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2010GMC Paper


Bill Eckert – Beta Machinery Analysis

In 2008, three centrifugal compressors at this compressor station were retrofitted with higher head impellers. For the next two years, the owner experienced continual vibration problems that caused failures with RTDs, transmitter and position switches. Most of the failures were on the discharge side, but failures did occur on the suction side as well. The cause of the failures was assumed to be flow induced pulsations (also referred to as vortex shedding). Many attempts were made to modify the thermowells and RTDs, but they were not successful in reducing the failures. In early 2010, Beta Machinery Analysis traveled to the site and conducted a vibration and pulsation analysis. After assessing the situation, it was determined that shell mode piping vibration excited by blade pass pulsation was responsible for the problems and not flow induced pulsations as originally assumed. This case study outlines the factors that contributed to the vibration problem and recommended solutions; it predicts interferencesbetween the compressor and sell mode piping natural frequencies and potential excitation sources such as flow induced and/or blade passing pulsations; and it also highlights why a centrifugal vibration study may be good practice during the initial design (or retrofit) as it is much easier and less costly to make adjustments at the design stage compared to searching for, and solving, the problem in the field.

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