Oil well pipe connection structure

Abstract

To provide an oil well pipe connecting structure that connects threaded oil well pipes with a simple structure, without increasing the size, fits within the inner and outer diameters of components, and has strength significantly exceeding the limits of conventional technology. [Solution] The oil country tubular goods connection structure connects tubular members having the same inner and outer diameters, and comprises a first tubular member having, on its outer circumferential surface, a parallel first male threaded portion and a second male threaded portion that is located more distal than the first male threaded portion and that gradually reduces in diameter to form a tapered shape; and a second tubular member having, on its inner circumferential surface, a parallel first female threaded portion that screws into the first male threaded portion and a second female threaded portion that screws into the second male threaded portion and that gradually reduces in diameter to form a tapered shape, wherein the shape of each of the threads of the first male threaded portion and the first female threaded portion is a sawtooth shape with a triangular cross section, and the flank angle of the flank surface of each thread that receives pressure when the tubular members are pulled in the screwing / unscrewing direction is set to an angle of less than a right angle with respect to the axis of the tubular members.

Description

[Technical Field]

[0001] The present invention relates to an oil country tubular goods connection structure for connecting oil country tubular goods having substantially the same inner and outer diameters. [Background technology]

[0002] It is generally known that multiple hollow rod-shaped components such as pillars, pipes, and tubes are connected in the axial direction for use, and known means for connecting them include joining the two components with adhesives or welding, or connecting the two components with a separate component (such as a sleeve or pipe thread joint).

[0003] For example, in a structure in which one steel pipe has a male joint end with a thread on its outer periphery and the other steel pipe has a female joint end with a thread on its inner periphery that screws into the male joint end, and the joint ends are screwed together, a structure is known in which a bolt with an uneven tip is screwed into a through hole that extends from the outer surface of the female joint end to the inner surface of the female joint end, and the tip is pressed against the outer surface of the male joint end, thereby preventing the steel pipe from loosening (see Patent Document 1).

[0004] Also known is a method of joining steel pipes by providing flanges at the ends of the pipes, butting the flanges together, and fastening nuts by passing bolts through the flange holes (see Patent Document 2). For such flanged steel pipes, the shape of the flanges, the number of bolts, etc. are usually determined based on the design pressure of the steel pipe. In other words, they are designed to ensure strength against the internal pressure that acts constantly, and to ensure that sufficient surface pressure is applied to the flange joint surfaces to prevent leakage.

[0005] Also, there is known a hydraulic cylinder in which a cylinder bottom is connected to one end of a cylinder tube and a cylinder head is connected to the other end (see Patent Document 3). In order to increase the strength of this hydraulic cylinder, flanges are provided on the cylinder tube, cylinder bottom, and cylinder head, and the flanges are butted together to fix the cylinder bottom and cylinder head to the cylinder tube with bolts. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-163781 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-040074 [Patent Document 3] Japanese Patent Application Publication No. 2017-044238 Summary of the Invention [Problem to be solved by the invention]

[0007] However, joining components by welding takes time and reduces workability, and using adhesives to connect components has the problem that the adhesives have poor long-term durability compared to threaded joints and can peel due to temperature changes.

[0008] Furthermore, when a male or female straight thread is formed on a pipe as in Patent Document 1, there is a problem in that the strength of the pipe in the axial direction can only be at most about 50% of the overall cross-sectional strength. Although the strength of the pipe in the axial direction can be improved by changing the straight thread to a tapered thread, the reality is that the strength of the pipe in the axial direction still only reaches about 70% of the overall cross-sectional strength of the pipe.

[0009] Therefore, if pipes are connected via a general threaded joint, strength equivalent to the total cross-section strength can be obtained, but the threaded joint has a larger diameter than the pipes, and the area where the threaded joint is installed becomes larger. Therefore, when installing pipes connected via a threaded joint underground, work such as making the hole larger is time-consuming.

[0010] In the case where a fluid passes through a pipe, when the pipes are connected by directly screwing together as in Patent Document 1, the surface contact between the pipes and the surface contact between the threaded joint and both pipes ensures a seal that prevents fluid leakage from the pipes, and even when the pipes are joined by welding, the joint ensures a seal. However, when the pipes expand at high temperatures, or when they are deformed by bending or stretching under high load, or when cracks occur at the joint, gaps form between the pipes, causing a loss of sealability.

[0011] Furthermore, when joining flanged steel pipes as described in Patent Document 2, it is not uncommon for external forces such as axial force and bending to act in addition to internal pressure. Even flanges that are strong enough to withstand internal pressure can be deformed by a moment in an environment where external forces act, resulting in surface pressure on the flange joint surface and causing leakage. Another problem is that the flanges must be enlarged to prevent such flange deformation. Another problem is that arranging flanged steel pipes together and storing them requires a larger storage space.

[0012] Furthermore, even when a flange is provided on the hydraulic pressure cylinder as in Patent Document 3, there is a problem in that the provision of the flange increases the size and weight of the entire hydraulic pressure cylinder.

[0013] Although the above-mentioned patent documents relate to the connection of pipes, similar problems can occur in supports and the like connected by similar means.

[0014] The present invention was made in consideration of the above-mentioned problems and is the result of extensive research by the present inventors, and has an object to provide an oil well pipe connection structure that connects threaded oil well pipes together using a simple structure, without increasing the size, that can be contained within the inner and outer diameters of components, and that has strength that significantly exceeds the limits of conventional technology.

[0015] Another object of the present invention is to provide an oil country tubular goods connection structure for forming a seal structure that maintains high sealing performance even under high temperature, high load, and other conditions. [Means for solving the problem]

[0016] An oil country tubular goods connection structure according to one aspect of the present invention is an oil country tubular goods connection structure for connecting tubular members having the same inner and outer diameters, comprising: a first tubular member having, on its outer peripheral surface, a first male threaded portion parallel to an axis and a second male threaded portion disposed distally of the first male threaded portion and tapered such that the diameter gradually decreases toward the distal end; and a second tubular member having, on its inner peripheral surface, a first female threaded portion parallel to the axis and threadably mates with the first male threaded portion, and a second female threaded portion disposed distally of the first female threaded portion and tapered such that the diameter gradually decreases toward the distal end so as to threadably mate with the second male threaded portion, wherein the thread shapes of the first male threaded portion and the first female threaded portion are sawtooth-shaped with triangular cross sections, and the flank angles of the flank faces of the threads that receive pressure when the first tubular member and the second tubular member are pulled in the screwing / unscrewing direction are set to an angle that is equal to or smaller than a right angle with respect to the axial centers of the first tubular member and the second tubular member.

[0017] The oil well pipe connection structure is also characterized in that the shape of each thread of the second male thread portion and the second female thread portion is a sawtooth shape with a triangular cross section, and the flank angle of the flank surface of each thread that receives pressure when pulled in the screwing / unscrewing direction is set to an angle that is equal to or smaller than a right angle with respect to the axis of the first tubular member and the second tubular member.

[0018] The oil well pipe connection structure is characterized in that the first tubular member has a third male threaded portion that is arranged closer to the tip than the second male threaded portion and is parallel to the axis, the second tubular member has a third female threaded portion that is arranged inside the member closer to the tip than the second female threaded portion and is parallel to the axis and screws into the third male threaded portion, the shape of each thread of the third male threaded portion and the third female threaded portion is a sawtooth shape with a triangular cross section, and the flank angle of the flank surface of each thread that receives pressure when pulled in the screwing / unscrewing direction is set to an angle that is equal to or less than a right angle with respect to the axial center of the first tubular member and the second tubular member.

[0019] The oil country tubular good connection structure is also characterized in that the first tubular member has a first interference mitigation portion that is provided in a boundary region that is convex in the outer diameter direction and is formed between the first male thread portion and the second male thread portion, and that has a curved first interference mitigation portion that mitigates interference between the first male thread portion and the second female thread portion.

[0020] The oil country tubular good connection structure is also characterized in that the first interference mitigation portion has a threaded portion whose height is determined along a curve that is closer to the inner diameter side of the first tubular member than a straight imaginary line connecting the crests of each thread of the first male threaded portion and a tapered imaginary line connecting the crests of each thread of the second male threaded portion.

[0021] The oil country tubular good connection structure is characterized in that the threaded portion of the first interference reduction portion is positioned along the curve.

[0022] The oil country tubular good connection structure is also characterized in that the second tubular member has a second interference mitigation portion that is provided in a boundary region that is convex in the inner diameter direction and is formed between the second female thread portion and the third female thread portion, and that has a curved second interference mitigation portion that mitigates interference between the second female thread portion and the third male thread portion.

[0023] The oil country tubular good connection structure is also characterized in that the second interference mitigation portion has a thread portion whose height is determined along a curve that is closer to the outer diameter side of the second tubular member than a straight imaginary line connecting the crests of the threads of the first female thread portion and a tapered imaginary line connecting the crests of the threads of the second female thread portion.

[0024] The oil country tubular good connection structure is characterized in that the threaded portion of the second interference mitigation portion is positioned along the curve.

[0025] The oil country tubular good connection structure is characterized in that the maximum outer diameter or maximum effective diameter of the second male thread portion is set larger than the maximum inner diameter or maximum effective diameter of the second female thread portion.

[0026] The oil country tubular good connection structure is characterized in that the minimum outer diameter or minimum effective diameter of the second male thread portion is set larger than the minimum inner diameter or minimum effective diameter of the second female thread portion.

[0027] An oil well tubular goods connection structure according to another aspect of the present invention is an oil well tubular goods connection structure for connecting tubular members having the same inner and outer diameters, comprising: a first tubular member having, on its outer peripheral surface, a first male threaded portion that gradually reduces in diameter toward the tip side and forms a tapered shape; and a second male threaded portion that is arranged more tip-side than the first male threaded portion and is parallel to the axis; and a second tubular member having, on its inner peripheral surface, a first female threaded portion that threadably engages with the first male threaded portion and that gradually reduces in diameter toward the tip side; and a second female threaded portion that is arranged more tip-side than the first female threaded portion and is parallel to the axis so as to threadably engage with the second male threaded portion, wherein the shape of each of the threads of the first male threaded portion and the first female threaded portion is saw-tooth shaped with a triangular cross section, and the flank angle of the flank surface of each thread that receives pressure when the first tubular member is pulled in the screwing / unscrewing direction is set to an angle that is equal to or smaller than a right angle with respect to the axial center of the first tubular member and the second tubular member.

[0028] The oil well pipe connection structure is also characterized in that the shape of each thread of the second male thread portion and the second female thread portion is a sawtooth shape with a triangular cross section, and the flank angle of the flank surface of each thread that receives pressure when pulled in the screwing / unscrewing direction is set to an angle that is equal to or smaller than a right angle with respect to the axis of the first tubular member and the second tubular member.

[0029] The oil country tubular goods connection structure is also characterized in that the first tubular member has a third male threaded portion that is arranged closer to the tip than the second male threaded portion and that is tapered relative to the axis, the second tubular member has a third female threaded portion that is arranged inside the member closer to the tip than the second female threaded portion and that is tapered and that screws into the third male threaded portion, the shape of each thread of the third male threaded portion and the third female threaded portion is a sawtooth shape with a triangular cross section, and the flank angle of the flank surface of each thread that receives pressure when pulled in the screwing / unscrewing direction is set to an angle that is equal to or smaller than a right angle with respect to the axial center of the first tubular member and the second tubular member.

[0030] The oil country tubular good connection structure is characterized in that the maximum outer diameter or maximum effective diameter of the third male thread portion is set larger than the maximum inner diameter or maximum effective diameter of the third female thread portion.

[0031] The oil country tubular good connection structure is characterized in that the minimum outer diameter or minimum effective diameter of the third male thread portion is set larger than the minimum inner diameter or minimum effective diameter of the third female thread portion.

[0032] The oil well pipe connection structure is also characterized in that the first tubular member has a second interference mitigation portion that is provided in a boundary region that is convex in the outer diameter direction and is formed between the second male thread portion and the third male thread portion, and that has a curved second interference mitigation portion that mitigates interference between the second male thread portion and the third female thread portion.

[0033] The oil country tubular good connection structure is also characterized in that the second tubular member has a first interference mitigation portion that is provided in a boundary region that is convex in the inner diameter direction and is formed between the first female thread portion and the second female thread portion, and that has a curved first interference mitigation portion that mitigates interference between the second female thread portion and the first male thread portion.

[0034] The oil country tubular good connection structure is characterized in that the maximum outer diameter or maximum effective diameter of the first male thread portion is set larger than the maximum inner diameter or maximum effective diameter of the first female thread portion.

[0035] The oil country tubular good connection structure is characterized in that the minimum outer diameter or minimum effective diameter of the first male thread portion is set larger than the minimum inner diameter or minimum effective diameter of the first female thread portion.

[0036] The oil country tubular good connection structure is characterized in that the flank angle is 70°.

[0037] The oil well pipe connection structure is characterized in that the outer diameter of the tip of the second male thread portion and the inner diameter of the tip of the second female thread portion are set so that the outer peripheral surface of the tip of the second male thread portion and the inner peripheral surface of the tip of the second female thread portion are in close contact with each other.

[0038] The oil well pipe connection structure is also characterized in that the outer diameter of the tip of the third male thread portion and the inner diameter of the tip of the third female thread portion are set so that the outer peripheral surface of the tip of the third male thread portion and the inner peripheral surface of the tip of the third female thread portion are in close contact with each other.

[0039] The oil well pipe connection structure is also characterized in that the base end outer diameter of the first male thread portion and the base end inner diameter of the first female thread portion are set so that the base end outer peripheral surface of the first male thread portion and the base end inner peripheral surface of the first female thread portion are in close contact with each other. [Effects of the Invention]

[0040] According to the oil country tubular good connection structure of the present invention, threaded oil country tubular goods can be connected together using a simple structure without increasing the size, while being able to fit within the inner and outer diameters of the components and having strength that significantly exceeds the limits of conventional technology.

[0041] Furthermore, the oil country tubular good connection structure of the present invention can form a seal structure that maintains high sealing performance even under high temperature and high load environments. [Brief explanation of the drawings]

[0042] [Figure 1] 1 is a perspective view showing two threaded pipes that have the connection structure of the first embodiment and can be connected to each other. FIG. [Figure 2] FIG. 1 is a cross-sectional view showing a threaded pipe according to a first embodiment. [Figure 3]FIG. 1 is a cross-sectional view showing connected threaded pipes. [Figure 4] FIG. 1 is a diagram showing the threads of a male screw. [Figure 5] 10A and 10B are diagrams showing other examples of thread shapes. [Figure 6] FIG. 1 is a cross-sectional view showing a threaded pipe. [Figure 7] FIG. 10 is a cross-sectional view showing another example of the shape of the threaded pipe. [Figure 8] 10A and 10B are diagrams showing examples of the tapered shape of a second male thread portion. [Figure 9] FIG. 10 is a cross-sectional view showing another example of the shape of the threaded pipe. [Figure 10] FIG. 10 is a diagram showing an example of a thread shape. [Figure 11] FIG. 10 is a diagram showing an example of a thread shape. [Figure 12] FIG. 10 is a diagram showing a sealing structure between a male threaded portion and a female threaded portion. [Figure 13] 10A and 10B show other examples of the shape of a threaded pipe having a male thread portion, where (a) is a cross-sectional view and (b) is a view showing annular regions A to C. FIG. [Figure 14] FIG. 1 is a view showing the outer surface of a threaded pipe having a male thread portion. [Figure 15] 10A and 10B show other examples of the shape of a threaded pipe having an internal thread portion, where (a) is a cross-sectional view and (b) is a view showing annular regions D to F. FIG. [Figure 16] 10A and 10B are diagrams illustrating examples of positions of sealing portions. [Figure 17] FIG. 10 is a diagram showing an example of a tip portion. [Figure 18] FIG. 2 is a diagram showing the axial length of each part of each threaded pipe. [Figure 19] FIG. 10 is a diagram showing an example in which the present invention is applied to a cylinder. [Figure 20] FIG. 1 shows the results of a tensile test and a compression test on a threaded pipe. [Figure 21] FIG. 10 is a view showing an interference mitigation portion of the male thread portion. [Figure 22] FIG. 10 is a cross-sectional view showing another example of the shape of the threaded pipe. [Figure 23] FIG. 10 is a view showing an interference mitigation portion of the female thread portion. [Figure 24]FIG. 10 is a diagram showing the position of an interference mitigation portion in a threaded pipe. DETAILED DESCRIPTION OF THE INVENTION

[0043] An embodiment of a connection structure for threaded pipes (threaded members) of the present invention will be described below with reference to the drawings. Fig. 1 is a perspective view showing two threaded pipes 1, 1A that can be connected to each other using an oil country tubular goods connection structure according to a first embodiment, and Fig. 2 is a cross-sectional view of the threaded pipes 1, 1A according to the first embodiment. Note that Figs. 1 and 2 show the essential parts for connecting the threaded pipes 1, 1A, but do not show the entire structure. That is, Figs. 1 and 2 show one end of the threaded pipe 1 where the male thread portion is formed, and one end of the threaded pipe 1A where the female thread portion is formed. Furthermore, the outer diameter of the male thread portion and the inner diameter of the female thread portion, which will be described later, are set so that the outer diameters of the threaded pipes 1, 1A are approximately uniform even when connected.

[0044] The threaded pipes 1 and 1A are threaded tubular members made of metal, such as so-called steel pipes having a hollow structure with a substantially uniform outer diameter and an axial through-hole 2 for transporting fluids. Therefore, the threaded pipes 1 and 1A are intended for use in wells containing extracted resource fluids at mining sites, such as oil wells and gas wells. That is, they are intended for use exclusively with non-extractable resource fluids (air, water, non-extractable natural gas, hydraulic oil, etc.) other than oil well tubular goods. Therefore, as a member used to contain and / or transport non-extractable resource fluids, the threaded pipes 1 and 1A can be used, for example, as water pipes, boiler pipes, etc.

[0045] The threaded pipe 1 has one end with a reduced outer diameter, and an external thread portion 10 on the outer circumferential surface of the one end. The external thread portion 10 has a first external thread portion 12 with a straight thread having a substantially constant outer diameter, and a second external thread portion 14 that is disposed closer to the one end than the first external thread portion 12 and has a so-called tapered thread in which the outer diameter of the external thread gradually reduces. Furthermore, the second external thread portion 14 has a longer region along the axial direction than the first external thread portion 12.

[0046] The second male threaded portion 14 is formed with threads such that the outer diameter of the male thread gradually decreases toward one end. Specifically, the threads of the second male threaded portion 14 are formed at the same pitch as the threads of the first male threaded portion 12, and so that the outer diameter and thread height gradually decrease toward one end. Note that the threads of the first male threaded portion 12 and the threads of the second male threaded portion 14 are formed continuously at the same pitch, but this is not limited to this, and the pitch of one may be set larger or smaller than that of the other, or the pitch may be configured to change gradually.

[0047] The threaded pipe 1A has an expanded inner circumferential surface at one end, which has a female thread portion 20. The female thread portion 20 has a first female thread portion 22 and a second female thread portion 24, with the first female thread portion 22 being located closer to the one end than the second female thread portion 24. Furthermore, the second female thread portion 24 has a longer region along the axial direction than the first female thread portion 22.

[0048] The first female thread portion 22 has a straight thread with a substantially constant diameter. The second female thread portion 24 has a tapered thread with a gradually changing diameter. Specifically, the second female thread portion 24 is formed with a thread such that the inner diameter of the female thread gradually increases toward one end (i.e., the first female thread portion 22 side). Furthermore, the threads of the second female thread portion 24 are set to the same pitch as the threads of the first female thread portion 22. As a result, the threads of the female thread portion 20 are formed to form a straight thread at the first female thread portion 22, and are formed to form a tapered thread at the second female thread portion 24, where the inner diameter gradually decreases from the first female thread portion 22 (one end) side.

[0049] The threads of the first female thread portion 22 and the threads of the second female thread portion 24 are formed continuously at the same pitch, but this is not limited to this, and the pitch of one may be set larger or smaller than that of the other, or the pitch may be configured to change gradually.

[0050] The thread shapes of the male thread portion 10 and the female thread portion 20 are not particularly limited, but may be, for example, sawtooth-shaped. Figure 4 shows the thread shape of the male thread portion 10. As shown in Figure 4, the thread shape is such that when the threaded pipes 1, 1A are threaded together and then pulled in a direction that pulls them apart axially, the flank angle θ of the flank surface 4 of the thread that receives pressure is approximately perpendicular to the axis of the threaded pipe 1. Note that the flank angle θ here refers to the exterior angle in the triangular cross section of the thread.

[0051] The thread shape of the female thread portion 20 is set to the same as that of the male thread portion 10. That is, in the female thread portion 20, the flank angle of the flank surface that abuts against the flank surface 4 of the male thread portion 10 is set to the same flank angle θ as that of the male thread portion 10. Of course, the flank angles of the male thread portion 10 and the female thread portion 20 may be set to an angle other than a right angle, as long as the flank surfaces of the male thread portion 10 and the female thread portion 20 abut against each other over substantially the entire surface. For example, the flank angle θ of the male thread portion 10 may be set to an angle exceeding a right angle, or conversely, the flank angle θ may be set to an angle less than a right angle, as shown in FIG. 5, i.e., a so-called counter-angle.

[0052] The threaded pipes 1 and 1A are connected to each other by threading the male thread portion 10 and the female thread portion 20 together. Specifically, one end of the threaded pipe 1 is inserted into the inner circumferential surface of one end of the threaded pipe 1A. At this time, the second male thread portion 14 located at the tip of the threaded pipe 1 is first passed through the inner circumferential surface surrounded by the first female thread portion 22 at the opening side of the threaded pipe 1A, and the threaded pipe 1 is positioned so that the first male thread portion 12 can be threadedly engaged with the first female thread portion 22, as shown in Figure 3(a). Next, the threaded pipe 1 is rotated relative to the threaded pipe 1A in the direction of tightening the threads so that the first male thread portion 12 is threadedly engaged with the first female thread portion 22.

[0053] As a result, the threaded pipe 1 gradually displaces to a position where the second male threaded portion 14 can be threaded into the second female threaded portion 24, and by further rotating, the male thread of the second male threaded portion 14 and the female thread of the second female threaded portion 24 become threaded together, as shown in Figure 3(b).

[0054] Therefore, the threaded pipes 1, 1A are connected with the male thread portion 10 and the female thread portion 20 threadedly engaged. That is, the first male thread portion 12 is threadedly engaged with the first female thread portion 22, and the second male thread portion 14 is threadedly engaged with the second female thread portion 24. Furthermore, when the male thread portion 10 and the female thread portion 20 are mated, an imaginary line connecting the crests of the threads of the male thread portion 10 aligned in the axial direction is parallel to an imaginary line connecting the crests of the threads of the female thread portion 20 aligned in the axial direction. That is, the imaginary line in the first male thread portion 12 is parallel to the imaginary line in the first female thread portion 22, and the imaginary line in the second male thread portion 14 is parallel to the imaginary line in the second female thread portion 24.

[0055] Here, the axial strength of the connected threaded pipes 1, 1A differs at the point where the first male threaded portion 12 and the first female threaded portion 22 are threaded together and at the point where the second male threaded portion 14 and the second female threaded portion 24 are threaded together.

[0056] First, in the first male thread portion 12 of the threaded pipe 1, load is concentrated at the point where the pipe wall thickness is thinnest near the start of the thread, i.e., around position P1 in Figure 6. Therefore, the strength of the first male thread portion 12 depends on the strength at position P1, and the ratio of the strength at position P1 to the total cross-sectional strength roughly corresponds to the ratio of the cross-sectional area at position P1 to the total cross-sectional area. For example, if the ratio of the cross-sectional area at position P1 to the total cross-sectional area at position P0 is about 90%, the strength will be about 90% of the total cross-sectional strength.

[0057] The second male threaded portion 14 of the threaded pipe 1 has tapered threads whose outer diameter changes toward the tip, and therefore threads onto the threads of the second female threaded portion 24 of the threaded pipe 1A with almost no gap in the section where the threads are effectively engaged. In other words, the shear strength corresponds to the shear cross-sectional area of ​​the threads according to the effective thread engagement length, and in the second male threaded portion 14, the load is distributed to the threads over the effective thread engagement length, and as a result, when the second male threaded portion 14 is set so that the effective thread engagement length is maximized, a strength of approximately 70% of the total cross-sectional strength is obtained.

[0058] The strength of the first female thread portion 22 and the second female thread portion 24 of the threaded pipe 1A is determined in substantially the same manner as the strength of the first male thread portion 12 and the second male thread portion 14 of the threaded pipe 1. That is, in the first female thread portion 22, load is concentrated at the point where the wall thickness is thinnest near the start of the thread (position P3 in FIG. 6). Therefore, the strength of the first female thread portion 22 is determined by the ratio of the cross-sectional area at position P3, where the wall thickness is thinnest, to the total cross-sectional area (the cross-sectional area at position P4 in FIG. 6), and the total cross-sectional strength. Furthermore, because the second female thread portion 24 has a tapered thread, it can achieve a strength of up to approximately 70% of the total cross-sectional strength.

[0059] Because the male thread portion 10 and the female thread portion 20 have different strengths in the straight thread region and the tapered thread region, as described above, their overall tensile strength is determined by the sum of the tensile strengths in each region. Specifically, the tensile strength of the male thread portion 10 is determined by the sum of the tensile strengths of the first male thread portion 12 and the second male thread portion 14. As in the above example, if the tensile strength of the first male thread portion 12 region is approximately 10% of the tensile strength of the entire cross section, and the tensile strength of the second male thread portion 14 region is approximately 70% of the tensile strength of the entire cross section, then the overall tensile strength is approximately 80% of the tensile strength of the entire cross section. In addition, in the female thread portion 20, the overall tensile strength is the sum of the tensile strength of the first female thread portion 22 region and the tensile strength of the second female thread portion 24 region.

[0060] As explained above, by providing male and female threaded portions on the threaded pipes 1, 1A, respectively, and by threading the straight threads of the first male and first female threaded portions together, and by threading the tapered threads of the second male and second female threaded portions together, it is possible to improve the axial strength compared to when the male and female threads are simply threaded together with straight threads, or when the male and female threads are threaded together with tapered threads.

[0061] In the above-described embodiment, the male thread portion 10 is formed so that the first male thread portion 12 and the second male thread portion 14 are arranged in this order from the middle of the threaded pipe 1 toward one end. However, as shown in FIG. 7, the male thread portion 10 may be formed so that the first male thread portion 12, the second male thread portion 14, and the third male thread portion 16 having a straight thread are arranged in this order from the middle of the threaded pipe 1 toward one end.

[0062] Furthermore, the female thread portion 20 is formed by arranging the first female thread portion 22 and the second female thread portion 24 in this order from one end of the threaded pipe 1A, but it may also be formed by arranging the first female thread portion 22, the second female thread portion 24, and the third female thread portion 26 having a straight thread in this order from one end, as shown in Figure 7.

[0063] In addition, threaded pipes are typically connected via a separate fitting to improve strength, but because the outer diameter of the fitting is larger than that of the threaded pipe, installing such a threaded pipe requires the creation of a large-diameter well, hole, etc. to accommodate the fitting. However, the threaded pipe of the present invention has very high axial strength while preventing the outer diameter of the pipe from becoming too large, thereby reducing the labor required to excavate wells, holes, etc. and reducing the cost of excavation.

[0064] Furthermore, when the threaded pipes 1 and 1A are connected, the straight threads of the first male and first female threads are threaded together, and the tapered threads of the second male and second female threads are threaded together. This eliminates the need for a radially protruding flange, improving axial strength compared to connecting flanged steel pipes. Furthermore, by eliminating the flange, the threaded pipes 1 and 1A can be prevented from becoming larger, reducing the space required for installation and achieving space savings. Furthermore, even when the threaded pipes 1 and 1A are stored in an array, storage space can be saved. Furthermore, since fluid leakage due to gaps occurring at the flange joint surfaces is prevented, more stable fluid transfer can be achieved.

[0065] In the above-described embodiment, the tapered shapes of the tapered threads of the second male thread portion 14 and the second female thread portion 24 can be set as appropriate. For example, in the cross-sectional shape of the male thread portion 10 shown in FIG. 8( a), the imaginary line connecting the tips of the threads of the second male thread portion 14 can be set to a linear tapered shape inclined at a predetermined gradient, or the imaginary line connecting the tips of the threads of the second male thread portion 14 shown in FIG. 8( b) can be set to a tapered shape inclined in a curved manner. Furthermore, the imaginary line connecting the tips and / or valleys of the threads of the second female thread portion 14 along the axial direction shown in FIG. 8( c) can also be set to a curved shape similar to a tangent curve. Of course, the tapered thread of the second female thread portion 24 of the female thread portion 20 can also be set to a tapered shape inclined at a predetermined gradient as described above, or a tapered shape inclined in a curved manner.

[0066] Furthermore, in the above-described embodiment, continuous threads are provided across the first male threaded portion 12 and the second male threaded portion 14. However, this is not limited thereto, and the threads of the first male threaded portion 12 and the threads of the second male threaded portion 14 may be formed separately. Furthermore, as shown in FIG. 9 , a non-threaded portion 18 may be provided between the first male threaded portion 12 and the second male threaded portion 14. The non-threaded portion 18 has an outer diameter set to be at least equal to or smaller than the root diameter of the threads of the first male threaded portion 12. In other words, the non-threaded portion 18 is set to an outer diameter that does not interfere with the threads of the female threaded portion 20 and hinder the threading when the male threaded portion 10 and the female threaded portion 20 are threaded together. Furthermore, it is desirable that the outer diameter of the non-threaded portion 18 is constant along the axial direction.

[0067] Furthermore, when a non-threaded portion 18 is provided in the male threaded portion 10, a non-threaded portion may also be provided in the female threaded portion 20. Furthermore, a metal seal structure may be provided in the non-threaded portion 18, or a sealing material such as an O-ring, D-ring, or gasket may be attached. By interposing a sealing material between the male threaded portion 10 and the female threaded portion 20, airtightness can be further improved, making it possible to prevent leakage of the fluid flowing inside the pipe.

[0068] Furthermore, the thread shapes of the male thread portion 10 and the female thread portion 20 are not limited to sawtooth shapes and can be set as appropriate. For example, they can be triangular thread shapes as shown in FIG. 10(a), round thread shapes as shown in FIG. 10(b), square thread shapes as shown in FIG. 10(c), trapezoidal thread shapes as shown in FIG. 10(d), etc. Also, they can be sawtooth shapes in which the tip surfaces of the threads are widened as shown in FIG. 11(a), or recurved shapes in which the tip surfaces of the threads are widened as shown in FIG. 11(b). Furthermore, they can be sawtooth shapes in which the tip surfaces and root portions of the threads are curved as shown in FIG. 11(c), or recurved shapes in which the tip surfaces and root portions of the threads are curved as shown in FIG. 11(d).

[0069] In the male thread portion 10, the thread shapes of the first male thread portion and the second male thread portion may be different, for example, the threads of the first male thread portion, which is a straight thread, may be set to a triangular thread shape, and the threads of the second male thread portion, which is a tapered thread, may be set to a sawtooth shape, etc. The same applies to a male thread portion having first to third male thread portions as shown in Figure 7, and the threads of the first male thread portion may be set to a triangular thread shape, the threads of the second male thread portion may be set to a sawtooth shape, and the threads of the third male thread portion may be set to a round thread shape, etc.

[0070] Furthermore, the outer diameter of the male thread portion 10 and the inner diameter of the female thread portion 20 can be set as appropriate. Therefore, the outer diameter of the male thread portion 10 and / or the inner diameter of the female thread portion 20 may be set to improve the sealing performance between the male thread portion 10 and the female thread portion 20. In other words, the second male thread portion 14 may press the second female thread portion 24 from the inside outward, causing elastic deformation and / or plastic deformation of at least one of the second male thread portion 14 and the second female thread portion 24 to improve the sealing performance.

[0071] For example, in a fully threaded state, the maximum outer diameter (or maximum effective diameter) of the second male thread portion 14 is set larger than the maximum inner diameter (or maximum effective diameter) of the second female thread portion 24, and / or the minimum outer diameter (or minimum effective diameter) of the second male thread portion 14 is set larger than the minimum inner diameter (or minimum effective diameter) of the second female thread portion 24, so that the female thread portion 20 can expand slightly radially outward. This allows at least a portion of the second male thread portion 14 and the second female thread portion 24 to interfere with each other in the radial direction, and as the male thread portion 10 and the female thread portion 20 are threaded together, the female thread portion 20 expands in diameter while undergoing elastic and / or plastic deformation, resulting in close contact between the male thread portion 10 and the female thread portion 20 and improved sealing performance.

[0072] Of course, the size of the inner diameter of the second female thread portion 24 relative to the outer diameter of the second male thread portion 14 may be set so that the second male thread portion 14 elastically deforms and / or plastically deforms radially inward. Furthermore, although the outer diameter of the second male thread portion 14 and the inner diameter of the second female thread portion 24 are set as described above, the thickness of the pipe at the second male thread portion 14 and / or the second female thread portion 24 may also be set.

[0073] Furthermore, if the second male threaded portion 14 and the second female threaded portion 24 are configured to interfere with each other, when they are screwed together to the correct position (threaded all the way in), the tip of the thread of the first male threaded portion 12 near the second male threaded portion 14 is located radially outward of the thread root portion of the second female threaded portion 24 near the end of the second female threaded portion 24 on the first female threaded portion 22 side, causing interference. In this interfered state, further screwing is not possible. Therefore, the end region of the first male threaded portion 12 that interferes with the second female threaded portion 24 is configured to have a reduced diameter, reducing or eliminating the amount of interference.

[0074] The length of the diameter reduction is preferably equal to or greater than the interference length between the end of the first male threaded portion 12 and the second female threaded portion 24. In addition, the end region of the first male threaded portion 12 is reduced in diameter by providing various shapes such as stepped, tapered, curved, or unthreaded.

[0075] Specifically, since the first male thread portion 12 may interfere with the second female thread portion 24 in the axial direction, in order to avoid such interference, an interference mitigation portion 13 as shown in Figure 21 is provided in the outwardly convex (i.e., radially outwardly convex) boundary region between the first male thread portion 12 and the second male thread portion 14.

[0076] For example, the imaginary line 13a (see FIG. 21) connecting the tips of the threads of the interference mitigation section 13 forms a curve closer to the axial center than the straight imaginary line 12a connecting the tips of the threads of the first male threaded section 12 and the tapered imaginary line 14a connecting the tips of the threads of the second male threaded section 14, and the height and position of the threads are determined to follow this curve. In addition, the maximum radius r (see FIG. 21) of the interference mitigation section 13 is equal to or smaller than the minimum inner diameter of the second female threaded section 24.

[0077] Therefore, by providing the interference mitigation portion 13, it is possible to mitigate or avoid interference between the first male threaded portion 12 and the second female threaded portion 24. Furthermore, the interference mitigation portion 13 may have a surface shape that mitigates or avoids interference with the second female threaded portion 24, or may have a shape that includes threads that can be threadedly engaged with the first female threaded portion 22 and / or the second female threaded portion 24.

[0078] While the male thread portion 10 has been described as having a shape that has a first male thread portion 12 with straight threads and a second male thread portion 14 with tapered threads from the midpoint of the threaded pipe 1 toward one end, it goes without saying that it may have a shape that has a second male thread portion 14 and a first male thread portion 12 from the midpoint to one end, as shown in Figure 22. In that case, the female thread portion 20 that can be threaded onto the male thread portion 10 will have a shape that has a second female thread portion 24 and a first female thread portion 22 from one end toward the back, as shown in Figure 22. Furthermore, the male thread portion 10 may be provided with a seal portion 19 that is annular nearer to the midpoint than the second male thread portion 14 and that can be in close contact with the inner surface of the threaded pipe 1A around the entire circumference.

[0079] 22, when the second male threaded portion 14 and the second female threaded portion 24 are configured to interfere with each other and are screwed together to the correct position (threaded all the way in), the end of the second male threaded portion 14 on the first male threaded portion 12 side interferes with the vicinity of the end of the first female threaded portion 22 on the second female threaded portion 24 side. Therefore, the end region of the first female threaded portion 22 that interferes with the second male threaded portion 14 is expanded in diameter to reduce or eliminate the amount of interference.

[0080] The length of the expanded diameter is preferably equal to or greater than the interference length between the end of the first female threaded portion 22 and the second male threaded portion 14. In addition, the end region of the first female threaded portion 22 is expanded in diameter by providing it with various shapes such as stepped, tapered, curved, or unthreaded.

[0081] Specifically, an interference mitigation portion 23 (see FIG. 23 ) is provided in an outwardly convex (i.e., radially inwardly convex) boundary region between the first female thread portion 22 and the second female thread portion 24. For example, an imaginary line 23a (see FIG. 23 ) connecting the tips of the threads of the interference mitigation portion 23 forms a curved line located outside the imaginary line 22a connecting the tips of the threads of the first female thread portion 22 and the tapered imaginary line 24a connecting the tips of the threads of the second female thread portion 24, and the height and position of the threads are determined along this curve. Furthermore, the maximum radius R (see FIG. 23 ) of the interference mitigation portion 23 is equal to or greater than the minimum outer diameter of the second male thread portion 14. By providing the interference mitigation portion 23, interference between the first female thread portion 22 and the second male thread portion 14 can be mitigated or avoided. In addition, the interference mitigation portion 23 may have a surface shape that mitigates or avoids interference with the second male threaded portion 14, or it may have a shape that includes threads that can be threaded onto the first male threaded portion 12 and / or the second male threaded portion 14.

[0082] 12, the outer peripheral surface 30 at the tip of the male threaded portion 10 of the threaded pipe 1 may be brought into close contact with the inner peripheral surface 40 at the base end of the female threaded portion 20 of the threaded pipe 1A. In other words, in the insertion direction between the threaded pipe 1A and the threaded pipe 1, the outer peripheral surface 30 located on the front side of the male threaded portion 10 may be brought into close contact with the inner peripheral surface 40 located on the rear side of the threaded pipe 1A in the insertion direction.

[0083] In this case, the outer diameter of the outer peripheral surface 30 is set to be slightly larger than the inner diameter of the inner peripheral surface 40. Therefore, when the male threaded portion 10 and the female threaded portion 20 are mated, an elastic force acts so that the outer peripheral surface 30 presses the inner peripheral surface 40 outward, or the inner peripheral surface 40 presses the outer peripheral surface 30 inward. As a result, the outer peripheral surface 30 and the inner peripheral surface 40 come into close contact all around, providing sealing performance.

[0084] Alternatively, the outer peripheral surface 32 at the base end of the male threaded portion 10 of the threaded pipe 1 may be brought into close contact with the inner peripheral surface 42 at the tip end of the female threaded portion 20 of the threaded pipe 1A. In this case, the outer diameter of the outer peripheral surface 32 is set to be slightly larger than the inner diameter of the inner peripheral surface 42.

[0085] Even in this case, when the male thread portion 10 and the female thread portion 20 are mated, an elastic force acts so that the outer peripheral surface 32 presses the inner peripheral surface 42 outward or the inner peripheral surface 42 presses the outer peripheral surface 32 inward, causing the outer peripheral surface 32 and the inner peripheral surface 42 to come into close contact all around, thereby achieving sealing performance. Note that the outer peripheral surfaces 30, 32 and the inner peripheral surfaces 40, 42 may be inclined surfaces that are inclined with respect to the axes of the male thread portion 10 and the female thread portion 20.

[0086] Next, threaded pipes with other configurations will be described. Figure 13 shows another example of the configuration of a threaded pipe having an external thread, where (a) is a cross-sectional view and (b) is a diagram showing annular regions A to C. Threaded pipe 300 has, from the tip end connected to threaded pipe 400, a first seal portion 310, an external thread portion 320, and a second seal portion 330 arranged in that order. Threaded pipe 300 also has a tip end 300a that limits the depth of insertion into threaded pipe 400.

[0087] As shown in Fig. 14, the first seal portion 310 has at least one, and preferably a plurality of, annular protrusions 312 that extend around the entire circumferential direction of the outer circumferential surface and protrude radially outward. The first seal portion 310 also defines annular recesses 314 between the annular protrusions 312 by arranging the annular protrusions 312 in parallel in the axial direction, the annular recesses 314 being recessed relative to the annular protrusions 312. The protruding length of the annular protrusions 312 is set to at least a length that does not interfere with the threaded engagement between a first male threaded portion 322 and a first female threaded portion 422 (see Fig. 15), which will be described later, and that allows the annular protrusions 312 to come into close contact with (or slightly interfere with) the inner circumferential surface of the first unthreaded portion 410 (see Fig. 15).

[0088] The male thread portion 320 is composed of, in order from the base end, a first male thread portion 322 which is a straight thread, a second male thread portion 324 which is a tapered thread, and a third male thread portion 326 which is a straight thread. The effective diameter of the second male thread portion 324 is equal to or smaller than the effective diameter of the first male thread portion 322, and the effective diameter of the third male thread portion 326 is equal to or smaller than the effective diameter of the second male thread portion. The effective diameter of the second male thread portion 324 is larger at the base end than at the tip end. Note that, here, the threads of the first male thread portion 322 to the third male thread portion 326 form a continuous spiral shape so that the maximum effective diameter of the second male thread portion 324 approximately corresponds to the effective diameter of the first male thread portion 322 and the minimum effective diameter approximately corresponds to the effective diameter of the third male thread portion 326.

[0089] The threaded pipe 300 includes any one of the first male thread portion 322 to the third male thread portion 326. The threaded pipe 300 has three concentric annular regions A (first annular region), B (second annular region), and C (third annular region) that are radially divided into three regions when viewed in the axial direction. As shown in FIG. 13(b), the radial region extending from the outer circumferential surface of the threaded pipe 300 to the effective diameter portion of the first male thread portion 322 is referred to as annular region A. The radial region extending from the maximum effective diameter portion of the second male thread portion 324 (i.e., the effective diameter portion of the first male thread portion 322) to the minimum effective diameter portion of the second male thread portion 324 is referred to as annular region B. The radial region extending from the effective diameter portion of the third male thread portion 326 (i.e., the minimum effective diameter portion of the second male thread portion 324) to the inner circumferential surface of the threaded pipe 300 is referred to as annular region C.

[0090] The area of ​​annular region A is set to be one-third or less of the total cross-sectional area of ​​the transverse cross-section of threaded pipe 300. The area of ​​transverse cross-sectional region B is set to be one-third or more of the total cross-sectional area of ​​the transverse cross-section of threaded pipe 300. The area of ​​transverse cross-sectional region C is set to be one-third or less of the total cross-sectional area of ​​the transverse cross-section of threaded pipe 300.

[0091] The shape of the thread region of the first male thread portion 322 is set so that the shear area of ​​the entire thread that threadably engages with the first female thread portion 422 is equal to or greater than the square root of the area of ​​the annular region A. Therefore, the effective thread engagement length, the number of threads, the pitch, etc. are set so that the total shear area of ​​the threads of the first male thread portion 322, which is formed by continuously shearing in a spiral shape at the effective diameter portion of the threads, is equal to or greater than the square root of 3 times the area of ​​the annular region A.

[0092] Additionally, the shape of the thread region of the second male thread portion 324 is set so that the shear area of ​​the entire thread that threadably mates with the second female thread portion 424 is equal to or greater than the square root of 3 multiplied by the area of ​​the annular region B. Therefore, the effective thread engagement length, the number of threads, the pitch, etc. are set so that the total shear area of ​​the threads of the second male thread portion 324, which are formed by continuously shearing in a spiral shape at the effective diameter portion of the threads, is equal to or greater than the square root of 3 times the area of ​​the annular region B.

[0093] Furthermore, the shape of the thread region of the third male thread portion 326 is set so that the shear area of ​​the entire thread that threadably engages with the third female thread portion 426 is equal to or greater than the square root of 3 multiplied by the area of ​​the annular region C. Therefore, the effective thread engagement length, the number of threads, the pitch, etc. are set so that the total shear area of ​​the threads of the third male thread portion 326, which is formed by continuously shearing in a spiral shape at the effective diameter portion of the threads, is equal to or greater than the square root of 3 times the area of ​​the annular region C.

[0094] The second seal portion 330 has one or more, preferably a plurality of, annular protrusions 332, similar to the first seal portion 310, and defines annular recesses 334 between the annular protrusions 332. The protruding length of the annular protrusions 332 is set to a length that allows them to come into close contact with (or slightly interfere with) the inner circumferential surface of the second unthreaded portion 430 (see FIG. 15).

[0095] The distal end portion 300a may have a shape that allows it to abut against the threaded pipe 400 and regulate its position in the depth direction, and preferably has a shape that allows it to be guided in to facilitate insertion, and for example, this may be formed by chamfering the distal end of the first seal portion 310 as shown in Figure 14. Also, a proximal end portion 300b, which serves as a regulating means that can abut against the threaded pipe 400 and regulate its position in the depth direction, may be formed on the proximal end side of the second seal portion 330 in place of or together with the distal end portion 300a.

[0096] 15 shows another example of the configuration of a threaded pipe having an internally threaded portion, where (a) is a cross-sectional view and (b) is a diagram showing annular regions D to F. Threaded pipe 400 has a first unthreaded portion 410, an internally threaded portion 420, and a second unthreaded portion 430. When threaded pipe 400 is connected to threaded pipe 300, first unthreaded portion 410 corresponds to first seal portion 310, and second unthreaded portion 430 corresponds to second seal portion 330.

[0097] The threaded pipe 400 also has a receiving portion 400a that restricts insertion of the threaded pipe 300, and the receiving portion 400a is disposed at a location corresponding to the distal end portion 300a (or proximal end portion 300b). The first unthreaded portion 410 has a circumferential inner surface with a constant inner diameter along the axial direction, which is set to be less than the crest diameter of a third female threaded portion 426, which will be described later. The second unthreaded portion 430 also has a circumferential inner surface with a constant inner diameter along the axial direction, which is set to be greater than or equal to the root diameter of a first female threaded portion 422, which will be described later.

[0098] The female thread portion 420 is composed of, arranged in order from the inserted end side, a first female thread portion 422 which is a straight thread, a second female thread portion 424 which is a tapered thread, and a third female thread portion 426 which is a straight thread. The second female thread portion 424 has at least a minimum effective diameter equal to or larger than the effective diameter of the first female thread portion 422, and the third female thread portion 426 has an effective diameter equal to or larger than the maximum effective diameter of the second female thread portion 424. The first female thread portion 422 threadably mates with the first male thread portion 322, the second female thread portion 424 threadably mates with the second male thread portion 324, and the third female thread portion 426 threadably mates with the third male thread portion 326.

[0099] The threaded pipe 400 has three concentric annular regions, D (fourth annular region), E (fifth annular region), and F (sixth annular region), which are radially divided into three parts when viewed in the axial direction and include any of the first female thread portion 422 to the third female thread portion 426. As shown in FIG. 15(b), the radial region extending from the outer circumferential surface of the threaded pipe 400 to the effective diameter portion of the first female thread portion 422 is referred to as annular region D. Furthermore, the radial region extending from the maximum effective diameter portion of the second female thread portion 424 (i.e., the effective diameter portion of the first female thread portion 422) to the minimum effective diameter portion of the second female thread portion 424 is referred to as annular region E. Furthermore, the radial region extending from the effective diameter portion of the third female thread portion 426 (i.e., the minimum effective diameter portion of the second female thread portion 424) to the inner circumferential surface of the base pipe portion of the threaded pipe 400 is referred to as annular region F.

[0100] The area of ​​annular region D is set to be one-third or less of the total cross-sectional area of ​​the transverse cross-section of threaded pipe 400. The area of ​​transverse cross-sectional region E is set to be one-third or more of the total cross-sectional area of ​​the transverse cross-section of threaded pipe 400. The area of ​​transverse cross-sectional region F is set to be one-third or less of the total cross-sectional area of ​​the transverse cross-section of threaded pipe 400. Here, it is assumed that annular region D has an area approximately corresponding to annular region A, annular region E has an area approximately corresponding to annular region B, and annular region F has an area approximately corresponding to annular region C.

[0101] The shape of the thread region of the first female thread portion 422 is set so that the shear area of ​​the entire thread that threadably mates with the first male thread portion 322 is equal to or greater than the square root of 3 multiplied by the area of ​​the annular region D. In other words, the effective thread engagement length, the number of threads, the pitch, etc. are set so that the total shear area of ​​the threads of the first female thread portion 422, which are formed by continuously shearing in a spiral shape at the effective diameter portion of the threads, is equal to or greater than the square root of 3 times the area of ​​the annular region D. Here, the above conditions are satisfied by setting the shape of the thread region of the first female thread portion 422 to correspond to the effective thread engagement length, the number of threads, and the pitch of the first male thread portion 322.

[0102] Furthermore, the shape of the thread region of the second female thread portion 424 is set so that the shear area of ​​the entire thread that threadably engages with the second male thread portion 324 is equal to or greater than the square root of the area of ​​the annular region E. In other words, the effective thread engagement length, the number of threads, the pitch, etc. are set so that the total shear area of ​​the threads of the second female thread portion 424, which are formed by continuously shearing in a spiral shape at the effective diameter portion of the threads, is equal to or greater than the square root of 3 times the area of ​​the annular region E. Here, the above conditions are satisfied by setting the shape of the thread region of the second female thread portion 424 to correspond to the effective thread engagement length, the number of threads, and the pitch of the second male thread portion 324.

[0103] Furthermore, the shape of the thread region of the third female thread portion 426 is set so that the shear area of ​​the entire thread that threadably mates with the third male thread portion 326 is equal to or greater than the square root of 3 multiplied by the area of ​​the annular region F. In other words, the effective thread engagement length, the number of threads, the pitch, etc. are set so that the total shear area of ​​the threads of the third female thread portion 426, which are formed by continuously shearing in a spiral shape at the effective diameter portion of the threads, is equal to or greater than the square root of 3 times the area of ​​the annular region F. Here, the above conditions are satisfied by setting the shape of the thread region of the third female thread portion 426 to correspond to the effective thread engagement length, the number of threads, and the pitch of the third male thread portion 326.

[0104] The first unthreaded portion 410 and the first seal portion 310 have approximately the same axial length, but are set so that the first unthreaded portion 410 is longer. The female threaded portion 420 and the male threaded portion 320 have approximately the same axial length. The second unthreaded portion 430 and the second seal portion 330 have approximately the same axial length, but are set so that the second unthreaded portion 430 is longer.

[0105] It is preferable to set the axial length of the first seal portion 310 so that it does not engage with the first non-threaded portion 410 before the male threaded portion 320 and the female threaded portion 420 are screwed together. Specifically, when the axial length of the first seal portion 310 shown in FIG. 18(a) is L1 and the axial length of the third male threaded portion 326 axially adjacent to the first seal portion 310 is L2, it is desirable to set each axial length so as to satisfy L1 < L2. Similarly, it is preferable to set the axial length of the second seal portion 330 so that it does not engage with the second non-threaded portion 430 before the male threaded portion 320 and the female threaded portion 420 are screwed together. Specifically, when the axial length of the second seal portion 330 shown in FIG. 18(a) is L3 and the axial length of the first male threaded portion 322 axially adjacent to the second seal portion 330 is L4, it is desirable to set each axial length so as to satisfy L3 < L4.

[0106] It is also preferable to set the axial lengths of the first non-threaded portion 410 and the second non-threaded portion 430 in the same manner corresponding to the axial lengths of the first seal portion 310 and the second seal portion 330. Specifically, when the axial length of the first non-threaded portion 410 shown in FIG. 18(b) is L1' and the axial length of the third female threaded portion 426 axially adjacent to the first non-threaded portion 410 is L2', it is desirable to set each axial length so as to satisfy L1' < L2'. When the axial length of the second non-threaded portion 430 is L3' and the axial length of the first female threaded portion 422 axially adjacent to the second non-threaded portion 430 is L4', it is desirable to set each axial length so as to satisfy L3' < L4'.

[0107] If the axial lengths of each part are set as described above, after the male threaded portion 320 and the female threaded portion 420 start to be screwed together and until the tightening is completed, the first seal portion 310 and the first non-threaded portion 410 (and the second seal portion 330 and the second non-threaded portion 430) can engage to form a sealing structure.

[0108] With these threaded pipes 300, 400, when the threaded pipe 300 is inserted into the threaded pipe 400 and rotated, the male threaded portions 322 to 326 threadably engage with the female threaded portions 422 to 426. The first seal portion 310 is press-fit into the first unthreaded portion 410, and the annular protrusion 312 tightly contacts the inner circumferential surface of the first unthreaded portion 410. The second seal portion 330 is press-fit into the second unthreaded portion 430, and the annular protrusion 332 tightly contacts the inner circumferential surface of the second unthreaded portion 430.

[0109] It is also possible to configure the tip portion 300a of the threaded pipe 300 to engage or abut against the receiving portion 400a of the threaded pipe 400, thereby preventing excessive tightening of each male thread portion 322 to 326 and each female thread portion 422 to 426.

[0110] Furthermore, the annular convex portion 312 is in close contact with the first unthreaded portion 410, and the annular convex portion 332 is in close contact with the second unthreaded portion 430, and the annular convex portions 312, 332 are pressed against the first unthreaded portion 410 or the second unthreaded portion 430, thereby forming a seal structure that can cope with situations involving relative displacement between the threaded pipes 300, 400 due to input such as tension or compression of the threaded pipes 300, 400, and can also form a seal structure with high sealing performance that can follow deformations such as bending of the threaded pipes 300, 400.

[0111] Furthermore, a sealing structure may be provided in the annular recess 314. Specifically, a solid grease (described in detail later) that softens and expands above a predetermined temperature may be accommodated in the annular recess 314, and a resin ring such as polyethylene or polypropylene may be fitted and / or embedded in the annular recess 314 to form a sealing structure, which can further improve the sealing performance.

[0112] As described above, the shape of the thread region of the first male thread portion 322 is set so that the total cross-sectional area of ​​the entire thread is equal to or greater than the area of ​​the annular region A multiplied by the square root of 3, and therefore the first male thread portion 322 has a higher shear strength than the tensile strength of the mother pipe corresponding to the area of ​​the annular region A. Similarly, the second male thread portion 324 has a higher shear strength than the tensile strength of the mother pipe corresponding to the area of ​​the annular region B, and the third male thread portion 326 has a higher shear strength than the tensile strength of the mother pipe corresponding to the area of ​​the annular region C.

[0113] Therefore, the entire male thread portion 320 has a shear strength higher than the tensile strength of the area of ​​the threaded pipe 300 where the male thread portion 320 is not formed, and when the two threaded pipes 300, 400 are pulled axially away from each other while threaded with the female thread portion 420, it is possible to prevent shear failure of the male thread portion 320 before axial breakage of the threaded pipe 300 occurs.

[0114] Similarly, the shape of the thread region of the first female thread portion 422 is set so that the total cross-sectional area of ​​the entire thread is equal to or greater than the area of ​​the annular region D multiplied by the square root of 3, and therefore the first female thread portion 422 has a higher shear strength than the tensile strength of the mother pipe corresponding to the area of ​​the annular region D. Similarly, the second female thread portion 424 has a higher shear strength than the tensile strength of the mother pipe corresponding to the area of ​​the annular region E, and the third female thread portion 426 has a higher shear strength than the tensile strength of the mother pipe corresponding to the area of ​​the annular region F.

[0115] Therefore, the entire female thread portion 420 has a shear strength higher than the tensile strength of the area of ​​the threaded pipe 400 where the female thread portion 420 is not formed, and when the two threaded pipes 300, 400 are pulled in a direction separating them from each other along the axial direction while threaded with the male thread portion 320, it is possible to prevent shear failure of the female thread portion 420 before axial breakage of the threaded pipe 400 occurs.

[0116] As described above, the shear strength of the male threaded portion 320 and the female threaded portion 420 is higher than the tensile strength of the non-threaded areas of each threaded pipe 300, 400, and when a tensile force is applied in a direction that separates the threaded pipes 300, 400 while they are connected, it is possible to reliably cause axial fracture of one of the threaded pipes 300, 400 before the threads shear.

[0117] The tensile strength of each of the first male threaded portion 322, the second male threaded portion 324, the third male threaded portion 326, or the first female threaded portion 422, the second female threaded portion 424, and the third female threaded portion 426 is the smallest of the total shear area a when the approximate effective diameter portion of the mating region where the target male threaded portion or female threaded portion is threadedly sheared continuously in a spiral shape along the threads, the cross-sectional area b of the cross section at the effective diameter portion of the target male threaded portion, and the cross-sectional area c of the cross section at the effective diameter portion of the target female threaded portion. However, the relationship a ≥ √3 · b ∧ a ≥ √3 · c can be set, in which case the tensile strength of the target male threaded portion or female threaded portion can be calculated by multiplying b and / or c by the tensile strength per unit area of ​​the material.

[0118] Furthermore, by arranging the first male threaded portion and the third male threaded portion before and after the second male threaded portion in the forward direction, and by arranging the first female threaded portion and the third female threaded portion before and after the second female threaded portion in the forward direction, the male threaded portion and the female threaded portion are threaded together over the entire helical thread region. This eliminates the formation of non-engaging portions at the distal and proximal ends of the tapered thread portion that exist in conventional joints known as flush joints, preventing a decrease in strength due to the presence of non-engaging portions and, as a result, enabling threaded pipes to be firmly connected to each other.

[0119] Furthermore, with the threaded pipes 300, 400 constructed as described above, the strength of the joint can be increased when the male threaded portion 320 and the female threaded portion 420 are threaded together and tightened. In evaluating the tensile strength, the yield ratio of the joint, which is the ratio of the tensile strength of the joint to the yield strength of the base pipe portion of the threaded pipes 300, 400, can be considered as a criterion. The yield ratio of the joint can be expressed as {fracture strength of the joint} / {full cross-section yield strength of the base pipe portion}.

[0120] For example, if a steel material with a strength classification equivalent to 10.9 in the bolt strength classification is used and the cross-sectional area of ​​the joint is S1 (mm 2 ), the cross-sectional area of ​​the raw tube is S0 (mm 2 ), the yield ratio can be expressed as equation (1).

[0121] [Formula 1] TIFF2026042909000002.tif19170

[0122] Here, the number 10 before the strength classification is the minimum tensile strength of 1040 (N / mm 2 The 9 at the end is the yield strength, and the tensile strength is 1040 (N / mm 2 ) is 90 percent. That is, the yield strength is 1040 x 0.9 = 936 (N / mm 2 )

[0123] The cross-sectional area S1 is determined by the cross-sectional area of ​​the male thread portion 320 or the cross-sectional area of ​​the female thread portion 420. That is, the size of the cross-sectional area of ​​the male thread portion 320 is affected by the range from the inner diameter of the threaded pipe 300 shown in Figure 13 to the effective diameter of the first male thread portion 322. The size of the cross-sectional area of ​​the female thread portion 420 is affected by the range from the outer diameter of the threaded pipe 400 shown in Figure 15 to the effective diameter of the third female thread portion 426.

[0124] Therefore, if the male thread portion 320 is set so that the first male thread portion 322 is expanded in diameter, and the female thread portion 420 is set so that the third female thread portion 426 is reduced in diameter, and the cross-sectional area S1 is set to be approximately 80% of the cross-sectional area S0, for example, the cross-sectional area S1 in Equation 1 can be expressed as the cross-sectional area S0 × 0.8.

[0125] Equation 2 is shown by substituting each value into equation 1.

[0126] [Formula 2] As shown in Equation 2, a yield rate of approximately 89 percent can be obtained.

[0127] Furthermore, the lower the ratio of yield strength to tensile strength of the material selected, the higher the yield percentage that can be obtained. For example, if a material with a yield strength to tensile strength ratio of 70 percent is selected and the cross-sectional area S1 is approximately 80% of the cross-sectional area S0, a yield percentage of approximately 114 percent can be obtained.

[0128] Furthermore, even if a material with a high ratio of yield strength to tensile strength is selected, the closer the cross-sectional area S1 is to the cross-sectional area S0, the higher the yield rate of the threaded pipe 300, 400. Of course, in reality, it must be considered that it is not desirable to make the thickness below a certain level due to issues such as machining accuracy and the strength of the thinnest portions of the first female threaded portion 422, second unthreaded portion 430, third male threaded portion 326, and first seal portion 310.

[0129] For example, the tensile strength is 965 (N / mm 2 ) and the yield strength is 862 (N / mm 2 In a threaded pipe manufactured from a material having a yield strength to tensile strength ratio of approximately 89 percent, if the base pipe portion has an outer diameter of 400 mm and a wall thickness of 19 mm, and the thinnest portions of the first female threaded portion 422, the second unthreaded portion 430, the third male threaded portion 326, and the first seal portion 310 are set to 1.4 mm, a yield rate of approximately 103 percent can be obtained according to Equation 1. Note that, conventionally, the yield rate of threaded pipes manufactured from the same material has been approximately 70%. Therefore, by threading the male threaded portion 320 and the female threaded portion 420 according to the present invention, i.e., by threading two straight threads together and two tapered threads together, it is possible to set a thinner wall thickness, resulting in a much higher yield rate than conventional threaded pipes.

[0130] The thread shape of the male thread portion 320 may be different for each of the first male thread portion 322, the second male thread portion 324, and the third male thread portion 326, or they may all have the same shape. For example, each of the male thread portions 322 to 326 may have a sawtooth-shaped thread, or the threads of the first male thread portion 322 and the third male thread portion 326, which have a straight thread shape, may have symmetrical thread shapes such as triangular threads or trapezoidal threads, and the threads of the second male thread portion 324, which has a tapered thread shape, may have a sawtooth-shaped thread. Note that, because the female thread portion 420 is threadably mated with the male thread portion 320, it is preferable that the thread shapes of each of the female thread portions 422 to 426 correspond to the thread shapes of the male thread portions 322 to 326 and basically have the same pitch.

[0131] 20 is a diagram showing the tensile strength and compressive strength of a test specimen of an oil country tubular goods connection structure in which a threaded pipe 300 and a threaded pipe 400 corresponding to two different thread shapes are threadedly connected to each other. The breaking strength of the oil country tubular goods connection structure is affected by the thread shape of the male thread portion 320 and the thread shape of the corresponding female thread portion 420.

[0132] Specifically, threaded pipe 300 has the above-mentioned annular regions A, B, and C, and threaded pipe 400 has the above-mentioned annular regions D, E, and F, which are threadedly coupled to form the test specimen. Furthermore, the area of ​​annular region A is set to one-third or less of the total cross-sectional area of ​​the transverse section of threaded pipe 300, and the effective thread engagement length, number of threads, pitch, etc. are set so that the total shear cross-sectional area of ​​the threads of first male thread portion 322 is at least the square root of three times the area of ​​annular region A.

[0133] In addition, the area of ​​cross-sectional region B is set to be at least one-third of the total cross-sectional area of ​​the cross section of the threaded pipe 300, and the effective thread engagement length, number of threads, pitch, etc. are set so that the total shear area of ​​the threads of the second male threaded portion 324 is at least three times the square root of the area of ​​the annular region B.

[0134] In addition, the area of ​​the cross-sectional region C is set to one-third or less of the total cross-sectional area of ​​the cross section of the threaded pipe 300, and the effective thread engagement length, number of threads, pitch, etc. are set so that the total shear area of ​​the threads of the third male thread portion 326 is at least three times the square root of the area of ​​the annular region C.

[0135] The area of ​​annular region D is set to be one-third or less of the total cross-sectional area of ​​the transverse cross-section of threaded pipe 400. The area of ​​transverse cross-sectional region E is set to be one-third or more of the total cross-sectional area of ​​the transverse cross-section of threaded pipe 400. The area of ​​transverse cross-sectional region F is set to be one-third or less of the total cross-sectional area of ​​the transverse cross-section of threaded pipe 400. Annular region D has an area approximately equivalent to annular region A, annular region E has an area approximately equivalent to annular region B, and annular region F has an area approximately equivalent to annular region C.

[0136] Two types of test specimens were prepared for the threaded pipes 300 and 400 configured as described above, each with a different thread shape, and tensile and compression tests were conducted. The results are shown in Figure 20. The effective thread engagement length, number of threads, pitch, etc. of each test specimen were set to be the same.

[0137] Here, one of the thread shapes was a sawtooth shape with a thread angle of 60°, and the other was a triangular thread with a symmetrical cross section and a thread angle of 70°. In Figure 20, the dashed line shows the results of a tensile test on a member connection (test specimen) with a thread angle of 70°. The dotted-dash line shows the results of a tensile test on a member connection (test specimen) with a sawtooth shape and a thread angle of 60°. The solid line shows the results of a compression test on a member connection (test specimen) with a sawtooth shape and a thread angle of 60°. The two-dot-dash line shows the results of a compression test on a member connection (test specimen) with a thread angle of 70°.

[0138] In the tensile test, the threaded pipe 300 and the threaded pipe 400, which constitute the component connection body (test body), were each attached to a testing machine via a jig, and the component connection body was pulled until it broke while the male threaded portion 320 and the female threaded portion 420 were screwed together.

[0139] In addition, in the compression test, the threaded pipe 300 and the threaded pipe 400 that constitute the member connection body (test body) were threaded together in advance, attached to a testing machine via a jig, and compressed until they collapsed.

[0140] Comparing the dashed and solid lines in Figure 20, i.e., comparing the compression test results, it was found that the component connection body (test specimen) with a symmetrical thread shape in cross section with a thread angle of 70° had a higher compressive strength than the component connection body (test specimen) with a sawtooth-shaped thread with a thread angle of 60°.

[0141] On the other hand, when comparing the dashed-dotted line and the double-dashed-dotted line in Figure 20, that is, when comparing the tensile test results, the component connection (test specimen) with saw-tooth shaped threads and a thread angle of 60° had a higher tensile strength than the component connection (test specimen) with threads at a thread angle of 70°. From these results of the compression test and the tensile test, it can be said that thread shapes that are strong against compression and thread shapes that are strong against tension are different.

[0142] Therefore, it is desirable to appropriately set the thread shape depending on the location where the component connector (test specimen) will be used. For example, a component connector (test specimen) that will be placed in an environment where it is likely to be subjected to tensile stress preferably has a sawtooth-shaped thread. Furthermore, a component connector (test specimen) that will be placed in an environment where it is likely to be subjected to compressive stress preferably has a thread that is symmetrical in cross-section with a thread angle of 70°. Alternatively, when placed in an environment where it is likely to be subjected to both tensile stress and compressive stress, or when used for purposes where it is likely to be subjected to both tensile stress and compressive stress, it is preferable to select a component connector that has a thread that is symmetrical in cross-section with a thread angle of 70°.

[0143] Furthermore, although annular projections 312, 332 and annular recesses 314, 334 are provided on the outer periphery of each seal portion 310, 330, annular projections and annular recesses may alternatively be provided on the threaded pipe 400 side. That is, annular projections and annular recesses may be formed on the inner circumferential surface of each unthreaded portion 410, 430, and the annular projections may be tightly attached to the outer circumferential surface of each seal portion 310, 330. In this case, the outer periphery of each seal portion may be formed into a circular or approximately conical circumferential surface.

[0144] Furthermore, while the first seal portion 310 and the second seal portion 330 are provided at the distal and proximal ends of the threaded pipe 300, a seal portion may be provided at only one of the distal or proximal ends. That is, as shown in FIG. 16(a), the seal portion 310 may be provided only at the distal end of the threaded pipe 300, or as shown in FIG. 16(b), the seal portion 330 may be provided only at the proximal end of the male thread portion 320 of the threaded pipe 300. In these cases, the threaded pipe 400 only needs to have an unthreaded portion formed at a location corresponding to the seal portion. That is, an unthreaded portion may be formed at only one end or the other end of the female thread portion.

[0145] The shape of the tip portion 300a, which restricts the insertion of the threaded pipe 300 into the threaded pipe 400, can be appropriately designed. For example, the tip portion 300a may be inclined at a shallow angle, e.g., less than 45°, relative to the direction perpendicular to the axis, as shown in FIG. 17(a). Alternatively, the tip portion 300a may be curved, as shown in FIG. 17(b), i.e., formed by chamfering the tip portion of the threaded pipe 300. Alternatively, the tip portion 300a may be the end face of the threaded pipe 300 with right-angled corners, as shown in FIG. 17(c). If the tip portion 300a is inclined or curved, a load may be concentrated radially outward on the receiving portion 400a via the inclined tip portion 300a, potentially causing the diameter of the threaded pipe 400 to expand. Therefore, if the tip portion 300a is made to come into surface contact with the receiving portion 400a over a wide area including the end face of the threaded pipe 300, the load is dispersed accordingly, preventing the radially outward load from acting on the receiving portion 400a. Of course, the shape of the base end 300b located on the base end side of the male threaded portion 320 of the threaded pipe 300 can also be set appropriately. In addition, the shape of the receiving portion 400a can be set to correspond to the shape of the tip end 300a or the base end 300b.

[0146] Furthermore, insertion of the threaded pipe 300 into the threaded pipe 400 may be restricted by means other than providing the distal end 300a or the proximal end 300b. For example, the pitch of the threads of either or both of the male and female threads 320 may be shortened. That is, the pitch of at least one of the threads on the proximal end of the male thread 320 and the threads on the far end of the female thread 420 in the insertion direction may be shortened. This allows a braking structure to be provided that restricts threading at the location of the shortened pitch when the male and female threads 320 are threaded together. Of course, in this case, the distal end 300a and the receiving portion 400a do not need to contact each other, but they may be in contact to distribute the load between the braking structure.

[0147] Furthermore, the outer diameter of the male thread portion 320 and / or the inner diameter of the female thread portion 420 may be set to improve the sealing performance between the male thread portion 320 and the female thread portion 420. That is, within the male thread portion 320, the second male thread portion 324 of the tapered thread presses the second female thread portion 424 of the tapered thread from the inside toward the outside, thereby elastically and / or plastically deforming at least one of the second male thread portion 324 and the second female thread portion 424 to improve the sealing performance.

[0148] For example, in order to allow the female thread portion 420 to expand slightly radially outward when fully threaded, the maximum outer diameter (or maximum effective diameter) of the second male thread portion 324 is set larger than the maximum inner diameter (or maximum effective diameter) of the second female thread portion 424, and / or the minimum outer diameter (or minimum effective diameter) of the second male thread portion 324 is set larger than the minimum inner diameter (or minimum effective diameter) of the second female thread portion 424. This allows at least a portion of the second male thread portion 324 and the second female thread portion 424 to interfere with each other in the radial direction, and as the male thread portion 320 and the female thread portion 420 are threaded together, the female thread portion 420 expands in diameter while undergoing elastic deformation and / or plastic deformation, resulting in close contact between the male thread portion 320 and the female thread portion 420 and improved sealing performance.

[0149] Of course, the size of the inner diameter of the second female thread portion 424 relative to the outer diameter of the second male thread portion 324 may be set so that the second male thread portion 324 elastically deforms and / or plastically deforms radially inward. Furthermore, although the outer diameter of the second male thread portion 14 and the inner diameter of the second female thread portion 24 are set as described above, the thickness of the pipe at the second male thread portion 324 and / or the second female thread portion 424 may also be set.

[0150] In addition, when the second male thread portion 324 and the second female thread portion 424 are configured to interfere with each other, a first interference mitigation portion 323 (see Figure 24(a)) may be provided between the first male thread portion 322 and the second male thread portion 324, and a second interference mitigation portion 425 (see Figure 24(b)) may be provided between the second female thread portion 424 and the third female thread portion 426.

[0151] The first interference mitigation portion 323 is disposed in an outwardly convex (radially outwardly convex) boundary region between the first male thread portion 322 and the second male thread portion 324, and is configured by forming it, for example, in a stepped, tapered, curved, or non-threaded region so as not to interfere with the second female thread portion 424 in the axial direction. The second interference mitigation portion 425 is disposed in an outwardly convex (radially inwardly convex) boundary region between the second female thread portion 424 and the third female thread portion 426, and is configured by forming it, for example, in a stepped, tapered, curved, or non-threaded region so as not to interfere with the third male thread portion 324 in the axial direction.

[0152] By providing both interference mitigation portions 323, 425, interference between the first male thread portion 322 and the second female thread portion 424 can be avoided, and interference between the third female thread portion 426 and the second male thread portion 324 can also be avoided.

[0153] Furthermore, the first interference mitigation portion 323 and / or the second interference mitigation portion 425 may have a surface shape that mitigates or avoids interference with the second female threaded portion 424 (or the second male threaded portion 324), but the first interference mitigation portion 323 may be provided with a thread so that it can be threaded into the second female threaded portion 424, and similarly, the second interference mitigation portion 426 may be provided with a thread so that it can be threaded into the second male threaded portion 324.

[0154] The solid resin may be, for example, a thermoplastic resin, a glass fiber reinforced resin blended with the thermoplastic resin, a thermoplastic elastomer, etc. Examples of the thermoplastic resin include general-purpose plastics (polyethylene, high-density polyethylene, medium-density polyethylene, low-density polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl acetate, polyurethane, polytetrafluoroethylene, acrylonitrile butadiene styrene resin, AS resin, acrylic resin, etc.), engineering plastics (polyamide, nylon, polyacetal, polycarbonate, modified polyphenylene ether, polyethylene terephthalate, glass fiber reinforced polyethylene terephthalate, polybutylene terephthalate, cyclic polyolefin, etc.), and super engineering plastics (polyphenylene sulfide, polytetrafluoroethylene, polysulfone, polyethersulfone, amorphous polyarylate, liquid crystal polymer, polyetheretherketone, thermoplastic polyimide, polyamideimide, etc.), and the thermoplastic resin is selected based on the applicable temperature, thermal expansion coefficient, required chemical resistance, etc.

[0155] The threaded pipe may be a steel pipe (carbon steel pipe for piping, carbon steel pipe for pressure piping, galvanized steel pipe for water piping, arc-welded carbon steel pipe for piping, etc.), lined steel pipe (hard polyvinyl chloride-lined steel pipe for water supply, heat-resistant hard polyvinyl chloride-lined steel pipe for water supply, hard polyvinyl chloride outer-coated steel pipe for fire extinguishing, hard polyvinyl chloride-lined steel pipe for drainage, polyethylene powder-lined steel pipe for water supply, tar epoxy-coated steel pipe for drainage, polyethylene-coated steel pipe, etc.), cast iron pipe (ductile cast iron pipe, cast iron pipe for drainage, etc.), copper pipe (copper pipe for piping, coated copper pipe, etc.), SUS steel pipe (stainless steel pipe for general piping), lead pipe (lead pipe for drainage, ventilation, drainage lead pipe, etc.), etc., excluding oil country pipes.

[0156] Furthermore, the location and application of threaded pipes are not particularly limited, except for use at oil mining sites and for crude oil mining applications, and may be buried underground or used indoors or outdoors. Threaded pipes may also be used to transport fluids such as liquids, gases, and powders, or as piping for power transmission lines or communication lines used for transmitting telegraph signals. Specifically, threaded pipes may be used as boiler pipes, water pipes, drainage pipes, gas pipes, fire extinguishing pipes, air pipes, instrument pipes, electrical equipment pipes, electrical conduits, etc.

[0157] 19, male threads 320 may be provided on both ends of a cylinder tube 500, and female threads 420 may be provided on a cylinder bottom 510 and a cylinder head 520. In this way, a cylinder that is small and lightweight yet has sufficient strength to withstand the stress generated by the sliding of a piston 530 can be provided without providing a flange. [Explanation of symbols]

[0158] 1,1A...threaded pipe 2...through hole 10...male threaded portion 12...first male threaded portion 14...second male threaded portion 16...third male threaded portion 18...non-threaded portion 20...female threaded portion 22...first female threaded portion 24...second female threaded portion 26...third female threaded portion 300,400...threaded pipe 310...first seal portion 312...annular convex portion 314...annular concave portion 320...male threaded portion 322...first male threaded portion 324...second male threaded portion 326...third male threaded portion 330...second seal portion 410...first unthreaded portion 420...female threaded portion 422...first female threaded portion 424...second female threaded portion 426...third female threaded portion 430...second unthreaded portion.

Claims

1. An oil well pipe connection structure for connecting tubular members having the same inner and outer diameters, a first tubular member having, on its outer circumferential surface, a first male threaded portion parallel to the axis and a second male threaded portion disposed distally of the first male threaded portion and tapered toward the distal end by gradually reducing in diameter; a second tubular member having an inner circumferential surface provided with a parallel first female thread portion that threadably engages with the first male thread portion, and a second female thread portion that is disposed inside the first female thread portion on the distal end side and has a tapered shape that gradually reduces in diameter so as to threadably engage with the second male thread portion; and an oil well pipe connection structure, characterized in that the shape of each thread of the first male thread portion and the first female thread portion is a sawtooth shape with a triangular cross section, and the flank angle of the flank surface of each thread that receives pressure when pulled in the screwing / unscrewing direction is set to an angle that is equal to or smaller than a right angle with respect to the axial center of the first tubular member and the second tubular member.

2. 2. The oil well pipe connection structure according to claim 1, wherein the shape of each thread of the second male thread portion and the second female thread portion is a sawtooth shape with a triangular cross section, and a flank angle of the flank surface of each thread that receives pressure when pulled in the screwing / unscrewing direction is set to an angle that is equal to or smaller than a right angle with respect to the axial center of the first tubular member and the second tubular member.

3. the first tubular member has a third male thread portion that is disposed closer to the tip end than the second male thread portion and is parallel to the axis, the second tubular member has a parallel third female thread portion disposed inside the second female thread portion on the distal end side and threadedly engaging with the third male thread portion, 3. The oil well pipe connection structure according to claim 1 or 2, characterized in that the shape of each thread of the third male thread portion and the third female thread portion is a sawtooth shape with a triangular cross section, and the flank angle of the flank surface of each thread that receives pressure when pulled in the screwing / unscrewing direction is set to an angle that is equal to or smaller than a right angle with respect to the axial center of the first tubular member and the second tubular member. Construction.

4. 4. The oil well pipe connection structure according to claim 1, wherein the first tubular member has a first interference mitigation portion that is provided in a boundary region that is convex in the outer diameter direction and is formed between the first male thread portion and the second male thread portion, and that has a curved first interference mitigation portion that mitigates interference between the first male thread portion and the second female thread portion.

5. 5. The oil well pipe connection structure according to claim 4, wherein the first interference reduction portion has a threaded portion whose height is determined along a curve that is closer to an inner diameter side of the first tubular member than a straight imaginary line connecting the crests of the threads of the first male threaded portion and a tapered imaginary line connecting the crests of the threads of the second male threaded portion.

6. 6. The oil country tubular good connection structure according to claim 5, wherein the threaded portion of the first interference mitigation portion is positioned along the curve.

7. 4. The oil well pipe connection structure according to claim 3, wherein the second tubular member has a second interference mitigation portion that is provided in a boundary region that is convex in the inner diameter direction and is formed between the second female thread portion and the third female thread portion, and that has a curved second interference mitigation portion that mitigates interference between the second female thread portion and the third male thread portion.

8. 8. The oil well pipe connection structure according to claim 7, wherein the second interference reduction portion has a thread portion whose height is determined along a curve that is closer to an outer diameter side of the second tubular member than a straight imaginary line connecting the crests of the threads of the first female thread portion and a tapered imaginary line connecting the crests of the threads of the second female thread portion.

9. 9. The oil country tubular good connection structure according to claim 8, wherein the threaded portion of the second interference mitigation portion is positioned along the curve.

10. 10. The oil well pipe connection structure according to claim 1, wherein a maximum outer diameter or a maximum effective diameter of the second male thread portion is set to be larger than a maximum inner diameter or a maximum effective diameter of the second female thread portion.

11. 11. The oil well pipe connection structure according to claim 1, wherein a minimum outer diameter or a minimum effective diameter of the second male thread portion is set to be larger than a minimum inner diameter or a minimum effective diameter of the second female thread portion.

12. An oil well pipe connection structure for connecting tubular members having the same inner and outer diameters, a first tubular member having a first male threaded portion on its outer circumferential surface, the first male threaded portion gradually reducing in diameter from the base end toward the tip end, and a second male threaded portion disposed on the tip end side of the first male threaded portion and parallel to the axis; a first female threaded portion that threads with the first male threaded portion and has a tapered shape that gradually reduces in diameter toward the tip side; and a second tubular member that has a second female threaded portion on its inner circumferential surface that is disposed inside the first female threaded portion on the tip side and is parallel to the first male threaded portion so as to thread with the second male threaded portion, in this order from the base end side; and an oil well pipe connection structure, characterized in that the shape of each thread of the first male thread portion and the first female thread portion is a sawtooth shape with a triangular cross section, and the flank angle of the flank surface of each thread that receives pressure when pulled in the screwing / unscrewing direction is set to an angle that is equal to or smaller than a right angle with respect to the axial center of the first tubular member and the second tubular member.

13. 13. The oil well pipe connection structure according to claim 12, wherein the shape of each thread of the second male thread portion and the second female thread portion is a sawtooth shape with a triangular cross section, and the flank angle of the flank surface of each thread that receives pressure when pulled in the screwing / unscrewing direction is set to an angle that is equal to or smaller than a right angle with respect to the axial center of the first tubular member and the second tubular member.

14. the first tubular member has a third male thread portion that is disposed closer to the tip end than the second male thread portion and that is tapered relative to the axis, the second tubular member has a tapered third female thread portion that is disposed inside the second female thread portion and is closer to the tip end side than the second female thread portion and that threadably engages with the third male thread portion, 14. The oil well pipe connection structure according to claim 12 or 13, characterized in that the shape of each thread of the third male thread portion and the third female thread portion is a sawtooth shape with a triangular cross section, and the flank angle of the flank surface of each thread that receives pressure when pulled in the screwing / unscrewing direction is set to an angle that is equal to or smaller than a right angle with respect to the axial center of the first tubular member and the second tubular member.

15. 15. The oil well pipe connection structure according to claim 14, wherein the maximum outer diameter or maximum effective diameter of the third male thread portion is set to be larger than the maximum inner diameter or maximum effective diameter of the third female thread portion.

16. 16. The oil well pipe connection structure according to claim 14 or 15, wherein the minimum outer diameter or minimum effective diameter of the third male thread portion is set to be larger than the minimum inner diameter or minimum effective diameter of the third female thread portion.

17. 17. The oil well pipe connection structure according to claim 14, wherein the first tubular member has a second interference mitigation portion that is provided in a boundary region that is convex in the outer diameter direction and is formed between the second male thread portion and the third male thread portion, and that has a curved shape that mitigates interference between the second male thread portion and the third female thread portion.

18. 18. The oil well pipe connection structure according to claim 12, wherein the second tubular member has a first interference mitigation portion that is provided in a boundary region that is convex in an inner diameter direction and is formed between the first female thread portion and the second female thread portion, and that has a curved shape that mitigates interference between the second female thread portion and the first male thread portion.

19. 19. The oil well pipe connection structure according to claim 12, wherein a maximum outer diameter or a maximum effective diameter of the first male thread portion is set to be larger than a maximum inner diameter or a maximum effective diameter of the first female thread portion.

20. 20. The oil well pipe connection structure according to claim 12, wherein a minimum outer diameter or a minimum effective diameter of the first male thread portion is set to be larger than a minimum inner diameter or a minimum effective diameter of the first female thread portion.

21. 21. The oil country tubular good connection structure according to claim 1, wherein the flank angle is 70°.

22. 13. The oil well pipe connection structure according to claim 1 or 12, wherein a tip outer diameter of the second male thread portion and a tip inner diameter of the second female thread portion are set so that a tip outer peripheral surface of the second male thread portion and a tip inner peripheral surface of the second female thread portion are in close contact with each other.

23. 15. The oil well pipe connection structure according to claim 3 or claim 14, wherein a tip outer diameter of the third male thread portion and a tip inner diameter of the third female thread portion are set so that a tip outer peripheral surface of the third male thread portion and a tip inner peripheral surface of the third female thread portion are in close contact with each other.

24. 24. The oil well pipe connection structure according to claim 1, wherein a base end outer diameter of the first male thread portion and a base end inner diameter of the first female thread portion are set so that a base end outer peripheral surface of the first male thread portion and a base end inner peripheral surface of the first female thread portion are in close contact with each other.

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