Cyclic Life Assessment of the Gas Turbine Rotor With Variable Fast Start Using Operational Data

This paper develops an innovative method to assess the cyclic life of a gas turbine rotor undergoing the variable load gradient starts using operational data from a remote monitor system (RMS). Using rotational speed and compressor discharge temperature, the method combines a lumped capacitance method and response surface approach to assess metal temperatures of rotor components with different temperature response rates and then determine the stress at the critical location for low cycle fatigue (LCF). The LCF lives are estimated with Neuber’s rule and the Coffin-Mansion-Basquin equation. Using the method outlined in this paper, the LCF life of a compressor disc and exit stub shaft of a gas turbine rotor are assessed during fast starts. The result shows that the disc, which is not affected by the fast start in terms of LCF life because the total stress is dominated by mechanical stress. On the other hand, the LCF life of the exit stub shaft balance hole is dominated by thermal stress, therefore, the LCF life is influenced by the fast start. The exit stub shaft is an example whereby with a feature, at which the thermal stress has a different impact than that in the disc. The method enables a customized service interval and parts replacement plan to be developed using real time measured operational data.