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Cost Effective Ways to Protection Steel Structures from Environments

Steel corrodes when exposed to myriad conditions including outdoor atmosphere. It is noteworthy that all types of steel including the low alloy type are prone to rust in moist atmosphere. Rusting is an electrochemical process characterized by exchange of electrons. In some cases, the additions of 0.3% copper to carbon steel can reduce the rate of rusting to a greater extent. The elements Cu, P, Cr and Ni have all been shown to improve resistance to atmospheric corrosion. Formation of a dense, tightly adhering rust scale is responsible in lowering the corrosion rate leading to use without protection and can also extend paint life by decreasing the amount of corrosion underneath the paint. The rate of rusting is usually higher in the first year of exposure to atmosphere than in subsequent years, and increase significantly with the degree of pollution and moisture in the air. Alloying elements contribute to a more compact and less porous corrosion product as surface film. Adherent, protective films on these steels seal the surface against further penetration of water, which does not easily wet the oxide surface. Compact surface oxide films develop more rapidly in industrial atmospheres containing SO2, which is probably involved in film formation in presence of moisture by forming sulphurous and sulphuric acids which are very corrosive. This theory was based largely on the observation that the corrosion products formed on steel when exposed to industrial atmosphere were usually rich in sulphates. However, the corrosion rates of weathering steels are not reduced in industrial atmospheres to levels lower than those in non corrosive rural or semi rural atmosphere. Periodic drying is required for the surface film to develop its protective properties.Further the development of improved weather resistant steel & high performance paints/coatings system can protect the steel even in most aggressive environments. Normally the lifetime of the protection system is not the same as the lifetime of the steel structure it protects. The protective system usually required has various lifespan. All Civil structures are designed for specific life spans based on durability as given in Table 1 Table 1: Lifetime of Structure & Durability