Metal corrosion impact

Anaerobic conditions are traditionally a major concern when dealing with microbial-induced transformations of wastewater in a collection system. The problem is primarily associated with the risk of hydrogen sulfide and odorous organic compounds. The corresponding problems appear as concrete and metal corrosion, health-related impacts and malodors. Such in-sewer process-related problems have been reported as early as over 50 years ago (Parker, 1945a, 1945b Pomeroy and Bowlus, 1946). 

Utility systems for equipment and space heating and cooling frequently use heavy metal corrosion inhibitors in their heat transfer fluids. Chromate compounds are among the best corrosion inhibitors available. Nonchromate inhibitors that have proved to be feasible substitutes include polyphosphates, organophosphates, zinc, molybdates, and aromatic azoles. Some of these compounds have their own environmental impacts, however. Azoles, for instance, can be quite dangerous to human health. 

The concentrations of specific elements can be useful indicators of some coal quality characteristics. Huggins et al. (5) and Reid (6) demonstrated that the aluminum, silicon, potassium, calcium, magnesium, and sodium values of a coal ash can be used to estimate ash fusion temperature. The Si/Al ratio of coal ash has been used as an indicator of the abrasiveness of a coal. Sodium is a major contributor to boiler fouling and metal corrosion and contributes to agglomeration in fluidized-bed reactors. Trace elements are generally defined as those elements with concentrations below 0.1 wt. % (1000 ppm). Despite concentrations in the parts-per-million range, certain trace elements can have a significant impact on coal... 

The built-in costs of corrosion of automobiles were identified as corrosion protection for steel body panels such as metallic zinc coatings, paint, adhesives and sealants, nonferrous metals, corrosion-resistant materials, rust-proofing heat exchanger components, mufflers, and tail pipe corrosion. The greatest impact on the cost of corrosion for automobiles was the adverse effect of corrosion on the cost of replacement of the automobile. Both the lO model and focused sector study showed that in both models the cost of replacement of the automobiles dominated the total cost and avoidable cost estimation. 

Since the invention of metal technology several thousand years ago, the prevention of metal corrosion has been a problem of fundamental practical importance. To try to solve corrosion problem, several methods can be adopted, depending on environment aggressiveness, corrosion heaviness and materials costs. In this section, some of the most diffuse protection methods are described, in order of efficacy and impact on corroding systems (environments, type and aspect of materials). 

B. Little, M. McNeil, and F. Mansfeld, The impact of alloying elements on microbiologically influenced corrosion—2l review. Proceedings 12th International Congress on Metal Corrosion, NACE, Houston, 1993, pp. 3680-3686. 

The enormous economic impact of corrosion of metallic stractures in aggressive environments is a very important issue worldwide. The most typical corrosive environments are the natural waters atmospheric moisture containing man-generated pollutants and man-made solutions. Therefore, metallic stractures operated in such environments suffer from continual and strong corrosion attack. This is especially important for transport systems, often used in a wide variety of environments that can combine different corrosive impact factors. 

When antifreeze becomes unsuitable for use, either because of depletion of inhibitors, presence of corrosion products or corrosive ions, or degradation of the fluid, recycling and reuse of the antifreeze, rather than disposal, may be considered. Although ethylene glycol is readily biodegraded in typical municipal waste treatment faciHties, antifreeze disposal becomes problematic because the coolant may contain hazardous quantities of heavy metals picked up from the cooling system. Recycling may be economically preferred over coolant disposal and reduces the concern for environmental impact. 

Impingement or erosion attack can occur when Hquids or gases impact metal surfaces at high velocity. The corrosion rate is high under such circumstances because any corrosion product films that can be protective if adherent are swept away as quickly as they are formed to leave exposed fresh surface. 

Cavitation Formation of transient voids or vacuum bubbles in a liquid stream passing over a surface is called cavitation. This is often encountered arouna propellers, rudders, and struts and in pumps. When these bubbles collapse on a metal surface, there is a severe impact or explosive effec t that can cause considerable mechanical damage, and corrosion can be greatly accelerated because of the destruction of protective films. Redesign or a more resistant metal is generally required to avoid this problem. 

Second, deformation twins were observed in metal grains at the damaged surfaces. Deformation twinning cannot result from corrosion but is the consequence of shock loading of the metal, precisely the effects of microjets of water impacting on the metal surface. 

Film is locally removed by dissolution, surface shear stress or particle/bubble impact but it can repassivate. Erosion corrosion rate is a function of the frequency of film removal, bare metal dissolution rate and subsequent repassivation rate. 

It is possible to envisage what might happen if an electrical intervention was made in the corrosion reaction by considering the impact on the anodic and cathodic reactions. For example, if electrons were withdrawn from the metal surface it might be anticipated that reaction 10.2 would speed up (to replace the lost electrons) and reaction 10.3 would slow down, because of the existing shortfall of electrons. It follows that the rate of metal consumption would increase. 

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