Corrosion-related bacteria

Biofilm samples and microbial contamination of drinking water flowing through the model in result of biofilm formation were analyses with standard methods (APHA, 1992). Number of heterotrophic bacteria (R2A/22°C/7d) coliforms and bacteria from different physiological groups, including corrosion related bacteria were determined. 

Biofilm samples collected from carbon steel and concrete pipes of the DWSS Yovkovtsy had different appearance, content of water, organic and corrosion products, while ones from concrete pipe and water tank s surfaces were the same. Biofilm community mainly consisted of heterotrophic bacteria and some fungi, actinomyces and autotrophic bacteria. Corrosion related bacteria were determined in some of the biofilm samples. 

We have been using the term corrosion-related bacteria throughout this chapter without really defining it. It must be noted that bacteria do not always accelerate corrosion, but under certain circumstances, as mentioned earlier, bacteria can decelerate corrosion. That is why we preferred the term corrosion-related bacteria to address both corrosion accelera-tion and deceleration by these microorganisms. 

In fact, in nature there is no such a thing as a pure culture of this or that bacteria [4], and it is quite possible to have a rather complex picture of all possible microbial reactions that may happen simultaneously or in sequence. Figure 4.13a shows a typical biomass formed on a steel pile being exposed to seawater conditions. Such a mass can easily harbour various types of corrosion-related bacteria. Figure 4.13b is a schematic presentation of possible bacterial types and their interactions within a typical biofilm. 

What is meant by untreated water is water in which no specific physical/chem-ical treatment has been done to remove (mainly) corrosion-related bacteria. This water can be sea, river, or well water used for industrial activities. 

As far as corrosion-related bacteria are concerned, in this chapter we will focus on both external and internal corrosion systems of a buried metallic pipeline. 

Farquhar, G.B. 1996. The Effect of Polycrylamide Polymers and Formaldehyde on Selected Strains of Oilfield Related Bacteria. Paper 96281 presented at the NACE International CORROSION 96 51 Annual Conference and Exposition, Denver, 24-29 March. 

Introduction. In the natural gas industry, MIC has been estimated to cause 15 to 30 percent of corrosion-related pipeline failures. The growth of bacteria on surfaces in cooling and process-water systems can lead to significant deposits and corrosion problems. Once the severity of these problems is understood, the importance of controlling biofilms becomes quite clear. 

Manganese and iron oxidation are coupled to cell growth and metabolism of organic carbon. Microbially deposited manganese oxide on stainless and mild steel alters electrochemical properties related to the potential for corrosion. Iron-oxidizing bacteria produce tubercles of iron oxides and hydroxides, creating oxygen-concentration cells that initiate a series of events that individually or collectively are very corrosive. 

Sulfate-reducing bacteria (SRB) are some of the most common and problematic microorganisms of environmental and economic importance in petroleum industry. The effects caused by SRB activity are mainly the souring of oil and gas deposits and in problems related with microbially influenced corrosion (MIC). The toxic hydrogen sulfide produced may also present a health hazard to workers and may decrease oil quality by the souring of oil and gas [1],... 

It is extremely diflScult to estimate the eosts related with corrosive processes attributed to the activity of microorganisms (SRB and other bacteria) in the oil industry. In recent years, the costs involving the control of the activity of SRB were significant with annual values estimated at approximately 150,000 per platform when only biocides are used to control microbial activity [2],... 

One of the primary causes of external corrosion is exposure to corrosive soils. The electrical and chemical characteristics of soil and water are closely related to corrosivity. Variations in soil characteristics because of soil type, fill compaction, amount of moisture, bacteria, chloride concentration help establish corrosion cells. Over a period of time, if untreated, the corrosion process can result in wall thickness reduction and can lead to leaks. The 6 o clock position of the USTs is one of the most critical locations because that is the rest point where the tank bottom touches the bottom of the hole dug for the tank. At such a location, the layer of backfill is relatively thin therefore, the soil characteristics can be different from the adjacent soil, setting up conditions for macrocell corrosion. 

This form of corrosion is defined as corrosion influenced by the presence and activities of microorganisms including bacteria and fungi. About 20-30% of all corrosion on pipelines is MIC related. MIC can affect either the external or internal surfaces of a pipeline. Microorganisms located on the metal surface do not directly attack... 

There are very interesting features of the sessile bacteria that could be related to corrosion. Some of these interesting points are as follows ... 

Pseudomonas spp. are IRB species reported to have corrosive effects. " - However, there is an increasing body of evidence that IRB could actually slow down corrosion. Hernandez et al. reported that in the presence of bacteria like aerobic Pseudomonas sp. and facultative anaerobic Serratia marcescens in synthetic seawater, corrosion of mild steel is inhibited. The effect seemed to disappear with time in natural seawater. Although no particular mechanism was proposed to address this phenomenon, it seems that it is related to the biofilm produced, thus reducing the contribution of factors such as diffusion gradients that normally enhance corrosion. 

In Figure 4.1a, it is mentioned that the highest LoA about microbial corrosion occurs when there is also a good understanding about Clostridia. Very few, if any, books on corrosion and MIC have explained about this group of bacteria. Apart from the undeniable attraction of SRB, another factor in paying much less attention to Clostridia, perhaps, has been the fact that relatively few case histories, again in comparison with SRB, related to these bacteria have been published. 

The changes in jet fuel and jet fuel additives that have taken place in recent years have also brought about a shift in the microbial community in aircraft fuel. The bacteria isolated from aircraft jet fuel tanks have been found to be closely related to Bacillus, and they do have the potential to cause microbiologically influenced corrosion (MIC) [11,17,18]. 

Anaerobic bacteria have been reported to accelerate the normtd corrosion process and convert noncorrosive soil to a very aggressive environment (Fig. 3). The environmental conditions under which the microorganisms normally operate are temj)erature from 20 to 30°C, pH from 6 to 8, and soil resistivity from 500 to 20 000 ohm-cm. Rate and extent of corrosion are related directly to bacterial growth in contact with the metallic surface. Bacteria have been found that are capable of growing on many kinds of coating materials, including hydrocarbons. 

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. 

Sulfate-reducing bacteria have also been reported to be responsible for pitting corrosion on stainless steels in aqueous environments. The mechanisms proposed are mostly related to iron and steel. However, a different mechanism has been proposed in which the role of thiosulfate in the microbial pitting of stainless steel has been emphasized [137]. The same authors have also demonstrated clearly that SRB-induced pitting corrosion of stainless steel is unlikely to occur in a uniformly anaerobic SRB medium, whereas it will occur when the anaerobic sites are coupled to an oxygen cathode [136]. 

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