Dovetail connection for pin and box joints

Claim 1

In a tubular pin member adapted to be coupled to a tubular box member, thereby to form a joint having an axis, (a) first thread means on the pin member adapted to interfit second thread means on the box member, and third thread means on the pin member adapted to interfit fourth thread means on the box member, said first and third thread means defining a two-step thread, (b) a first frusto-conical make-up shoulder on the pin member located between said first and third thread means and adapted to interfit a corresponding first make-up shoulder on the box member, (c) said first and third thread means having flanks angled negatively in axial radial planes, and relative to planes normal to said axis and intersecting said flanks, said flanks facing in one axial direction being negatively angled to lesser extent than the flanks facing in the opposite axial direction, and (d) a second frusto-conical make-up shoulder on the pin member proximate the end of one of said first and third thread means remote from said first make-up shoulder, said first and second shoulders being positively angled in axial radial planes and relative to planes normal to said axis and intersecting said shoulders, said second shoulder on said pin member being adapted to be in a spaced relation from a corresponding second shoulder on the box member on normal make-up of said pin member to such box member, said second frusto-conical make-up shoulder on said pin member being adapted to engage the corresponding second shoulder on the box member in the event of sufficient coining of said first frusto-conical make-up shoulder on said pin member and of said corresponding first make-up shoulder on such box member.