Back shield gas supply method

Abstract

To provide a back shield gas supplying method capable of reducing the consumption of a back shield gas.SOLUTION: A back shield gas supply method for supplying a back shield gas G into a pipe P using a back shield gas supply device 10 that is inserted into the pipe P and supplies the back shield gas G into the pipe P, the back shield gas supply method including an arrangement step of arranging the back shield gas supply device 10 inside one pipe P, and an approach step of bringing the other pipe P close to the one pipe P after the arrangement step, wherein the approach step is performed in a state where a pulling wire W for taking out the back shield gas supply device 10 from the inside of the pipe P is arranged inside the other pipe P.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present disclosure relates to a back shield gas supply method. [Background technology]

[0002] Conventionally, back shielding gas is supplied to the welded portion of a pipe to suppress oxidation of the welded portion, thereby ensuring welding quality. Patent Document 1 discloses that the inside of a pipe is sealed by expanding an annular sealing tube, and a back shield gas (inert gas) is supplied into the sealed pipe. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-51893 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, back shielding gas may be introduced into the piping without being sufficiently sealed, which means that more back shielding gas than necessary is used, posing a challenge in reducing the amount of back shielding gas used.

[0005] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a back shield gas supply method that can reduce the amount of back shield gas used. [Means for solving the problem]

[0006] A back shielding gas supply method according to one aspect of the present disclosure is a method for supplying back shielding gas into pipes using a back shielding gas supply device that is inserted into the pipes and supplies back shielding gas into the pipes, the method including: an arrangement step of arranging the back shielding gas supply device inside one of the pipes; and an approach step of bringing the other pipe close to the one pipe after the arrangement step, wherein the approach step is performed in a state where a traction wire for removing the back shielding gas supply device from inside the pipe is arranged inside the other pipe. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a back shield gas supply method that can reduce the amount of back shield gas used. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a cross-sectional view of the back shield gas supply system taken along the tube axis direction. [Figure 2] 2 is a cross-sectional view of the back shield gas supply device taken along the tube axis direction. FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2. [Figure 4] FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. 2. [Figure 5] FIG. 1 is a first diagram showing a pipe welding process. [Figure 6] FIG. 2 is a second diagram showing the welding process for piping. [Figure 7] FIG. 3 is a third diagram showing the welding process for piping. [Figure 8] FIG. 4 is a fourth diagram showing the welding process for piping. [Figure 9] FIG. 5 is a diagram showing the piping welding process. [Figure 10] FIG. 6 is a diagram showing the piping welding process. [Figure 11] FIG. 7 is a diagram showing the piping welding process. [Figure 12] FIG. 8 is an 8th diagram showing the welding process of the pipe. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a back shield gas supply device and a back shield gas supply method according to an embodiment of the present disclosure will be described with reference to the drawings. The back-shielding gas supply device supplies back-shielding gas to the periphery of the weld when welding the ends of pipes together, thereby suppressing oxidation of the weld and contributing to ensuring the quality of the weld. In this embodiment, the back shield gas is an inert gas such as argon, helium, nitrogen, etc. Preferably, the back shield gas is an inert gas that is heavier than air, such as argon, but an inert gas that is lighter than air, such as helium or nitrogen, may also be used.

[0010] FIG. 1 is a cross-sectional view of a back shield gas supply system 1 taken along the tube axis direction. FIG. 2 is a cross-sectional view of the back shield gas supply device 10 taken along the tube axis direction. As shown in FIG. 1, the back shielding gas supply system 1 includes a pipe P, a back shielding gas supply device 10, and a gas supply means 20. 1 or 2, the back shielding gas supply device 10 is inserted into the pipe P and supplies the back shielding gas G into the pipe P. The welding of the ends of the pipe P described above is performed in a state in which the back shielding gas G is supplied into the pipe P by the back shielding gas supply device 10. In this embodiment, the welding of the ends of the pipe P is performed in a state in which the pipe P is arranged in a horizontal direction (including a substantially horizontal direction). The substantially horizontal direction of the pipe P means that the crossing angle between the center CP of the pipe P and the horizontal direction is 1° or less.

[0011] In this embodiment, when the back shielding gas supply device 10 is disposed in the pipe P, the orientation of the back shielding gas supply device 10 around the axis of the pipe P is set to be in the first place because air (oxygen) is lighter than argon gas and the oxygen concentration in the 12 o'clock direction (upward) is higher than in other directions. Therefore, when the back shielding gas supply device 10 is inserted into the pipe P, the gas inlet 11b2h (described later) where the oxygen concentration is measured faces upward.

[0012] The back shielding gas G is sent from gas supply means 20 to the back shielding gas supply device 10. The gas supply means 20 includes, for example, a tube 21 inserted inside the piping P and a gas cylinder 22 connected to the tube 21. Hereinafter, in this embodiment, with respect to the path through which the back shielding gas G flows, the side closer to the gas cylinder 22 is referred to as the upstream side, and the side closer to the back shielding gas supply device 10 is referred to as the downstream side. In this embodiment, as shown in FIG. 1, a region to which back shield gas G is supplied when the pipe P is welded is referred to as a back shield gas region A.

[0013] The back shield gas supply device 10 supplies the back shield gas G, which flows from the tube 21 of the gas supply means 20 into the inside of the pipe P, to the back shield gas region A. In this embodiment, the flow path of the back shield gas G supplied to the back shield gas region A is referred to as a back shield gas supply path R1, as shown in FIG. The back shielding gas supply device 10 may also use the back shielding gas G flowing from the tube 21 to expand the diameter of a diameter expanding member 12, which will be described later. In this embodiment, the flow path of the back shielding gas G used to expand the diameter of the diameter expanding member 12 is called a diameter expanding gas supply path R2, as shown in FIG. That is, in this embodiment, the back shield gas supply device 10 or the back shield gas supply system 1 includes, as shown in FIG. 1, a back shield gas supply path R1 that supplies the back shield gas G to the back shield gas nozzle 14a, and an expanding-diameter gas supply path R2 that supplies the back shield gas G to the expanding-diameter member 12.

[0014] In this embodiment, the expanded-diameter gas supply passage R2 and the back shielding gas supply passage R1 are partially common to each other, i.e., the back shielding gas supply passage R1 and the expanded-diameter gas supply passage R2 are formed so as to branch off from a common portion R3, which is a common portion, at a branch point RB, as shown in FIG. The use of the back shield gas G is determined by whether it flows through the back shield gas supply passage R1 or the expanded-diameter gas supply passage R2. In this embodiment, the path through which the back shield gas G flows is determined by a switching means 16 (described in detail later).

[0015] After the welding of the pipes P is completed, the back shielding gas supply device 10 passes through the inside of one of the two pipes P that have been welded together and is removed from the inside of the pipes P. Specifically, for example, as shown in FIG. 1 , a traction wire W is attached to the back shielding gas supply device 10. Then, the back shielding gas supply device 10 is removed from the inside of the pipe P by an operator pulling the traction wire W. 1, in the present embodiment, the side of the back shielding gas supply apparatus 10 to which the traction wire W is attached will be referred to as the inlet side S1 of the pipe P. The side of the back shielding gas supply apparatus 10 to which the traction wire W is not attached will be referred to as the deep side S2 of the pipe P. In addition, the pipe axis direction of the pipe P will be simply referred to as the pipe axis direction. As shown in FIG. 2, the back shield gas supply device 10 includes a moving member 11, a diameter expanding member 12, a sealing member 13, a gas supply member 14, a tubular member 15, and a switching means 16.

[0016] The movable member 11 is a member that is movable along the inner peripheral wall Pw of the pipe P. As shown in FIG. 2 , each component of the back shielding gas supply device 10 is directly or indirectly connected to the movable member 11. The movable member 11 enables the back shielding gas supply device 10 to move inside the pipe P. As shown in FIG. 2, the moving member 11 includes a first moving member 11a located on the inner side S2 of the pipe P and a second moving member 11b located on the inlet side S1 of the pipe P. The first moving member 11a and the second moving member 11b have a common structure. Below, the first moving member 11a will be described in detail, and the second moving member 11b will be described with respect to differences from the first moving member 11a.

[0017] Fig. 3 is a cross-sectional view taken along the line III-III in Fig. 2. Fig. 3 is a view showing the first moving member 11a as viewed in the axial direction of the pipe P. 1 to 3, the first moving member 11a has a plurality of rolling members 11a1 that can roll along the inner circumferential wall Pw of the pipe P, and a main body portion 11a2 to which the rolling members 11a1 are attached. That is, the first moving member 11a is configured by attaching the rolling members 11a1 to the main body portion 11a2. The main body 11a2 is, for example, a cylindrical member with a bottom, as shown in Fig. 2. The bottom of the main body 11a2 faces the inlet side S1. A rolling member 11a1 is attached to a side surface 11A of the main body 11a2. A diameter expansion member 12 is attached to a bottom 11B of the main body 11a2 (details will be described later). Note that the bottom 11B of the main body 11a2 may be provided with a through-hole H through which a bolt B can be inserted to attach the diameter expansion member 12.

[0018] As shown in FIG. 3 , for example, a known spring ball plunger is preferably used for the rolling member 11a1. By using the spring ball plunger, the ball portions 11BL of the multiple rolling members 11a1 are configured to be movable in the radial direction of the pipe P. Each of the rolling members 11a1 is biased toward the inner circumferential wall Pw of the pipe P. Specifically, the ball portions 11BL of the rolling members 11a1, which are spring ball plungers, are pressed against the inner circumferential wall Pw of the pipe P by a spring or the like (not shown). By pressing the ball portions 11BL of the rolling members 11a1 against the inner circumferential wall Pw of the pipe P, for example, when an operator pulls the back shielding gas supply apparatus 10 via a pulling wire W, the ball portions 11BL of the rolling members 11a1 rotate. This allows the back shielding gas supply apparatus 10 to move inside the pipe P.

[0019] In this embodiment, the first moving member 11a has three rolling members 11a1 as shown in Fig. 3. However, the first moving member 11a may have two rolling members 11a1, four or more rolling members 11a1, one rolling member 11a1, or no rolling member 11a1. 3, one of the three rolling members 11a1 is disposed above the center CP of the pipe P. More preferably, one of the three rolling members 11a1 is provided at a position corresponding to the upper end of the pipe P when viewed in the axial direction of the pipe P. As shown in Fig. 3, of the two rolling members 11a1 other than the rolling member 11a1 provided on the upper side of the pipe P, one rolling member 11a1 and the other rolling member 11a1 are arranged below the center CP of the pipe P. When viewed in the pipe axis direction shown in Fig. 3, the one rolling member 11a1 and the other rolling member 11a1 are arranged on one side and the other side of the center CP of the pipe P in the left-right direction. In this embodiment, the plurality of rolling members 11a1 may be arranged at equal intervals in the circumferential direction of the pipe P, as shown in Fig. 3. For example, when there are three rolling members 11a1, the rolling member 11a1 provided at a position corresponding to the upper end of the pipe P as described above may be used as a reference, and the other two rolling members 11a1 may be arranged at intervals of 120°. This may satisfy the above-mentioned conditions for the arrangement of the rolling members 11a1.

[0020] 2, the second moving member 11b may be formed with a part of the back shielding gas supply path R1, a part of the diameter-expanding gas supply path R2, and a gas inlet 11b2h in addition to the components of the first moving member 11a described above. Also, the second moving member 11b may be provided with an attachment part E (for example, an eyebolt) to which the traction wire W is attached.

[0021] The main body 11b2 of the second movable member 11b is cylindrical with a bottom, similar to the main body 11a2 of the first movable member 11a. In the main body 11b2 of the second movable member 11b, a portion of the back shielding gas supply channel R1 and a portion of the expanded-diameter gas supply channel R2 are formed at the bottom 11B of the main body 11b2. The bottom 11B of the main body 11b2 faces the rear side S2. As shown in FIG. 2, the back shielding gas supply channel R1 and the expanded-diameter gas supply channel R2, which are partially shared at the shared section R3, branch off at a branch point RB located in the main body 11b2. As shown in FIG. 2, a tube 21 for supplying the back shielding gas G is connected to the upstream end of the back shielding gas G flow path in the shared section R3 of the main body 11b2.

[0022] The gas inlet 11b2h is a portion that takes in gas inside the pipe P. For example, an oxygen concentration measuring device (not shown) may be connected to the gas inlet 11b2h. This may make it possible to measure the oxygen concentration of the gas taken in through the gas inlet 11b2h. In this embodiment, as shown in FIG. 2, the gas inlet 11b2h is disposed closer to the inlet side S1 of the pipe P than the seal member 13. The seal member 13 will be described in detail later. As described above, when back shielding gas G is supplied to back shielding gas region A shown in FIG. 1, the air in back shielding gas region A is forced out of back shielding gas region A through gap C between seal member 13 and inner peripheral wall Pw of pipe P. Gas inlet port 11b2h takes in the gas thus forced out of back shielding gas region A. A measuring device connected to gas inlet port 11b2h measures the oxygen concentration of the gas taken in by gas inlet port 11b2h as described above. This makes it possible to evaluate whether back shielding gas G has sufficiently filled back shielding gas region A. 2, when viewed in a direction perpendicular to the pipe axis of the piping P, the gas inlet 11b2h preferably does not overlap with the diameter expansion member 12 and the switching means 16. Moreover, the gas inlet 11b2h is preferably disposed above the center CP of the piping P. Moreover, the gas inlet 11b2h preferably opens upward.

[0023] 2, in the back shielding gas supply apparatus 10, the components other than the movable member 11, including the diameter expanding member 12 and the switching means 16, are arranged between the first movable member 11a and the second movable member 11b. The components other than the movable member 11 in the back shielding gas supply apparatus 10 are arranged so as not to be adjacent to the first movable member 11a and the second movable member 11b in the radial direction of the pipe P. This prevents the back shielding gas supply apparatus 10 from becoming larger in the radial direction of the pipe P. It also makes it easier to prevent the components other than the movable member 11 in the back shielding gas supply apparatus 10 from coming into contact with the inner circumferential wall Pw of the pipe P.

[0024] 2, the diameter expanding member 12 is a member that can be expanded in diameter by the back shielding gas G and come into contact with the inner peripheral wall Pw of the pipe P. The diameter expanding member 12 is, for example, an air picker. By the diameter expanding member 12 coming into contact with the inner peripheral wall Pw of the pipe P, for example, the position of the back shielding gas supply device 10 can be fixed inside the pipe P. Alternatively, the back shielding gas G supplied into the inside of the pipe P can be prevented from leaking from between the diameter expanding member 12 and the inner peripheral wall Pw of the pipe P. As shown in FIG. 2, the diameter expanding member 12 has an expanded diameter portion 12a and a main body portion 12b.

[0025] As shown in FIG. 2, the expanded diameter portion 12a is a portion of the expanded diameter member 12 that can be expanded in diameter. The expanded diameter portion 12a is a bag-shaped member provided on the outer periphery of the main body portion 12b. The expanded diameter portion 12a expands in diameter by being filled with back shielding gas G. This allows the expanded diameter portion 12a to come into contact with the inner circumferential wall Pw of the pipe P. A flexible material such as rubber is preferably used for the expanded diameter portion 12a.

[0026] As shown in FIG. 2, the main body 12b is a block-shaped member located at the center of the enlarged-diameter portion 12a. The main body 12b has an enlarged-diameter gas outlet 12b1 that ejects back shielding gas G into the enlarged-diameter portion 12a. The enlarged-diameter gas outlet 12b1 is connected to the enlarged-diameter gas supply path R2. That is, the enlarged-diameter gas outlet 12b1 is a portion that ejects back shielding gas G that has flowed through the enlarged-diameter gas supply path R2 into the enlarged-diameter portion 12a. Furthermore, a portion of the enlarged-diameter gas supply path R2 is formed inside the main body 12b. In this embodiment, at least a portion of the enlarged-diameter gas supply path R2 formed in the main body 12b of the enlarged-diameter portion 12a may be located above the center CP of the pipe P.

[0027] 2, the expanded diameter gas outlet 12b1 is disposed above the center CP of the pipe P. In other words, a space through which the back shielding gas G passes is formed in the portion of the main body 12b above the center CP of the pipe P. This reduces the weight of the portion of the main body 12b above the center CP of the pipe P by the amount of the space, which contributes to lowering the center of gravity of the main body 12b and the back shielding gas supply device 10. In this embodiment, the expanded-diameter gas outlet 12b1 opens upward as shown in Fig. 2. This allows the inside of the expanded-diameter portion 12a to be efficiently filled with the back shielding gas G when a gas heavier than air is used as the back shielding gas G. Note that when a gas lighter than air is used as the back shielding gas G, the expanded-diameter gas outlet 12b1 may also open downward.

[0028] 2, the diameter expansion member 12 is disposed between the first movable member 11a and the gas supply member 14. More specifically, the diameter expansion member 12 is located adjacent to the first movable member 11a in the axial direction of the pipe P. The gas supply member 14 is disposed adjacent to the diameter expansion member 12 in the back shield gas region A. The diameter expanding member 12 is fixed to the first moving member 11a by a bolt B, for example, as shown in FIG. The gas supply member 14 and the diameter expansion member 12 are connected, for example, by screwing together threads (not shown) formed on each other. At this time, the gas supply member 14 and the diameter expansion member 12 are fixed so that parts of the expanded diameter gas supply passages R2 formed in the gas supply member 14 and the diameter expansion member 12 are connected to each other, as shown in FIG.

[0029] The seal member 13 is a member capable of sealing the inside of the pipe P. In this embodiment, as shown in FIG. 2 , the seal member 13 is a plate-shaped member made of silicone resin or the like. Any other material may be used for the seal member 13 as long as it has sufficient heat resistance and flexibility. In this embodiment, the diameter expansion member 12 and the seal member 13 are arranged on one side and the other side of a back shield gas ejection port 14a (described later) in the axial direction of the pipe P. More specifically, as shown in FIG. 2 , the diameter expansion member 12 is located next to the first moving member 11a, while the seal member 13 is located next to the second moving member 11b. A back shield gas region A filled with a back shield gas G in the pipe P is formed between the diameter expansion member 12 and the seal member 13. In this embodiment, as shown in Fig. 2, a gap C is formed between the inner peripheral wall Pw of the pipe P and the outer peripheral edge of the seal member 13. The gap C preferably has a size of, for example, about 0.5% of the diameter of the pipe P when converted into an equivalent diameter. The gap C is formed around the entire outer periphery of the seal member 13. This allows air present in the pipe P to be pushed out from the gap C (such as the portion of the gap C located above the pipe P) when back shield is supplied to the back shield gas region A.

[0030] The gas supply member 14 supplies the back shielding gas G toward the diameter expansion member 12 and the inside of the pipe P. As shown in FIG. 2, the gas supply member 14 is formed in a block shape, and has a flow path formed therein for flowing the back shielding gas G. 2, the gas supply member 14 includes an expanded-diameter gas supply channel R2 and a back-shielding gas supply channel R1. A portion of the expanded-diameter gas supply channel R2 and a portion of the back-shielding gas supply channel R1 are formed in the gas supply member 14. In this embodiment, at least a portion of the expanded-diameter gas supply channel R2 formed in the gas supply member 14 may be disposed above the center CP of the pipe P.

[0031] 2, the gas supply member 14 is connected to the diameter expansion member 12. As a result, one end of the diameter expansion gas supply path R2 provided in the gas supply member 14 is connected to the diameter expansion gas supply path R2 provided in the diameter expansion member 12. The other end of the diameter expansion gas supply path R2 provided in the gas supply member 14 is connected to the tubular member 15. As a result, the back shield gas G for expanding the diameter of the diameter expansion member 12 flows into the diameter expansion member 12 via the gas supply member 14.

[0032] As shown in FIG. 2, the gas supply member 14 has a plurality of back shield gas outlets 14a that eject back shield gas G into the pipe P (back shield gas region A). The plurality of back shield gas outlets 14a are arranged at predetermined intervals (e.g., equal intervals) around the center of the gas supply member 14 (the center CP of the pipe P). One end of a back shield gas supply path R1 formed in the gas supply member 14 is connected to the back shield gas outlets 14a. As a result, the back shield gas supply path R1 formed in the gas supply member 14 supplies back shield gas G to the back shield gas outlets 14a. As shown in FIG. 2, a switching means 16 is connected to the other end of the back shield gas supply path R1 formed in the gas supply member 14. As a result, the switching means 16 determines whether or not back shield gas G is supplied to the back shield gas supply path R1 formed in the gas supply member 14. As shown in FIG. 2, it is preferable that the back shield gas ejection port 14a does not overlap with the diameter expansion member 12 and the switching means 16 when viewed in the direction perpendicular to the pipe axis of the pipe P. In this embodiment, a back shield gas ejection port 14 a , which will be described later, is disposed between the diameter expansion member 12 and the seal member 13 on the side closer to the diameter expansion member 12 .

[0033] As shown in FIG. 2, the tubular member 15 has a diameter-expanding gas supply path R2 that supplies the back shielding gas G to the diameter-expanding member 12. In other words, the tubular member 15 is a part of the diameter-expanding gas supply path R2 that supplies the back shielding gas G to the diameter-expanding member 12. The tubular member 15 is, for example, a cylindrical member. The tubular member 15 is connected to the diameter-expanding gas supply path R2 formed in the gas supply member 14. In this embodiment, the tubular member 15 is disposed between the gas supply member 14 and the second moving member 11b as shown in FIG. 2. More specifically, the tubular member 15 is disposed between the gas supply member 14 and the seal member 13. The tubular member 15 is disposed adjacent to the switching means 16 in the radial direction of the piping P.

[0034] The switching means 16 switches whether or not to supply the back shield gas G to the back shield gas nozzle 14a, depending on the pressure of the back shield gas G. More specifically, the switching means 16 switches whether or not to supply the back shield gas G to the back shield gas nozzle 14a, depending on the pressure of the back shield gas G supplied to the diameter expansion member 12 via the diameter expansion gas supply path R2. In this embodiment, the switching means 16 is configured by a switching valve (not shown). 2, the switching means 16 is provided in a portion of the back shielding gas supply passage R1 that is not shared with the expanded-diameter gas supply passage R2. That is, the switching means 16 is provided downstream of the branch point RB in the flow path of the back shielding gas G. In this embodiment, the switching means 16 may be configured to be long in the tube axis direction, as shown in Fig. 2. That is, the size of the switching means 16 in the tube axis direction may be configured to be larger than the size of the switching means 16 in the direction perpendicular to the tube axis.

[0035] As shown in FIG. 2, the switching means 16 has a cylinder portion 16a and a valve body 16b. The cylinder portion 16a is a tubular (for example, cylindrical) member that houses the valve body 16b. The cylinder portion 16a is disposed adjacent to the tubular member 15 in the radial direction of the pipe P. The cylinder portion 16a is a part of the back shielding gas supply path R1. The valve element 16b is configured to be movable along the pipe axis direction. More specifically, the valve element 16b is movable along the pipe axis direction inside the cylinder portion 16a. The radial movement of the valve element 16b is restricted by the cylinder portion 16a.

[0036] In this embodiment, the valve element 16b is biased from the downstream side toward the upstream side of the back shielding gas supply path R1 inside the cylinder portion 16a. For example, as shown in FIG. 2, a spring S for biasing the valve element 16b may be provided inside the cylinder portion 16a. By being biased as described above, the valve element 16b closes the upstream end of the back shielding gas supply path R1 of the cylinder portion 16a. This prevents the back shielding gas G from passing inside the cylinder portion 16a.

[0037] 2, the expanded-diameter gas supply passage R2 and the back shielding gas supply passage R1 are formed so as to branch off at a branch point RB from a common portion R3 where they are common to each other. The expanded-diameter gas supply passage R2 is connected to the expanded-diameter gas outlet 12b1 through a tubular member 15, a gas supply member 14, and the expanded-diameter member 12. The back shielding gas supply passage R1 is connected to the back shielding gas outlet 14a through a switching means 16 and the gas supply member 14. As described above, in the back shielding gas supply passage R1, the cylinder portion 16a is closed by the valve body 16b. As a result, the back shielding gas G supplied from the tube 21 is first supplied to the diameter-expanding member 12 through the diameter-expanding gas supply passage R2. As a result, the diameter of the diameter-expanding member 12 is expanded before the back shielding gas G is injected into the inside of the pipe P.

[0038] As the diameter expansion of the diameter expansion member 12 continues, and the diameter expansion portion 12a of the diameter expansion member 12 comes into contact with the inner peripheral wall Pw of the pipe P as shown in FIG. 2, back shielding gas G is no longer supplied to the diameter expansion member 12, and the pressure in the diameter expansion gas supply path R2 increases. Then, the pressure in the tube 21 exceeds the force of the spring S biasing the valve body 16b. As a result, inside the cylinder portion 16a, the valve body 16b is pushed from the upstream side to the downstream side of the back shielding gas supply path R1, and the state in which the cylinder portion 16a is blocked by the valve body 16b is released. This causes the back shielding gas G to flow into the cylinder portion 16a. Therefore, the back shielding gas G flows into the back shielding gas supply path R1 of the gas supply member 14 and is sprayed into the inside of the pipe P from the back shielding gas ejection port 14a. As described above, after the diameter expanding member 12 expands in diameter, the switching means 16 opens in response to the pressure of the back shield gas G, and the back shield gas G is supplied to the back shield gas outlet 14a.

[0039] In this embodiment, the switching means 16 is disposed, for example, between the gas supply member 14 and the second moving member 11b. More specifically, the switching means 16 is disposed between the gas supply member 14 and the seal member 13 in the axial direction of the piping P, as shown in FIG. 2, it is preferable that the diameter expansion member 12 and the switching means 16 do not overlap when viewed in a direction perpendicular to the pipe axis of the pipe P. When viewed in the pipe axis direction of the pipe P, the diameter expansion member 12 and the switching means 16 may overlap.

[0040] Fig. 4 is a cross-sectional view taken along the line IV-IV shown in Fig. 2. Fig. 4 is a cross-sectional view of switching means 16 disposed inside pipe P, taken along a direction perpendicular to the pipe axis direction. In the present embodiment, the switching means 16 may be disposed below the center CP of the pipe P, as shown in Fig. 4. More specifically, for example, the switching means 16 may be disposed between one rolling member 11a1 and another rolling member 11a1 when viewed in the axial direction of the pipe P. That is, the switching means 16 may be disposed between two rolling members 11a1 located below the center CP of the pipe P, as shown in Fig. 3. That is, the switching means 16 may be disposed at a position corresponding to the lower end of the pipe P.

[0041] The back shield gas supply device 10 according to this embodiment is configured with the above components. In this embodiment, the back shielding gas outlet 14a, the diameter expansion member 12, and the switching means 16 are preferably aligned in the tube axis direction, as shown in Fig. 2. Furthermore, the back shielding gas outlet 14a, the diameter expansion member 12, the switching means 16, and the gas inlet 11b2h may be aligned in the tube axis direction.

[0042] (Back shield gas supply method) Next, a back shielding gas supplying method according to this embodiment will be described with reference to Figures 5 to 12. That is, a back shielding gas supplying method using the above-described back shielding gas supplying device 10 will be described. The back shielding gas supplying method according to this embodiment includes at least a diameter expansion step and a switching step. Below, a welding step for welding pipes P together will be described, along with a method for supplying back shielding gas G that is performed in conjunction with the welding step. FIG. 5 is a first diagram showing a welding process for the pipe P. FIG. FIG. 6 is a second diagram showing the welding process of the pipe P. FIG. 7 is a third diagram showing the welding process of the pipe P. FIG. 8 is a fourth diagram showing the welding process of the pipe P. FIG. 9 is a fifth diagram showing the welding process of the pipe P. FIG. 10 is a sixth diagram showing the welding process of the pipe P. FIG. 11 is a seventh diagram showing the welding process of the pipe P. FIG. 12 is an eighth diagram showing the welding process of the pipe P. As shown in FIG.

[0043] First, as shown in FIG. 5, a back shielding gas supply device 10 is placed inside one of the pipes P to be welded together. 6, the other of the pipes P to be welded together is brought close to one of the pipes P. At this time, a traction wire W may be placed inside the other of the pipes P to remove the back shielding gas supply device 10 from the pipe P after welding. As shown in Fig. 7, the ends of one end of the pipe P and the other end of the other pipe P are aligned with each other. Specifically, the ends are aligned so that the central axes of the one end of the pipe P and the other end of the other pipe P coincide with each other. At this time, the ends of the one end of the pipe P and the other end of the other pipe P are not in contact with each other. Then, the back shielding gas supply device 10 is arranged to straddle the two ends of the pipe P. This allows the back shielding gas region A to be arranged so as to include the welded parts of the one end of the pipe P and the other end of the other pipe P. At this time, it is preferable that the position of the back shielding gas supply device 10 be visually confirmed from between the two ends of the pipe P.

[0044] After the back shield gas supply device 10 is aligned as described above, a diameter expansion step is carried out. That is, as shown in Fig. 8, the supply of the back shield gas G to the back shield gas supply device 10 through the tube 21 is started. The supplied back shielding gas G is first supplied to the diameter expansion member 12 through the diameter expansion gas supply path R2. This causes the diameter of the diameter expansion member 12 to expand. Then, as shown in FIG. 8, the expanded diameter portion 12a of the diameter expansion member 12 is brought into contact with the inner peripheral wall Pw of the pipe P. This completes the fixing of the position of the back shielding gas supply device 10 in the pipe P and the sealing of the inside of the pipe P by the diameter expansion member 12. After the diameter expansion member 12 has been sufficiently expanded, one end and the other end of the pipe P are brought close enough to be welded to each other, as shown in Fig. 9. At this time, the ends of the pipe P may be brought into contact with each other, or a groove may be provided between the ends of the pipe P. This forms a back shield gas region A.

[0045] 9, after the back shielding gas region A is formed, the switching step is performed. That is, after the diameter expanding step, when the back shielding gas G is further supplied from the tube 21, the pressure in the portion of the back shielding gas supply path R1 downstream of the switching means 16 increases. As a result, the back shielding gas G presses the valve element 16b of the switching means 16. 10, back shield gas G is supplied to back shield gas supply path R1 via cylinder portion 16a. As a result, back shield gas G is supplied to back shield gas region A. As a result, air located in back shield gas region A is discharged to the outside of back shield gas region A through gap C. The discharged air is taken in by gas intake port 11b2h, and the oxygen concentration is measured. Thus, in the switching step, the switching means 16 switches whether or not the back shield gas G is supplied to the back shield gas ejection port 14a depending on the pressure of the back shield gas G.

[0046] After the back shield gas G is sufficiently supplied into the back shield gas region A by the switching step, the pipes P are welded together as shown in FIG. After the welding of the pipes P is completed, the supply of the back shield gas G is stopped. 12, the diameter expansion portion 12a of the diameter expansion member 12 contracts and moves away from the inner peripheral wall Pw of the pipe P. After this state is reached, the back shielding gas supply device 10 is removed from the inside of the pipe P by pulling the traction wire W. Through the above-described steps, the back shielding gas supply method and the welding of the pipe P according to this embodiment are performed.

[0047] As described above, according to the back shielding gas supply apparatus 10 of this embodiment, the diameter expanding member 12 can be expanded in diameter by the back shielding gas G and come into contact with the inner peripheral wall Pw of the pipe P. By expanding the diameter of the diameter expanding member 12 and coming into contact with the inner peripheral wall Pw of the pipe P, for example, the inside of the pipe P can be reliably sealed when the back shielding gas G is supplied. Furthermore, the back shielding gas supply apparatus 10 can be positioned inside the pipe P. Therefore, the operation of supplying the back shielding gas G can be performed stably. Furthermore, the switching means 16 switches whether or not to supply the back shield gas G to the back shield gas nozzle 14a depending on the pressure of the back shield gas G. This allows the back shield gas G to be ejected from the back shield gas nozzle 14a at appropriate timing. This prevents the back shield gas G from being ejected more than necessary. This allows the amount of back shield gas G used to be reduced.

[0048] Furthermore, after the diameter expansion member 12 expands in diameter, the switching means 16 opens in response to the pressure of the back shielding gas G, and the back shielding gas G is supplied to the back shielding gas outlet 14a. Therefore, the diameter expansion member 12 expands in diameter and comes into contact with the inner peripheral wall Pw of the pipe P, sealing the inside of the pipe P, and then the back shielding gas G is ejected from the back shielding gas outlet 14a. This makes it possible to prevent the back shielding gas G from leaking from the inside of the pipe P. Therefore, the amount of back shielding gas G used can be reduced.

[0049] Furthermore, the switching means 16 switches whether or not to supply the back shield gas G to the back shield gas ejection port 14a, depending on the pressure of the back shield gas G supplied to the diameter expansion member 12. This makes it possible to more reliably switch whether or not to supply the back shield gas G to the back shield gas ejection port 14a.

[0050] The back shielding gas supply device 10 further includes a diameter-expanding gas supply passage R2 that supplies back shielding gas G to the diameter-expanding member 12, and a back shielding gas supply passage R1 that supplies back shielding gas G to the back shielding gas ejection port 14a. As a result, for example, the diameter of the diameter-expanding member 12 can be expanded by supplying back shielding gas G to the diameter-expanding member 12 via the diameter-expanding gas supply passage R2. As a result, the back shielding gas G can be ejected into the piping P by supplying back shielding gas G to the back shielding gas ejection port 14a via the back shielding gas supply passage R1. The diameter-expanding gas supply passage R2 and the back shielding gas supply passage R1 are partially common to each other. As a result, the back shielding gas supply device 10 can be made smaller.

[0051] Here, when the diameter expansion member 12 is sufficiently expanded by the back shielding gas G and the diameter expansion member 12 comes into contact with the inner peripheral wall Pw of the pipe P, if further back shielding gas G is supplied to the diameter expansion gas supply path R2, the back shielding gas G will not be supplied to the diameter expansion member 12, and the pressure in the diameter expansion gas supply path R2 and the common portion R3, which is the portion where the diameter expansion gas supply path R2 and the back shielding gas supply path R1 are common to each other, will increase. Therefore, switching means 16 is provided in a portion of back shielding gas supply path R1 that is not shared with the expanded-diameter gas supply path R2. As a result, for example, when the pressure in the shared portion R3 increases as described above, the pressure of the back shielding gas G can switch switching means 16 to a state in which back shielding gas G is supplied to back shielding gas outlet 14a. Therefore, whether back shielding gas G is supplied to back shielding gas outlet 14a can be reliably switched depending on the pressure of the back shielding gas G supplied to diameter-expanding member 12.

[0052] Furthermore, when viewed in the direction orthogonal to the tube axis, the diameter expansion member 12 and the switching means 16 do not overlap. This makes it possible to prevent the back shielding gas supply device 10 from becoming larger in the radial direction of the pipe P due to the arrangement of the diameter expansion member 12 and the switching means 16, for example. Therefore, the back shielding gas supply device 10 can be made thinner.

[0053] Furthermore, when viewed in the tube axis direction, the diameter expansion member 12 and the switching means 16 overlap. That is, the diameter expansion member 12 and the switching means 16 are arranged side by side along the tube axis direction. This arrangement of the diameter expansion member 12 and the switching means 16 makes it possible to prevent the back shielding gas supply device 10 from becoming larger in the radial direction of the piping P. Therefore, the back shielding gas supply device 10 can be made thinner.

[0054] Furthermore, when viewed in the direction orthogonal to the tube axis, the back shielding gas outlet 14a does not overlap with the diameter expansion member 12 and the switching means 16. This makes it possible to prevent the back shielding gas supply device 10 from becoming larger in the radial direction of the pipe P, for example, due to the arrangement of the back shielding gas outlet 14a, the diameter expansion member 12, and the switching means 16. This allows the back shielding gas supply device 10 to be made thinner.

[0055] Furthermore, the back shielding gas outlet 14a, the diameter expansion member 12, and the switching means 16 are aligned in the axial direction of the pipe. This arrangement of the back shielding gas outlet 14a, the diameter expansion member 12, and the switching means 16 prevents the back shielding gas supply device 10 from becoming larger in the radial direction of the pipe P. This allows the back shielding gas supply device 10 to be made thinner.

[0056] The back shielding gas supply device 10 further includes a gas inlet 11b2h that takes in gas from within the pipe P. This allows the gas from within the pipe P to be taken in through the gas inlet 11b2h, enabling the concentration of the gas remaining within the pipe P to be evaluated. Furthermore, when viewed in a direction perpendicular to the pipe axis, the gas inlet 11b2h does not overlap with the diameter expansion member 12 and the switching means 16. This makes it possible to prevent the back shielding gas supply device 10 from becoming larger in the radial direction of the pipe P, for example, by arranging the gas inlet 11b2h, the diameter expansion member 12, and the switching means 16. This allows the back shielding gas supply device 10 to be made thinner.

[0057] Furthermore, the back shielding gas outlet 14a, the diameter expansion member 12, the switching means 16, and the gas inlet 11b2h are aligned in the axial direction of the pipe. This arrangement of the back shielding gas outlet 14a, the diameter expansion member 12, the switching means 16, and the gas inlet 11b2h makes it possible to prevent the back shielding gas supply device 10 from becoming larger in the radial direction of the pipe P. This allows the back shielding gas supply device 10 to be made thinner.

[0058] Moreover, the switching means 16 is disposed below the center CP of the pipe P. This allows the back shielding gas supply device 10 to have a lower center of gravity.

[0059] Furthermore, the switching means 16 is configured to be long in the axial direction of the pipe, which reduces the size of the switching means 16 in the radial direction of the pipe P. This allows the back shielding gas supply device 10 to be made thinner.

[0060] The switching means 16 also has a valve element 16b. As a result, for example, by moving the valve element 16b due to the pressure of the back shield gas G, it is possible to switch between supplying the back shield gas G to the back shield gas nozzle 14a and not supplying it. Furthermore, the valve element 16b is configured to be movable along the pipe axis direction, which reduces the size of the switching means 16 in the radial direction of the pipe P. This allows the back shielding gas supply device 10 to be made thinner.

[0061] Further, the diameter expansion member 12 has an expandable diameter portion 12a, and an expandable diameter gas ejection port 12b1 for ejecting the back shield gas G into the expandable diameter portion 12a, thereby enabling the diameter of the diameter expansion member 12 to be expanded efficiently. Moreover, the expanded diameter gas outlet 12b1 is disposed above the center CP of the pipe P. This allows a space to be formed in the portion of the expanded diameter member 12 above the center CP of the pipe P. Therefore, the portion of the expanded diameter member 12 above the center CP of the pipe P can be made lighter by the amount of the space. Therefore, the center of gravity of the back shielding gas supply device 10 can be lowered.

[0062] Here, a gas heavier than air may be used as the back shielding gas G. Therefore, the expanded diameter gas outlet 12b1 is open upward. This allows the back shielding gas G to be efficiently filled inside the expanded diameter portion 12a when a gas heavier than air is used as the back shielding gas G. Therefore, the diameter of the expanded diameter member 12 can be efficiently expanded.

[0063] Furthermore, the gas inlet 11b2h is disposed above the center CP of the pipe P. This allows, for example, a space to be formed in the portion of the main body 11b2 of the second moving member 11b in which the gas inlet 11b2h is formed, above the center CP of the pipe P. This allows the portion of the main body 11b2 above the center CP of the pipe P to be lighter by the amount of the space. This allows the center of gravity of the back shielding gas supply device 10 to be lowered.

[0064] Here, when a gas heavier than air is used as the back shield gas G, the air remaining inside the pipe P is pushed out from above the pipe P to the outside of the back shield gas region A. Therefore, the gas intake port 11b2h is open upward. This makes it easier to take in the air pushed out from the back shield gas region A, for example, when a gas heavier than air is used as the back shield gas G. This makes it easier to evaluate the concentration of air remaining inside the pipe P.

[0065] Moreover, at least a portion of the expanding-diameter gas supply passage R2 is disposed above the center CP of the pipe P. In this manner, by disposing the relatively light expanding-diameter gas supply passage R2 above, the center of gravity of the back shielding gas supply device 10 can be lowered. Furthermore, by utilizing a location inside the pipe P where the expanding-diameter gas supply passage R2 is not disposed, other components such as the switching means 16 can be easily disposed.

[0066] The back shielding gas supply device 10 further includes a moving member 11 that has a plurality of rolling members 11a1 that can roll along the inner peripheral wall Pw of the pipe P and that can move along the inner peripheral wall Pw of the pipe P. This makes it easier to move the back shielding gas supply device 10 inside the pipe P. This makes it easier to arrange and retrieve the back shielding gas supply device 10.

[0067] The movable member 11 has a first movable member 11a located on the deep side S2 of the pipe P and a second movable member 11b located on the inlet side S1 of the pipe P. By providing a plurality of movable members 11 in this way, the back shielding gas supply apparatus 10 can be more stably moved inside the pipe P. Furthermore, when the back shielding gas supply apparatus 10 is moved, each component of the back shielding gas supply apparatus 10 can be prevented from coming into contact with the inner peripheral wall Pw of the pipe P. Therefore, each component of the back shielding gas supply apparatus 10 can be protected. Moreover, the diameter expanding member 12 and the switching means 16 are disposed between the first moving member 11a and the second moving member 11b. This prevents the back shielding gas supply device 10 from becoming larger in the radial direction of the piping P. This allows the back shielding gas supply device 10 to be made thinner.

[0068] Furthermore, one rolling member 11a1 and the other rolling members 11a1 of the plurality of rolling members 11a1 are disposed below the center CP of the pipe P, and are disposed on one side and the other side of the center CP of the pipe P as viewed in the pipe axis direction. This allows the movable members 11 to be disposed in a well-balanced manner inside the pipe P. Therefore, the weight of the back shielding gas supply apparatus 10 can be easily supported by the rolling members 11a1. Therefore, the back shielding gas supply apparatus 10 can be easily moved inside the pipe P more stably.

[0069] Furthermore, as viewed in the pipe axis direction, a switching means 16 is disposed between one of the plurality of rolling members 11a1 and another of the plurality of rolling members 11a1. This improves the balance of the back shielding gas supply device 10. Therefore, for example, inside the pipe P, the back shielding gas supply device 10 can be more stably moved more easily.

[0070] Furthermore, the rolling member 11a1 is configured to be movable in the radial direction of the pipe P and is biased toward the inner peripheral wall Pw of the pipe P. This allows the moving member 11 to easily climb over steps caused by, for example, reverse beading or misalignment on the inner peripheral wall Pw of the pipe P. Therefore, manufacturing errors in the pipe P can be absorbed.

[0071] The pipe P further includes a seal member 13 capable of sealing the inside of the pipe P. The diameter expansion member 12 and the seal member 13 are arranged on one side and the other side of the back shielding gas ejection port 14a in the pipe axial direction. This makes it easier to retain the back shielding gas G injected into the inside of the pipe P within the pipe P. This makes it easier to fill the inside of the pipe P with the back shielding gas G.

[0072] Furthermore, a gap C is formed between the inner peripheral wall Pw of the pipe P and the outer peripheral edge of the seal member 13. This allows the back shielding gas G to be ejected into the inside of the pipe P while the air inside the pipe P is discharged through the gap C. This makes it easier to fill the inside of the pipe P with the back shielding gas G. Furthermore, after the inside of the pipe P is filled with the back shielding gas G, welding the pipe P in a state where the back shielding gas G is being discharged from the gap C can prevent defects from occurring in the welded portion.

[0073] The back-shielding gas supply device 10 further includes a gas supply member 14 having a back-shielding gas outlet 14a, an expanded-diameter gas supply passage R2, and a tubular member 15 having the expanded-diameter gas supply passage R2. The switching means 16 and the tubular member 15 are disposed between the gas supply member 14 and the second moving member 11b. This allows the switching means 16 and the tubular member 15 to be disposed by effectively utilizing the space between the gas supply member 14 and the second moving member 11b. This allows the back-shielding gas supply device 10 to be made smaller.

[0074] Moreover, the diameter expanding member 12 is disposed between the first moving member 11a and the gas supply member 14. This allows the diameter expanding member 12 to be disposed by effectively utilizing the space between the first moving member 11a and the gas supply member 14. Therefore, the back shielding gas supply device 10 can be made smaller in size.

[0075] Furthermore, a back shield gas region A filled with back shield gas G is formed between the diameter expansion member 12 and the seal member 13. The gas supply member 14 is disposed adjacent to the diameter expansion member 12 in the back shield gas region A. This allows the gas in the back shield gas region A to face the seal member 13. Therefore, for example, it is possible to efficiently discharge air in the back shield gas region A from the gap C formed between the inner circumferential wall Pw of the pipe P and the outer circumferential edge of the seal member 13. This makes it easier to fill the inside of the pipe P with back shield gas G.

[0076] Furthermore, according to the back shielding gas supply method of this embodiment, after the diameter expansion step in which the diameter expansion member 12 is expanded to contact the inner circumferential wall Pw of the pipe P, a switching step is performed in which whether or not to supply the back shielding gas G to the back shielding gas ejection port 14a is switched depending on the pressure of the back shielding gas G. As a result, the diameter expansion member 12 expands to contact the inner circumferential wall Pw of the pipe P, and the inside of the pipe P is sealed, and then the back shielding gas G can be ejected from the back shielding gas ejection port 14a. This makes it possible to prevent the back shielding gas G from leaking from the inside of the pipe P. Therefore, the amount of back shielding gas G used can be reduced.

[0077] The technical scope of the present disclosure is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present disclosure. For example, the movable member 11 may be provided with a drive source. This allows the back shielding gas supply device 10 to be self-propelled without using the traction wire W, and the back shielding gas supply device 10 may be removed from inside the piping P. In this case, the drive source may be provided for only either the first movable member 11a or the second movable member 11b, or for both. Furthermore, the switching means 16 may be provided with a pressure sensor instead of the valve body 16b described above. In this way, the supply destination of the back shield gas G may be switched according to the pressure of the back shield gas G. Furthermore, the switching means 16 does not have to be disposed below the center CP of the pipe P. Furthermore, the switching means 16 does not have to be configured to be long in the tube axis direction. Further, the expanded diameter gas outlet 12b1 does not have to be disposed above the center CP of the pipe P. Further, the expanded diameter gas outlet 12b1 does not have to be open upward. Furthermore, the gas intake port 11b2h does not have to be disposed above the center CP of the pipe P. Furthermore, the gas intake port 11b2h does not have to be open upward. Furthermore, the diameter-enlarged gas supply passage R2 does not have to be located above the center CP of the pipe P. Furthermore, the gap C between the inner peripheral wall Pw of the pipe P and the outer peripheral edge of the seal member 13 may be provided below the center CP of the pipe P. The gas supply member 14 does not have to be disposed adjacent to the diameter expansion member 12 in the back shield gas region A. An arbitrary member may be disposed between the gas supply member 14 and the diameter expansion member 12.

[0078] In addition, within the scope of the present disclosure, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described modified examples may be combined as appropriate.

[0079] (Addendum) The back shield gas supply device and the back shield gas supply method according to the above embodiment can be understood, for example, as follows.

[0080] <1> A back shielding gas supply device according to one aspect of the present disclosure is a back shielding gas supply device that is inserted into a pipe and supplies a back shielding gas into the pipe, and is characterized by comprising: a back shielding gas outlet that injects the back shielding gas into the pipe; a diameter expanding member that is expanded in diameter by the back shielding gas so as to be able to contact an inner peripheral wall of the pipe; and switching means that switches whether or not back shielding gas is supplied to the back shielding gas outlet depending on the pressure of the back shielding gas.

[0081] According to the back shielding gas supply device, the diameter expanding member can be expanded by the back shielding gas and come into contact with the inner peripheral wall of the pipe. By expanding the diameter of the diameter expanding member and coming into contact with the inner peripheral wall of the pipe, for example, the inside of the pipe can be reliably sealed when supplying back shielding gas. Furthermore, the back shielding gas supply device can be positioned inside the pipe. Therefore, the operation of supplying back shielding gas can be performed stably. Furthermore, the switching means switches whether or not to supply back shielding gas to the back shielding gas nozzle depending on the pressure of the back shielding gas. This allows the back shielding gas to be ejected from the back shielding gas nozzle at an appropriate timing. This prevents the back shielding gas from being ejected more than necessary, thereby reducing the amount of back shielding gas used.

[0082] <2> the above <1> In the back shield gas supply device according to the above, a configuration may be adopted in which, after the diameter expanding member expands in diameter, the switching means opens in response to the pressure of the back shield gas, and the back shield gas is supplied to the back shield gas outlet.

[0083] Furthermore, after the diameter expansion member expands, the switching means opens in response to the pressure of the back shielding gas, and the back shielding gas is supplied to the back shielding gas outlet. Therefore, the back shielding gas is injected from the back shielding gas outlet after the diameter expansion member expands and contacts the inner peripheral wall of the pipe, sealing the inside of the pipe. This makes it possible to prevent the back shielding gas from leaking from inside the pipe. Therefore, the amount of back shielding gas used can be reduced.

[0084] <3> the above <1> or <2> In the back shield gas supply device according to the above, a configuration may be adopted in which the switching means switches whether or not to supply the back shield gas to the back shield gas jet port, depending on the pressure of the back shield gas supplied to the diameter expansion member.

[0085] The switching means switches whether or not to supply the back shield gas to the back shield gas outlet depending on the pressure of the back shield gas supplied to the diameter expansion member, thereby more reliably switching whether or not to supply the back shield gas to the back shield gas outlet.

[0086] <4> the above <1> from <3> The back shield gas supply device according to any one of the above aspects may further include an expanding diameter gas supply path that supplies a back shield gas to the expanding diameter member, and a back shield gas supply path that supplies a back shield gas to the back shield gas outlet, and the expanding diameter gas supply path and the back shield gas supply path may be configured to be partially common to each other.

[0087] The device further includes a diameter-expanding gas supply passage for supplying back shielding gas to the diameter-expanding member, and a back shielding gas supply passage for supplying back shielding gas to the back shielding gas outlet. This allows the diameter of the diameter-expanding member to be expanded, for example, by supplying back shielding gas to the diameter-expanding member via the diameter-expanding gas supply passage. By supplying back shielding gas to the back shielding gas outlet via the back shielding gas supply passage, the back shielding gas can be ejected into the piping. The diameter-expanding gas supply passage and the back shielding gas supply passage are partially commonalized. This allows the back shielding gas supply device to be miniaturized.

[0088] <5> the above <4> In the back shielding gas supply device according to the present invention, a configuration may be adopted in which the switching means is provided in a portion of the back shielding gas supply path that is not shared with the expanded-diameter gas supply path.

[0089] Here, if further back shielding gas is supplied to the diameter-expanding gas supply path after the diameter-expanding member has been sufficiently expanded by the back shielding gas and is in contact with the inner peripheral wall of the pipe, the back shielding gas will not be supplied to the diameter-expanding member, and the pressure in the diameter-expanding gas supply path and in the portion where the diameter-expanding gas supply path and the back shielding gas supply path are shared will increase. Therefore, a switching means is provided in a portion of the back shielding gas supply path that is not shared with the expanding-diameter gas supply path. As a result, for example, when the pressure in the expanding-diameter gas supply path and the portion where the expanding-diameter gas supply path and the back shielding gas supply path are shared increases as described above, the switching means can be switched to a state in which back shielding gas is supplied to the back shielding gas nozzle by the pressure of the back shielding gas. Therefore, whether back shielding gas is supplied to the back shielding gas nozzle can be reliably switched depending on the pressure of the back shielding gas supplied to the expanding-diameter member.

[0090] <6> the above <1> from <5> In the back shielding gas supply device according to any one of the above aspects, a configuration may be adopted in which the diameter expanding member and the switching means do not overlap when viewed in a direction perpendicular to the tube axis.

[0091] Furthermore, when viewed in the direction perpendicular to the tube axis, the diameter expansion member and the switching means do not overlap. This makes it possible to prevent the back shielding gas supply device from becoming larger in the radial direction of the piping due to the arrangement of the diameter expansion member and the switching means, for example. Therefore, the back shielding gas supply device can be made thinner.

[0092] <7> the above <1> from <6> In the back shielding gas supply device according to any one of the above aspects, a configuration may be employed in which the diameter expanding member and the switching means overlap each other as viewed in the tube axis direction.

[0093] Furthermore, when viewed in the tube axis direction, the diameter expansion member and the switching means overlap. That is, the diameter expansion member and the switching means are arranged side by side along the tube axis direction. This arrangement of the diameter expansion member and the switching means makes it possible to prevent the back shielding gas supply device from becoming larger in the radial direction of the piping. Therefore, the back shielding gas supply device can be made thinner.

[0094] <8> the above <1> from <7> In the back shielding gas supply device according to any one of the above aspects, a configuration may be adopted in which the back shielding gas outlet does not overlap with the diameter expansion member and the switching means when viewed in a direction perpendicular to the tube axis.

[0095] Furthermore, when viewed in the direction perpendicular to the tube axis, the back shielding gas outlet does not overlap with the diameter expansion member and the switching means. This prevents the back shielding gas supply device from becoming larger in the radial direction of the piping, for example, due to the arrangement of the back shielding gas outlet, diameter expansion member, and switching means. This allows the back shielding gas supply device to be made thinner.

[0096] <9> the above <1> from <8> In the back shield gas supply device according to any one of the above aspects, a configuration may be adopted in which the back shield gas outlet, the diameter expanding member, and the switching means are aligned in the tube axis direction.

[0097] Furthermore, the back shielding gas nozzle, the diameter expansion member, and the switching means are aligned in the axial direction of the pipe. This arrangement of the back shielding gas nozzle, the diameter expansion member, and the switching means prevents the back shielding gas supply device from becoming too large in the radial direction of the pipe. This allows the back shielding gas supply device to be made thinner.

[0098] <10> the above <1> from <9> The back shielding gas supply device according to any one of the above aspects may further include a gas inlet port that takes in gas from within the piping, and may have a configuration in which the gas inlet port does not overlap with the diameter expanding member and the switching means when viewed in a direction perpendicular to the tube axis.

[0099] The device further includes a gas inlet for taking in gas from the piping. This allows the gas from the piping to be taken in through the gas inlet, enabling the concentration of gas remaining in the piping to be evaluated. Furthermore, when viewed in a direction perpendicular to the tube axis, the gas inlet does not overlap with the diameter expansion member and the switching means. This allows, for example, the arrangement of the gas inlet, diameter expansion member, and switching means to prevent the back-shielding gas supply device from becoming larger in the radial direction of the piping. This allows the back-shielding gas supply device to be made thinner.

[0100] <11> the above <10> In the back shielding gas supply device according to the above, a configuration may be adopted in which the back shielding gas outlet, the diameter expanding member, the switching means and the gas inlet are aligned in the tube axis direction.

[0101] Furthermore, the back shielding gas outlet, the diameter expansion member, the switching means, and the gas inlet are aligned in the axial direction of the pipe. This arrangement of the back shielding gas outlet, the diameter expansion member, the switching means, and the gas inlet prevents the back shielding gas supply device from becoming too large in the radial direction of the pipe. This allows the back shielding gas supply device to be made thinner.

[0102] <12> the above <1> from <11> In the back shielding gas supply device according to any one of the above aspects, the switching means may be arranged below the center of the piping.

[0103] In addition, the switching means is disposed below the center of the piping, which allows the back shielding gas supply device to have a lower center of gravity.

[0104] <13> the above <1> from <12> In the back shield gas supply device according to any one of the above aspects, the switching means may be configured to be long in the tube axis direction.

[0105] In addition, the switching means is configured to be long in the axial direction of the pipe, which reduces the size of the switching means in the radial direction of the pipe, thereby allowing the back shielding gas supply device to be made thinner.

[0106] <14> the above <1> from <13> In the back shielding gas supply device according to any one of the above aspects, the switching means may have a valve body, and the valve body may be configured to be movable along the tube axis direction.

[0107] The switching means has a valve element, and thereby, for example, the valve element is moved by the pressure of the back shield gas, thereby switching whether or not the back shield gas is supplied to the back shield gas nozzle. The valve element is also configured to be movable along the pipe axis, which reduces the radial size of the switching means, allowing the back shielding gas supply device to be made thinner.

[0108] <15> the above <1> from <14> In the back shielding gas supply device according to any one of the above aspects, a configuration may be adopted in which the expansion member has an expansion portion that can be expanded in diameter, and an expansion gas outlet that ejects back shielding gas into the expansion portion, and the expansion gas outlet is located above the center of the piping.

[0109] The diameter expansion member has an expandable diameter portion and an expandable diameter gas outlet that ejects back shielding gas into the expandable diameter portion. This allows the diameter of the expandable member to be expanded efficiently. The expandable diameter gas outlet is located above the center of the pipe. This allows a space to be formed in the portion of the diameter expansion member above the center of the pipe. This allows the weight of the portion of the diameter expansion member above the center of the pipe to be reduced by the amount of the space. This allows the center of gravity of the back shielding gas supply device to be lowered.

[0110] <16> the above <15> In the back shield gas supply device according to the above, the enlarged diameter gas outlet may be configured to open upward.

[0111] Here, a gas heavier than air may be used as the back shielding gas. Therefore, the expansion gas outlet is open upward. This allows the back shielding gas to be efficiently filled inside the expansion portion when a gas heavier than air is used as the back shielding gas. Therefore, the expansion member can be efficiently expanded in diameter.

[0112] <17> the above <1> from <16> In the back shielding gas supply device according to any one of the above aspects, a configuration may be adopted in which the back shielding gas supply device further includes a gas inlet for taking in gas from the piping, and the gas inlet is located above the center of the piping.

[0113] Furthermore, the gas inlet is disposed above the center of the piping. This allows, for example, a space to be formed in the part of the member in which the gas inlet is formed above the center of the piping. This allows the weight of the part of the member in which the gas inlet is formed above the center of the piping to be reduced by the amount of the space. This allows the center of gravity of the back-shielding gas supply device to be lowered.

[0114] <18> the above <17> In the back shield gas supply device according to the above, the gas intake port may be configured to open upward.

[0115] Here, when a gas heavier than air is used as the back shield gas, the air remaining inside the pipe is pushed out from above the pipe to the outside of the back shield gas region. Therefore, the gas intake port is open upward. This makes it easier to take in air pushed out from the back shield gas region when a gas heavier than air is used as the back shield gas. This makes it easier to evaluate the concentration of air remaining inside the pipe.

[0116] <19> the above <1> from <18> In the back shielding gas supply device according to any one of the above aspects, a configuration may be adopted in which the back shielding gas supply device further includes an expanding diameter gas supply passage that supplies back shielding gas to the expanding diameter member, and at least a portion of the expanding diameter gas supply passage is arranged above the center of the piping.

[0117] Furthermore, at least a portion of the expanding-diameter gas supply passage is disposed above the center of the pipe. By disposing the relatively light expanding-diameter gas supply passage at the upper position, the center of gravity of the back-shielding gas supply device can be lowered. Furthermore, it is possible to easily dispose other components, such as a switching means, by utilizing the space inside the pipe where the expanding-diameter gas supply passage is not disposed.

[0118] <20> the above <1> from <19> In the back shielding gas supply device according to any one of the above aspects, a configuration may be adopted in which the back shielding gas supply device has a plurality of rolling members that can roll along the inner circumferential wall of the piping, and further includes a moving member that can move along the inner circumferential wall of the piping.

[0119] The back shielding gas supply device further includes a movable member that has a plurality of rolling members that can roll along the inner peripheral wall of the pipe and that can move along the inner peripheral wall of the pipe. This makes it easier to move the back shielding gas supply device inside the pipe, thereby facilitating the placement and retrieval of the back shielding gas supply device.

[0120] <21> the above <20> In the back shielding gas supply device according to the above, a configuration may be adopted in which the movable member has a first movable member located at the back side of the piping and a second movable member located at the inlet side of the piping, and the expanding member and the switching means are disposed between the first movable member and the second movable member.

[0121] The movable member includes a first movable member located at the back of the pipe and a second movable member located at the inlet side of the pipe. By providing a plurality of movable members in this manner, the back shielding gas supply device can be more stably moved inside the pipe. Furthermore, when the back shielding gas supply device is moved, each component of the back shielding gas supply device can be prevented from coming into contact with the inner peripheral wall of the pipe. Therefore, each component of the back shielding gas supply device can be protected. Furthermore, the diameter expanding member and the switching means are disposed between the first moving member and the second moving member, which prevents the back shielding gas supply device from becoming large in the radial direction of the piping, thereby enabling the back shielding gas supply device to be made thinner.

[0122] <22> the above <20> or <21> In the back shielding gas supply device according to the above, a configuration may be adopted in which one rolling member and another rolling member among the plurality of rolling members are arranged below the center of the pipe, and are arranged separately on one side and the other side of the center of the pipe when viewed in the pipe axis direction.

[0123] Furthermore, one rolling member and the other rolling members among the plurality of rolling members are disposed below the center of the pipe, and are disposed on one side and the other side of the center of the pipe as viewed in the pipe axis direction. This allows the moving members to be disposed in a well-balanced manner inside the pipe. Therefore, the rolling members can easily support the weight of the back-shielding gas supply device. Therefore, the back-shielding gas supply device can be moved more stably inside the pipe.

[0124] <23> the above <22> In the back shielding gas supply device according to the present invention, a configuration may be adopted in which the switching means is disposed between the one rolling member and the other rolling member as viewed in the tube axis direction.

[0125] Furthermore, a switching means is disposed between one of the rolling members and another of the rolling members as viewed in the axial direction of the pipe. This improves the balance of the back shielding gas supply device. Therefore, for example, the back shielding gas supply device can be more stably moved inside the pipe.

[0126] <24> the above <20> from <23> In the back shielding gas supply device according to any one of the above aspects, a configuration may be adopted in which the rolling members are configured to be movable in the radial direction of the piping and are biased toward the inner wall of the piping.

[0127] The rolling members are configured to be movable in the radial direction of the pipe and are biased toward the inner peripheral wall of the pipe, which makes it easier for the moving members to overcome steps on the inner peripheral wall of the pipe caused by, for example, reverse beading or unevenness, thereby absorbing manufacturing errors in the pipe.

[0128] <25> the above <1> from <24> The back shielding gas supply device according to any one of the above aspects may further include a sealing member capable of sealing the inside of the piping, and the diameter expansion member and the sealing member may be arranged on one side and the other side of the back shielding gas outlet in the axial direction of the pipe.

[0129] The pipe further includes a sealing member capable of sealing the inside of the pipe. The diameter expansion member and the sealing member are arranged on one side and the other side of the back shielding gas outlet in the pipe axial direction. This makes it easier to retain the back shielding gas injected into the inside of the pipe within the pipe. This makes it easier to fill the inside of the pipe with back shielding gas.

[0130] <26> the above <25> In the back shielding gas supply device according to the present invention, a configuration may be adopted in which a gap is formed between an inner peripheral wall of the piping and an outer peripheral edge of the sealing member.

[0131] In addition, a gap is formed between the inner peripheral wall of the pipe and the outer peripheral edge of the seal member. This allows air inside the pipe to be discharged through the gap while back shielding gas is ejected into the inside of the pipe. This makes it easier to fill the inside of the pipe with back shielding gas. After the inside of the pipe is filled with back shielding gas, welding the pipe while the back shielding gas is being discharged through the gap can prevent defects from occurring in the welded joint.

[0132] <27> the above <21> The back shielding gas supply device according to the above may further include a gas supply member having the back shielding gas outlet, an expanding-diameter gas supply path that supplies back shielding gas to the expanding-diameter member, and a tubular member having the expanding-diameter gas supply path, and the switching means and the tubular member may be configured to be disposed between the gas supply member and the second moving member.

[0133] The back-shielding gas supply device further includes a gas supply member having a back-shielding gas outlet, an expanding-diameter gas supply passage, and a tubular member having the expanding-diameter gas supply passage. The switching means and the tubular member are disposed between the gas supply member and the second moving member. This allows the switching means and the tubular member to be disposed while effectively utilizing the space between the gas supply member and the second moving member. This allows the back-shielding gas supply device to be miniaturized.

[0134] <28> the above <27> In the back shielding gas supply device according to the above, a configuration may be adopted in which the diameter expanding member is disposed between the first moving member and the gas supply member.

[0135] Furthermore, the diameter expanding member is disposed between the first movable member and the gas supply member, which allows the space between the first movable member and the gas supply member to be effectively utilized for disposing the diameter expanding member, thereby enabling the back shielding gas supply device to be made smaller.

[0136] <29> the above <27> or <28> The back shield gas supply device according to the above aspect may further include a sealing member capable of sealing the inside of the piping, and a back shield gas region filled with back shield gas may be formed between the diameter expansion member and the sealing member, and the gas supply member may be disposed adjacent to the diameter expansion member in the back shield gas region.

[0137] Furthermore, a back shield gas region filled with back shield gas is formed between the diameter expansion member and the seal member. The gas supply member is disposed adjacent to the diameter expansion member in the back shield gas region. This allows the gas in the back shield gas region to face the seal member. Therefore, for example, it is possible to efficiently discharge air in the back shield gas region from a gap formed between the inner peripheral wall of the pipe and the outer peripheral edge of the seal member. This makes it easier to fill the inside of the pipe with back shield gas.

[0138] <30> The back shield gas supply method according to one aspect of the present disclosure includes the steps of: <1> from <29> a back shielding gas supplying method for supplying a back shielding gas into the piping by using the back shielding gas supplying device according to any one of the above aspects, the method comprising: a diameter expanding step of expanding the diameter expanding member to bring it into contact with an inner peripheral wall of the piping; and a switching step of switching, by the switching means, whether or not to supply a back shielding gas to the back shielding gas outlet after the diameter expanding step, depending on a pressure of the back shielding gas.

[0139] According to the above-described back shielding gas supply method, after the diameter expansion step in which the diameter expansion member is expanded to contact the inner peripheral wall of the pipe, a switching step is performed in which whether or not back shielding gas is supplied to the back shielding gas outlet is switched depending on the pressure of the back shielding gas. As a result, the back shielding gas can be ejected from the back shielding gas outlet after the diameter expansion member expands to contact the inner peripheral wall of the pipe and the inside of the pipe is sealed. This makes it possible to prevent back shielding gas from leaking from the inside of the pipe. Therefore, the amount of back shielding gas used can be reduced. [Explanation of symbols]

[0140] 1 Back shield gas supply system 10 Back shield gas supply device 11 Moving parts 11a first moving member 11A side 11a1 Rolling member 11a2 Main body 11b Second moving member 11B Bottom 11b2 Main body 11b2h Gas intake port 11BL ball part 12 Expanding member 12a Expanded diameter part 12b Main body 12b1 Expanded gas outlet 13 Sealing material 14 Gas supply member 14a Back shield gas outlet 15 Tubular member 16 Switching Methods 16a Cylinder section 16b Valve body 20 Gas supply means 21 tubes 22 Gas Cylinder A Back shield gas area B Bolt C Gap CP center E Mounting part G Back shield gas H through hole P piping Pw Inner wall R1 Back shield gas supply line R2 Expanded gas supply channel R3 common part RB Junction S1 entrance side S2 back side W Towing Wire

Claims

1. A back shield gas supplying method for supplying a back shield gas into a pipe using a back shield gas supplying device that is inserted into the pipe and supplies a back shield gas into the pipe, comprising: an arrangement step of arranging a back shield gas supply device inside one of the pipes; and an approaching step of bringing the other pipe close to the one pipe after the arranging step, The back shielding gas supply method, wherein the approaching step is performed in a state where a traction wire for removing the back shielding gas supply device from inside the pipe is disposed inside the other pipe.

2. 2. The back shield gas supply method according to claim 1, wherein the approaching step is performed in a state where a tube of a gas supply means for supplying back shield gas to the back shield gas supply device is disposed inside the other pipe.

3. The back shield gas supply method according to claim 1 , wherein the traction wire is disposed substantially on the center of the pipe when viewed in the pipe axis direction.

4. 4. The back shield gas supply method according to claim 3, wherein a tube of a gas supply means for supplying the back shield gas to the back shield gas supply device is disposed in a state of being displaced from the center of the piping when viewed in the tube axis direction.

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