Prox Probe X,Y Vibration Discrepency

Dear Wrench,

First of all, accept my sincere gratitude... Really, appreciate your input.

Yes, it has been a 6-year-old issue, nobody solved yet, and fortunately, I have been assigned new machinery engineer in this unit L

Answer for your questions:-

1. No; we don't have a cavitation issue
2. It's not accelerometer sensor, it's a non-contact eddy probe (3300XL probe),
3. Yes, instrument calibrated recently,
4. Couplings are rightly installed
5. Based on last maintenance report, bearings condition are good, and we also trending lube oil temp, it also good
6. Yes, we have enough lubrication, our PdM team monitoring well
7. Maint. Are update
8. We also suspect some pipe stress, based on current orbit
9. No, the issue started on Y2009 only, we do not have any vibration before that. Offline casing reading shows only 1.5mm/sec, and lube oil properties within range. We do not have any bearing failure or other failures too since 2009 with this level of vibration.
10. Nope
11. More than 10 years
12. Changed the probe, proximeter, cable, BN relay card and other instrument related troubleshoot...

We are struggling lot to identify the issue. I sincerely expect your valuable input.

One more question for now, What are your probes mounted to and is there maybe something that could induce the readings through the mounts that is not related to the turbine, such as another pump or other ancillary equipment.

The reason I ask is if this vibration had been present in the turbine for this long you would have seen some type of damage by now.

Yes, i agree.. if its real failure is imminent. infact, machine runs fine. Possible from instrument side only. About mounting we also suspect, and one more thing the probe view, whether the probe target are different than other probe. this also my doubt.

but im confusing that how to check and confirm those items in field?

Describe how the probes are mounted, their support rigidity could be one of the reasons.

Have you a polar graph of the vibrations ? Could you show how it looks ?

Probes measure the relative displacement between the support and the shaft surface so that influences could come from both ends.

45 degree right angle from TDC, sorry we don't have a polar graph. Yes, if it's a real vibration both probe should read. But we have a concern here from only one side.

Make an inversion probe X to Y and vice versa If results are the same as before for each direction probes are not the reason but their position if values change the probes could be "guilty".

we did, this, the reading are same as well. but same time, when we over haul the turbine, we found nothing, bearings , oil properties all are in good condition..

Hi we using 3300XL proximeter system and we did set -10V as Gap voltage, hence we observe X,Y vibration discrepancy.. Where one is showing high vibration 55 mic and other one showing very low vib 15 mic.as per theory, when gap voltage decrease then vibration gets up. I found for this system has a linear range Up to -13 v, if we change the concern probe ( the one having high vibration) gap voltage to -13 V, will vibration can come down? We again did open the turbine, nothing found, clearance,lube oil properties, journal bearing, pipe stress, soft foot all are in range. Though we changed probe, proximeter, cable, card, etc etc.. No result. We decided to play with gap settings, shall we go forward?

Dear Wrench,

What is the reason, if steam turbine vibration jumps sudden from 0 microns to 60 microns in less than a sec.