• Easily used by ships maintenance staff right out of the box

  • Instant indication of condition for motor bearings, gears, compressors, slewing rings, hoists, winches...

  • Plan maintenance and have the spares available on time. Minimise off-hire and demurrage.
Quick Contact
CAPTCHA
This question is for testing whether you are a human visitor and to prevent automated spam submissions.
Image CAPTCHA
Enter the characters shown in the image.

AN Testing Equipment

AN is one of two common Neutralisation Numbers. It is performed for purposes of determining the amount of acidic constituents in an oil, expressed as a concentration.

Oil on bearing

A few grams of oil are diluted with an appropriate solvent and the subsequent mixture titrated with an alkaline reagent, potassium hydroxide (KOH). The resulting answer at the completion of the titration is called the “Acid Number”. The history of this test includes a number of changes in the method, some of them ad hoc, such that the term, TAN (Total Acid Number), is being phased out. The original method allowed for Strong Acid Number and Total Acid Number - and Weak Acid Number, by inference, if one subtracted Strong from Total. None of these is commonly separated anymore, thus the test simply became “Acid Number”, and it is ‘total’.

On-Site: A titration test suitable for Strong Acid Number, typically not very user friendly Including the chemical test from Parker Kittiwake). However new portable IR device (FTIR3) is now available and acurately mirrors ASTM methodology in a format suitable for use in the field.  These types of devices have been around for a while but true ASTM replicability is an industry first!

Off-Site: Auto-titrators comprise the predominant method in use

A rather new one-step procedure that involves use of FTIR and new chemistries is now an approved ASTM method
Any of these methods should prove adequate for in-service analysis needs.

Reporting Units: Lube oil acid number is reported as milligrams of KOH/gram of oil. The most referenced method is ASTM D664. NOTE: It is imperative to have a New Lube baseline as additives can impart AN componentry to an oil.

Failure due to acidic constituents in oil

Above: Failure due to acidic constituents in oil

General information regarding AN:

Lube oil acid number can indicate these possibilities, among others:

  • Oxidation (best if correlated with VIS)
  • Corrosive tendency of the lubricant (may need to know strong acid number to glean better corroboration)
  • Depletion of BN (Base Number, formerly TBN)


Lube oil acid number does not usually allow one to distinguish between ‘strong’ and ‘weak’ acids, but it is possible to determine the difference when it is deemed important to do so. In such case a special section of the D664 method would have to be strictly followed.

On & Off-line Lube Oil

Latest News

Parker Kittiwake Launches New CAT Fines Test Kit
Test kit detects catalytic fines to prevent irreparable damage to fuel pumps, injectors, piston ring... Read More...
Switching Fuel Oil and the Risk of Loss of Propulsion
Nearly nine months have passed since the 0.1% sulphur limit for marine fuels in designated Emissions... Read More...
Measuring Ferrous Wear: the FWM vs. the Analex fdMplus
When it comes to detecting and analysing machine wear, testing for ferrous density – the prese... Read More...