Objective Under China’s carbon peaking and carbon neutrality targets, hydrogen blending in natural gas pipeline networks has emerged as a key pathway for the large-scale deployment of hydrogen energy. However, differences in physical properties between hydrogen and natural gas introduce entirely new safety risks to pipeline network systems, while existing studies still lack a systematic, coupled assessment of risks across the entire retrofit chain. This study is therefore undertaken to ensure the safe implementation and scaled deployment of hydrogen-blending retrofits, and to provide a foundation for engineering practice, standards development, and risk management.

Methods A systematic literature review and theoretical analysis were conducted to comprehensively compare the key physical property parameters of hydrogen and methane and to elucidate how hydrogen blending affects the leakage, dispersion, and combustion–explosion characteristics of the blended gas. A full-chain risk analysis framework covering resource supply, pipeline transmission and distribution, station operation, and end use was subsequently constructed. Critical risk points across the entire process were then systematically identified in terms of hydrogen-induced damage to pipe materials, leakage in sealing systems, station-equipment compatibility, fluctuations in operating conditions, and the adaptability of end-use gas appliances. Qualitative and quantitative risk assessment methods were further integrated to compare the safety boundaries of different hydrogen-blending processes, thereby forming a comprehensive risk control system covering the full life cycle.

Results The study established that hydrogen blending alters key physical property parameters of the gas mixture, including density, minimum ignition energy, burning velocity, and explosion limits, which directly narrows the safety envelope of urban gas systems. The full risk transmission pathway from changes in physical properties to facility damage, operational instability, and end-user accidents was also clarified. At a hydrogen blending ratio of 20％, the selection of low-strength pipeline steel, reinforcement of sealing systems, and adoption of precise gas-blending processes were shown to be technically feasible; aging pipeline facilities, transient operating conditions, and end-use gas-appliance compatibility were identified as the three core risk sources. Existing risk assessment methods and Computational Fluid Dynamics (CFD) simulation techniques were further shown to support risk identification and quantification in hydrogen-blending scenarios, while also indicating the need to update failure data and model parameters to reflect the specific characteristics of hydrogen blending. Ultimately, an integrated “materials–monitoring–management–standards” framework for full-process risk prevention and control was established.

Conclusion Retrofitting urban natural gas pipeline networks for hydrogen blending is technically feasible. However, the associated safety risks extend across the entire industry chain, making systematic risk assessment and end-to-end risk control essential. Future research should prioritize the accumulation of long-term operational data, the development of coupled risk models, and the refinement of dedicated standards and coordinated regulatory mechanisms to support the safe and large-scale deployment of hydrogen-blending technology.