Turbine Lub oil particle count 1

[irishal]

Hi, We have a 150MW steam turbine with associated lub oil system. We recently suffered a major bearing failure, the root cause is still not clear, however we suspect foreign object damage to the bearing from lub oil contamination. The turbine was repaired and the complete oil system including tank were flushed and cleaned through a 3 micron filter. The lub oil is normally filtered through a 34 micron (0.034mm) filter. We get monthly lub oil analysis done by our oil supplier and the oil cleanliness has starting to deteriorate since start up one month ago. Here are the results taken shortly after recommissioning and 3 weeks later:-
2 - 5 µm/100ml 23683 149893
5 -15 µm/100ml 3683 5320
15 - 25 µm/100ml 203 60
25 - 50 µm/100ml 17 20
50 - 100µm/100ml 10 0
>100 µm/100ml 3 0

The NAS cleanliness rating is 4.

Would these results be worrying?

We have no other oil cleaning or purifying facility on this system. Is this unusual?

Thanks,
Irish Al

 

[unclesyd]

These analysis would definitely trigger a closer look at the lub system with these increases in your time frame.


Did the lab try to identify the smaller particulate matter?

 

[irishal]

We also had a wear debris analysis carried out so I'll ask them to look at the sample again? The report concentrated more on the larger of the particles.

 

[byrdj]

I Know you said "the complete oil system ...was cleaned", however I have heard that before and there were two areas not inspected and usally found full of trash. That would be the Air and the H2 detraining tanks. A dirty Air detraining would gradully contaminate the lube oil system after going back in service.

As far as the origianl root cause, I would also look for water contimination or cooler temp excursion.

Most older systems I've seen have an original small continous filtering "bowser". Nearly every plant now has a high volume fine filter skid that is run ocassionally and shared if more than one unit at site. Before a tank mod is performed during outage, it was common to run the two hoses trough a top tank door.



Good look

 

[rmw]

Look on

http://www.hilliardcorp.com

for oil filtering equipment that can help your situation.

rmw

 

[byrdj]

Saw post concerning your air cooled generator so comments about generator Air and H2 detraining tanks does Not apply.

The filters rmw refer to are used in the skids I have seen

 

[irishal]

I have seen these filters elsewhere as well. Our plant was supplied with connections for one but it was not fitted - to save money I bet! I get the impression they are more or less standard nearly all power stations.

 

[abeltio]

the results are very bad.
as a first measure i would change lube oil filters and see if the situation improves.
check oil weekly, analize particulates to determine origin... if the material is babbit the bearings are losing material
check the oil for water content too.

saludos.
a.

 

[BladeHerb]

3 micron final filtration is industry standard. Failed bearing may have contaminated LO system with babbitt and/or hard particles from shaft journal if damage was significant. A 150 MW plant should have good delta pressure instrumentation on the final filter and possibly a by-pass relief valve around the filter. Check that the relief valve is not by-passing contaminated oil -- this would happen if the valve is hanging open due to dirt on the seat or is set too low so that it is always bypassing the filter.

LO system should have been flushed after the bearing failure. Flushing procedure should have included high velocity oil flow with line orifices and bearings removed or as a minimum, with by-passes around the bearings if the bearings are not removed for oil flush. There are companies which specialize in oil flushing to assure that the LO system does not remain a problem after this type of incident and also for good preventive maintenance during the planned outage.

http://www.fostercove.com

Herb

 

[MAH82]

1-have you accomplished thermal shock during the flushing process? the particles can be stayed on the welding joints and during the operation are releasing through the bearing. oil analysis can not show any thing in this regard.
2-have you used mesh to detect the particles on intrance of the bearing? I always belive this test is necassary to make sure that oil pipe line is ready to connect to bearing.