Pitting Corrosion Behavior of Type 904L Stainless Steel in Sodium Bromide Solutions

Potentiodynamic cyclic anodic polarization, scanning electron microscopy (SEM), and energy dispersive x-ray (EDX) techniques were used to study pitting corrosion behavior of type 904L (UNS N08904) stainless steel (SS) in aerated or argon-deaerated 0.6 M sodium bromide (NaBr) solutions at 25°C. Type 904L SS was shown to undergo pitting corrosion even though the steel has a high molybdenum content (4.5% Mo). Effects of temperature, air, pH, bromide ion concentration (CBr–), and bromide/chloride ratio on pitting corrosion were studied. The critical pitting potential (Epit) was found to decrease with increasing temperature and CBr–. Changing the pH of the 0.6 M NaBr solution did not affect Epit from pH 2 to 11. At pH ≥ 12, pitting corrosion was prevented. Addition of chloride ions to bromide at a fixed halide concentration of 0.6 M inhibited pitting corrosion attack. Morphology of the pits produced was inspected by SEM after anodic polarization treatment in different bromide solutions.