An in-situ investigation of the passive film on stainless steel and Inconel 600 in high temperature, pressurized, impurity containing water

An in situ investigation of the films that formed on stainless steel and Inconel 600 at 288°C and 1500psi were performed using Surface Enhanced Raman Spectroscopy (SERS). By examining the changes in the films that formed on these materials, information was obtained about how these films affect the Intergranular Stress Corrosion Cracking (IGSCC) of these two metals. Stainless steel was examined in water with dilute amounts of sulfate added, which is known to enhance IGSCC. It was observed that the addition of sulfates in no way affected the films that formed on the stainless steel. The enhanced susceptibility for IGSCC of stainless steel is due to an increase in the conductivity of the water. The increased conductivity, due to the added sulfate, reduced the potential drop down a crack, so the minimum concentration of oxygen required to cause IGSCC is less than in high purity water. Thus, the sulfate additions led to an enhancement in the IGSCC. Incone1 600 was studied in boron and lithium containing solution at 288°C. The results showed that in the corrosion potential region where IGSCC occurs, an M3O4 oxide enriched in chromium was stable. This suggested that the M3O4 was the deleterious film that enhanced SCC in the Inconel 600. Once the potential was increased above the SCC region, NiO formed, which must counteract the effects of the chromium enriched M3O4. The results from this study suggested that there is a correlation between film formation and SCC susceptibility.