JPH0716750A - Method and equipment for tack welding of large diameter tube to be welded - Google Patents

Abstract

PURPOSE:To provide a means which eliminates the defective welds immediately after starting the welding until the arc is started and reaches the stable normal condition and obtains the excellent bead in the tack welding of a large diameter tube to be welded where the tub plate is mounted on the tube end and welded by the gas shielded metal-arc welding method. CONSTITUTION:In executing the continuous tack welding of a UO-formed tube stock over the whole length of the seam by the gas shielded metal-arc welding method, the tub plate and/or the tube end part on the side where the welding is started are preheated to the temperature >=400 deg.C by the welding heat of a TIG welding machine or the like. In this condition, the tack welding is executed, and the arc start quality of the gas shielded metal-arc welding is improved. Thus, the quality of the tack welding of the large diameter tube to be welded can be improved, and the repair man-hours after the tack welding can be greatly reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tack welding method and apparatus for a UO-molded raw pipe in a method for manufacturing a large diameter welded pipe.

[0002]

2. Description of the Related Art In a method for manufacturing a large-diameter welded pipe, a UO-molded raw pipe is preliminarily welded by seam alignment in advance by tack welding or the like, but recently a tack welding method is used. Has been adopted. There are two tack welding methods: a continuous tack welding method that tacks the entire length of the seam and an intermittent welding method that is performed at an appropriate pitch. Welding used in tack welding. As for the method, both methods are gas shields (CO ₂ , CO ₂ + A).
The metal arc welding method by r. However, the CO ₂ gas shielded arc welding method has poor arc startability, and the bead is discontinuous immediately after the start of welding, that is, from the arc start to the steady state. There is a drawback that the arc stops due to a short circuit between the wire and the molten pool. Further, not only immediately after the start of welding, but also at the end of welding is an unstable portion such as a crater portion at the time of arc stop, and defects are likely to occur.

Therefore, in tack welding of a UO-molded blank pipe, a tab plate is attached to both ends of the pipe, welding is started or finished on this plate, and then only this portion is cut off. ing.

However, unlike conventional CO ₂ gas arc welding, tack welding in the manufacture of large diameter welded pipes is usually performed with a large diameter wire and at a high current and a high speed, as shown in the table below.

[0005]

In tack welding under such severe conditions, even if welding is started on the tab plate from the arc start to the steady state, the tab plate-like stuffing causes the stapling to occur. It may continue up to the main body, which requires maintenance of the welding bead after tack welding, resulting in an increase in man-hours.

On the other hand, as a countermeasure other than the tab plate, there is a method of stabilizing the arc by reducing the welding speed at the start of welding. However, if the welding speed is lowered, the proper range of the electric current also shifts to the lower side, so that it is necessary to control the electric current in conjunction with the welding speed, and the voltage also slightly changes when the electric current changes due to the characteristics of the transformer. For this reason, it is difficult to obtain proper welding conditions according to each welding speed by the method of starting the welding by decreasing the welding speed at the start of welding and then gradually increasing the welding speed. Is a less effective solution.

[0008]

DISCLOSURE OF THE INVENTION The present invention is directed to tacking welding of large diameter welded pipes by attaching a tab plate to the pipe end, and particularly to the occurrence of stapping defects immediately after the start of welding from the arc start to the steady state. The present invention intends to propose a tack welding method and apparatus that can solve the above problems and obtain good beads without defects.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing a large-diameter welded pipe, in which a UO-molded raw pipe is subjected to continuous tack welding over the entire seam length by a gas shielded arc welding method at the welding start side. Is characterized in that the tab plate and / or the pipe end part of No. 1 are pre-heated to a predetermined temperature to perform temporary welding, and the tab plate part on the welding start side is welded by a TIG welder to obtain the welding heat. It is characterized by performing temporary tack welding with the pipe end preheated to a predetermined temperature, and the preheating temperature of the tab plate on the welding start side and / or the pipe end is 400 ° C.
The gist is a tack welding method characterized by the above.

Further, as an apparatus for carrying out the above method, a TIG welding machine for welding the tab plate portion on the welding start side is provided, and the TIG welding machine can be evacuated by an automatic mechanism for temporary attachment gas. A gist is a temporary welding device for a large-diameter welded pipe, which is provided integrally with a shield arc welder.

[0011]

In the present invention, the method of preheating the tab plate and / or the pipe end portion on the welding start side during temporary tack welding of the UO-molded blank pipe is based on the following reasons. In general, the arc phenomenon is a phenomenon in which free electrons move in a space between an electrode (a wire in the case of CO ₂ gas welding) and a base metal, and this free electron is easy to fly when the arc voltage is activated (transition). It will improve the starting ability of the arc. On the other hand, the free electrons are activated as the ambient temperature rises, and their free energy increases. Therefore, in the present invention, in order to improve the arc startability of the gas shielded arc welding, the method of raising the temperature of the groove portion at the time of arc start is adopted in advance.

In the present invention, as a means for increasing the temperature of the groove portion at the time of arc start, a method of preheating the tab plate and / or the pipe end portion on the welding start side is provided.
This improves the arc startability of gas shielded arc welding.

Thus, the arc startability is improved by preheating the tab plate and / or the tube end portion on this side at the start of welding, but this preheating effect differs in its appearance depending on the preheating temperature. FIG. 1 is a diagram showing the relationship between the preheating temperature of the tab plate and the CO ₂ arc start property obtained by the experiment,
If the preheating temperature is 200 ° C or lower, the effect of preheating does not appear at all,
The preheating effect appears from around 300 ° C to over 200 ° C. 4
It can be seen that the preheating effect appears remarkably at 00 ° C or higher. Therefore, in the present invention, the preheating temperature of the tab plate on the welding start side and / or the pipe end is limited to 400 ° C or higher. The upper limit of the preheating temperature is not particularly limited, but as shown in FIG. 1, the preheating effect reaches a saturated state from around 500 ° C., so about 500 to 600 ° C. is appropriate.

FIG. 2 shows an example of changes in arc current at the time of arc start when preheated to a temperature of 400 ° C. or higher and when there is no preheat.
The arc starting current when preheated to the above temperature is (B)
Shows the arc starting current without preheating. As is clear from this data, 4 tabs
It can be seen that the current at the time of arc start is stable when preheated to a temperature of 00 ° C. or higher.

Various methods are conceivable as means for preheating the tab plate and / or the pipe end portion on the welding start side to a temperature of 400 ° C. or more. In the present invention, the arc of TIG welding is used as a heat source for preheating. And That is, in order to obtain the preheating effect, the tab plate or the tube end portion has to be preheated to a high temperature of 400 ° C. or higher as described above. Therefore, in order to easily obtain such a high temperature, the arc heat of TIG welding is used. It is because it is advantageous to use it in terms of efficiency and equipment.

When the tab plate portion on the welding start side is welded by a TIG welding machine, the welding heat preheats the tab plate and the tube end portion of the raw pipe to a high temperature of 400 ° C. or higher, so this high temperature state. Then, temporary welding with the gas shield arc welder will start, and the defect occurrence rate at the pipe end will be greatly reduced, and good beads can be obtained.

The reason why the TIG welding machine for preheating is provided integrally with the gas shielded arc welding machine for temporary attachment is to simplify the system and to save efficiency and labor. The TIG welding machine is provided so as to be retractable because the welding machine is intended only for welding the tab plate portion and the tack welding is performed by the gas shield arc welding machine. Therefore, in the device of the present invention,
When the tab plate portion is welded by the TIG welding machine, the welding machine is evacuated, and then the tack shield welding is started by the gas shield arc welding machine. As a means for retracting the TIG welder, for example, a method of attaching the TIG welder to an arm or the like that operates horizontally or vertically by a fluid pressure cylinder, a motor or the like can be used.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 is a schematic view showing an apparatus configuration example for carrying out the tack welding method for a large diameter welded pipe according to the present invention.
DESCRIPTION OF SYMBOLS 1 is a UO molded tube, 2 is a tab plate, 3 is a gas shield arc welding torch for temporary attachment, 4 is a TIG welding torch for preheating, 5 is a gas shield arc welding torch support, and 6 is T.
IG welding torch support, 7 is a torch slide board, 8 is a gas shield arc welding machine operation board, and 9 is a TIG welding machine operation board.

The torch slide plate 7 can be moved at a predetermined speed in the axial direction of the raw pipe 1 by a drive motor (not shown). The gas shielded arc welding torch 3 for temporary attachment is attached to this slide plate. A support base 5 is attached. The preheating TIG welding torch 4 is attached to one end of a gas shield arc welding torch support 5 so as to be vertically and horizontally movable, and the attachment means is a horizontal cylinder 6-1 on the gas shield arc welding torch support 5. TIG welding torch support base 6 that can be moved forward and backward in the direction perpendicular to the pipe axis.
A slide base 6-3 that moves vertically with a motor 6-2 is attached to the torch clamp arm 6-4 fixed to the slide base, and the preheating TIG welding torch 4 is attached to the torch clamp arm 6-4.
The torch clamp arm 6-4 is lowered when welding the tab plate 2, and when the welding of the tab plate 2 is completed, the torch is raised to a predetermined height and retracted by the horizontal cylinder 6-1. You can do it. Horizontal evacuation cylinder 6-1 and vertical movement motor 6-
The control of No. 2 is performed by the TIG welding machine operation panel 9.

When the temporary welding of the UO-molded raw pipe 1 is performed by the above apparatus, first, the torch slide plate 7 is operated to attach the preheating TIG welding torch 4 to the tab plate 2 on the welding start side.
Position, and the TIG welding machine operation panel 9 is operated to lower the torch by the vertical movement motor 6-2 to a position in contact with the tab plate groove. At this time, the temporary attachment gas shield arc welding torch 3 is located above the tab plate 2. When the tab plate 2 is welded in this state, the welding heat heats the tab plate 2 and the tube end portion of the base pipe 1 to a temperature of 400 ° C. or higher. When the welding of the tab plate is completed, the vertical movement motor 6-2 is controlled again to raise the preheating TIG welding torch 4 to a predetermined height, and the horizontal cylinder 6-1 retracts it to the designated position, and then the gas is removed. The shield arc welder operation panel 8 is operated to start the temporary attachment of the raw pipe 1 with the temporary attachment gas shield arc welding torch 3. At this time, the tube 1
Since the end of the pipe is preheated to a temperature of 400 ° C. or higher by the welding heat of the tab plate, the current at the time of arc start is stable and a good continuous bead can be obtained.

Example 1 With the apparatus shown in FIG. 3, an outer diameter of 609.6 mm and a wall thickness of 1
The tube-end defect occurrence rate when temporary tack welding (continuous tacking) of a large-diameter welded pipe having a length of 2.7 mm, a length of 12 m, and a tab plate of 200 mm was carried out under the conditions shown in Table 1 The results are shown in Table 2 in comparison with the case where the plate is temporarily attached. As is clear from the results of Table 2, in the conventional method, the pipe end defect occurrence rate was 35% when the number of target pipes was 205, whereas in the method of the present invention, the pipe end defects were generated when the target number was 250, which was larger than the conventional method. The rate was remarkably reduced to only 0.5%.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

As described above, according to the present invention, the current at the start of the temporary arc can be stabilized by the preheating effect of the tab plate and / or the tube end portion, so that a continuous good bead can be obtained. As a result, the quality of tack welding of large-diameter welded pipes can be significantly improved, and the number of maintenance steps after tack welding can be greatly reduced. Further, by utilizing the welding heat of the tab plate by the TIG welding machine as the preheating means for the tab plate and / or the pipe end portion, not only the desired preheating temperature can be easily obtained, but also the TIG welding machine is temporarily attached. Since it can be easily attached to a gas shield arc welder,
Simplification of the device and efficiency and labor saving can be achieved. Therefore, the effect brought about in the production of the large diameter welded pipe of the present invention is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a preheating temperature of a tab plate and CO ₂ arc startability in the present invention.

FIG. 2 is a graph showing a change in arc current at the time of arc start when the tab plate is preheated to a temperature of 400 ° C. or higher in the present invention, and (A) shows the tab plate of 400 ° C. or higher. It is a figure which shows the arc starting current at the time of pre-heating to the temperature of FIG.

FIG. 3 is a schematic diagram showing the overall configuration of a device according to an embodiment of the present invention.

[Explanation of symbols]

 1 UO-molded blank tube 2 Tab plate 3 Gas shield arc welding torch for temporary attachment 4 TIG welding torch for preheating 5 Gas shield arc welding torch support 6 TIG welding torch support 7 Torch slide machine 8 Gas shield arc welding machine operation Panel 9 TIG welding machine operation panel

Claims (4)

[Claims] 1. In a method for producing a large diameter welded pipe, when a UO-molded raw pipe is subjected to continuous tack welding over the entire seam length by a gas shield arc welding method, a tab plate and / or a pipe end on the welding start side are formed. A tack welding method for a large diameter welded pipe, characterized in that tack welding is performed in a state where a portion is preheated to a predetermined temperature. 2. In a method for producing a large diameter welded pipe, when performing a temporary tack welding of a UO-molded raw pipe over the entire seam length by a gas shield arc welding method, the tab plate portion on the welding start side is a TIG welding machine. A method for tack welding a large-diameter welded pipe, characterized in that the tack welding is performed in a state where the pipe end is preheated to a predetermined temperature by the welding heat. 3. The temporary welding method for a large-diameter welded pipe according to claim 1, wherein the preheating temperature of the tab plate and / or the pipe end portion on the welding start side is 400 ° C. or higher. 4. A device for performing temporary tack welding of a UO-molded raw pipe with a gas shield arc welder over the entire length of the seam, which is a TIG welder for welding a tab plate portion on the welding start side. A temporary welding apparatus for a large-diameter welded pipe, characterized in that the TIG welding machine is provided integrally with the gas shield arc welding machine so as to be retractable by an automatic mechanism.