High vibrations in 300kW motor during no load after tightening of foundation bolts

[Manish Waykole]

We have a 300kW motor for a multistage Union centrifugal pump. After installation of pump after last maintenance activity the vibrations of the pump ran very high where the motor outboard vibrations ran upto 17mm/s in horizontal direction. On checking the it was observed that there is soft foot in motor foot. The same was correceted by independently blue matching the baseframe and motor foots against the same glass surface. The motor has 2 nos outboard foot and 1 nos inboard foot bolts for tightening with baseframe.

However, even after the blue matching the motor no load vibration remains at 14mm/s in outboard horizontal direction. The soft foot has been checked again after removal of all shims, the same was found to be within 1-2 thou on all foot.
At the Motor outboard foots the vibrations are 180degree out of phase. Inboard and outboard feet of motor of any side of motor have in phase vibrations. The front feet of the motor have vibration phase difference of 66-70 degrees. On loosening the motor inboard 3 o'clock bolt (looking from motor outboard end towards the pump) the vibrations reduced to 7mm/s.

The baseframe was checked for irregularities and we found that the baseframe pads are inadequately supported at the outboard of motor.

I want some suggestions for further course of action here. The multistage pump is critical for the unit and has been a constant source of unreliability currently.

Regards,
Manish Waykole

 

[electricpete]

What is the frequency of the vibration? is it twice line frequency? is this a 2-pole motor?

 

[IRstuff]

What was the vibration before the maintenance?

What maintenance was done? It seems pretty obvious that some level of mechanical change occurred because of the maintenance, so some sort of imbalance of the rotor, or some mechanical distortion of the housing.

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[Basit Shafi]

electricpete , sorry I am new to this forum could you respond to a thread titled "Shaft Critical Speed Calculator Based on Melvin prohls Method "

 

[Tmoose]

" the baseframe pads are inadequately supported at the outboard of motor."

I do not doubt that is the case, but Information about how this was determined would be helpful.

Pictures of your actual pump and motor arrangement would be more than helpful.

Sometimes structural deficiencies are easy to correct.
Sometimes they are not.
Efficiently Arriving at a good solution absolutely depends on the quality of the up front investigation. Measurements of various forms are the key. Thoughtful observation is important too.

What vibration analysis equipment do you have?

Modifications based on Rules of thumb or anecdotal stories are really based on hope.
In my experience machines are often wily, and really good at finding and exploiting even subtle design and installation defects.

 

[Manish Waykole]

We have Emerson vibration monitoring handheld devices and 1 nos of rpm detector which helps is taking the phase wise readings of vibrations.

P305D – Vib Report
P305D - RPM20590Y (18-Jul-23)
OVERALL LEVEL 1xTS 2xTS 3-8xTS
MOH 9.399 mm/Sec 9.123 mm/Sec 1.245 mm/Sec 1.641 mm/Sec
OVERALL LEVEL 2xTS 3xTS 4-12xTS
MOP .080 G-s .028 G-s .027 G-s .042 G-s
OVERALL LEVEL 1xTS 2xTS 3-8xTS
MOV 2.045 mm/Sec 1.025 mm/Sec .967 mm/Sec 1.107 mm/Sec
MOA 1.970 mm/Sec .121 mm/Sec .529 mm/Sec 1.231 mm/Sec
MIH 9.586 mm/Sec 9.327 mm/Sec .823 mm/Sec 1.816 mm/Sec
OVERALL LEVEL 2xTS 3xTS 4-12xTS
MIP .219 G-s .035 G-s .037 G-s .126 G-s
OVERALL LEVEL 1xTS 2xTS 3-8xTS
MIV 2.189 mm/Sec .896 mm/Sec 1.061 mm/Sec 1.168 mm/Sec
MIA 2.011 mm/Sec .965 mm/Sec .452 mm/Sec .832 mm/Sec
MOT 36.00 Deg C
MIT 41.00 Deg C
The above set of vibration readings have been captured in motor solo-run condition:-
Motor DOR: CCW
Motor NL Current: Electrical to please provide

P305D - Dewaxed Oil Pump D (19-Jul-23)
OVERALL LEVEL 1xTS 2xTS 3-8xTS
MOH 15.16 mm/Sec 15.99 mm/Sec 1.293 mm/Sec 1.595 mm/Sec
OVERALL LEVEL 2xTS 3xTS 4-12xTS
MOP .108 G-s .024 G-s .022 G-s .062 G-s
OVERALL LEVEL 1xTS 2xTS 3-8xTS
MOV 2.744 mm/Sec 1.656 mm/Sec 1.306 mm/Sec 1.224 mm/Sec
MOA 2.928 mm/Sec 2.360 mm/Sec 1.107 mm/Sec 1.088 mm/Sec
MIH 16.26 mm/Sec 16.00 mm/Sec 1.049 mm/Sec 2.555 mm/Sec
OVERALL LEVEL 2xTS 3xTS 4-12xTS
MIP .234 G-s .062 G-s .053 G-s .124 G-s
OVERALL LEVEL 1xTS 2xTS 3-8xTS
MIV 3.767 mm/Sec 2.770 mm/Sec 1.616 mm/Sec 1.304 mm/Sec
MIA 3.398 mm/Sec 2.703 mm/Sec .677 mm/Sec .700 mm/Sec
PIH 9.335 mm/Sec 8.976 mm/Sec 1.416 mm/Sec 2.036 mm/Sec
OVERALL LEVEL 2xTS 3xTS 4-12xTS
PIP .187 G-s .048 G-s .048 G-s .116 G-s
OVERALL LEVEL 1xTS 2xTS 3-8xTS
PIV 3.909 mm/Sec 2.523 mm/Sec 1.466 mm/Sec 2.262 mm/Sec
PIA 1.198 mm/Sec .542 mm/Sec .811 mm/Sec .437 mm/Sec
POH 5.963 mm/Sec 5.083 mm/Sec 2.276 mm/Sec 2.103 mm/Sec
OVERALL LEVEL 2xTS 3xTS 4-12xTS
POP .247 G-s .073 G-s .074 G-s .096 G-s
OVERALL LEVEL 1xTS 2xTS 3-8xTS
POV 1.751 mm/Sec 1.011 mm/Sec .437 mm/Sec 1.331 mm/Sec
POA 1.147 mm/Sec .557 mm/Sec .796 mm/Sec .442 mm/Sec
MOB 45.00 Deg C
MIB 65.00 Deg C
PIB 35.00 Deg C
POB 55.00 Deg C
The above set of vibration readings have been captured in load condition:-
Motor Load Current: 30A
D/C Pressure: 5-25kg/cm² (fluctuating)

Observation and Analysis:

• Equipment no load trial run has been taken at site after motor overhauling job and vibration levels are observed to be higher side. Initially maximum vibration observed around 4-5mm/sec and after some time (20-30minutes of motor running), vibration readings increased up to 10mm/sec at motor bearings.
• The maximum vibration is in no load condition around 9.5mm/sec observed at motor IB bearing in horizontal direction. Load trial run also taken and maximum vibration is 16.26mm/sec observed at motor IB bearing in horizontal direction and 9.33mm/sec observed at pump IB bearing in horizontal direction.
• FFT spectrum indicates dominant frequency 1Xrpm in H-direction at motor bearings & 1Xrpm and its harmonics in V & A direction at motor bearings and 1Xrpm & its harmonics at pump bearings.
• There is abnormal noise from NDE side under full tight operation and significantly reduced noise conditions when bolts loosened.
• Vibration spectra and Time wave form data indicates presence of running speed harmonics and impacting phenomenon respectively.
• The source of the high vibration and noise appears to be the motor NDE bearing. The spectral data suggests possible loose mount/improper fitment of the NDE bearing.
• The foundation bolts tight and loose conditions must be influencing bearing fitment resulting in modified vibration response.


Regards,
Manish Waykole

 

[Manish Waykole]

It is a Marelli Motor and we have filled the contact form but to no avail.
A level 4 vibration expert Mr. S Ganti had following recommendation:
We have collected vibration data on the motor in solo operation under two conditions, all bolts in full tight condition and loose condition.
The following are my observations and recommendations.
1. There is abnormal noise from NDE side under full tight operation and significantly reduced noise conditions when bolts loosened.
2. The same behavior was the seen with vibration on both bearings, predominantly, in horizontal direction.
3. The noise from NDE side is predominantly impacting in nature and could be heard during motor coasting down.
4. Vertical vibration survey on the motor feet and base indicates relatively high amplitude, about 2.5 mm/s peak. Phase data suggests out of phase movement on either side of the motor base.
5. Vibration spectra and Time wave form data indicates presence of running speed harmonics and impacting phenomenon respectively.
Analysis..
1. The source of the high vibration and noise appears to be the motor NDE bearing. The spectral data suggests possible loose mount/improper fitment of the NDE bearing.
2. The foundation bolts tight and loose conditions must be influencing bearing fitment resulting in modified vibration response.
3. The high 1X amplitude and gradually increasing behavior after start of motor, is mostly likely due to an induced bow or eccentric conditions by the NDE bearing.
4. Some influence on the vibration behavior from the motor foundation is possible but might not be primary source.
5. Cooler fan mounted on the NDE might also partiallly contribute to the observed vibration behavior.
Recommendations..
1. Please remove motor cover on NDE side and inspect the Cooler fan for any signs of loose mounting or other abnormalities.
2. If nothing nothing is observed from Sr.1, please inspect the NDE bearing for signs of loose mount or excessive clearance etc.
Repair accordingly.
3. Install the motor on its foundation after repair and then fine tune the soft foot issues,if any, as required.

The recommendations could not be executed till date but work is ongoing.

Regards,
Manish Waykole

 

[electricpete]

That's a lot of data. I'm going to summarize what I read (feel free to correct anything if I said it wrong)
[ul]
[li]Overvations: noise coming from NDE area, baseframe pads appear inadequately supported at NDE end.[/li]
[li]Vibration: velocity shows high 1x uncoupled, increases by about 50% when coupled. Directional, with H about 4x more than V. No significant difference from NDE to DE (outboard to inboard that I could see. Harmonics at 2x and 3x about 10% of 1x. Not much showing up on peakvue. Soft foot corrected, didn't change anything. Vibration is time sensitive (grows over time). [/li]
[li]History: Vibration showed up after pump work. Fixed soft foot and that didn't correct the vib.[/li]
[/ul]

The source of the high vibration and noise appears to be the motor NDE bearing

I understand the noise part, but I don't understand the high vibration part. The vibration readings look same on inboard and outboard of the motor... what leads you to say the source of high vibration is on the outboard?

Did I read right that the unusual vibration first showed up after pump work? Nothing was done to the motor and everything was running fine before that?

Is it a TEFC motor? (I saw mention of checking the fan). What is the motor speed? A photo as Tmoose requested might help focus things a little.

I see the peakvue overalls are pretty good, I'm curious if the peakvue spectrum shows any bearing patterns.

You mentioned time dependent (increasing over time) vibration in uncoupled state... is that repetable?

... if so (repeatable observation of vib increasing over time after start), that is quite a distinctive symptom. Thermal rotor bow is what comes to mind for me on that. I have seen some strange rotor problems in my day and symptoms have included vibration increasing 1x as the motor warms after start, and also harmonics (that was a larger sleeve bearing motor so may not be comparable).

Some things related to rotor:
[ol 1]
[li]While running, do a current signature analysis (looking for pole pass sidebands around line frequency) if you have that capacity[/li]
[li]Take vib with high frequency resolution look for pole pass sidebands around running speed.[/li]
[li]I would suggest if you get an opportunity, check TIR on shaft extension as soon as you can after machine shutdown while it's still relatively warm. Then check it again later when cool again at shaft extension. And if you inspect the fan as recommended by your consultant, might as well check TIR there too. [/li]
[/ol]
I only suggest those because they're relatively easy /non-intrusive and the time dependence (and possible connection to rotor) is what jumps out at me. I don't have a really good feel for what's going on, will look forward to more info if you can answer some of the question.

 

[Tmoose]

Did I miss a description of the bearing types in the motor and pump?
Ball, roller, or plain/.sleeve type ?

The coupling type is worth thinking about.

Pictures of your actual pump and motor arrangement would be more than helpful.

 

[Daren Samy]

It is probably soft foot problem.

Daren!