PSI - Issue 68

Jan Kec et al. / Procedia Structural Integrity 68 (2025) 1091–1097 Jan Kec / Structural Integrity Procedia 00 (2025) 000–000

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Fig. 5. (a) typical micromorphology of crack extension of all FT samples; (b) micromorphology in delaminations of all FT samples.

3. Conclusions The mechanical properties of X70 steel pre-charged in blend of hydrogen and methane were evaluated. The most important findings in the TT results are that a noticeable reduction in strength properties occurs after only 3000 hours of pre-charging. Subsequently, the strength properties remain at approximately the same values even after pre-charging for 6000 hours. The decrease in average CVN energy values was 30 J for circumferential specimens and 20 J for longitudinal specimens. Also, the CVN results did not reveal that higher pre-charge time further reduced the CVN energy of X70 steel. For FT, the decrease in the size-independent fracture mechanical parameters J i and J 0,2 was 50% and 40%, respectively. A decrease of 22% was observed for the size-dependent parameter J u(20) . Furthermore, the studied fractographic features of all tested samples did not confirm the formation of quasi-cleavage fractures in the X70 steel under the given test conditions. Acknowledgements The authors would like to thank the Technology Agency of the Czech Republic (TACR) for financial support of the project TK04020336. References Topolski, K., Reznicek, E. P., Erdener, B. C., San Marchi, Ch. W., Ronevich, J. A., Fring, L., Simmons, K., Fernandez, O. J. G., Hodge, B. M., Chung, M., 2022. Hydrogen Blending into Natural Gas Pipeline Infrastructure: Review of the State of Technology. Technical Report NREL/TP-5400-81704, CO: National Renewable Energy Laboratory. NREL/TP-5400-81704. https://www.nrel.gov/docs/fy23osti/81704.pdf. May, L. M., Matthew, C., Zachary N. B., Peter, E. B., Damian, L., Andrew, J. S., 2022. Evaluating a natural gas pipeline steel for blended hydrogen service. Journal of Natural Gas Science and Engineering 101, 104529. Golisch, G., Genchev, G., Wanzenberg, E., Mentz, J., Brauer, H., Muthmann, E., Ratke, D., 2022. Application of line pipe and hot induction bends in hydrogen gas. Journal of Pipeline Science and Engineering 2 (3), 100067. Bradley, P. E., Martin, M. L., Connolly, M. J., Amaro, R. L., Lauria, D. S., Slifka, A. J., 2023. Modification to a testing assembly to enable strain life measurements in pressurized hydrogen gas. Review of Scientific Instruments 94 (8), 083906. Zafra, A., Álvarez, G., Benoit, G., Henaff, G., Martinez-Pañeda, E., Rodríguez, C., Belzunce, J., 2023. Hydrogen-assisted fatigue crack growth: Pre-charging vs in-situ testing in gaseous environments, Materials Science and Engineering: A 871, 144885. Zafra, A., Belzunce, J., Rodríguez, C., Fernández-Pariente, I., 2019. Hydrogen embrittlement of the coarse grain heat affected zone of a quenched and tempered 42CrMo4 steel. International Journal of Hydrogen Energy 45 (33), 16890-16908.