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 threaded connection includes a first tubular member having a pin end defining an external thread profile, and a second tubular member having a box end defining an internal thread profile threadably engageable with the external thread profile of the pin end. At least one of the external and internal thread profiles includes a first section that extends at a first taper angle relative to a longitudinal axis of the threaded connection, a second section extending from the first section at a second taper angle relative to the longitudinal axis, and a third section extending from the second section at a third taper angle relative to the longitudinal axis. The second taper angle is greater than each of the first and third taper angles.

A threaded connection includes a first tubular member having a pin end defining an external thread profile, and a second tubular member having a box end defining an internal thread profile threadably engageable with the external thread profile of the pin end. At least one of the external and internal thread profiles includes a first section that extends at a first taper angle relative to a longitudinal axis of the threaded connection, a second section extending from the first section at a second taper angle relative to the longitudinal axis, and a third section extending from the second section at a third taper angle relative to the longitudinal axis. The second taper angle is greater than each of the first and third taper angles.

Threaded connections of casing pipes comprising male and female members with trapezoidal tapered threads arranged on outer and inner surfaces of end sections. Radial sealing surfaces and stop end surfaces contact forming an internal sealing zone. Threads on male and female members have a 1:16 taper ratio, a 23-25 stab flank angle, and a 3 to 5 load flank angle. During assembly, crests and stab flanks of thread profile form clearances. Radial sealing surfaces on male and female members are tapered and positioned at a 71-73 angle relative to the normal. Stop end surfaces on male and female members are positioned at a 14-16 angle relative to the normal. Stop end thickness of male member constitutes at least 50% of wall thickness. Tight sealing of connection is preserved under considerable combined loads, including high-torque exposure.

A threaded connection that provides high sealing performance is provided. A threaded connection (10) includes a pin (1) and a box (2). An inner male thread (13) of the pin (1) includes a parallel portion (131). The parallel portion (131) is located at an end portion of the inner male thread (13) adjacent to the pin inner sealing surface (11), and has thread roots parallel to the pipe axis. An inner female thread (23) of the box (2) includes a tapered portion (231). The thread height in the tapered portion (231) is larger than that in the parallel portion (131). Da<Db is satisfied, where Da is the difference in diameter between adjacent thread crests (231a) in the tapered portion (231) in a longitudinal cross section of the pin (1) and box (2) as found when the connection is not made up, and Db is the difference between the diameter of the thread root (131a) in the parallel portion (13) and the maximum diameter of the pin inner sealing surface (11).

In a pipe joint where two pipe sections (14, 16) have threadably engaged end portions (17, 18), joint ends (32, 34) are substantially sealed to each other by a sealing surface (40, 50) on one pipe section that substantially abuts a sealing surface (42, 52) on the other pipe section. In one joint, a ring-shaped cutout (121, FIG. 7) is formed in a first pipe section and a ring-shaped spacer (120) is located in the cutout. The spacer is chosen from several that have slightly different lengths so the spacer end contacts the corresponding sealing surface (130). In a pipe string used to carry corrosive fluid, the inner surface (44) of adjacent pipe sections is covered with a corrosion resistant coating (70, 72). Where the sealing surface is connected to a rounded corner (82, 84), the coating extends to and along the sealing surfaces (40, 42). Where there are sharp corners (80) at the intersection of the inside surface (40) with the sealing surface (40B, 42B), the coating does not extend along the sealing surfaces.

A threaded joint is constructed of a pin and a box. The pin includes, in order from a tubular body having the pin toward the free end thereof: a male threaded portion and a lip portion including a sealing surface. The box includes: a female threaded portion corresponding to the male threaded portion of the pin; and a recessed portion corresponding to the lip portion, the recessed portion including a sealing surface. The lip portion includes, in order from a male threaded portion toward the free end of the pin: a neck portion; and a sealing head portion including the sealing surface. The maximum outside diameter of the region of the sealing surface in the sealing head portion is larger than an outside diameter of the neck portion at a boundary between the neck portion and the male threaded portion.

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.

A tubular connection includes a first joint of casing having an integral box end with an internal female wedge threaded zone having wedge threads disposed on a portion of the integral box end, and a second joint of casing having an integral pin end with an external male wedge threaded zone having wedge threads disposed on a portion of the integral pin end. The external male wedge threads engage with the internal female wedge threads. The second joint of casing has an internal diameter D1, and also includes an internal annular recess with an internal diameter D2. D2 is greater than D1, and the annular recess is disposed longitudinally along an inner surface of the second joint of casing. The annular recess is positioned radially adjacent to a portion of the external male threads disposed on a lower portion of the pin end.

A threaded joint for pipes including a pin and a box, characterized in that the relationship 0.05 degrees.sub.sb.sub.sp2.0 degrees is satisfied, where .sub.sb is an angle of an insertion surface of the female thread on the box side relative to a plane perpendicular to an axis of pipe, and .sub.sp is an angle of an insertion surface of the male thread, which faces the insertion surface of the female thread, on the pin side relative to the plane perpendicular to the axis of pipe.