Mineral Oil Contamination of a Phosphate Ester

We photographed sulfuric acid reacting with the mineral oil that’s contaminating a customer’s sample of phosphate ester. Notice the cloudy swirl reaction in the photo, which will eventually settle as a top layer that we can measure into percent contamination of the sample. This sample happens to be 2% contaminated with mineral oil which is a MONITOR. 3% is ABNORMAL, and 4% is the condemning limit. The sulfuric acid reacts with the mineral oil and ultimately rests at the bottom of the graduated cylinder in its own layer, while the mineral oil rises to the top above the fire-resistant hydraulic fluid. 

This is a very useful test. In a large petrochemical facility, it is not difficult to mistakenly contaminate a fire-resistant phosphate ester hydraulic fluid with one of the many mineral oil lubricants used in the plant. Don’t do it! It will accelerate EHC fluid degradation, reduce the fluid’s fire-resistance, and in certain cases soften seals if they are specifically engineered to work exclusively with phosphate ester fluids. We recommend this test on an annual basis for all phosphate ester fluids.