cwip 3.2 notları 1.pdf

8/11/2019 CWIP 3.2 Notlar 1.pdf

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SENIOR WELDING INSPECTION

CONTENTS

Section Subject

1.0 Duties of the Senior Welding Inspector

2.0 Terms and Defin itions

3.0 Planning

4.0 Codes and Standards

5.0 Calibration of Welding Equipment

6.0 Destructive Testing

7.0 Heat Treatment

8.0 WPS and Welder Qualifications

9.0 Materials Inspection

10.0 Residual Stress and Distor tion

11.0 Weldabil ity of Steels

12.0 Weld Fractures

13.0 Welding Symbols

14.0 NDT

15.0 Welding Consumables

16.0 GMAW

17.0 SMAW

18.0 SAW

19.0 GTAW

20.0 Weld Imperfections

21.0 Weld Repairs

22.0 Welding Safety

23.0 Appendices

Rev 1 Jul 08Senior Welding Inspection

CopyrightTWI Ltd 2008


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Section 1

Duties of the Senior Welding Inspector


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1 General

The Senior Welding Inspector has primarily a supervisory/managerial role,which could encompass the management and control of an inspectioncontract. The role would certainly include leading a team of Welding

Inspectors, who will look to the Senior Welding Inspector for guidance,especially on technical subjects. The Senior Welding Inspector will beexpected to give advice, resolve problems, take decisions and generallylead from the front, sometimes in difficult situations.

The attributes required by the Senior Welding Inspector are varied and theemphasis on certain attributes and skills may differ from project to project.Essentially though the Senior Welding Inspector will require leadershipskills, technical skills and experience.

2 Leadership Skills

Some aspects on the theory of leadership may be taught in the classroom,but leadership is an inherent part of the character and temperament of anindividual. Practical application and experience play a major part in thedevelopment of leadership skills and the Senior Welding Inspector shouldstrive to improve and fine tune these skills at every opportunity.

The skills required for the development of leadership include:

A willingness and ability to accept instructions or orders from senior staffand to act in the manner prescribed.

A willingness and ability to give orders in a clear and concise manner,whether verbal or written, which will leave the recipient in no doubt as towhat action or actions are required.

A willingness to take responsibility, particularly when things go wrong,perhaps due to the Senior Welding Inspectors direction, or lack of it.

A capacity to listen (the basis for good communication skills) if and whenexplanations are necessary, and to provide constructive reasoning andadvice.

A willingness to delegate responsibility to allow staff to get on with thejob and to trust them to act in a professional manner. The SeniorWelding Inspector should, wherever possible, stay in the background,managing.

A willingness and ability to support members of the team on technicaland administrative issues.

Rev 1 July 2008Duties of the Senior Welding Inspector.

Copyright TWI Ltd 2008


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3 Technical Skills

A number of factors make up the technical skills required by the SeniorWelding Inspector and these are a knowledge of:

Technology; Normative documents;

Planning;

Organisation;

Auditing;

4 Knowledge of Technology

Welding technology knowledge required by the Senior Welding Inspector isvery similar to that required by the Welding Inspector, but with someadditional scope and depth.

Certain areas where additional knowledge is required are:

A knowledge of quality assurance and quality control.

A sound appreciation of the four commonly used non-destructive testingmethods.

A basic understanding of steel metallurgy for commonly weldedmaterials and the application of this understanding to the assessment offracture surfaces.

Assessment of non-destructive test reports, particularly the interpretationof radiographs.

5 Knowledge of Normative Documents

It is not a requirement for Inspectors at any level to memorise the content ofrelevant normative documents, except possibly with the exception of takingexaminations.

Specified normative documents (specifications, standards, codes ofpractice, etc) should be available at the workplace and the Senior WeldingInspector would be expected to read, understand and apply therequirements with the necessary level of precision and direction required.

The Senior Welding Inspector should be aware of the more widely usedstandards as applied in welding and fabrication. For example:

BS EN ISO 15614 / ASME IX Standards for welding procedureapproval

BS 4872, BS EN 287 / ASME IX Standards for welder approval.

PED BS 5500 / ASME VIII Standards for quality of fabrication.

BS EN ISO 9000 2000 Standards for quality management.




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6 Knowledge of Planning

Any project or contract will require some planning if inspection is to becarried out effectively and within budget.

See unit: Planning for more detailed information.

7 Knowledge of Organisation

The Senior Welding Inspector must have good organisational skills in orderto ensure that the inspection requirements of any quality/inspection plan canbe met, within the allocated time, budget and using the most suitablepersonnel for the activity. Assessment of suitable personnel may requireconsideration of their technical, physical and mental abilities in order toensure that they are able to perform the tasks required of them. Otherconsiderations would include availability of inspection personnel at the time

required, levels of supervision and the monitoring of the inspectors activitiesform start to contract completion.

8 Knowledge of Quality/Auditing

There are many situations in manufacturing or on a project where the SeniorWelding Inspector may be required to carry out audits.

See section on: Quality Assurance/Quality Control and Inspection for moredetailed information.

9 Man ManagementAs mentioned above, the Senior Welding Inspector will have to direct andwork with a team of Inspection personnel which he may well have to pick.He will have to liaise with Customer representatives, sub-contractors andthird party Inspectors. He may have to investigate non-compliances, dealwith matters of discipline as well as personal matters of his staff.

To do this effectively he needs skills in man management.

10 Recruitment

When recruiting an individual or a team the SWI will first have to establishthe requirements of the work. Among them would be:

What skills are definitely required for the work and what additional oneswould be desirable?

Are particular qualifications needed?

Is experience of similar work desirable?

What physical attributes are needed?

Is the work local, in-shop, on-site, in a third world country?

Does the job require working unsociable hours being away from home

for long periods?




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Is the job for permanent staff or for a fixed term?

If overseas what are the leave and travel arrangements?

What is the likely salary?

During subsequent interviews the SWI will need to assess other aspects of

the candidates suitability:

Has he the ability to work on his own initiative?

Can he work as part of a team?

If overseas has the person been to a similar location?

What is his marital/home situation?

Are there any Passport/Visa problems likely?

11 Morale and Motivation

The morale of a workforce has a significant effect on its performance so theSWI must strive to keep the personnel happy and motivated and be able todetect signs of low morale.

Low morale can lead to among other things:

Poor productivity, less good workmanship, lack of diligence, taking shortcuts, ignoring safety procedures and higher levels of absenteeism.

The SWI needs to be able to recognise these signs and others such aspersonnel not starting work promptly, taking longer breaks, talking in groups

and grumbling about minor matters.

A good supervisor should not allow his workforce to get into such a state.

He must keep them motivated by:

His own demeanour does he have drive and enthusiasm or is heseen to have no energy and generally depressed. The workforce willreact accordingly.

Is he seen to be leading from the front in a fair and consistent manner?

Favouritism in the treatment of staff, on disciplinary matters, the

allocation of work, allotment of overtime, weekend working andholidays are common causes of problems

Keep them informed in all aspects of the job and their situation.Rumours of impending redundancies or cuts in allowances etc will notmake for good morale.




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12 Discipline

Any workforce must be working in a disciplined manner, normally to rulesand standards laid down in the Companys conditions of employment orrelevant company handbook. The SWI must have a good understanding of

these requirements and be able to apply them in a fair and equitablemanner.

He must have a clear understanding as to the limits of his authority knowing how far he can go in disciplinary proceedings.

The usual stages of disciplinary procedure are:

The quiet word

Formal verbal warning

Written warning

Possible demotion, transfer, suspension Dismissal with notice

Instant dismissal.

Usually after the written warning stage the matter will be handled by theCompanys Personnel or Human Resources Department.

It is of vital importance that the company rules are rigorously followed asany deviation could result in claims for unfair or constructive dismissal.

In dealing with disciplinary matters the SWI must:

Act promptly

Mean what he says

Treat everyone fairly and as an adult.

Avoid constant complaining on petty issues

Where there are serious breaches of company rules by one or two peoplethe rest of the workforce should be informed of the matter so that rumourand counter-rumours can be quashed.

Some matters of discipline may well arise because of incorrect workingpractices, passing off below quality work, signing for work which has notbeen done, etc.




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In all such cases the SWI will need to carry out an investigation and applydisciplinary sanctions to the personnel involved. To do this:

First establish the facts by interviewing staff, from the relevantrecords, by having rechecks on part of the job.

If any suspicions are confirmed, transfer/remove suspect personnelfrom the job pending disciplinary proceedings. If the personnel areemployed by a sub-contractor then a meeting with the sub-contractorwill be needed to achieve the same end.

Find out the extent of the problem, is it localised or widespread?

Is there need to inform the customer and third party inspector?

Formulate a plan of action, with other company departments wherenecessary, to retrieve the situation.

Carry out the necessary disciplinary measures on the personnelinvolved.

Convene a meeting with the rest of the workforce to inform them of thesituation and ensure that any similar lapses will be dealt with severely.

Follow up the meeting with a written memo.

13 Summary

The Senior Welding Inspectors role can be varied and complex, a numberof skills need to be developed in order for the individual to be effective in therole. Every Senior Welding Inspector will have personal skills and attributeswhich can be brought to the job, some of the skills identified above mayalready have been mastered or understood. The important thing for the

individual to recognise is not only do they have unique abilities which theycan bring to the role, but they also need to strive to be the best they can bystrengthening identifiable weak areas in their knowledge and understanding.Some ways in which these goals may be achieved is through:

Embracing facts and realities.

Being creative.

Being interested in solving problems.

Being pro-active not reactive

Having empathy with other people.

Having personal values.

Being objective.




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Section 2

Terms and Definitions


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Note:The following definitions are taken from BS 499-1:1991 Welding terms andsymbols Glossary for welding, brazing and thermal cutting

Welding:

An operation in which two or more parts are united by means of heat orpressure or both, in such a way that there is continuity in the nature of themetal between these parts.

Brazing:A process of joining generally applied to metals in which, during or afterheating, molten filler metal is drawn into or retained in the space betweenclosely adjacent surfaces of the parts to be joined by capillary attraction. In

general, the melting point of the filler metal is above 450C but always belowthe melting temperature of the parent material.

Braze welding:The joining of metals using a technique similar to fusion welding and a fillermetal with a lower melting point than the parent metal, but neither usingcapillary action as in brazing nor intentionally melting the parent metal.

Weld:A union of pieces of metal made by welding.

Joint:A connection where the individual components, suitably prepared andassembled, are joined by welding or brazing.

Rev 1 July 2008Terms and Definitions



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Type of joint Sketch Definition

Butt joint A connection between the endsor edges of two parts making an

angle to one another of 135 to

180inclusive in the region of thejoint

T joint A connection between the end oredge of one part and the face ofthe other part, the parts makingan angle to one another of more

than 5up to and including 90inthe region of the joint

Corner joint A connection between the endsor edges of two parts making anangle to one another of more

than 30but less than 135in theregion of the joint

Edge joint A connection between the edgesof two parts making an angle to

one another of 0to 30inclusive

in the region of the joint

Cruciform joint A connection in which two flatplates or two bars are welded toanother flat plate at right anglesand on the same axis

Lap joint A connection between twooverlapping parts making an

angle to one another of 0 to 5inclusive in the region of the weldor welds




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1 Types of Welds

1.1 From configuration point of view

Butt weld Fillet weld

Autogenous weld:A fusion weld made without filler metal. Can be achieved by TIG, plasmaelectron beam, laser or oxy-fuel gas welding.

Slot weld:A joint between two overlapping components made by depositing a filletweld round the periphery of a hole in one component so as to join it to thesurface of the other component exposed through the hole.

In a butt oint

In a T oint

In a corner oint

Butt weld




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Plug weld:A weld made by filling a hole in one component of a workpiece with fillermetal so as to join it to the surface of an overlapping component exposedthrough the hole (the hole can be circular or oval).

1.2 From the penetration point of view

Full penetration weld:A welded joint where the weld metal fully penetrates the joint with completeroot fusion. In US the preferred term is complete joint penetration weld or

CJP for short (see AWS D1.1.)

Partial penetration weld:A welded joint without full penetration. In US the preferred term is partialjoint penetration weld or PJP for short.

2 Types of Joint (see BS EN ISO 15607)

Homogeneous jo int:Welded joint in which the weld metal and parent material have no significantdifferences in mechanical properties and/or chemical composition. Example:two carbon steel plates welded with a matching carbon steel electrode.

Heterogeneous joint:Welded joint in which the weld metal and parent material have significantdifferences in mechanical properties and/or chemical composition. Example:a repair weld of a cast iron item performed with a nickel base electrode.

Dissimilar joint:Welded joint in which the parent materials have significant differences inmechanical properties and/or chemical composition. Example: a carbonsteel lifting lug welded onto an austenitic stainless steel pressure vessel.




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3 Features of the Completed Weld

Parent metal:Metal to be joined or surfaced by welding, braze welding or brazing.

Filler metal:Metal added during welding, braze welding, brazing or surfacing.

Weld metal:All metal melted during the making of a weld and retained in the weld.

Heat-affected zone (HAZ):The part of the parent metal that is metallurgically affected by the heat ofwelding or thermal cutting, but not melted.

Fusion line:

The boundary between the weld metal and the HAZ in a fusion weld. This isa non-standard term for weld junction.

Weld zone:The zone containing the weld metal and the HAZ.

Weld face:The surface of a fusion weld exposed on the side from which the weld hasbeen made.

Root:

The zone on the side of the first run farthest from the welder.

Toe:The boundary between a weld face and the parent metal or between runs.This is a very important feature of a weld since toes are points of high stressconcentration and often they are initiation points for different types of cracks(eg fatigue cracks, cold cracks). In order to reduce the stress concentration,toes must blend smoothly into the parent metal surface.

Excess weld metal:Weld metal lying outside the plane joining the toes. Other non-standardterms for this feature: reinforcement, overfill.




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Root

Parentmetal

Weldmetal

HAZ

Weldzone

Fusionline

Weldface Toe

Parent

metal

Excessweld metal

Excessweld metal

Butt weld

Fusionline

Weldmetal

Root

Parentmetal

HAZ

Weldzone

Weldface

Toe

Parentmetal

Excessweld metal

Fillet weld




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4 Weld Preparation

A preparation for making a connection where the individual components,suitably prepared and assembled, are joined by welding or brazing.

4.1 Features of the weld preparationAngle of bevel:The angle at which the edge of a component is prepared for making a weld.In case of a V preparation for a MMA weld on carbon steel plates, this angle

is between 25-30. In case of a U preparation for a MMA weld on carbon

steel plates, this angle is between 8-12. In case of a single bevelpreparation for a MMA weld on carbon steel plates, this angle is between

40-50.In case of a single J preparation for a MMA weld on carbon steel

plates, this angle is between 10-20.

Included angle:The angle between the planes of the fusion faces of parts to be welded. Inthe case of single V, single U, double V and double U this angle is twice thebevel angle. In case of single bevel, single J, double bevel and double J, theincluded angle is equal to the bevel angle.

Root face:The portion of a fusion face at the root that is not bevelled or grooved. Itsvalue depends on the welding process used, parent material to be weldedand application; for a full penetration weld on carbon steel plates, it has avalue between 1-2mm (for the common welding processes).

Gap:The minimum distance at any cross section between edges, ends orsurfaces to be joined. Its value depends on the welding process used andapplication; for a full penetration weld on carbon steel plates, it has a valuebetween 1-4mm.

Root radius:The radius of the curved portion of the fusion face in a component preparedfor a single J, single U, double J or double U weld. In case of MMA,MIG/MAG and oxyfuel gas welding on carbon steel plates, the root radiushas a value of 6mm in case of single and double U preparations and 8mm incase of single and double J preparations.

Land:The straight portion of a fusion face between the root face and the curvedpart of a J or U preparation. Can be 0. Usually present in case of weldpreparations for MIG welding of aluminium alloys.




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4.2 Types of preparation

Open square butt preparation

This preparation is used for welding thin components, either from one sideor both sides. If the root gap is zero (ie if components are in contact), thispreparation becomes a closed square butt preparation (unrecommendeddue to the lack of penetration problems!).

Single V preparation

The V preparation is one of the most common preparations used in welding;it can be produced using flame or plasma cutting (cheap and fast). Forthicker plates a double V preparation is preferred since it requires less fillermaterial to complete the joint and the residual stresses can be balanced onboth sides of the joint resulting in lower angular distortion.

Angle ofbevel

Included angle

Gap Root face


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Double V preparation

The depth of preparation can be the same on both sides (symmetric doubleV preparation) or the depth of preparation can be deeper on one sidecompared with the opposite side (asymmetric double V preparation).Usually, in this situation the depth of preparation is distributed as 2/3 of thethickness of the plate on the first side with the remaining 1/3 on thebackside. This asymmetric preparation allows for a balanced welding

sequence with root back gouging, giving lower angular distortions. Whilstsingle V preparation allows welding from one side, double V preparationrequires both sides access (the same applies for all double sidepreparations).

Single U preparation

U preparation can be produced only by machining (slow and expensive).However, tighter tolerances obtained in this case provide for a better fit-upthan in the case of V preparations. Usually it is applied for thicker platescompared with single V preparation (requires less filler material to completethe joint and this lead to lower residual stresses and distortions). Similar withthe V preparation, in case of very thick sections a double U preparation canbe used.

Included angle

Angle ofbevel

Root

radius

Root faceGap

Land




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Double U preparation

Usually this type of preparation does not require a land (exception:aluminium alloys).

Single V preparation with backing strip

Backing strips allow the production of full penetration welds with increasedcurrent and hence increased deposition rates/productivity without thedanger of burn-through. Backing strips can be permanent or temporary.Permanent types are of the same material being joined and are tack weldedin place. The main problems related with this type of weld are poor fatigueresistance and the probability of crevice corrosion between the parent metaland the backing strip. It is also difficult to examine by NDT due to the built-increvice at the root of the joint. Temporary types include copper strips,ceramic tiles and fluxes.

Single bevel preparation




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Double bevel preparation

Single J preparation

Double J preparation

All these preparations (single/double bevel and single/double J) can be usedon T joints as well. Double preparations are recommended in case of thicksections. The main advantage of these preparations is that only onecomponent is prepared (cheap, can allow for small misalignments).

For further details regarding weld preparations, please refer to BS EN ISO

9692 standard.




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5 Size of But t Welds

Full penetration but t weld

Partial penetration butt weld

Actual throatthickness

Design throatthickness

As a general rule:

Actual throat thickness = design throat thickness + excess weld metal.

Full penetration butt weld ground flush

Butt weld between two plates of d ifferent thickness

Actual throat thickness=design throatthickness



Actual throat thickness =maximumthicknessthrough the joint

Design throat thickness= thickness ofthethinner plate

Run (pass):

The metal melted or deposited during one passage of an electrode, torch orblowpipe.

Single run weld Multi run weldLayer:

A stratum of weld metal consisting of one or more runs.




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Types of butt weld (from accessibil ity poin t of view):

Single side weld Double side weld

6 Fillet Weld

A fusion weld, other than a butt, edge or fusion spot weld, which isapproximately triangular in transverse cross section.

6.1 Size of fil let welds

Unlike butt welds, fillet welds can be defined using several dimensions.

Actual throat th ickness:The perpendicular distance between two lines, each parallel to a line joiningthe outer toes, one being a tangent at the weld face and the other beingthrough the furthermost point of fusion penetration

Design throat thickness:The minimum dimension of throat thickness used for purposes of design.Also known as effective throat thickness. Symbolised on the drawing with

a.

Leg length:The distance from the actual or projected intersection of the fusion facesand the toe of a fillet weld, measured across the fusion face. Symbolised onthe drawing with z'.

Leg length



Leg length




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6.2 Shape of fil let welds

Mitre fillet weld:A flat face fillet weld in which the leg lengths are equal within the agreedtolerance. The cross section area of this type of weld is considered to be a

right angle isosceles triangle with a design throat thickness a and a leglength z. The relation between design throat thickness and leg length is:

a = 0,707 z. or z = 1,41 a.

Convex fi llet weld:A fillet weld in which the weld face is convex. The above relation betweenthe leg length and the design throat thickness written in case of mitre filletwelds is also valid for this type of weld. Since there is an excess weld metalpresent in this case, the actual throat thickness is bigger than the designthroat thickness.

Concave fillet weld:A fillet weld in which the weld face is concave. The above relation betweenthe leg length and the design throat thickness written in case of mitre fillet

welds is not valid for this type of weld. Also, the design throat thickness isequal to the actual throat thickness. Due to the smooth blending betweenthe weld face and surrounding parent material, the stress concentrationeffect at the toes of the weld is reduced compared with the previous type.This is why this weld is highly desired in case of applications subjected tocyclic loads where fatigue phenomena might be a major cause for failure.




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Asymmetrical fi llet weld :A fillet weld in which the vertical leg length is not equal with the horizontalleg length. The relation between the leg length and the design throatthickness written in case of mitre fillet welds is not valid for this type of weldbecause the cross section is not an isosceles triangle.

Throatsize

Verticalleg size

Horizontal

leg size

Deep penetration fillet weld:A fillet weld with a deeper than normal penetration. It is produced using highheat input welding processes (ie SAW or MAG with spray transfer). Thistype of weld uses the benefits of greater arc penetration to obtain therequired throat thickness whilst reducing the amount of deposited metalneeded, thus leading to a reduction in residual stress level. In order toproduce a consistent and constant penetration, the travel speed must bekept constant, at a high value. As a consequence, this type of weld isusually produced using mechanised or automatic welding processes. Also,the high depth-to-width ratio increases the probability of solidificationcentreline cracking. In order to differentiate this type of welds from theprevious types, the throat thickness is symbolised with s instead of a.




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6.3 Compound of but t and fil let welds

A combination of butt and fillet welds used in case of T joints with full orpartial penetration or butt joints between two plates with different thickness.Fillet welds added on top of the groove welds improve the blending of weld

face towards parent metal surface and reduce the stress concentration atthe toes of the weld.

Double bevel compound weld

Filletweld

Bevelweld

7 Welding Posit ion, Weld Slope and WeldRotation

Weld posi tion:The orientation of a weld expressed in terms of working position, weld slopeand weld rotation (for further details, please see ISO 6947).

Weld slope:The angle between root line and the positive X axis of the horizontalreference plane, measured in mathematically positive direction (ie counter-

clockwise).

Weld rotationThe angle between the centreline of the weld and the positive Z axis or aline parallel to the Y axis, measured in the mathematically positive direction

(ie counter-clockwise) in the plane of the transverse cross section of theweld in question.




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Welding position Sketch Definition

Flat A welding position in whichthe welding is horizontal,with the centreline of

the weld vertical. Symbolaccording ISO 6947 PA.

Horizontal-vertical A welding position in whichthe welding is horizontal(applicable in case of filletwelds). Symbol accordingISO 6947 PB

Horizontal A welding position in whichthe welding is horizontal,with the centreline of theweld horizontal. Symbolaccording ISO 6947 PC

Vertical up A welding position in which

the welding is upwards.Symbol according ISO 6947 PF.

Vertical down A welding position in whichthe welding is downwards.Symbol according ISO 6947 PG

Overhead A welding position in which

the welding is horizontal andoverhead, with the centre-line of the weld vertical.Symbol according ISO 6947 PE.

Horizontal-overhead

A welding position in whichthe welding is horizontal andoverhead (applicable incase of fillet welds). Symbolaccording ISO 6947 PD.

PG

PF




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Tolerances for the welding positions

8 Weaving

Transverse oscillation of an electrode or a blowpipe nozzle during thedeposition of weld metal. This technique is generally used in case of vertical

up welds.

Stringer bead:

A run of weld metal made with little or no weaving motion.




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Section 3

Planning


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1 General

The Senior Welding Inspector would almost certainly be involved in planningfor inspection at one or more of the following stages of a project;

Pre-contract Identification of the job requirements, recruiting andallocating suitably trained and qualified staff, gathering together

relevant normative documents, technical data and drawings, producingwork/inspection schedules and quality plans as well as generaladministration.

In-contract Application of inspection methodologies to therequirements of the contract specification, production and collection ofinspection and test reports/documentation.

Post-contract Compilation of inspection reports, certification and testdata.

There are a number of methods of planning for inspection activities, themethod selected being dependant on a number of factors, primarily therequirements of the client and the specific project.

The various methods are as follows;

In-situ inspection; an inspector(s) placed permanently at the work place. Theinspector would be expected to work independently, responsible for usingthe allocated inspection time in a useful and expedient manner. Periodicvisits to the work place would be made by the Senior Inspector.

2 Gantt ChartsGantt charts define stages of production and estimated work time for eachstage.

A Gantt chart is a popular type of bar chart/graph that illustrates a projectscheduleie list of a project's terminal elements. Terminal elements comprisethe work breakdown structure (WBS) of the project and are the lowestactivity or deliverable, with intended start and finish dates. Terminalelements are not further subdivided,

Terminal elements are the items that are estimated in terms of resourcerequirements, budget and duration linked by dependencies and schedules.

An example of a typical Gantt chart that could be used to plan inspectionactivities for either manufacturing or construction is shown below.

The WBS/task elements are listed on the left hand side and the start andcompletion of each activity is represented by a bar to the right of the activity.

The time period in this example is represented in months, both planned andactual. Some Gantt charts may show time in weeks, which can also bebroken down into days.

Rev 1 July 2008Planning.

http://../wiki/Bar_charthttp://../wiki/Schedule_%28project_management%29http://../wiki/Schedule_%28project_management%29http://../wiki/Projecthttp://../wiki/Terminal_elementhttp://../wiki/Work_breakdown_structurehttp://../wiki/Work_breakdown_structurehttp://../wiki/Terminal_elementhttp://../wiki/Projecthttp://../wiki/Schedule_%28project_management%29http://../wiki/Schedule_%28project_management%29http://../wiki/Bar_chart


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3 Critical Path Analysis (CPA)

Critical path analysis (CPA) is a powerful project management tool thathelps to schedule and manage complex projects. Developed in the 1950s tocontrol large defence projects, CPA has been used routinely since then. As

with Gantt charts, CPA helps plan all tasks that must be completed as partof a project. They act as the basis both for preparation of a schedule, and ofresource planning. During management of a project, they allow monitoringof achievement of project goals.

CPA can also show where remedial action needs to be taken in order to geta project back on course.

The benefit of using CPA over Gantt charts is that CPA formally identifiestasks which must be completed on time in order for the whole project to becompleted on time, and also identifies which tasks can be delayed for a

while if resources needto be reallocated to catch up on missed tasks.

A further benefit of CPA is that it helps to identify the minimum length of timeneeded to complete a project. Where there is a need to run an acceleratedproject, fast track, it helps to identify which project steps should beaccelerated in order to complete the project within the available time. Thishelps to minimise cost while still achieving objectives.

The disadvantage of CPA is that the relation of tasks to time is not asimmediately obvious as with Gantt charts. This can make them more difficultto understand for someone who is not familiar with the technique.

CPA are presented using circle and arrow diagrams. These circles showevents within the project, such as the start and finish of tasks. Circles arenormally numbered to allow identification of them. An arrow runningbetween two event circles shows the activity needed to complete that task.A description of the task is written underneath the arrow. The length of thetask is shown above it. By convention, all arrows run left to right.

An example of a very simple diagram is shown below:

This shows the start event (circle 1), and the completion of the Recruit &allocate inspection staff task (circle 2). The arrow between the two circlesshows the activity of carrying out Recruit & allocate inspection staff. Thetime allocated for this activity is 4 weeks.

1 24 Wks

Recruit & allocate

inspection

staffSimple Circle and Arrow

0 4A

START




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In the example above, the numbers above the circles show the earliestpossible time that this stage of the project will be reached.

Where one activity cannot start until another has been completed and whenother activities need to be scheduled it is useful to tabulate the terminal

elements and allocate time against each activity. For example the inspectionactivities for a project could be shown as:

The above tabulated terminal elements can now be shown as an algorithm,see the following example

IDENTIFICATIO

NTERMINAL ELEMENT /

ACTIVITY

SCHEDULED

COMPLETION

TIME

ALLOCATED

A Recruit & allocateins ection staff To be completed first 4 weeks

B

Review fabrication

drawings, material &

consumable certificates

Start when A is

completed 2 weeks

CReview WPSs, WPQRs

& WATCs Start when A is

completed 2 weeks

D

Witness & test WPSs &

WPQRs

Start when B is

completed

3 weeks

E

Witness welder qualificationtests

Start when C is

completed 2 weeks

F

Prepare quality plans &

identify inspection

requirements

Start when C, D & Eare completed

2 weeks

GVisual inspection andtesting of production

welds

Start when F is

completed 9 weeks

TOTAL TIME ALLOCATED 24 weeks


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Critical path analysis for inspection project.

1 2 3 5 6

4

AB D

CE

F

4 Wks 2 Wks 3 Wks 2 Wks

2

Wks

2

Wks0 4 6

6

11 13

ev 1 Jul 08Planning.


START

R


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In the example, the activities of B & C' cannot be started until 'A' has beencompleted.

This diagram also brings out a number of other important points:

Within CPA, reference to activities is made by the numbers in thecircles at each end. For example, task A would be called 'activity 1 to2'.

Task 'B' would be 'activity 2 to 3'.

Activities are not drawn to scale. In the diagram above, activities are 8,4, 3 and 2 weeks long.

In the example the numbers above the circles indicate the earliestpossible time that this stage in the project will be reached.

CPA is an effective and powerful method of assessing:

What tasks must be carried out

Where parallel activity can be performed

The shortest time in which you can complete a project

Resources needed to execute a project

The sequence of activities, scheduling and timings involved

Task priorities

The most efficient way of shortening time on urgent projects.

An effective Critical Path Analysis can make the difference between

success and failure on complex projects. It can be very useful forassessing the importance of problems faced during the implementation ofthe plan.

4 Programme Evaluation and Review Technique (PERT)

PERT is a variation on CPA but takes a slightly more sceptical view of timeestimates made for each project stage. To use it, estimate the shortestpossible time each activity will take, the most likely length of time, and thelongest time that might be taken if the activity takes longer than expected.

The formula below is used to calculate the time for each project stage:

Shortest time + 4 x likely time + longest time6

This helps to bias time estimates away from the unrealistically short time-scales normally assumed.

A variation of both CPA and PERT is a technique known as reversescheduling, which the completion date for the last terminal element for theproject is determined and then all other operations are worked back from

this date, each operation having its own target date.

Rev 1 Jul 08Planning.



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Rev 1 Jul 08Planning.


5 Summary

The Senior Welding Inspector doe not need to have an in-depth knowledgeof planning and would not be responsible for the planning of inspectionactivities on a large project or contract, this would be the responsibility of

the planning team or planning department.IHowever the SWI does need to have a basic understanding of projectplanning as inspection tasks must link in with other terminal activities toensure that inspection tasks are carried out on a timely and cost effectivebasis, in accordance with the planning system being used on a particularproject or contract.


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Section 4

Codes and Standards


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GeneralThe control of quality in a fabrication and welding situation is achieved byworking to company procedures and codes of construction or standards.The latter may be international, national, companys own or specific to theparticular client or contract.

Company procedures are usually covered in Quality Manuals the scope ofwhich may vary widely depending upon the size of company, its range ofwork, its working practices and many other factors.

1 Company Manuals

1.1 Quality assurance manual

Quality assurance is defined in IS0 9000 as; part of quality managementfocused on providing confidence that quality requirements will be fulfilled.

Essentially what the QA manual sets out is how the company is organised,to lay down the responsibilities and authority of the various departments,how these departments interlink. The manual usually covers all aspects ofthe company structure, not just those aspects of manufacture.

1.2 Quality control manual

Quality control is defined in ISO 9000 as; part of quality managementfocused on fulfilling quality requirements.

The QC manual will be the manual most often referred to by the SWI as itwill spell out in detail how different departments and operations areorganised and controlled.

Typical examples would be: production and control of drawings, howmaterials and consumables are purchased, how welding procedures areproduced, etc.

Essentially all operations to be carried out within the organisation will havecontrol procedures laid down.

In particular it will lay down how the Inspection function, whether visual,dimensional or NDT, will be performed. Inspection being defined as theactivity of measuring, examining and testing characteristics of a product orservice and comparing these to a specified requirement. Such requirementsare laid down in codes of practice and standards.

Rev 1 July 2008Codes and Standards



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2 Auditing

Auditing is a term originating from accountancy practice which involves anindependent accountant checking the accounts of a company to see if theaccounts are fair and accurate. A similar checking process is now widely

practised in manufacturing and construction industries and inspectionpersonnel will be involved in the carrying out of this operation.

Different types of audits may be performed:

Full audit of a company, usually carried out by a third party such as aCertifying Authority, checking the company for the award of a QAaccreditation system such as ISO 9000 or ASME Stamp.

Major audit by a potential customer prior to placement of a largecontract. This is usually carried out to demonstrate the company has allthe necessary facilities, plant, machinery, personnel and quality systems

in place to enable them to successfully complete the contract. Part audits carried out as ongoing demonstration that the quality system

is working properly.

An example of the latter case would be where a Senior Inspector isresponsible for signing-off the data book or release certificate for a product.After checking that all the necessary documents are in the package and thatthey have been correctly completed and approved where necessary, theSWI would look at a part of the job a beam, a piece of pipework etc andcrosscheck against the drawings, mill certificates, inspection reports etc thatall comply with the job requirements.

3 Codes and Standards

It is not necessary for the Inspector to carry a wide range of codes andstandards in the performance of his/her duties. Normally the specification ormore precisely the contract specification is the only document required.However the contract specification may reference supporting codes andstandards and the inspector should know where to access these normativedocuments.

The following is a list of definitions relating to codes and standards whichthe Inspector may come across whilst carrying inspection duties

3.1 Definitions

Normative document:A document that provides rules, guidelines or characteristics for activities ortheir results.

The term normative document is a generic term, which covers documentssuch as standards, technical specifications, codes of practice andregulations.*




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Standard:A document that is established by consensus and approved by a recognisedbody.

A standard provides, for common and repeated use, guidelines, rules, andcharacteristics for activities or their results, aimed at the achievement of theoptimum degree of order in a given context. *

Harmonised standards:Standards on the same subject approved by different standardising bodies,that establish interchangeability of products, processes and services, ormutual understanding of test results or information provided according tothese standards*

Code of practice:

A document that recommends practices or procedures for the design,manufacture, installation, maintenance, utilisation of equipment, structuresor products.

A code of practice may be a standard, a part of a standard or independentof a standard*

Regulation: A document providing binding legislative rules that is adopted by anauthority.*

Author ity: A body (responsible for standards and regulations legal or administrativeentity that has specific tasks and composition) that has legal powers andrights.*

Regulatory authority: Authority that is responsible for preparing or adopting regulations*

Enforcement authority:Authority that is responsible for enforcing regulations*

Specification:Document stating requirements. Meaning full data and its supportingmedium stating needs or expectations that is stated, generally implied orobligatory.**

Procedure:Specified way to carry out an activity or a process*. Usually it is a writtendescription of all essential parameters and precautions to be observed whenapplying a technique to a specific application following an establishedstandard, code or specification




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Instruction: A written description of the precise steps to be followed based on anestablished procedure, standard, code or specification.

Quality plan:A document specifying which procedures and associated resources shall beapplied by whom and when to a specific project, product, process orcontract*

* ISO IEC Guide 2 Standardisation and related activities General vocabulary** EN ISO 9000 2000 Quality management systems Fundamentals andvocabulary

4 Summary

Application of the requirements of the quality manuals, the standards andcodes of practice ensure that a structure or component will have anacceptable level of quality and be fit for the intended purpose.

Applying the requirements of a standard, code of practice or specificationcan be a problem for the inexperienced Inspector. Confidence in applyingthe requirements of one or all of these documents to a specific applicationonly comes with use over a period of time.

If in doubt the Inspector must always refer to a higher authority in order to

avoid confusion and potential problems.




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BS NUMBER TITLE

BS499: Part 1 Glossary of Welding Terms.

BS 709 Methods of destructive testing fusion welded joints and weld metal in steel.

BS 1113 Specification for design and manufacture of water-tube steam generatingplant.

BS 1453 Specification for filler materials for gas welding.

BS 1821 Specification for class I oxy -acetylene welding of ferritic steel pipe work forcarrying fluids.

BS 2493 Low alloy steel electrodes for MMA welding

BS 2633 Specification for class I arc welding of Ferritic steel pipe work for carryingfluids.

BS 2640 Specification for class II oxy - acetylene welding of carbon steel pipe workfor carrying fluids.

BS 2654 Specification for manufacture of vertical steel welded non-refrigeratedstorage tanks with butt-welded shells for the petroleum industry.

BS 2901 Part 3: Filler rods and wires for copper and copper alloys.

BS 2926 Specification for chromium & chromium-nickel steel electrodes for MMA

BS 2926 Specification for chromium & chromium-nickel steel electrodes for MMA

BS 3019 TIG welding.

BS 3604 Steel pipes and tubes for pressure purposes; Ferritic alloy steel withspecified elevated temperature properties for pressure purposes.

BS 3605 Specification for seamless tubes.

BS 4515 Specification for welding of steel pipelines on land and offshore.

BS 4570 Specification for fusion welding of steel castings.

BS 4677 Specification for arc welding of austenitic stainless steel pipe work forcarrying fluids.

BS 4872 Part 1: Approval testing of welders when procedure approval is not required. Fusionwelding of steel.

BS 4872 Part 2: TIG or MIG welding of aluminium and its alloys.

BS 6323 Specification for seamless and welded steel tubes for automobile,mechanical and general engineering purposes.

BS 6693 Method for determination of diffusible hydrogen in weld metal.

BS 6990 Code of practice for welding on steel pipes containing process fluids or theirresidues.

BS 7191 Specification for weldable structural steels for fixed offshore structures.

BS 7570 Code of practice for validation of arc welding equipment.




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BS EN NUMBER TITLE

BS EN 287 Part 1: Qualification test of welders - Fusion welding - Steels.

BS EN 440 Wire electrodes and deposits for gas shielded metal arc of non-alloyand fine grain s teels.

BS EN 499 Covered electrodes for manual metal arc welding of nonalloy and finegrain steels.

BS EN 3834-Parts 1 to 5

Quality requirements for fusion welding of metallic materials

BS EN 756 Wire electrodes and flux wire combinations for submerged arc welding ofnon-alloy and fine grain steels.

BS EN 760 Fluxes for submerged arc welding.

BS EN 970 Non-destructive examination of fusion welds - visual examination.

BS EN 910 Destructive tests on welds in metallic materials - Bend tests.

BS EN 12072 Filler rods and wires for stainless steels.

BS EN ISO 18274 Aluminium and aluminium alloys & magnesium alloys. Nickel & nickelalloys.

Note:The Inspector should have an awareness of s tandards that are printed in bold.

BS EN NUMBER TITLE

BS EN 1011Part 1:Part 2:Part 3

Part 4.

Welding recommendations for welding of metallic materials.General guidance for arc welding.Arc welding of ferr it ic steels.Arc welding of stainless steels

Arc welding of aluminium and aluminium alloys.EN 1320 Destructive tests on welds in metallic materials.

EN 1435 Non-destructive examination of welds - Radiographic examination of weldedjoints.

BS EN 10002 Tensile testing of metallic materials.

BS EN 10020 Definition and classification of grades of steel.

BS EN 10027 Designation systems for steels.

BS EN 10045 Charpy impact tests on metallic materials.

BS EN 10204 Metallic products - types of inspection documents.

BS EN 22553 Welded, brazed and soldered joints - symbol ic representation on

drawings.BS EN 24063 Welding, brazing, soldering and braze welding of metal. Nomenclature

of processes and reference numbers for symbolic representation ondrawings.

BS EN 25817 Arc welded joints in steel. Guidance on quality levels forimperfections.

BS EN 26520 Classifi cation of imperfections in metallic fusion welds, withexplanations.

BS EN 26848 Specification for tungsten electrodes for inert gas shielded arc welding andfor plasma cutting and welding.




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ISO NUMBER: TITLE:

ISO 857 - 1 Welding and allied processes - Vocabulary - Part 1 - Metal weldingprocesses.

ISO 6947 Welds - Working posit ions - definitions of angles of slope and rotation.

ISO 9606 2 Qualification test of welders fusion welding.Part 2 Aluminium & aluminium alloys.

ISO 15607 Specification and qualification of welding procedures for metallicmaterials - General rules.

ISO 15608 Welding - Guidelines for a metallic material grouping system.

ISO 15609 - 1 Specification and qualification of welding procedures for metallicmaterials - Welding procedure specification - Part 1: Arc welding.

ISO 15610 Specification and qualification of welding procedures for metallic materials-Qualification based on tested welding consumables.

ISO 15611 Specification and qualification of welding procedures for metallic materials-Qualification based on previous welding experience.

ISO 15613 Specification and qualification of welding procedures for metallic materials -Qualification based on pre - production-welding test.

ISO 15614 Specification and qualification of welding procedures for metallicmaterials - Welding procedure test.

Part 1:Part 2:Part 3:Part 4:Part 5:Part 6:Part 7:

Part 8:Part 9:Part 10Part 11Part 12Part 13

Arc and gas welding of steels and arc welding of nickel and nickel alloys.Arc welding of aluminium and its alloys*Welding procedure tests for the arc welding of cast irons*Finishing welding of aluminium castings*Arc welding of titanium, zirconium and their alloys.Copper and copper alloys*Not used

Welding of tubes to tube-plate joints.Underwater hyperbaric wet welding*Hyperbaric dry welding*Electron and laser beam weldingSpot, seam and projection welding*Resistance butt and flash welding*

Note:The Inspector should have an awareness of s tandards that are printed in bold.*Proposed

.




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Section 5

Calibration of Welding Equipment


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Rev 1 July 2008Calibration of Welding Equipment


1 Introduction

BS 7570 - Code of practice for validation of arc welding equipment is astandard that gives guidance to:

Manufacturers about the accuracy required from output meters fitted towelding equipment to show welding current, voltage etc

End users who need to ensure that the output meters provide accuratereadings

The Standard refers to two grades of equipment - standard grade andprecision grade.

Standard grade equipment is suitable for manual and semi-automaticwelding processes.

Precision grade equipment is intended for mechanised or automatic weldingbecause there is usually a need for greater precision for all weldingvariables as well as the prospect of the equipment being used for higherduty cycle welding.

2 Terminology

BS 7570 defines the terms it uses - such as:

Calibration:Operations for the purpose of determining the magnitude of errors of a

measuring instrument etc

Validation:Operations for the purpose of demonstrating that an item of weldingequipment, or a welding system, conforms to the operating specification forthat equipment or system

Accuracy:Closeness of an observed quantity to the defined, or true, value

Thus, when considering welding equipment, those that have output meters

for welding parameters (current, voltage, travel speed etc.) can be calibratedby checking the meter reading with a more accurate measuring device and adjusting the readings appropriately.

Equipment that does not have output meters (some power sources forMMA, MIG/MAG) cannot be calibrated but they can be validated, that is tomake checks to see that the controls are functioning properly.


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3 Calibration Frequency

BS 7570 recommends re-calibration/validation:

At yearly intervals (following an initial consistency test at 3 monthly

intervals) for standard grade equipment At 6 monthly intervals for precision grade equipment.

However, the Standard also recommends that re-calibration/validation maybe necessary more frequently. Factors that need to be considered are:

The equipment manufacturers recommendations

The users requirements

If the equipment has been repaired re-calibration should always becarried out

There is reason to believe the performance of the equipment has

deteriorated

4 Instruments for Calibration

Instruments used for calibration should:

Be calibrated by a recognised calibrator - using standards that aretraceable to a national standard

Be at least twice, and preferably five times, more accurate than theaccuracy required for the grade of equipment

For precision grade equipment it will be necessary to use instrumentswith much greater precision for checking output meters

5 Calibration Methods

The Standard gives details about the characteristics of power source types,how many readings should be taken for each parameter and guidance onprecautions that may be necessary.


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The Standard gives guidance about minimising any drop in line voltage byensuring that:

The current return cable is as short as practical and is heavy, lowresistance, cable

The current-return connector is suitably rated and is firmly attached andso does not overheat due to high resistance

The standard gives data for line voltage drops (DC voltage) according tocurrent, cable cross section and cable length (for both copper andaluminium cables).

Wire feed speedFor constant voltage (self-adjusting arc) processes such as MIG/MAG thestandard recognises that calibration of the wire feeder is generally notneeded because it is linked to current.

If calibration is required, it is recommended that the time be measured (inseconds) for ~1m of wire to be delivered (using a stopwatch or an electronictimer).

The length of wire should then be measured (with a steel rule) to anaccuracy of 1mm and the feed speed calculated.

Travel speedWelding manipulators, such as rotators and robotic manipulators, as well as

the more conventional linear travel carriages, influence heat input and otherproperties of a weld and should be checked at intervals.

Most of the standard devices can be checked using a stopwatch andmeasuring rule, but more sophisticated equipment, such as a tacho-generator, may be appropriate.


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Power

Source

Wire Feeder

17

{arc voltage

4

5

32

6

An example of a welding circuit (for MIG/MAG)




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Section 6

Destructive Testing


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1 Introduction

European Welding Standards require test coupons that are made forwelding procedure qualification testing to be subjected to non-destructivetesting and then destructive testing.

The tests are called destructive tests because the welded joint is destroyedwhen various types of test piece are taken from it.

Destructive tests can be divided into 2 groups, those used to:

Measure a mechanical property quantitative tests

Assess the joint quality qualitative tests

Mechanical tests are quantitative because a quantity is measured amechanical property such as tensile strength, hardness and impact

toughness.

Qualitative tests are used to verify that the joint is free from defects theyare of sound quality - and examples of these are bend tests, macroscopicexamination and fracture tests (fillet fracture and nick-break).

2 Test Types, Test Pieces and Test Object ives

Various types of mechanical test are used by material manufacturers/suppliers to verify that plates, pipes, forgings etc have the minimum propertyvalues specified for particular grades.

Design engineers use the minimum property values listed for particulargrades of material as the basis for design and the most cost-effectivedesigns are based on an assumption that welded joints have properties thatare no worse than those of the base metal.

The quantitative (mechanical) tests that are carried out for weldingprocedure qualification are intended to demonstrate that the joint propertiessatisfy design requirements.

The emphasis in the following sub-sections is on the destructive tests and

test methods that are widely used for welded joints.

Rev 1 July 2008Destructive Testing



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2.1 Transverse tensile tests

Test objectiveWelding procedure qualification tests always require transverse tensile teststo show that the strength of the joint satisfies the design criterion.

Test specimensA transverse tensile test piece typical of the type specified by EuropeanWelding Standards is shown below.

Parallellength

Standards, such as EN 895, that specify dimensions for transverse tensiletest pieces require all excess weld metal to be removed and the surface tobe free from scratches.

Test pieces may be machined to represent the full thickness of the joint butfor very thick joints it may be necessary to take several transverse tensiletest specimens to be able to test the full thickness.

Test methodTest specimens are accurately measured before testing. Specimens arethen fitted into the jaws of a tensile testing machine and subjected to acontinually increasing tensile force until the specimen fractures.

The tensile strength (Rm) is calculated by dividing the maximum load by thecross-sectional area of the test specimen - measured before testing.

The test is intended to measure the tensile strength of the joint and therebyshow that the basis for design, the base metal properties, remains the validcriterion.

Acceptance cri ter iaIf the test piece breaks in the weld metal, it is acceptable provided thecalculated strength is not less than the minimum tensile strength specified,which is usually the minimum specified for the base metal material grade.

In the ASME IX code, if the test specimen breaks outside the weld or fusionzone at a stress above 95% of the minimum base metal strength the test

result is acceptable.




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2.2 All-weld tensile tests

Test objectiveThere may be occasions when it is necessary to measure the weld metalstrength as part of welding procedure qualification particularly for elevated

temperature designs.

The test is carried out in order to measure not only tensile strength but alsoyield (or proof strength) and tensile ductility.

All weld tensile tests are also regularly carried out by welding consumablemanufacturers to verify that electrodes and filler wires satisfy the tensileproperties specified by the standard to which the consumables are certified.

Test specimensAs the name indicates, test specimens are machined from welds parallel

with their longitudinal axis and the specimen gauge length must be 100%weld metal.

Round tensile specimen from awelding procedure qualification testpiece

Round tensile specimen from anelectrode classification test piece




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Test methodSpecimens are subjected to a continually increasing force in the same waythat transverse tensile specimens are tested.

Yield (Re) or proof stress (Rp) are measured by means of an extensometer

that is attached to the parallel length of the specimen and is able toaccurately measure the extension of the gauge length as the load isincreased.

Typical load extension curves and their principal characteristics are shownbelow.

Load-extension curve for a steelthat shows a distinct yield point atthe elastic limit

Load-extension curve for a steel (orother metal) that does not show adistinct yield point; proof stress is ameasure of the elastic limit

Tensile ductility is measured in two ways:

% elongation of the gauge length (A%)

% reduction of area at the point of fracture (Z%)




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The schematics below illustrate these two ductility measurements.

2.3 Impact toughness tests

Test objectiveCharpy V notch test pieces have become the internationally acceptedmethod for assessing resistance to brittle fracture by measuring the energyto initiate, and propagate, a crack from a sharp notch in a standard sizedspecimen subjected to an impact load.

Design engineers need to ensure that the toughness of the steel that is usedfor a particular item will be high enough to avoid brittle fracture in serviceand so impact specimens are tested at a temperature that is related to the

design temperature for the fabricated component.

C-Mn and low alloy steels undergo a sharp change in their resistance tobrittle fracture as their temperature is lowered so that a steel that may havevery good toughness at ambient temperature may show extreme brittlenessat sub-zero temperatures as illustrated in following figure.




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-50 -40 -30 -20 -10 0 10 20 30 40

Ductile fracture(0% crystallinity)

Britt le fracture(100% crystall inity)

Upper shelf

Lower shelf

Transition Range

Test temperature, C

Impactenergy

The transition temperature is defined as the temperature that is mid-waybetween the upper shelf (maximum toughness) and lower shelf (completelybrittle). In the above the transition temperature is 20C.

Test specimensThe dimensions for test specimens have been standardised internationallyand are shown below for full sized specimens. There are also standarddimensions for smaller sized specimens, for example 10mm x 7.5mm and

10mm x 5mm.




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Charpy V notch test piece dimensions for fu ll sized specimens

Specimens are machined from welded test plates with the notch positionlocated in different locations according to the testing requirements buttypically in the centre of the weld metal and at positions across the HAZ asshown below.

Typical notch positions for Charpy V notch test specimens from double Vbutt welds

Test methodTest specimens are cooled to the specified test temperature by immersion inan insulated bath containing a liquid that is held at the test temperature.




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After allowing the specimen temperature to stabilise for a few minutes it isquickly transferred to the anvil of the test machine and a pendulum hammerquickly released so that the specimen experiences an impact load behindthe notch.

The main features of an impact test machine are shown below.

Impact testing machine

Impact specimen on the anvil showingthe hammer position at point of impact

Charpy V notch test pieces before and after test ing




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The energy absorbed by the hammer when it strikes each test specimen isshown by the position of the hammer pointer on the scale of the machine.Energy values are given in Joules (or ft-lbs in US specifications).

Impact test specimens are taken in triplicate (3 specimens for each notch

position) as there is always some degree of scatter in the results particularly for weldments.

Acceptance cri ter iaEach test result is recorded and an average value calculated for each set ofthree tests. These values are compared with the values specified by theapplication standard or client to establish whether specified requirementshave been met.

After impact testing, examination of the test specimens provides additionalinformation about their toughness characteristics and may be added to the

test report:

% crystallinity the % of the fracture face that has crystallineappearance which indicates brittle fracture; 100% indicates completelybrittle fracture

Lateral expansion the increase in width of the back of the specimenbehind the notch as indicated below; the larger the value the tougherthe specimen

A specimen that exhibits extreme brittleness will show a clean break. Bothhalves of the specimen having a completely flat fracture face with little or nolateral expansion.

A specimen that exhibits very good toughness will show only a small degreeof crack extension, without fracture and a high value of lateral expansion.




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2.4 Hardness testing

Test objectivesThe hardness of a metal is its resistance to plastic deformation. This isdetermined by measuring the resistance to indentation by a particular type

of indenter.

A steel weldment with hardness above a certain maximum may besusceptible to cracking, either during fabrication or in service, and weldingprocedure qualification testing for certain steels and applications that requirethe test weld to be hardness surveyed to ensure that are no regions of theweldment that exceed the maximum specified hardness.

Specimens prepared for macroscopic examination can also be used fortaking hardness measurements at various positions of the weldment referred to as a hardness survey.

Test methodsThere are 3 widely used methods for hardness testing:

Vickers hardness test uses a square-base diamond pyramid indenter

Rockwell hardness test uses a diamond cone indenter or steel ball

Brinell hardness test uses a ball indenter

The hardness value being given by the size of the indentation producedunder a standard load. The smaller the indentation, the harder the metal.




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The Vickers method of testing is illustrated below.

2

ddd 21

+=

Both Vickers and Brinell methods are suitable for carrying out hardnesssurveys on specimens prepared for macroscopic examination of weldments.

A typical hardness survey requires the indenter to measure the hardness inthe base metal (on both sides of the weld), in the weld metal and across theHAZ (on both sides of the weld).

The Brinell method gives an indentation that is too large to accuratelymeasure the hardness in specific regions of the HAZ and is mainly used tomeasure hardness of base metals.




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A typical hardness survey (using Vickers hardness indenter) is shownbelow:

Hardness values are shown on test reports as a number followed by lettersindicating the test method, for example:

240HV10 = hardness 240, Vickers method, 10kg indenter load

22HRC = hardness 22, Rockwell method, diamond cone indenter (scale C)

238HBW = 238 hardness, Brinell method, tungsten ball indenter

2.5 Crack tip opening displacement (CTOD) testing

Test objectiveCharpy V notch testing enables engineers to make judgements about risksof brittle fracture occurring in steels, but a CTOD test measures a materialproperty - fracture toughness.

Fracture toughness data enables engineers to carry out fracture mechanicsanalyses such as:

Calculating the size of a crack that would initiate a brittle fracture undercertain stress conditions at a particular temperature

The stress that would cause a certain sized crack to give a brittle fractureat a particular temperature

This data is essential for making an appropriate decision when a crack isdiscovered during inspection of equipment that is in-service.

Test specimensA CTOD specimen is prepared as a rectangular (or square) shaped bar cuttransverse to the axis of the butt weld. A V notch is machined at the centreof the bar, which will be coincident with the test position - weld metal orHAZ.

A shallow saw cut is then put into the bottom of the notch and the specimenis then put into a machine that induces a cyclic bending load until a shallowfatigue crack initiates from the saw cut.




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The specimens are relatively large typically having a cross section B x 2Band length ~10B (B = full thickness of the weld). The test piece details areshown below.

Test methodCTOD specimens are usually tested at a temperature below ambient andthe temperature of the specimen is controlled by immersion in a bath of

liquid that has been cooled to the required test temperature.

A load is applied to the specimen to cause bending and induce aconcentrated stress at the tip of the crack and a clip gauge, attached to thespecimen across the mouth of the machined notch, gives a reading of theincrease in width of the mouth of the crack as the load is graduallyincreased.

For each test condition (position of notch and test temperature) it is usualpractice to carry out three tests.




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The schematics below illustrate the main features of the CTOD test.

Fracture toughness is expressed as the distance that the crack tip openswithout initiation of a brittle crack.

The clip gauge enables a chart to be generated showing the increase inwidth of the crack mouth against applied load from which a CTOD value iscalculated.

Acceptance cri ter iaAn application standard or client may specify a minimum CTOD value thatindicates ductile tearing. Alternatively, the test may be for information so thata value can be used for an engineering critical assessment.

A very tough steel weldment will allow the mouth of the crack to open widelyby ductile tearing at the tip of the crack whereas a very brittle weldment willtend to fracture when the applied load is quite low and without any extensionat the tip of the crack.

CTOD values are expressed in millimetres - typical values might be


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2.6 Bend testing

Test objectiveBend tests are routinely taken from welding procedure qualification testpieces and sometimes have to be taken from welder qualification test

pieces.

Subjecting specimens to bending is a simple method of verifying that thereare no significant flaws in the joint. Some degree of ductility is alsodemonstrated.

Ductility is not actually measured but it is demonstrated to be satisfactory iftest specimens can withstand being bent without fracture or fissures abovea certain length.

Test specimens

There are 4 types of bend specimen:

Face bendSpecimen taken with axis transverse to butt welds up to ~12mm thicknessand bent so that the face of the weld is on the outside of the bend (face intension).

Root bendTest specimen taken with axis transverse to butt welds up to ~12mmthickness and bent so that the root of the weld is on the outside of the bend(root in tension).

Side bendTest specimen taken as a transverse slice (~10mm) from the full thicknessof butt welds >~12mm and bent so that the full joint thickness is tested (sidein tension).

Longitud inal bendTest specimen taken with axis parallel to the longitudinal axis of a butt weld;specimen thickness is ~12mm and the face or root of weld may be tested intension.




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Test method

Bend tests for welding procedure qualification (and welder qualification) areusually guided bend tests.

Guided means that the strain imposed on the specimen is uniformlycontrolled by being bent around a former with a certain diameter.

The diameter of the former used for a particular test is specified in the code,having been determined by the type of material that is being tested and theductility that can be expected from it after welding and any PWHT.

The diameter of the former is usually expressed as a multiple of thespecimen thickness and for C-Mn steel it is typically 4t (t is the specimenthickness) but for materials that have lower tensile ductility the radius of theformer may be greater than 10t.

The standard that specifies the test method will specify the minimum bendangle that the specimen must experience and this is typically 120-180.

Acceptance cri ter iaBend test pieces should exhibit satisfactory soundness by not showingcracks or any signs of significant fissures or cavities on the outside of the

bend.




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Small indications less than about 3mm in length may be allowed by somestandards.

2.7 Fracture tests

2.7.1 Fillet weld fractures

Test objectiveThe quality/soundness of a fillet weld can be assessed by fracturing testpieces and examining the fracture surfaces.

This method for assessing the quality of fillet welds may be specified byapplication standards as an alternative to macroscopic examination.

It is a test method that can be used for welder qualification testing accordingto European Standards but is not used for welding procedure qualification toEuropean Standards.

Test specimens

A test weld is cut into short lengths (typically 50mm) and a longitudinalnotch is machined into the specimen as shown below. The notch profile maybe square, V shaped or U shaped.

Test methodSpecimens are made to fracture through their throat by dynamic strokes(hammering) or by pressing, as shown below. The welding standard orapplication standard will specify the number of tests (typically 4).

Moving pressHammer stroke


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Acceptance cri ter iaThe standard for welder qualification, or application standard, will specify theacceptance criteria for imperfections such as lack of penetration into the rootof the joint and solid inclusions and porosity that are visible on the fracture

surfaces.

Test reports should also give a description of the appearance of the fractureand location of any imperfection

2.7.2 Butt weld fractures (nick-break tests)

Test objectiveThe objective of these fracture tests is the same as for fillet fracture tests.

These tests are specified for welder qualification testing to EuropeanStandards as an alternative to radiography. They are not used for weldingprocedure qualification testing to European Standards.

Test specimensTest specimens are taken from a butt weld and notched so that the fracturepath will be in the central region of the weld. Typical test piece types areshown below.

Test methodTest pieces are made to fracture by hammering or three-point bending.

Acceptance cri ter iaThe standard for welder qualification, or application standard, will specify theacceptance criteria for imperfections such as lack of fusion, solid inclusionsand porosity that are visible on the fracture surfaces.




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Test reports should also give a description of the appearance of the fractureand location of any imperfection.

3 Macroscopic Examination

Transverse sections from butt and fillet welds are required by the EuropeanStandards for welding procedure qualification testing and may be requiredfor some welder qualification testing for assessing the quality of the welds.

This is considered in detail in a separate section of these course notes.

Macro examination Micro examination

Objectives Detecting weld defects. (macro)

Measuring grain size. (micro)

Detecting brittle structures, precipitates.

Assessing resistance toward brittle fracture, cold cracking and corrosionsensitivity




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European Standards for Destructive Test Methods

The following Standards are specified by the European Welding Standardsfor destructive testing of welding procedure qualification test welds and forsome welder qualification test welds.

EN 875 Destructive tests on welds in metallic materials Impacttests Test specimen location, notch orientation andexamination

EN 895 Destructive tests on welds in metallic materials Transverse tensile test

EN 910 Destructive tests on welds in metallic materials Bend tests

EN 1321 Destructive tests on welds in metallic materials

Macroscopic and microscopic examination of weld

BS EN 10002 Metallic materials - Tensile testing. Part 1: Method of test atambient temperature

BS EN 10002 Tensile testing of metallic materials. Part 5: Method of testat elevated temperatures




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Section 7

Heat Treatment


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1 Introduction

The heat treatment given to a particular grade of steel by the steelmaker/supplier should be shown on the material test certificate and may bereferred to as the supply condition.

Welding inspectors may need to refer to material test certificates and it isappropriate that they be familiar with the terminology that is used and havesome understanding of the principles of some of the most commonly appliedheat treatments.

Welded joints may need to be subjected to heat treatment after welding(post-weld heat treatment) and the tasks of monitoring the thermal cycle andchecking the heat treatment records are often delegated to weldinginspectors.

2 Heat Treatment of SteelThe main supply conditions for weldable steels are:

As rol led, hot ro lled, hot finishedPlate is hot rolled to finished size and allowed to air cool; the temperature atwhich rolling finishes may vary from plate to plate and so strength andtoughness properties vary and are not optimised;

Appl ied to Relatively thin, lower strength C-steel

TMCP*, control-rolled, thermo-mechanically rolledSteel plate given precisely controlled thickness reductions during hot rollingwithin carefully controlled temperature ranges; final rolling temperature isalso carefully controlled;

Appl ied toRelatively thin, high strength low alloy steels (HSLA) and for some steelswith good toughness at low temperatures, eg, cryogenic steels* TMCP =thermo-mechanical controlled processing

NormalisedAfter working the steel (rolling or forging) to size, it is heated to ~900C andthen allowed to cool in air to ambient temperature; this optimises strengthand toughness and gives uniform properties from item to item for aparticular grade of steel;

Appl ied to C-Mn steels and some low alloy steels

Rev 1 July 2008Heat Treatment



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Because the main reason for (and benefit of) PWHT is to reduce residualstresses, PWHT is often called stress relief.

Note 1: There are circumstan