Cause of high NAS value(NAS )

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?

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.