It is a steel that contains copper. This improves the adherence of the rust
to the surface. This provides some corrosion resistance. Applications need
to be controled. Don't use it where it will get rubbed, such as a hand rail.
Don't use it in a buried or partially buried application. To work well it
needs to be able to drain and dry. The splash zone in marine use ought to be
terrible for this material.
Go to Rautaruukki Steel's web site at http://www.ruukki.com /
Then click on Products and Services, and on the left click on Brochures
and Publications, and under Hot Rolled Strip and Plate products, click
on Weathering Structural steels. This will download a big Acrobat file
(1.86 Mb). See Table 4 for compositions (Cu-Cr-Ni).
Be carefull if specifying weathering steels, they are excellent in the right
application but some applications are not suitable.
You are correct, design must be done carefully, and sea coasts are
not suitable places for conventional weathering steels. (Recently the
Japanese have made some 3% Ni seacost weathering steels though).
For older US experience on bridges, see the FHWA
TECHNICAL ADVISORY : UNCOATED WEATHERING STEEL IN STRUCTURES
T 5140.22, October 3, 1989
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