Can a basic sample test at T.A.N.=0.8 mgKOH/g 3

[electricpete]

ok, I'm a long-time poster on the elctrical motor forum but first time poster in this forum. I'm sure there are lots of folks here that can help me straighten something out.

We sent a mixture contaminated oil/water to lab #1 and they gave us result TAN= 0.8mg KOH / g.

We sent similar mixture to lab #2 and they said the sample is basic.

Knowing whether the sample was acidic or basic is critical to analysing a suspect contaminant. (let's not go into the details of the contaminant and what other tests can be done... it's a whole 'nother subject).

My understanding of TAN is the amount of KOH which must be added to bring the sample to neutral. If anything > 0, that would equate to acid sample, right?

Lab #1 says the ph is unknown (could be acidic or basic)... the only thing they know is that TAN tested in accordance with ASTM xxx gives 0.8.

Does this last statement by lab#1 make sense to you? It doesn't make any sense to me.
Thx

 

[electricpete]

To clarify my wordy post:

I thought that T.A.N.=0.8 mgKOH/g means the sample is acidic.

Is this wrong?

 

[25362]

Both labs may be right. TAN (total acid number) and TBN (total base number) values can simultaneously be present in lubes. To add to the confusion, both are expressed in mg KOH/g, and both are called neutralization numbers.

TAN measures the amount of KOH needed to neutralize acids or acid-like contaminants (that may not affect pH) present in the oil with no regard to their stength. These are organic and inorganic acids, esters, phenolic compounds, lactones, resins, salts of heavy metals, salts of weak bases and of ammonia, acid salts of polybasic acids, and some additives. TAN doesn't discern whether acids were formed by oxidation, and cannot discriminate them from those entering as contaminants or from antiwear additives, detergents and corrosion inhibitors. Freshly formulated engine lubes may have TAN values of 2.5 stemming from the acidic nature of some additives, however, their TBN is the highest one they'll possess.
TAN measurement is mainly used for non-engine systems (for example, industrial uses) because there is no combustion process taking place.

TBN expresses the equivalent amount of KOH that would neutralize the HCl needed to removed the basicity in one gram of oil. The basicity is that contained in the additives, and TBN is mainly intended to measure the oil's ability to absorb corrosive acids formed during combustion processes. Marine lubes have the highest TBN values. TBN values are are mainly provided by Ca and Mg salts (soaps), but can be also the result of the presence of organic and inorganic bases, amino compounds, basic salts of polyacidic compounds, and some salts of heavy metals.

Both TAN and TBN are used in conjuction with other parameters, such as interfacial tension, viscosity increase, to measure the lubricant's condition. TAN values are considered to be acceptable when the TBN is sufficient. However, not all the basicity, as given by the TBN, is effective to neutralize acids.
Therefore, the depleted TBN value when compared with the original in the fresh formulated lube, can give a better idea on whether a TAN of 0.8 mg KOH/g is acceptable or not for the particular application.

As a ROT when the TBN drops to 1/2 of the original value the oil should be changed, regardless of its TAN.
And at TAN values of around 3, engine oils need to be replaced, regardless of their TBN values, because they have reached, what is called in the literature, the end of their "induction period", or, better, their "useful working lifetime".

If you tell the experts in this forum the TAN and TBN values of the unused and the used oil, and what is the oil used for, I pressume industrial applications, they surely will tell you more about the causes for the TAN value found, its probable effects, and what maintenance corrective actions should be taken if at all. Good luck.

 

[electricpete]

Thanks for the detailed response. I have to take some time to digest it.

This is an upper lube oil reservoir for 4000hp motor.
Sent out a sample to Lab #1 for routine analysis. Lab came back and told us it was 99% water. The only thing they could test was T.A.N which was 0.8 mg KOH/g.

We investigated furthe and found about a pint of free water and several gallons of cloudy water while draining the reservoir.

Since this is a water-cooled reservoir with cooling coils, most likely suspect was leak in coils. (This has in fact now been confirmed.)

The coolant water has an additive named Surecool made by Nalco. We had another lab #2 test the water to see if that was present. They identified Nitrites which are a component of Surecool. They also said the sample had a basic pH which is expected for Surecool/water solution.

As I said, the problem is solved we know the source of contamination is the Surecool.

My question pertains to Lab #1 who told us this had 0.8 TAN. (Note they never said TBN).

My simple thinking: if I have to add 0.8mgKOH/g to make something neutral, doesn't that mean it was acid to begin with?? If I had a basic compound, wouldn't I just keep adding KOH forever and never get to ph=7 (would be getting more basic).

Sorry it's a basic question (no pun intended). Just can't quite grasp it.

 

[25362]

to electricpete, my explanation: kindly imagine acid and base molecules fixed in a glassy solid material, they wouldn't react, wouldn't they ? Many industrial catalysts contain acids and bases at the same time, don't they ?

One tends to get confused with neutralizations of acids and bases because one has been weaned, so to say, on water solutions, with pH concepts and the like.

Hydrocarbon lube oils aren't electrolytic, as water and other solvents are, so they may contain bases and acids at the same time without these neutralising (reacting) themselves.