THE RELIABILITY ESTIMATION OF THE LOW-CYCLE FATIGUE LIFE OF STEAM-TURBINE ROTORS

In this paper, a technique to define the low-cycle fatigue life damage and its cumulative effects on steam turbine rotors using the reliability estimation method is presented. Because of the dispersion of external load spectra and the fatigue strength of materials, the dispersion coefficient is defined to describe the probability relationship between reliability and life damage. The definition of the dispersion coefficient differs according to the probability distribution of service life. The situation for both the logarithmic normal distribution and the Weibull distribution is analysed in this paper. Using this technique, the internal relationship between the crack initiation life damage and the crack propagation life damage is investigated under any selected reliability. It is helpful for managers of power stations to evaluate the state of turbines and to manage the service life of turbine rotors. This technique is useful in evaluating the residual fatigue life of rotors and determining the optimal detecting date. An example is presented in the paper and some valuable results are obtained.