Stainless steel against internal and external atmospheric corrosion
Introduction
Atmospheric corrosion of stainless steel is not a single form of corrosion, but a collective term to denote the corrosion of surfaces in the atmosphere.
It can be indoors or outdoors. Corrosion of stainless steels is most often induced by halides and chlorides due to their abundance in our environment, for example coastal and marine environments.
When stainless steel is exposed to an aggressive atmosphere, it mainly stains. But it can also be attacked by localized corrosion, particularly at high chloride levels. It should be noted that discoloration of stainless steel is not automatically the result of atmospheric corrosion of the stainless steel, i.e. it may be discoloration from foreign dirt or rust that is in contact with the stainless steel but does not actually affect it.
There are two large areas of application where the application of corrosion knowledge is needed, in the architectural and structural use of stainless steel. Surface appearance is much more important for architectural use, while surface corrosion attack can be neglected in structural applications. Huge possibilities are offered for the use of stainless steels in these areas. Long-term durability and very low metal ion dissolution pairs make stainless steels a very environmentally friendly choice, with low life cycle costs.
Atmospheric Corrosion Classification
Traditionally, environments have been divided into four different categories: rural, urban, industrial, and marine. In general, corrosivity decreases in the order: industrial, marine, urban and finally rural. However, this classification is not self-evident, for example, an urban environment can be more aggressive than a marine one. Industrial emissions have been regulated of late, resulting in industrial environments with lower corrosivity.
