The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) Committee has recently developed a new Section XI (Nuclear Components Inspection) Division 2 Code named “Reliability and Integrity Management (RIM).” RIM incorporates a new concept known as “System-Based Code (SBC)” originally due to Asada and his colleagues (2001–2004), where an integrated approach from design to service inspection is introduced using three new types of statistical quantities: (1) “system reliability index,” or “system co-reliability target” for any system consisting of structures and components, (2) “structural co-reliability,” for any structure, and (3) “component co-reliability” for any component, where co-reliability is defined as “1 – reliability” and is equal to failure probability. In a recent paper published in the International Journal of Pressure Vessels and Piping (Vol. 173 (2019), pp. 79–93). Fong, Heckert, Filliben, and Freiman developed a new theory of fatigue and creep rupture life modeling for metal alloys at room and elevated temperatures such that the co-reliability of a smooth component can be estimated from fatigue and creep rupture test data with simple loading histories. In this paper, we extend the theory to include a methodology to estimate the failure probability (or, co-reliability) of a stainless steel 316L(N) component undergoing a complex loading history such as a thermal fatigue cycle. To illustrate an application of this new modeling approach, we present a numerical example using (a) the experimental test data of 7 specimens of S.S. 316L(N) in creep at 565 C as published by Kilian Wasmer in his Ph.D. thesis (Imperial College London, 2003), (b) the experimental test data of 10 specimens of S.S. 316L(N) in creep at 650 C also by Wasmer (Ph.D. thesis, 2003), and (c) a thermal fatigue loading history of 1 hour of creep at 650 C at an operating creep stress of 73 MPa, and 300 hours of creep at 565 C at the same creep stress to simulate a hypothetical powerplant thermal fatigue operation. The significance and limitations of this new damage-state-based approach to modeling creep and to estimate the component failure probability (or, co-reliability) of steel components in creep at elevated temperatures with complex histories are discussed.

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