CN212377489U

CN212377489U - Threaded joint

Info

Publication number: CN212377489U
Application number: CN202020281700.3U
Authority: CN
Inventors: 川井孝将; 吉川正树; 高野顺; 米山毅; 后藤城吾
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2019-03-14
Filing date: 2020-03-09
Publication date: 2021-01-19
Anticipated expiration: 2030-03-09
Also published as: JPWO2020183860A1; CN111692439A; AR118313A1; WO2020183860A1

Abstract

The utility model provides a compression resistance and the excellent screwed joint of leakproofness. In a threaded joint (1), a male thread portion (4a) is joined by the thread of a tapered thread (4) so that both a thread top surface (7) and a thread bottom surface (8) are in contact with a female thread portion (4b) on both an insertion surface (9) and a load surface (10) with a clearance between the female thread portion (4b), the insertion surface flank angle (alpha) of the tapered thread (4) is 30 degrees or more and 50 degrees or less, the load surface flank angle (beta) of the tapered thread (4) is-10 degrees or more and less than 0 degree, the taper, which is the amount of change in diameter per unit length in the axial direction of the tapered thread (4), is 1/10 or more and 1/4 or less, and the seal taper angle (gamma) of the female thread seal portion (11b) is 3 degrees or more and 10 degrees or less.

Description

Threaded joint

Technical Field

The present invention relates to a threaded joint, and more particularly to a threaded joint including: the present invention is suitably used for connection of steel pipes such as oil country tubular goods including pipes and casings, i.e., OCTG (oil country tubular goods), risers, and line pipes, which are generally used for exploration and production of oil wells and gas wells, and has excellent compression resistance and sealability.

Background

Threaded joints are widely used for connecting steel pipes used in oil production industrial facilities such as oil country tubular goods. Conventionally, a standard threaded joint defined by API (american petroleum institute) standards has typically been used for connecting steel pipes used for oil and gas exploration and production.

In recent years, deep drilling of crude oil and natural gas wells has progressed, and since horizontal wells, directional wells, and the like have been added to vertical wells, the excavation and production environment has become more severe. Further, as well development in severe environments such as the ocean and polar regions is increasing, the performance required for threaded joints, such as compression resistance, bending resistance, and external pressure sealing performance (external pressure resistance), is becoming more and more diverse. Due to such required performance, in recent years, the use of a high-performance special threaded joint called a special joint has increased.

The special joints described above are typically provided with tapered threads, seals (metal contact seals), and torque shoulders, respectively, at the ends of the pipes that are connected to each other. These structures constitute each of a male snap, which is a male threaded portion provided on one pipe, and a female snap, which is a female threaded portion provided on the other pipe and screwed or fitted to the male threaded portion. These elements are designed so that the elements of the same name of the internal and external threads face each other when the joint (meaning of a threaded joint, the same hereinafter) is tightened.

The tapered threads described above are necessary to securely fix the joint. In addition, the sealing portion ensures sealability by metal contact between the box and the pin in the region of the sealing portion. The seal portion is generally formed such that a male snap seal portion provided in the male snap has a convex tubular axial sectional shape, and a female snap seal portion provided in the female snap has a tapered tubular axial sectional shape. The torque shoulder portion serves as a shoulder surface that serves as a stopper for fastening the joint.

In addition, in order to reduce the excavation amount in the development of a well, it is required to make the joint slim. In order to make the joint slim, it is effective to exclude the torque shoulder, in which case the threaded portion is burdened with the action of the stopper and is subjected to the action of axial forces. In order to achieve the above-described effects, the male thread portion needs to be engaged by the thread of the tapered thread, and the female thread portion needs to be in contact with both the load surface and the insertion surface in a state where a clearance is left between both the thread top surface and the thread bottom surface and the female thread portion. The tapered thread of this type is referred to as a tube axis direction interference tapered thread. The joint having the axial interference tapered thread has a high compression resistance because the total of the areas of the bearing force increases as the axial force is received by the thread surface.

An example of a conventional technique for interfering a tapered thread in the axial direction of a pipe is described in patent document 1. Problems of the utility model described in patent document 1 are: taking into account the machining tolerances in actual manufacture, contact is always made at the thread joining on both the load and insert faces in any machining result within the tolerances. In addition, in the utility model described in patent document 1, a formula is proposed in which the relationship between the load surface flank angle, the insertion surface flank angle, the clearance generated between the thread top surface and the thread bottom surface, and the pipe axis direction clearance assumed by the machining tolerance is defined, and according to this formula, it is described that the contact can be generated inevitably at the time of the thread joining between the load surface and the insertion surface.

Patent document 1: japanese patent No. 3714199

The formula described in patent document 1 is as follows: when the tapered thread is tightened, contact at the thread top surface and the thread bottom surface is prevented, and contact at both the load surface and the insertion surface is always ensured. However, the fastening amount required to achieve contact is not taken into consideration, and the degree of dimensional variation in the position in the pipe axial direction at the time of fastening completion is greatly affected by the machining. Since the pipe axial direction stop position at the time of screw fastening greatly affects the contact state of the seal portion, if the contact state is too small due to dimensional variations of the tapered thread, the sealability becomes insufficient, and conversely, if the contact state is too large, there is a concern that the seizure may occur.

SUMMERY OF THE UTILITY MODEL

In view of the above problems, an object of the present invention is to provide a threaded joint having excellent compression resistance and sealing performance.

The present invention has been made in order to solve the above problems, and the following findings have been obtained. First, in the conventional technique, the dimensional deviation causes insufficient sealability and heat adhesion because the dimensional deviation greatly affects the contact state of the seal portion (hereinafter, also referred to as a seal interference amount). Therefore, it is important to design the tapered thread and the seal portion so as to suppress the influence of the dimensional variation on the seal interference amount. In a tapered thread composed of a substantially trapezoidal thread ridge, the amount of change in the clearance in the pipe axial direction with respect to the amount of rotation during fastening of the tapered thread can be increased by increasing the difference between the width of the thread ridge portion and the width of the thread ridge bottom portion. Therefore, by increasing the difference in width between the thread crest portion and the thread root portion, the influence of dimensional deviation (deviation in clearance in the pipe axial direction) on the pipe axial direction stop position at the time of fastening completion can be suppressed. However, since the load surface is desirably formed at a negative angle to prevent the jump-out, the absolute value is designed to be small at the negative angle, and the insertion surface needs to be designed at a large angle to secure the width difference. By setting the amount of change in the diameter of the tapered thread per unit length in the axial direction of the thread, i.e., the taper, to a slightly large amount, the thread is tightened by a small tightening amount, and therefore the influence of dimensional variations on the axial stop position at the end of tightening can be suppressed. Further, by reducing the seal taper angle of the box seal portion, the influence of the pipe axial direction stop position at the time of fastening end on the seal interference amount can be suppressed.

The gist of the present invention completed based on the above findings is as follows.

1. A threaded joint having:

a pin formed at a pipe end portion and including a male screw portion having a tapered thread and a pipe mouth portion outer peripheral surface located closer to the pipe end side than the male screw portion; and

a female snap provided with a female screw portion of the tapered thread and an inner peripheral surface of the seal hole facing the outer peripheral surface of the pipe opening,

the male screw portion is engaged with the female screw portion by the thread of the tapered thread so as to contact both the insertion surface and the load surface with the female screw portion with a clearance left between both the thread top surface and the thread bottom surface and the female screw portion,

the outer peripheral surface of the pipe opening has a male seal portion having a convex pipe axial sectional shape,

the inner peripheral surface of the seal hole has a box seal portion which is joined to the pin seal portion by the screw thread and which is in metal contact with the pin seal portion in a pipe radial direction to form a seal portion for sealing fluid, and the box seal portion has a tapered tubular axial sectional shape,

the insertion face flank angle of the tapered thread is 30 degrees or more and 50 degrees or less, and the load face flank angle of the tapered thread is-10 degrees or more and less than 0 degree,

the amount of change in diameter per unit length in the axial direction of the tapered thread, i.e., the taper, is 1/10 or more and 1/4 or less,

the seal taper angle of the female snap seal portion is 3 degrees or more and 10 degrees or less.

In addition, the shape, angle, and dimension of the tapered thread and the seal portion defined in the present application mean the shape, angle, and dimension in a state before the tapered thread is fastened (in other words, a state in which no load is applied).

2. The threaded joint according to claim 1, wherein the thread height T of the male thread portion is 0.04 inches or more and 0.10 inches or less.

3. According to the threaded joint of the above 1 or 2, a ratio T/W of the width W of the thread bottom portion of the male thread portion to the thread height T is 0.2 or more and 1.0 or less.

According to the utility model discloses, can obtain the screwed joint that resistance to compression nature and leakproofness are excellent.

Drawings

Fig. 1 is a tubular shaft sectional view showing a one-piece threaded joint which is an example of the embodiment of the present invention.

Fig. 2 is a tubular shaft sectional view showing a combination type threaded joint which is an example of the embodiment of the present invention.

Fig. 3 is an enlarged view of a portion a of fig. 1 and 2. Indicating a state in which both the insertion surface and the load surface are in contact.

Fig. 4 is an enlarged view of a portion B of fig. 1 and 2. The drawing showing the same dimensions of both the pin and the box shows the state of overlap of the seal portions when the insertion surface of the screw portion and both the load surfaces are overlapped in contact as shown in fig. 3.

Description of reference numerals:

1 … threaded joint; 2 … male buckle; 3 … female buckle; 4 … tapered threads; 4a … external threaded portion; 4b … internal threaded portion; 5 … pipe mouth peripheral surface; 6 … sealing the inner periphery of the hole; 7. 7' … thread top surface; 8. 8' … thread bottom; 9. 9' … inset face; 10. 10' … load plane; 11 … sealing part; 11a … male seal; 11b … female snap seal; α … stab flank angle; beta … load face flank angle; gamma … seal taper angle; x … tube core; s … reference plane; t … thread height; w … width of thread root.

Detailed Description

Hereinafter, embodiments of the present invention will be described by way of example with reference to the accompanying drawings.

As shown in fig. 1 and 2, a threaded joint 1 according to an embodiment of the present invention is a special joint for connecting oil country tubular goods by a pin 2 and a box 3. The threaded joint 1 may be a single-piece type in which steel pipes are directly connected to each other by the pin 2 and the box 3 as shown in fig. 1, or may be a combined type in which steel pipes having the pin 2 are connected to each other via a combination having the box 3 as shown in fig. 2. In fig. 1 and 2, only one side of the tube axis X is shown in cross section. The threaded joint 1 can also be applied to connection of steel pipes and the like other than oil country tubular goods.

The pin 2 is formed at a pipe end portion, and has a male screw portion 4a having a tapered thread 4 and a pipe end portion outer peripheral surface 5 located closer to the pipe end side than the male screw portion 4 a. The box 3 has a female screw portion 4b of the tapered thread 4 and a seal hole inner peripheral surface 6 facing the pipe mouth outer peripheral surface 5.

As shown in fig. 3, the male screw portion 4a is configured to: the thread engagement of the tapered thread 4 causes both the thread top surface 7 and the thread bottom surface 8 to contact the female thread portion 4b on both the insertion surface 9 and the load surface 10 with a clearance left between the female thread portion 4 b. That is, the tapered thread 4 is constituted such that: by the screw engagement, in a state where a clearance remains between the thread top face 7 of the male thread portion 4a and the thread bottom face 8 'of the female thread portion 4b and a clearance remains between the thread bottom face 8 of the male thread portion 4a and the thread top face 7' of the female thread portion 4b, the insertion face 9 of the male thread portion 4a and the insertion face 9 'of the female thread portion 4b are in contact with each other and the load face 10 of the male thread portion 4a and the load face 10' of the female thread portion 4b are in contact with each other. The "clearance" mentioned above means a clearance sufficient to bring about the tightening of both the insertion surfaces 9, 9 'and the load surfaces 10, 10' at the time of the threaded engagement of the tapered threads 4, i.e. at the end of the tightening.

The tapered thread 4 achieves a firm connection by making contact at both the insertion surfaces 9, 9 'and the load surfaces 10, 10'. An acute angle formed by the insertion surface 9 and a straight line perpendicular to the tube axis X in a cross section including the tube axis X, that is, a tube axis cross section is defined as an insertion surface flank angle α, and as shown in fig. 3, a reference numeral of the insertion surface flank angle α is positive when the insertion surface 9 is inclined toward a radially outer side (hereinafter, also simply referred to as a radially outer side) of the tube axis X and toward the load surface 10. In addition, an acute angle formed by the load surface 10 and a straight line perpendicular to the pipe axis X in the pipe axial cross section is a load surface flank angle β, and a case where the reference numeral of the load surface flank angle β is inclined toward the insertion surface 9 side while the load surface 10 is directed radially outward is positive (the reference numeral of the load surface flank angle β shown in fig. 3 is negative).

In order to secure a difference in width between the thread crest and the thread root, the flank angle α of the insertion surface needs to be set to 30 degrees or more. By setting the insertion surface flank angle α to 30 degrees or more, the amount of change in the clearance in the pipe axial direction (in other words, the direction along the pipe axis X) when the tapered thread 4 is fastened (in other words, the clearance at the insertion surfaces 9, 9 'and the load surfaces 10, 10') with respect to the amount of rotation can be increased, and the influence of dimensional variations (variations in the clearance in the pipe axial direction) on the pipe axial direction stop position can be suppressed. However, if the insertion surface flank angle α is excessively increased, the compressive force in the tube axial direction is no longer efficiently received, and therefore, it is necessary to be 50 degrees or less. In order to prevent the jump-out, the load surface flank angle β needs to be a negative value, and needs to be less than 0 degree, but if the absolute value is excessively increased, the difference in width between the thread crest and the thread root is no longer ensured, and thus needs to be-10 degrees or more. The load face flank angle β is preferably-10 degrees or more and-3 degrees or less.

The thread taper, which is the amount of change in diameter per unit length in the tubular axial direction of the reference surface S of the male thread portion 4a that coincides with the thread bottom surface 8, needs to be 1/10 or more. By setting the screw taper to 1/10 or more, the tapered screw 4 can be tightened with a small tightening amount, and the influence of dimensional deviation on the pipe axis direction stop position at the time of completion of tightening can be suppressed. However, if the thread taper is excessively increased, the thickness of the pin seal portion 11a, which will be described later, cannot be ensured any more, and the sealability cannot be ensured any more, so that the thread taper needs to be 1/4 or less.

As shown in fig. 4, the nozzle portion outer peripheral surface 5 has a male seal portion 11a, and the male seal portion 11a has a pipe axial sectional shape (in other words, a shape at the pipe axial sectional surface) curved in a convex shape. However, the cross-sectional shape of the male seal portion 11a in the pipe axis direction is not limited to a convex shape in a curved shape, and may be a convex shape. The seal hole inner peripheral surface 6 has a box seal portion 11b, the box seal portion 11b is in metal contact with the pin seal portion 11a in the pipe radial direction (in other words, the radial direction of the pipe axial center X) by screw engagement of the tapered thread 4, and forms a seal portion 11 that seals fluid, and the box seal portion 11b has a tapered pipe axial sectional shape. In other words, the seal portion 11 of the radial seal structure is constituted by the pin seal portion 11a and the box seal portion 11 b.

The box seal portion 11b is a conical surface having a truncated cone shape. An acute angle formed by the female snap seal portion 11b and a line parallel to the pipe axis X in the pipe axis cross section is set as a seal taper angle γ. In order to reduce the influence of the pipe axial direction stop position at the time of screwing of the tapered thread 4 on the contact state (seal interference amount) of the seal portion 11, the seal taper angle γ needs to be 10 degrees or less. However, if the seal taper angle γ is excessively reduced, the sliding distance becomes long and the risk of thermal sticking increases, and therefore the seal taper angle γ needs to be set to 3 degrees or more. Further, if the seal taper angle γ is less than 3 degrees, a large step can be easily formed at the boundary between the seal portion and the threaded portion, and in this case, it is hard to say that the design itself is established. This is because the pin is likely to be thermally bonded when it comes into contact with the step portion during the screw-fastening.

The thread height T of the male thread portion 4a is preferably 0.04 inch (0.04 inch × 25.4 mm/inch ═ 1.016mm) or more and 0.10 inch (0.10 inch × 25.4 mm/inch ═ 2.54mm) or less. Here, the thread height T is a distance between an intersection of a straight line perpendicular to the tube axis X and the reference plane S and an intersection of the straight line and the thread top surface 7 in the tube axis cross section. In the case where the thread height T is less than 0.04 inch, there is a concern that: the contact surface cannot be sufficiently secured and excessive plastic deformation occurs in the tapered thread 4 due to the axial force, and the function as a joint is lost. On the other hand, if the thread height T exceeds 0.10 inches, the cross-sectional area of the critical cross-section may be reduced, and the tensile strength of the joint may not be sufficiently ensured.

Preferably, the ratio T/W of the width W of the thread root portion of the male thread portion 4a to the thread height T is 0.2 or more and 1.0 or less. Here, the width W of the thread bottom portion is a distance between a straight line perpendicular to the tube axis X and including an intersection of a straight line including the load surface 10 and a straight line including the reference surface S, and a straight line perpendicular to the tube axis X and including an intersection of a straight line including the insertion surface 9 and a straight line including the reference surface S, in the tube axis cross section. If T/W is less than 0.2, the contact surface may not be sufficiently ensured. If T/W exceeds 1.0, the cross-sectional area of the critical cross-section may not be sufficiently ensured.

As described above, the threaded joint 1 satisfies the conditions that the insertion surface flank angle α is 30 degrees or more and 50 degrees or less, the load surface flank angle β is-10 degrees or more and less than 0 degrees, the thread taper is 1/10 degrees or more and 1/4 degrees or less, and the seal taper angle γ is 3 degrees or more and 10 degrees or less, and can exhibit excellent compression resistance and sealability.

The present embodiment has been described above by way of example, but the present invention is not limited thereto, and can be appropriately modified in the claims.

Examples

A sample was prepared for a threaded joint comprising a pin, which was formed by machining an end of a steel pipe of API 5CT steel type P110 having an outer diameter of 5.5 inches × a wall thickness of 0.415 inches (outer diameter 139.70mm × wall thickness 10.54mm), and a box corresponding thereto, and the sample was subjected to a pressure treatment in ISO 13679: 2002, and air tightness test. In this case, experiments were carried out under the experimental conditions at the respective levels shown in table 1. As an influence of the variation due to the dimensional tolerance, as shown in the drawing, the case where the clearance exists in the pipe axis direction when the screw is screwed in was set to be positive, and the case where the interference exists was set to be negative, and the case where the variation with the absolute value of 0.004 inches was evaluated. As experimental conditions not shown in table 1, the number of threads per 1 inch was set to 5(5TPI), the thread height T of the male thread portion was 0.05 inch, and the thread width (in the direction parallel to the tube axis X) at a height of 0.03 inch (from the reference plane S toward the direction perpendicular to the tube axis X) was set to 0.1 inch (half pitch) in common in all levels. The width W of the thread root of the male thread portion can be calculated from the stabbing surface flank angle alpha and the load surface flank angle beta, and the ratio T/W of the width W of the thread root to the thread height T is 0.38-0.47. Joint efficiency was designed to be 75% at all levels and in the hermetic test, the test was performed with 75% load applied while applying tension/compression relative to 95% VME.

In the example of the utility model satisfying the above conditions, the influence of the dimensional deviation on the amount of seal interference can be suppressed to a level free from problems, and the test result is acceptable. On the other hand, in comparative examples that do not satisfy the above conditions (particularly, the conditions that the stabbing face flank angle is 30 degrees or more, the thread taper is 1/10 or more, and the seal taper angle is 10 degrees or less), hot sticking or leakage occurs, and the test results are failed. In the comparative example, the heat adhesion occurred during the fastening relaxation test under the condition that the pipe axis direction stop position was largely positive and the seal interference amount was excessively large, and on the contrary, the leakage occurred during the airtight test under the condition that the pipe axis direction stop position was largely negative and the seal interference amount was excessively small.

[ Table 1]

Claims

1. A threaded joint, having:

a box having a female screw portion of the tapered thread and a seal hole inner peripheral surface facing the pipe mouth portion outer peripheral surface,

the male screw portion is engaged with the female screw portion at both an insertion surface and a load surface by the thread of the tapered thread, with a clearance left between both a thread top surface and a thread bottom surface and the female screw portion,

the outer peripheral surface of the pipe opening part is provided with a male buckle sealing part which has a convex pipe shaft section shape,

the inner peripheral surface of the seal hole has a box seal portion that is joined to the pin seal portion by the screw thread and that forms a seal portion for sealing fluid by making metal contact with the pin seal portion in a pipe radial direction, and the box seal portion has a tapered tubular axial sectional shape,

the amount of change in diameter per unit length in the axial direction of the tapered thread, i.e., the taper, is 1/10-1/4 inclusive,

the seal taper angle of the box seal portion is 3 degrees or more and 10 degrees or less.

2. The threaded joint as set forth in claim 1,

the thread height T of the external thread portion is 0.04 inches or more and 0.10 inches or less.

3. The threaded joint according to claim 1 or 2,

the ratio T/W of the width W of the thread root of the male thread portion to the thread height T is 0.2 to 1.0.