TAN of Compressor Oil

Mikhail

In fresh compressor oil TAN represents the additive content in the lubricant. As additves are consumables they are consumed during use and after a certain level when the additives get used up the TAN increases exponentialy indicating oxidation.

Hope this clarifies your query.

Franky,thanks.
Do you want to tell that in this case the plot TAN vs. operation time has minimum near 0 mg KOH/g and then it (TAN) will increase?

Hi Mikhail,
What Franky says is exactly correct. But to say that the plot Tan vs. operation time isn't quite correct.
As Franky has suggested consider the initial "new" Tan as an inherent built in reserve. Once that is used up then as you have suggested the Tan increasses...however it increasses significently faster than the initial reserve was used up(at least 2X under similar operating conditions). Also the speed or time is dependent on the load and hence the operational temperature of compressor. Generally the more severe the duty the quicker the TAN will raise.
So if you are tracking the TAN and you see a decrease and then it climbs again to the origional it means that it is time to scheduule an oil change soon or someone (your customer) has already topped up the oil or changed it without telling you...you tell them to change the oil and you end up looking like &^%#&^.
regards......

Hi Alan,
Thanks for your explanation.
But I do not understand how “acidity” can be placed initially. It is clearly if we are telling about TBN. In this case additive package has initial “alkalinity” for struggle against acidity components, for example against combustion materials. What purpose pursues initially “acidity”? Well, “acidity” containes in additive package, e.g. in amphoteric antiwear add. These additives are spent during operation and so the acidity drops. There is simultaneous process of form organic acids. It is products of oil oxidation. And acidity drop is become slower. When additives will finish the acidity will grow very strong. Ha ha, I began to ask you and myself understand the mechanism.
But now appear next question. What will be the signal of end oil life in this case? May be it will when TAN becomes equal to zero and when additives (antiwear agents) will be used up? Or it will be when TAN becomes equal to 1 mg KOH/g when in oil volume will accumulate large quality of organic acids?

Mikhail,

Petro-Canada NGS 1000 is a PAO synthetic product, so the starting TAN of 0.2 mg/KOH is consistent with PAO compressor products. For this product the condemning limit would be approximately 1.0 mg/KOH, depending on the trend analysis.

TAN level does drop off when the anti-oxidant additive has been depleted (as the nascent anti-oxidant additive is itself acidic), however, a drop to 0.01 mg/KOH is not typical.

Other possible causes for the TAN drop are;

1. Incorrect oil make-up: In order to drop the TAN level that significantly I would suspect mixture with a highly-refined R&O mineral oil. The mixing of a PAO and R&O mineral oil is not going to have serious consequences. A VI test would reveal if a mineral oil has been introduced into the system. PAO oils have a high VI, and mineral a low VI. Have your lab conduct a viscosity at both 40, and 100C and give you a VI.

2. Inaccurate TAN test by your laboratory. You should have this result confirmed. Best to take a fresh sample and submit it to the laboratory for a follow-up before doing any serious maintenance.

A follow-up sample is my recommendation. I believe that the NGS product has a high level of P in it. If this level has dropped off dramatically it could indicate that a different oil has been added. If this is the case, then you need to investigate what oil was added. If the oil is not compatible with PAO, then you need to drain and flush the compressor.

If the TAN on the next sample is very high ( > 1.0 mg/KOH ) then the anti-oxidant has been used up, and an oil change should be immediately scheduled.

If the TAN is in the 0.2 - 0.9 mg/KOH level then most likely the previous TAN result was inaccurate.

Best Regards

Mikhail's letter dated Jan18 has not been replied clearly by anybody. Acid and Alkali neutralize each other, so how TAN and TBN coexist in some oil. I have seen many test reports where the same oil had TAN and TBN both.

How can TAN be the representative of additives, yes, TBN can be.

So if someone says that TAN of any oil will go down first upto zero, then it will start rising , how is it possible?Yes, TBN may go down upto zero, then TAN will start rising.

I think I have some serious misunderstanding of TAN and TBN, will somebody clarify it as many people like me will be benefited.

Prabhakar

TBN is mostly measured for engine;engine cum transmission & transmission oils only because it has to combat acidity due to fuel sulfur.

Whereas TAN can be referred in most engine and industrial lubricants.

For most industrial lubricants TAN is normally referred to and measured to evaluate oil's performance.(There are exceptions)

For more information you can contact me on my mail ID frankyxavier@yahoo.co.uk

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Originally posted by Prabhakar Agrawal:
Mikhail's letter dated Jan18 has not been replied clearly by anybody. Acid and Alkali neutralize each other, so how TAN and TBN coexist in some oil. I have seen many test reports where the same oil had TAN and TBN both.
+ How can TAN be the representative of additives, yes, TBN can be.
+ So if someone says that TAN of any oil will go down first upto zero, then it will start rising , how is it possible?Yes, TBN may go down upto zero, then TAN will start rising.
+ I think I have some serious misunderstanding of TAN and TBN, will somebody clarify it as many people like me will be benefited.

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Let me clarify as much I understand about the lube oil formulation. Engine oils and industial oils such as compressor oils, Turbine oils do contain anti oxidants; they are mostly amine based or DBPC type additive components. These components are acidic type but not harmful to metallic corrosion or rusting and also will not react with alkaline additive (TBN booster) present in the engine oils. Because of this reason, Fresh industrial oils will have TAN value. WE call this TAN value as pseudo TAN number. Psedo TAN value will gradually decrease to zero. TAN incresae from zero is to watched carefully for oil detrioration. Due to this phenomena, fresh engine oils will have TAN and TBN values.kumartr@petrominoils.com Kumar