JP2874615B2 - Screw joint for pipe connection - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an oil well, a gas well, a geothermal well for exploring and producing oil and natural gas, steam and hot water, and an injection well or an oil and natural gas for injecting industrial waste underground. The present invention relates to a threaded joint for pipe connection forming a press-fit well for secondary and tertiary recovery, and particularly to a threaded joint for pipe connection suitable for use in deep wells or in severe corrosive environments. . In the following description, the present invention will be described by taking a typical example of a threaded joint for oil country tubular goods as a threaded joint for pipe connection.

[0002]

2. Description of the Related Art Conventional threaded joints for oil country tubular goods have API standards
(American Petroleum Institute Standard) round threaded joints and buttressed threaded joints have been widely used, but with the deepening of oil and gas wells and the severeness of pressure, temperature, corrosive environment, etc.,
There is a need for a joint that has high strength against breakage due to the weight of the pipe and has good airtightness.

FIG. 1 is a sectional view showing a coupling type oil country tubular good threaded joint as an example. FIG. 1A is a side view showing a part of the entire structure in a cross section, and FIG. 1B is an enlarged view showing a cross section of a box portion 21 of the coupling 20.
FIG. 1C is an enlarged sectional view of the pin portion 11 of the steel pipe 10.

[0004] As shown in Fig. 1 (a), steel pipes 10 'and 10 as oil country tubular goods are screw-connected by couplings 20, box parts 21 are provided on both sides of the coupling 20, and steel pipes 10 and 10 are provided. ′ Are provided with pin portions 11 respectively.

As shown in FIG. 1 (b), the box portion 21 has a tapered female screw 22. As shown in FIG. 1 (c), the pin portion 11 has a tapered male screw 12 as well. Is provided.

As described above, the coupling type threaded joint comprises the pin portion 11 having the tapered male screw 12 provided at the end of the steel pipe 10 and the tapered female screw 22 provided inside the coupling 20. The two steel pipes 10 and 10 'are connected by screwing with the box portion 21 having the same.

However, oil country tubular goods threaded joints used under the deteriorated environment in recent years, particularly for production casings (production casings) and tubing pipes, are constituted only by a screw element consisting of a male screw 12 and a female screw 22. As shown in FIGS. 1 (b) and 1 (c), the pin 11 and the box 21 have metal seals 13, 23 and torque shoulders 14, 24 at the same time. Many.

That is, a tapered metal seal portion 13 and a torque shoulder portion are provided at the tip of the pin portion 11 of the threaded joint portion.
14, a tapered metal seal portion 23 corresponding to the tapered metal seal portion 13 of the pin portion and a torque shoulder portion 24 corresponding to the torque shoulder portion 14 of the pin portion are provided inside the box portion 21. Is provided.

In this metal seal portion, the amount of interference in the radial direction, that is, the outer diameter of the metal seal portion 13 of the pin portion is larger than the inner diameter of the metal seal portion 23 of the box portion, and this difference is called the amount of interference. When the joint is screwed together, a surface pressure is generated on the contact surfaces of the two metal seal portions due to the amount of interference, and good airtightness is expected to be maintained by the surface pressure.

[0010] The torque shoulder portions 14 and 24 do not generate a high contact surface pressure on the metal seal portions 13 and 23 such that excessive plastic deformation occurs by abutting the pin portion 11 and the box portion 21 against each other. Thus, the fastening of the threaded joint is ensured. The angle of the torque shoulder portions 14, 24 with respect to the vertical plane is referred to as a shoulder angle, which has conventionally been about 0 to 3 degrees.

FIG. 2 is a schematic explanatory view showing a metal seal portion 13 and a torque shoulder portion 14 having improved airtightness and resistance to external force disclosed in Japanese Patent Application Laid-Open No. 60-260792. This is the metal seal part 13 and the torque shoulder part
14 is constituted by a curved surface having a curvature different from that of R ₁ , R ₂ , and R _{3 so} as to apply a triaxial compression force. Although the above publication does not refer to the shoulder angle,
It is about 25 to 30 degrees from the drawing.

[0012]

A threaded joint for an oil country tubular good having a metal seal portion shown in FIG. 1 has a metal seal portion 13 on the tip end side of a tapered male screw 12 of a pin portion 11 and usually has a metal seal portion. The thickness of 13 is remarkably thinner than the tube, and it has good radial tightness against internal pressure due to the amount of interference in the radial direction, and may maintain the internal pressure until the tube breaks . However, the oil well is composed of multiple steel pipes, and a liquid with a high specific gravity is maintained between the steel pipes to maintain the earth pressure (geological pressure, geological pressure) that works according to the depth.

Occasionally, however, this balance is lost and the external pressure can act directly on the steel pipe. In this case, the external pressure reaches the metal seal portion 13 through the gap of the engagement screw portion between the coupling and the pin portion, and the seal lip portion 17 at the tip of the pin portion (from the torque shoulder portion 14 in FIG. (The part near the part 16) is pressed and bent toward the center of the shaft. As a result, the two metal seal portions 23 and 13 are pushed open, and the airtightness is broken.

On the other hand, as disclosed in Japanese Patent Application Laid-Open No. 60-260792, a method in which a metal seal portion 13 and a torque shoulder portion 14 are configured to apply a triaxial compression force by three curves having different curvatures. However, there is a disadvantage that the structure is complicated and manufacturing is difficult, and the inclination of the torque shoulder portion 14, that is, the shoulder angle is large, so that the tip of the lip portion becomes thin and the rigidity is reduced.

Thus, an object of the present invention is to provide a coupling or integral type threaded joint having excellent airtightness even when a higher pressure acts on the outside than on the inside of the pipe.

[0016]

In order to solve the above-mentioned problems, the present inventor has conducted a detailed investigation on the cases where the sealability has been broken by external pressure. Something that is too big,
It has been found that the lip base thickness (S _{1 in} FIG. 1 (c)) of the metal seal portion is considerably thinner than the pipe wall thickness (WT).

Based on these findings, (1) the inclination of the torque shoulder portion, that is, the shoulder angle (θ) is 5 to 20 °
And (2) a joint in which the lip ratio defined by the following equation [1] between the base thickness (S ₁ ) of the lip seal portion of the metal seal portion and the pipe thickness (WT) is 0.52 or more. It was confirmed that the oil country tubular goods connected by the method can maintain the sealing property against the external pressure up to the compression deformation fracture (collapse) pressure of the API, and completed the present invention.

Here, the gist of the present invention is, for example, as shown in FIG.
As shown in (c), a pipe connection screw composed of a pin portion 11 and a box portion 21 and having metal seal portions 13 and 23 and torque shoulder portions 14 and 24 in the pin portion 11 and the box portion 21, respectively. A joint, the torque shoulder portion 14,
24 has a shoulder angle (θ) of 5 to 20 °, and the thickness (S ₁ ) at the base of the metal seal lip 17 of the pin portion and the pipe thickness
(WT) and a lip ratio defined by the following [1] is 52% or more. (S ₁ /DB)/(WT/OD)≧0.52 [1] where DB is the inner diameter at the root of the seal lip, and OD is the outer diameter of the tube.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The reason why the structure of the threaded joint according to the present invention is defined as described above will be described together with its operation.

In the present invention, 5 to 5
The reason for providing the inclination of 20 degrees, that is, the shoulder angle, is to prevent radial deformation when external pressure acts on the lip portion. If the shoulder angle is less than 5 °, a sufficient supporting force for preventing the deformation cannot be obtained. On the other hand, if the angle exceeds 20 °, the tip portion of the pin portion and the peripheral portion of the torque shoulder portion of the box portion become acute angles. Therefore, in the present invention, this shoulder angle is limited to between 5 and 20 degrees. Preferably, 10-
15 °.

Next, in the present invention, the base thickness S ₁ and the seal lip portion of the seal lip portion of the metal seal part of the pin portion the ratio of the root diameter DB, outside the pipe thickness of WT and tube body The ratio of the diameter OD should be 52% or more (relationship of equation [1]).
This is to reduce the deformation of the seal lip portion of the pin portion with respect to the minimum collapse pressure specified in I and to give the seal lip portion the rigidity necessary to maintain the sealing performance of the metal seal portion. With a lip thickness of 20 °, it is not always possible to maintain such excellent sealing properties by providing a predetermined external pressure resistance function. In other words, if the seal lip portion of the pin portion is deformed to some extent, the sealing mechanism of the metal seal portion is broken, and the external pressure seal resistance cannot be maintained.

The upper limit of the lip ratio is not particularly limited,
Preferably it is 55 to 65%. The thickness of the root of the seal lip 17 is the thickness of the starting portion of the incomplete thread 15 on the side of the metal seal 13 of the pin 11 shown in FIG. and a thickness of S _1.

Here, as a means for satisfying the above-mentioned equation [1], the following equation may be satisfied with respect to the diameter DB at the root of the seal lip portion 17 with respect to the tube outer diameter OD. Here, ID is the pipe inner diameter, and WT is the pipe wall thickness.

DB ≧ (ID + α) OD / (OD−0.52WT) (2) where α is a chamfer allowance of the inner diameter of the seal lip portion 17,
Although it should be changed slightly depending on the outer diameter, in general, α ≒
2.0 mm is usually fine. In some cases, α = 0 may be used.

Thus, the DB satisfying the above equation (2)
And place a screw between the diameter of the DB and the outside diameter of the tube.
FIG. 3 schematically illustrates a method of determining the thread shape in the pin portion in this manner. In the figure, once the DB is determined, the screw shape can be easily designed based on the required screw length.

Next, when the DB is determined in this manner, the range of S ₁ is obtained from the equation (1) based on the DB.
The thickness of the base of the lip seal portion 17 satisfying this, S ₁ , S ₁ ′,
S ₁ ". That is, as shown in FIG. 4, the root thickness S ₁ of the lip seal portion 17 is adjusted to the shape of the recess (chamfer) of the inner surface of the seal lip portion, and A: S ₁ or B: S ₁ ', or C: S ₁ "and the possible changes respectively, employing a S ₁ satisfying formula (1) from them.

Note that the bevel portion of the screw does not need to be determined because it is usually almost constant in shape. In addition, since the length of the seal lip portion is generally in a range of 10 to 15 mm (depending on the outer diameter), it is assumed that the length is not specified.

As described above, the shape of the screw is given by equation (2).
Once the DB is necessary thread length depends, rule by selecting the taper of the dimensions of the ridge and appropriately in accordance with FIG. 3, then S ₁ is determined in accordance with FIG. 4, as described above. Next, the effects of the present invention will be described more specifically based on examples.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In this embodiment, the threaded joint is shown in FIGS.
As shown in Table 1, a box part and a pin part were formed with the following tube and screw specifications to produce a coupling shape shown in Table 1. Note that the shoulder angle is provided symmetrically in the box portion and the pin portion.

Outer diameter of pipe body: 177.8 mm (7 ") Wall thickness of pipe body: 14.19 mm (0.559") Outer diameter of coupling: 195.98 to 201.68 mm Material of pipe and coupling: Yield strength 70.31 kgf / mm ² Low alloy steel Screw shape: Trapezoidal screw Thread pitch: 5.08mm (5 ridges / inch) Thread taper: 1/16 Thread height: 1.575 mm Surface treatment: Phosphate coating

[0031]

[Table 1]

As shown in FIG. 4, the shape of the seal lip portion of the test sample was obtained by cutting the inner diameter side of the seal lip portion, and the wall thickness (WT) after the cut and the thickness of the root of the metal seal lip portion. (S ₁ ) is determined by the above equation.
(1) was set to 50 to 60%, and the shoulder angle (θ), which is the inclination angle of the torque shoulder portion, was also variously changed.

FIG. 5 is a schematic explanatory view of a method of reducing the inner diameter of the pin portion in order to produce test samples having various “lip ratios (λ)” from the same material. The screw length,
The length of the lip, the dimensions of the metal seal part, etc. were kept constant.

In the figure, the description of each symbol and λ ₁ , S ₁ , WT ₁
Is as follows. A: pin lip length B: pin seal length C: Pin complete thread portion length D: Nejitepa (strain number) E: Pinriseru turning length H: thread height (Nejihaito) t ₁ ~t _4: Case 1-4 WT _{1 to} WT ₄ : Pipe wall thickness in cases 1 to 4 S ₁ : Lip base thickness in case 1 Lip rate λ ₁ = {S ₁ /[170.5+Bx (metal seal section wafer)] ]｝ / ｛WT ₁ /177.8｝ S ₁ = t ₁ +1/2 Bx (metal seal part wafer) + [At ₁ xtan (short angle: θ ₁ )] tan 6 ° WT ₁ = 1/2 [177.8- {170.5-2t ₁ -2 (Et ₁ tan θ ₁ ) tan6 °}] Since A, B, E and the taper of the metal seal portion are constant, the lip ratio λ ₁ is determined by the shoulder angle θ ₁ and the shoulder width t. Determined by ₁ . That is, if the shoulder angle is fixed, the target lip ratio λ ₁ can be set by determining the specific t ₁ .

A lubricating grease (containing molybdenum dioxide) was applied to the thread portion of the joint thus configured, and connected with a specified torque to obtain a test specimen. After sealing both ends of the test piece, the test piece was charged into a cylindrical pressure vessel, and an external pressure was applied to the test piece via a pressure medium (water). If the pressure is maintained for 30 minutes and there is no abnormality, a test is performed in which the pressure is further increased stepwise (3.43 MPa / 1 stage), and the pipe body is compressed and deformed (collapse)
Or until the sealability of the joint was broken. Table 2 shows the obtained results.

[0036]

[Table 2]

From these results, it can be seen that the threaded joints A to G according to the present invention maintain the sealing property up to the minimum collapse guarantee value of the pipe specified by the API, and leak at a value higher than the minimum collapse guarantee value. Alternatively, the tube collapsed due to compression deformation.

The threaded joints H and I of the comparative examples have lip thicknesses of 5.18 mm and 5.09 mm (the lip-to-tube (T / D) ratio is 50
%), The joint leaked at 54.3 and 57.1 MPa.

Since the thread joints J and L have a small shoulder angle of 3 °, leakage occurred from the joints at 75.7 and 78.5 MPa. Since the threaded joints K and M had a large torque shoulder angle of 25 °, leakage occurred from the joints at 69.3 and 80.9 MPa.

In the case of this example, the minimum collapse guarantee pressure of the tube of each sample is the value in the column of [API minimum collapse guarantee value] in Table 2 when calculated by the calculation formula specified by the API.

In the above-described embodiment, the case of the coupling method has been described. However, the same effect can be obtained in the case of the integral method (in the case where both a pin screw and a box screw are machined directly on a pipe).

[0042]

The threaded joint for oil country tubular goods according to the present invention has an excellent sealing performance against external pressure because the thickness of the lip portion is large and the inclination angle of the torque shoulder is specified, and the minimum collapse of the pipe defined by the API is achieved. (Crush) It can withstand external pressure up to the guaranteed pressure.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a kind of a special threaded joint for oil country tubular goods of a coupling type, and FIG. 1 (a) is a side view showing the whole;
FIG. 1B is an enlarged sectional view of the box portion, and FIG. 1C is an enlarged sectional view of the pin portion.

FIG. 2 is a partial cross-sectional view of a lip portion of a joint excellent in airtightness and resistance to external force as a prior art.

FIG. 3 is a schematic explanatory view of a method for determining a thread shape of a pin portion.

4 is a schematic explanatory view showing the relationship between the root thickness S ₁ and the pin inner surface recess shape of the sealing lip.

FIG. 5 is a schematic explanatory view of a method of reducing the inner diameter of a pin portion so as to set a lip ratio to a target value for a sample used in a current test.

[Explanation of symbols]

10: Steel pipe 11: Pin part
12: Male thread 20: Coupling 21: Box
22: Female thread 13, 23: Metal seal part 14, 24: Torque shoulder part 15: Incomplete thread part 16: Bevel part
17: seal lip portion WT: pipe thickness of _{S 1, S 1 ', S} 1 ": lip root thickness
θ: Shoulder angle DB: Lip base diameter

Claims (1)

(57) [Claims] 1. It comprises a pin part and a box part,
A pipe connection threaded joint having a metal seal portion and a torque shoulder portion at each of the pin portion and the box portion, wherein a shoulder angle of the torque shoulder portion is 5 to 20 °, and the metal portion of the pin portion is A threaded joint for pipe connection, characterized in that a lip ratio of a seal portion is 52% or more.