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1. Appearance and color: The appearance and color of oil are the most straightforward indicators for assessing its quality. If sediment or turbidity is observed in the oil, or if its color darkens significantly during operation, it is necessary to promptly test parameters such as the acid value and resistivity of the oil. Determine whether the oil is contaminated or has deteriorated. 2. Kinematic viscosity. Viscosity is one of the most important properties of turbine lubricating oil; it plays a crucial role in establishing an oil film between the shaft journals and bearing surfaces, as well as in determining the performance and stability of the bearings. At the same time, viscosity also determines the flow capacity of the oil, as well as its ability to support loads and transfer heat. Therefore, excessive (reduced) viscosity has an adverse effect on the lifespan of rotating components. 3. Flash point: A decrease in the flash point of the oil used to operate steam turbines indicates an increase in the volatile, flammable components present in the oil, thereby increasing the risk of fire. 4. Mechanical impurities and cleanliness: Due to the special nature of lubrication systems, the particle size requirement for turbine lubricants is generally NAS1638 grade 7–8. If the particle size does not meet these standards, it can lead to wear in the turbine system, resulting in serious safety incidents. 5. Acid value: The acid value is a chemical indicator that reflects the degree of degradation of turbine oil. An increased acid value indicates that the turbine oil has degraded and acidic substances have been formed. The higher the acid value, the faster its increase rate. The acidic products formed as a result of oil degradation affect properties such as the demulsification degree, particle size, foam formation, and air release value of the oil to varying degrees. At the same time, oils with a high acid value can cause corrosion to metal components and seals; during operation, the acid value of the oil should be kept below 0.2 mgKOH/g (for turbine oils containing rust inhibitors, this value should be below 0.3 mgKOH/g). 6. Liquid-phase corrosion: The presence of water in the turbine lubricating oil in amounts exceeding the specified limits not only causes rusting on the metal surfaces of the moving parts, but also accelerates the oxidation and deterioration of the lubricating oil. Rust formation occurs in turbine oil when the water content exceeds 0.1%. If water-soluble acids are also present in the oil, corrosion will be more severe. Therefore, rust resistance is an important indicator for turbine oil. 7. Demulsification degree: The demulsification degree is an important performance indicator for controlling turbine oil. When the water content in turbine oil reaches saturation, the presence of surfactants in the oil that can cause emulsification, along with the stirring effect resulting from the oil’s circulation within the system, leads to emulsification of the oil. This not only destroys the oil’s film-forming and extreme-pressure properties and deteriorates its film characteristics, severely affecting its lubricating performance and threatening the safe operation of the turbine, but the water in an emulsified state also accelerates the degradation of the oil and can cause rusting on metal surfaces. 8. Moisture: The presence of water in turbine oil accelerates the aging of the oil and leads to emulsification. It also reacts with the additives present in the oil, causing them to decompose and resulting in corrosion of the equipment. Therefore, the turbine oil should ensure that the moisture level is within acceptable limits. The presence of water may be caused by a leak in the cold oil cooler, moisture from the atmosphere entering the oil tank, or poor sealing of the shaft seal components, which allows steam to enter the oil. 9. Foam properties and air release value: Excessive foam can lead to an accumulation of too much foam inside the tank, which poses a risk to the safe operation of the unit. Firstly, bubbles in the oil accelerate its oxidative degradation. Under high pressure, the bursting of these bubbles affects the lubricating properties of the oil. When bubbles enter the oil pump, it can cause cavitation in the pump. Excessive foam may also disrupt the proper operation of the oil pump, and in some cases, the foam can even overflow from the breather opening at the top of the oil tank. 10. Rotating oxygen bomb: The rotating oxygen bomb can be used to evaluate the antioxidant properties of oils, thereby assessing their service life. If the rotational oxygen index of the oil is low, it indicates that the quality of the oil may deteriorate within a short period of time.