In spite of current world economic climates, recognition that alternative energy sources to the traditional fossil fuels has to be explored and understood. One potential energy source being researched and developed is hydrogen gas. Currently the most economical method of transporting large quantities of hydrogen gas is through steel pipelines. It is well known that hydrogen embrittlement has the potential to degrade steel’s mechanical properties when hydrogen migrates into the steel matrix. Consequently, the current pipeline infrastructure used in hydrogen transport is typically operated in a conservative fashion. This operational practice is not conducive to economical movement of significant volumes of hydrogen gas as an alternative to fossil fuels.

The degradation of the mechanical properties of steels in hydrogen service is known to depend on the microstructure of the steel. Understanding the levels of mechanical property degradation of a given microstructure when exposed to hydrogen gas under pressure can be used to evaluate the suitability of the existing pipeline infrastructure for hydrogen service and guide alloy and microstructure design for new hydrogen pipeline infrastructure. To this end, the microstructures of relevant steels and their mechanical properties in relevant gaseous hydrogen environments must be fully characterized to establish suitability for transporting hydrogen.

Previously data from a US Department of Energy/private sector funded project to evaluate four commercially available pipeline steels alloy/microstructure performance in the presences of gaseous hydrogen was presented in 2010. Interest in this previous work from industry and the ASME B31.12 Hydrogen Piping and Pipeline Systems codes and standards committee resulted in additional funding for continued evaluation of additional pipeline steel alloys/microstructures in the presences of gaseous hydrogen. Samples from API grades X52 (1960’s and current vintage designs), X70 (1980’s and current vintage) and X80 along with various samples from an X52 induction bend pipe and one pressure vessel steel A516 Gr 70 are being evaluated. Microstructural characterization, fracture toughness and fatigue testing in the presence of gaseous hydrogen at 800 psig and 3,000 psig are being conducted.

This paper will describe the fracture toughness results achieved to date on various commercially available pipeline steels used in the existing North American pipeline infrastructure in the presence of gaseous hydrogen at pressures relevant for transport in pipelines. Microstructures and fracture toughness performances will be compared between these in this study along with those published previously. In addition, recommendations for future work related to gaining a better understanding of steel pipeline performance in hydrogen service will be discussed.

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