Corrosion of an Oil Storage Tank

A 3-mm hole developed at the bottom of an oil storage tank after 25 months of service. This premature failure of the tank raised questions as to the construction material of the tank as well as the possibility of corrosive elements (i.e., water) present in the contents of the tank. 

The tank was received with two sections removed for analysis. One section was taken from the top, where minimal corrosion was expected to be seen, while the second section was taken from the bottom, where the tank had failed. 

The chemical composition of the steel, determined by spectrographic analysis, is listed in Table 7.14. Based upon this composition, the steel is most likely SAE-AISI 1006 or 1010. The thickness of the steel averaged 1.84 mm. 

The overall dimensions of the larger section, cut from the bottom of the tank, are 70 cm long by 33 cm wide. The section appears to be about 80% corroded on the surface. The surface corrosion along the edge appears to be smeared and brushed as a result of the cutting. The underlying metal substrate has mill scale attached and is blue-gray in appearance. 

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