JP2019196527A - Cr-CONTAINING ELECTROSEAMED STEEL PIPE, AND MANUFACTURING METHOD THEREOF - Google Patents

Abstract

To provide an electroseamed steel pipe excellent in corrosion resistance, and containing Cr over 3%.SOLUTION: In a Cr-containing electroseamed steel pipe containing Cr as much as 3.0-32.0 mass%, concerning Cr oxide defects existing on a welding surface, an evaluation length L, the maximum defective length Lin L, and a ratio Lbetween the evaluation length Land a total defect length (total of line lengths of exposed defects) satisfy following formulas (1), (2), and thereby corrosion resistance of a weld zone becomes equivalent to that of a parent metal: L[mm]≤0.1...(1) (100×L/L)[%]<-0.5×L[mm]+0.1...(2).SELECTED DRAWING: Figure 5

Description

  The present invention relates to a Cr-containing ERW steel pipe suitable for use as an oil well pipe, a line pipe, and the like, and a method for manufacturing the same.

  ERW welding can produce steel pipes with high roundness and small uneven thickness with high productivity, and is widely used for structural pipes, line pipes, oil well pipes, etc. However, since it is a welded pipe, the quality of the steel pipe is often determined by the quality of the welded portion, and it has been difficult to manufacture the material with a material in which the quality of the welded portion is difficult to ensure.

  In oil well pipes and line pipes for producing and transporting oil and gas, carbon steel and low alloy steel materials are used in a normal neutral wet environment. However, oil and gas containing a large amount of carbon dioxide gas has a much faster corrosion rate than corrosion under normal neutral and humid environments and atmospheric corrosion. For oil well pipes and line pipes for the production and transportation of steel, stainless steel seamless steel pipes containing more than 13% Cr with excellent corrosion resistance to carbon dioxide as a material, and adding oil to the oil Alternatively, arc welded pipes have been mainly used.

  However, the use of corrosion inhibitors in oil is not desirable from the viewpoint of environmental protection, and the application of stainless steel to line pipes is expensive, and the usage period is limited or the corrosion conditions are not so severe. It is over-spec in terms of cost-effectiveness for application to a new environment. In addition, since seamless steel pipes and arc welded steel pipes are less productive than ERW welding, steel pipes with lower alloy costs than stainless steel are desired for ERW welded pipes. Therefore, it is necessary to ensure high ERW welding quality with a material of an alloy component system necessary and sufficient for the use environment. From the viewpoint of securing corrosion resistance that is clearly superior to that of carbon steel, it is desirable that the Cr addition amount covers a range of more than 3%.

  On the other hand, Japanese Patent Application Laid-Open No. 56-93856, which is Patent Document 1, and Japanese Patent No. 4,499,949, which is Patent Document 2, can improve the local corrosion of the welded portion as well as the general corrosion caused by carbon dioxide gas. Steel for line pipes is disclosed. However, these publications do not describe an electric resistance welding method. Since steel containing about 1% or more of Cr is likely to generate oxide defects, consideration for suppressing oxide defects is indispensable in order to achieve stable welding quality.

  Moreover, in patent 4890609 which is patent document 3, the technique which suppresses a defect area ratio to 0.01% or less with the steel which contains about 0.5 to 26% or more of Cr by the electric resistance welding using a plasma shield. is suggesting. To ensure corrosion resistance, which is an advantage of steel containing Cr, it is necessary to reduce defects, and it is desirable that the amount of defects on the entire butt surface be low, but the amount of weld defects related to corrosion resistance is specified not on the butt surface but on the surface. There is a need to. This is because the corrosion of the material occurs on the material surface of the steel pipe, and even if the defect rate is low on the surface of the butt portion, if the defect is exposed on the surface, the corrosion resistance of the steel pipe is deteriorated.

  Therefore, it is necessary to clarify an index more suitable than the area ratio of weld defects for ensuring corrosion resistance, and to establish a steel pipe that satisfies the index and a manufacturing method that enables it.

JP-A-56-93856 Japanese Patent No. 4499949 Japanese Patent No. 4890609

Therefore, the object of the present invention is to solve the above-mentioned conventional problems, and is suitable for use in an environment containing a large amount of carbon dioxide (CO ₂ ) or for transporting oil and gas containing a large amount of CO ₂ . It is to provide an electric resistance welded steel pipe containing Cr and a method for manufacturing the same.

The present invention made to solve the above-described problems is as follows (1) to (9).
(1) The ingredient is mass%,
Cr: 3.0 mass% or more and 32.0 mass% or less,
C: 0.01 mass% or more and 0.45 mass% or less,
Si: 0.02 mass% or more and 1.00 mass% or less,
Mn: 0.05 mass% or more and 2.00 mass% or less,
P: 0.0008 mass% or more and 0.0450 mass% or less,
S: 0.0003 mass% or more and 0.0300 mass% or less,
Al: 0.005 mass% or more and 1.000 mass% or less,
N: 0.0005 mass% or more and 0.4000 mass% or less,
In a Cr-containing ERW steel pipe comprising residual Fe and unavoidable impurities, the evaluation length L _w , the maximum defect length L _dmax in L _w , and the evaluation length L for Cr oxide defects present on the weld surface A Cr-containing electric-welded steel pipe, _wherein the ratio of _w to the total defect length (total length of exposed defect lines) L _dtot satisfies the following formulas (1) and (2).
L _dmax [mm] ≦ 0.1 (1)
(100 × L _dtot / L _w ) [%] <− 0.5 × L _dmax [mm] +0.1 (2)

(2) In addition, the component is mass%,
B: 0.0001 mass% or more and 0.0200 mass% or less,
Ni: 0.03 mass% or more and 28.00 mass% or less,
Mo: 0.02 mass% to 7.00 mass%,
W: 0.02 mass% or more and 8.0 mass% or less,
Cu: 0.01 mass% or more and 4.00 mass% or less,
Ti: 0.01 mass% or more and 1.00 mass% or less,
Nb: 0.01 mass% or more and 1.00 mass% or less,
Zr: 0.01 mass% or more and 1.00 mass% or less,
V: 0.01 mass% or more and 1.00 mass% or less,
(1) Cr-containing ERW steel pipe characterized by containing one or more of the above.

(3) The component is mass%,
Cr: 3.0 mass% or more and 32.0 mass% or less,
C: 0.01 mass% or more and 0.45 mass% or less,
Si: 0.02 mass% or more and 1.00 mass% or less,
Mn: 0.05 mass% or more and 2.00 mass% or less,
P: 0.0008 mass% or more and 0.0450 mass% or less,
S: 0.0003 mass% or more and 0.0300 mass% or less,
Al: 0.005 mass% or more and 1.000 mass% or less,
N: 0.0005 mass% or more and 0.4000 mass% or less,
As a power supply coil used for ERW welding, one of the outer surface and the back surface of the coil main body is formed as a Cr-containing ERW steel pipe by making a Cr-containing steel sheet containing residual Fe and inevitable impurities. Alternatively, a method for producing a Cr-containing electric-welded steel pipe, characterized in that both are partitioned by a water channel and electro-welded using a power supply coil covered with a cover that covers the water channel and prevents leakage of cooling water.

(4) The method for producing a Cr-containing ERW steel pipe according to (3), wherein the water channel and the cover are electro-welded using a power feeding coil arranged outside the coil body.
(5) The Cr-containing battery according to (3) or (4), wherein the water channel is electro-welded using a power feeding coil disposed so as to preferentially cool the pipe-forming side downstream of the power feeding coil. Manufacturing method of sewn steel pipe.
(6) In the power feeding coil provided with the water channel, at the connection portion between the cooling water main pipe and the power feeding coil side water channel, the cooling water main pipe side should be electro-welded using a power feeding coil having the same or wider pipe. The method for producing a Cr-containing electric resistance welded steel pipe according to any one of (3) to (5) 5.
(7) The method for producing a Cr-containing ERW steel pipe according to any one of (3) to (6), wherein the feeding coil is provided upstream of a squeeze roll.
(8) The method for producing a Cr-containing ERW steel pipe according to any one of (3) to (7), further comprising plasma shielding the ERW weld.

(9) In addition, the component is mass%,
B: 0.0001 mass% or more and 0.0200 mass% or less,
Ni: 0.03 mass% or more and 28.00 mass% or less,
Mo: 0.02 mass% to 7.00 mass%,
W: 0.02 mass% or more and 8.0 mass% or less,
Cu: 0.01 mass% or more and 4.00 mass% or less,
Ti: 0.01 mass% or more and 1.00 mass% or less,
Nb: 0.01 mass% or more and 1.00 mass% or less,
Zr: 0.01 mass% or more and 1.00 mass% or less,
V: 0.01 mass% or more and 1.00 mass% or less,
The method for producing a Cr-containing electric-welded steel pipe according to any one of (3) to (8), comprising one or more of the following.

  By using the technique of the present invention, it is possible to provide an ERW steel pipe containing 3% or more of Cr and having excellent corrosion resistance.

It is a figure which shows the precipitation condition of Cr oxide in Cr steel. It is a figure which shows the relationship between the size and density of the defect exposed on the surface of a steel pipe, and deterioration of corrosion resistance. It is a figure which shows the relationship between the size and density of the defect exposed to the inner surface of a steel pipe, and deterioration of corrosion resistance. It is a graph which shows the relationship between _Ldmax and deterioration of corrosion resistance. The horizontal axis is L _dmax and the vertical axis is (L _dtot / L _w ), which is a graph plotting experimental data below L _dmaxt . It is a perspective view which shows the coil main body of a feed coil. It is a disassembled perspective view which shows the state which formed the water channel in the coil main body. It is a figure which shows the channel pattern without a partition used in the Example. It is a figure which shows the channel pattern with a partition used in the Example.

Embodiments of the present invention will be described below.
Corrosion resistance in an environment where surface corrosion is a problem does not corrode if there are many defects on the weld surface unless they are exposed to the surface. However, even if there are very few defects on the weld surface, if it comes out on the weld surface, it causes local corrosion and deteriorates the corrosion resistance compared to the base metal. Particularly in a CO ₂ humid environment, the surface of the steel material is H ₂ O + CO ₂ → H ⁺ + HCO ₃ ⁻
It is exposed to a low pH corrosive environment. Therefore, corrosion will progress unless the corrosion resistance of the steel material surface is ensured. Therefore, the inventors focused on the corrosion resistance of Cr steel and tried to improve it by utilizing Cr steel. It is known as an experimental fact that the corrosion resistance of Cr steel in a CO ₂ wet environment is determined by the Cr content if Cr is dissolved. However, even in the case of Cr steel, the corrosion resistance as a base material is improved by the inclusion of Cr, but depending on the size and distribution of the Cr compound on the welded part, particularly the welded surface, and also the Cr oxide on the welded surface Similarly, it has been found to affect the corrosion resistance.

  FIG. 1 shows the state of precipitation of Cr oxide. When Cr oxide is generated in Cr steel, the Cr content around the compound decreases with the concentration of Cr in the oxide, so that the corrosion resistance of the oxide generation position deteriorates as compared with the base material. A larger oxide results in a wider Cr-depleted layer. Therefore, compounds that are detrimental to corrosion resistance have a lower size limit. In other words, if the oxide is smaller than a certain size, the degradation allowance of corrosion resistance alone is small. However, even with small oxides, if the density is large, the corrosion resistance is degraded. Therefore, in the present invention, an index for determining the presence or absence of deterioration of corrosion resistance due to Cr oxide is defined, and a process satisfying the index has been found. Details will be described below.

(Rules related to Cr oxide defects that make the corrosion resistance of welds equal to that of the base metal)
As described above, the oxide defects in the Cr steel weld are mainly composed of Cr oxides, and at the same time, a form in which a Cr-depleted layer is generated around the defects. In electric resistance welding of Cr steel, an oxidation reaction occurs on the butt surface during heating before butting, and most of the Cr oxide defects are discharged while being stretched during upsetting. It is impossible to completely eliminate physical defects. And since a Cr oxide defect is extended along a butt | matching surface, the Cr oxide defect exposed on the steel pipe surface will be located substantially linearly along the weld line on the steel pipe surface.

When the Cr oxide defect is located on the outer surface in this manner, the corrosion resistance of the surface on the surface is deteriorated with respect to the base material, which can be a starting point for corrosion in a CO ₂ wet environment. That is, as shown in FIG. 2, the corrosion resistance is deteriorated depending on the size and density of the exposed defects. Specifically, when a coarse defect is exposed, the corrosion resistance deteriorates. However, even if a coarse defect is not exposed, the corrosion resistance does not deteriorate. Further, even if fine defects are exposed, the corrosion resistance is not deteriorated if the density is low, and if the fine defects are exposed at a high density, the corrosion resistance is deteriorated.

Similarly, when the defect is located on the inner surface, the corrosion resistance of the surface at the position is deteriorated with respect to the base material, so that it can be a starting point of corrosion when the CO ₂ wet fluid is transported. That is, as shown in FIG. 3, the corrosion resistance deteriorates depending on the size and density of the exposed defects.

As described above, since it is the Cr oxide defects present on the weld surface that affect the corrosion resistance, the distribution of the Cr oxide defects along the weld line on the surface can specify whether or not the corrosion resistance deteriorates. there is a possibility. The Cr oxide defect is linear as described above, and the maximum defect length L _dmax within a predetermined evaluation length (for example, sample length) L _w and L _w is used as a parameter representing deterioration due to the Cr oxide defect. It was organized corrosion resistance ratio of (the total length of the exposed defect line) L _dtot evaluation length L _w and the total defect length as a parameter representing the dense degree of defect. The deterioration of corrosion resistance was evaluated by the occurrence of visible dents. As a result, it has been found that the Cr oxide defects on the weld surface simultaneously satisfy the following expressions (1) and (2), whereby the corrosion resistance of the welded portion is equivalent to that of the base material.
L _dmax [mm] ≦ 0.1 (1)
(100 × L _dtot / L _w ) [%] <− 0.5 × L _dmax [mm] +0.1 (2)

  The evaluation length Lw is 200 mm, a sample is taken, the weld bead is cut, the position of the weld line is confirmed by picric acid etching, the surface of the mirror-polished surface is along the weld line, and the center of the weld line is 500 μm. The area is 500 times and the length of 200 mm is observed by SEМ, and in the reflected electron image, the brightness is less than half that of the base material (the light element is darker in the reflected electron image, so the oxide has lower brightness than the steel) )), An oxide that was analyzed by EDS was regarded as a defect.

(About formula (1))
The basis for this is as follows. The electric resistance welding of Cr-containing steels were tested for immersion in 5MPa of CO ₂ environment, to observe the recess described above. FIG. 4 shows the result. When the maximum defect length L _dmax is larger than 1 × 10 ⁻⁴ m (= 0.1 mm), it was revealed that a visible dent was surely observed and the corrosion resistance deteriorated.

Further, when L _dmax was smaller than 1 × 10 ⁻⁴ m (= 0.1 mm), the degree of corrosion resistance deterioration varied. A result of attempting a determination of deterioration presence in various indicators, found that organize the ratio of the weld wire length _{L w} of evaluating the sum _{L dtot} defect length _(L dtot / _{L w).} FIG. 5 shows a plot of experimental data below L _dmaxt , where the horizontal axis is L _dmax and the vertical axis is (L _dtot / L _w ). It can be seen that the presence or absence of deterioration can be discriminated by the dotted line in the equation (2) in the figure.

(About the component range of Cr-containing steel)
The component ranges of the Cr-containing steel in the present invention are as follows. Examples of the Cr-containing steel used in the steel pipe include low alloy Cr steel, martensitic stainless steel, ferritic stainless steel, austenitic stainless steel, and duplex (ferrite-austenitic) stainless steel. Is as follows.
Cr: 3.0 mass% or more and 32.0 mass% or less C: 0.01 mass% or more and 0.45 mass% or less Si: 0.02 mass% or more and 1.00 mass% or less Mn: 0.05 mass% or more and 2.00 mass% or less P: 0.0008 mass% to 0.0450 mass% S: 0.0003 mass% to 0.0300 mass% Al: 0.005 mass% to 1.000 mass% N: 0.0005 mass% to 0.4000 mass%

Furthermore, it is also preferable to contain one or more of the following elements as selective elements.
B: 0.0001 mass% or more and 0.0200 mass% or less Ni: 0.03 mass% or more and 28.00 mass% or less Mo: 0.02 mass% or more and 7.00 mass% or less W: 0.02 mass% or more and 8.0 mass% or less Cu: 0.01 mass% to 4.00 mass% Ti: 0.01 mass% to 1.00 mass% Nb: 0.01 mass% to 1.00 mass% Zr: 0.01 mass% to 1.00 mass% V: 0.00% 01 mass% or more and 1.00 mass% or less

The reason for limiting the numerical value of each component will be described below.
Cr imparts corrosion resistance to the steel material. In order to ensure corrosion resistance in a CO ₂ environment, a content of 3.0 mass% or more is required. In addition, as the amount of added Cr increases, the cost increases and there is no merit exceeding the upper limit of 26.0 mass% (JIS G 4304) used in general stainless steel, so the appropriate range is 3.0 ≦ Cr ≦ 32.0 mass. %.

  C improves strength. If it is less than 0.01 mass%, the strength is not improved. If it exceeds 0.45 mass%, Cr and C are combined to reduce the effective Cr amount and the corrosion resistance is remarkably reduced. Therefore, the appropriate range is 0.01 ≦ C ≦ 0. .45 mass%.

  Si improves oxidation resistance. If it is less than 0.03 mass%, the oxidation resistance will not be improved, and if it exceeds 1.00 mass%, the toughness of HAZ will be significantly reduced and it will be easily cracked during processing. Therefore, the appropriate range is 0.03 ≦ Si ≦ 1.00 mass%. is there.

  Mn improves strength. If it is less than 0.05 mass%, the strength is not improved, and if it exceeds 5.00 mass%, the oxidation resistance is remarkably lowered. Therefore, the appropriate range is 0.05 ≦ Mn ≦ 5.00 mass%.

  Since P causes internal scratches and lowers toughness, the smaller the amount, the better. If it exceeds 0.045 mass%, the occurrence of internal defects and a decrease in toughness become remarkable. Therefore, P must be 0.045 mass% or less. The lower limit is set to 0.0008 mass% from the viewpoint of cost and productivity.

  S causes a decrease in corrosion resistance and a decrease in toughness. Since corrosion resistance will deteriorate remarkably when it exceeds 0.0300 mass%, S must be 0.0300 mass%. The lower limit is set to 0.0003 mass% from the viewpoint of cost and productivity.

  Al is a deoxidizing material and improves oxidation resistance. If it is less than 0.005 mass%, there is no effect, and if it exceeds 1.000 mass%, inclusions are remarkably increased and ductility and toughness are greatly impaired. Therefore, the appropriate range is 0.005 ≦ Al ≦ 1.000 mass%. .

  N is inevitably mixed, and Cr-containing steel has an effect of improving corrosion resistance. It is difficult to reduce to less than 0.0005 mass%, and if it exceeds 0.4000 mass%, blowholes during welding increase remarkably, so the appropriate range is 0.0005 ≦ N ≦ 0.4000 mass%.

  Ni improves toughness and corrosion resistance. If less than 0.003 mass%, there is no effect, and if the amount of Ni added increases, the cost increases, and the upper limit of 28.00 mass% (for example, JIS G 4304) used for Cr-containing steels such as general stainless steel. Since there is no merit to exceed, the appropriate range is 0.03 mass% ≦ Ni ≦ 28.00 mass%.

  Mo improves corrosion resistance and high temperature strength. If the amount is less than 0.02 mass%, the effect is not obtained, and if the amount of added Mo increases, the cost increases, and the upper limit of 7.00 mass% used for Cr-containing steel such as general stainless steel (for example, JIS G 4304). Since there is no merit to exceed, an appropriate range is 0.03 mass% <= Mo <= 7.00 mass%.

  W improves corrosion resistance and high temperature strength. If it is less than 0.02 mass%, there is no effect, and if the amount of added W increases, the cost increases, and there is no merit exceeding the upper limit of 3.00 mass% (for example, JIS G 4312) used in general heat-resistant steel. Therefore, the appropriate range is 0.02 mass% ≦ W ≦ 3.00 mass%.

  Cu improves corrosion resistance. If it is less than 0.01 mass%, the effect is not obtained, and if it exceeds 4.00 mass%, the toughness is remarkably lowered. Therefore, the appropriate range is 0.01 ≦ Cu ≦ 4.00 mass%.

  B improves hardenability. If it is less than 0.0001 mass%, the effect is not obtained, and if it exceeds 0.0200 mass%, the toughness is remarkably lowered. Therefore, the appropriate range is 0.0001 ≦ B ≦ 0.0200 mass%.

  Ti improves high temperature strength. If it is less than 0.01 mass%, the effect is not obtained, and if it exceeds 1.00 mass%, the toughness of the welded portion is remarkably lowered. Therefore, the appropriate range is 0.01 ≦ Ti ≦ 1.00 mass%.

  Nb improves high temperature strength. If it is less than 0.01 mass%, the effect is not obtained, and if it exceeds 1.00 mass%, the toughness of the welded portion is remarkably lowered. Therefore, the appropriate range is 0.01 ≦ Nb ≦ 1.00 mass%.

  Zr improves high temperature strength. If it is less than 0.01 mass%, the effect is not obtained, and if it exceeds 1.00 mass%, the toughness of the welded portion is remarkably lowered. Therefore, the appropriate range is 0.01 ≦ Zr ≦ 1.00 mass%.

  V improves high temperature strength. If it is less than 0.01 mass%, the effect is not obtained, and if it exceeds 1.00 mass%, the toughness of the welded portion is remarkably lowered. Therefore, the appropriate range is 0.01 ≦ V ≦ 1.00 mass%.

(Manufacturing method with the specified Cr oxide defect to make the corrosion resistance of the welded part equal to the base metal)
It is the same as in the past that Cr oxide defects cannot be suppressed simply by optimizing welding-related conditions such as electric welding current. Therefore, we examined quality assurance by suppressing oxide formation by improving the surrounding environment during ERW welding.

  Conventionally, it has been recommended to use a plasma shield as a measure for improving the surrounding environment and welding quality. However, the plasma shield is also disturbed by the water vapor caused by the cooling water, or has suffered from the deterioration of the quality of the weld due to the intrusion of water vapor or water droplets. Therefore, we investigated the suppression of the generation of water vapor and water droplets caused by cooling water, which is the main cause of quality deterioration of welds. As a result, it was found that the following structure of the feeding coil is preferable. The feeding coil is provided upstream of a squeeze roll of a well-known electric sewing pipe facility.

  Instead of making a hole in the power supply coil itself, making it hollow, or connecting a water cooling pipe, the surface of the power supply coil is partitioned by a water channel and covered with a cover that prevents the cooling water from leaking. The partition and the cover may not necessarily be made of the same material as that of the power feeding coil as long as the cooling is sufficient. However, the partition and the cover are preferably made of the same material from the viewpoint of construction and thermal expansion. It is preferable to install the water channel and its cover on the inside (side through which the steel pipe in the pipe passes) and / or outside (the opposite side) of the feeding coil. However, the heating capacity of the feeding coil and the ease of construction of the water channel Therefore, it is preferable to be disposed outside the feeding coil.

  6 and 7 show an example of the structure of the feeding coil. The coil body 20 of the power feeding coil has a shape as shown in FIG. 6 and includes a circular portion 21 and a flat plate portion 22 connected to a high frequency power source. The coil body 20 is preferably made of a copper plate. As shown in FIG. 7, a zigzag water channel 24 is formed on the surface of the coil body 20 by brazing a partition bar 23 on the surface of the coil body 20. The length of the partition bar 23 is set short so that the water flow is not hindered. And it is set as the structure where a cooling water does not leak by covering the cover 25 from the top. The partition bar 23 is not essential and can be omitted. It is preferable that the water channel 24 preferentially cools the pipe-forming downstream side of the power feeding coil, and it is preferable that the water channel is partitioned as such. This is because the pipe-forming downstream side of the power feeding coil is exposed to the heat of the plasma shield and ERW welding.

  In the connection portion between the cooling water main pipe and the power feeding coil side water passage, it is preferable that the cooling water main pipe side has the same or wider pipe passage. This is because when the power supply coil side water channel is wider, stagnation occurs at the corner of the connecting portion, resulting in insufficient cooling, and the coil, water channel, and cover may be damaged or melted. Needless to say, if the amount of cooling water is large, breakage and dissolution of the feeding coil, water channel and cover are reduced. Similarly, if the heat input is not properly maintained, the power supply coil, the water channel, and the cover may be damaged or melted regardless of other conditions.

  The supply of cooling water to the power supply coil is preferably performed from the upstream side of the pipe making. In view of the cooling effect, it is preferable to cool from the downstream as described above, but there are squeeze rolls for pipe making and electric sewing downstream from the feeding coil, and it may be difficult to secure the path of the cooling water pipe. Because there is. By using such a power supply coil, the cooling water becomes water vapor or water droplets and does not adhere to the welded portion, so that the quality of the welded portion is improved, that is, the prescribed Cr oxide defect is achieved. It will be. Furthermore, it goes without saying that the use of a plasma shield improves the quality of the weld.

  Tables 1-A to 1-J show the results of cooling the power supply coil according to the water channel arrangement. FIG. 8 shows a water channel pattern without a partition used in the test, and FIG. 9 shows a water channel pattern with a partition. The steel pipe component is steel grade G shown in Table 2 to be described later, the feeding coil is for a steel pipe having an outer diameter of 11-3 / 4 inch, the current-carrying part (coil body 20) is made of copper and has a wall thickness of 3 mm, and a flow path. The partition was also made of copper, and a 6 mm thick partition rod 23 was brazed, and a thin cover 25 (t1.5 mm) was overlapped to close the end portion by brazing. This structure is common regardless of the dimensions of the feeding coil, the welding power source, and the structure of the forming roll.

  Next, the test which changed the component of Cr containing ERW steel pipe as shown in Table 2 was done, and the quality evaluation result is shown in Table 3. In Table 3, the water drainage was made using a water-cooled coil (partitioned 11). Heating method is high frequency induction heating, butting is I type, without water draining, using an external water-cooled work coil (normal pipe making), with water draining, using an internal water-cooled work coil, ERW steel pipe size: outer diameter 298mm, plate thickness 9.5mm, Evaluation length: 200 mm each.

As shown in Examples 1 and 2 described above, according to the present invention, it is excellent in corrosion resistance, suitable for use in an environment containing a large amount of carbon dioxide (CO ₂ ) or for transporting oil and gas containing a large amount of CO _2. In addition, it is possible to provide an ERW steel pipe containing more than 3% Cr.

20 coil body 21 circular portion 22 flat plate portion 23 partition bar 24 water channel 25 cover

Claims (9)

Ingredient is mass%,
Cr: 3.0 mass% or more and 32.0 mass% or less,
C: 0.01 mass% or more and 0.45 mass% or less,
Si: 0.02 mass% or more and 1.00 mass% or less,
Mn: 0.05 mass% or more and 2.00 mass% or less,
P: 0.0008 mass% or more and 0.0450 mass% or less,
S: 0.0003 mass% or more and 0.0300 mass% or less,
Al: 0.005 mass% or more and 1.000 mass% or less,
N: 0.0005 mass% or more and 0.4000 mass% or less,
In a Cr-containing ERW steel pipe comprising residual Fe and unavoidable impurities, the evaluation length L _w , the maximum defect length L _dmax in L _w , and the evaluation length L for Cr oxide defects present on the weld surface A Cr-containing electric-welded steel pipe, _wherein the ratio of _w to the total defect length (total length of exposed defect lines) L _dtot satisfies the following formulas (1) and (2).
L _dmax [mm] ≦ 0.1 (1)
(100 × L _dtot / L _w ) [%] <− 0.5 × L _dmax [mm] +0.1 (2) In addition, the ingredients are mass%,
B: 0.0001 mass% or more and 0.0200 mass% or less,
Ni: 0.03 mass% or more and 28.00 mass% or less,
Mo: 0.02 mass% to 7.00 mass%,
W: 0.02 mass% or more and 8.0 mass% or less,
Cu: 0.01 mass% or more and 4.00 mass% or less,
Ti: 0.01 mass% or more and 1.00 mass% or less,
Nb: 0.01 mass% or more and 1.00 mass% or less,
Zr: 0.01 mass% or more and 1.00 mass% or less,
V: 0.01 mass% or more and 1.00 mass% or less,
The Cr-containing ERW steel pipe according to claim 1, comprising one or more of the following. Ingredient is mass%,
Cr: 3.0 mass% or more and 32.0 mass% or less,
C: 0.01 mass% or more and 0.45 mass% or less,
Si: 0.02 mass% or more and 1.00 mass% or less,
Mn: 0.05 mass% or more and 2.00 mass% or less,
P: 0.0008 mass% or more and 0.0450 mass% or less,
S: 0.0003 mass% or more and 0.0300 mass% or less,
Al: 0.005 mass% or more and 1.000 mass% or less,
N: 0.0005 mass% or more and 0.4000 mass% or less,
As a power supply coil used for ERW welding, one of the outer surface and the back surface of the coil main body is formed as a Cr-containing ERW steel pipe by making a Cr-containing steel sheet containing residual Fe and inevitable impurities. Alternatively, a method for producing a Cr-containing electric-welded steel pipe, characterized in that both are partitioned by a water channel and electro-welded using a power supply coil covered with a cover that covers the water channel and prevents leakage of cooling water.   4. The method for producing a Cr-containing ERW steel pipe according to claim 3, wherein the water channel and the cover are ERW welded using a power feeding coil disposed outside the coil body.   5. The Cr-containing ERW steel pipe according to claim 3, wherein the water channel is ERW welded using a power feeding coil disposed so that the downstream side of the feeding coil can be preferentially cooled. Production method.   In the power feeding coil provided with the water channel, at the connection portion between the cooling water main pipe and the power feeding coil side water channel, the cooling water main pipe side is electro-welded using a power feeding coil having the same or wider pipe. A method for producing a Cr-containing ERW steel pipe according to any one of claims 3 to 5.   The method for producing a Cr-containing ERW steel pipe according to any one of claims 3 to 6, wherein the feeding coil is provided upstream of a squeeze roll.   The method for producing a Cr-containing ERW steel pipe according to any one of claims 3 to 7, further comprising plasma shielding the ERW weld. In addition, the ingredients are mass%,
B: 0.0001 mass% or more and 0.0200 mass% or less,
Ni: 0.03 mass% or more and 28.00 mass% or less,
Mo: 0.02 mass% to 7.00 mass%,
W: 0.02 mass% or more and 8.0 mass% or less,
Cu: 0.01 mass% or more and 4.00 mass% or less,
Ti: 0.01 mass% or more and 1.00 mass% or less,
Nb: 0.01 mass% or more and 1.00 mass% or less,
Zr: 0.01 mass% or more and 1.00 mass% or less,
V: 0.01 mass% or more and 1.00 mass% or less,
1 or 2 types or more of these are contained, The manufacturing method of the Cr containing ERW steel pipe of any one of Claim 3 thru | or 8 characterized by the above-mentioned.