Technical field
[0001]
　The present disclosure relates to a threaded joint for use in connecting steel pipes.
BACKGROUND
[0002]
　For example, oil wells and natural gas wells and the like exploration or production, the development of unconventional resources such as oil sand and shale gas, the carbon dioxide recovery and storage (CCS (Carbon (hereinafter, also collectively referred to as "oil wells") dioxide Capture and Storage)), in geothermal, or springs or the like, the steel pipe called oil well pipe is used. The connection of steel pipes, threaded joints are used.
[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 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 joint inner and outer diameters of the steel pipe inner and outer diameters and screw joints are comparable is frequently used. Such threaded joint by using, it is possible to reduce the clearance of oil well pipes to each other are arranged in multiple utmost, deeper in the well of the diameter can be developed efficiently oil well not so large. Under such an inner diameter and an 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]
　As threaded joints for securing the sealing performance, metal - are known to have a sealing portion by the metal contact. 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]
　As a threaded joint which is inner and outer diameters approximately the same inner and outer diameter steel pipe joints, for example, a flash-type, semi-flash type, slim type, and special clearance type (hereinafter, collectively referred to as "slim") there is what is called an equal. The slim-type threaded joint, the inner diameter and the outer diameter is strictly limited, the sealing surface of the inner pressure the thickness of the tip of the pin (pin in sealing surface) is provided is small, in the pin sealing surface acoustic it is not possible to sufficiently increase the resilience.
[0008]
　To improve the sealing performance with respect to internal pressure, there is known a technique further on the distal end side of the pin providing the nose than the pin sealing surface. For example, Figure 1 of EP 1836426, and in U.S. Patent No. 1 of 4,795,200 Pat and 2, threaded joints having a nose portion at the tip of the pin is disclosed.
[0009]
　Nose because it does not interfere with the box, has a function of amplifying the elastic recovery force of the pin sealing surface. That is, since the adhesion between the pins within the sealing surface and the box sealing surface is amplified by the nose portion, the sealing performance is improved with respect to the internal pressure.
Summary of the Invention
[0010]
　By providing a nose portion at the tip of the pin, it is possible to improve the sealing performance with respect to pressure. However, in the slim-type threaded joint, the wall thickness of the nose portion by the constraints of the size becomes very small, it may not be able to sufficiently ensure the sealing performance for the internal pressure. Increasing the thickness of the tip portion of the pin in order to enhance the sealing performance against internal pressure, the other portion of the pin, i.e. also increased uniform diameter, such as an outer seal portion to the male screw portion and below, the outer diameter of the resulting joint constraints opposite side of the box is generally smaller wall thickness by the sealing performance against external pressure is reduced becomes smaller thickness of the outer seal portion of the box side.
[0011]
　The present disclosure, without lowering the sealing performance against external pressure, and to provide a tubular threaded joint which can improve the sealing performance with respect to pressure.
[0012]
　Tubular threaded joint according to the present disclosure includes a pin tubular and a tubular box. Box, having an outer diameter less than 8% of the outside diameter of the steel pipe body. Box, the pin is fastened to the inserted into the pin. Pin includes a pin lip portion, and Pinshoruda surface, and the male screw portion, and a pin outer sealing surface. Pin lip portion includes a pin in the seal surface, and a nose portion. Pin the sealing surface is provided on the outer peripheral surface of the distal end portion of the pin. Nose portion is provided on the distal end side of the pin than the pin sealing surface. The outer peripheral surface of the nose portion has a smaller diameter than the diameter of the inner peripheral surface of the opposing boxes. The outer peripheral surface of the nose portion has a shape and discontinuous shapes in the pin sealing surface. Pinshoruda surface is provided on an end of the steel pipe main body of the pin. Male screw portion is provided on the outer periphery of the pin between the pin lip portion and Pinshoruda surface. Male screw portion is composed of a taper screw having a dovetail shape. Pin outside the sealing surface is provided on the outer peripheral surface of the pin between the pin lip portion and Pinshoruda surface. Box includes a box sealing surface, and the box shoulder surface, and the female screw portion, and a box outer sealing surface. Box sealing surface is provided on the inner peripheral surface of the box in correspondence with the pin sealing surface. Box sealing surface is in contact with the pin in the sealing surface in the engaged state. Box shoulder surface is provided on the end face of the box in response to Pinshoruda surface. Box shoulder surface contacts the Pinshoruda surface in engagement state. Internal thread portion is provided on the inner periphery of the box corresponding to the external thread portion. Internal thread portion is composed of a taper screw having a dovetail shape. Internal thread portion has an insertion flank surface facing spaced insert flanks and clearance of the male screw portion in the engaged state. Out of box sealing surface is provided corresponding to the pin outside the sealing surface on the inner peripheral surface of the box. Out of box sealing surface is in contact with the pin outside the sealing surface in the engaged state. D the distance tube axis direction of the male screw portion and the pin in the sealing surface, the length of the tube axis direction of the nose portion L, and screw pitch of the male screw portion as P, satisfies the following equation (1) to (3) .
　≧ P × D 1.5
　(1) L> P
　(2) | D-L | ≦ P (3)
[0013]
　According to a threaded joint for steel pipes according to the present disclosure, without lowering the sealing performance against external pressure, it is possible to improve the sealing performance with respect to pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014]
[1] Figure 1 is a longitudinal sectional view showing a schematic configuration of a tubular threaded joint according to the embodiment.
FIG. 2 is an enlarged view of a threaded portion of the threaded joint shown in Figure 1.
FIG. 3 is an enlarged view of the inner end portion in the tube axis direction of the threaded joint shown in Figure 1.
[4] FIG. 4 is an enlarged view of a threaded portion of the threaded joint shown in Figure 1.
FIG. 5 is a longitudinal sectional view of a conventional threaded joint for steel pipes.
DESCRIPTION OF THE INVENTION
[0015]
　The tubular threaded joint, the screw portion in the wall thickness is limited, the seal portion, and while arranging the necessary components, such as the shoulder portion, it is necessary to secure the sealing performance against external pressure and internal pressure. Particularly slim type threaded joint, since very severe constraints dimensions as described above, it is no longer possible to achieve high sealing performance for both external pressure and internal pressure only seal portion at one location. Therefore, in the slim-type threaded joint, in order to achieve both the sealing performance for sealing performance and pressure against external pressure, and an outer seal portion to exhibit sealing performance against external pressure, among the seal portion to exhibit sealing performance against pressure there is a need for a separately provided.
[0016]
　Inner seal portion is generally provided at the inner end of the tube axis direction of the threaded joint. That is, the inner seal portion is often disposed inside the threaded portion in the tube axis direction. Inner seal portion is constituted by the pin sealing surface and box seal surfaces. Pin the sealing surface is provided on the outer peripheral surface of the pin lip portion constituting the distal end portion of the pin. By doing so, the wall thickness of the pin lip portion is reduced, pin lip portion is easily pressed against the box by the load of the internal pressure acting on the inner peripheral surface thereof. As a result, adhesion between the pin within the sealing surface and the box sealing surface amplifies, sealing performance is improved with respect to the internal pressure. Amplification effect of adhesion due to the load of the internal pressure is increased by a sufficient distance between the threaded portion and the pin in the seal surface.
[0017]
　Besides amplification of the adhesion by the load of the internal pressure, there is preferably reason of providing an inner seal portion on the inner end of the tube axial direction of the threaded joint. For example, when fastening the pin and the box, it is possible to apply the lubricant on the surface and / or surface of the seal portion of the threaded portion. By providing the inner seal portion on the inner side of the tube axis direction than the threaded section, in engagement, or during use of the fastening steel tube, the lubricant can be inhibited from flowing into the interior of the steel pipe.
[0018]
　Further, by providing the inner seal portion on the inner side of the tube axis direction than the threaded portion, can be internal fluid, such as crude oil and natural gas can be inhibited from entering the threaded portion. Therefore, crevice corrosion is generated by the internal fluid that has entered the narrow gap threaded portion, the hole in the screw portion can be prevented Aitari, from thread portion or broken.
[0019]
　Incidentally, in the slim-type threaded joint, the wall thickness of the pin lip portion inner sealing surface is provided, inevitably very small. Therefore, increasing the amount of interference of the inner seal portion, there is no possibility that the elastic resilience of the pin sealing surface is greatly amplified. Therefore, in the slim-type threaded joint, even added effect of load pressure acting on the inner peripheral surface of the pin lip portion, not the adhesion of the pin in the sealing surface for the box sealing surface is greatly amplified, the internal pressure it is impossible to greatly improve the sealing performance against.
[0020]
　Here, the sealing performance against internal pressure, does not mean sealing performance in a state where only the load of the internal pressure is acting. The sealing performance against internal pressure, the other load pressure, for example, a tube axial direction of tension or compression, bending, load, etc. of external pressure, when various loads expected in actual use is repeatedly loaded, or loaded It means sealing performance in later. The sealing performance of the threaded joint under the repeated combined loads of as a method for evaluating in real samples, for example, there is evaluation test specified in API5C5 or ISO13679.
[0021]
　As described above, in the slim-type threaded joint, due to restrictions of the dimensions, it is difficult to ensure only the inner sealing portion a good sealing performance against pressure. To improve the sealing performance with respect to the internal pressure in the slim-type threaded joint, it is known to provide a nose portion at the tip of the pin lip portion.
[0022]
　Nose portion is configured so as not to interfere with the box. Therefore, the nose portion has a function pin in sealing surface that is reduced in diameter by interference with the box sealing surface to amplify the elastic recovery force of returning to the original diameter. Therefore, by providing the nose portion to the pin lip portion, without increasing the amount of interference of the inner seal portion amplifies the adhesion of the inner sealing portion is also considered to sealing performance is improved with respect to the internal pressure.
[0023]
　However, in practice, simply providing the nose portion to the pin lip portion, it is impossible to greatly amplify the adhesion of the inner seal portion. The slim-type threaded joint, due to restrictions of the dimensions, because the thickness of the nose portion becomes extremely small.
[0024]
　Also, the nose section, since it does not interfere with the box, the load of the internal pressure in both the inner and outer peripheral surfaces act. In other words, the nose section is intended to be to stay in place when the load of the internal pressure is applied, no amplification effect of the adhesion force by the load of the internal pressure.
[0025]
　Furthermore, the rigidity of the pin lip portion by providing the nose portion is increased, deformation of the pin lip portion is less likely to occur. According to the study of the inventor, etc. of a threaded joint according to the embodiment, in this case, it is obtained by securing the distance between the threaded portion and the pin in the sealing surface, the amplification effect of the adhesion due to the load of the internal pressure eroded.
[0026]
　Accordingly, the slim type threaded joint, in order to effectively amplify the adhesion of the inner seal portion, the distance tube axis direction between the threaded portion and the pin in the seal surface, and the length of the tube axis direction of the nose portion the balance of it is important. However, in the conventional slim-type threaded joint, the balance is not taken into consideration.
[0027]
　In order to improve the sealing performance with respect to internal pressure, it is also important to appropriately contact the pin in the seal surface and the box sealing surface.
[0028]
　The slim-type threaded joint, the limitations of size, small wall thickness of the pin lip portion. Therefore, when the load of internal pressure on the inner surface of the pin lip portion is applied, the portion between the threaded portion and the pin in the sealing surface is seen bulging to the outer peripheral side, the pin within the sealing surface is inclined with respect box sealing surface. According to the studies of the inventor, the inclination of such pins the sealing surface increases as the distance tube axis direction between the threaded portion and the pin in the sealing surface increases. When the pin within the sealing surface is inclined with respect box sealing surface, the contact position between the pin within the sealing surface and the box sealing surface ends up moving, sealing performance becomes unstable with respect to internal pressure. That is, the contact position between the pin within the sealing surface and the box sealing surface is shifted from the position familiar with each other by sliding in the engagement, may leak internal fluid occurs becomes high.
[0029]
　Tube axis direction of displacement of the mobile, or pins in the sealing surface and / or the box sealing surface of the contact position between the pin within the sealing surface and the box sealing surface, also generated by the load of compression. Slim-type threaded joint are the relatively large diameter thin walled, relative displacement between the pin and the box caused by the load of the compression is large compared with other types of screw joints. In order to improve the sealing performance, it is necessary to suppress the relative displacement between such pin and the box.
[0030]
　Conventionally, a threaded joint with different types of screws have been devised. Among them, a screw that can minimize the relative displacement between the pin and the box due to the load of compression is of the type and the insertion flank and the internal thread of the insert flank of the external thread is in contact in the engaged state. Negative angle each insert flank, that is, if the intended shape inclined to the tube axis direction and a plane perpendicular to the front end side of the pin, it is possible to further reduce the relative displacement between the pin and the box.
[0031]
　Typical examples, a threaded width that varies progressively along the lead, the cross-sectional shape dovetail shape of the screw (hereinafter referred to as dovetail screw) it is. Dovetail screw generally has a self 緊作. Accordingly, threaded joints Dovetail screw has been applied, typically, no shoulder for limiting the screwing of the pin relative to the box.
[0032]
　Screw Dovetail screw is applied joints, contacts inserted flank faces and load flank faces each other, fastening by mate the male screw and the female screw is completed. Such threaded joint, for example, a read error, the angle error of the insertion flanks and / or load flanks by elliptical error, or screws width errors, etc., may be fastened is completed position changes significantly. Therefore, it is difficult to introduce the amount of interference of the seal portion stably, sealing performance becomes unstable.
[0033]
　Other dovetail screw with a self 緊作, as a screw which can reduce the relative displacement between the pin and the box, the cross-sectional shape is dovetail shape, and the insertion flank and the internal thread of the insert flank of the external thread in engagement state there is a gap is formed between. Invention have found that by adopting this type of screw in a slim type of threaded joint, it is possible to reduce without adverse effects relative displacement between the larger tends pin and the box slim type threaded joint, a stable sealing performance I thought that it is possible to obtain.
[0034]
　Threaded joint gap is formed between the insertion flank and the internal thread of the insert flank of the external thread in the fastening state is not susceptible to various errors described above. Further, by providing the shoulder portion to the threaded joint, it is possible to manage the completion position of the fastening by the shoulder. Therefore, it is possible to prevent the completion position of the fastening changes, interference amount of the seal portion can be stabilized to stably sealing performance.
[0035]
　Based on the above findings, inventor, etc., while maintaining the sealing performance against external pressure, they devised a tubular threaded joint which can improve the sealing performance with respect to pressure.
[0036]
　Tubular threaded joint according to the embodiment includes a pin tubular and a tubular box. Box, having an outer diameter less than 8% of the outside diameter of the steel pipe body. Box, the pin is fastened to the inserted into the pin. Pin includes a pin lip portion, and Pinshoruda surface, and the male screw portion, and a pin outer sealing surface. Pin lip portion includes a pin in the seal surface, and a nose portion. Pin the sealing surface is provided on the outer peripheral surface of the distal end portion of the pin. Nose portion is provided on the distal end side of the pin than the pin sealing surface. The outer peripheral surface of the nose portion has a smaller diameter than the diameter of the inner peripheral surface of the opposing boxes. The outer peripheral surface of the nose portion has a shape and discontinuous shapes in the pin sealing surface. Pinshoruda surface is provided on an end of the steel pipe main body of the pin. Male screw portion is provided on the outer periphery of the pin between the pin lip portion and Pinshoruda surface. Male screw portion is composed of a taper screw having a dovetail shape. Pin outside the sealing surface is provided on the outer peripheral surface of the pin between the pin lip portion and Pinshoruda surface. Box includes a box sealing surface, and the box shoulder surface, and the female screw portion, and a box outer sealing surface. Box sealing surface is provided on the inner peripheral surface of the box in correspondence with the pin sealing surface. Box sealing surface is in contact with the pin in the sealing surface in the engaged state. Box shoulder surface is provided on the end face of the box in response to Pinshoruda surface. Box shoulder surface contacts the Pinshoruda surface in engagement state. Internal thread portion is provided on the inner periphery of the box corresponding to the external thread portion. Internal thread portion is composed of a taper screw having a dovetail shape. Internal thread portion has an insertion flank surface facing spaced insert flanks and clearance of the male screw portion in the engaged state. Out of box sealing surface is provided corresponding to the pin outside the sealing surface on the inner peripheral surface of the box. Out of box sealing surface is in contact with the pin outside the sealing surface in the engaged state. D the distance tube axis direction of the male screw portion and the pin in the sealing surface, the length of the tube axis direction of the nose portion L, and screw pitch of the male screw portion as P, satisfies the following equation (1) to (3) (first configuration).
　≧ P × D 1.5
　(1) L> P
　(2) | D-L | ≦ P (3)
[0037]
　In the first configuration, the distance D of the tube axis direction of the male screw portion and the pin in the sealing surface is more than 1.5 times the thread pitch P of the external thread portion. The length L in the tube axis direction of the nose portion is greater than the thread pitch P. The difference between the length L of the distance D and the nose portion of the male screw portion and the pin in the sealing surface is made within the thread pitch P. By placing the pin in the sealing surface and the nose portion to the pin lip portion in such a balance, while the adhesion of the pin in the sealing surface for the box sealing surface is amplified by the nose portion, the male screw portion and the pin in the seal surface the amplification effect of adhesion due to internal pressure loads in accordance with the distance the nose portion can be prevented from lowering. Therefore, it is possible to effectively amplify the adhesion between the pins within the sealing surface and the box sealing surface.
[0038]
　In a first configuration, the nose portion is provided on the pin lip portion, large flexural rigidity of the pin lip portion, deformation is unlikely to occur in the pin lip portion. Therefore, the load of the internal pressure, the pin within the sealing surface can be prevented from being inclined with respect to the box sealing surface. Therefore, movement of the contact position between the pin within the sealing surface and the box sealing surface is suppressed, thereby preventing deterioration of sealing performance against pressure.
[0039]
　According to the first configuration, each of the external thread portion and the female threaded portion is constituted by a taper screw having a dovetail shape. A gap is formed between the insertion flank the insertion flank of the internal thread portion of the male screw portion in the engaged state, the influence of various errors threaded joint becomes less susceptible. Further, in the fastening state, the contact between Pinshoruda surface and the box shoulder surface, it is possible to stabilize the completion position of the fastening. Therefore, the amount of interference of the seal portion can be stably introduced, the sealing performance against internal pressure and external pressure can be stabilized.
[0040]
　As described above, according to the first configuration, without changing the components for sealing performance against external pressure, it is possible to ensure a high and stable sealing performance against pressure. In other words, without lowering the sealing performance against external pressure, it is possible to improve the sealing performance with respect to pressure.
[0041]
　Pin the sealing surface may be a tapered surface whose diameter decreases toward the distal end side of the pin, the convex surface including the arcuate surface continuous with both ends of each of the tapered surfaces is. Box sealing surface may also include a long tapered surface than the pin sealing surface (second configuration).
[0042]
　In general, the pin within the sealing surface is composed of single arcuate surface is large radius of curvature. Such a shape of the pin within the sealing surface, when the pin within the sealing surface by the load of the internal pressure is inclined relative to the box sealing surface, causing the contact position between the pin within the sealing surface and the box sealing surface moves largely Become.
[0043]
　On the other hand, in the second configuration, the pin within the sealing surface, a tapered surface, a continuous radius of curvature and opposite ends of the tapered surface is constituted by a relatively small arcuate surface. According to this configuration, in most fastening process, the tapered surface of the pin sealing surface to slide in contact with the tapered surface of the box sealing surface, after completion of the final stage and the fastening of the fastening, the steel body arcuate surface is in contact with the tapered surface of the box sealing surface. Thus, by the curvature radius contacting the relatively small arc face in box sealing surface, even as a pin in the sealing surface is inclined against the box sealing surface, the pin within the sealing surface and the box sealing surface it is possible to reduce the amount of movement of the contact position of. Therefore, it is possible to stabilize the sealing performance against pressure.
[0044]
　The radius of curvature of the arcuate surface may be a 3 mm ~ 30 mm (third configuration).
[0045]
　Pin outside sealing surface, which may be located at the end of the steel pipe main body of the pin (fourth configuration).
[0046]
　According to a fourth configuration, across each of the tube axis direction, the seal portion constituted by the pin within the sealing surface and the box sealing surface, and a outer sealing between the pin outer sealing surface and the box outside the sealing surface parts are arranged. Therefore, it is to be disposed between the male thread portion and the inner seal portion threaded portion is composed of female screw portion and an outer seal portion, for example, it is possible to constitute a threaded portion at one stage of the screw. In this case, since the wall thickness can be used for the threaded portion is increased, it is possible to sufficiently ensure the complete thread portion region. As a result, it is possible to suppress a decrease in the tensile strength of the screw connection, it is possible to secure the joint strength.
[0047]
　Distance D may be equal to or less than 3 times the screw pitch P (fifth configuration).
[0048]
　According to a fifth configuration, pin lip portion is not too long, it is possible to reduce material costs and / or production costs.
[0049]
　Threaded portion constituted by the male screw portion and the female screw portion may have a screw width that varies along the lead (sixth configuration).
[0050]
　In the sixth configuration, in most fastening process, the gap between the insertion flank the insertion flank of the internal thread portion of the male thread portion is large, the gap is smaller at the last minute completion of fastening. Therefore, a threaded constant width of the screw portion, in comparison gap also inserted flank faces in fastening the small threaded joint, seizure is unlikely to occur.
[0051]
　Gap between the insertion flank the insertion flank of the internal thread portion of the male screw portion may also be 100μm or less (seventh configuration).
[0052]
　Threaded portion constituted by the male screw portion and the female screw portion may be a single-thread screw or threaded screw (eighth configuration).
[0053]
　[Embodiment]
　Hereinafter will be described with reference to the accompanying drawings, embodiments of the tubular threaded joint. Given the same reference and the corresponding configuration in the figure does not repeat the same description.
[0054]
　Figure 1 is a longitudinal sectional view showing a schematic configuration of a tubular threaded joint 1 according to the embodiment. Threaded joint 1 is an integral-type threaded joint. However, a threaded joint 1 can also be applied to the coupling type.
[0055]
　Threaded joint 1 is provided with a respective tubular pins 10 and box 20 of. Pin 10 is inserted into the box 20, the pin 10 and the box 20 is fastened.
[0056]
　Threaded joint 1 is directed to those slim small difference between the outer diameters of the steel pipe joint portion. Therefore, the outer diameter of the box 20 is less than 8% of the outside diameter of the steel pipe body of the pin 10. The outer diameter of the box 20 is at least 100% of the outer diameter of the steel pipe body of the pin 10. The inner diameter of the pin 10, API greater than the drift diameter defined by the standard (American Petroleum Institute (American Petroleum Institute)).
[0057]
　The steel body of the pin 10 in the present embodiment refers to a portion in the steel pipe comprising a pin 10 not inserted into the box 20. 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 pile body side is referred to as outer tube axis direction.
[0058]
　As shown in FIG. 1, the pin 10 includes a pin lip portion 11, a Pinshoruda surface 12, a male screw portion 13, and a pin outer sealing surface 14.
[0059]
　Pin lip portion 11 constitutes a leading end portion of the pin. Pin lip portion 11 includes a pin within the sealing surface 11a, a nose portion 11b, and a base 11c. Pin the sealing surface 11a is provided on the outer peripheral surface of the pin lip portion 11. The nose portion 11b is provided on the distal end side of the pin 10 than the pins in the sealing surface 11a. That is, the nose portion 11b is disposed at the cutting edge of the pin 10. The base 11c, of the pin lip portion 11 is a portion of the male screw portion 13 than the pins in the sealing surface 11a.
[0060]
　Pinshoruda surface 12 is provided on an end of the steel pipe main body of the pin 10. In the present embodiment, Pinshoruda surface 12 is substantially perpendicular annular surface to the tube axis CL. More specifically, Pinshoruda surface 12 is shaped to be slightly tilted in the screwing direction of travel of the pin 10 than the outer peripheral side the inner peripheral side.
[0061]
　External thread portion 13, between the pin lip portion 11 and the Pinshoruda surface 12, is provided on the outer periphery of the pin 10. External thread portion 13 is constituted by a one-stage tapered thread. In the external thread portion 13, longitudinal sectional shape of the screw (hereinafter, simply referred to as screw shape) is dovetail shaped.
[0062]
　Pin outer sealing surface 14, between the pin lip portion 11 and the Pinshoruda surface 12 is provided on the outer peripheral surface of the pin 10. Pin outer sealing surface 14 is arranged on the outside of the tube axis direction than the external thread portion 13.
[0063]
　Box 20 includes a box sealing surface 21, and the box shoulder surface 22, an internal thread portion 23, and a box outer sealing surface 24.
[0064]
　Box sealing surface 21, corresponding to the pin within the sealing surface 11a, provided on the inner peripheral surface of the box 20. Box sealing surface 21 contacts the pin within the sealing surface 11a in an engaged state.
[0065]
　Pin the sealing surface 11a and the box sealing surface 21 has an interference amount. That is, the diameter of the pin within the sealing surface 11a is slightly larger than the diameter of the box sealing surface 21. Therefore, pin in sealing surface 11a and the box sealing surface 21 is in contact with each other with the screwing of the pin 10 relative to the box 20, a fit state interference fit in close contact with the fitting in the engagement state. Thus, the pin within the sealing surface 11a and the box sealing surface 21, forming the inner seal portion by the metal contact.
[0066]
　Box shoulder surface 22 corresponds to Pinshoruda surface 12 is provided on the end surface of the outer tube axial direction in the box 22. Box shoulder surface 22 is substantially perpendicular annular surface to the tube axis CL. More specifically, the box shoulder surface 22 is shaped to be slightly tilted in the screwing direction of travel of the pin 10 than the outer peripheral side the inner peripheral side. Box shoulder surface 22 contacts the Pinshoruda surface 12 in the engaged condition.
[0067]
　Pinshoruda surface 12 and box shoulder surface 22 is pressed in contact with each other by screwing of the pin 10 relative to the box 20. Pinshoruda surface 12 and box shoulder surface 22 forms a shoulder portion by the pressing contact of such another. Pinshoruda surface 12 and box shoulder surface 22 is responsible stopper for limiting the screwing of the pin 10. Pinshoruda surface 12 and box shoulder surface 22, inside the joint, responsible for generating a clamping axial force of the screw.
[0068]
　Internal thread portion 23, corresponding to the external thread portion 13 is provided on the inner periphery of the box 20. Internal thread portion 23 is composed of a one-stage tapered thread that meshes with tapered threads constituting the male screw portion 13. Thread form of the female screw portion 23 is a dovetail shape.
[0069]
　Screw width of the threaded portion constituted by the male screw portion 13 and the internal thread portion 23 is changed to the screwing direction of travel of the pin 10. Specifically, screws Yamahaba the external thread portion 13 narrows in tapered in the direction of travel of the right screw along the screw chord winding (lead). Thread groove width of the opposite internal thread portion 23 is also narrower tapered in the direction of travel of the right screw along the helical line of the thread. Threaded portion is preferably a single-thread screw or double threaded screw.
[0070]
　Out of box sealing surface 24, corresponding to the pin outside the sealing surface 14 is provided on the inner peripheral surface of the box 20. Out of box sealing surface 24 is arranged outside the tube axis direction than the female threaded portion 23. Out of box sealing surface 24 contacts the pin outside sealing surface 14 in the engaged state.
[0071]
　Pin outer sealing surface 14 and out of box sealing surface 24 has an interference amount. That is, the diameter of Pimpin outer sealing surface 14 is slightly larger than the diameter of the out of box sealing surface 24. Thus, the pin outer sealing surface 14 and out of box sealing surface 24 is in contact with each other with the screwing of the pin 10 relative to the box 20, a fit state interference fit in close contact with the fitting in the engagement state. Thus, the pin outer sealing surface 14 and out of box sealing surface 24 forming the outer seal portion due to metal contact.
[0072]
　Figure 2 is a partially enlarged view of FIG. 1 shows a schematic configuration of a threaded portion of the threaded joint 1.
[0073]
　As shown in FIG. 2, the external thread portion 13, viewed in cross section taken along a plane passing through the tube axis CL, a plurality of screws crest surfaces 13a, thread root bottom surface 13b, the insertion flank 13c (hereinafter, "insertion surface" also referred), and load flank surfaces 13d (hereinafter, having also referred to as "load surface"). Each insertion face 13c is a face that precedes by screwing of the pin 10 relative to the box 20. Each load surface 13d is a surface of the insertion face 13d opposite.
[0074]
　Internal thread portion 23, viewed in cross section taken along a plane passing through the tube axis CL, a plurality of screws crest surfaces 23a, thread root bottom surface 23b, the insertion flank 23c (hereinafter, also referred to as "insertion surface"), and load flank surface 23d (hereinafter also referred to as "load surface") with a. 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.
[0075]
　As described above, the screw shape of the external thread portion 13 and the female threaded portion 23 is a dovetail shape. Therefore, insertion face 13c, the flank angle of 23c is the negative angle of less than 0 °. The flank angle in this embodiment is that the angle between the perpendicular surface and the flank surface to the tube axis CL. 2, insertion face 13c, the flank angle of 23c to the counterclockwise direction as positive. That is, each insertion face 13c, 23c, when viewed in cross section taken along a plane passing through the tube axis CL, are inclined to the distal end side of the pin 10.
[0076]
　Load surface 13d, also the flank angle of the 23d is a negative angle of less than 0 °. 2, the load surface 13d, the flank angle of the 23d to the clockwise and positive. Each load surface 13d, 23d, when viewed in cross section taken along a plane passing through the tube axis CL, the insertion face 13c, are inclined 23c opposite, that is, steel pipe main body of the pin 10.
[0077]
　The engagement state, a screw crest surface 23a of the thread root bottom surface 13b and the internal thread portion 23 of the external thread portion 13 are in contact with each other. Load surface 13d of the external thread portion 13 and the female threaded portion 23, 23d with each other also in contact with each other. On the other hand, they do not contact each other and the thread root bottom surface 23b of the thread crest surface 13a and the internal thread portion 23 of the male screw portion 13. Insertion face 13c of the externally threaded portion 13 and the female threaded portion 23, 23c to each other also do not contact each other.
[0078]
　In the engaged state, insertion face 13c of the externally threaded portion 13 is opposed spaced insertion face 23c and the gap G of the internal thread portion 23. Insertion face 13c, 23c gap G of, in cross-section including the pitch line PL of the screw, the point of intersection with the pitch line PL on the insertion face 13c of the externally threaded portion 13, the insertion surface of the opposite internal thread portion 23 on the insertion face 13c 23c is a distance in the tube axis direction to the. Pitch line PL, in longitudinal section including the tube axis CL, a line formed by connecting the points with a on the load surface 13d of the external thread portion 13 to half the load surface height. Gap G can be appropriately determined in consideration of the degree of read error and the like. Although not particularly limited, gap G is preferably 100μm or less.
[0079]
　External thread portion 13 has a constant thread pitch P. Thread pitch P is the distance between the load surface 13d of adjacent threads. More specifically, the thread pitch P, in a cross section including the pitch line PL of the screw, from the intersection of the load surface 13d and the pitch line PL of a thread, the thread of the load surface 13d is located next to the thread and it refers to the distance in the tube axis direction to an intersection between the pitch line PL. In short, the screw pitch P is a load surface pitch of the external thread portion 13. In the present embodiment, 1-threaded screw, regardless of the multiple thread, the thread pitch P of the external thread portion 13 is thus defined.
[0080]
　Figure 3 is a partially enlarged view of FIG. 1 shows a schematic configuration of the inner end portion in the tube axis direction of the threaded joint 1.
[0081]
　As shown in FIG. 3, the pin within the sealing surface 11a is a convex surface formed on the outer peripheral surface of the pin lip portion 11. Pin the sealing surface 11a is shaped and discontinuous shape of the outer peripheral surface of the nose portion 11b. Pin the sealing surface 11a is also the shape of the outer peripheral surface of the base portion 11c having a discontinuous shape. Accordingly, the outer peripheral surface of the pin lip portion 11, between the nose portion 11b and the pin in the sealing surface 11a, and between the pin within the sealing surface 11a and the base 11c are clear boundary respectively exist. The nose portion 11b is formed in a concave shape recessed on the inner peripheral side of the pin 10 than the pins in the sealing surface 11a. Proximal portion 11c is formed in a concave shape recessed on the inner peripheral side of the pin 10 than the male screw portion 13 and the pin within the sealing surface 11a.
[0082]
　The outer diameter of the nose portion 11b is smaller than the diameter of the inner peripheral surface of the box 20 which faces the nose portion 11b. Thus, the nose portion 11b does not interfere with the box 20 in both during and after fastening and fastening. That is, between the outer peripheral surface and the inner surface of the box 20 of the nose portion 11b, is always a gap.
[0083]
　In this embodiment, the nose portion 11b is cylindrical substantially has a constant outer diameter. However, the shape of the nose portion 11b is not particularly limited. For example, the nose portion 11b may be a hollow truncated cone shape.
[0084]
　The outer diameter of the base end portion 11c is smaller than the diameter of the inner peripheral surface of the box 20 which faces the base portion 11c. Accordingly, the base end portion 11c, like the nose portion 11b, does not interfere with the box 20 after being fastened and the fastening. Also between the inner circumferential surface of the outer peripheral surface and the box 20 of the base end portion 11c, is always a gap.
[0085]
　Referring to FIGS. 2 and 3, the tube axis direction length of the base end portion 11c, i.e. the distance D in the tube axis direction of the male screw portion 13 and the pin within the sealing surface 11a is in the tube axis direction of the nose portion 11b It is determined in consideration of the relationship between the length L and the thread pitch P of the external thread portion 13. Distance D between the male screw portion 13 and the pin within the sealing surface 11a, from the inner end of the external thread portion 13 refers to the length of the tube axis direction to the boundary between the base portion 11c and the pin in the seal surface 11a. In the present embodiment, the distance D, of the outer peripheral surface of the pin lip portion 11, is substantially the length of the tube axis direction of the step is not part between the external thread portion 13 and the pin within the sealing surface 11a. The length L of the nose portion 11b from the boundary between the pin within the sealing surface 11a and the nose portion 11b, refers to the length of the tube axis direction to the tip of the pin lip portion 11. In the present embodiment, the length L, of the outer peripheral surface of the pin lip portion 11, the tube axis direction of the substantially stepped portion without the inner end of the pin within the sealing surface 11a to the tip of the pin lip portion 11 with a length is there.
[0086]
　Distance D between the male screw portion 13 and the pin within the sealing surface 11a is more than 1.5 times the thread pitch P of the external thread portion 13. The length L of the nose portion 11b is greater than the thread pitch P of the external thread portion 13. The difference between the distance D and the length L is within the thread pitch P. In other words, the thread pitch P of the external thread portion 13 and the distance D between the pin within the sealing surface 11a, the length of the nose portion 11b L, and the external thread portion 13 is determined so as to satisfy the following equation (1) to (3) that.
　≧ P × D 1.5
　(1) L> P
　(2) | D-L | ≦ P (3)
[0087]
　For example, distance D may be from the viewpoint of cost and the like of the material or manufacturing, less three times the thread pitch P. However, the upper limit of the distance D is not particularly defined. Similarly, the upper limit of the length L is also not particularly defined.
[0088]
　Figure 4 is a partially enlarged view of FIG. 1 shows a schematic configuration of the seal portion of the threaded joint 1.
[0089]
　Pin the sealing surface 11a is a convex surface including a tapered surface 111, and arcuate surface 112, 113. Tapered surface 111, reduced in diameter toward the distal end side of the pin 10. Tapered surface 111, rather than the steel pipe main body having a shape corresponding to the peripheral surface of the conical diameter of the distal end side is smaller base. At both ends of each of the tapered surfaces 111, arcuate surface 112, 113 a small radius of curvature are connected.
[0090]
　Arcuate surface 112 is smoothly connected with the inner end of the tube axis direction of the tapered surface 111. Arcuate surface 113 is disposed on the opposite side of the arcuate surface 112 is smoothly connected to the outer end of the tube axis direction of the tapered surface 111. Arcuate surface 112 and 113, respectively, having a shape corresponding to the peripheral surface of the rotary body obtained by rotating an arc about the tube axis CL.
[0091]
　Each radius of curvature of the arcuate surface 112 and 113, for example, be a R3 ~ R30 (3mm ~ 30mm). However, the radius of curvature of the arcuate surface 112 is not limited thereto. Each radius of curvature of the arcuate surface 112 and 113, taking into account the inclination and the like of the tapered surface 111 can be appropriately determined.
[0092]
　Box sealing surface 21 includes a tapered surface 211. Tapered surface 211 is longer than the pin in the seal surface 11a. For example, in the fastening state, the tapered surface 211 extends to the outside of the tube axis direction than the pin in the seal surface 11a. Tapered surface 211 has an inclination corresponding to the inclination of the tapered surface 111 of the pin within the sealing surface 11a.
[0093]
　[Effects of Embodiment]
　In the above embodiment, in balance can be effectively improved sealing performance with respect to the internal pressure, the length of the tube axis direction of the distance D and the nose portion 11b of the male screw portion 13 and the pin within the sealing surface 11a L is defined is. That is, the distance D between the male screw portion 13 and the pin within the sealing surface 11a is not less than 1.5 times the thread pitch P of the external thread portion 13, the length L of the nose portion 11b is greater than the thread pitch P. Moreover, the difference between the distance D and the length L is made within the thread pitch P. Thus, while amplifying the adhesion of the inner sealing portion by the nose portion 11b, the amplification effect of the adhesion force by the load of the resulting pressure in accordance with the distance D can be prevented from being lowered by the nose portion 11b. Therefore, it is possible to effectively amplify the adhesion of the inner seal portion.
[0094]
　In the above embodiment, pin lip portion 11 has a nose portion 11b. Thus, pin lip portion 11, the flexural rigidity is large, deformation is unlikely to occur. Therefore, it is possible to pin lip portion 11 due to the load of the internal pressure bulge on the outer peripheral side, the pin within the sealing surface 11a can be inhibited from tilting relative to the box sealing surface 21. Thus, movement of the contact position between the pin within the sealing surface 11a and the box sealing surface 21 is suppressed, the sealing performance against internal pressure can be stabilized.
[0095]
　Threaded joint 1 according to the embodiment, since the gap is formed between the insertion face 23c of the insertion face 13c and the internal thread portion 23 of the male screw portion 13 in the fastening state, less susceptible to various errors. Further, in the engaged state because the contact between Pinshoruda surface 12 and the box shoulder surface 22, it is possible to manage the completion position of the fastening. Thus, it is possible to stably introduce the seal interference amount, it is possible to secure stable sealing performance against internal pressure and external pressure.
[0096]
　Thus, a threaded joint 1 according to the embodiment described above, for example, or to increase the amount of interference of the inner seal portion, or without or a design of adjustment as to lower the sealing performance of the outer seal portion also, it is possible to improve the adhesion of the inner seal portion. Therefore, it is possible while maintaining the sealing performance against external pressure, it may be an excellent sealing performance against pressure stable.
[0097]
　In the above embodiments, the pin within the sealing surface 11a is a tapered surface 111 is a convex surface constituted by an arc surface 112, 113. Box sealing surface 21 has a single tapered surface 211 longer than the pin in the seal surface 11a. With this configuration, in most fastening process, in contact with tapered surface 211 of the tapered surface 111 and the box sealing surface 21 of the pin within the sealing surface 11a slides, after completion of the final stage and the fastening of the fastening , arcuate surface 113 of the pin within the sealing surface 11a contacts the tapered surface 211 of the box sealing surface 21. Arcuate surface 113, since constitute the ends of the pin within the sealing surface 11a, the whole as compared with the conventional pin in sealing surface which consists of a single arcuate surface, a small radius of curvature. Therefore, even if the pin within the sealing surface 11a is inclined with respect to box sealing surface 21, it is possible to reduce the amount of movement of the contact position between the pin within the sealing surface 11a and the box sealing surface 21. As a result, it is possible to further stabilize the sealing performance against pressure.
[0098]
　In the above embodiments, the pin outer sealing surface 14 is located at the end of the steel pipe main body of the pin 10. That is, the screw portion is disposed between the inner seal portion and an outer seal portion. Therefore, the threaded portion can be composed of one stage of the screw, that in comparison with the case of dividing into two stages threaded portion by the outer seal portion, increasing the wall thickness can be used for the threaded portion it can. As a result, fully threaded region number becomes able to suppress a decrease in the tensile strength of the screw connection, it is possible to secure the joint strength.
[0099]
　If the screw width of the threaded joint having a constant screw portion, in the fastening process, since the gap between stabbing flanks and the stabbing flanks of the female thread portion of the male screw portion is small, it tends to burn occurs. In contrast, in the above embodiment, a screw width of the screw portion is changed along the lead. Therefore, between the load surface 23d of the load surface 13d and the internal thread portion 23 of the external thread portion 13, and in the presence of a large gap between the stabbing flanks 23c of the insertion face 13c and the internal thread portion 23 of the external thread portion 13, fastening most of the process is carried out. Therefore, it is possible to prevent the seizure occurs.

The scope of the claims
[Requested item 1]
　A threaded joint for steel pipes,
　and the pin of the tubular,
　has an outer diameter smaller than 8% of the outside diameter of the steel pipe body, a tubular box which pin is fastened to the pin is inserted,
provided with,
　the pin includes
　a pin within the sealing surface provided on the outer peripheral surface of the distal end portion of the pin, than the pin in the sealing surface provided on the distal end side of the pin, the diameter of the inner peripheral surface of the box outer peripheral surface thereof, facing a pin lip portion, comprising, a nose portion having a shape and discontinuous shape of the pin within the sealing surface and having a smaller diameter than
　the Pinshoruda surface provided at the end of the steel pipe main body of the pin,
　the pin lip portion It said provided on an outer periphery of the pin between the Pinshoruda surface, and a male screw portion formed in a taper screw having a dovetail shape,
　front between the said pin lip portion the Pinshoruda surface And the outer peripheral surface the pin outside the sealing surface provided on the pin,
wherein the
　said box,
　in correspondence with the pin in the sealing surface provided on the inner peripheral surface of the box in contact with the pin in the sealing surface in engagement state a box sealing surface,
　in correspondence with the Pinshoruda surface provided on an end face of the box, and the box shoulder surface in contact with the Pinshoruda surface in engagement state,
　in response to the external thread portion provided on an inner periphery of the box , it is composed of a taper screw having a dovetail shape, a female screw portion having an insertion flank surface facing spaced insert flanks and clearance of the male screw portion in the engaged state,
　among the boxes in correspondence with the pin outer sealing surface provided on the peripheral surface, and out of box sealing surface in contact with the pin outer sealing surface in the engaged state
wherein the
　external thread portion and the front The tube axis direction of the distance between the pin in sealing surface D, and the length of the tube axis direction of the nose portion L, and the screw pitch of the male screw portion as P, satisfies the following equation (1) to (3), screw joint.
　≧ P × D 1.5
　(1) L> P
　(2) | D-L | ≦ P (3)
[Requested item 2]
　A tubular threaded joint according to claim 1,
　wherein the pin in the seal surface includes a tapered surface whose diameter decreases toward the distal end side of the pin, and arcuate surface continuous with both ends of each of the tapered surfaces, the a convex surface including,
　the box sealing surface includes a long tapered surface than the pin within the sealing surface, threaded joint.
[Requested item 3]
　A tubular threaded joint according to claim 2,
　the radius of curvature of the arcuate surface is 3 mm ~ 30 mm, screw joint.
[Requested item 4]
　A threaded joint for steel pipes according to any one of claims 1 to 3,
　the pin outer sealing surface is disposed at an end of the steel pipe main body of the pin, a threaded joint.
[Requested item 5]
　A tubular threaded joint according to claim 1, any one of 4,
　the distance D is more than 3 times the thread pitch P, a threaded joint.
[Requested item 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 internal thread portion has a thread width that varies along the lead, screw joint .
[Requested item 7]
　A threaded joint for steel pipes according to any one of claims 1 to 6,
　wherein the gap between the insert flank and the insertion flank of the internal thread portion of the male screw portion is 100μm or less, screws joint.
[Requested item 8]
　A threaded joint for steel pipes according to any one of claims 1 to 7,
　the screw portion composed of the external thread portion and the female screw portion is a single-thread screw or double threaded screw, threaded joint.