TAN Analizi — ASTM D664 / ASTM D974 / ISO 6618

What Is TAN?

Total acid number (TAN) is the amount of potassium hydroxide (mg KOH/g) required to neutralize the acidic components in one gram of sample. The sample is dissolved in the appropriate solvent and titrated with alcoholic KOH; The turning point is determined potentiometrically or by color indicator.

Purpose of TAN

The aim is to monitor the level of oxidation products and acidic components in the oil. Increased TAN indicates that the oil has deteriorated and the risk of corrosion increases.

Which Products Is TAN Applied To?

Turbine and hydraulic oils
Transformer oils
Gear and compressor oils
Crude oil (acidic corrosion assessment)
Industrial lubricating oils

In Which Sectors Is TAN Used?

Oil & GasPetrokimyaEnergyEnergyIndustrial Equipment

Standards Related to TAN

ASTM D664 (acid number by potentiometric titration)
ASTM D974 (color indicator titration)
TS ISO 6618 (acid and base number — with color indicator)
IEC 62021 series (acidity in insulating oils)

TAN Conditions

Method: Potentiometric method is required for dark colored and used oils
Solvent: Toluene-isopropanol-water mixture defined in the standard
Reference: New oil TAN value required for comparison
Unit: mg KOH/g

Equipment for TAN

Automatic potentiometric titrator
Analytical balance
magnetic stirrer
Titration electrodes

Sample Requirements for TAN

A clean sample container should be used
New oil reference value must be provided
Oil type and service period must be declared
The sample must be homogenized

Duration of TAN

Titration is rapid; The results are usually obtained the same day or the next day.

TAN Procedure

1The sample is weighed and dissolved in the solvent.
2It is transferred to the titration cell.
3Electrodes are placed.
4It is titrated with alcoholic KOH.
5The turning point is determined.
6TAN is calculated as mg KOH/g.

TAN Acceptance Criteria

There is no fixed universal limit. The evaluation is based on the new oil value and the equipment manufacturer defines its own warning and intervention thresholds; For turbine and transformer oils, the relevant monitoring guides (e.g. IEC 60422) recommend action values.

Evaluation of Results

It is not the absolute value of TAN that is meaningful, but its increase and rate of increase compared to the new oil. A sudden rise usually indicates overheating, water intrusion, or incorrect oil addition. The color indicator method does not show the turning point in dark samples; In this case the potentiometric method is mandatory.

TAN Report

Oil type, equipment and service time
Standard and method applied
TAN sonucu (mg KOH/g)
New oil reference value
Trend assessment

Accreditation

EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.

Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.

Scope and authorisations

Related Regulations

Fuel and LPG market technical regulations (EPDK)
EU 2009/30/EC (fuel quality directive)
Communiqués on the placing of lubricating oils on the market

Petroleum, Fuel and Oil Analysis — What Does This Testing Field Cover?

The section below describes the field that the TAN test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.

Petroleum, fuel and oil analysis determines whether a fluid meets its specification and how it behaves in use. Standards in this field consist largely of ASTM and EN publications, with a separate method defined for each parameter.

What distinguishes this family is that product specifications are written as PARAMETER LISTS. Specifications such as EN 590 (diesel), EN 228 (petrol), EN 14214 (biodiesel) and ISO 8217 (marine fuels) state for each parameter both the limit and the method by which that limit is to be measured. If the method changes the result may change too; the specification therefore binds the method as well, and the use of an "equivalent method" is possible only where the specification allows it.

On the fuel side, parameters describe three different properties of the product. Physical properties (density, viscosity, distillation curve, pour point, cloud point) determine pumpability and cold weather behaviour. Combustion properties (cetane number, octane number, calorific value) indicate performance in the engine. Contaminant and stability parameters (sulphur, water, sediment, oxidation stability, copper strip corrosion) affect both emissions and storage life.

Oil analysis is carried out for two different purposes and the two must not be confused. Analysis of NEW oil verifies the conformity of the product to its specification: viscosity index, additive content, flash point. Analysis of USED oil, by contrast, is done to read the condition of the machine — elemental analysis shows wear metals (iron, copper, chromium, aluminium), water and fuel contamination point to leaks, and oxidation and acid number determine the remaining life of the oil.

Used oil analysis is therefore a PREDICTIVE MAINTENANCE tool. The trend of samples taken at regular intervals is followed; it is the trend rather than a single result that is meaningful. Iron levels climbing over the course of months allow intervention before a failure occurs.

Marine fuels are the most active sub-body of the field. The global tightening of sulphur limits has brought new blended fuels onto the market; for these fuels stability, compatibility (whether two fuels form deposits when mixed) and catalytic fines content have become critical parameters.

Sampling is part of the result in this family too. A sample taken from the bottom of a tank shows different water and sediment content from one taken from the upper level; in commercial deliveries the sampling point and method are set by contract.

Method groups in this field

Physical properties
Density (oscillating U-tube and hydrometer), kinematic viscosity, distillation, pour and cloud point, flash point.
Combustion properties
Cetane number and cetane index, research and motor octane number, calorific value.
Sulphur and elements
Sulphur by UV fluorescence and XRF; elemental analysis and additive content by ICP.
Stability and corrosion
Oxidation stability, copper strip corrosion, water and sediment, filter blocking tendency.
Composition analysis
Boiling range distribution by gas chromatography, hydrocarbon types (FIA), benzene and aromatics content, fatty acid methyl ester content.
Used oil
Wear metals, contamination (water, fuel, soot), oxidation, acid and base number, change in viscosity.

Commonly confused in this field

The specification binds the method as well; a result measured by a different method may not be accepted for specification conformity.
A single result on used oil is not meaningful; the decision is made on the trend.
The sampling point determines the result; the tank bottom and the upper level show different water and sediment.
The cetane index is a calculated value and is not the same thing as a measured cetane number.
Fuels blended with biodiesel behave differently in terms of storage life and microbial growth; classical diesel parameters are not sufficient.
Mixing marine fuels from different sources can cause deposits; compatibility is assessed separately.

Which decisions these results support

Conformity of a fuel lot to specification and commercial delivery
Predictive maintenance decisions based on used oil analysis
Determining parameters for customs and tax classification
Quality verification after storage, blending and transport
Compliance with sulphur limits under emissions legislation

Related Tests

Frequently Asked Questions About TAN

TAN has increased, should we change the oil immediately?

It is not right to decide alone. TAN increase is evaluated together with other parameters (viscosity, oxidation, water, particles). However, a rapid and sustained increase is a strong indicator that the oil is nearing the end of its life.