PredictionofcrackcoalescenceofsteamgeneratortubesinnuclearpowerplantsOriginalResearchArticle

Predictionoffailurepressuresofcrackedsteamgeneratortubesofnuclearpowerplantsisanimportantingredientinschedulinginspectionandrepairoftubes.Predictionisusuallybasedonnondestructiveevaluation(NDE)ofcracks.NDEoftenrevealstwoneighboringcracks.Ifthecracksinteract,thetubepressureunderwhichtheligamentbetweenthetwocracksfailscouldbemuchlowerthanthecriticalburstpressureofanindividualequivalentcrack.Theabilitytoaccuratelypredicttheligamentfailurepressure,called“coalescencepressure,”isimportant.Thefailurecriterionwasestablishedbynonlinearfiniteelementmodel(FEM)analysesofcoalescenceoftwo100%through-wallcollinearcracks.Theligamentfailureisprecipitatedbylocalinstabilityoftheligamentunderplanestrainconditions.Asaresultofthislocalinstability,theligamentthicknessintheradialdirectiondecreasesabruptlywithpressure.GoodcorrelationofFEManalysisresultswithexperimentaldataobtainedatArgonneNationalLaboratory’sEnergyTechnologyDivisiondemonstratedthatnonlinearFEManalysesarecapableofpredictingthecoalescencepressureaccuratelyfor100%through-wallcracks.ThisfailurecriterionandFEAworkhavebeenextendedtoaxialcracksofvaryingligamentwidth,cracklength,andcaseswherecracksareoffsetbyaxialorcircumferentialligaments.