JPH06198452A - Welding method for spiral steel pipe - Google Patents

Abstract

PURPOSE:To reduce formation of a recessed part of a bead and to increase the welding speed by cooling a preceding weld zone between outside submerged arc welding and inside submerged arc welding after edges of a strip steel sheet are subjected to electric welding. CONSTITUTION:This method is the welding of the spiral steel pipe F where the edges of the strip steel sheet A are welded in the order of electric resistance welding C, outside submerged arc welding D and inside arc welding E. A cooling water spray 1 is arranged between outside submerged are welding D and inside submerged arc welding E to cool the part of an outside submerged arc weld bead J and the base metal temperature at the time of inside welding is lowered. The flow of molten steel by inclined welding is reduced by cooling the weld zone formed by preceding submerged arc welding, by which the depth of the recessed part H formed at the center of the bead G is reduced. Consequently, the bead shape can be improved without decreasing the welding speed and the welding speed can be increased. In addition, since the recessed part H of the bead becomes smaller, the time and labor of correction of the surface state can be saved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of the bead shape of inner surface latent arc welding in manufacturing spiral steel pipe by compound welding.

[0002]

2. Description of the Related Art Japanese Patent Publication No. 3-28259 discloses a method for manufacturing a spiral steel pipe, which is a combination of electric resistance welding, outer surface arc welding, and inner surface arc welding combined in that order. A welding method is disclosed. Spiral steel pipes manufactured using this composite welding method are fast welded by electrical resistance welding, and the welded surface of the incomplete joints on the front and back surfaces generated by electrical resistance welding is welded by latent arc welding to ensure reliable welding of the seam. By combining the above and the above, a dramatic increase in speed was achieved compared to the conventional manufacturing method using only submerged arc welding.

[0003]

However, in such a high-speed welding, in the case of submerged arc welding, particularly in the subarc welding of the inner surface, the bead portion for forming the inclined state during welding of the spirally formed steel sheet. A deep recess is formed by the molten steel flow of

4 to 6 show a process of forming a deep concave portion by this gradient welding.

In FIG. 4 showing a conventional welding mode of a spiral steel pipe, the coil-side strip steel A is immediately joined by electric resistance welding C immediately after being formed by a forming stand B, and then the outer surface and the inner surface thereof are sequentially hidden. The spiral steel pipe F is manufactured by welding by arc welding D and E. In these latent arc welds D and E, in the latent arc weld E of the inner surface joint, as shown in FIG.
The molten steel forming the bead G causes a flow of molten metal by the rotation of, and as a result, as shown in FIG. 6 showing the cross section, a large concave depression H is formed at the center of the cross section of the bead G. When the inner surface is coated after the manufacture, the dent H needs to be reworked because the paint is less likely to adhere to it. In order to prevent the generation of the depression H, it is necessary to slow down the rotation speed of the spiral steel pipe to regulate the welding speed, and for that purpose, there is a problem that the manufacturing efficiency must be reduced.

It is an object of the present invention to provide a means for reducing the formation of bead depressions in latent arc welding when manufacturing spiral steel pipes.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a method for welding a spiral steel pipe in which the edges of a strip-shaped steel sheet are welded in the order of electric resistance welding, outer surface arc welding, and inner surface arc welding in the order of outer surface arc welding and inner surface welding. It is characterized in that the preceding weld portion is cooled with respect to the latent arc welding.

When cooling the preceding welded portion, it is practical to employ means for cooling the welded portion from the outer surface of the pipe with water after the outer surface arc welding.

[0009]

The depth of the recess formed at the center of the bead is reduced by cooling the weld formed by the preceding latent arc welding and reducing the molten steel flow of the inclined welding.

[0010]

FIG. 1 shows an embodiment of the present invention. As in the prior art, immediately after the coil side strip A is formed by the forming stand B, it is once joined by electric resistance welding C, and then the outer surface and the inner surface are joined. Are sequentially welded by latent arc welding D and E to manufacture a spiral steel pipe F.

A water-cooled spray 1 is arranged between the preceding outer surface arc welding D and the subsequent inner surface arc welding E to cool the portion of the outer surface arc welding bead J, and the mother for the inner surface welding. Lower the material temperature. As a result, the flow of molten metal in the conventional bead G portion as shown in FIG. 5 is reduced.

FIG. 2 shows the relationship between the base material temperature T and the length L of the pool formed at the bead portion by the inner surface welding.

As shown in the figure, the base material temperature T and the bead pool length L are in a substantially linear relationship, and the bead pool length L decreases in proportion to the decrease in the base material temperature T. Therefore, the depth of the concave portion shown in FIG. 6 formed in the bead is reduced accordingly.

FIG. 3 shows a typical shape of the bead portion when the outer surface is water-cooled as shown in FIG. To the depth of the recess of the bead G by conventional welding when the temperature immediately before the inner surface welding is 700 ° C without water cooling the outer surface, after the outer surface is subjected to the latent arc welding, the bead portion of the surface is cooled from the outer surface to form the inner surface. The depth in the case of this embodiment in which the temperature of the spiral steel pipe F immediately before welding was lowered to 550 ° C. and the inner surface welding was performed, the depth was reduced to almost half, and the shape of the recess was as shown in FIG. Was loose.

As a result, almost no deep recess was formed in the weld seam on the inner surface of the manufactured spiral steel pipe, and there was almost no effect on the inner surface coating.

[0016]

The present invention has the following effects.

(1) The bead shape can be improved without reducing the welding speed, and the welding speed can be increased.

(2) Since the concave portion of the bead is small, it is possible to save the trouble of modifying the surface condition of the product.

(3) High-speed welding can be performed by using a general-purpose flux instead of a highly viscous flux that does not easily flow molten metal.

[Brief description of drawings]

1 illustrates an embodiment of the present invention.

FIG. 2 shows a relationship between a base metal temperature and a length of a pool formed in a bead portion by inner surface welding.

FIG. 3 shows a typical shape of the bead portion when the outer surface is water-cooled.

FIG. 4 shows a welding mode of a conventional spiral steel pipe.

FIG. 5 shows a state of molten metal flow of molten steel due to rotation of a spiral steel pipe.

FIG. 6 shows a cross-sectional shape of a welding bead according to a conventional method.

[Explanation of symbols]

 1 water-cooled spray 2 bead formed by the welding method of the present invention A coil side strip steel B forming stand C resistance welding D, E latent arc welding F spiral steel pipe G bead H recess J outer surface arc welding bead

Claims (1)

[Claims] 1. A method for welding a spiral steel pipe in which an edge of a strip-shaped steel plate is welded in the order of electric resistance welding, outer surface latent arc welding, and inner surface latent arc welding in advance. Welding method for spiral steel pipes that cools the weld.