Thermal Stress and Fatigue Analysis in Turbine Rotors

Abstract

A method of thermal stress and fatigue analysis under triaxial stress conditions is presented. A rotor of a marine steam turbine is taken as a typical example to illustrate the detailed method of analysis in assessing the cycle damage life of the rotor. A computer technique of iterative block relaxation is devised for the thermal stress calculation as the physical geometry of the problem under consideration is fairly complex. This technique is particularly advantageous for such a system as (a) damping the magnitude of the oscillation in the solution of the ill-conditioned stress equations and (b) keeping the number of nodal points required in a converging solution to a minimum. Three different operating procedures of starting and loading the marine turbine have been studied with full three-dimensional stress and fatigue considerations. One of the three procedures which is found to be more desirable is recommended with the descriptions of detailed steam history and main features of the cold start throughout its whole operation.