Transmission, Distribution & Storage

The aim of this study is to review and identify H2 storage suitability in geological reservoirs of the Republic of Lithuania. Notably Lithuania can store clean H2 effectively and competitively because of its wealth of resources and well-established infrastructure. The storage viability in Lithuanian geological contexts is highlighted in this study. In addition when it comes to injectivity and storage capacity salt caverns and saline aquifers present less of a challenge than other kinds of storage medium. Lithuania possesses sizable subterranean reservoirs (Cambrian rocks) that can be utilized to store H2. For preliminary assessment the cyclic H2 injection and production simulation is performed. A 10-year simulation of hydrogen injection and recovery in the Syderiai saline aquifer demonstrated the feasibility of UHS though efficiency was reduced by nearly 50% when using a single well for both injection and production. The study suggests using separate wells to improve efficiency. However to guarantee economic injectivity and containment security a detailed assessment of the geological structures is required specifically at the pore scale level. The volumetric approach estimated a combined storage capacity of approximately 898.5 Gg H2 (~11 TWh) for the Syderiai and Vaskai saline aquifers significantly exceeding previous estimates. The findings underscore the importance of detailed geological data and further research on hydrogen-specific factors to optimize UHS in Lithuania. Addressing technical geological and environmental challenges through multidisciplinary research is essential for advancing UHS implementation and supporting Lithuania’s transition to a sustainable energy system. UHS makes it possible to maximize the use of clean energy reduce greenhouse gas emissions and build a more sustainable and resilient energy system. Hence intensive research and advancements are needed to optimize H2 energy for broader applications in Lithuania.

The UK net zero strategy aims to fully decarbonize the power system by 2035 anticipating a 40–60% increase in demand due to the growing electrification of the transport and heating sectors over the next thirteen years. This paper provides a detailed technical and economic analysis of the role of energy storage technologies and transmission lines in balancing the power system amidst large shares of intermittent renewable energy generation. The analysis is conducted using the cost-optimizing energy system modelling framework REMix developed by the German Aerospace Center (DLR). The obtained results of multiple optimization scenarios indicate that achieving the lowest system cost with a 73% share of electricity generated by renewable energy sources is feasible only if planning rules in England and Wales are flexible enough to allow the construction of 53 GW of onshore wind capacity. This flexibility would enable the UK to become a net electricity exporter assuming an electricity trading market with neighbouring countries. Depending on the scenario 2.4–11.8 TWh of energy storage supplies an average of 11% of the electricity feed-in with underground hydrogen storage representing more than 80% of that total capacity. In terms of storage converter capacity the optimal mix ranges from 32 to 34 GW of lithium-ion batteries 13 to 22 GW of adiabatic compressed air energy storage 4 to 24 GW of underground hydrogen storage and 6 GW of pumped hydro. Decarbonizing the UK power system by 2035 is estimated to cost $37–56 billion USD with energy storage accounting for 38% of the total system cost. Transmission lines supply 10–17% of the total electricity feed-in demonstrating that when coupled with energy storage it is possible to reduce the installed capacity of conventional power plants by increasing the utilization of remote renewable generation assets and avoiding curtailment during peak generation times.

Hydrogen (H2) has the potential to become a cleaner fuel alternative to increase energy mix versatility as part of a low-carbon economy. Geological H2 storage represents a key component of the emerging H2 value chain since large-scale energy generation linked to energy generation and large-scale industrial applications will require significant upscaling of geological storage. Geological H2 storage can take place in both salt domes and bedded salt formations. Bedded salt formations offer a significant advantage for H2 storage over salt domes because of their widespread availability. This research focuses on evaluating the H2 storage potential of the Salado Formation a bedded salt deposit in the Permian Basin of West Texas in the United States. Using data from 3268 well logs this study analyzes an area of 136100 km2 to identify suitable depth and net halite thickness for H2 storage in salt caverns. In addition this work applies a novel geostatistical workflow to quantify the uncertainty in the formation’s storage potential. The H2 working gas potential of the Salado Formation ranges from 0.62 to 17.53 Tsm3 (1.75–49.68 PWh of stored energy) across low-risk to high-risk scenarios with a median potential of 1.19 Tsm3 (3.37 PWh). The counties with the largest storage potential are: Lea in New Mexico and Gaines and Andrews in Texas. These three counties account for more than 75 % of the formation’s total storage potential. This is the first study to quantify uncertainty in H2 storage estimates for a bedded salt formation while providing a detailed breakdown of results by county and 1 km2 grid sections. The findings of this work offer critical insights for developing H2 infrastructure in the Permian Basin. The Permian Basin of West Texas has the potential to become an important hub for H2 production from both natural gas and/or renewable energy. Estimating H2 storage potential is an important contribution to assess the feasibility of the entire H2 value chain in Texas. An interactive map accompanies this work allowing the readers to explore the results visually.

Underground hydrogen storage in aquifers is a promising solution to address the imbalance between energy supply and demand yet its practical implementation requires optimized strategies to ensure high efficiency and economic viability. To improve the storage and production efficiency of hydrogen it is essential to select the appropriate cushion gas and to study the influence of reservoir and process parameters. Based on the conceptual model of aquifer with single-well injection and production three potential cushion gas (carbon dioxide nitrogen and methane) were studied and the changes in hydrogen recovery for each cushion gas were compared. The effects of temperature initial pressure porosity horizontal permeability vertical to horizontal permeability ratio permeability gradient hydrogen injection rate and hydrogen production rate on the purity of recovered hydrogen were investigated. Additionally the impact of different well pattern on the purity of recovered hydrogen was studied. The results indicate that methane is the most effective cushion gas for improving hydrogen recovery in UHS. Different well patterns have significant impacts on the purity of recovered hydrogen. The mole fractions of methane in the produced gas for the single-well line-drive pattern and five-spot pattern were 16.8% 5% and 3.05% respectively. Considering the economic constraints the five-spot well pattern is most suitable for hydrogen storage in aquifers. Reverse rhythm reservoirs with smaller permeability differences should be chosen to achieve relatively high hydrogen recovery and purity of recovered hydrogen. An increase in hydrogen production rate leads to a significant decrease in the purity of the recovered hydrogen. In contrast hydrogen injection rate has only a minor effect. These findings provide actionable guidance for the selection of cushion gas site selection and operational design of aquifer-based hydrogen storage systems contributing to the large-scale seasonal storage of hydrogen and the balance of energy supply and demand.

The use of rare earth elements in hydrogen storage processes offers significant advantages in terms of increasing technological efficiency and ensuring system security. However this process also creates some serious problems in terms of environmental and economic sustainability. It is necessary to determine the most critical indicators affecting the sustainable use of these elements. Studies on this subject in the literature are quite limited and this may lead to wrong investment decisions. The main purpose of this study is to determine the most important indicators to increase the sustainable use of rare earth elements in hydrogen storage processes. An original decision-making model in which Siamese network logarithmic percentage-change driven objective weighting (LOPCOW) fractal fuzzy numbers and weighted influence super matrix with precedence (WISP) approaches are integrated in the study. This study provides an original contribution to the literature by identifying the most critical indicators affecting the sustainable use of rare earths in hydrogen storage processes by presenting an innovative model. Fractal structures such as Koch Snowflake Cantor Dust and Sierpinski Triangle can model complex uncertainties more successfully. Fractal structures are particularly effective in modeling linguistic fuzziness because their recursive nature closely mirrors the layered and imprecise way humans often express subjective judgments. Unlike linear fuzzy sets fractals can capture the patterns of ambiguity found in expert evaluations. Hydrogen storage capacity and government supports are determined as the most vital criteria affecting sustainability in rare earth use.

This paper provides authors’ perspective on the current advances and challenges in utilising polymers and composites in hydrogen economy. It has originated from ‘Polymers and Composites for Hydrogen Economy’ symposium organised in March 2025 at the University of Warwick. This paper presents views from the event and thus provides a perspective from academia and industry on the ongoing advances and challenges for those materials in hydrogen applications.

The erosion behavior and the service life of a hydrogen transmission tube with high velocity suitable for a hydrogen fuel aviation engine are not clear which is the bottleneck for its application. In this study a coupled model considering the fluid flow field of hydrogen and discrete motion of particles was established. The effects of the geometry parameters and erosion parameters on the hydrogen erosion behavior were investigated. The maximum erosion rate increased exponentially with the increased hydrogen velocity and increased linearly with the increased erosion time. The large bend radius and inner diameter of the bend tube contributed to the decreased erosion rate. There was an optimized window of the bend angle for a small erosion rate. The relationship between the accumulated thickness loss and maximum erosion rate was established. The prediction model of the service life was established using fourth strength theory. The service life of the tube was sensitive to the hydrogen velocity and erosion time. The experiments were conducted and the variations in thickness and hardness were measured. The simulated models agreed with the experiments and could provide guidance for the parameter selection and prediction of the service life of a bend tube.

This study examines the pricing and assesses resilience methods in hydrogen supply chains by thoroughly analyzing two main disruption scenarios. The model examines a scenario in which a hydrogen production company depends on a Renewable Power plant (RP) for its electricity supply. Ensuring a steady and efficient hydrogen supply chain is crucial but outages at renewable power sources provide substantial obstacles to sustainability and operational continuity. Therefore in the event of disruptions at the RP the company has two options for maintaining resilience: either sourcing electricity from a Fossil fuel Power plant (FP) through a grid network to continue hydrogen production or purchasing hydrogen directly from another company and utilizing third-party transportation for delivery. Using a game theoretic approach we examine how different methods affect demand satisfaction cost implications and environmental sustainability. The study employs sensitivity analysis to evaluate the impact of different disruption probabilities on each scenario. In addition a unique sensitivity analysis is performed to examine the resilience of transmission security to withstand disruptions. This study evaluates how investments in security measures affect the strength and stability of the supply chain in various scenarios of disruption. Our research suggests that the first scenario offers greater reliability and cost-effectiveness along with a higher resilience rate compared to the second scenario. Furthermore the examination of the environmental impact shows that the first scenario has a smaller amount of CO2 emissions per kg of hydrogen. This study offers important insights for supply chain managers to optimize resilience measures hence improving reliability reducing costs and minimizing environmental effects.

Hydrogen is considered a key alternative to fossil fuels in the broader context of ecological transition. Repurposing natural gas pipelines for hydrogen transport is one of the challenges of this approach. However hydrogen can diffuse into metallic lattices leading to hydrogen embrittlement (HE). For this reason typically ductile materials can experience unexpected brittle fractures and it is therefore necessary to assess the HE propensity of the current pipeline network to ensure its fitness for hydrogen transport. This study examines the relationship between the microstructure of the circumferential weld joint in X52 pipeline steel and hydrogen concentration introduced electrolytically. Base material heat affected zone and fused zone were subjected to 1800 3600 7200 and 14400 s of continuous charging with a current density J = − 10 mA/cm2 in an acid solution. Results showed that the fusion zone absorbed the most hydrogen across all charging times while the base material absorbed more hydrogen than the heat-affected zone due to the presence of non-metallic inclusions. Fracture toughness was assessed using single edge notch tension specimens (SENT) in air and electrolytic hydrogen. Results indicate that the base material is particularly vulnerable to hydrogen environments exhibiting the greatest reduction in toughness when exposed to hydrogen compared to air.

Green hydrogen is likely to play a major role in decarbonising the aviation industry. It is crucial to understand the effects of microstructure on hydrogen redistribution which may be implicated in the embrittlement of candidate fuel system metals. We have developed a multiscale finite element modelling framework that integrates micromechanical and hydrogen transport models such that the dominant microstructural effects can be efficiently accounted for at millimetre length scales. Our results show that microstructure has a significant effect on hydrogen localisation in elastically anisotropic materials which exhibit an interesting interplay between microstructure and millimetre-scale hydrogen redistribution at various loading rates. Considering 316L stainless steel and nickel a direct comparison of model predictions against experimental hydrogen embrittlement data reveals that the reported sensitivity to loading rate may be strongly linked with rate-dependent grain scale diffusion. These findings highlight the need to incorporate microstructural characteristics in hydrogen embrittlement models.

This review provides a comprehensive examination of artificial intelligence methods applied to the design optimization and performance prediction of composite-based hydrogen storage vessels with a focus on composite overwrapped pressure vessels. Targeted at researchers engineers and industrial stakeholders in materials science mechanical engineering and renewable energy sectors the paper aims to bridge traditional mechanical modeling with evolving AI tools while emphasizing alignment with standardization and certification requirements to enhance safety efficiency and lifecycle integration in hydrogen infrastructure. The review begins by introducing HSV types their material compositions and key design challenges including high-pressure durability weight reduction hydrogen embrittlement leakage prevention and environmental sustainability. It then analyzes conventional approaches such as finite element analysis multiscale modeling and experimental testing which effectively address aspects like failure modes fracture strength liner damage dome thickness winding angle effects crash behavior crack propagation charging/discharging dynamics burst pressure durability reliability and fatigue life. On the other hand it has been shown that to optimize and predict the characteristics of hydrogen storage vessels it is necessary to combine the conventional methods with artificial intelligence methods as conventional methods often fall short in multi-objective optimization and rapid predictive analytics due to computational intensity and limitations in handling uncertainty or complex datasets. To overcome these gaps the paper evaluates hybrid frameworks that integrate traditional techniques with AI including machine learning deep learning artificial neural networks evolutionary algorithms and fuzzy logic. Recent studies demonstrate AI’s efficacy in failure prediction design optimization to mitigate structural risks structural health monitoring material property evaluation burst pressure forecasting crack detection composite lay-up arrangement weight minimization material distribution enhancement metal foam ratio optimization and optimal material selection. By synthesizing these advancements this work underscores AI’s potential to accelerate development reduce costs and improve HSV performance while advocating for physics-informed models robust datasets and regulatory alignment to facilitate industrial adoption.

Underground hydrogen storage (UHS) in salt caverns is emerging as a promising solution for the transition to a sustainable energy future. However a thorough understanding of hydrogen flow mechanisms through salt rock is essential to ensure safe and efficient storage operations. In this study we conducted hydrogen flow experiments in salt rocks using the pressure pulse decay (PPD) method covering a range of hydrogen pore pressures from 0.4 MPa to 7.5 MPa within the slip and transitional flow regimes (Knudsen numbers between 0.04 and 1.5). The Knudsen numbers were determined by measuring the pore size distribution (PSD) of the salt rock samples and assigning an average pore size to each sample based on the measured PSD. Our results indicate that the intrinsic permeability of the tested salt rock samples ranges from 5 × 10− 21 m2 to 1.0 × 10− 20 m2 . However a significant enhancement in apparent permeability up to 10 times the intrinsic permeability was observed particularly at lower pressures. This permeability enhancement is attributed to the nanoscale pore structure of salt rocks where the mean free path of hydrogen becomes comparable to the pore sizes leading to a shift from slip flow to the transitional flow regime. The results further reveal that the first-order slip model underestimates the apparent permeability in the transitional flow regime despite its satisfactory accuracy in the slip region. Moreover the higher-order slip model demonstrates acceptable accuracy across both the slip and transitional flow regimes.

As industry moves from fossil fuels to green energy substituting hydrocarbons with hydrogen as an energy carrier seems promising. Hydrogen can be stored in salt caverns depleted hydrocarbon fields and saline aquifers. Among other criteria these storage solutions must ensure storage safety and prevent leakage. The ability of a caprock to prevent fluid from flowing out of the reservoir is thus of utmost importance. In this review the main factors influencing fluid flow are examined. These are the wettability of the caprock formation the interfacial tension (IFT) between the rock and the gas or liquid phases and the ability of gases to diffuse through it. To achieve effective sealing the caprock formation should possess low porosity a disconnected or highly complicated pore system low permeability and remain strongly water-wet regardless of pressure and temperature conditions. In addition it must exhibit low rock–liquid IFT while presenting high rock–gas and liquid–gas IFT. Finally the effective diffusion coefficient should be the lowest possible. Among all of the currently reviewed formations and minerals the evaporites low-organic-content shales mudstones muscovite clays and anhydrite have been identified as highly effective caprocks offering excellent sealing capabilities and preventing hydrogen leakages.

The global energy sector is aiming to substantially reduce CO2 emissions to meet the UN climate goals. Among the proposed strategies underground storage solutions such as radioactive disposal CO2 NH3 and underground H2 storage (UHS) have emerged as promising options for mitigating anthropogenic emissions. These approaches require rigorous research and development (R&D) often involving laboratory-scale experiments to establish their feasibility before being scaled up to pilot plant operations. Microorganisms which are ubiquitous in laboratory environments can significantly influence geochemical reactions under variable experimental conditions of porous media and a salt cavern. We have selected a consortium composed of Bacillus sp. Enterobacter sp. and Cronobacter sp. bacteria which are typically present in the laboratory environment. These microorganisms can contaminate the rock sample and develop experimental artifacts in UHS experiments. Hence it is pivotal to sterilize the rock prior to conduct experimental research related to effects of microorganisms in the porous media and the salt cavern for the investigation of UHS. This study investigated the efficacy of various disinfection and sterilization methods including ultraviolet irradiation autoclaving oven heating ethanol treatments and gamma irradiation in removing the microorganisms from silica sand. Additionally the consideration of their effects on mineral properties are reviewed. A total of 567 vials each filled with 9 mL of acid-producing bacteria (APB) media were used to test killing efficacy of the cleaning methods. We conducted serial dilutions up to 10−8 and repeated them three times to determine whether any deviation occurred. Our findings revealed that gamma irradiation and autoclaving were the most effective techniques for eradicating microbial contaminants achieving sterilization without significantly altering the mineral characteristics. These findings underscore the necessity of robust cleaning protocols in hydrogeochemical research to ensure reliable reproducible data particularly in future studies where microbial contamination could induce artifacts in laboratory research.

This study examined the effects of microstructural alterations by controlling the surface carbon gradient via a thermal decarburizing process on hydrogen evolution adsorption and permeation along with neutral aqueous corrosion behavior of an ultra-high-strength steel with a tensile strength of 2.4 GPa. Microstructural analyses showed that an optimized decarburizing process at 1100 ◦C led to partial transformation to ferrite without precipitating Fe3C in a marked fraction. Electrochemical impedance spectroscopy along with the permeation results revealed that there was a notable decrease in hydrogen evolution and subsurface hydrogen concentration. Moreover immersion test in a neutral aqueous condition showed slower corrosion kinetics with a comparatively uniform corroded surface indicating improved corrosion resistance. However the extent of improvement is significantly limited under non-optimized decarburizing conditions specifically when the temperature is below or above 1100 ◦C due to insufficient decarburization or the formation of coarse-spheroidized Fe3C particles accompanied by a porous subsurface layer. In particular a far greater adsorption tendency at bridge sites on Fe3C (001) in a pre-charged surface is highlighted. This study provides insight that the adjustment of the carbon gradient through an optimized annealing process can be an effective technical strategy to overcome the critical drawbacks of ultrastrong martensitic steels under hydrogen-rich or corrosive conditions.

The adoption of hydrogen as a clean energy carrier depends heavily on the development of materials capable of enduring the extreme conditions associated with its production storage and transportation. This review critically evaluates the performance of metals polymers and composites in hydrogen-rich environments focusing on degradation mechanisms such as hydrogen embrittlement rapid gas decompression and long-term fatigue. Metals like carbon steels and high-strength alloys can experience a 30–50 % loss in tensile strength due to hydrogen exposure while polymers suffer from permeability increases and sealing degradation. Composite materials though strong and lightweight may lose up to 15 % of their mechanical properties over time in hydrogen environments. The review highlights current mitigation strategies including hydrogen-resistant alloys polymer blends protective coatings composite liners and emerging technologies like predictive modeling and AI-based material design. With hydrogen production expected to reach 500 GW globally by 2030 improving material compatibility and developing international standards are essential for scaling hydrogen infrastructure safely and cost-effectively. This work presents an integrated analysis of material degradation mechanisms highlights key challenges across metals polymers and composites in hydrogen environments and explores recent innovations and future strategies to enhance durability and performance in hydrogen infrastructure.

This review evaluates the current state of the art on polymeric materials for hydrogen transportation and storage highlighting the importance of developing a sustainable hydrogen infrastructure worldwide. It analyses different polymeric materials used for hydrogen transportation and storage applications including high-density polyethylene (HDPE) polytetrafluoroethylene (PTFE) polyimides (PI) polyether ether ketone (PEEK) polyamide ethylene propylene diene monomer (EPDM) polyvinylidene fluoride (PVDF) and fluorinated ethylene propylene (FEP). These materials are assessed using key characteristics such as hydrogen permeability mechanical strength chemical resistance and thermal stability. The review finds that while PEEK and polyimides exhibit the highest thermal stability (up to 400 °C) and pressure resistance (300–400 bar) HDPE remains the most cost-effective option for low-pressure applications. PTFE and FEP offer the lowest hydrogen permeability (<0.01 cm³ mm/m²·day·bar) making them ideal for sealing and lining in hydrogen storage systems. Furthermore key research gaps are identified and suggestions for future research and development directions are outlined. This comprehensive review is a valuable resource for researchers and engineers working towards sustainable hydrogen infrastructure development.

Hydrogen is a key enabler of the energy transition and repurposing existing natural gas pipelines offers a costeffective pathway for large-scale hydrogen transport. However hydrogen embrittlement raises integrity concerns and current design standards such as ASME B31.12 Option A adopt highly conservative safety margins without a quantified reliability basis. This study evaluates whether the conservative safety margins in ASME B31.12 Option A for hydrogen pipelines can be safely relaxed. A semi-elliptical flaw (depth 0.25t length 1.5t) is assessed using the Failure Assessment Diagram (FAD) method and Monte Carlo simulations with up to 2.5 × 107 iterations. Fracture toughness is fixed at 69.3 MPa√m while wall thickness and yield strength vary statistically. Three design scenarios explore safety factor products from 0.388 to 0.720 at 0 ◦C and 20 ◦C. Results show that flaw acceptability is maintained in all deterministic cases and the probability of failure remains below 10− 6 . No failures occur when the safety factor product drops below 0.637. The analysis uses only codified flaw assumptions and public material data. These findings confirm that Option A provides a highly conservative envelope and demonstrate the value of a reliability-based approach for assessing hydrogen pipeline repurposing while addressing the gap between prescriptive standards and quantified reliability. This integrated FAD–probabilistic framework demonstrates that Option A includes significant conservatism and supports a reliability-based approach to evaluate hydrogen pipeline repurposing without experimental inputs.

This study investigates the performance degradation of X70 steel weld material in highpressure natural gas pipelines in the Sichuan-Chongqing region and its impact on pipeline safety by investigating their behavior under multiphysics environments including varying gas media (nitrogen methane hydrogen-blended) pressure conditions (0.1–10 MPa) and material regions (base metal vs. weld). A key novelty of this work is the introduction of a “degradation rate” metric to quantitatively assess the deterioration of weld mechanical properties. A key novelty of this work is the explicit introduction of a “degradation rate” metric to quantitatively assess the deterioration of weld mechanical properties. Slow strain rate tensile tests combined with fracture morphology and microstructure analysis reveal that welds exhibit inferior mechanical properties due to microstructural inhomogeneity and residual stresses including a yield stress reduction of 15.2–18.7%. The risk of brittle fracture was highest in the hydrogen-blended environment while nitrogen exhibited the most benign effect. Material region changes were identified as the most significant factor affecting degradation. This research provides crucial data and theoretical support for pipeline safety design and material performance optimization.

The cooling effect from the para-ortho hydrogen conversion (POC) combined with a vaporcooled shield (VCS) and multi-layer insulation (MLI) can effectively extend the storage duration of liquid hydrogen in cryogenic tanks. However there is currently no effective and straightforward empirical correlation available for predicting the catalytic POC efficiency in VCS pipelines. This study focuses on the development of correlations for the catalytic conversion of para-hydrogen to ortho-hydrogen in pipelines particularly in the context of cryogenic hydrogen storage systems. A model that incorporates the Langmuir adsorption characteristics of catalysts and introduces the concept of conversion efficiency to quantify the catalytic process’s performance is introduced. Experimental data were obtained in the temperature range of 141.9~229.9 K from a cryogenic hydrogen catalytic conversion facility where the effects of temperature pressure and flow rate on the catalytic conversion efficiency were analyzed. Based on a validation against the experimental data the proposed model offers a reliable method for predicting the cooling effects and optimizing the catalytic conversion process in VCS pipelines which may contribute to the improvement of liquid hydrogen storage systems enhancing both the efficiency and duration of storage.

This study investigated the hydrogen embrittlement behavior of 304 stainless steel under the combined condition of sensitization and hydrogen pre-charging. Specifically hydrogen trapping analysis and martensite transformation mapping were used to examine the respective roles of carbide precipitation and chromium depletion and key factors were identified through fractographic observations. Sensitization was simulated at 650 ◦C for 50 h followed by hydrogen pre-charging at 250 ◦C under 50 MPa for 3.5 days. Under hydrogen pre-charging sensitized specimens showed a 9.3 % drop in ultimate tensile strength a 17.3 % reduction in elongation and a 16 % decrease in relative reduction of area indicating higher hydrogen embrittlement susceptibility. Hydrogen desorption analysis revealed a redistribution of hydrogen from reversible to irreversible traps consistent with 139 nm coarsened Cr23C6 carbides while phase mapping revealed extensive formation of strain-induced martensite along grain boundaries and within grains. These martensitic regions accelerated hydrogen transport and promoted strain localization leading to the disappearance of intragranular dimples and the development of intergranular cracking. The results demonstrate that strain-induced martensite formed in chromiumdepleted regions is the dominant factor governing post-sensitization hydrogen embrittlement emphasizing the necessity of controlling chromium depletion to maintain the stability of the austenitic matrix in hydrogen environments.

Underground hydrogen storage (UHS) is a relatively new technology that demonstrates notable potential for the efficient storage of large quantities of green hydrogen. Its large-scale implementation requires a comprehensive understanding of numerous factors including safe and effective storage methods as well as overcoming various thresholds and challenges. This article presents strategies for accelerating the implementation of this technology identifying the thresholds and challenges affecting the development and future scale-up of UHS. It characterises challenges and constraints related to geology (including the type and geological characterisation of structures hydrogen storage capacity and hydrogen interactions with underground environments) the technological aspects of hydrogen storage (such as infrastructure management and monitoring) and economic and legal considerations. The need for the rapid implementation of demonstration projects has been emphasised. The identified thresholds and challenges along with the resulting recommendations are crucial for paving the way for the large-scale implementation of UHS. Addressing these issues will significantly influence the implementation of this technology post-2030.

The rapid adoption of hydrogen fuel cell vehicles (HFCVs) in the Beijing–Tianjin–Hebei (BTH) hub accentuates the mismatch between renewable-based hydrogen supply in Hebei and concentrated demand in Beijing and Tianjin. We develop a mixed-integer linear model that co-configures a hydrogen pipeline network and optimizes hourly flow schedules to minimize annualized cost and CO2 emissions simultaneously. For 15000 HFCVs expected in 2025 (137 t d−1 demand) the Pareto-optimal design consists of 13 production plants 43 pipelines and 38 refueling stations delivering 50767 t yr−1 at 68% pipeline utilization. Hebei provides 88% of the hydrogen 70% of which is consumed in the two megacities. Hourly profiles reveal that 65% of electrolytic output coincides with local wind–solar peaks whereas refueling surges arise during morning and evening rush hours; the proposed schedule offsets the 4–6 h mismatch without additional storage. Transport distances are 40% < 50 km 35% 50–200 km and 25% > 200 km. Raising the green hydrogen share from 10% to 70% increases total system cost from USD 1.56 bn to USD 2.73 bn but cuts annual CO2 emissions from 142 kt to 51 kt demonstrating the trade-off between cost and decarbonization. The model quantifies the value of sub-day pipeline scheduling in resolving spatial–temporal imbalances for large-scale low-carbon hydrogen supply.

Hydrogen (H2) is a promising energy carrier for decarbonization; however efficient storage remains a key challenge. Porous materials offer potential for enhanced H2 densification and may enable the development of next-generation lightweight storage systems. A major limitation of such materials is their fine powder form which hampers retention and processability. In this study composite membranes comprising a polymer of intrinsic microporosity (PIM-1) matrix and a polytriphenylamine (PTPA)-based conjugated microporous polymer (CMP) filler were developed. The composites are mechanically robust forming self-standing membranes that retain stability under high temperatures and humidity. H2 storage capacities of the membranes showed excess gravimetric uptakes of 1.03 wt% at 1 bar and 1.84 wt% at 50 bar (77 K) with total capacities reaching 3.22 wt% at 100 bar. These values are significantly higher than those of pristine PIM-1 which achieved 0.87 wt% 1.64 wt % and 2.89 wt% under the same conditions. Net adsorption isotherms demonstrate the potential of the composites to outperform conventional compression storage up to 10 bar at 77 K. Additionally the composites exhibit high mass transfer coefficients (3.42 min− 1 ) indicating strong H2 affinity and faster charging rates compared with the pristine PIM-1 membrane (2.79 min− 1 ).

In the present work a new analytical model of polytropic flow in constant-diameter pipelines is developed to accurately describe the flow of compressible gases including natural gas and hydrogen explicitly accounting for heat exchange between the fluid and the environment. In contrast to conventional models that assume isothermal or adiabatic conditions the proposed model simultaneously accounts for variations in pressure temperature density and entropy i.e. it is based on a realistic polytropic gas flow formulation. A system of differential equations is established incorporating the momentum continuity energy and state equations of the gas. An implicit closed-form solution for the specific volume along the pipeline axis is then derived. The model is universal and allows the derivation of special cases such as adiabatic isothermal and isentropic flows. Numerical simulations demonstrate the influence of heat flow on the variation in specific volume highlighting the critical role of heat exchange under real conditions for the optimization and design of energy systems. It is shown that achieving isentropic flow would require the continuous removal of frictional heat which is not practically feasible. The proposed model therefore provides a clear reproducible and easily visualized framework for analyzing gas flows in pipelines offering valuable support for engineering design and education. In addition a unified sensitivity analysis of the analytical solutions has been developed enabling systematic evaluation of parameter influence across the subsonic near-critical and heated flow regimes.

This study enhances regional integrated energy systems by proposing a Stackelberg planning–operation model with seasonal hydrogen storage addressing source–network separation. An equilibrium algorithm is developed that integrates a competitive search routine with mixed-integer optimization. In the price–energy game framework the hydrogen storage operator is designated as the leader while energy producers load aggregators and storage providers act as followers facilitating a distributed collaborative optimization strategy within the Stackelberg game. Using an industrial park in northern China as a case study the findings reveal that the operator’s initiative results in a revenue increase of 38.60% while producer profits rise by 6.10% and storage-provider profits surge by 108.75%. Additionally renewable accommodation reaches 93.86% reflecting an absolute improvement of 20.60 percentage points. Total net energy imbalance decreases by 55.70% and heat-loss load is reduced by 31.74%. Overall the proposed approach effectively achieves cross-seasonal energy balancing and multi-party gains providing an engineering-oriented reference for addressing energy imbalances in regional integrated energy systems.

Liquid hydrogen (LH2 ) is a promising energy carrier for future clean fuel technologies. However its cryogenic storage and handling pose significant challenges particularly due to self-pressurisation and boil-off from ambient heat ingress. Accurate modelling of these phenomena is essential for the safe and efficient design of LH2 storage systems. A key aspect of such modelling is the selection and implementation of an appropriate interfacial phase change model. This study presents a comparative assessment of three widely used phase change models; the Schrage model the Modified Energy Jump (MeJ) model and the Lee model. A parametric study was conducted across three coefficients for each model with validation performed against five experimental benchmark cases from NASA’s K-Site and MHTB cryogenic tanks focusing on planar interface problems with thermally induced phase change under normal gravity. A CFD approach using STAR-CCM+ was employed to evaluate each model’s ability to predict tank pressure temperature and boil-off behaviour. The Schrage model demonstrated the most robust and accurate results exhibiting minimal sensitivity to coefficient variation and offering both numerical stability and physical fidelity. It demonstrated a maximum mean absolute percentage error (MAPE) of just 3.0% in its pressurisation predictions. The MeJ model showed comparable accuracy when its heat transfer coefficient was appropriately selected highlighting its reliance on an empirically derived coefficient. In contrast the Lee model performed the poorest exhibiting numerical divergence at high coefficient values and substantial deviation in its prediction of self-pressurisation with errors of up to 11% MAPE. These findings provide practical guidance for the selection and implementation of phase change models in CFD simulations and highlight key considerations for modelling LH2 storage tanks in industrial applications.

The HyPurge project aimed to explore the comparative challenges in purging gas network pipes to hydrogen compared to purging to Natural Gas. A comparative study has been carried out investigating the purging performance of hydrogen and methane on pipe diameters across the range of sizes to be used by SGN in the H100 Fife project.

The most significant discovery of the project is that the very low density of hydrogen does not make direct purging between air and hydrogen impossible or even difficult. In many cases direct purging a system in like for like conditions is more efficient for hydrogen than for methane. At the time of writing it is believed that this is due to the higher coefficient of diffusion for hydrogen.

These findings should provide SGN with confidence that direct purging is a viable option for commissioning and decommissioning the networks for H100 Fife.

Over 750 direct purges or purge related tests have been carried out during this project. The results provide evidence to fill the knowledge gap regarding direct purging performance between air and hydrogen.

Key messages from this work are: 1) Hydrogen purges are generally more efficient than Natural Gas purges. The total volume of air-fuel mixture created in a purge involving hydrogen is likely to be less than one involving Natural Gas.

In tests purges from air to hydrogen have been consistently more efficient than purges from air to methane. Purges from both fuel gases back to air have a relatively similar performance to each other. The low density of hydrogen did not present any challenges for direct purging operations. This means that less fuel-air mix and less fuel in total is released for a hydrogen purge compared to a Natural Gas purge. 2) Hydrogen purges are generally more flammable than Natural Gas purges. The flammable volume of air-fuel mixtures created inside the pipe during a purge involving hydrogen is likely to be greater than one involving Natural Gas.

Although less air-fuel mixture is created during a hydrogen purge the wider flammable range of hydrogen means that the volume of mixture that is flammable inside the pipe is greater for a hydrogen purge than for a Natural Gas purge. 3) The total volume of flammable air-fuel mixtures generated outside of the pipe during a purge involving hydrogen is likely to be less than one involving Natural Gas. The upper flammable limit does not prevent vented fuel becoming flammable once it mixes with air outside of the pipe.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

This study conducted theoretical modelling and experimental work to investigate if there were differences in particle transportation behaviour in hydrogen compared to natural gas. It was found that both experimental data and predictions indicate that the majority of particles are currently mobile at the standard maximum natural gas velocity of 20m/s thus an increase in velocity to 70m/s with hydrogen should not result in an increase in particle transportation. The experimental observations are that natural gas can transport particles at lower velocities than hydrogen and this is thought to be due to the higher density of natural gas. The consequence is that at a velocity of 20m/s natural gas would transport all mobile particles as would hydrogen at higher velocities and this means that high velocity hydrogen cannot transport more particles already transported by natural gas.

Therefore this study indicates that the mitigations for example filtration requirements and engineering policies and procedures should be unaffected by changing to hydrogen as no change to particle loading is anticipated.

CONCLUSIONS

• Modelling has been undertaken to predict particle flight and rolling velocities in 100% hydrogen and 100% natural gas to support experiments.

    o Initial comparison between the CFD modelling and British Gas modelling indicates results are similar for both particle        rolling and flight velocities for 100% hydrogen at 2barg.

    o For 100% methane the British Gas model results are 32-38% lower than those predicted by CFD modelling.

• Initial particle transportation experiments have been conducted using a purpose built test facility at Spadeadam to investigate particle transportation in 100% hydrogen and 100% natural gas at 2barg and 40mbarg.

    o Initial experimental results indicate that particle transportation occurred at lower velocities in natural gas than for             hydrogen.

    o From experimental data rolling and flight of particles occurs over a range of velocities and there is not one specific velocity to instigate rolling or flight.

    o Tests were performed for services in hydrogen. However a limited amount of sand was observed to travel up the service compared to the mains.

• Both experimental data and predictions indicate that the majority of particles are currently mobile at the standard maximum natural gas velocity of 20m/s (for unfiltered gas) thus an increase in velocity to 70m/s with hydrogen should not result in an increase in particle transportation.

• This study indicates that the mitigations used for natural gas should still be effective for hydrogen service

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

SGN are undertaking the LTS Futures Project which forms part of the UK’s national hydrogen research programme to deliver a net zero decarbonisation solution for customers. The project seeks to research develop test and evidence the compatibility of the Great Britain (GB) Local Transmission System (LTS) assets pipelines associated plant and ancillary fittings for hydrogen service.

The aim of the project is to demonstrate that the LTS can be repurposed to convey hydrogen providing options for the decarbonisation of power industry heat and transport by delivering a safe supply of energy to all customers both during and after the energy transition. The LTS Futures project includes a repurposing trial of the Grangemouth to Granton pipeline.

Prior to repurposing to convey hydrogen the Grangemouth to Granton pipeline is to be audited in accordance with the requirements of IGEM/TD/1 Edition 6 clause 12.4.2.1 noting the requirements of Supplement 2 for High Pressure Hydrogen Pipelines [1 2]. This is a formal assessment of the integrity of the pipeline and an assessment of the risk posed on the surrounding population.

This report presents the assessment of TD/1 compliance of the Grangemouth to Granton pipeline.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

The current UK natural gas networks operated by the Gas Distribution Networks have the potential to flow blended hydrogen and to be re-purposed to flow 100% hydrogen. The hydrogen networks would therefore have the potential to contribute to Ofgem’s strategic innovation fund (SIF) decarbonisation of heat challenge to help meet national 2030 and 2050 emissions targets.

To demonstrate how the current gas networks can be intelligently and efficiently transitioned to provide low carbon heating the gas velocity constraints for hydrogen applied at the design stage need to be identified. These constraints will directly impact the level of capital investment required in the transition of the system to accommodate blended and 100% hydrogen.

However hydrogen gas does not contain the same level of energy by volume as natural gas so the volume of hydrogen flowing to consumers would have to increase a little over 3 times for an 100% hydrogen network to deliver energy at an equivalent rate compared to natural gas. Without network reinforcement this increase in flow could require a significant increase to the pressure and/or velocity of gas.

Currently IGEM standards specify a nominal maximum velocity of 20 m/s mainly to avoid the risk of debris within the pipes being picked up by the gas stream and causing wear to pipe components possibly then resulting in early failure. A velocity limit of 40 m/s is assumed where the pipe assets are assumed to be clean.

Debris may be present in the system particularly in the lower pressure tiers in the form of dust mainly as a product of the historic manufacture of towns gas. Whilst many metallic mains particularly in the LP pressure tier have been replaced with PE (polyethylene) piping under the ongoing replacement scheme it is anticipated that debris will still be present in the pipes that have not been replaced and may have already been transported into the plastic pipes. Hydrogen has different properties to natural gas so it is not known if debris may be picked up to the same degree or if any other factor will limit velocity. Other factors such as noise and/or vibration may also constrain the design velocity of gas in the system.

Building on this initial work it was envisaged that validation of the pipe network behaviour would require full scale testing to investigate the erosion vibration and noise behaviour associated with transportation of hydrogen and hydrogen blends with natural gas to support the objective of validating and enhancing existing models. To develop the requirements for such testing the “Alpha phase” (this phase) of the SIF project was initiated with the intention of delivering conceptual designs of the full-scale test facilities a detailed test programme and to undertake any associated laboratory testing which would be required to support these activities.

This report summarises the SIF alpha phase conclusions and recommendations from work packages 1 to 5:

Work package 1 Conceptual design of test facilities

Work package 2 Detailed test plan

Work package 3 Laboratory testing

Work package 4 Network engagement

Work package 5 Cost-benefit analysis

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

Concerns relating to the production of carbon dioxide (CO2) and its effects on global background temperatures have led to international efforts to reduce CO2 emissions. A contributor to CO2 emissions is the burning of natural gas in domestic and commercial fuel supplies. The H21 project endeavours to explore the use of hydrogen gas as an alternative to natural gas.

As part of the work associated with delivering H21’s 100% hydrogen gas network a requirement was identified to develop a method of assessing the suitability of gas distribution network assets (e.g. pipes valves regulators) for use with hydrogen up to 7 barg. This project has developed such a methodology and this report summarises the work conducted and signposts the main deliverables.

The methodology developed for hydrogen suitability is based on a component-level analysis components being the individual items that make up an asset. The methodology structure is shown below where first the risk of the asset failing when operating on natural gas is determined. Next the asset is broken down to the component level and the individual risk of the components failing when operating on 100% hydrogen is determined. If the combination of these two risks is greater than is considered acceptable by the methodology the asset is considered not suitable for use with hydrogen without further mitigation.

The methodology is supported by the following key inputs delivered through the project:

♦ A list of assets on the gas distrbution network.

♦ A database of materials with their suitabiltiy for use with hydrogen quantified.

The method has been demonstrated on eight case studies and the next step will be for the project stakeholders to apply it to the population of network assets the results of which will gauge the networks readiness for hydrogen.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

Greater assurance regarding the integrity of current domestic gas installation pipework is sought to enable its repurposing to hydrogen. This project needs to be viewed in the context of current leaks from natural gas (NG) of sufficient magnitude to create a fire explosion or injury incident. Gas systems do leak and roughly 400000 publicly reportable escapes (PRE’s) are made each year from 24 million connections. This represents a risk per property of about one PRE every 60 years. The overwhelming majority of these leaks are extremely small and probably better described as weeps.

Odorised gas (as distributed through the low-pressure gas network) can be smelt at about 1000ppm gas in air concentration [1] which is about 2.5% of the published lower flammable limit (LFL) of hydrogen (4% gas in air concentration). This roughly equates to a leak of 10 l/h (0.01 m3/h) in a 25 m3 room. The amount of gas from such a leak is small but still large compared to the leak detectable by a standard IGEM/UP/1/B Edition 3 20 mbarg tightness test which can detect a leak greater than about 0.2 l/h (0.0002 m3/h) [2] for a typical natural gas domestic installation.

Spontaneous leaks (rather than weeps) in domestic and small commercial gas systems are extremely rare. The pressure within these systems (nearly always ca. 20 mbarg) is sufficiently low that it does not cause impromptu pipework failure. The pipes used in these systems do not corrode from the inside and even with external corrosion the nature of this effectively results in a small leak (initially a weep) which only grows slowly with time.

During the period from 2016 to 2022 there was an average of 25 domestic gas incidents a year that were attributed to meters meter outlet pipes (effectively the gas carcass) or appliances but of these only about 0.4 to 1.5 injury incidents arose from spontaneous failure of internal pipework. Therefore risk exposure from the internal pipework itself is very much at the lower end of the ‘Broadly Acceptable’ range defined by the Health and Safety Executive (HSE) and so existing controls under natural gas service should be deemed adequate.

Provided appropriate precautions are taken during the conversion of each property from natural gas to hydrogen it is expected that the risk exposure will remain Broadly Acceptable.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

In line with the UK government’s de-carbonisation strategy Northern Gas Network’s (NGN) H21 project aims to demonstrate the feasibility of converting the existing <7barg gas distribution network to 100% hydrogen. Following progress on Phase 1 of the H21 programme Phase 2 was proposed to build on the knowledge acquired to provide further quantified safety-based evidence on the suitability of the GB networks to transport 100% hydrogen. Phase 2 consisted of a number of Project Phases. Phase 2b evaluates network operational procedures in use with 100% hydrogen. Conducted on a repurposed part of the natural gas distribution network and identifying which of these are suitable for a 100% hydrogen network and those that may require adjustments. To achieve this a gas demonstration facility centred around an existing part of the gas network was built at South Bank Middlesbrough to accommodate operations within low pressure network parameters and typical network components. A Master Test Plan (MTP) for Phase 2 was subsequently developed by NGN in collaboration with the HSE and DNV to address various aspects of existing network procedures and operations including:

♦ Emergency Response and bad practice demonstrations

♦ Finding Leaks

♦ Accessing Leaks

♦ Assessment of repair techniques

♦ Planned live gas operations

♦ Isolation techniques

♦ Commissioning and decommissioning activities

♦ Pressure regulation and maintenance procedures

♦ Pressure and flow validation

Each practical test was derived from one of the above subcategories within the master test plan. This report details the work conducted within the Planned Live Gas Operation remit completed at the NGN H21 testing facility at South Bank. The programme included eight live gas operations undertaken on the buried hydrogen low pressure network within the South Bank test facility the network contained both metallic and PE mains with different diameters throughout the grid. This allowed operations to be undertaken in conditions mirroring real life as they would be completed out on the network. The objective of these experiments is to prove routine operations that are undertaken on a day-to-day basis on the NG distribution network can be completed on 100% hydrogen networks. This report details the experimental set-up operation procedures and method statements used in Section 3; the results and main observations in Section 4 followed by interpretation of results and conclusions in Section 5.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

In line with the UK government’s de-carbonisation strategy Northern Gas Network’s (NGN) H21 project aims to demonstrate the feasibility of converting the existing <7barg gas distribution network to 100% hydrogen. After conversion of the gas networks hydrogen could be transported from various sources through new and existing gas networks to industrial and domestic customers.

Following progress on Phase 1 of the H21 programme Phase 2 was proposed to build on the knowledge acquired to provide further quantified safety-based evidence on the suitability of the GB networks to transport 100% hydrogen. Phase 2 consisted of a number of Project Phases. Phase 2a evaluates network operational procedures identifying which of these are suitable for a 100% hydrogen network and those that may require adjustments. To achieve this a gas demonstration network was built at DNV Spadeadam Research and Development to accommodate full scale network parameters including typical network components. A Master Test Plan (MTP) was subsequently developed by NGN in collaboration with the HSE Science and Research Centre (HSE S\&RC) and DNV to address various aspects of existing network procedures and operations including:

♦ Emergency Response and bad practice demonstrations

♦ Finding leaks

♦ Accessing leaks

♦ Assessment of repair techniques

♦ Live gas operations

♦ Isolation techniques

♦ Commissioning and decommissioning activities (i.e. purging)

♦ Pressure regulation and maintenance procedures

♦ Pressure and flow validation

Each of these areas of testing and assessments were then divided in individual tests or tasks and identified with a unique ID name.

The current report details the work conducted on the H21 demonstration grid herein referred to as “Microgrid” in relation to planned live gas operations and isolation techniques. The programme included assessing the effectiveness of existing flow stopping techniques by measurement of the let-by rate downstream of the flow stopping device. The flow stopping techniques demonstrated included: a metallic stopple squeeze off ALH bag off and an MLS bag off. These techniques were performed by third parties according to Method Statements and Risk Assessments modified for the application to hydrogen. Principally the outcome of the Procedural Review conducted by HSE S\&RC1 was that flammable atmospheres within and around the tools pipework and vents as currently operated could not be tolerated as for hydrogen operations. As such the techniques were all conducted with the introduction of nitrogen inerting steps to avoid hydrogen and air mixing within any confined geometries.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

HyNTS is a programme of work that seeks to identify the opportunities and address the challenges that transporting hydrogen within the National Transmission System (NTS) and Local Transmission System (LTS) presents. This will unlock the potential of hydrogen to deliver the UK’s 2050 Net Zero targets. The programme is being executed alongside other ongoing UK hydrogen initiatives such as National Grids Project Union and Cadent’s HyNet projects.

A key element of repurposing feasibility and therefore central to the overall HyNTS initiative is the requirement to have an improved understanding of the ‘fingerprint’ of pipeline assets prior to hydrogen injection. The Pipeline Dataset SIF project has two primary objectives:

♦ Defining and gathering the data necessary to ultimately facilitate repurposing of above 7 bar pipelines on the NTS and LTS

♦ Developing the tools and processes to store align and visualise data

Split into 3 phases the first ‘Discovery’ phase aims to develop the high-level data and data management requirements for repurposing as well as the current data availability across the NTS and LTS to meet these requirements. Subsequent Alpha and Beta phases involve detailed planning and subsequent execution of the data collection and data management activities identified in the Discovery phase.

The Discovery phase comprises four Workpacks as shown in the diagram below designed to cover the project objectives.

ROSEN and Cadent have partnered with National Grid (NGG) to deliver the Discovery phase. Close collaboration between NGG Cadent and ROSEN has been required to conduct all Workpacks particularly in terms of appraising the current data held and current Data Management arrangements within both organisations.

This report presents the findings from the Discovery Phase as well as providing recommendations to feed into shaping subsequent Alpha and Beta phase activities.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

National Gas has identified the need to understand the effects of hydrogen on various pipeline materials commonly found in the UK National Transmission System (NTS) to determine their potential for a hydrogen use case. Accordingly National Gas is interested in investigating the potential use of oxygen as a mitigation of hydrogen embrittlement (HE) the detrimental effect of hydrogen on the mechanical properties of metallic materials. This report presents the laboratory findings part of the project “Inhibition of hydrogen embrittlement effects in pipeline steels” in which ROSEN has been requested to investigate the potential use of oxygen as a mitigation of hydrogen effects.<br/>Three pipe materials were investigated which included a ERW X52 commissioned in 1993 a DSAW X60 commissioned in 1973 and a DSAW X80 constructed in 2004. The test programme aimed to characterise the effectiveness of oxygen on mitigating hydrogen embrittlement and included an in-air baseline characterisation and three main hydrogen tests: threshold stress intensity factor KIH fracture toughness and two types of fatigue crack growth rate tests (frequency scans and Paris curve). Fracture toughness and fatigue crack growth rate tests were performed in pure hydrogen and at various oxygen concentrations ranging from 50 to 1000 ppm.<br/>The baseline in-air characterisation showed that some of the mechanical properties of the X52 and X60 were below the T/SP/PIP/1 requirements. For the X52 the yield strength of transverse parent material specimens was below the 360 MPa required by its designation. For the X60 both the longitudinal and transverse yield strength of the parent material were below the 415 MPa required for this grade. Furthermore CVN energies were also below the T/SP/PIP/1 requirements for parent metal and seam weld metal for the X60 pipe. The X80 was within specifications.<br/>Threshold stress intensity factor KIH tests were performed on the three investigated materials on base and weld metal in pure hydrogen. Crack extension was not seen in any of these tests for the applied stress intensity factors as high as 73 MPa√m. The absence of crack growth was verified by means of SEM examination which showed the direct transition from the fatigue pre-crack region to the final fracture region. For this reason KIH tests with oxygen additions were not conducted.<br/>Fracture toughness testing showed that the fracture resistance was reduced when testing in pure hydrogen. This was seen in X60 specimens that had a fracture resistance JQ of 31 kJ/m2 35% of that in air. The addition of oxygen resulted in an increase of the average JQ which at 250 ppm O2 was 85% of the in air value. At concentrations above this value the fracture resistance continued to approach in-air values although at a decreased rate. Increasing the oxygen concentration also resulted in smaller standard deviations of the fracture resistance decreasing from 13 to 2 kJ/m2 as the O2 concentration was increased from 50 to 500 ppm. These findings indicate there is a smaller variability of the performance when oxygen is added. The recovery of the fracture resistance was consistent with the SEM examination of fracture surfaces of tested specimens. In pure hydrogen fracture surfaces were consistent with a quasi-cleavage fracture characterised by planar facets with visible river marks. As oxygen was increased the fracture surface became more dimpled and areas with signs of plastic strain became evident. At concentrations of 250 ppm O2 the fracture surface resembled those obtained in air suggesting the same ductile failure mode. Obtaining quantitative fracture toughness data for the X52 and X80 specimens in oxygen additions was not possible due to material related challenges. However fractographic examination showed that in pure hydrogen and low oxygen concentrations e.g. 50 ppm the failure mode was predominantly brittle while at 250 ppm O2 and in air the failure mode was ductile and was accompanied of limited crack growth.<br/>The inhibiting effects of oxygen were also seen in fatigue crack growth rate tests. Frequency scan tests on X60 showed that the exposure to hydrogen resulted in high crack growth rates up to 2 orders of magnitude above the BS7910 in-air mean depending on the testing conditions. Crack growth rates were affected by the choice of the frequency. For the test performed with a Kmax of 45 ksi√in (49 MPa√m) crack growth rates continued to increase above 1 mm/cycle as the frequency was reduced to 1E-4 Hz. For the test performed with a Kmax of 38 ksi√in (42 MPa√m) crack growth rates reached a plateau at a frequency of 0.1 Hz. The additions of oxygen resulted in a reduction of crack growth to values a few times above the BS7910 in-air mean. Furthermore the effect of frequency was visibly reduced in 250 ppm O2 as reducing the frequency 40000 times resulted only in a 2 times increase of the crack growth rates. The effect of oxygen was also seen in Paris curve types of tests. In pure hydrogen crack growth rates were comparable with ASME B31.12 and Sandia National Laboratories reference curves and were in general up to an order of magnitude above the BS7910 in-air mean depending on ΔK and other parameters. The additions of oxygen at concentrations as low as 50 ppm resulted in reductions in fatigue crack growth rates to values closer to those in air. Further increases in the oxygen concentration resulted in slight reductions of crack growth rates that were more noticeable at higher ΔK and Kmax. The recovery of the fatigue performance was consistent with the fractography observations. The addition of oxygen resulted in an overall increase of the plastic strain seen on the fracture surfaces. In pure hydrogen fracture surfaces were consistent with quasi-cleavage failure and had planar cleavage facets with river marks and very fine striations that were mostly visible at high frequencies and ΔK under high magnifications (55800x). The fracture surfaces of specimens tested in presence of oxygen resembled those seen in the in-air fatigue pre-crack region especially at high frequencies and high ΔK. At low frequencies and low ΔK the fracture surfaces resembled that of quasi-cleavage fracture although they had a ‘fibrous’ aspect with visible signs of plastic strain. Striations were readily visible on the fracture surfaces of all specimens tested in presence of oxygen and were more defined than those seen in pure hydrogen.<br/>Based on the data generated in this work a concentration of 250 ppm O2 is recommended as the minimum value to achieve inhibition of hydrogen effects. This concentration provided a recovery of 85% of the in-air fracture resistance and resulted in crack growth rates close to in-air levels. The fracture surfaces of specimens tested at this oxygen concentration generally showed ductile features consistent with higher toughness failure mechanisms.

The project between DNV and NGT innovation is exploring the future impact of introducing hydrogen into the National Transmission System (NTS) network and specifically looking at the impact on the compressor station equipment. The consequent failure modes associated with the introduction of hydrogen will be assessed through Failure Mode Effect Analysis (FMEA).

The work scope includes:

• Perform a staged approach FMEA study  Qualitative assessments determining the risk levels associated with the various components of the compressor trains.

• Perform the FMEA on each selected train type assessing the operational safety and environmental impact of H2 introduction.

Assessment has been made for two potential network gas types:

• 25% H2/NG blend

• 100% H2

The output is an FMEA on each generic compressor stations indicating the risk areas from H2 operation. This output will allow NGT to identify areas which require further assessment / action before H2 is introduced.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

Distribution Network Operators have investigated the potential to utilise iron mains and fittings in hydrogen service.

Iron mains operate at low (<75 mbarg.) or medium (<2 barg.) pressure iron fittings at up to intermediate pressure (<7 barg.) depending on design. No iron mains have been laid since the 1980s although certain grades of iron are still used to construct fittings which includes valves.

The work was conducted by DNV. It examined the impact that hydrogen might have on iron of different grades and also the risk of explosion posed by hydrogen if it escapes from a buried main. In carrying out the analysis no account was taken of additional mitigation measures associated with hydrogen conversion (e.g. in home detection) which would reduce risk to members of the public.

To enhance confidence at the request of Operators IGEM assembled a ‘Peer review panel’ of material science and risk modelling experts from a range of backgrounds. Their role was to express their professional opinion of the findings. The reports produced by DNV and the peer review panel are attached to this report in the appendix.

The conclusion is that iron fittings and most iron mains expected to be in operation after the current replacement programme is completed in December 2032 can operate in hydrogen service.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

This Networks Innovation Allowance (NIA) funded project (NIA_NGGT0176) comprised a feasibility study on an exemplar National Grid Gas Transmission (NGGT) National Transmission System (NTS) compressor station. The study has examined safety environmental technical operational and economic issues in blending hydrogen/methane for combustion in a gas turbine (GT) driving NTS compression. The project also determined how to establish an innovative green hydrogen production storage and supply facility to fuel GTs on varying hydrogen/methane blends.

This strategic study is preparatory work ahead of demonstration on an NTS compressor station which precedes hydrogen blending in NTS compressors as ‘business as usual’. Higher hydrogen concentrations may be achieved in the GTs in advance of similar blends within the transmission pipes. As such this strategic and innovative project could de-risk the hydrogen transition of GT compression operations and bring forward CO2 and NOx reductions.

For the feasibility study two scenarios have been assessed: co-firing with 25%/75% vol hydrogen/natural gas blend and 100% vol hydrogen.

The study found it is viable to run the Siemens Energy SGT-A20 GTs on blends of hydrogen and natural gas up to 100% hydrogen and there are historic examples of this type of GT doing so without detriment.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz

HyNTS is a programme of work that seeks to identify the opportunities and address the challenges that transporting hydrogen within the National Transmission System (NTS) presents. This will unlock the potential of hydrogen to deliver the UK’s 2050 Net Zero targets. The programme will feed into a number of ongoing hydrogen initiatives such as Project Union which has the aim of creating a UK hydrogen transmission backbone for the UK using repurposed and new-build infrastructure.

The Pipeline Dataset SIF project has two primary objectives.

♦ Defining and gathering the data necessary to ultimately facilitate repurposing of above 7 bar pipelines on the NTS and LTS.

♦ Developing the tools and processes to store align and visualise data to facilitate effective Integrity Management decision-making during post-repurposing service.

This report provides a summary of the work completed in the HyNTS Pipeline Dataset project Alpha phase to address these objectives.

This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.

Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.

The accurate analysis of the sealing performance of underground lined cavern hydrogen storage is critical for enhancing the stability and economic viability of storage facilities. This study conducts an innovative investigation into hydrogen leakage behavior by developing a multiphysical coupled model for a composite system of support structures and surrounding rock in the operation process. By integrating Fick’s first law with the steady-state gas permeation equation the gas leakage rates of stainless steel and polymer sealing layers are quantified respectively. The Arrhenius equation is employed to characterize the effects of temperature on hydrogen permeability and the evolution of gas permeability. Thermalmechanical coupled effects across different materials within the storage system are further considered to accurately capture the hydrogen leakage process. The reliability of the established model is validated against analytical solutions and operational data from a real underground compressed air storage facility. The applicability of four materials— stainless steel epoxy resin (EP) ethylene–vinyl alcohol copolymer (EVOH) and polyimide (PI)—as sealing layers in underground hydrogen storage caverns is evaluated and the influences of four operational parameters (initial temperature initial pressure hydrogen injection temperature and injection–production rate) on sealing layer performance are also systematically investigated. The results indicate that all four materials satisfy the required sealing performance standards with stainless steel and EP demonstrating superior sealing performance. The initial temperature of the storage and the injection temperature of hydrogen significantly affect the circumferential stress in the sealing layer—a 10 K increase in initial temperature leads to an 11% rise in circumferential stress while a 10 K increase in injection temperature results in a 10% increase. In addition the initial storage pressure and the hydrogen injection rate exhibit a considerable influence on airtightness—a 1 MPa increase in initial pressure raises the leakage rate by 11% and a 20 kg/s increase in injection rate leads to a 12% increase in leakage. This study provides a theoretical foundation for sealing material selection and parameter optimization in practical engineering applications of underground lined caverns for hydrogen storage.