Effect of Oxidizing All-Volatile Treatment on Alumina-Forming Austenitic Oxidation Behavior in Supercritical Water

The corrosion behavior of a novel alumina-forming austenitic stainless (14Cr-24Ni-2.5Al) after 1000 hours of exposure to supercritical water (SCW) with deaerated and AVT(O) water chemistry. X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy was used to investigate the microstructure evolution of oxide layers and to explain the likely mechanism. Although the corrosion weight gain in deaerated supercritical water was lower than in AVT(O), the weight gain curves of AFAs in deaerated SCW followed near-linear rate equations, whereas the kinetic weight gain curves in AVT(O) followed the near-parabolic rate equations. The oxide film of AFAs could be separated into two distinct layers in both water chemistry environments, an exterior Fe-rich later and an inner Cr-Al internal oxidation layer, and neither formed a visible continuous alumina film, which was attributed to the lower Cr concentration. The development of amorphous Fe2O3 oxide filling the magnetite spinel interstices may explain the reduced porosity of the outer iron oxide in the AVT(O) environment compared to the deaerated environment. The reasons for the differences in corrosion behavior between the two chemical feedwater conditions were discussed and explained. These findings revealed that while AVT(O) was not effective in short corrosion resistance, it can help with long-term corrosion resistance.