GT Lube Oil Consumption High

Q

Thread Starter

Qurban Ali

Dear Sir,

Sir we have issue of lube oil consumption high. please help me!

Our machines GE frame 9E gas turbines lube oil consumption weekly basis more than 300 liters. It looks like a leakage somewhere but I have not been able to trace the place. But the unit indicates that lube oil is reducing. Please kindly assist with your knowledge. We also checked the machine exhaust temperature found normal.

Performed Checks,

1. Check negative pressure in the LO tank it is as per OEM recommendations

2. The centrifugal motor-driven type mist eliminator filter installed. New set SAI Brand

3. The OEM had increased the size of the vent piping from 6 10 Inches

4. There is no and external oil leakage

Qurban
KEPCO KPS
 
Qurban,

Use the L.O. P&ID to identify all the possible areas that L.O. may be lost when the unit is running.

GE-design Frame 9E heavy duty gas turbines have three bearings--one of them is in the middle of the machine between the axial compressor and the turbine sections. If you see no evidence of external leakage, a good place to check is the #2 bearing tell-tale leak-off (see the L.O. P&ID).

The #2 bearing is supplied by a feed pipe inside the drain pipe which both enter the axial compressor casing at the 6 o'clock position (the bottom of the casing). I believe there are some manual hand valves which are manipulated during Off-line Water Washing which can be left in the wrong position and lead to problems. Do you notice any increase in the gas turbine drains tank(s) levels?

Also, leaks of the #1 bearing sometimes are drawn into the axial compressor inlet, and can be detected by an oily film on the IGVs and bellmouth.

The L.O. Coolers operate with the Cooling Water system pressure slightly lower than L.O. pressure--so that if a leak develops in the tube nest L.O. will contaminate the Cooling Water instead of Cooling Water contaminating the L.O. (if the Cooling Water pump runs when there is no L.O. pressure, water can still "leak" into the L.O.).

If the unit has a hydrogen-cooled generator, has there been an increase in Seal Oil Flow-rate, and any Generator Casing Liquid Level High or High-High alarms? If the generator is air-cooled, has there been any Generator Casing Liquid Level alarm(s)? Have you checked the generator casing drain for any L.O.?

Please write back to let us know what you find.
 
Have you started maintaining a higher main oil tank level than OEM recommendation? This can increase oil consumption significantly. Also, you mentioned no external oil leakage -- is this during loaded condition or FSNL? Ideally, to check for oil leakages one should do them at three conditions --- 1] barring 2] cranking without firing 3] FSNL. After loading, it becomes more difficult to check for leakages in turbine & load compartments due to high temperatures. Be sure to check bearings 2 & 3. As for bearing#1, you may need an IGV & compressor 1st stage blade inspection.
 
Thanks for your reply. We are maintaining tank level as per OEM recommendations. IGV is quite clear and does not have any symptoms of oil leakage. Furthermore, we will check the external leakages on all the three conditions during next outage.
 
@ CSA:

Thanks for your reply. Our generator is water cooled. IGV is found clear and there are no signs of leakages at bearing # 1. however we will check bearing # 2 in the upcoming outage. We will let you know once we are done with investigation.

Regards
 
@ KRManish & CSA

i had another query about the vacuum in lube oil tank. How will the lube oil consumption be effected if the vacuum in lube oil tank deviates from OEM recommendations?
 
Both higher & lower vacuums than OEM recommendation increases oil consumption. If we go for higher vacuum, the mist eliminator fans will suck out more oil vapour [you can check this by opening any drain {if any} in your mist eliminator fan discharge or the oil vent piping. This could be a possibility in your case, since you had recently increased your oil vent piping diameter. However, in your original post, you had mentioned that it is within OEM specified limit, so I don't think that is the case. But, of course, I am assuming that you had increased the vent piping diameter in consultation with your OEM [if that is not the case, it could be your reason].
If you have lower vacuum, since seal air for the labyrinth seals for the bearings is taken from the compressor itself, there is a possibility of oil spillage from bearings due to improper sealing, though not a very common occurrence.
 
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