Technical Issues of Non-Conservatism in Design of High-Temperature Piping Subjected to Long-Term Operation in Creep Range When Using ASME B31.1

ASME B31.1 is widely used in the design of power piping, but it does not explicitly consider creep effects. Therefore, there are concerns over non-conservative design for power piping undergoing long-term operation at high temperatures within the creep range. In this study, sensitivity analyses were conducted over a range of hold times at high temperatures to quantify the conservative qualities of ASME B31.1. For the analyses, a high-temperature nuclear design code of RCC-MRx that explicitly considers creep was applied, and the two evaluation results were compared. Analysis using RCC-MRx showed that creep-fatigue failure occurred as the hold time at high temperature gradually increased, but integrity was maintained regardless of the hold time in the case of evaluations using ASME B31.1. It was therefore shown that ASME B31.1 might cause non-conservative design in the case of pipes subjected to long-term operation within the creep range.