Use and preparation of A588 weathering steel uncoated and coated

Weathering steel is a class of alloy steels that have been developed to form a stable, corrosion-resistant surface after years of exposure to the weather, potentially eliminating the need for painting in many environments. The United States Steel Corporation (USS) holds a registered trademark name COR-TEN, which refers to two remarkable properties of this type of steel: cor rosion and 10 Dassler strength. The original COR-TEN received the standard designation A242 (COR-TEN A) from ASTM International. Newer ASTM grades are A588 (COR-TEN B) and A606 (for thin sheet). All alloys can be produced and used together.

Weather resistance refers to the chemical composition of these steels, which give them a higher resistance to atmospheric corrosion than other steels. This is because steel develops a protective rusty patina on its surface when exposed to the weather. The corrosion inhibition effect of the protective layer is produced by the distribution and concentration of alloying elements in the alloy
. When subjected to the weather, a layer is formed that protects the surface. In other words, the steel is required to rust in order to form a protective layer.

Using weathering steel in construction presents several challenges. Special welding techniques or materials may be required to ensure that welds are as weather resistant as other materials. Weathering steel itself is not rustproof. If water accumulates in pockets or if the steel is kept wet all the time, these areas will have a higher corrosion rate, so provision must be made to drain or dry out. Weathering steel is sensitive to humid subtropical climates, in which case the protective patina may not be stable and will continue to corrode instead.

Weathering steel does not perform well in areas that experience significant chloride exposure. The normal surface weathering of weathering steel can also cause rust on nearby surfaces. For example, the U.S. Steel Tower in Pittsburgh, Pennsylvania, part of America's Built Steel showcases COR-TEN steel. The initial weathering of the material causes discoloration of surrounding city sidewalks and other nearby buildings, known as "seepage" or "runoff."

The rate at which certain weathering steels develop the desired patina is largely influenced by atmospheric pollutants that catalyze corrosion. While the process is usually done successfully in large urban centers, in more rural environments the rate of weathering is much slower.

As mentioned earlier, weathering steels, in the right environment, will form an adherent protective rust "spot" that inhibits further corrosion. The corrosion rate of weathering steel is so low that bridges made of unpainted weathering steel can achieve a design life of 120 years with minimal maintenance. Therefore, the use of detailed weathering steel bridges in the appropriate environment can provide a very low maintenance and economical solution.