Steam turbine bearin house oil leakage 1

[maozmen]

We have oil leakage from front bearing housing seal towards the coupling. There is a closed cover in the coupling space and oil leaked is discharged through the piping placed under this cover.

Our turbine is made by GE Thermodyn. It is an impulse type turbine. Is there anybody who has such experience.

 

[byrdj]

Is this backpressure or condensor, varible speed or genertor? Just curious.

I assume this is the inboard bearing with the coupling going to the driven device. The oil feed to the turbine bearing would be inside the external drain line leaving the bearing pedastal,towards the coupling, then turning down and back towards the turbine oil tank. GE use to be very strick about all pressurized oil lines were inside a guard drain line. If the oil is coming from the line from the turbine bearing back to the oil tank it will be drain flow back. A loose flange or damaged gasket would be the problem

If you say it is coming from the oil deflector seal (around the shaft), there could be a drain vent problem accross the bearing. This will require doing some maching on the internal bearing ring.

GE may not be so strick to pressurized oil lines going to the driven equipment, thus any oil feed lines going to the inboard driven equipment my be your leak.

If the unit is a condensing, and the bearing leak is at the LP end, the oil leak is not as dangerous as an oil leak at the hot, insulated, end.

If the leak is just a nuesance type drip from a drain flange, or around the shaft the oil tank vapor extraction vacumm may not be present. Increasing the vapor extraction vacumm beyound recomend may cause problems with sucking in water into the oil or dust in to the deflector teeth.

 

[maozmen]

Thanks byrdj for this valuable information.

The turbine is a part of a combined cycle plant. It is a condensing turbine with fixed 4200 rpm speed.

During mechanical running test of steam turbines in the factory, we have noticed lube oil leakage from front bearing housing through the seal to coupling part where gearbox is installed.

There is a coupling guard where underneath is a 11/2" pipe discharges the oil leakage to the oil tank. We have objected the situation claiming that there should be no oil leakage at all from the bearing housing. However, Thermodyn explains that this is a usual design and they can only minimize the leakage but bot guarantee absence.

I wonder if this is a general design feature in all the steam turbines manufacturers.

 

[byrdj]

Making oil deflectors leak free is not a given, but becomes the challange to a persistant engineer and mechanics.

Besides verifing that the test runs have the lube oil drain tank under a slight vacumm, if the oil pressure supply to the bearings is excessive (greater than 150% design) could cause deflector seal leakage.

Another possiblity, I doubt if they are still using shaft riding vibration probes, but if so there would be a lubricating spray tubing on the upper half of the bearing that could be spraying towards the deflector.

A minor item that could contribute if the bearing bore is eleptical, and the bearing oil dam rings were bored eliptical (to bore dam rings cylindercal to reduce spray, requirs a second machining setup, thus boring it same as bearing is cheaper)

With similar units (MDT,FPTs), back in the 70's, there was a design deffenciency with the drain and ventinting between the two sides of the bearing, causing this seal to leak.

A quick "war story". As a consultant, I always reccomended a customer install a tank vapor extractor to help with a unit with a lot of little leaks. When I went to work for this plant, the management was suprised when I did not continue to persue. my response to managenent was "as long as there was no extractor, I had an excuse for not fixing the leaks"

I wonder if this leak was at the other end, the hot end where fire would be a problem, would this leak be accptable?
Good luck

 

[maozmen]

Is there any ASME or other standart stipulating oil tightness of bearing housingin steam turbines?

 

[byrdj]

I have never heard of any. I would recomend read thru plant's boiler insurance policy or fire protection standard