We are facing high vibration an axial Flow Morris Type 54” MPAF pump which is designed for re-circulation of Caustic Liquid. This is an overhung design pump with no bearing support on the Non drive end side and pump is directly installed to elbow of a large pipe.

Following are the specifications of equipment

Flow:   20,000 m3/ hr.

RPM:    242

Driver: 1185rpm, 530 kW Motor        

Driven through a Gear box and universal coupling

Observations:-

  • Highest Vibration at P1H (Pump Inboard Horizontal) of 0.5-0.6 IPS. Which keeps on fluctuating. Overall trend rose after the replacement of complete pump with an overhauled pump in June-2015
  • Biggest Peak is at 10.95 Hz (2.717 x) which is around 0.25 IPS.
  • In P-P Mils spectrum another peak is around 2.001 Hz (0.497x) which is very close to FTF of Taper Roller bearing.
  • P1H Peakvue doesn’t show any abnormality.

 

Please have a look at the attached data and provide your feedback.

  • Whether it’s a bearing related. What type of issue? Why it’s not being shown in Peakvue.
  • Structural resonance as pump has no independent support and is directly bolted to the flange @ elbow of pipe.
  • Whether universal joints in the coupling can cause this issue.

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Original Post

Can you provide a multiple point waterfall, include HVA directions, at each bearing location on the gearbox and pump, if you can get the motor in there also that would help. 18 points maximum allowed in AMS software

Resolution of your data is not sufficient enough to determine what frequencies are present, can you take a set of velocity readings on this machine with a 6000 cpm fmax, 1600 LOR, 4 avgs, 50% overlap. Also collect peakvue with 60,000 fmax, 1600 LOR, 500hz and 1000hz filters, 1 avg, 2 separate readings. Post this data once collected, again in a multiple point waterfall, shown in velocity.

Was the pump completely replaced, elbow and all in June or was the pump rebuilt in place?

Your data indicates the vibration is direction sensitive, this could indicate change in structural stiffness of the piping and its supports, can you provide an equipment image? Do you know how many impeller vanes are in the pump? Was there a designed change in the system when the pump was replaced like increased impeller size, speed change?

Dave

First of all sorry for the late response; I could only make to the pump yesterday. Please find below the required information 1. I have attached multiple point waterfall for all the points except Peakvue plots. 2. I have attached different plot for the Pump with better resolution as required. 3. Two readings of Peakvue also attached. 4. Pump was completely replaced with an overhauled one, elbow is part of pipe and we didn’t replaced it. 5. I will take bump test reading in the next shutdown of pump. 6. Pump has 04 vanes. 7. I have attached drawing for the pump and the elbow. 8. There was no design change made to the system while replacing the pump. 9. Maintenance guys informed that they didn’t replace the coupling in some years; and am not sure that whether proper parallel offset was maintained for this coupling. So can anything from universal coupling can cause this problem?

Response definitely looks like resonant energy.  Have you checked all of the supporting piping connections and supports to ensure they ?  I don't suspect a flow condition because the axial direction and vertical directions look OK.  Check any supports that would affect horizontal stiffness.

Ron Brook

 

In that case the CSI Function of Bump Test "Equipment Running" will be on any help? Actually as discussed earlier and can be seen in the above attachment of Pump general drawing, there is no separate support for the pump, it's just directly bolted to the flange on the elbow. However the suction 86" line which is coming from a Caustic crystallizer must have some supports (which am not very aware of). However as mentioned earlier this problem started after replacing the complete pump in Plant Turnaround in June 2015. Therefore I inquired maintenance guys about any job that was performed during TA on suction/ discharge piping, supports or flanges? Their answer was NO. But let me get into this a bit deeper.

look like, that cavitation problem due to flow recirculation inside of pump. comparing to your waterfall that second peak frequency already exist before overhaul and after overhaul become higher. perhaps you can check operation. i assume pump discharge pressure increasing due to restriction at discharge line that cause pump internal recirculation.

Regards,

Abdillah

I think your spectral data indicates you have two problems that were more likely caused by maintenance actions of replacing the pump. The first problem is the vibration at essentially one half shaft speed that may be caused by impeller rub condition. My understanding is that this pump design does not have an impeller wear ring like a centrifugal pump. The impeller vane tip clearance is critical, so a rub could occur if the shaft is not correctly centered in the housing.

The second vibration peak near 2.7 times shaft speed is non-synchronous and has a broad base indicating a resonant amplification of the structure. The excitation force is probably fluid pulsation. The resonant amplification factor may have increased simply due to the replacement pump attachment to the piping being different than original. Fluid flow turbulence may have increased if there was any changes to the upstream piping; including internal cleaning and air in-leakage. I would look for additional indications of impeller rubbing by measuring high-frequency vibrations or ultrasound around the periphery of the pump case in the area of the impeller to detect possible rubbing. Could also try hand rotation of the pump shaft to determine if it moves freely, but this may be inconclusive. A structural impact test on the pump housing and piping and possibly an operating deflection shape (ODS) test could confirm that the resonant structure is present. You can then decide whether it should be changed or not. Maintenance actions can sometimes create new problems!
Walt

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