Preparation and Hydrogen Barrier Property of FexAly/Al/Al2O3 Composite Coating on X80 Steel Surface

Hydrogen-induced embrittlement is a significant safety concern for steel pipelines used in the transmission of hydrogen-blended natural gas. To mitigate this issue, hydrogen barrier coatings can be applied to the surface of steel substrates to reduce hydrogen permeation. In this study, rare earth oxides were optimized via first-principles calculations to identify the most effective doping agents. Subsequently, a FexAly/Al/Al2O3 composite coating doped with La2O3 and Ce2O3 was successfully applied to the surface of X80 steel using hot-dip aluminum plating combined with anodic oxidation. The coating was characterized using various techniques, including SEM, EDS, XRD, XPS, and hydrogen permeation tests. The results demonstrated that co-doping La2O3 and Ce2O3 resulted in a lower adsorption energy of Al2O3 to hydrogen molecules, and improved the surface quality of the aluminizing layer and the composite coating. Electrochemical hydrogen permeation tests showed that the FexAly/Al/Al2O3 composite coating significantly improved the hydrogen barrier property of X80 steel. The anodizing current density was found to have a significant effect on the coating's morphology, which in turn affected the hydrogen barrier property of the coating. The composite coating obtained at an anodizing current density of 2 A/dm(2) was uniform and dense, without noticeable defects, and exhibited the best hydrogen barrier property.