Our gas turbine control oil had NAS6 value. During last outage in february 2007 we changed control oil and flushed it.But Oil test sample from Australia shows Nas 12 now.Would any one tell me about the cause and possible solution.

Regards
Anis
anisur.rahman@haripur.globeleq.com

Dear Anis,
Please give us a little more information. What is the make/model/year/operating hours of your turbine. What was the control oil used before the change out. Please describe the flushing. Was the flush oil discarded or was it purified and used in the system. were any mods installed to the control oil system during the outage? What is the control oil you are using now?

DearDear Gerald,CLS
Thank you for your reply. our machine is Mitsubishi made /Model M701F gas turbine/year 2000 and operating our 40000 hours.We use only Mobil DTE light for conterol oil( no other oil).Before change out also ewe used Mobil DTE light. Actually we used new filters in different filtration points. we use pall cart and control oil purifier.Filters of these units also were being changed during flushing.After flushing we are using now new filters,flushing filters had been discarded.And
thyythe same flushed oil(Mobil DTE light) is being used through the purifier.
Regards Anis

Without knowing the engineering, my only advice has to be to check on sampling point(s), sample taking and confidence in the lab results.
NAS 12 is V.V Dirty and very suprising in view of what you say.
I would carefully resample and send samples to 2 labs for confirmation.

Dear Anus,

My suggestion would be to check the varnish potential.
One lab involved in this tests is analysts inc.
http://www.analystsinc.com
if the varnish potential is high then there are other issues to attend to.

I agree with many of the comments above. Resample paying attention to sampling techniques, hardware and sampling points. You can also get "clean bottles" for sampling as well - the lab should be able to advise.

If the laboratory is using an automatic particle counter,it is known that air bubbles, water and certain additives can interfere with the number of counter particles particularly at the lower end ie 5um or 6um. The counts are higher than what it should be. It may also pay to ask the lab if they can perform ISO cleanliness via the filterpatch method, magnify the particles to 100X 200X and take some photos. This way you may be able to identify what these particles are.

You also mentioned that you changed filters - has the filter media changed at all? I have seen certain bag type filters - contribute fibres. Check with the filter supplier.

I hope this helps.