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TAN is dropping

H halMember
Have a 1500 gallon sump of Royal Purple Synergy 320 oil to lubricate a large mill drive gearbox. Routine oil analysis has indicated normal conditions in all areas except for the TAN. Reference reading for TAN was 4.190. The last five tri-annual readings have been showing a decrease - 3.139 - 2.686 - 2.458 - 1.825 - 0.722.
This is the first time I've seen a decreasing TAN rather than an increasing number. Can anyone explain this one to me?
Info:
Visc. 321cSt @ 40C is steady
KF 57 ppm
Water .006%
Water FTIR 12.0
Oxidation 5.0
The only additive in reference is phosphorus at 364 ppm, with only slight variations.
Thanks for any help, Hal
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R rttechMember
Hi Hal,
I don't think it will be critical change, I think track the ISO 4406 particle count and PQ and if they remain steady I would expect the rate of wear will be low, ISO Pct would want to be ISO 16/13- to 17/13 for a low rate of wear, any more elevated I would inclined to check by microscope what the particles are.
What was the base line for PQ when the lubricant was new?
ReAgards
Rob S
H halMember
Hi Rob,
Thanks for the quick reply. I'm not sure that I understand your term "PQ". If you mean particulates, they have very slowly trended up from 1.2 to 35.7. Overall I can see no problem with this gearbox. Like I had stated before, I've never come across the TAN dropping off like it is and wondered if I am missing something.
Cheers,
Hal
R rttechMember
Hi Hal,
This article has an explanation PQ and some worthwhile reading, http://www.machinerylubricatio...4/oil-analysis-tests
Note TAN is not mentioned and the TAN on your new oil appears to be more elevated than I’ve noted as typically TAN would be lower and elevate, yours appears elevated and then dropping making suspect it’s part of the EP chemistry.
The reality for efficient monitoring of gear drives is particle count and PQ, if those two commence to elevate then other parameters could be checked but we would normally check by microscope to identify what the particle are elevating the count and maintain accordingly.
Rob S
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