Corrosion classification

Table 18.4 Skin Corrosion Classifications and pH Data for 44 Chemicals... 

PACER LIME algorithm for atmospheric corrosion classification... 

The International Standard Organization (ISO) developed a corrosivity classification system verified through exposure that has been carried worldwide. The ISO classification system is based on the assumptions that only the time of wetness and the concentration of pollutants in the atmosphere, SO2 and chlorides, control the corrosion rates of metals. Table 10.1 shows the Hst of ISO standards related to atmospheric corrosion of metals [39]. 

In reality the mechanism of concrete deterioration as a consequence of acid corrosion, if it is sulphuric acid, is the same as in case of sulphate corrosion. For this reason in both environments the matrix based on Portland cement with reduced Cj A content is more resistant. This example shows the imperfection of kind of corrosion classification, presented above. 

Knotkova, D. (1993). Atmospheric corrosivity classification. Results of the international testing programme ISOCORRAG. Paper presented to International Corrosion Conf, Houston, TX, typescript, 16 pp. 

The corrosivity of indoor atmospheres must be determined by standard panel exposures. Currently ISO/TC 156 is developing standards on indoor corrosivity classification. These standards have not yet been adopted. 

Corrosivity of waste is determined by measuring the pH of the waste to identify its relative acidity or alkalinity. In this test, waste is corrosive, and therefore hazardous, if its pH is less than 2.0 or greater than 12.5. (Several currently used throwaway sulfur recovery systems, such as fluidized bed combustion and sorbent injection, have problems meeting the RCRA corrosivity classification because of high pH levels due to large amounts of free lime in their waste.)... 

The assessment is directed at ferrous materials (steels, cast irons, and high-alloy stainless steels), hot-dipped galvanized steel, and copper and copper alloys. Summation of the individual ratings produces an overall corrosivity classification into one of four categories with scores less than -10 indicating a highly corrosive soil and positive values (>0), a noncorrosive environment (Table 10.7). It has been pointed out that sea or lake beds cannot be assessed using this worksheet. 

Table 10.7 Overall Soil Corrosivity Classification in Dechema Soil Corrosivity Worksheet [5]...

While it is generally important to rank macro-level environments according to a normalized corrosivity classification, specific information about atmospheric corrosivity and corrosion rates is often required on the micro level. For example, a corrosion risk assessment may be required for a military aircraft operating out of a specific air base environment. One such requirement resulted in a report of the... 

The nature and rate of atmospheric corrosive attack are dependent on the composition and properties of the thin-film surface electrolyte. Time of wetness and the type and concentration of gaseous and particulate pollutants in the atmosphere largely affect these in turn. The classification of atmospheric corrosivity is important for specifying suitable materials and corrosion protection measures at the design stage and for asset maintenance management to ensure adequate service life. Two fundamental approaches to classifying atmospheric corrosivity have been followed, as shown in Fig. 2.7. These two approaches to environmental classification can be used in a complementary manner to derive relationships between atmospheric corrosion rates and the dominant atmospheric variables. Ultimately, the value of atmospheric corrosivity classifications is enhanced if they are linked to estimates of actual corrosion rates of different metals or alloys. 

The ISO methodology. A comprehensive corrosivity classification system has been developed by the International Standards Organization (ISO). The applicable ISO standards are listed in Table 2.1. Verification and evolution of this system is ongoing through the largest exposure program ever, undertaken on a worldwide basis. ... 

Procedure and limitations. The ISO corrosivity classification from atmospheric parameters is based on the simplifying assumption that the time of wetness (TOW) and the levels of corrosive impurities determine the corrosivity. Only two types of corrosive impurities are considered, namely, sulfur dioxide and chloride. Practical definitions for all the variables involved in calculating an ISO corrosivity index follow. 

Knotkova D., Boschek P., Kreislova K., Results of ISO-CORRAG program processing of one-year data in respect to corrosivity classification, ASTM, STP 1239, 1995, p. 38-55. 

All corrosive materials and solutions have the EPA hazardous waste number D002. The following is one of the more commonly used corrosive classification... 

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