JPH10211597A - Gas shield arc welding wire for line pipe and circumference automatic welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide gas shield arc welding which is excellent in selective corrosion resistance, crack resistance, welding workability of a circumference weld metal for a line pipe to transport petroleum, natural gas, etc., obtains a weld metal excellent in strength/low temp. toughness and enables high efficiency welding. SOLUTION: The welding wire has a composition, by weight, consisting of 0.02-0.20% C, 0.20-1.50% Si, 0.50-2.0% Mn, <=0.030% P, <=0.030% S, 0.0030-0.050% O, 0.10-2.00% Cr, 0.10-5.50% Ni, 0.005-0.30% one kind or two kinds or more among Bi, Sb, Se and the balance Fe.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a welding method using a welding wire for a line pipe, which is used as a means of transporting petroleum, natural gas, and the like.
Excellent weldability with excellent crack resistance, excellent weld metal strength and low-temperature toughness, and good workability in all positions.
Moreover, the present invention provides a gas shielded arc welding method that enables high-speed and high-efficiency welding.

[0002]

2. Description of the Related Art In recent years, fluid transportation by line pipes worldwide has rapidly developed both at sea and on land, and at present, long-distance mass transportation piping for gas and liquid such as oil and natural gas, city gas piping, and water transportation. It is used for transportation of industrial piping, district heating and cooling piping, etc., and tends to increase in the future.

[0003] On the other hand, for circumferential welding, which is one of the important technologies that affect the quality and cost of line pipes,
In addition to being all-position welding and on-site welding work, it is required that Uranami bead formability is required in the Uranami welding of the first layer, and butt welding is performed for the purpose of high welding efficiency. With the tendency to have a narrow groove and a tendency to increase the welding speed, there is a need for welding materials that can secure welding techniques with few welding defects and high accuracy and that can obtain weld metal with excellent strength and low-temperature toughness. I have.

[0004] In recent years, it has become a problem that transport of oil, gas, and the like through these line pipes causes selective corrosion of the pipe circumferential weld metal portion, and corrosion resistance is also required.

It has been disclosed that Cr addition is effective for CO ₂ corrosion (Journal of the Japan Petroleum Institute, No. 5).
0, No. 2, FIGS. 9 and 10). Further, Japanese Unexamined Patent Publication No.
No. 230 proposes a method of adding Cr to improve the CO ₂ corrosion resistance of a steel pipe base material. Japanese Patent Laid-Open No. 5-5
No. 7478 proposes a gas shielded arc welding wire for a pipe, but little consideration is given to welding workability. Further, Japanese Patent Application Laid-Open No. 62-240193 proposes a steel wire for TIG welding to be used for back wave welding, which is excellent in non-solder-type TIG welding using an inert gas as a shielding gas. The purpose is to obtain a back wave bead, and CO ₂ corrosion resistance and selective corrosion resistance are not considered.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and relates to the welding of line pipes for transporting oil and natural gas and the like, and relates to the selective corrosion resistance and the resistance of a circumferential weld metal portion to the welding. Gas shielded arc welding with excellent cracking properties, weld metal parts with excellent strength and low-temperature toughness of weld metal, good welding workability in all positions, and high speed and high efficiency welding It relates to a wire and a welding method.

[0007]

[Means for Solving the Problems]

[Claim 1] In a gas shielded arc welding wire for a line pipe, C is expressed as a percentage by weight based on the total weight of the wire.
: 0.02 to 0.20%, Si: 0.20 to 1.50
%, Mn: 0.50 to 2.0%, P: ≦ 0.030
%, S: ≦ 0.030%, O: 0.0030-0.
050%, Cr: 0.10 to 2.00%, Ni: 0.1
0 to 5.50%, a total of one or more of Bi, Sb and Se containing 0.005 to 0.300%, with the balance being Fe For gas shielded arc welding wire. [Claim 2] In the circumferential automatic gas shielded arc welding of a steel pipe using the wire according to claim 1, the number of oscillations is set to 0.5 to 50 Hz, and the gas shielded arc welding is performed without sorting welding. Automatic gas shield arc welding method.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the circumferential welding of a line pipe, the present inventors have conducted various studies by changing various wire components for gas shielded arc welding in order to solve the above-mentioned problems. A gas-shielded arc welding wire that has good selective corrosion resistance in the part, has excellent crack resistance, strength, and low-temperature toughness, has good welding workability, and good bendability, and can perform high-speed, high-efficiency welding. Was.

The reasons for limiting the chemical components of the gas shielded arc welding wire of the present invention are as follows. C: 0.02 to 0.20% C is added in an appropriate amount mainly to adjust the strength. However, the amount of C also affects the quality of welding workability due to arc length variation, and the amount of C increases. As a result, the arc length is shortened, the number of short circuits is increased, the droplet transfer characteristics are improved, and the welding workability tends to be improved by improving the stability of the arc. However, when a large amount of C is contained, the weld metal is remarkably hardened, ductility and toughness are reduced, cracking resistance is deteriorated, and spatter is frequently generated. Therefore, the upper limit is set to 0.20%. Further, if it is less than 0.02%, effects such as securing strength and improving workability are not recognized, so the range is made 0.02 to 0.20%.

Si: 0.20 to 1.50% Si is an indispensable component as a main deoxidizing agent for a weld metal.
It is added to clean the weld metal and ensure toughness, but if added excessively, it causes solid solution hardening of ferrite during solidification of the weld metal, lowers toughness, increases the amount of slag generated, and increases welding workability. Is deteriorated, the range is set to 0.20 to 1.50%.

Mn: 0.50 to 2.0% Mn is an element effective for improving the strength and low-temperature toughness of the weld metal in addition to acting as a deoxidizing agent together with Si. However, if it is less than 0.50%, the integrity of the weld is impaired due to insufficient deoxidation, and if it exceeds 2.0%, the hardenability is increased, the hardness of the weld metal is increased, the crack resistance is deteriorated, and the amount of spatter is reduced. Therefore, the range is set to 0.50 to 2.0%.

P: ≦ 0.030% P is an impurity, and it is desirable that the content of P is small, because the toughness is reduced by the increase of P, and the content should not exceed 0.030%.

S: ≦ 0.030% S not only forms a low melting point compound at the time of solidification of the weld metal and lowers cracking resistance, but also is a hot crack inducing element.
The amount added should not exceed 0.030%.

O: 0.0030% to 0.050% O is necessary for ensuring the weldability in attitude welding and bead formation in high-speed welding, and also has the effect of reducing the generation of spatter. In the structure of the present invention, the effect becomes remarkable at 0.0030% or more, but when it exceeds 0.050%, the effect is not only saturated, but also the arc becomes unstable and spatter occurs frequently. 0.050%. O
May exist uniformly in the wire as a solid solution or an oxide, but more preferably, it is concentrated on the wire surface as an internal oxide layer and a grain boundary oxide layer.

Cr: 0.10 to 2.00% Cr is used to improve the CO ₂ corrosion resistance and the selective corrosion resistance of the weld metal, improve the quenchability, and obtain good mechanical properties by forming fine carbides. In particular, the effect of corrosion resistance is small when less than 0.10%, and when it exceeds 2.00%, the strength of the weld metal becomes excessive and the weld cracking sensitivity increases, so that the Cr content is 0.10 to 2.0. 00%.

Ni: 0.10% to 5.50% Ni has an effect of improving the resistance to CO ₂ corrosion and the resistance to selective corrosion together with Cr, and also has an effect of precipitating nitride formation and suppressing pore formation. If it is added, the effect is insufficient if it is less than 0.15%, and the crack sensitivity increases if it exceeds 5.50%. Therefore, the range is set to 0.10 to 5.50%.

Since Bi, Sb, and Se have low melting points, the surface tension of the molten metal is greatly reduced, so that the viscosity is reduced, thereby increasing the arc concentration, improving the droplet transferability, and increasing the penetration depth. This has the effect of reducing poor fusion and improving arc stability. In addition, the addition reduces the slag encapsulation rate, has the advantage of making it difficult to cover uniformly, and the difference in interfacial tension between the slag and the weld metal during solidification increases the slab removability. It is an effective element. Further, the weld bead shape and the state of adaptation to the end of the bead toe can be made good, so that insufficient penetration into the wall surface of the narrow groove can be reduced, and welding defects such as poor fusion can be prevented. However, if contained in a large amount, the amount of spatter increases remarkably and welding workability deteriorates. Therefore, the total content of one or more of Bi, Sb, and Se is set to 0.005 to 0.300%.

In the above gas shielded arc welding using a welding wire, the number of oscillations is set to 0.5 to 50 Hz.
The reason for limiting the welding method performed in one pass and one layer without sorting is as follows.

For the purpose of improving the welding efficiency, the shape of the pipe butt groove, which is the welded portion, tends to be narrow and the cross-sectional area of the groove tends to be small to improve the efficiency. It is close to vertical and defective fusion defects are likely to occur. In addition, since welding is performed in all positions, it was necessary to significantly change welding conditions in order to prevent the molten metal from sagging depending on the welding position.

In order to solve these problems, 0.5 Hz
With the above-mentioned oscillating, high-speed welding with little dripping of the molten metal and few welding defects such as poor fusion of the groove can be performed without changing welding conditions such as current and voltage in each position of the pipe. Thus, one-pass one-layer welding can be performed, and the welding efficiency can be greatly improved.

However, if the number of oscillations exceeds 50 Hz, the occurrence of spatters increases significantly and a large amount adheres to the groove, making it difficult to continue welding. Further, the arc state tends to be unstable, and welding defects such as poor fusion occur. Therefore, it was set to 0.5 to 50 Hz. Hereinafter, examples of the present invention will be described.

[0022]

EXAMPLE A test steel sheet having a chemical composition shown in Table 1 and a thickness of 20 mmt was formed into a tube having an outer diameter of 900 mm, and then, under the welding conditions shown in Table 2, a 1.2 mmφ chemical composition shown in Tables 3 and 4 was welded. Gas shielded arc welding was carried out using a wire by the butt groove in FIG. Table 5 shows the workability of the welding and the overall evaluation of the penetration bead formation, weld cracking, corrosion resistance, tensile strength and impact toughness of the weld metal part.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

[Table 5]

Inspection of the internal defect of the welded portion is performed by setting the total length of the welded portion to X
Evaluated by X-ray transmission test, corrosion resistance was measured by 10% Na
Bubbling 1 atm CO ₂ into a Cl aqueous solution, 80 ° C, p
H was adjusted to 5.0, and the test piece was immersed for 96 hours or more, and the corrosion amount was 0.55 mm / y or less. In addition, the tensile strength was measured according to JIS Z 2203 No. 3 test piece.
2241 Evaluated according to the tensile test method for metallic materials, 640
N / mm ² or more was judged to be acceptable. Impact toughness is JIS Z
JIS Z 224 according to No. 4 test piece specified in 2202
The test was performed at a test temperature of −30 ° C. according to the impact test method of No. 2, and 140 J or more was accepted. When a weld crack occurred, the tensile test and the impact test were omitted because a normal test piece could not be collected. As shown in Table 4, no. No. 1 to No. In the circumferential welding using the wire of the present invention No. 7, a good back bead in the first pass is obtained, the spatter is small, the welding workability is good, the corrosion resistance is excellent, the strength and the impact toughness are good. Was confirmed to be obtained.

However, the comparative wire No. 8 to No. 8
It is difficult to obtain a good weld metal because the wire composition of No. 20 is inferior in the formation of the backside bead and the workability of welding, the lack of corrosion resistance and strength / impact toughness, and the occurrence of weld cracks. Unable to make joints.

The wire No. 8, wire No. 9, wire No. Sample No. 10 was out of the range of Bi, Sb, and Se. Therefore, the arc state became unstable, the amount of spatter was increased, and welding defects such as poor penetration occurred. Wire N
o. 11, wire No. In No. 12, each of Cr and Ni was outside the claimed range, and the corrosion resistance was deteriorated. Wire No. 1
3, No. In No. 14, Cr and Ni were each within the claimed range, and weld cracks occurred in the first-layer weld metal. Wire N
o. In No. 15, C was more than the range, the crack resistance was inferior, and welding cracks occurred. Wire No. In the case of No. 16, C is below the range, the strength of the weld metal also decreases, and satisfactory workability cannot be ensured due to insufficient strength, unstable arc state, and rapid arc fluctuation due to short circuit. No. No. 17 is Mn, and No. 17 18 is S
Since i is less than the component range, blowholes occur due to insufficient shielding, so that a healthy weld metal cannot be obtained, and the weld metal strength is also insufficient. Further, the wire No.
19, no. In No. 20, Si and Mn were more than the claimed range, spatter generation was significantly increased, slag was generated, welding workability was poor, and weld metal cracks were generated.

In the above gas shielded arc welding using a welding wire, the number of oscillations is set to 0.5 to 50 Hz.
The following are the reasons for the limitations specified in the above. If the number of oscillations is less than 0.5 Hz, the molten metal tends to sag in the upright position and the upward position, and welding defects such as poor fusion occur in the next pass welding. On the other hand, when the vibration is higher than 50 Hz, the generation of spatter becomes abnormally large, and a large amount of the spatter adheres to the inside of the groove, making it impossible to continue welding. Further, the arc state becomes unstable and welding defects such as poor fusion occur. Therefore, the number of oscillations is set to 0.5 to 50 Hz.

As described above, the wire and the welding method of the present invention are excellent in selective corrosion resistance, crack resistance, strength and low-temperature toughness in circumferential welding of line pipes used as transportation means of oil, natural gas and the like. This is a gas-shielded arc welding method that enables high-efficiency, single-pass, single-layer welding without distributing welding at high speed. Can be obtained.

[0033]

Industrial Applicability According to the present invention, in welding using a welding wire of a line pipe used as a transportation means of oil and natural gas, etc., the circumferential welded portion has excellent selective corrosion resistance and crack resistance, and the strength of the weld metal. -A welded part with excellent low-temperature toughness is obtained, and welding workability is good in all positions, and gas shielded arc welding that enables high-speed and high-efficiency welding is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a joint groove shape of a test plate.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yasutomo Ichiyama 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Shinji Kodama 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division

Claims (2)

[Claims] 1. In a gas shielded arc welding wire for a line pipe, based on the total weight of the wire, C: 0.02 to 0.20%, Si: 0.20 to 1.50%, Mn: 0.50 to 2.0%, P: 0.030%, S: 0.030%, O: 0.0030 to 0.050%, Cr: 0.10 to 2.00%, Ni: 0 .10 to 5.50% and Bi, Sb, Se
0.005 to 0.3 in total of one or two or more
A gas-shielded arc welding wire for a line pipe, characterized in that the wire contains 00% and the balance is made of Fe. 2. The circular automatic gas shielded arc welding of a steel pipe using the wire according to claim 1, wherein the number of oscillations is set to 0.5 to 50 Hz and gas shielded arc welding is performed without sorting welding. Automatic gas shield arc welding method.