WELDING AND BRAZING QUALIFICATIONS

CHAPTER

24

24.1 INTRODUCTION

This chapter covers the qualification of welding and brazingprocedures and the qualification of individuals performing thoseprocedures as prescribed in Section IX of the ASME Boiler &Pressure Vessel Code. It reviews the qualification rules and pro-vides commentary on those requirements. Where comments areprovided, they represent the personal opinion of the author andshould not be regarded as the position of the ASME Code or itsSubcommittee on Welding.

The information presented herein is based on the 2007 edition.The author’s writing may have simplified some of the Code rulesin summarizing the cited requirements; therefore, all of the detailsof the rules might not have been addressed. The reader is advisedto consult Section IX as well as the applicable Construction Codefor the specific rules.

24.2 HISTORY OF SECTION IX

Riveting was the main fabrication method for the manufactureof boilers and pressure vessels in the ASME Boiler & PressureVessel Code in the early twentieth century. It was the SecondWorld War, with its urgency for ships and other components thatpropelled welding to the forefront of manufacturing processes.

The fledgling ASME Boiler & Pressure Vessel Code Committeerecognized welding when in 1918 Section I, “Power Boilers,” per-mitted welding, but only when it was used in applications wheresafety did not depend on the weld. Over the next two decades,welding was adopted by more sections of the Code includingSection VIII, “Unfired Pressure Vessels,” and Section IV, thentitled “Low Pressure Heating Boiler Code.” Rules for the qualifica-tion of welding and welders were introduced into Section VIIIthroughout the 1930s as part of an ongoing approval to use weld-ing in pressure boundary applications. In the mid-1930s, as the dif-ferent sections began to develop their own rules regarding welding,the Boiler & Pressure Vessel Committee formed Subcommittee IXas a joint committee of American Welding Society (AWS) andASME. One aspect of its charter was to write a common set ofrules for the qualification of welding and welders usable by all ofthe book’s sections, an effort that resulted in the publication of thefirst edition of Section IX in 1941. That edition had variables (i.e.,welding details that effect welding operations; see Section 24.6),16 of which were for the qualification of welding procedures and

4 of which were for a welder’s performance qualification. The2007 edition of Section IX has a total of 229 variables coveringboth welding procedure and performance and 23 variables cover-ing brazing procedure and performance.

24.3 ORGANIZATION OF SECTION IX

Since its first publication as a separate ASME document in1941, Section IX has seen a number of changes in its arrangementand makeup. The format of the 2007 edition is in two parts: PartQW, covering welding; and Part QB, covering brazing. Each partis further divided into four articles. The following is the organiza-tion of Section IX:

• Foreword. • Statement of Policy. • Introduction, an explanation of the purpose and organization

of Section IX. • Part QW—Welding.

• Article I, general requirements for welding procedure andwelder performance qualification.

• Article II, welding procedure qualifications. • Article III, welder performance qualifications. • Article IV, those variables applicable to welding procedure

and welder performance qualification.• Article V, standard welding procedure specification.

• Part QB—Brazing.• Article XI, general requirements for brazing procedure and

brazer performance qualification.• Article XII, brazing procedure qualifications.• Article XIII, brazer performance qualifications.• Article XIV, those variables applicable to brazing proce-

dure and brazer performance qualification.• Appendices, suggested forms of documenting welding and

brazing qualifications and the standard welding procedurespecifications acceptable for use.

24.4 WELDING PROCESSES

Before we discuss weld qualifications, it is wise to first review thescope of weld processes that Section IX addresses. Section IX con-tains rules for the qualification of the following weld processes:

WELDING AND BRAZING

QUALIFICATIONS

Joel G. Feldstein

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• Oxyfuel welding (OFW) • Shielded metal arc welding (SMAW) • Submerged arc welding (SAW) • Gas metal arc welding (GMAW) • Gas tungsten arc welding (GTAW) • Plasma arc (PAW) • Electroslag welding (ESW) • Electrogas welding (EGW) • Electron beam welding (EBW) • Laser beam welding (LBW) • Stud welding • Inertia and continuous drive friction welding • Resistance spot and projection welding • Flash welding

The requirements for the qualification of these weldingprocesses (referred to as variables) are given in QW-250 throughQW-286. When a welding process is not addressed in Section IXbut is permitted to be used by the Code of Construction (e.g.,induction welding), the qualification rules of Section IX should befollowed to the extent that they are applicable.

24.4.1 Oxyfuel Welding Although arc welding dominates the weld processes used today,

oxyfuel welding is still occasionally used, and oxy-acetylene is

the most familiar of the gas–welding heat sources. Other gasmixtures such as oxygen-propane, oxygen–natural gas, and oxygen–methylacetylene–propadiene (MAPP) are also used. Although theforthcoming discussion deals with oxygen–acetylene, the sameprinciples apply to any oxyfuel process in which a combustible gasis used as the heat source.

In the oxyacetylene process, heat is produced by the energyreleased while the gases burn in the flame. Figure 24.1 shows aschematic view of the oxyacetylene flame. When the acetylene(C2H2) is burnt in the presence of oxygen (O2), the followingreaction takes place:

C2H2 � O2 � 2CO � H2 � Heat (24.1)

The production of heat provides the energy to raise the temper-ature of gases in the flame and the workpiece to a point wherewelding is possible. Flame tip temperatures of about 6000�F canbe achieved.

When oxyacetylene welds are made, the tip of the flame ispositioned near the work to give the maximum heating affect; themajority of the gases surrounding the work are concentrations ofcarbon monoxide (CO) and hydrogen (H2) that protect the weldfrom oxidation. If there is any O2 near the weld, either from theair or as a dissolved element in the weld puddle itself, it will

FIG. 24.1 OXYACETYLENE WELDING PROCESS


COMPANION GUIDE TO THE ASME BOILER & PRESSURE VESSEL CODE • 219

combine chemically with either the CO or H2 in the protectiveatmosphere to form carbon dioxide (CO2) or water (H2O) and notgo into the weld metal.

24.4.2 Arc Welding In arc welding, heat is produced by an electrical discharge

through an ionized gas. An electric arc is a far more intense heatsource than a chemically produced flame; the maximum tempera-ture of the arc is well above 10,000�F. The heating effect of thearc is also more localized, resulting in much less heat being lost tothe surroundings than with a flame heat source. The arc, there-fore, is an extremely efficient heat source.

The nature of the arc as a heat source varies with the differenttypes of welding processes: gas-shielded arc, submerged arc, andshielded metal arc. To examine what happens during arc welding,the arc processes are divided into two groups: slag-shielded arcand gas-shielded arc. Although each group has a number of indi-vidual weld processes, they have both common and differentmeans of providing a shield for the weld deposit and sources ofchemical changes.

24.4.2.1 Slag-Shielded Arc Welding For the purpose of thisdiscussion, this group of welding processes includes submergedarc, shielded metal arc, flux-cored arc, and, to a somewhat lesserextent, electroslag. Figure 24.2 schematically illustrates shieldedmetal arc welding with covered electrode as the representativeprocess in the group. The arc is established between the consum-able electrode and the work, and the electrode becomes the fillermetal as it melts from the heat of the arc. One can envision theweld puddle as a miniature crucible in which the weld metal iscast. The arc sup-plies the heat, the base metal and electrode arethe raw materials for the molten bath (weld puddle), and the elec-trode coating provides protection of the molten metal duringsolidification.

The electrode coating’s ingredients perform two major func-tions. The first is to shield the arc by covering it and the moltenweld metal with gas, which prevents the collection of oxygen andnitrogen from the atmosphere and also prevents the formation ofoxides and nitrides in the weld deposit. The second function is to

provide a molten slag covering over the solidifying weld metal.The molten slag, having a lower density than the weld metal,floats on the surface weld pool and solidifies after the weldmetal. For example, when cellulose (C2H10O5) is used in the elec-trode coating, it decomposes into CO and H2 gas to shield theweld puddle. Other electrodes use calcium carbonate (CaCO3) togive gas shielding in the form of CO2 and slag shielding in theform of calcium oxide (CaO). Other sources of protective slagshielding come from silicon dioxide (SiO2) and titanium dioxide(TiO2) added to the electrode’s coating. Although the chemicalconstituents of the flux coating vary greatly from electrode toelectrode, their function remains constant—a source of shieldingand, when required, chemical change.

Submerged arc welding is distinguished from the other slag-shielded arc welding processes by the “submergence” of the arcand molten weld puddle beneath a granular fusible flux (seeFig. 24.3). In addition to shielding the arc from view, the flux(as in the shielded metal arc welding process) provides a slagthat protects the weld pool as it cools and deoxidizes the weldmetal. Although filler metal is provided primarily from a bareelectrode wire fed continuously from a spool, supplementalfiller metal in the form of metal powder or an additional weldwire may also be used.

Submerged arc welding is a versatile production weldingprocess that can be used in three modes: semiautomatic, machine,and automatic. In the semiautomatic mode, a hand-held weldinggun is used to deliver the filler wire and flux to the weld area. Thefiller metal is taken from a continuous spool of wire by a wirefeeder; the flux may be supplied by gravity from a hopper mountedon the gun or by air pressure through a hose. In the machinemode, the process uses equipment that performs all of the weldingoperations but requires a welding operator to position the work, tostart and stop the welding, and to adjust the welding controls(e.g., current, voltage, and travel speed). In automatic welding,the equipment performs the welding operation without the weld-ing operator continuously monitoring the process.

Flux-cored arc welding, like submerged arc welding, producesheat from a welding arc established between a continuous fillermetal and the work. In this process the filler metal is actually acomposite tubular product fabricated of a thin outer metal sheathsurrounding a core of granular powders providing metal alloyadditions and fluxing ingredients. In construction, it is the reverseof a stick electrode that has an inner solid wire core and an out-side flux covering.

Actually, there are two variations of flux-cored arc welding thatdiffer in their methods of shielding the arc and weld pool. Onetype, termed self-shielded, relies on decomposition of the fluxingingredients under the heat of the welding arc to provide both gasprotection to the welding arc and an extensive slag covering forthe solidifying weld metal, as do other slag-shielded arc weldingprocesses. The other type of flux-cored arc welding, gas shield-ing, makes use of a protective gas flow in addition to the fluxingingredients. Both types use the flux ingredients contained in thecore of the wire to provide a substantial slag covering for thesolidifying weld puddle.

Flux-cored arc welding in its semiautomatic mode represents asignificant improvement over shielded metal arc welding in thatbetter deposition rates can be achieved from a higher burn-off ofthe electrode. This results from a higher welding current and fromthe elimination of lost time for changing electrodes. However,unlike shielded metal arc welding, flux-cored arc welding canalso be used in the machine and automatic process forms. FIG. 24.2 SHIELDED METAL ARC WELDING PROCESS


220 • Chapter 24

24.4.2.2 Gas-Shielded Arc Welding While the gaseous pro-tection in the slag-shielded arc welding processes develops fromthe decomposition of the flux ingredients, the gas protection withthe gas-shielded arc welding processes is provided by an exter-nally supplied gas directed onto the work from a nozzle sur-rounding the electrode and engulfing the weld zone. Althoughinert gases such as argon (Ar) and helium (He) are frequently usedas shielding gases, for some gas-shielded welding processesactive gases such as CO2 or mixtures of inert gases with CO2 andO2 are often used.

When inert gases are used, a significant difference between gas-shielded arc welding processes and slag-shielded welding arcprocesses is that the only chemical changes taking place in the welddeposit under the inert gases occur through the alloy additions ofthe filler metal. CO2, CO2–O2 containing Ar, Ar–He gas mixturesare all being used extensively as shielding gases with consumableelectrode processes. When CO2 and O2 are used, they can besources of chemical change because they interact with the weld.The basic gas-shielded arc welding processes are the following: gastungsten arc; gas metal arc (including gas-shielding-flux-cored arc);plasma arc; and, to a lesser extent, electrogas.

Figure 24.4 is a schematic illustration of the gas tungsten arcwelding process. Although it is often referred to as the tungsteninert gas (TIG) process, the correct term is gas tungsten arc weld-ing (GTAW) process because gas-shielding mixtures that are nottruly inert can be used with it. The notable difference between theGTAW process and the slag-shielded and gas-shielded arc weld-ing processes is that the GTAW process uses a welding arc estab-lished between a nonconsumable tungsten electrode and thework-piece. The tungsten electrode is held in a torch throughwhich the shielding gas flows. The ionized shielding gas acts as a

conductor to transfer the arc current as well as to protect the tung-sten electrode, weld pool, and solidifying weld metal from atmos-pheric contamination. Heat produced by the arc is used to meltthe base metal and filler metal, if added. The GTAW process pro-duces high quality welds in nearly all metals and alloys. Its versa-tility ranges from the welding of the reactive family of metals(e.g., titanium, zirconium, and hafnium) to root pass welding forexcellent penetration control. Because of lower deposition ratescompared with consumable electrode welding processes, GTAWis used mostly in thinner sections or where the weld quality is ofcritical importance.

The gas metal arc welding (GMAW) process is distinguishedfrom the GTAW process by the fact that the arc is transferredfrom a consumable electrode (filler wire) to the work. When it

FIG. 24.4 GAS TUNGSTEN ARC WELDING OPERATION

FIG. 24.3 SUBMERGED ARC WELDING PROCESS



was initially developed, GMAW was thought of as also being aninert gas shielded process; hence, it was commonly called the metalinert gas (MIG) process. Later work showed that significantimprovements in the welding process could be achieved with reac-tive gases (CO2) and inert–reactive gas mixtures (e.g., Ar–CO2 andAr–O2); thus the correct term for the process is gas metal arc weld-ing. The process, illustrated in Fig. 24.5, reveals an arc between acontinuous filler wire electrode and the base metal shielded byexternally supplied gas. The filler metal may take the form of a baresolid wire, a tubular wire with predominantly metal powders in thecore (metal-cored wire), or a tubular wire with both metal powdersand slag shielding ingredients (flux-cored wire). This latter variantis referred to as the gas-shielded-flux-cored arc welding process,which Section IX considers to be a GMAW process.

One of the unique aspects of the GMAW process is that themetal transfer from the electrode to the workpiece may take placein three modes: short-circuiting, globular, or spray arc transfer.Short-circuiting transfer takes place in the low voltage, low currentregime of the GMAW process during the portion of the arc weld-ing cycle when the electrode is in contact with the workpiece,which generally occurs 100–200 times/s. When the electrode andworkpiece are separated by a gap, no metal transfer takes place.This mode of metal transfer, although prone to spattering, is usefulfor welding thin gauge metals and for out-of-position welding.

Globular transfer takes place at slightly higher welding currentsthan those used for short circuiting transfer. Here the filler metalis transferred from the electrode tip to the workpiece in largedroplets across the arc. The droplet size is usually larger than thediameter of the electrode and is dependent on gravity for itsdetachment and transfer to the workpiece. The transfer rate is inthe range of 5–20 drops/s. Both the large droplet size and thenature of the metal transfer limit the suitability of this transfermethod for out-of-position welding.

A very stable, spatter-free spray transfer mode can be achievedwhen an argon-rich shielding gas is used. This type of transferoccurs at and above a critical current value called the transitioncurrent. Below the transition current, transfer occurs in the globu-lar mode; above the current, spray transfer occurs as very small

drops that are formed and detached at the rate of hundreds persecond across the arc. Since arc-streaming forces, rather thangravity, propel the arc toward the work, the process under certainconditions can be used in all positions. With its high depositionrate, it is well suited for heavy section welding.

Plasma arc welding, like gas tungsten arc welding, uses a non-consumable electrode to develop an arc with which welding cantake place. The arc can be established between the tungsten elec-trode and the work or between the tungsten electrode and a con-stricting nozzle. This constricting nozzle forces the hot “plasma”gas through a relatively small orifice (see Fig. 24.6) and producesa higher arc density and a higher arc temperature (about30,000�F) than with GTAW, resulting in better arc stability, fasterwelding speeds, and higher depth-to-width ratios of the weldbead. Because of a greater number of process control variablesand the higher cost for equipment, GTAW is the more commonlyused of the two nonconsumable arc welding processes.

24.4.3 Other Weld Processes Although they deploy different types of “beams,” laser beam

welding (LBW) and electron beam welding (EBW) are often spo-ken of together, as they both use high-energy beams to producefusion welding. With EBW, the energy source is a stream of elec-trons that are produced in a vacuum and then collimated andfocused through a series of magnetic focusing lenses. With LBW,the energy source is a coherent beam of electromagnetic radiation(light) that is concentrated through the use of lenses or reflectors.Both processes, because of their high beam densities, can producevery high depth-to-width ratio welds—up to to 1 in. in a singlepass for laser welding and up to 4 in. (of carbon steel) for electronbeam welding. Similarly, because of the small cross-sectional sizeof their beams, both processes can join small, closely spacedcomponents with tiny welds. However, because the beams aresmall and must melt both pieces simultaneously, accurate fit-upand positioning of the weld joint are critical for a high qualityweld. Another limitation of these processes is the environments inwhich they must operate. To maintain the density of the electronbeam, welding must be performed in either a high or medium

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FIG. 24.5 GAS METAL ARC WELDING PROCESS


222 • Chapter 24

vacuum. This necessitates a chamber to contain the part duringwelding, resulting in a process with high equipment costs.Though the laser energy source is not similarly affected by weld-ing in air, it can be affected by the formation of a metal vapor (or plasma) above the workpiece. It is often necessary to flow gasacross the weld where the beam impinges to control the plasmaand provide shielding for the molten puddle as it solidifies.

As noted in Section IX, stud welding is a general term for join-ing a metal stud, pin, or similar fastener to a larger workpiece. Itis typically accomplished by placing the stud into a pistol-shapedtool called a stud gun, which is positioned by the operator overthe location where the weld is to be made. The stud often has aceramic shield at its tip, called a ferrule, to protect the weld pud-dle during this process. When the operator pulls the trigger, cur-rent flows through the stud, which is lifted slightly, creating anarc. After a short arcing period, the stud is then plunged into theweld puddle created on the workpiece. Typically, this weld cycletakes less than a second. The process is used for attaching a vari-ety of stud materials including carbon and alloy steels, stainlesssteels, aluminum and other nonferrous alloys.

Flash welding is part of the family of resistance weldingprocesses used to weld simultaneously the entire cross section ofa part without the addition of filler metal. The process producesmelting at the cross sectional faces to be welded by applying avoltage to the two parts and slowly bringing them together. Whenthe parts contact one another resistance heating produces a flash-ing action, caused by high current densities, producing meltingand vaporization at the points of contact. This continues until theentire cross sectional surface reaches a selected temperature atwhich point the flashing voltage is terminated and the parts areforced together by the application of a force sufficient to producea forged weld. When this occurs the molten metal is forced out ofthe weld joint producing what is referred to as flash.

24.5 CLASSIFICATION OF MATERIALS

24.5.1 P-Numbers To reduce the number of tests required to qualify procedures

and welders (or brazers), Section IX has adopted a system of cate-gorizing ASME base materials (i.e., those contained in Section II,

Parts A and B) of similar composition, weldability (or braze-ability),and mechanical properties. Each category of similar basematerials is assigned a P-Number. The general breakdown of P-Numbers is as follows:

FIG. 24.6 PLASMA ARC WELDING TORCH

P-number Description

1 Carbon steels, C–Mn, and C–Mn–Si steels3 Low-alloy steels with additions of Mo, Mn–Mo,

Si–Mo, and Cr–Mo (Cr � 43% and total alloycontent � 2%)

4 Cr–Mo low-alloy steels with Cr between %and 2%; total alloy content �2 %

5A Cr–Mo low-alloy steels with Cr � 3% and� 85,000 psi minimum tensile strength

5B Cr–Mo low-alloy steels with �3% Cr and �85,000 psi minimum tensile strength

5C Cr–Mo low-alloy steels with Cr between 2 %and 3%; �85,000 psi minimum tensile strength

6 Martensitic stainless steels 7 Ferritic stainless steels—essentially

nonhardenable 8 Austenitic stainless steels

9A, 9B, 9C Nickel alloy steels with 4.5% Ni 10A–10K Mn–V and Cr–V steels, 26% Cr–3% Ni–3%

Mo, and 29% Cr–4% Mo–2% Ni steels and duplex stainless steels

11A, 11B Low-alloy quenched and tempered steels with � 95,000 psi minimum tensile strength

21–25 Aluminum and aluminum-base alloys 31–35 Copper and copper-base alloys 41–49 Nickel and nickel-base alloys 51–53 Titanium and titanium-base alloys 61, 62 Zirconium and zirconium-base alloys

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Within the P-Number categories for ferrous alloys (i.e., P-Numbers 1 through 11B), the base metals are further brokendown into a subset category called group numbers. Group num-bers are required on procedure qualification records and proce-dure specifications when the referencing book section specifies



impact property testing as a requirement. Otherwise, the use ofgroup numbers is not mandatory.

24.5.2 S-Numbers While the P-Numbers are used for categorizing the weldability

of ASME base metals, another system, called S-numbers, areused for base metals in pressure and nonpressure applicationswithin certain Code Cases and the ASME B31 Code. These aremostly ASTM specification materials that have not been adoptedwithin Section II, Part D but that are referenced within CodeCases and the ASME B31 Code. The grouping of S-numbers isidentical to that of P-Numbers and they are listed along with P-Numbers in Table QW/QB-422.

As with P-Numbers, qualification of one base metal within anS-number category qualifies all base metals within the same S-number. Additionally, a qualification of a base metal within a P-Number grouping also qualifies all base metals within the sameS-number grouping. However, the opposite is not true:Qualification of a procedure with an S-number material does notqualify that procedure for the corresponding P-Number material.Base metals that have not been assigned a P- or S-number are con-sidered unassigned and require separate procedure qualifications.

24.5.3 F-Numbers With a purpose similar to that of P-Numbers, Section IX cate-

gorizes filler metals by their usability characteristics to reduce thenumber of tests required to qualify procedures and welders (orbrazers). F-Numbers are assigned to filler metal classificationsthat appear in the filler metal specifications in Section II, Part C.These specifications are those issued by the AWS and adopted byASME as SFA specifications. Assigned F-Numbers for weldingfiller metals are listed in Table QW-432; the F-Numbers for braz-ing filler metals are listed in Table QB-432. The general break-down of F-Numbers for weld filler metals is as follows:

Similar to Section IX’s treatment of base metals, filler metalsthat have not been assigned an F-Number are considered unas-signed and, as such, require separate procedures and performancequalifications.

24.5.4 A-Numbers The A-number is another material classification of Section IX.

It is used to describe weld deposit chemistry and is applicableonly to the ferrous metals for the qualification of a welding proce-dure. A-number classifications are based on chemical analysis ofthe weld deposit and are found in Table QW-442, given here asTable 24.1.

The usefulness of A-numbers to the procedure qualificationeffort stems from the wide range of chemical compositions thatmake up ferrous alloys. The F-Number classification system, devel-oped from usability characteristics of filler metals, is not appropri-ately divided to separate the very broad range of ferrous alloy weldchemistries. An example is the F-No. 6 classification that covers allsolid and tubular ferrous filler metals spanning a range of alloysthat includes carbon as well as low-alloy, high-alloy, stainless, andheat-resisting steels. This is too broad of a range for the purpose ofweld qualification. Rather than requiring every change in welddeposit composition to be qualified, Section IX has divided the fer-rous alloys into twelve discrete composition ranges or A-numbers.Like its P-Number counterpart, the A-number categories provides ameans to reduce the number of tests required to qualify weld proce-dures involving changes of weld metal.

It is not known for certain why the elements carbon (C),chromium (Cr), manganese (Mn), molybdenum (Mo), nickel (Ni),and silicon (Si) were selected as the principal elements for classi-fying the weld metal composition when, in 1952, A-numberswere first introduced into Section IX. One may speculate that theywere selected because they are the elements having a major effecton carbon alloy, low-alloy, and stainless steels. Chromium pro-vides resistance to high-temperature oxidation and (along withmolybdenum) improves the creep resistance of the weld deposit;manganese is important for reducing solidification cracking andimparts strength and toughness to the weld metal; molybdenumand nickel are both strengtheners and are additions used toimprove toughness; and silicon is important in that it improveswetting of the weld puddle and (along with manganese) is a pow-erful deoxidizer.

24.6 QUALIFICATION OF WELDINGPROCEDURES

The welding procedure aspect of qualification involves thepreparation of two documents—the procedure qualification record(PQR) and the welding procedure specification (WPS).

The purpose of the PQR is to demonstrate that the weldmentproposed for construction is suitable for its intended application.This is accomplished by establishing the properties of the weld-ment—tensile strength and bend ductility as a minimum. In addi-tion to these mechanical property tests, when required by theBook Sections; impact property (notch toughness) tests may alsobe conducted. For conducting the weldment fabrication and testingthat becomes a PQR, it is presupposed that the welder or weldingoperator performing the procedure qualification test possesses therequisite welding skills. Thus, the PQR establishes the mechani-cal properties of the weldment, but not the skill of the welder orwelding operator.

F-number Description

1 Carbon steel and low-alloy steel, (EXX2X) and certain EXXX-26 stainless steel electrodes

2 Carbon and low_alloy steel all position titania- coated (EXX12, EXX13, EXX14, and EXX19)electrodes

3 Carbon and low_alloy steel all position cellulose-coated (EXX10 and EXX11) electrodes

4 Carbon steel and low-alloy steel all-position, low-hydrogen (EXX15, EXX16, EXX18, and EXX48) electrodes; and martensitic, ferritic, and precipitation-hardening stainless steel all-position (EXX15, EXX16, and EXX17) electrodes

5 Austenitic and duplex stainless steel all-position (EXXX-15, EXXX-16, and EXXX-17) electrodes

6 Solid, flux-cored, and composite ferrous electrodes and rods

21–25 Aluminum and aluminum-alloy electrodes and rods

31–37 Copper and copper-alloy electrodes and rods 41–45 Nickel and nickel-alloy electrodes and rods 51–54 Titanium and titanium-alloy electrodes and rods

61 Zirconium and zirconium-alloy electrodes and rods 71, 72 Hard-facing electrodes and rods


224 • Chapter 24

The WPS is intended to provide direction for the welder orwelding operator. It lists the welding variables—essential, supple-mentary essential (when required), and nonessential—that are tobe controlled to make a satisfactory weld. The values or accept-able ranges for each of the welding variables are based on theresults of the supporting PQR(s) that must be referenced on theWPS.

Beginning with the 2000 addenda of the ASME Code, a newtype of welding procedure specification was approved for use bymanufacturers and contractors: it is the ANSI/AWS StandardWelding Procedure Specification (SWPS). To date a total of 33SWPS have been approved by subcommittee IX for use in ASMEcode construction. Preapproved SWPSs offer the manufacturersand contractors an alternative to qualifying its own welding pro-cedures within the following range:

Material P-No. 1, Groups 1 and 2; P-No. 8, Group 1 Weld Processes SMAW, GTAW, FCAW PWHT As-welded and stress-relieved Thickness 1 inches

In the absence of a procedure qualification, Section IX wantedthe manufacturer to provide evidence of its competence to controlits welding. Therefore, a requirement for the use of SWPSs is thata welder, employed by the manufacturer, must weld and test aweld coupon for certain of the SWPSs and record the weldingvariables and test results. Additionally, as an administrative mat-ter the manufacturer must enter its name on the SWPSs and signand date them as acknowledgment of responsibility for their use.

Regardless of whether a manufacturer uses a WPS or SWPS,an individual involved in welding is required to be qualified bythe manufacturer before he/she can be employed in construction

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work. The purpose of this qualification test is to demonstrate thewelder’s ability to deposit sound weld metal with the type ofequipment he/she will be using that is appropriate for each weld-ing process. This is accomplished by evaluating the resultingweldment by using either radiography or a bend test to ensure thatthe weld deposit is sound. The test and its results are recorded bythe manufacturer on a third document–the welder (or weldingoperator) performance qualification (WPQ).

24.6.1 Procedure Qualification Record The PQR is a record of the welding variables recorded during

the welding of the test coupon and the results of the tests conductedon the resulting weldment. The variables required to be recordedare those essential and, when specified, supplementary essentialvariables appropriate for each weld process. In the context of pro-cedure qualification, an essential variable is one that is deemed tohave an effect on the weldment’s tensile or bend properties, whilea supplementary essential variable is one that has an effect onnotch toughness properties. The actual value, or range of values,for each variable is recorded. The recorded value or range usuallyrepresents a subset of the range that will be used in productionwelding. Nonessential variables used in welding the test couponare not required to be recorded but may be included in the PQR atthe manufacturer’s option. While nonessential variables are con-sidered to have no effect on the weldment’s mechanical proper-ties, they are nonetheless important in providing direction to thewelder. The essential, supplementary essential, and nonessentialvariables for each welding process are found in Tables QW-252through QW-265.

Section IX specifies that each organization performing weldingis the responsible entity for welding of the qualification test



coupons, testing of the required specimens, and recording of thewelding data and test results in a PQR document to qualify itswelding procedures. What is meant by the term responsible? Inperforming the welding of the test coupon, Section IX requiresthis effort to be conducted solely by the manufacturer.Specifically, Section IX states:

The welders or welding operators used to produce weldmentsto be tested for qualification of procedures shall be under thefull supervision and control of the manufacturer or contractorduring the production of these weldments. The weldments tobe tested for qualification of procedures shall be weldedeither by direct employees or by individuals engaged by con-tract for their services as welders or welding operators underthe full supervision and control of the manufacturer or con-tractor. It is not permissible for the manufacturer or contrac-tor to have the supervision and control of welding of the testweldments performed by any other organization.

The applicability of these requirements to the manufacturer orcontractor performing Code work can be seen in recentInterpretation IX-92-92. (Interpretations are issued by the Code toprovide the meaning of or the intent of existing rules in the Codeand are in a question and reply form.)

Background: Two companies are contracted by a client com-pany to undertake pipe work installation on its facility. Allstages of the welding procedure qualification processes forthe two contracted companies are witnessed by the clientcompany’s representative and the documentation is dulystamped and signed by the client.

Question (1): May these procedures be used by the clientcompany?

Reply (1): No.

Question (2): Does the client company have to requalify theseprocedures to perform in-house maintenance at a later dateusing all the same essential and nonessential variables withits own qualified welders?

Reply (2): Yes.

The following aspects of the qualification test effort may besubcontracted: any or all of the work involved in the preparationof the base metal test coupon for welding; subsequent work on thepreparation of the test specimens from the completed weldment;and the performance of nondestructive examination and mechani-cal tests. This subcontracting is permissible provided the manu-facturer or contractor takes full responsibility for all such work.

The importance of the PQR is evidenced by the requirementthat the manufacturer sign the document certifying that the state-ments in the record are correct and that the test welds were pre-pared, welded, and tested in accordance with the requirements ofSection IX of the ASME Code. This certification must be per-formed by the manufacturer. The Code specifically prohibits thesubcontracting of this function to another organization. This posi-tion was reinforced in Interpretation IX-92-78, wherein an inquir-er asked:

Question (1): May a company subcontract weld proceduredevelopment and qualification including certification of thePQR without a company representative present to witness thewelding, testing, and certification?

Reply (1): No. Question (2): May a company subcontract weld proceduredevelopment and qualification including certification of thePQR with a company representative present to witness thewelding, testing, and certification?

Reply (2): No.

One question that is often asked pertains to the format that thePQR document must take. The position that Section IX takes inthis matter is that any format that fits the manufacturer’s or con-tractor’s need is acceptable so long as each essential and, whenrequired, supplementary essential variable for the qualified weldprocess(es) is recorded. It is also required that the type of tests,number of tests, and test results be listed on the PQR. Form QW-483 (Suggested Format for Procedure Qualification Record) isprovided by Section IX as a non-mandatory guide for the PQR.

It has long been recognized that within an organization theremay be more than one location performing manufacturing (i.e.,welding). Under these circumstances, is each manufacturing cen-ter required to have its own PQRs? Not necessarily; if two ormore companies of different names exist in a single organizationand these companies operate under a common operational control(an analogy would be the different manufacturing plants that buildsuch vehicles as the Blazer, the Camaro, the Cavalier, theCorvette, the Lumina, and the Monte Carlo under the ChevroletAutomotive Company), they may share procedure qualifications ifthey describe in their quality control system/quality assuranceprogram the common operational control of procedure qualifica-tion. Under such circumstances, separate welding procedure qual-ifications are not required.

Another matter that has been the topic of much discussion withSubcommittee IX over the past several years is the “ownership”of PQRs (and WPSs) when business entities within an organiza-tions are split off and sold to another corporation. Under theseconditions, the question arises of who has “ownership” of thePQRs. In the 1997 addenda, Section IX addressed this matter inparagraph QW-201.1. The paragraph stated:

The Code recognizes that manufacturers or contractors maymaintain effective operational control of PQRs and WPSsunder different ownership that existed during the original pro-cedure qualification. When a manufacturer or contractor or partof a manufacturer or contractor is acquired by new owner(s),the PQRs and WPSs may be used by the new owner(s) withoutrequalification, provided all of the following are met:

(a) the new owner(s) takes responsibility for the WPSs andPQRs;

(b) the WPSs reflect the name of the new owner(s); and (c) the quality control system/quality assurance program

reflects the source of the PQRs as being from the formermanufacturer or contractor.

24.6.2 Welding Procedure Specification The WPS document serves two purposes. First, it is a written,

qualified welding procedure prepared to provide direction to thewelder or welding operator for making production welds to Coderequirements. Second, it is the document the Authorized Inspectorreviews at the location of the manufacturer to ensure that produc-tion welding is being performed in accordance with the Code. Itdescribes all of the essential, nonessential, and, when required,supplementary essential variables appropriate for each welding


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process. (The essential, supplementary essential, and nonessentialvariables for each welding process are found in Tables QW-252through QW-264.) Additionally, the WPS must reference the sup-porting PQR(s) that have qualified it. Other information that themanufacturer thinks may be beneficial to the welder in makingthe Code weldment may also be included.

Some users take liberties with the recording of information onthe WPS. They assume that variables may be self-evident or redun-dant, such as listing the mode of metal transfer for gas metal arcwelding when they have already listed the welding parameters, orelse assuming that the absence of a response for a variable impliesthat the variable is not applicable. Section IX maintains that allvariables, including those that are nonessential, must be documentedon the WPS. This position is reinforced with a number of interpre-tations, two examples of which are IX-83-03 and IX-86-03.

Interpretation IX-83-03:

Question: Is it required that all of the essential and nonessen-tial variables listed in QW-250 through QW-280 for eachwelding process be addressed in the WPS, even though someof these variables are not applicable?

Reply: Yes.

Interpretation IX-86-03:

Question: Is omission of an essential, nonessential (or sup-plementary essential) variable from a WPS interpreted to bea negative response for that variable?

Reply: No. The Code requires that every variable for theappropriate welding process or processes (QW-252 throughQW-282) be listed on the WPS.

However, although it is strict in its position of documenting allessential and nonessential variables on the WPS, Section IX is notrigid in the manner in which this information is recorded. Usersfrequently ask if certain phrases or nomenclature are acceptablefor use on a WPS, as noted in the following interpretation:

Question: Is it acceptable to indicate on the WPS and PQRthat the variable QW-407.1 is addressed by indicating the let-ters “NA” to mean PWHT not used?

Reply: Section IX does not specify the terminology to be used.

Section IX is less concerned with the terminology used than itis with the provided information being comprehensible to thewelder. This should be the principle that guides the Code user infilling out the WPS.

Because we have been dealing with the recording of informationon the WPS, now is a good time to indicate that Section IX doessuggest a non-mandatory format for a WPS in Form QW-482. Thisform includes the required data for the common welding processes(SMAW, GTAW, GMAW, and SAW). Those using this form forother welding processes need to supplement the form to cover theadditional variables. As with the case of the PQR, the manufactureris free to provide its own format for the WPS as long as everyessential, nonessential and, when required, supplementary essentialwelding variable is included or referenced. Such a form may bemore practical for a multiple process WPS (such as SMAW rootpass and SAW fill pass), as the QW-482 form does not lend itself todocumentation for more than one process.

The variables for the procedure qualification of weld processesare given in Tables QW-252 through QW-264 and are subdividedinto essential variables, supplementary essential variables, andnonessential variables. Each variable is listed in the tables with abrief description that is intended for the user’s convenience only.The complete description of each variable is in Article IV(Welding Data). As an example, we will review the details of theessential and nonessential variables for qualifying a procedureinvolving the SMAW process as shown in Table QW-253, hererepresented by Table 24.2. We will start the discussion of the vari-ables with QW-402.1 (Groove Design), a nonessential variable,and then we will discuss each of the other variables in turn. Thosesupplementary essential variables listed in Table 24.2 will be dis-cussed later in Section 24.8.

QW-402.1 A change in the type of groove (e.g., V-groove,U-groove, single-bevel, and double-bevel,etc.).

While all of the variables in QW-402 (Joints) are identified asnonessential for the WPS, the WPS must address each variableidentified for the welding process. An appropriate means ofaddressing this variable is by description or sketch of the type ofjoint(s) that can be welded. However, this is not the only means,the WPS can also make reference to the joint styles in productiondrawings as well as make reference to a joint style manual or ashop traveler, to name a few acceptable alternatives. In fact, nearlyany means of providing the welder with the description of thetype of joint(s) to be welded in production is satisfactory. Termsthat are meant to be all-encompassing but that are lacking in defi-nition of the weld joint should be avoided. In fact, InterpretationIX-82-02 states the following:

Question: Currently, a manufacturer states “All groovedesigns” under [QW-402.1] Joints Design in the WPS. Is thispractice acceptable, or is it required to either include these inthe WPS or reference another document that illustrates allpossible joint configurations?

Reply: The practice of stating “all groove designs” on theWPS is not acceptable. Because the WPS is for the guidanceof the welder or welding operator, a manufacturer must stateon the WPS the types of joints permitted in production.Alternatively, a reference to a drawing or other document thatdescribes the allowable production joints is permitted.

QW-402.4 The deletion of the backing in single-weldedgroove welds. Double-welded groove weldsare considered welding with backing.

As referred to here, backing involves placing a material(including both metallic and nonmetallic) at the root of a grooveweld for the purpose of supporting the molten weld metal. Asexamples, the backing may take the form of a solid material suchas a backing ring for a pipe or tube and a copper backup bar forplate. Note that when a groove is welded from both sides (i.e.,double-welded), this activity is considered welding with backingbecause the original root has been removed (e.g., by backgoug-ing) and replaced with new weld metal from the opposite side.Fillet welds and partial penetration groove welds are consideredwelds with backing since the base metal to be welded providesbacking for the weld metal. Gas backing, although not a variablefor the SMAW process (it is one for the GTAW, GMAW, and



PAW processes, however), is not considered backing here underQW-402.4 for the WPS. It is covered as a variable under QW-408(Gas) for the WPS.

QW-402.10 A change in the specified root spacing.

The root spacing is the opening at the joint root between thework-pieces. Although it is a nonessential variable, the user

must still specify a dimension and, very importantly, a tolerance,as exact dimensions are difficult to achieve in production appli-cations. The nominal root spacing dimension must take intoaccount the weld process, the weld joint preparation, andwhether the joint is open root or has a consumable insert orbacking. Typical examples of specified root spacing are shownin the following table:


228 • Chapter 24

QW-402.11 The addition or deletion of nonmetallicretainers or nonfusing metal retainers.

Retainers are nonconsumable materials (both metallic and non-metallic) that are used to contain or shape the molten weld metal.If the weld involves a copper backup bar, a ceramic strip (or othershaped configuration), a water-cooled aluminum backup bar, or awelding flux, it must be identified on the WPS. However, when aweld joint involves no backing (e.g., a partial penetration grooveweld) and is indicated as such on the WPS, this variable is non-relevant and need not be addressed.

QW-403.8 A change in the base metal thickness beyondthe range qualified in QW-451, except asotherwise permitted by QW-202.4(b).

The range of base metal thickness that may be used in produc-tion must be specified on the WPS. This is based on the qualifiedtest coupon thickness and the range can be obtained from QW-451. For a PQR qualified using transverse bends tests, TableQW451.1, given here as Table 24.3, provides this range.

In referencing QW-202.4(b), QW-403,8 provides an exception tothe requirements of QW-451. For dissimilar base metal thickness

involving P-No. 8 (austenitic stainless steels), P-No. 41 through P-No. 49 (nickel-base alloys), P-No. 51 through P-No. 53 (titanium-base alloys), and P-No. 61 and P-No. 8 (zirconiumbase alloys), allmaterials in which notch toughness is not a requirement, a qualifica-tion on a in. thick test coupon will qualify unlimited base metalthickness. This exemption to the requirements of QW-451 was pro-vided because of the difficulty in obtaining thick sections of testpieces of these materials for procedure qualification testing.

One additional exception to the ranges of qualified base metalthickness given in QW-451 is found in QW-403.8. It further limitsthe base metal (and weld metal) thickness qualified over 8 in.for theSMAW, SAW, GTAW, and GMAW processes to 1.33 times thethickness of the test coupon. Thus, for a weldment involving one(or more) of these processes, a 10 in. thick production weldmentwould require a PQR conducted on a 7 in. thick test coupon.

QW-403.9 For single-pass or multipass welding inwhich any pass is greater than in. thick, anincrease in base metal thickness beyond 1.1times that of the qualification test coupon.

It is necessary to address on the WPS the thickness of the weldpass. When “none exceed in. thickness,” this statement is suffi-cient and the base metal thickness range is that given in QW-451.However, should any pass in the qualification test exceed a thick-ness of in., this variable limits the qualification range of the basemetal thickness to only 1.1 times that of the test coupon.

QW-403.11 Base metals specified in the WPS shall bequalified by a procedure qualification testthat was made using base metals inaccordance with QW-424.

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Weld Joint Description Root Spacing

GTAW process, 37 deg. bevel, in., � in., 0 in.open root 1SAW process, 7 deg. bevel with in. minimumbackingSMAW process, 25 deg. bevel, No gap tight butt

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QW-403.13 A change from one P-No. 5 to any other P-No. 5 (viz P-No. 5A to P-No. 5B or P-No.5C, or vice versa). A change from P-No. 9Ato P-No. 9B but not vice versa. A changefrom one P-No. 10 to any other P-No. 10(viz P-No. 10A to P-No. 10B or P-No. 10C,etc., or vice versa).

QW-403.11 requires that the P-Number(s) of the base metals bespecified on the WPS to the extent that they are supported by aqualified PQR. When P-Numbers are used the relationshipbetween base metals used in the procedure qualification test andthose qualified for production welding is provided in Table QW-424,given here as Table 24.4.

As can be seen from Table 24.4, a base metal used in a qualifi-cation that has an assigned P-Number (by QW/QB-422) qualifiesall base metals assigned the same P-Number. For base metals upto P-No. 5A, some additional latitude on the range of base metalsqualified is also provided in Table 24.4. Not all materials areassigned P-Numbers. When these are used in production welding,they are termed unassigned materials (meaning they have notbeen assigned a P-Number). As explained in Table 24.4, unas-signed materials may only be welded to themselves or, whenwelded to a P-Number metal, may be welded to any metalassigned the same P-Number.

There are additional requirements relating to specifying basemetals on the WPS in QW-403.13. These relate to the P-No. 5, P-No. 9, and P-No. 10 grouping of metals. Each of these P-Numbershave been further divided into P-No. 5A, 5B, 5C, 10A, 10B, 10C,

and so forth. These must each be treated as separate P-Numbercategories and, when specified on the WPS, must be appropriatelyqualified as indicated by QW-403.13.

QW-404.4 A change from one F-Number in QW-432 toany other F-Number or to any other fillermetal not listed in QW-432.

This is an essential variable requiring that the user identify onthe WPS the filler metal that is intended to be used. One methodto accomplish this is to specify the filler metal’s F-Number. (F-Numbers were discussed earlier in the Section 24.5.) As areminder, F-Numbers, like P-Numbers, are a categorizationdesigned to reduce the number of tests required to qualify proce-dures and welders.) Filler metal must be produced to a SFA specifi-cation in Section II, Part C, to have an assigned F-Number in TableQW-432. Any material not meeting this requirement is consideredan “other filler metal” and must be listed on the WPS using themanufacturer’s designation or trade name (e.g., CrMo-1 andFluxofil 6). The use of “other filler metals” must be supported by aprocedure qualification conducted with that specific filler metal.

QW-404.5 (For ferrous metals only) A change in thechemical composition of the weld depositfrom one A-Number to any other A-Numberin QW-442. Qualification with A-No. 1 shallqualify for A-No. 2 and vice versa.

Like the QW-404.4 variable for F-Numbers, QW-404.5 is anessential variable requiring that the user identify on the WPS theA-number. The A-number is the chemical composition of theweld deposit. There are several methods that QW-404.5 allows fordetermining the chemical composition (and hence the A-number)of the weld deposit. One is by the straightforward chemical analy-sis of the weld deposit from the supporting PQR; a secondmethod allows the use of the chemical composition from a welddeposit prepared according to the filler metal specification; and athird method allows the use of the chemical composition reportedin the filler metal specification or the manufacturer’s certificate ofcompliance. When the use of an A-number designation is imprac-tical or not possible, indicating the nominal chemical compositionof the weld deposit on the WPS will satisfy QW-404.5.

QW-404.6 A change in the nominal size of the electrodeor electrodes specified in the WPS.

Reporting the nominal sizes of electrodes (e.g., , , and in.)that will be used with the WPS can satisfy QW-404.6. As it is anonessential variable, the supporting PQR does not need to beconducted with all of the electrode sizes listed.

QW-404.30 A change in the deposited weld metalthickness beyond the range qualified in QW-451 for procedure qualification.

The WPS must list the maximum weld metal deposit thicknessthat is qualified. Table 24.3 provides this value based on the PQRtest coupon thickness, T. For a single weld process, the qualifieddeposited weld metal thickness, t, is twice the test coupon thick-ness, 2T or 2t. When multiple weld processes or procedures areused in the test coupon, the qualified deposited weld metal thick-ness is twice the weld thickness deposited by each process, 2t.When the deposited weld metal thickness in the test coupon is at

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230 • Chapter 24

least 43 in., then the qualified thickness is 2T when the testcoupon thickness is at least in. but less than 1 in. The qualifiedthickness (t) increases to 8 in. for the SMAW, SAW, GTAW, andGMAW processes when the test coupon thickness is � 1 in.

QW-404.33 A change in the filler metal classification inan within an SFA specification or, if notconforming to an filler metal classificationwithin an SFA classification, a change in themanufacturer’s trade name for the fillermetal.

QW-404.33 is a nonessential variable that is an addition to thefiller metal variable QW-404.3. It requires that the Code userspecify on the WPS the filler metal not simply by F-Number, butby SFA specification and AWS classification unless they areabsent, in which case the manufacturer’s trade name should beused. Thus, a typical WPS for a production welding would identifyan E7018 electrode as an F-No. 4, and identify the filler metalSFA specification filler metal classification as ASME SFA-5.1E7018 (AWS A5.1 is also acceptable) or list the manufacturer’strade name (e.g., Atom-Arc 7018).

QW-405.1 The addition of other welding positions tothose already qualified.

QW-405.3 A change from upward to downward, or fromdownward to upward, in the progressionspecified for any pass of a vertical weld,except that the cover or wash pass may be upor down. The root pass may also be run eitherup or down when the root pass is removed tosound weld metal in preparation for thewelding of the second side.

Both QW-405.1 and QW-405.3 are nonessential variables thatrequire weld position(s) and progression, when welding in the ver-tical position, to be specified on the WPS. A qualified weld proce-dure in any position will support a WPS for any and all positions aswell as both vertical up and vertical down progression. However,the reader should be warned that not all SMAW electrodes aredesigned to run in all positions and in both vertical progressions.Therefore, the information provided on the WPS for these variablesshould be consistent with the selection of filler metal and weldprocess, whether for SMAW or for other weld processes.

QW-406.1 A decrease of more than 100�F in thepreheat temperature qualified. Theminimum temperature for welding shallbe specified in the WPS.

To understand the variables of QW-406 (Preheat), it is necessaryto understand the Section IX definitions of preheating, preheatingtemperature, preheating maintenance, and interpass temperature.

Preheating—the application of heat to the base metal immedi-ately before a welding or cutting operation to achieve a specifiedminimum preheat temperature.

Preheat temperature—the minimum temperature in the weldjoint preparation immediately prior to the welding or, in the caseof multipass welds, the minimum temperature in the section of thepreviously deposited weld metal immediately prior to welding.

Preheat maintenance—the practice of maintaining the mini-mum specified preheat temperature, or some specified higher

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temperature, for some required time interval after welding is fin-ished or until postweld heat treatment.

Interpass temperature—the highest temperature in the weldjoint immediately prior to welding or, in the case of multiple passwelds, the highest temperature in the section of the previouslydeposited weld metal immediately before the next pass.

Since preheat temperature can have an effect on both themechanical properties and the soundness of the weldment, especial-ly in higher alloy ferrous materials, QW-406.1 requires the user tospecify on the WPS a minimum preheat temperature (WPS Tmin).Note that in a multipass weldment, preheat temperature occurs atthe very start of welding and prior to the start of each successivepass. Since the temperature of the weldment gradually rises as theweld is being completed, it is the lowest preheat temperature mea-sured during the welding of the PQR test coupon that is to berecorded. It is from the lowest preheat temperature used in the PQRtest coupon (PQR Tmin) that the minimum preheat temperature isestablished for the WPS. The WPS minimum preheat temperature(WPS Tmin) may be equal to but no more than 100�F lower than thepreheat temperature recorded on the PQR—that is, WPS Tmin �(PQR Tmin 100�F). This 100�F range is believed to provide a rea-sonable temperature tolerance for preparing the WPS without com-promising the properties of the weldment.

QW-406.2 A change in the maintenance or reduction ofpreheat upon completion of welding prior toany required postweld heat treatment.

This nonessential variable requires that the user specify whatwill happen to the preheat temperature following the completionof welding. There are a number of options that can be taken, someexamples of which follow.

• No maintenance of preheat temperature • Weldment maintained at 400�F for a minimum of 4 hr fol-

lowing welding and then allowed to drop to room temperature • Preheat temperature maintained until postweld heat treatment

QW-407.1 A separate procedure qualification isrequired for each of the following conditions:

(a) For P-No. 1, P-No. 3, P-No. 4, P-No. 5, P-No. 6, P-No. 9,P-No. 10, and P-No. 11 materials, the following post-weld heat treatment conditions apply: (1) No PWHT; (2) PWHT below the lower transformation tempera-

ture; (3) PWHT above the upper transformation tempera-

ture (e.g., normalizing);(4) PWHT above the upper transformation tempera-

ture followed by heat treatment below the lowertransfor-mation temperature (e.g., normalizing orquenching followed by tempering); and

(5) PWHT between the upper and lower transforma-tion temperatures.

(b) For all other materials, the following postweld heattreatment conditions apply: (1) No PWHT, and (2) PWHT within a specified temperature range.

QW-407.4 For ferrous base metals other than P-No. 7, P-No.8, P-No.45, when procedure qualifica-tion test coupon receiving a postweld heattreatment in which the upper transformation



temperature is exceeded, the maximumqualified thickness for production welds is1.1 times the thickness of the test coupon.

For the ferritic alloys given in QW-407.1(a), the PWHT condi-tions listed as (1) through (5) each can have a significant effect onthe mechanical properties of the weld metal. Hence, Section IXrequires that for each PWHT condition, a separate procedurequalification be conducted and subjected to the PWHT conditionsupporting the WPS. When PWHT is required, the test couponmerely needs to have been heat treated at any temperature thatmeets the requirements of the condition. Thus, for carbon steelsthat are deemed by B31.1 to have a lower transformation tempera-ture of 1340�F, PWHT at any temperature up to 1340�F wouldmeet the requirements of QW-407.1 (a)(2). (Note that book sec-tions such as Section VIII do not regard heat treatment below800�F as PWHT.) The user may enter on the PQR the specifictemperature at which heat treatment was performed or indicatethat heat treatment was conducted in accordance with one of theconditions, such as heat treatment conducted below the lowertransformation temperature, or conducted between the upper andlower transformation temperatures.

Should PWHT exceed the upper transformation temperature, asin conditions QW-407.1 (a)(3) and (a)(4), QW-407.4 wouldimpose restrictions on the range of base metal thickness qualified.Rather than finding the maximum qualified thickness in Table24.3, the maximum thickness qualified would be limited to 1.1times the thickness of the test coupon. Thus, while a 2 in. thicktest coupon would qualify a WPS for up to 8 in. with a PWHTbelow the lower transformation temperature, the same test couponthickness would only qualify a WPS for up to 2.2 in. if the PWHTis above the upper transformation temperature.

For the alloys covered in QW-407.1 (b) (P-No. 7, P-No. 8, andP-No. 21 and higher), only two PWHT conditions apply: one isno PWHT, the other is PWHT within a specified temperaturerange. For a weldment that will be subjected to PWHT, unlike thealloys of QW-407.1 (a), the WPS must identify the specific tem-perature range of heat treatment following welding and have asupporting PQR that covers this temperature range. Thus, if300series stainless steel (P-No. 8) was to be welded and subjectedto a solution annealing heat treatment at 1950�F-2100�F, then asuitable supporting PQR should list the actual heat treatment tem-perature such as 2000 25�F.

QW-409.4 A change from AC to DC, or vice versa; andin DC welding, a change from electrodenegative (straight polarity) to electrodepositive (reverse polarity) or vice versa.

QW-409.8 A change in the range of amperage or,except for SMAW and GTAW welding, achange in the range of voltage. A change inthe range of electrode wire feed speed maybe used as an alternative to amperage.

Both of these variables are nonessential variables, but QW-409.4is also a supplementary essential variable when notch toughnesstesting is required (for more on QW-409.4, see Section 24.8).Together, the two variables require that the WPS specify the type ofcurrent as either alternating current (AC), direct current (DC), orboth, and for direct current the type of polarity—straight polarity,reverse polarity, or both. Additionally, the WPS must specify therange of amperage (current) and voltage (for processes other thanSMAW and GTAW) that will be used. The choice of current type

and polarity are dictated by a number of factors including weldprocess, electrode type, application, and welder preference.

QW-410.1 For manual or semiautomatic welding, a{OK as published in the book — KR Rao,editor} change from the stringer beadtechnique to the weave bead technique, orvice versa.

QW-410.5 A change in the method of initial andinterpass cleaning (brushing, grinding, etc.).

QW-410.6 A change in the method of back gouging.

QW-410.25 A change from manual or semiautomatic tomachine or automatic welding and viceversa.

QW-410.26 The addition or deletion of peening.

All of the aforementioned QW-410 “technique” variables arenonessential for the SMAW process but are required to beaddressed on the WPS. For QW-410.1, the user needs to identifywhether the weld procedure will be performed using a stringerbead, a weave bead, or both. It is advisable to quantify theseterms to minimize disagreements between the person preparingthe WPS, the welder, the Authorized Inspector, and the customer,who often requests to review WPS. The width of the weld bead iscommonly used to describe the bead technique. For the SMAWprocess it is common to specify the bead as 2 or 3 times the corediameter of the electrode for a stringer bead and 4, 5, and 6 timesthe core diameter (depending on electrode size) for a weave bead.Another method suitable for SMAW and other weld processes isto specify a dimension such as in. maximum weave width.

All of the ASME Pressure Codes have a requirement that dealswith cleaning of the base metals before welding. In Section I, it iscovered in PW-29; in Section VIII, it is addressed in UW-32; andin B31.1, it is covered in 127.3. QW-410.5 requires that the userspecify how the base metal will be prepared suitable for weldingand, if the weld is multipass, how cleaning between passes will beaccomplished. Common methods for weld surface preparationinclude machining, grinding, and thermal cutting with grinding,whereas for interpass cleaning with the SMAW process one mightspecify wire brushing, chipping hammer, or grinding as accept-able methods. These same methods are also frequently used todescribe the method of back gouging required by QW-410.6.

For QW-410.25, the user is required to identify the type ofwelding process that is being used. In referring to “type of weld-ing process,” Section IX requires that the WPS state what modeof the process will be used - manual, semiautomatic, machine, orautomatic. All of the common welding processes are usable inmore than one “type,” as illustrated in the following table:

Weld Process Type of Process

SMAW Manual, semiautomatic SAW Semiautomatic, machine, automatic

GTAW Manual, semiautomatic, machine, automatic GMAW Semiautomatic, machine, automatic

The last SMAW technique variable, QW-410.26, requires theuser specify whether peening will be used. Peening is normally

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used as a means of controlling weld distortion or to produce com-pressive stresses on the top surface of the weld. Peening is themechanical working of the weld metal using impact blows and isusually performed manually by using a ball peen hammer or byusing a pneumatically driven tool with a radius tip end. It shouldbe noted that both Section III in NB-4422 and Section VIII inUW-39 prohibit peening on the initial (root) and final (face) layersunless the weld is subsequently postweld heat treated.

24.7 QUALIFICATION OF WELDERS ANDWELDING OPERATORS

This activity completes the process of welding qualification forCode construction. Every welder and welding operator is requiredto pass a qualification test to demonstrate his/her ability to depositsound weld metal with each weld process that he/she will use.This test, called the welder performance qualification test (WPQ),must be administered by the manufacturer or contractor for whomthe welder or welding operator will be working using a qualifiedWPS. As with the PQR, this responsibility cannot be delegated toanother organization.

In the 2001, an inquirer asked whether when a new companyacquires part or all of an existing company, whether the newowner may continue the use of existing welder performance qual-ifications. After some consideration the Subcommittee concludedthat such a situation would be acceptable and in 2002 providedrules for the continued use of welder performance qualificationsby a new owner (patterning the requirements after those for pro-cedure qualifications). The new rules stated:

When a manufacturer or contractor or part of a manufacturer orcontractor is acquired by a new owner(s), the WPQs [welderperformance qualifications] may be used by the new owner(s)without requalification, provided all of the following are met:

(1) the new owner(s) takes responsibility for the WPQs; (2) the WPQs reflect the name of the new owner(s); (3) the Quality Control System/Quality Assurance Program

reflects the source of the WPQs as being from the formermanufacturer or contractor.

24.7.1 Welder Performance Qualification The essential variables for the performance qualification of a

welder are given in QW-352 through QW-357, while the essentialvariables for the qualification of a welding operator are given inQW-361 through QW-363. As an example, we will review the details of the essential variables for qualifying a welder to the SMAW process as shown in Table QW-353, given here as Table 24.5. We will begin with the discussion of the variable QW-402.41 (Backing), and then discuss each of the other essentialvariables in turn.

QW-402.4 The deletion of backing in single-weldedgroove welds. Double-welded groove weldsare considered welding with backing.

This variable, when used in the welding performance qualifica-tion, is an essential variable not only for the SMAW process butalso for the GTAW, GMAW, and PAW processes. As referred tohere, backing can take several forms. The first involves materialplaced at the root of a weld groove that can take the form of asolid metal such as a carbon steel backing strip for plate, a back-ing ring for pipe or tube, and a copper backup bar. Nonmetallic

backing materials such as welding flux (often held in place bytape) or ceramic strips are also considered backing. Note thatwhen a groove is welded from both sides (i.e., double-welded),this activity is considered welding with backing since the originalroot has been removed (e.g., by backgouging) and replaced withnew weld metal from the opposite side. Other types of welds thatare considered welding with backing include fillet welds and par-tial penetration groove welds. Here, the base metal to be weldedprovides backing for the weld metal. Gas backing, although not avariable for the SMAW process (it is one for the GTAW, GMAW,and PAW processes, however) is not considered backing hereunder QW-402.4 for the WPQ. It is covered as an essential vari-able for certain base materials under QW-408.8 for procedurequalification.

QW-403.16 A change in the pipe diameter beyond therange qualified in QW-452, except asotherwise permitted in QW-303.1, QW-303.2, QW-381(c) or QW-382(c).

QW-452.3 specifies the diameter limits for a groove-weldedperformance qualification pipe or tube test coupon. For circumfer-ential weld joints in components greater than 2 in. diameter, thewelder has the option of having his performance qualification testconducted on a test coupon of plate or pipe. However, when theCode weld is to be made in a component with a diameter less than2 in., the qualification test must be conducted on a pipe or tubein accordance with the requirements in Table QW-452.3, givenhere as Table 24.6. Thus, if the welder were joining tubing of a 2in. outside diameter, he would be required to perform his WPQ ona pipe or tube with an outside diameter less than 2 in.

One issue that QW-403.16 and QW-452.3 always seem toevoke is how to handle the matter of a set-on versus a set-throughnozzle. Section IX addresses this matter in Interpretation IX-80-67.When the nozzle is set on the vessel (Fig. 24.7) and the weld ismade through the thickness of the nozzle, performance qualifica-tion with the appropriate diameter pipe test coupon is required.When the nozzle is set through the vessel and the weld is madethrough the thickness of the vessel, diameter is not considered a

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factor and performance qualification can be accomplished on aflat plate. Where fillet welds are added to the set-through nozzlegroove welds or fillet welds alone attach the set-through nozzle,the welder making these fillet welds is not limited when his quali-fication is by a groove weld WPQ. However, when the welderapplying the fillet welds has been qualified by a fillet weld test,the diameter limits of QW-453.4 (which are similar to QW-453.3)apply.

QW-403.18 A change from one P-Number to any otherP-Number or to a base metal not listed inQW/QB-422 except as permitted in QW-423,and in QW-420.2.

Although this variable states that a change in P-Numberrequires the welder to requalify, the reference to QW-423 (givenhere as Table 24.7) provides a large measure of relief from thisrequirement. A welder may use any base metal from the P-No. 1through P-No. 11, P-No. 34, or P-Nos. 41–49 groupings forhis/her qualification test coupon and, upon passing the WPQwould be qualified to weld on any of these materials as well asunassigned (non–P-Number) materials of similar chemical com-positions. This essential variable is quite liberal in its position onqualified production base metals for the WPQ; Section IXbelieves that within the groupings specified in Table 24.7, thebase metal has little effect on the welder’s ability to make soundwelds. Fundamentally, it is the weld process and filler metal (F-Number) that is most critical for the welder’s control. Hence, awelder may qualify using a plain carbon steel base metal (P-No. 1)test coupon and also be qualified to weld in production all carbon,

low-alloy, and stainless steels (P-Nos. 1–11), copper-base alloys(P-Nos. 31–35), and nickel-base alloys (P-Nos. 41–49). Note thatthe reference to QW-420.2 refers to the rules for S-number materi-als. As it relates to performance qualification, this paragraphpermits S-number materials to be qualified using P-Number mate-rials and vice versa. Thus, in Table 24.7 the rules for P-Number base metals are completely interchangeable with S-number base metals.

In 1998, in response to the ASME Code’s position on acceptingcertain foreign material specifications for Code construction,Section IX added paragraph QW-432.2. This paragraph permitsthe use (in performance qualification) of base metals, other thanP- or S-number materials that conform to a recognized national orinternational standard, to be considered as having the same P- orS-number as an assigned metal provided it meets the same chemi-cal and mechanical properties. Thus, a foreign manufacturerbuilding a Code component would be allowed to qualify hiswelders using DIN, JIS, or BS base metals that were comparableto ASME base metals.

QW-404.15 A change from one F-Number in QW-432 toany other F-Number or to any other fillermetal, except as permitted in QW-433.

This essential variable requires requalification whenever thereis a change in the F-Number to another F-Number or to any otherfiller metal that does not have an assigned F-Number. Somenotable exceptions to this general statement that apply to F-Nos.1–5 are given in Table 24.8. In general, qualification with an elec-trode of up to F-No. 4 qualifies the welder for all electrodes oflower F-Numbers. Thus, a welder that qualifies with an F-No. 4electrode is qualified to weld F-No. 4, F-No. 3, F-No. 2, and F-No. 1 with the same limitation on backing as was used in his

FIG. 24.7 SET-ON VERSUS SET-THROUGH NOZZLE


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qualification test coupon, that is a qualification with backing qual-ifies that F-Number and lower F-Number electrodes but only withbacking. Should the welder qualify without backing, he/she isqualified for that specific F-Number electrode both with and with-out backing; while qualification of lower F-Number electrodes isgiven but only without backing.

Table 24.8 also provides that qualification with any F-No. 6 fillermetals (solid- and metal-sheathed ferrous alloy wires) will qualifyall F-No. 6 filler metals. Note (1) allows filler metals for which no F-Number exists (this covers some stainless steels and Cr-Mowires), but in which weld deposit chemical analysis is covered by anA-number in Table 24.1, to be treated as an F-No. 6 filler metal.

QW-404.30 A change in the deposited metal thicknessbeyond the range qualified in QW-451 forprocedure qualification or QW-452 forperformance qualification, except asotherwise permitted in QW-303.1 and QW-303.2. When a welder is qualified usingradiography, the thickness ranges of QW-452.1 apply.

One of the basic tenets of performance qualification is that thewelder is not allowed in a production weldment to deposit a weldthickness (for each welding process) greater than what he/she isqualified for. The limits of deposited weld metal thickness forwhich he/she is qualified are dependent upon the thickness of theweld metal he/she deposits with each welding process. This thick-ness is given in Table 24.9.

When the welder qualifies a single process in a WPQ testcoupon, the thickness of the test coupon equals the thickness ofthe weld deposit. In this case, the welder is qualified for a welddeposit thickness twice the thickness of the test coupon (2t) up tocoupon thickness of in. A test coupon greater than in. providesa qualification of unlimited weld deposit thickness. When theWPQ test coupon is used to test multiple welders or a singlewelder with multiple processes, the total weld deposit thicknessapplicable to the welder or process cannot exceed the thickness ofthe test coupon. It is worth noting here that welder qualification isalways in terms of weld metal thickness (t), not base metal thick-ness (T). Base metal thickness is not an essential variable forwelder qualification.

Section IX does provide in QW-306 for a welder or weldingoperator to be qualified with a combination of welding processes

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in a single test coupon. Similarly, two or more welders using thesame or different welding processes may be qualified in a singletest coupon. When combination qualifications are performed, thenweld deposited thickness shall be considered individually for eachwelder or welding operator and each welding process wheneverthere is a change in an essential variable (e.g., an F-No. 3 [E6010]electrode without backing combined with an F-No. 4 [E7018]electrode with backing). When a welder or welding operator doesqualify in combination on a single test coupon, he/she is qualifiedto weld in production using any of his/her processes providedhe/she welds within the limits of his/her qualification for thatprocess [see Note (1) in Table 24.9]. One penalty that does comewith performing multiple qualifications in a single test coupon isthat failure of any portion of a combination test constitutes failureof the entire test coupon.

Beginning with the 2000 addenda, Section IX changed the testcoupon thickness requirements for welder performance qualifica-tion testing. After considerable discussion, the Committee decid-ed to reduce the test coupon thickness from its current require-ment of in. to in. for a welder to be qualified for unlimiteddeposited weld metal thickness in production. The Committeereasoned that if a welder could demonstrate capability of deposit-ing a sound root pass, fill pass, and cap pass, additional welddeposition in the test coupon would be superfluous. A in. testcoupon thickness was deemed sufficient to allow the root, fill, andcap pass deposition. This philosophy can be seen in anotherchange made in the 2000 addenda, as the Committee has added asan additional requirement to qualifying with the new in. testcoupon thickness that the weld deposit must consist of threelayers of weld metal.

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QW-405.1 The addition of other welding positions tothose already qualified. See QW-120, QW-130,and QW-303.

While QW-405.1 is a nonessential variable for procedure quali-fication, it is an essential variable for welder performance qualifi-cation. The basic test positions for grooves in plate and pipe areshown in Fig. 24.8 (QW-461.3) and Fig. 24.9 (QW-461.4),respectively. Note that the letter G is used to designate grooveweld test positions (e.g., 1G represents the flat position and 2Grepresents the horizontal position). A similar system is used fordesignating fillet weld test positions; however, in this case the let-ter F is used in place of the letter G.

Table 24.10 (QW-461.9) shows the limits of positions qualifiedbased on the qualification test(s) performed as a part of the WPQ.Thus, a plate-groove weld test in the 1G position would only quali-fy the welder for flat position welding of plate, pipe (2 in. diame-ter and over), and fillets. QW-405.1 requires that a welder whowants to weld in other positions to have additional qualifications.A typical qualification test for a Code welder in a pipe fabricationshop would be the pipe-groove weld test in the 6G position. Thiswould qualify the welder for all position welding of plate, pipe (2 in. diameter and over), and fillets. For pipe diameters less than 2in., the essential variable QW-403.16 previously discussed wouldapply.

QW-405.3 A change from upward to downward, orfrom downward to upward, in theprogression specified for any pass of avertical weld, except when the cover or wash

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FIG. 24.8 GROOVE WELDS IN PLATE—TEST POSITIONS (Source: FIG. QW-461.3, Section IX of the ASME B&PV Code)


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pass may be up or down. The root pass mayalso be run either up or down when the rootpass is removed to sound weld metal in thepreparation for welding the second side.

This variable only applies when the qualification test requiresthat some portion of the test coupon be welded in the verticaldirection. Specifically, this would involve 3G, 5G, 6G, and 3F testpositions. When such test positions are used in the WPQ, thewelder is only qualified to make welds in the vertical position inproduction in same progression as used in the qualification test.Thus, a vertical up progression used in the 3G test coupon limitsthe welder to only this progression. He would need to qualify twotest coupons: one vertical-up and one vertical-down, to be quali-fied for both progressions.

Note that in carbon steel pipe welding a common weld proce-dure would involve a vertical down E6010 (F-No. 3) root pass,and a vertical up E7018 (F-No. 4) fill pass(es). If the WPQ test isconducted to duplicate this situation, Section IX requires that thewelder’s progression be associated with the other qualificationvariables. Thus, in this case the welder’s progression would belimited by the F-Number electrode used—vertical-up for F-No. 4and vertical-down for F-No. 3 electrodes.

24.7.2 Expiration and Renewal of WelderPerformance Qualifications

Although welding procedures once qualified remain qualified,welder performance qualifications are not similarly treated.Section IX regards the skill that a welder or welding operatordemonstrates during the initial qualification test as time depen-dent, meaning that these skills can be diminished or lost if notused for a lengthy period. Therefore, QW-322 specifies that whena welder or welding operator has not welded with a process for aperiod of six months, his/her qualifications for that process shallexpire. As a result of this requirement, nearly every manufacturerhas a system that records the welder’s activity from the time of hisWPQ test (or last renewal test) to demonstrate that the individualhas continuously maintained his qualification. The exact nature of

such a “welder’s maintenance” system is not specified by SectionIX, but it must be rigorous enough to satisfy the AuthorizedInspector. Nor does Section IX consider the maintenance of thewelding skill to be limited solely to Code work the welder per-forms, as noted by Interpretation IX-83-159:

Question: May a welder maintain his qualification by weldingon non-Code work?

Reply: Yes.

When a welder’s or welding operator’s qualifications in aprocess have expired because of the six month rule, he/she mayrenew those qualifications by welding a single WPQ test coupon.If the welder or welding operator was previously qualified in theSMAW, GTAW, and GMAW processes, he/she would need onetest in each process to renew the qualifications for all three of theprocesses. A successful test renews the welder’s or welding oper-ator’s previous qualifications for that process for all materials,thicknesses, diameters, positions, and other variables for whichhe/she was previously qualified.

Additionally, the welder or welding operator may lose his/herqualifications when a specific reason exists to question his/her abili-ty to make welds that meet the specification. If that happens, asstated in QW-322. 1(b), the qualifications that support the work thewelder is doing are revoked. Note that not all of the welder’s quali-fications with that process(es) are revoked—only those appropriateto the work being performed. Thus, if the welder’s ability is ques-tioned while performing shielded metal arc welding in the verticaldown position with an E6010 (F-No. 3) electrode, only the qualifi-cations supporting this work would be lost; other qualifications,such as those supporting a vertical up procedure using an E7018electrode, would remain valid. Those qualifications revoked may bereinstated, but by a method other than renewal. In this case, thewelder is required to requalify following the same requirements asthose for the first-time welder. QW-322.2(b) specifies that therequalification uses a test coupon that is appropriate for the plannedproduction work and has been tested by bend testing or radiogra-phy. A successful test will restore the welder’s qualifications.

FIG. 24.9 GROOVE WELDS IN PIPE—TEST POSITIONS (Source: Fig. QW-461.4, Section IX of the ASME B&PV Code)



24.8 IMPACT TESTED WELDPROCEDURES

In Section 24.6, it was stated that the purpose of a procedurequalification test is to demonstrate that a weldment, produced byspecified essential variables, is suitable for its intended serviceand that this is accomplished by establishing the properties of theweldment—tensile strength and bend ductility. When a notchtoughness welding application is identified, another mechanicalproperty is added to the testing requirements of the PQR—CharpyV-notch impact testing—to establish the weldment’s resistance tobrittle fracture.

The requirement to perform Charpy V-notch impact tests on theprocedure qualification test coupon is not initiated by Section IXbut by a referencing Code Section (i.e., a Construction Code) thatspecifies notch toughness testing of the weld procedure qualifica-tion. In “turning on” the requirement for notch toughness testing,the Construction Code also provides the acceptance criteria for theimpact test as well as information on the number, location, and ori-entation of the test specimens. [There is one exception, that beingwhen the qualification is performed on pipe in the 5G or 6G posi-tion. For this specific situation, because of concern for the variationin heat input as the test coupon is welded, QW-463.1(f) specifiesthe location for notch toughness specimen removal.]

24.8.1 Welding Procedure Qualification While essential variables adequately control the weld produre

to ensure the required strength and ductility, they are not suffi-cient in themselves to assure that the weldment also achievesadequate notch toughness. To accomplish this, an additionalgroup of welding variables, called supplementary essential vari-ables, is imposed by Section IX when notch toughness isrequired. The supplementary essential variables for the procedurequalification of weld processes are given in Tables QW-252through QW-265 along with the essential and nonessential vari-ables. When notch toughness testing is imposed by aConstruction Code for qualification of the welding procedurespecification, the supplementary essential variable may be con-sidered an additional essential variable. Each of the variables islisted in the tables by a brief description that is for the user’sconvenience only. The complete description of each variable islisted in Article IV (Welding Data). As an example, we willreview the details of the supplementary essential variables forqualifying a notch toughness weld procedure involving theSMAW process as shown in Table 24.2 in Section 24.6.2. Wewill start the discussion of the supplementary essential variableswith QW-403.5 (Group Number), and then discuss each of theother supplementary essential variables in turn.


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QW-403.5 Welding procedure specifications shallbe qualified using one of the following:

(a) the same base metal (including type or grade) to be usedin production welding

(b) for ferrous materials, a base metal listed in the same P-Number Group Number in QW/QB-422 as the basemetal to be used in production welding

(c) for nonferrous materials, a base metal listed in the sameP-Number UNS Number in QW/QB-422 as the basemetal to be used in production welding

This is the first of the supplementary essential variables that mustbe addressed when the Construction Codes require notch toughnesstesting. Within each ferrous P-Number (i.e., P-No. 1 through P-No. 11B) is a subgrouping of the material specifications intogroup numbers. Group numbers are required only when notchtoughness is imposed. QW-403.5 requires requalification of theprocedure when the base metal to be welded in production is a dif-ferent P-Number, group number (UNS number for nonferrousmaterial), material specification, or type/grade than that used on thesupporting PQR. Thus, when a procedure qualification is conductedon SA-516 Grade 60 material (P-No. 1, Group 1), it can be used tosupport WPSs involving other P-No. 1, Group 1 materials such asSA-36 or SA-106 Grade B. However, it cannot be used to supportproduction welding SA-516 Grade 70 or SA-106 Grade C (P-No. 1,Group 2) where notch toughness is a requirement.

QW-403.5 also specifies that when base metals of two differentP-Number–group number combinations are to be welded (e.g., P-No. 1, Group 1–P-No. 1, Group 2), a supporting PQR mustexist for this combination of base metals. This requirement iswaived if individually qualified WPSs exist for welding each P-Number–group number base metal to itself with the sameessential variables as those that will be used for welding the com-bination of base metals. Note that in the full text of QW-403.5,the reader will find that this variable also allows a qualified WPSmade with base metals of two different P-Number–group numbersto be used for welding each P-Number–group number to them-selves with the same variables.

QW-403.6 The minimum base metal thickness qualified

is the thickness of the test coupon T or in.

whichever is less. however, when T is less than

in., the minimum thickness qualified is T.

Like QW-403.5 this, too, is a supplementary essential variablewhen the book sections require notch toughness testing. Thisvariable further limits the qualified minimum base metal thick-ness compared with that for the essential variable requirements

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of QW-403.8. (A discussion of QW-403.8 was presented in Section 24.6.2.)

As shown in Table 24.11, for test coupons at least in. thick,the minimum qualified base metal thickness for notch toughnessapplications is in. rather than the normal in. For test couponsless than in., the minimum qualified thickness is that of the testcoupon, T; below in., the minimum qualified thickness is T ofthe test coupon.

The concern here is that as the thickness of the base metaldecreases, so does the cooling rate of the base metal heat-affectedzone. Slower cooling rates may lead to a deterioration of the notchtoughness, and Section IX is most concerned with this effect whenthe base metal is less than in. Hence, this supplementary essentialvariable requires that the minimum base metal thickness be limitedto in. Additional impact property data from test coupons less than in. in thickness is necessary to support production welding compo-nents thinner than in.

QW-404.7 A change in the nominal diameter of theelectrode to over in.

Section IX is concerned that the higher heat input of electrodeswith diameters exceeding in. may result in a reduction of notchtoughness properties. Therefore, this supplementary essential vari-able requires requalification when a WPS specifies an electrodewith a diameter greater than in. when the supporting PQR wasconducted with electrodes less than in. If the electrode diameterwill not exceed 41 in. in production, QW-4404.7 can be satisfied onthe WPS by simply stating that no electrodes larger than 41 in. areto be used. Another approach is to report the electrode diameters(e.g., , and in.) that will be used with the WPS.

QW-404.12 A change in the filler metal classificationwithin an SFA specification or to a fillermetal not covered by an SFA specification, orfrom one filler metal not covered by an SFAspecification to another filler metal that isnot covered by an SFA specification.

QW-404.12 is a supplementary essential variable that representsa further restriction of the filler metal variable QW-404.4 (seeSection 24.6.2) when notch toughness testing is specified. QW-404.4allows the electrode to be specified by F-Number classificationalone. However, QW-404.12 requires that the WPS specify thefiller metal not simply by F-Number but by SFA specification andAWS classification as well. Additionally, the WPS must be sup-ported by a PQR conducted with this SFA specification and AWSclassification electrode. Thus, a notch toughness production appli-cation requiring an E7018-A1 electrode must be welded with aWPS listing this filler metal classification/SFA specification rather

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than a F-No. 4 electrode that not only includes the E7018-A1 butmany other electrodes as well, such as E7018, E8018-D1, andE9018-B9. QW-404.12 does provide some exceptions to thisrequirement; for example, when the electrode’s classification ischanged for coating type (e.g., EXX15 versus EXX18) or position-al use (e.g., EXX18 versus EXX28) in a way that does not effectthe notch toughness of the weld deposit. One further point: Shouldan electrode not conform to a SFA specification, this variablerequires a separate procedure qualification for that electrode.

QW-405.2 A change from any position to the verticalposition uphill progression. Vertical uphillprogression (e.g., 3G, 5G, or 6G position) qual-ifies for all positions. In uphill progression, achange from stringer bead to weave bead.

As was indicated earlier, both QW-405.1 and QW-405.3 arenonessential variables that require weld position(s) and progression(when welding in the vertical position) to be specified on the WPS.When notch toughness is not required, a qualified weld procedurein any position will support a WPS for all positions and progres-sions (vertical up and vertical down). However, when notch tough-ness is required both position and progression become supplemen-tary essential variables through QW-405.2. Now, a change from the1G, 2G, or 4G positions to the 3G, 5G, or 6G positions with uphillprogression requires a new qualification. The concern here is thatthe notch toughness properties of the qualification done in otherweld positions may not well represent those of the higher heatinput–vertical position–uphill progression weld. It is for the verysame reason that QW-405.2 requires requalification if the weld pro-cedure will be changed from stringer bead to weave bead.

QW-406.3 An increase of more than 100��F in the maxi-mum interpass temperature recorded on thePQR.

The specification of an interpass temperature on the WPS isrequired when the book sections require impact testing, as it isfelt that too high an interpass temperature could lead to degrada-tion of notch toughness properties. Like the preheat variable QW-406.1, the user is required to record the highest interpasstemperature used in the PQR test coupon (PQR Tmax)from whichthe maximum interpass temperature is established for the WPS.Following the parallel for the preheat temperature, the WPS maxi-mum interpass temperature (WPS Tmax) may be equal to but notmore than 100�F greater than the interpass temperature recordedon the PQR (i.e., WPS Tmax � [PQR Tmax � 100�F]). Thus, if thePQR Tmax is recorded as 600�F, the WPS Tmax cannot exceed700�F. As with preheat temperature, this 100�F maximum limita-tion is felt to provide a reasonable interpass temperature tolerancefor preparing the notch toughness WPS.

QW-407.2 A change in the postweld heat treatment (seeQW-407.1) temperature and time range. Theprocedure qualification test shall be subject-ed to PWHT essentially equivalent to thatencountered in the fabrication of productionwelds, including at least 80% of the aggre-gate times at temperature(s). The PWHTtotal time(s) at temperature(s) may beapplied in one heating cycle.

This supplementary essential variable requires that the user, inaddition to specifying and qualifying his/her welding procedure

for the PWHT conditions stated in QW-407.1 (see Section24.6.2), to include the time at PWHT temperature. The time atPWHT temperature used for the PQR must represent no less than80% of the total time to which the production weldment will besubjected. Thus, a production weld that will be given a PWHT at1150�F for 5 hr must have a supporting PQR postweld heat treat-ment for least 4 hr (80% of 5 hr). A word of caution here:Production welds often see more time at temperature thanrequired by the book sections based on thickness alone. Somecomponents see more than one heat treatment cycle during fabri-cation. It is common for very thick components to be given anintermediate heat treatment prior to the component’s final heattreatment. Further, if a weld repair is required this may add addi-tional time at PWHT temperature for the weld. Thus, it is theCode user’s responsibility to assure that supporting qualificationshave been run with sufficient time at PWHT temperature to coverthese variances. The writer is familiar with one fabricator whoconducts notch toughness qualifications for low-alloy steels with40 hr PWHT time to assure that the PQRs will meet the requirednotch toughness for up to 50 hr of production PWHT.

QW-409.1 An increase in heat input, or an increase involume of weld metal deposited per unitlength of weld, over that qualified. Theincrease may be measured by either of thefollowing:

(a)

(b) Volume of Weld Metal measured by(1) an increase in bead size (width x thickness), or(2) a decrease in the length of weld bead per unit length

of electrode.

Because of the concern that increasing heat input will producedegradation in notch toughness, this supplementary essential vari-able requires the Code user to specify the maximum heat inputused for the qualification test coupon. In specifying this heatinput, the Code user also has to define a method for controllingthe heat input so that production welding will not be conducted ata heat input higher than that used in qualification. To accomplishthis task, the variable offers two options. The first involves awidely used equation—item (a) of the foregoing list—to calculatethe heat (energy) developed by an arc during welding. For exam-ple, arc welding with a current of 250 amperes and a voltage of 20 volts at a weld travel speed of 6 in./min will produce a heatinput to the weld in the amount of 50,000 J/in. If this is the quali-fied heat input limit, the user may vary the voltage, amperage, andtravel speed values as long as the calculated value of heat inputdoes not exceed the value of 50,000 J/in. For example, reducingthe current to 125 amperes and the travel speed to 3 in./min wouldproduce the same acceptable value of 50,000 J/in. heat input.

The second option for calculating heat input involves using thelength of deposited weld bead. In the example previously used, letus assume that the filler metal is an electrode 14 in. long and thatthe weld is made with the same current of 250 amperes and thesame voltage of 20 volts but with a travel speed increased to 10 in./min. The heat input for this situation would be 30,000 J/in.,and the faster weld speed would produce a longer weld beaddeposit length from the 14 in. long electrode than when travellingat 6 in./min. This correlation between deposited weld bead lengthversus original electrode length for the SMAW process can beused to control heat input. As long as the production welder is

Heat Input (J/in.) =

Voltage * Amperage * 60

Travel Speed (in./min), or


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depositing weld beads of equal or longer length than those mea-sured in the procedure qualification, he/she is not exceeding thequalified maximum heat input. When the length of weld bead perlength of electrode is shorter, the welder has exceeded the maxi-mum heat input and a new qualification is required.

As an alternative to controlling heat input based on welddeposit length, one could also limit heat input based on weld-based cross section. A practical application of this relationship isto determine the number of weld passes used in a weld qualifica-tion and then limit production welding in the same groove geome-try/thickness to an equivalent or greater number of weld passes.

QW-409.4 A change from AC to DC, or vice versa, andin DC welding, a change from electrode neg-ative (straight polarity) to electrode positivereverse polarity or vice versa.

When notch toughness is required by the Construction Codes,QW-409.4, which is normally a nonessential variable, nowbecomes a supplementary essential variable. As a nonessentialvariable it still requires that the WPS specify the type of current,either alternating current (AC), direct current (DC), or both, andfor direct current the type of polarity—straight polarity, reversepolarity, or both. However, as a supplementary variable QW-409.4now has the additional requirement that the PQR must be con-ducted with the type of current (AC or DC) and polarity (reverseor straight) specified on the WPS. A change from DC reversepolarity to DC straight polarity (or vice versa) or a change fromAC to DC (or vice versa) requires requalification. Thus, forSMAW electrodes such as E7018 capable of running both AC andDC (in both polarities), three qualification tests are required to usethis electrode in its full range of electrode conditions.

QW-410.9 A change from multipass per side to singlepass per side.

As with QW-409.4 this variable too, which is normally anonessential variable, becomes a supplementary essential variablewhen notch toughness is required. As a nonessential variable theuser must simply list on the WPS whether the weld procedure isfor multiple passes per side, single pass per side, or both. Thesupporting PQR may have been conducted with either one pass ormultiple passes. However, as a supplementary essential variablethe user cannot utilize a PQR performed with multiple passes tosupport a production weld procedure involving only one pass perside. The requirement is driven by the concern that impact proper-ties of multipass welds, with their grain refinement and tempering(in the case of ferritic alloys), may not represent the weld metal orHAZ toughness of single pass deposited welds. Thus, a single

pass per side weld procedure in a notch toughness applicationmust be qualified by a single weld pass procedure qualification.

24.8.2 Notch Toughness Testing When notch toughness testing is required, QW-401.3 provides

a means for the Code user to not repeat all of the qualificationtesting of a weld procedure. If a qualification exists that satisfiesall requirements other than notch toughness, QW-401.3 allows anadditional test coupon to be prepared to provide only the notchtoughness test specimens. This additional test coupon must bewelded with the same essential variables as the original couponplus the additional supplementary essential variables required bythe notch toughness application. QW-401.3 allows similar latitudeif a weld procedure has been previously qualified to satisfy all therequirements including notch toughness, but one or more supple-mentary essential variables is changed. In such a situation, it isonly necessary to prepare an additional test coupon for only notchtoughness testing using the same welding procedure and the newsupplementary variable(s). The important aspect of QW-401.3 isthat notch toughness may be conducted on a separate test coupon.

When notch toughness testing is required by other ConstructionCodes, QW-170 makes it clear that the number of impact speci-mens, their notch location, and orientation shall be as specified bythe Book Section requiring such tests. To see an example of howthis works, we will consider what is required by Section VIII,Division 1 for a notch toughness application.

Paragraphs UG-84(g)(1) and UG-84(g)(2) require both weldmetal and HAZ impact specimens with the weld metal specimensto be located near the surface of the material (within in.). TheHAZ specimens are to include as much HAZ material as possiblein the resulting fracture, but these paragraphs do not include anyrequirements for locating the HAZ impact specimens with regardto depth from the surface, weld heat input, or any other variables.

When the procedure qualifications are made on materialsgreater than 1 in. thick, UG-84(h)(3) requires an additional set ofweld metal impact specimens (a total of two sets) and one set ofHAZ impact specimens. One weld metal set is required to belocated near the surface of the material (within in.); the other setis required to be taken from the opposite side of the weld at adepth midway between the center of the plate and the surface (thisis commonly referred to as the T location). Only one set of HAZimpact specimens is required, and its location need not be speci-fied.

The weld metal and HAZ testing requirements to satisfy theSection VIII, Division 1 rules are summarized in Table 24.12:Two sets of impact specimens (one weld and one HAZ) for platethickness 1 in. or less, and three sets of impact specimens (twoweld and one HAZ) for plate thickness over 1 in. 1

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Many Code users are surprised that Section VIII does not spec-ify HAZ impact specimen location. However, this has been con-firmed by Interpretation (VIII-1-89-267):

Question: Does Section VIII, Division 1 provide any rules inlocating an impact specimen notch other than that given inUG-84(g)(2)?

Reply: No.

A second, more recently approved Interpretation that will bepublished shortly further reinforces this position:

Question: Does Section VIII, Division 1 provide rules on therequired number or location of heat-affected zone impact testspecimens to qualify one or more welding processes or pro-cedures, other than that given in UG-84(g)(2)?

Reply: No.

24.8.3 Welder Performance Qualification There are no supplementary essential variables applicable to

welder performance qualification testing. Thus, a welder qualifiedusing the performance qualification variables of QW-350 (QW-360for a welding operator) is also qualified for notch toughness appli-cations required by the Construction Codes.

24.9 TESTING AND EXAMINATIONREQUIREMENTS

In conducting qualification testing, whether for the welding pro-cedure or welder/welding operator performance, the weldcoupon(s) prepared in these qualification efforts are required to betested to ensure that they meet the requirements of Section IX. Inthe case of a groove weld and pressure-retaining fillet weld

procedure qualification, testing is to assure that the weldment iscapable of providing the required mechanical properties for itsintended application. The basic properties of interest are the tensilestrength and bend ductility. When toughness is an added specialconsideration, as determined by the other Book Sections of theCode, then impact testing is an additional requirement. For thecase of procedure qualifications for non–pressure-retaining filletwelds (as defined by other Code sections), testing verifies not themechanical properties of the fillet weld but rather soundness.Similarly, for a welder/welding operator performance qualification,testing is to confirm the welder’s ability to produce sound welds.For the performance qualification, the basic tests to confirm this arevisual examination and guided-bend tests or radiographic examina-tion. For the procedure qualification of non-pressure -retaining fil-let welds, the basic tests are macroexamination and fracture test.

Paragraph QW-202 for procedure qualification and paragraphQW-302 for performance qualification provide information on thetypes of tests required for different types of qualification welds.QW-451.1 and QW-452.1, which were discussed earlier, providethe type and number of test specimens from groove weld couponsrequired for procedure qualification and performance qualification,respectively. Similarly, Tables QW-451.3 and QW-452.5 providethe type and number of test specimens from fillet weld couponsrequired for procedure qualification and performance qualification.

For groove weld qualification tests, Section IX provides theCode user with the manner in which the test specimens are to beremoved from the test coupon. This is shown in Fig. QW-463.1(a)and (b), given here as Fig. 24.10, and Fig. QW-463.2(a) and (b),given here as Fig. 24.11, for procedure and performance qualifica-tion plate test coupons, respectively. The ends of the test couponwhere the welder starts and stops the weld process are marked fordiscard. The center portion is used for the required mechanicalproperty test specimens. No discards are available when the quali-fication test uses a pipe test coupon. Removal of test specimens is

FIG. 24.10 TEST SPECIMEN REMOVAL FROM PLATE PROCEDURE QUALIFICATION (Source: Fig. QW-463.1(a) and (b),Section IX of the ASME B&PV Code)


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shown in Fig. QW-463.1(d) and (e), given here as Fig. 24.12, andFig. QW-463.2(d) and (e), given here as Fig. 24.13, for procedureand performance qualification. Note that the tension test speci-mens for the procedure qualification test coupon are taken at thesix and twelve o’clock positions and that the four bend test speci-mens are taken 45–60 degrees from these clock positions.

For the performance qualification test coupon, only bends spec-imens are taken and these, as with the procedure qualification, aretaken 45–60 degrees from the six and twelve o’clock positions.When performance qualification position is 5G or 6G, four bendsspecimens are required; however, when the performance qualifi-cation position is 2G, only two bend specimens 180� apart need tobe taken.

24.9.1 Tension Test For the weld procedure qualification test, as a minimum, two

tension tests are required. The rules regarding the removal of ten-sion test specimens from a test coupon are covered in QW-151,which specifies the following:

(1) full thickness tension specimens must be used for a testcoupon not more than 1 in. thick; and

(2) either full thickness or multiple specimens (representingthe full thickness) may be used for tension testing a testcoupon greater than 1 in. thick.

When the multiple specimen option is used, the thickness of thetest coupon is to be cut into a minimum number of test specimens

FIG. 24.11 TEST SPECIMEN REMOVAL FROM PLATE PERFORMANCE QUALIFICATION (Source: Fig. QW-463.2(a) and (b),Section IX of the ASME B&PV Code)

FIG. 24.12 TEST SPECIMEN REMOVAL FROM PIPE PROCEDURE QUALIFICATION (Source: Fig. QW-463.1(d) and (e), Section IX of the ASME B&PV Code)



of roughly equal size and tested. Each set of the multiple speci-mens represents a single tension test. Figures 24.14 and 24.15illustrate single and multiple tension test specimen removal fromtest coupons not more than 1 in. thick and greater than 1 in.,respectively. Section IX recognizes that in welding a test couponthere will be some distortion in the completed weldment, as illus-trated in Fig. 24.14. As was explained in Interpretation IX-92-79,the Code user’s responsibility is to remove the minimum amountof metal until parallel specimen surfaces can be achieved. Thus,producing a suitable tension specimen for testing from a 1 in. testcoupon may result in a in. thick test specimen.

Section IX also allows the use of turned (rather than flat) speci-mens for tension testing. When this type of specimen is used fortesting, Section IX requires the use of the largest diameter speci-men that can be cut from the test coupon. For a 1 in. thick testcoupon, this would be the standard 0.505 in. diameter specimen.Although the use of this turned, reduced section specimen repre-sents a seeming contradiction to the requirement to remove a min-imum amount of metal, recall that this requirement is for a full-thickness specimen. The use of a 0.505 in. diameter specimenfrom a 1 in. thick test coupon is the largest full-thickness turnedtension specimen that can be removed.

The acceptance criteria for the tension test are covered in QW-153.1. The tensile strength recorded from each tension testspecimen shall not be less than the following:

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(1) the minimum specified tensile strength of the base metal; or (2) the minimum specified tensile strength of the weaker of the

two, if base metals of different minimum tensile stengthsare used; or

(3) the minimum specified tensile strength of the weld metalwhen the applicable Code section provides for the use ofweld metal having lower room temperature strength thanthe base metal; but

(4) if the specimen breaks in the base metal outside of the weldor fusion line, the test shall be accepted as meeting therequirements, provided the strength is not more than 5%below the minimum specified tensile strength of the basemetal.

The minimum specified tensile values for the acceptance crite-ria for qualification are those values listed in QW/QB-422

FIG. 24.13 TEST SPECIMEN REMOVAL FROM PIPE PERFORMANCE QUALIFICATION (Source: Fig. QW-463.2(d) and (e),Section IX of the ASME B&PV Code)

FIG. 24.14 REMOVAL OF FULL-THICKNESS TENSIONTEST SPECIMEN

FIG. 24.15 REMOVAL OF MULTIPLE TENSION TESTSPECIMENS


244 • Chapter 24

(P-Number table). For most materials, the minimum specified ten-sile values in QW/QB-422 are identical to the values found in thematerial specifications of Section II, Parts A and B. However, forsome nonferrous materials such as copper alloys, this is not thecase. While copper alloys can be provided in a hardened condi-tion, during welding the material softens in the heat-affectedzone. As a result, the minimum specified tensile value given foracceptance in QW/QB-422 is the strength in the annealed condi-tion. Similarly, for 6061 and 6063 heat-treatable aluminum alloysthe acceptance values given in QW/QB-422 for qualification arebased on the as-welded condition of these alloys.

24.9.2 Guided-Bend Tests For the weld procedure qualification test, as a minimum, four

guided-bends tests are required. QW-451.1 specifies the followingfor the bend test.

• Two face- and two root-bend tests are to be used for a testcoupon in. thick.

• Either two face- and two root- or four side-bend tests may beused for a test coupon in. and greater but less than in. thick.

• Four side-bend tests are to be used for test coupon at least in. thick.

For the weld performance qualification test, as a minimum, twoguided-bend tests are required. QW-452.1(a) specifies the follow-ing for the bend test.

• One face- and one root-bend test are to be used for a testcoupon in. thick.

• Either one face- and one root- or two side-bend tests may beused for a test coupon in. and greater but less than in.thick.

• Two side-bend tests are to be used for test coupon at least in.thick.

The rules regarding the removal of guided-bend test specimensfrom a test coupon are covered in QW-161. It specifies that thequalification test coupon shall be cut from specimens of rectangular

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cross section for the guided-bend test specimens. In preparing thespecimens, the cut surfaces are designated the sides of the specimenand the other two surfaces are called the face and the root. The faceis the top or widest part of the weld while the root is the bottom ornarrowest portion of the weld (see Fig. 24.16). As was the case forthe tension test, multiple specimens may be used for the guided testwhen the test coupon thickness exceeds 1 in. The specimens mustbe between in. and 1 in. wide for testing, and each set of the mul-tiple specimens represents a single guided-bend test.

The guided-bend testing that was mentioned previously is fortransverse-oriented specimens—that is, the specimens are cut per-pendicular to the direction of the weld length. However, SectionIX recognizes that there are occasions when this type of test ori-entation is not suitable for the weldment’s evaluation. When thequalification test coupon is made of two different base metalswith markedly different bend characteristics, or when the same istrue for the weld metal and base metal, a transverse test will notbend the weldment uniformly in all regions. When this is the case,a longitudinal-bend test may be used. Here the test specimen iscut parallel to the weld length and all the regions are bent uni-formly when the specimen is tested.

For both a transverse-bend or a longitudinal guided-bend speci-men, a test jig is required to subject the test specimen to therequired bending. Three types of bend jigs are provided inQW466.1, QW-466.2, and QW-466.3: QW-466.1 is a plunger type(see Fig. 24.17) that forces the specimen into a bend fixture or dieof fixed dimensions; QW-466.2 is a roller-type fixture that allowsfor the specimen to be ejected from the bottom of the jig; and QW-466.3 is a wraparound jig that uses a forming roll to bend the spec-imen over a mandrel. Regardless of the type of jig used, its dimen-sions and the dimensions of the guided-bend specimen mustconform to the values given in the table presented in Fig. 24.17.Doing so ensures that when the specimen is bent through 180� it isstrained to the required value. For the ferrous alloys (except for P-No. 11 materials), this value is 20% outer fiber elongation. Whenone or both of the base metals has known ductility less than 20%,the jig dimensions and specimen thickness are calculated from thetable to provide an outer fiber elongation at least equal to that ofthe base metal with the lowest minimum elongation.

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FIG. 24.16 FACE-, ROOT-, AND SIDE-BEND SPECIMENS



Acceptance criteria for the guide-bend tension test are providedin QW-163, which specifies the following:

• No open discontinuities in the weld or heat-affected zonegreater than in. in any direction on the convex surface.

• Cracks at the corners of the specimen during testing may beignored unless they result from lack of fusion, slag, or otherinternal defects.

For a transverse-bend specimen, an additional requirement isthat the weld and heat-affected zone portions of specimen becompletely within the bent portion of the specimen after testing.If this requirement is difficult to achieve because the bend propertiesof the base metal are markedly different, the user may have toresort to a longitudinal-bend test as discussed earlier.

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24.9.3 Visual Examination When the test coupon is for a performance qualification test

and qualification testing will be by mechanical (i.e., guided-bend) testing, Section IX requires the Code user to visuallyexamine the test coupon prior to cutting the bend specimens.When the test coupon is pipe, all surfaces inside and outsideshall be examined; when the test coupon is a plate, all surfacesexcept those marked as discard are to be examined. The visualexamination criteria are given in QW-194, which states that thetest coupon shall show complete joint penetration with com-plete fusion of the weld metal and base metal. Thus, anyapparent defects such as lack of penetration, trapped slag, andlack of fusion are unacceptable and require failure of the testcoupon.

FIG. 24.17 GUIDED-BEND TEST JIG DIMENSIONS (Source: Fig. QW-466.1, Section IX of the ASME B&PV Code)


246 • Chapter 24

24.9.4 Radiographic Examination Another examination procedure unique to the performance

qualification test is radiographic examination. For the more com-mon weld processes, Section IX allows the substitution of radiog-raphy for the required guided-bend tests. The minimum length ofplate or pipe coupon that is required for examination is 6 in. forboth welder and welding operator qualification. If the pipecoupon circumference is less than 6 in., multiple coupons will beneeded. However, regardless of the pipe diameter, Section IXrequires that the entire weld circumference for the pipe weld testcoupon be radiographically examined. The acceptance criteria forradiographic examination are covered in QW-191.2, which speci-fies the following defects as cause for failure.

• Any crack, incomplete fusion or lack of penetration. • Slag greater than

— in. for test coupons in. thick, and — t for test coupon greater than in. but not more than 2

in. thick. • Grouped slag having a length greater than t in a length of 12t. • Rounded indications (length-to-width not more than 3)

exceeding the smaller of t or in. • Rounded indications in quantity and size in excess of that

given by Section IX in Appendix I.

Performance qualification may also be performed by radi-ographic examination on the first production weld of a welder orwelding operator. When the individual is a welder, as with a platetest coupon, 6 in. of the production weld is required to be radi-ographically examined, and evaluation is to the Section IX criterialisted above. When the individual is a welding operator, 3 ft of theproduction weld is required to be radiographically examined, andevaluation is to the acceptance standards of the referencing Codesection. One additional requirement, should the production weldsinvolve pipe welded in the 5G, 6G, or special positions, then theentire production weld circumference made by the welder orwelding operator is to be radiographed.

24.9.5 Macroexamination When the procedure or performance qualification is a fillet

weld test, Section IX requires evaluation by a macroexamina-tion. The type of test coupon and the manner in which the testspecimens are to be removed is shown in Fig. QW-462.4(a) and(d), given here as Fig. 24.18, for procedure qualification, andFig. QW-462.4(b) and (c), given here as Fig. 24.19, for perfor-mance qualification.

For the plate-to-plate procedure qualification, the ends of thetest coupon where the welder starts and stops the weld process aremarked for discard and the center portion is used for the requiredfive macro test specimens, each approximately 2 in. long. Whenthe procedure qualification test is a pipe-to-pipe or pipe-to-platetest coupon, no discards are available and the test coupon is cutinto four quarter sections for macro test specimens.

For the plate-to-plate performance qualification, the welder’s startand stop is in the center of the test coupon. A center section approxi-mately 4 in. long and two end sections approximately 1 in. long arecut from the test coupon. When the performance qualification test isa pipe-to-pipe/plate test coupon, no discards are available and thetest coupon is cut to provide two quarter sections opposite eachother. From the plate-to-plate and pipe-to-pipe/plate coupons, one 1 in.long and one quarter section, respectively, are for macro test speci-mens (the 4 in. long specimen will be discussed later).

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The rules regarding the preparation and acceptance criteria forthe macroexamination test are given in QW-183 (procedure) andQW-184 (performance). The cross-sectional faces of each of thetest specimens are required to be made smooth and etched toclearly define the weld metal and heat-affected zone. The crosssections are then visually examined. For procedure qualification,the following defects are cause for failure.

• Any crack or incomplete fusion. • A difference in the length of the legs of the fillet greater than

in.

For performance qualification, the following defects are causefor failure.

• Any crack or incomplete fusion. • Any root linear indication greater than in. • Weld concavity or convexity greater than in. • A difference in the length of the legs of the fillet greater than in.

24.9.6 Fracture Test In addition to the macroexamination, when the fillet weld test

coupon is for a welder performance qualification, Section IXrequires an additional evaluation test—a fracture test. The 4 in.specimen mentioned previously is for this purpose and is testedby applying a load that puts the root of the weld in tension. If thespecimen bends upon itself without breaking, it is acceptable.Should the specimen fracture during the application of the load,the following defects are cause for failure.

• Any crack or incomplete root fusion. • The sum of the length of inclusions and porosity that exceeds

— in. for plate-to-plate test coupon, or — 10% of quarter section for pipe-to-pipe/plate test coupon.

24.10 CORROSION-RESISTANT ANDHARDFACING OVERLAY

Corrosion-resistant weld metal overlay and hardfacing overlayare regarded as special weld processes and, as such, are not quali-fied in accordance with the essential variables and test couponsused for groove and fillet welds. The reason is that those vari-ables, tests, and coupons are designed to ensure that the propertiesof the weldments are the equivalent to the base metals beingjoined. In the case of corrosion-resistant and hardfacing overlaywe seek different attributes in the weld deposits. Typically, thecorrect chemical composition to ensure corrosion resistance and ahardness level that will provide a wear-resistant overlay.

To accomplish this, these special processes are qualified tothe rules of QW-214 and QW-216, respectively. These para-graphs are merely advisory in that they tell the user where tofind the requirements for overlay qualification coupons, typesof tests, test specimens, essential variables, and qualificationlimits. As noted previously for groove and fillet welds, theessential, supplementary essential, and nonessential variablesfor procedure qualification of each of the weld processes aregiven in Tables QW-252 through QW-264. The variables forthese special processes are found in the tables designated QW-252.1 through QW-264.1. As a reminder, only a brief descrip-tion of each variable is listed in the tables for the user’s conve-nience; the complete description of the variable is listed inArticle IV (Welding Data).

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24.10.1 Welding Procedure Qualification Let us review the details of the essential variables for qualifying

a corrosion-resistant overlay procedure using the SMAW process asshown in Table QW-253.1, given here as Table 24.13. We will startthe discussion of the variables with QW-402.16 (finished thicknessor t) and then discuss each of the other variables in turn.

QW-402.16 A decrease in the distance between theapproximate weld interface and the final sur-face of the production corrosion-resistant orhard-facing weld metal overlay below theminimum thickness qualified as shown inQW-462.5(a) through QW-462.5(e). There isno limit on the maximum thickness for cor-rosion-resistant or hard-facing weld metaloverlay that may be used in production.

Section IX defines the minimum qualified thickness of the cor-rosion-resistant overlay procedure qualification as the distancefrom the approximate fusion line to the welded surface height atwhich a satisfactory chemistry is determined. To establish thechemical analysis from a fixed height in the weld overlay deposit,QW-462.5(a) provides the Code user with the three methods ofestablishing the minimum overlay thickness. The first methodinvolves performing chemical analysis directly on the as-weldedsurface or from chips taken from the as-welded surface. If thedeposit meets the chemistry requirements specified in the WPS,the minimum thickness qualified is the as-deposited overlay thick-ness. Should the Code user choose to remove some of the overlaydeposit thickness (in production he/she might machine smooth thecorrosion-resistant overlay deposit), in the second method, chemi-cal analysis must be performed on the prepared surface eitherdirectly or from chips. If the specified chemistry requirements are

FIG. 24.18 PLATE AND PIPE FILLET WELD PROCEDURE QUALIFICATION TEST (Source: Fig. QW-462.4(a) and (d), Section IXof the ASME B&PV Code)


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met, the minimum thickness qualified is the prepared overlaythickness. The third method allows the Code user to take a hori-zontal drilled sample from the corrosion-resistant overlay deposit.With satisfactory chemistry results, the minimum overlay thick-ness qualified is from the uppermost side of the drill hole to theapproximate fusion line.

Reference in QW-402.16 to QW-462.5(b) though QW-462.5(e)simply provides figures illustrating specimen removal from pipeand plate test coupons. These in turn refer the Code user to QW-453,which establishes the qualification test coupons, type, and numberof required tests (for corrosion-resistant overlay - bends, chemicalanalysis, and a liquid-penetrant examination), and range of quali-fied base metal thickness for production.

QW-403.20 A change from a base metal, listed under oneP-Number in QW/QB-422, to a metal underanother P-Number or to any other basemetal, or from a base metal of one subgroupto any other grouping in P-No. 10 or 11.

This variable applies to the base metal on which the corrosion-resistant overlay is applied. Once qualified, the WPS is suitablefor any base metal with the same P-Number as that used in thequalification test coupon. Thus, if the qualification was performedon SA-516 Grade 70, which is a P-No. 1 material, it is suitable foroverlaying SA-216 WCB, SA-105, and SA-508 CL.1—all P-No.1 materials. If the base metal change involves a different P-Number, a new qualification is required to support the WPS as

this change may effect the resulting deposit chemistry. Similarly,because of the large range of base metal compositions in P-No. 10and P-No. 11, this variable also makes a change from one P-No. 10 or P-No. 11 to another P-No. 10 or P-No. 11 (e.g., P-No. 10A to P-No. 10B or P-No. 10C, or vice versa) a require-ment for a new qualification.

QW-403.23 A change in the base metal thickness beyondthe range qualified in QW-453.

Table 24.14 that follows is excerpted from QW-453. One cansee for corrosion-resistant overlay that a test coupon 1 in. thickwill qualify for production overlays on base metals at least 1 in.thick (not T to 2T as in groove weld qualifications). For overlay-ing a base metal whose thickness is less than 1 in., there is con-cern with the effect of increasing dilution and slower cooling rateson the integrity of the overlay and its bond. Therefore, a proce-dure qualification at or below that specific base metal thickness tobe overlaid in production is required. Thus, when overlaying a in. thick pipe, qualification is required on a in. thick or smallertest coupon.

QW-404.12 A change in the filler metal classificationwithin an SFA specification or to a fillermetal not covered by an SFA specification, orfrom one filler metal not covered by an SFAspecification to another filler metal that isnot covered by an SFA specification.

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This variable is only applicable to hard-facing overlay and con-trols the filler metal used in the overlay procedure. It requires theuser to requalify whenever there is a change in the filler metal thatdoes not have an AWS classification or a change in the AWS clas-sification of the filler metal. AWS classification is used rather thanan A-number classification because many of the hard-facing fillermetals are nonferrous; A-numbers are limited to ferrous metalsonly. (Note that although ASME adopts AWS filler metal specifi-cations as SFA specifications, the designations of filler metalscovered in the SFA documents are still referred to as AWS—notASME or SFA—classifications.) If an AWS classification existsfor a hard-facing filler metal, requalification is not required whendifferent filler metal producers manufacture the same classifica-tion, but when there is no AWS classification for the filler metal, achange of manufacturer will require a separate qualification.

QW-404.37 A change in the composition of the depositedweld metal from one A-Number in QW-442to any other A-Number, or to an analysis notlisted in the table.

This variable controls the ferrous weld deposit used in makingcorrosion-resistant overlays and allows the user to specify this byA-number. For those who may not have read the description of asimilar variable (QW-404.5) in the section on groove and filletweld qualifications, the A-number is the chemical composition ofthe weld deposit. There are several methods for determining theweld deposit chemical composition and hence the A-number: oneis by the straightforward chemical analysis of the weld from thesupporting PQR; a second allows the use of the chemical compo-sition from a weld deposit prepared according to the filler metalspecification; and a third allows the use of the chemical composi-tion reported in the filler metal specification or the manufacturer’scertificate of compliance. Lastly, when it is not possible orimpractical to use an A-number designation, indicating the nomi-nal chemical composition of the weld deposit on the WPS willsatisfy this variable.

QW-404.38 A change in the nominal electrode diameterused for the first layer of deposit.

For a corrosion-resistant overlay, a change in the electrodediameter of the first layer can have a significant impact on thedilution and hence chemistry of the weld deposit and on the qualityof fusion to the base metal. Typically, smaller electrodes mean

lower current and therefore lower dilution. For the SMAWprocess, this variable makes any change of nominal diameter(e.g., in., in., and in.) a requirement for requalification.

QW-405.4 Except as specified, the addition of otherwelding positions than already qualified.

Unlike groove weld procedure qualifications in which weldingposition is a nonessential variable, welding position is an essentialvariable for corrosion-resistant overlay. This is because the posi-tion in which the overlay is applied has a significant effect on theamount of dilution obtained (and hence weld deposit chemistry)and may affect fusion to the base metal or previously depositedweld metal. In terms of decreasing affect on dilution, weld posi-tions may be ranked as follows.

• Vertical up (highest dilution) • Horizontal • Flat • Overhead (lowest dilution)

Therefore, as shown in Table 24.15, Section IX has establishedthat corrosion-resistant overlay procedures qualified using the testpositions shown under “Qualification Test” are only usable for thepositions listed under the “Position(s) Qualified” column. Additionalpositions, beyond those listed, require a new qualification test.

QW-406.4 A decrease of more than 100�� F in the preheattemperature qualified or an increase in themaximum interpass temperature recorded onthe PQR. The minimum temperature forwelding shall be specified in the WPS.

The requirement regarding preheat temperature in this variableis consistent with that specified for the groove weld procedurequalification requirement in QW-406.1. However, the interpasstemperature requirement is more stringent here than in QW-406.3(a supplementary essential groove weld variable). QW-406.3allows a 100�F increase in maximum interpass temperature, whilefor corrosion-resistant overlay no increase in the maximum inter-pass temperature is permitted without requalification. The con-cern here is that increasing interpass temperature leads toincreased dilution of the weld deposit and adversely effectsdeposit chemistry. Hence, there can be no increase in interpasstemperature without requalification.

532

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250 • Chapter 24

QW-407.6 A change in the postweld heat treatment con-dition in QW-407.1 or an increase of 25% ormore in total time at postweld heat treatingtemperature.

Prior to 2004, QW-407.6 addressed the postweld heat treatmentrequirements for both hard-facing and corrosion-resistant weldmetal overlay. Starting in 2004, a split was made and QW-407.6addressed the PWHT requirements of hard-facing and QW-407.9(discussed below) addressed the PWHT requirements of corro-sion-resistant overlay.

Postweld heat treatment of weld overlays can pose interestingproblems due to metallurgical differences between base metal andoverlay. Postweld heat treatment commonly applied for the bene-fit of the ferritic base metal can be problematic for the overlaymaterial. A classic example is the embrittlement of a stainlesssteel overlay with a high ferrite level when exposed to a highPWHT temperature resulting from the transformation of ductileferrite to brittle sigma phase. As a result, Section IX has made thePWHT qualification requirements for groove welding (given inQW-407.1) applicable to corrosion-resistant overlay along withthe additional requirement of time at PWHT temperature. An as-welded overlay qualification will not support production workinvolving PWHT (and vice versa), nor will a PWHT overlay qual-ification support PWHT production work in which the time atPWHT temperature exceeds that applied in the qualification by atleast 25%. For both these situations, a new overlay qualification isrequired to support production. Many Code users apply far moretime to their PWHT overlay qualification test coupons than thatnormally required to cover unexpected additional heat treatmentcycles from changes in manufacturing sequence or needed weldrepairs.

QW-407.9 A separate procedure qualification isrequired for each of the following conditions:

(a) For weld corrosion-resistant overlay of A-No. 8 on allbase materials, a change in the postweld heat treatmentin QW-407.1, or when the total time at postweld heattreatment encountered in fabrication exceeds 20 hr, anincrease of 25% or more in total time at post-weld heattreatment temperature.

(b) For weld corrosion-resistant overlay of A-No. 9 on allbase materials, a change in the postweld heat treatmentin QW-407.1, or an increase of 25% or more in totaltime at postweld heat treatment temperature.

(c) For all other weld corrosion-resistant overlays on allbase materials, a change in the postweld heat treatmentin QW-407.1.

In 2004 Section IX created this new variable for the postweldheat treatment requirements of corrosion-resistant weld metaloverlays. It differs from the QW-407.6 requirements for hard-facing (above) in that it eliminates for high nickel alloy complete-ly and for austenitic stainless steel overlays of A-No. 8 depositchemistry with less than 20 hours of production PWHT time, therequirement to requalify when the time of production PWHTexceeds 25% of the procedure qualification time. This is anacknowledgement that most high nickel alloys and manyaustenitic stainless steels show little change in mechanical proper-ties with PWHT. [By contrast, the hardness of hard-facing over-lays will change (decrease) with an increase in PWHT time.]Thus, the rules of this variable require that as with PWHT forgroove welding (given in QW-407.1) and hard-facing overlay(given in QW-407.6), an as-welded overlay qualification will notsupport production work involving PWHT (and vice versa).Additionally, for austenitic stainless steel overlays of A-No. 9deposit chemistry and austenitic stainless steel overlays of A-No. 8deposit chemistry with more than 20 hours of production PWHTtime, a PWHT overlay qualification will not support PWHT pro-duction work in which the time at PWHT temperature exceedsthat applied in the qualification by 25%. As mentioned in QW-407.6, many Code users apply far more time to their PWHToverlay qualification test coupons than that normally required tocover unexpected additional heat treatment cycles from changesin manufacturing sequence or needed weld repairs.

QW-409.4 A change from AC to DC, or vice versa, andin DC welding, a change from electrode neg-ative (straight polarity) to electrode positive(reverse polarity) or vice versa.

This variable requires a requalification whenever there is achange from alternating current to direct current (and vice versa)

ASME_Ch24_p217-252.qxd 5/22/09 2:35 PM Page 250


or a change in the polarity of an overlay procedure using directcurrent. Both the type of current and the polarity have a signifi-cant effect on the penetration characteristics of the weld bead intothe underlying material, whether it is base metal or previouslydeposited weld metal. This will significantly affect both the welddeposit chemistry and, depending on the change, the quality offusion to the base metal.

QW-409.22 An increase of more than 10% in the amper-age used in application of the first layer.

Increasing amperage (current) increases the heat of the weldingarc, producing a more deeply penetrating weld bead that meltsmore of the base metal and increases dilution. The strong influ-ence that dilution has on the overlay properties prompts SectionIX to require an upper limit control on amperage for the firstlayer. Any time that production corrosion-resistant overlayingexceeds the amperage value recorded on the procedure qualifica-tion test by more than 10%, a new qualification is required. Thus,as with PWHT time, the Code user frequently qualifies at thehighest amperage that will produce a satisfactory result to providea broad first layer current range for production application.

QW-410.38 A change from multiple-layer to single-layercladding/hardfacing, or vice versa.

Because it is far easier to achieve required overlay chemistrywith two (or more) layers than with a single layer, Section IX hasadded this essential variable to the qualification requirement for acorrosion-resistant overlay. It requires the Code user intending todo production overlay with a single layer to be qualified with a sin-gle layer, or qualified with multiple layers if the production activitywill be a multiple-layer type. Should the Code user find that he/shehas a need for both single- and multiple-layer production, he/she isrequired to be qualified with both welding procedures.

24.10.2 Welder Performance Qualification Like procedure qualification, welder performance qualification

of corrosion-resistant (and hard-facing) overlay is considered aspecial process. Prior to 2005 a welder or welding operator quali-fied for groove or fillet welding is not qualified for corrosion-resistant overlay. In 2005 Subcommittee IX relaxed this provisionby permitting welders qualified on groove welds to be qualifiedfor corrosion resistant overlay when the base metals and weldmetals are the same as qualified for groove welding and welddeposit chemistry was not specified in the WPS for the weldmetal overlay. Otherwise, the individual must qualify using a cor-rosion-resistant weld metal overlay test coupon of the same sizeas that used for procedure qualification. The test coupon’s dimen-sions, the required examinations, and the number of test speci-mens are specified in QW-453. The essential variables for such aperformance qualification are the same as those for a groove weldperformance qualification, and the reader is referred to Section24.7 for a discussion on this matter. There are two differences inthe performance qualification rules that are worth noting: The firstis that a welder qualified for corrosion-resistant overlay is quali-fied for unlimited maximum deposit thickness (if a welder hasdemonstrated an ability to deposit a in. thick overlay, depositinga thicker layer does not require any additional skill on his/herpart), and the second difference involves the welding of a com-posite clad or lined base metal. A welder qualified for corrosion-resistant overlay is also qualified to apply the corrosion-resistantoverlay portion of a groove weld joining these materials.

14

In 2004 Subcommittee IX approved a change to the perfor-mance qualification requirements for weld corrosion-resistantweld overlay. Beginning with the 2005 Addenda, when chemicalcomposition is not specified on the weld overlay WPS, thenwelders and welding operators who have a groove weld perfor-mance qualification test that meet the test requirements for a trans-verse bend (qualification by radiography will not be accepted) willalso be qualified for corrosion-resistant overlay welding.

24.11 BRAZING

Brazing is a process that joins metals by heating them in thepresence of a filler metal having a liquidus above 840�F but belowthe solidus of the base metals. The filler metal distributes itselfbetween the closely fitted surfaces of the joint by capillary action.Viewed another way, a joining process must meet the followingcriteria to be considered brazing:

(1) The parts must be joined without the melting of the basemetals.

(2) The filler metal must have a liquidus temperature above840�F. (A liquidus temperature below 840�F is consideredsoldering.)

(3) The filler metal must wet the base metal surfaces and bedrawn into or held in the joint by capillary action.

While brazing is not as widely used in the fabrication of boilersand pressure vessels as welding, it is nonetheless a joiningprocess that is employed in pressure-retaining and structuralapplications in the Code. Accordingly, Section IX has rules forthe procedure and performance qualification aspects of brazing,which are found in Part QB of Section IX. Because these rulesclosely follow the philosophy and format of the QW rules forwelding, they are covered briefly in the following paragraphs.

As Part QW has different welding processes, there are differentbrazing processes covered by Part QB. Section IX contains rulesfor the qualification of the following brazing processes:

• Torch brazing (TB) • Furnace brazing (FB) • Induction brazing (IB) • Resistance brazing (RB) • Salt or flux bath dip brazing (DB) • Molten metal bath dip brazing (DB)

There are a number of essential and nonessential variables thatare important to the brazing process having a close parallel to thevariables for welding. First of these is the classification of basemetals. Like welding, brazing classifies base metals into P-Numbers to reduce the number of procedure qualificationsrequired (QB-402.1). However, brazing has its own P-Numberclassification, as the important base metal characteristics—mechanical properties and chemical composition—have a differenteffect on brazing than on welding. As a result the brazing P-Number system, which is a three-digit designation (e.g., P-No.101, P-No. 107, and P-No. 115), is not interchangeable with thewelding P-Number system.

In a very similar manner, brazing filler metals are assigned F-Numbers based on their usability (QB-403.1), to reduce thenumber of procedure qualifications. Like brazing P-Numbers, thebrazing F-Number system is a three-digit designation. Fillermetals are broken down into classifications such as silver alloys


252 • Chapter 24

(F-Nos. 101 and 102), copper-phosphorus alloys (F-No. 103),copper-zinc alloys (F-No. 106), aluminum-silicon alloys (F-No.104), nickel-base alloys (F-No. 107), and gold alloys (F-No. 108).One notable filler metal differences between brazing and welding isthat for brazing a change in filler metal product form (e.g., pre-formed ring, paste, and powder) requires requalification (QB-403.2).

Yet another similarity with welding is the treatment of the heattreatment variable. For ferrous base metals, changes in the post-braze heat treatment relative to the lower and upper transformationtemperatures requires requalification of the brazing procedure as withwelding. And for nonferrous materials, the addition of a post-brazeheat treatment also requires requalification (QB 409.1). One aspect ofheat treatment where welding and brazing differ is in the treatment oftime at heat treatment temperature. For brazing, time at post-brazeheat treatment temperature is an essential variable (QB-409.2),whereas for welding it is only a supplementary essential variablewhen notch toughness is specified. (This is a good place to note thatthere are no supplementary essential variables for brazing.)

The variables in brazing begin to diverge from welding wherethey represent the unique characteristics of brazing processes thatare critical to the strength and quality of the brazement. Oneexample is joint design. Though a nonessential variable in weld-ing, this is a critically important variable for brazing (QB-408.4).Although there are a number of different kinds of braze joints,there are two basic types—lap and butt (see Fig. 24.20), of whichall other types, such as the scarf and rabbet, are modifications.The strength of the lap joint is created by the amount of overlapof the two members. Typically, an overlap of three times thethickness of the thinner member will produce a brazement asstrong as the base metals. Butt joints are used where the thicknessof a lap joint presents a problem and where the strength of abrazed butt joint will satisfactorily meet service requirements.

Another variable of critical importance is joint clearance. Thejoint clearance between base metal surfaces helps to establish thecapillary action for the filler metal flow, which has a major effecton the mechanical properties of a brazed joint. Smaller clearancesare used because the smaller the clearance, the easier it is for thecapillary action to distribute the braze filler metal throughout thejoint area and the less likely it is that voids will form as the braz-ing filler metal solidifies. Typically, joint clearances that rangefrom 0.001 to 0.003 in. are designed for the best capillary actionand greatest joint strength. QB-408.2 specifies that changes injoint clearance beyond the range specified in the braze procedurespecification require requalification.

The flow of braze filler metal can be significantly enhanced by theuse of a braze flux. This material is capable of dissolving metaloxides on the surface of the base metals that would hinder wetting,and it also protects against the further oxidation. Braze fluxes aretypically composed of inorganic salts and mild acids and are avail-able in the form of a liquid, slurry, paste, or powder. The flux isapplied to areas of the base metals that will be brazed. During thebrazing operation, the filler metal displaces the flux, and upon

cooling the joint is filled with solid filler metal and the solid flux isfound at the joint periphery. The importance of a brazing flux is suchthat its addition or deletion, or a change in its chemical composition,requires requalification of the brazing procedure (QW-406.1).

Another major difference between welding and brazing proce-dure variables involves flow position. While position is anonessential variable for welding (note, however, that vertical-upversus vertical-down progression becomes a supplementaryessential welding variable for notch toughness applications), it isan essential variable for both procedure and performance qualifi-cation in brazing (QB-407.1). This is because during brazing, twophysical forces must be contended with—capillary flow and grav-ity. In certain flow positions, such as flat flow, the effect of gravityis constant. In vertical flow, the effect of gravity can complementcapillary flow when the flow is in the downward direction.However, when the flow is upward vertically, gravity and capil-lary flow compete with each other. In horizontal flow the effect ofgravity is at a right angle to the capillary flow. This situation canresult in a void area at the top portion of a plate or pipe braze jointwhile the rest of the joint is satisfactory.

It is for the variable effect of gravity that each of the braze flowpositions needs to be qualified. A single exception is that vertical-downflow can be qualified by flat, horizontal, or vertical-up flow.

While the number of variables for brazing is far fewer than thatfor welding, the reader is cautioned against the assumption thatqualification with brazing is therefore more simple. Quite the con-trary; because a number of the variables are unique to this joiningprocess, they must be considered and understood in a differentway by the Code user experienced solely in welding qualification.

24.12 FUTURE ACTIONS FOR SECTION IX’SCONSIDERATION

As the world continues its global reduction there is a need forharmonizing the requirements of different Codes and Standards tomake truly international usability of (pressure) components possi-ble. Such an opportunity exists in the area of welding, and in par-ticular that of qualification. Imagine having one standard thatwould be the basis for welding qualification in such diverse areasas the Americas, Europe, Asia, the Pacific Rim and Australia. Acommon standard would ease a manufacturer’s job in providingqualifications for jobs in different geographic regions. Advantagesinclude both cost and schedule savings in not having to duplicatequalifications because of administrative (rather than technical)differences between national codes.

The fundamental precepts for welding qualification—validationof procedure, certification of a welder’s performance, control offiller materials - are the same worldwide. The differences betweenstandards are only in the details. A long-term goal for ASME andother standards writing bodies should be the collaborative devel-opment of a common weld qualification standard.

Should historical or technical differences make adoption of acommon standard difficult to achieve, another option is forregional codes to use the common standard and supplement thedocument with their specific requirements. Such an approachwould still keep a uniform basis for qualification while merelysupplementing the basic requirements of the common standard.

Whether a common standard can be adopted directly or, in stan-dards writing parlance, supplemented by normative annexes or madea cohabited standard (more than one approach within a standard), itis effort meriting the consideration of those involved in specifyingthe qualification requirements for fabrication by welding. FIG. 24.20 BASIC LAP AND BUTT JOINTS FOR BRAZING


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WELDING AND BRAZING QUALIFICATIONS