Invention name: Threaded joint
Technical field
[0001]
This disclosure relates to threaded joints used to connect steel pipes.
Background technology
[0002]
In oil wells, natural gas wells, etc. (hereinafter collectively referred to as "oil wells"), in order to mine underground resources, casings that construct multiple well walls and oil and gas placed in the casings Tubing is used to produce. These casings and tubing are made by sequentially connecting a large number of steel pipes, and a threaded joint is used for the connection. Steel pipes used in oil wells are also called oil well pipes.
[0003]
The types of threaded joints are roughly divided into integral type and coupling type.
[0004]
In the integral type, the well pipes are directly connected to each other. Specifically, a female threaded portion is provided at one end of the well pipe, and a male threaded portion is provided at the other end. Be concatenated.
[0005]
In the coupling type, the well pipes are connected to each other via a tubular coupling. Specifically, female threaded portions are provided at both ends of the coupling, and male threaded portions are provided at both ends of the well pipe. Then, one male threaded portion of one oil country tubular goods screw is screwed into one female threaded portion of the coupling, and one male threaded portion of the other oil country tubular goods is screwed into the other female threaded portion of the coupling. Are concatenated. That is, in the coupling type, of the pair of pipe materials to be connected, one pipe material is an oil well pipe and the other pipe material is a coupling.
[0006]
Generally, the end of the well pipe on which the male thread portion is formed is called a pin because it contains an element inserted into the female thread portion formed on the oil well pipe or the coupling. The end of the well pipe or coupling in which the female thread is formed is referred to as a box because it contains an element that accepts the male thread formed in the well pipe.
[0007]
In recent years, further development of high temperature and high pressure deep wells has progressed. In deep wells, the maximum outer diameter of the joint, that is, the outer diameter of the box, is about the same as the outer diameter of the main body of the oil well pipe, because the number of casing stages needs to be increased due to the complexity of the depth distribution of the formation pressure. Slim type threaded joints may be used. A threaded joint whose box outer diameter is approximately equal to the outer diameter of the pipe body of the oil country tubular goods is also called a flush type threaded joint. Further, a threaded joint having a box outer diameter of less than approximately 108% of the outer diameter of the pipe body of the oil country tubular goods is also referred to as a semi-flash type threaded joint. Not only are these flush-type and semi-flash-type threaded joints required to have high strength and sealing performance, but also because the threaded structure and the sealing structure are arranged within a limited pipe wall thickness, each part is strict. Dimensional restrictions are imposed.
[0008]
In flush type and semi-flash type threaded joints with large dimensional restrictions, an intermediate shoulder surface is provided in the middle of the joint in the axial direction, and a male threaded portion and a female threaded portion are formed by two-step threads in which threaded portions are arranged before and after the intermediate shoulder surface. Fitting designs are often adopted. Such a threaded joint having a two-step screw structure is disclosed in, for example, Patent Documents 1 and 2 below. Further, for example, the following Patent Documents 3 and 4 disclose screw joints having a two-stage thread structure provided with hook-type intermediate shoulder structures that are fitted to each other instead of the intermediate shoulder surfaces.
[0009]
In these two-step threaded threaded joints, as mentioned in Patent Document 1, a dangerous cross section (PICCS and BICCS) exists in the middle of the joint portion.
[0010]
The dangerous cross section (CCS) is the cross section of the joint portion that has the smallest area that can withstand a tensile load in the fastened state. When an excessive axial tensile load is applied, the possibility of fracture near the dangerous cross section increases.
[0011]
In the case of a threaded joint with a general one-step thread structure, the propagation of the tensile load from the pin to the box is distributed axially over the entire thread fitting range. Therefore, the cross-sectional part of the pin on which all the tensile load acts is on the tube body side of the pin from the screw fitting range, and the cross-section part of the box on which all the tensile load acts is on the tube body side of the box rather than the screw fitting range. It becomes. Of the cross sections on which all of the tensile load acts, the one with the smallest cross section is the dangerous cross section. That is, among the meshing ends of the male threaded portion and the female threaded portion in the fastened state, the cross section of the box including the thread valley bottom position of the female threaded portion corresponding to the meshing end on the tip end side of the male threaded portion is the box danger cross section (BCCS). .. Further, among the meshing ends of the male threaded portion and the female threaded portion in the fastened state, the cross section of the pin including the thread valley bottom position of the male threaded portion corresponding to the meshing end on the pipe body side of the male threaded portion is the pin danger cross section (PCCS). Become. Of the box dangerous cross section and the pin dangerous cross section, the smaller area is the dangerous cross section (CCS) of the threaded joint. The ratio of the area of ​​the dangerous cross section to the cross-sectional area of ​​the pipe body of the oil well pipe is called the joint efficiency, and is widely used as an index of the tensile strength of the joint portion with respect to the tensile strength of the oil well pipe body.
[0012]
The above-mentioned box dangerous cross section and pin dangerous cross section also exist in a threaded joint having a two-step thread structure. Further, in the threaded joint having a two-step screw structure, as described above, there is a portion where the cross-sectional area of ​​the joint that can withstand the tensile load becomes small also in the axial intermediate portion of the joint portion. That is, in a threaded joint having a two-step thread structure, there is a section without screw fitting in the middle in the axial direction. In this non-screwed section, the tensile load shared by the pins and the box propagates axially without increasing or decreasing. Therefore, the cross section of the pin having the smallest cross section in the section without screw fitting is the pin intermediate dangerous cross section (PICCS), and the cross section of the box having the smallest cross section in the section without screw fitting is the box intermediate dangerous cross section (PICCS). BICCS). In order to prevent the occurrence of breakage in the intermediate portion of the joint, it is preferable to make the sum of the area of ​​the pin intermediate dangerous cross section and the area of ​​the box intermediate dangerous cross section as large as possible.
Prior art literature
Patent documents
[0013]
Patent Document 1: Japanese Patent Application Laid-Open No. 2013-536339
Patent Document 2: Japanese Unexamined Patent Publication No. 2002-357287
Patent Document 3: Japanese Patent Application Laid-Open No. 7-504483
Patent Document 4: Japanese Patent Application Laid-Open No. 2013-51854
Outline of the invention
Problems to be solved by the invention
[0014]
However, in a threaded joint with a two-step thread structure, an intermediate shoulder surface is provided in the section where there is no thread fitting. In order to improve the torque resistance performance, it is necessary to secure the radial dimensions of the intermediate shoulder surfaces and increase the contact area between the intermediate shoulder surfaces. As a result, it is difficult to secure a large cross-sectional area of ​​the pin intermediate dangerous cross section and the box intermediate dangerous cross section in the flush type and semi-flash type two-stage threaded screw joints.
[0015]
In addition, the pin intermediate dangerous cross section and the box intermediate dangerous cross section exist at positions close to the intermediate shoulder surface. Since the cross-sectional area of ​​the pin and the box changes abruptly before and after the intermediate shoulder surface, large distortion is likely to occur in the pin intermediate dangerous cross section and the box intermediate dangerous cross section existing in the vicinity thereof.
[0016]
Further, in the conventional threaded joint, as shown in Patent Documents 1 and 2, the base portion of the intermediate shoulder surface is chamfered from the viewpoint of securing the contact area between the intermediate shoulder surfaces and securing the pipe wall thickness in the vicinity of the intermediate shoulder surface. The diameter of the part is made as small as possible. Therefore, it is difficult to process the intermediate shoulder surface.
[0017]
Note that Patent Document 2 discloses a threaded joint in which an annular relief that gives flexibility to expansion or bending of the threaded joint portion is formed. This annular relief is formed by an annular groove provided on the outer peripheral surface of the pin and the inner peripheral surface of the box in the vicinity of the intermediate shoulder. This annular groove is provided separately from the intermediate shoulder surface and is not related to the workability of the intermediate shoulder. Further, Patent Document 2 does not mention the fracture in the intermediate dangerous cross section when a tensile load is applied.
[0018]
Further, the hook-shaped intermediate shoulder structure disclosed in Patent Documents 3 and 4 has a complicated structure, and the workability is further deteriorated.
[0019]
The present disclosure prevents a threaded joint having a two-step thread structure including an intermediate shoulder surface from breaking near a pin intermediate dangerous cross section and / or a box intermediate dangerous cross section when a tensile load is applied, and also prevents the intermediate shoulder. The purpose is to improve productivity by making the surface easier to process.
Means to solve problems
[0020]
The threaded joint according to the present disclosure is a threaded joint composed of a tubular pin and a tubular box, and the pin is screwed into the box to fasten the pin and the box. On the outer circumference of the pin, a first male screw, a second male screw that is axially separated from the first male screw and has a smaller diameter than the first male screw, and the first male screw and the second male screw are provided. An intermediate shoulder surface formed by a step portion located between the intermediate shoulder surfaces and a first peripheral surface formed by the outer peripheral surface of the pin between the intermediate shoulder surface and the second male screw are provided. On the inner circumference of the box, a first female screw to which the first female screw fits in the fastened state, a second female screw to which the second male screw fits in the fastened state, the first female screw and the second female screw are formed. It is composed of an intermediate shoulder surface that is in contact with the intermediate shoulder surface of the pin in the fastened state, and an inner peripheral surface of the box between the intermediate shoulder surface and the first female screw. A second peripheral surface is provided. One of the first peripheral surface and the second peripheral surface has a curved surface smoothly continuous with the intermediate shoulder surface related to the peripheral surface as at least a part of the inner wall surface of the groove. A directional groove is provided.
The invention's effect
[0021]
According to the present disclosure, in a threaded joint having a two-step thread structure including an intermediate shoulder surface, it is prevented from breaking near the pin intermediate dangerous cross section or the box intermediate dangerous cross section when a tensile load is applied, and the intermediate shoulder is prevented. Productivity can be improved by making the surface easier to process.
A brief description of the drawing
[0022]
FIG. 1 is a vertical cross-sectional view showing a fastening state of a threaded joint for steel pipe according to an embodiment.
[Fig. 2] Fig. 2 is an enlarged vertical sectional view of a main part of a threaded joint for a steel pipe.
FIG. 3 is a cross-sectional view for explaining a profile in the vicinity of an intermediate shoulder of a pin and a box.
FIG. 4 is a side view of a cutting tip blade for machining an intermediate shoulder surface.
FIG. 5 is a process diagram showing a processing process of an intermediate shoulder surface.
FIG. 6A is a graph showing the equivalent plastic strain generated in the vicinity of the pin intermediate dangerous cross section when a simple tensile load is applied to the specimens # 1 and # 2.
[FIG. 6B] FIG. 6B is a graph showing the equivalent plastic strain generated in the vicinity of the pin intermediate dangerous cross section when the specimens # 1 and # 2 are repeatedly loaded.
6C is a cross-sectional view of the bottom of the second male thread near the pin intermediate danger cross section, showing the strain measurement positions at each point on the horizontal axis of the graphs of FIGS. 6A and 6B.
[FIG. 7A] FIG. 7A is a graph showing the equivalent plastic strain generated in the vicinity of the box intermediate dangerous cross section when a simple tensile load is applied to the specimens # 1 and # 2.
[FIG. 7B] FIG. 7B is a graph showing the equivalent plastic strain generated in the vicinity of the box intermediate dangerous cross section when the specimens # 1 and # 2 are repeatedly loaded.
FIG. 7C is a cross-sectional view of the bottom of the thread valley of the first female thread near the box intermediate danger cross section, showing the strain measurement positions at each point on the horizontal axis of the graphs of FIGS. 7A and 7B.
FIG. 8A is a graph showing the equivalent plastic strain generated in the vicinity of the pin intermediate dangerous cross section when a simple tensile load is applied to the specimens # 3 and # 4.
[FIG. 8B] FIG. 8B is a graph showing the equivalent plastic strain generated in the vicinity of the pin intermediate dangerous cross section when the specimens # 3 and # 4 are repeatedly loaded.
FIG. 9A is a graph showing the equivalent plastic strain generated in the vicinity of the box intermediate dangerous cross section when a simple tensile load is applied to the specimens # 3 and # 4.
[FIG. 9B] FIG. 9B is a graph showing the equivalent plastic strain generated in the vicinity of the box intermediate dangerous cross section when the specimens # 3 and # 4 are repeatedly loaded.
Embodiment for carrying out the invention
[0023] The threaded joint according to the present embodiment is composed of a tubular pin and a tubular box. The pin and the box are fastened by screwing the pin into the box. The pin may be provided at the end of a steel pipe such as an oil well pipe. The box may be provided at the end of the coupling or at the end of another steel pipe. The oil country tubular goods pipe and the coupling may be made of a metal such as stainless steel or a nickel-based alloy.
[0024]
On the outer circumference of the pin, it is located between the first male screw, the second male screw which is separated from the first male screw in the axial direction and has a smaller diameter than the first male screw, and the first male screw and the second male screw. An intermediate shoulder surface formed by a step portion and a first peripheral surface formed by an outer peripheral surface of a pin between the intermediate shoulder surface and the second male screw may be provided. The intermediate shoulder surface may be composed of the side surface of the step portion (that is, the end surface facing the tip side in the axial direction). The first male screw and the second male screw can be composed of a tapered screw whose diameter gradually decreases toward the axial tip side of the pin. In this case, the fact that the diameter of the second male screw is smaller than that of the first male screw means that the diameter of the base end portion of the second male screw is smaller than the diameter of the tip portion of the first male screw.
[0025]
Further, the outer pin outer sealing surface can be provided on the outer peripheral side of the pin on the base end side of the first male screw, and the inner pin inner sealing surface can be provided on the outer peripheral side of the pin on the tip end side of the second male screw. A pin intermediate sealing surface may be provided on the outer circumference of the pin between the intermediate shoulder surface and the first male screw, or between the intermediate shoulder surface and the second male screw. One or more of these sealing surfaces may be provided depending on the required sealing performance and the joint structure.
[0026]
The inner circumference of the box is located between the first female screw to which the first female screw fits in the fastened state, the second female screw to which the second male screw fits in the fastened state, and the first female screw and the second female screw. An intermediate shoulder surface formed by a step portion and a second peripheral surface formed by an inner peripheral surface of the box between the intermediate shoulder surface and the first female screw may be provided. The intermediate shoulder surface of the box may be composed of the side surfaces of the stepped portion. The intermediate shoulder surface of the box contacts the intermediate shoulder surface of the pin in the fastened state. The 1st and 2nd female threads have a thread profile that matches the thread profile of the 1st and 2nd male threads, and gradually become smaller in diameter toward the axial tip side of the box (that is, the axial base end side of the pin). It can be configured with a tapered screw.
[0027]
The male and female threads may be buttress threads, and are wedge-shaped threads having a dovetail shape in vertical cross section and a thread width gradually narrowing toward the tip side along the spiral direction of the screw. It may be an appropriate screw.
[0028]
Further, a sealing surface corresponding to the sealing surface provided on the outer periphery of the pin can be provided on the inner circumference of the box. That is, when the pin outer seal surface is provided, the box outer seal surface that comes into contact with the pin outer seal surface in the fastened state can be provided. When the inner seal surface of the pin is provided, the inner seal surface of the box that comes into contact with the inner seal surface of the pin in the fastened state can be provided. When the pin intermediate seal surface is provided, a box intermediate seal surface that comes into contact with the pin intermediate seal surface in the fastened state can be provided. A predetermined amount of interference in the radial direction is set between the sealing surfaces that come into contact with each other, and when they are fitted together, they are brought into close contact with each other by the elastic restoring force that tries to return to the original diameter, thereby demonstrating the sealing performance. Will be done.
[0029]
The intermediate shoulder surface of the pin and the box may be a flat surface orthogonal to the tube axis, or may be a tapered surface having a tapered bus slightly inclined with respect to a straight line orthogonal to the tube axis in the cross section. .. Further, the intermediate shoulder surface of the pin and the box may be a single surface over substantially the entire radial width of the step.
[0030]
One of the first peripheral surface and the second peripheral surface described above has a curved surface smoothly continuous with the intermediate shoulder surface related to the peripheral surface as at least a part of the inner wall surface in the groove in the first circumferential direction. Grooves can be provided. The first circumferential groove has a radial groove depth. In the conventional structure without this circumferential groove, the rigidity of the part near the intermediate shoulder surface of the pin and the box is relatively high, while the pin intermediate danger cross section and the box intermediate danger cross section existing near the intermediate shoulder surface are relatively high. Due to the low rigidity of the pin, a large strain exceeding the elastic region occurs in the vicinity of the pin intermediate dangerous cross section and the box intermediate dangerous cross section, and the fracture is likely to occur. On the other hand, in the structure of the present embodiment, the extensibility due to the tensile load of the portion is improved by providing the first circumferential groove in the portion where the pipe wall thickness is sharply thinned by the step portion constituting the intermediate shoulder surface. It is possible to suppress the amount of strain generated in the pin intermediate dangerous cross section or the box intermediate dangerous cross section. Further, by smoothly continuing the curved surface forming the first circumferential groove to the corresponding intermediate shoulder surface, the stress concentration in the first circumferential groove can be relaxed. Further, even if the radius of curvature of the curved surface is relatively large, the contact area between the intermediate shoulder surfaces can be secured by fitting all or a part of the curved surface within the groove depth. Further, by increasing the radius of curvature of the curved surface, it is possible to use a cutting tip having a larger radius of curvature than before as a cutting tip for cutting the intermediate shoulder surface and each threaded portion, and per rotation of lathe processing. The amount of axial advance of can be increased. As a result, the life of the cutting tip is shortened, and the productivity of the pin and the box is improved.
[0031]
The other peripheral surface of the first peripheral surface and the second peripheral surface described above has a second peripheral surface having a curved surface smoothly continuous with the intermediate shoulder surface related to the peripheral surface as at least a part of the inner wall surface of the groove. A directional groove can be provided. The second circumferential groove has a radial groove depth. By providing both the pin and the box with a circumferential groove continuous with the intermediate shoulder surface, the above-mentioned advantages can be obtained in both the pin intermediate dangerous cross section and the box intermediate dangerous cross section. The cross-sectional shape and size of the second circumferential groove may be the same as that of the first circumferential groove.
[0032]
Preferably, the first circumferential groove and / or the second circumferential groove can be an annular groove over the entire circumference of the pin or box. This will further improve productivity.
[0033]
Preferably, the radius of curvature of the curved surface of the first circumferential groove is equal to the radius of curvature of the curved surface of the second circumferential groove. This makes it possible to machine the first and second circumferential grooves using a common cutting tip.
[0034]
The first circumferential groove may be provided on the first peripheral surface. According to this, it is possible to prevent breakage in the intermediate dangerous cross section of the pin and improve the workability of the intermediate shoulder surface of the pin.
[0035]
When the pin is provided with the first circumferential groove, the first peripheral surface is further provided with an unthreaded portion located between the first circumferential groove and the second male thread and having an axial length. Can be done. The threadless portion may have an outer peripheral surface having an outer diameter larger than the diameter of the thread valley bottom of the second male thread adjacent to the threadless portion. According to this, the rigidity of the portion between the first circumferential groove and the pin intermediate dangerous cross section can be ensured by the screwless portion, and the resistance to the compressive load and the bending load can be ensured.
[0036]
The first circumferential groove provided on the pin may further have a tapered surface continuous with the end portion of the curved surface in the axial direction opposite to the intermediate shoulder surface as a part of the inner wall surface of the groove. The curved surface can be connected to the outer peripheral surface of the screwless portion via the tapered surface. According to this, the cutting edge of the cutting tip can be inserted along the tapered surface to the curved surface forming position of the first circumferential groove, and the intermediate shoulder surface is continuously machined after the curved surface is machined. This will further improve productivity. In the case of the above configuration, the first peripheral surface includes the outer peripheral surface of the screwless portion, the curved surface and the tapered surface of the first circumferential groove, and the first circumferential groove is determined by the shape of the first peripheral surface. Will be defined.
[0037]
The pin includes a pin intermediate dangerous cross section PICCS located near the end of the second male screw that is closer to the intermediate shoulder surface (see FIG. 3). Preferably, the cross-sectional area AP1 of the cross section of the pin including the bottom of the first circumferential groove provided in the pin is larger than the cross-sectional area AP2 of the pin intermediate dangerous cross section. According to this, it is possible to secure the strength of the portion where the first circumferential groove is provided.
[0038]
Preferably, the connection point P1 between the curved surface of the first circumferential groove provided on the pin and the intermediate shoulder surface is positioned radially inward with respect to the radial inner end P2 of the intermediate shoulder surface of the box. Can be done (see Figure 3). According to this, even if the radius of curvature of the curved surface is relatively large, a large contact area between the intermediate shoulder surfaces can be secured. The radial inner end P2 of the intermediate shoulder surface of the box is the inner end of the straight line portion in the vertical cross section of the intermediate shoulder surface, and does not include the R portion provided at the corner portion.
[0039]
The first circumferential groove may be provided on the second peripheral surface. According to this, it is possible to prevent breakage in the intermediate dangerous cross section of the box and improve the workability of the intermediate shoulder surface of the box.
[0040]
When the box is provided with the first circumferential groove, the second peripheral surface may be further provided with an unthreaded portion located between the first circumferential groove and the first female thread and having an axial length. can. The threadless portion may have an inner peripheral surface having an inner diameter smaller than the diameter of the thread valley bottom of the first female thread adjacent to the threadless portion. According to this, the rigidity of the portion between the first circumferential groove and the box intermediate dangerous cross section can be ensured by the screwless portion, and the resistance to the compressive load and the bending load can be ensured.
[0041]
The first circumferential groove provided in the box may further have a tapered surface continuous with the end of the curved surface in the axial direction opposite to the intermediate shoulder surface as a part of the inner wall surface of the groove. The curved surface and the inner peripheral surface of the screwless portion can be connected via the tapered surface. According to this, the cutting edge of the cutting tip can be inserted along the tapered surface to the curved surface forming position of the first circumferential groove, and the intermediate shoulder surface is continuously machined after the curved surface is machined. This will further improve productivity. In the case of the above configuration, the first peripheral surface includes the inner peripheral surface of the screwless portion and the curved surface and the tapered surface of the first circumferential groove, and the first peripheral direction is determined by the shape of the first peripheral surface. A groove will be defined.
[0042]
The box includes a box intermediate dangerous cross section located near the end of the first female screw that is closer to the intermediate shoulder surface (see FIG. 3). Preferably, the cross-sectional area AB1 of the cross section of the box including the bottom of the first circumferential groove provided in the box is larger than the cross-sectional area AB2 of the box intermediate dangerous cross section BICCS. According to this, it is possible to secure the strength of the portion where the first circumferential groove is provided.
[0043]
Preferably, the connection point P3 between the curved surface of the first circumferential groove provided in the box and the intermediate shoulder surface is positioned radially outward from the radial outer end P4 of the intermediate shoulder surface of the pin. Can be done (see Figure 3). According to this, even if the radius of curvature of the curved surface is relatively large, a large contact area between the intermediate shoulder surfaces can be secured. The radial outer end P3 of the intermediate shoulder surface of the pin is the outer end of the straight line portion in the vertical cross section of the intermediate shoulder surface, and does not include the R portion provided at the corner portion.
[0044]
The threaded joint according to the present embodiment can be suitably implemented as a semi-flash type threaded joint in which the maximum outer diameter of the box is less than 108% of the pipe diameter of the steel pipe having a pin, and the box is particularly the end portion of another steel pipe. It can be suitably carried out as an integral type semi-flush thread joint provided in.
[0045]
In the present disclosure, each of the above dangerous cross sections does not include the cross section of the thread, and the cross section of each dangerous cross section is the area of ​​the cross section excluding the thread of the complete thread portion and the incomplete thread portion of each tapered screw. Is defined as.
[0046]
[Structure of threaded joints for oil country tubular goods]
With reference to FIG. 1, the oil country tubular goods threaded joint 1 according to the present embodiment is an integral type threaded joint, and has a tubular pin 2 and a pin 2 screwed into the pin 2.It includes a tubular box 3 to be fastened. The pin 2 is provided at one end of a pair of well pipes connected to each other, and the box 3 is provided at the end of the other well pipe. Although the structure is such that the pin 2 formed at the end of one well pipe is fitted inside the box 3 formed at the end of the other well pipe, the thickness of the pin 2 and the box 3 is increased. In order to secure as large as possible, the end of the well pipe on which the pin 2 is formed is subjected to diameter reduction processing, and the end of the well pipe on which the box 3 is formed is subjected to diameter expansion processing. The pin 2 and the box 3 are formed by turning after these diameter reduction or expansion processing.
[0047]
The pin 2 extends from the end of the main body of one of the well pipes to the outer end side (right side in FIG. 1) along the axial direction. On the outer periphery of the pin 2, there is no screw having an outer peripheral surface connected to the bottom surface of the thread valley of the pin outer sealing surface 21, the first male screw 22 composed of a tapered screw, and the first male screw 22 in order from the pipe body side to the outer end side. A second portion consisting of a portion 23, a step portion including an intermediate torque shoulder surface 24, a circumferential groove 25, an unthreaded portion 26 having an outer peripheral surface connected to the thread top surface of the second male screw 27, and a tapered screw having a diameter smaller than that of the first male screw 22. A 2-male screw 27 and a pin inner sealing surface 28 are provided. The circumferential groove 25 is provided on the outer peripheral surface of the pin 2 between the intermediate shoulder surface 24 and the second male screw 27.
[0048]
Box 3 extends from the end of the main body of the other oil country tubular goods pipe to the outer end side (left side in FIG. 1) along the axial direction. On the outer periphery of the box 3, a screw having an inner peripheral surface connected to the thread top surface of the box outer sealing surface 31, the first female screw 32 composed of a tapered screw, and the first male screw 32 in order from the outer end side to the pipe body side. No portion 33, circumferential groove 34, step portion including the intermediate torque shoulder surface 35, threadless portion 36 connected to the bottom surface of the thread valley of the second female thread 37, and a second female thread 37 composed of a tapered thread having a diameter smaller than that of the first female thread 32. , And a box inner sealing surface 38 is provided. The circumferential groove 34 is a box 3 between the intermediate shoulder surface 35 and the first female screw 32.
It is provided on the inner peripheral surface of.
[0049]
As shown in FIG. 1, the threaded joint 1 having a two-stage thread structure of the present embodiment has a pin danger cross section PCCS near the end of the pin tube main body in the meshing range of the first male thread 22 and the first female thread 32. , The box danger cross section BCCS is provided in the vicinity of the end of the box tube main body in the meshing range of the second male screw 27 and the second female screw 37. Further, a box intermediate dangerous cross section BICCS is provided near the end of the meshing range of the first male screw 22 and the first female screw 32 on the intermediate shoulder surface side, and the intermediate shoulder surface of the meshing range of the second male screw 27 and the second female screw 37. It has a pin intermediate hazard cross section PICCS near the side end.
[0050]
With the pin 2 and the box 3 fastened, the pin outer seal surface 21 and the box outer seal surface 31 come into contact with each other over the entire circumference to form a metal-metal seal, and the first male screw 22 is fitted to the first female screw 32. , The intermediate shoulder surfaces 24 and 35 come into contact with each other to bear the fastening torque, the second male screw 27 fits into the second female screw 37, and the inner pin inner seal surface 28 contacts the inner box seal surface 38 over the entire circumference. Metal-Consists of a metal seal.
[0051]
Further, in the fastened state, the unscrewed portion 23 of the pin 2 is inserted into the unscrewed portion 33 of the box 3, and the unscrewed portion 26 of the pin 2 is inserted into the unscrewed portion 36 of the box 3. A gap is formed between the screwless portion 23 and the screwless portion 33, and between the screwless portion 26 and the screwless portion 36.
[0052]
The circumferential grooves 25 and 34 are each composed of an annular groove that is continuous over the entire circumference. The circumferential groove 25 of the pin 2 has a curved surface 25a that is smoothly continuous with the intermediate shoulder surface of the pin 2 and has a constant radius of curvature, and both ends of the curved surface 25a in the axial direction opposite to the intermediate shoulder surface 24. It has a tapered surface 25b continuous with the end portion as a groove inner wall surface. The tapered surface 25b connects the curved surface 25a and the outer peripheral surface of the screwless portion 26. The circumferential groove 34 of the box 3 has a curved surface 34a that is smoothly continuous with the intermediate shoulder surface 35 of the box 3 and has a constant radius of curvature, and an axial end portion of the curved surface 34a that is opposite to the intermediate shoulder surface 35. It has a tapered surface 34b continuous with the end portion of the groove as an inner wall surface of the groove. The tapered surface 34b connects the curved surface 34a and the inner peripheral surface of the screwless portion 33.
[0053]
The groove depth of the circumferential groove 25, that is, the depth based on the outer peripheral surface of the threadless portion 26, is the thread valley bottom depth near the end portion of the second male thread 27 on the axial inner end side (that is, the intermediate shoulder surface side). It may be about the same as. With reference to FIG. 3, preferably, the cross-sectional area AP1 of the cross section of the pin 2 including the bottom of the circumferential groove 25 is larger than the cross-sectional area AP2 of the pin intermediate dangerous cross section PICCS. Further, in order to sufficiently bring about the effect of the circumferential groove 25, the groove depth can be set so that the cross-sectional area AP1 is preferably smaller than 110% of the cross-sectional area AP2. More preferably, the groove depth of the circumferential groove 25 can be set so that the cross-sectional area AP1 is smaller than 105% of the cross-sectional area AP2.
[0054]
The groove depth of the circumferential groove 34, that is, the depth based on the inner peripheral surface of the threadless portion 33, is the thread valley bottom near the end of the first female thread 32 on the axial inner end side (that is, the intermediate shoulder surface side). It may be about the same as the depth. With reference to FIG. 3, preferably, the cross-sectional area AB1 of the cross section of the box 3 including the bottom of the circumferential groove 34 is larger than the cross-sectional area AB2 of the box intermediate dangerous cross section BICCS. Further, in order to sufficiently bring about the effect of the circumferential groove 34, the groove depth can be set so that the cross-sectional area AB1 is preferably smaller than 110% of the cross-sectional area AB2. More preferably, the groove depth of the circumferential groove 34 can be set so that the cross-sectional area AB1 is smaller than 105% of the cross-sectional area AB2.
[0055]
The intermediate shoulder surfaces 24 and 35 are constructed by flat surfaces orthogonal to the pipe axis in the illustrated embodiment, respectively.
It is made. As shown in detail in FIG. 3, the radial inner end P1 of the intermediate shoulder surface 24 of the pin 2 is located at substantially the same radial position as the outer peripheral surface of the screwless portion 26, and the radial outer end of the intermediate shoulder surface 24. P 4 is located at substantially the same position in the radial direction as the outer peripheral surface of the screwless portion 23. Further, the radial inner end P 2 of the intermediate shoulder surface 35 of the box 3 is located at substantially the same radial position as the inner peripheral surface of the screwless portion 36, and the radial outer end P 3 of the intermediate shoulder surface 35 is the screwless portion. It is located at almost the same position in the radial direction as the inner peripheral surface of 33. The inner end of the intermediate shoulder surface 24 of the pin 2, that is, the connection point P1 between the intermediate shoulder surface 24 and the curved surface 25a of the circumferential groove 25 is radially inward with respect to the radial inner end P2 of the box intermediate shoulder surface 35. Is located in. The outer end of the intermediate shoulder surface 35 of the box 3, that is, the connection point P3 between the intermediate shoulder surface 35 and the curved surface 34a of the circumferential groove 34 is radially outer than the radial outer end P4 of the pin intermediate shoulder surface 24. Is located in. By connecting the curved surfaces 25a and 34a to the intermediate shoulder surfaces 24 and 35, respectively, the radius of curvature of the curved surfaces 25a and 34a can be increased without reducing the contact area between the intermediate shoulder surfaces 24 and 35, respectively. ..
[0056]
[Processing method for circumferential groove]
FIG. 4 is an enlarged side view of the tip blade portion 4 of the cutting tip (blade) for turning each screw 22, 27, 32, 37 and the circumferential groove 25, 34. The blade portion 4 has a tip R portion 41 having a predetermined radius of curvature R and left and right side edge portions 42, 43. The left and right edge portions 42 and 43 are provided with a blade angle α so as to gradually widen as the distance from the tip R portion 41 increases.
[0057]
The blade portion 4 has a clearance angle K', K'required with respect to the machined surface during cutting. That is, as shown in FIG. 5, the left and right side edge portions 42, 43 and the machined surface Machining cannot be performed unless the angle θ', θ "between is larger than the clearance angle K', K'. Therefore, when machining the pin intermediate shoulder surface 24 and the circumferential groove 25, as shown in FIG. Further, by inserting the blade portion 4 into the work at an angle satisfying the relationship of θ'> K'and θ "> K", the circumferential groove 25 and the intermediate shoulder surface 24 can be continuously machined. Since the circumferential groove 25 has the tapered surface 25b, the blade portion 4 can be inserted while ensuring the gap angle K'. Further, the radius of curvature R of the tip R portion 41 is the curvature of the curved surface 25a to be machined. Although it needs to be smaller than the radius, since the circumferential groove 25 according to the present disclosure has a depth, the radius of curvature R'of the curved surface 25a can be made relatively large without sacrificing the contact area between the intermediate shoulder surfaces. Along with this, a cutting tip having a large radius of curvature R of the tip R portion 41 can be used. The same applies to the processing of the circumferential groove 34 and the box intermediate shoulder surface 35.
[0058]
This disclosure can be applied not only to integral type but also to coupling type threaded joints. Further, each screw may be a trapezoidal screw, an API round screw, an API buttless screw, a wedge screw, or the like. In addition, the present disclosure is not limited to the above-described embodiment, and various changes can be made without departing from the spirit of the present disclosure.
Example
[0059]
In order to confirm the effect of the threaded joint for steel pipes according to this embodiment, a numerical analysis simulation by the elasto-plastic finite element method was carried out.
[0060]

Regarding the integral type threaded joints for oil well pipes shown in FIGS. 1 to 3, any of the specimens # 2 and # 4 (analysis model) provided with circumferential grooves 25 and 34 for two types of pipe diameter sizes, large and small. Specimens # 1 and # 3 without circumferential grooves were created, and elasto-plastic finite element method analysis was performed for each specimen. The plastic strain and the equivalent plastic strain generated at the bottom of the thread valley of the first female thread including the box intermediate dangerous cross section were compared.
[0061]

The size of the well pipes of specimens # 1 and # 2 is 9-5 / 8 ”47.0 # (pipe body outer diameter: 244.48 m).
m, inner diameter of the pipe body: 220.50 mm), and the joint efficiency (ratio of the cross-sectional area of ​​the box dangerous cross section BCCS to the cross-sectional area of ​​the pipe body) is 67.3%.
[0062]
The size of the well pipes of specimens # 3 and # 4 is 13-3 / 8 ”72.0 # (pipe body outer diameter: 339.73)
mm, inner diameter of the pipe body: 313.61 mm), and the joint efficiency is 70.5%.
[0063]
In all the specimens, the screw taper angle of each screw was 1.591 °, the screw height was 1.3 mm, and the screw pitch was 5.08 mm.
[0064]
The shapes of the circumferential grooves 25 and 34 are such that the radius of curvature of the curved surfaces 25a and 34a is 1.7 mm, the groove depth is 1.2 mm, and the angle between the tapered bus and the pipe axis of the tapered surfaces 25b and 34b is 15 °. Unified with.
[0065]

API standard oil country tubular goods Q125 (nominal yield strength YS = 862MPa (125ksi))
[0066]

First, after performing an analysis simulating fastening for each specimen, a repeated composite load simulating the Series A test specified by API 5C5 2017 CAL-IV is applied to the model in the fastening state, and the combined load initial stage. The equivalent plastic strain immediately after the simple tensile load and the equivalent plastic strain after the completion of the entire process of the repeated combined load were compared and compared for each specimen.
[0067]

The graphs of FIGS. 6A, 6B, 7A, and 7B show the comparison results between the small diameter size specimens # 1 and # 2. FIG. 6A shows the equivalent plastic strain distribution near the pin intermediate dangerous cross section immediately after a simple tensile load, FIG. 6B shows the equivalent plastic strain distribution near the pin intermediate dangerous cross section after the completion of the entire process of repeated compound loading, and FIG. 7A shows the equivalent plastic strain distribution near the pin intermediate dangerous cross section. The equivalent plastic strain distribution near the box intermediate dangerous cross section immediately after the simple tensile load is shown, and FIG. 7B shows the equivalent plastic strain distribution near the box intermediate dangerous cross section after the completion of the entire process of the repeated combined load. The "axial coordinates" on the horizontal axis are the pipe axial distance from the intermediate shoulder surface, and the tube body side of the pin is indicated by a positive value from the intermediate shoulder surface, and the pin tip side is indicated by a negative value from the intermediate shoulder surface. .. In addition, considerable plasticity The points at which the stain was measured are shown by dots in FIGS. 6C and 7C.
[0068]
As is clear from these graphs, the specimen # 2 provided with the circumferential grooves 25 and 34 is the specimen without the circumferential groove # in both the vicinity of the pin intermediate dangerous cross section and the vicinity of the box intermediate dangerous cross section. It was confirmed that the considerable plastic strain was reduced over the entire area as compared with 1. In the graphs of FIGS. 6A and 6B, the peak on the right side is that of the R portion of the bottom of the load surface of the second male screw 27, and the peak on the left side is that of the R portion of the bottom of the insertion surface.
[0069]
The difference between the specimens # 1 and # 2 is more remarkable immediately after the simple tensile load than after the completion of the whole process. The reason is that the plastic strain of each part is accumulated by the repeated combined load. It is thought that this is due to doing so.
[0070]
Similarly, the graphs of FIGS. 8A, 8B, 9A, and 9B show the comparison results between the large-diameter specimens # 3 and # 4. As is clear from these graphs, the large diameter size has the same tendency as the small diameter size, and the plastic strain generated on the bottom surface of the thread valley near the intermediate dangerous cross section by providing the circumferential groove regardless of the pipe diameter size. Was confirmed to be able to be reduced.
Code description
[0071]
1: Threaded joint,
2: Pin, 22: 1st male screw, 24: Intermediate shoulder surface
25: Circumferential groove, 25a: Curved surface, 25b: Tapered surface
26: Screwless part, 27: Second male screw
3: Box, 32: 1st female screw, 33: No screw part
34: Circumferential groove, 34a: Curved surface, 34b: Tapered surface
35: Intermediate shoulder surface, 37: 2nd female screw
PICCS: Pin intermediate dangerous cross section, BICCS: Box intermediate dangerous cross section
The scope of the claims
[Claim 1]
A threaded joint composed of a tubular pin and a tubular box, in which the pin is screwed into the box and the pin and the box are fastened.
On the outer circumference of the pin, a first male screw, a second male screw that is axially separated from the first male screw and has a smaller diameter than the first male screw, and the first male screw and the second male screw are provided. An intermediate shoulder surface formed by a step portion located between the intermediate shoulder surfaces and a first peripheral surface formed by the outer peripheral surface of the pin between the intermediate shoulder surface and the second male screw are provided.
On the inner circumference of the box, a first female screw to which the first female screw fits in the fastened state, a second female screw to which the second male screw fits in the fastened state, the first female screw and the second female screw are formed. It is composed of an intermediate shoulder surface that is in contact with the intermediate shoulder surface of the pin in a fastened state, and an inner peripheral surface of the box between the intermediate shoulder surface and the first female screw. The second peripheral surface is provided,
One of the first peripheral surface and the second peripheral surface has a curved surface smoothly continuous with the intermediate shoulder surface related to the peripheral surface as at least a part of the inner wall surface of the groove. A threaded joint with a directional groove.
[Claim 2]
In the threaded joint according to claim 1, on the other peripheral surface of the first peripheral surface and the second peripheral surface, a curved surface smoothly continuous with the intermediate shoulder surface related to the peripheral surface is formed on the inner wall surface of the groove. A threaded joint provided with a second circumferential groove having at least as part of.
[Claim 3]
The threaded joint according to claim 2, wherein the radius of curvature of the curved surface of the first circumferential groove is equal to the radius of curvature of the curved surface of the second circumferential groove.
[Claim 4]
In the threaded joint according to claim 1, 2, or 3, the first circumferential groove is a threaded joint provided on the first peripheral surface.
[Claim 5]
In the threaded joint according to claim 4,
The first peripheral surface is further provided with a screwless portion located between the first circumferential groove and the second male screw and having an axial length, and the screwless portion is the screwless portion. It has an outer peripheral surface having an outer diameter larger than the diameter of the thread valley bottom of the second male thread adjacent to the threadless portion.
The first circumferential groove further has a tapered surface continuous with the end portion of the curved surface in the axial direction opposite to the intermediate shoulder surface as a part of the inner wall surface of the groove, and the tapered surface is provided. A threaded joint in which the curved surface and the outer peripheral surface of the threadless portion are connected via a screw joint.
[Claim 6]
In the threaded joint according to claim 4 or 5,
The pin includes a pin intermediate dangerous cross section located near the end of the second male thread closer to the intermediate shoulder surface, and crosses the pin including the bottom of the first circumferential groove. A threaded joint whose surface cross-section is larger than the pin intermediate cross-section.
[Claim 7]
In the threaded joint according to claim 4, 5 or 6,
A threaded joint in which the connection point between the curved surface of the first circumferential groove and the intermediate shoulder surface is located radially inward from the radial inner end of the intermediate shoulder surface of the box.
[Claim 8]
In the threaded joint according to claim 1, 2, or 3, the first circumferential groove is a threaded joint provided on the second peripheral surface.
[Claim 9]
In the threaded joint according to claim 8,
The second peripheral surface is further provided with a screwless portion located between the first circumferential groove and the first female screw and having an axial length, and the screwless portion is the screwless portion. Adjacent to the screwless part
It has an inner peripheral surface having an inner diameter smaller than the diameter of the thread valley bottom of the first female screw.
The first circumferential groove further has a tapered surface continuous with the end portion of the curved surface in the axial direction opposite to the intermediate shoulder surface as a part of the inner wall surface of the groove, and the tapered surface is provided. A threaded joint in which the curved surface and the inner peripheral surface of the threadless portion are connected via a screw joint.
[Claim 10]
In the threaded joint according to claim 8 or 9,
The box includes a box intermediate dangerous cross section located near the end of the first female screw that is closer to the intermediate shoulder surface, and crosses the box including the bottom of the first circumferential groove. A threaded joint whose surface cross-section is larger than the box mid-hazard cross-section.
[Claim 11]
In the threaded joint according to claim 8, 9 or 10.
A threaded joint in which the connection point between the curved surface of the first circumferential groove and the intermediate shoulder surface is located radially outward from the radial outer end of the intermediate shoulder surface of the pin.