JPH06335768A - Method for welding fixed tube - Google Patents

Abstract

PURPOSE:To provide a method for welding a fixed tube with a high speed and high efficiency. CONSTITUTION:In the first pass of the welding of fixed tubes which are butted in a horizontal or an inclined position, the southern hemisphere part of the circumference of the fixed tube is welded (A) from the inner surface side of the fixed tube, and the northern hemisphere part of the circumference of the fixed tube is welded (B) from the outer surface side of the fixed tube. When the welding from the inner surface side of the fixed tube is executed simultaneously with the welding from the outer surface side of the fixed tube, the welding efficiency is further improved. When the keyhole welding is executed with the plasma as the heat source, the welding efficiency is improved. After this first pass of the welding, the all position welding is executed on the inner surface and/or the outer surface of the fixed tube over the whole circumference of the joint. In the case of the plasma arc welding, it is preferable to provide a lap part to the first bead and the second bead. This welding method is suitable for the welding of the horizontal fixed tube of medium to large diameter.

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 a fixed pipe, and is particularly suitable for welding a medium to large diameter horizontal fixed pipe.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
When welding a medium- or large-diameter fixed pipe, a method of welding around the 360 ° circumference from the inner or outer surface, or half from the inner surface to the half or from the outer surface to the top side The method of welding was adopted. For example, JP-A-55-141395 and JP-A-4-322884 are proposed.

However, in the prior art, both
We will perform all posture welding from downward to vertical to upward, from the first layer to the final layer, and in terms of efficiency, we will have to match the welding conditions of all postures to the upward posture with the lowest efficiency. There was such a problem.

Inefficiency, the first layer is TIG and the second and subsequent layers must be changed by another welding method. For example, when the first layer is welded from the outer periphery, there is excessive back wave near the sky. On the contrary, in the vicinity of the ground, back waves tend to be insufficient, and it is difficult to form stable beads.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for welding a fixed pipe at high speed and with high efficiency.

As a result of earnest studies to solve the above-mentioned problems, the present inventor has conducted a tandem welding method in which the outer circumference and the inner circumference are welded to each other in half, and a portion to be welded from an upright position to an upright position is welded. This is the finding of a new fixed pipe welding method that has achieved a significant reduction and improved efficiency.

That is, according to the present invention, in the first layer welding of fixed pipes which are butted in a horizontal or inclined posture, the southern hemisphere of the fixed pipe circumference is welded from the inner surface of the fixed pipe, and the northern hemisphere of the fixed pipe circumference is welded. The gist is a method of welding a fixed pipe, which is characterized in that welding is performed from the outer surface side of the fixed pipe.

The present invention will be described in more detail below.

[Action]

In the present invention, the welded portion of the fixed pipe is divided into the southern hemisphere and the northern hemisphere and welded. Here, the southern hemisphere and the northern hemisphere are convenient names, and the half including the top side of the pipe cross section is the northern hemisphere. The half including the ground side is separated from the southern hemisphere.
Therefore, as shown in FIG. 1, it is not necessary to strictly divide the upper side into the northern hemisphere, the lower side and the southern hemisphere by the line connecting O-O, and the O'-O 'line with the O-O line slightly shifted, or Even if the O "-O" line is used as a dividing line between the northern hemisphere and the southern hemisphere, there is no practical problem.

In view of the fact that the welding efficiency depends on the efficiency particularly in the upward posture, in the present invention, as shown in FIG.
Weld the southern hemisphere (A) of the circumference of the fixed pipe from the inside of the fixed pipe,
Weld the northern hemisphere (B) of the circumference of the solid pipe from the outer surface side of the fixed pipe. As a result, the entire welding can be performed in the downward posture, or most of the welding can be performed in the downward posture and a part of the welding can be performed in the vertical posture, so that the welding in the upward posture can be avoided and the efficiency can be improved.

Various modes are possible for the welding method, welding procedure, and the like in this welding method.

Welding method: The welding method is not particularly limited. Welding methods that use high-energy beams such as lasers and plasmas as heat sources, as well as TIG and MI
Even with the conventional welding method such as G, high efficiency can be achieved.

A welding method using a high energy beam as a heat source is effective, but keyhole welding using plasma as a heat source is particularly suitable in terms of efficiency improvement. Here, keyhole welding is the most characteristic backside welding method of plasma welding (Fig. 3). A plasma arc with a relatively large current is narrowed down and locally heats the base material, and at the same time, the plasma gas ejected at a high speed strongly pushes down the molten metal.
(Keyhole) occurs. As the welding progresses, the tip of the keyhole advances while melting the base metal, but the molten metal moves backward along the wall surface of the molten pool and blocks the rear of the keyhole.
The keyhole is a welding method that maintains an almost constant shape.

Welding procedure: Even if the welding from the inner surface side of the fixed pipe and the welding from the outer surface side of the fixed pipe are performed with a temporal shift,
Alternatively, they can be performed simultaneously. If two welding machines are used at the same time, the welding efficiency can be further improved.

The present invention can be applied not only in the case of welding work in which only the first layer welding is sufficient, but also in the case of multilayer welding as the first layer welding. In the case of multi-layer welding, for example, 2
After the second layer, the inner surface and / or the outer surface of the fixed tube are welded in all positions over the entire circumference of the joint.

Of course, it goes without saying that the welding conditions of various welding methods can be appropriately determined. At that time, in the case of plasma arc welding, it is preferable to consider the following points.

The efficiency of welding of the fixed pipe generally decreases at the upward welding points, and it is desirable to minimize the upward welding points. FIG. 11 shows a bead splicing method in which the outer side and the inner side of the fixed tube are connected, in which the number of upward welding points is minimized. That is,
This is a method in which welding beads from the inside and outside of the first layer keyhole welding are wrapped by a certain width (L ₁ , L ₂ ) to eliminate discontinuous points and complete the bead joining.

Regarding the lap width L, depending on the diameter of the fixed tube, the plate thickness, the groove shape, and the welding conditions, if the lap width is less than 5 mm, the overlapping portion is insufficient, and it is difficult to adjust the bead shape, and undercut or the like occurs. Since a welding defect is likely to occur, the lap width L is preferably 5 mm or more in order to obtain a stable bead overlapping portion.

This bead splicing method can be applied to the same welding method after the second pass after finishing the keyhole welding of the first layer, and also to the case of performing all-position welding, but more preferably, It is possible to perform more reliable welding if the lap portion of the bead does not overlap the lap portion.

Further, it is desirable that at least one of the welding current and the flow rate of the plasma gas in any of the lap portions is not higher than the welding condition of the welding portion other than the lap portion. If these conditions are reversed, the weld bead height in the lap portion becomes extremely large, and as a result, not only the next bead is difficult to form, but also fusion failure or the like eventually occurs. If necessary, the welding speed of the lap portion may be reduced or a stop time may be provided.

Next, examples of the present invention will be described.

[0022]

Example 1 This example is an example in which after welding the first layer by the plasma arc welding method, all the positions were welded from both the inner surface and the outer surface of the fixed tube.

First, in the groove joint of the fixed pipe shown in FIG. 4, the first layer welding was simultaneously performed by the keyhole welding method from the inner surface of the southern hemisphere and the outer surface of the northern hemisphere. In the figure, the bead 1 is the first layer. Then, the second to third layers were simultaneously formed from the inner surface and the outer surface by the non-keyhole welding method. In the figure, 2 and 3 are external beads, and 4 and 5 are internal beads.

The test material used was API 5L-X60 steel (plate thickness 19 mm) and had a tube diameter of 20 inches. Table 1 shows the plasma arc welding conditions.

[0025]

[Table 1]

[0026]

[Embodiment 2] This embodiment is an example in which after the first layer welding by the laser welding method, all the posture welding is performed from both the inner surface and the outer surface of the fixed tube.

First, in the grooved joint of the fixed pipe shown in FIG. 5, the first layer welding was simultaneously carried out by laser welding from the inner surface of the southern hemisphere and the outer surface of the northern hemisphere. In the figure, the bead 1 is the first layer. Then, 2-3 by laser welding method
Layers were formed from the inner surface and the outer surface, respectively. In the figure, 2 is an outer bead and 3 is an inner bead.

The test material used was API 5L-X60 steel (plate thickness 15 mm) and had a tube diameter of 20 inches. The laser welding conditions are shown in Table 2.

[0029]

[Table 2]

[0030]

[Embodiment 3] This embodiment is an example in which the first layer welding is performed by the plasma arc welding method, and then all the positions are welded from the outer surface of the fixed tube.

First, in the groove joint of the fixed pipe shown in FIG. 6 (Y groove having a groove only on the outer side), the first layer welding is performed simultaneously by the keyhole welding method from the inner surface of the southern hemisphere and the outer surface of the northern hemisphere. Carried out. In the figure, the bead 1 is the first layer. Then, the second to third layers were formed from the outer surface by a non-keyhole welding method. In the figure, 2 and 3 are outer beads.

The test material used was API 5L-X60 steel (plate thickness 19 mm) and had a tube diameter of 30 inches. Table 3 shows the plasma arc welding conditions.

[0033]

[Table 3]

[0034]

[Embodiment 4] This embodiment is an example in which the first layer welding is performed by the plasma arc welding method, and then all the positions are welded from the inner surface of the fixed tube.

First, in the groove joint of the fixed pipe shown in FIG. 7 (Y groove having a groove only on the inner side), the first layer welding is performed simultaneously by the keyhole welding method from the inner surface of the southern hemisphere and the outer surface of the northern hemisphere. Carried out. In the figure, the bead 1 is the first layer. Then, the second layer was formed from the inner surface by a non-keyhole welding method. In the figure, 2 is an inner bead.

The test material used was API 5L-X60 steel (plate thickness 19 mm) with a tube diameter of 30 inches. Table 4 shows the plasma arc welding conditions.

[0037]

[Table 4]

[0038]

[Embodiment 5] This embodiment is an example in which the welding of the fixed pipe is completed only by the first layer welding by the plasma arc welding method. For example,
For pipelines, it is suitable for welding thin pipes.

First, the groove joint (I groove) of the fixed pipe shown in FIG. 8 is keyhole welded from the inner surface of the southern hemisphere and the outer surface of the northern hemisphere by using a backing material (made of Cu or ceramic). The first layer welding was performed simultaneously by the method. In the figure, the bead 1 is the first layer.

The test material used was API 5L-X60 steel (plate thickness 12 mm) and a pipe diameter of 20 inches. Table 5 shows the plasma arc welding conditions. Hydrogen was not used as a shielding gas because it may crack if the amount of hydrogen is large.

[0041]

[Table 5]

[0042]

[Embodiment 6] This embodiment is an example in which after the first layer welding by the plasma arc welding method, the whole position welding is performed from both the inner surface and the outer surface of the fixed tube.

First, in the grooved joint (I groove) of the fixed pipe shown in FIG. 9, the first layer welding was simultaneously performed by the non-keyhole welding method from the inner surface of the southern hemisphere and the outer surface of the northern hemisphere. In the figure, the bead 1 is the first layer. Then, the second layer was formed from the inner surface by a non-keyhole welding method. In the figure, 2 is an inner bead.

The test material used was API 5L-X65 steel (plate thickness 19 mm) with a tube diameter of 30 inches. Table 6 shows the plasma arc welding conditions.

[0045]

[Table 6]

[0046]

[Embodiment 7] This embodiment is an example in which welding of a fixed pipe is completed only by first layer welding by the plasma arc welding method. For example,
For pipelines, it is suitable for welding thin pipes.

First, the grooved joint (I
Groove), unlike Example 5, without using a backing material,
First layer welding was performed simultaneously from the inner surface of the southern hemisphere and the outer surface of the northern hemisphere by the keyhole welding method. In the figure, the bead 1 is the first layer.

The test material used was API 5L-X65 steel (plate thickness 12 mm) and had a tube diameter of 20 inches. Table 7 shows the plasma arc welding conditions.

[0049]

[Table 7]

[0050]

Example 8

In this example, the grooved joint of the fixed tube shown in FIG. 12 was first layer welded by the keyhole welding method, and then the fixed tube was welded in all positions, and a lap portion was provided. In the figure,
Bead 1 is the first layer, 2 is the outer bead, and 3 is the inner bead. The test material is API5L-X60 steel (plate thickness 16 m
m) with a pipe diameter of 20 inches was used. Table 8 shows the plasma arc welding conditions.

[0052]

[Table 8]

In each of the examples, stable welding was possible and no welding defects were observed.

[0054]

As described in detail above, according to the present invention,
Fixed pipes can be welded at high speed and with high efficiency. It is also effective when welding from the top of the tank to the ground.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the northern hemisphere and the southern hemisphere.

FIG. 2 is a sectional view for explaining the welding procedure of the present invention,
Shows the inner surface welding of the southern hemisphere around the circumference of the fixed pipe, and (B) shows the outer surface welding of the northern hemisphere.

FIG. 3 is a diagram illustrating keyhole welding.

FIG. 4 is a cross-sectional view showing a joint shape and a formation method in Example 1.

5 is a cross-sectional view showing a joint shape and a formation method in Example 2. FIG.

FIG. 6 is a cross-sectional view showing a joint shape and a formation method in Example 3.

FIG. 7 is a cross-sectional view showing a joint shape and a formation method in Example 4.

FIG. 8 is a cross-sectional view showing a joint shape and a formation method in Example 5.

FIG. 9 is a cross-sectional view showing a joint shape and a formation method in Example 6.

FIG. 10 is a cross-sectional view showing a joint shape and a formation method in Example 7.

11 (a) and 11 (b) are views explaining a bead joining method in welding of a fixed pipe.

FIG. 12 is a cross-sectional view showing a joint shape and a formation method in Example 8.

Claims (7)

[Claims] 1. In the first layer welding of a fixed pipe that is butted in a horizontal or inclined posture, the southern hemisphere portion of the circumference of the fixed pipe is welded from the inner surface of the fixed pipe, and the northern hemisphere portion of the circumference of the fixed pipe is the outer surface of the fixed pipe. A method for welding a fixed pipe, characterized by further welding. 2. The method according to claim 1, wherein the welding from the inner surface side of the fixed tube and the welding from the outer surface side of the fixed tube are performed at the same time. 3. The method according to claim 1, wherein the keyhole welding is performed using plasma as a heat source. 4. The method according to claim 1, 2 or 3, wherein after the initial layer welding, the inner surface and / or the outer surface of the fixed tube are welded over the entire circumference of the joint. 5. In welding using a plasma arc,
The method according to claim 3, wherein the first bead and the second bead are provided with a lap portion L to perform welding. 6. The method according to claim 5, wherein the lap portion L is 5 mm or more. 7. The method according to claim 5, wherein the welding current and / or the plasma gas flow rate at the lap portion are always kept lower than those at other welding points.