Acid number progression during TOST test 1

[tmoritz]

I am preparing a specification for turbine oil for use in our hydroelectric generators. Our guide specification calls for a maximum acid number of 0.5 mg KOH/g after 1000 hours TOST. Most literature lists the the total TOST time or time to reach 2.0mg KOH/g. Does anybody know what the acid number vs. time graph looks like for high quality R&O inhibited turbine oil? I would expect to see something like a slow increase for about 2/3 of the total time followed by a rapid increase in the acid number. I'm trying to get an idea of where the 0.5 mg KOH/g point would fall on the time scale in percent total time. This would allow me to estimate if the product being considered would meet or exceed our oxidation resistance specifications.

Thanks,

Tom Moritz
Mechanical Engineer
US Bureau of Reclamation

 

[electricpete]

Does the TOST ASTM standard (D-943) say anything about it?

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[tmoritz]

D-943 requires the analyst test the acid number starting at 500 hours then at least once every 168 hours (one week) thereafter until 3000 hours. After 3000 hours the analyst can reduce the frequency of AN testing to once every 500 hours. There is a formula to calculate the TOST duration if the AN exceeds 2.0mg KOH/g inbetween AN tests.

I posted this question because all I've seen are the end results, the total duration to the 2.0mg KOH/g acidity level. I assume a certified lab would record the intermediate test results to document their testing procedure. I'm wondering if anybody else has seen a chart of AN vs. TOST time. If so, what does the curve look like.

Thanks,



Tom Moritz
Mechanical Engineer
US Bureau of Reclamation