Open Access

Polymeric components in hydrogen infrastructure face a significant challenge: the risk of damage from rapid gas decompression (RGD), which can ultimately compromise operational safety. This study investigates the impact of high-pressure hydrogen exposure on various rubber formulations: carbon black (CB) and silica (Sil) filled acrylonitrile butadiene rubber (NBR), as well as CB-filled ethylene-propylene-diene monomer rubber (EPDM). The materials were subjected to both static and dynamic high-pressure hydrogen environments. Their physical, mechanical, and chemical properties immediately after decompression and 48 h later were analysed. Our findings reveal a trend of the material to undergo tensile stiffening up to 24% after cyclic hydrogen exposure. The mechanism behind the increased stiffness is associated with a combination of microstructural mechanisms, polymer-filler interfacial rearrangement, and possible additive migration, depending on the grade. Silica-filled NBR demonstrates a faster volume recovery among all grades, but lower mechanical stability compared to its CB-filled counterparts, while the presence of plasticisers appears to accelerate crack formation under both static and dynamic loading conditions. The non-plasticised CB-filled NBR grade showed the best overall balance amongst the tested materials, particularly in tensile property retention, structural integrity, and resistance to crack formation under the applied exposure conditions. These findings contribute to the development of safer and more resilient materials for operational performance in hydrogen applications.

Delayed hydrogen-assisted cold cracking (HACC) in high-strength steels is rare, yet still a common phenomenon during welding. The occurrence of HACC largely depends on the both the time-depended hydrogen concentration and the geometry of the weld joint. Numerical modelling and calculation of the diffusion and time-dependent distribution of hydrogen concentration are increasingly being used to evaluate the necessary minimum waiting time (MWT) before non-destructive testing (NDT) for HACC, or to prevent it through adequate post-weld hydrogen removal heat treatment (HRHT). However, the quality of these calculations depends significantly on the diffusion coefficients of hydrogen used. This results in a situation where there is a range of diffusion coefficients spanning several orders of magnitude, even for low-alloy steels. The same applies at elevated temperatures, which consequently has a major influence on the calculation of time-dependent, local hydrogen concentrations. For this reason, evaluation routines supported by software were used to compile over 300 references into a scatterband for temperature-dependent diffusion coefficients of low-alloy steels. These are now available as an open-access database, enabling the targeted selection and analysis of data based on factors such as material, chemical composition, determination method (e.g. permeation), sample geometry and more. This enables the influence of material and determination method on the diffusion coefficient to be separated and evaluated for the first time. This provides explanatory models for the extreme variation in diffusion coefficients, as well as recommendations for using “realistic diffusion coefficients”. Using the MWT and HRHT as examples, this prevents overly conservative assessments resulting in excessively long holding times, as well as the underestimation of diffusion through the use of 'rule-of-thumb values'.

A total of 30 tensile carbon‑fiber‑reinforced polymer (CFRP) specimens and five type‑IV CFRP pressure vessels are tested using acoustic emission (AE) monitoring. Building on previously established approaches, Felicity, Shelby, and signal‑derived ratios are extracted from the AE data and used as input features for a neural network trained to predict failure loads. The ratio trends were found to be broadly consistent across the different test objects. For the tensile specimens with varying layup structures, the individually predicted failure loads show an average error of 4 kN (≈8% of failure load). Approximate burst pressures of the vessels can also be predicted using a model trained only on tensile‑sample data, albeit with larger uncertainties. Incorporating vessel data into the training set improves prediction accuracy. The study identifies a strong dependence on the chosen loading scheme, which represents a key limitation of the method and should be addressed in future work.

Hydrogen is set to become the energy carrier of the future, with most countries planning to transport it on a large scale by converting the natural gas grid and constructing new pipelines. However, the interaction between hydrogen and pipeline materials differs fundamentally from that of natural gas (NG), as hydrogen is readily absorbed into the material. Taking into account the possibility of hydrogen embrittlement (HE), the compatibility of pipeline materials (low-alloy steels with a wide range of strengths and thicknesses) must be investigated. However, pipelines require maintenance, repair or expansion of the grid, which involves welding onto the pipelines while they are in service, the well-known 'hot tapping' and 'plugging' processes. Compared to NG, the challenges can be broadly divided into the possible austenitization of the inner pipe material exposed to hydrogen and the welding itself. Both result in a significant increase in hydrogen solubility and could potentially pose challenges in terms of HE. Emphasis is placed on the word 'could' because knowledge of 'hot tapping' on hydrogen pipelines is scarce due to a lack of service experience. This article therefore provides an overview of research conducted over the past three years as part of the DVGW/BAM 'H2SuD' project. As part of this project, a representative portfolio of existing and new pipeline materials and their welded joints was investigated. Circumferential pipe girth welds, for example, are of central importance for “hot tapping”. To this end, extensive welding tests were conducted, with the respective temperature fields being measured during welding. These measurements were then used to evaluate the inner pipe wall temperature. Tests on hydrogen-pressurized demonstrators demonstrated the safe feasibility of in-service welding on pressurized hydrogen pipelines. These results are being incorporated into applicable regulations (e.g. DVGW Worksheet GW 350 in Germany). Both the construction of a new gas grid infrastructure for pure hydrogen and the conversion of existing NG grids raise a wide range of safety-related issues that must be resolved in order to ensure the safe and long-term operation of the infrastructure. For this purpose, the study introduces the possibilities for materials and component testing under realistic conditions at BAM’s new test facility “ModuH2Pipe”.

Composite overwrapped pressure vessels are increasingly being used for hydrogen storage. However, durability and safety assessment are crucial during the lifetime. In this view, the ultrasonic guided wave (UGW)-based structural health monitoring is applied to a pressure vessel during burst testing campaign to investigate the evolution and behavior of guided wave propagation under extreme loading conditions up to final failure. A full-scale vessel is instrumented with a distributed network of piezoelectric transducers, and guided wave measurements are conducted throughout a controlled pressurization cycle until burst. Signal changes are evaluated as a function of the pressurization cycle and progressive structural degradation. Guided wave features processed using machine learning algorithms, together with selected damage indices, are analyzed to assess their sensitivity and behavior under near-burst conditions. The results show the sensitivity of guided waves to extreme pressure conditions. In addition, the study Highlights the challenges due to multi-modal behavior of Lamb waves, which needs to be accounted for in metrics selection. Valuable support in visualizing structural degradation under extreme load is provided by principal component analysis, which allows clustering data and, as such, highlighting structural changes. This work provides valuable experimental reference for the validation of guided wave-based Structural Health Monitoring strategies for Composite overwrapped pressure vessels under critical conditions.