Critical Pitting Temperature Measurements for Evaluating Superaustenitic Stainless Steels Resistance to Solutions Modeling Wastewater Treatment of Flue Gas Desulfurization Plants

B. Eremiáš, V. Číhal, E. Kalabisová and L. Turek

Abstract
Critical pitting temperature (CPT) determination by potenciostatic procedure is often used as a method of screening stainless steels in solutions with activity range 0.067 – 4.3. Values of activity of chloride ions as well as pH values for those solutions are quite different from the values of the same parameters in solutions modeling wastewater treatment of flue gas desulfurization plants. In those waters the soluble components, mainly calcium chloride (which must be treated by evaporation and crystallization) can give solutions with pH values below 4and activities of chloride ions much more higher. Thus, even small changes of CaCl2 concentration can give an increase in chloride ions activity. In the work reported here the effect of two different activities of chloride ions was investigated using potenciostatic CPT measurements on superaustenitic stainless steels in c = 5.685 and 5.88 mol L–1 CaCl2 solutions with pH values below 4. The results demonstrated that an increase in the activity of chloride ions causes a decrease in the potential at which, for given a temperature, the growth of stable pits is possible.

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Keywords
Electrochemical tests, stainless steels, flue gas desulfurization plants