JP2563684B2 - Welding method of stainless clad steel pipe - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses stainless steel based on Ni, Cr, etc. on the inside, stainless clad steel using carbon steel or low alloy steel (hereinafter referred to as low alloy steel) as a base material, such as UOE. The present invention relates to a seam welding method when manufacturing a steel pipe by the method.

[0002]

2. Description of the Related Art In recent years, the development environment for petroleum resources has become more severe, and the line pipes to be laid have been required to have excellent corrosion resistance. The life of low alloy steels is extremely short, and there is a tendency that stainless steels or high alloy steels having a nobler component than stainless steels are used.
However, if a line pipe is laid only with stainless steel or high alloy steel, the cost will be enormous. Therefore, only the inner side of the steel pipe requiring corrosion resistance is stainless steel or high alloy steel, and the low alloy steel is used on the outside. Clad steel pipes have been receiving attention. This type of clad steel pipe is manufactured by rolling stainless steel, high alloy steel, and low alloy steel by rolling, then forming the pipe body by the UOE method, and butt welding the seam portion in the longitudinal direction of the pipe body.

However, there is a problem that defects are generated in the butt welded portion of the seam, particularly the welded portion inside the steel pipe. It is because the stainless steel or high alloy steel part clad on the inside is melted by welding, and the low alloy steel part is also melted. Therefore, the characteristics such as corrosion resistance of the welded portion cannot be maintained.

In order to prevent such defects of the welded portion, in Japanese Patent Publication No. 1-38597, particularly in welding of a stainless clad steel pipe, the bead width is set by forming the butted portion as the X groove and the inner side as the double groove. Is disclosed to facilitate levitation of slag during latent welding, and to perform band arc welding using a strip electrode on the inner stainless steel portion to reduce the dilution rate. However, in arc welding using a strip electrode, the arc may not be uniform over the strip width and a sound weld may not be obtained.

On the other hand, in Japanese Patent Laid-Open No. 63-10095, the depth and angle of the X groove are specified, and the inner low alloy portion is M.
It is disclosed that the IG welding and the high alloy removed portion can be subjected to one run welding by latent welding. That is, the publication discloses that the dilution ratio at the time of latent welding can be suppressed to a low level by eliminating a width in the high alloy butt portion that does not interfere with the inner groove of the low alloy steel.

However, both methods require two kinds of welding methods. Particularly, in the former case, it is necessary to finish the arc welding of the low alloy steel portion and then perform the arc welding of the stainless steel portion with the strip electrode. Once the slag on the bead surface of the low alloy steel part must be removed, the overall welding time becomes long and the productivity becomes low. It is premised on the application of welding materials, and it is essential that the stainless steel part is not melted during welding. However, since the groove cross section of the seam welded portion in the actual UO process is not always constant, there remains the problem of cracking of the welded metal portion due to melt dilution of the stainless steel portion.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and in producing a clad steel of stainless steel and low alloy steel into a steel pipe, particularly by the UOE method. It is an object of the present invention to provide a simple method for producing a stainless clad steel pipe that suppresses the inner groove shape and its welding conditions in welding the formed pipe longitudinal seam butt welding and has no welding defects. .

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention has the following structures. (1) Ni, Cr as base material and clad material for low alloy steel
A clad steel plate made of austenitic stainless steel containing aluminum is formed into a tubular shape such that the inside is made of stainless steel, and an X-shaped groove is formed on the butted portion to form the X-shaped groove portion. When manufacturing a clad steel pipe by seam welding, the groove depth inside is 80 to 1 of the stainless steel thickness.
00%, a groove with an angle of 20 to 120 ° is provided, and the outer groove portion is tack welded, and then the inner stainless steel groove portion is welded in the range of 400 to 800 A, and the inner and outer portions are made of stainless steel. A welding method for a stainless clad steel pipe, characterized in that a welding wire containing more Ni and Cr than that of the above is used, and each layer is subjected to latent arc welding. (2) The method for welding a stainless clad steel pipe according to the above item 1, wherein the inner stainless steel has a thickness of 2 to 4 mm.

Further, in the present invention, it is desirable to adopt the following conditions for the latent welding of the inner stainless steel portion. That is, the welding wire is preferably in the range of 2.4 to 4.8 mm in view of the stability of the welding arc. The number of welding electrodes is 1-2 for inside and 2 for outside.
A range of 3 electrodes is preferable. The order of welding is
Performing outer arc welding after inner arc welding is
Although it is preferable from the viewpoint of effectively utilizing the O step, there is no particular problem even if the welding sequence is reversed. The flux for latent welding may be either melt type or bond type.

Hereinafter, the present invention will be described in detail. The stainless clad steel to which the present invention is applied has a base material such as low alloy steel, and has stainless steel such as SUS304 or S on its surface.
US316 and the like are bonded as a bonding material, and the clad steel itself is manufactured by a conventional method. The stainless clad steel (plate) is formed into a tubular shape in the UO process, and the groove is provided at both ends to be seam welded portions. As the groove shape, various general shapes for butting can be used, but an X-shaped groove shape is usually used in the UO process.

FIG. 1 shows an example of the groove shape of the present invention. The clad steel composed of the outer low alloy steel 1 and the inner stainless steel 2 has a depth h ₁ in the range of 0.6 to 0.8 t relative to the outer low alloy steel 1 at the seam butting portion 3 with respect to the steel thickness t. And the groove 5 is provided so that the angle θ _{1 is} 60 to 80 °. On the other hand, the depth h _{2 of} the inner stainless steel is 0.8 to 1.0 t with respect to the thickness t of the stainless steel.
A groove 5 of 0 to 120 ° is formed.

The first feature of the present invention is that the groove shape of the inner stainless steel portion is provided as described above. The reason for this is to obtain a sound inner weld by one-layer arc welding. Inner groove depth h ₂ is 0.8 to
The reason for setting it to 1.0t is that it is difficult to obtain a wide and smooth bead when it is 0.8t or less. On the other hand, at 1.0 t or more, the welding arc directly acts on the low alloy steel portion below the stainless steel, the dilution ratio of the low alloy steel in the weld metal portion becomes large, and a healthy weld portion cannot be obtained. The reason why the angle is set to 20 to 120 ° is that if the angle is 20 ° or less, the groove cross-sectional area becomes too small and a wide and smooth weld bead cannot be obtained. On the other hand, if it exceeds 120 °, the welding arc directly acts on the low alloy steel portion below the stainless steel, and the dilution ratio increases, so that a sound weld portion cannot be obtained.

In the production of UO steel pipes using only ordinary low alloy steel, the dilution ratio of the low alloy steel is considered to be about 60 to 70%. Therefore, it is considered difficult to perform latent welding by the inner one layer of the stainless clad steel pipe. The reason is that if the dilution ratio of the low alloy steel part is as high as 60%, Ni, Cr, etc. components are diluted even if a welding wire having a component of stainless steel or higher is used as a wire for latent welding, and it becomes a weld metal. This is because not only the necessary Ni and Cr components cannot be secured, but also a martensite structure is generated in the weld metal and hot cracking occurs. In this respect, the present invention is characterized in that the groove shape is such that the dilution ratio of the low alloy steel can be kept low and a sound weld can be obtained in the single layer latent welding of the stainless clad steel pipe, in particular. The outer groove shape is set within the above range in order to make the welding bead shape and the welding portion appropriate by using a welding wire (described later) for high alloy steel.

FIG. 2 shows the welding process of the present invention. First, a welding wire for low alloy steel is temporarily welded 6 to the outer groove 4 by carbon dioxide welding (FIG. A), and then to the inner groove 5. A single layer of arc welding is performed using a welding wire having a composition higher than that of stainless steel (Fig. B). However, the present invention provides the arc welding current range in addition to the groove shape of the inner stainless steel portion. There are features. That is, the inner arc welding current range is 4
It is necessary to set the current to 0 to 800 A, and low dilution single-layer latent welding without welding defects is possible only in this welding current range. That is, on the high current side outside this condition range, the penetration depth of the low alloy steel portion becomes deep even in the above inner groove shape, and the dilution rate increases, which is not preferable. On the other hand, on the other hand, on the low current side, the dilution rate is small, but the welding speed must be extremely slowed down in order to obtain an appropriate amount of weld metal, resulting in inefficiency. In the present invention, the number of welding electrodes is not particularly limited to one electrode in the inner one-layer arc welding, and even if two electrodes are used, the operating current range of each electrode is set within the above range to further increase the welding current. It goes without saying that it will be an efficient latent welding method.

Next, after the inner arc welding, the outer low alloy steel portion is subjected to a one-layer arc welding 8 as shown in FIG. 2 (c). The present invention is for the outer welding of the outer low alloy steel portion. The method is characterized by using a welding wire having a composition of stainless steel or higher as the wire. That is, according to the study by the present inventors, the welding method of the present invention was possible only when a welding wire having a component higher than that of stainless steel was applied to the outer low alloy steel. The reason is that when a welding wire having a composition of stainless steel or more is applied for the inner welding and a welding wire for the low alloy steel is applied to the outer low alloy steel portion, in particular, it is welded to the outer latent arc welding metal 8. A defect has occurred. This welding defect is caused by the formation of a martensite structure as a result of the Ni and Cr components of the inner weld metal being mixed in the outer weld metal by dilution, and the welding wire having a component of stainless steel or more on the outer side. By applying
It is possible to perform single-layer latent welding without generation of welding defects.

[0016]

EXAMPLES As shown in Table 2, a groove shape of the present invention as shown in Table 2 and a conventional groove shape as a comparative method were prepared on a stainless clad steel tube having a total thickness of 20 mm shown in Table 1 and 3 mm of SUS316 stainless steel clad therein. A welding part was formed under the welding conditions shown in Table 4 by the welding wire shown in Table 3. In the table, examples are shown in which the inner one electrode and the outer two electrodes and the inner two electrodes and the outer three electrodes respectively are used. The welding wires are all as shown in Table 3, and the flux is the bond type.

Table 5 shows the results of investigating the chemical composition of the inner weld metal after the above welding was performed. At the end of each table, the calculation results of Ni and Cr equivalents based on the Schaeffler structure chart are also shown. As is clear from the table, the chemical composition of the inner weld metal in the case of performing the latent welding by the method of the present invention is equal to or more noble than the clad material of the test clad steel plate in both Ni and Cr equivalents. Although the composition was shown, the chemical composition of the inner weld metal when performing latent welding by the comparative method was significantly different from the chemical composition of the clad material of the test clad steel sheet, that is, a composition that is less base than the clad material. Became.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

[Table 4]

[0022]

[Table 5]

[0023]

As described above, according to the method of the present invention, in the butt welding of the seam portion of the stainless clad steel pipe, it is possible to obtain a stainless steel welded portion free from defects due to component dilution and the like. It is possible to perform stable and efficient production in line with the production of pipes.

[Brief description of drawings]

FIG. 1 shows the groove of stainless clad steel,

FIG. 2 is a diagram showing a welding process and a welding example of the present invention.

[Explanation of symbols]

1 Outer Low Alloy Steel 2 Inner Stainless Steel 3 Seam Butt 4 Outer Groove 5 Inner Groove 6 Temporary Welding 7 Inner Arc Welding 8 Outer Arc Welding

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B23K 9/235 8315-4E B23K 9/235 B 33/00 33/00 A // B23K 101: 06 103: 16

Claims (2)

(57) [Claims] 1. A low alloy steel base material and N as a clad material.
From austenitic stainless steel containing i, Cr
In order to manufacture a clad steel pipe by forming a clad steel pipe into a tubular shape so that the inside is stainless steel, and subjecting the butted portion to an X-shaped groove processing and seam welding the X-shaped groove portion, 8 depth of stainless steel thickness
0 to 100%, a groove having an angle of 20 to 120 ° is provided, and after temporarily welding the outer groove portion, the inner stainless steel groove portion is welded in the range of 400 to 800 A, both inside and outside. Contains more Ni and Cr than stainless steel
Welding using a wire, welding method of a stainless clad steel tube, characterized in that the latent arc welding of single layer that. 2. The method for welding a stainless clad steel pipe according to claim 1, wherein the inner stainless steel has a thickness of 2 to 4 mm.