JPH04319075A - Inside seam welding method for high alloy clad steel pipe - Google Patents

Abstract

PURPOSE:To provide the MIG welding method with high efficiency without generation of an oxide film and spatter sticking on the bead surface in inside welding of a high alloy clad steel pipe according to this invention. CONSTITUTION:In multiple electrode MIG multilayer one-run inside seam welding of the high alloy clad steel pipe, conventional MIG welding is performed from a first layer to a layer right before a last electrode, welding type flux is dispersed extending over 2-8mm thickness and 60mm width with the bead as a center right after the layer bead right before the last electrode is formed, then, MIG welding of a last layer is performed, the last high alloy bead surface is covered by slag and the high alloy weld bead without generation of the oxide film and spatter sticking on the bead surface is obtained even in high- speed welding.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal seam welding method for manufacturing high-alloy clad steel plates and steel pipes based on Ni, Cr, etc.

0002

BACKGROUND OF THE INVENTION In recent years, as the oil resource development environment has become increasingly severe, corrosion resistance has become important for line pipes to be laid. However, the cost of constructing line pipes using high-alloy steel is enormous. Therefore, in order to be economically practical, only the inner side where corrosion resistance is required is made of a high alloy based on Ni and Cr, and the rest is made of conventional low alloy steel, which has both corrosion resistance and strength. High alloy clad steel pipe is applied.

[0003] This clad steel pipe is manufactured by cladding high-alloy steel and low-alloy steel, rolling and UOE processing, and seam welding the longitudinal end faces. Taking the seam welding method used here as an example,
As shown in Japanese Unexamined Patent Publication No. 59-137191, an X groove is provided on the welding surface, and the inner surface is submerged arc welded to a height that does not create a weld bead on the high alloy layer, and then the outer surface is submerged arc welded. Then, returning to the inner surface, the high alloy layer is welded at low dilution using a co-metallic wire. Therefore, in this method, the pipe handling work becomes more complicated than before, and there is a concern that productivity will decrease. On the other hand, in Japanese Patent Application Laid-open No. 60-154875, T
A method has been proposed in which this internal welding is performed using multi-layered IG welding. However, the welding speed of TIG welding is 10
cm/min, it takes a long time to weld to the finish layer, and productivity is low, making it difficult to meet increasing demand.

0004

[Problem to be solved by the invention] To improve this welding speed, it is necessary to increase the amount of wire deposited per unit time, and for this purpose, welding methods that can apply a higher welding current than TIG welding, such as MIG welding, are considered. It will be done. However, as welding speeds increase, welding input also increases, and the weld metal is exposed to high temperature conditions for a longer period of time after welding is completed. For this reason,
When a solid wire is used, the surface oxidation of the high alloy layer becomes significant, and a strong oxide film of Cr, Ti, etc. is formed on the bead surface. Because it takes a considerable amount of man-hours to clean the bead surface to remove this oxide film, it has not been very effective in improving overall productivity. Also,
MIG welding cannot completely prevent the occurrence of spatter, and especially when high-alloy wire based on Ni is used, high-Ni spatter, which has a low melting point, can reach the high-alloy cladding surface without an oxide film. Since it is easily fused, there were also problems in its processing. Therefore, in the present invention, the welded upper surface layer of high-alloy clad steel pipes, etc., can be coated with MI without the formation of a surface oxide film on the weld bead, which becomes a high-alloy layer, and without spatter adhesion.
This provides a G welding method.

[0005]

[Means for Solving the Problems] The present invention has been made to realize an internal MIG welding method for high-alloy clad steel pipes that solves the above-mentioned problems. In multi-electrode MIG multi-layer one-run inner seam welding of high-alloy clad steel pipes with a high-alloy layer on the top surface welded, normal MIG welding is performed from the first layer to the layer immediately before the final electrode, and Immediately after forming a layer bead, a molten flux is spread around the bead to a thickness of 2 mm to 8 mm and a width of 60 mm or more, and then MIG welding of the final layer is performed. be.

[0006]

[Operation] Fig. 1 is a schematic side view of a welded part showing an example of an embodiment in which inner seam welding of a high alloy clad steel pipe according to the present invention is carried out in three passes and one run. Also, Figure 2 is Figure 1A
, A' section. Here, 1,
3 and 5 are the first, second and third electrode torches, 2, 4 and 6 respectively.
are 1, 2, and 3 electrode wires, 7 is a high alloy layer, and 8 is a high alloy layer.
9, 10 and 11 are the 1st, 2nd and 11th, respectively.
3-electrode arc, 12, 13, 14 are each low alloy first
pass (hereinafter abbreviated as the first layer), high alloy second pass (hereinafter abbreviated as buffer layer, therefore the buffer layer is the layer immediately before the final electrode), high alloy third pass (hereinafter abbreviated as final layer), 15 is The final layer slag, 16 is a sputter, 17 is an outer surface tacking bead, 18 is a flux spreading device, and 19 is a molten type flux.

In FIG. 1, first, a first layer bead 12 is formed by MIG welding on the groove of a low alloy steel base material 8 using a low alloy wire 2 for the first electrode, and then a high alloy wire is used for the second electrode. 4 to form the buffer layer 13. Immediately after forming the buffer layer, the molten flux 19 is spread from the flux spreading device 18 around the bead to a thickness of 2 mm to 8 mm and a width of 60 mm or more, and then a high alloy solid wire 6 is used as the third electrode of the final layer. , perform MIG welding to form the final layer bead. With this configuration, the molten flux sprinkled on the welding part is melted by the third electrode arc 11, forms the final slag layer 15, and covers the surface of the final layer bead 14, so that a surface oxide film is formed. A high-alloy weld bead with no cracks can be obtained.

[0008] That is, the higher the welding speed, the higher the temperature of the produced weld metal even at a location away from the gas shield torch, and the oxidation progresses further until it is cooled, forming a strong oxide film. However, in the present invention, the molten flux sprinkled just before the final electrode is melted by the final electrode arc, and the generated slag covers the surface of the final layer weld metal, preventing oxidation from the atmosphere and preventing high alloys with no surface oxide film. In the vicinity of the weld where a weld bead is obtained and spatter is most likely to adhere, a thinly sprinkled molten flux acts as a buffer material to prevent spatter from adhering to the high alloy clad surface. This makes it possible to obtain a welded portion free from spatter adhesion.

[0009] After the inner surface welding is performed in this manner, the outer surface is welded using the conventional submerged arc welding method, thereby making it possible to manufacture high-alloy clad steel pipes with high efficiency. The reason why we limited the flux used here to molten type is that sintered type flux has a small bulk density and is blown away by the shielding gas used in the final electrode before it is melted by the arc, which makes the present invention effective. This is because it cannot be done. Furthermore, if the particle size of the melting type flux used here is coarser than 1 mm, arc ignition and defective melting tend to occur, so it is preferable to use powder or fine particles with a diameter of less than 1 mm. Although the composition of the flux is not particularly critical, it is better to avoid fluxes that have a melting point that is too high compared to weld metals, such as high-MgO fluxes, as they tend to cause poor melting.

[0010] In the present invention, the flux is sprayed at the position immediately before the final electrode after the formation of the layer, because when the molten flux is sprayed from the initial layer, the groove is filled with flux equal to the groove depth and the spraying thickness. This is because the molten slag is too thick, resulting in poor arc ignition at the next electrode, or in some cases, submerged arc welding. The reason why the thickness of the molten flux was limited to 2 mm to 8 mm is as follows. That is, if it is less than 2 mm,
Slag thickness when melted flux is 0.5
This is because when the thickness is less than 1 mm, the slag coverage on the bead surface becomes unstable, and the slag does not cover parts of the bead surface, forming an oxide film and generating bead protrusions. Further, if the thickness of the molten flux exceeds 8 mm, submerged arc welding may occur. Submerged arc welding has deeper penetration than gas-shielded arc welding, and when low-alloy wire is used in the layer immediately before the final electrode, the proportion of diluted high-alloy wire used in the final electrode increases, reducing corrosion resistance. This is not desirable as it may cause problems such as

[0011] Next, the molten flux spreading width must be at least 60 mm or more. This is because even if high-alloy wire is used to suppress welding input and minimize spatter generation, spatter will still adhere within 30 mm of one side of the weld line. The degree of spatter adhesion depends on welding conditions,
Although it depends on the size and temperature of the spatter, the shorter the distance from sputtering to adhering to the clad steel surface, the more likely it is to be fused to the surface without being able to solidify. Therefore, the width may be increased or decreased to 60 mm or more depending on the welding conditions. In addition,
Spatter may also occur when a high-alloy wire is used in the electrode immediately before the final layer, and it may be attached to the surface of the inner cladding layer, but when the arc is ignited within the groove, the spatter is captured on the side surface of the groove. It rarely sticks to surfaces and is not a problem.

0012

[Example] A groove shape as shown in Fig. 3 was made in a clad steel pipe with an outer diameter of 500 mm, a wall thickness of 20 mm, and 3 mm of the inner surface made of a high alloy layer of alloy 825, and a shielding gas of 80% Ar + 20% CO2 and a flow rate of 20 liters. /m
Using the wire shown in Table 1 and the flux shown in Table 2, one-run three-layer welding was performed on the inner surface under the welding conditions shown in Table 3, and the bead formation was evaluated. The molten flux was sprayed after the buffer layer was formed, but the comparative test No.
．． Only J was sprayed from the front of the first electrode (initial layer). In addition,
In the final layer, wire oscillation with an amplitude of about 15 mm is performed to widen the bead width.

[0013]

[Table 1]

[0014]

[Table 2]

[0015]

[Table 3]

[0016] Table 4 shows the welding results for each layer, and the evaluation of the arc ignition condition, the thickness of the generated slag, the final bead surface shape, the oxide film formation, and the degree of sputter adhesion to the cladding surface. Here, in the arc condition, ○ indicates stable arc ignition, △ indicates transition to submerged arc, × indicates arc breakage, and slag thickness is the measured value at the center of the bead. The mark ○ on the bead surface indicates that the bead is completely covered with slag, there is no oxide film formed, and the bead shape is good.The mark △ indicates that the oxide film is partially formed or the bead shape is somewhat unstable. Indicating formation or bead shape defects. Regarding spatter, those with almost no adhesion are marked with ○, those with sporadic adhesion are marked with △, and those with spatter adhering all over are marked with x.

[0017] In the example of the present invention, after the formation of the final layer, the molten flux was spread over a thickness of 2 mm to 8 mm and a width of 60 mm or more in test symbols A to E, in which the slag thickness in the final layer was ensured to be 0.5 mm or more. The final bead surface is completely covered with slag and no oxide film is formed.
A good bead appearance was exhibited, and there was almost no spatter adhesion to the cladding surface. On the other hand, in test code F, a comparative example in which the molten flux distribution thickness is thin and the distribution width is narrow, the final layer slag is as thin as 0.3 mm, and cannot stably cover the bead surface, resulting in partial There were areas where there was no slag coverage, and a protruding oxide film was formed. In addition, spatter penetrated through the molten flux layer and adhered near the bead, and sputter adhered sporadically at positions farther away than the spray width. In addition, in test symbol G, which used a molten flux that contained a large amount of coarse particles of 1 mm or more, the final electrode arc became unstable, causing short circuits and arc breaks, and a good bead could not be formed.

In test symbols H and J in which the molten flux was spread too thick, the electrode arc after the molten flux was spread became a submerged arc. That is,
In test symbol H, in which the thickness of the molten flux at the final electrode was 10 mm, the bead shape became unstable because the arc became a gas-shielded arc or shifted to a submerged arc. On the other hand, in test code J in which molten flux was sprayed from the front of the first electrode, the initial layer became a submerged arc, and the thickness of the generated slag was 3.8 m.
m, the second electrode arc ignition became unstable, welding became unstable, and the final bead could not be formed. In addition, test symbol I where no flux was sprayed
In this case, an oxide film was deposited on the bead surface and a large amount of spatter was deposited on the cladding layer surface.

[0019]

[Table 4]

[0020]

As described above, according to the present invention, it is possible to prevent the formation of an oxide film on the bead surface of the final high-alloy layer in seam welding of high-alloy clad steel pipes in which the welded upper surface is a high-alloy layer, and the adhesion of spatter. Moreover, compared to the conventional TIG welding method, the welding speed can be greatly improved, and the bead surface care can be reduced, which has a large labor-saving effect on industry.

[Brief explanation of drawings]

FIG. 1 is a schematic side view of a welded part showing an example of an embodiment in which inner seam welding of a high-alloy clad steel pipe according to the present invention is performed in three passes and one run.

FIG. 2 is a cross-sectional view of part A' in FIG. 1A.

[Figure 3] Outer diameter is 500mm, wall thickness is 20mm, including inner surface 3
U consisting of a high alloy cladding layer with mm of alloy 825
It is a figure showing the groove shape of an OE clad steel pipe.

[Explanation of symbols]

1 First electrode torch 2 First electrode wire 3 Second electrode torch 4 Second electrode wire 5 Third electrode torch 6 Third electrode wire 7 High alloy layer 8 Low alloy steel base material 9 First electrode arc 10 Second electrode arc 11 Third electrode arc 12 First layer 13 Buffer layer 14 Final layer 15 Final layer slag 16 Spatter 17 External basting bead 18 Flux spraying device 19 Melting type flux

Claims (1)

[Claims] [Claim 1] In multi-electrode MIG multilayer one-run inner seam welding of a high alloy clad steel pipe with a high alloy layer based on Ni, Cr, etc. A high alloy characterized in that MIG welding is performed, and immediately after forming a bead in the layer immediately before the final electrode, molten flux is spread around the bead to a thickness of 2 mm to 8 mm and a width of 60 mm or more, and then MIG welding of the final layer is performed. Method for welding inner seams of clad steel pipes.