JP2003126965A - Welding method for steel pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welding method for a steel pipe enabling the continuous rolling at high efficiency with saving energy by shortening the flash butt welding time of the steel pipe. SOLUTION: In the welding method for a steel pipe which applies the flash butt welding to the rear end of the precedent steel pipe and the tip of the following steel pipe accompanied by the continuous rolling, projection parts (step parts 2, ridge parts 4 and projections 5 or the like) having 0.03-1.5 mm of the projection height are provided in two or more parts, in the circumference direction of the end faces to be welded of the precedent steel pipe and/or the following steel pipe, and the starting points of a spark are dispersed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining steel pipes, and more particularly, to a method for joining steel pipes which enables sufficient joining in a short time when the steel pipes are continuously rolled while being joined one after another.

[0002]

2. Description of the Related Art In order to join a plurality of steel pipes one after another and to continuously roll them, a technique is required which can join the trailing end of the preceding steel pipe and the leading end of the following steel pipe to the extent that they do not break during rolling. It is said that As a technique related to such a joining technique, for example, Japanese Patent Laid-Open No. 60-44108 discloses a method of joining a leading end of a preceding steel pipe and a leading end of a succeeding steel pipe by high frequency induction welding or high frequency resistance welding. However, with these joining methods, equipment cost and running cost (electric power)
Has the drawback of being expensive. Also, for example, Japanese Patent Publication Sho 63
-63282 and the like disclose a method of mechanically connecting the trailing end of the preceding steel pipe and the leading end of the following steel pipe. However, in this joining method, there is a possibility of breakage when high tension is applied by stretch reducer rolling. In addition, JP-A-8-267107 and JP-A-10-5803.
Japanese Patent Laid-Open Publication No. 2003-242242 discloses a flash butt joining method for billets and solid materials and a continuous rolling method using the same. According to this flash butt joining method, it is considered that the equipment cost and the running cost are lower than those of the high frequency induction welding and the high frequency resistance welding, and it is considered that a sufficient joining that does not break even if high tension is applied by the stretch reducer is obtained. .

[0003]

However, when the conventional flash butt joining method is applied to a steel pipe during continuous diameter reduction rolling, it takes too much time to obtain sufficient joining, which not only reduces the rolling efficiency. Since it is a hollow material, it cools faster than the solid material, and the material temperature drops below the start temperature of the reducer rolling during joining, and it was found that extra energy is required for reheating. did.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve this problem and to provide a steel pipe joining method which shortens the flash butt joining time of the steel pipe and enables continuous rolling with high efficiency and energy saving.

[0005]

DISCLOSURE OF THE INVENTION As a result of intensive studies made by the present inventors in order to achieve the above-mentioned object, in the case of flash butt joining, where the end surface of the steel pipe is finished to be smooth as usual, in the case of solid material Unlike, the flash (spark) emitted from one point with an unspecified position in the circumferential direction of the pipe is transmitted in the circumferential direction of the pipe to complete the joining, and this spark circulation time determines the joining time. I found out that
Furthermore, it has been found that it is effective to provide a plurality of protrusions, which are the starting points of sparks, on the joined end surface of the steel pipe in order to reduce the spark circulation time.

That is, the present invention relates to a method for joining steel pipes, wherein the rear end of the preceding steel pipe and the tip of the succeeding steel pipe subjected to continuous rolling are subjected to flash butt joining.
Alternatively, it is a method of joining steel pipes, characterized in that protrusions having a protrusion height of 0.03 to 1.5 mm are provided at two or more locations in the circumferential direction of the end face to be joined of the subsequent steel pipe. Further, it is preferable that the projecting portion is a step portion or a ridge portion that forms a boundary of the inclined portion, or a projecting portion in which a flat portion locally projects. When the protrusion is the protrusion, the total bottom area of the protrusion is preferably 5.0% or less of the cross-sectional area of the steel pipe.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, protrusions are provided at two or more locations in the circumferential direction on the joined end surface of the steel pipe. The protrusion may be provided on either the rear end of the preceding steel pipe, the leading end of the subsequent steel pipe, or both. By providing such protrusions, when performing flash butt joining of the preceding steel pipe and the following steel pipe, the first mutual contact occurs at the locations of the plurality of protrusions almost simultaneously, and the welding current is preferentially concentrated there. , That is the starting point of the spark. In other words, sparks are emitted from multiple points in the circumferential direction that are provided with protrusions, and
If you move less than 1/2 lap, you will reach the spark starting point next to it. Therefore, even if it takes a long time to circulate the sparks,
It will be reduced to 2 or less, and the bonding time can be significantly shortened.

To obtain the effect of shortening the joining time,
The protrusion height of the protrusion should be 0.03 to 1.5 mm. If the height of the protrusion is less than 0.03 mm, there is no significant difference from the normal roughness of the end face, and the place where the protrusion is provided does not become the spark starting point. On the other hand, when the protrusion height exceeds 1.5 mm, the spark is generated at the place where the protrusion is provided, but it is difficult for the spark emitted from the spark to move in the circumferential direction. The definition of the protrusion height is shown in FIGS.

Although the form of the protrusion is not particularly limited, from the viewpoint of ease of processing, the stepped portion which forms the boundary of the inclined portion 3 as shown in FIGS. 1 and 2, for example. 2 (FIG. 1) or ridge 4 (FIG. 2), or
For example, as shown in FIG. 3, it is preferable to form a convex portion 5 formed by locally projecting a flat portion 6. The number of protrusions is not limited to that shown in the figure, and may be two or more. It is preferably 3 or more. Further, it is preferable that the plurality of protrusions are arranged at equal points on the circumference of the circle as much as possible.

The step portion or the ridge portion can be formed by, for example, a method of cutting an end portion of a steel pipe using an end face cutting machine formed by combining a plurality of rotary blades 7 as shown in FIG. The rotary blade 7 in FIG. 4 is arranged with an inclination of about 1 to 2 degrees with respect to a plane orthogonal to the tube axis, and the blade body (eg, circular saw) rotates about its own axis and The heart rotates around the tube axis.

Further, for the convex portion, for example, an end face processing machine having a concave surface 8 as shown in FIG. 5 is used to press the joined end surface of the steel pipe 1 against the concave surface 8 to form the concave portion 9 into the convex portion. Can be formed by a method such as transfer. The cross-sectional shape of the convex portion is not limited to the circular shape shown in FIG. 3, and may be any shape such as an elliptical shape or a polygonal shape. Further, the three-dimensional shape of the convex portion is not limited to the columnar shape shown in FIG. 3, and may be any shape such as a conical shape or a frustum shape.

Further, in the case where the protrusion is the protrusion, when the total bottom area of the protrusion exceeds 5.0% of the cross-sectional area of the steel pipe, the portion where the protrusion is provided is stably dispersed as a spark starting point. The total bottom area of the protrusions is 5.0%.
It is preferable to form the following. More preferably, it is 0.05% or more and 5.0% or less. The definition of the bottom area of each convex portion is shown in FIG.

[0013]

(Example) (Example 1)
After perforating and rolling with a mandrel mill, adjusting the outer diameter with a sizer, and pipe-making to the dimensions (outer diameter and wall thickness) shown in Table 1 before diameter-reducing rolling,
The resulting steel pipe was reheated in a reheating furnace to the cutting temperatures shown in Table 1 and then using an edge cutting machine of the kind illustrated in FIG.
Cutting the rear end of the preceding steel pipe with the number of blades shown in Table 1 shows the steps (the number of steps is 0 when the number of blades is 1 and equal to the number of blades when the number of blades is 2 or more). Note that the steps are formed at approximately equal points on the circumference.) Then, the flash butt welding machine is used to join the subsequent steel pipe tip under the current and voltage conditions shown in Table 1, and then to the burr. After removing the burrs from the joint with a removing device, heat it with an induction heating type temperature compensating device to reach the reduction rolling start temperature shown in Table 1, then descale it with a mechanical descaler, and then use a stretch reducer. Then, continuous rolling was performed to reduce the diameter to a target dimension (outer diameter / thickness) shown in Table 1.

Table 1 shows the required joining time (the time required to obtain sufficient joining by flash butt welding) investigated under each condition of this continuous rolling. As shown here, according to the present invention, a predetermined projection height (step: 0.03
In the example of the present invention in which the protrusions (steps) having a thickness of 1.5 mm) are provided at a plurality of positions in the circumferential direction, the required joining time is significantly shortened as compared with the comparative example which deviates from the scope of the present invention.

[0015]

[Table 1]

(Example 2) A billet of the steel type shown in Table 2 was formed into the dimensions (outer diameter / wall thickness) shown in Table 2 before diametric rolling by adjusting the outer diameter with a sizer after piercing and rolling with a mandrel mill. The obtained steel pipe is reheated in a reheating furnace to the cutting temperature shown in Table 2, and then the end face processing machine of the kind illustrated in FIG. The location of the pipe is set to approximately equal points around the circumference.) After the rear end of the preceding steel pipe is end-face processed to form a columnar protrusion having the dimensions shown in Table 2, it is shown in Table 1 with a running flash butt welding machine. After joining with the subsequent steel pipe tip under current and voltage conditions, and then removing burrs from the joint with a burr remover, heat it with an induction heating type temperature compensator and reach the diameter reduction rolling start temperature shown in Table 2. After descaling with a mechanical descaler, shrink with a stretch reducer Rolled to was continuously rolling finish target dimension shown in Table 2 (the outer diameter and wall thickness).

Table 2 shows the required joining time (the time required to obtain sufficient joining by flash butt welding) investigated under each condition of this continuous rolling. As shown here, according to the present invention, a predetermined projection height (0.03-1.5 m
In the example of the present invention in which the protrusions (projections) having m) were provided at a plurality of positions in the circumferential direction, the required joining time was significantly shortened as compared with the comparative example which deviates from the scope of the present invention. In addition, among the examples of the present invention, a better result was obtained when the total bottom area of the convex portions was within a suitable range (5% or less of the cross-sectional area of the steel pipe).

[0018]

[Table 2]

In the above-mentioned Examples 1 and 2, the case where the present invention is applied to the method for producing a seamless steel pipe by the Mannesmann mandrel mill system has been described, but the present invention is not limited to this and, for example, electric The present invention can be applied to reheated diameter-reducing rolling of welded steel pipe such as a sewn pipe, and further, it can be applied to cold rolling without heating.

[0020]

EFFECTS OF THE INVENTION According to the present invention, the required joining time of flash butt joining, which is advantageously used when joining a plurality of steel pipes for continuous rolling, can be significantly shortened, and high efficiency and energy-saving continuous rolling of steel pipes can be achieved. It has an excellent effect that is possible.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example in which a protrusion is formed by a step portion.

FIG. 2 is an explanatory diagram showing an example in which a protrusion is formed by a ridge.

FIG. 3 is an explanatory diagram showing an example in which a protrusion is a protrusion.

FIG. 4 is an explanatory view illustrating a method for providing a step portion on the end surface of a steel pipe.

FIG. 5 is an explanatory diagram illustrating a method for providing a convex portion on the end surface of a steel pipe.

[Explanation of symbols]

1 steel pipe 2 steps 3 slope 4 ridge 5 convex 6 Flat part 7 rotary blades 8 Recessed surface 9 recess 10 Guide

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hideo Sato             1-1 Kawasaki-cho, Handa-shi, Aichi Made in Kawasaki             Chita Works of Iron Co., Ltd. (72) Inventor Nobuhiko Morioka             1-1 Kawasaki-cho, Handa-shi, Aichi Made in Kawasaki             Chita Works of Iron Co., Ltd.

Claims (3)

[Claims] 1. A method of joining steel pipes, wherein flash trailing joining of a trailing end of a preceding steel pipe and a leading end of a succeeding steel pipe to be subjected to continuous rolling is carried out, wherein a circumferential direction 2 of a joined end face of the preceding steel pipe and / or the following steel pipe. Protrusion height above the point = 0.03 to 1.
A method for joining steel pipes, characterized in that it is provided with a protrusion of 5 mm. 2. The method for joining steel pipes according to claim 1, wherein the protrusion is a step or a ridge that forms a boundary of the inclined portion, or a protrusion formed by locally projecting a flat portion. . 3. The total bottom area of the protrusions is the cross-sectional area of the steel pipe.
It is 5.0% or less, The joining method of the steel pipe of Claim 2 characterized by the above-mentioned.