Effect of CO2 corrosion on repeated impact fatigue properties of drill pipe materials

The work aims to investigate the effect rules of CO2 corrosion on the repeated impact fatigue properties of drill pipe materials and analyze whether surface corrosion products have serious impact on multiple impact properties. The cumulative impact energy of V150 and S135 after immersion in saturated CO2 solution for different corrosion time at normal temperature and ordinary pressure was tested by the independently developed repeated impact fatigue testing machine. The corrosion rate of each sample was calculated by weight loss method. The surface morphology after corrosion and fracture morphology were observed by scanning electron microscope (SEM). The main components of corrosion products were tested by XRD. The corrosion rates of the two materials in the CO2 corrosion environment reached more than 0.05 mm/a, which belonged to moderate corrosion, but the corrosion rate of Sl35 was slightly lower than that of Vl50. With the increase of corrosion time, the cumulative impact energy of the two materials decreased continuously, but the cumulative energy decline rate (19.68%) of S135 with lower corrosion rate was lower than that (22.54%) ofV150. The CO2 corrosion caused the crack morphology and crystalline corrosion products on the surface of the drill pipe materials which mainly consisted of Fe(HCO3)2. The CO2 corrosion did not affect the internal structure obviously or cause the brittle fracture of the drill pipe materials. The corrosion rate of drill pipe materials under corrosion environment is higher, but the effect of CO2 corrosion on the repeated impact fatigue properties is smaller than H2S. Therefore, the corrosion rate is not the key factor affecting the repeated impact fatigue properties of drill pipe materials. © 2019, Chongqing Wujiu Periodicals Press. All rights reserved.