Publications

This project has investigated equipment used to carry out purging of gas networks with a view to providing tooling for commissioning SGN’s H100 Fife project.

It has built on work including the HyPurge NIA2_SGN0008 and Lot 1 of the Hydrogen Skills and Standards for Heat projects. The project has further advanced the body of purge theory founded and developed in those previous projects. The HyPurge project showed that direct purging was feasible with hydrogen; this project has investigated some of the hazards presented and recommended tooling to mitigate those hazards.

Flame arrestors are specified for certain network operations involving Natural Gas. It is recommended that the current procedures regarding flame arrestors are kept for hydrogen and a range of flame arrestors suited to hydrogen use has been identified.

Purge tables specify minimum speeds for purging related to pipe diameter. These minimum purge speeds are used to suppress the buoyancy driven effect of a less dense gas to preferentially flow over a denser gas. The lower buoyancy of hydrogen suggests an increase in purge speed of 1.7x those recommended for methane. This increase is not required in smaller diameters (100 mm and below) where it has been found that diffusion effects dominate purge performance resulting in greater flexibility for purging. Therefore purge tables have been produced giving recommended minimum purge speeds for methane and hydrogen according to the PE pipe diameters proposed in the H100 Fife project.

A purge stack with additional features to assist with hydrogen purging has been developed in this project. The features include a restriction at the end of the stack to mitigate burn-back in the event of a vent ignition. Specific restriction sizes are linked to the diameter of network pipes being purged and each individual restriction is tailored to achieve the correct purge speed for the given network pipe diameter. A pressure gauge on the stack indicates sufficient back pressure showing the correct purge flow is being achieved. The stack also includes a hydrogen wHystle (developed by Steer independently) to provide feedback on purge progress in real time.

A review of non-sparking tool requirements has been carried out. Purge operations are such that it is unlikely that non-sparking tools will provide a significant reduction in hazard. The conclusions from this are that the current recommendations from SGN’s mainlay procedures on non-sparking tools and ignition prevention will be suitable for hydrogen use.

A preliminary investigation into the consequences of in-pipe ignitions has been carried out. The investigation has shown that the overpressures generated are affected by several different factors. The proportion of the pipe that contains the flammable mixture affects the ability of the system to absorb the overpressure through non-flammable gas buffer zones. Once detonable zones increase in size then the absolute length of the detonable zone in relation to pipe diameter becomes a dominant factor. The most significant hazard to be prevented is an in-pipe detonation therefore the volume of detonable mixture is an important factor that may result in a limit to the permitted length for direct purging in a given pipe diameter.

The hazards presented during purging have been investigated and three specific hazards have been studied. These are ignition of the vent in-pipe ignition and burn back from a vent ignition into the pipe. Although none of these events are likely to occur ignition of the vent is the most likely and the consequence of this is similar with hydrogen and methane. In-pipe ignition is the event with the greatest consequence and although very unlikely this should be avoided.

Proposed further work includes: data mining from the body of purge studies to date identification of the growth of flammable and detonable zones vs. purge length a study into static electricity generation and consequence testing on ignitions in a variety of 90 mm and 125 mm PE pipes of different lengths.

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.

There is a requirement for gas distribution network (GDN) operators to understand the cost safety and practicality of converting network pipelines from Natural Gas to Hydrogen in multi-occupancy buildings (MOBs). Previous work undertaken during project ‘MOBs Work Pack 2 Asset Information Review’ [1] considered the requirements for pressure testing commissioning and decommissioning of MOBs following a conversion to Hydrogen and identified the following gaps in technical evidence.

“How does Hydrogen affect the requirements for ventilation and explosion relief?”

“Work is required to understand the ventilation requirements of meters installed inside dwellings whether existing ventilation in MOBs is adequate and the practicalities of increasing the ventilation should it be required. Work has already been undertaken under the NIA project ‘NIA_WWU_2_12 – Ventilation Within Buildings’[2]. It was proposed that ROSEN review the NIA_WWU_2_12 work and confirm its applicability to MOBs”.

"Further work is required including a study consisting of a review of relevant British Standards (BS 8313 [77] BS 6891 [75] and BS 5925 [78]) and validation through case studies to determine how duct dimensions and ventilation requirements are affected by Hydrogen. This work would also need to determine whether the size and positioning of existing vents are adequate with Hydrogen.

“Further work is required to determine whether the ventilation in dwellings is adequate for risers and laterals located within and passing through dwellings.”

SGN is leading a feasibility project with some applied testing to understand the steps needed to convert MOBs to Hydrogen including any testing required to address any evidence gaps. This report focuses on the ventilation requirements associated with the conversion of MOBs from Natural Gas to Hydrogen. The objectives of this task are to:

• Determine ventilation requirements for meters risers and laterals inside buildings.

• Determine ventilation requirements for typical meter banks and energy centres with Hydrogen and how they compare with ventilation requirements for Natural Gas and update Table 6 of IGEM/G/5 Edition 3 [2]

• Determine ventilation requirements for typical ducts with Hydrogen and how they compare with ventilation requirements for Natural Gas and update Table 8 of IGEM/G/5 Edition 3.

• Investigate the feasibility of adding ventilation to MOBs which will need to be positioned so as not to compromise fire safety if located in a fire compartment.

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 project has built on the Hazardous Area Impact Mitigation (HAIM) Phase 1 project (NIA2_SGN0041) results that identified a disparity between hazardous zones measured during initial testing and those specified in the IGEM/SR/25 Hydrogen supplement. The aim of the HAIM Phase 2 project is to scale up the measurements to confirm the behaviour of larger vents equivalent to the test cases presented in the ATEX Equipment & IGEM/SR/25 Modification Assessment (NGNG_NIA_346) project.

The formation of a technical review group has informed the project team of the parameters and some of the assumptions used for the modelling leading to the development of the SR/25 Hydrogen Supplement. The difference between the modelled and measured data seen in the HAIM Phase 1 project has been attributed to the modelled data being carried out under a minimum of 0.5 m/s cross winds. Completely still conditions are not expected to occur hence this 0.5 m/s minimum. The result of this wind on the model leads to a significant reduction of the height of the resulting plume and a corresponding increase in the radial displacement of the plume from the vent tip. This has shifted the focus of this project towards examining wind influenced vents.

Two sets of experiments are provided in this interim report: measurements of plumes from wind influenced vents and plumes from fixtures and fitting leaks. The report also includes early results from plume ignition studies which have shown that ignition is not instantaneous for high velocity plumes.

The wind influenced plume tests have measured 0.0005 kg/s hydrogen releases from 50 mm and 15 mm vent pipes. The largest hazardous zone for these releases stipulated in IGEM/SR/25 hydrogen supplement is Xr = 2.5 m and Xh = 1.5 m so these were used as the extent of measurement. With no wind the plume rises vertically from the vent tip with no radial deflection. Measured concentration peaks have exceeded the lower flammable limit (LFL) at the 1.5 m measurement height. The influence of wind radially displaces the plume the higher the wind the larger the displacement. Concentration peaks are reduced but a wind of 0.5 m/s still permitted levels above the 4 % LFL value. Wind levels of 1.0 m/s displaced the plume to the end of the 2.5 m measurement array. Wind levels of 1.5 m/s broke up the plumes potentially driving pockets of gas beyond the 2.5 m measurement array.

Partial ignition of both vent types was possible at 1.5 m above the vent tip but complete sustained ignition was only possible when closer than 1 m to the vent tip.

Plumes from higher pressure (above 0.1 barg) fixture and fitting leaks have shown a good correlation between the shapes of modelled and measured vents. Except for the lowest pressure leaks which are momentum-dominated jets the resulting plumes are long and thin unaffected by buoyancy. The concentration decay in measured plumes is observed to be faster with distance compared to modelled values. Typically the measured distance to reach 2 % volume from the leak position is about half of the specified zone distances.

Limited ignition tests have been conducted but ignition from a 2 barg adverse downward pointing leak was challenging beyond 30 cm from the leak. The hydrogen jet also repeatably extinguished the methane flame used as pilot light during tests.

The next steps for the project are to carry out more measurements and to scale up the magnitude of the gas releases. This will provide more evidence supporting specified magnitudes of hazardous zones. In addition it is proposed that mitigation measures are explored that could reduce the specified hazardous zones for given vents. This could include design guidelines for hydrogen vents.

Further ignition tests will also be conducted to assess required conditions such as flow direction and gas concentration required to achieve both partial and stable ignition of hydrogen vents.

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 feasibility study has investigated the potential of repurposing existing gas installations for hydrogen use in Multi-Occupancy Buildings (MOBs). MOBs is a broad term extending from a single floor of flats over a shop to large tower blocks. For this study a MOB is defined as a building having at least one meter point and which meets one of these two criteria:

• The building contains at least three domestic dwellings

• The building contains a mixture of domestic dwellings and commercial units with there being at least three dwellings and units in total.

Due to the diverse nature of MOBs and the assets meter positions and appliances used in them it is necessary to sub-divide the population into archetypes and separately assess the risk posed in each category. Customers should only be exposed to Broadly Acceptable risk as defined as an individual risk of fatality of no more than 1 in 1 million per year in the HSE guidance document Reducing Risk Protecting People [1]. Due to the potential for multiple fatalities in MOBs it is important to understand how each building might respond to an incident and reduce risk to As Low As Reasonably Practicable (ALARP).

It is also reasonable to suggest that a customer’s risk after conversion to hydrogen should be comparable to that which currently exists for natural gas. Therefore risk to individuals within a building once converted to hydrogen should be no worse than either the risk faced by them prior to conversion or the average risk for that building height prior to conversion.

Based on SGN’s data the analysis has shown that with universally applied risk mitigation measures and up to two additional mitigations where required around 99% of MOBs can converted to hydrogen using repurposed assets. Detail can be located in Table 7 on page 12 of this report.

There are around 1% of MOBs where it is likely that existing natural gas installations cannot be repurposed for hydrogen use at an economic cost. The following options are available for this small proportion of buildings:

1. Accept a small individual risk increase in a small minority of building types.

2. Implement additional risk mitigation measures that would reduce those individual risks but at a disproportionate cost.

3. Remove gas supplies to these buildings and install an alternative energy source.

Based on the results the following recommendations are given:

• All MOBs to be divided into archetypes and subdivided by installation type prior to a pre-conversion site survey to identify the most practicable and cost-effective energy solution

• The survey will assess all the existing equipment which includes gas pipelines meter locations installation pipes and appliance locations against Gas Industry Standards

• Non-compliant installations will require further analysis and risk assessment on a case-by-case basis to determine their suitability for conversion to hydrogen

• It is proposed that where significant work will be required to re-purpose the existing installation to the required level of safety an economic assessment will be undertaken to determine the optimum solution for customers

• Further work should continue to develop and refine the risk assessment of hydrogen in MOBs. This will support the development of strategic decisions related to conversion. The risks associated with decommissioning gas installations in MOBs could also be assessed in future iterations

• Further work is required to assess Great Britain’s populations of MOBs and gas installation configurations

• Further work is required to provide a detailed cost benefit analysis across the Great Britain distribution networks to ensure that any proposals appropriately address societal expectations of risk versus investment and legal obligations

• Further work is required to define duty holders’ roles responsibilities and interoperability to convert MOBs to hydrogen

• The project has demonstrated that in most cases it is feasible to convert MOBs to hydrogen. The next steps include scoping of resource and operational strategies for conversion

• The additional MOB safety evidence recommendations detailed in Work Pack 3 - Task 12 of Appendix D should also be addressed.

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.

Multiple Occupancy Buildings (MOBs) account for 21% of the UK’s domestic heating demand and tackling the challenge to decarbonise these properties will be key to meeting Government net zero targets.1 There is therefore a requirement for gas distribution network operators (GDNOs) to understand the cost safety and practicality of converting gas supplies to hydrogen. This project aimed to address evidence gaps centred around commissioning and decommissioning of risers associated with MOBs in particular purging operations.

The project has carried out a review of processes procedures and tooling used for purging MOBs examined site surveys and discussed purging with operators. Riser systems in MOBs are branched systems often comprising many vertical and horizontal elements taking a single supply source and distributing it to multiple individual dwellings in the building. Purging this network of elements is caried out in a routine manner as dictated by standards and procedures. Routine purging of MOBs is not challenging and this will continue to be the same when using hydrogen. The greatest challenge identified to purging MOBs is when each individual dwelling needs to be accessed to complete the purge. If an individual dwelling is inaccessible and individual lateral isolation valves are not installed then unpurged branches can remain. A consequence of leaving branches unpurged is a mixing of the air and fuel into a flammable mixture in the riser.

An experimental programme of work has been developed to investigate dispersion in unpurged branches of risers using methane and hydrogen. The experiments started with single pipes and developed in complexity to a branched system with six laterals. The main conclusions are: • If an unpurged branch is left over time the flammable volume at the interface between purged and unpurged sections will increase. Pipe diameter is the dominant parameter that dictates the speed of mixing of the two gases. • Gas dispersion occurs through a combination of buoyancy and diffusion buoyancy effects are diameter dependent becoming more dominant in pipe diameters greater than 50 mm. Below 50 mm gas dispersion is slow being dominated by diffusion alone. • Diffusion driven dispersion acts in the direction of concentration gradient from high to low. This acts to reduce the driving concentration gradient and slows down subsequent diffusion. In vertical pipes concentration gradients have been seen to act upwards or downwards. • Buoyancy effects act preferentially upwards but also promote mixing of different density gases in horizontal pipes. • In tests hydrogen dispersion was up to twice as fast as methane dispersion.

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.

In order to utilise the existing gas transmission and distribution network to transport 100% hydrogen the effects of the changes in characteristics of hydrogen from natural gas need to be reviewed and the resultant effect on the network assessed. Hydrogen features a substantially larger range of flammable concentrations than natural gas which could potentially cause safety concerns if the existing network is not reviewed. Hazardous area zoning of equipment present on the gas transmission and distribution network is modelled in accordance with standard IGEM/SR/25 Ed. 2. A hazardous area is defined in this standard as “an area in which explosive gas/air mixtures are or may be expected to be in quantities as such as to require special precautions for the construction installation and use of electrical apparatus or other sources of ignition.” A supplement to this standard compatible with the use of hydrogen blends up to 20% in addition to pure hydrogen was published by IGEM in November 2022. This hydrogen supplement has been utilised to establish the hazardous area zoning of hydrogen gas in 13 sites across multiple networks.

Hydrogen possesses a lower molar mass than natural gas therefore the mass flow rate of gas escaping relief vent pipework during venting operations is expected to decrease during pressure-driven release. Due to the larger flammable concentration range of hydrogen-air mixtures the impact on the sizes of hazardous areas was not immediately present. Across all sites the size of hazardous areas was seen to increase upon calculating the hydrogen mass flow rate for a given vent. It was observed on several sites that the hazardous areas of relief vents extended beyond the site boundaries.

Additional consideration was paid to vent pipe geometry in relation to sections 7.8.3 and 7.8.4 of IGEM/TD/13 Ed. 2 Supplement 1 – Pressure Regulating Installations for Hydrogen at Pressures Exceeding 7 bar. These clauses require that the Length/Diameter ratio of a vent pipe be kept below 60:1 to reduce the chance of combustion or detonation due to depressurisation in the vent pipe. This is due to hydrogen experiencing an increase in temperature during depressurisation as opposed to natural gas which decreases in temperature. This affects all sites due to the prevalence of small-bore pipework (10-15mm) used in impulse and instrumentation pipework. This also has potential to affect smaller relief vent pipework such as that used on district governors (typically 1”/25NB) depending on specific pipe and valve placement.

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 order to utilise the existing gas transmission and distribution network to transport 100% hydrogen the effects of the changes in characteristics of hydrogen from natural gas need to be reviewed and the resultant effect on the network assessed. Hydrogen features a substantially larger range of flammable concentrations than natural gas which could cause safety concerns if the existing network is not reviewed.

By surveying the electrical and instrumentation assets on site it was identified that many of the existing instruments currently in operation are not certified for the hydrogen environment (minimum Gas Group IIC) and require replacement.

There are a large quantity of instruments not suitable for the hydrogen environment due to asset condition / age and the effect of corrosion overtime affecting instruments such as missing or illegible faceplates resulting in being unable to verify ATEX certifications. A smaller percentage of existing instrumentation are in good condition but not certified for the hydrogen environment.

Equipment without a faceplate have been considered as not suitable for Hydrogen pending a review of certification for validation within a hydrogen atmosphere a replacement may not be required.

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.