welding Geometric Shape Imperfections general review

8/11/2019 welding Geometric Shape Imperfections general review

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A general review of geometric shape imperfections - types and causes

Job Knowledge Part 1. Introduction

Inthejobknowledgeseriesweldingimperfectionssuchascracks,lackoffusion,penetrationandporosityhavebeendiscussed.Thisarticlelooksatthoseimperfectionsrelatedtopoorgeometricshapeandwillconcentrateonthefollowing:

Excessweldmetal

Undercut

Overlap

Linearmisalignment Incompletelyfilledgroove

Suchimperfectionsmightbeconsideredasanomaliesinthejointandtheywillalwaysbepresenttosomedegreesothatitbecomesnecessarytoseparatetheacceptablefromtheunacceptable.Thisisdonebyfollowingguidancegivenbytheapplicationstandard,whichwasthebasisforthecomponentdesign,and/orbydirection,assetoutinthejobcontract.Examplesofstandardsthatmightbereferredtoare:

PD5500Specificationforunfiredfusionweldedpressurevessels.

BSENISO5817Welding.Fusion-weldedjointsinsteel,nickel,titaniumandtheiralloys(beamweldingexcluded).Qualitylevelsforimperfections

AWSD1.1Structuralweldingcode-Steel

Excess weld metal

also called cap height, overfill or reinforcement)

Fig.1.Excessweldmetal

Thisisweldmetallyingoutsidetheplanejoiningtheweldtoes.Notethattheterm'reinforcement',althoughusedextensivelyintheASME/AWSspecificationsisavoidedinEuropeasitimpliesitaddsstrengthtotheweldedjoint,whichisrarelythecase.

Common causes

Thisimperfectionisformedwhenexcessiveweldmetalisaddedtothejoint,whichisusuallyaresultofpoorweldertechniqueformanualprocessesbutmaybeduetopoorparameterselectionwhentheprocessismechanised.Thatis,toomuchfillermetalforthetravelspeedused.Inmulti-runweldingapoorselectionofindividualbeadsizescanresultinabeadbuild-uppatternthatoverfillsthejoint.Differentprocessesandparameters( egvoltage)canresultindifferentexcessweldmetalshapes.

Acceptance

Theacceptabilityofthisimperfectionisverydependentontheapplicationinwhichtheproductwillbeused.Moststandardshavelimit,relatedtomaterialthickness(eg10%),butalsohaveamaximumupperlimits.Boththeratioandthemaximummayberelatedtotheseverityofservicethatthecomponentisexpectedtosee.ThefollowingtablegivesexamplestakenfromBSENISO5817.

Excess weld metal limits for quality levels:

Severityofservice Moderate,D Stringent,B

Limit(uptomaximum) h=1mm+0.25b h=1mm+0.1b


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Maximum 10mm 5mm

Transitionrequired Smooth smooth

Where:h=heightofexcess&b=widthofbead(see figure1)

Animportantreasonforlimitingtheheightofexcessweldmetalisthatitrepresentsanon-valueaddedcost.However,itmustberememberedthattheheightoftheweldcapinfluencestheresultanttoeblend.Asharptransitioncausesalocalstressconcentrationthatcancontributetolossofstrength,whichisparticularlyimportantinfatiguesituations.Asaresultmostspecificationsstatethat'smoothtransitionisrequired'.

Avoidance

Iftheimperfectionisaresultofweldertechniquethenwelderretrainingisrequired.Formechanisedtechniquesanincreaseintravelspeedorvoltagewillhelptoreducecapheight.

Undercut

Fig.2.Undercut

Thisisanirregulargrooveatthetoeofarunintheparentmetal.Thefigureshowsundercutatsurfaceofacompletedjointbutitmayalsobefoundatthetoesofeachpassofamulti-runweld.Thelattercanresultinslagbecomingtrappedintheundercutregion.

Common causes

Whenarcandgaswelding,undercutisprobablythemostcommonshapeimperfection.Withsingle-sidedpipeweldsitmayalsobefoundattheboresurface.Itmayalsobeseenontheverticalfaceoffilletweldsmadeinthehorizontalverticalposition.Awidespreadingarc(higharcvoltage)withinsufficientfill(lowcurrentorhightravelspeed)istheusualcause.However,weldertechnique,especiallywhenweaving,andthewaytheweldingtorchisangledcanbothcauseandbeusedtoovercomeundercutting(ieangledtopushtheweldmetaltofillthemeltedgroove).Highweldingcurrentwillalsocauseundercut-thisisgenerallyassociatedwiththeneedforahightravelspeedtoavoidoverfillingofthejoint.

Acceptance

Largelybecausethisimperfectioniswidespread,moststandardspermitsomelevelofundercutalthoughtheydorequirethata'smoothtransitionisrequired.ThelimitsinBSENISO5817rangefrom0.5mm(stringent)to1mm(moderate)forthickness(t)greaterthan3mm(morestringentlimitsarerequiredfort0.5to3mm),whileAWSD1.1hasalimitof1mm.Measuringundercutcanbeaproblembecauseofthesmallsizeoftheimperfectioncomparedwiththegeneralenvironmentwheretherecanbemillscale,irregularitiesinthesurfaceandspatter.

Incriticalapplicationstheimperfectioncanbe'corrected'byblendgrindingorbydepositinganadditionalweldbead.

Avoidance

Thisimperfectionmaybeavoidedbyreducingtravelspeedand/ortheweldingcurrentandbymaintainingthecorrectarclength.

Overlap cold lapping)


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Fig.3.Overlap

Thisisanimperfectionatatoeorrootofaweldcausedbymetalflowingontothesurfaceoftheparentmetalwithoutfusingtoit.Itmayoccurinbothfilletandbuttwelds.

Common causes

Thisisoftencausedbypoormanipulationoftheelectrodeorweldinggun,especiallywhentheweldpoolislargeand'cold',wherethewelderallowsgravitytoinfluencetheweldshapebeforesolidification.Tightlyadherentoxidesorscaleonthemetalsurfacecanalsopreventtheweldmetalfusingwiththeparentmetaltocausetheoverlapimperfection.

Avoidance

Avoidanceisachievedthroughanacceptablelevelofwelderskillandareductioninweldpoolsize(obtainedbyreducingcurrentorincreasingtravelspeed).Adequatecleaningoftheparentplateisalsoimportant.

Acceptance

Standardsrarelyallowthepresenceofthisimperfection,unlessthelengthisshort( egBSENISO5817formoderatequalitylevelD).Overlapcanbeverydifficulttodetect,especiallyifitisextremelysmall.

Linear misalignment

Fig.4Linearmisalignment

(AlsoknownintheUSAashigh-low).Thisimperfectionrelatestodeviationsfromthecorrectposition/alignmentofthejoint.

Common causes

Thisisprimarilyaresultofpoorcomponentfit-upbeforewelding,whichcanbecompoundedbyvariationsintheshapeandthicknessofcomponents(egoutofroundnessofpipe).Tacksthatbreakduringweldingmayallowthecomponentstomoverelativetooneanother,againresultinginmisalignment.

Acceptance

Theacceptabilityofthisdefectisrelatedtothedesignfunctionofthestructureorpipelineeitherintermsoftheabilitytotakeloadacrossthemisalignmentorbecausesuchastepimpedestheflowoffluid.Acceptancevarieswiththeapplication:BSENISO5817relatesmisalignmenttowallthicknessbutsetsmaximumlimits( egformaterialthicknesst>3mmandmoderatelimitsofimperfectionsD,=0.25xt,withamaximumof5mm).


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AWSD1.1allows10%ofthewallthicknessuptoamaximumof3mm.Theconsequenceoflinearmisalignmentcan,whenweldingiscarriedoutfromoneside,belackofrootorsidewallfusiontogiveasharpcontinuousimperfectionalongthehigherweldfacetoe.Insomesituationslinearmisalignmentintheboreofapipecanleadtoin-serviceproblemswhereturbulenceofthecarrierfluidinthepipecreatessubsequenterosion.

Incomplete filled groove

Incompletefilledgroove

Thisisacontinuous,orintermittent,channelinthesurfaceofaweld,runningalongitslength,duetoinsufficientweldmetal.

Common causes

Thisproblemariseswhentherehasbeeninsufficientfillermetal(currentorwirefeedtoolowortoohighatravelspeed)sothatthejointhasnotbeensufficientlyfilled.Theresultisthatthethicknessofweldmentislessthanthatspecifiedinthedesign,whichcouldleadtofailure.

Acceptance

Moststandardswillnotacceptthistypeofimperfection,exceptperhapsovershortlengthsandeventhenasmoothtransitionisrequired.Thedesignerexpectsthejointtobeadequatelyfilled,butnottoomuchso(seeexcessweldmetal).Oftenthepresenceofthisimperfectionisanindicationofpoorworkmanshipandcouldsuggestthatfurthertrainingisrequired.

Continuation

Part2looksatshapeimperfectionssuchasexcesspenetrationandrootconcavityandhighlightsshapeimperfectionsrelatedtofilletweldedjoints.

Thissecondarticleonshapeimperfectionsrefersmostlytofilletweldsbuttherearetwoadditionalbuttweldimperfectionsthatrequiresomecomment.Excessive penetration Excess penetration bead)

Fig.1.ExcesspenetrationExcessweldmetalprotrudingthroughtherootofafusion(butt)weldmadefromonesideonly.Withpipeweldingthistypeofimperfectionmaycauseeffectsinthefluidflowthatcancauseerosionand/orcorrosionproblems.Common causes

Penetrationbecomesexcessivewhenthejointgapistoolarge,therootfacesaretoosmall,theheatinputtothejointistoohighoracombinationofthesecauses.
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Acceptance

Thecriteriawhichsetsthelevelofacceptablepenetrationdependsprimarilyontheapplicationcodeorspecification.BS2971(Class2arcwelding)requiresthatthe'penetrationbeadshallnotexceed3mmforpipesuptoandincluding150mmboreor6mmforpipesover150mmbore'.BS2633(Class1arcwelding)givesspecificlimitsforsmallerdiameterspipes,egforpipesize25-50mmthemaximumallowedborepenetrationis2.5mm.ASMEB31.3basesacceptabilityonthenominalthicknessoftheweld,forinstance,allowingforathicknessrangeof13-25mmupto4mmofprotrusion.However,ASMEnotesthat'morestringentcriteriamaybespecifiedintheengineeringdesign'.BSENISO5817(Qualitylevelsforimperfections),whichsupersedesBSEN25817,relatestheacceptableprotrusionto

thewidthoftheunder-beadasfollows:

Severity of service Moderate, D Stringent, B

Limit(uptomaximum) h1mm+1.0b h1mm+0.2b

Maximum 5mm 3mm

Forthicknesses>3mmwhere:h=heightofexcess&b=widthofroot (seeFig.1)

Avoidance

Itisimportanttoensurethatjointfit-upisasspecifiedintheweldingprocedure.Ifweldertechniqueistheproblemthenretrainingisrequired.Root concavity suck-back; underwashing)

Fig.2.RootconcavityAshallowgroovethatmayoccurintherootofabuttweld.Common causes

Rootconcavityiscausedbyshrinkageoftheweldpoolinthethrough-thicknessdirectionoftheweld.Meltingoftherootpassbythesecondpasscanalsoproducerootconcavity.ThisimperfectionisfrequentlyassociatedwithTIGweldingwiththemostcommoncausebeingpoorpreparationleavingtherootgapeithertoosmallor,insomecases,toolarge.Excessivelyhighweldingspeedsmaketheformationofrootconcavitymorelikely.Acceptance

Therootconcavitymaybeacceptable.Thiswilldependontherelevantstandardbeingworkedto.Forexample:BS2971requiresthat:a)thereiscompleterootfusionb)thethicknessoftheweldisnotlessthanthepipethickness.ASMEB31.3requiresthatthe'totaljointthickness,includingweldreinforcement,mustbegreaterthantheweldthickness'BSENISO5817setsupperlimitsrelatedtothequalitylevel,egforthicknesses>3mmModerate,(D),h0.2tbutmax2mmforStringent,(B),h0.05tbutmax0.5mm.Furthermore,asmoothtransitionisrequiredattheweldtoes. Ineffectthestandardsrequirethattheminimumdesignthroatthicknessofthefinishedweldmentisachieved.Ifthefirsttwoconditionsofacceptancearemetbuttheweldfacedoesnothaveasufficientlyhighcap,additionalweldmetalmaybedepositedtoincreasethethroat.Avoidance

Itisimportanttoensurethatjointfit-upisasspecifiedintheweldingprocedureandthatthedefinedparametersarebeingfollowed.Ifweldertechniqueistheproblemthenretrainingisrequired.Fillet welded joints

ThisSectionshouldbereadinconjunctionwithJobKnowledge66Filletweldedjoints-areviewofthepracticalities. Excessive convexity
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Fig.3.ExcessiveconvexityThisfeatureisalsocoveredbythedefinitionforexcessweldmetal,seePart1,andmaybedescribedasweldmetallyingoutsidetheplanejoiningtheweldtoes.Notethattheterm'reinforcement',althoughusedextensivelyintheASME/AWSspecificationsisavoidedinEuropeasitimpliesthatexcessmetalcontributestothestrengthoftheweldedjoint.Thisisrarelythecase.Common causes

Poortechniqueandthedepositionoflargevolumesof'cold'weldmetal.Acceptance

Theidealiseddesignrequirementofa'mitre'filletweldisoftendifficulttoachieve,particularlywithmanualweldingprocesses.

BSENISO5817acceptanceisbasedonamitrefilletweldshapewithaspecificdesignthroatandanyexcessweldmetalismeasuredinrelationtothismitresurface.Thelimitsforthisimperfectionrelatetheheightoftheexcessmetaltothewidthofthebeadwithmaximumvaluesrangingfrom3mmforastringentqualitylevelto5mmforamoderatequalitylevel.Surprisingly,thereisnoreferencetoa'smoothtransition'beingrequiredattheweldtoesforsuchweldshape.AWSD1.1alsohaslimitsrelatingwidthtoacceptableexcessasfollows:

Width of weld face Maximum convexity

W8mm 2mm

W


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Undersized fillet welds fillet welds smaller than those specified)

Fig.5.UndersizedfilletweldCommon causes

Theweldingrelatedcausesareassociatedwithhighweldingspeedsandlowweldingcurrents.Acceptance

Therefore,itisnormallyassumedthatfilletweldswillbeatleastofthesizespecified.BSENSIO5817statesthatlimitstoinsufficientthroatthicknessarenotapplicabletoprocesseswithproofofgreaterdepthofpenetration,thereforeafilletweldwithanapparentthroatthicknesssmallerthatthatprescribedshouldnotberegardedasbeingimperfectiftheactualthroatthicknesswithacompensatinggreaterdepthofpenetrationcomplieswiththenominalvalue.Thatisifwecanbe

surethereisgoodpenetrationthesmallerfilletmaybeacceptable,however,thisshouldbediscussedwiththedesignerofthefabrication.Thelimitssetbythestandard.Relyingupondeeppenetrationtoprovidetherequiredminimumdesignthroatthicknesscanbedifficulttojustify.Penetrationisaweldcharacteristicthatishardtomeasuredirectlyandreliancemustbeplacedonthestringentcontrolofboththeweldingprocessandthewelder.Manualweldingcanrarelybereliedupontoprovidetherequiredconsistencybutitisanoptionwithmechanisedweldingsystems.

Imperfection: fillet weld

having a throat

thickness smaller than

the nominal value

Quality levels

ModerateD IntermediateC StringentB

LongimperfectionsNOTpermitted NOTpermitted

Shortimperfections(seeFig.5)h0.3mm+0.1a

max2mm max1mm

Avoidance

Adheretothespecifiedweldingprocedureandparameters.Usesufficientcurrentandappropriatetravelspeed.Wherepossiblemechanisetheweldingoperation.Asymmetric fillet weld a fillet weld where the legs are of unequal length)

Fig.6.AsymmetricfilletweldCommon causes

Duetoincorrectelectrodepositioningortogravitypullingthemoltenpooltowardsonefaceofthejoint.Itisanmainlyaproblemwithfilletweldsmadeinthehorizontal/vertical(PB)position.Acceptance

Thereareinstanceswhereasymmetrymaybespecified(egtoplacethetoestressconcentrationinaparticularregion).BSENISO5817would,fora10mmleglengthfilletweld( ie7.1mmthroat)allowadifferenceinleglengthsofabout2.5mmatthestringentqualityleveland3.4mmatthemoderatequalitylevel.Acceptanceisrelatedtothethroatthickness.


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Theconsequenceofthisimperfectionisasignificantincreaseinweldvolume.Providedtheleglengthrequirementisachievedtherewouldnotbealossofstrength.Perhapsthisiswhy,inotherstandards,arequirementisnotspecifiedandtheacceptabilityislefttotheinspectionpersonneltomakethe'engineeringjudgement'!Poor fit-up

Fig.7.Poorfit-upThemostcommonimperfectionisanexcessivegapbetweenthematingfacesofthematerials.Common causes

Poorworkshoppractice,poordimensioningandtolerancedimensionsondrawings.

AcceptanceAmajorproblemwithfilletweldsisensuringthegapbetweenthecomponentsiswithindefinedlimits.BSENISO5817specifiestheacceptancecriteriaasfollows:

Qualitylevels

ModerateD IntermediateC StringentB

h1mm+0.3ah0.5mm+0.2ah0.5mm+0.1a

max4mm max3mm max2mm

Whereh=fit-upgapanda=filletwelddesignthroat

Figure7showsthatthegapresultsinareductionintheleglengthontheverticalplateandthis,inturn,resultsinareductioninthethroatthicknessofthejoint.A10mmleglengthfilletwitharootgapof3mmgivesaneffectivelegof7mm(athroatof4.9mminsteadoftheexpected7mm).WhentheapplicationofBSENISO5817isnotrequired,theguidanceofBSEN1011-2canbefollowed,which

recommendsamaximumgapof3mm.Thisstandardalsostatesthatthesizeofthefilletweldcanbeincreasedtocompensateforalargegap.ThisdiscrepancyisaddressedwithinAWSD1.1.whichpermitsarootgapofupto5mmformaterialthicknessupto75mm.However,'ifthe(joint)separationisgreaterthan2mmthelegofthefilletweldshallbeincreasedbytheamountoftherootopening,orthecontractorshalldemonstratethattheeffectivethroathasbeenobtained'.

Fillet welded joints - a review of the practicalities

Job Knowledge

Filletweldedjointssuchastee,lapandcornerjointsarethemostcommonconnectioninweldedfabrication.Intotaltheyprobablyaccountforaround80%ofalljointsmadebyarcwelding.Itislikelythatahighpercentageofotherjoiningtechniquesalsousesomeformofafilletweldedjointincludingnon-fusionprocessessuchasbrazing,brazeweldingandsoldering.Thelattertechniquesareoutsidethescopeofthisarticle.

Althoughthefilletweldissocommon,thereareanumberofaspectstobeconsideredbeforeproducingsuchaweld.Thisarticlewillreviewanumberoftopicsthatrelatetofilletweldedjointsanditishopedthateventhemostseasonedfabricatororweldingpersonwillgainfromthisarticleinsomeway.CommonjointdesignsforfilletweldsareshownbelowinFig.1.


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Fig1.Commonjointdesignsforfilletwelds

Fillet weld features

ISO2553(EN22553)usesthefollowingnotationasFigs.2and3show.a=throatthicknessz=leglengths=deeppenetrationthroatthicknessl=lengthofintermittentfillet

Fig.2.Mitrefillet

Fig3.Deeppenetrationfillet

Fillet weld shapes

Over specified fillet welds or oversized fillet welds


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Fig4.Weldsizesinrelationtotherequiredleglengthsorthroatthickness

Oneofthegreatestproblemsassociatedwithfilletweldedjointsisachievingthecorrectweldsizeinrelationtotherequiredleglengthsorthroatthickness(Fig.4).Thedesignermaycalculatethesizeandallowa'safetyfactor'sothattheweldspecifiedonthefabricationdrawingislargerthanisrequiredbydesignconsiderations.Theweldsizeiscommunicatedbyusinganappropriateweldsymbol.IntheUKtheweldsizeisfrequentlyspecifiedbyreferringtotheleglength'z'inISO2553wherethenumbergivestheweldsizeinmillimetresasshowninFig.5.

Fig5.Weldsizespecification(UK)

InEurope,itismorecommontofindthedesignthroatthickness,'a'specified( Fig.6).

Fig6.Weldsizespecification(Europe)

Oncethedrawinghasbeenissuedtotheshopfloor,itisusualtofindanadditionalsafetyfactoralsobeingappliedonbythewelderorinspector.Itisalsocommontohear'addabitmoreitwillmakeitstronger'.Theoutcomeisanoversizedweldwithperhapsan8mmleglengthratherthanthe6mmspecifiedbythedesigner.Thisextra2mmconstitutesanincreaseinweldvolumeofover80%.Thiscoupledwiththealreadyoverspecifiedweldsizefromthedesigner's'safetyfactor'mayleadtoaweldthatistwicethevolumeofacorrectlysizedfilletweld.Bykeepingtheweldtothesizespecifiedbythedrawingoffice,fasterweldingspeedscanbeachieved,thereforeincreasingproductivity,reducingoverallproductweight,consumableconsumptionandconsumablecost.


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Theotherbenefitisthat,inthecaseofmostarcweldingprocesses,aslightincreaseintravelspeedwouldinmostcasesseeanincreaseinrootpenetrationsothattheactualthroatthicknessisincreased:Anoversizedweldisthereforeverycostlytoproduce,maynothave'betterstrength'andiswastefulofweldingconsumablesandmayseeotherfabricationproblemsincludingexcessivedistortion.

Lap joints welded with fillet welds.

Asdiscussedearlier,oversizedweldsarecommonplaceandthelapjointisnoexception.ThedesignermayspecifyaleglengththatisequaltothematerialthicknessasinFig.7.

Fig7.Lapjoint-leglengthspecification

Strengthconsiderationsmaymeanthatthefilletweldsizeneednotbeanywhereneartheplatethickness.Inpracticetheweldmayalsobedeficientinotherwaysforexample:

Fig8.Exampleshowinganundersizedfilletweld

Duetomeltingawayofthecorneroftheupperplate(Fig.8),theverticalleglengthisreducedmeaningthatthedesignthroathasalsobeenreduced;thereforeanundersizedweldhasbeencreated.Careisthereforeneededtoensurethatthe

corneroftheupperplateisnotmeltedaway.Ideallytheweldshouldbesome0.5-1mmclearofthetopcorner( Fig.9).

Fig9.Ideallytheweldshouldbe0.5-1mmclearofthetopcorner

Itmaybethedesignermaythereforespecifyaslightlysmallerleglengthcomparedtothethicknessofthecomponent.Tocompensateforthisreductioninthroatthicknessitmaybenecessarytospecifyadeeppenetrationfilletweld.Thisamountofadditionalpenetrationwouldneedtobeconfirmedbysuitableweldtests.Additionalcontrolsmayalsobeneededduringproductionweldingtoensurethatthisadditionalpenetrationisbeingachievedconsistently.Inadditiontothereductioninthroatthicknessthereisthepotentialforadditionalproblemssuchasoverlapattheweldtoeduetothelargerweldpoolsize(Fig.10)oranexcessivelyconvexweldfaceandconsequentialsharpnotchesattheweldtoe(Fig.11).


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Fig10.Overlapattheweldtoeduetothelargerweldpoolsize

Fig11.Excessivelyconvexweldfaceandconsequentialsharpnotchesattheweldtoe

BoththepotentialproblemsshowninFigs.10and11couldadverselyinfluencethefatiguelifeoftheweldedjointduetotheincreasedtoeangle,whichactsasagreaterstressconcentration.Poorfit-upcanalsoreducethethroatthicknessasinFig.12.Thecorneroftheverticalcomponenthasbeenbevelledinthesketchinanexaggeratedmannertoillustratethepoint.

Fig12.Throatthicknessmaybereducedbypoorfit-up

Summary

Filletweldedjointsarenotonlythemostfrequentlyusedweldjointsbutarealsooneofthemostdifficulttoweldwithanyrealdegreeofconsistency.Filletweldsrequireahigherheatinputthanabuttjointofthesamethicknessand,withlessskilledweldersthiscanleadtolackofpenetrationand/orfusiondefectsthatcannotbedetectedbyvisualexaminationandotherNDTtechniques.FilletweldedjointsarenotalwaysopentoNDTorareindeedtimeconsumingtomanynon-destructivelytestingtechniquessuchasradiographyorultrasonictestingandtheresultsareoftendifficulttointerpret.Inspectionmethodssuchasvisualinspection,magneticparticleinspectionandpenetrantinspectionaresurfaceexaminationtechniquesonlyandwithvisualinspection,muchoftheeffortisexpendedinmeasuringthesizeoftheweldratherthanidentifyingother

qualityaspects.Filletweldedjointsarethereforemuchmoredifficulttoweldandinspect.Oftentheweldsthatareproducedarelargerthantheyneedtobeortheymaybeofapoorshapewhichcanadverselyinfluencetheirserviceperformance.Toovercomethesedifficulties,designersneedtospecifyaccuratelythemostappropriatethroatsizeandweldingpersonnelshouldstrivetoachievethespecifieddesignsize.Weldersalsoneedtobeadequatelytrainedandsufficientlyskilledtobecapableofmaintaininganacceptableweldquality.ThisarticlewaswrittenbyMark Cozens of Weld-Class Solutions.AnyenquiriesregardingthecontentofthearticleshouldbeaddressedinitiallytotheEditor,Connect.

A review of the application of weld symbols on drawings - Part 2

Job Knowledge

Part1ofthisarticlewhichappearedintheMay/JuneissueofConnect,dealtwiththemostbasicweldsymbolsasthey

appearonengineeringdrawings.Aspreviouslymentioned,itisessentialthatallconcernedinanyprojectareawareofwhichStandardisbeingapplied.

Weld sizing

Inorderthatthecorrectsizeofweldcanbeapplied,itiscommontofindnumberstoeithertheleftortotherightofthesymbol.Forfilletwelds,numberstotheleftofthesymbolindicatethedesignthroatthickness,leglength,orbothdesignthroatthicknessandleglengthrequirements.Figure1givesexamplesofsymbolsusedindifferentStandards.
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Fig.1

Forfilletwelds:SupersededBS499Pt2gives

a=designthroatthicknessb=leglength

ISO2553/EN22553requirements

a=designthroatthicknessz=leglength

s=penetrationthroatthickness

Forbuttjointsandwelds,anSwithanumbertotheleftofasymbolreferstothedepthofpenetrationasshownin Fig.2.

Fig.2

Whentherearenospecificdimensionalrequirementsspecifiedforbuttweldsonadrawingusingweldsymbols,itwouldnormallybeassumedthattherequirementisforafullpenetrationbuttweld( Fig.3).

Fig.3

Numberstotherightofasymbolorsymbolsrelatetothelongitudinaldimensionofwelds, egforfillets,thenumberofwelds,weldlengthandweldspacingfornon-continuouswelds,asFig.4.


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Fig.4

Onfilletweldedjointsmadefrombothsides,astaggeredweldcanbeshownbyplacinga'Z'throughthereferenceline(Fig.5).

Fig.5

Supplementary symbols

Weldsymbolsindicatethetypeofpreparationtouseortheweldtype.However,theremaystillbeoccasionswhereotherinformationisrequired.ThebasicinformationcanthereforebeaddedtoinordertoprovidefurtherdetailsasshowninFigs.6,7and8.


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Fig.6

Fig.7

Fig.8

Weld all round

ForaRectangularHollowSection(RHS)weldedtoaplate,forexample:

Weld in the field or on site

Theboxattachedtothearrowcanbeusedtocontain,orpointto,otherinformation.

Welding process type

ISO4063givesweldingprocessesspecificreferencenumbers.AsshowninFig.9theappropriateprocessnumberisplacedinthetailofthearrow.Otherprocessesaregivenauniquenumber.Inthisexample,135referstoMAGwelding.


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Fig.9

ThereareanumberofadditionalsymbolsgivenintheStandards(egISO22553)whichrefertoadditionalweldingorjointrequirements.Figure10showstherequirementforasealingrun.

Fig.10

Compound joints/welds

Acompoundweldcouldbea'T'buttweldwhichrequiresfilletweldstobeaddedtoincreasethethroatthicknessasshowninFig.11.

Fig.11

The broken reference line


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Fig.12

ThemainfeaturethatdistinguishesweldsymbolstandardsisthatforISO2553andBSEN22553,thereisanadditionalfeatureofabrokenreferenceline.Thismethodisusedwhenaweldmentorweldpreparationneedstobespecifiedonthe'otherside'ofthearrowasshowninFig.12.

Anysymbolthatisusedtoshowajointorweldtypefeatureontheothersideofthearrowlineisalwaysplacedonadottedline.BS499andAWSrequiresymbolstobeplacedabovethereferenceline(whichindicatetheotherside)orbelowthereferenceline(indicatingthearrowside).

Summary

Weldsymbolsareaveryusefulwayofcommunicatingweldingrequirementsfromthedesignofficetotheshopfloor.Itisessentialthatthe'rules'ofthestandardusedarecorrectlyappliedbydrawingofficepersonnel.However,itisalsoimportantthatshopfloorpersonnelareabletoreadandunderstandthedetailsofweldsymbols.Muchofthisrequirementcanbemetbyreferencetothestandardbeingusedwithintheorganisationandbythedrawingofficepersonnelconsideringtheneedsoftheendusersuchasthewelders,weldingsupervisors,weldinginspectionpersonnelandweldingengineersinordertominimisecostlymistakesduetomisinterpretation.

Trainingofallpersonnelinthecorrectuseofweldsymbolspecificationsalsoplaysanimportantroleinensuringthatweldsymbolsarebothcorrectlyappliedandcorrectlyread.ThisarticlewaswrittenbyMark CozensofWeld-Class Solutions.

welding Geometric Shape Imperfections general review

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