Environmental consideration corrosion

With the increasing emphasis on energy conservation and environmental considerations, additives for fuels that can correct combustion-related problems have aroused considerable interest. Many commercial fuel additives are combinations of organometaHics, dispersants, emulsifiers, and carrier solvents. The organometaHic, often a metal soap, acts as a combustion catalyst, increasing efficiency with reduction of smoke, deposits, and corrosion. 

Although transformers suitable for other industrial installations are generally suitable for producing applications, certain options may be desirable— primarily due to environmental considerations. At locations subject to harsh environmental conditions, and particularly at locations subject to washdown with high-pressure hoses, non-ventilated enclosures are desirable, if not necessary. Likewise, at locations subjected to salt water and salt-laden air, it often is desirable to specify copper windings and lead wires. Most manufacturers provide standard units with aluminum windings and lead wires. Even if aluminum coils are used, it is almost always desirable to require stranded copper lead wires. This will lessen corrosion and loose terminal problems when transformers arc interconnected to the facility electrical system with copper conductors. If the transformers are to be installed outdoors in corrosive environments, cases should be of corrosion-resistant material (e.g., stainless steel) or be provided with an exterior coating suitable for the location. 

Important characteristics determining the quality of a feedstock are the C/H ratio as determined by elemental analysis and the BMC Index [4.7] (Bureau of Mines Correlation Index), which is calculated from the density and the mid-boiling point resp. the viscosity. Both values give some information on the aromaticity and therefore the expected yield. Further characteristics are viscosity, pourpoint, alkaline content (due to its influence on the carbon black structure), and sulfur content, which should be low because of environmental and corrosion considerations. 

Geochemistry and Environmental Considerations. The geochemistry of steam-dominated geothermal resources is concerned primarily with condensable and noncondensable gases in the steam. The amounts and composition of noncondensable gases in Geysers steam vary rather widely within the steamfield as shown in Table 1. The predominant gas is carbon dioxide (qv) in all cases. The most important noncondensable gas, however, is hydrogen sulfide, because H2S can present both corrosion and environmental problems. 

The high profile of environmental considerations ensures that the development of non-corrosive decontamination systems with biodegradable components remains a high priority. The use of A-alkyl-2-pyrrolidones as the major organic biodegradable component of a hypochlorite-based liquid system has been shown to be effective in the decontamination of the major CW agents The use of strong base in A-ethyl-2-pyrrolidone has been shown to function in the same way as DS2 . 

As described already, not only the property of corrosion resistance, but other desired functions are required for materials. Therefore, the best surface finishing processes need to be selected for specific materials in certain environments. Figure 8 shows the concept to design the surface finishing for corrosion control. In addition to the conventional concept, we have to take the possibility of environmental harmfulness into consideration. Corrosion often leads to the contamination of our environment, since the anodic dissolution is the essence in most cases. Therefore, sacrificial corrosion protection might be prohibited in some cases. From that perspective, the appropriate surface coating will be more versatile in the future. Chapter The Application of Corrosion Protection presents and discusses surface finishing processes. 

Metal coatings are applied by dipping, electroplating, spraying, cementation, and diffusion. The selection of a coating process for a specific application depends on several factors, including the corrosion resistance that is required, the anticipated lifetime of the coated material, the number of parts being produced, the production rate that is required, and environmental considerations. 

Historically, various investigators in Europe have used hydrochloric acid-px>tassium dichromate solutions for testing the exfoliation susceptibility of all types of aluminum alloys. An example is the Russian Stanchtid GOST 9.904-82, Aluminium Alloys Methods of Accelerated Exfohation Corrosion Testing [22]. It should be noted, however, that hexavalent chromium (Cr ) solutions are considered undesirable for health and environmental considerations and have been prohibited in some countries. 

The alumina and the Cr(OH)3 formed together serve as a chemical barrier to corrosion. This barrier is however not entirely immune to pinholes and cracks. Additionally, the chromates are highly toxic, and there is a strong movement at present to eventually replace them due to environmental considerations. Commercially available chromate conversion coatings include Elf-Atochem s "Alumigold" and Accelagold" and Parker Amchem s "Alodine 1200S". 

In general, as the corrosiveness of the environment increases, the rate of crack growth also increases. Environmental factors constituting corrosiveness vary with the metal under consideration. 

The effective use of metals as materials of construction must be based on an understanding of their physical, mechanical and chemical properties. These last, as pointed out earlier, cannot be divorced from the environmental conditions prevailing. Any fundamental approach to the phenomena of corrosion must therefore involve consideration of the structural features of the metal, the nature of the environment and the reactions that occur at the metal/environment interface. The more important factors involved may be summarised as follows ... 

The implications of the terms predictable and unpredictable used in the context of corrosion require further consideration, since they are clearly dependent on the knowledge and expertise of the engineer, designer or corrosion designer who takes the decision on the metal or alloy to be used, or the procedure to be adopted, to control corrosion in a specific environmental situation. On this basis a corrosion failure (i.e. failure of the function of the metal due to corrosion within a period that is significantly less than the anticipated life of the structure) may be the result of one or more of the following possibilities ... 

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