JP3180257B2 - Inner surface seam welding method for clad steel pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention uses a clad steel sheet obtained by bonding a stainless steel or a high Ni-based alloy steel having excellent corrosion resistance to a surface layer of a low alloy steel by rolling and pressure bonding, and forming a clad steel pipe by a method such as UOE. It relates to the inner seam welding method for manufacturing.

[0002]

2. Description of the Related Art In recent years, the environment for developing petroleum resources has become severe, and the corrosion resistance of line pipes and the like laid has been required. However, if all the line pipes to be laid are made of stainless steel or high alloy steel, the cost is not only enormous, but also because the strength is lower than that of low alloy steel, the wall thickness is increased due to strength. It is disadvantageous because it is necessary. Therefore, for economical practical use, stainless steel or high Ni alloy steel is used for the inner surface where corrosion resistance is required, and conventional low alloy steel is used for the remaining outer surface, which has both corrosion resistance and strength. Clad steel pipes are gaining attention.

[0003] The clad steel pipe is made of stainless steel or high N
After pressing the i-based alloy steel and low alloy steel by rolling etc.,
Usually, a tube body is formed by the UOE method so that the clad material is on the inside, a groove is formed on an end face in a longitudinal direction, and the groove portion is butted and the inner and outer surfaces are seam-welded to produce a clad steel pipe. . However, the inner surface welding of the clad steel pipe has many welding problems because the low alloy steel and the high alloy steel are layered. Generally, welding is performed using a low-alloy welding wire for the low-alloy steel groove and a high-alloy welding wire for the high-alloy steel groove. In welding, it is necessary to perform welding with a small dilution ratio and few welding defects.

However, taking the inner surface side welding method used here as an example, see JP-A-59-13719.
In Japanese Patent Publication No. 1 (1996), in welding stainless clad steel pipes, the butt portion is an X-shaped groove, and the inner surface side is a two-step groove in which the stainless steel portion is further reduced in thickness to a certain width.
A welding method is disclosed in which a low alloy steel groove portion is subjected to a submerged method, and a stainless steel groove portion is subjected to band arc welding with a band electrode to reduce a dilution ratio. However, in this method, it is necessary to remove the slag from the low alloy steel welded portion before welding the stainless steel portion, and there is a concern that the productivity may be reduced. In addition, Japanese Unexamined Patent Publication
Japanese Patent Application Laid-Open No. 3-10095 proposes that a depth and an angle of an X-shaped groove can be designated to enable one-run welding by MIG welding of an inner carbon steel part and submerging of a high alloy removed part. That is, the publication states that the removal of the width that does not interfere with the inner groove of the carbon steel at the butted portion of the steel reduces the dilution ratio at the time of welding, and that the welding speed is increased by the combination of the MIG method and the SAW method. It is planning to make it. However, when ordinary submerged welding is applied to the high alloy steel groove, the welding current becomes high in order to achieve high-speed welding, and high dilution is a concern. Japanese Patent Application Laid-Open No. 60-154875 proposes a method in which a low-alloy steel portion having a two-step groove is welded by submerging and a high-alloy steel groove portion is multi-layer welded by TIG welding. However, this method also requires the removal of slag after the welding of the low-alloy steel portion on the inner surface, so there is a concern that the productivity may be reduced. Of course, the application of TIG welding to the trapezoidal groove portion is particularly difficult at the groove corner. There is a possibility that welding defects are likely to occur in the part. In addition, in TIG welding, the welding speed is as long as about 10 cm / min, which takes a long time, and there is a problem in that it is difficult to cope with an increasing demand inevitably due to a decrease in the production capacity of UOE itself.

[0005]

The groove shape on the inner surface side is 2
It is very useful as a method for manufacturing a clad steel pipe if the inner surface can be welded at high speed by one-run welding without using a step groove. In order to increase the welding speed, it is necessary to secure the amount of deposited metal per unit time.
It is conceivable to employ a MIG welding method that can apply a higher welding current than welding. However, especially in MIG welding using a high alloy wire, the bead shape tends to be poor due to the increase in speed and current, and in extreme cases, there is a possibility that defective fusion defects occur between layers during multilayer welding. is there. This is because the weld metal is exposed to a high temperature even after the end of welding, so that an oxide film such as Cr and Ti is formed on the bead surface, and the time required for removing the oxide film is effective in improving productivity. Did not. In addition, it is difficult to completely prevent the occurrence of spatter in MIG welding. In particular, since high-alloy welding wires contain a large amount of low-melting-point Ni components, scattered spatter adheres to the surface. There was a drawback that it took time. Furthermore, weaving is necessary for welding the surface layer where the groove width is wide, but under conditions of high speed and high current, the weaving width and speed are larger and higher, so that the viewpoint of bead formation and spattering is increased. Was also a problem.

An object of the present invention is to provide a MIG welding method which is excellent in bead forming ability and has few welding defects and spatter adhesion in the inner surface welding of a clad steel pipe using a high alloy welding wire.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and its gist is as follows. (1) A clad steel pipe whose outer surface is made of low alloy steel and whose inner surface is made of stainless steel or high Ni-based high alloy steel, etc. In the welding method, the middle electrode on the inner surface side is weaved in a direction perpendicular to the welding line direction, and two welding wires are arranged and welded to the succeeding electrode at right angles to the welding line direction. Inner seam welding method of clad steel pipe.

(2) The clad according to the above item 1, wherein the number of times of weaving of the intermediate electrode is 2 to 4 Hz, the width is 2 to 6 mm, and the distance between two wires of the succeeding electrode is 6 to 12 mm. Inner seam welding method for steel pipes. (3) The method for welding an inner surface seam of a clad steel pipe according to the above (1) or (2), wherein the leading electrode is welded by using a welding wire for low alloy, and the intermediate electrode and the trailing electrode are welded by using welding wire with flux for high alloy. .

(4) The groove angle on the inner surface side is 65 to 75
°, depth 8-10mm, and 2-3mm on the inner surface
The inner seam welding method for a clad steel pipe according to any one of the above items 1 to 3, characterized by having a high alloy steel of (1). Hereinafter, the present invention will be described in detail. FIG. 1 is a side view (a) of a welded portion and a schematic plan view (b) showing an example of an embodiment in which the inner surface seam welding of a clad steel pipe according to the present invention is performed in one run of three layers. FIG. 2 shows a cross section taken along the line AA 'in FIG. 1A, and FIG. 3 shows a groove shape. Here, 1 is a low alloy steel base material portion, 2 is a high alloy steel portion, 3 is a groove on the outer surface side, 4 is a groove on the inner surface side, 5 is a groove root portion, 6 is an outer side temporary tacking bead, 7 is a welding electrode (leading electrode) at the groove of the low alloy steel, 9 is a welding electrode (intermediate electrode) at the boundary between the low alloy steel and the high alloy steel, 11 is a weaving mechanism for the intermediate electrode 9, and 12 is the final layer. In this case, two wires are arranged in a single electrode in a state of being electrically insulated. 8,1
0, 13, 14 are welding wires, 8 is a welding wire for low alloy steel, 10, 13, and 14 is a flux-cored welding wire for high alloy steel, 15, 16, 17, and 18 are welding arcs of each electrode. , 19, 20, and 21 indicate the MI of each electrode.
G welding beads, 22, and 23 are welding slags formed by flux-cored welding wires.

In FIG. 1, first, tack welding 6 of a groove 3 of a low alloy steel base material portion on the outer surface side is performed. This tack welding,
This is welding that is usually performed when manufacturing a UO steel pipe, and is not particularly limited in the present invention. After that, the low-alloy steel groove portion of the groove 4 is welded to the leading electrode 7 on the inner surface side by using a low-alloy steel welding wire 8 to form a first layer weld bead 1
9 is formed. At this time, it is necessary to adjust the amount of the weld metal so that the amount of the weld metal is too large to melt the high alloy steel portion.

Next, a second intermediate bead 20 is formed to a position near the surface of the high alloy steel 2 using a flux-cored welding wire 10 for high alloy steel as the intermediate electrode 9.
Here, the first feature of the present invention is to weave the intermediate electrode in a direction perpendicular to the direction of the welding line. That is, the groove shape after the welding of the first layer has a trapezoidal shape. If weaving is not performed, the welding arc acts directly on the center of the low alloy steel welding bead, so that a high dilution ratio or trapezoidal opening is required. This is because there is a tendency that a welding defect is easily generated at the corner of the tip. Therefore, by performing weaving, the arc point constantly moves in the direction perpendicular to the direction of the welding line, so that the intermediate layer having a low dilution ratio and few welding defects can be welded.

The number of times of weaving of the intermediate electrode is 2 to 4H
z and the amplitude were limited to 2 to 6 mm. The reason is that if the number of times of weaving is less than 2 Hz, the number of times of weaving is too slow, so that defective fusion defects are sometimes found at the corners of the trapezoidal groove. This is because the droplets are sputtered by inertia, which tends to promote spatter scattering. On the other hand, the reason for limiting the amplitude of the weaving to the above range is that if the amplitude is less than 2 mm, the amplitude is smaller than the groove shape shown in FIG. 3, so that it is difficult to completely prevent welding defects at the corners. On the contrary, if it exceeds 6 mm, the amplitude becomes too large, the arc acts on the surface of the high alloy steel, and the fluctuation of the welding voltage becomes large. still,
The welding wire was limited to a flux-cored welding wire. The reason is that a weld bead without surface oxidation can be obtained because the bead surface after welding is covered with slag.

Further, without removing the welding slag generated in the second layer, a third-layer final layer bead 21 is formed on the succeeding electrode 12 by using a flux-cored welding wire for high alloy steel. A second feature of the present invention is that the welding wires are arranged at right angles to the welding line direction and welded. That is, the decorative weld bead of the final layer needs to form a wide and good weld bead, and in the conventional welding of low alloy steel, weaving is generally applied. However, it has been clarified that the application of weaving is not always preferable in aiming at more efficient welding of high alloy steel as in the present invention. The reason is,
When weaving a wide bead using a welding wire for high alloy steel by weaving, the occurrence of welding spatter becomes remarkable with an increase in welding speed, and it becomes difficult to secure a good bead shape. . Therefore, the present invention employs a method of welding by arranging two welding wires at right angles to the welding line direction without using weaving for welding the final layer (hereinafter referred to as twin arc). According to this method, a wide bead can be formed without performing weaving, and the generation of welding spatter can be extremely reduced even at a high welding speed.

In the present invention, the wire interval between the two twin arcs is limited to the range of 6 to 12 mm. The reason is that if the length is less than 6 mm, the bead width becomes narrow because the wire interval is narrow with respect to the above groove shape, and it is impossible to completely cover the bead of the intermediate layer. The molten pool by wire is divided into each,
This is because it becomes difficult to secure a smooth final layer weld bead. In the present invention, the welding wire used for the third layer is also limited to the flux-cored welding wire. The reason is that since the bead surface is covered with slag, a good final layer decorative weld bead without surface oxidation can be obtained.

Incidentally, in order to realize the above-mentioned inner surface seam welding by three-layer one-run MIG welding, the inner surface groove shape has an angle of 65 to 75 ° and a groove depth of 8 to 10 mm.
And it was set as the range which has a high alloy steel of 2-3 mm on the inner surface. The reason is that the groove angle is less than 65 ° and the groove depth is 8
If it is less than mm, the groove cross section is too small to make welding difficult. Conversely, if the angle is more than 75 ° and the groove depth is more than 10 mm, the current balance in each layer welding is large. This is because good welding results cannot be obtained. In addition, the reason why the thickness of the high alloy steel portion is set to the range of 2 to 3 mm is that if the thickness is less than 2 mm, the thickness of the high alloy steel portion becomes too thin, so that the life as a clad steel pipe is shortened. On the contrary, if the thickness exceeds 3 mm, the thickness of the high alloy steel portion is too large, and the economic effect as a clad steel pipe is reduced, so that the practicality is reduced.

After the welding of the inner surface is completed, welding is performed to the groove 3 on the outer surface side by using a welding wire for a low alloy to complete the seam welding of the clad steel pipe. The welding here is a normal U
A multi-electrode submerged welding method similar to the O process can be applied, and is not particularly limited in the present invention.

[0017]

Next, examples of the present invention will be described. Outer diameter is 2
0 inch, wall thickness 20 mm, 3 mm of the inner surface of which is made of a high alloy steel of Incoloy 825, is processed into a groove shape as shown in FIG. 3 and welded into the outer side groove using a welding wire shown in Table 1. After performing the tack welding at a heat of 3.1 kJ / cm, a MIG welding test of three runs of one layer on the inner surface side was performed. The shielding gas is 20% CO ₂ +8 for all three electrodes.
Using a 0% Ar composition gas, the welding current, voltage and welding speed conditions of the first layer, the middle layer and the last layer are kept constant, and the type of welding wire applied to the middle layer and the last layer, or the presence or absence of weaving, and further, The evaluation was performed on the wire spacing and welding results in the twin arc of the final layer.
The evaluation was performed by generation of spatter during welding and the state of adhesion to the surface of the high alloy steel, the appearance of the weld bead of each layer, the X-ray inspection of the weld bead, and the observation of the cross section of the weld.

Tables 2 and 3 (continued from Table 2) show combinations of test conditions and evaluation results. In the table, in the results of the welding of the intermediate layer, ○ indicates that the internal quality, appearance, bead surface oxidation, and welding spatter resistance are good, and △ indicates that welding defects occur rarely, and □ indicates Indicates that the bead surface oxidation is remarkable, Δ indicates that the welding arc becomes unstable, and X indicates that welding defects are likely to occur. On the other hand, in the welding result of the final layer, the mark ○ is as good as the intermediate layer, the mark △ is good in the inner quality, but the bead shape is poor, the mark □ is the bead surface is partially oxidized, The symbol “◇” indicates that the generation of spatter and adhesion to the surface were remarkable, and the symbol “X” indicates the generation of welding defects.

In the example of the present invention, a flux-cored welding wire is used for the intermediate layer and the final layer, an amplitude of 2 to 6 mm and a weaving frequency of 2 to 4 Hz are used for the intermediate layer, and the distance between the two wires is 6 to 6 in the final layer. By using a twin arc of 12 mm, good results can be obtained not only in the internal quality of the welded portion, but also in any of the appearance, the bead surface oxidation resistance, and the welding spatter resistance.

On the other hand, in the test symbol H in which no weaving was applied to the intermediate layer, a linear slag entrainment defect sometimes occurred at the corner of the groove on the trapezoid. In addition, even if weaving is applied, the occurrence of welding defects cannot be completely prevented with the test symbols J and K in which the weaving conditions are out of the above-mentioned range. It acts up to the shoulder of the shape groove, and the welding voltage becomes unstable. Further, the test symbol I using a solid wire for the intermediate layer was not preferable because the surface oxidation of the intermediate layer bead affected the final layer. Next, in the test symbols N and O in which weaving was applied without applying the twin arc to the final layer, a large amount of welding spatter occurred regardless of the type of the welding wire, and adhered much to the surface of the high alloy steel. In addition, when the welding wire is a solid wire even when the twin arc is applied, the entire slag amount is insufficient even when the flux-cored welding wire is applied to the intermediate layer. Was. Further, even when the twin arc is applied, the test symbol P in which the distance between the two welding wires is too small results in a convex bead having a narrow bead width, and cannot completely cover the bead of the intermediate layer. Formation became difficult. Conversely, the test code Q is too wide
In the case of the above, the weld bead formed by the two welding wires was formed independently in parallel with each other, so that it was easy to cause welding defects.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

As described above, according to the present invention, in the inner surface seam welding of a clad steel pipe using a high alloy welding wire, it is possible to prevent welding defects and spatter adhesion and to obtain a good weld with less surface oxidation. Can be Compared with the conventional TIG welding method or the two-step groove method, the welding efficiency can be greatly improved and existing groove processing equipment can be used effectively.
The effect on the industry is great.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view (a) and a schematic plan view (b) showing an example of an embodiment in which the inner surface seam welding of a clad steel pipe according to the present invention is performed in one run of three layers.

FIG. 2 is a diagram showing a cross section taken along the line AA ′ of FIG.

FIG. 3 is a diagram showing a groove shape.

[Explanation of symbols]

 1: Low alloy steel base material 2: High alloy steel part 3: Outer side groove 4: Inner side groove 5: Groove root part 6: Outer side temporary tacking bead 7: Lead electrode 8: Welding for low alloy steel Wire 9: Intermediate electrode 10: High alloy steel welding wire 11: Intermediate electrode weaving mechanism 12: Trailing electrode 13: High alloy steel welding wire 14: High alloy steel welding wire 15: Leading electrode welding arc 16: Intermediate electrode welding arc 17: Trailing electrode welding arc 18: Trailing electrode welding arc 19: First layer welding bead 20: Middle layer welding bead 21: Final layer welding bead 22: Middle layer welding slag 23 : Welding slag of the last layer

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI B23K 9/173 B23K 9/173 E 35/34 35/34 (72) Inventor Masayoshi Kitamura 20-1 Shintomi, Futtsu-shi, Chiba New Japan (72) Inventor Yukihiko Horii 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation Technology Development Headquarters (56) References JP-A-55-112181 (JP, A) JP-A-5-220573 (JP, A) JP-A-61-262484 (JP, A) JP-A-62-45480 (JP, A) JP-A-58-47573 (JP, A) 40002 (JP, A) JP-A-3-94980 (JP, A) JP-A-61-286072 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B23K 9/23 B21C 37 / 14 B23K 9/00 B23K 9/025 B23K 9/12 B23K 9/173 B23K 35/34

Claims (4)

(57) [Claims] 1. A clad in which a clad steel pipe whose outer surface is made of low alloy steel and whose inner surface is made of stainless steel or high Ni-based high alloy steel is welded by three-electrode one-run MIG welding and the outer surface is welded by multi-electrode submerging. In the method of welding steel pipes, weaving the inner electrode on the inner surface in a direction perpendicular to the direction of the welding line and arranging two welding wires at right angles to the direction of the welding line for the succeeding electrode and welding. Features a method of seam welding the inner surface of clad steel pipe. 2. The number of times of weaving of the intermediate electrode is 2 to 4.
The inner seam welding method for a clad steel pipe according to claim 1, wherein the welding is performed at a frequency of 2 Hz to 6 mm in Hz, and a distance between two wires of the succeeding electrode is set to 6 to 12 mm. 3. The inner surface of a clad steel pipe according to claim 1, wherein the leading electrode is welded using a low alloy welding wire, and the intermediate electrode and the trailing electrode are welded using a high alloy flux-cored welding wire. Seam welding method. 4. The high-alloy steel according to claim 1, wherein the groove angle on the inner surface side is 65 to 75 °, the depth is 8 to 10 mm, and a high alloy steel of 2 to 3 mm is provided on the inner surface. An inner seam welding method for a clad steel pipe according to any one of the above.