JPWO2020183860A1 - Threaded joint - Google Patents

Abstract

Provided is a threaded joint having excellent compression resistance and sealing property. In the threaded joint (1), the male threaded portion (4a) has a gap between the female threaded portion (4b) on both the screw top surface (7) and the thread bottom surface (8) due to the screw connection of the tapered screw (4). When the insertion surface flank angle (α) of the taper screw (4) is 30 degrees or more and 50 degrees or less, it comes into contact with the female screw portion (4b) on both the insertion surface (9) and the load surface (10). At the same time, the load surface flank angle (β) of the tapered screw (4) is -10 degrees or more and less than 0 degrees, and the screw taper is the amount of change in the diameter of the tapered screw (4) per unit length in the pipe axis direction. Is 1/10 or more and 1/4 or less, and the seal taper angle (γ) of the box seal portion (11b) is 3 degrees or more and 10 degrees or less.

Description

The present invention relates to threaded joints, and more particularly to oil well pipes, including tubing and casings commonly used in the exploration and production of oil wells and gas wells, namely OCTG (oil country tubular goods), riser pipes, line pipes and the like. The present invention relates to a threaded joint having excellent compression resistance and sealing property, which is suitable for use in connecting steel pipes.

Threaded joints are widely used to connect steel pipes used in oil production equipment such as oil country tubular goods. Traditionally, standard threaded joints specified in API (American Petroleum Institute) standards have been typically used to connect steel pipes used in the search and production of oils and gases.

In recent years, crude oil and natural gas wells have become deeper, and the number of vertical wells, horizontal wells, and inclined wells has increased, and the drilling and production environment has become more severe. In addition, due to the increasing development of wells in adverse environments such as the ocean and polar regions, there are various performance requirements for threaded joints such as compression resistance, bending resistance, and external pressure sealing performance (external pressure resistance). It has become. Due to such required performance, the use of high-performance special threaded joints called premium joints has been increasing in recent years.

The above-mentioned premium joint usually includes a taper screw, a seal portion (metal touch seal portion), and a torque shoulder portion at the pipe end portions of the pipes connected to each other. These are the elements that make up each of the pin, which is a male-shaped portion provided in one tube, and the box, which is a female-shaped portion provided in the other tube and screwed or fitted to the male-shaped portion. These elements are designed so that male and female elements of the same name face each other when tightening a joint (meaning a threaded joint, the same applies hereinafter).

The taper screw described above is necessary to firmly fix the joint. Further, the seal portion secures the seal property by metal contact between the box and the pin in the region of the seal portion. In the seal portion, the pin seal portion provided on the pin usually has a convex pipe shaft cross-sectional shape, and the box seal portion provided on the box has a tapered pipe shaft cross-sectional shape. Further, the torque shoulder portion is a shoulder surface that acts as a stopper during tightening of the joint.

By the way, in order to reduce the amount of excavation during well development, there is a demand for slimming the joint. Elimination of the torque shoulder portion is effective for slimming the joint, and in that case, the screw portion is responsible for the role of the stopper and the role of receiving the axial force. In order to exert the above effect, the male thread portion is connected to the load surface and the insertion surface in a state where a gap is left between the female thread portion on both the screw top surface and the screw bottom surface due to the screw connection of the tapered screw. Both need to be in contact with the female thread. This form of taper screw is referred to as a tube axial interference taper screw. A joint having a pipe axial interference taper thread has high compressibility because the total area of the area to receive the force is large because the axial force is received by the thread surface.

Patent Document 1 describes an example of a prior art of a tube axial interference taper screw. The subject of the invention described in Patent Document 1 is that, in consideration of the processing tolerance in actual production, contact is always made at the time of screw connection on both the load surface and the insertion surface regardless of the processing result within the tolerance. To make it happen. The invention described in Patent Document 1 defines the relationship between the load surface flank angle, the insertion surface flank angle, the gap generated on the screw top surface and the screw bottom surface, and the pipe axial clearance assumed from the machining tolerance. The equation is presented, and it is explained that by following this equation, contact can always occur at the time of screw connection on both the load surface and the insertion surface.

Japanese Patent No. 3714199

The formula described in Patent Document 1 prevents contact on the screw top surface and the screw bottom surface when the taper screw is tightened, and always guarantees contact on both the load surface and the insertion surface. is there. However, the amount of tightening required to realize contact is not taken into consideration, and the position in the pipe axial direction at the time of completion of tightening is greatly affected by the degree of dimensional variation during processing. Since the stop position in the pipe axial direction when tightening the screw has a great influence on the contact state of the seal portion, if the contact state becomes too small due to the dimensional variation of the taper screw, the sealing property becomes insufficient, and conversely, the contact is excessive. If it becomes a state, there is a concern that seizure may occur.

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

The present inventors have diligently studied to solve the above problems and obtained the following findings. First, in the conventional technique, the dimensional variation causes insufficient sealing property and seizure because the dimensional variation has a great influence on the contact state of the seal portion (hereinafter, also referred to as the seal interference amount). Therefore, it is important to design the taper screw and the seal portion that can suppress the influence of the dimensional variation on the amount of seal interference. In a tapered screw composed of substantially trapezoidal threads, by increasing the difference between the width of the thread top and the width of the thread bottom, the gap in the pipe axis direction changes with respect to the amount of rotation when the taper screw is tightened. The amount can be increased. Therefore, by increasing the width difference between the thread top and the thread bottom, it is possible to suppress the influence of the dimensional variation (variation in the gap in the tube axis direction) on the stop position in the tube axis direction at the completion of tightening. However, since it is desirable to set the load surface to a negative angle to prevent jump-out, design the absolute value to be restrained at a negative angle, and design the insertion surface to a large angle to secure the width difference. There is a need. Regarding the screw taper, which is the amount of change in diameter per unit length in the pipe axis direction for tapered screws, by setting this to a large value, the screw is tightened with a small tightening amount, so the pipe shaft when tightening is completed due to dimensional variation. The influence on the direction stop position can be suppressed. Further, by reducing the seal taper angle of the box seal portion, it is possible to suppress the influence of the stop position in the pipe axial direction on the amount of seal interference when tightening is completed.

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

1. 1. A pin formed at the end of the pipe and having a male threaded portion of a tapered screw and an outer peripheral surface of a nose portion located on the pipe end side of the male threaded portion.
It has a female threaded portion of the tapered screw and a box having an inner peripheral surface of a seal hole facing the outer peripheral surface of the nose portion.
The male threaded portion comes into contact with the female threaded portion on both the insertion surface and the load surface with a gap left between the female threaded portion on both the screw top surface and the thread bottom surface due to the threaded coupling of the tapered screw. And
The outer peripheral surface of the nose portion has a pin seal portion having a convex tube shaft cross-sectional shape.
The inner peripheral surface of the seal hole has a box seal portion having a tapered tube shaft cross-sectional shape in which a seal portion is formed by metal contact with the pin seal portion in the radial direction of the pipe by the screw connection. ,
The flank angle of the insertion surface of the taper screw is 30 degrees or more and 50 degrees or less, and the flank angle of the load surface of the taper screw is -10 degrees or more and less than 0 degrees.
The screw taper, which is the amount of change in diameter per unit length in the pipe axis direction in the taper screw, is 1/10 or more and 1/4 or less.
The seal taper angle of the box seal portion is 3 degrees or more and 10 degrees or less.
Threaded joint.

The shape, angle, and dimensions of the taper screw and the seal portion specified in the present application mean the state before tightening the taper screw (that is, the state in which no load is applied).

2. The threaded joint of 1 above, wherein the thread height T of the male threaded portion is 0.04 inch or more and 0.10 inch or less.

3. 3. The threaded joint of 1 or 2 having a ratio T / W of the width W of the thread bottom portion and the thread height T of the male threaded portion of 0.2 or more and 1.0 or less.

According to the present invention, a threaded joint having excellent compression resistance and sealing property can be obtained.

It is a pipe shaft sectional view which shows the integral type threaded joint which is an example of embodiment of this invention. It is a pipe shaft sectional view which shows the coupling type threaded joint which is an example of embodiment of this invention. It is an enlarged view of the part A of FIG. 1 and FIG. Indicates a state in which both the insertion surface and the load surface are in contact with each other. It is the B part enlarged view of FIG. 1 and FIG. As shown in FIG. 3, the same scale drawings of both the pin and the box are superposed so that both the insertion surface and the load surface of the screw portion are in contact with each other, and the overlapping state of the seal portion is shown.

Hereinafter, embodiments of the present invention will be illustrated with reference to the drawings.

As shown in FIGS. 1 and 2, the screw joint 1 according to the embodiment of the present invention is a premium joint that connects an oil well pipe by a pin 2 and a box 3. The threaded joint 1 may be of an integral type in which steel pipes are directly connected to each other by a pin 2 and a box 3 as shown in FIG. 1, or steel pipes having pins 2 as shown in FIG. 2 are connected to each other. It may be a coupling type connected via a coupling having a box 3. Note that FIGS. 1 and 2 show only a cross section on one side of the tube axis X. The threaded joint 1 may be applied to a connection of a steel pipe or the like other than an oil well pipe.

The pin 2 is formed at the end of the pipe and has a male screw portion 4a of the taper screw 4 and an outer peripheral surface 5 of the nose portion located on the pipe end side of the male screw portion 4a. The box 3 has a female threaded portion 4b of the tapered screw 4 and an inner peripheral surface 6 of the seal hole facing the outer peripheral surface 5 of the nose portion.

As shown in FIG. 3, the male screw portion 4a is loaded with the insertion surface 9 in a state where a gap is left between the female screw portion 4b on both the screw top surface 7 and the screw bottom surface 8 due to the screw connection of the taper screw 4. It is configured to come into contact with the female threaded portion 4b on both sides of the surface 10. That is, the taper screw 4 leaves a gap between the screw top surface 7 of the male screw portion 4a and the screw bottom surface 8'of the female screw portion 4b due to the screw connection, and the screw bottom surface 8 of the male screw portion 4a and the screw of the female screw portion 4b. With a gap left between the top surface 7', the insertion surface 9 of the male threaded portion 4a and the insertion surface 9'of the female threaded portion 4b come into contact with each other, and the load surface 10 of the male threaded portion 4a and the female threaded portion 4b It is configured so that the load surface 10'is in contact with each other. The above-mentioned "gap" means a gap sufficient to cause tightening on both the insertion surface 9, 9'and the load surface 10, 10'when the tightening of the taper screw 4 is completed.

The taper screw 4 achieves a strong connection by contacting both the insertion surfaces 9, 9'and the load surfaces 10, 10'. The acute angle formed by the insertion surface 9 as a straight line perpendicular to the tube axis X in the cross section including the tube axis X is defined as the insertion surface flank angle α, and the reference numerals of the insertion surface flank angle α are shown in FIG. As shown, the case where the insertion surface 9 is inclined toward the lateral side of the pipe axis X (hereinafter, also simply referred to as the radial outer side) toward the load surface 10 is positive. Further, the angle of a sharp angle formed by the load surface 10 as a straight line perpendicular to the tube axis X in the pipe axis cross section is defined as the load surface flank angle β, and the sign of the load surface flank angle β is such that the load surface 10 is directed outward in the radial direction. The case where the load surface is inclined toward the insertion surface 9 is positive (the sign of the load surface flank angle β shown in FIG. 3 is negative).

The flank angle α of the insertion surface needs to be 30 degrees or more in order to secure the width difference between the top of the thread and the bottom of the thread. By setting the flank angle α of the insertion surface to 30 degrees or more, the gap in the pipe axis direction (that is, the direction along the pipe axis X) with respect to the amount of rotation when the taper screw 4 is tightened (that is, the insertion surfaces 9, 9'and The amount of change in the load surface (gap at the load surfaces 10 and 10') can be increased, and thus the influence of the dimensional variation (variation in the gap in the pipe axial direction) on the stop position in the pipe axial direction can be suppressed. However, if the flank angle α of the insertion surface is made too large, the compressive force in the tube axis direction cannot be efficiently received, so the angle must be 50 degrees or less. The load surface flank angle β needs to be a negative value to prevent jump-out and must be less than 0 degrees, but if the absolute value is made too large, the width difference between the thread top and thread bottom will increase. Since it cannot be secured, it is necessary to set the temperature to -10 degrees or higher. The load surface 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 pipe axis direction on the reference surface S corresponding to the thread bottom surface 8 of the male thread portion 4a, needs to be 1/10 or more. By setting the screw taper to 1/10 or more, the taper screw 4 is tightened with a small tightening amount, so that it is possible to suppress the influence on the pipe axial stop position at the completion of tightening due to dimensional variation. However, if the screw taper is made too large, the wall thickness at the pin seal portion 11a, which will be described later, cannot be secured and the sealing property cannot be guaranteed. Therefore, the screw taper must be 1/4 or less.

As shown in FIG. 4, the outer peripheral surface 5 of the nose portion has a pin seal portion 11a having a pipe shaft cross-sectional shape (that is, a shape in the pipe shaft cross section) that is curved in a convex shape. However, the cross-sectional shape of the pipe shaft of the pin seal portion 11a is not limited to the one that is curved in a convex shape, and may be a convex shape. The inner peripheral surface 6 of the seal hole forms a seal portion 11 that seals the fluid by metal contact with the pin seal portion 11a in the radial direction of the pipe (that is, the radial direction of the pipe axis X) by the screw connection of the taper screw 4. It has a box seal portion 11b having a tapered tube shaft cross-sectional shape. That is, the pin seal portion 11a and the box seal portion 11b form a seal portion 11 having a radial seal structure.

The box seal portion 11b is a tapered surface having a conical face. The acute angle formed by the box seal portion 11b with a straight line parallel to the tube axis X in the cross section of the tube axis is defined as the seal taper angle γ. The seal taper angle γ needs to be 10 degrees or less in order to reduce the influence of the stop position in the pipe axial direction on the contact state (seal interference amount) of the seal portion 11 when the taper screw 4 is screwed. However, if the seal taper angle γ is made too small, the sliding distance becomes long and the risk of seizure increases. Therefore, the seal taper angle γ needs to be set to 3 degrees or more. If the seal taper angle γ is less than 3 degrees, a large step is likely to be formed at the boundary between the seal portion and the screw portion, and in that case, it cannot be said that the design itself is established. This is because seizure easily occurs when the pin comes into contact with the stepped portion during screw connection.

The screw height T of the male thread portion 4a is 0.04 inch (= 0.04 inch × 25.4 mm / inch = 1.016 mm) or more and 0.10 inch (= 0.10 inch × 25.4 mm / inch = 2). It is preferably .54 mm) or less. Here, the screw height T is the distance between the intersection of the straight line perpendicular to the pipe axis X and the reference surface S in the cross section of the pipe shaft and the intersection of the straight line and the screw top surface 7. When the screw height T is less than 0.04 inch, there is a concern that the contact surface cannot be sufficiently secured and the tapered screw 4 is excessively plastically deformed due to the axial force, and the function as a joint is lost. On the other hand, when the screw height T exceeds 0.10 inch, there is a concern that the cross-sectional area of the dangerous cross section becomes small and the tensile strength of the joint cannot be sufficiently secured.

The ratio T / W of the width W of the thread bottom portion and the screw height T in the male thread portion 4a is preferably 0.2 or more and 1.0 or less. Here, the width W of the thread bottom includes a straight line including the intersection of a straight line including the load surface 10 and a straight line including the reference surface S in the cross section of the pipe axis and perpendicular to the pipe axis X, and the insertion surface 9. It is the distance between the straight line including the intersection of the including straight line and the straight line including the reference plane S and the straight line perpendicular to the tube axis X. If the T / W is less than 0.2, there is a concern that a sufficient contact surface cannot be secured. If the T / W exceeds 1.0, there is a concern that the cross-sectional area of the dangerous cross section cannot be sufficiently secured.

As described above, the threaded joint 1 has an insertion surface flank angle α of 30 degrees or more and 50 degrees or less, a load surface flank angle β of -10 degrees or more and less than 0 degrees, and a screw taper of 1/10 or more and 1 Excellent compression resistance and sealing property can be exhibited by satisfying the condition that the seal taper angle γ is 3 degrees or more and 10 degrees or less.

Although the present embodiment has been illustrated above, the present invention is not limited to this, and can be appropriately modified within the scope of the claims.

From a pin made by processing the end of a steel pipe with an outer diameter of 5.5 inches x a wall thickness of 0.415 inches (outer diameter of 139.70 mm x a wall thickness of 10.54 mm) of the steel grade P110 of API 5CT, and a box corresponding to this. A sample was prepared for the threaded joint and subjected to a tightening / tightening test and an airtightness test based on ISO13679: 2002. In carrying out this experiment, the experiments were carried out under the experimental conditions of each level shown in Table 1. As an effect of variation due to dimensional tolerance, the case where there is a gap in the pipe axis direction when tightened as shown in the drawing is regarded as positive, and the case where it interferes is negative, and the case where there is a variation of absolute value 0.004 inch is evaluated. Was done. Further, as experimental conditions not shown in Table 1, the number of threads per inch is 5 (5 TPI) and the thread height T of the male thread portion is 0.05 inch, which is common to all levels. The screw width (in the direction parallel to the tube axis X) at a height of 0.03 inch (from the reference plane S in the direction perpendicular to the tube axis X) was 0.1 inch (half pitch). The width W of the thread bottom of the male thread can be calculated from the insertion surface flank angle α and the load surface flank angle β, and the ratio T / W of the thread bottom width W and the thread height T is 0.38 to 0. It became .47. The joint efficiency was designed to be 75% at all levels, and in the airtightness test, a load of 75% was applied to 95% VME for both tensile and compression.

In the invention example satisfying the above conditions, the influence of the dimensional variation on the amount of seal interference could be suppressed to a level where there was no problem, and the test result was acceptable. On the other hand, in a comparative example that does not satisfy the above conditions (particularly, the insertion surface flank angle is 30 degrees or more, the screw taper is 1/10 or more, and the seal taper angle is 10 degrees or less), seizure or leakage occurs. However, the test result was unsuccessful. In the comparative example, seizure occurs during the tightening tightening test under the condition that the stop position in the pipe axis direction is large and the seal interference amount is excessive, and conversely, the stop position in the pipe axis direction is large and minus and the seal interference amount is too small. Under these conditions, a leak occurred during the airtightness test.

1 Threaded joint 2 Pin 3 Box 4 Tapered thread 4a Male threaded part 4b Female threaded part 5 Nose part outer peripheral surface 6 Seal hole inner peripheral surface 7,7'Screw top surface 8,8'Screw bottom surface 9,9' Insertion surface 10,10' Load surface 11 Seal portion 11a Pin seal portion 11b Box seal portion α Insertion surface flank angle β Load surface flank angle γ Seal taper angle X Pipe axis S Reference surface T Thread height W Thread bottom width

Claims (3)

A pin formed at the end of the pipe and having a male threaded portion of a tapered screw and an outer peripheral surface of a nose portion located on the pipe end side of the male threaded portion.
It has a female threaded portion of the tapered screw and a box having an inner peripheral surface of a seal hole facing the outer peripheral surface of the nose portion.
The male threaded portion comes into contact with the female threaded portion on both the insertion surface and the load surface with a gap left between the female threaded portion on both the screw top surface and the thread bottom surface due to the threaded coupling of the tapered screw. And
The outer peripheral surface of the nose portion has a pin seal portion having a convex tube shaft cross-sectional shape.
The inner peripheral surface of the seal hole has a box seal portion having a tapered tube shaft cross-sectional shape in which a seal portion is formed by metal contact with the pin seal portion in the radial direction of the pipe by the screw connection. ,
The flank angle of the insertion surface of the taper screw is 30 degrees or more and 50 degrees or less, and the flank angle of the load surface of the taper screw is -10 degrees or more and less than 0 degrees.
The screw taper, which is the amount of change in diameter per unit length in the pipe axis direction in the taper screw, is 1/10 or more and 1/4 or less.
The seal taper angle of the box seal portion is 3 degrees or more and 10 degrees or less.
Threaded joint. The threaded joint according to claim 1, wherein the thread height T of the male threaded portion is 0.04 inch or more and 0.10 inch or less. The threaded joint according to claim 1 or 2, wherein the ratio T / W of the width W of the thread bottom to the thread height T in the male threaded portion is 0.2 or more and 1.0 or less.

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