JPH09152067A - Threaded joint for oil well pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain high-degree airtightness and clearance corrosion resistance suitable in searching and collecting deposits under high pressure, or those containing highly corrosive impurities, such as gas and oil. SOLUTION: This threaded joint for an oil well pipe has an inner-surface shoulder forming sealing parts and torque shoulder parts. (a) The effective diameter of a pin side seal forming surface 13 is greater than that of time box side one. (b) The difference θ of inclination between the pin-and box-side torque shoulder forming surface meets 0.5 deg.<=θ<=4.0 deg., with θ=θ2 -θ1 , and (c) θis proportional to both D /(t) and δr where D is the outside diameter of the pipe, (t) is the wall thickness of the pipe, and δr equals (the radial fitting tolerance of the seal forming surface)-(the radial fitting tolerance of the screw forming surface).

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 buried underground. In particular, the joint is suitable for pumping gas or oil containing a large amount of corrosive impurities under a high pressure at a deep depth.

[0002]

2. Description of the Related Art Today, threaded joints are widely used as joints for connecting oil country tubular goods used for exploration and production of natural gas fields and oil fields having a depth of several thousand meters. There are two types of screw joints for oil country tubular goods. An integral system that connects the pipes with a pin section at one end and a box section at the other end, and a coupling system that connects a coupling with two box sections and a tube with pin sections at both ends Is.
The following performances are commonly required for these threaded joints.

Can withstand axial tensile force due to its own weight of connected pipes, can withstand internal pressure by internal fluid or external pressure by external fluid, can be used several tens of times repeatedly, corrosion by internal and external fluids And able to withstand erosion.

In recent years, wells have become deeper and are often used in severe environments such as polar regions. Furthermore, the deposits containing a large amount of corrosive and oxidative impurities, which have not been targeted so far, are now being mined, and the performance of joints is rapidly improving in order to meet the above requirements.

FIG. 3 is a view showing an example of a coupling joint having a seal portion and a torque shoulder portion, which is an oil well pipe threaded joint in the case of an inner shoulder. FIG.
(A) is a drawing showing a state in which the coupling is fastened to the pipe body. FIG. 3B is a drawing showing the screw part, the seal forming part, and the torque shoulder forming part of FIG. 3A.

The "torque shoulder portion" controls the fastening torque to an appropriate value so that a high contact pressure that causes plastic deformation does not occur in the seal portion by abutting the mutual torque shoulder forming surfaces. It was installed in. "Inner surface shoulder" refers to a type of joint having torque shoulder forming portions 14 and 24 on the inner surface side of the pipe, or a portion of the torque shoulder.

FIG. 2 is a drawing showing an example of a threaded joint for oil country tubular goods having both an inner shoulder and an outer shoulder. FIG.
(A) is drawing which shows the cross section of the pipe and coupling after fastening. FIG. 2B is a drawing showing the inclination of the torque shoulder forming surface on the pin side and the box side forming the outer surface shoulder. The "outer surface shoulder" refers to a type of joint that forms a torque shoulder portion by the torque shoulder forming surface 64 at the box-side tip abutting against the torque shoulder forming surface 54 at the base of the male thread on the outer surface of the pipe, or the torque shoulder portion thereof. .

In the following description, unless otherwise specified,
The joint shall be a coupling type inner shoulder joint having a seal portion and a torque shoulder portion.

In FIG. 3B, a male screw 12 provided on the tip of the pipe 10 and a female screw 22 provided inside the coupling 20 are screwed together. The seal forming surface 13 at the tip of the pin portion 11 which is a rotating surface of a tapered curve or an arc having a large radius of curvature, and the seal forming surface 2 which is a rotating surface of a tapered curve at the screw root of the box portion 21.
3 and 3 contact each other at the time of fastening to form a seal portion. Here, the "tapered curve" is a curve that lies in a plane including the tube axis (which is also the axis of the coupling), and is a curve that is closer to the tube axis as it approaches the center of the box. "Rotating surface" refers to a curved surface formed by rotating the above-mentioned tapered curve or arc around the tube axis (which is also the axis of the coupling).
By forming a metal seal with this seal portion, airtightness is maintained against the internal pressure due to the fluid inside the oil well pipe or the external pressure due to the fluid outside the pipe.

The pin side torque shoulder forming surface 14 at the tip of the seal forming surface 13 and the torque shoulder forming surface 24 at a portion closer to the box center of the box side seal forming surface 23 abut against each other to abut the torque shoulder. To form a part.

In addition to the airtightness with respect to the high-pressure fluid, the performance that the oil well pipe threaded joint must have is corrosion resistance against crevice corrosion that causes leakage and breakage from the threaded portion. Crevice corrosion is a phenomenon in which a corrosive fluid penetrates into the minute gaps between the pin member and the box member, stays and is concentrated, so that the high stress load inside the joint exposed to this fluid , Refers to the phenomenon of damage such as general corrosion and stress corrosion cracking. Crevice corrosion does not occur unless a minute gap exists on the pipe inner surface side or the pipe outer surface side where the corrosive fluid exists.

In order to meet the above-mentioned demands, the following seal-shaped and torque-shoulder-shaped joints have been proposed by improving the joint shown in FIG. These are α)
Joint that covers the contact surface with a soft material, β) Joint that uses packing, γ) Joint that improves the airtightness of the seal part by elastic deformation of the pin tip, δ) Seal part by devising the contact of the torque shoulder forming surface Are roughly classified into four types of joints with improved air tightness.

Α) There is a joint proposed in JP-A-56-109975 and JP-A-1-199088, in which the pin-side and box-side seal forming surfaces are covered with a soft metal or the like. This is done by contacting the seal forming surface and the torque shoulder forming surface coated with the soft material,
The sealing effect of the seal portion and the torque shoulder portion is improved.

However, this method has a drawback that the airtightness is deteriorated because the coating material is missing or worn during repeated fastening and releasing of the joint, and it cannot withstand several tens of uses.

Β) FIG. 4 shows a joint disclosed in Japanese Utility Model Laid-Open No. 142242/1983, which is made of a ring-shaped soft material between the pin-side torque shoulder forming surface 14 and the box-side torque shoulder forming surface 24. It is drawing showing the joint which inserted the other packing 30. In the figure, packing 3
With 0, variation in the tightening length of the pin 11 in the axial direction is allowed. Therefore, regardless of manufacturing tolerances of the seal forming portion, the seal forming portion is always fitted with a constant contact pressure by tightening by torque control, and stable airtightness can be obtained.

This joint has a problem in that it takes time and cost during manufacturing such as manufacturing and inserting of packing. further,
Originally, this joint does not have the function of controlling the tightening torque to an appropriate value, which is required for the torque shoulder part, so it is necessary to strictly control the torque when tightening on site, which deteriorates handleability. Leads to. Further, there is a problem that a gap is generated between the packing and the torque shoulder surface depending on a manufacturing error, and crevice corrosion occurs.

Γ) FIG. 5 is a joint shown in Japanese Patent Application Laid-Open No. 60-26878, in which the tip end (lip portion) of the pin portion is made thin so as to have high sealing performance by utilizing elastic deformation. It is a drawing showing. FIG. 5A shows a seal forming surface and a torque shoulder forming surface of the pin portion and the box portion before fastening. FIG. 5B shows a contact pressure distribution of the seal portion and the torque shoulder forming portion after fastening. This joint has a smooth groove 3 on the inner surface of the pipe across the pin tip lip portion 15 and the box side torque shoulder portion.
Has 1. Further, the inclination θ _{2 of} the box-side torque shoulder surface 24 is larger than the inclination θ _{1 of the} pin-side torque shoulder surface 14, and the effective diameter of the pin-side seal forming surface 13 is smaller than the effective diameter of the box-side seal forming surface 23. Since the pin tip lip portion 15 has a thin wall due to the groove 31, elastic deformation easily occurs. Pin tip torque shoulder surface 1 by screwing
When 4 is strongly pressed against the box-side torque shoulder surface 24, the seal forming surface 13 near the center of the pin tip lip portion 15 bulges outward due to the difference in inclination. Therefore, the sealing surface 32 is formed by coming into contact with the box-side seal forming surface 23. As a result, there are two sealing surfaces, the sealing surface 33 of the torque shoulder forming portion formed by pressing and the sealing surface 32 of the sealing portion.

This joint is similar to the structure of the present invention in that the inclination θ ₁ of the pin side torque shoulder forming surface 14 is slightly smaller than the inclination θ _{2 of} the box side torque shoulder forming surface as shown in FIG. ing. However, the difference in inclination θ ₂ −θ ₁ of the torque shoulder portion is due to the thin pin tip lip portion 15 pressed against the box side torque shoulder forming portion 24.
It is provided to inflate the center of. Since the pin-side seal forming surface 13 comes into contact with the box-side seal forming portion 23 only after this bulging deformation occurs, the effective diameter of the pin-side seal forming surface is smaller than that on the box side. In the above two points, the present joint differs from the joint of the present invention described later.

In this joint, in order to obtain a sealing surface having a sufficient contact pressure in the seal forming portion, a large bending deformation of the pin tip lip portion must be realized. For that purpose, it is necessary to press the pin tip lip portion against the box-side torque shoulder forming surface with a very large force. For this reason, there is a problem that excessive plastic deformation occurs particularly in the portion 26 of the box-side torque shoulder forming surface that is close to the inner surface of the pipe, and the predetermined airtightness cannot be exhibited.

Δ) FIG. 6 shows a joint disclosed in Japanese Unexamined Patent Publication No. 52-11765, in which the torque shoulder forming surfaces on the pin side and the box side are in contact with each other and the pipe outer diameter direction occurs near the tip of the pin portion. 5 is a view showing a joint in which the sealing performance of the seal portion is improved by bulging into the joint. Pin side seal forming surface 1
3 is an arc-shaped rotating surface with a large radius of curvature, and the box-side seal forming surface is a conical surface (tapered linear rotating surface).
And The pin side torque shoulder forming surface 14 and the box side torque shoulder forming surface 24 have different curvatures R ₂
And R ₃ with convex and concave surfaces. The radius of curvature R ₂ of the pin-side torque shoulder forming surface is made smaller than the radius of curvature R ₃ of the box-side torque shoulder forming surface, and R
_The center position of the radius of curvature of ₂ is inside the tube with respect to that of R ₃ .
With this structure, the deflection of the pin side lip portion 15 toward the inner surface of the pipe is reduced, and the non-uniform contact pressure in the circumferential direction of the seal portion due to a manufacturing error is automatically redistributed into a uniform contact pressure.
Therefore, a good sealed state can be obtained at the two locations of the torque shoulder portion and the seal portion.

In this joint, the contact of the torque shoulder portion is
It is maintained by circumferential line contact at the portions 16 and 26 near the inner surface of the tube. For this reason, the contact pressure at this portion becomes very high, and as in the case of γ), there is a problem that excessive plastic deformation occurs and the airtightness deteriorates.

[0022]

DISCLOSURE OF THE INVENTION The present invention provides a joint which does not cause crevice corrosion and maintains a high degree of airtightness even after repeated use for several tens of times without increasing manufacturing cost and deteriorating handleability. The task was to do.

[0023]

In order to solve the above-mentioned problems of the conventional joint, the present inventor has made the seal portion and the torque shoulder portion of the joint portion fastened and when the tensile stress acts in the axial direction. The behavior was examined in detail, and the following was confirmed.

1) In the seal portion of the oil well pipe threaded joint, usually, the effective diameter of the pin side seal forming surface 13 is made larger than the effective diameter of the box side seal forming surface 23, and the contact pressure is generated by fitting them together. A metal seal with good airtightness is formed. Here, the "effective diameter" of the pin-side seal forming surface and the box-side seal forming surface means the diameter of the "reference position" defined in each seal forming surface portion before fitting,
That is, it means the average distance from the tube axis or the box axis to the "reference position" of each seal forming surface. The "reference position" corresponds to the "portion where the pin-side and box-side seal forming surfaces are in contact with each other" when the fastening is completed, and the "position before fitting" Point

2) Due to the difference in effective diameter, stress acts on the pin side in the diameter reducing direction. In particular, bending deformation occurs at the tip of the pin.

FIG. 7 is a drawing showing a state in which the pin side torque shoulder forming surface is inclined by θa with respect to the box side torque shoulder forming surface due to the diameter-reducing deformation of the pin side seal forming surface. As shown in the figure, in the case of a joint in which the seal forming portion and the torque shoulder forming portion are arranged near the tip of the pin portion, the contact pressure generated in the seal forming portions 13 and 23 at the time of fastening causes the pin tip lip portion 15 to move. Bending deformation occurs in the direction of diameter reduction. Due to this bending deformation, the pin-side torque shoulder forming surface 14 is inclined toward the inner surface side of the pipe by θa with respect to the box-side torque shoulder forming surface 24.

3) In a normal joint in which the inclinations of the torque shoulder forming surfaces on the pin side and the box side are the same, the contact pressure at the pipe inner surface side portions 16 and 26 of the torque shoulder portion is small due to the above bending deformation. . Therefore, when a large tensile stress acts on the pipe body including the joint in the fastened state, the contact pressure almost disappears, and in some cases, there is a gap in the inner surface of the torque shoulder.

4) The inclination of the pin side torque shoulder forming surface and that on the box side are made different in advance, and after bending deformation by fitting, the torque shoulders on both sides are flush with each other or slightly overlap on the pipe inner surface side. By adjusting the inclination of the forming surface, a desired contact pressure distribution can be obtained.

Based on these results, the oil country tubular goods threaded joint of the present invention was completed.

FIG. 1 is a diagram illustrating the structure of the inner surface shoulder vicinity of smaller than the inclination theta ₂ of the inclination theta ₁ of the pin-side torque shoulder forming face box side torque shoulder forming face. FIG. 1A is a drawing showing the pin side and box side seal portions and the torque shoulder forming portion of the joint before fastening. FIG. 1B is a drawing showing a distribution of contact pressure (calculation result) generated in the seal portion and the torque shoulder portion after fastening. From the figure, it is understood that a uniform contact pressure can be obtained by preliminarily anticipating the bending deformation of the pin side torque shoulder forming surface described above and reducing the inclination of the pin side torque shoulder forming surface accordingly.

The invention also applies to the case of external shoulders. As shown in FIGS. 2 (a) and 2 (b), the technical idea of providing a uniform contact pressure by providing a difference in the inclination of the torque shoulder forming surface is maintained even in the case of the outer surface shoulder.

Here, the gist of the present invention is the structure of a joint for oil country tubular goods in which durability and airtightness are improved by providing a difference in the inclination of the torque shoulder forming surface on the pin side and the box side as shown below. (See FIGS. 1 and 2) (1) As shown in FIG. 1, a seal forming surface 13 provided on the outer surface of the tip of the pin portion 11 having a male screw and a seal provided on the inner surface of the box portion 21 having a female screw. A seal portion is formed by fitting the forming surface 23 to each other, and the torque shoulder forming surface 14 provided on the most distal end of the pin and the corresponding torque shoulder forming surface 24 provided on the box side are butted. A threaded joint for oil country tubular goods having the following characteristics for forming an inner shoulder.

(A) The pin-side and box-side seal forming surfaces are rotating surfaces, and the pin-side seal forming surface 1
The effective diameter of 3 is larger than the effective diameter of the box-side seal forming surface 23.

(B) The inclination θ ₁ of the pin-side torque shoulder forming surface is slightly smaller than the inclination θ ₂ of the box-side torque shoulder forming surface, and the difference (θ) between both inclinations is 0.5 ° ≦.
Satisfies θ ≦ 4.0 °. However, the difference between θ = θ ₂ -θ ₁ (c) the slope of the pin-side torque shoulder forming face inclination theta ₁ and the box-side torque shoulder forming face of the theta ₂ theta is, D / t
And δr are almost proportional to each other, and when the value of D / t or δr is large, the difference θ between the inclinations of the torque shoulder forming surfaces on the pin side and the box side is increased, and conversely, D / t or δr If the value is small, the inclination difference θ of the torque shoulder forming surface is made small.

However, D, t and δr are as follows.

D = outer diameter of tube, t = wall thickness of tube, δr = (radial fit of seal forming surface)-(radial fit of thread forming surface) (2) As shown in FIG. , The seal forming surface 53 provided on the outer surface of the base of the pin having the male screw and the seal forming surface 63 provided on the inner surface of the tip of the box having the female screw are fitted to form a seal portion, and the box leading edge is formed. Torque shoulder forming surface 6 provided on the
A threaded joint for oil country tubular goods having the following features in which an outer surface shoulder is formed by abutting 4 and a corresponding torque shoulder forming surface 54 provided on the outer surface of the pin root.

(A) The pin-side and box-side seal forming surfaces are rotating surfaces, and the pin-side seal forming surface 5
The effective diameter of 3 is larger than the effective diameter of the box-side seal forming surface 63.

(B) The inclination θ ₁ of the pin-side torque shoulder forming surface is slightly larger than the inclination θ ₂ of the box-side torque shoulder forming surface, and the difference (θ) between both inclinations is 0.5 ° ≦.
Satisfies θ ≦ 4.0 °. However, θ = θ ₁ -θ ₂ (c) the difference between the inclination theta ₂ of inclination theta ₁ and the box-side torque shoulder forming face of the pin-side torque shoulder forming face theta is, D / t
And δr are almost proportional to each other, and when the value of D / t or δr is large, the difference θ between the inclinations of the torque shoulder forming surfaces on the pin side and the box side is increased, and conversely, D / t or δr If the value is small, the inclination difference θ of the torque shoulder forming surface is made small.

However, D, t and δr are as follows.

D = coupling outer diameter, t = coupling wall thickness, δr = (radial fitting allowance of seal forming surface)-(radial fitting allowance of thread forming surface)

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limitation of the present invention will be described below.

1. Difference in Inclination of Pin-side and Box-side Torque Shoulder Forming Surface The pin-side seal forming surface is a tapered curved surface or an arcuate rotating surface with a large radius of curvature. Further, the box-side seal forming surface is composed of a tapered curved rotating surface.

The effective diameter of the pin-side seal forming surface must be larger than the effective diameter of the box-side seal forming surface. As described above, the effective diameter refers to the diameter of the reference portion of each of the pin-side seal forming surface and the box-side seal forming surface.

When fitting, the one that fits inside (pin side)
When the effective diameter of is large, the tip of the pin having low rigidity must be reduced in diameter when it is forcibly fitted. When the tip of the pin is deformed by reducing its diameter, the tip of the pin is bent and deformed toward the inner surface of the pipe. Therefore, the inclination of the pin side torque shoulder forming surface changes by the amount of this bending deformation (FIG. 7).
reference).

In the joint shown in FIG. 1A, the inclination θ ₁ of the pin side torque shoulder forming surface 13 is smaller than the inclination θ _{2 of the} box side torque shoulder forming surface 23 by θ (= θ ₂ −θ ₁ ). This angle difference θ is set to be equal to or slightly larger than the change θa of the inclination actually caused by the bending deformation described above. As shown in FIG. 7, the change in inclination θa due to the bending deformation that actually occurs is the deflection angle θ ′ of the pin side torque shoulder portion 14 when the pin tip lip portion 15 is bent and deformed by the contact pressure of the seal forming portion. Is almost equivalent to. Here, the deflection angle means the lip portion 15 at the tip of the pipe.
Is the angle that is deflected by a lateral load or bending moment.

By providing such an angle difference in the inclination of the torque shoulder forming surface of the pin portion and the box portion, the following contact pressure distribution can be obtained.

Almost uniform contact pressure distribution over the entire surface of the torque shoulder forming surfaces 14 and 24 on the pin side and the box side, or the contact pressure on the pipe inner surface sides 16 and 26 is high, and as the seal forming portion sides 17 and 27 are approached. The contact pressure distribution gradually decreases. Therefore, stress concentration to the extent that excessive plastic deformation occurs in the vicinity of the pipe inner surface 16 and 26 of the torque shoulder portion does not occur, and there is sufficient contact to eliminate gaps in this portion. The pressure can be secured. Therefore, it can withstand several tens of uses,
Moreover, a threaded joint for oil country tubular goods in which crevice corrosion does not occur can be obtained.

In this manner, the torque shoulder forming surfaces 14 and 24 on the pin side and the box side are provided with a substantially uniform contact pressure.
Since they are in contact with each other, local plastic deformation due to stress concentration does not occur. Therefore, when tensile stress is applied to the pipe main body including the joint that is fastened in this state, the contact pressure of the torque shoulder part decreases almost uniformly over the entire surface, so that it is better than the conventional joint having a torque shoulder shape. The tensile load value at which the torque shoulder opens is much higher. Therefore, when the contact pressure at the time of fastening is sufficiently high, a torque shoulder portion that does not open even if a tensile stress equivalent to the yield strength of the pipe body is applied is formed, and excellent crevice corrosion resistance is obtained.

Torque shoulder surface 1 on the pin side and the box side
In a joint in which the inclinations of 4 and 24 are the same, the torque shoulder surface does not have a uniform contact pressure distribution, and the contact pressure on the seal forming portion side is high and that on the inner surface side of the pipe is low. As a result, when tensile stress such as own weight is applied after fastening,
The contact pressure on the inner surface side becomes extremely small. In extreme cases, this part opens up. When used in this state for a long time, the high-pressure and corrosive fluid inside penetrates into the joint from the gap between the pipe inner surface side portions 16 and 26 of the torque shoulder portion. As a result, the seal portion and further the high stress load portion of the screw portion are corroded, and in the worst case, leakage occurs or the joint is broken. The joint of the present invention can prevent such a problem from occurring until it has been used several tens of times.

On the contrary, even when a compressive force is applied, the contact pressure of the torque shoulder portion is almost uniform over the entire surface.
Local plastic deformation due to stress concentration or the like is less likely to occur in the torque shoulder portion, and therefore "excessive plastic deformation that cannot be repeatedly used" does not occur. Here, "to the extent that repeated use is impossible" means that the torque control and sub-seal functions cannot be fulfilled due to permanent deformation of the torque shoulder on the box side, making proper joint fastening impossible, and It means that the performance of can not be exhibited.

The inclination difference θ cannot be too large. If θ is too large, stress concentration occurs on the inner surface side of the torque shoulder portion, causing local plastic deformation. There is an appropriate range for θ as described later.

2. Appropriate range of inclination difference Pin side seal forming surface 13 and box side seal forming surface 23
The bending angle θ ′ (see FIG. 7) of the bending deformation in the diameter reducing direction of the pin side lip portion 15 caused by fitting the can be obtained by a calculation formula based on the classical shell theory. Furthermore, the correspondence between the deflection angle θ'obtained by this calculation formula and the actual change in inclination θa has been confirmed by experiments. Therefore, by obtaining the deflection angle θ ′ of the pin tip portion, it is possible to obtain the change θa in the inclination of the pin side torque shoulder forming surface that actually occurs. The inclination difference θ between the pin side torque shoulder surface and the box side torque shoulder surface is set to be equal to or slightly larger than this inclination change θa. The inclination difference θ depends on the size, the wall thickness, the fitting allowance, and the mechanical properties of the joint material of the oil country tubular goods threaded joint, but is 0.5 ° to 4.0 ° for the oil well tubular threaded joint in the practical range. The following can be set. here,
The term "fit" means the difference in effective diameter.

Threading of the joint including the seal portion and the shoulder portion is usually performed by computer control by an NC lathe. The above-mentioned angle can be manufactured with accuracy that is practically problem-free without special precision control by a computer-controlled NC lathe.

3. Factors Affecting Difference in Inclination A) The difference in inclination θ set in this way is approximately proportional to D / t = (outer diameter of pipe body) / (wall thickness) in the case of an inner shoulder. When D / t is large, the rigidity against bending becomes small, so that bending becomes easy and the difference in inclination becomes large. Therefore, it is necessary to change the magnitude of θ according to the magnitude of D / t.

B) θ is also substantially proportional to δr = (fitting margin of seal forming portion) − (fitting margin of screw forming portion). The fitting margin is a difference between the effective diameters of the pin portion and the box portion, and thus causes the diameter reduction. As described above, the "fitting margin of the seal forming portion" is effective for both the diameter reduction of the pin tip and the bending of the torque shoulder forming surface. But,
When the "fitting margin of the seal forming portion" is the same as the "fitting margin of the screw forming portion", only a uniform diameter reduction occurs and no bending occurs. The "fitting margin of the thread forming portion" close to the pipe body only produces uniform diameter reduction deformation. "Match of thread forming part"
If it is equal to, the "fitting margin of the seal portion" is only balanced with the fitting margin of the screw portion, and is balanced. Of the "fitting margins of the seal forming portion", the fitting margin (= δr) obtained by subtracting the "fitting margin of the screw forming portion" that does not contribute to bending causes bending deformation. Θ, which is set to be substantially equal to the bending angle of bending in the inner surface of the pipe, is approximately proportional to δr, which is obtained by subtracting the “fitting margin of the screw forming portion” from the “fitting margin of the seal forming portion”. The difference between the inclinations of the torque shoulder forming surfaces on the pin side and the box side must be set so as to be changed substantially in proportion to δr.

4. In case of outer shoulder As shown in FIG. 2B, the box side seal forming surface 63
When the effective diameter of is smaller than that of the pin side seal forming surface 53, the box side torque shoulder forming surface 64 is bent outward by fastening and the inclination changes. In the case of the outer surface shoulder, unlike the inner surface shoulder, the bending rigidity of the coupling is related, so D = coupling outer diameter, t = coupling wall thickness. The box-side tip is bent and deformed because the box-side tip is thin and has a free end, and therefore the bending rigidity of the box-side tip is smaller than that at the pin root. The inclination θ ₂ of the box-side torque shoulder forming surface is set to be smaller than the inclination θ ₁ of the pin-side torque shoulder forming surface by the change amount θa of the inclination or an angle slightly larger than θa. At this time, a substantially uniform contact pressure or a slightly higher contact pressure on the outer surface sides 56 and 66 and a slightly lower contact pressure on the seal forming portion sides 57 and 67 can be obtained.

As a result, in the case of the outer surface shoulder, the outer surface side does not open even when tensile stress is applied. In addition, the above-described effects in the case of the inner shoulder are directly applied to the case of the outer shoulder.

Needless to say, the joint having both the inner shoulder and the outer shoulder has the structure of the present invention applied as it is.

In the above description, the case of the coupling system is described. However, when the present invention is applied to the integral system, one end of the pipe is equipped with a male screw forming a pin member, a seal and a shoulder forming surface. , The other end is a female screw that forms a box member after overlaying,
Since the seal and the shoulder forming surface may be provided, the configuration of the present invention can be applied as it is.

[0060]

Next, the effects of the present invention will be described based on embodiments.

Tables 1, 2, 3, and 4 are tables showing the inclination of the torque shoulder forming surface and the joint type of the joints of the invention examples and comparative examples used in the test. Joints A, B, C, D, E, F, G, H, I shown in Table 1 and Table 2
And J (Hereinafter, when referring to all these joints, joint A
Etc.) “D / t and δ _r are all 1
7.78 and 0.4 ". The joints K and L shown in Tables 3 and 4 have" D / t = ", respectively.
13.78, δ _r = 0.199 "and" D / t = 2
1.72, δ _r = 0.528 ", and D / t and δ _r are changed to high and low as compared with the joint A and the like. Both D / t and δ _r are smaller than the joint A and the like. K makes the difference in inclination θ of the torque shoulder forming surface approximately proportional and decreases, and conversely, for joint L in which D / t and δ _r are larger than joint A, the difference in inclination θ is set proportionally large. is there.

The joints of the invention examples of Tables 1 to 4 are the joints of the inner shoulder, the outer shoulder and the inner and outer shoulders shown in FIGS. 1 and 2. The comparative example shown in Table 2 is a joint having the same inclination of the pin side and box side torque shoulder forming surfaces, a joint having a sealing surface covered with a soft metal, and a joint having a thin lip portion with a smooth groove (Fig. 5) Alternatively, joints (Fig. 6) in which the torque shoulder forming surfaces on the pin side and the box side are convex and concave with different radii of curvature were investigated.

[0063]

[Table 1]

[0064]

[Table 2]

[0065]

[Table 3]

[0066]

[Table 4]

These joints were tested in the following tests to evaluate their performance.

A. Repeated fastening test Lubrication grease was applied to the threaded portion and the non-threaded portion, the joint was fastened and disassembled 10 times, and then the changes in the seal portion and the torque shoulder portion were investigated.

B. Gap generation test under tensile stress After the above test, the joint was fastened and the pipe body was subjected to a torque with a tensile force (245.2 ton) in the axial direction so as to generate a stress equivalent to 80% of the yield strength. The presence or absence of a gap on the inside or outside of the shoulder was investigated.

C. Corrosion test under combined load b. The mixed gas of hydrogen sulfide and carbon dioxide was sealed inside the tube including the joint while the tensile stress of 1. was applied.
The pressure of the mixed gas was set to 5.24 kgf / mm ² which causes a stress corresponding to 80% of the yield strength in the tube body. After holding in that state for 500 hours, the joint was disassembled and the corrosion site was investigated.

Tables 5 and 6 are tables showing the test results of the above-mentioned three kinds of tests (a., B. And c.). From the table, in the comparative example, a failure occurs in any test, but the joint according to the present invention has a good result in any test.

[0072] Table 6 is a test result of D / t and [delta] _r joint K and joint L is varied in proportion to the difference between θ of inclination in accordance with, by substantially proportional to D / t and [delta] _r This result clearly shows that it is effective to change the inclination difference θ.

[0073]

[Table 5]

[0074]

[Table 6]

[0075]

EFFECTS OF THE INVENTION The threaded joint for oil country tubular goods according to the present invention has a clearance on the inner surface side of the torque shoulder portion on the inner shoulder or on the outer surface side of the shoulder portion on the outer shoulder even under a tensile load due to the weight of the connected pipes. Does not occur. Therefore, it is possible to prevent crevice corrosion caused by the penetration of internal or external fluid into the inside of the joint from the gap of the torque shoulder, and because excessive plastic deformation does not occur in the torque shoulder, it is possible to use it repeatedly for dozens of times. Can bear. In the future, it will be possible to provide joints with excellent durability without increasing the cost significantly under the increasingly severe mining conditions.

[Brief description of the drawings]

FIG. 1 is a coupling type joint having a seal portion and a torque shoulder portion, in the vicinity of an inner surface shoulder having a structure in which the inclination of a torque shoulder forming surface on a pin side is smaller than the inclination of a torque shoulder forming surface on a box side. FIG. 5A is a drawing showing (a) a seal forming surface and a torque shoulder forming surface on a pin side and a box side before fastening, and (b) is a contact pressure distribution (calculation calculated on a seal portion and a torque shoulder portion after fastening). FIG.

FIG. 2 is a drawing showing a threaded joint for oil country tubular goods having both an inner shoulder and an outer shoulder, wherein (a) is the pin portion and box portion after fastening, and (b) is the outer shoulder shown in (a). 3 is a drawing showing a structure in which the inclination of the torque shoulder forming surface on the box side is made smaller than the inclination of the pin side torque shoulder forming surface at the portion.

FIG. 3 is a drawing showing an example of a threaded joint for oil country tubular goods in the case of an inner shoulder, which is a coupling joint having a seal portion and a torque shoulder portion, and FIG. The state where the ring is fastened, (b) is (a)
3 is a view showing a thread portion, a seal forming portion, and a torque shoulder forming portion of FIG.

FIG. 4 is a drawing showing a joint in which a ring-shaped packing made of a soft material is inserted between the pin-side torque shoulder forming surface and the box-side torque shoulder forming surface.

FIG. 5 is a drawing showing a joint in which the tip end (lip portion) of the pin portion is thinned to provide high sealing performance by utilizing elastic deformation, and (a) is a pin portion and a box before fastening. The respective seal forming surfaces and the torque shoulder forming surfaces of the section, and (b) represents the contact pressure distribution of the seal section and the torque shoulder forming section after fastening.

FIG. 6 is a pin side torque shoulder forming surface (convex surface).
And a box-side torque shoulder forming surface (concave surface) with the respective centers of curvature displaced from each other.

FIG. 7 is a drawing showing a state in which a pin side torque shoulder surface is inclined by θa with respect to a box side torque shoulder surface due to bending deformation in a diameter reducing direction that occurs in a pin side seal forming portion having a large effective diameter. .

[Explanation of symbols]

θ '... Deflection angle of pin tip lip, θa ... Change in inclination of pin side torque shoulder forming surface due to bending deformation of pin tip lip, θ ₁ ... Inclination of pin side torque shoulder forming surface, θ ₂ ... Box side torque Inclination of shoulder forming surface, θ ... Difference of inclination of pin side and box side torque shoulder forming surface Where, for inner shoulder: θ = θ ₂ −θ ₁ (>
0), external shoulder: θ = θ ₁ −θ ₂ (> 0) 10 ... Pipe body, 11 ... Pin part, 12 ... Male screw, 20 ... Coupling, 21 ... Box part, 22 ... Female screw, 30 ... Ring Packing, 31 ... Smooth grooves provided in the circumferential direction, 32 ... Seal forming portion at the time of fastening, 33 ... Torque shoulder forming portion at the time of fastening-The following symbols are limited to the case of the inner surface shoulder. 13 ... Pin forming seal forming surface, 23 ... Box forming seal forming surface, 14 ... Pin forming torque shoulder forming surface, 24 ... Box forming torque shoulder forming surface, 16 ... Pin forming torque shoulder forming surface End portion, 26 ... End portion of the torque shoulder forming surface of the box portion on the pipe inner surface side, 17 ... End portion of the torque shoulder forming surface of the pin portion on the seal forming side, 27 ... Seal forming side of the torque shoulder forming surface Ends: -The following symbols are limited to external shoulders. 53 ... Pin portion seal forming surface, 63 ... Box portion seal forming surface, 54 ... Pin portion torque shoulder forming surface, 64 ... Box portion torque shoulder forming surface, 56 ... Pin portion torque shoulder forming surface End portion of the torque shoulder forming surface of the box portion, the end portion of the torque shoulder forming surface of the box portion on the tube outer surface side, 57 ... the end portion of the torque shoulder forming surface of the pin portion on the seal forming side, 67 ... the seal forming side of the torque shoulder forming surface edge

Claims (2)

[Claims] 1. A seal forming surface (13) provided on an outer surface of a tip of a pin portion (11) having a male screw and a seal forming surface (2) provided on an inner surface of a box portion (21) having a female screw.
3) is fitted to form a seal portion, and a torque shoulder forming surface (14) provided at the tip of the pin,
A threaded joint for oil country tubular goods having the following characteristics (a), (b) and (c), which forms an inner shoulder by abutting against a corresponding torque shoulder forming surface (24) provided on the box side. (A) The pin-side and box-side seal forming surfaces are respectively rotating surfaces, and the effective diameter of the pin-side seal forming surface (13) is larger than the effective diameter of the box-side seal forming surface (23). (B) The inclination of the pin-side torque shoulder forming surface (θ ₁ ) is smaller than the inclination of the box-side torque shoulder forming surface (θ ₂ ), and the difference (θ) between the two is 0.5 ° ≦ θ ≦ 4. Satisfies 0 °. However, θ = θ ₂ −θ ₁ (c) The difference (θ) between the inclination of the pin side torque shoulder forming surface (θ ₁ ) and the inclination of the box side torque shoulder forming surface (θ ₂ ) is the difference between D / t and δr. When the values of D / t or δr are large in proportion to each other, increase the difference (θ) in the inclination of the torque shoulder forming surface on the pin side and box side, and conversely, the value of D / t or δr. When is small, the difference (θ) in the inclination of the torque shoulder forming surface is made small. However, D, t, and δr are as follows. D = outer diameter of tube, t = wall thickness of tube, δr = (radial fit of seal forming surface) − (radial fit of thread forming surface) 2. A seal part by fitting a seal forming surface (53) provided on the outer surface of the base of a pin having a male screw and a seal forming surface (63) provided on the inner surface of the tip of a box having a female screw. And the torque shoulder forming surface (64) provided on the top of the box and the corresponding torque shoulder forming surface (54) provided on the outer surface of the pin base corresponding thereto are formed to form an outer shoulder (see below). ), (B), and (c) are screw joints for oil country tubular goods. (A) The pin-side and box-side seal forming surfaces are respectively rotating surfaces, and the effective diameter of the pin-side seal forming surface (53) is larger than the effective diameter of the box-side seal forming surface (63). (B) The inclination of the pin side torque shoulder forming surface (θ ₁ ) is slightly larger than the inclination of the box side torque shoulder forming surface (θ ₂ ), and the difference (θ) between the two is 0.5 ° ≦ θ ≦
Satisfies 4.0 °. However, θ = θ ₁ − θ ₂ (c) The difference (θ) between the inclination of the pin side torque shoulder forming surface (θ ₁ ) and the inclination of the box side torque shoulder forming surface (θ ₂ ) is the difference between D / t and δr. When the values of D / t or δr are large in proportion to each other, increase the difference (θ) in the inclination of the torque shoulder forming surface on the pin side and box side, and conversely, the value of D / t or δr. When is small, the difference (θ) in the inclination of the torque shoulder forming surface is made small. However, D, t and δr are as follows. D = coupling outer diameter, t = coupling wall thickness, δr = (radial fitting allowance of seal forming surface) − (radial fitting allowance of screw forming surface)