JPH0825050A - Welding method of fixed tube in pipeline - Google Patents

Abstract

PURPOSE:To improve the welding efficiency by running two welding trucks installing welding torches on the outer circumference, and avoiding the upward welding by a plasma keyhole welding. CONSTITUTION:In a pipeline fixed tube welding method to butt a pipeline fixed tube 3 and to weld the butted end faces in the circumferential direction, two welding trucks 1, 2 moving in the circumferential direction on the outer circumference of the fixed tube 3 are installed. While both trucks 1, 2 are moved from the position of 12 of the upper part of the fixed tube 3 toward the lower part in mutually opposite directions, the initial layer welding is executed with plasma keyhole welding by using the welding torch installed on each welding truck, after the welding trucks 1, 2 are made reach the lower part of the fixed tube 3, they are turned back toward the upper part and the secondary layer is welded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for plasma-welding a fixed pipe for a pipeline, and more particularly to a method for welding a fixed pipe for a pipeline in which two welding carriages are run on the outer peripheral surface of the fixed pipe to perform welding with high efficiency.

[0002]

2. Description of the Related Art In the conventional all-position welding method for a horizontal fixed pipe, usually, one welding carriage which moves in the circumferential direction is provided on the outer peripheral surface of the fixed pipe, and a welding torch having a single electrode is attached to this welding carriage. Is installed and the welding carriage is run in one direction along the circumference of the fixed pipe, and one-side welding is performed.

In this conventional single-electrode welding, when attempting to continuously weld a fixed pipe, it is inevitable that all-position welding including all positions is performed.

On the other hand, in plasma keyhole welding, a high frequency voltage is applied between a non-consumable electrode and a material to be welded in the presence of a plasma gas flow to generate a plasma column, which is fixed at an I-shaped groove. The pipes are welded to each other in the circumferential direction. Then, in this keyhole welding, the plasma column penetrates the material to be welded in the thickness direction thereof, and forms and holds the molten metal behind the welding torch moving direction. This plasma keyhole welding has an advantage that the welding efficiency is extremely high because the plasma penetrates the material to be welded and welds.

[0005]

However, if all positions are welded in the circumferential direction by the plasma keyhole welding, there are welding positions that are extremely inefficient among the positions that change from moment to moment. That is, in the all-position welding in which the outer peripheral surface of the fixed tube is welded while moving in the clockwise direction from the 12 o'clock position to the 6 o'clock position to the 12 o'clock position, 1
Downward welding is performed when moving clockwise from the position 2 to 6 o'clock, and upward welding is performed when moving back from the 6 o'clock position to the 12 o'clock position.
In this case, in the plasma keyhole welding, since the keyhole penetrates, in the case of upward welding, the molten pool is easily pushed down by gravity, in order to retain the molten metal and obtain a good weld bead, There is no choice but to make the upward welding slower than the downward welding. For this reason, the welding efficiency decreases during the upward welding.

The present invention has been made in view of the above problems, and a welding carriage having a welding torch provided on the outer peripheral surface is provided.
An object of the present invention is to provide a pipeline fixed pipe welding method in which welding efficiency is improved by traveling on a platform and avoiding upward welding by plasma keyhole welding.

[0007]

A pipeline fixed pipe welding method according to the present invention is a pipeline fixed pipe welding method in which pipeline fixed pipes are butted and their abutting end faces are circumferentially welded to each other. Two welding carriages that move the outer peripheral surface in the circumferential direction are provided, and using the welding torches provided to each welding carriage while moving the two carriages in opposite directions from the upper part to the lower part of the fixed pipe. First layer welding is performed by plasma keyhole welding, and after the welding carriage reaches the bottom of the fixed pipe, fold it back to the top 2
It is characterized by layer welding.

[0008]

In the present invention, two welding carriages are run on the outer peripheral surface of the fixed pipe in opposite directions, and the right half portion of the fixed pipe is downwardly welded by the welding torch mounted on one of the welding carriages. The welding torch mounted on the other welding carriage downwardly welds the left half of the fixed pipe. Then, when these welding carriages are folded back at the lower part of the fixed pipe and directed upward, a two-layer welding is carried out in which the weld metal is placed on the initial welding.

Therefore, the keyhole welding in which the keyhole is formed is only the downward welding when the trolley is in the first layer, and the welding efficiency is high. On the other hand, since the upward welding is performed in the case of the two-layer welding in which the first layer has already been formed or the subsequent laminated welding, unlike the case of forming the keyhole, the welding efficiency does not decrease. . in this way,
The present invention has extremely high welding efficiency because inefficient upward welding is avoided by plasma keyhole welding.

[0010]

Embodiments of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 1 is a schematic diagram for explaining the method of the first embodiment of the present invention. This figure is a view showing a state in which two welding carriages 1 and 2 move on the outer peripheral surface of the fixed pipe 3 along the circumferential direction.
The lowermost part of the fixed tube 3 will be described at 6 o'clock of the timepiece. Although not shown, the welding carriages 1 and 2 are
The welding torch is installed, the welding voltage is supplied from the welding power source to the welding torch, and the plasma gas is ejected from the welding torch in the state of being surrounded by the shield gas flow, thereby generating plasma. .

As shown in FIG. 1, first, both welding carriages 1 and 2 are located at the 12 o'clock position. Then, the welding carriage 1 starts welding at this 12 o'clock position, moves clockwise in the drawing along the locus R1, and downwardly welds the right half of the fixed pipe 3 via the 3 o'clock position. . This welding method is plasma keyhole welding. The welding carriage 2 moves counterclockwise from the 12 o'clock position along the locus R3, and downwardly welds the left half of the fixed pipe 3 via the 9 o'clock position. Also in this case, plasma keyhole welding is used.

When the welding carriage 1 reaches the position of the lower portion of the fixed pipe at 6 o'clock, it is folded back and moves the right half of the fixed pipe 3 along the locus R2 in the direction of 5 o'clock. From this 6 o'clock position to the 5 o'clock position, the vehicle runs idle and welding is stopped. Then, the welding is restarted from the 5 o'clock position, the upward welding is performed, the 3 o'clock position is passed, the 12 o'clock position is passed, and the welding is continued until the 11 o'clock position. By the movement in the counterclockwise direction from the position of 5 o'clock to the position of 11 o'clock, the welding carriage 1 deposits the weld metal on the initial overlay of the welding carriage 1 itself and the initial overlay of the welding carriage 2. Perform two-layer filling.

On the other hand, the welding carriage 2 is keyhole down welded to the 6 o'clock position, and then continues the lap welding by the plasma non-keyhole welding until 5 o'clock, and is folded back at the 5 o'clock position, and the bottom 6 Weld up through the hour position to the 12 o'clock position. Therefore, the movement of the welding carriage 2 in the clockwise direction causes the welding carriage 1 to move from 5 o'clock to 11 o'clock.
The two-layer welding with the weld metal is performed on the first welding and the first welding of the welding carriage 2 itself, and the lap welding is performed from 11:00 to 12:00 and the welding is completed.

Thus, as shown in the cross section of the welded portion in FIG. 2, a first layer buildup portion by plasma keyhole welding and a two layer buildup portion by plasma non-keyhole welding are formed.

In the case of three-layer welding, the right and left halves of this fixed pipe are similarly lap-welded in the same manner, while running on separate welding carriages 1 and 2 and repeated. Welding sequentially.

In this welding method, only the downward welding is used for the first layer deposition by plasma keyhole welding, and the downward welding is more efficient than the upward welding in terms of welding speed and stability. Is taking advantage of that. That is, in the first layer build-up welding in which the keyhole is formed, the upward welding is avoided. As a result, the welding efficiency is improved and the welding quality is ensured.

Also, when overlay welding of two or more layers is performed on it, the welding carriage is reversing the downward route and
Since the welding is performed in the upward direction, the idle time of the welding carriage is minimized, and the work of rewinding and returning the cable is unnecessary. Therefore, welding is performed with extremely high efficiency.

When considering welding of a large-diameter pipe having a diameter of more than 400 mm, high-speed and high-efficiency plasma welding is possible by the two-electrode distribution welding method as described above, which is extremely useful. In the case of a large diameter pipe having a large thickness, the welding time can be further shortened by providing a third welding carriage and a welding torch inside the pipe as shown below.

In FIG. 3, a welding carriage 4 running in the circumferential direction along the inner peripheral surface of the fixed pipe is provided inside the fixed pipe.
Is rotated once along the locus R5. During this time, the welding carriage 4
Plasma non-keyhole welding is performed to form a backside bead by a welding torch mounted on.

As a result, as shown in FIG. 4, a weld metal portion formed by plasma keyhole welding of the first layer, a weld metal portion formed by plasma non-keyhole welding of the two layers, and a plasma non-key formed by the backside bead formation. A weld metal portion is formed by hole welding.

In the two-electrode distribution welding method shown in FIG. 1,
The backside bead shape is formed by keyhole welding of the first layer, and the welding is completed in that state. Even in the downward welding position where the bead shape can be maintained in high quality, in order to maintain the bead shape in high quality, the welding speed is limited to some extent, and higher speed and higher efficiency are achieved. This becomes a limiting factor for the conversion.

In other words, as in the embodiment shown in FIG.
If the backside wave shape is formed by the third welding carriage, the shape of the backside bead does not need to be a problem in the first build-up by the welding carriages 1 and 2, so the outer peripheral surface of the fixed pipe 3 The two welding carriages 1 and 2 provided in the above can perform higher efficiency welding.

Thus, the problem of the backside bead shape, that is, the problem of unevenness of the bead surface and the dent of the bead itself does not occur, and the speed can be further increased.
In particular, in the case of a large-diameter pipe, since the time zone of the upward welding posture where the backside bead formation is most difficult becomes long, it becomes difficult to obtain a high-quality bead by one-way welding from the outside, but in the present embodiment, Solves this problem and is particularly useful for large diameter pipes.

Further, by installing the welding carriage 4 inside, a good bead like that formed on the front surface can be easily formed on the rear surface of the fixed tube, and further, the welding carriages 1 and 2 for surface use.
It is also effective in shortening the welding time, because the amount of welding that is taken care of by can be reduced.

Next, the total welding time when welding is actually performed by the method of the embodiment of the present invention is shown in Table 1 below in comparison with the conventional example. However, the numerical values in Table 1 represent the required time (%) required for welding in each example when the required time for welding by the conventional single electrode welding method is 100.

[0026]

[Table 1]

As is apparent from Table 1, the embodiment of the present invention significantly improves the welding speed.

[0028]

As described above, according to the present invention, two welding carriages are used, and the two welding carriages are moved in the opposite directions from the upper portion of the fixed pipe while any of the carriages for the first layer welding is used. In this case, since the downward welding is used, the inconvenience of plasma keyhole welding by upward welding is avoided, and the advantage of high efficiency plasma keyhole welding is that the fixed pipeline pipe can be circled at high speed. Plasma welding can be performed in the circumferential direction.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a method according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a weld metal obtained by this method.

FIG. 3 is a diagram illustrating a second embodiment method of the present invention.

FIG. 4 is a cross-sectional view showing a weld metal obtained by this method.

[Explanation of symbols]

 1, 2, 4: Welding trolley 3: Fixed pipe

 ─────────────────────────────────────────────────── ─── Continued Front Page (71) Applicant 591278666 Shinko Plant Construction Co., Ltd. 4-5-22 Iwayakitamachi, Nada-ku, Kobe-shi, Hyogo (72) Inventor Mitsunori Komori 1144-3, Miyazawa-cho, Seya-ku, Yokohama, Kanagawa (72) Inventor Yasushi Yamamoto 19-18 Sakurada-cho, Atsuta-ku, Nagoya-shi, Aichi Toho Gas Co., Ltd., Supply Control Department, Pipeline Technology Center (72) Inventor Shinya Suezawa 4-chome, Hirano-cho, Chuo-ku, Osaka-shi, Osaka 1-2 No. 2 in Osaka Gas Co., Ltd. (72) Inventor Fumito Yoshino 100-1 Urakawachi, Miyamae, Fujisawa-shi, Kanagawa Incorporated company Kobe Steel Works, Fujisawa Works (72) Inventor Noriaki Okubo Iwaya, Nada-ku, Kobe-shi, Hyogo 4-5-22 Kitamachi Shinko Plant Construction Co., Ltd.

Claims (4)

[Claims] 1. A pipeline fixed pipe welding method for abutting pipeline fixed pipes and welding the abutting end faces thereof in the circumferential direction, wherein two welding carriages for moving the outer peripheral surface of the fixed pipe in the circumferential direction are provided. The welding torch is fixed by plasma keyhole welding using the welding torch provided on each welding trolley while moving both trolleys from the upper part to the lower part of the fixed pipe in opposite directions. After reaching the lower part of the pipe, the pipe is folded and welded in two layers toward the upper part, so that the fixed pipe welding method for a pipeline is characterized. 2. The three-layer welding or more welding includes a step of moving the welding carriage from the upper part to the lower part of the fixed pipe, and a step of folding it back at the lower part and moving it from the lower part to the upper part. The pipeline fixed pipe welding method according to claim 1, wherein the method is performed sequentially and repeatedly. 3. The two-layer welding is characterized in that a starting point thereof is a position where a lowermost portion of the fixed tube is removed and an end point thereof is a position where an uppermost portion of the fixed tube is removed. Pipeline fixed pipe welding method described in. 4. One fixed welding carriage is provided inside the fixed pipe, the inner circumference of which is moved in the circumferential direction, and the welding carriage is interlocked with the movement of two welding carriages provided on the outer circumference of the fixed pipe. The pipe according to any one of claims 1 to 3, wherein the inner peripheral surface side portion of the fixed tube is welded by a welding torch provided on the inner peripheral surface of the welding carriage while moving the welding carriage. Line fixed pipe welding method.