Dear People

We have experimenting a problem with a Centrifugal Compressor of a Ethylene Unit.

The compressor has 3,000 Gallons of ISO VG 46 Turbine Oil, and we found a high temperature in the sleeve bearing of the first stage of the compressor. The temperature increase in the night when the enviroment temperature is low. In the day, when the enviroment temperature is higher, the bearing temperature decrease. We have registered values of 117 °C in the bearing, with the env. temp. is 19°C, and values of 114 °C in the bearing with the env. temp. is 29°C. This relationship appears only in this bearing. For the others one, the relationship between env. temp. and bearing temperature is direct.

We have performed oil analysis, and we found good results, like ISO Code 14/12/10; Water content 37 ppm, TAN 0.07, Colour 3, and Varnish Potential Rating 40.

We don´t thing that the problem could be related with oil.

One of our team commented that maybe some kind of sludge of varnishing could be being accumulated in the surface of the bearing. This sludge interrumps the oil film and increase the temperature. Due the high temperature, the sludge of varnishing become solved in the oil and removed.

We don't think that this could be the cause of the problem.

Please, if anyone of you have experimented a situation like this one, it could be good for us have your comments.

Kind Regards,

Cristian

Could it be something like when the ambient temperature is low the temperature in the compressor oil reservoir is low and the oil temperature at the suction of the bearing is low as well. As the temperature is lower the viscosity of the oil is thicker and the friction in the sleeve increase increasing the temperature of the bearing. The change of temperature does not appear on the other bearing because the clearances are slightly larger. I suppose the rotational speed of the compressor is high.

Otherwise the problem might be related to metal expansion.

What is the lube oil supply temp to this bearing?

Shaft RPM?

Bearing type: straight sleeve bearing, tilt pad bearing, fluid pivot bearing or elliptal bore bearing?

ow long has this bearing been in service?

Dear pepelepew and Fritz

Thanks for your answers.

The lube oil supply is 43°C., the shaft rpm is 7700 rpm. Type of bearing is tilt pad bearing. It has been in service for 5 years.

Kind Regards,

Cristian,

I guess I should have asked if the temperature indication is from a drain temp or imbedded white metal indication. From the temperature I'm assuming it's a imbedded RTD.

We operate many compressors with the same bearings and speed in natural gas service. Your oil inlet temp is right in the ballpark (or soccer pitch if you will) We try for a lube oil header temp of 110 F. If this has been a problem since installation I would look at the viscosity of the oil you are using. In our service we use ISO VG 32. What leads me to think your oil might be borderline viscus is that when the ambient temps go up the bearing temp goes down and just the opposite at night.

If this is a problem that has just started and is unique to just this bearing then I would suspect a bearing related problem, clearance and or varnishing of the bearing surface that should trigger a planned inspection at your next scheduled outage.

Any corresponding changes in vibration amplitude and or signature between day and night? Viscosity changes could cause oil whirl that will show up in a vibration spectrum at .4 to .48X.

Fritz

Fritz