Importance

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Abstract

A fatigue-resistant threaded connector for connecting adjacent sections of a tubing string subject to cyclic dynamic stress variations is disclosed. The connector comprises a pin member which is threadedly engageable with a corresponding box member. In its preferred embodiment, the connector is radially preloaded. The connector has tapered threads with a straight load path having substantially no eccentricity. The preferred thread form is a modified buttress thread having a zero (or near zero) degree load flank, a 45 degree stab flank, and a large root radius. Additionally, the thread may include a small stab flank relief to reduce stress concentrations, and a differential between the pitch of the pin threads and the pitch of the box threads to compensate for the Poisson's ratio effect of the radial preload. The connector utilizes an elliptical stress relief groove at the base of the pin threads and elliptical contours on all thickness transitions to reduce peak stresses. The fully assembled and preloaded connector has a maximum stress-concentration-factor of less than 1.5 and its weight is less than 2.5 times the weight of an equivalent length of tubing.

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First Claim