عنوان مقاله [English]
Degradation of underground buried pipelines due to corrosion imposes enormous financial damages on industry and environment. Hence, recognition of soil nature as a non-homogeneous electrolyte in corrosion of pipelines is an important issue, which should be taken into consideration during design and execution of cathodic protection (CP). The most important factors regarding soil composition, which affect the corrosion or protection of a buried pipeline, are: soil resistivity, various dissolvable salts in earth, relative humidity, soil composition and grain size, mineral materials, micro organisms, etc. In this study, a length of 5 kilometers from a long cathodicaly protected coated pipeline near Tehran was selected for laboratory and on-site investigations, which had noticeable lack of protection. Five soil samples were collected from five positions adjacent to the pipeline with one kilometer distance between each collect sample. Prior to sample collection, the selected positions were subjected to resistivity measurement, using Wenner measuring device. The soil samples were transferred immediately to the laboratory for further investigation, whereby the pH, grain size and chemical composition of each sample was calculated using standard measuring methods including XRF and Loss on ignition (LOI) for grain size specification and chemical composition, respectively. Furthermore, the corrosion rate of steel specimens with similar composition to the pipeline exposed to each soil sample was obtained via potentiostatic polarization measurement. Also the relative amount of current required with respect to the area of the steel specimen (i.e. I/S) exposed to each soil sample was obtained for a period of 400 hours in each case. Finally, the results for all selected samples were compared and contrasted against each other and the effective parameters on corrosion of steel samples were specified.