Creep-Fatigue Life Property of P91 Welded Piping Subjected to Bending and Torsional Moments at High Temperature

Abstract

In recent years, the role of thermal power plants has shifted from providing a baseload to providing supplemental supply due to fluctuations in the energy output of renewable energy sources. Thus, it is expected that the operation of these plants involves frequent startup and shutdown cycles, which lead to extensive damage caused by creep and fatigue interactions. In addition, the piping utilized in thermal plants is subjected to a combined stress state composed of bending and torsional moments. In this study, a high-temperature fatigue testing machine that is capable of generating such a bending-torsional loading was developed. Creep-fatigue tests were conducted on P91 steel piping with weldment. The obtained results clarified that the creep-fatigue life was reduced by the superposition of the torsional and bending moments and that it was further reduced by a holding load. It was also shown that the creep-fatigue life of piping welds can be estimated accurately by the modified ductile exhaustion rule.