EP2964988B1

EP2964988B1 - Double shoulder tool joint

Info

Publication number: EP2964988B1
Application number: EP13877149.8A
Authority: EP
Inventors: Koji Sakura; Nobuhide SATO; Tomoyuki NARIKAWA
Original assignee: NKKTubes KK
Current assignee: NKKTubes KK
Priority date: 2013-03-05
Filing date: 2013-03-05
Publication date: 2018-10-24
Anticipated expiration: 2033-03-05
Also published as: WO2014136139A1; CN105008785A; JP6151793B2; EP2964988A4; EP2964988A1; CN105008785B; JP2016513214A

Description

[Technical Field]

This invention relates to a double shoulder tool joint, and more particularly, to a double shoulder tool joint, which has excellent liquid sealability even when repeatedly subject to make-up and break-out operations.

[Background Art]

Drill pipes used for deepwater drilling and horizontal well drilling have conventionally been connected to each other by a tool joint. The tool joint is defined and detailed by API (American Petroleum Institute) standards 5DP. To transmit high torque required for drilling, the tool joint has been formed to have a greater outer diameter than an outer diameter of a pipe body and a smaller inner diameter than an inner diameter of the pipe body. Since there are limits in size of the outer diameter and the inner diameter of the tool joint, the torque performance of the tool joint has generally been lower than the torque performance of the pipe body. Thus, for this case, the use of a double shoulder tool joint having a high torque performance has been suggested (See e.g. JP-T-2007-530875 , hereafter referred to as: Patent Literature 1).
The tool joint disclosed by Patent Literature 1 is a double shoulder tool joint which comprises a pipe joint whereby a box with a female threaded portion formed at one end of a drill pipe and a pin with a male threaded portion formed at one end of another drill pipe are screwed together. The drill pipes are configured so as to be connected together successively by the tool joints with the box and the pin.
The box is provided with a box access sleeve formed parallel to a tip of the box, a female threaded portion formed with a predetermined taper relative to the box access sleeve, a box end sleeve formed parallel to the end of the box, an internal shoulder formed perpendicular to a pipe axis and extended from an end of the box end sleeve, a pipe inner diameter portion to provide a hollow portion along the pipe axis, and a box outer diameter portion to form an outer surface of the box. Also, the pin is provided with a pin nose having an outer surface parallel to the pipe axis, a male threaded portion formed adjacent to the pin nose and having the same taper as the taper of the box, a pin base formed adjacent to the male threaded portion and having an outer surface parallel to the pipe axis, a pin outer diameter portion to form an outer surface of the pin, and an external shoulder formed perpendicular to the pipe axis and extended from the pin outer diameter portion.
The Patent Literature 1 describes that, in the double shoulder tool joint thus configured, since the inner surface of the box access sleeve and the outer surface of the pin base are formed parallel to the pipe axis, and the inner surface of the box end sleeve and the outer surface of the pin nose are formed parallel to the pipe axis, it is possible to increase the thickness of the pin nose and the thickness of the box access sleeve, in comparison to the prior art. This allows for increasing a contact surface area between the tip of the box access sleeve and the external shoulder as well as a contact surface area between the tip of the pin nose and the internal shoulder, enhancing the torque resistance performance and prolonging the life of the tool joint.

[Patent Literature]

JP-T-2007-530875 and JP2012-214863 disclose tool joints.
However, due to the repeated use and repeated making-up operations of the tool joint shoulder functioning as a pressure-receiving surface of a tightening torque, it is difficult to maintain the surface roughness of the tool joint shoulder, so that excellent liquid sealability cannot be expected. Also, when a tool joint alone or a plurality of tool joints joined together are stood on a floor of a rig, no adequate liquid sealability is likely to be achieved due to a possibility of damage to the tip of the pin nose of the pin functioning as a pressure-receiving inner surface.
Accordingly, it is an object of the present invention to provide a double shoulder tool joint, whose a sealing surface (including a pin sealing surface and a box sealing surface) is less subject to damages so that the tool joint has excellent liquid sealability when the drill pipes are interlocked and used.
For achieving the above object, the present invention provides a double shoulder tool joint comprising: a box comprising a box access sleeve including a first contact surface perpendicular to a pipe axis, a female threaded portion having a taper relative to the pipe axis, a box backward sleeve including a second contact surface perpendicular to the pipe axis; and a pin comprising a pin base including a third contact surface to contact the first contact surface, a male threaded portion to be screwed and engaged to the female threaded portion, a pin nose including a fourth contact surface perpendicular to the pipe axis to contact the second contact surface, wherein the double shoulder tool joint further comprises a guard portion including a fifth contact surface provided in a tip portion of the box extended forward from the first contact surface and a sixth contact surface provided in a tip portion of the pin extended forward from the fourth contact surface, wherein the dimensions of the contact surfaces of each of the box and the pin are configured such that the third contact surface firstly contacts the first contacts surface to provide an external surface receiving pressure when the box and pin are engaged with each other in use by screwing the female threaded portion and the male threaded portion to provide threaded engagement.

[2] In the double shoulder tool joint according to [1], the sixth contact surface of the guard portion provided in the tip portion of the pin may be configured to contact a seventh contact surface provided at a position extended backward from the second contact surface of the box backward sleeve.
[3] In the double shoulder tool joint, according to [1] or [2], the fifth contact surface of the guard portion provided in the tip portion of the box may be configured to contact an eighth contact surface provided at a position extended backward from the third contact surface of the pin base.
[4] In the double shoulder tool joint, according to [1] or [2], a seal width between the fourth contact surface and the second contact surface may be 1 mm to 2 mm.
[5] In the double shoulder tool joint, according to [1] or [2], the fourth contact surface may be formed at a position receded from the sixth contact surface of the pin nose with a distance of 2 mm to 5 mm.
[6] In the double shoulder tool joint according to [4] or [5], a surface roughness of each of the second contact surface and the fourth contact surface may be not more than 32S.

According to the invention, it is possible to provide the double shoulder tool joint whose sealing surface (including a pin sealing surface and a box sealing surface) is less subject to damage so that the tool joint has excellent liquid sealability when the drill pipes are interlocked and used.

[FIG. 1]
FIG. 1 is a diagram showing an entire configuration of a double shoulder tool joint and drill pipes in the first embodiment according to the present invention.
[FIG. 2]
FIG. 2 is a cross-sectional view along a pipe axis in FIG. 1 showing the double shoulder tool joint in the first embodiment according to the present invention, wherein the pin and the box are not yet screwed together.
[FIG. 3]
FIG. 3 is a cross-sectional view along a pipe axis in FIG. 1 showing the double shoulder tool joint in the first embodiment according to the present invention, wherein the pin and the box are screwed together.
[ FIG. 4 ]
FIG. 4 is a diagram showing an entire configuration of a double shoulder tool joint and drill pipes in the second embodiment according to the present invention.
[ FIG. 5 ]
FIG. 5 is a cross-sectional view along a pipe axis in FIG. 4 showing the double shoulder tool joint in the second embodiment according to the present invention, wherein the pin and the box are not yet screwed together.
[ FIG. 6 ]
FIG. 6 is a cross-sectional view along a pipe axis in FIG. 4 showing the double shoulder tool joint in the second embodiment according to the present invention, wherein the pin and the box are screwed together.
[ FIG. 7 A]
FIG. 7A is a partial detailed cross-sectional view showing a pin nose.
[ FIG. 7 B]
FIG. 7B is a partial detailed cross-sectional view showing a box backward sleeve.
[ FIG. 7 C]
FIG. 7C is a partial detailed cross-sectional view showing a contact state between the pin nose and the box backward sleeve with the tool joint fastened thereto.
[ FIG. 8 ]
FIG. 8 is a graph showing a relationship between a rotation angle theta and a tightening torque T when the drill pipes are fastened by screwing.
[ FIG. 9 A]
FIG. 9A is an appearance diagram showing the double shoulder tool joint (drill pipe) in the embodiments according to the present invention.
[ FIG. 9 B]
FIG. 9B is an appearance diagram showing a comparative conventional double shoulder tool joint (drill pipe).
[ FIG. 10 ]
FIG. 10 is a VME curve showing a loading condition where the horizontal axis is an axial load, and the vertical axis is a pressure.
[ FIG. 11 ]
FIG. 11 is a cross-sectional view along a pipe axis in FIG. 4 showing the double shoulder tool joint in the third embodiment according to the present invention, wherein a pin 3 comprises a pin guard portion 30 and a box 2 has a box guard portion 20.

[Description of Embodiments]

(The first embodiment of the present invention)

(Entire configuration of a tool joint and drill pipes)

FIG. 1 is a diagram showing an entire configuration of a double shoulder tool joint 1 and drill pipes 4 in the first embodiment according to the present invention. This double shoulder tool joint 1 is a pipe joint of one drill pipe 4 comprising a box 2 with a female threaded portion 23 formed at one end thereof and a pin 3 with a male threaded portion 33 formed at another end thereof, which is configured to be successively connected to the other drill pipe 4 at a female threaded portion 23 of a box 2 or a male threaded portion 33 of a pin 3 of the other drill pipe 4 by screwing. The drill pipes 4 are configured to be connected successively by the tool joint comprising the box 2 and the pin 3.

(Configuration of the tool joint)

FIG. 2 is a cross-sectional view along a pipe axis in FIG. 1 showing the double shoulder tool joint in the first embodiment according to the present invention, wherein the pin and the box are not yet screwed together. FIG. 3 is a cross-sectional view along a pipe axis in FIG. 1 showing the double shoulder tool joint in the first embodiment according to the present invention, wherein the pin and the box are screwed together. The tool joint 1 comprises the box 2 with the female threaded portion 23, and the pin 3 with the male threaded portion 33.
The double shoulder tool joint 1 in the first embodiment of the present invention comprises a box 2 comprising a box access sleeve 22 including a box access sleeve end surface 21 which is a first contact surface perpendicular to a pipe axis 50, a female threaded portion 23 having a taper relative to the pipe axis 50, a box backward sleeve 24 including a box sealing surface 28 which is a second contact surface perpendicular to the pipe axis 50, and a pin 3 comprising a pin base 34 including an external shoulder end surface 35 which is a third contact surface to contact the first contact surface (the box access sleeve end surface 21), a male threaded portion 33 to be screwed and engaged to the female threaded portion 23, a pin nose 32 including a pin sealing surface 39 which is a fourth contact surface perpendicular to the pipe axis 50 to contact the second contact surface (the box sealing surface 28), and further comprises a guard portion (a box guard portion 20 or a pin guard portion 30) including a box access guard surface 20b which is a fifth contact surface provided in a tip portion of the box 2 extended forward (preceded) from the first contact surface (the box access sleeve end surface 21) or a pin nose end surface 31 which is a sixth contact surface provided in a tip portion of the pin 3 extended forward (preceded) from the fourth contact surface (the pin sealing surface 21). Here, the term --forward-- or --preceded-- means the direction shifting toward either of pipe ends from a pipe center of the drill pipe 4 along the pipe axis 50.
Here, the box 2 or the pin 3 includes the guard portion (box guard portion 20 or pin guard portion 30) at its tip portion. It is possible to adopt either of the configuration having the box guard portion 20 only at the box 2, the configuration having the pin guard portion 30 only at the pin 3, and the configuration having the box guard portion 20 and the pin guard portion 30 at the box 2 and the pin 3. The guard portion (box guard portion 20 or pin guard portion 30) and the drill pipe 4 (box 2 or pin 3) are formed as one piece from the same material.
In the configuration having the box guard portion 20 at the box 2, the guard portion (box guard portion 20) is formed to protrude with the box access guard surface 20b which is the fifth contact surface formed at a position preceded from the box access sleeve end surface 21 which is the first contact surface of the box 2 (namely along a direction toward the box access sleeve 22 from the box backward sleeve 24). In the case of the above configuration, the box access guard surface 20b contacts an external shoulder guard end surface 36b which is an eighth contact surface formed at a position extended backward (receded) from the external shoulder end surface 35 of the pin base 34 (namely along a direction returning to the pin base 34 from the pin guard portion 30). Here, the term --backward-- or --receded-- means the direction shifting toward the pipe center from either of pipe ends of the drill pipe 4 along the pipe axis 50.
Df shown in FIG. 2 shows a diameter of the box diameter portion 26, excluding the guard portion, in the box 2. Df is a value prescribed as Rotary Shoulder Connection Bevel Diameter in the API 5DP. The outer diameter dimension Df of the box outer diameter portion 26, which is reduced in diameter by being provided with the guard portion (box guard portion 20), is determined to satisfy the standards of the API 5DP, so that the torque resistance property is secured by sufficiently obtaining a contact surface between the box 2 and the pin 3. According to this structure, even in the configuration with the guard portion, it is possible to obtain a contact width between the box access sleeve end surface 21 and the external shoulder end surface 35 enough, thereby securing the torque resistance property and providing the tool joint and the drill pipe pursuant to the API standards. Further, a diameter of the inner surface 35a in the pin 3 is such configured to fit the above guard portion (box guard portion 20) with keeping a clearance, and satisfies the purpose of the Df value prescribed in the API 5DP, similarly to the box 2.
In the configuration having the pin guard portion 30 at the box 3, the guard portion (pin guard portion 30) is formed to protrude with the pin nose end surface 31 which is the sixth contact surface formed at a position preceded from the pin sealing surface 39 which is the fourth contact surface of the pin 3. In the case of the above configuration, the pin nose end surface 31 contacts an internal shoulder end surface 25b which is a seventh contact surface formed at a position receded from the box sealing surface 28 of the box backward sleeve 24 (namely along a direction returning to the box backward sleeve 22 from the box access sleeve 24).
The box 2 includes a box access sleeve 22 including a box access sleeve end surface 21 which is the first contact surface perpendicular to the pipe axis 50 and an inner surface 22a, the female threaded portion 23 having a taper of 1/6 relative to the pipe axis 50, and the box backward sleeve 24 including the box sealing surface 28 which is the second contact surface perpendicular to the pipe axis 50 and an inner surface 24a.
In addition, the box 2 is provided with a pipe inner diameter portion 41 which provides a hollow portion along the pipe axis 50, and a box outer diameter portion 26 which forms an outer surface of the box 2.
The box outer diameter portion 26 is formed from the pipe outer diameter portion 40 and through a box side tapered shoulder 27 so that the box outer diameter portion 26 gradually increases in diameter. It should be noted that, for clarity of tapering, the threads of the female threaded portion 23 and the male threaded portion 33 are omitted in FIGS. 2 and 3 . Here, the box access sleeve 22 and the box backward sleeve 24 are shown as having their inner surfaces parallel to the pipe axis 50, but are not limited thereto. The box access sleeve 22 and the box backward sleeve 24 may have a taper smaller than the taper of the female threaded portion 23 or the male threaded portion 33, and may, in particular, have a taper of not greater than 1/12 relative to the pipe axis 50. In addition, the term --parallel-- in the present invention includes --substantially parallel having such a small taper--. Further, by the term --perpendicular to the pipe axis-- is meant --not only perpendicular, but also substantially perpendicular thereto--.
The pin 3 includes a pin nose 32 including the pin sealing surface 39 which is the fourth contact surface perpendicular to the pipe axis 50 and an outer surface 32a in correspondence to the inner surface 24a of the box backward sleeve 24, the male threaded portion 33 to be screwed and engaged to the female threaded portion 23, and a pin base 34 including an external shoulder end surface 35 which is the third contact surface perpendicular to the pipe axis 50 and an outer surface 34a in correspondence to the inner surface 22a of the box access sleeve 22a.
In addition, the pin 3 is provided with a pipe inner diameter portion 41 which provides a hollow portion along the pipe axis 50, and a pin outer diameter portion 36 which forms an outer surface of the pin 3.
The pin outer diameter portion 37 is formed from the pipe outer diameter portion 40 and through a pin side tapered shoulder 38 so that the pin outer diameter portion 37 gradually increases in diameter. Here, the pin nose 32 and the pin base 34 are shown as having their outer surfaces parallel to the pipe axis 50, but are not limited thereto. The pin nose 32 and the pin base 34 may have a taper smaller than the taper of the female threaded portion 23 or the male threaded portion 33, and may, in particular, have a taper of not greater than 1/12 relative to the pipe axis 50.
According to the first embodiment of the present invention, the box 2 or the pin 3 includes, at its tip portion, the guard portion (box guard portion 20) which is formed to protrude with the box access guard surface 20b at the position preceded from the box access sleeve end surface 21 or the guard portion (pin guard portion 30) which is formed to protrude with the pin nose end surface 31 at the position preceded from the pin sealing surface 39. Therefore, even though the drill pipe 4 is leaning on a floor surface on the rig, it is possible to suppress of the damage due to the impact of the box access sleeve end surface 21 or the pin sealing surface 39 which should exhibit the sealing function. Namely, the guard portion (box guard portion 20 or pin guard portion 30) can provide both the guard function and the sealing function.

(The second embodiment of the present invention)

The second embodiment of the present invention provides a configuration in that the guard portion (pin guard portion 30) is provided only in the pin 3 in the first embodiment. Therefore, the repetitive explanation is omitted, and the sealing function for keeping the liquid sealability of the inside and outside of the drill pipes 4 and the like will be explained based on the second embodiment.
FIG. 4 is a diagram showing an entire configuration of a double shoulder tool joint and drill pipes in the second embodiment according to the present invention. FIG. 5 is a cross-sectional view along a pipe axis in FIG. 4 showing the double shoulder tool joint in the second embodiment according to the present invention, wherein the pin and the box are not yet screwed together. FIG. 6 is a cross-sectional view along a pipe axis in FIG. 4 showing the double shoulder tool joint in the second embodiment according to the present invention, wherein the pin and the box are screwed together. FIG. 7A is a partial detailed cross-sectional view showing a pin nose. FIG. 7B is a partial detailed cross-sectional view showing a box backward sleeve. FIG. 7C is a partial detailed cross-sectional view showing a contact state between the pin nose and the box backward sleeve with the tool joint fastened thereto.
As shown in FIGS. 4 , 5 , 6 and 7A, the tip of the pin nose 32 is provided with the pin nose end surface 31 as the most prominent portion and the pin sealing surface 39 at a backward extension in the direction toward the pin base 34 from the pin nose end surface 31. Both the pin nose end surface 31 and the pin sealing surface 38 are the surfaces that are perpendicular to the pipe axis 50. Here, when the drill pipes 4 are connected together by screwing the male threaded portion 33 of the pin 3 and the female threaded portion 23 of the box 2, the pin sealing surface 39 is in contact with the box sealing surface 28 in the state where the surface pressure is applied to the pin sealing surface 39 due to the tightening torque. Therefore, the surface roughness of the pin sealing surface 39 is preferably not more than 32S, so as to ensure the sealing function for maintaining the liquid sealability of the inside and outside of the drill pipes 4.
On the other hand, as shown in FIG. 7B, the box backward sleeve 24 is provided with the internal shoulder end surface 25 as the most recessed portion and the box sealing surface 28 at a forward extension in the direction of the box access sleeve 22 from the internal shoulder end surface 25. Both the internal shoulder end surface 25 and the box sealing surface 28 are the surfaces that are perpendicular to the pipe axis 50. Here, when the drill pipes 4 are connected together by screwing the male threaded portion 33 of the pin 3 and the female threaded portion 23 of the box 2, the box sealing surface 28 is in contact with the pin sealing surface 39 in the state where the surface pressure is applied to the box sealing surface 28 due to the tightening torque. Therefore, the surface roughness of the box sealing surface 28 is preferably not more than 32S, so as to ensure the sealing function for maintaining the liquid sealability of the inside and outside of the drill pipes 4.
Here, a distance between the pin sealing surface 39 and the pin nose end surface 31 is set to be L1 as shown in FIG. 7A, and a distance between the box sealing surface 28 and the internal shoulder end surface 25b is set to be L2 as shown in FIG. 7B. When the drill pipes 4 are connected together, in accordance with the male threaded portion 33 being screwed into the female threaded portion 23, the external shoulder end surface 35 firstly contacts the box access sleeve end surface 21, then the pin sealing surface 39 contacts the box sealing surface 28, and further being screwed, the pin nose end surface 31 contacts the internal shoulder end surface 25b. As described above, so as to achieve successive contacts, the dimensions are set as L1 < L2. Here, the dimensions L1 and L2 are set to be within the range of from 2 mm to 5 mm. Namely, the pin sealing surface 39 is formed at a position receded (in the direction returning toward the pin base 34 from the pin guard portion 30) from the sixth contact surface (pin nose end surface 31) of the pin nose 32 with a distance of 2 mm to 5mm. It is provided for making the pin sealing surface 39 less susceptible to the damage such as deformation, dents, even though the drill pipe 4 is leaning on a floor surface over the rig. In addition, assuming that both the tolerances of L1 and L2 are + or - 0.01 mm, the dimensions are set to satisfy L2> L1 +0.02 mm to achieve L1<L2,
A width of a contacting portion between the pin sealing surface 39 and the box sealing surface 28, i.e., a seal width W shown in FIG. 7C, is preferably set to be within a range from 1 mm to 2 mm, in order to ensure the liquid sealability and prevent the poor contact such as uneven contact. Here, the seal width W is a dimension excluding R portions formed at recessed corner portions and C-chamfered portions formed at protruded corner portions.
As shown in FIG. 7C, a width of a clearance between the outer surface 32a of the pin nose 32 and of the inner surface 24a of the box backward sleeve 24 (a pin nose clearance) is configured to be not less than 0.5 mm and not more than 1.2 mm. Similarly, a width of a gap between the outer surface 34a of the pin base 34 and the inner surface 22a of the box access sleeve 22 (a pin base gap) is configured to be not less than 0.5 mm and not more than 1.2 mm. These dimensions are optimal dimensions by which the strength of the structure can be maximized and the structure will not be damaged when the drill pipes 4 are connected successively by the pin 3 and the box 2.

(Dimension example)

For example, the dimensions of each part as shown above can be applied to a drill pipe 4 having an entire length of 13500 mm or less, a pipe outer diameter of 60.2 mm to 168.3 mm, a pipe inner diameter of 38.1 mm to 127.0 mm, and a pin nose length of 12.7 mm to 38.1 mm.
The materials of the box 2 and the pin 3 are not particularly limited, and may be selected appropriately as long as they have the strength to satisfy the requirements of the API standard 5DP.

(Connection of the tool joint)

In the box 2 and the pin 3, the dimensions of the contact surfaces of each of the box 2 and the pin 3 are such configured that the box access sleeve end surface 21 and the external shoulder end surface 35, the box sealing surface 28 and the pin sealing surface 39, and the internal shoulder end surface 25b and the pin nose end surface 31 contact successively with each other, when the box 2 and the pin 3 are engaged with each other by screwing the female threaded portion 23 and the male threaded portion 33, to be made up by threaded engagement. For connecting the drill pipes 4 with the use of the tool joint 1 having the aforementioned dimensions, the box 2 and the pin 3 are firstly positioned to face each other, then the tip of the pin 3 is inserted into an opening of the box 2 and at least one of the box 2 and the pin 3 is rotated, so that the box access sleeve end surface 21 contacts the external shoulder end surface 35, then the box sealing surface 28 contacts the pin sealing surface 39, and the internal shoulder end surface 25 contacts the pin nose end surface 31, successively.
FIG. 8 is a graph showing a relationship between a rotation angle theta and a tightening torque T when the drill pipes are fastened by screwing. In a section R1 (from 0 to theta1) from the contact between the box access sleeve end surface 21 and the external shoulder end surface 35 to the contact between the box sealing surface 29 and the pin sealing surface 39, the tightening torque T increases up to T1 in accordance with the increase in the rotation angle theta. As a result, the external surface receiving pressure is firmly provided. Next, in a section R2 (from theta1 to theta2) to the contact between the internal shoulder end surface 25b and the pin nose end surface 31, the tightening torque T increases up to T2 in accordance with the increase in the rotation angle theta. Further, the tightening torque T increases up to T2 by tightening the box 2 and pin 3 with increasing the rotation angle up to the angle theta3. As a result, the internal surface receiving pressure is firmly provided.
As described above, the contact surface between the internal shoulder end surface 25b and the pin nose end surface 31 acts as internal pressure-receiving surfaces that are closest to the pipe inner diameter portion 41. The contact surface between the pin sealing surface 39 and the box sealing surface 28 that are located in the vicinity of and in parallel with the contact surface between the internal shoulder end surface 25b and the pin nose end surface 31 act as sealing surfaces. In addition, the contact surface between the box access sleeve end surface 21 and the external shoulder end surface 35 that are closest to the pipe outer diameter portion 40 acts as an outer pressure-receiving surface.

(Make-up/break-out test)

The performance evaluation of the tool joint 1 in the embodiment according to the present invention, i.e. double shoulder tool joint with a sealing surface has been conducted in comparison with a double shoulder tool joint with no sealing surface, i.e. without a box sealing surface and a pin sealing surface.
FIG. 9A is an appearance diagram showing the double shoulder tool joint (drill pipe) in the embodiment according to the present invention, and FIG. 9B is an appearance diagram showing a comparative conventional double shoulder tool joint (drill pipe). As shown in FIG. 4A, the double shoulder tool joint in the embodiment according to the present invention is formed with the pin sealing surface 39 at a position receded from the pin nose end surface 31 at the tip of the pin nose 32. On the other hand, the double shoulder tool joint in the comparative example has no portion corresponding to the pin sealing surface, in which the tip of the pin nose 32 is entirely a pin nose end surface.
Here, specific configurations of the drill pipe and tool joint are as follows.

Drill pipe: Outer diameter of 88.9 mm and pipe thickness of 11.40 mm Grade G105 (according to AIP 5DP)
Tool joint: DSTJ-SST39

The test results for performance evaluation are shown as follows. Prior to the pressure test, the make-up/break-out operations have been carried out for 50 times in order to provide the pin sealing surface, the box sealing surface, the pin nose end surface and the internal shoulder end surface as watertight and airtight surfaces with wears corresponding to the actual work. After the make-up/break-out operations for 50 times have been completed, the baking process has been carried out. The baking process is to remove the influence on the sealing property of the lubricant used during the make-up/break-out operations. For the two specimens shown in FIGS. 4A and 4B for which the aforementioned operations have been finished, the internal pressure and tensile complex load test including the bending load was carried out. This test was carried out in order to confirm the advantages in the internal pressure-resistant property thanks to the sealing effect achieved by the contact between the box sealing surface 28 and the pin sealing surface 39.
FIG. 10 is a VME curve showing a loading condition where the horizontal axis is an axial load and the vertical axis is a pressure.

(Test condition)

As to the test condition, the points of the occurrence of leakage from the joint when the internal pressure is increased from LP (Load Point) 1 to LP13 along the VME curve shown in FIG. 10 were investigated. When the load is applied to the LP2 to LP2B, only the bending load (7.5 degrees/100ft) (7.5 degrees/30.5 meters) was applied toward the LP2B. Subsequently, the internal pressure was raised by 137.9 bar/step (2000 psi/step).

(Test results)

Specimen No. 1 (with seal)

No leakage occurred in the specimen No. 1 (the double shoulder tool joint according to the present invention) as shown in FIG. 9A.
Final LP13: Total axial load of 1286 kN (289.0 kips, 131 tonf), tensile load of 667.7 kN (150.1 kips, 68 tonf), and internal pressure of 27000 psi (186.2 MPa).
The test was terminated due to the limitation of the test facility FST.

Specimen No. 2 (without seal)

The leakage occurred in the specimen No. 2 (the conventional double shoulder tool joint) as shown in FIG. 9B.
LP6: Total axial load of 2111kN (474.5 kips, 215 tonf), tensile load of 1767kN (397.3 kips, 180 tonf), and internal pressure of 15000 psi pressure (103.4 MPa)
The pressure drop was actually observed at LP5 (Tensile load of 2151kN (483.5 kips) and internal pressure of 89.632 MPa (13000 psi)) which is prior to LP6.
According to the second embodiment of the present invention, the following effects are achieved.

(1) The pin sealing surface 39 as the sealing surface is provided at a portion (another surface) receded from the pin nose end surface 31, so that the pin sealing surface 39 is not contiguous to the end surface pressure-receiving surface of the pipe. Therefore, even though the drill pipe 4 is leaning on a floor surface on the rig, the sealing surface will not be damaged by the contact of the sealing surface, and also become less susceptible to the damage applied from the side surfaces.
(2) Apart from the contact surfaces of the internal shoulder end surface 25b and the pin nose end surface 31 that function as an internal pressure-receiving surface, the too joint 1 is configured such that the box sealing surface 28 contacts the pin sealing surface 39 firmly, so that there is no need for the strict dimensional control or the like for controlling a tightening margin in the radial direction. In addition, since the sealing surfaces are perpendicular to the pipe axis and the sealing surface is neither spherical nor inclined with respect to the pipe axis, the dimension measurement during the production can be easily performed so that there is no need to prepare a special measuring instrument.
(3) In the technique of the DSTJ (double shoulder tool joint), the tightening (make-up) torque as in the prior art makes the external pressure-receiving surfaces (external pressure-receiving surfaces in contact between the external shoulder end surface 35 and the box access sleeve end surface 21) firstly contact with each other, then makes the internal pressure-receiving surfaces (the internal pressure-receiving surfaces in contact between the internal shoulder end surface 25b and the pin nose end surface 31. At this time, the sealing surfaces that are the contact surfaces between the box sealing surface 28 and the pin sealing surface 39 according to the present invention are located in the portion closest to the internal pressure-receiving surfaces. Accordingly, it is possible to provide a configuration that is less susceptible to the damage while the strength of the pin tip is maintained, and to suppress the leakage due to the rise of the internal pressure securely. Therefore, it is possible to provide a double shoulder tool joint in which the sealing surface (at the tip pin nose) of the tool joint is less susceptible to the damage and excellent in liquid sealability when the drill pipes are connected with each other.
(4) By configuring the seal width to be from 1 mm to 2 mm, a level difference from the internal pressure-receiving surface to the sealing surface to be from 2 mm to 5 mm, and the roughness of the sealing surface to be not more than 32S, it is possible to provide the tool joint and the drill pipe with the same which can withstand the average drilling mud pressure of 48.26 MPa (7000 psi) as the internal pressure.
(5) The water hole becomes a large opening after being repeatedly eroded by hydraulic pressure via a through-crack such as gap, fatigue crack as a leakage path, thereby causes the pressure loss which will reduce the drilling efficiency of the drill pipe tip bit, or the rupture of the water hole which will lead to the troubles in operation and a large loss in time. However, the present embodiment is configured to comprises a sealing surface by the box sealing surface 28 and the pin sealing surface 39 apart from the internal pressure-receiving surface, it is possible to suppress the water hole by the sealing performance, to prevent a large trouble in operation of the rig, to shorten the downtime, and to improve the lifetime of the drill pipe per se.

(The third embodiment of the present invention)

The third embodiment of the present invention provides the configuration in which the box 2 is provided with a guard portion (box guard portion 20) in the first embodiment. Therefore, the repetitive explanation is omitted, and the configuration in which the pin 3 comprises the pin guard portion 30 and the box 2 comprises the box guard portion 20 will be explained with referring to FIG. 11 .
FIG. 11 is a cross-sectional view along a pipe axis in FIG. 4 showing the double shoulder tool joint in the third embodiment according to the present invention, wherein a pin 3 comprises a pin guard portion 30 and a box 2 has a box guard portion 20.
In the box 2 and the pin 3, the dimensions of the contact surfaces of each of the box 2 and the pin 3 are such configured that the box access guard surface 20b and the external shoulder guard end surface 36b, the box access sleeve end surface 21 and the external shoulder end surface 35, the box sealing surface 28 and the pin sealing surface 39, and the internal shoulder end surface 25b and the pin nose end surface 31 contact successively with each other, when the box 2 and the pin 3 are engaged with each other by screwing the female threaded portion 23 and the male threaded portion 33, to be made up by threaded engagement. For connecting the drill pipes 4 with the use of the tool joint 1 having the aforementioned dimensions, the box 2 and the pin 3 are firstly positioned to face each other, then the tip of the pin 3 is inserted into an opening of the box 2 and at least one of the box 2 and the pin 3 is rotated, so that the box access guard surface 20b firstly contacts the external shoulder guard end surface 36b, the box access sleeve end surface 21 secondly contacts the external shoulder end surface 35, the box sealing surface 28 thirdly contacts the pin sealing surface 39, and the internal shoulder end surface 25 fourthly contacts the pin nose end surface 31, successively.
According to the third embodiment, it is configured such that the pin 3 comprises the pin guard portion 30 and the box 2 comprises the box guard portion 20, so that it is possible to exhibit the guard function by the guard portion (box guard portion 20, pin guard portion 30) and to enhance the seal function of the drill pipe against the internal pressure and the external pressure.
In addition, the present invention, various modifications are possible within the scope is not limited to the embodiments described above, without departing from the spirit or change techniques of the present invention.
Although the invention has been described with respect to the specific embodiments for complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.

[Industrial Applicability]

[Reference Sings List]

1: Tool joint
2: Box
3: Pin
4: Drill pipe
20: Guard portion (box guard portion)
20a: Inner surface
20b: Box access guard surface (Fifth surface)
21: Box access sleeve end surface (First surface)
22: Box access sleeve
23: Female threaded portion
24: Box backward sleeve
24a: Inner surface
25a: Inner surface
25b: Internal shoulder end surface (Seventh surface)
26: Box outer diameter portion
27: Box side tapered shoulder
28: Box sealing surface (Second surface)
30: Guard portion (pin guard portion)
31: Pin nose end surface (Sixth surface)
32: Pin nose
32a: Outer surface
33: Male threaded portion
34a: Outer surface
35: External shoulder end surface (Third surface)
36a: Inner surface
36b: External shoulder guard end surface (Eighth surface)
37: Pin outer diameter portion
38: Pin side tapered shoulder
39: Pin sealing surface (Fourth surface)
40: Pipe outer diameter portion
41: Pipe inner diameter portion
50: Pipe axis

Claims

A double shoulder tool joint (1) comprising:
a box (2) comprising a box access sleeve including a first contact surface (21) perpendicular to a pipe axis (50), a female threaded portion (23) having a taper relative to the pipe axis, a box backward sleeve (24) including a second contact surface (28) perpendicular to the pipe axis; and

a pin (3) comprising a pin base (34) including a third contact surface (35) to contact the first contact surface (21), a male threaded portion (33) to be screwed and engaged to the female threaded portion, a pin nose (32) including a fourth contact surface (39) perpendicular to the pipe axis to contact the second contact surface (28),

wherein the double shoulder tool joint further comprises a guard portion (20, 30) including a fifth contact surface (20b) provided in a tip portion of the box extended forward from the first contact surface and a sixth contact surface (31) provided in a tip portion of the pin extended forward from the fourth contact surface (39),

wherein the sixth contact surface (31) of the guard portion provided in the tip portion of the pin is configured to contact a seventh contact surface (25b) provided at a position extended backward from the second contact surface (28) of the box backward sleeve, and

wherein the dimensions of the contact surfaces of each of the box and the pin are configured such that the first contact surface (21) and the third contact surface (35), the second contact surface (28) and the fourth contact surface (39), and the sixth contact surface (31) and the seventh contact surface (25b) contact successively with each other when the box and pin are engaged with each other by screwing the female threaded portion and the male threaded portion to provide threaded engagement.
The double shoulder tool joint (1), according to claim 1, wherein the fifth contact surface (20b) of the guard portion provided in the tip portion of the box (2) is configured to contact an eighth contact surface (36b) provided at a position extended backward from the third contact surface (35) of the pin base.
The double shoulder tool joint (1), according to claim 1, wherein a seal width between the fourth contact surface (39) and the second contact surface (28) is 1 mm to 2 mm.
The double shoulder tool joint (1), according to claim 1, wherein the fourth contact surface (39) is formed at a position receded from the sixth contact surface (31) of the pin nose with a distance of 2 mm to 5 mm.
The double shoulder tool joint (1) according to claim 3 or 4, wherein a surface roughness of each of the second contact surface (28) and the fourth contact (39) surface is not more than 32S.