Corrosion of the inner surface of the tanks with sulfurous oil and pyrophoric properties of formed deposits

Abstract

The corrosion rate of the inner surface of the tanks in contact with the natural vapor-gas phase of the tanks can reach 3 mm/year. On the surface of the metal simultaneously occur two corrosion reactions, namely, the first with the formation of iron oxides and hydroxides, the second - with the formation of sulfide compounds. The resulting corrosive deposits are pyrophoric ones and cause spontaneous combustion of the tanks. Replacement of the natural vapor-gas phase with a mixture of N2 + O2 (nitrogen protection) with an O2 content of not more than 7 vol.% leads to a decrease in the corrosion rate by more than 2 orders of magnitude and is up to 0.013…0.015 mm/year. Continuous operation of nitrogen system provides fire and explosion safety operation of the tanks as a result of the termination of the formation of pyrite. In tanks, steel corrodes by an electrochemical mechanism, since the thickness of the moisture film on their walls (105…106 monolayers) is commensurate with the thickness of the diffusion layer at the steel – electrolyte solution interface.