CN202417340U - Threading connector for oil well pipe - Google Patents

Abstract

The utility model provides a threading connector for an oil well pipe. The threading connector for the oil well pipe (10-1) comprises: a male buckle (11) and a female buckle (21), wherein the male buckle is provided with an external thread part (12), a first sealing part (13), a first circular bead part (14) and a front-section unthreaded part (15); and the female buckle is provided with an internal thread part (22), a second sealing part (23) and a second circular bead part (24). The inclined angles of the first sealing part and the second sealing part (23) relative to an axis line are respectively 14 degrees-30 degrees; the front-section unthreaded part and the first sealing part are connected through an arc part with the radius being 3mm-11mm; a line of the second circular bead part (24), which is vertical to the axial line, has the inclined angle being 5 degrees-20 degrees; a front end part (16) of the male buckle is formed by an arc part with the radius being 0.6mm-0.9mm; and a part (25) of the female buckle (21), corresponding to the front end part (16) of the male buckle, is formed by an arc part with the radius being below 0.5mm.

Description

Threaded joints for oil well pipe

technical field

The utility model relates to a threaded joint for oil well pipes used in the exploration and production of oil and natural gas, in particular to a metal-sealed threaded joint for oil well pipes.

Background technique

As threaded joints for oil well pipes for connecting oil well pipes, API standard circular threaded joints and buttress threaded joints are generally used. However, in view of the cruelty of production conditions as the depth of oil wells and gas wells increases year by year, the threaded joints for oil well pipes will bear a large three-dimensional load and be exposed to severe stress states. Especially in production wells, since circumferential stress is applied from the inside of the pipe, it is not easy to fully maintain the airtight performance under triaxial stress for circular threaded joints and partial trapezoidal threaded joints.

Therefore, Patent Document 1 discloses a metal-seal type oil country tubular threaded joint having a metal sealing surface. Fig. 6(a) is an explanatory view showing the overall structure of the threaded joint 0 for oil country tubular goods, and Fig. 6(b) is when the pin 1 and the box 5 of the threaded joint 0 for oil country tubular goods are connected. Partial sectional view of enlarged representation of the condition. In addition, FIG. 7( a ) is an explanatory diagram schematically showing the state of the connection between the pin 1 and the box 5 of the threaded joint 0 for oil country tubular goods, and FIG. 7( b ) is a diagram schematically showing the threaded joint 0 for oil country tubular goods. It is an explanatory diagram of the situation when the connection of the pin 1 and the box 5 is completed, and (c) of FIG. 7 is an explanatory diagram showing an enlarged connection portion between the front unthreaded portion and the sealing portion.

As shown in FIG. 6( a ) and FIG. 6( b ), the oil well pipes P and P are connected by a coupling C (coupling). Reference numeral 1 is an end portion of the oil country pipe P inserted into the coupling C, and denotes a pin portion, and reference numeral 5 denotes a box portion formed in the coupling C for receiving the pin 1 . The threaded joint 0 for oil well pipe is a metal-sealed threaded joint in which a pin 1 and a box 5 are screwed together. The pin 1 has a tapered external thread portion 2 on its outer surface that gradually decreases in diameter toward the front end. A tapered sealing portion 3 whose diameter gradually decreases toward the tip is provided at the tip of the male thread portion 2 . A shoulder portion 4 steeply inclined in a direction opposite to the external thread portion 2 and the sealing portion 3 is formed at the tip of the pin 1 . On the other hand, the female snap 5 has an internal thread portion 6 corresponding to the external thread portion 2 on its inner surface, and a sealing portion 7 corresponding to the sealing portion 3 is provided at the inner end of the internal thread portion 6, and a sealing portion 7 corresponding to the sealing portion 3 is provided at the inner end. A shoulder portion 8 corresponding to the shoulder portion 4 is provided.

By screwing the external threaded part 2 into the internal threaded part 6, the sealing parts 3 and 7 are in contact, and the male buckle 1 and the female buckle 5 are sealed by the butt joint of the shoulder parts 4 and 8 . In order to generate sufficient surface pressure on the sealing surface, a radial difference called an interference amount S is provided between the pin-side sealing portion 3 and the box-side sealing portion 7 . The interference amount S is defined as S=D _PX -D _BX (D _PX : the minimum diameter of the pin side seal, D _BX : the minimum diameter of the box side seal), S>0, that is, D _PX >D _BX . By applying the interference amount S, the sealing parts 3 and 7 start to interfere during the screwing (see FIG. 7( a )), and the shoulder parts 4 and 8 come into contact with each other to complete the connection. The axial stroke from the start of interference of the sealing parts 3 and 7 to the completion of the coupling is referred to as the tightening amount MOS.

In this metal surface seal type threaded joint 0 for oil well pipes, due to the diameter difference between the seal parts 3 and 7, the period from the start of interference of the seal parts 3 and 7 to the completion of the connection, that is, the period of screwing in the tightening amount MOS , The sealing parts 3 and 7 slide in a helical shape while maintaining high surface pressure. Therefore, the sealing parts 3 and 7 are prone to sticking (Japanese: 焼付き). If sticking occurs, the sealing surface will become rough, and local gaps and excessive interference will occur, thereby impairing the sealing performance.

Therefore, Patent Document 2 discloses a threaded joint for oil well pipes, that is, in a surface seal type threaded joint 0 for oil well pipes having a metal sealing surface, the sealing parts 3 of the pin 1 and the box 5, The inclination of 7 is made into a taper shape of more than 1/6, so that the inclination is greater than the inclination of the threaded parts 2 and 6, so that the length L _B of the sealing part 7 of the female buckle 5 is greater than the length of the sealing part 3 of the male buckle 1 L _P , between the external threaded part 2 of the pin 1 and the sealing part 3, a front-stage unthreaded part 9a with an inclination smaller than the inclination of the sealing part 3 is formed, and the front-stage unthreaded part 9a is formed by a curve 9b tangent to the sealing part 3. and the sealing part 3, so that the distance from the apex of the arc that exists in the curve 9b and is closest to the tangent point of the curve 9b and the sealing part 3 to the tangent point or from the distance between the front unthreaded part 9a and the sealing part 3 Any one of the smaller distances from the border to the tangent point is 1.45 mm or more.

In brief, the threaded joint for oil well pipes forms a front unthreaded portion 9a with an inclination smaller than the inclination of the sealing portion 3 between the external threaded portion 2 of the pin 1 and the sealing portion 3, and utilizes the arc 9b of the front unthreaded portion 9a. It is connected with the sealing part 3, and the distance up to the intersection point of the arc 9b and the sealing part 3 is 1.45 mm or more to prevent the sealing part 3 from sticking.

Patent Document 1: Japanese Patent Application Laid-Open No. 5-87275

Patent Document 2: Japanese Patent Application Laid-Open No. 8-135855

However, the threaded joint for oil country tubular goods disclosed in Patent Document 2 has problems (i) and (ii) listed below.

(i) As can be seen from the value of "seal portion taper" specifically disclosed as an example of the present invention in Table 2 of Patent Document 2, the taper of seal portions 3 and 7 is as small as 1/6 to 1/2, converted The angle is about 5°～14°. In addition, it is clear from the value of "curvature radius R (mm) of the tangential arc" that the R of the connecting portion between the front unthreaded portion 9a of the pin 1 and the sealing portion 3 is as large as 12 mm to 32 mm. Although this structure can reduce contact stress and is effective for anti-sticking properties, the shape of the sealing portion becomes large.

(ii) Whether the pin 1 and the box 5 interfere at the sealing portions 3, 7 or at the shoulders 4, 8, there is no disclosure on how to prevent the shoulders 4, 8 from sticking.

Contents of the invention

The utility model is as follows.

(1) A threaded joint for oil well pipes, comprising: a pin having a tapered external thread portion, a tapered first seal portion provided at the front end of the external thread portion, and a first tapered seal portion provided at the top end. A shoulder portion and a front unthreaded portion provided between the externally threaded portion and the first sealing portion with an inclination angle smaller than that of the first sealing portion; a box having a tapered internal thread threadedly engaged with the externally threaded portion part, the tapered second sealing part which is arranged at the inner end of the internal thread part and interferes with the first sealing part in the radial direction, and the second sealing part which is arranged at the innermost end and is in the axial direction of the pin with the first shoulder part The second shoulder portion that interferes; it is characterized in that the inclination angles of the first sealing portion and the second sealing portion are both 14° to 30° relative to the axis along the axial direction, and the front unthreaded portion and the first sealing portion utilize The arc portion with a radius of 3mm to 11mm is connected, the inclination angle of the first shoulder and the second shoulder with respect to a line perpendicular to the axis is 5° to 20°, and the front end of the male buckle is formed by a radius of The arc portion of 0.6 mm to 0.9 mm is formed, and the portion of the female snap corresponding to the front end portion of the pin snap is formed of an arc portion with a radius of 0.5 mm or less.

(2) The threaded joint for oil well pipes according to item (1), wherein the external thread portion and the internal thread portion have stabbing flank angles (stabbing flank angles) of 5° to 35°, respectively, and load flank angles ( The load flank angle) is -1°～-5°, and the height of the internal thread part is 0.2mm～0.4mm higher than the height of the external thread part.

(3) The threaded joint for oil country tubular goods according to item (2), wherein the insertion flank clearance when the external thread portion and the internal thread portion are combined is 30 μm to 150 μm.

(4) The threaded joint for oil country tubular goods according to any one of items (1) to (3), wherein the surface roughness of the sealing surfaces of the first sealing part and the second sealing part is averaged on the center line. The roughness meter is 0.8 μm to 3.2 μm.

(5) The threaded joint for oil country tubular goods according to any one of (1) to (4), wherein the pin has an inner peripheral surface in a shape satisfying the following three conditions (A) to (C) : (A) The inner peripheral surface has substantially the same inner diameter as the inner peripheral surface of the box at the connecting portion with the first shoulder; (B) Along the connecting portion from the inner peripheral surface and the first shoulder Towards the axial direction of the rear end side of the pin, a parallel portion with a constant inner diameter is formed from the connecting portion to 2mm or more; (C) an inclined portion is formed following the parallel portion along the axial direction toward the rear end side of the male snap, the The inclined portion is inclined at an angle of ±6° or less with respect to the axial direction.

(6) The threaded joint for oil country tubular goods according to any one of items (1) to (5), wherein when the outer diameter of the pipe is less than 5 inches, the second shoulder is the same as that of the same joint. The distance between the shoulders of adjacent box snaps in the hoop, that is, the shoulder width SW is 25 mm or more, and when the pipe outer diameter is 5 inches or more, the shoulder width SW is 50 mm or more.

According to the utility model of technical solution 1, it is possible to provide a threaded joint for oil well pipes, that is, by increasing the inclination angle of the sealing part to 14° to 30°, and forming it with a circular arc portion with a radius of 3mm to 11mm The sealing part and the front unthreaded part can achieve both small size and excellent adhesion resistance and sealing performance by reducing the distance between the sliding surfaces while ensuring the lowest contact surface where the sealing performance is unstable. In addition, according to the utility model of technical solution 1, the angle of the shoulder surface is in the range of 5° to 20°, and the shape of the front end of the male buckle is made into a circular arc portion with a radius of 0.6mm to 0.9mm, and The shape of the part of the female snap corresponding to the front end of the male snap is made into a circular arc with a radius of 0.5mm or less, which can take advantage of the lifting effect of the sealing part during connection (due to the inclination of the shoulder surface, the male snap and the female snap After the sealing surfaces of the pin and box are in contact with each other, partial pressure is generated in the radial direction of the sealing surfaces of the pin and box, so the surface pressure of the sealing surfaces of the pin and box rises, and stable sealing performance can be exhibited) Stable sealing performance is exhibited, and sticking due to stress concentration at the connecting portion between the shoulder portion and the sealing portion can be prevented.

According to the present invention of Claim 2, it is possible to maintain the compression performance in contact with the stabbing flanks of the threads while suppressing the degree of damage to the stabbing flanks of the threads during stabbing. In addition, according to the present invention of Claim 2, it is possible to maintain cutting performance while suppressing generation of notches or the like on the bearing surface during cutting. Furthermore, according to the present invention of Claim 2, the lubricating pressure generated during the connection can be quickly released without increasing the outer diameter of the box.

In the present invention adopting the technical solution 3, after the shoulder portion is plastically deformed by compression, the insertion flanks of the threads contact each other to support the compressive force, thereby fully satisfying the sealing performance.

According to the present invention of Claim 4, no welding occurs in the sliding phase when joints are connected, and desired sealing performance can be maintained.

The utility model adopting the technical solution 5 can prevent the fluid flow of oil and the like even when the pin buckle and the box buckle are fastened.

Furthermore, according to the present invention of claim 6, stable connection performance can be obtained without being affected by adjacent joint parts.

Description of drawings

FIG. 1 is an explanatory diagram schematically showing a state of a pin and a box of an example of a threaded joint for oil country tubular goods according to the present invention when they are connected.

Fig. 2 is an explanatory diagram partially enlarged showing a pin and a box of the threaded joint for oil country tubular goods.

Fig. 3 is an explanatory diagram schematically showing a state of a pin and a box of another example of the threaded joint for oil country tubular goods according to the present invention being connected.

Fig. 4 is an explanatory diagram partially enlarged showing a pin and a box of the threaded joint for oil country tubular goods.

Fig. 5 is an explanatory view showing the shapes of an externally threaded portion and an internally threaded portion.

6( a ) is an explanatory view showing the overall structure of a conventional threaded joint for oil country tubular goods, and FIG. 6( b ) is an enlarged partial cross-sectional view showing the state when the pin and box of the threaded joint for oil country tubular goods are connected.

Fig. 7(a) is an explanatory diagram schematically showing a state in the middle of connecting a pin and a box of a conventional threaded joint for oil country tubular goods, and Fig. 7(b) is a diagram schematically showing a pin and box of a threaded joint for oil country tubular goods As an explanatory diagram of the situation when the connection is completed, Fig. 7(c) is an enlarged view of the connecting portion between the front non-threaded part and the sealing part, showing enlarged part A of the male buckle in Fig. 7(b).

Detailed ways

The threaded joint for oil well pipe of the present invention will be described with reference to the accompanying drawings.

Fig. 1 is an explanatory diagram schematically showing the state when the pin 11 and the box 21 of an example 10-1 of the threaded joint for oil well pipes of the present invention are connected, and Fig. 2 is the pin of the threaded joint 10-1 for oil well pipes 11 and a partially enlarged explanatory diagram of the female snap 21.

On the other hand, FIG. 3 is an explanatory diagram schematically showing the state of the connection between the pin 11 and the box 21 of another example 10-2 of the threaded joint for oil country tubular goods of the present invention, and FIG. 4 is an illustration of the threaded joint for oil well tubular goods 10-2 is an explanatory diagram showing partially enlarged male buckle 11 and female buckle 21.

In addition, the reference sign Slb in Fig. 2 and Fig. 4 represents the sealing length of the female snap 21, the reference symbol Sab represents the sealing angle of the female snap 21, the reference symbol Bnr represents the radius of the front end of the female snap 21, and the reference symbol Bsa represents the shoulder angle of the female snap 21, the reference symbol Slp represents the sealing length of the male snap 11, the reference symbol Sap represents the sealing angle of the male snap 11, the reference symbol Spr represents the sealing radius of the male snap 11, and the reference symbol Pnr Represents the radius of the front end of the male buckle 11, the reference symbol Pra represents the progressive angle (Japanese: レセス angle: recess angle) of the male buckle 11, the reference symbol Psa represents the shoulder angle of the male buckle 11, and the reference symbol Stp represents the male buckle 11. The front stage of the buckle 11 has no threaded portion, and reference symbol Ttp denotes a threaded tapered surface of the pin buckle 11 . In addition, reference symbol Pil in FIG. 4 represents the length of the parallel portion (inner cylindrical portion) in the inner peripheral surface of the pin 11 .

As shown in Figures 1 and 2, the threaded joint 10-1 for oil well pipes includes a male buckle 11 and a female buckle 21, and, as shown in Figures 3 and 4, the threaded joint 10-2 for oil well pipes also includes a male buckle 11 and a female buckle 21. Buckle 21.

The pin 11 includes an external thread portion 12 , a first sealing portion 13 , a first shoulder portion 14 and a front unthreaded portion 15 .

The external thread portion 12 is formed in a tapered shape on the outer surface of the pin 11 . The first sealing portion 13 is provided in a tapered shape at the tip of the external thread portion 12 . The first shoulder portion 14 is provided in a stepped shape at the tip of the male buckle 11 . Furthermore, the front unthreaded portion 15 is provided between the externally threaded portion 12 and the first seal portion 13 so that the inclination angle with respect to the axis is smaller than the inclination angle of the first seal portion 13 with respect to the axis.

The male snap 11 has an inner peripheral surface 11 a having a shape satisfying three conditions (A) to (C) enumerated below.

(A) The inner peripheral surface 11 a has substantially the same inner diameter as the corresponding position 21 b of the inner peripheral surface 21 a of the box snap 21 at the connection portion 11 b to the first shoulder portion 14 .

(B) Along the axial direction (the left direction in FIG. 2 and FIG. 4 ) from the connecting portion 11 b of the inner peripheral surface 11 a and the first shoulder portion 14 toward the rear end side of the pin 11 , the parallel portion with a constant inner diameter 11c is formed 2 mm or more from the connection part 11b.

(C) Following the parallel portion 11c, an inclined portion 11d is formed along the axis direction (left direction in FIGS. 2 and 4 ) toward the rear end side of the male buckle 11, and the inclined portion 11d is formed at an angle with the axis direction. Tilt at an angle of ±6° or less. Fig. 1, Fig. 2 is the case where the inclined part 11d inclined at an angle formed with the axis direction is +6° or less; The case of the inclined portion 11d inclined at an angle of less than °.

The threaded joint 10-1 for oil well pipes and the threaded joint 10-2 for oil well pipes of the present utility model include a pin 11 having an inner peripheral surface 11a in a shape that satisfies the three conditions (A) to (C). Even when the buckle and the box are fastened, the fluid flow such as oil will not be hindered.

On the other hand, the box snap 21 includes an internal thread portion 22 , a second seal portion 23 , and a second shoulder portion 24 .

The internal thread portion 22 is formed in a tapered shape on the inner peripheral surface 21 a of the box 21 , and is screwed to the external thread portion 12 of the pin 11 . The second sealing portion 23 is tapered at the inner end of the female thread portion 22 and interferes with the first sealing portion 13 of the pin 11 in the radial direction. Furthermore, the second shoulder portion 24 is provided at the innermost end of the box snap 21 and interferes with the first shoulder portion 14 of the pin snap 11 in the axial direction of the pin snap 11 .

In addition, the distance SW in FIGS. 1 and 3 is called a shoulder width. Shoulder width SW is the spacing between the 2nd shoulder and the shoulder of the adjacent box in the same coupling, 2-3/8 for pipe outside diameters less than 5 inches, such as API specifications (19/8) inches to 4-1/2 (9/2) inches of tubing, the shoulder width SW is preferably 25 mm or more, and the outer diameter of the tube is 5 inches or more, for example, 5 inches under the API standard In a casing of ~16 inches or more, the shoulder width SW is preferably 50 mm or more. In the case of threaded joints, the dimension in the radial direction changes subtly once the connection is completed, but by ensuring the above-mentioned shoulder width, a stable joint can be obtained without being affected by fluctuations caused by the connection of adjacent joint parts. link performance.

The inclination angles with respect to the axis of the first seal portion 13 and the second seal portion 23 are both 14° to 30° with respect to the axis along the axial direction. In a material such as a high alloy, if the inclination angle is less than 14°, the distance between the sliding surfaces where the first sealing portion 13 and the second sealing portion 23 slide becomes longer, and sticking tends to occur. On the other hand, when the inclination angle is larger than 30°, although adhesion does not occur, the width of the portion where surface pressure is generated during stretching is 0.5 mm or less, and the sealing performance is unstable.

The front unthreaded portion 15 and the first sealing portion 13 are connected by an arc portion with a radius of 3 mm to 11 mm. The reason for this is that when connecting with an arc portion with a radius of less than 3 mm, the surface pressure locally rises, and the sealing portion tends to stick. On the other hand, when connecting with an arc portion with a radius larger than 11 mm, there is no problem in the anti-sticking property, but the shape of the sealing portion becomes large.

The inclination angle of the first shoulder portion 14 and the second shoulder portion 24 with respect to a line perpendicular to the axis (hereinafter also referred to as “sub-shoulder angle”) is 5° to 20°. When the auxiliary shoulder angle is less than 5°, the surface pressure rise caused by the lifting effect on the metal seal cannot be reflected when connecting with the male buckle 11. When the auxiliary shoulder angle is greater than 20°, the metal seal of the female buckle 21 and the second The stress concentration at the corner portion formed by the shoulder portion 24 increases, which is not preferable.

The front end 16 of the male snap 11 is formed by an arc with a radius of 0.6 mm to 0.9 mm, and the portion 25 of the female snap 21 corresponding to the front end 16 of the male snap 11 is formed by an arc with a radius of 0.5 mm or less.

The radius of the arc portion of the front end 16 of the male snap 11 is larger than the radius of the arc of the portion 25 of the female snap 21 corresponding to the front end 16 of the male snap 11 . The reason for this is that they interfere with each other and do not stick together. In addition, since making the height of the shoulder extremely high is effective for compression performance and torque performance, in the conventional threaded joint for oil well pipes, the radius of the arc portion of the front end 16 of the pin 11, the distance between the box 21 and the It is preferable that the radius of the arc portion of the portion 25 corresponding to the front end portion 16 of the male buckle 11 is extremely small.

In the threaded joint 10-1 for oil well pipe and the threaded joint 10-2 for oil well pipe having the above elements, the inclination angle of the sealing parts 13 and 23 is increased to 14° to 30°, and the seal is formed by an arc portion with a radius of 3 mm to 11 mm. Parts 13, 23 and the connection part of the front unthreaded part 15, therefore, by reducing the distance of the sliding surface while ensuring the lowest contact surface that does not cause unstable sealing performance, small size and excellent adhesion resistance can be achieved. tightness.

In addition, in the threaded joint 10-1 for oil well pipe and the threaded joint 10-2 for oil well pipe, the angle of the secondary shoulder is in the range of 5° to 20°, and the shape of the front end 16 of the pin 11 is made into a radius of 0.6 mm to 0.9 mm. mm, and the shape of the portion 25 of the female snap 21 corresponding to the front end portion 16 of the male snap 11 is made into an arc portion with a radius of 0.5mm or less, so that the sealing portion 13, The lifting effect of 23 exhibits stable sealing performance, and can prevent sticking due to stress concentration at the connecting portion of the shoulder portions 14, 24 and the sealing portions 13, 23.

FIG. 5 is an explanatory view showing the shapes of the externally threaded portion 12 and the internally threaded portion 22 . Reference numeral θ ₁ in Fig. 5 represents the stabbing flank angle, reference numeral θ ₂ represents the load flank angle, reference numeral H _P represents the height of the external thread portion 12, and reference numeral H _B represents the height of the internal thread portion 22. Height, the reference symbol C _S represents the insertion flank clearance, and T _ta represents the thread taper.

The externally threaded part 12 and the internally threaded part 22 have an insertion flank angle _θ1 of 5° to 35°, a load flank angle _θ2 of -1° to -5°, and the height H of the internal thread portion 22 is higher than _B The height H _P of the external thread portion 12 is a trapezoidal thread higher than 0.2 mm to 0.4 mm.

The BTC specification of API has been used in the market for many years, and the insertion flank angle of about 10° is a common sense dimension. When the insertion flank angle is less than 5°, the degree of damage to the insertion flank of the thread during stabbing is relatively large. On the other hand, when the stabbing flank angle is larger than 35°, the compression performance under contact of the stabbing flanks of the thread decreases. Therefore, in the present invention, the stabbing flank angle θ ₁ is preferably 5° to 35°.

In addition, in view of bending stretching, etc., if the load flank angle is a negative angle, it is difficult to slip out (jump out), but the cutting performance is poor. Therefore, the load flank angle should not be larger than -5°. The angle is better, but when the load flank angle is 0°, there will be notches on the load surface during cutting, so it cannot be completely negative angle. Therefore, in terms of accuracy, the load flank angle is preferably -1° or more. Therefore, the load flank angle θ ₂ is preferably -1° to -5°.

Furthermore, when the height H _B of the internal thread portion 22 is the same as the height H _P of the external thread portion 12, the lubricating pressure generated during the connection increases, and the box cannot be completely disengaged from the end surface. When the difference between the height H _B of the internal thread portion 22 and the height H _P of the external thread portion 12 is less than 0.2 mm, the release of the lubricating pressure at the time of connection is slow, and even when entering the well after 24 hours from the connection, there remains with lubrication pressure. And, when the height H _B of the internal thread part 22 is 0.4mm higher than the height H _P of the external thread part 12, although the lubricating pressure during connection is released, the height H _B of the internal thread part 22 is too high. The same thread efficiency cannot be obtained by increasing the outer diameter of the box snap 21 . Therefore, a trapezoidal thread in which the height H _B of the internal thread portion 22 is 0.2 mm to 0.4 mm higher than the height H _P of the external thread portion 12 is preferable.

When the insertion flank clearance _CS of the combination of the external thread portion 12 and the internal thread portion 22 is 30 μm or less, due to Poisson’s ratio, the insertion flanks contact each other at the time of connection, resulting in an increase in the torque or the insertion flank may Side bonding. In addition, as the insertion flank clearance C _S becomes larger, the threaded portions 11, 21 become out of contact, and the insertion flanks of the threads contact each other after the shoulder portions 14, 24 are plastically deformed by compression, thereby supporting the compressive force. role. The limit value of the insertion flank clearance C _S is about 150 μm. When the insertion flank clearance C _S becomes larger than 150 μm, the shoulders 14 and 24 undergo large plastic deformation, which cannot meet the sealing performance. Therefore, the insertion flank clearance C _S is preferably 30 μm to 150 μm.

The surface roughness of the sealing surfaces of the first sealing part 13 and the second sealing part 23 is small, and the sealing performance is high. However, in the sliding stage when the joint is connected, the surface roughness is less than 0.8 μm in terms of centerline average roughness. will result in welding. In addition, when the surface roughness becomes larger than 3.2 μm in terms of the center line average roughness, the undulation in the longitudinal direction becomes large, thereby deteriorating the sealing performance. Therefore, the surface roughness of each sealing surface of the first sealing portion 13 and the second sealing portion 23 is preferably 0.8 μm to 3.2 μm in terms of center line average roughness.

Explanation of reference signs

0. The threaded joint for oil well pipes disclosed by Patent Document 1; 1. Male thread; 2. External thread; 3. Seal; 4. Shoulder; 5. Box; 6. Internal thread; 7. Seal 8, shoulder portion; 9a, front section without thread portion; 9b, curve tangent to sealing portion; 10-1, 10-2, threaded joint for oil well pipe of the present utility model; 11, male buckle; 11a, inner circumference 11b, connection part; 11c, parallel part; 11d, inclined part; 12, external thread part; 13, first sealing part; 14, first shoulder part; 15, front section without thread part; 16, front end part; 21. Female buckle; 21a, inner peripheral surface; 21b, corresponding position; 22. Internal thread part; 23. Second sealing part; 24. Second shoulder part; 25. The part corresponding to the front end of the male buckle .

Claims (10)

1. A threaded joint for oil well pipes, the threaded joint for oil well pipes comprising: The pin has a tapered external thread portion, a tapered first sealing portion provided at the front end of the external thread portion, a first shoulder portion provided at the top end, and a seal provided between the external thread portion and the first sealing portion, the front unthreaded portion whose inclination angle is smaller than the inclination angle of the above-mentioned first sealing portion; A box having a tapered internal thread portion screwed to the external thread portion, and a tapered second sealing portion provided at the inner end of the internal thread portion and interfering with the first sealing portion in the radial direction and a second shoulder portion disposed at the innermost end and interfering with the first shoulder portion in the axial direction of the pin buckle; characterized in that, The inclination angles of the first sealing portion and the second sealing portion are both 14° to 30° with respect to the axis along the axial direction, The front unthreaded portion and the first sealing portion are connected by an arc portion with a radius of 3 mm to 11 mm, The inclination angle of the above-mentioned first shoulder portion and the second shoulder portion with respect to a line perpendicular to the above-mentioned axis is 5° to 20°, and The front end of the male snap is formed by an arc with a radius of 0.6 mm to 0.9 mm, and the portion of the female snap corresponding to the front end of the pin is formed by an arc with a radius of 0.5 mm or less. 2. The threaded joint for oil well pipe according to claim 1, characterized in that: The above-mentioned male thread portion and the above-mentioned internal thread portion have an insertion flank angle of 5° to 35° and a load flank angle of -1° to -5°, and the height of the above-mentioned internal thread portion is higher than the height of the above-mentioned external thread portion. Trapezoidal threads with a height of 0.2mm to 0.4mm. 3. The threaded joint for oil well pipe according to claim 2, characterized in that: When the above-mentioned external thread portion and internal thread portion are combined, the insertion flank clearance is 30 μm to 150 μm. 4. The threaded joint for oil country tubular goods according to any one of claims 1 to 3, characterized in that: The surface roughness of each sealing surface of the said 1st sealing part and the said 2nd sealing part is 0.8 micrometer - 3.2 micrometers in centerline average roughness. 5. The threaded joint for oil country tubular goods according to any one of claims 1 to 3, characterized in that: The above-mentioned male buckle has an inner peripheral surface of a shape satisfying the following three conditions (A) to (C): (A) The inner peripheral surface has substantially the same inner diameter as that of the inner peripheral surface of the box at the connection portion with the first shoulder; (B) A parallel portion with a constant inner diameter is formed at least 2 mm from the connection portion along the axis direction from the connection portion between the inner peripheral surface and the first shoulder portion toward the rear end side of the pin; (C) Next to the parallel portion, an inclined portion is formed along the axial direction toward the rear end side of the pin, and the inclined portion is inclined at an angle of ±6° or less with the axial direction. 6. The threaded joint for oil well pipe according to claim 4, characterized in that: The above-mentioned male buckle has an inner peripheral surface of a shape satisfying the following three conditions (A) to (C): (A) The inner peripheral surface has substantially the same inner diameter as that of the inner peripheral surface of the box at the connection portion with the first shoulder; (B) A parallel portion with a constant inner diameter is formed at least 2 mm from the connection portion along the axis direction from the connection portion between the inner peripheral surface and the first shoulder portion toward the rear end side of the pin; (C) Next to the parallel portion, an inclined portion is formed along the axial direction toward the rear end side of the pin, and the inclined portion is inclined at an angle of ±6° or less with the axial direction. 7. The threaded joint for oil country tubular goods according to any one of claims 1 to 3, characterized in that: When the outer diameter of the pipe is less than 5 inches, the distance between the above-mentioned second shoulder and the shoulder of the adjacent box snap in the same coupling, that is, the shoulder width is 25mm or more. When the shoulder width is 5 inches or more, the shoulder width is 50 mm or more. 8. The threaded joint for oil well pipe according to claim 4, characterized in that: When the outer diameter of the pipe is less than 5 inches, the distance between the above-mentioned second shoulder and the shoulder of the adjacent box snap in the same coupling, that is, the shoulder width is 25mm or more. When the shoulder width is 5 inches or more, the shoulder width is 50 mm or more. 9. The threaded joint for oil well pipe according to claim 5, characterized in that: When the outer diameter of the pipe is less than 5 inches, the distance between the above-mentioned second shoulder and the shoulder of the adjacent box snap in the same coupling, that is, the shoulder width is 25mm or more. When the shoulder width is 5 inches or more, the shoulder width is 50 mm or more. 10. The threaded joint for oil well pipe according to claim 6, characterized in that: When the outer diameter of the pipe is less than 5 inches, the distance between the above-mentioned second shoulder and the shoulder of the adjacent box snap in the same coupling, that is, the shoulder width is 25mm or more. When the shoulder width is 5 inches or more, the shoulder width is 50 mm or more.

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