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 connections with high tensile strength and sealing performance are necessary. As for the high tensile strength, jump-out tensile failure, by which the tensile strength and the elongation of connections are decreased, should be prevented. The mechanical behavior and preventive conditions of the 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 the jump-out tensile failure, in addition to the negative load flank angle thread for maintaining the engagement of the threads and the incomplete 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 the jump-out tensile failure by decreasing the deformation of the threads and the expansion of the box.