Distribution of cathodic protection current and residual corrosion in insulation defects of large-diameter oil and gas pipelines

The results of long-term corrosion tests of 17GS pipe steel samples under field conditions at a specially equipped landfill using a pipe with a diameter of 1220 mm are presented. It is established that seasonal freezing of the soil does not have a noticeable effect on the flow of currents of corrosive macroparticles of differential aeration. The redistribution of the loss of mass of samples due to the flow of macroparticles of differential aeration in high-resistance soils of the taiga–swamp zone of the central part of Western Siberia does not exceed 2…5% of the total loss of mass of samples, which indicates that the currents of corrosive microparticles are most effective in these conditions.

Based on the results of long-term corrosion tests, it was found that when the cathodic protection current density is equal to the oxygen limit current density, with cathodic polarization of 0,15…0,30 V, the residual corrosion rate due to the effect of self-regulation of cathodic protection on all samples decreases to values not exceeding 0,005…0,010 mm/year, although in the absence of cathodic The corrosion protection rates of these samples under various oxygen delivery conditions were 0,08…0,13 mm/year. It is shown that the ratio of the cathodic protection current density to the oxygen limit current can serve as the decisive criterion for choosing the optimal cathodic protection modes, which allows determining the residual corrosion rate of steels in express mode under various cathodic protection modes and reducing the cathodic decomposition reaction of water with the release of hydrogen on the protected surface to a controlled minimum.

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