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Issues and solutions for integrity of pressure vessels and piping subjected to long-term creep exposure in supercritical thermal plants

ABSTRACT ASME BPVC Section VIII Division 2 (‘ASME VIII(2)’) and ASME B31.1 are being used not only for low-temperature design but also for high-temperature design in the creep range in supercritical thermal power plants. However, creep effects in ASME VIII(2) and B31.1 are taken into account implicitly, and there could be significant technical issues in terms of conservatism in the case of long-term operation in the creep range because their design evaluation results do not change across plant operation time. The conservatisms of ASME VIII(2) and B31.1 have been quantified based on comparisons with nuclear-grade design rules of ASME BPVC Section III Division 5 and RCC-MRx which take creep hold time into account explicitly. It was shown that ASME VIII(2) and B31.1 results could be non-conservative if operation time exceeds a certain time limit, which raises concerns around non-conservatism in the case of long-term operation within the creep range.