Causes and harms of turbine oil oxidation deterioration
November 25, 2022
Turbine oil belongs to a kind of lubricating oil, which is formulated from Base Oil and additives, and the base oil accounts for the majority. The base oil is mainly divided into two types, synthetic oil and mineral oil. The mineral base oil is refined from petroleum. Most of the turbine oil today is mineral oil. Mineral base oil itself has the functions of lubrication and anti friction. A small amount of additives have been added to modern turbine oil to improve the performance of turbine oil and increase the strength of oil film.
Common causes of turbine oil oxidation deterioration:
1. High temperature: The turbine oil circulates in the lubrication system of the turbine and flows to all parts that need lubrication. In addition to lubrication, the turbine oil also plays a cooling role. The turbine oil flows through high-temperature shafts, gears, bearings, oil pumps and other parts, taking away heat and raising the temperature of the turbine oil. In addition, the surrounding high-temperature air can also raise the oil temperature, and some of it will dissolve into the oil, causing the oil temperature to rise. High temperature will significantly increase the oxidation rate of turbine oil and accelerate the deterioration of turbine oil. The general rule is that after the temperature is higher than 60 ℃, the service life of turbine oil will be halved every 10 ℃ increase. When the temperature is higher than 82 ℃, the oxidation rate has increased significantly. The higher the temperature is, the more severe the oxidation rate is. After oxidation, the color of the turbine oil will become darker, the viscosity will increase, and the acid value will increase, resulting in sludge, colloidal sediment, and insoluble substances. These oxidation products in turn accelerate the deterioration of turbine oil, and also cause corrosion to metals. After the turbine oil deteriorates, it will cause the wear of components in the lubrication system, and the generated acidic substances will also corrode metals. Therefore, the oil quality of the turbine oil should be monitored to check the content of antioxidant additives in the oil and the oxidation stability of the oil, so as to understand the oxidation resistance and oxidation degree of the oil. Through the oil detection, we can know the oil quality, as well as the internal conditions of the machine, find out the wear and failure, and prevent and deal with them as early as possible. 2. Moisture: Water is another main reason for damaging turbine oil. The main source of water is cooling water leakage, as well as steam and condensate. The oil contains a small amount of dissolved water (generally less than 0.01%). With the increase of water content, the turbine oil becomes turbid gradually. In severe cases, the oil is emulsified, the color of the oil turns white, which damages the lubrication of the oil and causes oil oxidation. The turbine oil shall have good demulsibility. The measurement method of demulsibility is ASTM D1401, which can measure the speed of oil and water separation. 3. Oil is polluted: The turbine oil shall be kept clean. The dust and impurities brought in will not only cause wear of components, but also cause oil oxidation. The metal scraps in the oil, such as iron, copper, lead, will catalyze the oxidation of the oil to some extent if they are not filtered out. Avoid mixing other oil into the oil, pay attention to the cleanliness of the oil, pay attention to the filtration and purification of the oil, and keep it well sealed.
Hazards of oxidation products: The oxidation of turbine oil will generate insoluble substances, which will not only accelerate the oxidation of the oil, but also gather into clusters as the oil circulates in the system, forming sludge, blocking the filter element, forming paint film on some parts, and forming a layer of sediment on the metal surface in serious cases, affecting heat dissipation. To optimize the performance of turbine oil (including its oxidation resistance), it is essential to use high-quality turbine oil and do a good job of oil maintenance at the same time - from storage and use, always keep the oil clean, dry (waterproof intrusion), control the oil temperature, do a good job of oil filtration and purification, keep the system running stable, prevent local overheating, and insist on oil detection. The oil supply to the oil ring of the bearing may also be affected by oxidation: the viscosity of the oil increases after oxidation, and the oil sludge adhered to the bearing may affect the normal rotation of the oil ring, resulting in insufficient oil supply to the bearing. It should be noted that we should not blindly add antioxidants to solve the problem of oil oxidation. We should first consult the oil supplier and find out the cause of oil oxidation. First, the antioxidant additives used by users may not be compatible with other components of the oil (base oil, other additives), and may not work, or even affect other aspects of performance. In addition, the amount of additives is not enough. As users, it is difficult to know the exact amount of additives. Moreover, the solubility of base oil to different additives may be different (for example, the solubility of Class I oil and Class II oil to additives is different).
