Outdoor applications are subject to the effects of weather, air pollution and in winter, de-icing salt.  Under certain environmental conditions, even stainless steel can corrode, so it is important to choose the right grade of material.

In rural areas or towns where industrial emissions are low, standard autenitic grades such as EN 1.4301 and EN 1.4307 have proved themselves to be an excellent choice.  In areas subject to greater air pollution from industrial emissions, molybednum alloy stainlss steels such as EN 1.4401, EN 1.4404 and EN 1.4571 can be considered. However, where the environmental conditions are classed as aggressive, for example in coastal areas that also suffer from industrial air pollution, or where higher temperatures of humidity are a problem, higher-alloy steels are recommended.

In the structural design, too, it is important to avoid the possibility of corrosion. In particular, with components subject to weathering, seams should be fully welded to prevent dirt collecting in gaps and having a corrosive impact. When different metals are used, measures should be taken to avoid galvanic corrosion. 

For components of stainless steel many different surface finishes are available, from factory-finished hot or cold-roolled to ground, brushed and polished, as well as patterned designs. All of these finishes have an invisible oxide layer, just a few atoms thick, on the surface of the stainless steel.  Each time this passive layer, as it is known, is damaged, it reforms under the influence of oxygen in the air or in the water, which means there is no need to add any additional corrosion protection, such as surface coating. 

[text from "Public Spaces, stainless steel in the urban environment", by Euro Inox]