DURABILITY AND LIFE EXPECTANCY FOR STAINLESS STEELS IN EXTERNAL ENVIRONMENTS
The most important corrosion consideration with stainless steels is pitting. Micro pitting is manifested as surface rust staining and is generally considered unacceptable for a material basically selected for its aesthetic appearance and corrosion resistance. Analysis and extrapolation of pit depth data gathered from atmospheric exposure test programs can be used as a durability guide. (This work was done by Corus (British Steel) Technical.) It must be borne in mind that staining from micro pitting may result in rejection of the steel on aesthetic grounds, long before pitting has perforated it.
Factors Affecting Durability
The durability of the stainless steel depends on:
- Steel Grade
- Surface Finish
Chloride ions are the most aggressive environmental hazard when assessing the pitting corrosion risk. Marine sites tend to be the most aggressive and so give the lowest projected durability.
Acid conditions, sometimes found in industrialized atmospheres, are also aggressive.
It is also important to consider the effects of local ‘micro climates’ that may influence how aggressive the environment is.