Corrosion of steel is an electrochemical reaction that requires the presence of water (H2O), oxygen (O2) and ions such as chloride ions (Cl¯), all of which exist in the atmosphere. Atmospheric chloride ions are in greatest abundance anywhere near the coastline. This electrochemical reaction starts when atmospheric oxygen oxidises iron in the presence of water. In addition, if any two dissimilar metals are in contact with each other, the more reactive metal will corrode in preference to the less reactive metal.
In: steel Australia, vol. 31, no. 1, pp.20-27.