Inspections and Repair Enhance Pump Performance


Written by:
Bob Bluse, Hydro East
Published:
January 23, 2012

Improvement can result from repair opportunities.

Often all that is needed to improve a pump’s dependability and performance is a high quality inspection and repair. Over time, a pump may have been repaired by more than one service provider with varying levels of engineering and technical experience.

Tolerances may have been opened, fits and concentricities may have been lost and materials may have been changed, all of which contribute to reduced performance, loss of reliability and more frequent repairs.than one service provider with varying levels of engineering and technical experience. 

This article highlights the opportunity seized by a coal-fired power generating facility located in Western Pennsylvania, to upgrade a Westinghouse vertical pump.

Column pipe upper flange as received
Column pipe upper flange as-received

 

Close-up of the broken pipe
Close-up of the broken pipe

 

Background

The Power Plant’s Unit 4 “Alpha” circulating water pump was scheduled for repair.  In the process of removal, the sister pump 4 “Bravo,” exhibited severe vibration and failed in a manner that was believed to have been a result of a broken shaft. The Alpha pump was put back into service and the Bravo pump removed and sent to the repair facility for inspection and emergency repair.

This circulating water pump performs a critical function in the power plant, by cooling the low-pressure steam in the condenser to use as feedwater for the boiler. A loss of one of these pumps in the summer means that the plant will not be able to produce to its maximum capacity until the pump returns to service.

Observed Pump Condition

The general condition of the Bravo pump when received at the repair facility was much worse than anticipated with the top column flange broken about half way around. The entire pump had been hanging from this broken joint leaving a gap of ¼ inch to ½ inch at the opening.

The keyed coupling (internal to the pump) used to join its two shafts was broken in several pieces. The shaft journals were severely worn to one side, and the impeller vanes and suction bell liner surface were also severely worn as expected, considering the significant pump damage.

 

After disassembly of the pump, the repair engineers also observed that the shaft enclosing tubes had spun in their fits because they were not fitted with any anti-rotation mechanism. This rotation caused damage to the O-ring fit areas at both ends of the enclosing tube assembly, which resulted in the loss of a proper flush water supply to the pump bearings below the packing box. Another issue observed during the inspection was that part to part alignment of major pump components used dowel pins, which are very difficult, if not impossible, to verify.

Close-up of the broken pipe flange
Close-up of the broken pipe flange
 
 
 
Destroyed shaft coupling and hardware
Destroyed shaft coupling and hardware

Opportunity for Improvement 

While the typical repair scope of bearing, wear ring and small part replacement was employed, several issues identified during the inspection were corrected with improvement to the design:

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