Case analysis of on-site repair for sulfuric acid storage tank leaks

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1. Leakage in the sulfuric acid storage tank: A leakage was detected at the weld joint where the top of the 88% sulfuric acid storage tank meets its barrel body in a certain chemical plant (see Figure 1). The sulfuric acid storage tank is made of carbon steel; the length of the leaking weld is approximately 1 meter, and there is also a gap about 10 cm long. Although the liquid level has dropped to one meter, acidic gas can still be clearly seen escaping. 2. Analysis of the causes of leakage: The corrosion at the welds between the top of the sulfuric acid storage tank and its barrel is mainly pitting and crevice corrosion. In conditions of high air humidity, the upper part inside the tank is exposed to a wet SO3 environment, while the exterior of the tank top suffers from corrosion caused by acid rain. Carbon steel can form a passivation film in concentrated sulfuric acid, and dry SO3 will not corrode the welds on the tank top. However, during welding, situations such as unwetted electrodes or a humid environment can cause welding defects such as pores and slag inclusions on the inner and outer surfaces of the weld. These minor defects can lead to an incomplete passivation layer on the surface of the metal material; once this passivation layer is locally damaged, the metal at the site of the damage becomes the anode. The large area of passivation film surrounding it serves as the cathode. This causes the corrosion to progress rapidly inward, forming a corrosion source. 3. On-site repair of sulfuric acid storage tank leaks: Currently, for leaks in sulfuric acid tanks, polymer composite materials are commonly used for rapid on-site repairs. The chemical resistance, adhesion properties, and versatility of polymer composite materials enable them to avoid the drawbacks associated with traditional patch welding. Moreover, they possess advantages that conventional corrosion-resistant materials lack, satisfying the requirements for use in various environments. Compared to traditional methods, the advantage of polymer composite material technology lies in its ability to enable companies to carry out rapid and effective on-site repairs promptly. On one hand, this helps to avoid losses in productivity resulting from prolonged equipment downtime or shutdowns; on the other hand, using this technology for on-site repair of leaking sulfuric acid tanks also reduces safety risks associated with the equipment, ensuring its safe and stable operation ； It effectively avoids various factors such as transportation costs, lifting expenses, and construction safety issues, ensuring personal safety and minimizing corporate losses, thereby saving the company valuable production time. 4. Repair steps for leaks in sulfuric acid storage tanks: (1) Remove surface impurities, loose rust, dirt, and corrosion layers ； (2) Rinse and wipe the leaking area repeatedly with a NaCO3 solution to neutralize any acidic residues on the surface of the metal substrate, and use a pH test strip for testing, so as to keep the substrate surface as neutral as possible ； (3) Then use tools such as sanding belts to grind the leaking area and extend it 10 cm around it to expose the original color of the metal, and clean it thoroughly with alcohol. (4) Blend the EE-121K corrosion inhibitor material in proportion ； (5) Apply the blended EE-121K material to the leak site and knead it repeatedly to ensure full bonding with the metal. (6) Strengthen the surface of the leaking area using EE-121K material mixed with glass fiber cloth ； (7) Wait for the EE-121K material to cure, then use 2211F metal repair material to reinforce the repaired area once again ； (7) After repair, wait for the material to cure (24°C/24 hours; for every 11°C increase in material temperature, the curing time is reduced by half). Case image: