JPH0117032B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Application> The disclosed technology belongs to the technical field of couplings between unit double pipes of corrosion-resistant double pipes such as oil country tubular goods.

<Summary of the gist> Accordingly, the present invention provides a corrosive fluid transport pipe such as an oil country tubular goods, which is made up of a connected body of unit pipes consisting of a corrosion-resistant inner pipe and a pressure-resistant outer pipe to which the corrosion-resistant inner pipe is tightly connected. This invention relates to a structure in which a pipe joint between unit pipes used in this process is screwed together using a box type screw and a pin type screw. A one-piece stainless steel corrosion-resistant material of the same property is formed with a metal touch surface perpendicular to the axial direction, including its thick part, and is integrally fixed in a ring shape from the inner tube to the outer tube by welding to improve corrosion resistance. This invention relates to a double pipe joint structure as described above.

<Prior Art> As is well known, so-called corrosion-resistant double pipes, in which a corrosion-resistant inner pipe is tightly connected to a pressure-resistant and heat-resistant outer pipe, are used for corrosive fluid transport pipes such as oil country tubular goods. The length of unit pipes is limited due to shipping conditions, etc., and therefore pipes are generally joined and connected to a desired set length on site.

There are various types of connection methods at the site, but for example, the one shown in FIG.
Coupling joints are widely used.

That is, as shown in FIG. 1, a pair of unit tubes 3, 3 each having an inner tube 1 made of, for example, a stainless steel liner and an outer tube 2 made of carbon steel with a predetermined lining, are provided with a tapered male thread 4 at opposite ends. , 4 are engraved,
Put on the coupling ring 5, and the female screws 6 on the inside of both ends,
6 is tightly screwed to the male screws 4, 4.

As disclosed in the applicant's prior invention, an end tube 7 made of stainless steel or the like is integrated with the lining at the center of the inner surface of the coupling ring 5 made of carbon steel or the like.
The inner corrosion-resistant liner of the connecting unit pipes 3, 3 is flush with the inner pipes 1, 1.

<Problems to be Solved by the Invention> However, in the conventional type of coupling joint, apart from carving the male thread 4 of each unit pipe 3, manufacturing of the coupling 5 is extremely difficult from the viewpoint of accuracy, etc. In addition, there is a disadvantage that the cost is high, and there are two screw connection parts in the longitudinal direction, so the screw management to ensure sealing performance is extremely complicated. There is no guarantee that compressive stress will be applied to the joint joint to ensure that the tensile load due to the connection length is eliminated.
There was a problem with the possibility of stress corrosion cracking.

To deal with this, for example, JP-A-56-90578
Although technologies such as the invention disclosed in the publication No. 1 have been developed, this type of known technology is a so-called coupling type joint,
When such a technique is used for on-site coupling of oil country tubular goods, etc., tensile stress is generally generated at the joint between the two ends of the coupling, and there is a risk that stress corrosion cracking may occur as described above. As shown in the figure, since a so-called underhang restraint is formed at the joint between the coupling part and the pipe end, an outward expansion force is generated at the pipe end. is applied, therefore,
As mentioned above, not only is the tensile stress applied in the longitudinal direction of the tube due to the coupling, but also a tube expansion force is applied at the tube end, and as a result, tensile stress is applied in all directions, resulting in stress corrosion during operation. Cracks are more likely to occur, and in particular stress corrosion cracks occur in joints where corrosion is most likely to occur.

Therefore, there are so-called pin box type joints as threaded joints between unit pipes, for example, there is an invention disclosed in Japanese Patent Application Laid-open No. 56-109975. It is a joint, and cannot be used as an oil supply pipe for corrosive regulating fluid such as oil country tubular goods.In particular, there are problems with leakage and corrosion resistance in the joint part.

On the other hand, there is also a pin box type threaded joint, such as the invention disclosed in JP-A-55-47082 (particularly shown in Fig. 5), but the opposing unit pipes of the joint are single-layer pipes as described above. In addition, the sealing material interposed between the facing surfaces of the opposing unit pipes is not a corrosion-resistant double pipe, and is a member with low strength that easily softens. Although the durability is guaranteed, compressive stress is not applied, so there is a problem that it is difficult to sufficiently deal with stress corrosion cracking due to corrosive fluid during operation, and furthermore, maintenance, inspection, etc. are required repeatedly. In some cases, the plastically deformed portion of the easily softened sealing material loosened, resulting in a negative point that the reproducibility of a reliable seal was not guaranteed.

The purpose of this invention is to solve the technical problems of the coupling joints in the conventional corrosion-resistant double pipe connection based on the above-mentioned prior art, and to omit the couplings by using a pin box type joint.
Corrosion-resistant material is fixedly interposed on the abutting surfaces of the box screw side and pin screw side to improve sealing performance and ensure corrosion resistance. Furthermore, compressive stress is applied in the axial direction to the joint, and tensile stress is applied in the radial direction. It is an object of the present invention to provide an excellent double-pipe joint structure that is free from stress corrosion cracking and is beneficial to piping technology application fields in various industries.

<Means/effects for solving the problems> In order to solve the problems mentioned above, the structure of the present invention, which is based on the scope of the above-mentioned claims, is as follows:
Insert the male thread of the pin of the other unit pipe into the male and female female threads of one box of the unit pipe in which the corrosion-resistant inner pipe is joined to the pressure-resistant outer pipe, and screw the latter male thread into the former's female thread. and tighten.
An integral corrosion-resistant stainless steel material having the same properties as the inner pipe is interposed in at least one of the two pipes, and is formed so as to be perpendicular to the axial direction, including its thickness, to form a metal touch surface. By being provided at the butt part of the box screw and pin screw, when the pin box is screwed together, both are tightened with metal touch, ensuring a seal due to one screw connection, and axial compressive stress is applied to the inner tubes of both tubes. In addition, technical measures have been taken to prevent radial tension from acting on the metal touch surface and reliably prevent stress corrosion cracking from occurring during operation.

<Example> Next, an example of the present invention will be described below based on the drawings from FIG. 2 onwards. Furthermore, the first
Components having the same features as those in the drawings will be described using the same reference numerals.

In the embodiment shown in FIGS. 2 to 5, an outer tube made of carbon steel is formed by tightly joining an inner tube 1 made of stainless steel by a predetermined technical means such as the so-called heat expansion method disclosed in the applicant's earlier application. One of the unit tubes 3 of the double tube type having a tube 2 is a blank tube in which a box 8 is formed on the outer tube 2 at the end.On the other hand, as shown in FIG. Boring machining is performed to form a stepped portion 9, and a corrosion-resistant material 10 is formed on the stepped portion 9 by overlaying a high-hardness stainless steel made of the same material continuously and integrally with the inner tube 1.

Next, as shown in FIG. 4, a tapered female thread 11 is carved on the inner surface of the box 8 by an appropriate screw processing means, and the corrosion-resistant material 10 has a thickness perpendicular to the axial direction including the thick part. Metal touch surface 12
is formed sufficiently over the stepped portion 9 from the inner tube 1 to the outer tube 2.

On the other hand, the outer tube 2 which is also tightened and joined to the inner tube 1
As shown in FIG. 5, the other unit tube 3' having
A pin 15 with a tapered male thread 14 is formed on the outer surface, and a step surface 16 serving as a stopper for one box 8 is connected to one unit pipe 3.
The pin box joint is designed so that the abutting surfaces 12 and 13 come into contact with the end surfaces of the pin box after the metal touches.

In the above configuration, when the pin 15 of the other unit pipe 3' is exposed to the box 8 of one unit pipe 3, and the male thread 14 is rotatably screwed into the female thread 11 and tightened, the pin 15 will be tightened with a predetermined stroke. The tip abutting surface 13 is brought into close contact with the metal touch surface 12 of the abutting surface of the corrosion resistant material 10 in a metal touch state, and at this time, since the corrosion resistant material 10 is a highly hard corrosion resistant material that is the same material as the inner tube 1, the screw In the tightened state, the stepped surface 16 as a stopper of the pin 15 faces the end surface of the box 8 of one of the unit tubes 3 in a state where the threaded portion, which does not undergo plastic deformation and is subjected to large compressive stress in the axial and radial directions during the fastening process, is tightened. It hits and comes into close contact.

Therefore, both unit pipes 3, 3' have abutting surface 1
2, 13, and 16 are metal-touchly pressed to form a complete seal, and a strong compressive stress is applied to the inner tubes 1, 1 in the axial direction, particularly in the vicinity of the abutting surfaces 12, 13.

As shown in the figure, a highly hard corrosion-resistant material 10 is interposed on both sides thereof in a direction perpendicular to the inner tube 1, and furthermore, from the inner tube 1 to the outer tube 2 there is a step 9 in depth. Since the corrosion-resistant material 10 is provided with a sufficient size, metal touches appear in the direction perpendicular to the inner tube 1 and the outer tube 2 on both axial sides of the corrosion-resistant material 10. Also at the end of the tube, expansion in the radial direction does not occur due to the large frictional force of the metal touch, and no tensile stress occurs in the radial direction at the end of the tube, resulting in compressive stress. Therefore, no tensile stress is applied to each tube 3, 3' in the length direction and radial direction, especially at the joint portion, and only compressive stress is applied.

Therefore, even if they are connected to a specified length as oil country tubular goods and installed vertically, the axial tensile force is canceled out and eliminated or relaxed, and compressive stress acts on the corrosive crude oil being transported. Stress corrosion cracking does not occur, and no leakage occurs from the abutting surfaces 12 and 13.

In another embodiment shown in FIG. 6, the inside of the box 8 of the outer tube 2 of the raw material unit tube 3 is bored as shown in FIG. 7 to form a stepped portion 9. As shown in FIG. 8, a plate-shaped stainless steel ring 10' made of the same material as the inner tube 1 and having a predetermined thickness is welded and fixed to the end of the inner tube 1 by electron beam welding 17 as a corrosion-resistant material. A metal touch surface 12 that is perpendicular to the axial direction of the abutting surface is formed, and then, as shown in FIG. 8, threading is performed to form a female threaded portion 11, and similar to that shown in FIG. It may also be screwed to the pin 15 of the tube 3'.

It should be noted that the embodiments of the present invention are of course not limited to the above-mentioned embodiments. For example, the corrosion-resistant material that is integrally joined to the inner pipe of one double pipe may be fixed to the pin side. You can also use the pin side,
Various embodiments can be adopted, such as providing it on both sides of the box.

In addition to the upset type, the lateral type can also be used, and in addition to oil country tubular goods, it can also be applied to transportation pipes, nuclear power plant piping, etc.

<Effects of the Invention> As described above, according to the present invention, the joint portion of a unit pipe of a pair of double pipes consisting of a corrosion-resistant inner pipe and a pressure-resistant outer pipe tightly joined to the corrosion-resistant inner pipe is a pin box screw joint. Furthermore, at least one of the abutting surfaces of the pin screw and the box screw is fixedly interposed at the tube end with an integral stainless steel corrosion-resistant material having the same properties as those of the inner tube, and the thickness thereof is perpendicular to the axial direction. By forming the metal touch surface from the inner tube to the outer tube, the coupling is basically connected via a pin box screw connection, but there is no need to manufacture a coupling, making it easier to manufacture and lower costs. Not only does it have the excellent effect of making it easy to manage the screws, but in the threading process of both tubes, not only the inner tube but also the outer tube can be tightened and crimped due to the metal touch surface of the corrosion-resistant material whose abutting surfaces are perpendicular to the axial direction. Moreover, the corrosion-resistant stainless steel material prevents plastic deformation, and the inner tube receives axial and radial compressive force through the metal touch surface perpendicular to the axial direction. Therefore, not only does the corrosive fluid not leak, but also the excellent effect that stress corrosion cracking does not occur during operation is achieved.

In addition, as mentioned above, by providing the corrosion-resistant material at the pipe end of a pin box joint that has one threaded connection, it is possible to reduce tension when connecting through two threaded connections in a coupling such as a coupling joint. Compared to the stress, the compressive stress caused by screwing in the pin box acts in both the axial and radial directions of the joint, and therefore, axial compressive stress is formed at least at the pipe end of the joint. Not only does stress corrosion cracking not occur, but as mentioned above, the stainless steel corrosion-resistant material has a sufficient depth from the inner tube side to the outer tube side, so that it does not damage the tube ends at both end faces in the length direction, that is, even in the thick part. Since the compression caused by the metal touch occurs at right angles to the axial direction, radial expansion of the tube ends toward the outside does not occur, and therefore no radial tensile stress is generated. is the axial direction,
Moreover, the excellent effect that radial tension does not occur and stress corrosion cracking does not occur throughout is achieved.

Moreover, the corrosion-resistant material has the advantage that it can be formed into a shape that can be reliably touched by metal by employing overlay welding, beam welding, etc.

In addition, a corrosion-resistant material such as stainless steel, which has the same properties as the inner tubes of both tubes, is interposed on the opposing surfaces of both unit tubes at the pin box joint, so that both unit tubes can be connected through the pin box joint. When they are fastened and screwed together, the axial pressure causes both pipes and the corrosion-resistant material to come into metal-touch contact, so compressive stress is applied not only in the axial direction but also in the radial direction as described above, which reduces corrosion during operation. It has the effect of not causing stress corrosion cracking due to fluid, and since it is made of corrosion-resistant stainless steel, plastic deformation does not occur when connecting, making it easy to reconnect after the two unit pipes have been separated due to frequent maintenance, inspection, etc. The metal touch is always guaranteed with good reproducibility, sealing performance is reliably guaranteed, and long-term compressive stress is always applied, so stress corrosion cracking during operation can be prevented, which is an excellent effect.

Furthermore, since the bulging portion of the box portion has a block shape that is more rigid than that of the coupling joint, this also has the effect of guaranteeing the strength of the metal touch portion of the corrosion-resistant material.

[Brief explanation of drawings]

Fig. 1 is a schematic partial sectional view of a threaded joint based on the prior art, Fig. 2 and the following are explanatory views of embodiments of the present invention, and Figs. The partial side view, FIGS. 6, 7, 8, and 5 are partial cross-sectional views of the manufacturing and screwing process of other embodiments. 1... Inner pipe, 2... Outer pipe, 3, 3'... Unit pipe, 8, 15... Joint, 11... Box screw, 14... Pin screw, 8... Box, 15...
...Pin, 10,10'...Corrosion-resistant material, 12...Metal touch surface.

Claims (1)

[Claims] 1. In a structure in which a connecting joint of a pair of unit pipes having an outer pipe integrally joined with a corrosion-resistant inner pipe consists of a box screw of one unit pipe and a pin thread of the other unit pipe, the box thread side of the one pipe and the At the abutting surface of the stepped portion near the inner tube on the other pin screw side, a corrosion-resistant material made of stainless steel having the same properties as the inner tube is integrally installed with the inner tube on at least one of the box screw side and the pin screw side, including its thick part. A double pipe joint structure characterized in that a metal touch surface is formed from the inner pipe to the outer pipe part and fixedly interposed in a ring shape by welding to the other pipe end at right angles to the axial direction. .