PSI - Issue 68

Robert Sundström et al. / Procedia Structural Integrity 68 (2025) 1081–1090 Robert Sundström / Structural Integrity Procedia 00 (2025) 000–000

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These studies show mixed effects of specimen geometry on fatigue lives in water reactor environments, but they do firmly point towards the influence of wall thickness. It is also possible that it depends on which type of alloy is being tested.

3. Summary and outlook Hydrogen embrittlement is present in many applications and mechanical testing is required to evaluate properties in gaseous hydrogen. Tests using high-pressure chambers are expensive (Vesely et al. 2002), so a new specimen geometry has been developed (Ogata 2018). The hollow specimen has been used for in-situ slow strain rate testing in hydrogen gas (Ogata 2008a, b, 2010, 2012, 2015, 2018, Ogata and Ono 2019, Michler et al. 2021, Ebling et al. 2022, Michler et al. 2022, Michler et al. 2023, Freitas et al. 2024, Michler et al. 2024), fatigue testing in hydrogen gas (Ogata 2018, Ebling et al. 2022) and fatigue testing in air (Bae and Lee 2011), argon (Van Den Avyle 1983) and reactor water (Twite et al. 2016). Various studies indicate that low wall thicknesses should be avoided as it can affect the ductility (Ogata and Ono 2019) and fatigue life (Van Den Avyle 1983, Twite et al. 2016). The inner surface condition requires consideration as it can influence slow strain rate testing results in hydrogen (Ogata and Ono 2019, Michler et al. 2022, Michler et al. 2023, Michler et al. 2024) and fatigue testing results in argon (Van Den Avyle 1983). For slow strain rate testing in hydrogen gas, it generally shows a higher relative reduction of area compared to the solid specimen (Michler et al. 2022, Michler et al. 2023, Michler et al. 2024). When ranked in embrittlement categories from negligibly embrittled to extremely embrittled, this causes some results to be categorized differently than solid specimens, unless a correction factor is applied (Michler et al. 2024). Studies comparing the two specimen geometries in fatigue testing are lacking for gaseous hydrogen but exist for other environments. Results from these studies are mixed but differences in fatigue life and crack propagation have been observed (Twite et al. 2016). A recently published standard for the hollow specimen method in slow strain rate testing (ISO 2024) establishes limits and recommendations for testing parameters, including gas purity, strain rate and diameter dimensions. But there remains work to be done as more precise recommendations for hole machining, diameter ratios, wall thickness requirements and inner surface condition are needed. Round-robin tests have not been performed using this method but are required to estimate the reproducibility and repeatability of the method. Previous work with testing in autoclaves has indicated higher variability for tests in gaseous hydrogen than air (Vesely et al. 2002) and it remains to be seen whether the hollow specimen method can fare better in this regard. A round-robin program is planned within an ongoing project, TransHyDE-H2Hohlzug, in Germany (Freitas et al. 2024). Acknowledgements This work is part of a project that is financially supported by the Swedish Foundation for Strategic Research. References Johnson, W. H. (1875). II. On some remarkable changes produced in iron and steel by the action of hydrogen and acids. Proceedings of the Royal Society of London 23(156-163): 168-179. DOI: https://doi.org/10.1098/rspl.1874.0024 Lee, J. A. (2016). Hydrogen Embrittlement. Huntsville, Alabama, USA, National Aeronautics and Space Administration. Ustolin, F., Paltrinieri, N. and Berto, F. (2020). Loss of integrity of hydrogen technologies: A critical review. International Journal of Hydrogen Energy 45(43): 23809-23840. DOI: https://doi.org/10.1016/j.ijhydene.2020.06.021 Briottet, L., Batisse, R., Bernard, P., Duret-Thual, C., Heuzé, J.-L., Martin, F., Thebault, F. and Vucko, F. (2019). 10 - Industrial Consequences of Hydrogen Embrittlement. Mechanics - Microstructure - Corrosion Coupling . C. Blanc and I. Aubert, Elsevier: 223-244 DOI: https://doi.org/10.1016/B978-1-78548-309-7.50010-7 Kobayashi, H., Kobayashi, H., Sano, T., Maeda, T., Tamura, H., Ishizuka, A., Kimura, M., Yoshikawa, N., Iijima, T., Yamabe, J., Matsuoka, S. and Matsunaga, H. (2018). Methods of material testing in high-pressure hydrogen environment and evaluation of hydrogen compatibility of metallic materials – current status in Japan. ASME 2018 Pressure Vessels and Piping Conference, Prague, Czech Republic. DOI: https://doi.org/10.1115/PVP2018-84112 Jewett, R. P. and Halchak, J. A. (1991). The Use of Alloy 718 in the Space Shuttle Main Engine. Superalloys: 749-760. Sutton, G. P. (2003). History of Liquid Propellant Rocket Engines in the United States. Journal of Propulsion and Power 19(6): 978-1007. DOI: