Pitting Corrosion Behavior of UNS N08904 Stainless Steel in a Chloride/Sulfate Solution

Type 904L (UNS(1) N08904) stainless steel exhibits pitting corrosion in certain environments at elevated temperature, even though the steel has a high molybdenum content. Potentiodynamic polarization techniques were used to establish the characteristic pitting conditions in a chloride/sulfate solution that simulates typical seawaters. The effects of chloride concentration, temperature, pH value, and chlorination on the pitting potential were studied. It was found that the critical pitting temperature for this steel is about 60°C in the solutions used. The free-corrosion potentials and cathodic reduction kinetics of chlorine and oxygen were measured in order to obtain an indication of the pitting corrosion tendency in seawater environments. The morphology of corrosion pits produced was inspected by optical and scanning electron microscopy following anodic polarization treatments in both chlorinated and non-chlorinatβd solutions.