Influence of Surface Oxide Layers on the Hydrogen Permeation Behaviour through X65 Pipeline Steel

Abstract

The global transition to sustainable energy has accelerated the demand for hydrogen as a
clean fuel source. Carbon steel pipelines play a vital role in hydrogen transport and storage infrastructure, but their potential susceptibility to hydrogen embrittlement poses a significant challenge.
Hydrogen ingress, facilitated by environmental and operational factors, undermines the
structural integrity of these steel pipelines, making it critical to develop strategies to mitigate
hydrogen-induced degradation. The formation of internal surface oxide layers on these steels
significantly influences hydrogen-material interaction processes, underscoring the need for
further investigation and understanding, a focus of this study.
This study focuses on a naturally formed oxide layer on pipeline steel API 5L X65 and its role in
influencing hydrogen permeation behaviour. Using characterization techniques including optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Raman spectroscopy, the composition and thickness of the oxide layer were studied.
Electrochemical hydrogen permeation experiments using the Devanathan–Stachurski (D-S)
cell were performed on bare steel samples (with oxide removed from the surface) and oxide-covered steel samples. The results showed a significant delay in hydrogen permeation in the
case of oxide-covered steel. An estimation of the hydrogen diffusion coefficient (D_eff) was
carried out, showing significantly lower values for oxide-covered steel (5.57×10⁻¹⁰ cm²/s and
7.13 × 10⁻¹¹ cm²/s) compared to bare steel (3.46 × 10⁻⁶ cm²/s).
Electrochemical analysis by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) of the surface before and after hydrogen charging revealed a significant degradation of the barrier properties of the oxide after charging. Further optimization of the experimental conditions during the D-S method will be necessary to verify that the oxide integrity is solely affected by hydrogen ingress and not by the potential or current applied during charging.
This research provides a better understanding of the properties of naturally formed oxide layers on pipeline steel and their role in mitigating hydrogen permeation. These insights contribute to a deeper understanding of the role of oxide layers in the hydrogen transportation steel infrastructure.
Recognizing the significance of these interactions is crucial for developing accurate
testing and qualification protocols to ensure the reliability and performance of these materials in hydrogen transport applications.