Numerical Analysis of Fatigue Life Improvement by Optimizing the Startup Phase for a 1000 MW Supercritical Steam Turbine Inner Casing

The fatigue behavior of a specific inner casing of a 1000 MW supercritical steam turbine was investigated during a complete startup phase. The Ramberg-Osgood model and Manson-Coffin strain-life law were used to describe the stress-strain behavior and calculate the damage. The temperature variation during the startup phase revealed that the startup phase could be divided into a warming-up phase, transition phase, and elevated temperature phase. The thermal stress that dominated in the inner casing could also be divided into the same three phases. The damage caused by the alternating stress during the warming-up phase was around 70% of the total damage. The remaining 30% of the damage was contributed by the transition and elevated temperature phases. The fatigue life was improved by shortening the warming-up phase and extending the elevated temperature phase. The damage was reduced by approximately 20%.