Carbon steel is commonly used in Mauritius, and information related to its atmospheric corrosion behaviour in the Mauritian atmosphere is not readily available. Hence, the present study was performed to obtain relevant data and to develop a model for predicting the atmospheric corrosion degradation of carbon steel in Mauritius. Carbon steel samples were exposed outdoors at several sites, according to BS EN ISO 8565. They were removed after specific time periods, and their mass loss was determined. At the same time, the sites' environmental parameters were monitored. From the mass loss measurements and the environmental parameters considered, it was found that the corrosivity of the Mauritian atmosphere falls in category C3 to C4, according to ISO 9223. A model was developed using the SPSS software, and it was found that the atmospheric corrosion in Mauritius depends mainly on the time of exposure and the carbon content of carbon steel.

When carbon steel is subjected to atmospheric corrosion, the surface texture of the base metal becomes rougher due to corrosion attack. In this study, three-dimensional surface roughness analysis of the base metal of carbon steel samples exposed outdoors was performed to investigate this aspect of atmospheric corrosion. Corrosion loss was found to depend mainly on the number of days of exposure, the carbon content of the base metal and the core void volume. A high correlation coefficient was obtained, which suggests that analysis of surface texture can also be used as a means for determining atmospheric corrosion degradation.

ISO 9223 can be used to categorize the corrosivity of atmospheres through either corrosion loss measurements or the use of environmental data. Although both methods are expected to give the same result, discrepancies have been found to occur. The present paper analyses this aspect of ISO 9223, focusing on the effects of metal composition, when using carbon steel, in corrosivity categorisation. Low and medium carbon steel were, therefore, exposed outdoors at one site in Mauritius to determine its atmospheric corrosivity. It was found that for medium carbon steel, the corrosivity obtained from corrosion loss results, through the weight loss method, was not in conformance with that obtained through the environmental data. This was not the case with low carbon steel. Taking into consideration the various factors affecting atmospheric corrosion, it was concluded that the carbon content of carbon steel is an important parameter that should be considered in ISO 9223 for more reliable determination of the corrosivity of atmospheres.

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