Synergistic action of hydrogen and stress concentration on the fatigue properties of X80 pipeline steel

The objective of this study is to quantify the synergistic action of hydrogen and stress concentration on the fatigue properties of pipeline steel. Notch tensile tests and fatigue-life tests were performed on X80 specimens under both a hydrogen partial pressure of 0.6 MPa and a nitrogen environment. The notch tensile results indicate that hydrogen had little influence on the notch strength of the specimens with various stress concentration factor (Kt) values; however, as the Kt values increased, there was a decrease in the reduction of area (RA). The results of the fatigue-life tests suggest that the stress concentration severely impaired the fatigue properties, and that further deterioration would occur with hydrogen. The finite element analysis (FEA) results show that the weakest mechanical properties were obtained when Kt was equal to 3.3, due to the synergistic action of the strain and its distribution. This matter should be further considered before hydrogen is blended into existing natural gas pipelines that have been in service for a long period.