JP2019199894A - Threaded coupling for oil well pipe - Google Patents

Abstract

To more effectively suppress the deformation of a pin-side screw portion due to seal interference.SOLUTION: A threaded coupling for an oil well pipe is provided that comprises a pin 1 and a box 2, the pin 1 having: a male screw part 1A formed with a male screw 10; and a pin 1 side seal part formed at a position more on the shaft end side than the male screw part 1A, the box 2 having: a female screw part 2A formed with a female screw 20 threadedly engaged with the male screw 10; and a box 2 side seal part in contact with pin 1 side seal part. A first hook part 11 is provided on the stubbing surface 10A of some of the male screws 10, and a second hook part 21 is formed on the stubbing surface 20A of some of the female screws 20. When the male screw 10 and the female screw 20 look to displace in a direction in which both screws are radially separated from each other, the opposite surface 11a of the first hook part 11 of the male screw 10 and the opposite surface 21a of the second hook part 21 of the female screw 20 abut on each other.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a threaded joint for oil well pipes (hereinafter also simply referred to as a threaded joint) for connecting oil well pipes used for exploration and production of natural gas fields and oil fields.

  There are two types of connection of oil well pipes: an integral system in which pipes are directly connected and a coupling system in which two pipes are connected via a coupling. In the integral method, a male screw is provided at the end of one oil well pipe to form a pin, a female screw is provided to the end of the other oil well pipe to form a box, and the female screw of the box and the male screw of the pin are screwed together to connect the tubes. Connect. In the coupling method, a male screw is provided at the end of the oil well pipe to form a pin, a female screw is provided at each end of the coupling to form a box, and the female screw at one end of the box and the end of one oil well pipe are configured. The male screw of the pin is screwed, and the female screw on the other end side of the box is screwed with the male screw of the pin of another oil well pipe, thereby connecting the two pipes via the coupling.

The pin has a male screw portion in which a male screw is formed and a pin side seal portion formed on the tube end side of the male screw portion. The box has an internal thread portion in which an internal thread is formed and a box-side seal portion.
An oil well pipe threaded joint is a pipe joint of a box and a pin, and is generally constituted by a metal seal formed by abutment between a female screw of a box and a male screw of a pin and a seal portion. When the screw is tightened, for example, the shoulder portions of the pin and the box come into contact with each other and the tightening amount is regulated, and the nose portion of the pin and the box is locally in metal contact (metal-metal contact) and the contacted portion Plays the role of a seal.

  The cross-sectional shape of the thread provided in the threaded joint in the tube axis direction is generally a trapezoid with a load flank angle of 3 ° and a stubbing flank angle of 10 ° as defined in API (American Petroleum Institute) standards. The load flank angle is an inclination angle of the screw load surface with respect to the tube axis orthogonal line. The load flank angle is positive (+) when the tip is on the tip side of the screw shaft when viewed from the base end of the screw load surface, and negative (-) when the tip is on the opposite side. The stubbing flank angle is an inclination angle of the screw insertion surface with respect to the tube axis orthogonal line. The stubbing flank angle is negative when the tip is on the tip side of the screw portion when viewed from the base end of the screw insertion surface and positive when the tip is on the opposite side.

Here, in the above screw shape, when a compressive force is applied in the axial direction of the oil well pipe, the thread may float and the seal may be incomplete. A solution for making the load flank angle negative is known (Patent Documents 1 and 2).
Also, if the load flank angle is negative, the load surface of the male and female threads will come into strong contact during oil well pipe connection work, and excessive stress concentration may damage the screw corners, resulting in an incomplete seal. . To solve this problem, a solution is known in which the load surface of the screw is vertically divided into two in the height direction of the male screw, and the upper load flank angle is made smaller than the lower load flank angle (Patent Document 3). ).

JP-A-6-28059 JP-A-6-281061 Republished patent WO00 / 06937

In screw design, it is important to secure airtightness as well as galling resistance.
When the screw is tightened, the male screw and the female screw come into contact with each other in the geometrically interfering seal portion and screw portion. Therefore, in a threaded joint, airtightness is ensured by designing and producing a seal interference amount appropriately.
Here, the seal interference amount is a diameter difference (= pin side diameter (outer diameter) −box side diameter (inner diameter)) at the metal seal position (seal point) of the seal portion where the pin and the box face each other. Also, the amount of screw interference that is set appropriately to maintain the tightened state is the difference in the screw diameter at each position in the tube axis direction where the pin and the box face each other (= pin screw root diameter (outer diameter) −box thread). Part diameter (inner diameter)). The amount of screw interference is generally positive (+).

That is, the general threaded joint has a positive seal interference amount (pin seal diameter> box seal diameter) and a positive screw interference amount (pin screw valley diameter> box thread diameter).
In order to improve airtightness, the amount of seal interference may be increased. However, when the seal interference amount is increased, the hermetic performance is improved, but the larger the seal interference amount is, the more likely seizure (goling) occurs. Further, as the seal interference amount is increased, the pin is more deformed inward as the position is closer to the seal portion, and the pin and the box screw are separated in the radial direction.

That is, as the seal interference amount is increased in order to improve the airtightness, the screw portion on the pin side near the seal portion is deformed inward due to the seal interference, and the screw portion is separated from the box. Due to the deformation of the screw part on the pin side, the actual values of the screw interference amount and the seal interference amount become smaller than the design values, so that the contact pressure on the thread surface decreases and the contact pressure on the load flank also decreases. There is a problem of end.
Such problems cannot be sufficiently solved by the techniques described in Patent Documents 1 to 3.
The present invention has been made paying attention to the above points, and aims to more effectively suppress the deformation of the pin-side thread portion due to seal interference.

  In order to solve the problem, according to one aspect of the present invention, a male screw portion in which a male screw is formed, a pin having a pin-side seal portion formed on the shaft end side of the male screw portion, and a female screw that is screwed into the male screw are formed. And a box having a box-side seal portion in contact with the pin-side seal portion, and a threaded joint for an oil well pipe, wherein the first hook portion is provided on a part of the stubbing surface of the male screw. At the same time, when the second hooking portion is formed on a part of the stubbing surface of the female screw and the male screw and the female screw are to be displaced in the direction of relatively radial separation, the opposing surface of the first hooking portion of the male screw and the female screw The gist is that the opposing surface of the second hook part comes into contact.

According to the aspect of the present invention, the separation of the male screw and the female screw in the radial direction on the stub side is prevented by the first hook portion and the second hook portion, so that the pin side generated by the seal interference can be prevented. It becomes possible to suppress the deformation of the screw.
As a result, according to the aspect of the present invention, the airtight performance can be improved. In addition, since the deformation of the pin screw due to the seal interference can be reduced, the designed seal interference amount can be reduced without reducing the airtightness.

It is sectional drawing of the pipe-axis direction explaining the threaded joint for oil country pipes concerning embodiment based on this invention. It is sectional drawing of the pipe-axis direct direction which shows the relationship between a 1st hook part and a 2nd hook part. It is sectional drawing of a pipe axis right direction explaining the deformation | transformation by screw fastening. It is sectional drawing of a pipe axis right direction explaining the deformation | transformation of a pin screw part. It is sectional drawing of a pipe axis right direction explaining the effect | action of a 1st hook part and a 2nd hook part. It is a figure explaining other examples of the 1st hook part and the 2nd hook part. It is a figure explaining other examples of the 1st hook part and the 2nd hook part.

Next, embodiments of the present invention will be described with reference to the drawings.
Here, the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each part, and the like are different from the actual ones. Further, the embodiment described below exemplifies a configuration for embodying the technical idea of the present invention, and the technical idea of the present invention is such that the shape and structure of the component parts are as follows. Not specific. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.
In the following example, a threaded joint to which a coupling method is applied will be described as an example. The present invention can also be applied to an integral system.

(Constitution)
As shown in FIG. 1, the threaded joint for oil well pipe of the present embodiment includes a pin 1 and a box 2. The pin 1 has a male screw portion 1A, a nose portion 1B (no screw portion) extending to the tube end side from the male screw portion 1A, and a shoulder portion 1C provided at a tip portion of the nose portion 1B. The male screw portion 1A is composed of a taper screw in which a plurality of male screws 10 are formed. Specifically, the nose portion 1B is a portion from the most distal portion of the pin 1 to the first thread of the male screw portion 1A.
The box 2 includes a female screw portion 2A, a nose portion 2B on the box 2 side facing the nose portion 1B on the pin 1 side in the radial direction, and a deepest end portion of the box 2 (a portion where the most distal portion of the pin 1 abuts 2) of the shoulder portion 2C on the box 2 side. The female screw portion 2A is formed of a taper screw formed with a female screw 20 that is screwed with the male screw 10 of the male screw portion 1A.

In the present embodiment, a case will be described in which seal portions are formed on the nose portions 1B and 2B, and positions close to the shoulder portions 1C and 2C constitute a seal surface that is metal-touched to each other. Although the shoulder portions 1C and 2C may be used as the seal portions, the airtightness can be improved by forming the seal portions on the nose portions 1B and 2B.
In the present embodiment, from the viewpoint of further improving airtightness and improving galling resistance, the outer peripheral surface 1Ba of the nose portion 1B on the pin 1 side is formed as a convex curved surface in the outer diameter direction at the sealing position, and the box 2 side The inner peripheral surface 2Ba of the nose portion 2B is a tapered surface (the shoulder side has a small diameter tapered surface). In FIG. 1, symbol SP indicates a seal point that is a center point of metal contact in the tube axis direction.

The cross-sectional shape in the tube axis direction of the male screw 10 provided in the male screw portion 1A and the female screw 20 provided in the female screw portion 2A, that is, the thread shape is a trapezoid. The basic shape of the screw thread may be a known shape as appropriate.
However, in the present embodiment, one or two or more first hooks 11 are provided on at least one stubbing surface 10A of the male screw 10 on the nose portion 1B side. In addition, a second hook portion 21 that can be engaged with the first hook portion 11 is provided on the stubbing surface 20A of the female screw 20 on the nose portion 1B side. Here, the engagement in the present embodiment refers to a state in which the other enters the space formed by one, and the two do not need to be in contact with each other.

  The first hook 11 has a cross-sectional shape that is at least one of a concave cross-section and a convex cross-section when viewed from the direction perpendicular to the tube axis. The first hook portion 11 and the second hook portion 21 have opposing surfaces 11 a and 21 a that face each other in the axial direction (radial direction) of the pin 1, and the opposing surface 11 a on the first hook portion 11 side. Facing the inner diameter side, the facing surface 21a on the second hook portion 21 side faces the outer diameter side, and the facing surfaces 11a, 21a forming a pair overlap in the axial direction of the pipe.

In the present embodiment, as shown in FIG. 2, the first hook portion 11 has a concave cross section. The second hook portion 21 has a convex cross section that is inserted into a concave space formed by the first hook portion 11.
In FIG. 2, the angle β represents the road flank angle, and the angle γ represents the stubbing flank angle. As described above, the load flank angle is positive (+) when the tip is on the tip side of the screw shaft as viewed from the base end of the screw load surface, and negative (-) when the tip is on the opposite side. The load flank angle β shown in FIG. 2 is a negative (−) case.

In this embodiment, the 1st hook part 11 is formed from one groove | channel extended along the helical extension direction of 10 A of stubbing surfaces of the external thread 10 by the side of the nose part 1B, for example. That is, the first hook portion 11 and the second hook portion 21 have a groove shape or a rail shape extending along the stub surface. The groove shape and rail shape extending along the stub surface may be formed from the first screw position on the seal portion side, but the opposing surface formed by the first hook portion 11 and the second hook portion 21 is: It may be formed from an intermediate position in the extending direction.
The first hook 11 preferably has a length of at least 360 degrees when viewed from the tube axis direction. The range of the screw for providing the second hook 21 may be the same as the range for providing the first hook 11. In addition, you may make the direction which becomes a cross-sectional convex side a little short.

A preferable range of the screw provided with the first hook 11 is that the length in the tube axis direction on the threaded portion side from the seal point SP which is a seal position formed by the pin 1 side seal portion and the box 2 side seal portion is L. When [mm] (see FIG. 1), the length L is a range represented by the following formula. The first hook 11 may be provided on the male screw 10 existing within the length L.
However,
L ≧ S / (2 × tan α)
S [mm]: Seal interference amount α [degree]: Inclination angle of taper screw

Here, the main range in which the screw portion on the pin side tends to move away from the box side due to the seal interference amount S is the distance from the seal position point SP to the length L (= S / (2 × tan α)). Therefore, it is defined as L ≧ S / (2 × tan α).
Here, the seal interference amount S is a diameter difference (= pin 1 side diameter (outside diameter) −box 2 side diameter (inside diameter)) at the metal seal position (seal point SP) of the seal portion.
The first hook 11 may be provided on all stubbing surfaces of the male screw 10.

In addition, in FIG. 2, although the example which formed the 1st hook part 11 in the root side (screw surface side) of a screw thread is shown, the formation position of the 1st hook part 11 is not limited to this position. For example, the first hook 11 may be formed on the center side in the height direction of the stub surface 10A.
Further, the length n in the tube axis direction of the opposing surface 11a on the male screw portion 1A side and the opposing surface 21a on the female screw portion 2A side in the axial direction (radial direction) is 0.05 times or more the screw pitch P. It is preferable that it is 0.25 times or less. More preferably, it is 0.10 times or more and 0.20 times or less of the thread pitch P.

Here, if the overlap length n is too short, the opposing surfaces tend not to overlap each other when the pins are deformed due to seal interference, and if the length n is too long, the first hook portion 11 and the second hook portion 11 are not overlapped. Considering that the strength of the stubbing surface side due to the hook portion 21 is insufficient, the length n is preferably 0.05 times or more and 0.25 times or less the screw pitch P as described above.
The effective height m of the opposing surfaces 11a, 21a is preferably 0.05 h times or more and 0.95 h times or less, more preferably 0.25 h times or more and 0.60 times or less when the height of the male screw 10 is h. .

Here, if the height for forming the first hook portion 11 and the second hook portion 21 is too low, the effect of the hook is small, and if the height is too high, the initial engagement (stubbing) property of the screw is lowered. Therefore, as described above, the effective height m is preferably 0.05 h times or more and 0.95 h times or less when the height of the male screw 10 is h.
The angle θ of the facing surfaces 11a, 21a with respect to the tube axis direction is, for example, 30 degrees to 85 degrees, preferably 45 degrees to 70 degrees. The smaller the angle θ, the more reliably the opposing surfaces 11a and 21a can be brought into contact with each other. However, the smaller the angle θ, the more difficult the processing becomes.

The minimum gap d between the facing surface 11a on the male screw portion 1A side and the facing surface 21a on the female screw portion 2A side is made smaller than the gap between the stubbing surface 10A of the male screw 10 and the stubbing surface 20A of the female screw 20. Just design. The gap between the opposed surfaces 11a and 21a does not need to be uniform. The minimum gap d between the opposed surface 11a on the male screw portion 1A side and the opposed surface 21a on the female screw portion 2A side satisfies, for example, the following formula: Set.
0 <d ≦ (S / (2 × tan θ))
Here, if d is too large, the hook portions do not come into contact with each other when the pin side is deformed due to seal interference, and the effect of the hook cannot be obtained. As described above, “0 <d ≦ (S / (2 × tan θ)) ”.

(Action and others)
“When the first hook portion 11 and the second hook portion 21 are not provided”
The pin 1 is less rigid than the box 2. Therefore, as the screw is tightened, the nose portions 1B and 2B of the pin 1 are deformed in the direction indicated by the arrow Y1 in FIG. 3 due to the seal interference, and the male thread portion 1A close to the seal portion as shown in FIG. In FIG. 4, the external thread 10 is deformed in the direction of the arrow Y <b> 2 (inner diameter side) and is displaced in a direction away from the internal thread 20. As a result, the contact pressure on the thread surface decreases and the contact pressure on the load flank also decreases. Since the actual values of the screw interference amount and the seal interference amount are smaller than the design values, it is necessary to set the design values larger.

“When the first hook portion 11 and the second hook portion 21 are provided”
On the other hand, in this embodiment, by providing the first hook portion 11 and the second hook portion 21, as shown in FIG. 5, it is deformed in the direction of arrow Y2 (inner diameter side) in FIG. When 10 is going to be displaced away from the female screw 20, the opposing surface 11a of the first hook 11 comes into contact with the opposing surface 21a of the second hook 21 to suppress deformation of the male screw 1A toward the inner diameter side. To do.
Thus, in this embodiment, as a result of suppressing the deformation of the male screw portion 1A on the seal portion side due to seal interference, it is possible to maintain the screw interference amount and the seal interference amount at values close to design values. . This can improve the airtight performance.

In addition, the design value of the seal interference amount can be reduced while improving the airtightness in some cases without lowering the same airtight performance as compared with the conventional case.
Here, the oil well is classified into a tube corresponding to a straw for sucking out oil and a casing for supporting an outer shell (ground pressure). Tubing needs to be removed and retightened after a certain amount of use, and ISO 13679 must be able to withstand 9 tightenings plus a final tightening. Although the casing is not as frequent as tubing, it requires 2 + 1 tightening performance under the same rule. The ability to reduce the design value of the amount of seal interference as in this embodiment leads to the same hermetic performance and an increase in the number of retightenings.

(Modification)
Here, the cross-sectional shapes of the facing surface 11a of the first hooking portion 11 and the facing surface 21a of the second hooking portion 21 need not be linear. As illustrated in FIGS. 6A and 6B, the cross-sectional shape of one of the opposing surfaces 11a and 21a may be curved. Both cross-sectional shapes of the opposing surfaces 11a and 21a may be curved. The contact between the facing surface 11a of the first hook 11 and the facing surface 21a of the second hook 21 may be linear or point-like.

Further, in the above embodiment, the case where the first hook portion 11 is a single line is illustrated, but two or more lines are provided so as to line up and down with respect to the stubbing surface 10A of the male screw 10 as shown in FIG. Also good.
Moreover, although the case where the cross-sectional shape of the 1st hook part 11 is concave shape is illustrated in the said embodiment, the cross-sectional shape of the 1st hook part 11 is made into convex shape, as shown in FIG. The cross-sectional shape of the hook portion 21 may be a concave shape. When the male screw 10 and the female screw 20 are about to be displaced in the radial direction, the opposing surface 11a of the first hook portion 11 of the male screw 10 and the opposing surface 21a of the second hook portion 21 of the female screw 20 come into contact with each other. As long as the shape is such that the cross-sectional shape is not limited.

The effect of the present invention was verified by FEM (finite element method).
The conditions of the oil well pipe were API5CT L80 7 ″ × 29.0 # (tube outer diameter 177.80 mm × tube thickness 10.36 mm).
The evaluation conditions were ISO 13679 CAL IV 100% compression, which is a screw tightness test. As an index of the effect, the seal portion contact pressure in LP2 (tension and internal pressure application), which generally tends to cause leakage, was used. In Table 1, it evaluated by the ratio with respect to the pressure of the verification example 2.
If the index value is large, the airtightness is high, and if the index value is small, the airtightness is low.

The test results are shown in Table 1.
In the table, the hook angle θ is the inclination θ of the opposing surfaces 11 a and 21 a of the first hook 11. The stub side distance d is a distance d between the opposing surfaces 11a and 21a.

Further, after the screw hermeticity test was performed with ISO 13679: 2002 1st Edition CAL IV 100% compression, a further hermeticity test was performed.
That is, in the airtight test, the seal interference amount S was set in two ways, and the stubbing-side screw interval d was set in several ways, and the airtight test was performed.
The results are shown in Table 2.

As can be seen from Table 2, those with a smaller interval d passed the hermetic test, and those with a larger d failed. In addition, since the deformation of the pin 1 screw due to seal interference can be reduced, the amount of seal interference in design can be reduced.
Although a conventional example in which the first hook portion 11 and the second hook portion 21 are not provided is not described, the case where the distance d is increased is close to the conventional example.
Therefore, it can be seen from Table 2 that when the first hook portion 11 and the second hook portion 21 are provided, compared to the case where the first hook portion 11 and the second hook portion 21 are not provided, after tightening. It can be seen that the seal interference amount can be close to the design value.

  In addition, the pass line of a test here is set higher than the airtightness level requested | required of the normal threaded joint for oil country pipes. Therefore, it does not mean that a threaded joint that fails in this test will fail in a normal test.

1 pin 1A male thread part 1B nose part 1C shoulder part 2 box 2A female thread part 2B nose part 2C shoulder part 11 first hook part 11a opposed surface 21 second hook part 21a opposed surface L range P where the first hook part is provided Pitch S Seal interference amount SP Seal point d Minimum gap (interval)
θ Inclination of facing surface α Angle of taper screw

Claims (4)

A box having a male screw part on which a male screw is formed and a pin having a pin-side seal part formed on the tube end side of the male screw part, a female screw part on which a female screw to be screwed onto the male screw is formed, and a box in contact with the pin-side seal part A box having a side seal part, and a threaded joint for oil country tubular goods,
A first hook or two or more first hooks provided on at least a part of the stubbing surface of the male screw;
A second hook portion formed on the stubbing surface of the female screw capable of facing the stubbing surface of the male screw having the first hook portion and engageable with the first hook portion;
The first hook portion and the second hook portion have opposing surfaces that face each other in the axial direction of the pin, and the opposing surface on the first hook portion side faces the inner diameter side and the second hook portion. An oil well pipe threaded joint, characterized in that the opposing surface on the hook portion side faces the outer diameter side and the opposing surfaces overlap in the axial direction of the pin. The first hook is one of a concave cross section or a convex cross section,
The said 2nd hook part is the other of a cross-sectional concave shape or a cross-sectional convex shape, The cross-sectional convex shape side hook part is inserted in the hook part of a cross-sectional concave shape side, It described in Claim 1 characterized by the above-mentioned. Threaded joint for oil well pipes. The first hook portion is provided on a stubbing surface existing in a range of L [mm] in the tube axis direction from a seal position formed by the pin side seal portion and the box side seal portion. The threaded joint for oil country tubular goods according to claim 1 or 2, characterized by being expressed by a formula.
However,
L ≧ S / (2 × tan α)
S [mm]: Seal interference amount α [degree]: Inclination angle of taper screw   The length in the tube axis direction where the opposing surfaces overlap each other in the direction perpendicular to the tube axis is not less than 0.05 times and not more than 0.25 times the screw pitch. 2. A threaded joint for oil country tubular goods according to item 1.

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