[0001]The present invention relates to a threaded joint for use in connecting steel pipes.
BACKGROUND
[0002]
　Oil wells, natural gas wells and the like in (hereinafter, also collectively referred to as "oil wells"), oil well pipe to mine underground resources: steel pipe called (OCTG Oil Country Tubular Goods) is used. Steel pipes are sequentially connected, a threaded joint is used for the connection.
[0003]
　Format tubular threaded joint is roughly classified into a coupling-type and integral type. For coupling type, a pair of tubing of consolidated, where one tube is steel, other tubing is coupled. In this case, a male screw portion is formed on an outer periphery of both end portions of the steel pipe, the internal thread portion is formed on the inner periphery of both end portions of the coupling. Then, it is linked and the steel pipe and the coupling. For integral type, a pair of tubing of consolidated are both steel pipe, without using a separate coupling. In this case, a male screw portion is formed on an outer periphery of one end portion of the steel pipe, the internal thread portion is formed on the inner periphery of the other end. Then, one of the steel pipe and the other steel pipe is connected.
[0004]
　Generally, the joint portion of the male screw portion the tube end portion formed, since the containing elements to be inserted into the female screw portion, it referred to as pin. On the other hand, the joint portion of the pipe end portion a female screw portion is formed, since it contains elements for receiving the external thread portion, referred to as boxes. These pin and the box are the ends of the tube, both of which are tubular.
[0005]
　Recently, high-depth reduction and ultra deep water of wells are increasingly developed. In such an environment, to develop efficient oil well, oil well pipe is disposed in multiple. The connection of OCTG multiple structure, the outer diameter of the box threaded joint is comparable to the outside diameter of the pin is often used. Since multiple structures of required inner clearance between the oil well pipe and the outer OCTG, because the inner diameter of the pin of the outer OCTG expansion of the outer diameter of the inner OCTG box is limited. Under such constraint, the threaded joint, pressure from the inside (hereinafter, also referred to as "internal pressure") and external pressure (hereinafter, also referred to as "external pressure") to, is required to have excellent sealing performance that.
[0006]
　For example, excellent as threaded joint for realizing the sealing performance, there is a dovetail-shaped tapered thread also called wedge screw adopted to the screw portion. The wedge screw, load flank surface (hereinafter, also referred to as "load surface") and insert flank (hereinafter, also referred to as "insertion surface") both of a flank angle of the negative angle, when the fastening is completed, load faces and insertion surfaces come into contact with each other. Thus, the entire threaded portion fit Mari firmly fitted. Furthermore, in the fastening state, the thread crest surfaces and the thread root bottom surface of the threaded portion are in contact closely with each other. Thus, a threaded joint employing a wedge screw, since there is no gap threaded portion, there is a possible to realize an excellent sealing performance.
[0007]
　U.S. Patent No. 7,690,696 (Patent Document 1) and U.S. Patent Application Publication No. 2006/0145480 Pat (Patent Document 2) discloses a threaded joint employing a wedge thread on the threaded portion.
[0008]
　In Patent Document 1 of the threaded joint is divided into two thread portion along the tube axis, the shoulder portion is provided further on the boundary of the screw portion of the two-stage. Its seal portion by surface contact adjacent the shoulder portion is provided. Threaded joint disclosed in Patent Document 1 includes a contact fitting without clearance in wedge screw, the locking effect of a combination of a pressing contact between the shoulder surface, thereby improving the sealing performance.
[0009]
　However, in the case of a threaded joint Patent Document 1, in order to achieve a close contact without a gap in the engaged state, none of the threaded portion and the shoulder portion of the wedge-shaped screw, the tolerance of the design dimension to be set is narrowed. Thus, not only the manufacturing cost increases, feature size can also happen that out of the tolerance. When the tolerance off occurs, locking effect is not exhibited sufficiently, there may not be obtained sealing performance as expected.
[0010]
　In contrast, in the threaded joint disclosed in Patent Document 2, similarly to the threaded joint disclosed in Patent Document 1, the shoulder portion and the seal portion is provided at the boundary of the screw portion of the two-stage. Additionally, in one of the threaded portion either of the screw portion of the two-stage, between the adjacent load surface during insertion faces, a gap is formed like between the screw crest surfaces and the thread valley bottom. With such a configuration, it spreads tolerance of design dimension set in the threaded portion. This makes it possible to reduce manufacturing costs, it is easy to keep the processing dimensions within the tolerance.
[0011]
　However, in the case of a threaded joint Patent Document 2, the sealing portion due to surface contact is not established only one place. Therefore, when it is loaded in excessive pressure (internal pressure and external pressure) screw joints, it may not be possible to maintain the sealing performance. In particular, the outer diameter of the box when the threaded joint is comparable to the outside diameter of the pin, coupled with the expansion of the wall thickness of the pin and box is limited, ensuring the sealing performance becomes difficult.
CITATION
Patent Document
[0012]
Patent Document 1: U.S. Patent No. 7,690,696 Pat
Patent Document 2: U.S. Patent Application Publication No. 2006/0145480 Pat
Summary of the Invention
Problems that the Invention is to Solve
[0013]
　An object of the present invention is to provide a tubular threaded joint which can reliably exhibit excellent sealing performance.
Means for Solving the Problems
[0014]
　A threaded joint for steel pipes according to an embodiment of the present invention, the pin of the tubular, is composed of a tubular box, a tubular threaded joint in which the box and the pin the pin is screwed into the box is fastened, the following including such as configuration.
(I) the outer diameter of the box is less than 110% of the outer diameter of the tube body of the pin.
(Ii) the pin, in order toward the tube body from the tip of the pin, first male threaded portion of the tapered threads of dovetail shape, a first sealing surface, a shoulder surface, the second sealing surface, and the taper thread of dovetail shape a second male screw portion.
(Iii) the first sealing surface has a first curved surface at both ends of the first tapered surface and the first tapered surface. It said second sealing surface has a second curved surface at both ends of the second tapered surface and the second tapered surface. The tube axis direction of the distance L1 from the first boundary between the tapered surface and the front end side of the first curved surface of the pin to the shoulder surface is 15mm or more. It said second tube axial direction distance L2 from the boundary between the tapered surface and the pipe main body side of the second curved surface of the pin to the shoulder surface is 15mm or more. Total distance L of the distance L1 and the distance L2 is 50mm or more.
(Iv) the box, in order toward the tip from the tube body of the box, first internally threaded portion of the tapered threads of dovetail shape, a first sealing surface, a shoulder surface, the second sealing surface, and the taper thread of dovetail shape a second female threaded portion.
(V) in the engaged state, the above threaded joint,
　in contact-the shoulder faces, the first sealing faces are in contact, said second seal faces are in contact,
　- the first male screw portion and with a gap is formed between the insertion flank faces of the first female threaded portion, between the screw crest surface of the thread root bottom and the first female threaded portion of the first male threaded portion, or the first external thread portion gap is formed between the thread crest surfaces and the thread root bottom surface of the first female threaded portion,
　with a gap is formed between the insertion flank faces of-the second male threaded portion and the second internally threaded portion, said between the thread root bottom and the screw crest surface of the second female threaded portion of the second male threaded portion, or a gap is formed between the thread root bottom surface of the thread crest surface of the second male threaded portion and the second female threaded portion that.
[0015]
　In the above-described threaded joint, it is preferable that the clearance between the screw crest surface and the thread root bottom surface is less than or 0.10 mm 0.20 mm.
[0016]
　The above threaded joint in longitudinal section along the tube axis, it is preferable to adopt a configuration the angle between the the tube axis shoulder surface is 75 ~ 105 °.
[0017]
　In the above-described threaded joint, it is preferable that the total distance L is 90mm or less.
[0018]
　In the above-described threaded joint, the first threaded portion formed between the first male threaded portion with the first female thread portion, and said second threaded portion formed in the second male threaded portion and the second internally threaded portion, Article 1 it is preferably a screw or double threaded screw.
Effect of the invention
[0019]
　A threaded joint for steel pipes of the present invention has a remarkable effect of the following:
　that the excellent sealing performance can be reliably exhibited.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020]
[1] Figure 1 is a longitudinal sectional view showing a threaded joint for steel pipes according to an embodiment of the present invention.
FIG. 2 is a vertical sectional view enlarging a vicinity of the boundary of the two-stage screw portion of a threaded joint for steel pipes shown in Figure 1.
FIG. 3 is a longitudinal sectional view of an enlarged first threaded portion of a threaded joint for steel pipes shown in Figure 1.
[4] FIG. 4 is a longitudinal sectional view of an enlarged second threaded portion of a threaded joint for steel pipes shown in Figure 1.
FIG. 5 is the pin of the present embodiment, showing the dimensional relationship between the first sealing surface and the shoulder surface.
FIG. 6 is the pin of the present embodiment, showing the dimensional relationship between the second sealing surface and the shoulder surface.
FIG. 7 is a region of the inner sealing portion by the surface contact is a longitudinal sectional view schematically showing.
[8] FIG. 8 is a longitudinal sectional view schematically showing a region of the outer seal portion due to surface contact.
DESCRIPTION OF THE INVENTION
[0021]
　As described above, in a threaded joint for steel pipes, since the enlargement of the outside diameter of the box is limited, the outer diameter of the box threaded joint is comparable to the outside diameter of the pin is often used. In this type of threaded joint, in order to ensure the sealing performance, it is often the seal portion due to surface contact is provided.
[0022]
　In a conventional threaded joint, for example, the inner sealing portion is disposed at the tip of the pin, the outer seal portion is placed on (the side opposite to the main pipe side of the box) Box tip. Inner seal portion contributes to sealing performance from being an inboard, primarily to internal pressure. Outer sealing portion contributes to sealing performance from being an outboard, primarily to external pressure. Then, in the area between the inner seal portion and an outer seal portion, the screw portion of the two stages is provided. Furthermore, the boundary of the screw portion of the two-stage, shoulder portion is provided. The threaded portion, for example, buttress-type taper thread is employed.
[0023]
　In such a conventional threaded joint of a structure, the thickness of the pin and box in the region of the seal portion (inner seal portion and an outer seal portion) becomes thinner. While securing the area of ​​risk section of the pin and box, because must seal portion is placed at the tip of each pin and box. A hazardous sectional here, refers to a end of the engagement region of the threaded portion, the position of the cross sectional area to bear the tensile load is minimized. Position and cross-sectional area thereof hazards section is an element for determining the tensile strength of the threaded joint.
[0024]
　When the thickness of the region of the seal portion is thin, when the excessive pressure in the threaded joint (internal pressure and external pressure) is loaded, the area of ​​the seal portion is excessively deformed, it may be impossible to maintain the sealing performance.
[0025]
　In contrast, the threaded joint of the Patent Document 2, it is possible to suppress excessive deformation of the region of the sealing portion during pressure loading. And in the patent document 2 of the threaded joint, because the sealing portion is provided adjacent to the shoulder portion at the boundary of the screw portion of the two-stage, because it is possible to ensure the thickness of the pin and box in the region of the seal portion .
[0026]
　Also, in the case of the Patent Document 2 threaded joint employing a threaded portion of the dovetail shape. Then, in one of the threaded portion either of the screw portion of the two-stage, between the adjacent load surface during insertion faces, a gap is formed between such a thread crest surface and the thread root bottom surface. That is, the screw portion is not in close contact fit without a gap over the entire region.
[0027]
　Here, a threaded joint having a threaded portion of the gap without wedge thread: If (eg Patent Document 1 of the threaded joint), there are the following problems. During fastening, adhesion fit in the threaded portion shouldering (that shoulder faces abut) occurs before the. For this reason, becomes excessive tightening torque at the time of the shoulder ring, trouble occurs in the fastening operation. In addition, a threaded portion is engaged already enough at the time of engagement completion, it is not possible to bear a sufficiently load in the shoulder portion. Therefore, damage of the screw portion is increased.
[0028]
　In contrast, a threaded joint having a threaded portion of the dovetail shape of the foregoing gap, specifically, there is a gap between the insertion faces, threaded portion with a further gap between the screw crest surface and the thread root bottom surface at the threaded joint having, upon engagement, the occurrence of plastic deformation of only threaded portion correspondingly to the presence of clearance is delayed, it is possible to bear sufficiently the load to the shoulder portion.
[0029]
　Therefore, a threaded joint having a threaded portion with a gap, compared to a threaded joint having a threaded portion with no gap, can exhibit excellent sealing performance.
[0030]
　Incidentally, even in a threaded joint having a threaded portion with a gap in the threaded joint of an excessive internal pressure and external pressure is loaded, rather than installing a seal portion only at one place (in the Patent Document 2 threaded joint see), it is preferably placed separately and outer seal portion for the inner seal portion and the external pressure of the inner pressure. The installation of the individual seal portions, it is possible to effectively share the internal pressure and external pressure, since the sealing performance more be ensured.
[0031]
　In this respect, in the patent document 2 of the threaded joint, as described above, the seal portion is not only installed in one location adjacent to the shoulder portion. If, when trying to set up in two places a seal in the Patent Document 2 threaded joint on both sides between which the shoulder portion and an outer seal portion sealing portion respectively be located adjacent the shoulder portion Become. In this case, the inner seal portion and an outer seal portion to close.
[0032]
　However, the inner case of the sealing portion and the outer seal portion and the screw joint to close, and active contact of the inner seal portion and the contact of the outer seal portion to each other in the fastening process, each of the sealing faces is fit enough not in close contact. Therefore, the interference amount of each seal portion becomes (interference) is insufficient, not be able to exhibit a sealing performance rather.
[0033]
　Therefore, a state where the inner seal portion and an outer seal portion to close is inadequate, the distance between the inner seal portion and an outer seal portion needs to be long to some extent. If secure the distance between the inner seal portion and an outer seal portion, the interaction between the contact of the contact with the outer seal portion of the inner seal portion at the conclusion of the process is reduced. Thus, fitting contact between the respective sealing surfaces becomes sufficiently reliably excellent sealing performance.
[0034]
　Further, with the ensuring the distance between the inner seal portion and an outer seal portion, the pin and box, respectively, the rigid portion of sufficient length between both seal portion is formed. The rigid portion acts to or reduced in diameter or is uniformly expanded the area of ​​the seal portion during pressure loading. This action is prevented from deflection in each of the sealing surfaces occurs, improving the sealing performance can be expected.
[0035]
　However, at first glance, when an excessive compressive load is applied to the threaded joint, between the inner seal portion and an outer seal portion each seal surface becomes aspects away in the axial direction of the tube, decrease in sealing performance is concerned. However, the shoulder portion is disposed between the inner seal portion and an outer seal portion, because this compressive load by the shoulder portion is borne, never between the individual sealing surface away in the axial direction of the tube, decrease in sealing performance It does not occur.
[0036]
　A threaded joint for steel pipes of the present invention has been completed based on these findings. Hereinafter, an embodiment of a threaded joint for steel pipes of the present invention.
[0037]
　Figure 1 is a longitudinal sectional view showing a threaded joint for steel pipes according to an embodiment of the present invention. Figure 2 is a vertical sectional view enlarging a vicinity of the boundary of the two-stage screw portion of a threaded joint for steel pipes shown in Figure 1. As shown in FIGS. 1 and 2, a threaded joint of the present embodiment is a integral type threaded joint, composed of the pin 10 and the box 20. However, a threaded joint of the present embodiment can also be applied to a coupling type of threaded joint.
[0038]
　Threaded joint of this embodiment, the outer diameter of the box 20 is directed to what is comparable to the outside diameter of the pin 10. Therefore, the outer diameter of the box 20, at least 100% of the outer diameter of the tube body of the pin 10, is less than 110%.
[0039]
　Pin 10, in order from the distal end side of the pin 10 to the tube main body includes a first male threaded portion 11, the first sealing surface 12, the shoulder surface 13, the second sealing surface 14, and a second male threaded portion 15. The first sealing surface 12 and the second sealing surface 14 are both tapered. Strictly speaking, the first sealing surface 12 and the second sealing surface 14, respectively, shape consisting of a surface corresponding to a peripheral surface of a truncated cone as the distal end side of the pin 10 diameter is reduced, or frustoconical circumferential surface thereof and , a shape of a combination of a surface corresponding to the peripheral surface of the rotary body obtained by rotating the curve of the circular arc or the like around the tube axis CL.
[0040]
　Shoulder surface 13 is substantially perpendicular annular surface to the tube axis CL. 1 and 2, the shoulder surface 13, showing a state in which slightly tilted in the screwing direction of travel of the pin 10 from the plane perpendicular to the tube axis CL. That is, the state in which the shoulder surface 13 is slightly inclined toward the front end side of the pin 10 about the outer periphery side.
[0041]
　On the other hand, the box 20 includes, in order toward the tip side from the tube main body side of the box 20 comprises a first internally threaded portion 21, the first seal surface 22, shoulder surface 23, the second sealing surface 24, and a second female threaded portion 25 . The first female screw portion 21 of the box 20, the first seal surface 22, shoulder surface 23, the second sealing surface 24 and the second female threaded portion 25, respectively, the first male threaded portion 11 of the pin 10, the first sealing surface 12, the shoulder surface 13, is provided corresponding to the second sealing surface 14, and the second male threaded portion 15.
[0042]
　The first first female threaded portion 21 of the male thread portion 11 and the box 20 of the pin 10, a taper thread of dovetail shape meshing with one another, constituting a first threaded portion of the inboard and (internal thread portion). The second female threaded portion 25 of the second male threaded portion 15 and the box 20 of the pin 10 is also a taper thread of dovetail shape meshing with one another, constituting a second threaded portion of the outboard (outer threaded portion).
[0043]
　3 and 4 are a longitudinal sectional view of an enlarged threaded portion of a threaded joint for steel pipes shown in Figure 1. Of these, FIG. 3 shows a first threaded portion, FIG. 4 shows a second threaded portion.
[0044]
　As shown in FIG. 3, it relates the inner threaded portion, the first male threaded portion 11 of the pin 10 is threaded crest surface 11a, a screw trough bottom 11b, insertion flank surfaces 11c preceding by screwing (hereinafter, also referred to as "insertion surface") , and its insertion surface 11c load flank surface 11d on the opposite side (hereinafter, also referred to as "load surface") having a. On the other hand, the first female threaded portion 21 of the box 20, the screw crest surface 21a facing the thread root bottom surface 11b of the first male threaded portion 11, the screw trough bottom 21b facing the thread crest surface 11a of the first male threaded portion 11, the first comprising insertion face 21c facing the insertion face 11c of the externally threaded portion 11, and the load surface 21d opposed to the load surface 11d of the first male threaded portion 11.
[0045]
　As shown in FIG. 4, relates to the external thread portion, the second male threaded portion 15 of the pin 10 is threaded crest surfaces 15a, thread root bottom surface 15b, insertion face 15c preceding by screwing, and opposite its insertion surface 15c with a load surface 15d. The second female threaded portion 25 of the box 20, the screw crest surface 25a facing the thread root bottom surface 15b of the second male threaded portion 15, the screw trough bottom 25b facing the thread crest surface 15a of the second male threaded portion 15, the second comprising insertion face 25c facing the insertion face 15c of the externally threaded portion 15, and the load surface 25d opposed to the load surface 15d of the second male threaded portion 15.
[0046]
　Load surface 11d of the first threaded portion, 21d and insertion surfaces 11c, 21c, and the load surface 15d of the second threaded portions, 25d and insertion surfaces 15c, 25c flank angle of each a negative angle of less than 0 °. The flank angle here means the angle between the perpendicular surface and the flank surface to the tube axis CL. For threaded joint shown in FIGS. 3 and 4, the load surface 11d, 21d, 15d, 25d flank angle clockwise is positive, the insertion surface 11c, 21c, 15c, the flank angle of 25c is counterclockwise positive to.
[0047]
　A first male threaded portion 11 and the first female screw portion 21 (internal thread portion) and a second male threaded portion 15 and the second female threaded portion 25 (external thread portion), respectively to allow mutual screwing, together mating contact in the engaged state and, the interference fit of the state. Between the first seal surface 12 and 22 and between the second seal surface 14 and 24, respectively, with the screwing of the pin 10 in contact with each other, closely fit in the fastening state, the interference fit state. Thus, between the first sealing surface 12 and 22, formed first sealing portion by surface contact (the inner sealing portion). Between the second seal surface 14 and 24 forms the second seal portion by surface contact (outer seal portion).
[0048]
　Shoulder surfaces 13 and 23 to each other is pressed in contact with each other with the screwing of the pin 10, responsible for the stopper for limiting the screwing of the pin 10. Shoulder surfaces 13 and 23 forms a shoulder portion by pressure contact of such other, responsible for the stopper. Shoulder surfaces 13 and 23, in the engaged state, the first threaded portion and a second threaded section load surface 11d of the respective pins 10, to 15d, with confers fastening axial force of the so-called screw bear the load due to the reaction force responsible for.
[0049]
　Relates inner threaded portion of the fastening state, the load surface 11d of the first male threaded portion 11 and the first female threaded portion 21, it is 21d with each other in contact with each other. Further, the screw crest surface 11a of the first male screw portion 11 and the thread root bottom surface 21b of the first female screw portion 21 are in contact with each other. Further, insertion face 11c of the first male threaded portion 11 and the first female threaded portion 21, a gap is formed between the 21c together. A gap is formed between the screw trough bottom 11b and the screw crest surface 21a of the first internally threaded portion 21 of the first male threaded portion 11. However, contrary to such an embodiment, the thread crest surface 21a of the thread root bottom surface 11b and the first internal thread portion 21 of the first male threaded portion 11 are in contact with each other, and the screw crest surface 11a of the first external thread portion 11 a it may be in a manner that a gap is formed between the thread root bottom surface 21b of the 1 internal thread portion 21.
[0050]
　Relates external threaded portion of the fastening state, the second male threaded portion 15 and a second load surface 15d of the female screw portion 25, it is 25d with each other in contact with each other. Further, a screw crest surface 25a of the thread root bottom surface 15b and the second female threaded portion 25 of the second male threaded portion 15 are in contact with each other. Moreover, the second male threaded portion 15 and the second insertion surface 15c of the internal thread portion 25, a gap is formed between the 25c together. A gap is formed between the thread root bottom surface 25b of the thread crest surface 15a and the second female threaded portion 25 of the second male threaded portion 15. However, contrary to such an embodiment, the thread root bottom surface 25b of the thread crest surface 15a and the second female threaded portion 25 of the second male threaded portion 15 are in contact with each other, and the thread valley bottom 15b of the second male threaded portion 15 a it may be in a manner that a gap is formed between the screw crest surface 25a of the 2 internal thread portion 25.
[0051]
　5, the pin of the present embodiment, showing the dimensional relationship between the first sealing surface and the shoulder surface. As shown in FIG. 5, the first sealing surface 12 of the pin 10 has a first tapered surface 12a and the first curved surface 12b, and the 12c. The first curved surface 12b, 12c are present on both ends of the first tapered surface 12a. Position P1 is a boundary between the first curved surface 12c of the front end side of the first tapered surface 12a and the pin 10. Position P3 is the position of the maximum diameter of the shoulder surface 13 of the pin 10. Distance L1 in the tube axis CL direction from position P1 to position P3 is 15mm or more.
[0052]
　6, the pin of the present embodiment, showing the dimensional relationship between the second sealing surface and the shoulder surface. As shown in FIG. 6, the second sealing surface 14 of the pin 10 has a second tapered surface 14a and the second curved surface 14b, and the 14c. The second curved surface 14b, 14c are present on both ends of the second tapered surface 14a. Position P2 is a boundary between the main pipe side of the second curved surface 14b of the second tapered surface 14a and the pin 10. Distance L2 in the tube axis CL direction from the position P2 to the position P3 is 15mm or more. Furthermore, the total distance L of the distance L1 and the distance L2 is 50mm or more.
[0053]
　In short, in the present embodiment, the inner seal portion (first seal portion) is formed by a surface contact between the first sealing surface 22 of the first seal surface 12 and the box 20 of the pin 10. Position of the inner seal portion is defined by a position P1 which is the boundary between the first tapered surface 12a and the first curved surface 12c of the first sealing surface 12 of the pin 10. Position outside the sealing portion (second seal portion) is defined by the second tapered surface 14a and the position P2 which is the boundary between the second curved surface 14b of the second sealing surface 14 of the pin 10. Furthermore, the shoulder portion is disposed between the inner seal portion and an outer seal portion. The position of the shoulder portion is defined by the position P3 of the shoulder surface 13 of the pin 10. Then, the tube axis direction of the distance between the inner seal portion and an outer seal portion, a distance L1 from the position P1 of the inner sealing portion to the position P3 of the shoulder portion, the position of the shoulder portion from the position P2 of the outer seal portion P3 It corresponds to the total distance L and the distance L2 to some extent longer.
[0054]
　Incidentally, as shown in FIG. 2, the pin 10 and the box 20, the gap C1 is formed between the inner seal portion and the shoulder portion, do not contact each other. Similarly, the pin 10 and the box 20, a gap C2 is formed between the outer seal portion and the shoulder portion, do not contact each other.
[0055]
　Thus, in the threaded joint for steel pipes of the present embodiment, the inner seal portion between the threaded portion of the dovetail shape which is divided into two regions, the shoulder portion and the outer sealing portion is provided in order, an outer seal from the inner seal portion distance to the part is ensured. Further, the threaded portion, there is a gap between the insertion faces, there is a further gap between the screw crest surface and the thread root bottom surface. With this configuration, a threaded joint of the present embodiment, with respect to pressure and external pressure, reliably excellent sealing performance.
[0056]
　Hereinafter, to complement the preferred embodiment of the primary site.
　Distance L between the inner seal portion and an outer seal portion]
　distance L between the inside seal portion and the outer sealing portion is 50mm or more. When the distance L is less than 50 mm, the contact of contact with the outer seal portion of the inner seal portion in the fastening of the process interact, we can not exhibit the sealing performance rather. A preferred lower limit of the distance L is 55 mm.
[0057]
　On the other hand, the upper limit of the distance L is not particularly defined. However, when the distance L is too long, it occurs following disadvantages. Since the length of the entire joint portion is increased, the manufacturing cost is increased. Further, since the area where the pressure is loaded with increasing length of the whole joint portion is increased, easily joint portion is plastically deformed, there is a risk of fracture in a corrosive environment. Therefore, to avoid these disadvantages occur, a preferred upper limit of the distance L is 90 mm. A more preferred upper limit of the distance L is 80 mm.
[0058]
　Distance L1, L2 of the seal portion from the (inner seal portion and an outer seal portion) to the shoulder portion]
　distance L2 of the distance from the sealing portion to the shoulder portion L1, and the outer seal portion to the shoulder portion, the inner seal portion It is set in relation to the distance L between the outer seal portion, both a 15mm or more. When the distance L1, L2 is less than 15 mm, ensuring the seal surface becomes difficult. A preferred lower limit of the distance L1, L2 is 20 mm.
[0059]
　[Shoulder]
　In longitudinal section along the tube axis, the angle between the tube axis and the shoulder surface is preferably a 75 ~ 105 °. If the angle is less than 75 °, the shoulder faces is largely tilted in the screwing direction of travel of the pin from a plane perpendicular to the tube axis, the state of pressure contact by the hook-like form. Therefore, easily shoulder portion is plastically deformed, the sealing performance becomes unstable. A more preferred lower limit of the angle of the shoulder surface is 85 °.
[0060]
　On the other hand, if it exceeds the angle of 105 °, the shoulder surfaces each other, in a state of being largely tilted in the direction opposite to the pin of the screw-advancing direction from the plane perpendicular to the tube axis. Therefore, with the pressure contact between the shoulder surface, forces that force reduced in diameter pin diameter simultaneously box to act acts, contact surface pressure between the sealing surfaces is reduced. A more preferred upper limit of the angle of the shoulder surface is 95 °. The optimum angle of the shoulder surface is 90 °. When the angle of the shoulder surface is at 90 °, the sealing performance is stabilized, and, since the processing of the shoulder portion is facilitated.
[0061]
　If the width of the shoulder surfaces of the pin and box is too small, it is impossible to bear sufficiently the load, resistance to compression is decreased. Therefore, the width of the shoulder surfaces of the pin and box may preferably be respective tube body wall thickness of more than 10%, more preferably 15% or more.
[0062]
　[Seal portion (inner seal portion and an outer seal portion)
　in the region of the sealing portion, when one thick one of the pin and box is too thick, correspondingly thinner wall thickness of the other, the other rigid There is reduced. Pin or box rigidity is decreased, pressure resistance performance is degraded. Therefore, the thickness of the wall thickness and the box pin in the region of the sealing portion is preferably 80% or less than 45% of the thickness each tube body. A preferred lower limit of the thickness is 10.5 mm. The preferable upper limit of the thickness is 17 mm.
[0063]
　Tapered sealing surface is made too steep, the sealing performance is lowered when the tensile load application. On the other hand, the taper of the sealing surface is too gentle gradient, the length of the entire seal portion is increased, the manufacturing cost is increased. Thus, the taper angle of the sealing surface is preferably 2 ~ 10 ° to the tube axis. A more preferred lower limit to the taper angle of the sealing surface is 3 °. A more preferred upper limit of the taper angle of the sealing surface is 7 °.
[0064]
　[Thread (internal thread portion and the external thread portion)
　taper of the threaded portion is made too steep, too short length of the entire screw part, torque performance is greatly reduced. On the other hand, the taper of the threaded portion is made too gentle gradient, the length of the entire screw portion is increased, the manufacturing cost is increased. Thus, the taper angle of the threaded portion is preferably 1.5 ~ 4 ° to the tube axis. A more preferred lower limit to the taper angle of the threaded portion is 2.0 °. A more preferred upper limit of the taper angle of the threaded portion is 3.6 °.
[0065]
　The gap between the screw crest surface and the thread root bottom of the screw portion is preferably less than or 0.10 mm 0.20 mm. When the gap of the threaded portion is less than 0.10mm, at the time of the fastening, the plastic deformation of the threaded portion begins at an early stage, the load burden on the shoulder portion becomes insufficient. A more preferred lower limit of the clearance of the thread portion is 0.12 mm. On the other hand, the clearance of the screw portion when is not less than 0.20 mm, the sealing performance of the inner seal portion is particularly reduced. A more preferred upper limit of the gap of the thread portion is 0.16 mm. Gap range of these threaded portion is the same in the gap between the stabbing flanks.
[0066]
　Threaded portion is practically is preferably 1 threaded screw or double threaded screw.
[0067]
　In addition, the present invention is not limited to the above embodiments, without departing from the scope of the present invention, various modifications are possible.
[0068]
　Each sealing surfaces forming the sealing portion by surface contact as described above (the inner seal portion and an outer seal portion) is shaped with the other parts by a series of machining. At that time, the feed speed of the tool when machining each seal surface is slower than when machining the other sites. Thus, each seal surface is significantly smoother than the working surface of the other portions.
[0069]
　7 and 8 are a longitudinal sectional view showing a region of the seal portion due to surface contact schematically. Figure 7 is an inner seal portion (first seal portion) is illustrated. 8, the outer seal portion (second seal portion) is illustrated. As shown in FIG. 7, the inner sealing portion refers to a region Sa to each other first sealing surface 12 and 22 are in contact with each other in the engaged state. The length of the tube axis direction of the inner seal portion 1 ~ 7 mm is preferred. On the other hand, the first seal surface 12 and 22 does not refer to only the area Sa in contact with each other by a fastening state, region processed into a smooth surface as a sealing surface Sb, it refers to the entire area of ​​Sc. Region Sc corresponds to the first tapered surface 12a of the pin 10 described above. That is, the first seal surface 12 and 22 is an area that slides while contacting each other at the conclusion of the process (including a region of possible sliding), equivalent to the area Sa in contact with each other by a fastening state machined area Sb on the surface accuracy of, including the entire area of ​​Sc. The same applies to the outer seal portion shown in FIG.
[0070]
　Remove the pin 10 from the box 20, by looking at the sealing surface, can recognize the seal portion. The sealing surface is because the seal section traces (strongly sliding regions) of (contact area Sa in the engagement state) is left.
Example
[0071]
　To confirm the effects of the present invention was performed numerical simulation analysis by the elasto-plastic finite element method.
[0072]
　
　In FEM analysis, a model of a threaded joint for steel pipes integral type shown in FIG. 1 and more produced. For these models, the distance L2 from the distance L1, and the outer seal portion from the inner sealing portion to the shoulder portion to the shoulder portion was variously changed. This change was to change the distance L between the inner seal portion and an outer seal portion. Furthermore, the angle of the shoulder surfaces were also variously changed.
[0073]
　As a conventional example for comparison, we were prepared the following model. This prior art model of joint inner seal portion is disposed on the tip portion of the pin, the outer seal portion is installed at the tip of the box. Further, in a region between the inner seal portion and an outer seal portion, a tapered threaded portion of the buttress type of two-stage are provided, and the boundary of the screw portion of the two-stage, shoulder portion is provided.
[0074]
　Main dimensions of each model are shown in Table 1 to Table 3 below. Of these tables, Table 2 shows the various dimensions of the pins, Table 3 shows the dimensions of the box.
[0075]
[Table 1]

[0076]
[Table 2]

[0077]
[table 3]

[0078]
　Other common conditions are as follows.
　- steel dimensions: 14 [inch], 115 [ lb / ft] ( outer diameter of 355.6 mm, an inner diameter of 314.35Mm, wall thickness 20.625Mm)
　- steel grade: the API standard Q125 (yield strength 125ksi (862MPa) carbon steel)
[0079]
　 The FEM analysis was successively a load simulating the Series A test ISO13679 each model of the fastening state. Sealing contact force of the outer seal portion (second seal portion) of the load [N / mm], that is, by comparing the minimum value of the "average contact surface pressure between the sealing surface" × "contact width", sealed against external pressure and evaluate the performance. Sealing performance enough seal portion is higher value of the contact force is meant that good. Similarly, by comparing the seal contact force even inner seal portion (first seal portion) were evaluated sealing performance against pressure.
[0080]
　
　The test results are shown in Table 4 below.
[0081]
[Table 4]

[0082]
　As shown in Table 4, the test of the present invention examples satisfy all of the conditions specified in the present invention No. 4-9 does not satisfy any of the conditions specified in the present invention Test No. Test of Conventional Example 1 and Comparative Example No. Compared to 2 and 3, the contact force of the outer seal portion and the inner seal portion was remarkably high. This trend was observed similarly be changed in a range of the angle of the shoulder surface 75 ° ~ 95 °. Therefore, by employing a tubular threaded joint of the present invention, it could be demonstrated that it is possible to reliably improve the sealing performance with respect to pressure and external pressure.
Industrial Applicability
[0083]
　Threaded joint of the present invention can be effectively used for connecting steel pipes used as OCTG.
DESCRIPTION OF SYMBOLS
[0084]
　10:
　Pin, 11: first male threaded
　portion, 11a: screw crest surface of the first male screw
　portion, 11b: thread root bottom surface of the first male threaded
　portion, 11c: insert flanks of the first external thread
　portion, 11d: first male threaded portion load flank surface
　of, 12: first sealing
　surface, 12a: first tapered
　surface, 12b, 12c: first curved
　surface, 13: shoulder surface,
　14: second sealing
　surface, 14a: second tapered
　surface, 14b, 14c : second curved
　surface, 15: second male threaded
　portion, 15a: screw crest surface of the second male threaded
　portion, 15b: thread root bottom surface of the second male threaded
　portion, 15c: insert flank of the second male threaded
　portion, 15d: second load flank surface of the external thread
　portion, 20:
　box, 21: first female threaded
　portion, 21a: screw crest surface of the first female threaded
　portion, 21b: thread root bottom surface of the first female threaded
　portion, 21c: insert flank of the first female threaded portion ,
　21D: Load flank surface of one internal thread
　portion, 22: first sealing
　surface, 23: shoulder
　surface, 24: second sealing
　surface, 25: second female threaded
　portion, 25a: screw crest surface of the second female threaded
　portion, 25b: second female thread thread root bottom parts,
　25c: insert flank of the second female threaded portion,
　25d: load flank face of the second female threaded portion,
　L: distance between the first sealing portion and the second sealing portion,
　L1: first seal distance from part to shoulder,
　L2: distance from the second sealing portion to the shoulder portion,
　P1: boundary position between the first tapered surface and the pin head side first curved surface of,
　P2: second tapered surface and the pin boundary position between the second curved surface of the pipe main body,
　P3: minimum diameter position of the contact area between the shoulder surfaces,
　C1: clearance,
　C2: clearance,
　CL: tube axis

WE CLAIM

[Requested item 1]
　A pin tubular, is composed of a tubular box, a tubular threaded joint in which the box and the pin the pin is screwed into the box is fastened,
　outside the outer diameter of the box is a tube body of said pin less than 110% of the diameter,
　said pins in order toward the tube body from the tip of the pin, first male threaded portion of the tapered threads of dovetail shape, a first sealing surface, a shoulder surface, the second sealing surface, and dovetail a second external thread portion of the tapered thread shape,
　the first sealing surface, and a first curved surface at both ends of the first tapered surface and the first tapered surface,
　the second sealing surface, the second and a tapered surface and the second curved surface at both ends of the second tapered surface,
　the tube axis direction from the boundary between the first tapered surface and the front end side of the first curved surface of the pin to the shoulder surface distance L1 is there in 15mm or more
　Wherein and the second tapered surface and the pipe axis direction of the distance L2 from the boundary between the main pipe side of the second curved surface of the pin to the shoulder surface is 15mm or more,
　the total distance L of the distance L1 and the distance L2 There is at least 50mm,
　the box, in order toward the tip from the tube body of the box, first internally threaded portion of the tapered threads of dovetail shape, a first sealing surface, a shoulder surface, the second sealing surface, and the dovetail-shaped a second female threaded portion of the tapered threads,
　the engaged state,
　the shoulder surfaces contact each other, the first sealing faces are in contact, said second seal faces are in contact,
　the first male screw portion and the second with a gap is formed between the insertion flank surfaces of 1 female thread portion, between the screw crest surface of the thread root bottom and the first female threaded portion of the first male threaded portion, or the first external thread portion Flip gap is formed between the crest face and thread root bottom surface of the first female threaded portion,
　with a gap is formed between the insertion flank faces of the second male threaded portion and the second female threaded portion, the first a gap is formed between the between, or thread crest surface of the second male threaded portion and the thread root bottom surface of the second female threaded portion of the screw trough bottom screw crest surface of the second internally threaded portion of 2 male thread portion , a threaded joint for steel pipes.
[Requested item 2]
　A tubular threaded joint according to claim 1,
　wherein the gap is less than or 0.10 mm 0.20 mm, tubular threaded joint between the thread root bottom and the screw crest surface.
[Requested item 3]
　A tubular threaded joint according to claim 1 or 2,
　in longitudinal section along the tube axis, the angle between the the tube axis shoulder surface is 75 ~ 105 °, tubular threaded joint.
[Requested item 4]
　A threaded joint for steel pipes according to any one of claims 1 to 3,
　wherein the total distance L is 90mm or less, a threaded joint for steel pipes.
[Requested item 5]
　A threaded joint for steel pipes according to any one of claims 1 to 4,
　wherein said first externally threaded portion of the first threaded portion formed of the first female screw portion, and a second male threaded portion first second threaded section consists of two female screw portion is a single-thread screw or double threaded screw, threaded joint for steel pipes.