Detection of Surface Roughness Evolution of Carbon Steel Subjected to Outdoor Exposure and Constant Humidity Corrosion Tests

The surface roughness evolution of carbon steel under corrosion was studied through outdoor exposure and constant humidity corrosion tests. The statistical analysis of the roughness parameters, such as the degree of skewness and kurtosis, are the good indicators to anticipate the corrosion stages. The results indicated that the corroded surface evolution could be classified into three stages of corrosion. The first stage showed shallow and sparsely distributed pits on the surface of the steel with a probability density function of negative skewness and a high degree of kurtosis (Ku > 3). The second stage exhibited pits distributed densely and partial overlapping of pits. In the third stage, the overlapping pits entirely covered the metal surface, thereby exhibiting uniform corrosion. Statistical analysis of the corroded surface indicated that the random depth variable of the uniform corrosion follows the normal distribution. The samples exposed to outdoor for one year exhibited the corrosion in the first stage only, while the samples exposed to constant humidity chamber for ten months showed all the three stages of corrosion.