Threaded joint for pipe

Abstract

In the present invention, a threaded joint (100) comprises a pin (10) and a box (20). The pin (10) includes a pin seal surface (12) and a tapered male thread part (13). The tapered male thread part (13) includes male thread parts (131, 132). The first male thread part (131) is disposed on the side of the pin seal surface (12) near the pipe body (31). The second male thread part (132) is disposed on the side of the first male thread part (131) near the pipe body (31). The box (20) includes a box seal surface (22) and a tapered female thread part (23). The tapered female thread part (23) includes female thread parts (231, 232). The first male thread part (131) and the first female thread part (231) have a first taper ratio (T1). The second male thread part (132) and the second female thread part (232) have a second taper ratio (T2) that is smaller than the first taper ratio (T1).

Description

Pipe threaded joints

[0001] The present disclosure relates to a threaded pipe joint.

[0002] In oil wells, natural gas wells, and other areas, large numbers of steel pipes known as oil country tubular goods (OCTG) are used to extract underground resources. These steel pipes are connected to one another by threaded joints.

[0003] Threaded joints are broadly divided into integral and coupling types. In the case of integral joints, each steel pipe has a male thread at one end and a female thread at the other end. The steel pipes are connected by screwing the male thread of one steel pipe into the female thread of the other steel pipe to fasten them together. In the case of coupling joints, steel pipes with male threads at both ends are connected by a coupling. A coupling is a tubular member separate from the steel pipes to be connected, and has female threads at both ends. The male threads of the steel pipe are screwed into each of the female threads of the coupling to fasten them together. Generally, the end of a steel pipe with a male thread is called a pin, and the end of a steel pipe or coupling with a female thread is called a box.

[0004] One of the basic performance requirements of a threaded joint is the ability to seal against pressurized fluids. Conventionally, threaded joints that include a seal portion as a means for ensuring sealing performance have been known. For example, Patent Document 1 discloses a threaded joint in which a seal surface is provided at the tip of the pin. The box also has a seal surface that corresponds to the seal surface of the pin. When the pin and box are fastened together, the seal surface of the pin and the seal surface of the box come into contact with each other to form a seal portion.

[0005] International Publication No. 2019 / 111803

[0006] In recent years, as drilling environments for oil wells and other structures have become deeper, the multi-string design in which pipes are buried in multiple layers has become even more multi-layered, and slim threaded joints, which have a small difference between the outer diameter of the box and the outer diameter of the pipe body, are widely used.In deep wells, the formation pressure is applied to the multi-string, so the threaded joints that connect the pipes must have high external pressure resistance.

[0007] The box has a critical cross-section (a cross-section perpendicular to the pipe axis) at the innermost end of the threaded portion. In conventional threaded joints, the outer diameter of the box is significantly larger than the outer diameter of the pipe body, and the critical cross-sectional area of ​​the box is larger than the cross-sectional area of ​​the pipe body. On the other hand, slim-type threaded joints require the outer diameter of the box to be approximately the same as the outer diameter of the pipe body. Simply reducing the outer diameter of the box from a conventional threaded joint while maintaining the radial position and shape of the threaded portion results in the critical cross-sectional area of ​​the box becoming smaller than the cross-sectional area of ​​the pipe body, resulting in a decrease in the tensile strength of the threaded joint. To ensure the tensile strength of the threaded joint, it is possible to maintain the ratio of the critical cross-sectional area of ​​the box to the cross-sectional area of ​​the pipe body by shifting the radial position of the threaded portion along with the outer diameter of the box toward the pipe axis (i.e., reducing the diameter of the threaded portion). However, because slim-type threaded joints used in multi-stage strings are subject to constraints on both the outer diameter and the inner diameter, the pins are thinned, reducing their rigidity. This can impair the external pressure resistance of the threaded joint.

[0008] Specifically, when a seal surface is provided at the tip of the pin, pressurized fluid (external pressure) from outside the threaded joint reaches the vicinity of the seal surface through the gap between the male and female threads or through the fluid lubricant applied to the surfaces of these threads. If the pin does not have sufficient rigidity, the pin will be deformed overall by contracting in diameter due to external pressure that extends over a wide area of ​​the threads, and sufficient contact between the seal surface of the pin and the seal surface of the box will not be ensured, which may result in a decrease in sealing performance against external pressure.

[0009] Furthermore, if the pin does not have sufficient rigidity, the box may contract due to the load of external pressure, causing the tip of the pin to plastically deform so that it bends toward the pipe axis (as if it is locally squeezed). In this case, sufficient contact between the sealing surface of the pin and the sealing surface of the box cannot be ensured, and the subsequent load of pressurized fluid (internal pressure) from inside the threaded joint may cause an internal pressure leak.

[0010] Therefore, an object of the present disclosure is to provide a tubular threaded joint that can achieve good resistance to external pressure while ensuring tensile strength.

[0011] A tubular threaded joint according to the present disclosure comprises a tubular pin and a tubular box. The pin is provided contiguous with the pipe body. The pin is inserted into the box. The box is fastened to the pin. The pin includes a pin seal surface and a tapered male thread portion. The pin seal surface is provided on the outer peripheral surface of the pin at the tip of the pin. The tapered male thread portion is provided on the outer peripheral surface of the pin. The tapered male thread portion includes a first male thread portion and a second male thread portion. The first male thread portion is arranged on the pipe body side of the pin seal surface. The second male thread portion is arranged on the pipe body side of the first male thread portion and is continuous with the first male thread portion. The box includes a box seal surface and a tapered female thread portion. The box seal surface is provided on the inner peripheral surface of the box corresponding to the pin seal surface. The tapered female thread portion is provided on the inner peripheral surface of the box. The tapered female thread portion includes a first female thread portion and a second female thread portion. The first female thread corresponds to the first male thread. The second female thread corresponds to the second male thread. The first male thread and the first female thread have a first taper rate. The second male thread and the second female thread have a second taper rate. The second taper rate is smaller than the first taper rate.

[0012] A tubular threaded joint according to the present disclosure can achieve good resistance to external pressure while ensuring its tensile strength.

[0013] Fig. 1 is a longitudinal cross-sectional view of a tubular threaded joint according to an embodiment. Fig. 2 is an enlarged view of a first male threaded portion and a first female threaded portion included in the threaded joint shown in Fig. 1. Fig. 3 is an enlarged view of a second male threaded portion and a second female threaded portion included in the threaded joint shown in Fig. 1. Fig. 4 is a schematic diagram for explaining the effects of the embodiment. Fig. 5 is a schematic diagram for explaining the effects of the embodiment.

[0014] A tubular threaded joint according to an embodiment comprises a tubular pin and a tubular box. The pin is provided contiguous with the pipe body. The pin is inserted into the box. The box is fastened to the pin. The pin includes a pin seal surface and a tapered male thread portion. The pin seal surface is provided on the outer peripheral surface of the pin at the tip of the pin. The tapered male thread portion is provided on the outer peripheral surface of the pin. The tapered male thread portion includes a first male thread portion and a second male thread portion. The first male thread portion is arranged on the pipe body side of the pin seal surface. The second male thread portion is arranged on the pipe body side of the first male thread portion and is continuous with the first male thread portion. The box includes a box seal surface and a tapered female thread portion. The box seal surface is provided on the inner peripheral surface of the box corresponding to the pin seal surface. The tapered female thread portion is provided on the inner peripheral surface of the box. The tapered female thread portion includes a first female thread portion and a second female thread portion. The first female thread corresponds to the first male thread. The second female thread corresponds to the second male thread. The first male thread and the first female thread have a first taper rate. The second male thread and the second female thread have a second taper rate. The second taper rate is smaller than the first taper rate (first configuration).

[0015] In a tubular threaded joint according to the first configuration, the tapered male thread portion of the pin includes a first male thread portion and a second male thread portion. The tapered female thread portion of the box includes a first female thread portion and a second female thread portion corresponding to the tapered male thread portion of the pin. The taper rate (second taper rate) of the second male thread portion and the second female thread portion on the pipe body side is smaller than the taper rate (first taper rate) of the first male thread portion and the first female thread portion on the tip side of the pin, i.e., the seal portion side. This allows the thickness and rigidity of the pin to be increased while maintaining the critical cross-sectional area of ​​the box within the dimensional constraints of the outer diameter and inner diameter imposed on the threaded joint. Therefore, good external pressure resistance can be achieved while ensuring the tensile strength of the threaded joint.

[0016] In the tubular threaded joint according to the first configuration, the length of the second male threaded portion in the axial direction of the pin may be greater than the length of the first male threaded portion (second configuration).

[0017] In the second configuration, the axial length of the second male thread portion having a small taper rate is longer than the axial length of the first male thread portion having a large taper rate. This allows the pin to have a larger area with a larger wall thickness. Therefore, the rigidity of the pin can be further increased, making it easier to improve its resistance to external pressure. Furthermore, within the constraints of the outer diameter and inner diameter of the threaded joint, when the axial length of the second male thread portion having a small taper rate is longer than when the axial length of the first male thread portion having a large taper rate is longer, the overall length of the tapered male thread portion is longer, and the meshing length of the tapered male thread portion and the tapered female thread portion is increased. This improves the tensile resistance of the threaded joint, making it less likely for jump-out to occur.

[0018] In a tubular threaded joint according to the first or second configuration, the tapered male thread portion may include a complete thread portion and an incomplete thread portion. The incomplete thread portion is located closer to the pipe body than the complete thread portion. In this case, the boundary between the first and second male thread portions may be located within the complete thread portion (third configuration).

[0019] In a tubular threaded joint according to any of the first to third configurations, the pin may further include a pin shoulder surface. The pin shoulder surface is provided, for example, on the tip surface of the pin. In this case, the box further includes a box shoulder surface, and the box shoulder surface is provided on the rear side of the box in correspondence with the pin shoulder surface (fourth configuration).

[0020] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In each drawing, the same or equivalent components are designated by the same reference numerals, and the same description will not be repeated.

[0021] 1 is a longitudinal cross-sectional view of a tubular threaded joint 100 according to this embodiment. The longitudinal cross-section of the threaded joint 100 is a cross-section obtained by cutting the threaded joint 100 along a plane that includes the pipe axis X. Hereinafter, the direction in which the pipe axis X extends will be referred to as the axial direction, and the radial direction of the threaded joint 100 will simply be referred to as the radial direction.

[0022] The threaded joint 100 is used to connect pipes to each other. The threaded joint 100 typically connects steel pipes to each other. The threaded joint 100 includes a tubular pin 10 and a tubular box 20. The pin 10 is provided continuous with the main body 31 of the pipe 30 to be connected. The pin 10 is provided at the end of the pipe 30. The pin 10 is inserted into the box 20 and fastened to the box 20. The box 20 may be provided at the end of the pipe to be connected, or may be provided at the end of a coupling separate from the pipe to be connected. In other words, the threaded joint 100 may be an integral type threaded joint or a coupling type threaded joint.

[0023] The pin 10 includes a pin shoulder surface 11, a pin seal surface 12, and a tapered male thread portion 13. The pin shoulder surface 11, the pin seal surface 12, and the tapered male thread portion 13 are arranged in this order from the tip side of the pin 10 toward the pipe body 31 side.

[0024] The pin shoulder surface 11 is provided on the tip surface of the pin 10. The pin shoulder surface 11 is an annular surface whose axis is the pipe axis X. In a longitudinal cross section of the threaded joint 100, the pin shoulder surface 11 may be perpendicular to the pipe axis X or may be inclined relative to the pipe axis X. The annular pin shoulder surface 11 may be inclined relative to the pipe axis X, for example, so that its outer circumferential edge is located closer to the tip of the pin 10 than the inner circumferential edge.

[0025] The pin seal surface 12 is provided on the outer peripheral surface of the pin 10 at the tip end of the pin 10. The pin seal surface 12 is disposed between the pin shoulder surface 11 and the tapered male thread portion 13. The pin seal surface 12 is a side surface of a rotationally symmetric body with the pipe axis X as its axis of rotation. In a vertical cross-sectional view of the threaded joint 100, the pin seal surface 12 may be, for example, a curve that is convex toward the box 20 side, or a straight line that is inclined relative to the pipe axis X so as to approach the pipe axis X toward the tip end of the pin 10. The pin seal surface 12 may be configured by combining two or more of such curves and / or straight lines.

[0026] The tapered male thread portion 13 is provided on the outer peripheral surface of the pin 10. The tapered male thread portion 13 is provided from the vicinity of the pin seal surface 12 to the vicinity of the pipe body 31. The tapered male thread portion 13 is configured as a tapered thread as a whole. Examples of the types of threads that make up the tapered male thread portion 13 include an API standard buttress thread, a trapezoidal thread formed based on a buttress thread, and a dovetail-shaped thread.

[0027] The tapered male thread portion 13 includes a first male thread portion 131 and a second male thread portion 132. The first male thread portion 131 is disposed on the pipe body 31 side relative to the pin seal surface 12. The first male thread portion 131 is provided in a region of the tapered male thread portion 13 that is close to the pin seal surface 12. The second male thread portion 132 is disposed on the pipe body 31 side relative to the first male thread portion 131. The second male thread portion 132 is continuous with the first male thread portion 131. In other words, no other components, such as a seal surface or a shoulder surface, are interposed between the first male thread portion 131 and the second male thread portion 132. The second male thread portion 132 is directly connected to the first male thread portion 131.

[0028] The box 20 has an outer diameter D ｂ The box 20 has an outer diameter D ｂ is, for example, the outer diameter D of the pipe body 31 ０ 110%。 In other words, the threaded joint 100 may be a so-called slim type (semi-flush type) threaded joint. The box 20 includes a box shoulder surface 21, a box seal surface 22, and a tapered female thread portion 23. The box shoulder surface 21, the box seal surface 22, and the tapered female thread portion 23 are provided on the box 20 in correspondence with the pin shoulder surface 11, the pin seal surface 12, and the tapered male thread portion 13, respectively.

[0029] The box shoulder surface 21 is provided on the back side of the box 20 in correspondence with the pin shoulder surface 11. Like the pin shoulder surface 11, the box shoulder surface 21 is an annular surface whose axis is the pipe axis X. When the pin 10 and box 20 are fastened together, the box shoulder surface 21 comes into contact with the pin shoulder surface 11 and forms a shoulder portion together with the pin shoulder surface 11. The pin shoulder surface 11 and the box shoulder surface 21 come into contact during fastening rotation and cause a sudden increase in torque resistance, thereby detecting the completion of make-up, and also play a role in generating a make-up axial force inside the threaded joint 100, thereby strengthening the engagement of the threaded portions 13, 23.

[0030] The box seal surface 22 is provided on the inner peripheral surface of the box 20 in correspondence with the pin seal surface 12. The box seal surface 22 is disposed between the box shoulder surface 21 and the tapered female thread portion 23. The box seal surface 22 is a side surface of a rotationally symmetric body with the pipe axis X as its axis of rotation. In a vertical cross-sectional view of the threaded joint 100, the box seal surface 22 may be, for example, a curve that is convex toward the pin 10 side, or a straight line that is inclined with respect to the pipe axis X so as to approach the pipe axis X toward the back side of the box 20. The box seal surface 22 may be configured by combining two or more types of such curves and / or straight lines.

[0031] In a fastened state, the pin seal surface 12 and the box seal surface 22 form a seal portion through metal-to-metal contact. Specifically, the box seal surface 22 has a diameter smaller than the diameter of the pin seal surface 12 when the pin 10 and the box 20 are not fastened together. The difference between the diameter of the pin seal surface 12 and the diameter of the box seal surface 22 is called the radial interference amount. Due to this interference amount, in a fastened state, the box seal surface 22 interferes with the pin seal surface 12, causing the pin seal surface 12 to contract in diameter and the box seal surface 22 to expand in diameter. Due to the elastic recovery force of the contracted pin seal surface 12 and the expanded box seal surface 22, the box seal surface 22 comes into interference contact with the pin seal surface 12 over the entire circumference, generating high contact pressure between the pin seal surface 12 and the box seal surface 22.

[0032] The tapered female thread portion 23 is provided on the inner peripheral surface of the box 20. The tapered female thread portion 23 is provided from the vicinity of the box seal surface 22 to the vicinity of the pipe end portion of the box 20. The tapered female thread portion 23 is configured as a tapered thread as a whole. The tapered female thread portion 23 is configured with a thread having a shape corresponding to the tapered male thread portion 13.

[0033] The tapered female thread portion 23 includes a first female thread portion 231 and a second female thread portion 232. The first female thread portion 231 is disposed closer to the pipe end of the box 20 than the box seal surface 22. The first female thread portion 231 is provided in a region of the tapered female thread portion 23 that is close to the box seal surface 22. The second female thread portion 232 is disposed closer to the pipe end of the box 20 than the first female thread portion 231. The second female thread portion 232 is continuous with the first female thread portion 231. That is, no other components, such as a seal surface or a shoulder surface, are interposed between the first female thread portion 231 and the second female thread portion 232. The second female thread portion 232 is directly connected to the first female thread portion 231. The first female thread portion 231 corresponds to the first male thread portion 131, and the second female thread portion 232 corresponds to the second male thread portion 132.

[0034] Fig. 2 is an enlarged view of the first male threaded portion 131 and the first female threaded portion 231. Fig. 3 is an enlarged view of the second male threaded portion 132 and the second female threaded portion 232.

[0035] 2, the first male thread portion 131 includes a thread crest surface 131a, a thread groove bottom surface 131b, a stab flank surface 131c, and a load flank surface 131d. The thread crest surface 131a is connected to the thread groove bottom surface 131b via the stab flank surface 131c and the load flank surface 131d. The stab flank surface 131c is located closer to the tip of the pin 10 than the thread crest surface 131a. The load flank surface 131d is located closer to the pipe body 31 than the thread crest surface 131a.

[0036] The first female thread portion 231 includes a thread crest surface 231a, a thread groove bottom surface 231b, a stab flank surface 231c, and a load flank surface 231d. When the pin 10 and the box 20 are fully fastened, the load flank surface 231d of the first female thread portion 231 contacts the load flank surface 131d of the first male thread portion 131, and the stab flank surface 231c of the first female thread portion 231 faces the stab flank surface 131c of the first male thread portion 131 with a gap therebetween. Furthermore, when the fastening is completed, the thread crest surface 231a of the first female thread portion 231 contacts the thread groove bottom surface 131b of the first male thread portion 131, and the thread groove bottom surface 231b of the first female thread portion 231 faces the thread crest surface 131a of the first male thread portion 131 with a gap therebetween. Alternatively, the bottom surface 231b of the thread groove of the first female thread portion 231 may be in contact with the crest surface 131a of the thread ridge of the first male thread portion 131, and the crest surface 231a of the thread ridge of the first female thread portion 231 may face the bottom surface 131b of the thread groove of the first male thread portion 131 with a gap therebetween, or may be in contact with the bottom surface 131b of the thread groove of the first male thread portion 131.

[0037] The first female thread portion 231 has a radial interference with the first male thread portion 131. That is, when the pin 10 and the box 20 are not fastened to each other, for example, the diameter of the thread crest 231 a of the first female thread portion 231 is smaller than the diameter of the thread groove bottom 131 b of the first male thread portion 131. More specifically, when the diameters of the thread crest 231 a of the first female thread portion 231 and the thread groove bottom 131 b of the first male thread portion 131 are compared at positions equiaxially distant from the pin shoulder surface 11 and the box shoulder surface 21 ( FIG. 1 ) in the not fastened state, the diameter of the thread crest 231 a is smaller than the diameter of the thread groove bottom 131 b. Furthermore, when the pin 10 and the box 20 are not fastened together, the diameter of the thread groove bottom 231b of the first female threaded portion 231 may be smaller than the diameter of the thread crest 131a of the first male threaded portion 131. That is, when the diameters of the thread groove bottom 231b of the first female threaded portion 231 and the thread crest 131a of the first male threaded portion 131 are compared at positions equiaxially distant from the pin shoulder surface 11 and the box shoulder surface 21 ( FIG. 1 ) in the non-fastened state, the diameter of the thread groove bottom 231b may be smaller than the diameter of the thread crest 131a. When the pin 10 and the box 20 are fastened together, at least one of the thread crest 231a and the thread groove bottom 231b of the first female threaded portion 231 comes into interference contact with the first male threaded portion 131.

[0038] The taper rate of the first male thread portion 131 is the taper rate of a taper line L11 formed by connecting the centers of the load flank surfaces 131d of the multiple complete threads in a vertical cross-sectional view of the threaded joint 100. The taper rate of the first female thread portion 231 is the taper rate of a taper line L21 formed by connecting the centers of the load flank surfaces 231d of the multiple complete threads in a vertical cross-sectional view of the threaded joint 100. The taper rate of the first female thread portion 231 is equal to the taper rate of the first male thread portion 131. However, the taper rate of the first female thread portion 231 only needs to be the same as the taper rate of the first male thread portion 131 in terms of design, and differences between the two within the manufacturing tolerances are permitted. Examples of manufacturing tolerances include those specified in API Spec. 5B:2008. API Spec. 5B:2008 specifies that the manufacturing tolerances for the thread taper of the buttress thread are +0.45% to -0.25% for the female thread portion of the box (coupling thread), +0.35% to -0.15% for the complete male thread portion of the pin, and +0.45% to -0.15% for the incomplete male thread portion of the pin. The taper ratio of the first male thread portion 131 and the first female thread portion 231 is a first taper ratio T1. The first taper ratio T1 is, for example, 10.00% or more (1 / 10 taper or more). The first taper ratio T1 may be 30.00% or less (3 / 10 taper or less). Note that FIG. 2 shows only one side of the taper lines L11 and L21 relative to the pipe axis X.

[0039] 3, the second male thread portion 132 includes a thread crest surface 132a, a thread groove bottom surface 132b, a stab flank surface 132c, and a load flank surface 132d. The thread crest surface 132a is connected to the thread groove bottom surface 132b via the stab flank surface 132c and the load flank surface 132d. The stab flank surface 132c is located closer to the tip of the pin 10 than the thread crest surface 132a. The load flank surface 132d is located closer to the pipe body 31 than the thread crest surface 132a.

[0040] The second female thread portion 232 includes a thread crest surface 232a, a thread groove bottom surface 232b, a stab flank surface 232c, and a load flank surface 232d. When the pin 10 and the box 20 are fully fastened, the load flank surface 232d of the second female thread portion 232 contacts the load flank surface 132d of the second male thread portion 132, and the stab flank surface 232c of the second female thread portion 232 faces the stab flank surface 132c of the second male thread portion 132 with a gap therebetween. Furthermore, when the fastening is completed, the thread crest surface 232a of the second female thread portion 232 contacts the thread groove bottom surface 132b of the second male thread portion 132, and the thread groove bottom surface 232b of the second female thread portion 232 faces the thread crest surface 132a of the second male thread portion 132 with a gap therebetween. Alternatively, the bottom surface 232b of the thread groove of the second female threaded portion 232 may be in contact with the crest surface 132a of the thread ridge of the second male threaded portion 132, and the crest surface 232a of the thread groove of the second female threaded portion 232 may face the bottom surface 132b of the thread groove of the second male threaded portion 132 with a gap therebetween, or may be in contact with the bottom surface 132b of the thread groove of the second male threaded portion 132.

[0041] The second female thread portion 232 has a radial interference with the second male thread portion 132. That is, when the pin 10 and the box 20 are not fastened to each other, for example, the diameter of the thread crest 232a of the second female thread portion 232 is smaller than the diameter of the thread groove bottom 132b of the second male thread portion 132. More specifically, when the diameters of the thread crest 232a of the second female thread portion 232 and the thread groove bottom 132b of the second male thread portion 132 are compared at positions equiaxially distant from the pin shoulder surface 11 and the box shoulder surface 21 ( FIG. 1 ) in the not fastened state, the diameter of the thread crest 232a is smaller than the diameter of the thread groove bottom 132b. Furthermore, when the pin 10 and the box 20 are not fastened together, the diameter of the thread groove bottom surface 232b of the second female thread portion 232 may be smaller than the diameter of the thread crest surface 132a of the second male thread portion 132. That is, when the diameters of the thread groove bottom surface 232b of the second female thread portion 232 and the thread crest surface 132a of the second male thread portion 132 are compared at positions equiaxially distant from the pin shoulder surface 11 and the box shoulder surface 21 ( FIG. 1 ) in the non-fastened state, the diameter of the thread groove bottom surface 232b may be smaller than the diameter of the thread crest surface 132a. When the pin 10 and the box 20 are fastened together, at least one of the thread crest surface 232a and the thread groove bottom surface 232b of the second female thread portion 232 comes into interference contact with the second male thread portion 132.

[0042] The taper rate of the second male thread portion 132 is the taper rate of a taper line L12 formed by connecting the centers of the load flank surfaces 132d of the multiple complete threads in a vertical cross-sectional view of the threaded joint 100. The taper rate of the second female thread portion 232 is the taper rate of a taper line L22 formed by connecting the centers of the load flank surfaces 232d of the multiple complete threads in a vertical cross-sectional view of the threaded joint 100. The taper rate of the second female thread portion 232 is equal to the taper rate of the second male thread portion 132. However, as with the first thread portions 131, 231, the taper rate of the second female thread portion 232 only needs to be the same as the taper rate of the second male thread portion 132 in terms of design, and differences between the two within manufacturing tolerances are permitted. The taper rate of the second male thread portion 132 and the taper rate of the second female thread portion 232 are the second taper rate T2. The second taper ratio T2 is, for example, 1.50% or more (3 / 200 taper or more). The second taper ratio T2 may be 10.00% or less (1 / 10 taper or less). Note that Fig. 3 shows only one side of the tapered lines L12 and L22 with respect to the tube axis X.

[0043] As shown in Fig. 2, the first male thread portion 131 and the first female thread portion 231 have a first taper rate T1. As shown in Fig. 3, the second male thread portion 132 and the second female thread portion 232 have a second taper rate T2. The second taper rate T2 is smaller than the first taper rate T1. The ratio T1 / T2 of the first taper rate T1 to the second taper rate T2 is, for example, 1.25 or more. T1 / T2 may also be 15.00 or less.

[0044] Returning to FIG. 1 , in the axial direction of the pin 10, the length B of the second male thread portion 132, which extends at the second taper rate T2, is preferably greater than the length A of the first male thread portion 131, which extends at the first taper rate T1. However, the length B of the second male thread portion 132 may be less than the length A of the first male thread portion 131. The ratio of the length B of the second male thread portion 132 to the length A of the first male thread portion 131 is, for example, 0.25 or greater (B / A≧0.25). When the length B of the second male thread portion 132 is greater than the length A of the first male thread portion 131, the ratio of the length B to the length A may be 1.50 or greater (B / A≧1.50). The ratio of the length B of the second male thread portion 132 to the length A of the first male thread portion 131 may be 3.00 or less (B / A≦3.00). The first male thread portion 131 includes, for example, at least three threads in a vertical cross-sectional view of the threaded joint 100. The upper limit of the number of threads included in the first male thread portion 131 in a vertical cross-sectional view of the threaded joint 100 is naturally determined by the thickness of the pin 10.

[0045] In the axial direction of the threaded joint 100, the boundary 233 between the first female thread portion 231 and the second female thread portion 232 in the tapered female thread portion 23 is located at substantially the same position as the boundary 133 between the first male thread portion 131 and the second male thread portion 132 in the tapered male thread portion 13. Specifically, the boundary 233 between the first female thread portion 231 and the second female thread portion 232 is located within a range calculated from the manufacturing tolerances of the other elements of the threaded joint 100, using the boundary 133 between the first male thread portion 131 and the second male thread portion 132 as a reference. For example, the boundary 233 between the first female thread portion 231 and the second female thread portion 232 is located preferably within a range of ±0.50 times the thread pitch of the first male thread portion 131, and more preferably within a range of ±0.20 times the thread pitch of the first male thread portion 131, from the boundary 133 between the first male thread portion 131 and the second male thread portion 132 in the axial direction of the threaded joint 100. The boundary 133 between the first male thread portion 131 and the second male thread portion 132 is the intersection of the taper line L11 and the taper line L12. The boundary 233 between the first female thread portion 231 and the second female thread portion 232 is the intersection of the taper line L21 and the taper line L22. In Figure 1, to simplify the drawing, the taper line L11 of the first male thread portion 131 and the taper line L21 of the first female thread portion 231 are shown by a common double-dashed line, and the taper line L12 of the second male thread portion 132 and the taper line L22 of the second female thread portion 232 are shown by a common double-dashed line.

[0046] Continuing to refer to FIG. 1 , the tapered male thread portion 13 includes a complete thread portion 134 and an incomplete thread portion 135. The complete thread portion 134 extends from near the pin seal surface 12 toward the pipe body 31. The incomplete thread portion 135 is located closer to the pipe body 31 than the complete thread portion 134. The incomplete thread portion 135 is a portion of the tapered male thread portion 13 in which the thread crest surface is gradually reduced as it approaches the pipe body 31. Therefore, the thread height of the incomplete thread portion 135 is smaller than the thread height of the complete thread portion 134. A boundary 133 between the first male thread portion 131 and the second male thread portion 132 is located, for example, within the complete thread portion 134 of the tapered male thread portion 13. In this case, the complete thread portion 134 of the tapered male thread portion 13 exists across the first male thread portion 131 and the second male thread portion 132, and the incomplete thread portion 135 exists within the second male thread portion 132.

[0047] [Effect] In the tubular threaded joint 100 according to this embodiment, the tapered male thread portion 13 of the pin 10 includes a first male thread portion 131 and a second male thread portion 132, and correspondingly, the tapered female thread portion 23 of the box 20 includes a first female thread portion 231 and a second female thread portion 232. The second taper rate T2 of the second male thread portion 132 and the second female thread portion 232 on the pipe body 31 side is smaller than the first taper rate T1 of the first male thread portion 131 and the first female thread portion 231 on the tip end side of the pin 10, i.e., the seal surface 12, 22 side. This makes it possible to increase the wall thickness and rigidity of the pin 10 while maintaining the critical cross-sectional area of ​​the box 20 within the dimensional constraints on the outer diameter and inner diameter imposed on the threaded joint 100. This will be explained in more detail below.

[0048] Figure 4 is a longitudinal cross-sectional view showing the schematic configuration of a threaded joint 100 according to the present embodiment, and Figure 5 is a longitudinal cross-sectional view showing the schematic configuration of a threaded joint 900 in which the design of each component is the same as that of the threaded joint 100 shown in Figure 4, except for the taper rate of the threaded portions 13, 23. In the threaded joint 100 of Figure 4, the taper rate of the threaded portions 13, 23 changes from a first taper rate T1 to a second taper rate T2 (T1 > T2) from the seal surface 12, 22 side toward the pipe main body 31 side, whereas in the threaded joint 900 of Figure 5, the threaded portions 13, 23 have a uniform taper rate T0 throughout. 4 and 5 , the critical cross-sectional area S of the box 20 in the threaded joint 100 (the cross-sectional area of ​​the box 20 at the engagement end of the threaded portions 13, 23) is equal to the critical cross-sectional area S of the box 20 in the threaded joint 900, but the thickness of the portion of the pin 10 where the tapered male thread portion 13 is provided is greater in the threaded joint 100 than in the threaded joint 900. In this way, by making the threaded portions 13, 23 two-stage tapered threaded portions, the thickness of the pin 10 can be increased while ensuring the critical cross-sectional area of ​​the box 20, thereby increasing the rigidity of the pin 10. Therefore, overall diametrical contraction deformation of the pin 10 due to the intrusion of external pressure into the threaded portions 13, 23 can be reduced. Furthermore, in the threaded joint 100 according to this embodiment, the thickness of the box around the box seal surface 22 from the critical cross section of the box 20 to the box shoulder surface 21 is equivalent to that of the threaded joint 900 in Figure 5, and therefore plastic deformation of the tip of the pin 10 due to the load of external pressure and the diameter reduction deformation of the box 20 can be suppressed to the same extent as in the threaded joint 900 in Figure 5. Therefore, the threaded joint 100 according to this embodiment can achieve good external pressure resistance.

[0049] For example, if the tapered male thread portion 13 is composed of a first male thread portion 131 extending at a first taper rate T1 and a second male thread portion 132 extending at a second taper rate T2, and the tapered female thread portion 23 is a female thread portion with a uniform taper rate, the intended radial interference between the tapered male thread portion 13 and the tapered female thread portion 23 may not be obtained, resulting in performance not being achieved due to insufficient interference, or excessive interference between the tapered male thread portion 13 and the tapered female thread portion 23 may cause seizure. However, in the threaded joint 100 according to this embodiment, both the tapered male thread portion 13 and the tapered female thread portion 23 are two-step tapered thread portions, and the positions of the taper change points of the tapered male thread portion 13 and the tapered female thread portion 23 are configured so that they substantially coincide in the axial direction. This ensures the meshing length between the tapered male thread portion 13 and the tapered female thread portion 23. Therefore, when a tensile load is applied to the threaded joint 100, jump-out (disengagement) is less likely to occur in the threaded joint 100. In addition, excessive interference between the tapered male thread portion 13 and the tapered female thread portion 23 is less likely to occur, and seizure when the pin 10 and the box 20 are fastened together can be prevented.

[0050] In this embodiment, the axial length B of the second male thread portion 132 is preferably greater than the axial length A of the first male thread portion 131. This allows the pin 10 to have a larger area with a larger wall thickness. Therefore, the rigidity of the pin 10 can be further increased, making it easier to improve its resistance to external pressure. Furthermore, within the constraints of the outer and inner diameters of the pin 10, the overall length of the tapered male thread portion 13 is greater when the axial length B of the second male thread portion 132, which has a relatively small second taper rate, is greater than when the axial length A of the first male thread portion 131, which has a relatively large first taper rate T1, is long, thereby increasing the engagement length between the tapered male thread portion 13 and the tapered female thread portion 23. This improves the tensile resistance of the threaded joint 100 and suppresses jump-out.

[0051] For example, if a component such as a seal surface, shoulder surface, or other unthreaded portion is provided between the first male thread portion 131 and the second male thread portion 132, the component requires a thick wall. Furthermore, the maximum diameter of the crest surface 131a of the first male thread portion 131 must be smaller than the diameter of the component, resulting in a smaller wall thickness at the tip of the pin 10. This reduces the external pressure resistance of the threaded joint 100. Furthermore, if a component other than a threaded portion is disposed between the first male thread portion 131 and the second male thread portion 132, the threaded joint 100 will have a structure with an intermediate danger cross section. The area of ​​the intermediate danger cross section is typically smaller than the area of ​​the danger cross section of the pin 10 or box 20 when no component other than a threaded portion exists between the first male thread portion 131 and the second male thread portion 132. This may reduce the tensile resistance of the threaded joint 100.

[0052] In contrast, in the present embodiment, the second male thread portion 132 is provided contiguous with the first male thread portion 131. That is, the first male thread portion 131 and the second male thread portion 132 are disposed adjacent to each other, and no other components are interposed between the first male thread portion 131 and the second male thread portion 132. This prevents a reduction in the thickness of the tip portion of the pin 10 due to components other than the first male thread portion 131 and the second male thread portion 132. As a result, it becomes easier to ensure the rigidity of the pin 10, and good external pressure resistance can be ensured. Furthermore, because the threaded joint 100 does not have an intermediate critical cross section, the tensile resistance of the threaded joint 100 can be ensured.

[0053] In the threaded joint 100 according to the present embodiment, when the pin 10 and the box 20 are fastened together, at least one of the thread crest 231 a and the thread groove bottom 231 b of the first female threaded portion 231 comes into interference contact with the first male threaded portion 131. Furthermore, in the fastened state, at least one of the thread crest 232 a and the thread groove bottom 232 b of the second female threaded portion 232 comes into interference contact with the second male threaded portion 132. By causing the first male threaded portion 131 and the second male threaded portion 132 to interfere with the first female threaded portion 231 and the second female threaded portion 232 in this manner, it is possible to maximize the tensile resistance performance of the threaded joint 100 within its limited wall thickness. More specifically, by configuring the tapered thread portions 13, 23 using first thread portions 131, 231 and second thread portions 132, 232 with different taper rates, the actual critical cross-sectional area S of the box 20 at the engagement ends of the tapered thread portions 13, 23 is maximized, while by providing a radial interference amount in the tapered thread portions 13, 23 to make the engagement reliable and strong, the tensile resistance performance of the threaded joint 100 can be maximized within the constraints of the wall thickness.

[0054] 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.

[0055] In the threaded joint 100 according to the above embodiment, the pin 10 includes a pin seal surface 12 provided at its tip. In addition to the pin seal surface 12 as an inner pin seal surface, the pin 10 may include another pin seal surface as an outer pin seal surface. The outer pin seal surface is provided on the pipe body 31 side relative to the tapered male thread portion 13. In this case, the box 20 includes a box seal surface 22 as an inner box seal surface, as well as an outer box seal surface corresponding to the outer pin seal surface. The outer pin seal surface and the outer box seal surface can provide sealing performance primarily against external pressure. However, the threaded joint 100 according to the above embodiment can achieve good external pressure resistance with only the inner seal surfaces 12 and 22. Therefore, the threaded joint 100 does not particularly require an outer pin seal surface or an outer box seal surface.

[0056] In the threaded joint 100 according to the above embodiment, the pin 10 includes a pin shoulder surface 11 provided on its tip end surface. The box 20 includes a box shoulder surface 21 corresponding to the pin shoulder surface 11. However, the pin 10 and the box 20 do not have to include shoulder surfaces.

[0057] Alternatively, the pin 10 can include another pin shoulder surface in addition to or instead of the pin shoulder surface 11. The other pin shoulder surface is provided on the pipe body 31 side with respect to the tapered male thread portion 13. In this case, the box 20 includes a box shoulder surface corresponding to this pin shoulder surface. These shoulder surfaces can exhibit a certain level of sealing performance against external pressure. However, the threaded joint 100 according to the above embodiment can achieve good external pressure resistance performance with only the inner seal surfaces 12, 22. Therefore, in the threaded joint 100, of the multiple components provided on the pin 10 and box 20, the components located closest to the pipe body 31 may be the tapered male thread portion 13 and the tapered female thread portion 23.

[0058] In the threaded joint 100 according to the above embodiment, when the pin 10 and the box 20 are fastened together, the load flank surface 131d of the first male thread portion 131 contacts the load flank surface 231d of the first female thread portion 231, and the stab flank surface 131c of the first male thread portion 131 faces, with a gap, the stab flank surface 231c of the first female thread portion 231. Furthermore, in the fastened state, the load flank surface 132d of the second male thread portion 132 contacts the load flank surface 232d of the second female thread portion 232, and the stab flank surface 132c of the second male thread portion 132 faces, with a gap, the stab flank surface 232c of the second female thread portion 232. However, in the fastened state, the load flank surface 131d of the first male thread portion 131 and the load flank surface 132d of the second male thread portion 132 may be in contact with the load flank surface 231d of the first female thread portion 231 and the load flank surface 232d of the second female thread portion 232, respectively, and the stab flank surface 131c of the first male thread portion 131 and the stab flank surface 132c of the second male thread portion 132 may be in contact with the stab flank surface 231c of the first female thread portion 231 and the stab flank surface 232c of the second female thread portion 232, respectively. In other words, the tapered male thread portion 13 and the tapered female thread portion 23 may be configured as wedge threads.

[0059] In the above embodiment, the tapered male thread portion 13 is composed of a first male thread portion 131 and a second male thread portion 132. However, the tapered male thread portion 13 may further include other male thread portions. That is, the tapered male thread portion 13 may be a male thread portion having a two-stage thread taper as in the above embodiment, but may also be a male thread portion having a three-stage or more thread taper. The tapered female thread portion 23 is configured to have a thread taper corresponding to the tapered male thread portion 13.

[0060] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited to the following examples.

[0061] To confirm the effects of the present disclosure, an analysis was conducted on multiple threaded joint specimens using the elastic-plastic finite element method (FEM). In this analysis, after the pin and box were tightened on each specimen, a repeated combined load simulating the test specified in API RP 5C5:2017 was applied to evaluate the external pressure resistance.

[0062] The main common conditions for this analysis are as follows: ・Pipe size: 9-5 / 8" 53.5# (pipe body outer diameter 244.5 mm, wall thickness 13.8 mm) ・Material: API standard Q125 steel (yield stress 862 MPa, elastic modulus 205 GPa) ・Thread pitch: 5.08 to 5.11 mm ・Load flank surface height of male thread: 1.40 to 1.45 mm ・Outer diameter of box: 252.5 mm ・Tightening conditions: After pressure contact between shoulder surfaces, a further 1 / 100th turn

[0063] The external pressure resistance was evaluated by the seal contact force under a simple external pressure load after applying internal pressure + tension, internal pressure + compression, and external pressure + compression equivalent to 100% of the yield stress of the pipe body. The higher this seal contact force, the better the external pressure resistance. Table 1 shows the analysis conditions and evaluation results for each test specimen.

[0064]

[0065] In the threaded joints of specimens 1 to 5, the threads are composed of a first threaded portion having a taper rate T1 and a second threaded portion having a taper rate T2 smaller than T1 (Examples). In the threaded joint of specimen 6, the threaded portion is formed with a uniform taper rate throughout (Comparative Example). In Table 1, the external pressure resistance (seal contact force) of specimen 6 is set to 1, and the external pressure resistance (seal contact force) of each specimen is shown as a relative value.

[0066] As shown in Table 1, all of the examples, specimens 1 to 5, showed improved resistance to external pressure compared to the comparative example, specimen 6. In other words, when the threaded portion is formed of a first threaded portion on the tip side (seal portion side) of the pin and a second threaded portion on the pipe body side, and the taper rate T2 of the second threaded portion is smaller than the taper rate T1 of the first threaded portion, it was confirmed that the resistance to external pressure is improved compared to when the threaded portion is formed with a single taper.

[0067] With respect to the length A of the first threaded portion and the length B of the second threaded portion in the axial direction of the threaded joint, specimens 2 to 4, in which length A was greater than length B, had improved external pressure resistance compared to specimen 6, which is a comparative example. However, specimens 1 and 5, in which length B of the second threaded portion was greater than length A of the first threaded portion, had even better external pressure resistance. For this reason, it is preferable that length B of the second threaded portion be greater than length A of the first threaded portion.

[0068] 100: Pipe threaded joint 10: Pin 11: Pin shoulder surface 12: Pin seal surface 13: Tapered male thread portion 131: First male thread portion 132: Second male thread portion 133: Boundary 134: Complete thread portion 135: Incomplete thread portion 20: Box 21: Box shoulder surface 22: Box seal surface 23: Tapered female thread portion 231: First female thread portion 232: Second female thread portion 233: Boundary 31: Pipe body

Claims

1. A pipe threaded joint comprising: a tubular pin provided contiguous with a pipe body; and a tubular box into which the pin is inserted and fastened, wherein the pin includes: a pin seal surface provided on an outer circumferential surface of the pin at a tip portion of the pin; and a tapered male thread portion provided on the outer circumferential surface, the tapered male thread portion including a first male thread portion arranged on the pipe body side with respect to the pin seal surface and a second male thread portion arranged on the pipe body side with respect to the first male thread portion and continuous with the first male thread portion; and the box includes: a box seal surface provided on an inner circumferential surface of the box corresponding to the pin seal surface; and a tapered female thread portion provided on the inner circumferential surface, the tapered female thread portion including a first female thread portion corresponding to the first male thread portion and a second female thread portion corresponding to the second male thread portion; and the first male thread portion and the first female thread portion have a first taper rate, the second male threaded portion and the second female threaded portion have a second taper rate that is smaller than the first taper rate.

2. A tubular threaded joint as claimed in claim 1, wherein the length of the second male threaded portion in the axial direction of the pin is greater than the length of the first male threaded portion.

3. A tubular threaded joint as described in claim 1, wherein the tapered male thread portion includes a complete thread portion and an incomplete thread portion located on the pipe body side of the complete thread portion, and the boundary between the first male thread portion and the second male thread portion is located within the complete thread portion.

4. A tubular threaded joint as claimed in any one of claims 1 to 3, wherein the pin further includes a pin shoulder surface provided on the tip surface of the pin, and the box further includes a box shoulder surface provided on the rear side of the box corresponding to the pin shoulder surface.

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