Q & A > Question Details
Recently we encountered a failure in one of the Boiler feed water pump. Observations were as below.
1. Pump tripped after running for 30 sec when it reached its full disch pressure of 100kg/cm2G.
2. Trip was due to high bearing vibration on NDE side.
3. Rotor was moved towards DE by about 2mm.
4. Rotor was seized( could not rotate with hand).
5. NDE oil decolorised slightly.
6. upon dismantling we found that NDE bearing inner race was seized to shaft. NDE bearing was totally damaged.
7. DE bearing was fine and no change in oil color too.
8. While operation, discharge valve was fully closed( according to operations min circulation as well as balancing lines were fully open).
Online probes not able to provide required spectrum.
Now we are struggling to analyze the cause. Pls suggest the way forward and also if you have link to similar failures.
 
Answers
29/03/2018 A: Shridhar Shenoy, OMPL, shridharbshenoy@gmail.com
I too suspect the problem to be with balancing line. though its been a year since this happened, still we are not fully certain about possible cause. I think its not possible to post the drawings here.
I would be happy to share findings on email: shridharbshenoy@gmail.com
09/01/2017 A: Eric Hennings, Technip Stone & Webster, EHennings@technip.com
Generally, parallel pumps in high head service require “Automatic Recirculation Valves” within the pump discharge piping. These special ARV valves are mechanically linked to the individual check valves. If the ARV’s are isolatable, special procedures are mandatory to prevent deactivation of this feature.
Common “minimum flow” control valves in the common discharge piping are not appropriate. There have been cases of “deadhead” of one pump while a parallel pump remains in service. This condition can occur when one driver (such as turbine) is running slower than the constant speed electrical drivers.
05/01/2017 A: Bruce Carr, Suncor Inc, bcarr@suncor.com
Without seeing the drawing of the pump it is hard to troubleshoot. If it was a cavitation issue because of pumping water at near saturated temp at low flow and flashing I would expect to see the seals go long before the bearing. From what I see here the most likely cause would be the labbys on the balance piston which would account for the movement towards the drive end putting stress on the NDE bearing.