Highlights  A new thermal desorption spectroscopy (TDS) apparatus was used to study hydrogen in a 3.5NiCrMoV steel  The hydrogen concentration increased with increasingly negative charging potential and increasing hydrogen gas pressures.  The equivalent hydrogen fugacity versus charging overpotential relationship was derived.  A two-site model for Sieverts' Law explained the positive Y-intercept, as the density of already filled hydrogen traps.

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Thermal desorption spectroscopy (TDS) is used to analyze hydrogen in 980DP after (i) electrochemical charging, and (ii) gaseous charging. The hydrogen concentration increases with (i) a more negative charging potential and (ii) an increasing hydrogen gas pressure. For charging in 0.1 M NaOH, the hydrogen fugacity for 980DP is similar to that for (i) low interstitial steel, and (ii) MS1500, and is greater than that for the 3.5NiCrMoV steel. This indicates an influence of steel chemistry on the hydrogen evolution reaction. The de‐trapping activation energies are 40.5 and 50.2 kJ mol−1, indicating hydrogen traps at boundary defects.