High-temperature fatigue behavior of a steam turbine rotor under flexible operating conditions with variable loading amplitudes

Abstract

This study investigated the high-temperature fatigue behavior of a steam turbine rotor under long-term operation with multiple startup types including one cold, three warm and 16 hot-startups at intervals of 45 days. To better describe the mechanical behavior of the rotor material, a unified viscoplastic constitutive model was experimentally validated then implemented with a user-defined material. Analysis initially focused on the inlet region, where thermal loads dominated. Next, the stress and damage at three selected positions with differences in temperature and load were compared and analyzed in detail. The effect of different startup types on the fatigue damage was statistically assessed. The equivalent hot startup (EHS) ratio was calculated to compare the risk level of each position under each startup type in flexible operation mode. Investigation of the inlet region showed that the warm startup conditions adopted here were more damaging than cold startup due to the higher warmup rate. The analysis of fatigue damage showed a temperature-dependent characteristic of the thermo-mechanical load-dominated positions. The EHS ratio of Groove-1 was larger than that of Groove-4, indicating a higher risk level in Groove-1 under flexible operating conditions. For the inlet region, the accumulation of viscoplastic strain made this region a fatigue-damageable position.