軸方向表面き裂を有する鋳造ステンレス鋼管の破壊評価法

抄録

Since the ductility of cast austenitic stainless steel pipes decreases due to thermal aging embrittlement after long term operation, not only plastic collapse failure but also unstable ductile crack propagation (elastic-plastic failure) should be taken into account for the structural integrity assessment of cracked pipes. In the fitness-for-service code of the Japan Society of Mechanical Engineers (JSME), Z-factor is used to incorporate the reduction in failure load due to elastic-plastic failure. However, the JSME code does not provide the Z-factor for axial cracks. In this study, Z-factor for axial cracks in aged cast austenitic stainless steel pipes was derived. Furthermore, an optimized failure assessment curve (FAC) for the two-parameter method, which can also derive elastic-plastic failure load, was obtained. Then, a comparison was made for the elastic-plastic failure load obtained from different analysis procedures. It was shown that the optimized FAC as well as the obtained Z-factor could derive reasonable elastic-plastic failure loads, although the failure loads were more conservative than those obtained by the two-parameter method using FAC obtained J-value solutions. The reference stress method was found to be applicable to evaluation of the FAC. It was concluded that elastic-plastic failure loads could be derived by the Z-factor and two-parameter methods in which FAC was obtained using J-value solutions, the optimized curve and the reference stress method.