposithas a pronounced influence in the preventionof both centerline cracking and fissuring. Theamount of delta ferrite in as-welded materialis largely, but not completely, controlled by abalance in the weld metal compositionbetween the ferrite-promoting elements(chromium, silicon, molybdenum, and colum-bium are the most common) and the austen-ite-promoting elements (nickel, manganese,carbon, and nitrogen are the most common).

Excessive delta ferrite, however, can haveadverse effects on weld metal properties. Thegreater the amount of delta ferrite, the lowerwill be the weld-metal ductility and tough-ness. Delta ferrite is also preferentiallyattacked in a few corrosive environments(such as urea). And in extended exposure totemperatures in the range of 900 to 2700°F(480 to 930°C) ferrite tends to transform inpart to a brittle intermetallic compound(sigma phase) that severely embrittles theweldment.

15.11.2 Delta Ferrite Verification and Mea-surement. For the reasons previously men-tioned, control over ferrite content inaustenitic stainless weld metal is oftenrequired. This, in turn, requires a method ofmeasurement. In the past, estimation of ferritecontent by metallographic examination ofprepared specimens has been used to deter-mine the volume percent ferrite present. How-ever, nonuniform ferrite distribution in weldmetal, the sensitivity of the volume percentferrite measurement to the sample preparationprocedure, and the difficulty in preparing andexamining the sample have led to this methodbeing largely discarded. Estimation of ferritecontent by chemical composition through aconstitution diagram (the Schaeffler and theDeLong diagrams are the most popular) hasbeen more common, but it is subject to ana-lytical errors and uncertainties concerningalloying influences. Since ferrite is magneticand austenite is not, ferrite content can also bemeasured by magnetic responses of the mate-rial, and this is currently the most commonmethod of ferrite measurement, reproducible

from laboratory to laboratory with properlycalibrated instruments. Most instruments con-vert the force holding a standard magnet tothe surface into a ferrite measurement.

Because agreement between laboratories asto the absolute percent ferrite in an austeniticstainless steel weld metal has thus far provenimpossible to achieve, an arbitrary ferritenumber (FN) scale has been established andis presented in AWS A4.2, Standard Proce-dure for Calibrating Magnetic Instruments toMeasure the Delta Ferrite Content of Austen-itic Stainless Steel Weld Metal. The FN scale,though arbitrary, is believed to approximatethe true volume percent ferrite at least up to10 FN.

The ferrite content recommended in weldfiller metal is usually between 3 and 20 per-cent. A minimum of 3 percent ferrite is desir-able to avoid microfissuring in welds. Up to20 percent ferrite is permitted when needed tooffset dilution losses. Delta ferrite verificationcan be made by tests on undiluted welddeposits using magnetic measuring devices.AWS A5.4, Specification for Corrosion-Resisting Chromium and Chromium-NickelSteel Covered Electrodes, describes a proce-dure for test-pad preparation and ferrite mea-surement. The magnetic measuring devicesused for examination of the weld pad for deltaferrite should be calibrated prior to use, fol-lowing the procedure given in AWS A4.2.

15.11.3 Austenitic Stainless Steels. Austen-itic chromium-nickel stainless steel types arethe most widely used stainless steels. Thevariations in composition among the standardaustenitic types are important, both in the per-formance of the steel in service and in itsbehavior in welding. As examples, Types 302,304, and 304L, represent the so-called “18-8”stainless steels. They differ chiefly in carboncontent. Types 316, 316L, and 317 contain anaddition of molybdenum for improved corro-sion resistance. Types 321, 347, and 348 are“stabilized” with titanium, columbium, andsome tantalum to avoid intergranular chro-mium carbide during welding.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


15.11.4 Behavior in Welding. An importantpart in the successful welding of austeniticstainless steels is the control of compositionsand microstructures through proper selectionof electrode type, welding procedure, andpostweld treatment. Base-metal composi-tions, fully austenitic in wrought form, willoften show the presence of small islands ofdelta ferrite in an austenite matrix in the castor weld metal form. Figure 15.53 shows themicrostructure of a typical austenitic weldspecimen containing some delta ferrite. Fullyaustenitic weld deposits are occasionally sus-ceptible to hot-short cracking.

Weld-metal cracking in austenitic stainlesssteels can be separated into four types: (1)crater cracks, (2) star cracks, (3) hot cracks ormicrofissures, and (4) root cracks. All fourtypes of cracking are believed to be manifes-tations of the same basic kind of cracking:namely, “hot cracking” or, when present in itsearliest, least severe stage, “microfissuring.”Hot cracks or microfissures occur intergranu-

larly. The segregation of low-melting com-pounds to the grain boundaries appears topromote fissuring susceptibility. Microfis-sures can develop in the as-deposited weldmetal shortly after solidification.

Microfissures can also occur in the heat-affected zones (HAZ) of previously depositedsound beads of weld metal.

The presence of ferrite usually inhibits thistendency to crack. Many manufacturersdesign austenitic stainless steel electrodes todeposit a weld metal containing sufficient fer-rite to reduce the susceptibility toward hotcracking. Thus, the weld metal for many ofthe standard austenitic grades may containferrite, although the same grade base metaldoes not contain any. Postweld heat treat-ments may decrease or even eliminate the fer-rite in a weld deposit.

The presence or absence of ferrite ina weld-metal structure will depend princi-pally upon composition. Since many ofthe corrosion-resistant stainless steels have

Figure 15.53—Microstructure of Austenitic Weld Specimen


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


borderline phase distribution, a single type ofweld metal may be fully austenitic or partiallyferritic, depending upon the composition bal-ance. The constitution of a weld metal depositis indicated in Figure 15.54. This figure iscalled a Schaeffler diagram, named for itsoriginator. A subsequent variation of this dia-gram is the W. T. DeLong diagram shown inFigure 15.55. The DeLong diagram providesmore accuracy and accounts for the contribu-tion of nitrogen content.

15.11.5 Ferrite Values and Testing. Ferritecontent has traditionally been expressed asthe volume percent ferrite in the weld beaduntil the recent application of the term ferrite

number (FN). Key factors in the recom-mended procedure for testing ferrite are thefollowing:

(1) Use of the term ferrite number (FN)instead of percent ferrite

(2) Use of National Institute of Standardsand Technology (NIST) coating thicknessspecimens as reference and calibration stan-dards, and ferrite numbers assigned by Weld-ing Research Council (WRC) for calibratingferrite gauges

(3) Provisions for calibration of all othermagnetic instruments through weld metalstandards that have been rated for ferrite num-ber (FN)

Figure 15.54—Schaeffler Diagram for Stainless Steel Weld Metal


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Figure 15.55—DeLong Diagram for Stainless Steel Weld Metal


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


The magnetic ferrite phase is most com-monly measured using a portable instrument,such as the Ferritescope by Twin City TestingCorp., the Ferrite Content Meter by InstitutDr. Forster, and the Severn gauge by SevernEngineering Co. The WRC procedure isbased on a sensitive instrument, the Magne-Gauge Tester by American Instrument Co.,well known for its laboratory applications.

Portable ferrite indicators are designed foron-site use. Ferrite content of the welddeposit may be indicated in percent ferrite orFN numbers and may be bracketed betweentwo values. This provides sufficient control inmost applications where minimum ferritecontent or a ferrite range is specified.

15.12 Nondestructive Examination Procedures

The previous sections of this chapter havebeen devoted to fundamental concepts ofindividual NDE methods. In applying theseNDE methods to weld inspections, the weld-ing inspector will discover that each particu-lar NDE method has numerous variables thatmay be traded off to optimize (1) economics,(2) adaptability of the technique to a particu-lar weld type; and (3) technical resultsdesired. In addition, the welding inspectorwill discover that acceptance criteria varydepending upon the job and its specificationrequirements. Many contractors are workingmultiple jobs that require different techniqueand acceptance requirements. In order to pro-vide the desired assurance of quality in thecustomer’s product, specific NDE proceduresare commonly employed to ensure uniformityand continuity in the inspection process. Pre-planned NDE procedures provide the follow-ing advantages:

(1) Consolidate all of the customer’s basicinspection criteria into a single document

(2) Promote efficient integration of manu-facturing and inspecting operations

(3) Provide interpretation by experienced,knowledgeable, and responsible personnel

To give the welding inspector some back-ground in the usefulness of NDE procedures,

the following text expands upon some of thetypical sources of requirements.

15.12.1 Engineering a Procedure. There areseveral approaches to engineering nonde-structive examination procedures. Theapproach that will prove most effective willdepend upon a particular contractor’s policiesgoverning the engineering, manufacturing,technical, and administrative factors involved.Each factor should receive due considerationif the nondestructive examination operation isto function successfully. The flow diagram(see Figure 15.56) shows how requirementsinvoked in the contract may be transformedinto a written operational procedure.

15.12.2 Specifications, Codes, and OtherStandards. The requirements for the techni-cal content of a typical NDE procedureusually begin with the contractual “package”of detailed specifications for building or man-ufacturing the product. As may be seen in ourflow diagram, a contractor specifies the basicfabrication standard or code to be used inconjunction with internal requirements orparticular needs. This fabrication standardbecomes the “backbone” for the job package,which establishes engineering conditions forconstruction and allied processes, i.e., inspec-tions. The fabrication standard usually furtherrefines building requirements by invoking astandard or practice especially tailored toprovide specific, detailed inspection require-ments. These detailed inspection require-ments may be modified at almost any stagedepending upon the customer’s requirements.It is not uncommon to discover that specifi-cations and associated documents employextensive cross-referencing to related variousdetails. Some networks of cross-referencingcan generate a complicated situation forselection of applicable inspection conditions.In addition, such specifications and docu-ments are characteristically comprehensiveand require careful interpretation by experi-enced, knowledgeable, and responsible per-sonnel. Most contractual requirements willgenerally address the following inspectionrelated variables:


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


(1) Extent of examination coverage (whatis required?)

(2) Examination method required(3) NDT techniques for the method(4) Qualification of examination technique

methods(5) Acceptance criteria for the welds using

that method(6) Personnel qualification and certifications(7) Safety practices and miscellaneousIn addition, the contractual requirements

will usually stipulate when the examinationshould be performed and what examinationmethods are to be used for weld repairs,should any be necessary. If any of theseimportant conditions are not fully understoodby the contractor, further discussion shouldensue until a finalized agreement is reachedon the complete requirements for examinationof the welds. At this point, an NDE proceduremay be beneficial to both customer and con-tractor in that an approved system may be

agreed upon and uniformly followed through-out the manufacturing process.

15.12.3 NDE Procedures. Nondestructiveexamination Procedures generally fall intotwo basic categories: (1) company proce-dures, and (2) general standard operating pro-cedures (S.O.P.s). Company proceduresnormally consolidate requirements and final-ize interpretations concerning a particularNDE method into a single package (i.e., cus-tomer requirements, specification require-ments, necessary modifications, etc.). Thecompany procedure therefore represents anagreed upon consolidation and interpretationof contractual requirements. Standard operat-ing procedures (S.O.P.s) are generallyintended to serve as “recipe” or step-by-stepprocedures or methods to carry out the exami-nation or portions of it. Examples of S.O.P.scould typically include equipment calibra-tions, job lay-out procedures, equipmentmaintenance, personnel qualifications, etc.

Figure 15.56—Typical Flow Diagram from Contractto Approved Operations Procedures


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


S.O.P.s can provide an efficient method ofadministering procedures in that they tendtoward minimizing redundant or repetitivemention in the specific operating procedures,especially where examination areas overlapor where multiple procedures are usedextensively.

Fundamental rules for developing the pro-cedural text can apply to both categories sincetheir basic differences are determined by theirscope and their functional objective. A com-pany procedure may reference a series ofstandard operating procedures for perfor-mance of specific functions (e.g., personnelqualification, equipment calibration and stan-dardization, etc.) but the standard operatingprocedure generally represents the “end of theline” for respective written requirements.

15.12.3.1 Procedure Mechanics. An effec-tively written procedure sustains the primaryobjective of providing nondestructive exami-nation personnel with simplified instructions.This objective should always be kept in mindwhen phrasing the respective requirementsfor incorporation into the procedure. A verba-tim transfer of the applicable requirementsfrom the involving document as the proceduretext may defeat the objective of the procedureand may not suffice. Although this methodmay succeed in achieving technical compli-ance, it may not complement the overall pro-cedure program. The respective requirementsshould be interpreted by an experienced per-son and refined as necessary to provide a pre-cise but simplified account of acceptablepractices and policies.

The mechanics associated with procedurepreparation may vary with different situations,but certain fundamental rules will apply. Theprocedure will generally be evaluated on thebasis of organization, content, and ability tocommunicate and function effectively. Therespective requirements should be arranged inlogical sequence. Commonly, a basic outlinestructure is used. The format or an indexshould provide a convenient means for locat-ing and identifying any particular require-ment. Generally, procedure wording is brief

and to the point, producing a text that is accu-rate and concise without undue sacrificing ofnecessary details. Redundancies and repetitionshould be avoided unless they are considerednecessary for emphasizing or clarifying a cer-tain point. Tables, charts, and sketches usuallyprove effective in describing certain condi-tions and depicting various situations.

The distribution of nondestructive exami-nation procedures is generally controlled as tothe number of copies and the locations ofeach. This control assures that the proceduresare distributed to only those parties requiringtheir use. The distribution control systemshould also encompass procedure changesand revisions that may be required as a resultof changing policies and practices. The con-trol system ensures that each procedureholder receives a copy of the respectivechange. An effectively maintained proceduraldistribution system will provide assurancethat all related examination is being per-formed in accordance with up-to-daterequirements.

15.13 References and Suggested Reading Material

1. American Society for Metals (ASM).“Nondestructive inspection and qualitycontrol.” ASM Metals Handbook, Vol. II,105-156. Materials Park, OH: ASM.

2. American Society for NondestructiveTesting (ASNT). Personnel Qualificationand Certification in Nondestructive Test-ing. ASNT No. SNT-TC-1A, Columbus,Ohio: The American Society for Non-destructive Testing.

3. American Welding Society (AWS). A3.0,Standard Welding Terms and Definitions.Miami, FL: American Welding Society.

4. American Welding Society (AWS).B1.10, Guide for the NondestructiveExamination of Welds. Miami, FL:American Welding Society.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

215

Nondestructive examination (NDE) per-sonnel must be properly qualified in order toeffectively do their jobs. The process of qualifi-cation gives some assurance that the NDE oper-ator is knowledgeable in the theory andapplication of the method being used, as well asits advantages, disadvantages, and limitations.Experience, training, and ethical conduct areimportant elements that all NDE personnelshould possess. The most widely used documentfor NDE personnel qualifications in the U.S. is

Recommended Practice No. SNT-TC-1A

, writtenand published by The American Society forNondestructive Testing, Inc. While this docu-ment is a recommended practice, various codes,other standards, or specifications require its use,thus making it a minimum requirement. Thewelding inspector is cautioned that SNT-TC-1Ais an ever changing document and the weldinginspector should confirm that the applicable edi-tion is being used. The welding inspector shouldreview the manufacturer’s written practice forNDE personnel qualifications to assure that it isin compliance with job requirements.

In today’s NDE industry there are threelevels of qualification. Recommended Prac-tice No. SNT-TC-1A defines the capabilitiesof each level as follows:

16.1 Level I

A Level I individual should be qualified toproperly perform specific calibrations, spe-cific tests, and specific evaluations for accep-tance or rejection determinations according towritten instructions and to record results.

The Level I shall receive the necessaryinstruction or supervision from a certifiedLevel II or III individual.

16.2 Level II

A Level II individual should be qualified toset up and calibrate equipment and to interpret

and evaluate results with respect to applicablecodes, other standards, and specifications. TheLevel II should be thoroughly familiar with thescope and limitations of the methods for whichthe individual is qualified and should exerciseassigned responsibility for on-the-job trainingand guidance of trainees and Level I personnel.The Level II should be able to prepare writteninstructions, and to organize and report theresults of nondestructive examinations.

16.3 Level III

A Level III individual should be capable ofestablishing techniques and procedures; inter-preting codes, other standards, specifications,and procedures; and designating the particulartest methods, techniques, and procedures to beused. The Level III should be responsible forthe NDE operations for which qualified and towhich assigned, and should be capable of inter-preting and evaluating results in terms of exist-ing codes, other standards, and specifications.The Level III should have sufficient practicalbackground in applicable materials, fabrica-tion, and product technology to establish tech-niques and to assist in establishing acceptancecriteria where none are otherwise available.The Level III should have general familiaritywith other appropriate NDE methods, andshould be qualified to train and examine Level Iand Level II personnel for certification.

Before being certified, a person working inNDE is considered a

Trainee

. Trainees shouldnot be allowed to perform any NDE functionwithout DIRECT supervision.

In order for the welding inspector to evalu-ate the performance of an NDE operator, it isnecessary to have some familiarity with themethod(s) used. This book lists numerous ref-erences that can be used to become morefamiliar with the various methods of nonde-structive examination.

Chapter 16Qualification of Nondestructive

Examination Personnel


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

217

17.1 Definitions

This chapter is intended to familiarize thewelding inspector with the basic documentsthat govern or guide welding activities. Thesedocuments serve to assure that (1) only safeand reliable welded products will be pro-duced, and (2) those persons associated withwelding operations will not be exposed toundue danger or other conditions that wouldbe harmful to their health. Publications relat-ing only to the manufacture of welding mate-rials or welding equipment are not covered inthis chapter. However, the publications maybe referenced in the basic documents, andtheir relationship to safety and reliabilityshould not be underestimated.

The American Welding Society uses thegeneral term

standards

to refer to documentsthat govern and guide welding activities.Standards describe the technical requirementsfor a material, process, product, system, orservice. They also indicate, as appropriate,the procedures, methods, equipment, or testsused to determine that the requirements havebeen met.

Standards include codes, specifications, rec-ommended practices, classifications, methods,and guides. These documents have many simi-larities, and the terms are often used inter-changeably, but sometimes incorrectly.

Codes

and

Specifications

are similar typesof standards that use the words

shall

and

will

to indicate the mandatory use of certain mate-rials or actions, or both. Both become manda-tory when specified by one or moregovernmental jurisdictions or when they arereferenced by contractural or other procure-ment documents.

Recommended Practices and Guides

arestandards that are offered primarily as aids to

the user. They use words such as

should

and

may

because their use is usually optional.However, if these documents are referencedby codes or contractural agreements, their usemay become mandatory. If the codes oragreements contain non-mandatory sectionsor appendices, the use of referenced guidesor recommended practices is at the user’sdiscretion.

Classifications

and

methods

generally pro-vide lists of established practices or catego-ries for processes or products. The mostcommon example is a standard testingmethod.

The user of a standard should becomeacquainted with its scope and intended use,both of which are usually included within the

Scope

or

Introduction

section of the standard.It is equally important, but often more diffi-cult, to recognize subjects that are not cov-ered by the document. These omissions mayrequire additional technical consideration. Adocument may cover the details of the prod-uct form without considering special condi-tions for which it will be used. Examples ofspecial conditions would be corrosive envi-ronments, elevated temperatures, or dynamicrather than static loading.

Standards vary in their method of achievingcompliance. Some have specific requirementsthat do not allow for alternative actions. Oth-ers permit alternative actions or procedures solong as they result in properties that meetspecified criteria. These criteria are oftengiven as minimum requirements.

17.2 Sources

Private and governmental organizationsdevelop, issue, and update standards thatapply to their particular areas of interest.

Chapter 17Codes and Other Standards


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

218/Codes and Other Standards

Section 17.3.25 lists the organizations of con-cern to the welding industry and their currentaddresses. The interests of many of thesegroups overlap with regard to welding, andsome agreements have been made to reduceduplication of effort.

Many standards that address welding, braz-ing, and allied processes are prepared by theAmerican Welding Society (AWS) becausethese subjects are of primary interest to AWSmembers. Standards that apply to a particularproduct are usually prepared by the group thathas overall responsibility. For example, thosefor railroad freight cars are published by theAssociation of American Railroads (AAR).However, freight cars are basically structures,and the applicable AAR specification cur-rently refers to AWS for the qualification ofwelding procedures, welders, and weldingoperators. In 1986, the American WeldingSociety published AWS D15.1,

RailroadWelding Specification

. Future revisions to theAAR standards will reference AWS D15.1.

Each organization that prepares consensusstandards has committees or task groups toperform this function. Members of these com-mittees or task groups are specialists in theirfields. They prepare drafts of standards thatare reviewed and approved by a larger group.Each main committee is selected to includepersons with diverse interests from producers,users, and government representatives. Toavoid control or undue influence by one inter-est group, consensus should be achieved by ahigh percentage of all members.

The federal government develops or adoptsstandards for items and services that are in thepublic rather than the private sector. Themechanisms for developing federal or mili-tary documents are similar to those of privateorganizations. Standard-writing committeesusually exist within a federal department oragency that has responsibility for a particularitem or service.

The American National Standards Institute(ANSI) is a private organization responsiblefor coordinating national standards for usewithin the United States. ANSI does not actu-ally prepare standards. Instead, it forms

national interest review groups to determinewhether proposed standards are in the publicinterest. Each group is composed of personsfrom various organizations concerned withthe scope and provisions of a particular docu-ment. If there is consensus regarding the gen-eral value of a particular standard, then it maybe adopted as an American National Stan-dard. Adoption of a standard by ANSI doesnot, of itself, give it mandatory status. How-ever, if the standard is cited by a governmen-tal rule or regulation, or imposed by contractrequirements, it may then be backed by forceof law.

Other industrial countries also develop andissue standards on the subject of welding. Thefollowing are examples of other national stan-dards designations and the bodies responsiblefor them:

BS—British Standard issued by the BritishStandards Association

CSA—Canadian Standard issued by theCanadian Standards Association

DIN—West German Standard issued by theDeutsches Institute fuer Normung

JIS—Japanese Industrial Standard issuedby the Japanese Standards Association

NF—French Standard issued by the Asso-ciation Française de Normalisation

There is also an International Organizationfor Standardization (ISO). Its goal is theestablishment of uniform standards for use ininternational trade.

17.3 Applications

The minimum requirements of a particularstandard may not satisfy the special needs ofevery user. Therefore, a user may find it nec-essary to invoke additional requirements toobtain desired quality.

There are various mechanisms by whichmost standards may be revised. These areused when a standard is found to be in error,unreasonably restrictive, or not applicablewith respect to new technological develop-ments. Some standards are updated on a regu-lar basis, while others are revised as needed.The revisions may be in the form of addenda,


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Codes and Other Standards/219

or they may be incorporated in supersedingdocuments. If there is a question about a par-ticular standard regarding either an interpreta-tion or a possible error, the user shouldcontact the responsible organization.

When the use of a standard is mandatory,whether as a result of a government regula-tion or a legal contract, it is essential to knowthe particular edition of the document to beused. It is unfortunate, but not uncommon, tofind that an outdated edition of a referenceddocument has been specified, and should befollowed to be in compliance. If there is aquestion concerning which edition or revisionof a document is to be used, it should beresolved before commencement of work.

Organizations responsible for preparingstandards that relate to welding are discussedin the following sections. The publications arelisted without reference to date of publication,latest revision, or amendment. New publica-tions relating to welding may be issued, andcurrent ones may be withdrawn or revised.The responsible organization should be con-tacted for current information on the stan-dards it publishes.

17.3.1 American Association of State High-way and Transportation Officials.

Themember agencies of the association known asAASHTO are the U.S. Department of Trans-portation, and the Departments of Transporta-tion and Highways of the fifty states,Washington DC, and Puerto Rico. AASHTOspecifications are prepared by committeesmade up of employees of the member agen-cies. These documents are the minimum rulesto be followed by all member agencies or oth-ers in the design and construction of highwaybridges.

17.3.2 American Bureau of Shipping.

Thefunction of the American Bureau of Shipping(ABS) is to verify the quality of ship, boat,and offshore platform construction. Eachyear, ABS reissues the

Rules for Building andClassing Steel Vessels.

ABS also publishes a list of weldingconsumables, entitled

Approved WeldingElectrodes, Wire-Flux, and Wire-Gas Combi-

nations.

These consumables are produced byvarious manufacturers around the world.They are tested under ABS supervision andapproved for use under the ABS rules.

17.3.3 American Institute of Steel Con-struction.

The American Institute of SteelConstruction (AISC) is a non-profit tradeorganization for the fabricated structural steelindustry in the United States. The Institute’sobjectives are to improve and advance the useof fabricated structural steel through researchand engineering studies, and to develop themost efficient and economical design of struc-tures. The organization also conducts pro-grams to improve and control product quality.

17.3.4 American National Standards Insti-tute.

The American National Standards Insti-tute (ANSI) is the coordinating organizationfor the U.S. voluntary standards system; itdoes not develop standards directly. The Insti-tute provides the means for determining theneed for standards, and ensures that organiza-tions competent to fill these needs undertakethe development work. The approval proce-dures of ANSI ensure that all interested per-sons have an opportunity to participate in thedevelopment of a standard or to comment onprovisions of the standard prior to publica-tion. ANSI is the U.S. member of nontreatyinternational standards organizations, such asthe International Organization for Standard-ization (ISO), and the International Electro-technical Commission (IEC).

17.3.5 American Petroleum Institute.

TheAmerican Petroleum Institute (API) publishesdocuments in all areas related to petroleumproduction, storage, and transportation.

17.3.6 American Railway EngineeringAssociation.

The American Railway Engi-neering Association (AREA) publishes the

Manual for Railway Engineering.

This man-ual contains specifications, rules, plans, andinstructions that constitute the recommendedpractices of railway engineering.

17.3.7 American Society of MechanicalEngineers.

Two standing committees of the


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


American Society of Mechanical Engineers(ASME) are actively involved in the formula-tion, revision, and interpretation of standardscovering products that may be fabricated bywelding. These committees are responsiblefor preparing the

ASME Boiler and PressureVessel Code

and the

Code for Pressure Pip-ing

, which are American National Standards.

17.3.8 ASTM.

ASTM (formally The Ameri-can Society for Testing and Materials) devel-ops and publishes specifications for use in theproduction and testing of materials. The com-mittees that develop the specifications arecomprised of producers and users as well asothers who have an interest in the subjectmaterials. The specifications cover virtuallyall materials used in industry and commercewith the exception of welding consumables,which are covered by AWS specifications.

17.3.9 American Water Works Associa-tion.

The American Water Works Association(AWWA) currently has two standards thatpertain to the welding of water storage andtransmission systems. One of these standardswas developed jointly with and adopted bythe American Welding Society.

17.3.10 American Welding Society.

TheAmerican Welding Society (AWS) publishesnumerous documents covering the use andquality control of welding. These documentsinclude codes, specifications, recommendedpractices, classifications, methods, and guides.The general subject areas covered are thefollowing:

(1) Definitions and symbols(2) Filler metals(3) Qualification and testing(4) Welding processes(5) Welding applications(6) Safety(7) Standard Welding Procedures

17.3.11 Association of American Railroads.

The primary source of welding informationrelating to the construction of new railwayequipment is the

Manual of Standards andRecommended Practices

prepared by the

Mechanical Division, Association of Ameri-can Railroads (AAR).

17.3.12 Canadian Standards Association.

The Canadian Standards Association (CSA)is a voluntary membership organizationengaged in standards development and alsotesting and certification. The CSA is similarto ANSI in the United States, but ANSI doesnot test and certify products. A CSA Certifi-cation Mark assures buyers that a productconforms to acceptable standards.

17.3.13 Compressed Gas Association.

TheCompressed Gas Association (CGA) pro-motes, develops, represents, and coordinatestechnical and standardization activities in thecompressed gas industries, including end usesof products.

17.3.14 Federal Government.

Severaldepartments of the Federal Government,including the General Services Administra-tion, are responsible for developing weldingstandards or adopting existing standards orboth. There are in excess of 48 000 standardsadopted by the federal government.

17.3.15 Consensus Standards.

The U.S.Departments of Labor, Transportation, andEnergy are primarily concerned with adoptingexisting national consensus standards, butthey also make amendments to these stan-dards or create separate standards, as neces-sary. For example, the Occupational Safetyand Health Administration (OSHA) of theDepartment of Labor issues regulations cov-ering occupational safety and health protec-tion. The welding portions of standardsadopted or established by OSHA are pub-lished under the Title 29 of the

United StatesCode of Federal Regulations.

Part 1910 cov-ers general industry, while Part 1926 coversthe construction industry. These regulationswere derived primarily from national consen-sus standards of ANSI and of the NationalFire Protection Association (NFPA).

Similarly, the U.S. Department of Trans-portation is responsible for regulating thetransportation of hazardous materials, petro-leum, and petroleum products by pipeline in


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


interstate commerce. Its rules are publishedunder Title 49 of the

United States Code ofFederal Regulations

, Part 195. Typical of themany national consensus standards incorpo-rated by reference in these regulations are APIStandard 1104 and ASME B31.4, which werediscussed previously.

The U.S. Department of Transportation isalso responsible for regulating merchant shipsof American registry. It is empowered to con-trol the design, fabrication, and inspection ofthese ships by Title 46 of the

United StatesCode of Federal Regulations.

The U.S. Coast Guard is responsible forperforming the inspections of merchant ships.The

Marine Engineering Regulations

incor-porate references to national consensus stan-dards, such as those published by ASME,ANSI, and ASTM. These rules cover repairsand alterations that should be performed withthe cognizance of the local Coast GuardMarine Inspection Officer.

The U.S. Department of Energy is respon-sible for the development and use of stan-dards by government and industry for thedesign, construction, and operation of safe,reliable, and economic nuclear energy facili-ties. National consensus standards, such asthe ASME

Boiler and Pressure Vessel Code

,Sections III and IX, and AWS D1.1,

Struc-tural Welding Code—Steel

are referred to infull or in part. These standards are supple-mented by separate program standards,known as RDT Standards.

17.3.16 Military and Federal Specifica-tions.

Military specifications are prepared bythe Department of Defense. They cover mate-rials, products, or services specifically formilitary use, and commercial items modifiedto meet military requirements.

17.3.17 International Organization forStandardization.

The International Organi-zation for Standardization (ISO) promotes thedevelopment of standards to facilitate theinternational exchange of goods and services.It is comprised of the standards-writing bod-ies of more than 80 countries, and hasadopted or developed over 4000 standards.

The American National Standards Instituteis the designated U.S. representative to ISO.ISO standards and publications are availablefrom ANSI.

17.3.18 National Board of Boiler and Pres-sure Vessel Inspectors.

The National Boardof Boiler and Pressure Vessel Inspectors(NBBPVI), often referred to as the NationalBoard, represents the enforcement agenciesempowered to assure adherence to the ASME

Boiler and Pressure Vessel Code.

Its membersare the chief inspectors or other jurisdictionalauthorities who administer the boiler andpressure vessel safety laws in the variousjurisdictions of the United States and prov-inces of Canada.

17.3.19 National Fire Protection Associa-tion.

The mission of the National Fire Protec-tion Association (NFPA) is the safeguardingof people and their environment from destruc-tive fire through the use of scientific and engi-neering techniques and education. NFPAstandards are widely used as the basis of leg-islation and regulation at all levels of govern-ment. Many are referenced in the regulationsof the Occupational Safety and HealthAdministration (OSHA). The standards arealso used by insurance authorities for riskevaluation and premium rating.

17.3.20 Pipe Fabrication Institute.

The PipeFabrication Institute (PFI) publishes numer-ous documents for use by the piping industry.Some of the standards have mandatory statusbecause they are referenced in one or morepiping codes. The purpose of PFI standards isto promote uniformity of piping fabrication inareas not specifically covered by codes. OtherPFI documents, such as technical bulletins,are not mandatory, but they aid the piping fab-ricator in meeting the requirements of codes.

17.3.21 Society of Automotive Engineers.

The Society of Automotive Engineers (SAE) isconcerned with the research, development,design, manufacture, and operation of all typesof self-propelled machinery. Such machineryincludes automobiles, trucks, buses, farmmachines, construction equipment, airplanes,


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


helicopters, and space vehicles. Related areasof interest to SAE are fuels, lubricants, andengineering materials.

17.3.22 Unified Numbering System.

TheUnified Numbering System (UNS) provides amethod for cross referencing the differentnumbering systems used to identify metals,alloys, and welding filler metals. With UNS,it is possible to correlate over 3500 metalsand alloys used in a variety of specifications,regardless of the identifying number used bya society, trade association, producer, or user.

UNS is produced jointly by SAE andASTM, and designated SAE HSJ1086/ASTMDS56. It cross references the numbered metaland alloy designations of the following orga-nizations and systems:

(1) AA (Aluminum Association)(2) ACI (Steel Founders Society of America)(3) AISI (American Iron and Steel Institute)(4) ASME (American Society of Mechani-

cal Engineers)(5) ASTM (Formerly American Society for

Testing and Materials)(6) AWS (American Welding Society)(7) CDA (Copper Development Association)(8) Federal Specifications(9) MIL (Military Specifications)

(10) SAE (Formerly Society of AutomotiveEngineers)(11) AMS (SAE Aerospace Materials

Specifications)Over 500 of the listed numbers are for

welding and brazing filler metals. Numberswith the prefix

W

are assigned to weldingfiller metals that are classified by depositedmetal composition.

17.3.23 Underwriter’s Laboratories, Inc.

Underwriter’s Laboratories, Inc., (UL) is anot-for-profit organization which operateslaboratories for the examination and testing ofdevices, systems, and materials to determinetheir relation to hazards to life and property.UL Standards for Safety are developed undera procedure which provides for participationand comment from the affected public as wellas industry. This procedure takes into consid-

eration a survey of known existing standards,and the needs and opinions of a wide varietyof interests concerned with the subject matterof a given standard. These interests includemanufacturers, consumers, individuals asso-ciated with consumer-oriented organizations,academicians, government officials, industrialand commercial users, inspection authorities,insurance interests, and others.

UL should be contacted if no standard canbe found for a particular product. The ULStandards for Safety pertain to more than11 000 product types in over 500 genericproduct categories.

17.3.24 Manufacturers’ Associations.

Thefollowing organizations publish literaturewhich relates to welding. The committees thatwrite descriptive literature are comprised ofrepresentatives of equipment or material man-ufacturers. They do not generally includeusers of the products. Although some biasmay exist, there is a lot of useful informationthat can be obtained from this literature. Theorganization should be contacted for furtherinformation.

Aluminum Association

900 19th Street, N.W., Suite 300Washington, DC 20006(202) 862-5100 Tel.(202) 862-5164 Faxwww.aluminum.org

American Association of State Highway and Transportation Officials

444 North Capitol Street, N.W., Suite 249Washington, DC 20001(202) 624-5800 Tel.(202) 624-5806 Faxwww.aashto.org

American Bureau of Shipping and Affiliated Companies

Two World Trade Center, 106th FloorNew York, NY 10048(212) 839-5000 Tel.(212) 839-5209 [email protected] E-mail


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


American Conference of Governmental Industrial Hygienists

1330 Kemper Meadow Drive, Suite 600Cincinnati, OH 45240-1634(513) 742-2020 Tel.(513) 742-3355 Faxwww.acgih.org

American Gas Association

400 North Capitol Street, N.W.Washington, DC 20001(703) 841-8400 Tel.(703) 841-8689 Faxwww.aga.com

American Institute of Steel Construction

One East Wacker Drive, Suite 3100Chicago, IL 60601-2001(312) 670-2400 Tel.(312) 670-5403 Faxwww.aiscweb.org

American Iron and Steel Institute

1101 17th Street, N.W., Suite 1300Washington, DC 20036-4700(202) 452-7100 Tel.(202) 463-6573 Faxwww.steel.org

American National Standards Institute

11 West 42nd Street, 13th FloorNew York, NY 10036-8002(212) 642-4900 Tel.(212) 398-0023 Faxwww.ansi.org

American Petroleum Institute

1220 L Street, N.W.Washington, DC 20005(202) 682-8000 Tel.(202) 682-8115 Faxwww.api.org

American Railway Engineering and Maintenance of Way Association

8201 Corporate Drive, Suite 1125Landover, MD 20785(301) 459-3200 Tel.(301) 459-8077 Fax

American Society for Nondestructive Testing

1711 Arlingate Lane, P.O. Box 28518Columbus, OH 43228-0518(614) 274-6003; (800) 222-2768 Tel.(614) 274-6899 Faxwww.asnt.org

American Society for Quality

P.O. Box 3005611 East Wisconsin AvenueMilwaukee, WI 53201-3005(414) 272-8575; (800) 248-1946 Tel.(414) 272-1734 Faxwww.asq.org

American Society for Testing and Materials

100 Barr Harbor DriveWest Conshohocken, PA 19428(610) 832-9500 Tel.(610) 832-9555 Faxwww.astm.org

American Society of Civil Engineers

1801 Alexander Bell DriveReston, VA 20191-4400(703) 295-6000; 800 548-2723 Tel.(703) 295-6351 Faxwww.asce.org

American Society of Mechanical Engineers

Three Park AvenueNew York, NY 10016-5990(212) 591-7000 Tel.(212) 591-7674 Faxwww.asme.org

American Society of Safety Engineers

1800 East Oakton StreetDes Plaines, IL 60018-2187(847) 699-2929 Tel.(847) 296-3769 Faxwww.asse.org

American Water Works Association

6666 W. Quincy AvenueDenver, CO 80235-3098(303) 794-7711 Tel.(303) 795-1989 Faxwww.awwa.org


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


American Welding Society

550 N.W. LeJeune RoadMiami, FL 33126(305) 443-9353; (800) 443-9353 Tel.(305) 443-7559 Faxwww.amweld.org

ASM International

9639 Kinsman RoadMaterials Park, OH 44073-0002(440) 338-5151 Tel.(440) 338-4634 Faxwww.asm-intl.org

Association of American Railroads

50 F Street, N.W.Washington, DC 20001-1564(202) 639-2100 Tel.(202) 639-2558 Faxwww.aar.org

Compressed Gas Association

1725 Jefferson Davis Highway, Suite 1004Arlington, VA 22202-4102(703) 412-0900 Tel.(703) 412-0128 Faxwww.cganet.com

Copper Development Association, Inc.

260 Madison AvenueNew York, NY 10016-2401(212) 251-7200; (800) 232-3282 Tel.(212) 251-7234 Faxwww.copper.org

Electronic Industries Association

2500 Wilson BoulevardArlington, VA 22201(703) 907-7500 Tel.(703) 907-7501 Faxwww.eia.org

Fabricators and Manufacturers Association, International

833 Featherstone RoadRockford, IL 61107(815) 877-7633 Tel.(815) 399-7279 Fax

Institute of Industrial Engineers

25 Technology Park/AtlantaNorcross, GA 30092-2901(770) 449-0460 Tel.(770) 441-3295 Faxwww.iienet.org

NACE InternationalP.O. Box 218340Houston, TX 77218-8340(281) 228-6200 Tel.(281) 228-6300 Faxwww.nace.org

National Board of Boiler and Pressure Vessel Inspectors1055 Crupper AvenueColumbus, OH 43229(614) 888-8320 Tel.(614) 888-0750 Faxwww.nationalboard.org

National Electrical Manufacturers Association1300 N. 17th Street, Suite 1847Rosslyn, VA 22209(703) 841-3200 Tel.(703) 841-3351 Faxwww.nema.org

National Fire Protection AssociationP.O. Box 91011 Battery March ParkQuincy, MA 02269-9101(617) 770-3000 Tel.(617) 770-0200 Faxwww.nfpa.org and www.sparky.org

National Safety Council1121 Spring Lake DriveItasca, IL 60143-3201(630) 285-1121 Tel.(630) 285-1315 Faxwww.nsc.org

National Welding Supply Association1900 Arch StreetPhiladelphia, PA 19103-1498(215) 564-3484 Tel.(215) 564-2175 Faxwww.nwsa.com


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


Pipe Fabrication InstituteBox 173612 Lenore AvenueSpringdale, PA 15144-1518(514) 634-3444 Tel.(514) 634-9736 Fax

Resistance Welder Manufacturers Association1900 Arch StreetPhiladelphia, PA 19103-1498(215) 564-3484 Tel.(215) 963-9785 Faxwww.rwma.org

Society of Automotive Engineers International400 Commonwealth DriveWarrendale, PA 15096-0001(724) 772-7168 Tel.(724) 776-1830 Faxwww.sae.org

Society of Manufacturing EngineersP.O. Box 930One SME DriveDearborn, MI 48121-0930(313) 271-1500; (800) 733-4763 Tel.(313) 271-2861 Faxwww.sme.org

Underwriters Laboratories, Inc.333 Pfingsten RoadNorthbrook, IL 60062(312) 272-8800 Tel.www.ul.com

Uniform Boiler and Pressure Vessel Laws Society308 N. Evergreen Road, Suite 240Louisville, KY 40243-1010(502) 244-6029 Tel.(502) 244-6030 Fax

U.S. Government Printing OfficeSuperintendent of DocumentsWashington, DC 20402(202) 783-3238 Tel.www.gpo.gov

Welding Research Council3 Park Avenue, 27th FloorNew York, NY 10016-5902(212) 705-7956 Tel.(212) 591-7183 Faxwww.forengineers.org/wrc


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

227

18.1 Introduction

The American Welding Society is activelypromoting the adoption of the InternationalSystem of Units (SI) within the U.S. weldingindustry.

Every inspector should have or shouldacquire a working knowledge of the metricsystem of measurements because of theincreasing use of SI units to replace thecustomary U.S. units in American industry.The latest revision of the AWS A1.1,

MetricPractice Guide for the Welding Industry

, maybe referred to for more information.

18.2 Units

SI consists of seven base units, two supple-mentary units, a series of derived units, and aseries of prefixes for the forming of multiplesor sub-multiples of the units.

Base and supplementary units and theirsymbols are shown in Table 18.1.

Derived units and their symbols are shownin Table 18.2.

Prefixes are used in the SI system toindicated orders of magnitude. This simpli-fies numeric terms and may be more conve-nient than writing powers of ten as isgeneral in computation. As an example,12 900 meters or 12.9

×

10

3

meters wouldbe written 12.9 kilometers. The tabulationin Table 18.3 shows the factors, prefixes,and symbols.

Other units are in widespread use and areacceptable for use with, although not a partof, the SI system. The term “weight,” as com-monly used in commerce, is a measure offorce that depends on the acceleration due togravity. The SI system does not have a unitfor weight. The kilogram is the SI unit for“mass,” the term that is used extensively inscientific documents. Other units are in wide-spread use and are acceptable for use with,although not a part of, the SI system. Theseare shown in Table 18.4.

18.3 Welding—Recommended Units and Conversion Factors

Table 18.5 shows the recommended SIunits for welding nomenclature and someuseful conversion factors. The recommendedSI units are given in parentheses.

18.4 Conversions—General

Table 18.6 presents factors for convertingnumerous U.S. Customary Units to SI Units.These values, though not exact, are useful formaking everyday conversions.

Rules for conversion and rounding off havebeen published by AWS in document AWSA1.1,

Metric Practice Guide for the Welding

Chapter 18Metric Practice

Table 18.1SI Base and Supplementary

Units and Symbols

Measure Unit Symbol

length meter mmass kilogram kgtime second selectric current ampere Athermodynamic

temperaturekelvin K

luminous intensity candela cdamount of substance mole molplane angle radian radsolid angle steradian sr


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

228/Metric Practice

Table 18.2SI Derived Units and Symbols

Measure Unit Symbol Formula

acceleration—linear—angular

meter per second squaredradian per second squared

nonenone

m/s

2

rad/s

2

area square meter none m

2

density kilogram per meter cubed none fg/m

3

electromotive force volt V W/A

energy, work, heat, and impact strength

joule J N m

force newton N kg m/s

2

luminous flux lumen lm cd sr

frequency hertz Hz s

–1

magnetic flux weber Wb V s

power watt W J/s

pressure, stress pascal Pa N/m

2

velocity—linear—angular

meter per secondradian per second

nonenone

m/srad/s

volume cubic meter none m

3

Table 18.3SI Factors, Prefixes, and Symbols

Expression Multiplication Factor Prefix Symbol

10

6

10

3

10

2

10

0

–

10

–1

–

10

–2

–

10

–3

–

10

–6

–

10

–9

1 000 0001000100100.10.010.0010.000 0010.000 000 001

megakilohecto*deka*deci*centi*millimicronano

Mkhdadcmµn

*Not recommended. Prefixes should be selected in steps of 10

3

so that the resultant number before the prefix isbetween 0.1 and 1000.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Metric Practice/229

Industry

, as well as by other organizationssuch as ASTM. Generally, rounding and con-version are needed during a transition period,but since they may continue throughout theuseful life of this revision of “WeldingInspection,” the following guidelines areoffered:

(1) Exact conversion from one system toanother is seldom used, since most often thisresults in long decimal numbers that imply ahigher degree of precision than was intendedoriginally.

(2) The closest practical equivalencybetween inch and millimeter values will occurwhen the SI value contains one less decimalplace than its inch equivalent. For example,0.365 in. equals 9.27 mm. Fractional inchconversions are especially tricky, however,since these usually exaggerate the intendedprecision. For example, when changing 1-7/8in. to mm, unless the 1-7/8 in. dimension wasintended to be 1.875 in., 47.63 mm may bemore precise than necessary. For interchange-ability of parts, allowed and required toler-ances should be kept in mind in making inch-millimeter conversion, or vice versa, so that

neither excessively tight tolerances nor excessclearances are inadvertently introduced. Inthese cases, the function of the assembly orfeature should be addressed. If this requiresthat maximum and minimum limits in milli-meters be within inch limits, maximum limitsare rounded down and minimum limits arerounded up.

(3) Two round-off methods, designated Aand B are described in document AWS A1.1and in Appendix B of the AWS

WeldingHandbook

, Volume One, Eighth Edition. Oneof these sources should be consulted whenmore detailed information is needed.

The commonly used inch-millimeter con-versions are listed in Table 18.7.

Table 18.8 may be used to obtain SI equiva-lents of values expressed in psi or ksi. SI val-ues are usually expressed in kPa when originalvalue is in psi and in MPa when original valueis ksi. This table may be extended to valuesbelow 1 or above 100 psi (or ksi) by manipula-tion of the decimal point and addition.

Conversions for Fahrenheit—Celsius tem-perature scales are shown in Table 18.9.

Table 18.4Units Not Part of the SI System

Units Symbol Value

minute min 1 min = 60 s

hour h 1 h = 60 min = 3600 sday d 1 d = 24 h = 1440 min = 86 400 sdegree (angular) ˚ 1

°

= (/180) rad = 0.0175 radbar* bar 1 bar = 0.1 MPa = 10

5

Paliter L 1 L = 0.001 m

3

= 1 dm

3

degree Celsius ˚C 1

°

C = 1 K (interval)angstrom* A 1 A = 0.1 nm = 10

–10

matmosphere* atm 1 atm = 101 325 Paweight kg 1 kgf = 9.806 650 N

*The lower case “ell” is the recognized symbol for liter but on most typewriters (and typesetting machines) thelower case “ell” and the figure one are nearly identical. Accordingly, it is preferable to spell the word in full oruse capital L. However, ml may be used for milliliter, because confusion would no longer be possible.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

230/Metric Practice

Table 18.5 SI Unit Conversion Factors

Property To Convert From To Multiply By

area dimensions(mm

2

)in.

2

mm

2

mm

2

in.

2

6.451 600

×

10

2

1.550 003

×

10

–3

current density(A/mm

2

)A/in.

2

A/mm

2

A/mm

2

A/in.

2

1.550 003

×

10

–3

6.451 600

×

10

2

deposition rate**(kg/h)

lb/hkg/h

kg/hlb/h

0.45**2.2**

electrical resistivity(

Ω

m)cmm

mcm

1.000 000

×

10

–2

1.000 000

×

10

2

electrical force(N)

pound-forcekilogram-forceN

NNlbf

4.448 2229.806 6502.248 089

×

10

–1

energy, work, heat, and impact energy

foot pound forcefoot poundalBtu*calorie*watt hour

JJJJJ

1.3564.214

×

10

–2

1.054

×

10

3

4.1843.600

×

10

3

flow rate(L/min)

ft

3

/hgallon per hourgallon per minutecm

3

/minliter/mincm

3

/min

L/minL/minL/minL/minft

3

/hft

3

/h

4.719 475

×

10

–1

6.309 020

×

10

–2

3.785 4121.000

×

10

–3

2.1192.119

×

10

–3

fracture toughness(MN m

–3/2

)ksi in.

1/2

MN m

–3/2

MN m

–3/2

ksi in.

1/2

1.098 8550.910 038

heat input(J/m)

J/in.J/m

J/mJ/in.

3.937 008

×

102.540 000

×

10

–2

linear measurements(mm)

in.ftmmmm

mmmmin.ft

2.540 000

×

103.048 000

×

10

2

3.937 008

×

10

–2

3.280 840

×

10

–3

power density(W/m

2

)W/in.

2

W/m

2

W/m

2

W/in.

2

1.550 003 × 103

6.451 600 × 10–4

pressure (gas and liquid)(kPa)

psilb/ft2

N/mm2

kPakPakPa

kPakPakPapsilb/ft2

N/mm2

6.894 7574.788 026 × 10–2

1.000 000 × 103

1.450 377 × 10–1

2.088 543 × 101.000 000 × 10–3

(Continued)


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Metric Practice/231

tensile strength(MPa)

psilb/ft2

N/mm2

kg/mm2 (kgf/mm2)MPaMPaMPa

MPaMPaMPaMPapsilb/ft2

N/mm2

6.894 757 × 10–3

4.788 026 × 10–5

1.000 0009.806 6501.450 377 × 102

2.088 543 × 104

1.000 000

thermal conductivity(W/[m K])

cal/(cm s °C) W/(m K) 4.184 000 × 102

travel speed, wire feed speed(mm/s)

in./minmm/s

mm/sin./min

4.233 333 × 10–1

2.362 205

Table 18.6 General Conversion Factors


acceleration (angular) revolution per minute squared

rad/s2 1.754 329 × 10–3

acceleration (linear) in./min2

ft/min2

in./min2

ft/min2

ft/s2

m/s2

m/s2

mm/s2

mm/s2

m/s2

7.055 556 × 10–6

8.466 667 × 10–5

7.055 556 × 10–3

8.466 667 × 10–2

3.048 000 × 10–1

angle, plane degminutesecond

radradrad

1.745 329 × 10–2

2.908 882 × 10–4

4.848 137 × 10–6

area in.2

ft2

yd2

in.2

ft2

acre (U.S. Survey)

m2

m2

m2

mm2

mm2

m2

6.451 600 × 10–4

9.290 304 × 10–2

8.361 274 × 10–1

6.451 600 × 102

9.290 304 × 104

4.046 873 × 103

density pound mass per cubic inchpound mass per cubic foot

kg/m3

kg/m32.767 990 × 104

1.601 846 × 10

(Continued)

Table 18.5 (Continued)SI Unit Conversion Factors



--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

232/Metric Practice

energy, work, heat, and impactenergy

foot pound forcefoot poundalBtu*calorie*watt hour

JJJJJ

1.355 8184.214 011 × 10–2

1.054 350 × 103

4.184 0003.600 000 × 103

force kilogram-forcepound-force

NN

9.806 6504.448 222

impact strength length (see energy)in.ftydmile (statute)

mmmm

2.540 000 × 10–2

3.048 000 × 10–1

9.144 000 × 10–1

1.609 300 × 103

mass pound mass (avdp)metric tonton (short, 2000 lbm)slug

kgkgkgkg

4.535 924 × 10–1

1.000 000 × 103

9.071 47 × 102

1.459 390 × 10

power horsepower (550 ft lbf/s)horsepower (electric)Btu/min*calorie per minute*foot pound-force per minute

WWWWW

7.456 999 × 102

7.460 000 × 102

1.757 250 × 106.973 333 × 10–2

2.259 697 × 10–2

pressure pound force per square inchbaratmospherekip/in.2

kPakPakPakPa

6.894 7571.000 000 × 102

1.013 250 × 102

6.894 757 × 103

temperature degree Celsius, tCdegree Fahrenheit, tFdegree Rankine, tRdegree Fahrenheit, tFkelvin, tK

KKKC°C°

tK = tC + 273.15tK = (tF + 459.67)/1.8tK = tR/1.8)tC = (tF – 32)/1.8tC = tK – 273.15

tensile strength (stress) ksi MPa 6.894 757

torque inch pound forcefoot pound force

N mN m

1.129 848 × 10–1

1.355 818

velocity (angular) revolution per minutedegree per minuterevolution per minute

rad/srad/sdeg/min

1.047 198 × 10–1

2.908 882 × 10–4

3.600 000 × 102

(Continued)

Table 18.6 (Continued)General Conversion Factors



--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Metric Practice/233

velocity (linear) in./minft/minin./minft/minmile/hour

m/sm/smm/smm/skm/h

4.233 333 × 10–4

5.080 000 × 10–3

4.233 333 × 10–1

5.080 0001.609 344

volume in.3

ft3

yd3

in.3

ft3

in.3

ft3

gallon

m3

m3

m3

mm3

mm3

LLL

1.638 706 × 10–5

2.831 685 × 10–2

7.645 549 × 10–1

1.638 706 × 104

2.831 685 × 107

1.638 706 × 10–2

2.831 685 × 103.785 412

*Thermochemical

Table 18.6 (Continued)General Conversion Factors



--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

234/Metric Practice

Table 18.7Commonly Used Metric Conversions (Inch–Millimeter Conversion)

1 in. = 25.4 mm exactly.

To convert inches to millimeters, multiply the inch millimeter value by 25.4.To convert millimeters to inches, divide the value by 25.4.

Inch and Millimeter Decimal Equivalents of Fractions of an Inch

Inch

Millimeter

Inch

MillimeterFraction Decimal Fraction Decimal

1/641/323/641/165/64

3/327/641/89/645/32

11/643/16

13/647/32

15/64

1/417/64

9/3219/64

5/16

21/6411/3223/64

3/825/64

13/3227/64

7/1629/6415/32

31/641/2

0.015 6250.031 2500.046 8750.062 5000.078 125

0.093 7500.109 3750.125 0000.140 6250.156 250

0.171 8750.187 5000.203 1250.218 7500.234 375

0.250 0000.265 6250.281 2500.296 8750.312 500

0.328 1250.343 7500.359 3750.375 0000.390 625

0.406 2500.421 8750.437 5000.453 1250.468 750

0.484 3750.500 000

0.396 8750.793 7501.190 6251.587 5001.984 375

2.381 2502.778 1253.175 0003.571 8753.968 750

4.365 6254.762 5005.159 3755.556 2505.953 125

6.350 0006.746 8757.143 7507.540 6257.937 500

8.334 3758.731 2509.128 1259.525 0009.921 875

10.318 75010.715 62511.112 50011.509 37511.906 250

12.303 12512.700 000

33/6417/3235/64

9/1637/64

19/3239/64

5/841/6421/32

43/6411/1645/6423/3247/64

3/449/6425/3251/6413/16

53/6427/3255/64

7/857/64

29/3259/6415/1661/6431/32

63/641

0.515 6250.531 2500.546 8750.562 5000.578 125

0.593 7500.609 3750.625 0000.640 6250.656 250

0.671 8750.687 5000.703 1250.718 7500.734 375

0.750 0000.765 6250.781 2500.796 8750.812 500

0.828 1250.843 7500.859 3750.875 0000.890 625

0.906 2500.921 8750.937 5000.953 1250.968 750

0.984 3751.000 000

13.096 87513.493 75013.890 62514.287 50014.684 375

15.081 25015.478 12515.875 00016.271 87516.668 750

17.065 62517.462 50017.859 37518.256 25018.653 125

19.050 00019.446 87519.843 75020.240 62520.637 500

21.034 37521.431 25021.828 12522.225 00022.621 875

23.018 75023.415 62523.812 50024.209 37524.606 250

25.003 12525.400 000


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Metric Practice/235

Tab

le 1

8.8

Pre

ssur

e an

d S

tres

s E

quiv

alen

ts—

psi a

nd k

si to

kP

a an

d M

Pa

1 ps

i = 6

894.

757

Pa

To c

onve

rt p

si to

pas

cals

, mul

tiply

the

psi v

alue

by

6.89

4 75

7 ×

103

To c

onve

rt p

asca

ls to

psi

, div

ide

the

pasc

al v

alue

by

6.89

4 75

7 ×

103

psi o

r ks

i

01

23

45

67

89

kPa

or M

Pa

00.

0000

6.89

4813

.789

520

.684

327

.579

034

.473

841

.368

548

.263

355

.158

162

.052

810

68.9

476

75.8

423

82.7

371

89.6

318

96.5

266

103.

4214

110.

3161

117.

2109

124.

1056

131.

0004

2013

7.89

5114

4.78

9915

1.68

4715

8.57

9416

5.47

4217

2.36

8917

9.26

3718

6.15

8419

3.05

3219

9.94

8030

206.

8427

213.

7375

220.

6322

227.

5270

234.

4217

241.

3165

248.

2113

255.

1060

262.

0008

268.

8955

4027

5.79

0328

2.68

5028

9.57

9829

6.47

4630

3.36

9331

0.26

4131

7.15

8832

4.05

3633

0.94

8333

7.84

3150

344.

7379

351.

6326

358.

5274

365.

4221

372.

3169

379.

2116

386.

1064

393.

0012

399.

8959

406.

7907

6041

3.68

5442

0.58

0242

7.47

4943

4.36

9744

1.26

4544

8.15

9245

5.05

4046

1.94

8746

8.84

3547

5.73

8270

482.

6330

489.

5278

496.

4225

503.

3173

510.

2120

517.

1068

524.

0015

530.

8963

537.

7911

544.

6858

8055

1.58

0655

8.47

5356

5.37

0157

2.26

4857

9.15

9658

6.05

4459

2.94

9159

9.84

3960

6.73

8661

3.63

3490

620.

5281

627.

4229

634.

3177

641.

2124

648.

1072

655.

0019

661.

8967

668.

7914

675.

6862

682.

5810

100

689.

4757

Rep

rint

ed b

y pe

rmis

sion

of A

STM

.


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

236/Metric Practice

Table 18.9 Conversions for Fahrenheit–Celsius Temperature Scales

Find the number to be converted in the center (boldface) column. If converting Fahrenheit degrees, readthe Celsius equivalent in the column headed “C°”. If converting Celsius degrees, read the Fahrenheitequivalent in the column headed “F°”.

˚C ˚F ˚C ˚F ˚C ˚F ˚C ˚F

–273 –459 –40.0 –400 –40 24.4 76 168.8 199 390 734–268 –450 –34.0 –300 –22 25.6 78 172.4 204 400 752–262 –440 –29.0 –200 –4 26.7 80 176.0 210 410 770–257 –430 –23.0 –100 14.0 27.8 82 179.6 216 420 788–251 –420 –17.8 0 32.0 28.9 84 183.2 221 430 806–246 –410 –16.7 2 35.6 30.0 86 186.8 227 440 824–240 –400 –15.6 4 39.2 31.1 88 190.4 232 450 842–234 –390 –14.4 6 42.8 32.2 90 194.0 238 460 860–229 –380 –13.3 8 46.4 33.3 92 197.6 243 470 878–223 –370 –12.2 10 50.0 34.4 94 201.2 249 480 896–218 –360 –11.1 12 53.6 35.6 96 204.8 254 490 914–212 –350 –10.0 14 57.2 36.7 98 208.4 260 500 932–207 –340 –8.9 16 60.8 37.8 100 212.0 266 510 950–201 –330 –7.8 18 64.4 43.0 110 230.0 271 520 968–196 –320 –6.7 20 68.0 49.0 120 248.0 277 530 986–190 –310 –5.6 22 71.6 54.0 130 266.0 282 540 1004–184 –300 –4.4 24 75.2 60.0 140 284.0 288 550 1022–179 –290 –3.3 26 78.8 66.0 150 302.0 293 560 1040–173 –280 –2.2 28 82.4 71.0 160 320.0 299 570 1058–168 –270 –454 –1.1 30 86.0 77.0 170 338.0 304 580 1076–162 –260 –436 0.0 32 89.6 82.0 180 356.0 310 590 1094–157 –250 –418 1.1 34 93.2 88.0 190 374.0 316 600 1112–151 –240 –400 2.2 36 96.8 93.0 200 392.0 321 610 1130–146 –230 –382 3.3 38 100.4 99.0 210 410.0 327 620 1148–140 –220 –364 4.4 40 104.0 100.0 212 414.0 332 630 1166–134 –210 –346 5.6 42 107.6 1040. 220 428.0 338 640 1184–129 –200 –328 6.7 44 111.2 110.0 230 446.0 343 650 1202–123 –190 –310 7.8 46 114.8 116.0 240 464.0 349 660 1220–118 –180 –292 8.9 48 118.4 121.0 250 484.0 354 670 1238–112 –170 –274 10.0 50 122.0 127.0 260 500.0 360 680 1256–107 –160 –256 11.1 52 125.6 132.0 270 518.0 366 690 1274–101 –150 –238 12.2 54 129.2 138.0 280 536.0 371 700 1292

–96 –140 –220 13.3 56 132.8 1430. 290 554.0 377 710 1310–90 –130 –202 14.4 58 136.4 149.0 300 572.0 382 720 1328–84 –120 –184 15.6 60 140.0 154.0 310 590.0 388 730 1346–79 –110 –166 16.7 62 143.6 1600. 320 608.0 393 740 1364–73 –100 –148 17.8 64 147.2 166.0 330 626.0 399 750 1382–68 –90 –130 18.9 66 150.8 171.0 340 644.0 404 760 1400–62 –80 –112 20.0 68 154.4 1770. 350 662.0 410 770 1418–57 –70 –94 21.1 70 158.0 1820. 360 680.0 416 780 1436–51 –60 –76 22.2 72 161.6 1880. 370 698.0 421 790 1454–46 –50 –58 23.3 74 165.2 1930. 380 716.0 427 800 1472

(Continued)


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Metric Practice/237

432 810 1490 738 1360 2480 1043 1910 3470 1349 2460 4460438 820 1508 743 1370 2498 1049 1920 3488 1354 2470 4478443 830 1526 749 1380 2516 1054 1930 3506 1360 2480 4496449 840 1544 754 1390 2534 1060 1940 3524 1366 2490 4514454 850 1562 760 1400 2552 1066 1950 3542 1371 2500 4532460 860 1580 766 1410 2570 1071 1960 3560 1377 2510 4550466 870 1598 771 1420 2588 1077 1970 3578 1382 2520 4568471 880 1616 777 1430 2606 1082 1980 3596 1388 2530 4586477 890 1634 782 1440 2624 1088 1990 3614 1393 2540 4604482 900 1652 788 1450 2642 1093 2000 3632 1399 2550 4622488 910 1670 793 1460 2660 1099 2010 3650 1404 2560 4640493 920 1688 799 1470 2678 1104 2020 3668 1410 2570 4658499 930 1706 804 1480 2696 1110 2030 3686 1416 2580 4676504 940 1724 810 1490 2714 1116 2040 3704 1421 2590 4694510 950 1742 816 1500 2732 1121 2050 3722 1427 2600 4712516 960 1760 821 1510 2750 1127 2060 3740 1432 2610 4730521 970 1778 827 1520 2768 1132 2070 3758 1438 2620 4748527 980 1796 832 1530 2786 1138 2080 3776 1443 2630 4766532 990 1814 838 1540 2804 1143 2090 3794 1449 2640 4784538 1000 1832 843 1550 2822 1149 2100 3812 1454 2650 4802543 1010 1850 849 1560 2840 1154 2110 3830 1460 2660 4820549 1020 1868 854 1570 2858 1160 2120 3848 1466 2670 4838554 1030 1886 860 1580 2876 1166 2130 3866 1471 2680 4856560 1040 1904 866 1590 2894 1171 2140 3884 1477 2690 4874566 1050 1922 871 1600 2912 1177 2150 3902 1482 2700 4892571 1060 1940 877 1610 2930 1182 2160 3920 1488 2710 4910577 1070 1958 882 1620 2948 1188 2170 3938 1493 2720 4928582 1080 1976 888 1630 2966 1193 2180 3956 1499 2730 4946588 1090 1994 893 1640 2984 1199 2190 3974 1504 2740 4964593 1100 2012 899 1650 3002 1204 2200 3992 1510 2750 4982599 1110 2030 904 1660 3020 1210 2210 4010 1516 2760 5000604 1120 2048 910 1670 3038 1216 2220 4028 1521 2770 5018610 1130 2066 916 1680 3056 1221 2230 4046 1527 2780 5036616 1140 2084 921 1690 3074 1227 2240 4064 1532 2790 5054621 1150 2102 927 1700 3092 1232 2250 4082 1538 2800 5072627 1160 2120 932 1710 3110 1238 2260 4100 1543 2810 5090632 1170 2138 938 1720 3128 1243 2270 4118 1549 2820 5108638 1180 2156 943 1730 3146 1249 2280 4136 1554 2839 5126643 1190 2174 949 1740 3164 1254 2290 4154 1560 2840 5144649 1200 2192 954 1750 3182 1260 2300 4172 1566 2850 5162654 1210 2210 960 1760 3200 1266 2310 4190 1571 2860 5180660 1220 2228 966 1770 3218 1271 2320 4208 1577 2870 5198

(Continued)

Table 18.9 (Continued)Conversions for Fahrenheit–Celsius Temperature Scales


˚C ˚F ˚C ˚F ˚C ˚F ˚C ˚F


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

238/Metric Practice

666 1230 2246 971 1780 3236 1277 2330 4226 1582 2880 5216671 1240 2264 977 1790 3254 1282 2340 4244 1588 2890 5234677 1250 2282 982 1800 3272 1288 2350 4262 1593 2900 5252682 1260 2300 988 1810 3290 1293 2360 4280 1599 2910 5270688 1270 2318 993 1820 3308 1299 2370 4298 1604 2920 5288693 1280 2336 999 1830 3326 1304 2380 4316 1610 2930 5306699 1290 2354 1004 1840 3344 1310 2390 4334 1616 2940 5324704 1300 2372 1010 1850 3362 1316 2400 4352 1621 2950 5342710 1310 2390 1016 1860 3380 1321 2410 4370 1627 2960 5360716 1320 2408 1021 1870 3398 1327 2420 4388 1632 2970 5278721 1330 2426 1027 1880 3416 1332 2430 4406 1638 2980 5396727 1340 2444 1032 1890 3434 1338 2440 4424 1643 2990 5414732 1350 2462 1038 1900 3452 1343 2450 4442 1649 3000 5432

°C = 5/9 (F – 32) °F = 9/5 C + 32

Table 18.9 (Continued)Conversions for Fahrenheit–Celsius Temperature Scales


˚C ˚F ˚C ˚F ˚C ˚F ˚C ˚F


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

239

A

Acoustic Emission Examination, 204Summary, 205

Austenitic Stainless Steel, 40

B

Base Metal Discontinuities, 63Delamination, 63Lamellar Tearing, 64Laminations, 63Seams and Laps, 64

C

Certification of Qualification, 17Chemical Tests, 100

Chemical Composition Tests, 100Corrosion Tests, 100

Codes and Other Standards, 217Applications, 218Consensus Standards, 220Definitions, 217Federal Government, 220Manufacturers’ Associations, 222Military and Federal Specifications, 221Sources, 217Unified Numbering System, 222

Communication, 3Computerization of Welding Inspection and

Quality, 93Summary, 97

Control Data, 93Hardware, 95Quality Assurance and Inspector Computer

Interfaces, 95Quality Trends Identification and Control

Charts, 97Software, 95Special Purpose Programs, 96

Statistical Process Control, 97Use of Computers, 95Welding Inspection Applications, 93

D

Delayed Cracking, 36Causes of Delayed Cracking, 36Low Temperature, 38Presence of Hydrogen, 37Presence of Stress, 37Susceptible Microstructure, 37

Destructive Testing of Welds, 99Bend Specimens, Welded Joints, 109Fillet Weld Test, 116Fracture Toughness Tests, 119Tensile Strength Test Specimens, 115Test Specimen, the, 82Testing of Qualification Welds, 82Welded Joints, 109

Discontinuities, Classifications of, 49Base Metal, 63Metallurgical, 62Procedure/Process, 50

Drawings, Specifications, and Manufacturing Instructions, Review of, 19

E

Eddy Current (Electromagnetic) Examination, 192

Advantages, 204Alternating Current Saturation, 199Application, 204Electric and Magnetic Properties of

Metals, 193Electrical Conductivity, 193Electromagnetic Examination, 202Electromagnetic Properties of Coils, 195Equipment Calibration and Quality

Assurance Standards, 203

Index


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

240/Index

General, 192History, 192Magnetic Induction, 195Properties of Eddy Currents, 196Theory, 192

Electrical Hazard

(See also

Safety), 27Electromagnetic Testing (ET), 26Evaluation of Test Results, 21

F

Ferrite Content Examination, 206Austenitic Stainless Steels, 207Behavior in Welding, 208Delta Ferrite Verification and

Measurement, 207Effects of Ferrite Content, 206Ferrite Values and Testing, 209

Ferrous Welding Metallurgy, 33

I

Image Quality Indicators, 149Inspection By Radiographic Examination, 134

Acceptance Criteria, 155Advantages, 156Coverage Requirements, 155Essential Elements, 136Exposure Geometry, 148Exposure Techniques, 151Film Artifacts, 154Film Contrast, 146Film Viewing Conditions, 154Graininess of the Film, 149Interpretation of Radiographs, 153Limitations, 156Object to be Radiographed, 137Pitfalls in Interpretation, 155Procedure Approvals, 156Processing the Film, 140Radiographic Acceptance Standards in

Specification, Codes, and Other Standards, 155

Radiographic Contrast, 143Radiographic Definition, 148Radiographic Techniques, 143Radiographs of Weld Discontinuities, 156Skilled Person to Interpret the Radiograph,

142Source of Radiation, 136

Subject Contrast, 143Technique Conditions, 155Trained Person to Produce an Acceptable

Radiograph, 139X-Ray Film Enclosed in a Lightproof Film

Holder (Cassette), 137Inspection by Visual Examination, 125Inspection Safety Considerations

(See also

Safety), 25Inspector Classifications, 13Inspector, Welding Attributes, 13

Ethical, 15Personal, 16Physical, 14Technical, 14

L

Lamellar Tearing, 41Avoidance, 42Causes, 42Design to Avoid Through-Thickness

Stress, 43Fabricating Techniques, 43Joint Design, 42Joint Restraint, 42Material, 42Material Selection, 43Welding Procedures, 43

Leak Examination, 205Acoustic Methods, 206Bubble Testing, 206Flow Detection, 206Gas Specific Detectors, 206Techniques, 206

Liquid Penetrant Testing (PT), 25

M

Magnetic Characteristics, Change in, 187Magnetic Particle Testing (MT), 25Magnetic-Particle Examination, 172

Alternating Current, 179Amount of Magnetizing Current, 179Common Applications, 183Continuous Method Sequence of

Operations, 180Crater Cracks, 185Demagnetization, 182Direct Current, 180


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Index/241

Dry Method, 180Equipment, 183Evaluation, 187Inadequate Joint Penetration or Gap

Between Plates at the Weld Root, 185

Incomplete Fusion, 185Inspection Media, 180Inspection of Large Weldments, 183Inspection of Light Weldments (Aircraft

Type), 184Interpretation of Patterns, 184Irrelevant Indications, 186Longitudinal Magnetization, 177Orientation of Magnetic Field, 177Overall Circular Magnetization, 177Plate Inspection, 184Principles, 173Prod Magnetization, 178Repair or Rework Examination, 184Residual Method Sequence of Operations,

180Seams, 186Slag Inclusions, 186Standards, 187Subsurface Discontinuity Indications, 185Subsurface Porosity, 185Surface Cracks, 185Type of Magnetizing Current, 179Undercut, 185Wet Method, 181

Magnetic-to-Nonmagnetic Metal, 187Master Chart of Welding, Allied Processes,

and Thermal Cutting, 6Materials with Differing Magnetic Properties,

187Mechanical Tests, 102

Brinell, 104Ductility, 108Hardness Tests, 103Mechanical Properties, 103Rockwell, 104Standard Tension Test, 109Summary, 105Tensile Strength, 106Vickers, 105Yield Point, 106Yield Strength, 106

Metallographic Tests, 100

Macro Specimens, 101Micro Specimens, 101

Metallurgical Considerations, Other, 43Metallurgical Discontinuities, 62

Base Metal Properties, 62Chemistry, 63Corrosion Resistance, 63Mechanical Properties, 62Tensile Strength, 62Yield Strength, 62

Metric Practice, 227Conversions—General, 227Introduction, 227Units, 227Welding—Recommended Units and

Conversion Factors, 227

N

Nondestructive Examination Methods, 125Introduction, 125References and Suggested Reading

Material, 213Nondestructive Examination Procedures, 211

Engineering a Procedure, 211NDE Procedures Categories, 212Procedure Mechanics, 213Specifications, Codes, and Other

Standards, 211

P

Penetrant Examination, 187Applications, 190Comparator Application, 192Evaluation of Indications, 192Fluorescent Penetrant Method, 188Liquid Penetrant Comparator, 191Technique, 188Visible Dye Penetrant Methods, Type B,

189Performance Qualification Requirements, 81

Essential Variables, 81Personnel, Verification of Approved

Procedures for Qualifying Welding and Inspection, 21

Physical Contour, 186Postweld Heat Treating (PWHT), 46

Heat Treating Inspection, 47Precautions, 47


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

242/Index

Preheating, 45Preparation of Test Reports and Maintenance

of Records, 22Prevention of Delayed Cracking, 38

Controlling the Presence of Hydrogen, 38Microstructural, 39Restraint, 39Temperature, 39

Procedure/Process Discontinuities, 50Base Metal Cracking, 59Concavity, 54Convexity, 52Cracks, 57Distortion, 50Final Dimensions, 51Geometric, 50Inclusions, 56Incomplete Fusion, 54Incomplete Joint Penetration, 54Misalignment, 50Overlap, 51Porosity, 60Surface Irregularities, 61Undercut, 56Underfill, 56Weld Metal Cracking, 57Weld Profile, 52Weld Reinforcement, 54Weld Size, 51Weld/Structural, 54

Production Test Samples, Selection and Examination of, 21

Proof Tests, 123Hardness Test, 123Nondestructive Examination, 123

Q

Qualification of Nondestructive Examination Personnel, 215

Level I, 215Level II, 215Level III, 215

Qualification of Welders and Welding Operators, 81

Qualification of Welding Procedure Specifications, 68

Employment of Mock-up Tests, 73

Employment of Prequalified Welding Procedures, 68

Employment of Standard Qualification Tests, 73

Qualification Records, 84Qualifications, Procedure and Personnel

Verification of, 20Quality Assurance, 29Quality Assurance Program, 29

Audits, 31Document Control, 30Identification and Control of Material, 30Inspection, 30Nonconforming Materials or Items, 31Organization Requirements, 29Process Control, 30Purchasing, 29Records, 31

Quality Assurance/Quality Control Program, Review of the Manufacturer’s Approved, 19

R

Radiographic Testing (RT), 26Access Control, 26Radiation Monitoring, 26

Recording the Indications, 183

S

Safety Guidelines, Observance and Monitoring of Recommended, 23

Safety Information, General, 27Scope and Application, Handbook, 1Standardization of Tests, 84Standards Developers, 219

American Association of State Highway and Transportation Officials, 219

American Bureau of Shipping, 219American Institute of Steel Construction,

219American National Standards Institute,

219American Petroleum Institute, 219American Railway Engineering

Association, 219American Society of Mechanical

Engineers, 219American Water Works Association, 220


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

Index/243

American Welding Society, 220Association of American Railroads, 220ASTM, 220Canadian Standards Association, 220Compressed Gas Association, 220International Organization for

Standardization, 221National Board of Boiler and Pressure

Vessel Inspectors, 221National Fire Protection Association, 221Pipe Fabrication Institute, 221Society of Automotive Engineers, 221Underwriter’s Laboratories, Inc., 222

Steel, Carbon, 33Steels, Low-Alloy, 36Symbols, 3

Nondestructive Examination, 6

T

Training Welder, or Welding Operator, 84

U

Ultrasonic Examination of Welds and Weld Related Materials, 158

Calibration, 163Coupling, 168Determinate Variables, 165Equipment, 158Equipment Qualification, 160Equipment Selection, 168Flaw Location and Interpretation, 168General Principle, 158Geometry, 160Interpretation, 159Procedures, 169Reporting, 172Sound Behavior, 159Ultrasonic Attenuation and Wave Form,

160Ultrasonic Testing (UT) and Acoustic

Emission Testing (AET), 26

V

Visual Examination Practice, 129Examination During Welding, 130Examination Prior to Welding, 129Inspection After Welding, 132

Marking Welds For Repair, 133Summary, 133

Visual Testing (VT), 25

W

Weld and Weld Related Discontinuities, 49General, 49

Welder Performance, 84Welding Certification, 84Welding Inspection Operations, 19Welding Inspector, Attributes, 13

Completing and Maintaining Inspection Records, 17

Conflict of Interest, 16Inspection Experience, 15Integrity, 15Interpretation of Drawings and

Specifications, 14Knowledge of Examination Methods, 15Knowledge of Welding, 15Learning Potential, 17Physical Condition, 14Professional Attitude, 16Public Statements, 16Responsibility to the Public, 15Solicitation of Employment, 16Technical Ability, 14

Welding Inspector, Requirements for the, 13Welding Procedure Specifications, 65

Arc Voltage and Travel Speed, 66Base Metals and Applicable Specifications,

66Description and Important Details, 65Heat Input, 67Joint Designs and Tolerances, 66Joint Preparation and Cleaning of Surfaces

for Welding, 66Joint Welding Details, 67Peening, 67Positions of Welding, 67Post Weld Heat Treatment, 68Preheat and Interpass Temperatures, 67Prequalified WPSs, 68Removal of Weld Sections for Repair, 67Repair Welding, 68Root Preparation Prior to Welding From

Second Side, 67Scope, 66


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---

244/Index

Standard WPSs, 68Summary of Important Details, 68Tack Welding, 67Type of Current and Current Range, 66Type, Classification, Composition, and

Storage of Filler Metals, 66Welding Processes, 66

Welding Procedure, Steps for Qualification of, 73

Approval of Qualification Tests and Procedure Specifications, 79

Changes in a Qualified Procedure, 74

Evaluation of Test Results, 74

Preparation of Procedure Qualification Test Joints, 73

Testing of Procedure Qualification Welds, 73


--`,```,,``,,`,`,``,,,,``````,-`-`,,`,,`,`,,`---