Inhibition of Bromide-Pitting Corrosion of Type 904L Stainless Steel

Pitting corrosion of Type 904L (UNS N08904) stainless steel was investigated using the potentiodynamic polarization technique in different bromide concentrations, as well as in 0.6 M sodium bromide (NaBr) in the presence of some inorganic compounds at elevated temperatures. The critical pitting potential (E_pit) of the steel decreased linearly with logarithm bromide ion concentrations. The addition of various concentrations of molybdate $(MoO4−2)$⁠, dichromate $(CrO4−2)$⁠, tetraborate $(B2O7−2)$⁠, and nitrate $(NO3−)$ anions to 0.6 M NaBr increased E_pit values. E_pit values in 0.6 M NaBr, with and without 0.1 M $MoO4−2$⁠, $CrO4−2$⁠, and $NO3−$ anions, were found to be virtually independent of bulk pH, in the range from 3 to 10. At the same concentration of these anions, the pitting inhibition efficiency decreased in the following succession: $NO3−>MoO4−2>Cr2O7−2>B4O7−2$⁠. Scanning electron microscope inspection showed that lace-like pits were formed on Type 904L in the bromide solution.