JPH08135855A - Oil well pipe threaded joint - Google Patents

Abstract

(57) [Summary] [Purpose] In a face-sealing type oil country tubular goods threaded joint, prevents seizing of the seal portion. [Structure] Between the pin side screw portion 11 and the seal portion 12, a pre-stage screwless portion 14 having a smaller inclination than the seal portion 12 is provided.
To provide. The front unthreaded portion 14 and the seal portion 12 are connected by an arc 15 tangent to each other. Distance L from the apex of arc 15 to the intersection X of arc 15 and seal portion 12
Is 1.45 mm or more.

Description

Detailed Description of the Invention

[0001]

[Field of Industrial Application] The present invention is for the prospecting of petroleum and natural gas.
The present invention relates to a threaded joint used for connecting oil country tubular goods used for production and the like, and particularly to a face seal type threaded joint.

[0002]

2. Description of the Related Art As a threaded joint for connecting an oil country tubular good, a round threaded joint and a buttressed threaded joint of API standard are generally used. However, the depth of oil wells and gas wells has become deeper year by year, and due to the severer mining conditions that accompany this, threaded joints are now subject to large three-dimensional loads and are exposed to severe stress conditions. In particular, in the production well, the circumferential stress from the inside of the pipe acts, and it is necessary to maintain the airtight performance under triaxial stress.

In response to such demands, round screw joints and buttress screw joints have become insufficient.
What was developed there was a face-seal type screw joint having a metal seal surface as shown in Japanese Patent Laid-Open No. 5-87275, and it has already begun to be used in many wells. A schematic configuration of a face seal type screw joint will be described with reference to FIGS. 1 and 2.

Here, the oil country tubular goods P, P are coupling C
Connected by. Reference numeral 10 denotes an end portion of the oil country tubular good P inserted into the coupling C, which is a pin portion. Further, 20 is a box portion formed in the coupling C to receive the pin portion 10. A screw joint is one that screw-connects the pin portion 10 and the box portion 20.

In the face-seal type screw joint, the pin portion 10 has a tapered male screw portion 11 whose diameter gradually decreases toward the tip.
On the outer surface. At the tip of the male screw portion 11, there is provided a taper-shaped seal portion 12 whose diameter gradually decreases toward the tip. The tip of the pin portion 10 is a shoulder portion 13 that is steeply inclined in a direction opposite to the male screw portion 11 and the seal portion 12. The box portion 20 has a female screw portion 21 corresponding to the male screw portion 11 on the inner surface, a seal portion 22 corresponding to the seal portion 12 is provided in the inner portion thereof, and a shoulder portion 13 is provided further in the inner portion thereof. A corresponding shoulder portion 23 is provided.

When the male screw portion 11 is screwed into the female screw portion 21, the seal portions 12 and 22 come into contact with each other, and the shoulder portions 13 and 23 are butted against each other, whereby the pin portion 10
The box portion 20 is face-sealed. In order to generate a sufficient surface pressure on the seal surface, a diameter difference called an interference amount is provided between the pin-side seal portion 12 and the box-side seal portion 22.

The interference amount S is expressed by S = D _PX -D _BX D _PX : minimum diameter of pin side seal portion D _BX : minimum diameter of box side seal portion, and S> 0, that is, D _PX > D _BX . . By giving the amount of interference, the sealing parts 12, 2
2 begins to interfere [FIG. 2 (a)], and the shoulder portion 13,
23 abuts and the coupling ends (FIG. 2 (b)). The axial stroke from the start of the interference of the seal portions 12 and 22 to the completion of the coupling is referred to herein as the tightening amount MOS.

[0008]

In such a metal surface seal type oil country tubular goods threaded joint, due to the difference in diameter between the seal portions 12 and 22, the interference between the seal portions 12 and 22 starts and the coupling is completed. In the meantime, that is, while the tightening amount MOS is screwed in, the seal portions 12 and 22 slide in a spiral shape while maintaining a high surface pressure. Therefore, the seal parts 12, 2
2 is likely to be seized. When this seizure occurs, the sealing surface is roughened, a gap is locally formed or an excessive interference portion is formed, and the sealing property is impaired.

Particularly, in a joint used for an oil country tubular good having a relatively large diameter called a casing size, the seal portion 1
Since the sliding distance L _{S of} 2 and 22 (the distance that the rubbing roller moves in the spiral direction) is long and the contact surface pressure P is large, seizure easily occurs. If the oil country tubular goods are made of stainless steel, which is an alloy of nickel or chrome, or pure titanium / titanium alloy, the thermal conductivity is lower than that of steel, and the heat accumulation in the sliding part is large, so the tubing size of the small diameter is small. However, seizure often occurs.

An object of the present invention is to provide a face-seal type threaded joint for oil country tubular goods which suppresses seizure of the seal surface.

[0011]

[Means for Solving the Problems] In order to prevent the seizure of the seal surface, the inventors of the present invention conducted investigation and examination on the occurrence of the seizure, and as a result, the following facts were found.

1) In a face-seal type oil country tubular goods threaded joint having a tapered metal seal surface as shown in FIGS. 1 and 2, due to a difference in diameter between the seal portions 12 and 22, a pin side seal is formed at the time of screwing and coupling. The tip 12 'of the portion 12 collides with the inlet 22' of the seal portion 22 on the box side, and the portion is likely to be flawed. If the screwing is further continued, seizure occurs in the seal portions 12 and 22 with the flaw as the starting point. In the drill pipe, the pipe is sequentially discharged to the outside of the well while performing a so-called break for uncoupling the drill bit, etc., but the flaws attached at the time of joining break the other parts at the time of the break, and the seal portion 12, Since a large number of flaws are induced in 22, it is easy for seizure to occur.

2) The seizure of the seal portion in the face seal type oil country tubular goods threaded joint mechanically causes frictional heat generated by sliding under a face pressure load to accumulate above a limit value in a part of the sliding face. ,
It is generated by melting a part of the contact surface metal. Therefore, if the same material is used and the other conditions are the same, it can be said that the larger W represented by W = P (contact pressure) × L _S (sliding distance) is, the more easily seizure occurs. Here, the surface pressure P is proportional to the amount of interference S (= D _PX -D _BX ) in the elastic region, but the amount of interference S cannot be reduced in order to secure good sealability.

3) The sliding distance (L _S ) of the seal portion is generally expressed by the following equation. L _S = MOS × π × D _S ÷ p S × T _S × π × D _S ÷ p where S: interference amount (= D _PX −D _BX ) MOS: tightening amount 1 / T _S : seal part inclination ( Taper) π: Circumferential ratio D _S : Seal part diameter p: Thread part pitch

The seal diameter D _S is the above-mentioned D
_PX (minimum diameter of pin side seal), D _BX (minimum diameter of box side seal), DB (maximum diameter of pin side seal), and other representative diameters of seals.

As can be seen from the above equation, the thread pitch p,
If the diameter D _{S of} the seal portion and the interference amount S are the same, the sliding distance L _S of the seal portion decreases T _S, and the inclination of the seal portion (1
The larger / T _S ) is, the smaller it is. That is, if the inclination (1 / T _S ) of the seal portion is increased from 1/10 to 1/4, the sliding distance L _S becomes 4/10 (= 1 / 2.5).
Decrease to.

4) In the face seal type oil country tubular goods threaded joint, as shown in FIG. 2, a pre-stage screwless portion 14 having a smaller inclination than the seal portion 12 is provided between the male thread portion 11 on the pin side and the seal portion 12. May be provided. In that case, the pre-stage screwless portion 14 and the seal portion 12 are normally connected by an arc 15 tangent to each other, as shown in FIG. FIG. 3B is an enlarged view of part A in FIG. Then, the pin side seal portion 12 and the box side seal portion 2
A peak of the contact surface pressure D occurs at a portion where 2 starts to separate from each other, that is, a portion x on the arc side close to the contact point X of the arc 15 and the seal portion 12, and in fact, seizure frequently occurs at this portion x.

According to the investigation by the present inventors, when the radius of curvature of the arc 15 connecting the pre-stage screwless part 14 and the seal part 12 is relatively small and the contact point X is close to the apex of the arc 15, FIG. As indicated by the solid line in the graph in (a), the peak value of the surface pressure P becomes extremely large. However, when the radius of curvature of the circular arc 15 is increased and the contact point X is moved away from the apex of the circular arc 15, the peak generation position of the surface pressure P moves as shown by the broken line, and in addition, the peak value decreases. . Therefore, image sticking hardly occurs. The reason why the peak value of the surface pressure P is small is that since the radius of curvature of the contact portion boundary is large, the change from contact to non-contact becomes gradual, so that the contact stress of so-called Hertz decreases.

Based on these findings, the threaded joint for oil country tubular goods of the present invention effectively suppresses seizure of the seal portion without deteriorating the sealing property. Characterize. The inclination of the seal portions 12 and 22 is tapered to 1/6 or more, and the inclination is made larger than the inclination of the screw portions 11 and 21. The length L _B of the box-side seal portion 22 is made larger than the length L _P of the pin-side seal portion 22. Between the pin side male screw portion 11 and the seal portion 12, a pre-stage screwless portion 14 having a smaller inclination than the seal portion 12 is provided, and a curve tangent to the seal portion 12 is provided between the pre-stage screwless portion 14 and the seal portion 12. Connect by 15. Or the distance L _a from the nearest arc vertex contact X of present in the curve 15 curve 15 and the sealing portion 12 to the contact point X,
From the boundary Y between the pre-stage screwless portion 14 and the seal portion 12 to the contact point X
The smaller one of the distances L _b up to 1.45 mm is set.

The apex angle of the arc closest to the contact point X in the curve 15 is defined because the contact of the seal begins to separate at the portion having the maximum curvature. This part is the boundary where the sealing surfaces are actually in contact. In addition, the pre-stage screwless part 14
And the boundary Y of the seal portion 12 are where the respective extension lines intersect. The smaller one of L _a and L _b is specified because the contact of the sealing surface is up to L _b .
If a minute R is provided at the boundary Y, the contact is made up to that part, and a peak of the surface pressure occurs near the point Y [Fig.
(A)].

As shown in FIG. 3, when the curves 15 connecting the pre-stage screwless portion 14 and the seal portion 12 are arcs tangent to each other, the apex of the arc 15 is located at the boundary Y. Also, the distances L _a and L _b match. Therefore, is arc 15
The distance L from the apex to the contact point X will be 1.45 mm or more.

In Japanese Patent Laid-Open No. 5-87275, the
Although a joint satisfying the condition (1) is shown, nothing is shown about the condition (1), and not all of these are indispensable from the viewpoint of preventing seizure.

[0023]

The conditions in the present invention will be described in detail below.

The inclination of the seal portions 12 and 22 is set to the screw portion 11,
The inclination of 21 is made larger than the tip of the seal portion 12 on the pin side when the screw is screwed in is the seal portion 22 on the box side.
This is to avoid a situation in which the vehicle collides with the entrance 22 '. When this collision occurs, the seal portions 12 and 22 are flawed, and due to the sliding of the seal portions 12 and 22 due to the subsequent screwing, seizure occurs in the seal portions 12 and 22 starting from the flaw. By avoiding the collision between the tip 12 ′ of the seal portion 12 and the inlet 22 ′ of the seal portion 22, the seal portion 1
One of the causes of seizure 2,2 is removed. If the inclination of the seal part is α and the inclination of the thread part is β, then 4/3 ≦ α / β
≤14.6 is desirable. If α / β is too large, it is not preferable from the viewpoint of maintaining the sealing property under axial load.

The length L _B of the box-side seal portion 22 is made larger than the length L _P of the pin-side seal portion 12 because the diameter difference between the inlet diameter of the seal portion 22 and the tip diameter of the seal portion 12 is set. This is to make the size larger so as to avoid the collision between the tip 12 ′ of the seal portion 12 and the inlet 22 ′ of the seal portion 22. Desirable L _B / L _P is as shown in Equation 1. If L _B / L _P is too large, the box-side seal portion 22 and the screw portion 21 are too close to each other, which makes machining difficult.

[0026]

[Equation 1]

The length L of the box side seal portion 22
_{Even if B} is smaller than the length L _P of the seal portion 12 on the pin side, if the length of the mutual contact portions of the seal portions 12 and 22 is increased, the inlet diameter of the seal portion 22 and the tip diameter of the seal portion 12 become However, in the present invention, the inclination of the seal portions 12 and 22 is reduced to 1 /
The length L _B of the box-side seal portion 22 needs to be greater than the length L _P of the pin-side seal portion 12 because the mutual contact portion cannot be made longer by making the length as sudden as 6 or more.

The taper of the inclination α of the seal portions 12 and 22 is ⅙ or more, and the sliding distance L _S between the seal portions 12 and 22 is made small so that W = P (contact pressure) × L _S ( This is because seizure is less likely to occur by reducing W represented by (sliding distance). Desirable slope is 1/4 ≦ α
≦ 1 / 1.373. If α is too large, it is not preferable from the viewpoint of maintaining the sealing property under axial load.

Between the male thread portion 11 on the pin side and the seal portion 12, the pre-stage screwless portion 14 having a smaller inclination than the seal portion 12
In order to connect the pre-stage unscrewed portion 14 and the seal portion 12 by the curve 15 tangent to the seal portion 12, the portion x where the seal portions 12 and 22 are separated is lengthened so that the seal portions 12 and 22 are This is because the peak value of the contact surface pressure P is lowered by gradually separating them.

The curve 15 and the seal portion 1 exist within the curve 15.
Distance L from the vertex of the arc closest to the contact point 2 to the contact point X
_a or the distance L _b from the boundary Y to the contact point X, whichever is smaller,
As for 1.45 mm or more, the sealing parts 12, 22 are
This is because the portion x where is separated is made longer so that the seal portions 12 and 22 are gradually separated, and the peak value of the contact surface pressure P is lowered.

When the curve 15 connecting the pre-stage screwless portion 14 and the seal portion 12 is an arc tangent to each other, the distance L from the apex of the arc 15 to the contact point X is 1.45 mm.
That is all. Assuming that the front-stage unthreaded portion 14 is a straight surface parallel to the pipe axis, the radius R of the arc 15 required to realize L ≧ 1.45 mm is 1 / the taper of the seal portion.
In the case of 2, the taper of the seal is 1/4 or more, and is 1/4.
In the case of, it is 24 mm or more.

The seizure resistance varies depending on the surface treatment, but when the taper of the seal portion is 1/2, R ≧ 13 m
m, R ≧ 26m when the taper of the seal part is 1/4
If a combination of m, that is, the taper of the seal portion and the radius R at which the distance L is 1.6 mm or more is adopted, good seizure resistance can be obtained regardless of the type of surface treatment. From this point, the distance is preferably 1.6 mm or more.

The upper limit of the distance, L ≦ (L _P -
Tip radius R _P ) -2, that is, a minimum of 2 m on the pin side seal part
It is preferable to have a taper portion (straight portion) of about m from the viewpoint of measuring the seal diameter. It is also preferable from the viewpoint of surface pressure distribution on the sealing surface. If there is no taper portion, the seal surface pressure distribution becomes mountainous, and seizure is likely to occur at that portion. Further, it is difficult to measure the pin side seal diameter, and the amount of interference with the box side seal surface cannot be set correctly.

[0034]

Next, the effects of the present invention will be clarified by showing Examples of the present invention and comparing them with Comparative Examples.

In the coupling type threaded joint for oil country tubular goods shown in FIGS. Lubrication compound was applied to the threads of various prototype joints, and joints and breaks were repeated until seizure occurred at the seal. The maximum number of repetitions was 10 times. The results are shown in Tables 4 and 5.

As can be seen from Table 3, in each of the comparative examples, seizure occurred due to early joining / breaking, and subsequent joining / breaking became impossible. It was possible to combine and break up to once. The maximum number of repetitions of bonding / breaking is set to 10 because the number of repetitions usually adopted in the test for examining the seizure resistance of the joint for tubing is 10.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

[Table 4]

[0041]

[Table 5]

In the above embodiment, the case of the coupling system has been described, but the same effect can be obtained even in the case of the integral system.

The curve connecting the pre-stage screwless part on the pin side and the seal part has been described in the case of a single arc.
Similar effects can be obtained when this single arc is approximated by a multi-order curve or a combination thereof.

Regarding the pre-stage screwless portion, the case where it is parallel to the pipe axis has been described. However, even if this portion has an inclination, the inclination of the sealing portion is changed so that the angle with the sealing portion is the same as that of the embodiment. Then, when the radius R of the connecting arc is the same, the distance from the boundary Y to the contact point X can be made the same, and the same effect can be obtained.

[0045]

As described above, in the oil well pipe threaded joint of the present invention, seizure of the seal portion, which is a problem in the face seal type, can be significantly suppressed. Moreover, since it is not necessary to reduce the amount of interference required to secure the sealing property, there is no fear of reducing the sealing property.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a face seal type screw joint.

FIG. 2 is a schematic cross-sectional view showing the vicinity of the seal portion of the threaded joint.

FIG. 3 is a schematic diagram showing a connection portion between a pre-stage screwless portion and a seal portion and an influence of a shape of the connection portion on a surface pressure distribution.

[Explanation of symbols]

 10 pin part 20 box part 11,21 screw part 12,22 seal part 13,23 shoulder part 14 pre-stage screwless part 15 connection curve

Claims (1)

[Claims] 1. A pin portion (10) having a tapered seal portion (12) at the tip of the tapered male screw portion (11) and a shoulder portion (13) at the tip, and a tapered female screw portion ( Provide a tapered seal part (22) at the back of 21) and shoulder part at the back.
In a face seal type oil country tubular goods threaded joint in which the box part (20) provided with (23) is screwed and connected, the seal parts are brought into contact, and the shoulder parts are butted, the inclination of the seal parts (12, 22) Is 1/6 or more, and the inclination is larger than the inclination of the screw part (11, 21),
The length L _B of the box side seal part (22) is made larger than the length L _P of the pin side seal part (22), and the pin side male screw part (11)
A pre-stage screwless part (14) having a smaller inclination than the seal part (12) is provided between the seal part (12) and the seal part (12), and the seal part (12) is provided between the pre-stage screwless part (14) and the seal part (12). ) Is connected by a curve (15) that is tangent to the curve (15) and exists inside the curve (15) and the seal (12).
Whichever is smaller, the distance from the apex of the arc closest to the contact point (X) to the contact point (X) or the distance from the boundary (Y) between the pre-stage screwless part (14) and the seal part (12) to the contact point (X). To 1.45
A threaded joint for oil country tubular goods characterized by having a thickness of at least mm.