General Guidance on Babbitt Bearing Running Temperatures.

[MacMcMacmac]

Good Day. We have a large turbo exhauster here that we are trying to solve a vibration issue on. It will peg the vibration monitoring meter at startup, but gradually level out within acceptable limits after running for an hour or so. We are trying out various theories as to why the vibration has come about after the main driver was overhauled a few months ago after a drive bearing failure (roller type). The vibe meter pegged when the motor bearing began to overheat. I hit the e-stop and it coasted down normally. The motor was overhauled, re-installed, and aligned to within acceptable parameters using a PrufTeknik Rotalign.

What is bothering me is the seemingly absurdly low temperature alarms on this machine. The oil temperature is going into warning at 107F, and will go into alarm at 115F. This seems way too low. Shaft speeds are 1775 input, 4500 output, and 1775 input, 7000 output. 2 motors, 2 exhausters in series.

What bothers me, is that these alarm levels are colder than what we keep the oil warmed up to in the sump of our other 4 machines when standing idle. Offline temperature for these is in the 120F range. Rotor speeds on one of those machines is 39,0000rpm. The alarm temperature on our 5MW compressor, which is from the same manufacture and of similar general design, is 138F, which still seems low to me, but is a bit more reasonable.

My question is, do you think the oil temperature is too low and will this contribute to vibration issues? Is there a rule of thumb as to what an ideal temperature range is for a plain babbitt bearing?

We have a 6MW Cooper-Cameron MSG turbocompressor that would trip out on startup until we upped the resting oil temperature another 10F.

Oil is Shell Tellus 32.

We have virtually no information on the first machine as it was war booty taken from the Nazis. Brown-Boveri circa 1933 or so.

 

[Tmoose]

How many bearings in the train are being monitored for vibration ?
I'm expecting prox probes on the plain bearings.
Are frequency data and orbits available?
How high is high?


How many bearings in the train are being monitored for temperature ?
Are the temp sensors in contact with the outer surface of the bearing shells?
Or in a well in the bearing housing? Heat transfer fluid is needed in one or both interfaces.

If the start up vibration is high on the exhauster I'd suspect a thermal bow from sitting with some hot fluid flow hitting the stationary rotor.

 

[MacMcMacmac]

Hello. There are 6 bearings being monitored on this machine. Peak to peak has our Bentley Nevada gauge pegged at over 100 microns at the motor d.e. Temperature probes are in wells machined into the steel bearing carriers. The oil temperature is monitored leaving the oil cooler.

The probes themselves are ancient and about to be replaced, as is the monitoring system itself. What bugs me is that motor vibration has been measured at two motor overhaul facilities and found to be quite low. When coupled to the exhauster, it starts very high and gradually settles out during operation. We had a Bentley Nevada tech come through this week and he said the vibration is coming from the motor. Another company came in and said it is definitely coming from the gearbox. BN said vibes were motor/radial. The other company swore it was gearbox/axial, so I am quite skeptical about the whole process. It was not a cheap exercise. I figured if we had the oil starting out warmer and ran the overall lube system hotter we could get the vibrations down faster and maybe keep them lower at startup, which should at least help keep the vibration down until we find the root cause.