WO2023238864A1

WO2023238864A1 - Threaded joint for steel pipe

Info

Publication number: WO2023238864A1
Application number: PCT/JP2023/021005
Authority: WO
Inventors: 景太井瀬; 賢栗生; 琢也辻村; 優嘉佐々木; 崇夫倉西
Original assignee: 日本製鉄株式会社; バローレック・オイル・アンド・ガス・フランス
Priority date: 2022-06-07
Filing date: 2023-06-06
Publication date: 2023-12-14

Abstract

Provided is a threaded joint which is for a steel pipe and which can improve seizure resistance performance and manufacturability. A threaded joint 1 for a steel pipe comprises: a pin 10; and a box 20. The pin 10 has a male screw 11, an inner pin seal surface 12, and an outer pin seal surface 13. The box 20 has a female screw 12, an inner box seal surface 12, and an outer box seal surface 23. The male screw 11 includes a tapered region 111 positioned on the outer pin seal surface 13 side, and a tapered region 112 positioned on the inner pin seal surface 11 side. The gradient β1 of the tapered region 112 is smaller than the gradient α1 of the tapered region 111. The insertion surface pitch of screw threads included in the male screw 112 is constant. The screw threads included in the tapered region 112 have a screw thread width wider than that of screw threads included in the tapered region 111.

Description

Threaded joints for steel pipes

The present disclosure relates to a threaded joint used for connecting steel pipes.

In oil wells, natural gas wells, etc. (hereinafter also collectively referred to as "oil wells"), oil country pipes such as casings and tubing are used to extract underground resources. Oil country tubular goods are made up of steel pipes connected one after another, and threaded joints are used to connect them.

This type of threaded joint for steel pipes is broadly divided into coupling type and integral type. In the case of a coupling type, one of the pair of pipe materials to be connected is a steel pipe, and the other pipe material is a coupling. In this case, male threads are provided on the outer periphery of both ends of the steel pipe, and female threads are provided on the inner periphery of both ends of the coupling. Then, the male thread of the steel pipe is screwed into the female thread of the coupling, thereby fastening and connecting the two. In the case of the integral type, the pair of pipes to be connected are both steel pipes, and separate couplings are not used. In this case, a male thread is provided on the outer periphery of one end of the steel pipe, and a female thread is provided on the inner periphery of the other end. Then, the male threaded portion of one steel pipe is screwed into the female threaded portion of the other steel pipe, thereby fastening and connecting the two.

In general, the joint portion at the end of the tube in which the male thread is formed is called a pin because it includes an element that is inserted into the female thread. On the other hand, the joint portion at the end of the tube in which the female thread is formed is called a box because it includes an element for receiving the male thread. These pins and boxes are both tubular because they are the ends of tubing.

In recent years, oil wells have become deeper. In deep wells, oil country tubular goods having high pressure resistance are usually used. Threaded joints for connecting oil country country tubular goods are not only required to have high strength and sealing performance, but also have strict restrictions on outer diameter dimensions due to the multiple arrangement of oil country country tubular goods.

Threaded joints for oil country tubular goods exhibit high sealing performance at the sealing part. Generally, the diameter of the seal on the pin is larger than the diameter of the seal on the box. Therefore, in the fastened state, both seal portions fit into each other and come into close contact with each other to form an interference fit, forming a seal portion through metal contact. The difference between the pin seal diameter and the box seal diameter is called the "seal interference". The larger the amount of seal interference, the higher the seal contact force, and the better the sealing performance.

In order to improve the sealing performance against external pressure, it is effective to increase the thickness of the seal portion of the pin on which external pressure acts. This increases the resistance to diameter reduction of the seal portion of the pin when external pressure is applied to the threaded joint, so that the actual amount of seal interference decreases and the decrease in seal contact force decreases. In addition, in order to exhibit stable sealing performance even under high tensile/compressive loads, certain thread lengths and shoulder surface areas are required.

On the other hand, in order to reduce the outer diameter of the joint portion, at least one of the pin and the box may be made thinner. An example of a threaded joint in which the pin and/or box are made thinner is a so-called slim type. The slim type threaded joint has an outer diameter that is approximately the same as the outer diameter of the oil country tubular body. Since the slim type threaded joint has a thinner wall, it is difficult to ensure the wall thickness of the seal portion and the area of the shoulder surface.

International Publication No. 2019/224345 (Patent Document 1) discloses a tubular threaded connection. The tubular threaded connection has a tubular male end (pin) and a tubular female end (box). The tubular male end includes an outer male sealing surface, an inner male sealing surface, outer male threads, inner male threads, and a male shoulder located between the outer male threads and the inner male threads. The tubular female end has an outer female seal surface that corresponds to the outer male seal surface, an inner female seal surface that corresponds to the inner male seal surface, an outer female thread that meshes with the outer male thread, an inner female thread that meshes with the inner male thread, and a male shoulder. and a female shoulder that contacts the. Further, Patent Document 1 discloses that the outer female thread and the inner female thread that engage with the outer male thread and the inner male thread, respectively, are tapered along the same taper angle, and the pitch and lead of the load surface and the insertion surface are exactly the same. There is.

Patent No. 6916277 (Patent Document 2) discloses a threaded joint for steel pipes. A threaded joint for steel pipes consists of a tubular pin and a tubular box. The pin includes, in order from the tip end of the pin toward the tube body side, an inner sealing surface, an inner male threaded portion, a shoulder portion, an outer male threaded portion, and an outer sealing surface. The box includes, in order from the tube body side to the distal end side of the box, an inner sealing surface, an inner female threaded portion, a shoulder portion, an outer female threaded portion, and an outer sealing surface. Threaded joints for steel pipes have some of the teeth of the inner male thread of the pin accommodated in the inner groove provided between the inner sealing surface of the box and the inner female thread, or the outer sealing surface of the pin and the outer Some of the teeth of the external female threaded portion are accommodated in the outer groove provided between the male threaded portion and the external female threaded portion. Further, Patent Document 2 discloses that the inner sealing surface of the pin, the inner sealing surface of the box, the outer sealing surface of the pin, and the outer sealing surface of the box are all tapered.

International Publication No. 2019/224345 Patent No. 6916277

An object of the present disclosure is to provide a threaded joint for steel pipes that can improve seizure resistance and manufacturing cost.

The threaded joint for steel pipes according to the present disclosure may include a tubular pin and a tubular box into which the pin is screwed and fastened to the pin. The pin is located between an internal sealing surface formed at the tip of the pin, an internal sealing surface of the pin, and the steel pipe body, and a male thread formed on the outer peripheral surface of the pin, and a connection between the steel pipe main body and the male thread. and a pin outer sealing surface formed therebetween. The box has an internal sealing surface that faces the internal sealing surface of the pin and contacts the internal sealing surface of the pin when the pin and box are fastened, and a female thread that corresponds to the external thread and is formed on the internal peripheral surface of the box. , a box outer sealing surface that faces the pin outer sealing surface and contacts the pin outer sealing surface when the pin and box are fastened. The male thread has a first tapered region located between the pin inner sealing surface and the pin outer sealing surface, and a first tapered region located between the pin inner sealing surface and the first tapered region, and having a slope smaller than the first tapered region. and a second tapered region. The female thread has a third tapered region located between the box inner sealing surface and the box outer sealing surface, and a third tapered region located between the box outer sealing surface and the third tapered region, and has a slope smaller than the third tapered region. and a fourth tapered region. The threads included in the second tapered region may have a wider width than the threads included in the first tapered region. The threads included in the fourth tapered region may have a width wider than the thread width of the threads included in the third tapered region. The insertion surface pitch of the male thread and the female thread may be constant.

FIG. 1 is a longitudinal sectional view showing how the threads of a threaded joint for steel pipes are cut. FIG. 2 is a longitudinal sectional view showing the threaded joint for steel pipes according to the first embodiment. FIG. 3 is an enlarged sectional view of the threaded joint for steel pipes shown in FIG. 2. FIG. 4 is a longitudinal cross-sectional view showing how the threads of the threaded joint for steel pipes shown in FIG. 2 are cut. FIG. 5 is a longitudinal sectional view showing a threaded joint for steel pipes according to a second embodiment. FIG. 6 is a longitudinal sectional view showing a threaded joint for steel pipes according to a third embodiment.

The above-mentioned tubular threaded connection part is provided with an outer male sealing surface, an inner male sealing surface, an outer female sealing surface corresponding to the outer male sealing surface, and an inner female sealing surface corresponding to the inner male sealing surface. Similarly, the above-described threaded joint for steel pipes improves the sealing performance against external pressure and internal pressure by providing an inner sealing surface and an outer sealing surface of the pin, and an inner sealing surface and an outer sealing surface of the box. As mentioned above, slim type threaded joints for steel pipes are required to have a sufficient wall thickness at the sealing part in order to obtain excellent sealing performance under strict outer diameter restrictions. There is room for further consideration regarding ensuring the wall thickness of the seal portion. In a threaded joint having a tapered threaded section, the present inventors have determined that the bottom surface of the male thread at the tip of the pin and the bottom surface of the female thread at the tip of the box are connected to the steel pipe body. It was considered to make the taper parallel to the tube axis, or to make the slope of the taper of the thread bottom surface at the tip of the male thread and the tip of the female thread smaller than the slope of the taper of the male thread and the female thread excluding these tips. This makes it possible to increase the thickness of the pin inner sealing surface and the box outer sealing surface to improve rigidity and improve sealing performance.

Here, the joint efficiency of the slim type threaded joint is less than 1. Joint efficiency is the ratio of the tensile strength of the joint part to the tensile strength of the steel pipe body, and the cross section of the joint part where the area that can withstand tensile load is the smallest in the connected state (generally referred to as the "dangerous cross section"). It is defined as the area of / cross-sectional area of the oil country tubular body. In order to obtain appropriate joint efficiency, it is important that the male and female threads mesh reliably and that when a tensile load is applied to the threaded joint, the tensile load is borne by both the pin and the box. In order to reliably engage the male thread and the female thread, it is preferable that the load surface pitch and the insertion surface pitch be the same.

However, as described above, if the thread bottom surface of the male thread tip and the thread bottom surface of the female thread tip are made parallel, or if the slope of the taper of the male thread tip and the taper slope of the female thread tip are made smaller, 1 It is not possible to make the load surface pitch and insertion surface pitch the same in the cutting process. That is, it is necessary to cut the load surface and the insertion surface separately, which reduces manufacturability. Further, from the viewpoint of ensuring tensile strength after completion of fastening, only the load surface pitch can be made the same by one cutting process, but the insertion surface pitch cannot be made the same.

More specifically, with reference to FIG. 1, a method for cutting the male thread 11 using one chaser 100 will be described. From the above-mentioned viewpoint, cutting is performed so that the load surface pitch is constant, that is, the load surface pitch LPα and the load surface pitch LPβ are the same. When cutting with a taper slope β smaller than a taper slope α with respect to the tube axis CL, the amount of cutting by the chaser 100 (the amount of movement of the chaser 100 downward in the figure) becomes smaller, as shown in the figure. Furthermore, the chaser 100 for cutting a trapezoidal thread is tapered toward the cutting direction (downward in the figure) in a longitudinal cross-sectional view. Therefore, when cutting is performed so that the load surface pitches LPα and LPβ are constant, the insertion surface pitch changes between the tapered region with the slope α and the taper region with the slope β. That is, compared to the case where the slope α and the slope β are constant, the insertion surface moves by the difference Δ in the figure so that the thread width becomes wider in the tapered region of the slope β. If the width of the thread in the tapered region with the slope β becomes wide as described above, the insertion surfaces come into excessive contact with each other during the process of fastening the pin and the box, and seizure is likely to occur.

As a result of extensive studies, the present inventors have newly discovered that when the slope α and the slope β are different, if the insertion surface pitch is kept constant, it is possible to improve seizure resistance and manufacturability while ensuring sealing performance. . Based on this knowledge, the present inventors invented the following threaded joint for steel pipes.

The threaded joint for steel pipes according to the present embodiment may include a tubular pin and a tubular box into which the pin is screwed and fastened to the pin. The pin is located between an internal sealing surface formed at the tip of the pin, an internal sealing surface of the pin, and the steel pipe body, and a male thread formed on the outer peripheral surface of the pin, and a connection between the steel pipe main body and the male thread. and a pin outer sealing surface formed therebetween. The box has an internal sealing surface that faces the internal sealing surface of the pin and contacts the internal sealing surface of the pin when the pin and box are fastened, and a female thread that corresponds to the external thread and is formed on the internal peripheral surface of the box. , a box outer sealing surface that faces the pin outer sealing surface and contacts the pin outer sealing surface when the pin and box are fastened. The male thread has a first tapered region located between the pin inner sealing surface and the pin outer sealing surface, and a first tapered region located between the pin inner sealing surface and the first tapered region, and having a slope smaller than the first tapered region. and a second tapered region. The female thread has a third tapered region located between the box inner sealing surface and the box outer sealing surface, and a third tapered region located between the box outer sealing surface and the third tapered region, and has a slope smaller than the third tapered region. and a fourth tapered region. The threads included in the second tapered region may have a wider width than the threads included in the first tapered region. The threads included in the fourth tapered region may have a width wider than the thread width of the threads included in the third tapered region. The insertion surface pitch of the male thread and the female thread may be constant.

The threads included in the second taper region have a width wider than the thread width of the threads included in the first taper region, and the threads included in the fourth taper region have a width larger than that of the threads included in the first taper region. It has a width wider than the thread width of the included threads, and the insertion surface pitch of the male thread and the female thread is constant. That is, the load surface pitch of the male thread and the female thread is changing. The load surface pitch of the threads included in the second and fourth tapered regions is smaller than the load surface pitch of the threads included in the first and third regions. Note that in the present disclosure, the slopes of the second and fourth tapered regions include cases where the slopes are parallel to the tube axis CL (or a straight line parallel thereto).

Thereby, it is possible to improve the anti-seizure performance and manufacturability in the process of fastening the pin and box.

A threaded joint for steel pipes may include a tubular pin and a tubular box into which the pin is screwed and fastened to the pin. The pin is located between the internal sealing surface formed at the tip of the pin, the internal sealing surface of the pin, and the steel pipe body, and the internal male thread formed on the outer peripheral surface of the pin, and the internal male thread between the steel pipe main body and the internal male thread. The pin may include an outer male thread located therebetween and formed on the outer peripheral surface of the pin, and a pin intermediate sealing surface formed between the inner male thread and the outer male thread. The box has an inner seal surface formed on the inner peripheral surface of the box that faces the inner seal surface of the pin and that contacts the inner seal surface of the pin when the pin and box are fastened, and an inner male thread that corresponds to the inner male thread. An outer female thread formed on the inner peripheral surface of the box that corresponds to the female thread and the outer male thread, and a box intermediate seal that faces the pin intermediate seal surface and comes into contact with the pin intermediate seal surface when the pin and box are fastened. may include a surface. The internal male thread has a fifth tapered region located between the pin internal sealing surface and the pin intermediate sealing surface, and a fifth tapered region located between the pin internal sealing surface and the fifth tapered region, and has a slope smaller than the fifth tapered region. and a sixth tapered region. The external male thread includes a seventh tapered region located between the pin intermediate sealing surface and the steel pipe body, and a seventh tapered region located between the pin intermediate sealing surface and the seventh tapered region and having a smaller slope than the seventh tapered region. 8 tapered regions. The internal female thread has a ninth tapered region located between the box inner sealing surface and the box intermediate sealing surface, and a ninth tapered region located between the box intermediate sealing surface and the ninth tapered region, which has a smaller slope than the ninth tapered region. and a tenth tapered region. The external female thread has an 11th tapered region located between the box intermediate sealing surface and the top end of the box, and a tapered region located between the top end of the box and the 11th taper region, which has a smaller slope than the 11th taper region. and a twelfth tapered region. The threads included in the sixth and eighth tapered regions may each have a wider width than the threads included in the fifth and seventh tapered regions. The threads included in the tenth and twelfth tapered regions may have a wider width than the threads included in the ninth and eleventh tapered regions. The insertion surface pitch of the internal male thread and the internal female thread may be constant. The insertion surface pitch of the outer male thread and the outer female thread may be constant. Thereby, it is possible to improve seizure resistance and manufacturability in the process of fastening the pin and box.

A threaded joint for steel pipes may include a tubular pin and a tubular box into which the pin is screwed and fastened to the pin. The pin has an inner seal surface formed at the tip of the pin, an outer seal surface formed between the steel pipe body and the inner seal surface of the pin, and an inner seal surface formed between the inner seal surface and the outer seal surface of the pin. an inner male thread located between the pin outer sealing surface and the inner male thread, an outer male thread located between the pin outer sealing surface and the inner male thread, and an inner male thread and an outer male thread located between the pin outer seal surface and the inner male thread; and a pin intermediate shoulder surface formed on the outer peripheral surface of the pin. The box faces the inner sealing surface of the pin and contacts the inner sealing surface of the pin when the pin and box are fastened. The outer sealing surface of the box that sometimes contacts the outer sealing surface of the pin, the inner female thread formed on the inner circumferential surface of the box corresponding to the inner male thread, and the outer sealing surface formed on the inner circumferential surface of the box corresponding to the outer male thread. The box may include an internal thread and a box intermediate shoulder surface that faces the pin intermediate shoulder surface and contacts the pin intermediate shoulder surface when the pin and box are fastened. The internal male thread has a fifth tapered region located between the pin internal sealing surface and the pin intermediate shoulder surface, and a fifth tapered region located between the pin internal sealing surface and the fifth tapered region, which has a smaller slope than the fifth tapered region. and a sixth tapered region. The external male thread has a seventh tapered region located between the pin intermediate shoulder surface and the pin external sealing surface, and a seventh tapered region located between the pin intermediate shoulder surface and the seventh tapered region, which has a smaller slope than the seventh tapered region. and an eighth tapered region. The internal female thread has a ninth tapered region located between the box inner sealing surface and the box intermediate shoulder surface, and a ninth tapered region located between the box intermediate shoulder surface and the ninth tapered region, which has a smaller slope than the ninth tapered region. and a tenth tapered region. The external female thread has an eleventh tapered region located between the box intermediate shoulder surface and the box outer sealing surface, and an eleventh tapered region located between the box outer sealing surface and the eleventh tapered region, which has a smaller slope than the eleventh tapered region. and a twelfth tapered region. The threads included in the sixth and eighth tapered regions may each have a wider width than the threads included in the fifth and seventh tapered regions. The threads included in the tenth and twelfth tapered regions may have a wider width than the threads included in the ninth and eleventh tapered regions. The insertion surface pitch of the inner male thread and the inner female thread is constant, and the insertion surface pitch of the outer male thread and the outer female thread is constant. Thereby, it is possible to improve seizure resistance and manufacturability in the process of fastening the pin and box.

The pin may further include an annular pin groove that faces the twelfth tapered region of the external female thread and is spaced apart from the twelfth tapered region when the pin and box are fastened. The box may further include an annular box groove that faces the sixth tapered region of the internal male thread and is spaced apart from the sixth tapered region when the pin and box are fastened. Thereby, excessive interference between the load surfaces of the threads included in the sixth taper region and the twelfth taper region can be suppressed, and better sealing performance can be ensured.

The male and female threads may include a fully threaded portion having a threaded top surface and a threaded bottom surface. The threaded top surface and threaded bottom surface may be parallel to the pipe axis of the steel pipe body.

The threaded joint for steel pipes may be an integral threaded joint.

The threaded joint for steel pipes may have an outer diameter of 105% or less of the steel pipe body.

Either one of a solid lubricant coating and a semi-solid lubricant coating may be formed on at least one of the outer circumferential surface of the pin and the inner circumferential surface of the box.

Hereinafter, this embodiment will be described in detail with reference to the drawings. Identical or corresponding parts in the figures are denoted by the same reference numerals, and their descriptions will not be repeated.

[Structure of threaded joint for steel pipes]
[First embodiment]
Referring to FIG. 2, the threaded joint 1 for steel pipes according to the first embodiment is a slim threaded joint, which includes a tubular pin 10 and a tubular box into which the pin 10 is screwed and fastened to the pin 10. 20. The threaded joint 1 for steel pipes according to the present disclosure can be more suitably used in the slim-type threaded joint 1 for steel pipes. The slim type threaded joint 1 for steel pipes has, for example, an outer diameter of 105% or less of the steel pipe main body 2.

The pin 10 is provided at the pipe end of one of the steel pipe main bodies 2. The pin 10 includes a tapered external thread 11, an internal pin sealing surface 12, an external pin sealing surface 13, and an internal pin shoulder surface 14.

The male thread 11 is formed on the outer peripheral surface of the pin 10. The internal pin shoulder surface 14 is formed at the tip of the pin 10. The pin shoulder surface 14 is an annular surface substantially perpendicular to the tube axis CL. The inner pin sealing surface 12 is formed on the outer peripheral surface of the pin 10 between the male thread 11 and the inner pin shoulder surface 14 . The pin outer sealing surface 13 is formed on the outer circumferential surface of the pin 10 between the male thread 11 and one steel pipe main body 2.

The male thread 11 includes a tapered region 111 and a tapered region 112. Tapered region 112 is formed on the tip side of pin 10 . Tapered region 111 is formed between region 112 and pin outer sealing surface 13 . Tapered region 111 has a taper gradient α1. Tapered region 112 has a slope β1 smaller than slope α1 of tapered region 111. The slope β1 of the tapered region 112 is smaller than the taper slope α1. Thereby, compared to the case where the taper of the male thread 11 is formed with a constant slope α1, the wall thickness at the pin internal sealing surface 12 can be ensured more, contributing to internal pressure sealing performance. Note that in the present disclosure, the slope β1 includes a case where the slope β1 is parallel to the tube axis CL (or a straight line parallel thereto).

When the thread bottom surface of the male thread 11 is parallel to the thread taper, the gradients α1 and β1 are the straight line connecting the thread bottom surface of the male thread 11 and the pipe axis CL (or a straight line parallel to this) in the longitudinal section of the pin 10 including the pipe axis CL. ) is the gradient between On the other hand, when the thread bottom surface of the male thread 11 is parallel to the tube axis CL, the taper gradients α1 and β1 are equal to the extension line of the bottom surface of the male thread 11 and the extension line of the load surface in the longitudinal section of the pin 10 including the tube axis CL. This is the slope between the straight line connecting the intersection points and the tube axis CL (or a straight line parallel to this).

The male thread 11 is a trapezoidal thread, as shown in FIG. The male thread 11 has a thread bottom surface 1111, a thread top surface 1112, an insertion surface 1113, and a load surface 1114. Insertion surface 1113 has a positive flank angle. Loading surface 1114 has a negative flank angle. The absolute value of the flank angle of the insertion surface 1113 is greater than the absolute value of the flank angle of the load surface 1114. The flank angle refers to the angle between a straight line perpendicular to the tube axis CL and the insertion surface or load surface in the longitudinal section of the threaded joint 1 for steel pipes. Regarding the flank angle of the insertion surface 1113, the positive direction is counterclockwise in the drawing. Therefore, the insertion surface 1113 is inclined such that the outer circumferential portion is located further back in the tube axis direction than the inner circumferential portion. Regarding the flank angle of the load surface 1114, the counterclockwise direction in the figure is the negative direction. Therefore, the load surface 1114 is inclined such that the outer circumferential portion is located further back in the tube axis direction than the inner circumferential portion. In the fully threaded portion of the male thread 11, the thread bottom surface 1111 and the thread top surface 1112 are parallel to the thread taper in a longitudinal cross-sectional view. However, in the fully threaded portion of the male thread 11, the thread bottom surface 1111 and the thread top surface 1112 may be parallel to the tube axis CL in a longitudinal cross-sectional view.

The box 20 is provided at the pipe end of the other steel pipe main body 2. The box 20 includes a tapered internal thread 21, an inner box sealing surface 22, an outer box sealing surface 23, and an inner box shoulder surface 24.

The female thread 21 corresponds to the male thread 11 and is formed on the inner peripheral surface of the box 20. The in-box shoulder surface 24 corresponds to the in-pin shoulder surface 14 and is formed on the rear end side of the box 20. The in-box shoulder surface 24 is an annular surface substantially perpendicular to the tube axis CL. The in-box shoulder surface 24 contacts the in-pin shoulder surface 14 when the pin 10 and box 20 are fastened. The box inner sealing surface 22 corresponds to the pin inner sealing surface 12 and is formed on the inner peripheral surface of the box 20. The box inner sealing surface 22 contacts the pin inner sealing surface 12 when the pin 10 and the box 20 are fastened. The box outer sealing surface 23 corresponds to the pin outer sealing surface 13 and is formed on the inner peripheral surface of the box. The box outer sealing surface 23 contacts the pin outer sealing surface 13 when the pin 10 and the box 20 are fastened.

The female thread 21 includes a tapered region 211 and a tapered region 212. Tapered region 212 is formed on the distal end side of box 20 . Tapered region 211 is formed between tapered region 212 and box inner sealing surface 22 . Tapered region 211 has a taper gradient α2. Tapered region 212 has a slope β2 smaller than slope α2. The slope β2 is smaller than the slope α2. As a result, compared to the case where the taper of the female thread 21 is formed at a constant slope α1, a sufficient wall thickness can be ensured on the box outer sealing surface 23, contributing to external pressure sealing performance. Note that in the present disclosure, the taper slope β2 includes a case where the taper slope β2 is parallel to the tube axis CL (or a straight line parallel thereto).

When the bottom surface of the female thread 21 is parallel to the thread taper, the slopes α2 and β2 of the taper are the straight line connecting the bottom surface of the female thread 21 and the pipe axis CL (or a straight line parallel to this) in the longitudinal section of the pin 10 including the pipe axis CL. ) is the gradient between On the other hand, when the bottom surface of the female thread 21 is parallel to the tube axis CL, the taper gradients α2 and β2 are determined at the intersection of the extension line of the bottom surface of the female thread 21 and the extension line of the load surface in the longitudinal section of the pin 10 including the tube axis CL. This is the slope between the straight line connecting the lines and the tube axis CL (or a straight line parallel to this).

The female thread 21 is a trapezoidal thread, as shown in FIG. The female thread 21 has a thread bottom surface 2111, a thread top surface 2112, an insertion surface 2113, and a load surface 2114. Insertion surface 2113 has a positive flank angle. Loading surface 2114 has a negative flank angle. The absolute value of the flank angle of the insertion surface 2113 is greater than the absolute value of the flank angle of the load surface 2114. Regarding the flank angle of the insertion surface 2113, the positive direction is counterclockwise in the figure. Therefore, the insertion surface 2113 is inclined such that the outer circumferential portion is located further forward in the tube axis direction than the inner circumferential portion. Regarding the flank angle of the load surface 2114, the counterclockwise direction in the figure is taken as a negative direction. Therefore, the load surface 2114 is inclined such that the outer circumferential portion is located further forward in the tube axis direction than the inner circumferential portion. In the fully threaded portion of the female thread 21, the thread bottom surface 2111 and the thread top surface 2112 are parallel to the thread taper in a longitudinal cross-sectional view. However, in the fully threaded portion of the female thread 21, the thread bottom surface 2111 and the thread top surface 2112 may be parallel to the tube axis CL in a longitudinal cross-sectional view.

When the pin 10 and the box 20 are completely fastened, the thread bottom surface 1111 of the male thread 11 and the thread top surface 2112 of the female thread 21 come into contact at the fully threaded portion of the male thread 11 and the female thread 21, and the load surface 1114 of the male thread 11 and the female thread 21 load surfaces 2114 contact each other. Further, the insertion surface 1113 of the male thread 11 and the insertion surface 2113 of the female thread 21 face each other with a gap between them, and the top surface 1112 of the male thread 11 and the bottom face 2111 of the female thread 21 face each other with a gap between them.

The insertion surface pitch of the male thread 11 and the insertion surface pitch of the female thread 21 are constant. As shown in FIG. 4, by cutting with one chaser 100 so that the insertion surface pitch SPα and the insertion surface pitch SPβ are constant, the insertion surface pitch becomes constant. Thereby, in the process of fastening the pin 10 and the box 20, the load is not concentrated on the tapered region 112 at the tip of the male screw 11, but is distributed over each thread. As a result, the anti-seizure performance when the pin 10 and box 20 are fastened can be improved. In addition, the thread can be formed in a single cutting process, and productivity can be improved. Moreover, as shown in FIG. 4, the load surface of the male screw 11 moves by the difference Δ in the figure so that the thread width of the male screw 11 becomes wider. That is, the load surface pitch LPα and the load surface pitch LPβ change between the slopes α1 and β1. In this way, the thread width of the thread included in the tapered region 112 is wider than the thread width of the tapered region 111 because the gradient β1 is smaller than the gradient α1. That is, since the insertion surface pitch is constant, the thickness increases at the load surface 1114 of the male screw 11. As a result, an amount of interference in the tube axis direction is introduced between the load surface 1114 of the male thread 11 and the load surface 2114 of the female thread 21 in the tapered region 112 and the tapered region 212. This amount of interference increases toward the tip of the pin in the tapered region 112, and increases toward the tip of the box (toward the tube body side of the pin) in the tapered region 212. As a result, when the fastening is completed, the tapered region 112 and the tapered region 212 In this case, the load surfaces come into strong contact with each other. Further, this contact becomes stronger toward the tip of the pin in the tapered region 112, and stronger toward the tip of the box (the side of the pin toward the tube body) in the tapered region 212. By the way, in the threaded joint 1 for steel pipes shown in FIG. 2, the dangerous cross section of the pin 10 is the threaded end on the one steel pipe main body 2 side, and the dangerous cross section of the box 20 is the threaded end on the tip side of the pin 10. be. If sufficient engagement is not obtained between the male thread 11 and the female thread 21 in these dangerous cross-sections, the applied tensile load will not be reliably transmitted to the pin 10 and the box 20, and neither the pin 10 nor the box 20 will be properly engaged. Otherwise, an excessive load may be applied, leading to a decrease in tensile strength. As described above, the load surfaces of the tapered region 112 and the tapered region 212 are in strong contact with each other. That is, the contact between the load surfaces of the male thread 11 and the female thread 12 at these critical cross-sections becomes stronger. Thereby, the load surfaces can be reliably engaged with each other at these critical cross-sections, and the tensile load can be reliably transmitted to the pin 10 and the box 20. That is, the tensile strength can be improved.

[Second embodiment]
Next, with reference to FIG. 5, a threaded joint 1 for steel pipes according to a second embodiment will be described. Descriptions of the same configurations as in the first embodiment will be omitted, and basically configurations that are different from the first embodiment will be described in detail.

The threaded joint 1 for steel pipes according to the second embodiment is a so-called two-stage thread. The threaded joint 1 for steel pipes includes a pin 10 and a box 20. The pin 10 has an inner male thread 11a, an outer male thread 11b, and a pin intermediate sealing surface 15. The pin intermediate sealing surface 15 is formed on the outer peripheral surface of the pin 10 between the inner male thread 11a and the outer male thread 11b. The internal male thread 11a is formed on the outer peripheral surface of the pin 10 between the pin internal sealing surface 12 and the pin intermediate sealing surface 15. The external male thread 11b is formed on the outer peripheral surface of the pin 10 between the pin intermediate sealing surface 15 and the steel pipe body 2. In addition, in the threaded joint 1 for steel pipes according to the second embodiment, the pin outer seal surface 13 is not formed, but the pin outer seal surface 13 is formed on the outer peripheral surface of the pin 10 between the outer male thread 11b and the steel pipe main body 2. may be formed.

The box 20 has an inner female thread 21a, an outer female thread 21b, and a box intermediate sealing surface 25. The internal female thread 21a corresponds to the internal male thread 11a and is formed on the inner peripheral surface of the box 20. The outer female thread 21b corresponds to the outer male thread 11b and is formed on the inner peripheral surface of the box 20. The box intermediate sealing surface 25 corresponds to the pin intermediate sealing surface 15 and is formed on the inner peripheral surface of the box 20. When the pin 10 and the box 20 are fastened, the box intermediate sealing surface 25 contacts the pin intermediate sealing surface 15. In addition, when the above-mentioned pin outer sealing surface 13 is formed, a box outer sealing surface 23 corresponding to the pin outer sealing surface 13 may be formed.

The internal male thread 11a includes a tapered region 111a and a tapered region 112a. Tapered region 112a is formed on the tip side of pin 10. Tapered region 111a is formed between tapered region 112a and pin intermediate sealing surface 15. The tapered region 111a has a taper gradient α1. Tapered region 112a has a slope β1 smaller than slope α1. The slope β1 is smaller than the taper slope α1. Thereby, compared to the case where the taper of the male thread 11a is formed with a constant slope α1, it is possible to ensure a greater wall thickness on the pin internal sealing surface 12, contributing to internal pressure sealing performance. Note that in the present disclosure, the slope β1 includes a case where the slope β1 is parallel to the tube axis CL (or a straight line parallel thereto).

The internal female thread 21a includes a tapered region 211a and a tapered region 212a. Tapered region 212a is formed on the front end side of box 20. Tapered region 211a is formed between tapered region 212a and box inner sealing surface 22. The tapered region 211a has a taper gradient α2. Tapered region 212a has a slope β2 smaller than slope α2. The slope β2 is smaller than the slope α2. Thereby, compared to the case where the taper of the female thread 21a is formed with a constant slope α2, a sufficient wall thickness can be ensured at the box intermediate sealing surface 25, contributing to external pressure sealing performance. Note that in the present disclosure, the slope β2 includes a case where the slope β2 is parallel to the tube axis CL (or a straight line parallel thereto).

The external male thread 11b includes a tapered region 111b and a tapered region 112b. Tapered region 112b is formed on the pin intermediate seal surface 15 side. Tapered region 111b is formed between tapered region 112b and steel pipe main body 2. The tapered region 111b has a taper gradient α3. Tapered region 112b has a slope β3 smaller than slope α3. The slope β3 is smaller than the slope α3. As a result, compared to the case where the taper of the male thread 11b is formed with a constant slope α1, the wall thickness at the pin internal sealing surface 12 and the pin intermediate sealing surface 15 can be ensured more, contributing to internal pressure sealing performance. I can do it. Note that in the present disclosure, the slope β3 includes a case where the slope β3 is parallel to the tube axis CL (or a straight line parallel thereto).

The external female thread 21b includes a tapered region 211b and a tapered region 212b. The tapered region 212b is formed on the front end side of the box 20. Tapered region 211b is formed between tapered region 212b and box intermediate sealing surface 25. Tapered region 211b has a taper gradient α4. Tapered region 212b has a slope β4 smaller than slope α4. Thereby, compared to the case where the taper of the female thread 21b is formed with a constant slope α4, when the box outer sealing surface 23 is formed, a sufficient wall thickness can be ensured on the box outer sealing surface 23, It can contribute to external pressure sealing performance. Note that in the present disclosure, the taper slope β4 includes cases in which it is parallel to the tube axis CL (or a straight line parallel thereto).

Similar to the male thread 11 and female thread 21 according to the first embodiment, the insertion surface pitch of the inner male thread 11a and the inner female thread 21a is constant, and the insertion surface pitch of the outer male thread 11b and the outer female thread 21b is also constant. Thereby, in the steel pipe threaded joint 1 according to the second embodiment as well, seizure can be suppressed in the process of fastening the pin 10 and the box 20. Further, in the tapered region 112a of the internal male thread 11a and the tapered region 112b of the male thread 11b, the wall thickness on the load surface of the thread increases. Thereby, tensile strength can be improved.

[Third embodiment]
Next, with reference to FIG. 6, a threaded joint 1 for steel pipes according to a third embodiment will be described. The description of the same configurations as the second embodiment will be omitted, and basically the configurations that are different from the second embodiment will be explained in detail.

The threaded joint 1 for steel pipes according to the third embodiment includes a pin 10 and a box 20. The pin 10 has a pin intermediate shoulder surface 16, a pin outer seal surface 13, and a pin groove portion 17. The pin intermediate shoulder surface 16 is formed on the outer peripheral surface of the pin 10 between the inner male thread 11a and the outer male thread 11b. The pin intermediate shoulder surface 16 is an annular surface substantially perpendicular to the tube axis CL. The pin outer sealing surface 13 is formed on the outer circumferential surface of the pin 10 between the outer male thread 11b and one steel pipe main body 2.

The pin groove 17 is an annular groove formed on the outer peripheral surface of the pin 10, facing the tapered region 212b of the female thread 21b. The pin groove portion 17 is spaced apart from the tapered region 212b of the female thread 21b and does not come into contact with the tapered region 212b when the pin 10 and box 20 are fastened. That is, a gap is provided between the pin groove portion 17 and the tapered region 212b of the female thread 21b. As described above, the slope β4 of the tapered region 212b is smaller than the taper slope α4 of the tapered region 211b, so the thread width of the thread included in the tapered region 212b is the thread width of the thread included in the tapered region 211b. becomes wider than If the load surface of the thread included in the tapered region 212b and the load surface of the thread included in the tapered region 111b interfere excessively, it may affect the contact between the pin outer seal surface 13 and the box outer seal surface 23. be. Therefore, by providing the pin groove portion 17, excessive interference between the load surfaces can be suppressed, and external pressure sealing performance can be further improved.

The box 20 has a box intermediate shoulder surface 26, a box outer sealing surface 23, and a box groove 27. The box intermediate shoulder surface 26 corresponds to the pin intermediate shoulder surface 16 and is formed on the inner peripheral surface of the box 20. The box intermediate shoulder surface 26 is an annular surface substantially perpendicular to the tube axis CL. Box intermediate shoulder surface 26 contacts pin intermediate shoulder surface 16 when pin 10 and box 20 are fastened. The box outer sealing surface 23 corresponds to the pin outer sealing surface 13 and is formed on the inner peripheral surface of the box 20. The box outer sealing surface 23 contacts the pin outer sealing surface 13 when the pin 10 and the box 20 are fastened.

The box groove 27 is an annular groove formed on the outer peripheral surface of the box 20, facing the tapered region 112a of the internal male thread 11a. The box groove portion 27 is spaced apart from the tapered region 112a of the internal male screw 11a and does not come into contact with the tapered region 112a when the pin 10 and box 20 are fastened. That is, a gap is provided between the box groove portion 27 and the tapered region 112a of the male thread 11a. As described above, since the slope β1 of the tapered region 112a is smaller than the slope α1 of the tapered region 111a, the thread width of the thread included in the tapered region 112a is smaller than the thread width of the thread included in the tapered region 111a. It becomes wider. If the load surface of the thread included in the tapered region 112a and the load surface of the thread included in the tapered region 221a interfere excessively in the tube axis direction, it will affect the contact between the pin inner seal surface 12 and the box inner seal surface 22. It may cause Therefore, by providing the box groove portion 27, excessive interference between the load surfaces can be suppressed, and external pressure sealing performance can be further improved.

Since the gradient β2 of the tapered region 212a of the internal female thread 21a is smaller than the gradient α1 of the tapered region 111a, the thread width of the thread included in the tapered region 212a is smaller than the thread width of the thread included in the tapered region 111a. It becomes wider. Therefore, an amount of interference in the tube axis direction is introduced between the load surface of the thread included in the tapered region 212a and the load surface of the thread included in the tapered region 111a. Further, since the slope β3 of the tapered region 112b of the external male screw 11b is smaller than the slope α4 of the tapered region 211b, the thread width of the thread included in the tapered region 112b is the thread width of the thread included in the tapered region 211b. becomes wider than Therefore, an amount of interference in the tube axis direction is introduced between the load surface of the thread included in the tapered region 112b and the load surface of the thread included in the tapered region 211b. The amount of interference increases as the pin intermediate shoulder surface 16 and the box intermediate shoulder surface 26 are approached. As a result, at the positions of the pin intermediate dangerous cross section PCCS1 and the box intermediate dangerous cross section BCCS1, the inner male thread 11a and the inner female thread 21a reliably contact, and the outer male thread 11b and the outer female thread 21b reliably contact. A tensile load is transferred to the pin intermediate shoulder surface 16 and the box intermediate shoulder surface 26. As a result, tensile strength can be improved.

Note that the pin 10 includes a pin intermediate dangerous cross section PSSC1 and a pin dangerous cross section PSSC2. Box 20 includes a box intermediate dangerous section BCCS1 and a box dangerous section BCCS2. As mentioned above, the critical cross section is the cross section of the joint portion where the area that can withstand tensile load is the smallest in the fastened state. Normally, the pin intermediate dangerous cross section PSSC1 is located near the end of the internal male thread 11a on the pin intermediate shoulder 16 side. The pin dangerous cross section PSSC2 is located near the end of the external male thread 11b on the pin external sealing surface 13 side. The box intermediate dangerous cross section BSSC1 is located near the end of the external female thread 21b on the box intermediate shoulder surface 26 side. The box dangerous cross section BSSC2 is located near the end on the box inner sealing surface 22 side.

The threaded joint 1 for steel pipes according to the present disclosure can also be applied to coupling-type or integral-type threaded joints 1 for steel pipes. However, the threaded joint 1 for steel pipes of the present disclosure can achieve particularly great effects in slim-type threaded joints 1 for steel pipes where strict restrictions are imposed on the outer diameter dimension.

Furthermore, the steel pipe threaded joint 1 according to the present disclosure can be suitably applied to a so-called dope-free threaded joint. A dope-free threaded joint is a threaded joint in which dope is not applied when the pin 10 and box 20 are fastened, and a solid lubricant film or semi-solid lubricant film is preliminarily formed on either the pin 10 or the box 20 before fastening. It is. Dope-free threaded joints are repeatedly fastened and dismantled without reapplying dope. Therefore, excellent seizure resistance is required. Therefore, the threaded joint 1 for steel pipes of the present disclosure, which has excellent seizure resistance, can be suitably applied to dope-free threaded joints.

Although the embodiments have been described above, the present disclosure is not limited to the above embodiments, and various changes can be made without departing from the spirit thereof.

[First analysis (stubbing property evaluation)]
Using finite element analysis using a two-dimensional axisymmetric model, an elastic-plastic analysis was performed that simulated the state when a threaded joint was stubbed. Specifically, from the state where the pin and box shown in FIG. 6 were separated in the tube axis direction, an axial force load corresponding to the weight of the steel tube body was applied, and the contact state of the threaded portion during stabbing was evaluated.

[Analysis conditions]
14” 116# Slim type threaded joint for steel pipe Length of steel pipe body 12m
Q125 steel specified by API standards (nominal yield stress 125 ksi = 861.8 MPa)
Young's modulus 210GPa, Poisson's ratio 0.3
Thread shape Taper slope α1 to 4 1/18 [-] shown in Figure 6
Taper gradient β1 to 4 0 [-] shown in Fig. 6
Flank angle of load surface -3 [deg] (The tip of the pin is positive with respect to the plane perpendicular to the tube axis CL.)
Flank angle of insertion surface 10 [deg] (tube body side is positive with respect to the plane perpendicular to tube axis CL)
Load surface pitch 5.08 [mm]
Insertion surface pitch of

tapered regions

111a, 111b, 211a and 211b shown in FIG. 6: 5.08 [mm]

[Second analysis (sealing performance evaluation)]
For the model used in the first analysis, after conducting an analysis simulating the fastening of a threaded joint, a repeated combined load equivalent to the ISO13679 Series A test was applied to the inner seal (pin inner seal surface and box inner seal surface). The sealing performance of the outer seal (pin outer seal surface and box outer seal surface) was evaluated. The sealing performance is evaluated by the seal contact force [N/mm] per circumferential unit length of the inner seal and outer seal, and the larger the minimum value of the seal contact force during the load cycle load, the better the sealing performance. I decided that.

[Analysis result]
Table 1 shows the analysis results in the first and second analyses. Note that

specimens

1 and 2 are comparative examples, and specimen 3 is an example. Further, in Table 1, the contact pressure refers to the maximum contact pressure applied to the threaded portion during stabbing.

In the first analysis, since the insertion surface pitch of specimens 1 and 3 was constant, the load applied to the threads was dispersed, and the contact pressure at the threaded portion was suppressed. On the other hand, in specimen 2 where the insertion surface pitch changes (see Figure 1), only the threads at the ends of the internal male thread and internal female thread, and the ends of the external male thread and external female thread contact, and these screws Because the load was concentrated on the thread, extremely high contact pressure was generated on the threaded part.

The evaluation results of the sealing performance obtained in the second analysis are shown in Table 1, and it can be said that the sealing performances of specimens 1 to 3 are approximately the same.

In the above threaded joint where the taper slope changes, when both the load surface pitch and the insertion surface pitch are constant (specimen 1), it is necessary to cut the load surface and the insertion surface separately, and the cutting The process increases. Therefore, specimen 1 is evaluated as "B" because it has poor manufacturability, and specimens 2 and 3, which only need to be cut to align either the load surface pitch or the insertion surface pitch, are evaluated as "B" because they have excellent manufacturability. Rated "A".

From the above, it can be said that Specimen 3 has excellent seizure resistance and manufacturability, and is equivalent to

Specimens

1 and 2 in terms of sealing performance.

1: Threaded joint for steel pipes 2: Steel pipe body 10: Pin 11: Male thread 11a: Inner male thread 11b: Outer male thread 12: Pin inner seal surface 13: Pin outer seal surface 14: Pin inner shoulder surface 15: Pin intermediate seal surface 16: Pin intermediate shoulder surface 17: Pin groove 20: Box 21: Female thread 21a: Inner female thread 21b: Outer female thread 22: Box inner seal surface 23: Box outer seal surface 24: Box inner shoulder surface 25: Box intermediate seal surface 26: Box middle Shoulder surface 27: Box grooves α1 to α4, β1 to β4: Gradient of tapered region

Claims

A threaded joint for steel pipes for connecting steel pipe bodies,
tubular pin,
a tubular box into which the pin is screwed and fastened to the pin;
The pin is
an internal sealing surface formed at the tip of the pin;
a male thread located between the inner sealing surface of the pin and the steel pipe body and formed on the outer peripheral surface of the pin;
a pin outer sealing surface formed between the steel pipe body and the male thread,
The box is
a box inner seal surface that faces the pin inner seal surface and contacts the pin inner seal surface when the pin and the box are fastened;
a female thread corresponding to the male thread and formed on the inner peripheral surface of the box;
a box outer sealing surface that faces the pin outer sealing surface and contacts the pin outer sealing surface when the pin and the box are fastened;
The male thread includes a first tapered region located between the pin inner sealing surface and the pin outer sealing surface, and a first tapered region located between the pin inner sealing surface and the first tapered region. a second tapered region having a slope less than
The female thread includes a third tapered region located between the box inner sealing surface and the box outer sealing surface, and a third tapered region located between the box outer sealing surface and the third tapered region. a fourth tapered region having a slope less than
The threads included in the second tapered region have a wider width than the threads of the threads included in the first tapered region,
The thread included in the fourth tapered region has a width wider than the thread width of the thread included in the third tapered region,
A threaded joint for steel pipes, wherein the insertion surface pitch of the male thread and the female thread is constant.
A threaded joint for steel pipes for connecting steel pipe bodies,
tubular pin,
a tubular box into which the pin is screwed and fastened to the pin;
The pin is
an internal sealing surface formed at the tip of the pin;
an inner male thread located between the inner sealing surface of the pin and the steel pipe body and formed on the outer peripheral surface of the pin;
an outer male thread located between the steel pipe main body and the inner male thread and formed on the outer peripheral surface of the pin;
a pin intermediate sealing surface formed between the inner male thread and the outer male thread,
The box is
a box inner seal surface that faces the pin inner seal surface and contacts the pin inner seal surface when the pin and the box are fastened;
an internal female thread corresponding to the internal male thread and formed on the inner peripheral surface of the box;
an outer female thread corresponding to the outer male thread and formed on the inner peripheral surface of the box;
a box intermediate sealing surface that faces the pin intermediate sealing surface and contacts the pin intermediate sealing surface when the pin and the box are fastened;
The internal male thread includes a fifth tapered region located between the pin internal sealing surface and the pin intermediate sealing surface, and a fifth tapered region located between the pin internal sealing surface and the fifth tapered region. a sixth tapered region having a slope less than
The external male thread includes a seventh tapered region located between the pin intermediate sealing surface and the steel pipe main body, and a seventh tapered region located between the pin intermediate sealing surface and the seventh tapered region, and an eighth tapered region having a small slope;
The internal female thread includes a ninth tapered region located between the box inner sealing surface and the box intermediate sealing surface, and a ninth tapered region located between the box intermediate sealing surface and the ninth tapered region. a tenth tapered region having a slope smaller than the region;
The external female thread includes an eleventh tapered region located between the box intermediate sealing surface and the distal end of the box, and an eleventh tapered region located between the distal end of the box and the eleventh tapered region. a twelfth tapered region having a slope smaller than the region;
The threads included in the sixth and eighth tapered regions each have a wider width than the threads included in the fifth and seventh tapered regions,
The threads included in the tenth and twelfth tapered regions have a wider width than the threads included in the ninth and eleventh tapered regions,
A threaded joint for steel pipes, wherein the insertion surface pitch of the inner male thread and the inner female thread is constant, and the insertion surface pitch of the outer male thread and the outer female thread is constant.
A threaded joint for steel pipes for connecting steel pipe bodies,
tubular pin,
a tubular box into which the pin is screwed and fastened to the pin;
The pin is
an internal sealing surface formed at the tip of the pin;
a pin outer seal surface formed between the steel pipe body and the pin inner seal surface;
an internal male thread located between the pin inner sealing surface and the pin outer sealing surface and formed on the outer peripheral surface of the pin;
an outer male thread located between the pin outer sealing surface and the inner male thread and formed on the outer peripheral surface of the pin;
a pin intermediate shoulder surface located between the inner male thread and the outer male thread and formed on the outer peripheral surface of the pin;
The box is
a box inner seal surface that faces the pin inner seal surface and contacts the pin inner seal surface when the pin and the box are fastened;
a box outer seal surface that faces the pin outer seal surface and contacts the pin outer seal surface when the pin and the box are fastened;
an internal female thread corresponding to the internal male thread and formed on the inner peripheral surface of the box;
an outer female thread corresponding to the outer male thread and formed on the inner peripheral surface of the box;
a box intermediate shoulder surface that faces the pin intermediate shoulder surface and contacts the pin intermediate shoulder surface when the pin and the box are fastened;
The internal male thread includes a fifth tapered region located between the pin internal sealing surface and the pin intermediate shoulder surface, and a fifth tapered region located between the pin internal sealing surface and the fifth tapered region. a sixth tapered region having a slope less than
The outer male thread includes a seventh tapered region located between the pin intermediate shoulder surface and the pin outer sealing surface, and a seventh tapered region located between the pin intermediate shoulder surface and the seventh tapered region, and the seventh taper region located between the pin intermediate shoulder surface and the pin outer seal surface. an eighth tapered region having a slope smaller than the region;
The internal female thread includes a ninth tapered region located between the box inner sealing surface and the box intermediate shoulder surface, and a ninth tapered region located between the box intermediate shoulder surface and the ninth tapered region. a tenth tapered region having a slope smaller than the region;
The external female thread includes an eleventh tapered region located between the box intermediate shoulder surface and the box outer sealing surface, and an eleventh tapered region located between the box outer sealing surface and the eleventh tapered region. a twelfth tapered region having a slope smaller than the region;
The threads included in the sixth and eighth tapered regions each have a wider width than the threads included in the fifth and seventh tapered regions,
The threads included in the tenth and twelfth tapered regions have a wider width than the threads included in the ninth and eleventh tapered regions,
A threaded joint for steel pipes, wherein the insertion surface pitch of the inner male thread and the inner female thread is constant, and the insertion surface pitch of the outer male thread and the outer female thread is constant.
The threaded joint for steel pipes according to claim 3,
The pin further includes an annular pin groove facing the twelfth tapered region of the external female thread and spaced apart from the twelfth tapered region when the pin and the box are fastened,
The box further includes an annular box groove facing a sixth tapered region of the internal male thread and spaced apart from the sixth tapered region when the pin and the box are fastened.
The threaded joint for steel pipes according to any one of claims 1 to 4,
The male thread and the female thread include a fully threaded portion having a threaded top surface and a threaded bottom surface,
The threaded joint for steel pipes, wherein the threaded top surface and threaded bottom surface are parallel to the pipe axis of the steel pipe main body.
The threaded joint for steel pipes according to any one of claims 1 to 5,
The threaded joint for steel pipes is an integral threaded joint for steel pipes.
The threaded joint for steel pipes according to any one of claims 1 to 6,
The threaded joint for steel pipes has an outer diameter of 105% or less of the steel pipe main body.
The threaded joint for steel pipes according to any one of claims 1 to 7,
A threaded joint for steel pipes, wherein either a solid lubricant coating or a semi-solid lubricant coating is formed on at least one of the outer circumferential surface of the pin and the inner circumferential surface of the box.