Fire in bearing housing with roller bearings. 2

[Mech5656]

Hello All,

One of the boiler feed pump caught fire in bearing housing and I was wondering if you have seen something like this before and what was the root cause. Upon disassembly, the rollers from bearings were sitting freely in bearing bore of housing. I am separately working on analysis but I wanted to get your feedback. Do you think it is because of oil leaking from bearing housings (and eventually bearing rans without oil and caused the fire), or do you think bearing was not installed correctly or bearing was faulty?

Before disassembly:

Disassembled bearing housing parts:

 

[3DDave]

Lack of lubrication is high on the list. Was there a cage? I haven't seen all bearing designs, but I think roller bearings need a cage to prevent contact between the rollers. I have experienced a ball bearing with no lubrication that then eroded the cage until the ball bearings were able to gather together on one half the race which allowed the inner race to shift and then spit ball bearings out through the gap.

Edit: At first I wondered why you thought the lubrication was gone - then I saw the empty oil supply. It might be that the original failure is in the seal that let the oil leak out, but someone should have been checking the oil level; they do make sensors to remotely monitor oil levels to prevent this as well as oil distribution systems to ensure they are all filled, but how much to spend is a matter of what the cost of future incidents is like and how much human monitoring might make a difference. There are sensor button systems that are usually used to ensure property guards hit each point along their rounds; same thing could be used here.

 

[TugboatEng]

Is that a disconnected temperature sensor on the right side of the housing in the first pic?

 

[Tmoose]

An oil leak, or forgetful maintenance person should not cause a catastrophic failure or be a "root cause" on a decently instrumented machine.

"disconnected temperature sensor".
Stuff like that deserves to be the stinky old fish head on the root cause fishbone diagram.

https://media.istockphoto.com/photos/rotten-fish-with-maggots-on-the-river-bank-picture-id547046592

 

[electricpete]

It looks like there is a constant level oiler in the first photo which still has oil in the bulb. At first glance that doesn't look like lack of lube to me.

At our plant the sliding bearing machines have temperature monitoring, but the rolling bearing machines do not (with only a few exceptions). I presume that is partly based on the fact that the rolling bearing machines are smaller, but also we tend to look more toward vibration than temperature for early warning of rolling bearing degradation. Is there any vib monitoring history on this machine? (retrospective review of spectra etc might show some clues). How about oil sample history?

From the first glance at rollers and outer race and shaft, it does not look like typical bearing defect that started small and slowly propogated damage throughout the bearing. Instead it looks more like a relatively rapid failure if I had to guess. Lub failure might fit with rapid failure, but already discussed that. Like 3DDave mentioned, cage failure would fit with rapid failure if there was supposed to be a cage present (are there designs of cylindrical roller bearings without cage?) . If there was supposed to be a cage, I would suspect cage failure was a key event in the failure sequence. Do you have a drawing or sketch of what this bearing is supposed to look like (especially presence or absence of cage)?.

You described it as a fire, that's an unusual description. What was observed that led you to call it a "fire" (maybe it was just fumes from the overheating?)

Can you tell us about the machine history? How long had the machine been operating at the time of the failure (was it just started?, any recent maintenance?) How long had it been installed at the time of the failure? (is it a relatively new installation or operated successfully a long time). If it is a relatively new installation then you might want to look at bearing and lubricant selection parameters closer.

EDIT - added a few more notes:

Can you also describe the machine train in a little more detail? (what is the driver, describe all the bearings, what is the position of the failed bearing, what type of coupling). It may steer in certain directions. Also I'm a little curious how thermal growth is handled (given that a boiler feedpump would be subject to thermal growth, and cylindrical roller bearings are not particularly tolerant of misalignment, and it doesn't look like a spherical bearing seat in the photo as far as I can tell).

I also notice there was evidence of circumferential sliding between the inner ring and the shaft. I guess that could have been either an initiator (sliding causes inner ring heating which squeezes the bearing) or else a downstream effect (bearing failure for other reasons causes heating and maybe more friction torque which encouraged sliding of inner ring relative to shaft). Since the shaft and the inner ring ID are not as discolored as the rest of the bearing I'm inclined to think it was a consequence, but you never know - there are different conditions at play in these two areas. I think the photo is showing that the shaft was threaded for a bearing inner ring locknut... were there any observations about the locknut noted during disassembly? It also renews the interest in maintenance records (was shaft fit recorded and anything recorded about locknut torque or thread compound).

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(2B)+(2B)' ?

 

[dArsonval]

Wait, Wait, wait.

What is the purpose of a roller bearing in what appears to be an inline pump?

Would love to see a print of this pump.
The threaded portion of the shaft suggests a lock nut.

John