Pipe joints or couplings – Particular interface – Tapered
Reexamination Certificate
2000-07-13
2001-08-07
Nicholson, Eric K. (Department: 3627)
Pipe joints or couplings
Particular interface
Tapered
C285S390000
Reexamination Certificate
active
06270127
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to 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 without having to apply tremendous torque for make-up.
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.
The wedge thread has been proven to be a reliable sealing mechanism in threaded connections. The dovetail, wedging action of the threads create sufficient interference in roots, crests, load flanks, and stab flanks to effect the thread seal. The friction drag caused by the interference threads must be overcome with torque during the make-up process. The larger the area of thread interference, the greater the torque requirements are for make-up. As connection diameters increase, e.g., for diameters of 10″ or greater, the thread interference area increases until the point is reached where the make-up torque required is not practical for field operations.
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 flanks, roots, and crests of the respective threads to move into forcible engagement during rotational make-up of the connection and form sealing surfaces that resist the flow of fluids between the threads upon rotational 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.
SUMMARY OF THE INVENTION
A threaded pipe connection is disclosed that includes a box member and a pin member. The box and pin members are formed in a two-step configuration having a larger step and a smaller step. The box member has a tapered, internal, generally dovetail-shaped thread across both thread steps with stab flanks, load flanks, roots, and crests. The pin member also has a tapered, external, generally dovetail-shaped thread across both thread steps with stab flanks, load flanks, roots, and crests. The internal thread of the box member increases in width in one direction while the external thread increases in width in the other direction so that the complementary flanks of the respective threads move into engagement during rotational make-up of the connection and form sealing surfaces that resist the flow of fluids between the threads on at least one step of the box and pin members upon rotational make-up of the connection.
In accordance with one or more embodiments of the invention, a gap may exist between the complementary stab flanks of one of the thread steps of the box and pin members upon final make-up. A gap may exist between the complementary load flanks of one of the thread steps of the box and pin members upon final make-up. A gap may exist in the stab flank and the load flank of one of the thread steps upon final make-up. A gap may exist between the complementary roots and crests of the box and pin members of one of the thread steps upon final make-up. A gap may exist in one or more of the complementary load flanks, stab flanks and roots and crests of the box and pin members upon final make-up. The roots and crests of both thread steps may come into contact during make up prior to contact of both stab and load flanks of at least one thread step upon final makeup. One of the wedge thread steps may be an interference wedge thread step and the other may be a clearance wedge thread step. A greater amount of root and crest interference may occur on the interference wedge thread step than on the clearance wedge thread step upon final make-up. Root and crest interference may exist on the interference wedge thread step and root and crest clearance may exist on the clearance wedge thread step upon final make-up.
Advantages may include one or more of the following. By minimizing thread interference area without sacrificing sealing or structural integrity of the connector, it becomes practical for large diameter connectors to be installed at much lower make up torque. Also, by incorporating a two-step structure, high resistance to compression and/or impact loading can be achieved, while sensitivity to the torque. restrictions of existing field make up equipment is retained. Further, the two-step configuration of the invention will reduce the amount of torque required to generate the contact stress necessary for creating a seal, while still providing the necessary threads for structural purposes. Other advantages and features will become apparent from the following description including the drawings and claims.
REFERENCES:
patent: Re. 34467 (1993-12-01), Reeves
patent: 4244607 (1981-01-01), Blose
patent: 4662659 (1987-05-01), Blose et al.
patent: 4671544 (1987-06-01), Ortloff
patent: 4703954 (1987-11-01), Ortloff et al.
patent: 4753460 (1988-06-01), Tung
patent: 4822081 (1989-04-01), Blose
patent: 5154452 (1992-10-01), Johnson
patent: 6123368 (2000-09-01), Enderle
patent: 6158785 (2000-12-01), Beaulier et al.
patent: 6174001 (2001-01-01), Enderle
Hydril Company
Nicholson Eric K.
Rosenthal & Osha LLP
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