vibration/alignment/balance

To Mr Ali M Surafa
Dear Mr Ali
In our new plant we have Four NGL shipping Vertical pumps (Flowserve)with 8 stages
We are facing high vibration problem during commissioning time no pump succeed to run more than 10 minutes
- Pump tripped on high radial vibration (proximeter probe).
- CSI readings given only maximum 1.3mm/s rms on pump side
- seismic probes installed on motor casing
given Max vibration 1.7mm/s pk
- spectrum shows high pick @ 1X
- We are suspecting flow related problem (presence of Bubble on suction line or NGL specification not adequate with pump design

Could you please help us ?
Thanks in advance

Can you give more details on the pump's probes?

Motor vibrations are well withine the limits, right?

Is this a new project?

Can you post some plots of the high vibtation points?

Dear :Mr Ali
thanks for your reply
Yes it is a new project
Vibration probes installed on the pump bearing are proximeters

Vibration increase form 0 up to 130 micron just after start up .

Can you please post the vibration plots of the pump probe?

Is this probe submerged in the fluid? Mounted/threaded on the bushing housing?

The more details you give, the easier one can provide meaningful suggestions.

Dear Mr Ali
Those probes required by our company for more protection, installed on bearing housing (Near the disc) and not submerged in the fluid.
Both radial probes going high more than 150 microns

We are suspected maybe
1- Fluid instability (babbles, vapor or vortex)
2- Probes reliability

What's your recommendation?

Dear OULADALI ALI,

I hope I can help a little but still the information you give is limited. Vibration plots and drawing of the pump showing the location of the probes will add value to understand the problem. You can or cannot post them here?

The 150 micron (~6 mils) vibration you mentioned on the on the pump can be high and can be normal. In fact there are no well-established standards for pump' shaft vibration for vertical machines. Who provided the settings and based on what?

I have experience in vertical pump vibration on two locations: 1) on the top of the pump just above the stuffing box (seal) 2) on the stationery parts of the structure like spiders and bowl.

Dear Ali
As requested you Find attached all vibration trends and spectrum
For your information
To day one pump started 3 times every time tripped due to high vibration onboth vibration radial probes but tripped by seismic probes installed on Motor casing

waiting for your reply

I would suspect a resonant structure either shaft or stationary support as at lease part of your problem. Try one or more of these tests:
1) Impact vibration-response (bump) for motor and exposed shaft
2) Operating deflection shape (ODS) for motor and support structure
3) Coast-Down for shaft and housing (need speed sensor or Key Phasor)
Perhaps you can raise your Trip settings to accommodate tests 2 & 3 above.

Walt

have you gone for dynamic balancing? Up to what tolerance the rotor was balanced? May be, field balancing is required.
Vibmaster

Dear OULADALI ALI,

I agree with both Walt and Vibmaster. I would moreover emphasize on the possibility of multiple causes.

Based on the motor casing measurements (10.6 mm/sec or 0.42 in/sec), it seems that there is an actual vibration and it is high.

I would advise to review the pump data sheet (API forms) and see the natural frequency documented. Do the impact test and compare the results. Compare the documented natural frequencies versus measured values and measured values versus measured vibration frequency. Notice that the online spectra (System 1) are of a rough resolution and it would be better to collect the data using a higher resolution set up.

On the balance quality side, I would recommend to go to the performance sheets of the pump and motor and see the balancing and factory run test records. It is likely that the pump and motor rotors were well balanced and had acceptable vibration level. But this is the first point one should check.

Some symptoms on the balance problems would be found from vibration plots that you can extract from System1. Can you post the orbits and 1X amplitude and phase trends for example?

Again can you post a sketch/drawing to show the locations of the vibration probes/sensors?

Now, is the manufacture representative for this project aware of the high vibration problem? If he is not, somebody should communicate with him for many reasons. You might lose the warranty on the equipment if he is not officially informed about the problem.

Has the pumping system cooled down before starts? Could you be cavitating during the transient start conditions?

Thanks

The problem still under investigation with presence of the pump Vendor
He's suspecting cavitation/evaporation probelm due to
1- piping design problem
2- NGL specification (High C1 Level)

Good.

Please keep us posted on the findings.

It would be interesting to hear based on what the vendor suspected "cavitation/evaporation problem". From the limited data in above posts I do not see a strong symptom for that.