Experimental Study on Leakage and Diffusion of Buried Hydrogen Blended Natural Gas Pipeline

Abstract Hydrogen has emerged as a strategic priority in global energy transitions because it is a highly efficient, clean, and renewable energy carrier. However, the development of dedicated hydrogen transmission infrastructure faces significant economic barriers, necessitating the repurposing of existing natural gas pipeline networks. Although this hybrid transportation approach is cost-effective, it introduces critical safety challenges because of the unique physicochemical properties of hydrogen. This study systematically investigated the leakage and diffusion behaviors of hydrogen-blended natural gas in buried pipelines using controlled experiments. A custom-designed experimental soil box (6 m × 1.25 m × 0.8 m, L × H × W) was constructed to simulate subsurface conditions. A stainless-steel pipe with a diameter of Φ30 mm traversed the lower middle section of the right-side surface of the box and exited through the left-side surface. The centerline of the pipe was positioned 0.25 m above the lower surface of the box. Three remotely controllable valves were installed along the pipe to simulate the leakage scenarios. The distances from the center of each valve opening to the left side surface of the box were 0.39, 2.16, and 4.17 m. Additionally, the distance from the valve openings to the lower surface of the box was 0.58 m. The system was backfilled with soil to replicate realistic burial conditions, and hydrogen/methane sensors were deployed 0.67 m above the leak points on the soil surface. The key variables examined include: 1. Temporal evolution of surface gas concentrations; 2. Diffusion patterns under varying hydrogen blending ratios (1 VOL%–10 VOL%); 3. Operational pressures (0.2 Mpa–1 Mpa); 4. Leakage locations (central vs. terminal pipeline segments); 5. Environmental perturbations (crosswind velocities: 0 m/s–1 m/s; ambient temperatures: 0–10 °C). These findings establish quantitative correlations between operational parameters and hazard thresholds, providing critical insights for: 1. Optimizing real-time monitoring systems; 2. Implementing risk-based pipeline integrity management; 3. Developing secondary accident mitigation strategies is also important. This study advances the fundamental understanding of the behavior of hydrogen blended natural gas in legacy infrastructure, directly supporting the safe scaling of hydrogen economies.