Transmission, Distribution & Storage

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.