JPS623683B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The disclosed technology is applicable to, for example, chemical plants, oil country tubular goods,
This field belongs to the technical field related to the joining of double pipes used for oil pipes and heat exchanger pipes.

<Prior art> As is well known, chemical plants, oil country pipes, oil pipes,
For piping used in heat exchangers, etc., clad steel pipes made of high nickel material or carbon steel pipes are used as the outer pipes, and stainless steel pipes are fitted as the inner pipes to meet the objectives of high temperature resistance, high strength, and corrosion resistance. Double pipes are used.

Furthermore, recently there has been a strong demand for the development of pipes that have a high degree of corrosion resistance in addition to strength, but the material that controls the corrosion resistance function has to be used in a state where compressive stress is applied inside the material. It has been revealed that this is desirable from the viewpoint of maintaining corrosion resistance such as preventing stress corrosion cracking, and non-metallurgically bonded double pipes have been put into practical use.

<Problems to be solved by the invention> By the way, the unit length of pipes is generally determined due to restrictions on the size of manufacturing equipment and length restrictions for transportation to the installation site, and joints are used to connect the pipes. However, the problem with welded joints, which are most commonly used, is that the aforementioned tight connections loosen due to the high temperatures during welding.

To avoid heat effects during on-site welding,
For example, there are cases where a lining material is overlay welded to the end of the tube, but similar problems arise in this case as well.

Furthermore, in order to adopt other mechanical joint structures, there are cases in which high-strength materials are welded on the outside of the tube end, but tight fastening is required at the overlay weld and the weld heat-affected zone. The problem of loosening occurs in this case as well.

Commonly in these cases, the above-mentioned corrosion resistance becomes difficult to maintain because the fastening is loosened.
Furthermore, there was a problem in that tensile stress was generated in the weld metal part and the weld heat affected zone of the inner tube, leading to deterioration in corrosion resistance, particularly stress corrosion cracking resistance.

<Object of the Invention> The object of the present invention is to solve the above-mentioned problems at the end of the self-tightening, corrosion-resistant double pipe, and , applying a local mechanical spreading force to the inner wall surface area of the inner tube in the vicinity thereof,
An object of the present invention is to provide an excellent method for treating a double-walled pipe, which is capable of forming compressive stress in the inner pipe and increasing the corrosion-resistant ability of the corrosion-resistant pipe, thereby benefiting piping technology applications in various industries. It is.

<Means/effects for solving the problems> In order to solve the above-mentioned problems, the structure of the present invention, which is based on the above-mentioned claims, is to incorporate a stainless steel pipe or the like into an outer pipe such as a carbon steel pipe. When welding or overlaying the end of a double-walled pipe in which corrosion-resistant inner pipes are closely layered, short cylindrical rollers apply a predetermined mechanical spreading force to the inside of the inner pipe at the end of the pipe. Concentrated local application is applied continuously in the circumferential direction and axial direction of the pipe end to expand and expand the inner pipe, and the welded part and built-up part of the pipe end are Compressive stress is created in the inner tube at the end of the tube, including the adjacent heat-affected zone, to compensate for the lost self-tightening force and prevent stress corrosion cracking from occurring.

<Example> Next, an example of the present invention will be described below with reference to the drawings.

First, the principle is shown in FIG. 1. A short cylindrical spreading roller 3 is applied to a carbon steel outer tube 2 and a stainless steel inner tube 1 having a predetermined wall thickness with a predetermined external pressure. When the inner tube 1 is set and rotated while applying a spreading force, the spreading force is locally applied to the inner tube 1 by the spreading rollers 3, so that the thickness of that part is less than the initial thickness. The inner wall of the inner tube 1 is processed to have a thin wall thickness, and a thin inner wall skin portion of the inner tube 1 is formed by rotation of the rollers 3 in the circumferential direction.

Therefore, by moving the rotation of the spreading roller 3 along the axial direction, the set length and thickness can be reduced.

In this case, since the spreading roller 3 has a short cylindrical shape, the pressure of the spreading force is intensively applied as described above, and therefore the pressing force can be relatively small.

This spreading deformation of the inner wall at the end of the inner tube 1 is actually restrained by the outer tube 2, which is not affected by the spreading, and causes a self-tensioning effect on the skin of the inner tube 1. As a result,
Compressive stress is applied to the inner tube 1.

It is not necessary to limit the number of rollers 3 to one for spreading; FIG. 2 shows an embodiment in which two spreading rollers 3, 3' are set on opposite sides, and FIG. 3'', 3 are set in three pieces at intervals of 120° in the circumferential direction.

Specific embodiments of this invention are shown below as FIGS. 4 to 6.

The embodiment shown in FIG. 4 is a case in which two double-pipe single pipes 4, 4 are connected to a welded joint 5 to form a long pipe at the installation site, and when forming the welded joint 5, the single pipe 4 is , 4 are welded to each other by the spreading roller 3, which causes the loss of compressive stress in the loosening range H of the tight joint of the double pipe formed during the manufacture of the single pipe 4 in the range including the welded heat affected zone. This figure shows how recovery can be achieved by continuous application of spreading action.

A similar treatment can also be applied to the ends of the tubes as a preliminary treatment before forming the two double-walled single tubes 4, 4 into a long tube via a joint at the installation site.
Here, the first aspect of pre-treatment is that in a double pipe where the inner pipe 1 is made of stainless steel, the inner pipe wall in the range where the single pipe joint will be affected by heat due to welding is treated in advance even if it is not affected by heat. The pipe end treatment method shown in Fig. 5 involves overlay welding using a different type of stainless steel material with less deterioration in corrosion resistance and a width that is not affected by heat during welding as much as the stainless steel material of the inner pipe 1. .

That is, when overlay welding 6 is performed on the inner surface of the end of the double pipe single pipe 4 before the weld joint is formed, the end of the inner pipe 1 including the weld overlay metal part and the heat-affected zone of the inner pipe 1 Although the phenomenon of disappearance of compressive stress and the loosening of self-tightening force occur over the inner wall skin part H of You can recover and supplement your strength.

The second embodiment is shown in FIG. 6, in which overlay welding 7 is performed on the end of the outer tube 2 to form a coupling joint for connecting the single tube 4 of the double tube. After that, when forming a machined finished part for a joint at the end of the overlay weld 7, the inner wall skin of the inner pipe 1 at the tube end including the heat affected zone of the inner pipe 1 is removed by the overlay weld 7. Although a phenomenon in which the compressive stress disappears over the width H or a phenomenon in which the self-tightening force loosens occurs, the compressive stress can be reduced by using the pressing and spreading means of the roller 3 in this part as in the above embodiment. It becomes possible to recover self-control and self-control.

The present invention described above with reference to the drawings describes an embodiment in which the spreading roller is a short cylindrical spreading roller and rotates in the circumferential direction with respect to the tube axis on the inner surface of the end portion of the double pipe.

Even if the spreading roller rotates along the inner surface of the tube end of the inner tube of the double tube in the tube axis direction or in a diagonal direction with respect to the tube axis, the effects of the present invention remain unchanged.

<Effects of the Invention> As described above, according to the present invention, when welding is performed at the end of a double-layered pipe in which an inner pipe is tightly fastened to an outer pipe and the inner pipe is tightly fastened to the outer pipe, the welding or overlay metal This method ensures the loss of compressive stress and loosening of self-tightening force generated in the inner wall skin of the inner tube at the end of the tube, including the heat-affected zone of the inner tube.
In addition, the excellent effect of being able to recover easily at a low cost is achieved.

Further, according to the present invention, it is possible to prevent stress corrosion cracking due to insufficient compressive stress at the pipe end of a welded joint or a coupling joint of a corrosion-resistant double pipe whose inner pipe is a corrosion-resistant pipe. There are also effects such as being able to do it.

[Brief explanation of the drawing]

1, 2 and 3 are sectional views of the principle mode, FIG. 4 is a sectional view of an embodiment, and FIGS. 5 and 6 are partial sectional views of another embodiment. 2...outer pipe, 1...inner pipe, 3...spreading roller,
4...Double pipe, 6,7...Overlay welding.

Claims (1)

[Claims] 1. In a double pipe manufacturing method in which the inner pipe is non-metallurgically fastened to the outer pipe and the pipe ends are welded to form a joint part at the pipe end, the welded part or overlay of the joint part Continuously applying a localized mechanical spreading force using a short cylindrical spreading roller to the internal tube at the end of the pipe corresponding to the welding heat affected zone and the welding heat affected zone to restore the tightening effect lost due to welding. A double tube manufacturing method characterized by: