Industrial standards do not required any NDE tests that has to be performed on large induction motor sleeve bearings as a part of preventive maintenance activities. In our facility we has performed NDE test (UT and PT) since 2010.

We use ISO 4386-1 and ISO 4386-3 standards for acceptance criteria. We chose conservatively class B for our acceptance criteria. In few years we found out that most of our sleeve bearings are out of acceptance criteria. 

So, I am looking forward to hear industrial experiences especially from NPP on this topic.  Do anyone performs NDE (UT and PT) tests on  sleeve bearings? How often do you perform NDE tests? What standard do you use for acceptance criteria.

 

Original Post

At our power plant, we do periodic inspections of certain sleeve bearings and also of course have various monitoring strategies (temperature, vibration, oil sampling).

We do not do any periodic N.D.E. and I'm not understanding why it would be required.

Blue check is done after bearing replacement.

UT is looking primarily for integrity of bond between babbit and base metal. I view it as a quality check or installation check where bad babbit bond would be a result of manufacturing. If cracking should appear on the babbit surface or on certain bearings where cross section of babbit/steel interface is visible at the bearing end (no thrust bumper), then I might request UT.   Is it an expected phenomenon that healthy bond may develop into poor bond without other symptoms?

I guess some people might also use UT to look for babbit thickness. I don't expect any significant change in babbit thickness without change in bearing clearance.

I don't see the purpose of PT unless it happens to be a bearing where the babbit/steel interface is visible from the end… might make sense at that interface. I don't picture there are any cracks on the babbit working surface that we should be concerned if they are not at a level visible with the naked eye.

 That's just my view. I don't claim to be an expert on sleeve bearings. Interested to hear if you disagree with any parts of what I said.

Sorry but does NDE stand for Non Destructive Examination/Evaluation?

I'm familiar with NDTs (PT, Ut etc). In the small machine shop we have in the facility (or at the site), we do not perform such tests on bearing on regular basis.

 

In my company, we have a large repair shop where critical or large equipment are repaired. Even there, NDTs are not parts of the standard checks.

 

Of course, one can use any special tool/test (deemed appropriate) for special cases.

 

How many times, these tests you performed yielded findings otherwise could not be found?

 

Regards- Ali M. Al-Shurafa

First of all, yes we are talking about non destructive examination on sleeve bearings.

We should take in consider that we are nuclear power plant with a 35 years in operation. So, there is a quick review of our strategy:

- we perform NDT on split sleeve bearings that are installed in horizontal motors

- 120 months is frequency for motor overhaul

- during motor overhaul we do PT and UT tests

- acceptance criteria are ISO 4386-1 (acceptance criteria B1) and ISO 4386-3 (acceptance criteria B)

In that period we found out a lot of ''bad'' bearings. We could see porous sliding surface by PT and also discontinuity of white babbitt to bearing shell by UT. So, now we are looking for industry operation experience because we are planning to revise our NDT procedure with a new acceptance criteria  different for safety related motors and non safety motors.

And finally, there are a lot of factors which impact to sleeve bearings condition. Operation temperature, lubrication oil viscosity, load, RPM, aging.... are the most important factors...

I could see in other facility bearings that have more than 70% of discontinuity of white babbitt to bearing shell and there are still in operation.

I am looking forward to hear from you guys....

 

 

 

I reviewed two documents which provide overview of repair activities for electric motors (typically done in repair shop):

  • EPRI TR 1016679 is "NMAC: Repair and Reconditioning Specification Guidance for AC Squirrel-Cage and Salient Pole Synchronous Motors with Voltage Ratings of 2.3 to 13.2 kV"
  • IEEE 1068 (2009) - Standard for repair and rewind of electric motors in the Petrochemical, Chemical, and Process Industires

Both documents have fairly detailed instructions for inspecting sleeve bearings for things like surface appearance (visual) and clearance. The IEEE is more detailed and also includes guidelines for scraping and blue check. But neither says anything whatsoever about NDE on sleeve bearings.

So I think your plant is an outlier - doing checks that no other plant does. If you want to investigate further to what extent NDE is performed (other than bearing replacement), you might check with your local repair shop to see if they would do NDE during a motor refurbishment. Also you might query the EPRI Large Electric Motor User's Group (which can be done by email).  Or if you attend an EPRI LEMUG meeting, it would be a good discussion topic....I'm sure everyone would be interested to hear more about what you've found.

EDIT - I see your beginning statement was along the lines "Industrial Standards do not require NDE...".  So I'm not telling you much new.  It would be  a topic of interest for people in this group and also people that make the standards (EPRI LEMUG and IEEE PCIC).

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