An economical composite pipe threaded joint with an inner corrosion-resistant alloy layer

Abstract

This invention discloses an economical composite pipe thread joint with an inner corrosion-resistant alloy liner, belonging to the field of oil and gas development technology. Its sealing performance mainly relies on the direct and tight contact between the inner liner and the threaded connection. To ensure a tight bond, the outer thread substrate is slightly shorter than the inner liner, allowing the inner liner to contact first for sealing, followed by contact at the outermost end of the substrate to bear torque and prevent excessive deformation of the inner liner after contact. The angle between the second cylindrical surface of the outer thread and the outermost end of the outer thread is greater than 90°, ensuring sufficient contact even after slight tilting deformation due to the interference contact between the inner and outer threads, thus bearing the torque of the threading. This joint ensures that the corrosion-resistant alloy layer remains in contact with the corrosive medium after screwing, reducing pretreatment and on-site welding costs.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas development technology and relates to an economical composite pipe thread joint with an inner corrosion-resistant alloy layer. Background Technology

[0002] Joints are a crucial component of oil and gas pipelines. During oil and gas development and storage, a large number of oil pipes are required, such as well pipes connected at the ends with threaded joints to form pipe strings thousands or even tens of thousands of meters long, used to transport fluids such as oil, gas, and water. When the fluid medium has a high corrosive content, corrosion protection measures for these well pipes need to be considered, such as using high-alloy steel pipes, pipes with internal organic anti-corrosion coatings, or pipes lined with corrosion-resistant alloy layers. Among these, pipes lined with corrosion-resistant alloy layers are considered the lowest-cost method over their entire life cycle. However, the joints of steel pipes lined with corrosion-resistant alloy layers are a very weak point. When using welding methods, the pipe ends need to be pre-treated, and the on-site welding process and material requirements are very high, making the on-site construction cost comparable to the procurement cost of composite pipes.

[0003] Existing patented technologies for composite pipe threaded joints also require processing at the pipe ends. This involves either butt welding with nickel-based or nickel-iron alloys of equal or higher strength, or butt welding with nickel-iron or nickel-based alloys to ensure that the area of ​​the pipe end in contact with corrosive media after threaded connection is entirely composed of corrosion-resistant alloy. For cost-sensitive oil and gas development or storage pipelines, the use of welded or butt-welded threaded joints incurs substantial expenses for factory processing or on-site installation. Summary of the Invention

[0004] The purpose of this invention is to overcome the disadvantages of high processing and installation costs in the existing technologies, such as welding connections or post-weld threaded joints used in oil and gas development or storage pipelines, and to provide an economical composite pipe threaded joint with an inner corrosion-resistant alloy layer.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] An economical composite pipe threaded joint with an inner corrosion-resistant alloy layer includes a coupling and an external threaded joint connected to both ends of the coupling, the other end of which is connected to an external pipe body.

[0007] The external threaded connector has an external thread area, which includes the starting point of the large end thread and the ending point of the small end thread. A chamfer is provided at the ending point of the small end thread.

[0008] A first cylinder is provided at the end of the small end thread along the pipe end direction, and a second cylinder is provided at the end of the first cylinder;

[0009] The coupling has a first cylindrical surface in the middle, and a second cylindrical surface on each side of the first cylindrical surface;

[0010] The inner wall of the external threaded joint is provided with a corrosion-resistant alloy layer.

[0011] Preferably, the chamfer angle at the end of the small-end thread is no greater than 8°.

[0012] Preferably, the distance between the end of the small end thread and the first cylinder in the horizontal direction is not less than 2mm.

[0013] Preferably, the length of the first cylinder in the horizontal direction is 2.00–6.00 mm;

[0014] The second cylinder has a horizontal length of 1.50–2.00 mm;

[0015] The outer diameter of the second cylinder is 1.5 to 3 mm smaller than that of the first cylinder.

[0016] The included angle between the second cylinder and the outer end face of the external threaded connector is 90 to 90.5°.

[0017] Preferably, the ends of the external threaded connector are mechanically expanded.

[0018] The corrosion-resistant alloy layer extends to the outer end of the external threaded joint, and the extension dimension of the corrosion-resistant alloy layer relative to the outer end of the external threaded joint is 0.03 to 0.15 mm;

[0019] The wall thickness of the end of the external threaded connector is 1.50 to 2.00 mm.

[0020] The thickness of the corrosion-resistant alloy layer is greater than 1.00 mm.

[0021] Preferably, the inner walls at both ends of the coupling are machined with internal threads that mate with the external threaded joint.

[0022] Preferably, the length of the first cylindrical surface is 2.9 to 4.9 mm.

[0023] Preferably, the surface of the coupling is plated with copper or an organic coating.

[0024] Preferably, the outer diameter of the second cylindrical surface is 1.5 to 3.5 mm larger than the outer diameter of the first cylindrical surface.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention discloses an economical composite pipe thread joint with an inner corrosion-resistant alloy liner. The coupling does not require a corrosion-resistant alloy, reducing costs. Its sealing performance is primarily achieved through the direct and tight contact between the inner liner and the threaded connection. To ensure a tight bond, the outer thread substrate is slightly shorter than the inner liner. The inner liner contacts first, providing a seal, followed by contact at the outermost end of the substrate to bear the torque, preventing excessive deformation of the inner liner after contact. The angle between the second cylindrical surface of the outer thread and the outermost end of the outer thread is greater than 90°, ensuring sufficient contact even after slight tilting deformation due to the interference fit between the inner and outer threads, thus bearing the torque of the threading. This joint ensures that the corrosion-resistant alloy layer remains in contact with the corrosive medium after screwing, reducing pretreatment and on-site welding costs. Attached Figure Description

[0027] Figure 1 This is a schematic diagram showing the relative positions of the components after the threaded connector is screwed on.

[0028] Figure 2 This is a schematic diagram of the external thread end structure;

[0029] Figure 3 This is a schematic diagram of the structure at the middle position of the coupling.

[0030] Wherein: 1-coupling; 2-external threaded joint; 3-pipe body; 4-corrosion resistant alloy layer. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to the accompanying drawings:

[0032] Example 1

[0033] An economical composite pipe threaded joint with an inner corrosion-resistant alloy layer includes a coupling 1 and an external threaded joint 2 connected to both ends of the coupling 1. The other end of the external threaded joint 2 is connected to an external pipe body 3. The external threaded joint 2 has an external thread area engraved on it, which includes a large end thread start point and a small end thread end point. A chamfer is provided at the small end thread end point. A first cylinder is installed at the small end thread end point along the pipe end direction, and a second cylinder is installed at the end of the first cylinder. A first cylindrical surface is provided in the middle of the coupling 1, and second cylindrical surfaces are installed at both ends of the first cylindrical surface. The inner wall of the external threaded joint 2 is provided with a corrosion-resistant alloy layer 4.

[0034] Example 2

[0035] The processing and application methods for Φ88.9×6.45 (1.50 mm inner corrosion-resistant alloy lining) mm N80 base lined with 316L corrosion-resistant alloy oil well tubing used for carbon dioxide fluid transportation are as follows.

[0036] according to Figure 2The required machining is performed at the end of the external threaded connector 2. The external thread area has a large end thread start point and a small end thread end point A, where a = 1.86mm, b = 1.98mm, c = 1.40mm, d = 0.08mm, e = 7°, f = 2.10mm, g = 1.80mm, and the angle between BC and CD is 90.38°. Starting from the small end thread end point A, a chamfered surface is machined inward at e = 7°.

[0037] Starting from point A, the end of the small-end thread, machine a fine round thread of 10 teeth per inch according to API standards, and grind off the burrs on the surface of the black thread. Figure 3 As required, the middle of coupling 1 is machined, with EF being 3.60mm long and having the same diameter as the cylindrical surface BC, EG being 3.22mm long, and the chamfer radius at point G being 1.20mm. Coupling 1 is machined with a 10-pitch fine round thread per inch according to API standards, starting from the end. The end of the external threaded connector 2 is screwed onto one end of coupling 1 with a torque range of 5300±300 N·m. After delivery to the site, the other end of the threaded connector is screwed onto the other end of the coupling with a torque range of 5500±500 N·m to form a pipe string for use.

[0038] In this embodiment, the N80 material, the same as that used for the external thread base, is selected for coupling 1. The surface of coupling 1 is phosphated for the N80 material.

[0039] Example 3

[0040] For Φ114.30×6.35 (1.50mm corrosion-resistant alloy lining) L80-3Cr base lined with 625 corrosion-resistant alloy oil well tubing used for transporting fluids with high mineral, carbon dioxide, and hydrogen sulfide content, the processing and application methods are as follows:

[0041] according to Figure 2 The requirements are as follows: Machining is required at the end of the external thread, where a = 1.98 mm, b = 1.86 mm, c = 1.40 mm, d = 0.08 mm, e = 7°, f = 2.10 mm, g = 1.68 mm, and the angle between BC and CD is 90.26°. Starting from the end point A of the small end thread, a chamfered surface is machined inwards at e = 7°. Starting from the end point A of the small end thread, a 5-thread-per-inch trapezoidal thread is machined inwards according to API standards, and burrs on the black thread surface are ground off.

[0042] according to Figure 3 As required, machining is performed in the middle of the coupling, where EF is 3.85mm long and has the same diameter as the cylindrical surface BC, EG is 3.08mm long, and the chamfer radius of point G is 1.20mm.

[0043] The coupling is machined with a 5-thread-per-inch trapezoidal thread from the end according to API standards.

[0044] Tighten one end of the external thread to one end of the coupling with a torque of 8700±500 N.m. After delivery to the site, tighten the other end of the threaded connector to the other end of the coupling with a torque of 8700±500 N.m to form a pipe string for use.

[0045] The coupling is made of the same L80-3Cr material as the external thread base. The surface of the L80-3Cr material coupling is treated with a wear-resistant and lubricating organic coating.

[0046] The preparation method of the economical composite pipe thread joint with corrosion-resistant inner lining is as follows:

[0047] The threaded joint with couplings consists of a coupling with internal threads made of the same material as the pipe body, and a pipe body with external threads that is a composite pipe lined with a corrosion-resistant alloy layer. The relative cross-sectional structure of the threaded joint with the corrosion-resistant alloy layer after screwing is shown below. Figure 1 As shown, the thread can be a standard thread type such as a trapezoidal thread or a round thread.

[0048] Figure 2 Point A marks the end of the small-end thread. From point A towards the external thread area, a chamfer is machined, with an angle e not exceeding 8°. Starting from point A, a cylindrical structure is machined towards the pipe end, with a length f not less than 2mm and an outer diameter not greater than the outer diameter at point A. Continuing towards the pipe end, another cylindrical structure is machined, with an outer diameter equal to the outer diameter at point A minus dimension b. The length a is between 1.50 and 2.00mm. The specific values ​​of a and b are related to the pipe's outer diameter and wall thickness; the larger the outer diameter and wall thickness, the larger the values ​​of a and b. The line connecting points C and D... The angle between the end of the tube body and the line connecting BC is 90° and is related to the wall thickness. The larger the wall thickness, the smaller the value. The thickness dimension g ranges from 1.50 to 2.00 mm. The larger the wall thickness of the tube body, the larger the value. The dimension c is the thickness of the end of the inner alloy lining layer. The value should be greater than 1.00 mm. To ensure this value, the end of the tube body is mechanically expanded before machining to reduce the ellipticity at this position. The protruding dimension d relative to point D of the end of the base body is 0.03 to 0.15 mm.

[0049] Figure 3 The cross-section of the middle section of the coupling is designed, with the entire coupling symmetrical about the middle section along its axial length. EF is a machined cylindrical surface with a diameter not less than [missing information]. Figure 2 The diameter and length of the BC cylindrical surface should not exceed 2a-0.1 mm to ensure that the inner alloy lining layer makes priority contact after the joint is screwed on; EG is perpendicular to the pipe axis; a chamfered or beveled arc surface can be machined at point G to reduce stress concentration at this location, with a chamfer radius not exceeding 1.20 mm; continue machining a cylindrical surface away from the middle of the coupling, with a diameter not less than... Figure 2The diameter and length at point A shall not be less than 30mm. After the coupling thread and intermediate structure are machined, surface treatment shall be performed to enhance resistance to sticking damage. For ordinary carbon steel, the coupling surface may be phosphated, copper plated, or coated with a wear-resistant and lubricating organic coating. For couplings made of alloy steel, a wear-resistant and lubricating organic coating treatment shall be applied. The inner walls of both ends of coupling 1 are machined with internal threads that mate with the external threaded connector 2.

[0050] In summary, in order to reduce the on-site connection cost of composite pipes with corrosion-resistant alloy linings used in oil and gas development or storage where axial load requirements are not high, this invention proposes an economical composite pipe threaded joint with corrosion-resistant alloy linings suitable for connecting oil and gas pipelines where the tensile load is less than half of the axial tensile strength of the composite pipe body.

[0051] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. An economical, lined corrosion resistant alloy layer composite pipe threaded joint, characterized by, The coupling (1) and the external thread joint (2) connected with the two ends of the coupling (1) respectively, the other end of the external thread joint (2) is connected with the external pipe body (3); The external thread joint (2) has an external thread area, the external thread area includes a large end thread starting point and a small end thread ending point, and a chamfer is arranged at the small end thread ending point; A first cylinder is arranged at the small end thread ending point in the pipe end direction, and a second cylinder is arranged at the end of the first cylinder; The middle part of the coupling (1) is provided with a first cylindrical surface, and the two sides of the first cylindrical surface are respectively provided with a second cylindrical surface; The inner wall of the external thread joint (2) is provided with a corrosion-resistant alloy layer (4); The length of the first cylinder in the horizontal direction is 2.00-6.00mm; The length of the second cylinder in the horizontal direction is 1.50-2.00mm; The outer diameter of the second cylinder is smaller than that of the first cylinder by 1.5-3mm; The included angle between the second cylinder and the outer end face of the external thread joint (2) is 90-90.5°; The outer diameter of the second cylindrical surface is larger than that of the first cylindrical surface by 1.5-3.5mm; The size of the external thread base is slightly shorter than that of the inner liner layer, the inner liner layer is contacted first to play a sealing role, and then the outermost end of the base is contacted to play a torque bearing role.

2. The economic lined corrosion resistant alloy composite pipe threaded joint of claim 1, wherein, The angle of the chamfer at the small end thread ending point is not greater than 8°.

3. The economic lined corrosion resistant alloy composite pipe threaded joint of claim 1, wherein, The distance between the small end thread ending point and the first cylinder in the horizontal direction is not less than 2mm.

4. The economic lined corrosion resistant alloy composite pipe threaded joint of claim 1, wherein, The end of the external thread joint (2) is subjected to mechanical expansion treatment; The corrosion-resistant alloy layer (4) extends to the outer end of the external thread joint (2), and the protruding size of the corrosion-resistant alloy layer (4) relative to the outer end of the external thread joint (2) is 0.03-0.15mm; The wall thickness of the end of the external thread joint (2) is 1.50-2.00mm; The thickness of the corrosion-resistant alloy layer (4) is greater than 1.00mm.

5. The economic lined corrosion resistant alloy composite pipe threaded joint of claim 1, wherein, The inner wall of the two ends of the coupling (1) is processed with an internal thread matched with the external thread joint (2).

6. The economic lined corrosion resistant alloy composite pipe threaded joint of claim 1, wherein, The length of the first cylindrical surface is 2.9-4.9mm.

7. The economic lined corrosion resistant alloy composite pipe threaded joint of claim 1, wherein, The surface of the coupling (1) is plated with copper or organic coating.

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