Hydrogen infrastructure will play a critical role in meeting the future demand for decarbonization. Existing pipelines can be potentially repurposed, and new pipelines will be installed to transport hydrogen gas. Pipelines, especially offshore pipelines, are subjected to cyclic loading which can lead to potential fatigue damage and failure. The fatigue resistance of steel deteriorates under prolonged exposure to pressurized hydrogen due to the hydrogen embrittlement effect.
Hydrogen assisted fatigue crack growth rate (HA-FCGR) is investigated in this study. The influences of various test parameters including hydrogen gas pressure, cyclic load ratio and frequency, test temperature, and the yield strength of the steel are reviewed and analyzed. Existing models to predict the HA-FCGR are also assessed.
An updated Tri-Linear model is proposed to predict the HA-FCGR of carbon steel. The key values associated with the two knee points, which define the shape of the HA-FCGR curve, are expressed as functions of the test parameters and the yield strength of the steel. Fatigue test results digitized from existing literature are utilized to optimize the experimental constants required for the Tri-Linear model. The modeled HA-FCGR curves are compared against experimental data to demonstrate the agreement with the test results.
The updated Tri-Linear model directly correlates the hydrogen gas pressure, cyclic load ratio and frequency, test temperature, and the yield strength of the steel to the predicted HA-FCGR. Facilitated by the strong correlations, the number of experiments required to qualify the pipeline steel under the design and operating conditions can be reduced.