A HIGH-TIGHTNESS THREADED JOINT

RACCORD FILETE A DEGRE ELEVE D'ETANCHEITE

English Abstract

The invention relates to building oil and gas wells and can be used in casing
strings and tubings. The
inventive highly-tight screw joint comprises internal and external mating
elements with conical surfaces.
The internal and external elements are provided with a thread. Said thread has
supporting and embedded
faces. A sealing unit is made in the form of a wedge on the side of a small
diameter. The sealing unit is
provided on the internal and external elements. The sealing unit consists of
the parts of the internal and
external elements. The internal and external elements of the sealing unit are
formed by conical radial and
conical stop faces. The conical radial face is made at an angle of 25°-
35° to the normal to the thread axis.
The conical supporting surface is made at an angle of 10°-25° to
the normal to thread axis. The design
makes it possible to increase the reliability, the tightness and the strength
of the joint, to ease the assembly
and disassembly thereof, to improve the abrasion resistance of the joint and
to extend the service life
thereof.

French Abstract

L'invention concerne le domaine de la construction de puits pétroliers et gaziers et peut s'utiliser dans des tubages et des pipelines de transport. Un raccord fileté à degré élevé d'étanchéité est doté d'éléments raccordés extérieur et intérieur possédant des surfaces coniques. Les éléments raccordés extérieur et intérieur comportent un filetage. Ce filetage possède un côté d'appui et un côté d'insertion. Le bloc d'étanchéité est disposé du côté du diamètre inférieur du cône de filetage et a la forme d'un coin. Le bloc d'étanchéité est disposé sur les éléments raccordés extérieur et intérieur. Le bloc d'étanchéité est constitué des parties éléments raccordés extérieur et intérieur. Les éléments intérieur et extérieur du bloc d'étanchéité sont formés par des surfaces conique radiale et conique d'appui. Lasurface conique radiale présente un angle de 25° +/- 35° par rapport à la normale de l'axe de filetage. La surface conique d'appui présente un angle de 15° +/- 25° par rapport à la normale de l'axe de filetage. L'invention permet d'améliorer la fiabilité et l'étanchéité du raccord, d'augmenter la solidité du raccord et d'en faciliter l'assemblage et le désassemblage pendant l'utilisation ainsi que d'augmenter la résistance à l'usure et la durée de vie du raccord.

Claims

5
CLAIMS:
1. A high-tightness threaded joint that has an internal and external
interfacing elements with
tapered surfaces that have a thread with a bearing face and an inserted face,
and a sealing component
that is on a side of a smaller diameter of a thread taper, is made in the
shape of a wedge and comprises
parts of internal and external elements, distinct in that the internal and
external parts of the sealing
component are formed by tapered radial and tapered bearing surfaces, wherein
the tapered radial surfaces
are at a 25°-35° angle to the normal to a thread axis, and the
tapered bearing surfaces are at a 10°-25°
angle to the normal to the thread axis.
2. A joint per claim 1, characterized in that thread with a 1:16 taper is
used.
3. A joint per any one of claims 1, 2, characterized in that it uses thread
with the bearing face at a
1°-5° angle to the normal to the thread axis and the inserted
face at a 7°-25° angle.
4. A joint per claim 3, characterized in that the bearing face has a straight
section, the internal and
external parts having different thread radii along the straight section.

Description

CA 02706286 2010-05-18
A High-Tightness Threaded Joint
The invention pertains to the field of construction of building oil and gas
wells and can be used for
casings and tubing strings. A threaded joint for casings and tubing strings is
high-tight and is designed for
the use in wells characterized by high rate of shaft crookedness and/or severe
operating conditions, such
as high tension or compression loads, excessive internal and external
pressures, and an environment with
high concentrations of H2S and CO2.
Known is a technical solution protected by patent FR 1489013, priority
11.05.1965, describing a
high-tightness threaded joint. In the known technical solution, the threaded
joint has internal and external
interfacing elements with tapered surfaces. The tapered surfaces of the
elements have thread with a
bearing face and inserted face. On the side of the smaller diameter of thread
taper there is a sealing
component made in the shape of a wedge and comprising parts of the internal
element and external
element.
However, a shortcoming of this threaded joint is that the sealing component is
not sufficiently tight.
In addition, such design does not make it possible to achieve desired
interference at low axial movements
of the internal element, which lengthens the time between the first contact of
sealing surfaces and
achievement of the required interference. In addition, under severe operating
conditions (high tension or
compression loads, excessive internal and external pressures) there are
flexural deformations that disrupt
the contact of taper surfaces which results in unsealing of the threaded
joint.
This technical solution is used as the closest analogue of the claimed
technical solution.
In developing the invention, the objective was to design a high-tightness
threaded joint that would
make it possible to reassemble the threaded joint without damaging it,
ensuring high tightness, improving
behavior of the threaded joint in tension and bending, achieving guaranteed
contact along the straight
section of the thread bearing surface when screwing and unscrewing the joint,
and increasing the
resistance to compression loads.
The technical result being achieved is increased reliability and tightness of
the joint, increased joint
strength, simplified assembly-disassembly during operation, and increased wear
resistance and life of the
joint.
This technical result is achieved due to the fact that a high-tightness
threaded joint has internal and
external interfacing elements with tapered surfaces that have thread with
bearing and inserted faces, and
on the side of the smaller diameter of thread taper there is a sealing
component made in the shape of a
wedge and comprising parts of the internal and external elements. The sealing
component internal and
external parts are formed by a tapered radial surface and a tapered bearing
surface, wherein the tapered

CA 02706286 2010-05-18
=
2
radial surface is at a 250-350 angle to the normal to the thread axis, and the
tapered bearing surface is at a
100-250 angle to the normal to the thread axis.
The table vividly demonstrates the effect of the angles on the threaded joint
tightness, reliability
and life. The table second column shows the pressure a pipe and joints must
withstand while maintaining
tightness. The third and fourth columns show stress readings taken when
testing the joint; in the process,
the joint itself had remained tight.
Average Contact Stresses Average Contact Stresses
Hydrotesting
Angle Combination in the Radial Seal After in the Radial Seal After
Pressure, MPa
Assembly, MPa
Tension (0.801), MPa
250-100 793.7
690.2
300-150 64.5 1054.9
794.3
350-250 1158.5
865.1
These features are essential and interrelated, forming a stable set of
essential features that is
sufficient to achieve the stated technical result.
In the sealing component, the contact of the radial seal of the part of the
internal element in the
shape of a cone with the mating tapered surface of the part of an external
element takes place with
interference over a relatively small area. In this, high contact stresses
occur which ensures high tightness.
The design makes it possible to reassemble the threaded joint without damaging
the sealing surface, due
to rapid achievement of the desired radial interference during the assembly
process. In addition, such
design of the sealing component makes it possible for the threaded joint to
stay tight when exposed to
substantial flexural loads. In this, the bearing surfaces protect the radial
seal from excessive torque and
compression.
To enhance the technical result, one can use a series of the following
features.
In the high-tightness threaded joint, thread with a 1:16 taper is used.
The thread bearing face is at a 10-50 angle to the normal to the thread axis,
and the inserted face is
at a 70-250 angle. This angle of the thread bearing face ensures improved
operation of the threaded joint in
tension and bending, and the angle of the inserted face improves conditions
for joint assembly when
engaging the first several turns of the thread.
Along the bearing face straight section, the internal and external parts have
different thread radii.
Such design makes it possible to improve threading the joint together, and
increase its resistance to wear
and compression loads.
Figure 1 shows a high-tightness threaded joint of casings with the internal
and external elements.

CA 02706286 2014-12-02
3
Figure 2 shows the thread profile of Section A in Fig. 1.
Figure 3 shows the sealing component corresponding to section E. in Fig. 1.
In the high-tightness threaded joint, thread (1) with a 1:16 taper is used.
The thread profile has a
positive angle of 1 -5 along bearing face (2) and 70-250 along inserted face
(3). The height of the thread
profile of internal element (4) is lower than the height of the thread profile
of external element (5). Sealing
component (6) is on the side of the smaller diameter of thread taper, is made
in the shape of a wedge and
comprises parts of internal element (7) and external element (8). Parts of the
internal and external
elements are formed by tapered radial surfaces (9) and (10) and tapered
bearing surfaces (11) and (12).
The radial seal is at a 250-350 angle to the normal to the thread axis, and
the tapered seal is at a 100-250
angle to the normal to the thread axis.
The invention is explained using a specific example. It clearly demonstrates
the possibility to
achieve the above technical result. However, this is not the only possible
example.
In the high-tightness threaded joint, thread with a 1:16 taper is used. The
thread profile has a
positive angle of 30 along the bearing face and 100 along the inserted face.
The height of the thread profile
of the internal element is lower than the height of the thread profile of
external element. The sealing
component is on the side of the smaller diameter of thread taper, is made in
the shape of a wedge and
comprises parts of the internal element and the external element. Parts of the
internal and external
elements are formed by tapered radial and tapered bearing surfaces. The radial
seal is at a 300 angle to
the normal to the thread axis, and the tapered seal is at a 150 angle to the
normal to the thread axis.
The high-tightness threaded joint works as follows.
When performing operations of screwing and unscrewing the threaded joint, the
interaction of
internal (4) and external (5) elements by means of thread (1) occurs first.
When screwing the joint, the
surface of the external element is moving along the surface of the external
element. Then, the tapered
radial surface (7) and tapered bearing surface (8) of the internal element
interact with the tapered radial
surface (9) and tapered bearing surface (10) of the external element. Due to
diametrical deformations of
these surfaces, a "metal-to-metal" type sealing component is created.
When elements (4) and (5) move relative to each other, a forced contact of
bearing surfaces (7) and
(8) of the internal element and (9) and (10) of the external element occurs.
As a result, contact stresses
develop on their surfaces. Magnitude of the stresses must be within the limits
of elastic strains. All other
conditions being equal, the level of contact stresses is determined by the
size of contact areas of bearing
surfaces (7), (8), (9) and (10).
The advantage of the claimed threaded joint compared to the known one is
improved reliability of
tightness, increased joint strength, facilitation of assembling-disassembling
during operation, and
increased wear resistance and life of the joint.

CA 02706286 2010-05-18
4
The invention is new and commercially practicable because, by using known
processes used for
making threaded pipe ends, it can be put into practice based on a new
principle of interaction of mating
surfaces that is different from the known designs.

Representative Drawing