Fatigue and Fracture of Pipeline Steels in High-Pressure Hydrogen Gas

Decarbonizing natural gas networks is a challenging enterprise. Replacing natural gas with renewable hydrogen is one option under global consideration to decarbonize heating, power and residential uses of natural gas. Hydrogen is known to degrade fatigue and fracture properties of structural steels, including pipeline steels. In this study, we describe environmental testing strategies aimed at generating baseline fatigue and fracture trends with efficient use of testing resources. For example, by controlling the stress intensity factor (K) in both K-increasing and K-decreasing modes, fatigue crack growth can be measured for multiple load ratios with a single specimen. Additionally, tests can be designed such that fracture tests can be performed at the conclusion of the fatigue crack growth test, further reducing the resources needed to evaluate the fracture mechanics parameters utilized in design. These testing strategies are employed to establish the fatigue crack growth behavior and fracture resistance of API grade steels in gaseous hydrogen environments. In particular, we explore the effects of load ratio and hydrogen partial pressure on the baseline fatigue and fracture trends of line pipe steels in gaseous hydrogen. These data are then used to test the applicability of a simple, universal fatigue crack growth model that accounts for both load ratio and hydrogen partial pressure. The appropriateness of this model for use as an upper bound fatigue crack growth is discussed.