Service Life of Steam Turbine Rotor Material Made of Low-Alloy Cr-Mo-V Steels after Long-Term Use outside the Design Operating Time of Power Unit

Abstract

The purpose of the study was to assess the state and degree of exhaustion of turbine rotor materials made of low-alloy Cr-Mo-V steels after long-term operation. The tests were carried out for selected structure states defined on the basis of images of the structure observed using a scanning electron microscope, and the degree of development of precipitation processes based on the X-ray analysis of the phase composition of electrolytically isolated carbide deposits. For materials with such defined structure states and degree of development of precipitation processes, the following were determined: mechanical properties at room and elevated temperatures, residual life and available residual life on the basis of short-term creep tests, and creep rate from creep curves for temperature and stress parameters corresponding to operational parameters. Based on the results of short-term creep tests conducted at a temperature higher than the operational temperature and with a stress corresponding to the operational life, residual and available residual life were determined and the degree of exhaustion was estimated.