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TAN is total acid the TAN analysis is to measure the total acid(both inorganic and organic)content in the lube oil.It can be used for both fresh oil and used oil.But the neutralisation number is the TBN(total base number)in the oil.It is mainly the alkaline reserve incorporated in the engine oil to neutralise the acidic content generated during engine operation.
If the question is what is the difference between TAN and TBN then it is as KM correctly says.
TBN is almost exclusively measured for engine oil QC and condition monitoring. TBN deminishes in use(in diesel engines) until a threshold change value say 40% of new oil.
TAN can be measured for all types of oil and is affected by many things including additives and oxidation.
TAN can be used for QC purposes, but more so for oil oxidation.
Non additive new oil will have a TAN of ~0.01 mg/km KOH per gm (same units as TBN) this value will rise on increase in oxidation.As in all monitoring, trending values is more important than individual numbers
Originally posted by Pablo Dossier:
Can anybody help me? What`s the difference between TAN ANALYSIS and NEUTRALISATION NUMBER ANALYSIS?

Both terms represent absolutely the same thing. Neutralization Number (NN) is an older term for Acid Number (AN) in industrial oils, as no industrial lubricating or hydraulic oil had alkali characteristic. The term NN hints that the acid in oil was neutralized to the equilibrium or an inflection point by a base. Regardless which term is used; the result is always expressed in mgKOH/g. This is the case in EU and US, but the nomenclature may be different in India, providing that Krishnakumar Menon knows what he’s talking about.

It is best that you refer to the ASTM standards pertaining to Petroleum Products and Lubricants. If you look in the index section under "Neutralisation Numbers" you will see that is a "generic term" used for 4 other ASTM test methods namely, ASTM D664 Acid Number of Petroleum Products by Potentiometric Titration, ASTM D974 Acid and Base Number by Color Indicator Titration, ASTM D128 Analysis of Lubricating Grease and ASTM D5372 Evaluation of Hydrocarbon Heat Transfer Fluids. It is just how much of one titrant does it take to neutralise the acid or base present in solution.
I hope this helps.
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