Background: Leak-before-break technique is widely used in operating and abuilding nuclear plants

for which net-section-criteria is adopted by ASME to assess flawed pipes under full yielding condition.Purpose: However

net-section-criteria has been proved to overestimate the loading capacity of structure.Methods: For nuclear pipeline with internal surface crack

finite element method is used to simulate its deformation process under internal pressure

and initial plastic failure load is determined based on J integral curves of crack front.Results: Then

calculated value of initial plastic load is compared with theoretical one from ASME code

and the results show that the theoretical value overestimates the capacity load of structure.Conclusions: Finally

applicability of allowable membrance stress for level-A service restriction set by ASME-BPVC-XI code is evaluated.