Dramatic Ring-Section Pump Vibration Improvement Using ODS

MSI's ODS testing suggested modifications for the baseplate of a Boiler Feed Pump that greatly reduced the max vibration amplitude at the outboard bearing housing, solving the problem.

• Detected high vibration at the outboard bearing housing in the horizontal direction.
• Gradual vibration increment over time (from 0.06 in/s pk to 0.35 in/s pk).
• Over one year period, modifications recommended by preceding consultants were implemented to try and improve the erratic vibration amplitude, without success.
• Vibration Monitoring consisted of:
  • Monitoring test during transient and steady operation to monitor the vibration amplitude, natural frequencies, and phase angle.
  • Experimental Modal Analysis (EMA) test to determine the natural frequencies of the pump structure and the rotor system.
  

Cross-Section of Ring Section Boiler Feedwater Pump.

FFT plot of an accelerometer mounted to the outboard bearing housing before modifications.

Boiler Feed Pump baseplate before modifications.

The root cause was excessive flexibility at the baseplate due to softness/ delamination of the internal grout.  This phenomenon originated due to the looseness of the anchor J-bolts.  After all suggested modifications were performed on the baseplate, the maximum vibration amplitude at the OBB housing in the horizontal direction was greatly reduced.

Boiler Feed Pump baseplate with modifications.

FFT plot of an accelerometer mounted to the outboard bearing housing after modifications.

Click to view ODS animation showing soft foot between the baseplate and grout. The separation can be seen in the +y corner near the outboard bearing (top right and bottom left quadrants).

For a more in depth paper on this case study presented at the International Pump Users Symposium, click here.