Session: MF-02-02 Materials for Hydrogen Service (Joint with C&S): Hydrogen-Assisted Fatigue

Paper Number: 83958

83958 - Modelling the Effects of Hydrogen Pressure on Fatigue Crack Growth Behavior in SA372 Pressure Vessel Steels 

Low alloy ferritic steels used in fabricating cost-effective cylinders for hydrogen storage are susceptible to hydrogen embrittlement. A model first proposed by Amaro et al. (ARFiDS model) for predicting the effects of hydrogen pressure on the kinetics of hydrogen assisted fatigue crack growth (HA-FCG) in X-100 pipeline steels for pressure between 1 and 20 MPa is adapted in this study and used for predicting the HA-FCG behavior of SA372 Grade J Class 70 pressure vessel steels for pressures ranging between 10 and 102 MPa. The crack growth kinetics in these steels exhibit a typical two-region behavior labelled as transient and the steady-state regions, characterized by distinct power-law exponents in the relationship between fatigue crack growth rate, da/dN, and the cyclic stress intensity parameter, ∆K. The predicted HA-FCG behavior from the model are compared with experimental data for SA 372 steel for hydrogen pressures ranging from 10 to 102 MPa and are shown to perform remarkably well for load ratios, R, of 0.2 and 0.5 over a wide range of crack growth rates.

 

This paper bridges the gap existing between mechanistic understanding of various atomic-scale degradation processes involved in hydrogen assisted fatigue crack growth (HA-FCG) behavior and the empirical modeling of the behavior based only on experimental characterization. The phenomenological basis for the model is discussed.

Such models provide interpolation and extrapolation capabilities of HA-FCG behavior needed for making decisions during design of experimental programs and during design life calculations of pressure vessels for storing hydrogen. Following conclusions are reached from the modeling exercise undertaken as part of these studies.

·         The transient region of HA-FCG behavior is identified with crack growth during a cycle occurring entirely within a process zone of high hydrogen concentration that is embrittled. During steady state, the crack growth during a cycle exceeds the size of the high hydrogen concentration process zone, with the crack growth entering normal material.

·         The HA-FCG behavior shows significant increases in da/dN going from air to 10 MPa and then to 45 MPa. These affects tend to saturate between 45 and 102 MPa.

·         The modified Amaro et al. model, ARFiDS model, proposed in this paper, does an excellent job of representing the HA-FCG trends due to pressure over the range of  MPa in both regions.

Presenting Author: Ashok Saxena WireTough Cylinders, LLC

Presenting Author Biography: Low alloy ferritic steels used in fabricating cost-effective cylinders for hydrogen storage are susceptible to hydrogen embrittlement. A model first proposed by Amaro et al. (ARFiDS model) for predicting the effects of hydrogen pressure on the kinetics of hydrogen assisted fatigue crack growth (HA-FCG) in X-100 pipeline steels for pressure between 1 and 20 MPa is adapted in this study and used for predicting the HA-FCG behavior of SA372 Grade J Class 70 pressure vessel steels for pressures ranging between 10 and 102 MPa. The crack growth kinetics in these steels exhibit a typical two-region behavior labelled as transient and the steady-state regions, characterized by distinct power-law exponents in the relationship between fatigue crack growth rate, da/dN, and the cyclic stress intensity parameter, ∆K. The predicted HA-FCG behavior from the model are compared with experimental data for SA 372 steel for hydrogen pressures ranging from 10 to 102 MPa and are shown to perform remarkably well for load ratios, R, of 0.2 and 0.5 over a wide range of crack growth rates. <br/><br/>This paper bridges the gap existing between mechanistic understanding of various atomic-scale degradation processes involved in hydrogen assisted fatigue crack growth (HA-FCG) behavior and the empirical modeling of the behavior based only on experimental characterization. The phenomenological basis for the model is discussed.<br/>Such models provide interpolation and extrapolation capabilities of HA-FCG behavior needed for making decisions during design of experimental programs and during design life calculations of pressure vessels for storing hydrogen. Following conclusions are reached from the modeling exercise undertaken as part of these studies.<br/> The transient region of HA-FCG behavior is identified with crack growth during a cycle occurring entirely within a process zone of high hydrogen concentration that is embrittled. During steady state, the crack growth during a cycle exceeds the size of the high hydrogen concentration process zone, with the crack growth entering normal material.<br/> The HA-FCG behavior shows significant increases in da/dN going from air to 10 MPa and then to 45 MPa. These affects tend to saturate between 45 and 102 MPa.<br/> The modified Amaro et al. model, ARFiDS model, proposed in this paper, does an excellent job of representing the HA-FCG trends due to pressure over the range of 0≤P_H≤102 MPa in both regions.

Authors:

Ashok Saxena WireTough Cylinders, LLC
Kip Findley Colorado School of Mines