A PFM-based defect evaluation method for cast austenitic stainless-steel pipes

Cast Austenitic Stainless Steel (CASS) pipes with high δ-ferrite content undergo pronounced thermal aging during service in nuclear power plants. This aging process decreases the material’s fracture toughness, reducing the critical crack size to values that may be undetectable by ultrasonic testing. According to elastic-plastic fracture mechanics (EPFM) theory, crack stability is assessed by comparing the crack-driving force, represented by the J-integral, with the material’s fracture resistance as defined by the J-R curve. Fracture is predicted to occur when the applied J-integral exceeds the corresponding J-R curve value. Given the substantial scatter in properties of saturation-aged material, a modified defect evaluation method for CASS pipes based on probabilistic fracture mechanics is proposed. This methodology addresses the limitations of conventional non-destructive evaluation and provides a foundation for establishing in-service inspection acceptance criteria for this class of material.