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Hi expert

Kindly to support us to find the Cause of high Vibration at NDE of boiler feed Water Pump ,

Brief of problem :

The vibration observed High by operation section @ P NDE H , fluctuated in this bearing between ( 2.1-5.5 mm/s RMS ) When the load changed at Steam turbine ,after mechanical team do maintenance on Minimum flow valve & back pressure valve at discharge line , we taken vibration reading when the vibration @ 2.1 mm/s and at 4.9mm/s at pump bearing DE& NDE as attached file  , We observed changing the level of 1X and 10X @ DE H & NDE H direction @ pump and appears bearing frequency @ NDE A in HD ENV Technique as illustrated  below picture , and there is changing forces inside pump related to flow changing  , all pressure ( suction & discharge ) are acceptable valve compared with sister pump B , But Unfortunately there is no flow meter @ discharge line of pump C ,  only in common header  , all details about pump included in attached file

kindly to hear your opinion

Attachments

Tags: Boiler, Vibration, pump, NDE

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My guess is that the vibration goes up when the pump is operating at low flow or well below the BEP operating point. The main evidence is the increase at 10 X shaft speed which is probably from suction pulsation frequency and the appearance of Cavitation based on the high frequency vibrations shown on page 15 of your report. The increase in vibration at 1X shaft speed may be related to excessive clearance in the radial bearing or less damping from the thrust bearing. If the pump housing or NDE bearing housing has a natural frequency close to 1X shaft speed, as you say, then the suction or discharge piping supports may change the natural frequency at different flow rates. I have seen this problem on a booster pump on a large BFP. I found broken pipe supports and a support that had hard contact that was supposed to be floating.

Actions: check flow rate and valve position, inspect pipes and supports at different flow conditions, and check bearing clearance during normal shutdown.

Walt

RM
Last edited by Registered Member

I would test for natural frequency with pump running at low and high load to see if the natural frequency changes due to change in pipe support stiffness. The impact-response vibration method with negative averaging could be used. Consider installing a temporary ultrasonic flow meter on discharge pipe exterior to confirm flowrate at different load operating points. You might find that Pump-C flow is below BEP point evan at higher load, assuming there is another pump operating with it.

Walt

RM

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