射线检测常见缺陷图Word文档下载推荐.docx
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voidinthematerialitwillhavearadiographicdensitymorethanthesurroundingarea.
(密集气孔)iscausedwhenfluxcoatedelectrodesarecontaminatedwithmoisture.Themoistureturnsintogaseswhenheatedandbecomestrappedinthe
weldduringtheweldingprocess.Clusterporosityappearjustlikeregularporosityinthe
radiographbuttheindicationswillbegroupedclosetogether.
arenonmetallicsolidmaterialentrappedinweldmetalorbetweenweldandbasemetal.Inaradiograph,dark,jaggedasymmetricalshapeswithintheweld
oralongtheweldjointareasareindicativeofslaginclusions.
occurswhentheweld
metalfailstopenetratethejoint.Itisoneofthemost
objectionablewelddiscontinuities.
Lackofpenetrationallowsanaturalstressriserfromwhichacrack
maypropagate.The
appearanceonaradiographisadarkareawithwell-defined,straightedgesthatfollows
thelandorrootfacedownthecenteroftheweldment.
(未融合)isaconditionwheretheweldfillermetaldoesnot
properlyfusewiththebasemetal.Appearanceonradiograph:
usuallyappearsasadarklineor
linesorientedinthedirectionoftheweldseamalongtheweldpreparationorjoining
area.
isconditionwheretheweldmetalhascontractedasitcoolsandhasbeendrawnupintotherootoftheweld.Onaradiographitlooks
similartolackofpenetrationbutthelinehasirregularedgesand
itisoftenquitewidein
isanerosionofthebasemetalnexttotherootoftheweld.Inthe
radiographicimageitappearsasadarkirregularlineoffsetfromthecenterlineoftheweldment.UndercuttingisnotasstraightedgedasLOPbecauseit
isanerosionofthebasemetalnexttothecrown
oftheweld.Intheradiograph,itappearsasadarkirregularline
alongtheoutsideedge
aretermsassociatedwithaconditionwheretwopiecesbeingweldedtogetherarenotproperlyaligned.Theradiographicimageisanoticeable
differeneeindensitybetweenthetwopieces.Thediffereneeindensityiscausedbythe
differenceinmaterialthickness.Thedark,straightlineiscaused
byfailureoftheweld
metaltofusewiththelandarea.
isanareaofaweldwherethethicknessofweldmetaldepositedislessthanthethicknessofthebasematerial.Itisveryeasyto
determinebyradiographiftheweldhasinadequatereinforcement,becausetheimage
densityintheareaofsuspectedinadequacywillbemore(darker)thantheimagedensity
ofthesurroundingbasematerial.
isanareaofaweldthathasweldmetaladdedinexcessofthatspecifiedbyengineeringdrawingsandcodes.Theappearaneeonaradiographisalocalized,lighterareaintheweld.Avisualinspectionwilleasily
determineiftheweldreinforcementisinexcessofthatspecifiedbytheengineering
requirements.
canbedetectedinaradiographonlywhentheyarepropagatinginadirectionthatproducesachangeinthicknessthatisparalleltothex-raybeam.Cracks
willappearasjaggedandoftenveryfaintirregularlines.Crackscansometimesappear
as"
tails"
oninclusionsorporosity.
ThefollowingdiscontinuitiesarepeculiartotheTIGweldingprocess.These
discontinuitiesoccurinmostmetalsweldedbytheprocessincludingaluminumand
stainlesssteels.TheTIGmethodofweldingproducesacleanhomogeneousweldwhich
whenradiographediseasilyinterpreted.
Tungstenisabrittleandinherentlydensematerialusedin
theelectrodeintungsteninertgaswelding.Ifimproperweldingproceduresareused,
tungstenmaybeentrappedintheweld.Radiographically,tungstenismoredensethan
aluminumorsteel;
therefore,itshowsasalighterareawithadistinetoutlineonthe
radiograph.
areusuallyvisibleonthesurfaceofmaterialbeingwelded
(especiallyaluminum).Oxideinclusionsarelessdensethanthesurroundingmaterialsand,
therefore,appearasdarkirregularlyshapeddiscontinuitiesinthe
ThefollowingdiscontinuitiesaremostcommonlyfoundinGMAWwelds.
areshortlengthsofweldelectrodewire,visibleonthetoporbottomsurfaceoftheweldorcontainedwithintheweld.Onaradiographtheyappearaslight,"
wirelike"
indications.
resultswhentoomuchheatcausesexcessiveweldmetalto
penetratetheweldzone.Oftenlumpsofmetalsagthroughtheweldcreatingathick
globularconditiononthebackoftheweld.Theseglobsofmetalarereferredtoasicicles.
Onaradiograph,burnthroughappearsasdarkspots,whichareoftensurroundedby
lightglobularareas(icicles).
RadiographInterpretation—Castings
Themajorobjectiveofradiographictestingofcastingsisthedisclosureofdefectsthatadverselyaffectthestrengthoftheproduct.
Castingareaproductformthatoftenreceiveradiographicinspectionsincemanyofthedefectsproducedbythecastingprocessarevolumetricinnatureand,thus,relativelyeasytodetectwiththismethod.Thesediscontinuitiesofcourse,arerelatedtocastingprocessdeficiencies,which,ifproperlyunderstood,canleadtoaccurateaccept-rejectdecisionsaswellastosuitablecorrectivemeasures.Sincedifferenttypesandsizesofdefectshavedifferenteffectsoftheperformanceofthecasting,itisimportantthattheradiographerisabletoidentifythetypeandsizeofthedefects.ASTME155,StandardforRadiographsofcastingshasbeenproducedtohelptheradiographermakeabetterassessmentofthedefectsfoundcomponents.Thecastingsusedtoproducethestandardradiographshavebeendestructivelyanalyzedtoconfirmthesizeandtypeofdiscontinuitiespresent.Thefollowingisabriefdescriptionofthemostcommondiscontinuitytypesincludedinexistingreferenceradiographdocuments(ingradedtypesorassingleillustrations).
Gasporosityorblowholesarecausedbyaccumulatedgasorairwhichistrappedbythemetal.Thesediscontinuitiesareusuallysmoothwalledroundedcavitiesofaspherical,elongatedorflattenedshape.Ifthe
sprueisnothighenoughtoprovidethenecessaryheattransferneededtoforcethegasorairoutofthemold,
thegasorairwillbetrappedasthemoltenmetalbeginstosolidify.Blowscanalsobecausedbysandthatis
toofine,toowet,orbysandthathasalowpermeabilitysothatgascan'
tescape.Toohighamoisturecontentin
thesandmakesitdifficulttocarrytheexcessivevolumesofwatervaporawayfromthecasting.Anothercause
ofblowscanbeattributedtousinggreenladles,rustyordampchillsand
chaplets.
Sandinclusionsanddrossarenonmetallicoxides,appearingontheradiographasirregular,darkblotches.Thesecomefromdisintegratedportionsofmoldorcorewallsand/orfromoxides(formedinthemelt)which
havenotbeenskimmedoffpriortointroductionofthemetalintothemoldgates.Carefulcontrolofthemelt,
properholdingtimeintheladleandskimmingofthemeltduringpouringwillminimizeorobviatethissource
oftrouble.
Shrinkageisaformofdiscontinuitythatappearsasdarkspotsontheradiograph.Shrinkageassumesvarious
formsbutinallcasesitoccursbecausemoltenmetalshrinksasitsolidifies,inallportionsofthefinalcasting.
Shrinkageisavoidedbymakingsurethatthevolumeofthecastingisadequatelyfedbyriserswhich
sacrificiallyretaintheshrinkage.Shrinkagecanberecognizedinanumberofcharacteristicbyvarying
appearancesonradiographs.Thereareatleastfourtypes:
(1)cavity;
(2)dendritic;
(3)filamentary;
and(4)
spongetypes.Somedocumentsdesignatethesetypesbynumbers,withoutactualnames,toavoidpossible
misunderstanding.
Cavityshrinkageappearsasareaswithdistinctjaggedboundaries.
Itmaybeproducedwhenmetalsolidifies
betweentwooriginalstreamsofmelt,comingfromopposite
directionstojoinacommonfront;
cavity
shrinkageusuallyoccursatatimewhenthemelthasalmostreached
solidificationtemperatureandthereisno
sourceofsupplementaryliquidtofeedpossiblecavities.
isadistributenofveryfinelinesorsmallelongatedcavitiesthatmayvaryindensityandareusuallyunconnected.
usuallyoccursasacontinuousstructureofconnectedlinesorbranchesofvariablelength,widthanddensity,oroccasionallyasa
network.
showsitselfasareasoflacytexturewithdiffuseoutlines,
generallytowardthemid-thicknessofheaviercastingsections.Spongeshrinkagemaybe
dendriticorfilamentaryshrinkage;
filamentaryspongeshrinkageappearsmoreblurred
becauseitisprojectedthroughtherelativelythickcoatingbetweenthediscontinuities
andthefilmsurface.
arethin(straightorjagged)linearlydisposeddiscontinuitiesthatoccurafterthemelthassolidified.Theygenerallyappearsinglyandoriginateatcastingsurfa