Microbiologically Influenced Corrosion: Causes, Remedies, Facts & Semi-facts

Author(s): Reza Javaherdashti

Microbiologically Influenced Corrosion (MIC) is in essence an electrochemical corrosion process in which living organisms (either microscopic such as bacteria and macroscopic such as algae and fungi observable by naked eye) can influenced the course of corrosion by accelerating (and sometimes decelerating) the associated kinetics. While MIC encompasses both micro- and macro-organisms , the main focus –perhaps by a mistake that stemmed from first days of exploring MIC in late 19th century- has been on bacteria.The main organisms of interest from a corrosion point of view are bacteria, archaea, algae and fungi. Some of these organism accelerate corrosion by directly electron take up from the metal (this is called Electrical MIC or EMIC. In case of sulphate reducing bacteria (SRB) EMIC-driven corrosion could reach unbelievable rates of more than 30 mpy). Other organisms can modify the surrounding environment by changing its chemistry, for example sulphur oxidising bacteria (SOB) or Clostridia can lower pH by generating acids (in case of SOB, sulphuric acid and in case of Clostridia, it will be organic acids. In both cases, the normally neutral environment becomes acidic and aggressive to the metal. Producing acid could also be the way some fungi may use to attack metals such as Aluminium have Organisms such as algae that have day-night cycles during which they establish high and low oxygen partial pressure environments can contribute to corrosion by facilitating differential aeration cells.