Threaded joint

Abstract

Provided is a compact threaded joint which has excellent sealing performance against internal pressure and sealing performance against external pressure, has excellent strength against compressive loads, and can maintain sealing performance against external pressure even when repeated loads are applied. Provided is a compact threaded joint in which external pressure seal sections (21, 31) and internal pressure seal sections (23, 33) are provided in front of and behind threaded sections (22, 32), a nose section (24) for maintaining internal pressure sealing performance is provided at the tip of a pin (2), and torque shoulder surfaces (25, 35) are provided at the tip of the nose section (24). When a compressive load is applied, a portion of the compressive load is applied by contact between the insertion surfaces of the threaded portions (22, 32). Furthermore, by reducing the shoulder angle (theta) of the torque shoulder surfaces (25, 35), the amount of press-fit of the male buckle (2) with respect to the female buckle (3) and the amount of radially inward shrinkage deformation of the opening end of the female buckle (2) when a compressive load is applied are reduced, and accumulation of damage in the vicinity of the outer sealing surface is suppressed.

Description

Technical Field

[0001] The present disclosure relates to a threaded joint for connecting long pipes such as oil well pipes. Background Art

[0002] In oil wells, natural gas wells, etc. (hereinafter also collectively referred to as "oil wells"), in order to extract underground resources, casings for constructing the wellbore in multiple sections and tubing for producing oil and gas disposed within the casing are used. These casings and tubing are formed by sequentially connecting a number of steel pipes, and a threaded joint as shown in Patent Documents 1 to 4 below is used for their connection. The steel pipe used for an oil well is also referred to as an oil well pipe.

[0003] The forms of the threaded joint are roughly classified into an integral type and a coupling type.

[0004] In the integral type, the oil well pipes are directly connected to each other. Specifically, an internal threaded portion is provided at one end of the oil well pipe, and an external threaded portion is provided at the other end. The oil well pipes are connected to each other by screwing the external threaded portion of another oil well pipe into the internal threaded portion of one oil well pipe.

[0005] In the coupling type, the oil well pipes are connected to each other by means of a tubular coupling. Specifically, internal threaded portions are provided at both ends of the coupling, and external threaded portions are provided at both ends of the oil well pipe. Then, one external threaded portion of one oil well pipe is screwed into one internal threaded portion of the coupling, and at the same time, one external threaded portion of another oil well pipe is screwed into the other internal threaded portion of the coupling, thereby connecting the oil well pipes to each other. That is, in the coupling type, one of the pair of pipes to be connected is an oil well pipe, and the other pipe is a coupling.

[0006] Generally, the end portion of the oil well pipe formed with the external threaded portion includes an element to be inserted into the internal threaded portion formed in the oil well pipe or the coupling, and thus is called a male thread. The end portion of the oil well pipe or the coupling formed with the internal threaded portion includes an element for receiving the external threaded portion formed in the oil well pipe, and thus is called a female thread. In theory, a male thread may also be provided at the end portion of the coupling and a female thread may be provided at the end portion of the oil well pipe.

[0007] In recent years, the further development of high-temperature and high-pressure deep wells has been continuously progressing. In deep wells, due to the complexity of the depth distribution of formation pressure, the number of casing sections needs to be increased, etc. Therefore, sometimes a compact (slim type) threaded joint with the maximum outer diameter of the joint, that is, the outer diameter of the female thread, being approximately the same as the outer diameter of the pipe body of the oil well pipe is used. A compact threaded joint with the outer diameter of the female thread being approximately equal to the outer diameter of the pipe body of the oil well pipe is also called a standard flush type threaded joint. In addition, a compact threaded joint with the outer diameter of the female thread being slightly larger than the outer diameter of the pipe body of the oil well pipe is also called a semi-flush type threaded joint. For these compact threaded joints, not only high strength and sealing performance are required, but also strict dimensional constraints are imposed on each part in order to arrange the thread structure and sealing structure within the limited pipe wall thickness.

[0008] In Patent Document 1, a coupling type threaded joint that is not compact is disclosed. In the case of not being compact, the wall thickness of the male thread near the inner sealing part provided on the outer periphery of the tip of the male thread and the wall thickness of the female thread can both ensure sufficient sizes, and sufficient sealing performance against internal pressure and external pressure can be obtained only with the inner sealing part. Therefore, an outer sealing part is not provided in the threaded joint disclosed in Patent Document 1.

[0009] Prior art documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2013 - 29174

[0012] Patent Document 2: International Publication No. 2017 / 213048

[0013] Patent Document 3: International Publication No. 2018 / 135536

[0014] Patent Document 4: International Publication No. 2007 / 017082 Summary of the Invention

[0015] In the case of a compact threaded joint, the wall thickness of the male thread near the tip of the male thread and near the inner sealing part provided on the outer periphery of the male thread becomes thinner, and it is difficult to ensure the sealing performance against external pressure with the inner sealing part. Therefore, as disclosed in Patent Documents 2 to 3, an outer sealing surface is mostly provided on the outer periphery of the base end part of the male thread and the inner periphery of the tip of the female thread. The wall thickness of the female thread near the outer sealing part is relatively thin. If external pressure acts on the outer peripheral surface of the female thread, the contact pressure between the outer sealing surfaces increases. Therefore, external pressure sealing performance can be ensured. In addition, the wall thickness of the male thread near the inner sealing part is also relatively thin. If internal pressure acts on the inner peripheral surface of the male thread, the contact pressure between the inner sealing surfaces increases. Therefore, internal pressure sealing performance can be ensured.

[0016] An integral compact threaded joint is disclosed in Patent Document 2. In this threaded joint, external shoulder surfaces are provided at the base end portion of the male thread and the tip end portion of the female thread. In the case of this external shoulder structure, it is necessary to arrange the external shoulder surface within the wall thickness of the steel pipe. If the radial dimension of the external shoulder surface is ensured in such a way as to obtain sufficient torque resistance performance and compressive load resistance performance, it is difficult to ensure the radial width for forming the tapered thread and the wall thickness of the male thread of the internal seal portion.

[0017] An integral compact threaded joint is disclosed in Patent Document 3. This threaded joint has a two-thread structure in which thread portions are arranged before and after an intermediate shoulder. In order to ensure the wall thickness of the internal external thread portion (13) of the male thread on the tip end side relative to the intermediate shoulder (15), necking processing is applied to the male thread in the region including the internal external thread portion. As a result, the inner diameter of the tip end of the male thread is smaller than the inner diameter of the steel pipe having the female thread, and a step is formed between the inner peripheral surface of the steel pipe having the female thread and the inner peripheral surface of the steel pipe having the male thread. Such a step causes turbulence in the flow of the fluid inside the pipe, and thus is not preferable.

[0018] An integral compact threaded joint having internal shoulder surfaces (8, 9), internal seal surfaces (10, 12), thread portions (3, 4), external seal surfaces (34, 35), and external shoulder surfaces (32, 33) is disclosed in FIG. 7 of Patent Document 4. In this case, if both the internal shoulder and the external shoulder are arranged within the wall thickness of the steel pipe and the axial length of the thread portion formed by the tapered thread is ensured according to the required strength, the taper angle of the tapered thread becomes smaller, the amount of tightening rotation work required to complete the tightening increases, and the tightening work efficiency deteriorates.

[0019] The content capable of omitting the internal shoulder surfaces (8, 9), the internal seal surfaces (10, 12), and the housing (7) is mentioned on pages 13, lines 7 - 9 of Patent Document 4. In this case, it becomes a structure similar to the threaded joint disclosed in Patent Document 2, and the same problems are implied.

[0020] The present disclosure aims to provide a compact threaded joint having excellent sealing performance against internal pressure and external pressure, excellent strength against compressive load, and capable of maintaining the sealing performance against external pressure even when a repeated load is applied.

[0021] The inventors of the present application studied a solution in which a torque shoulder is arranged at the tip end of the male thread, and an internal seal portion and an external seal portion are arranged before and after the thread portion in order to ensure the contact area between the shoulder surfaces and the radial width for forming the thread portion even in a compact threaded joint.

[0022] However, when comparing the case where the torque shoulder is disposed at the top of the male thread and the case where the torque shoulder is disposed at the top of the female thread, even if the same radial width is ensured, the overall diameter will be smaller. Therefore, the cross-sectional area near the torque shoulder becomes smaller, and the compression load resistance performance is reduced.

[0023] Therefore, the inventors of the present application studied the following situation: when applying a compression load, by deforming the male thread and the female thread in the elastic region, the insertion surfaces of the external thread and the internal thread are brought into contact with each other, and a part of the compression load is borne between the insertion surfaces. However, it was found that as the axial load acting on the insertion surface of the internal thread of the female thread increases, the top opening of the female thread tends to shrink and deform. On the other hand, when the male thread is pressed into the female thread, the outer sealing surface of the female thread is forcibly pushed radially outward by the outer sealing surface of the male thread. As a result, damage is likely to accumulate near the outer sealing surface of the female thread.

[0024] In the compact threaded joint having the above structure, in order to reduce the damage generated near the outer sealing surface of the female thread when applying a compression load, it is necessary to minimize the axial movement amount of the male thread pressed into the female thread when applying a compression load. Therefore, the inventors of the present application focused on the torque shoulder angle. It is generally considered that the torque shoulder angle is preferably set to about -15° in anticipation of the holding effect of the female thread on the top end portion of the male thread. However, in the case of the compact threaded joint having the above structure studied by the inventors of the present application, a part of the compression load is borne by the threaded portion. Therefore, the compression load acting on the top end portion of the male thread becomes smaller. It is considered that it is preferable to limit the axial movement amount of the male thread relative to the female thread when applying a compression load by making it difficult for the top end portion of the male thread to deform in a radially outward expanding manner.

[0025] The present disclosure is made based on the above insights.

[0026] The threaded joint of the present disclosure is preferably a threaded joint composed of a tubular male thread and a tubular female thread, and the male thread is screwed into the female thread to fasten the male thread and the female thread.

[0027] It can be provided that the male thread includes: an external thread provided on the outer periphery of the male thread and composed of a tapered thread whose diameter gradually decreases toward the top end side; a male internal sealing surface provided on the outer periphery of the male thread at a position closer to the top end side than the external thread; a convex head portion provided at a position closer to the top end side than the male internal sealing surface and having an outer peripheral surface that is smoothly continuous with the male internal sealing surface; a torque shoulder surface formed by the top end surface of the convex head portion; and a male external sealing surface provided on the outer periphery of the male thread at a position closer to the base end side than the external thread.

[0028] It can be set that the female coupling includes: an internal thread provided on the inner circumference of the female coupling and meshing with the external thread in the tightened state; a female internal sealing surface provided on the inner circumference of the female coupling and contacting the male internal sealing surface in the tightened state; a non-threaded portion having an inner circumferential surface that has a clearance relative to the outer circumferential surface of the convex head portion and is radially opposed to the outer circumferential surface of the convex head portion in the tightened state; a torque shoulder surface axially opposed to the torque shoulder surface of the male coupling and contacting the torque shoulder surface of the male coupling in the tightened state; and a female external sealing surface provided on the outer circumference of the female coupling and contacting the male external sealing surface in the tightened state.

[0029] It is preferable that the external thread and the internal thread are configured as follows: in the tightened state, when no axial compressive load is applied, a clearance is formed between the insertion surface of the external thread and the insertion surface of the internal thread, and when a predetermined axial compressive load acts on the threaded joint, due to the elastic deformation of the male coupling and the female coupling, the insertion surface of the external thread contacts the insertion surface of the internal thread, so that a part of the axial compressive load is transmitted between the insertion surface of the external thread and the insertion surface of the internal thread.

[0030] It is preferable that the male external sealing surface and the female external sealing surface have the following shape: if the male coupling tightened to the female coupling is pressed into the tip side relative to the female coupling due to an axial compressive load, the diameter of the female sealing surface is expanded. The taper angle of the male external sealing surface and / or the female external sealing surface can be larger than the thread taper angle of the external thread and the internal thread. For example, when the inclination degree of the thread cone is 1 / 6, the inclination degree of the cone of the external sealing surface can be set to 1 / 4. In addition, the inclination degree of the cone is the amount of diameter displacement relative to the axial length (diameter displacement amount / axial length). The taper angle is represented by arctan (inclination degree of the cone / 2).

[0031] Preferably, the shoulder angle defined as the angle between the straight line passing through the radially outer end and the radially inner end in the longitudinal section of the torque shoulder surface of the female coupling and the plane orthogonal to the pipe axis is 0° or more and less than 10°, where the case where the radially outer end is located on the tip side relative to the radially inner end is set as a positive angle.

[0032] According to the present disclosure, a compact threaded joint can be provided, which has excellent sealing performance against internal pressure and external pressure, excellent strength against compressive load, and can maintain the sealing performance against external pressure even when a repeated load is applied. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is an overall longitudinal sectional view showing the tightened state of the threaded joint for an oil well pipe according to the embodiment.

[0034] Figure 2 is an enlarged longitudinal sectional view near the outer seal portion of the threaded joint.

[0035] Figure 3 is an enlarged longitudinal sectional view showing the thread engagement state of the threaded joint.

[0036] Figure 4 is an enlarged longitudinal sectional view showing the vicinity of the tip of the male thread of the threaded joint.

[0037] Figure 5 is a graph showing the results of numerical analysis simulation by the elastoplastic finite element method and the relationship between the shoulder angle and the minimum value of the contact pressure evaluation value between the outer seal surfaces when applying a repeated combined load. Detailed implementation mode

[0038] The threaded joint of the present embodiment is a threaded joint composed of a tubular male thread and a tubular female thread having an opening for receiving the male thread, and the male thread is screwed into the female thread to fasten the male thread and the female thread. It is preferable that the male thread is provided at the end of a long pipe such as an oil well pipe. It is preferable that the female thread is provided at the end of a coupling or the end of other long pipes. In a preferred embodiment, the male thread is formed at the end of the long pipe, and the female thread is formed at the end of the coupling. Further, the long pipe and the coupling are preferably made of metal such as steel like stainless steel or nickel-based alloy.

[0039] The threaded joint includes: a pipe including a pipe body and the above-mentioned male thread provided at the end of the pipe body; and a tubular coupling for connecting the pipe to other pipes, and the coupling can include a pipe body and the above-mentioned female thread provided at the end of the pipe body. In this case, the outer diameter of the pipe body and the female thread of the coupling is preferably 100% or more and 105% or less of the outer diameter of the pipe body of the pipe, and the inner diameter of the pipe body of the coupling is preferably 90% or more and less than 100% of the inner diameter of the pipe body of the pipe. When the inner diameter of the pipe body of the coupling is made smaller than the inner diameter of the pipe body of the pipe, it is preferable to perform necking processing on the vicinity of the tip of the male thread (that is, the convex head portion described later) so that its inner peripheral surface becomes the same diameter as the inner peripheral surface of the pipe body of the coupling. In an oil well pipe, the inner diameter of the pipe body of the coupling can be made larger than the drift diameter specified by the API standard.

[0040] The male joint can have an external thread provided on the outer periphery of the male joint. It is preferable that the external thread is a tapered thread whose diameter gradually decreases toward the top side. The male joint can have a male joint internal sealing surface provided on the outer periphery of the male joint at a position closer to the top side than the external thread. The male joint can have a convex head portion provided at a position closer to the top side than the male joint internal sealing surface, and it is preferable that the convex head portion has an outer peripheral surface that is smoothly continuous with the male joint internal sealing surface. The male joint can have a torque shoulder surface formed by the top surface of the convex head portion. The male joint can have a male joint external sealing surface provided on the outer periphery of the male joint at a position closer to the base end side than the external thread.

[0041] The female joint can have an internal thread formed by a tapered thread provided on the inner periphery of the female joint. The internal thread is a tapered thread whose diameter gradually increases toward the open end side of the female joint and has a screw profile suitable for the external thread. The internal thread meshes with the external thread in the tightened state. The female joint can have a female joint internal sealing surface provided on the inner periphery of the female joint at a position closer to the top side of the male joint than the internal thread, and the female joint internal sealing surface contacts the male joint internal sealing surface in the tightened state. The female joint can have a threadless portion that has an inner peripheral surface that has a gap with respect to the outer peripheral surface of the convex head portion in the tightened state and is radially opposed to the outer peripheral surface of the convex head portion. The threadless portion is provided at a position closer to the top side of the male joint than the female joint internal sealing surface. The female joint can have a torque shoulder surface that is axially opposed to the torque shoulder surface of the male joint, and the torque shoulder surface contacts the torque shoulder surface of the male joint in the tightened state. That is, when in the tightened state, even when no axial compressive load is applied, the torque shoulder surfaces of the male joint and the female joint are in contact with each other. Preferably, the radially inner end portion of the torque shoulder surface of the female joint is an end portion having the inner peripheral surface of the collar of the female joint or the pipe body of the steel pipe. The female joint can have a female joint external sealing surface provided on the outer periphery of the female joint at a position closer to the open end side than the internal thread, and the female joint external sealing surface contacts the male joint external sealing surface in the tightened state. The female joint can also have an external convex head portion extending from the female joint external sealing surface toward the top side (open end side) of the female joint, and in this case, the external convex head portion becomes the open end portion of the female joint. It is preferable that a gap is formed between the inner peripheral surface of the external convex head portion and the outer peripheral surface of the male joint that faces the inner peripheral surface of the external convex head portion.

[0042] The above-mentioned external thread and internal thread can also be serrated threads, or can be the following wedge-shaped threads: the longitudinal cross-sectional shape is a dovetail shape, and the width of the thread tooth gradually narrows as it goes toward the top side along the helical direction of the thread, or can be other suitable threads.

[0043] The external thread and the internal thread can be configured in the following manner: in the tightened state, when no axial compression load is applied, the load surfaces of the external thread and the internal thread are in contact, and on the other hand, a gap is formed between the insertion surface of the external thread and the insertion surface of the internal thread. Preferably, the external thread and the internal thread can be configured in the following manner: in the tightened state, the bottom surface of the thread tooth of the external thread is in contact with the top surface of the thread tooth of the internal thread, and on the other hand, a gap is formed between the top surface of the thread tooth of the external thread and the bottom surface of the thread tooth of the internal thread. Instead, the external thread and the internal thread can also be configured in the following manner: the top surface of the thread tooth of the external thread is in contact with the bottom surface of the thread tooth of the internal thread, and on the other hand, a gap is formed between the bottom surface of the thread tooth of the external thread and the top surface of the thread tooth of the internal thread. In this way, the thread groove depth of the male thread or the female thread can be made shallower, and a larger dangerous cross-sectional area of the male thread or the female thread can be ensured. Therefore, the tensile load resistance performance of the threaded joint can be maximized.

[0044] Moreover, it is preferable to configure the external thread and the internal thread in the following manner: when a predetermined axial compression load acts on the threaded joint, due to the elastic deformation of the male thread and the female thread, the insertion surface of the external thread and the insertion surface of the internal thread are in contact, and a part of the axial compression load is transmitted between these insertion surfaces. In addition, the elastic deformation of the male thread and the female thread only requires that the overall fastening structure of the male thread and the female thread undergoes elastic deformation without yielding, and yielding can also occur locally, such as in the surface layer part of the bottom corner of the thread tooth.

[0045] The predetermined axial compression load is preferably a load at which the insertion surfaces of the external thread and the internal thread can be in contact with each other due to the elastic deformation of the male thread and the female thread. As an example of a design index, if the yield compression load of the pipe body of the steel pipe provided with the male thread is set as Ly and the joint efficiency of the threaded joint is set as JE, then the above axial compression load is preferably Lc = Ly × JE. Among them, the joint efficiency JE is the ratio of the smaller of the dangerous cross-sectional areas of the male thread A PCCS and the female thread A BCCS to the cross-sectional area Ap of the pipe body of the long pipe (that is, A PCCS / Ap, or A BCCS / Ap). This joint efficiency JE is preferably 75% or more.

[0046] As Figure 1 shown, the dangerous cross-sectional area A PCCS of the male thread is the cross-sectional area of the male thread at the position of the bottom of the thread tooth at the engagement end on the base end side of the external thread (that is, the pipe body side of the male thread) among the two ends of the engagement range between the external thread and the internal thread in the tightened state. The dangerous cross-sectional area A BCCSIt is the cross-sectional area of the female thread at the meshing end on the base end side of the internal thread (i.e., the pipe body side of the female thread) at both ends of the meshing range between the external thread and the internal thread in the tightened state. It is preferable that the dangerous cross-sectional areas of these male and female threads are the cross-sectional areas of the parts other than the cross-sectional areas of the thread teeth of the external thread and the internal thread. Additionally, it is preferable that at the time point when an axial compressive load smaller than the above-mentioned Lc acts, the insertion surfaces of the external thread and the internal thread start to contact each other due to the elastic deformation of the male and female threads.

[0047] It is preferable that the external sealing surface of the male thread and the external sealing surface of the female thread have the following shapes: when the male thread tightened to the female thread is slightly pressed into the tip side relative to the female thread due to the axial compressive load, the sealing surface of the female thread is expanded in diameter. For example, it is preferable that both the external sealing surface of the male thread and the external sealing surface of the female thread are in a conical shape where the diameter gradually decreases toward the tip side of the male thread. Additionally, it may be that the external sealing surface of the male thread is in a conical shape where the diameter gradually decreases toward the tip side of the male thread, and the external sealing surface of the female thread is in a convex curved surface shape that contacts the external sealing surface of the male thread. Additionally, it may be that the external sealing surface of the female thread is in a conical shape where the diameter gradually decreases toward the tip side of the male thread, and the external sealing surface of the male thread is in a convex curved surface shape that contacts the external sealing surface of the female thread. Moreover, it may be that both the external sealing surface of the male thread and the external sealing surface of the female thread are in a convex curved surface shape such that when the male thread is pressed into the tip side relative to the female thread, the sealing surface of the female thread is expanded in diameter. Moreover, at least one of the external sealing surface of the male thread and the external sealing surface of the female thread may also be a composite surface shape including a conical surface portion and a curved surface portion.

[0048] It is preferable that the radially outer end portion in the longitudinal cross-section of the torque shoulder surface of the female thread and the male thread is located at a position closer to the tip side than the radially inner end portion. Thereby, when an axial compressive load is applied, deformation of the convex head portion of the male thread toward the radially inner side can be prevented. Additionally, the shoulder angle defined as the angle between the straight line passing through the radially outer end portion and the radially inner end portion of the torque shoulder surface of the female thread and the male thread and the plane orthogonal to the pipe axis is preferably 0° or more and less than 10°. This shoulder angle is more preferably 7.5° or less. Further preferably, the shoulder angle is preferably 4.5° or more and 5° or less.

[0049] In the threaded joint according to the present embodiment, a convex head portion is provided between the internal sealing surface of the male thread and the torque shoulder surface of the male thread. Therefore, even if the shoulder is deformed due to an excessive compressive load, the influence on the contact state between the internal sealing surfaces can be reduced, and the internal sealing performance can be maintained when an excessive compressive load is applied.

[0050] In addition, a convex head portion is provided at the top end of the male joint, and the top end surface of the convex head portion constitutes a torque shoulder surface. Therefore, there is no need to accommodate the open end portion of the female joint within the wall thickness of the pipe body of the long pipe provided with the male joint (hereinafter referred to as the "male joint pipe body") as disclosed in Patent Document 2. By making the outer diameter of the open end portion of the female joint slightly larger than the outer diameter of the male joint pipe body, it is possible to ensure the wall thickness of the female joint near the outer sealing surface and the wall thickness of the male joint near the inner sealing surface, and to ensure a relatively large radial width for the tapered threads constituting the external thread and the internal thread. Moreover, there is no need to make the diameter of the inner peripheral surface of the top end portion of the male joint smaller than the diameter of the inner peripheral surface of the pipe body of the long pipe or the coupling provided with the female joint (hereinafter referred to as the "female joint pipe body"), and these diameters can be made equal in such a way that no large step is generated between the inner peripheral surface of the top end portion of the male joint and the inner peripheral surface of the female joint pipe body.

[0051] In addition, in the tightened state, when no axial compression load is applied, a gap is formed between the insertion surface of the external thread and the insertion surface of the internal thread. Therefore, it is difficult for adhesion to occur between the external thread and the internal thread during the assembly process.

[0052] Moreover, when a predetermined axial compression load is applied, a part of the compression load is borne by the insertion surface of the internal thread of the female joint. Therefore, even if the cross-sectional area of the convex head portion of the male joint provided with the torque shoulder surface is relatively small, the required compression load resistance performance can be obtained.

[0053] In addition, if a part of the compression load acts on the insertion surface of the internal thread, internal stress is generated that deforms the female joint in such a way that the diameter near the outer sealing surface of the female joint is reduced. However, by setting the shoulder angle of the torque shoulder surfaces of the male joint and the female joint to a predetermined angle in the range of 0° or more and less than 10°, the expansion deformation of the convex head portion in the radial outward direction along the torque shoulder surface can be suppressed. By suppressing the deformation of the convex head portion, the axial movement amount of the male joint relative to the female joint caused by the compression load can also be suppressed, and the forced expansion amount of the outer sealing surface of the female joint caused by the outer sealing surface of the male joint can be suppressed. As a result, it is possible to prevent relatively large damage from accumulating in the female joint when the compression load is applied, and the outer sealing performance can also be maintained when the state changes to one where an axial tensile load is applied later.

[0054] In addition, in a threaded joint, generally, in order to prevent adhesion and the like, surface treatment such as chemical conversion treatment and plating is mostly applied to the threaded portions and the surfaces of the sealing faces of either or both of the male thread and the female thread. In the case of an integral-type threaded joint, it is necessary to perform surface treatment on the male thread and the coupling provided at the end of the long pipe, and large-scale equipment is required. In addition, in an integral-type threaded joint, generally, before forming the female thread by cutting, a tube expanding process is mostly performed from the tube end to a predetermined range in the axial direction by cold working of a metal long pipe. This not only requires large-scale equipment but also increases the processing steps, resulting in an increase in the processing cost of the female thread.

[0055] On the other hand, in the case where the threaded joint of the present disclosure is configured as a coupling-type compact threaded joint, since the coupling is short, surface treatment can be easily performed. Moreover, by prefabricating a coupling tube blank having a predetermined outer diameter and inner diameter, the tube expanding process of the tube blank can be omitted. In addition, it has the following advantages: by making the inner diameter of the tube body of the coupling slightly smaller than the inner diameter of the long pipe, it is easy to ensure the radial width of the torque shoulder surface.

[0056] 〔Structure of threaded joint for oil well pipe〕

[0057] Refer to Figure 1 FIG., the threaded joint 1 for an oil well pipe of the present embodiment is a coupling-type threaded joint, which is composed of a long oil well pipe P having a male thread 2 in a tubular shape and a short coupling C having a female thread 3 in a tubular shape. It is preferable that both the oil well pipe P and the coupling C are made of steel. The coupling C is provided with female threads 3 at both axial ends thereof, and a pair of oil well pipes P are connected by the coupling C.

[0058] The male thread 2 extends axially from the end of the pipe body P of the oil well pipe P body toward the tip side of the male thread 2 ( Figure 1 right side in FIG.). As also shown in detail in Figures 2 to 4 FIG., on the outer periphery of the male thread 2, a male external sealing surface 21, an external thread 22 composed of a tapered thread whose diameter gradually decreases toward the tip side, a male internal sealing surface 23, and a convex head portion 24 are sequentially provided from the pipe body P body side toward the tip side. The top surface of the convex head portion 24 functions as a torque shoulder surface 25.

[0059] In the threaded joint 1 of the illustrated embodiment, as shown in Figure 2 FIG., the male external sealing surface 21 is composed of a tapered surface whose diameter gradually decreases toward the tip side. The inclination degree of the taper of the male external sealing surface 21 is 1 / 4. As shown in Figure 3As shown, the external thread 22 is composed of a thread having a thread tooth with a trapezoidal longitudinal cross-sectional shape, and its load surface 22L has a negative thread profile half angle. The top surface and the bottom surface of the thread tooth are formed in an inclined shape with a gradually decreasing diameter as going toward the top side in the longitudinal cross-section. The top end portion of the external thread 22 is formed as an incomplete thread 22A as shown in Figure 4 The internal sealing surface 23 of the male joint is composed of a conical surface with a gradually decreasing diameter as going toward the top side. The convex head portion 24 has an outer peripheral surface that is smoothly continuous with the internal sealing surface 23 of the male joint. In addition, as shown in Figure 1 In the region midway between the top end portion of the male joint 2 and the region where the external thread 22 is provided, a necking process is performed on the male joint 2. As a result, the diameters of the inner peripheral surface of the portion where the internal sealing surface 23 of the male joint is provided and the inner peripheral surface of the convex head portion 24 are slightly smaller than the diameter of the inner peripheral surface of the male joint pipe body P body .

[0060] The female joint 3 extends axially from the end portion of the pipe body C of the coupling C body toward the top side of the female joint 3 (the left side in Figure 1 ). In this specification, the top side of the female joint 3 is sometimes referred to as the open end side. On the outer periphery of the female joint 3, an outer convex head portion 30, a female external sealing surface 31 corresponding to the male external sealing surface 21, an internal thread 32 corresponding to the external thread 22, a female internal sealing surface 33 corresponding to the male internal sealing surface 23, a non-threaded portion 34 corresponding to the convex head portion 24, and a torque shoulder surface 35 corresponding to the torque shoulder surface 25 of the male joint 2 are sequentially provided from the top side of the female joint toward the pipe body C body side of the coupling C.

[0061] The outer convex head portion 30 is a portion that extends from the female external sealing surface 31 toward the top side of the female joint 3, and the outer convex head portion 30 forms the open end portion of the female joint 3. A gap is formed between the inner peripheral surface of the outer convex head portion 30 and the outer peripheral surface of the male joint that faces the inner peripheral surface of the outer convex head portion 30.

[0062] The female external sealing surface 31 is composed of a convex curved surface that protrudes radially inward.

[0063] The internal thread 32 is composed of a tapered thread suitable for the external thread. The thread profile half angle of the load surface of the external thread 22 and the internal thread in the illustrated embodiment is -5°, and the thread profile half angle of the insertion surface is 15°. The negative thread profile half angle of the load surface means that the top of the thread tooth overhangs the base of the thread tooth in the load surface. In the illustrated embodiment, in Figure 3In the shown tightened state, the load surfaces of the external thread 22 and the internal thread 32 are in contact, but a minute gap S1 is formed between the insertion surfaces of the external thread 22 and the internal thread 32. The axial dimension of this gap S1 is preferably about 0.1 mm, for example. The gap S1 can be set to the following size: If the above-mentioned axial compressive load Lc acts on the male joint 2 and the female joint 3 in the tightened state, the male joint 2 is pressed into the female joint 3 and as in Figure 3 The insertion surfaces of the external thread 22 and the internal thread 32 are shown in phantom lines to be in contact with each other. Further, in the tightened state, the bottom surface of the thread tooth of the external thread 22 is in contact with the top surface of the thread tooth of the internal thread 32, but a gap S2 is formed between the top surface of the thread tooth of the external thread 22 and the bottom surface of the thread tooth of the internal thread 32.

[0064] As Figure 4 shown, the internal sealing surface 33 of the female joint is formed by a convex curved surface protruding radially inwards.

[0065] The non-threaded portion 34 and the torque shoulder surface 35 form a recess in the inner circumference of the female joint 2 for holding the convex head portion 24 of the male joint 2. The inner circumferential surface of the non-threaded portion 34 is a cylindrical surface that is smoothly continuous with the internal sealing surface 33 of the female joint, and a gap is formed between the inner circumferential surface of the non-threaded portion 34 and the convex head portion 24.

[0066] The torque shoulder surface 35 is axially opposed to the torque shoulder surface 25 of the male joint 2. These torque shoulder surfaces 25, 35 are preferably formed by substantially flat annular surfaces. That is, the longitudinal cross-sectional shape of the torque shoulder surfaces 25, 35 is preferably set to a single straight line shape that is substantially orthogonal to the pipe axis. Moreover, by making the shoulder angles θ of the torque shoulder surfaces 25, 35 of the male joint 2 and the female joint 3 equal, it is possible to prevent the contact pressure from becoming locally excessive during the tightening operation and causing adhesion.

[0067] The radially outer ends of the torque shoulder surfaces 25, 35 protrude slightly towards the top end side of the male joint 2 relative to the radially inner ends. The shoulder angle θ, which is defined as the angle between the straight line passing through the radially outer end and the radially inner end of the torque shoulder surfaces 25, 35 and the plane orthogonal to the pipe axis, is 5° in the illustrated embodiment.

[0068] This disclosure can be applied not only to the coupling type but also to the integral type of threaded joints. Further, each thread is preferably a trapezoidal thread, an API round thread, an API buttress thread, or a wedge thread, etc. In addition, the torque shoulder surfaces of the male joint and the female joint can also be respectively formed by two or more surfaces having different angles with respect to the plane orthogonal to the pipe axis. Furthermore, this disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the claims.

[0069] Examples

[0070] To confirm the effect of the threaded joint for oil well pipes of the present embodiment, a numerical analysis simulation based on the elastoplastic finite element method was carried out.

[0071] <Test Conditions>

[0072] For Figures 1 to 4 the shown coupling type threaded joint for oil well pipes, multiple specimens (analysis models) with only the shoulder angle θ of the torque shoulders 25 and 35 changed were fabricated, and the elastoplastic finite element method analysis was carried out for each specimen to compare the difference in external sealing performance between the external sealing surfaces 21 and 31. The shoulder angle θ of each specimen was set to 0.0°, 1.0°, 2.5°, 4.0°, 4.5°, 5.0°, 5.5°, 6.0°, 7.5°, 10°, 15°, 20°.

[0073] The following shows the test conditions common to all specimens.

[0074] <Dimensions of Oil Well Pipe>

[0075] Outer diameter of the pipe body of the oil well pipe: 355.6 mm, wall thickness of the pipe body: 20.62 mm

[0076] <Grade of Oil Well Pipe>

[0077] Oil well pipe material Q125 according to API standard (low alloy steel with a nominal yield stress of 125 ksi)

[0078] In addition, in the finite element analysis, a model in which each specimen was modeled in the following manner was used: the material was set as an isotropic hardening elastoplastic body, the elastic modulus was set to 210 GPa, and the yield strength was 125 ksi (861.9 MPa) as the 0.2% yield strength.

[0079] <Thread Profile>

[0080] Thread pitch: 6.35 mm, thread profile half angle of the load surface: -5°, thread profile half angle of the insertion surface: 15°, clearance S1 between insertion surfaces: 0.09 mm, thread taper: 1 / 6

[0081] <Coupling Profile>

[0082] Outer diameter: 365.3 mm (102.7% of the outer diameter of the pipe body of the oil well pipe)

[0083] <Joint Efficiency>

[0084] Joint efficiency JE = A BCCS / A P = 79.3%

[0085] <Evaluation Method>

[0086] First, after performing an analysis of simulated fastening on each specimen, a repeated combined load simulating the Series A test specified in ISO13679:2011 was applied, and an evaluation value obtained by dividing the contact force per circumferential unit length between the outer sealing surfaces 21 and 31 under each load condition of the repeated combined load by the external pressure at this time was calculated. The minimum evaluation value among these evaluation values was extracted for each specimen, and the minimum evaluation value was used as an index for evaluating the sealing performance, and comparison and evaluation were performed. The larger this minimum evaluation value, the more excellent the external pressure sealing performance.

[0087] <Evaluation Results>

[0088] As is clear from Figure 5 the chart shown, in specimens with a shoulder angle of 10° or more, the minimum evaluation value decreased to less than 6.0, and the minimum evaluation values of specimens with a shoulder angle of less than 10° were all greater than 6.5, obtaining good results. In particular, in specimens with a shoulder angle of 4.5° and 5.0°, extremely good results with a minimum evaluation value greater than 8.0 were obtained. Therefore, it was confirmed that the optimal range of the shoulder angle in the collar-type compact threaded joint of the present embodiment is 4.5° or more and 5.0° or less.

[0089] The reason for obtaining good results when the shoulder angle is less than 10° is that, as described above, when simple compression is not possible, the amount of press-in of the male external sealing surface relative to the female external sealing surface becomes smaller, and the internal stress that causes the open end of the female thread to deform by reducing the diameter radially inward becomes smaller, thereby reducing the damage accumulated near the female external sealing surface.

[0090] In addition, it is considered that the reason why the shoulder angle is 4.5° - 5° and the external pressure sealing performance reaches the maximum is that when it is less than 4.5°, due to the compressive load, the radially inner end side of the female shoulder deforms in an open manner, and thus cannot support the convex head portion of the male thread.

[0091] Explanation of Reference Numerals

[0092] 1, threaded joint; P, pipe; P body 、pipe body; 2, male thread; 21, male external sealing surface; 22, external thread; 23, male internal sealing surface; 24, convex head portion; 25, torque shoulder surface; C, collar; C body 、pipe body; 3, female thread; 31, female external sealing surface; 32, internal thread; 33, female internal sealing surface; 34, non-threaded portion; 35, torque shoulder surface.

Claims

1. A threaded joint, which is composed of a tubular male thread and a tubular female thread. The male thread is screwed into the female thread to fasten the male thread and the female thread. In this threaded joint, The male connector includes: an external thread provided on the outer periphery of the male connector and formed of a tapered thread whose diameter gradually decreases toward the top side; a male connector inner sealing surface provided on the outer periphery of the male connector at a position closer to the top side than the external thread; a convex head provided at a position closer to the top side than the male connector inner sealing surface and having an outer peripheral surface that is smoothly continuous with the male connector inner sealing surface; a torque shoulder surface, which is formed by the top end surface of the convex head portion; and an outer sealing surface of the male thread, which is provided on the outer periphery of the male thread at a position closer to the base end side than the outer thread, the female thread includes: an internal thread, which is provided on the inner periphery of the female thread and meshes with the outer thread in the fastened state; an inner sealing surface of the female thread, which is provided on the inner periphery of the female thread and contacts the inner sealing surface of the male thread in the fastened state; a non-threaded portion, which has an inner peripheral surface that has a gap with respect to the outer peripheral surface of the convex head portion in the fastened state and is radially opposed to the outer peripheral surface of the convex head portion, a torque shoulder surface, which is axially opposed to the torque shoulder surface of the male thread and contacts the torque shoulder surface of the male thread in the fastened state; and an outer sealing surface of the female thread, which is provided on the outer periphery of the female thread and contacts the outer sealing surface of the male thread in the fastened state, the outer thread and the inner thread are configured as follows: in the fastened state, when no axial compression load is applied, a gap is formed between the insertion surface of the outer thread and the insertion surface of the inner thread, and if a predetermined axial compression load acts on the threaded joint, then due to the elastic deformation of the male thread and the female thread, the insertion surface of the outer thread contacts the insertion surface of the inner thread, so that a part of the axial compression load is transmitted between the insertion surface of the outer thread and the insertion surface of the inner thread, the outer sealing surface of the male thread and the outer sealing surface of the female thread have the following shape: if the male thread fastened to the female thread is pressed into the top end side with respect to the female thread due to the axial compression load, the outer sealing surface of the female thread is expanded in diameter, the shoulder angle, which is defined as the angle between the straight line passing through the radially outer end portion and the radially inner end portion in the longitudinal section of the torque shoulder surface of the female thread and the plane orthogonal to the pipe axis, is 0° or more and less than 10°. Here, the case where the radially outer end portion is located at a position closer to the top end side than the radially inner end portion is set as a positive angle.

2. The threaded joint according to claim 1, wherein the shoulder angle is 7.5° or less.

3. The threaded joint according to claim 1, wherein the shoulder angle is 4.5° or more and 5° or less.

4. The threaded joint according to claim 1, 2 or 3, wherein the female thread has the following structure: internal stress is generated due to the load acting on the insertion surface of the internal thread, which causes the female thread to deform in a manner of shrinking in diameter near the outer sealing surface of the female thread.

5. The threaded joint according to any one of claims 1 to 4, wherein the threaded joint includes: a pipe, which includes a pipe body and the male thread provided at the end of the pipe body; and a tubular coupling, which is used to connect the pipe to other pipes, and this coupling includes a pipe body and the female thread provided at the end of the pipe body, The outer diameter of the pipe body of the coupling and the female thread is more than 100% and less than or equal to 105% of the outer diameter of the pipe body of the pipe, and the inner diameter of the pipe body of the coupling is more than 90% and less than 100% of the inner diameter of the pipe body of the pipe.

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