Fatigue Crack Growth Prediction of a Pipe With a Circumferential Surface Flaw Using ΔJ and Reference Stress Method

Fatigue crack growth calculation method beyond ΔK in codes and standards, like ASME Sec. XI or JSME rules for Fitness for Service has not been established even in Mode I. In the FDF-II Subcommittee of the nuclear research committee of the Japan Welding Engineering Society, an evaluation procedure for fatigue crack growth beyond small scale yielding using ΔJ has been investigated for several years. Since the evaluation procedure in the Subcommittee is to be incorporated into codes and standards, it should not be complex. Therefore the reference stress approach was tried to apply to calculate J-integral as a simplified procedure. Several formulae for J-integral calculation based on the reference stress approach were proposed by researchers. The authors joined the Subcommittee and performed finite element analyses for a sample problem to confirm the accuracy of those formulae, which were for a pipe with a circumferential part-through wall flaw subjected by bending load. The reference stress-based J, whose accuracy was confirmed by the authors, was applied to predict crack growth behaviors of pipes with a circumferential surface flaw under cyclic bending load conducted by other researches a decade ago. The difference of the failure cycles between the prediction and the experiment were nearly within a factor of 2. Since the verification of the simplified procedure was performed for just one case, more verification cases were needed to incorporate the procedure into codes and standards.