JPH05208277A - Shielded metal arc welding method for pipe - Google Patents

Abstract

PURPOSE:To improve selective corrosion resistance, toughness and crack resistance of weld metal in circumferential welding of the pipe by regulating the difference between the weld metal and base metal, and Mo and welding conditions. CONSTITUTION:In circumferencial welding of the pipe, the pipe base metal, a high cellulose type electrode and the welding conditions are regulated. The inequality DELTAMo >=0.03% determined by the difference between the weld metal and the base metal, and Mo and the inequality PCM <=0.30% calculated from chemical composition of the weld metal are satisfied. Further, the welding conditions regulate the electrode diameter, a kind of a current, a welding current, the welding speed and the welding position.

Description

Detailed Description of the Invention

[0001]

The present invention relates to oil and gas containing CO ₂ or circumferential welding method for line pipe for transporting CO _2, especially resistance to preferential corrosion resistance and low-temperature toughness of the weld metal,
The present invention relates to a circumferential welding method having excellent crack resistance.

[0002]

2. Description of the Related Art Conventionally, there are the following publications regarding selective corrosion of welded parts of low alloy steel. 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, No.12, s1266, 1986). 2) Similarly, localized corrosion of welded steel in ice-sea steels, where Ni and Cu influence and 3.8 ΔCu + 1.1 ΔNi + 0.3 influences selective corrosion (Kametaro Ito et al .;
"Iron and Steel" Vol.72, No.12, s1265, 1986). 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; Material Vol.38, No.424, p62-p68, 1989). 4) Addition of Ni and Mo is effective for preventing selective corrosion of welded steel pipe vertical seam welds (Suga et al .; JP-A-3-70641).

As described above, as a method for improving the selective corrosion of the weld metal in a corrosive environment such as seawater containing oxygen such as ice sea, a method of adding Ni and Cu and an improvement of the selective corrosion characteristic of the welded steel pipe vertical seam. A method of adding Ni and Mo has been found, but it has been found that Mo addition is effective for suppressing selective corrosion of circumferential welds of line pipes used in corrosive environments containing CO _2, and the base metal A covered arc welding method has not been obtained in consideration of the combination with the above and considering practicality such as hardness and crack resistance of the weld metal.

[0004]

The welded steel pipe or seamless steel pipe INVENTION SUMMARY is], using the inclusive of oil and natural gas or CO ₂ transport CO _2, circumferential weld metal is selectively corroded, so-called weld-alloying May occur.
This is because the chemical composition and structure of the weld metal and the base material are different and the weld metal part becomes electrochemically base, and the weld metal part is selectively corroded. In the case of the line pipe used in the environment as described above, the circumferential welding method considering the selective corrosion has not been studied so far. However, in a real environment, this type of selective corrosion often poses a problem, and this examination is awaited.

Therefore, the inventors of the present invention have variously changed the chemical composition of the circumferential weld metal and the composition values thereof, so that the selective corrosion characteristic of the welded portion and its mechanical property resistance in a corrosive environment containing CO ₂ and seawater. Thorough investigations were conducted on crackability. The present invention is based on the findings obtained as a result of this investigation,
By adjusting the base metal, welding material, and welding method to adjust the chemical composition of the weld metal part, selective corrosion of the circumferential weld metal part was prevented and sufficient strength, toughness, and crack resistance were provided. An object of the present invention is to provide a covered arc welding method for pipes to obtain a circumferential weld metal.

[0006]

The first aspect of the present invention is that the chemical composition of the weld metal (% by weight) is C: 0.05 to 0.20% Si; 0.05 to 0.45% Mn; 0.50 to 2.00% The balance consists of Fe and unavoidable impurities, and is calculated from the following formula (1) determined by the difference in Mo between the weld metal and the base metal and the chemical composition of the weld metal ( It is a covered arc welding method for pipes with a high-cellulosic welding rod that satisfies 2). ΔMo ≧ 0.03% (1) P _CM ≦ 0.30% (2) (P _CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5
B) At this time, the inevitable impurities shall satisfy the following range. P; ≤0.030% S; ≤0.030% Al;
≤0.10% N; ≤0.050% Nb; ≤0.10% V;
≤0.10% Ti; ≤0.10% Cr; ≤1.00% Ca;
≦ 0.0025% O 2 ≦ 0.10% Zr; ≦ 0.05%

A second aspect of the present invention is a high-cellulosic welding rod in which the chemical composition (% by weight) of the weld metal contains, in addition to the above chemical composition, one or more of the following components. This is a covered arc welding method for pipes. Cu; 0.15-2.00% Ni; 0.15-2.00% Cu + Ni; 0.15-2.00% B; 0.0005-0.0050%

The chemical components and welding conditions of the pipe base material and the high-cellulosic welding rod applied to the first and second inventions are as follows. Chemical composition (% by weight) of base material C; 0.03 to 0.15% Si; 0.05 to 0.50% Mn; 0.50 to 2.00% Al; 0.005 to 0.10% Contained, or in addition to the above chemical components, further contains one or more of the following components: Cu; 0.05 to 2.0% Ni; 0.05 to 2.0% Cr; 0.05-2.0% Mo; 0.05-1.0% Nb; 0.005-0.20% V; 0.005-0.20% Ti; 0.005-0.20% B; 0.0005 to 0.0020% Ca; 0.0005 to 0.0050% The balance contains Fe and unavoidable impurities. Composition of welding rod A coating material obtained by kneading a coating material raw material containing a large amount of cellulose together with a binder, in a high cellulose-based coated arc welding rod formed by coating the outer circumference of a mild steel core wire or a low alloy steel core wire,
In the coating agent, the following chemical components (wt%) MgO; 0.1-7.0% iron oxide (FeO conversion); 7-25% TiO ₂ ; 8-19% SiO ₂ ; 10-30% Mn; It is a welding rod containing 5 to 27%, and Mo; 0.06 to 1.10% added singly or in combination with respect to the total weight of the welding rod, and the weight ratio of the coating agent is 0.10 to 0. .19 or in addition to the above chemical components, a high cellulosic welding rod containing one or more of the following components. Cu; 0.30 to 2.00% Ni; 0.30 to 2.00% Cu + Ni; 0.30 to 2.00% B; 0.05 to 0.5% Welding conditions Rod diameter (core diameter): 3.2 to 4.8 mm Type of current: DCEP Welding current: 90 to 240 A Welding speed: 100 to 450 mm / min Welding posture: All postures (downward welding)

[0009]

As described above, the present invention limits the chemical composition of the weld metal by limiting the chemical composition of the base metal and the welding rod and the range of welding conditions, and provides sufficient strength and high toughness with rich selective corrosion resistance. It is a circumferential welding method that has excellent crack resistance.

Next, the reason why each chemical component in the weld metal is limited will be described. C: 0.05 to 0.20% C is 0.05 to 0.20% in the weld metal in order to obtain good workability and mechanical properties of the weld metal. In the range of the amount of cellulose in the high-cellulosic coated arc welding rod that provides good welding workability, the amount of C in the weld metal is 0.05%.
As described above, if the amount is set to be less than 0.05%, the workability for welding is significantly reduced. On the other hand, if it exceeds 0.20%, the strength and hardness of the weld metal increase, and cold cracking tends to occur. Si: 0.05 to 0.45% Si is 0.05 to 0.45% in the weld metal in order to obtain good workability and mechanical properties of the weld metal. 0.0
If it is less than 5%, deoxidation becomes insufficient, and the amount of O in the weld metal increases, so that good mechanical properties cannot be obtained. 0.45%
If it is added to the weld metal in excess of 1.0, the amount of slag increases and welding becomes difficult. Mn: 0.50 to 2.00% Mn is also set to 0.50 to 2.00% in the weld metal in order to obtain good welding workability and mechanical properties. If it is less than 0.50%, deoxidation becomes insufficient and good mechanical properties cannot be obtained. If more than 2.00% is added to the weld metal, pits are likely to occur on the bead surface. Mo: 0.03 to 1.05% Mo is 0.03 to 1.03% in the weld metal so that ΔMo is 0.03% or more in order to prevent selective corrosion of the weld metal.
Add 1.05%. As shown in FIG. 1, when the difference ΔMo in Mo content between the weld metal and the base metal is 0.03% or more,
Selective corrosion of the weld metal can be prevented in a corrosive environment containing CO ₂ . However, if added in excess of 1.05%, the hardness of the weld metal increases and weld cracking (cold cracking) tends to occur. It should be noted that FIG. 1 shows ΔMo that affects the selective corrosion characteristics.
Is a graph showing the effect of, the vertical axis represents the selective corrosion current (μA) flowing between the base metal and the weld metal, and the horizontal axis represents ΔM.
It is shown by taking o (%). When the selective corrosion current is positive, the selective corrosion of the weld metal does not occur. ΔMo
Is 0.03% or more, the selective corrosion current turns to positive.

Next, in the second aspect of the present invention, in addition to the above-mentioned components, the above-mentioned optional components and their compositions are limited. Cu; 0.15 to 2.00% Ni; 0.15 to 2.00% Cu + Ni; 0.15 to 2.00% Cu and Ni are used alone to improve the toughness of the weld metal and the selective corrosion property. In both cases of composite addition, 0.15 to 2.00% may be added to the weld metal. If it is less than 0.15%, these effects are not recognized, and if it exceeds 2.00%, solidification cracking easily occurs in the weld metal. Cu
Although addition of Ni and Ni is effective in preventing selective corrosion of the weld metal, these effects are smaller than Mo and play an auxiliary role, and it is not always necessary to add Cu. When Ni is added, it is effective to add it to the same extent as the base material. B: 0.0005 to 0.0050% When low temperature toughness of the weld metal is required, B can be added so as to be 0.0005 to 0.0050% in the weld metal. If it is less than 0.0005%, the toughness improving effect is small, and if it exceeds 0.0050%, the hardness of the weld metal increases and cold cracking easily occurs.

Next, the reasons for limiting the chemical composition of the steel pipe base material will be described. C: 0.03 to 0.15% Carbon in steel is an element effective in increasing the strength of steel, but excessive addition causes deterioration of toughness. Therefore,
The upper limit of the carbon content is 0.15% in order to manufacture a steel pipe having both good strength and toughness. The reduction of the carbon amount improves the toughness, but if it is 0.03% or less, the toughness deteriorates. Further, 0.03% of carbon is required to effectively utilize stable precipitation hardening of Nb, V, Ti, etc., so the lower limit of the amount of carbon is set to 0.03%. The reasons for limiting the other components are as follows. Si; 0.05 to 0.50% Si is necessary for deoxidation, but if added in excess, it deteriorates toughness, so the lower limit is 0.05% and the upper limit is 0.50%.
And Mn: 0.50 to 2.00% Mn is required to be 0.50% or more for deoxidation, but 2.0
If it exceeds 0%, the weldability deteriorates, so the upper limit is 2.00.
%. Al: 0.005-0.10% Al is necessary for deoxidation, but if it is less than 0.005%, deoxidation is insufficient, so the lower limit is made 0.005%. On the other hand, if it exceeds 0.10%, the cleanliness of the steel and the HAZ toughness deteriorate, so the upper limit is made 0.10%. Cu; 0.05 to 2.0% Ni; 0.05 to 2.0% Cu and Ni improve the strength and toughness of the base material without adversely affecting the HAZ toughness, but when it exceeds 2.0%. Since the HAZ hardenability and toughness are adversely affected, the upper limit is 2.0%. Cr: 0.05 to 2.0% Cr increases the strength of the base material and the welded portion, but if it exceeds 2.0%, the hardenability and toughness of the HAZ are deteriorated, so the upper limit is made 2.0%. Mo: 0.05-1.0% Mo improves the strength and toughness of the base material, but 1.0%
If it exceeds 0.1%, the hardenability of the HAZ increases and the weldability deteriorates, so the upper limit is made 1.0%. The lower limit of the amount of addition of these elements is the minimum required amount to obtain the effect on the material, and 0.05
%. Ti: 0.005 to 0.20% Ti has the effect of preventing coarsening of austenite during slab heating by adding 0.005% or more, so the lower limit is made 0.005%, and if added excessively, the weld zone The toughness deteriorates, so the upper limit is made 0.20%. Nb; 0.005 to 0.20% V; 0.005 to 0.20% Nb and V are found to have an effect on strength and toughness.
If it exceeds 20%, the toughness of the base material and the welded part deteriorates, so the upper limit is made 0.20%. The lower limit is set to 0.005% at which improvement in material is recognized. B: 0.0005 to 0.0020% B is effective in increasing the strength of the base material, but excessive addition causes deterioration of weldability and HAZ toughness, so the upper limit is 0.002.
0%, the lower limit is 0.00, which is effective in increasing strength.
05%. Ca: 0.0005 to 0.0050% Addition of Ca improves hydrogen-induced cracking resistance, and the lower limit is made 0.0005% at which the effect is recognized. Excessive addition forms an oxide and is harmful, so the upper limit is 0.0050%.
And

The reasons for limiting the chemical composition (% by weight) of the high cellulosic welding rod in the present invention are as follows. MgO: 0.1-7.0% (ratio in coating material) MgO does not cause dripping of molten metal or slag even when the welding speed is greatly changed and used, and pit resistance and joint part Although it has the effect of improving X-ray performance,
If it is less than 0.1%, these effects cannot be obtained, and if it exceeds 7.0%, the fluidity of the slag becomes excessive and it becomes difficult to perform downward welding. Therefore, the ratio of MgO in the coating agent is 0.1 to 7.
0 wt. The range is%. Iron oxide (calculated as FeO): 7 to 25% (ratio in coating agent) Iron oxide has the effect of making the slag porous to improve the slag releasability and also to prevent the formation of pits due to excess deoxidation. .. 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 downward welding becomes difficult. Therefore, the ratio of iron oxide in the coating agent is 7 to 25 wt. The range is%. The iron oxide may be added in the form of FeO ₂ other than FeO. In this case, the FeO conversion amount should be within the above range. TiO ₂ ; 8 to 19% (ratio in coating material) TiO ₂ has an effect of improving arc stability. However, if it is less than 8%, the arc is not stable, and if it exceeds 19%, the arc force becomes weak and it becomes difficult to perform downward welding. Therefore, the ratio of TiO _{2 in} the coating material is 8 to 19 wt. The range is%. SiO ₂ ; 10 to 30% (ratio in coating material) SiO ₂ is an essential component for improving arc strength, crater spread, and conformability, but if it is less than 10%, those effects can be obtained. On the other hand, if it exceeds 30%, the amount of slag increases and the fluidity becomes excessive, which makes downward welding difficult. Therefore, the ratio of SiO _{2 in} the coating material is 1
0-30 wt. The range is%. It should be noted that SiO ₂ can be added in the form of water glass, silicate mineral, or the like. Mn: 5 to 27% (ratio in coating material) Mn is an essential component as a deoxidizer and for securing strength and toughness, but if it is less than 5%, deoxidation becomes insufficient and a clean weld metal is obtained. If it exceeds 27%, deoxidation becomes excessive and pits are likely to occur on the bead surface. Therefore, the ratio of Mn in the coating agent is 5 to 27 wt. The range is%. In addition to Mn, Mn is Fe-Mn, Mn.
It can be added in the form of an oxide, but in the latter case, the Mn conversion amount should be within the above range. Mo: 0.06 to 1.10% (ratio to the total weight of the welding rod) In order to adjust the strength of the weld metal and to improve selective corrosion resistance, 0.06 to 1.10 wt. %Added. This range is 0.03 to 1.05w in the weld metal
t. % Is the amount required for addition. Mo can be added to the coating material in the form of metallic Mo, Fe-Mo, etc., as well as to the core wire. Cu: 0.30 to 2.00% (ratio to the total weight of the welding rod) To improve the selective corrosion resistance of the weld metal, 0.30 to 2.00 wt. %Added. This range is 0.15-2.00 wt. % Is the amount required for addition. Cu can be added to the coating in the form of metallic Cu, copper oxide, etc., as well as to the core wire. Ni: 0.30 to 2.00% (ratio to the total weight of the welding rod) To improve the selective corrosion resistance of the weld metal, 0.30 to 2.00 wt. %Added. This range is 0.15-2.00 wt. % Is the amount required for addition. Ni is metallic Ni, Fe- in the coating material.
Not only can it be added in the form of Ni, Ni oxide, etc., but it can also be added to the core wire. Cu + Ni: 0.30 to 2.00% (ratio to the total weight of the welding rod) Cu and Ni can be added in combination to improve the selective corrosion resistance of the weld metal, but Cu + Ni is 0.30 relative to the total weight of the welding rod. ~ 2.00 wt. Add in the range of%. This range is 0.15 to 2.00w Cu + Ni in the weld metal.
t. % Is the amount required for addition. B: 0.05 to 0.5% (ratio in coating material) 0.05 to 0.5 wt.% In the coating material in order to refine the structure and obtain good toughness. % Can be added. This range is 0.0005 to 0.0050 wt.
% Is the amount required for addition. Weight ratio of coating material to welding rod; 0.10 to 0.19 The weight ratio of coating material to welding rod (covering ratio) is an important condition for facilitating the downward welding, and therefore the coating ratio is 0. 10 or more is required. 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 burnt. Further, the coating ratio is 0.
When it exceeds 19, the concentration of the arc is lowered and it becomes difficult to form the back bead. 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. In addition,
The balance of the coating agent is mainly composed of cellulose. Also usually
Other components added to the coating material for high cellulosic coated arc welding rods, such as Na ₂ O, Al ₂ O ₃ , Zr.
A minute amount of metal components such as O ₂ and K ₂ O and Fe and Cr can be added.

The reason for limiting the welding conditions in the present invention is as follows. Rod diameter: 3.2 to 4.8 mm Welding using a rod diameter outside this range is also possible, but in consideration of welding efficiency and ease of circumferential welding of pipes, 3.2
~ 4.8mm. Type of current: DCEP DCEP (direct current, rod plus) generally used when using a high cellulosic welding rod. Welding current, welding speed: 90-240A, 100-450
mm / min Weld current and welding speed generally used according to the groove shape, welding position, and rod diameter. Welding position: All positions All positions should be set considering the circumferential welding of the pipe. In the case of inclined welding, downward welding (downward welding) is performed.

[0015]

EXAMPLES Examples of the present invention will be described. Table 1 shows the chemical composition (% by weight) of the test base metal. After manufacturing a welded steel pipe having an outer diameter of 38 inches and a total length of 12 m using the A to D steels shown in Table 1, circumferential welding is performed by covered arc welding, and the strength, toughness, and seawater environment of the weld metal (CO ₂ bubbling) The selective corrosion rates in the above were measured respectively. Tables 2 and 3 show the selective corrosion rate of the weld metal, strength, toughness, and the presence or absence of cracks.
For strength YS, JIS Z2201 No. 3 (6 mmφ) test piece was used, and for toughness, JIS Z3128 No. 4 test piece was used.
It was evaluated by the absorbed energy at 0 ° C. The presence or absence of weld cracking is determined by observing 5 cross-sections after welding, and the selective corrosion rate is 50 cm long steel pipe including circumferential welds, artificial seawater is put inside, and CO ₂ gas is blown into it to form a base metal. It is a value measured by obtaining the difference in plate thickness of the weld metal part.

As shown in Tables 2 and 3, the yield strength (350 N / mm ² or more), toughness (50 J or more), and selective corrosion are found in the circumferential welded portion where the chemical composition of the weld metal satisfies the claims. It was confirmed that the circumferential welded portion has excellent properties (the weld metal portion does not selectively corrode, indicated by 0 in Table 2), has a low hardness (Hv 300 or less), and has excellent crack resistance.

[Table 1]

[Table 2]

[Table 3]

[0017]

As described above, according to the present invention, since the chemical composition of the weld metal portion is adjusted by the base material, the welding material and the welding method, it is exposed to a corrosive environment such as a seawater environment containing CO _2. In the selective corrosion of the circumferential welded portion, by specifying the Mo difference between the weld metal portion and the base metal as described above, it has sufficient strength and high toughness, and also has weld crack resistance and selective corrosion resistance. It is possible to obtain an excellent circumferential weld metal part.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a selective corrosion current (μA) flowing between a base material and a weld metal and ΔMo.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location B23K 35/365 R 7362-4E // B23K 101: 06 (72) Inventor Motokiyo Itoh Chiyoda, Tokyo 1-1-2, Marunouchi-ku Nihon Kokan Co., Ltd. (72) Inventor Takeshi Sugino 100-1 Urakawachi, Miyamae, Fujisawa-shi, Kanagawa Kobe Steel Works, Fujisawa Works (72) Inventor Shozo Naruse Kanagawa 100-1 Urakawachi, Fujimae, Fujisawa Prefecture

Claims (2)

[Claims] 1. A method for covering arc welding of a pipe by combining a pipe base material, a high-cellulosic welding rod and welding conditions so that a weld metal having the following chemical composition (% by weight) can be obtained in the circumferential welding of the pipe. .. C; 0.05 to 0.20% Si; 0.05 to 0.45% Mn; 0.50 to 2.00% Mo; 0.03 to 1.05% The balance consists of Fe and inevitable impurities, and The following formula (1) determined by the difference in Mo between the weld metal and the base metal and the formula (2) calculated from the chemical composition of the weld metal are satisfied. ΔMo ≧ 0.03% (1) P _CM ≦ 0.30% (2) However, P _CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15
+ V / 10 + 5B At this time, unavoidable impurities shall satisfy the following range. P; ≤0.030% S; ≤0.030% Al;
≤0.10% N; ≤0.050% Nb; ≤0.10% V;
≤0.10% Ti; ≤0.10% Cr; ≤1.00% Ca;
≤0.0025% O; ≤0.10% Zr; ≤0.05% Chemical composition (% by weight) of base material C; 0.03 to 0.15% Si; 0.05 to 0.50% Mn; 0.50 to 2.00% Al; 0.005 to 0.10%, or one or more of the following components in addition to the above chemical components: Cu; 0.05 to 2.0% Ni; 0.05 to 2.0% Cr; 0.05 to 2.0% Mo; 0.05 to 1.0% Nb; 0.005 to 0.20% V; 005 to 0.20% Ti; 0.005 to 0.20% B; 0.0005 to 0.0020% Ca; 0.0005 to 0.0050% The balance contains Fe and unavoidable impurities. Composition of welding rod A coating material obtained by kneading a coating material raw material containing a large amount of cellulose together with a binder, in a high cellulose-based coated arc welding rod formed by coating the outer circumference of a mild steel core wire or a low alloy steel core wire,
In the coating agent, the following chemical components (wt%) MgO; 0.1-7.0% iron oxide (FeO conversion); 7-25% TiO ₂ ; 8-19% SiO ₂ ; 10-30% Mn; It is a welding rod containing 5 to 27%, and Mo; 0.06 to 1.10% added singly or in combination with respect to the total weight of the welding rod, and the weight ratio of the coating agent is 0.10 to 0. .19, or in addition to the above chemical components, one or more of the following components are contained, a high cellulosic welding rod. Cu; 0.30 to 2.00% (based on the total weight of the welding rod) Ni; 0.30 to 2.00% (based on the total weight of the welding rod) Cu + Ni; 0.30 to 2.00% (welding B: 0.05 to 0.5% (relative to the total weight of the coating) Welding conditions Rod diameter (core diameter): 3.2 to 4.8 mm Current type: DCEP Welding current : 90-240A Welding speed: 100-450mm / min Welding posture: All postures (downward welding) 2. The weld metal, in addition to the chemical composition,
The method for coating arc welding of pipes according to claim 1, wherein one or more of the following components are contained. Cu; 0.15-2.00% Ni; 0.15-2.00% Cu + Ni; 0.15-2.00% B; 0.0005-0.0050%