we have Propylene Transfer Pump Motor. The unit is newly repaired and overhauled, but after operating for a period of 10 to 15 minutes, it trips and found broken bearing inside. I would like to know what’s the real reason of bearing damage.

highlights:
1. The pump motor unit running hours before the most recent overhaul is approximately 26,760 hours.
2. The pump motor unit started twice in reverse direction for approximately 15 minutes and 8 minutes respectively (time difference was 45 minute)
3. The direction of the pump motor unit rotation was corrected after interchanging the connection and it runs for 10 minutes, then trips.
4. After removal of the pump motor unit from the tank, nitrogen was applied to the pump motor unit to melt/remove the ice (the unit was already on the ground and they applied nitrogen with two hoses on the holes of the pump directly. Reference to this, is there any effect on the pump casing and/or is there any thermal stress?)

Best Regards,

There are a few questions to answer. Was this a motor with an anti-reverse ratchet if on a pump. Vertical hollow shaft or solid shafts typically will have this feature and should "not" be reversed without severe damage resulting. If this was in a severe application and pumping material or subjected to less than -25*C it would require Arctic Duty grease and possibly a special bearing assemble to accommodate the thermal stresses associated.
Was the bearing assembly properly packed to 30% and run in or was additional grease added at installation? If over packed or not greased properly this would also lead to bearing failures.

Ali,

If you send photographs of the bearing, I can offer more insights. However, reversing the pump should not cause a "broken bearing". That description raises the possibility that the nitrogen and ice shrunk the components and shattered the bearing. Sub-zero operation requires special alloys for shaft steel, etc. and can cause bearing components to literally "break". Bob's comment about lubricant also extends to suitable lubricants being needed for low-temperature operation.
Hence the request for photographs of the bearing.
By the way, what is the HP or KW rating, and RPM, of the motor in question?

Ali - in addition to the points raised by Bob and Chuck, there is one other thing that is not mentioned that might have some bearing (pardon the pun) on the re-start event.

Was the pump trying to start with material already in the pipeline? Operating the impeller in the reverse rotation against a "loaded" line and/or chamber is probably going to introduce some severe vibration issues ... which in turn may ultimately cause damage to both the shaft and bearing. It is unlikely that the vibration would be sufficient to literally "break" the bearing all on its own, though.

Reverse operation of a pump can in some cases cause high pressure steam or gas that can break the casing and the second failure would be the bearing . Most protection would let the motor operate until lit was overloaded. I expect that you have learned that the unit should have been bumped to check rotation. This probably would have prevented the failure.