JP5660308B2 - Threaded joints for steel pipes - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a threaded joint for steel pipes, and in particular, oil well pipes including tubing and casings generally used for exploration and production of oil wells and gas wells, that is, OCTG (oil country tubular goods), riser pipes, line pipes, etc. The present invention relates to a threaded joint for steel pipes that is suitable for use in connecting steel pipes and has excellent sealing properties and compression resistance.

  Threaded joints are widely used to connect steel pipes used in oil industry equipment such as oil well pipes. Conventionally, standard threaded joints defined in API (American Petroleum Institute) standards have been used to connect steel pipes used in the search and production of oil and gas. However, in recent years, wells for crude oil and natural gas have been deepened, and horizontal wells and inclined wells have increased from vertical wells, and the drilling and production environment has become severe. In addition, the demand for screw joints such as compression resistance, bending resistance, and external pressure seal performance (external pressure resistance) has diversified due to the increased development of wells in poor environments such as the ocean and polar regions. ing. Therefore, the use of high-performance special threaded joints called premium joints is increasing.

  The premium joint is usually a joint in which a pin member and a box member each having a taper screw, a seal portion (specifically, a metal touch seal portion), and a shoulder portion (specifically, a torque shoulder portion) are combined. The taper screw is important for firmly fixing the pipe joint, and the seal part plays a role of ensuring the sealing performance by the metal contact between the box member and the pin member at this part, and the shoulder part is tightening the joint. It becomes the shoulder surface that plays the role of the stopper.

  FIGS. 2-4 is typical explanatory drawing of the premium joint for oil well pipes, These are the longitudinal cross-sectional views of the threaded joint of a circular pipe. The threaded joint includes a pin member 3 and a box member 1 corresponding thereto, and the pin member 3 (pin 3) is provided on the outer surface thereof adjacent to the male screw 7 and on the tip end side of the pin 3 adjacent to the male screw 7. And a no-thread portion called a nose portion 8 (pin nose 8). The nose portion 8 has a seal portion 11 on its outer peripheral surface and a torque shoulder portion 12 on its end surface. The opposing box member 1 has, on its inner surface, a female screw 5, a seal portion 13, and a portion that can be screwed or contacted with the male screw 7, the seal portion 11, and the shoulder portion 12 of the pin 3, respectively. The shoulder portion 14 is provided.

  Patent documents 1-6 are mentioned as conventional technology about the premium joint.

Japanese Patent No. 4535064 Japanese Patent No. 4208192 Japanese Utility Model Publication No. 61-44068 Japanese Patent No. 4300187 JP 2001-124253 A Japanese Patent No. 2705506

  2 to 4, the metal touch seal portion is at the tip of the pin nose 8. However, in Patent Document 1, a metal touch seal portion is provided near the screw portion of the pin nose 8 in order to increase the external pressure resistance. In addition, it has been proposed to extend the nose part from the seal part to the shoulder part. In the threaded joint disclosed in Patent Document 1, the pin nose that is not in contact with the box member is configured to be elongated so as to be discontinuous with the seal portion so that the thickness of the pin nose is not reduced. In addition to the above-mentioned external pressure resistance, the axial compression resistance is also improved.

Similarly, in Patent Document 2, an appendix is formed from the seal portion to the pin nose tip, which also has a portion having a discontinuous shape with the seal portion to ensure radial rigidity and lower axial rigidity. It is described that this appendix is deformed at the time of tightening and the tensile resistance is improved by recovering the appendix when loaded.
As described in Patent Documents 1 and 2, placing the seal part near the screw part of the pin and separating it from the tip of the pin nose is stable against the screw as well as improving the external pressure resistance and tensile resistance. It is effective in giving a realistic performance, and it can be confirmed from FEM simulations and the like. Further, the pin nose that has a shape discontinuous with the seal portion is deformed itself when a strong axial compressive force is applied, and has an effect of reducing plastic deformation of the torque shoulder portion of the box member. However, on the other hand, unauthorized deformation may occur in the discontinuous portion, which is considered to depend on the tightening torque.

  Since the tightening torque is affected by lubrication conditions, surface properties, etc., a design that does not depend greatly on this is a radial seal method in which the radial contact pressure is increased. For example, Patent Document 3 discloses an example of a radial seal method having a large pin seal R shape and a small seal taper angle. However, a problem with the radial seal method in which the seal taper angle is thus reduced is that goling is likely to occur during tightening. Further, in the radial seal method, it is necessary to increase the amount of seal interference in order to ensure sealing performance and seal stability, and the ease of occurrence of goling is further increased.

  In Patent Document 4, in order to solve these problems, the radius of the toroidal (conical curved rotating surface shape) pin seal surface is specified to be large, thereby increasing the seal contact area and reducing the contact pressure. This measure is effective, and can greatly reduce the goling risk of the metal touch seal part. However, by taking a large R and lowering the contact pressure, there is a problem that the contact pressure is lowered with some slight trouble, and if a minute leak path is formed in the metal touch seal part, the leak does not stop easily. . Also, because of the large R, it is physically difficult to separate the metal touch seal part from the nose tip. When the length of the metal touch seal part and the pin nose tip is secured to a certain extent, the thickness of the pin nose tip is It leads to becoming too small.

Regarding the axial compression resistance, as described in Patent Document 5 and Patent Document 6, it is effective to reduce the gap on the stub flank side in the threaded portion. However, if this gap is too small, goling tends to occur in the threaded portion, so it is necessary to take an appropriate gap.
As described above, the conventional threaded joints still have some problems, and diversify the performance requirements for threaded joints, such as the above-mentioned compression resistance, bending resistance, and external pressure seal performance. There is room for further improvement in order to fully respond. In view of such circumstances, it is an object of the present invention to provide a threaded joint for steel pipes that has improved sealing properties, compression resistance, and galling resistance.

In order to find out the means for solving the above-described problems, the inventors have conducted intensive studies and have come to achieve the present invention having the following gist. That is, the present invention is as follows.
(1) a pin member having a male screw part, a nose part extending from the male screw part toward the tube end side, and a shoulder part provided at the tip of the nose part;
A female screw part that is screw-coupled to the male screw part, a nose part inner peripheral surface that faces the outer peripheral surface of the nose part of the pin member, and a box member that has a shoulder part that contacts the shoulder part of the pin member,
The pin member and the box member are connected by the screw connection, and the nose portion outer peripheral surface of the pin member and the nose portion inner peripheral surface of the box member are in metal-metal contact at two locations in the joint axial direction, and the two contact locations are Each of the threaded joints for steel pipes that forms a first seal portion that is relatively long and far from the tip of the nose portion, and a second seal portion that is relatively short near the shoulder portion,
In the first seal portion forming portion of the pin member, a plurality of arcs having different curvature radii R on the outer peripheral surface of the nose portion on the outer peripheral surface of the cylindrical portion adjacent to the male screw portion are outward in a cross-sectional view in the pin axial direction. It is a first composite R curve that is sequentially and smoothly connected so as to have a convex shape, and the first composite R curve has a radius of curvature R that increases as the distance from the male thread portion increases.
The angle formed by each arc in the first composite R curve is larger as the arc is closer to the male screw part,
The inner peripheral surface of the nose portion of the box member includes first and second tapered surfaces that respectively interfere with the first and second seal portion forming portions of the pin member during the screw connection. , Threaded joints for steel pipes.
(2) One of the connection points of the circular arcs in the first composite R curve is a tangent point of the first tapered surface of the box member. The threaded joint for steel pipes according to (1), .
(3) The threaded joint for steel pipes according to (1) or (2) , wherein the angle formed between the first tapered surface and the box axis direction is within 10 degrees.
(4) The length of the nose part of the said pin member is 20 mm or more, The threaded joint for steel pipes in any one of said (1)- (3) characterized by the above-mentioned.
(5) In the second seal portion formation portion of the pin member, a bus line on the outer peripheral surface of the nose portion is a curve smoothly connected to the first composite R curve, and has a plurality of different radii of curvature R The second composite R curve is formed by sequentially connecting arcs so as to be convex outward in a cross-sectional view in the pin axis direction, and the second composite R curve has a smaller radius of curvature as the distance from the male screw portion increases. The threaded joint for steel pipes according to any one of the above (1) to (4) , wherein
(6) The threaded joint for steel pipes according to any one of (1) to (5) , wherein an angle formed between the second tapered surface and the box axis direction is within 45 degrees.
(7) The threaded joint for steel pipes according to any one of (1) to (6) , wherein the male thread part and the female thread part have a stub flank angle in a range of 0 degrees to 30 degrees. .
(8) The screw for a steel pipe according to any one of (1) to (7) , wherein the male screw part and the female screw part have a load flank angle within a range of −5 degrees to 4 degrees. Fittings.
(9) The male threaded part and the female threaded part have a screw gap in the range of 0.01 to 0.1 mm when screwed together, in any one of the above (1) to (8) Threaded joint for steel pipe.
(10) The threaded joint for steel pipes according to any one of (1) to (9) , wherein a shoulder angle of the shoulder portion is in a range of 0 degrees to 20 degrees.
(11) The threaded joint for steel pipes according to any one of (1) to (10) , wherein a thread taper amount of the male thread part and the female thread part is within a range of 1/32 to 1/12.
(12) The steel pipe according to any one of (1) to (11) , wherein a seal interference amount of the second seal portion is equal to or smaller than that of the first seal portion. Threaded joint.
(13) In any one of the above (1) to (12) , instead of a curve that is sequentially and smoothly connected, a curve that is sequentially and smoothly connected directly or via a line segment is used. Threaded joint for steel pipes.

In addition, in said (1)- (13) , connecting smoothly means that two circular arcs connected mutually have a common tangent on a mutual connection point.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to obtain the screw joint for steel pipes which improved the sealing performance, compression resistance, and also galling resistance.

Sectional drawing which shows the nose part vicinity of the threaded joint for steel pipes concerning embodiment of this invention Sectional view showing a conventional threaded joint for steel pipes Enlarged sectional view showing the vicinity of the pin nose in FIG. The expanded sectional view which shows the screw part in FIG. Sectional view showing definitions of screw clearance, load flank angle, and stub flank angle Chart showing load history in leak test simulation Sectional drawing which shows the nose part vicinity of the threaded joint for steel pipes which concerns on embodiment (different from that of FIG. 1) of this invention

  As described above, providing a seal part at a position away from the tip of the nose and extending the nose part from the seal part to the shoulder part for a long time has improved external pressure resistance and tensile resistance, as well as stable performance against screws. It is effective in having it. Therefore, the inventors further studied the shape of the periphery of the seal portion so that the seal portion can be brought closer to the screw portion and the thickness of the pin nose tip does not become too small.

as a result,
(i) During screw connection, the nose part outer peripheral surface of the pin member and the nose part inner peripheral surface of the box member are in metal-metal contact at two locations in the joint axial direction, and the two contact locations are separated from the tip of the nose, respectively. Forming a long first seal portion and a relatively short second seal portion near the shoulder portion;
(ii) In the pin member first seal portion forming portion, a plurality of arcs having different radii of curvature R in the pin axis cross-sectional view in the bus line on the outer peripheral surface of the nose portion are different from the bus bar of the cylindrical portion adjacent to the male screw portion It is a curve that is smoothly connected sequentially (directly or via a line segment) so as to be convex outward, that is, a first composite R curve, and the first composite R curve has a curvature as it goes away from the male screw portion. The radius R shall be increased, and
(iii) The inner peripheral surface of the nose portion of the box member includes first and second tapered surfaces that respectively interfere with the first and second seal portion forming portions of the pin member when the screw is coupled.
By satisfying this condition, the inventors have come up with the idea that the seal portion can be brought closer to the screw portion without reducing the thickness of the tip of the pin nose.

  FIG. 1 is a cross-sectional view showing a nose portion of a threaded joint for steel pipes according to an embodiment of the present invention, where (a) shows a pin member 3, (b) shows a box member 1, and (c) shows a pin member 3. And the box member 1 are shown in a coupled state. The pin member 3 is provided at an end portion of the steel pipe, and includes a male screw portion 7, a nose portion 8 connected to the pipe end side from the male screw portion 7, and a shoulder portion 12 provided at the tip of the nose portion 8. Have. On the other hand, the box member 1 includes a female screw portion 5 screwed to the male screw portion 7 of the pin member 3, and an outer peripheral surface (nose portion) of the nose portion 8 in a coupled state of the pin member 3 and the box member 1 by the screw coupling. The inner peripheral surface (the inner peripheral surface of the nose portion) of the box member 1 facing the outer peripheral surface) and the shoulder portion 14 that abuts the shoulder portion 12.

  As shown in FIG. 1 (c), the pin member 3 and the box member are metal at two locations in the joint axial direction between the outer peripheral surface of the pin member 3 and the inner peripheral surface of the nose portion of the box member 1 as shown in FIG. -Metal contact and the two contact points are designed to form a first seal 20 that is relatively long away from the tip of the nose and a second seal 30 that is relatively short near the shoulder 12 ing.

As the design conditions, such as in FIG. 1 (a), a first bus bar of the nose portion outer peripheral surface in the sealing portion formation portion of the pin member 3, different curvatures bus N ₀ of the cylindrical portion adjacent to the external thread portion A curve formed by sequentially and smoothly connecting a plurality of (for example, three) arcs having radii R ₁ , R ₂ , R ₃ so as to be convex outward in a cross-sectional view in the pin axis direction, that is, a first composite R curve 22 In the first composite R curve 22, the radius of curvature R increases as the distance from the male screw portion 7 increases, that is, R ₁ <R ₂ <R ₃ .

  Note that, at the second seal portion forming portion of the pin member, a bus line on the outer peripheral surface of the nose portion is a curve smoothly connected to the first composite R curve 22, and a plurality of arcs having different curvature radii R Is a curve that is smoothly connected in sequence (directly or via a line segment) so as to be convex outward in a cross-sectional view in the pin axis direction, that is, a second compound R curve 32, and the second compound R curve It is preferable that No. 32 has a radius of curvature that decreases as the distance from the male screw portion increases.

On the other hand, as shown in FIG. 1 (b), the inner peripheral surface of the nose portion of the box member 1 is formed with the first and second sealing portion forming portions (the first and second composite Rs) of the pin member 3 when the screw is coupled. It is assumed that the curved surfaces 22 and 32 include first and second tapered surfaces 21 and 31 that respectively interfere with the nose portion inner peripheral surface portions that serve as buses. The taper angles α ₁ and α ₂ of the first and second taper surfaces 21 and 31 are defined by angles formed between the respective taper surfaces and the box axis direction.

When the pin member 3 and the box member 1 are coupled, the first taper surface 21 interferes with the outer peripheral surface portion of the nose portion having the first composite R curve 22 as a bus, and the first seal portion 20 is formed. And the 2nd taper surface 31 interferes with the nose part outer peripheral surface location which makes the 2nd compound R curve 32 a generating line, and the 2nd seal part 30 is formed. The taper angles α ₁ and α ₂ are cross-sectional views in the joint axial direction when the pin member 3 and the box member 1 are virtually incoherently coupled, and the generatrix of the first taper surface 21 is the first composite R curve 22 It intersects at two points, and the generatrix of the second taper surface 31 is set so as to intersect with the second composite R curve 32 at two points. Actually, the first and second points are within the range between the two intersecting points. The seal portions 20 and 30 are formed. The seal interference amounts S ₁ and S ₂ of the first and second seal portions 20 and 30 are respectively measured from the first and second tapered surfaces to the outside on the pin nose outer peripheral surface in the virtual no-interference coupling state. A virtual overhang portion is generated, and is defined by the maximum overhang amount of the virtual overhang portion from the first and second tapered surfaces.

For example, as shown in FIG. 7, the inner peripheral surface of the box member may have a surface shape formed by connecting the first tapered surface 21 and the second tapered surface 31 via a cylindrical surface portion 40.
By increasing the radius of curvature R of the arc in the first compound R curve so as to be farther away from the male screw portion 7 (R ₁ <R ₂ <R ₃ ), the thickness of the shoulder portion 12 at the tip of the pin nose 8 (shoulder thickness) ) T can be increased.

  For comparison, a single R curve M (single arc with a radius of curvature R) is used instead of the first composite R curve 22, and the joint axial lengths of the first seal portion 20 are the same in FIG. As shown by the broken line, it can be seen that the shoulder thickness becomes smaller in the single R curve M than in the case of the first composite R curve 22. When the shoulder thickness is reduced, the rigidity of the pin nose 8 is insufficient, and the contact surface pressure of the first seal portion 20 cannot be properly secured. Conversely, if the shoulder thickness is to be secured with a single R curve, the position of the first seal portion 20 approaches the shoulder portion, which is not preferable from the viewpoint of securing external pressure resistance and tensile resistance.

In addition, since the first and second composite R curves are formed by smoothly connecting a plurality of arcs having different Rs, the first and second composite R curves have a continuous curve shape with no inflection points on the curves, and the nose portion is illegal. Deformation is suppressed. The two arcs to be connected may be directly connected or may be connected via a line segment that overlaps a common tangent line between the arcs.
Here, the angles θ ₁ , θ ₂ , θ ₃ formed by the arcs N ₁ , N ₂ , N ₃ in the first composite R curve are larger as the arc is closer to the male screw portion 7 (that is, θ ₁ > It is preferable that θ ₂ > θ ₃ . Otherwise, the length of the nose portion 8 of the limited pin member 3 (pin nose length L in FIG. 1A) or the length of the limited first seal portion (first seal contact length) It is difficult to design the first composite R curve.

Furthermore, any one of the connection points of the arcs in the first composite R curve, for example, the connection points of the arcs N ₁ and N ₂ and the connection points of the arcs N ₂ and N ₃ is the first tapered surface. It is preferably coincident with the tangent point which means the point of first contact with 21. By setting one of the connection points of the arcs in the first composite R curve as a tangent point, the contact surface pressure distribution of the first seal portion 20 is a region where R is large, the surface pressure is low, and the contact length is long. As a result, it is possible to form a region where R is small, the surface pressure is high, and the contact length is short, and it is difficult to form a leak path and the ultimate sealing performance is improved.

  The tangent point is preferably placed at a position where the distance from the tip of the male screw portion is 0.7 L or less (L is the pin nose length as described above) from the viewpoint of separating the first seal portion from the tip of the nose. . Furthermore, if the distance from the tip of the male screw portion at the tangent point is less than 0.2L, interference between the seal portion and the screw portion is likely to occur during tightening, so 0.2L or more is preferable. Furthermore, 0.3L or more is good for safety.

Taper angle alpha ₁ of the first tapered surface 21 of the box member 1 is preferably within 10 degrees. Within the taper angle alpha ₁ 10 degrees, more preferably not be within 5 degrees, radial sealing method can be preferably achieved, tightening torque dependent sealing performance is relatively low.
The pin nose length L is preferably 20 mm or more. According to this, the seal portion is sufficiently separated from the tip of the pin nose, and as a result, damage to the seal portion can be greatly reduced by elastic deformation within this separation distance range, which is effective in stabilizing the sealing performance. . Since the sealing performance is stabilized, the first seal interference amount S ₁ (see FIG. 1 (c)) can be relatively small as the radial seal method, and the goling risk is small.

  The two or more types of R in the first composite R curve are preferably 1 inch or less for a relatively small R, 2 inches or more for a relatively large R, and 3 inches or more for a larger R. . Specifically, at least one of the plurality of Rs of the first composite R curve is 2 inches or more (more preferably 3 inches or more), and at least one R is less than 2 inches (more preferably 1 inch or less). It is preferable that By making at least one of a plurality of Rs of the composite R curve 2 inches or more (more preferably 3 inches or more), it becomes easy to secure the contact length of the seal portion, and at least one of the remaining Rs is 2 By making it less than 1 inch (preferably 1 inch or less), it becomes easy to achieve high surface pressure.

  Further, the number of arcs in the first composite R curve (the number of arcs having different R) may be two, may be three illustrated in FIG. 1, or may be four or more. As the number of arcs increases, the seal contact length becomes larger and it is easier to improve the sealing performance. However, the load and dimension confirmation in actual manufacturing may increase, so the number of arcs is actually a threaded joint. It is better to design according to the performance required for the system.

In addition, the inventors have found that the effect obtained by providing the second seal portion is that the external pressure sealability is slightly improved from the axial compression state. However, this effect, when the second taper angle alpha ₂ of the tapered surface involved in the formation of the second sealing portion is greater than 45 degrees, it becomes inconspicuous, alpha ₂ is preferably within 45 degrees. Furthermore, this effect has a good effect on improving the sealing performance when axial tension + internal pressure (the most severe test condition) is applied after axial compression.

Further, the inventors have shown that the overall seal performance is improved by making the seal interference amount S2 of the _second seal portion the same as or smaller than the seal interference amount S1 of the _first seal portion. I found it. Incidentally, preferably, and _{S 1/2} ≦ _S 2, is _{S 2} ≦ _{S 1.}
In addition to the shape limitation of the nose part described above, by defining one or more of the load flank angle, the stub flank angle, the screw gap, and the thread taper amount within a suitable range for the male screw part and the female screw part. As a result, it was confirmed that the overall sealing performance was improved by the combined effect. Here, the load flank angle is the load flank angle β shown in FIG. 5, that is, the angle β formed by the load flank surface 18 with respect to the joint axis orthogonal plane (meaning the plane orthogonal to the axial direction of the threaded joint, hereinafter the same). It is. The stub flank angle is the stub flank angle γ shown in FIG. 5, that is, the angle γ formed by the stub flank surface 19 with respect to the joint axis orthogonal surface. Further, the screw gap is the screw gap G shown in FIG. 5, that is, the gap G between the thread 7a of the male screw and the screw groove 5a of the female screw meshing with the screw thread 7a. Further, the thread taper amount is a tangent value of an angle formed by a taper surface passing through the thread crest (or thread groove bottom) of the male thread (or female thread) and the joint axial direction.

The preferred range of the load flank angle β is -5 ° to 4 °. The lower limit of the preferred range is determined from the viewpoint of galling resistance and tool life of the threaded portion, and the upper limit is determined from the viewpoint of bending resistance.
The preferable range of the stub flank angle γ is 0 ° to 30 °, and the lower limit of the preferable range is determined from the viewpoint of galling resistance and tool life of the threaded portion, and the upper limit is determined from the viewpoint of axial compression resistance.

  The preferable range of the screw gap G is 0.01 to 0.1 mm. The lower limit of the preferable range is determined from the viewpoint of reducing the goling risk, and the upper limit is determined from the viewpoint of reducing the load on the pin tip during the axial compression load. It was. In consideration of the lead error at the time of threading, the screw gap G is preferably about 0.03 mm at least. Moreover, since it discovered that the screw gap G was about 0.045 mm and can exhibit sufficient performance effectively, it is good also as about 0.045 mm according to a condition.

A preferable range of the screw taper amount is 1/32 to 1/12.
By defining one or more of the load flank angle, stub flank angle, screw gap, and screw taper amount as described above, the overall improvement effect of the sealing performance is particularly significant after the shaft compression is once applied. It is remarkable under the condition of applying tension + internal pressure or external pressure.
In addition, the shoulder angle of the shoulder portion (the angle formed by the end surface of the shoulder portion in the joint axis direction with respect to the joint axis orthogonal surface, and the pin outer peripheral side of the interface protruding from the pin inner peripheral side to the outer side in the joint axial direction) The positive angle is preferably 0 to 20 degrees. If the shoulder angle is less than 0 degree, it is disadvantageous in terms of sealing performance and tightening characteristics, whereas if it exceeds 20 degrees, it is disadvantageous in that plastic deformation of the box shoulder part and local deformation of the seal part are likely to occur. Preferably it is 15 degrees or less. Furthermore, depending on the situation, 7 degrees or less is preferable.

  As an example of the invention, a threaded joint for steel pipes according to the present invention shown in FIG. 1 or FIG. 7 or in which any two arcs of the first composite R curve in FIG. 1 are connected via line segments. The leakage test in accordance with ISO 13679 was simulated, and the contact area pressure (ksi · inch) at the seal portion at this time was determined by FEM analysis. Note that contact area pressure = contact surface pressure × seal contact length, and is obtained by integral calculation. In this leak test, a biaxial stress corresponding to 95% of the yield condition of the material, an internal pressure, and an external pressure are applied to the threaded joint for steel pipes according to the history shown in FIG.

In addition, as an index indicating the risk of goling during screw tightening, a Goring index (defined by the product of sliding distance (inch) and contact surface pressure (psi) at each axial position of the seal part from the start to the end of tightening. (psi · inch) = contact surface pressure × sliding distance, was obtained by FEM analysis. This is also obtained by integral calculation. It can be said that the smaller the Goring index, the smaller the Goring risk.
For comparison,
Comparative Example 1: The bus bar on the outer peripheral surface of the pin nose 8 has a convex curve shape having a single R (single R curve M indicated by a broken line in FIG. 1), and the second seal portion is not provided. if you did this,
-Comparative example 2: Although the generating line of the nose part outer peripheral surface of the 1st seal part formation location of a pin member was made into the 1st compound R curve, it does not satisfy the requirements that R of a circular arc becomes so large that it goes away from the external thread part 7. If
In the same manner, the contact area pressure and Goling index were obtained.

  Table 1 shows the contact area pressure and Goling index determined by FEM calculation for the inventive example and the comparative example, together with the dimensions of each part of the threaded joint. In all cases, the contact area pressure showed a minimum value (corresponding to a state in which leakage is most likely to occur) in the vicinity of the load step L18 (biaxial tensile stress + internal pressure) in the history of FIG. This load point is not specified in ISO13679, but the internal pressure + tension condition is the most severe condition and may be required, so it was compared here. In addition, since the load performance at the load step L18 after receiving the compression history is lower than that at the same load point L3 before receiving the compression history, the comparison at L18 is good. In Table 1, the minimum value of the contact area pressure in each example is displayed as a relative minimum value (the minimum value in all examples is 100, and the others are expressed as ratios relative thereto). In addition, the joint axis direction position showing the maximum value (corresponding to the state with the highest goling risk) of the Goling index was different for each example. In Table 1, the maximum value of the Goring index of each example is displayed as a relative maximum value (the maximum maximum value is 100 among all examples, and the others are expressed as ratios relative thereto). In addition, several samples were made and a physical test was performed, and it was confirmed that there was no leakage under the external pressure condition at the interference level in this example. The only problem is Q1, and when the amount of interference is reduced, a leak occurs at L18 after axial compression.

  From Table 1, it can be seen that, in all of the inventive examples, compared with the comparative example, although the contact area pressure is high, the Goling index is comparable, and a threaded joint excellent in sealing performance and anti-goling resistance has been realized.

1 Box material
3 Pin (Pin material)
5 Female thread (Female thread)
5a Female thread groove
7 Male thread (Male thread)
7a Male thread thread
8 Nose (pin nose)
11, 13 Seal part (Details are metal touch seal part)
12, 14 Shoulder part (For details, torque shoulder part)
18 Road flank surface
19 Stub flank surface
20 First seal
21 First taper surface
22 First composite R curve
30 Second seal
31 Second taper surface
32 Second composite R curve
40 Cylindrical surface

Claims (13)

A pin member having a male screw part, a nose part extending from the male screw part to the tube end side, and a shoulder part provided at the tip of the nose part;
A female screw part that is screw-coupled to the male screw part, a nose part inner peripheral surface that faces the outer peripheral surface of the nose part of the pin member, and a box member that has a shoulder part that contacts the shoulder part of the pin member,
The pin member and the box member are connected by the screw connection, and the nose portion outer peripheral surface of the pin member and the nose portion inner peripheral surface of the box member are in metal-metal contact at two locations in the joint axial direction, and the two contact locations are Each of the threaded joints for steel pipes that forms a first seal portion that is relatively long and far from the tip of the nose portion, and a second seal portion that is relatively short near the shoulder portion,
In the first seal portion forming portion of the pin member, a plurality of arcs having different curvature radii R on the outer peripheral surface of the nose portion on the outer peripheral surface of the cylindrical portion adjacent to the male screw portion are outward in a cross-sectional view in the pin axial direction. It is a first composite R curve that is sequentially and smoothly connected so as to have a convex shape, and the first composite R curve has a radius of curvature R that increases as the distance from the male thread portion increases.
The angle formed by each arc in the first composite R curve is larger as the arc is closer to the male screw part,
The inner peripheral surface of the nose portion of the box member includes first and second tapered surfaces that respectively interfere with the first and second seal portion forming portions of the pin member during the screw connection. , Threaded joints for steel pipes. 2. The threaded joint for steel pipes according to claim 1, wherein any one of connection points of arcs in the first composite R curve is a tangent point of the first tapered surface of the box member. Wherein the first tapered surface is a threaded joint for steel pipes according to claim 1 or 2, angle between the box-axis direction, characterized in that is within 10 degrees. The length of the nose part of the said pin member is 20 mm or more, The threaded joint for steel pipes in any one of Claims 1-3 characterized by the above-mentioned. In the second seal portion forming portion of the pin member, the bus on the outer peripheral surface of the nose portion is a curve smoothly connected to the first composite R curve, and a plurality of arcs having different curvature radii R are pinned It is a second composite R curve that is sequentially and smoothly connected so as to be convex outward in an axial sectional view, and the second composite R curve has a radius of curvature that decreases as the distance from the male screw portion increases. The threaded joint for steel pipes according to any one of claims 1 to 4 characterized by things. The second tapered surface is a threaded joint for steel pipes according to any one of claims 1 to 5, characterized in that the angle formed with the box-axis direction is within 45 degrees. The threaded joint for steel pipes according to any one of claims 1 to 6 , wherein the male screw part and the female screw part have a stub flank angle in a range of 0 to 30 degrees. The threaded joint for steel pipes according to any one of claims 1 to 7 , wherein the male thread part and the female thread part have a load flank angle within a range of -5 degrees to 4 degrees. The threaded joint for steel pipes according to any one of claims 1 to 8 , wherein the male screw part and the female screw part have a screw gap in the range of 0.01 to 0.1 mm at the time of screw connection. The threaded joint for steel pipes according to any one of claims 1 to 9 , wherein a shoulder angle of the shoulder portion is in a range of 0 degrees to 20 degrees. The threaded joint for a steel pipe according to any one of claims 1 to 10 , wherein a thread taper amount of the male thread part and the female thread part is within a range of 1/32 to 1/12. The threaded joint for steel pipes according to any one of claims 1 to 11 , wherein a seal interference amount of the second seal portion is the same as or smaller than that of the first seal portion. The threaded joint for steel pipes according to any one of claims 1 to 12 , characterized in that, instead of a curve that is sequentially and smoothly connected, a curve that is successively and smoothly connected directly or via a line segment.

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