09 welding procedures and qualifcations as per asme sec ix

7/30/2019 09 Welding Procedures and Qualifcations as Per ASME SEC IX

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VI.WeldingProceduresandqualifcationsasPerASMESECIXPage1

WELDINGPROCEDURES &QUALIFICATIONS Mostofthepeopleconsidertheweldingqualificationsastotallytheoreticalandhenceitisnotveryuncommontosee

people totally ignoring this aspect in a manufacturing setup. One would often meet several people in the related

industries

unaware

of

difference

between

a

welding

procedure

qualification

and

a

welder

qualification.

This

paper

is

preparedwiththeintentofthrowinglightonaspectsrelatedtotheweldingqualifications.

Whenanitemisdesignedforaparticularapplication,thematerialusedfortheconstructionofsuchanitemisassumed

to have certain properties. Mechanical strength and chemical composition are the two such properties that are

considered very commonly in almost all the engineering designs. Naturally a weldjoint which forms a part of the

componentalso isassumedtohavetheseproperties.Duetotheadvancements intheWeldingTechnologyandNDT

methods ithasbeenpossible toobtain weldjointswhich areasstrongastheparentmaterial.Hence,these days, in

mostcasesweldsareconsideredtohavethestrengthsameasthatofbasematerial.

To check that they have the desired properties, one can carry out any type of tests (either destructive or

nondestructive)fortheparentmetals,inmostofthecases.Butsameisnotthecasewiththeweldmetals.Inmostof

thecases

NDTs

are

the

only

methods

available

for

testing

the

properties.

But

with

NDTs

one

cannot

determine

the

strengthoftheweld.Henceonewouldthinkofmakingasampleoftheweldandtestfortherequiredproperties.This

wouldcallforatesting,foreverynewjobandeverynewjoint.Thisiswheretheconceptofweldingprocedureshelps

onetoreducethenumberoftestsandhencethecost.

WELDINGPROCEDURE: Awelder/weldingengineermustknowseveraldetailsbeforestartingthewelding,suchasbasematerialcomposition,

thickness, process to be used, etc.. These details which a welder/ welding engineer must know before commencing

weldingarecalledWeldingVariables.

Adocument

showing

all

the

applicable

welding

variables

is

called

WPS

(Welding

Procedure

Specification).

ItisnotenoughifonehasonlytheWPS.OnemustensurethattheweldmadeasperWPSmeetsalltherequirements,

whicharenothingbutthepropertiesofthematerialofconstructionassumedbythedesignerwhiledesigningtheitem.

Normally,thepropertiesassumedaremechanicalstrengthandchemicalcomposition.Additionallyitmayalsoinclude

notchtoughness,hardness,corrosionresistanceetc.

Howtoensurethattheweldmadehavetheseproperties?

WeldacouponasperWPSandtest, if itmeetstherequirementsonecanassumethatweldsimilarlymadealsowill

have similar properties. The document in which the actual values of the variables and the results of the test are

recordediscalledaPQR(ProcedureQualificationRecord).Inotherwords,PQRisarecord,whichservesasaprooffor

thesatisfactoryperformanceoftheweldmadeasperthespecificWPSwithinthespecificrangespermitted.

TheaboveprocessoftestingtoensurethepropertiesiscalledProcedureQualificationTest

TheWPS&PQRtogetherconstituteaQualifiedWeldingProcedureorinshortaprocedure.


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Whetheritisrequiredtocarryoutthetestingforeverynewjoint?

No.

Ithas

been

established

that

a

change

in

the

value

of

the

variable

need

not

necessarily

change

the

properties.

Accordinglythevariablesareclassifiedundertwogroups.

Variables,whosechangeresultsinthechangeinthepropertiesarecalledasEssentialVariables. Variables,whosechangedoesnothaveanyeffectontheproperties,arecalledasNonEssentialVariables.

Variables are listed under one more head known as Supplementary Essential Variables. These become essential

variablewhennotchtoughnessisrequiredfortheweldasperapplicablecode.

Nowthatweknow'whataweldingprocedureis',letusunderstandwhatismeantbythequalificationofthewelding

procedure'. One must notice that welding procedure is only a mock up that can represent welding done in a shop

undersimilar

conditions.

But,

in

certain

cases

where

lesser

factor

of

safety

is

considered

this

may

not

be

sufficient.

Hence, most of the codes call for a production weld coupons as an additional measure. One must note that these

productioncouponsthemselvesalsoactasqualificationtestsfortheweldingprocedures.

WELDERQUALIFICATION: Welderqualificationisthesecondtypeofqualificationrequired.

Itisverymuchsimilartoadrivinglicenseissuedtothedrivers. Thisauthenticatesapersontoperformwelding.Justas

a person capable of manipulating a steering wheel, brakes, clutch etc., can act as a driver, a person capable of

depositingsoundweldmetalcanbecomeawelder. Whatisrequiredforawelderisskilltodepositsoundweldmetal

byproperly

interpreting

the

welding

procedure.

A

document

similar

to

driving

license

authorizing

the

driver

to

drive

is

theWPQ(WelderPerformanceQualificationrecord)forthewelder.Theprocessoftestingthecapabilityofthewelderisknownas"WelderPerformanceQualificationtest".Onemustnoticethatmostofthecodesallowwelderqualificationonthejobsignifyingthefactthatwhatisimportant

isthesoundnessoffinalweld.Hence,onemustviewWelderQualificationmoreasatooltogetarepairfreejointin

thefirstinstance.

INTRODUCTIONTO

SEC

IX

OF

ASME

Throughoutthispaperareference ismadetoASMEboilerandpressurevesselcodeforthesakeofconvenience.But

thediscussionsarenormallyvalidforanycodes.

SECIXofASMEcoversvariousaspectsrelatingtotheweldingqualifications.Thefollowingpointsmustclarifysomeofthedoubts/confusionscommonlyseeninthebeginners.


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1. Thissectionmustbereferredonlywhenthedesigncode(suchasSECVIIIdiv.1),crossreferstothissection2. Thissectiondoesnotguideintheselectionofelectrode3. Thissectiondoesnotguideinthedesignofjoints4. Thissectiondoesnotspecifythetypeandextentofradiography/NDTtobeused5. Thissectiondoesnotspecifytheacceptancecriteria(i.e.typesandextentofdiscontinuitiesacceptable).6.

This

section

does

not

specify

Energy

value

for

impact

testing

For points specified in 3, 4, 5 and 6 one must refer the Design code. Knowledge of how the contents (and their

organization)ofSECIXshouldgreatlyhelpthereaderstosolvethecommonlyseenstartingtrouble.

Thissectionhastwoparts,weldingandbrazing.Under Welding,thereare4chapters(Article ItoIV), inadditionto

initialintroduction.

ArticleI:General.Mainlycovers

Positionsofwelding Examinations(VariousTypesofTests,TestingProcedures,SpecimenDetails,AcceptanceCriteria)etc.

ArticleII WeldingProcedureQualifications WPS,PQR Theircontents,Format Listofvariables Qualifiedranges Typeandnumberofexaminationsrequired

ArticleIII WeldingPerformanceQualifications WPQ ListofVariables Qualifiedranges Typeandnumberofexaminationsrequired

ArticleIV CompiledweldingdatameantforusingwitharticlesI,II,III

Hence,forexample,onewhowantstoqualifyaweldercandirectlyreferarticleIII.

FollowingTipsmusthelpreaderwhenreadingtheweldingdata:

NeverreadtheweldingdatagiveninarticleIVunlesscalledupontodosobyarticlesI,IIorIII Normally adding "a new qualification shall be done when " before reading data against essential variable

givenin

the

tables

of

Article

II

and

III(such

as

QW

253/6),

makes

the

reading

easy

Normallyadding"anewqualification isnotrequiredwhen"beforereadingthedataagainstnonessentialvariablegiveninthetablesofarticleII(suchasQW253/6),makesthereadingeasy


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ThicknessofthetestcouponThicknessselectionistheimportantandmostlyconfusedparameter

WeldingprocedureFollowing

parameters

shall

be

considered

in

the

selection

of

thickness

Testcouponthickness governstherange Impactrequirement governsthelowerlimit Normalizingrequirement governstheupperlimit

AppendixIdescribesthicknessselectioninmoredetail.

WeldersQualificationOnemustpreferablyqualifyawelderwithacouponof20mmthicknessormorewhichwillqualifyhimtowelddeposit

ofanythickness.

GroupingofmaterialsBase materials and electrodes / filler materials are grouped variously due to their similarity of

composition, mfg., Practice etc., to reduce the number of qualification tests to be carried out.

Belowwewilldiscussfewofthem.

BasemetalsPnumber

This is the grouping of BaseMaterials based on their chemical composition, weldability mechanicalproperties etc. P

standsfor

Parent

metal.

Table

QW422

lists

the

P

numbers

of

various

materials.

QW422

and

QW424

describe

the

rules

for usingthe P numbers ofqualifications.With thehelpof Pnumbersthenumberof qualificationtestsrequiredare

greatlyreduced.Forexampleallplaincarbonsteels(SA105,SA106,SA515,SA516etc.)areassignedaPnumberof1.

GnumberThisisasubgroupingofferrousBaseMaterialshavingspecifiedimpacttestrequirements,withinaPnumber.Gstands

for Group. Table QW422 lists the G numbers of various materials. This willbe an additionalrestriction on P number

whenimpacttestingisrequiredforthebase/weldmetalinthejobspecification.

AsimpleexampleofusageofPnumberandgroupnumberisasfollows

A

procedure

qualified

using

a

plates

confirming

to

SA516

Gr.60

can

be

used

to

weld

ajoint

between

the

pipes

confirmingtoSA106Gr.Bassumingthatallotherparametersremainunaffected.

In the WPS it is enough if only P number and group number are specified. When they are not known, material

specificationshallbewritten(ex..ifbasematerialIS2062).Whenspecificationalsoisnotknown,chemicalcomposition

shallbewritten.Thelatteroptionsactuallyreducetherangequalified


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FillermaterialsFnumberThis

is

the

grouping

of

electrodes

and

filler

materials

based

on

their

usability

characteristics

mainly

governed

by

flux

or

shielding medium used (which also govern their electrical characteristics). F stands for F Filter metal. These aredescribedinQW430

AnumberThis is the grouping of electrodes and filler materials based on the weld metal chemical composition. 'A' stands for

weldmetalAnalysis.ThesearedescribedinQW440

SomefactsrelatingtoWPS,PQR,WPQ Adoublewelded(weldedfromboththesides)jointisconsideredasajointwithbacking.Weldmetalbecomes

theBackingmaterial.

Size of base metal, normally designated as T and size of weld deposit normally designated as t must beconsideredseparately.

WPS/PQR A procedure qualified using plates can be used for welding the pipes, provided the P number G number

criteriaismet.

Aprocedurequalifiedinanyonepositioncanbeusedtoweldinanyotherpositionprovidedjobspecificationsdo

not

specify

impact

test.

Aprocedurequalifiedusinggroveweldscanbeusedforfilletweldsofanysize. Onemustalwayscarryout impacttestingatthe lowestpossibletemperature, intheprocedurequalification

test.Thiscanbeusedforthejobshavingimpactrequirementornot

Technically,aprocedurequalificationtest,whichhasfailedtomeettherequiredtensilestrengthcanbeusedforjobswithmaterialsoflowerstrength.Forexample,ifthetensiletestresultsshowedavalueof65ksiwhen

testedwithacouponmaterialofSA516Gr.70,E7018electrode,onnormalizingcanbeusedforweldsmade

onequipmentofSA516Gr.60,provided,allotherparametersremainsame

A test coupon of thickness 40mm used for procedure qualification test covers largest range from 5 mm to200mm(withoutheattreatmentorimpactrequirements).

TheformatrecommendedbySECIX,commonlyusedforWPS/PQR,iscommonforprocessesSMAW,GTAW,SAW

and

GMAW.

Hence,

one

must

be

careful

when

using

them,

since,

some

of

the

points

are

not

applicable

forsomeprocesses.

WPQ Normallyaweldercanbequalifiedusingonlyaradiographictest. Achangeoffillermetal(Fnumber)needsarequalificationofwelder


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Presence or absence of impact test or normalizing does not affect the welder's skill and hence thequalification.

A small diameter pipe requires more skill for welding. Hence, a welder qualified on lower diameters canalwaysweldhigherdiameters(plateisapipewithinfinitediameter).


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AppendixIDeterminationoftestcouponthicknessforweldingprocedurequalification

IdeallyonemuststartwithtablessuchasQW253/256,proceedtoweldingdatasuchasQW403.8(asspecifiedinthe

tables)andthenproceedtoQW451(asspecified inthedata) andselectthethickness insuchawayastocoverthe

largestrange.

Letustakeanexampletoillustratetheabovepoint.Forthejointconfigurationshownontheright,variousstepstobe

followedtoarriveattheoptimumthicknessareasfollows.

Step1: Startwiththicknesssameasthejob.But,codedoesnotpermitdissimilarthicknessforthetestcouponStep2: Choose16mm(arbitrary),Thiswillqualifyusfor,Reference Thickness

Tofbasemetal tofweldmetal,max

From To GTAW SMAW

AsperQW450(BasedonThicknessofthecoupon) 5 32 16 16

AsperQW407.4(duetonormalizing) 18 8.8 8.8

AsperQW403.6(duetoimpacttestrequirement) 16

Result 16 18 8.8 8.8

Step3: Choose32mm(arbitrary).ThiswillqualifyusforReference Thickness

Tofbasemetal tofweldmetal,max

From To GTAW SMAW

AsperQW450(BasedonThicknessofthecoupon) 5 64 64 64

AsperQW407.4(duetonormalizing) 35 35 35

AsperQW403.6(duetoimpacttestrequirement) 16

Result 16 35 35 35

Onemustnotethatthestep3givesusthelargestrange.Onemay,however,chooseanythicknesshigherthan32mm,

but this would not yield any additional benefit due to the presence of normalizing in thejob requirement in this

example.AdditionallyQW407.2indirectlyrestrainsusfromchoosingathicknessvaryingtoomuchfromthatofjob.

Whathappens

when

a

production

weld

has

two

dissimilar

metal

thicknesses?

This

shall

be

arrived

at

in

two

steps

1. ThicknessofthethinnermembershallbeaspermittedbyQW4512. Thicknessofthethickermembershallbe

i. Unlimitedforspecifiedmaterialprovideda) MaterialsareofsamePnumber.b) qualificationismadeon>

ii. limitedwithintherangeofqw451***********

Process(assumption) 2layers(root

andhotpass)ofGTAWandrestby

SMAW(fillupandfinal).

Heattreatment Normalizing

Min.designtemperature. 48C

16 32SS CS

09 welding procedures and qualifcations as per asme sec ix

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