Microbial corrosion metals

Corrosion associated with the action of micro-organisms present in the corrosion system. The biological action of organisms which is responsible for the enliancement of corrosion can be, for instance, to produce aggressive metabolites to render the environment corrosive, or they may be able to participate directly in the electrochemical reactions. In many cases microbial corrosion is closely associated with biofouling, which is caused by the activity of organisms that produce deposits on the metal surface. 

Many of the by-products of microbial metaboHsm, including organic acids and hydrogen sulfide, are corrosive. These materials can concentrate in the biofilm, causing accelerated metal attack. Corrosion tends to be self-limiting due to the buildup of corrosion reaction products. However, microbes can absorb some of these materials in their metaboHsm, thereby removing them from the anodic or cathodic site. The removal of reaction products, termed depolari tion stimulates further corrosion. Figure 10 shows a typical result of microbial corrosion. The surface exhibits scattered areas of localized corrosion, unrelated to flow pattern. The corrosion appears to spread in a somewhat circular pattern from the site of initial colonization. 

A.K. Tiller. Is stainless steel susceptible to microbial corrosion In Microbial Corrosion, Proceedings of the conference sponsored and organized jointly by the National Physics Laboratory and the Metals Society, The Metals Society, London, 1983. 

Hamilton, W, A., The Sulphate-Reducing Bacteria Then-Physiology and Consequent Ecology, Proceedings, Microbial Corrosion, The Metals Society, London, U.K, 1983, p. 1. 

Dexter, S. C., Chandrasekaran, P., Zhang, H. J, and Wood, S., "Microbial Corrosion in Marine Environments Effect of Mi-crofouling Organisms on Corrosion of Passive Metals," Proc., Biocorrosion and Biofouling, H. Videla, Z. Lewandowski, R. Lutey, Eds., Buckman Laboratories, Int., Memphis, TN 1993, p. 171. 

Microbial corrosion is probably not caused by a direct bacterial attack on the metallic phase. It is affected by metabolic products which interfere with diverse steps of the corrosion process (Gordon et al., 1981 Hamilton, 1985 Morton, 1987 N. N., 1990 a, b, 1991 Rose, 11981 Summers and Silver, 1978 Thierry, 1987 Weiner et al., 1988). Taking into consideration the living conditions of microorganisms, it appears... 

Stott JFD (1988) Assessment and control of microbially induced corrosion. Metals and... 

Tiller AK (1983) Electrochemical aspects of microbial corrosion An overview proceedings of microbial corrosion, 8-10 March 1983, The Metals Society, London Rainha VL, Fonseca ITE (1997) Kinetics studies on the SRB influenced corrosion of steel A first approach. Corrosion Science 39(4) 807-813... 

Alloying elements are added to improve mechanical and electrochemical properties of the metal. For exanple, it is a well-known practice to add chromium to steel to increase its corrosion resistance. However, alloying elements can sometimes have other inpacts as well they may affect the way the metal responds to the environment from a microbial corrosion point of view. 

Duddridge JE, Pritchard AM (1983) Factors affecting the adhesion of bacteria to surfaces. Proceedings of Microbial Corrosion, 8-10 March 1983 The Metals Society London... 

MICROBIAL CORROSION OF CONSTRUCTIONAL MATERIALS Metallic Materials... 

In summary, all known cases of microbial corrosion of metals can be attributed to known corrosion mechanisms. In the following sections, the mechanisms of microbially induced corrosion for different metals and alloys are discussed. 

The mechanisms involved during microbial corrosion of metals are the following (1) stimulation of an anodic or cathodic process by bacterial metabolites, (2) breakdown of the protective layers, and (3) enhanced conductivity near the surface liquid environment. However, bacteria may also inhibit corrosion processes (O Fig. 12.8) by electrochemical processes (Hernandez et al. 1994 Jayaraman et al. 1997, 1999 Manila et al. 1997 Potekhina et al. 1999). Bacteria may also (1) neutralize the corrosive substances, (2) form protective layers on materials, or (3) decrease the corrosiveness of the aqueous environment. 

Ford T, Maki J, Mitchell R (1988) Involvement of bacterial exopolymers in biodeterioration of metals. In Houghton DR, Smith RN, E ins HOW (eds) Biodeterioration, vol 7. Elsevier Science, New York, pp 378-384 Ford T, MitcheU R (1990a) Metal embrittlement by bacterial hydrogen — an overview. Marine Technol Soc J 24 29-35 Ford T, MitcheU R (1990b) The ecology of microbial corrosion. In MarshaU KC (ed) Advances in microbial ecology, vol 11. Plenum Press, New York, pp 231-262... 

Gu J-D, Ford TE, Mitchell R (2000a) Microbial corrosion of metals. In Revie W (ed) The H. H. Uhlig corrosion handbook, 2nd edn. Wiley, New York, pp 915-927 Gu J-D, Ford TE, Mitchell R (2000b) Microbial corrosion of concrete. In Revie W (ed) The H. H. Uhlig corrosion handbook, 2nd edn. Wiley, New York,... 

---