The abbreviation MIC stands for Microbiologically Influenced Corrosion. This term is used for the process in which corrosion is either or both initiated or accelerated by the activities of microorganisms. Generally, this corrosion mechanism can only play a role in those situations when there is water involved. The adhesion of microorganisms on the surface area, usually through a biofilm, is a crucial starting point for MIC-related processes, which results into material loss.
What is MIC?Generally speaking, corrosion is an interfacial process. It doesn’t happen in the water, but it happens on or in proximity to a metallic surface. The kinetics of corrosion are determined by the physio-chemical environment at the interface, like the oxygen concentration, pH value, salts, conductivity and redox potential are some of the parameters that are influenced by the microorganisms in the environment. After the microorganisms attach to the surfaces, they are embedded into extracellular polymeric substances (EPS) and form layers which are then defined as the biofilms. Thanks to these biofilms, microorganisms can attach to a food source, exchange nutrients and other metabolites and create different zones. This process also supports to create specific conditions that meet the requirements of a particular microorganism. For example, that some microorganisms need oxygen for their survival, while other microorganisms thrive in conditions without oxygen (anaerobic). From a biological perspective, the second advantage of this biofilm is that the nested microorganisms are able to protect themselves against harsh external environmental conditions. For instance very low or high pH ranges, shear stress through high flow velocities, but also anti-microbial agents (biocides). At the metallic surface, several microbiological mechanisms can lead to corrosion. In general, two mechanisms are known:
1. The forming of a chemical substance that will lead to corrosion (CMIC)
2. Direct use of electrons on the metallic surface by microorganisms (EMIC)