JPH08247351A - Oil well pipe threaded joint - Google Patents

Abstract

(57) [Summary] [Purpose] It has excellent airtightness and can be used repeatedly,
Develop a threaded joint for oil country tubular goods without the risk of seizure. [Structure] The unthreaded part for forming the seal part has a two-step taper structure, and the taper on the pin tip side is 1/10 or more and less than 1/4,
The taper on the pin root side should be 1/4 or more and 1 or less and larger.

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 an oil country tubular good used for exploration and production of natural gas or crude oil produced underground, and is particularly suitable for use in wells in the ocean. The present invention relates to a fitting suitable for use in pumping underground deposits such as high-pressure groundwater, mud, and gas layers.

[0002]

2. Description of the Related Art Today, threaded joints are widely used as a technique for connecting oil well pipes used for exploration and production in natural gas fields, crude oil fields, etc. having a depth of several thousand meters. For such oil country tubular goods threaded joints, a pin portion is formed at one end of the pipe, a box portion is formed at the other end, and an integral system in which the pipes are directly connected, and a coupling in which two box portions are formed on both sides There is a coupling system in which this is connected to a pipe having pin portions formed at both ends.

No matter which method is used for these threaded joints, 1) they can withstand the axial tensile force due to the weight of the connected pipes, and 2) they can withstand the internal pressure of the fluid inside. Performance is required such as obtaining, 3) being able to withstand external pressure from an external fluid or earth and sand, and 4) being able to be used repeatedly several tens of times.

In recent years, the depth of wells has tended to increase,
In addition, in many cases, it is used under a special environment such as on the ocean or in polar regions, and the above-mentioned required performance becomes more severe. By the way, a threaded joint as described above is provided with a threaded portion and a non-threaded portion, and in particular, a non-threaded portion is provided with a seal portion and a torque shoulder portion. By contacting with, the sealability, the seizure resistance, and the fastening force are secured. Therefore, many proposals have been made regarding the structure of the seal portion and the torque shoulder portion of the oil country tubular goods joint in response to the above-described performance improvement.

As an example thereof, an example of a coupling type oil well pipe joint is shown in FIG. That is, as shown in FIG.
In the example shown in (b), the tapered seal-forming threadless portion 13 at the tip of the pin portion 11 having the male thread 12 provided at the end of the steel pipe 10 and the female thread 22 provided inside the coupling 20 are provided. The seal portion is formed by bringing the tapered seal-forming screwless portion 23 inside the box portion 21 that it has into contact. This is because the metal seal is configured in this contact region to improve the airtight performance against an internal pressure load due to the fluid inside the oil well pipe or an external pressure load due to the fluid outside the pipe.

Further, as can be seen from FIG. 1 (b), the torque shoulder forming screwless portion 14 further at the tip of the seal forming screwless portion 13 of the pin portion 11 and the seal forming screw of the box portion 21. The torque shoulder portion is formed by abutting the torque shoulder forming screwless portion 24 located further inward of the absence portion 23. This is because the engagement torque is controlled to an appropriate value so that the contact surface pressure that causes excessive plastic deformation is not generated in the seal portion by abutting these portions.

In the example shown in FIG. 1, the seal-forming unscrewed portions 13 and 23 have a single-step taper shape. In the prior art, the taper amount is as shown in Japanese Patent Publication No. 27557/1990. Many are specified in the range of about 1/16 to 1/10.

Further, it is not a straight taper but a Japanese patent publication 2-
As shown in Japanese Patent No. 31271, the non-threaded portion 13 for forming a seal on the pin side is formed into a spherical surface having a relatively large radius of curvature, and as shown in Japanese Patent Publication No. 59-44552, The tip unthreaded part is composed of two shoulder-shaped shoulders and a conical surface for seal formation in the middle, and the shoulder on the pin base side has torque shoulder performance and high airtightness. However, even in these cases, the seal portion has a single shape.

[0009]

As described above, in the conventional one-stage seal shape, the one having the taper of 1/16 to 1/10 is generally used, but the taper amount is small. In the one-stage tapered seal part, when an axial tensile force acts on the pipe body, the force in the direction to separate the unthreaded part for forming the seal part that is in metal-to-metal contact is small, so it is airtight There is an advantage that there is little deterioration in performance. In addition, even when internal pressure is applied, the internal pressure acts to press the unthreaded part for forming the seal part at the tip of the pin side against the unthreaded part for forming the seal part on the box side. have.

However, when external pressure is applied, the force exerted by the operating external pressure that has penetrated to the dope reservoir immediately before the unthreaded portion for forming the seal portion is large in the direction to open the unthreaded portion for seal formation, so that the airtight performance is high. May decrease, and in the worst case, leakage may occur. In addition, since the amount of feeding the pin portion is increased in order to ensure a predetermined airtight performance, it is necessary to unnecessarily lengthen the seal forming screwless portion, and seizure easily occurs at this portion, and at the same time the material There is a problem that it causes an increase in cost.

Also, in the case of a shape having two shoulder portions and a seal forming portion in the middle thereof as shown in Japanese Patent Publication No. 59-44552, there is a gap in the shoulder portion at the tip of the pin. Since it does not play the role of the torque shoulder portion, it is functionally similar in shape to the conventional seal portion having one shoulder portion forming portion and one seal portion forming portion. Therefore, the same problem as described above also occurs in a joint having such a seal portion shape.

On the other hand, when the non-threaded portion 13 for forming the seal portion on the pin side is spherical as shown in FIG. 2, a high contact pressure can be obtained at the contact portion, so that good airtightness can be obtained. Further, by making the taper of the unthreaded portion 23 for forming the seal portion on the box side small like the seal portion having the above-mentioned one step taper, good airtightness can be obtained even when tension or internal pressure acts. Further, even when external pressure is applied, the contact pressure at the contact portion is high, and therefore the airtight performance is not significantly deteriorated.

However, since a high contact pressure is generated in a very narrow contact width, excessive plastic deformation may occur in the contact portion, and there is a problem that it cannot withstand repeated use of a dozen or more times.

[0014]

The object of the present invention is to solve the above-mentioned problems of the prior art, to provide excellent airtightness, to allow repeated use, and to prevent seizure from occurring in an oil well. It is to develop a threaded joint for pipes.

[0015]

As a result of various researches and developments, the present inventors have obtained the idea that the above-mentioned problems can be effectively achieved by improving the contact form of the seal portion found in a threaded joint. The inventors have completed the present invention, knowing that the problem of the above-mentioned prior art can be solved by providing two-step taper on the unthreaded portion for seal formation.

That is, the gist of the present invention is that
The seal forming screwless part and the torque shoulder forming screwless part provided on the pin part having the male screw and the seal forming screwless part and the torque shoulder forming screwless part provided on the box part having the female screw are respectively brought into contact with each other. Alternatively, in the oil well pipe threaded joint in which the seal portion and the torque shoulder portion are formed by abutting, the seal forming unthreaded portion has a two-step taper structure, and the taper on the pin tip side is smaller than the taper on the pin base side. This is a threaded joint for oil country tubular goods.

According to a preferred embodiment of the present invention, in the two-step taper structure of the unthreaded portion for seal formation, the taper on the pin tip side is 1/10 or more and less than 1/4 and the taper on the pin base side is 1 /
4 or more and 1 or less.

[0018]

Next, the operation of the present invention will be described in detail together with the reasons for limiting the above-mentioned constituent elements. First, in the present invention, the seal forming portion of the joint has a two-step taper structure, and the taper on the pin tip side is made smaller than the taper on the pin root side in order to reduce both the tensile force acting on the joint and the internal pressure and the external pressure. This is to improve the airtightness of the seal forming portion.

That is, as shown in FIG. 3, when a tensile force is applied to the joint in the axial direction, an axial force F for pulling out the pin is generated in the unthreaded portion 13 for forming the seal on the pin side. F is decomposed into a component F · sin α (α is the angle between the surface of the unthreaded portion and the axis) perpendicular to the surface of the unthreaded portion for seal formation and a horizontal component F · cos α.

Of these, the pinless seal forming screwless portion 13
Force to separate the unit from the unthreaded part 23 on the box side F ・ sin
α decreases as the angle α, that is, the taper of the unthreaded portion for seal formation is smaller.

When an internal pressure is applied to the joint, as shown in FIG. 4, a radial force P ₁ is generated on the pin-side unthreaded portion 13 for forming seal as a result of the acting internal pressure. This force P ₁ is decomposed into a force P ₁ · cos α in the vertical direction and a force P ₁ · sin α in the horizontal direction with respect to the surfaces of the seal forming unscrewed portions 13 and 23.

Of these, the pinless seal forming screw-less portion
Horizontal force P ₁ to slide 13 in the direction of loosening
sin α becomes smaller as α, that is, the taper of the seal forming unthreaded portions 13 and 23 becomes smaller.

Further, as shown in FIG. 5, the external pressure that has penetrated to the dope reservoir 27 immediately before the seal forming unscrewed portions 13 and 23 acts in the direction in which the dope reservoir 27 is inflated, particularly in the thin portion. Strong force P ₀ that pushes in the radial direction
Occurs.

Of this force P ₀ , there is no screw for seal formation
The force to open the mouths 13 and 23 is
Is a component P ₀ · cos α'perpendicular to the surface of, and the larger the inclination α'of the unthreaded portion is, the more P ₀ · cos α '
Becomes smaller.

For the above reasons, the seal forming portion is the non-screw forming portion 13 for the seal forming on the pin base side where the external pressure enters.
The taper of 23 is large, and the taper of the unthreaded portions 13 and 23 for forming seals on the tip end side of the pin has a two-step taper structure that is smaller than that. Next, the reason for limiting the taper range of each unthreaded portion for seal formation in the preferred embodiment of the present invention will be described.

No-screw portion 13 for forming a seal on the tip side of the pin,
The lower limit of the taper of 23 is set to 1/10 or more in order to prevent seizure and reduce the material cost. That is,
If the taper of this portion is too small, the amount of the pin portion fed in to ensure a predetermined contact pressure becomes large and seizure easily occurs. Furthermore, the seal forming unthreaded portion must be unnecessarily long. This is because it will be eliminated and the material cost will be increased.

On the other hand, the upper limit of the taper of this portion is set to less than 1/4, in order to distinguish the airtightness against the internal pressure from the taper that is too large and the taper provided on the pin root side.

Next, the upper limit of the taper of the non-screw forming parts 13 and 23 on the pin root side is set to 1 unless the two-step non-screw forming part is provided within a limited thickness range. This is because there is naturally a limit to the taper size.Because a certain contact pressure is generated in this seal-less screw part, the tightening torque increases when the joint is fastened, and the seizure occurs on the screw surface. Is more likely to occur and it becomes impossible to withstand repeated use for several tens of times. Further, the lower limit of the taper of this portion is set to 1/4, as described above, in order to distinguish it from the taper on the tip side of the pin, if the taper is too small, the airtightness against external pressure is deteriorated.

The lengths and proportions of the tapered regions on the pin tip side and the pin root side are not limited as long as they maintain a predetermined contact pressure and do not affect the airtightness against the internal pressure and the external pressure, respectively. Therefore, for example, the boundary of each taper region can be set at the midpoint between the seal forming unscrewed portions 13 and 23, and the length ratio of each taper region can be changed depending on the external pressure and the contact pressure. Good. Next, the working effects of the present invention will be described more specifically by way of examples.

[0030]

EXAMPLE FIG. 6 shows an example of the shape in the vicinity of the seal portion according to the present invention. In this example, in the joint having the shape of FIG. 1, the seal forming screwless portions 13 and 23 are changed to a two-stage taper structure as shown in FIG. 6, and the screwless portions 15 and 16 and the screwless portion 2 respectively.
The taper of the unthreaded portions 15, 25 on the pin tip side is made smaller than the taper of the unthreaded portions 16, 26 on the pin root side.

In FIG. 6, the regions of the unscrewed portions 16 and 26 have a large taper in order to improve the airtightness against external pressure (for example, pressure from the ground). External pressure has entered the dope reservoir 27. External pressure must be prevented from entering the pipe interior by the areas of the unthreaded parts 16, 26. Further, the taper is reduced in the regions of the unscrewed portions 15 and 25 in order to enhance the airtightness with respect to the internal pressure (for example, hydraulic pressure and steam pressure). Oil inside the pipe does not have screws for torque shoulder formation
It leaks through a gap such as 14th magnitude. Therefore, the screwless part 1
The area of 5, 25 is sealed to prevent leakage. next,
The effects of the present invention will be shown based on examples.

As a coupling type joint having the structure shown in FIG. 1, various joint specifications of the seal portion were changed as shown in Table 1 and trial production was performed. At this time, the following conditions were the same for all joints. Pipe body outer diameter: 177.8 mm, Pipe body wall thickness: 11.51 mm, Coupling outer diameter: 194.49 mm, Pipe and coupling material: L80 carbon steel (yield strength 5
6.2kgf / mm ² ) Screw shape: Trapezoidal screw, Screw pitch: 5.08mm, Screw taper: 1/18, Thread height: 1.575 mm, Torque shoulder angle: 15 °, Seal length: 10.3mm (1st step) (Seal length 6.5 mm, second stage seal length 3.8 mm) However, in case of only one stage seal, Table 1 shows the seal length.

The length of the first-stage seal is set to 6.5 mm, but this is usually about this regardless of the outer diameter of the pipe. Also 2
The length of the step seal is set to 3.8 mm, but this is usually this level regardless of the pipe outer diameter, and if it is too long, seizure may occur when connecting the pipe and the joint.

[0034]

[Table 1]

These joints were tested in the following tests to evaluate their performance. Repeated fastening test: Lubrication grease was applied to the threaded portion and the non-threaded portion, the joint was fastened and removed, and this was repeated until seizure occurred on the threaded portion. The maximum number of repetitions was 10 times.

Simple external pressure test: After fastening the joint, external pressure was applied and the pressure at which breakage or leakage of external pressure occurred was recorded.

Combined load test: After fastening the joint, after applying a tensile force in the axial direction such that a stress equivalent to 95% of the yield strength is generated in the pipe body, it is equivalent to 80% of the yield strength in the pipe body Internal pressure was applied so that stress was generated, and leakage of internal pressure was investigated. The above test results are summarized in Table 2.

[0038]

[Table 2]

From the results shown in Table 2, it can be seen that in the comparative examples, a failure occurred in any of the tests, but the joint of the present invention showed good results in all the tests. By the way, although the case of the coupling method has been described in the above-described embodiments, it is apparent that the same effect can be obtained by the technique of the present invention even in the case of the integral method.

[0040]

EFFECTS OF THE INVENTION The oil well pipe threaded joint according to the present invention has excellent airtightness against both internal pressure and external pressure, and its airtightness does not deteriorate even under tensile load. It can be used satisfactorily.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a configuration example of a coupling type threaded joint for oil country tubular goods, FIG. 1 (a) is an overall view thereof, and FIG.
Is a partially enlarged view of FIG.

FIG. 2 is an explanatory view showing a seal forming portion having a spherical threadless portion.

FIG. 3 is an explanatory diagram showing how the axial tensile force F is shared on the surface of the seal forming unthreaded portion.

FIG. 4 is an explanatory diagram showing how the radial force P ₁ is shared on the surface of the seal forming unthreaded portion.

FIG. 5 is an explanatory diagram showing how the force P ₀ due to external pressure is shared at the end of the seal forming screwless portion.

FIG. 6 is an explanatory view showing a shape of a two-step taper structure of a seal forming screwless portion.

[Explanation of symbols]

 10: Pipe body 11: Pin part 12: Male screw 20: Coupling 21: Box part 22: Female screw 13, 23: No screw for forming seal 14, 24: No screw for forming torque shoulder 15, 25: Two-stage seal Forming pin tip side screwless part 16, 26: Two-stage seal forming pin root side screwless part 27: Dope reservoir part

Claims (2)

[Claims] 1. A seal forming screwless portion and a torque shoulder forming screwless portion provided on a pin portion having a male screw, and a seal forming screwless portion and a torque shoulder forming screwless portion provided on a box portion having a female screw. In a threaded joint for oil country tubular goods in which a seal portion and a torque shoulder portion are formed by making contact with or abutting each other, the seal forming unthreaded portion has a two-step taper structure, and the taper on the pin tip side is the pin root Threaded joint for oil country tubular goods characterized by being smaller than the taper on the side. 2. The threaded joint for oil country tubular goods according to claim 1, wherein the taper on the pin tip side is 1/10 or more and less than 1/4 and the taper on the pin root side is 1/4 or more and 1 or less.