JPH06270B2 - One-sided first layer welding method for pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a single-sided first layer welding method for pipes in pipeline laying work.

[Prior Art] Generally, the groove shape in the circumferential butt welding of pipes is the third
It is formed as shown in Figure (a), and welding is performed as shown in Figure (b). That is, first, the root path I is welded by the inner surface welding machine. The welding speed of this route pass I is about 75 cm / minute, and the torch is not weeped.

Next, after the completion of this route pass I, welding is performed from the outer face of the pipe in the order of hot pass H, filler pass F and cap pass C by an outer surface welding machine.

The welding speed of the hot path H is about 100 cm / minute, and the torch is not weeped.

Welding speed of fly pass F and cap pass C is 30-40
Welding is performed in cm / quantile while weaving (usually 6 to 7 mm) according to the groove width of the joint.

[Problems to be Solved by the Invention] The present invention is intended to improve the welding speed of initial layer welding in circumferential butt welding of pipes and to ensure stable welding quality.

As described in the previous section, in the prior art, the welding speed of the initial layer root pass welding is about 75 cm / min, and weaving is not performed. That is, since weaving is not performed in the conventional technology, it is not possible to perform groove automatic copying control by the arc sensor, so it takes time and labor to align the welding torch of the first layer welding machine with the groove center of the joint. However, sometimes there was a problem that defects were likely to occur in the first-layer welding bead due to factors such as the bending of the wire and displacement of the target position of the welding torch.

The arc sensor swings the welding torch in the groove width direction inside the groove, detects the positional deviation in the groove of the welding torch from the waveform of the welding current and arc voltage, and corrects it to make the welding line. Is a method of automatically following. But,
Since the arc sensor in the prior art adopts the vibration type weaving method, the weaving frequency cannot exceed 10 Hz due to the mechanical constraint, so that the welding speed that can be applied is limited due to the responsiveness of the arc sensor and the bead shape. Therefore, it cannot be applied at the welding speed of 75 cm / min in the first layer root pass welding of the prior art.

In addition, the welding current of the first-layer root-pass welding of the prior art is about 2
It is 00A. This is because the welding torch is not moved (weaving), and if a larger current than this is applied, the bead shape becomes convex especially in the upward posture, so the welding current is limited to about 200A. Therefore, higher speed welding was not possible.

The above two problems are summarized as follows.

(1) In the welding of the first layer route pass in the conventional technology, since weaving of the torch cannot be performed, the groove automatic copying control by the arc sensor cannot be applied, and it takes time and labor to position the welding torch, and sometimes it is necessary. Disturbance causes defects.

(2) Welding current is 200A due to the problem of the bead shape because the weaving of the welding torch cannot be performed.
Due to the limited extent, higher speed welding was not possible.

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a consumable electrode type arc welding method by a high speed rotating arc method is adopted as a welding process.

In this method, the arc rotation speed N is 10 Hz to 15 Hz.
0Hz (the lower limit is the upper limit of the weaving frequency of the conventional vibration type arc sensor, the upper limit depends on the current track record), the rotating diameter D of the arc is 1 to 4 mm, the welding current is 200 to 500 A (the lower limit is the conventional value The welding current and the upper limit are the upper limit of the welding process, and the welding speed is 75 to 300 cm / min (the lower limit is the welding speed of the prior art, and the upper limit is the current arc sensor performance).

[Operation] In this method, since the arc is rotated and weaved at a high speed of 10 to 150 Hz per second, it is 75 to 300 cm.
The problem of (1) is solved because the automatic groove chamfering by the arc sensor can be achieved even in high-speed welding of / min.

Further, the high speed rotation of the arc disperses the pressure and heat input of the arc and smoothes the bead surface shape.
The problem (2) is solved because a good bead shape can be obtained even at a high current of 500 A and high speed welding of 75 to 300 cm / min.

That is, in the butt-circumferential welding of pipes, if the rotating arc method described above is used, the number of rotations of the arc can be easily increased, and the bottom formed at the pipe end automatically moves in the V-shaped annular groove. Can be imitated. Therefore, while the automatic welding machine is running along the circumferential guide rail temporarily attached to the outer surface of the pipe, the arc rotation speed is 10 to 1
If welding is performed under the action of a high-speed rotating arc sensor with a rotating diameter of the arc of 50 Hz and an arc rotating diameter of 1 to 4 mm, the first layer can be circumferentially welded in all positions, and the welding current is 200 to 50.
By welding with the backing material under a large current of 0 A, normal backwater is formed at the same time as the first layer welding, and high-speed welding with a welding speed of 75 to 300 cm / min is realized. Further, the filler pass and the cap pass can be continuously welded continuously based on the first layer welded in this way.

[Examples] Hereinafter, a welding method of the present invention will be described with reference to the drawings. First
The figure is a schematic configuration diagram of an automatic welding machine. The welding machine body 1 is installed so as to be self-propelled along a circumferential guide rail 12 temporarily attached to the outer surface of the pipe 10. A welding torch 2 provided in the welder body 1 is rotated by a motor 3 via a gear mechanism 4, and an x-axis slide block 5 that is movable in the width direction of the groove 14 (x-axis) and a torch axial direction ( y-axis slide block 6 that can move to y-axis)
Is supported through. The rotation speed N of the torch 2 is the rotation speed of the arc, and the rotation speed and rotation position are detected by a rotation detector (not shown). The welding wire 7 is automatically fed to the current-carrying tip having the eccentric hole of the torch 2, and the rotating diameter D of the arc is determined by the eccentric distance. This allows the rotating arc method to be implemented.
Reference numeral 16 is a backing material such as a copper plate arranged facing the groove 14.

2 (a) and 2 (b) are enlarged sectional views of the groove shape according to the present invention. The groove 14 is formed in a straight annular groove 14b having a V-shaped bottom 14a. The inclination angle θ of the bottom portion 14a is set to 30 ° to 60 °. Also, the a dimension is 1
The groove width b is set to 7 to 8 mm or less when the pipe thickness is 2 mm and the wall thickness t of the pipe is 8 to 25 mm. A small root face 14c may be provided on the inner surface of the groove 14 on the inner surface of the pipe as shown in FIG. 2 (b).

By forming the bottom portion 14a of the groove 14 in the V-shape in this manner, the welding torch 2 shown in FIG. 1 can be accurately positioned at the center of the bottom portion 14a under the action of the rotary arc sensor under a constant arc length. Can be copied, and the external hot path H (first layer 1
7) can be circumferentially welded in all positions. Moreover, the back seam 18 can be normally produced simultaneously with the welding of the first layer 17.

Explaining a specific example, a solid wire of 0.9 mmφ is used, the arc rotation speed N = 50 Hz, the arc rotation diameter D = 2 to 3 mm, the welding current I _a = 300 A, and the welding speed v =
When the first layer 17 was welded in an atmosphere of 100% CO ₂ gas at 2.0 m / min, a smooth bead shape as shown in FIG. 2 (c) was obtained. Therefore, also in the case where the filler path F and the cap path C are sequentially laminated and welded on the bead of the first layer 17 next, welding may be performed under the action of the rotary arc sensor with the first layer 17 as a reference. Since it can be performed continuously, the butt circumferential welding of pipes can be performed at high speed.

[Effects of the Invention] As described above, according to the present invention, the hot path is welded using the rotary arc method only from the outer surface of the pipe without using the inner surface welding machine as in the conventional method, and the welding conditions at that time are described above. Since it is set as follows, it is possible to perform excellent first layer welding with no welding defects by high current and high speed welding, and furthermore, it is possible to perform all laminated welding continuously based on this first layer. Butt circumferential welding can be performed at high speed. Therefore, according to the present welding method, there is an effect that the construction period can be shortened to about 1/4 or less as compared with the conventional method, and the equipment and the personnel can be greatly reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an automatic welding machine used in the welding method of the present invention, and FIGS. 2 (a) and 2 (b) are enlarged sectional views of a groove shape.
Figure (c) shows the state of laminated welding at the groove,
FIG. 3 (a) is an enlarged sectional view of a conventional groove shape, and FIG. 3 (b)
FIG. 4 is an explanatory view showing a state of laminated welding at the groove. 1 ... Welder main body 2 ... Welding torch 3 ... Motor 4 ... Gear mechanism 5 ... X-axis slide block 6 ... Y-axis slide block 7 ... Welding wire 10 ... Pipe 12 ... Circumferential guide rail 14 ... Groove 16 ... Backing material

Claims (1)

[Claims] 1. In butt-circumferential welding of pipes, a groove having a V-shaped bottom of an annular groove is formed on the butt end face of the pipe, and a backing material is arranged on the inner surface side of the pipe. While traveling on a circumferential guide rail attached to the outer surface of the pipe, while performing automatic groove tracking control by a high-speed rotating arc welding method with an arc rotation speed of 10 to 150 Hz and an arc rotation diameter of 1 to 4 mm, Welding current 200-500
A, a single-sided first-layer welding method for a pipe, characterized in that the first layer is welded from the outer surface of the pipe in all positions on one side at a welding speed of 75 to 300 cm / min.