Corrosion growth model for buried pipes

Corrosion is known as the main cause of the most of material degradation and structural deterioration. Many researchers use different corrosion rate models to estimate life time of steel structures in order to prevent failures, breakage, leakage, and many other catastrophic consequences. In this study a new model for corrosion rate and pit depth is presented by considering the concentration of aggressive and inhibitor ions which are not covered implicitly in previous theoretical studies. These concentration parameters are used to relate the corrosion rate to the environmental factors which can be measured by periodic soil analysis. The model is based on Point Defect Model (PDM) which assumes a thin porous oxide layer for the metal structure carries cations and ions. The result of the developed model verified by some experimental data and then the effect of parameters on the pit growth was studied. The results shows the role of water, aggressive and inhibitor ions in the competition of reacting with metal cations to create an oxide passive layer, corrosion pit, or protective layer. The study also suggests the critical amount of the inhibitor ions to control the corrosion growth.