The current IGEM standards for requirements of qualification testing of onshore pipelines do not contain guidance on specific tests for hydrogen. SGN has engaged PIE to develop a material qualification procedure for inclusion in standards for assets in hydrogen service
When completed, the project will identify relevant criteria for fracture toughness, fatigue and any relevant material aspects impacted by hydrogen. Learning from this project can be applied to other operations to facilitate safe transition to 100% hydrogen.
Benefits
A primary threat to steel pipelines in hydrogen transportation is the ingress of hydrogen into the steel structure and the resulting degradation of material properties through Hydrogen embrittlement. Current standards for hydrogen pipelines, (ASME B31.12 and IGEM/TD/1 Edition 6 Supplement 2) require that:
· the stress in the pipeline is limited to 180 N/mm2, which is equivalent to an X52 grade pipeline operating at a design factor of 0.5, and
· the pipeline material is qualified for hydrogen service.
The key benefit following completion of this project will be to have a full understanding of current global research. This will define relevant criteria for fracture toughness and other testing procedure for material qualification for steel hydrogen pipelines based on small scale material tests. This will subsequently define a consistent standard for the UK gas industry enabling the transition to a hydrogen network.
The project will provide unique and referenceable information for Network licensees and Industry for the manufacture of new Hydrogen steel pipelines. The learning gained from the project can be applied to Network Licensees and their network operations to facilitate safe transition to hydrogen from natural gas.
Learnings
Outcomes
Hydrogen embrittlement of steel occurs at low partial pressures of hydrogen, and involves significant reductions in ductility, fracture resistance and fatigue resistance. Current research is actively quantifying the impact on material properties through material properties. Variations in reported results, and states this may be due to variations in the applied testing standards as well as in materials and hydrogen purity. With regard to testing standards, a number of different standards are referenced
in published research. Research has moved to the measurement of elastic plastic rather than linear elastic fracture mechanics parameters, and Best Practice Guidelines based on this approach have now been published by EPRG.
This report considered the requirements for a standard test specification for the qualification of steel for high pressure pipelines. ASME B31.12 is the recognised international standard for hydrogen pipelines. IGEM/TD/1 Edition 6 Supplement 2 – High Pressure Hydrogen Pipelines is based on ASME B31.12 , and specifies equivalent requirements for hydrogen pipelines, and includes a procedure for repurposing. Comments on the application of IGEM/TD/1 Supplement 2 to the selection of material for a new hydrogen pipeline were included in the report and identify additional issues to be taken into account in the development of standard test procedure.
The requirements for a procedure for testing for hydrogen service are considered in this report, finding that as well as the requirements for design of standard test specimens which can be extracted from pipeline geometries and measurement of elastic plastic fracture properties, it is identified that a standard test procedure should consider the correlation of Charpy and fracture toughness tests in air with fracture toughness test results in hydrogen, noting that this approach is not recommended in current research paper. The procedure must address the requirements for hydrogen pre-charging, and management of the test environment.
Existing experimental results were analysed, considering results of the evaluation of fracture mechanics parameters required for the assessment of pipeline and component steels for hydrogen service by the DVGW Project SyWeSt H2 Project. These results confirm that tests on a range of typical pipeline steels used in Germany carried out on base metal, weld and HAZ were demonstrated as suitable for hydrogen. The report notes that pipe geometries (diameter and wall thickness) limit the sample size, standard samples were too small to be tested, so modifications to the test specimen (CT20) were needed to ensure comparability. The impact of these modifications is not evaluated. It is noted that the DVGW test method does not comply with the EPRG draft best practice guidelines.
Lessons Learnt
The study identified gaps and constraints which influence the development of a standard test procedure for qualification of pipeline material for hydrogen service, as outlined below.
Gaps
· Consideration of sub critical crack growth in hydrogen (related to hydrogen pressure and hydrogen concentration in steel)
· Quantification of lower bound comparisons between fracture toughness in hydrogen and Charpy and fracture toughness values in air.
Constraints:
· Limited international capacity for material testing in hydrogen
· Long testing times required for material testing in hydrogen
· Timescale over which hydrogen qualification of existing and new pipeline materials is required
