JPH0550235A - Welding method for steel tube - Google Patents

Abstract

PURPOSE:To improve the welding production efficiency of a steel tube by executing submerged arc welding to the outside surface side of a press formed tube under a specific welding condition. CONSTITUTION:After a plate-like steel plate is formed in a circular shape by press working, at the time of executing welding of the inside and the outside surfaces of a tube along a seam in the longitudinal direction of the tube, tack welding and submerged arc welding of the outside surface side are executed by the same welding pass of the beginning. In this case, at the time of executing submerged arc welding of the outside surface side, the welding heat input quantity and groove depth of the inside surface side are set to a range of oblique lines shown in the figure. In such a way, the number of welding passes can be reduced, and the production efficiency can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a large diameter welded steel pipe, and more particularly to a method for efficiently performing seam welding after forming a steel pipe by a UOE process or the like.

[0002]

2. Description of the Related Art A large diameter steel pipe is manufactured by a UOE method, a continuous forming method,
Or it is classified as a bending method. Regardless of which forming method is adopted, the steel pipe after forming is generally subjected to independent welding stages in the order of tack welding → inner surface welding → outer surface welding. For the main welding of the inner and outer surfaces of the steel pipe, multi-electrode submerged arc welding (SAW) using two or more electrodes is generally adopted in order to achieve high efficiency and high speed.

In recent years, in the seam welding method for steel pipes, various welding methods have been proposed for high efficiency, high quality and high speed. For example, in Japanese Examined Patent Publication No. 63-17554, after U → O molding, the inner surface side groove has an asymmetrical shape with a smaller cross-sectional area than the outer side groove, the inner surface side is subjected to submerged arc welding, and the outer surface side is There is a disclosure of a method in which the first layer is subjected to MIG welding with a predetermined current and then the second layer is subjected to submerged arc welding.

In Japanese Patent Laid-Open No. 61-253174, tack welding is omitted and main welding from the outer surface of the first-stage pipe is performed by plasma arc welding which does not require a filler material.
20 to 150 mm downstream side, TIG welding is performed from the inner surface side to smooth the back bead generated on the inner surface of the pipe, and finally TI welding is performed to sufficiently build up the outer surface of the pipe during the same pass.
There is a disclosure of a welding method in which the number of welding passes and the number of welding wires are reduced by performing G, MIG, or submerged arc.

Further, in Japanese Patent Publication No. 2-52586, in producing solid and clad steel pipes such as stainless steel, nickel-base alloy steel and non-ferrous metal as UOE steel pipes, a blank pipe formed by U-forming after U-forming is By performing TIG welding from the inner surface side, simultaneously performing plasma welding from the outer surface side, and further performing TIG or MIG welding on the plasma welding from the outer surface side, efficient welding is performed, and welding such as welding cracks and slag inclusion are also performed. There is a disclosure of a welding method that eliminates defects.

[0006]

However, the welding method disclosed in Japanese Patent Publication No. Sho 63-17554 is basically the same as the conventional method except that the steps of tack welding (from the outer surface side) → inner surface welding → outer surface welding are performed. In addition, the setup / refilling work for each welding stage is required, which causes a problem that the work is not efficient. Further, the above-mentioned JP-A-61-253
In the welding methods of Japanese Patent Publication No. 174 and Japanese Patent Publication No. 2-52586, the cost of the welding material can be reduced, but since the welding method inserts plasma welding into the welding path, the overall welding speed is increased by this plasma welding. Since the rate is controlled and the welding speed is about 50 cm / min at the maximum, the number of welding passes can be reduced by simultaneous welding, but as a result, such a high efficiency cannot be expected.

[0007] Therefore, the main object of the present invention is to review a conventional welding sequence to reduce the number of welding passes and, at the same time, to control a welding heat input amount and a groove depth. Is provided.

[0008]

[Means for Solving the Problems] The above-mentioned problems are solved by at least temporary welding and outer surface welding when the inner and outer surfaces of a pipe are welded along a joint in the pipe longitudinal direction after a plate-shaped steel plate is formed into a cylindrical shape by press working. Side submerged arc welding is performed in the same welding pass, then inner surface side submerged arc welding is performed, and at the time of the outer surface side submerged arc welding, the welding heat input and the inner surface side groove depth are shown in FIG. The problem can be solved by setting the shaded area.

[0009]

[Function] In the conventional submerged arc welding method, the inner surface is basically welded first and then the lower surface (pipe inner surface side).
After forming the inner bead on the outer surface, by welding the outer surface side,
Prevents burn-through during external surface welding. On the other hand, in the case of the welding method in which tack welding is omitted as in JP-A-61-253174, it is still difficult to stabilize the abutting state of both edges of the steel plates to be welded at the time of outer surface side welding. Offset due to the deviation generated during welding,
Since welding defects such as bead cracks may occur, it is not a good idea to omit the tack welding pass. Therefore, in the present invention, first, in order to reduce the number of welding passes, welding which was conventionally performed in the order of inner surface side welding → outer surface side welding is performed in the order of outer surface side welding → inner surface side welding, and temporarily performed first. Adhesive welding and outer surface side welding can be continuously performed in the same pass. However, when the steps are performed in this order, the inner surface bead is not formed during the outer surface side welding, and thus the burn-through is likely to occur. Therefore, by controlling the relationship between the welding heat input and the groove depth within the range shown in FIG. 1 according to each plate thickness, the required penetration amount is secured and the burn-through is prevented.

[0010]

EXAMPLES The present invention will be described in detail below based on examples. In FIG. 2, the cylindrical steel pipe 1 is a steel pipe manufactured into a cylindrical shape by the UO pressing method. In the UO press, the edge planer is used to cut into a predetermined plate width, the groove is processed with high precision, and then only the plate end is bent with the clipping press. Then, after being formed into a U shape by U press, it is formed into an O shape to obtain a cylindrical tube having a predetermined shape. The cylindrical steel pipe 1 is subjected to a cleaning and drying process after forming, and then enters a welding process shown in the drawing. The cylindrical steel pipe 1 traveling along the guide rolls 4, 4, ... Is subjected to tack welding by the tack welding torch 3 during one pass, and is jointed by the multi-electrode submerged arc welder 2 at the subsequent stage. Submerged arc welding is performed along the outer surface side of 1a.

The tack welding is gas shielded arc welding using carbon dioxide gas or carbon dioxide gas + Ar gas,
The welding method may be either a continuous tacking method or an intermittent tacking method. According to the continuous tacking method, the welding speed can be remarkably increased, but as shown in FIG. 4, a good bead range in which the stapling bead or the humping bead does not occur as the tacking speed increases. Since the arc voltage range is narrowed at the same time as the arc voltage is narrowed, it is important to operate under close control. The diameter of the wire used is in the range of about φ2.4 to φ4.0 mm, and the arc current is in the range of about 600A to 1300A, depending on the plate thickness. The flow rate of the shielding gas is 50 l
/ min to 100 l / min.

Table 1 shows a summary of the examples of the tack welding conditions by plate thickness in this embodiment.

[0013]

[Table 1]

A multi-electrode submerged arc welding machine 2 is disposed in front of the cylindrical steel pipe 1 in the traveling direction with a separation distance 1 of the tack welding torch 3. The separation distance l is 10
The range is from 00 to 2000 mm. When it is less than 1000 mm, spatter of tack welding adheres to the submerged arc welder 2, causes a failure in wire feeding, and cannot secure a space for groove-like flux dispersion. On the other hand, if it exceeds 2000 mm, it will come out of the constraint of the temporary tacking continuous tightening machine (cage roll), causing angular deformation of the seam during scavenged arc welding, causing solidification cracking in the weld. .. Further, when the twist of the seam portion is large, the seam following of the subsequent welding head itself becomes impossible.

In the illustrated example, the submerged arc welding machine 2 in this embodiment has six electrodes, but the number of electrodes can be set appropriately according to the plate thickness, welding speed and the like. In order to suppress the arc interference and keep the molten pool stable in accordance with a usual example, a combination of direct current and alternating current or a phase difference in the case of alternating current and alternating current is provided.

The welding conditions for submerged arc welding differ depending on the number of electrodes, plate thickness, etc., but the current is about 500 to 1600 A for each electrode, the voltage is 30 to 50 V, and the welding speed is 100 to 500 cm / min. Wire diameter is φ4.0
The range is φ8.0 mm.

In this embodiment, immediately after tack welding,
Since the outer surface is welded, there is a concern that it will burn through from the back side. Therefore, the welding heat input amount and the inner surface side groove depth are managed according to the graph shown in FIG. Figure 1 is for each plate thickness
This shows the relationship between the welding heat input and the groove depth X corresponding to the plate thickness in order to secure the required amount of penetration P and perform outer surface side welding without causing burn-through. The symbols in FIG. 1 are, as shown in FIG. 2, T: base metal plate thickness,
P: Range of penetration amount necessary for welding one layer on the inner and outer surfaces of the base metal, X: Maximum groove depth on the inner surface side determined by plate thickness T and welding heat input to prevent burn-through ..

In the graph shown in FIG. 1, the line for each plate thickness shows the case where the X value at each plate thickness is changed from the value marked with ◯ to X = 0 and submerged arc welding is performed with 6 electrodes. Was determined as the appropriate amount of penetration required for. In addition, the range of the required penetration amount P in the figure is the optimum penetration amount on the outer surface side from the efficiency (welding speed) balance between the outer surface tacking-SAW welding line and the lower surface inner surface welding line in consideration of the operation efficiency of the mill. Is set.

Table 2 shows examples of welding conditions for each plate thickness in this embodiment.

[0020]

[Table 2]

After the above-mentioned outer surface side welding is completed, subsequently, the inner surface side welding is performed in the next welding pass. Inner surface side welding
Submerged arc welding is performed in the same way as outer surface welding,
Regarding the welding conditions and the like, the welding can be performed according to the above-mentioned outer surface side welding.

[Example] With respect to a steel pipe that was O-formed after U-forming, various internal surface groove depths and welding heat input amounts were changed in the range of a plate thickness of 6 to 40 mm, and the presence or absence of burn-through and the penetration depth were investigated. I went. The results are shown in Table 3.

[0023]

[Table 3]

From Table 3, it was found that when there was a relationship between X plotted on each plate thickness line and the heat input amount, there was no burn-through, the penetration depth was appropriate, and good welding was performed. It

[0025]

As described above, according to the present invention, since the outer surface side welding is performed prior to the inner surface side welding, the tack welding and the outer surface side welding can be performed in the same welding pass. The production efficiency can be improved by reducing the number of passes. In addition, since the heat input amount and the groove depth are precisely controlled during welding on the outer surface side, burn-through does not occur.

[Brief description of drawings]

FIG. 1 is a relationship diagram of welding heat input and groove depth for each plate thickness.

FIG. 2 is an explanatory diagram of symbols in FIG.

FIG. 3 is a perspective view of tack welding and outer surface side welding in the present embodiment.

FIG. 4 is a diagram showing the relationship between tacking speed and arc voltage in tack welding.

[Explanation of symbols]

1 ... Cylindrical steel pipe, 2 ... Submerged arc welder, 3 ...
Temporary welding torch, 4 ... Guide roll

Claims (1)

[Claims] 1. When a plate-shaped steel sheet is formed into a cylindrical shape by press working and then the inner and outer surfaces of the pipe are welded along a joint in the longitudinal direction of the pipe, at least tack welding and submerged arc welding on the outer surface are the same. It is performed by a welding pass, and then submerged arc welding on the inner surface side is performed, and at the time of the submerged arc welding on the outer surface side, the welding heat input amount and the inner surface side groove depth are set within the range of the diagonal line in FIG. Welding method for steel pipes.