Research on the fatigue properties of S135 drill pipe steel under a variety of conditions

Through rotating bending fatigue test, the fatigue properties of S135 drill pipe steel were investigated under various conditions (a): the smooth specimens; (b): the notched specimens; (c): the notched specimens with H2S corrosion). The experimental results show that the fatigue life of smooth specimens is about 107 cycles at fatigue limit (540 MPa); the fatigue life of notched specimens is about 3 × 105 cycles at fatigue limit (320 MPa); and the fatigue life of notched specimens with H2S corrosion is about 5 × 104 cycles at fatigue limit (300 MPa). By analyzing the surface of fracture, it can be shown that the propagation direction of fatigue crack in the notched specimens is changed little and the propagation speed is faster than the smooth specimens. The cracks of notched specimens with H2S corrosion occur at the high-speed propagation earlier stage, and the initiation and propagation of crack are caused by hydrogen embrittlement and fatigue stress. Compared with H2S corrosion affect S135 drill pipe steel, the effect of the notch is greater on the fatigue life.