Metals processing factors influencing corrosion

Atmospheric corrosion is an electrochemical process with the electrolyte being a thin layer of moisture on the metal surface. The composition of the electrolyte depends on the deposition rates of the air pollutants and varies with the wetting conditions. The factors influencing the corrosivity of atmospheres are gases in the atmosphere, critical humidity and dust content. Two rural environments can differ widely in average yearly rainfall and temperature and can have different corrosive... 

In designing an effective laboratory test program, it is important to consider factors that influence corrosion in a freshwater environment. The following discussion summarizes these factors, but the complexity of the topic does not permit a detailed discussion in this chapter. Details on corrosion processes affecting metals in freshwaters are found in the references provided at the end of this chapter [7--5]. 

Atmospheric corrosion is a complicated electrochemical process taking place in corrosion cells consisting of base metal, metallic corrosion products, surface electrolyte, and the atmosphere. Many variables influence the corrosion characteristics of an atmosphere. Relative humidity, temperature, sulfur dioxide content, hydrogen sulfide content, chloride content, amount of rainfall, dust, and even the position of the exposed metal exhibit marked influence on corrosion behavior. Geographic location is also a factor. 

No corrosion occurs in a completely dry environment. In soil, water is needed for ionisation of the oxidised state at the metal surface. Water is also needed for ionisation of soil electrolytes, thus completing the circuit for flow of a current maintaining corrosive activity. Apart from its participation in the fundamental corrosion process, water markedly influences most of the other factors relating to corrosion in soils. Its role in weathering and soil genesis has already been mentioned. 

Atmospheric corrosion is influenced by a number of meteorological factors of which humidity is the most important. This is because the electrochemical corrosion process on metals requires moisture. 

Tribocorrosion can be defined as the study of the influence of environmental factors (chemical and/or electrochemical) on the tribological behavior of surfaces. In other words, the process leading to the degradation of a metaUic and/or non-metallic material resulting from a mechanical contact (sliding, friction, impact,...) combined to a corrosive action of the surrounding environment. 

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