TAILIEUCHUNG - Corrosion Engineering Principles and Practice2
corrosion is surely the most visible of all , for example, rusty bridges, flag poles, buildings, and . The large segment of the paint industry committed to and application of products for the protection of metals,.as well as the large-scale operations of the galvanizing industry the importance of controlling atmospheric corrosionEconomic losses caused by atmospheric corrosion are therefore account for the disappearance of a significant metal produced. Consider, for instance, agricultural machinery,.steel structures, fences, exposed metals on buildings, or bodies, and the myriad of other metal items that are the scrap yard when they become unusable as a result of corrosionThese constitute direct losses from corrosionAtmospheric corrosion has been reported to account for in terms of cost and tonnage than any other type of processes. This particular type of material recently received more attention, particularly by the , since the Aloha incident in 1988, when a Boeing 737 lost portion of the upper fuselage in full flight at 7300 m [1]All of the general types of corrosion attack occur in the atmosphereSince the corroding metal is not bathed in large quantities of electrolyte,.most atmospheric corrosion operates in highly localized corrosion cells,.sometimes producing patterns difficult to explain as in the example rusting galvanized roof shown in Fig. , calculation of the electrode potentials on the basis of , the determination of polarization characteristics, electrochemical operations are not as simple in as they are in liquid immersion corrosion. However, all electrochemical factors which are significant in corrosion operate in the © 2008 by The McGraw-Hill Companies, Inc. Click here for terms of use330Chapter 9FIGURE Rusting galvanized roof with regular bands of Types of Corrosive atmospheres have been traditionally classified into four , most environments are in fact mixed and present no . Furthermore, the type of atmosphere may vary with pattern, particularly where corrosive pollutants are present, local conditions (Fig. ) [2]. industrial atmosphere is characterized by pollution of sulfur compounds such as sulfur dioxide (SO2), a precursor rain, and nitrogen oxides (NOx), the backbone of smog in . Sulfur dioxide from burning coal or other fossil fuels is picked moisture on dust particles as sulfurous acid. This is oxidized by process on the dust particles to sulfuric acid, which settles droplets and fall as acid rain on exposed surfaces. is that contaminants in an industrial atmosphere, plus dew or fog,.produce a highly corrosive, wet, acid film on exposed surfacesIn addition to the normal industrial atmosphere in or plants, other corrosive pollutants may be present. These various forms of chloride which may be much more the acid sulfates. The reactivity of acid chlorides with is more pronounced than the reactivity of other as phosphates and nitratesAtmospheric CorrosionFIGURE Bird damage to a 1931 bronze statue commemorating the battles in WW I. (Courtesy of Kingston Technical Software) marine atmosphere is laden with fine particles of sea mist the wind to settle on exposed surfaces as salt crystals. The salt deposited may vary greatly with wind velocity and it may, weather conditions, even form a very corrosive sal
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