Acceptable oil temperature for journal bearing lubrication 1

[eeprom]

Hello,
I am working with an old GE generator/turbine with babbitted journal bearings. I am looking for information which will help me to determine how to set my temperature alarms for the bearing RTDs. I have found little information on the web. I was hoping that someone here might be able to point me in the right direction.

thanks

 

[MintJulep]

This might get you started.

http://www.machinerylubrication.com/article_detail.asp?articleid=779

http://www.noria.com/learning_cente...p?articleid=243&relatedbookgroup=Lubrication2

 

[TheTick]

We had GE turbines in the navy. Typically 110-150F. Anything over 180F meant failure was imminent.

 

[IceStationZebra]

I know that with hydraulic oil we try to keep it below 180°F, 220°F absolute max. I've been told that the oxidation rate doubles for every 10° the temp increases.

ISZ

 

[tbuelna]

Journal bearings are essentially "oil-cooled" bearings. You will need enough oil flow to maintain the bearing materials within their allowable limits.

Unfortunately, there is no analytical method to determine this , unless you have detailed properties of the bearing materials, heat transfer characteristics of the supporting structure, physical properties of the lube oil, exact running clearance of the journal in the bearing, oil flow volume past the bearing, etc.

 

[eeprom]

Thank you all for your help. But I do not want numbers, I want justification for numbers. What kind of engineer would set vibration and temperature limits for a 10 million dollar piece of equipment based on what someone told him on the internet? If any of you have knowledge of professional papers or the mathematics behind the numbers, please help me out.

thanks

 

[hydtools]

You might find some authority here:

http://www.kingsbury.com/pdfs/kng_tech_biblio.pdf

Ted

 

[hydtools]

Or here:

http://www.kingsbury.com/pdfs/universe_brochure.pdf

Ted

 

[byrdj]

How about the OEMs recomendations as provided in GEKs

I do not have access to the current editions but you should find them in the instruction book or corespondaces (TILS)

By the way were you looking for bearing oil drain or bearing metal temps. I was thinking TCs were for metal and there was an RTD opition for drains.

As far as the GE engineering that use to applied to sizing the orificed supply and bearing loading, It was fairly constaint on the LSTG type units. for example I have seen swapped orifices provide an indication outside of the norm values that resulted in securing the unit before damage had occured (and also indicated an excessive flow)

 

[RossABQ]

But I do not want numbers, I want justification for numbers. What kind of engineer would set vibration and temperature limits for a 10 million dollar piece of equipment based on what someone told him on the internet?

I would not set limits for a $1,000 machine that were not in accord with the manufacturer's recommendations, regardless of what justification I could find on the internet.

Call GE with your serial number, they are the only ones who can provide the relevant data particular to your specific machine.

 

[Artisi]

RossABQ - I can only agree with your comments re contacting the manufacturer. It beats me why "engineers" constantly post for information when all they have to do is pick up the phone and ask the manufacturer, who better to ask?

 

[sms]

The original post is asking about bearing RTDs, which I am assuming means bearing metal temp. A number of the responses so far seem to be related to oil drain temp.

Bearing metal temp is a function of load and babbitt melt temp. I have experienced smearing of babbit on turbine thrust and journal bearings at metal temps about 250F. I would not go any more than that.

Having said that, I agree with the other posters, go ask GE.

"Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?" Oddball, "Kelly's Heros" 1970

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[sms]

Went and reread the post title and now I am very confused.

Eeprom, are you talking about oil supply temp, oil drain temp or bearing metal temp?

"Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?" Oddball, "Kelly's Heros" 1970

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[hydtools]

I had to reread the post and he is asking how to set the temperature alarms. He didn't ask for numbers or justification. Sound like he needs the manual for the RTD monitor(s) and alarm system.

Ted

 

[eeprom]

Guys,
Why are people trying to turn this thread into an insult forum? I want to know how the bearing temp (and vibration) limits are derived. I already have the numbers. I just want to know where they came from.
And of course I started with GE. Have you ever called GE and asked for information? I would guess not. You can get information from GE in one of two ways: 1. Hire a GE field engineer to do your work for you. 2. Ask GE to send you the documentation you need (GE charges $2500 a day for document searches, which does not include the cost of the documents).

 

[electricpete]

I think three factors to consider will be
1 – Max temp of the oil film. As oil film temperature goes up, viscosity goes down and oil film thickness goes down which may result in wipe. A 20C change in oil film results in approx halving of operating viscosity for VI=95%. Not as much of a change for higher VI oils including many synthetic oils.
2 – Max temp of babbit – often given as 140C.
3 – Babbit mechanical damage (fatigue or plastic deformation) where damage threshhold load may decrease as temperature increases. I saw a lecture from Kingsbury, and they had a curve of bearing temperature limit vs loadingg (pressure). It is flat (140C max operating limit, 120C recommended limit) up until 800 psi. Then it starts decreasing at 10C per 100 psi. When I asked the presenter about it, he was adamant this was not an oil film thickness issue... it was babbit mechanical damage with threshhold affected by temperature.

A few other tidbits:

Babbit melt temperatures ASTM grades 1,2,3,5, 7. The lowset is 180C.

There are also a variety of locations to monitor bearings and if the hottest is not selected, the alarms/trips need to be more conservative. For center-pivot tilting pad, the hottest spot is about half way from center to trailing endge. For offset tilting pad, it can be almost at trailing edge. For tilting pad, it is often 75/75 location.

Another excerpt from Kingsbury presentation:
•Typical sliding bearing rating limits:
–500 psi unit loading
–.001” minimum film thickness
–240 F maximum film temperature

Note on the link below they show item #1 above more likely to be limiting at low speed, item 2/3 at higher load:

http://books.google.com/books?id=Oo...&lr=&as_brr=3&sig=2x84NZ0PNGPinsSHm8Aa6i0f7ko

http://books.google.com/books?id=EK...rr=3&sig=-9Zt9FaQUVyQPb6r1fjSFtlOqlA#PPA58,M1

So I think you can see that there are a lot of factors to consider.

Why are people trying to turn this thread into an insult forum?

By no means do I want to create any negative feelings. But I think the tone you have conveyed in earlier posts and continuing to the latest post is slightly ungrateful. People give you suggestions and you responded "what kind of engineer would set vibration and temperature limits for a 10 million dollar piece of equipment based on what someone told him on the internet?" OK, that's a fair enough comment, and in the full spirit of your comment, people suggested you contact the OEM (after all we don't know you or your equipment). In response to that suggestion you had another snappy comeback "Have you ever called GE and asked for information? I would guess not."

Everyone here is just trying to help. Any negative tone in this thread was originated with you imo

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[electricpete]

Correction in bold:
"Note on the link below they show item #1 above more likely to be limiting at low speed, item 2/3 at higher speed"

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[electricpete]

Another correction:
"For thrust tilting pad, it is often 75/75 location."


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[electricpete]

For run-of the mill applictions, a very common thumbrule is:

80C - Highest expected temp during normal operation
90C - Alarm
100C - Trip

It is prevalent in EASA documents for sleeve beairng motors.
Needless to say, just a thrumbrule.

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[sms]

1) Vibration and bearing metal temp alarm and shutdown recommendations are in the GE operations manual. BTW maybe you posted a different thread, but your OP here mentions nothing about vibration. A conservative recommendation for vibration is to shut down at 50% bearing clearance (to avoid babbitt fatigue) and to alarm at a level of 150% of normal levels. I have often used much higher levels, because on critical process machinery I don't want to automatically trip the machiney unless damage is being done. So in that case I would use bearing clearence for trip.

2) You did not answer my question, are you talking about bearing lube oil supply temp, bearing lube oil drain temp, or bearing metal temp, until you clarify that, I can't help you. I already gave you a number for bearing metal.

3) I deal with GE all the time. For a question like "what is the design basis for vibration and bearing temp alarms?" I have found them to be very willing to help for free.

Assuming you did insult them off the bat with your attitude.



"Why don't you knock it off with them negative waves? Why don't you dig how beautiful it is out here? Why don't you say something righteous and hopeful for a change?" Oddball, "Kelly's Heros" 1970

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.