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 threaded joints, which have large dimensional restrictions, have an intermediate shoulder surface in the middle of the joint in the axial direction. often adopted.
[0009]
Patent Document 1 discloses a technique for stably ensuring sealing performance in such a threaded joint having a two-step thread structure. That is, in the technique of Patent Document 1, a repeated load is applied by constructing the inner groove portion provided between the inner sealing surface of the box and the inner male thread portion to accommodate a portion of the inner male thread portion of the pin. To stably secure the sealing performance even after being sealed.
[0010]
Further, Patent Document 2 discloses that, in flush type and semi-flush type threaded joints, an annular portion having a length in the pipe axis direction longer than the thread pitch of the female thread is provided between the outer seal surface of the box and the female thread. discloses a technique for reliably ensuring the sealing performance of an outer seal.
prior art documents
patent literature
[0011]
Patent Document 1: International Publication No. 2018/211873
Patent Document 2: International Publication No. 2016/056222
Patent Document 3: JP 2012-149760 A
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0012]
　In order to maintain the sealing performance due to the interference between the sealing surfaces, it is effective to improve the compression resistance performance of the threaded joint. This is because if the compressive load deforms each part of the threaded joint and shifts the position of the seal faces in the axial direction, an appropriate amount of interference cannot be introduced between the seal faces, which adversely affects the sealing performance.
[0013]
However, in threaded joints with two-stage screw structures, such as integral, flush and semi-flush, it is difficult to secure a large contact width between the intermediate shoulder surfaces (that is, the radial width of the contacting portion) due to thickness restrictions. is difficult. If the contact width between the intermediate shoulder surfaces is increased, the thickness of the threaded portion of the pin and the box and the thickness of the seal portion will be sacrificed, resulting in a decrease in sealing performance, etc., and also making it difficult to secure the area of ​​the intermediate dangerous cross section of the pin and box. , the tensile strength and sealing performance of the threaded joint are lowered.
[0014]
On the other hand, due to the development of further high-temperature, high-pressure deep wells in recent years, further improvement in compression resistance performance is required, and the technology disclosed in Patent Document 1, which bears the compression load only on the intermediate shoulder surface, is sufficient for compression resistance. performance is not obtained.
[0015]
In the above-mentioned Patent Document 3, in a threaded joint for pipes in which a shoulder surface is provided at the tip of the nose portion extending from the male thread portion of the pin to the pipe end side, the screw gap G between the insertion surfaces of the male and female screws is set to 0.01. By making it within the range of ~ 0.1 mm, when an axial compressive load is applied, the insertion surfaces of the male and female threads are brought into contact with each other so as to bear a part of the axial compressive load, thereby improving compression resistance performance. Techniques are disclosed.
[0016]
However, Patent Document 3 is a document relating to a threaded joint of a type different from a threaded joint having a two-step thread structure, and Patent Document 3 does not cause undesirable deformation on the intermediate shoulder surface of the threaded joint having a two-step thread structure. There is no disclosure of the size of the inter-insertion surface gap for this purpose.
[0017]
An object of the present disclosure is to further improve compression resistance performance in a threaded joint for pipes with a two-step screw structure.
Means to solve problems
[0018]
The inventor of the present application focused on how the intermediate shoulder surface deforms when a compressive load is applied in a threaded joint for pipes with a two-step screw structure, and the amount of deformation, and mainly by elasto-plastic analysis using computer simulation. Analysis was carried out. As a result, it was confirmed that the intermediate shoulder surfaces of the pin and the box have the characteristic that the larger the axial compressive load applied, the larger the shoulder rotation angle θ. Furthermore, when the axial compressive load is borne only by the intermediate shoulder surface, as shown in FIG. It was found that the unit increment Δθ increased sharply.
[0019]
In this specification, as shown in FIG. 2, the shoulder rotation angle .theta. It is the angle formed by the straight line L1 and the straight line L2 passing through the outer end P2 of the intermediate shoulder surface of the pin and the inner end B2 of the intermediate shoulder surface of the box in the longitudinal section under axial compressive load. In FIG. 2, the intermediate shoulder surface at the time of completion of fastening is indicated by a phantom line, and the intermediate shoulder surface when an axial compressive load is applied is indicated by a solid line. In FIG. 2, the B2 point is superimposed on the B1 point, but in reality, the B1 point and the B2 point do not always overlap. The outer end of the intermediate shoulder surface of the pin is the outer end of the contact surface that is in contact with the intermediate shoulder surface of the box, and is not the outer end of the chamfer provided on the outer peripheral edge of the intermediate shoulder surface of the pin. . In addition, the inner end of the intermediate shoulder surface of the box is the inner end of the contact surface that is in contact with the intermediate shoulder surface of the pin, and is not the inner end of the chamfer provided on the inner peripheral edge of the intermediate shoulder surface of the box. .
[0020]
Also, in this specification, the "time of completion of fastening" means the time when neither the axial load nor the internal and external pressure is applied to the threaded joint after fastening the pin to the box. On the other hand, the 'fastened state' means a state in which the pin and the box are fastened regardless of whether or not an axial load and internal and external pressure are applied, and the threaded joint is not broken or the pin and box are sealed. If the pin and the box are fastened even after the axial load and the internal and external pressure are applied within the range where the contact surface pressure of the surfaces is not lost, more preferably within the elastic range, they are in the "fastened state". In the present disclosure, the “axial load and internal/external pressure within the elastic range” may be the axial load and internal/external pressure within the yield ellipse where the threaded joint of interest guarantees strength.
[0021]
If the shoulder rotation angle of the intermediate shoulder surface becomes too large, plastic strain tends to accumulate in the vicinity of the intermediate shoulder surface, which is not preferable. In addition, a large shoulder rotation angle induces crushing deformation near the outer end of the intermediate shoulder surface of the pin and near the inner end of the intermediate shoulder surface of the box, thereby reducing the subsequent substantial shoulder contact area. It is possible.
[0022]
Therefore, at time X (see FIG. 1) before the unit increment Δθ of the shoulder rotation angle θ abruptly increases, the gap between the insertion surfaces at the completion of fastening is large enough so that the insertion surfaces of the male and female screws start to come into contact with each other. By setting the thickness, the compressive load acting on the intermediate shoulder surface can be reduced even when a relatively large compressive load is applied, and as shown by the two-dot chain line in FIG. It is considered that the amount of increase in the rotation angle θ can be moderated.
[0023]
Next, the inventor of the present application verified the angle at which the unit increment Δθ of the shoulder rotation angle θ abruptly increases for threaded joints of a plurality of pipe diameter sizes. It was found that the unit increment .DELTA..theta. of the shoulder rotation angle .theta.
[0024]
When an axial compressive load is applied to a two-stage threaded joint having an intermediate shoulder, compressive strain occurs in the pin and box, and the axial contraction amount α of the pin and box increases as the distance from the intermediate shoulder increases in the axial direction. Therefore, when the size of the gap between the insertion surfaces is uniform over the entire length, when the compressive load is gradually increased, the contact between the insertion surfaces starts from the portion far from the intermediate shoulder, and the insertion proceeds to the portion closer to the intermediate shoulder. Face-to-face contact tends to progress.
[0025]
Also, the amount of relative displacement between the insertion surfaces of the pin and the box is affected by the amount of axial deviation β of the pin and the box due to rotational deformation of the intermediate shoulder, in addition to the amount of contraction α. Dsh is the distance between the radially outer end of the intermediate shoulder surface of the pin and the radially inner end of the intermediate shoulder surface of the box (i.e., the radial width of the contact portion between the intermediate shoulder surfaces) in the longitudinal section at the completion of fastening. Then, as shown in FIG. 2, the amount of deviation β is given by Dsh×tan θ.
[0026]
　The above relative displacement amount of the part where the insertion surfaces of the pin and box start to contact each other is
Therefore, in order to start the contact between the insertion surfaces at a shoulder rotation angle of less than 1°, the following equation (1) should be established.
　G≦α+β=α+Dsh×tan1° (1)
Here, α is the amount of axial displacement due to compressive strain based on the intermediate shoulder of the portion where the insertion surfaces start contacting each other when an axial compressive load is applied at which the insertion surfaces start contacting each other.
[0027]
The inventors of the present application determined the insertion surface gap G at which the insertion surfaces start contacting each other when the shoulder rotation angle θ is 1° or less for two types of specimens with shoulder contact widths Dsh of 1.80 mm and 1.92 mm. As a result of verification by elasto-plastic analysis by computer simulation, it was confirmed that if the insertion surface gap G is 0.15 mm or less, the insertion surfaces start contacting each other when the shoulder rotation angle θ is 1° or less. However, for a larger shoulder contact width Dsh, a larger insertionEven with the face gap G, it is considered possible to suppress the shoulder rotation angle θ to 1° or less.
[0028]
When α is obtained by substituting G=0.15 and Dsh=1.80 mm or 1.92 mm into the above formula (1), α=0.12 mm is obtained.
[0029]
The greater the shoulder contact width Dsh, the greater the axial compressive load for rotating the intermediate shoulder by 1°. Furthermore, normally, the larger the pipe diameter, the larger the shoulder contact width Dsh. Therefore, it can be assumed that the value of α when the shoulder rotation angle θ is 1° is substantially constant regardless of the pipe diameter size.
[0030]
This disclosure has been made based on these findings.
[0031]
A threaded joint for pipes according to the present disclosure includes a tubular pin and a tubular box, and the pin and the box are fastened by screwing the pin into the box. The pin has an external thread including axially spaced internal and external threads, and an intermediate shoulder surface disposed between the internal and external threads of the external thread. The box includes a female thread including an inner threaded portion into which the inner threaded portion of the male thread is fitted and an outer threaded portion into which the outer threaded portion of the male thread is fitted in a fastened state, the inner threaded portion of the female thread and the outer threaded portion. an intermediate shoulder surface provided between the threaded portion and contacting the intermediate shoulder surface of the pin in a fastened state. The male thread and the female thread are configured such that the load surfaces of the male thread and the female thread are in contact with each other and a gap is formed between the insertion surfaces of the male thread and the female thread when fastening is completed. The gap formed between the insertion surfaces of the male thread and the female thread at the time of completion of fastening is such that the pin and the box are compressed when a predetermined axial compressive load smaller than the yield compressive load of the pin and the box is applied. , the insertion surfaces of the male thread and the female thread start contacting each other so as to bear part of the axial compressive load.
[0032]
A threaded joint for pipes according to the present disclosure satisfies the following formula (1).
　G ≤ 0.12 + Dsh x tan1° (1)
Here, G is the size of the gap formed between the insertion surfaces of the male thread and the female thread at the time of completion of fastening in the direction along the pipe axis direction, and Dsh is the vertical cross section of the pin at the time of completion of fastening. is the distance between the radially outer edge of the intermediate shoulder surface of the box and the radially inner edge of the intermediate shoulder surface of said box.
Effect of the invention
[0033]
According to the present disclosure, in a threaded joint having a two-step thread structure, when a gradually increasing axial compressive load is applied, the insertion surfaces of the male and female threads come into contact with each other before the unit increment Δθ of the intermediate shoulder surface becomes large. and having these insertion surfaces bear a portion of the axial compressive load,
Even when a relatively large axial compressive load is applied, the shoulder rotation angle θ of the intermediate shoulder surface, that is, the amount of rotational deformation of the longitudinal cross-sectional shape of the intermediate shoulder surface, can be made relatively small, and damage accumulated on the intermediate shoulder surface can be reduced. can be suppressed. As a result, the compression resistance performance of the threaded joint having the two-step thread structure can be further improved.
Brief description of the drawing
[0034]
1] Fig. 1 is a graph showing the relationship between the axial compressive load and the shoulder rotation angle in a threaded joint for pipes having a two-step screw structure, in the case where only the intermediate shoulder surface bears the axial compressive load.
2] Fig. 2 is a simplified enlarged cross-sectional view showing a deformation state of an intermediate shoulder surface when an axial compressive load is applied to a threaded joint for pipes having a two-step screw structure. [Fig.
3] FIG. 3 is a longitudinal sectional view showing a fastened state of the threaded joint for oil country tubular good according to the embodiment. [FIG.
4] Fig. 4 is a diagram showing paths of a combined load applied to specimens #1 to #10. [Fig.
5] Fig. 5 is a diagram showing paths of combined loads applied to specimens #11 to #20. [Fig.
6] FIG. 6 is a graph showing the relationship between the compressive load and the shoulder rotation angle when a simple compressive load is gradually applied to specimens #1 to #5. [FIG.
7] FIG. 7 is a graph showing the relationship between the compressive load and the shoulder rotation angle when a gradually increasing simple compressive load is applied to specimens #6 to #10. [FIG.
8] FIG. 8 is a graph showing the relationship between the compressive load and the shoulder rotation angle when a gradually increasing simple compressive load is applied to specimens #11 to #15. [FIG.
9] FIG. 9 is a graph showing the relationship between the compressive load and the shoulder rotation angle when a gradually increasing simple compressive load is applied to specimens #16 to #20. [FIG.
10] Fig. 10 is a graph showing the shoulder rotation angle at each load step of two specimens #1 and #6 with different axial lengths of inner grooves. [Fig.
11] Fig. 11 is a graph showing the shoulder rotation angle at each load step of two specimens #2 and #7 having inner grooves with different axial lengths. [Fig.
12] Fig. 12 is a graph showing the shoulder rotation angle at each load step of two specimens #3 and #8 with different axial lengths of inner grooves. [Fig.
13] Fig. 13 is a graph showing the shoulder rotation angle at each load step of two specimens #4 and #9 with different axial lengths of inner grooves. [Fig.
14] FIG. 14 is a graph showing the shoulder rotation angle at each load step of two specimens #5 and #10 with different axial lengths of inner grooves. [FIG.
15] Fig. 15 is a graph showing the shoulder rotation angle at each load step of two specimens #11 and #16 with different axial lengths of inner grooves. [Fig.
16] Fig. 16 is a graph showing shoulder rotation angles at each load step of two specimens #12 and #17 having inner grooves with different axial lengths. [Fig.
17] Fig. 17 is a graph showing shoulder rotation angles at each load step of two specimens #13 and #18 having inner grooves with different axial lengths. [Fig.
18] Fig. 18 is a graph showing the shoulder rotation angle at each load step of two specimens #14 and #19 having inner grooves with different axial lengths. [Fig.
19] Fig. 19 is a graph showing the shoulder rotation angle at each load step of two specimens #15 and #20 in which the axial length of the inner groove is changed. [Fig.
MODE FOR CARRYING OUT THE INVENTION
[0035]
The threaded joint according to this embodiment is composed of a tubular pin and a tubular box. The pin and box are fastened together by screwing the pin into the box. A pin is provided at the tube end of the first tube and a box is provided at the tube end of the second tube. The first pipe may be a long pipe such as an oil well pipe. The second pipe may be a long pipe such as an oil well pipe, or may be a coupling for connecting long 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.
[0036]
The pin may comprise an external thread including axially spaced internal and external threads, and an intermediate shoulder surface provided between the internal and external threads of the external thread. Preferably, the internal and external threads each comprise a tapered thread. The inner threaded portion can be arranged closer to the pipe end than the outer threaded portion. Preferably, the tapered generatrix of the tapered thread forming the inner threaded portion is located radially inwardly of the taper generatrix of the tapered thread forming the external threaded portion. The intermediate shoulder surface may comprise a side surface of a step formed on the outer circumference of the pin between the inner and outer threads. The intermediate shoulder surface faces the tube end side of the pin. The internal and external threads may each be trapezoidal threads, API round threads, API buttress threads, dovetail threads, or the like.
[0037]
The box can include internal threads including axially spaced internal and external threads, and an intermediate shoulder surface provided between the internal and external threads of the internal threads. Preferably, the internal and external threads of the female thread comprise tapered threads that match the internal and external threads of the male thread, respectively. The inner threaded portion of the female thread is fitted with the inner threaded portion of the male thread in a fastened state. The outer threaded portion of the female thread is fitted with the outer threaded portion of the male thread in a fastened state. The intermediate shoulder surface of the box can be constituted by the side surface of a step formed on the inner circumference of the box between the inner threaded portion and the outer threaded portion of the female thread. The intermediate shoulder surface of the box faces the tube end side of the box and faces the intermediate shoulder surface of the pin. The intermediate shoulder surfaces of the box contact intermediate shoulder surfaces of the pin in the fastened state, and these intermediate shoulder surfaces act as torque shoulders. The internal and external threads of the female threads may be trapezoidal threads, API round threads, API buttress threads, dovetail threads, or the like that match the internal and external threads of the male threads, respectively.

The scope of the claims

[Claim 1]
A threaded joint for pipes, comprising a tubular pin and a tubular box, wherein the pin is screwed into the box to fasten the pin and the box,
the pin comprises an external thread including axially spaced internal and external threaded portions, and an intermediate shoulder surface provided between the internal and external threaded portions of the external thread;
The box includes a female thread including an inner threaded portion into which the inner threaded portion of the male thread is fitted and an outer threaded portion into which the outer threaded portion of the male thread is fitted in a fastened state, the inner threaded portion of the female thread and the outer threaded portion. an intermediate shoulder surface provided between the threaded portion and in contact with the intermediate shoulder surface of the pin in a fastened state;
The male and female threads are configured so that the load surfaces of the male and female threads are in contact with each other and a gap is formed between the insertion surfaces of the male and female threads at the time of completion of fastening,
The gap formed between the insertion surfaces of the male thread and the female thread at the time of completion of fastening is such that the pin and the box are compressed when a predetermined axial compressive load smaller than the yield compressive load of the pin and the box is applied. The deformation of the male screw and the female screw is sized to start contact so that the insertion surfaces of the male screw and the female screw bear a part of the axial compressive load,
A threaded joint for pipes that satisfies the following formula (1).
　G ≤ 0.12 + Dsh x tan1° (1)
Here, G is the size of the gap formed between the insertion surfaces of the male thread and the female thread at the time of completion of fastening in the direction along the pipe axis direction, and Dsh is the vertical cross section of the pin at the time of completion of fastening. is the distance between the radially outer edge of the intermediate shoulder surface of the box and the radially inner edge of the intermediate shoulder surface of said box.
[Claim 2]
The threaded joint for pipes according to claim 1, wherein G≦0.15 mm is satisfied.
[Claim 3]
The threaded joint for pipes according to claim 1 or 2, wherein G≧0.06 mm is satisfied.
[Claim 4]
In the threaded joint for pipes according to claim 1, 2 or 3,
The pin has a sealing surface provided on the tip side of the pin from the male thread,
The box has a seal surface that contacts the seal surface of the pin in a fastened state, and extends along a circumferential direction provided at a portion of the inner circumference of the box between the seal surface of the box and the female thread. an internal groove, the internal groove receiving a portion of the external thread of the pin in a fastened state;
A threaded joint for pipes, wherein the inner groove has a groove bottom with an axial width smaller than twice the thread pitch of the male thread.
[Claim 5]
In the threaded joint for pipes according to any one of claims 1 to 4,
The intermediate shoulder surfaces of the pin and the box have a characteristic that the larger the axial compressive load applied to them, the larger the shoulder rotation angle θ. , wherein the shoulder rotation angle θ at the time when contact starts to bear is less than 1°.
Here, the shoulder rotation angle ? It is the angle formed by a straight line passing through the radially outer end of the intermediate shoulder surface of the pin and the radially inner end of the intermediate shoulder surface of the box in the longitudinal section under load.