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Building Pathology: stainless steel

a presentation hosted by A. Sebastian Engineering Investigation Services

Contrary to the perception most people have, stainless steel is not only one material, but rather many specialty steels. There are probably over 100 different stainless steels readily available in the North American market, and many more that can be had if one is willing to go through the trouble of special ordering.
To oversimplify things, steel is an alloy of iron and carbon (steels of various types contain from 0.04 percent to 2.25% carbon); by adding not less 10.5% chromium (by weight) to the basic low carbon steel the properties change drastically: it makes the steel less prone to rust and staining (thus "stain less").

There are three general types of classifications used to identify stainless steels, which ultimately give the name of a particular steel:

Corrosion resisting properties.
The chromium present within the steel structure oxidates and allows the formation of a relatively rough, yet invisible, protective film. This film of corrosion-resisting chromium oxide on the steel surface is self-healing: whenever damaged, be it mechanically or chemically, it will regenerate itself in the presence of oxygen. The corrosion resistance is generally enhanced by an increased chromium content, as well as other alloying elements such as molybdenum and nickel.

An application to be seriously considered: metal roofs...
...such as standing seam roofs, may last well over 100 years without any major need for maintenance, repair, or replacement. Material costs on such project will vary with the size of each project; they may be as low as $1.00 per square foot for stainless steel ( about the same as for copper). Coastal applications where the salt air environment may void the traditional roof warranty are key target areas

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