常见缺陷图.docx

常见缺陷图.docx

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常见缺陷图

GeneralWeldingDiscontinuities

Thefollowingdiscontinuitiesaretypicalofalltypesofwelding.

Coldlapisaconditionwheretheweldfillermetaldoesnotproperlyfusewiththebasemetalorthepreviousweldpassmaterial（interpasscoldlap）.Thearcdoesnotmeltthebasemetalsufficientlyandcausestheslightlymoltenpuddletoflowintobasematerialwithoutbonding.

Porosity（气孔）istheresultofgasentrapmentinthesolidifyingmetal.Porositycantakemanyshapesonaradiographbutoftenappearsasdarkroundorirregularspotsorspecksappearingsingularly,inclustersorrows.SometimesporosityiselongatedandmayhavetheappearaneeofhavingatailThisistheresultofgasattemptingtoescapewhilethemetalisstillinaliquidstateandiscalledwormholeporosity.Allporosityisavoidinthematerialitwillhavearadiographicdensitymorethanthesurroundingarea.

Clusterporosity（密集气孔）iscausedwhenfluxcoatedelectrodesare

contaminatedwithmoisture.Themoistureturnsintogaseswhenheatedandbecomestrappedintheweldduringtheweldingprocess.Clusterporosityappearjustlikeregularporosityintheradiographbuttheindicationswillbegroupedclosetogether.

Slaginclusions（夹渣）arenonmetallicsolidmaterialentrappedinweldmetalorbetweenweldandbasemetal.Inaradiograph,dark,jaggedasymmetricalshapeswithintheweldoralongtheweldjointareasareindicativeofslaginclusions.

Incompletepenetration（IP）orlackofpenetration（LOP）（未焊透）occurswhen

theweldmetalfailstopenetratethejoint.Itisoneofthemostobjectionablewelddiscontinuities.Lackofpenetrationallowsanaturalstressriserfromwhichacrackmaypropagate.Theappearanceonaradiographisadarkareawithwell-defined,

straightedgesthatfollowsthelandorrootfacedownthecenteroftheweldment.

Incompletefusion（未融合）isaconditionwheretheweldfillermetaldoesnot

properlyfusewiththebasemetal.Appearanceonradiograph:

usuallyappearsasadarklineorlinesorientedinthedirectionoftheweldseamalongtheweldpreparationorjoiningarea.

Internalconcavityorsuckback（内凹）isconditionwheretheweldmetalhas

contractedasitcoolsandhasbeendrawnupintotherootoftheweld.Onaradiographitlookssimilartolackofpenetrationbutthelinehasirregularedgesanditisoftenquitewideinthecenteroftheweldimage.

Internalorrootundercut（根部咬边）isanerosionofthebasemetalnexttothe

rootoftheweld.Intheradiographicimageitappearsasadarkirregularlineoffsetfromthecenterlineoftheweldment.UndercuttingisnotasstraightedgedasLOPbecauseitdoesnotfollowagroundedge.

Externalorcrownundercut（外咬边）isanerosionofthebasemetalnexttothe

crownoftheweld.Intheradiograph,itappearsasadarkirregularlinealongtheoutsideedgeoftheweldarea.

Offsetormismatch（错边）aretermsassociatedwithaconditionwheretwopiecesbeingweldedtogetherarenotproperlyaligned.Theradiographicimageisanoticeablediffereneeindensitybetweenthetwopieces.Thediffereneeindensityiscausedbythedifferenceinmaterialthickness.Thedark,straightlineiscausedbyfailureoftheweldmetaltofusewiththelandarea.

Inadequateweldreinforcement（未焊满）isanareaofaweldwherethethicknessofweldmetaldepositedislessthanthethicknessofthebasematerial.Itisveryeasytodeterminebyradiographiftheweldhasinadequatereinforcement,becausetheimagedensityintheareaofsuspectedinadequacywillbemore（darker）thantheimagedensityofthesurroundingbasematerial.

Excessweldreinforcement（焊缝余高过高）isanareaofaweldthathasweldmetaladdedinexcessofthatspecifiedbyengineeringdrawingsandcodes.Theappearanceonaradiographisalocalized,lighterareaintheweld.Avisualinspectionwilleasilydetermineiftheweldreinforcementisinexcessofthatspecifiedbytheengineeringrequirements.

Cracks（裂纹）canbedetectedinaradiographonlywhentheyarepropagatinginadirectionthatproducesachangeinthicknessthatisparalleltothex-raybeam.

Crackswillappearasjaggedandoftenveryfaintirregularlines.Crackscansometimesappearas"tails"oninclusionsorporosity.

DiscontinuitiesinTIGwelds

ThefollowingdiscontinuitiesarepeculiartotheTIGweldingprocess.Thesediscontinuitiesoccurinmostmetalsweldedbytheprocessincludingaluminumandstainiesssteels.TheTIGmethodofweldingproducesacleanhomogeneousweldwhichwhenradiographediseasilyinterpreted.

Tungsteninclusions（夹钨）.Tungstenisabrittleandinherentlydensematerialusedintheelectrodeintungsteninertgaswelding.Ifimproperweldingproceduresareused,tungstenmaybeentrappedintheweld.Radiographically,tungstenismoredensethanaluminumorsteel;therefore,itshowsasalighterareawithadistinctoutlineontheradiograph.

Oxideinclusionsareusuallyvisibleonthesurfaceofmaterialbeingwelded（especiallyaluminum）.Oxideinclusionsarelessdensethanthesurroundingmaterialsand,therefore,appearasdarkirregularlyshapeddiscontinuitiesintheradiograph.

DiscontinuitiesinGasMetalArcWelds（GMAW）

ThefollowingdiscontinuitiesaremostcommonlyfoundinGMAWwelds.

Whiskersareshortlengthsofweldelectrodewire,visibleonthetoporbottomsurfaceoftheweldorcontainedwithintheweld.Onaradiographtheyappearaslight,"wirelike"indications.

Burn-Through（烧穿）resultswhentoomuchheatcausesexcessiveweldmetaltopenetratetheweldzone.Oftenlumpsofmetalsagthroughtheweldcreatingathickglobularconditiononthebackoftheweld.Theseglobsofmetalarereferredtoasicicles.Onaradiograph,burnthroughappearsasdarkspots,whichareoftensurroundedbylightglobularareas（icicles）.

-Castings（铸件）

RadiographInterpretation

Themajorobjectiveofradiographictestingofcastingsisthedisclosureofdefectsthatadverselyaffectthestrengthoftheproduct.Castingareaproductformthatoftenreceiveradiographicinspectionsincemanyofthedefectsproducedbythecastingprocessarevolumetricinnatureand,thus,relativelyeasytodetectwiththismethod.Thesediscontinuitiesofcourse,arerelatedtocastingprocessdeficiencies,which,ifproperlyunderstood,canleadtoaccurateaccept-rejectdecisionsaswellastosuitablecorrectivemeasures.Sincedifferenttypesandsizesofdefectshavedifferenteffectsoftheperformaneeofthecasting,itisimportantthattheradiographerisabletoidentifythetypeandsizeofthedefects.ASTME155,StandardforRadiographsofcastingshasbeenproducedtohelptheradiographermakeabetterassessmentofthedefectsfoundcomponents.Thecastingsusedtoproducethestandardradiographshavebeendestructivelyanalyzedtoconfirmthesizeandtypeofdiscontinuitiespresent.Thefollowingisabriefdescriptionofthemostcommondiscontinuitytypesincludedinexistingrefereneeradiographdocuments（ingradedtypesorassingleillustrations）.

RADIOGRAPHICINDICATIONSFORCASTINGS

Gasporosityorblowholesarecausedbyaccumulatedgasorairwhichistrappedbythemetal.Thesediscontinuitiesareusuallysmooth-walledroundedcavitiesofaspherical,elongatedorflattenedshape.

Ifthesprueisnothighenoughtoprovidethenecessaryheattransferneededtoforcethegasorairoutofthemold,thegasorairwillbetrappedasthemoltenmetalbeginstosolidify.Blowscanalsobecausedbysandthatistoofine,toowet,orbysandthathasalowpermeabilitysothatgascan'tescape.Toohighamoisturecontentinthesandmakesitdifficulttocarrytheexcessivevolumesofwater

vaporawayfromthecasting.Anothercauseofblowscanbeattributedtousinggreenladles,rustyor

Sandinclusionsanddrossarenonmetallicoxides,appearingontheradiographasirregular,darkblotches.Thesecomefromdisintegratedportionsofmoldorcorewallsand/orfromoxides（formedinthemelt）whichhavenotbeenskimmedoffpriortointroductionofthemetalintothemoldgates.Carefulcontrolofthemelt,properholdingtimeintheladleandskimmingofthemeltduringpouringwillminimizeorobviatethissourceoftrouble.

Shrinkageisaformofdiscontinuitythatappearsasdarkspotsontheradiograph.Shrinkageassumesvariousformsbutinallcasesitoccursbecausemoltenmetalshrinksasitsolidifies,inallportionsofthefinalcasting.Shrinkageisavoidedbymakingsurethatthevolumeofthecastingisadequatelyfedbyriserswhichsacrificiallyretaintheshrinkage.Shrinkagecanberecognizedinanumberofcharacteristicbyvaryingappearancesonradiographs.Thereareatleastfourtypes:

（1）cavity;

（2）

dendritic;（3）filamentary;and（4）spongetypes.Somedocumentsdesignatethesetypesbynumbers,

Cavityshrinkageappearsasareaswithdistinetjaggedboundaries.Itmaybeproducedwhenmetalsolidifiesbetweentwooriginalstreamsofmelt,comingfromoppositedirectionstojoinacommonfront;cavityshrinkageusuallyoccursatatimewhenthemelthasalmostreachedsolidificationtemperatureandthereisnosourceofsupplementaryliquidtofeedpossiblecavities.

Dendriticshrinkageisadistributionofveryfinelinesorsmallelongatedcavitiesthatmayvaryindensityandareusuallyunconnected.

Filamentaryshrinkageusuallyoccursasacontinuousstructureofconnectedlinesorbranchesofvariablelength,widthanddensity,oroccasionallyasa