PSI - Issue 54

Daria Pałgan et al. / Procedia Structural Integrity 54 (2024) 322 –331

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Daria Pałgan et al./ Structural Integrity Procedia 00 (2023) 000 – 000

charging time and temperature. The hydrogen levels measured in these steels was notably higher as compared to A516 steel. This was expected due to large difference in solubility of hydrogen in these steels (Kiuchi and McLellan, 1983). Note that this is also valid for the cathodic charging where higher hydrogen uptake was measured for the austenitic steel grades as compared to the ferritic steel. Also, as for A516 steel after 24 hours of gaseous charging saturation with hydrogen occurred. It should be noted that the hydrogen uptake after gaseous hydrogen charging was more pronounced in irreversible traps contradicting the observations made after cathodic charging of these steels where the hydrogen uptake was more pronounced in reversible trapping sites. Hence, it can be concluded that gaseous hydrogen charging results in preferential and more pronounced hydrogen uptake in irreversible trapping sites while cathodic charging results in higher hydrogen uptake in reversible trapping sites. Although it seems that changes of the cathodic charging parameters might assist in influencing the uptake of hydrogen in irreversible trapping sites.

Figure 7. Effect of charging time on hydrogen uptake at 180 °C in a) A516 steel; at 360 °C in b) A516 steel; at 180 °C and 360 °C in c) 304L steel and at 180 °C and 360 °C in d) 316L steel. Note that the scale of the y-axis is different between the diagrams

3.4 T emperature influence on hydrogen uptake ( cathodic versus gaseous charging ) Figure 8 shows the effect of temperature on hydrogen uptake measured for all steels using cathodic and gaseous charging at various temperatures for 24 hours. Only the total hydrogen uptake is compared since there is a notable difference, as discussed above, whether hydrogen is trapped in reversible or irreversible sites depending on charging method used. Hence, for all studied steels the following comparable total hydrogen contents were measured: • for A516 about 1 wppm was measured when the samples were cathodically charged in an electrolyte composed of 3.5 wt.% NaCl + 0.3 wt.% NH 4 SCN at 80 °C using a current density of 1 mA/cm 2 or charged in pure H 2 gas with a pressure of 200 bar at 360 °C, • about 15-16 wppm of total hydrogen content was measured for 304L when the samples were cathodically charged in an electrolyte composed of 0.1 M NaOH + 0.3 wt.% NH 4 SCN at 50 °C using a current density of 20 mA/cm 2 or charged in pure H 2 gas with a pressure of 200 bar at 180 °C, and finally • for the 316L about 13 wppm of total hydrogen content was measured when samples were cathodically charged in an electrolyte composed of 0.1 M NaOH + 0.3 wt.% NH 4 SCN at 50 °C using a current density of 20 mA/cm 2 or charged in pure H 2 gas with a pressure of 200 bar at 180 °C.