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At higher process temperatures, the degradation of heat transfer oil can significantly affect system performance and operating costs; therefore, we need to take precautions to prevent such degradation when using heat transfer oil. So, under what circumstances does heat transfer oil degrade? Depending on its quality and inherent properties, heat transfer oil degrades when the temperature rises and the molecular chains within it break. The rate of degradation increases as the temperature rises. For organic heat transfer oils, the degradation rate generally doubles for every 12°C increase in temperature. Under normal operating conditions, the temperature of the heat transfer oil film on the wall of the heating tube should be 50–75°F (30–40°C) higher than the temperature of the oil itself. Close contact between the flame and the heating tube can raise the temperature of the heat transfer oil by several hundred degrees, leading to degradation of the oil. Unreasonable system design or improper operation can also lead to rapid degradation of the heat transfer oil. In some cases, the degradation of heat transfer oil may be considered inevitable. When heat transfer oil degrades, certain degradation products have very low molecular weights and vaporize at process temperatures; these are what are known as \"low-boiling substances\" or \"light components\". Under normal operating conditions, low-boiling substances must be discharged regularly, and new heat transfer oil must be added. If the heat transfer oil degrades to produce more light hydrocarbons, more new oil will need to be added. However, not all degradation products are light hydrocarbons; when degradation occurs, bonds break and certain molecules recombine to form high-molecular-weight components. Until their concentration exceeds the level recommended by the manufacturer, they are all good heat transfer oils. During operation, heat transfer oil heating systems are generally exposed to high temperatures and operate continuously throughout the year. As time goes by, the heat transfer oil inevitably undergoes a series of physical and chemical changes, such as oxidation, thermal cracking, and polycondensation. As it changes, its color deepens accordingly, and its physical and chemical properties deteriorate until it becomes unusable. This not only affects the heat transfer efficiency of the heat transfer oil, but severe coking can also occur, directly threatening the safety of the equipment, production processes, and the entire system. Therefore, when selecting and using heat transfer oil, it is necessary to choose products of high quality, as well as manufacturers with strong technical capabilities who can provide users with technical support such as appropriate processing procedures and operating guidelines. This can effectively extend the service life of the heat transfer oil and reduce the frequency of its replacement due to degradation.