A rear-mounted self-sealing threaded fitting

Abstract

A post-installed adaptive sealing threaded joint includes a female joint and a male joint. The female joint's root portion comprises, in sequence: an axial anti-torsion shoulder, a sealing arc, a front connecting bevel, a relief cylindrical surface, a rear connecting bevel, and an internal thread. These parts are directly connected or transitioned via arcs. The male joint, from its end portion, comprises, in sequence: an internal bore, an axial anti-torsion shoulder, a connecting conical surface, a sealing conical surface, a threaded bevel, and an external thread. These parts are also directly connected or transitioned via arcs. The axial anti-torsion shoulders of the female joint and the male joint are pressed together, with the angles between these two axial anti-torsion shoulders and the axial vertical section of the steel pipe being -10° to -20° respectively. The sealing arc of the female joint and the sealing conical surface of the male joint form an arc-to-cone adaptive sealing structure. This invention solves the problem of insufficient sealing structure in existing gas-tight special threaded joints, providing a more stable gas sealing capability.

Description

Technical Field

[0001] This utility model relates to threaded joints, specifically to a rear-mounted adaptive sealing threaded joint. Background Technology

[0002] In the field of drilling and development of underground resources such as oil and gas, drill pipes are used to drill through the formation, casings are used to isolate the formation from the fluids inside the pipes, and tubing is used to transport oil and gas. Drill pipes, casings, and tubing are often connected by threads, with steel pipes connected one by one and lowered into the ground thousands of meters deep. Each pipe is about 10 meters long.

[0003] In practical applications, threaded connections need to withstand high tension and high internal pressure, and the connection point often becomes the weakest link in the entire tubing.

[0004] As easily exploitable oil reserves are gradually depleted, oil extraction is becoming increasingly difficult. The adoption of new extraction technologies, such as acid fracturing, long horizontal wells, and rotary drilling, is placing increasingly harsh conditions on the tubing. With the continuous development of high-temperature, high-pressure wells and deep-sea exploration, the deepest wells on land are approaching 10,000 meters, placing increasingly higher demands on the performance of oil casing threaded joints, particularly in terms of compression resistance and external pressure resistance.

[0005] In conventional gas-tight joints, both the shoulder and sealing surfaces are located at the end, and both the shoulder and sealing surfaces at the end serve as "torsional shoulders." When the joint is subjected to high torque and high compressive force, the sealing surface also shares part of the pressure. Furthermore, due to their proximity, when the shoulder undergoes plastic deformation, the sealing surface inevitably undergoes plastic deformation as well.

[0006] The male threaded connector requires boring at the end to ensure a smooth inner and outer diameter of the connector. To improve the compression and external pressure resistance of this traditional special threaded connector, the male end is typically thickened by reducing the diameter of the male nose. However, due to the limitation of the nominal diameter, the inner diameter of the end can only be reduced by about 1 mm after boring.

[0007] Since the sealing surface is the most critical part of the entire joint for sealing, ensuring that the sealing part remains in a stable and safe state is a key focus of product design. However, it is evident that the shoulder surface often withstands extremely high compressive forces during use. When the compressive force exceeds a certain limit, the coupling shoulder surface is most prone to yielding deformation, and the pipe end is also prone to diameter reduction, thus affecting sealing performance. To ensure performance, thin-walled pipes typically require a necking process at the pipe end to increase the thickness of the sealing surface. However, due to the limitation of the inner diameter by the nominal diameter, necking cannot be performed indefinitely. For pipes with slightly larger walls, necking is difficult. Furthermore, to ensure a smooth transition of the inner diameter, boring is required. To ensure 100% bore coverage, the boring amount needs to be at least 2-3 mm. Although the pipe end thickness is not too thin at this point, to achieve 100% compression resistance, the bored portion inevitably reduces the joint's compression resistance and sealing performance.

[0008] Under high compressive forces, the coupling shoulder of the gas-tight special threaded joint bears the brunt of the stress, experiencing the greatest compressive force. When the compressive force reaches or exceeds 100% of the pipe body's yield strength, the coupling shoulder is the first to undergo irreversible yield deformation. Under high tensile forces, the coupling shoulder and the pipe fitting end shoulder will separate slightly, and the sealing surfaces will also separate to a small extent. Due to the significant interference between the sealing surfaces, this separation, while not causing the sealing surfaces to detach completely, weakens the sealing performance to some extent. Because of the negative angle shoulder design, when there is contact pressure between the shoulder surfaces, the reaction force can enhance the contact pressure of the sealing surfaces, thereby improving the sealing performance. However, when the shoulder separates under high tensile forces, this reaction force disappears.

[0009] Chinese patent CN200880115451.2 discloses a threaded connector for steel pipes, comprising a pin and a housing. The pin has a male thread and a lip with a shoulder surface. The lip includes a sealing surface and a nose. The housing has a female thread, a sealing surface, and a shoulder surface. The male thread engages with the female thread. The sealing surface of the pin is in sealing contact with the corresponding sealing surface of the housing. The shoulder surface of the pin is disposed on the end face of the pin. The sealing surface of the pin is located near the pipe end side of the male thread. The nose is located between the sealing surface and the shoulder surface of the pin, and the nose of the pin does not contact the portion of the housing opposite to the nose.

[0010] The threaded joint for steel pipe is characterized in that the shoulder surface of the pin includes two adjacent different surfaces: an inner main shoulder surface and an outer secondary shoulder surface; the corresponding shoulder surface of the housing opposite to the shoulder surface of the pin includes two adjacent different surfaces: an inner main shoulder surface and an outer secondary shoulder surface; the main shoulder surface of the pin and the main shoulder surface of the housing are arranged to prevent radial inward deformation of the lip end; the secondary shoulder surface of the pin and the secondary shoulder surface of the housing are arranged to limit radial outward deformation of the lip end; the radial dimension of the main shoulder surface of the pin is greater than the radial dimension of the secondary shoulder surface of the pin; and at least the main shoulder surface of the pin axially abuts against at least the corresponding main shoulder surface of the housing.

[0011] The patented sealing surface employs a conical-to-conical sealing structure. Due to the numerous combinations of outer diameter, wall thickness, and steel grade in the oil casing, ensuring that the rearward-moving sealing surface maintains high gas-tight pressure under various varying and harsh test conditions and actual operating conditions is difficult to guarantee completely. This patent features an axial primary shoulder surface and a radial secondary shoulder surface structure.

[0012] Chinese patent CN201320838237.8 discloses a traditional gas-tight structure in which the sealing surface is close to the end shoulder surface. Summary of the Invention

[0013] The purpose of this invention is to design a rear-mounted adaptive sealing threaded joint, which solves the problem of insufficient sealing structure of existing gas-tight special threaded joints, has a more stable gas sealing capability, and its sealing surface has a deformation resistance capability that is about 2 to 3 times that of the traditional structure.

[0014] To achieve the above objectives, the technical solution of this utility model is as follows:

[0015] A post-positioned adaptive seal threaded joint includes a female connector and a male connector, wherein,

[0016] The female connector root consists of, in sequence: an axial anti-torsion shoulder, a sealing arc, a front connecting bevel, a retraction cylindrical surface, a rear connecting bevel, and an internal thread; the various parts are directly connected or transitioned through arcs.

[0017] The male connector, from end to end, consists of: an inner bore, an axial anti-torsion shoulder, a connecting conical surface, a sealing conical surface, a threaded bevel, and an external thread; the various parts are directly connected or connected by a circular arc transition.

[0018] The axial anti-torsion shoulder of the female connector and the axial anti-torsion shoulder of the male connector are pressed together, and the two axial anti-torsion shoulders form an angle with the axial vertical section of the steel pipe.

[0019] The sealing arc of the female connector and the sealing cone surface of the male connector form an arc-to-cone self-adaptive sealing structure.

[0020] The sealing arc of the female connector is a large arc with a radius of 10-80 mm and an arc length of 4-12 mm; the sealing cone of the male connector has a length of 3-6 mm and a taper of 30%-60%.

[0021] Preferably, the angles between the axial anti-torsion shoulder of the female connector, the axial anti-torsion shoulder of the male connector, and the axial vertical section of the steel pipe are -10° to -20°.

[0022] Preferably, the length of the connecting tapered surface of the male connector is 2–6 mm, and the taper is 0–20%.

[0023] Preferably, the sealing arc of the female connector is interference-fitted with the sealing cone surface 28 of the male connector, and preferably, the interference in the diameter direction is 0.2 to 1.5 mm.

[0024] Preferably, the sealing arc of the female connector and the connecting cone surface of the male connector are in clearance fit, and preferably, the clearance is 0.1 to 0.5 mm.

[0025] Preferably, the front connecting bevel, the retraction cylindrical surface, and the rear connecting bevel before the internal thread of the female connector form a groove.

[0026] Preferably, after machining, 0-70% of the 1-2 threads at the beginning of the male connector thread are cut off circumferentially. Correspondingly, on the premise of ensuring no interference with the starting thread of the male connector, the diameter of the retraction cylindrical or conical surface of the female connector thread is reduced to the diameter of the cylindrical or conical surface of the tooth tip at the beginning of the male connector thread.

[0027] Preferably, the starting part of the male connector thread is a cylindrical or conical surface, and the diameter of the retraction cylindrical or conical surface of the female connector thread is reduced to the diameter of the cylindrical or conical surface at the starting part of the male connector thread.

[0028] In the threaded joint with rear-mounted adaptive seal described in this utility model:

[0029] The sealing arc of the female connector and the sealing cone of the male connector form an arc-to-cone adaptive sealing structure; the sealing arc of the female connector is a large arc with a radius of 10-80mm and an arc length of 4-12mm; the sealing cone of the male connector has a length of 3-6mm and a taper of 30%-60%.

[0030] The sealing arc of the female connector is interference-fitted with the sealing cone of the male connector, preferably with an interference amount of 0.2 to 1.5 mm in the diameter direction.

[0031] The smaller the diameter, the thinner the wall, and the lower the steel grade (yield strength), the smaller the interference fit; the larger the diameter, the thicker the wall, and the higher the steel grade (yield strength), the larger the interference fit.

[0032] There are many specifications for steel pipes (outer diameter, wall thickness, material combination). The special threaded joints for airtightness developed for each specification need to be tested in actual airtightness. The workload of actual testing is huge. The influence of "machining deviation" and "threading torque" on sealing performance is also very significant. Seal leakage occurs from time to time in actual testing, which shows that the "sealing safety margin" is limited.

[0033] The threaded connector described in this utility model is a "rear-mounted" threaded connector with an "adaptive" metal-to-metal sealing structure.

[0034] In practical use, it has been found that traditional airtight joints (such as...) Figure 6 As shown, under high torque pressure, 100% axial compression, and high temperature expansion strain, the torque shoulder is most prone to plastic deformation, and since the sealing surface is close to the shoulder, the sealing performance will be significantly reduced.

[0035] The sealing arc of the female connector and the sealing cone of the male connector in this utility model design form a "circular arc to cone" self-adaptive sealing structure. The self-adaptive means that no matter how the upper screwing position, sealing interference, load strain, and high temperature strain change, there is always a section of the circular arc that forms a seal with the cone.

[0036] The sealing cone surface of the male connector described in this invention is located away from the end anti-torsion shoulder, forming a "rear-mounted" sealing structure. Both the front and rear portions of the annular cone surface of the sealing cone surface are supported by annular steel pipes. This contrasts with traditional gas-tight connectors, where the sealing surface is located at the end and only has rear annular support. The deformation resistance of the sealing surface of this invention is approximately 2 to 3 times that of traditional structures.

[0037] To achieve the best sealing fit, there should be a matching relationship between the taper and length of the sealing cone of the male connector, the taper and length of the connecting cone, and the radius of the sealing arc of the female connector. This will result in a greater contact length and contact pressure between the sealing cone of the male connector and the sealing arc of the female connector, but not exceeding the yield strength of the materials.

[0038] Compared with the prior art, the advantages of this utility model are:

[0039] This invention designs a more reliable sealing structure with more stable gas sealing capability. By moving the sealing surface to the root of the thread, the shoulder surface is separated from the sealing surface, effectively avoiding the problem of reduced sealing performance caused by the shoulder surface undergoing a certain degree of plastic deformation.

[0040] However, due to the numerous combinations of outer diameter, wall thickness, and steel grade in the oil casing, ensuring that the rearward-positioned sealing surface maintains high gas-tight pressure under various changing and harsh test conditions and actual working conditions remains difficult to guarantee completely. Therefore, this utility model, based on the rearward-positioned sealing surface, designs the sealing surface mating structure as a large arc-to-conical surface seal, which can automatically adapt to different outer diameters, wall thicknesses, material properties, processing deviations, load strains, and temperature strains, ensuring that a section of the sealing interference fit is always under high contact pressure.

[0041] Under actual service conditions, such as high torsional forces, test compression exceeding 100%, bending reaching 65° / 100ft, or temperatures reaching 240°C or higher, or several of these conditions acting simultaneously, the sealing surface and shoulder surface of traditional joints are subjected to exceptionally harsh stresses. The sealing surface and shoulder surface of the joint described in this invention are separated, thus preventing mutual interference. An annular relief groove is machined at the female end position corresponding to the starting thread of the male end, eliminating thread interference at this location and reducing the impact of the thread segment on the sealing surface, thus placing the sealing surface in a relatively stable environment.

[0042] The most significant feature of this novel sealing structure is that the sealing surface is located between the rear annular steel tube and the extended nose end at the front. The simultaneous action of both increases the contact stress of the sealing surface, rather than relying on the reaction force of the negative angle shoulder surface. Regardless of the reaction force of the negative angle shoulder, the new structure can enhance the contact stress of the sealing surface without reducing the inner diameter of the end.

[0043] The female connector has a groove pre-machined on the internal thread. This groove can act as a container for excess thread grease, preventing the grease from accumulating and causing pressure.

[0044] Chinese patent CN200880115451.2 discloses a conical-to-conical sealing structure for the sealing surface, while this utility model employs a self-adaptive sealing structure with a "large arc to conical surface" (i.e., a large radius and long arc at the sealing surface of the female joint). Due to the numerous combinations of outer diameter, wall thickness, and steel grade in the oil casing, ensuring that the rearward-moving sealing surface maintains high gas-tight pressure under various changing and harsh test conditions and actual working conditions is difficult to guarantee completely. Therefore, the sealing surface mating structure of this utility model is a large arc to conical surface seal, which can automatically adapt to different outer diameters, wall thicknesses, material properties, processing deviations, load strains, and temperature strains, ensuring that a section of the sealing interference fit is always under high contact pressure.

[0045] Furthermore, this patent features an axial main shoulder surface and a radial secondary shoulder surface structure, while this utility model only has a main shoulder surface and no secondary shoulder surface. The two are different.

[0046] Chinese patent CN201320838237.8 discloses a traditional gas-tight structure, in which the sealing surface is close to the end shoulder surface, which is different from the structure of this utility model. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the structure of an embodiment of the present utility model;

[0048] Figure 2 This is an exploded view of the structure of an embodiment of the present utility model;

[0049] Figure 3 This is a schematic diagram of the male connector in an embodiment of the present utility model;

[0050] Figure 4 This is a schematic diagram of the female connector in an embodiment of the present utility model;

[0051] Figure 5 This is a diagram showing the mating of the male and female connector sealing structures in an embodiment of this utility model.

[0052] Figure 6 Diagram showing the fit of a traditional joint sealing structure;

[0053] Figure 7 This is a schematic diagram of the structure of Embodiment 2 of the present invention;

[0054] Figure 8 This is a structural schematic diagram of Embodiment 3 of the present invention.

[0055] Figure 9 The contact pressure curve of the sealing surface of a traditional joint;

[0056] Figure 10 The contact pressure curve of the sealing surface of the connector of this utility model;

[0057] Figure 11 The contact pressure curve of the sealing surface of a traditional joint under combined load;

[0058] Figure 12 The contact pressure curve of the sealing surface of the connector of this utility model under combined load;

[0059] Figure 13 The weighted energy integral of the contact pressure of the sealing surface of a traditional joint;

[0060] Figure 14 The weighted energy integral of the contact pressure on the sealing surface of the connector of this utility model. Detailed Implementation

[0061] See Figures 1-5 , Figure 7 , Figure 8The threaded joint with a rear-mounted adaptive seal according to this utility model includes a female joint 1 and a male joint 2, wherein,

[0062] The female connector 1 has the following components in sequence: axial anti-torsion shoulder 11, sealing arc 12, front connecting bevel 13, retraction cylindrical surface 14, rear connecting bevel 15, and internal thread 16. The components are directly connected or transitioned through arcs.

[0063] The male connector 2, from end to end, consists of: an inner bore 21, an axial anti-torsion shoulder 22, a connecting cone surface 23, a sealing cone surface 24, a threaded bevel 25, and an external thread 26; the parts are directly connected or transitioned by arcs.

[0064] The axial anti-torsion shoulder 11 of the female connector 1 and the axial anti-torsion shoulder 22 of the male connector 2 are pressed together, and the angles between the two axial anti-torsion shoulders 11 and 22 and the axial vertical section of the steel pipe are -10° to -20° respectively.

[0065] The sealing arc 12 of the female connector and the sealing cone surface 24 of the male connector form an arc-to-cone adaptive sealing structure.

[0066] Preferably, the sealing arc 12 of the female connector 1 is a large arc with a radius of 10 to 80 mm and an arc length of 4 to 12 mm.

[0067] Preferably, the sealing cone surface 24 of the male connector 2 has a length of 3-6 mm and a taper of 30%-60%.

[0068] Preferably, the length of the connecting tapered surface 23 of the male connector 2 is 2-6 mm, and the taper is 0-20%.

[0069] Preferably, the sealing arc 12 of the female connector 1 and the sealing cone surface 24 of the male connector 2 are interference fit, and preferably, the interference in the diameter direction is 0.2 to 1.5 mm.

[0070] Preferably, the sealing arc 12 of the female connector 1 and the connecting cone surface 23 of the male connector 2 are in clearance fit, preferably with a clearance of 0.1 to 0.5 mm.

[0071] Preferably, the front connecting bevel 13, the retraction column surface 14, and the rear connecting bevel 15 before the internal thread 16 of the female connector 1 form a groove. This groove can act as a container for excess thread grease, preventing the accumulation of thread grease and the resulting pressure.

[0072] Preferably, after the male connector thread starts with 1 to 2 threads, 0 to 70% of the threads can be cut off circumferentially. Correspondingly, on the premise of ensuring no interference with the male connector thread, the diameter of the female connector thread retraction cylinder 14 or cone can be reduced to the diameter of the cylinder or cone at the tooth tip of the male connector thread starting point (external thread 26).

[0073] Preferably, the starting point of the male connector thread (external thread 26) can be a cylindrical or conical surface, and the diameter of the female connector thread retraction cylindrical or conical surface 14 can be reduced to the diameter of the cylindrical or conical surface at the starting point of the male connector thread (external thread 26).

[0074] See Table 1 for embodiments of this utility model.

[0075] The sealing cone surface 24 of the male connector 2 of this utility model, with its axial anti-torsion shoulder 22 away from the end, is a "rear-mounted" sealing structure. Figure 5 As shown, the annular conical seal 27 of the sealing conical surface 24 of the male connector 2 is supported by annular steel pipes at the front 28 and rear 29. This contrasts with the traditional gas-tight connector 4, where the sealing surface 41 is located at the end and is only supported by the rear annular 42. Figure 6 As shown. The sealing surface of this invention has approximately 2 to 3 times the deformation resistance of the traditional structure.

[0076] like Figure 9 , Figure 10 As shown, this is a pressure curve of the sealing surface of a traditional connector and the connector of this invention under 10 different combinations of dimensional deviations and torque positions for an outer diameter of 88.9mm. Due to the self-adaptive sealing structure of the "large arc conical surface" designed in this invention, the pressure distribution of the sealing surface is a symmetrical dome shape, with the maximum contact pressure ranging from 1200 to 1500 MPa. In contrast, the traditional connector, not being a self-adaptive sealing structure, suffers from deformation caused by the initial interference, resulting in a pressure distribution that is lower on the left and higher on the right, with the maximum value being a narrow peak. The maximum contact pressure ranges from 750 to 1600 MPa, exhibiting poor stability.

[0077] like Figure 11 , Figure 12As shown, this is a graph illustrating the contact pressure curves of the sealing surfaces of a conventional connector and the connector of this invention under combined internal / external pressure and tensile / compression loads, with a nominal outer diameter of 88.9 mm and an intermediate torque. Due to the self-adaptive sealing structure of the "large arc-cone surface" designed in this invention, the contact pressure distribution shape of the sealing surface remains a symmetrical dome shape, with the maximum contact pressure ranging from 600 to 1400 MPa. In contrast, the conventional connector, not being a self-adaptive sealing structure, suffers from deformation caused by the initial interference fit, resulting in a left-low and right-high contact pressure distribution shape, with the maximum value being a narrow peak, and the maximum contact pressure ranging from 400 to 1200 MPa, exhibiting poor stability.

[0078] like Figure 13 , Figure 14 The figure shows the weighted energy integral curves of the sealing surface contact pressure of a conventional connector and the connector of this invention under 12 different combinations of dimensional deviations and torque positions for an outer diameter of 88.9 mm. The comparison shows that the weighted energy integral of the sealing surface of the connector of this invention is 2 to 3 times that of the conventional connector.

[0079] Table 1

[0080]

Claims

1. A threaded joint with a rear-mounted adaptive seal, comprising a female joint and a male joint, characterized in that, The female connector root consists of, in sequence: an axial anti-torsion shoulder, a sealing arc, a front connecting bevel, a retraction cylindrical surface, a rear connecting bevel, and an internal thread; the various parts are directly connected or transitioned through arcs. The male connector, from end to end, consists of: an inner bore, an axial anti-torsion shoulder, a connecting conical surface, a sealing conical surface, a threaded bevel, and an external thread; the various parts are directly connected or connected by a circular arc transition. The axial anti-torsion shoulder of the female connector and the axial anti-torsion shoulder of the male connector are pressed together, and the two axial anti-torsion shoulders form an angle with the axial vertical section of the steel pipe. The sealing arc of the female connector and the sealing cone surface of the male connector form an arc-to-cone self-adaptive sealing structure. The sealing arc of the female connector is a large arc with a radius of 10-80 mm and an arc length of 4-12 mm; the sealing cone of the male connector has a length of 3-6 mm and a taper of 30%-60%.

2. The rear seat self-sealing threaded joint of claim 1, wherein, The angles between the axial anti-torsion shoulder of the female connector and the axial anti-torsion shoulder of the male connector and the axial vertical section of the steel pipe are -10° to -20°, respectively.

3. The rear seat self-sealing threaded joint of claim 1, wherein, The length of the connecting tapered surface of the male connector is 2–6 mm, and the taper is 0–20%.

4. The rear seat self-sealing threaded joint of claim 1, wherein, The sealing arc of the female connector is interference-fitted with the sealing cone surface of the male connector.

5. The rear seat self-sealing threaded joint of claim 1, wherein, The sealing arc of the female connector is interference-fitted with the sealing cone of the male connector, and the interference in the diameter direction is 0.2 to 1.5 mm.

6. The rear seat self-sealing threaded joint of claim 1, wherein, The sealing arc of the female connector is clearance-fitted with the connecting cone surface of the male connector.

7. The rear seat self-sealing threaded joint of claim 1, wherein, The sealing arc of the female connector is clearance-fitted with the connecting cone surface of the male connector, with a clearance of 0.1 to 0.5 mm.

8. The rear seat self-sealing threaded joint of claim 1, wherein, The front connecting bevel, the retraction cylindrical surface, and the rear connecting bevel of the female connector form a groove.

9. The rear seat self-sealing threaded joint of claim 1, wherein, After machining, 0-70% of the 1-2 threads at the beginning of the male connector thread are cut off circumferentially. Correspondingly, on the premise of ensuring no interference with the starting thread of the male connector, the diameter of the retraction cylindrical or conical surface of the female connector thread is reduced to the diameter of the cylindrical or conical surface of the tooth tip at the beginning of the male connector thread.

10. The rear seat self-sealing threaded joint of claim 1, wherein, The starting point of the male connector thread is a cylindrical or conical surface, while the diameter of the retracted cylindrical or conical surface of the female connector thread is reduced to the diameter of the cylindrical or conical surface at the starting point of the male connector thread.

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