Abstract
There are opportunities to increase energy resilience by adapting existing pipeline and pressure vessel infrastructure for hydrogen usage. Both existing and new infrastructure is manufactured from ferritic and martensitic steels due to the low cost and versatility of these steels. While these steels are commonly used in hydrogen service, the challenge remains that these steel microstructures are susceptible to hydrogen-assisted fatigue and fracture, which must be characterized and managed to ensure structural integrity of gaseous storage and distribution assets.
Assessing a material’s susceptibility to gaseous hydrogen requires testing in environments relevant to the application—in this case, gaseous hydrogen at high pressure—and measurement of relevant mechanical properties for structural engineering assessment. Fracture mechanics-based approaches to structural integrity, for example, evaluate crack propagation and fracture resistance, which must be measured in the presence of gaseous hydrogen. Fatigue crack growth rates have been evaluated in gaseous hydrogen for various pipeline and pressure vessel steels. Despite differences in microstructure and strength, fatigue design curves have been established based on consistent behavior and codified in ASME code cases. The effects of hydrogen on fracture resistance have also been studied; however, the fracture behavior appears more nuanced than for fatigue. While broad trends with strength/hardness are observed for fracture resistance in hydrogen, significant variability in measured fracture resistance exists for lower strength steels.
In this study, rising displacement fracture tests were conducted in gaseous hydrogen over a range of pressures on low-carbon and low-alloys steels to evaluate hydrogen-assisted fracture. The steels examined feature a variety of microstructures, including ferrite, pearlite, bainite, and martensite. The examined steels include vintage pipeline steels dating back to the 1940s, as these steels are of interest in the U.S. for potential repurposing of existing pipelines for hydrogen blends. For a given strength, steels with higher pearlite fractions exhibited lower fracture resistance compared to steels with microstructures consisting of acicular ferrite and polygonal ferrite. Low-alloy quenched and tempered martensitic steels demonstrated comparable, or improved, fracture resistance in gaseous hydrogen and higher strength than many pipeline steels. As expected, higher strength steels generally display lower fracture resistance, but unexpectedly, this trend is observed regardless of microstructure.