STP1186

    Prediction of Thermal-Mechanical Fatigue Life for Gas Turbine Blades in Electric Power Generation

    Published: Jan 1993


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    Abstract

    Thermal-mechanical fatigue (TMF) cracking is the primary mode of mechanical failure of first stage blades in gas turbines used for electric power generation. Because of the high replacement costs of these superalloy components, it is important that accurate predictions of TMF life be made so that blades can be reconditioned before cracks initiate and propagate beyond repair limits. This paper describes the development of a TMF life prediction methodology for first stage blades, which is part of a Life Management System developed by the Electric Power Research Institute (EPRI).

    The TMF life model is based on laboratory TMF tests of the superalloy IN-738LC in both the coated and uncoated conditions. Results for TMF crack initiation life are presented and modeled. The life model is based upon the strain range, the dwell time, and the strain A-ratio. The dwell time term accounts for the time dependence of the fatigue life due to environmental attack and creep. The strain ratio term helps account for the effect of mean stress in the cycle. The ability of the life model to predict the fatigue lives of the current test data and the fatigue lives of IN-738 test samples for various test conditions reported in the literature is presented. The effect of coatings and environment upon the TMF life is also discussed.

    The strain-temperature response of the blade was obtained from the manufacturer. The life prediction methodology is presented and applied to the prediction of TMF life of blades from a number of engines. Miner's rule is used to sum cumulative damage from the different engine cycles that occur. Good agreement is obtained between the service experience and the life predictions.

    Keywords:

    thermal-mechanical fatigue, nickel-base superalloys, IN-738LC, gas turbine blades, life prediction, high-temperature coatings


    Author Information:

    Bernstein, HL
    Principal engineer, engineer, and senior research engineer, Southwest Research Institute, San Antonio, TX

    Grant, TS
    Principal engineer, engineer, and senior research engineer, Southwest Research Institute, San Antonio, TX

    McClung, RC
    Principal engineer, engineer, and senior research engineer, Southwest Research Institute, San Antonio, TX

    Allen, JM
    Formerly, project managerconsulting engineer, Electric Power Research Institute, Palo AltoCupertino, CACA


    Paper ID: STP24258S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP24258S


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