Corrosive Environment of Underground Pipes and Prediction of Corrosion

Abstract

Marine clay beds in Japan are often distributed in coastal plains and inland basins. This clay is composed of marine sediments and is very corrosive. We tried to predict the degree of external corrosion of water main exposed to agressive soils containing marine clay. It is used in the equation of prediction model that the growing rate of the pitting depth (P) follows a power law equation of time (t): P=ktⁿ. Parameter “k” and “n” were decided by the results of regression analysis. By assuming that “k” means the corrosiveness of environment, “n” could be given by the statistical analysis. Parameter “n” did not depend on the environmental factors. The corrosion of cast iron pipes installed in areas where marine clay is distributed is statistically described in terms of environmental factors in the present paper. We established the correlation between the depth of corrosion pit and the period after the installation of mains, and found a useful equation for predicting the depth of corrosion pit.