Specification
Title of invention: Steel pipe threaded joint
Technical field
[0001]
　The present disclosure relates to a threaded joint for steel pipes.
Background technology
[0002]
　For example, exploration or production of oil wells and natural gas wells (hereinafter also collectively referred to as “oil wells”), development of unconventional resources such as oil sands and shale gas, carbon dioxide capture and storage (CCS (Carbon) (Dioxide Capture and Storage)), geothermal power generation, hot springs, etc., steel pipes called oil well pipes are used. A threaded joint is used to connect the steel pipes together.
[0003]
　The type of threaded joint for steel pipes of this kind is roughly classified into a coupling type and an integral type. In the case of the coupling type, one of the pair of pipe members to be connected is a steel pipe and the other pipe member is a coupling. In this case, male threads are formed on the outer circumferences of both ends of the steel pipe, and female threads are formed on the inner circumferences of both ends of the coupling. Then, the male thread of the steel pipe is screwed into the female thread of the coupling, whereby the both are fastened and connected. In the case of the integral type, the pair of pipe materials to be connected are both steel pipes, and separate couplings are not used. In this case, a male screw is formed on the outer circumference of one end of the steel pipe and a female screw is formed on the inner circumference of the other end. Then, the male screw of one steel pipe is screwed into the female screw of the other steel pipe, whereby both are fastened and connected.
[0004]
　Generally, the male threaded tube end fitting portion is referred to as a "pin" because it includes the elements that are inserted into the female thread. On the other hand, the female threaded end of the pipe is referred to as a "box" because it includes an element for receiving a male thread. These pins and boxes are tubular because they are the ends of the tubing.
[0005]
　In the oil well, the well wall is reinforced by the oil well pipe so that the well wall does not collapse during the excavation, and the digging proceeds. Therefore, the oil well pipe has a structure in which it is multiply arranged. In recent years, deepening and deepening of oil wells are progressing more and more, but in such an environment, in order to efficiently develop an oil well, the inner and outer diameters of the joint part should be Threaded joints that are as large as or slightly larger than the inner and outer diameters are often used. By using such a screw joint, it is possible to minimize the gap between the oil well pipes that are arranged in a multiple manner, and it is possible to efficiently develop the oil well without increasing the diameter of the well even if it is deep. Under such restrictions of the inner diameter and the outer diameter, the threaded joint has a fluid pressure from the inside (hereinafter, also referred to as “internal pressure”) and a fluid pressure from the outside (hereinafter also referred to as “external pressure”). On the other hand, excellent sealing performance is required. Further, for example, when used in a deep oil well, thermal expansion of the oil well pipe causes a large tensile load or compressive load on the threaded joint. Even in such an environment, the threaded joint is required to have excellent sealing performance.
[0006]
　As a threaded joint for ensuring the sealing performance, a threaded joint having a metal-to-metal contact seal (hereinafter referred to as "metal seal") is known. A metal seal means that the diameter of the pin sealing surface is slightly larger than the diameter of the box sealing surface (the difference in this diameter is called the "interference amount"), and the screw joints are fastened to fit the sealing surfaces together. Then, the seal surface of the pin contracts due to the amount of interference, the seal surface of the box expands, and the elastic recovery force that causes each seal surface to return to its original diameter creates contact pressure on the seal surface. It is a structure that closely adheres to the circumference and exhibits sealing performance.
[0007]
　Japanese Patent Publication No. 2006-526747 (Patent Document 1) discloses a steel pipe threaded joint including a pin and a box. The pin has a male thread, a sealing surface, and a shoulder surface. Correspondingly, the box has an internal thread, a sealing surface and a shoulder surface. The pin has a nose portion provided between the seal surface and the shoulder surface. The nose part is not in contact with the corresponding part of the box. It is described that the shoulder angle is preferably 4 to 16 degrees with respect to the plane perpendicular to the tube axis.
[0008]
　Japanese Unexamined Patent Publication No. 2013-29176 (Patent Document 2) discloses a threaded joint for steel pipes, which includes a pin and a box. The pin has a male screw portion, a nose portion extending toward the pipe end side from the male screw portion, and a shoulder portion provided at the tip of the nose portion. The box has a female threaded portion that is screwed to the male threaded portion to form a threaded portion, a sealing surface that faces the outer peripheral surface of the nose portion of the pin, and a shoulder portion that abuts the shoulder portion of the pin. The outer peripheral surface of the nose portion of the pin has a curved surface shape that is convex outward. The sealing surface of the box has a single taper shape. The outer peripheral surface of the nose portion of the pin and the sealing surface of the box make metal-to-metal contact, and the contact portion forms the sealing portion.
[0009]
　Japanese Unexamined Patent Application Publication No. 2014-13052 (Patent Document 3) discloses a threaded joint for a pipe including a pin member and a box member. The pin member has a male screw portion, a nose portion extending toward the pipe end side from the male screw portion, and a shoulder portion provided at the tip of the nose portion. The box member has a female screw portion that is screwed to the male screw portion, an inner peripheral surface that faces the outer peripheral surface of the pin nose that is the nose portion of the pin member, and a shoulder portion that abuts the shoulder portion of the pin member. The outer peripheral surface of the pin nose is a convex curved surface. The inner peripheral surface of the box member is a tapered surface that interferes with the convex curved surface of the pin nose when coupled to the pin member. The shoulder angle of the shoulder portion is 0 degree or more. The pin member and the box member are connected by screw connection, the convex curved surface of the pin nose and the tapered surface of the box member are in metal-metal contact, and the contact interface forms a seal portion.
[0010]
　This specification incorporates the following documents by reference.
Patent Document 1: Japanese
Patent Laid-Open No. 2006-526747 Patent Document 2: Japanese Patent Laid-Open No. 2013-29176
Patent Document 3: Japanese Patent Laid-Open No. 2014-13052
Summary of disclosure
[0011]
　An object of the present disclosure is to provide a steel pipe threaded joint capable of improving sealing performance against internal pressure and external pressure.
[0012]
　The present inventors have diligently studied factors that affect the sealing performance against internal pressure and external pressure in addition to the shoulder angle. As a result, the inventors have newly found that the distance from the tip of the pin to the metal seal affects the sealing performance. In addition to this finding, the present inventors have newly found that the wall thickness ratio between the pin and the box in the metal seal, which has not been studied in the past, affects the sealing performance. Based on these new findings, the present inventors have invented the following threaded joint.
[0013]
　A steel pipe threaded joint according to the present disclosure includes a tubular pin formed at one end of a steel pipe, and a tubular box into which the pin is inserted and fastened to the pin. The pin has a male screw formed on the outer periphery of the pin, a nose formed on the tip of the pin and having an outer diameter smaller than the inner diameter of the facing portion of the box in a state where the pin and the box are fastened, and a nose. And a pin seal surface formed on the outer peripheral surface of the pin between the male screw and the nose. The pin seal surface is a first curvature surface located closer to the pin shoulder surface, a second curvature surface located farther from the pin shoulder surface, and a first taper located between the first curvature surface and the second curvature surface. Including faces. The box corresponds to the male screw and faces the female screw formed on the inner circumference of the box, the pin shoulder surface, and the box shoulder surface that contacts the pin shoulder surface when the pin and the box are fastened, and the pin seal surface. , And a box seal surface that contacts the pin seal surface when the pin and the box are fastened. The box sealing surface is located between the third curvature surface located closer to the box shoulder surface, the fourth curvature surface located farther from the box shoulder surface, and between the third curvature surface and the fourth curvature surface. And a second taper surface. The box seal surface has a seal point located at a midpoint in the tube axial direction on the second tapered surface. The seal point distance between the tip of the nose and the seal point in the tube axis direction is 13 mm or more. The shoulder angle between the pin shoulder surface or box shoulder surface and the plane perpendicular to the tube axis is 2 to 13 degrees. The seal wall thickness ratio of the box wall thickness to the pin wall thickness at the seal point is 1.7 or more. Here, the seal point distance may be 13 to 25 mm. The shoulder angle may be 2-10 degrees. The seal wall thickness ratio may be 1.8 to 3.0.
Brief description of the drawings
[0014]
FIG. 1 is a vertical cross-sectional view of a coupling type threaded joint for steel pipes according to an embodiment, taken along the pipe axis direction.
[FIG. 2] FIG. 2 is a vertical cross-sectional view of an integral type threaded joint for steel pipes different from that of FIG. 1, taken along the pipe axis direction.
FIG. 3 is an enlarged vertical sectional view of a portion II in FIG.
[FIG. 4] FIG. 4 is an enlarged vertical cross-sectional view of the vicinity of the seal and the nose in FIG. 3.
FIG. 5 is a graph showing a route of load conditions used in FEM analysis.
FIG. 6 is a graph showing evaluation results of torque performance.
FIG. 7 is a graph showing evaluation results of sealing performance under a composite load.
FIG. 8 is a graph showing evaluation results of sealing performance against external pressure.
FIG. 9 is a graph showing evaluation results of sealing performance with respect to internal pressure.
MODE FOR CARRYING OUT THE INVENTION
[0015]
　Hereinafter, a threaded joint for steel pipes according to the present embodiment will be described with reference to the drawings. In the drawings, the same or corresponding components are designated by the same reference numerals, and the same description will not be repeated.
[0016]
　Referring to FIG. 1, a steel pipe threaded joint 1 according to the present embodiment includes a tubular pin 10 and a tubular box 20. The pin 10 is formed at one end of the steel pipe 2. In the box 20, the pin 10 is inserted and fastened to the pin 10. Hereinafter, the portion other than the tip end portion of the steel pipe 2 may be particularly referred to as "steel pipe main body".
[0017]
　The threaded joint 1 shown in FIG. 1 is a coupling type and includes two pins 10 and 10 and a coupling 3. One pin 10 is formed at the tip of one steel pipe 2. The other pin 10 is formed at the tip of the other steel pipe 2. The coupling 3 includes two boxes 20, 20 and an annular protrusion 31. One box 20 is formed at one end of the coupling 3. The other box 20 is formed at the other end of the coupling 3. The protrusion 31 is formed at the center of the coupling 3. One box 10 is inserted into one box 20 and fastened to the other pin 10. The other box 20 is formed on the opposite side of the one box 20, and the other pin 10 is inserted and fastened to the other pin 10.
[0018]
　However, the threaded joint 1 may be an integral type. As shown in FIG. 2, the integral type threaded joint 1 is for connecting two steel pipes 2 to each other, and includes a pin 10 and a box 20. In the integral type threaded joint 1, one steel pipe 2 includes a pin 10 and the other steel pipe 2 includes a box 20.
[0019]
　With reference to FIGS. 1 and 3, the pin 10 includes a male screw 11, a nose 12, a pin shoulder surface 13, and a pin seal surface 14. The male screw 11 is formed on the outer periphery of the pin 10. The nose 12 is formed at the tip of the pin 10 and has an outer diameter smaller than the inner diameter of the facing portion of the box 20 in a state where the pin 10 and the box 20 are fastened. Therefore, a minute gap is formed between the outer peripheral surface of the nose 12 of the pin 10 and the inner peripheral surface of the box 20 facing the pin 10, as shown in FIG. The pin shoulder surface 13 is formed at the tip of the nose 12. The pin seal surface 14 is formed on the outer peripheral surface of the pin 10 between the male screw 11 and the nose 12.
[0020]
　The pin seal surface 14 includes a curvature surface 141 located closer to the pin shoulder surface 13, a curvature surface 143 located farther from the pin shoulder surface 13, and a taper surface 142 located between the curvature surface 141 and the curvature surface 143. including. That is, the pin seal surface 14 includes the curved surface 141, the tapered surface 142, and the curved surface 143. The curvature surface 141, the taper surface 142, and the curvature surface 143 are arranged in order along the tube axis direction CL.
[0021]
　The box 20 includes an internal thread 21, a box shoulder surface 23, and a box sealing surface 24. The female screw 21 corresponds to the male screw 11 and is formed on the inner circumference of the box 20. The box shoulder surface 23 faces the pin shoulder surface 13, and contacts the pin shoulder surface 13 in a state where the pin 10 and the box 20 are fastened. The box sealing surface 24 faces the pin sealing surface 14, and contacts the pin sealing surface 14 in a state where the pin 10 and the box 20 are fastened.
[0022]
　The box sealing surface 24 has a curvature surface 241 located closer to the box shoulder surface 23, a curvature surface 243 located farther from the box shoulder surface 23, and a taper located between the curvature surface 241 and the curvature surface 243. Surface 242. That is, the box sealing surface 24 includes the curved surface 241, the tapered surface 242, and the curved surface 243. The curvature surface 241, the taper surface 242, and the curvature surface 243 are arranged in order along the tube axis direction CL.
[0023]
　The male screw 11 and the female screw 21 are trapezoidal screws whose shape is changed based on a buttress screw.
[0024]
　With reference to FIGS. 3 and 4, the box sealing surface 24 has a sealing point SP. The seal point SP is located on the taper surface 242 of the box seal surface 24 at the midpoint of the box seal surface 24 in the tube axis direction CL. The seal point distance L SP is 13 mm or more. The seal point distance L SP is the distance between the tip of the nose 12 and the seal point SP in the tube axis direction CL. The shoulder angle α is 2 to 13 degrees. The shoulder angle α is an angle between the pin shoulder surface 13 or the box shoulder surface 23 and the plane VP perpendicular to the tube axis CL. The seal wall thickness ratio T B /T P is 1.7 or more. The seal wall thickness ratio T B /T P is the wall thickness of the box 20 relative to the wall thickness of the pin 10 at the seal point SP (hereinafter referred to as “pin seal wall thickness”) T P (hereinafter referred to as “box seal wall thickness”). ) The ratio of T B. In FIG. 3, W indicates the outer diameter of the box 20, and ID indicates the inner diameter of the tube body 2.
[0025]
　Here, the lower limit value of the seal point distance L SP is preferably 14 mm, more preferably 15 mm. Sealing point distance L SP so manufacturability is too long is not reduced, the sealing point distance L SP upper limit of, for example, may be 25 mm, preferably 24 mm, more preferably 23 mm. The lower limit value of the shoulder angle α is preferably 3 degrees, more preferably 4 degrees. The upper limit of the shoulder angle α is preferably 10 degrees, more preferably 9 degrees. The lower limit of the seal wall thickness ratio T B /T P is preferably 1.8, and more preferably 1.9. The upper limit of the seal wall thickness ratio T B /T P is, for example , so that the outer diameter of the coupling 3 is not too large and interferes with the inner surface of the outer pin 10 when a plurality of steel pipes are inserted in a well in a multilayer manner. Although it may be 3.0, it is preferably 2.9, more preferably 2.8.
[0026]
　In the above-described embodiment, since the seal point distance L SP is 13 mm or more, the rigidity of the nose 12 is high, and even when a compressive load is applied to the threaded joint 1, the nose 12 bears the compressive load so that the metal is Deflection of the seal surface of the seal can be suppressed, and a decrease in contact surface pressure can be suppressed. In addition, since the seal wall thickness ratio T B /T P is 1.7 or more, the rigidity of the box 20 becomes high, and the pushing resistance of the box 20 due to the internal pressure becomes particularly high, so that the close contact of the seal surface is maintained. Therefore, it is possible to suppress a decrease in the contact surface pressure of the metal seal. As a result, the sealing performance against internal pressure and external pressure can be improved.
[0027]
　Although the embodiment has been described above, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the invention.
Example
[0028]
　In order to verify the effect of this embodiment, torque performance and sealing performance were evaluated by the finite element method (FEM). The evaluation target was a buttress threaded joint, and the following steel pipes were used.
　Size: 7 inches, 26# (outer diameter of pipe body: 177.8 mm, inner diameter of pipe body: 159.41 mm)
　Material: API well oil well pipe material L80 (nominal yield strength YS=552 MPa (80 ksi))
[0029]
　Tables 1 and 2 show the dimensions and evaluation results of 42 types of experimental examples used for the analysis. Here, the outer diameter of the pipe body 2, the inner diameter ID of the pipe body 2, the outer diameter W of the box 20, the pin seal wall thickness T P , the box seal wall thickness T B , and the seal wall thickness ratio T B /T P are made constant. , The seal point (SP) distance L SP and the shoulder angle α were changed. Table 1 is sorted by the seal point distance L SP , and shows the yield torque as the evaluation result of the torque performance. Table 2 is sorted by the shoulder angle α and shows the minimum seal contact force as the evaluation result of the sealing performance. The yield torque and the minimum seal contact force will be defined later. The shoulder angle α of the pin 10 and the shoulder angle α of the box were the same.
[0030]
[table 1]

[0031]
[Table 2]

[0032]
　Table 3 shows the dimensions of eight different experimental examples different from the above except the substitute 5 (the same as the substitute 33 in Tables 1 and 2) and the evaluation results of the sealing performance. Here, the outer diameter of the pipe body 2, the inner diameter ID of the pipe body 2, the pin seal wall thickness T P , the seal point distance L SP , and the shoulder angle α are kept constant, and the outer diameter W of the box 20 and the box seal wall thickness T B are set. seal thickness ratio T by varying the B / T P was varied. In addition, as a result of evaluation of sealing performance against external pressure and internal pressure, the minimum seal contact force when external pressure and internal pressure are applied is shown.
[0033]
[Table 3]

[0034]
　Regarding the torque performance, a value MTV (Maximum Torque Value) at which the fastening torque diagram starts to yield is defined as “yield torque”, and the value is used for evaluation. Regarding the sealing performance, analysis was performed under the combined load condition simulating the ISO13679 series A test shown in FIG. , And evaluated using that value. Moreover, when evaluating the influence of the seal wall thickness ratio T B /T P , the sealing performance under simple external pressure and simple internal pressure was also considered. Only the external pressure or the internal pressure was gradually increased without applying the axial force, and the minimum seal contact force at that time was evaluated.
[0035]
　FIG. 6 shows the yield torque obtained by FEM. From FIG. 6, it was found that the yield torque depends on the seal point distance L SP and the shoulder angle α. It is considered that the torque performance is improved because the rigidity is increased as the seal point distance L SP is increased. On the other hand, when the shoulder angle α was 5 degrees, the yield torque became maximum, and when the shoulder angle α was larger than 5 degrees, the yield torque decreased. As described above, since the torque performance is greatly affected by the shoulder angle α, it has been found that the shoulder angle α is preferably 2 to 13 degrees.
[0036]
　FIG. 7 shows the evaluation results of the sealing performance under a composite load. The minimum seal contact force was generated by the simple external pressure of load step (12) in FIG. From FIG. 7, it was found that if the seal point distance L SP is 13 mm or more, the sealing performance is improved regardless of the shoulder angle α. From these evaluation results, it was found that the shoulder angle α is 2 to 13 degrees and the seal point distance L SP is 13 mm or more in order to achieve both high sealing performance and high torque performance .
[0037]
　In addition, as shown in Table 3, the shoulder angle α was fixed at 5 degrees, the seal point distance L SP was fixed at 13 mm, and the seal wall thickness ratio T B /T P was changed. In order to investigate the effect of the seal wall thickness ratio T B /T P on the sealing performance, the sealing performance was evaluated using the load paths of simple internal pressure and simple external pressure shown in FIG. FIG. 8 shows the evaluation results of the sealing performance under a simple external pressure and FIG. 9 under a simple internal pressure. In either case , the sealing performance improved as the seal wall thickness ratio T B /T P increased, but especially from FIG. 9, the sealing performance against the internal pressure is remarkable when the seal wall thickness ratio T B /T P is less than 1.7. Very low and saturated above 1.7. Therefore, it was found that the seal wall thickness ratio T B /T P is preferably 1.7 or more.
Explanation of symbols
[0038]
1: Threaded joint
2: Steel pipe (steel pipe main body)
3: Coupling
10: Pin
11 : Male screw
12: Nose
13: Pin shoulder surface
14: Pin seal surface
20: Box
21: Female screw
23: Box shoulder surface
24: Box seal surface
141, 143,241,243: curvature surface
142, 242: tapered surface
SP: seal point
L SP : seal point distance
alpha: shoulder angle
T B / T P : seal thickness ratio
CL: tube axis
The scope of the claims
[Claim 1]
　A threaded joint for steel pipes,
　comprising a tubular pin formed at one end of the steel pipe,
　and a tubular box into which the pin is inserted and fastened to the
　pin , wherein the pin is provided on
　the outer periphery of the pin. A male screw formed,
　a nose formed at the tip of the pin and having an outer diameter smaller than the inner diameter of the facing portion of the box with the pin and the box fastened, and
　the tip of the nose. A
　pin shoulder surface formed on the outer peripheral surface of the pin between the male screw and the nose, the pin
　seal surface being a first curvature surface located closer to the pin shoulder surface. And a second curvature surface located farther from the pin shoulder surface and a first taper surface located between the first curvature surface and the second curvature surface, the
　box
　corresponding to the male screw. A female screw formed on the inner circumference of the box,
　a box shoulder surface that
　faces the pin shoulder surface and that contacts the pin shoulder surface while the pin and the box are fastened, and a pin seal surface that faces the box shoulder surface. A box seal surface that contacts the pin seal surface when the pin and the box are fastened together,
　The box sealing surface includes a third curvature surface positioned closer to the box shoulder surface, a fourth curvature surface positioned farther from the box shoulder surface, the third curvature surface and the fourth curvature surface. A second taper surface located between the
　box seal surface and the box seal surface , the box seal surface having a seal point located on the taper surface at a midpoint in the
　tube axis direction, and the tip of the nose and the seal in the tube axis direction. sealing point distance between the points is at 13mm or more,
　the shoulder angle between the plane perpendicular to the Pinshoruda surface or the box shoulder surface and the pipe axis is from 2 to 13 degrees, and
　the at the seal point A threaded joint for steel pipes, wherein a seal wall thickness ratio of the wall thickness of the box to the wall thickness of the pin is 1.7 or more.
[Claim 2]
　The threaded joint for steel pipes according to claim 1,
　wherein the seal point distance is 13 to 25 mm, the
　shoulder angle is 2 to 10 degrees, and the
　seal wall thickness ratio is 1.8 to 3. 0, a threaded joint for steel pipes.