TOFD厚壁压力容器焊接检测超声成像计算机技术Word格式文档下载.docx
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TOFD厚壁压力容器焊接检测超声成像计算机技术Word格式文档下载.docx
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▪Scanningdirection
▪Realtimeacquisitionandrecords
▪Imageevaluation
▪Experiencesonexaminationofwelds
▪Conclusions
▪Bibliography
Abstract
ThepaperpresentsTOFD,theTimeofFlightDiffractionTechnique,currentlythemostpromisingultrasonictechniqueforexaminationofheavywallthicknessweldsonPressureVesselsTOFD,isacomputerizedultrasonicsystem,abletoscan,store,andevaluateindicationsintermsofheight(throughthicknessweld),length,position,withadegreeofaccuracyneverachievedwithotherultrasonictechniques.ArecordofexaminedsectionsisavailableinunprocessedformonfloppydiskorCDandreadableinWordforWindows95.TheASMECode,withCodeCaseno.2235hasacceptedthismethodinlieuofradiographyexaminationforthicknessesover4"
(1).Experienceson75mmupto300mmthickweldsof2.5/3%Q1Mo,0.25VandCarbonsteelarediscussed.Thetechniquehasbeenappliedonlongitudinal,circumferentialandnozzle-shell/beadwelds.ScanningPlanDataanditsvalidationarereportedwithusedtestblocks.CladdedlayersinTOFDimagesarepresented.Basedonexperiencetodate,prospectsforthisnewtechniqueareofgreatinterest.
FundamentalsoftheTOFDtechnique
TheTOFDtechniquewasfirstappliedin1985attheHarwellCenter(UK)inresponsetoinsistentrequeststosizecracksinnuclearreactorwelds
(2).
TheTOFDtechniqueisafullycomputerizedsystemabletoscan,store,andevaluateindicationsintermsofheight,length,andpositionwithagradeofaccuracyneverachievedbyotherultrasonictechniques.
TheTOFDtechniqueisbasedondiffractionofultrasonicwavesontipsofdiscontinuities,insteadofgeometricalreflectionontheinterfaceofthediscontinuities.
ThisphenomenamakesTOFDidealforidentifyingcracks,lackoffusionlocatedalongtheverticalaxisoftheweld(inparticularfornarrowgappreparation)orwithanyotherorientations,becausedetectionisnotaffectedbythenegativeconsequenceofultrasonicbeamdeviationfromthereceiverduetounfavourableorientationofthediscontinuity.
ThesefeatureshaveextendedtheuseofTOFDtoreplaceRadiographyandcomplexUltrasonicinspectionbytandemtechniquewhereverplanardefects(cracks,lackoffusion)arethemainobjectofexamination.
ThemaindisadvantagestoboththeaforementionedtechniquesareexpensivemanipulationforRadiographyonbigpartsandtheamountoftimerequiredtoperformthetandemtechniqueduetotheaccuracynecessaryforreliabletesting.
TOFDovercomesbothtechniquesintermsofspeedofexaminationandhigheraccuracy.
TOFDnorms
ExperienceacquiredinapplicationofTOFDhasfullydemonstrateditsreliabilityanddetectioncapacitywithrespecttoothermethods(3).ThishasinducedpotentialuserstoestablishproceduresforcodingTOFDinrecognizedstandardizednorms.
TheBritishStandardInstitutehasissuedthefirstdraft:
BSNo7706(4)
ASMECodehasincludedinSectionV,art.4,AppendixE,thecomputerizedultrasonicsystemandTOFDtechniqueforultrasonicexaminationofwelds(5).
An"
adhoc"
WorkgrouphasbeennominatedfromwithintheASMETechnicalCommitteetoprepareadocumentestablishingtheconditionsforusingcomputerizedsystems,suchasTOFDinreplacingRadiographyexaminationsofwelds,intheover4"
thicknessrange(seeCodeCase).
CEN(comiteEuropeendeNormalisation)hasissuedthedocumentCEN/138/WGonpracticalapplicationofTOFDforultrasonicexaminationofwelds(6).
TOFDApplications
OneofthemajorapplicationsofTOFDistheultrasonicexaminationofweldsafterfinalheattreatmentand/orhydraulictesting,toverifytheabsenceofcracksnotdetectablebyRadiographyandtoproveconformitywithpriorultrasonicmanualexaminationcarriedoutduringconstruction.
Inadditiontohighersensitivity,theTOFDtechniqueallowsthefullexaminationdatatoberecordedonharddisk,displayingalldiscontinuitiesinC/scanimages.Thisenables"
offline"
evaluationofindicationsbycomputerusingdedicatedsoftware.Veryaccuratesizingofdefectscanbeachievedandprintedfordocumentation.
AnotheradvantageandcurrentapplicationofTOFDisitsuseinmonitoringweldsduringtheservicelifeofcomponents.Storeddataacquiredfrominitialexaminations,madeduringthefinalstageofconstruction,canbecomparedwithnewdataobtainedfromin-serviceinspection.Thisallowsthestabilityofexistingindicationstobedeterminedwithhighaccuracyandreliability.
ThemoreaccuracyguaranteedbyTOFDinsizingthruwallextentionofflawsallowsmorereliablefracturemechaniccalculationfortheresiduallifeevaluation.
CompanieslikeExxon,Shell,FluorDaniel,Texaco,Chevronetc.areusingTOFDtoreplaceradiographyinexaminationofweldsafterPVMTorhydraulictesting.ThemaininspectionagencieshaveapprovedproceduresoftheTOFDTechniqueanditsvalidation.
PhysicalprincipleofTOFD
Fig1:
TOFDwavespatternandcorrespondingA-Scanpresentation
Fig2:
Compressionalwaves(left)crossingthetipofadiscontinuitygenerateawidebeamofsphericalwaves(right)
Fig.3:
TOFDmapofthecalibrationonASMEtestblockof185mm(7.28inch)withthreeholesof7.5nun(1/3inch.)diameter.TheTOFDmapshowsthethreeholeswithsymmetricalmodeconversionindication.ThestraightlinesatleftandrightoftheTOFDmaparerespectivelythelaterwave(scanningsurface)andtheback-wallwaves(oppositesurface).Thespacebetweenthesetwolinerepresentsthethicknessoftheweld.
TypicalpatternofwavesinvolvedinTOFDtechnique
FourdifferenttypesofwavesareinvolvedintheconstructionofaTOFDimage:
▪longitudinalwavegeneratedbythetransmitterandpartiallytransformedinsphericalwavewhenthebeamcrossthetipofdefect
▪thelateralwavethatflowsonthesurfacebetweenthetwotransducers
▪thelongitudinalwavereflectedbythebackwall
▪theshearwavesgeneratedbythemodeconversionL/Tontheinterfaceofdiscontinuities
InFigure1TOFDwavespatternandthecorrespondingA-SCANimagearerepresented.
TheFigure2showshowsphericalwavesaregeneratedonthetipsofthecrackswhenincidentlongitudinalwavescrossthetip.
TheFigure3showsatypicalTOFDimageobtainedduringcalibrationofequipmentontwocylindricalholes.
TheFigure4representsthemathematicalandgeometricalmodelonwhichTOFDsoftwareisbased.
MATHEMATICMODELOFTOFD
Fig.4-OnPitagoraprincipleisbasedthesoftwareto
measurethetroughthicknessdimensioninTOFDTechnique.
Configurationofsystem
Fig5:
BlockdiagramofTOFDultrasoniccomputerizedsystem.
Fig5a:
TheTOFDsysteminitspracticalaspect.
TheFigure5representstheblockdiagramofTOFDsystemforexaminationofweld.Thesystemiscomposedby:
▪computerwithdedicatedboards(P/R,A/D)andTOFDsoftware
▪probesassembledonaspecialholdertoallowscanningparallelandtransversaltotheweldsaxis
▪Printertoprinttheresult
ProbesneedspecialcharacteristicstoemitshortpulsestoimproveaccuracymTimeOfFlightmeasurement.Incaseofsmallthicknesseshighfrequencycanbeused,4-8MHz.
Computer'
sfeatures
Portablecomputer,Pentium,withminimum3slotfreeforinstalledtheboards,colorscreenactivematrixTFT,Window'
s95.
Scanningplan
ParametersaffectingtheapplicationofTOFDtechniquearethefollowing:
▪PCS(ProbeCenterSpacing)
▪DZ(DepthZone)foreachrangeofthicknessanappropriatevalueshallbeestablishedandvalidatedontestblock
▪Probecenterline
▪Probefrequency
▪Probeangle
▪Crystaldiameter
▪Testblock
Allthementionedparameters,aftervalidation,arereportedintherelevantSCANNINGPLAN,seeanexampleonFigure6.
SCANPLANTAB.1
Fig.6-ScanPlanindicatingthemainparametersvaluetouseinrelationofthethicknessexamined.
Block
Ident
Thickness
ofweld
calibration
block
Calibration
hole
ø
(mm)
grove
Angle
Beam
DZ
DepthZone
PCS-ProbeCenter
Spacing
BC:
Beam
Centerline
mm
0
Location
depth
degree
1
85
90
2.5
1/4T
1/2T
3/4T
3,28mm
52°
0-90
BC=57mm
PCS=184mm
2
164
170
35°
0-90
90-170
PCS=184mm
BC=125mm
PCS=175mm
Scanningdirection
Fig7a:
-Scanningdirection-paralleltotheweldaxis.
Fig:
7b-Scanningdirection-perpendiculartotheweldaxistoimprovesizingaccuracyofindication.
Thescanningdirectionsforexaminationofweldedjointhascarriedoutmovingtheholderparalleltotheweldaxis,seeFigure7a.Incaseofflaws,inordertobettercharacterizetheshapeanditsdimensionanadditionalscanningperpendiculartotheweldaxisshallbeperformed(Figure7b).
Whentransversalcrackshavetobeinvestigatedascanin90°
orientationwithrespecttotheprimaryscanningshallbeapplied
Realtimeacquisitionandrecords
Fig8:
B-ScanimageinrealtimecreateandvisualizeonPCduringthescanningof1meterlengthweldand135mm(5.3inch.)ofthickness.
Alldataofexaminationarecollectedinrealtimebythe
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- 关 键 词:
- TOFD 压力容器 焊接 检测 超声 成像 计算机技术