Corrosion anaerobic

Oxidation-reduction potential Because of the interest in bacterial corrosion under anaerobic conditions, the oxidation-reduction situation in the soil was suggested as an indication of expected corrosion rates. The work of Starkey and Wight , McVey , and others led to the development and testing of the so-called redox probe. The probe with platinum electrodes and copper sulphate reference cells has been described as difficult to clean. Hence, results are difficult to reproduce. At the present time this procedure does not seem adapted to use in field tests. Of more importance is the fact that the data obtained by the redox method simply indicate anaerobic situations in the soil. Such data would be effective in predicting anaerobic corrosion by sulphate-reducing bacteria, but would fail to give any information regarding other types of corrosion. 

Starkey, R. L. and Wight, K. M., Anaerobic Corrosion of Iron in Soil, Amer. Gas Assoc., New York (1945)... 

Pankhania 1.1988. Hydrogen metabolism in sulphate-reducing bacteria and role in anaerobic corrosion. Biofouling 1 27-47. 

Scheme showing proposed pathways for reductive dehalogenation in Fe0-H2O systems (A) direct electron transfer from iron metal at the metal surface (B) reduction by Fe2+, which results from corrosion of metal (C) catalyzed hydrogenolysis by the H2 that is formed by reduction of H20 during anaerobic corrosion. Stoichiometries are shown. (From Matheson, L.J. and Trat-nyek, P.G., Environ. Sci. Technol., 28, 2045-2053, 1994. With permission.)... 

Even if the mechanisms or the extent of passivation of iron by mineral reactions are still unknown in detail the inorganic reactions most probably effect the degradation behaviour of CHC. A simplified model is capable of simulating the effects of these reactions on CHC reduction at different flow velocities on the assumption that mineral precipitation as well as continuous anaerobic corrosion decrease the reactive iron surface. PHREEQC (Parkhurst and Apello, 1999) can be used for qualitative simulation after modification of the data set integrating ethene and chlorinated ethene species as well as some iron minerals. Figure 13.6 shows the results of two simulations at five times different pore velocities and the model assumptions in Table 13.1. 

Iverson WP. An overview of die anaerobic corrosion of underground metallic structures. Evidence for a new mechanism, In Escalante E. editor. Underground Corrosion. ASTM STP 741. American Society for Testing and... 

W.P. Iverson. Possible source of a phosphorus compound produced by sulfate-reducing bacteria that cause anaerobic corrosion of iron. Materials Performance, Vol. 37, No. 5, pp. 46-49,1998. 

D.T. Hang. Microbiological study of the anaerobic corrosion of iron. PhD Dissertation, University of Bremen, Bremen, Germany, 2003. 

S. Deckena, K.H. Blotevoge. Fe oxidation in the presence of methanogenic and sulfate-reducing bacteria and its possible role in anaerobic corrosion. Biofouling, Vol. 5, No. 4, pp. 287-293, 1992. 

Anaerobic a-no- ro-bik an- a(-o), - e(-o)- (ca. 1881) adj. Free of oxygen and/or air. Used in connection with bacteria, developing without air. Important for anaerobic corrosion (tanks and ship bottoms). 

Iverson, W. P., "An Overview of the Anaerobic Corrosion of Underground Metallic Structures, Evidence for a New Mechanism, Underground Corrosion, ASTM STP 741, ASTM International, West Conshohocken, PA, 1981. 

Weight loss corrosion rates, which represent an average of corrosion over the test period, are useless from a predictive point of view, but are often used in conjunction with other measurements for quality assessments. Corrosion kinetics can be measured in different ways. Most favored are electrochemical techniques. They are, however, contrary to common belief, indirect techniques and must be properly calibrated and interpreted to be useful. If corrosion products are soluble in solution (as, for instance, iron carbonate), the buildup of such in solution can be used to monitor how corrosion progresses. Hydrogen, a byproduct of anaerobic corrosion, can also be used to monitor kinetics. Less common, but equally direct, are methods that use the removal of radioactivity from irradiated surfaces. Kinetic measurements have also been carried out with electrical resistance probes. As a general principle, no one method is in itself without some problems and should, therefore, always... 

Iverson, W. P., Olson, O. J., and Heverly, L. F., The Role of Phosphorous and Hydrogen Sulphide in the Anaerobic Corrosion of Iron and the Possible Detection of this Corrosion by an Electrochemical Noise Technique, Proceedings, Biologically Induced Corrosion, S. C. Dexter, Ed., NACE-8, National Association of Corrosion Engineers, Houston, TX, 1986, p. 154. 

The anaerobic corrosion of iron was noted in the nineteenth century and many theories were proposed about its mechanism. Decades of scientific research projects and investigations on the complex influence of microbes on increasing or decreasing corrosion rates have provided a much deeper insight in the role microorganisms play on the life of systems exposed to waters and grounds where they proliferate (see Chap. 10 for more details). 

In 1934 in Holland, VonWolzogen Kuhr and Van der Vlugt provided significant evidence that anaerobic corrosion was caused by the activity of SRB. The two scientists suggested a theory that was named the cathodic depolarisation theory or classical theory . From that time on, noodifications to which we collectively refer as alternative theories have bem made to this original theory. 

In this study, [95] model anaerobic corrosion of iron without the involvement of hydrogen. They postulate that the SRB that grow in very close contact with the iron surface can take electrons directly from the metal surface (in a slept they call electron pick-up ) and transfer these electrons to the sulphate-reducing system (SRS). While this proposed mechanism is certainly a breakthrough, there are still serious questions to be answered. For example, it is unknown how the electron pick-up step works and what mechanisms are involved there. As we will see later. Little et al. [32] have also demonstrated that for another group of bacteria which are important in corrosion (i.e., Shewanella purefaciens which are iron-reducing bacteria), the reduction of metal requires contact between the cell and the surface where the reduction rate is directly related to the surface area. The same researchers also found that the location of pits induced by these bacteria on carbon steel coincided with sites of bacterial colonisation. 

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