Durability of Building Materials and Components in the Agricultural Environment, Part II: Metal Structures

Metals in agricultural structures are often subjected to adverse environmental conditions resulting in high corrosion rates (up to 200 µm/yr). The different factors enhancing metal corrosion in farm buildings include high humidity and temperature, high concentrations of aggressive gases, acids, and salts (from silage and feed residues, cleaning agents, manure, fertilizers, preservatives), mechanical destruction and bacteria causing microbially induced corrosion. The importance of microbially induced corrosion is not yet clarified and a reduction in corrosion by biofilms on metals has also been reported. Corrosion products found in animal houses are similar to those resulting from classic corrosion mechanisms, which may lead to the conclusion that the fundamental mechanisms of metal corrosion in animal buildings are similar to the classic ones. Different methods to detect, measure and predict corrosion are described. The economic losses by corrosion in agriculture are evaluated. By corrosion prevention, a reasonable amount of expense can be saved. Prevention includes: (1) the choice of corrosion resistant materials such as stainless steel or non-metallic materials; (2) designing against corrosion; (3) control of the aggressive environment; and (4) application of coatings. When protective coatings are used, such as zinc layers and painting systems, surface preparation of the metal is of the utmost importance. Zinc layers should be thick enough (>50 µm), and zinc-coated steel should be protected in areas of extreme aggressiveness, such as fittings at floor level. Reports about the durability of different painting systems in agricultural structures are reviewed. The development of new environmentally friendly products is discussed. Guidelines for maintenance of previously painted steelwork are formulated.