JPS60241596A - Pipe joint for oil well pipe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pipe joint for oil country tubular goods that are vertically inserted deep underground in order to extract natural gas and crude oil produced from underground. This invention relates to pipe joints with excellent tensile strength.

The depth of wells that produce crude oil is several thousand meters, and in recent years the depth has been increasing further to reach 10,000 meters. A huge number of oil country tubular goods are inserted vertically into such wells, and they are all connected in series with pipe joints. Various severe forces act on pipe joints. Firstly, axial tensile force due to the accumulation of the weight of the connected pipes and pipe joint bodies, secondly compressive force on the outer circumferential surface due to earth pressure, etc. Thirdly, internal fluid This includes the pressing force on the inner circumferential surface due to the Needless to say, these forces become even more severe as the well deepens. The two most important requirements for pipe fittings subjected to such severe conditions are to withstand strong tensile loads and to maintain reliable airtight sealing performance. In order to meet this demand, many proposals regarding pipe joints have been made in the past.

[Prior Art] Among the conventional pipe joints, the most basic one is as shown in FIG.

The pipe joint of the liner OCTG shown in Fig. 3 is connected to the OCTG main body 3.
It is composed of a female joint part 1 formed at the left end of the pipe, and a male joint part 2 formed on the right side of the oil country tubular body 3' so as to be screwed into the female joint part 1.

On the inner periphery of the female joint part 1, a buttress-type female thread 1d whose inner diameter decreases with an appropriate taper as it goes deeper in the axial direction from near the left end is carved, and from the part where the female thread 1d is cut off, the inner diameter is reduced. , there is a tapered unthreaded portion following the female thread 1d, and the inner circumferential surface of this unthreaded portion serves as an inner circumferential sealing surface 1C.

The innermost end of the inner circumferential sealing surface 1G is terminated by a shoulder portion 1b that projects in the axial direction. Further, a non-threaded mouth portion 1a is formed at the tip of the female joint portion 1 beyond the portion into which the female thread 1d is cut. The inner peripheral surface of the mouth portion 1a is a tapered inner peripheral sealing surface 1a', and the tip surface of the mouth portion 1a is a tip sealing surface 1a'.

On the other hand, on the outer periphery of the male joint part 2, a male thread 2d is carved to correspond to the female thread 1d and to obtain a threaded relationship, so that the outer diameter increases as it progresses from the right end toward the base in the axial direction. , there is a tapered unthreaded part following the male thread 1d near the base of the part where the male thread 1d is cut off,
The outer circumferential surface of this non-threaded portion serves as an outer circumferential sealing surface 2C corresponding to the inner circumferential sealing surface 1a'. Outer seal surface 2
The base of C is terminated by a shoulder 2b that projects in the radial direction, and the side surface of the shoulder 2b forms an abutment sealing surface 2b' corresponding to the tip sealing surface 1a'. Further, a non-threaded mouth portion 2a is formed at the tip of the male joint portion 2 beyond the portion into which the male thread 2d is cut. The tapered outer peripheral surface of the mouth portion 2a is formed with an outer peripheral sealing surface 2a' corresponding to the inner peripheral surface 1C. When the female joint part 1 and the male joint part 2 are tightly screwed together, the pairing seal surfaces come into contact with each other, creating an airtight seal state in which metal surfaces become metal surfaces. is obtained, and the inner sealing surface 1C of the female joint part 1 closer to the inside and the inner sealing surface 2a' of the male joint part 2 form an inner peripheral seal part 4, and the inner peripheral sealing surface 1C of the female joint part 1 closer to the mouth part An outer seal part 5 is formed by the inner seal surface 1a' of the male joint part 2 and the outer seal surface 2C of the male joint part 2, and further, the tip seal surface 1a' of the female joint part 1 and the abutting seal surface 2b' of the male joint part 2. As a result, a shoulder seal portion 6 is formed.

Since the pipe joint for oil country tubular goods is as described above, the tensile strength and sealing performance, which are the most important requirements for a pipe joint, are ultimately ensured by the threaded connection between the female joint part 1 and the male joint part 2. If a failure occurs in this threaded connection, both of the above-mentioned most important matters cannot be fulfilled. However, when a conventional pipe joint is vertically inserted deep underground, the threaded portion is deformed due to the huge tensile force acting on it as described above, and the male joint part 2 eventually separates from the female joint part 1. There was even fear.

Such a failure will be explained based on the force relationship acting on a pair of threads of the male thread 2d' and the female thread 1d' shown in FIG. That is, when a tensile force P in the direction of the outlined arrow is applied to the male joint part 2, at a point O on the thread slope where the female thread 1d' of the female joint part 1 and the male thread 2d' of the male joint part 2 contact, Regarding the female thread 1d', f in the vertical direction of the thread slope
The force of is applied. This force f acts as two components: a force f1 in the axial direction and a force f2 in the direction perpendicular to the axis. The component force f2 acts to expand the diameter of the female joint portion 2. Since this component force f2 acts on all the female screw threads 1d' of the female joint part 1, the diameter expansion strain generated by the component force f2 is accumulated near the tip, and therefore the female The diameter of the joint portion 1 near the mouth portion 1a is greatly expanded. The force f' acting as a reaction force on the point O of the thread slope is the same for the male thread 2d', and the action of the force on them is shown by a broken line. A component force ft2 in the axial direction acts on the male joint portion 2, causing a diameter reduction phenomenon. Male joint part 2
The synergistic effect of the diameter reduction phenomenon of the female joint part 1 and the diameter expansion phenomenon of the female joint part 1 causes the threaded relationship to become loose, reducing not only the strength of the thread itself but also the tensile strength of the pipe joint as a whole, and at the same time reducing the sealing performance. It also makes things worse. As a result, for conventional pipe fittings, the specified tensile strength of the pipe fitting, which is naturally determined by the fitting efficiency (the joint efficiency refers to the value obtained by dividing the dangerous cross-sectional area of the fitting by the pipe body cross-sectional area), is lower than the specified tensile strength of the pipe fitting. Even when a small tensile load is applied, the male joint part 2 may break away from the female joint part 1 and cause the OCTG to fall deep into the oil well, making it extremely difficult to connect the OCTG, so the oil well must be abandoned. It may lead to the worst situation.

[Problems to be Solved by the Present Invention] In view of the above-mentioned drawbacks of the pipe joint, the present invention provides excellent tensile strength and sealing performance without loosening the threaded engagement between the male and female joints. The objective is to provide pipe fittings that can be secured. The inventor of the present invention repeated many experiments to perfect such a pipe joint, and as a result, established a technique that can improve the tensile strength. In other words, if the thread height, fully engaged thread length, and thread O-flank angle are each within the specified ranges, even if a strong tensile force is applied to the oil country tubular body, the threads at the female joint will The component force acting on the inclined surface in the direction orthogonal to the axis effectively acts in the direction of reducing the diameter of the female joint, contrary to the conventional method, tightening the threaded relationship between the female and male joints. , it was discovered that improvement in tensile strength was ensured, and the present invention was completed based on this knowledge.

[Means for Solving the Problems] The present invention provides a threaded joint for oil country tubular goods with a thread height of 1.0 to 2.0 cm, a fully engaged thread length of three times or more of the wall thickness of the pipe body, and a screw thread height of 1.0 to 2.0 cm. By setting the load flank angle to -8 to -10 degrees, the threaded relationship between the male and female joints is tightened, resulting in a pipe joint with excellent tensile strength and sealing performance. .

[Example] Hereinafter, a pipe joint for oil country tubular goods (hereinafter referred to as a main pipe joint) according to the present invention will be described based on an example shown in FIGS. 1 and 2. FIG. 1 is a schematic sectional view showing the upper half of the main pipe joint. Female joint portion 7 formed at the left end of the oil country tubular body 9
A male joint portion 8 formed on the right side of the oil country tubular body 9' is screwed into the male joint portion 8.

When the female joint part 7 and the male joint part 8 are tightly screwed together, the inner seal part 10 is formed by the inner seal surface 7C and the inner seal surface 8a'.
The outer seal portion 11 is formed by the inner seal surface 18' and the outer seal portion 8C, and the shoulder seal portion 12 is further formed by the tip seal surface 7a' and the abutment seal surface 8b'. In these respects, there is no essential difference from conventional pipe joints. The main pipe joint differs from the conventional one in that the thread height of the female thread 1d and male thread 8d is set to 1.0 to 2.0 cm, and the thread length L at which the female thread 7d and male thread 8d are completely engaged is set to the oil country tubular body. 9 (or 9'), and the load flank angle θ of the male thread 7d is limited to -8 to -10 degrees.

[Function] FIG. 2 is an enlarged schematic diagram showing a state in which a pair of threads of the male thread 8d and the female thread 7d are engaged. The contact surface of the male thread 8d' has an inclination angle of -8 to -10 degrees (in the figure, an angle that advances in the clockwise rotation direction is a positive angle) with respect to the perpendicular V made on the base 8e of the male thread 8d'. It is formed with θ. When a strong tensile force P in the direction of the white arrow is applied to the male joint part 8, the male thread 8d' and the female thread 7
At point 0 on the slope where d' is in contact, a force F acts in the vertical direction of this slope. In this case, the force F is the internal thread 7d
', the component force Fl along the axis C of the oil country tubular body 9' (see Fig. 1) and the component force F2 in the direction orthogonal to the axis are 2.
Acts as component force. The component force F2 acts to reduce the diameter of the female joint portion 7. This diameter reduction effect is F2−F x
Since it is Sin θ, it increases as the inclination angle θ becomes larger. However, increasing the inclination angle θ makes the internal angle of intersection between the inclined surface of the male thread 8d' and the base 8e acute, and the reaction force F' acting in response to the force F causes the male thread to The internal stress generated at 8d' is the root part 8d'
This results in a stress concentration phenomenon where the external thread 8d' is concentrated, and the strength of the external thread 8d' is extremely reduced. In particular, when the male thread 8d' is made of a brittle material with a small elongation at break, there is a risk that the root portion 8d' will suffer brittle fracture even under a low tensile load P. Conversely, if the inclination angle θ is made small, the diameter reduction effect cannot be sufficiently exerted. Therefore, when the load flank angle θ of the screw is set to -8 to -10 degrees, a sufficient diameter reduction effect can be exerted without reducing the strength of the root portion 8d' of the male thread 8d'. .

A reaction force F' acting on the slope of the male thread 8d' in response to the force F generates bending stress and shear stress at the root portion 8d'. This bending stress has the greatest effect on the breakage of the male thread 8d', and its thickness is proportional to the thread height H. As for the thread height H, the male thread height is 8.
In order to ensure the screw engagement between d' and the female thread 7d', it is necessary to make it large, but in order to increase the strength and joint efficiency of the male thread 8d/, it is necessary to make it small.

However, the fully engaged screw length L, which will be described later, is 3 times the wall thickness of the tube body.
If the thread height H is set to 1.0 to 2.01 under conditions where the height is more than twice as high, it is necessary to adjust such contradictory matters and ensure screw engagement while maintaining the strength of the male thread 8d'. This makes it possible to do this.

As shown in FIG. 1, the magnitude of the force F acting on the slope where the male thread 8d' and the female thread 7d' contact is determined by the length L at which the male thread 8d and the female thread 7d completely engage. . In other words, increasing the length L of the fully engaged screw means increasing the total area of the slope where the male thread 8d and the female screw 7d contact, so the tensile force P can be obtained by dividing the total area of this slope. This means that the value of the force F can be reduced. Reducing this force F not only reduces the internal stress generated in the male thread 8d', but also reduces the component force F1 (Ft') along the axis C shown in FIG. 2. Incidentally, the component force F1 acts to stretch the inner surface layer of the female joint portion 7, and expands the diameter of the female joint portion 1.

Furthermore, the component force Fl′ acts to stretch the outer surface layer of the male joint portion 8, thereby reducing the diameter of the female joint portion 8. Therefore, by increasing the length L of the fully engaged screw to reduce the component force Fl (Fl'), the amount of diameter expansion of the female joint portion 1 and the amount of diameter reduction of the female joint portion 8 are reduced. In particular, under the conditions that the load flank angle θ of the screw is -8 to -10 degrees and the screw height H is 1.0 to 2.0+v as described above, the length of the fully engaged screw is equal to the wall thickness T of the tube body. If it is 3 times or more, the amount of diameter expansion of the female joint portion 7 and the amount of diameter reduction of the female joint portion 8 caused by the stretching action are suppressed, and the male thread 8d' becomes the female thread 7d/
You can prevent them from escaping. In addition, it is generally preferable that the fully engaged thread length L be 5 times or less than the wall thickness T of the tube body, since if it is made longer, it will be difficult to cut the thread.

[Test Example] The present inventor investigated how the thread height, fully engaged thread length, and load flank angle of the thread affect tensile strength and the like.

Table 1 shows the experimental conditions.

(The following is a blank space) As is clear from Table 1, it was confirmed that in the pipe joint for oil country tubular goods of the present invention, the female joint part did not separate from the male joint part before breaking inside the pipe joint part.

[Effects of the Invention] The pipe joint for oil country tubular goods according to the present invention can be a pipe joint for oil country tubular goods in which the female joint part does not separate from the male joint part.
At a tensile load lower than a predetermined tensile strength naturally determined by joint efficiency, the male joint part does not separate from the female joint part, and sealing performance is ensured. Therefore, the pipe joint for oil country tubular goods according to the present invention has an excellent effect of being able to avoid an unexpected accident in which the male joint part separates from the female joint part.

[Brief explanation of drawings]

1 and 2 are diagrams showing an embodiment of a pipe joint for oil country tubular goods according to the present invention, in which FIG. 1 is a sectional view showing the upper half of the pipe joint portion, and FIG. 2 is a male thread and a female thread. FIG. 3 and FIG. 4 are diagrams showing a conventional oil country pipe joint, and FIG. 3 is a cross-sectional view showing the upper half of the pipe joint. , FIG. 4 is an enlarged schematic diagram showing a state in which the male thread and the female thread are engaged. 1...Female joint part 1d...Female thread part 8...Male joint part 8d...Male thread θ...Thread load flank angle] (...Thread height shi...Full meshing thread Length patent applicant Sumitomo Metal Industries Co., Ltd. Representative Patent attorney 1) Toshihiko

Claims (1)

[Claims] 1. For threaded joints for oil country tubular goods, the thread height should be set to 1.
0 to 2.0 ms, the length of the fully engaged screw is at least 3 times the wall thickness of the tube body, and the load flank angle of the screw is -8 to -10.
A pipe joint for oil country tubular goods characterized by its hardness.