Guide to weathering steel

Weathering steel definition: steels that are chemically formulated to develop a protective patina layer – rust-like in appearance – that eliminates the need for paint. The dense oxide patina layer of weathered steel seals it off from the atmosphere. If a weathered steel panel is scratched, its patina will self-heal. The weathered steel is only not protected against further corrosion: it also delivers a unique finish that is an aesthetically pleasing – a warm, dark-brown, textured appearance that needs low or no maintenance.

Once it’s exposed to alternating wet and dry conditions, weathering steel begins to rust in the same fashion as non-weathering steel. However, as time passes, the rust layer transforms into a patina layer, and its color changes from a fresh, newly developed orange-brown to a light or dark brown.

The speed of change and the final color of a weather-resistant steel sheet are dependent on the atmospheric conditions of a site and the level of pollution. Sulfur-dense atmospheres will speed up the oxidation process and result in a darker patina. Frequent cycles of wet and dry conditions will also speed up oxidation. The entire oxidation process for this corrosion-resistant steel usually takes between 2–6 years.

Weathering steel’s patina process has no effect on the steel’s mechanical properties, including its strength. As a result, structures made from SSAB Weathering steel require low- to no-maintenance for as long as the structure stands. Weathering steel from SSAB is strong, reliable, and guaranteed to last, as will its vivid natural appearance.