Pump Rotor Critical Speeds Diagnosis And Solutions

Abstract

Delmarva Power Indian River Power Station’s Unit 4 has had boiler feed pump reliability problems since startup in 1980. The pump has been rebuilt nine times with post overhaul operability ranging from 30 minutes to 16 months. Many of the failures have been attributed to high shaft vibration. The analysis techniques used to diagnose and develop solutions to the chronic rotor critical speed problems are described. The analysis techniques described are general in nature and can be applied to all rotating equipment, but are particularly well suited to high speed multistage pumps where some rotor “bearings” that determine the rotor behavior are difficult to characterize. There have been many papers written concerning pump rotordynamic computer modelling [1, 2, and 3] and modal analysis [4] of pump rotors, but there is no published case study where the computer modelling and field modal testing have been combined to diagnoses and develop solutions to a real problem. The combination of the two methods provides a powerful tool that accurately represents the behavior of the rotor and allow designers to engineer proper solution without trial and error experiments on the pump.