CORROSION RESISTANCE OF ALLOYS IN CALCIUM BROMIDE AND CALCIUM CHLORIDE SOLUTIONS

摘要

Calcium bromide is used in the coal fire power plant industry to help control mercury emissions. Adding bromide ions to the flue gas can cause the total halide ion content of the downstream Wet Flue Gas Desulfurization (WFGD) slurry to increase. The objective of this study was to determine the effect of bromide additions in chloride-rich WFDG slurries on the crevice corrosion resistance of commercially-available corrosion resistant alloys. Cyclic potentiodynamic polarization (CPP) was used to collect voltage-current traces for each alloy. The traces were analyzed to estimate the performance of three alloys in model solutions with varying concentrations of calcium chloride, calcium bromide, and a mixture of calcium chloride and calcium bromide. The alloys had pitting resistance equivalent numbers of 35, 44, and 66. Three factors from the CPP tests were assessed: the open circuit potential, the breakdown potential, and the repassivation potential. The following conclusions were drawn from the CPP study: 1 Alloys with increasing PREn values require increasing total halide ion concentrations to shift breakdown or protection potentials. 2 Chlorides are more aggressive than bromides to the alloys tested using model electrolytes. A multi-variable regression analysis was performed to help reveal the statistically significant relationship(s) between open circuit potential, the breakdown potential, the repassivation potential, and the total halide ion concentration. A conservative ratio of bromides to chlorides can be used to estimate total effective chloride concentrations in slurry solutions containing mixtures of chlorides and bromides.