Hydrogen permeation in co-electrodeposited SiC and MWCNT-COOH Ni coatings in H ₂ S environments

Hydrogen embrittlement remains a critical damage mechanism for structural materials commonly used in oil and gas pipeline and well, particularly under H 2 S-containing sour conditions. Nickel coatings can enhance corrosion resistance for structural carbon steels avoiding the selection of corrosion resistant alloys. In this study, Ni-based composite coatings containing silicon carbide (SiC) and multi-walled carbon nanotubes (MWCNT-COOH) were co-electrodeposited to improve hydrogen barrier performance by limiting hydrogen ingress. The influence of deposition current density on microstructure and hydrogen permeation was investigated under identical deposition time and charging conditions. Hydrogen permeation was assessed using the Devanathan–Stachurski cell as a comparative electrochemical method relevant to aqueous H 2 S-related environments. Results indicate that the composite coating deposited at 5 A/dm 2 exhibited the most compact and homogeneous morphology, with well-dispersed SiC and MWCNT-COOH within the nickel matrix. The modified microstructure was associated with reduced surface defects and lowered hydrogen permeation. Compared to conventional nickel coating, the composite coating achieved a 75% reduction in effective hydrogen permeation coefficient, demonstrating that hydrogen permeation resistance is governed by microstructure-controlled transport rather than coating thickness alone. These findings highlight the potential of Ni-based composite coatings as hydrogen barrier layers for oil and gas pipeline steels in sour environments.