Vibration Reduction of a Centrifugal Compressor for Gas Transmission

Abstract

Centrifugal compressors used in gas transmission produce strong pressure pulsations, piping vibration, and noise. These are undesirable by-products of the compressor operation that is inherently an unsteady process. This is particularly true for compressors that use a vane diffuser, rather than a vaneless scroll type of diffuser. High vibration levels can potentially cause structural damage in the piping, particularly instrumentation connections, which can cause unnecessary machine down-time and production loss, and is a potential safety hazard. This paper discusses a unique technique to reduce centrifugal compressor piping vibration. This technique reduces aeroacoustics excitation by mounting a duct resonator array inside a compressor diffuser. The effectiveness of this technique is demonstrated by a recent field application to address a noise and vibration concern of a compressor installed in a pipeline station. This compressor had run successfully for several years with a high (but not excessive) level of high frequency vibration in the unit piping. Recent changes in pipeline operating conditions resulted in a significant increase in vibration and associated problems including failure of thermowells and resistance temperature detectors (RTDs). A preliminary measurement of gas pressure pulsations and piping vibration revealed a severe level of high frequency vibration that could lead to a fatigue failure of the unit piping, if operation continued under these conditions. Additional vibration data were measured from the compressor to characterize the noise and vibration and to establish the baseline for future comparison. The baseline vibration data are characterized with a dominant component at the blade passing frequency that makes the duct resonator array an ideal solution. Consequently, a resonator array was designed, manufactured, and installed to reduce the compressor piping vibration and noise. A final test was conducted to verify the effectiveness of the resonator array. Comparing the data acquired before and after the resonator array shows that the dominant vibration level at the blade passing frequency was reduced by 93% on average. The compressor is now able to operate safely at the new pipeline conditions, and it runs much quieter over the full operating range.