Turbine shaft journal damage with no corresponding babbitt damage 1

[Zimann]

Has anyone seen this? Have you seen a case where the shaft gets scored/phonographed, but the sleeve bearing has no damage?

Side info:
Oil sample clean - as far as I'm told.
I'm told the bearing was not replaced.
Only 3 year old turbine.
Scoring in the non-feed area of the pressure dam bearing.

 

[sms]

Yes it is called wire wooling and while it is fairly rare, it is pretty well known, all the bearing companies and machinery OEMs should be well aware of it. A partical of something of much harder material than the shaft comes in to the bearing from the oil system and gets imbedded in the babbit of the bearing, which holds that particle much like a bit in a lathe. Contact between the hard particle and the shaft machines the shaft.

Look at the bearing surface again, you should find something embedded in it some where...

-The future's so bright I gotta wear shades!

 

[electricpete]

I had never heard wire wooling described that way. It makes some sense. I remember it is limited to certain shaft materials containing chrome, correct?

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[Zimann]

Thanks.
Looking at the sleeves, the grooves almost look polished. My initial thought was that something larger than the bearing clearance made it into the pressure dam area and slowly wore away at the shaft over time - therefore, no shaft cutting or raised edges to break down the babbitt. I suppose the same theory could hold true, like you say, if a hard particle entered the babbitt and slowly polished the shaft.
I'll get the sleeves looked at professionally. If wire wooling is the culprit in this case, the particle(s) is pretty small.
Thanks again.

 

[sms]

It doesn't have to be a very large particle size, clearance is generally 1.5 mil per inch, so an average turbine might have a 6-9 mil diametral clearance, a particle that imbeds and has just a few mils of protrusion can causes some damage.

Here is a picture and description I found:

http://www.tribology.co.uk/services/investigate/pb09-2.htm

-The future's so bright I gotta wear shades!

 

[Zimann]

http://www.bearings.machinedesign.com/guiEdits/Content/BDE_6_1/bdemech6_21.aspx

No appreciable babbitt damage in my case. I'm tending to think this may be a very minor case of wire wooling which occurs at startup when film thickness is not yet established.
Thanks again for your help, and the link.

 

[electricpete]

Do you know the shaft material?

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[sms]

Pete, I have seen this on just normal 4140 steels, but I do recall high chrome steel being more susceptible.

I had one machine where polymer build up in the interstage seal on a compressor machined the rotor from a six inch diameter to a three inch diameter. The polymer built up, hard stuff imbedded in it, machined the rotor like sand paper, and as the clearance opened up more polymer built up to fill the gap. The cycle repeated itself.

-The future's so bright I gotta wear shades!

 

[Zimann]

The shaft is normal 4140. I'll be sure to let you know if I find anything in the babbitt upon closer inspection....

Have you ever seen something larger than bearing clearance get stuck in the pressure dam area and slowly polish the shaft?

 

[sms]

I haven't. But most machinery in my world has moved to tilt pad bearings, so there is not much with pressure dams around anymore.

-The future's so bright I gotta wear shades!

 

[electricpete]

It sounds like that certainly may be the culprit.

Just to play devil's advocate. From the link:

"The best solution is to limit the chromium content of the steel to 1.5% where surface speeds are greater than 25 m/sec."
A440 has -.8 - 1.1% so should not be susceptible. But the books aren't always right and Steve has specific experience to to the contrary.

"Identified by extensive damage to both bearing and the journal"
No extensive damage to the bearing mentioned in this case.

Also I have heard the reason they call it wire wooling is because you will often see shavings like from machining.

Once again, I defer to Steve's experience on this one. I certainly don't have any alternate theory. But just wanted to throw in those comments.

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[electricpete]

A440 was a typo - I meant 4140.

Even with A4140, perhaps there might be a possibility the shaft journal area had previously been repaired with a chrome process? We prohibit that in our repair specification for motors.

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[Zimann]

Not a repaired shaft. Just a straight 4140 journal. I like your "devil's advocate" thought, since I originally ruled out the possibility of something getting into the bearing clearance since I was sure there would be subsequent babbitt damage. Then Steve helped me think that the particle could be small enough so that it didn't leave cuttings or raised edges, but rather just took microns at a time and not hurt the babbitt.....I haven't yet ruled out that something may have gotten in the pressure dam and acted similarly. I'm confident that a good inspection of the babbitt and the leading edge of the babbitt in the dam area will help solve this.

 

[JJPellin]

Unless you are absolutely certain of the repair history of the turbine, there is another possibility. I have found scored shafts with perfect bearings. But I later found that there had been a catastrophic bearing failure and someone (perhaps in the middle of the night, on an emergency basis) had installed a new bearing around the damaged shaft. Even if the turbine is relatively new at your facility, might it have had some problems on the test stand before it was shipped to you? Just a thought based on my experience.

Johnny Pellin

 

[adamjt]

Steve,
I am having a wire wooling problem with a large vertical pump with a type 431 shaft sleeve and babbit tilting pad journal bearings.
We were looking into using 4140 as a replacement for the 431 shaft sleeve to solve our wire wooling problem.

You said you have seen wire wooling on 4140? I was for 4140 until I just read you post. What was the case where this happened?
Any help is appreciated...thanks

 

[sms]

I suppose if you look at the definition of wire wooling it really has to be a high chrome steel.

So I stand corrected in that regard. Now I have seen shafts machined by debris even in 4140 steels, as I mentioned above, but that literally would not be wire wooling.

I think 4140 is probably the most common rotor material out there. Unless this is a very unusual application then you can't really go wrong with a 4140 shaft.

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[adamjt]

Steve,

I am looking for proof of 4140 in shaft sleeve/shaft applications for documentation purposes (pump, turbines, etc...) before we make any material changes.....if you can be of any help in that regard I would greatly appreciate it.

 

[Tmoose]

Automotive engines need to have their journals ground and polished in a particular direction to remove directional grinding fuzz and surface flaps and nuggets. I have to wonder if chrome steel's bad rap is related to that phenomenon, and might be remedied just as easily.

http://motorheadheaven.com/it_crankgrind.asp

go here and click on accelerated wear

http://motorheadheaven.com/it_bearingfailures.asp