Causes Of Subsynchronous Vibration In Integrally Geared Compressors

TutorialIntegrally geared centrifugal compressors (IGC’s) are a well-established and continually growing segment of the turbomachinery industry. They have proven to provide a high level of reliability, efficiency and design flexibility. Although the applications and technology of IGC’s have continued to grow and advance, there are few publications that address subsynchronous vibration (SSV) specific to IGC’s. Subsynchronous vibration can be either destructive or harmless depending on the root cause. Misdiagnosing the root cause can lead to destructive failure or unnecessary design changes. As integrally geared compressor design and applications evolve traditional design limits are tested. Pressure ratios, rotor flexibility, bearing loads and compressor operating range continue to be increased to satisfy the end users process requirements in the most efficient way possible. When addressing a SSV issue on an IGC one must keep in mind that there can be multiple root causes and each call for a different and sometimes unique approach to eliminate. Although some consider interpreting and diagnosing machinery vibration is an ‘art’, following a systematic approach will save time and money. This paper will review some of the known causes of SSV in IGC’s, typical characteristics of each, and how vibration monitoring techniques can be applied and interpreted in order to determine the root cause and solution. Several examples will be presented to illustrate the vibration characteristics associated with the root cause