JP2013029177A - Steel pipe screw joint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel pipe screw joint in which a shoulder part and a seal part are hardly subject to plastic deformation and that secures excellent sealing performance even when a high axial compression force is applied since there has been a room to be improved in a conventional steel screw joint of radial-sealing type for securing the sealing performance when the high axis compression force is applied.SOLUTION: In the steel pipe screw joint, a nose part outer circumferential surface of a pin 3 is tapered, a seal surface 21 of a box 1 has an outwardly convex curved shape, an angle α formed by a pin tapered surface 31 and a tube axis direction line 2 is 2 to 10°, and an angle θ formed by a shoulder surface 16 and a tube axis orthogonal surface 10 is 3 to 10°.

Description

  TECHNICAL FIELD The present invention relates to a threaded joint for steel pipes, and in particular, oil well pipes including tubing and casings generally used for exploration and production of oil wells and gas wells, that is, OCTG (oil country tubular goods), riser pipes, line pipes, etc. The present invention relates to a threaded joint for steel pipes that is suitable for use in connecting steel pipes and has excellent sealing properties and compression resistance.

  Threaded joints are widely used to connect steel pipes used in oil industry equipment such as oil well pipes. Conventionally, a standard threaded joint specified in the API (American Petroleum Institute) standard has been typically used for connecting steel pipes used for oil and gas exploration and production. However, in recent years, the wells for crude oil and natural gas have been deepened, and the number of vertical wells, horizontal wells, inclined wells, etc. has increased, and the drilling and production environment has become severe. In addition, the demand for screw joints such as compression resistance, bending resistance, and external pressure seal performance (external pressure resistance) has diversified due to the increased development of wells in poor environments such as the ocean and polar regions. ing. For this reason, the use of high-performance special threaded joints called premium joints is increasing, and the demands on the performance are also increasing.

  A premium joint usually has a male screw member (hereinafter referred to as a pin) formed on a pipe end portion, each having a taper screw, a seal portion (specifically, a metal touch seal portion), and a shoulder portion (specifically, a torque shoulder portion). It is a coupling type joint in which a female screw member (hereinafter referred to as a box) for connecting pins to each other is coupled. The taper screw is important for firmly fixing the pipe joint, and the seal part plays a role of securing the sealing performance by metal contact between the box and the pin at this part, and the shoulder part is a stopper of the joint during tightening. It becomes the shoulder side that plays the role.

  FIG. 2 is a schematic longitudinal sectional view of a threaded joint of a circular pipe as an explanatory diagram of a premium joint for oil well pipes, (a) is an overall view, (b) is an enlarged view showing a threaded portion in (a), c) is an enlarged view showing the vicinity of the pin nose in (a). The threaded joint includes a pin 3 and a box 1 corresponding to the pin 3, and the pin 3 has a male screw portion 7 on the outer surface thereof and a screwless portion provided adjacent to the male screw portion 7 on the distal end side of the pin 3. It has a nose portion 8 (pin nose 8) which is a length portion. The nose portion 8 has a seal portion 11 on its outer peripheral surface and a torque shoulder portion 12 on its end surface. The opposing box 1 has a female screw part 5, a seal part 13, a part that can be screwed or contacted with the male screw part 7, the seal part 11, and the shoulder part 12 of the pin 3 on the inner surface thereof, respectively. A shoulder portion 14 is provided.

Patent document 1 is mentioned as a prior art regarding the said premium joint.
In the conventional example of FIG. 2, the seal portion is at the tip of the pin nose 8, and a desired sealing performance can be realized by applying an appropriate tightening torque.
On the other hand, since the tightening torque is affected by lubrication conditions, surface properties, etc., a design that does not depend greatly on this is a radial seal method in which the radial component of the seal contact pressure is relatively strong. For example, Patent Literature 1 discloses an example of a radial seal method having a large pin seal R shape and a small seal taper angle. However, the problem with the radial seal method with such a small seal taper angle is that goling is likely to occur during tightening, and in particular, the amount of seal interference for the purpose of ensuring seal performance and sealing stability. When a large value is set, the ease of occurrence of goling is remarkably increased.

Japanese Utility Model Publication No. 61-44068

The seal part 11, 13 in FIG. 2 or the seal part of the above-mentioned radial direction seal method (hereinafter also referred to as radial seal type) is loaded with a necessary and sufficient pressure, so that a healthy seal part that does not cause leak or goling Is formed.
However, according to a study by the inventors, it has been found that the following problems still remain in order to ensure sealing performance in the radial seal type steel pipe threaded joint. That is, as the tightening of the screws proceeds, the pin and the box generally come into contact in the order of the seal portion and the shoulder portion. Here, when the contact at the seal portion is started, the pin is elastically deformed together with the box, approaches the shoulder surface of the box along the seal taper, and finally the shoulder surfaces of both the pin and the box come into contact with each other. However, when a high axial compression force is applied to the threaded joint, plastic deformation occurs in the seal portion as well as the shoulder portion, and if the axial force changes to an axial force in the tensile direction, the seal portion cannot maintain airtightness. There is. In particular, when the taper of the seal portion has a large angle with respect to the tube axis, the seal portion is directly damaged by the axial force, the plastic deformation is increased, and the airtightness is impaired. In addition, if the angle formed by the shoulder surface and the tube axis orthogonal plane (= plane perpendicular to the tube axis) is large, the reaction force of the axial compression force is greatly propagated from the shoulder portion to the seal portion, and the plastic deformation of the seal portion increases. .

  There has been no knowledge of the above-mentioned problems and solutions.

In order to solve the above-mentioned problems, the inventors appropriately set the angle formed by the seal taper to the tube axis, the angle formed by the shoulder surface and the tube axis orthogonal surface, or the angle formed by the shoulder surface formed by the taper of the seal portion. The guideline to be found was found by various experimental studies.
That is, the present invention is as follows.
(1)
A pin having a male screw part, a nose part extending from the male screw part to the tube end side, and a shoulder part provided at the tip of the nose part;
A female screw part that is screw-coupled with the male screw part to form a screw part, a seal surface that faces the outer peripheral surface of the nose part of the pin, and a box that has a shoulder part that contacts the shoulder part of the pin, A screw joint for a steel pipe in which the pin and the box are coupled by screw coupling, and the outer peripheral surface of the pin and the seal surface of the box are in metal-metal contact, and the contact portion forms a seal portion,
The outer peripheral surface of the nose part of the pin is a tapered shape, and the sealing surface of the box is a curved surface shape convex outward,
An angle formed by a pin taper surface, which is an outer peripheral surface of the taper-shaped nose portion of the pin, and a tube axis direction line is 2 degrees or more and 10 degrees or less, and a shoulder surface which is a contact surface between shoulder portions of the pin and the box; A threaded joint for steel pipes, characterized in that an angle formed with a plane perpendicular to the pipe axis is 3 degrees or more and 10 degrees or less.
(2)
The threaded joint for steel pipes according to (1) above, wherein an angle formed between the shoulder surface and the pin taper surface is 85 degrees or more and 95 degrees or less.

  According to the present invention, the shoulder joint and the seal portion are hardly plastically deformed even when subjected to a high axial compression force, and a threaded joint for steel pipes that can ensure excellent sealing performance is realized.

It is a longitudinal cross-sectional schematic diagram which shows one example of embodiment of this invention. It is a longitudinal cross-sectional schematic diagram which shows the conventional threaded joint for steel pipes.

  As shown in FIG. 1, a threaded joint for steel pipes according to the present invention includes a male screw part 7, a nose part 8 extending from the male screw part 7 toward the pipe end side, and a shoulder provided at the tip of the nose part 8. A pin 3 having a portion 12, a female screw portion 5 screwed to the male screw portion 7 to form a screw portion, a seal surface 21 facing the outer peripheral surface of the nose portion of the pin 3, and a shoulder portion 12 of the pin 3 And a box 1 having a shoulder portion 14 in contact with the pin, and the pin 3 and the box 1 are connected by the screw connection, so that the outer peripheral surface of the nose portion of the pin 3 and the seal surface 21 of the box 1 are metal-metal It was assumed that this was a steel pipe threaded joint that contacted and the contact part formed the seal part 20 (a threaded joint equivalent to a conventional radial seal type premium joint).

  In the present invention, based on the above assumption, as shown in FIG. 1 (c), the outer peripheral surface of the nose portion of the pin 3 is a taper-shaped pin taper surface 31, and the seal surface 21 of the box 1 is an outwardly convex curved surface. On the other hand, the angle (hereinafter referred to as pin taper angle) α between the pin taper surface 31 and the tube axis direction line 2 is not less than 2 degrees and not more than 10 degrees, and the pin 3 and the shoulder portions 12 and 14 of the box 1 are in contact with each other. The angle (hereinafter referred to as the shoulder angle) θ formed by the shoulder surface 16 that is the contact surface and the tube axis orthogonal surface 10 is 3 degrees or more and 10 degrees or less.

  By setting the pin taper angle α to 2 degrees or more and 10 degrees or less, it is possible to ensure sufficient sealing performance at the time of tightening and to effectively relieve plastic deformation of the seal portion due to axial compression force. If α is less than 2 degrees, the contact surface pressure at the time of tightening is insufficient and the sealing performance becomes insufficient. On the other hand, if α exceeds 10 degrees, the effect of reducing plastic deformation of the seal portion due to the axial compression force is poor. Therefore, α needs to be 2 degrees or more and 10 degrees or less. Preferably, α is 2 degrees or more and 5 degrees or less.

  However, if the shoulder angle θ is greater than 10 degrees, plastic deformation is likely to occur on the seal surface 21 due to the reaction force on the shoulder surface 16, while if θ is less than 3 degrees, the torque becomes unstable during tightening. Thus, during actual operation, the pin 3 and the box 1 are easily separated from the external pressure applied to the gap communicating with the outside on the seal surface 21, and it is difficult to ensure airtightness. Therefore, θ needs to be 3 degrees or more and 10 degrees or less. Preferably, θ is 7 degrees or more and 10 degrees or less.

  In the present invention, it is further preferable that an angle (hereinafter referred to as a shoulder-to-pin taper angle) φ formed by the shoulder surface 16 and the pin taper surface 31 is 85 degrees or more and 95 degrees or less. This is because, by setting φ to 85 degrees or more, it is possible to make the influence of the reaction force on the shoulder surface 16 difficult to exert on the seal surface 21, while by setting φ to 95 degrees or less, it communicates with the outside. This is because the resistance to the external pressure applied to the gap can be further increased.

  A threaded joint consisting of a steel tube end with an outer diameter of 9 + 5/8 inch and a wall thickness of 0.545 inch and a box corresponding to this pin is subjected to ISO13679 series A test by finite element analysis (FEA). A simulation was carried out under the same conditions, and a sample was produced with a design in which the same contact area pressure (an index obtained by integrating the surface pressure over the contact length) was obtained with the first LP2 of ISO 13679. A test was conducted. In carrying out this experiment, the experiment was conducted at various levels shown in Table 1. The results are shown in Table 1 together with the contact area pressure at the second LP2 in the simulation conducted by FEA.

  As shown in Table 1, it is clear that the inventive examples have better sealing properties than the comparative examples.

1 box
2 Pipe axis line
3 pin
5 Female thread
7 Male thread
8 Nose (pin nose)
10 Pipe axis orthogonal plane
11,13,20 Seal (Details are metal touch seal)
12,14 Shoulder (For details, Torque shoulder)
16 Shoulder surface
20 Seal part
21 Seal surface
31 Pin taper surface

Claims (2)

A pin having a male screw part, a nose part extending from the male screw part to the tube end side, and a shoulder part provided at the tip of the nose part;
A female screw part that is screw-coupled with the male screw part to form a screw part, a seal surface that faces the outer peripheral surface of the nose part of the pin, and a box that has a shoulder part that contacts the shoulder part of the pin;
A screw joint for a steel pipe in which the pin and the box are connected by the screw connection, the outer peripheral surface of the pin and the seal surface of the box are in metal-metal contact, and the contact portion forms a seal portion,
The outer peripheral surface of the nose part of the pin is a tapered shape, and the sealing surface of the box is a curved surface shape convex outward,
An angle formed by a pin taper surface, which is an outer peripheral surface of the taper-shaped nose portion of the pin, and a tube axis direction line is 2 degrees or more and 10 degrees or less, and a shoulder surface which is a contact surface between shoulder portions of the pin and the box; A threaded joint for steel pipes, characterized in that an angle formed with a plane perpendicular to the pipe axis is 3 degrees or more and 10 degrees or less.   2. The threaded joint for steel pipes according to claim 1, wherein an angle formed by the shoulder surface and the pin taper surface is not less than 85 degrees and not more than 95 degrees.

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