Microbially influenced corrosion microbial biofilm

Biofilms can promote corrosion of fouled metal surfaces in a variety of ways. This is referred to as microbiaHy influenced corrosion. Microbes act as biological catalysts promoting conventional corrosion mechanisms the simple, passive presence of the biological deposit prevents corrosion inhibitors from reaching and passivating the fouled surface microbial reactions can accelerate ongoing corrosion reactions and microbial by-products can be directly aggressive to the metal. 

The sheer complexity of the corrosion process in the presence of microoiganisms and microbial biofilms makes data interpretation difficult. Thus, whenever possible, multiple techniques should be used for assessing any microbial corrosion situation before conclusions are drawn. An outline of the laboratory techniques used most successfully in the past, along with any cautions for applying those techniques when the corrosion is influenced by microorganisms will be given below. 

Sd] Zhang, H. J. and Dexter, S. C. The Effect of Biofilms on Critical Pitting Potentials for Stainless Steels S30400 and S31600 in Seawater, Proceedings, 1995 International Conference on Microbially Influenced Corrosion, P. Angel, et al., Eds., NACE International, Houston, TX, 1995, p. 70/1. 

Biofilms are of great importance for microbially influenced corrosion. Unfortunately, the investigation/research of these systems has just begun. Interested readers may see Flemming and Geesey (1991). 

The remote crevice assembly technique (see Chapter 19) is a research tool that allows one to separate the anode and cathode areas of a crevice corrosion test sample so that the current flowing between them can be measured with a zero-resistance ammeter. This technique is similar to the dual cell method, and it lends itself well to studies of microbial effects on crevice corrosion [7]. It allows direct measurement of microbial effects on both the initiation time and propagation rate for crevice attack, provided again that a suitable control experiment without the microbial influence can be done concurrently. The scime technique of separating the anode and cathode can be used to study the influence of microbes in biofilms on galvanic corrosion [li]. 

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