Effect of incomplete threads on the jump-out tensile failure of premium connections for oil or gas wells.

Abstract

In order to develop deep wells in corrosive conditions, premium con-nections with high joint tensile strength and high seal integrity have been required. As for the high joint tensile strength, jump-out tensile failure, by which tensile strength and the elongation of connections are decreased, should be prevented. The mechanical behavior and preventive conditions of jump-out tensile failure are investigated through the failure analysis of connections with varied box-end profiles and thread length. Incomplete pin threads are necessary to prevent jump-out tensile failure, in addition to the negative load flank angle thread for main-taining the mating of the threads and the complete thread lenIn order to develop deep wells in corrosive condition5, premium connections with high joint tensile strength and high seal integrity have been required. As for the high joint tensile strength, jump-out tensile failure, by which tensile strength and the elongation of connections are decreased, should be prevented. The mechanical behavior and preventive conditions of jump-out tensile failure are investigated through the failure analysis of connections with varied box-end profiles and thread length. Incomplete pin threads are necessary to prevent jump-out tensile failure, in addition to the negative load flank angle thread for maintaining the mating of the threads and the complete thread length for ensuring the shearing resistance. The rigidity of the box-end increased by a longer incomplete thread length and an unthreaded ring added to a box-end can help prevent jump-out tensile failure by decreasing the deformation of the threads and the expansion of the box.