Hydrogen is key to carbon neutrality; blending into existing natural gas pipelines enables large-scale deployment. Based on energy supply-demand balance, this paper proposes a four-dimensional “source-storage-transmission-utilisation” resilience indicator system and aggregates a comprehensive resilience index (RI) via a geometric mean that captures short-board effects, establishing a resilience assessment framework oriented toward end-use heating value assurance. Taking the Shandong pipeline network as a case, a baseline diagnosis of eight candidate injection points shows that Zibo, a mid-section industrial hinterland with abundant local hydrogen, achieves the highest RI, outperforming topologically central hubs. To address offshore LNG disruption, three supply-constrained scenarios are defined; energy balance quantifies hydrogen compensation needs and safe blending ratios. A staged strategy is proposed, namely, single-point injection, multi-point coordination, and then onshore gas increase plus storage replenishment plus low-ratio blending. When LNG supply falls to 65% of baseline, hydrogen blending alone would require a global ratio of 39.6%, far exceeding safety limits. After activating onshore augmentation and storage, the ratio drops to 9.02%, yet comprehensive resilience still declines by 7.8% relative to baseline. The study reveals that when crisis intensity exceeds operational thresholds, the decisive resilience constraint shifts from dispatch optimisation to gas source structure; heavy dependence on a single deep-sea LNG channel fundamentally limits overall network resilience.

In view of the shortcomings of the existing CO2 pipeline leakage and diffusion models, such as large fluctuations in prediction errors, insufficient depiction of heavy gas effects, and poor adaptability to phase states, this paper constructs a phase-state adaptive leakage rate model, an SLAB model adapted to CO2 properties, and an improved Gaussian plume model, achieving more accurate predictions of leakage rate and hazardous distance. Experimental validation showed that the average relative error of the leakage rate model in predicting density and leakage rate is respectively <= 5.20% and 6.90%. The prediction error under all verification conditions is <= 15%, which is higher than that of the existing models. The SLAB model based on CO2 physical properties exhibited an average relative error of <= 14.90% in concentration-distance predictions, while the improved Gaussian plume model showed average relative errors of 15.20% and 12.40% for 4% medium-risk and 1% low-risk concentration-distance predictions, respectively. Under most operating conditions, the model prediction errors were <= 20%, outperforming traditional Gaussian plume models and the Phast model. Engineering case study results indicate that the dense-phase CO2 leakage rate is the highest for the same leakage orifice diameter. For a 100 mm leakage orifice, the leakage rates for the dense-phase, supercritical, and gas-phase states are 500.39 kg/s, 370.47 kg/s, and 96.19 kg/s, respectively; For a 100 mm leak aperture, the maximum low-risk, medium-risk, and high-risk distances predictedby the diffusion model for dense-phase CO2 reached 952.50 m, 342.10 m, and 138.70 m, respectively. These research findings provide reliable model data support for CO2 pipeline safety design, risk assessment, and emergency response.

Integrating hydrogen into urban gas pipeline networks is a pivotal technology for energy transition yet poses critical safety threats, thus necessitating comprehensive risk assessment of hydrogen-blended natural gas pipelines. This study performs full quantitative risk assessment of leakage failure and accident evolution by proposing a novel framework that integrates causal inference (Bow-Tie analysis) with probabilistic machine learning (Bayesian networks), enabling systematic failure factor identification and dynamic accident progression simulation. Key findings indicate human factors and pipeline material degradation as primary triggers. The studied pipeline exhibits a low baseline failure probability, with dispersion emerging as the most likely consequence of leakage. Higher hydrogen blending ratios significantly elevate jet fire risk due to hydrogen’s low ignition energy, while hydrogen’s inherent buoyancy and high diffusivity notably mitigate the likelihood of flash fire and vapor cloud explosion. The case study verifies the model’s practicability, and macro-micro analyses provide holistic insights, offering a reliable method to guide pipeline safety and reliability improvement amid energy transition.

This study systematically investigates the hydrogen embrittlement (HE) behavior of X65 pipeline steel base metal (BM) and weld metal (WM) in gaseous hydrogen environments. The hydrogen permeation characteristics, fatigue properties and fracture behaviour of both the BM and WM under various hydrogen partial pressure environments were considered intensively. Electron backscatter scanning diffraction (EBSD) was employed to characterize crystallographic features of the BM and WM. The results indicate that the BM exhibits no pronounced texture and contains a low proportion of high angle grain boundaries (HAGBs). The WM shows distinct texture and possesses relatively low dislocation density. Under in-situ gaseous hydrogen charging conditions, the hydrogen diffusivity for various regions of WM are about half an order of magnitude greater than that of the BM. With the increase of hydrogen partial pressure, the correlation between partial pressure and the fatigue crack growth rate (FCGR) weakens. At the hydrogen partial pressure of 1.26 MPa, the FCGRR of WM is approximately 1.4 times that of the BM, which is more susceptible to hydrogen effects. Macroscopic and microscopic analyzes of the specimen fracture surfaces were conducted using a 3D super depth of field microscope and a scanning electron microscope (SEM). Comparing with BM specimens, WM specimens accompany more abundant brittle fracture characteristics and exhibit lower fracture toughness. Under the identical hydrogen partial pressure, the embrittlement index (EI) of BM and WM are comparable, whereas the fracture toughness of WM was approximately 37.7 % and 14.6 % lower than those of BM respectively.

ObjectiveThe formation of hydrogen atoms on the surface of hydrogen pipeline steel serves as the critical link between the external hydrogen environment and internal hydrogen-induced damage. While existing research predominantly concentrate on hydrogen diffusion, hydrogen trapping, and macroscopic mechanical property degradation, systematic reviews regarding the dissociative adsorption of hydrogen on pipeline steel surfaces remain insufficient, which fails to supply direct theoretical basis for safety assessment of operational hydrogen pipelines. MethodsCentering on of the dissociative adsorption of hydrogen, recent research regarding gaseous hydrogen embrittlement and hydrogen behavior in pipeline steel was summarized across three dimensions: theoretical foundations, experimental testing, and numerical simulations. The application scopes of multiple methodologies were systematically compared, including surface characterization, hydrogen permeation testing, densityfunctional theory, ab initio molecular dynamics, and the finite element method. Furthermore, influencing factors such as surface states, corrosion product films and passive films, impurity gases, alloying elements, temperature, and stress were integrated into a unified analytical framework. ResultsStatistical analysis indicated that in the field of gaseous hydrogen embrittlement, studies on macroscopic mechanical properties and hydrogen embrittlement mechanisms accounted for approximately 72％, those on hydrogen diffusion in steel accounted for roughly 15％, and only around 8％ directly addressed surface dissociative adsorption—revealing insufficient research on this initial process. Comparative analysis of typical numerical simulation methods revealed that density functional theory was applicable to analyzing stable adsorption sites, adsorption energy, and dissociation energy barriers at a scale of 0.1–10.0 nm. Ab initio molecular dynamics described dynamic interfacial processes at finite temperatures for scales of 0.1–20.0 nm, though it was limited by system size and time scale. The finite element method could reach micrometer scales and even component scales, but it relied on atomic-scale input parameters. Experimental results further demonstrated that surface roughness, grain boundaries, dislocation emergences, and inclusion interfaces increased local active site density. The integrity and compactness of corrosion product films/passive films significantly affect hydrogen ingress, and compact films generally show a hydrogen-barrier effect, gas impurities introduced distinct chemical behaviors: O2 and CO primarily induced competitive adsorption and surface poisoning, CO2 exhibited environment-dependent characteristics, and H2S tended to facilitate the ingress of atomic hydrogen into the steel matrix. ConclusionThe dissociative adsorption of hydrogen on pipeline steel surfaces should not be regarded as an isolated surface reaction, but rather as the starting point of the entire degradation sequence: surface hydrogen generation – interfacial hydrogen ingress – bulk hydrogen diffusion – hydrogen trapping and enrichment – damage evolution. Future research should focus on in-situ characterization under high-pressure gas phases, standardized gaseous hydrogen permeation testing, and multi-scale coupling models to provide quantitative benchmarks for material selection, gas quality management, and the safety evaluation of in-service hydrogen pipelines.

Gravity-induced stratification of hydrogen–methane(H₂–CH₄) mixtures remains a debated safety concern in hydrogen-blended natural gas pipelines, particularly in vertical and quiescent sections. In this work, a unified thermodynamic–transport framework is developed to quantitatively evaluate both the equilibrium distribution and the transient timescale of H₂–CH₄ mixtures under gravity. The framework integrates(i) a minimum-energy model based on Helmholtz free energy minimization with the Peng–Robinson real-gas equation of state and(ii) a transient convection–diffusion model coupling gravitational drift with molecular diffusion. Model predictions agree with benchmark literature and experimental data within 2%. Results show that temperature accelerates diffusion, pressure delays equilibration without altering steady-state distributions, and pipe height primarily controls the stratification timescale rather than its magnitude. Even under extreme conditions (−10°C, 10 MPa, 30 vol% H₂, 1 km height), the steady-state top–bottom hydrogen volume fraction difference remains below 1.5%, while more than 2.7 × 10³ years are required to reach equilibrium. Under typical urban gas conditions, the concentration difference after 10 days is below 0.01%. These findings demonstrate that gravity-induced stratification of H₂–CH₄ mixtures is physically possible but engineering-irrelevant within practical pipeline lifetimes, providing a time-explicit and quantitatively justified basis for pipeline design and safety assessment.

With growing global recognition of methanol as a versatile energy carrier, establishing safe and efficient transnational supply chains is urgent. Pipeline transportation, known for its economy and efficiency, is pivotal in this context. Repurposing existing refined oil pipelines for green methanol transport offers a strategic solution, improving infrastructure utilization and avoiding the high costs of new construction. Despite this potential, systematic reviews on large-scale green methanol transport infrastructure, particularly pipeline repurposing, remain scarce. Based on a comprehensive survey of the literature, this review synthesizes key findings on establishing a large-scale green methanol pipeline infrastructure, covering material compatibility, equipment adaptability, and operational safety for green methanol pipeline transport. A primary conclusion is that repurposing existing refined oil pipelines, integrated with multimodal transportation methods offers a viable path to enhance pipeline utilization and ensure a stable supply. However, significant technical challenges must be addressed. Material compatibility studies indicate that impurities can induce corrosion and swelling; equipment requires specialized designs for safety; Leakage dispersion behavior is complex, and during sequential transport, mixing lacks efficient predictive models. Compounding these hurdles is the absence of dedicated national standards. By identifying these key knowledge gaps, this review proposes a methodology for assessing the feasibility of converting refined oil pipelines to transport green methanol, considering process, technical, economic, and environmental safety aspects. It provides a research roadmap for future technological innovation and strategic planning to support the emerging green methanol economy. (230 words)

This work presents an experimental investigation of hydrogen-induced degradation in X52 pipeline steel, evaluating both base metal and weld metal behavior under varying hydrogen pressures. Through in-situ hydrogen-charged mechanical testing combining fatigue crack growth analysis and single-point J₀ toughness measurements, the research quantifies hydrogen's impact on fracture resistance. Advanced microstructural characterization techniques, including EBSD and SEM fractography, provide mechanistic insights into embrittlement phenomena. The results reveal two critical hydrogen effects: first, a pressure-dependent acceleration of fatigue crack propagation, with weld metal showing 25-40% faster growth rates than base metal at equivalent pressures. Second, substantial toughness reduction occurs through hydrogen's selective impairment of plastic deformation mechanisms, decreasing J₀ values by up to 85% at 4MPa H₂ pressure. The vulnerability of the weld zone may be linked to its characteristic grain boundary structure. Observations indicate a significantly higher proportion (estimated at 30-50%) of high-angle boundaries compared to the base metal. As these boundaries are widely hypothesized to be effective hydrogen traps, they could be a key factor contributing to the observed higher hydrogen embrittlement susceptibility.

Research on hydrogen flame safety is currently rapidly expanding, supported by a substantial theoretical framework. However, existing studies predominantly adopt a singular perspective, lacking a comprehensive analysis of the entire accident chain. Furthermore, available reviews fail to accurately characterize the diverse scenarios of hydrogen accidental release and the complete process of flame evolution. To address these gaps, this review reports the detailed process of flame generation induced by hydrogen jets and summarizes the experimental/simulation methods for high-pressure hydrogen ignition and their corresponding results. Furthermore, considering discrepancies between laboratory-scale experiments and field-scale hydrogen release scenarios, the limitations of current research on hydrogen flame safety are analyzed. Finally, the practical application of current quantitative risk assessment is discussed, emphasizing the need for more reliable data and rational dynamic Bayesian models to assess and control the consequences arising from failures. The objective of this review is to reduce the risks of safety issues induced by hydrogen jets and to provide actionable guidance in advancing the theoretical perfection and technological innovation of hydrogen safety.

China’s hydrogen scale-up hinges on resolving midstream bottlenecks that move volumes from resource-rich northern and western basins to demand-dense coastal corridors. A structured synthesis of policy, engineering practice, and techno-economic evidence compares compressed gas, liquefied hydrogen, chemical carriers, and dedicated or repurposed pipelines under distance, throughput, and utilization constraints. Two findings dominate: persistent geographic (and water-resource) mismatch creates a durable need for bulk cross-regional logistics, and once flows are continuous and large, pipelines minimize levelized transport cost relative to trucking or liquefaction, while carrier routes remain case-dependent for maritime chains. System integrity depends on materials, sealing, metering, and leak detection, with hydrogen embrittlement setting design and operating limits. International benchmarks underscore China’s early stage of pipeline build-out relative to European backbone plans, highlighting urgency for standardization and coordinated development. A staged roadmap emerges: near term—local distribution and limited blending; medium term—interprovincial trunk lines supplied mainly by renewable hydrogen; long term—a meshed pure-hydrogen backbone coupled with power and gas networks to provide seasonal flexibility and industrial offtake at scale.

Welds of hydrogen transportation pipelines exhibit high hydrogen embrittlement (HE) susceptibility. To obtain the optimum welding process, the hydrogen compatibility of the 20# steel welds with different welding processes was tested by in-situ gaseous hydrogen permeation and slow strain rate tensile (SSRT) tests. The fracture surface analysis of the welds was also presented. The welding process with the best HE resistance was selected. Moreover, the mechanism between the HE susceptibility and microstructure of the welds was discussed. This study provides a reference for the selection of welding process for long-distance hydrogen pipelines.

Hydrogen is widely considered a key energy carrier for net-zero targets, particularly in hard-to-abate sectors, yet its small size and high diffusivity make it prone to leakage across the value chain, raising safety, energy-loss, and climate concerns. This review treats hydrogen leakage as an infrastructure-management problem linking leak pathways, detection capability, climate-relevant accounting, and mitigation. Rather than treating reported values as directly comparable leakage rates, we classify the evidence by system boundary and measurement basis, distinguishing physical leakage from broader operational losses. We synthesize advances in acoustic, optical, and catalytic detection, some reaching parts-per-billion sensitivity; atmospheric-chemistry ensembles assess hydrogen’s indirect global warming potential and its dependence on leakage rate, production pathway, and time horizon. We assess mitigation through barrier coatings, sealing materials, and modular design and identify key gaps in leakage quantification, soil-sink uncertainty, long-term material performance, and leakage-specific regulation.

In actual engineering applications, blending equipment is rarely used at low flow conditions (Q <= 100 m3/h) due to its high cost. In such cases, Proper direct blending can achieve a mixture that meets industrial requirements. To analyze and optimize structural parameters of the direct blending pipeline, the orthogonal test method was used to orthogonally construct 27 CFD simulation schemes from the eight structural parameters, with each parameter having three levels. CFD simulations are conducted by Fluent software. The results indicate that the optimized pipeline design achieves effective mixture without introducing flow disturbance components. In addition, it significantly reduces the required blending distance and pressure loss. Among the various structural parameters, the diameter of the variable-diameter straight pipe section is identified as the key factor influencing the blending performance. This study offers practical engineering recommendations for the blending of hydrogen and natural gas in pipelines under low flow conditions.

This study investigates the spontaneous ignition phenomenon resulting from high-pressure hydrogen release through tubes into the atmosphere and subsequent flame transition in the near-field region of the nozzle. The effects of release pressure (2-10 MPa) and tube length (360-2260 mm) on the ignition and flame characteristics were systematically explored. Results indicate that increasing release pressure generates stronger leading shock waves, thereby enhancing the probability of spontaneous ignition and jet fire formation. As pipe length increases from 360 mm to 2260 mm, the critical release pressure for spontaneous ignition initially drops from 8 MPa to 4 MPa, then gradually rises and stabilizes at 5-6 MPa. Interestingly, jet fires were observed to form outside tubes >= 1540 mm even in the absence of internal spontaneous ignition or a sustained internal flame. Furthermore, the critical pressure for external ignition may be lower than that for internal ignition, suggesting that the formation of jet fire does not necessarily require a complete and continuous internal flame. At a tube length of 2260 mm and near-critical release pressures, two Mach disks were observed outside the tube, providing insights into complex flow structures under these conditions.

Constructing new hydrogen pipelines or utilizing existing natural gas networks represents an effective pathway for large-scale hydrogen energy transport. However, the permeation of hydrogen atoms into metallic materials during transport can induce hydrogen embrittlement (HE), posing a severe threat to pipeline safety. Developing hydrogen barrier coatings (HBCs) with superior pipeline adaptability is a critical strategy to mitigate this issue. This paper systematically reviews four HBC material systems: metal-based, ceramic-based, 2D materials, and polymer-based composites. Beyond a comparative analysis of their barrier performance, we deeply elucidate the hydrogen barrier mechanisms, including the physical/chemical barriers and hydrogen trapping effects in inorganic materials, as well as the synergistic mechanisms between organic polymer matrices and functional fillers. A key contribution of this review, which distinguishes it from existing literature, is the construction of a comprehensive full-chain evaluation framework. This framework integrates “Preparation Quality (density, adhesion, thickness) – Hydrogen Barrier Efficiency (permeation rate, permeation reduction factor) – Protection Performance (HE resistance, fatigue resistance) – Pipeline Applicability (environmental coupling, coating–substrate interactions)”, thereby providing a standardized basis for assessment. Finally, considering the specific requirements of hydrogen transport scenarios, the paper outlines current pipeline coating application requirements and proposes future research directions to support the development of safe and efficient hydrogen transport infrastructure.

Corrosion product films are inevitably present in natural gas pipelines, these corrosion product films on the pipeline surface are considered a naturally formed protective film layer that markedly reduces the corrosion rate of the pipeline. In addition, corrosion product films can significantly influence the hydrogen diffusion characteristics of the pipeline steel, which in turn affects the safety of the pipeline. The hydrogen-blocking effect and mechanism of these films remain unclear, which severely limits the evaluation of hydrogen compatibility for inservice natural gas pipelines. In this study, for CO2 corrosive environments, density functional theory, first principle molecular dynamics, and hydrogen permeation test were used to investigate the process of hydrogen adsorption and dissociation on FeCO3 corrosion product surface and diffusion through the steel matrix. The adsorption sites of hydrogen on the FeCO3 corrosion films surface were clarified, the kinetics and thermodynamics of the hydrogen dissociative adsorption were calculated, and the form of hydrogen adsorption was elucidated. The findings indicate that the FeCO3 corrosion product film accomplishes the hydrogen blocking effect by impeding the hydrogen dissociative adsorption and diffusion processes. This work highlights the possibility of using corrosion product films on the inner walls of pipelines as a natural hydrogen barrier.

ObjectiveWith increasing demand for large-scale hydrogen storage and transport, underground hydrogen storage (UHS) has gained prominence due to its high capacity and low construction costs. However, the competitive adsorption mechanisms of hydrogen and cushion gases within clay mineral pores remain inadequately elucidated. This study clarifies these processes at the molecular level, providing a theoretical foundation for optimizing UHS operation strategies and cushion gas selection. MethodsA Na+-montmorillonite slit pore model was constructed using Grand Canonical Monte Carlo (GCMC) simulation. Adsorption behaviors were simulated under varying pressures, temperatures, pore sizes, cushion gas types, and mixing ratios. Key parameters—including hydrogen adsorption isotherms, molecular density distributions, and selectivity coefficients—were analyzed alongside visual characterization of equilibrium configurations. The spatial distribution and interaction mechanisms of gas molecules within the pores were directly demonstrated, providing more reliable microscopic explanations. ResultsHydrogen adsorption capacity increased with pressure and decreased with temperature, exhibiting no significant variation across pore sizes of 2.0–6.5 nm. Cushion gases notably reduced hydrogen adsorption, with nitrogen exerting more pronounced inhibitory effect than methane. In a H2-N2 mixture (60％:40％ molar fraction), hydrogen adsorption plateaued near 6 MPa due to intense competitive adsorption of nitrogen. Selectivity coefficients of methane and nitrogen relative to hydrogen declined with pressure but remained above 1, with nitrogen’s selectivity coefficient decreasing more rapidly. ConclusionUHS facilities should adopt high-temperature and high-pressure operation strategies to minimize hydrogen adsorption losses in caprocks while maintaining sealing integrity. Nitrogen is superior to methane as a cushion gas for suppressing excessive hydrogen adsorption. From a selectivity coefficient perspective, increasing pressure may rapidly diminish montmorillonite’s hydrogen selectivity; the performance of different cushion gases at elevated pressures warrants further investigation. Although based on an idealized model, the revealed microscopic competitive adsorption mechanisms provide theoretical guidance for caprock sealing evaluation, cushion gas selection, and operational optimization in UHS engineering. Future research should prioritize developing complex models that better represent real geological conditions and conducting experimental validation to enhance engineering applicability.