Engineering behaviour of soil materials on the corrosion of mild steel

Underground pipelines and steel structures are usually expected to have a long working life. The risk of corrosion should be estimated before installing such pipelines so this paper is aiming at the investigation of the surrounding and incorporating medium (soil filling materials). Many problems related to soil application are due to the unfavorable interaction between water and soil. Underground corrosion is primarily influenced by the following factors: the presence of soil moisture, the supply of oxygen, the redox potential, the pH value, the soil resistivity, and also by microbial activity. From engineering aspects an increase in soil water content has a number of disadvantages e.g. swelling, shrinkage and cohesion decreases which affect directly on the interaction of pipelines, causing deterioration of pipeline materials "corrosion" and also cause damage of infrastructure above this soil due to the occurrence of general and localized corrosion (pitting formation) which is present in different sites of steel structures. The presence of water is a prerequisite for the functioning of corrosion cells. Corrosion of mild steel is affected by grain size, swelling, shrinkage and clay mineral content. The finer soil particles, owing to the increase in swelling, shrinkage, and plasticity, are considered as corrosive medium for underground pipelines and steel structures. The clay mineral contents are also the main quality control to the mild steel corrosion for example montmorillonite and illite absorbed water more than kaolinite clay minerals so it is highly effective in the deterioration of metals. (C) 2008 Elsevier B.V. All rights reserved.