SAE ARP5991

The test method describes the procedure for the direct determination of water concentration in polyol ester and diester based aerospace lubricants by the commercially available automated coulometric Karl Fischer titration instrument. The method was validated to cover the water concentration range of 150 to 3500 \gmg/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. Knowledge of the water concentration in polyol and diester aerospace lubricants is required since the presence of excess amounts of water can lead to hydrolysis of the lubricant, resulting in corrosion and wear of the lubricated components and degradation of the lubricant. Significant variability observed in inter-laboratory Karl Fischer test results for these lubricants highlighted the need for a standardized Karl Fischer test procedure, specifically suited for these lubricants.