Weathered Steel

Weathered Steel is a unique product that has an aesthetic like no other. Weathering Steel is high-strength, low-alloy steel that under normal atmospheric conditions gives an enhanced resistance to rusting compared with that of other carbon steels.

In the presence of moisture and air, low-alloy steels have a tendency to rust, the rate of which depends on the access of oxygen, moisture and atmospheric contaminants to the metal surface. As the process progresses, the rust layer forms a barrier to the ingress of oxygen, moisture and contaminants, and the rate of rusting slows down.

The rust layers formed on most ordinary structural steels are porous. This porosity leads to the rust detaching from the metal surface after a certain time, causing the corrosion cycle to commence again. Hence, the rusting process repeats over and over without a protective layer remaining on the steel at the end of each process.

With Weathering Steel, the rusting process is initiated in the same way, but the specific alloying elements in the steel produce a stable rust layer that adheres to the base metal and is much less porous. This rust ‘patina’ develops under conditions of alternate wetting and drying to produce a protective barrier that impedes further access of oxygen, moisture, and pollutants. The result is a much lower corrosion rate than would be found on other structural steels. The mechanical properties and rate of weathering are dependent upon which alloys are found in the steel, the concentration of those alloys, and how thick the steel substrate is.

Weathered Steel products are found in a wide variety of applications where a specific aesthetic is desired and corrosion resistance is required. End-use applications well suited for Weathering Steel include bridges, pilings, marine transportation (containers), wall panel applications, sculptures, and other architectural applications.

Using Weathering Steel in construction may present several challenges. Weathering Steel is not rustproof in itself (i.e. if water is allowed to accumulate in pockets, those areas will experience higher corrosion rates). Weathering Steel is sensitive to humid subtropical climates and environments laden with sea salt. In such environments, it is possible that the protective patina may not stabilize but instead continue to corrode. Weathering Steel’s normal surface weathering can also lead to rust stains on nearby surfaces, also known as “bleeding” or “runoff”. Staining can be prevented if the structure can be designed so that water does not drain from the steel onto concrete or other building surfaces where stains would be visible.