Damage Analysis and Startup Schedule Optimization of Steam Turbine Rotors With an Anisotropic Damage Coupled Viscoplastic Constitutive Model

The optimization of the operation scheme is of great significance for improving the flexibility of thermal power plants in energy systems dominated by renewable energy. However, thermal stress and corresponding thermomechanical fatigue damage are the main limitations. A unified viscoplastic constitutive model coupled with anisotropic damage is introduced and validated by comparing the experimental and simulated hysteresis loops and cyclic softening curves. The model is implemented into the ansys software by using the USERMAT subroutine to numerically investigate the high-temperature fatigue behavior of a 1000 MW steam turbine rotor on different startup schedules. The critical areas of the rotor are studied in terms of temperature, stress, accumulated inelastic strain, and damage. Based on the damage analysis, the hot start schedule is optimized and validated. The startup time can be significantly shortened within permitted fatigue damage. Moreover, the life expenditure under different loading-up rates is calculated and the extra startup costs can be evaluated accordingly for wider application.