Acoustic Emission monitoring of hydrogen-assisted cracking mechanisms during slow strain rate tests in pure and blended hydrogen atmosphere

Hydrogen is becoming the most important energetic vector in the energetic transition process in particular energy transport and energy storage. There is therefore a growing interest in using hydrogen blends in natural gas to reduce carbon emissions. However, the debate on the compatibility of the current natural gas network with hydrogen gas is still open, and there is no harmonization of allowable hydrogen concentration in natural gas. Indeed, national laws and EU Directives set different limits for hydrogen injection into the Gas Grid. The Acoustic Emission technique has been successfully used to study hydrogen-assisted cracking mechanisms in metal alloys. The technique was used here to monitor the cracking mechanisms during slow strain rate tests on tubular carbon steel specimens pressurized with pure hydrogen and methane blended hydrogen gas. Mechanical as well as morphological analysis of fracture surfaces evidenced the influence of partial pressure on cracking mechanisms. Acoustic Emission allowed the identification of different data clusters correlated with the specific observed cracking modes.