Bacteria Corrosion, microorganisms

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Waters While MIC-causing bacteria may arrive at the surface of their corrosion worksite by almost any transportation system, there is always water present to allow them to become ac tive and cause MIC to occur. There are plenty of examples of even superpure waters having sufficient microorganisms present to feed, divide, and multiply when even the smallest trace of a viable food-stuff is present (e.g., the so-called watei for injection in the pharmaceutical industiy has been the observed subject of extensive corrosion of pohshed stainless steel tanks, piping, and so on). 

These microorganisms become a problem when their numbers are large enough to produce corrosives such as carbon dioxide and hydrogen sulfide. Pseudomonas, Bacillus and Flavobacterium are examples of slime-forming bacteria. 

Polarization techniques have also been used to determine mechanisms by which microorganisms induce localized corrosion in the forms of pitting or crevice corrosion. In most cases itpit was determined in the presence and absence of bacteria, itpit provides data as to the tendency for pitting, but not the rate for pit propagation. Salvarezza et ah " and De Mele... 

Active microbiologically influenced corrosion (MIC) of metal due to bacteria is quite complex. It can involve several species of microorganisms and is affected by temperature, TOC, pH, and other factors. Examples of bacterial species which are associated with MIC are described below ... 

Production of biofilms. The bacteria implicated in corrosion may begin their lives on a metal surface as a scatter of individual cells. As the biofilm matures, however, the organisms are usually found as individuals or in colonies embedded in the matrix of a semicontinuous and highly heterogeneous biofilm (Figure 6.33). (Dexter)5 Microorganisms start on the surface from scattered individual bacteria to thick, semicontinuous films or colonies (slime or polymer) which can influence corrosion. 

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],... 

Growth and metabolism depends on the availability of water as microorganisms take up the nutrients present in water and produce cell material (51). Under favorable conditions, some bacteria can double in number every 20 min or less. Thus a single bacterium can produce a mass of over a million microorganisms in <7 h. The bacteria can survive from -10 to >100°C, pH 0-10.5, dissolved oxygen 0 to saturation, pressure of vacuum to >31 MPa, and a salinity of ppb to 30%. Most of the bacteria encountered in corrosion grow best at 15-45 C and pH of 6-8 (41). 

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... 

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