This invention builds up on technical features and on the industry experience with the use of Merlin™ family connectors. In addition to friction, structural means utilized to transfer high torsional loads include keys and may also include: interlocked thread systems, shear pins, dog-clutch teeth and splines, all used in isolation or in arbitrary combinations. Static and fatigue bending load capacities of the connectors remain high, while the axial load capacities may or may not be high, depending on the design requirements. Connectors according to this invention can be built as new, carefully optimized designs. In some cases upgrading existing Merlin™ family connector designs to increase they torque transfer capacities may be also feasible.

A threaded tubular connection comprises a first tubular (12) component and a second tubular component (14). The first tubular component (12) includes a female portion (10) defined on an interior surface of the first tubular component. The female portion includes an inner threaded portion (16d) and an outer threaded portion (16b) which are offset radially with respect to a longitudinal axis of the first tubular component by a first shoulder (26). The second tubular component (14) includes a male portion (18) defined on an exterior surface of the second tubular component. The male portion is to be inserted into the female portion, and includes an inner threaded portion (18d) and an outer threaded portion (18b) which are offset radially with respect to a longitudinal axis of the second tubular component by a second shoulder (28). The second shoulder is to abut the first shoulder once the male portion is connected to the female portion. The threaded tubular connection comprises an inner short length fluid tight seal.

A threaded connection includes a pin and a box. The pin includes, in the order from a free end side of the pin toward a tubular body side thereof, an inner sealing surface, an inner male threaded portion, a shoulder portion, an outer male threaded portion, and an outer sealing surface. The box includes, in the order from a tubular body side of the box toward a free end side thereof, an inner sealing surface, an inner female threaded portion, a shoulder portion, an outer female threaded portion, and an outer sealing surface. Between the inner sealing surface and the inner female threaded portion of the box, an inner groove along a circumferential direction is provided, and some threads of the inner male threaded portion of the pin are contained in the inner groove.

A telescopically assembled, Merlin™ Family Connector is provided with one or more sets of threads on substantially matching frustoconical surfaces of a pin and a box of the connector. Strengthening means are introduced involving at least one of: a mechanical stiffening clamp interacting with an outside surface of the box or a mechanical stiffening clamp interacting with an inside surface of the pin. The stiffening clamps may include systems of arbitrarily oriented ribs and/or fairing surfaces. The said strengthening means may be essentially annular clamps that would have relatively regular shapes essentially conforming to the external or internal surfaces of the box or the pin, respectively. The above modifications can be introduced to traditional connectors and to connectors designed to transfer high torsional loads.

A threaded connection for a steel pipe includes a box which is an opening end of a second pipe and a truncated cone shaped pin which is an end of a first pipe and is inserted into the box, wherein the pin includes a male thread portion which is a tapered thread and a seal portion which includes a tapered surface, the box includes a female thread portion which is a tapered thread and a seal portion which includes a tapered surface, and in a state before make-up between the pin and the box, a minimum diameter of the tapered surface of the pin is smaller than a maximum diameter of the tapered surface of the box.

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 tubular connection includes either or both of a pin or a box. The pin includes an external male threaded zone having external male threads disposed on a portion of the pin, and the box includes an internal female threaded zone having internal female threads disposed on a portion of the first box. The internal female threads are configured to engage with the external male threads of the first pin. At least one of the pin or the box includes a torque shoulder surface that includes a surface roughness that is greater than or equal to 100 microns. In some instances, the torque shoulder surface can include a knurled surface profile that is continuous along the torque shoulder surface. In certain instances, a second mating torque shoulder surface has a surface roughness greater than or equal to 100 microns.

A downhole assembly that includes tubulars rotationally coupled to one another. An interface is between adjacent tubulars that makes up at least a portion of the rotational coupling. Certain surfaces of adjacent tubulars come into contact with one another when adjacent tubulars are rotationally coupled; and which are defined as contact surfaces. Each contact surface is profiled with facets that are complementary to facets on a corresponding contact surface of an adjacent tubular. The profiling of the contact surfaces is such that when a contact surface is brought together with a corresponding contact surface; facets on the contact surface abut facets on the corresponding contact surface along planes that are oblique or parallel with an axis of the tubular. At least some of a rotational torque transmitted between adjacent tubulars occurs across the abutting facets.

A vibration isolating coupler including a first coupler portion, a second coupler portion including an external surface and an internal surface portion, and a vibration isolating portion extending between the first coupler portion and the second coupler portion. The vibration isolating portion including a first solid annular portion and a second solid annular portion. The vibration isolating portion including a plurality of slots extending from the first solid annular portion toward the second solid annular portion forming a plurality of vibration isolating elements. Each of the plurality of vibration isolating elements is disconnected from adjacent ones of the plurality of vibration isolating elements by a corresponding one of the plurality of slots. The plurality of vibration isolating elements enabling torsional rotation of the first coupler portion relative to the second coupler portion.

In a threaded connection for pipe with a two-step thread construction, including intermediate shoulders, during stabbing, the internal-pressure sealing surface of the pin near its tip is prevented from contacting the intermediate shoulder of the box and thus receiving damage. L.sub.P, L.sub.B, h.sub.P and h.sub.B shown in FIG. 2 satisfy Expressions (1) and (2), provided below. θ.sub.seal is the angle of slope of the straight line connecting the two ends, as determined along the axial direction, of the internal-pressure sealing surface of the pin. Expression (3), provided below, is also satisfied.

L.sub.P<L.sub.B  (1)

h.sub.B<h.sub.P(L.sub.B−L.sub.P)×tan θ.sub.seal  (2)

L.sub.SP<L.sub.B−L.sub.P  (3)