Pitting susceptibility of UNS NO. 8904 stainless steel in bromide-sulphide solution

The effect of sulphide ion on the pitting corrosion behaviour of UNS* no. 8904 (904L) stainless steel (SS) in 0.6 M NaBr at 25°C has been investigated by using potentiodynamic anodic polarization and electrochemical impedance spectroscopy techniques. The pitting potential, Epit, in 0.6 M NaBr + 10-2 M Na2S was more negative than that obtained in 0.6 M NaBr, and decreased with increasing temperature in the range 25-60°C. Scanning electron microscopy observation showed that elemental sulphur formed on the steel surface before Epit was reached in 0.6 M NaBr + 10-2 M Na2S at 60°C. Epit of 904L SS was pH independent in the pH range from 3-10 of 0.6 M NaBr + 10-2 M Na2S at 25°C, while at high pH values the pitting was suppressed. The impedance measurements showed that the charge transfer resistance, Rt, decreased with time, when the controlled potential became higher than Epit. © 1998 Kluwer Academic Publishers.