JPH09239536A - Magnetic stirring welding method of steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the welding speed in the seam welding of a steel tube in a UOE process by surrounding a tip part of a terminal electrodes among multiple electrodes with a coil, energizing the coil to form the magnetic field, and giving the magnetic stirring to the molten metal to achieve the welding. SOLUTION: The AC current is applied to a coil in which an enamel copper wire is wound between an outer steel skin 1 and an inner steel skin 2 from an AC magnetic field power source 11 to generate the magnetic field. Welding arcs 18-21 are generated covering a part in the vicinity of a part to be welded with the flux 17 for submerged arc welding between a welding wire and a base metal 16 from each center through welding electrodes 12-15. The welding current of the fourth electrode 15 flows parallel to the surface of the base metal 16 through an arc 21 and a molten pool 22 in the radial direction. The AC current is crossed therewith, the rotational force is applied to the molten pool 22 formed by the fourth electrode 15 to stir the molten metal. This method is effective in the welding at higher speed and suppression in the undercut accompanied thereby.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for welding seams in a UOE steel pipe manufacturing process.

[0002]

2. Description of the Related Art Steel pipes are very useful as a means of transporting oil, gas and the like, and the amount thereof is large, so that most of them are manufactured by the UOE process which enables mass production. Generally, when manufacturing steel pipes by the UOE process,
Using the steel plate for UOE steel pipe manufactured in the thick plate process, the UOE steel pipe is manufactured by the following process. (1) First, start and end tabs are attached to the steel sheet at both ends in the longitudinal direction of the steel sheet in the tab attachment process.
(2) Next, in a groove processing step, the steel sheet is processed into a groove at both ends in the longitudinal direction by an edge planer, an edge mirror or the like. (3) In the next forming step, the above-described steel sheet subjected to the groove processing is pressed so that the cross-sectional shape becomes U to O, that is, the shape of a steel pipe. (4) Further, the formed steel pipe material is welded along the line of the grooved longitudinal seam in the longitudinal direction.

In seam welding, (5) First, full-length tack welding is first performed on the bottom of the groove on the outer surface side by carbon dioxide arc welding or the like. (6) Next, one layer welding is performed on the inner surface side groove by the latent arc welding method, and (7) One layer welding is further performed on the outer surface side residual groove portion by the latent arc welding method to complete the seam welding of the steel pipe. To do.
After the seam welding is completed, the steps of (8) inspection of welded portion, (9) pipe expansion correction by a pipe expanding machine, (10) water pressure inspection, etc. are followed, and the basic production of UOE steel pipe is completed for the time being.

The present invention is concerned with the above-mentioned seam welding. For seam welding, however, in all UOE manufacturing factories, the inner surface side is currently a 3-4 electrode latent arc welding method, and the outer surface side is a 4 arc electrode welding method.
The application of the latent arc welding method of electrodes has become common. 3-4
The purpose of adopting the multi-electrode latent arc welding method of electrodes is to achieve a high welding speed, that is, to achieve mass production of steel pipes.
However, most UOE steel pipes for line pipes are manufactured for export, but under the recent trend of yen appreciation, reduction of manufacturing cost has become an issue that each company should solve immediately. .

As a cost reduction measure in seam welding, it goes without saying that the welding material and the electric power consumption rate are reduced.
Improving productivity is an important issue. Behind the importance of improving productivity more than ever before is the versatility of line pipe applications. Specifically, due to the problem of the mining environment for oil and natural gas, there is an increasing demand for special component materials. For this reason, it is necessary to manufacture a large number of steel pipes in small quantities in a limited facility scale, and improvement of productivity is a key to cost reduction measures.

In order to improve productivity in seam welding, it is an effective means to further increase the current welding speed. However, in the current method, as a means for increasing the welding speed, it is general to set the welding current value of each multi-electrode welding electrode to a higher value and to increase the welding speed accordingly. But,
When the welding current is extremely increased and the welding speed is increased, there is a problem that various welding defects occur remarkably. As welding defects that are promoted with the increase in welding speed, (1) defects that occur in the weld metal, and (2)
It can be roughly classified into appearance defects that occur near the surface of the weld metal.

The former defects include blowhole defects caused by gas entrainment of molten slag and gas generated when slag is generated, and further defects such as cracking of weld metal. Both slag inclusion defect and blowhole defect are related to the levitation of molten slag and gas bubbles generated in the molten state of the weld metal.The faster the welding speed, the shorter the solidification time of the weld metal, and Bubbles are more likely to be trapped in the weld metal. The defects of weld metal cracks include solidification cracks (or high temperature cracks) and low temperature cracks (or delayed cracks). Solidification cracking is explained by a mechanism similar to shrinkage cavities that occur during solidification of castings. That is,
Even in welding, if the welding speed becomes high, the solidification rate of the weld metal will increase even if the welding heat input is constant, and the molten metal will be replenished to the deformation of the pipe that occurs during solidification, that is, the restraining force to open the weld metal. Is due to being unable to keep up with.

The latter appearance defect is that the bead surface shape is made convex due to the increased welding speed, and the undercut is generated accordingly. Generally, when the welding current is increased, the arc plasma becomes large, and with a strong digging effect, large kinetic energy is applied to the molten steel flow of the weld metal, and a strong molten steel flow is generated in the direction opposite to the welding proceeding direction. Usually, in the case of multi-electrode welding, such as the 4-electrode SAW method,
The action of each electrode can be qualitatively explained as follows. That is, the preceding first and second electrodes mainly contribute to the digging of the base material, and the digged molten steel flow is vigorously pushed backward. Next, the third electrode has the function of suppressing the flow force of the molten steel flow dug up by the first and second electrodes and widening the bead width. Further, the fourth electrode, that is, the last electrode has a function of further weakening the momentum of the molten steel flow pushed backward by the first to third electrodes and stabilizing the solidification.

Therefore, in order to achieve a high welding speed in the multi-electrode welding method such as the 4-electrode SAW method, the balance of the current, voltage or electrode angle, electrode interval, etc. of each electrode is very important. . Weldability of the flux used as another element is also important for increasing the welding speed. Therefore, at each of the current UOE manufacturing plants, steel pipes are manufactured by applying the conditions of the highest balanced welding speed in the multi-electrode SAW method.

Therefore, even if the welding current is simply increased by the existing method to further increase the welding speed, it is difficult because the undercut is generated and the bead becomes convex. On the other hand, welding defects such as extreme convex beads and undercuts that occur with high current and high speed,
There is a problem that it is necessary to repair the convex bead by the grinder and repair welding. At present, a method of applying magnetic stirring for the purpose of solving the above-mentioned various problems has been proposed and partially put to practical use. However, the application of this method is limited to only the one-electrode method, and the one-electrode method has a limitation in increasing the welding speed, and there is a problem that it cannot be applied to the UOE process for mass production of steel pipes.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and improves the welding speed in seam welding of steel pipes in the UOE process to improve productivity and welding quality thereof. The present invention provides a method for welding a steel pipe which can significantly improve

[0012]

Means for Solving the Problems The present invention is to solve the above problems, and in a method of welding a steel pipe by a multi-electrode latent arc welding method, the electrode tip of the final electrode of the multi-electrode is surrounded by a coil, A magnetic stir welding method for a steel pipe, characterized in that the coil is energized to form a magnetic field and the molten metal is magnetically stirred to weld.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings. 1 is a side sectional view showing a magnetic stir welding method of a steel pipe seam by a multi-electrode (four-electrode) latent arc welding method according to the present invention, and FIG. 2 is a diagram showing a front section of FIG. 1 in the figure
Is a steel outer shell of a magnetic stirring coil, 2 is a steel inner shell,
3 is a coil in which an enamel copper wire is wound between a steel inner skin and a steel outer skin. Reference numeral 4 is an indirect water cooling tube of a coil, 5 is a cooling water inlet, 6 is a cooling water outlet, 7 is a cooling water partition wall, 8 is a jig for fixing a coil to an electrode, 9 is a space between the electrode and the steel endothelium 2. Insulating material, 10 is a set screw for fixing the coil part to the electrode,
11 is an alternating magnetic field power source connected to the coil 3, 12 is a first electrode (leading electrode) for latent arc welding, 13 is a second electrode, 14 is a third electrode, 15 is a fourth electrode (final electrode), 16 is Base material of steel pipe, 17 is a flux for latent arc welding, 18-21 is a welding arc of each electrode, 22 is a molten pool, 23 is a latent arc welding bead, 24 is a latent arc welding slag, and 25 is a magnetic field by a coil. .

In the above drawings, an alternating magnetic field power source 11 supplies an alternating current to a coil 3 in which an enamel copper wire is wound several hundred to several thousand times between a steel outer skin and a steel inner skin to generate a magnetic field.
Since the magnetic field is formed by winding the enamel copper wire in the circumferential direction of the final electrode 15, an alternating magnetic field 25 in the axial direction is obtained with respect to the welding electrode on the steel inner side of the coil. On the other hand, welding electrode 1
Welding arcs 18 to 21 are generated while covering the vicinity of the welded portion between the center of each of the welding wires 2 to 15 and the welding wire and the base material with the flux 17 for latent arc welding. A weld pool 22 is formed immediately below the welding arc of the base metal portion, and a welding bead 2 covered with a latent arc welding slag 24 is provided behind it.
3 is formed.

Here, the welding current of the fourth electrode flows radially and in parallel with the surface of the base material 16 via the arc 21 and the molten pool 22. On the other hand, the alternating magnetic field crosses, and according to Fleming's left-hand rule, a rotating force acts on the molten pool formed by the fourth electrode to stir the molten metal. At this time, in order to protect the coil from heat during welding, cooling water is supplied from the cooling water introduction port 5 of the indirect water cooling pipe 4 of the coil, the coil is indirectly cooled, and then discharged from the cooling water discharge port 6. . The cooling water partition wall 7 is for rotating water in the circumferential direction of the coil to enhance the cooling ability.

[0016]

EXAMPLES Examples of carrying out the method of the present invention using the above apparatus will be described below. Thickness of X65 grade as base material 2
A groove similar to the outer surface side of UOE as shown in FIG. 3 was formed on one surface of a steel plate having a length of 0 mm, a length of 2000 mm, and a plate width of 500 mm. A temporary bead having a heat input of 3 kJ / cm for a material having a thickness of 20 mm was placed in the groove by the carbon dioxide arc welding method in the same manner as in the normal UOE process. Using this test material, a welding test with or without magnetic stirring was carried out under the conditions shown in Table 1.

[0017]

[Table 1]

As described above, from the viewpoint of improving productivity by applying magnetic stirring to the latent arc welding, the length is 20 m.
Standard welding conditions for m-thick UOE, namely welding current,
The current was increased stepwise based on the voltage and speed, and the welding speed was changed to match the welding heat input under standard conditions. In addition, a comparative test was also performed between the conventional method without magnetic stirring and the method of the present invention to which magnetic stirring was applied, in which only the welding speed was gradually increased with standard current and voltage. Welding material is wire,
The same flux as the normal UOE was applied. The magnetic stirring condition, that is, the output current from the alternating magnetic field power source, the magnetic field frequency, and the coil height were set under the condition that a magnetic field strength of 350 gauss, which was confirmed to be effective in the preliminary test, was obtained.

After welding, X-ray transmission test of bead portion, undercut occurrence rate, and three macro test pieces of penetration cross section were collected under each condition, and after polishing and corrosion, dimension measurement of each bead portion was performed and measured. Practicality was evaluated by the average value. Table 2 shows the test results. The undercut occurrence rate was expressed as the ratio of the total undercut length and the total bead length. As a practical evaluation, the ○ marks are those that were judged to be applicable without any practical problems, and the Δ marks were those that required some reworking of the bead grinder. The mark X indicates that some chipping and repair welding were judged necessary.

[0020]

[Table 2]

In the case of the conventional method without magnetic stirring, there was no particular problem with the test code A2 of the current standard conditions. However, the test symbols B2, C2, and D2 with high current and high speed have a gradually narrower bead width, higher surplus height, and undercut occurrence rate with higher current and higher speed. An increasing tendency was confirmed. Especially welding speed 2.4m /
An internal defect was recognized in the test symbol D2, which was min, in the X-ray transmission test. Further, in the test symbols E2 and F2, in which the welding speed was gradually increased under the standard conditions of current and voltage, the undercut occurrence rate increased as the welding speed increased. On the other hand, with the test symbols A1 to F1 materials to which magnetic stirring was applied, practicable results were obtained under all conditions, and by applying magnetic stirring welding to the final electrode in the multi-electrode latent arc welding method, high welding speed and It was confirmed that it was effective in suppressing undercut.

[0022]

As described above, according to the present invention, U
It is possible to improve the welding speed of the seam welded portion in the manufacturing process of the OE steel pipe, improve the productivity, and significantly improve the welding quality.

[Brief description of drawings]

FIG. 1 is a transverse sectional view of a welded portion for explaining a magnetic stir welding method according to the present invention.

FIG. 2 is a vertical sectional view of a welded portion for explaining a magnetic stir welding method according to the present invention.

FIG. 3 is a diagram showing a groove shape in an example.

[Explanation of symbols]

 1 Steel Skin 2 Steel Endothelium 3 Coil 4 Indirect Water Cooling Pipe 5 Cooling Water Inlet 6 Cooling Water Outlet 7 Cooling Water Partition Wall 8 Coil Fixing Tool 9 Insulating Material 10 Set Screw 11 Alternating Magnetic Field Power Supply 12 First Electrode 13 2nd electrode 14 3rd electrode 15 4th electrode 16 Base material 17 Flux 18, 19, 20, 21 Welding arc 22 Molten pool 23 Submerged arc welding bead 24 Submerged arc welding slag 25 Magnetic field by coil

Claims (1)

[Claims] 1. A method for welding a steel pipe by a multi-electrode latent arc welding method, wherein an electrode tip portion of the final electrode of the multi-electrode is surrounded by a coil, and the coil is energized to form a magnetic field to give magnetic stirring to the molten metal. Magnetic stir welding method for steel pipes, which is characterized by welding by welding.