JPH06331070A - Oil well pipe threaded joint - Google Patents

Abstract

PURPOSE:To attain repeated use by increasing thread groove depth of an external thread in a pipe joint end part nearest to a metal seal part and in a screw part position most distant from the metal seal part, so as to improve seizure resistance, in a threaded joint formed by providing the metal seal part and a screw part continued to this metal seal part. CONSTITUTION:In an oil well pipe joint for connecting adjacent steel pipes 1, 1 by a coupling 2, each steel pipe 1 has a taper, where its connection point end side periphery is formed into a small diameter toward the point end, to provide an external thread part 3 of engraving an external thread, and a seal part 5 connected to the external thread part 3 is formed in the point end part. In the coupling 2, an internal thread part 4 screwable to the external thread part 3 of the steel pipe 1 is formed in the internal peripheral surface, and also forming a seal part 6 engageable with the seal part 5 of the steel pipe 1, to constitute a metal seal part 7 of both the seal parts 5, 6. Here is increased thread groove depth of an external thread in a pipe point end part side nearest to the metal seal part 7 and in a screw part position most distant from the metal seal part, to improve seizure resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a threaded joint used for mining oil and gas, and more particularly to an oil country tubular goods threaded joint characterized by the engraved screw shape.

[0002]

2. Description of the Related Art In recent years, the depth of oil wells has reached a depth of about several thousand meters to 10,000 meters with the exhaustion of resources and the progress of drilling technology. To achieve this, a huge number of oil country tubular goods are used, and the huge number of oil country tubular goods are connected in series by coupling.

In such a pipe joint portion, an axial tensile force due to the weight of the oil well pipe and the coupling, a ground pressure exerted from the surroundings to the outer peripheral surface, a pressing force exerted on the inner peripheral surface by a fluid flowing inside, etc. Needless to say, various kinds of severe forces act, and these forces become more severe as the depth of the oil well increases. In order to be used under such severe conditions, the pipe joint is required to withstand a large tensile load and at the same time have a reliable sealing property.

Many proposals have been made in order to meet this demand, and with respect to the tensile load resistance, the required joint tensile strength is secured by improving the thread shape and pitch of the threaded portion in the joint portion, and the sealing property is improved. With regard to (1), airtightness and liquid tightness are secured based on a metal seal by metal contact between the pipe tip and the torque shoulder of the coupling when they are fastened.

However, when a coupling is fastened to the pipe, a large force acts on the threaded portion, so that a defect such as seizure or damage is likely to occur on the threaded surface, and the number of times the steel pipe can be repeatedly used decreases as it is. Conventionally,
To solve the above problem, for example, Japanese Patent Publication No. 1-129.
As disclosed in JP-A-95-95 and JP-A-1-219173, the surface of the screw portion is coated with copper, zinc, or the like, or a manganese phosphate coating is formed to improve the resistance of the screw surface. The image sticking property is improved. In addition,
When the pipe and coupling are made of stainless steel, shot peening is generally performed on one thread surface of the male thread or the female thread and the above coating is performed on the other thread surface.

[0006]

However, in the improvement of the seizure resistance as in the above-mentioned conventional method, although the occurrence of defects such as seizure can be almost prevented at the time of the first tightening, the tightening at the second and third times is difficult. ， Often, the coating film comes off during repeated tightening,
As a result, there is a problem that defects such as seizure and damage occur on the screw surface.

The present invention has been made in view of the above problems, and an object thereof is to provide a structure of an oil country tubular goods threaded joint that can be repeatedly used.

[0008]

In order to achieve the above object, the oil well pipe threaded joint of the present invention comprises a metal seal portion and a threaded portion following the metal seal portion, and when the pipe and the coupling are fastened, In the oil well pipe threaded joint where the thread crests of the female thread engraved on the inner circumference of the coupling and the thread roots of the male thread engraved on the outer circumference of the pipe contact at the same gradient, at the pipe tip side closest to the metal seal part. The depth of the thread groove of the male screw is increased, and the depth of the thread groove of the male screw is increased at the position of the thread portion farthest from the metal seal portion.

At this time, the thread height of the female screw located on the pipe tip side closest to the metal seal portion is lowered, and the thread height of the female screw at the thread portion position farthest from the metal seal portion is adjusted. You may use together making it low. In addition, when the pipe and the coupling are fastened, a metal seal portion and a threaded portion following the metal seal portion are provided, and when the pipe and the coupling are fastened, a female screw thread crest engraved on the inner circumference of the coupling and a male screw engraved on the outer circumference of the pipe. In the oil well pipe threaded joint where the screw roots of the contact with the same gradient, while reducing the thread height of the female screw located on the pipe tip side closest to the metal seal part,
It is characterized in that the thread height of the female screw at the position of the screw portion farthest from the metal seal portion is lowered.

[0010]

The inventor of the present invention has conducted extensive research and studies on seizure resistance of oil well pipe threaded joints, and has found that the shape of the screw portion greatly affects seizure resistance. After further research, only the thread shape of the thread near the metal seal and the thread at the thread farthest from the metal seal have a large seizure resistance. I confirmed that I was involved.

That is, the shallower the thread groove depth of the male screw at the tip of the pipe closest to the metal seal portion and the thread groove depth of the incomplete thread portion farthest from the metal seal portion, the more easily seizure occurs, In addition, the higher the thread height of the female screw at the position of the pipe tip closest to the metal seal portion in the coupling and the height of the screw thread of the female screw farthest from the metal seal, the more likely seizure will occur. It became clear.

As described above, the seizure resistance is greatly influenced by the shape of the pipe tip portion closest to the metal seal portion and the shape of the screw portion farthest from the metal seal portion. , When tightening, since the screw part at the pipe tip side near the metal seal part and the screw part farthest from the metal seal part are more likely to make strong contact than the screw part at the center of the joint, baking etc. It is thought that the defect of (3) is likely to occur.

From the above-described examination results, in the present invention, only the threaded portion at the pipe tip side near the metal seal portion and the threaded portion farthest from the metal seal portion have the male screw threads. By increasing the groove depth or lowering the thread height of the female screw, a gap is provided between the thread root of the male thread and the crest of the female thread in the threaded portion, and the above It reduces contact and improves seizure resistance.

For example, for a threaded joint having a standard thread height and thread groove depth defined by a standard such as the API standard, the thread groove depth of the male screw closest to the tip of the pipe is δ. Just deeper and the thread groove depth that follows is (1/2) ・ δ
When designed to be deeper, a predetermined gap is provided between the crest of the female thread and the bottom of the male thread in the threaded portion of the portion closest to the pipe tip to mitigate the strong contact, In actual experiments, it was confirmed that the seizure resistance was improved. Further, it was confirmed that the seizure resistance was improved by changing the thread groove depth of the male screw farthest from the metal seal portion in the same manner.

As described above, even if the tightening and tightening are repeated, seizure occurs in the pipe tip side position closest to the metal seal part where seizure is likely to occur during tightening and in the screw part farthest from the metal seal part. Suppressed. In addition, from the viewpoint of mitigating the strong contact,
In the invention described in claim 2, the thread height on the female screw side is reduced to provide a predetermined gap between the crest of the female thread and the bottom of the male thread. In the described invention, the shapes of both the male screw and the female screw are changed to bring about the above effect.

[0016]

Embodiments of the present invention will be described with reference to the drawings.
First, the structure will be described. As shown in FIG. 2, the basic structure is the same as that of the conventional oil well pipe threaded joint, and the outer periphery of the steel pipe 1 on the tip side has a taper that becomes smaller in diameter toward the tip, and thus has a male thread. Is engraved to form a male screw portion 3, and a pipe-side seal portion 5 following the male screw portion 3 is formed at the tip thereof.

On the inner peripheral surface of the coupling 2, the steel pipe 1 is attached.
A female threaded portion 4 that can be screwed into the male threaded portion 3 is formed, and a seal portion 6 on the coupling 2 side that is engageable with the seal portion 5 of the steel pipe 1 is formed. The metal seal portion 7 is composed of the elements 5 and 6. Further, the screw shapes of the oil well pipe 1 and the coupling 2 are as shown in FIG.
The trapezoidal screw as shown in FIG. 2 is configured so that there is a predetermined clearance between the thread crest 3a of the steel pipe 1 and the root 4a of the thread groove of the coupling 2 in the tightened state.

The bottom 3b of the thread groove of the steel pipe 1 and the crest 4b of the screw thread of the coupling 2 have the same slope except the position closest to the metal seal portion 7 and the position 9 farthest from the metal seal. It is formed of K and is designed to make strong linear contact when tightened. Further, as shown in FIG. 1, the thread height closest to the metal seal portion 7 is defined by the standard for the thread portions of the two female threads on the tube tip 5 side closest to the tube 1 tip. Lower than the standard screw thread height (the height of the screw crest along the above-mentioned slope K) by δ, and the subsequent thread height is lower than the standard value (1/2).
・ It is set to be lower by δ.

Further, the thread height of the female screw of the incomplete thread portion 9 farthest from the metal seal portion 7 is set to δ, which is larger than the standard thread height defined by the standard, in the same manner as described above.
The thread height is set to (1/2) / δ lower than the standard value. By constructing the oil well pipe threaded joint in this manner, the female screw 4 at the screw portion at the portion closest to the tip of the pipe 1 and the screw portion at the position 9 farthest from the metal seal portion 7 that largely contributes to the occurrence of seizure Screw crest 4b and male screw 3 thread trough 3b
By providing a predetermined gap between and, when tightening, strong contact at the screw position is relaxed, and seizure resistance of the oil well pipe threaded joint is improved.

In order to confirm the improvement of the seizure resistance, actually, the API standard is L80, the outer diameter is 139.7 mm,
When a threaded joint for an oil country tubular goods with a wall thickness of 7.72 mm was processed to have the above-mentioned threaded structure and tightened under the same conditions, the results shown in Table 1 were obtained. The reference male screw depth is 1.575 mm and the reference female screw height is 1.500 mm.

[0021]

[Table 1]

This table is a result of investigating the state of seizure occurring on the joint surface by tightening each screw joint with the same torque and then re-tightening it 10 times.
The amount of change in the height of the internal thread shown in the table corresponds to δ in the above description. As can be seen from Table 1, it was confirmed that seizure did not occur in any of the joints whose screw shape was changed based on the present invention, whereas seizure occurred in the comparative example. It was confirmed.

That is, it was confirmed that the oil well pipe threaded joint according to the present invention does not cause seizure even after repeated use, and is excellent in seizure resistance. by this,
The number of times of reuse can be increased more than ever before. In addition, conventional means such as coating may be applied in addition to the means for improving the seizure resistance according to the above embodiment.

In the above embodiment, the height of the thread on the female screw 4 side is lowered so that a clearance is provided between the thread crest 4b of the female screw 4 and the thread root 3b of the male screw 3 to form the screw thread. This is an example in which the strong contact at the part position is relaxed, but the male screw 3
The thread shape may be changed to increase the depth of the thread groove on the side to widen the gap to mitigate the strong contact at that position and improve seizure resistance. Four
By lowering the thread height on one side and increasing the thread groove depth on the opposite male thread 3 side, a predetermined gap is provided between the thread crest 4b on the female thread 4 side and the thread trough bottom 3b on the male thread 3 side. May be provided to mitigate the strong contact.

[0025]

As described above, in the oil country tubular goods threaded joint of the present invention, the occurrence of defects such as seizure and damage on the screw surface is suppressed even if the tightening and unfastening are repeated twice and three times. As a result, seizure resistance is improved, and thus reliability in repeated use is improved.

[Brief description of drawings]

FIG. 1 is a side sectional view (detailed view of portion A in FIG. 2) showing a screw shape of a threaded joint of an embodiment according to the present invention.

FIG. 2 is a side sectional view showing a tightened state of the threaded joint of the embodiment according to the present invention.

[Explanation of symbols]

 1 Steel pipe 2 Coupling 3 Male screw part 3a Screw crest of male screw part 3b Screw root of male screw part 4 Female screw part 4a Screw root of female screw part 4b Screw crest of female screw part 7 Metal seal part 8 Screw part

Claims (3)

[Claims] 1. A metal seal portion and a thread portion following it are provided, and when a pipe and a coupling are fastened, the thread crest of a female screw engraved on the inner periphery of the coupling and the outer periphery of the pipe are engraved. In an oil well pipe threaded joint in which the screw roots of the male screw contact at the same gradient, the thread groove depth of the male screw on the pipe tip side closest to the metal seal part is deepened,
An oil country tubular goods threaded joint in which the thread groove depth of the male thread at the threaded portion position farthest from the metal seal portion is increased. 2. A metal seal portion and a thread portion following the metal seal portion are provided, and when the pipe and the coupling are fastened, the thread crest of a female screw engraved on the inner periphery of the coupling and the outer periphery of the pipe are engraved. In oil well pipe threaded joints where the screw thread bottoms of the male threads contact at the same gradient, lower the thread height of the female screw located on the pipe tip side closest to the metal seal part, and move it farthest from the metal seal part. An oil country tubular goods threaded joint characterized in that the thread height of the female thread at the threaded portion is reduced. 3. The thread height of the female screw located on the side of the pipe tip closest to the metal seal portion is lowered, and the thread height of the female screw at the thread portion farthest from the metal seal portion is lowered. Claim 1 characterized in that
Oil well pipe threaded joint described.