Patent ID: 6406070
Filing Date: 2002-06-18
Classification: E21B

Abstract:
An oilfield tubular string comprising a plurality of elongate joints each having one or both ends threaded for engagement with another elongate joint having one or both ends threaded, the threaded ends of each joint being structurally interconnected by a coupling, the coupling comprising:a generally sleeve shaped coupling body having a central axis and a tapered upstream thread profile for threaded engagement with a mating thread profile on an upstream elongate joint; the coupling body having a tapered downstream thread profile for threaded engagement with a mating profile on a downstream elongate joint; and the coupling body having a low stress flex groove along a radially inner surface of the coupling body and axially between the tapered upstream thread profile and the tapered downstream thread profile, the flex groove having a selected upstream thread runout bevel angle and a selected downstream thread runout bevel angle each greater than 0Â° relative to the central axis of the coupling body, each bevel angle being functionally related to thread height and thread taper, with all transitions in the flex groove between surfaces being radiused to greater than 0.100 inch to minimize stress risers.