JPH0615447A - Manufacture of welded tube - Google Patents

Abstract

PURPOSE:To attain high toughness and high corrosion resistance and to suppress the formation of welded defect such as penetrator by reforming dealloying component layer formed on a welded surface. CONSTITUTION:At the position apart from a plane included with both rotating axial centers of one pair of squeeze rolls 3, 3 by 30-70mm at the upstream side, i.e., the side of an induction heating coil 2, an arc is ignited between a wire 4b continuously supplied from a consumable electrode type gas sealed arc welder 4 and both side edge parts E, E of an open pipe OP. The oscillating frequency of a high frequency power source 6 is measured by a counter 7, and this measured data are read in a controller 5. For example, a driving part 4d for adjusting the position of the wire 4b is operated so that the standard deviation in the fluctuation of this oscillating frequency becomes 0.15% so as to ignite the arc between the edge parts E, E of the part where the gap between the edge end surfaces and the wire 4b is set in the range of 0.3-0.7mm and the wire 4b.

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 in which a metal strip-shaped material is curved in the width direction thereof and is abutted and welded while the edges on both sides are heated and melted.

[0002]

2. Description of the Related Art Generally, there are submerged arc welding method, plasma welding method, TIG welding method, high frequency electric resistance welding method, etc. in this type of pipe welding method. Widely adopted as the most efficient process in the process.

FIG. 4 is a schematic diagram showing a manufacturing method of a welded pipe by the high frequency electric resistance welding method. A group of forming rolls ( Only the seam guide roll is shown in the figure), and after forming it into an open pipe OP, this open pipe
A high-frequency current is passed through the induction heating coil 2 to both side edge portions to heat and melt this portion, and the squeeze roll 3 makes the both side edge portions E, E asymptotically close to a V shape.
The pipe P is manufactured by butt welding.

A problem with such a high-frequency electric resistance welding method is that there are many welding defects caused by the fact that an oxide called a penetrator, which is generated by high temperature oxidation of the edge portion, remains between the welding surfaces. It is known that the remaining penetrator deteriorates the workability of the welded portion such as pipe expansion and bending, and also deteriorates the toughness and corrosion resistance of the welded portion, which is 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 electric resistance welding method. For this reason, in actual operation, when using a material that easily causes a penetrator, a method of shielding the heating part with an inert gas is adopted, but even this method has not yet completely prevented the defect of the penetrator. .

As a conventional technique for preventing the occurrence of such a penetrator, for example, there is a technique disclosed in Japanese Patent Laid-Open No. 56-168981. According to this method, the edge portion is heated to a melting temperature or a temperature in the vicinity thereof by the first heating means using a high frequency current, and then the edge portion is heated to a temperature equal to or higher than the melting temperature by the second heating means to perform abutting welding. Is. Japanese Patent Publication No. 51-33512 discloses a method of butt welding by combining electric resistance welding and plasma welding.

However, in these conventional methods, the fusion welding method is used only as a means for heating and melting the welded portion, and is therefore referred to as a ferrite band between the welding surfaces, as in general electric resistance welding. A dealloying component layer with a thickness of several hundred μm is generated, and it is difficult to make the toughness and corrosion resistance of the welded part equivalent to the base metal.

As a countermeasure against this, both edges of the open pipe disclosed in Japanese Patent Laid-Open No. 63-220977 are heated by a high frequency electric current, and a gap between the electrode and both edges is consumed by a consumable electrode type gas shield arc welding method of opposite polarity. There is a method of performing butt welding while igniting an arc that is buried in.

[0009]

However, in this conventional method, the gap between the edge faces directly below the position where the arc is ignited is an important factor that determines the welding quality. Estimate the gap between the edge faces directly below the arc during welding from the gap between the edge faces of the weld, or take the photograph from above the weld during actual welding to find the proper position and set the arc position in the longitudinal direction of the pipe. However, in the actual manufacturing process, the V-shape of the edge part to be electric resistance welded varies depending on the pipe outer diameter, wall thickness, material, welding speed, etc.
It is necessary to check the proper position, not only lowering the operation rate and yield, but also not being able to follow the shape change caused by a slight change in the coil width, material plate thickness, etc. there were.

For example, when the gap between the edge faces directly under the arc is narrower than an appropriate value, it is difficult to prevent penetration of the penetrator, and it is difficult to modify the dealloying component layer peculiar to the electric resistance welded portion. The heated and melted edge end surface promotes the extrusion of molten metal to the inside and outside surfaces of the open pipe, resulting in a significant decrease in the upset force during butt welding, and insufficient discharge of oxides generated on the end surface due to heating. It becomes difficult to secure the welding quality.

The present inventor has conducted experiments and researches to accurately detect the gap between the edge faces directly under the arc ignition, and as a result, found that the gap between the edge faces is closely related to the fluctuation amount of the high frequency oscillation frequency. did.

Generally, the load impedance is a factor of fluctuation in the oscillation frequency of the high frequency power source used for manufacturing welded pipes. The load impedance is roughly classified into a load in the oscillation circuit and a load in the high frequency current path flowing in the welded pipe. Here, since the load in the oscillation circuit is constant, it is considered that the cause of the oscillation frequency fluctuation is on the welded pipe side. However, if the size of the welded pipe to be welded is constant, the oscillation frequency does not fluctuate because the high-frequency current path is basically constant.

However, the oscillation frequency actually fluctuates due to the following causes. That is, in the consumable electrode type arc welding method, the wire molten metal melted by the arc is supplied to between the end faces of the edges to temporarily short-circuit both edges, so that the high frequency current flowing originally through the abutting welding point O flows. The path is shortened and the impedance is reduced. Therefore, the oscillation frequency increases.

Therefore, the present inventor has paid attention to this short circuit and, as a result of research, has obtained the following knowledge. Directly below the arc position,
That is, when the gap between the edge and end faces at the position where the molten metal is added is wide, the molten metal wire is not added to the position to be welded and reaches the inner surface of the open pipe OP, so a short circuit between edges does not occur, and oscillation frequency fluctuations caused by changes in the high frequency current path occur. The quantity is small. On the contrary, when the gap between the edge faces is narrow, that is, when the gap is close to the abutting welding point O, the amount of change in the current path is small even if this short circuit occurs, and thus the amount of oscillation frequency fluctuation is also small.

By monitoring the variation frequency and variation amount of the oscillation frequency of the high frequency power source used for welding in this way, it is possible to know whether or not the arc is ignited at the proper position. The present invention has been made based on such knowledge, and monitors the arc ignition position during pipe manufacturing by the amount of fluctuation of the oscillation frequency of the high frequency power source, and based on this result, moves the arc welding electrode appropriately. It is an object of the present invention to provide a method for manufacturing a welded pipe which can stably obtain the defect generation preventing effect and the dealloying component layer modifying effect by setting the position to the position.

[0016]

In the method for manufacturing a welded pipe according to the present invention, the edge portions on both sides of the open pipe facing each other are heated and melted by a high frequency current, and the edge portions on both sides are opposed to the edge portions. In a method for manufacturing a welded pipe in which the edges on both sides are butt-welded with a squeeze roll while igniting an arc with a consumable electrode supplied from a consumable electrode type gas shielded arc welder, a high frequency wave that emits the high frequency current It is characterized in that the fluctuation amount of the oscillation frequency of the power supply is detected, and the position of the consumable electrode with respect to the edge portion is monitored and changed based on the detection result.

[0017]

According to the present invention, the position of the consumable electrode which should be ignited with the edge of the open pipe is monitored and changed based on the fluctuation amount of the oscillation frequency of the high frequency power source. Can be recognized easily and accurately. Since the arc ignition position is controlled based on this value, a large dealloying component layer reforming effect and a welding defect generation preventing effect can be obtained.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings showing the embodiments thereof. FIG. 1 is a schematic side view showing an implementation state of a method for manufacturing a welded pipe according to the present invention (hereinafter referred to as a method of the present invention), and FIG. 2 is a schematic plan view of the same.
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 controller, 6
Is a high frequency power supply, and 7 is a counter. For open pipe OP, skelp is applied to the forming roll group (only the seam guide roll 1 at the final stage is shown), and both side edges E, E
Is bent from a U-shaped section to a substantially O-shaped section facing each other.

After the seam guide roll 1 exits the open pipe OP, it is passed through an induction heating coil 2 to heat both side edge portions E, E, and both side edge end faces E, E are mutually moved toward the squeeze roll 3 side. Are asymptotically V-shaped, upset by the squeeze roll 3, butt-welded to each other at the welding point O, and transferred to the finishing process in the arrow direction toward the finishing process. .

The consumable electrode type gas shielded 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), and the reel 4c is consumed through the welding torch 4a. The wire 4b serving as the electrode is pulled out, and the opposite edge portions E, E of the open pipe OP are abutting welded by the squeeze roll 3, that is, the edge portions E, E between the welding point O and the induction heating coil 2.
An arc is ignited between the wire and the wire 4b to melt and supply the arc.

Further, the consumable electrode type gas shield arc welding machine 4 is provided with a drive unit 4d for moving and adjusting the position of the wire 4b opposed to the edge portions E, E in the pipe axis direction of the open pipe OP. By operating the drive unit 4d toward the side of the induction heating coil 2 from the plane including both rotation axes of the pair of squeeze rolls 3, 3 within a range of, for example, 30 mm to 70 mm,
Desirably, the position of the wire 4b with respect to the edge portions E, E is moved and adjusted in the forward and backward directions within a range of 40 to 50 mm.

The counter 7 measures the high frequency voltage frequency of the high frequency power source 6 of the induction heating coil 2 on the side of the vacuum tube plate, for example, every 0.5 msec. The control device 5 reads this measurement data and obtains the frequency fluctuation amount and its standard deviation.
Then, a control signal is output to the drive unit 4d so that the standard deviation becomes, for example, 0.15%, in other words, the ignition is performed within the gap between the edge surfaces on both sides of 0.3 to 0.7 mm, and the position of the welding torch 4a is changed. It is designed to make adjustments.
Then, the arc is ignited at this adjusting position to melt the continuously supplied wire 4b, and the molten metal is added to the surface to be welded, and the squeeze roll 3 is used for abutting welding to monitor to obtain a welded pipe P. And control.

By adopting such a monitoring method, insufficient addition of the molten metal to the surface to be welded due to the gap between the edge faces directly below the arc ignition is too narrow, that is, the effect of preventing penetration of the penetrator is insufficient, On the contrary, it is too wide to promote the extruding 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 surely avoid the occurrence of cracks due to the decrease in the upsetting force.

(Test Example) C: 0.07%, Si: 0.23%, Mn:
ERW steel pipe with an outer diameter of 50.8 mm and a wall thickness of 4.9 mm was manufactured from a strip steel containing 1.30%, Nb: 0.066%, Ti: 0.046%. At the time of manufacture, C: 0.19%, Si: 0.23%, Mn: 2.09%, Nb: 0.066% with a consumable electrode type gas shield arc welder 4 placed between the induction heating coil 2 and the abutting welding point O. ,
A 1.2 mm diameter wire containing Ti: 0.046% was continuously melted, and the molten metal was added to the welded surface of the open pipe OP. The ignition position of the arc is the induction heating coil 2 from a plane including both rotation axes of the pair of squeeze rolls 3 and 3.
It was above the open pipe 30 to 70 mm apart in the direction of. The current and voltage of the welding power source in the consumable electrode type gas shield arc welder 4 were 300 A and 30 V, respectively, and 99.999% pure Ar was used as the shield gas.

Arc firing position (distance from the plane including both rotation axes of the pair of squeeze rolls 3 and 3) when the pipe was produced under the above welding conditions, and a photograph was taken from above the abutting weld point. Fig. 3 shows 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.

In FIG. 3, the horizontal axis indicates the distance mm measured from the position corresponding to the center of the squeeze roll to the induction heating coil 2 side, and the vertical axis indicates the edge end face gap mm [FIG. 3 (a)], the oscillation frequency fluctuation amount. Standard deviation% [Fig. 3 (b)], welding defect length mm /
m [Fig. 3 (c)].

The arc firing position is 40 mm or more and 50 mm or less from the plane including both rotation axes of the pair of squeeze rolls 3, 3.
By maintaining the gap between the edge faces of 0.3 mm or more and 0.7 mm or less and the standard deviation of the oscillation frequency fluctuation amount in each range of around 0.15%, the length of the welding defect recognized by the flatness test after welding can be significantly reduced. I understand.

Further, as is clear from FIGS. 3 (b) and 3 (c), there is a close correlation between the standard deviation of the oscillation frequency fluctuation amount and the welding defect length. It is understood that by monitoring the standard deviation, the proper ignition position of the arc that reduces the welding defect length can be determined.

The present embodiment shown in FIG. 3 uses the standard deviation of the oscillation frequency fluctuation amount as the monitoring parameter. However, in the case of many frequency measurement data processing methods, that is, when the gap between the edge faces is narrow, the oscillation frequency Similar results can be obtained by monitoring with a parameter considering that the fluctuation frequency of the oscillation frequency decreases when the fluctuation amount is small or wide. Further, the same effect can be obtained when the contact tip is directly energized instead of the induction heating coil.
The optimum arc firing position, in other words, the optimum value of the gap between the end faces of the edges may be appropriately determined according to the pipe manufacturing specification conditions.

[0030]

As described above, according to the method of the present invention, the appropriateness of the arc ignition position can be accurately grasped during the pipe manufacturing, and the stable arc ignition can be performed at the optimum position. It is possible to suppress the occurrence of welding defects such as, moreover, it is also possible to modify the dealloying component layer, it is possible to manufacture a welded pipe having high toughness, high corrosion resistance, etc. The present invention has excellent effects is there.

[Brief description of drawings]

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

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

FIG. 3 is a graph showing the 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 part 1 Seam guide roll 2 Induction heating coil 3 Squeeze roll 4 Consumable electrode type gas shield arc welder 4a Welding torch 4b Wire 4c Reel 4d Motor 5 Control device 6 High frequency power supply 7 Counter

Claims (1)

[Claims] 1. An open pipe is provided with a consumable electrode supplied from a consumable electrode type gas shielded arc welding machine, which is heated and melted at opposite side edges by a high-frequency current, and the opposite side edge portions are opposed to each other. In a method of manufacturing a welded pipe in which both edges are butt-welded with a squeeze roll while igniting an arc between, the oscillation frequency fluctuation amount of the high frequency power source that emits the high frequency current is detected, and based on this detection result A method for manufacturing a welded pipe, wherein the position of the consumable electrode with respect to the edge portion is monitored and changed.