Investigation of a Compressor Coupling Failure by Torsional Excitation

Abstract

This case study examines a repeat compressor coupling failure that was a result of a complex, dynamic interaction of components that excited the 2nd torsional natural frequency of the train. The mature unit had operated successfully for 17 years until a seemingly insignificant series of compromising events created degradation which triggered the excitation of the natural frequencies. The couplings exhibited evidence of fatigue fractures leading to catastrophic failure due to high alternating torsional stress. A natural frequency modal analysis showed that a mode shape of the compressor train bull gear enabled it to interact within the total system torsional modal response to create an excitation frequency at the 2nd torsional natural frequency. Further, discussion on practical design, operation and equipment monitoring shows limitations in guarding against the vulnerabilities mentioned.