Corrosion factors, weathering steel

Environmental Factors Affecting Corrosion of Weathering Steel... 

The coefficients in Table 3 provide a better theoretical understanding of how the different factors affect the corrosion of weathering steel. The 3 coefficients affect the solubility of the protective oxide layer and the a coefficients affect the diffu-sivity through the layer. The large ratio of a/3 confirms the relative insolubility of the rust on weathering steel in most environments. Sulfur dioxide increases the solubility of the film while NO2 and rain decrease the solubility. Rain apparently washes away acidic components (deposited during dew formation) that increase the solubility. 

Haynie, F.H. Environmental Factors Affecting the Corrosion of Weathering Steel. To be published in Proceedings of ACS Meeting, Degradation of Materials Due to Acid Rain, Arlington, Va., June 1985. 

Haynie, F. H., Spence, J. W., and Upham, J. B. (1976 and 1978). Effects of air pollutants on weathering steel and galvanized steel A chamber study. Atmospheric Factors Affecting the Corrosion cf Engineering Metals. ASTM STP 646, Proc. Golden Anniversary Symposium. ASTM, Philadelphia, pp. 30-47. Also report EPA-600/3-76-015 (1976), 85 pp. 

Weathering steels are steels to which small amounts of copper, chromium, nickel, phosphorus, silicon, manganese, or various combinations thereof have been added. This results in a low-alloy carbon steel that has improved corrosion resistance in rural areas or in areas exhibiting relatively low pollution levels. Factors that affect the corrosion resistance of these steels are ... 

Iron and the Environment The natural geological iron cycle comprises weathering of rocks and subsequent water-mediated re-sedimentation. The amount of mined iron exceeds the natural circulation by an estimated factor of 8. Approximately 25% of iron production is estimated to be destroyed by corrosion and dispersed into the environment. Additional iron is emitted by combustion of iron-containing coal, but approximately 70% of scrap is returned into the steel production process. The re-utilization of scrap requires 60% less energy than smelting ores. Zinc from coated steel scrap vaporizes during crude steel production and is recovered in dust filters (Ullmann 1989). 

Each polymer has its own distinctive chemical nature. Some are affected by fuels and lubricants, others are attacked by battery acid, and all are visually affected to some degree by weathering. However, none is susceptible to factors like acid rain, sea spray and road salt which can do so much damage to unprotected sheet steel, requiring the automotive industry to spend huge sums on corrosion protection. 

The most widely used simulated service test for static atmospheric testing is described in ASTM G 50, Practice for Conducting Atmospheric Corrosion Tests on Metals. It is used to test coated sheet steels for a variety of outdoor applications. Test materials, which are in the form of flat test panels mounted in a test rack (Fig. 16), are subjected to the cyclic effects of the weather, geographical influences, and bacteriological factors that cannot be realistically duplicated in the laboratory. Test durations can last from several months up to many years. Some zinc-coated steel specimens have undergone testing for more than 30 years. 

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