JPS6251695B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The disclosed technology belongs to the field of hydraulic expansion and fastening technology of an inner pipe to an outer pipe of a corrosion-resistant double pipe used for plant piping and the like.

In this invention, an inner tube made of stainless steel or the like having a cross-sectional area smaller than that of the outer tube made of carbon steel or the like is smoothly inserted, and then expansion pressure is applied to the inner tube to increase the diameter of the inner tube. This invention relates to a double tube manufacturing method in which the double tube is tightly integrated with the outer tube.In particular, a die is brought into surface contact with the inner surface of the outer tube in advance, and the die has a surface area larger than the contact area of the outer tube. The inner tube is made to have a large contact area, and the inner tube with a small cross section is inserted into the outer tube through the die, and expansion pressure is applied to the inner tube in advance so that the inner tube is at least pressed against the die. The inner tube is deformed so that the outer circumference of the inner tube is larger than the inner circumference of the outer tube in cross section, and then the application of tube expansion pressure is stopped and the die is pulled out. After that, the tube expansion liquid pressure is applied again and the tube is tightly fitted by compressive stress in the circumferential direction. This relates to a method for manufacturing a double pipe in which the pipes are made to fit together.

As is well known, many rotary pipes such as plant pipes and oil country tubular goods are used for transporting corrosive liquids, and these pipes have not only pressure resistance and pressure resistance but also corrosion resistance. Corrosion-resistant double pipes have come to be used in order to improve the durability and other properties.

Since the double-pipe type requires a considerable amount of material, it is inherently much more expensive than the single-ply type pipe, so it should be manufactured at the lowest possible cost. There is a strong need for this to be done.

On the other hand, since the occurrence of problems such as cracking and implosion can lead to fatal troubles in the long-term operation of corrosion-resistant double pipes, it is also required that the strength of the connection between the inner and outer pipes be high. It is becoming more and more like this.

To deal with this, double pipes have been developed, such as clad double pipes, in which the inner and outer pipes are relatively heavily loaded and the two pipes are tightly connected. The main method used is the shrink fitting method, which has the disadvantage that it is extremely difficult to insert long pipes due to relatively heavy loading.Additionally, there is also the problem that precision is required, and with the hydraulic pipe expansion method, it is difficult to insert the inner and outer pipes. The required condition is that there is a considerable difference in yield point between the tubes, which imposes material constraints, and the disadvantage is that a large amount of power is required to expand the tubes to fit them together.

However, a thermal tube expansion method such as a hydraulic tube expansion method based on a diameter difference based on a temperature difference, as seen in the applicant's prior invention, has the disadvantage of requiring a large-scale heating device.

The purpose of the present invention is to solve the problems of the method of manufacturing a corrosion-resistant double pipe based on the above-mentioned prior art, and to create a method that allows a circumferential length to be formed with respect to that of the outer pipe so as to provide sufficient interference with the outer pipe. The inner tube is formed into a small cross-section that is easy to insert, and the outer tube is a perfect circle.
The inner tube is inserted through a die, and the inner tube is once plastically deformed by internal pressure expansion to make the circumference of the inserted inner tube longer than the inner circumference of the outer tube in the cross section.
The object of the present invention is to provide an excellent double tube manufacturing method in which the die is then removed and the inner tube is tightly connected to the outer tube by compression fitting through internal pressure tube expansion.

The structure of the present invention in accordance with the above-mentioned object is to place at least one die in an outer tube with a perfect circular cross section and abut the inner surface of the outer tube over the entire length, insert an inner tube with a small cross section through the die, and insert the inner tube in that state. Stress is applied by applying expansion pressure inside the pipe.
The tube is expanded according to the strain curve, plastically deformed as it comes into close contact with the die, and then the tube expansion pressure is temporarily reduced, and the die is pulled out using the gap created by the elastic return of the inner tube.Finally, the tube expansion liquid pressure is applied to the inner tube. is further applied to increase the diameter of the inner tube through plastic deformation, causing the concave portion formed by the die to protrude, making it tightly adhere to the outer tube all around the circumference, and a tight fit is achieved by compression fitting based on the difference in the circumferential length of the inner and outer tubes. This is a summary of what was done.

Next, embodiments of the present invention will be described below with reference to the drawings.

First, for a carbon steel outer tube 1 having a set diameter and a perfect circle in cross section, dies 2, 2 whose cross section has an outer circumferential curvature that matches that of the inner circumference of the outer tube 1 and whose inner circumference is longer than the outer circumference are placed. The inner space section formed by the die 2 and the outer tube 1 is inserted from both ends of the pair so that its outer peripheral surface is in contact with the outer tube 1, as shown in FIG. A stainless steel inner tube 4 (the cross-sectional shape does not need to be concave) is inserted, which has a small cross-sectional area that can sufficiently fit into the area.

In addition, due to the post-stage tube expansion, the inner tube is extended outward from the outer tube 1 by the amount of axial reduction, and is made longer at both ends, and the same-shaped two-split short tube 1' is connected to the tube end of the outer tube 1. .

In this state, a cap 6 having the same cross-sectional shape as the inner pipe 4 is connected to the end of the inner pipe 4 through a seal 5 in a watertight manner, and a liquid supply pipe 8 is connected to one end and a liquid supply pipe 8 is connected to the other end through a valve 7. Connect the drain pipe 8' to the drain pipe 8'.

Therefore, the valve 7 on the drain pipe 8' side is closed and the liquid supply 8' is closed.
When more tap water is pumped to fill the inner pipe 4 and the water pressure is further increased to expand the pipe, the diameter of the inner pipe 4 increases along the stress and strain curve, and after yielding, it becomes plastically deformed. The outer tube 1 changes from the state shown in Fig. 1 to the state shown in Fig. 2.
Then, it comes into contact with the inner circumferential surface of the die 2 and is deformed so that its outer circumferential length is longer than the inner circumferential length of the outer tube 1.

In addition, the tube end is similarly applied with water pressure to expand the tube and is pressed against the exposing die 2, and is then pressed against the two-split connecting end tube 1'.

Therefore, close the liquid supply side valve 7, stop applying liquid pressure to expand the tube, open the drain side valve 7 slightly, drain a small amount of water, close the valve 7, and return the short tube 1' to the two halves. At the same time, the dies 2, 2 are pulled out from inside the tube via the support bars 3, 3, and then, as shown in FIG. Split seal tube 1″,
1'' through clamps 9, 9.

Therefore, the drain side valve 7 is closed and the liquid supply side valve 7 is closed.
When the tube is opened and expansion pressure is applied again, the inner tube 4 is plastically deformed by the space removed by the die 2, and the inner tube 4 is expanded as shown in FIG. Since the inner circumference of the die 2 is longer than the outer circumference, the outer circumference of the inner tube 4 is longer than the inner circumference of the outer tube 1. Therefore, the compression allowance corresponding to the difference length becomes the fitting allowance, and the inner tube 4 is tightly tied to the outer tube 1.

During this time, the tube end is restrained by the end of the short tube 1'', so the diameter is not increased and the seal is ensured, and the axial reduction relative to the increase in the diameter of the general section is compensated for by the slide inside the short tube 1''. Ru.

When the diffusion bonding is completed, the liquid supply side valve 7 is closed, the liquid drain side valve 7 is opened, the liquid is drained, the clamps 9, 9 are released, the two short pipes 1'', 1'' are removed, and the seal 5 is removed. , 5. Remove the caps 6, 6, remove the material double tube, and trim the tube end of the inner tube 4 to obtain a unit double tube.

Furthermore, although the number of dice 2 is one, it is also possible to use a plurality of dice 2, 2, etc. as in the embodiment shown in FIG. It is also possible to use a plurality of dies 2'', 2 having different amounts.

It goes without saying that the embodiments of this invention are not limited to the above-mentioned embodiments; for example, various embodiments may be adopted, such as making the die a high-hydraulic expansion type and retracting it when drawing it out. It is possible.

Therefore, the target double pipe is not limited to plant piping.
Of course, it can also be used for various purposes such as oil country tubular goods and transport pipes.

As described above, according to the present invention, in the double pipe manufacturing method, in order to hydraulically expand and connect the inner pipe to the outer pipe, the die is placed inside the outer pipe so that the inner pipe contact circumference is smaller than the outer pipe contact circumference. By inserting a longer tube and inserting the inner tube there, there is no need for complicated processes such as processing the inner tube to make its outer circumference longer than the inner circumference of the outer tube. Since it is sufficient to simply insert an inner tube with a small set cross-sectional area, manufacturing is easy, and there is also the advantage that initial dimensional accuracy is not required.

Also, the dies are manufactured separately from the inner and outer tubes,
It has the advantage that it can be inserted into the outer tube, pulled out, and used repeatedly, and is easy to handle.

Therefore, the outer circumference length can be made longer than the inner circumference length of the outer tube simply by performing primary processing of the inner tube by hydraulic expansion using a die and plastically deforming it, and this can be done while being inserted into the outer tube. Therefore, there is the advantage that there is no difficulty in inserting the preformed inner tube, and the inner tube can be temporarily press-fitted to the inner surface of the outer tube other than the die, preventing displacement due to pulling out of the die. It's also effective.

Furthermore, since the tube can be expanded by hydraulic pressure without using heat, there is no need for heat management during manufacturing, and there is also the effect that an arbitrary degree of fitting can be obtained by selecting the die size.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention. Figures 1, 2, and 3 are explanatory diagrams of the manufacturing process of one embodiment, Figures 4 and 5 are perspective illustrations of the same process, and Figures 6 and 7 are separate diagrams. It is a schematic explanatory view of an example. 1...Outer tube, 4...Inner tube, 2, 2', 2''...Dice.

Claims (1)

[Claims] 1. In the double pipe manufacturing method described above, in which an inner pipe having a cross-sectional area smaller than the inner cross-sectional area of the outer pipe is inserted into the outer pipe, and then a pipe expansion pressure is applied to the inner pipe to tighten the inner pipe to the outer pipe. A die with an inner circumference longer than the abutting circumference of the outer tube is inserted into the outer tube, and an inner tube is inserted into the outer tube. Expansion pressure is applied to the inner tube in advance so that the outer circumference of the inner tube is outside. After plastically deforming the tube for a length longer than the inner circumference, the pressure application is stopped and the die is taken out.
A double tube manufacturing method characterized in that the tube expansion pressure is then applied again to tightly fit the inner tube to the inner surface of the outer tube.