With a view to reduction of greenhouse gas emissions, hydrogen is expected to play a fundamental role as future energy carrier. Clarifying product requirements is therefore essential to ensure safe operation of hydrogen pipelines. Recently, the interaction of pressurized hydrogen gas with line pipe steel has been studied in more detail and test methods relevant to qualify carbon-manganese steels have been proposed. Upon these test methods, fracture mechanics tests, both quasi-static and dynamic, were found to be most suitable to support life-cycle assessment of large-diameter pipes. However, challenges in laboratory testing under pressurized hydrogen still exist and relate to selection of test equipment, control of purity, oxygen content and humidity of hydrogen as test medium as well as to the details of test execution.

This paper provides an overview of fracture mechanics testing and recent results to prove the suitability of longitudinally submerged-arc-welded large-diameter pipes for transport of pressurized hydrogen. The test program included fracture mechanics testing of different steels with different grades, chemistries and microstructures. The focus was set on steel grades between L415 to L485, as the hydrogen performance of those steels is considered more critical than of lower grades. Test methods included fracture toughness testing to ASTM E1820 and comparison with the ASTM E1681 method. The latter, which allows to determine threshold stress intensity factors, is referred to in ASME B31.12:2019 as qualification requirement. Fatigue crack growth testing to ASTM E647 was also considered. All tests were performed under pure hydrogen pressurized between 100 and 250 bar.

The significance and robustness of the determined characteristic values are discussed considering the background of the most-recent developments on test requirements.