Analysis of Rotor Rub in a Large Centrifugal Refrigeration Compressor

Case StudyThe purpose of this case study is to present an investigation of substantial damage to the rotor of a large centrifugal propane refrigeration compressor that is installed in an 800 MTPA Ethylene plant. After ten years of normal operation since its commissioning, the compressor was shut down during the plant’s scheduled turnaround to carry out peripheral inspection. As the speed of the compressor–steam turbine train was reduced; an abnormal sound was heard by the field operators. Instead of looking for the possible cause(s), the shutdown sequence was completed. Even twenty four hours after shutdown, the compressor’s casing remained unusually hot. This was a cause of concern. After deliberations, the train was isolated and released for external inspection. On decoupling the compressor, it was noticed that its rotor could not be moved axially and many attempts to turn the shaft to verify if there was binding proved to be unsuccessful. This case study outlines the sequence of events, the details of inspection, and the root cause analysis of the failure. It concludes with an understanding of thermal rub phenomenon and the primary causes which resulted in rotor-to-stator scuffing