PSI - Issue 77

Behzad Vasheghani Farahani et al. / Procedia Structural Integrity 77 (2026) 424–431 Behzad V. Farahani et al./ Structural Integrity Procedia 00 (2026) 000–000

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Fig. 4: 3D simulation results of NRB-R6: force–elongation curves for HMG and HTG materials under air and hydrogen (H) exposure.

Referring to Fig. 4, the force/elongation curves show that the HTG material reaches a higher maximum force than the HMG, which can be attributed to the higher yield strength of WM compared to the BM. While the same damage parameters have been assigned to different regions in the HTG model, the strength difference among BM, WM, and HAZ results in a reduction in ductility compared to the homogeneous model of the BM. Hydrogen exposure reduces ductility in both HMG and HTG models. The HMG model in air shows the highest ductility, while HTG under hydrogen has the lowest ductility. These results show the importance of considering local material heterogeneity effects on the hydrogen embrittlement of pipeline components. 5. Concluding Final Remarks This study presents a numerical framework to capture the hydrogen assisted degradation of mechanical properties in pipeline steels, considering the local heterogeneity in girth-welded joints. Element-specific property assignment effectively captures these local variations. The simulation results demonstrate that the variation of local mechanical properties in the weld region, with higher hardness and yield strength in the WM than the BM, leads to a reduction in the tensile ductility compared to the homogeneous BM. These findings emphasize the importance of accounting for material heterogeneity when predicting structural integrity under hydrogen exposure. Acknowledgements The authors gratefully acknowledge funding from the European Union’s Research Fund for Coal and Steel (RFCS) for the HYSCORE project – Hydrogen Storage and Carriage as Opportunity for Renewable Energy Transition – under grant agreement No. 101112571. References Campari, A., Ustolin, F., Alvaro, A., & Paltrinieri, N. (2023). A review on hydrogen embrittlement and risk-based inspection of hydrogen technologies. International Journal of Hydrogen Energy , 48 (90), 35316–35346. https://doi.org/10.1016/j.ijhydene.2023.05.293 Depraetere, R., De Waele, W., & Hertelé, S. (2021). Fully-coupled continuum damage model for simulation of plasticity dominated hydrogen embrittlement mechanisms. Computational Materials Science , 200 , 110857. https://doi.org/https://doi.org/10.1016/j.commatsci.2021.110857 Dwyer, R. A. (1987). A faster divide-and-conquer algorithm for constructing delaunay triangulations. Algorithmica , 2 (1–4), 137–151. https://doi.org/10.1007/BF01840356 Gurson, A. L. (1977). Continuum Theory of Ductile Rupture by Void Nucleation and Growth: Part I—Yield Criteria and Flow Rules for Porous Ductile Media. Journal of Engineering Materials and Technology , 99 (1), 2–15. https://doi.org/10.1115/1.3443401 Hertelé, S., De Waele, W., Verstraete, M., Denys, R., & O’Dowd, N. (2014). J-integral analysis of heterogeneous mismatched girth welds in clamped single-edge notched tension specimens. International Journal of Pressure Vessels and Piping , 119 , 95–107. https://doi.org/10.1016/j.ijpvp.2014.03.006 Hertelé, S., O’Dowd, N., Van Minnebruggen, K., Verstraete, M., & De Waele, W. (2015). Fracture mechanics analysis of heterogeneous welds: Numerical case studies involving experimental heterogeneity patterns. Engineering Failure Analysis , 58 , 336–350.

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