Weathering steel (also known by the trademark COR-TEN steel) is a form of high-strength, low alloy steel originally developed in the 1930's by United States Steel. It is a steel alloy, chemically composed to form a stable rust-like appearance that can resist corrosion and abrasion, by forming a protective surface layer, or patina.
The protective layer’s increased resistance is produced by the alloying elements and their particular distribution and concentration. When subjected to the influence of the weather, the protective surface layer continuously develops and regenerates, allowing the rust to form.
Weathering steel is often used in external sculptures, the most iconic of which is the Angel of the North in Gateshead. It can be used in bridges and other large structural applications, such as the New River Gorge Bridge, and it is becoming an increasingly popular design choice for buildings, often used alongside materials such as glass and terracotta. An example of such a building is the distinctive Broadcasting Tower in Leeds (see top image).
The advantages of weathering steel are that because it is already weathered and ‘rusted’, there are very low maintenance costs, it can be installed easily, and the need for a protective paint system is removed. Studies have found that bridges fabricated from unpainted weathering steel can achieve a design life of 120 years with only nominal maintenance, due to the low corrosion rate.
However, there are several challenges to weathering steel. It is unsuitable for use in marine or coastal environments, and in humid subtropical climates the patina may continue to corrode instead of stabilising into a protective layer. In addition, interface details require careful design as run-off water from wet rusted steel may negatively impact on other materials, such as staining glass. This is a particular problem in the first years after installation.
 Related articles on Designing Buildings Wiki
Featured articles and news
Christiania is an anarchist 'freetown' in Copenhagen where strange and experimental architecture has flourished.
“UK waste data needs improving” say BRE specialists, in this summary of their report into construction waste.
UandI announce new joint venture with US developer to work on office refurbishment projects.
BSRIA give critical response to Theresa May's speech on leaving the EU.
Why buildings crack, how cracks are categorised and what can be done.
Inaugurated last week, the new Elbphilharmonie concert venue; a soaring new addition to Hamburg's skyline.
Summary of a new ICE Transport journal which says improving transport infrastructure is essential to eradicating global poverty.
BRE look at a new government report into the accuracy of heat meters.
Herzog & de Meuron get planning permission for revamp of Chelsea FC football stadium.
UK-GBC green paper proposes more powers for cities on new-build housing.
The Pompidou Centre – not a monument but an event.
Designing Buildings Wiki talks to the founder of the world's first indoor biophilic gym, now open in London.