The present disclosure relates to a threaded joint for steel pipes.
BACKGROUND
[0002]
　For example, oil wells and natural gas wells and the like exploration or production, the development of unconventional resources such as oil sand and shale gas, the carbon dioxide recovery and storage (CCS (Carbon (hereinafter, also collectively referred to as "oil wells") dioxide Capture and Storage)), in geothermal, or springs or the like, the steel pipe called oil well pipe is used. The connection of steel pipes, threaded joints are used.
[0003]
　Format tubular threaded joint is roughly classified into a coupling-type and integral type. For coupling type, a pair of tubing of consolidated, where one tube is steel, other tubing is coupled. In this case, a male screw portion is formed on an outer periphery of both end portions of the steel pipe, the internal thread portion is formed on the inner periphery of both end portions of the coupling. Then, the male screw portion of the steel pipe is screwed into the female screw portion of the coupling, which both are connected is fastened by. For integral type, a pair of tubing of consolidated are both steel pipe, without using a separate coupling. In this case, a male screw portion is formed on an outer periphery of one end portion of the steel pipe, the internal thread portion is formed on the inner periphery of the other end. Then, the male screw portion of one of the steel pipe is screwed into the female screw portion of the other steel pipe, which both are connected is fastened by.
[0004]
　Generally, the joint portion of the male screw portion the tube end portion formed, since the containing elements to be inserted into the female screw portion, it referred to as pin. On the other hand, the joint portion of the pipe end portion a female screw portion is formed, since it contains elements for receiving the external thread portion, referred to as boxes. Pin and box are the ends of the tube, both of which are tubular.
[0005]
　The threaded joint for steel pipes, pressure from internal fluid (hereinafter, also referred to as "internal pressure") and the pressure fluid from the outside (hereinafter, also referred to as "external pressure") excellent sealing performance for is required. Therefore, the threaded joint, a metal - seal part due to metal contact is provided. Seal portion is composed of a pin seal surface provided on an outer peripheral surface of the pin, the box sealing surface provided on the inner peripheral surface of the box. Diameter of pin seal surface is slightly larger than the diameter of the box sealing surface. Pin seal surface and the difference between the diameter of the box sealing surface interfering amounts of from. When the screw joint is fitted is has been sealed faces fastened by interference amount, diameter and box seal surfaces of the enlarged diameter of the pin seal surface is generated. The elastic recovery force of each of the sealing surfaces to return to the original diameter, the contact pressure on the seal surface all around closely occurring, sealing performance is exhibited.
[0006]
　JP Kohyo 2007-504420, a threaded joint is disclosed in which the purpose of effective contact length of the seal surface to maximize. In this threaded joint, with pin seal surface is constituted by a circular arc surface, the box sealing surface is constituted by a tapered surface. The same publication, such a configuration has been described as a very effective contact width in the axial direction, a substantially parabolic contact pressure distribution along the effective contact zone is formed.
[0007]
　JP-A-2014-101983 discloses, a threaded joint for the purpose of securing the sealing performance and resistance to compression are disclosed. The threaded joint includes a Pinshoruda surface provided on the distal end portion of the pin, and a box shoulder surface provided on the inner end of the box. Pinshoruda surface and the box shoulder surface constitutes a shoulder portion in contact with each other in the engaged state. The same publication, box contact reaction force from the shoulder surface to Pinshoruda surface toward centripetal or component does not contribute to the shrink deformation of the tip portion of the pin without or contraction of the front end portion of the pin there is a countercurrent centrifugal component It has been described as to resist diameter change shape.
[0008]
　In the publication of the threaded joint, shoulder angle is set to 20 ° or less 0 ° over a crossing angle between a plane perpendicular to the shoulder surface and the tube axis. According to the publication, the shoulder angle exceeds 20 °, the damage is generated in the seal portion the direction centrifugal component becomes excessive.
[0009]
　In the publication of the threaded joint, the outer diameter of Pinshoruda surface is smaller than the outer diameter of the box shoulder surface. According to the publication, this configuration can prevent the occurrence of reduced diameter direction of the push force to the distal end portion of the pin from the box, it can be suppressed contact weakening of the seal portion due to the pressing force.
SUMMARY OF THE DISCLOSURE
[0010]
　Details will be described later, the threaded joint of the above patent documents, there is room for further improving the sealing performance. The present disclosure is intended to provide a tubular threaded joint which can be obtained more excellent sealing performance.
[0011]
　Tubular threaded joint according to the present disclosure includes a pin tubular and a tubular box. Pin is connected to the steel tube body. Box, the pin is fastened to the inserted into the pin. Pin includes a Pinshoruda surface, and the male screw portion, and a pin seal surface. Pinshoruda surface is an annular surface provided at the distal end portion of the pin. Pinshoruda surface is inclined so as the outer peripheral edge portion is located on the pin tip side than the inner peripheral edge. Male screw portion is provided on the outer peripheral surface of the pin. Male screw portion is composed of a wedge screw. Pin seal surface is provided on the outer peripheral surface of the pin between the Pinshoruda surface and the male screw portion. Box has a box shoulder surface, and the female screw portion, and a box seal surface. Box shoulder surface is an annular surface provided at the rear end portion of the box in response to Pinshoruda surface. Box shoulder surface is inclined so as the outer peripheral edge portion is located on the rear end side of the box than the inner periphery. Internal thread portion is provided on the inner peripheral surface of the box corresponding to the external thread portion. Internal thread portion is composed of a wedge screw. Box sealing surface is provided on the inner peripheral surface of the box in correspondence with the pin seal surface. In the engaged state, contact Pinshoruda surface and box shoulder surface, insertion surface and load flanks of the male thread portion respectively in contact with the insert surface and the load flanks of the female thread portion, and, pin seal surface is in contact with the box sealing surface. Shoulder angle is 4 ° or more. Shoulder angle, each of Pinshoruda surface and box shoulder surface is an angle formed between the plane perpendicular to the tube axis in the disengaged state.
[0012]
　According to the screw joint according to the present disclosure, it is possible to obtain a better sealing performance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013]
[1] Figure 1 is a longitudinal sectional view showing a schematic configuration of a tubular threaded joint according to the embodiment.
FIG. 2 is a partially enlarged view of a threaded joint shown in Figure 1.
FIG. 3 is a partially enlarged view of a threaded joint shown in Figure 1.
[4] FIG. 4 is a graph showing the relationship between the seal contact force and shoulder angle.
FIG. 5 is a graph showing the relationship between the torque resistance performance and shoulder angle.
DESCRIPTION OF THE INVENTION
[0014]
　As a threaded joint for steel pipes to achieve high torque resistance performance threaded joints wedge screw is applied is known. Wedge screw has a screw width that varies progressively along the lead has an insertion surface and the load flank angle is negative angle. Wedge screw has a self 緊作. That is, in the threaded joint wedge screw is applied, when fastening is completed, the insertion faces of the male screw portion and the female threaded portion, as well as the contact load faces of the male screw portion and female screw portion together, the male screw portion and the female screw portion and There suit fits.
[0015]
　Generally, the threaded joint wedge thread has been applied, not the shoulder portion is provided. For example, JP-threaded joint Kohyo Publication 2007-504420 is provided with a screw portion constituted by a wedge-type screws, not provided with a shoulder portion. On the other hand, the threaded joint comprising a shoulder portion, generally does not wedge screw is applied. For example, in the threaded joint of JP 2014-101983, although the shoulder portion is provided, trapezoidal thread is applied to the insertion surfaces of the threaded portion does not contact during engagement completion.
[0016]
　Thus, in a threaded joint for steel pipes, typically, it will not be provided by combining the wedge-shaped screw and the shoulder portion. Apply the Kusabigata threaded into the threaded joint, and the case of providing a shoulder portion, a contact between the insertion faces and load faces (locking), the contact between the shoulder surface must be controlled so as (shouldering) and occur at the same time there is. If occur simultaneously and locking the shouldering of wedge screw, a predetermined amount of interference is not introduced into the seal portion and / or the threaded portion, there is a possibility that the weak point occurs for combined loads. It is also possible that the phenomenon that the yield separately for each is generated of the threaded portion and the shoulder portion in the fastening torque line occurs. To prevent these situations, it is necessary to strictly set the manufacturing tolerances of the threaded joint. Therefore, the combination of the wedge screw and shoulder portion are normally avoided.
[0017]
　However, except for the problem of manufacturing tolerances, by combining the wedge-shaped screw and the shoulder portion, it is possible to expect an improvement in sealing performance. That is, the locking effect and shouldering effect of the wedge-type thread upon engagement completion, it is contemplated that the contact force generated in the seal portion can be increased.
[0018]
　The present inventors have both of the threaded portion and the shoulder portion of the wedge-shaped thread on which is provided a threaded joint, was examined angle proper shoulder surfaces to obtain an excellent sealing performance. As a result, the present inventors have completed the threaded joint according to the embodiment.
[0019]
　Tubular threaded joint according to the embodiment includes a pin tubular and a tubular box. Pin is connected to the steel tube body. Box, the pin is fastened to the inserted into the pin. Pin includes a Pinshoruda surface, and the male screw portion, and a pin seal surface. Pinshoruda surface is an annular surface provided at the distal end portion of the pin. Pinshoruda surface is inclined so as the outer peripheral edge portion is located on the pin tip side than the inner peripheral edge. Male screw portion is provided on the outer peripheral surface of the pin. Male screw portion is composed of a wedge screw. Pin seal surface is provided on the outer peripheral surface of the pin between the Pinshoruda surface and the male screw portion. Box has a box shoulder surface, and the female screw portion, and a box seal surface. Box shoulder surface is an annular surface provided at the rear end portion of the box in response to Pinshoruda surface. Box shoulder surface is inclined so as the outer peripheral edge portion is located on the rear end side of the box than the inner periphery. Internal thread portion is provided on the inner peripheral surface of the box corresponding to the external thread portion. Internal thread portion is composed of a wedge screw. Box sealing surface is provided on the inner peripheral surface of the box in correspondence with the pin seal surface. In the engaged state, contact Pinshoruda surface and box shoulder surface, insertion surface and load flanks of the male thread portion respectively in contact with the insert surface and the load flanks of the female thread portion, and, pin seal surface is in contact with the box sealing surface. Shoulder angle is 4 ° or more. Shoulder angle, each of Pinshoruda surface and box shoulder surface is an angle formed between the plane perpendicular to the tube axis in the disengaged state.
[0020]
　The above threaded joint, the male screw portion and the female threaded portion made of a wedge screw, and a Pinshoruda surface and box shoulder surface are provided. In the engaged state, the insertion faces and load faces of the male screw portion and the female thread portion is in contact, contact between Pinshoruda surface and the box shoulder surface. That is, locking and shouldering of Kusabigata screw upon engagement completion occurs. Accordingly, when the action of the load, the deformation of the pin seal surface and the box sealing surface disposed between the threaded portion and the shoulder portion is less likely to occur, contact force between the sealing surfaces is expected to increase. In addition, each shoulder surface has a shoulder angle of at least 4 °. Details will be described later, if the shoulder angle, it is possible to obtain excellent sealing performance in comparison with conventional threaded joint.
[0021]
　The shoulder angle may be 40 ° or more.
[0022]
　Details will be described later, by setting the shoulder angle 40 ° or more, it is possible to obtain an excellent torque resistance performance.
[0023]
　The shoulder angle may be 60 ° or less.
[0024]
　In general, increasing the shoulder angle, sealing performance is lowered rigidity of the tip portion of the pin is lowered. However, in the configuration of a threaded joint according to the embodiment, if the shoulder angle of 60 ° or less, less susceptible to the effects of decreased rigidity of the front end portion of the pin, it is possible to maintain excellent sealing performance. This point will be described later.
[0025]
　Hereinafter, embodiments will be described specifically with reference to the drawings. Given the same reference and the corresponding configuration in the figure does not repeat the same description. For convenience of explanation, in each figure, or are simplified or schematized configuration, in some cases or are omitted a part of the configuration.
[0026]
　[Configuration of the threaded joint]
　FIG 1 is a longitudinal sectional view showing a schematic configuration of a tubular threaded joint 1 according to the embodiment. The longitudinal section means a cross-section that is cut along a plane including the tube axis CL of the threaded joint 1. Threaded joint 1 may be a integral type threaded joint, it may be a coupling type of threaded joint.
[0027]
　As shown in FIG. 1, a threaded joint 1 is provided with a pin 10 and a box 20. Pin 10 and box 20 are each tubular. Pin 10 is inserted into the box 20, the pin 10 and the box 20 is fastened.
[0028]
　Pin 10 is connected to the steel tube body 30. Pin 10 is formed by cutting is performed on the end of the steel pipe. The steel body 30 refers to a portion in the steel pipe comprising a pin 10 not inserted into the box 20. Hereinafter, in the tube axis CL extends direction (tube axis direction), the inner tip end of the pin 10, before or back, sometimes referred to as outer or after the steel pipe pile body 30 side.
[0029]
　Pin 10 includes a Pinshoruda surface 11, a pin seal surface 12, and a male screw portion 13. Pinshoruda surface 11, pin seal surface 12, and the external thread portion 13 are arranged in this order from the front of the tube axis direction toward the rear.
[0030]
　Pinshoruda surface 11 is provided on the distal end portion of the pin 10. Pinshoruda surface 11 is disposed on the distal end surface of the pin of the tubular. Therefore, Pinshoruda surface 11 is an annular surface.
[0031]
　Pin seal surface 12 is provided on the outer peripheral surface of the pin 10. Pin seal surface 12 is disposed between the Pinshoruda surface 11 and the male screw portion 13. Pin seal surface 12 is constituted, for example, an arc or elliptical arc peripheral surface of the rotated rotator around the tube axis CL, or the tube axis CL in the circumferential surface of the truncated cone to the shaft. Alternatively, pin seal surface 12 is formed by a combination of these peripheral surfaces of two or more.
[0032]
　External thread portion 13 is provided on the outer peripheral surface of the pin 10. External thread portion 13 is disposed in the steel pipe main body 30 side of the pin seal surface 12. External thread portion 13 is composed of a wedge screw. The wedge screw thread width towards the base from the top of the screw thread is a thread having a gradually narrowed shape. Male screw portion 13 includes a tapered external thread screw outer diameter decreases toward the tip of the pin 10. Screw Yamahaba external thread portion 13 is gradually narrowed toward the tip of the pin 10.
[0033]
　Box 20 includes a box shoulder surface 21, the box sealing surface 22, and a female thread portion 23. Box shoulder surface 21, the box sealing surface 22, and the internal thread portion 23 is positioned from the front of the tube axis direction in this order toward rearward.
[0034]
　Box shoulder surface 21, corresponding to Pinshoruda surface 11 is provided on the inner end portion of the box 20. Box shoulder surface 21, like the Pinshoruda surface 11 is an annular surface. Box shoulder surface 21 contacts the Pinshoruda surface 11 in engagement state, to form a shoulder portion with Pinshoruda surface 11. Pinshoruda surface 11 and box shoulder surface 21 is responsible stopper for limiting the screwing of the pin 10. Pinshoruda surface 11 and box shoulder surface 21, inside the joint, responsible for generating a clamping axial force of the screw.
[0035]
　Box sealing surface 22, corresponding to the pin seal surface 12 is provided on the inner peripheral surface of the box 20. Box sealing surface 22 is arranged between the box shoulder surface 21 and the internal thread portion 23. Box sealing surface 22 is constituted, for example, an arc or elliptical arc peripheral surface of the rotated rotator around the tube axis CL, or the tube axis CL in the circumferential surface of the truncated cone to the shaft. Alternatively, the box sealing surface 22 is formed by combining these peripheral surfaces of two or more. Box sealing surface 22 contacts the pin seal surface 12 in the fastening state, the metal with pin seal surface 12 - to form a sealing portion by the metal contact.
[0036]
　Internal thread portion 23, corresponding to the external thread portion 13 is provided on the inner peripheral surface of the box 20. Internal thread portion 23 is constituted by a wedge-type screw that meshes with wedge screw which constitutes the male threaded portion 13. Internal thread portion 23 is composed of a tapered female thread which screws inside diameter becomes smaller toward the rear end of the box 20. Internal thread portion 23 forms a threaded portion with the external thread portion 13 in the engaged state. Threaded portion is preferably a single-thread screw or double threaded screw.
[0037]
　Threaded portion constituted by the male screw portion 13 and the female screw portion 23 has a screw width that varies progressively along the lead. However, it may be made to the screw constant width in some of the threaded portion. For example, the inner end of the tube axis direction of the screw portion and / or the outer end may be threaded constant width.
[0038]
　Figure 2 is a partially enlarged view of the threaded joint 1. 2 shows a threaded portion of the threaded joint 1 is shown enlarged.
[0039]
　As shown in FIG. 2, the external thread portion 13 has a thread crest surface 131, a thread root bottom surface 132, an insertion face 133, and a load surface 134. Insertion surface 133 and load flanks 134, a flank surface which connects the thread crest surface 131 and the thread valley bottom 132. Insertion surface 133 is a surface that precedes by screwing of the pin 10 relative to the box 20. Load surface 134 is disposed on the opposite side of the insertion surface 133 across the screw crest surface 131.
[0040]
　Insertion surface 133 and load flanks 134, has a negative flank angle. The flank angle, the longitudinal section of the threaded joint 1, refers to an angle between the perpendicular line and flank surfaces to the tube axis CL.　
[0041]
　The flank angle of the insert surface 133, the clockwise and negative direction. Therefore, insertion surface 133 having a negative flank angle is inclined so as to be positioned in front of the tube axis direction than the inner peripheral portion is the outer peripheral portion. The flank angle of the load flanks 134, the counterclockwise and negative direction. Therefore, load surface 134 having a negative flank angle is inclined so as to be positioned behind the tube axis direction than the inner peripheral portion is the outer peripheral portion.
[0042]
　Internal thread portion 23 has a thread root bottom surface 231, the screw crest surface 232, an insertion surface 233, and a load surface 234. Insertion surface 233 and load flanks 234, a flank surface which connects the thread root bottom surface 231 and the screw crest surface 232. Load surface 234 faces the insertion surface 233 across the thread root bottom surface 231.
[0043]
　Insertion surface 233 and load flanks 234, has a negative flank angle. The flank angle of the insert surface 233, the clockwise and negative direction. Therefore, insertion surface 233 is inclined so as to be positioned in front of the tube axis direction than the inner peripheral portion is the outer peripheral portion. The flank angle of the load flanks 234, the counterclockwise and negative direction. Therefore, the load surface 234 is inclined so as to be positioned behind the tube axis direction than the inner peripheral portion is the outer peripheral portion.
[0044]
　In the engaged condition, the screw trough bottom 231 of the internal thread portion 23 is opposed with a gap and a screw crest surface 131 of the male thread portion 13. In the engaged condition, the screw crest surface 232 of the female screw portion 23 contacts the thread root bottom surface 132 of the external thread portion 13. However, in the engaged state, contact screw crest surface 131 of the thread root bottom 231 and the external thread portion 13 of the female screw portion 23 to each other, the screw trough bottom 132 of the thread crest surface 232 and the external thread portion 13 of the internal thread portion 23 is a contactlessly it may be.
[0045]
　In the engaged state, insertion face 233 of the female screw portion 23 is in contact with the insert surface 133 of the male thread portion 13. In the engaged condition, the load surface 234 of the female screw portion 23 contacts the load surface 134 of the male thread portion 13. In this case, it is not necessary to the whole of the insertion face 233 of the female screw portion 23 is in contact with the insert surface 133 of the male thread portion 13. For example, by manufacturing tolerances and the like, in the insertion surface 233 of the female screw portion 23, there may be a portion not in contact with the insert surface 133 of the male thread portion 13.
[0046]
　Figure 3 is a partially enlarged view of the threaded joint 1. In FIG. 3, the front portion of the threaded joint 1 of the non-fastening state is shown.
[0047]
　As shown in FIG. 3, Pinshoruda surface 11 is inclined so as to be positioned on the distal end side of the pin 10 than the inner peripheral portion outer peripheral edge portion. Pinshoruda surface 11 has a shoulder angle .theta.1. Shoulder angle θ1 is at pin 10 of the state of not being fastened to the box 20, the Pinshoruda surface 11, which is the angle between a plane perpendicular to the tube axis CL.
[0048]
　Box shoulder surface 21 is inclined so as to be positioned on the rear end side of the box 20 than the inner peripheral portion outer peripheral edge portion. Box shoulder surface 21 has a shoulder angle .theta.2. Shoulder angle θ2, in box 20 in a state that is not fastened to the pin 10, the box shoulder surface 21, which is the angle between a plane perpendicular to the tube axis CL.
[0049]
　Shoulder corner of the box shoulder surface 21 .theta.2 is shoulder angle Pinshoruda surface 11 .theta.1 substantially equal. A shoulder angle θ1 and the shoulder angle θ2 is the substantially equal, it means that the difference between the shoulder angle θ1 and the shoulder angle θ2 is within the range of manufacturing tolerances. For example, the difference between the shoulder angle θ1 and the shoulder angle θ2 is in the range of ± 1 °. For convenience of explanation, the shoulder angle .theta.1, .theta.2 especially when not distinguished, that the shoulder angle theta.
[0050]
　The shoulder angle θ of Pinshoruda surface 11 and box shoulder surface 21, from the viewpoint of excellent sealing performance, at 4 ° or more. To the sealing performance further improved, the shoulder angle theta, is preferably 7 ° or more, and more preferably 20 ° or more.
[0051]
　In order to improve the torque resistance performance, the shoulder angle theta, it is preferably 40 ° or more.
[0052]
　The shoulder angle theta, to ensure the necessary rigidity at the distal end of the pin 10, is preferably 60 ° or less. Also in terms of practical production, the tool for cutting the outer peripheral surface and the inclination angle and the respective inner peripheral surfaces of the box 20 to be continuous in the box shoulder surface 21, the pin 10 and box 20 of the pin 10 that is continuous with Pinshoruda surface 11 in view of the angle, the upper limit of the shoulder angle θ is 60 °.
[0053]
　The shape of pin seal surface 12 and the box sealing surface 22 is not particularly limited, pin seal surface 12 of the present embodiment is a convex curved surface radially outward of the pin 10. On the other hand, the box sealing surface 22 is a generally tapered surface. Diameter of the box sealing surface 22 is gradually decreased toward the rear end of the box 20.
[0054]
　At pin 10 of the non-engaged state, the position P1 of the maximum diameter of the pin seal surface 12, from the tip of the pin 10 at a position separated by a predetermined distance D1 in the axial direction of the tube. The distance D1 is, for example, 5mm or more. In the pin 10, the rigid portion 14 is provided in front of the pin seal surface 12. Rigid section 14 of the pin 10, a forward section in the tube axis direction than the pin seal surface 12, including Pinshoruda surface 11.
[0055]
　Rigid part 14 has an outer diameter becomes smaller toward the tip of the pin. In longitudinal cross section of the pin 10, the outer peripheral surface of the rigid portion 14 is slightly inclined to the tube axis CL. At least part of the outer peripheral surface of the rigid portion 14 does not contact the inner peripheral surface of the box 20 in the engaged state. Rigid part 14, when the compressive load is applied to the threaded joint 1, absorbs the plastic deformation of the pin seal surface 11. The rigid part 14, lowering of the contact surface pressure of the pin seal surface 11 for box sealing surface 21 is suppressed.
[0056]
　[Effect]
　A threaded joint 1 according to the present embodiment includes a Pinshoruda surface 11 and box shoulder surface 21, and a male screw portion 13 and the female screw portion 23 made of a wedge screw. In the engaged state, Pinshoruda surface 11 is brought into contact with the box shoulder surface 21, and the insertion surfaces 133 and 233 and between the load surface 134, 234 to each other of the male thread portion 13 and the female threaded portion 23 is in contact. Thus, the threaded joint 1, the locking of the shoulder ring and the screw portion is generated during engagement completion. Accordingly, when a load is applied to the threaded joint 1, the deflection of the deployed seal portion between the shoulder portion and the threaded portion is less likely to occur, the contact force between the pin seal surface 12 and the box sealing surface 22 is increased it can be expected. Furthermore, since the shoulder angle of Pinshoruda surface 11 and box shoulder surface 21 is 4 ° or more, it is possible to obtain an excellent sealing performance.
[0057]
　Having described embodiments, the present disclosure is not intended to be limited to the above embodiments but can be variously modified without departing from the spirit.
Example
[0058]
　To verify the effect of the present disclosure were performed finite element analysis that target a threaded joint for steel pipes wedge screw is applied. Specifically, the threaded joint model having the basic structure shown in FIGS. 1 to 3, it analyzes by changing the shoulder angle (theta) of Pinshoruda surface (11) and box shoulder surface (21), sealing performance and it was evaluated the anti-torque performance. Dimensions of the steel pipe used in the analysis, 7 "26 # (nominal outer diameter 177.80Mm, nominal wall thickness 9.19mm), the material of the steel pipe, in the API standard L80 steel (nominal yield strength YS = 552MPa (80ksi)) is there.
[0059]
　For each model, using a mixed-loading conditions simulating the ISO13679 Series A test to evaluate the value of seal contact force at each loading step. Of the sealing contact force which changes in the conditions and the minimum value (minimum seal contact force) as an indicator of the sealing performance.
[0060]
　Furthermore, for each model, and conducting an assay simulating the fastening of the threaded joint was evaluated torque resistance performance value of considered one by MTV indicator of breakdown torque (Maximum Torque Value).
[0061]
　The results of the evaluation of the sealing performance is shown in FIG. Figure 4 is a graph showing the relationship between the minimum seal contact force and shoulder angle (theta). In Figure 4, for comparison with threaded joint (Example) provided with a shoulder portion and Kusabigata screws, also it shows the minimum seal contact force of the threaded joint of the wedge-shaped screw without a shoulder (Comparative Example).
[0062]
　As shown in FIG. 4, the threaded joint according to the embodiment, the minimum seal contact force enough to increase the shoulder angle (theta) is a tendency to increase. In general, increasing the shoulder angle (theta), reduced stiffness of the distal end portion of the pin (10) is, sealing performance is considered to be reduced for the particular external pressure. However, the threaded joint according to the embodiment, the seal portion is sandwiched between the locking has been threaded portion and the shoulder portion amplifies the contact surface pressure of the seal portion, the deflection of the pin seal surface during load application (12) Decrease. Therefore, even when increasing the shoulder angle (theta), decrease in sealing performance caused by the reduction in the rigidity of the tip portion of the pin (10) is presumed to have been suppressed.
[0063]
　Specifically, the minimum seal contact force of the screw joint according to the embodiment rises with increasing shoulder angle (theta), when the shoulder angle (theta) became 4 °, the threaded joint of the comparative example It becomes larger than the minimum seal contact force. Minimum seal contact force is also increased with increasing shoulder angle (theta) after shoulder angle (theta) exceeds 4 °, once to level off the shoulder angle (theta) is 7 ° or more. However, the shoulder angle (theta) is 20 ° or more, again, the minimum seal contact force is increased with increasing the shoulder angle (theta).
[0064]
　Therefore, if the shoulder angle (theta) is 4 ° or more, than the threaded joint of the conventional wedge-type screw without the shoulder portion can be enhanced sealing contact force, it is possible to ensure excellent sealing performance. If the shoulder angle (theta) is 7 ° or more, the seal contact force is stable at a higher value than conventional threaded joint, it is possible to obtain an excellent sealing performance more reliably. If the shoulder angle (theta) is 20 ° or more, the sealing contact force increases considerably, it is possible to obtain a better sealing performance.
[0065]
　However, the shoulder angle (theta) exceeds 60 °, the seal contact force be increased shoulder angle (theta) is not increased. This is the influence of the stiffness reduction of the front end portion of the pin (10) is considered to be because becomes excessive. Therefore, the shoulder angle (theta) is preferably not less than 60 °.
[0066]
　The results of the evaluation of the anti-torque performance shown in FIG. Figure 5 is a graph showing the relationship between the value of MTV obtained with characteristic (torque resistance performance) shoulder angle and (theta). In Figure 5, for comparison with threaded joint (Example) provided with a shoulder portion and Kusabigata screw also shows MTV of wedge screw without a shoulder threaded joint (Comparative Example).
[0067]
　As shown in FIG. 5, the threaded joint according to the embodiment, has a tendency that the value of the MTV enough to increase the shoulder angle (theta) increases. When the shoulder angle (theta) is equal to or greater than 40 °, the value of the MTV of the threaded joint according to the embodiment is larger than the value of the MTV of the threaded joint according to the comparative example. Therefore, if the shoulder angle (theta) is 40 ° or more, it is possible to obtain high torque resistance performance than threaded joints of the conventional wedge-type screw without a shoulder.
[0068]
　From the above, designed shoulder angle of the shoulder surface in the disengaged state (11, 21) a (theta) to 4 ° or more, and, the insertion surface (133, 233) and between the load flanks of the threaded portion at the time of engagement completion (134 , 234) optionally with contacting each other contacting the shoulder surfaces (11, 21) with each other, it can be confirmed that it is realized an excellent sealing performance. In order to obtain more excellent sealing performance, the shoulder angle (theta) preferably 7 ° or more, more preferably if 20 ° or more. Further, if the shoulder angle (theta) and 40 ° or more, it was possible to confirm that you can achieve both excellent sealing performance, and excellent resistance to torque performance. The upper limit of the shoulder angle (theta) is not particularly limited, is preferably 60 °.

WE claims

A threaded joint for steel pipes,
　and the pin of the tubular connected to the steel pipe body,
　a tubular box which pin is fastened to the pin is inserted,
provided with,
　the pin is
　provided at the distal end portion of the pin ring a surface, and Pinshoruda surface inclined so as to be positioned on the distal end side of the pin than the inner peripheral portion outer peripheral edge portion,
　provided on the outer peripheral surface of the pin, and the male screw portion formed in wedge-shaped screw,
　the , a pin seal surface provided on the outer peripheral surface of the pin between the Pinshoruda surface and the external thread portion
has a,
　the box is
　located in the annular surface provided corresponding to said Pinshoruda face the back end of the box , and the box shoulder surface inclined to the outer peripheral edge of the inner peripheral edge portion positioned on the rear end side of the box,
　in correspondence with the male screw portion provided on the inner peripheral surface of the box, configured with wedge-shaped screw And the internal thread portion which,
　in correspondence with the pin seal surface has a box sealing surface provided on the inner peripheral surface of the box,
　in the engaged state, the Pinshoruda surface is in contact with the box shoulder surface, the male thread portion insertion surface and the load surface is in contact with insert surfaces and load flanks of each of the female screw portion, and the pin seal surface is in contact with the box sealing surface,
　Shoulder angle each of said Pinshoruda surface and the box shoulder surface is an angle formed between the plane perpendicular to the tube axis in a disengaged state is 4 ° or more, a threaded joint.
[Requested item 2]
　A threaded joint according to claim 1,
　wherein the shoulder angle is 40 ° or more, a threaded joint.
[Requested item 3]
　A threaded joint according to claim 1 or 2,
　wherein the shoulder angle is 60 ° or less, a threaded joint.