JPH0577047A - Method for butt-welding steel pipe - Google Patents

Abstract

PURPOSE:To omit a backing strip in a U-shaped groove. CONSTITUTION:In a butt-welding for steel pipe, a root surface of the groove is abutted and by using gas having four elements composed of 40-70% Ar, 3-10% CO2, 0.1-1% O2 and the balance He as the shield gas in the inner surface welding, a consumable electrode type arc welding is executed. The four-element gas having the above component ratio has higher potential gradient, generates more intense plasma gas stream and makes the energy density larger and can form the wider bead having deep depth of fusion in the comparison with single gas of Ar and CO2 or Ar-CO2 mixed gas usually used as a shield gas. Therefore, even if the core of a torch is shifted a little to the groove faced surfaces from the inner surface of the pipe, the welding metal from the inner surface of the pipe and the welding metal from the outer surface are surely joined and the reliability of the welded part can be improved. Further, the depth of the fusion can be obtd. at about 10mm, and the depth of the is made shallow by the above depth and the welding time from the outside can be shortened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a butt welding method for steel pipes.

[0002]

2. Description of the Related Art Butt welding of steel pipe is performed by MAG,
By MIG, TIG, or SAW, SMAW, etc., U groove (2) in Fig. 5a or V groove (21) in Fig. 5b and backing plate
One-sided welding from the outer surface using (3), or double-sided welding from the inner and outer surfaces using the X groove (22) in Fig. 5c and the H groove (23) in Fig. 5d. ing.

If the steel pipe (1) is used as a structural material, the existence of the backing metal (3) does not interfere, but if it is used as a fluid pipe, the backing metal (3) has a fluid resistance. There is a problem. There is also a welding method in which the backing metal (3) is omitted and the back wave is exposed from the outer surface to the inner surface of the joint part of the pipe by back wave welding, and then the groove is filled with weld metal.
In low alloy steel, backside welding by MAG or MIG from one side is quite difficult.

In order to fill the weld metal in the groove inside and outside the pipe by double-sided welding, the number of welding passes increases, which is inefficient. In addition, the filler metal that fills the groove, that is, the welding wire is supplied. It requires a large amount, resulting in high cost.

In order to omit the backing metal in the groove shape of one-sided welding, the Applicant performs MAG or MIG welding for one or two layers from the back side of the pipe, and then performs welding from the outside of the pipe. An attempt was made to fill the groove with filler material.

However, as shown in FIG. 3, MAG, MI
The cross-sectional shape of the 1-pass G weld bead (4) has a sharp tip and the penetration width and penetration depth of the tip are small. Therefore, if the core of the welding torch deviates from the groove alignment surface, the 1-pass weld bead (4) from the pipe inner surface and the weld metal (5) from the outer surface are not connected as shown in FIG. It turned out that he lacked sex.

Applicants have found that Ar 40-70%, CO ₂ 3-10
%, O ₂ 0.1 to 1% The known TIME (Transfered Ionized M) using a quaternary gas consisting of the balance He as a shield gas
oltenEnergy) process (Japanese Patent Laid-Open No. 59-45084)
Paying attention to the fact that the penetration depth and the penetration width increase,
By performing this welding process on the inner surface welding, a welding method that can omit the backing metal (3) will be clarified.

[0008]

According to the present invention, in butt welding of steel pipes, Ar 40 to 70%, CO ₂ 3 to 10%, and O ₂ 0.1 to 1 are used.
%, The remaining gas He is used as a shield gas to perform a consumable electrode type arc welding over the entire circumference of the inner surface of the pipe for a single pass to form a single weld bead, and the groove is welded with the weld metal on the outer surface. fill in.

[0009]

[Action and effect] Ar 40-70%, CO ₂ 3-10%, O ₂
The consumable electrode type arc welding using a quaternary gas consisting of 0.1 to 1% and the balance He as a shield gas, so-called TIMEE process, is commonly used as a shield gas such as Ar, CO ₂ alone gas or Ar- Generates a strong plasma flow having a higher potential gradient and a higher energy density than the CO ₂ mixed gas. Further, since the generated arc can be formed into a stable rotation arc, it is possible to obtain a wide bead with deep penetration.

Therefore, when the TIME process is applied to the inner surface of the pipe, a wide bead having a deep penetration can be formed even if the core of the torch is slightly displaced. ) And the weld metal (5) from the outer surface are reliably connected, and the reliability of the welded portion can be improved.

The penetration depth in the TIME process can be about 10 mm, and the groove depth can be reduced correspondingly, and the welding time from the outside can be shortened.

[0012]

EXAMPLES Two steel pipes to be welded were mounted on a turning roller, and the root surfaces of the grooves were brought into contact with each other and rotated, and automatic welding was carried out by a welding torch held on a manipulator.

The following data is shown. Steel pipe material SCW490-CF (JIS G5201) Outer diameter 500mm Wall thickness 50mm

Groove (U groove) Groove depth 40 mm Groove angle 4 ° Root face length 10 mm Root interval 0 mm

Inner surface welding (TIME process) Shield gas component ratio Ar 40%, CO ₂ 3%, O ₂ 0.1%, balance H
e Shield gas usage 20 liters / min Consumable electrode wire Diameter 1.2 mm Wire supply 20 m / min Current 400A Voltage 44V Welding speed 270 mm / min Number of passes 1 pass

External surface welding CO ₂ shield welding Number of passes: 11 passes

According to the above welding conditions, as shown in FIG.
Butt welding in which the inner surface one-pass weld bead (4) and the outer surface weld metal (5) were completely connected was realized.

The quaternary gas produced by the TIME process increases the arc voltage by increasing the arc voltage by adding He, which has a large potential gradient, in addition to Ar, which is a general MAG shielding gas. By increasing the plasma flow and energy to deepen the rigidity and penetration of the arc, it is possible to obtain the arc physical phenomenon that the droplet exists only in the arc plasma column. O ₂ is necessary to facilitate ionization of these gases, and CO ₂ is important for increasing the rigidity of the arc plasma and increasing the penetration. 4-way gas by T.I.M.E process is mixed in a ratio such as to exhibit the characteristics of the four gas is excellent, respectively, the ratio is Ar 40~70%, CO ₂ 3~10
%, O ₂ 0.1 to 1%, and the balance He.

If the Ar content is 40% or less, the arc voltage will be high and the arc stability will be poor, and the amount of spatter will be large. If the Ar content is 70% or more, it will be difficult to exhibit the characteristics of the time process. If CO ₂ is 3% or less, it is difficult to generate arc concentration and rigidity.
If it is above, the arc voltage will rise and the amount of spatter and the amount of slag will become large. If O ₂ is 0.1 or less, the arc voltage cannot be lowered, and if it is 1% or more, the amount of slag and the amount of spatter increase significantly. He
If the ratio is less than the minimum value of the mixing ratio, the spread of the arc is small and the amount of energy generated is a little, and if it is more than the maximum value of the mixing ratio, the arc voltage rises significantly, causing spatter and lack of stability. Occurs.

By separating the root surfaces of the grooves of the steel pipes to be weld-joined from each other by 2 to 4 mm, the welding torch is weaved during the TIME process to weld the inner surfaces of the pipes. The same effect as described above is achieved.

The present invention is not limited to the configuration of the above embodiment, and various modifications can be made within the scope of the claims.

[Brief description of drawings]

FIG. 1 is a sectional view of a welded joint manufactured by the welding method of the present invention.

FIG. 2 is a cross-sectional view of a 1 pass bead according to the TIME process.

FIG. 3 is a cross-sectional view of a 1-pass bead of MAG or MIG.

FIG. 4 is a cross-sectional view of the welded joint in a state where the inner surface welding position is deviated from the groove butting surface.

FIG. 5 is a sectional view of a groove shape.

[Explanation of symbols]

 (1) Steel pipe (2) Groove

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[Procedure amendment]

[Submission date] November 12, 1991

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

[Procedure amendment]

[Submission date] June 11, 1992

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Kato 488-11 Nakamachi, Kodaira-shi, Tokyo (72) Inventor Hobo Kuura 8-11-10-3-10 Nishimaiko, Tarumi-ku, Kobe-shi, Hyogo Prefecture

Claims (1)

[Claims] 1. Ar 40 to 70 in butt welding of steel pipes.
%, CO ₂ 3 to 10%, O ₂ 0.1 to 1%, and the balance He as a shield gas, a consumable electrode type arc welding is performed for only one pass over the entire circumference of the inner surface of the pipe to form a further welding bead. Butt welding method for steel pipes in which a groove is formed and the groove is filled with weld metal by external surface welding.