Paper No. 39
J. C. Wachel, AICHE Ammonia and Related Plants Safety Symposium, Minneapolis, MN, August 26-30, 1972 .
This paper discusses several types of vibration and failure problems which occurred in a steam turbine-compressor string in a methanol plant resulting in considerable downtime of the process. The vibrations which occurred are representative of those which can occur in most modern high speed installations. By using new and effective ways of presenting data utilizing signature analysis techniques, the causes of the excessive vibrations and failures were established. Vibrations encountered were caused by 1) unbalance, 2) misalignment, 3) mechanical resonances of attached structural components, 4) running near critical speeds, 5) sleeves which shifted during operation, 6) nonsynchronous instabilities, and 7) intermittent faulty operation of governor control and overspeed trip. The nonsynchronous instabilities caused several compressor failures, even though tilted pad bearings were used to eliminate instabilities. By monitoring and recording vibration data on startups, it was possible to replay and study transient vibration phenomena which typical control board instruments cannot accurately display. The spectral time history plots and diagnostic techniques presented in this paper can be used to identify similar vibration problems on other units.