Multilayer pipe system and joining method

Abstract

To provide a multilayer pipe system and a joining method that are able to inhibit deterioration of thermal insulation.SOLUTION: A multilayer pipe system 100 includes: a first multilayer pipe 10 comprising a first inner pipe 11 and a first outer pipe 12 into which the first inner pipe 11 is inserted; and a second multilayer pipe 20 comprising a second inner pipe 21 and a second outer pipe 22 into which the second inner pipe 21 is inserted. An end of the first inner pipe 11 protrudes from an end of the first outer pipe 12, and an end of the second inner pipe 21 protrudes from an end of the second outer pipe 22. The end of the first inner pipe 11 and the end of the second inner pipe 21 are joined together.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a multi-pipe system and a joining method. [Background technology]

[0002] There is a multi-pipe system that includes an outer pipe and an inner pipe disposed inside the outer pipe, and that provides thermal insulation between the outer pipe and the inner pipe by creating a vacuum between the outer pipe and the inner pipe. For example, Patent Document 1 discloses a technique for maintaining a superconducting state by disposing a superconducting conductor inside an insulated inner tube as described above. In Patent Document 1, the multi-tube is bent in order to transport a long multi-tube system to an installation site. Then, at the installation site, the multi-tube is unbent and flattened. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7098037 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional technology, the inner and outer tubes are reduced in diameter by bending and unbending the multi-walled tube, which may result in a problem that the heat insulating radiation layer provided around the inner tube is compressed, resulting in a decrease in heat insulating properties.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a multi-pipe system and a joining method capable of suppressing a decrease in thermal insulation properties. [Means for solving the problem]

[0006] <1> A multi-pipe system according to a first aspect of the present invention is a multi-pipe system comprising a first multi-pipe including a first inner pipe and a first outer pipe into which the first inner pipe is inserted, and a second multi-pipe including a second inner pipe and a second outer pipe into which the second inner pipe is inserted, wherein the first outer pipe and the second outer pipe are steel pipes, an end of the first inner pipe protrudes from an end of the first outer pipe, an end of the second inner pipe protrudes from an end of the second outer pipe, and the end of the first inner pipe and the end of the second inner pipe are joined in a state in which the end of the first inner pipe protrudes from the end of the first outer pipe and the end of the second inner pipe protrudes from the end of the second outer pipe.

[0007] According to the first aspect, the multi-pipe system includes a first multi-pipe and a second multi-pipe. In other words, the first multi-pipe and the second multi-pipe are joined together at an installation site or the like to form a multi-pipe system. This makes it possible to transport a long multi-pipe in a bent state and then bend it back into a straight line at an installation site or the like, thereby preventing a decrease in the heat insulating properties due to deformation of the heat-resistant radiation layer caused by the diameter reduction of the pipe. Here, when a long multi-pipe system is constructed with one outer pipe and one inner pipe, problems occur such as increased frictional resistance when inserting the inner pipe into the outer pipe, and bending of the outer pipe or inner pipe due to friction, making the work difficult. By constructing a multi-pipe system by joining multiple multi-pipes at installation locations, etc., as described above, the occurrence of the above problems can be suppressed.

[0008] In addition, the end of the first inner pipe protrudes from the end of the first outer pipe, and the end of the second inner pipe protrudes from the end of the second outer pipe. This makes it possible to prevent the first outer pipe and the second outer pipe from being positioned around the end of the first inner pipe and the second inner pipe when the ends of the first inner pipe and the second inner pipe are butted against each other. In this state, the end of the first inner pipe and the end of the second inner pipe are joined. Therefore, the joining operation of the first inner pipe and the second inner pipe can be easily performed from the outside of the first inner pipe and the second inner pipe. In addition, for example, when welding the first inner pipe and the second inner pipe, the welding operation and the repair operation when a welding defect occurs can be easily performed.

[0009] <2> A multi-pipe system according to a second aspect of the present invention is characterized in that in the multi-pipe system according to the first aspect, the first inner pipe and the second inner pipe are steel pipes.

[0010] <3> A multi-tube system according to aspect 3 of the present invention is characterized in that, in the multi-tube system according to aspect 1 or aspect 2, the length of the first inner tube is longer than the length of the first outer tube, and the length of the second inner tube is shorter than the length of the second outer tube.

[0011] According to the third aspect, the length of the first inner tube is longer than the length of the first outer tube. As a result, when the positions of one end of each of the first inner tube and the first outer tube are aligned, the other end of the first inner tube protrudes from the other end of the first outer tube. Therefore, the first multi-layer pipe and the second multi-layer pipe can be joined in a state in which the positions of the first inner tube and the first outer tube are aligned in advance. This makes it unnecessary to align the first inner tube and the first outer tube after joining, thereby improving workability.

[0012] Furthermore, the length of the second inner tube is equal to or shorter than the length of the second outer tube. For example, when the length of the second inner tube is shorter than the length of the second outer tube, the difference in length between the second inner tube and the second outer tube is set to be the same as the difference in length between the first outer tube and the first inner tube, so that when the first multiple tube and the second multiple tube are joined, the combined length of the first inner tube and the second inner tube can be made the same as the combined length of the first outer tube and the second outer tube. This makes it possible to improve workability by eliminating the need to adjust the lengths and positions of the inner tube and the outer tube in a multiple tube system in which the first multiple tube and the second multiple tube are joined.

[0013] Furthermore, for example, if the length of the second inner tube is the same as the length of the second outer tube, when the first multi-layer tube and the second multi-layer tube are joined, the end of the second inner tube opposite the side joined to the first inner tube protrudes from the end of the second outer tube opposite the side joined to the first outer tube. This makes it easier to join more multi-layer tubes in addition to the first and second multi-layer tubes. This makes it easier to make a multi-tube system longer.

[0014] <4> A multi-tube system according to aspect 4 of the present invention is characterized in that, in the multi-tube system according to aspect 3, the difference between the length of the second inner tube and the length of the second outer tube corresponds to the length by which the end of the first inner tube protrudes from the end of the first outer tube.

[0015] According to aspect 4, the difference between the length of the second inner tube and the length of the second outer tube corresponds to the length by which the end of the first inner tube protrudes from the end of the first outer tube. This makes it possible to make the combined length of the first inner tube and the second inner tube the same as the combined length of the first outer tube and the second outer tube when the first multi-layer tube and the second multi-layer tube are joined together. This eliminates the need to adjust the lengths and positions of the inner tube and the outer tube in a multi-tube system in which the first multi-layer tube and the second multi-layer tube are joined together, thereby improving workability.

[0016] <5> A multi-pipe system according to aspect 5 of the present invention is characterized in that, in the multi-pipe system according to any one of aspects 1 to 4, the end of the first inner pipe and the end of the second inner pipe are welded.

[0017] According to the fifth aspect, the end of the first inner pipe and the end of the second inner pipe are welded together. This allows the outer circumferential surface of the connection between the first inner pipe and the second inner pipe to be flatter than when the end of the first inner pipe and the end of the second inner pipe are joined together by a flange or a ferrule. This allows the inner diameters of the first outer pipe and the second outer pipe to be smaller. Therefore, for example, the outer diameter of the outer pipe can be reduced to make the multi-pipe system more compact.

[0018] <6> A multi-tube system according to a sixth aspect of the present invention is characterized in that, in the multi-tube system according to the fifth aspect, a supply tube is provided on the outer surface of the second inner tube for supplying a back shielding gas to an end of the second inner tube.

[0019] According to the sixth aspect, a supply tube is provided on the outer circumferential surface of the second inner pipe to supply a back shielding gas to the end of the second inner pipe. This allows the back shielding gas to be supplied between the first and second inner pipes and the first and second outer pipes in the vicinity of the joint when the first and second outer pipes are joined. This makes it possible to prevent welding defects caused by poor shielding from occurring at the joint between the first and second outer pipes.

[0020] <7> A multi-pipe system according to aspect 7 of the present invention is characterized in that, in the multi-pipe system according to any one of aspects 1 to 6, the system further comprises a first insulating material and a second insulating material, wherein a first heat-resistant radiation layer is provided on the outer peripheral surface of the first inner pipe, the first insulating material is provided between the first outer pipe and the first heat-resistant radiation layer, and is provided at a predetermined interval in the tube axis direction of the first inner pipe, and a second heat-resistant radiation layer is provided on the outer peripheral surface of the second inner pipe, and the second insulating material is provided between the second outer pipe and the second heat-resistant radiation layer, and is provided at a predetermined interval in the tube axis direction of the second inner pipe.

[0021] According to aspect 7, a first heat-resistant radiation layer and a second heat-resistant radiation layer are provided on the outer circumferential surfaces of the first inner tube and the second inner tube, respectively. Furthermore, a first insulating material is provided between the first outer tube and the first heat-resistant radiation layer, and a second insulating material is provided between the second outer tube and the second heat-resistant radiation layer. This makes it possible to more reliably suppress heat conduction from the outer tube to the inner tube, for example, when insulating the space between the inner tube and the outer tube in a multi-pipe system, after creating a vacuum state between the inner tube and the outer tube. The first and second insulating materials are provided at a predetermined interval in the pipe axis direction of the first and second inner pipes, respectively. This allows the position of the outer pipe relative to the inner pipe to be constant throughout the pipe axis direction of the multi-pipe system. Furthermore, by making the first and second insulating materials function as guides, it is possible to facilitate the work of inserting the first inner pipe into the first outer pipe and the work of inserting the second inner pipe into the second outer pipe.

[0022] <8> A multi-tube system according to aspect 8 of the present invention is characterized in that, in the multi-tube system according to any one of aspects 1 to 6, a first heat-resistant radiation layer is provided on the outer peripheral surface of the first inner tube, a second heat-resistant radiation layer is provided on the outer peripheral surface of the second inner tube, a first protrusion protruding toward the tube axis of the first outer tube is formed on the inner peripheral surface of the first outer tube, and the first protrusion is formed continuously along the tube axis direction of the first outer tube, and a second protrusion protruding toward the tube axis of the second outer tube is formed on the inner peripheral surface of the second outer tube, and the second protrusion is formed continuously along the tube axis direction of the second outer tube.

[0023] According to aspect 8, the first inner tube and the second inner tube are provided on their outer circumferential surfaces with a first heat-resistant radiation layer and a second heat-resistant radiation layer, respectively, which can suppress heat conduction from the outside to the first inner tube and the second inner tube. A first protruding portion protruding toward the tube axis of the first outer tube is formed on the inner circumferential surface of the first outer tube, and a second protruding portion protruding toward the tube axis of the second outer tube is formed on the inner circumferential surface of the second outer tube. As a result, when the first inner tube is inserted into the first outer tube, only the first protruding portion contacts the first heat-resistant radiation layer provided on the first inner tube. Also, when the second inner tube is inserted into the second outer tube, only the second protruding portion contacts the second heat-resistant radiation layer provided on the second inner tube. Therefore, for example, when insulating the space between the inner tube and the outer tube in a multiple tube system, the space between the inner tube and the outer tube is made into a vacuum state, and then heat conduction from the outer tube to the inner tube can be further suppressed. Moreover, the first protrusion and the second protrusion are formed continuously along the tube axis direction of the first outer tube and the second outer tube, respectively. This allows the position of the outer tube relative to the inner tube to be constant along the tube axis direction of the multi-tube system. Furthermore, by making the first protrusion and the second protrusion function as guides, it is possible to facilitate the relative movement of the first inner tube and the first outer tube, and the second inner tube and the second outer tube, in the tube axis direction of the multi-tube system. This makes it easier to insert the first inner tube into the first outer tube, and the second inner tube into the second outer tube.

[0024] <9> A ninth aspect of the present invention relates to a joining method for a multi-pipe system including a first multi-pipe including a first inner pipe and a first outer pipe into which the first inner pipe is inserted, and a second multi-pipe including a second inner pipe and a second outer pipe into which the second inner pipe is inserted, wherein an end of the first inner pipe protrudes from an end of the first outer pipe and an end of the second inner pipe protrudes from an end of the second outer pipe, the method including an inner pipe protrusion joining step in which the end of the first inner pipe protruding from the end of the first outer pipe and the end of the second inner pipe protruding from the end of the second outer pipe are butted together. the inner pipe butting process; an inner pipe joining process for joining the end of the first inner pipe and the end of the second inner pipe that have been butted together in the inner pipe butting process; an outer pipe butting process for butting the end of the first outer pipe and the end of the second outer pipe by moving the second outer pipe in the axial direction of the second outer pipe; and an outer pipe joining process for joining the end of the first outer pipe and the end of the second outer pipe that have been butted together in the outer pipe butting process, wherein the inner pipe joining process and the outer pipe joining process are performed at a location where the multiple pipe system is laid.

[0025] According to the ninth aspect, when joining the first and second multi-layer pipes, the first and second inner pipes are joined in the inner pipe joining step, and then the first and second outer pipes are joined in the outer pipe joining step. In other words, a plurality of prefabricated multi-layer pipes are joined at the installation site of the multi-layer pipe system. This makes it possible to facilitate the installation work and shorten the work time when installing a long multi-layer pipe system, as compared with the case where a long inner pipe is inserted into a long outer pipe at the installation site. In addition, it is possible to prevent the reduction in diameter of the pipe caused by transporting the long multi-layer pipe in a bent state and bending it back into a straight line at the installation site, and the deterioration of the heat insulating property caused by the deformation of the heat-resistant radiation layer due to the reduction in diameter of the pipe.

[0026] <10> The joining method of aspect 10 of the present invention is characterized in that, in the joining method of aspect 9, it further comprises an installation process of providing a heat-resistant radiation layer on the end of the first inner tube and the end of the second inner tube after the inner tube joining process and before the outer tube butting process.

[0027] Here, if a heat-resistant radiation layer is provided on the end of the first inner pipe and the end of the second inner pipe before the inner pipe joining step, the heat-resistant radiation layer interferes with the operation of the inner pipe joining step. According to aspect 10, the installation step of providing a heat-resistant radiation layer on the end of the first inner pipe and the end of the second inner pipe is performed after the inner pipe joining step and before the outer pipe butting step. In other words, the end of the first inner pipe and the end of the second inner pipe are not provided with a heat-resistant radiation layer during the inner pipe joining step. This makes it possible to suppress the heat-resistant radiation layer from interfering with the inner pipe joining step. In addition, after the first multi-layer pipe and the second multi-layer pipe are joined, a heat-resistant radiation layer is provided at the joint between the end of the first inner pipe and the end of the second inner pipe, so that in the multi-pipe system, heat conduction from the outer pipe to the inner pipe due to radiant heat or the like can be suppressed.

[0028] <11> The joining method of aspect 11 of the present invention is characterized in that, in the joining method of aspect 9, it further includes an installation process of providing a heat-resistant radiation layer and an insulating material on the end of the first inner pipe and the end of the second inner pipe after the inner pipe joining process and before the outer pipe butting process.

[0029] According to the eleventh aspect, the installation step of providing a heat-resistant radiation layer and a heat insulating material on the end of the first inner pipe and the end of the second inner pipe is performed after the inner pipe joining step and before the outer pipe butting step. In other words, the end of the first inner pipe and the end of the second inner pipe are not provided with a heat-resistant radiation layer and a heat insulating material during the inner pipe joining step. This makes it possible to suppress the heat-resistant radiation layer and the heat insulating material from interfering with the work of the inner pipe joining step. In addition, after the first multi-layer pipe and the second multi-layer pipe are joined, the heat-resistant radiation layer and the heat insulating material are provided at the joint between the end of the first inner pipe and the end of the second inner pipe, so that in the multi-pipe system, heat conduction from the outer pipe to the inner pipe due to radiant heat or the like can be suppressed. In addition, by making the insulating material provided in the installation process function as a guide, the second outer pipe can be easily moved in the pipe axis direction of the second outer pipe in the outer pipe butting process, thereby improving workability.

[0030] <12> A joining method according to a twelfth aspect of the present invention is the joining method according to a ninth aspect, further comprising an inner pipe manufacturing process, an outer pipe manufacturing process, and a multi-pipe manufacturing process, wherein the first inner pipe and the second inner pipe are composed of a plurality of inner pipes for lengthening, and the first outer pipe and the second outer pipe are composed of a plurality of outer pipes for lengthening, and in the inner pipe manufacturing process, the first inner pipe and the second inner pipe are manufactured by joining the plurality of inner pipes for lengthening before the inner pipe butting process, and in the outer pipe manufacturing process, the first outer pipe and the second outer pipe are manufactured by joining the plurality of outer pipes for lengthening before the inner pipe butting process, and in the multi-pipe manufacturing process, a first heat-resistant radiation layer is disposed on the first inner pipe and inserted into the first outer pipe before the inner pipe butting process, to manufacture a first multi-pipe, and a second heat-resistant radiation layer is disposed on the second inner pipe and inserted into the second outer pipe, to manufacture a second multi-pipe.

[0031] According to aspect 12, the first inner pipe and the second inner pipe are manufactured in an inner pipe manufacturing process before the inner pipe butting process. The first outer pipe and the second outer pipe are manufactured in an outer pipe manufacturing process before the inner pipe butting process. This allows the lengths of the first inner pipe, the second inner pipe, the first outer pipe, and the second outer pipe to be the longest possible within a range that can be transported from a manufacturing factory to an installation site of the multi-pipe system, etc. This reduces the number of welding operations at the installation site of the multi-pipe system, etc., and shortens the time required for installation. Furthermore, by manufacturing the first multi-pipe and the second multi-pipe in advance in a multi-pipe manufacturing process before the inner pipe butting process, the amount of work at the installation site of the multi-pipe system, etc., can be reduced.

[0032] <13> A joining method according to aspect 13 of the present invention is characterized in that, in the joining method according to any one of aspects 9 to 12, it further comprises an inner pipe centering step of, after the inner pipe butting step, approximately aligning the pipe axis of the first inner pipe with the pipe axis of the second inner pipe, and an outer pipe centering step of, after the outer pipe butting step, approximately aligning the pipe axis of the first outer pipe with the pipe axis of the second outer pipe.

[0033] According to the thirteenth aspect, after the inner pipe butting step, the pipe axis of the first inner pipe is substantially aligned with the pipe axis of the second inner pipe by an inner pipe centering step. Also, after the outer pipe butting step, the pipe axis of the first outer pipe is substantially aligned with the pipe axis of the second outer pipe by an outer pipe centering step. This ensures the positional accuracy of the first inner pipe and the second inner pipe, and the first outer pipe and the second outer pipe. Effect of the Invention

[0034] According to the present invention, it is possible to provide a multi-pipe system and a joining method capable of suppressing a decrease in thermal insulation properties. [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 is a front view of a multi-pipe system according to a first embodiment. [Diagram 2] FIG. 2 is an exploded front view of the multi-pipe system according to the first embodiment. [Diagram 3] FIG. 3 is an enlarged view of part III shown in FIG. [Figure 4] FIG. 2 is a diagram showing a state before a first multi-layer pipe and a second multi-layer pipe are joined together. [Diagram 5] 13 is a modified example of a state after the first and second multiple pipes are joined together. [Figure 6] FIG. [Figure 7] FIG. [Figure 8] FIG. [Figure 9] FIG. [Figure 10] FIG. 11 is a front view of a second multi-pipe system according to a second embodiment. [Figure 11] FIG. 11 is a side view of a first multiple pipe according to a second embodiment. [Figure 12] FIG. 11 is a side view of a second multiple pipe according to a second embodiment. [Figure 13] FIG. 11 is a front view of a third multiple pipe system according to a third embodiment. [Figure 14]FIG. 13 is an exploded front view of a third multiple pipe system according to a third embodiment. [Figure 15] 13 is a diagram showing a state after a start-end multi-layer pipe and an intermediate-end multi-layer pipe have been joined in the third embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] (First embodiment) Hereinafter, a multi-pipe system 100 and a method for joining the multi-pipe system 100 according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a front view of a multi-pipe system 100 according to an embodiment. The multi-pipe system 100 according to the present embodiment is used, for example, as a thermally insulating multi-pipe. Specifically, the multi-pipe system 100 is used to keep the temperature of a superconducting cable disposed therein below a specific transition temperature and to make the electrical resistance of the superconducting cable zero. As shown in FIG. 1, a multi-tube system 100 according to this embodiment includes an inner tube IP, an outer tube OP, and a heat-resistant radiation layer SI.

[0037] The inner pipe IP is, for example, a straight pipe. A superconducting cable is inserted inside the inner pipe IP. A gap is formed between the superconducting cable and the inner pipe IP. The inner pipe IP is made of stainless steel. For example, the material of the inner pipe IP is appropriately selected from SUS316, SUS316L, SUS304, SUS304L, etc. The inner pipe IP is cylindrical. For example, the inner pipe IP has an outer diameter of 60.5 mm and a thickness of 2.0 mm.

[0038] The outer pipe OP is provided outside the inner pipe IP. A gap is formed between the inner pipe IP and the outer pipe OP. The outer pipe OP is made of stainless steel. For example, the material of the outer pipe OP is appropriately selected from SUS316, SUS316L, SUS304, SUS304L, etc. The outer pipe OP is cylindrical. For example, the outer diameter of the outer pipe OP is 76.3 mm and the thickness is 2.0 mm.

[0039] The heat-resistant radiation layer SI is provided on the outer peripheral surface of the inner pipe IP. The heat-resistant radiation layer SI is provided over the entire length of the inner pipe IP. The heat-resistant radiation layer SI is provided so as to cover the entire outer surface of the inner pipe IP. The heat-resistant radiation layer SI is made of a sheet called super insulation, which is a laminate of a resin film with aluminum vapor deposition and a polyester net. The heat-resistant radiation layer SI is used by wrapping the same sheet in multiple layers. The heat-resistant radiation layer SI has a thickness of, for example, about 1 mm (total thickness after multiple windings is about 1 mm). The heat-resistant radiation layer SI suppresses the penetration of radiant heat from the outside. In other words, the heat-resistant radiation layer SI can suppress the transfer of radiant heat from the outer tube OP side to the inner tube IP side. In addition, it is preferable to use a heat-resistant radiation layer SI having a small friction resistance in order to reduce the resistance when inserting the inner tube IP into the outer tube OP.

[0040] Here, the multi-pipe system 100 is laid over a long distance corresponding to the length of the superconducting cable, for example. At this time, if an attempt is made to construct the multi-pipe system 100 using a long inner pipe IP and an outer pipe OP, problems arise in that the frictional resistance increases when inserting the inner pipe IP into the outer pipe OP, and that the outer pipe OP or the inner pipe IP is deflected due to friction, making the work difficult. To prevent this, the multi-pipe system 100 according to this embodiment is constructed by joining a plurality of multi-pipes at the laying site, as described below.

[0041] FIG. 2 is an exploded front view of the multi-pipe system 100 according to the embodiment. 1 and 2, the multi-pipe system 100 includes a first multi-pipe 10 and a second multi-pipe 20. The multi-pipe system 100 is constructed by joining the first multi-pipe 10 and the second multi-pipe 20 at an installation location.

[0042] The first multi-layer pipe 10 includes a first inner pipe 11, a first outer pipe 12, a first heat-resistant radiation layer 13, and a first insulating material 14. The first inner pipe 11 is a part of the inner pipe IP described above. An end of the first inner pipe 11 is connected to an end of a second inner pipe 21 described below. The first inner pipe 11 is composed of a plurality of elongation inner pipes. The first outer pipe 12 is a part of the outer pipe OP described above. The first inner pipe 11 is inserted into the first outer pipe 12. An end of the first outer pipe 12 is connected to an end of a second outer pipe 22 described later. The first outer pipe 12 is composed of a plurality of outer pipes for lengthening.

[0043] The first heat-resistant radiation layer 13 is a part of the heat-resistant radiation layer SI described above. The first heat-resistant radiation layer 13 is provided on the outer peripheral surface of the first inner tube 11 and suppresses heat conduction from the first outer tube 12 to the first inner tube 11. Therefore, the first heat-resistant radiation layer 13 is provided between the outer peripheral surface of the first inner tube 11 and the inner peripheral surface of the first outer tube 12. In order to avoid interference with the work due to melting during the joining operation of the first inner pipe 11 and the second inner pipe 21, the first heat-resistant radiation layer 13 is preferably not provided near the joint between the first inner pipe 11 and the second inner pipe 21 before the joining operation, as shown in Fig. 2. Specifically, the first heat-resistant radiation layer 13 is preferably not provided in a region approximately 200 mm in absolute value from the welded part at the end of the first inner pipe 11 in the axial direction of the first inner pipe 11.

[0044] The first insulating material 14 is provided between the first outer pipe 12 and the first heat-resistant radiation layer 13, and suppresses heat conduction from the first outer pipe 12 to the first inner pipe 11. The first insulating material 14 is cylindrical. The first insulating material 14 is disposed around the entire circumference between the cylindrical inner pipe IP and the outer pipe OP. The first insulating material 14 is provided at a predetermined interval in the tube axis direction of the first inner pipe 11. The predetermined interval is preferably a distance such that the deflection of the first inner pipe 11 when the first outer pipe 12 is supported by the first insulating material 14 is 1 mm or less. By disposing the first insulating material 14 in this manner, the position of the first outer pipe 12 relative to the first inner pipe 11 can be made constant by the first insulating material 14 throughout the tube axis direction of the first multi-layer pipe 10. Note that, like the first heat-resistant radiation layer 13, the first insulating material 14 is also preferably not provided near the joint between the first inner pipe 11 and the second inner pipe 21.

[0045] Furthermore, the first insulating material 14 is also used as a guide when inserting the first inner pipe 11 into the first outer pipe 12. That is, the first insulating material 14 is also used to facilitate movement of the first inner pipe 11 in the axial direction of the first outer pipe 12. For this reason, the first insulating material 14 is preferably made of a material that has low thermal conductivity and low frictional resistance. That is, the first insulating material 14 may be, for example, a fluororesin (polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polychlorotrifluoroethylene) or a glass fiber reinforced plastic in which a fibrous filler is added to a fluororesin. Alternatively, glass fiber insulating paper in which silica aerogel is added is preferable. However, the material of the first insulating material 14 is not limited to this. For example, the first insulating material 14 may be formed by wrapping super insulation around the first heat-resistant radiation layer 13 multiple times.

[0046] The second multi-layer pipe 20 includes a second inner pipe 21 , a second outer pipe 22 , a second heat-resistant radiation layer 23 , and a second insulating material 24 . The second inner pipe 21 is a part of the inner pipe IP described above. An end of the second inner pipe 21 is connected to an end of the first inner pipe 11. The second inner pipe 21 is composed of a plurality of elongation inner pipes. The second outer pipe 22 is a part of the outer pipe OP described above. The second inner pipe 21 is inserted into the second outer pipe 22. The end of the second outer pipe 22 is connected to the end of the first outer pipe 12. The second outer pipe 22 is composed of a plurality of outer pipes for lengthening.

[0047] The second heat-resistant radiation layer 23 is a part of the heat-resistant radiation layer SI described above. The second heat-resistant radiation layer 23 is provided on the outer peripheral surface of the second inner tube 21, and suppresses heat conduction from the second outer tube 22 to the second inner tube 21. Therefore, the second heat-resistant radiation layer 23 is provided between the outer peripheral surface of the second inner tube 21 and the inner peripheral surface of the second outer tube 22. In order to avoid interference with the work due to melting during the joining operation of the first inner pipe 11 and the second inner pipe 21, the second heat-resistant radiation layer 23 is preferably not provided near the joint between the first inner pipe 11 and the second inner pipe 21 before the joining operation, as shown in Fig. 2. Specifically, the second heat-resistant radiation layer 23 is preferably not provided in a region approximately 200 mm in absolute value from the welded part at the end of the second inner pipe 21 in the axial direction of the second inner pipe 21.

[0048] The second insulating material 24 is provided between the second outer pipe 22 and the second heat-resistant radiation layer 23, and suppresses heat conduction from the second outer pipe 22 to the second inner pipe 21. The second insulating material 24 is cylindrical. The second insulating material 24 is disposed over the entire circumference between the cylindrical inner pipe IP and the outer pipe OP. The second insulating material 24 is provided at a predetermined interval in the tube axis direction of the second inner pipe 21. The predetermined interval is preferably a distance such that the deflection of the second inner pipe 21 when the second outer pipe 22 is supported by the second insulating material 24 is 1 mm or less. By disposing the second insulating material 24 in this manner, the position of the second outer pipe 22 relative to the second inner pipe 21 can be made constant over the tube axis direction of the second multi-layer pipe 20 by the second insulating material 24. Note that, like the second heat-resistant radiation layer 23, the second insulating material 24 is also preferably not provided near the joint between the first inner pipe 11 and the second inner pipe 21.

[0049] Furthermore, the second insulating material 24 is also used as a guide when inserting the second inner pipe 21 into the second outer pipe 22. That is, the second insulating material 24 is also used to facilitate movement of the second inner pipe 21 in the axial direction of the second outer pipe 22. For this reason, a material that has low frictional resistance in addition to low thermal conductivity is preferably used for the second insulating material 24. The material of the second insulating material 24 is the same as that of the first insulating material 14 described above, and therefore a description thereof will be omitted.

[0050] In this embodiment, the inner pipe IP in the multi-pipe system 100 is formed by joining a first inner pipe 11 and a second inner pipe 21. In this embodiment, an end of the first inner pipe 11 and an end of the second inner pipe 21 are welded. For this reason, it is preferable to provide, for example, a groove (not shown) between the end of the first inner pipe 11 and the end of the second inner pipe 21 that are joined to each other. In this embodiment, the outer pipe OP in the multi-pipe system 100 is configured by joining a first outer pipe 12 and a second outer pipe 22. In this embodiment, an end of the first outer pipe 12 and an end of the second outer pipe 22 are welded to each other.

[0051] FIG. 3 is an enlarged view of part III shown in FIG. Here, when the first outer pipe 12 and the second outer pipe 22 are welded together, if gas such as oxygen is present between the inner pipe IP and the outer pipe OP, the gas reacts with the molten metal during welding, causing welding defects due to poor shielding. To prevent this, as shown in Fig. 3, a supply tube 21t is provided on the outer circumferential surface of the second inner pipe 21 to supply back shield gas to the end of the second inner pipe 21. In this embodiment, the first outer pipe 12 and the second outer pipe 22 are welded together while supplying back shield gas from this supply tube 21t. A notch 24s may be provided in a portion of the second insulating material 24 in the circumferential direction so that the supply tube 21t can be disposed along the outer circumferential surface of the second inner pipe 21. Furthermore, the supply tube 21t may be removed after the first multiple pipe 10 and the second multiple pipe 20 are joined together.

[0052] FIG. 4 is a diagram showing the state before the first multiple pipe 10 and the second multiple pipe 20 are joined together. In this embodiment, when joining the first multiple pipe 10 and the second multiple pipe 20, the first inner pipe 11 and the second inner pipe 21 are joined first, and then the first outer pipe 12 and the second outer pipe 22 are joined (details will be described later). In this embodiment, in order to facilitate the above process, the first multiple pipe 10 and the second multiple pipe 20 each have the following structure.

[0053] That is, before the first multiple pipe 10 and the second multiple pipe 20 are joined, the end of the first inner pipe 11 in the first multiple pipe 10 that faces the second outer pipe 22 protrudes from the end of the first outer pipe 12. The end of the second inner pipe 21 that faces the first inner pipe 11 protrudes from the end of the second outer pipe 22, as shown in FIG. In order to satisfy the above, the length of the first inner tube 11 is longer than the length of the first outer tube 12, as shown in Fig. 2. In other words, when the ends of the first inner tube 11 and the first outer tube 12 that do not face the second multi-layer tube 20 are aligned in the tube axial direction of the first multi-layer tube 10, the end of the first inner tube 11 that faces the second inner tube 21 protrudes from the end of the first outer tube 12 that faces the second outer tube 22. The length of the second inner pipe 21 is equal to or shorter than the length of the second outer pipe 22. In other words, the length of the second inner pipe 21 is shorter than the length of the second outer pipe 22 or equal to the length of the second outer pipe 22.

[0054] When the length of the second inner pipe 21 is shorter than the length of the second outer pipe 22, as shown in Fig. 2, it is preferable that the difference between the lengths of the second inner pipe 21 and the second outer pipe 22 corresponds to the length by which the end of the first inner pipe 11 protrudes from the end of the first outer pipe 12. This makes it possible to make the combined length of the first inner pipe 11 and the second inner pipe 21 the same as the combined length of the first outer pipe 12 and the second outer pipe 22 when the first multiple pipe 10 and the second multiple pipe 20 are joined. In other words, the lengths of the inner pipe IP and the outer pipe OP can be made the same.

[0055] FIG. 5 shows a modified example of the state after the first multiple pipe 10 and the second multiple pipe 20 are joined together. In the case where the length of the second inner pipe 21 is the same as the length of the second outer pipe 22, when the first multi-layer pipe 10 and the second multi-layer pipe 20 are joined, the end of the second inner pipe 21 opposite to the side joined to the first inner pipe 11 protrudes from the end of the second outer pipe 22 opposite to the side joined to the first outer pipe 12, as shown in Fig. 5. In other words, when the first multi-layer pipe 10 and the second multi-layer pipe 20 are joined, the positional relationship between the end of the second inner pipe 21 and the end of the second outer pipe 22 becomes the same as the positional relationship between the end of the first inner pipe 11 and the end of the first outer pipe 12 described above. This embodiment is the same as the third embodiment described later.

[0056] (Method of joining multiple pipe systems) Next, a joining method for the multiple pipe system 100 according to this embodiment will be described. That is, the joining method according to this embodiment includes an inner pipe manufacturing process, an outer pipe manufacturing process, a multiple pipe manufacturing process, an inner pipe butting process, an inner pipe centering process, an inner pipe joining process, an installation process, an outer pipe butting process, an outer pipe centering process, and an outer pipe joining process. FIG. 6 is a front view of the inner pipe centering step. FIG. 7 is a side view of the inner pipe centering step. FIG. 8 is a front view of the outer tube centering step.

[0057] The inner pipe manufacturing process is a process for manufacturing the first inner pipe 11 and the second inner pipe 21 by joining a plurality of inner pipes for lengthening before the inner pipe butting process. The plurality of inner pipes for lengthening are welded, for example. The outer pipe manufacturing process is a process for manufacturing the first outer pipe 12 and the second outer pipe 22 by joining a plurality of outer pipes for lengthening before the inner pipe butting process. The plurality of outer pipes for lengthening are, for example, welded. The multi-wall pipe manufacturing process is a process in which, prior to the inner pipe butting process, a first heat-resistant radiation layer 13 and a first insulating material 14 are placed on a first inner pipe 11 and inserted into a first outer pipe 12 to manufacture a first multi-wall pipe 10, and a second heat-resistant radiation layer 23 and a second insulating material 24 are placed on a second inner pipe 21 and inserted into a second outer pipe 22 to manufacture a second multi-wall pipe 20. After the first multiple tube 10 and the second multiple tube 20 are manufactured by the above-mentioned steps, the following steps are carried out.

[0058] The inner pipe butting step is a step of butting an end of the first inner pipe 11 with an end of the second inner pipe 21. That is, the end of the first inner pipe 11 and the end of the second inner pipe 21 are moved to a position where they can be joined.

[0059] The inner pipe centering process is a process of substantially aligning the pipe axis of the first inner pipe 11 and the pipe axis of the second inner pipe 21 after the inner pipe butting process. In this embodiment, substantially aligning means that the misalignment between the first inner pipe 11 and the second inner pipe 21 is within a range of ±0.5 mm or less. Specifically, first, the wall thickness in the circumferential direction at each end of the first inner pipe 11 and the second inner pipe 21 is measured. Next, based on the measurement results, the phases of the first inner pipe 11 and the second inner pipe 21 are aligned so that the portions of the first inner pipe 11 and the second inner pipe 21 with their respective representative thicknesses are positioned downward. The representative thickness is, for example, the thickness of the portions of the first inner pipe 11 and the second inner pipe 21 where the thicknesses are equal. In this way, by positioning the portions of the first inner pipe 11 and the second inner pipe 21 with their respective same thicknesses downward, a step caused by the difference in thickness between the first inner pipe 11 and the second inner pipe 21 is not positioned downward. This prevents the superconducting cable or the like from interfering with the step and affecting the installation work when the cable or the like is installed inside the inner pipe IP. 6 and 7, the first inner pipe 11 and the second inner pipe 21 are aligned using a jig J including a backing plate J1 and a pressing tool J2. That is, first, the backing plate J1 having a shape that conforms to the outer circumferential surfaces of the first inner pipe 11 and the second inner pipe 21 is placed so as to be in contact with the underside of the joint between the first inner pipe 11 and the second inner pipe 21. Then, the pressing tool J2 is used to press the first inner pipe 11 and the second inner pipe 21 against the backing plate J1. 7, a plurality of pressing tools J2 are preferably provided at positions at least 90° away from the backing plate J1 in the circumferential direction of the first inner pipe 11 and the second inner pipe 21. Specifically, the pressing tools J2 are preferably provided at positions 60° away from the top to one side and the other side in the circumferential direction of the first inner pipe 11 and the second inner pipe 21. Also, the pressing tools J2 are preferably provided at positions away from the ends of the first inner pipe 11 and the second inner pipe 21 so as not to interfere with the welding operation of the first inner pipe 11 and the second inner pipe 21. By performing the inner pipe centering process, the positional accuracy of the first inner pipe 11 and the second inner pipe 21 is ensured, and the welding quality when the first inner pipe 11 and the second inner pipe 21 are welded together is ensured.

[0060] The inner pipe joining process is a process of joining the end of the first inner pipe 11 and the end of the second inner pipe 21 that have been butted together in the inner pipe butting process. More specifically, the inner pipe joining process is a process of joining the end of the first inner pipe 11 and the end of the second inner pipe 21 whose pipe axes have been substantially aligned in the inner pipe centering process. That is, it is a process of welding the end of the first inner pipe 11 and the end of the second inner pipe 21 together.

[0061] The installation process is a process of providing a heat-resistant radiation layer SI and a thermal insulation material I on the end of the first inner pipe 11 and the end of the second inner pipe 21 after the inner pipe joining process and before the outer pipe butting process. As described above, in order to avoid interfering with the joining operation of the first inner pipe 11 and the second inner pipe 21, the first heat-resistant radiation layer 13, the first thermal insulation material 14, the second heat-resistant radiation layer 23, and the second thermal insulation material 24 are not provided near the joint between the first inner pipe 11 and the second inner pipe 21. 8, in the installation process, a heat-resistant radiation layer SI and a thermal insulating material I are provided near the joint between the first inner pipe 11 and the second inner pipe 21, thereby reliably suppressing heat conduction from the outer pipe OP to the inner pipe IP after the first multiple pipe 10 and the second multiple pipe 20 are joined. Note that the thermal insulating material I has the same configuration as the first insulating material 14 and the second insulating material 24.

[0062] The outer pipe butting step is a step of butting an end of the first outer pipe 12 with an end of the second outer pipe 22 by moving the second outer pipe 22 in the pipe axis direction of the second outer pipe 22. In this way, the second outer pipe 22 is moved to a position where the end of the first outer pipe 12 and the end of the second outer pipe 22 can be joined.

[0063] The outer pipe centering process is a process of approximately aligning the pipe axis of the first outer pipe 12 and the pipe axis of the second outer pipe 22 after the outer pipe butting process. In this embodiment, approximately aligning means that the misalignment between the first outer pipe 12 and the second outer pipe 22 is within a range of ±0.5 mm or less. The outer pipe centering process is performed in the same manner as the above-mentioned inner pipe centering process, using a jig J as shown in Fig. 9.

[0064] The outer pipe joining process is a process of joining the end of the first outer pipe 12 and the end of the second outer pipe 22 that have been butted together in the outer pipe butting process. More specifically, the outer pipe joining process is a process of joining the end of the first outer pipe 12 and the end of the second outer pipe 22 whose pipe axes have been approximately aligned in the outer pipe centering process. That is, it is a process of welding the end of the first outer pipe 12 and the end of the second outer pipe 22 together. Through the above process, the first multiple tube 10 and the second multiple tube 20 are joined together. After the first multiple tube 10 and the second multiple tube 20 are joined together, a vacuum is created between the outer tube OP and the inner tube IP to ensure thermal insulation. The multiple pipe system 100 according to this embodiment is constructed through the above steps.

[0065] As described above, the multi-pipe system 100 according to the present embodiment includes the first multi-pipe 10 and the second multi-pipe 20. In other words, the multi-pipe system 100 is constructed by joining the first multi-pipe 10 and the second multi-pipe 20 at the installation site. This makes it possible to transport a long multi-pipe in a bent state and then bend it back into a straight line at the installation site, thereby preventing reduction in pipe diameter and deterioration in thermal insulation due to deformation of the heat-resistant radiation layer SI caused by the pipe diameter reduction. Here, when a long multiple pipe system 100 is constructed with one outer pipe OP and one inner pipe IP, problems occur that the frictional resistance increases when inserting the inner pipe IP into the outer pipe OP, and that the friction causes the outer pipe OP or the inner pipe IP to bend, making the work difficult. By constructing the multiple pipe system 100 by joining multiple multiple pipes at their installation locations as described above, the occurrence of the above problems can be suppressed.

[0066] In addition, the end of the first inner pipe 11 protrudes from the end of the first outer pipe 12, and the end of the second inner pipe 21 protrudes from the end of the second outer pipe 22. This makes it possible to prevent the first outer pipe 12 and the second outer pipe 22 from being positioned around the first inner pipe 11 and the second inner pipe 21 when the ends of the first inner pipe 11 and the second inner pipe 21 are butted against each other. In this state, the end of the first inner pipe 11 and the end of the second inner pipe 21 are joined. Therefore, the joining work of the first inner pipe 11 and the second inner pipe 21 can be easily performed from the outside of the first inner pipe 11 and the second inner pipe 21. In addition, for example, when the first inner pipe 11 and the second inner pipe 21 are welded, the welding work and the repair work when a welding defect occurs can be easily performed.

[0067] Furthermore, the length of the first inner pipe 11 is longer than the length of the first outer pipe 12. As a result, when one end of each of the first inner pipe 11 and the first outer pipe 12 is aligned, the other end of the first inner pipe 11 protrudes from the other end of the first outer pipe 12. Therefore, the first multiple pipe 10 and the second multiple pipe 20 can be joined together with the first inner pipe 11 and the first outer pipe 12 aligned in advance. This makes it unnecessary to align the first inner pipe 11 and the first outer pipe 12 after joining, improving workability.

[0068] Moreover, the length of the second inner pipe 21 is equal to or shorter than the length of the second outer pipe 22. For example, when the length of the second inner pipe 21 is shorter than the length of the second outer pipe 22, the difference in length between the second inner pipe 21 and the second outer pipe 22 is set to be the same as the difference in length between the first outer pipe 12 and the first inner pipe 11, so that when the first multiple pipe 10 and the second multiple pipe 20 are joined, the combined length of the first inner pipe 11 and the second inner pipe 21 can be made the same as the combined length of the first outer pipe 12 and the second outer pipe 22. This makes it possible to improve workability by eliminating the need to adjust the lengths and positions of the inner pipe IP and the outer pipe OP in the multiple pipe system 100 in which the first multiple pipe 10 and the second multiple pipe 20 are joined.

[0069] Furthermore, for example, if the length of the second inner pipe 21 and the length of the second outer pipe 22 are the same, when the first multiple pipe 10 and the second multiple pipe 20 are joined, the end of the second inner pipe 21 opposite the side joined to the first inner pipe 11 protrudes from the end of the second outer pipe 22 opposite the side joined to the first outer pipe 12. This makes it easier to join even more multiple pipes in addition to the first multiple pipe 10 and the second multiple pipe 20. This makes it easier to make the multiple pipe system 100 longer.

[0070] Furthermore, the difference between the length of the second inner pipe 21 and the length of the second outer pipe 22 corresponds to the length by which the end of the first inner pipe 11 protrudes from the end of the first outer pipe 12. This makes it possible to make the combined length of the first inner pipe 11 and the second inner pipe 21 the same as the combined length of the first outer pipe 12 and the second outer pipe 22 when the first multiple pipe 10 and the second multiple pipe 20 are joined together. This makes it possible to improve workability by eliminating the need to adjust the lengths and positions of the inner pipe IP and the outer pipe OP in the multiple pipe system 100 in which the first multiple pipe 10 and the second multiple pipe 20 are joined together.

[0071] Furthermore, the end of the first inner pipe 11 and the end of the second inner pipe 21 are welded together. This allows the outer circumferential surface of the connection between the first inner pipe 11 and the second inner pipe 21 to be flatter than when, for example, the end of the first inner pipe 11 and the end of the second inner pipe 21 are joined together by a flange or a ferrule. This allows the inner diameters of the first outer pipe 12 and the second outer pipe 22 to be smaller. Therefore, for example, by reducing the outer diameter of the outer pipe OP, the multi-pipe system 100 can be made more compact.

[0072] Furthermore, a supply tube 21t is provided on the outer circumferential surface of the second inner pipe 21 for supplying back shielding gas to the end of the second inner pipe 21. This allows back shielding gas to be supplied between the first inner pipe 11 and the second inner pipe 21 and the first outer pipe 12 and the second outer pipe 22 in the vicinity of the joint when the first outer pipe 12 and the second outer pipe 22 are joined. This makes it possible to prevent welding defects caused by poor shielding from occurring in the joint between the first outer pipe 12 and the second outer pipe 22.

[0073] Furthermore, a first heat-resistant radiation layer 13 and a second heat-resistant radiation layer 23 are provided on the outer circumferential surfaces of the first inner pipe 11 and the second inner pipe 21, respectively. Furthermore, a first insulating material 14 is provided between the first outer pipe 12 and the first heat-resistant radiation layer 13, and a second insulating material 24 is provided between the second outer pipe 22 and the second heat-resistant radiation layer 23. Thereby, for example, when insulating the space between the inner pipe IP and the outer pipe OP in the multi-pipe system 100, it is possible to more reliably suppress heat conduction from the outer pipe OP to the inner pipe IP after creating a vacuum state between the inner pipe IP and the outer pipe OP. Moreover, the first insulating material 14 and the second insulating material 24 are provided at a predetermined interval in the pipe axis direction of the first inner pipe 11 and the second inner pipe 21, respectively. This makes it possible to keep the position of the outer pipe OP relative to the inner pipe IP constant throughout the pipe axis direction of the multi-pipe system 100. Furthermore, by making the first insulating material 14 and the second insulating material 24 function as guides, it is possible to facilitate the work of inserting the first inner pipe 11 into the first outer pipe 12 and the work of inserting the second inner pipe 21 into the second outer pipe 22.

[0074] According to the joining method of the present embodiment, when joining the first multi-layer pipe 10 and the second multi-layer pipe 20, the first inner pipe 11 and the second inner pipe 21 are joined in the inner pipe joining step, and then the first outer pipe 12 and the second outer pipe 22 are joined in the outer pipe joining step. In other words, a plurality of prefabricated multi-layer pipes are joined at the installation site of the multi-layer pipe system 100. This makes it possible to facilitate the installation work and shorten the work time when installing the long multi-layer pipe system 100, compared to the case where the long inner pipe IP is inserted into the long outer pipe OP at the installation site. In addition, it is possible to prevent the reduction in the diameter of the pipe caused by transporting the long multi-layer pipe in a bent state and bending it back to a straight line at the installation site, and the deterioration of the heat insulation caused by the deformation of the heat-resistant radiation layer SI due to the reduction in the diameter of the pipe.

[0075] Here, if a heat-resistant radiation layer SI is provided on the end of the first inner pipe 11 and the end of the second inner pipe 21 before the inner pipe joining step, the heat-resistant radiation layer SI interferes with the operation of the inner pipe joining step. Therefore, the installation step of providing a heat-resistant radiation layer SI on the end of the first inner pipe 11 and the end of the second inner pipe 21 is performed after the inner pipe joining step and before the outer pipe butting step. In other words, the end of the first inner pipe 11 and the end of the second inner pipe 21 are not provided with a heat-resistant radiation layer SI during the inner pipe joining step. This makes it possible to suppress the heat-resistant radiation layer SI from interfering with the work of the inner pipe joining step. In addition, after the first multi-layer pipe 10 and the second multi-layer pipe 20 are joined, the heat-resistant radiation layer SI is provided at the joint between the end of the first inner pipe 11 and the end of the second inner pipe 21, so that in the multi-pipe system 100, heat conduction from the outer pipe OP to the inner pipe IP due to radiant heat or the like can be suppressed.

[0076] In addition, the installation step of providing the heat-resistant radiation layer SI and the heat insulating material I on the end of the first inner pipe 11 and the end of the second inner pipe 21 is performed after the inner pipe joining step and before the outer pipe butting step. In other words, the heat-resistant radiation layer SI and the heat insulating material I are not provided on the end of the first inner pipe 11 and the end of the second inner pipe 21 during the inner pipe joining step. This makes it possible to suppress the heat-resistant radiation layer SI and the heat insulating material I from interfering with the work of the inner pipe joining step. In addition, after the first multi-layer pipe 10 and the second multi-layer pipe 20 are joined, the heat-resistant radiation layer SI and the heat insulating material I are provided at the joint between the end of the first inner pipe 11 and the end of the second inner pipe 21, so that in the multi-pipe system 100, heat conduction from the outer pipe OP to the inner pipe IP due to radiant heat or the like can be suppressed. In addition, by making the insulating material I provided in the installation process function as a guide, it is possible to facilitate the movement of the second outer pipe 22 in the axial direction of the second outer pipe 22 in the outer pipe butting process. This improves workability.

[0077] Moreover, the first inner pipe 11 and the second inner pipe 21 are manufactured in an inner pipe manufacturing process before the inner pipe butting process. The first outer pipe 12 and the second outer pipe 22 are manufactured in an outer pipe manufacturing process before the inner pipe butting process. This allows the lengths of the first inner pipe 11, the second inner pipe 21, the first outer pipe 12, and the second outer pipe 22 to be the longest possible within a range that can be transported from a manufacturing factory to the installation site of the multi-pipe system 100. This reduces the number of welding operations at the installation site of the multi-pipe system 100, and shortens the time required for installation. Furthermore, by manufacturing the first multi-pipe 10 and the second multi-pipe 20 in advance in a multi-pipe manufacturing process before the inner pipe butting process, the amount of work at the installation site of the multi-pipe system 100 can be reduced.

[0078] Furthermore, after the inner pipe butting step, the pipe axis of the first inner pipe 11 and the pipe axis of the second inner pipe 21 are substantially aligned by an inner pipe centering step. Furthermore, after the outer pipe butting step, the pipe axis of the first outer pipe 12 and the pipe axis of the second outer pipe 22 are substantially aligned by an outer pipe centering step. This ensures the positional accuracy of the first inner pipe 11 and the second inner pipe 21, and the first outer pipe 12 and the second outer pipe 22.

[0079] Second embodiment Next, a second multiple pipe system 200 according to a second embodiment of the present invention will be described with reference to FIGS. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and their description will be omitted, with only the differences being described.

[0080] FIG. 10 is a front view of the second multi-pipe system according to the second embodiment. FIG. 11 is a side view of the first multiple pipe according to the second embodiment. FIG. 12 is a side view of the second multiple pipe according to the second embodiment. As shown in FIG. 10, the second multi-pipe system 200 is common to the first embodiment in that it includes a first multi-pipe 10 and a second multi-pipe 20. The second multi-layer pipe system 200 differs from the first embodiment in that the first multi-layer pipe 10 and the second multi-layer pipe 20 have the following configuration instead of the first insulating material 14 and the second insulating material 24.

[0081] That is, in the first multiple pipe 10 of the second multiple pipe system 200, a first protruding portion 12p that protrudes toward the pipe axis of the first outer pipe 12 is formed on the inner circumferential surface of the first outer pipe 12, as shown in FIG. The first protrusion 12p is, for example, integrally formed on the inner peripheral surface of the first outer tube 12. A plurality of first protrusions 12p are provided at intervals in the circumferential direction of the first outer tube 12. The first protrusions 12p contact the first heat-resistant radiation layer 13 provided on the outer peripheral surface of the first inner tube 11. In this way, only the first protrusions 12p contact the first heat-resistant radiation layer 13, thereby suppressing heat conduction from the first outer tube 12 to the first inner tube 11. The first protrusions 12p are formed continuously along the tube axis direction of the first outer tube 12. In addition to this, the contact points between the first protrusions 12p and the first inner tube 11 via the first heat-resistant radiation layer 13 are located at a plurality of points in the circumferential direction of the first inner tube 11, so that the position of the first outer tube 12 relative to the first inner tube 11 can be kept constant throughout the tube axis direction of the first multi-layer tube 10.

[0082] In the second multi-tube 20 of the second multi-tube system 200, a second protruding portion 22p protruding toward the tube axis of the second outer tube 22 is formed on the inner circumferential surface of the second outer tube 22, as shown in FIG. The second protrusion 22p is, for example, integrally formed on the inner peripheral surface of the second outer tube 22. A plurality of second protrusions 22p are provided at intervals in the circumferential direction of the second outer tube 22. The second protrusions 22p contact the second heat-resistant radiation layer 23 provided on the outer peripheral surface of the second inner tube 21. In this way, only the second protrusions 22p contact the second heat-resistant radiation layer 23, thereby suppressing heat conduction from the second outer tube 22 to the second inner tube 21. In addition, the second protrusions 22p are continuously formed along the tube axis direction of the second outer tube 22. In addition, the contact points between the second protrusions 22p and the second inner tube 21 via the second heat-resistant radiation layer 23 are located at a plurality of points in the circumferential direction of the second inner tube 21, so that the position of the second outer tube 22 relative to the second inner tube 21 can be constant throughout the tube axis direction of the second multi-tube 20.

[0083] (Method of joining the second multi-pipe system) In the joining method in the second embodiment, during the installation process, only the heat-resistant radiation layer SI is provided on the end of the first inner pipe 11 and the end of the second inner pipe 21. In other words, the second embodiment differs from the first embodiment only in that the first insulating material 14 and the second insulating material 24 are not provided during the installation process.

[0084] As described above, according to the second multi-pipe system 200 according to the second embodiment, the first heat-resistant radiation layer 13 and the second heat-resistant radiation layer 23 are provided on the outer circumferential surfaces of the first inner pipe 11 and the second inner pipe 21, respectively. This makes it possible to suppress heat conduction from the outside to the first inner pipe 11 and the second inner pipe 21. A first protruding portion 12p protruding toward the tube axis of the first outer tube 12 is formed on the inner peripheral surface of the first outer tube 12, and a second protruding portion 22p protruding toward the tube axis of the second outer tube 22 is formed on the inner peripheral surface of the second outer tube 22. As a result, when the first inner tube 11 is inserted into the first outer tube 12, only the first protruding portion 12p contacts the first heat-resistant radiation layer 13 provided on the first inner tube 11. Also, when the second inner tube 21 is inserted into the second outer tube 22, only the second protruding portion 22p contacts the second heat-resistant radiation layer 23 provided on the second inner tube 21. Therefore, for example, when insulating the space between the inner tube IP and the outer tube OP in the multiple tube system 100, the space between the inner tube IP and the outer tube OP is made vacuum, and then the heat conduction from the outer tube OP to the inner tube IP can be further suppressed. Moreover, the first protrusion 12p and the second protrusion 22p are formed continuously along the tube axis direction of the first outer tube 12 and the second outer tube 22, respectively. This allows the position of the outer tube OP relative to the inner tube IP to be constant throughout the tube axis direction of the multi-tube system 100. Furthermore, by making the first protrusion 12p and the second protrusion 22p function as guides, it is possible to facilitate the relative movement of the first inner tube 11 and the first outer tube 12, and the second inner tube 21 and the second outer tube 22 in the tube axis direction of the multi-tube system 100. This makes it possible to facilitate the work of inserting the first inner tube 11 into the first outer tube 12, and the work of inserting the second inner tube 21 into the second outer tube 22.

[0085] Third embodiment Next, a third multiple pipe system 300 according to a third embodiment of the present invention will be described with reference to FIGS. In the third embodiment, the same components as those in the first and second embodiments are denoted by the same reference numerals, and their description will be omitted, with only the differences being described.

[0086] FIG. 13 is a front view of the third multiple pipe system according to the third embodiment. FIG. 14 is an exploded front view of the third multiple pipe system according to the third embodiment. FIG. 15 is a diagram showing a state after a start end multi-layer pipe and an intermediate portion multi-layer pipe are joined in the third embodiment. In the third embodiment, three types of multiple pipes are provided as described below. That is, the third multiple pipe system 300 includes a start end multiple pipe 310, a middle multiple pipe 320, and an end end multiple pipe 330, as shown in FIG. The start end multiple tube 310 includes a start end inner tube 311 and a start end outer tube 312 into which the start end inner tube 311 is inserted. The intermediate multiple tube 320 includes an intermediate inner tube 321 and an intermediate outer tube 322 into which the intermediate inner tube 321 is inserted. The end portion multiple pipe 330 includes an end portion inner pipe 331 and an end portion outer pipe 332 into which the end portion inner pipe 331 is inserted. The starting end multi-layer pipe 310, the middle section multi-layer pipe 320, and the ending section multi-layer pipe 330 each have a structure therein equivalent to the first heat-resistant radiation layer 13 or the second heat-resistant radiation layer 23, and the first insulating material 14 or the second insulating material 24 (not shown).

[0087] In the third embodiment, the inner pipe IP in the third multi-pipe system 300 is configured by joining a start end portion inner pipe 311, a middle portion inner pipe 321, and a terminal end portion inner pipe 331. The joining is performed by welding the respective ends to each other. In the third embodiment, the outer pipe OP in the third multi-pipe system 300 is configured by joining a starting end outer pipe 312, a middle outer pipe 322, and a terminal end outer pipe 332. The joining is performed by welding the respective ends to each other.

[0088] In the third embodiment, the start end multi-layer pipe 310, the middle portion multi-layer pipe 320, and the end portion multi-layer pipe 330 have the following structures to facilitate joining of each of them. That is, as shown in FIG. 14 , one end of the starting end inner tube 311 protrudes from one end of the starting end outer tube 312, one end of the intermediate section inner tube 321 protrudes from one end of the intermediate section outer tube 322, and one end of the terminal section inner tube 331 protrudes from one end of the terminal section outer tube 332.

[0089] In order to satisfy the above, the length of the starting end inner tube 311 is longer than the length of the starting end outer tube 312. This structure is similar to that of the first multiple tube 10 included in the multiple tube system 100 of the first embodiment. The length of the intermediate section inner tube 321 and the length of the intermediate section outer tube 322 are approximately the same. In the third embodiment, approximately the same means that the error between the length of the intermediate section inner tube 321 and the length of the intermediate section outer tube 322 is 100 mm or less in absolute terms. This structure is similar to the case where the length of the second inner tube 21 and the length of the second outer tube 22 are the same in the second multiple tube 20 included in the multiple tube system 100 of the first embodiment. That is, when one end of the start end multiple tube 310 and one end of the intermediate section multiple tube 320 having the above-mentioned structures are joined, the other end of the intermediate section inner tube 321 protrudes from the other end of the intermediate section outer tube 322 as shown in FIG. 15. The length of the terminal inner tube 331 is shorter than the length of the terminal outer tube 332. The difference between the length of the terminal inner tube 331 and the length of the terminal outer tube 332 preferably corresponds to the length by which the end of the starting inner tube 311 protrudes from the end of the starting outer tube 312. This makes it possible to make the combined length of the starting inner tube 311, the intermediate inner tube 321, and the terminal inner tube 331 the same as the combined length of the starting outer tube 312, the intermediate outer tube 322, and the terminal outer tube 332. In other words, the lengths of the inner tube IP and the outer tube OP can be made the same.

[0090] (Method of joining the third multi-pipe system 300) Next, a joining method of the third multiple pipe system 300 will be described. That is, the joining method according to this embodiment includes an inner pipe manufacturing step, an outer pipe manufacturing step, a start end inner pipe butting step, a start end inner pipe centering step, a start end inner pipe joining step, a start end installation step, a start end outer pipe butting step, a start end outer pipe centering step, a start end outer pipe joining step, a terminal end inner pipe butting step, a terminal end inner pipe centering step, a terminal end inner pipe joining step, a terminal end installation step, a terminal end outer pipe butting step, a terminal end outer pipe centering step, and a terminal end outer pipe joining step.

[0091] The inner pipe manufacturing process and the outer pipe manufacturing process are performed in the same manner as in the first embodiment. That is, by joining a plurality of elongation inner pipes, a starting end portion inner pipe 311, a middle portion inner pipe 321, and a terminal end portion inner pipe 331 are manufactured. Also, by joining a plurality of elongation outer pipes, a starting end portion outer pipe 312, a middle portion outer pipe 322, and a terminal end portion outer pipe 332 are manufactured. As in the first embodiment, after the start end multiple tube 310, the middle portion multiple tube 320, and the end portion multiple tube 330 are constructed, the following steps are carried out.

[0092] The starting end portion inner pipe butting step is a step of butting one end of the starting end portion inner pipe 311 and one end of the intermediate portion inner pipe 321 together. The starting end portion inner pipe centering step is a step of aligning the pipe axis of the starting end portion inner pipe 311 and the pipe axis of the intermediate portion inner pipe 321 substantially in agreement with each other after the starting end portion inner pipe butting step. The starting end inner pipe joining process is a process of joining one end of the starting end inner pipe 311 and one end of the intermediate end inner pipe 321 which have been butted together in the starting end inner pipe butting process and then centered with each other in the starting end inner pipe centering process. The start end installation process is a process of providing a heat-resistant radiation layer SI and a heat insulating material I to the end of the start end inner pipe 311 and the end of the middle section inner pipe 321 after the start end inner pipe joining process and before the start end outer pipe butting process.

[0093] The starting end outer tube butting step is a step of butting one end of the starting end outer tube 312 and one end of the intermediate outer tube 322 by moving the intermediate outer tube 322 in the tube axial direction of the intermediate outer tube 322 . The starting end portion outer tube centering step is a step of aligning the tube axis of the starting end portion outer tube 312 and the tube axis of the intermediate portion outer tube 322 substantially in agreement with each other after the starting end portion outer tube butting step. The starting end outer tube joining process is a process of joining one end of the starting end outer tube 312 and one end of the intermediate end outer tube 322 that have been butted together in the starting end outer tube butting process and then centered with each other in the starting end outer tube centering process.

[0094] The terminal end inner pipe butting step is a step of butting the other end of the intermediate section inner pipe 321 and one end of the terminal end inner pipe 331 together. The terminal end inner pipe centering step is a step of aligning the pipe axis of the intermediate portion inner pipe 321 and the pipe axis of the terminal end inner pipe 331 substantially in agreement with each other after the terminal end inner pipe butting step. The terminal portion inner pipe joining process is a process of joining the other end of the intermediate portion inner pipe 321 and one end of the terminal portion inner pipe 331 which have been butted together in the terminal portion inner pipe butting process and then centered with each other in the terminal portion inner pipe centering process. The terminal installation process is a process of providing a heat-resistant radiation layer SI and a heat insulating material I on the ends of the intermediate inner pipe 321 and the terminal inner pipe 331 after the terminal inner pipe joining process and before the terminal outer pipe butting process.

[0095] The terminal outer pipe butting step is a step of butting the other end of the intermediate outer pipe 322 and one end of the terminal outer pipe 332 by moving the terminal outer pipe 332 in the tube axis direction of the terminal outer pipe 332 . The end portion outer pipe centering step is a step of aligning the pipe axis of the intermediate outer pipe 322 and the pipe axis of the end portion outer pipe 332 substantially in agreement with each other after the end portion outer pipe butting step. The terminal outer pipe joining process is a process of joining the other end of the intermediate outer pipe 322 and one end of the terminal outer pipe 332 which have been butted together in the terminal outer pipe butting process and then centered with each other in the terminal outer pipe centering process.

[0096] In the third embodiment, the starting end portion inner pipe butting step and the terminal end portion inner pipe butting step are similar to the inner pipe butting step in the first embodiment. In the third embodiment, the starting end portion inner pipe centering step and the terminal end portion inner pipe centering step are similar to the inner pipe centering step in the first embodiment. In the third embodiment, the starting end portion inner pipe joining step and the terminal end portion inner pipe joining step are similar to the inner pipe joining step in the first embodiment. In the third embodiment, the start end portion installation step and the end end portion installation step are similar to the installation steps in the first embodiment. In the third embodiment, the starting end portion outer pipe butting step and the terminal end portion outer pipe butting step are similar to the outer pipe butting step in the first embodiment. In the third embodiment, the starting end portion outer pipe centering step and the terminal end portion outer pipe centering step are similar to the outer pipe centering step in the first embodiment. In the third embodiment, the starting end portion outer pipe joining step and the terminal end portion outer pipe joining step are steps similar to the outer pipe joining step in the first embodiment.

[0097] The above steps join the start end multi-layer pipe 310, the middle section multi-layer pipe 320, and the end section multi-gap pipe 330. After joining the start end multi-layer pipe 310, the middle section multi-layer pipe 320, and the end section multi-gap pipe 330, a vacuum is created between the outer pipe OP and the inner pipe IP to ensure thermal insulation. The third multi-pipe system 300 is constructed through the above steps.

[0098] As described above, according to the third multi-pipe system 300 and joining method of the third embodiment, the start end multi-pipe 310, the middle multi-pipe 320, and the end end multi-pipe gap 330 are joined at the installation location of the multi-pipe system 100. This makes it possible to prevent the tube from shrinking in diameter when the long multi-pipe is transported in a bent state and then bent back into a straight line at the installation location, and to prevent deterioration of the heat insulating property due to deformation of the heat-resistant radiation layer SI caused by the tube shrinking. Furthermore, compared to the case where a long inner pipe IP is inserted into a long outer pipe OP at the installation location, the installation work can be made easier and the work time can be shortened. Moreover, one end of the starting end inner pipe 311 protrudes from one end of the starting end outer pipe 312, and one end of the intermediate portion inner pipe 321 protrudes from one end of the intermediate portion outer pipe 322. This makes it easier to perform the starting end inner pipe joining step of joining one end of the starting end inner pipe 311 and one end of the intermediate portion inner pipe 321. Moreover, one end of the terminal portion inner pipe 331 protrudes from one end of the terminal portion outer pipe 332, and the length of the intermediate portion inner pipe 321 and the length of the intermediate portion outer pipe 322 are substantially the same. Here, if the length of the intermediate portion inner pipe 321 and the length of the intermediate portion outer pipe 322 are substantially the same, the other end of the intermediate portion inner pipe 321 protrudes from the other end of the intermediate portion outer pipe 322 by moving the intermediate portion outer pipe 322 in the tube axis direction of the intermediate portion outer pipe 322 in the starting end outer pipe butting step. This makes it easier to perform the terminal portion inner pipe joining step of joining the other end of the intermediate portion inner pipe 321 and one end of the terminal portion inner pipe 331.

[0099] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, although the first inner pipe 11 and the second inner pipe 21 are described as being welded, this is not limiting. That is, the first inner pipe 11 and the second inner pipe 21 may be joined by a flange or a ferrule. In this case, it is preferable to place the heat-resistant radiation layer SI on the outside of the flange or ferrule in the installation process. In addition, it is preferable that the inner diameters of the first outer pipe 12 and the second outer pipe 22 are set to a degree that allows the flange or ferrule and the heat-resistant radiation layer SI to be placed. In addition, although the first outer pipe 12 and the second outer pipe 22 are described as being welded to each other, the present invention is not limited to this. That is, the first outer pipe 12 and the second outer pipe 22 may be joined by a flange or a ferrule.

[0100] In addition, within the scope of the invention, the components in the above-described embodiments may be replaced with well-known components, and the above-described modified examples may be combined as appropriate. [Explanation of symbols]

[0101] 10 1st multiplex tube 11 1st inner pipe 12 First outer tube 12p 1st protrusion 13 First heat-resistant radiation layer 14 First insulation material 20 2nd multiplex tube 21 2nd inner pipe 21t supply tube 22 Second outer tube 22p 2nd protrusion 23 Second heat-resistant radiation layer 24 Second insulation material 24s notch 100 Multi-Tube System 200 Second Multiple Tube System 300 3rd Multi-Tube System 310 Starting end multiple pipe 311 Inner pipe at start 312 Starting end outer tube 320 Middle part multiple tube 321 Middle inner tube 322 Middle outer tube 330 Termination Multiplex 331 End inner tube 332 End part outer tube I Insulation IP inner tube J Jig J1 Backing plate J2 Pressing tool OP outer tube SI heat resistant radiation layer

Claims

1. a first multi-layer pipe including a first inner pipe and a first outer pipe into which the first inner pipe is inserted; a second multi-pipe system including a second inner pipe and a second outer pipe into which the second inner pipe is inserted, the first outer tube and the second outer tube are steel tubes, an end of the first inner tube protrudes beyond an end of the first outer tube; an end of the second inner tube protrudes beyond an end of the second outer tube; A multi-pipe system, characterized in that an end of the first inner pipe and an end of the second inner pipe are joined in a state in which the end of the first inner pipe protrudes from the end of the first outer pipe and the end of the second inner pipe protrudes from the end of the second outer pipe.

2. 2. The multi-pipe system according to claim 1, wherein the first inner pipe and the second inner pipe are steel pipes.

3. The length of the first inner tube is longer than the length of the first outer tube, 2. The multi-pipe system according to claim 1, wherein a length of the second inner pipe is equal to or less than a length of the second outer pipe.

4. 4. The multi-pipe system according to claim 3, wherein a difference between a length of the second inner pipe and a length of the second outer pipe corresponds to a length by which an end of the first inner pipe protrudes from an end of the first outer pipe.

5. 5. The multi-pipe system according to claim 1, wherein an end of the first inner pipe and an end of the second inner pipe are welded to each other.

6. 6. The multi-pipe system according to claim 5, wherein a supply tube is provided on an outer circumferential surface of the second inner pipe for supplying a back shielding gas to an end of the second inner pipe.

7. A first insulating material; A second insulating material; Further comprising: A first heat-resistant radiation layer is provided on an outer circumferential surface of the first inner tube, the first insulating material is provided between the first outer tube and the first heat-resistant radiation layer, and is provided at predetermined intervals in a tube axis direction of the first inner tube, A second heat-resistant radiation layer is provided on an outer circumferential surface of the second inner tube, The second insulating material is provided between the second outer tube and the second heat-resistant radiation layer, and is provided at a predetermined interval in a tube axis direction of the second inner tube.

5. The multi-pipe system according to claim 1, wherein the multi-pipe system is a multi-pipe system.

8. A first heat-resistant radiation layer is provided on an outer circumferential surface of the first inner tube, A second heat-resistant radiation layer is provided on an outer circumferential surface of the second inner tube, a first protruding portion protruding toward a tube axis of the first outer tube is formed on an inner circumferential surface of the first outer tube; the first protrusion is formed continuously along the tube axis direction of the first outer tube, A second protruding portion is formed on an inner circumferential surface of the second outer tube, the second protruding portion protruding toward a tube axis of the second outer tube, The second protruding portion is formed continuously along the tube axis direction of the second outer tube.

5. The multi-pipe system according to claim 1, wherein the multi-pipe system is a multi-pipe system.

9. a first multi-layer pipe including a first inner pipe and a first outer pipe into which the first inner pipe is inserted; a second multi-pipe system including a second inner pipe and a second outer pipe into which the second inner pipe is inserted, an end of the first inner tube protrudes beyond an end of the first outer tube; an end of the second inner pipe protrudes beyond an end of the second outer pipe, an inner pipe butting process of butting an end of the first inner pipe protruding from an end of the first outer pipe with an end of the second inner pipe protruding from an end of the second outer pipe; an inner pipe joining step of joining the end of the first inner pipe and the end of the second inner pipe that have been butted together in the inner pipe butting step; an outer tube butting process of butting an end of the first outer tube against an end of the second outer tube by moving the second outer tube in a tube axis direction of the second outer tube; an outer pipe joining step of joining the end of the first outer pipe and the end of the second outer pipe that have been butted together in the outer pipe butting step; Equipped with A joining method, characterized in that the inner pipe joining step and the outer pipe joining step are performed at a location where the multiple pipe system is laid.

10. an installation step of providing a heat-resistant radiation layer on an end portion of the first inner pipe and an end portion of the second inner pipe after the inner pipe joining step and before the outer pipe butting step; The bonding method according to claim 9, further comprising:

11. The joining method according to claim 9, further comprising an installation process for providing a heat-resistant radiation layer and an insulating material to the ends of the first inner pipe and the second inner pipe after the inner pipe joining process and before the outer pipe butting process.

12. Inner pipe manufacturing process, Outer tube manufacturing process, A multiple tube manufacturing process; Further comprising: the first inner tube and the second inner tube are constituted by a plurality of elongation inner tubes, the first outer tube and the second outer tube are composed of a plurality of elongation outer tubes, In the inner pipe manufacturing step, the first inner pipe and the second inner pipe are manufactured by joining the plurality of elongation inner pipes before the inner pipe butting step; In the outer pipe manufacturing process, the first outer pipe and the second outer pipe are manufactured by joining the plurality of outer pipes for elongation before the inner pipe butting process; 10. The joining method according to claim 9, characterized in that in the multi-pipe manufacturing process, before the inner pipe butting process, a first heat-resistant radiation layer is placed on the first inner pipe and inserted into the first outer pipe to manufacture a first multi-pipe, and a second heat-resistant radiation layer is placed on the second inner pipe and inserted into the second outer pipe to manufacture a second multi-pipe.

13. an inner pipe centering step of substantially aligning a pipe axis of the first inner pipe with a pipe axis of the second inner pipe after the inner pipe butting step; an outer pipe centering step of substantially aligning a pipe axis of the first outer pipe with a pipe axis of the second outer pipe after the outer pipe butting step; The bonding method according to claim 9, further comprising:

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