STP408

    Erosion of Steam Turbine Blade Shield Materials

    Published: Jan 1967


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    Abstract

    The physical processes preceding blade erosion by wet steam in low-pressure turbines have been traced from the collection of water droplets larger than 30 μ by the stationary blading to the stripping of this water into drops at the blade trailing edges and the impact of these drops with the following moving blade row. Experiments indicate that the maximum stable drop diameter before the last row of a 500-Mw turbine is 800 μ, being a function of downstream Mach number as well as the Weber number. Stresses produced by impact of drops have been calculated by existing theories to be sufficiently high to initiate damage in shield materials. Turbine experience and our experiments show that erosion rate is time dependent, with three successive zones: a primary zone with a low erosion rate, a secondary zone where the rate rises to a maximum, and finally, a tertiary zone, where the rate diminishes to a steady-state value. Experiments on artificially roughened specimens suggest that this reduction in erosion rate may be partially caused by droplet breakup on the peaks of the eroded surface and partially by the retention of water in the cavities. The terminal rate dictates the life of a turbine erosion shield, and materials must be tested well into the tertiary zone before a valid assessment can be made.

    Keywords:

    steam, turbines, impact, erosion, hardness, liquid impact, impingement


    Author Information:

    Smith, Allen
    Head, LP turbine and compressor group, chief metallurgist, and research metallurgist, C. A. Parsons and Co., Ltd., Newcastle Upon Tyne

    Kent, R. P.
    Head, LP turbine and compressor group, chief metallurgist, and research metallurgist, C. A. Parsons and Co., Ltd., Newcastle Upon Tyne

    Armstrong, R. L.
    Head, LP turbine and compressor group, chief metallurgist, and research metallurgist, C. A. Parsons and Co., Ltd., Newcastle Upon Tyne


    Paper ID: STP46048S

    Committee/Subcommittee: G02.10

    DOI: 10.1520/STP46048S


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