Microbiologically induced corrosion of stainless steels in paper machines

The phenomenon of microbiologically influenced corrosion (MIC) of stainless steels has been known for decades, but its causative factors and the mechanisms involved remain to be clarified. The first reports of corrosion of stainless steels associated with micro-organisms appeared during the early 1970s. However, there are only a few studies available on MIC of stainless steels in the pulp and paper industry. The deleterious effects of micro-organisms in the pulp and paper industry typically occur alongside the presence of biofilms. The corrosion of stainless steels under paper and/or board mill conditions is usually localized and unexpected. Paper and board mill waters provide an ideal environment for the growth of microorganisms. There are several sources of organic and inorganic nutrients in the paper-making process and the temperature is at an appropriate level. MIC is not a new form of corrosion, but rather a modified electrochemical corrosion in which microbes or their metabolic by-products induce changes in either chemical or physical conditions or both. Therefore, the effects of biofilm formation on the electrochemical behaviour of stainless steels can be studied by different electrochemical methods used in conventional corrosion studies. In this paper, a brief review is presented of the mechanisms and the methods for studying MIC of stainless steels in the paper industry.