ComparisonofexperimentalandfiniteelementanalyticalresultsforthestrengthandthedeformationofpipeswithlocalwallthinningsubjectedtobendingmomentOriginalResearchArticle

Fracturebehaviorsofpipeswithlocalwallthinningareveryimportantfortheintegrityofpowerplantpipingsystem.Inthisstudy,monotonicbendingtestswithoutinternalpressureareconductedon48.6mmdiameterSchedule80(thickness,5.1mm)STS370full-scalecarbonsteelpipespecimens.Fracturestrengthsoflocallywall-thinnedpipeswerecalculatedbyelasto-plasticanalysisusingfiniteelementmethod.Theelasto-plasticanalysiswasperformedbyFEcodeANSYS.Wesimulatedvarioustypesoflocalwallthinningthatcanbeoccurredatpipesurfaceduetocoolantflow.Locallywallthinnedshapesweremachinedtobedifferentinsizealongthecircumferentialoraxialdirectionofstraightpipes.Weinvestigatedfracturestrengthsandfailuremodesoflocallywallthinnedpipesbyfourpointbendingtest.And,theallowablelimitofpipeswithlocalwallthinningwasinvestigated.Inaddition,wecomparedthesimulatedresultsbyfiniteelementanalysiswithexperimentaldata.Thefailuremode,fracturestrengthandfracturebehaviorobtainedfromFEanalysesshowedwellagreementwithexperimentalresults.Fromthetestresults,weidentifiedthreetypesoffailuremodesintoovalization,localbucklingandcrackinitiation.Thesefailuremodescouldbeclassifiedaccordingtothinneddepth,thinnedlengthandthinnedangleofapipe.Forlocallywall-thinnedspecimens,maximummoments(Mmax)wereestimatedbyusingthenet-sectionstresscriterion.Pipeswithlocalwallthinningcanbeestimatedusingσuinsteadofσfbecauseof1.19σf≅σu.Also,theaxialstrainaffectsfailuremodesoccurredonlocalwallthinning.theallowablelimitoflocalwallthinningforcarbonsteelpipeusedcanbegivenasfollows;inthecaseofMmax≥My,if10≤l<25mm,d/tcanbeallowedtoabout55%,andif25≤l<100mm,d/tcanbeallowedtoabout50%.Also,if100≤l≤120mm,d/tcanbeallowedtoabout29%.