Hydrogen-Assisted Fatigue and Fracture of Pipeline Materials in Natural Gas Infrastructure: Trends and Implications on Structural Integrity

Decarbonization of natural gas networks is a significant challenge, but a necessary step to meeting global targets to reduce carbon emissions. One strategy to reduce carbon in these networks is the displacement of natural gas with hydrogen in gas networks. The ‘embrittling’ effects of hydrogen on steel pipe, however, is a relevant safety concern. This presentation provides an overview of the state of knowledge of hydrogen-assisted fatigue and fracture of pipeline steels, specifically with respect to hydrogen uptake from the gas phase. Concurrent gaseous hydrogen exposure substantially increases fatigue crack growth and reduces fracture resistance (toughness) of most steels. While this fact is well known, the implications of blending hydrogen into gas networks and the relevant variables for structural integrity analysis are often misunderstood. For example, gaseous hydrogen degrades the fatigue and fracture behavior yet hydrogen partial pressure (often incorrectly described as percentage of hydrogen) has a relatively modest effect compared to other characteristics of a system analysis, such as applied stresses. This presentation seeks to place the materials response in gaseous hydrogen into a context that is meaningful for structural integrity assessment.