Dear Experienced panel 

I would like to share one concern about high casing vibration (1x rpm) in horizontal direction of pedestal showed in picture attached. 

the vibration is 10 mm/sec -rms.

the another Steam Turbine pedestal vibration is 1 mm/sec.

the question are?

1.- can we allow this part of machine vibrate with this severity?

2.- can the grouting issue to be the cause of this high vibration?

3.- can some resonance frequency be the cause?

4.- can be possible this pedestal has design problem?STEAM TURBINE PEDESTAL

please I will wait your appreciate comments. 

Rest Regards.



Ramon Ruiz (vibration CAT II)


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Original Post

I would like to know some information

Do you have the historical vibration data?

Was it a gradual or sudden increase?

Have you received maintenance lately?

Is it just at this point or is it all over the pedestal?

Do you have displacement sensors?

oil pressure and bearing temperature how are they found?


Dear Carlos.

Thanks for your questions.

 1.-Was it a gradual or sudden increase?

the vibration has long time, but nobody took reading in this pedestal before, they took reading in horizontal direction of bearing housing, if the load reduce or the speed reduce at 5%, the vibration reduce 70%.. the speed is 8600 rpm with normal load. 

2.- Have you received maintenance lately? 

the last overhaul was five month ago, also the vibration in casing of bearing housing was present since 2016.

3.- Is it just at this point or is it all over the pedestal? 

the bigest vibration is showed by the arrow, also in the same point at right side, but near to the grouting vibration is almost 1.5 mm/sec. 

4.- Do you have displacement sensors?

I will attached information about displacement sensors. 

5.- oil pressure and bearing temperature how are they found?

the oil pressure is 1,2 kg/cm2, temperature about 70 ° C.

tomorrow I will share more vibration in several points in pedestal, also in vertical direccion I found 3.3 mm/sec. 

orbit rear bearing



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Hi, Vibration Guy

1.- Is your found 10mm/s rms occur during steady state normal operating condition of your turbine?

the vibration only appear with load, 

more than 8600 rpm is load condition,  but when the load reduce at 8100 rpm, the vibration reduce 70% in pedestal and bearing casing .

Of course the vibration comes from the bearing housing, and when the vibration is low in bearing housing also de vibration in pedestal reduce. 

but why the other pedestal (turbine front side)  the maximum vibration is 1 mm/sec at all directions?

2.-Is there any problem found or high vibration on the shaft relative vibration? 

I attached full spectrum about shaft spectrum.full spectrum rear brg


Photos (1)

Hello Ramon

In the orbit an instability is observed, which is confirmed in the spectrum by the presence of an amplitude at approx 0.4x, this phenomenon can be related to a oil whip or surge problems (very rare).

What is the alarm limit of the protection system for that bearing?

In this case I would do the following:

1.- impact test to determine the natural frequency of the pedestal.

2.- increase the oil pressure and observe the behavior (2.2 kg / cm2)

3.- perform a transitory analysis, focusing on the shaft centerline, bode plot, orbit, cascade.

If this condition has always remained, it may possibly be due to a misalignment between bearings, resulting in greater eccentricity between the rotor and the bearing causing the oil whip.

ramonruiz posted:

BODE VI-6901Cascade VI-6901SCLWaterfall VI-6901

Dear sir

Do you have phase information about this issue ? Does it stable ?how about amplitude ? According to shaft center line graph shows some  excessive radial load deu to bearing misalignment .this issue cause eccentric shaft and so oil instability that see at orbit shape .

But if you have cross phase between vertical position and base plate of    pedestal , you should check foundation  defect like crack grouting .


Dear Panel, 

Please see the vibration in both pedestals, and comparing you will see, some differences , both of them have same vibration pattern respect to shaft. 

the question now is, why the pedestal front side don't have high vibration?

as soon as possible we will try to do ODS analysis. 

what is your opinion about that case..comparative pedestals


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Are you seeing high 1X in the shaft spectrum also..??

Are you seeing high vibrations/High 1X on the pinion input bearing..?? if yes how much, if no how much..??

How does the time waveform on the pedestal (Turbine rear) bearing looks like

Take a shutdown and do the impact test as others have suggested. There may be a local resonance coming into play as soon as the turbine reaches rated speed.

Your comment says there is a reduction by 70% in vibs as soon as the speed drops from rated to 8100 rpm. This is the hint that there may be a local resonance along Turbine rear end and no such resonance near turbine front due to which its vibs are low. I have sen this kind of problem in a couple of turbines.

Hope this helps.


I agree with Mr. Nagaraja that it looks like resonance problem. 

I have a similar case with condenser turbine which i see high casing vibration at rear side but not front side in axial direction. We did a lot of test and finally, the root cause is LP control valve of turbine having problem (oil leaking) and the valve knocking/vibrating with frequency near/equal natural frequency of bearing support making it high. After we repair the valve and vibration reduced to normal value of 3-4mm/s. So, i suggest you conduct impact test to evaluate the natural frequency of bearing support.

I do not think oil whip/whirl/misalignment is a case.


thanks at All for your comments, 

we are planning to do some actions next 2020 March,  all your recommendations will be take in count, 

some test, also Dye penetrant test over Metal pedestal will be done, 

civil engineers told me this foundation suffered  fire almost in 2014. we are considering some concrete test, 

thanks a lot for your coments. 



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