Abstract: The causes of corrosion in the three- phase area for the storage tank (oily sewage area, oil phase area, gas phase area) were analyzed and summarized,then the areas that are liable to corrosion and leakage were determined. The affected range model of released liquid after corrosion of tank was established. Taking the leakage of oily sewage area in a gasoline tank of an oil depot as an example, the involved area of released liquid was calculated and analyzed to provide basis for determining safety protection distance and emergency rescue of oil tank leakage. Compared with oil- phase area and gas- phase area, the oil- bearing sewage area has serious corrosion on the inner wall of the tank. Compared with the oil- gas interface, the oil-bearing sewage oil interface is corroded seriously.

Key words: oil tank, causes of corrosion, leakage, affected range, safety protection distance