JPS6341678B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Application> The disclosed technology belongs to the field of manufacturing process technology for clad pipes used for plant piping and the like.

<Summary of the gist> Therefore, the present invention involves inserting and overlapping an inner tube such as a stainless steel tube into an outer tube such as a carbon steel tube to mechanically tighten the inner tube, and then performing diffusion welding on the mating surfaces of both tubes. This invention relates to a manufacturing method for manufacturing a clad pipe, and in particular, the invention relates to a method of manufacturing a clad pipe by applying heat to increase the degree of fit by applying a temperature difference between the two pipes in a polymerization process to expand the pipe through the initial diameter difference, causing yield plastic deformation, and increasing the degree of fit. This invention relates to a method for manufacturing a clad pipe in which a tube expansion method is used to increase the degree of adhesion, and after self-stretching, the boundary surface of the tube end is seal welded and diffusion welded in a HIP device.

<Prior art> As is well known, double pipes are widely used in plant piping to provide pressure, heat, and corrosion resistance functions for transporting corrosive fluids such as petroleum. Clad pipes have come to be used to prevent distortion, misalignment, and the occurrence of cracks and implosion caused by these.

By the way, in general, metal plate cladding involves stacking multiple metal plates, seal-welding the ends of their polymerized interfaces, storing them in a HIP device, processing them at high temperature and high pressure in an inert gas, and performing diffusion welding. It is generally believed that, in order to improve the diffusion welding effect as designed, it is known that the stronger the tightness of the joint surface before the cladding, the better.

<Problems to be Solved by the Invention> However, with special metal bodies such as cylindrical bodies such as tubes and elongated bodies of considerable length, it is difficult to obtain a strong bond between joint surfaces. However, there was a drawback that conventional double pipes using hydraulic pressure expansion, shrink fitting, etc. were not possible.

The purpose of the present invention is to solve the technical problem of the double pipe cladding technology based on the prior art described above, and to achieve self-tightening of the inner and outer pipes with a high degree of fitting.
It is an object of the present invention to provide an excellent method for manufacturing clad pipes which is useful for piping technology applications in various industries by ensuring that the ends of the pipes are sealed.

<Means/effects 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 sufficiently polish the joining surfaces of the inner and outer tubes. Keep it smooth, give a relative temperature difference between the two during relative polymerization to create a latent diameter difference, expand the tube using hydraulic pressure, yield, plastically deform, release the expansion force at a predetermined amount of strain, and return to natural temperature. By doing this, a high degree of fitting is obtained, and the boundary surfaces of both tubes are strongly self-tightened.The ends of the self-tightened double tube thus obtained are sealed and welded to the boundary surfaces of both tubes, and HIP is performed.
This is a technical measure that allows diffusion welding to be carried out at high temperature and high pressure in an inert gas atmosphere by storing the weld in a device.

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

The carbon steel outer tube 1 and the stainless steel inner tube 2 inserted into the outer tube 1 have their inner surfaces 1' and outer surfaces 2' polished as smooth as possible by a predetermined appropriate means, respectively, as shown in FIG. Each is manufactured separately in steps A and A'.

Then, the outer tube 1 and the inner tube 2 are heated and cooled from room temperature with a heater and cold water to increase and decrease their diameters, and are smoothly inserted relative to each other as shown in FIG. The polymerization process is carried out in step B of FIG.

In this case, as shown in Figure 6, the horizontal axis represents the diameter (strain ε).
In the stress-strain curve for tube expansion, where the stress F is taken on the vertical axis, the outer tube follows the graph _C1 , and the inner tube follows the graph _C2 , but the former changes from the initial state diameter A' to the heating diameter increase B'. The latter is made to cool down from the initial state diameter A to obtain the insertion allowance ΔD.

Next, when the cooling fluid is pressurized with both ends of the inner tube 2 sealed and the process moves to step C of the tube expansion process in FIG. ′, the tube enters the state of integral expansion, then yields and plastically deforms sequentially, removes the expansion force at the set diameter, eliminates the expansion liquid, returns the double tube 3 to its natural temperature, and the inner and outer tubes 2, 1 are C, C′ to D, respectively.
Furthermore, the diameter of the outer tube 1 decreases from D to E due to natural cooling after heating, while the diameter of the inner tube 2 increases as the temperature rises from cooling, and the diameter decreases from D to Hol. Therefore, a large fitting allowance ΔD' can be obtained.

In this way, a strong degree of fitting is obtained, and the tightness of the interface between the inner and outer tubes 2, 1 is reliably guaranteed due to the close contact between the joining surfaces 1', 2' as described above. .

Of course, since the degree of fitting of the self-tightening double pipe 3 is large and the boundary surface is polished, the whole surface is in a tight state even from a microscopic point of view.

Therefore, as shown in step D in Figure 1, the self-containing double pipe 3
As shown in FIG. 5, electron beam welding 4 is applied to the end of the tube between the opposing surfaces 1' and 2' of the inner and outer tubes to form a ring-shaped seal.

Thus, the sealed tubing is not shown.
The inner and outer tubes 1 are stored in a HIP device and subjected to a predetermined high temperature and high pressure in argon gas for a predetermined time.
2 is diffusion welded at the close joint surface and clad as step E in FIG.

Diffusion welding is ensured because the welding surface is in extremely good adhesion and is microscopically applied over the entire surface.

It goes without saying that the embodiments of the present invention are not limited to the above-mentioned embodiments. For example, before fitting the inner and outer tubes, an insert material such as nickel may be applied to the inner surface of the outer tube or the outer surface of the inner tube. It is also possible to add it in the form of plating foil, etc. Seal welding can also be done by TIG welding, etc. Furthermore, thermal expansion of self-sealing double pipes can be done by either heating the outer pipe or cooling the inner pipe. Various embodiments can be adopted, such as a single one.

<Effects of the Invention> As described above, according to the present invention, in order to manufacture a clad steel pipe such as a stainless steel clad steel pipe, the inner and outer pipes are self-tightened, the joint surfaces of which have been polished as smooth as possible by a heat expansion method, and By tightly crimping the joining surfaces with an extremely high degree of fit, diffusion welding in the HIP device is performed extremely well, which is an excellent effect.Also, it is possible to achieve self-tight double pipe end sealing using the heat expansion method. This also has the effect that seal welding can be reliably performed by electron beam welding or the like.

In addition, self-tight joining of double tubes can increase the degree of fit by applying a temperature difference in advance to give a diameter difference, and returning to the natural temperature after yielding and plastic deformation, so it has the advantage of contributing greatly to the above-mentioned diffusion welding. be.

[Brief explanation of the drawing]

The drawings show one embodiment of the invention,
Figure 1 is a manufacturing process flow sheet diagram, Figures 2 and 3
The figure is a perspective view of the outer tube and inner tube, and Figure 4 is a perspective view of the joint.
FIG. 5 is a sectional view of the tube end seal welded, and FIG. 6 is a stress-strain curve graph during tube expansion. 1... Outer pipe, 2... Inner pipe, 1', 2'... Fitting (joining) surface, 4... Seal welding.

Claims (1)

[Claims] 1. In a clad pipe manufacturing method in which the inner and outer tubes are self-tightly joined together and then the fitting surfaces of both tubes are diffusion welded, a temperature difference is applied to the inner and outer tubes before and after they are polymerized to cause them to yield by expansion. After that, the expansion force is removed and the tube is naturally cooled to self-tighten. After that, the fitting end is sealed and welded, and diffusion welding is performed on the fitting surface under high temperature and pressure. Method.