Experimental determination of equivalent hydrogen gas pressure from electrochemical hydrogen charging

This study describes a novel approach for determining the electrochemical charging conditions corresponding to the hydrogen gas pressures associated with transportation of hydrogen in X65 pipeline steel, using a custommade setup. Electrochemical charging conditions representing cathodic protection at -1050 mV vs. Ag/AgCl are found to be equivalent to a hydrogen pressure of 15-20 bar. Additions of recombination poisons increase the equivalent pressure up to 200 bar, which is the desired pressure for transportation of hydrogen gas in existing pipelines. The results are compared with data from fracture mechanical testing of a X65 steel under equivalent charging conditions, thereby verifying the reliability of the new custom-made setup. The electrochemical production of hydrogen on the outer wall and its diffusion into the sample is simulated with a transient, 1-D diffusion model. The model predicts the evolution of hydrogen pressure, elucidating the impact of varying operational and material parameters, such as increased pressure with more negative potentials and increased time to reach steady state with larger internal volume. The model is validated with experimental pressure measurements.