A nuclear power plant was trying to understand why their new feed water pumps exhibited high vibration amplitude (1x rpm) at the drive end (DE), showed step changes in vibration over time, and demonstrated inconsistent results associated with the alignment before and after shut-downs.
- Problem Statement (Challenge)
- What (type of machine): Single Stage Double Suction Feed Water Pump in Nuclear Service
- Where (State/ Country): Wisconsin
- Why (problem/reason): A nuclear power plant was trying to understand why their new feed water pumps exhibited high vibration amplitude (1x rpm) at the drive end (DE), showed step changes in vibration over time, and demonstrated inconsistent results associated with the alignment before and after shut-downs. The plant wanted a second opinion on whether it was safe to continue running the pumps or take the entire plant off line for a costly and unexpected outage.
- Work Performed
- Results/ Solution
- Findings: The high vibration of the pump DE was due to excessive piping strain on the suction and discharge nozzles measure with weldable strain gauges. In this particular case, the pump casing was acting as an anchor support for the piping. When the piping load was applied, the south end of both pumps was pushed downward, changing the angular alignment of the pump and motor shafts. In addition, changes in the phase angle at the DE of Bravo FWP indicated a change in the rotor heavy spot.
- Impact: The findings suggested that since no bearing damage or shaft overheating was observed, MSI determined that the Bravo FWP can be maintained in service. During a future outage, MSI recommended that the loads for the suction and discharge piping should be corrected based on a piping flexibility analysis.
Strain gauges installed
Top view bending loads. Bottom view axial loads.
Nozzle loads results summary table using strain gauges
