The serviceability of a product or structure utilizing the type of information presented herein is, and must be, the sole responsi-bility of the builder/user. Many variables beyond the control of The James F. Lincoln Arc Welding Foundation or The LincolnElectric Company affect the results obtained in applying this type of information. These variables include, but are not limited to,welding procedure, plate chemistry and temperature, weldment design, fabrication methods, and service requirements.

This guide makes extensive reference to the AWS D1.1 Structural Welding Code-Steel, but it is not intended to be a comprehen-sive review of all code requirements, nor is it intended to be a substitution for the D1.1 code. Users of this guide are encouragedto obtain a copy of the latest edition of the D1.1 code from the American Welding Society, 550 N.W. LeJeune Road, Miami,Florida 33126, (800) 443-9353.

Fabricators and Erectors Guide toWelded Steel Construction

By Omer W. Blodgett, P.E., Sc.D.R. Scott FunderburkDuane K. Miller, P.E., Sc.D.Marie Quintana, P.E.

This information has been provided byThe James F. Lincoln Arc Welding Foundation

to assist the general welding industry.

Copyright 1999

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

2 Welding Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12.1 SMAW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12.2 FCAW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32.3 SAW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62.4 GMAW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82.5 ESW/EGW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

3 Welding Process Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .113.1 Joint Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .113.2 Process Capabilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123.3 Special Situations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

4 Welding Cost Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

5 Welding Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155.1 Effects of Welding Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155.2 Purpose of Welding Procedure Specifications (WPSs) . . . . . . . . . . .175.3 Prequalified Welding Procedure Specifications . . . . . . . . . . . . . . . .185.4 Guidelines for Preparing Prequalified WPSs . . . . . . . . . . . . . . . . . .205.5 Qualifying Welding Procedures By Test . . . . . . . . . . . . . . . . . . . . . .205.6 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .225.7 Approval of WPSs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

6 Fabrication and Erection Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . .236.1 Fit-Up and Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .236.2 Backing and Weld Tabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .236.3 Weld Access Holes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .246.4 Cutting and Gouging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .256.5 Joint and Weld Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .256.6 Preheat and Interpass Temperature . . . . . . . . . . . . . . . . . . . . . . . . . .256.7 Welding Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .266.8 Special Welding Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .296.9 Weld Metal Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . .296.10 Intermixing of Weld Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Table of Contents

Fabricators and Erectors Guide toWelded Steel Construction

7 Welding Techniques and Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . .357.1 SMAW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .357.2 FCAW-ss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .367.3 FCAW-g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .377.4 SAW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .387.5 GMAW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .397.6 ESW/EGW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

8 Welder Qualification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40

9 Weld Cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .409.1 Centerline Cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .419.2 Heat Affected Zone Cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .429.3 Transverse Cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44

10 Weld Quality and Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4410.1 Weld Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4410.2 Weld Quality and Process-Specific Influences . . . . . . . . . . . . . . . . .4610.3 Weld Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46

11 Arc Welding Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49

1Fabricators and Erectors Guide toWelded Steel Construction

1 Introduction/Background

This Fabricators and Erectors Guide to Welded SteelConstruction has been produced by The Lincoln ElectricCompany in order to help promote high quality and cost-effective welding. This guide is not to be used as a sub-stitute for the AWS D1.1 Structural Welding Code, or anyother applicable welding code or specification, and theuser bears the responsibility for knowing applicablecodes and job requirements. Rather, this documentincorporates references to the D1.1-96 code, and addsexplanation, clarification, and guidelines to facilitatecompliance with the code. At the time of writing, thisguide reflects the current industry views with respect tosteel fabrication, with specific emphasis on the new pro-visions that have been recently imposed for fabrication ofstructures designed to resist seismic loads. These provi-sions are largely drawn from the Federal EmergencyManagement Administration (FEMA) Document No.267, produced by the SAC Consortium, whose membersinclude the Structural Engineers Association ofCalifornia, Applied Technology Council, and CaliforniaUniversities for Research and Earthquake Engineering.Another cited document is the AWS D1 StructuralWelding Committees Position Statement on theNorthridge earthquake. Research is still underway, andadditional provisions may be found that will furtherincrease the safety of welded steel structures. The userof this document must be aware of changes that mayoccur to codes published after this guide, specific jobrequirements, and various interim recommendations thatmay affect the recommendations contained herein.

The January 1994 Northridge earthquake revealed anumber of examples of lack of conformance to D1.1code mandated provisions. Lack of conformance to codeprovisions, and the poor workmanship revealed in manysituations, highlight the need for education. This docu-ment is one attempt to assist in that area.

The information contained herein is believed to be cur-rent and accurate. It is based upon the current technolo-gy, codes, specifications and principles of weldingengineering. Any recommendations will be subject tochange pending the results of ongoing research. Asalways, it is the responsibility of the Engineer of Record,

and not The Lincoln Electric Company, to specify therequirements for a particular project. The prerogative tospecify alternate requirements is always within theauthority of the Engineer of Record and, when morerestrictive requirements are specified in contract docu-ments, compliance with such requirements would super-sede the preceding recommendations. Acceptance ofcriteria by the Engineer of Record that are less rigorousthan the preceding does not change the recommendationsof The Lincoln Electric Company.

2 Welding Processes

A variety of welding processes can be used to fabricateand erect buildings. However, it is important that all par-ties involved understand these processes in order toensure high quality and economical fabrication. A briefdescription of the major processes is provided below.

2.1 SMAW

Shielded metal arc welding (SMAW), commonly knownas stick electrode welding or manual welding, is the old-est of the arc welding processes. It is characterized byversatility, simplicity and flexibility. The SMAWprocess commonly is used for tack welding, fabricationof miscellaneous components, and repair welding. Thereis a practical limit to the amount of current that may beused. The covered electrodes are typically 9 to 18 inch-es long, and if the current is raised too high, electricalresistance heating within the unused length of electrodewill become so great that the coating ingredients mayoverheat and break down, potentially resulting in weldquality degradation. SMAW also is used in the field forerection, maintenance and repairs. SMAW has earned areputation for depositing high quality welds dependably.It is, however, slower and more costly than other meth-ods of welding, and is more dependent on operator skillfor high quality welds.

The American Welding Society (AWS) publishes a vari-ety of filler metal specifications under the jurisdiction ofthe A5 Committee; A5.1 addresses the particular require-ments for mild steel covered electrodes used with theshielded metal arc welding process. The specificationA5.5 similarly covers the low alloy electrodes.

2For welding on steels with minimum specified yieldstrengths exceeding 50 ksi, all electrodes should be of thelow hydrogen type with specific coatings that aredesigned to be extremely low in moisture. Water, orH2O, will break down into its components hydrogen andoxygen under the intensity of the arc. This hydrogen canthen enter into the weld deposit and may lead to unac-ceptable weld heat affected zone cracking under certainconditions. Low hydrogen electrodes have coatingscomprised of materials that are very low in hydrogen.

The low hydrogen electrodes that fit into the A5.1 classi-fication include E7015, E7016, E7018, and E7028. TheE7015 electrodes operate on DC only. E7016 electrodesoperate on either AC or DC. The E7018 electrodes oper-ate on AC or DC and include approximately 25% ironpowder in their coatings; this increases the rate at whichmetal may be deposited. An E7028 electrode containsapproximately 50% iron powder in the coating, enablingit to deposit metal at even higher rates. However, thiselectrode is suitable for flat and horizontal welding only.

Under the low alloy specification, A5.5, a similar format isused to identify the various electrodes. The most signifi-cant difference, however, is the inclusion of a suffix letterand number indicating the alloy content. An examplewould be an E8018-C3 electrode, with the suffix -C3 indicating the electrode nominally contains 1% nick-el. A -C1 electrode nominally contains 2.5% nickel.

In AWS A5.1, the electrodes listed include both lowhydrogen and non-low hydrogen electrodes. In AWSD1.1-96, Table 3.1, Group I steels may be welded withnon-low hydrogen electrodes. This would include A36steel. For Group II steels and higher, low hydrogen elec-trodes are required. These steels would include A572grade 50. For most structural steel fabrication today, lowhydrogen electrodes are prescribed to offer additionalassurance against hydrogen induced cracking. When lowhydrogen electrodes are used, the required levels of pre-heat (as identified in Table 3.2 of D1.1-96) are actuallylower, offering additional economic advantages to thecontractor.

All the low hydrogen electrodes listed in AWS A5.1 haveminimum specified notch toughnesses of at least 20 ft.lb. at 0F. There are electrode classifications that have no

notch toughness requirements (such as E6012, E6013,E6014, E7024) but these are not low hydrogen elec-trodes. Although there is no direct correlation betweenthe low hydrogen nature of various electrodes and notchtoughness requirements, in the case of SMAW electrodesin A5.1, the low hydrogen electrodes all have minimumnotch toughness requirements.

Care and storage of low hydrogen electrodes Lowhydrogen electrodes must be dry if they are to performproperly. Manufacturers in the United States typicallysupply low hydrogen electrodes in hermetically sealedcans. When electrodes are so supplied, they may beused without any preconditioning; that is, they need notbe heated before use. Electrodes in unopened, hermeti-cally sealed containers should remain dry for extendedperiods of time under good storage conditions. Onceelectrodes are removed from the hermetically sealedcontainer, they should be placed in a holding oven tominimize or preclude the pick-up of moisture from theatmosphere. These holding ovens generally are electri-cally heated devices that can accommodate several hun-dred pounds of electrodes. They hold the electrodes at atemperature of approximately 250-300F. Electrodes tobe used in fabrication are taken from these ovens.Fabricators and erectors should establish a practice oflimiting the amount of electrodes discharged at anygiven time. Supplying welders with electrodes twice ashift at the start of the shift and at lunch, for example minimizes the risk of moisture pickup. However, theoptional designator R indicates a low hydrogen elec-trode which has been tested to determine the moisturecontent of the covering after exposure to a moist envi-ronment for 9 hours and has met the maximum level per-mitted in ANSI/AWS A5.1-91. Higher strengthelectrodes will require even more rigorous control.Electrodes must be returned to the heated cabinet forovernight storage.

Once the electrode is exposed to the atmosphere, itbegins to pick up moisture. The D1.1 code limits thetotal exposure time as a function of the electrode type(D1.1-96, paragraph 5.3.2.2, Table 5.1). Electrodes usedto join high strength steels (which are particularly sus-ceptible to hydrogen cracking) must be carefully caredfor, and their exposure to the atmosphere strictly limited.

3Some electrodes are supplied in cardboard containers.This is not commonly done for structural fabrication,although the practice can be acceptable if specific andappropriate guidelines are followed. The electrodes mustbe preconditioned before welding. Typically, this meansbaking them at temperatures in the 700 to 900F range toreduce moisture. In all cases, the electrode manufactur-ers guidelines should be followed to ensure a bakingprocedure that effectively reduces moisture without dam-age to the covering. Electrodes removed from damagedhermetically sealed cans should be similarly baked athigh temperature. The manufacturers guidelines shouldbe consulted and followed to ensure that the electrodesare properly conditioned. Lincoln Electrics recommen-dations are outlined in Literature # C2.300.

Redrying low hydrogen electrodes When containersare punctured or opened so that the electrode is exposedto the air, or when containers are stored under unusuallywet conditions, low hydrogen electrodes pick up mois-ture. The moisture, depending upon the amountabsorbed, impairs weld quality in the following ways:

1. If the base metal has high hardenability, even a smallamount of moisture can contribute to underbead cracking.

2. A small amount of moisture may cause internal poros-ity. Detection of this porosity requires X-ray inspec-tion or destructive testing.

3. A high amount of moisture causes visible externalporosity in addition to internal porosity. Proper redry-ing restores the ability to deposit quality welds. Theproper redrying temperature depends upon the type ofelectrode and its condition (D1.1-96, paragraph5.3.2.4, Table 5.1).

2.2 FCAW

Flux cored arc welding (FCAW) uses an arc between acontinuous filler metal electrode and the weld pool. Theelectrode is always tubular. Inside the metal sheath is acombination of materials that may include metallic pow-der and flux. FCAW may be applied automatically orsemiautomatically.

The flux cored arc welding process has become the mostpopular semiautomatic process for structural steel fabri-cation and erection. Production welds that are short, thatchange direction, that are difficult to access, that must bedone out-of-position (e.g., vertical or overhead), or thatare part of a short production run, generally will be madewith semiautomatic FCAW.

The flux cored arc welding process offers two distinctadvantages over shielded metal arc welding. First, theelectrode is continuous. This eliminates the built-instarts and stops that are inevitable with shielded metal arcwelding. Not only does this have an economic advantagebecause the operating factor is raised, but the number ofarc starts and stops, a potential source of weld disconti-nuities, is reduced.

Another major advantage is that increased amperagescan be used with flux cored arc welding, with a corre-sponding increase in deposition rate and productivity.With the continuous flux cored electrodes, the tubularelectrode is passed through a contact tip, where electricalenergy is transferred to the electrode. The short distancefrom the contact tip to the end of the electrode, known aselectrode extension or stickout, limits the build up ofheat due to electrical resistance. This electrode extensiondistance is typically 3/4 in. to 1 in. for flux cored elec-trodes, although it may be as high as two or three inches.

Within the category of flux cored arc welding, there aretwo specific subsets: self shielded flux core (FCAW-ss)and gas shielded flux core (FCAW-g). Self shielded fluxcored electrodes require no external shielding gas. Theentire shielding system results from the flux ingredientscontained within the core of the tubular electrode. Thegas shielded versions of flux cored electrodes utilize anexternally supplied shielding gas. In many cases, CO2 isused, although other gas mixtures may be used, e.g.,argon/CO2 mixtures. Both types of flux cored arc weld-ing are capable of delivering weld deposits that meet thequality and mechanical property requirements for moststructure applications. In general, the fabricator will uti-lize the process that offers the greatest advantages for theparticular environment. Self shielded flux cored elec-trodes are better for field welding situations. Since no

4externally supplied shielding gas is required, the processmay be used in high winds without adversely affectingthe quality of the deposit. With any of the gas shieldedprocesses, wind shields must be erected to preclude inter-ference with the gas shield in windy weather. Many fab-ricators have found self shielded flux core offersadvantages for shop welding as well, since it permits theuse of better ventilation.

Individual gas shielded flux cored electrodes tend to bemore versatile than self shielded flux cored electrodes,and in general, provide better arc action. Operator appealis usually higher. While the gas shield must be protectedfrom winds and drafts, this is not particularly difficult inshop fabrication situations. Weld appearance and qualityare very good. Higher strength gas shielded FCAW elec-trodes are available, while current technology limits selfshielded FCAW deposits to 90 ksi tensile strength or less.

Filler metals for flux cored arc welding are specified inAWS A5.20 and A5.29. A5.20 covers mild steel elec-trodes, while A5.29 addresses low alloy materials.Positive polarity is always used for FCAW-g, althoughthe self shielded electrodes may be used on either polar-ity, depending on their classification. Under A5.29 foralloy electrodes, a suffix letter followed by a numberappears at the end. Common designations include Ni1indicating a nominal nickel content in the depositedmetal of 1%. The letter M could appear at the end ofthe electrode classification. If this is done, the electrodehas been designed for operation with mixed shieldinggas, that is an argon-CO2 blend that consists of 75 - 80%argon. Other suffix designators may be used that indicateincreased notch toughness capabilities, and/or diffusiblehydrogen limits.

Table 2.1 describes various FCAW electrodes listed inAWS A5.20 and A5.29. Some of the electrodes haveminimum specified notch toughness values although oth-ers do not. Some are gas shielded, while others are selfshielded. Some are restricted to single pass applications,and others have restrictions on the thickness for theirapplication. The electrical polarity used for the variouselectrodes is also shown. For critical applications inbuildings that are designed to resist seismic loading asdetermined by the Engineer of Record, only electrodesthat are listed in Table 2.1 as having the required mini-

mum specified notch toughness levels should be used.The corresponding Lincoln Electric products are alsoshown.

Shielding gases for FCAW-g Most of the gas shield-ed flux cored electrodes utilize carbon dioxide for theshielding media. However, electrodes may also beshielded with an argon-CO2 mixture. All gases should beof welding grade with a dew point of -40F or less. Thecarbon dioxide content is typically 10% to 25%, with thebalance composed of argon. This is done to enhancewelding characteristics. In order to utilize the argonbased shielding gases, arc voltages are typically reducedby two volts from the level used with carbon dioxideshielding.

The selection of shielding gas may affect mechanicalproperties, including yield and tensile strength, elonga-tion, and notch toughness. This is largely due to the dif-ference in alloy recoverythat is, the amount of alloytransferred from the filler material to the weld deposit.Carbon dioxide is a reactive gas that may cause some ofthe alloys contained in the electrode (Mn, Si and others)to be oxidized, so that less alloy ends up in the deposit.When a portion of this active carbon dioxide is replacedwith an inert gas such as argon, recovery typicallyincreases, resulting in more alloy in the weld deposit.Generally, this will result in higher yield and tensilestrengths, accompanied by a reduction in elongation.The notch toughness of the weld deposit may go up ordown, depending on the particular alloy whose recoveryis increased.

Storing FCAW electrodes In general, FCAW elec-trodes will produce weld deposits which achievehydrogen levels below 16 ml per 100 grams of deposit-ed metal. These electrodes, like other products whichproduce deposits low in hydrogen, must be protectedfrom exposure to the atmosphere in order to maintainhydrogen levels as low as possible, prevent rusting ofthe product and prevent porosity during welding. Therecommended storage conditions are such that theymaintain the condition of 90 grains of moisture perpound of dry air. Accordingly, the following storageconditions are recommended for FCAW electrodes intheir original, unopened boxes and plastic bags.

5Table 2.1 FCAW Electrode Classification

6For best results, electrodes should be consumed as soonas practicable. However, they may be stored up to threeyears from the date of manufacture. The Lincoln distrib-utor or sales representative should be consulted if there isa question as to when the electrodes were made.

Once the electrode packaging is opened, Innershield andOutershield electrodes can be subject to contaminationfrom atmospheric moisture. Care has been taken in thedesign of these products to select core ingredients thatare essentially resistant to moisture pick-up; however,condensation of the moisture from the atmosphere ontothe surface of the electrode can be sufficient to degradethe product.

The following minimum precautions should be taken tosafeguard product after opening the original package.Electrode should be used within approximately 1 weekafter opening the original package. Opened electrodeshould not be exposed to damp, moist conditions orextremes in temperature and/or humidity where surfacecondensation can occur. Electrodes mounted on wirefeeders should be protected against condensation. It isrecommended that electrode removed from its originalpackaging be placed in poly bags (4 mil minimum thick-ness) when not in use.

In the case of FCAW-s, excessively damp electrodes canresult in higher levels of spatter, poorer slag cover andporosity. FCAW-g electrodes will display high moisturelevels in the form of gas tracks, higher spatter and poros-ity. Any rusty electrode should be discarded.

Products used for applications requiring morerestrictive hydrogen control The AWS specificationfor flux cored electrodes, ANSI/AWS A5.20, states thatFlux cored arc welding is generally considered to be alow hydrogen welding process. To further clarify theissue, this specification makes available optional supple-mental designators for maximum diffusible hydrogenlevels of 4, 8 and 16 ml per 100 grams of deposited weldmetal.

Some Innershield and Outershield products have beendesigned and manufactured to produce weld depositsmeeting more stringent diffusible hydrogen require-ments. These electrodes, usually distinguished by an Hadded to the product name, will remain relatively dryunder recommended storage conditions in their original,unopened package or container.

For critical applications in which the weld metal hydro-gen must be controlled (usually H8 or lower), or whereshipping and storage conditions are not controlled orknown, only hermetically sealed packaging is recom-mended. Innershield and Outershield electrodes areavailable in hermetically sealed packages on a specialorder basis.

Once the package has been opened, the electrode shouldnot be exposed to conditions exceeding 80% relativehumidity for a period greater than 16 hours, or any lesshumid condition for more than 24 hours. Conditions thatexceed 80% RH will decrease the maximum 16 hourexposure period.

After exposure, hydrogen levels can be reduced by con-ditioning the electrode. Electrodes may be conditioned ata temperature of 230F 25F for a period of 6 to 12hours, cooled and then stored in sealed poly bags (4 milminimum thickness) or equivalent. Electrodes on plasticspools should not be heated at temperatures in excess of150F. Rusty electrodes should be discarded.

2.3 SAW

Submerged arc welding (SAW) differs from other arcwelding processes in that a layer of fusible granularmaterial called flux is used for shielding the arc and themolten metal. The arc is struck between the workpieceand a bare wire electrode, the tip of which is submergedin the flux. Since the arc is completely covered by theflux, it is not visible and the weld is made without theflash, spatter, and sparks that characterize the open-arcprocesses. The nature of the flux is such that very littlesmoke or visible fumes are released to the air.

Typically, the process is fully mechanized, although semi-automatic operation is often utilized. The electrode is fedmechanically to the welding gun, head, or heads. In semi-automatic welding, the welder moves the gun, usuallyequipped with a flux-feeding device, along the joint.

Maximum %Ambient Temperature Relative Humidity

Degrees F Degrees C60 - 70 16 - 21 8070 - 80 21 - 27 6080 - 90 27 - 32 4590 - 100 32 - 38 30

7High currents can be used in submerged arc welding andextremely high heat input levels can be developed.Because the current is applied to the electrode a short dis-tance above its arc, relatively high amperages can beused on small diameter electrodes, resulting in extreme-ly high current densities. This allows for high depositionrates and deep penetration.

Welds made under the protective layer of flux are excel-lent in appearance and spatter free. Since the processdevelops a minimum amount of smoke, the surroundingplate surfaces remain clear of smoke deposits. The highquality of submerged arc welds, the high depositionrates, the deep penetration characteristics, and the easyadaptability of the process to full mechanization make itpopular for the manufacture of plate girders and fabricat-ed columns.

One of the greatest benefits of the SAW process is free-dom from the open arc. This allows multiple arcs to beoperated in a tight, confined area without the need forextensive shields to guard the operators from arc flash.Yet this advantage also proves to be one of the chief draw-backs of the process; it does not allow the operator toobserve the weld puddle. When SAW is applied semiau-tomatically, the operator must learn to propel the guncarefully in a fashion that will ensure uniform bead con-tour. The experienced operator relies on the uniform for-mation of a slag blanket to indicate the nature of thedeposit. For single pass welds, this is mastered fairlyreadily; however, for multiple pass welding, the degree ofskill required is significant. Therefore, most submergedarc applications are mechanized. The nature of the jointmust then lend itself to automation if the process is toprove viable. Long, uninterrupted straight seams are idealapplications for submerged arc. Short, intermittent weldsare better made with one of the open arc processes.

Two electrodes may be fed through a single electricalcontact tip, resulting in higher deposition rates.Generally known as parallel electrode welding, theLincoln trade name for this is Tiny Twin or Twin Arc.The equipment is essentially the same as that used forsingle electrode welding, and parallel electrode weldingprocedures may be prequalified under AWS D1.1-96.

Multiple electrode SAW refers to a variation of sub-merged arc which utilizes at least two separate powersupplies, two separate wire drives, and feeds two elec-trodes independently. Some applications such as themanufacture of line pipe may use up to five independent

electrodes in a multiple electrode configuration. ACwelding currently is typically used for multi-electrodewelding. If DC current is used, it usually is limited to thelead electrode to minimize the potentially negative inter-action of magnetic fields between the two electrodes.

Submerged arc filler materials are classified underAWS A5.17 for mild steel and AWS A5.23 for low alloyfiller materials. Both fluxes and electrodes are coveredunder these specifications. Since submerged arc is a two-component process, that is, flux and electrode, the classi-fication system is slightly different than for other fillermaterials.

Electrodes are classified based on the composition of theelectrode. Under A5.17, the electrode will carry a classi-fication that consists of two letters, one or two numericaldigits and, in some cases, a final letter. The first letter isan E, which stands for electrode. The second letter willbe L, M, or H, referring to a low, medium, or high levelof manganese in the electrode. The next one or two dig-its refer to the nominal carbon content in hundredths of apercent. A 12 in this location, for example, wouldindicate a nominal carbon content of 0.12%. It should beemphasized that this is the nominal value; it is possible tohave higher and lower carbon contents in a specific elec-trode. In some cases, the electrode will be made of killedsteel. When this is the case, silicon normally is addedand the electrode will have a K at the end of the clas-sification (e.g., EM13K).

Electrodes classified under A5.23, the low alloy variety,have a more complex nomenclature, because of the vari-ety of alloys that may be involved. The most importantalloys for structural welding are the Ni, or nickelalloys, and W, or weathering alloys (e.g., ENi1K).

Fluxes are always classified in conjunction with an elec-trode. The flux-electrode combination must meet specif-ic mechanical property requirements. After a flux isselected and a classification test plate welded, a flux-electrode classification may be established. Specimensare extracted from the weld deposit to obtain the mechan-ical properties of the flux-electrode combination. Theclassification will follow the format of an F followedby a single or two digit number, an A or P, a singledigit and a hyphen which separates the electrode classifi-cation. Thus, a typical flux-electrode may be classifiedas an F7A2-EM12K. The F stands for flux, and the7 indicates all of the following: a 70-95 ksi tensilestrength deposit, a 58 ksi minimum yield strength, and a

8minimum of 22% elongation. The A indicates thedeposit is tested in the as-welded condition. The 2indicates 20 ft. lbf. at -20F, and the balance of the clas-sification identifies the electrode used.

Because of the popularity of the submerged arc processfor pressure vessel fabrication where assemblies are rou-tinely stress relieved, submerged arc products may beclassified in the post weld heat treated, or stress relieved,condition. When this is done, a P replaces the A. Forstructural work, which is seldom stress relieved, the Aclassification is more common.

For products classified under A5.23, a format similar tothat of A5.17 is used, with this major exception: at theend of the flux-electrode classification, a weld depositcomposition is specified. For example, an F7A2-ENi1-Ni1 would indicate that the electrode, an ENi1, deliversan F7A2 deposit when used with a specific flux. In addi-tion, the deposit has a composition that meets therequirements of an Ni1. In this case, a nickel bearingelectrode deposits a weld that contains nickel. Theexample is straightforward. However, it is also possibleto use alloy fluxes which, with mild steel electrodes, arecapable of delivering alloy weld metal. In this case, atypical classification may be an F7A2-EL12-Nil. In thisexample, an EL12 electrode (a non-alloy electrode thatcontains a low level of manganese) is used with an alloyflux. The result is an alloyed deposit. This is common-ly done when nickel bearing deposits are desired onweathering steel that will not be painted.

Only part of the flux deposited from a hopper or a gun isfused in welding. The unfused, granular flux may berecovered for future use and is known as reclaimed flux.The unmelted flux does not undergo chemical changesand may therefore be capable of delivering quality weldswhen used the next time. However, this flux can be con-taminated in the act of recovery. If it comes in contactwith oil, moisture, dirt, scale or other contaminants, theproperties of the weld deposit made with reclaimed fluxmay be adversely affected. Care should be exercised toensure that flux is not thus contaminated. Another prob-lem with reclaimed flux is the potential for the break-down of particles and the modification of the particle sizedistribution. This can affect the quality and/or proper-ties. The method of flux recovery can range from sweep-ing up the flux with broom and pans, to vacuum recoverysystems; the method chosen should take into account theneed to avoid contamination.

Larger pieces of fused slag should be separated from therecovered flux in order to avoid flux feeding problems.The automated systems typically have screening to han-dle this. The fused slag may be chemically different thanthe unfused flux. For less critical applications, this slagmay be crushed and thoroughly intermixed with newflux. This is sometimes called recycled flux, but sincereclaimed flux is sometimes referred to by the same term,a better description for this product is crushed slag.Performance and mechanical properties of crushed slagmay differ from those of virgin flux. AWS D1.1-96requires that crushed slag must be classified in much thesame way as new flux. (See AWS D1.1-96, paragraph5.3.3.4)

Flux must be stored so that it remains dry. The manu-facturers guidelines regarding storage and usage of theflux must be followed. In use, granules of flux must notcome in direct contact with water since weld crackingcan result. Fluxes can be contaminated with moisturefrom the atmosphere, so exposure should be limited.When not in use, flux hoppers should be covered or oth-erwise protected from the atmosphere. Lincoln Electricsrecommendations for storage and handling of flux areoutlined in Literature # C5.660.

2.4 GMAW

Gas metal arc welding (GMAW) utilizes equipmentmuch like that used in flux cored arc welding. Indeed,the two processes are very similar. The major differencesare: gas metal arc uses a solid or metal cored electrode,and leaves no appreciable amount of residual slag. Gasmetal arc has not been a popular method of welding inthe typical structural steel fabrication shop because of itssensitivity to mill scale, rust, limited puddle control, andsensitivity to shielding loss. Newer GMAW metal coredelectrodes, however, are beginning to be used in the shopfabrication of structural elements with good success.

A variety of shielding gases or gas mixtures may be usedfor GMAW. Carbon dioxide (CO2) is the lowest cost gas,and while acceptable for welding carbon steel, the gas isnot inert but active at elevated temperatures. This hasgiven rise to the term MAG (metal active gas) for theprocess when (CO2) is used, and MIG (metal inert gas)when predominantly argon-based mixtures are used.

While shielding gas is used to displace atmospheric oxy-gen, it is possible to add smaller quantities of oxygen into

9mixtures of argon generally at levels of 2 - 8%. Thishelps stabilize the arc and decreases puddle surface ten-sion, resulting in improved wetting. Tri- and quad-mixes of argon, oxygen, carbon dioxide and helium arepossible, offering advantages that positively affect arcaction, deposition appearance and fume generation rates.

Short arc transfer is ideal for welding on thin gaugematerials. It is generally not suitable for structural steelfabrication purposes. In this mode of transfer, the smalldiameter electrode, typically 0.035 in. or 0.045 in., is fedat a moderate wire feed speed at relatively low voltages.The electrode will touch the workpiece, resulting in ashort in the electrical circuit. The arc will actually go outat this point, and very high currents will flow through theelectrode, causing it to heat and melt. Just as excessivecurrent flowing through a fuse causes it to blow, so theshorted electrode will separate from the work, initiatinga momentary arc. A small amount of metal will be trans-ferred to the work at this time.

The cycle will repeat itself again once the electrodeshorts to the work. This occurs somewhere between 60and 200 times per second, creating a characteristic buzzto the arc. This mode of transfer is ideal for sheet metal,but results in significant fusion problems if applied toheavy materials. A phenomenon known as cold lap orcold casting may result where the metal does not fuse tothe base material. This is unacceptable since the weldedconnections will have virtually no strength. Great cau-tion must be exercised in the application of the short arcmode to heavy plates. The use of short arc on heavyplates is not totally prohibited however, since it is theonly mode of transfer that can be used out-of-positionwith gas metal arc welding, unless specialized equipmentis used. Weld joint details must be carefully designedwhen short arc transfer is used. Welders must pass specific qualification tests before using this mode oftransfer. The mode of transfer is often abbreviated asGMAW-s, and is not prequalified by the D1.1 code.

Globular transfer is a mode of gas metal arc weldingthat results when high concentrations of carbon dioxideare used, resulting in an arc that is rough with larger globsof metal ejected from the end of the electrode. This modeof transfer, while resulting in deep penetration, generatesrelatively high levels of spatter. Weld appearance can bepoor and it is restricted to the flat and horizontal position.Globular transfer may be preferred over spray transferbecause of the low cost of CO2 shielding gas and thelower level of heat experienced by the operator.

Spray arc transfer is characterized by high wire feedspeeds at relatively high voltages. A fine spray of moltendrops, all smaller in diameter than the electrode diame-ter, is ejected from the electrode toward the work. Unlikeshort arc transfer, the arc in spray transfer is continuous-ly maintained. High quality welds with particularly goodappearance are the result. The shielding used for sprayarc transfer is composed of at least 80% argon, with thebalance made up of either carbon dioxide or oxygen.Typical mixtures would include 90-10 argon-CO2, and95-5 argon-oxygen. Other proprietary mixtures areavailable from gas suppliers. Relatively high arc volt-ages are used with the spray mode of transfer. However,due to the intensity of the arc, spray arc is restricted toapplications in the flat and horizontal position, becauseof the puddle fluidity, and lack of a slag to hold themolten metal in place.

Pulsed arc transfer utilizes a background current that iscontinuously applied to the electrode. A pulsing peakcurrent is optimally applied as a function of the wire feedspeed. With this mode of transfer, the power supplydelivers a pulse of current which, ideally, ejects a singledroplet of metal from the electrode. The power supplyreturns to a lower background current which maintainsthe arc. This occurs between 100 and 400 times per sec-ond. One advantage of pulsed arc transfer is that it canbe used out-of-position. For flat and horizontal work, itmay not be as fast as spray transfer. However, used out-of- position, it is free of the problems associated with gasmetal arc short circuiting mode. Weld appearance isgood and quality can be excellent. The disadvantage ofpulsed arc transfer is that the equipment is slightly morecomplex and more costly. The joints are still required tobe relatively clean, and out-of-position welding is stillmore difficult than with processes that generate a slagthat can support the molten puddle.

Metal cored electrodes are a relatively new develop-ment in gas metal arc welding. This is similar to fluxcored arc welding in that the electrode is tubular, but thecore material does not contain slag forming ingredients.Rather, a variety of metallic powders is contained in thecore. The resulting weld is virtually slag-free, just aswith other forms of GMAW. The use of metal coredelectrodes offers many fabrication advantages. Theyhave increased ability to handle mill scale and other sur-face contaminants. Finally, metal cored electrodes per-mit the use of high amperages that may not be practicalwith solid electrodes, resulting in potentially higherdeposition rates. The properties obtained from metal

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cored deposits can be excellent. Appearance is verygood. Because of the ability of the filler metal manufac-turer to control the composition of the core ingredients,mechanical properties obtained from metal coreddeposits may be more consistent than those obtainedwith solid electrodes. However, metal cored electrodesare in general more expensive.

2.5 ESW/EGW

Electroslag and electrogas welding (ESW/EGW) areclosely related processes that offer high deposition weld-ing in the vertical plane. Properly applied, these process-es offer significant savings over alternativeout-of-position methods and in many cases, a savingsover flat position welding. Although the two processeshave similar applications and mechanical set up, thereare fundamental differences in the arc characteristics.

Electroslag and electrogas are mechanically similar inthat both utilize copper dams or shoes that are applied toeither side of a square edged butt joint. An electrode ormultiple electrodes are fed into the joint. A starting sumpis typically applied for the beginning of the weld. As theelectrode is fed into the joint, a puddle is established thatprogresses vertically. The copper dams, which are com-monly water cooled, chill the weld metal and prevent itfrom escaping from the joint. The weld is completed inone pass.

These processes may be used for groove welds in butt,corner and tee joints. Typical applications involve heav-ier plate, usually 1 or thicker. Multiple electrodes maybe used in a single joint, allowing very heavy plate up toseveral inches thick to be joined in a single pass.Because of the sensitivity of the process to the variety ofvariables involved, specific operator training is required,and the D1.1-96 code requires welding procedures to bequalified by test.

In building construction, applications for ESW/EGWwith traditional connection designs are somewhat limit-ed. However, they can be highly efficient in the manu-facture of tree columns. In the shop, the beamflange-to-column welds can be made with the column inthe horizontal plane. With the proper equipment andtooling, all four flange welds can be made simultaneous-ly. In addition, continuity plate welds can be made withESW/EGW. Future connection designs may utilize con-figurations that are more conducive to these processes.

Another common application is for the welding of conti-nuity plates inside box columns. It is possible to weldthree sides of the continuity plate to the interior of thebox prior to closing the box with the fourth side.However, once this closure is made, access to the finalside of the continuity plate is restricted. It is possible touse these processes to make this final closure weld byoperating through a hole in the outside of the box col-umn. This approach is very popular in Asia, where boxcolumns are widely used.

In electroslag welding, a granular flux is metered into thejoint during the welding operation. At the beginning, anarc, similar to that of submerged arc welding, is estab-lished between the electrode and the sump.

After the initial flux is melted into a molten slag, thereaction changes. The slag, which is carefully designedto be electrically conductive, will conduct the weldingcurrent from the electrode through the slag into thepieces of steel to be joined. As high currents are passedthrough the slag, it becomes very hot. The electrode isfed through the hot slag and melts. Technically, elec-troslag welding is not an arc welding process, but a resis-tance welding process. Once the arc is extinguished andthe resistance melting process is stabilized, the weld con-tinues vertically to completion. A small amount of slagis consumed as it chills against the water cooled coppershoes. In some cases, steel dams instead of copper damsare used to retain the puddle. After completion of theweld, the steel dams stay in place, and become part of thefinal product. Slag must be replenished, and additionalflux is continuously added to compensate for the loss.

One aspect of electroslag welding that must be consid-ered is the very high heat input associated with theprocess. This causes a large heat affected zone (HAZ)that may have a lower notch toughness. Electrogas weld-ing is different from electroslag, inasmuch as no flux isused. Electrogas welding is a true arc welding processand is conceptually more like gas metal arc or flux coredarc welding. A solid or tubular electrode is fed into thejoint, which is flooded with an inert gas shield. The arcprogresses vertically while the puddle is retained by thewater cooled dams.

The Lincoln Vertishield system uses a self shieldedflux cored electrode, and while no gas is required, it isclassified as EGW since it is an open arc process.

11

The HAZ performance is dependent not only on the heatinput, but also on the nature of the steel. While allprocesses develop a heat affected zone, the large size ofthe electroslag heat affected zone justifies additionalscrutiny. Advances in steel technology have resulted inimproved steels, featuring higher cleanliness and tough-ness, that better retain the HAZ properties in ESW/EGWwelds.

3 Welding Process Selection

Any of the common arc welding processes can be used toachieve the quality required for structural steel applica-tions. While each may have a particular area of strengthand/or weakness, the primary consideration as to whichprocess will be used is largely driven by cost. The avail-ability of specialized equipment in one fabrication shop,compared to the capabilities of a second shop, may dic-tate significantly different approaches, both of whichmay prove to be cost effective. A history of successfulusage offers a strong incentive for the fabricator to con-tinue using a given process. The reasons for this go wellbeyond familiarity and comfort with a specific approach.When welders and procedures are established with agiven process, significant costs will be incurred with anychange to a new approach.

3.1 Joint Requirements

Each individual weld joint configuration and preparationhas certain requirements of the welding process in orderto achieve low cost welding. Four characteristics mustbe considered: deposition rate, penetration ability, out-of-position capability, and high travel speed capacity.Each process exhibits different capabilities in theserealms. Once the joint and its associated requirementsare analyzed, they should be compared to the variousprocess options and the ability of the process to achievethose requirements. A proper match of weld jointrequirements and process capabilities will lead todependable and economical fabrication.

Some welds, such as large fillet welds and groove weldsrequire that high deposition rate welding be used (Fig.3-1) for the most economical fabrication. The cost ofmaking these welds will be determined largely by thedeposition rate of the process. The amount of weld mate-rial required may be measured in pounds per foot ofjoint. Once the deposition rate of a process in pounds perhour is known, it is possible to determine the number of

feet of weld that can be made in a given hour assuming100% arc time. This, of course, translates directly to pro-ductivity rates.

The second criterion imposed by weld joints is therequirement for penetration. Examples are listed underFig. 3-2 and would include any complete joint penetra-tion groove weld that has a root face dimension. Thesejoints will be made by welding from one side and backgouging from the second to ensure complete fusion.With deeper penetration afforded by the welding process,a smaller amount of base metal will be required to beremoved by back gouging. Subsequent welding will thenbe proportionately reduced as well.

While all welding requires fusion, not all joints requiredeep penetration. For example, simple fillet welds arerequired by AWS D1.1-96 to have fusion to the root of thejoint, but are not required to have penetration beyond theroot. This has a practical basis: verification of penetrationbeyond the root is impossible with visual inspection.Fusion to the root, and not necessarily beyond, ensuresthat sufficient strength is generated, provided the weld isproperly sized. While penetration can be verified withultrasonic inspection, fillet welds routinely receive onlyvisual or magnetic particle inspection. Thus, no penetra-

Figure 3-1 Joints requiring substantial fill

Figure 3-2 Joints requiring substantial penetration

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tion beyond the root is required, nor is design credit givento deeper penetration in fillet welds if it happens to be pre-sent. Figure 3-3 illustrates this requirement.

The out-of-position capability of a given welding processrefers to the ability to deposit weld metal in the verticalor overhead positions. It is generally more economical toposition the work in the flat and horizontal positions.However, this is usually impossible for field erection,and may be impractical under other conditions.

The ability to obtain high travel speeds is important forsmall welds. It may not be possible for a high depositionwelding process to be used at high travel speeds. Thesize of the droplet transferred, puddle fluidity, surfacetension, and other factors combine to make someprocesses more capable of high travel speeds than others.

3.2 Process Capabilities

After the joint is analyzed and specific requirementsdetermined, these are compared to the capabilities of var-ious processes. The process with capabilities most close-ly matching the requirements typically will be the bestand most economical option.

Submerged arc welding and electroslag/electrogas weld-ing have the greatest potential to deliver high depositionrates. Multiple electrode applications of submerged arcextend this capability even further. For joints requiringhigh deposition rates, submerged arc andelectroslag/electrogas welding are ideal processes to con-tribute to low cost welding. When the specific conditionsare not conducive to SAW but high deposition rates arestill required, flux cored arc welding may be used. Thelarger diameter electrodes, which run at higher electricalcurrents, are preferred.

Deep penetration is offered by the submerged arc weld-ing process. While electroslag/electrogas also offersdeep penetration, the joints on which electroslag are usedtypically do not require this capability. Where open arcprocesses are preferred, gas shielded flux cored weldingmay offer deep penetration.

Out-of-position capability is strongest for the flux coredand shielded metal arc welding processes. The slag coat-ings that are generated by these processes can be instru-mental in retaining molten weld metal in the vertical andoverhead positions. Submerged arc is not applicable forthese joints.

The requirement for high travel speed capability is fairlylimited in terms of welding structural steel members.This typically consists of the travel speed associated withmaking a 1/4 in. fillet weld. All of the popular process-es, with the exception of electroslag/electrogas, are capa-ble of making 1/4 in. fillet welds under the properconditions. Among the variables that need to be consid-ered are electrode size and procedure variables. A com-mon mistake of fabricators is to utilize a process andprocedure capable of extremely high deposition rates, butlimited travel speeds. Oversized welds can result fromthe inability to achieve high travel speeds. A more eco-nomical approach would be to optimize the procedureaccording to the desired travel speed. This may result ina lower deposition rate but a lower overall cost becauseoverwelding has been eliminated.

3.3 Special Situations

Self shielded flux cored welding is ideal for outdoor con-ditions. Quality deposits may be obtained without theerection of special wind shields and protection fromdrafts. Shielded metal arc welding is also suitable forthese conditions, but is considerably slower.

Figure 3-3 Fillet weld requirements

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The welding process of choice for field erectors for thelast 25 years has been FCAW-ss. It has been the com-monly used process for fabrication of steel structuresthroughout the United States. Its advantages arereviewed in order to provide an understanding of why ithas been the preferred process. In addition, its limita-tions are outlined to highlight areas of potential concern.

The chief advantage of the FCAW-ss process is its abili-ty to deposit quality weld metal under field conditions,which usually involve wind. The graph shown in Figure

3-4 illustrates the effect of shielding gas loss on welddeposits, as well as the resistance to this problem withthe FCAW-ss process. The code specifically limits windvelocity in the vicinity of a weld to a maximum of 5miles per hour (2.3 m/s) (D1.1-96, paragraph 5.12.1). Inorder to utilize gas shielded processes under these condi-tions, it is necessary to erect windshields to precludemovement of the shielding gas with respect to the moltenweld puddle. While tents and other housings can be cre-ated to minimize this problem, such activities can becostly and are often a fire hazard. In addition, adequateventilation must be provided for the welder. The mostefficient windshields may preclude adequate ventilation.Under conditions of severe shielding loss, weld porositywill be exhibited. At much lower levels of shielding loss,the mechanical properties (e.g., notch toughness andductility) may be negatively affected, although there willbe no obvious evidence that this is taking place.

A variety of other gas-related issues are also eliminated,including ensuring availability of gas, handling of highpressure cylinders (always a safety concern), theft ofcylinders, protection of gas distribution hosing underfield conditions, and the cost of shielding gas. Leaks inthe delivery system obviously waste shielding gas, but aleak can also allow entry of air into the delivery system.Weld quality can be affected in the same way as shield-ing loss. Most field erectors have found it advantageousto utilize the self-shielded process and circumvent allsuch potential problems.

Some projects permit multiple welding heads to besimultaneously operated in the same general vicinity. Forsuch applications, submerged arc is an ideal choice.Because of the lack of arc flash, one operator can controlmultiple arcs that are nearly impossible to control in a sit-uation where the arc intensity from one arc would make itdifficult to carefully control another. A typical examplewould be the use of welding systems that simultaneouslymake fillet welds on opposing sides of stiffeners.

The easiest way to control smoke and fumes in thewelding environment is to limit their initial generation.Here, submerged arc is ideal. Smoke exhaust guns areavailable for the flux cored arc welding processes. Themost effective process for use with these smoke exhaustguns is FCAW-ss. Because the process is self shielded,there is no concern about the disruption of the gas shield-ing. See 11 on arc welding safety.

Figure 3-4a Comparison of the effect of side wind ontensile elongation of: (a) CO2-shielded and (b) selfshielded ferritic steel weld metals.(source: Self-Shielded Arc Welding. T. Boniszewski, 1992.)

Figure 3-4b Comparison of the effect of side wind speedon Charpy V-notch impact toughness of: (a) CO2 -shield-ed at room temperature and (b) self shielded ferritic steelweld metals at 0C.(source: Self-Shielded Arc Welding. T. Boniszewski, 1992.)

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4 Welding Cost Analysis

Welding is a labor intensive technology. Electricity,equipment depreciation, electrodes, gases, and fluxesconstitute a very small portion of the total welding cost.Therefore, the prime focus of cost control will be reduc-ing the amount of time required to make a weld.

The following example is given to illustrate the relativecosts of material and labor, as well as to assess the effectsof proper process selection. The example to be consid-ered is the groove weld of beam flange to column con-nections. Since this is a multiple pass weld, the mostappropriate analysis method is to consider the weldingcost per weight of weld metal deposited, such as $/lb.Other analysis methods include cost per piece, ideal formanufacturers associated with the production of identicalparts on a repetitive basis. Another method is cost perlength, appropriate for single pass welds with substantiallength. The two welding processes to be considered areshielded metal arc welding and flux cored arc welding.Either would generate high quality welds when properlyused.

To calculate the cost per weight of weld metal deposited,an equation taking the following format is used:

The cost of the electrode is simply the purchase cost ofthe welding consumable used. Not all of this filler metalis converted directly to deposited weld metal. There arelosses associated with slag, spatter, and in the case ofSMAW, the stub loss (the end portion of the electrodethat is discarded). To account for these differences, anefficiency factor is applied. The following efficiency fac-tors are typically used for the various welding processes:

The cost to deposit the weld metal is determined bydividing the applicable labor and overhead rate by thedeposition rate, that is, the amount of weld metal deposit-ed in a theoretical, continuous one hour of production.This cannot be maintained under actual conditions sincewelding will be interrupted by many factors, includingslag removal, replacement of electrode, repositioning of

the work or the welder with respect to the work, etc. Toaccount for this time, an operating factor is used whichis defined as the arc-on time divided by the total timeassociated with welding activities. For SMAW, replace-ment of electrodes takes place approximately everyminute because of the finite length of the electrodes used.The following operating factors are typically used for thevarious processes and method of application:Operating factors for any given process can vary widely,

depending on what a welder is required to do. In shopsituations, a welder may receive tacked assemblies andbe required only to weld and clean them. For field erec-tion, the welder may hang iron, fit, tack, bolt, clean thejoint, reposition scaffolding and other activities in addi-tion to welding. Obviously operating factors will be sig-nificantly reduced under these conditions.

The following examples are the actual procedures usedby a field erector. The labor and overhead cost does notnecessarily represent actual practice. The operating fac-tors are unrealistically high for a field erection site, buthave been used to enable comparison of the relative costof filler metals vs. the labor required to deposit the weldmetal, as well as the difference in cost for differentprocesses. Once the cost per deposited pound is known,it is relatively simple to determine the quantity of weldmetal required for a given project, and multiply it by thecost per weight to determine the cost of welding on theproject.

Method Operating FactorManual SMAW 30%Semiautomatic 40%Mechanized 50%

Process EfficiencySMAW 60%FCAW 80%GMAW 90% (CO2 shielding)

98% (Mixed gas)SAW 100% (Flux not included)

Process SMAW FCAWElectrode Classification E7018 E70TG-K2Electrode Diameter 3/16 7/64Amperage 225 430Voltage N.A. 27Electrode Efficiency 60% 80%Electrode Cost $1.23/lb. $2.27/lb.Operating Factor 30% 40%Deposition Rate 5.5 lb./hr. 14.5 lb./hr.Labor and Overhead Rate $50/hr $50/hr.

Cost perweight = +

Electrode CostEfficiency

Labor + Overhead Rate(Deposition Rate) (Operating Factor)

Cost perweight = $2.05 + $30.30 = $32.35/lb.= +

$1.2360%

$50.00(5.5) (30%)

Cost perweight = +

$2.2780%

$50.00(14.5) (40%) = $2.84 + $8.62 = $11.46/lb.

For SMAW:

For FCAW:

15

In the SMAW example, the electrode cost is approxi-mately 6% of the total cost. For the FCAW example, pri-marily due to a decrease in the labor content, theelectrode cost is 25% of the total. By using FCAW, thetotal cost of welding was decreased approximately 65%.While the FCAW electrode costs 85% more than theSMAW electrode, the higher electrode efficiency reducesthe increase in electrode cost to only 39%.

The first priority that must be maintained when selectingwelding processes and procedures is the achievement ofthe required weld quality. For different welding methodswhich deliver the required quality, it is generally advan-tageous to utilize the method that results in higher depo-sition rates and higher operating factors. This will resultin reduced welding time with a corresponding decreasein the total building erection cycle, which will generallytranslate to a direct savings for the final owner, not onlylowering the cost of direct labor, but also reducing con-struction loan costs.

5 Welding Procedures

Within the welding industry, the term WeldingProcedure Specification (or WPS) is used to signify thecombination of variables that are to be used to make acertain weld. The terms Welding Procedure, or simplyProcedure, may be used. At a minimum, the WPS con-sists of the following:

WPS Variables

Process (SMAW, FCAW, etc.)Electrode specification (AWS A5.1, A5.20, etc.)Electrode classification (E7018, E71T-1, etc.)Electrode diameter (1/8 in., 5/32 in., etc.)Electrical characteristics (AC, DC+, DC-)Base metal specification (A36, A572 Gr50, etc.)Minimum preheat and

interpass temperatureWelding current (amperage)/wire feed speedArc voltageTravel speedPosition of weldingPost weld heat treatmentShielding gas type and flow rateJoint design details

The welding procedure is somewhat analogous to acooks recipe. It outlines the steps required to make aweld of the required quality under specific conditions.

5.1 Effects of Welding Variables

The effects of the variables are somewhat dependent onthe welding process being employed, but general trendsapply to all the processes. It is important to distinguishthe difference between constant current (CC) and con-stant voltage (CV) electrical welding systems. Shieldedmetal arc welding is always done with a CC system.Flux cored welding and gas metal arc welding generallyare performed with CV systems. Submerged arc mayutilize either.

Amperage is a measure of the amount of current flowingthrough the electrode and the work. It is a primary vari-able in determining heat input. Generally, an increase inamperage means higher deposition rates, deeper penetra-tion, and more admixture. The amperage flowingthrough an electrical circuit is the same, regardless ofwhere it is measured. It may be measured with a tongmeter or with the use of an electrical shunt. The role ofamperage is best understood in the context of heat inputand current density considerations. For CV welding, anincrease in wire feed speed will directly increase amper-age. For SMAW on CC systems, the machine settingdetermines the basic amperage, although changes in thearc length (controlled by the welder) will further changeamperage. Longer arc lengths reduce amperage.

Arc voltage is directly related to arc length. As the volt-age increases, the arc length increases, as does thedemand for arc shielding. For CV welding, the voltageis determined primarily by the machine setting, so the arclength is relatively fixed in CV welding. For SMAW onCC systems, the arc voltage is determined by the arclength, which is manipulated by the welder. As arclengths are increased with SMAW, the arc voltage willincrease, and the amperage will decrease. Arc voltagealso controls the width of the weld bead, with highervoltages generating wider beads. Arc voltage has a directeffect on the heat input computation.

The voltage in a welding circuit is not constant, but iscomposed of a series of voltage drops. Consider the fol-lowing example: assume the power source delivers a totalsystem voltage of 40 volts. Between the power sourceand the welding head or gun, there is a voltage drop ofperhaps 3 volts associated with the input cable resistance.From the point of attachment of the work lead to thepower source work terminal, there is an additional volt-age drop of, say, 7 volts. Subtracting the 3 volts and the

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7 volts from the original 40, this leaves 30 volts for thearc. This example illustrates how important it is toensure that the voltages used for monitoring welding pro-cedures properly recognize any losses in the welding cir-cuit. The most accurate way to determine arc voltage isto measure the voltage drop between the contact tip andthe work piece. This may not be practical for semiauto-matic welding, so voltage is typically read from a pointon the wire feeder (where the gun and cable connectionis made), to the workpiece. For SMAW welding, voltageis not usually monitored, since it is constantly changingand cannot be controlled except by the welder. Skilledwelders hold short arc lengths to deliver the best weldquality.

Travel speed, measured in inches per minute, is the rateat which the electrode is moved relative to the joint. Allother variables being equal, travel speed has an inverseeffect on the size of the weld beads. As the travel speedincreases, the weld size will decrease. Extremely lowtravel speeds may result in reduced penetration, as the arcimpinges on a thick layer of molten metal and the weldpuddle rolls ahead of the arc. Travel speed is a key vari-able used in computing heat input; reducing travel speedincreases heat input.

Wire feed speed is a measure of the rate at which theelectrode is passed through the welding gun and deliv-ered to the arc. Typically measured in inches per minute(ipm) the wire feed speed is directly proportional todeposition rate, and directly related to amperage. Whenall other welding conditions are maintained constant(e.g., the same electrode type, diameter, electrode exten-sion, arc voltage, and electrode extension), an increase inwire feed speed will directly lead to an increase inamperage. For slower wire feed speeds, the ratio of wirefeed speed to amperage is relatively constant and linear.

For higher levels of wire feed speed, it is possible toincrease the wire feed speed at a disproportionately highrate compared to the increase in amperage. When theseconditions exist, the deposition rate per amp increases,but at the expense of penetration.

Wire feed speed is the preferred method of maintainingwelding procedures for constant voltage wire feedprocesses. The wire feed speed can be independentlyadjusted, and measured directly, regardless of the otherwelding conditions. It is possible to utilize amperage asan alternative to wire feed speed although the resultantamperage for a given wire feed speed may vary, depend-

ing on the polarity, electrode diameter, electrode type,and electrode extension. Although equipment has beenavailable for twenty years that monitors wire feed speed,many codes such as AWS D1.1 continue to acknowledgeamperage as the primary method for procedure docu-mentation. D1.1 does permit the use of wire feed speedcontrol instead of amperage, providing a wire feed speedamperage relationship chart is available for comparison.Specification sheets for various Lincoln electrodes pro-vide data that report these relationships.

Electrode extension, also known as stickout, or ESO,is the distance from the contact tip to the end of the elec-trode. It applies only to the wire fed processes. As theelectrode extension is increased in a constant voltage sys-tem, the electrical resistance of the electrode increases,causing the electrode to be heated. This is known asresistance heating or I2R heating. As the amount ofheating increases, the arc energy required to melt theelectrode decreases. Longer electrode extensions may beemployed to gain higher deposition rates at a givenamperage. When the electrode extension is increasedwithout any change in wire feed speed, the amperage willdecrease. This results in less penetration and less admix-ture. With the increase in electrode stickout, it is com-mon to increase the machine voltage setting tocompensate for the greater voltage drop across the elec-trode.

In constant voltage systems, it is possible to simultane-ously increase the electrode stickout and wire feed speedin a balanced manner so that the current remains con-stant. When this is done, higher deposition rates areattained. Other welding variables such as voltage andtravel speed must be adjusted to maintain a stable arc andto ensure quality welding. The ESO variable shouldalways be within the range recommended by the manu-facturer.

Electrode diameter Larger electrodes can carry high-er welding currents. For a fixed amperage, however,smaller electrodes result in higher deposition rates. Thisis because of the effect on current density discussedbelow.

Polarity is a definition of the direction of current flow.Positive polarity (reverse) is achieved when the electrodelead is connected to the positive terminal of the directcurrent (DC) power supply. The work lead is connectedto the negative terminal. Negative polarity (straight)occurs when the electrode is connected to the negative

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terminal and the work lead to the positive terminal.Alternating current (AC) is not a polarity, but a currenttype. With AC, the electrode is alternately positive andnegative. Submerged arc is the only process that com-monly uses either electrode positive or electrode negativepolarity for the same type of electrode. AC may also beused. For a fixed wire feed speed, a submerged arc elec-trode will require more amperage on positive polaritythan on negative. For a fixed amperage, it is possible toutilize higher wire feed speeds and deposition rates withnegative polarity than with positive. AC exhibits a mixof both positive and negative polarity characteristics.The magnetic field that surrounds any DC conductor cancause a phenomenon known as arc blow, where the arc isphysically deflected by the field. The strength of themagnetic field is proportional to the square of the currentvalue, so this is a more significant potential problem withhigher currents. AC is less prone to arc blow, and cansometimes be used to overcome this phenomenon.

Heat input is proportional to the welding amperage,times the arc voltage, divided by the travel speed. Higherheat inputs relate to larger weld cross sectional areas, andlarger heat affected zones, which may negatively affectmechanical properties in that region. Higher heat inputusually results in slightly decreased yield and tensilestrength in the weld metal, and generally lower notchtoughness because of the interaction of bead size andheat input.

Current density is determined by dividing the weldingamperage by the cross sectional area of the electrode. Forsolid electrodes, the current density is therefore proportion-al to I/d2. For tubular electrodes where current is conduct-ed by the sheath, the current density is related to the area ofthe metallic cross section. As the current density increases,there will be an increase in deposition rates, as well as pen-etration. The latter will increase the amount of admixturefor a given joint. Notice that this may be accomplished byeither increasing the amperage or decreasing the electrodesize. Because the electrode diameter is a squared function,a small decrease in diameter may have a significant effecton deposition rates and plate penetration.

Preheat and interpass temperature are used to controlcracking tendencies, typically in the base materials.Regarding weld metal properties, for most carbon-man-ganese-silicon systems, a moderate interpass temperaturepromotes good notch toughness. Preheat and interpasstemperatures greater than 550F may negatively affect

notch toughness (AWS Position Statement, p. 7). Whenthe base metal receives little or no preheat, the resultantrapid cooling may also lead to a deterioration of notchtoughness. Therefore, careful control of preheat andinterpass temperatures is critical.

5.2 Purpose of Welding Procedure Specifications

The particular values for the variables discussed in 5.1have a significant effect on weld soundness, mechanicalproperties, and productivity. It is therefore critical thatthose procedural values used in the actual fabrication anderection be appropriate for the specific requirements ofthe applicable code and job specifications. Welds thatwill be architecturally exposed, for example, should bemade with procedures that minimize spatter, encourageexceptional surface finish, and have limited or no under-cut. Welds that will be covered with fireproofing, in con-trast, would naturally have less restrictive cosmeticrequirements.

Many issues must be considered when selecting weldingprocedure values. While all welds must have fusion toensure their strength, the required level of penetration is afunction of the joint design and the weld type. All weldsare required to deliver a certain yield and/or tensilestrength, although the exact level required is a function ofthe connection design. Not all welds are required todeliver minimum specified levels of notch toughness.Acceptable levels of undercut and porosity are a functionof the type of loading applied to the weld. Determinationof the most efficient means by which these conditions canbe met cannot be left to the welders, but is determined byknowledgeable welding technicians and engineers whocreate written Welding Procedure Specifications (WPSs)and communicate those requirements to welders by themeans of these documents. The WPS is the primary toolthat is used to communicate to the welder, supervisor, andthe inspector how a specific weld is to be made. The suit-ability of a weld made by a skilled welder in conformancewith the requirements of a WPS can only be as good asthe WPS itself. The proper selection of procedural vari-able values must be achieved in order to have a WPSappropriate for the application. This is the job of thewelding expert who generates or writes the WPS. Thewelder is generally expected to be able to follow theWPS, although the welder may not know how or whyeach particular variable was selected. Welders are expect-ed to ensure welding is performed in accordance with theWPS. Inspectors do not develop WPSs, but should ensurethat they are available and are followed.

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The D1.1-96 Structural Welding Code - Steel requireswritten welding procedures for all fabrication performed(D1.1-96, paragraph 5.5). The inspector is obligated toreview the WPSs and to make certain that productionwelding parameters conform to the requirements of thecode (D1.1-96, paragraph 6.3.1). These WPSs arerequired to be written, regardless of whether they are pre-qualified or qualified by test (sections 5.3 and 5.5). Eachfabricator or erector is responsible for the developmentof WPSs (D1.1-96, paragraph 4.1.1.1, 4.6). Confusionon this issue apparently still exists since there continue tobe reports of fabrication being performed in the absenceof written welding procedure specifications. One preva-lent misconception is that if the actual parameters underwhich welding will be performed meet all the conditionsfor prequalified status, written WPSs are not required.This is not true. As has been shown in the cited code ref-erences, the requirement is clear.

The WPS is a communication tool, and it is the primarymeans of communication to all the parties involvedregarding how the welding is to be performed. It musttherefore be readily available to foremen, inspectors andthe welders.

The code is not prescriptive in its requirements regardingthe availability and distribution of WPSs. Some shopfabricators have issued each welder employed in theirorganization with a set of welding procedures that aretypically retained in the welders locker or tool box.Others have listed WPS parameters on shop drawings.Some company bulletin boards have listings of typicalWPSs used in the organization. The AWS D1. PositionStatement suggest that WPSs should be posted near thepoint where welding is being performed. Regardless ofthe method used, WPSs must be available to those autho-rized to use them.

It is in the contractors best interest to ensure efficientcommunication with all parties involved. Not only canquality be compromised when WPSs are not available,but productivity can suffer as well. Regarding quality,the limits of suitable operation of the particular weldingprocess and electrode for the steel, joint design and posi-tion of welding must be understood. It is obvious that theparticular electrode employed must be operated on theproper polarity, that proper shielding gases are used, thatamperage levels be appropriate for the diameter of elec-trode, and appropriate for the thickness of material onwhich welding is performed. Other issues may not be soobviously apparent. The required preheat for a particular

application is a function of the grade(s) of steel involved,the thickness(es) of material, and the type of electrodeemployed (whether low hydrogen or non-low hydrogen).The required preheat level can all be communicated bymeans of the written WPS.

Lack of conformance with the parameters outlined in theWPS may result in the deposition of a weld that does notmeet the quality requirements imposed by the code or thejob specifications. When an unacceptable weld is made,the corrective measures to be taken may necessitate weldremoval and replacement, an activity that routinelyincreases the cost of that particular weld tenfold.Avoiding these types of unnecessary activities by clearcommunication has obvious quality and economic rami-fications.

Equipment such as Lincoln Electrics LN-9 wire feeder,which has the ability to have preset welding parameters,coupled with a digital LED display that indicates opera-tional parameters, can assist in maintaining and monitor-ing WPS parameters. Analog meters can be used onother wire feeders.

The code imposes minimum requirements for a givenproject. Additional requirements may be imposed bycontract specifications. The same would hold trueregarding WPS values. Compliance with the minimumrequirements of the code may not be adequate under allcircumstances. Additional requirements can be commu-nicated through the WPS. For example, the D1.1-96code permits the use of an E71T-11 FCAW electrode formultiple pass welding without any restriction on platethickness. The Lincoln Electric product, InnershieldNR211MP, has a maximum thickness restrictionimposed by the manufacturer of 1/2 in. This additionalrequirement can be incorporated into the applicableWPS. Other recommendations that may be imposed bythe steel producer, electrode manufacturer, or others canand should be documented in the WPS.

5.3 Prequalified Welding Procedure Specifications

The AWS D1.1 code provides for the use of prequalifiedWPSs. Prequalified WPSs are those that the AWS D1Committee has determined to have a history of acceptableperformance, and so they are not subject to the qualifica-tion testing imposed on all other welding procedures. Theuse of prequalified WPSs does not preclude their need tobe in a written format. The use of prequalified WPSs stillrequires that the welders be appropriately qualified. All

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the workmanship provisions imposed in the fabricationsection of the code apply to prequalified WPSs. The onlycode requirement exempted by prequalification is thenondestructive testing and mechanical testing required forqualification of welding procedures.

A host of restrictions and limitations imposed on pre-qualified welding procedures do not apply to weldingprocedures that are qualified by test. Prequalified weld-ing procedures must conform with all the prequalifiedrequirements in the code. Failure to comply with a sin-gle prequalified condition eliminates the opportunity forthe welding procedure to be prequalified (D1.1-96, para-graph 3.1).

The use of a prequalified welding procedure does notexempt the engineer from exercising engineering judg-ment to determine the suitability of the particular proce-dure for the specific application (D1.1-96, paragraph 3.1).

In order for a WPS to be prequalified, the following con-ditions must be met:

The welding process must be prequalified. OnlySMAW, SAW, GMAW (except GMAW-s), and FCAWmay be prequalified (D1.1-96, paragraph 3.2.1).

The base metal/filler metal combination must be pre-qualified. Prequalified base metals, filler metals, andcombinations are shown in D1.1-96, paragraph 3.3,Table 3.1.

The minimum preheat and interpass temperatures pre-scribed in D1.1-96, paragraph 3.3, Table 3.2 must beemployed (D1.1-96, paragraph 3.5).

Specific requirements for the various weld types mustbe maintained. Fillet welds must be in accordancewith D1.1-96, paragraph 3.9, plug and slot welds inaccordance with D1.1-96, paragraph 3.10, and groovewelds in accordance with D1.1-96, paragraphs 3.11,3.12, and 3.13, as applicable. For the groove welds,whether partial joint penetration or complete joint pen-etration, the required groove preparation dimensionsare shown in D1.1-96, Figures 3.3 and 3.4.

Even if prequalified joint details are employed, the weld-ing procedure must be qualified by test if other prequali-fied conditions are not met. For example, if aprequalified detail is used on an unlisted steel, the weld-ing procedures must be qualified by test.

Prequalified status requires conformance to a variety ofprocedural parameters. These are largely contained inD1.1-96, Table 3.7, and include maximum electrodediameters, maximum welding current, maximum rootpass thickness, maximum fill pass thicknesses, maxi-mum single-pass fillet weld sizes, and maximum singlepass weld layers (D1.1-96, Table 3.3).

In addition to all the preceding requirements, weldingperformed with a prequalified WPS must be in confor-mance with the other code provisions contained in thefabrication section of AWS D1.1-96 Structural WeldingCode.

The code does not imply that a prequalified WPS willautomatically achieve the quality conditions required bythe code. It is the contractors responsibility to ensurethat the particular parameters selected within the require-ments of the prequalified WPS are suitable for the spe-cific application. An extreme example will serve as anillustration. Consider a (hypothetical) proposed WPS formaking a 1/4 in. fillet weld on 3/8 in. A36 steel in the flatposition. The weld type and steel are prequalified. SAW,a prequalified process, is selected. The filler metalselected is F7A2-EM12K, meeting the requirements ofD1.1-96, Table 3.1. No preheat is specified since itwould not be required according to D1.1-96, Table 3.2.The electrode diameter selected is 3/32 in., less than the1/4 in. maximum specified in D1.1- 96, Table 3.7. Themaximum single pass fillet weld size in the flat position,according to D1.1-96, Table 3.7, is unlimited, so the 1/4in. fillet size can be prequalified. The current levelselected for making this particular fillet weld is 800amps, less than the 1000 amp maximum specified inD1.1-96, Table 3.7.

However, the amperage level imposed on the electrodediameter for the thickness of steel on which the weld isbeing made is inappropriate. It would not meet therequirements of D1.1-96, paragraph 5.3.1.2, whichrequires that the size of electrode and amperage be suit-able for the thickness of material being welded. Thisillustration demonstrates the fact that compliance with allprequalified conditions does not guarantee that the com-bination of selected variables will always generate anacceptable weld.

Most contractors will determine preliminary values for aprequalified WPS based upon their experience, recom-mendations from publications such as Lincoln ElectricsProcedure Handbook of Arc Welding, the AWS Welding

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Handbooks, AWS Welding Procedures Specifications(AWS B2.1), or other sources. It is the responsibility ofthe contractor to verify the suitability of the suggestedparameters prior to applying the actual procedure on aproject, although the verification test need not be subjectto the full range of procedure qualification tests imposedby the code. Typical tests will be made to determinesoundness of the weld deposit (e.g., fusion, tie-in of weldbeads, freedom from slag inclusions, etc.). The platecould be nondestructively tested or, as is more common-ly done, cut, polished, and etched. The latter operationsallow for examination of penetration patterns, beadshapes, and tie-in. Welds that are made with prequalifiedWPSs meeting the physical dimensional requirements(fillet weld size, maximum reinforcement levels, and sur-face profile requirements), and that are sound (that is,adequate fusion, tie-in and freedom from excessive slagcharacterized by inclusions and porosity) should meetthe strength and ductility requirements imposed by thecode for welding procedures qualified by test. Weldsoundness, however, cannot be automatically assumedjust because the WPS is prequalified.

5.4 Guidelines For Preparing Prequalified WPSs

When developing prequalified WPSs, the starting point isa set of welding parameters appropriate for the generalapplication being considered. P