Microbiologically influenced corrosion in B35 carbon steel storage tank: The influence of diesel blend sludge mixed culture in the oil-water interphase

Biodiesel is a renewable biofuel that is more environmentally friendly. Biodiesel is used in Indonesia as a blend of 35%-v biodiesel and 65%-v petrodiesel. Consequently, diesel storage systems initially designed for petrodiesel are now being used to store diesel blends, which increases the risk of microbiologically influenced corrosion (MIC). In this research, the characteristics and risks of MIC phenomena in the diesel blend storage system were studied. MIC caused by the naturally occurring diesel blend sludge was studied by immersing carbon steel coupon at the oil-water interphase of the diesel blend. Microorganisms detected in the mixed culture diesel blend sludge were dominated by Streptomyces sp. and Bacillus aerophilus, while Pseudomonas sp. and several anaerobes ( Dialister sp., Blautia sp., Prevotella sp., etc.) were also detected. The immersion test showed that the sludge can cause uniform corrosion at a rate of 0.05 mm/year (Moderate Category). Additionally, an increase in biofuel acid number exceeding the allowable limit was also found, indicating fuel biodegradation by the presence of microorganisms. Two different layers were formed on the carbon steel samples, namely biofilms (water, alcohol, fat, protein, and carbohydrates) on the upper part and the corrosion product (iron oxide and iron phosphate) on the lower part. Pitting corrosion was more prominent in the water phase due to biofilm unevenness. A dense biofilm was detected at the oil-water interphase, which potentially inhibits the oxygen diffusion from the oil to the water phase, resulting in anaerobic conditions.