JP3233049B2 - Spiral steel pipe manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a spiral steel pipe, and more particularly to a method for manufacturing a spiral steel pipe using only a submerged arc welding method.

[0002]

2. Description of the Related Art Spiral steel pipes are manufactured by spirally winding and forming a steel strip as a raw material while welding and joining the seams thereof. The greatest feature of this spiral steel pipe manufacturing method is that the outer diameter can be determined only by adjusting the entry angle of the steel strip with respect to the pipe mill, and there is no need to replace the tool with a specially shaped tool such as a hole type roll.

[0003] On the other hand, as a welding method for welding and joining seams, a submerged arc welding method capable of large current, deep penetration and high speed welding is generally employed. The mainstream is a two- to three-electrode submerged arc welding method.

As a welding process, an inner surface welding for joining a pipe edge and a steel strip edge near a lowermost point of a pipe bent in a horizontal state is first performed.
Outer surface welding is performed near the uppermost point rotated by 80 °. However, since the welding line is spiral, for molten metal,
A complicated force due to gravity that does not occur in normal horizontal welding is applied.

FIG. 7 and FIG. 8 are diagrams for explaining this fact. FIG. 7 shows the case of inner surface welding, and FIG. 8 shows the case of outer surface welding.

As shown in FIG. 7A, in the case of inner surface welding, uphill welding is performed in the vicinity of a welding point (arc generating point), and the molten metal in the molten pool is hollowed out by the influence of gravity. Flows in the same direction as the rotation direction of the pipe, in other words, in the direction opposite to the welding progress direction. Conversely, downhill welding occurs near the solidification point (end of the molten pool), and the molten metal flows in the same direction as the welding progress direction due to the influence of gravity. As a result, the sectional shape of the weld bead is shown in FIG.
As shown in the figure, the shape becomes an overfilled shape having a concave portion having a depth D in the center.

As shown in FIG. 8 (a), in the case of outer surface welding, downhill welding is performed near the welding point, and the molten metal flows in the direction opposite to the welding progress direction due to the influence of gravity. . Conversely, uphill welding occurs near the solidification point, and the molten metal flows in the same direction as the welding progress direction due to the influence of gravity. As a result, as shown in FIG. 8B, the cross-sectional shape of the weld bead becomes an overfilled shape having a convex portion having a height H at the center.

The above is the effect of uphill welding and downhill welding only in the welding traveling direction. However, in actual welding, uphill welding and downhill welding are performed even in a direction orthogonal to the welding traveling direction. , But very slightly.

[0009] Since a specific phenomenon in the pipe welding of the spiral steel pipe is the effect of gravity due to the spiral shape of the welding line, when the temperature and the amount of the molten metal are the same, the distance between the welding point and the solidification point is increased. The longer the distance, that is, the longer the length of the molten pool, the more noticeable.
8B, and the height H of the convex portion shown in FIG. 8B becomes excessively large, resulting in insufficient thickness of the welded portion and a local increase in the outer diameter, which are problems.

[0010] The length of the molten pool becomes longer as the welding conditions are increased in current, increased in speed, and increased in number of electrodes, which is an obstacle to further increasing the speed of pipe production. ing.

For this reason, various methods have been conventionally proposed for solving the above-mentioned problems due to the increase in the length of the molten pool and achieving an increase in the pipe-making speed. For example, a method in which outer surface welding performed after submerged arc welding of an inner surface is performed in two steps of carbon dioxide gas welding and submerged arc welding (Japanese Patent Laid-Open No. 6-23553), and a method in which inner and outer surfaces are subjected to submerged arc welding after laser penetration welding (Japanese Unexamined Patent Publication (Kokai) No. 4-190989), a method of performing submerged arc welding of inner and outer surfaces after high-frequency resistance welding (Japanese Patent Publication No. 61-254).
62 publication).

[0012]

However, any of the above-mentioned methods has a disadvantage that workability is reduced because the number of welding conditions to be managed increases with the use of different welding means. In addition, even if the welding speed can be increased, there is a disadvantage that it does not lead to an improvement in overall productivity such as an increase in the number of workers engaged in welding.

For this reason, it is possible to obtain a product having a small welding management condition and having a small recess depth D of the inner bead and a small height H of the convex bead of the outer bead even when welding at a high speed without increasing the number of workers. It has been desired to develop a method for manufacturing a spiral steel pipe that can be used.

SUMMARY OF THE INVENTION The present invention has been made in view of the above situation, and has as its object to perform high-speed welding with a welding current as low as possible using only a submerged arc welding method which has been considered impossible in the past. And energy saving can be achieved.
In addition, it is an object of the present invention to provide a method of manufacturing a spiral steel pipe capable of obtaining a product pipe in which the depth D of the concave portion of the inner surface bead and the height H of the convex portion of the outer surface bead are both small.

[0015]

The gist of the present invention resides in the following method (1) to (6) for manufacturing a spiral steel pipe.

(1) A method for manufacturing a spiral steel pipe using a single-electrode submerged arc welding method, wherein the length L of a welding wire protruding from the leading end of a power feeding portion of an electrode is set to 50 mm or more, and welding is performed. Production method.

(2) In a method for manufacturing a spiral steel pipe using a multi-electrode submerged arc welding method, at least one
Length L of the welding wire protruding from the feeder tip of the two electrodes
A method for manufacturing a spiral steel pipe, wherein the welding is performed with the length of the steel pipe set to 50 mm or more.

(3) A method of manufacturing a spiral steel pipe using a single electrode submerged arc welding method, wherein the welding is performed while inserting a non-arc firing wire into a molten pool downstream of the electrode. Manufacturing method.

(4) A method for manufacturing a spiral steel pipe using a multi-electrode submerged arc welding method, wherein welding is performed while inserting a non-arc firing wire only into a molten pool downstream of the final electrode. Manufacturing method of spiral steel pipe.

(5) In a method for manufacturing a spiral steel pipe using a single-electrode submerged arc welding method, a length L of a welding wire protruding from a leading end of a power supply portion of an electrode is set to 50 mm or more, and a molten pool downstream of the electrode. A method for manufacturing a spiral steel pipe, wherein welding is performed while a non-arc firing wire is inserted therein.

(6) In a method for manufacturing a spiral steel pipe using a multi-electrode submerged arc welding method, at least one
Length L of the welding wire protruding from the feeder tip of the two electrodes
And welding while inserting a non-arc firing wire only into the molten pool downstream of the final electrode.

The above (1), (2), (5) and (6)
In the method, the upper limit of the protrusion length of the welding wire is:
There is no particular limitation. However, as will be described later, there is an appropriate upper limit depending on the magnitude of the welding current. Therefore, it is preferable to set the upper limit to a value corresponding to the welding current.

The present inventors have paid attention to the temperature of the molten metal in the submerged arc welding method and have conducted many experiments. As a result, they have found the following, and have accomplished the present invention.

That is, the temperature of the molten metal in the submerged arc welding is selected from the viewpoints of improving the wettability with the base material and preventing the occurrence of welding defects, and promoting the deoxidation and denitrification of the molten metal. It is well known that higher welding yields better welding results. For this reason, the technology development which lowers the temperature of a molten metal is not performed conventionally.

Therefore, the inventors changed the idea, and if the temperature of the molten metal could be reduced without reducing the welding speed, the length of the molten pool could be shortened even if the amount of the molten metal was the same. The inner surface weld bead having the concave portion having the excessive depth D and the outer surface bead having the convex portion having the excessive height H as shown in FIGS. 7B and 8B are not formed. I thought it might be.

As means for lowering the temperature of the molten metal, the length of the welding wire protruding from the feeding point of the copper tip constituting the electrode and the insertion of a non-arc firing wire into the molten pool behind the electrode are considered. As a result of conducting experiments on the two methods, the following was found.

First, the results of a test for increasing the length of the welding wire protruding from the electrode will be described.

The molten metal is divided into a portion where the base material is melted and a portion where the welding wire is melted, and the length of the welding wire protrusion (the feed point (tip end) of the copper tip constituting the electrode and the distance between the surface of the base material). The separation distance which is usually set to 20 to 40 mm) has an effect on a portion where the welding wire is melted.

It is well known that if the welding wire protrusion length, which is usually set to 20 to 40 mm, is further increased, the amount of welding wire increases and the droplet temperature decreases, and the temperature of the molten metal decreases. It is. This is because the welding wire itself is preheated to a higher temperature due to resistance heating as the protruding length of the welding wire is increased, but the droplets slide down from the tip of the welding wire with only a short arc exposure and the arc It is said that this is because the base material falls into the molten metal without being substantially heated by the heat.

FIGS. 1 and 2 show the results of experiments conducted by the present inventors by varying the welding wire protrusion length and welding current under the following conditions. FIG. 1 shows the welding wire protrusion length and the welding current. FIG. 2 shows the relationship between the welding wire protruding length and the crater length of the solidified weld metal measured after removing the slag, in other words, the length of the molten pool.

<< Welding conditions >> Welding method: single electrode submerged arc welding, welding wire: outer diameter 4 mm, welding speed: 50 cm / min.

As can be seen from FIG. 1, when the welding wire protrusion length is increased, the welding wire melting amount is greatly increased at any welding current. Also, as can be seen from FIG. 2, when the welding wire protrusion length is increased, the crater length (the length of the molten pool) is significantly increased with increasing welding wire melting amount at any welding current. .

However, an important point at the time of pipe welding of a spiral steel pipe is whether or not a correlation is established between the above-described melting amount of the welding wire and the crater length. That is,
In the case of pipe welding of a spiral steel pipe, if the welding speed is constant, the welding wire melting amount required to fill the groove and the butt gap must be constant. Therefore, the problem is how the crater length at the same welding wire melting amount changes when the welding wire protrusion length is increased, but such a relationship has not been considered so far. Was.

Then, the present inventors arranged the experimental results of FIGS. 1 and 2 above based on the welding wire melting amount and the crater length, and found that the relationship shown in FIG. 3 was obtained.

That is, as is apparent from FIG. 3, when the welding wire protrusion length is the conventional 30 mm, the welding wire melting amount when the welding current is, for example, 1400 A is about 210 g.
/ Min, the crater length is as long as about 140 mm.

On the other hand, in order to obtain the same welding wire melting amount of about 210 g / min as in the prior art, if the welding wire protrusion length is 70, 110 and 150 mm, the necessary welding currents are about 1100 A, 900 A and 800 A, respectively. Energy saving, and the crater length is about 1 each.
It has been found that the weld bead becomes as short as 15, 105, and 100 mm, and a small weld bead having a depth D and a height H is formed.
And it was confirmed that the protrusion length of the welding wire was required to be 50 mm or more.

Next, the insertion of a non-arc firing wire into the molten pool behind the electrode (after the final electrode in the case of multiple electrodes) will be described.

The non-arc firing wire insertion method into the molten pool is a well-known technique applied when it is necessary to increase the amount of molten metal, such as a multi-pass welding method in a groove. However, when this non-arc firing wire insertion method was applied to submerged arc welding of spiral steel pipes, it was unknown whether it was effective in lowering the temperature of the molten metal, in other words, reducing the length of the molten pool. .

In order to apply the non-arc ignition wire insertion method to the submerged arc welding of a spiral steel pipe, the present inventors have applied a non-arc ignition wire having an outer diameter of 1.6 mm to a welding wire under the following conditions. The experiment was carried out by inserting at an elevation angle of 30 ° at a rear position separated by 20 mm from the position, and changing the insertion amount and the welding current variously.

<< Welding conditions >> Welding method: single electrode submerged arc welding, welding wire: outer diameter 4 mm, welding wire protrusion length: 30 mm, welding speed: 50 cm / min.

FIG. 4 is a diagram showing the results of the experiment, in which the horizontal axis indicates the non-arc firing wire insertion amount and the vertical axis indicates the crater length.

As is apparent from FIG. 4, when the non-arc firing wire is inserted into the weld pool at a position behind the welding wire, any welding current consumes heat to melt the wire. The crater length (the length of the molten pool) decreases due to the decrease in the temperature of the molten metal, and as a result, the depth D
And that a weld bead with a small height H was formed.

Further, although illustration of data is omitted, it has been confirmed that the insertion position of the non-arc firing wire in the case of multi-electrode welding needs to be behind the final electrode. This is because when inserted at other positions, the non-arc firing wire is easily melted by the arc of the welding wire, the temperature of the molten metal hardly decreases, and the effect of reducing the length of the molten pool is lost. is there.

There is a limit to the insertion amount of the non-arc firing wire, and if the insertion amount is shown in the unmelted wire area in the figure, the tip of the wire hits the bottom of the molten pool and welding becomes unstable. Therefore, it is important to set the insertion amount to a value smaller than the unmelted wire area shown in the figure.

[0045]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the method of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 5 is a schematic view showing an embodiment of the present invention. In the drawing, reference numeral 1 denotes a material to be welded, 2 denotes a torch for supplying a welding wire 3, 4 denotes an AC power source, 5 denotes a flux, and 6 denotes a flux. An arc, 7 is a weld pool, and 8 is a non-arc firing wire.

In the welding of a spiral steel pipe to which the present invention is applied, the torch 2 is fixedly arranged, and the material 1 to be welded is moved in the direction indicated by the white arrow.

First, the first and second aspects of the present invention will be described.

The torch 2 used in the first and second inventions comprises a copper nozzle body 2a in which a power supply portion 2a 'having an inner diameter slightly larger than the outer diameter of the welding wire 3 is formed at an intermediate portion. It has a guide member 2b made of an insulating and heat-resistant material such as ceramics and having a through-hole whose inner diameter is substantially the same as that of the power supply section 2a '.

When the torch 2 is constructed as described above, the protrusion length L of the welding wire 2, that is, the distance from the tip of the power supply portion 2a 'formed on the conductive nozzle body 2a to the surface of the material 1 to be welded. When the separation distance is increased to 50 mm or more, even when the winding habit of the welding wire 2 is severe, the welding wire 2 can be supplied as straight as possible.

Of course, a torch which does not have the above-mentioned guide member 2b at the tip but has only a conventional copper nozzle body having a feeder 2a 'formed at the tip is used, and the height of the torch is increased. Needless to say, a desired protrusion length L may be ensured.

When welding is performed with the protrusion length L of the welding wire 3 set to 50 mm or more as described above, the temperature of the molten metal decreases and the length of the molten pool decreases. As a result, as described above, at the time of inner surface welding, the flow of the molten metal to the central portion in the longitudinal direction of the molten pool is suppressed, and a weld bead having a small depth D (see FIG. 7) is formed. Further, at the time of outer surface welding, the flow of the molten metal to both ends in the longitudinal direction of the molten pool is suppressed, and a weld bead having a small height H (see FIG. 8) is formed.

The above effect is obtained by arranging two or more torches 2 in the welding direction, that is, at the time of so-called multi-electrode welding, at least one of the torch protrusion length L.
Is set to 50 mm or more. This is clear from the results of the examples described later.

However, if the welding current is too high with respect to the protrusion length L of the welding wire, the amount of the molten metal becomes too large and the height of the entire weld bead becomes excessive. vice versa,
If the welding current is too low with respect to the protrusion length L of the welding wire, the amount of the molten metal is insufficient and undercut occurs. On the other hand, if the protruding length L of the welding wire is too long while the welding current is increased, the temperature of the welding wire due to resistance heating increases, and the welding wire is melted before reaching the arc point, making welding impossible.

Therefore, the protrusion length L of the welding wire is
It is important to set an appropriate value according to the welding current.

Next, the third and fourth aspects of the present invention will be described.

In the third and fourth aspects of the present invention, the non-arc firing wire is placed in the molten pool 7 downstream of the torch 2 with the protrusion length L of the welding wire 2 set to 40 mm or less as in the prior art. 8 is supplied. For this reason, it is not necessary to use the torch 2 shown in FIG. 5 as the torch, and it is sufficient to use a conventional torch having a power supply portion formed at the tip.

According to the third and fourth aspects of the invention, the heat of the molten metal in the molten pool 7 is consumed in melting the inserted non-arc firing wire 8 to lower the temperature, and the length of the molten pool is reduced. Becomes shorter. As a result, the protrusion length L of the welding wire 3 is set to 50
Similarly to the case where the thickness is set to be equal to or more than mm, at the time of inner surface welding, the flow of the molten metal to the center in the longitudinal direction of the molten pool is suppressed, and a weld bead having a small depth D (see FIG. 7) is formed. Further, at the time of outer surface welding, the flow of the molten metal to both ends in the longitudinal direction of the molten pool is suppressed, and a weld bead having a small height H (see FIG. 8) is formed.

However, in the case of so-called multi-electrode welding in which two or more torches 2 are arranged in the direction of progress of welding, a non-arc firing wire is inserted and supplied only into the molten pool downstream of the final torch. There is a need to. This is because, as described above, when the non-arc firing wire is inserted and supplied to a portion other than in the molten pool downstream of the final torch, the non-arc firing wire is easily melted by the arc of the welding wire, and the temperature of the molten metal increases. Is hardly reduced.

Preferably, the non-arc firing wire 8 has an outer diameter of about 0.3 to 0.8 times the outer diameter of the welding wire 3. The insertion position is preferably a position where the distance l from the welding wire 3 is about 15 to 30 mm, and the insertion angle θ is preferably about 20 to 40 °.

The reason is that if the outer diameter of the non-arc firing wire 8 is less than 0.3 times the outer diameter of the welding wire 3, it is necessary to feed the non-arc firing wire 8 at a high speed and the molten pool 7 slightly fluctuates, the phenomenon that the tip of the non-arc firing wire 8 abuts against the bottom of the molten pool 7 easily occurs. Conversely, if it exceeds 0.8 times, the non-arc firing wire 8 This is because the high rigidity causes an increase in the size of the feeding device and deteriorates workability.

The distance l between the insertion positions is 15 m.
m, the non-arc firing wire 8 becomes the welding wire 3
When the temperature exceeds 30 mm, the solidification of the molten pool 7 has already progressed and the molten metal required to melt the non-arc firing wire 8 is reduced. This is because the amount is insufficient and the effect of lowering the temperature of the molten metal is reduced.

Further, if the insertion angle θ is less than 20 °, the feeding of the non-arc firing wire 8 is unstable because the slag generated and formed on the upper surface of the molten pool 7 is hindered from progressing. This is because if it exceeds 40 °, on the other hand, the contact length between the non-arc firing wire 8 and the molten metal is shortened, and the melting efficiency is reduced.

The first and third inventions and the second and fourth inventions can be implemented in combination, and these are the fifth and sixth inventions according to the present invention. Among these inventions, in the sixth invention in which multi-electrode welding is performed, the insertion and supply position of the non-arc firing wire 8 needs to be only in the molten pool 7 downstream of the final electrode. This is because, as described above, even if the non-arc firing wire 8 is inserted and supplied into a weld pool other than the weld pool 7 downstream of the final electrode, a desired effect cannot be obtained. According to the fifth and sixth aspects, more remarkable effects can be obtained.

[0065]

EXAMPLES In order to manufacture a spiral steel pipe having an outer diameter of 508 mm and a wall thickness of 19 mm, pipe welding was performed under various conditions shown in Table 1.

At this time, the butted shape of both edges of the steel strip had the shape and dimensions shown in FIG. Further, a welding wire having an outer diameter of 4.0 mm was used. In addition, a non-arc firing wire having an outer diameter of 1.6 mm is used, and in the case of single electrode welding, behind the final electrode in the case of multi-electrode welding and at an insertion angle of 30 ° at a position of 20 mm behind the final electrode. Feed inserted into.

Then, while observing the presence or absence of erosion of the welding wire and the welding stability during pipe welding, observing the weld bead after pipe welding, measuring the occurrence of undercut and measuring the shape and dimensions of the weld bead. In the case of inner surface welding, the case where the depth D shown in FIG. 7 (b) is 2 mm or less is preferable, and the case where the depth H is more than 2 mm occurs, and in the case of outer surface welding, the height H shown in FIG. Was evaluated as good, and a case of more than 5 mm was evaluated as occurrence of a convex bead. These results are also shown in Table 1.

[0068]

[Table 1]

As can be seen from the results shown in Table 1, No. 1
Nos. 1 to 15 are the cases of single electrode inner surface welding, and the conventional example (No. 1, No. 1) in which the protrusion length of the welding wire is as short as 40 mm or less.
In 2), a concave bead having a depth D exceeding 2 mm occurred in each case. In addition, in the conventional examples (Nos. 8 to 12) in which the welding current was reduced in order to shorten the length of the molten pool, the amount of molten metal was insufficient in each case, and the groove could be completely filled. No undercut occurred.

On the other hand, in the case of the present invention in which the protruding length of the welding wire was set to 50 mm or more (Nos. 3 to 7 and N
o. 13 to 15), except for No. 15, were good with no concave bead having a depth D exceeding 2 mm.
However, in No. 13, since the welding current was too large with respect to the protruding length of the welding wire, the extra height of the entire weld bead was excessive. In No. 14, the welding current was too low with respect to the length of the protrusion of the welding wire, and the amount of the molten metal was insufficient to cause undercut. Further, in No. 15, both the protrusion length of the welding wire and the welding current were too large, so that the welding wire melted before reaching the arc point and could not be welded.

Nos. 16 and 17 show the case of single electrode outer surface welding. In the conventional example (No. 16) in which the protrusion length of the welding wire was 30 mm, a convex bead having a height H exceeding 5 mm occurred.

On the other hand, in the example of the present invention (No. 17) in which the protruding length of the welding wire was set to 150 mm, the convex bead having the height H exceeding 5 mm was not generated and was good.

No. 18 to No. 21 show the case of two-electrode inner surface welding. In the conventional example (No. 18) in which the protrusion length of the welding wire is set to 30 mm for both electrodes (torch), the depth D is 2 mm. Concave beads were generated.

On the other hand, in the case of the present invention (No. 19 to No. 19) in which the protruding length of the welding wire of one or both electrodes was set to 50 mm or more, and the welding current was appropriately set according to the protruding length. 21) In either case,
A concave bead having a depth D exceeding 2 mm was not generated and was good.

Nos. 22 to 25 show the case of two-electrode outer surface welding. In the conventional example (No. 22) in which the protrusion length of the welding wire was set to 30 mm for both electrodes (torch), the height H was 5 mm. Of convex beads.

On the other hand, in the present invention example (No. 23 to No. 23) in which the protruding length of the welding wire of one or both electrodes was set to 50 mm or more, and the welding current was appropriately set according to the protruding length. 25) In either case,
A convex bead having a height H exceeding 5 mm was not generated and was good.

Nos. 26 to 29 show the case of three-electrode outer surface welding. In the conventional example (No. 26) in which the protrusion length of the welding wire was set to 30 mm for all three electrodes (torch), the height H was 5 mm. Of convex beads.

On the other hand, the length of the protrusion of the welding wire of one or two of the electrodes was set to 50 mm or more, and the welding current was appropriately set according to the length of the protrusion (No. 27). -29) In either case,
A convex bead having a height H exceeding 5 mm was not generated and was good.

The above are the results of the first and second inventions according to the present invention and the results of the prior art. If the welding speed is the same, the conventional method cannot obtain a good result, so that the welding speed is reduced. In contrast to the necessity, the method of the present invention does not require it, and it is clear that high-speed pipe production is possible.

Nos. 30 to 35 are cases where the third and fourth inventions and the fifth and sixth inventions according to the present invention are applied. Except for No. 31 which was too much, good results were obtained in all cases. That is, the welding conditions except the effect of the second invention and the non-arc firing wire insertion supply into the molten pool are the same.
No. 1 and No. 30 welding results, and No. 22 and No. 3 welding results
This is apparent from the welding result of No. 3. The effect of the third invention is clear from the results of Nos. 32, 34 and 35.

[0081]

According to the method of the present invention, since the length of the molten pool is shortened, the size of the concavo-convex portion formed at the center in the width direction is as small as possible or has no concavo-convex portion. Spiral steel pipe having a normal weld bead without excessive or excessive overall welding can be welded at high speed. Further, since the required welding current can be reduced, energy saving can be achieved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a welding wire protrusion length and a welding wire melting amount.

FIG. 2 is a diagram showing a relationship between a welding wire protrusion length and a crater length.

FIG. 3 is a diagram showing a relationship between a welding wire melting amount and a crater length.

FIG. 4 is a diagram showing a relationship between a non-arc firing wire insertion amount and a crater length.

FIG. 5 is a schematic view showing an example of an embodiment of the method of the present invention.

FIG. 6 is a view showing a groove shape and dimensions of a material to be welded used in Examples.

7A and 7B show a welding state in the inner surface welding of the spiral steel pipe, wherein FIG. 7A is a view for explaining the flow state of the molten metal, and FIG. 7B is a view showing the shape of the obtained weld bead. .

8A and 8B show a welding state in the outer surface welding of the spiral steel pipe; FIG. 8A is a view for explaining a flow state of a molten metal; and FIG. 8B is a view showing a shape of a weld bead obtained. .

[Explanation of symbols]

 1: Material to be welded, 2: Torch, 2a: Nozzle body, 2b: Guide member, 2a ': Power supply part, 3: Welding wire, 4: AC power, 5: Flux, 6: Arc, 7: Weld pool, 8 : Arc-fired wire.

Continuation of the front page (56) References JP-A-4-284975 (JP, A) JP-A-4-143075 (JP, A) JP-A-9-295138 (JP, A) JP-A-54-155166 (JP) , A) JP-A-60-118386 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 9/032 B21C 37/12 B23K 9/12 B23K 9/18

Claims (6)

(57) [Claims] 1. A method of manufacturing a spiral steel pipe using a single electrode submerged arc welding method, wherein welding is performed by setting a length L of a welding wire protruding from an end of a power feeding portion of an electrode to 50 mm or more. Method. 2. A method of manufacturing a spiral steel pipe using a multi-electrode submerged arc welding method, wherein a length L of a welding wire protruding from a leading end of a power supply portion of at least one electrode is set to 50.
mm. 3. A method for manufacturing a spiral steel pipe using a single electrode submerged arc welding method, wherein the welding is performed while a non-arc firing wire is inserted into a molten pool downstream of the electrode. Production method. 4. A method of manufacturing a spiral steel pipe using a multi-electrode submerged arc welding method, wherein the welding is performed while inserting a non-arc firing wire only into a molten pool downstream of a final electrode. Manufacturing method of steel pipe. 5. A method for manufacturing a spiral steel pipe using a single-electrode submerged arc welding method, wherein a length L of a welding wire protruding from a leading end of a power feeding portion of an electrode is set to 50 mm or more, and a length of a welding pool downstream of the electrode is reduced. A method for manufacturing a spiral steel pipe, wherein welding is performed while a non-arc firing wire is inserted into a pipe. 6. A method of manufacturing a spiral steel pipe using a multi-electrode submerged arc welding method, wherein a length L of a welding wire protruding from a leading end of a power supply portion of at least one electrode is set to 50.
mm or more, and welding while inserting a non-arc firing wire only into the molten pool downstream of the final electrode.