Thermal oil inspection includes seven key factors due to the various physical properties of thermal oil, also known as heat-conducting fluid, such as viscosity, vapor pressure, boiling range, initial boiling point, flash point, ignition point, and pour point. The viscosity of thermal oil directly impacts heat transfer efficiency, with lower viscosity allowing for faster flow and higher efficiency. The vapor pressure, flash point, and ignition point of thermal oil are factors indicating its volatility and flammability. Oils with lower vapor pressure, higher flash and ignition points are less likely to cause fires. The initial boiling point of thermal oil is related to its safety and operating temperature, with higher boiling points offering greater safety and allowing for higher operating temperatures. The pour point of thermal oil refers to the lowest temperature at which it can flow, making low-pour-point oils suitable for use in cold climates where high-pour-point oils could hinder system startup.

4 Methods to Determine the Properties of Thermal Conductive Oil
Flashpoint generally refers to the low temperature at which thermal oil emits a spark when approaching a flame under specific conditions. Its size indicates the oil's tendency to evaporate and its safety. When the flashpoint is lower, the oil contains lighter fractions with higher volatility and lower safety; when the flashpoint is higher, the oil contains heavier fractions with lower volatility and higher safety. What role does the flashpoint play in safety, and can it lead to combustion or fire?
Famously, combustion is an oxidation reaction in chemistry. Combustion has three essential elements: combustion = fuel + temperature + oxygen. This means that combustible materials will only burn at a certain temperature and in the presence of oxygen, with none of these elements being dispensable.
We learned from thermal oil indicators both domestically and internationally that different thermal oils have varying flash points, ranging from as low as 140 degrees to over 200 degrees. These thermal oils with different flash points, when used in thermal oil heaters, do not ignite. This is primarily because the thermal oil is used in a closed system within the thermal oil heater, which does not allow for the three elements of combustion to be present, thus preventing combustion. If there is a leakage in the system, smoking occurs first, and only when exposed to an open flame would a flash fire occur, even then, it would not ignite. Moreover, the flash points of most thermal oils rise when used in thermal oil heaters, indicating that the flash point is not a critical factor for the discard criteria of thermal oil. As long as it is properly managed, thermal oil will not ignite and will not affect the safety of the thermal oil heater.
2. The acid value represents the total amount of organic and inorganic acids in the thermal oil, which is the total amount of potassium hydroxide consumed per gram of thermal oil. Organic acids are further categorized into low molecular weight organic acids and high molecular weight organic acids. Both low molecular weight organic acids and inorganic acids are corrosive to metals, and corrosion is exacerbated in the presence of water molecules. The majority of the acids in thermal oil are high molecular weight organic acids, which cause minimal corrosion to equipment.
Thermal oil undergoes a coking process during high-temperature operation, involving stages such as induction, adsorption, hardening, and shedding. These processes lead to the formation of a thermal oil residue in the pipeline of a thermal oil furnace, affecting its heat transfer efficiency. Additionally, they isolate the thermal oil from contact with the metal tube walls, preventing the acid from corroding the equipment. Therefore, controlling the acidity of thermal oil is crucial in preventing corrosion of the metal.
3. Viscosity refers to the thickness and fluidity of thermal oil under specified conditions. When the mechanical load and rotational speed are the same, the higher the viscosity of the thermal oil used, the greater the power loss. Since most oils in China are used in the high-temperature heat transfer stage, almost all thermal oils have similar viscosities at high temperatures. Generally, manufacturers consider a thermal oil's viscosity change of ±15% to be a failure. Through analyzing a large amount of thermal oil data, it was found that if the viscosity changes by ±20%, the oil can still be used. Therefore, the size of viscosity has little impact on the use of thermal oil. The key issue is that as viscosity increases, the flow point of the thermal oil also increases. During cooling, asphalt-like or solid phenomena may occur inside the hot oil furnace tubes, causing blockages and preventing the hot oil pump from rotating. This makes it impossible for the hot oil furnace to heat up. Cleaning the hot oil furnace at this point requires a significant amount of manpower and resources to clear the hot oil furnace tubes, and sometimes it can lead to the furnace being scrapped.