Study on the role of niobium in corrosion mechanism of low-alloy pipeline steel in H2S-saturated solution

In this study, the role of Nb addition on the corrosion behavior of low-alloy steel exposed to H2S solution is studied by means of microstructure, macro/microsurface morphology characteristics, type of corrosion product, cross-sectional structure and elemental distri-bution. The addition of Nb is a route to refine grains and improve corrosion resistance. The surface formation process of iron sulfides changes from homogeneity to dispersion at the initial corrosion stage when Nb is added to steel. However, the transformation process and crystal structure of iron sulfides are not affected by the addition of Nb. The elemental distribution of corrosion products is not affected by Nb addition although thick and compact corrosion products are formed on the specimen surface of Nb steel. A schematic model is proposed to clarify the difference of the corrosion mechanism in atomic and molecular level.& COPY; 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.