Implication of Elastic Stress Range at Structural Discontinuity

Abstract

This paper illustrates that in addition to the elastic stress intensity range it is necessary to evaluate the stress intensities (and corresponding material properties) at specific times during a postulated thermal transient to characterize inelastic response at a structural discontinuity. The specific case of an austenitic flued head operating in a temperature range of 600 to 1050°F (316 to 538°C) is used to calculate ratcheting strain accumulation due to cyclic primary and secondary loads. Detailed inelastic analyses were performed to evaluate two designs. Both designs have essentially the same stress intensity range; however, only the design with lower stress intensity during steady-state elevated temperature operation satisfied the ASME Code Case N-47 strain accumulation limits.