Determination of Demulsibility of Petroleum Products

Overview

Petroleum products such as turbine oil and hydraulic oil, as well as synthetic fluids, are widely applied in steam turbines and hydraulic power systems. During equipment operation, water vapor inevitably intrudes into the oil system and forms an oil-water emulsion under circulating agitation. The demulsibility (water separability) of oil refers to the capacity of oil and water to separate from each other after contact. Poor demulsibility will keep the emulsified state for a long time, resulting in reduced oil film strength, corrosion of metal components, hydrolysis failure of additives, aggravated equipment wear, and even unit shutdown in severe cases.

Test Purpose

The demulsibility of oil products is evaluated by measuring the separation time of the emulsion layer after mixing petroleum products with water, so as to judge the quality of new oil and the deterioration state of in-service oil. The test is conducted in accordance with GB/T 7305-2003 Determination of Water Separability of Petroleum Oils and Synthetic Fluids and GB/T 7605-2008 Determination of Demulsibility of In-Service Turbine Oils. The SH122 Petroleum Demulsibility Tester is designed and manufactured in full compliance with the two national standards, and can complete the detection of oil demulsibility.

Test Sample

Turbine oil / petroleum synthetic fluid to be tested

Test Instruments

1. SH122 Petroleum Demulsibility Tester
2. Matched glass graduated cylinders, distilled water (1% sodium chloride solution or synthetic seawater is applicable for special marine oils)
3. Auxiliary consumables such as cleaning reagents

Operating Procedures

1. Before powering on the instrument, add pure water to the water bath to the specified liquid level, complete circuit connection, reliably ground the instrument, and confirm the equipment is in normal condition.
2. Add 40 mL of test water and 40 mL of oil sample successively into a clean glass graduated cylinder with no water droplets adhering to the inner wall, making the total liquid level reach the 80 mL graduation mark. Place the cylinder in the constant temperature bath, and let it stand at 54℃±1℃ or 82℃±1℃ to ensure the temperature of the oil-water sample inside the cylinder is consistent with the bath temperature. The maximum constant temperature duration shall not exceed 30 minutes.
3. Set test parameters on the touch screen interface: test temperature and stirring time (the standard stirring time is set to 5 minutes), then confirm and save the parameters.
4. Click the start button on the measurement interface. The instrument will automatically lower the stirring paddle to mix oil and water. After stirring, the paddle will rise automatically, and the timer will start simultaneously to observe the oil-water separation process.
5. Observe the changes of the oil layer, water layer and emulsion layer in the cylinder in real time. When the volume of the emulsion layer decreases to ≤3 mL, click to end the test and record the separation time, which is the demulsification time of the sample. If the emulsion layer is still more than 3 mL after 30 minutes of standing, record the actual volumes of the oil layer, water layer and emulsion layer as the test result.
6. After the test, the instrument will automatically store the test data, and historical records can be retrieved at any time. The next group of samples can be tested directly without shutting down the instrument.

Data Analysis and Result Evaluation

In accordance with GB/T 7305-2003 and GB/T 7605-2008, stratification is observed after 40 mL of oil sample and 40 mL of water are stirred for 5 minutes to form an emulsion:

1. Excellent performance: Separation time ≤15 min; the emulsion layer quickly reduces to ≤3 mL; the oil layer is bright and transparent, the water layer is clear, with only a very thin transition emulsion layer. The oil has good demulsibility and can continue to be used in the unit.
2. Critically qualified: Separation time 15~30 min, and the emulsion layer is just ≤3 mL at 30 min; the oil layer is slightly turbid, with a small amount of suspended oil droplets in the water layer. The oil performance is degraded, so the detection frequency should be increased to track water ingress and aging conditions.
3. Unqualified (oil deterioration): After standing for 30 minutes, the emulsion layer is >3 mL. Record the actual volumes of the oil layer, water layer and emulsion layer. The oil-water interface is blurred, and a large amount of oil phase is suspended in water, indicating oil oxidation, additive loss or impurity contamination. It is recommended to evaluate oil filtration and purification treatment. If the retest still fails to meet the standard, replace the oil to avoid risks such as bearing corrosion, oil film failure and unit shutdown.

Note

The test temperature for ordinary turbine oil is 54℃±1℃, while 82℃±1℃ is selected for high-viscosity oils. When measuring the initial sample at room temperature, the total liquid will expand by 2-3 mL at 82℃. Be sure to correct the cylinder reading to ensure that the total volume of oil, water and emulsion layer does not exceed 80 mL, so as to guarantee accurate judgment.