JPS6152351B2 - - Google Patents

Description

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

The present invention relates to a corrosion-resistant double tube structure in which a corrosion-resistant inner tube made of stainless steel or the like is fitted and tightly connected by heat expansion into an outer tube made of a carbon steel tube or the like, and the inner and outer tubes are seal-welded at the tube ends. It is an invention,
In particular, another corrosion-resistant outer tube is integrally connected to the end of the outer tube in a short tube shape by friction welding, etc., a corrosion-resistant inner tube is fitted and tightly connected to the inner surfaces of both outer tubes, and the inner and outer tubes are further connected at the end of the tube. This invention relates to a corrosion-resistant double pipe structure in which the pipes are sealed and welded.

<Prior art> As is well known, corrosive fluid flow pipe bodies such as oil country tubular goods have a so-called corrosion-resistant structure, in which an inner pipe made of stainless steel or the like having a corrosion-resistant function is fitted into an outer pipe made of carbon steel, which has a pressure- and heat-resistant function. A double tube is used.

Therefore, the pipe length of one unit pipe is determined by standards depending on the manufacturing equipment mechanism, facility space, etc., as well as transportation constraints to the site. When installing a considerable length of piping, it is necessary to connect each unit pipe to the set length using coupling joint processing or the like on site.

During this time, the unit pipes are actually piled up in the open and exposed.

For this reason, factory-produced corrosion-resistant double-pipe pipes are designed to prevent rust and corrosion from entering at the boundary between the inner and outer pipes before being used in actual piping, and to provide corrosion resistance to coupling joints. Furthermore, in order to prevent the inner and outer tubes from shifting in the axial direction during operation, means are used to seal-weld the inner and outer tubes at the tube ends.

For example, as shown in FIG. 1, after manufacturing a double-walled corrosion-resistant double-walled pipe 1 consisting of a carbon steel outer tube 2 and a stainless steel inner tube 3, seal welding 5 is performed at the tube end 4 by penetration welding. Also, as shown in Figure 2,
The pipe end of the inner pipe 3 is made longer than the outer pipe 2 of the double pipe 1' by a set length, and a seal weld 5' is performed on the pipe end using stainless steel build-up welding, and the seal is integrated at the pipe end and post-processing is performed. A pin thread is machined to the coupling joint to provide the pin thread with a corrosion-resistant function.

<Problems to be solved by the invention> However, in this type of technology, the number of man-hours for welding, etc. is large, the sealing work is cumbersome, and since welding is performed between dissimilar materials such as carbon steel and stainless steel, heat generated by welding heat is This method has the disadvantage that the strain is non-uniform and complicated, and metallurgical thermal degeneration occurs, making it undesirable as a tube end treatment.

The purpose of this invention is to solve the technical problem of seal welding between the outer tube and the inner tube at the end of a corrosion-resistant double tube based on the above-mentioned prior art, and to ensure sufficient sealing performance at the end of the tube. , an excellent corrosion-resistant double-pipe structure that ensures integration, facilitates post-processing such as threading, and allows the pipe end to function as a joint, benefiting piping applications in various industries. This is what we intend to provide.

<Means and operations for solving the problems> In order to solve the above-mentioned problems, the structure of the present invention, which is summarized in the above-mentioned claims, is to form a corrosion-resistant double pipe with pressure resistance and heat resistance. A short tube made of a corrosion-resistant material with the same diameter and wall thickness is welded and connected to the end of the outer tube by means such as friction welding, and an inner tube made of the same material and made of a corrosion-resistant material is fitted into the outer tube that is connected to both. The inner and outer tubes are fitted together by a predetermined means, and the corrosion-resistant short outer tube and inner tube are seal-welded at the ends of the tubes, and the welding is easily performed because it is made of the same material. , prevents different thermal effects from appearing, maintains sealing performance, and maintains pipe fitting corrosion resistance,
Technical measures have been taken to increase the reliability of the double pipe.

<Embodiment - Configuration> Next, one embodiment of the present invention will be described as follows based on the drawings from FIG. 3 onwards. Note that the same parts as in FIGS. 1 and 2 will be described using the same reference numerals.

As shown in FIG. 3, the tube end 6 of the carbon steel outer tube 2 having a predetermined wall thickness and length is formed into an end surface perpendicular to the axial direction by mechanical grinding or the like as appropriate.

On the other hand, as shown in FIG. 4, a stainless steel short tube 7 having the same wall thickness and diameter as the outer tube 2 and a set short length, for example, a length equal to the female pin thread length of the coupling joint, corresponds to the outer tube 2. A short outer tube is prepared by mechanically grinding the corresponding surface 8 to be a surface perpendicular to the axial direction.

Then, the outer tubes 2 and 7 are brought into relative rotational pressure contact via an appropriate friction welding device to form an integral outer tube 10 with a friction weld connection 9 as shown in FIG.

Thereafter, as shown in FIG. 6, the stainless steel inner tubes 11 are layered relative to each other by, for example, the so-called thermal tube expansion method of the applicant's earlier patented invention, and are tightly fitted to form a double tube 12.

Next, as shown in FIG. 7, the stainless steel inner tube 1
The end surface 13 of 1 is the end surface 14 of the stainless steel short outer tube 7.
Cut the inner tube 11 of both stainless steel materials by mechanical grinding, etc., so that it is on the inside by a set amount.
Stainless steel build-up welding 15 is performed between the short outer tube 7 and the short outer tube 7 for seal welding.

In this way, the unit corrosion-resistant double pipe 16 is manufactured.

Then, as shown in FIG. 8, the inner surface of the seal weld 15 of the build-up weld is processed to be smooth and then stored in the open or transported to the site.

<Embodiment - Effect> In the above structure, the produced unit corrosion-resistant double pipe 16 has its pipe ends sealed and welded by the short outer pipe 7 and inner pipe 11 made of the same stainless steel material, so that corrosion does not occur even in an open state. There is no penetration, there is no material change due to welding heat unlike when welding different materials, and there is no axis misalignment.

In addition, in the joint processing, if the pin thread processing 17 of the coupling joint is performed as shown in FIG.
Since the corrosion-resistant materials are directly screwed together and tightly connected, corrosion resistance is automatically imparted.

It goes without saying that the embodiments of the present invention are not limited to the above-mentioned embodiments. For example, the pipe end of the unit corrosion-resistant double pipe shown in FIG. Various aspects can be adopted, such as combining the two.

<Effects of the Invention> According to the present invention, basically, a corrosion-resistant outer pipe is formed into a short pipe and integrally connected to a general non-corrosion-resistant outer pipe at the pipe end of a corrosion-resistant double pipe. By integrally fitting the corrosion-resistant inner tube to the tube and seal-welding it to the corrosion-resistant outer tube, the metallurgical properties will not change due to welding heat because the seal welding is a welding of the same corrosion-resistant material, making it possible to operate. Excellent effects such as no corrosion at the ends of the tubes are achieved.

In addition, since it is easy to weld, it has the excellent effect of increasing the reliability of the corrosion-resistant double pipe product.

Furthermore, since the inner and outer tubes at the tube ends are made of the same corrosion-resistant material and are sealed and integrated, the expansion and contraction are the same not only during manufacturing but also during operation, which prevents stress corrosion cracking, etc. There is.

Furthermore, there is the advantage that non-corrosion resistant parts such as coupling joints and flange joints do not require overlay welding.

[Brief explanation of the drawing]

Figures 1 and 2 are partial sectional views explaining the seal welding structure of a corrosion-resistant double pipe based on the prior art, Figure 3 and the following are explanatory views of an embodiment of the present invention, and Figure 3 is a partial sectional view of the outer tube; Figure 4 is a partial cross-sectional view of the short outer tube;
The figure is a partial cross-sectional view of the connecting outer pipe, Figure 6 is a partial cross-sectional view of the inner pipe fitting, Figures 7 and 8 are partial cross-sectional views of the product unit double pipe, and Figure 9 is a partial cross-sectional view of the pipe end joint processing. be. 2...Outer tube, 11...Inner tube, 15...Seal welding, 16...Corrosion-resistant double tube, 7...Corrosion-resistant short outer tube.

Claims (1)

[Claims] 1 In a double pipe structure in which a corrosion-resistant inner pipe is fitted to an outer pipe and the inner and outer pipes are seal-welded at the end of the pipe, a short corrosion-resistant outer pipe is integrally connected to the end of the outer pipe by welding, and A corrosion-resistant double pipe structure characterized in that a corrosion-resistant inner pipe is fitted and tightly connected to both outer pipes, and the outer pipe end and the inner pipe end are seal-welded.