Why is it recommended to coat the outer walls of towers, containers, etc., with a temperature-indicating coating when they have a non-metallic lining?

The temperature-indicating coating (thermochromic paint) applied to the outer wall is used primarily to **monitor the temperature of the equipment’s outer surface in real time and in a straightforward manner**, thereby **indirectly assessing the condition of the internal non-metallic linings (such as insulation linings)**. The specific reasons are as follows: 1. **Failure of the monitoring lining**: Once the internal inorganic material lining (such as the heat-insulating and wear-resistant lining) suffers damage such as cracking or peeling, the local heat-insulation effect is reduced, and heat is transferred directly to the metal outer wall, causing the temperature of that part of the outer wall to rise abnormally. Thermochromic paint **changes color significantly** when the temperature exceeds a set threshold (for example, changing from one color to another or the color disappearing), allowing inspectors to quickly detect abnormal hot spots without the need for a thermometer, simply by eye. 2. **Preventing equipment damage and safety accidents**: * **Preventing a decrease in the strength of metal materials**: Excessively high wall temperatures can significantly reduce the strength of the metal materials used in equipment, posing a risk of deformation or even rupture of the equipment. * **Prevent medium leakage or spontaneous combustion**: In the reactors and regenerators of heavy oil catalytic units, the temperature of the internal medium is very high. If the lining is damaged, causing localized overheating of the outer wall, it may lead to leaks or spontaneous combustion of certain materials at high temperatures, resulting in safety accidents. 3. **Achieve efficient inspections**: The temperature-indicating coating acts like a \"thermometer\" that covers the entire outer surface of the equipment, providing **continuous, large-area visualizations of the temperature distribution**. Compared to point temperature measurement, it can locate the problematic area more comprehensively and quickly, thereby greatly improving inspection efficiency and reliability. **In summary: Applying temperature-indicating paint to the outer surface of high-temperature equipment with non-metallic linings is an economical, effective, and intuitive method for online monitoring. By monitoring abnormalities in the outer wall temperature, it provides early warnings of internal lining failure, serving as an important protective measure to ensure the safe, stable, and long-term operation of such equipment. The temperature-indicating coating that plays this crucial monitoring role is precisely the one applied to the outer walls of the reactor and regenerator in the image you provided. .