modern welding technology (ch. 13, 21, 22 & 25)

OUTLINE

2 1 - 1 Weld Reliability 2 1 -2 Welding Codes and

Specifications 2 1-3 Welding Procedures and

Qualifying Them 2 1-4 Standard Welding

Procedure Specifications

Welding Codes, Standards, Specifications, and Procedures 21 - 1 WELD RELIABILITY

The demand for more reliable products, increasingly complex technology, and the need to conserve resources makes weld quality increasingly important. A "welding manufacturing system"(" as part of a total manufacturing system will provide good-quality welded products by establishing the engineering capabilities to:

I. Select, properly apply, and inspect suitable welding processes and equipment-the quality control program

2. Select or generate and apply qualified welding procedures for each welding operation-the welding procedure qualification

3. Direct, train, and qualify welding personnel to produce weldments-the welder performance qualification

The manufacturing system provides management support through policy and delegated authority. The system includes documentation to establish designs, manufacturing techniques, and quality control methods. From a welding point of view it includes welding procedure qualifications, welder performance qualifications, and an overall total welding quality control program.

The purpose of a welding procedure qualification(*) is to show that the proposed weldment will have the required properties for its intended application, that is, to determine the properties of a sound weld. The document that does this is the Procedure Qualification Record (PQR). This provides the actual welding variables used to produce an acceptable test weld and the results of tests conducted.

The purpose of the welder performance qualification test is to determine the ability of the welder or welding operator to deposit sound weld metal following a welding procedure specification. The document that does this is the Performance Qualification Test Record. This qualifies the welder or welding operator for specific processes, for different welds, positions, and thicknesses.

Neither the welding procedure qualification nor the welder performance qualification establish the capabili- ty of the organization or the welding equipment to make an acceptable welded product. Therefore, a quality control program must be developed and implemented. The quality control or assurance program establishes: the authority and responsibility; the design basis, procurement and material contro;, manufacturing technology, the selection and application of welding processes and equipment; the necessary fixtures and tooling; pre- and postheating requirements; the calibration of the equipment; the training and indoctrinating of welders and supervision; and the commitment of all levels of management to high-quality products.

The remaining portion of this section concerns the quality control plan and offers a suggested quality control program. It can be adopted by companies desiring to improve weld quality and is very similar to programs established by some of the nuclear codes.

Quality welding on any product must be judged with respect to a specific quality standard, which must be based on the intended service of the product. It must be balanced between the service requirements and the con- sequence of failure versus economic factors. For many products, in many industries, weld quality requirements are controlled by applicable codes and specifications. However, when no codes or specifications apply, the producer must maintain high product quality in order to sur- vive. The success of maintaining the balance between high quality and high cost is decided in the field and in the marketplace, where quality and price determine the producer's continuing success.

The weldments included in space vehicles and nu-

clear vessels are exposed to environments unheard of in the recent past. The weld perfection demanded and obtained by this class of work has been possible thanks to excellent procedures, extensive training, and stringent quality assurance methods. This quality level is attained because of extensive preparation and time-consuming procedures, testing, and qualification, which contribute to high cost. However, perfect welds are not required on every type of weldment. The welding industry must guard against establishing super-quality requirements when they are not required.

The responsibility for producing high-quality products rests on many people. It is the responsibility of management to create the proper cooperative spirit among designers, managers, welders and other production workers, supervisors, and quality control and inspection personnel to make sure that the quality requirement is reasonable and in agreement with the service expected. The responsibility for producing high-quality welds rests on the welder. Each welder must accept this responsibility. The welding supervisor has the responsibility for the welders and for their performance. The welding inspectors must verify that quality standards are met. The welding standards or specifications and procedures are the basis for weld quality, and these factors coupled with the weldment design are the responsibility of designers, welding engineers, material managers, and quality assurance personnel. It is a total responsibility with all involved. This interrelationship is very complex.

The designers, the specification writers, material specifiers, and others must keep close contact with field requirements and problems. They must be sensitive to needs for change and they must be able to relax or tighten standards when needed. Welding supervisors and production managers must be continually alert for evidence of substandard workmanship.

The need to differentiate between the adequate and the perfect weld had led to research concerning the ac- ceptability of weld imperfection and how these imperfec- tions affect service life. This has led to investigations of the degree of imperfection and the fitness for purpose of the weldment. Through the years these data have been translated into codes and specifications for different types of equipment. The knowledge gained from field experience and experience producing weldments is reflected in the revisions of the codes.

A major problem encountered in weldment production is the suspicion of the designer that the weldment will not be manufactured as designed. The suspicion occurs when designers consider workmanship factors that are seemingly beyond their control. They feel that the welder can produce joints equal to the design requirements under ideal conditions and that the welder did produce a good-quality weld when the performance qualification test was passed; however, they want assurance

CH. 21 1

that every weld in the weldment will be of this quality. For positive assurance it is necessary to implement a quality control program. Such programs save money in the long run, as they eliminate the problem of premature field failures, catastrophic disasters, or the cost of overwelding to overcome suspected shop malpractice.

Quality Control Program

For certain classes of work quality control requirements are well established. These requirements make it necessary to write a quality control program. Strict requirements which are found in the nuclear codes require a quality assurance program that is based on the technical and manufacturing aspects of the product. The program must ensure adequate quality from the design, acquisition, and manufacture, to final shipment. The program must define authority and responsibility for each portion of the work. The quality assurance plan must include the following:

1. Organization. The organization for quality must be clearly prescribed. It should define and show charts for responsibility and authority and the organiza- tional freedom to identify and evaluate quality problems. Quality control personnel should not report to production personnel.

2. Quality assurance program. The producer must conduct a review of the requirements of the quality required of the product. The various factors, such as specialized controls, processes, testing equipment, and skills, for assuring product quality must be identified. This program must be documented by written policies, procedures, and instructions.

3. Design control. The design control must provide for verifying or checking the adequacy of the design, via performance testing and independent review. It should include qualification and testing of prototypes and must conform to specifications. Measures must be established to ensure that the design specifications and code requirements are cor- rectly translated into drawings, procedures, and instructions.

4. Procurement document control. The program requires that specifications be written for each item purchased and that the specification ensure the quality required by the end product. These specifications also require quality assurance programs from vendors.

5. Instructions, procedures, and drawings. The quality program must ensure that all work affecting quality must be prescribed in clear and complete documented instructions of a type appropriate to the work. Compliance with instructions must be monitored.

6. Document control. The quality program must include a procedure for maintaining the completeness and correctness of drawings and instructions, and the like, showing dates, control, effective point, and so on. These drawings, procedures, and instructions must be maintained and continuity explained by change notices.

7. Control of purchased material, equipment, and services. The program must include a control system for purchasing from qualified vendors. This means that vendors must have similar quality programs for producing their items. A qualified products list is required and only those vendors having adequate quality programs and providing quality parts will be included. The program requires receiving inspection systems so that purchased parts can be checked against the specifications. Raw materials, purchased parts, and the like will be inspected by means of instruments, laboratory procedures, and so on, to ensure that the products meet the specifications.

8. Identification and control of materials. The program must provide for identification of all parts, materials, components, and so on, from receipt throughout all processing to the final item. Records shall provide traceability of all materials, components, and so on. A checklist shall be established for all characteristics to be reported and to record that the test reports have been received, reviewed, and found acceptable.

9. Control of specialprocesses. The quality program must ensure that all manufacturing operations including welding are accomplished under controlled conditions. These controlled conditions involve the use of documented work instructions, drawings, special equipment, and so on. It further requires that such instructions be provided, with space for reporting results of inspection by the manufacturer and the inspector, including the date and initials.

10. Inspection. The quality assurance program should ensure a system of inspection and testing for all products. Such testing should simulate the product service and records must be maintained of the adequacy of the product to meet these specifications.

11. Test control. The program must assure that all tests are performed according to written instructions. In- structions must provide requirements and acceptance limits. Test results must be documented and evaluated to assure that test requirements are met.

12. Control of measuring and testing equipment. The program should provide for methods of maintaining the accuracy of gauges, testing devices, meters, and other precision devices, showing that they are calibrated against certified measurement standards on a periodic basis.

SEC. 21-1 WELD RELIABILITY 621

13. Handling, storage, and delivery. The program should provide for adequate instructions for handling, storage, preservation, packaging, shipping, and so on, that the product is protected from its time of manufacture until its time of use.

14. Inspection test and operating status. The program must include methods of identifying parts to determine its status as far as inspection and approval are concerned.

15. Nonconforming materials, parts, or comgonents. There should be a procedure established to maintain an effective and positive system for controlling nonconforming material. It may include and allow for rework; however, records must be maintained of such work. Resolution of nonconformities should be in conformance with paragraph 7 of this program.

16. Corrective actions. The quality program must establish methods of dealing promptly with any conditions that are adverse to quality, including design, procurement, manufacturing, testing, and so on. The program should also include methods of overcoming defects, taking corrective action to produce a part to meet the required quality.

17. Quality assurance records. Program requires that records be maintained, including all data essential to the economical and effective operation of the quality program. Records must be complete and reliable and include measurements, inspections, observations, and so on, and these records must be available for review.

18. Cost related to quality. The program should allow for maintenance and use of cost data for identifying the cost of the program and for the prevention and correction of defects encountered.

19. Production tooling and inspection equipment. Various items of tooling, including fixtures, templates, patterns, and so on, may be used for inspection purposes provided that their accuracy be checked at periodic intervals.

20. Audits. The program must include a system of planned and periodic audits to verify compliance with all aspects of the quality assurance program. The audit must be done by personnel not normally involved in the areas being audited. Audits must be documented and reviewed, and action must be taken to correct any deficiencies found.

The preceding list is an abbreviated outline of the requirement of a quality assurance program necessary for critical products. As time goes on and as requirements for higher quality continue, similar programs may be required for other products.

21-2 WELDING CODES AND SPECIFICATIONS

There are many codes and specifications that relate to welding (Figure 21-1). To properly understand these codes and where they are used, it is best to consider the industries that employ welding specifications. Certain products are regulated by codes and specifications regarding welding. For the purposes of classifying the codes, they are listed according to the products involved.

The products that utilize welding specifications are as follows:

1. Pressure vessels

2. Nuclear reactors 3. Piping 4. Bridges and buildings 5. Ships

6. Storage tanks and vessels 7. Railroad rolling stock

8. Aerospace and aircraft 9. Construction and agriculture equipment

10. Industrial machinery 11. Automotive

Specifications applying to similar products are similar with regard to welding. In some cases the qualifications of one specification may be acceptable by another for the same products. Most manufacturers and contractors usually produce weldments that are similar or come under the sank? general types of specifications. Efforts are continuing to make specifications more

I

FIGURE 21-1 Popular codes and specifications.

628 WELDING CODES, STANDARDS, SPECIFICATIONS, AND PROCEDURES CH. 21

uniform and to make the interchange of qualifications easier between different specifications. Following is a listing of welded product followed by the specifications that apply.

Pressure Vessels

In North America the manufacturer of pressure vessels and all other items defined as pressure vessels comes under the specifications of the ASME boiler and pressure vessel code.") This code consists of 11 sections:

Section I

-- Section 11

Section 111 Section 1V

- Section V 1 Section VI

Section VII

- Section VIII

Section IX - Section X

- Section XI

Power boilers

Material specifications-ferrous Material specifications-nonferrous Material specifications-welding rods, electrodes, and filler metals

Nuclear power plant components Heating boilers

Nondestructive examination Recommended rules for care and operation of heating boilers

Recommended rules for care of power boilers Pressure vessels division I , 11, and I11 Welding qualifications

Fiberglass-reinforced plastic pressure vessels Rules for in-service inspection of nuclear reactor coolant system

All products manufactured under the requirements of these codes may also be manufactured under the rules and regulations of different states and provinces which either reference or reprint different sections of the boiler and pressure vessel code. In general, Section IX is universally used throughout North America and in other parts of the world as the method of qualifying procedures and welders for work on pressure vessels.

Nuclear Reactors

The nuclear reactors, components, and materials used in nuclear power plants are covered by the provisions of Sec- tion 111 of the ASME pressure vessel code or the Nuclear Regulatory Commission Spe~ification.(~) Any part that is utilized in a nuclear plant must be manufactured under the jurisdiction of t h e codes. The exceptions are those components for navy ship use which are covered by a similar but different code issued by the Department of Defense Naval Ship Division. This is known as "Stand-

ard for Welding of Reactor Coolant and Associated Systems and Components for Naval Nuclear Power Plants."(s) This is a specialized code that includes additional restrictions. It requires the certification of materials and traceability of all materials, including welding filler metals to the point of origin. It also includes strict control systems of inspection during the manufacture of nuclear power plant components.

Pressure Piping

Codes, specifications, and procedures for all piping is covered in Chapter 25.

Bridges and Buildings

Structural welding is done under the requirements of many large cities, and for bridges under the jurisdiction of state or provincial highway departments. The basis for these codes either by reference or by direct copy is the "Structural Welding Code" published by the American Welding Society.c6) This code incorporates the requirements of the Department of Transportation, Bureau of Public Roads, of the U.S. government. The Bureau of Public Roads has interest in state structural specifications. They are all similar; however, each state publishes its own welding code. Welding on highway bridges is under the jurisdiction of the state highway departments, and in many states welders are examined yearly and certified by the state to work on bridges. Many state highway departments also require yearly certification of welding electrodes and filler metals. The "Standard Specifications for Highway Bridges,"(') adopted by the American Association of State Highway Officials, and the "Specifications for Steel Railway Bridges,"cs) published by the American Railway Engineering Association, are in substantial agreement with the AWS structural welding code from the welding point of view.

Large steel buildings welded in the major cities in North America are covered by city codes and specifications. These codes and specifications are in substantial agreement with the AWS structural welding code. Only the larger cities publish welding codes; others reference the AWS code. Some cities require qualification of welders and certification of filler metals for structures welded under their jurisdiction.

Ships

Welding on ships is covered by different specifications and codes. In the United States, all federal government vessels are covered by codes issued by the U.S. Coast Guard(" or the Navships Division of the Department of Defense.(lo) These requirements are nearly identical as to welding procedure qualification and welder qualification.

SEC. 21-2

They are also very similar to the requirements of the Maritime Administration for commercial ships.(Il) Qualification of welders is usually transferable among these three organizations. The American Bureau of Ship- ping has similar requirements for welding on ships that they survey.(12) Lloyd's and other classification societies also publish specifications that cover welding. Certifica- tion of filler metal is required. The American Welding Society publishes two guides related to ship welding: "Guide for Steel Hull Welding"(I3) and "Guide for Aluminum Hull Welding."(I4)

Storage Tanks and Vessels

There are two major codes for the welding of storage tanks. One is for the welding of elevated storage tanks and is published by AWS and the American Water Works Association, "Standard for Welded Steel Elevated Tanks, Standpipes, and Reservoirs for Water Storage."(15) The other one is for oil or petroleum products storage tanks published by American Petroleum Institute, "Standard for Welded Steel Tanks for Oil Storage."(16) Both of these codes refer to Section IX of the ASME boiler code as far as welding qualification is concerned.

Railroad Rolling Stock

Specifications for manufacturing of rolling stock for North American railroads is under the jurisdiction of the Department of Transportation in the United States. However, as far as welding qualification and welding design requirements are concerned, the controlling specifications are issued by the Association of American Railroads. Various specifications are involved including "Specifications for Tank Cars"(I7) and "Specifications for Design, Fabrication, and Construction of Freight Cars."(I8) These specifications provide information concerning the design of welds and the qualification of

the Department of Defense Military (Mil) Standards and Specifications. The one pertaining primarily to welding on aircraft is "Qualification of Aircraft, Missile and Aerospace Fusion Welders."(24) This standard covers many welding processes, metals, and levels of proficien- cy for testing welders and must be adhered to when welding on aircraft. Qualification under this standard is done under the supervision of government inspectors.

Construction Equipment

Construction equipment is made to company standards which have been found acceptable based on the product acceptance in the field. Most manufacturers of construction equipment have their own specifications. The American Welding Society has issued specifications that establish common acceptance standards for weld performance known as "Welding on Earth moving and Con- struction Equipment."(2s) Qualification of welders is not a major issue in this standard.

Industrial Machinery

Most industrial machinery utilizing weldments is not covered by code or specification. The American Welding Society has issued specifications which establish common accepted standards for weld performance and process application. Some of these are:

- "Welding Industrial and Mill Cranes"(26) - "Metal Cutting Machine Tool Weldment~"~~')

"Specifications for Welding of Presses and Press

- "Specification for Rotating Elements of Equipment"cZ9)

- "Classification and Application of Welded Joints for Machinery and Equipment"(30'

welders' manufacturing these products. They are in substantial agreement with requirements of the AWS The welder qualification requirements are similar

"Railroad Welding Specification."(lY) to the requirements of AWS structural code.

The Department of Transportation also has codes covering the manufacture of tanks for transporting gas under high pressure(20) and for tanks carrying liquid petroleum and similar products.(*l)

Aerospace and Aircraft

Weldments intended for use in aircraft and spacecraft are welded to the requirements of U.S. government specifications. There are other groups that write specifications for materials that might be utilized, including the Society of Automotive engineer^'^^) and the Aerospace Industries Association of America.(23) Welding codes or requirements are covered by specifications of the National Aeronautics and Space Administration (NASA) and of

Automotive

The American Welding Society has issued a number of documents relating to welding of automobiles and trucks. They are:

, "Recommended Practices for Automotive Welding Design"(31)

- "Recommended Practices for Automotive Portable Gun-Resistance Spot Welding"c3?) : "Standard for Automotive Resistance Spot Welding

Electrodes"(33) "Specifications for Automotive Welding Quality- Resistance Spot Welding"(34)

CH. 21 I

"Specifications for Automotive Frame Weld Quality-Arc Welding"(3s)

General

The American Welding Society document "Standard for Welding Procedure and Performance Qualifica- t i o n ~ " ' ~ ~ ) may become the reference document for qualifying procedures and performance for all AWS product codes, standards, or specifications. It may be used in contract documents. In using any code or specification it is important to use the latest edition or the specific edition involved.

21-3 WELDING PROCEDURES AND QUALIFYING THEM

The subject of welding procedures has become extremely complicated because of the different terminology and definitions of the various welding codes. In view of this it is necessary to consult the latest or specified edition of the code involved and follow it in detail.

In general, "a welding procedure is the detailed methods and practices involved in the production of a ~eldrnent ." '~~) This is a very broad definition and covers two types of procedures. The first is the legal requirements of a code or specification. The second is broader and can be step-by-step directions for making a specific weldment. Procedures of this type are written to maintain consistency, to help reduce weld distortion, or to show how a weldment should be built.

The written welding procedure, required by codes, comprises the step-by-step directions for making a specific weld and proof that the weld is acceptable. This type of procedure consists of three parts:

1. A written explanation describing the conditions involved

2. A drawing of the weld joint and a table giving the welding parameters

3. An information data sheet showing the results of testing the welds and stating that they met the requirements

All welding codes and specifications are similar with respect to procedures. In every case it is necessary to write up the welding procedure and then to prove or qualify it. The problem is with the terminology, which is different in many codes.

Most codes also require proof that welders and welding operators have the necessary skill and ability to follow the welding procedure successfully. This requires that welders and welding operators make specific welds, which are then tested to prove that the welder can produce the weld quality required. This routine is different in

different codes and was briefly covered in the section "Qualifying and Certifying Welders."

Many consensus standards, codes, and specifications are adopted by political subdivisions such as cities, states, and provinces. When this is done, the provisions of the referenced code or specifications become a legal document. They may also become legal documents when specified by a contract or purchase order.

Companies develop and qualify welding procedures necessary to manufacture their products that are built under code. Contractors have qualified welding procedures enabling them to install code products. Utilities, with power plants, also have qualified procedures and personnel. In addition, certain special associations have qualified procedures and qualified personnel. This is done in metropolitan areas or where similar work is performed. For example, piping contractors in a large city may form an association to qualify welding procedures and welders. The welders are hired from a labor pool and may work for different contractors on each new job. With this arrangement they are covered by the association's qualified procedures and need not retest for each job. Even with an association the contractor is responsible for the procedures and the welders and for enforcing quality control practices.

The three most popular welding codes cover boilers and pressure vessels, bridges and buildings, and the welding on cross-country transmission pipelines. Each of these codes will be explained by showing examples of the documents required.

Boilers and Pressure Vessels

Section IX of the ASME Boiler and Pressure Vessel Code covers welding and brazing qualifications. It is entitled "Qualification Standard for Welding and Brazing Pro- cedures, Welders, Brazers, and Welding and Brazing Operators. "c3)

This code makes the following statement concerning responsibility: "Each manufacturer or contractor is responsible for the welding done by his organization and shall conduct the tests required to qualify the welding procedures he uses in the construction of the weldments built under this code, and the performance of 'welders and welding operators who apply these procedures." It further states: "Each manufacturer, or contractor, shall maintain a record of the results obtained in welding procedures and welder and welding operator performance qualifications. These records shall be certified by the manufacturer or contractor and shall be accessible to the authorized inspector."

The ASME code calls the welding procedure a welding procedure specification (WPS). This document provides in detail the required conditions for specific applications to assure repeatability by properly trained

SEC. 21-3 WELDING PROCEDURES AND QUALIFYING THEM 63 1

welders and welding operators. A WPS is a written welding procedure prepared to provide direction for making production welds to code requirements. The ASME provides a sample form, which may be used or modified provided that it covers all information. The WPS provides directions to the welder or welding operator to assure compliance with the code requirements. The completed WPS describes all of the essential, nonessential, and supplementary essential (when required) variables for each welding process. The WPS should reference the supporting procedure qualification record (PQR). A PQR is a record of the welding data used to weld the test coupons. It shows all conditions that were used when welding the test coupons and the actual results of the tested specimens: The completed PQR should record all essential and supplementary essential (when required) variables for each welding process used to weld the test coupon. Nonessential or other variables used during the welding of test coupons need not be recorded. The PQR should be certified accurate by the manufacturer or contractor. This certification is the manufacturer's or contractor's verification that the information is a true record of the variables that were used during the welding of the test coupon and that the test results are in compliance with Section IX of the code. The manufacturer or contractor cannot subcontract this certification function.

There are three types of variables for welding procedure specifications WPS. "Essential variables" are those in which change is considered to affect mechanical properties of the weld joint or weldment. "Supplemen- tary essential variables" are required for metals for which notch toughness tests are required. "Nonessential variables" are those in which a change may be made in the WPS without requalification. The variables for each welding process is listed in detail in Section IX. For this reason it is necessary that you refer to the code when writing, testing, or certifying the welding procedures.

Welding Procedure Specification To help explain the welding procedure specification (WPS), an example is shown in Figures 21-2 to 21-4, which are similar to ASME QW-482. In this example, the ABC Pressure Vessel Com- pany is using the gas metal arc welding process, semi- automatically applied for welding P-1 grade steel pipe in the horizontal fixed and vertical positions. Each entry will be explained briefly.

Joints. The joint design is a single V groove with a 60 to 70" included angle. It is recommended that a sketch be drawn on the form in the area under details. If more space is needed, use a third sheet, such as sheet 3 of 3 (Figure 21-4) in the example. The welding parameters are placed in the table provided. Backing is not used, and backing material need not be described. However, if backing is used, it must be described.

Base Metals. To reduce the number of WPSs required, P numbers are assigned to base metals depending

on characteristics such as composition, weldability, and mechanical properties. Groups within P numbers are assigned for ferrous metals for the purpose of procedure qualifications where notch toughness requirements are specified. The same P numbers group the different base metals having comparable characteristics. The P numbers and groupings of most of the different steels are given in the Section IX. Base metal classifications and groupings in AWS B2.1 are slightly different. If a P number is not available for the material involved, its ASTM specification number may be used. If an ASTM specification number is not available, the chemical analysis and mechanical properties can be used. Under base metals the thickness range must be shown, and if it is in pipe, the pipe diameter range must be shown.

Filler Metals. Electrodes and welding rods are grouped according to their usability characteristics, which determines the ability of the welders to make satisfactory welds with a given filler metal. This grouping is made to reduce the number of WPSs needed. The groups are given F numbers, which relate to the composition and usability. This is filled in on the form. This block also requires ASME specification number and the AWS classification number of the filler metal used. The ASME specification numbers are the same as the AWS specification number with the addition of the letters SF. These data are given in ASME Section IX and in the AWS B2.1 document. The AWS classification number for the filler metal specification is also given on the label on the filler metal box. The A number is the classification of weld metal analysis. For example, A-1 has a mild steel weld metal deposit. This classification system is given in both specifications. The size of the filler metal, which is its diameter, must be shown as well as deposited weld metal thickness range for groove or fillet welds. In the case of submerged arc welding, electrode flux class must be shown and the flux trade name must be shown. For gas tungsten arc, the consumable insert analysis should be shown. Other information relating to filler metals not mentioned above should be given, when available.

Position. The welding position of the groove or fillet weld must be described according to AWS terminology. If vertical welding is involved, it should be mentioned whether progression is upward (uphill) or downward (downhill).

Preheat. A minimum temperature shall be given as well as the maximum interpass temperature. Preheat maintenance temperature should be given. Where applicable, special heating should be recorded.

Postweld Heat Treatment. If a postweld heat treatment is used, it must be described. This includes the temperature range and the time at temperature. If there is no postweld heat treatment, write in "none."

Gas. The shielding gas should be identified, and

CH. 21

if it is a mixture, should be described. The shielding gas should be shown as alternating (ac) or direct current (dc). flow rate should be recorded. If backing gas or trailing If direct current is used, the polarity of the electrode shield gas is used, the gas composition should be given should be reported. The amperes and voltage range and flow rate recorded. should be recorded for each electrode size, position, and

Electrical Characteristics. The welding current thickness. This is also presented in a tabular form, as

- - - pp

FIGURE 21-2 ASME weldlng procedure specifications (WPS), sheet 1.

WELDING PROCEDURE SPECIFICATION (WPS) (See QW-201.1, Section IX, ASME Boiler and Pressure Vessel Code)

Company Name_&&C Pressure Vessd Co " BY: Frank J n n ~ Weld ~n_o/ . Welding Procedure .Specification No.~~ISupporting POR N0.h) 101

Revision No. - Date - Welding Process(es) Cos /eta/ Afc Weidino - short Circv~ t i Type($) Semi- A u t o d i c

(Automatic. Manual. Machine. or Semi-Auto.)

1 JOINTS (QW-402) Details I Joint Design SIAO/P Vee Backing (Yes) ( N O ) X

Backing Material (Type) -

(Refer to both backing and retainers.)

Metal Nonfusing Metal

Nonmetallic Other

Sketches, Production Drawings, Weld Symbols or Written Description

should show the general arrangement of the parts to be welded. Where

applicable, the root spacing and the details of weld groove may be

specified.

design, weld layers and bead sequence, e.g. for notch toughness proce-

dures, for multiple process procedures, etc.)

/ (A t the option of the Mfgr., sketches may be attached to illustrate joint

'BASE METALS (QW-403)

~ - ~ o . L ~ r o u ~ No. f t o P-No. 7 Group No. 7 OR

Specification type and grade - to Specification type and grade

- OR

Chem. Analysis and Mech. Prop. - to Chem. Analysis and Mech. Prop. - Thickness Range:

Base Metal: Groove (ID to f-lnch Fillet - Pipe Dia. Range: Groove m//ml'f ed Fillet -

I

"FILLER METALS (QW-404)

Spec. No. (SFA) 5. f8 AWS NO. (Class) ER 705 - 3

A-No. 1 Size o f Filler Metals 0. 35 - /j7 Deposited Weld Metal -

Thickness Range:

Groove 7/s - hch Fillet

- Electrode-Ptux (Class) None 1 - Flux Trade Name

Consumable Insert Nofie i Other

- I 1

'Each bare metal-filler metal combination should be recorded individually.

SEC. 21-3

POSITIONS (QW-405)

Position(s) of Growe 7 C PI;DC A X ~ S ~ @ ~ ~ I ' c c I /

Welding Progression: Up - Down - Position(s) o f Fillet -

PREHEAT (OW-)

Preheat Temp. Min. /OO°F lnterpass Temp. Max. 20o0f Preheat Maintenance / O O e f (Continuous or special heating where applicable should be recorded)

WPS NO.I Rev. - POSTWELD HEAT TREATMENT (QW-407)

Temperature Range None Time Range -

GAS (QW-408)

Percent Composition

Gas(es) (Mixture) Flow Rate

Shielding Co2 100% n Trailing A - - Backing A - -

ELECTRICAL CHARACTERISTICS (QW-409)

Current AC or DC D. C. polarity-

Amps (Range) /50 -170 Volts (Range) 21 - 23 (Amps and volts range shw ld be recorded for each electrode size, position, and thickness, etc. This information may be l ined in a tabular form similar t o that shown below.)

AXIS OF PlPE VERTICAL PlPE SHALL NOT BE TURNED OR ROLLED WHILE WELDING

Tungsten Electrode Size and Type None (Pure Tungsten, 2% Thoriated, etc.)

Mode of Metai Transfer for GMAW Short ~ i r c u i t i n a orc (Spray arc, short circu7ting arc, etc.)

Electrode Wire feed speed range 230 t o 300 i ~ r n

TECHNIQUE (QW-410)

String or Weave Bead See Details Sketch ' Orifice or Gas Cup Size VZ -inch I. D. 1/16 MAX Initial and lnterpass Cleaning (Brushing, Grinding, etc.) Bvcdsh f o clean metal

Method of Back Gouging None Oscillation As reouired Contact Tube to Work Distance +" t o 34 -inch Multiple or Single Pass (per side) / M L ( ( ~ ( D / ~ Multiple or Single Electrodes S in ole lik 4 1/16 MAX

Travel Speed (Range) 21 t o 2% ; ~ r n

Peening None Other All tack welds I% be around to feathev edoe. All starts and stoos fo be =round to

Sound metal. All suv~a:e cracks or holesJto be removed bq&e rnd/n; tno. , ,

Filler Metal Current

Travel

Speed

Class Dia. Polar. Range Range Range

ER 705-3 0.035.m E/ec + / 5 0 - I 7 0 2 / - 2 3 2/-26

I ,

Other

(e.g., Remarks, Com-

ments, Hot Wire

Addition. Technique,

Torch Angle, Etc.)

increase shl'e/d,np gas

//ow 50% when we/dl'ng

outdoors .

FIGURE 21-3 ASME welding procedure s p e c i f i c a t i o n s (WPS), s h e e t 2.


WPS N 0 . I Rev. - I POSITIONS (OW-405) I POSTWELD HEAT TREATMENT IQW407) 1

Position(s) of Groove 5 c P(0e A U S F/ot - f / x e d Welding Progression: Up P own -

I Position(s) of Fillet - PREHEAT ( Q W 4 M I

Preheat Temp. Min. 100-F Interpass Temp. Max. 200°F Preheat Maintenance /0O0/ (Continuous or special heating where applicable should be recorded)

ELECTRICAL CHARACTERISTICS (OW-409)

Current AC or D C ~ Polarity Electrode $ Amps (Range) 150 - 170 Volts (Range) 2/- 23

(Amps and volts range should be recorded for each electrode size, position, and thickness, etc. This information may be listed in a tabular form similar t o that shown below.)

Temperature Range None Time Range - I

GAS (QW-408)

Percent Composition

O d e s ) (Mixture) Flow Rate

Shielding f o o , ~ ~ - Trailing None - - Backing A - -

5G

AXIS OF PlPE HORIZONTAL PlPE SHALL NOT BE TURNED OR ROLLED WHILE WELDING

Tungsten Electrode Size and Type N0np (Pure Tungaten, 2% Thoriated, etc.) 1

Mode of Metal Transfer for GMAW Short circuitlno arc (Spray arc, short cyrcuiting arc, etc.)

230 ta 300 lorn 1 Electrode Wire feed speed range I TECHNIQUE (OW-410)

String or Weave Bead See Defails ske t ch - Orifice or Gas Cup Size PZ - ~ n c h LO.

tQl 1132 TO 1/16

Initial and lnterpass Cleaning (Brushing, Grinding, etc.) B ~ u s h to d e a n me

Method o f Back Gouging None Oscillation AS requi red L Contact Tube to Work Distance to '3'f

rp? Multiple or Single Pass (per side) r*ru/f(de

7 1116 MAX

Multiple or Single Electrodes sinqle Travel Speed (Range) 21 to 26 {cvn

Peening None Other AN hack weIds lo be qround b feather edqe . A// s t a r t s and stops to be qround

fo sound metal. All s t r ~ a c e cracks ov ho/<s to be fernoved beiore con$ny,nq

Filler Metal I Current

Travel

Speed

Range

2 1 - 26

Other

(e.g., Remarks, Com-

ments, Hot Wire

Addition, Technique,

Torch Angle, Etc.)

FIGURE 21-4 ASME welding procedure specifications (WPS), sheet 3.

I

SEC. 21-3

~ h r e /d;ng Y U S

{/ow 50%

when welding

out do0 fs.

PROCEDURE QUALIF ICATION RECORD (PQR) (See OW-201.2, Section I X , ASME Boiler and Pressure Vessel Code)

Record Actual Conditions Used to Weld Test Coupon.

Company Name ABC P ~ P S S U ~ ~ V ~ s ~ e l Co. Procedure Q u a l ~ f ~ c a t t o n Record No._ 10 7

BnutoH/n= l7 34C; Date AUO 8 1985

2

WPS NO. - . L - _ _ _ _ -

Weld~ng Process(es) -6-0- /MetalArr LY/a/d;nY) Types (Manual, Au tomat~c , Semi-Auto.) S e m i - ~ u f o m u t i r

FIGURE 21-5 ASME procedure qualification record (PQR), sheet 1.

JOINTS (QW-402)

5G

A X l S OF PlPE H O R I Z O N T A L PlPE S H A L L N O T BE T U R N E D OR R O L L E D WHILE WELDING

3/32 * 1/32 1/16 t 1/32 A X I S OF PIPE V E R T I C A L

PlPE S H A L L N O T BE T U R N E D OR R O L L E D WHILE WELDING

3/32 t 1 132

0.562 1/16 M A X

Groove Des~gn of Test Coupon

CH. 21

th~ckness shall be recorded for each f ~ l l e r metal or process used.)

P O S W E L D H E A T T R E A T M E N T IQW-407)

Temperature None - T ~ m e - Other

GAS (QW-408) Percent Composit ion

Gas(es) (Mixture) Flow Rate

Shie ld~ng c 0, 100% 20 CFH N o n ~ - -

Trail ing None -

Backing

ELECTRICAL CHARACTERISTICS (QW-409)

current D. C . P ~ I ~ ~ ~ ~ ~ E/ecfro de Positive Amps. I 5 O -180 Volts 21-23 Tungsten Electrode S ~ z e None other Shor t c~rcu i t inq arc

TECHNIQUE (QW-410)

Travel Speed 21 - 26 <prn string or weave ~~~d as vequived - see sketch -

osclllatlon as ~equiied - See skcr'ch Mult~pass or S~ngle Pass (per s~de) M U / ~ / , $ ~ S~ngle or Mul t ip le Electrodes Smn-qle - Other . .-___

(For comb lna t~on q u a l ~ f ~ c a t ~ o n s , the depos~ted weld metal

BASE M E T A L S (QW-403)

Mater~al spec. A STM A 53 ,Q ,P~ A Type or Grade

.I P-No. t o P-No. f

ThicknessofTestCoupon 0 . 5 6 2 - 1 n c h Diameter o f Test Coupon 24 - ;rich 0. D. Other -

FILLER METALS ( ~ w - 4 0 4 )

SFA Specification

AWS Classification

Fil ler Metal F-No.

Weld Metal Analysis A-No.

Size o f Fil ler Metal

Other

Deposited Weld Metal

5.18 ER 705 - 3

6 I

0 . 0 3 5 - l ‘ n - "8 - inch

POSITION (QW-405)

P o s ~ t ~ o n of Groove 2 G qnd 5C --

Weld Progress~on (UP~II I , D o w n h ~ l l ) Downhill Other

- _ _ _

PREHEAT (QW-4061

Preheat Temp.-- /ooO f lnterpass Temp. 2000 Ma* Other

shown on sheet 3 of 3. In the case of gas tungsten arc welding the tungsten electrode size and type should be described. For gas metal arc welding the mode of metal transfer must be described. The electrode wire feed speed range should be recorded.

Technique. Under technique, describe the weld as made with stringer or weave beads. Oscillation should be used to make weave beads. This should also show in the sketch. Often, both techniques are used in the same weld. For the gas-shielded process the nozzle inside diameter should be recorded. The method of cleaning before welding and between passes must be recorded. If back gouging is employed, it should be described. The contact tip-to-work distance should be described as a minimum-to-maximum dimension. It should be stated whether multiple- or single-pass technique is used. It is also necessary to indicate whether a single electrode or multiple electrodes are used. The travel speed range should be described. Peening, if used, must be described, and any other pertinent information concerned with making the weld should be mentioned. For example, pulsing, if employed, would need to be described.

Procedure Qualification Record To support the welding procedure specification (WPS), it is necessary to test and certify the weld results. This is done by making the welds described in the WPS, machining them, and testing the specimen in accordance with the code. This is done by the procedure qualification record (PQR), defined as a document providing the actual welding variables used to produce an acceptable test weld, and the results of tests conducted on the weld for the purpose of qualifying a welding procedure specification (WPS). It must reference a specific WPS. An example of a procedure qualification record is shown in Figures 21-5 and 21-6, which are similar to ASME QW-483. This sample PQR is a record of actual conditions used to weld the coupons made in accordance with WPS-1, the example shown previously. Many of the data required by the PQR are the same as the information on the referenced WPS. In fact, the data on the front sheets are almost identical. The back (sheet 2 of 2) of the PQR is straightfor- ward and is a record of the mechanical test, the tensile test, the guided bend test, the toughness test when required, and the fillet weld test, when used. A toughness test, either impact or drop weight, is not required by Sec- tion IX of the code. These tests may be required by other sections of the code and must be made according to other provisions of the code or an ASTM specification. The example shows typical data that would be entered. If the test data meet the requirements of the code, the form is then signed by the manufacturer's representative, certifying that the statements in the record are correct and that the test welds were prepared, welded, and tested in accordance with requirements of Section IX of the ASME code. The test record of the PQR qualifies the WPS and

fulfills the requirements for the code. All changes to a PQR require recertification by the manufacturer or contractor.

It is necessary to have specific WPSs and PQRs to cover all the weld processes, combination of welding processes, different P groupings of base materials, and so on, to comply with the variables involved. Every process and base metal used in production of the product must be covered by a WPS, which must be qualified by a PQR.

Record of Welder Qualification Tests With the WPS and PQR documents in order, it is then necessary to test the welders and welding operators for the work to be done. Each welder and welding operator involved in manufacturing or installing the products covered by the ASME Boiler and Pressure Vessel Code must be qualified.

The welder who prepares the procedure qualification record (PQR) specimens that pass code requirements is personally qualified within his or her performance qualification variables. All other welders and welding operators are qualified by specific welding tests, which are designed to determine the ability of the welder or welding operator to make welds required by the WPS that will cover the work. An example of the "Record of Welder or Welding Operator Qualification Tests" is shown by Figure 21-7, which is similar to ASME QW-484.

The record of welder or welding operator performance qualification tests should include the essential variables, the type of test and test results, and the ranges qualified, for each welder and welding operator. Each welder and welding operator should be assigned an identifying number, letter, or symbol. It is used to identify the work of that person. The tests assigned are in accordance with the code and the mechanical tests should meet the requirements applicable by the code. Radiographic examination may be substituted for mechanical tests ex- cept for GMAW using short-circuiting metal transfer. The radiographic technique and acceptance criteria should be in accordance with the code. In general, welders who meet the code requirements for groove welds are also qualified for fillet welds, but not vice versa. A welder qualified to weld in accordance with one qualified WPS is also qualified to weld in accordance with other qualified WPSs using the same welding process, within the limits of the essential variables according to the code.

If a welder has not welded for a period of three months or more, his or her qualifications shall be expired. If there is reason to question the welder's ability to make welds that meet the specifications, his or her qualification shall be considered expired. There are various other conditions relative to welder qualifications listed in the code. The code must be consulted for this information.

Symbol Stamps Manufacturers or contractors who regularly build or install pressure vessels or pressure pip-

SEC. 21-3 WELDING PROCEDURES AND QUALIFYING THEM 637

POR No. /0 Tonrile Test (QW-150)

Guided-Bend Tests (OW-1 60)

Toughness Tests (OW-170)

Type and F~gure No

51de bend 97.1 - Side bend 47 .1 -

51de bend 0 7 . 1 -

51de bend 07.1

Result

.. /Vode/ect - ---

NO de&ct .& d e [ e d - -

No detect

Fillet-Weld Test (OW-180)

Result - Sat~sfactory Yes X No - Penetrat~on lnto Parent Metal Yes - X - No

Macro-Results N o r m a l . - -

Other Tests

Drop We~qht

Type of Test - None -- -

Depos~t Analys~s _ - _ None - --- - -- - -

Other - None - -- -

Break

-

Lateral EXD

welder's ~ a m e P e t e r _J/,k- - - C l o c k No 3 5 0 6 Stamp No 506 Tests conducted by Hobart Procedure Laboratory Laboratory Test No 7- 376 We cen~fy that the statements In t h ~ s record are correct and that the test welds were prepared, welded, and tested In accordance wlth the

requirements of Sect~on IX of the ASME Code

Test Temp

-- -

-

. - - --

Notch Type

- . --

- -

Spec~men No

None

--

No Break % Shear

- - -- .

. - -

-

.~ - -

Manufacturer -A6-CP!re5%!Ee Vegee/ Co

Impact Values

- - - - .

~. - --

-

- -

Notch Locat~on

- -

-- - . -

- --

M ~ l s

. - - - .

-

-

- -

Date Au4. 11: 1985 -- --

(Detail of record of tests are ~l lustrat~ve only and may be m o d ~ f ~ e d to conform to the type and number of tests requ~red by the Code 1

FIGURE 21-6 ASME procedure qualification record (PQR), sheet 2.

CH. 21

MANUFACTURER'S RECORD OF WELDER OR WELDING OPERATOR QUALIFICATION TESTS (WPQ)

(See QW-301, Section IX, ASME Boiler and Pressure Vessel Code)

Welder ~ame- check No. 3506 Stamp No. 506

Using WPS NO.I Rev. - Date 8!1/!85 the above welder is qualified for the following ranges.

Record Actual Values

Variable

Process

Process T V D ~

Used i n Qualification

C/HAW Semi- a s

Backing [metal, weld metal, flux, etc. (OW402)I A Material Spec. (QW-403) -to & Thickness

Groove 0.562 - in

Qualification Range

I;MAW Semi- au-

Fillet - -

Diameter

Groove

Fillet

Filler Metal (OW-404)

Spec. No.

Class

F-No.

Deposited Weld Metal Thickness

Groove - X Fillet

Position (QW-405)

Weld Progression

Gas Type (OW-408)

Backlng Gas (QW-408) None Electrical Characteristics (OW409)

2G and 5C A// ~osl t ion

Current

Polarity Electrode 4 f / m ~ t r o d e + Guided Bend Test Results QW-462.2(a), QW-462.3(a), QW-462.3(b)

Type and Fig. No. Result

Radiographic Test Results (QW-304 & QW-305) For alternative qualification of groove welds by radiography

Rad~ographlc Results. None Fillet Weld Test Results [See QW462.4(a), QW462.4(b)l

Fracture Test (Describe the locat~on, nature and stze of any crack or tearlng of the specimen)

- -

Length and Per Cent of Defects - Inches - Yo

Macro Test-Fus~on None In. x - -

Appearance-Ftllet Sue (leg) - ~ n . Convextty in. or Concavity - In

Test Conducted by H o b a r t Weldin? P r o c e d u r e L Q ~ ~aboratory-Test No. /065 We cenlfy that the statements In thts record are correct and that the test welds were prepared, welded and tested i n accordance with the

requirements of Sect~on IX of the ASME Code

Organization A6C P r e s s w e Vessel Co

(Detail of record of tests are illustrative only and may be modif ied to conform to the type and number of tests required by the Code.)

NOTE: Anv essential vartables In addition to those above shall be recorded.

FIGURE 21-7 ASME record of welder qualification tests WPQ.

SEC. 21-3

ing will usually have an ASME "symbol stamp." This means that the particular contractor or manufacturer has been approved by the American Society of Mechanical Engineers as an authorized manufacturer or installer of the type of equipment specified. Various stamps are used to mark the installation or the product manufactured. Some of the symbol stamps are:

7 7 N Nuclear vessel

Y P P Pressure piping

7 U Pressure vessel ; S Power boilers 1 H Heating boilers

To obtain an ASME symbol stamp, a manufacturer or contractor must contact the American Society of Mechanical Engineers, Boiler and Pressure Code Com- mittee, and apply for the code symbol required. The actual mechanics are quite involved but include obtaining a contract with an authorized inspection agency, normally one of the states or provinces or a casualty insurance company. The American Society of Mechanical Engineers will advise of the exact requirements. The requirements include at least the need to prepare a written quality control manual describing a controlled manufacturing system for the scope of the proposed ASME certificates of authorization. The ASME will send a survey team to inspect your facilities and review the quality control manual and a demonstration of all items affecting quality within the scope of the certificate. This demonstration must include material control, drawings, design, inspection sign- off, welding procedure specifications, welding procedure qualifications, welding performance qualifications, heat treatment, and so on. If everything is satisfactory, ASME will issue a certificate of authorization and the applicable code symbol stamp.

Structural Welding

Requirements for the AWS Structural Welding Code(6) are not as involved as the ASME Pressure Vessel Code. However "each manufacturer or contractor shall conduct the tests required by this code to qualify the welding procedures." In addition, "the engineer, at his discretion, may accept evidence of previous qualification of welders, welding operators and tackers to be employed." Thus the manufacturer or contractor is totally responsible for qualification of procedures and personnel.

AWS allows the use of prequalified welding procedures. They must conform in all respects to the provisions of the code described in a table "Mandatory Code Re- quirements for Pre-Qualified Joint Welding Procedures." There is an exception to the prequalified procedures, and that is if high-strength (90,000 psi) filler metals are used. By "prequalified," AWS means that they should be ex-

empt from tests or qualifications provided that they conform in all respects to the applicable code requirements. Even so, the code requires that the manufacturer or contractor prepare a written procedure specification for the joint welding procedure to be used. This is a record of materials and welding variables which shows that the joint welding procedure meets the requirements for prequalified status. It is therefore necessary to prepare welding procedure specifications that cover the work to be done under the requirements of the AWS Structural Welding Code, D1.l.

There are other qualification requirements by AWS, and these relate to many types of weldments other than structural. To have a broader qualification record, it is best to conform to the requirements of the AWS "Stand- ard for Welding Procedure and Performance Qualifi- cation."(2) This is because the provisions of B2.1 will fill the requirements of structural code Dl . 1, but also the requirements of any other welded products covered by AWS codes or specifications. In view of this, the example will describe the requirements of the Standard for Welding Procedure and Performance Qualification and utilize the forms recommended. In this example, the X,Y,Z Structural Company is qualifying a procedure for flux-cored arc welding of carbon steel using the semiautomatic method of application, and using carbon di- oxide shielding gas.

For the AWS standard for welding and performance, the welding procedure is known as a welding procedure specification, and an example is shown in Figure 21-8. The information to fill in this form is essentially the same as the information used by ASME welding procedure specification.

The welding procedure specification is then qualified by making specific welds as described and testing them. An example of the AWS procedure qualification record (PQR) is shown in Figures 21-9 and 21-10. These data are also very similar to those used by the ASME procedure qualification record. One difference would be that filler metal specifications and classifications are to AWS numbers, and these numbers are all presented in the Standard B2.1.

For qualifying the welder, the AWS B2.1 uses a form called the performance qualification test record (PQTR). This is for recording the results of tests made by welders or welding operators. An example of this test record is shown in Figure 21-1 1. The data to be filled in are similar to ASME data. Upon completion of the tests, and if they meet the code requirements, this record is then signed by the qualifier, which qualifies the welder or welding operator. In the case of AWS, the qualification record is continuous unless no welding is done for a period of six months or if there is reason to question the ability of the welder. You must refer to the specific code or specification involved and follow it.

FIGURE 21-10 AWS procedure qualification record (PQR), sheet 2.

I M Page 2 of 2 r

TENSILE TEST SPECIMENS: PROCEDURE OUALlFlCATlON RECORD POR No 2 Type Reduced Sectton Tensile speclmen slze 1 x3/4 -Inch Area 3'4 9. ' I - .

Groove ( x ) Re~n fo rc~ng bar ( - ) Stud welds ( - ) 8 Tensile test results (M ln~mum requ~red UTS 62. 0 0 0 PSI)

z Max load Type failure and Soec~men no Wldth ~n Thickness ~n Area in Ibs UTS PSI location

V1 -8751 -C1 0.990 0.796 0.7376 56.700 76.870 Bqse Metol -8751-C2 0.99 0.746 0.74/5 57.275 77.24-0 B a s e Metel

,991 0.790 0.7829 68.000 87.000 Aose Metal 0.789 0 7835 69.850 8 9 1 1 5 0 0 ~ s e Mete/

GUIDED BEND TEST SPECIMENS - SPECIMEN SIZE: 3/8 x 1 -loch g (f/at) Type Result ( ~ o r r ~ o n t o l ) ~ ~ p e Result

$ 5,d.- bend Passed I S~de bend Pussed Slde bend Passed 1 Slde bend Passed

MACRO-EXAMINATION RESULTS: Reinforcing bar ( - ) Stud ( - ) M 1 - 4 -

2 - 5 G None

- 3

- SHEAR TEST RESULTS - FILLETS 1

- 3 - 2 - 4 -

2 None 7

IMPACT TEST SPECIMENS Type C r lo V - n o size /O m n x /O m n

-5 ~ e s t temperatu:: '-ZOsc. F20-F: - 6O0F; -Boo/= Specimen locatlon WM = weld metal BM = base metal. HAZ = heat-affected zone

tr Test results 'd Weld~ng Specimen Energy absorbed Ductlle fracture Lateral expansion

posltlon location (it -Ibs ) area (percent) (mils)

F ls t WM 95 ' /oo 8 0 F/at W M 82 l o o 7 5

u Flat W M 65 100 70 Flet W M 50 (00 50

m M IF APPLICABLE

Hardness tests: ( - ) Values - Visual (special weldments 2.4.2) ( - ) Torque ( - ) psi

Proof test ( - ) Method

Chemical analysis ( - )

Non-destructive exam ( - ) Process

Other None - Mechanical Testing by (Company) -

RESULTS

Acceptable ( ) Unacceptable ( )







Lab No. TWB-707-C

Wecertify that the statements in this Record arecorrect and that the test welds were prepared, welded, and tested in accordance with the requirements of the American Welding Society Standard for Welding Procedure and Perfor- mance Qualification (AWS 02.1-83).

Qualifier: X Y Z Strucfuva[ Comoonv Revlewed by: Date: /ov 12. /985 Approved by:

Employer

E

FIGURE 21-11 AWS performance qualification test record.

PERFORMANCE QUALIFICATION TEST RECORD

Name John Doe ldentiflcatlon 7w6- 707- C Welder ( % i Operator ( i

Soc~al securlty number /23 - 4-5 - 432/ O u a l ~ f ~ e d to WPS no 200 Process(es) FCAC)' Manual ( ) Semi-Automat~c ( X ) Automat~c ( ) Machlne i i

Test base metal s p e c ~ f ~ c a t ~ o n A S W 8-4.41 - T~ ASTM A - 4 4 1 Mater~al number M 7 - - To M-l

Fuel gas (OFW) None -. - -- --

AWS f~l ler metal c lass~ f~ca t~on A 5 . 2 0 F 707-5 F n o 2- Back~ng Current Consumable lnsert Root sh~elding

TEST WELDMENT

GROOVE: P ~ p e Plate Rebar

Yes ( X i No i ! AC i I DC i X J

Yes 1 ) No ( u I Yes ( ) No ( x 1

POSITION TESTED

FILLET: Pipe ( ) I F ( ) 2 F i ) 3 F ( 1 4 F i Plate ( ) I F ( ! 2 F ( ) 3 F i I 4 F (

Double ( 1 or Slngle s ~ d e i x )

Shor t -c~rcu~ t~ng arc (GMAW) Yes 1 ) No ( 1

WELDMENT THICKNESS (T)

6GR ( I Dlameteris) ( T i - iT1 f - / n & Bar s~ze A Butt i 1

Spllced butt i )

) 5F i 1 Diameter f T ) 1 i T i -

Other (describe) -

Test results Remarks

V I S U ~ ~ test results NIA ( % ) Pass i ) Fall ( I

Bend test results NIA i Pass ( m ) Fall ( J

Macro test results N/A ( x J Pass ( J Fall I )

Tension test NfA ( 1 Pass ( x ) F a ~ i ( 1 Radiographic test results NIA ( x ) Pass ( ) Fail i i Penetrant test NIA ( x 1 Pass ( ) Fall ( j

QUALIFIED FOR, PROCESSES GROOVE: THICKNESS

P ~ p e 1G ( j 2G ( ) 5G ( j 6G ( ) 6GR ( ) (T ) Mln __ Max __ Dla - Plate l G ( x j 2 G ( x ) 3 G ( ) 4 G ( ) (T ) Mln k Max Med Rebar 1G ( ) 2G ( j 3G ( ) 4G ( Bar size Mln Max -

FILLET: P ~ p e I F ( ) 2 F ( ) 4 F ( j 5 F ( j (T) Mln Max - Plate 1F ( ) 2F ( ) 3F ( ) 4F ( j (T) Mln 3/8 Max &bJ?kX

Rebar I F ( ) 2F ( j 3F ( ) 4F ( ) Bar slze Min Max - Weld claddlng ( ) Pos~tlon(s) T Min Max Clad Mln -

Consumable lnsert ( ) Backing type ( ) Vert~cal Up ( ) Down ( ) Slngle s ~ d e ( ) Double s ~ d e ( j No backlng ( ) Short-c~rcuit lng arc ( ) Spray arc ( ) Pulsed arc ( ) Relnforc~ng bar - butt ( ) or Spliced butt ( )

The above named person IS q u a l ~ f ~ e d for the welding process(es) used In thls test w i th~n the llmlts of essential var~ables lncludlng materlalsand f~ l le r metal var~ables of the AWS Standard for Welding Procedure and Performance Qual~ficatlon (AWS B2 1) .

Date tested NO#. 17, 1985 Slgned by -7- R m Ouallfier

Cross-Country Pipelines

The API Standard 1 104(38) for welding pipelines and related facilities requires procedure and welder qualification. This code was designed so that qualification tests can be made in the field. It is used worldwide. The procedure specification includes the process, the base metal material, the size of pipe, diameter and wall thickness, the joint detail, the filler metal type, size and number of passes, and the electrical characteristics utilized. For gas welding, the flame characteristics, direction of welding, welding position, type of flux, and so on, must be made known. If any of the essential variables are changed, the welding procedure must be reestablished and completely

F G.U. Cross Country f i f e Line CO

STANDARD PROCEDURE SPECIFIC4TION YO. 3

Date 11 30 82 For .$MhW. .Welding of x.-.?? .Pipe and Fittings , or

A Process Shie /ded Metsi Avc !4'eld,ng

B Material A , P. I . Std p$~:pe X - 52

C D~ameter and Wall Thickness 4%' f0 /z3/+ 9 3'?6 b 3/4

D Joint Des~gn S/n$e Vee Cvoovsr 60' to 75" $6 RO + k RF

E Filler Metal and Number of Beads see Sketch s l d Sched.clz

F Electrical or Flame Character~stics C Electrode & s / t l v e

G Pos~t~on & o r ( $ , ~ n t a / f / x e d - 5 G

H D~rection of Welding P ~ w / l h / l l

I Number of Welders

J T ~ m e Lapse between Passes Unilmlted

K Type of Llne-up Clamp bone

L Removal of L~ne-up Clamp requcrcd

M Clearung f l echo~cs l to &move C1// 519

N Preheat, Stress Relief None

0 Shield~ng Gas and Flow Rate None

P Sh~eldlng Flux Nooe

Q speed of Travel Total T/me f ~ r Joint 23 n l ~ p

R Sketches and Tabulations (to be attached) See S h t t t 2 o[ 3

Tested Welder L Welder Approved Weld~ng Sup 5 JOM* Adopted Chief Eng~neer C E Smltb

FIGURE 21-12 API standard procedure specification: data sheet.

requalified. This includes a change in the welding process, a change in the pipe material or size, a change in the joint design, a change in the position, a change in filler metal, a change in filler metal size, and so on. These changes are described in detail. The code must be referred to in writing a qualified welding procedure. An example of an API qualified welding procedure is given in Figures 21-12 to 21-14. These illustrations utilize the API forms found in the code.

Other codes may reference the three codes just described, and in these cases the same provisions would apply. It must be reemphasized that the code in question must be studied in order to write an intelligent welding procedure and qualify it.

FIGURE 21-13 API standard procedure specification: sketches and tabulation.

f G ci C r o s s Country fipe f ne

S T A N D A R D PROCEDURE SPECIF ICATIONS "eC " 3

SKETCHES & TABULATIONS Date lo 30 82

Sheet 2 of 3

r-' 3f1:3021T1061 16 x(-yj$ t

APPROX 1/16 1 1 6 f 1 3 2

r A P P R O X 1 1 6

'l--s$-T] L

ELECTRODE SIZE LL NUMBERS OF BEADS

NUMBER OF BEADS

PIPE WALL TOTAL NUMBER THICKNESS ELECTRODE ELECTRODE ELECTRODE OF BEADS

0 203 E6010 1- ' 7 0 0 1-5 /J2 €7010 3

NOTE FIRST PASS ONLY 66010 REMAINING PASSES USE E 7010 COVER BEAD MAY BE MADE WITH E7010

VOLTAGE LL AMPERAGE RANGE

ELECTRODE DIAMETER AMPERAGE ARC VOLTS

$ EbOlO / / O 1 7

'4 E 7010 /10 7 7

'/& ,E 7010 / 3 0 2 6

SEC. 21-3

-1 volves different joint details, welding positions, metal

F L H Cvoss Country Ptpe i o

COUPON TEST REPORT

Test No 7242 I t,Lrtlc,n 507, Ohio I)at< 1/ 3 0 8 5 \talc KI,II Weld NO I (xed p,\ltlon Weld yes Welder John C Mtckman Mak 3 5 0 9 Weld~ny tlmc 2 3 mi05 l lntr 01 clay /O 00 A& M Temperature 70°F weather c,,nd,tl,,n We/dtny was done ~ncloors W ~ n d hrerk u\etl Voqe rollage 25 28 amperage ( 1 0 -130 rype of weldan8 mach~nr Hobart DC Cen S u e 300 Amp

r l l l r r mrtal Hob~rrt # 10. Hobart R 885 51rc of relntor~emrnt V5.1 ( o ''16 P ~ p e Kind and (nr.idr 5 C X X - 52 W.111 th l~kne\ \ 203 [)la 0 0 8"

Bead NIB S I L C of E l r ~ t r o d r

Coupon \ t rnr~ led Ortglnal D ~ m e n \ ~ o n of plate O r ~ g n area of plate Mar lmum load Tenule S/ln plate u e d Fra~ture locdt!on

Meto1 Aehi

N o 01 Electrode

M Procedurr Q u a l ~ f y ~ n g Test @ a l ~ h e d n Welder n L ~ n e Test Dlsqualtfted

M a r ten*~ l r 80 000 Man tens~le 79,200 Avg tenslle 79.500 Remark5 on ten\~le

I Faded tn bqse rneCsl 2' krn w e @ 2 Faded /n base rneCsl 1-1/z f r o m weld 3

. . . . . . 4 Remarks on Bend Te\ta . . . . . . .

1 Root bend, no defects,psssed . . . . . . . . . . . . . . . 2 Root bend, one m,nQr defect, pqued . . . . . . . . . 3 Face bend, no defects ,passed . . . . . . 4 Face bevd, mlnor de~ec.Cs,p~ssed . . . . .

Remarks on Ntck Tests . . . . . . . I No s'ejrcts . . . . . . . . . 2 No de(ecfs . . . . . . . .

. . . . . . . 3 . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . Tett made at Hobart irchnrcsl Cenfcr. Date 71.2.3; 85 Tested by . Supervised by . . . . . . . . . . . . .

1 2 3 4 5 6 7

4

FIGURE 21-14 API standard procedure specification: coupon test report.

3

21-4 STANDARD WELDING PROCEDURE SPECIFICATIONS

A major expense of welding fabricators, contractors, construction companies, and weldment manufacturers is the necessity to design, write, prepare, test, and qualify welding procedures. This expense becomes excessive because of the necessity of requalifying the same procedures and personnel over and over. The requalification of welding procedures and welders is due to code requirements, customer requirements, or legal reasons.

Welding companies are required to have qualified welding procedures for welding similar or different metals together in different thickness ranges using different welding processes and welding filler materials. This in-

products, and joint welding techniques. Many companies have hundreds of qualified welding procedures to enable them to manufacture their products.

The use of standard welding procedure specifications can greatly reduce this expense. The standard welding procedure specifications will satisfy all of the technical requirements of most welding codes and specifications. A standard welding procedure specification (Std. WPS) would list ranges of all variables acceptable for the application of the particular specification. Each standard WPS is based on data from hundreds of proven procedure qualification records (PQRs) and/or extensive tests. These provide directions for making acceptable welds with specific processes on specific metals, and so on, by a skilled welder or welding operator. The standard welding procedure specifications have a broader technical base than those normally qualified by a single organization. They are supported by more test data, including the results from research programs

The standard procedure specifications will provide ranges of the welding variables that will be practical for the applications for which they are to be used. These will be narrow enough so that acceptable welds can be made at the extremities of the ranges.

The standard welding procedure specifications are permitted to be used on work covered by the code or specification for which it has been approved. They do not require further testing or qualification work by the welding company. Thus it will no longer be necessary for the welding company to develop and qualify specific welding procedures specifications. However, new welding processes, materials, or filler metals must still be tested and qualified as in the past.

The standard WPS do not replace the applicable code or standard. They merely replace individual company's own WPSs and PQRs. Standard welding procedure specifications will still require engineering judg- ment so that the ranges of variables are suitable for the application.

The standard welding procedure specifications are approved by the American Welding Society and by the American National Standards Institute (ANSI). They would also be approved by the code- or specification- writing organization.

The standard welding procedure specifications adopted so far are shown by Figure 21-15. All standard welding procedure specifications will follow a standardized format similar to AWS and ASME forms. They will use filler metal and base metal specifications used by existing codes and specifications. The Standardized Welding Procedure Specifications can be obtained from the American Welding Society, Miami, Florida. It is an- ticipated that the standard WPSs will save the welding industry tremendous sums of money and may enable them to become more competitive throughout the world.


Standard WPS Welding Process Application Base Miscellaneous

Number Process Variation Method Metal Position Information

SMAW

GTAW

GMAW

GMAW

GMAW

GMAW

GTAW

GTAW

GTAW

GTAW

-

-

Short circu~ting

Short c i rcu~t ing

Short circuiting

Short circuiting

-

-

-

M.A.

M.A.

S. A.

S.A.

S.A.

S.A.

M.A.

M.A.

M.A.

M.A.

Carbon steel

Carbon steel

Galvanized steel

Carbon steel

Austenitic SS

CS to austenitic SS

Galvanized steel

Carbon steel

Austenitic SS

CS t o austenitic SS

All

All

All

All

All

All

All

All

All

All

3/r6-3'-in.-thi~k L.H.

%6-3/8-in.-thick-argon dc

Sheet metal-argon + CO,

Sheet metal-argon + CO,

Sheet metal

9 0 % He, 7 % argon, 2 %

coz Sheet metal

9 0 % He, 7 % argon, 2 % coz

Sheet metal - argon

Sheet metal-argon

Sheet metal-argon

Sheet metal-argon

FIGURE 21-15 Standard welding procedure specifications.

QUESTIONS

21-1. What are the three components of a welding manufacturing system?

21-2. What is the purpose of a procedure qualification record (PQR)?

21-3. What is the purpose of a welder performance qualification (WPQ) test?

21-4. Why are perfect welds required for some classes of work and not others?

21-5. Who is responsible for a good-quality product?

21-6. Who is responsible for a good-quality weld? 21-7. There are 20 factors included in a quality assurance

plan. Name as many as you can.

21-8. Codes and specifications are related to industries. What industries use welding specifications?

21-9. What is a welding procedure specification (WPS)? 21-10. What is a welding procedure? Name two types. 21-11. Is the ASME Section IX, welding qualifications, en-

forceable by law?

REFERENCES

1. Howard Woodward, "The Importance of a Welding Manufacturing System," Welding Journal, Sept. 1986.

2. "Standard for Welding Procedure and Performance Qualification," AWS B2.1, American Welding Society, mi am^, Fla.

3. "Boiler and Pressure Vessel Code," American Society of Mechanical Engineers, New York.

Can welders be certified by a contractors' association? Who does this, and how?

What is an ASME symbol stamp? Who can use it?

What welded products are covered by the AWS structural code? What materials?

What are prequalified welding processes? Explain.

What welded products are covered by API Standard 1 104?

How are automatic welding equipment and operators qualified? What method does API 1104 use for fracture toughness testing?

How will standard WPSs reduce the cost of weldments?

Who makes standard welding procedure specifications available to the industry?

4. "Code of Federal Regulations," Section 10, Energy Part 50, Appendix B (lOCFR50-B), Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants.

5 . "Standard for Welding of Reactor Coolant and Asso- ciated Systems and Components for Navel Nuclear Power Plants," Navships 250-1 500- 1 .

"Structural Welding Code," AWS D l . 1, American Welding Society, Miami, Fla.

"Standard Specifications for Highway Bridges," American Association of State Highway Officials, Washington, D.C.

"Specifications for Steel Railway Bridges," American Railway Engineering Association, Chicago, 1969.

U.S. Coast Guard, Department of Transportation, "Marine Engineering Regulations," Sub Chapter F, Part 57, "Welding and Brazing," Code of Federal Regulations, Washington, D.C.

"Fabrication, Welding and Inspection of Ship Hulls," Navships 0900-000-1000, Dept. of the Navy, Naval Ship Systems Command, Washington, D.C.

"Standard Specification for Merchant Ship Construc- tion," U.S. Maritime Administration, Washington, D.C.

"Rules for Building and Classing Steel Vessels," American Bureau of Shipping, New York.

"Guide for Steel Hull Welding," AWS D3.5, American Welding Society, Miami, Fla.

"Guide for Aluminum Hull Welding," AWS D3.7, American Welding Society, Miami, Fla.

"Standard for Welded Steel Elevated Tanks, Standpipes and Reservoirs for Water Storage," AWS D5.2, American Welding Society, Miami, Fla.

"Standard for Welded Steel Tanks for Oil Storage," API Standard 650, American Petroleum Institute, Washington, D.C.

"Specifications for Tank Cars," Association of American Railroads, Washington, D.C.

"Specifications for Design, Fabrication, and Construc- tion of Freight Cars," Association of American Railroads, Chicago.

"Railroad Welding Specifications," AWS D15.1, American Welding Society, Miami, Fla.

"General Design and Construction Requirements," Code of Federal Regulations, Title 49, Transportation Section 178.340, Part D, Superintendent of Documents, Washington, D.C.

"Specification for Cargo Tanks," ML.33 1, Code of Federal Regulations, Title 49, Transportation Section 178.337, Superintendent of Documents, Washington, D.C. "Aerospace Material Specifications," Society of Auto- motive Engineers, Warrendale, Pa.

"National Aerospace Standards," Aerospace Industries Association of America, Washington, D.C.

"Qualification of Aircraft, Missile and Aerospace Fusion Welders," Military Standard MIL-T-1595A, Department of Defense, Washington, D.C. "Welding on Earthmoving and Construction Equip- ment," AWS D14.3, American Welding Society, Miami, Fla. I

"Welding Industrial and Mill Cranes," AWS D14.1, American Welding Society, Miami, FLa.

"Metal Cutting Machine Tool Weldments," AWS D14.2, American Welding Society, Miami, Fla. "Specifications for Welding of Presses and Press Corn- ponents," AWS D14.5, American Welding Society, Miami, Fla.

"Specifications for Rotating Elements of Equipment," AWS D14.6, American Welding Society, Miami, Fla.

"Classification and Application of Welded Joints for Machinery and Equipment," AWS D14.4, American Welding Society, Miami, Fla.

"Recommended Practices for Automotive Welding Design," AWS D8.4, American Welding Society, Miami, Fla.

"Recommended Practices for Automotive Portable Gun- Resistance Spot Welding," AWS D8.5, American Weld- ing Society, Miami, Fla.

"Standard for Automotive Resistance Spot Welding Electrodes," AWS D8.6, American Welding Society, Miami, Fla.

"Specifications for Automotive Welding Quality- Resistance Spot Welding," AWS D8.7, American Welding Society, Miami, Fla.

"Specifications for Automotive Frame Weld Quality- Arc Welding," AWS D8.8, American Welding Society, Miami, Fla.

"Standard for Welding Procedure and Performance Qualifications," AWS B2.1, American Welding Society, Miami, Fla.

"Standard Welding Terms and Definitions," AWS A3.0, American Welding Society, Miami, Fla.

"Standard for Welding Pipelines and Related Facilities," API Standard 1104, American Petroleum Institute, Washington, D.C.

OUTLINE

25-1 Tubular Products

25-2 Pipe and Tube Welding

2 5-3 Manual and Semiautomatic Pipe Welding

25-4 Mechanized Pipe and Tube Welding

25- j Automated Pipe Welding

25-6 Tube t o Sheet Welding

Pipe and Tube Welding

TUBULAR PRODUCTS

Tubular products, known as pipe or tubing, are hollow items, normally circular, used for transmitting gases or liq- uids, or for structural, mechanical, or decorative functions. They can range in diameter from the smallest to the largest and with wall thicknesse? from very thin to relatively heavy. Tubular products can be manufactured as seamless or welded. Welded tubular products are the most popular and are the only one considered here. There are many different ways of classifying pipe and tubing, but are usually based on shape arid intended use. General classifications are as follows:

1. Standard pipe: used for transmission of low- pressure air, steam, other gases, water, oil, and/or other fluids. Used primarily in buildings, sprinkler systems, irrigation systems, and in machinery.

2. Line pipe: used for the transportation of gas, oil, water, and so on, in cross-country pipelines and for utility distribution systems.

3. Oil country goods: tubular products used by the oil and gas industries with three subdivisions: casings for well walls, tubing used within the casings, and drill pipe used to carry rotary drilling tools.

4. Pressure tubing: used to transmit fluids or gases at elevated temperatures or pressures or both.

5. Mechanical tubing: used to manufacture industrial, construction, and agriculture equipment.

6 . Structural pipe and tube: used for structural or load-bearing purposes, for architectural or structural purposes, and can be of different shapes.

7. Thin-wall tubing: used for instrument tubing, aircraft control tubing, air conditioning, and miscellaneous applications; can be of different sizes and of stainless steels and nonferrous metals.

Each classification can be made of different materials. Standard pipe is normally made of carbon steel. It may be uncoated, galvanized, or plastic coated, and is made in different wall thicknesses, known as standard, extra-strong, double-extra strong, and others. Wall thickness may be indicated by schedule number (Figure 25-1). Schedule 40 is standard-weight pipe.

Line pipe is made of carbon steel or of low-alloy high-strength steel. They are made of weldable steels since line pipe is normally joined by welding. Line pipe is made to API specifications.

Oil country goods are made of carbon steel and alloy steels, and some items are made of extremely high- alloy high-strength materials.

Pressure tubing, which is made to exact dimensions of outside diameter arid wall thickness, is made of carbon steels, alloy steels, creep-resisting steels, heat-resisting steels, and stainless steels of different types.

Structural steel pipe and tube is made of low-carbon weldable steels. The analysis of the steel used for making the pipe is normally specified by the producer, or by specifications for the material.

Thin-wall tubing is made of low-alloy steels and stainless steels. Stainless steel tubing is available in almost any alloy of stainless available. In addition to steels, tubing is available in aluminum, copper, titanium, and nickel alloys.

The dimensions used for pipe and tubing depend on the product classification and the country of origin. See standard pipe sizes mentioned above and metric sizes shown in Figure 25-2.

In specifying pipe and tubing, it is necessary to provide exact dimensions and the material classification or composition in order to obtain the type requested.

Methods for Manufacturing

Welded tubing is preferred over seamless tubing since it has more uniform wall thickness and is normally less ex- pensive. The following welding processes are used to make pipe and tubing:

1. The continuous butt welding process 2. The resistance welding processes

3. The arc welding processes

4. The high-energy beam (electron and laser) processes

There are two types of weld joints employed. The most common is the straight longitudinal joint from end to end of pipe, used for all sizes from smallest to largest. The spiral joint, which is used for medium- and larger- sized tubular products, is usually welded with the submerged arc welding processes.

The continuous mill for making tubular products, when the weld joint is longitudinal, is similar for all of the welding processes.(') A continuous mill (Figure 25-3) consists of the following:

1. The coil of strip or skelp 2. The splicing operation for the skelp

3. Strip flattening and trimming station (optional) 4. Multiple forming rolls, including closing rolls 5. Welding station, including the squeeze or pressure

rolls 6. Sizing rolls, or die

7. Cut off operation

The number and size of rolls, number of stations, and so on, will vary depending on the manufacture of the mill and the size and type of tubular products being produced.

The welding station produces a high-quality weld with full penetration, minimum root and face reinforcement, and minimum bead widths. The weld must be smooth, uniform, and clean without cracks and without undercutting and the reinforcement of the weld should not exceed 10% of the wall thickness.

The so-called butt welding process, commonly called the CW (continuous welding) process, is the oldest welding process for welding pipe. It is actually forge welding in which the flat stock, known as skelp, is formed into a tubular shape while very hot and pulled through a die. This causes the abutting edges to come together under very high pressure and high temperatures in a continuous welding mill, to make a forge weld. This process is used to manufacture standard pipe of %, to 4 in. nominal diameter at high rate of speed on a continuous butt-welded pipe mill.

There are three electric resistance welding processes employed for continuous mill welding. The choice of the welding process variation depends on the diameter of the tubular product, the wall thickness, and the production rate. In all three methods the power for welding is provided either by low-frequency current through revolving electrode wheels, or by radio-frequency current through sliding contacts or induction coils.

Gas tungsten arc welding is popular for thin-wall stainless tubing and tubing made of nonferrous alloys. As wall thickness increases, more torches may be used

SEC. 25-1

FIG

UR

E 25-1

Sta

nd

ard

pip

e s

ize

an

d w

all

th

ickn

ess

.

Nom

inal

P

ipe

NO

MIN

AL W

AL

L TH

ICK

NE

SS

F

OR

:

Siz

e O

uts

ide

S

ched

. S

ched

. S

ched

. S

ched

. S

ched

. S

ched

. E

xtra

S

ched

. S

ched

. S

ched

. S

ched

. S

ched

. X

X

(in

.)

Dia

. 5

10

2 0

30

Sta

nd

ard

4

0

60

Str

on

g

80

100

120

140

160

Str

on

g

Nominal Outside Wall

Size schedule Diameter Thickness

in. rnm Number in. mm in. rnm

Nominal Outside Wall

Pipe Size Schedule Diameter Thickness

in. mm Number in. mm in. mm

1 '12 3 8 5 1.900 48.3 0 .065 1.7 1 0 0 .109 2.8 4 0 0 .145 3.7 8 0 0 .200 5.1

FIGURE 25-2 Metr ic p ipe size and wal l thickness.

FIGURE 25-3 Continuous m i l l for making tubular products.

SEC. 25-1 TUBULAR PRODUCTS 73 1

Wall Thickness

Travel Speed

in. mm in./min mmlmin

Current Arc Shield (A) Voltage Gas

DCEN (V) Type

Joint Detail

TY pe

Argon Argon + 5% H, Argon Argon 9 5 argon + 5 % H2 9 5 argon + 5% H2 9 5 argon + 5% H, 9 5 argon + 5% H2

Square butt Square butt Square butt Square butt 60° V 60° V 60° V 60° V

FIGURE 25-4 We ld ing schedule for G T A W welding stainless steel tubing.

and filler wire may be employed. Plasma arc welding is finding increased use for stainless steel tube mills. Gas metal arc welding is often employed where thickness is greater and filler metal is required. For thick-wall pipe made in short lengths, flux-cored arc welding or submerged arc welding can be used. These processes are used for making spiral joint pipe.

The gas tungsten arc welding process produces high- quality welds in tube mills in square groove welds from 0.020 in. (0.5 mm) to 0.118 in. (3 mm) thick without the addition of filler wire. The wall thickness of the tubing and the metal composition greatly influence the welding parameters. Most procedure tables for mechanized welding relate to average conditions. Tubular product mills use welding data that are modified for maximum travel speed. The welding parameters must be analyzed and each adjusted to provide for maximum travel speed.

The primary variables are travel speed, welding current, and arc voltage. This is the heat input into the weld. The secondary adjustable variables include the torch travel angle and the arc direction when a magnetic arc deflecting system is used. The distinct level variables include the electrode size, type and point geometry, the composition of the shielding gas, and trailing gas shield

I if used. The use of more than one torch and their spac- t ing, and the use of oscillation either mechanical or 1 magnetic. j The fixed conditions include thickness and com-

I position of the metal. Increasing productivity means increasing the speed of the tube, which can be done by

I I

increasing the energy employed in making the weld. A combination of improvements can increase the welding speed of the tube mill. Revise the welding procedure by examining each variable and adjusting them independ- ently until the right combination has been obtained. Figure 25-4 gives parameters for single-arc gas tungsten arc welding for stainless steel of the wall thicknesses shown.

Adjust the primary variables, which relate to heat input. Increase the welding current; as the welding current increases, the travel speed must also increase, to avoid burn-through. The travel speed must be continuously adjustable so that it can be changed as the cur-

732 PIPE AND TUBE WELDING

rent is increased. The top limit of current seems to be approximately 250 to 300 A.

Arc voltage is a more complex variable which relates to arc length; it can be varied between narrow limits. The minimum arc length should not be less than one diameter of the electrode. The maximum arc length should not be more than twice the diameter of the elecrode. The torch should be adjustable so that the arc length can be varied easily. Many GTAW mills use automatic arc length control (ALC or AVC), which allows setting the torch to a specific arc voltage.

Travel speed must be increased. The practical maximum speed, approximately 1 m (39 in.) per minute is limited by the quality of the weld. As travel speed increases beyond this rate, undercutting will occur. The weld bead may be high and crowned, and after there will be a depression in the center of the bead which introduces a notch and reduces the cross section along the weld centerline (Figure 25-5).

UNDERCUT UNDERCUT AND CENTERLINE NOTCH

FIGURE 25-5 Undesirable weld cross section.

These defects occur because of a dragging arc (Figure 25-6). This makes the arc longer as travel speed increases. As the arc length increases it flares, is less concentrated, does less work, and has a higher voltage. Giving the torch a lead angle overcomes the lagging arc, reduces the arc length, and generally allows travel speed to be increased without undercutting. A push angle of up to 20" will move the undercutting occurrence to a higher speed and tends to flatten the weld bead. This can also be accomplished by a magnetic arc deflection system, which corrects for the arc lag and reduces arc length. This system is adjusted to cause the arc to lead, which preheats the weld area and allows higher travel speeds before undercutting occurs. The torch must be adjustable across

CH. 25

t----------

TUBE TRAVEL TUBE T R A V E L

(a) LAGGING ARC - LONGER (b) TORCH WITH PUSH ANGLE

1 1 STATIONARY

. T U B E TRAVEL

(c) WITH MAGNETICS P R O V I D I N G LEADING ARC

FIGURE 25-6 A r c length factors.

the joint so that it is always located on the center of the seam.

The optimum arc length is approximately 1 I/ , times the electrode diameter, which provides optimum arc voltage for tube welding. The torch angle adjustment is required for the best welding conditions.

Another way to increase the heat input in the arc is to use a shielding gas that provides a higher arc voltage at the same arc length.

Helium provides more heat in the arc, hence travel speed can be increased. Increased production must be re-

lated to the higher cost and greater flow rate of helium gas. A mixture of 50:50 argodhelium can be used to reduce gas cost. Another way to increase the heat of the arc is to use hydrogen in the argon shielding gas. Up to 10% hydrogen can be used for welding nickel and nickel alloys and some stainless steels. Hydrogen mixtures should not be used for welding carbon and low-alloy steels.

The use of helium or hydrogen mixtures will increase travel speed up to 50%. Special nozzles are required to shield the longer molten weld pool. Heavy- duty, water-cooled, automatic torches with adjusting rack should be used. The torch rating should be at least 50% greater than the welding current, since tube mill operation is highly demanding.

The tungsten electrode for tube mill use must be selected for heavy duty. For welding ferrous metals, direct-current electrode negative is used. The 2% thoria type (EWTh2) should be used. The ground finish should be specified since this improves heat transfer and increases electrode life and time between regrinding the point. The size of the electrode should be the largest for the welding current to be used. The electrode should be precision ground to a point of 30" included angle, but the end of the point should be flattened.

The use of an additional GTAW torch ahead of the welding arc will allow increased speed since more energy is being put into the material to preheat it. The use of an additional torch following the welding torch will reduce the undercut problem. The use of three torches will increase tube travel speed by up to 100% while producing a good-quality weld joint. The leading (preheat) torch should operate at about 50% of the current of the welding torch. The trailing torch will operate at about 33% of the welding torch. The spacing between the torches should be the minimum.

The plasma arc welding keyhole process can be used in place of the gas tungsten arc to increase the production rate. Speed increase of from 33% to 100% is possible with the greatest improvement on thicker metal. Increased production is due to the higher temperature plasma and the constricted stiffer arc which improves heat transfer to the work. The welding schedule shown in Figure 25-7 shows the productivity improvement.

FIGURE 25-7 We ld ing Wall Travel Orifice Gas Shield schedule for plasma arc

Current Thickness Speed Size and Plasma weld ing stainless steel

Amperes in. mm (in.lmin) mmlmin DCEN in. mm Type tubing.

SEC. 25-1 TUBULAR PRODUCTS 733

Analysis and adjustment of all variables would be universally adopted in this field. Screw-thread connec- similar to that described for Gas Tungsten Arc welding. tions, soldered copper tubing, and plastic pipe are used

In submerged arc, gas metal or flux cored arc for certain applications. The steel pipe is usually stand- welding applications multiple torches can be used. With ard wall thicknesses in the small and medium sizes. Quali- submerged arc using ac three torches are often used. fication tests may not be required, although qualified

Electron beam and laser beam welding processes are welders and qualified procedures are often used. both used for welding speciality type tubular products. Welding pipe and tubular products is normally done

in accordance with established written procedures. There

25-2 PIPE AND TUBE WELDING are literally thousands of welding procedures in existence based on different processes, codes or specifications,

In the United States approximately 10% of the steel produced is made into tubular products, essentially pipe. Ex- cept for the small sizes, the majority of pipe is installed by welding.

The piping industry is roughly divided into three major categories:

Pressure or power piping -1 Transmission and distribution piping

Noncritical piping

The welding of pressure piping used in thermal and nuclear power stations, refineries, chemical plants, on ships, and so on, is done in accordance with the ASME code for pressure piping.c2) All of the ASME piping codes of B31 are shown in Figure 25-8. The pipe employed normally has a medium to thick wall thickness in medium to large sizes. Welding procedures, qualifications, and so on, are largely in accordance with Section IX of the ASME pressure vessel code.(3'

Transmission and distribution pipelines transmit gas and petroleum products from the producing fields to the consumers. Welding this type of pipe utilizes special techniques and procedures, and is governed by API Standard 1 104.(4) This specification is in general agreement with B31.8, "Gas Transmission and Distribution Piping Systems." The pipe employed is usually of medium to high strength and has relatively thin walls in medium to large diameters. Distribution piping is normally carbon steel standard-size pipe of smaller diameter.

The noncritical piping field includes many different pipes, ranging from domestic hot water supply systems through sprinkler systems, sanitary systems, gas and air lines, and many other applications. Welding has not been

FIGURE 25-8 ASME c o d e fo r pressure piping.

Power piping Fuel gas piping Chemical plant and petroleum refinery piping Liquid petroleum transportation piping systems Refrigeration piping Gas transmission and distribution piping systems Building services piping Slurry pipelines

piping materials, and applications. Pipe welds and procedures that will meet the requirements of one specification or code may or may not meet the requirements of others. The specific code involved must be consulted. Welding procedures are designed based on the pipe material, pipe diameter, and wall thickness. Welding position depends on the job and the code, but the procedure must indicate the welding process and progression of travel. The method of application depends on the process and equipment available. The filler metal is selected based on the composition of the pipe material and the quality requirement. A listing of pipe welding procedure schedules is given in Figure 25-9. This list is based on the pipe or tubing size, which is categorized as small [4 in. (100 mm) and smaller], medium [4 in. (100 mm) to 12 in. (300 mm)], and large [12 in. (300 mm) and larger]. The wall thickness is categorized as thin (less than standard), standard (Schedule 40), and heavier (greater than standard). This is followed by the welding position, the welding process, and the method of application. In some cases, combinations of welding processes and methods of application are used.

With these data, welding procedures can be designed to meet the job requirements based on the specification involved. Welding procedure specifications must be qualified to meet the code requirements.

Joint Design I

The joint designs for pipe welding have been fairly well standardized and are shown in Figure 25-10. For thinner- wall pipe the joint design is the square groove weld. As thickness increases, a single-V-type joint is used. The included angle of the V groove has been standardized at 60 and 75 ". The 75" included angle is more common in pressure piping, and the 60" included angle is common in cross-country transmission-line piping. The root face and root opening are approximately the same. As the wall thickness increases, the joint design will change so that less weld metal will be required. This means that the included angle changes to a narrower angle partially up the joint. These types of joint designs are more commonly used in power plant piping, where heavy wall thickness pipe is used. Other variations in joint design depend on the composition of the pipe. Some automatic procedures require special joint designs. For aluminum pipe special

CH. 25 I

Tube & Pipe Diameter Method of &Wall Thickness Welding Position Welding Process Applying

Small tubing-thin wall All position GTAW MA Small tubing-th~n wall All position PAW MA Small tubing-thin wall All position GTAW-No FM A U

Small pipe-std. wall Small pipe-std. wall

All position OFG MA All position GTAW-with FM A U

Small to medium-std. wall All position GMAW SA Small to medium-std. wall All position SMAW MA

Medium-std. & heavv wall

Medium & large-thin & std. Medium & large-thin & std. Medium & large-thin & std.

Medium & large-all wall Medium & large-all wall Medium & large-all wall

Medium & large-all wall

All position Comb. GTAW & SMAW MA

All downhill SMAW All up or down GMAW All up or down FCAW

All uphill SMAW MA Flat roll (1G) SAW AU Flat roll (1G) Comb. GMAW SA or AU

& SAW & AU Flat roll (1G) Comb. GMAW SA or AU

& FCAW & AU

Small, medium & large-std. to thick All position FCAW SA Small, medium & large-std. to thick All position Comb. GTAW

& FCAW M A & SA Small, medium & large-std. to thick All position Comb. GTAW

& GMAW MA & SA FIGURE 25-9 Pipe welding procedure schedules.

- 60" FIGURE 25-10 Pipe welding ,I' 3> joint designs.

-m

( A ! THIN W A L L ( B ) THICKER WALL (C! STD W A L L D O W N H I L L

iD! H E A V E R WALL-AUTO GTAW ( E l STD WALL-UP H ILL

( F i HEAVY WALL-ELECTRODE PROCESSES (G) HEAVY W A L L ALUMINUM

CLASS 1 CLASS 2 CLASS 4 CLASSES 3 AND 5

joint details have been developed, and these are normally associated with combination process procedures. This allows a root weld to be made in much the same manner as the weld on thin-wall tubing.

The rectangular backing ring is rarely used when fluids are transmitted through the piping system. It may be used for structural applications in which pipe and tubular members are used to transmit loads rather than materials. Consumable insert rings are often used for critical piping. In these situations the GTAW process is used for the root pass and the rings are fused into the root of the joint. A variety of designs of insert rings are used. Socket joints and bell and spigot joints which utilize fillets are sometimes used, but they are becoming less popular. Internal gas purging is used for critical pipe work. Special dams of soluble paper or balloons are used to contain the purge gas in the area of the pipe joint. This is most often used with GTAW.

Joint Alignment and Fitup

The most important factor in obtaining a high-quality pipe joint is to make sure that the fitup of the joint prior to welding is perfect. It must be in accordance with the joint detail and uniform throughout the circumference of the pipe joint. This is relatively difficult to obtain because pipe is not always exactly round and the diameter may vary within limits of the pipe size. Tubing is made to closer size tolerances and is easier to fit up. The nonroundness or ovality of pipe presents a major welding problem. This is particularly true with larger-diameter pipe.

The most common method of preparing joints for welding is by oxygen flame cutting. Mechanized torches that revolve around the pipe are used. Preparation equipment of this type is shown in Figure 25-1 1. Automatic and computer-controlled cutting machines are used in the shop. Mechanical cutters are also used to make a uniform joint preparation on pipe. End preparation is prepared at the steel mill on each length of pipe. Forged fittings have the joint preparation prepared at the manufacturer's plant. Special bevels are prepared by mechanical means as a part of some automatic welding machines.

Fitting the pipe is the most difficult part of piping installations. For small assemblies this is relatively easy and much of this work is done in pipe-fabricating shops. Setup and welding subassemblies of different kinds of fittings and pipe sections are welded there under ideal conditions. A typical shop fabrication welded with semiautomatic equipment is shown in Figure 25-12. These assemblies are then transported to the erection site for field welding. Assembly in the field is usually more difficult since dimensional variations are more difficult to control.

A variety of alignment devices are used for pipe installations. For small-diameter pipe, external-type clamps

PIPE AND TUBE WELDING

are normally employed. Figure 25-13 shows an assortment of these. Some of these clamps have sufficient force to re-form the pipe into a perfect circle to facilitate fitup. This is possible on the thin-wall pipe but becomes increasingly difficult as the pipe wall thickness increases.

FIGURE 25-11 Preparation of bevels on pipe.

CH. 25

Cross-Country Pipelines

FIGURE 25-12 Shop fabrication of pipe subassembly.

FIGURE 25-13 Variety of external line-up clamps.

The cross-country transmission pipeline welding techniques have become extremely sophisticated. Normally, the "stove pipe" method of installing pipe is used. This means that each section or length of pipe is added on to the existing pipe installation. The crew for doing this moves along the right-of-way from the beginning to the end of the pipeline. Welding procedures and techniques vary based on the diameter of the pipe.

Special techniques were established for cross- country pipe utilizing the downhill technique and E6010-type electrodes. This technique is still used for large-diameter relatively thin wall cross-country pipeline - work. More and more cross-country pipelines are being welded with semiautomatic or automatic equipment.

For the large-diameter pipe welds an internal lineup clamp is utilized (Figure 25-14). The clamp is inserted in the end of the last section of the pipeline and is operated remotely by air pressure. The air pressure clamps the internal lineup clamp to the section already welded to the pipeline and then as the new section is being placed in position, it clamps, locates, and spaces the new section. It helps round out the pipe due to the strength of the clamp. Some of these clamps include a copper backing ring. Normally, the clamps are left in the pipe joint until the first or stringer pass is made. In some cases, the second pass is also made before the clamp is released and removed from the joint. In welding large-diameter pipes there is usually one welding crew that makes the root pass and second pass, commonly known as the stringer and hot pass. They move on with the lineup clamp crew and work on the next pipe joint, and other welding crews come in to finish the weld. These crews make the so-called filler passes, which are those that fill the weld joint; the stripper passes, which are usually made in the vertical portion of the pipe joint; and the last pass, known as the

FIGURE 25-14 Pneumatic internal line-up clamps.

SEC. 25-2 PIPE AND TUBE WELDING 737

cap pass. The stringer crew and the other crews may represent three or four pipe welding groups that are pro- gressing along the pipeline during its construction.

Semiautomatic welding using gas metal arc welding is also utilized for cross-country pipe welding. The welding equipment is placed on a flatbed truck or a tractor with a boom supporting the welding cables and guns over the pipe to be welded. This technique has almost doubled the production rates over manual shielded metal arc welding and has beome very popular in many parts of the world. Figure 25-15 shows the semiautomatic welding of small pipe, and Figure 25-16 shows the welding of a large-diameter cross-country pipe.

FIGURE 25-17 Air view of pipe laying barge. FIGURE 25-15 Welding small-diameter pipeline

FIGURE 25-16 Welding large-diameter pipeline.

Gas metal arc welding will meet the requirements of the API 1104 specification for medium and large pipe with relatively thin wall.

Pipe work very similar to the cross-country transmission pipeline welding is done on "lay-barges" (Figure 25-17). This is the welding of pipelines that will be lowered to the bottom of the ocean. Underwater pipelines bring gas and oil in from offshore wells to dry land. Manual, semiautomatic, mechanized, and automatic welding are employed by different lay-barge operations.

A high level of skill is required to make pipe welds manually or with semiautomatic equipment either uphill or downhill. Stringent qualification tests apply to pipe work. Trained and experienced welders are used for pipe welding.

Quality Assurance

The quality of butt welds in piping systems must be close- ly monitored. Visual inspection is always used; however, there is increasing use of ultrasonic inspection. Tradi- tionally, x-ray inspection has been employed. The quality level, level of acceptable defects, and so on, are established by the code involved.

25-3 MANUAL AND SEMIAUTOMATIC PIPE WELDING

Neither screw-thread joints nor mechanical joints develop the full strength of pipe; hence one of the earliest applications of welding was to join pipe. The oxyacetylene welding process was used for many years to make pipe welds. Oxyacetylene welds develop the full strength of the pipe. Oxyacetylene welding is a slow welding process, so the time involved for making heavy-wall large-diameter pipe welds was excessive. However, even today the welding of 2-in. and smaller standard wall pipe is still done by the oxyacetylene welding process. It is used for radiant

FIGURE 25-19 Shielded metal a rc welding of heavy-wall pipe.

FIGURE 25-18 Oxyacetylene welding of small pipe.

heating systems, cooling systems for ice rinks, and similar applications. Figure 25-18 shows the oxyacetylene welding of small-diameter pipe.

Electric arc welding has been used for pipe joining for many years. Initially, bare or lightly coated electrodes were used, and the welds produced that developed the full strength of the pipe. Recently pipelines welded with bare electrodes over 50 years ago, have been uncovered and inspection with indications that the welds were still good. The advent of the covered electrode made manual shielded metal arc welding of pipe a very popular process.

For pressure piping, primarily medium diameter, heavy wall, an uphill technique is used. This technique meets the requirements of the ASME piping codes, and literally thousands of procedures have been qualified using this technique with E6010 electrodes.

With the advent of low-alloy, high-strength steels for powerhouse construction, a new type of electrode was used. These are the low-hydrogen types with low-alloy deposited metal which will match the analysis of the pipe. This development led to welding procedures using low- alloy, low-hydrogen electrodes for powerhouse work. An illustration showing this type of application is shown in Figure 25-19.

For special applications of critical piping the root pass is made with the gas tungsten arc welding process. This is done using the open root technique or using consumable insert rings and fusing them to the root of the joint. A second pass may be made with the gas tungsten

arc welding and the remaining weld deposit by shielded metal arc welding. This produces an excellent weld joint with an extremely smooth inner surface. Procedures have been developed for many different low-alloy steels, including the low-chrome-molybdenum steels.

Gas tungsten arc and shielded metal arc welding applied manually is a relatively low production welding method. When gas metal arc welding was developed, it was soon applied to pipe welding. It was used for roll welding (lG) with the hand-held gun, and for fixed position (5G) welding at construction sites. Figure 25-20 shows the use of semiautomatic gas metal arc welding in a factory installation. Both the small wire short-circuiting

FIGURE 25-20 Semiautomatic welding of power plant piping.

SEC. 25-3 MANUAL AND SEMIAUTOMATIC PIPE WELDING 739

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technique and the spray technique are employed. Elec- trode wire compositions were developed to match the composition of various base metals. Flux-cored electrode wires were also formulated to match the composition requirements for pressure piping.

The work just described is governed by codes and specifications. A summary of pipe welding schedules is given in Figure 25-21. Assistance in developing pipe welding procedures is provided by the welding society in the form of recommended practices. A listing of these is given in Figure 25-22. These are available from AWS, Miami, Florida.

D l 0.4 Austenitic chromium-nickel, stainless steel piping and tubing

D10.6 Gas tungsten arc welding of titanium piping and tubing

D10.7 Gas shielded arc welding of aluminum and aluminum alloy pipe

D l 0.8 Chromium-molybdenum steel piping and tubing D l 0.1 0 Local heat treatment of welds in piping and tubing D l 0.1 1 Root pass welding and gas purging D l 0.1 2 Welding plain carbon steel pipe

FIGURE 25-22 A W S recommended practices for p ipe welding.

25-4 MECHANIZED PIPE AND TUBE WELDING

Mechanized welding systems are available for welding pipe and tubing. Two basic types of procedures are used for different applications. One is "roll welding" pipe in the flat or downhand position, the 1G position, when the joint is rotated under the welding head. The second, known as "orbital welding," is used when the pipe is in the fixed position, with the axis of the pipe horizontal or vertical, and the machine rotates about the pipe to make the weld. A further subdivision is for thin- or heavy- wall pipe, or for small- or large-diameter pipe or tubing. A further subdivision relates to the weld process. Submerged arc welding is used for roll welding only; other processes, such as gas metal arc, flux-cored arc, and gas tungsten arc, are used for making pipe welds in any position.

Roll welding, that is, rotating the pipe under the welding head, was the first application of machine or automatic welding. In the field this is known as "double jointing" (Figure 25-23). This means the welding together of two sections of straight pipe normally done for cross- country pipelines. Double jointing is done at the pipe storage yard using standard lengths of pipe which are welded and then transported to the construction site. Roll welding is more productive than orbit welding and reduces the total number of welding hours to construct a pipeline.

FIGURE 25-23 Double joining pipe b y roll welding.

Submerged arc welding has historically been used for roll welding. An internal line-up clamp, usually con- taining a backup bar, is used. Roll welding is also done in the fabricating shop on subassemblies. Normally straight pipe sections are joined to ells, flanges, and so on. (Figure 25-24). This provides higher efficiency since welds can be made more rapidly in the flat or roll position than in the fixed position. In some cases, the first or root pass, and even a second pass, is made by gas metal arc welding, shielded metal arc welding, or gas tungsten

FIGURE 25-24 Roll welding in pipe fabrication shop.

SEC. 25-4 M E C H A N I Z E D PIPE AND TUBE W E L D I N G 741

arc welding. Flux-cored arc welding or gas metal arc welding can be used for subsequent passes, as well as submerged arc welding.

The plasma arc process using the keyhole mode is also used for roll welding. This requires complex controls since there are a large number of variables involved and the closing of the keyhole requires simultaneous coor- dinated change in parameters. This is used on medium- wall alloy and stainless steel pipe.

Orbital welding of thin-wall tubing and standard wall pipe is being done with the gas tungsten arc welding process. Mechanized orbital tube and pipe welding systems are used (Figure 25-25). They are available as complete systems consisting of the power source, programmer, welding head, and so on (Figure 25-26). Remote control pendants or controls on the head allow operation at the point of welding. This equipment can weld tubes with an outside diameter from ;/4 in. (6.35 mm) to over 8 in. (200 mm), with wall thicknesses from 0.01 5 in. (0.35 mm) up to % in. (6.35 mm). Exact capabilities depend on the welding head design as well as the joint design and pipe material. The head shown in Figure 25-27 is designed with a minimum radial clearance of 1'%, in. (46 mm), so that it can be used to weld pipe in clusters. These mechanized orbital heads for pipe and tubing are compact and rugged and clamp on the pipe or tube. A family of heads is required to weld the smallest to the larger tubes. The welding torch rotates around the pipe and carries the tungsten electrode. In some designs, slip rings are used to avoid rotating or twisting cables and hose. These heads will rotate the torch around the pipe

FIGURE 25-26 Complete system for welding small-diameter tubing.

continuously. Other heads, which do not include slip rings, allow the cable and hose to wrap around the pipe. Three revolutions are usually the maximum used. A clamshell head design (Figure 25-28) is used for smaller tubes.

The three joint types commonly used are shown in Figure 25-29. This includes the square groove joint, socket joint, and U-groove joint. The square groove joint is used for thin-wall tubing and only a single pass is used. Socket joints provide easy fitup and the weld is a fillet. Groove joints, U and V, are used for thicker-wall tubing where full-penetration welds are required. Multiple passes with filler metal are used for groove joints.

Specialized programmers having upslope and

FIGURE 25-25 Orbital head welding tubing.

FIGURE 25-27 Tube-to-tube orbital head for GTAW

CH. 25

FIGURE 25-28 FIGURE 25-30 Mechanized pipe welding head for heavy-wall pipe.

FIGURE 25-29 - I \ I I

A (a) BUTT W E L D

r-++7 !->I-+ (b) SOCKET W E L D

feeder and various collets to weld different sizes of pipe. It can also be used for welding pipe when it is in the vertical position (Figure 25-31). Groove joints are normally employed.

Similar machines have been developed that utilize a combination of welding processes. The first pass will use gas tungsten arc, and subsequent passes may use the gas metal arc. Torches are changed for making the total weld. This equipment is becoming increasingly popular for welding pressure piping. Complex controllers and two power sources or combination power sources with CC and CV characteristics are required.

Mechanized welding machines for welding large- diameter pipe, primarily cross-country pipelines, use the gas metal arc welding process. These are large machines that fit around the circumference of the pipe and will make gas metal arc welds in the field, on lay-barges, or in the shop. Different types are available that utilize dif-

A (c) GROOVE W E L D

downslope of welding current plus control of rotation, preflow and postflow of gas, and high frequency for arc initiation are all included. Pulsing is normally used for most mechanized welding procedures.

For larger-diameter pipe with thicker wall, a different type of gas tungsten welding head is used. A head of this type rotates around the pipe but is held to the pipe by means of a split-ring or chain-drive assembly (Figure 25-30). Some units have a low profile and can weld pipe with minimum clearance. This machine includes a wire

FIGURE 25-31 Mechanized pipe welding with pipe vertical.

SEC. 25-4

ferent weld joint details. In some cases, welds are made on the inside diameter of the pipe as well as the outside diameter. The inside welding head is combined with a line-up clamp and is made prior to the outside weld. Equipment of this type is shown in Figure 25-32.

Mechanized pipe welding systems will continue to advance and in some cases become automatic or automated.

FIGURE 25-32 GMAW welding machine for large pipe.

25-5 AUTOMATED PIPE WELDING

Further efforts to reduce the cost of pipe welding have resulted in a fully automated pipe welding system that is computer driven. Figure 25-33 shows the automated pipe welding system for making all-position gas tungsten arc welds on small-diameter pipe. The cabinet on the left

FIGURE 25-33 Automated pipe welding system.

FIGURE 25-34 Automated head and remote pendant

includes the microprocessor controller, computer keyboard and display screen, and a 150-A inverter power source. This equipment includes a remote teaching pen- 25-35 Pipe head On pipe.

dant, shown with the automatic head in Figure 25-34. The welding head on the pipe is shown in Figure 25-35. This head weighs approximately 25 Ib and will weld pipe sizes from 1X to 2% in. nominal with a standard wall to the heaviest pipe wall available. This head was designed for minimum radial clearance between adjacent pipes, so that welds can be made when the pipe is separated by only 2:: in. The head hinges in the middle in a clamshell

744 PIPE AND TUBE WELDING CH. 25

tion. This allows the head to mechanically oscillate during setup to determine the centerline of the weld joint prior to striking an arc. The arc will sense the joint at each end of the oscillation stroke. The controller will reverse the stroke and keep the weld head centered on the joint. This can be modified for a split weave technique and can be different for each layer.

Practical application in a fabrication shop utilizes two heads with one controller and power source panel. While one head is making welds, the other head is being attached and aligned to another joint. When the first joint

FIGURE 25-36 Program menu. is completed, the controller switches to the second head and makes the weld. Meanwhile the first head is removed

The heart of this automated welding system is the microprocessor controller. The input to the controller is by means of the keyboard and the readout on the monitor screen. The microprocessor controls all functions; however, the arc length control may be a subroutine using a separate system. The key to operation is the soft- ware program, which is extremely complex but is user friendly. The initial readout observed by the operator is the mode of operation and menu (Figure 25-36). The operator selects the teach mode, which is the next display. Specific instructions for orbital welding is given in the next display. The operator will then key in the welding parameters as requested and they will appear on the next display, which is the operating mode. This input provides welding parameters for making the weld utilizing a specific procedure based on pipe size, wall thickness, joint details, pipe analysis, and so on. This procedure can be modified and the procedure can be recorded by means

from the completed pipe joint and attached to a new joint ready to be welded.

This machine can be utilized for remote welding in dangerous or radioactive atmospheres.

Automated welding has been applied to the plasma arc welding, keyhole mode process for roll welding. In this case the torch is stationary, but adjustable, while the pipe joint rotates under the arc. The welding head has automatic X, Y, and Z adjustments. The angle of the torch is preset. The microprocessor initiates the plasma arc and all other functions, including torch adjustment, pipe rotation, and gas coverage. Welding parameters are programmed to initiate the keyhole and to provide filler metal. This equipment is designed for high-alloy steel piping and is normally used with single-pass operation. Upon completion of the weld, the computer programs the closing of the keyhole, which involves simultaneous chang- ing of four variables. This equipment is shown in Figure ? C 17 L J - 3 1 .

of a hard-copy printout at any step. Welding operators learn to program this equipment in a short time, based on their experience. FIGURE 25-37 Roll pipe welding equipment: plasma.

In operation, the head is normally clamped on the pipe and lined up with the joint. The root pass does not require oscillation; however, subsequent passes may utilize oscillation as required. Oscillation is programmed with the exact dimensions, which change for each layer. Dwell time is programmed for each end of the stroke, and for each layer, the speed of oscillation is also programmed and welding current pulsing is synchronized with oscillation. When the second pass is completed, the programmer automatically changes to the third pass without stopping the weld. Welding parameters can be changed each 10" around the pipe. The welding is uninter- rupted from root to cap pass and provides 100% arc time. When the final pass is completed, the controller turns off the machine.

Welds produced by this automated system meet the requirements of the most stringent codes. Radiographs of welds produced are water clear.

The teach pendant shown earlier is used to input information to the microprocessor to establish the total welding procedure. Arc sensing is used to control oscilla-

SEC. 25-5 AUTOMATED PIPE WELDING 745

25-6 TUBE TO SHEET WELDING

Mechanized equipment is widely used for welding tubes to tube sheets or heads. This equipment is used primarily by the heat-exchanger industry. A heat exchanger consists of many tubes between two headers, where the tubes must be attached to the headers with perfect, leakproof connections. Each heat exchanger may have hundreds of tube-to-header joints. Previously, these were mechanically connected or manually welded with gas tungsten arc welding, which was a tedious boring job. The transition from manual to machine welding has improved quality and reduced the cost per weld.t5)

Complete welding systems are available, including the mechanized orbital welding head, the welding power source, and the programmer, which completely mechanize the welding operation.

The welding head is a compact lightweight device that rotates the gas tungsten arc welding torch around the periphery of the tube to sheet joint. The head includes a mandrel which fits inside the tube to be welded and locates the torch. The head will rotate the torch 360" plus overlap in each direction. Slip rings are incorporated so that the hose and cables do not twist. Figure 25-38 shows this equipment in use welding a small heat exchanger. This photograph shows the tube sheet in the vertical position; however, the equipment can be used if the tube sheet is horizontal and the weld is flat or even if the weld is overhead.

Heads of this type can weld tubes with outside diameter from 1/8 in. (16 mm) to 6 in. (150 mm) with a tube wall thickness of 0.015 in. (0.4 mm) and larger.

FIGURE 25-38 Tube-to-sheet mechanized welding machine.

FIGURE 25-39 Tube-to-tube sheet welding head.

A close-up of the welding head is shown in Figure 25-39. The head includes the GTAW torch, rotation motor and filler wire, and drive motor. The tungsten electrode is the 2% thoriated type (AWS Spec. EWTh2) and %, in. diameter is normally used. Filler metal can be added for certain types of welds. When filler metal is added, the arc length should be slightly greater than the electrode diameter. When filler metal is not added, the arc length is slightly less than the electrode diameter.

The tungsten electrode position is adjustable and critical for tube-to-header welds. Figure 25-40 shows the electrode position for the most common joint designs.

The programmer is the same as used with mechanized tube-to-tube welding heads. It starts the gas preflow, torch rotation, high frequency, and welding current, which normally changes during the weld cycle. Puls- ing is normally used for making tube-to-tube sheet welds. The controller has various delays and ends with postflow of shielding gas, required to produce high-quality welds. The equipment may also include a weld control pendant, which is used when remote welding is required.

The joint detail used for this type of welding is shown in Figure 25-41. The three most common joint designs are the extended tube, flush tube, and recessed tube. There are variations of each design. Some applications require only a seal bead between the tube and the tube sheet. Filler metal is normally added for the extended tube or the recessed tube joint design. Nuclear specifications require that the weld metal thickness be equal to the thickness of the tube, which dictates the J-groove joint design. The fillet weld design normally will not produce the desired cross section dimension since the fillet weld throat dimension is less than the thickness of the tube. The design selected must have sufficient filler metal so that the weld is stronger through its shortest dimension than the thickness of the wall of the tube. Joint design is based on the specifications involved. The welding procedure shown is with the tube sheet vertical. With the tube sheet flat, higher currents can be used. Any metal welded by the gas tungsten arc process can be welded with mechanized GTAW tube-to-tube sheet welding heads.

CH. 25 I

FLUSH TUBE WELD EXTENDED TUBE WELD

FIGURE 25-4L1 Tungsten electrode position for welds.

FIGURE 25-41 Tube-to-tube sheet welding schedule.

A . Extended Tube 8. Flush Tube C. Recessed Tube

Tube Wall J o ~ n t We'd O.D. I Th~ckness I Type / Current

Flller Rod Type

Weld T ~ m e (set)

18

18

31

~ t a l n ~ k s s steel iube-to stainless steel' tube shee'f

E304

None

E304

in, I I I I I

mm

- Stainless steel to ml ld ster

0 62 1 15.7 1 0062

(Amperes) ~ n .

;; ;I 1 0 083

CUNI CUNI

0 062

C U N I - m ~ d steel

rn m

I I Mi ld steel t o mi ld steel

SEC. 25-6

1.6

3.2

3.2

0.75

1 .OO

1.00

8

B

C

19.1

25

25'

140

140

180

0.062

0.125

0 125

QUESTIONS

What are the seven different classifications of pipe and tubing?

What schedule number pertains to standard wall pipe?

Briefly describe a continuous pipe mill.

What arc welding process is used to make spiral joint pipe? What percentage of steel produced is made into tubular products?

What code applies to most high-pressure pipe welding? Cross-country pipe? Can more than one welding proccss be used to make a pipe weld? Explain.

Why are different pipe weld joint designs used? Where is each used?

Explain the difference between internal and external line-up clamps. What determines the type to be used?

Explain the difference between uphill and downhill pipe welding.

REFERENCES

1. Harold E. McGannon, ed., "The Making, Shaping and Treating of Steel," Association of Iron and Steel Engineers, Pittsburgh, Pa.

2. Hoobasar Rampaul, Pipe Welding Procedures, Industrial Press, New York.

3. "Power Piping," ASME Code for Pressure Piping B31, American Society of Mechanical Engineers, New York.

What type of covered electrode is widely used on cross- country pipe welding?

What is stove pipe welding?

What is double jointing?

What is the difference between roll welding and fixed- position welding?

Can submerged arc welding be used for fixed-position welding? For roll welding?

Are low-hydrogen welding electrodes used for pressure piping?

What is the advantage of consumable inserts for pipe welding? Can gas metal arc welding be used on pipelines?

What is the advantage of mechanized orbital welding of tubes? What are the three joint types for tube-to-tube sheet welds?

4. "Standard for Welding Pipe Lines and Related Facilities." API Standard 1104, American Petroleum Institute, Washington, D.C.

5. W. Hebert, "Mechanized Tube Welding Speeds Heat Ex- changer Fabrication," Welding Journal, May 1986.