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"), a casing, an oil well pipe such as tubing 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, the steel pipe and the coupling is coupled. 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 steel and other steel pipes are 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 is developed, along with this, an oil well environment has become severe environment of high corrosion at high temperature and high pressure. To accommodate such harsh environment, steel thick are increasingly being used as oil well pipes. The threaded joint for connecting these steel pipes, pressure from the inside (hereinafter, also referred to as "internal pressure") and external pressure (hereinafter, also referred to as "external pressure") to be required to have excellent sealing performance.
[0006]
　As a conventional technique for improving the sealing performance for the threaded joint of the thick steel pipes, there is the following. WO WO01 / 029476 (Patent Document 1) discloses a threaded joint having two positions sealing portion by surface contact. In this technique of Patent Document 1, the pin is provided, in order from the distal end side of the pin to the tube body, the shoulder surface, a first sealing surface, the first male threaded portion, the second sealing surface, and a second male threaded portion. Box comprises corresponding to each of the pins of the various parts, the shoulder surface, a first sealing surface, the first internally threaded portion, the second sealing surface, and a second female threaded portion. The first threaded portion constituted by the first male screw portion and the first female screw portion is a trapezoidal thread taper thread. The second threaded portion constituted by the second male threaded portion and the second female threaded portion is the same.
[0007]
　The first threaded portion and the second threaded section, respectively, fastening closely fitting in a state of completion, the interference fit state. The first sealing faces and second sealing faces, respectively, with the screwing of the pin contact each other, and because of the state interference fit in close contact with the fitting in a state in which fastening has been completed. Shoulder faces are pressed in contact with each other with the screwing of the pin, responsible of the stopper for limiting the screwing of the pin. Shoulder surface, together with the role of the stopper, in a state in which fastening is completed, the load flanks of the first threaded portion and a second threaded portion each pin, responsible for imparting clamping axial force of the so-called screw.
[0008]
　When the first threaded portion and a second threaded portion disclosed in Patent Document 1, in a state in which fastening has been completed, together with the load flank surfaces of the pin and box are in contact, a screw crest surface of the screw trough bottom and the box pin There contacts, also contacts thread root bottom surface of the further thread crest surfaces of the pin and the box.
[0009]
　In such an arrangement Patent Document 1 of the threaded joint, the fitting contact mating contact and a second threaded portion of the first threaded portion, a robust screw connection is secured. Additionally, the adhesion fitting between the first sealing surface, the sealing portion of the inboard is formed by surface contact, the sealing performance is secured in the main internal pressure. Further, the contact fit of the second sealing faces are formed sealed portions of the outboard by surface contact, primarily sealing performance against external pressure is ensured.
CITATION
Patent Document
[0010]
Patent Document 1: International Publication No. WO01 / 029476 No.
Summary of the Invention
Problems that the Invention is to Solve
[0011]
　Threaded joint used in recent harsh environments, particularly threaded joint of the thick steel pipes, with respect to pressure and external pressure, further improvement of the sealing performance is required.
[0012]
　An object of the present invention is to provide a tubular threaded joint having the following characteristics:
　while maintaining the sealing performance against pressure, improving the sealing performance against external pressure.
Means for Solving the Problems
[0013]
　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, the box and the pin the pin is screwed into the box is a threaded joint to be fastened.
　It said pin is provided in order from a tip end thereof, the shoulder surface, a first sealing surface, the first male threaded portion of the tapered thread, a second sealing surface, and a second male threaded portion of the tapered thread.
　The box is provided in order toward the tip side from the tube body, the shoulder surface, a first sealing surface, the first internally threaded portion of the tapered thread, a second sealing surface, and a second female threaded portion of the tapered thread.
　The first male screw portion has thread crest surface, thread root bottom insert flanks and load flanks.
　The first internally threaded portion, said first screw trough bottom opposite to the thread crest surface of the male screw portion, a screw crest surface facing the thread root bottom surface of the first male screw portion, the insertion flank of the first male threaded portion insert flank face opposite to the face, and has a load flank surface facing the load flank surface of the first male screw portion.
　Flank angle of the load flanks of each of the first male screw portion and the first female threaded portion is less than 0 °.
　The first male screw portion, in order from the side closer to the second sealing surface is divided incomplete thread region, and a fully threaded area.
　The incomplete thread portion region is an in the length along the tube axis than three times the thread pitch of the first male screw portion is lower than the thread height is thread height of the complete thread portion region.
　In a state in which the fastening has been completed,
　Wherein in the fully threaded region, said together with the thread root bottom surface of the thread crest surface and the first female thread portion is in contact, the first male screw portion and the load flanks of each of the first female threaded portion of the first male threaded portion contact each other, wherein with a gap is formed between the thread root bottom and the screw crest surface of the first female threaded portion of the first male threaded portion, of each of the first male screw portion and the first female threaded portion a gap is formed between the said insert flanks,
　wherein in the incomplete thread portion region, a gap is formed between the thread root bottom surface of the thread crest surface and the first female threaded portion of the first male threaded portion that.
[0014]
　In the above-described threaded joint, it is preferable to the incomplete thread portion length along the tube axis of the region is less than 8 times the thread pitch of the first male screw portion configured.
[0015]
　In the above-described threaded joints, said pins, between said first externally threaded portion and the second sealing surface, it is desirable to employ an arrangement wherein an annular portion which does not contact the box in a state where the fastening is complete. In this threaded joint, it is preferable length along the tube axis of the annular portion is not more than three times the thread pitch of the first external thread portion.
[0016]
　In the above-described threaded joints, the gap between the screw crest surface of the thread root bottom and the first female threaded portion of the first male screw portion is preferably configured at 0.05mm or more.
[0017]
　In the above-described threaded joint, it is preferable to employ the following configuration.
　The second male threaded portion has thread crest surface, thread root bottom insert flanks and load flanks.
　The second female threaded portion, the thread root bottom surface facing the thread crest surface of the second male threaded portion, the screw crest surface facing the thread root bottom surface of the second male threaded portion, the insertion flank of the second male threaded portion insert flank face opposite to the face, and has a load flank surface facing the load flank surface of the second male threaded portion.
　Flank angle of the load flanks of each of the second male threaded portion and the second female threaded portion is less than 0 °.
　In a state where fastening is completed, the screw with the screw crest surface of the trough bottom and the second female screw portion is in contact, the second male threaded portion and the load flanks of each of the second female threaded portion of the second male threaded portion contact each other, wherein with a gap is formed between the thread crest surface of the second male threaded portion and the thread root bottom surface of the second female threaded portion, of each of the second male threaded portion and the second female threaded portion a gap is formed between the said insert flanks.
Effect of the invention
[0018]
　A threaded joint for steel pipes of the present invention has a remarkable effect of the following:
　while maintaining the sealing performance against internal pressure, it can improve the sealing performance against external pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019]
[1] Figure 1 is a longitudinal sectional view showing a threaded joint for steel pipes according to the first embodiment.
FIG. 2 is a longitudinal sectional view of an enlarged second sealing portion near the threaded joint for a steel pipe shown in Figure 1.
FIG. 3 is a longitudinal sectional view showing a threaded joint for steel pipes according to the second embodiment.
[4] FIG. 4 is a longitudinal sectional view of an enlarged second sealing portion near the threaded joint for a steel pipe shown in FIG.
DESCRIPTION OF THE INVENTION
[0020]
　The present inventors have found that in order to achieve the above object, focusing the sealing portion due to surface contact with the threaded joint comprises two portions, superimposed intensively examined configuration capable maximize the sealing performance by the individual seal. The main structure of the screw joint is as follows. Shoulder surface is provided on the tip of the pin. Threaded portion has a first threaded portion of the inboard (hereinafter, also referred to as "inner threaded portion") and a second threaded portion of the outboard (hereinafter, also referred to as "external thread portion") is divided into two and, any of the first threaded portion and a second threaded portion is a trapezoidal thread taper thread. Between the shoulder surface and the first threaded portion, the first sealing portion by the surface contact between the first sealing surface (hereinafter, also referred to as "inner seal portion") is provided. Between the first threaded portion and a second threaded portion, the second sealing portion by the surface contact between the second sealing surface (hereinafter, also referred to as "intermediate seal portion") is provided. Inner seal portion is mainly contributes to the sealing performance against pressure. Intermediate seal portion is mainly contributes to the sealing performance against external pressure. The results of the study, was first obtained the following findings.
[0021]
　As a technique for improving the sealing performance against external pressure, it can be considered the following methods. The first approach is to increase the fitting margin of the intermediate seal portion (interference amount). This is because the contact surface pressure between the sealing surfaces is increased in the intermediate seal portion.
[0022]
　In the first approach, when inserting the pin into the box, the contact between the first male threaded portion of the pin and the second sealing surface of the box, and the contact between the second sealing surface and the second female threaded portion of the box pin it is necessary to avoid. Therefore, smaller than the smallest diameter of the second female threaded portion of the maximum diameter of the second sealing surface of the pin box, so that the minimum diameter of the second sealing surface of the box is larger than the maximum diameter of the first male screw portion of the pin to, must be designed dimensions. To increase the amount of interference at the intermediate seal portion, there is a method for the thread taper of the first threaded portion and a second threaded portion to steep. Alternatively, in a region close to the intermediate seal portion of the area of ​​the second female threaded portion of the first male threaded portion and a box pin, thread height there is a method of installing a low incomplete thread section than the full thread portion.
[0023]
　However, if you too steep screw taper, the area of ​​the shoulder surface which is placed on the pin tip is reduced, resistance to compression is decreased. Moreover case, meshing length of the threaded portion is reduced, the risk of jump-out (pin situation in which pulled out inadvertently from the box) occurs increases. These problems, in that the threaded taper steeper is limited. In the first approach, excessively too large amount of interference, there is a possibility that seizure is generated when fastening the pin and the box. Therefore, there is a limit to increasing the amount of interference.
[0024]
　The second approach is to thicken the region of the intermediate seal portion of the pin. The reason for this is as follows. And pins with the load shrink-deformed external pressure to the threaded joint, the contact of the sealing surfaces of the intermediate seal portion is loosened. In this regard, reduced diameter resistance is increased by the thickening of the pin. However, the inner diameter of the pin is defined by the standard of API (American Petroleum Institute (American Petroleum Institute)), expansion of the outer diameter of the pin is a finite constraints on the structure of the oil well. Therefore, to thickening the regions of the intermediate seal portion of the pin is limited.
[0025]
　Therefore, as a technique for improving the sealing performance against external pressure, only the first and second methods described above have limitations.
[0026]
　Accordingly, the present inventors have, when high threaded joint external pressure is loaded, if it becomes possible to shrink the area of ​​the intermediate seal portion of the box, amplifies the contact surface pressure of the sealing surfaces of the intermediate seal portion I thought that if not can do. Result of intensive studies, have found that the following configuration is effective.
[0027]
　The inner threaded portion of the intermediate seal portion inner threaded portion sandwiching (second seal portion) (first threaded portion) and an outer threaded portion (second threaded section) of the pin of the male screw portion and the box engage with each other internally threaded among parts, to reduce the thread height of the male screw portion of the pin closer to the intermediate seal portion region. With such a configuration, adhesion mating screws in incomplete thread portion region thread height is lower to relax. Thus, when the high threaded joint external pressure is loaded, the box, the region of the intermediate seal portion is so reduced in diameter leading to the incomplete thread portion region and the incomplete thread portion region of the internal thread portion. As a result, the contact surface pressure between the sealing surfaces is amplified in the intermediate seal portion, thereby improving the sealing performance against external pressure.
[0028]
　However, it should be noted the following points. First, the flank angle of the load flanks of the internal thread portion is a conformal greater than 0 °, even if an attempt is reduced in diameter box with the load of the external pressure, the reaction force from the load flank of the pin (male screw portion) order to receive a reduced diameter of the box is blocked. Thus, to tolerate the diameter of the box, the flank angle of the load flanks of the internal thread portion is a negative angle of less than 0 °.
[0029]
　Furthermore, as in the screw joint the Patent Document 1, when the fastening screw crest surface of the screw trough bottom and the box pin has adopted an internal thread portion, such as contact in a state of completion, in a region close to the intermediate seal portion be lower the thread height of the pin (male screw portion), the contact state between the screw crest surface of the incomplete thread portion region pin thread root bottom and the box is maintained. Therefore, diameter of the box due to the load of the external pressure is inhibited. Further, in the threaded joint described in Patent Document 1, lowering the thread height of the first female threaded portion of the box in the area close to the intermediate seal portion, it reduces the contact area between the load flank surface. Accordingly, when the tensile and compressive loads on the threaded joint is loaded, a stress acting becomes relatively high in the inner threaded portion, there is a possibility that the internal thread portion is plastically deformed. Moreover, there is a possibility that jump-out occurs. Thus, to tolerate the diameter of the box, thread root bottom surface of the thread crest surface and the box pin to adopt internal threaded portion such that contact.
[0030]
　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.
[0031]
　[First Embodiment]
　FIG. 1 is a longitudinal sectional view showing a threaded joint for steel pipes according to the first embodiment. Figure 2 is a vertical sectional view enlarging a vicinity of the second sealing portion at the threaded joint for steel pipes. As shown in FIGS. 1 and 2, a threaded joint of the present embodiment is a coupling type of threaded joint, composed of the pin 10 and the box 20.
[0032]
　Pin 10 is provided in order from the distal end side of the pin 10 to the tube body, the shoulder surface 11, a first sealing surface 12, the first male threaded portion 13, 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 has 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.
[0033]
　Shoulder surface 11 is substantially perpendicular annular surface to the tube axis CL. Strictly speaking, the shoulder surface 11 is an annular surface which is inclined in the screwing direction of travel of the pin 10 from the plane perpendicular to the tube axis CL, are inclined toward the front end side of the pin 10 about its outer periphery.
[0034]
　On the other hand, the box 20 is provided in order toward the tip side from the tube main body side of the box 20, the shoulder surface 21, the first seal surface 22, the first female threaded portion 23, second sealing surface 24, and a second female threaded portion 25 . Shoulder surface 21 of the box 20, the first seal surface 22, the first female threaded portion 23, second sealing surface 24 and the second female threaded portion 25, respectively, the shoulder surface 11 of the pin 10, the first sealing surface 12, the first male screw portion 13 is provided so as to correspond to the second sealing surface 14, and the second male threaded portion 15.
[0035]
　The first female threaded portion 23 of the first male screw portion 13 and the box 20 of the pin 10 is a trapezoidal screw tapered thread meshing with each other, 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 trapezoidal thread taper thread meshing with each other, it constitutes the second threaded portion of the outboard (outer threaded portion). For the threaded joint of the first embodiment, since the only the second sealing surface 14, 24 has been added between the first threaded portion and a second threaded portion, the tapered surface of the first threaded portion and a second screw the tapered surface of the part to match.
[0036]
　As shown in FIG. 2, it relates to the internal threaded portion, the first male threaded portion 13 of the pin 10 is inserted flank surfaces 13c preceding thread crest surfaces 13a, thread root bottom surface 13b, in screwing, and contrary to the insertion flanks 13c having a load flank surface 13d side. On the other hand, the first female threaded portion 23 of the box 20, the screw crest surface 23a facing the thread root bottom surface 13b of the first male screw portion 13, the screw trough bottom 23b facing the thread crest surface 13a of the first male screw portion 13, the first comprising inserting flank 23c facing the insert flanks 13c of the external thread portion 13, and a load flank surfaces 23d opposed to the load flank surface 13d of the first male screw portion 13.
[0037]
　It relates external threaded portion, the second male threaded portion 15 of the pin 10 is threaded crest surfaces 15a, thread root bottom surface 15b, the insertion flank surfaces 15c preceding by screwing, and the load flank surface 15d opposite to the insertion thereof flanks 15c a. 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 inserting flank surfaces 25c facing the insert flanks 15c of the external thread portion 15, and the second load flank surfaces 25d opposed to the load flank surface 15d of the external thread portion 15.
[0038]
　Taper thread of the first threaded portion in this embodiment is a buttress-type tapered threads, the load flank surfaces 13d, the flank angle of the 23d is a negative angle of less than 0 °. The flank angle here is that the angle between the perpendicular surface and the flank surface to the tube axis CL, where the clockwise and positive (see Figure 2). Tapered thread of the second threaded portion is the same.
[0039]
　Here, it relates inner threaded portion, the first male threaded portion 13 of the pin 10, in order from the side closer to the second sealing surface 14 is divided into the incomplete thread portion region 31b and the fully threaded region 31a. The length along the tube axis CL of the incomplete thread portion region 31b is more than three times the thread pitch of the first male screw portion 13. Further, the first male threaded portion 13, thread height of the incomplete thread portion region 31b is lower than the thread height of the complete thread portion area 31a. Thread root bottom surface 13b of the incomplete thread portion region 31b in the first male threaded portion 13 is on the thread root bottom surface 13b and the same tapered surface of the complete thread portion area 31a. Screw crest surface 13a of the incomplete thread portion region 31b in the first external thread portion 13 are on a cylindrical surface parallel from the boundary between the complete thread portion area 31a and the incomplete thread portion region 31b in the tube axis CL.
[0040]
　It relates external threaded portion, the second female threaded portion 25 of the box 20, in order from the side closer to the second sealing surface 24 is divided into the incomplete thread portion region 32b and the fully threaded region 32a. Tube axis length along the CL of the incomplete thread portion region 32b is not particularly limited, in practice, a 3-8 times the thread pitch of the second female threaded portion 25. Further, in the incomplete thread portion region 32b, thread height of the second female threaded portion 25 is lower than the thread height of the complete thread portion area 32a. Thread root bottom surface 25b of the incomplete thread portion region 32b in the second female threaded portion 25 is on the thread root bottom surface 25b and the same tapered surface of the complete thread portion area 32a.
[0041]
　Thread root bottom surface 13b of the first male threaded portion 13 is on an extension plane of the taper of the thread root bottom surface 15b of the second male threaded portion 15.
[0042]
　The first male screw portion 13 and the first female screw portion 23 (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, each other in a state in which fastening has been completed fitting in close contact, 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, it becomes a fit state interference fit in close contact with the fitting in a state in which fastening has been completed, forming first sealing portion by surface contact (inner seal portion) and a second seal portion (intermediate seal portion). Between the shoulder surfaces 11 and 21 is pressed in contact with each other with the screwing of the pin 10, in a state in which fastening is completed, the load flank surfaces 13d of the pin 10, the axial fastening force to 15d grant.
[0043]
　It relates inner thread portion in a state in which fastening has been completed, either fully threaded region 31a and the incomplete thread portion region 31b, a state below. Load flank surfaces 23d of the load flank surface 13d of the first male threaded portion 13 first internally threaded portion 23 are in contact with each other. A gap is formed between the screw crest surface 23a of the thread root bottom surface 13b and the first female threaded portion 23 of the first male screw portion 13. A gap is formed between the insertion flank 23c of the insertion flank 13c and the first female threaded portion 23 of the first male screw portion 13. However, the complete thread portion area 31a, a state where the screw trough bottom 23b of the thread crest surface 13a and the first female threaded portion 23 of the first male screw portion 13 is in contact with one another. In contrast, in the incomplete thread portion region 31b near the second seal surface 14 and 24 (intermediate seal portion), between the thread root bottom surface 23b of the thread crest surface 13a and the first female threaded portion 23 of the first male screw portion 13 gap is formed, the adhesion fit in the first threaded portion is relaxed.
[0044]
　It relates external thread portion in a state in which fastening has been completed, either fully threaded region 32a and the incomplete thread portion region 32b, a state below. Load flank surfaces 25d of the load flank surface 15d and the second female threaded portion 25 of the second male threaded portion 15 are in contact with each other. 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. A gap is formed between the insertion flank 25c of the insertion flank 15c and the second female threaded portion 25 of the second male threaded portion 15. However, the complete thread portion area 32a, a state where the 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 is in contact with one another. In contrast, in the incomplete thread portion region 32b near the second seal surface 14 and 24 (intermediate seal portion), between the thread crest surface 25a of the thread root bottom surface 15b and the second female threaded portion 25 of the second male threaded portion 15 gap is formed, the adhesion fit in the second threaded portion is relaxed.
[0045]
　However, with respect to the external thread portion in a state in which fastening has been completed, contrary to the above embodiments, either fully threaded region 32a and the incomplete thread portion region 32b, the screw crest surface 15a of the second male threaded portion 15 a thread root bottom surface 25b of the 2 internal thread portion 25 may be performed in a mode of contact. In this case, the 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, either fully threaded region 32a and the incomplete thread portion region 32b, without contacting with each other, both a gap is formed between.
[0046]
　The threaded joint of this first embodiment of the configuration, the load flank surfaces 13d of the first screw part (internal thread portion), the flank angle of the 23d is less than 0 °. In the incomplete thread portion region 31b of the first threaded portion, adhesion is relaxed fit of the first threaded portion. Thus, when the high threaded joint external pressure is loaded, the box 20, the incomplete threaded portion region 31b of the first threaded portion, and a second sealing surface which is an intermediate seal portion continuous to the incomplete thread portion region 31b 24 region is such that diameter of. As a result, it amplifies the contact surface pressure between the second seal surface 14 and 24 side, thereby improving the sealing performance against external pressure.
[0047]
　Sealing performance against internal pressure is maintained by surface contact of the first seal surface 12 and 22 to each other is an internal seal.
[0048]
　In the incomplete thread portion region 31b of the first threaded portion, the first male threaded portion 13 and the contact region is load flank surfaces 13d of the first female screw portion 23, and 23d only. In this case, at first glance, since the engagement area of ​​the first threaded portion is reduced, it may engagement state becomes unstable. However, in practice, since the second threaded portion on the outer side of the first threaded portion is disposed, the engagement state by engagement of the second threaded portion is stabilized.
[0049]
　Hereinafter, to complement the preferred embodiment of the primary site.
[0050]
　In the incomplete thread portion region 31b and the fully threaded region 31a of the first threaded portion, a gap between the screw crest surface 23a of the thread root bottom surface 13b and the first female threaded portion 23 of the first male screw portion 13, when external pressure load diameter of box 20 is set so as not to be inhibited. For example, it is preferable that the gap is 0.05mm or more. The upper limit of the gap is not specified in particular, if the gap is too large, reduction of the engagement area of ​​the first threaded portion is significantly. Accordingly, when the tensile and compressive loads on the threaded joint is loaded, a stress acting on the first threaded portion is relatively high, there is a possibility that the first threaded portion is plastically deformed. Moreover, the pin 10 is likely to situation where pulled out inadvertently from the box 20 (jump-out) occurs. Thus, light of practicality, the upper limit of the gap is preferably about 0.25 mm.
[0051]
　When the length of the incomplete thread portion region 31b of the first threaded portion is too short, box 20 when external pressure load effectively not reduced in diameter. Accordingly, the lower limit of the length of the incomplete thread portion region 31b is three times the thread pitch of the first male screw portion 13. A more preferred lower limit of the length of the incomplete thread portion region 31b is four times the thread pitch of the first male screw portion 13.
[0052]
　On the other hand, if the length of the incomplete thread portion region 31b of the first threaded portion is too long, there is a disadvantage follows. Improvement of sealing performance due to the reduced diameter of the box 20 due to outside pressure load is saturated. Also, reduction in the engagement area of ​​the first threaded portion is significantly. Accordingly, when the tensile and compressive loads on the threaded joint is loaded, the first thread portion or plastically deformed, which may or cause jumping out. Therefore, the upper limit of the length of the incomplete thread portion region 31b is preferably set to 8 times the screw pitch of the first male screw portion 13. A preferred upper limit than the length of the incomplete thread portion region 31b is 7 times the thread pitch of the first male screw portion 13.
[0053]
　The lower limit of the load flank surfaces 13d, 23d flank angle of the first threaded portion (internal thread portion) is not particularly specified. Load flank surfaces 13d, flank angles of 23d is do not inhibit the diameter of the box 20 when external pressure load if it is negative angle of less than 0 °. However, given the utility of thread cutting, load flank surfaces 13d, the lower limit of the flank angle of the 23d, the - (minus) preferably set to 15 °. Its more preferred lower limit of the flank angle is -10 °.
[0054]
　[Second Embodiment]
　FIG. 3 is a longitudinal sectional view showing a threaded joint for steel pipes according to a second embodiment of the present invention. Figure 4 is a vertical sectional view enlarging a vicinity of the second sealing portion at the threaded joint for steel pipes. Threaded joint of the second embodiment shown in FIGS. 3 and 4, is a modification of the threaded joint of the first embodiment shown in FIGS. 1 and 2, description overlapping the first embodiment will be appropriately omitted .
[0055]
　As shown in FIGS. 3 and 4, the pin 10, between the first male screw portion 13 and the second sealing surface 14 comprises an annular portion 16. On the other hand, the box 20 includes a first internally threaded portion 23 an annular groove is formed between the second seal surface 24, an annular portion 26 which is shaped by the formation of the annular groove. Annular portion 26 of the box 20 is provided in correspondence with the annular portion 16 of the pin 10 does not contact the annular portion 16 of the pin 10 in a state in which fastening has been completed. That is, in the state in which fastening has been completed, the gap between the annular portion 26 of the annular portion 16 and the box 20 of the pin 10 is formed. Coated excess lubricant during tightening (hereinafter, also referred to as "dope") because it can accommodate the gap, inadvertent reduction in contact surface pressure of the second sealing surface 14, 24 with each other due to the pressure rise in the dope is avoided It is.
[0056]
　Here, the length along the tube axis CL of the annular portion 16 of the pin 10 when too long, there is a disadvantage follows. In the case where the total length of the threaded joint is constant, the entire length of the first threaded portion and the second threaded portion is substantially shortened. Accordingly, when the tensile and compressive loads on the threaded joint is loaded, a stress acting on the first threaded portion and the second threaded portion is relatively high, the first threaded portion and the second threaded portion is plastically deformed I fear there is. Moreover, there is a possibility that jump-out occurs. Therefore, the length of the annular portion 16 is preferably equal to or less than 3 times the screw pitch of the first male screw portion 13.
[0057]
　By a threaded joint of the second embodiment, the same effect as the first embodiment.
[0058]
　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. For example, in the above embodiment, the tapered surface thread crest surface 13a of the incomplete thread portion region 31b in the first male threaded portion 13 is located on a cylindrical surface parallel to the tube axis CL, which is inclined to the tube axis CL it may be in the top. Further, in the above embodiments, the screw trough bottom 13b of the first male screw portion 13 is located on the extension surface of the taper of the thread root bottom surface 15b of the second male threaded portion 15, and the extended surface, from its extended surface a be between twice partial outer diameter smaller tapered surface of the thread height of 2 male threaded portion 15 may be.
[0059]
　Furthermore, a threaded joint of the above embodiments can be applied to any of the integral type and coupling type.
Example
[0060]
　To confirm the effects of the present invention was performed numerical simulation analysis by the elasto-plastic finite element method.
[0061]
　
　In FEM analysis, a coupling model of an oil well pipe threaded joint for a plurality prepared. For these models, the flank angle of the load flanks of the first threaded portion, the area where and gap dimension of the gap in the first threaded portion, the area where the gap in the second threaded portion, incomplete thread portion of the first threaded portion the length of the region, as well as variously changed the length of the annular portion.
[0062]
　Common conditions are as follows.
　- steel dimensions: 10-1 / 8 [inch] × 0.8 [inch] ( outer diameter 257.2Mm, wall thickness 20.3 mm), the outer diameter of the coupling: 276.6Mm
　-steel and grade of the coupling : the API standard Q125 (carbon steel yield stress 125 [ksi])
　· thread shape (first threaded section and a second threaded section): taper 1/10, thread height (full thread portion region) 1. 575 [mm], the screw pitch of 5.08 [mm], flank angles 10 ° insertion flank, a gap between the insert flank 0.15 [mm]
[0063]
　The FEM analysis, the elasto-plastic body of isotropic hardening the material, the elastic modulus 210 [GPa], the nominal yield strength of the 0.2% proof stress is 125 [ksi] (= 862 [MPa]) to become as Model It was used as ized. Tightening was performed to a state where the shoulder surfaces of the pin and the box has further 1.5 / 100 rotate after contact.
[0064]
　The changed conditions are shown in Table 1 below.
[table 1]

[0065]
　Test No. 1, 3, 4 and 11 are comparative examples not satisfying the conditions defined by the present invention. Test of the No. 1, 3 and 11, in the fully threaded region of the first threaded portion, there is a gap between the thread root bottom surface of the thread crest surface and the internal thread portion of the male screw portion (pin) (box), incomplete thread portion region It is not provided. Test No. 4, the flank angle of the load flank surface is conformal to 3 °. On the other hand, test No. 2, 5 to 10 are satisfying the present invention embodiment as defined in the present invention. Test of the No. 2 is based on the threaded joint of the first embodiment shown in FIGS. 1 and 2. Test No. 5-10 is based on a threaded joint of the second embodiment shown in FIG. 3 and FIG. 4.
[0066]
　 In FEM analysis, conclusion is sequentially loaded with Series load simulating the A test of the model to the ISO13679 2011 years version of the state has been completed. The second sealing portion in the load contact force (intermediate seal portion) [N / mm], that is, by comparing the minimum value of the "average contact surface pressure between the sealing surface" × "contact width", sealing performance against external pressure It was evaluated. Sealing performance enough seal portion is higher value of the contact force is meant that good. Similarly, by comparing the contact force even first seal portion (inner seal portion) were evaluated sealing performance against pressure. Evaluation of sealing performance, the test No. The sealing performance for sealing performance and external pressure relative to pressure in 1 and respectively 1, the Test No. Ratio was performed as an index for the 1.
[0067]
　Evaluation of sealing performance was carried out in the following four levels.
　· ◎: Yu. Sealing performance of the intermediate seal portion is 1.15 or more with respect to external pressure, and sealing performance of the inner seal portion against the internal pressure is 1.0 or more.
　· ○: Good. Sealing performance of the intermediate seal portion is 1.10 or more with respect to external pressure, and sealing performance of the inner seal portion against the internal pressure is 1.0 or more.
　· △: Yes. Sealing performance of the intermediate seal portion is 1.05 or more with respect to external pressure, and sealing performance of the inner seal portion against the internal pressure is 1.0 or more.
　· ×: No. Sealing performance of the intermediate seal portion is less than 1.05 for the external pressure, or sealing performance of the inner seal portion against the internal pressure is less than 1.0.
[0068]
　
　The test results are shown in Table 1 above.
[0069]
　Test of Comparative Example No. In 1 and 3, due to the length of the incomplete thread portion region of the first threaded portion is short, because the diameter of the box is limited, improvement in sealing performance against external pressure is not observed.
[0070]
　Test of Comparative Example No. In 4, the flank angle of the load flanks of the first threaded portion is due to a positive angle, since the diameter of the box is limited, improvement in sealing performance against external pressure is not observed.
[0071]
　Test of Comparative Example No. In 11, although the length of the incomplete thread portion region of the first threaded portion is short, improvement of sealing performance against external pressure is observed. This is due to the long annular portion is provided, because the diameter of the box is substantially acceptable. However, the installation of a long annular part, because the reduction in the engagement area of ​​the first threaded portion is remarkably, sealing performance against internal pressure is lowered.
[0072]
　Testing of the present invention example No. In 2,5-10, incomplete thread portion is sufficiently long length of the region of the first threaded portion, since the box due to the effective diameter, improving the sealing performance is observed for the external pressure, for pressure sealing performance was also maintained. Among them, test No. In 5, 7 and 9, the length of the incomplete thread portion region following seven times more than four times the screw pitch of the male screw portion, improvement of the sealing performance against external pressure was remarkable.
[0073]
　The test of the present invention example No. In 8, due to the interference of the second screw part (external thread portion) had occurred to the vicinity of the intermediate seal portion, since the substantial amount of interference intermediate seal portion is lowered, the improvement in the sealing performance against external pressure degree was relatively small.
[0074]
　From the above results, by adopting a tubular threaded joint of the present invention, while maintaining the sealing performance against internal pressure, it was proven to be improved sealing performance against external pressure.
Industrial Applicability
[0075]
　Threaded joint of the present invention can be effectively used for connecting a thick steel pipe used as an oil well pipe in harsh environments.
DESCRIPTION OF SYMBOLS
[0076]
　10: Pin, 11: shoulder surface, 12: first sealing
　surface, 13: first male threaded
　portion, 13a: screw crest surface of the first external thread
　portion, 13b: thread root bottom surface of the first male screw
　portion, 13c: first external thread insertion flank
　parts, 13d: load flanks of the first external thread
　portion, 14: second sealing
　surface, 15: second male threaded
　portion, 15a: screw crest surface of the second male threaded
　portion, 15b: second male threaded portion of the screw valley bottom,
　15c: insert flank of the second male threaded
　portion, 15d: load flank surfaces of the second male threaded
　portion, 16: annular
　portion, 20: box, 21: shoulder surface, 22: first sealing
　surface, 23: first internal thread
　portion, 23a: screw crest surface of the first female threaded
　portion, 23b: thread root bottom surface of the first female threaded
　portion, 23c: insert flank of the first female threaded
　portion, 23d: load flank face of the first female thread
　portion, 24: second 2 seal ,
　25: second female threaded
　portion, 25a: screw crest surface of the second female threaded portion,
　25b: thread root bottom surface of the second female threaded
　portion, 25c: insert flank of the second female threaded
　portion, 25d: load flank face of the second female threaded
　portion, 26: annular
　portion, 31a: complete thread portion region of the first threaded portion,
31b: incomplete thread portion region of the first threaded
　portion, 32a: complete thread portion region of the second threaded
　portion, 32 b: incomplete thread portion region of the second threaded
　portion, CL: tube axis

WE CLAIM

A pin tubular, is composed of a tubular box, the pin is a threaded joint for steel pipes in which the box and the pin is screwed into the box is fastened,
　said pins, in order from the distal end side of the pin, shoulder surface, the first sealing surface, the first male threaded portion of the tapered thread, a second sealing surface, and a second male screw portion of the tapered threads,
　the box, in order toward the tip side from the tube main body of the box, the shoulder surface, the first internally threaded portion of the first sealing surface, tapered threads, the second sealing surface, and a second female threaded portion of the tapered threads,
　the first male screw portion is threaded crest surface, thread root bottom insert flanks, and has a load flank surface,
　the first internally threaded section, the thread root bottom surface facing the thread crest surface of the first male threaded portion, the screw crest surface facing the thread root bottom surface of the first male screw portion, wherein the Insert flank surfaces facing the insertion flanks of the external thread portion, and the first has a load flank surface facing the load flanks of the external thread portion,
　the first male screw portion and the first female thread portion respectively of the load flank angle of the flank surface is less than 0 °,
　the first external thread portion includes, in order from the side closer to the second sealing surface, is divided into incomplete thread region, and a complete thread region,
　said incomplete thread part region, there is the length along the tube axis than three times the thread pitch of the first external thread portion, thread height are lower than thread height of the complete thread portion region,
　state the fastening is completed in,
　Wherein in the fully threaded region, said together with the thread root bottom surface of the thread crest surface and the first female thread portion is in contact, the first male screw portion and the load flanks of each of the first female threaded portion of the first male threaded portion contact each other, wherein with a gap is formed between the thread root bottom and the screw crest surface of the first female threaded portion of the first male threaded portion, of each of the first male screw portion and the first female threaded portion a gap is formed between the said insert flanks,
　wherein in the incomplete thread portion region, a gap is formed between the thread root bottom surface of the thread crest surface and the first female threaded portion of the first male threaded portion that, a threaded joint for steel pipes.
[Requested item 2]
　A tubular threaded joint according to claim 1,
　wherein the length along the tube axis of the incomplete thread portion region is less than 8 times the thread pitch of the first male threaded portion, a tubular threaded joint.
[Requested item 3]
　A tubular threaded joint according to claim 1 or 2,
　wherein the pin is between said first externally threaded portion and the second sealing surface, an annular portion which does not contact the box in a state where the fastening is complete comprising, a tubular threaded joint.
[Requested item 4]
　A tubular threaded joint according to claim 3,
　is 3 times or less of the length along the tube axis of the annular portion is screw pitch of the first male threaded portion, a tubular threaded joint.
[Requested item 5]
　A threaded joint for steel pipes according to any one of claims 1 to 4,
　the gap between the screw crest surface of the thread root bottom and the first female threaded portion of the first male screw portion is more than 0.05mm in it, a threaded joint for steel pipes.
[Requested item 6]
　A threaded joint for steel pipes according to any one of claims 1 to 5,
　wherein the second external thread portion has thread crest surface, thread root bottom insert flanks and load flanks,
　the first 2 female screw portion is threaded trough bottom opposite to the thread crest surface of the second male threaded portion, the screw crest surface facing the thread root bottom surface of the second male threaded portion, the insertion flank of the second male threaded portion insert flank surface facing, and the second has a load flank surface facing the load flanks of the external thread portion,
　the flank angle of the load flanks of each of the second male threaded portion and the second female screw portion is 0 ° less than,
　in a state in which fastening has been completed, together with the thread crest surface of the thread root bottom surface and the second female threaded portion of the second male threaded portion is in contact, of each of the second male threaded portion and the second female threaded portion the load Flank surfaces contact each other, with a gap is formed between the thread crest surface of the second male threaded portion and the thread root bottom surface of the second female threaded portion, the second male threaded portion and the second female threaded portion a gap is formed between the each of the insertion flank, a threaded joint for steel pipes.