:::::: Total Acid Number

Total Acid Number (TAN)

This test will generally only be carried out on Premium mineral oils from main engine crankcase systems. The TAN is a measurements of the total acids present in the oil. In turbine oils these derive from oxidation (weak acids), in diesel engine oils acidic products from fuel combustion may also be present (strong acids). The value is measured in units of mgKOH/g. The corrective action limit is +0.5 mgKOH/g of the new oil value in the premium mineral oils.

Corrective actions :

The acid value of premium mineral oils for slow speed crosshead engines can be controlled as below.

Correct leaking pistons or lod glands.
Discontinue manual addition of cylinder oil drainings or other slop oils to the system.
Water wash the oil charge.

If the oil TAN has not dropped the O.K. range after above action, the following action is required or change to alkaline system oil.
(1) On engines with a small oil charge, change the oil.
(2) On engines with a large oil charge, replace sufficient oil to restore TAN to below the maximum value.