Pipe joints or couplings – Particular interface – Tapered
Reexamination Certificate
1999-02-19
2001-03-27
Barrett, Suzanne Dino (Department: 3629)
Pipe joints or couplings
Particular interface
Tapered
C285S390000
Reexamination Certificate
active
06206436
ABSTRACT:
FIELD OF THE INVENTION
The present invention involves threaded tubular joints usable in oil and gas well drilling and production, such as tubing, casing, line pipe, and drill pipe, commonly known collectively as oilfield tubular goods. More particularly, the invention relates to a tubular joint for connecting male (pin) and female (box) members.
BACKGROUND OF THE INVENTION
The use of threaded tubular connections for joining flow conduits in an end-to-end relationship to form a continuous flow path for transporting fluid under pressure is well known. Oilfield tubular goods all use threaded connections for connecting adjacent sections of conduit or pipe. Examples of such threaded end connections designed for use on oilfield tubular goods are disclosed in U.S. Pat. Nos. 2,239,942; 2,992,019; 3,359,013; RE 30,647; and RE 34,467, all of which are assigned to the assignee of the present invention.
In U.S. Pat. No. RE 30,647 by Blose, a particular thread form or structure is disclosed for a tubular connection that provides an unusually strong joint while controlling the stress and strain in connected pin and box members within acceptable levels. The pin member is equipped with at least one generally dovetail-shaped external thread whose width increases in one direction along the pin, while the box member is equipped with at least one matching generally dovetail-shaped internal thread whose width increases in the other direction. In this manner, the mating set of helical threads provide a wedge-like engagement of opposing pin and box flanks that limit the extent of relative rotation between the pin and box members, and define a forcible make-up condition that completes the connection. In this thread structure, the flank shoulder angles as well as the thread width can be used to control the stress and strain preload conditions induced in the pin and box members for a given make-up torque. Thus, by tailoring the thread structure to a particular application or use, the tubular connection or joint is limited only by the properties of the materials selected.
As shown in
FIG. 1
, a prior art connection
10
includes a pin member
11
and a box member
12
. Box member
12
has a tapered, internal, generally dovetail-shaped thread structure
14
formed thereon and adapted for engaging complementary tapered, external, generally dovetail-shaped thread structure
15
formed on pin member
11
to mechanically secure the box and pin members in a releasable manner.
Internal thread
14
of box member
12
has stab flanks
18
, load flanks
16
, roots
20
, and crests
24
. The thread increases in width progressively at a uniform rate in one direction substantially the entire helical length of thread
14
. External thread
15
of pin member
11
has stab flanks
19
, load flanks
17
, roots
21
, and crests
25
. The thread increases in width progressively at a uniform rate in the other direction substantially the entire helical length of thread
15
. The oppositely increasing thread widths and the taper of threads
14
and
15
, cause the complementary roots and crests of the respective threads to move into engagement during make-up of the connection in conjunction with the moving of complementary stab and load flanks into engagement upon make-up of the connection.
The pin member
11
or the box member
12
defines the longitudinal axis
13
of the made-up connection
10
. The roots and crests of the box and pin members are flat and parallel to the longitudinal axis of the connection and have sufficient width to prevent any permanent deformation of the threads when the connection is made up.
FIG. 2
shows a profile of the wedge thread on box member
12
. The dimension A represents the location of the thread start and dimension B represents the thread depth. The stab flank and load flank leads are denoted C and D respectively.
FIG. 3
shows a profile of the wedge thread on box member
12
, for example formed in a two-step configuration. The dimension W represents the basic wedge width and dimension R represents the wedge ratio.
When trying to incorporate a wedge thread with a conical metal-to-metal seal in the prior art, it was necessary to have a very shallow seal angle to compensate for the linear variability of the wedge thread torque stop.
SUMMARY OF THE INVENTION
In general, in one aspect, the invention includes a box member having a tapered, internal, generally dovetail-shaped thread incorporated in a two-step configuration and a pin member having a tapered, external, generally dovetail-shaped thread incorporated in a two-step configuration. The internal thread of the box member has stab flanks, load flanks, roots, crests and a wedge ratio and increases in width in one direction. The external thread of the pin member has stab flanks, load flanks, roots, crests and a wedge ratio and increases in width in the other direction so that the complementary roots and crests of the respective internal and external threads move into engagement during make-up of the connection in conjunction with the moving of complementary stab and load flanks into engagement upon make-up of the connection. The wedge ratio of one step is an aggressive wedge ratio with a larger magnitude, while the wedge ratio of the other step is a conservative wedge ratio with a smaller magnitude.
In accordance with one or more embodiments of the invention, the number of threads on the step with the conservative wedge thread ratio may exceed the number of threads on the step with the aggressive wedge ratio. The two-step configuration may include a larger step and a smaller step and the aggressive wedge thread ratio may be on the larger step while the conservative wedge thread ratio may be on the smaller step.
The make-up sequence may start with the roots and crests of one or both steps making contact during the initial phase of make-up, followed by the stab and load flanks of the step with the conservative wedge ratio coming into contact as make-up continues and followed, upon final make-up, by the stab and load flanks of the step with the aggressive wedge ratio coming into contact.
The make-up sequence may start with the stab and load flanks of the step with the conservative wedge ratio coming into contact during the initial phase of make-up, followed by the roots and crests of one or both steps making contact as make-up continues and followed, upon final makeup, by the stab and load flanks of the step with the aggressive wedge ratio coming into contact.
The make-up sequence may start with the roots and crests of one or both steps and the stab and load flanks of the step with the conservative wedge ratio making contact simultaneously during make-up followed, upon final make-up, with the stab and load flanks of the step with the aggressive wedge ratio coming into contact. Upon final make-up the stab and load flanks may form sealing surfaces that resist the flow of fluids between the threads.
In general, in one aspect, the invention includes a box member having a plurality of tapered, internal, generally dovetail-shaped threads, each with stab flanks, load flanks, roots, crests and a wedge ratio and a pin member having a plurality of tapered, external, generally dovetail-shaped threads, each with stab flanks, load flanks, roots, crests and a wedge ratio. The internal threads of the box member increase in width in one direction while the external threads of the pin member increase in width in the other direction so that the complementary roots and crests of the internal and external threads move into engagement during make-up of the connection in conjunction with the moving of complementary stab and load flanks into engagement upon make-up of the connection. The wedge ratio of one thread is an aggressive wedge ratio with a larger magnitude while the wedge ratio of another thread is a conservative wedge ratio with a smaller magnitude.
In accordance with one or more embodiments of the invention, the number of threads on the thread with the conservative wedge thread ratio may exceed the number of threads on the thread with the aggressive we
Barrett Suzanne Dino
Hydril Company
Rosenthal & Osha L.L.P.
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