JP2005144533A - Welding method for piping, shielding gas blockade member, shielding gas injection tube, ascending current shielding means, and cover - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out preparation for welding in a short period of time in welding and connecting of vertical piping on a building site etc., and to perform satisfactory welding by making it possible to easily and surely protect a weld zone by a small amount of shielding gas. <P>SOLUTION: In welding vertically arranged upper and lower piping 1 and 2, water-soluble shielding gas blockade members 4 and 5 are housed and fixed at the prescribed positions within the upper and lower piping 1 and 2 and a shielding gas injection tube 6 is inserted into a welding chamber formed between the shielding gas blockade components 4 and 5 from a gap G formed at a groove 3 at the opposite ends of the upper and lower piping 1 and 2. The shielding gas 8 heavier than air is then injected to the part upper than the groove 3 of the welding chamber from the shielding gas injection tube 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a shield gas welding method for stainless steel pipes arranged vertically in a construction site, and more particularly to a pipe welding method capable of effectively protecting a back shield gas for piping during welding.

  In butt welding of stainless steel pipes, it is necessary to shield the welded portion with an inert gas such as argon or helium in order to prevent pores or cracks during welding. In particular, in the case of piping, in order to prevent oxidation of the inner surface, it has been conventionally performed to protect the inside of the piping with a back shield gas (hereinafter simply referred to as shield gas) with an inert gas.

  For example, when butt welding of a small diameter stainless steel pipe is performed, a shield gas is flown into the pipe to reduce the oxygen concentration in the pipe. Patent Document 1 is an example of such a conventional example. In Patent Document 1, two stainless steel pipes to be welded are butt-arranged, and a gas injection pipe in which a large number of pores are formed in the pipe is inserted from a small hole formed in the butt section. The butt portion is welded while injecting an inert gas into the pipe from the small holes.

  For example, when performing butt welding of intermediate or large diameter stainless steel pipes, the inside of the pipe is partitioned by a simple partition member around the weld groove, and the space between the partition members is a simple welding chamber. The welding gas is injected into the welding chamber from the gap of the groove portion, and welding is performed while releasing the shielding gas in the welding chamber little by little from the gap of the groove portion. As such a conventional example, There exists patent document 2. FIG. In Patent Document 2, each of the two stainless steel pipes butt-arranged with the tip to be welded (welded part) separated from the welded part by a predetermined distance so as not to be affected by the heat of welding. Insert the water-soluble polyvinyl alcohol membrane bag into the tube, close the inside of the pipe, inject argon gas into the pipe from the gap of the welded part, replace the air inside with argon gas, and weld the welded part Yes.

  Further, the inside of the vertical pipe is partitioned by a simple partition member centering on the weld groove portion, the space between the partition members is made a simple welding chamber, and a shielding gas is injected into the weld chamber from the gap of the groove portion. Patent Document 3 is a conventional example of welding while carrying out welding. In Patent Document 3, a conical water-soluble paper main body and an open end of the water-soluble paper main body are folded outward in a longitudinal pipe that is butt-welded in an inert gas atmosphere, and the diameter of the folded base portion is vertical. A water-soluble paper plug composed of a flange formed so as to have substantially the same diameter as the inner diameter of the arranged pipe is inserted so as to form an inert gas filling space around the welded portion inside the pipe.

  The inside of the vertical pipe is divided by a partition member around the weld groove, and the space between the partition members is used as a welding chamber, and welding is performed while injecting a shielding gas into the welding chamber from the gap of the groove. A conventional example is shown in FIG. In FIG. 12, a is a stainless steel pipe arranged vertically, b is a stainless steel pipe arranged vertically on the upper part of the pipe a, and c is a groove formed at a butt portion of the pipes a and b. , D is a sponge shield gas blocking member housed in the pipe a at a position not affected by heat below the groove c, and e is housed in the pipe a at a position not affected by heat above the groove c. This is a shield gas blocking member made of sponge.

  Further, f is a shield gas injection pipe which is inserted into the pipe b from the upper end opening of the pipe b and penetrates the shield gas closing member e and extends in the pipe a to the vicinity of the upper portion of the shield gas closing member d. The injection pipe f is formed with a large number of small holes g for injecting a shielding gas h that is an inert gas such as argon into the welding chamber between the shielding gas closing members d and e. In the figure, H1 is the height of the pipe b.

  During the welding of the pipes a and b, welding is performed while injecting the shielding gas h into the welding chamber in the pipes a and b formed between the shield gas closing members d and e through the small hole g of the shielding gas injection pipe f. . At this time, the shield gas h in the welding chamber flows out from the gap of the groove c little by little, so that the welding arc portion is protected.

  By the way, as a characteristic of the installation location of vertical pipes at the site, the fire prevention compartment may be a pit hole compartment, and the housing side is vertically divided into a chimney from the ground floor or the basement floor to the higher floor. ing. In this case, an ascending air current is generated around the outside of the pipe due to the chimney effect, and there is a risk of disturbing the shield gas (inert gas) on the welded part and causing poor welding. Generally, the wind speed is 2 m / sec on site. In the above case, welding is difficult. For this reason, conventionally, the work area including the welded part is surrounded by a curing disaster prevention sheet to prevent the wind, the screen is provided with windscreens to weaken the wind, and the shield gas flow rate is increased to prevent the harmful effects caused by the dissipation of the shield gas. In this way, the influence of the wind on the welding arc portion is reduced.

  Further, Patent Documents 4 and 5 are conventional examples in which a welding torch is held and wind protection is performed when a vertical pipe is welded using an automatic welder. In Patent Document 4, the entire welding torch is covered with a surrounding body, and the arc portion at the tip of the welding torch is locally windproof. In Patent Document 5, the entire welding torch is surrounded by a windbreaker for welding.

In addition, the vertical pipe may be 10 m or longer. In this case, a chimney effect is produced in the pipe, and the circulating air flows in the pipe. Therefore, conventionally, waste or air is filled in the piping to prevent air circulation. Moreover, since the inert gas which prevents the oxidation of a welding part is disturbed by the circulation | circulation air which flows in piping, there exists patent document 6 as a prior art example which prevented this. In Patent Document 6, bubbles are filled so as to be positioned in the vertical position of the groove in a vertically oriented pipe arranged in abutment to prevent welding defects.
Japanese Patent Laid-Open No. 9-295147 JP-A-5-245633 JP-A-9-10933 Japanese Utility Model Publication No. 55-55281 JP 2000-238771 A Japanese Patent Laid-Open No. 11-170050

  In the case of Patent Document 1, there is no problem in the case of a horizontal pipe. However, when the shield gas is argon heavier than air when used in a vertical pipe, the argon gas is more than the gas injection pipe inserted horizontally. However, the shield gas concentration behind the bead portion of the liver kidney is not sufficiently high, and good welding cannot be performed.

  In the case of Patent Document 2, leakage of shielding gas is prevented by a water-soluble polyvinyl alcohol film bag, but when the bag is installed in a vertically oriented pipe, the bag falls, There is a possibility that the welding chamber is not formed at a predetermined position.

  In the case of Patent Document 3, the shape of the water-soluble paper plug is complicated.

  In the case of the one shown in FIG. 12, the length of the shield gas injection pipe f is used to connect unit pipes having a length of 10 m or more for two floors or three floors by welding, as in the case of vertical pipes for buildings. Since it is necessary to extend the shield gas injection pipe f through the shield gas closing member e in the pipe b, the preparation work is troublesome. Further, it is difficult to take out the shield gas blocking members d and e such as sponges from the pipes a and b after the pipes a and b are welded, and the shield gas blocking members d and e are applied to a pipe through which a fluid flows. It ’s bad to do.

  On the other hand, in order to prevent the upward air flow generated around the outside of the vertical pipe due to the chimney effect and reduce the influence of the wind on the welding arc part, the work range including the welded part is surrounded by a curing disaster prevention sheet, If a partition is provided, it takes time for the welding work, the work efficiency is poor, and increasing the flow rate of the shielding gas causes an increase in cost.

  In the case of Patent Documents 4 and 5, the welding torch can be protected from the airflow flowing outside the pipe, but since the welding torch is covered by the enclosure or the windbreaker for welding, the field of view of the weld is deteriorated and welding is performed. Even if the operation of the torch is not performed well, it is difficult to confirm.

  Also, in order to prevent the chimney effect from occurring in the piping and the flow of air through the piping, if the waste is clogged in the piping, the waste will be forgotten, causing problems. In the case of Document 6, a large-scale filling device is required to fill the bubbles in the pipe, and there is a possibility that the workability is deteriorated due to the filling time of the bubbles and the circulation air is regenerated due to the bubbles being blown out.

  The first object of the present invention is to enable welding preparation in a short time when welding vertically connected pipes at a construction site or the like, and to make a welded portion easily and reliably with a small amount. It is to be able to perform good welding by protecting with a shielding gas. In addition, the second object of the present invention is to prevent the updraft by a simple means and prevent the shield gas from being disturbed even when an updraft is generated around the outside of the vertical pipe due to the chimney effect. It is to be able to perform good welding. Furthermore, the third object of the present invention is to prevent the circulation air by a simple and reliable means when the circulation air flows in the vertically oriented pipe, and perform good welding so that the shield gas is not disturbed. Is to do so.

  In the pipe welding method according to claim 1, when the upper and lower pipes arranged in the vertical direction are welded, the water-soluble shield gas blocking members are respectively housed and fixed at predetermined positions in the upper and lower pipes, and the upper and lower pipes are opposed to each other. A shield gas injection pipe is inserted into the welding chamber formed between the upper and lower shield gas closing members from the gap formed in the groove between the end portions, and the groove of the welding chamber is inserted from the shield gas injection pipe. The shield gas heavier than air is injected into the upper part.

  The shield gas blocking member according to claim 2 includes a water-soluble sheet and an edge formed by bending an end of the sheet, and the edge can be attached to the inner periphery of the pipe with a water-soluble adhesive tape. It is a thing.

  The shield gas injection pipe according to claim 3 is inserted into a welding chamber formed between the upper and lower shield gas closing members through a gap formed in a groove between opposed ends of the upper and lower pipes, and the welding chamber. Inside, the vertical member in which the small hole for inject | pouring shielding gas in a welding chamber was formed is comprised so that it may be located above the said groove | channel.

  According to a fourth aspect of the present invention, there is provided a pipe welding method in which ascending air current blocking means is provided so as to be positioned below a groove between opposing ends of the upper and lower pipes when the upper and lower pipes arranged vertically are welded. The ascending airflow flowing from below to above along the outer periphery is blocked.

  The ascending air flow blocking means according to claim 5 is divided into a plurality of parts in the circumferential direction, and is provided on each support body and a support body that is attached to the outer periphery of a pipe arranged vertically. And an ascending airflow blocking plate having a flange shape whose outer shape is larger than the pipe diameter as a whole.

  According to a sixth aspect of the present invention, the ascending air current blocking means includes two sets of support bodies attached to the pipe, and one of the opposing end portions of the support bodies is connected by a hinge.

  In the upward flow blocking means according to the seventh aspect, the upward air flow blocking plate positioned below the welding torch at the time of pipe welding is provided with a wall extending downward from three sides of the blocking plate.

  In the pipe welding method according to the eighth aspect, when the upper and lower pipes arranged in the vertical direction are welded, a lid is fitted to the upper end of the upper pipe to prevent the flowing air flowing through the pipe.

  The lid body according to claim 9 is formed in a cap shape and can be fitted to the upper end portion of the pipe.

  According to the first to third aspects of the present invention, since preparation for welding work can be performed easily and in a short time, the work efficiency can be improved, and a shield gas having a predetermined concentration exists in the groove. Therefore, good welding can be performed, and furthermore, since a small amount of shielding gas flows out from the groove, various excellent effects such as advantageous cost can be obtained.

  According to invention of Claims 4-7, the ascending airflow that has risen along the outer periphery of the pipe is blocked by the updraft blocking means that is simple in structure and inexpensive, and is not blown onto the groove portion. Therefore, the shielding gas in the groove is not disturbed, and good welding can be performed. Also, since the welding torch is not shielded, an excellent effect that the welding state can be easily confirmed can be achieved. .

  According to the inventions of claims 8 and 9, since it is possible to reliably prevent the circulation air from flowing in the pipe, the shield gas is not disturbed, and good welding can be performed. Since the lid has a simple configuration, various excellent effects such as low cost can be achieved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 4 show an example of an embodiment of the present invention for achieving the first object of the present invention. In the figure, 1 is a stainless steel pipe arranged vertically, 2 is a stainless steel pipe installed vertically on the upper part of the pipe 1, and 3 is a groove formed at the butt of the pipes 1 and 2. Yes, the gap G between the pipes 1 and 2 in the groove 3 is about 4 mm.

  4 is a water-soluble and paper shield gas blocking member housed in the pipe 1 at a position not affected by heat below the groove 3, and 5 is inside the pipe 2 at a position not affected by heat above the groove 3. It is a water-soluble paper-made shielding gas blocking member housed in the container. The height H2 from the center of the gap G between the shield gas blocking members 4 and 5 is H2≈300 mm.

  6 is a stainless steel shield gas injection pipe to which a hose 7 is connected at the rear end and can be inserted into the pipe 2 through a gap G between the grooves 3 formed between the pipes 1 and 2. In the vertical member 6a of the gas injection pipe 6, a large number of small gases for injecting a shield gas 8 which is an inert gas such as argon into a welding chamber formed between the shield gas closing members 4 and 5 of the pipes 1 and 2 are provided. A hole 6b is formed. The shield gas injection pipe 6 has a side surface formed in an L shape, and the cross-sectional shape is flat so that it can be easily inserted into the welding chamber between the shield gas closing members 4 and 5 from the gap G. The shield gas injection pipe 6 may be formed in a U shape instead of the L shape.

  9 is a bracket fixed to the outer side of the pipe 2, 10 is a bracket disposed on the beam 11 provided in the field, and the pipe 2 is fixed to the beam 11 by bolting the brackets 9 and 10, It has come to be supported.

  As shown in FIG. 2, the shield gas blocking members 4 and 5 are arranged in a radial direction at predetermined intervals in the circumferential direction around a water-soluble paper sheet 12 formed by a predetermined dimension larger than the inner diameters of the pipes 1 and 2. A cut 12a is made in the direction, and the cut 12a is bent as shown in FIG. 3 to form an edge 12b, and the cross-sectional shape is formed in a substantially cylindrical shallow dish shape. Thus, when the shield gas blocking members 4 and 5 are set in the pipes 1 and 2, about 300 mm from the opening end side forming the groove in both the pipes 1 and 2 installed in the horizontal state. The shield gas blocking members 4 and 5 can be inserted into the pipes 1 and 2 by inserting the shield gas blocking members 4 and 5 into the closed member set position. The fixing is performed by adhering the edge portion 12b of the paper sheet 12 to the pipe end 1 and the inner wall circumference of the pipe 1 and 2 with the single-sided adhesive tape 13 with the edge portion 12b facing the tube end front side. 3 and 4, the openings of both the shield gas blocking members 4 and 5 are shown upward. However, the direction of the shield gas blocking member 5 is upside down. The side is facing down.

Next, the operation of the illustrated example will be described.
When welding the vertically oriented pipes 1 and 2, the water is soluble at a predetermined position inside the pipe 1, which is vertically erected downward and has a water-soluble shield gas blocking member 4 attached at a predetermined position inside. The pipe 2 to which the shield gas blocking member 5 is attached is conveyed in a vertical direction by a conveying means such as a crane with the end portion to be welded down, and lowered to a predetermined state above the pipe 1. The pipe 2 is set in a predetermined state by fastening the brackets 9 and 10 with bolts. Thereby, the groove | channel 3 of the clearance gap G is formed in the butt | matching part of the piping 1 and 2. FIG. Since the shield gas blocking members 4 and 5 are attached to the inner circumferences of the pipes 1 and 2 via the single-sided adhesive tape 13, the shield gas blocking members 4 and 5 do not fall off. Further, when the pipe 2 is attached, fine adjustment is performed so as to be concentric with the pipe 1.

  Next, the worker puts the vertical member 6a of the shield gas injection pipe 6 in a horizontal state and inserts it into the welding chamber formed between the shield gas closing members 4 and 5 provided in the pipes 1 and 2 from the gap G. Then, the orientation of the vertical member 6a is changed by 90 degrees so that the vertical member 6a is placed upright so as to be positioned in the pipe 2 in the welding chamber. For this reason, the vertical member 6a is located on the pipe 2 side of the welding chamber. Thus, the shield gas 8 which is an inert gas heavier than air such as argon sent from a cylinder (not shown) or the like is formed from the hose 7 to the vertical member 6a of the shield gas injection pipe 6. It is injected into the welding chamber so as to be positioned above the groove 3 of the welding chamber through the small hole 6b.

  Since the shielding gas 8 injected into the welding chamber is heavier than air, it descends and flows out little by little from the gap G of the groove 3. As a result, the shielding gas 8 having a predetermined concentration exists in the groove 3. . For this reason, the welding arc by a welding torch is protected and the groove | channel 3 can be welded favorably.

  According to the illustrated example of the present invention, the preparation of the welding operation can be performed easily and in a short time, so that the efficiency of the operation can be improved. Moreover, since the shield 3 has a predetermined concentration in the groove 3, good welding can be performed. Furthermore, since the flow rate of the shield gas flowing out from the gap G of the groove 3 is small, it is advantageous in terms of cost.

  FIG. 5 shows another example of the embodiment of the present invention for achieving the first object of the present invention. In the illustrated example, 3 to 6 guide bodies 15 are fixed to the lower end of the vertically oriented pipe 2 by tack welding so that the lower end protrudes below the pipe 2 at predetermined intervals in the circumferential direction. Yes. According to the illustrated example, when the pipe 2 is set to the pipe 1, if the suspended pipe 2 is lowered, the guide body 15 is lowered along the outer periphery of the pipe 1. Is reliably aligned. Therefore, in the illustrated example, the pipe 2 can be set to the pipe 1 more easily, quickly and accurately. When the pipe 2 is set with respect to the pipe 1, the guide body 15 is removed. Welding is performed in the same manner as described with reference to FIG.

6 and 7 show an example of an embodiment for achieving the second object of the present invention.
In the figure, 16 is a building pillar, 17 is a work scaffold provided in the portion of the vertically oriented pipe 1, 18 is a curing smoke-proof sheet stretched around the pipes 1 and 2, and 19 is a pipe. The skirt is arranged at a predetermined position below the groove 3 formed between 1 and 2 and fixed to the outer periphery of the pipe 1 so as to block the rising airflow 20 flowing on the outer peripheral surface of the pipes 1 and 2.

  As shown in FIG. 7, the skirt 19 has a two-part structure, is assembled and fixed to the outer periphery of the pipe 1, and is paired with a pair of semi-cylindrical skirt supports 19a that are cylindrical. A pair of semicircular flange-shaped skirt main bodies 19b that are formed into a plate shape and a bracket 19c that serves as a fastening portion when assembled are provided. The skirt body 19b is fixed to the lower end of the skirt support 19a, and the bracket 19c is connected to the circumferential end of the skirt support 19a and the circumferential end of the skirt body 19b at an angle of approximately 90 degrees. Is fixed.

  When welding the pipe 2 to the pipe 1, the skirt 19 is fixed to the outer periphery of the pipe 1 at a predetermined position below the groove 3 formed between the pipes 1 and 2. The fixing is performed by aligning the skirt support portion 19a with the outer periphery of the pipe 1 and fastening the opposing bracket 19c with bolts. As a result, the rising airflow 20 rising along the outer periphery of the pipe 1 is blocked by the skirt body 19b of the skirt 19 and is not blown onto the groove 3 portion. For this reason, by providing the skirt 19 with a simple structure, the shield gas 8 flowing out little by little from the gap G of the groove 3 is not disturbed, and good welding can be performed.

  FIG. 8 shows another example of the skirt shown in FIG. In the skirt 19 of the illustrated example, a hinge 21 for opening and closing the skirt support portion 19a and the skirt body 19b is attached to one end of the bracket 19c. With such a configuration, the skirt 19 can be easily and quickly attached to and detached from the pipe 1. Also in the illustrated example, the shield gas 8 flowing out from the groove 3 is not disturbed.

  9 and 10 show still another example of the skirt shown in FIG. In the illustrated example, in order to prevent the shield gas 8 at the position where the groove 3 is currently welded from being disturbed by the rising airflow 20 rising along the outer periphery of the pipe 1, The area of one skirt body 19b of 19b is expanded to form a skirt body 22 having a flat rectangular shape at the tip, and a wall portion 22a extending downward is attached to the tip of the skirt body 22, and the skirt body 22 is lowered to both sides of the skirt body 22. A side wall 22b extending to is fixed. In FIG. 10, reference numeral 23 denotes a welding torch.

  When welding the groove 3, the skirt 19 is attached to the pipe 1 so as to be positioned below the groove 3 as shown in FIG. 10. During welding, the skirt 19 is also moved in the circumferential direction of the pipe 1 as the welding torch 23 moves along the groove 3 so that the skirt body 22 is positioned below the welding torch 23. By doing in this way, the ascending air current 20 is guided to the side wall 22b and the wall portion 22a, and ascends while avoiding the welding torch 23. For this reason, the ascending airflow 20 is not blown to the location where welding is currently performed, and the disturbance of the shield gas 8 at the tip of the welding torch 23 is further reliably prevented, and a better welding can be obtained.

  FIG. 11 is an example of an embodiment for achieving the third object of the present invention. In the figure, 24 is a cap-like lid that is fitted on the top of the pipe 2, and H 3 is the height of the pipe 2, and H≈10 m. Since the lid 24 is fitted on the top of the pipe 2 to reliably prevent the flowing air from flowing in the pipes 1 and 2, the shield gas 8 is disturbed by the flowing air in the pipes 1 and 2. And good welding can be performed. Further, since the lid 24 has a simple configuration, the cost is low.

  In addition, the same code | symbol is attached | subjected to the same part in FIGS.

  In the present invention, the case where the pipe is made of stainless steel has been described. However, the present invention can be applied to pipes other than stainless steel, and various modifications can be made without departing from the scope of the present invention. Of course.

It is a perspective view of an example of an embodiment of a welding method of piping of the present invention for achieving the first object. It is a top view which shows the state which made the cut | interruption in the sheet | seat in order to create the shield gas obstruction | occlusion member applied to the welding method of piping of FIG. It is sectional drawing of the shield gas obstruction | occlusion member formed by bending the edge part of the sheet | seat shown in FIG. It is sectional drawing which shows the state which inserted the shield gas obstruction | occlusion member shown in FIG. 3 in vertical piping. In the pipe welding method shown in FIG. 1, it is a perspective view which shows the state which attached the guide body to the lower end of the upper piping which should be welded, was guided by the guide body, and was set to the upper end of the lower piping. It is a perspective view which shows an example of embodiment of the welding method of piping of this invention for achieving the 2nd objective. It is a perspective view which shows the detail of the skirt applied to the welding method of piping of FIG. It is a perspective view which shows the other example of the skirt applied to the welding method of piping of FIG. It is a perspective view which shows the further another example of the skirt applied to the welding method of piping of FIG. It is a side view which shows the state which mounted | wore piping with the skirt shown in FIG. It is a perspective view which shows an example of embodiment of the welding method of piping of this invention for achieving the 3rd objective. It is a perspective view which shows an example of the welding method of the conventional piping.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piping 2 Piping 3 Groove 4 Shield gas obstruction member 5 Shield gas obstruction member 6 Shield gas injection pipe 6a Vertical member 6b Small hole 8 Shield gas 12 Paper sheet (sheet)
12b Edge 13 Single-sided adhesive tape (adhesive tape)
19 Skirt (updraft blocking means)
19a Skirt support (support)
19b Skirt body (updraft block)
20 Ascending current 21 Hinge 22 Skirt body (Updraft blocking plate)
22a Wall (wall)
22b Side wall (wall body)
23 welding torch 24 lid (lid)
G gap

Claims (9)

  When welding the upper and lower pipes arranged vertically, the water-soluble shield gas blocking member is housed and fixed at predetermined positions in the upper and lower pipes, respectively, and formed at the groove between the opposite ends of the upper and lower pipes. A shield gas injection pipe is inserted into the welding chamber formed between the upper and lower shield gas closing members from the gap, and the shield heavier than air is placed above the groove of the welding chamber from the shield gas injection pipe. A method for welding pipes, characterized by injecting gas.   A shield gas blocking member comprising a water-soluble sheet and an edge formed by bending an end of the sheet, and the edge can be attached to the inner periphery of the pipe with a water-soluble adhesive tape. .   Inserted into the welding chamber formed between the upper and lower shield gas closing members from the gap formed in the groove between the opposite ends of the upper and lower pipes, and in the welding chamber, the shield gas is introduced into the welding chamber. A shield gas injection pipe characterized in that a vertical member in which a small hole for injection is formed is positioned above the groove.   When welding upper and lower pipes arranged vertically, ascending airflow that flows upward from below along the pipe outer periphery is provided so that it is located below the groove between the opposing ends of the upper and lower pipes Pipe welding method characterized by shutting off.   A support body that is divided into a plurality of parts in the circumferential direction and that is attached to the outer periphery of a pipe arranged vertically, and provided on each support body and attached to the pipe, as a whole An ascending air current blocking means comprising an ascending air current blocking plate having a flange shape whose outer shape is larger than a pipe diameter.   6. The ascending current blocking means according to claim 5, further comprising two sets of supports attached to the pipe, wherein one of the opposing ends of the supports is connected by a hinge.   The upflow blocking means according to claim 5 or 6, wherein a wall extending from the three sides of the blocking plate to the lower side is provided on the rising airflow blocking plate located below the welding torch during pipe welding.   A pipe welding method, wherein, when welding upper and lower pipes arranged vertically, a lid is fitted to an upper end of an upper pipe to prevent a flowing air flowing in the pipe.   A lid body formed in a cap shape and configured to be fitted to an upper end portion of a pipe.

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