Acid number curve from TOST

[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