Reliability and Representativeness of Hydrogen Charging Methods for Assessing Hydrogen Embrittlement in Metals

Industries seeking to reduce carbon emissions are considering hydrogen as an alternative fuel or reductive reagent. However, the addition of hydrogen into new and existing infrastructure has triggered concerns for materials compatibility, forming a significant barrier to its implementation. Hydrogen is known to damage and embrittle metals, and despite growing efforts to generate compatibility data for structural materials under hydrogen environments, there is no consensus on how hydrogen degrades such material. This is due to the complex mechanisms in which hydrogen interacts with metals but more so the lack of standardised testing methods. Electrochemical methods are being used increasingly to generate hydrogen materials compatibility data. However, for industries to use electrochemical methods the conditions must be representative of those of gaseous hydrogen environments. Currently, when comparing mechanical properties by samples produced under gaseous and electrochemical environments, results show inconstancies in the mechanical properties produced and reliability issues. In this work, methods of electrochemical hydrogenation are reviewed in comparison to those under gaseous environments. Differences in the charging fugacity, surface effects and damage mechanisms are assessed between gaseous and electrochemical charging that may contribute to the disparities seen in the literature. Based on this comparative assessment, we identify key knowledge gaps and provide an approach for future research to address existing uncertainties.