This orbit is by "wet" rubbing?

Hi everyone,

I have a case in pump with 6500rpm. From the orbit, I see that the wet rubbing could happen inside the pump but phase is not change (you can see from polar plot). Anybody have a different ideal on the case.

At the moment, the vibration around 66um and the last running is 46um. The increase just happen after the pump is restarted without any maintenance activities (the plant shutdown by an accident and then restarted up right away).

 

N.V.Đ

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Original Post

You said this increase just happened after the pump was re-started. What day was that?

Page 1 of your plots (dated Jan 6 - today) does show some restriction of motion in the horizontal direction at the pump drive end; as I can see it in both the orbit and time waveform (looks a bit truncated).  I am not sure of the reason and I wouldn't necessarily jump to a wet rub conclusion at this time.

Can you provide the SAME plots as this just prior to the re-start?    (I'm asking so that I can correlate your concern of "increase suddenly happening" after a restart to what it might have looked like prior to this recent restart).

The 2nd page shows the range of 1X from December 18 to 28th, 2016. Not sure why you chose that time range if your concern seems to be more recent....as in today?? Is the 1X vector in the same general range of amp & phase?  Again, I would ask if you could include the most recent data in these historical plots.

Jim P

Dear John and Jim,

please see file attached for trend of vibration and from that you can see how the vibration behaved after shutdown.

Please re-inform that there is nor maintenance activity is made in recent time. It just shutdown and restart. I think rubbing could be make by orbit show the limit on horizontal as Jim said. the frequency is mainly is 1X at NDE side where high vibration but not in DE side. I see that the vibration at DE side decrease a little bit 3um but NDE side increase 10um. It could be by change load at both bearings change stiffness by alignment change.

The thing I concern is why phase is not change (in normally, it could be). But what happen if the rubbing happen slightly at a stage at center of pump and with carbamate fluid lubrication?

 

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Ngo Dinh posted:

Hi everyone,

I have a case in pump with 6500rpm. From the orbit, I see that the wet rubbing could happen inside the pump but phase is not change (you can see from polar plot). Anybody have a different ideal on the case.

At the moment, the vibration around 66um and the last running is 46um. The increase just happen after the pump is restarted without any maintenance activities (the plant shutdown by an accident and then restarted up right away).

 

hi dinh

do u have strainer or filter in  pump suction? ,do u have check valve on discharge side?

i had experience  high vibration when starting pump with dirty strainer and check valve malfunction

 

On page 5 of 6, you show the comparison of orbit displays at the NDE  (with the ~ 20um p-p increase).

Can you also post the same orbit comparison (i.e. current orbit vs. that of Dec 18)  at the DE?  

As far as rubbing and effect on phase is concerned, my understanding is that this is attributed to rubbing of the shaft (vs. pump impeller itself) resulting in a thermal bow. I am having trouble understanding how rubbing of the impeller (localized spot heating) would affect the phase to any significant degree (I could be wrong).

I am more concerned about the DE side (even though the levels are lower) due to the unusual TWF and orbit display. 

Jim P 

NGO DINH

Thanks for the additional information. Based on the comparisons at DE end, it seems this "flattened" orbit shape in horiz direction has been there even before the recent re-start.      Hmmm...   

I don't have extensive experience with disc type couplings; I suspect John has more than I and he may be suspecting some issues there. My understanding is that these type of couplings are fairly easy to inspect, even while running (with strobe). Others can weigh in on this and provide better direction.   Regardless, it would be nice to know the actual as-is alignment condition based on the still unusual orbit display - even though it may not explain the changes in the NDE. 

Is it safe to assume your comment "... with misalignment axial: +-2mm, axial: 0.77mm." is the allowed SPEC and not the actual as-is condition?

The only other thing I can suggest is to see if these readings and displays are sensitive to flow or temperature. Does this pump generally run at constant conditions?

Lastly, AZIZ58 seems to have had experience with these pumps running with strainer/filter issues, can you rule them out?

Keep us informed

Jim P

Thanks Jim,

As the vibration quite stable without increasing trend, so, now I still suggest the operator keep pump running.

"... with misalignment axial: +-2mm, axial: 0.77mm." is tolerance of coupling which the maximum value of shaft misalignment that the coupling can absorbed.

The alignment issue is one of problem I suspect and I require the maintenance guy to check and correct alignment whenever it is available; however, as my limited experience with type pump and disk coupling, together with alignment issue through shaft centerline, the alignment is not likely a cause make vibration here. So, it still question me why the vibration behaves like that (see shaft centerline compared between present and last shutdown).

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A common method of pump journal repair includes chrome plating and often the chrome extends into the proximity probe area.  Minor axial shifts in rotor position  can cause changes in radial behavior.  Do you know if these journals have ever had chrome plating applied?  

Have you ever applied compensation to the data to see if the levels go up or down and by how much?

 

Dear John,

Thanks for your ideal. I try to find the information about coating material but it is not available. The shaft material is A276 type 316L.

I know that the difference axial position could make difference of radial vibration; however, in the case the difference is around 4-8um, I am not sure that it is enough for changing the radial value (see file attached).

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