Aeration cell corrosion of carbon steel in soil: In situ monitoring cell current and potential

Abstract

Aeration cell corrosion in soil has been studied in situ in the soil at a test site in Göteborg, Sweden. The aeration cell consisted of two carbon steel sheets, the anodic, buried in a lump of clay, and the cathodic, buried in the surrounding filling material. Two aeration cells were used, one with a cathodic sheet of the same size as the anodic sheets, and an other with a cathodic sheet 10 times larger. The anode-cathode area ratio of the cells were 1:1 and 1:10. Both corrosion current and potential was measured during the 2.67 y test period. As a reference, the corrosion potential of sheets with no connection to any aeration cells were measured. The corrosion of the anodic sheets in clay can be calculated from the cell current to 31.7 μm/y (2.59 μA/cm 2) for the cell with area ratio 10 and 5.0 um/y (0.47 μA/cm 2) with area ratio 1. The difference in cell current between the cells increased with time; from about three times larger in the beginning to about eight times larger. This can be explained by deposition of corrosion products on the cathodic sheet, causing a larger part of the anodic dissolution to be transferred to the anodic sheet. The difference in cell current will be 10 with no corrosion of the cathodic sheets and 1.82 with the same corrosion rates on both anodic and cathodic sheets.