Soils, corrosion plant piping

The hot brine found in crystallization plants can be quite corrosive. Inconel, Monel, and stainless steel are used in most of the major equipment. Nonmetallic piping, including FRP, is common, within its serviceable temperature range, and Schedule 80 carbon steel pipe is often used in pump lines. The soil in a salt-processing plant can itself become corrosive as a result of spillage. Underground carbon steel lines therefore are protected by sacrificial anodes of magnesium or zinc or by application of direct electrical current. 

The danger of corrosion on buried installations in industrial plants is increased by various soils and by cell formation with cathodes of steel in concrete. The rest potentials of these foreign cathodes are between t/cu-cuS04 = and -0.5 V [4-6]. Factors that affect cell formation are the type of cement, the water/cement ratio and the aeration of the concrete [6]. Figure 12-1 shows schematically the cell action and the variation of the pipe/soil potential where there is contact with a steel-concrete structure. The cell current density is determined by the large area of the cathode [see Fig. 2-6 and Eq. (2-44)]. In industrial installations the area of steel surface in concrete is usually greater than 10 m ... 

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