weathering steel Restrictions

The hygroscopic nature of salt adversely affects the 'patina' as it maintains a continuously damp environment on the metal surface. Consequently, as a general rule, unprotected weathering steel should not be used within 2km of the coastline

The texture of weathering steel is influenced by the orientation of the structure and the degree of shelter it provides. Surfaces facing south and west, and those subject to frequent wet and dry cycles, develop a smoother fine-grained texture. Sheltered structures, and surfaces facing north and east (slower drying), tend to develop a coarse granular texture.

Concrete, stone and unglazed brick may suffer from oxide staining when in contact with weathering steel. Connections to dissimilar materials, such as zinc or cadmium plated bolts, should be avoided.

It is possible to paint weather-resistant steel. The requirements of such a paint system do not differ from those required for normal grades of steel. One significant advantage that occurs when doing this (as is common in containerised storage) is that damage to the paint does not result in under-creep corrosion to the surrounding painted area.

Weathering steels are high strength, low alloy, weldable structural steels that possess good weather resistance in many atmospheric conditions without the need for protective coatings. They contain up to 2.5% alloying elements, e.g. chromium, copper and nickel. On exposure to air, a protective rust patina forms that adheres to the surface of the steel. This layer causes the rate of corrosion to slow so that after 2-5 years, corrosion almost ceases. Requirement for the formation of the protective corrosion product layer is regular wetting and curing of the surface. Long wet periods may prevent the formation of the protective layer.