JPH05192789A - High-cellulosic coated electrode - Google Patents

Abstract

PURPOSE:To provide the high-cellulosic coated electrode which prevents the selective corrosion of a circumferential weld metal part in particular and with which the circumferential weld metal having sufficient strength, toughness and crack resistance is obtainable. CONSTITUTION:This coated electrode contains, by weight%, 0.1 to 7.0% MgO, 7 to 25% iron oxide (in terms of FeO), 8 to 19% TiO2 10 to 30% SiO2, 5 to 27% Mn by the total weight of a coating material in the coating material, in addition, 0.06 to 1.10% Mo by the weight of the electrode. The weight ratio of the coating material is specified to 0.10 to 0.19. Further, either or both of 0.30 to 2.005 Cu+Ni by the total weight of the electrode and 0.05 to 0.5% B of the total weight of the coating material may be incorporated in addition to the above-mentioned components into the coated electrode. A mild steel core wire or low alloy steel core wire is used for the core wire. This coated electrode is suitable for circumferential welding of pipelines for transporting highly corrosive petroleum and natural gases.

Description

Detailed Description of the Invention

[0001]

The present invention relates to oil and gas containing CO _2, or CO ₂ relates high cellulosic covered electrode suitable for circumferential welding of line pipes for transporting,
In particular, the present invention relates to a high-cellulosic coated arc welding rod for circumferential welding, which is excellent in selective corrosion resistance, low temperature toughness, and crack resistance of weld metal.

[0002]

2. Description of the Related Art Conventionally, the following documents have been published regarding the selective corrosion of welded parts of low alloy steels, and their improvement measures have been proposed. (1) It is said that the difference in the amount of Ni added between the base metal and the weld metal has an effect on the local corrosion of welded joints in the ice sea (Takashi Abe et al., "Iron and Steel," Vol. 72 (1988), p.126
6). (2) Similarly, due to local corrosion of welded sea ice steel, Ni and Cu
Influences the amount of 3.8 × Cu + 1.1 × Ni + 0.3, which affects the selective corrosion (Kametaro Ito et al.
"Iron and Steel," Vol. 72 (1989), p. 1265). (3) Use of low alloy welding rods containing Cu and Ni is effective for preventing selective corrosion of carbon steel pipe circumferential welds (Yuki Hideaki, "Materials" Vol. 38 (1989), No. 42).
4, p. 62-68). (4) The addition of Ni and Mo is effective for preventing selective corrosion of welded steel pipe vertical seam welds (Suga et al., Japanese Patent Application No. 1-206985).

As described above, N is a method for improving the selective corrosion of the weld metal in a corrosive environment containing oxygen such as ice sea.
It has been proposed that a method of adding i and Cu to the weld metal and a method of adding Ni and Mo to improve the selective corrosion characteristics of the welded steel pipe vertical seam are effective.

However, it has been found that the addition of Ni and Mo is effective for suppressing the selective corrosion of the circumferential weld of the line pipe used in the corrosive environment including the CO ₂ environment, the hardness of the weld metal and the crack resistance. No high-cellulosic welding rod has been found in consideration of the above. However, JP-A-63-220994
According to the publication, Mo and the like can be added for the purpose of improving the mechanical properties, but the specific range has not been clarified, and the hot crack resistance and cold crack resistance during addition have not been examined. Further, no relation between Mo and selective corrosion resistance has been suggested.

[0005]

[SUMMARY OF THE INVENTION] welded steel pipe or a seamless steel pipe, including the CO ₂ oil and natural gas or CO ₂
When used for transportation, the circumferential weld metal will corrode to your choice,
So-called selective weld corrosion may occur. this is,
The chemical composition and structure of the weld metal and the base material are different, the weld metal becomes electrochemically base, and the weld metal field is selectively corroded.

Conventionally, in the circumferential welding of a line pipe used in such an environment, a high-cellulosic welding rod in consideration of the selective corrosion, weldability and mechanical properties has not been studied. However, in a real environment, this type of selective corrosion often poses a problem, and the fact is that this study is awaited.

That is, in the high-cellulosic coated arc welding rod, in order to obtain good selective corrosion characteristics by adding Cu or Ni alone or in combination, it is necessary to consider weld cracks and mechanical properties of weld metal. .. Regarding Mo,
The knowledge that Mo addition is effective in suppressing selective corrosion of circumferential welds, and Mo-added high cellulosic coated arc welding rods have not been developed in consideration of practicality such as hardness and crack resistance of weld metal. .. As described above, in the conventional method, a high-cellulosic coated arc welding rod has not been able to provide a circumferential weld having excellent practicability such as selective corrosion characteristics and its weldability and mechanical properties.

The present invention has been made in order to meet such a request, and its purpose is to prevent the selective corrosion of the circumferential welded metal portion and to provide sufficient strength, toughness and crack resistance. It is intended to provide a high-cellulosic coated arc welding rod which can provide a circumferential weld metal having the above.

[0009]

In order to solve the above-mentioned problems, the inventors of the present invention have variously changed the coating material component of the high cellulosic coated arc welding rod and its component value and the chemical composition of the core wire. As a result of thorough investigations on the selective corrosion characteristics of welds and their mechanical properties, crack resistance, etc. in a corrosive environment containing CO, CO ₂ and seawater, Mo or Mo in the coating material and / or core wire , Cu, Ni (Cu and Ni can be added individually or in combination), a high-cellulosic coated arc welding rod capable of effectively preventing selective corrosion of the circumferential weld metal portion was found.

That is, according to the present invention, a coating material prepared by kneading a coating material raw material containing a large amount of cellulose together with a binder is applied to the outer circumference of a mild steel core wire or a low alloy steel core wire to form a high-cellulosic coated arc welding rod. in, in the coating agent relative to the total weight coating agent, MgO: 0.1 to 7.0%, iron oxide (FeO in _{terms): 7~25%, TiO 2:} 8~19%, SiO 2: 10 -30%, Mn: 5-27%, and based on the total weight of the welding rod, Mo: 0.06
-1.10%, and the weight ratio of the coating agent is 0.10-0.1.
The high-cellulosic coated arc welding rod excellent in selective corrosion resistance of the welded portion is characterized in that it is set to 19.

According to another aspect of the present invention, in addition to the above chemical components, Cu + Ni: 0.30-based on the total weight of the welding rod.
2.00%, and B in the coating based on the total weight of the coating:
One or both of 0.05 to 0.5% is contained.

The present invention will be described in more detail below.

[0013]

[Action]

As described above, the present invention provides a circumferential welded portion having high strength, high toughness and excellent crack resistance, which is rich in selective corrosion resistance, by mainly controlling the chemical components of the high cellulosic coated arc welding rod. Obtainable.

The reasons for limiting the chemical composition and the coating ratio in the high-cellulosic coated arc welding rod of the present invention are as follows.

MgO: 0.1-7.0% (relative to the total weight of the coating) MgO does not cause dripping of molten metal or slag even when the welding speed is changed greatly, and also has pit resistance and This has the effect of improving the X-ray performance of the joint. But 0.
If it is less than 1%, the effect cannot be obtained, and if it exceeds 7.0%, the fluidity of the slag becomes excessive and it becomes difficult to perform the downward welding. Therefore, the amount of MgO is 0.1 to 7.
The range is 0%.

Iron oxide (converted to FeO): 7 to 25% (based on the total weight of the coating agent) Iron oxide makes the slag porous to improve the slag releasability and prevents the formation of pits due to excess deoxidation. Has the effect of However, if it is less than 7%, these effects cannot be obtained, and if it exceeds 25%, the fluidity of the slag becomes excessive and it becomes difficult to perform the downward welding. Therefore, the amount of iron oxide is FeO
The range is from 7 to 25% based on the total weight of the coating agent. The iron oxide may be added in the form of Fe ₂ O ₃ in addition to FeO, and in this case, the FeO conversion amount should be within the above range.

TiO ₂ : 8 to 19% (based on the total weight of the coating material) TiO ₂ has the effect of improving the stability of the arc. But 8
If it is less than%, the arc is not stable, and if it exceeds 19%, the arc force becomes weak and it becomes difficult to perform downward welding. Therefore Ti
The amount of O ₂ is 8 to 19% based on the total weight of the coating material.

SiO ₂ : 10 to 30% (relative to the total weight of the coating material) SiO ₂ is an essential component for improving arc strength, crater spread, and conformability, but if it is less than 10%, its effect is obtained. Is not obtained, and if it exceeds 30%, the amount of slag increases, and the fluidity becomes excessive, which makes downward welding difficult. Therefore, the amount of SiO ₂ is 10 to the total weight of the coating material.
The range is 30%. Incidentally, SiO ₂ can be added in the form of water glass, silicate mineral, or the like.

Mn: 5 to 27% (relative to the total weight of the coating agent) Mn is an essential component as a deoxidizing agent and for securing strength and toughness, but if it is less than 5%, deoxidizing becomes insufficient and clean. No weld metal can be obtained, and if it exceeds 27%, deoxidation becomes excessive and pits are easily generated on the bead surface. Therefore, the amount of Mn is set in the range of 5 to 27% based on the total weight of the coating material. It should be noted that Mn can be added in the form of Fe-Mn or Mn oxide in addition to the metal Mn, but in the latter case, the amount converted to Mn is within the above range.

Mo: 0.06 to 1.10% (based on the total weight of the welding rod) Mo is added to adjust the strength of the weld metal and to improve selective corrosion resistance. If it is less than 0.06%, good selective corrosion resistance cannot be obtained, while if it exceeds 1.10%, the weld metal becomes too hard and cold cracking (delayed cracking due to hydrogen) is likely to occur. Therefore, the amount of Mo is 0.0 with respect to the total weight of the welding rod.
The range is 6 to 1.10%. In addition, Mo can be added to the coating material in the form of metal Mo, Fe-Mo, or the like, and can also be added to the core wire.

In order to obtain better selective corrosion resistance of the welded portion, the ratio of Mo to the total weight of the welding rod should be Mo content (%) in the base metal + 0.06% or more. desirable. FIG. 1 shows the selective corrosion current (μA) flowing between the base metal and the weld metal, and the difference (ΔMo) between the Mo content in the total weight of the welding rod and the Mo content (wt%) in the base metal. It is a figure which shows the relationship with.
When the selective corrosion current is positive, the selective corrosion of the weld metal does not occur. The selective corrosion current turned positive when ΔMo was 0.06% or more.

Although the above components are contained as essential components,
If necessary, one or both of the following Cu + Ni and B can be contained in an appropriate amount.

Cu + Ni: 0.30 to 2.00 (based on the total weight of the welding rod) Cu and Ni can be added to improve the selective corrosion resistance of the weld metal. In order to obtain this effect, the total of Cu + Ni is in the range of 0.30 to 2.00 with respect to the total weight of the welding rod. If the total of Cu + Ni is less than 0.30%, it does not contribute to the selective corrosion resistance, and if it exceeds 2.00%, solidification cracking easily occurs in the weld metal, which is not preferable.
Cu and Ni are metallic Cu, metallic Ni and Fe in the coating material.
It can be added in the form of —Ni, copper oxide, nickel oxide, etc., as well as in the core wire.

B: 0.05 to 0.5% (based on the total weight of the coating material) B can be added in order to make the structure fine and to obtain good toughness. If it is less than 0.05%, the effect of improving the impact resistance is small, and if it exceeds 0.5%, the weld metal becomes hard and cold cracking easily occurs. Therefore, the amount of B is set in the range of 0.05 to 0.5% based on the total weight of the coating.

The balance of the coating material is mainly composed of cellulose and contains a binder. In addition, other components that are usually added to the coating material for high-cellulosic coated arc welding rods, such as Na ₂ O, Al ₂ O ₃ , ZrO ₂ , K ₂ O, and F
A small amount of metal components such as e and Cr can be added.

Weight ratio of coating agent: 0.10 to 0.19 (based on the total weight of the welding rod) The weight ratio of the coating agent to the welding rod (covering ratio) is an important condition for facilitating the downward welding. Therefore, the coating ratio needs to be 0.10 or more. If the coating ratio is less than 0.10%, the function as a protective cylinder becomes insufficient, the arc becomes unstable, and the stick is easily burned. Further, when the coverage ratio exceeds 0.19, the concentration of the arc is reduced and the back bead becomes difficult to be formed. In addition, the arc becomes weaker in the welding of the second and subsequent layers, and the amount of slag increases. Therefore, the coating ratio is set in the range of 0.10 to 0.19.

As the core wire, a mild steel core wire or a low alloy steel core wire is used. Of course, it goes without saying that the composition of these steels is not limited.

The high cellulosic coated arc welding rod of the present invention can be applied to welding of various steel types. Especially suitable for circumferential welding of steel pipes, Cu ≤ 2.00%, Ni ≤ 2.00%, M
o ≤ 1.00%, the total content of alloying elements excluding Cu, Ni, Mo and Mn is 1.00% or less, and the balance of steel and inevitable impurities in the balance, the selection in the circumferential weld zone of the steel pipe. The corrosion prevention effect is remarkable.

Next, examples of the present invention will be shown.

【Example】

[0031]

[Table 1] External diameter 38 in x total length 12 using the test steel with the chemical composition shown in
After producing m welded steel pipe,

[Table 2] Circumferential welding was performed with a high-cellulosic welding rod having the configuration shown in. The rod diameter used was 4.0 mm (1 to 2 layers) and 4.8 mm (3 to final layers), and the welding current was 100 A to 240 A. After welding, weld metal strength, toughness, weld cracking, seawater environment (CO ₂
The selective corrosion rate in bubbling) was investigated. Those results

[Table 3] Shown in.

The yield strength was evaluated using JIS Z 2201 No. 3 test piece (6 mmφ), and the toughness was JIS Z 3128.
The No. 4 test piece was used to evaluate the absorbed energy at O ° C. The presence or absence of weld cracking was judged by observing 5 cross sections after welding. Selective corrosion rate is 50 cm in total length including circumferential weld
It is a value measured by inserting artificial seawater into the steel pipe of No. ₂ , blowing CO ₂ gas into it, and obtaining the difference in plate thickness between the base metal and the weld metal part, and the weld metal part does not corrode selectively. The case was displayed as "0.0".

As shown in Table 3, the circumferential welded portion welded with the high-cellulosic coated arc welding rod of the present invention has a yield strength of 350 N / mm ² or more and a toughness of 50 J or more and is excellent in selective corrosion characteristics. In addition, it was confirmed that the circumference welded portion had excellent welding workability and crack resistance.

[0034]

As described above in detail, when the high cellulose-based welding rod of the present invention is used for welding, it has sufficient strength and high toughness, and also has excellent weld cracking resistance and selective corrosion resistance. A welded metal part is obtained. Particularly suitable for welding line pipes that transport highly corrosive oil and natural gas,
It is possible to obtain a circumferential weld metal portion which is not easily selectively corroded with respect to the base metal.

[Brief description of drawings]

FIG. 1 Selective corrosion current flowing between base metal and weld metal
(μA) is a diagram showing the relationship between the Mo content in the total weight of the welding rod and the difference (ΔMo) between the Mo content in the base metal (wt%).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Motokiyo Ito 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. Company Kobe Steel Works, Fujisawa Works (72) Inventor Sansho Naruse 100-1, Urakawachi, Miyamae, Fujisawa-shi, Kanagawa Stock Company Kobe Steel Works, Fujisawa Works

Claims (3)

[Claims] 1. A high-cellulosic coated arc welding rod formed by coating a coating material obtained by kneading a coating material raw material containing a large amount of cellulose together with a binder on the outer circumference of a mild steel core wire or a low alloy steel core wire, in wt%. in (hereinafter, the same), in the coating agent relative to the total weight coating agent, MgO: 0.1 to 7.0%, iron oxide (FeO in _{terms): 7~25%, TiO 2:} 8~19% , SiO ₂ : 10-30%, Mn: 5-27%, and Mo: 0.06 with respect to the total weight of the welding rod.
-1.10%, and the weight ratio of the coating agent is 0.10-0.1.
A high-cellulosic coated arc welding rod excellent in selective corrosion resistance of welded portions, characterized by being No. 19. 2. In addition to the above chemical components, Cu + Ni: 0.30 to 2.00% based on the total weight of the welding rod, and B: 0.05 to 0.05% based on the total weight of the coating material in the coating material. The high cellulosic coated arc welding rod according to claim 1, which contains one or both of 0.5%. 3. The high cellulose-based coated arc welding rod according to claim 1, which is for circumferential welding of a line pipe.