Biologically influenced corrosion

See Chap. 5, Oxygen Corrosion Chap. 6, Biologically Influenced Corrosion and Chap. 17, Graphitic Corrosion. ... 

The importance of biologically influenced corrosion (particularly micro-biologically influenced corrosion) has been underestimated for many years. Recently, more attention has been paid to biological forms of corrosion— yet more attention does not always mean an improved situation. 

Many forms of corrosion resemble each other. However, it is just as true that each form of corrosion produces a unique fingerprint by which it can be differentiated from all other forms of attack. Biologically influenced corrosion is no exception. 

The presence of organisms (large or small) in proximity to corrosion by itself is not proof of biologically influenced corrosion, any more than a correlation of lunar phases with stock market fluctuations establishes a lunar-financial connection. It should be stressed vigorously that all evidence must be consistent with any single corrosion mode before a definitive diagnosis can be made (see Critical Factors above). Further, all alternative explanations must be carefully examined. 

The triggering mechanism for the corrosion process was localized depassivation of the weld-metal surface. Depassivation (loss of the thin film of chromium oxides that protect stainless steels) can be caused by deposits or by microbial masses that cover the surface (see Chap. 4, Underdeposit Corrosion and Chap. 6, Biologically Influenced Corrosion ). Once depassivation occurred, the critical features in this case were the continuity, size, and orientation of the noble phase. The massive, uninterrupted network of the second phase (Figs. 15.2 and 15.21), coupled... 

R.E. Tatnall, Introduction, A Practical Manual on Micro-biologically Influenced Corrosion, Gregory Kobrin, Ed., NACE International, 1993, p 1-9... 

More recently, attention has been directed to the "ninth form of corrosion, biologically influenced corrosion, which includes studies on an area referred to as "ennoblement. The presence of biofilms on metals and alloys immersed in natural seawater produces a complex, heterogeneous chemistry along the metallic surface. It has usually been observed that passive alloys such as aluminum, stainless steels, nickel-base alloys, or titanium show an increase to more noble (electropositive) potentials or ennoblement of several hundred millivolts with exposure time in natural seawater, thus magnifying the potential differences that may exist between dissimilar alloys [26,55-64]. Ennoblement is likely caused by the formation of microbiological films, which increase the kinetics of the cathodic reaction [55-63],... 

Al-Darbi MM, Agha K, Islam MR. Modeling and simulation of the pitting micro-biologically influenced corrosion in different industrial systems. In CORROSION 2005, Paper 505. Houston, Tex. NACE International, 2005. 

C. C. Gaylarde and J. M. Johnston, Anaerobic metal corrosion in cultures of bacteria from estuarine sediments. Proceedings Biologically Influenced Corrosion (S. C. Dexter, ed.), NACE-8, Houston, 1986, pp. 137-143. 

Iverson WP, Olsen GJ, Heverly LF (1986) The role of phosphorus and hydrogen sulfide in the anaerobic corrosion of iron and the possible detection of this corrosion by an electrochemical noise technique. In Dexter SC (ed) Biological influenced corrosion. National Association of Corrosion Engineers, Houston, pp 154—161... 

---