The present invention relates to a threaded joint for use in connecting steel pipes.
BACKGROUND
[0002]
　Oil wells, natural gas wells and the like (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 pipe are sequentially linked. The screw joint is used to join.
[0003]
　Format tubular threaded joint is roughly classified into a coupling-type and integral type. For coupling type of threaded joint, 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 threaded joint, 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]
　Joint part of the pipe end portion a male screw portion is formed, since the containing elements to be inserted into the female screw portion, 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]
　Moreover, the form of a threaded joint for steel pipes, there by the outer diameter of the box, a flash type, semi-flash type, also be classified in a slim type or the like. Slim-type threaded joint, the cross-sectional area of ​​danger section of box approximately equal coupling (hereinafter, referred to as "standard coupling") and tube body of the pin is determined by the index. Specifically, in the slim-type threaded joint, the maximum outer diameter of the box is smaller than the outer diameter of a standard coupling. Flash and semi flash type of the threaded joint is defined by a tube body of the pin as an index. Specifically, the flash of the threaded joint, the maximum outer diameter of the box is substantially equal to the outer diameter of the tube body of the pin. The semi-flash type threaded joint, the maximum outer diameter of the box is in the flash-type threaded fittings and slim-type threaded joint intermediate. In short, in order from the maximum outer diameter of the box to the outside diameter of the tube body of the pin is small, flash-type threaded joint, semi flush-type threaded joint, and a slim-type threaded joint. Flash-type, semi-flash type, and there is no clear division to define a slim type. However, in a threaded joint for steel pipes in circulation, generally referred to as flash or semi-flash type up to about 110% of the outside diameter of the tube body of the maximum outer diameter pin boxes.
[0006]
　In general, the risk section refers to the cross-section at the position of the end of the action area of ​​the threaded portion. Normally, the position of the dangerous section, 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.
[0007]
　Recently, high-depth reduction and ultra deep water of wells is progressing. In such oil well environment, threaded joint, the fluid present in the external and internal (e.g. gas, liquid) subjected to high pressures from. Furthermore, a threaded joint is subjected repeatedly load compression and tension. In the above oil well environment, oil well pipes are arranged in multiple. Normally, the connection of OCTG multiple structure, the outer diameter of the box Semi flash type of threaded joint is comparable to the outside diameter of the pin is often used. The inner diameter of the pin is defined by the standard of the API (American Petroleum Institute (American Petroleum Institute)), because even the outside diameter of the box is limited accordingly. Such a restriction under 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 be required to have excellent sealing performance . Moreover, even for tensile and compressive loads, it is required to have excellent sealing performance.
[0008]
　For example JP-A 9-126366 (Patent Document 1) discloses pressure, external pressure, the threaded joint for steel pipes with improved sealing performance against tensile and compressive loads. The threaded joint described in Patent Document 1, as the screw portion composed of a male screw portion and the box of the female thread portion of the pin, buttress-type taper thread is employed. The screw portion, the shoulder portion is divided into an inner threaded portion and the externally threaded portion. That is, the internal thread portion is provided on the distal end side of the pin. External thread portion is provided on the distal end side of the box. Shoulder portion is provided between the internal thread portion and the external thread portion. Further, the inner seal portion is provided on the inner side of the inner threaded portion (pin tip side). Outer sealing portion is provided on the outer side of the outer threaded portion (box on the distal end side).
[0009]
　Time of fastening, by screwing the pin into the box, the shoulder surface included in the shoulder portion of the pin is in contact with shoulder surfaces included in the shoulder portion of the box. Moreover, the respective external thread portion and the female screw portion of the inner threaded portion and the externally threaded portion is fitted. Accordingly, thread seal portion is formed in each of the inner threaded portion and the externally threaded portion. The inner sealing surface that is included in the inner sealing portion of the pin, interferes with the inner sealing surface that is included in the inner sealing portion of the box, in contact with a high surface pressure. Outer sealing surface included in the outer seal portion of the pin interferes with the outer sealing surfaces included in the outer seal portion of the box, in contact with a high surface pressure. Thus, the sealing portion by the surface contact with each of the inner seal portion and an outer seal portion.
[0010]
　Inner seal portion is mainly responsible for the fluid inside the threaded joint can be prevented from inadvertently entering the region of the threaded seal part. That is, the inner seal portion contributes to the improvement of the sealing performance against pressure. Outer seal portion is mainly responsible for fluid of the threaded joint outside is prevented from inadvertently entering the region of the threaded seal part. That is, the outer seal portion contributes to the improvement of the sealing performance against external pressure.
[0011]
　The threaded joint described in Patent Document 1, an inner female thread portion of the inner male screw portion and the box pin constituting the internal thread portion is engaged over the entire area. However, in some areas is close to out the seal portion of the region of the inner female thread portion of the box, the tip of the tooth is cut parallel to the tube axis, and has a low incomplete thread of thread height. If the region is a complete thread, there is a risk of damaging the inner sealing surface of the pin at the fastening. However, the inner male screw portion and the inner female thread portion is engaged in the region of the incomplete thread.
[0012]
　Similarly, the outer female screw portion of the outer male thread portion and the box pin constituting the external thread portion is engaged over the entire area. However, in some areas close to the out outside the sealing portion of the region of the outer male thread portion of the pin, the tip of the tooth is cut parallel to the tube axis, and has a low incomplete thread of thread height. If the region is a complete thread, there is a risk of damaging the outer sealing surface of the box during fastening. However, meshing the outer male threaded portion and an outer internally threaded section in the region of the incomplete thread.
CITATION
Patent Document
[0013]
Patent Document 1: Laid-Open Publication No. 9-126366
Summary of the Invention
Problems that the Invention is to Solve
[0014]
　For threaded joint described in Patent Document 1, the internal pressure, external pressure, as long as the tensile and compressive loads are simply loaded once, sealing performance is good. However, according to the test conducted by the present inventors, if the repeated tensile load and internal pressure on the threaded joint for example certain count is loaded, the leakage of the internal pressure was sometimes occur in the inner seal portion. That is, the sealing performance of the threaded joint described in Patent Document 1 is unstable.
[0015]
　An object of the present invention is to provide a threaded joint for steel pipes having the following properties:
　pressure, external pressure, tensile load and sealing performance even in an environment in which compressive load is repeatedly loaded stably can be secured.
Means for Solving the Problems
[0016]
　A threaded joint for steel pipes according to an embodiment of the present invention is composed of a pin and a tubular box of the tubular. Pin includes a order from the distal end side of the pin to the tube body, and the inner sealing surface, and an inner male screw portion, and a shoulder portion, and the outer male threaded portion, and the outer sealing surface. Box includes sequentially toward the front end side from the tube main body of the box, and an inner sealing surface, and an inner female thread portion, and a shoulder portion, and the outer internally threaded section, and the outer sealing surface. Threaded joint is provided with at least one component of the following features (1) and (2).
　(1) between the inner sealing surface and an inner female thread of the box, among groove portions are provided along the circumferential direction, a portion of the teeth of the inner male screw portion of the pin is accommodated in the inner groove portion,
　(2) Pin of between the outer sealing surface and the outer male threaded portion, the outer groove is provided along the circumferential direction, a portion of the teeth of the external female thread of the box is accommodated in the outer groove.
The invention's effect
[0017]
　A threaded joint for steel pipes according to an embodiment of the present invention has a remarkable effect of the following:
　pressure, external pressure, tensile load and sealing performance even in an environment in which compressive load is repeatedly loaded stably can be secured.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018]
[Figure 1A] Figure 1A is a schematic view of the pressure leak was observed a longitudinal section of the inner male screw portion of the inner seal portion near the threaded joint occurs.
FIG 1B] Figure 1B is a schematic view of the pressure leak was observed a longitudinal section of the inner female thread portion of the inner seal portion near the threaded joint occurs.
[Figure 2A] Figure 2A is a longitudinal sectional view showing an inner seal portion and its vicinity in threaded joint pressure leak has occurred.
[Figure 2B] Figure 2B is a longitudinal sectional view of an enlarged internal thread portion in the vicinity of the inner seal portion of Figure 2A.
[Figure 3A] Figure 3A is a longitudinal sectional view showing the outer seal portion and its vicinity in a threaded joint which external pressure leak has occurred.
[Figure 3B] Figure 3B is a longitudinal sectional view of an enlarged external thread portion in the vicinity of the outer seal portion of Figure 3A.
[4] FIG. 4 is a longitudinal sectional view showing a tubular threaded joint according to the present embodiment.
FIG. 5 is a longitudinal sectional view showing an inner seal portion and its vicinity in a threaded joint shown in FIG.
FIG. 6 is a longitudinal sectional view showing the outer seal portion and its vicinity in a threaded joint shown in FIG.
[Figure 7A] Figure 7A is a diagram showing the test results of the inner seal portion.
[Figure 7B] Figure 7B is a diagram showing the test results of the outer seal portion.
DESCRIPTION OF THE INVENTION
[0019]
　The present inventors have found that in order to achieve the above object, the threaded joint described in Patent Document 1, to prepare samples of various sizes, were performed internal pressure, external pressure, tensile load and the cyclic loading test the compressive load.
[0020]
　In both samples, when the tensile load and internal pressure is loaded, the leakage of the internal pressure occurs in the inner seal portion. Further, in any of the samples, when the tensile load and external pressure is loaded, the leakage of external pressure occurs in the outer seal portion. In some cases, internal pressure leakage and external pressure leak occurs when the compressive load is applied. Therefore, due to the design of the thread profile, pressure leak and external pressure leak is presumed to occur.
[0021]
　Therefore, to decompose a threaded joint for pressure leak has occurred, we examine each pin and box in detail. Similarly, to decompose the threaded joint for external pressure leak has occurred, was examined each pin and box in detail.
[0022]
　1A and 1B, when the internal pressure leak was observed a longitudinal section of the inner threaded portion of the inner seal portion near the threaded joint occurs, which is a schematic diagram showing an example of a view state. Of these figures, FIG. 1A shows a part of the inner male screw portion of the pin, Fig. 1B shows a portion of an inner female thread of the box. The cross-sectional observation of the respective inner threads of the pin and box, each 90 ° around the tube axis was performed at each position (each convenience 0 °, 90 °, expressed as 180 ° and 270 °). Figure 1A shows the situation at the location of 180 °. Figure 1B shows the situation at the location of 270 °.
[0023]
　As shown by the dotted line circle in FIG. 1A, the inner male screw portion of the inner seal portion near the tip of the load flank surface is deformed. In other words, the inner male screw portion of the inner seal portion near traces that an excessive load is applied to the distal end portion of the load flank surface was observed. As shown by the dotted line circle in FIG. 1B, a similar phenomenon in the internal female thread portion of the inner seal portion near had occurred.
[0024]
　Although not shown, when the threaded joint external pressure leak occurs, the outer male thread portion of the outer seal portion near traces excessive load is applied to the distal end portion of the load flank surface was observed. On the other hand, the outer internally threaded section of the outer seal portion near traces excessive load is applied to the distal end portion of the load flank surface was observed.
[0025]
　In short, if a threaded joint pressure leak occurs in the vicinity of the inner seal portion, a portion of the teeth of the inner male screw portion of the pin (in particular, the load flank surface) that is improperly interfere with the inner female thread of the box all right. For a threaded joint external pressure leak occurs in the vicinity of the outer seal portion, a portion of the teeth of the external female thread of the box (especially load flank surface) were found to be improperly interfere with the outer male thread portion of the pin .
[0026]
　Accordingly, the present inventors focused on the improper interference of the inner threaded portion of the inner seal portion near was examined for the occurrence mechanism of the internal pressure leak due to the interference. Further, the present inventors focused on the improper interference of the externally threaded portion of the outer seal portion near was examined for the occurrence mechanism of external pressure leak due to the interference.
[0027]
　2A and 2B are schematic views for explaining the mechanism of pressure leaks. Of these figures, FIG. 2A is a longitudinal sectional view showing an inner seal portion and its vicinity in the threaded joint. Figure 2B is a longitudinal sectional view of an enlarged internal thread portion in the vicinity of the inner seal portion of Figure 2A.
[0028]
　Referring to FIGS. 2A and 2B, the threaded joint described in Patent Document 1, (refer to the outlined arrow in FIG. 2A) when the internal pressure is loaded, the tip portion 10a of the pin 10 is elastically to enlarged deformation to. In particular, a portion of the inner seal portion 1 near the inner female thread portion 22 is a low incomplete thread of thread height. Therefore, even in mesh with the inner male screw portion 12 and the incomplete screw until the screw crest surface and the thread valley bottom surface of mutual contact, the tip portion 10a of the pin 10 can be modified as the diameter increases. Thus, (refer to the outlined arrow in FIG. 2A) the inner contact surface pressure of the seal portion 1 is enhanced, the sealing performance is improved with respect to the internal pressure.
[0029]
　However, when the internal pressure is unloaded (the white arrow the absence in Fig. 2A), the distal end portion 10a of the pin 10 is restored to diameter. Thus, as shown in FIG. 2B, the tip portion of the load flank surface 22d of the incomplete thread (part of the inner female thread portion 22), and the distal end portion of the load flank surface 12d of the inner male thread portion 12 are in contact with each other. The contact area is narrow. If the tensile load is applied at this time (see the shaded arrows in FIG. 2A), an excessive load is applied to the tip portion of each of the load flanks 12d and 22d. Thus, the distal end portion of each of the load flanks 12d and 22d are deformed further, the teeth of the part of the inner female thread portion 22 of the part of the tooth box 20 of the external thread portion 12 within the deformed (incomplete thread) rides. If this occurs, then the internal pressure be loaded, expanded deformation of the tip portion 10a of the pin 10 is restrained. Thus, the contact surface pressure of the inner seal portion 1 is not increased. As a result, the sealing performance decreases for pressure.
[0030]
　3A and 3B are schematic views for explaining the mechanism of the external pressure leaks. Of these figures, FIG. 3A is a longitudinal sectional view showing the outer seal portion and its vicinity in the threaded joint. Figure 3B is a longitudinal sectional view of an enlarged external thread portion in the vicinity of the outer seal portion of Figure 3A.
[0031]
　Referring to FIGS. 3A and 3B, the threaded joint described in Patent Document 1, (refer to the outlined arrow in FIG. 3A) when the external pressure is loaded, elastic deformation as the tip portion 20a of the box 20 decreases in diameter to. In particular, part of the outer seal portion 5 near the outer male thread portion 14, a lower incomplete thread of thread height. Therefore, even in mesh with the incomplete thread and the outer internally threaded section 24 until the mutual thread crest surfaces and the thread root bottom surface contacts, the tip portion 20a of the box 20 can be deformed to diameter. This increases the contact surface pressure of the outer seal portion 5 (refer to the outlined arrow in FIG. 3A), the sealing performance is improved with respect to external pressure.
[0032]
　However, external pressure when it is unloaded (the white arrow the absence in Fig. 3A), the distal end portion 20a of the box 20 is restored to diameter. Thus, as shown in FIG. 3B, the tip portion of the load flank surface 14d of the incomplete thread (part of the outer male thread portion 14), and the distal end portion of the load flank surface 24d of the outer internally threaded section 24 are in contact with each other. The contact area is narrow. If the tensile load is applied at this time (see the shaded arrows in FIG. 3A), an excessive load is applied to the tip portion of each of the load flanks 14d and 24d. Thus, the distal end portion of each of the load flanks 14d and 24d are deformed further, the teeth of a portion of the outer male thread portion 14 of the part of the tooth pins 10 of the outer female screw portion 24 which is deformed (incomplete thread) rides. If this happens, then it is external pressure load, shrink deformation of the tip portion 20a of the box 20 is restrained. Thus, the contact surface pressure of the outer seal portion 5 is not increased. As a result, the sealing performance decreases for external pressure.
[0033]
　From the above, in the vicinity of the inner seal portion, if prevented that some of teeth of the external thread portion of the pin rides on the teeth of the internal female thread of the box, can be stably ensured sealing performance against pressure to become, and it can be said. Further, in the vicinity of the outer seal portion, if prevented that some of the teeth of the external female thread of the box rides on the teeth of the outer male thread portion of the pin, it is possible to stably secure a sealing performance against external pressure, it can be said that.
[0034]
　A threaded joint for steel pipes of the present invention has been completed based on the above findings.
[0035]
　A threaded joint for steel pipes according to an embodiment of the present invention is composed of a pin and a tubular box of the tubular. Pin includes a order from the distal end side of the pin to the tube body, and the inner sealing surface, and an inner male screw portion, and a shoulder portion, and the outer male threaded portion, and the outer sealing surface. Box includes sequentially toward the front end side from the tube main body of the box, and an inner sealing surface, and an inner female thread portion, and a shoulder portion, and the outer internally threaded section, and the outer sealing surface. Threaded joint is provided with at least one component of the following features (1) and (2).
　(1) between the inner sealing surface and an inner female thread of the box, among groove portions are provided along the circumferential direction, a portion of the teeth of the inner male screw portion of the pin is accommodated in the inner groove portion,
　(2) Pin of between the outer sealing surface and the outer male threaded portion, the outer groove is provided along the circumferential direction, a portion of the teeth of the external female thread of the box is accommodated in the outer groove.
[0036]
　According to such a threaded joint, if the configuration of the above (1) is adopted, in the vicinity of the inner seal portion due to contact with the inner sealing surface and the inner sealing surface of the box pin, the inner male screw portion of the pin one part of the tooth (particularly, a load flank surface) can be prevented from inappropriately interfere with the inner female thread of the box. The inner seal portion near although of teeth of the external thread portion is present, because the internal thread portion does not exist among meshing with teeth of the inner male screw portion. Accordingly, even when the load and internal pressure tension on the threaded joint is loaded, a portion of the teeth of the inner male screw portion of the pin can be prevented from rides on the teeth of the internal female thread of the box. As a result, reduction in contact surface pressure of the inner sealing portion is suppressed, it is possible to stably secure a sealing performance against pressure.
[0037]
　On the other hand, if the configuration of (2) is adopted, in the vicinity of the outer seal portion due to contact with the outer sealing surface and the outer sealing surface of the box pin, a portion of teeth of the external female thread of the box (especially load flank surfaces) it can be prevented from improperly interfere with the outer male thread portion of the pin. Outside the seal vicinity, although the teeth of the external female thread portions are present, because the outer male threaded portion meshing with the teeth of the outer female screw portion is not present. Accordingly, even when the load and external pressure tensile threaded joint is loaded, it is possible to prevent the portion of the teeth of the external female thread of the box rides on the teeth of the outer male thread portion of the pin. As a result, reduction in contact surface pressure of the outside seal portion is suppressed, it is possible to stably secure a sealing performance against external pressure. To ensure the sealing performance for both pressure and external pressure stable may be adopted both the configuration (1) and (2).
[0038]
　As a typical example, a threaded joint of this embodiment is integral type threaded joint. However, the form of the threaded joint is not particularly limited, and may be a coupling type.
[0039]
　As a typical example, a threaded joint of the present embodiment is a semi-flash type or flash type referred threaded joint. In other words, more than 100% of the outer diameter of the pin of the pipe body of the box is 110% or less. However, the form of the threaded joint is not particularly limited, and may be a slim type.
[0040]
　As a typical example, a screw portion formed of an inner male screw portion and the inner female thread portion, and a threaded portion formed of an outer male thread portion and the outer internally threaded section are each buttress-type tapered thread. In this case, each of the tapered threads, including thread crest surface, thread root bottom surface, the insert flanks and the load flanks. Then, the the thread root bottom surface of the thread crest surface and the inner female thread portion of the inner male thread portion is in contact with the load flank of the load flank surface and the inner female thread portion of the inner male thread portion is in contact. With a thread root bottom surface of the outer male threaded portion and an outer internally threaded portion of the screw crest surfaces are in contact, a load flank surface of the load flank surface and the outer internally threaded section of the outer male thread portion is in contact. Flank angle of the load flank surface is a negative angle.
[0041]
　However, the state meshing with the meshing state, and the outer male thread portion and the outer internally threaded section of the inner male screw portion and the inner female thread portion, as long as the load flanks contact each other, is not particularly limited. For example, instead of the contact between the thread root bottom surface of the thread crest surface and the inner female thread portion of the inner male screw portion, and the screw crest surface of the inner female thread portion and the thread root bottom surface of the inner male screw portion may contact. Instead of the contact between the thread root bottom and the screw crest surface of the outer internally threaded section of the outer male thread portion, and a thread root bottom surface of the thread crest surface of the outer male threaded portion and an outer female screw portion may contact.
[0042]
　In the above-described threaded joints, the length along the tube axis of the inner groove of the box is preferably greater than the thread pitch of the inner female thread portion. The length of the groove inner referred to herein means the length from the end portion of the inner sealing surface. The length along the tube axis of the outer groove of the pin is preferably greater than the thread pitch of the external male thread portion. The length of the outer groove referred to herein means the length from the end of the outer sealing surface.
[0043]
　In a threaded joint in this case, the length along the tube axis of the inner groove of the box is preferably not more than 4 times the thread pitch of the internal female threaded portion. More preferred length is less than 2.5 times the thread pitch. Thus, it is possible to ensure the engagement length of the inner male screw portion and the inner female thread portion. Further, it is preferable length along the tube axis of the outer groove of the pin is less than four times the thread pitch of the external male thread portion. More preferred length is less than 2.5 times the thread pitch. Thus, it is possible to ensure the engagement length of the outer male thread portion and the outer internally threaded section. As a result, tensile load does not decrease permitted by a threaded joint.
[0044]
　In the above-described threaded joint, the depth of the inner groove portion of the box, or thread height of the inner female threaded portion is preferably not less than 2 times its thread height. The depth of the grooves in the present specification means a depth from the thread crest surface on the assumption that the internal female threaded portion is extended to the inner groove region. This allows securing the area of ​​risk section box. The depth of the outer pin grooves, or thread height of the outer male threaded portion is preferably not less than 2 times its thread height. The depth of the outer groove referred to herein means a depth from the thread crest surface when the outer male thread portion is assumed to have been extended to a region of the outer groove. This allows securing the area of ​​risk section of the pin.
[0045]
　Shape of the inner groove portion of the box is not particularly limited. For example, the inner groove may include a tube axis parallel to the cylindrical surface. The inner groove may comprise a tapered surface having a diameter closer to the inner sealing surface is reduced. The tapered surface is adjacent to the inner sealing surface. The taper angle of the tapered surface is smaller than the greater 90 ° than 0 °. However, if the taper angle is too small, it may become difficult to secure the area of ​​risk section box. On the other hand, if the taper angle is too large, it may be stress concentration occurs. Therefore, the tapered surface taper angle of 1 ° or more, and preferably 50 ° or less. More preferred taper angle 1 ° or more and 30 ° or less, still more preferably taper angle 3 ° or more and 15 ° or less. Taper angle of the tapered surface may be the same as the taper angle of the inner female thread portion.
[0046]
　The inner groove may comprise a tapered surface having a diameter closer to the inner female thread portion is reduced. The tapered surface is adjacent to the inner female thread portion. The taper angle of the tapered surface is smaller than the greater 90 ° than 0 °. However, if the taper angle is too small, it may become difficult to ensure the engagement length of the inner male screw portion and the inner female thread portion. On the other hand, if the taper angle is too large, it may be stress concentration occurs. Therefore, the taper angle of the tapered surface is 5 ° or more and 45 ° or less. More preferred taper angle 10 ° or more and 30 ° or less.
[0047]
　Similarly, the shape of the outer groove portion of the pin is not particularly limited. For example, the outer groove may include a tube axis parallel to the cylindrical surface. Further, the outer groove may comprise a tapered surface having a diameter closer to the outer sealing surface is increased. The tapered surface is adjacent to the outer sealing surface. The taper angle of the tapered surface is smaller than the greater 90 ° than 0 °. However, if the taper angle is too small, it may become difficult to secure the area of ​​risk section of the pin. On the other hand, if the taper angle is too large, it may be stress concentration occurs. Therefore, the tapered surface taper angle of 1 ° or more, and preferably 50 ° or less. More preferred taper angle 1 ° or more and 30 ° or less, still more preferably taper angle 3 ° or more and 15 ° or less. Taper angle of the tapered surface may be the same as the taper angle of the outer male thread portion.
[0048]
　Further, the outer groove may comprise a tapered surface having a diameter closer to the outer male thread portion is increased. The tapered surface is adjacent to the outer male thread portion. The taper angle of the tapered surface is smaller than the greater 90 ° than 0 °. However, if the taper angle is too small, it may become difficult to ensure the meshing length of the outer male thread portion and the outer internally threaded section. On the other hand, if the taper angle is too large, it may be stress concentration occurs. Therefore, the taper angle of the tapered surface is 5 ° or more and 45 ° or less. More preferred taper angle 10 ° or more and 30 ° or less.
[0049]
　Hereinafter, with reference to the drawings, a specific example of a tubular threaded joint according to the present embodiment.
[0050]
　Figure 4 is a longitudinal sectional view showing a tubular threaded joint according to the present embodiment. Figure 5 is a longitudinal sectional view showing an inner seal portion and its vicinity in a threaded joint shown in FIG. Figure 6 is a longitudinal sectional view showing the outer seal portion and its vicinity in a threaded joint shown in FIG. As shown in FIGS. 4 to 6, a threaded joint of the present embodiment is a integral type threaded joint, composed of the pin 10 and the box 20.
[0051]
　Pin 10, in order from the distal end side of the pin 10 to the tube main body includes an inner sealing surface 11, an inner male screw portion 12, a shoulder portion 13, the outer male thread portion 14, an outer sealing surface 15. Box 20 includes in the order toward the tip side from the tube main body side of the box 20, the inner sealing surface 21, an inner female thread portion 22, a shoulder portion 23, an outer female screw portion 24, an outer sealing surface 25. Inner sealing surface 21 of the box 20, the inner female thread portion 22, shoulder portion 23, the outer female threaded portion 24 and outer sealing surface 25, respectively, the inner sealing surface 11 of the pin 10, the inner male screw portion 12, shoulder portion 13, the outer male thread part 14, and is provided so as to correspond to the outer sealing surface 15.
[0052]
　Inner female thread portion 22 of the male thread portion 12 and the box 20 of the pin 10 is a buttress-type taper thread meshing with each other, forming the inner threaded portion 2 of the inboard (leading end side side of the pin 10). External female thread portions 24 of the outer male thread portion 14 and the box 20 of the pin 10 is a buttress-type taper thread meshing with each other, forming the outer threaded portion 4 of the outboard (tip side toward the box 20).
[0053]
　Shoulder portion 13 of the pin 10 comprises a shoulder surface 13a. Shoulder 23 of the box 20 includes a shoulder surface 23a. Shoulder surfaces 13a and 23a are substantially perpendicular annular surface to the tube axis. However, the shoulder surfaces 13a and 23a may be annular surface which is inclined in the screwing direction of travel of the pin 10 from the plane perpendicular to the tube axis. In other words, the shoulder surface 13a and 23a may be inclined toward the front end side of the pin 10 about its outer periphery.
[0054]
　Shoulder 13 and 23 is disposed between the inner threaded portion 2 and the external thread portion 4. The shoulder portion 13 and 23, the tapered surface and the tapered surface of the outer thread portion 4 of the screw portion 2 is offset.
[0055]
　Relates inner threaded portion 2, the inner male thread portion 12 of the pin 10 is threaded crest surfaces 12a, thread root bottom surface 12b, the insertion flank surfaces 12c preceding by screwing, and the load flank surface 12d opposite to the insertion thereof flanks 12c provided. On the other hand, the inner female thread portion 22 of the box 20 is provided with screw crest surfaces 22a, thread root bottom surface 22b, inserted flanks 22c, and a load flank surfaces 22d. Screw crest surface 12a of the inner male screw portion 12 facing the thread root bottom surface 22b of the inner female thread portion 22. Thread root bottom surface 12b of the inner male screw portion 12 facing the thread crest surface 22a of the inner female thread portion 22. Insert flank 12c of the inner male screw portion 12 faces the insert flanks 22c of the inner female thread portion 22. Load flank surfaces 12d of the inner male screw portion 12 is opposed to the load flank surface 22d of the inner female thread portion 22. Flank angle of the load flank surface 12d and 22d are negative angle, load flanks 12d and 22d with each other are pressed strongly engaged. Flank angle of the insert flanks 12c and 22c may be either positive angle and a negative angle.
[0056]
　Similarly, relates external thread portion 4, the outer male thread portion 14 of the pin 10 is threaded crest surfaces 14a, thread root bottom surface 14b, the insertion flank surfaces 14c preceding by screwing, and the opposite side of the load flank and the insertion flanks 14c provided with a surface 14d. On the other hand, the outer female thread portion 24 of the box 20 is provided with screw crest surfaces 24a, thread root bottom surface 24b, inserted flanks 24c, and a load flank surfaces 24d. Screw crest surface 14a of the outer male thread portion 14 facing the thread root bottom surface 24b of the outer internally threaded section 24. Thread root bottom surface 14b of the outer male thread portion 14 facing the thread crest surface 24a of the outer internally threaded section 24. Insert flank 14c of the outer male thread portion 14 faces the insert flanks 24c of the outer internally threaded section 24. Load flank surfaces 14d of the outer male thread portion 14 faces the load flank surface 24d of the outer internally threaded section 24. Flank angle of the load flank surface 14d and 24d are negative angle, load flanks 14d and 24d with each other are pressed strongly engaged. Flank angle of the insert flanks 14c and 24c may be either positive angle and a negative angle.
[0057]
　Inner sealing surface 11 and 21, and the outer sealing surface 15 and 25 are both tapered. Strictly speaking, the inner sealing surface 11 and 21 and outer sealing surfaces 15 and 25, respectively, shape composed of a surface corresponding to the frusto-conical peripheral surface as the tip end of the pin 10 diameter is reduced, or the truncated cone and the peripheral surface, 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.
[0058]
　The engaged state, the inner male screw portion 12 and the inner female thread portion 22 is fitted. That is, the thread crest surface 22a of the thread root bottom surface 12b and the inner female thread portion 22 of the male thread portion 12 is in contact. A load flank surface 22d of the load flank surface 12d and the inner female thread portion 22 of the male thread portion 12 is in contact. Between the thread root bottom surface 22b of the thread crest surface 12a and the inner female thread portion 22 of the male thread portion 12, a gap is formed. Between the insertion flank 22c of the insertion flank 12c and the inner female thread portion 22 of the male thread portion 12, a gap is formed. Lubricant is filled in these gaps. Thus, the inner thread portion 2 Deneji seal portion is formed.
[0059]
　Further, the outer male thread portion 14 and the outer internally threaded section 24 is fitted. That is, the thread root bottom surface 24b of the thread crest surface 14a and the outer internally threaded section 24 of the outer male thread portion 14 contacts. A load flank surface 24d of the load flank surface 14d and the outer internally threaded section 24 of the outer male thread portion 14 contacts. Between the thread crest surface 24a of the thread root bottom surface 14b and the outer internally threaded section 24 of the outer male thread portion 14, a gap is formed. Between the insertion flank 24c of the insertion flank 14c and the outer internally threaded section 24 of the outer male thread portion 14, a gap is formed. Lubricant is filled in these gaps. Thus, external thread portion 4 Deneji seal portion is formed.
[0060]
　Inner sealing surface 11 of the pin 10 interfere with the inner sealing surface 21 of the box 20, in contact with a high surface pressure. Thus, the sealing portion by the surface contact with the inner seal portion 1 is formed. The outer sealing surface 15 of the pin 10 interferes with the outer sealing surface 25 of the box 20, in contact with a high surface pressure. Thus, the sealing portion by the surface contact with the outer seal portion 5 is formed.
[0061]
　Shoulder surfaces 13a and 23a with each other are in contact with each other with the screwing of the pin 10 relative to the box 20, is pressed against. The engaged state, to impart axial fastening force to each of the load flank surface 12d and 14d of the inner male threaded portion 12 and an outer male thread portion 14 of the pin 10.
[0062]
　In this exemplary embodiment, the inner periphery of the box 20, the inner groove 16 along the circumferential direction is provided. Specifically, the inner groove portion 16 is provided between the inner female thread portion 22 and the inner sealing surface 21 of the box 20. In the vicinity of the inner sealing surface 21 (inner seal portion 1), although the teeth of the inner male screw portion 12 is present, the teeth of the inner male screw portion 12 is received in the inner groove portion 16. That is, the internal thread portion 22 is not present among meshing with the teeth of the inner male screw portion 12. Therefore, in the vicinity of the inner seal portion 1, a portion of the teeth of the inner male thread portion 12 of the pin 10 can be prevented from improperly interfere with the inner female thread portion 22 of the box 20. Accordingly, even when the load and internal pressure tension on the threaded joint is loaded, a portion of the teeth of the inner male thread portion 12 of the pin 10 can be prevented from rides on the teeth of the inner female thread portion 22 of the box 20. As a result, reduction in contact surface pressure of the inner seal portion 1 is suppressed, it is possible to stably secure a sealing performance against pressure.
[0063]
　In the present embodiment, the outer periphery of the pin 10, the outer groove 26 along the circumferential direction are provided. Specifically, the outer groove 26 is provided between the outer sealing surface 15 and the outer male thread portion 14 of the pin 10. In the vicinity of the outer sealing surface 15 (outer seal portion 5), although the teeth of the external female thread portions 24 are present, the teeth of the external female thread portion 24 is accommodated in the outer groove 26. In other words, there is no external male threaded portion 14 that engages with the teeth of the outer internally threaded section 24. Therefore, in the vicinity of the outer seal portion 5 it can be prevented that a part of the teeth of the external female thread portions 24 of the box 20 is improperly interfering with the outer male thread portion 14 of the pin 10. Accordingly, even when the load and external pressure tensile threaded joint is loaded, it is possible to prevent the portion of the teeth of the external female thread portions 24 of the box 20 rides on the teeth of the outer male thread portion 14 of the pin 10. As a result, reduction in contact surface pressure of the outside seal portion 5 is suppressed, it is possible to stably secure a sealing performance against external pressure.
[0064]
　The inner groove portion 16 of this embodiment, the order from the inner sealing surface 21 side to the inner female thread portion 22 includes a first tapered surface 16a, and the cylindrical surface 16b, and a second tapered surface 16c, a. Taper angle of the first taper surface 16a is 6 °. The taper angle is the same as the taper angle of the inner female thread portion 22. Taper angle of the second tapered surface 16c is 15 °.
[0065]
　Outer groove 26 of this embodiment comprises from the outer sealing surface 15 side toward the outer male thread portion 14 includes a first tapered surface 26a, and the cylindrical surface 26b, and a second tapered surface 26c, a. Taper angle of the first taper surface 26a is 6 °. The taper angle is the same as the taper angle of the outer male thread portion 14. Taper angle of the second tapered surface 26c is 15 °.
[0066]
　In addition, the present invention is not limited to the above embodiments, without departing from the scope of the present invention, it is needless to say various modifications are possible.
Example
[0067]
　To confirm the effects of the present invention was performed numerical simulation analysis by the elasto-plastic finite element method (FEM analysis).
[0068]
　[Test Conditions]
　The FEM analysis was made models of a threaded joint for steel pipes shown in FIG. 4. As a comparative example, by extending the inner female thread portion in the inner groove region model by extending the outer male thread portion in the region of the outer grooves, i.e. to produce a model of a threaded joint for steel pipes described in Patent Document 1.
[0069]
　The main characteristics regarding the material and dimensions of the steel tube is as follows.
　- steel dimensions: 13-5 / 8 [inch], 88.2 [lb / ft] ( outer diameter 346.1Mm, wall thickness 15.9 mm)
　, steel grade: as defined in Q125 (API 5CT of API standard that in oil well pipe for carbon steel, tensile yield strength 125 ksi (862N / mm 2 ))
[0070]
　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.
[0071]
　[Evaluation
　Method] The FEM analysis, load step simulating the Series A test ISO13679 2011 2011 Edition the fastening state model (internal pressure, external pressure, tensile and compressive loads) were sequentially loaded. Pressure cycle (first, second quadrant) of the load steps history and external pressure cycle (third, fourth quadrant) were compared inner seal portion and each of the contact force of the outer seal portion [N / mm] in. The contact force of the seal portion, the minimum value of the "average contact surface pressure between the sealing surface" × "contact width" means the sealing performance of the seal portion The higher the value is good. They were evaluated sealing performance against pressure from the contact force of the inner seal portion. They were evaluated sealing performance against external pressure from the contact force of the outer seal portion.
[0072]
　Each of the contact force of the extraction of the inner seal portion and an outer seal portion, 0 ° of the tube axis, 90 °, was carried out at each position of 180 ° and 270 °.
[0073]
　[Result]
　Figures 7A and 7B are diagrams summarizing the test results. Of these figures, FIG. 7A shows the results of the inner seal portion, FIG. 7B shows the results of the outer seal portion. As shown in FIG. 7A, the variation of the contact force of the inner seal portion according to the embodiment was smaller than that of the comparative example. As shown in FIG. 7B, variation in the contact force of the outer seal portion according to the embodiment was smaller than that of the comparative example. From these, the threaded joint of the present embodiment, it can be ensured sealing performance against internal pressure and external pressure stably was demonstrated.
Industrial Applicability
[0074]
　Threaded joint of the present invention can be effectively used for connecting steel pipes used as OCTG.
DESCRIPTION OF SYMBOLS
[0075]
　10 pin
　11 in the sealing surface
　12 in the male screw portion
　12a screw crest surfaces
　12b thread root bottom surface
　12c inserted flank
　12d load flank surface
　13 shoulder
　13a shoulder surface
　14 outer male threaded portion
　14a screw crest surfaces
　14b thread root bottom surface
　14c inserted flank
　14d load flank
　15 outer sealing surface
　16 in the groove portion
　20 box
　21 the sealing surface
　22 the internal thread portion
　22a screw crest surfaces
　22b thread root bottom surface
　22c inserted flank
　22d load flank surface
　23 shoulder
　23a shoulder surfaces
　24 the outer internally threaded section
　24a screws crest surfaces
　24b screw valley bottom
　24c inserted flank
　24d load flank surface
　25 outer sealing surface
　26 outside the groove

WE claims

A threaded joint for steel pipes comprising a pin and a tubular box of the tubular,
　the pin is in the order toward the tube main body from the front end side of the pin, and the inner sealing surface, and an inner male screw portion, and a shoulder portion, the outer and the male screw portion, comprising an outer sealing surface, and
　the box, in order toward the tip side from the tube main body of the box, and an inner sealing surface, and an inner female thread portion, and a shoulder portion, and the outer internally threaded section, the outer It includes a sealing surface, and
　comprises at least one component of the following features (1) and (2), a threaded joint for steel pipes.
　(1) between the inner sealing surface and the inner female thread portion of the box, grooves among along the circumferential direction is provided, a part of the teeth of the inner male thread portion of the pin is received in said groove it,
　(2) between the outer sealing surface of the pin and the outer male threaded portion, the outer groove is provided along the circumferential direction, housed part of the teeth of the outer internally threaded section of the box to the outer groove is is it.
[Requested item 2]
　A tubular threaded joint according to claim 1,
　in the case with the arrangement (1) has a length along the groove portion of the tube axis of the box is greater than the thread pitch of the inner female thread portion ,
　wherein (2) the case with the arrangement, the outer groove tube axis along the length of the pin is greater than the thread pitch of said outer male threaded portion, a tubular threaded joint.
[Requested item 3]
　A tubular threaded joint according to claim 2,
　in the case with the arrangement (1) has a length along the groove portion of the tube axis of the box four times the thread pitch of the inner female thread portion or less,
　in the case with the arrangement of (2) has a length along the outer groove of the tube axis of the pin is less than four times the thread pitch of said outer male threaded portion, a tubular threaded joint.
[Requested item 4]
　A threaded joint for steel pipes according to any one of claims 1 to 3,
　in the case with the arrangement of (1), the groove portion of the depth of the box is screw in said female screw portion more height, or less twice its thread height,
　when having the configuration of (2), said outer groove depth of the pins, or thread height of the outer male threaded portion, the screw it is 2 times or less the height, 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 the box outer diameter is less than 110% of the outside diameter of the tube body of said pin, a threaded joint for steel pipes.
[Requested item 6]
　A threaded joint for steel pipes according to any one of claims 1 to 5,
　a screw portion formed of the inside female screw portion and the inner male screw portion, and a threaded portion formed of the outer internally threaded section and the outer male thread portion a buttress type of taper thread, respectively, a threaded joint for steel pipes.
[Requested item 7]
　A tubular threaded joint according to claim 6,
　wherein each of the tapered thread, wherein the screw crest surface, thread root bottom surface, the insert flanks and load flanks
　the said thread crest surface of the inner male screw portion together with the thread root bottom surface of the inner female thread portion is in contact, wherein the external thread portion and the load flank surface and the load flank surface of the inner female thread portion is in contact, and
　the outer and the thread root bottom surface of the outer male thread portion together with the screw crest surface of the female screw portion is in contact, the load flank surface of the outer male thread portion and said outer internally threaded section the load flank surfaces of the contacts, a threaded joint for steel pipes.