Dear friends ,

In these days I experienced a bearing failure on our centrifugal compressor.

So far,The compessor just run for 3 months. And the same bearing failure type was happened three times on another two same type of new CAMERON compressor.
The damaged bearing type: NACHI 7214BMUC3

Some prictures and related drawings are attached below.
To this kind of compressor during normal running the axial force is toward NDE . In other words the inboard bearing of two thrust bearings will be mainly forced. But the damaged bearing at every time is the outbard bearing.
before, the rootcause of bearing failure from vendor is due to inadequated lubrication. The radius at the bearing outer race is not enough. (TO the two thrust bearing lubrication method the pressure oil is coming into bearing through the radius and small groove on the bearing outer race. ( TO the small groove you can see in the attachment)
In addition, a strange finding is that some tar accumulate at the radius of two bearings inner race positon and just exist at this postion. at other places we didnot find this . And during past repair for the another two compressors we also didnot findd this.

Now It is time to rest for me. Tommorrow continute talking about this.

Any comments and thoughs will be welcome.

Thanks
Lux

Cameron_compressor_(7).doc (381 KB, 72 downloads)

The pictures attached above is not successful. Repost again

Cameron_compressor122_(7).doc (1,119 KB, 57 downloads) pictures

Pl. check whether the bearings are installed face to face, back to back or tandem. Thrust bearings can be installed in only these three orientations and depends upon the direction of thrust. Sometimes, the bearing thinner portion is facing the lock nut due to misorientation and breaks on thrust. Pl. confirm or post a bigger drawing of bearing arrangement. May be some lubrication issue but it will not result in breakage of only one bearing always.
Regards
Irshad

Continue talking.......
To these tar accumulating at the radius of bearing inner race , it is very strange for me. In the whole gear box except this postion didnot find this at other places. Commonly,the reason of the situatin happening is due to deteriorative lubricating oil. But for this compressor lubricant we just did a oil sample analysis a month ago, the analysis result also is in a good condition. In addition, At the radius position between the two bearing inner race the lubricating oil cannot come into the area after two bearings are assembled and tighten the two bearings inner race with . And even if the clearance between two inner bearings the oil can come into site, But this also is able to come out due to machine running.

the possible causes what I am guessing is that the oil is come into inside as vendor assembled the bearing . And is locked at the area. Over a period of machine running these oil is gradually deteriorative to current status.

Above is I am thinking aloud.


Thanks
Lux

Hi Irshad, Thanks a lot for your response.
The two thrust bearings arrangement is face to face .

Thanks
Lux

attached some clear pictures , you may see there is much oil coke existing at the radius of bearing inner race. In whole compressor gear box we didnot find this except this radius postion. It is very strange for me.

Cameron_compressor_bearing.doc (1,350 KB, 32 downloads) pictures

Sorry lux, I have a slow connection and can't open the pictures.
I'm not sure if you are having compressor thrust bearing failures or gear box bearing failures.
The centrifugal compressor thrust bearing failures I have experienced have been caused by poor balance piston performance or by compressor surge.

The cause of this "coke" is a loose bearing fit or fretting. The interference fit is too loose and the rust is coming from the bearing inner race moving on the shaft. The shaft should also show this same "coke" appearance. Shaft will need to be repaired to get the correct bearing fit to the shaft. If you were taking vibration data on this machine, you should see a gradual rise in 3x turning speed....
Dave

I agree spinning of inner ring would be a big problem.

Shaft dimensions at bearing seat need to be checked now as during every replacement.

I would suggest to also examine carefully the method of setting the preload of those face-to-face bearings. A scenario I would propose: perhaps preload was not properly established, the unloaded (outboard) bearing had dramatic skidding, and the heating caused the inner race to intermittently come free.

imo, it could be either scenario (original problem was improper shaft fit or original problem was improper preload), along with perhaps others. I lean towards the preload because:
1 - checking and adjusting preload is a trickier evolution than checking shaft dimension.
2 - there are large areas of the bearing bore that seem relatively unaffected.

Just an opinion. Examination of inside of bearing might give some more clues (I didn't seee any photos of that)

Thank you for your response.
Attached are some picture fyi.

Thanks
Lux

TA3000_Bullgear_bearing_.doc (1,608 KB, 13 downloads) picture

another pictures

TA3000_Bullgear_bearing_.doc (1,339 KB, 11 downloads) pictures

another picture .

Some supplements:

When dismantling the two bearings ,the bearings locknut and lockwasher is still in tight condition. And observe the end face of the two bearings inner race, we didnot find any inner race spin track . the shaft fit size still within tolerance ( shaft diameter 2.7562 / 2.7559
shaft fit (- = interference) 0.000 / -0.0008.

TA3000_Bullgear_bearing_.doc (488 KB, 9 downloads) picture

attached is vibration spectrum at that time .
The bull gear shaft DE thrust bearing : 7214BMUC3(nachi). NDE: SKF 6311C3.

MAC_Vibration_Spectrum_Data_Collection_.xls (160 KB, 11 downloads) picture.

quote:

Originally posted by Dave Reynolds:
If you were taking vibration data on this machine, you should see a gradual rise in 3x turning speed....
Dave

Where does 3X come from?

D

3 X can come from a loose inner race to a shaft. Seen this dozens of times with motors and several types of pillow block bearings. Keeping in mind the machine you are looking at does not have a 3x forcing frequency.
If you had a machine or demo unit, you could try this for yourself by leaving the inner race loose to the shaft, how things in OH, 1-3" of fresh snow in lovely Nebraska
Dave

Lux, you state shaft size is 2.7562 / 2.7559

The shaft should be 2.7565 to 2.7560

Did you "polish" the shaft prior to taking your readings?

The "coke" is taking up space. Meaning that if you are supposed to have .0008" of "interference" fit, the coke is taking up at least .001" of this measurement.
If you took your bearing that you show in the images and measure it with the coke on the bearing surface and it measures X. Now clean the inner race of the bearing and measure again, your measurement will be larger.
Can you repost vibe data with more lines of resolution? Like double what you have right now

Hope this helps
Dave