JP2666647B2 - Manufacturing method of welded pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a welded pipe by bending a metal strip in its width direction and performing abutment welding while heating and melting both edges.

[0002]

2. Description of the Related Art Generally, there are submerged arc welding, plasma welding, TIG welding, high-frequency electric resistance welding, etc., of this type of pipe welding. It is widely adopted as the most efficient process among the processes.

FIG. 4 is a schematic view showing a method of manufacturing a welded pipe by a high-frequency electric resistance welding method. A metal roll is formed by forming a metal strip so that both side edges E, E in the width direction face each other. (Only the seam guide roll is shown in the figure) to form an open pipe OP, and then pass the open pipe OP through the induction heating coil 2 to pass high-frequency current to both side edges, thereby heating and melting this portion while squeezing. The pipes P are manufactured by assembling the side edge portions E, E with each other by the roll 3 into a V-shape, and performing abutment welding.

A problem with such a high-frequency electric resistance welding method is that there are many welding defects which occur when oxides generated by high-temperature oxidation of an edge called a penetrator remain on a welding surface. It is known that the residual penetrator 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 is a practical problem.

[0005] The penetrator can be reduced to some extent by selecting appropriate welding conditions, but it is extremely difficult to eliminate it by the conventional ERW method. For this reason, in the actual operation, when a material that easily generates a penetrator is used, a method of shielding the heating part with an inert gas is adopted, but even this method has not yet completely prevented the penetrator defect. .

As a conventional technique for preventing the occurrence of such a penetrator, there is a technique disclosed in Japanese Patent Application Laid-Open No. 56-168981, for example. In this method, the edge is heated to a melting temperature or a temperature close to the melting temperature by a first heating means using a high-frequency current, and then the edge is heated to a temperature equal to or higher than the melting temperature by a second heating means to perform an impact welding. It is.

However, in this conventional method,
Since the fusion welding method is simply used as a means to heat and melt the weld, a dealloyed component layer called a ferrite band with a thickness of several hundred μm is formed on the weld surface, similar to general ERW. In addition, it is difficult to make the toughness and corrosion resistance of the welded parts equal to those of the base metal.

As a countermeasure, both edges of the open pipe disclosed in Japanese Patent Application Laid-Open No. 63-220977 are heated by a high-frequency current, and a consumable electrode type gas shielded arc welding method of opposite polarity is used to form a gap between the electrode and both side edges. There is a method of performing abutment welding while igniting a buried arc.

[0009]

However, in this conventional method, the gap between the edge end faces immediately below the position where the arc is ignited is an important factor that affects the welding quality. Estimate the gap between the edge end faces immediately below the arc at the time of welding from the gap between the edge end faces, or take a picture from the upper part of the weld during the actual welding to determine the appropriate position and set the arc position in the pipe longitudinal direction However, in the actual manufacturing process, the V-shape of the edge portion to be ERW welded due to various disturbances varies depending on the pipe outer diameter, wall thickness, material, welding speed, etc. It is necessary to confirm the proper position, not only lowering the operation rate and yield, but also not being able to follow the shape change caused by the slight fluctuation of the coil width and material thickness. There is a problem that is not.

For example, if the gap between the edge end faces immediately below the arc is smaller than an appropriate value, it becomes difficult to prevent the occurrence of a penetrator, and it becomes difficult to modify the dealloying component layer peculiar to the ERW weld. Heating and melting of the edge end surface promotes the extrusion of the molten metal to the inside and outside of the open pipe, causing a significant decrease in upset force at the time of abutment welding and insufficient discharge of oxides generated on the end surface by heating As a result, it becomes difficult to secure welding quality.

The present inventor conducted experiments and studies to accurately detect the gap between the edge end faces immediately below the arc firing, and found that the gap between the edge end faces is closely related to the arc voltage or the arc current. did.

In general, in the consumable electrode type arc welding method, when the arc length is short, when a droplet of the wire melted by the arc separates from the wire, an instantaneous short circuit occurs between the wire and the welded portion. It is necessary to keep the arc length short in order to stably add the molten metal to the welded part, and it is difficult to avoid such a short-circuit occurrence phenomenon, and the number of short-circuits in normal arc welding reduces the arc length Increase according to. The number of short-circuits also greatly depends on the surface to be welded immediately below the arc firing position, that is, the gap between the edge end surfaces. For example, if the gap between the edge end surfaces immediately below the arc is wide, the arc is buried between the edge portions E and E of the open pipe edge OP. The number of contacts, that is, the number of short circuits, increases.

On the other hand, when the gap between the edge end surfaces E, E immediately below the arc is narrow, or when the arc is ignited after the butt welding, the repulsive force of the high-frequency current flowing through the opposing edge end surfaces E, E causes the outer surface of the open pipe OP to be closed. The molten metal is extruded irregularly, the arc length fluctuates greatly, the arc becomes unstable, and the arc current and arc voltage fluctuate.

Therefore, by monitoring the arc current or the arc voltage that changes depending on the number of short circuits and the arc length, it is possible to know whether or not the arc is being fired at an appropriate position.

The present invention has been made based on the above findings, and is based on the distance from the squeeze roll and the arc voltage.
More adjusting the supply position of the consumable electrode Te aims to defect prevention effect and de-alloy component layers modifying effect obtained stably.

[0016]

According to a method of manufacturing a welded pipe according to the present invention, opposite edges of an open pipe are heated and melted by a high-frequency current, and the edges are opposed to the edges. In a method for manufacturing a welded pipe in which both edges are butt-welded with a squeeze roll while igniting an arc between consumable electrodes supplied from a consumable electrode type gas shielded arc welding machine, the rotating shaft of the squeeze roll The supply position of the consumable electrode with respect to the edge portion is adjusted so that the variation of the arc voltage of the ignited arc is 6 V or less within a range of 40 to 50 mm from the center.

[0017]

In the present invention, the supply position of the consumable electrode to be ignited between the open pipe and the edge of the open pipe is set within the range of 40 to 50 mm from the rotation axis of the squeeze roll. By adjusting the variation of the value to be 6 V or less, it is possible to accurately set the position of the consumable electrode, and to obtain a large dealloying component layer reforming effect and a welding defect generation preventing effect.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the state of implementation. FIG. 1 is a schematic side view showing an embodiment of a method for manufacturing an electric resistance welded tube according to the present invention (hereinafter referred to as the method of the present invention), and FIG. 2 is a schematic plan view thereof.
OP indicates an open pipe, P indicates a pipe, 1 indicates a seam guide roll, 2 indicates an induction heating coil, 3 indicates a squeeze roll, 4 indicates a consumable electrode type gas shielded arc welder, and 5 indicates a control device. Open pipe OP forms skelp rolls
(Only the last seam guide roll 1 is shown), both side edge portions E, E are bent from a U-shaped cross section to a substantially O-shaped cross section facing each other.

After leaving the seam guide roll 1, the open pipe OP is passed through an induction heating coil 2 to heat both side edges E, E, and to move toward both sides of the squeeze roll 3 so that both end surfaces E, E are mutually opposed. The pipe is gradually asymptotically shaped into a V shape, is upset by a squeeze roll 3, is abutted and welded to each other at a welding point O, and is transferred in a direction of an arrow toward a finishing process in a pipe P state. .

The consumable electrode type gas shielded arc welding machine 4 includes a predetermined wire feeder and a welding torch 4a connected to a welding power source (not shown), and is consumable from the reel 4c through the welding torch 4a. The wire 4b, which is an electrode, is drawn out, and the opposing edges E, E of the open pipe OP are joined by a squeeze roll 3 at a point of welding, that is, the edges E, E between the welding point O and the induction heating coil 2.
An arc is ignited between the wire and the wire 4b, and the melt is supplied while being melted.

The consumable electrode type gas shielded arc welding machine 4 is provided with a drive unit 4d for moving and adjusting the position of the wire 4b facing the edges E, E in the direction of the pipe axis of the open pipe OP. By operating the driving unit 4d, a range from 30 mm to 70 mm, preferably from 40 to 50 mm, from a plane including both rotation axes of the pair of squeeze rolls 3 toward the induction heating coil 2 side. Wire for edges E, E
The position of 4b is adjusted to move forward and backward.

The control device 5 reads an arc current or an arc voltage from the consumable electrode type gas shielded arc welding machine 4, and
For example, in the case of arc voltage, the variation is 6
V or less, in other words, a control signal is output to the drive unit 4c so as to cause ignition within a range of 0.3 to 0.7 mm between the end faces on both side edges to adjust the position of the welding torch 4a. ing.

In the method of the present invention,
The consumable electrode type gas shielded arc welding machine 4 has its wire 4b
The wire 4b is sequentially melted by igniting an arc between the edge of the open pipe OP and the edges E, E of the open pipe OP, and abutting welding is performed while adding the molten metal to the edges E, E, which are the surfaces to be welded. It will be.

During this time, the control device 5 detects the arc current or the amount of fluctuation of the arc voltage, which changes when the droplet melted by the arc is short-circuited to the edges E, E of the open pipe OP. In other words, at a point where the voltage becomes 6 V or less, in other words, at a point where the gap between the end faces on both sides is in the range of 0.3 to 0.7 mm, the continuously supplied wire 4b is melted and the molten metal is welded to the surface to be welded. Is monitored and controlled in order to obtain a welded pipe P by performing abutment welding with the squeeze roll 3 while adding the steel.

The arc voltage fluctuation (V) to 6V or less, to the other words in the range edge end face gap (mm) of the 0.3 ～0.7Mm if the length weld defects caused by penetrator like above which is Exceeds the allowable range.

By adopting such a monitoring method, insufficient addition of the molten metal to the surface to be welded due to too small a gap between the edge end surfaces immediately below the arc firing, that is, insufficient penetrator prevention effect, Or, conversely, it is too wide to promote the extrusion of the molten metal to the inner and outer surfaces of the open pipe due to overheating of the edge portion, and it is possible to reliably avoid the occurrence of cracks due to a decrease in upset force.

(Test Example) C: 0.07%, Si: 0.23%, Mn:
An electric resistance welded steel pipe having an outer diameter of 50.8 mm and a wall thickness of 4.9 mm was manufactured from a steel strip containing 1.30%, Nb: 0.066%, and Ti: 0.046%. At the time of manufacture, the consumable electrode type gas shielded arc welding machine 4 arranged between the induction heating coil 2 and the abutment welding point O is C: 0.19%, Si: 0.23%, Mn: 2.09%, Nb: 0.066%. ,
A wire having a diameter of 1.2 mm containing Ti: 0.046% was continuously melted, and the molten metal was added to the surface to be welded of the open pipe OP. The ignition position of the arc is determined from the plane including the rotation axes of the pair of squeeze rolls 3 and 3 by the induction heating coil 2.
Above the open pipe separated by 30 mm to 70 mm in the direction of.

The current and voltage of the welding power source in the consumable electrode type gas shielded arc welding machine 4 were 300 A and 30 V, respectively.
Ar having a purity of 99.99% was used as a shielding gas.

An arc firing position (distance from a plane including both rotation axes of the pair of squeeze rolls 3 and 3) when the pipe is manufactured under the above welding conditions, and a photograph taken from above the abutting welding point. FIG. 3 shows the relationship between the gap between the edge end faces measured by the above method, the variation of the arc voltage measured during pipe production, and the weld defect length per 1 m of the pipe determined by the flattening test after welding.

In FIG. 3, the horizontal axis indicates the distance mm measured from the position corresponding to the center of the squeeze roll toward the induction heating coil 2, the vertical axis indicates the edge end surface gap mm [FIG. V [Fig. 3 (b)], welding defect length mm / m [Fig.
(C)].

The arc firing position is set at 40 mm or more and 50 mm or less from a plane including both rotation axes of the pair of squeeze rolls 3 and 3.
By maintaining the gap between the edge end faces in the range of 0.3 mm or more and 0.7 mm or less and the arc voltage fluctuation (V) in the range of 6 V or less, the length of welding defects recognized in the flattening test after welding can be significantly reduced. I understand.

As apparent from FIGS. 3 (b) and 3 (c), there is a close correlation between the arc voltage fluctuation and the welding defect length. Thus, it can be understood that the appropriate firing position of the arc for reducing the length of the welding defect can be determined.

Although the present embodiment shown in FIG. 3 uses an arc voltage as a monitoring parameter, a similar result can be obtained by monitoring with an arc current.

[0034]

As described above, according to the method of the present invention, the supply position of the consumable electrode during pipe production is within the range of 40 to 50 mm from the rotation center of the squeeze roll, and the fluctuation of the arc voltage . By adjusting the amount to be 6 V or less, stable arc ignition at an optimum position becomes possible, the occurrence of welding defects such as a penetrator can be suppressed, and the dealloying component layer can be reformed. The present invention has excellent effects such as the ability to manufacture a welded pipe having toughness and high corrosion resistance.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing an embodiment of the method of the present invention.

FIG. 2 is a schematic plan view showing an embodiment of the method of the present invention.

FIG. 3 is a graph showing test results of the method of the present invention.

FIG. 4 is a schematic plan view showing an implementation state of a conventional method.

[Explanation of symbols]

 OP Open pipe P pipe E Edge 1 Seam guide roll 2 Induction heating coil 3 Squeeze roll 4 Consumable electrode type gas shielded arc welding machine 4a Welding torch 4b Wire 4c Reel 4d Motor 5 Control device

Claims (1)

(57) [Claims] 1. An opposite end of an open pipe is heated and melted by a high-frequency current by means of a high-frequency current, and the opposite end and a consumable electrode supplied from a consumable electrode type gas shielded arc welding machine facing the edge are connected to each other. In a method for manufacturing a welded pipe in which both edges are butt-welded with a squeeze roll while igniting an arc, the arc is ignited within a range of 40 to 50 mm from the rotation axis of the squeeze roll. A method for manufacturing a welded pipe, comprising: adjusting a supply position of the consumable electrode with respect to the edge so that a variation amount of an arc voltage of the arc is equal to or less than 6V.