Exhaust boiler inlet expansion joint

Then doesn’t the expansion joint used for external insulation come with a protective cover?

I’ve never seen insulation on the expansion joints of waste heat boilers

1. The components of the flue gas in waste heat boilers play a key role in causing corrosion of metal U-shaped bellows. For example, the flue gas from catalytic cracking units in the oil refining industry contains elements such as sulfur and nitrogen, which can condense into dilute solutions of sulfuric acid and nitric acid at low temperatures, thereby causing corrosion and damage to the metal. 2. Therefore, the issue raised by the original poster involves several aspects: 2.1. Whether the material chosen for the bellows can resist corrosion; 2.2. The high-temperature performance of the material used for the bellows; 2.3. The arrangement of the bellows, whether vertically or horizontally; 2.4. The corrosiveness of the medium; 2.5. Ambient temperature and wind speed; 2.6. The use of internal guide tubes and insulation materials. 3. Since these various factors have an impact, here are some examples: 3.1. Assuming the medium is corrosive, generally speaking, as the temperature decreases, corrosivity increases. At lower temperatures, acidic substances tend to condense and accumulate at the bottom of the horizontally arranged U-shaped sections. Therefore, it is necessary to prevent the metal of the bellows from dropping below the acid dew point, and insulation materials should not be used on the guide tubes inside the expansion joint. 3.2. For a medium temperature of 600°C, austenitic stainless steel or higher-grade alloys should suffice in terms of strength. However, it is advisable to consult the designer regarding the design temperature of the bellows. Even if external insulation is used to prevent the metal temperature from dropping too low, an appropriate thickness of protective layer should be selected to ensure that the metal temperature does not exceed the design temperature. 4. Regarding the protection measures proposed by the original poster for the expansion joint, it should be noted that protection applies only to the bellows portion of the expansion joint, not to the entire expansion joint. 5. If the temperature of the medium passing through the bellows is 600°C, it is more appropriate to install a protective cover against wind, rain, and snow rather than applying external insulation