Standard test methods for TAN assessment and modifications thereof

摘要

Present market trends require lubricants to function under demanding conditions for extendedrnperiods. To avoid damage to the equipment or unscheduled maintenance calls, monitoring of inservicernlubricants is essential. Measurable consequences of lubricant degradation are, forrnexample, viscosity increase, discoloration, sludge and acid formation. The latter is quantitativelyrnassessed by titration and reported as Total Acid Number (TAN in mg KOH/g oil). The TAN isrnindicative of the degree of oxidation and hydrolysis of the lubricant in use, warning limits forrnwhich have been stipulated in industry standards such as ASTM D 4378. Lubricant acidity levelsrnabove these limits trigger end-users to change the oil before damage to the installation can takernplace.rnThe TAN is also a quality indicator employed in many bench tests to assess the robustness of arnfinished fluid against aging and acid formation. Commonly employed methods to assess thernTAN of oils are described in ASTM D 974 and ASTM D 664. Several bench tests, such ASTM Drn2619 and IP 280, require the measurements of TAN of aqueous phases. In this paper, limitationsrnof these TAN methods are discussed and modifications are proposed. The focus is onrnrepeatability by automation and the use of commercially available, low toxic aqueous calibrationrnfluids, which do not compromise accuracy.