[0001]The present disclosure relates to a threaded joint for use in connecting steel pipes.
Background technique
[0002]
　Oil wells, natural gas wells and the like in (hereinafter collectively referred to as "oil wells"), a casing, an oil well pipe such as tubing are used to mine underground resources. The oil well pipe is frequently used steel, threaded joint is used for the connection.
[0003]
　The format of this type of 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 male screw portion of the steel pipe is screwed into the female screw portion of the coupling, which both are connected is fastened by. 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, the male screw portion of one of the steel pipe is screwed into the female screw portion of the other steel pipe, which both are connected is fastened by.
[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]
　Oil wells, as Anakabe during drilling does not collapse, since the burrows with reinforced anti wall OCTG will result in oil well pipes are arranged in multiple structure. Recently, high-depth reduction and ultra deep water of wells are increasingly progress, in such environments, for developing efficient oil well, the connection of the oil well pipe, the inner diameter and the outer diameter of the joint portion is steel inner diameter, threaded joint is comparable to the outside diameter is often used. Such threaded joint by using, it is possible to minimize the gap OCTG each other are arranged in multiple, deep efficiently wells not also the diameter of the well is too large can be developed. Such an inner diameter, under the outer diameter restriction, the threaded joint, the pressure from the internal fluid to (hereinafter also referred to as "internal pressure") and the pressure fluid from the outside (hereinafter, also referred to as "external pressure"), excellent sealing performance is required.
[0006]
　For example, a threaded joint for ensuring sealing performance, the metal in the engaged state - is what constitutes the sealing portion by the metal contact has been known. Each following patent documents disclose a threaded joint having such a seal. Metal described here - a sealing portion by the metal contact, slightly larger than the diameter of the sealing surface of the diameter of the sealing surface of the pin box (called the difference between the diameter and the amount of interference), and entered into a threaded joint seal When faces thereof is fitted, interference amount sealing surface of the pin is reduced in diameter, the larger diameter the sealing surface of the box, the contact pressure on the sealing surfaces each seal face by the elastic restoring force of returning to the original diameter There entire circumference in close contact occurs, a structure to exhibit sealing performance.
[0007]
　Threaded joint KOKOKU 2-31271 discloses adopts the taper screw one stage to the screw portion, has an inner seal portion on the distal end side of the pin. The inner seal portion is composed of a sealing surface provided on the tip of the pin, the sealing surface provided on the box so as to correspond to the sealing surface of the pin. The threaded joint KOKOKU 2-31271 discloses, when the pin and the box is fastened, closely fit the sealing faces.
[0008]
　Threaded joint U.S. Patent No. 4,494,777, as well as the threaded joint KOKOKU 2-31271 discloses adopts a tapered thread of one stage to the screw portion. However, U.S. Patent No. 4,494,777 Pat of the threaded joint, the outer seal portion is provided on the steel body of the pin. The outer seal portion is composed of a concave and convex surfaces provided on the steel pipe body end of the pin, the convex and concave surfaces provided on the box so as to correspond to each of the concave and convex of the pin. In U.S. Patent No. 4,494,777 Pat of the threaded joint, when the pin and the box is fastened, concave and convex surfaces of the pin contacts the convex and concave, respectively box.
[0009]
　Patent No. 3426600 discloses a threaded joint employs a tapered thread in two stages in the threaded portion, having a sealing portion between the two stages of taper thread. The seal portion is constituted by a shoulder structure provided in the intermediate portion of each pin and box. Surface of each shoulder structure is formed in the reverse S-shape in longitudinal cross section. Thus, the threaded joint of Japanese Patent No. 3426600, when the pin and the box is fastened, in contact so that the shoulder structures mutually meshing.
[0010]
　Threaded joint U.S. Patent Application Publication No. 2012/0043756 and U.S. Patent No. 5,687,999 employs a tapered thread in two stages in the threaded portion, each of the distal end side and the steel pipe main body side of the pin It has an inner seal portion and an outer seal portion. Inner seal portion is composed of a sealing surface provided on the distal end portion of the pin, the sealing surface provided on the box so as to correspond to the seal surface by. Outer seal portion is composed of a sealing surface provided on an end portion of the steel pipe main body of the pin, the sealing surface provided on the box so as to correspond to the seal surface. In US Patent Application Publication No. 2012/0043756 Pat and U.S. Pat. No. 5,687,999 Pat of the threaded joint, when the pin and the box is fastened, the corresponding seal surfaces come into contact with each other.
Disclosure of the Invention
[0011]
　For example, the difference is small flash of the outer diameter of the steel pipe pile body boxes, semi-flash type, and a slim-type (hereinafter, collectively referred to as "slim") there is a threaded joint called. The slim-type threaded joint, inner and outer diameters are strictly limited. Therefore, the case of providing a seal on the end of the slim-type threaded joint, the wall thickness of the pin and / or box in the portion where the seal portion is provided is small.
[0012]
　Threaded joint KOKOKU 2-31271 discloses has only inner seal portion provided on the distal end side of the pin. According to this configuration, when the internal pressure in the screw joint is loaded, there is also the leading end portion of the pin is pushed towards the box, it is possible to maintain the sealing performance against pressure. On the other hand, readily gap between when the external pressure is loaded to the threaded joint, the distal end portion of the pin thin by external pressure penetrates into the joint is pressed down along the gap screw, the pin and the box at the inner seal portion It occurs. Therefore, the threaded joint KOKOKU 2-31271 discloses, it is difficult to ensure the sealing performance against external pressure.
[0013]
　Threaded joint U.S. Patent No. 4,494,777 has only a outer seal portion provided on the steel pipe main body of the pin. According to this arrangement, when the external pressure is loaded to the threaded joint, there is also the end portion of the box is pushed toward the pins, it is possible to maintain the sealing performance against external pressure. On the other hand, when the internal pressure in the screw joint is loaded, the end of the thin-walled box internal pressure entered inside the joint is pushed along the gap of the screw, readily gap between the pin and the box at the outer seal portion It occurs. Thus, in U.S. Patent No. 4,494,777 Pat of the threaded joint, it is difficult to ensure the sealing performance for the internal pressure.
[0014]
　The threaded joint of Patent No. 3426600 publication, the sealing portion is provided at an intermediate portion of the pin and box. According to this arrangement, it is possible to ensure the thickness of the seal portion in the pin and box, as compared to the threaded joints such as KOKOKU 2-31271 Patent Publication and US Patent No. 4,494,777 sealing performance Te can be increased. However, when dividing the threaded portion in two stages by the seal portion, the wall thickness is reduced, which can be used to screw in each stage. As a result, it becomes a low screw entirely threaded region is small thread height, the strength of the screw connection, in particular the tensile strength decreases significantly. That is, when a high internal pressure or external pressure entering the interior fittings, low screw or incomplete thread is easily deviated radially, jump out even with a low tensile load (missing Suppo screws) occurs easily. Therefore, a threaded joint of Japanese Patent No. 3426600 is also not possible to sufficiently secure the joint strength and sealing performance.
[0015]
　Threaded joint U.S. Patent Application Publication No. 2012/0043756 and U.S. Patent No. 5,687,999 has both the inner seal portion and an outer seal portion. In this configuration, the inner seal portion work for the internal pressure acts outer seal portion for external pressure. However, US Patent Application Publication No. 2012/0043756 Pat and U.S. Pat. No. 5,687,999 Pat of the threaded joint, like the threaded joint of Japanese Patent No. 3426600, threaded portion is divided into two stages and for that, the strength of the screw connection is insufficient. Therefore, in the United States Patent Application Publication No. 2012/0043756 Pat and U.S. Pat. No. 5,687,999 Pat of the threaded joint, it is impossible to expect a sufficient joint strength and sealing performance.
[0016]
　Thus, in the threaded joint as disclosed in the patent documents described above, sufficient joint strength and internal pressure, it is impossible to ensure the sealing performance against external pressure both.
[0017]
　The present disclosure aims to provide internal pressure without lowering the joint strength, especially tensile strength, the tubular threaded joint capable of improving the sealing performance against external pressure both.
[0018]
　Tubular threaded joint according to the present disclosure is comprised of a pin of the tubular and the tubular box. The tubular threaded joint, pin screwed into the box and the pin and the box are tightened. The outside diameter of the box is less than 8% of the outside diameter of the steel pipe body. Pin comprises in sequence toward the steel body from the tip, pin lip portion, the male screw portion, and a second sealing surface. Pin lip portion includes a first sealing surface. Male screw portion is composed of one stage of the taper thread. Box includes a first sealing surface, a female screw portion, and a box lip. First seal surface corresponds to the first sealing surface of the pin. Internal thread portion corresponds to the external thread portion, and a single-stage tapered thread. Box lip includes a second sealing surface corresponding to the second sealing surface of the pin. In the fastening state, the first sealing faces are in contact, the second sealing faces are in contact. Male screw portion at an end of the pin lip portion, having a plurality of thread root bottom surface parallel to and radially the tube axis are the same. Internal thread portion at the end of the box lip portion, having a plurality of thread root bottom surface parallel to and radially the tube axis are the same.
[0019]
　According to a threaded joint for steel pipes according to the present disclosure, the internal pressure without lowering the joint strength, especially tensile strength, can be improved sealing performance against external pressure both.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020]
[1] Figure 1 is a longitudinal sectional view showing a threaded joint for steel pipes according to the embodiment.
FIG. 2 is a longitudinal sectional view of an enlarged threaded portion of a threaded joint for steel pipes shown in Figure 1.
FIG. 3 is a longitudinal sectional view of an enlarged inner end portion in the tube axis direction of the tubular threaded joint shown in Figure 1.
[4] FIG. 4 is a longitudinal sectional view of an enlarged outer end portion in the tube axis direction of the tubular threaded joint shown in Figure 1.
FIG. 5 is a longitudinal sectional view of an enlarged inner end portion in the tube axis direction of the tubular threaded joint according to a modification of the embodiment.
FIG. 6 is a longitudinal sectional view of an enlarged outer end portion in the tube axis direction of the tubular threaded joint according to another modification to the threaded joint for a steel pipe shown in FIG.
[7] FIG. 7 is a longitudinal sectional view of an enlarged inner end portion in the tube axis direction of the tubular threaded joint according to another modification to the threaded joint for steel pipes shown in FIGS.
[8] FIG. 8 is a longitudinal sectional view of an enlarged threaded portion of a threaded joint for steel pipes according to another modification to the threaded joint for steel pipes shown in FIGS. 5-7.
[9] FIG. 9 is a longitudinal sectional view showing a model of a threaded joint for steel pipes according to the examples and comparative examples.
[10] FIG 10 is a longitudinal sectional view of an enlarged outer end portion of the tube axis direction of a model of a threaded joint for steel pipes shown in Figure 9.
[11] FIG 11 is a longitudinal sectional view of an enlarged threaded portion of the model of a threaded joint for steel pipes shown in Figure 9.
DESCRIPTION OF THE INVENTION
[0021]
　As described above, in the slim-type threaded joint, inner and outer diameters are strictly limited. Therefore, the necessary components, such as threaded portion and the sealing portion is arranged in a meat very limited thickness, while ensuring a predetermined joint strength, it is necessary to realize the excellent sealing performance. However, in the slim-type threaded joint, typically, it is difficult to sufficiently secure the thickness of the portion providing the seal portion.
[0022]
　For example, in the case of a threaded joint having only inner seal portion, there is also the internal pressure presses the distal end portion of the pin into the box, it can exhibit sealing performance against pressure. However, external pressure, along the clearance of the threaded portion reaches the tip of the pin, for pushing down the front end portion of the pin of the thin, occurs easily gap between the pin and box when external pressure is loaded put away. Thus, in the configuration in which only the inner seal portion, it is impossible to exert sealing performance against external pressure.
[0023]
　On the other hand, in the case of a threaded joint having only the outer seal portion, there is also be pressed against the pin end of the external pressure is box, it can exhibit sealing performance against external pressure. However, the internal pressure reaches the end of the box along the clearance of the screw portion, for pushing up the end portion of the thin-walled box, when the internal pressure is loaded readily create a gap between the pin and the box put away. Thus, in the configuration in which only the outer sealing portion can not exert sealing performance against pressure.
[0024]
　Also it is provided with a seal portion at an intermediate portion of the threaded joint. This configuration is a configuration that can be maximized thickness of the seal portion in a slim type of threaded joint. Moreover, if this arrangement, since there is screwed to both sides of the seal portion, it is possible to obtain high sealing performance.
[0025]
　However, when providing a seal portion in an intermediate portion of the threaded joint, threaded portion becomes to be composed necessarily a two-stage screw. That is, since the threaded portion is divided, the thickness that can be used to screw in each stage of course very small. As a result, a complete thread portion little area becomes a screw of incomplete thread portion covered region, the strength of the screw connection, in particular the tensile strength decreases significantly.
[0026]
　Configuration in which both the inner seal portion and an outer seal portion also. If this arrangement, the inner sealing portion work for the internal pressure acts outer seal portion for external pressure. Therefore, as compared with the configuration in which only one of the inner seal portion and an outer seal portion, it is possible to obtain pressure, excellent sealing performance against external pressure both. Moreover, if this configuration, it is possible to constitute a threaded portion at one stage of the screw, nor the strength of the threaded connection is significantly decreased.
[0027]
　Inventor, etc. of a threaded joint for steel pipes according to the embodiment has a sealing portion on both the tip side and the steel body of the pin, threaded portion for threaded joint constituted by one-stage screw, further sealing performance the research to improve've been doing. Invention have made intensive studies results, the tip of the pin the inner seal portion is provided (hereinafter, also referred to as "pin lip portion"), and an end of the box outer sealing portion is provided (hereinafter, "Box lip" by maximize the respective thickness of also referred) and found that is to improve the sealing performance considerably.
[0028]
　However, as described above, in the slim-type threaded joint, inner and outer diameters are strictly limited. Therefore, you can reduce the inner diameter in order to increase the thickness of the pin lip portion, it is not possible or increasing the outer diameter in order to increase the thickness of the box lip. For example, to shorten the length of the screw, or to lower the height of the screw thread, such as by or loose taper angle of the screw, saving thick threaded section is used, pin lip portion and box lip it is also conceivable to increase the thickness of the part. However, in this case, for example, or resulting situation that pulled out inadvertently destroyed or pin of the thread from the box (jump out) is insufficient and the strength of the screw connection is, the pin or box at the time of fastening the pin and the box very many or cause to be rotated, such as may become likely to occur eye difference screws, the strength and handling properties of the threaded joint may occur a problem that significantly reduced.
[0029]
　Accordingly, the present invention have found that focused on engagement state of the end portion of the screw portion of a conventional threaded joint. Since the screw portion is constituted by a tapered thread provided on the outer peripheral surface or inner peripheral surface of the tube, at the end of the threaded portion, the top portion of the threads of the external thread or internal thread is cut, the height of the thread gradually decreases Become. On the other hand, these depth of the screw groove corresponding to the screw thread does not become shallow, with the end of the threaded portion, a large space occurs between the screw crest surface and the thread root bottom even after threaded connection.
[0030]
　The constraints are severe slim type of threaded joints of size, space, such as described above is the height of the waste. The present invention have found that in the screw joint, by effectively using the area where the space is caused, thought to be able to further improve the sealing performance. The present invention have found, at the end of the threaded portion, by gradually shallower the depth of the screw groove according to the height of the thread gradually decreases, the thickness of the pin lip portion and the box lip It led to the idea of ​​a can be increased.
[0031]
　Tubular threaded joint according to the embodiment, it has been completed based on the above findings. A threaded joint for steel pipes according to the embodiment is constituted by a pin of the tubular, the tubular box. The tubular threaded joint, pin screwed into the box and the pin and the box are tightened. The outside diameter of the box is less than 8% of the outside diameter of the steel pipe body. Pin comprises in sequence toward the steel body from the tip, pin lip portion, the male screw portion, and a second sealing surface. Pin lip portion includes a first sealing surface. Male screw portion is composed of one stage of the taper thread. Box includes a first sealing surface, a female screw portion, and a box lip. First seal surface corresponds to the first sealing surface of the pin. Internal thread portion corresponds to the external thread portion, and a single-stage tapered thread. Box lip includes a second sealing surface corresponding to the second sealing surface of the pin. In the fastening state, the first sealing faces are in contact, the second sealing faces are in contact. Male screw portion at an end of the pin lip portion, having a plurality of thread root bottom surface parallel to and radially the tube axis are the same. Internal thread portion at the end of the box lip portion, having a plurality of thread root bottom surface parallel to and radially the tube axis are the same. Note the term "diameter same" here, the cutting device such as used by those skilled in the art usually NC lathe, the cutting tool, a "same" size when processed in the usual precision, several hundred microns even larger in average diameter the difference of the order of meters means that there is only. Further, the external thread portion and the female screw portion is a "parallel and diameter and the tube axis has a plurality of thread root bottom surface is the same", in longitudinal cross section of the threaded joint, each threaded portion, parallel and diameter and the tube axis It says that a plurality of screws valley bottom is the same there.
[0032]
　In the above-described threaded joint, the male screw portion at an end of the pin lip portion, having a plurality of thread root bottom surface parallel to and radially the tube axis are the same. According to this configuration, in comparison with the case of placing all of the thread root bottom surface of the male screw portion along a tapered surface whose diameter decreases toward the pin lip portion, increasing the wall thickness of the pin lip portion. Therefore, it is possible to considerably increase the elastic recovery force due to interference of the first sealing surface of the pin, it is possible to improve the sealing performance with respect to pressure.
[0033]
　In the above-described threaded joint, at the end of the box lip portion, having a plurality of thread root bottom surface parallel to and radially the tube axis are the same. According to this configuration, in comparison with the case where all the thread root bottom surface of the female screw portion along a tapered surface whose diameter increases toward the box lip, to increase the thickness of the box lip. Therefore, it is possible to considerably increase the elastic recovery force due to interference of the second sealing surface of the box, it is possible to improve the sealing performance against external pressure.
[0034]
　In the above-described threaded joint, the external thread portion and the female threaded portion is formed of one-stage tapered thread. Therefore, as compared to threaded joint constituting the threaded portion in two stages, the thickness that can be used in the screw portion is increased, the fully threaded region can be sufficiently secured. Therefore, it is possible to suppress a decrease in the tensile strength of the screw connection, it is possible to secure the joint strength.
[0035]
　In the above-described threaded joint, pin may further comprise a shoulder surface provided on at least one end face of the tip and the steel pipe body side. Box may further comprise a shoulder surface corresponding to the shoulder surface of the pin. In the engagement state, the corresponding shoulder faces may contact.
[0036]
　According to this configuration, it is possible to set a limit to the screwing of the pin relative to the box. Further, by shoulder faces corresponding in engaged state are in contact, fastening axial force of the screw is generated inside the joint, it is possible to further strengthen the engagement state of the screw.
[0037]
　In the above-described threaded joint, pin may further comprise a first nose portion disposed between the distal end surface and the first sealing surface of the pin.
[0038]
　According to this configuration, it is possible to further improve the rigidity of the pin lip portion (elastic recovery force of the first sealing surface of the pin). Therefore, it is possible to further improve the sealing performance with respect to pressure.
[0039]
　In the above-described threaded joints, box may further comprise a second nose portion disposed between the end surface and the second sealing surface of the box corresponding to the end surface of the steel pipe main body of the pin.
[0040]
　According to this configuration, it is possible to further improve the rigidity of the box lip (elastic recovery force of the second sealing surface of the box). Therefore, it is possible to further improve the sealing performance against external pressure.
[0041]
　In the above-described threaded joints, threaded portion constituted by the male screw portion and the female screw portion, (hereinafter referred to simply screw shape) cross-sectional shape of the screw is dovetail shaped, screw width changes gradually along the lead it may be the one.
[0042]
　In the above-described threaded joints, threaded portion constituted by the male screw portion and the female screw portion may be a single-thread screw or double threaded screw.
[0043]
　In the above-described threaded joint, the distance in the tube axis direction from the externally threaded portion to the first sealing surface of the pin, may be more than 1.5 times the thread pitch in the male screw portion.
[0044]
　In the above-described threaded joint, the distance in the tube axis direction from the internally threaded portion to the second sealing surface of the box, may be more than 1.5 times the thread pitch in the internal thread portion.
[0045]
　[Embodiment]
　Hereinafter will be described with reference to the accompanying drawings, embodiments of the tubular threaded joint. Identical and the phase in the drawing
the same reference numerals are used for configuration of those is not repeated the same description.
[0046]
　Figure 1 is a longitudinal sectional view showing a threaded joint for steel pipes 1 according to the embodiment. Threaded joint 1 is an integral-type threaded joint, composed of the pin 10 and the box 20. However, a threaded joint 1 can also be applied to a coupling type of threaded joint.
[0047]
　Threaded joint 1 is directed to what difference between the outer diameter of the outer diameter of the steel tube body 30 of the box 20 is small slim type. Therefore, the outer diameter of the box 20 is less than 8% of the outside diameter of the steel pipe body 30. The outer diameter of the box 20 is at least 100% of the outer diameter of the steel pipe body 30. The steel body 30, of the steel pipe to be connected by the threaded joint 1, a portion other than the pin 10 and box 20.
[0048]
　Pin 10 is provided in order from the tip to the steel body 30, pin lip portion 12 includes a first sealing surface 11, the male screw portion 13, and a second sealing surface 14. Pin 10 further includes a shoulder surface 15 on the end of a steel pipe body 30 side. Incidentally, the inner diameter of the pin 10 is greater than the drift diameter defined by the standards of API (American Petroleum Institute (American Petroleum Institute)). For convenience of explanation, there are cases where the inside of the distal end side of the tube axis direction of the pin 10, the pin 10 of the steel pipe body 30 side is referred to as outer tube axis direction.
[0049]
　The first seal surface 11 is provided on the outer peripheral surface of the pin lip portion 12 extending distally from the male screw portion 13. The second sealing surface 14, the outer peripheral surface of the pin 10, provided on the steel pipe main body 30 side than the male screw portion 13. Accordingly, the outer peripheral surface of the pin 10, the external thread portion 13 is disposed between the first sealing surface 11 and the second sealing surface 14.
[0050]
　The first seal surface 11 and the second sealing surface 14 are both tapered. Strictly speaking, the first seal surface 11 and the second sealing surface 14, respectively, and the shape, or frustoconical circumferential surface consisting of a surface corresponding to a peripheral surface of a truncated cone as the distal end side diameter is reduced, the arc or the like shape composed of curved from the surface corresponding to the peripheral surface of the rotary body obtained by rotating around the pipe axis CL or are combined to form the both.
[0051]
　Shoulder surface 15 is substantially perpendicular annular surface to the tube axis CL. In Figure 1, the state shoulder surface 15, screwing the traveling direction in a state of slightly tilting the pin 10 from the plane perpendicular to the tube axis CL, i.e., a slightly inclined toward the front end side of the pin 10 about its outer periphery the shows.
[0052]
　Box 20, the order from the inside of the tube axis direction outwardly, includes a box lip 22 including a first sealing surface 21, a female screw portion 23, and a second sealing surface 24. Box 20 further comprises a shoulder surface 25 at its outer end. The first seal surface 21 of the box 20, the female screw portion 23, the second sealing surface 24, and the shoulder surface 25, respectively, the first sealing surface 11 of the pin 10, the external thread portion 13, second sealing surface 14, and the shoulder surface 15 It is provided so as to correspond to.
[0053]
　A female thread portion 23 of the male thread portion 13 and the box 20 of the pin 10 is composed of a one-stage tapered thread meshing with each other. Thread form of the external thread portion 13 and the female threaded portion 23 is a dovetail shape.
[0054]
　Screw width of the external thread portion 13 and the female threaded portion 23 is changed to the screwing direction of travel of the pin 10. Specifically, the thread width of the external thread portion 13 is narrow tapers in the direction of travel of the right screw along the screw chord winding (lead), chord winding thread groove width of the screw of the opposite female threaded portion 23 It narrows in tapered in the direction of travel of the right screw along.
[0055]
　The male thread portion 13 and the female screw portion 23, to allow mutual screwing. Between the first sealing surface 11, 21 and between the second seal surface 14 and 24, respectively, with the screwing of the pin 10 in contact with each other, and because of the state interference fit in close contact with the fitting in the engagement state. Thus, between the first sealing surface 11, 21 forms a first sealing portion by the metal contact (inner seal portion). Between the second seal surface 14 and 24 forms the second seal portion by the metal contact (outer seal portion).
[0056]
　Shoulder surface 15 and 25 is pressed in contact with each other by screwing the pin 10 into the box 20, responsible for the stopper for limiting the screwing of the pin 10. Furthermore, the shoulder surface 15, 25 in the engaged state, to the external thread portion 13 of the pin 10, the load in the opposite direction (backward) to the screwing direction of travel (forward), the role of imparting the fastening axial force of the so-called screw responsible. Shoulder surface 15, 25 forms a shoulder portion by the pressing contact of such another.
[0057]
　Figure 2 is a longitudinal sectional view of an enlarged threaded portion of the threaded joint 1. Threaded portion, and a female screw portion 23 of the male thread portion 13 and the box 20 of the pin 10. Although not particularly limited, threaded portion is preferably a single-thread screw or double threaded screw.
[0058]
　As shown in FIG. 2, the external thread portion 13 of the pin 10, a plurality of screws crest surfaces 13a, thread root bottom surface 13b, the insertion flank surfaces 13c preceding by screwing (hereinafter, also referred to as "insertion surface"), and insert the load flank surface 13d opposite to the surface 13c (hereinafter, also referred to as "load surface") having a. Internal thread portion 23 of the box 20 is provided with a plurality of screws crest surfaces 23a, thread root bottom surface 23b, insertion face 23c, and the load surface 23d. Each thread crest surface 23a of the female screw portion 23 is opposed to the screw trough bottom 13b of the external thread portion 13. Each thread root bottom surface 23b of the female screw portion 23 is opposed to the screw crest surface 13a of the male screw portion 13. Each insertion surface 23c of the internal thread portion 23 faces the insertion face 13c of the externally threaded portion 13. Each load surface 23d of the female screw portion 23 faces the load surface 13d of the male thread portion 13.
[0059]
　Load surface 13d of the external thread portion 13 and the female threaded portion 23, 23d and insertion face 13c, the flank angle of 23c are both negative angle of less than 0 °. The flank angle here means the angle between the perpendicular surface and the flank surface to the tube axis CL. For threaded joint shown in FIG. 2, the load surface 13d, 23d flank angle of positive in the clockwise insertion face 13c, flank angles of 23c to the counterclockwise direction as positive.
[0060]
　The engaged state, the load surface 13d of the external thread portion 13 and the female threaded portion 23, 23d and between the insertion face 13c, with 23c with each other are in contact with each other, and the screw crest surface 23a of the thread root bottom surface 13b and the internal thread portion 23 of the male thread portion 13 It comes into contact with each other. A gap is formed between the thread root bottom surface 23b of the thread crest surface 13a and the internal thread portion 23 of the male screw portion 13. However, contrary to such an embodiment, the screw crest surface 13a and the thread root bottom surface 23b of the female screw portion 23 are in contact with each other, the screw crest surface of the screw trough bottom 13b and the internal thread portion 23 of the external thread portion 13 of the male thread portion 13 it may be a mode in which a gap is formed between the 23a. Further, insertion face 13c of the externally threaded portion 13 and the female threaded portion 23 may have a gap is formed between the 23c.
[0061]
　Figure 3 is a longitudinal sectional view of an enlarged end portion of the pin lip portion 12 of the threaded joint 1 (inner end portion of the tube axis direction). As shown in FIG. 3, the external thread portion 13, at the end of the pin lip portion 12 side, it has a plurality of thread root bottom surface 131b parallel to and radially the tube axis CL is the same. Among a plurality of thread root bottom surface of the male screw portion 13, two or more thread root bottom surface 131b from the inner end of the tube-axis direction, respectively, have a substantially cylindrical surface shape. That is, each thread root bottom surface 131b is configured to tube axis CL in a cylindrical surface whose axial center.
[0062]
　In the tube axis direction, the depth of the screw groove in the inner end of the external thread portion 13 gradually decreases toward the pin lip portion 12. Among a plurality of thread root bottom surface of the male screw portion 13, other than the screw trough bottom 131b each have a shape along the circumferential surface of the truncated cone to be reduced in diameter of about approaches the pin lip portion 12.
[0063]
　Among the plurality of screw crest surface of the female screw portion 23, the screw crest surface 231a corresponding to the thread root bottom surface 131b of the external thread portion 13, parallel and diameter are configured the same as the tube axis CL. That is, in the internally threaded portion 23, two or more thread crest surface 231a from the inner end of the tube axis direction parallel to and radially the tube axis CL is the same. Screw crest surface 231a is disposed in each screw trough bottom 131b coaxial with the corresponding external thread portion 13 has the shape of a slightly cylindrical larger diameter section than the thread root bottom surface 131b. Therefore, in the engaged state, a clearance C1 is generated between each thread crest surfaces 231a, a thread root bottom surface 131b of the external thread portion 13 corresponding thereto. Among the plurality of screw crest surface of the female screw portion 23, those other than the thread crest surfaces 231a, respectively, having a shape along the circumferential surface of the truncated cone to be reduced in diameter toward the inside of the tube axis direction.
[0064]
　Clearance C1 is caused by the difference in the diameter of the cylindrical surface constituting the thread crest surface 231a of the internally threaded portion 23, the diameter of the cylindrical surface constituting the thread root bottom surface 131b of the external thread portion 13. Although not particularly limited, for example, the average diameter of C1 is greater than 0μm in the state where the threaded joint is fastened, or less 900 .mu.m, more preferably 500μm or less. Here the said mean diameter is the actual product has elliptical error, because it is rare that C1 over the entire circumference is uniform. Thus, in some cases to the C1 in the circumferential direction of the portion it may also be present a portion to be zero, may also be present a portion where the maximum gap is greater than 900 .mu.m.
[0065]
　As described above, the first sealing surface 11 of the pin lip portion 12 is in the engaged state, in contact with the first seal surface 21 of the box 20. Of the outer peripheral surface of the pin lip portion 12, a region other than the first seal surface 11 does not contact the box 20 in the engaged state.
[0066]
　Distance L1 in the tube axis direction from the externally threaded portion 13 to the first seal portion, for example, is preferably at least 1.5 times the thread pitch P1. Here, the distance L1 is in the tube axis direction from the outer end E11 of the first seal surface 11 in contact with the first seal surface 21 of the box 20 to the inner end E12 of the external thread portion 13 in length. Thread pitch P1 refers to the length of the tube axis direction between the load flanks of the threads adjacent the male threaded portion 13 (herein, the thread pitch in the case of double threaded screw also with this definition).
[0067]
　Figure 4 is a longitudinal sectional view of an enlarged end portion of the box lip portion 22 of the threaded joint 1 (outer end portion in the tube axis direction). As shown in FIG. 4, the internal thread portion 23, at the end of the box lip portion 22 side, it has a plurality of thread root bottom surface 231b parallel to and radially the tube axis CL is the same. Among a plurality of thread root bottom surface of the internally threaded portion 23, two or more thread root bottom surface 231b from the outer end of the tube-axis direction, respectively, have a substantially cylindrical surface shape. That is, each thread root bottom surface 231b is configured to tube axis CL in a cylindrical surface whose axial center. In the tube axis direction, the depth of the screw groove at the outer end of the internal thread portion 23 gradually decreases toward the box lip portion 22. Among a plurality of thread root bottom surface of the internal thread portion 23, those other than the thread root bottom surface 231b, respectively, having a shape along the circumferential surface of the truncated cone to be reduced in diameter of about away from the box lip portion 22.
[0068]
　Among the plurality of screw crest surface of the male screw portion 13, the screw crest surface 131a corresponding to the thread root bottom surface 231b of the female screw portion 23, parallel and diameter are configured the same as the tube axis CL. That is, the external thread portion 13, two or more thread crest surface 131a from the outer end of the tube axis direction is parallel to and radially the tube axis CL is the same. Screw crest surface 131a is disposed on the corresponding thread root bottom surface 231b coaxial with the female screw portion 23 has a slightly small diameter cylindrical surface shape than the thread root bottom surface 231b. Therefore, in the engaged state, a gap C2 is formed between the thread root bottom surface 231b of the female screw portion 23 corresponding to each thread crest surface 131a. Among the plurality of screw crest surface of the male screw portion 13, those other than the thread crest surfaces 131a, respectively, having a shape along the circumferential surface of the truncated cone to be reduced in diameter toward the inside of the tube axis direction.
[0069]
　Clearance C2 is caused by the difference in the diameter of the cylindrical surface constituting the thread crest surface 131a of the external thread portion 13, the diameter of the cylindrical surface constituting the thread root bottom surface 231b of the internal thread portion 23. Although not particularly limited, for example, the average diameter of the C2 is greater than 0μm in the state where the threaded joint is fastened, or less 900 .mu.m, more preferably 500μm or less. Here the said mean diameter is the same reason as C1 described above.
[0070]
　As described above, the second sealing surface 24 of the box lip portion 22, in the engaged state, in contact with the second sealing surface 14 of the pin 10. Of the inner peripheral surface of the box lip portion 22, a region other than the second sealing surface 24 and shoulder surface 25 does not contact the pin 10 in the engaged state.
[0071]
　Distance L2 in the tube axis direction from the internally threaded portion 23 to the second sealing portion, for example, is preferably at least 1.5 times the thread pitch P2. Here, the distance L2 is, in the tube axis direction from the inner end E21 of the second sealing surface 24 in contact with the second seal portion 14 of the pin 10 to the outer end E22 of the female screw portion 23 in length. Thread pitch P2 refers to the length of the tube axis direction between the load flanks of the threads adjacent the internal thread portion 23.
[0072]
　As described above, in a threaded joint for steel pipes 1 according to the present embodiment, the external thread portion 13, at the end of the pin lip portion 12 side, has a plurality of thread root bottom surface 131b parallel to and radially the tube axis CL is the same . Therefore, in comparison with the case of placing all of the thread root bottom surface of the male screw portion 13 along a tapered surface reduced in diameter toward the pin lip portion 12 side, increasing the wall thickness of the pin lip portion 12.
[0073]
　If all the thread root bottom surface of the male screw portion 13 provided along on the tapered surface, as shown by the broken line in FIG. 3, after forming the external thread portion 13, for releasing a tool that moves tilted with respect to the tube axis CL it is necessary to provide a space on the outer circumferential surface of the pin lip portion 12. On the other hand, as in this embodiment, if the thread root bottom surface 131b of the end portion of the pin lip portion 12 side of the external thread portion 13 is the same is parallel and diameter and the tube axis CL, the tool at the end of the pin lip portion 12 side tube to move parallel to the axis CL, there is no need to provide a space for releasing the tool the pin lip portion 12. Therefore, according to this embodiment, it is possible to prevent the thickness of the pin lip portion 12 in which the first sealing surface 11 is provided is reduced, it is possible to increase the rigidity of the pin lip portion 12. Therefore, it is possible to improve the sealing performance with respect to pressure.
[0074]
　In a threaded joint for steel pipes 1 according to the present embodiment, the internal thread portion 23, at the end of the box lip portion 22 side, has a plurality of thread root bottom surface 231b parallel to and radially the tube axis CL is the same. Therefore, in comparison with the case where all the thread root bottom surface of the female screw portion 23 along a tapered surface whose diameter increases as it approaches the box lip portion 22 side, increasing the wall thickness of the box lip portion 22.
[0075]
　If all the thread root bottom surface of the female screw portion 23 provided along on the tapered surface, as shown by the broken line in FIG. 4, after the formation of the internal thread portion 23, for releasing a tool that moves tilted with respect to the tube axis CL it is necessary to provide a space on the inner peripheral surface of the box lip portion 22. On the other hand, as in this embodiment, when parallel and radial thread root bottom surface 231b of the end portion of the box lip portion 22 side and the tube axis CL of the internal thread portion 23 is the same, the tool at the end of the box lip portion 22 side There to move parallel to the tube axis CL, there is no need to provide a space for releasing the tool on the inner peripheral surface of the box lip portion 22. Therefore, according to this embodiment, it is possible to prevent the thickness of the box lip portion 22 in which the second sealing surface 24 is provided is reduced, it is possible to increase the rigidity of the box lip portion 22. Therefore, it is possible to improve the sealing performance against external pressure.
[0076]
　In a threaded joint for steel pipes 1 according to the present embodiment, the external thread portion 13 and the female threaded portion 23 is composed of a one-stage tapered thread. Therefore, the threaded joint 1, as compared to the threaded joint constituting the threaded portion in two stages, that the thickness that can be used in the screw portion is increased, a sufficient fully threaded region it can. Therefore, it is possible to suppress a decrease in the tensile strength of the screw connection, it is possible to secure the joint strength.
[0077]
　Thus, according to this embodiment, it is possible to secure a respective wall thickness of the box lip 22 pin lip portion 12 and the outer seal portion inner sealing portion is disposed is disposed on both the internal pressure and external pressure it is possible to improve the sealing performance against. Further, joint strength in order to improve the sealing performance, nor that particularly tensile strength decreases.
[0078]
　Moreover, in the present embodiment, the screw trough bottom 131b arranged at the end of the pin lip portion 12 side in the external thread portion 13, the shape of the corresponding thread crest surface cylindrical surface slightly smaller diameter than 231a of the internal thread portion 23 having. Thus, the inner end of the threaded portion, the screw trough bottom 131b and the gap C1 between the screw crest surface 231a of the internally threaded portion 23 of the external thread portion 13 is reduced. Also, thread root bottom surface 231b which is disposed at the end of the box lip portion 22 side in the female screw portion 23 has a corresponding shape of the cylindrical surface slightly larger in diameter than the screw crest surface 131a of the external thread portion 13. Accordingly, the outer end of the threaded portion, the clearance C2 between the screw crest surface 131a of the thread root bottom surface 231b and the male screw portion 13 of the internal thread portion 23 is reduced. That is, in this embodiment, the space which was formed between the screw crest surface and the thread root bottom surface at the inside and outside edges of the formed threaded portion with tapered thread is smaller than before. According to the present invention have found, by adopting such a configuration, the thickness which can be used in the pin lip portion 12 and the box lip portion 22 is increased. Therefore, it is possible to further improve the sealing performance with respect to pressure and external pressure.
[0079]
　In this embodiment, the shoulder surface 15 is provided in the steel pipe body 30 end of the pin 10. The box 20, the shoulder surface 25 corresponding to the shoulder surface 15 of the pin 10 is provided. Each shoulder surface 15, 25 for contacting each other in the engaged state, can function as a stopper for limiting the screwing of the pin 10 relative to the box 20. Each shoulder surface 15, 25 can generate a clamping axial force of the screw inside the joint.
[0080]
　In this embodiment, threaded portion constituted by the male screw portion 13 and the female screw portion 23, the thread profile is dovetail-shaped, screw width changes. According to this configuration, in the engaged state, contact the load face each other, and since the thread crest surfaces and the thread root bottom surface is in close contact in contact with each other, it is possible to realize an excellent sealing performance. When contacted also inserted faces when engagement of the pin 10 and the box 20 is completed, the entire threaded portion fit Mari firmly fitted, it is possible to further improve the adhesion performance.
[0081]
　In engagement state, so that between the first sealing surface 11, 21 and between the second sealing surface 14, 24 can exhibit an adhesion to the sealing performance in the contact force of the corresponding over the entire circumference, the first seal portion and the second seal portion has allowance fitting respectively (interference amount). Therefore, if the distance tube axis direction between the first seal portion and / or the second seal portion and the threaded portion is too close, the internal thread portion 23 by the interference amount of the first seal portion and / or the second seal portion is external thread is peeled from the section 13, the strength of the screw connection is reduced at the end of the threaded portion.
[0082]
　In the present embodiment, so that the contact with the contact between the first sealing surface 11, 21 and the male screw portion 13 and the female threaded portion 23 does not affect each other, the distance L1 in the tube axis direction from the threaded portion to the first seal portion It is secured. Also, as contact with the second sealing surface 14, 24 to each other of the contact and the male screw portion 13 and the female threaded portion 23 does not affect each other, a distance L2 in the tube axis direction from the threaded portion to the second seal portion is ensured there. For example, the distance L1, L2, respectively, a screw pitch P1, 1.5 times or more the length of P2. This allows the strength of the threaded connection can be inhibited from reduction by the first seal portion and / or the second seal portion interference amount.
[0083]
　Hereinafter, to complement the preferred embodiment of the primary site.
[0084]
　(Threaded portion)
　As described above, the gap between the inner end of the tube axis direction of the screw portion, and a thread root bottom surface 131b of the external thread portion 13, and the screw crest surface 231a of the internally threaded portion 23 corresponding thereto C1 is present. At the outer end of the tube axis direction of the screw portion, a clearance C2 between each thread crest surfaces 131a, a thread root bottom surface 231b of the female screw portion 23 corresponding to the external thread portion 13 occurs. Gaps C1, C2 are Zorezore preferably set in accordance with the inner end of the tube axis direction of the screw portion and the roundness of the outer end portion variation of (ellipticity) (manufacturing tolerances). Roundness, for example, the outer diameter of the steel pipe, the thickness sizes and materials variously changed by the production method and the like. However, circularity, generally, be less than 50% approximately 5% or more complete threads and among lower load surface height of the complete thread of the internal thread portion 23 of the male thread portion 13 (radial dimension) , more preferably 30% or less than 10%.
[0085]
　Thread height and thread taper of the screw portion is not particularly limited. Thread height and thread taper, for example, can be appropriately adjusted in accordance with the outer diameter and wall thickness sizes, etc. of the steel pipe. When intended for oil well steel pipe, thread height may be generally set from 0.8mm in a range of 3 mm. When intended for oil well steel pipes, threaded taper may be generally set in the range of 1/21 1/4.
[0086]
　If the screw portion is constituted by a screw of dovetail shape, but are not particularly limited, the size of each flank angle of the load flanks and the stabbing flanks is practically and less -31 ° or 0 ° can do. The size of each flank angle of the load flanks and the stabbing flanks, from the viewpoint of manufacturability, more preferably -16 ° ~ -2 °. The size of the flank angle of the size and insertion face of the flank angle of the load surface may not be the same.
[0087]
　(Inner diameter and outer diameter of a threaded joint for steel pipes)
　in the present embodiment, in particular, the difference is small flash of the outer diameter of the steel tube body 30 of the box 20, a steel pipe called a semi-flash type, and slim like the screw joint is the target. As described above, in a threaded joint for steel pipes 1 according to the present embodiment, the outer diameter of the box 20 is less 8% of the outside diameter of the steel pipe body 30. In particular, when the difference between the outer diameter of the steel tube body 30 of the box 20 is less than the flash type and semi-flash type threaded joint, the outer diameter of the box 20, the following 104% of the outside diameter of the steel pipe body 30 is there. The inner diameter of the threaded joint 1 (inner diameter of the pin 10), for example, the lower limit drift diameter of SPEC5CT the API standard.
[0088]
　(Seal portions)
　each shape and size first seal surface 11, 21 and the second seal surface 14 and 24 is not particularly limited. In longitudinal section of the threaded joint 1 (section cut along a plane including the tube axis CL), the contour of the first seal surface 11, 21 and the second seal surface 14 and 24, lines, arcs, elliptical arcs or smooth convex curve, , or it can be composed of these combinations.
[0089]
　(The distance between the threaded portion and the seal portion)
　As described above, when the distance tube axis direction between the first seal portion and / or the second seal portion and the threaded portion is too close, the first seal portion and / or the internal thread portion 23 is peeled off from the external thread portion 13 by the interference of second seal portion, the strength of the threaded connection at the end of the threaded portion is reduced. Therefore, depending on the outer diameter and wall thickness sizes, etc. of the threaded joint 1, the distance in the tube axis direction from the threaded portion to the first seal portion L1, and the distance in the tube axis direction from the threaded portion to the second sealing portion L2 each is preferably a screw pitch P1, P2 1.5 times more. From the viewpoint of production cost and handling properties, the distance L1, L2, respectively, may be more than 5 times the thread pitch P1, P2.
[0090]
　(Circumferential direction of the tensile strength at the ends of the box)
　circumferential tensile yield strength at the end of the box 20 can be enhanced by cold pipe expanding or the like. For example, the circumferential direction of the tensile strength in the second sealing surface 24 of the box 20 is preferably increased at least 5% or more than the tensile strength of the steel pipe body 30, it is more preferable to increase more than 10%.
[0091]
　[Modification]
　Although embodiments have been described, the present disclosure is not intended to be limited to the above embodiments but can be variously modified without departing from the spirit. For example, as shown in FIGS. 5 and 6, the pin or box may be provided with a nose portion.
[0092]
　Figure 5 is a longitudinal sectional view of an enlarged inner end portion in the tube axis direction of the tubular threaded joint 2 according to a modification of the embodiment. Tubular threaded joint 2, in that the pin 10A is provided with a nose portion 16, differs from the tubular threaded joint 1 according to the embodiment.
[0093]
　As shown in FIG. 5, the nose portion 16 is installed in the innermost tube axis direction of the pin lip portion 12. The nose portion 16 is disposed between the first sealing surface 11 of the distal end surface and the pin 10A of the pin 10A. Although not shown, each outer end of the tube axis direction of the pin 10A and box 20A may be have shoulder surface similar to the above embodiment is provided, may not be the shoulder surface is provided .
[0094]
　In the engaged state, the outer peripheral surface of the nose portion 16 does not contact the box 20A. By providing such a nose portion 16 on the pin 10A, it is possible to increase the rigidity of the pin lip portion 12. As a result, it is possible to further improve the sealing performance with respect to pressure.
[0095]
　Figure 6 is a longitudinal sectional view of an enlarged outer end portion in the tube axis direction of the tubular threaded joint 3 according to a modification of the above embodiment. Tubular threaded joint 3, in that the box 20B is provided with a nose portion 26, it differs from the tubular threaded joint 1 according to the embodiment.
[0096]
　As shown in FIG. 6, the nose portion 26 is disposed at the outermost side in the tube axis direction of the box lip portion 22. The nose portion 26 is disposed between the shoulder surface 25 of the second sealing surface 24 and the box 20B box 20B. In other words, the shoulder surface 25 is provided at the distal end of the nose portion 26.
[0097]
　In the engaged condition, the shoulder surface 25 of the box 20B is in contact with the shoulder surface 15 likewise pin 10B in the above embodiment, the inner peripheral surface of the nose portion 26 does not contact the pin 10B. By providing such a nose portion 26 in the box 20B, it is possible to increase the rigidity of the box lip portion 22. As a result, it is possible to further improve the sealing performance against external pressure.
[0098]
　Circumferential direction of the tensile strength of the box lip portion 22 including a nose portion 26 and the second sealing surface 24 of box 20B can be enhanced by cold pipe expanding or the like. Circumferential direction of the tensile strength in the nose portion 26 and the second sealing surface 24 is preferably increased at least 5% or more than the tensile strength of the steel pipe body, it is more preferable to increase more than 10%.
[0099]
　5 and 6 show an example in which the nose portion to the pin or box. However, the nose portion may be provided on both the pin and box.
[0100]
　In the above embodiment, the tip of the pin has not shoulder surface is provided, as shown in FIG. 7, the tip of the pin 10C may be the shoulder surface 17 is provided. Box 20C is provided with a shoulder surface 27 corresponding to the shoulder surface 17 of the pin 10C. In the engaged condition, the shoulder surface 17 of the pin 10C is in contact with the shoulder surface 27 of the box 20C. The end surface of the steel pipe main body of the pin 10C may be have shoulder surface similar to the above embodiment is provided, may not be provided. Shoulder surfaces of the pin, whereas either of the end faces of the pin tip and the steel body, or may be provided in both. The box shoulder surface corresponding to one or more shoulder surfaces each pin is provided.
[0101]
　In the above embodiment, the threaded portion is constituted by a screw of dovetail shape, thread shape of the threaded portion is not particularly limited thereto. For example, as shown in FIG. 8, the external thread portion 13A (13) and the female thread portion 23A (23) may be constituted by a trapezoidal screw. Although not shown, also in this case, the male screw portion 13A (13) has a plurality of thread root bottom surface parallel to and radially the tube axis CL is the same at the inner end of the tube axis direction, the internal thread portion 23A (23 ) has a plurality of thread root bottom surface parallel to and radially the tube axis CL is the same at the outer end of the tube axis direction.
Example
[0102]
　To confirm the effects of a threaded joint for steel pipes according to the present disclosure was conducted numerical simulation analysis by elasto-plastic finite element method.
[0103]
　
　9, model threaded joint for steel pipes used in the elastoplastic finite element analysis, a seal portion in which is composed of a first sealing surface 11 and 21, the second sealing surface 14, 24 in comprising an outer sealing portion that is configured, the shoulder portion comprised of shoulder surfaces 15 and 25, and a nose portion 26 which is disposed between the outer seal portion and the shoulder portion. The basic construction of the model of the Examples and Comparative Examples described later are the same.
[0104]
　As an example, with respect to a threaded joint having the basic configuration as described above, to produce a model of applying the technology according to the present disclosure. That is, as shown in FIG. 10, at the outer end of the tube axis direction of the threaded portion, the screw crest surface of the male screw portion 13 corresponding plurality of thread root bottom surface of the female screw portion 23, and which includes a tube axis CL parallel it is. Although not shown, the inner end of the tube axis direction of the threaded portion, the screw crest surface of the female screw portion 23 corresponding plurality of thread root bottom surface of the male screw portion 13, and which is parallel to the tube axis CL. The wall thickness of the pin lip portion 6.11mm, the thickness of the box lip portion is 7.19mm.
[0105]
　In an embodiment, the distance in the tube axis direction to the inner seal portion from the male screw portion 13 is twice the thread pitch. Distance in the tube axis direction from the internally threaded portion 23 to the outer seal part was also twice the thread pitch.
[0106]
　As prior art (Comparative Example) for comparison, have a basic structure as described above, to prepare a model of the technology according to the present disclosure is not applied. The configuration of the outer end portion of the tube axis direction of the model according to the comparative example shown by the broken line in FIG. 10. In the model of the comparative example, the wall thickness of the pin lip portion 4.98 mm, the thickness of the box lip is 5.98 mm.
[0107]
　Common test conditions are as follows.
　- steel dimensions: 14 [inch], 115 [ lb / ft] ( nominal outer diameter of Fai355.6Mm, nominal wall thickness 20.63Mm)
　- steel grade: the API standard Q125 (wells defined by API 5CT pipe carbon steel, yield strength 125 ksi (862N / mm 2 ))
　· thread shape and size: see dovetail shape (FIG. 11), the thread width and thread groove width screwing direction of travel changes, the male screw portion in the engaged state There gaps between and between stabbing flanks of the thread root bottom surface of the thread crest surface and the internal thread portion, the thread height of about 2 mm, a screw pitch 0.3335inch, screw taper 1/10, Article screw
　in and screw seal parts and the distance between the outer seal portion: 19 mm
　· nose portion in the tube axis direction length: 20mm
[0108]
　
　In the elastic-plastic finite element analysis, for each model that was produced, the shoulder ring (shoulder surfaces 15 and 25 that abuts against each other) from further tube axis direction to 0.001 inches tightening, ISO13679: 2002-year version of the Series A test (under normal temperature repeated pressure, external pressure load test) were successively a load combination that simulates the. The minimum value of the sealing surface pressure of the inner and outer seal portion in the analysis process, were compared as a relative value to the value of Comparative Example as 1. The analysis results are shown in Table 1.
[0109]
[Table 1]

[0110]
　As shown in Table 1, the sealing surface pressure of the inner and outer seal portion in the embodiment is much higher than the sealing surface pressure of the inner and outer seal portion in the comparative example. Therefore, a threaded joint for steel pipes according to the present disclosure, the thickness of the pin lip portion and the box lip than in the prior art is large, as a result, found to have excellent sealing performance against external pressure and internal pressure.

claims

[Claim 1]Is composed of a tubular pin, the tubular box, the pin is a threaded joint for a steel pipe and the box and the pin is screwed into the box is fastened,
　the outer diameter of the box, the outer diameter of the steel tube body less than 8% of
　the said pin, provided in this order toward the steel body from the tip, pin lip portion including a first sealing surface, the male screw portion is constructed of a one-stage tapered thread, and a second sealing surface,
　wherein box, first sealing surface corresponding to the first sealing surface of the pin, against the external thread portion
the internal thread portion formed in the tapered thread of the first stage to respond, and a corresponding second sealing surface of the pin 2 comprising a box lip portion including a sealing surface,
　in the fastening state, the with the first sealing faces are in contact, said second seal faces are in contact,
　the external thread portion, an end portion of the pin lip portion side Contact Te, a plurality of thread root bottom surface parallel to and radially the tube axis are the same,
　the female screw portion, at the end of the box lip portion, a plurality of thread root parallel and diameter and the tube axis are the same having a face, a tubular threaded joint.
[Claim 2]
　A tubular threaded joint according to claim 1,
　wherein the pin further comprises a shoulder surface provided on at least one of the tip and the steel pipe pile body-side end face of
　the box, further, the shoulder surface of the pin with corresponding shoulder surface,
　in the engagement state, it said corresponding shoulder surfaces contact each other, a tubular threaded joint.
[Claim 3]
　A tubular threaded joint according to claim 1 or 2,
　wherein the pin further comprises a first nose portion disposed between the distal end surface and the first sealing surface of the pin, a threaded joint for steel pipes .
[Claim 4]
　A threaded joint for steel pipes according to any one of claims 1 to 3,
　wherein the box is furthermore provided between the end surface and the second sealing surface of the box corresponding to the end surface of the steel pipe main body side pin a second nose portion disposed, tubular threaded joint.
[Claim 5]
　A tubular threaded joint according to claim 1, any one of 4,
　the screw portion composed of the external thread portion and the internal thread portion, the thread profile is dovetail-shaped, screw width to the lead along changes, tubular threaded joint.
[Claim 6]
　A threaded joint for steel pipes according to any one of claims 1 to 5,
　threaded portion composed of the external thread portion and the female screw portion is a single-thread screw or double threaded screw, tubular threaded joint.