Characteristics of corrosion in large-scale steel structures and protection methods

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Characteristics of corrosion in large-scale steel structures and protection methods Large-scale steel structures such as bridges, television towers, high-voltage transmission tower foundations, storage tanks, spherical tanks, and offshore platform steel structures are all exposed to marine and industrial atmospheric corrosive environments for extended periods of time. For long-term use without the need for extensive repairs, long-lasting coating protection is the best option; it can last for 20–30 years, results in lower repair costs, and offers significant economic benefits. 1. Corrosion characteristics of steel structures in marine and industrial atmospheres. Steel structures in atmospheric environments are exposed to sunlight, wind and sand, rain and snow, frost, 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 a steel structure is to the coast, the more severe its corrosion becomes, with its corrosion rate being many times higher than that in inland areas. 2. Common protection methods for large-scale steel structures: Steel structures are often treated with zinc or aluminum spraying, or with corrosion-resistant coatings to create a long-lasting anti-corrosion layer; alternatively, they can be coated with specialized heavy-duty anti-corrosion coatings for protection. Metal zinc and aluminum possess excellent resistance to atmospheric corrosion. Zinc or aluminum is sprayed on steel components; zinc and aluminum have a negative potential, and they act as sacrificial anodes to protect the steel, thereby providing effective protection for it. Currently, aluminum spraying coatings are used to prevent corrosion in industrial and marine atmospheres, and their characteristics are as follows: 2.1 Zinc or aluminum spraying – Zinc and aluminum spraying coatings provide a strong bond with the steel substrate, have a long service life, and offer good economic benefits over time. Zinc or aluminum spraying followed by the application of an anti-corrosion coating can **extend the service life of the coating. Both theoretically and in practical applications, zinc or aluminum coatings serve as the best base layer for anti-corrosion coatings. The protective lifespan of a composite coating that combines a metal spray coating with an anti-corrosion coating is longer than the sum of the lifespans of the metal spray coating and the anti-corrosion coating alone, and it is several times longer than the lifespan of a coating applied as a single layer. 2.2 The heavy-duty anti-corrosion long-lasting coating consists of a primer, an intermediate coat, and a topcoat. The epoxy zinc-rich primer + epoxy ferrochrome intermediate coat + acrylic polyurethane long-term protection system offers good cost-effectiveness. Additionally, for the topcoat, fluorocarbon paint or acrylic polysiloxane coatings can be used, both of which offer excellent long-term corrosion resistance.