PITTING CORROSION BEHAVIOR OF SUPERFERRITIC STAINLESS-STEEL IN WATERS CONTAINING CHLORIDE

On a cost-performance basis, superferritic stainless steel (SFSS) grades can now be considered competitive choices for brackish and sea water cooling systems. The pitting corrosion of a SFSS (X2CrNiMoTi 25 3.6 3.5) was tested in a chloride/sulfate solution similar to sea water, as a function of temperature, pH, and salinity Potentiodynamic polarization techniques and experimental stability diagrams were used to evaluate the pitting conditions. The critical pitting temperature (CPT) was found to be above 50-degrees-C, and the re-passivation tendency under critical temperatures was satisfactory even when the pH was less than the depassivation pH, a condition which simulates a propagating occluded cell. The SFSS behavior in the presence of chlorine was evaluated by means of potentiodynamic tests and by studying the cathodic reduction kinetics of Cl2 and O2 (air).