Defect-Controlled Hydrogen Permeation in GO/Al2O3 Composite Coatings on X80 Pipeline Steel: Quantitative Correlation with Raman-Derived Defect Density

Abstract

To enhance the resistance of X80 pipeline steel to hydrogen ingress in hydrogen-containing environments, GO/Al2O3 composite coatings with varying GO contents were fabricated by a sol-gel route and systematically investigated. Coating microstructure, carbon-framework defect characteristics, and hydrogen permeation behavior were examined by microscopy, Raman spectroscopy, and electrochemical hydrogen permeation testing. As the GO content increased, the coatings became progressively denser, the Raman-derived defect density (ND) decreased from 2.89 x 1011 cm-2 to 2.01 x 1011 cm-2, and the hydrogen-barrier performance improved markedly. Among the investigated samples, the pure GO coating exhibited the lowest steady-state permeation current density (i∞, 1.61 μA cm-2) and apparent diffusion coefficient (Dapp, 2.33 x 10-7 cm2 s-1), together with the highest hydrogen permeation resistance factor (HPRF, 62.1%), relative to bare X80 steel. By contrast, the pure Al2O3 coating afforded only limited improvement, indicating that practical barrier efficiency was governed more by coating defects than by the nominal barrier character of the ceramic phase alone. To relate coating structure quantitatively to hydrogen transport behavior, a semi-empirical defect-controlled correlation model was established using Raman-derived ND as a measurable microstructural descriptor. The fitted correlations between ND and Dapp and between ND and HPRF gave R2 values of 0.951 and 0.969, respectively, and the deviations between fitted and experimental values remained within approximately 10% within the present dataset. These findings show that the superior hydrogen-barrier performance of the GO-containing coatings arises from suppressed defect-assisted transport and a more effective diffusion-barrier structure, providing a quantitative basis for the design and optimization of composite hydrogen-barrier coatings for pipeline steels.