A Facile Preparation of Black Oxide Coating with Favorable Corrosion Resistance, Hydrogen Barrier Property, and Adhesion to Epoxy Resin

Hydrogen transportation pipelines require steels with enhanced hydrogen barrier properties. This study aims to develop a composite coating with integrated functions of corrosion resistance and hydrogen barrier. Firstly, a dense black oxide layer was chemically formed on X65 pipeline steel at room temperature by a modified blackening process. Then, the traditional epoxy resin was applied onto the surface of black oxide layer, obtaining a novel black oxide/epoxy resin composite coating. For the blackening process, the effects of surface pretreatment methods (untreated, polished, sandblasted) and blackening solution pH (1.5, 2.5, 3.5) on the microstructure, corrosion resistance and hydrogen barrier performance were investigated, as well as the adhesion strength of composite coating. Results show that corrosion resistance and hydrogen barrier performance of coatings depended on both blackening solution pH and pretreatment method, with polished substrates and pH 2.5 yielding optimal results. Additionally, the black oxide layer served as an effective adhesion-promoting interlayer, enhancing the bonding and durability of the composite coating. This novel black oxide/epoxy composite coating system offers valuable insights for designing hydrogen barrier coatings for pipeline steels.