JP5906588B2 - Manufacturing method of threaded joint for steel pipe - Google Patents

Description

The present invention relates to a method for manufacturing a threaded joint for steel pipes, and in particular, an oil well pipe including a tubing and a casing generally used for exploration and production of oil wells and gas wells, that is, OCTG (oil country tubular goods), a riser pipe, and The present invention relates to a method for manufacturing a threaded joint for steel pipes, which is suitable for connecting steel pipes such as line 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. 3 is a schematic explanatory view of a premium joint for an oil well pipe, and these are longitudinal sectional views of a threaded joint of a circular pipe. 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 documents 1-3 are mentioned as conventional technology about the premium joint.
In the example of FIG. 3, the metal touch seal portion is at the tip of the pin nose 8. However, in Patent Document 1, a metal touch seal portion is provided near the screw portion of the pin nose 8 in order to increase the external pressure resistance performance. It has also been proposed to extend the length from the seal part to the shoulder part. In the threaded joint disclosed in Patent Document 1, the pin nose that is not in contact with the box member is configured to be elongated so as to be discontinuous with the seal portion so that the thickness of the pin nose is not reduced. In addition to the above-mentioned external pressure resistance, the axial compression resistance is also improved.

Similarly, in Patent Document 2, an appendix is formed from the seal portion to the pin nose tip, which also has a portion having a discontinuous shape with the seal portion to ensure radial rigidity and lower axial rigidity. It is described that this appendix is deformed at the time of tightening and the tensile resistance is improved by recovering the appendix when loaded.
As described in Patent Documents 1 and 2, placing the seal part near the screw part of the pin and separating it from the tip of the pin nose is stable against the screw as well as improving the external pressure resistance and tensile resistance. It is effective in giving a realistic performance, and it can be confirmed from FEM simulations and the like. Further, the pin nose that has a shape discontinuous with the seal portion is deformed itself when a strong axial compressive force is applied, and has an effect of reducing plastic deformation of the torque shoulder portion of the box member. However, on the other hand, unauthorized deformation may occur in the discontinuous portion, which is considered to depend on the tightening torque.

  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 contact pressure is increased. For example, Patent Document 3 discloses an example of a radial seal method having a large pin seal R shape and a small seal taper angle. However, a problem with the radial seal method in which the seal taper angle is thus reduced is that goling is likely to occur during tightening. Further, in the radial seal method, it is necessary to increase the amount of seal interference in order to ensure sealing performance and seal stability, and the ease of occurrence of goling is further increased.

Japanese Patent No. 4535064 Japanese Patent No. 4208192 Japanese Utility Model Publication No. 61-44068

The seal part 11, 13 in FIG. 3 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 no leak or goling occurs Is formed.
However, seamless steel pipes, which are threaded joint pipes, are subject to uneven thickness distribution (eccentric eccentric thickness) and integrity (elliptical shape) that cannot be avoided during manufacturing. It is assumed that a non-uniform distribution will occur. In radial seal type threaded joints, the surface of the seal part is cut with high accuracy, so the outer diameter of the seal part on the pin side and the inner diameter of the seal part on the box side are sufficiently accurate. Since the seal portion on the side has a large thickness and high rigidity as a whole, the adverse effect of eccentric eccentric thickness on the sealing performance is small. Furthermore, there is a circumstance where the outer diameter is cut off, and the accuracy of the outer diameter is high. However, since the pin has a smaller wall thickness and lower rigidity than the box, there may be a problem that the sealing performance is hindered by the eccentric thickness deviation. In other words, as shown in FIG. 2, if the pin 3 is eccentric in the seal section, the contact surface pressure becomes non-uniform due to the non-uniform thickness of the pin, and a leak occurs at a thin portion where the contact surface pressure is small. It's easy to do. Therefore, in order to obtain a stable sealing property, it is necessary to cut the inner diameter side of the pin (referred to as internal cutting for short) to eliminate the uneven thickness, which is a problem.

In threaded joints, mere internal cutting is often performed, but no knowledge has been found in the past that contributes to the guideline of internal cutting from the viewpoint of ensuring sealing performance. Further, since it takes extra time to perform the internal cutting, a guideline for the internal cutting length is also necessary, but there is no knowledge that contributes to such a guideline in the past.
An object of this invention is to provide the manufacturing method of the threaded joint for steel pipes which solves said subject and can eliminate the eccentric thickness deviation of a pin, and can ensure the stable sealing performance.

In order to solve the above-described problems, the inventors have provided a seal that is a portion on the pin-side nose portion outer peripheral surface that first comes into contact with the box-side nose portion inner peripheral surface during screw connection from the pin inner diameter-side tip. It was found by various experimental studies that it is necessary to cut the inner diameter side of the pin within a length range equal to or longer than the point to reduce the thickness deviation rate.
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 nose part inner peripheral surface that is opposed to an outer peripheral surface of the nose part of the pin, and a box that has a shoulder part that comes into contact with the shoulder part of the pin A method of manufacturing a threaded joint for a steel pipe in which the pin and the box are coupled by the screw coupling, and the outer peripheral surface of the nose portion of the pin and the inner peripheral surface of the nose portion of the box are in metal-metal contact, and the contact portion forms a seal portion. Because
The pin side nose portion outer peripheral surface is a curved surface shape convex outward, the box side nose portion inner peripheral surface is a taper shape,
The pin is intended to cut the outer diameter side and inner diameter side,
The length of the internal cutting length range, which is the axial length range to be cut on the inner diameter side, from the tip of the pin nose to the pin side nose portion that first contacts the inner peripheral surface of the nose portion on the box side when screwing The axial length to the seal point that is a part on the outer peripheral surface and the axial length to the rear end of the seal portion that is the threaded end of the seal portion , and the internal cutting length range pin of the inner may be in the same cross-sectional thickness deviation ratio defined by the following equation as 6% or less, Ru to stabilize the sealing performance by eliminating the thickness non-uniformity due to the pin eccentricity uneven thickness at the seal portion in the cross section A method for producing a threaded joint for steel pipes.
Unevenness rate = (Maximum thickness in the circumferential direction-Minimum thickness in the circumferential direction) / Average thickness in the circumferential direction * 100 (%)
(2)
In performing external cutting that is cutting on the outer diameter side of the pin and internal cutting that is cutting on the inner diameter side, the external cutting is performed prior to the internal cutting,
At the time of the external cutting, the external pipe is supported at two or more places in the raw pipe length direction as a fulcrum, and the external cutting is performed at a predetermined cutting tool feed speed while rotating,
In the internal cutting, the internal cutting is performed at the same cutting tool feed speed while supporting the blank tube with the same location as that of the external cutting as a fulcrum and rotating in the same rotation method. The manufacturing method of the threaded joint for steel pipes of Claim 1.

  According to the present invention, the eccentric thickness deviation of the pin nose is eliminated with the minimum necessary internal cutting time, and a threaded joint for steel pipes having a stable sealing property is realized.

It is sectional drawing which shows embodiment of this invention. It is sectional drawing of the seal | sticker part which shows the conventional problem. It is sectional drawing which shows the conventional threaded joint for steel pipes, (a) is whole sectional drawing, (b) is an expanded sectional view which shows the screw part in (a), (c) is an enlarged drawing which shows the pin nose vicinity in (a) It is sectional drawing.

  A threaded joint for steel pipes according to the present invention includes a male screw part, a pin having a nose part extending from the male screw part to the pipe end side, a shoulder part 12 provided at the tip of the nose part, and the male screw part. A screw thread-coupled female thread portion that forms a thread portion; a pin having a nose portion inner circumferential surface facing a nose portion outer circumferential surface of the pin; and a shoulder portion that contacts the shoulder portion of the pin; and the screw coupling Threaded joint for steel pipe in which the pin and the box are joined together, and the outer peripheral surface of the pin nose and the inner peripheral surface of the nose portion of the box are in metal-metal contact, and the contact portion forms a seal portion (specifically, a metal touch seal portion) (It is a threaded joint equivalent to a conventional radial seal type premium joint).

  In the present invention, based on the above premise, as shown in FIG. 1, the outer peripheral surface of the nose portion on the pin 3 side has a curved shape that protrudes outward, and the inner peripheral surface of the nose portion on the side of the box 1 has a tapered shape. The seal taper angle θ, which is the taper angle of the taper surface forming the taper shape, is defined as an angle θ that the taper surface forms with respect to the threaded joint axis. Further, the seal point sp is a portion on the outer peripheral surface of the nose portion on the pin 3 side that first comes into contact with the inner peripheral surface of the nose portion on the box 1 side during screw connection. Further, the seal portion rear end se is an end of the seal portion 20 on the threaded portion side.

  The pin 3 is formed by cutting the outer diameter side and the inner diameter side, and the length of the inner cutting length range that is the cut axial length range on the inner diameter side is from the tip of the pin nose 8 to the seal point se. It is the length more than the axial direction length. In addition, the pin 3 within the cutting length range has the thickness deviation rate of 6% or less in the same cross section. As a result, the eccentric thickness deviation of the pin in the seal portion 20 is eliminated, and the wall thickness is made uniform to obtain a stable sealing performance.

When the seal point sp is out of the internal cutting length range, the eccentric thickness deviation of the portion where the pressure is highest in the seal portion 20 is not eliminated, so that the effect of stabilizing the sealing performance is poor. Further, if the thickness deviation ratio is more than 6% within the machining length range, the degree of elimination of the eccentric thickness deviation is insufficient, and the effect of stabilizing the sealing performance is poor.
As long as the seal point sp is within the internal cutting length range, the length of the internal cutting length range may be large, but the part closer to the raw pipe side than the seal rear end se is within the internal cutting length range. In addition to not being able to expect a sealing part stabilizing effect beyond that, an increase in internal cutting time is caused and productivity is lowered. Therefore, the length of the internal cutting length range is preferably set to a length equal to or shorter than the axial length from the pin nose tip to the seal portion rear end se.

The following method is mentioned as a suitable internal cutting method of the internal cutting length range.
-Prior to the internal cutting, the outer diameter side of the pin nose is cut (referred to as external cutting for short).
-For external cutting, the raw pipe is supported at two or more locations in the length direction of the raw pipe, and outer diameter side cutting is performed at a predetermined cutting tool feed speed while rotating.
-For internal cutting, the inner tube is supported at the same location as that for external cutting, and the inner diameter side is cut at the same cutting tool feed speed while rotating by the same rotational method.

  According to this internal cutting method, even if there is a bending in the length direction of the pipe (small bending that inevitably occurs in the production of seamless steel pipes), the bending in the length direction of the pipe will cause a cross-section of the cutting part that is undergoing internal cutting. Since the change in the core position follows the same change as that at the time of external cutting, the internal cutting progresses while maintaining the same state as that at the time of external cutting. Therefore, according to this preferred internal cutting method, the thickness deviation rate can be stably reduced to 6% or less.

A finite element analysis (FEA) simulation was performed on a threaded joint consisting of a steel pipe end machined with an outer diameter of 9-5 / 8 inch and a wall thickness of 0.545 inch and a box corresponding to this pin under the conditions of ISO13679. The following samples were manufactured with the same contact area pressure (index obtained by integrating the contact pressure over the contact length) under LP2 under the same ISO13679 condition, and the ISO13679 series A test was performed.
(sample)
-Invention Example 1
Pin nose outer peripheral surface = curved shape convex outward, inward cutting length range = axial length range from the tip of the pin nose to the seal point, internal cutting method = the above preferred internal cutting method Nose inner peripheral surface of the box = Tapered shape, box seal taper angle θ = 3.5 degrees, Invention Example 2:
In Example 1 of the present invention, the internal cutting length range = the axial length range twice the axial length from the pin nose tip to the seal point (the axial length from the pin nose tip to the part farther from the seal portion rear end) Range), and other than this was the same as Example 1 of the present invention.

Comparative Example 1:
In Example 1 of the present invention, it was changed to no internal cutting (internal cutting length range = none, internal cutting method = none), and other than this, it was the same as Example 1 of the present invention.
Table 1 shows the thickness deviation ratio and sealing performance of each sample.
From Table 1, it is clear that the inventive examples have better sealing properties than the comparative examples. In addition, since Example 2 of the present invention was internally cut farther than the rear end of the seal portion, the productivity was lower than that of Example 1 of the present invention.

1 box
3 pin
5 Female thread
7 Male thread
8 Nose (pin nose)
11,13,20 Seal (Details are metal touch seal)
12,14 Shoulder (For details, Torque shoulder)

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 nose part inner peripheral surface that is opposed to an outer peripheral surface of the nose part of the pin, and a box that has a shoulder part that comes into contact with the shoulder part of the pin A method of manufacturing a threaded joint for a steel pipe in which the pin and the box are coupled by the screw coupling, and the outer peripheral surface of the nose portion of the pin and the inner peripheral surface of the nose portion of the box are in metal-metal contact, and the contact portion forms a seal portion. Because
The pin side nose portion outer peripheral surface is a curved surface shape convex outward, the box side nose portion inner peripheral surface is a taper shape,
The pin is intended to cut the outer diameter side and inner diameter side,
The length of the internal cutting length range, which is the axial length range to be cut on the inner diameter side, from the tip of the pin nose to the pin side nose portion that first contacts the inner peripheral surface of the nose portion on the box side when screwing The axial length to the seal point that is a part on the outer peripheral surface and the axial length to the rear end of the seal portion that is the threaded end of the seal portion , and the internal cutting length range pin of the inner may be in the same cross-sectional thickness deviation ratio defined by the following equation as 6% or less, Ru to stabilize the sealing performance by eliminating the thickness non-uniformity due to the pin eccentricity uneven thickness at the seal portion in the cross section A method for producing a threaded joint for steel pipes.
Unevenness rate = (Maximum thickness in the circumferential direction-Minimum thickness in the circumferential direction) / Average thickness in the circumferential direction * 100 (%) In performing external cutting that is cutting on the outer diameter side of the pin and internal cutting that is cutting on the inner diameter side, the external cutting is performed prior to the internal cutting,
At the time of the external cutting, the external pipe is supported at two or more places in the raw pipe length direction as a fulcrum, and the external cutting is performed at a predetermined cutting tool feed speed while rotating,
In the internal cutting, the internal cutting is performed at the same cutting tool feed speed while supporting the blank tube with the same location as that of the external cutting as a fulcrum and rotating in the same rotation method. The manufacturing method of the threaded joint for steel pipes of Claim 1.

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