Long term atmospheric corrosion in Mauritius

Abstract

Carbon steel is a commonly used metal in Mauritius. Short term exposure of the metal at several sites has shown that the corrosivity of the Mauritian atmosphere lies in the C3 category according to ISO 9223. Long term atmospheric corrosion behaviour of carbon steel in the Mauritian atmosphere has never been studied, though this can be considered as essential information in the design and maintenance of steel structures. Hence, this study investigates the atmospheric corrosion of carbon steel over an 18-year period through outdoor exposures of the metal. It was observed that the atmospheric corrosion of low carbon steel in Mauritius can be divided into two time periods. An initial time period extending over 4 years involves a high corrosion rate which would probably result due to the formation of porous rust layer on the surface. In the second time period, the corrosion degradation decreases to much lower levels over time. This can be due to a change in the corrosion mechanism and the formation of a more compact rust layer. Moreover, scanning electron microscope (SEM) tests have shown that goethite has formed in the rust layer after 18 years of exposure, which is more stable, as a corrosion product.