Characteristics of metal corrosion in marine and industrial atmospheres

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Steel structures in the atmospheric environment are exposed to sunlight, wind and sand, rain and snow, frost and dew, as well as changes in temperature and humidity throughout the year. Oxygen and moisture in the atmosphere are key factors that cause corrosion of outdoor steel structures, leading to electrochemical corrosion. Industrial gases contain substances such as SO2, CO2, NO2, Cl2, H2S, and NH3. Although their concentrations are low, their corrosive effects on steel cannot be ignored; among these, SO2 has the greatest impact, while Cl2 can destroy the passivation layer on the metal surface. When these gases dissolve in water, they become acidic, forming acid rain that corrodes metal structures. The marine atmosphere is characterized by a high content of salts, primarily NaCl. These salt particles settle on metal surfaces; due to their hygroscopic nature and their ability to increase the conductivity of the surface film, coupled with the strong corrosive properties of Cl-, this accelerates the corrosion of the metal surfaces. The closer steel structures are to the coast, the more severe the corrosion becomes, and their corrosion rate is many times higher than that in inland areas.