Vibration and NPSHr (NPSH₃), improvement of BB1 two stage pump reliability

Abstract

This case study discusses the impeller redesign of 10 8x15 BB1 two stages Amine pump in a Gas Sweeting Plant in Malaysia. The original pump was supplied in 1996 and after some design changes it had an history of recurring high vibration and impeller damages such as a cavitation erosion on inlet suction side and disk break at impeller outlet. Pump performance analysis revealed a service operative point close to Minimum Continuous Stable Flow showing vibration peak both on synchronous frequency and VPF (vane passing frequency) typical of secondary flow effect. After a FMEA analysis it was decided to redesign the impeller.CFD simulation and Static structural with pressure load profiles have been performed and a model test bench has been set up to compare new and old impeller design focusing on NPSHr curve and on interaction forces between impeller blades and volute lip. Currently the 10 pumps are operating without showing any vibration problem.