Due to the high cost and the environmental problems that changing the oil in turbines entails, in recent years there has been an increase in the interest in monitoring the in-service conditions of the oil of this equipment.
Turbine oil is generally subjected to conditions of high temperatures and pressures, so it must maintain good properties to ensure the continuous functioning of the turbine:
1. Appropriate viscosity. This depends on the turbine type, if they are small groups with ring bearings, large turbines or marine turbines with gear reducers.
2. High water separation capacity. Good demulsibility. In this type of turbine it is common for an emulsion of water in oil to form. The presence of water may be due to condensation, leaks, etc. and the oil has to be separated from the water quickly.
3. Non corrosive and prevents rust formation. Both effects occur on metal components, but it is advisable to differentiate them. Corrosion is a chemical reaction caused by the oxidation products present in the oil that may be corrosive to certain metals. Rusting is a reaction caused by the presence of water and air on iron and steel.
4. Stability against oxidation. Oils oxidise when subjected to high temperatures or when in contact with the air, giving rise to the formation of acids and oxidation compounds. At the same time, they may be corrosive and encourage the formation of deposits, giving rise to the valves and circuits, which causes the equipment to malfunction.
5. Resistance to foaming. Foam alters the properties of the lubricants and favours their oxidation, due to the continuous contact with air.
6. High air separation capacity. Deaeration. In this type of oil it is common for air to be retained and damage the pumps and bearings. It is important to eliminate the air from the oil quickly and for the design of the system to prevent the formation of oil/air emulsions.
7. Stability in long-term storage. Taking into account the long life of these oils, they must be stable and maintain their properties for long periods of time.