A modified API buttress threaded casing connection is disclosed for use in drilling oil and gas wells in lieu of using conventional drill pipe. The coupling threads only are modified to include a reduced thread height thread form to relieve thread stresses at axial ends of the coupling. The reduced thread height thread form may be mated with standard single tapered API buttress thread forms formed on the pin ends. The axial length of the coupling may be generally shortened to permit abutment of the mating pins at the center of the coupling.

A modified API buttress threaded casing connection is disclosed for use in drilling oil and gas wells in lieu of using conventional drill pipe. The coupling threads only are modified to include a reduced thread height thread form to relieve thread stresses at axial ends of the coupling. The reduced thread height thread form may be mated with standard single tapered API buttress thread forms formed on the pin ends. The axial length of the coupling may be generally shortened to permit abutment of the mating pins at the center of the coupling.

A leak-resistant pipe connection has an annular seal bulge on a pin end of the connection and a tapered seal area adjacent a secondary box shoulder of a box end of the connection. The annular seal bulge is coined on contact with the tapered seal area on initial make-up of the connection which provides a metal-to-metal seal that is very resistant to high-pressure fluid leakage even after the connection is subjected to extreme shear and tensile stresses.

A leak-resistant pipe connection has an annular seal bulge on a pin end of the connection and a tapered seal area adjacent a secondary box shoulder of a box end of the connection. The annular seal bulge is coined on contact with the tapered seal area on initial make-up of the connection which provides a metal-to-metal seal that is very resistant to high-pressure fluid leakage even after the connection is subjected to extreme shear and tensile stresses.

A drill pipe comprises a drill pipe body and a tool joint that comprises a rotary shoulder connection is disclosed. The rotary shoulder connection comprises: a box connection, wherein the box connection has a box outer adius, a box counter bore radius and a box inner radius, and box threads having a box thread form cut along a box taper: a pin connection, wherein the pin connection has a pin outer radius, a pin cylinder radius and a pin nose radius, and pin threads having a pin thread form cut along a pin taper to align with the box threads inside the box connection; and a primary shoulder connection comprising: a primary box shoulder that is angled or curved; and a primary pin shoulder that is angled or curved. Methods of using the drill pipe are also disclosed.

A drill pipe comprises a drill pipe body and a tool joint that comprises a rotary shoulder connection is disclosed. The rotary shoulder connection comprises: a box connection, wherein the box connection has a box outer adius, a box counter bore radius and a box inner radius, and box threads having a box thread form cut along a box taper: a pin connection, wherein the pin connection has a pin outer radius, a pin cylinder radius and a pin nose radius, and pin threads having a pin thread form cut along a pin taper to align with the box threads inside the box connection; and a primary shoulder connection comprising: a primary box shoulder that is angled or curved; and a primary pin shoulder that is angled or curved. Methods of using the drill pipe are also disclosed.

A coupling for connecting downhole tubulars includes a tubular body, and at least one thread of a male screw thread formed on an outer surface of the body, and a female screw thread formed in an inner surface of the body. The at least one thread has a thread-form including a crest, a root, and a pair of flanks. The crest and the root are each cambered about a respective first and second camber radius. Each camber radius is greater than an outer diameter of the coupling.

A coupling for connecting downhole tubulars includes a tubular body, and at least one thread of a male screw thread formed on an outer surface of the body, and a female screw thread formed in an inner surface of the body. The at least one thread has a thread-form including a crest, a root, and a pair of flanks. The crest and the root are each cambered about a respective first and second camber radius. Each camber radius is greater than an outer diameter of the coupling.

An optimized thread profile (140) for joining composite materials is presented. This thread profile (140) maintains a certain material strength when used as part of a composite threaded joint (101). The thread profile (140) comprises a repeating pattern of four components: a crest region (150), a first flank (162), a root region (170) and a second flank (164). The thread profile (140) is symmetrical, that is, the dimensions of the four components do not change throughout the length of the thread profile. The crest (152) has a flat profile and the root (172) has a rounded profile. When a shaft (120) is affixed to a joining shaft (110) using this optimized thread profile (140), the flat profiles of the crest (152) of the shaft (120) and corresponding rounded profiles of the root (172) of the joining shaft (110) create a gap to accommodate a substance such as an adhesive or a lubricant. Similarly, the flat profiles of the crest (152) of the joining shaft (110) and corresponding rounded profiles of the root (172) of the shaft (120) create a gap to accommodate a substance.

A threaded connection for steel pipe with improved sealing performance is provided. A threaded connection (1) includes a pin (10) and a box (20). The pin (10) includes a pin shoulder surface (11), a pin sealing surface (12) and a male thread (13). The box (20) includes a box shoulder surface (21), a box sealing surface (22) and a female thread (23). The male thread (13) and female thread (23) are constituted by wedge threads. When the connection has been made up, the pin shoulder surface (11) is in contact with the box shoulder surface (21), the stabbing flank and load flank of the male thread (13) are in contact with the stabbing flank and load flank, respectively, of the female thread (23), and the pin sealing surface (12) is in contact with the box sealing surface (22). The shoulder angle is 4° or larger. The shoulder angle is the angle formed by each of the shoulder surfaces (11, 21) with a plane perpendicular to the pipe axis (CL) when the connection is not made up.