How to solve the problem of stress corrosion cracking of weld beads in acid water tanks in oil refining systems?
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How to solve the problem of stress corrosion cracking of weld beads in acid water tanks in oil refining systems? The operating conditions of the acid water tank of the sulfur recovery unit of the refining system of the petrochemical plant are relatively harsh, and its main medium is: The H2S content of the raw water is 1.0~2.8g/L, the NH3 content is 5000ppm/L, and it also contains various media such as CO2, CN-, phenol and oil. The pH value is 10±5, and the temperature of the raw water is 65-70°C. When carbon steel works under such operating conditions, the form of metal corrosion of carbon steel is electrochemical corrosion. It is prone to stress corrosion cracking when the welding joint and the metal base material are subjected to bending force (such as the bending deformation of the steel plate under pressure near the bottom of the column in the tank). At the same time, uniform corrosion occurs on the metal surface. The protection effect of using general anti-corrosion coatings is very unsatisfactory. For example, anti-corrosion coatings using epoxy systems lose their effect within 4 months of use. From the pictures below you can see the weld bead cracks where acid stress corrosion cracking occurred.
Solving the problem of stress corrosion cracking of weld beads in acid water tanks in oil refining systems requires efforts in the following aspects:: 1. * * Material selection * * ： Choose materials that are more resistant to corrosion and stress, such as stainless steel or special corrosion-resistant alloys. These materials, while higher in initial cost, may become economical over the long term due to less maintenance and longer service life. 2. * * Welding quality control * * ： Weld bead stress corrosion cracking problems often begin at the center of stress introduced during the welding process. Therefore, ensure that proper welding procedures and techniques are used to reduce stress in the weld bead. For example, preheating materials, using low-hydrogen welding rods, post-weld heat treatment, etc. 3. * * Anti-corrosion coating * * ： Although you mentioned that using anti-corrosion coatings such as epoxy systems is not ideal, there are still other types of coatings that may be more effective. For example, use polyurethane coatings or ceramic coatings with higher chemical resistance. 4. * * cathodic protection * * ： By applying an electric current, the tank of acidic water becomes the cathode of the circuit, thus stopping the corrosion process. This method is often used to protect steel in corrosive environments. 5. * * Regular inspection and maintenance * * ： Regularly perform non-destructive testing, such as ultrasonic testing, to detect potential cracks or corrosion. By detecting a problem in its early stages, you can prevent it from getting worse by repairing or replacing damaged parts. The above are some possible solutions to solve the problem of stress corrosion cracking of weld beads in acid water tanks in oil refining systems. These options need to be selected and adapted to your specific situation. .