Case Histories » Insurance

Microbial Influenced Corrosion of Heating Fuel Oil Tanks

MIC of heating fuel oil tank - corrosion perforation at bottom of tank
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)
MIC of heating fuel oil tank - metallurgical cross section through tunnelling under corrosion pits
Corrosion pits which were not representative of typical pitting corrosion. Unusual pit morphology and tunnel-like bore holes (encircled) were indicative of microbial activity.

Specimen

Above ground, heating fuel oil tank: 935 litres (approximately 200 gallons)

Material

ASTM A569 (or equal) sheet steel.

Thickness

2mm.

Service Life

The heating fuel oil tank had been in service for approximately three 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 observed below the corrosion pits within the wall thickness of the tank. It was determined that the corrosion perforations that 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.