High Frequency Fatigue Failure In Silencer/Pulsation Dampers For Oil Free Screw Compressors.

Abstract

Oil-free screw (OFS) compressors are capable of producing high-pressure pulsations in the discharge gas stream, over a frequency range of 200 to 3000 Hz. The fundamental pressure pulsation is due to the opening cycle of the compressor lobes at the discharge porting and is referred to as the pocket passing frequency (PPF). Fatigue failures have been observed in discharge silencers/pulsation dampers as well as downstream piping components in oil-free screw compressor service where the frequencies were greater than 1000 Hz. A careful review of the pulsation damper design has shown that attenuation effectiveness is limited to frequencies less than 1000 Hz. The principal purpose of the pulsation damper is to reduce the line pressure pulsations in order to lessen the chances of downstream piping failures. The pulsation damper does very little to attenuate high frequency noise levels that are transmitted to the area surrounding the compressor. The principal purpose of this paper is to document failures of silencer/pulsation dampers in OFS compressor service and provide a root cause analysis of these failure modes. Pulsation dampers are not used at the inlet flange in many applications, due to the lowpressure pulsation in the inlet plenum of the compressor. It is not the intent of this paper to present any theoretical background in the design of acoustic dampers, but to provide an overview of the acoustic phenomenon and how it is used in screw compressor applications. The end result of this work will be to provide practical guidelines for specifying silencer/pulsation dampers for OFS compressor applications.