Let’s discuss how oxygen concentration difference corrosion in buried pipelines occurs
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The most common corrosion phenomenon in underground pipelines is the oxygen concentration cell. Due to the varying oxygen concentrations at different parts of the pipeline, the natural potential (non-equilibrium potential) of the pipeline in the oxygen-poor areas is low; these areas act as the anode of a corrosion galvanic cell. The rate of anodic dissolution in these areas is significantly higher than that on the other surfaces, resulting in corrosion. When pipes pass through the junctions of soils with different properties, the clay-rich sections become oxygen-poor and are prone to corrosion; corrosion is most severe at the junctions between the two types of soil or near the end of buried pipes where they emerge from the ground. For oil storage tanks, the oxygen concentration difference is mainly manifested in poor contact between the tank bottom plate and the sand base, as well as in the difference in air permeability between the periphery and the center of the tank. The lower oxygen concentration at the center leads to corrosion there as an anode.
Oxygen concentration difference corrosion of buried pipelines is mainly caused by the uneven distribution of oxygen in the soil. At different parts of underground pipelines, potential differences are generated due to variations in oxygen concentration. Areas with lower oxygen concentrations have a lower potential and become the anode, while areas with higher oxygen concentrations have a higher potential and become the cathode. This potential difference causes the metal material in the oxygen-deficient areas to dissolve more rapidly, leading to corrosion. Especially where the pipeline passes through soils of different properties or in areas where it emerges near the surface, the differences in oxygen concentration in the soil are more pronounced, leading to more severe corrosion in these areas. In oil storage tanks, poor contact between the tank bottom and the sand base, or differences in permeability around the tank and at its center, can also lead to oxygen concentration gradients that cause localized corrosion. .