JP5978953B2 - Threaded joints for pipes - Google Patents

Description

  The present invention relates to a threaded joint for 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 pipes excellent in sealing properties, compression resistance, and galling resistance, suitable for use in connecting steel pipes.

  Threaded joints are widely used to connect steel pipes used in oil industry equipment such as oil well pipes. Conventionally, a standard threaded joint specified in the API (American Petroleum Institute) standard has been typically used for connecting steel pipes used for oil and gas exploration and production. However, in recent years, the wells for crude oil and natural gas have been deepened, and the number of vertical wells, horizontal wells, inclined wells, etc. has increased, 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. For this reason, the use of high-performance special threaded joints called premium joints is increasing, and the demands on the performance are also increasing.

  A premium joint usually has a male screw member (hereinafter referred to as a pin) formed on a pipe end portion, each having a taper screw, a seal portion (specifically, a metal touch seal portion), and a shoulder portion (specifically, a torque shoulder portion). It is a coupling type joint in which a female screw member (hereinafter referred to as a box) for connecting pins to each other is coupled. The taper screw is important for firmly fixing the pipe joint, and the seal part plays a role of securing the sealing performance by metal contact between the box and the pin at this part, and the shoulder part is a stopper of the joint during tightening. It has a shoulder surface that plays a role.

  FIG. 7 is a schematic explanatory view showing a conventional example of a premium joint for an oil well pipe, and these are longitudinal sectional views of a threaded joint of a circular pipe. The threaded joint includes a pin 3 and a box 1 corresponding to the pin 3, and the pin 3 has a male screw portion 7 on the outer surface thereof, and has no screw provided adjacent to the male screw portion 7 on the tip end side of the pin 3. It has a nose portion (also called a pin nose) 8 that is a length portion. The nose portion 8 has a seal portion (specifically, a metal touch seal portion) 11 on its outer peripheral surface, and a shoulder portion (specifically, a torque shoulder portion) 12 on its end surface. The opposing box 1 has a female screw part 5, a seal part 13, and a part that can be screwed or brought into contact with the male screw part 7, the seal part 11, and the shoulder part 12 of the pin 3, respectively. And it has the shoulder part 14.

In the conventional example of FIG. 7, the seal portion 11 is at the tip of the pin 3 and a desired sealing performance can be realized by applying an appropriate tightening torque. However, the tightening torque depends on the lubrication conditions, surface properties, etc. As a design that does not greatly depend on these, there is a radial seal method (also referred to as a radial seal type) in which the radial component of the seal contact pressure is relatively strong.
In the radial seal type premium joint, the seal portion is usually a seal portion formed by contact between tapers (referred to as “prior art A”), or within the member boundary surface in a sectional view in the axial direction of the taper and the member. Any one of the seal portions formed by contact with a convex curved surface which is a curved surface formed by a rotation trajectory around a member axis of a convex arc which is an arc having a chord in the member (referred to as Prior Art B) It is.

  Prior art B allows, for example, the creation of long pipelines with excellent sealing properties for today's largest range of normal working conditions and ensures optimum performance even after several assembly and disassembly, Also, for the purpose of making the joint with a high resistance to the operating load, the joint axial cross-sectional shape of the seal part is a convex arc on the pin side, a straight line on the box side, and the radius of the convex arc of the pin side seal part ( It is known that the radius of curvature is limited to a value that varies depending on the pipe outer diameter (see Patent Document 1).

Japanese Patent No. 4300187

However, according to the study by the present inventors, the conventional technique A (the seal part formed by contact between the tapers) and the conventional technique B (the seal part formed by contact between the taper and the convex curved surface) have the following difficulties. Therefore, it has been found that there is a problem that it is difficult to sufficiently improve the sealing performance and galling resistance.
In the conventional technique A, when there is a mismatch in the taper angle (inclination angle on the acute angle side of the taper with respect to the joint shaft) between the tapers, one-sided contact occurs. Further, in the prior art A, an extremely high contact surface pressure is generated at both ends of the contact area between the tapers, so that goling easily occurs.

  In the prior art B, it is effective to reduce the seal taper angle in order to suppress a decrease in sealing performance (contact surface pressure decrease) in the pipe axis direction (= joint axis direction), but MU (= Make- The sliding distance at the time of Up (tightening) becomes long, and goling easily occurs. On the other hand, in the conventional technique B, when the radius of curvature of the convex arc is increased, the contact length is increased and the sealing performance is improved, and the maximum contact surface pressure is decreased, and the risk of goling can be reduced. However, if the radius of curvature is changed, the contact length and maximum contact surface pressure change in conjunction with each other. Therefore, in order to achieve a state where the contact length is long and the maximum contact surface pressure is high, an excessive amount of seal interference must be given. Goaling problems will occur.

  In this specification, the amount of seal interference refers to the cross-sectional views in the member axial direction of both the pin member on the pin side of the screw joint and the box member on the box side, and the shafts and the shoulder surfaces coincide with each other. Thus, in the joint assembly drawing formed by overlapping, the difference in the member diameter dimension at the position in the member axis (= joint axis) direction of the interference part of both members formed by the overlapping (the outer diameter of the pin and the box Difference in inner diameter = overlapping dimension per diameter). The interference portion corresponds to a seal portion of a threaded joint formed by screwing both members. The member axial position where the seal interference amount is maximum is referred to as a seal point.

As a result of intensive studies on means for solving the above problems, the present inventors have found that the inner peripheral surface portion of the member that forms the seal portion on the member side forming the box has two concavely curved surfaces, that is, members in a sectional view in the member axial direction. A compound curved surface connected via a curved surface formed by a rotation trajectory around the member axis of a concave arc, which is an arc having a chord outside the member within the boundary surface, and a seal portion on the member side forming a pin The member outer peripheral surface portion is a convex curved surface, that is, a curved surface formed by a rotation locus around the member axis of a convex arc which is an arc having a chord in the member in the member boundary surface in a sectional view in the member axial direction. Based on this finding, the present invention has the following gist configuration.
(1) a pin having a male screw portion, a nose portion extending from the male screw portion toward the tube end side, and a shoulder portion provided at the tip of the nose portion;
A female screw part that is screw-coupled with the male screw part to form a screw part, a seal surface that faces the outer peripheral surface of the nose part of the pin, and a box that has a shoulder part that contacts the shoulder part of the pin,
A screw joint for pipes in which the pin and the box are connected by the screw connection, the outer peripheral surface of the nose part of the pin and the seal surface of the box are in metal-metal contact, and the contact part forms a seal part,
The member outer peripheral surface portion to be the seal portion on the member side forming the pin is a rotation locus around the member axis of a convex arc which is an arc having a chord in the member in the member interface in a sectional view in the member axial direction. A convex curved surface,
The member inner peripheral surface portion to be the seal portion on the member side forming the box has a first taper located on the near shoulder portion side and a second taper located on the far shoulder portion side in the member axial direction sectional view. It is a compound curved surface formed by connecting through a concave curved surface that is a rotation locus around a member axis of a concave arc that is an arc having a string outside the member within the boundary surface,
A threaded joint for pipes, wherein a radius of curvature Rb of the concave arc in the complex curved surface and a radius of curvature Rp of the convex arc in the convex curved surface satisfy Rb ≧ Rp × 0.7.
(2) The threaded joint for pipes according to (1), wherein the taper angles α1 and α2 of the first and second tapers satisfy α1−α2 ≧ 0.5 degrees.
(3) The threaded joint for pipes according to (1) or (2), wherein a seal point, which is a position in the member axial direction that maximizes the amount of seal interference, is arranged in the concave curved surface.

  According to the present invention, by adopting the above-described configuration, a threaded joint for pipes that is more excellent in sealing performance and galling resistance than before can be obtained.

It is a joint axial direction sectional view showing an example of an embodiment of the present invention. It is a schematic diagram which shows the contact surface shape of the seal part by this invention. It is a diagram which shows the contact length direction distribution of the contact surface pressure by FEA (finite element analysis) at the time of Make-up. It is an equal strain area figure which shows the result of having carried out the FEA calculation of the equivalent plastic strain distribution after the composite load load prescribed | regulated to the ISO test about the example of this invention. It is a diagram which shows the contact length direction distribution of the Goring index by FEA (finite element analysis). It is the bar graph which compared the contact area pressure with respect to the load steps 2, 12, and 13 at the time of the compound load load by FEA (finite element analysis) with the example (level 4) of this invention, and the comparative example (level 11). It is a joint axial direction sectional view showing the conventional example which has a seal part in a pin tip part.

  FIG. 1 is an axial sectional view showing an example of an embodiment of the present invention. This figure shows a joint assembly state in which the axial sectional views of the pin 3 and the box 1 are overlapped so that the shafts and the shoulder surfaces 22 and 24 coincide with each other. In addition, the member axis | shaft which is either a pin axis | shaft (it is a concentric axis | shaft with a pipe axis | shaft) and a box axis | shaft which becomes a concentric axis | shaft at the time of a screw connection and becomes a coupling axis | shaft is abbreviate | omitting illustration. In this figure, the interference portion 20 between the outer diameter side of the pin 3 and the inner diameter side of the box 1 formed by the superposition serves as a seal portion 21 (see FIG. 2) when the pin 3 and the box 1 are screwed together.

  In the interference part 20, the outer peripheral surface on the pin 3 side is a convex curved surface 10 that is a rotation locus around the axis of the convex arc 9 that is an arc of curvature radius Rp having a chord (not shown) in the pin 3, The inner peripheral surface on the box side includes a first taper 15 located on the near shoulder portion side (side near the shoulder portion 14) and a second taper 16 located on the far shoulder portion side (the side far from the shoulder portion 14). , A composite curved surface 19 connected via a concave curved surface 18 which is a rotation locus around a member axis of a concave arc 17 which is a circular arc of curvature radius Rb having a string (not shown) outside the box 1.

The curvature radii Rb and Rp of the concave arc 17 and the convex arc 9 respectively satisfy Rb ≧ Rp × 0.7.
FIG. 2 is a schematic diagram showing the contact surface shape of the seal portion 21 corresponding to the seal shape of the interference portion 20 (the outer peripheral surface shape of the pin nose 8 and the inner peripheral surface shape of the pin nose facing portion on the box 1 side). , 30 is a seal arc portion in which the concave curved surface 18 and the convex curved surface 10 are in metal-metal contact, and 31 is a first seal taper portion in which the first taper 15 and the convex curved surface 10 are in metal-metal contact. , 32 is a second seal taper portion in which the second taper 16 and the convex curved surface 10 are in metal-metal contact, and 33 and 34 are connections between the concave arc 17 and the first and second tapers 15 and 16, respectively. Eyes.

The seal taper angle of the first seal taper portion 31 (inclination angle on the acute side of the seal taper portion with respect to the joint shaft) is almost equal to α1, and the seal taper angle of the second seal taper portion 32 is almost equal to α2. Become.
The outer peripheral surface portion on the pin 1 side to be the seal portion 21 is a convex curved surface 10, and the concave arc 17 is applied as a curve connecting the first and second tapers 15 and 16 on the box 3 side, thereby the seal arc portion 30. The contact surface pressure is suppressed, and the galling resistance is improved.

  The radius of curvature Rb of the concave arc 17 is preferably smaller than the radius of curvature Rp of the convex arc 9 because the contact surface pressure can be suppressed while ensuring the contact length, but if Rb is too small, the vicinity of the joints 33 and 34 A non-contact part (gap) is generated in the surface, and the compound remaining in the gap hinders the sealing performance. In order to avoid such a problem, it is necessary to satisfy Rb ≧ Rp × 0.7. However, if Rb> Rp × 2, the effect of reducing the contact surface pressure is reduced, and if it is excessive, it will be substantially the same as a single taper seal, so Rb ≦ Rp × 2 may be satisfied. preferable. That is, preferably, Rb is Rp × 0.7 or more and Rp × 2 or less.

  Further, from the viewpoint of suppressing a decrease in contact surface pressure during pulling in the tube axis direction, the taper angle α2 of the second taper 16 that is the taper on the far shoulder portion side of the box 3 (the seal taper angle of the second seal taper portion 32). For example, α2≈3 to 10 degrees. On the other hand, the taper angle α1 of the first taper 15 (which is almost equal to the seal taper angle of the first seal taper portion 31), which is a taper on the near shoulder portion side, is easily received by the force during compression in the tube axis direction. It is preferable to satisfy the angle difference Δα = α1−α2 ≧ 0.5 degrees with respect to α2. However, if Δα is excessive, contact at one or both of the first and second taper portions is lost, and a contact surface pressure with a large wrinkle obtained by contact at joints 33 and 34 is obtained. There is a concern that will not be obtained. In order to avoid this problem, Δα is more preferably Δα ≦ 4 degrees. That is, more preferably, Δα is not less than 0.5 degrees and not more than 4 degrees.

  By the way, in the conventional seal shape, the maximum contact surface pressure is generated at the seal point, which is the position in the axial direction of the member where the seal interference amount is maximum, and plastic deformation occurs upon receiving a composite load such as repeated tension-compression load. Will occur and the sealing performance is likely to deteriorate. On the other hand, in the present invention, the contact point pressure can be reduced by coordinating the seal point in the area of the concave arc 17 so that a decrease in the sealing performance can be suppressed. Therefore, in the present invention, a threaded joint in which a seal point is coordinated in the concave curved surface 18 is preferable.

  Finite element analysis (FEA) is performed on a threaded joint for a pipe consisting of a pin formed by machining a steel pipe end with an outside diameter of 9-5 / 8 "x wall thickness of 0.545" and a box corresponding to the pin. (Make-Up; tightening) contact area pressure (index obtained by integrating the contact surface pressure over the contact length in the tube axis direction) with the same design, Table 1 shows a sample showing the seal shape and evaluation parameters Produced and conducted a series A test of ISO 13679. In carrying out this experiment, the experiment was conducted at various levels shown in Table 1. In the experiment, the seal interference amount and the MU torque were adjusted so that the contact area pressure upon completion of MU was 6000 psi-inch.

  The experimental results are shown in Table 1. From Table 1, compared with the comparative example, in the present invention example, more excellent sealing performance is expressed, and in the present invention example, the seal point is arranged in the concave curved surface (concave arc), and further excellent. It is clear that a good sealing performance was developed.

  FIG. 3 is a diagram showing a contact length direction distribution of contact surface pressure by FEA (finite element analysis) at the time of Make-up. The curves in the figure are the results for level 4 (invention example) and level 11 (comparative example) in Table 1, respectively. The contact length and the contact surface pressure are displayed in a non-dimensional manner based on the distribution of level 11 (comparative example). From this figure, it can be seen that in the example of the present invention, the distribution during Make-up has a long contact length and the maximum surface pressure is not excessive.

FIG. 4 is an equal strain area diagram showing the result of FEA calculation of the equivalent plastic strain distribution after the combined load specified in the ISO test for the example of the present invention (level 4). From this figure, it can be seen that by arranging the seal point within the concave curved surface 18 (concave arc 17), the strain concentrated portion is divided into a plurality of portions, and plastic deformation hardly occurs.
FIG. 5 is a diagram showing a contact length direction distribution of a Goring index by FEA (finite element analysis). The curves in the figure are the results for level 4 (invention example) and level 11 (comparative example) in Table 1, respectively. The contact length and the contact surface pressure are displayed in a non-dimensional manner based on the distribution of level 11 (comparative example). Here, the Goring index is an integral calculation value of “friction coefficient μ × sliding distance × contact surface pressure” at each position of the contact point of the seal part from the start to the end of tightening as an index representing the risk of goling during screw tightening. The smaller the Goring index is, the smaller the Goring risk is. From this figure, it can be seen that in the present invention example, the contact surface pressure is suppressed even when the sliding distance is increased, and the Goling index can be reduced as compared with the comparative example.

  FIG. 6 shows the contact area pressure by FEA with respect to LP (Load Point) 2, 12 and 13 when combined load is applied by tension / compression and internal / external pressure of series A test in the seal evaluation test of ISO 13679: 2002. It is a bar graph which shows the result of calculation. Note that the bar graph displays the contact area pressure for the example of the present invention (level 4) and the comparative example (level 11) in a non-dimensional manner based on the value of each load step of level 11. The problem with the internal pressure resistant seal is LP (Load Point) 2 on which the maximum tensile force and internal pressure act. On the other hand, the problem with the external pressure-resistant seal is LP12 in which only the maximum external pressure acts and LP13 in which tensile force acts in addition to high external pressure. From this graph, it can be seen that the contact area pressure is improved in the example of the present invention and the sealing property is improved as compared with the comparative example.

1 Box 3 Pin 5 Female thread 7 Male thread 8 Nose (pin nose)
9 Convex arc 10 Convex curved surface 11, 13 Seal part (metal touch seal part)
12, 14 Shoulder (torque shoulder; 12 is pin side, 14 is box side)
15 First taper 16 Second taper 17 Concave arc 18 Concave surface 19 Compound curved surface 20 Interference part 21 Sealing parts 22 and 24 Shoulder surface (22 is pin side, 24 is box side)
30 Seal arc portion 31 First seal taper portion 32 Second seal taper portions 33 and 34 Joint (joint between concave arc and taper)

Claims (3)

A pin 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 with the male screw part to form a screw part, a seal surface that faces the outer peripheral surface of the nose part of the pin, and a box that has a shoulder part that contacts the shoulder part of the pin,
A screw joint for pipes in which the pin and the box are connected by the screw connection, the outer peripheral surface of the nose part of the pin and the seal surface of the box are in metal-metal contact, and the contact part forms a seal part,
The member outer peripheral surface portion to be the seal portion on the member side forming the pin is a rotation locus around the member axis of a convex arc which is an arc having a chord in the member in the member interface in a sectional view in the member axial direction. A convex curved surface,
The member inner peripheral surface portion to be the seal portion on the member side forming the box has a first taper located on the near shoulder portion side and a second taper located on the far shoulder portion side in the member axial direction sectional view. It is a compound curved surface formed by connecting through a concave curved surface that is a rotation locus around a member axis of a concave arc that is an arc having a string outside the member within the boundary surface,
A threaded joint for pipes, wherein a radius of curvature Rb of the concave arc in the complex curved surface and a radius of curvature Rp of the convex arc in the convex curved surface satisfy Rb ≧ Rp × 0.7.   2. The threaded joint for pipes according to claim 1, wherein the taper angles α <b> 1 and α <b> 2 of the first and second tapers satisfy α 1 −α 2 ≧ 0.5 degrees.   3. The threaded joint for pipes according to claim 1, wherein a seal point, which is a position in the axial direction of the member that maximizes the amount of seal interference, is arranged in the concave curved surface.