High temperature fatigue damage evaluation of steam turbine rotor steel

High temperature fatigue damage of heat relief grooves of HP rotor can be assessed by measurement of residual stresses present in the surface of the component. These stresses get accumulated in the surface due to cyclic operations such as start-up, shut downs and load transients. Changes in the residual stress values were examined in the laboratory by using X-ray residual stress measurements for Cr-Mo-V rotor steel specimens subjected to high temperature low cycle fatigue in order to develop a method for non-destructive damage detection. A linear variation of residual stress with fatigue cycles was observed. The method has been applied on a 62.5MW steam turbine operated for 1,56,456hrs to assess the fatigue damage.