Creep-fatigue interactions in type 316H under typical high-temperature power plant operating conditions

A micromechanical crystal plasticity self-consistent model (SCM) is used to analyse loading histories in 316H stainless steel. SCM predictions on changes in cyclic and creep properties are compared to analyses via the R5 assessment procedure. Plant-relevant cyclic-creep histories at 550 degrees C are examined with focus on the estimation of accumulated creep strain. The effect of cyclic plasticity on creep is quantified. The levels of creep strain accumulated during different dwells, following loading from different macroscopic stress states, is also evaluated and explained through experimental observations. Assessing the impact of displacement- and load-controlled dwells on the hysteresis loop evolution revealed how different assumptions for creep strain accumulation could employ SCM results to reduce uncertainty. Guidance is provided in the development of extrapolation frameworks for structural parameters based on the SCM results which could be used directly in structural assessment to estimate the inelastic strain accumulation with a lower degree of conservatism.