An assessment of thermo-mechanically induced fatigue damage of a steam turbine shaft

The increasing demands on the flexibility of steam turbines due to the use of renewable energy sources substantially alters the fatigue strength requirements of components of these facilities. The work summarized hereafter was initiated by the effort to develop the methodology of prediction of thermo-mechanical fatigue of steam turbine rotors. A significant effort was put into local thermo-mechanical stress-strain response modelling in the shaft material. An FE model of the structure assuming 2D axisymmetry idealisation was developed and verified. In-house codes based on a variety of approaches to assess critical location and fatigue damage, including the Manson-McKnight and the Nagode methods, were created. The experimental programme aimed to investigate the material fatigue behaviour under the thermo-mechanical conditions was initiated in order to provide data for calibrating and verifying the fatigue prediction procedures. A preliminary study on thermo-mechanical fatigue behaviour was conducted and the results are summarized in the paper.