Double wall drill pipe

Abstract

This invention discloses a double-walled drill pipe, comprising an upper short connector, an outer tube, and a lower short connector connected sequentially from top to bottom by threads, and an inner tube disposed within the central channel of the outer tube. Both the upper and lower short connectors have a central channel and an eccentric channel along their axial direction. The inner tube is fitted inside the outer tube with a gap, forming a double-walled tube with a central channel and an annular channel. Both ends are fixed to the walls of the central channels of the upper and lower short connectors, respectively, so that the central channels of the upper and lower short connectors communicate with the central channel of the inner tube to form a first fluid passage. The eccentric channels of the two short connectors communicate with the annular channel formed between the inner and outer tube walls to form a second fluid passage. Simultaneously, a shoulder seal is formed between the two threaded components, preventing the first and second fluid passages from communicating. This double-walled drill pipe effectively prevents the inner tube from jumping up and down during use, and significantly improves the sealing pressure-bearing capacity and reliability between the long inner and outer tubes.

Description

Technical Field

[0001] The invention relates to the technical field of drilling, and in particular to a double-wall drill pipe. Background Art

[0002] Double-wall drill pipe drilling method refers to the method of drilling using double-wall drill pipe and other auxiliary equipment, mainly including low-pressure drilling, center sampling drilling, RDM technology and double-wall gas-filled drilling, etc. This method has been continuously valued and promoted in the field of geological and mining departments and oil drilling.

[0003] At present, the double-wall drill pipe commonly used in the double-wall drill pipe drilling method consists of an inner pipe and an outer pipe. The inner pipe is installed in the outer pipe to form two flow channels, namely the annular gap between the inner and outer pipes and the internal channel of the inner pipe; the outer pipes are connected by threads, and the inner pipes are connected by plug-in radial sealing structures to achieve connection and prevent fluid communication between the two channels. However, the double-wall drill pipe of this structure has the following problems: ① The inner and outer drill pipes are both long, and their length can reach about 10m. The concentricity of the inner and outer pipes is difficult to ensure, resulting in a large gap between the male and female joints of the inner pipe plug-in seal. Under high pressure, the sealing ring is easily squeezed into the gap between the male and female joints to damage the assembly sealing ring, reducing the sealing pressure bearing capacity and reliability; ② Frequent disassembly and assembly of the drill pipe may cause the sealing ring to curl and squeeze, reducing the sealing pressure bearing capacity and reliability; ③ Due to the space limitation between the inner and outer pipes, the inner pipe needs to be suspended on the upper step of the outer pipe. Due to the small step surface and the up and down vibration of the inner pipe during the use of the double-wall drill pipe, it is easy to cause the suspension step to fail, and the inner and outer pipes are misaligned up and down; the up and down vibration of the inner pipe will also greatly reduce the service life of the sealing ring. The failure of the seal ring will lead to the failure of the double-wall drill pipe drilling method, which seriously hinders the promotion and application of the double-wall drill pipe drilling technology. Therefore, it is necessary to improve the life and reliability of the key equipment in the double-wall drill pipe drilling method, that is, the double-wall drill pipe seal, so as to further promote the development of the double-wall drill pipe drilling technology. Summary of the invention

[0004] The purpose of the present invention is to provide a double-wall drill pipe which can effectively improve the pressure bearing capacity and reliability of the seal between the inner tube and the outer tube.

[0005] To this end, the technical solution of the present invention is as follows:

[0006] A double-wall drill pipe comprises an upper short-circuit, an outer tube and a lower short-circuit which are sequentially connected from top to bottom, and an inner tube sleeved in a central hole of the outer tube; wherein:

[0007] The inner wall of the top end of the upper short-circuit is provided with an internal thread for connecting to the bottom end of the lower short-circuit, and the outer wall of the bottom end is provided with an external thread for connecting to the top end of the outer tube, and the upper short-circuit is provided with a central hole A and an eccentric hole A in the axial direction; the hole wall at the bottom end of the central hole B is sunken to form a first annular step;

[0008] The inner wall of the top end of the outer tube is provided with an internal thread for connecting to the bottom end of the upper short-circuit, and the outer wall of the bottom end is provided with an external thread for connecting to the top end of the lower short-circuit;

[0009] The inner wall of the top end of the lower short-circuit is provided with an internal thread for connecting to the bottom end of the outer tube, and the outer wall of the bottom end is provided with an external thread for connecting to the top end of the upper short-circuit, and a central hole C and an eccentric hole B are respectively opened in the axial direction on the lower short-circuit; the top end hole wall of the central hole C is sunken to form a second annular step;

[0010] The inner tube is inserted into the outer tube in the form of a gap to form a double-walled tube with a central channel B and an annular channel A; the top end of the inner tube is inserted into the central channel A of the upper short-circuit and its top surface is against the lower end surface of the first annular step, and the bottom end of the inner tube is inserted into the central channel C of the lower short-circuit and its bottom surface is against the upper end surface of the second annular step, so that the central channel A, the central channel B and the central channel C form a connected first liquid passage, and the eccentric channel A, the annular channel A and the eccentric channel B form a connected second liquid passage.

[0011] Among them, the outer tube adopts conventional single-wall drill pipe, and the inner tube is preferably made of aluminum alloy tube, which effectively reduces the overall weight while ensuring the strength requirements of the double-wall drill pipe.

[0012] Preferably, the upper short-circuit is composed of an outer short-circuit and an inner short-circuit arranged in the central channel of the outer short-circuit; wherein the inner wall of the top end of the outer short-circuit is provided with an inner thread for connecting to the bottom end of the lower short-circuit, and the outer wall of the bottom end is provided with an outer thread for connecting to the top end of the outer tube; the inner short-circuit is provided with a central channel A and an eccentric channel A in the axial direction;

[0013] The inner short link and the outer short link are integrally formed; or, the inner short link and the outer short link are fixed by welding or by fastening screws or other connecting fixings; or, an annular flange is provided on the outer wall of the top end of the inner short link, and a thrust step is provided on the inner wall of the outer short link located below the inner thread, so that the inner short link is installed on the thrust step of the outer short link through the annular flange to prevent the inner short link from descending relative to the outer short link.

[0014] Preferably, a seal A is provided between the outer wall of the inner tube and the hole wall of the central channel A, and a seal B is provided between the outer wall of the inner tube and the hole wall of the central channel C.

[0015] The seal A13 and the seal B53 are at least one sealing ring arranged between the outer wall of the inner tube and the corresponding hole wall, or at least one sealing ring and a sealing ring retaining ring located on the upper side and / or the lower side of each sealing ring. At least one guide ring can also be optionally arranged near the sealing ring to reduce eccentric extrusion of the seal.

[0016] Preferably, an annular shoulder is provided above the external thread of the lower short-connection, and the shoulder surface C of the annular shoulder is tightly fitted with the annular shoulder surface A formed by processing the top end face of the upper short-connection to form a shoulder seal, and an annular shoulder is formed below the internal thread of the upper short-connection, and the shoulder surface B of the annular shoulder is tightly fitted with the annular shoulder surface D formed by processing the bottom end face of the lower short-connection to form a shoulder seal, so that when the two double-wall drill pipes are threadedly connected and fixed, the first liquid passages of the two double-wall drill pipes are connected to each other, the second liquid passages of the two double-wall drill pipes are connected to each other, and the connected first liquid passages and the connected second liquid passages are not connected to each other through the shoulder seal formed between the shoulder surface B and the shoulder surface D.

[0017] Preferably, an annular groove provided with a sealing member C is opened on the shoulder surface B or the shoulder surface D, so that a seal is formed between the shoulder surface B and the shoulder surface D through the sealing member C.

[0018] Preferably, the shoulder surface B and the shoulder surface D are processed into mutually matching conical surfaces, and an annular groove provided with a sealing member C is opened on the shoulder surface B or the shoulder surface D, so that a seal is formed between the shoulder surface B and the shoulder surface D through the sealing member C;

[0019] More preferably, the taper angle of the shoulder surface B is equal to the taper angle of the shoulder surface D and both are 90°.

[0020] Preferably, the sealing member C is an O-ring, a rectangular sealing ring, or a combined sealing gasket formed by vulcanizing a rubber ring and a metal ring.

[0021] Preferably, the shoulder surface B is processed into an inner cylindrical surface that is concave inward, and the shoulder surface D is processed into an outer cylindrical surface that is convex outward and cooperates with the inner cylindrical surface. A U-shaped sealing ring is arranged between the inner cylindrical surface and the outer cylindrical surface, so that a seal is formed between the shoulder surface B and the shoulder surface D through the U-shaped sealing ring.

[0022] Preferably, at least one centralizer is provided between the inner tube and the outer tube so as to concentrically arrange the inner tube and the outer tube, and a plurality of liquid passages distributed along the circumferential direction are provided on the outer wall of the centralizer.

[0023] Compared with the prior art, the double-wall drill pipe has the following beneficial effects:

[0024] 1) The setting of the upper short-circuit and the lower short-circuit effectively prevents the inner tube from jumping up and down during use, and improves the precision and quality of the indoor assembly of the inner tube and the outer tube, so that the inner tube and the outer tube are sealed and connected, and there is no need to disassemble them on the well, thereby greatly improving the sealing pressure bearing capacity and reliability between the inner tube and the outer tube with a longer length;

[0025] 2) The upper shorting link and the lower shorting link are shorter in size, which is conducive to improving the processing accuracy of the two, thereby further improving the sealing pressure level and reliability after the two are connected and fixed;

[0026] 3) When two double-wall drill pipes are connected, a seal is set between the upper short-circuit and the lower short-circuit on the matching flat shoulder surface or the matching conical shoulder surface, which solves the problems of distortion, falling off and eccentricity caused by repeated disassembly of the seal and improves the service life of the seal. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic structural diagram of a double-wall drill pipe according to Embodiment 1 of the present invention;

[0028] Figure 2 It is a structural schematic diagram of the upper short-circuit and the lower short-circuit threaded connection state of two double-wall drill pipes in Example 1 of the present invention;

[0029] Figure 3 It is a structural schematic diagram of the upper short-circuit and the lower short-circuit threaded connection state of two double-wall drill pipes according to Example 2 of the present invention;

[0030] Figure 4 It is a structural schematic diagram of the upper short-circuit and the lower short-circuit threaded connection state of two double-wall drill pipes in Example 3 of the present invention;

[0031] Figure 5 It is a structural schematic diagram of the upper short-circuit and the lower short-circuit threaded connection state of two double-wall drill pipes according to Embodiment 4 of the present invention;

[0032] Figure 6 It is a structural schematic diagram of the upper short-circuit and the lower short-circuit threaded connection state of two double-wall drill pipes according to Example 5 of the present invention;

[0033] Figure 7 for Figure 1 A partial enlarged schematic diagram of

[0034] Figure 8 This is a schematic diagram of the double wall structure of Example 6 of the present invention.

[0035] In the figure, 1. upper short-circuit, 2. outer tube, 3. inner tube, 4. centralizer, 5. lower short-circuit, 10. shoulder surface B, 11. eccentric hole A, 12. center hole A, 13. seal A, 14. shoulder surface A, 15. inner short-circuit, 16. outer short-circuit, 17. thrust step, 20. annular hole A, 30. center hole B, 40. liquid passage C, 50. shoulder surface D, 51. eccentric hole B, 52. center hole C, 53. seal B, 54. shoulder surface C, 60. seal C, 1301. O-type rubber ring, 1302. O-type sealing ring retaining ring, 1303. guide ring. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but the following embodiments are by no means intended to limit the present invention in any way.

[0037] Example 1

[0038] like Figure 1 As shown, the double-wall drill pipe includes an upper short-circuit 1, an outer tube 2 and a lower short-circuit 5 connected in sequence from top to bottom, and an inner tube 3 sleeved in the central channel of the outer tube 2; wherein,

[0039] The upper short-circuit 1 is a cylindrical structure, with an internal thread concentric with its outer cylindrical surface processed on the inner wall of its top end, and an external thread concentric with its outer cylindrical surface processed on the outer wall of its bottom end, and a central hole A12 and an eccentric hole A11 penetrating vertically are respectively opened axially from the end face located below the internal thread;

[0040] The outer tube 2 is a conventional single-wall drill pipe, with an internal thread processed on the inner wall of the top end and an external thread processed on the outer wall of the bottom end; the internal thread processed on the inner wall of the top end of the outer tube 2 cooperates with the external thread processed on the outer wall of the bottom end of the upper short-circuit 1, so that the outer tube 2 and the upper short-circuit 1 are threadedly connected and fixed;

[0041] The lower short-circuit 5 is a cylindrical structure, with an internal thread concentric with its outer cylindrical surface processed on the inner wall of its top end, and an external thread concentric with its outer cylindrical surface processed on the outer wall of its bottom end, and a central hole C52 and an eccentric hole B51 are respectively opened axially from the center and adjacent sides of the end face below the internal thread; the internal thread processed at the top of the lower short-circuit 5 and the external thread processed at the bottom of the outer tube 2 cooperate with each other, so that the outer tube 2 and the lower short-circuit 5 are threadedly connected and fixed;

[0042] The inner tube 3 is an aluminum alloy tube, which is sleeved in the outer tube 2 with a gap to form a double-walled tube with a central channel B30 and an annular channel A20; at the same time, two centralizers 4 are respectively sleeved and fixed on the upper and lower parts of the outer wall of the inner tube 3, so that the inner tube 3 and the outer tube 2 are arranged concentrically; the outer wall of the centralizer 4 is provided with a plurality of liquid passages 40 evenly distributed in the circumferential direction, so that the liquid flowing to the centralizer 4 continues to flow into the annular space below through the liquid passages 40;

[0043] The bottom hole wall of the central hole A12 is sunken to form a first annular step, and the top hole wall of the central hole C52 is sunken to form a second annular step, so that the top end of the inner tube 3 is inserted into the central hole A12 of the upper short circuit 1 and its top surface is against the lower end surface of the first annular step, and the bottom end of the inner tube 3 is inserted into the central hole C52 of the lower short circuit 5 and its bottom surface is against the upper end surface of the second annular step. At this time, the central hole A12, the central hole B30 and the central hole C52 form a connected first liquid passage, and the eccentric hole A11, the annular hole A20 and the eccentric hole B51 form a connected second liquid passage. In order to ensure good sealing and isolation between the first liquid passage and the second liquid passage, a sealing member A13 is provided between the outer wall of the inner tube 3 and the hole wall of the central hole A12, and a sealing member B53 is provided between the outer wall of the inner tube 3 and the hole wall of the central hole C52. Specifically, as Figure 7 As shown, the seal A13 includes two O-rings 1301, four O-ring retaining rings 1302 and a guide ring 1303; wherein, three annular grooves are spaced apart from top to bottom on the hole wall of the central channel A12 and the hole wall of the central channel C52 that are in contact with the outer wall of the inner tube 3, and the guide ring 1303 is installed in the annular groove located in the middle, and an O-ring 1301 is arranged in each of the annular grooves located on both sides, and a seal retaining ring 1302 is arranged on the groove walls on both sides of each O-ring 1301 located in the annular groove; the structure and setting method of the seal B53 are consistent with the structure and setting method of the above-mentioned seal A13.

[0044] Before using the double-wall drill pipe, multiple identical double-wall drill pipes must be connected end to end in sequence to form a pipe string with a length that is suitable for the well conditions. To ensure the stability and sealing of the pipe string formed by connecting multiple double-wall drill pipes, Figure 2 As shown, the internal thread processed on the inner wall of the top end of the upper short-circuit 1 and the external thread processed on the outer wall of the bottom end of the lower short-circuit 5 cooperate with each other, so that the lower short-circuit 5 of the upper double-wall drill rod and the upper short-circuit 1 of the lower double-wall drill rod are fixed by threaded connection. At the same time, a shoulder seal is formed between the upper short-circuit 1 and the lower short-circuit 5, so that the first liquid passage channels of the two connected double-wall drill rods are interconnected, the second liquid passage channels of the two connected double-wall drill rods are interconnected, and the connected first liquid passage channels and the connected second liquid passage channels are not interconnected.

[0045] Specifically, the shoulder seal is formed in the following manner: the top hole wall of the central hole A12 of the upper short-circuit 1 is indented to form a third annular step, and the bottom center of the lower short-circuit 5 is axially extended downward to form a cylindrical protrusion, and the cylindrical protrusion is concentric with the central hole C52, and the eccentric hole B51 is located on the adjacent side of the cylindrical protrusion; the outer diameter of the cylindrical protrusion is adapted to the hole diameter above the third annular step, so that when the upper short-circuit 1 and the lower short-circuit 5 are threadedly connected and fixed, the cylindrical protrusion is inserted into the central hole A12 and the bottom end is pressed onto the upper end surface of the third annular step; the third annular step The upper end face and the bottom end face of the cylindrical protrusion are respectively processed into an annular shoulder surface B10 and an annular shoulder surface D50 that can fit tightly to form a shoulder seal; an annular shoulder is provided above the external thread of the lower short-circuit 5, and the shoulder surface C54 of the annular shoulder is tightly fitted with the annular shoulder surface A14 formed by the top end face of the upper short-circuit 1 to form a shoulder seal; wherein, in this embodiment, the shoulder surface B10 and the shoulder surface A14 are both processed into planes perpendicular to the axis of the internal thread of the upper short-circuit 1, and the shoulder surface D50 and the shoulder surface C54 are both processed into planes perpendicular to the axial direction of the external thread of the lower short-circuit 5.

[0046] Example 2

[0047] like Figure 3 As shown, the structure of the double-wall drill pipe is basically the same as that of the double-wall drill pipe in Example 1, except that: a sealing member C60 adapted to the shoulder surface 50 is provided between the shoulder surface B10 and the shoulder surface D50 of the upper short-circuit 1, so that a seal is formed between the shoulder surface B10 and the shoulder surface D50 through the sealing member C60; wherein the sealing member C60 is a combined sealing gasket formed by vulcanizing a rubber and metal ring into one.

[0048] Example 3

[0049] like Figure 4 As shown, the structure of the double-wall drill pipe is basically the same as that of the double-wall drill pipe in Example 1, except that: the end face located below the internal thread of the upper joint 1 is processed into a shoulder surface B10 that cooperates with the annular shoulder surface D50, and an annular groove with a rectangular ring cross-section is opened on the shoulder surface B10, and a rectangular sealing ring C60 is arranged in the annular groove, so that a seal is formed between the shoulder surface B10 and the shoulder surface D50 through the rectangular sealing ring; wherein the rectangular sealing ring is a rectangular rubber ring.

[0050] Example 4

[0051] like Figure 5As shown, the structure of the double-wall drill pipe is basically the same as that of the double-wall drill pipe of Example 1, except that: the shoulder surface B10 of the upper short-circuit 1 is processed into a conical surface with an inner diameter gradually decreasing from top to bottom, and correspondingly, the cylindrical protrusion of the lower short-circuit 5 is processed into a structure with an upper outer diameter greater than a lower outer diameter, and the diameter change portion is processed into a conical surface that cooperates with the shoulder surface B10 to form a shoulder surface D50; an annular groove is opened on the shoulder surface B10, and an O-ring C60 is arranged in the annular groove, so that the shoulder surface B10 and the shoulder surface D50 are sealed by the O-ring C60; wherein, the cone angle formed by the shoulder surface B10 and the shoulder surface D50 processed into a conical surface structure is 90°.

[0052] Example 5

[0053] like Figure 6 As shown, the structure of the double-wall drill pipe is basically the same as that of the double-wall drill pipe in Example 1, except that: the shoulder surface B10 is processed into an inner cylindrical surface that is recessed inward, the shoulder surface D50 is processed into an outer cylindrical surface that is convex outward and can cooperate with the inner cylindrical surface, and a U-shaped sealing ring C60 is arranged between the inner cylindrical surface and the outer cylindrical surface, so that a seal is formed between the shoulder surface B10 and the shoulder surface D50 through the U-shaped sealing ring C60.

[0054] Example 6

[0055] like Figure 8 As shown, the structure of the double-wall drill pipe is basically the same as that of the double-wall drill pipe of Example 1, except that: the upper short-circuit 1 is composed of an outer short-circuit 16 and an inner short-circuit 15 arranged in the central channel of the outer short-circuit 16; wherein, the outer short-circuit 16 is a cylindrical structure, and an inner thread for connecting the bottom end of the lower short-circuit 5 is provided on the inner wall of the top end, and an outer thread for connecting the top end of the outer tube 2 is provided on the outer wall of the bottom end, and a thrust step 17 is provided on the inner wall of the outer short-circuit 16 located below the inner thread; correspondingly, an annular flange is provided on the outer wall of the top end of the inner short-circuit 15, so that the inner short-circuit 15 is installed on the thrust step 17 of the outer short-circuit 16 through the annular flange; the inner short-circuit 15 is a cylindrical structure, and a central channel A12 and an eccentric channel A11 are respectively provided on it along the axial direction.

[0056] For the double-wall drill pipe described in the above-mentioned embodiment 6, the outer short connection 16 therein can also be processed with the outer tube 2 into an integrated structure.

[0057] When the double-wall drill pipe is hoisted, transported and placed vertically, a thread protector is installed at the lower end of the lower short-circuit 5 to prevent the external thread and other matching surfaces of the lower short-circuit 5 from being damaged.

[0058] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A double-wall drill pipe, characterized in that: The invention comprises an upper short-circuit (1), an outer tube (2) and a lower short-circuit (5) connected in sequence from top to bottom; the upper short-circuit (1) is composed of an outer short-circuit (16) and an inner short-circuit (15) arranged in the central hole of the outer short-circuit (16); the inner wall of the top end of the outer short-circuit (16) is provided with an internal thread for connecting to the bottom end of the lower short-circuit (5), and the outer wall of the bottom end is provided with an external thread for connecting to the top end of the outer tube (2); the inner short-circuit (15) is provided with a central hole A (12) and an eccentric hole A (11) in the axial direction; the hole wall at the bottom end of the central hole A (12) is sunken to form a first annular step; the inner wall of the top end of the outer tube (2) is provided with an internal thread for connecting to the bottom end of the upper short-circuit (1), a bottom thread for connecting to the bottom end of the lower short-circuit (5), and an eccentric hole A (11) in the axial direction. The outer wall of the end is provided with an external thread for connecting to the top end of the lower short-circuit (5); the inner wall of the top end of the lower short-circuit (5) is provided with an internal thread for connecting to the bottom end of the outer tube (2); the outer wall of the bottom end is provided with an external thread for connecting to the top end of the upper short-circuit (1); and the lower short-circuit (5) is provided with a central hole C (52) and an eccentric hole B (51) along the axial direction; the top end hole wall of the central hole C (52) is sunken to form a second annular step; the inner tube (3) is inserted into the outer tube (2) in the form of a gap to form a double-walled tube having a central hole B (30) and an annular hole A (20); the top end of the inner tube (3) is inserted into the central hole A (12) and its top surface abuts against the first hole. On the lower end surface of the annular step, the bottom end of the inner tube (3) is inserted into the central hole C (52) of the lower short-circuit (5) and its bottom surface abuts against the upper end surface of the second annular step, so that the central hole A (12), the central hole B (30) and the central hole C (52) form a first liquid passage that is connected, and the eccentric hole A (11), the annular hole A (20) and the eccentric hole B (51) form a second liquid passage that is connected; at least one centralizer (4) is provided between the inner tube (3) and the outer tube (2) so that the inner tube (3) and the outer tube (2) are concentrically arranged; an annular shoulder is provided above the external thread of the lower short-circuit (5), and the shoulder surface C (54) of the annular shoulder An annular shoulder surface A (14) formed by machining the top end face of the upper short-circuit (1) is tightly fitted to form a shoulder seal, an annular shoulder is formed below the internal thread of the external short-circuit (16), and a shoulder surface B (10) of the annular shoulder is tightly fitted to an annular shoulder surface D (50) formed by machining the bottom end face of the lower short-circuit (5) to form a shoulder seal, so that when the two double-wall drill pipes are threadedly connected and fixed, the first liquid passages of the two double-wall drill pipes are connected to each other, the second liquid passages of the two double-wall drill pipes are connected to each other, and the connected first liquid passages and the connected second liquid passages are not connected to each other through the shoulder seal formed between the shoulder surface B (10) and the shoulder surface D (50).

2. The double-wall drill pipe according to claim 1, characterized in that: The inner short link (15) and the outer short link (16) are integrally formed; or, the inner short link (15) and the outer short link (16) are fixed by welding or by fastening screws; or, an annular flange is provided on the outer wall at the top end of the inner short link (15), and a thrust step (17) is provided on the inner wall of the outer short link (16) located below the inner thread, so that the inner short link (15) is installed on the thrust step (17) of the outer short link (16) through the annular flange.

3. The double-wall drill pipe according to claim 1 or 2, characterized in that: A sealing member A (13) is provided between the outer wall of the inner tube (3) and the hole wall of the central hole A (12), and a sealing member B (53) is provided between the outer wall of the inner tube (3) and the hole wall of the central hole C (52).

4. The double-wall drill pipe according to claim 1, characterized in that: The shoulder surface B (10) and the shoulder surface D (50) are processed into mutually matching conical surfaces; an annular groove provided with a sealing member C (60) is opened on the shoulder surface B (10) or the shoulder surface D (50), so that a seal is formed between the shoulder surface B (10) and the shoulder surface D (50) through the sealing member C (60).

5. The double-wall drill pipe according to claim 4, characterized in that: The sealing member C (60) is an O-ring, a rectangular sealing ring or a combined sealing gasket formed by vulcanizing a rubber ring and a metal ring.

6. The double-wall drill pipe according to claim 4, characterized in that: The taper angle of the shoulder surface B (10) is equal to the taper angle of the shoulder surface D (50), both of which are 90°.

7. The double-wall drill pipe according to claim 1, characterized in that: The shoulder surface B (10) is processed into an inner cylindrical surface that is concave inwardly, and the shoulder surface D (50) is processed into an outer cylindrical surface that is convex outwardly and cooperates with the inner cylindrical surface. A U-shaped sealing ring is provided between the inner cylindrical surface and the outer cylindrical surface, so that a seal is formed between the shoulder surface B (10) and the shoulder surface D (50) through the U-shaped sealing ring.

8. The double-wall drill pipe according to claim 1, characterized in that: A plurality of liquid passages (40) distributed along the circumferential direction are provided on the outer wall of the centralizer (4).

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