System and object

Abstract

To provide a system and an object capable of filling a space between an inner pipe and an outer pipe with back shield gas at the time of welding the outer pipe being a multiple pipe.SOLUTION: A system includes: a multiple pipe DP including an inner pipe IP and one or more outer pipes OP to which the inner pipe IP is inserted; and a back shield gas supply device 100 for supplying back shield gas to one or more layers of the multiple pipe DP. The back shield gas supply device 100 includes a supply tube 10 for supplying the back shield gas to the multiple pipe DP. The supply tube 10 is arranged between the inner pipe IP and the outer pipe OP.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to systems and articles. [Background technology]

[0002] When the tubular members are welded together, the inside of the tubular members is filled with a back shield gas. Patent Document 1 discloses a technique in which a gas supply tube is inserted from a hole provided in the side surface of a tubular member, and a back shield gas is sprayed from a gas spray nozzle provided at the end of the gas supply tube. Patent Document 2 discloses a technique in which a seal member is disposed inside a tubular member, thereby filling the inside of the tubular member with a back shield gas. Patent Document 3 discloses a technique in which a foaming agent is filled inside a tubular member, thereby filling the inside of the tubular member with a back shielding gas. Patent Document 4 discloses a method for welding a double-pipe structure having an inner pipe and an outer pipe, in which the inner pipes are first welded together using a laser beam, and then a filler material is fitted into the groove of the outer pipe, and the outer pipes are welded together by TIG welding while flowing an inert gas between the inner pipe and the outer pipe. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-146771 A [Patent Document 2] JP 2014-97527 A [Patent Document 3] International Publication No. 2010 / 150422 [Patent Document 4] Japanese Patent Application Publication No. 10-34373 Summary of the Invention [Problem to be solved by the invention]

[0004] When welding outer tubes together in a multi-tube structure, there is a need to fill the gap between the inner tube and the outer tube around the welded part with back shielding gas. However, the techniques in Patent Documents 1 to 3 are based on the premise of welding a single tube, and cannot be used for multi-tube. The technique in Patent Document 4 does not specify a specific method for supplying inert gas between the inner tube and the outer tube around the welded part.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a system and product that can fill the space between the inner tube and the outer tube when welding the outer tube of a multi-wall pipe. [Means for solving the problem]

[0006] A system according to one aspect of the present invention comprises a multi-layer tube including an inner tube and one or more outer tubes into which the inner tube is inserted, and a back shielding gas supply device that supplies a back shielding gas to one or more layers of the multi-layer tube, wherein the back shielding gas supply device includes a supply tube that supplies the back shielding gas to the multi-layer tube, and the supply tube is positioned between the inner tube and the outer tube. Effect of the Invention

[0007] According to the present invention, it is possible to provide a system and an article capable of filling the gap between the inner tube and the outer tube of a multi-wall pipe with a back shielding gas when welding the outer tube of the multi-wall pipe. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a conceptual diagram of a welding operation for multiple pipes. [Diagram 2] 2 is a first example of a cross-sectional view taken along line II-II of FIG. 1. [Diagram 3] 2 is a second example of a cross-sectional view taken along line II-II of FIG. 1. [Figure 4] 4 is an enlarged cross-sectional view of the vicinity of a welded portion between multiple pipes, as viewed from the IV direction shown in FIG. 1. [Diagram 5]13 is a diagram showing a state in which the detachable part is broken by pulling the supply tube. FIG. [Figure 6] This is a first example of the location of the detachable part. [Figure 7] This is a second example of the location of the detachable part. [Figure 8] FIG. 13 is a diagram showing a state in which the supply tube comes into contact with the base. [Figure 9] FIG. 13 is a conceptual diagram of a welding operation for modified multi-wall pipes. [Figure 10] 10 is a cross-sectional view taken along the line XX in FIG. 9. [Figure 11] 10 is an enlarged cross-sectional view of the vicinity of a welded portion between modified examples of multi-wall pipes, as viewed from the XI direction shown in FIG. 9 . FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, a back shield gas supply device 100, a method for welding a multi-wall pipe DP, and a method for manufacturing a multi-wall pipe DP according to an embodiment of the present invention will be described with reference to the drawings. As shown in Fig. 1, the back shielding gas supplying device 100 according to this embodiment supplies a back shielding gas to one or more layers of a multi-tube DP including an inner tube IP and one or more outer tubes OP into which the inner tube IP is inserted, when the ends of the multi-tube DP including the inner tube IP and one or more outer tubes OP are welded together by a welding torch T. In this embodiment, the multi-tube DP is a double tube including an inner tube IP and one outer tube OP. That is, in this embodiment, the back shielding gas supplying device 100 supplies a back shielding gas between the inner tube IP and the outer tube OP shown in Fig. 1. In this embodiment, the back shielding gas is, for example, argon gas.

[0010] In this embodiment, as shown in FIG. 1, a ring-shaped pedestal IPs with a portion cut out in the circumferential direction is provided on the outer peripheral surface of the inner pipe IP. A plurality of pedestals IPs are provided at intervals along the longitudinal direction of the inner pipe IP. The interval between the pedestals IPs on the inner pipe IP is, for example, about 2 m to 3 m. The pedestals IPs contact the inner peripheral surface of the outer pipe OP. In this way, the pedestals IPs secure a gap between the outer peripheral surface of the inner pipe IP and the inner peripheral surface of the outer pipe OP in a portion of the inner pipe IP where the pedestals IPs are not provided. Note that an SI material (super insulation material) may be provided along the outer peripheral surface of the inner pipe IP in the gap between the outer peripheral surface of the inner pipe IP and the inner peripheral surface of the outer pipe OP. In the multiple pipe DP according to this embodiment, the seat IPs is preferably provided at a location at least 300 mm away from the ends of the inner pipe IP and the outer pipe OP. Details will be described below together with the location of the detachable part 20.

[0011] In this embodiment, the base IPs is partially cut out in the circumferential direction of the inner pipe IP, as shown in Fig. 2. Hereinafter, the cut-out part of the base IPs is referred to as a cut-out part IPsc. Alternatively, the base IPs has a part that is thinner than the other part of the base IPs, as shown in Fig. 3. Hereinafter, the part of the base IPs that is thinner is referred to as a thin-walled part IPst. In this embodiment, the cutout width of the cutout portion IPsc, i.e., the dimension A of the cutout portion IPsc in the circumferential direction of the inner pipe IP shown in Fig. 2, is about 30 mm, for example. The width of the thin-walled portion IPst, i.e., the dimension B of the thin-walled portion IPst in the circumferential direction of the inner pipe IP shown in Fig. 3, is about 30 mm, for example.

[0012] The cutouts IPsc or thin-walled portions IPst are provided in all of the multiple pedestals IPs provided along the longitudinal direction of the inner pipe IP. In addition, the cutouts IPsc or thin-walled portions IPst are arranged in a straight line in the multiple pedestals IPs. This allows a supply tube 10, which will be described later, to be placed in the cutouts IPsc or thin-walled portions IPst. During the welding operation of the multi-wall pipe DP, it is preferable that the cutouts IPsc or thin-walled portions IPst are located at the top as shown in Figures 2 and 3 (details will be described later).

[0013] As shown in FIG. 1, the back shield gas supply device 100 includes a supply tube 10. The supply tube 10 is a tube disposed between an inner pipe IP and an outer pipe OP. One end of the supply tube 10 is disposed at a joint between the multiple pipes DP, and the other end is connected to a gas tank or the like (not shown). The supply tube 10 is supplied with a back shield gas from a gas tank or the like (not shown). As a result, the supply tube 10 supplies the back shield gas between the inner pipe IP and the outer pipe OP of the multiple pipes DP. The outer diameter of the supply tube 10 is preferably, for example, 80% or less of the dimension of the gap between the inner pipe IP and the outer pipe OP. The inner diameter of the supply tube 10 is preferably, for example, a diameter that can keep the flow rate of the back shield gas at 0.6 L / min or more when the length of the supply tube 10 is 100 m.

[0014] In this embodiment, one end of the supply tube 10 is wound around the inner pipe IP as shown in Fig. 4. A portion of the supply tube 10 is kept wound around the outer circumferential surface of the inner pipe IP during the welding operation of the multi-wall pipe DP. In this embodiment, the supply tube 10 is detachably attached to the inner pipe IP. Specifically, as shown in Fig. 4, the supply tube 10 is maintained in a state of being wound around the inner pipe IP by a detachable part 20. The detachable part 20 is, for example, an aluminum tape. A loop formed by winding one end of the supply tube 10 around the inner pipe IP is fixed by the detachable part 20, which is the aluminum tape.

[0015] When the supply tube 10 is pulled, the detachable part 20 releases the supply tube 10 from the state where it is wound around the inner tube IP. Specifically, by pulling the other end of the supply tube 10 in a direction away from one end of the supply tube 10, the detachable part 20 breaks as shown in FIG. 5. This releases the supply tube 10 from the state where it is wound around the inner tube IP. This makes the supply tube 10 detachable from the inner tube IP.

[0016] As described above, the supply tube 10 is removed from the inner tube IP by being pulled. Therefore, it is preferable that the supply tube 10 has sufficient resistance to the pulling force. That is, the material of the supply tube 10 is preferably, for example, a polyurethane tube, and a nylon tube may also be used.

[0017] 4, the supply tube 10 includes an outlet 10n for ejecting the back shield gas. Specifically, the supply tube 10 has a plurality of outlets 10n provided along the circumferential direction of the inner peripheral surface of the outer tube OP. In other words, the plurality of outlets 10n are provided in a part of the supply tube 10 wound around the inner tube IP.

[0018] The nozzles 10n are formed, for example, by drilling through holes with a diameter of about 0.5 mm in the supply tube 10 with a drill bit or the like. In this case, it is preferable that a plurality of nozzles 10n are provided at intervals of about 20 mm along the length of the supply tube 10 in the supply tube 10 in a state where it is not wound around the inner tube IP. Note that the above dimensions are merely examples, and any other dimensions may be used.

[0019] (Location of supply tube 10) Next, a specific location of the supply tube 10 between the inner pipe IP and the outer pipe OP will be described. First, a location of the supply tube 10 other than the part wound around the inner pipe IP will be described. That is, the supply tube 10 is arranged so as to pass through the notch portion IPsc or the thin portion IPst provided in the base IPs, as shown in FIG. 2 or FIG.

[0020] Here, the weight of the inner pipe IP may reduce the size of the gap between the outer peripheral surface of the inner pipe IP and the inner peripheral surface of the outer pipe OP below the multiple pipe DP. In this case, if the cut-out portion of the pedestal IPs or the thin portion of the pedestal IPs is located below the multiple pipe DP, the supply tube 10 may be pinched between the outer peripheral surface of the inner pipe IP and the inner peripheral surface of the outer pipe OP, making it impossible to pull the supply tube 10 to remove it. For this reason, as described above, it is preferable that the cut-out portion of the pedestal IPs or the thin portion of the pedestal IPs is located above the multiple pipe DP.

[0021] Next, the location of the part of the supply tube 10 wound around the inner pipe IP will be described. As described above, a part of the supply tube 10 wound around the inner pipe IP is provided with a plurality of nozzles 10n at intervals. This allows the back shield gas supplied from the other end of the supply tube 10 to be evenly filled around the outer circumferential surface of the inner pipe IP through the nozzles 10n.

[0022] When welding the outer pipes OP of the multi-pipe DP together, the space between the inner pipe IP and the outer pipe OP is filled with back shielding gas by the supply tube 10. If the distance between the welded portion of the outer pipe OP, i.e., the end of the outer pipe OP, and the part of the supply tube 10 wrapped around the inner pipe IP, is short, there is a risk that the supply tube 10 will melt during the welding operation of the outer pipe OP. For this reason, for example, when the supply tube 10 is a polyurethane tube, it is desirable to set the surface temperature that the supply tube 10 receives due to radiant heat during welding to be equal to or lower than 200° C., which is the melting point of polyurethane tubes. To meet this requirement, as shown in FIG. 4, it is preferable that the distance D between the part of the supply tube 10 wound around the inner tube IP and the end of the outer tube OP is 50 mm or more.

[0023] (Location of the detachable part 20) Next, the location of the detachable part 20 that secures the supply tube 10 will be described. As described above, the supply tube 10 is secured to the inner tube IP by the detachable part 20. The detachable part 20 breaks when the supply tube 10 is pulled. In this way, the detachable part 20 enables the supply tube 10 to be detached from the inner tube IP. For this reason, it is preferable that the detachable part 20 is disposed in a position where it is likely to break when the supply tube 10 is pulled.

[0024] Here, the portion of the supply tube 10 wound around the inner pipe IP is positioned as follows: That is, for example, as shown in Fig. 4 or 5, when viewed from the end of the multiple pipe DP that is to be welded, the portion of the supply tube 10 wound around the inner pipe IP is positioned so that the supply tube 10 moves counterclockwise around the axis of the inner pipe IP from the side closer to the other end toward one end of the supply tube 10.

[0025] At this time, the portion of the supply tube 10 that passes through the pedestal IPs located at the position closest to the detachable part 20 is preferably disposed at a position that ensures a distance C from at least the notched part IPsc or the thin-walled part IPst of the pedestal IPs when viewed from one end side of the supply tube 10, as shown in, for example, Figures 2 to 4. Moreover, it is more preferable that the detachable part 20 is disposed at a position shifted about 10° to 30° in the clockwise direction from the upper end of the multiple tube DP when viewed from one end side of the supply tube 10, as shown in Figure 7.

[0026] Here, when the supply tube 10 is pulled and the supply tube 10 comes into contact with the base IPs as shown in Fig. 8, it becomes difficult for the supply tube 10 to apply a force in a direction that breaks the detachable part 20. For this reason, in order to make it easier for the detachable part 20 to break when the supply tube 10 is pulled, it is preferable that the distance E between the part of the supply tube 10 wound around the inner tube IP and the base IPs be 250 mm or more as shown in Fig. 4, for example. As described above, the distance D between the part of the supply tube 10 wound around the inner tube IP and the end of the outer tube OP is preferably 50 mm or more.

[0027] In order to satisfy these requirements, it is preferable that the distance F (see FIG. 4) between the ends of the inner pipe IP and the outer pipe OP and the base IPs is at least 300 mm. In other words, as described above, it is preferable that the base IPs is provided at a location at least 300 mm away from the ends of the inner pipe IP and the outer pipe OP.

[0028] (Welding method for multi-layer DP pipes) Next, a method for welding a multi-wall pipe DP according to the present embodiment will be described. That is, a method for welding a multi-wall pipe DP including an inner pipe IP to which a supply tube 10 capable of supplying back shielding gas is attached and an outer pipe OP into which the inner pipe IP is inserted will be described. The method for welding a multi-wall pipe DP according to this embodiment includes an attachment step, an insertion step, an inner pipe welding step, a jetting step, an outer pipe welding step, and a removal step.

[0029] (Installation steps) The mounting step is a process of mounting the supply tube 10 capable of supplying back shielding gas to the inner pipe IP. That is, first, one end of the supply tube 10 provided with the nozzle 10n is wound around the inner pipe IP. Next, the supply tube 10 is fixed to the inner pipe IP by wrapping the detachable part 20, which is an aluminum tape, around the supply tube 10. Then, the part of the supply tube 10 other than the part wrapped around the inner pipe IP is placed in the cutout part IPsc or the thin part IPst of the base IPs arranged along the axial direction of the inner pipe IP.

[0030] (Insertion step) The insertion step is a process of inserting the inner pipe IP to which the supply tube 10 is attached into the outer pipe OP. In the insertion step, first, one of the inner pipe IP and the outer pipe OP is fixed. In this state, the other of the inner pipe IP and the outer pipe OP is moved toward the fixed one of the inner pipe IP and the outer pipe OP. In this way, the inner pipe IP is inserted into the outer pipe OP.

[0031] (Inner pipe welding step) The inner pipe welding step is a step of welding the inner pipes IP of the multi-pipe DP together. In the inner pipe welding step, the inner pipes IP are welded together, for example, by TIG welding. After the inner pipes IP are connected together by the inner pipe welding step, the outer pipes OP are welded together by the following steps.

[0032] (Ejection step) The ejection step is a process of ejecting the back shielding gas from the supply tube 10. This fills the gap between the inner pipe IP and the outer pipe OP with the back shielding gas. At the time of the ejection step, it is preferable that the ends of the outer pipe OP are in close contact with each other. If an SI material is provided on the outer peripheral surface of the inner pipe IP, aluminum tape may be wrapped around the SI material before the ejection step in order to protect the SI material located directly below the welded portion of the outer pipe OP.

[0033] (Outer pipe welding step) The outer pipe welding step is a process of welding the outer pipes OP. In the outer pipe welding step, the outer pipes OP are welded together by, for example, TIG welding. In this way, the multiple pipes DP are connected together.

[0034] (Removal steps) The removal step is a process of removing the supply tube 10 attached to the inner tube IP. That is, the supply tube 10 is pulled to break the detachable portion 20, and the supply tube 10 is removed from between the inner tube IP and the outer tube OP. Through the above steps, the multi-wall pipe DP is welded.

[0035] (Manufacturing method of multi-tube DP) Next, a method for manufacturing the multiple tube DP according to this embodiment will be described. The method for manufacturing the multiple tube DP includes a mounting step and an insertion step. The attachment step is a step of attaching the supply tube 10 capable of supplying the back shielding gas to the inner pipe IP. The attachment step is the same as the step explained in the welding method for the multi-pipe DP. The insertion step is a process of inserting the inner pipe IP to which the supply tube 10 is attached into the outer pipe OP. The insertion step is the same as the process described in the welding method for the multi-wall pipe DP. Through the above steps, the multi-wall pipe DP is manufactured.

[0036] As described above, the back shield gas supply device 100 according to the present embodiment includes the supply tube 10 that supplies the back shield gas to the multi-wall pipe DP. This allows the back shield gas to be supplied to the multi-wall pipe DP by the supply tube 10 when the outer pipe OP is welded.

[0037] In addition, the supply tube 10 is disposed between the inner pipe IP and the outer pipe OP. This allows the supply tube 10 to supply back shield gas between the inner pipe IP and the outer pipe OP when welding the outer pipe OP.

[0038] In addition, the supply tube 10 is detachably attached to the inner tube IP. With this, for example, by inserting the inner tube IP into the outer tube OP while the supply tube 10 is attached to the inner tube IP, the supply tube 10 can be disposed between the inner tube IP and the outer tube OP. This makes it easier to dispose the supply tube 10 between the inner tube IP and the outer tube OP.

[0039] The supply tube 10 is maintained in a state of being wound around the inner pipe IP by the detachable part 20. The state is released in response to the supply tube 10 being pulled. This makes it possible to easily remove the supply tube 10 from between the inner pipe IP and the outer pipe OP after welding the outer pipe OP.

[0040] The supply tube 10 also includes an outlet 10n for ejecting the back shielding gas, so that the back shielding gas can be quickly filled into the outer tube OP.

[0041] Further, the supply tube 10 has a plurality of nozzles 10n provided along the circumferential direction of the inner peripheral surface of the outer tube OP, thereby making it possible to uniformly fill the inside of the outer tube OP with the back shielding gas.

[0042] In addition, a portion of the supply tube 10 is wound around the inner tube IP. The multiple nozzles 10n are provided in the portion of the supply tube 10 wound around the inner tube IP. This allows the multiple nozzles 10n to be arranged along the circumferential direction of the inner tube IP. This allows the back shield gas to be filled more evenly inside the outer tube OP.

[0043] In addition, a ring-shaped seat IPs with a portion cut out in the circumferential direction is provided on the outer peripheral surface of the inner pipe IP. The supply tube 10 passes through the portion cut out in the circumferential direction of the inner pipe IP. This makes it easy to arrange the supply tube 10 between the inner pipe IP and the outer pipe OP, even if the seat IPs is provided on the outer peripheral surface of the inner pipe IP.

[0044] In addition, a pedestal IPs is provided on the outer peripheral surface of the inner pipe IP. The supply tube 10 passes through a part of the pedestal IPs that is thinner than the remaining part of the pedestal IPs. This makes it easier to arrange the supply tube 10 between the inner pipe IP and the outer pipe OP, even if the pedestal IPs is provided on the outer peripheral surface of the inner pipe IP.

[0045] Furthermore, the method for welding a multi-wall pipe DP according to the present embodiment includes an inserting step of inserting the inner pipe IP to which the supply tube 10 is attached into the outer pipe OP. This makes it easier to arrange the supply tube 10 between the inner pipe IP and the outer pipe OP. The method includes a jetting step for jetting the back shield gas from the supply tube 10. This allows the back shield gas to fill the inside of the outer tube OP. The method includes a removal step for removing the supply tube 10 attached to the inner pipe IP. This makes it possible to prevent the supply tube 10 from being left behind between the inner pipe IP and the outer pipe OP after the outer pipe OP is welded.

[0046] In the insertion step, either the inner pipe IP or the outer pipe OP is fixed, which makes it easier to insert the inner pipe IP into the outer pipe OP.

[0047] In addition, the manufacturing method of the multi-tube DP according to the present embodiment includes an attachment step of attaching the supply tube 10 capable of supplying back shielding gas to the inner tube IP, and an insertion step of inserting the inner tube IP to which the supply tube 10 is attached into the outer tube OP. That is, the inner tube IP is inserted into the outer tube OP with the supply tube 10 attached to the inner tube IP. This makes it easier to arrange the supply tube 10 between the inner tube IP and the outer tube OP. Therefore, it is easier to manufacture the multi-tube DP capable of supplying back shielding gas between the inner tube IP and the outer tube OP.

[0048] The method also includes an ejection step of ejecting the back shielding gas from the supply tube 10. That is, the back shielding gas is ejected from the supply tube 10 disposed between the inner pipe IP and the outer pipe OP. This makes it easier to supply the back shielding gas between the inner pipe IP and the outer pipe OP when welding the outer pipe OP.

[0049] (Modification of multi-tube DP) Next, a modified example of the multi-tube DP according to this embodiment will be described with reference to FIGS. In this modification, the same components as those in the above-described embodiment are denoted by the same reference numerals, and their description will be omitted, with only the differences being described. The multiple pipe DP according to the modified example differs from the above-described embodiment in the structure for ensuring a gap between the outer circumferential surface of the inner pipe IP and the inner circumferential surface of the outer pipe OP.

[0050] That is, in the multi-wall pipe DP according to the modified example, ribs OPp are provided on the inner peripheral surface of the outer pipe OP along the pipe axis direction of the outer pipe OP, as shown in Fig. 9. A plurality of ribs OPp are provided on the inner peripheral surface of the outer pipe OP at intervals in the circumferential direction of the outer pipe OP, as shown in Fig. 10. The tips of the ribs OPp contact the outer peripheral surface of the inner pipe IP. This ensures a gap between the outer peripheral surface of the inner pipe IP and the inner peripheral surface of the outer pipe OP in areas other than the ribs OPp.

[0051] In the multi-wall pipe DP according to the modified example, the supply tube 10 is disposed so as to pass between a first ridge OPp1, which is one of the plurality of ridges OPp provided as described above, and a second ridge OPp2, which is a ridge OPp located adjacent to the first ridge OPp1. During welding of the multi-wall pipe DP, the portion between the first ridge OPp1 and the second ridge OPp2, where the supply tube 10 is disposed, is preferably located above.

[0052] As shown in Fig. 11, a notch OPc is provided on the inner peripheral surface of the end of the outer pipe OP according to the modified example. The notch OPc refers to a portion of the end of the outer pipe OP where the protrusion OPp is cut out. The notch OPc is formed by machining the end of the outer pipe OP by countersinking, thereby removing the protrusion OPp provided on the end of the outer pipe OP. In the modified multi-pipe DP, the end of the supply tube 10 is located at the position of the inner pipe IP, corresponding to the notch OPc.

[0053] As described above, in the multi-wall pipe DP according to the modified example, the first ridges OPp1 and the second ridges OPp2 are provided on the inner circumferential surface of the outer pipe OP along the pipe axis direction of the outer pipe OP. The supply tube 10 is passed between the first ridges OPp1 and the second ridges OPp2. This makes it easier to arrange the supply tube 10 between the inner pipe IP and the outer pipe OP, even if the first ridges OPp1 and the second ridges OPp2 are provided on the inner circumferential surface of the outer pipe OP.

[0054] Further, a notch OPc is provided on the inner peripheral surface of the end portion of the outer tube OP. The end portion of the supply tube 10 is disposed at a position corresponding to the notch OPc at the position of the inner tube IP. This makes it easier to fill the part of the outer tube OP where the notch OPc is provided, i.e., the part of the inner peripheral surface of the outer tube OP where the first protrusion OPp1 and the second protrusion OPp2 are not provided, with the back shielding gas.

[0055] (Modification of attachment of supply tube 10) Next, a modified example of the attachment of the supply tube 10 according to this embodiment will be described. In this modification, the same components as those in the above-described embodiment are denoted by the same reference numerals, and their description will be omitted, with only the differences being described. In a variant of the attachment of the supply tube 10, the supply tube 10 is detachably attached to the outer tube OP.

[0056] Specifically, both ends of the supply tube 10 are attached to the inner circumferential surface of the outer tube OP by sticking them with tape or the like. At this time, tension is generated between both ends of the supply tube 10 to prevent the portions of the supply tube 10 other than both ends from loosening. In this way, when the supply tube 10 is attached to the inner peripheral surface of the outer tube OP in advance, the attachment step is performed after the above-mentioned insertion step. That is, after the inner tube IP is inserted into the outer tube OP to which the supply tube 10 is attached in advance, the tape that attached the supply tube 10 to the outer tube OP is removed. Then, one end of the supply tube 10 is wrapped around the inner tube IP and fixed by the attachment / detachment part 20. The above-mentioned modified attachment of the supply tube 10 can be applied to both the multiple pipe DP described above in this embodiment and the modified multiple pipe DP.

[0057] As described above, according to the modified embodiment of the supply tube 10, the supply tube 10 is detachably attached to the outer tube OP. This makes it easier to insert the inner tube IP into the outer tube OP, for example.

[0058] 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, the detachable portion 20 may be fixed using adhesive, hook-and-loop fastener, or tube joint other than aluminum tape. The supply tube 10 may be made of any tubing material other than polyurethane and nylon tubing.

[0059] In addition, the portion of the supply tube 10 wound around the inner pipe IP may be positioned such that, when viewed from the end of the multiple pipes DP that is to be welded, the portion of the supply tube 10 wound around the inner pipe IP moves in a clockwise direction around the axis of the inner pipe IP from the side closer to the other end of the portion of the supply tube 10 wound around the inner pipe IP toward one end of the supply tube 10. In this case, the detachable portion 20 is preferably positioned, for example, at a position overlapping at least the notch portion IPsc or the thin-walled portion IPst of the base IPs when viewed from one end of the supply tube 10, and more preferably positioned at a position shifted approximately 10° to 30° counterclockwise from the upper end of the multiple tube DP when viewed from one end of the supply tube 10. In this embodiment, the multi-tube DP is described as a double tube including an inner tube IP and one outer tube OP, but the back shielding gas supply device 100 of this embodiment may also be used to supply back shielding gas to a triple tube or a multi-tube having even more layers.

[0060] 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]

[0061] 10 Supply Tube 10n spout 20 Detachable part 100 Back shield gas supply device A, B dimensions C, D, E, F distance DP multiple tube IP inner tube IPs Pedestal IPsc notch IPst thin section OP outer tube OPc cutout OPp protrusion OPp1 1st protrusion OPp2 2nd protrusion T welding torch

Claims

1. a multi-wall tube including an inner tube and one or more outer tubes into which the inner tube is inserted; and a back shield gas supply device for supplying a back shield gas to one or more layers of the multi-layer tube, the back shield gas supply device includes a supply tube that supplies the back shield gas to the multiple tubes, The supply tube is disposed between the inner tube and the outer tube. A system characterized by:

2. The supply tube is removably attached to the inner tube.

2. The system of claim 1 .

3. A detachable portion is further provided, The supply tube is maintained in a state of being wound around the inner tube by the detachable portion, The detachable unit releases the state in response to the supply tube being pulled.

2. The system of claim 1 .

4. The supply tube includes an outlet for ejecting the back shield gas.

2. The system of claim 1 .

5. The supply tube is removably attached to the outer tube.

2. The system of claim 1 .

6. a multi-wall tube including an inner tube and one or more outer tubes into which the inner tube is inserted; and a back shield gas supply device for supplying a back shield gas to one or more layers of the multi-layer tube, the back shield gas supply device includes a supply tube that supplies the back shield gas to the multiple tubes, The supply tube is disposed between the inner tube and the outer tube. An object characterized by:

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