Ultrasonic Mitigation of Microbiologically Influenced Corrosion

Power ultrasound was investigated as an environmentally benign technique for the mitigation of microbiologically influenced corrosion (MIC) in natural gas pipeline facilities. Bacterial kill tests were performed with simulated pipeline brine containing acid-producing bacteria, Enterobacter aerogenes. The effect of sonication on the concentration of viable bacteria was determined for different pulse duty cycles, flow rates, hydrocarbon (kerosene) contents, applied pressures, and sublethal doses of a biocide (gluteraldehyde). With a fresh sonicator horn-tip, the bacterial concentration in brine containing 20 vol% kerosene can be reduced by about three orders of magnitude for a double pass of the brine through a 550-W sonicator at a flow rate of 4.8 L/h. The combination of ultrasound and 5 ppm gluteraldehyde (OHC[CH₂]₃CHO) decreased the bacterial concentration to undetectable levels within 4 h after sonication. The polarization resistance of API 5L Grade X-52 pipeline steel was measured in recirculating deaerated brine in the sterile, unsonicated, and sonicated conditions. The degree and duration of corrosion mitigation by ultrasound depended on the concentration of acid-producing bacteria after sonication. The polarization resistance measured in four-day tests showed a correlation with the bacterial concentration. Reducing the bacteria to 10² to 10³ colony-forming units/mL resulted in a decrease in corrosion to a level approaching that for the sterile brine.