Effects of gaseous hydrogen on fatigue crack growth in pipeline steel

The effects of hydrogen on crack growth rates in a moderate-strength pipeline steel subjected to cyclic loads were studied. Fatigue crack growth experiments were conducted in high-pressure hydrogen and nitrogen environments, and the influences of stress ratio, stress intensity, and cyclic loading frequency on hydrogen-accelerated fatigue crack growth were investigated. Hydrogen acceleration of intermediate-rate (Stage II) crack growth was greatest at low stress ratios and decreased to approximately zero at a stress ratio of about 0.5. However, hydrogen promoted the premature onset of accelerated (Stage III) crack growth. This appeared to be related to a hydrogen-induced reduction of fracture toughnessJ _IC.