JP2819778B2 - High frequency ERW pipe welding equipment - Google Patents

Description

The present invention relates to a high-frequency electric resistance welded pipe welding apparatus.

B. Summary of the Invention The present invention relates to a high-frequency ERW pipe welding apparatus for a thick-walled pipe which is formed into a tube having a V-shaped gap, and which connects and welds opposed edges, wherein a heating conductor is provided between the opposed edges. An inductor for preheating the edge is provided in front of the V-seam weld, and this inductor is
By supplying power at a frequency of z or less, it is possible to perform good welding even when welding thick-walled pipes.

C. Prior Art For high frequency electric resistance welded pipe welding, Japanese Patent Application No. 61-45680 (Japanese Patent Application Laid-Open No. 62-203684) and Japanese Patent Application No. 61-55876 (Japanese Patent Application No. 62-176)
No. 085) has been proposed. In the former, the electromagnetic force induced by the high-frequency current is eliminated or reduced at a substantially constant period by applying a high-frequency current periodically, intermittently or intermittently or at an interval of 0.1 msec. On the other hand, in the latter case, a coil for preheating with electric power of a frequency of 20 kHz or less is disposed in front of the V seam welded portion of the tube material.

D. Problems to be Solved by the Invention In general, high frequency ERW pipe welding devices are generally applied to relatively thin ERW pipes. Occurs.

(B) Difficulty in welding thick wall.

(B) The range of welding conditions for good welding is narrow.

(C) In particular, when the material of the pipe is a material containing alloy components such as Cr, Mo, Mn, etc., the allowable range is narrowed because the alloy components are liable to become oxides. The reason will be described.

In the electric resistance welded pipe welding, it is preferable that the edge portion (edge portion) to be heated and joined is heated flat at the same depth from the tip end as shown in FIG. 14B. Then, when the tips are butted and joined by a squeeze roll section (pressing roll section), the heated and melted portions of both tip sections are extruded to the inner and outer peripheral sides to form a sound weld. This is the basic condition for ERW pipe welding.

However, in the case of a thick-walled tube, an increase in the wall thickness t makes it difficult to flatten the ends of both edges as shown in FIG. 14A. In particular, while the temperature of the inner and outer corners rises, the temperature of the central portion does not rise, and the heating portion tends to be a heating portion as shown in FIG. 14A. In this method, high-frequency electric power of 100 to 400 kHz is usually used to efficiently perform heat welding by using the proximity effect of current, and as a result, the edge effect also works strongly and most of the current flows intensively at the corner part That's why.
When the heating portions at both edges are in the state shown in FIG. 14A (hatched portion in the drawing), the molten metal generated at the inner and outer corners is scattered and discharged as spatter by the electromagnetic force, In addition, at the time of butt welding, as shown in FIG. 14C, the molten metal at both corners (shaded portions in the figure) is not completely discharged but remains in the welded portion, so that pinholes or oxides are involved. And the integrity of the weld is lost. This is a first problem in the electric resistance welded welding of a thick pipe.

In ERW pipe welding, a phenomenon as described in detail in JP-A-62-203684 occurs. Then, in order to obtain a healthy weld, it is necessary to control the amount of high-frequency power (weld heat input) supplied to the weld within an appropriate range. The above publication describes a heat input range in which the cycle T is 0 <T ≦ 0.1 seconds. This is true for ERW pipe welding in general, but the thicker the pipe, the more likely it is that high-frequency currents are likely to be concentrated at the corners. The adverse effect of the vibration of the abutment point w becomes remarkable, and the range (width) of the appropriate input condition becomes narrow, and the difficulty in obtaining a sound welded portion increases. This is the second problem.

As described in detail in the "Action" section of JP-A-62-203684, the discharge of the molten metal by the electromagnetic force near the welding point is repeated to generate spatter. In addition, in thick-walled pipes, the inner and outer corners are overheated as described above, and the molten metal generated in this area is discharged and overlapped, causing many spatters. This can lead to eaves on the tube or to rolls. This is the third problem.

Further, since the frequency of the heating power is high as described above, only the end portions of both edges are heated with a steep temperature gradient.
Therefore, after welding, the heat of the welded portion rapidly moves to both sides in the circumferential direction, and the welded portion is rapidly cooled. As a result, the hardness of the weld increases. Then, in order to recover the ductility of the welded portion, annealing by reheating is required, and thus a large amount of electric power is required. This is the fourth problem.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a high-frequency electric resistance welded pipe welding apparatus capable of performing satisfactory welding even in welding a thick-walled pipe.

E. Means for Solving the Problems The present invention is directed to a high-frequency electric resistance welded pipe welding line in which a tube material is formed into a tube having a V-shaped gap and opposing edges of the V-shaped gap are continuously subjected to electric welding. In an electric resistance welded tube welding apparatus provided with an inductor for preheating an opposing edge in front of a V-seam weld, the inductor has an edge heating conductor that is open and disposed between the opposing edges. And W ≧ S / 2 (W: dimension where the outer and inner cores wrap around one edge, S: between opposing edges ), And the edge is preheated by supplying power at a frequency of 50 kHz or less to the inductor.

Further, the present invention is characterized in that a power supply device for preheating and welding is provided, which shares a forward conversion unit and has inversion units each capable of adjusting the output in parallel.

In addition, a pre-heating means is provided for the edge facing the V seam weld, and a post seam heater is disposed in the vicinity of the V seam weld behind the V seam weld, and the residual heat of the weld is provided. The method is characterized in that a post-heat treatment is continuously performed on the welded portion by utilizing the above.

Furthermore, a preheating means for the facing edge portion is provided in front of the V seam welding portion, and the frequency of the welding power supplied to the V seam welding is at most 1.500 k, which is equivalent to approximately three times the conventional value.
It is characterized in that it is raised to around Hz.

F. Action Supply power at a frequency of 50 kHz or less to the inductor,
Preheat both edges of the material to a predetermined temperature below the melting point.
Due to this preheating, both edges have little edge effect and are heated over a wide range in the circumferential direction.

Further, since the power supply devices for preheating and welding are separately adjusted and transmitted, power consumption is reduced.

Further, after the welding is completed, reheating is performed to anneal the material to reduce the hardness of the welded portion and recover the toughness.

In addition, by preheating both edges of the material and increasing the welding power frequency supplied to the V seam weld,
Reduces electromagnetic repulsion at seam welds to improve weld quality.

G. Example Hereinafter, an example of the present invention will be described with reference to the drawings.
First, an embodiment that solves the first problem will be described.

FIG. 1 is a perspective view of the embodiment, in which 1 is a tube material, 2a and 2b are pressure rolls, 4 is a V seam welding point, 5 is a V-shaped gap, and 5a and 5b are both. The edges, 6a and 6b are contacts, and 7 is a power supply, and this portion is a V seam weld.
Opposite edges of tube blank 1 before this V seam weld
An inductor 11 for preheating is provided between 1a and 1b. Electric power is supplied to the inductor 11 from a power supply 19 having a relatively low frequency of, for example, 50 kHz or less to preheat the vicinity of the facing edges 1a and 1b. Inductor 1
Numeral 1 is configured such that a one-turn coil is formed by the outer conductors 12 and 13 and the plate-shaped edge heating conductor 14 disposed between the facing edges 1a and 1b. Reference numerals 15 and 16 denote a pair of terminals for connection to the power supply 19. 17 is an outer core.

2 to 4 show a detailed structure of the inductor 11, FIG. 2 is a plan view, FIG. 3 is a side view, and FIG. 4 is an enlarged cross-sectional view taken along line YY in FIG. It is. 2 to 4, an outer core 17 and an inner core 18 are arranged on the outer and inner sides of the edge heating conductor 14, respectively. Formed by 12a is a cooling water hole provided in the outer conductor 12, cooling water holes are similarly provided in the outer conductor 13 and the edge heating conductor 14, respectively. Cooling water is passed through.

In the inductor 11 configured as described above, the dimensional relationship of each part shown in FIG. 4 is set as follows.

 W ≧ S / 2, where S: distance between opposing edges.

W: The dimension where the outer and inner cores wrap around one edge.

The above as among the magnetic flux generated by an alternating current flowing through the edge heating conductor 14 to set an expression opposite allowed increase the effective magnetic flux phi ₁ for heating the edges 1a, the edge 1a by the intersection with 1b, and 1b The purpose of this is to reduce the ratio of the ineffective magnetic flux φ ₂ to increase the electrical heating efficiency of the edge by the edge heating conductor 14.

Here, means for deriving the equation of W ≧ S / 2 will be described.
This equation is for determining the condition of the magnetic resistance, and is for effectively linking the magnetic flux to the material. Magnetic resistance R
Is proportional to the length (L) of the magnetic flux path and inversely proportional to the cross-sectional area A.

R∝L / A R (valid) = (L / 2 + L / 2) / W = L / W R (invalid) = (L / 2 + t + L / 2) / (SB) / 2 = (2L + 2t) / (S -B) Here, if R (valid) <R (invalid), the above two equations are as follows.

 L / W <(2L + 2t) / (SB) Next, assuming that t << L, the above equation becomes (SB) / 2 <W.

 If S >> B, S / 2 <W.

The inductor 11 is supplied with power having a lower frequency than, for example, 50 kHz from the power supply 19. The lower the power frequency,
Since the edge effect is small and the depth of penetration of the conductive current from the surface is large, the opposite edge portions as shown in FIG.
The heating of 1a and 1b is substantially flat, and a wide range is heated from the end in the circumferential direction. Note that FIG. 4 shows a heated portion.

After preheating both edges to a predetermined temperature below the melting point in this manner, the V-seam weld shown in FIG.
A high frequency power of kHz is supplied to the edges 5a and 5b to
a, 5b is further heated to a temperature above the melting point,
Welding is performed by pressing the edges together at a and 2b.

FIG. 5 shows a temperature rise curve of the edges 5a and 5b at this time. In addition, according to the conventional temperature rise curve without the preheating, the characteristic curve as shown in FIG. 6 (A) indicates that the portions a, b, and a shown in FIG. It is a temperature distribution in c. In FIG. 5,, and also show the temperature distribution of the same parts as above.

When the above-described embodiment is used, the inside and outside corners a of the edges of the material 1 are not overheated, and the edges are heated almost flat over the corners a and the center b, so that the thickness is increased. In welding of a thin tube, a sound weld can be obtained as in the case of welding of a thin tube. This also means
While greatly reducing the difficulty of welding due to the narrowness of the appropriate heat conditions in the welding of the thick-walled pipe and facilitating welding,
This embodiment also solves the second and third problems because the amount of spatters can be greatly reduced.
Further, since a wide range including the portion C in FIG. 6 (B) is heated, rapid cooling of the welded portion is alleviated, and the hardness of the welded portion is reduced. Thereby, annealing after welding can be omitted depending on the material of the pipe. This is also an embodiment for solving the fourth problem.

Next, the power supplies 7, 19 shown in FIG. 1 will be described. Power supply 7,
19 may be independent power supplies, respectively, but as shown in the block diagram in FIG. 15, the forward converter 30 is replaced with an inverse converter 31 (50 kHz or less) for edge preheating and an inverse converter for V seam welding. It is preferable to adopt a configuration provided in common for both the unit 32 (150 to 450 kHz).

FIG. 16 is an example of a specific circuit diagram of the block diagram shown in FIG. 15, and in FIG. 16, 30a is a transformer, 30b is a rectifier circuit, 31a and 32a are electron tubes, 31b and 32b are electron tubes 31a and 32a. A semiconductor switch circuit using a GTO (gate / tan-off thyristor) and the like provided in the grid circuit of FIG. 1, and 31c and 32c are matching transformers.

As described above, the output of the common forward converter 30 is supplied to the reverse converters 31 and 32 for preheating and welding, but the semiconductor switch provided in the grid circuit of the electron tubes 31a and 32a of the reverse converters 31 and 32. The respective oscillation outputs are PWM-controlled by the circuits 31b and 32b and the ON period is adjusted, so that the respective outputs can be controlled independently of each other.

By providing the common forward conversion unit 30 in this manner, the power supply device can be downsized as compared with the case where separate forward conversion units are provided, and the required commercial power can be significantly reduced. Can be. For example, 700kW (30kHz) as the power for edge preheating and 50 as the power for V seam welding
When 0 kW (300 kHz) is required, a configuration in which a forward converter is separately provided consumes approximately 2,400 kVA of commercial power in total, but a configuration in which the forward converter 30 is shared as shown in FIG. By doing so, the consumption of commercial power can be reduced to 1,900 kVA, as indicated by numerical values in the figure.

Next, an embodiment for solving the second and third problems will be described.

As described above, an edge preheating portion provided with an inductor is provided in front of the V seam weld, and the opposite edge is preheated with power of a frequency of 50 kHz or less to heat the tip of the edge substantially flat. By raising the temperature, the second and third problems could be significantly improved.

However, as described above, the second and third problems are described in
This is largely due to the movement phenomenon of the welding point w in the V seam welded portion as described in detail in -203684. Further, in welding a thick-walled pipe, a further effect was obtained by intermittently reducing the welding current at least twice as fast as the moving cycle of the welding point w.

In practice, using the power supply whose circuit diagram is shown in Figure 16,
Oscillation output by the semiconductor switch circuit 32b so that the length of movement of the tube material in the V seam during intermittent or 1/2 periods of the height is 2 mm or less for each transfer speed (line speed) of the tube material 1. A great effect was obtained by selecting the PWM control frequency and performing the PWM control of the welding current. That is, the range of appropriate heat input conditions for obtaining a healthy weld in the welding of a thick-walled pipe is expanded, so that the difficulty of welding is greatly reduced, and the effect of greatly reducing the amount of spatters is obtained.

The PWM control frequency of the welding current may be selected according to the following equation.

 pitch (moving length) = vmm / sec × 1 / 2H <2 v: Conveying speed of tube material (line speed).

 H: PWM chopping frequency of high frequency welding current.

For example, when v = 60 m / min (v = 1000 mm / sec), H = 5
By setting to 00 Hz, pitch = 1000 × 1/2 × 500 = 1 mm When v = 180 m / min (v = 3000 mm / sec), by setting H = 1500 Hz, pitch = 3000 × 1/2 × 1500 = 1 mm Both The pitch (moving length) becomes 2 mm or less at 1 mm.

Next, an embodiment for solving the fourth problem will be described. Conventionally, since the welded portion is rapidly cooled after welding, the hardness increases, and the toughness is not good as it is. Therefore, it is necessary to perform reheating annealing in a subsequent process. FIG. 7 is a block diagram of a conventional welding-reheating annealing apparatus, and FIG. 8 shows a temperature schedule characteristic curve of a welded portion. In FIG. 7, TF is a matching transformer, and PH is a post-seam heater group.

Since the welded portion is heated by welding only at the tip of the opposite edge, the temperature drops rapidly after welding is completed, reheats from 200 ° C with a post-seam heater, performs annealing, and performs welding. It reduces hardness and restores toughness. For this reason, large electric power was required for reheating annealing.

Conventionally, in such a method, even if the post seam heater PH is brought close to immediately after the pressure rolls 2a and 2b in order to utilize the residual heat of the welded portion, cooling after welding is fast, so the desired effect cannot be obtained. Was. There is also difficulty in arranging the devices in order to bring the post seam heater PH immediately after the pressure rolls 2a and 2b. Therefore, even if it is devised and brought close to it, the effect of reducing the power of the post-seam heater PH was hardly obtained.

However, in the present embodiment, since the edge of the material is preheated at a low frequency, the opposing edges 1a and 1b are preheated not only at the tip but also over a wider range, and even at the corners and the center. Become so. The cooling rate of the weld after the completion of welding, including the center, is much slower than in the conventional case without preheating.

Therefore, depending on the material (steel type) of the tube material, annealing may not be required. Also, when reheating after welding is necessary, the post seam heater can be used to
By placing them close to immediately after 2a, 2b
A great effect such as reduction of the electric power of the seam heater can be produced.

FIG. 9 shows an example of a device configuration of the method according to the present embodiment, and FIG. 10 shows a temperature schedule characteristic curve diagram of a welded portion. As can be seen from Fig. 10, the temperature drop of the weld after completion of welding is much slower than before, so in the case of steel using the residual heat of the weld, the steel is kept at a temperature of 850-900 ° C etc. in the austenitic state. After keeping the heat for a predetermined time in the host seam heater PH, it is possible to prevent an increase in hardness and a decrease in toughness of the welded portion by cooling.

Therefore, unlike the conventional heat treatment by reheating after the temperature of the weld has dropped (200 ° C), the post-seam heater replenishes the amount of heat used to prevent the temperature of the weld from lowering by using the residual heat of the weld. Thus, the following effects can be obtained.

(1) As shown in the embodiment of FIGS. 7 and 9, the required power amount of the post-seam heater is 600 × 4 =
It can be greatly reduced from 2,400 kW (Fig. 7) to 700 kW (Fig. 9).

In addition, as shown in the embodiment of FIGS. 7 and 9, including the preheating of the edge portion before the V seam weld, the total power required for welding and post heating is also considered. From the conventional 700 + 2,400 = 3,100 kW (Fig. 7) to 700 +
500 + 700 = 1,900 kW (Fig. 9).

(2) When the material of the pipe is steel, it can be continuously heated by the post-seam heater at the temperature in the austenitic state, so that it can be subjected to constant temperature heat treatment or the like to impart excellent strength and toughness to the welded portion. .

Next, welding was performed with a preheating means for an edge facing the front of the V-seam welded portion, and a frequency of welding power supplied from the power supply to the V-seam welded portion being up to about three times higher than before. An embodiment will be described.

In FIG. 1, the power supplied from the power source 7 to the V-seam welding portion via the contacts 6a and 6b to perform welding at the V-seam welding portion generally has higher gravitational efficiency for welding. Can be increased. However, as described above, the higher the frequency, the stronger the edge effect, and the inner and outer corners of the edge are overheated as shown in FIG. 14 (A), so that flat heating from the end face cannot be obtained.

Further, as the frequency becomes higher, the skin effect becomes stronger, and the current concentrates on the surface portion, so that an effective heating depth from the end face cannot be obtained. From these facts, if the frequency is too high, a good welding result cannot be obtained, so that power having a frequency from 100 kHz to about 450 kHz has been conventionally used.

FIG. 11 illustrates the relationship between the capacity of electric power for welding supplied to the V seam weld and the frequency. In the figure, the curve of --- of the induction type using the induction heating coil,
Further, the curve of --- shows the example of the conventional case in each of the contact type shown in FIG. In both curves, the reason why the frequency is low in the range where the capacity is large is that it is difficult to effectively supply power to the welded portion until the frequency is high from the circuit configuration as the capacity increases. is there.

By the way, as described above, when power of a frequency of 50 kHz or less provided with a preheating means is provided in front of the V seam weld to preheat the opposing edges, the welding to be supplied to the V seam weld is performed. Power frequency can be made much higher than before.

FIG. 12 shows a device configuration example of the present embodiment system, and FIG. 13 shows a temperature schedule characteristic curve diagram of a welded portion. 11 is a preheating means for preheating from a power source 19 via a matching transformer TF. Power is supplied. Reference numeral 7 denotes a power supply for welding, and power of a frequency of 1.100 kHz is supplied to the V seam welded portion via the matching transformer TF.

As shown in FIG. 13, the edge of the tube material is heated to 900 ° C. by the preheating means 11. And since the frequency of the heating power at this time is as low as 50 kHz or less, as described above, the edge is heated almost flat across the corner and the center, and the heating is performed to a deep range from the end face. . And, in the V seam welded portion, welding is performed with additional heating up to the melting temperature, so that even if the frequency of the electric power for welding is increased, the above-mentioned disadvantages are significantly reduced. Also, when the material of the tube material is a steel tube, the edge is already heated to the temperature of the non-magnetic region above the Curie point by preheating, so that even if the frequency of the welding power is increased, the Penetration depth: (However, since the values of p: specific resistance (μΩ-cm) of the tube material, μ: relative magnetic permeability, and f: frequency (Hz)) are larger than those in the magnetic region, the influence of the skin effect is less likely to occur. Therefore, the frequency of the electric power for welding can be made much higher than in the past.

Then, as a result of performing welding by changing the frequency of the welding power in various ways, the frequency is equivalent to about three times or more the frequency of the conventional one.
Even at 500 kHz, better welding results could be obtained than before. The curve shown in FIG. 11 shows an example in which the preheating of the edge is performed in accordance with the method of the present embodiment in comparison with the conventional example. Also, good welding results could be obtained. The reason why the frequency is lowered in the range where the capacitance is large is for the same reason as described above.

By thus increasing the frequency of the electric power for welding, the electric efficiency was increased, and the capacity of the power supply was reduced. When the frequency is increased, the current value can be reduced by increasing the voltage value of the welding power supplied to the V seam welded portion. This means that the value of the welding current flowing through the V seam portion is reduced, so that the electromagnetic repulsion can be reduced. Therefore, the repetition of molten metal discharge and the generation of spatter due to the electromagnetic force near the welding point are reduced, the pulsation of the weld is reduced, the entrapment of oxides and the occurrence of penetrator defects are prevented, and the weld bead is smoothed. There was a great effect in obtaining good welding results such as possible. These facts greatly contribute to solving the third problem and the like.

H. Effects of the Invention As described above, according to the present invention, the following effects can be obtained in welding a thick-walled pipe.

(A) Since the generation of spatter during welding is drastically reduced, the generation of the eaves of the pipe itself is prevented, the quality of the pipe is improved, and damage to the pressure roll and the like and insulation deterioration can be prevented and protected.

(B) The occurrence of defects such as entrapment of oxides and pinholes in the welded portion can be prevented, and the quality of the welded portion can be improved by smoothing the weld bead.

(C) Since the range of allowable welding heat input conditions for sound welding is expanded, difficulties in thick-walled pipe welding are greatly eased, and welding work is facilitated and the defect rate can be reduced.

(D) Since the heating area of the edge (edge) of the material is almost flat and the temperature at the center becomes a sufficient welding temperature, it is necessary to use a pressure roll as in the past to obtain a good weld. No need to pressurize.

(E) It is possible to obtain a weld portion having excellent toughness due to a decrease in hardness of the weld portion, and to reduce damage to a cutting machine when cutting a pipe.

(F) When the pipe is made of steel, the welded portion can be post-heated (post-heat-treated) from the austenitic state, so that it can be given a constant-temperature heat treatment such as aus tempering to impart excellent strength and toughness.

(G) The amount of power required for post-heating (post-heat treatment) of the weld and the total amount of power required including welding can be significantly reduced.

[Brief description of the drawings]

1 is a perspective view showing an embodiment of the present invention, FIGS. 2 to 4 show details of the inductor in the embodiment of FIG. 1, FIG. 2 is a plan view, and FIG. FIG. 4 is an enlarged cross-sectional view taken along line YY of FIG. 3, FIG. 5 is a temperature rise curve of an edge in the embodiment of the present invention, and FIG. FIG. 6 (B) is an explanatory diagram showing a heating and heating distribution at the edge of the material, FIG. 7 is a configuration diagram showing a conventional example when a post heater is combined, and FIG. FIG. 9 is a temperature schedule characteristic curve diagram, FIG. 9 is a configuration diagram showing another embodiment of the present invention when a post heater is combined,
FIG. 10 is a temperature schedule characteristic curve diagram in FIG. 9;
FIG. 11 is a diagram showing the relationship between output power and frequency of the V seam weld,
FIG. 12 is a block diagram showing another embodiment of the present invention, FIG. 13 is a temperature schedule characteristic diagram in FIG. 12, and FIGS.
Is an explanatory diagram showing the state of heating and heating distribution at the edge of the material,
FIG. 15 is a block diagram showing another embodiment of the present invention, and FIG. 16 is a specific circuit diagram of FIG. 11… Inductor, 12,13… Outer conductor, 14… Edge heating conductor, 15,16… Terminal, 17,18… Iron core, 19… Power supply.

Claims (4)

(57) [Claims] 1. A high frequency ERW pipe welding line in which a tube material is formed into a tube having a V-shaped gap and opposing edges of the V-shaped gap are continuously subjected to electric welding. An electric resistance welded tube welding apparatus in which an inductor for preheating an opposing edge is disposed in the foreground, wherein the inductor has an edge heating conductor that is opened and disposed between the opposing edges, and a pipe of the conductor. A magnetic core is provided on the outer and inner peripheral sides of the body, and has a relationship of W ≧ S / 2 (W: dimension where the outer and inner peripheral cores wrap around one edge, S: interval between opposing edges). A high-frequency electric resistance welded tube welding apparatus, characterized in that an electric power having a frequency of 50 kHz or less is supplied to the inductor to preheat the edges. 2. A high-frequency electric resistance welded tube according to claim 1, further comprising a power supply device for preheating and welding, which shares a forward conversion section and has inversion sections each capable of adjusting the output in parallel. Welding equipment. 3. A welding apparatus, comprising: a preheating means for an edge facing the front of the V seam weld; and a post seam heater disposed rearward of the V seam weld and adjacent to the V seam weld. The high-frequency electric resistance welded tube welding device according to claim 1, wherein the post-heat treatment of the welded portion is continuously performed using the residual heat amount. 4. A welding method comprising: providing a preheating means for a facing edge portion in front of a V seam welding portion to supply power at a frequency of 50 kHz or less to preheat the edge portion and to supply welding from a power supply to the V seam welding portion; The power frequency is increased to a high frequency up to about 1.500 kHz.
Or the high frequency electric resistance welded pipe welding device according to 3.