Study on the hydrogen permeation resistance and protective mechanism of N80 pipeline steel coated with metal nitride coatings

Objective To address the risk of hydrogen embrittlement facing N80 pipeline steel in environments like hydrogen storage and transportation, the development of effective hydrogen permeation barrier coatings has become a crucial approach. However, a systematic, standardized comparison across successive generations of nitride coatings is still lacking, and the intrinsic structure–property correlation governing their hydrogen permeation resistance remains unclear. Therefore, this study comparatively evaluates the comprehensive protective performance of TiN, AlCrN, and (TiAlCrSiY)N coatings, elucidating their hydrogen barrier mechanisms to inform coating selection and design for hydrogen service environments. Methods Three types of nitride coatings were prepared on N80 steel substrates using multi-arc ion plating technology. The microstructure and mechanical properties of the coatings were characterized by scanning electron microscopy (SEM), digital microscopy, microhardness testing, and micro-scratch testing. Their corrosion resistance was evaluated via electrochemical polarization curves. A Devanathan-Stachurski dual electrochemical cell was employed to systematically evaluate the hydrogen permeation resistance of each coating under two distinct hydrogen charging modes: electrochemical (liquid-phase) and gaseous (gas-phase). Results The AlCrN coating exhibited the best overall performance, featuring the densest, flattest surface with the fewest defects, and it demonstrated the highest hardness and the strongest adhesion. Although the (TiAlCrSiY)N coating showed optimal corrosion resistance due to the synergistic effect of its multiple elements, it suffered from numerous surface agglomerates and micro-defects, resulting in the weakest adhesion among the three. Hydrogen permeation tests revealed that, regardless of the charging mode, the AlCrN coating provided the most effective barrier against hydrogen. Compared to the bare N80 substrate, it reduced the effective diffusion coefficient by 83.68%, with hydrogen blocking efficiencies reaching as high as 99.23% (gas-phase) and 84.76% (liquid-phase). The results clearly indicate a strong correlation between the hydrogen blocking efficiency of the coatings and their microstructural density. Conclusion A comprehensive evaluation confirms that all three nitride coatings provide good hydrogen resistance and other beneficial properties like corrosion resistance and adhesion. The microstructural density of the coatings is the primary factor determining their hydrogen permeation resistance. The AlCrN coating, with its superior microstructural density, balanced mechanical properties, and optimal hydrogen blocking efficiency, represents the most suitable protective solution for hydrogen service among the three options. Future development of hydrogen barrier coatings should prioritize process optimization to achieve low-defect, dense microstructures, followed by compositional optimization to enhance chemical stability and mechanical properties. This approach holds significant engineering guidance for ensuring the safety of hydrogen energy infrastructure.