To all vibration Guru,

Our FGD Flus Gas fan was recently experienced high vibration axially (13 mm/s) especially at fan inboard bearing. Oddly enough radial vibration was very low (1 mm/s) horizontally.

The fan was scheduled for new lubrication and the vibration was observed 1 hour after start-up. I only manage to get vibration at fan inboard since I did not wanna take the risk of further damaging the bearing by letting in run for a longer time.

Some info on the fan
1. Center hung type.
2. Use journal bearing with thrust pad at fan inboard side.
3. Using gear coupling type.
4. Fan weight is about 30 tonne, centrifugal type with guide vane to control the flow.

During the first 30 minutes after startup, we noticed oil bubbles coming out from the bearing pedestal bolts. Then we decided to tighten up the bolt onload at all fan bearing. The vibration was observed during tightening works in progress.

We also had our gear coupling re-tighten without any torque reference prior to startup.

my main question, can the tightening the bolt cause this kind of vibration? if it does, it would exhibit symptom of misalignment. Having said that, I would expect to see high radial vibration as well. It is more like resonance to me.

After the incident, we open up the fan inboard bearing and found its thrust pad was severely damaged. It looks like consequences of the high vibartion. Oddly enough, its journal is in good condition.

I'd appreciate if you guys can give some input on this. I dont wanna start back the fan without knowing whats the root cause of this problem. Thanks guys. Spectrum is as attached

FGD_Flue_Gas_Fan.rtf (222 KB, 18 downloads) Spectrum & Activity Log

Did the impacting and high vibration occur after tightening the pedestal hold down bolts? If so, could it be that the alignment was altered beyond the limits of the the coupling design and thrust bearing design? Was the thrust clearance checked or altered prior to the problem?

Was the oil, based on your quote, "The fan was scheduled for new lubrication and the vibration was observed 1 hour after start-up." of the correct viscosity.

OK, you found a bolt loose and tightened it. Did you do a re-alignment?

On your design consideration: thrust on inboard is an OEM spec?

On alignments: both cold and hot? 2.) no bow in rotor was observed when in the alignment process. 3.) air gap or spacing of coupling was kept within tolerance when in the alignment process? 4.) temps known? 5.) was bearing to shaft, bearing to bearing and shaft to shaft alignment on target.... It seems if it were, the looseness of anchor bolts made all null and it's time to do it over again unless you have hot data and can check via Acculign or optics.

Any know departures from ___________ I saw no big standouts except the broad-banded patters from 1X down. Comfortable with your data? Have more, especially in acceleration?