Understanding the Propagation of Nonuniform Corrosion on a Steel Surface Covered by Marine Sand

The corrosion progression of X65 pipeline steel, which was partly covered by a mineral deposit layer, was investigated in oxygen-containing artificial seawater using a multielectrode array (MEA) and electrical resistance method. Results show that the deposit covered area would act as the anodes due to the oxygen concentration difference between the bare steel area and deposit covered area. The most serious corrosion would occur at the bare steel area which was close to the sand deposit due to the diffusion of the cations from the deposit covered area to the bare steel area, leading to the decrease of local pH. Once the diffusion path between the bare steel area and the deposit covered area was blocked, the bare steel area would act as a constant cathode, resulting in the formation of a protective calcium carbonate layer on the bare steel surface.