Intergranular Corrosion of Stainless Steel in Nitric Media

Abstract Austenitic stainless steels are largely used as structural materials for equipment handling nitric acid media in reprocessing plants. In almost all nitric media, these materials remain in their passive state. However, in the presence of oxidizing ions, their corrosion potential may be shifted towards their transpassive domain. In this domain they can suffer intergranular corrosion which limits their lifetime. Oxidizing species of the medium can be involved in electrochemical processes. In nitric media, the overall cathodic reaction is known to be the reduction of HNO3, whereas in nitric media with oxidizing ions the cathodic reaction may be reduction of oxidizing species. This cathodic reaction change leads to increase corrosion potential and corrosion rate. Several factors may influence this potential shift: the nature of oxidizing ions, concentration of ions, reduction and oxidation kinetics. In addition, the metallurgic impurities in the grain boundaries may explain their sensibility to corrosion. This study deals with oxidizing ions vanadium in nitric media and a new model to predict the intergranular long term corrosion rate.