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Stress corrosion of metals in gas occurs when three key conditions are simultaneously met: the material itself, stress, and the corrosive environment. The specific causes are as follows: 1. Essential conditions: Sensitive materials – Metals are prone to stress corrosion; materials such as pipeline steel and stainless steel tend to crack under certain corrosive conditions. Tensile stress effects: These include the operating stress on pipes/equipment, as well as residual tensile stresses resulting from welding, cold working, etc. Stress concentration accelerates the initiation and propagation of cracks. II. Key corrosive agents in gas: Hydrogen sulfide (H₂S): It is the main corrosive component; when it dissolves in condensed water, it releases hydrogen atoms that penetrate into the metal, causing hydrogen embrittlement and sulfide stress corrosion, which in turn lead to brittle fracture. Carbon dioxide (CO₂): When dissolved in water, it forms a weak acid; together with H₂S, it creates an electrochemical corrosion system of H₂S-CO₂-H₂O, which accelerates the anodic dissolution of the metal surface and promotes crack propagation. Impurities such as chloride ions: Chloride ions present in gas can destroy the passivation layer on the metal surface; the locally exposed active metal forms microcells, significantly increasing the risk of stress corrosion. Condensate water: The water vapor in gas cools down and precipitates to form a liquid film, which allows corrosive gases to dissolve and create an electrolyte solution; this liquid film serves as a necessary medium for the occurrence of stress corrosion electrochemical reactions.