Part 1: Architect’s Guide 1 - 53 Insulation materials include rock wool or glass, polyurethane foam and polystyrene foam. The risk of direct temperature transfer between the metal parts in contact with the outside and the inside areas of the wall must be dealt with at the level of the fittings and joints. 6.5 Durability of steel structures This Section covers the durability of steel building components. Sustainability of the material itself, particularly in respect of recycling, is discussed in Section 7 of this document. Damage to a steel construction component arises mainly from two phenomena: fatigue and corrosion. Routine multi-storey buildings covered in this document are not affected by fatigue. This Section is therefore concerned only with the corrosion. It is important to note at the outset that the steel frame buildings do not generally suffer major damage as a result of atmospheric corrosion. Moreover corrosion is not an issue for internal steelwork. Even if, in the absence of adequate protection, structural elements subjected to normal atmospheric conditions may rust on the surface, this phenomenon is rarely the cause of damage to buildings, as long as a few elementary precautions are taken. In contrast, the atmospheric conditions in some regions, such as coastal areas with a saline climate, or where there are industries that give rise to corrosive vapours, may result in steel structures having to be protected and maintained. 6.5.1 The phenomenon of corrosion Corrosion is caused by the formation of metal salts on the surface of the steel component when a metal is combined with other elements. For example, iron corrosion leads to the production of iron oxide. The corrosion process may be: Chemical: through reaction between the metal and a gas phase or liquid. Electrochemical: formation by electric current and oxidation of the anode. Biochemical: by attacking bacteria. Steel corrosion Rust is the result of steel corrosion and is mainly composed of iron oxides and hydroxides, which grow in the presence of moisture and oxygen content in the atmosphere. The oxide layers are generally non-adherent and oxidation spreads steadily. The parts lose weight linearly as a function of time. The corrosion product does not protect the steel.
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