PSI - Issue 68

Birhan Sefer et al. / Procedia Structural Integrity 68 (2025) 1129–1139 Sefer et al. / Structural Integrity Procedia 00 (2025) 000–000

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3.3 Hydrogen analysis Figure 6 shows hydrogen desorption rate versus temperature curves recorded with TDMS from reference materials in as-delivered state, and for specimens extracted from the gauge section of SSRT specimen tested in 200 bar H 2 at room and high temperature. The respective hydrogen contents measured from duplicate samples are also given as bar plots below the respective desorption rate curves.

Figure 6. Hydrogen desorption rate versus temperature curves recorded from reference material in as-delivered state, and for specimens extracted from the gauge section of hollow SSRT test specimen tested in 200 bar hydrogen at room and high temperature for a) SiMo51, b) CGI and c) NCF3015. The respective hydrogen contents measured from duplicate samples are given as bar plots below the respective desorption rate curves. The hydrogen desorption rate vs. temperature curves and respective bar plots from Figure 6 indicate whether hydrogen uptake has occurred due to hydrogen-material interaction during SSRT. Hence, from Figure 6 plots can be seen that during testing at room temperature hydrogen uptake was measured only for the CGI material (higher total hydrogen content was measured for RT than reference specimen), while no hydrogen uptake was measured for SiMo51 and NCF3015 materials (lower total hydrogen content was measured in the RT than the reference specimen). On the other hand, for all materials tested at high temperature a hydrogen uptake was measured. The position of the hydrogen peak(s) at the temperature axis (low <400 °C vs. high > 400 °C) provide information about if the hydrogen that was absorbed is of diffusible or strongly trapped nature. Qualitatively, if the hydrogen peak appears at temperatures below 400 °C it is considered as diffusible and may be considered as a threat to the mechanical properties. However, if it appears above 400 °C, it is considered as strongly trapped and “locked” hydrogen. Thus, this “locked” type of hydrogen should not result in adverse effect on the mechanical properties of the material. For all materials tested at high temperature the hydrogen peak appeared > 400 °C indicating that the absorption of hydrogen is more favourable to strong traps present in the materials. Note that the focus of the present work was not to identify the trapping sites present in the materials. However, to obtain detailed picture with this regard additional work is in progress. Identifying the weak and strong trapping sites is especially relevant for the CGI material for which three to four hydrogen peak maximums can be seen in the hydrogen desorption rate vs. temperature curves measured after SSRT at room and high temperature. Interestingly, the position of these peaks can be correlated and agree with the mechanical degradation behaviour of CGI material seen in this work. The more pronounced degradation of the