Why RULER doesn't agree with oxidation stability test?

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Hi, I'm the chemical lab head office of a turbogas power plant that use TOTALFINA PRESLIA 32 as lubricant for own gas turbines (GE MS9001F).
In the last campaign of analysis I find contrasting results between RULER (Remaining Useful Life Evaluation Routine) and oil stability test.
The RULER, lead in according to ASTM D6810-02 showed 25%, while the O.S.T. lead in according to CEI standard showed > 200 hours. All the others measured parameters (viscosity, TAN, demulsibility, foam, ecc...) were good.
Is it possible that the RULER test doesn't find (recognized) particulars additives? Does someone have any explenation for this?
The oil at them sampling moment has worked for 9400 hours.
Thanks everybody

3/21/0512:47 AM

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andysittonMember

You give the RPVOT values in minutes, not percent. What is the calculated reminaing useful life, in percent, by RPVOT? Suggest that you do not use the RPVOT value given by the oil refiner in the calculation, you should actually test RPVOT of the new oil, RPVOT of theused oil, and calculate.

I am doing a study which shows that RULER is probably more accurate than the RPVOT values, your data would be helpful.

Thanks
Andy Sitton

3/21/058:58 PM

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johnmMember

RULER and RPVOT are two different methods, and their results are not interchangeable. That does not mean that one is better that the other. It all comes down to which one you want to use to track oil’s serviceability (or the remaining service life) based on the oxidation prevention characteristics. Once you decide which method you will use, establish a baseline using the same method. Historically, oil companies are reporting oxidation stability in RBOT minutes, but some end-users elected to use less expensive RULER method instead. However, neither of the methods would do you any good if they are not tracked regularly and interpreted properly.

3/22/0510:35 PM

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matteobrescianiMember

I premise that the tests was been performed by an external lab, so I didn't know how the test were been exactly conduct; I knew after, that the test was been performed in yellow solution only, which were monitoring the phenolic type of antioxidant. Afterward I asked that the test will be conduct with the green solution too, which were monitoring the aminic type of antioxidant. The new result was a 87% RULER, this probably mean that our oil is poor of phenolic antioxidant but the aminic antioxidant are already present in great quantity. This result now agree with the O.S.T.
What do you think about my explanation?

3/23/051:47 AM

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johnmMember

Good investigative work, Matteo! It looks that your oil has been additized predominantly with amino-based antioxidant. Therefore, the same method should be requested from lab in all future testing for tracking purposes for this particular lubricant.

3/23/0510:51 PM

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