SEA WATER INTAKE PUMP

Hi to All
We are facing one vibration issue in sea water intake pump. The pump is vertical pump driven by motor and the RPM is 740. The vibration issue started before 6 months. The pump vibration was varying from 3mm/sec to 8 mm/sec RMS. The vibration is high in one direction (towards flow directions). The vibration in other direction of the pump is normal with minimum variation up to 2.5 mm/sec.

History
Initial there was minor abnormal sound from the motor Non drive end bearing with bearing defects in the vibration spectrum. The motor solo run was tested and bearing replaced. 
The pump vibration shows variations at 3X. Upto 10mm/sec along with flow direction.Initially misalignment was suspected and also to review the gear coupling for any abnormalities. 
The alignment was checked and found severe misalignment. The coupling was found ok. The runout of the coupling also within normal.
The equipment started again and found same pattern with high vibration . Again alignment was out and decided to take the pump out and checked completely. No notable abnormalities. However the rubber bearings were replaced.
The pump started again and the problem still persist. Kindly share your ideas.

Original Post

Ask yourself why does the alignment keep changing? Sounds more like the support structure of your pump is suspect. When you say hi vibration in one direction this typically is a resonance related symptom, due to weak machine foundation, IF the machine is in good working order. 

What do you know about the hydraulics of this pump, any change in pump performance in the past 6 months?

Dave

Sreekumar posted:

Hi to All
We are facing one vibration issue in sea water intake pump. The pump is vertical pump driven by motor and the RPM is 740. The vibration issue started before 6 months. The pump vibration was varying from 3mm/sec to 8 mm/sec RMS. The vibration is high in one direction (towards flow directions). The vibration in other direction of the pump is normal with minimum variation up to 2.5 mm/sec.

History
Initial there was minor abnormal sound from the motor Non drive end bearing with bearing defects in the vibration spectrum. The motor solo run was tested and bearing replaced. 
The pump vibration shows variations at 3X. Upto 10mm/sec along with flow direction.Initially misalignment was suspected and also to review the gear coupling for any abnormalities. 
The alignment was checked and found severe misalignment. The coupling was found ok. The runout of the coupling also within normal.
The equipment started again and found same pattern with high vibration . Again alignment was out and decided to take the pump out and checked completely. No notable abnormalities. However the rubber bearings were replaced.
The pump started again and the problem still persist. Kindly share your ideas.

Since it is towards the flow why you try to jack the pipe or put a support if does not any, it seems that there some forces excite the misalignment. 

SREEKUMAR,

The seawater intake pumps I saw are deep underground and their motors are tall. The highest measurements are usually at the top of the motor and there no real access to the pump for vibration measurement. I'm not sure if your pump is of the same design or not.

It would be easier and more encouraging to help if you can post some vibration plots and pictures of the machine.

"The pump vibration was varying from 3mm/sec to 8 mm/sec RMS". Assuming the variation takes place at 3X, this might be an indication of a beat. I suggest to do the following (if not already done):

1. Take background vibration (while the pump is off).

2. Take long time waveform or trend of you do not have this feature on your device. Take at least 5 minutes.

3. Take a list of measurements from the top of the motor to the concrete foundation and analyze the variation.

4. Work with your operators to change the flow of this pump or other pumps if they work in parallel. If possible switch adjacent pumps off (temporarily). You should take the readings while doing so.

Please keep us posted on your findings.

Regards- Ali M. Al-Shurafa

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