Working Environmental Corrosion

Summitt and Fink [41] developed an environmental corrosion severity classification system for steel aluminum, magnesium, and titanium aircraft alloys. The corrosion damage algorithm (CDA) is shown in Fig. 10.10. This classification takes into account either the distance from saltwater or moisture levels. When the CDA considers the moisture levels in an atmosphere, the values of the concentration of the pollutants are compared with those listed in the Working Environmental Corrosion Standards (WECS) [42],... 

As demonstrated by the recent works on corrosion, it is worthwhile to have at our disposal (or to acquire) a perfect knowledge of the whole environmental conditions i.e. of the considered molten salt chemistry and its dependence on the nature of the cover gas. This allows us to predict, from a thermodynamic point of view, the operating conditions leading to reduced corrosion effects, the consistency of which is being further experimentally tested. 

Systems. Corrosion is usually studied in an isolated fashion in the laboratory, but in practice is clearly the result of interacting systems in the environment. Studies need to be conducted on the way in which the component parts of corroding systems Interact under actual environmental conditions, and on the way in which the components of the environment interact with the total corroding system. This would suggest not only design work for corrosion protection systems, but also additional work on the sensing and monitoring of corrosion in real hostile environments. 

Purposely added elements also often help to pinpoint an exact locus of failure as illustrated in Figure 11. Here a failure is shown to have occurred near the priner-aluminum alloy interface as indicated by SIMS and other spectra which showed elements of the corrosion inhibitor (strontium chromate) on the failure surfaces. Similar work using SIMS has been used to infer environmental corrosion resistance and to determine thickness of thin silanized surfaces... 

Galvanic corrosion typically involves two or more dissimilar metals. It should be recognized, however, that sufficient variation in environmental and physical parameters such as fluid chemistry, temperature (see Case History 16.3), flow velocity, and even variations in degrees of metal cold work can induce a flow of corrosion current even within the same metal. 

In the light of what has been said above, little further explanation of the implications of the title of the present work is required. Its treatment of the subject of corrosion will centre round the control of the environmental interactions of metals and alloys used as materials of construction. 

Ion vapor deposition (IVD) was developed from vacuum deposition by McDonnell Douglas Corporation. They used IVD of aluminum as a substitute for cadmium plating on steel aircraft parts. Aluminum provides corrosion protection similar to cadmium, it can withstand 925°F temperatures as opposed to 450°F for cadmium, and it is cheaper on a volume basis than either cadmium or zinc (Higgins 1989). Aluminum is also far less toxic than cadmium, and its use in an IVD system offers safer working conditions and less environmental risk. 

Sulfur chemistry is important both in combustion and in the petrochemical industry. Most fossil fuels contain sulfur, and also biofuels and household waste have a sulfur content. As a consequence sulfur species are often present in combustion processes. Knowledge of gas-phase sulfur chemistry occurring in combustion has bearing on pollutant emissions and on system corrosion. Air pollution by SO2 still constitutes a major environmental concern and search for control techniques has motivated research also on high-temperature homogeneous sulfur chemistry. However, more recent work on sulfur chemistry has been concerned mainly with the effect of sulfur on other pollutant emissions, such as NO and CO, and with the SO3/SO2 ratio, which is important for the corrosive potential of the flue gas and for formation of sulfur containing aerosols. 

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