what every engineer should know about welding

primary variable in determiningheat input. Generally, an increase inamperage means higher depositionrates, deeper penetration, and moreadmixture. The amperage flowingthrough an electrical circuit is thesame, regardless of where it is mea-sured. It may be measured with atong meter or with the use of anelectrical shunt. The role of amper-age is best understood in the contextof heat input and current densityconsiderations. For CV welding, anincrease in wire feed speed willdirectly increase amperage. ForSMAW on CC systems, the machinesetting determines the basic amper-age, although changes in the arclength (controlled by the welder) willfurther change amperage. Longerarc lengths reduce amperage.

Arc voltage is directly related toarc length. As the voltage increases,the arc length increases, as does thedemand for arc shielding. For CVwelding, the voltage is determinedprimarily by the machine setting, sothe arc length is relatively fixed inCV welding. For SMAW on CC sys-tems, however, the arc voltage isdetermined by the arc length, whichis manipulated by the welder. As arclengths are increased with SMAW,the arc voltage will increase, and theamperage will decrease. Arc voltagealso controls the width of the weldbead, with higher voltages generat-ing wider beads. Arc voltage has adirect effect on the heat input com-putation.

The voltage in a welding circuitis not constant, but is composed of aseries of voltage drops. Consider thefollowing example: assume thepower source delivers a total systemvoltage of 40 volts. Between thepower source and the welding head

Modern Steel Construction / May 1997

WITHIN THE WELDING INDUS-TRY, THE TERM WELDINGPROCEDURE SPECIFICATION(or WPS) is used to signify the com-bination of variables used to make acertain weld. At a minimum theWPS (or Welding Procedure orsimply Procedure) consists of:process (Shielded Metal Arc Welding[SMAW], Flux Cored Arc Welding[FCAW], etc.); electrode specification(AWS A5.1, A5.20, etc.); electrodeclassification (E7018, E71T-1, etc.);electrode diameter; electrical charac-teristics ( (AC, DC+, DC-); basemetal specification (A36, A572 Gr.50, etc.); minimum preheat andinterpass temperature; welding cur-rent (amperage)/wire feed speed; arcvoltage; travel speed; position ofwelding; post weld heat treatment;shielding gas type and flow rate; andjoint design details.

The welding procedure is some-what analogous to a cooks recipe: Itoutlines the steps required to makea quality weld under specific condi-tions.

EFFECTS OF WELDING VARIABLESThe effects of the variables are

somewhat dependent on the weldingprocess being employed, but generaltrends apply to all the processes. Itis important to distinguish the dif-ference between constant current(CC) and constant voltage (CV) elec-trical welding systems. Shieldedmetal arc welding is always donewith a CC system, while flux coredwelding and gas metal arc weldinggenerally are performed with CVsystems. Submerged arc may utilizeeither.

Amperage is a measure of theamount of current flowing throughthe electrode and the work. It is a

WHAT EVERYENGINEER

SHOULD KNOWABOUT WELDING

From amperageto preheat,

theres more towelding

procedures thanmeets the eyeBy Duane K. Miller, P.E.

or gun, there is a voltage drop of per-haps 3 volts associated with theinput cable resistance. From thepoint of attachment of the work headto the power source work terminal,there is an additional voltage dropof, say, 7 volts. Subtracting the 3volts and the 7 volts from the origi-nal 40 leaves 30 volts for the arc.This example illustrates how impor-tant it is to ensure that the voltagesused for monitoring welding proce-dures properly recognize any lossesin the welding circuit. The mostaccurate way to determine arc volt-age is to measure the voltage dropbetween the contact tip and thework piece. However, this may notbe practical for semiautomatic weld-ing, so voltage is typically read froma point on the wire feeder (where thegun and cable connection is made),to the workpiece. For SMAW weld-ing, voltage is not usually moni-tored, since it is constantly changingand cannot be controlled except bythe welder. Skilled welders holdshort arc lengths to deliver the bestweld quality.

Travel speed, measured in inch-es per minute, is the rate at whichthe electrode is moved relative to thejoint. All other variables beingequal, travel speed has an inverseeffect on the size of the weld beads.As the travel speed increases, theweld size will decrease. Extremelylow travel speeds may result inreduced penetration, as the arcimpinges on a thick layer of moltenmetal and the weld puddle rollsahead of the arc. Travel speed is akey variable used in computing heatinput (reducing travel speed increas-es heat input).

Wire feed speed is a measure ofthe rate at which the electrode ispassed through the welding gun anddelivered to the arc. Typically mea-sured in inches per minute (ipm),the deposition rates are directly pro-portional to wire feed speed anddirectly related to amperage. Whenall other welding conditions aremaintained constant, an increase inwire feed speed will directly lead toan increase in amperage. For slowerwire feed speeds, the ratio of wirefeed speed to amperage is relativelyconstant and linear. For higher wirefeed speeds, this ratio may increase,resulting in a higher deposition rateper amp, but at the expense of pene-tration.


Wire feed speed is the preferredmethod of maintaining welding pro-cedures for constant voltage wirefeed processes. The wire feed speedcan be independently adjusted andmeasured directly, regardless of theother welding conditions. It is possi-ble to utilize amperage as an alter-native to wire feed speed althoughthe resultant amperage for a givenwire feed speed may vary, dependingon polarity, electrode diameter, elec-trode type and electrode extension.Although equipment has been avail-able for two decades that monitorwire feed speed, many codes such asAWS D1.1 continue to acknowledgeamperage as the primary method forprocedure documentation. D1.1 doespermit the use of wire feed speedcontrol instead of amperage, provid-ing a wire feed speed-amperage rela-tionship chart is available for com-parison. Specification sheetssupplied by the filler metal manufac-turer provide data that supportthese relationships.

Electrode extension, also knownas electrical stickout or ESO, is thedistance from the contact tip to theend of the electrode. It applies onlyto the wire fed processes. As the

electrode extension is increased in aconstant voltage system, the electri-cal resistance of the electrodeincreases, causing the electrode to beheated. This is known as resistanceheating or I2R heating. As theamount of heating increases, the arcenergy required to melt the electrodedecreases. Longer electrode exten-sions may be employed to gain high-er deposition rates at a given amper-age. When the electrode extension isincreased without any change inwire feed speed, the amperage willdecrease. This results in less pene-tration and less admixture. With theincrease in electrical stickout, it iscommon to increase the machinevoltage setting to compensate for thegreater voltage drop across the elec-trode.

In constant voltage systems, it ispossible to simultaneously increaseboth the ESO and the wire feedspeed in a balanced manner so thatthe current remains constant. Whenthis is done, higher deposition ratesare attained. Other welding vari-ables, such as voltage and travelspeed, must be adjusted to maintaina stable arc and to ensure qualitywelding. The ESO variable should

always be within the range recom-mended by the manufacturer.

Electrode diameter is anothercritical variable. Larger electrodescan carry higher welding currents.For a fixed amperage, however,smaller electrodes result in higherdeposition rates. This is because ofthe effect on current density dis-cussed below.

Polarity is a definition of thedirection of current flow. Positivepolarity (reverse) is achieved whenthe electrode lead is connected to thepositive terminal of the direct cur-rent (DC) power supply. The worklead is connected to the negative ter-minal. Negative polarity (straight)occurs when the electrode is connect-ed to the negative terminal and thework lead to the positive terminal.Alternating current (AC) is not apolarity, but a current type. WithAC, the electrode is alternately posi-tive and negative. Submerged arc isthe only process that commonly useseither electrode positive and elec-trode negative polarity for the sametype of electrode. AC may also beused. For a fixed wire feed speed, asubmerged arc electrode will requiremore amperage on positive polaritythan on negative. For a fixedamperage, it is possible to utilizehigher wire feed speeds and deposi-tion rates with negative polaritythan with positive. AC exhibits amix of both positive and negativepolarity characteristics.

The magnetic field that sur-rounds any DC conductor can causea phenomenon known as arc blow,where the arc is physically deflectedby the field. The strength of themagnetic field is proportional to thesquare of the current value, so thisis a more significant potential prob-lem with higher currents. AC is lessprone to arc blow, and can some-times be used to overcome this phe-nomenon.

Heat input is proportional tothe welding amperage, times the arcvoltage, divided by the travel speed.Higher heat inputs relate to largerweld cross sectional areas, and larg-er heat affected zones, which maynegatively affect mechanical proper-ties in that region. Higher heatinput generally results in slightlydecreased yield and tensile strengthin the weld metal, and generallylower notch toughness because ofthe interaction of bead size and heat


input. Current density is determined

by dividing the welding amperage bythe cross sectional area of the elec-trode. For solid electrodes, the cur-rent density is therefore proportion-al to I/d2. For tubular electrodeswhere current is conducted by thesheath, the current density is relat-ed to the area of the metallic crosssection. As the current densityincreases, there will be an increasein deposition rates, as well as pene-tration. The latter will increase theamount of admixture for a givenjoint. Notice that this may beaccomplished by either increasingthe amperage or decreasing the elec-trode size. Because the electrodediameter is a squared function, asmall decrease in diameter mayhave a significant effect on deposi-tion rates and plate penetration.

Preheat and interpass tempera-ture are used to control crackingtendencies, typically in the basematerials. Regarding weld metalproperties, for most carbon-man-ganese-silicon systems, a moderateinterpass temperature promotesgood notch toughness. Preheat andinterpass temperatures greater than550 degrees F may negatively affectnotch toughness. When the basemetal receives little or no preheat,the resultant rapid cooling may alsolead to a deterioration of notchtoughness. Therefore, careful con-trol of preheat and interpass tem-peratures is critical.

PURPOSE OF WPSSThe particular values for the vari-

ables discussed above have signifi-cant affect on weld soundness,mechanical properties, and produc-tivity. It is therefore critical thatthose procedural values used in theactual fabrication and erection beappropriate for the specific require-ments of the applicable code and jobspecifications. Welds that will bearchitecturally exposed, for example,should be made with proceduresthat minimize spatter, encourageexceptional surface finish, and havelimited or no undercut. Welds thatwill be covered with fireproofing, incontrast, would naturally have lessrestrictive cosmetic requirements.

Many issues must be consideredwhen selecting welding procedurevalues. While all welds mustachieve fusion to ensure their

strength, the required level of pene-tration is a function of the jointdesign in the weld type. All weldsare required to deliver a certainyield and/or tensile strength,although the exact level required isa function of the connection design.Not all welds are required to deliverminimum specified levels of notchtoughness. Acceptable levels ofundercut and porosity are a functionof the type of loading applied to theweld. Determination of the mostefficient means by which these con-ditions can be met cannot be left tothe welders, but is determined byknowledgeable welding techniciansand engineers who create writtenwelding procedure specifications andcommunicate those requirements towelders by the means of these docu-ments. The WPS is the primary toolthat is used to communicate to thewelder, supervisor, and the inspectorhow a specific weld is to be made.The suitability of a weld made by askilled welder in conformance withthe requirements of a WPS can onlybe as good as the WPS itself.Procedural variable values must beproperly selected in order to have aWPS appropriate for the application.

The ability of a welder to follow awritten WPS is determined bywelder qualification tests (D1.1-96,paragraph C4.1.2). The welder maynot know how or why each particu-lar variable was selected, althoughthese values must be used in produc-tion. The inspector is required toensure that all welding is done inaccordance with the WPS, observingthe technique of each welder on aperiodic basis (D1.1-96, paragraph6.5.4). Inspectors do not developWPSs, but they must ensure the pro-cedures exist and are followed (D1.1-96, paragraph 6.3.1).

The D1.1-96 Structural WeldingCode - Steel requires written weld-ing procedures for all fabricationperformed (D1.1-96, paragraph 5.5).These WPSs are required to be writ-ten, regardless of whether they areprequalified or qualified by test.Each fabricator or erector is respon-sible for the development of WPSs(D1.1-96, paragraph 4.1.1.1, 4.6).Confusion about this issue apparent-ly still exists since there continue tobe reports of fabrication being per-formed in the absence of writtenwelding procedure specifications.One prevalent misconception is that

if the actual parameters underwhich welding will be performedmeet all the conditions for prequali-fied status, written WPSs are notrequired. This is not true. As hasbeen shown in the cited code refer-ences, the requirement is clear.

The WPS is a communicationtool, and it is the primary means ofcommunication to all the partiesinvolved regarding how the weldingis to be performed. It must thereforebe readily available to foremen,inspectors and the welders. Thecode is not prescriptive in itsrequirements regarding availabilityand distribution of WPSs. Someshop fabricators have issued eachwelder employed in their organiza-tion with a set of welding proceduresthat are typically retained in thewelders locker or tool box. Othershave listed WPS parameters on shopdrawings. Some company bulletinboards have listings of typical WPSsused in the organization. Regardlessof the method used, WPSs must beavailable to those authorized to usethem.

It is in the contractors best inter-est to ensure that efficient communi-cation is maintained with all partiesinvolved. Not only can quality becompromised when WPSs are notavailable, but productivity can sufferas well. Regarding quality, the lim-its of suitable operation of the par-ticular welding process and electrodefor the steel, joint design and posi-tion of welding must be understood.Obviously, the particular electrodeemployed must be operated on theproper polarity, proper shieldinggases must be used, and amperagelevels must be appropriate for thediameter of electrode, and for thethickness of material on which weld-ing is performed. Other issues maynot be as obvious. For example, therequired preheat for a particularapplication is a function of thegrade(s) of steel involved, the thick-ness(es) of material, and the type ofelectrode employed (whether lowhydrogen or non-low hydrogen). Allof this can be communicated bymeans of the written WPS.

Lack of conformance with theparameters outlined in the WPSmay result in the deposition of aweld that does not meet the qualityrequirements imposed by the code orthe job specifications. When anunacceptable weld is made, the cor-


rective measures to be taken maynecessitate weld removal andreplacement, an activity that rou-tinely increases the cost of that par-ticular weld tenfold. Avoiding thesetypes of unnecessary activities byclear communication has obviousquality and economic ramifications.

There are other economic issuesto be considered as well. In a mostgeneral way, the cost of welding isinversely proportional to the deposi-tion rate. The deposition rate, inturn, is directly tied to the wire feedspeed of the semiautomatic weldingprocesses. If it is acceptable, forexample, to make a given weld witha wire feed speed of 200 ipm, then aweld made at 160 ipm (which maymeet all the quality requirements)would cost approximately 25% morethan the weld made at the optimumprocedure. Conformance with WPSvalues can help ensure that con-struction is performed at rates thatare conducive to the required weldquality and are economical as well.

The code imposes minimumrequirements for a given project.Additional requirements may beimposed by contract specifications.The same would hold true regardingWPS values. Compliance with theminimum requirements of the codemay not be adequate under all cir-cumstances. Additional require-ments can be communicated throughthe WPS. For example, the D1.1-96code permits the use of an E71T-11FCAW electrode for multiple passwelding without any restriction onplate thickness. The LincolnElectric product, InnershieldNR211MP, has a maximum thick-ness restriction imposed by the man-ufacturer of 1/2. This additionalrequirement can be incorporatedinto the applicable WPS. Other rec-ommendations that may be imposedby the steel producer, electrode man-ufacturer, or others can and shouldbe documented in the WPS.

PREQUALIFIED PROCEDURESThe AWS D1.1 code provides for

the use of prequalified WPSs.Prequalified WPSs are those thatthe AWS D1 Committee has deter-mined to have a history of accept-able performance, and so does notsubject them to the qualificationtesting imposed on all other weldingprocedures. The use of prequalifiedWPSs does not preclude the require-

ment that they be written. The useof prequalified WPSs still requiresthat the welders be appropriatelyqualified. All the workmanship pro-visions imposed in the fabricationsection of the code apply to prequali-fied WPSs. The only code require-ment exempted by prequalificationis the nondestructive testing andmechanical testing required forqualification testing of welding pro-cedures.

A host of restrictions and limita-tions imposed on prequalified weld-ing procedures do not apply to weld-ing procedures that are qualified bytest. Prequalified welding proce-dures must conform with all the pre-qualified requirements in the code.Failure to comply with a single pre-qualified condition eliminates theopportunity for the welding proce-dure to be prequalified (D1.1-96,paragraph 3.1).

In order for a WPS to be prequali-fied, the following conditions mustbe met: The welding process must be pre-

qualified. Only SMAW, SAW,GMAW (except GMAW-s), andFCAW may be prequalified(D1.1-96, paragraph 3.2.1).

The base metal/filler metal com-bination must be prequalified.Prequalified base metals, fillermetals, and combinations areshown in D1.1-96, paragraph 3.3,Table 3.1.

The minimum preheat and inter-pass temperatures prescribed inD1.1-96, paragraph 3.3, Table3.2 must be employed (D1.1-96,paragraph 3.5).

Specific requirements for the var-ious weld types must be main-tained. Fillet welds must be inaccordance with D1.1-96, para-graph 3.9, plug and slot welds inaccordance with D1.1-96, para-graph 3.10, and groove welds inaccordance with D1.1-96, para-graph 3.11, 3.12, and 3.13 asapplicable. For the groove welds,whether partial joint penetrationor complete joint penetration, therequired groove preparationdimensions are shown in D1.1-96,Figures 3.3 and 3.4. Even if prequalified joint details

are employed, the welding proceduremust be qualified by test if otherprequalified conditions are not met.For example, if a prequalified detailis used on an unlisted steel, thewelding procedures must be quali-fied by test.

Prequalified status requires con-formance to a variety of proceduralparameters. These are largely con-tained in D1.1-96, Table 3.7, andinclude maximum electrode diame-ters, maximum welding current,maximum root pass thickness, maxi-mum fill pass thicknesses, maxi-mum single-pass fillet weld sizes,and maximum single pass weld lay-ers (D1.1-96, Table 3.3). In additionto all the preceding requirements,welding performed with a prequali-fied WPS must be in conformancewith the other code provisions con-tained in the fabrication section ofAWS D1.1-96 Structural WeldingCode.

The code does not imply that aWPS that is prequalified will auto-matically achieve the quality condi-tions required by the code. The com-mentary language for paragraph3.2.1 states the following:

The use of prequalified jointsand procedures does not necessarilyguarantee sound welds. Fabricationcapability is still required, togetherwith effective and knowledgeablesupervision to consistently producesound welds. (AWS D1.1-96, para-graph C3.2.1)

It is the contractors responsibili-ty to ensure that the particularparameters selected within therequirements of the prequalifiedWPS are suitable for the specificapplication. An extreme examplewill serve as an illustration.Consider the following example of ahypothetical proposed WPS formaking a fillet weld on 3/8 A36steel in the flat position. The weldtype and steel are prequalified.SAW, a prequalified process, isselected. The filler metal selected isF7A2-EM12K, meeting the require-ments of D1.1-96, Table 3.1. No pre-heat is specified since it would notbe required according to D1.1-96,Table 3.2. The electrode diameterselected is 3/32, less than the max-imum specified in D1.1-96, Table3.7. The maximum single pass filletweld size in the flat position, accord-ing to D1.1-96, Table 3.7, is unlimit-ed, so the fillet size can be pre-qualified. The current level selectedfor making this particular fillet weldis 800 amps, less than the 1000 ampmaximum specified in D1.1-96,Table 3.7.

However, the amperage levelimposed on the electrode diameter

for the thickness of steel on whichthe weld is being made is inappro-priate. It would not meet therequirements of D1.1-96, paragraph5.3.1.2 in the section entitledFabrication, which requires that thesize of electrode and amperage besuitable for the thickness of materialbeing welded. This illustrationdemonstrates the fact that compli-ance with all prequalified conditionsdoes not guarantee that the combi-nation of selected variables willalways generate an acceptable weld.

Most contractors will determinepreliminary values for a prequalifiedWPS based upon their experience,recommendations from publicationssuch as Lincoln Electrics ProcedureHandbook of Arc Welding, industrypublications such as the AWSWelding Handbooks, from AWSWelding Procedure Specifications(AWS B2.1), or other sources. It isthe responsibility of the contractorto verify the suitability of the sug-gested parameters prior to the appli-cation of the actual procedure on aproject, although the verificationtest need not be subject to the fullrange of procedure qualificationtests imposed by the code. Typicaltests will be made to determinesoundness of the weld deposit (e.g.,fusion, tie-in of weld beads, freedomfrom slag inclusions, etc.). The platecould be nondestructively tested or,as is more commonly done, cut, pol-ished, and etched. The latter opera-tions allow for examination of pene-tration patterns, bead shapes, andtie-in. Welds made with prequali-fied WPSs that meet the physicaldimensional requirements (filletweld size, maximum reinforcementlevels, and surface profile require-ments), and are sound (that is, hav-ing adequate fusion, tie-in and free-dom from excessive slag inclusionsand porosity) should meet thestrength and ductility requirementsimposed by the code for welding pro-cedures qualified by test. Weldsoundness, however, cannot beassumed just because the WPS isprequalified.

GUIDELINESWhen developing prequalified

WPSs, the starting point is a set ofwelding parameters appropriate forthe general application being consid-ered. Parameters for overhead weld-ing will naturally vary from those


required for down-hand welding.The thickness of material involvedwill dictate electrode sizes and corre-sponding current levels. The specificfiller metals selected will reflect thestrength requirements of the connec-tion. Many other issues must beconsidered.

Depending on the level of famil-iarity and comfort the contractor haswith the particular values selected,welding a mock-up may be appropri-ate. Once the parameters that aredesired for use in production areestablished, it is essential to checkeach of the applicable parametersfor compliance with the D1.1-96code.

To assist in this effort, Annex Hhas been provided in the D1.1-96code. This contains a check list thatidentifies prequalified requirements.If any single parameter deviatesfrom these requirements, the con-tractor is left with two options: (1)the preliminary procedure can beadjusted to conform with the pre-qualified constraints; or, (2) theWPS can be qualified by test. If thepreliminary procedure is adjusted, itmay be appropriate to reexamine itsviability by another mock-up.

The next step is to document, inwriting, the prequalified WPS val-ues. A sample form is included inAnnex E of the code. The fabricatormay utilize any convenient format(D1.1-96, paragraph 3.6). Also con-tained in Annex E are a series ofexamples of completed WPSs thatmay be used as a pattern.

QUALIFYING BY TESTConducting qualification tests

There are two primary reasons whywelding procedures may be qualifiedby test. First, it may be a contractu-al requirement. Secondly, one ormore of the specific conditionsencountered in production may devi-ate from the prequalified require-ments. In either case, a test weldmust be made prior to the establish-ment of the final WPS. The firststep in qualifying a welding proce-dure by test is to determine the pro-cedure one wants to qualify. Thesame sources cited for the prequali-fied WPS starting points could beused for WPSs qualified by test.These will typically be the parame-ters used for fabrication of the testplate, although this is not alwaysthe case, as will be discussed later.

In the simplest case, the exact condi-tions that will be encountered inproduction will be replicated in theprocedure qualification test. Thiswould include the welding process,filler metal, grade of steel, jointdetails, thicknesses of material, pre-heat values, minimum interpasstemperature level, and the variouswelding parameters of amperage,voltage, and travel speed. The ini-tial parameters used to make theprocedure qualification test platebeg for a name to define them,although there is no standard indus-try term. It has been suggested thatTWPS be used where the T couldalternately stand for temporary,test, or trial. In any case, it woulddefine the parameters to be used formaking the test plate since thevalidity of the particular parameterscannot be verified until they havesuccessfully passed the requiredtest. The parameters for the testweld are recorded on a ProcedureQualification Record (PQR). Theactual values used should be record-ed on this document. The targetvoltage, for example, may be 30 voltsbut, in actual fact, only 29 volts wereused for making the test plate. The29 volts would be recorded.

After the test plate has beenwelded, it is allowed to cool and theplate is subjected to the visual andnondestructive testing as prescribedby the code. The specific testsrequired are a function of the type ofweld being made and the particularwelding consumables. The types ofqualification tests are described inD1.1-96, paragraph 4.4.

In order to be acceptable, the testplates must first pass visual inspec-tion followed by nondestructive test-ing (NDT) (D1.1-96, paragraphs4.8.1, 4.8.2). At the contractorsoption, either RT or UT can be usedfor NDT. The mechanical testsrequired involve bend tests (forsoundness), macro etch tests (forsoundness), and reduced section ten-sile tests (for strength). For qualifi-cation of procedures on steels withsignificantly different mechanicalproperties, a longitudinal bend spec-imen is possible (D1.1-96, paragraph4.8.3.2). All weld metal tensile testsare required for unlisted filler met-als. The nature of the bend speci-mens, whether side, face, or root, isa function of the thickness of thesteel involved. The number and

type of tests required are defined inD1.1-96, Table 4.2 for complete jointpenetration groove welds, D1.1-96,Table 4.3 for partial joint penetra-tion groove welds, and D1.1-96,Table 4.4 for fillet welds.

Once the number of tests hasbeen determined, the test plate issectioned and the specimensmachined for testing. The results ofthe tests are recorded on the PQR.According to D1.1-96, if the testresults meet all the prescribedrequirements, the testing is success-ful and welding procedures can beestablished based upon the success-ful PQR. If the test results areunsuccessful, the PQR cannot beused to establish the WPS. If anyone specimen of those tested fails tomeet the test requirements, tworetests of that particular type of testmay be performed with specimensextracted from the same test plate.If both of the supplemental speci-mens meet the requirements, theD1.1-96 allows the tests to bedeemed successful. If the test plateis over 11/2 thick, failure of a speci-men necessitates retesting of all thespecimens at the same time fromtwo additional locations in the testmaterial (D1.1-96, paragraph 4.8.5).

It is wise to retain the PQRsfrom unsuccessful tests as they maybe valuable in the future whenanother similar welding procedure iscontemplated for testing.

The acceptance criteria for thevarious tests are prescribed in thecode. The reduced section tensiletests are required to exceed the min-imum specified tensile strength ofthe steel being joined (D1.1-96, para-graph 4.8.3.5). Specific limits on thesize, location, distribution, and typeof indication on bend specimens isprescribed in D1.1-96, paragraph4.8.3.3.

Writing WPSs from successfulPQRs When a PQR records thesuccessful completion of the requiredtests, welding procedures may bewritten from that PQR. At a mini-mum, the values used for the testweld will constitute a valid WPS.The values recorded on the PQR aresimply transcribed to a separateform, now known as a WPS ratherthan a PQR.

It is possible to write more thanone WPS from a successful PQR.Welding procedures that are suffi-ciently similar to those tested can be

supported by the same PQR.Significant deviations from thoseconditions, however, require addi-tional qualification testing. Changesthat are significant enough to war-rant additional testing are consid-ered essential variables, and theseare listed in D1.1-96, Tables 4.5, 4.6,and 4.7. For example, consider anSMAW welding procedure that isqualified by test using an E8018-C3electrode. From that test, it wouldbe possible to write a WPS that uti-lizes E7018 (since this is a decreasein electrode strength) but it wouldnot be permissible to write a WPSthat utilizes E9018-G electrode(because Table 4.5 lists an increasein filler metal classification strengthas an essential variable). It isimportant to carefully review theessential variables in order to deter-mine whether a previously conduct-ed test may be used to substantiatethe new procedure being contemplat-ed.

D1.1-96, Table 4.1 defines therange of weld types and positionsqualified by various tests. Thistable is best used, not as an after-the-fact evaluation of the applicabili-ty of the test already conducted, but

rather for planning qualificationtests. For example, a test plate con-ducted in the 2G position qualifiesthe WPS for use in either the 1G or2G position. Even though the firstanticipated use of the WPS may befor the 1G position, it may be advis-able to qualify in the 2G position sothat additional usage can beobtained from this test plate.

In a similar way, D1.1-96, Table4.7 defines what changes can bemade in the base metals used in pro-duction vs. qualification testing. Analternate steel may be selected forthe qualification testing simplybecause it affords additional flexibil-ity for future applications.

If WPS qualification is performedon a non-prequalified joint geometry,and acceptable test results areobtained, WPSs may be written fromthat PQR utilizing any of the pre-qualified joint geometries (D1.1-96,Table 4.5, Item 32).

EXAMPLESTo provide some insight into the

thought process that a welding engi-neer may follow to develop a WPS,two examples will be given. In bothcases, the weld is the same, namely,

a 5/16 fillet weld. The specific appli-cation conditions, however, willnecessitate that a separate WPS bedeveloped for each situation. A sam-ple WPS is included for each situa-tion.

Situation One: The weld to bemade is a 5/16 fillet weld that con-nects the shear tab to the column.This weld will be made in the fabri-cation shop with a column in thehorizontal position. The fillet weldis applied to either side of a 1/2 sheartab. It is welded to a W14x311 col-umn with a flange thickness of 21/4 .The shear tab is made of A36 steel,while the column is of A572 Gr 50.

The welding engineer recognizesthat for the grades of steel involved,and for the type of weld specified, aprequalified WPS could be written.The process of choice for this partic-ular shop fabricator is gas shieldedflux cored arc welding, a prequali-fied welding process. From Table3.1 of the D1.1-96 code, a list of pre-qualified filler metals is given.Outershield 70, an E70T-1 electrodeis selected because, for semiauto-matic welding, it is likely to be themost economical process consideringdeposition rate and cleanup time.The electrode operates on DC+polarity. From experience, the engi-neer knows that 3/32 diameter isappropriate for the application, andspecifies that the shielding gasshould be CO2 based upon the elec-trode manufacturers recommenda-tion and its low cost characteristics.From Table 3.2 of the D1.1-96 code,the preheat is selected. It is con-trolled by the thicker steel, that is,the column flange, and required tobe a minimum of 150 degree F sincethe column flange thickness is 21/4.From recommendations supplied bythe electrode manufacturer, thewelding engineer selects a weldingcurrent of 460 amps, 31 volts, andspecifies that the welding speedshould be 15-17 ipm. The final vari-able is determined based upon expe-rience. If any doubts still exist, asimple fillet weld test could be madeto verify the travel speed for thegiven amperage.

As a quick check, the engineerreviews Annex H to ensure that allthe prequalified conditions havebeen achieved. Finally, these aretabulated on the WPS.

Situation Two: The second weldto be made is also a 5/16 fillet weld,


but in this case, the weld will bemade in the field. The weld will bemade between the shear tabdescribed above, and the beam web.In this situation, the beam is aW36x150, specified to be of A36steel. Under field conditions, theweld must be made in the verticalposition.

The welding engineer again rec-ognizes that the WPS for this appli-cation could be prequalified if all theapplicable conditions are met. Selfshielded flux cored arc welding isselected in order to ensure highquality welds under windy condi-tions. This is a prequalified process.In D1.1-96, Table 3.1, the engineerlocates suitable filler metals andselects Innershield NR232, an E71T-8 self-shielded flux cored electrodewhich operates on DC negativepolarity. Because the welding willbe made in the vertical position, a0.068 in. diameter electrode is speci-fied. From technical literature sup-plied by Lincoln Electric, a middle-of-the-range procedure suitable forvertical position welding is selected.The engineer specifies the current tobe 250 amps, 19-21 volts, with atravel speed of 5.5-6.5 ipm. The con-trolling variable is the thickness ofthe beam web, which is 5/8. In thissituation, Table 3.2 of the D1.1-96code does not require any minimumpreheat.

The two welds to be made areremarkably similar, and yet theWPS values specified are significant-ly different. In order to ensure thatquality welds are delivered at eco-nomical rates, it is imperative that aknowledgeable individual establishWPS values. These values must beadhered to during fabrication anderection in order to ensure qualitywelds in the final structure.

REVIEW AND APPROVALAfter a WPS is developed by a

fabricator or erector, it is required tobe reviewed by the inspector (AWSD1.1-96, paragraph 6.3.1). Thisapplies whether the WPS has beenqualified by test, or whether it isprequalified. The code requiresWPSs that are qualified by test to besubmitted to the engineer forapproval (D1.1-96, paragraph 4.1.1).

Prequalified WPSs are requiredto be reviewed by the inspector whois required to make certain that theprocedures conform to the require-

ments of this code (D1.1-96, para-graph 6.3.1). The D1.1-96 code doesnot require prequalified WPSs to besubmitted to the engineer forapproval. Welding procedures thathave been qualified by test arerequired to be reviewed by the engi-neer (D1.1-96, paragraph 4.1.1).However, the use of a prequalifiedjoint does not exempt the engineerfrom using engineering judgment indetermining the suitability of appli-cation for these joints (D1.1-96,paragraph 3.1). The code is notexplicit with respect to engineeringresponsibility for the other aspectsof a prequalified WPS.

The code is clear that the inspec-tor is required to review all WPSs.For a prequalified WPS, Annex H,Contents of a Prequalified WPS, isparticularly helpful. This Annexprovides a list of the various ele-ments of a prequalified WPS, andhas a reference to the code para-graph where these restrictions arelisted. In the reorganized D1.1-96code format, user-friendly tables andfigures summarize many of the pre-qualified requirements. Theseinclude:

Table 3.1 - Prequalified BaseMetal - Filler Metal Combinationsfor Matching Strength

Table 3.2 - P r e q u a l i f i e dMinimum Preheat and InterpassTemperatures

Table 3.3 - Filler MetalRequirements for Exposed BareApplications of A588 Steel

Table 3.7 - Prequalified WPSRequirements

Figure 3.3 - P r e q u a l i f i e dGroove Weld Joint Details

Figure 3.4 - Prequalified CJPGroove Weld Details

In addition to the above tables,Table 4.5 lists the essential variablechanges required for WPS requalifi-cation. The limitation of variablesprescribed in Table 4.5 also apply toprequalified WPSs (D1.1-96, para-graph 3.6). Through the use of thesetables, the majority of the prequali-fied conditions can be easily checkedby the inspector as part of therequired review.

The fundamental premise onwhich the suitability of prequalifiedprocedures stands is stated in thecommentary as follows:

Certain shielded metal arc, sub-merged arc, gas metal arc(excluding the short circuitingmode of metal transfer across the

arc), and flux cored arc WPSs inconjunction with certain relatedtypes of joints have been thor-oughly tested and have a longrecord of proven satisfactory per-formance. (D1.1-96, paragraphC3.2.1).The review required by the

inspector in D1.1-96, paragraph6.3.1 does not specifically require adetermination regarding the suit-ability of the procedure for the par-ticular application, but ratherrequires that the procedure conformto the requirements of the code. Aspreviously stated, the engineer isnot exempted from exercising engi-neering judgment when prequalifiedjoint details are used.

The previously described respon-sibility of the inspector to review allWPSs applies equally to those quali-fied by test. However, D1.1-96,paragraph 4.1.1 additionallyrequires the following:

Except for prequalified WPSs inconformance with Section 3, aWPS for use in production weld-ing shall be qualified in confor-mance with Section 4, Part B, andshall be approved by the engi-neer.The apparent logic behind the dif-

ferences in approval approaches isthat while prequalified WPSs arebased upon well established, timeproven, and documented weldingpractices (see D1.1-96, paragraphC3.2.1), WPSs that have been quali-fied by test may utilize new,unproven and sometimes controver-sial concepts. WPSs that are quali-fied by test are not automaticallysubject to the same restrictions thatwould apply to prequalified WPSs.Even though the required qualifica-tion tests have demonstrated theadequacy of the particular WPSunder test conditions, further scruti-ny by the engineer is justified toensure that it is applicable for theparticular situation that will beencountered in production.

Two examples will be cited toillustrate the philosophical differ-ences a welding engineer may takewhen evaluating a WPS qualified bytest. In Situation One, the contrac-tor wishes to use a WPS that wouldotherwise be prequalified, except forone change in the joint detail. Basedupon experience and some informaltests, the contractor has determinedthat a modified groove detail willreduce the required volume of weld


metal without affecting quality. Thejoint detail is similar to a B-U2a-GF,except that the root opening andgroove angles deviate from the pre-qualified requirements shown inD1.1-96. Specifically, the combina-tion of a 1/8 root opening with a 45degree included angle when appliedto plate 1/2 thick provides a nearoptimum configuration for this con-tractors procedures that utilizeFCAW-g. Since these dimensionalchanges are beyond the limits per-mitted by the as-detailed tolerancesfor the specific joint, they must bequalified by test. If there were to bea problem associated with thisapproach, it would no doubt evi-dence itself as a fusion-type prob-lem. The required qualification testas outlined in Table 4.2 require twoReduce Section Tension Tests, andfour Side Bend Tests. Both of thesetests, and the Side Bend Test in par-ticular, will quickly reveal any prob-

lem with fusion problems associatedwith this technique. A successfulPQR should satisfy the engineer whois required to approve this proce-dure.

In Situation Two, the issue ismore complex. A new steel is beingcontemplated for construction, andthe claim of the steel producer isthat it can be welded with reducedpreheat levels. It cannot be prequal-ified because (a) the steel is notprequalified; and, (b) the preheatlevels are below the prequalified lim-its. In order to qualify the procedurefor unlimited thickness qualification,D1.1-96, Table 4.2 requires the testplate be 1 in. or thicker. The con-tractor qualifies the welding proce-dure on 1 in. steel, although theactual application will utilize 4 in.thick steel. The actual joint configu-ration used for qualification testingis a double V groove butt joint, weld-ed from two sides. The test plate is

not preheated prior to fabrication(although the air temperature insidethe shop where the qualificationtesting is being performed is at 70degree F). After the first weld passis applied, the steel temperaturerises well above ambient due to thethermal energy added by the weld-ing process. A second weld pass isapplied to the first side. Next, theplate is inverted and the root passmade from the opposite side isgouged out. While the interpasstemperature is still well above ambi-ent, the second side of the joint iswelded. Finally, the plate is flippedone more time, and the first side ofthe joint is welded out to completion.

The test plate is subject to all ofthe code-mandated tests, and suc-cessfully meets the code require-ments. With this information inhand, the contractor submits theprocedure to the engineer forapproval, claiming that these testshave proven the weldability of thenew steel, and that no preheat isrequired. While it is true that thecode-mandated requirements havebeen fulfilled, the suitability of thiswelding procedure for actual fabrica-tion has not been established. Therelatively small sizes associatedwith the test plate (1 thick x 14minimum wide x 30 minimum long,according to D1.1-96, Figure 4.10) isnot sufficient to duplicate therestraint or cooling rates that will beseen in actual structures. Theseissues will affect the resultant heataffected zone microstructure, hydro-gen diffusion rates, and residualstress levels - all elements thataffect the possibility of weld crack-ing. In addition, except for the rootpass, all of the weld passes had thebenefit of the higher interpass tem-perature. Furthermore, the rootpass that was made without preheatwas gouged out when the secondside was welded. Although no pre-heat was applied, the steel was atshop ambient temperature, qualify-ing a 70 degrees F preheat tempera-ture, not no preheat temperature.

The engineer ought to view thesecond WPS with a greater degree ofscrutiny than first. It would be rea-sonable, for example, to requireweldability tests (such as: G-BOP,TEKKEN, or CTS tests) in order tobetter understand the likely behav-ior of this proposed welding proce-dure. Larger scale, restrained mock-


ups would be necessary to evaluateactual restraint and cooling condi-tions.

When WPSs that have been qual-ified by test are reviewed, there arethree distinct elements of thatreview: First, the procedure qualifi-cation record should be evaluated toensure that all the required testshave been performed, verifying thatthe proper thicknesses of material,positions of welding, and number ofrequired tests have all been per-formed. Secondly, the results of thetesting must be examined to be cer-tain that the code requirementshave been met. The final aspect ofthe review is to compare the WPS tothe PQR. This will consist of a com-parison of the requirements of AWSD1.1-96, Table 4.5, as it relates toany differences between the PQRand the WPS. Requirements regard-ing the steels used in testing versusthose listed on the WPS areaddressed in D1.1-96, Table 4.7.

The opinions and explanationsexpressed above are the authorsalone and do not necessarily reflectthe opinions of the AWS or of theAWS D1 Committee. Official inter-pretations of the D1.1 code can onlybe made by the D1 Committee. D1.1-96, Annex F, provides informationdetailing how an official interpreta-tion can be obtained.

This article is based on a paperpresented at the 1997 National SteelConstruction Conference. Duane K.Miller, P.E., is a senior project leaderand design consultant at TheLincoln Electric Companys WeldingTechnology Center.In that capacity,he assists engineers and fabricatorsin welding design and metallurgicalproblems.


what every engineer should know about welding

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