Sweetening oil vs full change

quote:

Conoco Diamond Class Turbine Oil 32

as per experience, one of my clients have the same problem. their service oil for their turbine was being tested by RULER and found that the type II & III additives are depleting. we have suggested to sweeten their oil and not to full change. it is also advise to monitor the condition of your lube oil and the condition of the equipment. during sweetening do a routine oil analysis to monitor the generation of the fine and coarse wear metals. it is also advise to monitor the the general oil condition and contamination.

The rate of RPVOT value drop is closely related to the operating conditions; mainly temperature and exposure to air (actually, oxygen from air). Anti-oxidant additives are of a sacrificial nature, and in preventing formation of acids they got used up over time. Because of a significant difference in cost of AN and RPVOT tests many folks test and track AN with a legitimate premise: low AN means that oil still have good oxidation protection reserve. They also test track concentration of wear metals (especially bronze components), which acidic oil could affect.

In regard to your onsite oil testing...when was the last time you verified results you are getting with the results of the same samples but analyzed by a commercial oil lab? I am asking this because you should have noted an increase in AN as RPVOT was dropping at lower level.
Should the 30% of remained oxidation protection be labeled good, bad or ugly depends on the level of acidity in the oil. Even though the condemning limits are often set on 25% of RPVOT, I have seen oils running just fine with an increase of AN (but not near the condemning limit) even at RPVOT below 20%.

I would not suggest an immediate change of this oil, but rather would suggest sorting out what you are testing onsite and how much accurate are those numbers you’re getting. Also, at this level of RPVOT you need to run more frequently AN, and elemental spectroscopy (every 3 months at least) and RPVOT (at lest twice/year) so you can more closely monitor this oil.

You might also consider adding varnish potentials to John M's ideas.

And ask Conoco for help. ExxonMobil is helping me through some of the same problems on my steam turbines, 4 small, 2 large, that resulted in an on the fly 40% sweetening for one unit and another to come.

So yeah, expensive. But as my RULER and RPVOT values went south my MPCs went up, Dmuls, Air Release, and Foma tend were OK on standard tests but no in practice (I was seeing air entrained to the bearings)

Bearing on the main showed some varnish residue too. So in tot, this appears to have been a legitimate issue and I am now monitoring hard.

Also installing a Fluitec ESP this week, as the varnish precursors are still there and tend to be autocatylitic. So removing them or at least fighting them to a standstill is a priority

I will be running a baseline of everything (suitability for conitnued operation type) and MPCs and RULER bi monthly from here on out.