Influence of Hydrogen and Oxygen Impurity Content in a Natural Gas / Hydrogen Blend on the Toughness of an API X70 Steel

The European Union is intending to reduce their carbon emissions by up to 80–95% by 2050. This will imply the increase of electricity coming from variable renewable energy sources. Producing hydrogen from this electricity is one way to facilitate the integration of such intermittent sources. Currently, there is no consensus in the world on the allowed amount of hydrogen in the natural gas with the aim to use the natural gas existing transportation grid to transport such mixture. The object of the present study is to provide additional experimental data concerning the effect of the hydrogen content in a N2/H2 mixture on the toughness of an API X70 steel dedicated to gas transport. The toughness has been measured in terms of Crack Tip Opening Displacement under a total pressure of 85 bar. The mechanical results are compared to existing results. It is confirmed that 1% H2 induces a significant decrease of the material toughness. Moreover, the content of O2 impurity in the N2/H2 mixture has been considered and its effect on HE mitigation has been quantified for an O2 content ranging between 10 vol. ppm and 100 vol. ppm. Finally, several approaches to take into account the effect of H2 in the NG/H2 blend on the design or on the service life of gas pipelines will be discussed.