JPH1043859A - Method for welding steel tube having excellent defective welding resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the welding speed in multi electrode submerged arc welding of a steel tube and to improve the productivity and the welding quality by arranging a coil so that the coil height of a 1st electrode is specified. SOLUTION: An alternate current is made to flow through a coil 3 wound with many numbers of enamel copper wires between a steel sheath and a steel core from an alternate magnetic field power source 11 and a magnetic field is generated. In this magnetic field, since the copper wire is wound in the circumferential direction of weld electrodes 12 to 15, the alternate magnetic field in the axial direction is obtained against the weld electrode in the core side of the coil 3. On the other hand, the alternate current is crossed almost perpendicular to the alternate magnetic field, and based on the Fleming's left-hand rule, the rotation force is applied on a molten pool 26 and the molten metal is stirred. At this time, when the coil height of a 1st electrode part is arranged so as to be 1.1 to 2.0 times higher than the coil height of a final electrode, the strength of the magnetic field acting to the welding arc of the 1st electrode is made weak and the digging down action of a base material is not deteriorated. On one side, the molten pool is stirred with the sufficient rotation force.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a UOE steel pipe or SP
The present invention relates to a (spiral) steel pipe welding method.

[0002]

2. Description of the Related Art UOE steel pipes and SP steel pipes are used as means for transporting oil and natural gas. UOE steel pipe and S
For welding of P steel pipes, from the viewpoint of productivity such as improvement of welding speed, 3 to 4 to 4 to 4 in latent arc welding (SAW).
The application of a five-electrode multi-electrode latent arc welding method has become common. In addition, as a means for further improving the welding speed, it is general to set the welding current value of each welding electrode high and improve the welding speed.However, the welding current was set extremely high and the welding speed was increased. In this case, there is a problem that the occurrence of welding defects becomes significant.

In contrast, in the multi-electrode latent arc welding method, the inventors arrange a coil surrounding a welding tip of a multi-electrode, energize the coil to form a magnetic field, and apply magnetic stirring to the molten metal. Welding methods have been attempted with less welding defects. However, when a strong magnetic field is applied to each electrode, welding defects are reduced, but the penetration depth is reduced, and a problem has arisen that the metal touch of the inner and outer surface weld metal cannot be secured.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and has been made to improve the welding speed in multi-electrode latent arc welding of steel pipes, thereby improving productivity and welding quality. It is an object of the present invention to provide a method of welding a steel pipe that can be improved.

[0005]

SUMMARY OF THE INVENTION The gist of the present invention is that in a multi-electrode latent arc welding having two or more electrodes, a current-carrying coil surrounding each electrode is arranged at the same time to form a magnetic field in the coil. In a method of welding a steel pipe by stirring molten metal, the coil height of the first electrode portion is arranged to be 1.1 to 2.0 times the coil height of the final electrode portion.

[0006] Welding defects promoted as the welding speed increases include (1) defects occurring in the weld metal, and (2) appearance defects occurring near the surface of the weld metal. The former defects include blowhole defects caused by entrainment of molten slag and gas generated when slag is generated, and weld metal cracks. Slag entrainment defects and blowhole defects are caused by the molten slag and gas generated in the molten state. Easy to be.

[0007] On the other hand, defects in the appearance include projection of the bead surface shape due to an increase in welding speed and the generation of an undercut due to the projection. Generally, in the case of a four-electrode SAW, the preceding first and second electrodes mainly contribute to drilling of the base material, and the excavated molten steel flow is swept backward. The third electrode has the effect of suppressing the momentum of the molten steel flow excavated by the first and second electrodes and increasing the bead width. Further, at the fourth electrode, the momentum of the molten steel flow pushed backward by the first to third electrodes is further weakened to stabilize solidification. Therefore, in order to increase the welding speed in multi-electrode latent arc welding such as four-electrode SAW, it is very important to balance the current, voltage, electrode angle, electrode spacing, and the like of each electrode.

[0008] The inventors have already filed Japanese Patent Application No. 7-245972.
In the multi-electrode latent arc welding, a welding method with less welding defects by forming a magnetic field in the coil surrounding the electrodes and stirring the molten metal was shown. However, when all the electrodes are surrounded by the coil, the agitation function at the first electrode is weakened by stirring, the penetration depth is reduced, and when the inner and outer surfaces are welded, there is a problem that the inner and outer surface weld metal is difficult to metal touch. . Therefore, the inventors conducted intensive studies and changed the coil height of the first electrode and the final electrode when installing the coil on the electrode, thereby ensuring the digging action at the first electrode, and By sufficiently stirring the molten steel in the electrode, a sufficient penetration depth can be obtained, and a welding method with less welding defects such as blowholes and undercuts has been invented.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. FIG. 1 and FIG. 2 show a steel pipe welding method by a sub-arc welding method of a multi-electrode (four electrodes) according to the present invention. FIG. 3 is a front sectional view (a) of FIGS. 1 and 2 and a plan view (b) showing an aspect from above. In these figures, reference numeral 1 denotes a steel shell of a magnetic stirring coil, 2 denotes a steel inner shell, and 3 denotes a coil in which an enameled copper wire is wound between the steel inner shell and the steel shell. 4 is an indirect water cooling pipe 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 the coil to the electrode, 9 is an insulating material for the electrode and the steel sheath 1. , 10 is a set screw for fixing the steel sheath to the electrode, 11 is an alternating magnetic field power supply connected to the coil 3, 12 is a first electrode for latent arc welding, 13 is a second electrode, 14 is a third electrode, 15 is a fourth electrode, 16 to 19 are welding power supplies for four electrodes, 20 is a base material of a steel pipe, 21 is a flux for latent arc welding, 22 to 25 is a welding arc of each electrode, 26 is a weld pool,
27 is a latent arc welding bead, 28 is a latent arc welding slag, 29 is the final electrode (here, the height from immediately below the coil 3 at the fourth electrode to the surface of the welded steel plate, 30 is the welded steel plate from immediately below the coil 3 at the first electrode. The height up to the surface.

In FIG. 1 to FIG. 3, an alternating current is supplied from an alternating magnetic field power supply 11 to a coil 3 having an enameled copper wire wound several hundred to several thousand times between a steel outer skin and a steel inner skin to generate a magnetic field. . The magnetic field is enameled copper wire with welding electrodes 12-1.
5, an alternating magnetic field in the axial direction with respect to the welding electrode is obtained on the steel inner side of the coil.
On the other hand, welding arcs 22 to 25 are generated from the welding power sources 16 to 19 through the welding electrodes 12 to 15 while covering the vicinity of the welding portion between the welding wire and the base metal from the respective centers with the flux 21 for latent arc welding. Let it. A welding pond 26 is formed immediately below the welding arc in the base material portion, and a welding bead 27 covered with a submerged arc welding slag 28 is formed behind the welding pool 26. Here, the welding current flows through the arcs 22 to 25 and the molten pool 26 in parallel to the base material surface 20 and radially.

On the other hand, the alternating current crosses almost vertically, and a rotating force acts on the molten pool 26 according to Fleming's left-hand rule to agitate the molten metal. At this time, if the coil height of the first electrode portion is arranged to be 1.1 to 2.0 times higher than the coil height of the final electrode portion, the strength of the magnetic field acting on the welding arc of the first electrode is reduced, Does not impair the drilling action of the base material. On the other hand, in the welding arc of the final electrode, a predetermined magnetic field strength acts, so that the molten pool is stirred by a sufficient rotational force. By this welding method, a sufficient penetration depth can be obtained, and a weld having no welding defects can be obtained. Further, when the coil height of the first electrode portion is arranged to be greater than 2.0 times the coil height of the final electrode portion,
Since sufficient stirring is not performed even at the final electrode, welding defects such as undercuts occur.

In order to protect the coil from heat during welding, cooling water is supplied from the cooling water inlet 5 of the indirect water cooling pipe 4 of the coil, and after the coil is indirectly cooled, the cooling water is drained from the cooling water outlet 6. Is done. The water-cooling partition wall 7 is for rotating water in the circumferential direction of the coil to increase the cooling capacity.

Hereinafter, an example based on the above will be described. A 20 mm thick steel plate of API standard X65 grade was welded. Table 1 shows the welding conditions. After welding, an X-ray transmission test of a bead portion and a measurement of an undercut occurrence rate were performed. Table 2 shows the test results. The undercut occurrence rate was represented by the ratio of the total length of the undercut to the total length of the bead. In the evaluation of the practicality, a mark that is judged to be practically applicable is indicated by a circle, and a mark that is judged to be required to be removed and repair welding is indicated by a cross.

[0014]

[Table 1]

[0015]

[Table 2]

[0016] With reference numeral 1 according to the method of the present invention, a good weld bead having no welding defects was obtained, but welding by the comparative method caused welding defects and was not practically applicable. Reference numeral 2 applied magnetic stirring, but because the coil height of the final electrode and the first electrode was the same, there was no metal touch of the inner and outer surface welding, and welding defects occurred. Reference numeral 3 applied magnetic stirring, but the ratio of the coil heights of the final electrode and the first electrode was too large, so that the molten pool was not sufficiently stirred and an undercut occurred. In the code 4, undercut occurred because no magnetic stirring was applied.

[0017]

According to the present invention, the welding speed of a steel pipe can be increased, and high productivity and weld quality can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method for welding a steel pipe according to the present invention.

FIG. 2 is a view showing a method for welding a steel pipe according to the present invention.

3A is a front cross-sectional view of FIG. 1 and FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steel outer shell of magnetic stirring coil 2 Steel inner shell of magnetic stirring coil 3 Coil wound between steel inner shell and steel outer shell 4 Indirect water cooling tube 5 Cooling water inlet 6 Cooling water drain 7 Cooling water partition Wall 8 Jig for fixing coil to electrode 9 Insulating material of electrode and steel shell 10 Set screw 11 Alternating magnetic field power supply 12 First electrode 13 Second electrode 14 Third electrode 15 Fourth electrode 16 First electrode welding power supply 17th Welding power supply for two electrodes 18 Welding power supply for third electrode 19 Welding power supply for fourth electrode 20 Base material 21 Flux for latent arc welding 22 Welding arc for first electrode 23 Welding arc for second electrode 24 For third electrode Welding arc 25 Welding arc for fourth electrode 26 Weld pool 27 Latent arc welding bead 28 Latent arc welding slag 29 Height from just below coil 3 at final electrode to surface of welded steel plate 30 At first electrode Yl height 3 from just below to the surface of the welded steel

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location // B23K 101: 06

Claims (1)

[Claims] 1. In a multi-electrode latent arc welding having two or more electrodes, an energizing coil surrounding each electrode simultaneously is arranged,
In the method of forming a magnetic field in the coil and stirring the molten metal to weld the steel pipe, the coil height of the first electrode portion is arranged to be 1.1 to 2.0 times the coil height of the final electrode portion. A method for welding steel pipes having excellent resistance to welding defects.