Pumping sets are common but often critical operating assets in the industry. Such pumps often do not have adequate pressure and flow instrumentation that could detect abnormal hydraulic operating conditions. This paper presents field investigations of two submerged vertical pumps with suspected cavitation and flow induced vibrations in a power plant. These pumps had a history of catastrophic impeller failures.
The vibration analysis allowed an assessment to be made on the pump of concern; upon which visual examination of the newly installed impeller was made that confirmed the occurrence of cavitation. High frequency random vibration was shown to be a good indicator for flow excitation and cavitation. Comparison of results under service conditions between a cavitating and non-cavitating pump are presented. Failure modes showed cavitation erosion and a sheared impeller blade. Evidence of excessive clearance and/or sleeve bearing wear was also noted in the pump of concern. The investigations confirmed concern relating to operations during low tide and combined pumps operated in parallel where inadequate ubmergence was identified as a likely cause to the impeller failures. The investigations implied a system design problem and pump operating conditions compounding the system design error that had resulted in frequent failures of the pumps. To read more click here