JPH0910932A - Manufacture of welded tube - Google Patents

Abstract

PURPOSE: To stably manufacture a welded tube with extremely few defective welds attributable to scattered spatter and attributable to the residual penetrator by smoothly discharging the oxide on the incompletely welded surface without increasing the scattered spatter amount. CONSTITUTION: Edge parts E, E on each opposite side of an open pipe OP are heated and melted by the high frequency current, and wires 4b, 4c which are a plurality of consumable electrodes to be fed from a consumable electrode gas shielded arc welding machine 4 are fed from the positions opposite to the heated and melted edge parts E, E on each side with the prescribed space therebetween in the longitudinal direction. The arc is ignited between the consumable electrodes 4b, 4c and the edge parts E, E, and the edge parts E, E on each side are butt welded by a squeeze roll 3 while the edge parts E, E are heated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a welded pipe in which a metal strip is bent in the width direction thereof, and the edges of both sides are heated and melted while being abutted and welded together. .

[0002]

2. Description of the Related Art Generally, this type of pipe welding method includes submerged arc welding method, plasma welding method, TIG welding method,
There are high-frequency electric resistance welding methods and the like. Among them, the high-frequency electric resistance welding method is widely adopted as the most efficient process in the pipe welding process.

FIG. 6 is a plan view schematically showing a manufacturing method of a welded pipe by a high frequency electric resistance welding method, in which a metal strip is formed so that edges E on both sides in the width direction face each other. After forming with a roll group (only the seam guide roll 1 at the final stage is shown in FIG. 6) to form an open pipe OP, the open pipe OP is passed through the induction heating coil 2 and a high frequency wave is applied to the edge portions E, E on both sides. An electric current is passed through the squeeze roll 3 while heating and melting this portion, so that the edges E,
The pipes E are asymptotically V-shaped and abutted and welded together to manufacture the pipe P.

In the high-frequency electric resistance welding method, however, there is a problem in that many oxides called penetrators generated by high temperature oxidation of the edge portion remain on the welded surface, resulting in many welding defects. . It is well known that the remaining penetrator not only deteriorates the workability of the welded portion such as pipe expansion and bending but also deteriorates the toughness and corrosion resistance of the welded portion, which poses a practical problem.

The penetrator can be reduced to some extent by selecting proper welding conditions, but it is extremely difficult to eliminate it by the conventional high frequency electric resistance welding method. For this reason, in actual operation, when using a material in which a penetrator is easily generated, a method of shielding the heating part with an inert gas is adopted, but this method also completely prevents welding defects caused by the penetrator. The reality is that it has not arrived.

Therefore, in recent years, as a technique for preventing the occurrence of such a penetrator, both side edge portions of the open pipe are preheated by a high frequency current, and the electrode and both side edge portions are connected to each other by a consumable electrode type gas shield arc welding method of opposite polarity. A method of performing abutting welding while igniting an arc during heating was considered.

[0007]

However, according to this method, the arc generated between the electrode and both side edges is 1
Since there is only one, the range heated by the arc will be very small. As a result, the fluidized portion of the molten steel becomes narrow, and the oxide generated by the high temperature oxidation of the edge portion does not sufficiently float from the inside of the molten pool and remains as a penetrator on the welding surface, forming a welding defect.

By the way, in the above-mentioned conventional method,
It was necessary to make the arc current larger than usual in order to sufficiently discharge the oxides generated on the welding surface, but when a high current arc is ignited, the amount of spatter scattered from the molten pool also increases. A large amount of spatter adhered to the outer surface of the squeeze roll or the pipe and solidified is sandwiched between the squeeze roll and the pipe, and as a result, the outer surface of the pipe is dented or flawed. Also, when a high current arc is used, the welding torch will be severely damaged and it will be necessary to replace the torch enormously.Therefore, every time a situation such as welding of spatter to the squeeze roll or melting of the torch occurs, pipe production It was necessary to interrupt the work to remove spatter and replace the torch, which was a factor of deteriorating the operating rate, yield, and welding torch basic unit.

The present invention has been made in view of the above-mentioned problems of the prior art, and it is possible to smoothly discharge the insufficient oxide on the welded surface without increasing the amount of scattered spatter, and to remove the residual penetrator. It is an object of the present invention to provide a method capable of stably producing a welded pipe having extremely few recessed and flawed defects caused by welding defects and scattered spatter.

[0010]

Generally, in the consumable electrode type arc welding method, the larger the molten pool formed, the better the oxide discharge property, and the smaller the arc that jumps into the molten pool, the more the amount of spatter scattered. Less. Therefore, instead of igniting a high-current arc from one electrode as in the conventional art, a plurality of electrodes arranged in appropriate regions are used to disperse arcs of a relatively large current, which are smaller than the conventional one, into a plurality of arcs. When ignited, the amount of scattered spatter can be minimized, the high-temperature oxide generated at the edge can be discharged smoothly, the residual penetrator is extremely small, and the dent defects due to sputtering are also extremely small. The inventor has found out.

The present invention was made on the basis of the above-mentioned findings, and the edges of opposite sides of an open pipe are heated and melted by a high frequency current and supplied from a consumable electrode type gas shield arc welder. Multiple consumable electrodes,
The heated and melted edge portions are supplied from a position opposed to each other with a predetermined interval in the longitudinal direction, and an arc is ignited between these consumable electrodes and the edge portions to heat the edge portions and squeeze. This is a method for manufacturing a welded pipe, which is characterized in that the edges of both sides are butt-welded with a roll.

[0012]

In the method for producing a welded pipe of the present invention, since the consumable electrode type gas shielded arc welding machine supplies a plurality of consumable electrodes, the molten pool formed can be expanded as compared with the conventional one, and the edge portion The high temperature oxide can be discharged smoothly. In addition, since the heat can be widely supplied to the edge portion by the arc that is ignited between the plurality of consumable electrodes and the edge portion, the arc current can be made smaller than in the conventional case, and the generation of scattered spatter can be suppressed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a welded pipe according to the present invention will be described below with reference to an embodiment shown in FIGS. FIG. 1 is a schematic front view showing a concrete implementation state by the method for manufacturing a welded pipe of the present invention, and FIG. 2 is a schematic plan view of the same.

1 and 2, OP is an open pipe,
P is a pipe, 1 is a seam guide roll, 2 is an induction heating coil, 3 is a squeeze roll, 4 is a consumable electrode type gas shield arc welder, 5 is a control device, 6 is a high frequency power supply, and 7 is a counter. In the open pipe OP, a skelp is applied to a forming roll group (only the seam guide roll 1 at the final stage is shown in FIGS. 1 and 2), and a cross section of a substantially U-shaped cross section in which both edge portions E are opposed to each other. It was formed into a shape.

The open pipe OP, after exiting the seam guide roll 1, is passed through an induction heating coil 2 to heat the edge portions E, E on both sides, while the edge portions E on both sides are moved toward the squeeze roll 3 side. , E end faces are mutually V
The shape is asymptotic, upset by the squeeze roll 3, and butt-welded to each other at the welding point O, and the pipe P
In this state, they are transferred in the direction of the white arrow toward the finishing process.

By the way, the consumable electrode type gas shield arc welding machine 4 is provided with a predetermined wire feeding device and a welding torch 4a connected to a welding power source (not shown). Two wires 4 as consumable electrodes from one reel 4d and 4e
b, 4c are pulled out, and the opposite edge portions E, E of the open pipe OP are abutted and welded by the squeeze roll 3, that is, the edge portions E, E between the welding point O and the induction heating coil 2 and the wire 4b. , 4c, an arc is ignited to melt and supply the wires 4b, 4c.

Further, in the consumable electrode type gas shield arc welding machine 4, the wires 4b, 4 facing the edge portions E, E are provided.
A drive unit 4f for integrally moving and adjusting the position of c in the axial direction of the pipe of the open pipe OP is provided. By operating this drive unit 4f, both rotary shaft centers of the pair of squeeze rolls 3 and 3 are included. 3 from the plane toward the induction heating coil 2
The positions of the wires 4b, 4c with respect to the edge portions E, E can be moved and adjusted in the front-back direction within a range of 0 to 80 mm. Although not shown, the wire 4b is further included.
4c may be adjusted.

The counter 7 measures the high-frequency voltage frequency on the vacuum tube plate side of the high-frequency power source 6 of the induction heating coil 2 at intervals of, for example, 0.5 msec. Calculate the standard deviation. And this standard deviation is, for example, 0.15%
In other words, the distance between the edge end faces on both sides is 0.
A control signal is output to the drive unit 4f to adjust the position of the welding torch 4a so that the ignition is performed within the range of 3 to 1.1 mm. Then, the wires 4b, 4c that are continuously supplied by igniting an arc at this adjusting position are melted, and the molten metal is added to the surface to be welded, and the squeeze roll 3 is used for butt welding to form the welded pipe P. Monitor and control to obtain.

[Test Example] C: 0.07% by weight, S
i: 0.23%, Mn: 1.30%, Nb: 0.066%, T
i: Outer diameter of 50.8 m from steel strip containing 0.046%
An electric resistance welded steel pipe having a thickness of 4.9 mm and a wall thickness of 4.9 mm was manufactured. At the time of production, the consumable electrode type gas shielded arc welder 4 placed between the induction heating coil 2 and the welding point O was used for C: 0.19.
%, Si: 0.23%, Mn: 2.09%, Nb: 0.066
%, Ti: 0.046%, wire with a diameter of 1.2 mm is continuously melted and the molten metal is opened.
Added to the welded surface of OP. The ignition position of the arc was above the open pipe OP, which was separated by 20 to 80 mm in the direction of the induction heating coil 2 from the plane including both rotation axes of the pair of squeeze rolls 3, 3. The wire interval was fixed at 5 mm. The current and voltage of the welding power source in the consumable electrode type gas shield arc welder 4 are 300 and 300, respectively.
A, 30V, purity 99.999 as shield gas
% Ar was used.

An arc ignition position (distance from a plane including both rotation axes of the pair of squeeze rolls 3 and 3) and a photograph taken from above the abutting welding point when the pipe is manufactured under the above welding conditions. The relationship between the edge-to-end face gap measured by the method, the oscillation frequency fluctuation amount of the high-frequency power source 6 measured during pipe manufacturing, and the welding defect length per 1 m of the pipe determined by the flattening test after welding is shown in FIG.

FIG. 3 shows the distance measured from the position corresponding to the center of the squeeze roll 3 on the horizontal axis to the induction heating coil 2 side,
Further, the vertical axis shows the gap between the edge faces [FIG. 3 (a)], the standard deviation of the oscillation frequency fluctuation amount [FIG. 3 (b)], and the welding defect length [FIG. 3 (c)]. Further, in the figure, the measured values when the consumable electrodes (wires) are 1, 2 and 3 are respectively plotted.

When only one consumable electrode is used (□ in FIG. 3)
Mark), the arc firing position is 40 mm or more and 50 mm or less from a plane including both rotation axes of the pair of squeeze rolls 3, 3.
The gap between the edges of the edges is 0.3 mm or more and 0.7 mm or less, and the standard deviation of the oscillation frequency fluctuation amount is kept in each range of around 0.15% to reduce the length of welding defects recognized by the flatness test after welding. The possibilities are already disclosed.

However, when the number of consumable electrodes is set to two (marked with a circle in FIG. 3), the appropriate range in the case of the previous one, that is, the standard deviation of the oscillation frequency fluctuation amount becomes about 0.15%. The range is expanded, and the arc firing position is 35 mm for each.
65mm or less, the gap between the edge faces is 0.3mm
It is understood that the length of the welding defect can be reduced within the range of 1.1 mm or less. When using three consumable electrodes (● in Fig. 3)
The same result as when two lines were obtained was also obtained for the mark).

In FIG. 4, the horizontal axis shows the number of welding defects per 250 mm of pipe determined by the flatness test after welding, and the vertical axis shows the actual defect length of the welding defects. In FIG. 4, the curve indicated by the broken line is the measured value when one consumable electrode is used, the bar graph is the measured value when the consumable electrode is two, and the broken line shown by the solid line is the measured value when the consumable electrode is three. It represents.
When the number of consumable electrodes was 2 and 3, the actual welding defect length could be made shorter than when the number of consumable electrodes was 1. As a result, the welding defect length is reduced as shown in FIG.

In addition, when the distance between the arc firing position and the position corresponding to the center of the squeeze roll 3 is adjusted to 50 mm under the above welding conditions, the number of consumable electrodes is set to 2 and 3. FIG. 5 shows the relationship between the distance between the electrodes and the length of the welding defect per 1 m of the pipe determined by the flatness test after welding. Two consumable electrodes from Fig. 5 (○ in Fig. 5
(Marked) and 3 (marked with ● in FIG. 5), the length of the welding defect recognized by the flatness test after welding when the distance between the electrodes is 3.5 mm or more and 6.0 mm or less. It turns out that the size can be reduced.

[0026]

As described above, according to the method of manufacturing a welded pipe of the present invention, a plurality of consumable electrodes are used and an arc is ignited with a smaller current than in the prior art, so that scattered spatter is generated. It is possible to suppress the occurrence of welding defects caused by the dents and the penetrator caused by the above, and it is possible to manufacture a welded pipe having high toughness and high corrosion resistance, which is an excellent effect.

[Brief description of the drawings]

FIG. 1 is a schematic front view showing a concrete implementation state by the method for manufacturing a welded pipe of the present invention.

FIG. 2 is a schematic plan view of the same.

FIG. 3 is a graph showing test results of the method for manufacturing a welded pipe of the present invention.

FIG. 4 is a graph showing test results of the method for manufacturing a welded pipe of the present invention.

FIG. 5 is a graph showing test results of the method for manufacturing a welded pipe of the present invention.

FIG. 6 is a schematic plan view showing an implementation state of a conventional method.

[Explanation of symbols]

 OP Open pipe P pipe E Edge part 3 Squeeze roll 4 Consumable electrode type gas shield arc welder 4b wire 4c wire 6 High frequency power supply

Claims (1)

[Claims] 1. An edge part on both sides of an open pipe, which is opposed to each other, is heated and melted by a high-frequency current, and a plurality of consumable electrodes supplied from a consumable electrode type gas shield arc welder are heated and melted on both sides. Are supplied from a position facing each other at a predetermined interval in the longitudinal direction, and an arc is ignited between these consumable electrodes and the edge to heat the edge while the squeeze roll is applied to both edges. A method for manufacturing a welded pipe, which comprises subjecting the welded joints to butt welding.