JPH10169855A - Screw joints for large diameter oil country tubular goods - Google Patents

Abstract

(57) [Summary] (Modified) [Problem] To provide a threaded joint for a large diameter oil country tubular good. A male screw (12) and a threadless part (1) for forming a seal are provided.
3 is fastened to the box member 21 having the female screw 22 and the threadless portion 23 for forming a seal. Furthermore, the outer diameter of the pipe body is 219 mm or more, the screw shape is trapezoidal, the screw insertion surface has a contact or a small gap in the insertion surface in the fastened state, and the outer diameter of the pin member 11 side screwless portion 13 is the box member 21 side screw. The inner surface of the metal touch is larger than the inner diameter of the non-threaded portion 15, and the metal-touch seal surface is formed by contact fitting of both screwless portions,
A groove 33 is formed in the circumferential direction between the male screw 12 and the non-threaded portion 23 of the pin member. The depth of the groove 33 is within 1/4 of the thickness of the pin member 111, and the radius of curvature at the bottom of the groove 33 is 0.5 mm or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a threaded joint for oil country tubular goods used for exploration and production of natural gas and crude oil existing underground, and more particularly to a threaded joint having a large diameter and used for a casing. It is.

[0002]

2. Description of the Related Art Today, threaded joints have been widely used as a method of connecting oil country tubular goods for exploring natural gas fields and oil fields, which are several thousand meters deep, and for producing natural gas and crude oil. I have. The depths of these wells are typical
It is 2000-3000m, and when it is deep, it exceeds 6000m. In such a well, an oil well pipe connected by a threaded joint is buried deep underground, but only one oil well pipe does not pass through one well. Normally, a large-diameter oil well pipe is first buried vertically to a certain depth and buried therein, and then a small-diameter oil well pipe is sequentially and concentrically inserted into the inside to form a multi-tube structure. The smaller the diameter, the deeper it extends in the ground.

[0003] These oil well pipes not only have different outer diameters but also have significantly different purposes. The outer large-diameter oil well tube is called a casing, and has the role of preventing the pit wall dug deep in the ground from collapsing and also preventing outside earth and sand, groundwater and gas from entering the well. .
On the other hand, the innermost small-diameter OCTG is called tubing,
Used for pumping products.

[0004] In a threaded joint for connecting an oil country tubular good, as described above, the required performance is different depending on the outer diameter.
1) to 4).

1) Ability to withstand the axial tensile force due to the weight of the connected oil country tubular goods or the unexpected axial compressive force acting when the oil country tubular goods including the joints are inserted into the wells.

2) Able to withstand internal pressure due to fluid inside the oil country tubular good or external pressure due to external fluid.

3) It can be used repeatedly several tens of times.

4) Fast and easy screwing and disassembly can be performed on site.

However, in the case of a threaded joint used for an oil country tubular good for a casing, higher performance was not required compared with a threaded joint used for an oil country tubular good for tubing due to the following factors 1) and 2). .

1) Since the connection length is short, the tensile and compressive loads may be small.

2) Since it is used in the underground surface layer, the internal pressure resistance and the external pressure resistance performance need not be high.

However, in recent years, the depth of wells has tended to be deeper, and threaded joints have often been used in harsh environments such as the ocean and polar regions. It has become more and more severe in the threaded joints described above, and it has become necessary to satisfy the same performance as the threaded joints of tubing oil country tubular goods with regard to the performances of 1) to 4).

To cope with such a situation, threaded joints having various structures have been proposed and used. FIG. 5 shows an example.

FIG. 5 is a view showing an example of a conventional threaded joint of the coupling type and the inner surface sealing type. Fig. 5 (a)
5 is a partial longitudinal sectional view and a partial front view showing a main part of the joint structure, and FIG. 5 (b) is a longitudinal sectional view showing a main part of a screw part, a seal part and a torque shoulder part.

In this example, the pin member 11 is formed by providing a male screw 12 on the outer peripheral surface of the end of the oil country tubular good 10. Further, a threadless portion 13 for forming a seal having a tapered shape or a rotating body surface having a large radius of curvature is provided adjacent to the male screw portion 12 at the end thereof. On the other hand, the box member 21 is formed by providing a female screw 22 on the inner peripheral surface at the end of another coupling 20. Further, a taperless screwless portion 23 for forming a seal is provided at the innermost portion (deepest portion) of the tapered portion so as to be adjacent to the female screw portion 22 and correspond to the screwless portion 13.

As shown in FIG. 5 (b), the seal portion 15 connects the pin member 11 and the box member 21 by screwing and fastening.
It is formed by fitting the corresponding surfaces of the two threadless portions 13, 23 into contact with each other. By forming a metal touch seal with the seal portion 15 in this manner, the internal pressure load due to the fluid inside the oil well pipe 10 or the oil well pipe 10
The sealing performance against an external pressure load caused by an external fluid is improved.

Further, as shown in FIG.
A threadless portion 14 for forming a torque shoulder at the tip of a threadless portion 13 for forming a seal 11 and a torque shoulder for forming a torque shoulder at the innermost portion (deepest portion) of the threadless portion 23 for forming a seal of the box member 21. A threadless portion 24 is provided. The threadless portions 14, 24 for forming the torque shoulder are abutted to form the torque shoulder portion 16, so that
The screw fastening is completed.

At the time of abutting in this manner, the screw fastening torque is controlled to an appropriate value so that a high contact pressure that causes excessive plastic deformation does not occur in the seal portion 15.

The thread portion and the seal portion of the oil country tubular good thread joint are usually provided with a fitting allowance (see FIG. 6 described later).
(a)). After manually screwing the joint, it is further screwed in with a special fitting machine by the amount of fitting, so that screw connection, that is, screw engagement is strong, and sealing performance is exhibited by contact fitting. A sufficient contact pressure is generated in the seal portion.

Although the fitting allowance of the threaded portion does not change much even when the diameter becomes large, the fitting allowance of the seal portion increases as the diameter increases, and the difference from the fitting allowance of the threaded portion increases. In the case of a large diameter, the fitting margin of the seal portion must be larger than that of the screw portion for the following two reasons. One is that since the seal portion is located at the tip of the pin member, the bending rigidity of the seal portion becomes smaller as the diameter of the seal portion becomes smaller, so that the seal portion is easily bent even with a small force. Therefore, in order to ensure the contact pressure of the seal portion to be substantially the same as that of the small-diameter and thick-walled one, the fitting margin is increased. Another reason is that as the diameter increases, shape errors such as eccentricity and elliptical shape of the seal portion due to manufacturing errors are more likely to occur. Therefore, these fitting errors are allowed to some extent, and the fitting margin is increased so that a sufficient contact pressure can be secured over the entire peripheral surface of the seal portion.

Although not particularly limited to threaded joints for large-diameter oil country tubular goods, various measures have been taken to improve the axial tensile strength, compression resistance, and sealing performance, which are the basic properties of oil country tubular goods. Has been taken. The main ones thereof include the following a) to c).

A) As disclosed in Japanese Patent Application Laid-Open No. 60-241596, a hook screw is employed to tighten the screw connection to improve tensile strength and sealing performance.

B) As shown in JP-A-6-281061, a trapezoidal screw having a screw insertion surface in contact,
As disclosed in Japanese Patent No. 281059, a trapezoidal screw with a very small screw insertion surface gap is applied to improve compression resistance and sealing performance.

C) As shown in Japanese Patent Application Laid-Open No. Sho 59-170591, the height of the thread at the start end area of the screw engagement is made higher than a specified height, and the engagement of the screw at this start end area is strengthened. With improved tensile resistance.

[0025]

It goes without saying that the above-mentioned prior art screws exhibit excellent performance only when the female screw and the male screw are firmly engaged with each other. With so-called small-diameter tubing size and medium-diameter product line size, the fitting allowance of the screw portion and the fitting allowance of the seal portion are relatively close values, and there is no particular problem regarding the engagement of the screws. However, in the case of a large-diameter casing, the fitting allowance of the seal portion is much larger than the fitting allowance of the screw portion for the above-described reason. Therefore, as shown in FIG. The engagement of the threads is significantly deteriorated, and as a result, the axial load bearing performance of the joint is greatly reduced. Therefore, no effective means has been disclosed yet that can eliminate the poor meshing of the screws due to the difference in the fitting margin as described above.

An object of the present invention is to solve the above-mentioned problems relating to poor meshing of screws, to provide a high-performance large-diameter, which is easy to handle, has excellent axial load-bearing performance, and exhibits stable sealing performance. An object of the present invention is to provide a threaded joint for oil country tubular goods.

[0027]

The gist of the present invention resides in the following threaded joint for large diameter oil country tubular goods.

A threaded joint for a large-diameter oil country tubular good formed by screwing a pin member and a box member together (hereinafter simply referred to as "fastening"), wherein the pin member has no external thread and no thread for forming a seal on the outer peripheral surface of the pipe end. And a box member provided with a female screw and a threadless portion for forming a seal on the inner peripheral surface of another pipe end, and further satisfying the following conditions:

The outer diameter of the oil country tubular good must be a large diameter of at least 8-5 / 8 inch (219 mm).

The screw shape is trapezoidal and the screw insertion surface contacts or has a small gap in the screw insertion surface in the state of being screwed and fastened.

The outer diameter of the non-threaded portion for forming a seal on the pin member side is larger than the inner diameter of the non-threaded portion for forming a seal on the box member side. Being formed.

The groove is formed in the circumferential direction between a male screw provided on the outer peripheral surface of the pipe end of the pin member and a threadless portion for forming a seal.

Further, in the above, the depth of the groove to be engraved is within 1/4 of the thickness of the pin member at the engraved portion, and the shape of the groove bottom is a smooth circular arc having a radius of curvature of 0.5 mm or more. It is desirable that

A desirable upper limit of the above outer diameter is about 14 inches in consideration of a practical range. Further, "contact" means that there is no gap in the screw insertion surface, and "small gap" means that the gap in the screw insertion surface is about 0.06 mm or less and is very small.

Further, it is desirable that the above "outer diameter" be larger than the above "inner diameter" in a range of about 0.4 to 1.5 mm.

The joint of the present invention can be applied to the case of the inner surface sealing system regardless of the coupling system or the integral system.

The present inventors conducted a basic study in detail about the actual state of engagement of the threads inside the joint when the axial load was applied when the threaded joint for oil country tubular goods for casing use was fastened.
The following new findings (a) and (b) were obtained.

(A) A coupling type large diameter oil country tubular good threaded joint having a configuration as shown in FIG. 5, wherein the thread shapes are the following two types (a) and (b), A total of four types were prepared under the following two conditions (1) and (2) in terms of the manufacturing tolerance of the combination of the fitting allowance of the screw part and the fitting allowance of the seal part.

(A) A trapezoidal screw having a clearance in the screw insertion surface when fastened and having both the screw load surface and the bottom surface in contact.

(B) A trapezoidal screw having a gap between the screw top surface and the bottom surface when fastened, and having both the screw load surface and the insertion surface in contact.

(1) The screw fitting allowance and the seal fitting allowance are maximum and minimum, respectively.

(2) The screw fitting allowance and the seal fitting allowance are minimum and maximum, respectively.

For these four types of threaded joints,
After fastening with the specified torque, the yield strength of
%, And the joints were disassembled, the torque required for disassembly was compared, and the state of plastic deformation of the torque shoulder was observed.

As a result, the torque required for disassembly is
For both types of trapezoidal screws (a) and (b),
Under the manufacturing tolerance conditions, the case (1) was larger than the case (2), that is, less loose, and the amount of plastic deformation of the torque shoulder portion was smaller.

(B) Next, using the elasto-plastic finite element method, a simulation analysis on the fastening of a threaded joint for a large diameter oil country tubular good was performed. As a result, it was found that the bottom, the top, and the load surface of the several threads near the seal portion on the tip end side of the pin member were not in contact with each other, that is, not engaged.

FIG. 6 is a longitudinal sectional view of a main part showing a state of fitting at a seal part and a screw part near the seal part in the conventional threaded joint as described above. Fig. 6 (a) shows the state before fastening, that is, the state after processing based on the design, and Fig. 6 (b)
Is the state after fastening.

In the state when processing based on the design,
As shown in FIG. 6 (a), a threadless portion 13 for forming a seal,
The fitting margin 31 of 23 is considerably larger than the fitting margin 32 of the screws 12 and 22.

At the time of fastening, in order to secure the sealing performance, the sealing is performed so that the sealing surfaces of the threadless portions 13 and 23 are brought into contact with each other. However, because the fitting allowance 31 is large,
As shown in FIG. 6 (b), a large contact reaction force is generated in the seal portion 15 in the direction indicated by the deformation direction 25, and the distal end side of the pin member 11 is largely pushed inward in the oil well pipe 10 to reduce the diameter. On the other hand, the side of the box member 24 is also pushed outward to expand the diameter. At this time, since the absolute amount of the diameter reduction deformation of the pin member 11 and the diameter expansion deformation of the box member 24 increases, the screw portions 12 and 22 near the seal portion are affected, and the male screw 12 and the female screw
Acting in the direction of peeling off the screw 22, a gap is generated between the bottom, top and the load surface of the several threads near the seal portion 15, so that they do not contact each other.

It has been found that such a phenomenon when a screw joint having a large fitting margin 31 provided in the seal portion 15 is fastened causes the screws not to mesh as described above.

The inventors of the present invention have made the present invention based on the following technical idea in consideration of the above-mentioned new knowledge on the actual state of screw engagement in the vicinity of a seal portion of a threaded joint for a large diameter oil country tubular good.

The reason why the meshing of the screws is defective is that the sealing portion is affected by a large fitting margin as described above. Therefore, by preventing or reducing the influence of the fitting allowance from propagating to the screw portion by some structural improvement, it is possible to reduce poor engagement of the screw.

FIG. 1 is a view for explaining a deformed state near the seal portion. FIG. 1A shows a deformed state near the seal on the pin member side after fastening a conventional threaded joint for a large-diameter oil country tubular good. FIG. As shown in the figure, the tip of the pin member 11 is
5 'is forcibly reduced in diameter by the deforming material 36. In the screw start end region 17 of the screw portion adjacent to the seal portion 15 ', since the bending rigidity is continuous with the seal portion, the screw start end region 17 is bent due to the reduction in diameter of the seal portion.
Deformation becomes large.

FIG. 1B is a schematic view showing a deformed state in the vicinity of the seal portion in the case of the configuration of the present invention, in which a groove is formed in the outer surface on the tip end side of the pin member in the circumferential direction. . As can be seen from the figure, the deformation amount 36 'of the seal portion 15' which is reduced in diameter by the large fitting allowance of the seal portion is the deformation amount 36 'of the seal portion 15' without the groove shown in FIG. Is almost the same as However, by providing the groove 33, a discontinuous portion of bending rigidity is formed between the seal portion 15 'and the screw start end region 17,
As a result, the effect of the large diameter reduction deformation of the seal portion 15 ′ is reduced from propagating to the screw start end region 17. For this reason, the amount of deformation of the screw start end area 17 due to the diameter reduction of the seal portion is smaller than that of FIG.
It is dramatically smaller than the conventional one shown in (a). As a result, as shown in FIG. 6 (b), the screw portion is peeled off, the amount of deformation in the direction in which the screw is poorly connected is reduced, and the number of threads with insufficient meshing is reduced.

By forming a groove having the above-described action between the male screw and the threadless portion of the pin member, even in the case of a threaded joint having a large fitting allowance in the seal portion, the fastening is performed. In this case, it is possible to reduce the influence of the diameter reduction deformation caused by the large fitting allowance on the tip end side of the pin member on the screw portion, and it is possible to improve the screw engagement state.

[0055]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A configuration example of a threaded joint according to the present invention will be described with reference to FIG. FIG. 2 is a longitudinal sectional view of a main part showing a configuration example of the threaded joint of the present invention. The example of FIG. 2 shows a coupling type and inner surface sealing type joint in which the number of grooves to be engraved is one. FIG. 2 (a) shows a case where the shape of the groove is a U-shape, and FIG.

The screw joint shown in FIG. 2 comprises a pin member 11 and a box member 21 as in the case of FIG. 5, and is connected by fastening. The pin member 11 is provided with a male screw 12 on the outer peripheral surface of the end of the oil country tubular good 10 and a screwless portion 13 for forming a seal on the tip side of the male screw 12. Box member 21 is a separate tube,
That is, the inner peripheral surface at the end of the coupling 20 is provided with a female screw 22 and a threadless portion 23 for forming a seal at the innermost (deepest) side of the female screw 22.

The outer diameter of the oil country tubular good 10 is a large diameter of 8-5 / 8 inch or more. Medium diameter with outer diameter less than 8-5 / 8 inch,
In a small-diameter oil country tubular good, the screw fitting allowance and the seal fitting allowance are relatively close to each other, so that poor meshing in the screw start end region 17 due to the seal fitting allowance does not pose a practical problem. Therefore,
This is because even if the present invention is applied, no significant effect can be expected. The desirable upper limit of the outer diameter is about 14 inches as described above.

The seal portion 15 connects the pin member 11 and the box member 21 by fastening, and the two screwless portions 13 and
It is formed by bringing the corresponding sealing surfaces of the 23 into contact with each other. The formed seal surface is a so-called metal touch. In order to ensure the sealing performance,
The outer diameter of the threadless portion 13 for forming the seal on the side is made larger than the inner diameter of the threadless portion 23 for forming the seal on the box member 21 side.

The above “outer diameter” is more than the above “inner diameter” by 0.
It is desirable to increase the size in the range of about 4 to 1.5 mm.

The threadless portion 13 for forming the seal of the pin member 11
A threadless portion 14 for forming a torque shoulder and a screwless portion 24 for forming a torque shoulder are provided on the innermost (deepest) side of the threadless portion 23 for forming a seal of the box member 21 at the tip of the box. . The torque shoulder portion 16 is formed by abutting the corresponding surfaces of the screwless portion 14 and the corresponding surfaces of the torqueless portion 24 with each other, and the fastening is completed by forming the torque shoulder.

Further, a groove 33 is formed in the circumferential direction between the external thread 12 provided on the outer peripheral surface of the end of the tube 10 of the pin member 11 and the threadless portion 13 for forming a seal. The reason for limiting the engraving position of the groove 33 in this way is as follows.

That is, as described above with reference to FIG. 1B, the intention of the present invention is that, in the case of a threaded joint for a large-diameter oil country tubular good, the number of threads in the vicinity of the seal is poor due to a large fitting margin. Is to be prevented by the effect of the groove 33. In other words, if the outside diameter of the oil country tubular good is not as large as in the above range, and the difference in the fitting allowance between the seal portion and the screw portion is not so large, or the screw portion and the seal portion If they are not adjacent,
This is because the effect of engraving such a groove cannot be expected so much. The effect of the groove as described above is remarkable at the engraving position determined by the present invention.

As described with reference to FIG. 1B, the deflection angle 35 'at the tip of the pin member 11
It is larger than the case without. Therefore, the contact pressure distribution on the seal surface changes. That is, the peak surface pressure slightly increases, and conversely, the average surface pressure slightly decreases. The degree of change in the contact pressure distribution on the seal surface depends on the size of the groove, the engraving position, and the fitting allowance. Does not happen.

In the case where a large fitting allowance is provided in the seal portion, the engagement between the screws in the vicinity of the seal portion is improved by the action of the groove as described above, so that the tensile resistance and the compression resistance are significantly increased. Stable sealing performance can be secured.

In order to sufficiently exert the effect of the groove and the performance of the joint of the present invention, and to avoid a secondary adverse effect due to the formation of the groove, the size and shape of the groove which is practically desirable is determined by itself.

The desired depth of the groove 33 shown in FIG. 2 is desirably within one-fourth of the thickness of the pin member 11 at the carved portion. The reason why the desirable upper limit of the depth of the groove 33 is set to 1/4 of the thickness of the pin member 11 at the engraved portion is as follows. That is,
Normally, a torque shoulder portion 16 is formed between the tip end of the pin member 11 and the innermost (deepest) threadless portions 14 and 24 of the box member 21, and the reaction force of the torque shoulder portion 16 when fastening is reduced. By being transmitted to the screw 12 as a tightening force, the screw is connected. Therefore, when the depth of the groove 33 exceeds the desired upper limit, the thickness of the engraved portion becomes thinner, the stress value passing through the cross section of the engraved portion increases, and the groove 33 is engraved immediately near the seal portion 15. Therefore, the contact pressure on the sealing surface is significantly reduced. The desirable lower limit of the depth is about 1/8 of the thickness of the pin member 11 at the engraved portion.
In order to sufficiently exhibit the effects of the present invention, the depth of the groove is preferably as deep as possible.

The desired shape of the bottom of the groove 33 is a smooth arc shape having a radius of curvature of 0.5 mm or more, that is, a curved surface having a curvature smoothly connected from the side wall of the groove 33. The reason for this is that if the groove bottom has a small radius of curvature of less than 0.5 mm or a small radius or an acute angle, stress concentration will occur at the groove bottom, and the groove bottom is likely to be the starting point of cracking due to fatigue and corrosion. Because it becomes. The desirable upper limit of the radius of curvature is not particularly limited.

The axial width of the groove 33 is not particularly limited, but the desired minimum width is naturally determined by the minimum value of the radius of curvature described above, and the maximum width is, of course, between the male screw 12 and the sealless screwless portion 13. Is the distance between

The number of the grooves 33 is not particularly limited as long as a male screw and a threadless portion for forming a seal make a pair, and a joint of the inner surface sealing type having a structure as shown in FIG. do not do. However, in order to obtain the effect of the groove described above and the desired performance of the joint of the present invention, it is necessary to provide one between the thread and the seal.
Individual is enough.

In the joint according to the present invention, the screw shape is limited to a trapezoidal shape, and the screw insertion surface is limited to a contact or a small gap in a fastened state. This “contact” means that there is no gap between the screw insertion surfaces, and “there is a small gap” means that the range of the gap between the screw insertion surfaces is very small, about 0.02 to 0.06 mm.

Originally, a high-performance screw exhibits excellent performance only when the screws are sufficiently engaged with each other. If a poor engagement occurs, the function of the high-performance screw is significantly reduced. According to the joint having the screw having the configuration of the present invention, the meshing of the screw is strengthened, and the excellent performance inherent in the screw is fully exhibited.

FIG. 3 is a longitudinal sectional view of a main part showing an example of a thread shape and a contact state in the joint of the present invention. FIG.
(a) has a small gap in the screw insertion surface and when there is no contact,
FIG. 3B shows the case where the screw insertion surface is in contact.

In the case of FIG. 3A, the shape of the male screw 12 is trapezoidal,
There is a gap 45 on the insertion surface 43 side, and the insertion surface 43 is in a non-contact state. Further, there is a gap 45 at the screw top 42, and the screw load surface 41 and the bottom 44 are in contact. In the case of FIG. 3B, the shape of the male screw 12 is trapezoidal, there is no gap on the insertion surface 43 side, and the insertion surface 43 is in contact. Further, there is a gap 45 between the screw top 42 and the bottom 44, and the screw load surface 41 is in contact.

The joint of the present invention can be applied not only to the coupling system but also to an integral system and an inner surface sealing system as shown in FIG. In the case of the integral system, the concept and the embodiment of the coupling system described above may be used as a basis.

With the joint of the present invention as described above, even in a threaded joint for a large-diameter oil country tubular good, the state of poor meshing of the screw near the seal portion is improved, the tensile and compression resistance are improved, and the large-diameter oil country tubular good. Since a large margin for fitting the seal portion can be effectively utilized, stable sealing performance can be achieved.

[0076]

EXAMPLES In order to compare with the comparative example, all the joints to be tested were of the coupling type having the configuration shown in FIG. 5 and the inner surface sealing type. Table 1 shows the conditions of the test joints of the present invention and comparative examples.

[0077]

[Table 1]

At this time, the conditions were the same for all the test joints until the following fastening.

[Size] Outer diameter of oil country tubular good: 273.05 mm (10-3 / 4 inch) Thickness of oil country tubular good: 12.57 mm Outer diameter of coupling: 293.54 mm Mesh of pin member at groove cut position thickness: 8.57Mm [subjected試継hand material] carbon steel (yield strength: 56.2 kgf / mm ²⁾ [the shape of the seal portion] seal taper: 1/10 seal length: 6.5 mm seal Hamagodai (radial) : 0.8mm [Tightening conditions] Torque: 3500 kgf · m The following two types of screw shapes were used: Type 1 and Type 2.

[Type 1] Thread shape: Same as in FIG. 3 (a) Thread pitch: 6.35mm (four inches) Thread height: 1.982mm Thread taper: 1/18 Thread fitting allowance (radial direction): 0.272mm Thread clearance: 0.06mm [Type 2] Thread shape: Same as Fig. 3 (b) Thread pitch: Same as type 1 Thread height: Same as type 1 Thread taper: Same as type 1 Thread fitting margin ( (Radial direction): Same as type 1 The following composite load test was performed on these test joints, and the performance was evaluated based on the point of occurrence of leakage from the joints and the state of plastic deformation of the torque shoulder portion.

[Composite Load Test] FIG. 4 is an iso-stress diagram showing composite load conditions. After the fastening, a load was repeatedly applied according to the following procedures (1) to (4) according to FIG.

(1) After applying a tensile force in the axial direction such that a stress equivalent to 80% of the yield strength of the oil country tubular good is applied to the entire test body including the joint, the same stress as above is generated. Apply internal pressure and hold for 15 minutes ((o) → (a) shown in Fig. 4)
→ (b)).

(2) While applying an internal pressure so that a stress equivalent to 80% of the yield strength of the oil country tubular good is always applied to the entire test body including the joint, the yield corresponds to 50% of the yield strength. An axial compressive force that generates a stress is applied and held for 15 minutes ((b) → (c) shown in FIG. 4).

(3) Further, while applying an internal pressure so that a stress equivalent to 80% of the yield strength of the oil country tubular good is always applied to the entire test body including the joint, 80% tension is maintained for 15 minutes. A load of 50% compression and holding for 15 minutes is repeated five times in total ((c) ← → (b) shown in FIG. 4).

(4) Finally, the compression force and the internal pressure are simultaneously unloaded ((c) → (o) shown in FIG. 4).

In the above test, the time when the leak occurred was recorded, and after the test was completed, the joint was disassembled and the state of plastic deformation of the torque shoulder was observed. Table 2 shows the results.

[0087]

[Table 2]

As shown in Table 2, all of the examples of the present invention
It turns out that it has excellent tensile and compression resistance.

From the above results, it is clear that the same effect can be obtained even when the joint of the present invention is applied to the integral system and the inner surface sealing system.

[0090]

According to the present invention, it is possible to obtain a high-performance threaded joint for a large-diameter oil country tubular good having a strong screw engagement, excellent tensile and compression resistance, and stable sealing performance.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a deformed state near a seal portion.
(a) is a schematic diagram showing a deformed state near the seal on the pin member side after fastening the conventional large diameter oil country tubular goods threaded joint,
(b) is a schematic diagram showing a deformed state in the vicinity of the seal portion when a groove is engraved in the circumferential direction on the outer surface on the distal end side of the pin member in the configuration of the present invention.

FIG. 2 is a longitudinal sectional view of a main part showing a configuration example of a threaded joint of the present invention. (a) shows the case where the shape of the groove is U-shaped, and (b) shows the case where the shape is also an arc.

FIG. 3 is a longitudinal sectional view of a main part showing an example of a screw shape and a contact state in the joint of the present invention. (a) is the case where the screw insertion surface is not in contact, and (b) is the case where it is also in contact.

FIG. 4 is an iso-stress diagram showing a combined load condition in the example.

FIG. 5 is a diagram showing an example of a conventional threaded coupling of a coupling system. (a) is a partial longitudinal sectional view and a partial front view showing a main part of the joint structure, and (b) is a longitudinal sectional view showing a main part of a thread part.

FIG. 6 is a longitudinal sectional view of a main part showing a state of fitting in a seal part and a screw part near the seal part in a conventional threaded joint. (a) is the state before the conclusion, and (b) is the state after the conclusion.

[Explanation of symbols]

10: oil well pipe, 11: pin member, 12: male screw, 1
3, 23: Screwless part for forming seal, 14, 24: Screwless part for forming torque shoulder, 15, 15 ': Sealed part, 1
6: Torque shoulder part, 17: Screw start end area, 20: Coupling, 21: Box member, 22: Female screw,
25: Deformation direction due to seal fitting allowance, 31: Fitting allowance for seal part, 32: Fitting allowance for screw part, 33: Groove, 35, 35 ': Deflection angle, 36, 36': Depends on seal fitting allowance Deformation amount, 41: Screw load surface, 42: Screw top, 43: Screw insertion surface, 4
4: Screw bottom, 45: Screw clearance

Claims (2)

[Claims] 1. A threaded joint for a large-diameter oil country tubular good formed by screwing a pin member and a box member together, wherein the pin member has an external thread and a threadless portion for forming a seal on the outer peripheral surface of the pipe end,
A threaded joint for a large diameter oil country tubular good, characterized in that the box member has a female screw and a threadless portion for forming a seal on an inner peripheral surface of another pipe end, and further satisfies the following conditions. The outer diameter of the oil country tubular good shall be 8-5 / 8 inch (219 mm) or more. The screw shape must be trapezoidal and the screw insertion surface should be in contact with the screwed state or there should be a small gap in the screw insertion surface. The outer diameter of the threadless portion for forming the seal on the pin member side is larger than the inner diameter of the threadless portion for forming the seal on the box member side, and the sealing surface of the metal touch is formed by the contact fitting of the both threadless portions. That you are. The groove is engraved in the circumferential direction between a male screw provided on the outer peripheral surface of the pipe end of the pin member and a threadless portion for forming a seal. 2. Under the above conditions, the depth of the groove to be engraved is within 1/4 of the thickness of the pin member at the engraved portion, and the shape of the groove bottom is a smooth circle having a radius of curvature of 0.5 mm or more. The threaded joint for a large diameter oil country tubular good according to claim 1, wherein the threaded joint is formed in an arc shape.