TBN vs. TAN

Smiley,

Considering only TBN/TAN for Natural gas Engines
is insufficient.Other important tests like Oxidation,Nitration,Wear metals,Viscosity has to be run regualrly.TBN,TAN is of little importance since oil is been topped up regularly
due to intense heat produced by the combustion
of natural gas.Natural gas increases oxidation,
nitration by-products,causes corrosive punch in
engine components.The organic acids,Nitric acids
elevates Bearing corrosion.It is important to
remember that oil change intervals has to be
optimized based on Viscosity,Oxidation,Nitration
and wear analysis.....

Good Luck

Bala.

If TAN is the measurement of total acid present in the oil ,acid is undesirable, what should be the maximum TAN allowed for Hydraulic oil SAE 68. Shell people in Vietnam told me that their new Hydraulic oil Tellus 68 has TAN equal to 1, if acid is undesirable how new oil has so high a TAN, In any oil how TAN and TBN coexist. If oil is alkaline it will neutralize acid whenever it will be formed, still oil will be alkaline unless and untill total alkali is neutralized . So at any time oil is either alkaline or acidic, how it can be both

Prabhakar,

Any Oil can have an acid and base number at the same time because they measure different constituents with two different titration procedures.Infact some additives particularly
in engine oils are amphoteric-they can behave as either an acid or base.Both the values are
valid.Acid and Base numbers are not reciprocal
in nature,although acid numbers do trend up,as
base numbers trend down through an oils life span.

Hydraulic oil(ISO 68) is acidic in nature due to the ZDDP(Zinc Dialkyl Dithiophosphate)chemistry.Over a period of time additive depleates resulting in decreased TAN.Oxidised oil increases organic acids resulting in elevated TAN levels.Needless to say that treating the cause is good maintenance practice.

Bala.

Dear Bala,
I would request you to explain TAN more elaborately.You have given the example of Hydtaulic oil 68 which has a TAN due to ZDDP, Shell claims the TAN of new oil to be 1, if this oil is run its TAN will go on decreasing due to depletion of additives, but at the same time the oxidation products with moisture will generate acid which should increase TAN, how then this combined effect is taken into consideration?

Prabhakar,
-The first thing we need to clarify is the fact that AN and BN can coexist. There is a close relationship between both. However is not an absolute relationship. The presence of one does not mean the absence of the other.
- The AN value gave to you by Shell for their hydraulic fluid is measuring additives. During the operation of the oil the additive package experiment a normal adjustment and the base oil start to deteriorate (oxidation process) these cause a variation of the AN
- The best way to analyze AN is comparing the values with the base line

Velasco,
your reply is slightly not clear to me.Take the example of Tellus 68 of Shell for which they have declared a TAN equal to 1. Now this new oil is put into machine and run regularly, Oxidation products will combine with moisture to form acid which should increase the TAN value of the oil. Isn't it?
But you have said that the initial TAN represents the additive package present in oil, it means that with more and more use the additives will deplete and TAN should decrease.
In one case TAN is increasing , in another it is decreasing, how they will adjust.
Suppose after 4000 hours the TAN of this hydraulic oil comes to 1.5, now in comparison to intial TAN=1 what is the condition of oil? Every other parametres being within allowable limits, at what TAN this oil will have to be rejected. Kindly go through the whole case thoroughly, then reply. i have received many answers which have not satisfied me

Prabhakar,
Suggest to draw the sample at every 500 Hrs.
Apart from TAN,Run Viscosity @ 40'C,Particle
Count,Wear metal Analysis.At 4000 Hrs it's quite
obvious that TAN increases due to age.Particle
Count is essential for Hydraulic System.Sampling
at regualar intervals establishes trend/pattern
of wear elements,contaminants.Oil change periods
can be optimized based on these tests.Post your
analytical results,Hydraulic system details,Topup added oil etc..for interpretation.

Regards

Bala.

Mr Smiley,

The thumb rule is check TBN for engine oils and check TAN for oils other than engine oils. It should be no different for Gas engine oils.

Hussam Adeni

Bala and Adeni,
I don't think that you have read my posting carefully.I am talking about Hydraulic oil only, if all the parameters like viscosity, moisture and NAS value are within allowable limits , should the value of TAN be the deciding factor.What should be the limit of TAN at which the oil should be rejected? If the TAN of new Tellus 68 is 1, will it go down gradually or will increase with more and more use of oil. If TAN will go down, will it go upto zero and then again increase? Or it will go on increasing from the initial value 1. Kindly read my both the posts thoroughly, then if you have a clear concept of the whole thing , then reply.
Prabhakar

Mr Smiley,

I recently read an article by Mike Barnes of Noria, which answers your question. The article is pasted below.

Hussam Adeni

--------------------------------------------------------------------
Copy of articles by Mike Barnes, Noria is pasted below:

Which Acid Number Test is Best?

"In used oil analysis of natural gas engine oils, most original equipment manufacturers (OEM) have total acid number (TAN) as a criteria for an oil change. However, certain gas engine OEMs have strong acid number (SAN) as a criteria for oil change. Why do these OEMs prefer SAN over TAN?"

Strong acid number can be determined using the same methods as total acid number (ASTM D664 or D974). With total acid number, the test titrates to the final inflection end point and determines both strong acids, like sulfuric and nitric acids, and weaker acids like organic acids formed by oil degradation.

Strong acid number, however, titrates to the first inflection point, corresponding to a pH equivalent of around 6, which does not account for weaker acids.

For natural gas engines - particularly those burning sour gas (that is, a high content of sulfurous impurities), or other impure fuel sources like landfill and biogas, SAN can be instructive in determining the degree of contamination due to stronger, more corrosive acids formed by burning lower-quality fuel.
Under these circumstances, it may offer a more precise method of determining a condition-based oil change parameter.

Mark Barnes, Senior Technical Consultant, Noria Corporation

Prabhakar,

I was carried away by the original post, by Mr Smiley, which sought to know whether to "Analyse TBN or TAN for LNG Engines."

Coming to your query on TAN, I thought it apposite to paste two "Lube tips" that appeared in Noria.

Hussam Adeni
------------------------------------------------
Article appearing in Lube Tips.

ACID NUMBER

Oil Analysis Tip

Acid Number monitors the level of organic acids produced from the oxidation of the oil. All systems in which an extended drain interval is contemplated or in which the potential exists for acidic contamination should be monitored for an increase in acidic contaminates. As the oil ages and oxidizes, the acidic by-products cause the acid number to increase. An increase in acid number is an indication of oxidation in the lubricant, which could lead to lubricant degradation.

-------------------------------------------------
Article appearing in Lube Tips

Acid Number Helps Time Oil Changes

"Should I consider adding the acid number test to my predictive maintenance program?"
Acid number (AN) tests are typically performed as part of a proactive oil analysis strategy. The principal reason we would consider acid number is to determine a condition-based oil change interval rather than a time-based oil change interval.

Because acid number changes when organic acids build up in the oil due to oxidation, the test can be used to warn of incipient oxidation so that an oil change can be scheduled. Used correctly, it allows oil analysis users to optimize oil life, without jeopardizing equipment by leaving oil in service for too long.

It is typically used in large (>50-100 gallon) systems, where the cost to perform AN tests can be justified by the extended oil drain intervals and is applicable to most oils, with the exception of diesel engine oils.

Most quality labs are able to accurately determine AN. We do, However, strongly suggest the lab be requested to use ASTM D664 (potentiometric titration), rather than D974 (colorimetric) because this is generally more accurate for used oil analysis - particularly darker oils.

--------------------------------------------------

Adeni,
Do you think that you have answered my query ? I think you have not even read my posting. I would again request you to first read my posting , then answer it point by point. How can New oil have a TAN of 1, have you considered it.
Prabhakar

Prabhakar,
I think what you are looking for is why does the new oil have a TAN of 1. This can best be determined by the chemical make up of the oil. It has a great deal to do with the additives the company is using. In most hydraulic oils you want to keep the oxidation process down. The oxidation process in your hydraulic oils is what will drive the TAN up. I would refer you to George Totten's book titled "Handbook of Hydraulic Fluid Technology." Look in particular at chapter 14 and specifically section 6.1. While it may not give you all of the answers you are looking for, I am sure it will help give you a better understanding of some of the whys. If you do not have the book, it is available at Noria's book store. Good Luck.

Quoted from Prabhakar:

"If TAN is the measurement of total acid present in the oil ,acid is undesirable, what should be the maximum TAN allowed for Hydraulic oil SAE 68. Shell people in Vietnam told me that their new Hydraulic oil Tellus 68 has TAN equal to 1, if acid is undesirable how new oil has so high a TAN, In any oil how TAN and TBN coexist. If oil is alkaline it will neutralize acid whenever it will be formed, still oil will be alkaline unless and untill total alkali is neutralized . So at any time oil is either alkaline or acidic, how it can be both"

Prabhakar, you need to look up the chemical term 'amphoteric'. Some compounds can behave both as acids and bases, as strange as this may seem. As said above, some of the additives used in lubricants are amphoteric, especially the metal detergency additives.

From a web site with a reasonable definition of amphoteric:

Amphoteric
--------------------------------------------------------------------------------

(1) A compound that can behave both as an acid and as a base. For example, with strong acids aluminium hydroxide acts as a base, Al(OH)3, forming aluminium salts. With strong bases it behaves as an acid, H3AlO3, forming salts containing the ion AlO33-. The formation of amphoteric hydroxides is a characteristic of metalloids.

(2) Compounds that contain both basic and acidic functional groups. See, for example, the amino acid glycine.



As you pointed out, this behavior can make tracking oil condition by TAN very difficult. As a result, you cannot rely only on TAN to determine the oil condition. Several previous posters said the same thing when they told you to do other testing as well as tracking TAN. TAN will sometimes initially drop as the additives are consumed, and may then rise later as the oil is oxidized. Unless you are continually tracking the TAN value it is difficult to tell where you are in this process.

Guy
Thanks a lot, you have given a very clear concept. It means TAN is not a very important parameter for deciding the condition of used hydraulic oil.It may be due to additives which is desirable and at the same time it may be due to oxidation products which will be undesirable.
Just one question: I have taken 600 litres of oil from the hydraulic tank of a Melamine products producing machine, it has run for 6000 or even more hours, now this oil is cleaned resulting in Viscosity of 67.6 at 40 degree C , moisture 100ppm, NAS value 5, how to know whether this oil can be continued further in use or not. Will the measurement of TAN help in decision making? If yes, what decision you will take in 6 different cases when TAN is 0.33 or 1.02 or 1.3 or 1.5 or 1.9 or 2.4 Please remember topping up has been done with oil of different companies , but same viscosity 68 (+/- 5%), no info available about the oil charged initially. Should I perform any other test, which one?

Prabhakar,

1# NAS is Outdated.Current Particle count standard is NIST-ISO 11171 calibration method
with three ranges 4/6/14 microns.

2# FTIR Spectrum of used Hydraulic oil can show
Molecular Additive levels(organic anti-wear)and
Oxidation By-products.Comparing the Fresh oil and used oils helps identify the Additive and
Contaminant levels.

3# After cleaning the oil,Recommend to run the
oil property tests like Foaming characteristics,
Wear test by Four Ball method,Rotating Bomb
oxidation stability,Rust preventive test,
Demulsibility test.Compare the analytical results with fresh oils.

4# If the above oil property tests fails,discuss
with lube oil supplier for further action.If
test passes,it can be reused in hydraulic system
with periodic oil condition monitoring.

5# Treating the cause of High oxidation will
Extend both the machine and oil life.

Regards

Bala.

Bala,
Thanks. You have given very useful information , but have been silent on TAN-TBN of hydraulic oil. So far as I understand from your writing , they need not be given so much importance. Am I correct?
Will you please give me a chart of Particle-counts associated with NIST ISO 11171, however I think it does not make much difference as NAS also considers particles of many ranges.
Can you give me address of some labs in India which are considered authority, if they are Govt labs that will be better.
What do you think , for the tests whch you have mentioned except FTIR, how much will it cost to buy those apparatus, what should be the testing charges in some lab?

I have refrained from reacting to the TAN-TBN debate, as I belong to the old school. In my 18 years with Castrol in India, Burmah Castrol Technical experts taught us some thumb rules that I giving below:

1. Seek TBN values for Marine Engine oils on account of the high sulphur content of most of bunker fuels and poor fuel distillates.It is the quality ( poor quality of Fuels) that demand high TBN. For other engine oils (EO's), which largely run on HSD and possibly LDO, tracking of moisture, Flash, KV 40 will reveal good guestimates of the condition of lube.

2. Track TAN for Gas engine oils other than on LPG.

3. Check TAN for lubes (not EO's) that are aged, stored for a long time without use, or have been contaminated with water to check for organic acidity.

Hussam Adeni

Prabhakar,

Further to the last post I discovered an article in this very Noria and which I thought should be reproduced, with due acknowledgements. t does answer a number of basic queries on the forum.

-------------------------------------------
Interview Helps Clarify Questions Surrounding AN/BN Test Methods in Used Oil Samples

In an article written by W. Van Dam of Chevron Oronite Technology and published in Practicing Oil Analysis magazine’s July-August 2002 issue, a number of different ASTM test procedures were outlined for determining acid number (AN) and base number (BN). There are numerous test methods prescribed by ASTM for determining both BN and AN (Table 1). Although these methods use the same basic idea, a wet chemistry titration to neutralize either acidic or basic (alkalinic) components in an oil sample, they differ either in the titrant or the method used to determine the end point of the neutralization reagent.

To clear up some of the ambiguities surrounding the different test methods, we asked Janet Barker, research scientist in the Petroleum Products Research Department at Southwest Research Institute, to answer some questions about acid number and base number testing.

Q Why do we use AN and BN to test oil samples? Doesn’t pH measure acidity and alkalinity?

Strictly speaking, the pH of a solution is a measure of hydrogen ion concentration. In aqueous solutions, a pH of 0 to 6 is acidic, pH 7 is neutral, and a pH of 8 to 14 is alkaline. Acidic and alkaline character of fluids cannot be fully described by the pH alone because the pH describes the strength of an acid or alkali, not its concentration. Acid or base concentrations, not strengths, are actually being investigated when we talk about acid and base numbers. In fact, running either of these methods tests the fluid’s resistance to being neutralized. Acid and base number are used to measure the concentration of acidic components (organic acids formed by oil oxidation, certain additives, etc.) and basic components, for example, overbase detergent additives in engine oils, as a means of performing condition-based oil changes.

Q What is ASTM’s recommended test procedure for determining AN and BN for used oil samples?

ASTM does not specifically recommend any one procedure over another. ASTM is an entity that provides written instructions about how to perform reliable testing and monitoring. It provides several applicable methods from which to choose. Some testing may be more reliable or applicable to the given circumstances, but the final decision ultimately rests with the end user. ASTM currently does not prescribe AN or BN test procedures specifically for used oils, and care must be exercised to select the most appropriate procedure for a specific application.

Q Why do some test procedures, such as ASTM D974, have a colorimetric end point, while others use a potentiometric end point? What is the difference?

Colorimetric titrations use an indicator with a color change at a specific pH to detect the titration endpoint, while potentiometric titration uses an electrical activity reading to detect the same reading. Some indicators used for colorimetric titrations provide indistinct endpoints that are difficult to detect, even for trained individuals. In addition, some oils, especially highly colored or heavily contaminated oils such as diesel engine oils, are more suited to potentiometric endpoint titration than a colorimetric endpoint method. Oil darkens with age and this darkening can also contribute to indistinct endpoints. Potentiometric titrations will distinguish titration endpoints on samples otherwise obscured due to the oil’s colored nature. It is important to be consistent. Pick a test procedure that applies to your specific circumstance and run all samples to this method.

Q Some oils, such as natural gas engine oils, are listed in product guidebooks with both acid numbers and base numbers. How can oil have both an acid number and a base number?

Any oil can have an acid and base number at the same time because they measure different constituents with the two different titration procedures. In fact, some additives, particularly in engine oils, are amphoteric - they can behave as either an acid or a base. Both values are valid and it is wise to track both in some cases. In fact, the numeric crossing point of acid number and base number is sometimes used as an indicator of a condition-based oil change point for in-service natural gas engine oils. Acid and base numbers are not reciprocal in nature, although acid numbers do trend up as base numbers trend down through an oil’s life span.

Q In ASTM D664, the term “strong acid number” is mentioned. What is a strong acid number and how can it be used in oil analysis?

ASTM covers the determination of two parameters, strong acid number and acid number, sometimes referred to as weak acid number. When using ASTM D664 to determine strong acid number, the sample is titrated to a freshly prepared nonaqueous acidic buffer solution’s meter equivalent or well-defined inflection point. By contrast, a sample run for acid number is titrated to the freshly prepared basic buffer solution’s meter equivalent or well-defined inflection point. In simpler terms, this means that the strong acid number titration reaches the end-point sooner than the conventional acid number reported by most oil analysis labs. In general, strong acid number measures only strong acids and hence would provide a lower result than weak acid number. ...



... Conventional (weak) acid number measurement reflect total acidic components including, according to ASTM, organic and inorganic acids, esters, phenolic compounds, lactones, resins, salts of heavy metals, salts of ammonia with other weak bases, acid salts of polybasic acids, and additional agents such as inhibitors and detergents. Because used oils provide ill-defined or no inflection points, it is standard practice to run all used oils to the basic, buffer endpoint and report this as an oil’s acid number. Strong acid numbers are rarely requested or reported, especially for used oils, although they can be useful in determining the presence of strongly acidic contaminants such as hydrochloric and hydrofluoric acids, formed by freon decomposition in refrigeration compressors, and other sources of strong acids.

Q Some oils, such as those used for locomotive engines and marine diesel engines, have very high base numbers, often 15 and higher. Wouldn’t you want to select a high base number oil with high over-base detergent additive concentrations all the time, so that it lasts longer than a lower base number oil?

High over-based oils are specially formulated for these engines to provide the longer drain intervals that long-haul vehicles require, and to counteract the effects of higher fuel sulfur levels used in locomotive diesel fuel and bunker fuels used in marine applications. While a higher base number oil can potentially extend the useable life of the oil, it is important to remember that higher base numbers are provided by higher levels of metallic detergent additives. When these burn, they form ash, which can deposit on valve stems and other engine components. Such deposits can be detrimental to engine life. Most manufacturers set ash level limits for their engines.

-----------------------------------------------------------
Please reference this article as:
"Interview Helps Clarify Questions Surrounding AN/BN Test Methods in Used Oil Samples". Practicing Oil Analysis Magazine. May 2003

[QUOTE]Originally posted by Bala:
Prabhakar,
2# FTIR Spectrum of used Hydraulic oil can show
Molecular Additive levels(organic anti-wear)and
Oxidation By-products.Comparing the Fresh oil and used oils helps identify the Additive and
Contaminant levels.
3# After cleaning the oil,Recommend to run the
oil property tests like Foaming characteristics,
Wear test by Four Ball method,Rotating Bomb
oxidation stability,Rust preventive test,
Demulsibility test.Compare the analytical results with fresh oils.


Bala,
Thanks God, you have dropped the TAN from your suggested list of tests for cleaned oil, actually I am still not satisfied with the explanations given in different posts, I assume that TAN is a confusing thing with very few people having clear idea.Adeni has posted one article which gives some very valuable information , but it also does not satisfy my doubts about TAN. I don't know whether you people too have the same doubts or I have some mental block which is preventing me to understand it clearly. If you go through all my posters under this sub heading you may appreciate my honesty in admitting about my ignorance
Anyway, can you give name and address of some reliable labs which can perform these tests honestly and declare whether some cleaned oil can be used further or not.

Prabhakar,

Try this out.

1. IIPM - Orissa
Indian Institute for Production Management
Kansbahal - 770 034, Near Rourkela, Orissa, INDIA
Telephone Number +91-6624-280322/948/576 | FAX : +91-6624-280122

2. S & S Industries
C-15, Sector - 7
Noida, U.P. - 201301 (INDIA)

Tel : +91-120-2423191/ 207/ 523/ 382
Fax : +91-120-2423654
Email : ssengg@giasdl01.vsnl.net.in

Regards

Bala.

Bala,
I know about these two laboratories, they are not sophisticated. The tests which you were talking about can't be carried out by them.IIPM is expert in Wear Debris Analysis, other tests they are carrying with a portable oil testing kit supplied by SS Engineering , Noida. SSEngineering are supplying testing kit for used engine oil,containing Visgauge , TBN "GO Gauge , Not Go Gauge", both are approximately OK. But Hydro gauge and TAN Gauge are not very satisfactory. Have you any idea if they can perform all those tests you suggested to do on cleaned oil? Any other more reliable advanced lab? Tata Steel has also started taking samples from outside for testing, but they take littlr interest inoutside parties

quote:

---

Originally posted by Prabhakar Agrawal:
If TAN is the measurement of total acid present in the oil ,acid is undesirable, what should be the maximum TAN allowed for Hydraulic oil SAE 68. Shell people in Vietnam told me that their new Hydraulic oil Tellus 68 has TAN equal to 1, if acid is undesirable how new oil has so high a TAN, In any oil how TAN and TBN coexist. If oil is alkaline it will neutralize acid whenever it will be formed, still oil will be alkaline unless and untill total alkali is neutralized . So at any time oil is either alkaline or acidic, how it can be both

---

Mr. Prabhakar,

You can obtain TAN and TBN values while testing a fresh oil. You get TAN value due to acidic type inhibitors present in the oil and TBN vaue due to alkaline detegergents such as calcium/Magnesium sulfonates. Acidic type inbitors are not harmful. This is the reason, many turbine oils and hydraulic oils will have initial TAN value but reduces gradually and then increases due to oil degradation. Fresh oil TAN is called Pseudo TAN value.
Crankcase engine oils also contain either acidic or alkaline inhibitors whose TAN will reflect while testing but they are not harmful. What one should really worry is for TAN increase due to oil degradation/acid formation due to fuel sulfur;for this TBN additives will come to rescue by neautralizing.

Kumar, Petrolube, Saudi Arabia

Kumar,
Thanks, you have clearly mentioned that turbine /hydraulic oil will have some initial TAN which will decrease to some point and then will start increasing due to oxidation products.It means when it started decreasing that was a sign of that particular additive getting depleted. Once it starts rising due to oxidation , its value will not reflect the actual status of additives in the oil. Some people think that on the basis of TAN of hydraulic oil you can predict the status of additives in it.But here we dont find it true.
But in the case of engine oil, the value of TBN may be a reliable indicator of remaining additives in the oil. Very surprisingly all the experts who have posted their views in this column, have neither said 'No' to it nor agreed with this theory.I appeal to them to come out clearly in the open to clear the doubts of people like me.

if i may suggest,pl try out extensive facilities at:
iit,delhi
ioc,r&d centre,faridabad.

----

Sam,
Would you please give me the name of contact person, address, phone nos and email i.d of IIT, Delhi and R&D Centre , IOC, Faridabad if it is available with you.
What type of facilities they have got for testing various oils

quote:

Originally posted by Bala:
Prabhakar,

Any Oil can have an acid and base number at the same time because they measure different constituents with two different titration procedures.Infact some additives particularly
in engine oils are amphoteric-they can behave as either an acid or base.Both the values are
valid.Acid and Base numbers are not reciprocal
in nature,although acid numbers do trend up,as
base numbers trend down through an oils life span.

Hydraulic oil(ISO 68) is acidic in nature due to the ZDDP(Zinc Dialkyl Dithiophosphate)chemistry.Over a period of time additive depleates resulting in decreased TAN.Oxidised oil increases organic acids resulting in elevated TAN levels.Needless to say that treating the cause is good maintenance practice.

Bala.

quote:

Originally posted by Bala:
Prabhakar,

Any Oil can have an acid and base number at the same time because they measure different constituents with two different titration procedures.Infact some additives particularly
in engine oils are amphoteric-they can behave as either an acid or base.Both the values are
valid.Acid and Base numbers are not reciprocal
in nature,although acid numbers do trend up,as
base numbers trend down through an oils life span.

Hydraulic oil(ISO 68) is acidic in nature due to the ZDDP(Zinc Dialkyl Dithiophosphate)chemistry.Over a period of time additive depleates resulting in decreased TAN.Oxidised oil increases organic acids resulting in elevated TAN levels.Needless to say that treating the cause is good maintenance practice.

Bala.

============================================

Dear Sir,
I'am interested in knowing more about (Zinc Dialkyl Dithiophosphate)and its application.

Could I request you to please inform the same.

Thanks & Regards,
Arun Sikchi

FROM:
MARATHWADA CHEMICAL INDUSTRIES (P) LTD.,
S.NO.43/2, SATARA ROAD, USMANPURA,
AURANGABAD-431005 (M.S)
INDIA.
TEL: 0091-240-2376114, 3290738
FAX: 0091-240-2376918
Email: sikchi_agd@sancharnet.in

Total Base Number (ASTM D-2896)

Total Base Number (TBN) is the measurement of a lubricant’s reserve alkalinity, which aids in the control of acids formed during the combustion process. The higher a motor oil’s TBN, the more effective it is in suspending wear-causing contaminants and reducing the corrosive effects of acids over an extended period of time.

Testing for TAN is essential to maintain and protect your equipment, preventing damage in advance. A rise in TAN is indicative of oil oxidation due to time and/or operating temperature. Trend as well as absolute values should be used to monitor TAN levels.

Noureddine TOUHAMI

Mr SMiley,

For natural gas engines in automotive service, use TBN.

For the other guy asking about the hydraulic oil. TAN does increase in a close approximation for oxidation. To answer your question... You should change the oil when the TAN doubles from the original new oil value. Typically TAN does not go down on industrial oils, unless you add new oil. Then by dilution, the lower TAN new oil will lower the overall TAN of the mixture.

It is important to distinguish that TAN and TBN are not really the same as pH is in water. As was posted by another reader, an oil can have a TAN and a TBN.

Another interesting thing to note is that both TAN and TBN are measured in a laboratory in grams KOH.

Happy days!

Dear folks,

In reference to the initial problem of the ISO 68 results, is a bad practice refill whit different product, because you don't know if the additive package is going to react between it? the condemnatory limit for an Hydraulic oil ISO 68 for AN test is 50% lost of initial value, so if you are using TELLUS for example and the AN is below 0.5 mg KOH/gr than means that 50% of the additive package is lost! is you refill with MOBIL DTE 26 (AN = 1.5) or MOBIL HYDRAULIC AW 68 (AN=0.6) depending of the total volume and the volume added is the result of the AN? the problem is that you lost the track of what are you going to control? but any way you need to fix the problem! don't run costly analysis like mad! (rvot, foam test, emulsion test) why? if you don't know the initial values of the oil? is too expensive! simple and unexpensive request color ASTM D1500 all the ISO 68 got more or less the same value, if the color value increased is a clear indication of oxidation! also request the comparison of the spectrum from FTIR in the range of 1680 to 1750 and look for an unusual peak of oxidation, if you refill by any reason with mobil dte 16M you are not going to obtain nothing from the FTIR and the comparison of the spectrum because DTE 16M got signal in that range!

regards
pcancino,
pedro.cancino@gmail.com

Prabhakar,
As with any oil analysis, trending is critical in monitoring oil condition. With hydraulic oils, the initial TAN value comes from the additives which react to the TAN test. In service these will deplete leading to a drop in TAN but this is countered by increasing TAN from oil oxidation. What you are looking for is an increase in TAN over new oil conditions. Typically you would take an increase of say 2.0 over fresh oil value as an alert however the acidity is due to oxidation so you will see a corresponding increase in viscosity and oxidation products at the same time. Bear in mind also that the accuracy of the TAN test is quite poor and you should not action oil changes on a single value alone.
By the way it is not a good idea to top up with different brands of oil as this can lead to reactions between different additive systems leading to loss of performance and sludge formation.

Rule of thumb
TBN is going down. TAN is going up.
When the values are closed - the time for oil changing arrive. In general, the gap is at least 4-5 points. If it is closer than 1-2
ther is a problem.
Thanks

For Natural Gas Engine Oils, Cat, Waukesha, etc. TBN has terrible accuracy, and TAN is only second-best.

Try using Ruler (Linear Sweep Voltammetry) and calculate % remaining AO additive in the oil!!

Then try correlating the Ruler results with viscosity increase and FTIR oxidation absorbance. Then try correlating the Ruler results with viscosity increase and FTIR oxidation. It is so simple, it is difficult for the Chemists in this group to admit that a chemical titration is 19th century technology, especially with all the additive interference.

Join the 21st century and use Ruler!

Our data in a recent combustion study on engines, using a modified dual fuel system of diesel and CNG (gas), in multiple over the road vehicles, shows RUler (linear sweep voltammetry) as being very responsive and correlating almost perfectly with FTIR Ox and Nit, however, TBN (D-4739) is a flat line with noise...