Special steels such as stainless and weathering provide corrosion protection with qualification. Stainless is durable for many decades in most applications, but is extremely expensive and often ages with an uneven appearance. It is not available in many sizes and shapes and is difficult to weld. Its application tends to be in cases where small quantities make an OEM product superior to one that has no stainless.
Weathering steel, which contains small amounts of copper, develops a natural iron-oxide (rust) patina that is relatively stable once formed. However, because the patina is rust, use of weathering steel tends to be in rural areas where appearance doesn’t matter. Additionally, if the exposure area is damp much of the time or vegetation comes in contact with the steel, performance is severely degraded. Once attractive to designers because it was economical, staining of concrete bases of poles and bridge columns by rust runoff has made weathering steel less appealing.