Specification
Title of Invention : Threaded Joint for Pipes
Technical field
[0001]
The present disclosure relates to a threaded joint for pipes used for connecting steel pipes and the like.
Background technology
[0002]
In oil wells, natural gas wells, etc. (hereinafter also collectively referred to as "oil wells"), in order to extract underground resources, a casing that constructs a multi-stage well wall, and a casing that is arranged in the casing and contains oil and gas Tubing is used that produces These casings and tubings are made up of a large number of steel pipes connected in sequence, and threaded joints for pipes are used for the connections. Steel pipes used in oil wells are also called oil well pipes.
[0003]
The types of threaded joints for pipes are roughly divided into the integral type and the coupling type. Integral threaded joints for pipes are disclosed, for example, in Patent Documents 1 and 2 below, and coupling type threaded joints for pipes are disclosed, for example, in Patent Document 3 below.
[0004]
In the integral type, oil country tubular goods are directly connected. Specifically, one end of the oil country tubular good is provided with a female threaded portion, and the other end thereof is provided with a male threaded portion. concatenated.
[0005]
In the coupling type, oil country tubular goods are connected via tubular couplings. Specifically, both ends of the coupling are provided with female threads, and both ends of the oil well pipe are provided with male threads. One male threaded portion of one oil country tubular good is screwed into one female threaded portion of the coupling, and one male threaded portion of the other oil country tubular good is screwed into the other female threaded portion of the coupling, whereby the coupling is formed. The oil country tubular goods are connected to each other through the joint. That is, in the coupling type, one of a pair of directly connected pipe members is an oil well pipe and the other is a coupling.
[0006]
Generally, the end of an oil country tubular good having a male threaded portion is called a pin because it includes an element that is inserted into a female threaded portion formed in the oil country tubular good or coupling. The end of a female-threaded oil country tubular good or coupling is called a box because it includes an element that receives the male-threaded portion formed on the end of the oil country tubular good.
[0007]
In recent years, further development of high-temperature, high-pressure deep wells has progressed. In deep wells, it is necessary to increase the number of casing stages due to the complexity of the depth distribution of formation pressure. threaded joints may be used. A threaded joint whose box outer diameter is approximately equal to the outer diameter of the main body of the oil well pipe is also called a flush-type threaded joint. Further, a threaded joint whose box outer diameter is approximately less than 108% of the outer diameter of the main body of the oil well pipe is also called a semi-flush type threaded joint. These flush-type and semi-flush-type threaded joints are required not only to have high strength and sealing performance, but also to place the threaded structure and seal structure within the limited wall thickness of pipes. Dimensional constraints are imposed.
[0008]
Flush-type and semi-flush-type screw joints, which have large dimensional restrictions, adopt a joint design in which an intermediate shoulder is provided in the axial middle of the joint, and a two-step screw with threaded portions on the front and back of the shoulder forms male and female threads. It is often done. In such a threaded joint with a two-step thread structure, as disclosed in Patent Documents 1 and 2, in order to ensure sealing performance against internal pressure and sealing performance against external pressure under severe dimensional restrictions, An internal pressure seal is provided, and an external pressure seal is provided near the opening end of the box.
[0009]
Both Patent Documents 1 and 2 were filed by the applicants of the present application, and the drawings attached to these applications are schematic diagrams for explaining the features of the respective inventions in an easy-to-understand manner. The dimensions of each part are not exact. Therefore, it should be added that technical features not explicitly disclosed in the specification should not be extracted from the dimensions on the drawings of the parts not described in the specification of these applications.
prior art documents
patent literature
[0010]
Patent Document 1: Japanese Patent Publication No. 2018-536818
Patent Document 2: International Publication No. 2018/211873
Patent Document 3: JP 2012-149760 A
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0011]
In the case of a threaded joint with a two-step thread structure, there is a box intermediate shoulder near the center of the box in the axial direction. During centering, etc., the pin inner seal surface (internal pressure pin seal surface) provided near the tip of the pin may hit the corner of the box intermediate shoulder and be damaged.
[0012]
During actual excavation work, the pin is stubbed after the stabbing guide is attached to the opening edge of the box. Protected by the wing guide, it is less likely to be damaged by hitting the pin mid-shoulder. On the other hand, even if a stubbing guide is used, there is a risk that the seal surface inside the pin will contact the box mid-shoulder.
[0013]
In general, the internal pressure is higher than the external pressure in the oil country tubular goods usage environment. Avoiding is important.
[0014]
An object of the present disclosure is to prevent the box intermediate shoulder from hitting the pin inner seal surface during stubbing in a pipe threaded joint with a two-step thread structure, thereby making the pin inner seal less likely to be damaged.
Means to solve problems
[0015]
A threaded joint for pipes according to the present disclosure comprises a tubular pin and a tubular box, and the pin and the box are fastened by screwing the pin into the box.
[0016]
The pin is provided between a first male screw, a second male screw provided on the tip end side of the first male screw and having a smaller diameter than the first male screw, and the first male screw and the second male screw. A pin intermediate shoulder, a pin inner sealing surface provided distally of the second male thread, and a pin outer sealing surface provided proximally of the first male thread.
[0017]
The box is provided between a first female thread into which the first male thread is fitted in a fastened state, a second female thread into which the second male thread is fitted in a fastened state, and the first female thread and the second female thread. a box intermediate shoulder that contacts the pin intermediate shoulder in a fastened state; a box inner seal surface that contacts the pin inner seal surface in a fastened state; and a box outer seal surface that contacts the pin outer seal surface in a fastened state. Prepare.
[0018]
A threaded joint for pipes according to the present disclosure satisfies the following formulas (1) and (2).
[0019]
[Number 1]

[0020]
[Number 2]

[0021]
where L P is the axial distance between the pin intermediate shoulder side end of the pin inner seal surface and the radially outer end of the pin intermediate shoulder, and LB is the box outer seal surface intermediate the box. The axial distance between the shoulder-side end and the radially inner end of the box intermediate shoulder, hP is the pin intermediate shoulder-side end of the pin inner seal surface and the radially outer end of the pin intermediate shoulder. h B is the radial distance between the end of the box outer seal surface on the box intermediate shoulder side and the radial inner end of the box intermediate shoulder, θ seal is the pin inner seal It is the slope angle of the straight line connecting the axial ends of the face.
[0022]
Preferably, an inclination angle θP of a straight line connecting an end portion of the pin inner seal surface on the pin intermediate shoulder side and a radial outer end of the pin intermediate shoulder is equal to an inclination angle θP of the box outer seal surface on the box intermediate shoulder side. greater than the slope angle θ B of the straight line connecting the end and the radially inner edge of the box intermediate shoulder. More preferably, said slope angle θ P is less than 6°.
[0023]
Also, the present disclosure is particularly useful when LP is greater than 94% of LB.
[0024]
Further, according to the present disclosure, even when hB is larger than hP, it is possible to avoid damage to at least the seal point SP where the seal contact pressure is the largest among the seal surfaces in the pin, and the diameter of hB can be reduced. Since there is a margin in the design of the first female thread 31 provided within the direction range and the corresponding first male thread 21, this margin can be allocated to various performances.
[0025]
In order to protect the seal point SP more reliably, the seal point SP where the seal contact force is the highest due to contact with the seal surface in the box among the seal surfaces in the pin at the time of completion of fastening, and the pin intermediate seal surface of the seal surface in the pin. Preferably, the axial distance LSP to the shoulder-side end P1 is smaller than the difference between LB and LP.
Effect of the invention
[0026]
According to the present disclosure, it is possible to prevent the inner seal surface of the pin from being damaged by striking against the intermediate shoulder of the box during stubbing, and prevent deterioration of the internal pressure sealing performance after fastening.
Brief description of the drawing
[0027]
1] Fig. 1 is a longitudinal sectional view of a threaded joint for pipes according to an embodiment. [Fig.
2] Fig. 2 is a dimensional explanatory diagram of a characteristic portion of a pin and a box. [Fig.
3] Fig. 3 is an enlarged view of the vicinity of the tip of a pin. [Fig.
4] FIG. 4 is a cross-sectional view for explaining a state during stubbing. [FIG.
MODE FOR CARRYING OUT THE INVENTION
[0028]
As illustrated in FIGS. 1 to 4, a threaded joint 1 for pipes according to the present embodiment is composed of a tubular pin 2 and a tubular box 3. As shown in FIGS. The pin 2 and the box 3 are fastened together by screwing the pin 2 into the box 3 . The pin 2 is provided at the tube end of the first tube P1 and the box 3 is provided at the tube end of the second tube P2. The first pipe P1 may be a long pipe such as an oil well pipe. The second pipe may be a coupling for connecting long pipes, but is preferably a long pipe such as an oil well pipe. That is, the threaded joint 1 for pipes according to the present embodiment is preferably an integral threaded joint for pipes. Oil country tubular goods and couplings are typically made of steel, but may be made of metal such as stainless steel or nickel-based alloy.
[0029]
The pin 2 may be formed at one end of the first oil country tubular good P1 whose diameter has been reduced. The box 3 may be formed at the diameter-expanded one end of the second oil country tubular good P2. Preferably, the pin 2 can be formed at one end of each of the oil country tubular goods P1 and P2, and the box 3 can be formed at the other end. More specifically, the first oil country tubular good P1 is formed by reducing the diameter of one end of a raw pipe made of a long pipe, and then cutting the outer circumference of the diameter-reduced one end so as to form a component of the pin 2 . It can be manufactured by cutting. The second oil country tubular good P2 is formed by enlarging the diameter of one end of the base pipe made of a long pipe, and then cutting the inner circumference of the one end that has been diameter-enlarged so as to form a constituent element of the box 3. It can be manufactured by As a result, the thickness of the pin 2 and the box 3 can be ensured in the semi-flush type integral threaded joint.
[0030]
In this specification, the portion other than the pin 2 and the box 3 of the oil country tubular goods P1 and P2, which is neither diameter-reduced nor diameter-enlarged, is referred to as "tube body". The tube end side of the pin 2 means the direction from the tube main body of the pin 2 toward the tube end of the pin 2, and is sometimes referred to as the "tip side". The tube main body side of the pin 2 means the direction from the tube end of the pin 2 toward the tube main body of the pin 2, and is sometimes referred to as the "base end side". The open end side of the box 3 means the direction from the pipe body of the box 3 toward the open end of the box 3 .
[0031]
The pin 2 includes a first male screw 21, a second male screw 22 provided closer to the tube end of the pin 2 than the first male screw 21 and having a diameter smaller than that of the first male screw 21, and the first male screw 21 and the second male screw 22. a pin intermediate shoulder 23 provided between; a pin end shoulder 24 provided at the tube end of the pin 2; 25 and a pin outer sealing surface 26 provided between the first external thread 21 and the tube body of the pin 2 . First male screw 21 and second male screwIt is axially spaced from the screw 22 and may have a pin intermediate shoulder 23 therebetween.
[0032]
Preferably, the first and second male threads 21, 22 are tapered threads. Preferably, the first and second external threads 21, 22 have the same thread taper angle and the same thread pitch. Preferably, the tapered generatrix of the tapered thread forming the second male thread 22 is located radially inwardly of the taper generatrix of the tapered thread forming the first male thread 21 . The pin intermediate shoulder 23 can be constituted by the side surface of a step formed on the outer periphery of the pin between the first male thread 21 and the second male thread 22 . The pin intermediate shoulder 23 has a pin intermediate shoulder surface directed toward the tube end of the pin 2 . The first and second external threads 21, 22 may each be trapezoidal threads, API round threads, API buttress threads, wedge threads, or the like.
[0033]
The box 3 contacts the first female thread 31 into which the first male thread 21 is fitted at the completion of fastening, the second female thread 32 into which the second male thread 22 is fitted at the completion of fastening, and the pin intermediate shoulder 23 at the completion of fastening. A box intermediate shoulder 33, a box end shoulder 34 provided corresponding to the pin end shoulder 24, and a pin inner seal provided between the second female thread 32 and the box end shoulder 34 at the completion of fastening. A box-inside sealing surface 35 that contacts the surface 25 over the entire circumference, and a box-outside sealing surface 36 that is provided between the first female thread 31 and the box opening end and contacts the pin-outside sealing surface 26 over the entire circumference when fastening is completed. and The pin inner seal surface 25 and the box inner seal surface 35 can mainly function as internal pressure seals for exhibiting sealing performance against internal pressure. The pin outer seal surface 26 and the box outer seal surface 36 can mainly function as external pressure seals for exhibiting sealing performance against external pressure.
[0034]
The first internal thread 31 and the second internal thread 32 are axially separated, and a box intermediate shoulder 33 may be provided between them. Preferably, the first and second internal threads 31,32 comprise tapered threads that match the first and second external threads 21,22, respectively. The box intermediate shoulder 33 can be configured by a step formed on the inner circumference of the box 3 between the first female thread 31 and the second female thread 32 . The box intermediate shoulder 33 has a box intermediate shoulder surface directed toward the open end of the box 3 and faces the pin intermediate shoulder surface of the pin intermediate shoulder 23 . The box intermediate shoulder 33 contacts the pin intermediate shoulder 23 at least at the time of completion of fastening, and these intermediate shoulders 23, 33 function as torque shoulders for exhibiting torque performance. The first and second internal threads 31, 32 may be trapezoidal threads, API round threads, API buttress threads, wedge threads, or the like that match the first and second external threads 21, 22, respectively.
[0035]
The pin end shoulder 24 may be spaced from the box end shoulder 34 as shown in FIG. When these end shoulders 24, 34 are separated at the time of completion of fastening, when a predetermined axial compressive load smaller than the yield compressive load of the threaded joint is applied, the elastic deformation of the pin 2 and the box 3 causes the ends to move apart. The shoulders 24, 34 can also be configured to contact and carry a portion of the axial compressive load.
[0036]
The intermediate shoulders 23 and 33 of the pin 2 and the box 3 are formed by flat surfaces perpendicular to the tube axis, but the tapered surfaces in which the radially outer end inclines toward the tube end side of the pin 2 rather than the radially inner end. may be configured.
[0037]
The longitudinal cross-sectional shape of each of the seal surfaces 25, 35, 26, and 36 may be arbitrary. In the threaded joint 1 shown in FIGS. It is composed of Alternatively, one of the sealing surfaces that contact each other may be configured with a convex curved surface, or both sealing surfaces may be configured with a convex curved surface. Also, each sealing surface can be configured by a combination of a convex curved surface and a tapered surface having a straight generatrix. In any case, each sealing surface is configured such that the farther the pin 2 is pushed into the box 3, the greater the seal interference amount. That is, both the pin inner seal surface 25 and the box outer seal surface 26 are formed in a tapered shape with diameters gradually decreasing toward the tip of the pin, and the box inner seal surface 35 is tapered to match the pin inner seal surface 25. , and the outer box sealing surface 36 is tapered to match the outer pin sealing surface 26 .
[0038]
The gradient of the straight line connecting both ends in the axial direction of each seal face is preferably 5% (10% as a taper ratio) or more, more preferably 10% (20% as a taper ratio). In addition, the gradient of the straight line connecting both ends in the axial direction of each seal face is preferably 25% (50% as a taper ratio) or less, more preferably 17% (34% as a taper ratio) or less. . The slope angle θ seal of the straight line connecting both ends in the axial direction of the pin inner seal surface 25 is about 2.9° for a 5% slope, about 5.7° for a 10% slope, and about 5.7° for a 17% slope. 9.7°, about 14.0° for a 25% slope.
[0039]
The axial distance LP between the pin intermediate shoulder 23 side end P1 of the pin inner seal surface 25 and the radial outer end P2 of the pin intermediate shoulder 23 is, for example, 65, although it depends on the pipe diameter size and the like. ˜95 mm. The ratio of L P to the diameter of the radially outer end of pin intermediate shoulder 23 may be 20-45%.
[0040]
The axial distance LB between the end P2 of the box outer seal surface 36 on the box intermediate shoulder 33 side and the radial inner end P4 of the box intermediate shoulder 33 is, for example, 70 to It may be 100mm. The ratio of LB to the diameter of the radially inner end of box intermediate shoulder 33 may be 20-45%. The ratio of L P to L B may be between 94% and 98%.
[0041]
The radial distance hP between the pin intermediate shoulder 23 side end P1 of the pin inner seal surface 25 and the radial outer end P2 of the pin intermediate shoulder 23 is, for example, 5 .0 to 8.5 mm.
[0042]
The radial distance hB between the end P3 of the box outer seal surface 36 on the box intermediate shoulder 33 side and the radial inner end P4 of the box intermediate shoulder 33 is, for example, 5 .0 to 8.5 mm. Preferably h P and h B are equal.
[0043]
The inclination angle θP of the straight line connecting the pin intermediate shoulder 33 side end P1 of the pin inner seal surface 25 and the radial outer end P2 of the pin intermediate shoulder 33 is preferably less than 6°, more preferably less than 5.5°. The slope angle θB of the straight line connecting the end P3 of the box outer seal surface 36 on the box intermediate shoulder 33 side and the radially inner end P4 of the box intermediate shoulder 33 is preferably less than 5.5°, and more preferably less than 5.5°. It is preferably less than 5.3°.
[0044]
FIG. 3 shows the seal contact pressure distribution generated on the pin inner seal surface 25 in the fastened state and the seal point SP where the seal contact pressure peaks. The shape of the pin 2 before fastening is indicated by a phantom line, and the fastening state in which the pin 2 is slightly contracted radially inward due to interference between the seal surfaces 25 and 35 is indicated by a solid line.
[0045]
Since the internal pressure sealing performance is mainly exhibited at the sealing point SP, it is important to avoid damage to the surface of the pin inner sealing surface 25 especially in the vicinity of the sealing point SP in order to maintain the internal pressure sealing performance. On the other hand, the farther away from the seal point SP, that is, the closer to the end P1 of the pin inner seal surface on the pin intermediate shoulder 23 side, the less the seal contact pressure increases, so some superficial damage can be tolerated. . Therefore, it is considered that the internal pressure sealing performance can be maintained by designing so as to avoid damage to the seal point SP located radially inward of the end P1.
[0046]
When inserting the pin 2 into the box 3, as shown in FIG. With the outer edge P 2 aligned with the edge P 3 of the outer box sealing surface 36 , it is more likely that the pin inner sealing surface 25 will interfere with the box mid-shoulder 33 . In order to avoid damage to at least the seal point SP of the pin inner seal surface 25 in this state, first, the end portion P1 of the pin inner seal surface 25 should be located closer to the box opening end than the radially inner end of the box intermediate shoulder 33 . must be located in This leads to equation (1) above. Although the stabbing guide is omitted in FIG. 4, the stabbing guide can be used as necessary.
[0047]
Since the diameter of the pin inner seal surface 25 gradually decreases from the end P1 toward the tip side, in the situation shown in FIG. Using the axial distance between the end P4, that is, (LB-LP), and the slope angle θ seal of the pin inner seal surface 25, if the above equation (2) is satisfied, the box is formed on the pin inner seal surface 25. It follows that the intermediate shoulder 33 is less likely to strike.
[0048]
In order to more reliably avoid damage to the seal point SP, in the situation shown in FIG. From this, the distance between the seal point SP where the seal contact force is the highest due to contact with the box inner seal surface 35 of the pin inner seal surface 25 at the completion of fastening and the end portion P1 of the pin inner seal surface 25 A condition is introduced that the axial distance L SP is less than the difference between LB and LP.
[0049]
If the above conditions are satisfied, even if hB is greater than hP, it is possible to avoid contact of the box intermediate shoulder 33 with the seal point SP of the pin inner seal surface 25 during stubbing.
[0050]
In addition, the inclination angle θP of the straight line connecting the end P1 of the pin inner seal surface 25 and the radial outer end P2 of the pin intermediate shoulder 23 is equal to the end P3 of the box outer seal surface 36 and the box intermediate shoulder 33 is greater than the gradient angle θ B of the straight line connecting the radially inner end P 4 of the . This causes, in the situation shown in FIG. It can be positioned radially inward, and the possibility of contact of the box intermediate shoulder 33 with the pin inner seal surface 25 can be further reduced.
[0051]
Furthermore, the slope angle θ P is preferably less than 6°. According to this, damage to the pin inner sealing surface 25 can be avoided while limiting the thickness range in which the second male thread 22 and the pin intermediate shoulder 23 are provided.
[0052]
LP may be 90% or more of LB, more preferably 92% or more, and still more preferably 94% or more. As a result, it is possible to provide a threaded joint 1 that is well-balanced as a whole by equalizing the threaded state and strength of each of the two-step threaded structures.
[0053]
The present disclosure may be applied not only to integral type threaded joints but also to coupling type threaded joints. In addition, the present disclosure is not limited to the above embodiments, and various modifications are possible within the scope of the claims.

The scope of the claims

[Claim 1]
A threaded joint for pipes, which is composed of a tubular pin and a tubular box, wherein the pin is screwed into the box to fasten the pin and the box,
The pin is provided between a first male screw, a second male screw provided on the tip end side of the first male screw and having a smaller diameter than the first male screw, and the first male screw and the second male screw. A pin intermediate shoulder, a pin inner seal surface provided on the distal side of the second male thread, and a pin outer seal surface provided on the proximal side of the first male thread,
The box is provided between a first female thread into which the first male thread is fitted in a fastened state, a second female thread into which the second male thread is fitted in a fastened state, and the first female thread and the second female thread. a box intermediate shoulder that contacts the pin intermediate shoulder in a fastened state; a box inner seal surface that contacts the pin inner seal surface in a fastened state; and a box outer seal surface that contacts the pin outer seal surface in a fastened state. with
A threaded joint for pipes that satisfies the following formulas (1) and (2).
[Number 1]

[Number 2]

where L P is the axial distance between the pin intermediate shoulder side end of the pin inner seal surface and the radially outer end of the pin intermediate shoulder, and LB is the box outer seal surface intermediate the box. The axial distance between the shoulder-side end and the radially inner end of the box intermediate shoulder, hP is the pin intermediate shoulder-side end of the pin inner seal surface and the radially outer end of the pin intermediate shoulder. h B is the radial distance between the end of the box outer seal surface on the box intermediate shoulder side and the radial inner end of the box intermediate shoulder, θ seal is the pin inner seal It is the slope angle of the straight line connecting the axial ends of the face.
[Claim 2]
In the threaded joint for pipes according to claim 1,
The inclination angle θP of the straight line connecting the pin intermediate shoulder side end of the pin inner seal surface and the radially outer end of the pin intermediate shoulder is equal to the box intermediate shoulder side end of the box outer seal surface. A threaded joint for pipes, wherein the inclination angle θ B of a straight line connecting the box intermediate shoulder with the radially inner end thereof is greater.
[Claim 3]
In the threaded joint for pipes according to claim 2,
A threaded joint for pipes, wherein the inclination angle θ P is less than 6°.
[Claim 4]
The threaded joint for pipes according to claim 1, 2 or 3, wherein LP is greater than 94% of LB.
[Claim 5]
The threaded joint for pipes according to any one of claims 1 to 4, wherein hB is larger than hP.
[Claim 6]
A threaded joint for pipes according to any one of claims 1 to 5, wherein a seal point at which seal contact force is the highest due to contact with the box inner seal surface among the pin inner seal surfaces at the time of completion of fastening; A threaded joint for pipes, wherein the axial distance L SP between the seal face and the pin intermediate shoulder side end is smaller than the difference between LB and LP.