Abstract
As global efforts to decarbonize energy systems gain momentum, blending hydrogen into existing natural gas pipelines is being actively pursued. Many owners and operators have concerns about how to ensure the integrity of their natural gas infrastructure in the presence of hydrogen. It is true that hydrogen does degrade fatigue and fracture properties of pipeline steels, manifested as increased fatigue crack growth rates and decreased fracture resistance. It is also true that small amounts of hydrogen can result in significant reduction in fatigue and fracture resistance. Additionally, the partial pressure of hydrogen is the important parameter, not the percentage of hydrogen. However, in order to assess the integrity of the pipeline, a holistic view must be taken which examines the hydrogen environment, material, and stress conditions. Much of existing infrastructure consists of lower strength grades with pipe ages dating back more than half a century. Interestingly, fatigue crack growth rates in hydrogen are comparable for all vintages of steels (from present to at least the 1950s) and for all grades from X52 to X70, despite significant differences in microstructure and strength. One common misconception is that higher strength grade pipelines exhibit more sensitivity to hydrogen degradation; however, this was not observed with respect to fatigue crack growth rates. Fracture resistance in hydrogen is sensitive to material strength, especially for the higher strength grades, although the fracture resistance still remains greater than 55 MPa m1/2 for representative natural gas pipe grades (e.g. X80 and below) that have been tested to date.
In this paper, an overview of the hydrogen-assisted fatigue and fracture behavior of pipeline steels is presented and the common observed trends are described. Testing was performed in both pure hydrogen and hydrogen blends of 3% to explore the effects of low partial pressures of hydrogen. Despite degradation to the fatigue and fracture properties of linepipe steels, similar behavior is observed for both vintage and modern steels. Additionally, small amounts of hydrogen can have significant effects on fatigue crack growth and fracture resistance. Collectively, these observations demonstrate that the fatigue and fracture properties can be bounded. Questions remain, however, about the performance of vintage welds in the presence of hydrogen as data are still limited.