Reliable hydrogen transport requires pipeline steels with controlled hydrogen uptake and diffusion. This study investigates how temperature (−15 to 60 °C) and gaseous H₂ pressure (1, 4, 8 MPa) jointly influence hydrogen behaviour in X80 pipeline steel. Gas-phase permeation tests were conducted using a Devanathan–Stachurski double electrolytic cell coupled with a high-pressure autoclave to obtain hydrogen permeation curves for X80 under varying pressure and temperature conditions. Asymptotic analysis of the permeation kinetics was then performed to determine the densities of hydrogen trap sites, and a method was developed to compute nonlinear hydrogen concentration profiles resulting from hydrogen trapping. Finally, X80 samples were hydrogen-charged under different pressures and temperatures, and thermal desorption spectroscopy (TDS) was employed to measure the surface concentration, thereby verifying the results calculated from the nonlinear hydrogen concentration profiles.
Figure 1. Effect of temperature and pressure on hydrogen uptake and diffusion in X80 pipeline steel.
Key Findings:
- Diffusion accelerates with both temperature and pressure. The apparent diffusion coefficient follows Arrhenius behaviour across all pressures. Activation energies are approximately 27 kJ mol⁻¹ at 1 MPa and approximately 31 kJ mol⁻¹ at 4 to 8 MPa, consistent with faster transport at higher temperatures, albeit moderated by trapping.
- Pressure increases the effective population of traps. Elevated pressure raises the occupancy of microstructural traps, which initially slows diffusion at low lattice occupancy but ultimately increases the overall hydrogen inventory as charging continues.
- Total hydrogen shows distinct temperature trends depending on pressure. At 4 and 8 MPa, the total hydrogen concentration increases monotonically with temperature. At 1 MPa, it decreases slightly at low temperatures and then increases at higher temperatures. This behavior defines a transition temperature at which lattice solubility begins to dominate over trap depopulation.
- Guidance for sub-surface hydrogen. The sub-surface lattice hydrogen concentration follows Sieverts’ law and can be predicted from pressure and temperature without invoking detailed equations, providing a practical basis for design and assessment.
- Concentration sensitivity to hydrogen trapped sites and service condition. The transition temperature shifts lower as hydrogen pressure increases and shifts higher as trap density or trap strength increases, for example after plastic straining. Consequently, regions with high dislocation density—such as crack tips and deformed zones—are expected to display a “decrease then increase” trend in total hydrogen with temperature within typical pipeline operating ranges.
Implications:
The combined experimental and modeling results demonstrate that reported contradictions in the literature arise from the competition between endothermic lattice solubility and exothermic trap release, each weighed differently by pressure and microstructure. The validated nonlinear framework supports more reliable prediction of hydrogen content during pipeline service, informs material qualification for hydrogen transport, and provides clear parameters for fitness-for-service evaluations.
Project Summary by: Juan Shang, Assistant Professor, National University Corporation Kyushu University, Japan.
Paper Reference: Gao, R., Xing, B., Yang, C., Jiang, X., Shang, J. and Hua, Z. (2024) ‘Synergic effects of temperature and pressure on the hydrogen diffusion and dissolution behaviour of X80 pipeline steel.’ Corrosion Science. Elsevier BV, September, pp. 112468–112468. DOI: 10.1016/j.corsci.2024.112468.
Hiden Product: TPD Workstation (now known as TDSLab Series).
