Interpreting Oil Demulsibility Tests

Noria Corporation

"How do you interpret the results of DIN ISO 6614 demulsibility for turbine oils? I'm checking a data sheet of a proposed lubricant's separation power of water and oil, and the test yields a value of less than 30. Is this a good result for the test?"

The ability for water and oil to separate, also known as demulsibility, is an important factor in many industrial oils. The effects of water in oil can be very detrimental to machine surfaces and can greatly reduce machine life. This oil property must be closely monitored, especially in areas where water ingression is common (steam turbines, paper machines, etc.).

There are three states of water in oil: dissolved, free and emulsified. Dissolved water occurs when the molecules are dispersed one by one throughout the oil. As the amount of water in the oil increases, you begin to see emulsions, or water that is suspended in the oil, and then free water. Free water is the water that separates and settles out of the oil. It is typically found in the bottom of the sump or reservoir.

When testing for demulsibility, specific amounts of oil and water are mixed. The resulting solution is then left to separate. The results are reported in the following format: X/X/X (X). This correlates to the amount of oil/water/emulsion and time (in minutes) to reach that level of separation. The best results would be 40/40/0, with a lower number in parenthesis indicating quicker full separation. This result shows that the original 40 milliliters (ml) of oil fully separated from the 40 ml of water. As fluid ages, there tends to be a difference in these values, particularly in oils that have been contaminated with water.

Conversely, 0/0/80 would be the worst possible result. In this case, the oil and water never separate, and what is left is known as a stable emulsion. Of all states of water in oil, emulsified water is considered the most destructive. As oil flows through the system, the emulsified water flows with it and can cause increased machine damage through corrosion, impaired load-carrying capability and a long list of other issues.

A value of less than 30 means that the measured separation occurred in less than 30 minutes. Provided that the oil and water separated completely, the oil's demulsibility properties are likely still intact. The best way to know whether the results for used oil are satisfactory is to start with a good baseline. As new oils are delivered, they should be subjected to these types of tests to establish a baseline for comparison.

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