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1. Microcell corrosion: Water accumulation on the bottom of oil tanks is a major cause of electrochemical corrosion of that bottom surface. The aqueous solutions containing various ionic impurities in the tank bottom, together with the exposed metal surface resulting from the peeling off of the coating on the bottom, create numerous microcells. Charged ions such as Ca2+, Fe2+, and Mg2+ present in crude oil increase the conductivity of the electrolyte solution, thereby accelerating the corrosion process. Taking the rusting of the tank bottom plate as an example, the reaction product Fe(OH)2 formed during the corrosion process is oxidized by the dissolved oxygen in the accumulated water to produce Fe(OH)3, which is further oxidized into red rust, Fe2O3·3H2O. Microcellular corrosion begins at the surface and gradually spreads downward, causing bulging and delamination. As the corrosion deepens and expands further, large areas of rust formation appear on the bottom plate of the tank. 2. Corrosion by sulfur dioxide in accumulated water: Sulfur dioxide present in the water accumulated at the bottom of the tank can cause an acid regeneration cycle reaction that leads to the degradation of the anti-corrosion coating and the steel plates there. First, FeSO4 is formed from SO2, O2, and Fe; subsequently, FeSO4 hydrolyzes to produce oxides and free acid. The free acid further accelerates the corrosion of iron, resulting in the formation of more FeSO4. This cycle repeats, thereby accelerating the corrosion of the tank bottom plates. 3. H2S-H2O type corrosion