JP2008212994A - Welding equipment and method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply and easily realize highly efficient welding work and then to realize high-quality butt welding. <P>SOLUTION: The welding equipment comprises: mounting a butt arranged straight pipe 13 and elbow pipe 24 on a pipe cradle 15 and a joint pipe cradle 16; inserting a pipe centering-holding device 40 into the straight pipe 13; moving a travel unit 44 of the pipe centering-holding device 40 in the pipe and adjusting the position; driving a hydraulic mechanism 436 of its head section 43 to adjust a clamp claw 435 to elongate and contrast and to bring the clap claw into press contact with the inside of the pipes thereby centering and holding the pipes, tack welding the pipes in this state at a plurality of the points of the mutual grooves; mounting a preheater 30 to the outside near the butt portion of the elbow pipe 14 and heating the preheater 30; then thermally controlling the temperature fluctuation of the hydraulic mechanism 436 of the head section 43 of the pipe centering-holding device 40; and rotating the straight pipe 13 and the elbow 14 and performing groove downward welding to whole periphery of the butt portion of the pipe by a welding torch. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a welding apparatus and method used for performing butt welding of, for example, a large-diameter thick wall pipe.

  As is well known, as a welding method for welding pipes to each other, the gaps of the pipes to be welded are butt-matched, positioned and provisionally welded, and then the periphery of the butt portion is performed using a welding torch. (For example, refer to Patent Document 1).

  And when welding thick-walled pipes among such welding methods, the grooves of the pipes to be welded are butted together, and a piece as a holding member is attached to the outer peripheral portion of the pipe at a predetermined interval and centered. While holding, tack welding is performed and the welding torch which is a welding apparatus is used for the welding.

  However, with this method, the welded part is welded in the circumferential direction, and once it is welded to the position where the piece is located, the welding must be stopped, the piece removed, and then welded again, so that the work is very troublesome. It has the disadvantage of being. In addition, since the pieces are arranged outside the pipe, it is difficult to efficiently heat the vicinity of the welding site required in the case of a thick-walled pipe, and there is a problem that the welding accuracy is hindered.

Therefore, a hydraulic pipe centering / holding device is movably inserted into one of the pipes with which the grooves are butted together, and the pipe centering / holding device is moved to the butting part in the pipe, and the head is moved. A welding apparatus has also been developed that enables welding from the outer periphery of the butt portion of the pipe by centering and holding the butt portion from within the pipe.
JP-A-5-192793

  However, in the above welding apparatus, any of the methods is intended for so-called thin-walled pipes and has a problem that it is difficult to apply to the welding of thick-walled pipes. For example, when performing butt welding of thick-walled pipes, it is necessary to perform welding while heating the vicinity of the welding portion with a preheating device. For this reason, this preheating causes the temperature of the tube centering / supporting mechanism in the tube to rise, resulting in thermal fluctuations in the hydraulic mechanism of the centering / holding device, and the support force is reduced, making accurate centering and holding difficult. Have the problem.

  In addition, when applied to butt welding of thick-walled pipes, it is necessary to perform a seaming process for matching the welding root surface to the butt portion in the pipe. For this reason, a step is generated between the diameter of the seamed portion and the inner diameter of the pipe, and a gap is generated between the head portion and the seamed portion by the amount of the step, which makes it difficult to stably and accurately support. Have the problem of becoming.

  This invention has been made in view of the above circumstances, and can easily and easily realize high-efficiency welding work, and realizes high-quality butt welding without being affected by the wall thickness of the pipe. It is an object of the present invention to provide a welding apparatus and method that can be used.

  According to the present invention, pipes to be butt welded are mounted so as to be independently movable, and at least one of them is moved to butt-arrange each other, and a pipe moving means that can move in the axial direction within one of the pipes. A pipe centering / holding means having a hydraulic mechanism that is inserted into the inner wall of the pipe and is driven in contact with and separated from the inner wall of the pipe so that the clamp pawl is pressed against the inside of each butted portion of the pipe. A tube rotating means for rotationally driving the tube that has been centered and held via the tube centering / holding means and is tack-welded, and a butt portion of the tube is opened in conjunction with the rotational driving of the tube rotating means. And a welding means for welding first downward.

  According to the above configuration, the pipe to be welded is attached to the pipe moving means, and the pipe centering / holding means is inserted into one of the pipes whose grooves are abutted with each other. The mechanism is driven to adjust the expansion and contraction of the clamp pawl, and are temporarily welded to each other in a state where the clamp is pressed into the tube at the butted portion where the groove is butted and held. Then, the temporarily attached pipe is mounted on the pipe rotating means, and the pipe rotating means is driven and rotated. In the rotated state, the groove is welded downward by the welding means over the entire circumference of the butt portion. Is given.

  This makes it possible to continuously perform high-quality welding with the welding means while performing stable centering and holding of the abutting portion with the clamp claws of the pipe centering and holding means, and efficient welding work can be performed. Realized.

  As described above, according to the present invention, high-efficiency butt welding can be realized without being affected by the wall thickness of the pipe, and can easily and easily realize high-efficiency welding work. It is possible to provide a welding apparatus and method thereof.

  Hereinafter, a welding apparatus and a method thereof according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a welding apparatus according to an embodiment of the present invention. A torch stand 10 constituting welding means is mounted on a guide rail 11 so as to be movable in the directions of arrows A and B. The torch stand 10 is provided with, for example, a narrow groove HOTIG welding welding torch 12 that can be raised and lowered in the direction of the arrow. This welding torch 12 can be constructed in a pipe downward posture from the first layer backside welding to the extra welding.

  As shown in FIG. 2, the welding torch 12 is provided with a torch mounting body 20 that can be moved up and down on the torch stand 10, and a torch body 22 with a tungsten electrode 21 extended on the torch mounting body 20. It is provided so that it can be welded downward. In the torch body 22, a pair of gas nozzles 23, 23 for injecting a shielding gas such as argon gas is disposed via the nozzle support member 24 with the tungsten electrode 21 interposed therebetween.

  As a result, the tungsten electrode 21 of the torch body 22 can have a wide gap with the side wall at the groove butt portion of the straight pipe 13 and the elbow pipe 14 (see FIG. 1) used for the welding. Along with expansion, when an arc is generated, it is possible to prevent the arc from being generated on the side wall of the groove, the groove width can be further reduced, and high-precision welding with reduced welding amount is performed. Can do.

  In addition, a filler nozzle 25 constituting a filler material supply unit is disposed on the torch mounting body 20 via a position adjusting member 26 so that the position of the filler nozzle 25 can be adjusted. The filler nozzle 25 is adjusted in position to a predetermined position corresponding to the tungsten electrode 21 of the torch body 22 through a position adjusting member 26.

  Along with the torch stand 10, a pipe holder 15 called a support roller and a joint pipe holder 16 are mounted on the guide rail 11 so as to be movable in the directions of arrows A and B, respectively. The straight pipe 13 and the elbow pipe 14 are mounted on the base 15 and the joint pipe receiving base 16 with their grooves facing each other. The joint cradle 16 is provided with a preheating device 30 as preheating means, for example.

  The preheating device 30 is formed by combining a plurality of divided bodies, for example, first and second support frames 31 and 32 in a frame-like manner so as to be divided through a connecting portion 33 as shown in FIG. In the first and second support frames 31 and 32, first and second high-frequency heating coils 34 and 35 that are combined and divided in a ring shape corresponding to the outer diameter of the tube are supported by the support members 311 and 321. Supported through.

  The first and second high-frequency heating coils 34 and 35 are provided so as to be freely divided via a connecting portion 36, and the first and second support frames 31 and 32 are divided via a connecting portion 33. Similarly, when divided through the connecting portion 36, the first and second support frames 31, 32 are integrated and divided, for example, and attached to the outer peripheral portion of the elbow pipe 14 near the butted portion. In this mounted state, the first and second support frames 31 and 32 are combined into a frame shape via the connecting portion 33, and the first and second high-frequency heating coils 34 and 35 are connected via the connecting portion 36. It is united in a ring shape and arranged at a desired position in the vicinity of the butted portion of the elbow pipe 14.

  Here, the first and second high-frequency heating coils 34 and 35 are disposed so that their inner walls face each other with a gap of, for example, 20 to 30 mm from the outer wall surface of the butted portion of the elbow pipe 14, and are not shown. Is driven and controlled to heat the vicinity of the butted portion of the straight pipe 13 and the elbow pipe 14.

  As described above, the preheating device 30 is configured by dividing the first and second support frames 31 and 32 and the first and second high-frequency heating coils 34 and 35 when performing the preheating work. In this state, the elbow pipe 14 is connected in a ring shape so as to cover the outer peripheral portion near the butted portion. For example, during welding work, the first and second support frames 31 and 32 and the first and second high-frequency heating coils 34 and 35 are separated from the outer peripheral portion in the vicinity of the pipe butt portion. Separated and separated. As a result, it is possible to easily and easily attach the preheating device 30 to a position close to the tube butting site, and to realize efficient heat treatment to the butting site.

  At the base end portion of the guide rail 11, a positioner 17 constituting a tube rotating means is disposed. The positioner 17 is provided with a chuck portion 18 for gripping the tube, and the chuck portion 18 grips the proximal end of the straight tube 13 mounted on the tube support 15. The chuck unit 18 is connected to a rotation driving unit 19, and when the rotation driving unit 19 is driven to rotate via a control unit (not shown), a rotational force is transmitted to grip the straight pipe 13 and rotate. . The positioner 17 and the rotation drive unit 19 are provided with insertion holes 171 and 191, respectively. The insertion holes 171 and 191 are provided with hydraulic pressures of a tube centering / holding device 40, which will be described later, constituting tube centering / holding means. The hose 41 and the cooling water hose 42 are inserted.

  As shown in FIG. 4, the tube centering / holding device 40 includes a head unit 43 and a traveling unit 44 that are connected to each other. That is, a disc member 442 is attached to the tip shaft portion 441 of the traveling unit 44 as shown in FIG. 5, and this disc member 442 uses a flange member 432 and a screw member 433 with respect to the casing 431 of the head portion 43. And attached with a gap d in the radial direction. Then, the disk member 442 is pressed against the casing 431 of the head portion 43 via the spring member 434 and the movement in the axial direction is restricted.

  Accordingly, the head portion 43 is connected and arranged so as to be movable in the radial direction by the radial gap d of the disk member 442 in a state where movement in the axial direction is restricted with respect to the distal end shaft portion 441 of the traveling unit 44. The As a result, a clamp claw 435 (to be described later) of the head unit 43 can travel without being affected by the surface accuracy in the pipe due to the action of the gap d when the running roller member 443 of the running unit 44 moves in the straight pipe 13. The unit 44 is kept substantially perpendicular to the distal end shaft portion 441 and can move stably in the straight pipe 13.

  In other words, a plurality of, for example, a pair of the clamp claws 435 are provided on the head portion 43 independently of each other via the hydraulic mechanism 436 so as to freely extend and retract in the tube wall direction (radial direction). The hydraulic mechanism 436 is thermally coupled with a cooling mechanism 437 that constitutes a cooling means, and is cooled via the cooling mechanism 437 to prevent hydraulic pressure fluctuations.

  A hydraulic pump 45 is connected to the hydraulic mechanism 436 by piping through the hydraulic hose 41, and is driven and controlled via the hydraulic pump 45 so that the clamp claw 435 is independently expanded and contracted in the direction of the pipe wall. 13 and the inner side of the butted portion of the elbow pipe 14 are centered and held. A cooling water pump 46 is connected to the cooling mechanism 437 by piping through the cooling water hose 42, and cooling water is circulated and supplied through the cooling water pump 46 to cool the hydraulic mechanism 436 to be operable. Control. The hydraulic pump 45 and the cooling water pump 46 are arranged in parallel with the positioner 17, for example, and are driven and controlled together with the hydraulic mechanism 436 and the cooling mechanism 437 through the control unit (not shown).

  In the traveling unit 44, a plurality of pantograph mechanisms 444 are arranged radially around the tip shaft portion 441, for example. The plurality of pantograph mechanisms 444 are folded and unfolded in response to the operation of the operation handle 445. A traveling roller member 443 is provided at the tip of each pantograph mechanism 444 so as to be able to contact with and separate from the inside of the tube, and is folded and unfolded in conjunction with the operation of the operation handle 445 so that the traveling roller member 443 is brought into the tube. Make contact and separation. When the traveling roller member 443 of the pantograph mechanism 444 is moved in the axial direction along the tube wall while being in contact with the pipe of the straight pipe 13, the traveling unit 44 is moved in the same direction together with the head unit 43 along with the movement. Is guided to move.

  In the pair of clamp claws 435 of the head portion 43, for example, as shown in FIG. 6, a notch portion 435 a is formed on the inner side of the butted portion of the straight pipe 13 and the elbow pipe 14 on the peripheral wall surface serving as the contact surface. It is provided so as to face the seaming processing part for route alignment. The notch 435a of the clamp claw 435 forms a concave gas guide groove in cooperation with the seaming portion of the butted portion in a state where the butted portion of the straight pipe 13 and the elbow pipe 14 is centered and held ( (See FIG. 6).

  The concave gas guide groove formed by the notch 435a of the clamp claw 435 is filled with, for example, a gas such as an argon gas that constitutes a shielding gas. By the action of this gas, the straight pipe 13 and the elbow pipe 14 are prevented from being oxidized, for example, on the inner side (back wave) of the butt portion during welding.

  In the above configuration, when butt welding of the straight pipe 13 and the elbow pipe 14 is performed, a groove and a seamed portion are formed at each end, and first, a pipe pedestal mounted with the straight pipe 13 on the guide rail 11. 15, and then the tube centering / holding device 40 is inserted from the base end side of the straight tube 14 from the head portion 43 side. Here, the tube centering / holding device 40 first operates the operation handle 445 of the traveling unit 44 so that the pantograph mechanism 444 is deployed, and the traveling roller member 443 is brought into contact with the tube wall surface and guided to the wall surface. The traveling unit 44 is moved to a desired position for welding in the straight pipe 13.

  Subsequently, the tube centering / holding device 40 is driven by the hydraulic mechanism 436 on the straight pipe 13 side of the clamp claw 435 of the head portion 43 so that the clamp claw 435 is extended in the tube wall direction, and the peripheral wall abuts. The contact surface comes into contact with the seaming portion of the straight pipe 13. Here, the hydraulic hose 41 and the cooling water hose 42 extending from the head portion 43 are inserted into the insertion holes 171 and 191 of the positioner 17 and the rotation driving unit 19 and connected to the hydraulic pump 45 and the cooling water pump 46 by piping. The

  Next, the elbow pipe 14 is placed on the joint pipe cradle 16 attached to the guide rail 11, and the joint pipe cradle 16 is moved in the direction of arrow B along the guide rail 11 to open the elbow pipe 14. The front surface is matched with the groove surface of the straight pipe 13. Thereafter, the hydraulic mechanism 436 on the front side of the head portion 43 of the tube centering / holding device 40 is driven, the clamp claw 435 is extended in the tube wall direction, and the abutment surface of the peripheral wall is a seaming process of the elbow tube 14. The centering and holding of the straight pipe 13 and the elbow pipe 14 are completed here.

  Here, the straight pipe 13 and the elbow pipe 14 which are shifted to the welding process and are centered and held by the claws 435 of the head portion 43 are centered and held at a plurality of groove bottoms with respect to the welding length. The place is tack welded.

  In this tack welding state, the preheating device 30 on the joint pipe cradle 16 has the first and second support frames 31 and 32 and the first and second high-frequency heating coils 34 and 35 as described above. It is divided and attached to the outer peripheral portion in the vicinity of the groove of the elbow pipe 14 in a state where the centering and holding of the straight pipe 13 and the elbow pipe 14 is completed. When the preheating device 30 is driven by power supplied to the first and second high-frequency heating coils 34 and 35 from the drive source (not shown), the vicinity of the butted portion of the elbow pipe 14 is heated to Preheating is applied to the butted portion of the elbow pipe 14 and the straight pipe 13. At this time, in the tube centering / holding device 40, the cooling mechanism 437 is driven and controlled, the hydraulic mechanism 436 is cooled and thermally controlled, and stable centering and holding by the clamp pawl 435 is maintained.

  Next, the torch mounting body 20 of the welding torch 12 is adjusted up and down with respect to the torch stand 10, and the tungsten electrode 21 of the torch body 22 is opposed to the bottoms of the straight pipe 13 and the elbow pipe 14. A pair of gas nozzles 23 are arranged in the circumferential direction across the 21 (the front-rear direction of the tungsten electrode 21). Further, the filler nozzle 23 is adjusted in position with respect to the torch mounting body 20 via the position adjusting member 26 and is arranged corresponding to the tungsten electrode 21 of the torch main body 22.

  The welding torch 12 generates an arc at the tungsten electrode 21, and a shield gas is supplied from the gas nozzle 23 to the front and rear of the tungsten electrode 21, and a filler material is supplied from the filler nozzle 25. The groove downward welding is performed at the butt portion of the preheated straight pipe 13 and elbow pipe 14. At this time, the notch 435a of the clamp claw 435 is filled with gas from the gas nozzle 23, for example.

  Here, the rotation drive portion 19 of the positioner 17 is driven, and the straight pipe 13 held by the chuck portion 18 is rotationally driven, so that all of the butted portions of the straight pipe 13 and the elbow pipe 14 by the welding torch 12 are all driven. Continuously over the circumference, from the first layer back wave welding to the extra welding, the groove is directed downward. Thereby, the welding amount in groove downward welding can be improved, and high quality welding can be reliably performed.

  During the groove downward welding, the gas inside the notch 435a of the clamp claw 435 is prevented from oxidizing the inner side (back wave) of the butted portion of the straight pipe 13 and the elbow pipe 14.

  As described above, the welding apparatus includes the straight pipe 13 and the elbow pipe 14 that are arranged to face each other, mounted on the pipe receiving base 15 and the joint pipe receiving base 16, and the pipe centering / holding device 40 inside the straight pipe 13. Then, the travel unit 44 of the tube centering / holding device 40 is moved into the tube to adjust the position, and the hydraulic mechanism 436 of the head portion 43 is driven to adjust the expansion and contraction of the pair of clamp claws 435. In a state where the straight pipe 13 and the elbow pipe 14 are centered and held while being pressed against the butted part, a plurality of groove portions are temporarily welded together, and the preheating device 30 is mounted outside the elbow pipe 14 near the butted part. Then, the temperature fluctuation of the hydraulic mechanism 436 of the head portion 43 of the pipe centering / holding device 40 is thermally controlled by the cooling mechanism 437, and the straight pipe 13 and the elbow pipe 14 are rotated to thereby weld the torch. 12 And configured to perform a GMA downward welding the entire circumference of the butted portion of the more tubes.

  According to this, since the hydraulic mechanism 436 of the head portion 43 of the tube centering / holding device 40 is thermally controlled by the cooling mechanism 437 and the stable supply of hydraulic pressure is performed, high accuracy of the butt portion by the clamp claw 435 is achieved. While maintaining the centering and holding, the welding torch 12 can continuously perform groove downward welding efficiently and with high quality.

  In addition, according to this, it becomes possible to further reduce the groove width by the welding torch 12, to reduce the welding amount, and to improve the welding amount. It can be done easily.

  In the above embodiment, the case where the preheating device 30 is configured to be divided and arranged in two parts on the joint pipe receiving base 16 has been described. However, the present invention is not limited to this, and instead of the joint pipe receiving base 16, It is also possible to configure so as to be arranged on the tube cradle 15. The number of divisions of the preheating device 30 is not limited to two divisions, and the number of divisions may be two or more.

  Moreover, in the said embodiment, although the case where the butt welding of the straight pipe 13 and the elbow pipe 14 was performed was demonstrated, it is not restricted to this, Butt welding of various joint pipes, such as straight pipes and elbow pipes, is carried out. It is possible to apply to the same, and the same effective effect is expected.

  Therefore, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention at the stage of implementation. Further, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements.

  For example, even if some constituent elements are deleted from all the constituent elements shown in the embodiment, the problems described in the column of problems to be solved by the invention can be solved, and the effects described in the effects of the invention can be obtained. In some cases, a configuration from which this configuration requirement is deleted can be extracted as an invention.

It is the block diagram which showed the external appearance structure of the welding apparatus which concerns on one embodiment of this invention. It is the block diagram which showed the detail of the welding torch of FIG. It is the block diagram which took out and showed the preheating apparatus of FIG. It is the block diagram which extracted and showed the principal part of the tube centering and holding | maintenance apparatus of FIG. FIG. 5 is a configuration diagram showing a cross-sectional view of a connection configuration of a traveling unit, a head portion, and the like in FIG. It is the enlarged view which showed the state which centered and hold | maintained the straight pipe | tube and elbow pipe | tube of FIG. 1 with the clamp nail | claw of the head part of the pipe | tube centering / holding apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Torch stand, 11 ... Guide rail, 12 ... Welding torch, 13 ... Straight pipe, 14 ... Elbow pipe, 15 ... Pipe receiving stand, 16 ... Joint pipe receiving stand, 17 ... Positioner, 171 ... Insertion hole, 18 ... Chuck , 19: Rotation drive unit, 191 ... Insertion hole, 20 ... Torch mounting body, 21 ... Tungsten electrode, 22 ... Torch main body, 23 ... Gas nozzle, 24 ... Nozzle support member, 25 ... Filler nozzle, 26 ... Position adjustment member, DESCRIPTION OF SYMBOLS 30 ... Preheating apparatus 31, 32 ... 1st and 2nd support frame, 311 and 312 ... Support member, 33 ... Connection part, 34, 35 ... 1st and 2nd high frequency heating coil, 36 ... Connection part, 40 ... pipe centering / holding device, 41 ... hydraulic hose, 42 ... cooling water hose, 43 ... head part, 431 ... casing, 432 ... gutter member, 433 ... screw member, 434 ... spring member, 435 Clamp claw, 435a ... notch, 436 ... hydraulic mechanism, 437 ... cooling mechanism, 44 ... traveling unit, 441 ... tip shaft, 442 ... disc member, 443 ... traveling roller member, 444 ... pantograph mechanism, 445 ... operation handle 45 ... hydraulic pump, 46 ... cooling water pump.

Claims (11)

Pipe moving means for butt-welding the pipes to be independently movable, moving at least one of them and butt-arranging each other's groove;
The tube is inserted into one of the tubes so as to be movable in the axial direction, and a clamp claw provided in contact with and away from the inner wall of the tube is driven to press-contact the inside of each butted portion of the tube to maintain the centering. Tube centering / holding means having a hydraulic mechanism to
Tube rotating means for rotationally driving the tube that has been centered and held via the tube centering / holding means and is temporarily welded;
A welding means for welding the butt portion of the pipe downwardly in conjunction with the rotational drive of the pipe rotating means;
A welding apparatus comprising:   2. The welding apparatus according to claim 1, further comprising preheating means attached to an outer peripheral portion in the vicinity of the welding portion of the pipe to be butt welded, for heating the vicinity of the welding portion.   The welding apparatus according to claim 2, wherein the preheating means is formed of a plurality of divided bodies.   4. The welding apparatus according to claim 1, further comprising a cooling unit that cools a hydraulic mechanism of the tube centering / holding unit.   The tube centering / holding means is composed of a clamp claw provided on the inner wall of the tube and a head part that accommodates a hydraulic mechanism, and a traveling unit that supports the head part and travels in the pipe. The welding apparatus according to any one of claims 1 to 4, wherein the welding apparatus is provided.   The head portion of the tube centering / holding means and the traveling unit are provided such that their center axes can be displaced in the radial direction in a state where the clamp pawl is pressed against the inner wall of the tube. 5. The welding apparatus according to 5.   The welding apparatus according to any one of claims 1 to 7, wherein a notch that forms a gap in the circumferential direction inside the abutting portion of the pipe is provided opposite to the clamp pawl of the hydraulic mechanism.   The welding apparatus according to claim 1, wherein the clamp pawl of the hydraulic mechanism is independently driven and controlled.   The said welding means is equipped with the electrode, the shield gas supply part, and the filler material supply part, The said shield gas supply part is arrange | positioned in the circumferential direction of the said pipe | tube across the said electrode. The welding apparatus according to any one of 8. A centering / holding step in which the groove of the pipe to be butt welded is butt-arranged and centered and held from the inside of the pipe; and
A welding process in which the centered and held pipe is tack-welded and rotationally driven, and a butt portion of the pipe is welded downward in the groove;
The welding method characterized by comprising.   11. The welding according to claim 10, wherein in the welding step, the centered / held tube is tack-welded to pre-heat the butt portion, and the butt portion of the tube is welded downward by groove driving. Method.

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