Stress distribution of oil tubing thread connection during make and break process

Abstract The operations of make-up and break-out in oilfields have a strong impact on the service life of oil tubing thread connections. A series of full-scale tests were performed on samples of J 55 ∅ 73.03×5.51 mm API nonupset tubing thread connection. Forty foil gages were placed on the inner surface of the pin thread and the outer surface of the box thread along the axial and circumferential direction. Using XYQ3E type oil tubing hydraulic tongs that are used in oilfields and the DH5937 type dynamic strain testing system, the axial strain, hoop strain and shearing strain of the tubing connection were tested dynamically under the action of different make-up and break-out torque and velocity, and then the failure surfaces of the tubing thread were analyzed by SEM. Major factors, which affect thread gluing and the galling position of the tubing connection, were studied and their effects were summarized through analyzing the experimental data and results. The dynamic distribution of stress field in the location where the thread connection exists are ascertained during the whole process of make-up and break-out.