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Durability of zinc coating and corrosivity of steel

The corrosion resistance of steel is closely linked to the corrosivity of the environment itself. In this regard, so-called corrosivity categories have been introduced, which make it possible to estimate the service life of the coating and the choice of protection method. As for the protection period of the steel, an important aspect is the corrosion load and the thickness of the zinc coating. According to EN ISO 1461, in a steel structure with a minimum cross section of 6 mm, coating thickness is at least 85 µm. However, in practice, these thicknesses are considerably greater.

Zinc coatings as thin as 200 µm can be obtained already at the design stage of the structure by selecting suitable steel with specific wall thicknesses. Each corrosion category is assigned an annual coating loss expressed in micrometres for each year. Knowing the annual thickness loss of the zinc coating and bearing in mind the durability of the corrosion protection, it is therefore very easy to calculate the minimum thickness of the coating.

Zinc coatings can be used in different corrosivity categories. Details are given in PN-EN ISO 14713. It should be noted that in the case of zinc plating there is a difference in the way the corrosivity of the environment is defined compared to the standard for paint coatings.