Method of manufacturing screw joint unit

Abstract

To provide a method of manufacturing a screw joint unit enabling suppression of corotation of a coupling with a metal tube when coupled.SOLUTION: A method of manufacturing a screw joint unit (100) comprises a preparation step and a fastening step. In the preparation step, a metal pipe (10) and a coupling (20) are prepared. The metal pipe (10) comprises a pin (11M) at its pipe end portion. The coupling (20) comprises boxes (21M, 21F) at both pipe end portions. In the fastening step, the pin (11M) and box (21M) are fastened. The pin (11M) and box (21M) have rotation stop means which mechanically stops relative rotation of the pin (11M) and box (21M). First fastening torque for the pin (11M) and box (21M) is larger than second fastening torque for pin (11F) and box (21F). The pin (11F) is provided at a pipe end portion of the other metal pipe (10).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing a threaded joint unit. [Background technology]

[0002] 2. Description of the Related Art In oil wells, natural gas wells, and the like, a large number of metal pipes called oil country tubular goods are used to extract underground resources. The metal pipes are connected to each other by threaded joints.

[0003] The types of threaded joints for metal pipes are broadly classified into integral type and coupling type. In the case of the integral type, the metal pipes to be connected each have a male threaded portion at one pipe end and a female threaded portion at the other pipe end. The metal pipes are connected to each other by inserting the male threaded portion of one metal pipe into the female threaded portion of the other metal pipe and fastening them. In the case of the coupling type, metal pipes having male threaded portions at both pipe ends are connected to each other by a coupling. The coupling is a pipe material different from the metal pipes to be connected, and has female threaded portions at both pipe ends. The male threaded portions of the metal pipes are inserted into the female threaded portions of the coupling and fastened. In general, the pipe end of the metal pipe having the male threaded portion is called a pin, and the pipe end of the metal pipe or the coupling having the female threaded portion is called a box.

[0004] As described in Patent Document 1, when metal pipes are connected by a coupling-type threaded joint, one of the pins provided at both ends of the metal pipes is fastened to a coupling box at a factory, and the other pin is fastened to a coupling box at a site such as an oil well. The pin and box fastened at the factory are called a mill end, and the pin and box fastened at the site are called a field end. Each metal pipe is shipped from the factory to the site with a coupling fastened only to the pin at the mill end. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 195621 Summary of the Invention [Problem to be solved by the invention]

[0006] At the work site, a metal tube is inserted from the field end side into the coupling with the other metal tube attached to the mill end side. More specifically, the metal tube on the mill end side and the metal tube on the field end side are each held by a clamp, and the metal tube on the field end side is screwed into the coupling to fasten the pin and the box. At this time, since the coupling is not held by the clamp, when the metal tube on the field end side is screwed into the coupling, the coupling rotates together with the metal tube on the field end side, and the relative rotation amount between the metal tube on the field end side and the metal tube on the mill end side may increase. When the torque and the number of revolutions at the time of fastening are recorded to create a torque chart and the pass / fail of the fastening quality of the threaded joint is judged based on the shape of the chart, it becomes difficult to judge the pass / fail of the fastening quality if the coupling rotates together. More specifically, the inclination of the torque chart changes due to the coupling rotating together, and the shape of the chart becomes similar to the shape of the chart at the time of the threaded joint yielding, making it difficult to distinguish between the two. Therefore, even if the threaded joint does not yield, the fastening quality of the threaded joint may be judged to be poor. In this case, tasks such as pulling up the metal pipe, dismantling the threaded joint, and checking for deformation of the threaded joint are required, increasing the time and effort required for fastening the threaded joint.

[0007] Coupling rotation may also occur due to the lubricant (dope) applied to the threaded joint. For example, in threaded joints used in environments requiring high torque resistance, such as deep wells and horizontal drilling wells, wedge threads are sometimes used. A wedge thread is a thread whose thread width changes in the axial direction of the threaded joint, and torque can be generated by the wedge effect of the entire thread. In a threaded joint having a wedge thread, the stabbing surface of the male thread portion and the stabbing surface of the female thread portion come into contact with each other when the fastening is completed, and the load surface of the male thread portion and the load surface of the female thread portion come into contact with each other, eliminating any gaps between the stabbing surfaces and between the load surfaces. Therefore, the lubricant applied to the male thread portion and the female thread portion prior to fastening is sealed in the thread portion, and the pressure of this lubricant (dope pressure) increases rapidly. On the other hand, in a threaded joint having a parallel thread or a thread similar to a buttress thread of the American Petroleum Institute standard, a gap exists between the stabbing surface of the male thread portion and the stabbing surface of the female thread portion after fastening is completed, so the dope pressure is less likely to become as high as in a wedge thread. In a threaded joint having a wedge thread, the problem of the apparent torque increasing during fastening is likely to occur due to a sudden increase in dope pressure. For example, when the fastening of a threaded joint is torque-managed during fastening on the mill end side, if the apparent torque increases due to high dope pressure, it may be determined that the fastening is complete even though sufficient torque is not actually applied to the threaded joint. After the fastening of the threaded joint is completed, the dope pressure is released over time. However, since sufficient torque is not applied to the threaded joint on the mill end side, the coupling is likely to rotate when fastening is performed on the field end side.

[0008] The increased dope pressure in the threaded portion also makes the threaded joint more susceptible to low breakout torque problems. More specifically, regardless of whether it is the mill end or the field end, if the dope pressure during fastening is high and the apparent torque is high, the threaded joint is judged to be fastened without sufficient torque being applied. If sufficient torque is not applied to the threaded joint, breakout (loosening) of the threaded joint may occur at low torque. For example, if a problem such as a metal pipe getting stuck occurs in a horizontal drilling well and the threaded joint is rotated in the opposite direction to when it was fastened to resolve the problem, a breakout of the threaded joint may occur unintentionally.

[0009] An object of the present disclosure is to provide a method for manufacturing a threaded joint unit capable of suppressing co-rotation of a coupling during make-up. Alternatively, an object of the present disclosure is to provide a method for manufacturing a threaded joint unit capable of suppressing the low breakout torque problem of a threaded joint. [Means for solving the problem]

[0010] The manufacturing method of a threaded joint unit according to the present disclosure includes a preparing step and a fastening step. In the preparing step, a metal pipe and a tubular coupling are prepared. A first pin is provided at a pipe end of the metal pipe. The first pin includes a male thread portion. Boxes are provided at both pipe ends of the coupling. A first box, which is one of the boxes, and a second box, which is the other of the boxes, each include a female thread portion. The second box has the same shape and dimensions as the first box. In the fastening step, the first pin is inserted into the first box, and the first box is rotated relatively to the first pin to fasten the first pin and the first box. The first pin and the first box have a rotation stopping means. The rotation stopping means mechanically stops the relative rotation of the first box with respect to the first pin. A first fastening torque when the first pin is fastened to the first box is greater than a second fastening torque that is predetermined as a torque when the second pin is fastened to the second box after the fastening of the first pin and the first box is completed. The second pin is provided at an end of a metal pipe different from the metal pipe. The second pin includes a male thread. The second pin has the same shape and dimensions as the first pin.

[0011] Another method for manufacturing a threaded joint unit according to the present disclosure includes a preparing step, an applying step, and a fastening step. In the preparing step, a metal tube and a tubular coupling are prepared. A pin is provided at a pipe end of the metal tube. The pin includes a pin seal surface and a male thread portion. A box is provided at a pipe end of the coupling. The box includes a box seal surface and a female thread portion. In the applying step, a lubricant is applied to the pin seal surface and the male thread portion, and also to the box seal surface. However, in the applying step, the lubricant is not applied to the female thread portion. In the fastening step, the pin and the box are fastened together after the lubricant has been applied. When the fastening of the pin and the box is completed, the insertion surface of the male thread portion contacts the insertion surface of the female thread portion, the load surface of the male thread portion contacts the load surface of the female thread portion, and the pin seal surface contacts the box seal surface. Effect of the Invention

[0012] According to the manufacturing method of a threaded joint unit according to the present disclosure, it is possible to suppress co-rotation of the coupling during make-up. Alternatively, according to the manufacturing method of a threaded joint unit according to the present disclosure, it is possible to suppress the problem of low breakout torque of the threaded joint. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a vertical sectional view showing a schematic configuration of a threaded joint unit in a first embodiment. [Diagram 2] FIG. 2 is a diagram showing an example of a rotation stopping means in the threaded joint unit shown in FIG. [Diagram 3] FIG. 3 is a diagram showing another example of the rotation stopping means in the threaded joint unit shown in FIG. [Figure 4] FIG. 4 is a diagram illustrating an example of the configuration of a threaded portion when the threaded joint unit has the rotation stopping means shown in FIG. [Figure 5A] FIG. 5A is a schematic view illustrating the method for manufacturing the threaded joint unit according to the first embodiment. [Figure 5B] FIG. 5B is a schematic view for illustrating the method of manufacturing the threaded joint unit according to the first embodiment. [Figure 5C] FIG. 5C is a schematic view illustrating the method for manufacturing the threaded joint unit according to the first embodiment. [Figure 5D] FIG. 5D is a schematic view illustrating the method for manufacturing the threaded joint unit according to the first embodiment. [Figure 5E] FIG. 5E is a schematic view illustrating the method for manufacturing the threaded joint unit according to the first embodiment. [Figure 6] FIG. 6 is a torque chart on the field end side when the fastening torques on the mill end side and the field end side are substantially equal. [Figure 7A] FIG. 7A is a schematic view illustrating a method for manufacturing a threaded joint unit according to a second embodiment. [Figure 7B]FIG. 7B is a schematic view illustrating the method for manufacturing the threaded joint unit according to the second embodiment. [Figure 7C] FIG. 7C is a schematic view illustrating a method for manufacturing a threaded joint unit according to the second embodiment. [Figure 7D] FIG. 7D is a schematic view illustrating the method of manufacturing the threaded joint unit according to the second embodiment. [Figure 8] FIG. 8 is a graph showing the relationship between the amount / area of ​​lubricant applied to a threaded joint and the ratio of breakout torque to make-up torque. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] A manufacturing method of a threaded joint unit according to an embodiment includes a preparing step and a fastening step. In the preparing step, a metal pipe and a tubular coupling are prepared. A first pin is provided at a pipe end of the metal pipe. The first pin includes a male thread portion. Boxes are provided at both pipe ends of the coupling. A first box, which is one of the boxes, and a second box, which is the other of the boxes, each include a female thread portion. The second box has the same shape and dimensions as the first box. In the fastening step, the first pin is inserted into the first box, and the first box is rotated relatively to the first pin to fasten the first pin and the first box. The first pin and the first box have a rotation stopping means. The rotation stopping means mechanically stops the relative rotation of the first box with respect to the first pin. A first fastening torque when the first pin is fastened to the first box is greater than a second fastening torque that is predetermined as a torque when the second pin is fastened to the second box after the fastening of the first pin and the first box is completed. The second pin is provided at an end of a metal pipe different from the metal pipe. The second pin includes a male thread. The second pin has the same shape and dimensions as the first pin (first configuration).

[0015] In the manufacturing method of the threaded joint unit according to the first configuration, the first pin provided at the pipe end of the metal pipe is fastened to the first box of the coupling under torque management. That is, the first pin is fastened to the first box with a first fastening torque within a target range. The first fastening torque is greater than a second fastening torque, which is a torque when the second pin provided at the pipe end of another metal pipe is fastened to the second box of the coupling. In this way, by fastening the first pin and the first box with a high torque in advance, the coupling is less likely to rotate in a direction to tighten the first pin and the first box, that is, in a direction to load a torque on the first pin and the first box. Therefore, when the second pin is rotated relative to the coupling when the second pin and the second box are fastened, the coupling is less likely to rotate together with the second pin. Therefore, it is possible to suppress co-rotation of the coupling when the second pin and the second box are fastened.

[0016] In the first configuration, the yield torque of the threaded joint unit is T y When the predetermined standard fastening torque is T0, the first fastening torque is T1, and the second fastening torque is T2, T y , T0, T1, and T2 can satisfy the following formulas (second configuration): T0<0.95×T y T0 <T1<T y ·T0-6780[Nm]≦T2≦T0+6780[Nm]

[0017] In the second configuration, the first fastening torque T1 is T0×1.25≦T1 <T y It is preferable that the following is satisfied (third configuration).

[0018] In the third configuration, the first fastening torque T1 when fastening the first pin and the first box is ensured to be 125% or more of the standard fastening torque T0 that is the reference for the second fastening torque T2 when fastening the second pin and the second box. In this case, co-rotation of the coupling when fastening the second pin and the second box is more easily suppressed.

[0019] In any of the first to third configurations, the manufacturing method of the threaded joint unit may further include an applying step. In the applying step, a lubricant is applied to at least one of the first pin and the first box before the fastening step. In the fastening step, the first pin and the first box may be fastened together with the relative rotational speed of the first box with respect to the first pin set to 5 rpm or less (fourth configuration).

[0020] In the fourth configuration, after applying lubricant to at least one of the first pin and the first box, the first pin and the first box are fastened at a relatively low speed of 5 rpm. In this case, the pressure of the lubricant (dope pressure) in the male thread portion and the female thread portion is unlikely to become high, so that it is possible to prevent the torque load on the first pin and the first box from becoming insufficient due to the dope pressure. As a result, it is possible to suppress the co-rotation of the coupling when the second pin and the second box are fastened. It is also possible to suppress the low breakout torque problem of the first pin and the first box.

[0021] In any of the first to fourth configurations, when the fastening of the first pin and the first box is completed, the insertion surface of the male threaded portion of the first pin may contact the insertion surface of the female threaded portion of the first box, and the load surface of the male threaded portion of the first pin may contact the load surface of the female threaded portion of the first box (fifth configuration).

[0022] A manufacturing method of a threaded joint unit according to another embodiment includes a preparing step, an applying step, and a fastening step. In the preparing step, a metal pipe and a tubular coupling are prepared. A pin is provided at a pipe end of the metal pipe. The pin includes a pin seal surface and a male thread portion. A box is provided at a pipe end of the coupling. The box includes a box seal surface and a female thread portion. In the applying step, a lubricant is applied to the pin seal surface and the male thread portion, and also to the box seal surface. However, in the applying step, the lubricant is not applied to the female thread portion. In the fastening step, the pin and the box are fastened together after the lubricant has been applied. When the fastening of the pin and the box is completed, the insertion surface of the male thread portion contacts the insertion surface of the female thread portion, the load surface of the male thread portion contacts the load surface of the female thread portion, and the pin seal surface contacts the box seal surface (sixth configuration).

[0023] When the pin and the box are fastened, the lubricant is usually applied to the entire threaded portion and seal surface of both the pin and the box. However, in the sixth configuration, the lubricant is applied to the pin seal surface and the male threaded portion of the pin, and the lubricant is applied to the box seal surface of the box, but the lubricant is not applied to the female threaded portion. This reduces the amount of surplus lubricant, and the surplus lubricant is easily discharged from between the male threaded portion and the female threaded portion as the pin is screwed into the box. Therefore, even if the male threaded portion and the female threaded portion are configured as wedge threads, the lubricant pressure (dope pressure) in the male threaded portion and the female threaded portion can be reduced. Therefore, it is possible to prevent the torque load on the pin and the box from becoming insufficient due to high dope pressure. As a result, it is possible to suppress the low breakout torque problem of the pin and the box.

[0024] In the sixth configuration, the area of ​​the pin to which the lubricant is applied is defined as S [cm 2 ], the amount of lubricant applied to the pin is V [cm 3 ], it is preferable that 0.005×S≦V≦0.040×S (seventh configuration).

[0025] In the seventh configuration, the amount V of the lubricant applied to the pin is 0.005 times or more and 0.040 times or less of the lubricant application area S of the pin. In this case, the dope pressure in the male thread portion and the female thread portion is more likely to decrease. This makes it more difficult for the low breakout torque problem of the pin and the box to occur.

[0026] In the sixth or seventh configuration, in the fastening step, the pin and the box can be fastened together by setting the relative rotation speed of the pin to the box at 5 rpm or less (eighth configuration).

[0027] In the eighth configuration, the pin and the box are fastened at a relatively low speed of 5 rpm after applying lubricant to the pin and the box. In this case, the dope pressure in the male and female threads is unlikely to become high. Therefore, the low breakout torque problem of the pin and the box can be more unlikely to occur.

[0028] The method for manufacturing a threaded joint unit according to any of the sixth to eighth configurations can further include a step of re-tightening the pin and the box after the fastening step has been completed and a predetermined time has elapsed (ninth configuration).

[0029] Even if dope pressure is generated when the pin and the box are fastened, the dope pressure is released over time. Therefore, in the ninth configuration, the pin and the box are fastened again after the fastening of the pin and the box is completed and a predetermined time has passed and the dope pressure is released. This makes it possible to increase the breakout torque of the pin and the box. Therefore, the problem of low breakout torque of the pin and the box can be more effectively suppressed.

[0030] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and the same description will not be repeated.

[0031] First Embodiment [Threaded joint unit configuration] Fig. 1 is a diagram showing a schematic configuration of a threaded joint unit 100 in a first embodiment. Fig. 1 shows a cross section (longitudinal cross section) of the threaded joint unit 100 cut along a plane including a pipe axis X of the threaded joint unit 100.

[0032] 1, a threaded joint unit 100 includes a metal pipe 10 and a coupling 20. The metal pipe 10 is connected by the coupling 20 to another metal pipe 10 indicated by a two-dot chain line in FIG.

[0033] A pin 11M is provided at one pipe end of each metal pipe 10. A pin 11F is provided at the other pipe end of each metal pipe 10. Each of the pins 11M, 11F includes a pin seal surface 111 and a male thread portion 112. Hereinafter, the pins 11M, 11F will be collectively referred to as pin 11 unless there is a need to particularly distinguish between the pins 11M, 11F.

[0034] The pin seal surface 111 and the male thread portion 112 are provided on the outer peripheral surface of the pin 11. The pin seal surface 111 is a side surface of a rotationally symmetric body whose rotation axis is the pipe axis X. The pin seal surface 111 is disposed, for example, at the tip portion of the pin 11. In the example shown in FIG. 1 , the male thread portion 112 is disposed on the pipe main body 12 side with respect to the pin seal surface 111. The male thread portion 112 extends from the vicinity of the pin seal surface 111 to the vicinity of the pipe main body 12.

[0035] Boxes 21M, 21F are provided at both pipe ends of the coupling 20. The box 21M is fastened to the pin 11M of one metal pipe 10. The box 21F is fastened to the pin 11F of the other metal pipe 10. The boxes 21M, 21F each include a box seal surface 211 and a female thread portion 212. Hereinafter, when there is no need to particularly distinguish between the boxes 21M, 21F, the boxes 21M, 21F will be collectively referred to as the box 21.

[0036] The box seal surface 211 is provided on the inner peripheral surface of the box 21 corresponding to the pin seal surface 111. The box seal surface 211 is a side surface of a rotationally symmetric body whose rotation axis is the pipe axis X. When the fastening between the box 21 and the pin 11 is completed, the box seal surface 211 comes into contact with the pin seal surface 111 over the entire circumference.

[0037] In this embodiment, the box seal surface 211 corresponds to the pin seal surface 111 provided at the tip of the pin 11, and is provided at the back side of the box 21. However, the pin seal surface 111 may be provided, for example, at the end of the pin 11 on the pipe main body 12 side or at the middle part of the male thread portion 112. In this case, the box seal surface 211 corresponds to the pin seal surface 111 and is provided at the pipe end side of the box 21 or at the middle part of the female thread portion 212.

[0038] The female thread portion 212 is provided on the inner peripheral surface of the box 21 in correspondence with the male thread portion 112. The female thread portion 212 corresponds to the male thread portion 112 and extends from near the box seal surface 211 to near the pipe end surface of the box 21. The female thread portion 212 is configured to mesh with the male thread portion 112.

[0039] When the pin 11 and the box 21 are fastened, the pin 11 is inserted into the box 21, and the box 21 rotates around the tube axis X relative to the pin 11. The pin 11 and the box 21 have a rotation stopping means that mechanically stops the relative rotation of the box 21 with respect to the pin 11. The rotation stopping means substantially stops the relative rotation of the box 21 with respect to the pin 11 by abutting a part of the pin 11 with a part of the box 21. Fastening of the pin 11 and the box 21 is completed by stopping the relative rotation of the pin 11 and the box 21.

[0040] The rotation stopping means is, for example, the engagement between the male thread portion 112 and the female thread portion 212. Below, a case where the rotation stopping means is the engagement between the male thread portion 112 and the female thread portion 212 will be described with reference to Fig. 2. Fig. 2 is a partially enlarged view of the male thread portion 112 and the female thread portion 212 when viewed in vertical cross section of the threaded joint unit 100.

[0041] 2, the male thread portion 112 and the female thread portion 212 are configured by wedge threads. In the male thread portion 112, the width of the thread narrows toward the tip side of the pin 11. In the female thread portion 212, the width of the thread groove narrows toward the back side of the box 21, corresponding to the male thread portion 112.

[0042] 2, the male thread portion 112 includes a crest surface 112a, a groove root surface 112b, a stabbing flank 112c, and a load flank 112d. The crest surface 112a is connected to the groove root surface 112b via the stabbing flank 112c and the load flank 112d.

[0043] The female thread portion 212 includes a thread crest surface 212a, a thread groove bottom surface 212b, an insertion surface 212c, and a load surface 212d. When the pin 11 and the box 21 are in a state where the fastening of the pin 11 and the box 21 is completed, the insertion surface 112c of the male thread portion 112 contacts the insertion surface 212c of the female thread portion 212, and the load surface 112d of the male thread portion 112 contacts the load surface 212d of the female thread portion 212. The insertion surfaces 112c, 212c contact each other, and the load surfaces 112d, 212d contact each other, and the male thread portion 112 and the female thread portion 212 are engaged with each other, thereby stopping the relative rotation of the box 21 with respect to the pin 11.

[0044] 2, in the fastening completed state, the thread crest surface 112a of the male thread portion 112 faces the thread groove bottom surface 212b of the female thread portion 212 with a gap therebetween, and the thread groove bottom surface 112b of the male thread portion 112 contacts the thread crest surface 212a of the female thread portion 212. However, in the fastening completed state, the thread crest surface 112a of the male thread portion 112 may also contact the thread groove bottom surface 212b of the female thread portion 212. Also, in the fastening completed state, the thread groove bottom surface 112b of the male thread portion 112 may face the thread crest surface 212a of the female thread portion 212 with a gap therebetween.

[0045] Fig. 3 is a diagram showing another example of the rotation stopping means. In the example of Fig. 3, the pin 11 includes a pin shoulder surface 113. The pin shoulder surface 113 is provided, for example, on a tube end surface of the pin 11. The pin shoulder surface 113 may be provided on the end of the pin 11 on the tube main body 12 side (Fig. 1) or in the middle of the male thread portion 112.

[0046] The box 21 includes a box shoulder surface 213. The box shoulder surface 213 is provided on the box 21 in correspondence with the pin shoulder surface 113. When the fastening of the pin 11 and the box 21 is complete, the box shoulder surface 213 abuts against the pin shoulder surface 113. The abutment of the annular pin shoulder surface 113 and the box shoulder surface 213 stops the relative rotation of the box 21 with respect to the pin 11.

[0047] When the rotation stopping means is the abutment of the pin shoulder surface 113 and the box shoulder surface 213, the male thread portion 112 and the female thread portion 212 may not be configured as wedge threads. In other words, when the relative rotation of the box 21 with respect to the pin 11 is stopped by the pin shoulder surface 113 and the box shoulder surface 213, the load surface 112d of the male thread portion 112 may contact the load surface 212d of the female thread portion 212 in the fastening completed state of the pin 11 and the box 21, while the insertion surface 112c of the male thread portion 112 may not contact the insertion surface 212c of the female thread portion 212, as shown in Fig. 4. In this case, the thread crest surface 112a of the male thread portion 112 may face the thread groove bottom surface 212b of the female thread portion 212 with a gap therebetween in the fastening completed state, or may contact the thread groove bottom surface 212b. In addition, in the fastening completed state, the thread groove bottom surface 112b of the male thread portion 112 may be in contact with the thread crest surface 212a of the female thread portion 212, or may face the thread crest surface 212a with a gap therebetween.

[0048] Returning to FIG. 1, in the coupling 20, the box 21M provided at one pipe end has the same shape and dimensions as the box 21F provided at the other pipe end. In other words, the boxes 21M and 21F are provided substantially symmetrically with respect to the center of the pipe axis direction of the coupling 20. The boxes 21M and 21F having the same shape and dimensions means that the shapes and dimensions of the boxes 21M and 21F are the same in design. Naturally, the spiral directions of the female threads in the boxes 21M and 21F are also the same. For example, if the female thread of the box 21M is a right-handed thread, the female thread of the box 21F is also a right-handed thread, and the male threads of the corresponding pins 11M and 11F are also right-handed. The shapes and dimensions of the boxes 21M and 21F are the same in design, but if a difference in shape or dimension occurs between the boxes 21M and 21F in actual manufacturing due to a simple manufacturing error or the like, the boxes 21M and 21F are considered to have the same shape and dimensions.

[0049] Pin 11M fastened to box 21M also has the same shape and dimensions as pin 11F fastened to box 21F. Pins 11M, 11F having the same shape and dimensions means that the shapes and dimensions of pins 11M, 11F are the same by design. Although the shapes and dimensions of pins 11M, 11F are the same by design, if a difference in shape or dimensions occurs between pins 11M, 11F in actual production due to a simple manufacturing error or the like, pins 11M, 11F are considered to have the same shape and dimensions.

[0050] [Manufacturing method of threaded joint unit] A manufacturing method of the threaded joint unit 100 will be described below with reference to Figures 5A to 5E. The manufacturing method of the threaded joint unit 100 includes a preparation step and a fastening step. With reference to Figure 5A, in the preparation step, a metal pipe 10 and a coupling 20 are prepared. In the fastening step, a pin 11M of the prepared metal pipe 10 and a box 21M of the coupling 20 are fastened to each other.

[0051] Referring to Fig. 5B, in the fastening step, the metal pipe 10 and the coupling 20 are arranged side by side in the pipe axis direction with the pin 11M and the box 21M facing each other. The pipe body 12 of the metal pipe 10 and the coupling 20 are each gripped by a clamp 30. The metal pipe 10 and the coupling 20 approach each other relatively along the pipe axis direction, and the pin 11M is inserted into the box 21M. Then, the box 21M is rotated relatively to the pin 11M to fasten the pin 11M to the box 21M. As a result, a threaded joint unit 100 including the metal pipe 10 and the coupling 20 is obtained as shown in Fig. 5C.

[0052] The pin 11M of the metal pipe 10 and the box 21M of the coupling 20 are fastened to each other in a factory. That is, the pin 11M and the box 21M are joint parts on the mill end side. After the fastening step, the threaded joint unit 100 is shipped to a site such as an oil well.

[0053] Referring to FIG. 5D, at the site of an oil well, the box 21F of the coupling 20 is fastened to the pin 11F of the metal pipe 10 different from the metal pipe 10 on the mill end side. The pin 11F and the box 21F constitute a joint part on the field end side. The threaded joint unit 100 is arranged in line with the metal pipe 10 on the field end side in the pipe axis direction with the box 21F facing the pin 11F. The pipe body 12 of the metal pipe 10 on the mill end side and the pipe body 12 of the metal pipe 10 on the field end side are each held by a clamp 40. The coupling 20 is not held by the clamp 40. The metal pipe 10 on the field end side and the coupling 20 approach each other relatively along the pipe axis direction, and the pin 11F is inserted into the box 21F. Then, the pin 11F is rotated relatively to the box 21F to fasten the pin 11F to the box 21F. As a result, in the threaded joint unit 100, the metal pipe 10 on the mill end side and the metal pipe 10 on the field end side are connected by the coupling 20, as shown in FIG. 5E.

[0054] If the torque when the pin 11M on the mill end side is fastened to the box 21M is a first fastening torque T1 [Nm] and the torque when the pin 11F on the field end side is fastened to the box 21F is a second fastening torque T2 [Nm], the first fastening torque T1 is greater than the second fastening torque T2 (T1>T2). The second fastening torque T2 is predetermined as the torque when the pin 11F and the box 21F are fastened to the field end side after the fastening of the pin 11M and the box 21M is completed on the mill end side. It is preferable that the first fastening torque T1 and the second fastening torque T2 further satisfy the following formulas. T0<0.95×T y T0 <T1<T y ·T0-6780[Nm]≦T2≦T0+6780[Nm]

[0055] T y [Nm] is the yield torque of the threaded joint unit 100. That is, T y is the torque at which the joints yield when the pins 11M, 11F and the boxes 21M, 21F are fastened. T0 [Nm] is the standard fastening torque determined in advance based on the material, shape, dimensions, etc. of the joints. In the above formula, the second fastening torque T2 is set within the tolerance range of the standard fastening torque T0.

[0056] The first fastening torque T1 is significantly greater than the standard fastening torque T0. The first fastening torque T1 is T0×1.25≦T1 <T y It is more preferable that the following conditions are satisfied.

[0057] The standard tightening torque T0 is T0<0.80×T y It is more preferable that the second fastening torque T2 satisfies T0-2034 [Nm]≦T2≦T0+2034 [Nm].

[0058] The manufacturing method of the threaded joint unit 100 may further include a step of applying a lubricant. The lubricant is applied to at least one of the pin 11M and the box 21M before the step of fastening the pin 11M and the box 21M on the mill end side. The lubricant may be applied, for example, to the entire pin seal surface 111 and the male thread portion 112 of the pin 11M. In the box 21M, the lubricant can be applied to the box seal surface 211. The lubricant may be applied to the female thread portion 212, but may not be applied. The lubricant is in a fluid form containing oil, and is typically a dope.

[0059] When the step of applying a lubricant to the pin 11M and / or the box 21M is performed, in the step of fastening the pin 11M and the box 21M, it is preferable to fasten the pin 11M and the box 21M at a relative rotation speed (fastening speed) of the box 21M to the pin 11M of 5 rpm or less. The fastening speed here refers to the fastening speed at the end of the fastening process. Until the middle of the fastening process, the box 21M may rotate at a relatively high speed with respect to the pin 11M. However, at least at the end of the fastening process, it is preferable that the pin 11M and the box 21M rotate relatively at a low speed, that is, 5 rpm or less, until fastening is completed. The fastening speed is more preferably 3 rpm or less, and particularly preferably 1 rpm or less.

[0060] On the field end side, as on the mill end side, a lubricant can be applied to at least one of the pin 11F and the box 21F before fastening the pin 11F and the box 21F. In this case, too, the relative rotation speed (fastening speed) of the pin 11F with respect to the box 21F is preferably 5 rpm or less, at least at the end of the fastening process. The fastening speed is more preferably 3 rpm or less, and further preferably 1 rpm or less.

[0061] The fastening speed of the pin 11M and the box 21M, and the fastening speed of the pin 11F and the box 21F can be changed depending on the material of the metal tube 10. When the material of the metal tube 10 is carbon steel, the fastening speed can be, for example, 5 rpm or less. When the material of the metal tube 10 is high alloy steel such as 13Cr steel, the fastening speed can be, for example, 3 rpm or less.

[0062] [effect] In the manufacturing method of the threaded joint unit 100 according to the present embodiment, the pin 11 and the box 21 are fastened by torque management on both the mill end side and the field end side. More specifically, on the mill end side, the pin 11M of the metal tube 10 and the box 21M of the coupling 20 are fastened by applying a first fastening torque T1 within a target range, and on the field end side, the pin 11F of the other metal tube 10 and the box 21F of the coupling 20 are fastened by applying a second fastening torque T2 within a target range. The first fastening torque T1 when the pin 11M and the box 21M are fastened is greater than the second fastening torque T2 when the pin 11F and the box 21F are fastened. By fastening the pin 11M and the box 21M on the mill end side with a high torque in advance in this way, the coupling 20 is less likely to rotate in a direction that further applies torque to the pin 11M and the box 21M. Therefore, when the pin 11F is rotated relative to the coupling 20 to fasten the pin 11F and the box 21F at the field end side, the coupling 20 is unlikely to rotate together with the pin 11F. Therefore, when fastening the pin 11F and the box 21F at the field end side, co-rotation of the coupling 20 can be suppressed. Therefore, changes in the shape of the torque chart due to co-rotation are unlikely to occur, and erroneous judgment of the fastening quality at the field end side can be prevented.

[0063] Fig. 6 is a torque chart on the field end side when the fastening torques on the mill end side and the field end side are substantially equal. As shown in Fig. 6, the inclination of the torque chart changes at a position of about 80% of the fastening torque. When the pin 11F and the box 21F are fastened on the field end side, co-rotation of the coupling 20 occurs when about 80% of the fastening torque on the mill end side is loaded. From this result, it can be said that if about 80% of the fastening torque on the mill end side is equal to or greater than the fastening torque on the field end side, co-rotation of the coupling 20 is unlikely to occur.

[0064] In contrast, in this embodiment, the first fastening torque T1 when fastening the pin 11M and the box 21M on the mill end side is preferably 125% or more of a predetermined standard fastening torque T0. In this case, 80% of the first fastening torque T1 is equal to or more than the standard fastening torque T0. The second fastening torque T2 when fastening the pin 11F and the box 21F on the field end side is set within a range of the standard fastening torque T0 ± tolerance (6780 Nm), for example. This makes it easier to suppress co-rotation of the coupling 20 when fastening the pin 11F and the box 21F on the field end side.

[0065] In this embodiment, on the mill end side, a fluid lubricant containing oil can be applied to at least one of the pin 11M and the box 21M before the pin 11M and the box 21M are fastened. In this case, in fastening the pin 11M and the box 21M, it is preferable that the relative rotation speed (fastening speed) of the box 21M with respect to the pin 11M is 5 rpm or less at least at the end of fastening. The fastening speed is more preferably 3 rpm or less, and further preferably 1 rpm or less. When the fastening speed is set to a low speed in this way, the pressure (dope pressure) of the lubricant in the male thread portion 112 and the female thread portion 212 is unlikely to become high during fastening. Therefore, it is possible to prevent the torque load on the pin 11M and the box 21M from becoming insufficient due to the dope pressure. As a result, it is possible to suppress the low breakout torque problem of the pin 11M and the box 21M. In addition, it is possible to suppress the occurrence of co-rotation of the coupling 20 during fastening the pin 11F and the box 21F on the field end side.

[0066] Similarly, on the field end side, a fluid lubricant containing oil can be applied to at least one of the pin 11F and the box 21F before the pin 11F and the box 21F are fastened. At least at the end of the fastening period, the relative rotation speed (fastening speed) of the pin 11F with respect to the box 21F is preferably 5 rpm or less, more preferably 3 rpm or less, and even more preferably 1 rpm or less. In this case, the dope pressure in the male thread portion 112 and the female thread portion 212 is suppressed, so that a sufficient torque can be applied to the pin 11F and the box 21F. Therefore, the low breakout torque problem of the pin 11F and the box 21F can be suppressed.

[0067] <Second embodiment> [Manufacturing method of threaded joint unit] Next, a method for manufacturing the threaded joint unit 100 according to the second embodiment will be described with reference to Figures 7A to 7D. The configuration of the threaded joint unit 100 is similar to that of the first embodiment, so description thereof will be omitted.

[0068] The manufacturing method of the threaded joint unit 100 according to this embodiment includes a preparation step, an application step, and a fastening step. With reference to Fig. 7A, in the preparation step, a metal pipe 10 and a coupling 20 are prepared. In the example of Fig. 7A, a coupling 20 is prepared in which a pin 11M is already fastened to a box 21M on the mill end side. At the preparation step, a box 21F on the field end side is not fastened to the pin 11F. In this embodiment, the application step and the fastening step are performed at the site, such as an oil well.

[0069] Referring to FIG. 7B, in the application step, the lubricant 50 is applied to the pin seal surface 111 and the male thread portion 112 of the pin 11F of the prepared metal pipe 10. The lubricant 50 is applied over the entirety of the pin seal surface 111 and the male thread portion 112. In addition, in the application step, the lubricant 50 is applied to the box seal surface 211 of the box 21F of the coupling 20. However, in the application step, the lubricant 50 is not applied to the female thread portion 212 of the box 21F. The lubricant 50 used is a fluid lubricant containing oil, as in the first embodiment, and is typically a dope. In the example of FIG. 7B, in the pin 11F, the lubricant 50 is applied to the pin seal surface 111 and the male thread portion 112 as well as to the pipe end surface. In the box 21F, the lubricant 50 is applied to the box seal surface 211 as well as to the inner end surface thereof. However, the tube end surface of the pin 11F and the inner end surface of the box 21F do not need to be coated with the lubricant 50. The tube end surface of the pin 11F and the inner end surface of the box 21F do not come into contact with each other when the pin 11F and the box 21F are in a fully fastened state.

[0070] The area of ​​the outer circumferential surface of the pin 11F to which the lubricant 50 is applied is defined as S [cm 2 ], and the amount of lubricant 50 applied to pin 11F is V [cm 3 [0.005×S≦V≦0.040×S], the coating area S and coating amount V preferably satisfy 0.005×S≦V≦0.040×S. The coating area S and coating amount V more preferably satisfy 0.010×S≦V≦0.040×S, and further preferably satisfy 0.010×S≦V≦0.037×S.

[0071] Referring to FIG. 7C, in the fastening step, the pin 11F and the box 21F after the lubricant 50 (FIG. 7B) is applied are fastened together. In the fastening step, the coupling 20 is arranged in line with the metal tube 10 on the field end side in the tube axis direction with the box 21F facing the pin 11F. The tube bodies 12 of the metal tubes 10 on the mill end side and the field end side are gripped by clamps 40, respectively. The metal tube 10 on the field end side and the coupling 20 approach each other relatively in the tube axis direction, and the pin 11F is inserted into the box 21F. Then, the pin 11F is rotated relatively to the box 21F to fasten the pin 11F to the box 21F. In this embodiment, when the pin 11F and the box 21F are fastened, the insertion surface 112c of the male thread portion 112 contacts the insertion surface 212c of the female thread portion 212, and the load surface 112d of the male thread portion 112 contacts the load surface 212d of the female thread portion 212 (FIG. 2). That is, the rotation stopping means of the pin 11F and the box 21F in this embodiment is the engagement between the male thread portion 112 and the female thread portion 212. By fastening the pin 11F and the box 21F, a threaded joint unit 100 including the metal pipe 10 on the mill end side, the metal pipe 10 on the field end side, and the coupling 20 is obtained, as shown in FIG. 7D.

[0072] The relative rotation speed (fastening speed) of the pin 11F with respect to the box 21F in the fastening step can be 5 rpm or less, similar to the first embodiment. The fastening speed is preferably 3 rpm or less, and more preferably 1 rpm or less. The fastening speed here is the fastening speed at the end of the fastening process, similar to the first embodiment.

[0073] In this embodiment, the manufacturing method of the threaded joint unit 100 may further include a step of re-tightening the pin 11F and the box 21F. In this step, after the step of fastening the pin 11F and the box 21F is completed and a predetermined time has elapsed since the completion of the fastening, the pin 11F and the box 21F are re-tightened with a predetermined fastening torque. The predetermined time is the time required for the dope pressure of the threaded portion generated in the fastening step to be released. The predetermined time is, for example, one minute or more. There is no particular upper limit to the predetermined time.

[0074] [effect] In this embodiment, the lubricant 50 is applied to the pin seal surface 111 and the male thread portion 112 of the pin 11F, but the lubricant 50 is applied to the box seal surface 211 of the box 21F, but the lubricant 50 is not applied to the female thread portion 212. This reduces the amount of excess lubricant 50, and the excess lubricant 50 is easily discharged from the male thread portion 112 and the female thread portion 212 as the pin 11F is screwed into the box 21F. Therefore, the dope pressure in the male thread portion 112 and the female thread portion 212 can be reduced. Therefore, it is possible to prevent the torque load on the pin 11F and the box 21F from becoming insufficient due to high dope pressure, and the low breakout torque problem of the pin 11F and the box 21F can be suppressed.

[0075] FIG. 8 is a graph obtained by a breakout test of a threaded joint, and shows the relationship between the amount V of the lubricant 50 applied to the threaded joint / application area S and the ratio of the actual value of the breakout torque to the standard make-up torque (B / O torque ratio). From FIG. 8, it can be seen that the B / O torque ratio is 80% or more when V / S is in the range of 0.005 to 0.040. Therefore, in the manufacturing method of the threaded joint unit 100 according to this embodiment, it is preferable that the application area S and application amount V of the lubricant 50 satisfy 0.005×S≦V≦0.040×S. This makes it possible to sufficiently ensure the breakout torque of the pin 11F and the box 21F, and to suppress the problem of low breakout torque of the pin 11F and the box 21F.

[0076] In the manufacturing method of the threaded joint unit 100 according to this embodiment, the relative rotation speed (fastening speed) of the pin 11F with respect to the box 21F can be set in the same manner as in the first embodiment. The fastening speed is preferably 5 rpm or less, more preferably 3 rpm or less, and further preferably 1 rpm or less. In this case, the dope pressure in the male thread portion 112 and the female thread portion 212 is suppressed, so that a sufficient torque can be applied to the pin 11F and the box 21F. Therefore, the low breakout torque problem of the pin 11F and the box 21F can be suppressed.

[0077] In this embodiment, it is preferable that the pin 11F and the box 21F are fastened again after a predetermined time has elapsed after the fastening of the pin 11F and the box 21F is completed. This can increase the breakout torque of the pin 11F and the box 21F. Therefore, the low breakout torque problem of the pin 11F and the box 21F can be more effectively suppressed.

[0078] In this embodiment, the steps for fastening the pin 11F and the box 21F at the field end side have been described. However, the steps described in this embodiment can also be applied to fastening the pin 11M and the box 21M at the mill end side.

[0079] In this embodiment, the fastening is performed under torque management on both the mill end side and the field end side. For example, on the mill end side, the pin 11M of the metal tube 10 and the box 21M of the coupling 20 are fastened by applying a first fastening torque T1, and on the field end side, the pin 11F of another metal tube 10 and the box 21F of the coupling 20 are fastened by applying a second fastening torque T2. In this embodiment, unlike the first embodiment, the first fastening torque T1 when the pin 11M and the box 21M are fastened may not be larger than the second fastening torque T2 when the pin 11F and the box 21F are fastened. For example, both the first fastening torque T1 and the second fastening torque T2 may be set within the range of T0±tolerance (6780 [Nm]). That is, the first fastening torque T1 and the second fastening torque T2 may be substantially the same. However, the first fastening torque T1 and the second fastening torque T2 may be set to satisfy the same relationship as in the first embodiment.

[0080] In this embodiment, the pin 11M and the box 21M can be retightened after a predetermined time has elapsed since the fastening of the pin 11M and the box 21M has been completed. Also, the pin 11F and the box 21F can be retightened after a predetermined time has elapsed since the fastening of the pin 11F and the box 21F has been completed. Such retightening (retightening) of the pin 11M and the box 21M, and the pin 11F and the box 21F can also be applied to the manufacturing method of the threaded joint unit 100 according to the first embodiment.

[0081] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure. [Explanation of symbols]

[0082] 100: Threaded joint unit 10:Metal tube 11, 11F, 11M: Pin 111: Pin seal surface 112: Male thread 112c: Insertion surface 112d: Loading surface 20: Coupling 21, 21F, 21M: Box 211: Box seal surface 212: Female thread 212c: Insertion surface 212d: Load surface 50: Lubricants

Claims

1. A method for manufacturing a threaded joint unit, comprising: A step of preparing a metal pipe having a first pin including a male thread portion provided at a pipe end, and a tubular coupling having boxes provided at both pipe ends, a first box being one of the boxes, and a second box being the other of the boxes and having the same shape and dimensions as the first box, each including a female thread portion; a step of fastening the first pin and the first box by inserting the first pin into the first box and rotating the first box relatively to the first pin; Equipped with the first pin and the first box have a rotation stopping means for mechanically stopping the relative rotation of the first box with respect to the first pin; a first fastening torque when the first pin is fastened to the first box is greater than a second fastening torque that is predetermined as a torque when a second pin, which is provided at a pipe end of a metal pipe different from the metal pipe, includes a male thread portion, and has the same shape and dimensions as the first pin, is fastened to the second box after fastening of the first pin and the first box is completed.

2. A method for manufacturing a threaded joint unit according to claim 1, The yield torque of the threaded joint unit is T ｙ , a predetermined standard tightening torque is T ０ , the first tightening torque is T １ , the second tightening torque is T ２ Then, T ｙ , T ０ , T １ , and T ２ A manufacturing method that satisfies the following formulas. T ０ <0.95×T ｙ T ０ <T １ <T ｙ T ０ -6780[Nm]≦T ２ ≦T ０ +6780[Nm]

3. A method for manufacturing a threaded joint unit according to claim 2, The first fastening torque T １ Is T ０ ×1.25≦T １ <T ｙ A manufacturing method that satisfies the above requirements.

4. The method for manufacturing a threaded joint unit according to claim 1, further comprising: applying a lubricant to at least one of the first pin and the first box before the fastening step; In the fastening step, the first pin and the first box are fastened together at a relative rotation speed of the first box with respect to the first pin of 5 rpm or less.

5. A method for manufacturing a threaded joint unit according to any one of claims 1 to 4, a manufacturing method in which, when the first pin and the first box are completely fastened to each other, an insertion surface of the male threaded portion of the first pin contacts an insertion surface of the female threaded portion of the first box, and a load surface of the male threaded portion of the first pin contacts a load surface of the female threaded portion of the first box.

6. A method for manufacturing a threaded joint unit, comprising: Providing a metal tube having a pin at an end thereof, the pin having a pin seal surface and a male thread portion, and a tubular coupling having a box at an end thereof, the box having a box seal surface and a female thread portion; applying a lubricant to the pin seal surface and the male threads and to the box seal surface, while not applying the lubricant to the female threads; fastening the pin and the box together after the lubricant has been applied; Equipped with when the pin and the box are completely fastened, the insertion surface of the male threaded portion contacts the insertion surface of the female threaded portion, the load surface of the male threaded portion contacts the load surface of the female threaded portion, and the pin seal surface contacts the box seal surface.

7. A method for manufacturing a threaded joint unit according to claim 6, The area of ​​the pin to which the lubricant is applied is defined as S [cm ２ ], the amount of the lubricant applied to the pin is V [cm ３ ], 0.005×S≦V≦0.040×S.

8. A method for manufacturing a threaded joint unit according to claim 6, In the fastening step, the pin and the box are fastened together at a relative rotational speed of the pin with respect to the box of 5 rpm or less.

9. A method for manufacturing a threaded joint unit according to any one of claims 6 to 8, further comprising: re-clamping the pin and the box after a predetermined time has elapsed after completion of the fastening step; A manufacturing method comprising:

Images