Discuss the corrosion of equipment and other components caused by petrochemical wastewater systems, its causes, and countermeasures

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1. Corrosion condition: The tanks, vessels, pipes, etc. in the petrochemical wastewater system are severely corroded by sulfur-containing wastewater. Since the wastewater contains large amounts of H2S, NH3, HCN, and CO2, as well as numerous harmful ions such as Cl- and SO42-, along with a large number of bacteria, and the temperature is as high as 70–80°C, some of it also contains phenolic corrosive substances. Therefore, without effective anti-corrosion measures, corrosion of these devices can be quite severe, leading to phenomena such as reduced thickness of carbon steel, local perforations, bubbling, cracking, and stress corrosion cracking in welds, which can result in the premature disposal of the equipment. 2. Analysis of corrosion causes: Different crude oils and production processes result in varying corrosive agents in the wastewater; as a result, the causes and mechanisms of corrosion differ to some extent. Generally speaking, however, the following points apply: ① Corrosive agents such as H2S, NH3, and HCN present in sulfur-containing wastewater cause corrosion due to electrochemical reactions that generate H2S ； ②Hydrogen embrittlement corrosion caused by hydrogen atom penetration ； ③The wastewater contains large amounts of NH3, CN-, and Cl-. The substances formed as a result of their reaction with H2S, namely NH4HS and (NH4)2S, are highly corrosive ； ④Phenolic corrosion agents can damage the coating, exacerbating corrosion. 3. Selection of anti-corrosion materials: Practical applications of anti-corrosion coatings in various units have shown that conventional coatings (ordinary epoxy paint, epoxy coal tar pitch coating, epoxy phenolic paint, polyurethane paint, chlorosulfonated coating, highly chlorinated polyethylene coating, unsaturated polyester fiberglass) fail to meet the required standards; they develop color changes, delamination, and peeling within less than a year. Epoxy glass flake coatings, epoxy furan coatings, epoxy fiberglass, vinyl resins, and coatings have shown excellent performance in practical applications.