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Purpose This study aims to reveal the differential concentration corrosion (DCC) mechanism, which has been ignored by researchers for a long time. Design/methodology/approach The ionic conductive layer near the pipe wall was extracted and discretized. In the case of DCC, the equations of corrosion potential after polarization in units are derived according to Kirchhoff’s Law. By solving these equations, the corrosion potential and current on situation of DCC are calculated. Findings DCC can change origin distribution of (nature) potential and current greatly; it will cause polarization. The positions with original lower corrosion potential will produce anodic polarization; meanwhile, the speed of corrosion also increases; the position with original higher corrosion potential will produce cathodic polarization, and the corrosion current is also decreased. Generally speaking, the potential will be homogenized by DCC mechanism. Originality/value This model makes an in-depth analysis of the traditional FAC theory, greatly supplements it and enriches the theory.

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