Fatigue Failures Of Compressor Impellers And Resonance Excitation Testing

Abstract

The similarity of failures of impellers in centrifugal compressors soon after initial startup and failures of impellers in other compressors after about seven years of successful operation and the test programs to define the problems are described. Early failure of an impeller in a turbine driven air compressor followed by other failures in parallel constant speed process compressors installed at another Union Carbide process plant indicated resonance or response at known excitation frequencies. However, fatigue failure of an impeller without a known source of excitation soon after initial start-up was followed by an identical failure about four years later in the same constant speed machine. Concurrently, an impeller failed by fatigue in a turbine driven process compressor after about seven years of satisfactory operation. These failures led to extensive testing and quality control programs at several manufacturers’ plants for both new equipment and replacement impellers plus a revitalized series of field tests to identify the excitation sources. Shaker testing and field testing were effective in determining that, while the resonant frequencies and modal patterns may not correspond with any known source of excitation, the fluid flow at various load and speed conditions can excite a resonance and lead to failure. Both the shop and field testing, including corrective action, are discussed.