damaged shaft - repair or replace ?

[electricpete]

Motor description: 600hp, 3600rpm, horizontal sleeve bearing motor (3” shaft journals)

We had an event where the motor bearings (probably outboard) produced smoke shortly after startup.

Found both bearing insulating pins (mycarta) broke, bearings rotated, causes loss of oil flow since oil ring no longer works properly, causes bearing damage. (also if there were some other unknown cause of bearing damage, it may have led to anti-rotation pin damage to begin with).

Inspection showed the outboard bearing babbit was completely melted away. Inboard bearing babbit overheated, but not significantly missing.

As expected, outboard bearing lab seal (toward winding) had a very heavy rub with the shaft (slide 3). The rub pattern on the shaft is 360 degrees around, and looks to be up to 1 / 8” deep in places. Outboard bearing shaft journal was also slightly rough.

The inboard bearing lab seal (the one away from winding toward shaft extension) showed signs of a rub over approx 180 degree arc, with discoloration of the shaft, no significant metal lost (slide 6).

QUESTION: Would you expect the shaft could be repaired, or would this normally require shaft replacement?


=====================================
(2B)+(2B)' ?

 

[electricpete]

By the way (anticipating questions), there are no records of how hot the bearing got, because this particular motor has no bearing temperature monitoring. I realize that's not ideal, but that's the current situation.

=====================================
(2B)+(2B)' ?

 

[MikeHalloran]

The discoloration confirms localized heating.
The shaft's mechanical properties are now partly uknown, and nonuniform.
They were nonuniform before, but in a known way. No so much now.

I'd replace the shaft.
Yes, it's repairable, but I'd call any repair temporary.



Mike Halloran
Pembroke Pines, FL, USA

 

[spciesla]

Conservative Decision Making = Replace Shaft

 

[desertfox]

Hi Pete

Definitely replace the shaft, the heat the shaft as seen may have an impact on its properties as others have said.

desertfox

 

[petronila]

Hello pete,

I have a good experience with shaft repairs, with out shaft testing is premature to say something, for me the most important is the shaft is not bent.

If Yes: Replace by a new one.

If No: Repair it, you can machine all parts at reasonable cost, and this action is more quickly than the replacement.

The decolaration is normal due to friction forces.

Also you can contact the motor manufacturer in order to know if they have an available shaft, seals and sleeve bearings and to perform an economic analysis of the promptly retourn of the motor to the service.(Downtime cost)

Regards

Carlos