SAE ARP5991A

The test method describes the procedure for the direct determination of water concentration in polyol ester and diester based aerospace lubricants by commercially available automated coulometric Karl Fischer titration instruments. The method was validated to cover the water concentration range of 150 to 3500 µg/g. The method may also be suitable for the determination of water concentrations outside this range and for other classes of fluids; however, the precision statement shall not be applicable for such uses. The determination of the water content of polyol ester and diester aerospace lubricants is of importance in assessing the possibility of water corrosion of lubricant system components. Excessive amounts of water in these lubricants may also lead to hydrolysis of the lubricant, resulting in corrosion and wear of lubricated components and degradation of the lubricant properties. This SAE Aerospace Recommended Practice (ARP) has been tailored for determination of the water content in these types of lubricants. Revision A includes: (1) Incorporation of a rationale statement. (2) Removal of specific revision numbers in the reference ASTM standards. (3) Addition of ASTM D1193 reference in Section 2 (Applicable Documents). (4) Inclusion of the use of commercially available water standards for validation of the Karl Fischer apparatus/reagent system. (5) Revision of the repeatability criterion in 8.4. (6) Editorial changes for clarification of the procedure.