JPH05245633A - Shielding gas welding method for pipes - Google Patents

Abstract

PURPOSE:To reduce the quantity of blocking materials used in the pipes, to improve solubility into water and to discharge the blocking materials to the outside of the pipes by wash by inserting specified bags which are filled with gas and filled out into both side pipes of a weld zone of two stainless steel pipes and blocking up the insides of the pipes to perform welding. CONSTITUTION:When the weld zone 2 of the two stainless steel pipes 1 whose pipe ends are abutted on each other is subjected to shielding gas welding, water soluble polyvinylalcohol film bags 3 are filled with air and inserted into the stainless steel pipes 1 separately from the weld zone 2 to avoid a thermal effect of the weld zone 2 and both sides of the weld zone 2 are blocked up. After argon gas is blown into blocked space by an inside sealed jig from a gap of the weld zone 2 to replace the inside air and it is kept in an argon gas atmosphere, welding is performed by a TIG torch and an electrode. At this time, the water soluble polyvinylalcohol film bags 3 are deformed by the argon gas pressure and stuck to the pipe walls to maintain airtightness and it is carried till welding of a first layer is completed to perform welding. After welding is completed, water is filled into the pipes and these bags are carried away.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shield gas welding method for pipes.

[0002]

2. Description of the Related Art In butt welding of stainless steel pipes, chrome steel pipes, etc., it is necessary to shield the welded parts with an inert gas such as argon or helium and weld them in order to prevent defects such as pores and cracks during welding. This is necessary, and as a method for holding the shield gas in the welded portion and preventing the outflow of the welded gas, a suitable blockage is filled in a place that is not affected by heat at a distance of 30 cm or more on both sides of the welded portion. At this time, since the clogging material needs to be removed after welding, water-dispersible paper that can be removed by washing with water, rolled water-soluble polyvinyl alcohol film, and foaming a liquid mainly composed of alkanolamine of saturated fatty acid. What is made to be used is used.

However, although water-dispersible papers are well dispersed in water, they are basically insoluble in water because the fibers are scattered, which causes pollution problems such as turbidity of wastewater and high COD value. In addition, there are drawbacks such that clogging of the strainer occurs and fibers remain in the recesses of the pipe, making removal difficult.

Polyvinyl alcohol film dissolves in water, but since the film is rolled and packed tightly in a tube,
The solubility is extremely poor, and even if water penetrates, it becomes a gel-like mass, and it is difficult to discharge it from the pipe by washing with water. Especially, in the case of a thermal power plant, a long washing work and a large amount of water are required. If the removal is incomplete, the performance of the condensate desalination unit may be degraded.

Further, when the shielding gas is retained by the foaming agent, there is a problem in stability of the foaming agent, and it is necessary to perform welding work promptly after filling the foaming agent into the pipe. Also, in welding of vertical pipes, the foaming agent may drop by its own weight and the gas shield may become incomplete. In addition, when filling the pipe, the foaming agent may adhere to the vicinity of the groove of the welded portion, which may make welding impossible.

[0006]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above circumstances, and it is possible to accurately close both side pipes of a welded portion and reliably maintain the shield gas atmosphere of the welded portion. The welding quality is improved, the amount of blockages in the pipe is extremely small, the solubility in water is good, and it can be easily discharged out of the pipe by washing with water, which in turn improves the efficiency and economy of welding work. It is an object of the present invention to provide a shield gas welding method for a pipe that can be improved.

[0007]

To this end, the present invention provides two
When the ends of the pipes are butt-welded and shield gas is fed into the pipes for butt welding, a water-soluble polymeric material bag filled with gas is inserted into the pipes on both sides of the welded part to close the pipes. And then weld.

[0008]

In the shield gas welding method for pipes of the present invention,
By enclosing the gas in the water-soluble polymer bag, the bag is pressed against the entire inner surface of the pipe and adheres tightly, and remains at that position against the shield gas pressure due to the friction between the film surface and the inner surface of the pipe. , Keep the shield gas atmosphere. Even if some of the gas in the bag leaks and shrinks to some extent, the width of the bag, that is, the diameter when expanded, is larger than the inner diameter of the tube, so it is pressed against the inner surface of the tube by the shield gas and adheres tightly, creating a shield gas atmosphere Hold. Furthermore, compared to the conventional method in which polyvinyl alcohol film is rolled tightly and packed, the amount of water-soluble polymer material used is several tenths. Therefore, the bag made of water-soluble polymer material at the time of washing the pipe inner surface after welding is It can be easily dissolved and removed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the shield gas welding method for pipes of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of a pipe into which a water-soluble polyvinyl alcohol film bag is inserted, and FIG. 2 shows a shield gas welding procedure. A front view, FIG. 3 is a vertical cross-sectional view showing a deformation of the bag in a gas shield state, and FIG. 4 is an explanatory view of an example of a different mode of the bag.

Referring to FIG. 1, when welding the welded portions 2 of two stainless steel pipes 1 having an inner diameter of 30 mm with their ends abutted to each other with shield gas, a film thickness of 40 μm and 120 mm × 15 are used.
Air is sealed in a water-soluble polyvinyl alcohol film bag 3 of 0 mm by about 1/3 volume, and it is inserted into the stainless steel pipe 1 about 300 mm away from the weld 2 to avoid the heat effect of the weld 2. Block both sides of 2. Then, as shown in FIG. 2, argon gas is blown into the closed space by the inner shield jig 4 from the gap of the welded portion 2 to replace the internal air and maintain the argon gas atmosphere, and then the TIG torch 5 is used. , Welding is started by the welding rod 6. At this time, as shown in FIG. 3, the water-soluble polyvinyl alcohol film-made bag 3 is deformed by the argon gas pressure and adheres to the tube wall to keep airtightness, and the argon gas flow rate is 1 l / min. Continue welding until the welding is completed.

After the shield gas welding is completed in this way,
The pipe was filled with water and allowed to stand for a few minutes and then drained, but the water-soluble polyvinyl alcohol film-made bag 3 was completely dissolved and discharged, and no residue was observed. In addition, there was no defect in the inspection of the welded portion 2 by radiation, and formation of chromium oxide was not observed in the inspection of the back surface of the welded portion after the split pipe.

Next, referring to FIG. 4, a different embodiment of the water-soluble polyvinyl alcohol film bag 3 will be described. The water-soluble polyvinyl alcohol film bag 3 has an inner diameter of about 5 m on the bag wall 3a.
A water-soluble polyvinyl alcohol film-made cylinder 3b having a length of m and a length of about 50 mm is penetrated and adhered. The water-soluble polyvinyl alcohol film-made cylinder 3b with the air blowing nozzle 7 inserted therein is used. After the alcohol film bag 3 is inserted about 300 mm deep from the welded portion 2, air is blown from the air blowing nozzle 7 to inflate the bag 3 and bring it into close contact with the inner surface of the pipe, and the air blowing nozzle 7 is removed. When the air blowing nozzle 7 is pulled out, the inside of the bag of the water-soluble polyvinyl alcohol film cylinder 3b at the air sealing port is closed by the sealed air pressure to prevent air from leaking.

[0013]

In summary, according to the present invention, when two pipe ends are abutted with each other and a shield gas is fed into the pipes for butt welding, gas is sealed in both pipes of the welded portion and expanded. By inserting a water-soluble polymer bag and closing the inside of the pipe and welding, the inside of the pipe on both sides of the weld is accurately closed, the shield gas atmosphere at the weld is reliably maintained, and welding quality is improved. A pipe that can use a very small amount of blockage in the pipe, has good solubility in water, can be easily discharged outside the pipe by washing with water, and can improve the efficiency and economy of welding work. The present invention is extremely useful industrially because it provides the shield gas welding method of

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a pipe into which a water-soluble polyvinyl alcohol film bag is inserted in an embodiment of the shield gas welding method for a pipe of the present invention.

FIG. 2 is a front view showing a shield gas welding procedure.

FIG. 3 is a vertical sectional view showing deformation of the bag in a gas shield state.

FIG. 4 is an explanatory view of an example of a different mode of the bag.

[Explanation of symbols]

 1 Stainless steel pipe 2 Welded part 3 Water-soluble polyvinyl alcohol film bag 3a Bag wall 3b Water-soluble polyvinyl alcohol film tube 4 Inner shield jig 5 TIG torch 6 Welding rod 7 Air blowing nozzle

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Norihiro Hiramatsu 1-1 1-1 Atsunoura-machi Nagasaki-shi Nagasaki Shipyard Ltd. (72) Inventor Toshio Hosono 1-12-4 Marunouchi, Naka-ku, Nagoya Sugimura Chemical Industry Co., Ltd.

Claims (1)

[Claims] 1. A bag made of a water-soluble polymer material in which gas is enclosed and expanded in both side pipes of a welded portion when two pipe ends are butted and a shield gas is fed into the pipes for butt welding. A shield gas welding method for a pipe, characterized in that the pipe is inserted and the inside of the pipe is closed and welded.