Weathering steel
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Weathering steel, best-known under the trademark Cor-Ten steel, is a group of steel alloys which were developed to obviate the need for painting, and form a stable rust-like appearance if exposed to the weather for several years.
United States Steel (USS) held the original registered trademark on the name COR-TEN, which has now passed to International Steel Group (now Arcelor-Mittal) with the purchase of USS's heavy steel plate business.[1]
In some areas it may be known without the hyphen as "Corten steel".
The original Cor-Ten received the standard designation A 242 ("Cor-Ten A") from the ASTM International standards group. Newer ASTM grades are A 588 ("Cor-Ten B") and A 606 for thin sheet. All alloys are in common production and use.
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[edit] Properties
The mechanical properties of weathering steels depend on which alloy and how thick the material is. [2] [3] [4]
[edit] ASTM A 588
A 588 has a yield strength of at least 50 ksi (50,000 psi, 345 MPa), and ultimate tensile strength of 70 ksi (480 MPa) for all rolled shapes and plate thicknesses up to 4.0 inches thick. Plates from 4.0 to 5.0 inches have yield strength at least 46 ksi (320 MPa) and ultimate tensile strength at least 67 ksi (460 MPa), and plates from 5.0 to 8.0 inches thick have yield strength at least 42 ksi (290 MPa) and ultimate tensile strength at least 63 ksi (435 MPa).
[edit] ASTM A 242
The older A 242 alloy has a tensile to yield strength of 50 ksi (345 MPa) and ultimate tensile strength of 70 ksi (480 MPa) for light-medium rolled shapes and plates up to 0.75 inch thickness. It has yield strength of 46 ksi (320 MPa) and ultimate strength of 67 ksi (460 MPa) for medium weight rolled shapes and plates from 0.75 to 1.50 inch thick. The thickest rolled sections and plates from 1.50 to 4.0 inches thick have yield strength of 42 ksi (290 MPa) and ultimate strength of 63 ksi (435 MPa).
[edit] Usage
Weathering steel is popularly used in outdoor sculptures, such as in the large Chicago Picasso sculpture, and as exterior facades, for its rustic antique appearance.
It has also been used in bridge and other large structural applications such as the New River Gorge Bridge, the newer span of the Newburgh-Beacon Bridge and the creation of the Australian Centre for Contemporary Art (ACCA).
It is very widely used in marine transportation, in the construction of shipping containers.
[edit] Usage Challenges
The use of weathering steel in construction presents several challenges:
[edit] Weld-area corrosion
Ensuring that weld-points weather at the same rate as the other materials may require special welding techniques or material.
[edit] Trapped water corrosion
It is not a rustproof material. If water is allowed to accumulate in pockets, those areas will experience higher corrosion rates, so provision for drainage must be made.
[edit] Discoloration
Weathering steel's normal surface weathering can lead to rust stains on nearby surfaces.
The U.S. Steel Tower in Pittsburgh, Pennsylvania was constructed by U.S. Steel in part to showcase Cor-Ten steel. The initial weathering of the material resulted in a discoloration of the surrounding city sidewalks, as well as other nearby buildings. A cleanup effort was orchestrated by the corporation once weathering was complete to undo this damage, but the sidewalks still have a decidedly rusty tinge. This problem has been reduced in newer formulations of Cor-Ten steel.
[edit] References
- ^ http://www.uss.com/corp/products/plate.htm, Accessed Sept 21, 2006
- ^ http://www.chapelsteel.com/A588.html, accessed Sept 21, 2006
- ^ http://www.mittalsteel.com/documents/en/Inlandflats/ProductBrochure/weathering.pdf, Accessed December 28, 2006
- ^ Manual of Steel Construction, 8th Edition, Second Revised Printing, American Institute of Steel Construction, Chicago, 1987; chapter 1 page 1-5
[edit] External links
- Report on Performance of Weathering Steel in Highway Bridges from the American Iron and Steel Institute
- Report on Weathering Steel in TxDOT Bridges from the Texas Department of Transportation (4464 KB). Contains recommended details to avoid staining. Note: wrapping of piers was later found not to be cost-effective.
- A Primer on Weathering Steel: a white paper from the National Steel Bridge Alliance
- Corten FAQ from the American Institute of Steel Construction
- Weathering steel at the archINFORM database (Example projects)
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