JPH0257454B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for manufacturing a double-layer bent pipe for use in various piping systems, and particularly to a method for bending a straight double-layer pipe. [Prior Art] In recent years, there has been a rapid increase in demand for high-frequency bent pipes, which are extremely advantageous in terms of reliability and cost reduction, by reducing welded joints as much as possible in place of elbow joints in chemical, nuclear, and thermal power plant piping. Against the above background, high alloy steel and non-ferrous metal pipes are used particularly for highly corrosive piping systems. However, since the cost of raw materials for such metal tubes is high and the manufacturing method is difficult, two-layer tubes such as clad tubes having a two-layer cross section made of different metals on the inside and outside have been put into practical use. Generally speaking, there are many double-layer tubes that use carbon steel for the outer tube and stainless steel, nickel alloy, titanium, etc. for the inner tube, but recently, double-layer tubes that use a zirconium alloy for the outer tube and pure zirconium for the inner tube are becoming popular. There is also. A conventional method for manufacturing a bent pipe with a double-layer structure is to manufacture a straight pipe with a double-layer structure such as a clad pipe in which an outer pipe and an inner pipe are joined together in advance, and then subject the straight pipe to high-frequency bending. That is, by locally heating a straight two-layer tube in an annular manner using a high-frequency inductor, by moving the heating section in the axial direction of the tube, and at the same time continuously applying a bending moment to the heating section. This is a method of sequentially bending the two-layer pipe by plastically deforming the heating section. [Problems to be solved by the invention] However, when manufacturing bent pipes using the conventional bending method, not only the outer pipe but also the inner pipe become hot, and both the outer pipe and the inner pipe become hot during the heating and cooling process. expansion,
When shrinking, a peeling phenomenon occurs due to the difference in expansion coefficients between the inner tube and the outer tube, resulting in a gap between the outer tube and the inner tube of the bent tube. Furthermore, even in a double-layered tube in which the inner tube and the outer tube are joined together in this way, peeling may occur during bending. There is a gap between the outer tube and the inner tube).
It is not possible to eliminate the gap between the inner tubes, and therefore, in practice, bending cannot be performed using this method. Furthermore, due to the heating during bending, the inner tube may reach a high temperature and the surface may oxidize, the temperature may rise to an unstable temperature and phase transformation may occur, precipitates such as carbides and nitrides may be formed, and foreign phases may occur. There was also a problem in that the corrosion properties could be impaired. The present invention has been made in view of such conventional problems.Whether it is a two-layered tube in which the inner tube and the outer tube are in close contact with each other, or a two-layered tube with a gap between the inner tube and the outer tube. An object of the present invention is to provide a method for bending two layers of a two-layered tube, which can be bent while bringing the inner tube and outer tube into close contact with each other. [Means for solving the problems] The present invention has been made to achieve the above object.
While locally heating a two-layer pipe with a two-layer cross section made up of different metals on the inside and outside,
In the method of sequentially bending the two-layer pipe by moving the heating part in the axial direction of the pipe and simultaneously continuously applying a bending moment to the heating part, the heating part is plastically deformed. During the bending process of the double-layered pipe, the inside of the double-layered pipe is filled with or flows, and the fluid is pressurized so that the inner pipe of the double-layered pipe is plastically deformed toward the outside, and the heating is performed immediately after heating. The gist of this invention is a method for bending a two-layer tube, which is characterized by cooling the outer tube from the outside and shrinking the outer tube inward. Hereinafter, the present invention will be explained in detail with reference to the drawings. 1 and 2 show an example of an apparatus used to carry out the double-layer pipe bending method of the present invention, in which 1 is a straight double-layer pipe to be bent, an outer pipe 11 and an inner pipe. It consists of 12. Double-layer pipe 1 used in the present invention
is not limited to a case in which the outer tube 11 and the inner tube 12 are joined metallurgically or mechanically;
2 may be inserted, with a slight gap between the two. 2 is a guide roller that supports and guides the two-layer tube 1; 3 is a soaking coil consisting of a high-frequency inductor having a cooling tank and a spray nozzle, which locally heats the two-layer tube 1 in an annular manner from its outer periphery; 4
is a rotatable bending arm equipped with a clamp 5 at the tip; 6 is a tube end support that supports the rear end of the two-layer tube 1 and pushes it in the direction of arrow A; and 7 is attached to the rear end of the two-layer tube 1. 8 is a fluid outlet attached to the tip of the double-layer tube 1. The fluid inlet 7 is connected to a pressurizing supply device (not shown) for supplying and pressurizing a fluid for internal pressure, such as water, into the double-layer tube 1, while the fluid outlet 8 is connected to A valve (not shown) to keep the inside of the double-layer pipe 1 under pressure
are connected. Reference numeral 9 indicates cooling water sprayed from the soaking coil 3, and reference numeral 10 indicates fluid filling the pipe. Next, a bending method of the present invention using the above-mentioned apparatus will be explained. The tip of the two-layer tube 1 is fixed to the clamp 5 of the bending arm 4, the rear end is fixed to the tube end support 6, and the tube is filled with fluid 10 from the fluid inlet 7 and pressurized. As a result, internal pressure due to the fluid 10 acts on the inner surface of the tube as shown by arrow B in FIG. Here, this internal pressure is selected so that the inner tube 12 is plastically deformed in the radial direction and brought into close contact with the inner surface of the outer tube 11. At this time, the fluid outlet 8 may be closed to leave the inside of the two-layer tube 1 filled with the fluid 10, or the fluid 10 may be allowed to flow inside the two-layer tube 1 by allowing an appropriate amount of fluid to flow out. It may be set as a state. With the internal pressure of the internal fluid 10 acting on the inner surface of the double-layered pipe 1, the double-layered pipe 1 is locally heated to a high temperature by the soaking coil 3, and cooling water 9 is injected into the vicinity, and at the same time, the double-layered pipe 1 in the direction shown by arrow A. As a result, the part of the double-layered pipe 1 indicated by the hatched double-dashed line is heated in an annular manner, and the bending moment by the bending arm 4 acts on this heated part, so that this heated part plastically deforms and curves. Immediately after that, the heating section is cooled by the cooling water 9 and no longer undergoes plastic deformation. In this way, the straight two-layer pipe 1 is continuously bent. [Function] In the above bending process, when the two-layer pipe 1 is locally heated by the soaking coil 3, the heated part expands and expands in diameter, but is then cooled by the cooling water 9. As a result, it contracts and becomes smaller in diameter. now,
As shown in FIG. 4, when the two-layer tube 1 is not filled with any pressurizing fluid and therefore bent without applying internal pressure, the outer tube 11, the inner tube 1
Both the outer tube 11 and the inner tube 12 are heated to a high temperature and then cooled, and both the outer tube 11 and the inner tube 12 expand and contract. However, due to differences in the heating rate and cooling rate of the outer tube and the inner tube, as well as differences in linear expansion coefficients, the amount of expansion and contraction differs, and as a result, even if the outer tube 11 and the inner tube 1
Even if it is a two-layer tube with a structure in which the outer tube 1 and the outer tube 1 are in close contact with each other,
1 and the inner tube 12 may peel off, creating a gap 13 between them. However, in the present invention, as shown in FIG. 3, internal pressure is applied by the fluid 10 filled inside, so even if the double-layered pipe 1 has a gap between the outer pipe 11 and the inner pipe 12, Also, the inner tube 12 is deformed and pressed against the inner surface of the outer tube 11 in the straight tube section before heating, and the inner tube is thermally expanded due to the diameter expansion of the outer tube 11 in the heating section directly below the soaking coil 3. Even if the diameter expansion is small, the inner tube 12 is plastically deformed and comes into close contact with the inner surface of the outer tube 11. Furthermore, by cooling with the cooling water 9 immediately after that, the outer tube 11 thermally contracts and its diameter decreases, but the inner tube 12 does not contract much in diameter because it is under internal pressure.
2. It attaches more firmly. Thus, the outer tube 11
A bent tube with a two-layer structure in which the inner tube 12 and the inner tube 12 are tightly bonded is manufactured. Furthermore, the manufactured double-layer bent pipe is
The structure is such that the outer tube is tightly attached to the outer surface of the inner tube by reducing its diameter, so the inner tube is tightened by the outer tube.
Therefore, compressive residual stress is generated on the inner tube surface. This compressive residual stress is highly effective in preventing stress corrosion cracking. Further, by bending the double-layered tube 1 while applying pressure from the inside, there is also an effect of minimizing changes in the shape of the bent tube, that is, ovalization, caused by ordinary high-frequency bending. Above we have explained the effect of bending while applying internal pressure using the fluid inside the pipe, but the fluid that fills or flows inside the pipe can be used not only for applying internal pressure but also for cooling the inner pipe. . That is, by appropriately adjusting the temperature and flow rate of the fluid 10 supplied into the tube, the temperature of the inner tube 12 can be adjusted to a desired temperature lower than that of the outer tube 11. Cooling the inner tube 12 suppresses the temperature rise of the inner tube 12 during heating by the soaking coil 3, thereby preventing oxidation, structural changes, etc. on the inner surface of the inner tube. As mentioned above, most double-layer tubes are made of carbon steel for the outer tube and stainless steel, nickel alloy, titanium, etc. for the inner tube, but recently, the outer tube is made of zirconium alloy and the inner tube is made of pure metal. There are also double-layered zirconium tubes. When these inner tubes reach high temperatures of about 400°C or higher, precipitates and foreign phases are generated, which increases their susceptibility to pitting corrosion, intergranular corrosion, stress corrosion cracking, etc., and also promotes oxidation, resulting in poor corrosion resistance. For this reason, the inner pipe 12 is
It is preferable that the temperature of the inner tube is maintained at a temperature at which oxidation and structural changes do not occur, for example, 400° C. or lower, even in the heating section. In the above explanation, the internal pressure applied during the bending process was described as a pressure that can plastically deform the inner tube 12 in the straight tube portion before heating and bring it into close contact with the inner surface of the outer tube 11. However, the present invention is not limited to this case. The internal pressure applied to the inner tube is at least to the extent that the inner tube can be plastically deformed so that the inner tube is brought into close contact with the inner surface of the outer tube 11 after its diameter is reduced by cooling with the cooling water 9 immediately after heating. That's fine. Further, the fluid used to apply internal pressure to the inner tube is not necessarily limited to a liquid such as water, but may be a gas. [Example] Next, an example of the present invention will be described. The following processing was performed using the high frequency bending apparatus shown in FIG.

[Table] Bending radius: 1365mm (5D: D is the outer diameter) Bending propulsion speed: 1mm/S Cooling method: External spray water cooling Fluid supply into the pipe during bending: (1) None (Comparative example I) (2) No-pressure water flow (comparative example,
) (3) 50Kg/ ^cm2 water pressure (Example I) (4) 70Kg/ ^cm2 water pressure (Example) Bending was performed under the above conditions, and the outer surface temperature (℃) and inner tube thickness were Measure the temperature (℃) at the center, and measure the maximum gap (mm) between the outer tube and the inner tube, the aspect ratio (%), and the inner surface residual stress (Kg/mm ² ) of the obtained bent tube. The results shown in Table 1 were obtained. As shown in Table 1, when no internal pressure was applied during bending of the mechanically joined two-layer pipe in Comparative Example I, a gap was generated between the outer pipe and the inner pipe. In contrast, water pressure
Example I of the present invention, which was subjected to bending while applying 50 kg/cm ² , showed excellent values in inner tube temperature, peelability, aspect ratio, and residual stress. Further, in the case of rolled clad steel pipes, no peeling phenomenon occurred even in the conventional bending process without fluid supply in the pipe in the comparative example, but this cannot be said to be sufficient in terms of shape and residual stress. Both the treated products of the comparative example and the example have the performance as curved pipes, but the water pressure is 70 kg/cm ²
The example in which the bending process was carried out by bending was superior in both shape and residual stress value.

〔Effect of the invention〕

As explained above, in the present invention, fluid is supplied into the double-layered tube and bending is performed while applying internal pressure, so there is no separation between the outer tube and the inner tube. It is possible to manufacture a two-layered tube in which the two are tightly adhered and the inner tube has compressive residual stress. Moreover, when bending a double-layer pipe, the outer pipe and inner pipe do not need to be firmly joined; even if there is a slight gap, it is possible to bring them into close contact during the bending process. It is possible to reduce the manufacturing cost of bent pipes. Note that by cooling the inner tube with the fluid inside the tube during bending, oxidation and structural changes in the inner tube can be suppressed, and a two-layer tube with good corrosion resistance can be manufactured.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an example of a high-frequency bending device used to carry out the method of the present invention, FIG. 2 is a cross-sectional view of a main part showing a state in which bending is performed using the device shown in FIG. 1, and FIG. FIG. 4 is a cross-sectional view of a main part explaining bending by a conventional method. DESCRIPTION OF SYMBOLS 1... Double layer pipe, 2... Guide roller, 3... Soaking coil, 4... Bending arm, 5... Clamp, 6... Tube end support stand, 7... Fluid inlet, 8... Fluid outlet, 9... Cooling water, 10... Fluid, 11...outer tube, 12...inner tube.

Claims (1)

[Scope of Claims] 1. A two-layer tube having a cross section of two layers made of different metals inside and out, while locally heating it in an annular shape, moving the heating section in the axial direction of the tube, At the same time, in the method of sequentially bending the two-layer pipe by plastically deforming the heating part by continuously applying a bending moment to the heating part, during the bending process of the two-layer pipe, the inside of the two-layer pipe is The inner tube of the two-layer tube is filled with or flows fluid, and the fluid is pressurized so that the inner tube of the two-layer tube is plastically deformed toward the outside.The heating section immediately after heating is cooled from the outside, and the outer tube is turned inward. A method for bending a double-layered pipe, characterized by shrinking it as it approaches. 2. The method for bending a two-layered tube according to claim 1, characterized in that the temperature of the inner surface of the inner tube is maintained at a lower temperature than that of the outer tube by a fluid that is filled or made to flow inside the two-layered tube. . 3. Bending a double-layered pipe according to claim 2, characterized in that during the bending process, the temperature of the inner surface of the inner tube is maintained at 400° C. or lower to prevent oxidation of the inner surface of the inner tube and deterioration of the structure. Processing method.