Connecting oil country tubular goods
Ends of separate tubular members used in oil and gas drilling are connected pin-to-pin by a threaded coupling and made leak tight by an internal pressure seal, wherein the male or field end pin of a first tubular member has an integral geometry designed to mate with the female or mill end pin of a second tubular member. The coupling and tubular members possess a modified buttress thread form having a negative load flank angle and a positive stab flank angle. When assembled, the coupling connects the field end pin of the first tubular member with the mill end pin of the second tubular member, wherein integral geometries of the mated pin ends generate the interference necessary to produce a single, metal-to-metal, leak-tight, internal contact pressure seal.
1. A threaded connection for releasably coupling and sealing tubular members, the connection comprising:
a tubular coupling having a first box end and a second box end, wherein a longitudinal bore extends through the coupling from the first box end to the second box end, with a center plane disposed proximate the middle of the coupling;
a first internal thread profile at the first box end of the coupling, wherein the first internal thread profile has a torque shoulder that divides the first internal thread profile into two radially and axially separate thread profiles, with the torque shoulder having a flat face perpendicular to the longitudinal bore of the coupling and facing the terminus of the first box end;
a second internal thread profile at the second box end of the coupling, wherein the second internal thread profile has a torque shoulder that divides the second internal thread profile into two radially and axially separate thread profiles, with the torque shoulder having a flat face perpendicular to the longitudinal bore of the coupling and facing the terminus of the second box end;
a first tubular member having a longitudinal bore extending therethrough, wherein the first tubular member has a first pin end;
a second tubular member having a longitudinal bore, wherein the second tubular member has a second pin end;
a first external thread profile at the first pin end of the first tubular member, wherein the first external thread profile has a torque shoulder that divides the first external thread profile into two radially and axially separate thread profiles, with the torque shoulder having a concave face relative to terminus of the first pin end of the first tubular member;
a second external thread profile at the second pin end of the second tubular member, wherein the second external thread profile has a torque shoulder that divides the second external thread profile into two radially and axially separate thread profiles, with the torque shoulder having a concave face relative to the terminus of the second pin end of the second tubular member;
a conical surface at the terminus of the first pin end of the first tubular member, wherein the conical surface has an angled primary seal surface relative to the longitudinal bore of the first tubular member; and,
a lip at the terminus of the second pin end of the second tubular member, wherein the lip is designed to engagingly mate with the conical surface of the first tubular member when the first tubular member and the second tubular member are connected by the coupling, with the lip having an angle slightly greater than the angle of the primary seal surface relative to the longitudinal bore of the second tubular member.
2. A threaded connection according to claim 1 , wherein the coupling has an outer diameter no greater than 6 . 5 % of the outer diameter of either tubular member.
3. A threaded connection according to claim 1 , wherein the coupling has a beveled first box end and a beveled second box end.
4. A threaded connection according to claim 1 , wherein the thread form is a modified buttress thread having negative load flanks angled within in a range of −3 degrees and −10 degrees and positive stab flanks angled within a range of +10 degrees and +20 degrees, the load and flank angles being measured counterclockwise relative to an axis perpendicular to the axis of the longitudinal bore of the tubular members when connected.
5. A threaded connection according to claim 1 , wherein a pitch of the threads ranges from 3 threads to 8 threads per inch of tubular member length.
6. A threaded connection according to claim 1 , wherein the angle of the primary seal surface ranges from 2 degrees to 35 degrees relative to the longitudinal bore of the tubular members when connected by the coupling.