What are the methods for preventing corrosion in heat exchanger tube bundles?

Heat exchangers are important equipment in chemical production, accounting for 40% of the total weight of process equipment. Corrosion prevention methods: 1. Corrosion-resistant materials: Use materials such as stainless steel, titanium, and aluminum brass. 2. Electrochemical protection: Carbon steel heat exchangers are inexpensive but have poor corrosion resistance. For large heat exchangers, external current cathodic protection is generally used, while for smaller ones, sacrificial anode cathodic protection is more common; these methods can help reduce the corrosion of heat exchangers. 3. Ni-P electroless plating, coating: The heat exchanger is subjected to overall electroless plating to form a nickel-phosphorus coating, which acts as a cathodic coating and helps to mechanically isolate corrosive agents. The coating provides limited protection and is prone to peeling during maintenance. 4. Aluminum infiltration: Infiltrating aluminum elements into the working surface layer, using methods such as the powder method, gas phase method, and slurry method, can enhance the resistance of steels, non-ferrous metals, and alloys to high-temperature oxidation and gas corrosion; they also exhibit good corrosion resistance in environments exposed to air, H2S, CO2, and seawater. Aluminum-chromium codoping, aluminum-silicon codoping, and aluminum-chromium-silicon codoping, all based on aluminizing, are widely used. 5. Zinc coating: It is one of the most economical and common corrosion prevention methods. The zinc infiltration process operates at a relatively low temperature, around 400–500°C; as a result, the heat exchanger is less likely to deform. The layer formed through this process is uniform and does not tend to peel off. Acting as an anodic protection layer, the zinc infiltration layer provides better protection, thereby significantly extending the service life of the equipment.

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To improve heat transfer efficiency, corrosion allowance is generally not considered for the heat exchange tubes in the tube bundle; therefore, it is very important to protect these tubes from corrosion as they are key components. First is material selection; in addition to theory, practical experience in real-world applications is also very important. The second is processing and manufacturing, on-site installation, as well as operation and maintenance. Thirdly, under abnormal operating conditions such as emergency shutdowns or maintenance, it is necessary to protect the equipment in accordance with the established procedures. The selection of conventional dielectric metal materials is already well-established; in particularly demanding conditions, non-metallic solutions can be used, such as rubber lining, aluminum spraying, graphite tubes, fluoroplastics, and so on. The best fit is the best.

Depending on the operating conditions of the heat exchanger, they generally include coolers for gasoline, condensers, gas heaters, oil coolers for large compressors, and air-cooled oil-gas exchangers. Corrosion protection for the tube bundle can be applied when the medium temperature remains below 180 degrees Celsius over an extended period. However, there are some usage conditions that require special attention; for example, caution must be exercised when the medium is acidic or alkaline.