Out board bearing lube oil being dis coloured

[pkg80]

hello all

We have a 4 stage Centrifugal pump recently overhauled. After overhauling there was some abnormal noise from OB bearing ,We had changed that bearing(ANGULAR CONTACT BALL BEARING) ,now oil is being discolored in 3-4 days of running of pump. We have flushed and refill two times but getting same problem. I have observed temperature is also slightly higher than sister pump.
yesterday again drained whole oil and noted following points
1. It was discolored (dark brown )
2. No moisture observed
3. No any particle observed
4. Oil breather was found dirty
Following job done :
1. Drained whole oil from OB bearing housing
2. Flushed bearing housing with fresh oil (Three times)
3. Bearing housing filled by fresh oil (Turbine oil 46) up to the correct oil level
4. Oil breather & oil cup has cleaned


Skin temperature for OB bearing housing after running of 1/2 hrs of pump was 116 deg F ,for sister pump after 1 hrs it was 112 deg F.
Can any one suggest what may be the probable causes and what checks should be required for this type of problem?

 

[keyepitts]

The abnormal noise is concerning, the noise may indicate that some contaminates were getting ground up in the bearing, which may have already damaged the bearing. The temperature seems normal, certainly not high enough to cause the oil to start breaking down (unless you mean 116ºC). I would be looking for any way that outside contaminants might be making there way into the bearing housing, specifically through shaft seals (installed backwards?) and/or the breather.

 

[spciesla]

You need an oil analysis done to discern moisture levels, particle counts, wear particle concentrations, viscosity, etc. The eyeballs won't work for that analysis unless things are really bad. Is the angular contact bearing a thrust bearing? Is there a radial bearing? Slinger ring?

 

[romke]

the oil you mention is a turbine oil that at the temperature mentioned (116 F) should have no problem with overheating and consequent darkening. that it darkens may indicate that local temperatures have been much higher then measured, the darkening also can indicate that some water got into the oil - the darkening then will go together with a certain loss of transparency of the oil. since a turbine oil has excellent water shedding capabilities, a sample taken should clear up within say 1 hour with some water at the bottom of the container.

since before the change of the bearing everything was ok, i suspect something has gone wrong with the bearing. are you sure it is exactly the same type/size as the original, has it been mounted correctly, has anything else been changed? in normal operation the oil should last a lot longer, that same oil is used in steamturbines for decades without changing it running at temperatures of about 170 F.

 

[Strong]

Some multistage pump thrust-end bearings have shims that control axial bearing position. You could check whether the replacement bearings were identical in all dimensions and whether correct shims were used and installation procedure was followed. Vibration analysis possibly supplement with contact ultrasound measurements would help follow bearing deterioration. Might as well make plans to replace bearing. I assume there is no indication of pump shaft seal issue that would cause water to enter bearing.

Walt

 

[BoilingCrude]

Possible that who ever cleaned O.B. bearing housing did not do a good job and there could be debris leaching into the new oil and bearing.
Plan to remove O.B. housing and perform field brg. change out and inspect clean housing reinstall. You are relying on the shop that did the repairs ......