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 failure probability upper bound (FPUB) of a smooth component can be estimated from fatigue life and creep rupture time test data with simple loading histories. In this paper, we extend the theory to include a methodology to estimate not only the failure probability upper bound, but also the damage state of metal alloy components undergoing creep and fatigue with creep-fatigue interactions. To illustrate our methodology, we present numerical examples based on high temperature creep rupture time test data of stainless steel 316L(N) and room temperature fatigue life test data of AISI 4340 aircraft-quality steel. The significance and limitations of this new damage-state-based approach to modeling creep and fatigue reliability of steel components at elevated temperatures are presented and discussed.

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