A gaseous hydrogen environment is believed to have a deleterious effect on the fatigue properties of steel. Furthermore, it is theorized that the slower the cyclic loading rate, the greater the rate of crack growth. However, conducting tests at sufficiently slow rates in a gaseous hydrogen environment can be prohibitively long and expensive, so the question has not been definitively addressed. A series of tests have been conducted comparing different pipeline steels at cyclic loading rates of 1 Hz, 0.1 Hz, and 0.01 Hz in a hydrogen gas environment pressurized to 5.5 MPa or 34 MPa. Service conditions for the pipeline would generate a cyclic loading rate of approximately 2×10-5 Hz, if the pipeline is re-pressurized twice per day. Therefore, even these slow testing rates do not mimic service conditions; however with the aid of a predictive model based on these data, the effect can be extrapolated to the slower rate. The data for certain datasets show a small, but measurable, increase in the rate of fatigue crack growth as the cyclic loading rate decreases. In cases where a sensitivity appears to exist, our model indicates that this relationship may be simulated by testing under an increased hydrogen gas pressure.
SteelyHydrogen, 2nd International Conference on Metals and Hydrogen
May 5-7, 2014
cyclic loading, fatigue crack growth rate, hydrogen gas, pipeline steels, X70, X52, 1 Hz, 0.1 Hz, 0.01 Hz