Active biological corrosion

Biological Corrosion The metabohc activity of microorganisms can either directly or indirectly cause deterioration of a metal by corrosion processes. Such activity can (1) produce a corrosive environment, (2) create electrolytic-concentration cells on the metal surface, (3) alter the resistance of surface films, (4) have an influence on the rate of anodic or cathodic reaction, and (5) alter the environment composition. 

Two basic mechanisms cause biological corrosion. Biologically produced substances may actively or passively cause attack. Each mechanism either accelerates preexisting corrosion or establishes a new form of metal loss. Often the distinction between active and passive attack is vague. 

Localized biological corrosion of stainless steels. There are three general sets of conditions under which localized biological corrosion of austenitic stainless steel occurs (Figure 6.29). These conditions should be examined for metals that show active-passive corrosion behavior. Microbiological corrosion in austenitic steel weldments has been documented. (Wahid)61, (Krysiak)14... 

The review of inhibited paint coatings would be incomplete without mentioning coatings with Cl that inhibit biological corrosion. Microbiologically influenced corrosion is the deterioration of a metal by a corrosion process that occurs either directly or indirectly as a result of the activity of living organisms [85]. 

Static secondary ion mass spectrometry (SIMS) of polymers Static SIMS is a technique that obtains a mass spectrum of the upper 2nm of a surface. Knowledge about surfaces is very important in studies of adhesion, corrosion, catalytic activity, biological compatibility, etc. By limiting the total primary ion dose from a primary ion beam to less than 10 ions per cm, each primary ion interacts with a sample that has not been damaged by previous primary ion impacts. In this way less than 1% of the total surface will be damaged by primary ion impacts. 

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. 

Analysis of biological activity does not automatically lead directly to a corrosion-rate measurement. However, with detection and correlation with process conditions, such information may also lead to improvements in the corrosion lifetime of the process equipment. 

At this point in the investigation, the relationship between the pits and the arrowhead-shaped regions of corrosion was uncertain. Several possible causes for the pitting were considered, such as siphonic gas exsolution, biological and/or microbiological activity, and debris (concrete chips, etc.) lodged in the tubes, but each was tentatively dismissed as improbable since none of the proposed mechanisms adequately accounted for all observations. 

A large number of parameters are involved in the choice of the corrosion protection system and the provision of the proteetion eurrent these are deseribed elsewhere (see Chapters 6 and 17). In partieular, for new locations of fixed production platforms, a knowledge of, for example, water temperature, oxygen content, conductivity, flow rate, chemical composition, biological activity, and abrasion by sand is useful. Measurements must be carried out at the sea location over a long period, so that an increased margin of safety can be calculated. 

As mentioned earlier, there is an inverse relationship between water volumes and oxygen concentration in soil. As soils dry, conditions become more aerobic and oxygen diffusion rates become higher. The wet-dry or anaerobic-aerobic alternation, either temporal or spatial, leads to higher corrosion rates than would be obtained within a constant environment. Oxygen-concentration-cell formation is enhanced. This same fluctuation in water and air relations also leads to greater variation in biological activity within the soil. 

Another important relationship between the salts of the soil and corrosion has to do with biological activity. Since the growth of plants and microorganisms depends upon the proper inorganic mineral nutrients, the action of these forms of life varies with the mineral content of the soil. While many of the possible indirect effects, such as the role of various nitrogenous... 

Reaction of the host tissue to metallic implants is affected by many factors including shape and size of the implant, movement between the implant and tissue, extent of corrosion attack, general degradation of the implant, and the biological activity of the resulting by-products of corrosion or degradation. 

DISOLVED OXYGEN (DO). One t>r the- most important indicators of the condition of a water supply for biological, chemical, and sanitary investigations. Adequate dissolved oxygen is necessary for the life of fish and other aquatic organisms, and is an indicator of corrosivity or water, photosynlhctie activity, septieity. etc. 

---