JPH06285640A - Inner surface welding method for clad steel tube - Google Patents

Abstract

PURPOSE:To reduce a rate of dilution of a low alloy steel and weld metal by arranging a groove of the specific depth and angle on the inner surface side of X shape groove and welding with suppressing the welding quantity of low alloy part to the specific height from the boundary with high alloy steel. CONSTITUTION:X shape groove is machined at a seam part of clad steel tube consisting of an outer surface of low alloy steel 1 and an inner surface of high alloy 2 of stainless steel, high Ni alloy, etc. The inner surface is subjected to one run welding of three electrodes, subsequently the outer surface side to four electrode submerged welding so as to weld clad steel tube. At this time, the groove of 8-10mm depth t1, 65-75 deg. angle theta is arranged on the inner surface side of X shape groove. A low alloy part 1 of inner surface side is welded so that the welding metal quantity by low alloy welding wire is suppressed to the height t2 1-2mm lower than the boundary with the high alloy steel 2. The inner surface side is subjected to MIG welding with a welding speed of 35-45cm/min. By this method, at welding the initial layer of low alloy steel of inner surface side, melting of the groove part of high alloy steel is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a method such as UOE in which a clad steel plate obtained by rolling and pressure-bonding stainless steel having high corrosion resistance, high Ni alloy steel or the like to the surface layer of low alloy steel is used. The present invention relates to a seam welding method when manufacturing a steel pipe.

[0002]

2. Description of the Related Art In recent years, the environment for developing petroleum resources has become severe, and line pipes and the like to be laid have been required to have corrosion resistance. However, if all the line pipes to be laid are manufactured from stainless steel or high alloy steel, not only will the cost be extremely huge, but its strength will be lower than that of low alloy steel, so the wall thickness will be increased for strength design. Must be done, which is at an even greater disadvantage. Therefore, for economical commercialization, stainless steel or high Ni alloy steel is used for the inner surface side where corrosion resistance is required, and the remaining low alloy steel is used for the clad steel pipe that has both corrosion resistance and strength. Is becoming popular.

This clad steel pipe is made of stainless steel or high N
After crimping the i-based alloy steel and the low alloy steel by rolling etc.,
Usually, a clad steel pipe is manufactured by forming a clad material in the tube body by the UOE method so that the clad material is on the inside, and performing a groove processing on the end face in the longitudinal direction, and abutting the groove portions and seam welding the inner and outer surfaces. . However, as an example of the inner surface welding method used here, Japanese Patent Laid-Open No. 59-137.
In Japanese Patent No. 191, the groove shape on the inner surface side is a two-step groove,
It is disclosed that after submerged welding the low alloy steel portion with a welding wire for low alloy, welding on the outer surface side and further band arc welding the high alloy groove portion on the inner surface side with a strip electrode for high alloy are disclosed. ing. Also, JP-A-63-10095
According to Japanese Patent Laid-Open Publication No. 2004-242242, the groove shape on the inner surface side is a two-step groove, and the low alloy steel portion is MIG welded with a wire for carbon steel, and the high alloy removed portion is submerged welded with a cored wire or a solid wire for high alloy steel. Is disclosed. Further, Japanese Patent Laid-Open No. 60-154875 proposes a method in which a low alloy steel portion having a two-step groove is welded by submerge and a high alloy groove portion is multi-layer welded by TIG welding.

The above methods are all the same in that it is necessary to process the groove shape on the inner surface side into a two-step groove,
Therefore, the beveling machine used in a normal UOE cannot be used as it is, and it is necessary to reassemble the bite or the cutter of the beveling machine in each case, so that the production capacity of the UOE is unavoidably deteriorated. Further, in the processing, there is a problem that the uncut portion of the clad material is hardly permitted.

[0005]

The groove shape on the inner surface side is 2
The reason for forming the step groove is to prevent the occurrence of weld metal cracking due to partial melting of the clad material during welding of the low alloy steel portion. However, the processing of the two-step groove has the problems described in the previous section, and the possibility of causing the following welding problem due to the further two-step groove. First, since the groove width of the clad material part is wide, when the final layer is welded using a welding wire for high alloys, it is necessary to widen the bead width. You can not expect much speeding up. Secondly, since the groove width is wide, there is a concern that welding defects such as slag entrainment easily occur at the trapezoidal corners of the two-step groove. Thirdly, since the welding arc is likely to concentrate directly on the weld of the low alloy steel, the components of the weld metal are Ni and C even if a welding wire for high alloys is used.
The problem remains that components such as r are easily diluted.

Therefore, the present invention does not require a two-step groove forming of a groove shape and provides an inner surface welding method for a low alloy steel and a clad steel pipe having a small dilution rate of the weld metal even in welding of a clad material portion. The purpose is.

[0007]

The present invention is constructed to achieve the above object, and the gist thereof is as follows. (1) Forming an X-shaped groove on the seam part of a clad steel pipe made of a low alloy steel on the outer surface and a high alloy such as stainless steel or a high Ni alloy steel on the inner surface, and one run welding of three electrodes on the inner surface side,
After that, in the welding method of the clad steel pipe in which the outer surface side is welded by a four-electrode submerge, a groove with a depth t ₁ of 8 to 10 mm and an angle θ of 65 to 75 ° is provided on the inner surface side of the X-shaped groove. For the welding of the low alloy steel portion on the side, the amount of weld metal is t ₂ from the boundary with the high alloy steel by the welding wire for low alloy.
Is 1 A method for welding the inner surface of a clad steel pipe, which comprises welding while suppressing the height to 2 mm lower.

(2) The inner surface welding method for a clad steel pipe as recited in the aforementioned Item 1, wherein the inner surface side is MIG welded at a welding speed of 35 to 45 cm / min. (3) The thickness t ₃ of the high alloy steel portion on the inner surface of the clad steel pipe is 2
The inner surface welding method for a clad steel pipe according to the above 1 or 2, wherein the inner surface is 3 mm. The present invention will be described in detail below.

FIG. 1 is a welding cross section showing an example of an embodiment of seam welding of a clad steel pipe according to the present invention. FIG. 2 shows the groove shape of the seam portion of the clad steel pipe according to the present invention, and FIG.
Shows the order of welding in a schematic diagram. Where 1
Is a low alloy steel base metal part, 2 is a high alloy steel part, 3 is an outer surface groove,
Reference numeral 4 is an inner groove, 5 is a groove root portion, 6 is a temporary bead on the outer surface, 7 is a weld bead of a low alloy steel portion, 8 and 9 are weld beads of a high alloy steel portion, and 10 is a low bead on the outer surface side. The welding bead of the alloy steel groove part is shown.

The first feature of the present invention is the groove shape on the inner surface side shown in FIG. That is, the groove depth t ₁ on the inner surface side is 8
That is, the inner surface of the clad steel pipe can be welded with a V groove of 10 mm and an angle θ of 65 to 75 °. By the way, in a shallow and narrow groove material outside the above range, the welding current value of the low alloy steel portion and the high alloy steel groove portion becomes small, and the welding becomes unstable. On the contrary, when the groove depth is deeper than the above range and the angle becomes large, the welding current becomes too large.
In particular, it becomes difficult to form a weld bead in a groove portion of a high alloy steel using a welding wire for a high alloy. Therefore, if it is within the range of the groove shape described above, a great effect that the clad steel pipe can be manufactured by the same method as the manufacturing method in the normal low alloy steel pipe UO process can be expected.

Next, a welding embodiment of the clad steel pipe according to the present invention will be described. The welding is first performed by tack welding 6 of the groove 3 of the low alloy steel base material portion on the outer surface side using a welding wire for low alloy steel (Fig. 3a). This tack welding is a welding 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 on the inner surface side is subjected to first layer welding 7 using a welding wire for low-alloy steel (Fig. 3b). At this time, the amount of weld metal is the boundary of the high-alloy steel. From 1 to 2 mm lower. That is, it is necessary to secure t ₂ of 1 to ₂ mm (hereinafter, t _{2 is referred} to as the height of the first layer left). If the amount of the weld metal is too large to melt the groove portion of the high alloy steel, alloys such as Ni and Cr, which are the main components of the high alloy steel, are diluted and mixed in the weld metal to form martensite. This is because welding defects such as solidification cracking occur in the weld metal due to the generation of. The first layer is left with a height of 1-2 m
The reason why it is limited to m is that if it is less than 1 mm, the risk of melting the groove portion of the high alloy steel against the groove fluctuation increases, and conversely if it exceeds 2 mm, the groove shape is in the above range. On the other hand, it is necessary to make the welding current extremely low, which makes the welding unstable. The method to control the height of the first layer left against the groove accuracy is possible by measuring the groove depth and groove width in advance, or by using other groove shape measuring means. Is.

After welding the groove portion of the low alloy steel on the inner surface, the groove portion of the high alloy steel of groove 4 on the inner surface side is subjected to MIG welding of the second layer and the third layer using a welding wire for the high alloy steel. Perform steps 8 and 9 (Fig. 3c). In welding here, it is important that the composition of the weld metal is noble than the composition of the clad material,
Since the width of the groove is significantly smaller than that of welding using a two-step groove, and since two layers are welded with a welding wire for high alloys, low dilution welding is possible for the weld metal of the third layer.

Since the welding on the inner surface side enables 3-electrode 1-run welding by the MIG welding method, the welding speed is 3
The range was 5 to 45 cm / min. The welding speed is a parameter determined by the cross-sectional shape of the groove and the welding current. However, when the welding speed is less than 35 cm / min in the above-mentioned groove shape, the welding current of the first layer of low alloy steel becomes too small, which results in welding. Because it will be difficult. On the contrary, if the welding speed exceeds 45 cm / min, the welding current becomes high,
This is because spatter is significantly generated in the welding of the second and third layers using the welding wire for high alloys and it is not always preferable in terms of bead formation.

Further, the thickness t ₃ of the high alloy steel portion on the inner surface of the clad steel pipe targeted by the welding method of the present invention is set in the range of 2 to ₃ mm. If t ₃ is less than 2 mm, the thickness of the high alloy steel portion becomes too thin, which shortens the life as a clad steel pipe, and is impractical from the viewpoint of tolerance for misalignment in field welding, and conversely exceeds 3 mm. Since the thickness of the high alloy steel portion becomes too thick, the economical effect as a clad steel pipe is reduced and the practicality is reduced.

Further, welding 10 is performed on the groove 3 on the outer surface side by using a welding wire for low alloy (FIG. 3d). The welding here can be applied by the multi-electrode submerged welding method in a normal UO process, and is not particularly limited in the present invention.

[0016]

EXAMPLES Next, examples of the present invention will be described. Outer diameter is 2
An arc-shaped test piece was cut out from a clad steel pipe made of a high alloy steel having 0 inch, a wall thickness of 20 mm, and an inner surface of 3 mm and made of Incoloy 825, and a groove of the type shown in FIG. 4 and Table 1 was used. After using the welding materials shown in Table 2 and welding the temporary tack welding on the outer surface side under a constant condition of a welding heat input of 3.1 kJ / cm,
Welding was performed on the inner surface side. The welding speed on the inner surface side is 40 cm /
Shielding gas of Ar 80% + CO ₂ 20% was used for both the low alloy steel part and the high alloy steel part while keeping the min constant.
The welding conditions of the low alloy steel part were tested for various groove shapes shown in Table 1 by adjusting the welding current so that the initial layer residual height t ₂ was 0, 1, ₂ , 3 mm. The groove conditions, the height of the first layer left and the stability of the welding conditions were evaluated. Regarding the first layer weld material of the low alloy steel part according to the present invention, the second layer and the third layer were welded with a welding wire for high alloy.

Table 3 shows the groove conditions, the height of the first layer remaining and the welding conditions, and the welding results of the first layer. Here, in the welding result of the first layer, the ○ mark indicates that stable welding was possible, and the △ mark indicates that the first layer was manageable but the groove shape was 2
Since the welding current of the layer becomes too large, it is difficult to form beads or the occurrence of spatter increases (the expected current is shown in parentheses in the column of the welding current of the second layer in Table 3 as a reference value). ), □ indicates that welding of the first layer was possible but led to the occurrence of welding defects, and x indicates that welding became unstable because the welding current value of the first layer was extremely small.

In the examples of the present invention, in the test symbols A to J in which the groove angle is 65 to 75 ° and the groove depth is 8 to 10 mm, the high alloy steel portion is melted in the range of the height of the first layer remaining of 1 to 2 mm. It was possible and stable welding of the first layer was possible. On the other hand, in the test symbol K of the comparative example having a narrow groove angle, when the groove depth is 8 mm, the welding current becomes a small current of about 100 A and the welding arc becomes unstable when the first layer remaining height is 1 mm. No weld bead was obtained and welding defects due to poor fusion were found at the bottom of the penetration. Further, in the test symbol L having a groove depth of 12 mm and the initial layer remaining height of 3 mm, stable welding was possible, but similar to the test symbol K, the occurrence of welding defects was recognized. This is because the groove angle is narrow and the groove bottom cannot be sufficiently melted by the welding arc. Then, the groove angle is 70 °, the depth is 8 mm, and the height of the first layer is 0 m.
In the test symbol M with m, the welding arc was stable, but melting of the high alloy groove portion was observed in various places, and there was a concern that martensite was generated by dilution of Ni, Cr, etc. in the weld metal. . Conversely, the groove angle and depth are test symbols M
In the test symbol N, which is the same as the above and the height of the first layer is 3 mm,
The required welding current was about 70 A, and welding became unstable. The tendency is that the groove angle is 70 °, the depth is 6 mm, the height of the first layer is 2 mm, and the height is 2 mm.
The same was true for the test symbol R in which the height of the first layer was 0 mm and the depth was 6 mm and the height was 2 mm. On the other hand, groove angle 70 °, depth 1
In the test code P in which the height of the first layer is 2 mm and the height is 2 mm,
As the welding conditions for the first layer, stable welding was possible.
However, in this groove shape, since the groove depth is as deep as 12 mm, the required welding current in welding using the second-layer high-alloy welding wire becomes a high current of 380 A, which causes spatter generation and bead formation. Not practical from a point of view. This tendency becomes more remarkable in the test symbol Q in which the groove angle is 75 °. Further, in the test symbol S in which the groove angle is 80 °, the depth is 12 mm, and the height of the first layer is 1 mm, the welding current of the first layer is 4
It became a high current of 20 A, and it was difficult to obtain a smooth and favorable initial layer weld bead shape.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

[0022]

As described above, according to the present invention, it is possible to prevent melting of the groove portion of the high alloy steel in the first layer welding of the low alloy steel on the inner surface side without the need for the two-step groove forming of the groove shape. it can. Further, since one-run MIG welding of three electrodes becomes possible, the effect on the clad steel pipe manufacturing industry is great.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an embodiment of seam welding of a clad steel pipe.

FIG. 2 is a view showing a groove shape of a seam portion of a clad steel pipe.

FIG. 3 is a schematic view showing the order of welding.

[Fig. 4] Outer diameter is 20 inches, wall thickness is 20 mm, of which 3 mm
FIG. 3 is a view showing a groove shape of a clad steel pipe made of high alloy steel of Incoloy 825.

[Explanation of symbols]

 1: Low alloy steel base metal part 2: High alloy steel part 3: Outer surface side groove 4: Inner surface side groove 5: Groove root part 6: Outer surface side temporary attachment bead 7: Inner surface side low alloy steel welded part 8: Inner surface side high alloy steel weld zone 9: Inner surface side high alloy steel weld zone 10: Outer side low alloy steel weld zone

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B23K 9/18 A 7920-4E

Claims (3)

[Claims] 1. An X-shaped groove is formed in a seam portion of a clad steel pipe made of a low alloy steel on the outer surface and a high alloy such as stainless steel or a high Ni alloy steel on the inner surface, and one run welding of three electrodes on the inner surface side is performed. Then, in the welding method of the clad steel pipe in which the outer surface side is welded by four-electrode submergence, a groove having a depth t ₁ of 8 to 10 mm and an angle θ of 65 to 75 ° is provided on the inner surface side of the X-shaped groove. , A clad, characterized in that the welding of the low alloy steel portion on the inner surface side is carried out by a welding wire for low alloy while suppressing the amount of weld metal from the boundary with the high alloy steel to a height t ₂ lower by 1 to ₂ mm. Internal welding method for steel pipes. 2. The inner surface welding method for a clad steel pipe according to claim 1, wherein MIG welding is performed on the inner surface side at a welding speed of 35 to 45 cm / min. 3. The inner surface welding method for a clad steel pipe according to claim 1, wherein the thickness t ₃ of the high alloy steel portion on the inner surface of the clad steel pipe is 2 to ₃ mm.