Hi guys,
Happy Christmas and new year.

I am in seriou problem with similar type of failure in both main and standby naptha pumps one by one. The pump shaft sheared after seizing the thrust bearings.
I have observed that the all vibration parameters, operating temperatures,flow,pressures, density, oil mist parametsr and flow into the bearing housing found normal. Also one wonderful experience is that in both the pumps the radial bearings are fine but the thrust bearings were damaged.
Can any one please give some inputs why these pumps failed?
I am attaching some of the photographs for your refernce.

Didn't you have an excessive thrust force? Is the balancing line working properly?

This is single stage pump. The exessive thrust force reason couldn't be established as per the available data? Is there any contribution from resonance?If it is what are the things to be checked please advice?

Check compatibility of the pump. Was torsional analysis done prior to deciding shaft diameter? Can the roller bearing take the aial load? Would it be a good idea to use roller bearing. Design deficiency seems to be cause of the problem.

Corrections to the above:

replace aial load with axial load.

Wow, that is a mess.
Hard to tell just from pictures but I did notice severe ball indentation on the inner race.
Was this pump subjected to recent shock loads?
What was its history prior to failure?

Also, what was condition of the grease?
I see NO grease residue in these photos !!

Regards
Jim P

I have seen sudden failures of angular contact ball bearings,but never encountered failure of shaft like this.If vibration levels were quite ok just before failure,then the sudden failure might be due to failure of bearing cage. Vibration signatures donot indicate the problem with cages though we see some FTF in spectrums. This failure appears to be due to poor lubrication and subsequent cage failure leading to siezure.Surprisingly the failure of shaft cannot be explained unless it is fatigue related.One more thing is ,why the motor didnot trip when it was running in overload condition.Please check trip settings.Also observe the failed shaft for beach marks to establish fatigue type of failure.Since how long this pump was running with this shaft?

Dear Karun,
Thanks for yourreply , these pumps are running since 2005 with this shaft .
Also oil mist lubrication system is perfectly working without any abnormality.

Why both the pumps sized within 3 hrs of operation? can you suggest .

Regards

I have never seen anything like that in my experience, or in the many cases posted on these forums.

My guess would be the bearing went first, then created unusual stresses on the shaft. The types of increased stresses on the shaft resulting from bearing failure might include:
1 - unusal bending stresses as balls roll over chunks of cage.
2 - locked rotor motor torque transferred through this location if the bearing away from the driver locks up.
3 - Thermal expansion of an overheated back-to-back bearing puts the shaft in tension in the area between bearings (where your failured occured), especially if the arrangement was tight to begin with.
4 - Heat conducted from bearing to shaft increases local shaft temperature to the point that it's mechanical properties are affected, contributing to ductile failure.

A better picture of the shaft might help.

Now the question of what caused the bearings to fail is wide open. The fact that you had two pumps seize within three hours when apparently operating ok for years before that obviously suggests a likely common cause. The only ones I can think of:
1 - failure of your oil mist system, assuming it supplies both pumps.
2 - some kind of fluid system problem which dramatically changed the thrust.
3 - extreme ambient or process temperature change which affected thermal growth of machines and their operating alignment.


Just guesses.

Hello dear S KANTI!
It could be many things involved in this case such as , shaft bending, bad lubrication, damage bearing, high speed of the rotating shaft which ecxeed manufacturer recomandation, neglating of using VFD to steer the speed etc. I sugget that you use CBM (Condition Based Mainteance) to detect the failure in earlier stage, on the other hand its important to impleement VM specially in machines which contains rotating shaft.
Best Regards

Were the locking tabs on the lockwasher fully engaged in both the shaft and the nut?

Dear Danny,

I am no sure. But apparently it seems to be good fit as per the sample damage piece.

kanti

Mr. Kanti;

Please Provide informations as mentioned in the attached enquiry sheet for furthur.

as for as the bearings failure is concerned My observations -
Inner Ring - - Decolouration of the entire rings with normal tracks

Outer Ring Decolouration of the entire rings with normal tracks

Cage - In picture some damaged cage was there but my view says that there should be two window type cages in one bearing, what is the condition of both cages ? entirely damaged? or one side more damaged than the other?

balls - Plastic deformation and decoluration

Interpretations:
Lubrication failure due to failure of the lubriation system / Decreased operating clearance.

Excess Load - Due to lubrication faliure resulting in excess frication and melting of brass cages damage of bearing. and shearing of shaft


Note<< This double row angular contact bearing,Double row angular contact ball bearings 32 and 33 have filling slots on one side; they must be mounted in such a way that the main load is accommodated by the raceways which do not
have filling slots. i.e not in the thrust direction. whether it is followed ? >>

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