screw compressor, gas pulsation, vibration
The severe vibration of a screw compressor outlet piping system caused the fatigue failure of some thermowells and the unscheduled shut down of the system. The main reasons of the abnormal vibration in the outlet piping system were investigated by developing an acoustic model to simulate the gas pulsation and establishing two finite element models to conduct the mechanical vibration analyses. The acoustic analysis results showed that the pulsation amplitudes of most nodes in the outlet piping system exceeded the allowable values. The results of mechanical vibration analyses indicated that the insufficient stiffness of the outlet piping system and the first-order structure resonance occurred on thermowells were also the key factors inducing vibration. Several methods were put forward to attenuate vibration amplitude of the outlet piping system as well as the thermowells. A new pulsation attenuator was installed and the piping layout was rearranged to reduce pulsation amplitudes and shaking forces of all nodes in the outlet piping system. Several reasonable supports were added to improve the stiffness of the outlet piping system. After reinforcing the thermowells, the first-order natural frequency of the thermowells increased from 207.4Hz to 280.7Hz, away from the excitation frequency of 196.67Hz. The field measurement results showed that vibration amplitude and the vibration velocity decreased significantly after modifications.