Hydrogen permeation in uncoated and coated X60steel

The sustainable storage and transport of hydrogen represent major challenges for the deployment of renewable energy systems, requiring a comprehensive understanding of hydrogen–material interactions in pipeline steels and effective strategies to limit hydrogen uptake. This PhD research investigates hydrogen diffusion and permeation in API 5L X60 pipeline steel, with a focus on the development and validation of experimental and analytical methodologies to evaluate RF-magnetron-sputtered tungsten coatings as hydrogen permeation barriers. A combined electrochemical and surface analytical approach was employed to characterize hydrogen uptake, transport mechanisms, and barrier performance of both the steel substrate and tungsten coatings. Hydrogen permeation experiments enabled reliable evaluation of hydrogen transport behavior in X60 steel, highlighting the dominant role of bulk microstructure over surface condition in controlling hydrogen diffusion and accumulation. A novel non-destructive XPS-based method was developed to assess through-thickness porosity in tungsten coatings, allowing rapid evaluation of coating integrity and uniformity. Electrochemical permeation testing demonstrated a strong correlation between coating porosity and hydrogen barrier effectiveness. Dense and uniform tungsten coatings significantly reduced hydrogen permeation, while coatings with higher defect density showed limited barrier performance, indicating that coating quality and interfacial integrity are the key factors governing hydrogen permeation resistance. Depth-resolved spectroscopic analyses revealed near-surface chemical modifications in tungsten coatings, suggesting that both structural and chemical features contribute to hydrogen barrier behavior. Overall, this work provides experimentally validated methodologies and design guidelines for the development of effective hydrogen permeation barriers for pipeline steel applications.