Motor pump bearing problem 1

[Sofistioelevib]

Hy guys,
i have a boiler food pump 278Kw 6000Vac 3000RPM have a recursive bearing failure.
There are # 2 NU317 and #1 6317C3 on DE. The failure occur at 6317 bearing and it is a classic fatigue damage as described in bearing detection failure manual (SKF or FAG).
This bearing life is aprox 6 month after htat the damage occur.
The cold alignment left is aprox max 5/100 mm (parallel or angular).
The vibration measurement reveal a little (1mm/s) component on 2X.
It is possible to have a 6 month life time with little 2X?
Never before this problem appear and the bearing seems to be original.


Any idea? any other suggestion for vibration analisys?

Regards

 

[Tmoose]

"the bearing seems to be original."
The make and model of the bearing are exactly like the OEM original, or the actual bearing is the one installed by the OEM ?

Recursive means repeating.
So after the original pump lasted for years, all the replacement bearings have lasted just 6 months ?
If so it sounds like a workmanship issue.

Do you have any vibration history ?

Pictures of the uncleaned, damaged bearing just as the bearing was removed from the pump would be helpful.
I'd hope those pictures would help understand the condition of the lubricant.

Is the damage inner race, outer race, balls ?
If the outer race is damaged, does the damage extend 360 ° ? Or is it confined to 90° or so?
Is the damage and the ball path centered on the race, like the loading was purely radial?
Or, is the ball path off center, like the bearing was subjected to an axial load.

Does the boiler feed pump manufacturer have a cold alignment specification? I'd expect it to have some thermal growth compensation, even with a centerline mounted pump.

What type of coupling ?

I'd expect bearing race surface deterioration of most any kind to progress over time.
Vibration measurements should be more comprehensive than just looking at 1X and 2X.
To start, it would be helpful if they were configured along the lines of page E-28 here -

https://fred.hq.nasa.gov/Assets/Docs/2015/NASA_RCMGuide.pdf

How is the vibration sensor mounted to the machine during vibration measurements ?

11 down, 9 to go.

 

[electricpete]

Tmoose - What is this, 20 questions? ;-)

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

 

[JJPellin]

That is a large bearing for 3000 rpm. With a DN number close to 400,000, any failures will progress quickly. Verify the shaft fit to the inner race. Verify that the housing bore is round and not excessively tapered. Verify the fit from the outer race to the housing. Verify that the outer race has adequate axial clearance so that the radial bearing can not receive thrust loads. Verify that the proper lube oil is being used. I would use an ISO 46 or ISO 32 turbine oil. Measure the oil temperature with the pump running under normal conditions. If it is running hotter than about 180 F, cooling may be needed. Verify that the operators are running the pump between about 50 percent and 120 percent of best efficiency point flow.

Johnny Pellin

 

[Tmoose]

Hi E-pete,

It seems to me many OPs are indeed playing 20 questions, or What's my line, or etc.
As much as I enjoy following threads on Eng-Tips, I earnestly wish OPs would include a reasonable best effort at up-front information in the very first post.

I keep six honest serving-men
(They taught me all I knew);
Their names are What and Why and When
And How and Where and Who.

Rudyard Kipling

Dan T

 

[Sofistioelevib]

Tmoose i'mgoing to answer to all your questions as possible.
I could be agree with you regarding workmanship issue but i have to well discuss with the mechanical department and discuss him in tecnical details about this issue.
Unfortunately no vibration analysis made before so i've no idea about previous spectrum was.

If i've a chance i'm going to paste some spectra about the pump and motor vibration data.

Reagarding the lubricant, we had an inspection visit of 3 most important lubrication grase company with same response: Grease is in good condition and it is correct for the application.

"Or, is the ball path off center, like the bearing was subjected to an axial load." EXACTLY the damage seems due to an excessive axial load but i've no idea what type of axial force can damage the race in so fast manner.
The coupling is a gear type

JJPellin thank you for the very detailed analisys, i'm going to make your suggestion and i'll give you the response about.

 

[CouplingGuru]

That is a fairly fast application for a gear coupling. 3000 rpm tends to cause the grease to move away from the lubricated teeth which then can cause a binding scenario and put a lot of axial force on the shaft. and If you have thermal growth this scenario would resist movement, further increasing axial force. Lots of if's in there, but it is worth looking into and crossing the coupling of the cause list.

When it comes to couplings we are always here to help.

http://WWW.PSCCOUPLINGS.COM

 

[electricpete]

There are # 2 NU317 and #1 6317C3 on DE. The failure occur at 6317 bearing and it is a classic fatigue damage as described in bearing detection failure manual (SKF or FAG).

That is a large bearing for 3000 rpm. With a DN number close to 400,000, any failures will progress quickly

I concur, now that we know that the bearings are greased. We have had similar experience of repeated bearing failures with similar grease bearings 6316 at 3600rpm

https://www.eng-tips.com/viewthread.cfm?qid=152220

There are a few limits and references mentioned in the thread. Bearing manufacturer catalogues will imply you can go to the higher end of the D*N numbers. I think they used to include a lower limit for greased bearings than for oiled bearings and that separate limit has disappeared from all the catalogues after some iso standards Change. I don't believe 'em. There may be some machines which where greased bearings last a long life with such high D*N. But I tend to think those must have led a charmed life. I think at a minimum the bearings are more sensitive to other insults (non optimal lub practices, misalignment etc) when operated at high D*N.

I'm not saying you should jump to the conclusion that is the main problem. But after you do your due diligence on post mortem inspection, answer questions above, review grease selection, lubricating practices, alignment, fits, etc you may end up there. (that's where we ended up)


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

 

[Tmoose]

" EXACTLY the damage seems due to an excessive axial load but i've no idea what type of axial force can damage the race in so fast manner. "

√*!!- Was the ball wear path offset toward the coupling, or toward the pump impeller?

" 2 NU317 and #1 6317C3 on DE " .
√*!!- What is the bearing arrangement on the NDE? Or, are NU roller bearing on the NDE ?
√*!!- Do you have a picture cross section of the pump showing details of ALL the bearing arrangements?

√*!! - Was the pump "rebuilt" 6 months ago ?