Failure analysis of a sucker rod fracture in an oilfield

Abstract

The sucker rod was fracture after 729 days’ service in an oilfield. The fracture position is located at the welding seam that is connecting the sucker rod’s upsetting end and the polished rod end. The failure causes were analyzed by the nondestructive test (NDT) of penetration detection, direct-reading spectrometer, tensile strength test machine, impact test machine, vickers hardness tester, optical microscope (OM), macroscopic fracture morphology, scanning electron microscopy (SEM) in this paper. The process of the fracture is under cyclic loading and the stress concentration, the sucker rod’s outside weld was brittle cracking in the first fracture at the beginning. Then the crack in first facture is passed to the inside welding residual, which is corresponding to the source area of the second fracture. Finally, the crack in the second fracture propagation along the weld seam and connected with the first fracture surface lead the rod broke completely. The causes of sucker rod breaking for the sucker rod did not meet the requirements of the HL grade rod material and the friction welding defects.