Casing drilling connector with low stress flex groove

摘要

An oilfield tubular string (10, 60, 60A) comprising a plurality of elongated joints having one or both ends threaded. The joints may be connected by a coupling including a generally sleeveshaped coupling body having a tapered upstream thread profile and a tapered downstream thread profile for threaded engagement with a mating profile of a respective joint. The coupling body includes a low stress flex groove (30) having a selected box thread runout bevel angle, and all transitions in the flex groove between surfaces are radiused to greater than 0.100 inches to minimize stress risers. A pin-in-box connection between tubular joints includes mating tapered threads (72), engagement of end shoulder (74. 76, 78, 80), and a low stress hex groove (82). The present invention allows the elongate joints to be used as both a casing string and a drill string, thereby saving significant time and expense.