Creep-Fatigue Life Prediction of Stop and Regulating Valves on the Intermediate-Pressure Section of a 1000MW Steam Turbine

The stop&regulating integrated valve on the intermediate-pressure (IP) section of a 1000MW steam turbine is presented in this paper. A multiaxial model based on continuum damage mechanics (CDM) is applied to life prediction of the valve. The transient stress and the temperature fields of the valve in a 1000MW supercritical steam turbine are investigated by using finite element method (FEM) for fatigue-creep. Since the turbine typically runs 120 days between starts, a simplified mission profile for a 120-day block was created. Accordingly, the 120-day loading block with plasticity and creep was run repetitively to achieve a 22 years creep-fatigue life prediction. The interaction between creep and fatigue was considered in total damage in proper order. Due to highly complex stress and structure, the multiaxial factors for fatigue and creep are assessed from the temporal and spatial points of view respectively. Furthermore, the creep-fatigue damage of the integrated valve is discussed in relation to the multiaxial factors. The results drawn from the multiaxial CDM model give a satisfactory life prediction on the valve.