Oil well pipe connection structure

Abstract

This invention provides an oil well pipe connecting structure that connects threaded oil well pipes in a simple manner, without increasing size, within the inner and outer diameters of the components, and with strength significantly exceeding the limits of conventional technology. [Solution] The oil well pipe connecting structure connects tubular members having the same inner and outer diameters, and includes a first tubular member having a first male threaded portion parallel to the axis and a second male threaded portion located towards the tip of the first male threaded portion and gradually decreasing in diameter to form a tapered shape on its outer surface, starting from the base end; a second tubular member having a first female threaded portion parallel to the first male threaded portion and screwing into the first male threaded portion, starting from the base end, and a second female threaded portion located inside towards the tip of the first female threaded portion and gradually decreasing in diameter to screw into the second male threaded portion on its inner surface; and a first interference mitigation portion having a curved shape, provided in the outer diameter convex boundary region formed between the first male threaded portion and the second male threaded portion to mitigate interference between the first male threaded portion and the second female threaded portion.

Description

Technical Field

[0001] The present invention relates to a connection structure for oil well pipes that connects oil well pipes with substantially the same inner and outer diameters to each other.

Background Art

[0002] Generally, it is known to use a plurality of hollow rod-shaped members such as columns, pipes, and tubes connected axially. As means for connecting them, it is known to join and connect both members by an adhesive or welding, or to connect both members by a separate member (such as a sleeve or a pipe screw joint).

[0003] For example, in a structure in which one steel pipe having a male joint end portion with a thread on the outer circumference and another steel pipe having a female joint end portion with a thread on the inner circumference and screwing with the male joint end portion are joined by screwing their joint end portions together, with respect to a through hole extending from the outer circumferential surface to the inner circumferential surface of the female joint end portion provided in the female joint end portion, a bolt having an uneven shape at the tip is screwed, and by pressing the tip against the outer circumferential surface of the male joint end portion, a structure for preventing loosening of the steel pipe joint is known (see Patent Document 1).

[0004] Also, it is known to provide flanges at the ends of steel pipes, abut the flanges against each other, pass bolts through the flange holes and tighten nuts to join the steel pipes together (see Patent Document 2). Such steel pipes with flanges are usually designed based on the design pressure of the steel pipes, determining the shape of the flanges, the number of bolts, etc. That is, it is designed to ensure strength against the internal pressure acting constantly and to have sufficient surface pressure acting on the flange joint surface so that no leakage occurs.

[0005] Furthermore, in a hydraulic cylinder, there is a known type 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 this hydraulic cylinder, flanges are provided on the cylinder tube, cylinder bottom, and cylinder head to increase strength, and the flanges are butted together and the cylinder bottom and cylinder head are fixed to the cylinder tube with bolts. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-163781 [Patent Document 2] Japanese Patent Publication No. 2017-040074 [Patent Document 3] Japanese Patent Publication No. 2017-044238 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, joining components by welding is time-consuming and reduces work efficiency. Furthermore, when using adhesives to connect components, there are problems such as the adhesive's shorter lifespan compared to screw joints and the possibility of delamination due to temperature changes.

[0008] Furthermore, when a straight thread is formed on a pipe, such as in Patent Document 1, there is a problem that the axial strength of the pipe can only be obtained at most about 50% of the total cross-sectional strength. Although the axial strength of the pipe can be improved by changing the straight thread to a tapered thread, even then the axial strength of the pipe can only be obtained at about 70% of the total cross-sectional strength of the pipe.

[0009] Therefore, while connecting pipes using standard threaded joints can provide strength equivalent to the overall cross-sectional strength, threaded joints are larger in diameter than the pipes, resulting in a larger area where the joint is installed. Consequently, when laying pipes connected via threaded joints underground, the work involved in enlarging the hole becomes time-consuming.

[0010] Furthermore, when fluid passes through a pipe, if the pipes are directly screwed together as in Patent Document 1, sealing performance is ensured to prevent fluid leakage through surface contact between the pipes or surface contact between the threaded joint and both pipes. Similarly, when pipes are joined by welding, sealing performance is ensured by the joint. However, there is a problem that when the pipes expand at high temperatures, deform due to bending or elongation under high load, or cracks occur at the joint, a gap is created between the pipes, resulting in a loss of sealing performance.

[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 with sufficient strength against internal pressure can deform due to moments acting on them in environments where external forces are present, leading to surface pressure on the flange joint surface and causing leakage. Additionally, there is the problem that the flanges must be enlarged to prevent such deformation. Moreover, there is the problem that storing flanged steel pipes in an arrangement requires a larger storage space.

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

[0013] Although the aforementioned patent documents concern pipe connections, similar problems may occur with support columns and other structures connected by similar means.

[0014] This invention was made possible through the diligent research of the inventors in view of the above-mentioned problems, and aims to provide an oil well pipe connecting structure that connects threaded oil well pipes with a simple structure, without increasing size, within the inner and outer diameters of the members, and with strength that significantly exceeds the limits of the conventional technology.

[0015] Furthermore, the objective is to provide an oil well pipe connecting structure that maintains high sealing performance even in environments subject to high temperatures and heavy loads. [Means for solving the problem]

[0016] An oil well pipe connecting structure according to one aspect of the present invention is an oil well pipe connecting structure for connecting tubular members having the same inner and outer diameters, and is characterized by comprising: a first tubular member having a first male threaded portion parallel to the axis and a second male threaded portion located on the outer circumferential surface, positioned on the tip side of the first male threaded portion and gradually decreasing in diameter toward the tip side to form a tapered shape; a second tubular member having a first female threaded portion parallel to the first male threaded portion that screws into the first male threaded portion, and a second female threaded portion located inside the tip side of the first female threaded portion and gradually decreasing in diameter to screw into the second male threaded portion, positioned on the inner circumferential surface; and a first interference mitigation portion having a curved shape, provided in an outer diameter convex boundary region formed between the first male threaded portion and the second male threaded portion to mitigate interference between the first male threaded portion and the second female threaded portion.

[0017] Furthermore, the oil well pipe connecting structure is characterized in that the first tubular member is positioned closer to the tip than the second male threaded portion and has a third male threaded portion parallel to the axis, the second tubular member is positioned further inside closer to the tip than the second female threaded portion and has a third female threaded portion parallel to the third male threaded portion that screws into it, and a second interference mitigation portion is provided in an inwardly convex boundary region formed between the second female threaded portion and the third female threaded portion and has a curved shape that mitigates interference between the second female threaded portion and the third male threaded portion.

[0018] Further, the oil well pipe connection structure is characterized in that the screw portion of the second interference mitigation portion has a height defined along a curve closer to the outer diameter side of the second tubular member than a linear virtual line connecting the tops of the threads of the first female screw portion and a tapered virtual line connecting the tops of the threads of the second female screw portion.

[0019] Also, the oil well pipe connection structure is characterized in that the position of the screw portion of the second interference mitigation portion is defined along the curve.

[0020] Further, the oil well pipe connection structure is characterized in that the screw portion of the first interference mitigation portion has a height defined along a curve closer to the inner diameter side of the first tubular member than a linear virtual line connecting the tops of the threads of the first male screw portion and a tapered virtual line connecting the tops of the threads of the second male screw portion.

[0021] Also, the oil well pipe connection structure is characterized in that the position of the screw portion of the first interference mitigation portion is defined along the curve.

[0022] Also, the oil well pipe connection structure is characterized in that the maximum outer diameter or maximum effective diameter of the second male screw portion is set larger than the maximum inner diameter or maximum effective diameter of the second female screw portion.

[0023] Also, the oil well pipe connection structure is characterized in that the minimum outer diameter or minimum effective diameter of the second male screw portion is set larger than the minimum inner diameter or minimum effective diameter of the second female screw portion.

[0024] Another embodiment of the present invention is an oil well pipe connecting structure for connecting tubular members having the same inner and outer diameters, characterized in that it comprises: a first tubular member having a first male threaded portion that gradually decreases in diameter toward the tip, forming a tapered shape, and a second male threaded portion that is positioned toward the tip than the first male threaded portion and parallel to the axis, provided on its outer circumferential surface; a second tubular member having a first female threaded portion that screws into the first male threaded portion and gradually decreases in diameter toward the tip, forming a tapered shape, and a second female threaded portion that screws into the second male threaded portion and is positioned inside toward the tip than the first female threaded portion and parallel to the axis, provided on its inner circumferential surface; and a first interference mitigation portion that is provided in an inwardly convex boundary region formed between the first female threaded portion and the second female threaded portion, and has a curved shape to mitigate interference between the second female threaded portion and the first male threaded portion.

[0025] Furthermore, the oil well pipe connecting structure is characterized by having a first tubular member having a third male thread portion that is positioned closer to the tip than the second male thread portion and tapered with respect to the axis, a second female thread portion that is positioned further inside closer to the tip than the second female thread portion and tapered to screw with the third male thread portion, and a second interference mitigation portion that is provided in an outer diameter convex boundary region formed between the second male thread portion and the third male thread portion and has a curved shape to mitigate interference between the second male thread portion and the third female thread portion.

[0026] Furthermore, the oil well pipe connecting structure is characterized in that the second 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 the straight imaginary line connecting the tops of each thread of the second male threaded portion and the tapered imaginary line connecting the tops of each thread of the third male threaded portion.

[0027] Furthermore, the oil well pipe connecting structure is characterized in that the threaded portion of the second interference mitigation section is positioned along the curve.

[0028] Furthermore, the oil well pipe connecting structure is characterized in that the first interference mitigation section has a threaded section whose height is determined along a curve that is closer to the outer diameter side of the second tubular member than the tapered imaginary line connecting the tops of each thread of the first female thread section and the straight imaginary line connecting the tops of each thread of the second female thread section.

[0029] Furthermore, the oil well pipe connecting structure is characterized in that the threaded portion of the first interference mitigation section is positioned along the curve.

[0030] Furthermore, the oil well pipe connecting structure is characterized in that the shape of the threads in the third male threaded portion and the third female threaded portion are sawtooth-shaped.

[0031] Furthermore, the oil well pipe connecting structure is characterized in that the shape of the threads in the first male threaded portion and the first female threaded portion are sawtooth-shaped.

[0032] Furthermore, the oil well pipe connecting structure is characterized in that the shape of the threads in the second male threaded portion and the second female threaded portion are sawtooth-shaped.

[0033] Furthermore, the oil well pipe connecting structure is characterized in that each thread has a triangular cross-section, where the flank angle of the flank surface of each thread that receives pressure when the third male thread portion and the third female thread portion are pulled in the unthreading direction is set to an angle of perpendicular or less with respect to the axis of the first tubular member and the second tubular member.

[0034] Furthermore, the oil well pipe connecting structure is characterized in that each thread has a triangular cross-section, with the flank angle of the flank surface that receives pressure when the first male thread portion and the first female thread portion are pulled in the unthreading direction set to an angle of perpendicular or less with respect to the axis of the first tubular member and the second tubular member.

[0035] Furthermore, the oil well pipe connecting structure is characterized in that each thread has a triangular cross-section, where the flank angle of the flank surface of each thread that receives pressure when the second male thread portion and the second female thread portion are pulled in the unthreading direction is set to an angle of perpendicular or less with respect to the axis of the first tubular member and the second tubular member.

[0036] Furthermore, the oil well pipe connection structure is characterized by having a flank angle of 70°.

[0037] Furthermore, the oil well pipe connecting structure is characterized in that the minimum outer diameter or minimum effective diameter of the third male threaded portion is set to be larger than the minimum inner diameter or minimum effective diameter of the third female threaded portion.

[0038] Furthermore, the oil well pipe connecting structure is characterized in that the maximum outer diameter or maximum effective diameter of the first male threaded portion is set to be larger than the maximum inner diameter or maximum effective diameter of the first female threaded portion.

[0039] Furthermore, the oil well pipe connecting structure is characterized in that the minimum outer diameter or minimum effective diameter of the first male threaded portion is set to be larger than the minimum inner diameter or minimum effective diameter of the first female threaded portion.

[0040] Furthermore, the oil well pipe connecting structure is characterized in that the outer diameter of the tip of the second male threaded portion and the inner diameter of the tip of the second female threaded portion are set so that the outer circumferential surface of the tip of the second male threaded portion and the inner circumferential surface of the tip of the second female threaded portion are in close contact with each other.

[0041] Furthermore, the oil well pipe connecting structure is characterized in that the outer diameter of the tip of the third male threaded portion and the inner diameter of the tip of the third female threaded portion are set so that the outer circumferential surface of the tip of the third male threaded portion and the inner circumferential surface of the tip of the third female threaded portion are in close contact with each other.

[0042] Furthermore, the oil well pipe connecting structure is characterized in that the base end outer diameter of the first male thread and the base end inner diameter of the first female thread are set so that the base end outer circumferential surface of the first male thread and the base end inner circumferential surface of the first female thread are in close contact with each other. [Effects of the Invention]

[0043] According to the oil well pipe connecting structure of the present invention, threaded oil well pipes can be connected with a simple structure, without increasing their size, within the inner and outer diameters of the members, and with strength that significantly exceeds the limits of conventional technology.

[0044] Furthermore, the oil well pipe connecting structure of the present invention can provide a sealing structure that maintains high sealing performance even in environments subject to high temperatures or high loads. [Brief explanation of the drawing]

[0045] [Figure 1] This is a perspective view showing two threaded pipes having the connecting structure of the first embodiment and capable of being connected to each other. [Figure 2] This is a cross-sectional view showing a threaded pipe according to the first embodiment. [Figure 3] This is a cross-sectional view showing connected threaded pipes. [Figure 4] This diagram shows the threads of a male screw. [Figure 5] This figure shows examples of other screw thread shapes. [Figure 6] This is a cross-sectional view showing a threaded pipe. [Figure 7] This is a cross-sectional view showing other examples of threaded pipe shapes. [Figure 8] This figure shows an example of the tapered shape of the second male thread section. [Figure 9] This is a cross-sectional view showing other examples of threaded pipe shapes. [Figure 10] This figure shows examples of screw thread shapes. [Figure 11] This figure shows examples of screw thread shapes. [Figure 12] This diagram shows the sealing structure between the male and female threaded sections. [Figure 13] The following are examples of other shapes of threaded pipes having a male threaded portion, where (a) is a cross-sectional view and (b) is a diagram showing the annular region A to C. [Figure 14] This figure shows the outer surface of a threaded pipe having a male threaded portion. [Figure 15] The following are examples of other shapes of threaded pipes having an internal thread section, where (a) is a cross-sectional view and (b) is a diagram showing the annular region D to F. [Figure 16] This diagram shows an example of the location of the seal. [Figure 17] This figure shows an example of the tip section. [Figure 18]This diagram shows the axial length of each part of each threaded pipe. [Figure 19] This figure shows an example of its application to a cylinder. [Figure 20] This figure shows the results of tensile and compression tests on threaded pipes. [Figure 21] This diagram shows the interference mitigation section of the male screw portion. [Figure 22] This is a cross-sectional view showing other examples of threaded pipe shapes. [Figure 23] This diagram shows the interference reduction section of the female screw thread. [Figure 24] This diagram shows the location of the interference mitigation section in a threaded pipe. [Modes for carrying out the invention]

[0046] Embodiments of the threaded pipe (threaded member) connection structure of the present invention will be described below with reference to the drawings. Figure 1 is a perspective view showing two threaded pipes 1 and 1A that can be connected to each other using the oil well pipe connection structure of the first embodiment, and Figure 2 is a cross-sectional view showing the threaded pipes 1 and 1A of the first embodiment. Note that Figures 1 and 2 show the main parts for connecting the threaded pipes 1 and 1A, and do not show the whole structure. That is, Figures 1 and 2 show one end of threaded pipe 1 where the male thread portion is formed, and one end of 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 of threaded pipes 1 and 1A are set so that the outer diameter is substantially uniform even when connected, as will be described later.

[0047] Threaded pipes 1 and 1A are metal threaded tubular members, such as so-called steel pipes, which have a hollow structure with a substantially uniform outer diameter and an axial through-hole 2 that allows fluid to be transported. Therefore, threaded pipes 1 and 1A are used in wells for extractable resource fluids at extraction sites such as oil wells and gas wells, that is, they are used exclusively for non-extractable resource fluids (air, water, non-extractable natural gas, hydraulic oil, etc.) excluding oil well pipes, that is, they are applied exclusively to non-oil well pipes. Therefore, they are used to contain and / or allow non-extractable resource fluids to flow, and threaded pipes 1 and 1A can be used, for example, as water pipes, boiler pipes, etc.

[0048] The threaded pipe 1 has one end with a reduced outer diameter, and a male threaded portion 10 on the outer circumferential surface of this end. The male threaded portion 10 has a first male threaded portion 12 having a straight thread with a substantially constant outer diameter, and a second male threaded portion 14 located closer to the end than the first male threaded portion 12 and having a so-called tapered thread where the outer diameter of the male thread gradually decreases. Furthermore, the second male threaded portion 14 has a longer axial region compared to the first male threaded portion 12.

[0049] The second male threaded portion 14 has threads formed 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 with the same pitch as the threads of the first male threaded portion 12, and the outer diameter and thread height gradually decrease toward one end. The threads of the first male threaded portion 12 and the threads of the second male threaded portion 14 are formed continuously with the same pitch, but this is not limited to this, and the pitch of the other may be set to be larger or smaller than that of the other, or the pitch may be gradually changed.

[0050] The threaded pipe 1A has an enlarged inner circumferential surface at one end, and has a female threaded portion 20 on this inner circumferential surface. The female threaded portion 20 has a first female threaded portion 22 and a second female threaded portion 24, with the first female threaded portion 22 located closer to the one end than the second female threaded portion 24. In addition, the second female threaded portion 24 has a longer axial region compared to the first female threaded portion 22.

[0051] The first female threaded portion 22 has a straight thread with a substantially constant diameter. The second female threaded portion 24 has a tapered thread with a gradually changing diameter. Specifically, the threads of the second female threaded portion 24 are formed such that the inner diameter of the female thread gradually increases toward one end (i.e., toward the first female threaded portion 22). In addition, the threads of the second female threaded portion 24 are set to the same pitch as the threads of the first female threaded portion 22. As a result, the threads of the female threaded portion 20 are formed to form a straight thread in the first female threaded portion 22, and a tapered thread in the second female threaded portion 24, where the inner diameter gradually decreases toward the first female threaded portion 22 (one end).

[0052] Although the threads of the first female thread portion 22 and the threads of the second female thread portion 24 are formed continuously with the same pitch, the system is not limited to this, and the pitch of one may be set to be larger or smaller than the other, or the pitch may be gradually changed.

[0053] Furthermore, the thread shape of the male thread portion 10 and the female thread portion 20 is not particularly limited, but may be, for example, a sawtooth shape. Here, Figure 4 shows the thread shape of the male thread portion 10, and as shown in Figure 4, the thread shape is such that when the threaded pipes 1 and 1A are screwed together and pulled apart in the axial direction from the connected state, 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. Here, the flank angle θ represents the outer angle of the triangular thread cross-section.

[0054] The thread shape of the female thread portion 20 is set to be 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 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 male thread portion 10 and the female thread portion 20 can have flank angles other than right angles, as long as their flank surfaces abut each other over substantially their entire surfaces. For example, the flank angle θ in the male thread portion 10 can be set to an angle greater than right angle, or conversely, the flank angle θ can be set to a so-called inverted shape, which is less than right angle, as shown in Figure 5.

[0055] The connection between threaded pipes 1 and 1A is made by screwing the male threaded portion 10 and the female threaded portion 20 together. Specifically, one end of threaded pipe 1 is inserted into the inner circumferential surface of the end of threaded pipe 1A. At this time, first the second male threaded portion 14 located at the tip of threaded pipe 1 is passed through the inner circumferential surface surrounded by the first female threaded portion 22 on the opening side of threaded pipe 1A, and threaded pipe 1 is positioned so that the first male threaded portion 12 shown in Figure 3(a) can be screwed into the first female threaded portion 22. Next, threaded pipe 1 is rotated relative to threaded pipe 1A in the tightening direction so that the first male threaded portion 12 is screwed into the first female threaded portion 22.

[0056] As a result, the threaded pipe 1 is gradually displaced until the second male thread portion 14 can be screwed into the second female thread portion 24, and then rotates further until the male thread of the second male thread portion 14 and the female thread of the second female thread portion 24 are screwed together, as shown in Figure 3(b).

[0057] Therefore, the threaded pipes 1 and 1A are connected with the male threaded portion 10 and the female threaded portion 20 screwed together. That is, the first male threaded portion 12 is screwed into the first female threaded portion 22, and the second male threaded portion 14 is screwed into the second female threaded portion 24. Furthermore, when the male threaded portion 10 and the female threaded portion 20 are fitted together, the imaginary line connecting the peaks of the threads of the male threaded portion 10, which are aligned axially, and the imaginary line connecting the peaks of the threads of the female threaded portion 20, which are aligned axially, are parallel. That is, the imaginary line in the first male threaded portion 12 is parallel to the imaginary line in the first female threaded portion 22, and the imaginary line in the second male threaded portion 14 is parallel to the imaginary line in the second female threaded portion 24.

[0058] Here, the axial strength of the connected threaded pipes 1 and 1A differs at the point where the first male threaded portion 12 and the first female threaded portion 22 are screwed together, and at the point where the second male threaded portion 14 and the second female threaded portion 24 are screwed together.

[0059] First, in the first male threaded portion 12 of the threaded pipe 1, the load is concentrated at the point where the pipe wall thickness is thinnest, near the starting point of the thread, i.e., around position P1 in Figure 6. Therefore, the strength of the first male threaded portion 12 depends on the strength at position P1, and the ratio of the strength at position P1 to the total cross-sectional strength is approximately equivalent 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 approximately 90%, then the strength will be approximately 90% of the total cross-sectional strength.

[0060] The second male threaded portion 14 of the threaded pipe 1 has a tapered thread whose outer diameter changes towards the tip, so it screws into the threads of the second female threaded portion 24 of the threaded pipe 1A with virtually no gap in the section where the thread is effectively engaged. That is, 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 along the effective thread engagement length, and as a result, when the second male threaded portion 14 is set so as to maximize the effective thread engagement length, a strength of approximately 70% of the total cross-sectional strength is obtained.

[0061] Furthermore, the strength of the first female thread portion 22 and the second female thread portion 24 of the threaded pipe 1A is determined in much the same way as the first male thread portion 12 and the second male thread portion 14 of the threaded pipe 1. Specifically, in the first female thread portion 22, the load is concentrated at the point where the wall thickness is thinnest near the starting point of the thread (position P3 in Figure 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 (cross-sectional area at position P4 in Figure 6), and the total cross-sectional strength. In addition, since the second female thread portion 24 has a tapered thread, a maximum strength of approximately 70% of the total cross-sectional strength can be obtained.

[0062] As described above, the male threaded portion 10 and the female threaded portion 20 have different strengths in the areas where straight threads are arranged and the areas where tapered threads are arranged. Therefore, the total tensile strength is determined by the sum of the tensile strengths in each area. Specifically, the tensile strength of the male threaded portion 10 is determined by the sum of the tensile strength of the first male threaded portion 12 and the tensile strength of the second male threaded portion 14. As in the example above, if the tensile strength of the first male threaded portion 12 area is about 10% of the total tensile strength of the entire cross-section, and the tensile strength of the second male threaded portion 14 area is about 70% of the total tensile strength of the entire cross-section, then the total tensile strength will be about 80% of the total tensile strength of the entire cross-section. Similarly, in the female threaded portion 20, the sum of the tensile strength of the first female threaded portion 22 area and the tensile strength of the second female threaded portion 24 area equals the total tensile strength.

[0063] As explained above, threaded pipes 1 and 1A are provided with a male threaded section and a female threaded section, respectively. By screwing the straight threads of the first male threaded section and the first female threaded section together, and by screwing the tapered threads of the second male threaded section and the second female threaded section together, the axial strength can be improved compared to simply screwing straight threads together or screwing tapered threads together.

[0064] In the embodiment described above, the male threaded portion 10 was formed by arranging the first male threaded portion 12 and the second male threaded portion 14 in order from the middle of the threaded pipe 1 toward one end. However, as shown in Figure 7, it may also be formed by arranging the first male threaded portion 12, the second male threaded portion 14, and the third male threaded portion 16 having a straight thread in order from the middle of the pipe toward one end.

[0065] Furthermore, although the female thread portion 20 is formed by arranging a first female thread portion 22 and a second female thread portion 24 in order from one end of the threaded pipe 1A, it may also be formed by arranging a first female thread portion 22, a second female thread portion 24, and a third female thread portion 26 having a straight thread in order from one end, as shown in Figure 7.

[0066] Furthermore, while threaded pipes are generally connected via a separate joint to improve strength, the outer diameter of the joint is larger than that of the threaded pipe. Therefore, installing such threaded pipes required digging wells, holes, etc., with a larger diameter to accommodate the joint. However, the threaded pipe of the present invention has extremely high axial strength while suppressing the need to increase the outer diameter of the pipe. This reduces the labor involved in digging wells, holes, etc., and lowers the cost of excavation.

[0067] Furthermore, when threaded pipes 1 and 1A are connected, the straight threads of the first male thread and the first female thread are screwed together, and the tapered threads of the second male thread and the second female thread are screwed together. Compared to connecting flanged steel pipes, this method improves axial strength without requiring flanges that protrude radially. Also, by omitting flanges, the size of threaded pipes 1 and 1A can be kept down, reducing the space required for installation and saving space. In addition, even when threaded pipes 1 and 1A are stored in an arrangement, storage space can be saved. Furthermore, since fluid leakage due to gaps in the flange joint surface cannot occur, more stable fluid transfer can be achieved.

[0068] In the embodiments described above, the tapered shape of the tapered threads of the second male threaded portion 14 and the second female threaded portion 24 can be set as appropriate. For example, in the cross-sectional shape of the male threaded portion 10 shown in Figure 8(a), the imaginary line connecting the tips of each thread of the second male threaded portion 14 can be set to a straight tapered shape with a predetermined gradient, and the imaginary line connecting the tips of each thread of the second male threaded portion 14 shown in Figure 8(b) can be set to a curved tapered shape. Furthermore, the imaginary line connecting the tips and / or valleys of each thread of the second female threaded portion 14 shown in Figure 8(c) along the axial direction can be set to a tangent curve-like curve. Of course, in the second female threaded portion 24 of the female threaded portion 20, the tapered thread can also be set to a tapered shape with a predetermined gradient, or to a curved tapered shape, similar to the above.

[0069] Furthermore, in the above-described embodiment, continuous threads are provided across the first male threaded portion 12 and the second male threaded portion 14, but the invention is not limited to this, and the threads of the first male threaded portion 12 and the threads of the second male threaded portion 14 may be formed separately. Also, as shown in Figure 9, a non-threaded portion 18 may be provided between the first male threaded portion 12 and the second male threaded portion 14. The outer diameter of the non-threaded portion 18 is set to be at least less than or equal to the root diameter of the threads of the first male threaded portion 12. That is, the outer diameter of the non-threaded portion 18 is set so as not to interfere with the threads of the female threaded portion 20 when screwing the male threaded portion 10 and the female threaded portion 20 together. It is also desirable that the outer diameter of the non-threaded portion 18 be constant along the axial direction.

[0070] Furthermore, if a non-threaded portion 18 is provided on the male threaded portion 10, a non-threaded portion may also be provided on the female threaded portion 20. Alternatively, a metal seal structure may be provided on the non-threaded portion 18, or sealing materials such as O-rings, D-rings, or gaskets 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, preventing leakage of fluid flowing through the pipe.

[0071] Furthermore, the thread shape of the male thread portion 10 and the female thread portion 20 is not limited to a sawtooth shape, but can be set as appropriate. For example, there may be a triangular thread shape as shown in Figure 10(a), a round thread shape as shown in Figure 10(b), a square thread shape as shown in Figure 10(c), a trapezoidal thread shape as shown in Figure 10(d), etc. Also, there may be a sawtooth shape with a wide tip surface of the thread as shown in Figure 11(a), or a curved shape with a wide tip surface of the thread as shown in Figure 11(b). In addition, there may be a sawtooth shape with a curved tip surface or thread valley as shown in Figure 11(c), or a curved shape with a curved tip surface or thread valley as shown in Figure 11(d).

[0072] Furthermore, in the male thread portion 10, the thread shape may be different between the first male thread portion and the second male thread portion. For example, the thread of the first male thread portion, which is a straight thread, may be set to a triangular shape, and the thread of the second male thread portion, which is a tapered thread, may be set to a sawtooth shape. The same applies to a male thread portion having a first to third male thread portion as shown in Figure 7, where the thread of the first male thread portion may be set to a triangular shape, the thread of the second male thread portion to a sawtooth shape, and the thread of the third male thread portion to a round thread shape.

[0073] Furthermore, the outer diameter of the male threaded portion 10 and the inner diameter of the female threaded portion 20 can be set as appropriate. Therefore, the outer diameter of the male threaded portion 10 and / or the inner diameter of the female threaded portion 20 may be set to improve the sealing performance between the male threaded portion 10 and the female threaded portion 20. That is, the second male threaded portion 14 may press the second female threaded portion 24 from the inside out, causing elastic and / or plastic deformation of at least one of the second male threaded portion 14 and the second female threaded portion 24 to improve the sealing performance.

[0074] For example, the maximum outer diameter (or maximum effective diameter) of the second male thread portion 14 is set to be 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 to be larger than the minimum inner diameter (or minimum effective diameter) of the second female thread portion 24, so that when fully screwed together, the female thread portion 20 can expand slightly radially outward. In this case, the second male thread portion 14 and the second female thread portion 24 can interfere with each other radially in at least a part, and when the male thread portion 10 and the female thread portion 20 are screwed together, the female thread portion 20 expands in diameter while undergoing elastic and / or plastic deformation, and as a result the male thread portion 10 and the female thread portion 20 become tightly fitted together, improving the sealing performance.

[0075] 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 undergoes elastic and / or plastic deformation radially inward. Furthermore, although the above description assumes setting the outer diameter of the second male thread portion 14 and the inner diameter of the second female thread portion 24, the thickness of the pipe in the second male thread portion 14 and / or the second female thread portion 24 may also be set.

[0076] Furthermore, if the second male thread portion 14 and the second female thread portion 24 are configured to interfere with each other, when screwing them together to the correct position (screwed all the way in), the tip of the thread in the first male thread portion 12 near the second male thread portion 14 is located radially outward from the thread root near the end of the second female thread portion 24 on the first female thread portion 22 side, causing interference. In this interfered state, further screwing becomes impossible. Therefore, the end region of the first male thread portion 12 that interferes with the second female thread portion 24 is reduced in diameter to reduce or eliminate the amount of interference.

[0077] Preferably, the length to be reduced in diameter is greater than or equal to 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 provided with various shapes such as stepped, tapered, curved, or threadless to reduce the diameter.

[0078] Specifically, since the first male thread portion 12 may interfere with the second female thread portion 24 in the axial direction, an interference mitigation portion 13, as shown in Figure 21, is provided in the outwardly convex (i.e., radially outward convex) boundary region between the first male thread portion 12 and the second male thread portion 14 to avoid such interference.

[0079] For example, the imaginary line 13a (see Figure 21) connecting the tips of each thread in the interference mitigation section 13 is a curved line that is closer to the axis than the straight imaginary line 12a connecting the tips of each thread in the first male thread section 12 and the tapered imaginary line 14a connecting the tips of each thread in the second male thread section 14, and the height and position of the threads are determined to follow this curve. Also, the maximum radius r (see Figure 21) in the interference mitigation section 13 is less than or equal to the minimum inner diameter of the second female thread section 24.

[0080] Therefore, by providing the interference mitigation portion 13, interference between the first male thread portion 12 and the second female thread portion 24 can be mitigated or avoided. The interference mitigation portion 13 may have a surface shape that mitigates or avoids interference with the second female thread portion 24, but it may also have a shape that has threads that can be screwed into the first female thread portion 22 and / or the second female thread portion 24.

[0081] Although the male threaded portion 10 has been described as having a straight first male threaded portion 12 and a tapered second male threaded portion 14 extending from the middle of the threaded pipe 1 to one end, it goes without saying that it may also have a shape with a second male threaded portion 14 and a first male threaded portion 12 extending from the middle of the pipe to one end, as shown in Figure 22. In that case, the female threaded portion 20 that can be screwed into the male threaded portion 10 will have a shape with a second female threaded portion 24 and a first female threaded portion 22 extending from one end to the back, as shown in Figure 22. Furthermore, the male threaded portion 10 may be annular on the middle side of the second male threaded portion 14 and may have a sealing portion 19 that can tightly adhere to the inner circumferential surface of the threaded pipe 1A over its entire circumference.

[0082] Furthermore, in the threaded pipes 1 and 1A of Figure 22, the second male threaded portion 14 and the second female threaded portion 24 are configured to interfere with each other, and when they are screwed together to the correct position (screwed all the way in), the end of the second male threaded portion 14 on the side of the first male threaded portion 12 interferes with the end of the first female threaded portion 22 on the side of the second female threaded portion 24. Therefore, the end region of the first female threaded portion 22 that interferes with the second male threaded portion 14 is widened to reduce or eliminate the amount of interference.

[0083] It is preferable that the length to be expanded is greater than or equal to the interference length between the end of the first female thread portion 22 and the second male thread portion 14. Furthermore, the end region of the first female thread portion 22 may be provided with various shapes such as stepped, tapered, curved, or threadless to expand the diameter.

[0084] Specifically, an interference mitigation section 23 (see Figure 23) is provided in the outwardly convex (i.e., radially inwardly convex) boundary region between the first female thread section 22 and the second female thread section 24. For example, the imaginary line 23a (see Figure 23) connecting the tips of each thread in the interference mitigation section 23 is a curved shape located outside the imaginary line 22a connecting the tips of each thread in the first female thread section 22 and the tapered imaginary line 24a connecting the tips of each thread in the second female thread section 24, and the height and position of the threads are determined to follow this curve. Furthermore, the maximum radius R (see Figure 23) in the interference mitigation section 23 is greater than or equal to the minimum outer diameter of the second male thread section 14. By providing the interference mitigation section 23, interference between the first female thread section 22 and the second male thread section 14 can be mitigated or avoided. Furthermore, the interference mitigation portion 23 may have a surface shape that mitigates or avoids interference with the second male thread portion 14, but it may also have a shape that includes threads that can be screwed into the first male thread portion 12 and / or the second male thread portion 14.

[0085] Furthermore, in order to provide a sealing structure between the male threaded portion 10 and the female threaded portion 20, the outer circumferential surface 30 of the tip of the male threaded portion 10 of the threaded pipe 1 may be brought into close contact with the inner circumferential surface 40 on the base end side of the female threaded portion 20 of the threaded pipe 1A, as shown in Figure 12. That is, the outer circumferential surface 30 of the male threaded portion 10 located on the insertion side in the direction of insertion of the threaded pipe 1A and the threaded pipe 1 may be brought into close contact with the inner circumferential surface 40 located on the insertion side of the threaded pipe 1A.

[0086] In this case, the outer diameter of the outer circumferential surface 30 is set to be slightly larger than the inner diameter of the inner circumferential surface 40. Therefore, when the male threaded portion 10 and the female threaded portion 20 are fitted together, an elastic force acts such that the outer circumferential surface 30 presses the inner circumferential surface 40 outward or the inner circumferential surface 40 presses the outer circumferential surface 30 inward. As a result, the outer circumferential surface 30 and the inner circumferential surface 40 are in close contact around the entire circumference, providing a sealing performance.

[0087] Alternatively, the outer circumferential surface 32 on the base end side of the male threaded portion 10 of the threaded pipe 1 may be brought into close contact with the inner circumferential surface 42 on the tip side of the female threaded portion 20 of the threaded pipe 1A. In this case, the outer diameter of the outer circumferential surface 32 is set to be slightly larger than the inner diameter of the inner circumferential surface 42.

[0088] Even in this configuration, when the male threaded portion 10 and the female threaded portion 20 are fitted together, an elastic force acts such that the outer circumferential surface 32 presses the inner circumferential surface 42 outward or the inner circumferential surface 42 presses the outer circumferential surface 32 inward, causing the outer circumferential surface 32 and the inner circumferential surface 42 to be in close contact around the entire circumference, thereby providing a sealing performance. Note that the outer circumferential surfaces 30, 32 and the inner circumferential surfaces 40, 42 may be inclined surfaces tilted with respect to the axes of the male threaded portion 10 and the female threaded portion 20.

[0089] Next, a threaded pipe with other configurations will be described. Figure 13 shows another example of a threaded pipe having a male threaded portion, where (a) is a cross-sectional view and (b) is a diagram showing the annular regions A to C. The threaded pipe 300 has a first seal portion 310, a male threaded portion 320, and a second seal portion 330 arranged in order from the tip side connected to the threaded pipe 400. The threaded pipe 300 also has a tip portion 300a that restricts the insertion depth into the threaded pipe 400.

[0090] As shown in Figure 14, the first seal portion 310 has at least one, preferably multiple, annular projections 312 that extend along the entire circumference of the outer surface and project radially outward. Furthermore, by arranging the annular projections 312 in parallel in the axial direction, the first seal portion 310 defines annular recesses 314 that are concave relative to the annular projections 312. The projection length of the annular projections 312 is such that it does not interfere with the screwing of the first male threaded portion 322 and the first female threaded portion 422 (see Figure 15), which will be described later, and that it is in close contact (or slightly interfering) with the inner surface of the first unthreaded portion 410 (see Figure 15).

[0091] The male threaded portion 320 consists of a first straight male threaded portion 322, a second tapered male threaded portion 324, and a third straight male threaded portion 326, arranged in order from the base end. The effective diameter of the second male threaded portion 324 is less than or equal to the effective diameter of the first male threaded portion 322, and the effective diameter of the third male threaded portion 326 is less than or equal to the effective diameter of the second male threaded portion. The effective diameter of the second male threaded portion 324 is larger at the base end than at the tip end. Here, it is assumed that the threads of the first male threaded portion 322 to the third male threaded portion 326 form a series of helical shapes such that the maximum effective diameter of the second male threaded portion 324 is approximately equal to the effective diameter of the first male threaded portion 322, and the minimum effective diameter is approximately equal to the effective diameter of the third male threaded portion 326.

[0092] The threaded pipe 300 has three concentric annular regions, A (first annular region), B (second annular region), and C (third annular region), which are divided radially in an axial view and include any of the first to third male threaded portions 322 to 326. As shown in Figure 13(b), the radial region from the outer surface of the threaded pipe 300 to the effective diameter portion of the first male threaded portion 322 is defined as annular region A. The radial region from the maximum effective diameter portion of the second male threaded portion 324 (i.e., the effective diameter portion of the first male threaded portion 322) to the minimum effective diameter portion of the second male threaded portion 324 is defined as annular region B. The radial region from the effective diameter portion of the third male threaded portion 326 (i.e., the minimum effective diameter portion of the second male threaded portion 324) to the inner surface of the threaded pipe 300 is defined as annular region C.

[0093] The area of ​​the annular region A shall be set to be one-third or less of the total cross-sectional area of ​​the cross-section of the threaded pipe 300. The area of ​​the cross-sectional region B shall be set to be one-third or more of the total cross-sectional area of ​​the cross-section of the threaded pipe 300. The area of ​​the cross-sectional region C shall be set to be one-third or less of the total cross-sectional area of ​​the cross-section of the threaded pipe 300.

[0094] The shape of the thread region of the first male thread portion 322 is set such that the shear area of ​​the entire thread region that is screwed and fitted with the first female thread portion 422 is equal to or greater than the area of ​​the annular region A multiplied by the square root of 3. Accordingly, the effective thread engagement length, number of threads, pitch, etc. are set such that the total shear area of ​​the threads of the first male thread portion 322, which is formed by a series of spiral shears at the effective diameter portion of the thread, is equal to or greater than the square root of 3 of the area of ​​the annular region A.

[0095] Furthermore, the shape of the thread region of the second male thread portion 324 is set such that the shear area of ​​the entire thread region that is screwed and fitted with the second female thread portion 424 is equal to or greater than the area of ​​the annular region B multiplied by the square root of 3. Accordingly, the effective thread engagement length, number of threads, pitch, etc. are set such that the total shear area of ​​the threads of the second male thread portion 324, which is formed by a series of spiral shears at the effective diameter portion of the thread, is equal to or greater than the square root of 3 of the area of ​​the annular region B.

[0096] Furthermore, the shape of the thread region of the third male thread portion 326 is set such that the shear area of ​​the entire thread region that is screwed and fitted with the third female thread portion 426 is equal to or greater than the area of ​​the annular region C multiplied by the square root of 3. Accordingly, the effective thread engagement length, number of threads, pitch, etc. are set such that the total shear area of ​​the threads of the third male thread portion 326, which is formed by a series of spiral shears at the effective diameter portion of the thread, is equal to or greater than the square root of 3 of the area of ​​the annular region C.

[0097] The second sealing portion 330, like the first sealing portion 310, has one or more, preferably more, annular protrusions 332, with annular recesses 334 defined between the annular protrusions 332. The protruding length of the annular protrusions 332 is set to a length that allows them to be in close contact (or slightly interfere) with the inner circumferential surface of the second threadless portion 430 (see Figure 15).

[0098] The tip portion 300a should have a shape that can contact the threaded pipe 400 and regulate its position in the depth direction, preferably a shape that can guide it in to facilitate insertion. For example, as shown in Figure 14, it can be formed by chamfering the tip of the first seal portion 310. Alternatively, a base portion 300b, which can contact the threaded pipe 400 and regulate its position in the depth direction, may be formed on the base end side of the second seal portion 330, either in place of the tip portion 300a or together with the tip portion 300a.

[0099] Figure 15 also shows another configuration example of a threaded pipe having a female thread portion, where (a) is a cross-sectional view and (b) is a diagram showing the annular region D to F. The threaded pipe 400 has a first unthreaded portion 410, a female thread portion 420, and a second unthreaded portion 430. When the threaded pipe 400 is connected to the threaded pipe 300, the first unthreaded portion 410 corresponds to the first seal portion 310, and the second unthreaded portion 430 corresponds to the second seal portion 330.

[0100] Furthermore, the threaded pipe 400 has a receiving portion 400a that restricts the insertion of the threaded pipe 300, and the receiving portion 400a is positioned at a location corresponding to the tip portion 300a (or base portion 300b). The first unthreaded portion 410 has a circumferentially shaped inner surface with a constant inner diameter along the axial direction, and this inner diameter is set to be less than the thread diameter of the third female thread portion 426, which will be described later. The second unthreaded portion 430 also has a circumferentially shaped inner surface with a constant inner diameter along the axial direction, and this inner diameter is set to be greater than or equal to the root diameter of the first female thread portion 422, which will be described later.

[0101] The female thread portion 420 is comprised of a first female thread portion 422 with a straight thread, a second female thread portion 424 with a tapered thread, and a third female thread portion 426 with a straight thread, arranged in order from the insertion end side. The second female thread portion 424 has a minimum effective diameter that is equal to or greater than the effective diameter of the first female thread portion 422, and the third female thread portion 426 has an effective diameter that is equal to or greater than the maximum effective diameter of the second female thread portion 424. The first female thread portion 422 is screwed into the first male thread portion 322, the second female thread portion 424 is screwed into the second male thread portion 324, and the third female thread portion 426 is screwed into the third male thread portion 326.

[0102] The threaded pipe 400 has three concentric annular regions, D (fourth annular region), E (fifth annular region), and F (sixth annular region), which are divided radially in an axial view and include any of the first female thread portion 422 to the third female thread portion 426. As shown in Figure 15(b), the radial region from the outer surface of the threaded pipe 400 to the effective diameter portion of the first female thread portion 422 is defined as annular region D. The radial region 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 defined as annular region E. The radial region 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 surface of the raw pipe portion of the threaded pipe 400 is defined as annular region F.

[0103] The area of ​​the annular region D is set to be one-third or less of the total cross-sectional area of ​​the cross-section of the threaded pipe 400. The area of ​​the cross-sectional region E is set to be one-third or more of the total cross-sectional area of ​​the cross-section of the threaded pipe 400. The area of ​​the cross-sectional region F is set to be one-third or less of the total cross-sectional area of ​​the cross-section of the threaded pipe 400. Here, it is assumed that the annular region D has an area approximately equivalent to annular region A, the annular region E has an area approximately equivalent to annular region B, and the annular region F has an area approximately equivalent to annular region C.

[0104] The shape of the thread region of the first female thread portion 422 is set such that the shear area of ​​the entire thread region that is screwed and fitted with the first male thread portion 322 is equal to or greater than the area of ​​the annular region D multiplied by the square root of 3. That is, the effective thread engagement length, number of threads, pitch, etc. are set so that the total shear area of ​​the threads of the first female thread portion 422, which is formed by a series of spiral shears at the effective diameter portion of the thread, is equal to or greater than the square root of 3 of the area of ​​the annular region D. Here, the above condition is satisfied by setting the shape of the thread region of the first female thread portion 422 to correspond to the effective thread engagement length, number of threads, and pitch of the first male thread portion 322.

[0105] Furthermore, the shape of the thread region of the second female thread portion 424 is set such that the shear area of ​​the entire thread region that is screwed and fitted with the second male thread portion 324 is equal to or greater than the area of ​​the annular region E multiplied by the square root of 3. That is, the effective thread engagement length, number of threads, pitch, etc. are set so that the total shear area of ​​the threads of the second female thread portion 424, which is formed by a series of spiral shears at the effective diameter portion of the thread, is equal to or greater than the square root of 3 of the area of ​​the annular region E. Here, the above conditions are met by setting the shape of the thread region of the second female thread portion 424 to correspond to the effective thread engagement length, number of threads, and pitch of the second male thread portion 324.

[0106] Furthermore, the shape of the thread region of the third female thread portion 426 is set such that the shear area of ​​the entire thread region that is screwed and fitted with the third male thread portion 326 is equal to or greater than the area of ​​the annular region F multiplied by the square root of 3. That is, the effective thread engagement length, number of threads, pitch, etc. are set so that the total shear area of ​​the threads of the third female thread portion 426, which is formed by a series of spiral shears at the effective diameter portion of the thread, is equal to or greater than the square root of 3 of the area of ​​the annular region F. Here, the above conditions are met by setting the shape of the thread region of the third female thread portion 426 to correspond to the effective thread engagement length, number of threads, and pitch of the third male thread portion 326.

[0107] The first threadless portion 410 and the first seal portion 310 have approximately equal axial lengths, but the first threadless portion 410 is set to be longer. The female thread portion 420 and the male thread portion 320 have approximately equal axial lengths. The second threadless portion 430 and the second seal portion 330 have approximately equal axial lengths, but the second threadless portion 430 is set to be longer.

[0108] 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.

[0109] 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´.

[0110] 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.

[0111] With such threaded tubes 300 and 400, when threaded tube 300 is inserted into threaded tube 400 and rotated, each male threaded portion 322 to 326 screws into each female threaded portion 422 to 426. Also, the first seal portion 310 is press-fitted into the first unthreaded portion 410, and the annular projection 312 makes close contact with the inner circumferential surface of the first unthreaded portion 410. Furthermore, the second seal portion 330 is press-fitted into the second unthreaded portion 430, and the annular projection 332 makes close contact with the inner circumferential surface of the second unthreaded portion 430.

[0112] Furthermore, the tip portion 300a of the threaded pipe 300 can be configured to engage with or abut against the receiving portion 400a of the threaded pipe 400, thereby preventing excessive tightening between each male threaded portion 322 to 326 and each female threaded portion 422 to 426.

[0113] Furthermore, the annular projection 312 is in close contact with the first threadless portion 410, and the annular projection 332 is in close contact with the second threadless portion 430, and the annular projections 312 and 332 are in pressure contact with the first threadless portion 410 or the second threadless portion 430. As a result, a seal structure is formed that can cope even in situations involving relative displacement between the threaded pipes 300 and 400 due to inputs such as tension and compression of the threaded pipes 300 and 400, and a seal structure with high sealing performance that can follow deformations such as bending of the threaded pipes 300 and 400 is formed.

[0114] Furthermore, the annular recess 314 may be provided with a sealing structure. Specifically, a solid fat (described in detail later) that softens and expands at a predetermined temperature or higher can be placed inside the annular recess 314, and a resin ring such as polyethylene or polypropylene can be fitted and / or embedded in the annular recess 314 to form a sealing structure, thereby further improving the sealing performance.

[0115] Furthermore, as described above, the shape of the thread region of the first male thread portion 322 is set such that the total cross-sectional area of ​​the entire thread region is equal to or greater than the area of ​​the annular region A multiplied by the square root of 3, and therefore it has a shear strength higher than the tensile strength of the raw pipe corresponding to the area of ​​the annular region A. Similarly, the second male thread portion 324 has a shear strength higher than the tensile strength of the raw pipe corresponding to the area of ​​the annular region B, and the third male thread portion 326 has a shear strength higher than the tensile strength of the raw pipe corresponding to the area of ​​the annular region C.

[0116] Therefore, the entire male threaded portion 320 has a higher shear strength than the tensile strength of the area of ​​the threaded pipe 300 where the male threaded portion 320 is not formed. This prevents the male threaded portion 320 from shearing before the threaded pipe 300 undergoes axial fracture when both threaded pipes 300 and 400 are pulled apart along the axial direction while screwed together with the female threaded portion 420.

[0117] Similarly, the shape of the thread region of the first female thread portion 422 is set such that the total cross-sectional area of ​​the entire thread region is equal to or greater than the area of ​​the annular region D multiplied by the square root of 3, and therefore it has a shear strength higher than the tensile strength of the raw pipe corresponding to the area of ​​the annular region D. Likewise, the second female thread portion 424 has a shear strength higher than the tensile strength of the raw pipe corresponding to the area of ​​the annular region E, and the third female thread portion 426 has a shear strength higher than the tensile strength of the raw pipe corresponding to the area of ​​the annular region F.

[0118] Therefore, the entire female thread portion 420 has a higher shear strength than the tensile strength of the area of ​​the threaded pipe 400 where the female thread portion 420 is not formed. This prevents the female thread portion 420 from shearing before the threaded pipe 400 breaks when both threaded pipes 300 and 400 are pulled apart along the axial direction while screwed together with the male thread portion 320.

[0119] 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 and 400. When a tensile force is applied in a direction that separates the threaded pipes 300 and 400 while they are connected, it is possible to reliably cause axial fracture of either the threaded pipe 300 or 400 before the threads are sheared.

[0120] The tensile strength of the first male thread portion 322, the second male thread portion 324, the third male thread portion 326, or the first female thread portion 422, the second female thread portion 424, the third female thread portion 426 is the smallest of the following: the total shear area a when the approximately effective diameter portion of the fitting region where the male or female thread portions are screwed together is sheared in a continuous spiral manner along the threads; the cross-sectional area b of the cross-section at the effective diameter portion of the male thread portion; and the cross-sectional area c of the cross-section at the effective diameter portion of the female thread portion. However, the relationship a≧√3·b∧a≧√3·c can be set, in which case the tensile strength of the male or female thread portion can be calculated by multiplying b and / or c by the tensile strength per unit area of ​​the material.

[0121] Furthermore, by positioning the first and third male threads before and after the second male thread in the direction of threading, and the first and third female threads before and after the second female thread in the direction of threading, the male and female threads are screwed together across the entire helical threaded region. This prevents the formation of unthreaded sections at the tip and base ends of the tapered thread section, which was present in conventional joints known as flush joints, thus preventing a reduction in strength due to the presence of unthreaded sections, and as a result, threaded pipes can be firmly connected to each other.

[0122] Furthermore, with the threaded pipes 300 and 400 having the structure described above, the connection can be made highly strong when the male threaded portion 320 and the female threaded portion 420 are screwed together and tightened. In evaluating the tensile strength, a criterion called the yield ratio of the joint can be considered, which is the ratio of the tensile strength of the joint to the yield strength of the raw pipe portion of the threaded pipes 300 and 400. The yield ratio of the joint can be expressed as {breaking strength of the joint} / {total cross-sectional yield strength of the raw pipe portion}.

[0123] For example, if a steel material with a strength class equivalent to 10.9 in the bolt strength class is used, and the cross-sectional area of ​​the joint is S1 (mm²) 2 ), the cross-sectional area of ​​the raw tube part is S0 (mm 2 In the case of ), the yield rate can be expressed as shown in equation (1).

[0124] [Formula 1] TIFF2026062954000002.tif19170

[0125] Here, the number 10 before the strength classification represents the tensile strength, with a minimum of 1040 (N / mm²). 2 This number is approximately 1 / 100th of the yield strength, and the tensile strength is 1040 (N / mm²). 2 This guarantees that the ratio to ) is 90 percent. That is, the yield strength is 1040 × 0.9 = 936 (N / mm²). 2 )

[0126] The cross-sectional area S1 is determined by the cross-sectional area of ​​the male threaded portion 320 or the female threaded portion 420 as described above. Specifically, the size of the cross-sectional area of ​​the male threaded 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 threaded portion 322. The size of the cross-sectional area of ​​the female threaded 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 threaded portion 426.

[0127] Therefore, if the male thread portion 320 is set to enlarge the diameter of the first male thread portion 322, and the female thread portion 420 is set to reduce the diameter of the third female thread portion 426, for example, if the cross-sectional area S1 is set to be about 80% of the cross-sectional area S0, then the cross-sectional area S1 in Equation 1 can be expressed as cross-sectional area S0 × 0.8.

[0128] Equation 2, obtained by substituting the values ​​into Equation 1, is shown below.

[0129] [Formula 2] As shown in Equation 2 of TIFF2026062954000003.tif51170, a yield rate of approximately 89 percent can be obtained.

[0130] Furthermore, the lower the ratio of yield strength to tensile strength of the selected material, the higher the yield ratio 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 ratio of approximately 114 percent can be obtained.

[0131] Furthermore, even when selecting a material with a high ratio of yield strength to tensile strength, the closer the cross-sectional area S1 is to the cross-sectional area S0, the more threaded pipes 300 and 400 with high yield ratios can be obtained. Of course, in reality, it is necessary to consider that it is not desirable to reduce the thickness below a certain level due to issues such as machining accuracy and the strength of the thinnest parts of the first female threaded section 422, the second unthreaded section 430, or the third male threaded section 326 or the first seal section 310.

[0132] Also, for example, if the tensile strength is 965 (N / mm²) 2 ) and yield strength of 862 (N / mm²) 2 In a threaded tube manufactured from a material (a material with a yield strength-to-tensile strength ratio of approximately 89 percent), if the base tube has an outer diameter of 400 mm and a wall thickness of 19 mm, and the thinnest wall thickness of the first female threaded section 422, the second unthreaded section 430, or the third male threaded section 326 or the first seal section 310 is set to 1.4 mm, then according to Equation 1, a yield ratio of approximately 103 percent can be obtained. Conventionally, the yield ratio of threaded tubes manufactured from the same material is approximately 70 percent. Therefore, by screwing the male threaded section 320 and the female threaded section 420 according to the present invention, that is, by screwing straight threads together and tapered threads together, the wall thickness can be set to be thinner, and a very high yield ratio can be obtained compared to conventional threaded tubes.

[0133] The thread shape of the male thread portion 320 may be different for 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 male thread portion 322 to 326 may have a sawtooth-shaped thread, the threads of the straight-threaded first male thread portion 322 and the third male thread portion 326 may have a symmetrical shape such as a triangular thread or a trapezoidal thread, and the threads of the tapered second male thread portion 324 may have a sawtooth shape. Since the female thread portion 420 is screwed into the male thread portion 320, it is preferable that the thread shape of each female thread portion 422 to 426 corresponds to the thread shape of each male thread portion 322 to 326, and that the pitch is basically the same.

[0134] Here, Figure 20 shows the tensile and compressive strengths of a test specimen of an oil well pipe connection structure in which threaded pipes 300 and 400 corresponding to two different thread shapes are screwed together and connected. The fracture strength of the oil well pipe connection structure is affected by the thread shape of the male threaded portion 320 and the corresponding thread shape of the female threaded portion 420.

[0135] Specifically, the threaded pipe 300 has the aforementioned annular regions A, B, and C, and the threaded pipe 400 has the aforementioned annular regions D, E, and F, and these are screwed together and connected to form a test specimen. Furthermore, the area of ​​annular region A is set to be 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 first male threaded portion 322 is at least three times the square root of the area of ​​annular region A.

[0136] Furthermore, the area of ​​the 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 area of ​​the annular region B.

[0137] Furthermore, the area of ​​the cross-sectional region C is set to be 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 area of ​​the annular region C.

[0138] Furthermore, the area of ​​the annular region D is set to be one-third or less of the total cross-sectional area of ​​the cross-section of the threaded pipe 400. Also, the area of ​​the cross-sectional region E is set to be one-third or more of the total cross-sectional area of ​​the cross-section of the threaded pipe 400. Also, the area of ​​the cross-sectional region F is set to be one-third or less of the total cross-sectional area of ​​the cross-section of the threaded pipe 400. The annular region D has an area that is approximately equivalent to the annular region A, the annular region E has an area that is approximately equivalent to the annular region B, and the annular region F has an area that is approximately equivalent to the annular region C.

[0139] Figure 20 shows the results of tensile and compression tests conducted on two types of threaded pipes 300 and 400 with the above configuration, each with a different thread shape. The effective thread engagement length, number of threads, pitch, etc., of each test specimen were set to be the same.

[0140] Here, the thread shape was such that one end had a sawtooth shape with a thread angle of 60°, and the other end had a triangular thread with a symmetrical cross-section and a thread angle of 70°. In Figure 20, the dashed line shows the results of the tensile test of the member assembly (test specimen) with a thread angle of 70°. The dashed line shows the results of the tensile test of the member assembly (test specimen) with a sawtooth shape and a thread angle of 60°. The solid line shows the results of the compression test of the member assembly (test specimen) with a sawtooth shape and a thread angle of 60°. The dashed line shows the results of the compression test of the member assembly (test specimen) with a thread angle of 70°.

[0141] In the tensile test, the threaded tube 300 and threaded tube 400, which form the member connection (test specimen), were mounted on the testing machine via a jig, and the male threaded portion 320 and female threaded portion 420 were screwed together, and the member connection was subjected to tensile force until it broke.

[0142] In the compression test, the threaded pipe 300 and threaded pipe 400, which form the component assembly (test specimen), were pre-screwed together and mounted on the testing machine via a jig, and then compressed until they collapsed.

[0143] When comparing the dashed and solid lines in Figure 20, i.e., comparing the compression test results, the member assembly (test specimen) with a symmetrical cross-sectional shape and a thread angle of 70° had higher compressive strength than the member assembly (test specimen) with a sawtooth shape and a thread angle of 60°.

[0144] On the other hand, when comparing the dashed-dotted and dashed-dotted lines in Figure 20, that is, when comparing the tensile test results, the member assembly (test specimen) with a sawtooth-shaped thread and a thread angle of 60° showed higher tensile strength than the member assembly (test specimen) with a thread angle of 70°. From these results of the compression test and the tensile test, it can be said that the thread shape that is strong in compression is different from the thread shape that is strong in tension.

[0145] Therefore, it is desirable to appropriately set the thread shape according to the application of the component assembly (test specimen). For example, component assembly (test specimen) placed in an environment prone to tensile stress preferably has a sawtooth-shaped thread. Also, component assembly (test specimen) placed in an environment prone to compressive stress preferably has a symmetrical thread in cross-sectional view with a thread angle of 70°. Alternatively, when placed in an environment prone to both tensile and compressive stress, or in an application where the component assembly has a symmetrical thread in cross-section, and more preferably a component assembly with a symmetrical thread in cross-sectional view with a thread angle of 70°.

[0146] Furthermore, although annular projections 312, 332 and annular recesses 314, 334 are provided on the outer circumference of each sealing portion 310, 330, annular projections and annular recesses may also 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 non-threaded portion 410, 430, and the annular projections may be brought into close contact with the outer circumferential surface of each sealing portion 310, 330. In this case, the outer circumference of each sealing portion can be circular or substantially conical.

[0147] Furthermore, although the first seal portion 310 and the second seal portion 330 are provided on the tip and base ends of the threaded pipe 300, the seal portion may be provided on only one of either the tip or base end. That is, as shown in Figure 16(a), the seal portion 310 may be provided only on the tip end of the threaded pipe 300, or as shown in Figure 16(b), the seal portion 330 may be provided only on the base end of the male thread portion 320 of the threaded pipe 300. In these cases, the threaded pipe 400 only needs to have a non-threaded portion formed in the area corresponding to the seal portion. That is, the non-threaded portion may be formed on only one of either the end or the other end of the female thread portion.

[0148] Furthermore, the shape of the tip portion 300a that restricts the insertion of the threaded pipe 300 into the threaded pipe 400 can be set as appropriate. For example, the tip portion 300a may be inclined at a shallow angle of less than 45° with respect to the direction perpendicular to the axis, as shown in Figure 17(a), or it may be formed in a curved shape, that is, formed by rounding the tip portion of the threaded pipe 300, as shown in Figure 17(b). Alternatively, the end face of the threaded pipe 300, which has right-angle corners, may be used as the tip portion 300a, as shown in Figure 17(c). Note that if the tip portion 300a is an inclined or curved surface, a load may be concentrated radially outward on the receiving portion 400a via the inclined tip portion 300a, which may cause the diameter of the threaded pipe 400 to expand. Therefore, if the tip portion 300a is made to make surface contact with the receiving portion 400a over a wide area including the end face of the threaded pipe 300, the load will be distributed accordingly, and it will be possible to prevent a radially outward load from acting on the receiving portion 400a. Of course, the shape of the base end portion 300b located on the base end side of the male threaded portion 320 of the threaded pipe 300 can also be set appropriately in the same way. Furthermore, the shape of the receiving portion 400a can be set to correspond to the shape of the tip portion 300a or the base end portion 300b.

[0149] Furthermore, the insertion of the threaded pipe 300 into the threaded pipe 400 may be restricted by means other than providing the tip portion 300a or the base portion 300b. For example, the pitch of the end of the threads of either the male threaded portion 320 or the female threaded portion 420, or both, may be shortened. That is, the pitch of at least one of the threads on the base end side of the male threaded portion 320 and the threads on the inner side in the insertion direction of the female threaded portion 420 may be shortened. This provides a braking structure that restricts screwing when the male threaded portion 320 and the female threaded portion 420 are screwed together, at the point where the pitch is shortened. Of course, in this case, it is not necessary for the tip portion 300a and the receiving portion 400a to be in contact with each other, but they may be made to be in contact to distribute the load between them and the braking structure.

[0150] 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 sealing performance between the male thread portion 320 and the female thread portion 420. That is, the second male thread portion 324 of the tapered thread within the male thread portion 320 may press the second female thread portion 424 of the tapered thread from the inside out, causing elastic and / or plastic deformation of at least one of the second male thread portion 324 and the second female thread portion 424 to improve sealing performance.

[0151] For example, the maximum outer diameter (or maximum effective diameter) of the second male thread portion 324 is set to be 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 to be larger than the minimum inner diameter (or minimum effective diameter) of the second female thread portion 424, so that when fully screwed together, the female thread portion 420 can expand slightly radially outward. In this case, the second male thread portion 324 and the second female thread portion 424 can interfere with each other radially in at least a part, and when the male thread portion 320 and the female thread portion 420 are screwed together, the female thread portion 420 expands in diameter while undergoing elastic and / or plastic deformation, and as a result the male thread portion 320 and the female thread portion 420 become tightly fitted together, improving the sealing performance.

[0152] 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 undergoes elastic and / or plastic deformation radially inward. Furthermore, although the above description assumes that the outer diameter of the second male thread portion 14 and the inner diameter of the second female thread portion 24 are set, the thickness of the pipe in the second male thread portion 324 and / or the second female thread portion 424 may also be set.

[0153] Furthermore, if 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.

[0154] The first interference mitigation portion 323 is positioned in the outwardly convex (radially outward convex) boundary region between the first male thread portion 322 and the second male thread portion 324, and is configured to avoid axial interference with the second female thread portion 424 by forming it in a stepped, tapered, or curved shape, or by forming a threadless region. The second interference mitigation portion 425 is positioned in the outwardly convex (radially inward convex) boundary region between the second female thread portion 424 and the third female thread portion 426, and is configured to avoid axial interference with the third male thread portion 324 by forming it in a stepped, tapered, or curved shape, or by forming a threadless region.

[0155] By providing both interference mitigation sections 323 and 425, interference between the first male threaded section 322 and the second female threaded section 424 can be avoided, as can interference between the third female threaded section 426 and the second male threaded section 324.

[0156] 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 thread portion 424 (or the second male thread portion 324), but the first interference mitigation portion 323 may have threads so as to be screwed into the second female thread portion 424, and similarly the second interference mitigation portion 426 may have threads so as to be screwed into the second male thread portion 324.

[0157] Furthermore, as solid fats, for example, thermoplastic resins, glass fiber reinforced resins and thermoplastic elastomers mixed with such thermoplastic resins are also possible. Examples of thermoplastic resins that can be applied 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 selection is made according to the applicable temperature, thermal expansion coefficient, and required chemical resistance.

[0158] Threaded pipes may be steel pipes (carbon steel pipes for piping, carbon steel pipes for pressure piping, galvanized steel pipes for water piping, arc-welded carbon steel pipes for piping, etc.), lined steel pipes (rigid polyvinyl chloride lined steel pipes for water supply, heat-resistant rigid polyvinyl chloride lined steel pipes for water supply, rigid polyvinyl chloride outer-coated steel pipes for fire extinguishing, rigid polyvinyl chloride lined steel pipes for drainage, polyethylene powder lined steel pipes for water supply, tar epoxy coated steel pipes for drainage, polyethylene coated steel pipes, etc.), cast iron pipes (ductile cast iron pipes, cast iron pipes for drainage, etc.), copper pipes (copper pipes for piping, coated copper pipes, etc.), SUS steel pipes (stainless steel pipes for general piping), lead pipes (lead pipes for drainage and ventilation, lead drainage pipes, etc.), etc., excluding oil well pipes.

[0159] Furthermore, the location and use of threaded pipes are not particularly limited, except for use in crude oil extraction sites and for crude oil extraction purposes. For example, they may be used buried underground, indoors, or outdoors. Threaded pipes may also be used to transport fluids such as liquids, gases, and powders, and may be used as piping for power transmission lines and communication lines used for telegraph signaling. In other words, they may be used as boiler pipes, water pipes, drainage pipes, gas pipes, fire extinguishing pipes, air pipes, measuring pipes, electrical equipment pipes, and conduits.

[0160] Furthermore, threaded members may also be applied to cylinders. Specifically, as shown in Figure 19, male threaded portions 320 can be provided at both ends of the cylinder tube 500, and female threaded portions 420 can be provided at the cylinder bottom 510 and cylinder head 520. In this way, a cylinder can be made smaller and lighter while having high strength that can sufficiently withstand the stress generated by the sliding of the piston 530, without the need for flanges. [Explanation of symbols]

[0161] 1,1A...Threaded pipe 2...Through hole 10...Male threaded section 12...First male threaded section 14...Second male threaded section 16...Third male threaded section 18...Unthreaded section 20...Female threaded section 22...First female threaded section 24...Second female threaded section 26...Third female threaded section 300,400...Threaded pipe 310...First seal section 312...Annular protrusion 314...Annular recess 320...Male threaded section 322...First male threaded section 324...Second male threaded section 326...Third male threaded section 330...Second seal section 410...First unthreaded section 420...Female threaded section 422...First female threaded section 424...Second female threaded section 426...Third female threaded section 430...Second unthreaded section.

Claims

1. An oil well pipe connecting structure that connects tubular members having the same inner and outer diameters, A first tubular member has a first male threaded portion on its outer surface that is parallel to the axis, starting from the base end, and a second male threaded portion that is positioned closer to the tip than the first male threaded portion and gradually decreases in diameter toward the tip, forming a tapered shape. A second tubular member is provided on its inner surface, having a first female threaded portion parallel to the first male threaded portion that screws into the first male threaded portion, and a second female threaded portion located further inside than the first female threaded portion and tapering in diameter, so as to screw into the second male threaded portion. A first interference mitigation portion is provided in the outer diameter convex boundary region formed between the first male thread portion and the second male thread portion, and has a curved shape to mitigate interference between the first male thread portion and the second female thread portion. An oil well pipe connecting structure characterized by having the following features.

2. The first tubular member has a third male threaded portion that is positioned closer to the tip than the second male threaded portion and is parallel to the axis. The second tubular member has a third female thread portion that is located inside the tip side of the second female thread portion and is parallel to the third male thread portion and screws into it. A second interference mitigation portion is provided in the inwardly convex boundary region formed between the second female thread portion and the third female thread portion, and has a curved shape to mitigate interference between the second female thread portion and the third male thread portion. The oil well pipe connecting structure according to claim 1, characterized by having the following features.

3. The oil well pipe connecting structure according to claim 2, characterized in that the second interference mitigation portion has a threaded 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 tops of each thread of the first female thread portion and a tapered imaginary line connecting the tops of each thread of the second female thread portion.

4. The oil well pipe connecting structure according to claim 3, characterized in that the threaded portion of the second interference mitigation section is positioned along the curve.

5. The oil well pipe connecting structure according to any one of claims 1 to 4, 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 tops of each thread of the first male threaded portion and a tapered imaginary line connecting the tops of each thread of the second male threaded portion.

6. The oil well pipe connecting structure according to claim 5, characterized in that the threaded portion of the first interference mitigation section is positioned along the curve.

7. The oil well pipe connecting structure according to any one of claims 1 to 6, characterized in that the maximum outer diameter or maximum effective diameter of the second male threaded portion is set to be larger than the maximum inner diameter or maximum effective diameter of the second female threaded portion.

8. The oil well pipe connecting structure according to any one of claims 1 to 7, characterized in that the minimum outer diameter or minimum effective diameter of the second male threaded portion is set to be larger than the minimum inner diameter or minimum effective diameter of the second female threaded portion.

9. An oil well pipe connecting structure that connects tubular members having the same inner and outer diameters, A first tubular member having a first male threaded portion that gradually tapers in diameter from the base end towards the tip end, and a second male threaded portion that is positioned closer to the tip than the first male threaded portion and parallel to the axis, provided on its outer surface, A second tubular member comprising, in order from the base end, a first female threaded portion that screws into the first male threaded portion and gradually tapers toward the tip end, and a second female threaded portion that is positioned inside the first female threaded portion toward the tip end and parallel to it, which screws into the second male threaded portion, and provided on the inner circumferential surface of the second female threaded portion, A first interference mitigation portion is provided in the inwardly convex boundary region formed between the first female thread portion and the second female thread portion, and has a curved shape to mitigate interference between the second female thread portion and the first male thread portion. An oil well pipe connecting structure characterized by having the following features.

10. The first tubular member has a third male thread portion that is positioned closer to the tip than the second male thread portion and is tapered with respect to the shaft. The second tubular member has a third female thread portion that is tapered and positioned inside the tip side of the second female thread portion, and that screws into the third male thread portion. A second interference mitigation portion is provided in a curved 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 which mitigates interference between the second male thread portion and the third female thread portion. The oil well pipe connecting structure according to claim 9, characterized by having the following features.

11. The oil well pipe connecting structure according to claim 10, characterized in that the second 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 tops of each thread of the second male threaded portion and a tapered imaginary line connecting the tops of each thread of the third male threaded portion.

12. The oil well pipe connecting structure according to claim 11, characterized in that the threaded portion of the second interference mitigation section is positioned along the curve.

13. The oil well pipe connecting structure according to any one of claims 9 to 12, characterized in that the first interference mitigation portion has a threaded portion whose height is determined along a curve that is closer to the outer diameter side of the second tubular member than a tapered imaginary line connecting the tops of each thread of the first female thread and a straight imaginary line connecting the tops of each thread of the second female thread.

14. The oil well pipe connecting structure according to claim 13, characterized in that the threaded portion of the first interference mitigation section is positioned along the curve.

15. The oil well pipe connecting structure according to claim 2 or 10, characterized in that the shape of the threads of the third male thread portion and the third female thread portion are saw-tooth shaped.

16. The oil well pipe connecting structure according to any one of claims 1 to 15, characterized in that the shape of the threads of the first male thread portion and the first female thread portion is a sawtooth shape.

17. The oil well pipe connecting structure according to any one of claims 1 to 16, characterized in that the shape of the threads of the second male thread portion and the second female thread portion are saw-tooth shaped.

18. The oil well pipe connecting structure according to claim 2 or 10, characterized in that the third male thread portion and the third female thread portion have threads with a triangular cross-section, where the flank angle of the flank surface of each thread that receives pressure when pulled in the unthreading direction is set to an angle of perpendicular or less with respect to the axis of the first tubular member and the second tubular member.

19. The oil well pipe connecting structure according to any one of claims 1 to 18, characterized in that the first male threaded portion and the first female threaded portion each have a triangular cross-section thread, wherein the flank angle of the flank surface that receives pressure when pulled in the unthreading direction is set to an angle of perpendicular or less with respect to the axis of the first tubular member and the second tubular member.

20. The oil well pipe connecting structure according to any one of claims 1 to 19, characterized in that the second male thread portion and the second female thread portion have threads with a triangular cross-section, where the flank angle of the flank surface of each thread that receives pressure when pulled in the unthreading direction is set to an angle of perpendicular or less with respect to the axis of the first tubular member and the second tubular member.

21. The oil well pipe connecting structure according to any one of claims 18 to 20, characterized in that the flank angle is 70°.

22. The oil well pipe connecting structure according to any one of claims 10 to 12, characterized in that the minimum outer diameter or minimum effective diameter of the third male threaded portion is set to be larger than the minimum inner diameter or minimum effective diameter of the third female threaded portion.

23. The oil well pipe connecting structure according to any one of claims 10 to 22, characterized in that the maximum outer diameter or maximum effective diameter of the first male threaded portion is set to be larger than the maximum inner diameter or maximum effective diameter of the first female threaded portion.

24. The oil well pipe connecting structure according to any one of claims 10 to 23, characterized in that the minimum outer diameter or minimum effective diameter of the first male threaded portion is set to be larger than the minimum inner diameter or minimum effective diameter of the first female threaded portion.

25. The oil well pipe connecting structure according to claim 1 or 9, characterized in that the outer diameter of the tip of the second male threaded portion and the inner diameter of the tip of the second female threaded portion are set so that they are in close contact with the outer circumferential surface of the tip of the second male threaded portion.

26. The oil well pipe connecting structure according to claim 2 or 10, characterized in that the outer diameter of the tip of the third male threaded portion and the inner diameter of the tip of the third female threaded portion are set so that they are in close contact with the outer circumferential surface of the tip of the third male threaded portion.

27. The oil well pipe connecting structure according to any one of claims 1 to 26, characterized in that the base end outer diameter of the first male thread and the base end inner diameter of the first female thread are set so that the base end outer circumferential surface of the first male thread and the base end inner circumferential surface of the first female thread are in close contact.

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