Mechanisms of microbially influenced corrosion

Abstract

The chapter demonstrates that biofilms can influence the corrosion of metals (1) by consuming oxygen, the cathodic reactant; (2) by increasing the mass transport of the corrosion reactants and products, therefore changing the kinetics of the corrosion process; (3) by generating corrosive substances; and (4) by generating substances that serve as auxiliary cathodic reactants. These interactions do not exhaust the possible mechanisms by which biofilm microorganisms may affect the corrosion of metals; rather, they represent those few instances in which we understand the microbial reactions and their effect on the electrochemical reactions characteristic of corrosion. In addition, we can use electrochemical and chemical measurements to detect one or more products of these reactions. An important aspect of quantifying mechanisms of microbially influenced corrosion is to demonstrate how the microbial reactions interfere with the corrosion processes and,based on this, identify products of these reactions on the surfaces of corroding metals using appropriate analytical techniques. The existence of these products, associated with the increasing corrosion rate, is used as evidence that the specific mechanism of microbially influenced corrosion is active. There is no universal mechanism of MIC. Instead, many mechanisms exist and some of them have been described and quantified better than other. Therefore, it does not seem reasonable to search for universal mechanisms, but it does seem reasonable to search for evidence of specific, well-defined microbial involvement in corrosion of metals.