JPH0127805B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Application> The disclosed technology belongs to the technical field of manufacturing by expanding corrosion-resistant double pipes used for oil country tubular goods and the like.

<Summary of the gist> Therefore, the present invention is directed to a tube expansion medium such as liquid stored in the inner tube by inserting and layering an inner tube made of stainless steel or the like into an outer tube made of carbon steel or the like. This invention relates to a method for manufacturing a double pipe, in which the inner pipe is expanded in diameter and yielded by applying a pipe expansion force to the inner pipe, and the inner pipe is plastically deformed to tighten the two pipes. A tube expansion medium such as liquid is stored in the inner tube and sealed either before or after the outer tube is layered relative to the outer tube whose diameter has been increased by heating in advance,
With the inner tube inserted and set into the outer tube, compressive force is applied in the axial direction of the inner tube, compressing the inner tube in the axial direction and expanding it in the radial direction, compressing the inner tube in both the circumferential and axial directions. It is integrated with the outer tube to form residual stress and yielded, plastically deformed and bonded, then both tubes are brought to room temperature, the outer tube is naturally cooled and reduced in diameter, and the inner tube is naturally heated and increased in diameter. The invention also relates to a double pipe manufacturing method in which the expansion medium is removed by axial compressive force.

<Prior art> As is well known, many of the transport pipes used in oil country tubular goods, nuclear power plant piping, etc. are used to transport corrosive fluids, and these types of pipes have not only high pressure resistance and heat resistance. Therefore, it is important that the material also has corrosion resistance.

To deal with this, techniques such as layering a carbon steel outer tube with a stainless steel inner tube to provide corrosion resistance and use it as a double tube have been developed to provide pressure and heat resistance functions. Although widely adopted,
From the viewpoint of preventing cracking and implosion during operation, tight fitting of both pipes has become desirable, for example, the generally known hydraulic pipe expansion method or the applicant's many recently developed inventions. Heat expansion methods have been developed.

<Problems to be solved by the invention> By the way, as shown in FIG.
When a tube expansion force F such as water pressure is applied to the inner tube 2 inserted into the inside of the tube, it will contract in the axial direction by the increased diameter. Normally, if the inner tube 2 is allowed to shrink in the axial direction,
There is a drawback that it is difficult to seal 3 at the end of the tube.

Therefore, if the end of the inner tube 2 is made to protrude from the outer tube 1 by the amount of contraction, the contraction amount 4 will swell in the radial direction at the initial stage of tube expansion, which has the disadvantage of interfering with axial contraction. However, in order to prevent this, a complicated device is required, resulting in high cost and troublesome management.

Furthermore, when the inner tube 2 is expanded while restraining both ends thereof, tensile residual stress is generated in the inner tube 2, which causes so-called stress corrosion cracking during operation.

Therefore, as shown in Fig. 2, the axial stress σ _A is plotted on the horizontal axis,
If the vertical axis is the circumferential stress σ _H and the yield stress of the material is σ _Y , the yield condition is expressed as σ _Y = σ _A ² + σ _H ² −σ _A σ _H , and the descending condition curve is As shown in the figure, point P in the first quadrant indicates axial tension expansion because the axial stress σ _A is positive, and the yield stress S in the circumferential direction is extremely large, resulting in a significantly large expansion force. This requires a large amount of power, and the elastic return is also large, which is disadvantageous in that the fitting stress is reduced.

<Objective of the Invention> The object of the present invention is to solve the problems of the method for manufacturing a double-pipe tube using the tube expansion method based on the above-mentioned prior art, and to solve the problem by sealing an expansion medium such as a liquid inside the inner tube so that the tube expands in the axial direction. Applying compressive force to actively reduce the diameter of the inner tube in the axial direction while increasing the diameter of the inner tube to lower the yield stress in the circumferential direction, making it easier to expand the tube and reducing elastic return. It is an object of the present invention to provide an excellent double pipe manufacturing method which is beneficial to piping technology applications in various industries by imparting compressive residual stress in the axial direction to obtain a high degree of fit without stress corrosion cracking.

<Means/effects for solving the problem> In order to solve the above-mentioned object and the scope of the above-mentioned claims as a gist, the structure of the present invention is to provide an inner tube whose diameter is reduced by cooling in advance and which is not longer than the outer tube. Before or after layering the inner tube relative to the outer tube whose diameter has been increased by heating in advance, liquid or a tube expansion medium such as hard rubber is stored in the inner tube to seal the inner tube. An axial compressive force is applied to both ends of the inner tube housed inside to compress the inner tube, expand the tube, integrate both tubes, and expand the tube through axial pressure to reduce the yield stress and cause it to yield. , After being plastically deformed, the outer tube is heated at room temperature, and the diameter of the outer tube is naturally reduced by cooling, and the inner tube is naturally heated and increased in diameter, and the compressive force in the axial direction is removed, and then the inner tube is opened and expanded. By removing the medium, the elastic return of the inner tube is made smaller than that of the outer tube, providing a high degree of fit, and compressive residual stress is formed in both the circumferential and axial directions to prevent stress corrosion cracking during operation. This was achieved by taking technical measures to

<Example> Next, an example of the present invention will be described below with reference to FIG. 2 and the drawings from FIG. 3 onwards. Note that parts having the same features as those in FIGS. 1 and 2 will be described with the same reference numerals.

First, to explain the principle of this invention, the axial stress σ _A (horizontal axis) and circumferential stress σ _H (vertical axis) shown in FIG.
In the yield condition curve, point R in the second quadrant indicates axial compression tube expansion because the axial stress σ _A is negative, and circumferential yield stress S' indicates the axial tension tube expansion in the first quadrant (point P). It is significantly smaller than that of S, therefore, the tube expansion force is also small, and the elastic return is also small, so that a high fitting force can be obtained.

This invention applies this principle and utilizes the so-called thermal tube expansion method, which is the basic invention of the applicant's earlier application.First, as shown in FIG. A cap 7 is hermetically plugged into one end of the threaded portions 5, 5 at both ends via a sealing material 6, and filled with water 8 as a tube expansion medium.Then, as shown in FIG. 4, a cap 7' is attached to the other end. The container is sealed with a seal 6 and kept in a water-cooled state, for example, by immersing it in a tap water pool or the like.

As shown in FIG. 5, the outer tube 1 made of carbon steel is heated separately in advance with a heater 9 to increase its diameter.
Insert the inner tube 2 in which the cooled expansion medium water 8 resides.

The inner tube 2 is designed and set so that the length of the inner tube 2 is not longer than the outer tube 1 in the inserted state, that is, so that both ends of the inner tube 2 do not protrude from the outer tube 1.

Therefore, after setting, as shown in FIG. 6, compression rods 10, 10' connected to a predetermined pressing device such as a hydraulic jack (not shown) are immediately brought into contact with the caps 7, 7' at both ends of the inner tube 2. As shown in FIG. 6, the inner tube 2 is compressed in the axial direction and is expanded by applying a tube expansion force F due to the radial expansion of the compressible fluid water 8.
The diameter increases according to the stress strain curve.

However, as shown in FIG. 2, this tube expansion means expands the inner diameter 2 by compressing it in the axial direction, so the yield stress in the circumferential direction σ _H is small, and it yields early, contacts the outer tube 1, and is set. The outer tube 1 increases in diameter and plastically deforms to the same diameter as the outer tube 1.

After the tube has been expanded to the set diameter, heating by the heater 9 is stopped, and as shown in FIG.
When removed, both tubes 1 and 2 elastically contract in diameter, but even though the elastic return of the inner tube 2 is small, the elastic return of the outer tube 1 is large. The inner tube 2 is naturally cooled and reduced in diameter, and the inner tube 2 is naturally heated and increased in diameter, and together, a significantly large degree of fitting is obtained and a strong self-tightening double tube 11 is obtained.

In addition, as mentioned above, in the manufacturing process of the self-stressing double pipe 11, compressive residual stress is formed not only in the circumferential direction of the inner pipe 2 but also in the axial direction due to the axial compressive force. So-called stress corrosion cracking does not occur.

In the above embodiment, water was used as the tube expansion medium, but as shown in FIG. 8, hard rubber 8' was used instead of water.
You can also use

It goes without saying that the embodiments of the present invention are not limited to the above-mentioned embodiments; for example, various embodiments can be adopted, such as using a tube expansion medium containing water or oil in the inner tube. be.

In addition to the above-mentioned thermal tube expansion method, tube expansion at normal temperatures can also be used as the tube expansion means.

<Effects of the Invention> As described above, according to the present invention, in the double pipe manufacturing method by pipe expansion and tightening, the inner pipe, which has been previously cooled and reduced in diameter with respect to the outer pipe, is layered relative to the outer pipe, which has been heated and increased in diameter, either before or after. By sealing and storing a tube expansion medium such as water or rubber inside the tube, and then applying compressive force from the axial direction to the inner tube set inside the outer tube, basically the outer tube is Relative stacking of the inner tube to the outer tube can be carried out smoothly, and axial compression expansion is possible. Therefore, the yield stress can be reduced, and the elastic return can also be reduced, which reduces the elastic return of the outer tube. This provides an excellent effect of obtaining a large degree of fitting.

Further, since compressive residual stress is applied to the inner tube in both the circumferential direction and the axial direction, an excellent effect is achieved in that stress corrosion cracking does not occur on the entire surface of the joint between the two tubes during operation.

As mentioned above, since the yield stress of the inner tube is small, the tube expansion power is small, the cost is low, and the device can be small and easy to manage.

Furthermore, since the tube expansion pressure can be applied within the outer tube, there is no need to consider measures against swelling at the end of the inner tube, which also has the effect of simplifying the tube expansion operation.

Furthermore, since the tube expansion medium can be sealed, there is no need to manage the pressure from outside the system, and by using a cartridge type, it is easy to set and reset the tube expansion medium, and it is easy to remove. There is no need to dispose of it, and work efficiency is significantly improved.
Excellent effects are achieved which are also beneficial in terms of pollution prevention.

When both tubes are plastically deformed, by returning them to room temperature, the diameter of the outer tube is reduced by natural cooling, and the diameter of the inner tube is increased by natural temperature rise, making it possible to better demonstrate the fastening condition of both tubes. The effect is produced.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a double tube expansion manufacturing method based on the prior art, FIG. 2 is a graph of axial stress and circumferential stress yield conditions, and FIG. 3 and the following are explanatory diagrams of embodiments of the present invention. Figures 3 and 4 are cross-sectional views of the inner tube of one embodiment in which the expansion medium is stored, Figure 5 is a layered cross-sectional view of the inner tube and the outer tube, Figure 6 is a cross-sectional view of the expanded tube, and Figure 7
The figure is a cross-sectional view of the double pipe after pipe expansion is completed, and FIG. 8 is a cross-sectional view of another embodiment corresponding to FIG. 5. 1... Outer tube, 2... Inner tube, 8, 8'... Tube expansion medium, F... Tube expansion force.

Claims (1)

[Claims] 1. In a double pipe manufacturing method in which a pipe expansion medium is stored in an inner pipe layered relative to an outer pipe, and in this state, a pipe expansion force is applied to the inner pipe to increase the diameter of the inner pipe and connect the inner and outer pipes, the above-mentioned inner pipe is putting the tube in a cooling state, storing a tube expansion medium in the inner tube, and sealing both ends of the inner tube;
The inner tube is layered relative to the outer tube, which has been heated in advance to increase its diameter, and then compressive force in the axial direction is applied to the inner tube, the inner tube is expanded in diameter and integrated with the outer tube, and the inner tube is compressed in the circumferential and axial directions. Both tubes are yielded and plastically deformed so as to generate stress, then both tubes are returned to room temperature, the outer tube is naturally cooled and knitted, the inner tube is raised and lowered naturally to increase its diameter, and the compressive force in the axial direction is A method for manufacturing a double-walled tube, characterized in that the application of the above-mentioned tube expansion medium is removed after the application of the above-mentioned tube expansion medium is removed.