Boiler feed water pump Vibration 1

[Imanshines]

Gents,
We have a problem in our steam turbine driven BFW pump. We always getting high 1X vibration reading from turbine outboard radial direction. It is monitoring by proximate probe.Single stage steam turbine, speed is 4732RPM. Forced lubrication type.we suspected, steam pipeline layout issue.. but i am not sure about it. readings we received 70 microns..Pk-Pk

based on your exeperience what are the other possible cause for this issue? Though we checked alignment and ruled out no-unbalance. and hot and cold alignment also within the OEM specs.

Thanks

 

[dougarthur42]

Just a couple things to ponder. Could the turbine be operating at or near its critical speed. We have a multistage unit that has 2 critical speeds 1 at about 2120 and another at almost 3000 rpm. It shakes like crazy at these speeds but settles out well above or below these speeds. It is not allowed to operate at either speed. Another trouble shooting hint is; have you tried the turbine uncoupled from the BFW pump, and if so does it still shake, as you add load its characteristics may change. Some times when BFW pumps are hard coupled to a motor or turbine they can transmit vibrations from each other. I hope someone else adds to this.
Thanks Doug

 

[Imanshines]

Thanks a lot doug! Sounds good.. But as you said, if load characteristic is the cause while doing solo run test, what will be the best action to control those high vibration.

In same scenarion, this time we have BFW pump driven by motor and gearbox also there. We received high 1X vibration from pump inboard side, besides multiple orders but levels are so small.. compartively 1X is high..
we suspect : scratch in shaft or chrome plate thickness variation
Rubbing
very loose interanl component rattling such as impeller

 

[JJPellin]

Measure the vibration at slow roll (<200 rpm) to determine how much of the signal is run-out and how much is dynamic vibration. Proximity probes are not designed to look through chrome plating. If you have two orthogonal problem, review the orbit. A shaft scratch should be readily evident on the orbit. Compare the housing vibration to the prox probe readings.

Johnny Pellin

 

[Tmoose]

" always getting high 1X vibration reading from turbine outboard radial direction "

How long is always?
Do you have any vibration history?
Any repair history?

 

[Imanshines]

Hi Tmoose,

We changed whole casing and rotor recently.. However we suspect that sensor and instrument having malfunction since long time. That was the only reason why we have unbelievable reading like 160 microns PK -PK. Though they fixed, still we are getting 65 microns. We still unaware that this is the real instrument problem or from machinery.

The same pump but driven by electric motor connected with gearbox. We have high 1X in pump inboard x direction. Almost 40-50 microns. But the level are fluctuating.. some times it went upto 50 micron another time 45 or 35 microns. My question is, can the mechanical issue fluctuating thier level as like process issue?

These are our possible causes, for high pump vibration ; scratch in shaft
Rubbing
very loose interanl component rattling such as impeller