JPH0141875B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The disclosed technology belongs to the field of sealing technology between a coupling in a pipe joint of a transportation pipe and a pipe end connected thereto.

<Summary of the gist> The present invention provides a unit pipe joint structure for fluid transport piping such as oil country tubular goods, in which a male thread is carved on the outside of the pipe end, while a corresponding thread is carved on the inside of the coupling side. A female thread is carved into the male thread, and the end of the tube end seal in the center of the coupling is formed into a curved surface, protruding inward in the radial direction, and is made into a metal touch against the tube end. This invention relates to a pipe joint structure in which the pipe ends are tightly connected and sealed, and in particular, the pipe end seal part of the coupling is screwed onto the outside of the convex wall surface of the pipe at the pipe end connected to the coupling. It is a concave curved surface with the same cross-sectional curvature as the curved surface of a circle with a set radius having the center, and is formed so that both can slide in a metal-touch state, and is connected to the inner surface of the coupling at the base of the tube end seal part. This invention relates to a pipe joint structure in which an allowance gap is provided between the pipe end and the pipe end to allow sliding displacement of both curved surfaces.

<Prior art> As is well known, in oil country tubular goods, plant piping, etc.
Pipe bodies are made into unit pipes of a predetermined length due to manufacturing and transportation constraints, and therefore pipe ends are required to connect a predetermined number of unit pipes to each other in order to perform piping on site. .

Various types of joints such as welded joints, flange joints, and coupling joints are used for the pipe ends, but for example, they are used to connect field piping such as oil country tubular goods,
A so-called coupling joint is widely used as a joint that undergoes repeated disassociation and is suitable for severe conditions such as load application and corrosive fluid transport.

This kind of coupling joint has changed from its initial form, which had a coupling function by screwing and a sealing function, to a coupling coupling 1 as shown in Fig. 1 in order to reduce the number of parts and increase the speed of coupling and disassembly. Improvements have been developed and are now widely used.

That is, the double pipe 2 as a corrosion-resistant oil country pipe according to an exemplary embodiment
A male thread 4 is carved into a tapered shape on the outside of the tube end of the outer tube 3 made of carbon steel, and the tip with the inner tube 5 made of stainless steel is formed into a pointed protrusion 6. Female thread 8 screwed into male thread 4 inside coupling ring 7
A concave portion 10 into which the pointed protrusion 6 is metal-touched is formed in a reverse tapered shape at both ends of a tube end seal portion 9 made of stainless steel that protrudes inward from approximately the center.

<Problems to be Solved by the Invention> However, in this type of coupling joint structure, repeated connection and disconnection makes the screw threading loose, and the sharp protrusion 6 of the tube end and the recess 1 of the tube end seal portion 9.
0 becomes loose, or conversely, if the tightening is made stronger, the tube end seal can be maintained, but there is a drawback that the threaded connection becomes loose.

In addition, in corrosive fluid transport piping, there is a risk that so-called stress corrosion cracking may occur in the inner pipe 5. To deal with this, there is a technique to apply compressive residual stress to the inner pipe 5, but In this case, compressive residual stress disappears, which is a problem in that stress corrosion cracking occurs at the tube end seal.

Moreover, the above-mentioned problem of loosening can be solved by the single pipe 2' shown in Fig. 2.
The same thing happened in .

To deal with this, as shown in FIG.
There is also an embodiment in which a gap 11 is formed with the inner surface of the clasp so that the pointed protrusion 6 escapes upward as shown by the dotted line when tightening. There was a problem that the sealing properties deteriorated due to contact.

<Objective of the Invention> The object of the present invention is to solve the problems of the pipe joints based on the above-mentioned prior art, and to solve the problems of the pipe joints based on the above-mentioned prior art. The metal touch seal is always maintained on the curved surface of the circular arc, and an escape gap is formed between the inner surface of the coupling and the outer surface of the tube end, so that the tube and the coupling can be tightly connected and have good sealing performance. It is an object of the present invention to provide an excellent pipe joint structure that is useful in the field of piping technology used in various industries.

<Means/actions for solving the problem> In order to solve the above-mentioned object, the structure of the present invention, which is summarized in the above-mentioned claims, has the following features: The two are tightly connected by screw tightening, and in this process, the pipe end is brought into a metal touch state through the close contact between the curved surfaces of both sides of a circle with a set radius centered on the outside of the pipe wall at the pipe end sealing part of the coupling ring. If the connection is weak, the tube end can maintain a metal touch state through sliding contact between the curved surfaces of the tube end sealing portion of the coupling ring by increasing the tightness. , maintaining the state of close contact between the curved surfaces by sliding displacement,
By moving the pipe end into the clearance gap on the side, we are able to ensure strong tightening and sealing performance, and in addition, we have developed a technical measure that prevents stress corrosion cracking by generating compressive stress. It's a mess.

<Example> Next, an example of the present invention will be described below based on FIGS. 4 and 5.

Note that the same reference numerals are used to describe the same parts as in FIGS. 1, 2, and 3.

2″ is a unit pipe of a predetermined length for oil country tubing;
The outer tube 3 is made of carbon steel and the inner tube 5 is made of stainless steel.
The inner tube 5, which has a flange-shaped tube end, is given compressive residual stress in the axial direction to prevent stress corrosion cracking. Further, the outer tube 3 has a tapered male thread 4 carved on its outer surface at the tube end, and the outer end has an outer circumferential surface 12 having a set length parallel to the axial direction.

As shown in detail in FIG. 5, the tube end 6'' of the inner tube 5 has an outward flange-like cross section with a curved surface A for metal touch, and a circle with a set radius having its center outside the wall surface of the unit tube 2''. Curved surface A expanded outward of
is formed in a convex shape.

On the other hand, 7 is a coupling ring made of carbon steel, which is formed so that it can be screwed into the internally tapered female thread 8 or the above-mentioned male thread 4 from both sides. Inner surface 1 parallel to surface 12
3 is formed so as to form a clearance gap 11' of a set size between the outer circumferential surface 12 of the tube end of the outer tube 3 and the outer circumferential surface 12 of the tube end in the screwed state with the unit tube 2'', as shown in FIG. It is being done.

In addition, a tube end seal 9' made of stainless steel is fixed in the center of the inner surface 13 of the coupling ring 7 by electron beam welding 14, and its inner surface 15 is flush with the inner surface 16 of the inner tube 5. A curved surface A that matches the curved surface A of the tube end 6'' of the inner tube 5 is formed in a concave shape by the same circle with the same center on the lateral surface portion 10'' of the sealing surface, and is always connected to the tube end 6'', i.e. , so that the metal touch state between the tip of the inner tube 5 and the tube end seal portion 9' of the coupling 7 is maintained regardless of whether the unit tube 2'' is in a straight-extending condition or the tube end 6'' is in an expanded condition. has been done.

In the above configuration, when the unit tube 2'' is screwed into the coupling 7 as shown in FIG. Surfaces A and A are in close contact with each other in a metal-touch state, and are sealed as shown by the solid line in FIG.

In this case, due to the design, an axial pressing force is applied to the inner tube 5 due to the surface contact between the curved surfaces A and A, and the stress at the end of the tube is increased in response to the compressive residual stress in the general portion. It is possible to prevent corrosion cracking.

Therefore, if the pipe is used for transporting a corrosive fluid in this state, the pipe end seal portion 9' of the inner pipe 5 will be damaged.
Of course, the corrosive fluid is sufficiently prevented from penetrating into the curved surfaces A and A, and corrosion due to gas generation is also prevented.

Therefore, if the coupling ring 7 has become loose due to repeated use, or if stronger fastening is required for transportation under increased pressure, tightening the coupling ring 7 will increase the axial pressing force. Therefore, the curved surfaces A, A of the tube end 6'' and the tube end seal portion 9' are the same circle, and since their centers are outside the wall surface of the unit tube 2'', the curved surfaces A, A are Due to the sliding action of , an expansion force is applied to the tube end 6'' as shown by the arrow Q in the figure, and the tube end 6'' is bent from the solid line state to the dotted line state with respect to the clearance gap 11', and is expanded. .

Even in this state and during this bending displacement process, the metal touch is always maintained through the mutual sliding contact between the two curved surfaces A, A, and therefore the sealing performance is always maintained and the intrusion of corrosive fluid is prevented. In addition to being prevented in the same manner as described above, depending on the design radius of the curved surfaces A and A, the inner tube 5 receives compressive stress due to the constant application of axial pressing force at the tube end.
It can resist stress corrosion cracking.

It goes without saying that the embodiments of this invention are not limited to the above-mentioned embodiments, and the circle forming the curved surface of the tube end sealing surface may be composed of a curved surface of a composite circle with a plurality of radii, or The unit pipe to be used may be a single pipe in addition to a double pipe, and various embodiments can be adopted, such as being applicable not only to oil country tubular goods but also to oil pipes, plant piping, etc.

<Effects of the Invention> As described above, according to the present invention, in a pipe joint structure in which unit pipes such as oil country tubular goods are screwed together via a coupling, both the pipe end seal portion and the pipe end of the coupling can be slidably contacted with each other. It has a metal touch abutment surface of a curved surface consisting of a circle having its center outside the wall surface of the unit tube, and has an outer surface of the tube end that is in surface contact with the metal touch on the inner surface of the coupling at the base of the tube end seal. By forming a clearance gap between the coupling and the coupling, basically, when the coupling and the unit pipe are screwed together, the pipe end seal between the pipe end and the coupling is formed. The curved surfaces of the parts are brought into contact with each other in a metal touch state and tightened, ensuring a secure seal.
Therefore, not only is there an effect that the fluid to be transported does not infiltrate and corrosion caused by this is achieved, but also if the fastening is too loose, retightening can improve the sealing curved surface of the pipe end. The pipe slides in a metal-touch manner on the curved surface of the tube end sealing part of the coupling, expanding and displacing the pipe, but a tight metal-touch is guaranteed during this time and also in the posture after displacement.
In addition, the excellent effect that the displacement is absorbed by the above-mentioned relief gap and that no unreasonable stress occurs is achieved.

In addition, in the case of corrosion-resistant double pipes, since an axial pressing force is applied to the ends of the inner pipes, compressive stress acts, which has the excellent effect of preventing stress corrosion cracking.

[Brief explanation of drawings]

FIG. 1 is a schematic partial sectional view of a pipe joint based on the prior art, FIGS. 2 and 3 are enlarged sectional views of a tube end seal based on the prior art, and FIGS. 4 and 5 show an embodiment of the present invention. 4 is a schematic partial sectional view of the entire structure, and FIG. 5 is a partially enlarged sectional view thereof. 4...male thread, 6''...tube end, 7...coupling, 8...female thread, 9'...tube end seal part,
A... Curved surface, 11'... Relief gap, 13...
Inside.

Claims (1)

[Claims] 1 A male thread is carved on the outside of the tube end, and a female thread that engages with the male screw is carved on the inside of the coupling, so that the tube end seal part inside the center of the coupling has a concave curved surface and is curved on the inside. protrudes in the radial direction,
In a pipe joint structure in which a curved surface that abuts the curved surface is made into a metal touch shape with respect to the pipe end formed at the tip, the curved surface of the pipe end sealing portion of the coupling ring and the curved surface of the pipe end are both It is formed into a curved surface of a circle with a set radius centered on the outside of the pipe wall that is in close contact with each other in the connected state, so that the metal can be touched freely, and the pipe end has no clearance against the inner surface of the coupling at the base of the pipe end seal part. A pipe joint structure characterized in that the pipe joint is fastened with a gap formed therein.