This topic is aimed at accelerating the deployment of a safe, flexible, and efficient hydrogen grid by repurposing part of the gas networks, as this solution is expected to be particularly cost-effective compared to the development of new pipes. However, steel embrittlement by hydrogen may limit this possibility. To assess precisely which pipes might be repurposed on a shared basis between EU Member States’ authorities and gas transmission operators, Pre-Normative Research on pipe integrity is required to develop a European standard, as current US codes are not adapted to the projected use-cases in EU.

In its strategic vision for a climate-neutral EU in 2050, the European Commission forecasts the share of hydrogen in Europe’s energy mix to grow from the current less than 2% to 13-14% by 2050. According to the REPowerEU ambitions published in May 2022, about 20 million tonnes of renewable hydrogen should already be distributed throughout Europe in 2030. For hydrogen to claim such position in the energy mix and as explicitly mentioned in the EU Hydrogen Strategy, it is essential that it becomes an intrinsic part of an integrated energy system, being used for daily or seasonal storage providing buffering functions thereby enhancing security of supply in the medium term. The REPowerEU strategy also calls for an acceleration of the deployment of an EU-wide pipeline infrastructure to transport hydrogen from areas with large renewable potential to demand centres across EU. Consequently, a pan-European grid will have to be established. To do so, there is significant energy system benefit in using existing natural gas assets across Europe, as they have large seasonal storage potential and can also readily manage large swings in daily demand. Total investment needs for key hydrogen infrastructure categories are estimated by the European Commission to be in the range of EUR 28 – 38 billion for EU-internal pipelines by 2030. In light of the EC’s REPowerEU proposal and in response to accelerated hydrogen market developments, members of the European Hydrogen Backbone Initiative^[1] (gathering 31 European energy infrastructure operators from 28 countries) have shared an updated vision of the hydrogen grid, with a total length of 53,000 km in 2040 consisting of approximately 60% repurposed existing gas pipelines.

In a nearer term, to distribute hydrogen, EU gas grid operators are investigating the possibility to increase the content of hydrogen blends into natural gas from 2% in volume to 20% in existing Transmission gas grids. In its “Hydrogen and decarbonised Gas Package” revision proposal released in December 2021, the European Commission emphasises the need for a harmonised EU approach for cross-border interconnection points while leaving flexibility to the Member States, with a floor rate for hydrogen blends that could be set at 5% for all cross-border points as of October 2025.

However, first public bibliographic results of R&D supported projects (e.g.: NaturalHY^[2], HYready^[3], MultiHy^[4] or HIGGS^[5] ) have identified a potential embrittlement effect on some steels used for pipes or network equipment. EU gas Transmission System Operators (TSOs) are currently compelled to refer to US standards (mainly ASME B31.12) that seem to be strongly over-conservative for EU hydrogen transmission use-cases, leading to ineffective investments and slowing down the administrative authorisation processes.

As stated by the European Committee for Standardisation CEN [CEN/TR 17797, March 2022], the State of the Art on gas grid steel integrity show limited available knowledge and a need for additional Pre-Normative Research. Also, there is a strong need to investigate further on specific and critical topics that are insufficiently covered by existing programs, like weld embrittlement or fatigue crack growth (FCG) mechanisms due to atomic hydrogen ingress into the steel. Even if some private or public projects are currently ongoing in some Member States, very limited shared results don’t allow other gas TSOs to benefit from such results. Moreover, since their testing protocols and environment are not yet aligned, it would prove anyway very difficult to compare projects’ results, with a risk for national TSOs and Authorities to draw misaligned conclusions on each side of the same interconnection. Therefore, it is critical to launch a comprehensive and overarching project at EU level to overcome these hurdles.

Project results are expected to contribute to all of the following expected outcomes:

• De-risking of business cases for an accelerated H2-readiness assessment of existing EU Transmission gas grids for hydrogen and enabling expansion of new dedicated infrastructures.
• Increasing operator, regulator, authorities, and end user confidence in safety of repurposed gas grids by consolidated and exhaustive scientific data.
• Delivering harmonised matrix to assess the hydrogen effect on steels present in the gas grids to get a comprehensive view of the networks’ degree of compatibility across EU and reduce the current over-conservative and inefficient approach. These guidelines are aimed at providing impactful Pre-Normative Research key inputs to contribute to the development of Regulation, Codes and Standards and thus enabling a seamless interconnection between hydrogen gas grids.

Project results are expected to contribute to the following objectives and KPIs of the Clean Hydrogen JU SRIA:

• Development of technologies and materials to facilitate the transportation of H₂ via the natural gas Transmission grid.
• Enable through research and demonstration activities the safe and affordable transportation of hydrogen through the repurposed natural gas grid.

The following KPIs should be therefore achieved by the end of the project:

• Gas TSOs from the EU reviewed: 70% of EU Member States should be covered;
• Representative EU steels assessed by testing vs operational parameters (steel grade, pressure of H₂, pressure cycling, etc.): 8 to 10 steel grades assessed;
• Design codes & standards optimisation with reduced conservatism vs ASME B31.12: 60% constraint reduction (in terms of Capacity and/or manageable linepack);
• PNR reports delivered to relevant standardisation bodies: Inputs on matrix H₂-readiness assessment with proposed optimised mastercurves (toughness reduction and Fatigue Crack Growth;
• Guidelines for mitigation techniques:
  • Operational parameters guidelines (pressure, cycling…);.
  • Preliminary reports on Innovative technology

Embrittlement effect on metallic grid materials used for pipes or network equipment is directly linked to the pressure of hydrogen. The project should focus on specific critical issues that are insufficiently covered by existing publicly available knowledge, like hydrogen embrittlement in pipe and girth welds and heat affected zones (HAZ), Fatigue Crack Growth mechanisms and update of criteria for assessment of flaws. To date, no exhaustive characterisation of these effects on transmission grids is available, due to costly and time-consuming test methods and to the diversity of existing networks across the EU, in terms of material grades used, building protocols (e.g. welds) or day-to-day current and future operational parameters (e.g. pressure level and cycling). A particular effort is expected on quantifying these effects versus the main parameters (H₂ pressure, mechanical loading, steel microstructures…).

Modern new steel grades likely to meet the deployment needs of H2 networks should also be investigated (allowing connections of hydrogen producers and consumers to repurposed grids). It is expected that these results will have a strong impact on the development of competitive products by EU pipe manufacturers.

Currently different US standards are used for the design of steel components (e.g. ASME B31.12) or to assess their mechanical properties in the presence of hydrogen (ANSI/CSA CHMC 1, ASTM G142). This wide range of standards and the lack of commonly agreed mechanical guidelines are slowing down the definition of harmonised criteria to assess hydrogen-readiness of EU gas networks. Moreover, due to the lack of data, these standards propose very conservative design. A preliminary ASME B31.12 sensitivity analysis about the ascending influence of different parameters on the lifetime prediction of pipelines revealed for instance that the conservatism in ASME B31.12 could be potentially optimised in the range between a factor of 2-4. A pronounced optimisation potential is expected by a more precise knowledge of the fatigue crack growth behaviour and well-founded initial defect sizes determined by optimised non-destructive testing methods.

Finally, the gas industry has identified that solutions to mitigate the impact of hydrogen could enable a higher conversion rate for natural gas pipelines to hydrogen operation. Early-stage developments of internal coatings, inhibitors, and preparation of guidelines to adapt network operating conditions are ongoing and need to be accelerated.

This project should cover steel grades constitutive of the gas Transmission networks, that are particularly sensitive to hydrogen embrittlement due to some high strength grades, high service pressure and potentially impacting pressure cycling.

Proposals should:

• First conduct a preliminary bibliographic review to identify the gap analysis, taking into account existing results from former and ongoing projects (e.g. NaturalHY^[2], HYready^[3], HIGGS^[8], project supported under the topic HORIZON-JTI-CLEANH2-2022-05-03 ‘Safe hydrogen injection management at network-wide level: towards European gas sector transition’ and the German TransHyDE^[9] flagship project).
• Propose a testing approach covering the most relevant steel grades constitutive of EU transmission gas grids (with a particular attention to ensuring a good geographical coverage) and their different (current and envisioned future) operating conditions (maximum pressure, pressure cycling, etc.) for a 100% hydrogen service (natural gas/hydrogen mixtures are not in the scope of this topic; however, due to the partial pressure of hydrogen being the driving parameter, it is expected that studying various pressure conditions will contribute indirectly to qualifying grid for mixtures as well). This approach should combine mechanical tests and innovative modelling approaches.
• Deliver harmonised protocols and run material tests to measure the mechanical properties affected by the presence of hydrogen which are critical for its integration into networks, based upon the gap analysis performed, and focusing on critical effects (should include fatigue crack growth rate, fracture toughness, and impacts on welds and HAZ) and impact of chemical composition for grid components and future pipes. The shared protocols should ensure all results will be comparable between the different testing laboratories involved and should serve as a standardised reference guideline for future investigations.
• After the testing work-packages, deliver to relevant standardisation bodies a matrix of gas grid steel grades’ behaviour in the presence of hydrogen as a function of network operating conditions, assessing the compatibility of vintage and new components. Projects should also define design criteria including the allowed size of defects, depending on the hydrogen gas pressure. It is expected that the projects should propose new Pre-Normative assessment master-curves to reduce current over-conservatism of existing norms that is ineffectively slowing down H₂-readiness assessments. It is also expected that these Pre-Normative results will strongly limit the current redundancy of costly R&D actions conducted in the different EU Member States, and deliver common approval guidelines to national authorities. Therefore, it is expected that all the data and results from the projects will be made entirely public.
• Investigate and propose initial guidelines for mitigation techniques limiting hydrogen uptake and thus embrittlement (such as adapted network operating conditions, inhibitors, or coating) for repurposed or new hydrogen grids and document their impact.

In order to ensure an exhaustive geographical coverage, the consortium should include a large panel of TSOs from different EU Member States, whose operated networks represent the variety of EU gas transmission infrastructure. The knowledge and differences in the national networks can be very significant, therefore the EU wide coverage should guarantee full usability of results for EU companies.

Proposals are expected to collaborate and explore synergies with the activities of ENTSOG^[10] and those of the European Metrology Programme for Innovation (EMPIR161) and European Partnership on Metrology of EURAME (e.g Decarb^[11], MefhySto^[12] and Met4H2^[13] projects).

Given the scope of this topic), the involvement of formal standardisation bodies as part of the consortia is encouraged, with the aim of facilitating the uptake of the project results.

Applicants are encouraged to address sustainability and circularity aspects in the activities proposed.

Proposals are expected to contribute towards the activities of Mission Innovation 2.0 - Clean Hydrogen Mission. Cooperation with entities from Clean Hydrogen Mission member countries, which are neither EU Member States nor Horizon Europe Associated countries, is encouraged (see section 2.2.6.7 International Cooperation).

Activities are expected to start at TRL 3 and achieve TRL 5 by the end of the project - see General Annex B.

The JU estimates that an EU contribution of maximum EUR 4.00 million would allow these outcomes to be addressed appropriately.

Beneficiaries must, up to 4 years after the end of the action, inform the granting authority if the results could reasonably be expected to contribute to European or international standards.

The conditions related to this topic are provided in the chapter 2.2.3.2 of the Clean Hydrogen JU 2023 Annual Work Plan and in the General Annexes to the Horizon Europe Work Programme 2023–2024 which apply mutatis mutandis.

[1] https://www.ehb.eu/

[2] https://www.gerg.eu/projects/hydrogen/naturalhy

[3] https://www.dnv.com/article/hyready-219355

[4] https://cordis.europa.eu/project/id/263335

[5] https://higgsproject.eu/

[6] https://www.gerg.eu/projects/hydrogen/naturalhy

[7] https://www.dnv.com/article/hyready-219355

[8] https://higgsproject.eu/

[9] https://www.wasserstoff-leitprojekte.de/leitprojekte/transhyde

[10] https://entsog.eu/

[11] https://www.euramet.org/european-metrology-networks/energy-gases/activities-impact/projects/project-details/project/metrology-for-decarbonising-the-gas-grid

[12] https://mefhysto.eu/

[13] https://www.euramet.org/index.php?id=1913