IP 163: Petroleum products - Determination of sulfated ash in lubricating oils and additives

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  • Method adopted/last revised: 2012
  • Method reapproved: None
  • REF/ISBN: IP163-2936207
  • Status: Current
  • First printed in STM books: January 2012


This International Standard describes a procedure for the determination of the mass percentage of sulfated ash from unused lubricating oils containing additives and from additive concentrates used in compounding. These additives usually contain one or more of the following metals: barium, calcium, magnesium, zinc, potassium, sodium and tin. The elements sulfur, phosphorus and chlorine can also be present in combined form.

Application of this procedure to sulfated ash levels below 0,02 % (m/m) is restricted to oils containing ashless additives. The lower limit of applicability of the procedure is 0,005 % (m/m) sulfated ash.

NOTE 1 For the purposes of this International Standard, the terms "% (m/m)" and "% (V/V)" are used to represent the mass fraction and volume fraction of a material, respectively.

This International Standard is not intended for the analysis of used engine oils containing lead, nor is it recommended for the analysis of non-additive lubricating oils, for which ISO 6245 [1] is suitable.

NOTE 2 There is evidence that magnesium does not react in the same manner as alkali metals in this procedure. If magnesium additives are present, it is advisable to interpret the data with caution.

NOTE 3 There is evidence that samples containing molybdenum can give low results, since molybdenum compounds are not fully recovered at the temperature of ashing.

The sulfated ash may be used to indicate the concentration of known metal-containing additives in new lubricating oils. When phosphorus is absent, barium, calcium, magnesium, sodium and potassium are converted to their sulfates, and tin (IV) and zinc to their oxides.

NOTE 4 Since zinc sulfate slowly decomposes to its oxide at the ignition temperature specified in the procedure, samples containing zinc may give variable results unless the zinc sulfate is completely converted to the oxide.

Sulfur and chlorine do not interfere, but when phosphorus is present with metals, it remains partially or wholly in the sulfated ash as metal phosphates.

NOTE 5 Fatty acid methyl esters (FAME) conforming to EN 14213 [2] and EN 14214 [3], when tested using this International Standard, were shown to meet its precision.

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