Quantitative comparison of plasticity correction approaches for environmental fatigue assessment under secondary stress-dominated conditions

This study examines the origin of compounded conservatism in environmental fatigue evaluation under secondary stress–dominated conditions through a systematic assessment of plasticity correction methods. Conventional ASME BPVC Sec. III procedures correct elastic analysis results while treating secondary stresses as primary, neglecting stress redistribution and local strain-energy relaxation. Redistribution-based approaches, namely the Elastic Follow-Up (EFU) and Stress Redistribution Locus (SRL) methods, are employed to examine the causal chain linking strain amplitude, strain rate, environmental fatigue correction factor ( ), and fatigue life. Code-based linear elastic–plastic scaling fails to represent nonlinear hardening, leading to overestimation of strain amplitude and underestimation of average strain rate, which inflates and compounds conservatism. For stepped-pipe thermal shock tests, the ASME NB-3200 procedure predicts a fatigue life of 122 cycles, less than 10% of the experimental mean life of 1,543 cycles, while Code Case N-779 and N-904 provide partial improvement but remain conservative. In contrast, EFU and SRL apply correction coefficients derived from elastic–plastic analysis, significantly improving predictive accuracy and consistency with experimental results and elastic–plastic finite element analysis. These results demonstrate that redistribution-based plasticity correction offers a physically consistent means to mitigate excessive conservatism in secondary stress–dominated environmental fatigue assessments.