ASTM D4056 Standard Test Method for Estimation of Solubility of Water in Hydrocarbon and Aliphatic Ester Lubricants
4. Summary of Test Method
4.1 Data required are the density, refractive index, and molecular weight of a hydrocarbon. The saponification number is also required for an ester. From these are calculated the carbon distribution for a hydrocarbon, and then the partial solubility parameters. These in turn are used to calculate the volume fraction of water dissolved at 298 K at saturation. This is converted to mole fraction, and adjusted to system temperature. The mole fraction is then converted to solubility by weight. If the system atmosphere is not saturated, the solubility is multiplied by the relative humidity.
5. Significance and Use
5.1 Knowledge of the water content is important in lubrication, as large amounts of water can cause corrosion fatigue in steel bearings, and the complete absence of water can cause metal scuffing.
5.2 High water content has an accelerating effect on oxidation of lubricants, and can also contribute to foaming, especially at high altitude or temperature, or both.
