Microbial Influenced Corrosion of Heating Fuel Oil Tanks
Specimen: Above ground heating fuel oil tank: 935L (approx. 200 Gallons)
Material: ASTM A569 (or equal) sheet steel
Thickness: 2mm
Service Life: The heating fuel oil tank had been in service for approximately 3 years.
Findings: The observed corrosion features were found to be dissimilar to typical corrosion pitting. Pitting was found to be highly localized, and appeared as straight, bore-like holes, in contrast to typical concave pitting. Additionally, tunnel-like features were also observed below the corrosion pits within the wall thickness of the tank. It was determined that the corrosion perforations which caused the above-ground heating fuel oil storage tank to leak were caused by microbial influenced corrosion (MIC). MIC is the corrosion or deterioration of a material which is initiated and/or accelerated by the activities of micro-organisms.
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(a) Close-up view of the leak site and associated metal loss at the bottom of the tank. The metal loss was limited to a parabolic region at the end of the tank (fuel oil/water interface)
(b) Corrosion pits which were not representative of typical pitting corrosion. Unusual pit morphology and tunnel-like bore holes (encircled) were indicative of microbial activity.
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