Reliability-basedloadandresistancefactordesignforpiping:anexploratorycasestudyOriginalResearchArticle

ThispaperpresentsanexploratorycasestudyontheapplicationofLoadandResistanceFactorDesign(LRFD)approachtotheSectionIIIofASMEBoilerandPressureVesselcodeforpipingdesign.Thefailurecriterionfordefiningtheperformancefunctionisconsideredasplasticinstability.Presentlyuseddesignequationiscalibratedbyevaluatingtheminimumreliabilitylevelsassociatedwithit.IfthetargetreliabilityintheLRFDapproachissameasthatevaluatedforthepresentlyuseddesignequation,itisshownthatthetotalsafetyfactorsforthetwodesignequationsareidentical.Itisobservedthattheloadandresistancefactorsarenotdependentuponthediametertothicknessratio.Asensitivityanalysisisalsoconductedtostudythevariationsintheloadandresistancefactorsduetochangesin(a)coefficientsofvariationforpressure,moment,andultimatestress,(b)ratioofmeandesignpressuretomeandesignmoment,(c)distributiontypesusedforcharacterizingtherandomvariables,and(d)statisticalcorrelationbetweenrandomvariables.Itisobservedthatcharacterizationofrandomvariablesbylog-normaldistributionisreasonable.Considerationofstatisticalcorrelationbetweentheultimatestressandsectionmodulusgiveshighervaluesoftheloadfactorforpressurebutlowervalueforthemomentthanthecorrespondingvaluesobtainedbyconsideringthevariablestobeuncorrelated.Sincetheeffectofstatisticalcorrelationontheloadandresistancefactorsisrelativelyinsignificantfortargetreliabilityvaluesofpracticalinterest,theeffectofcorrelatedvariablesmaybeneglected.