Predicting Creep Initiation in Gas Turbine Blades

The demand for increased performance from combustion turbines has pushed firing temperatures to the point where the life consumption of the hot section components may no longer be accurately monitored based on traditional engineering practices. For rotating blades in particular, creep rupture criterion such as strain limits, tend to be arbitrary, subjective and prohibit the use of statistical data available from material tests. This inhibits the application of a probabilistic treatment as a basis to answer the fundamental question of an operator responsible for the life cycle management of these costly parts, i.e. how does the chance of an in-service failure increase over the lifetime of the component. Presented in this paper is a more direct engineering approach that has been used to predict the risk of crack initiation and propagation due to creep in hot section parts. Results are compared first against the traditional method of designing against creep rupture, and then conclude with the risk analysis of an actual first stage gas turbine blade.