JP6520876B2 - Manufacturing method of ERW welded clad steel pipe - Google Patents

Description

  The present invention relates to a method of manufacturing an electric resistance welded welded clad steel pipe.

  In general, ERW steel pipe is manufactured by forming a steel strip into a tubular shape, welding opposite end portions in the width direction of the steel strip heated and melted by a high frequency current by butting pressure with a squeeze roll. In the case of the ERW steel pipe, it is generally said that mechanical properties such as toughness and strength of the welded portion deteriorate compared to the steel strip before welding.

  The cause of the deterioration of the mechanical properties of the weld is an oxide-based weld defect called a penetrator. This penetrator remains in the weld and causes the decrease in the toughness and strength of the weld. Therefore, in order to prevent the penetrator from remaining in the welded portion, it is usual to take measures to discharge the oxide melt produced at the time of welding to the outer surface of the pipe by increasing the upset amount by the squeeze roll.

  By the way, as a means for improving the characteristic of ERW steel pipe, ERW welded clad steel pipe has been proposed. The ERW welded clad steel pipe is an ERW steel pipe manufactured using a clad steel band in which a metal band (joining material) made of a material different from the base material is clad on a steel band as the base material. By combining different materials in this manner, it is possible to obtain a steel pipe having excellent characteristics by making use of the characteristics possessed by the base material and the joining material. For example, when carbon steel is used as a base material and stainless steel is used as a joining material, it is considered that a seam-cladded steel pipe having both the corrosion resistance of stainless steel and the strength of carbon steel can be obtained.

  However, in the case of producing an electric resistance welded welded steel pipe using a clad steel strip as the raw material, when the upset amount is increased, as shown in FIG. 5, the molten steel and the heat affected zone of the base material 11 In this case, the phenomenon of invading the welded seam portion of the inner surface of the steel pipe occurs. In particular, when the amount of upset is excessive, the base material 11 is exposed to the joint material side surface of the steel pipe (in the case of FIG. 5, the inner surface of the steel pipe), and as a result, the performance as a clad steel pipe utilizing the excellent characteristics of the joint material. Will be lost.

  For example, a stainless steel clad steel band in which the base material 11 is a low carbon steel and the joining material 12 is a stainless steel, and the upset amount is increased, and an electric seam welded clad manufactured using the joining material as the inner layer and the base material as the outer layer. In a steel pipe, low carbon steel intrudes into the seam portion of stainless steel, or low carbon steel is exposed to the inner surface of the steel pipe as shown in FIG. Therefore, the corrosion resistance in the vicinity of the weld seam portion 14 on the inner surface of the steel pipe is significantly reduced. If such a seam welded welded steel pipe is used in an environment where corrosion resistance is required on the inner surface of the steel pipe, the required performance can not be exhibited.

  That is, in the prior art, there is a problem that it is difficult to simultaneously achieve not deteriorating the mechanical properties of the welded portion and not impairing the function as the clad steel pipe in the case of the electric seam welded clad steel pipe as it is. With respect to such a problem, a technology is known in which an additional process is applied to the ERW welded clad steel pipe.

  In Patent Document 1, at least a joint material side bead in a weld bead obtained by butt welding opposite edges of a clad steel plate or a steel strip bent into a tubular shape is cut and removed to a depth reaching a base material, and a cut and removed portion Discloses a method of manufacturing a clad tube to be subjected to build-up welding having the same properties as a laminated material.

  In Patent Document 2, after a clad steel strip is formed into a hollow tube and a seam edge portion is seam welded, first, along the weld seam where dissimilar metals infiltrated, melting and solidification to the depth of the clad interface portion Second, the seam portion in which the dissimilar metal has infiltrated is weld-backed with the same kind of metal as the joining material, and the weld-over portion is rolled to dilute the dissimilar metal A method of producing a clad steel pipe is disclosed.

  Patent Document 3 discloses a method of manufacturing a clad steel welded steel pipe in which the inner surface side is a composite material, in which at least a part of the joint material butt of a tubular body is formed by forming an original clad steel plate or an original coil and using an inner surface as a composite material. A method of manufacturing a clad steel welded steel pipe is disclosed which is seam welded and then weld butt welds welded on.

Japanese Patent Application Laid-Open No. 60-221173 Japanese Patent Application Laid-Open No. 62-156087 JP-A-5-154545

  However, the techniques described in the above-mentioned Patent Documents 1 to 3 cut and remove the joint material bead portion and weld them after electric resistance welding (Patent Document 1), TIG arc heat source along the welding seam, etc. Because additional welding processes such as melting / solidifying or welding in place (Patent Document 2), welding butt welds in place (Patent Document 3), etc. are required, productivity is reduced, and manufacturing costs are increased. Along with the increase, there has been a problem that additional overlay welding causes adverse environmental effects.

  Therefore, in view of the above problems, the present invention impairs the function as a clad steel pipe in the electric resistance welding as it is without performing additional welding processing such as build-up welding after electric resistance welding which is required in the prior art. It is an object of the present invention to provide a method of manufacturing an electric resistance welded welded clad steel pipe excellent in the mechanical characteristics of a welded portion.

  The present inventors obtained the following knowledge as a result of earnestly examining in order to solve the said subject. Both widthwise end portions of the clad steel strip become butt portions (i.e., welded portions) in an open tube formed into a tubular shape. Therefore, prior to ERW welding, both end portions in the width direction of the clad steel strip are pressed from the laminated material side to form a Y-shaped groove having a predetermined groove shape. It was possible to suppress the penetration of the molten steel and the heat affected zone into the weld seam of the laminated material.

  Therefore, the amount of upset can be increased in a situation where the function as the clad steel pipe is unlikely to be impaired, and as a result, the discharge of the penetrator from the weld can be promoted, and as a result, the decrease in toughness and strength of the weld can be prevented. The

  Furthermore, with the predetermined groove shape, the temperature distribution of the entire portion to be welded is uniformed, so the discharge of the penetrator from the weld portion is promoted, and as a result, the decrease in toughness and strength of the weld portion is prevented. did it.

The essential features of the present invention completed based on the above findings are as follows.
[1] Prepare a clad steel strip formed by pressure bonding a first layer of carbon steel or low alloy steel as a base material and a second layer of stainless steel or nickel-containing alloy as a joining material,
Both widthwise end portions of the clad steel strip are pressed from the second layer side, and the clad interface is directed from the second layer side to the thickness center side of the clad steel strip from the second layer side, and When the bevel angle is 10 ° or more and 50 ° or less, the groove depth d is 10% or more and 45% or less of the thickness t of the clad steel strip, and the projected cladding ratio R defined by the following equation (1) is 15% Perform bevel processing to make Y-shaped bevel that is 50% or less,
Thereafter, the clad steel strip is formed into a tubular shape,
Electric seam welding is characterized in that the widthwise end portions of the clad steel strip are butt-pressed and pressure-welded under conditions of upset amount of 0.2 t or more and 1.0 t or less, and electric seam welding is performed to obtain an electric seam welded clad steel pipe. Method of manufacturing clad steel pipe.
Description R = (t _c ^* + d) / t × 100 (%) (1)
Where R: projected cladding ratio
t _c ^* : thickness of the second layer on the root surface (mm)
d: Groove depth (mm)
t: thickness of the clad steel strip (mm)

[2] The electric resistance-welded clad steel pipe according to the above [1], wherein the flat value h / D in the 90 ° flat test in accordance with JIS G 3445 satisfies less than 0.3. Manufacturing method of sewing welded clad steel pipe.
Where h: Flat crack height (mm)
D: Tube outer diameter (mm)

  According to the present invention, welding is performed without any loss of the function as a clad steel pipe as it is in the electric resistance welding, without performing additional welding treatment such as overlay welding after electric resistance welding which is required in the prior art. It is possible to manufacture an electric resistance welded welded clad steel pipe excellent in the mechanical properties of the part.

FIG. 1 is a schematic view of an installation for producing a ERW welded clad steel pipe according to an embodiment of the present invention. (A) is sectional drawing which shows the groove shape of the width direction both-ends part (butt part) of clad steel pipe, (B) is sectional drawing which shows the welding part and its vicinity after electric resistance welding. It is a graph which shows the influence which the projection clad ratio R exerts on the clad ratio of the weld after electric resistance welding. It is a schematic diagram which shows the bevel processing machine which can be used by one Embodiment of this invention. It is sectional drawing which shows the metal flow in the weld part and its vicinity, and a clad interface.

  With reference to FIG. 1, a manufacturing process of a seam welded welded steel pipe according to an embodiment of the present invention will be described. The manufacture of a seam welded welded steel pipe in one embodiment of the present invention includes the following steps. First, the clad steel strip 10, which is a hot-rolled coil, is continuously discharged by the uncoiler 30. Subsequently, groove processing is performed by the groove processing machine 40 on both end portions in the width direction of the clad steel strip 10 that has been dispensed. Subsequently, the clad steel strip 10 is formed into a tubular shape by a roll forming machine 50. Subsequently, while heating the both end portions in the width direction to be a butt portion (welded portion) to the melting point or more with the high-frequency heating device 60, butt pressure is applied with the squeeze roll 70 to perform electric resistance welding. A clad steel pipe 20 is obtained. Subsequently, the bead cutting machine 90 cuts the weld bead on the outer and inner surfaces of the weld, and then the pipe 20 is cut to a predetermined length by the cutting machine 96.

  The high frequency heating device 60 may be either a direct current heating type or an induction heating type device. It is to be noted that there may be a case where an impeller (not shown) is inserted into the inner surface side of the pipe in the communication direction range including the current-carrying portion of the high frequency current to perform electric resistance welding. In addition, in the pressure welding process with the squeeze roll 5, in order to suppress the formation of a penetrator at the heated welding portion and further improve the mechanical characteristics of the welding portion, a shield box covering the entire circumference of the base pipe may be provided. preferable.

  In this embodiment, as shown in FIG. 2, a first layer 11 made of carbon steel or low alloy steel as a base material and a second layer 12 made of stainless steel or a nickel-containing alloy as a joining material are pressure bonded. The example which performs electric seam welding by making the 2nd layer 12 which is a joining material into an inner layer, and the 1st layer 11 which is a base material as an outer layer using clad steel strip 10 which becomes is shown. Here, in the present specification, the "base material" means a material of a layer having a large thickness among clad steel strips composed of two layers having different thicknesses and materials, and the "joining material" has a small thickness. It means the material of the layer. For example, in a clad steel strip used for manufacturing a clad steel pipe, a material for securing the strength of the steel pipe is selected as a base material, and as a joint material, to secure characteristics (for example, corrosion resistance etc.) which can not be secured by the base material. The choice of materials can be made.

  Although the carbon steel used as the base material in the present invention is not particularly limited, the mechanical properties of the clad steel pipe are governed by the properties of the base material occupying most of the volume of the steel pipe. It is preferable to select carbon steel having standards and mechanical properties.

  The low alloy steel used as a base material in the present invention is not particularly limited as long as the total content of alloying elements is 5 mass% or less, and it is selected in consideration of the application destination of clad steel pipe like carbon steel. Just do it.

  The stainless steel or nickel-containing alloy used as a joining material in the present invention is a corrosion resistant alloy. From the viewpoint of having particularly high corrosion resistance, SUS316L is preferable for stainless steel and Alloy625 and Alloy825 for nickel-containing alloys. Line pipes used in highly corrosive environments are required to have high corrosion resistance on the inner surface of the steel pipe through which the production fluid flows. Therefore, in the case of using a seam welded welded steel pipe for a line pipe, seam welding may be performed with the joint material as the inner layer and the base material as the outer layer. Conversely, in applications where high corrosion resistance is required on the outer surface of the steel pipe, electric seam welding may be performed with the base material as the inner layer and the laminated material as the outer layer.

In the present embodiment, it is important to perform the following beveling on both widthwise end portions of the clad steel strip. That is, referring to FIG. 2 (A), both widthwise end portions of clad steel strip 10 are pressed from the second layer 12 side, and both end portions in the widthwise direction are clad steel. Is directed to the thickness center side of the band, and the bevel angle θ is 10 ° to 50 °, and the groove depth d is 10% to 45% or less of the thickness t of the clad steel strip, according to the following equation (1) The Y-shaped groove has a defined projected cladding ratio R of 15% to 50%.
Description R = (t _c ^* + d) / t × 100 (%) (1)
Where R: projected cladding ratio
t _c ^* : thickness of the second layer at the root surface (mm)
d: Groove depth (mm)
t: thickness of the clad steel strip (mm)

  Here, the second layer side corner portions at both widthwise end portions of clad steel strip 10 are not cut off to form a Y-shaped groove, but both widthwise end portions of clad steel strip 10 are pressed from the second layer 12 side It is important to. As a result, the clad interface 13 is also pushed from the second layer side to the thickness center side of the clad steel strip. In addition, the bevel angle θ, the groove depth d, and the projected cladding ratio R are in the above ranges. Thereby, it can suppress that the molten steel and heat affected zone of a base material penetrate | invade into the welding seam part of a laminated material after electric resistance welding. As a result, the base material is not exposed to the joint material side surface (in this embodiment, the inner surface in the present embodiment) of the steel pipe at the weld, and after cutting the inner surface bead of the weld, the joint material is coated over the entire surface including the weld. It is possible to obtain a seam welded welded steel pipe having an inner surface.

  Further, as a result of the absence of the corners where current concentrates due to the above-mentioned groove shape, the temperature distribution of the entire portion to be welded is uniformed, so the discharge of the penetrator from the welded portion is promoted, and as a result the toughness of the welded portion And a reduction in strength can be prevented.

  If the bevel angle θ is less than 10 °, the uniformity of the temperature distribution across the weld zone can not be maintained, and as a result, the discharge of the penetrator tends to be insufficient. Therefore, mechanical properties such as toughness and strength of the weld zone Will be inadequate.

  On the other hand, when the bevel angle θ is more than 50 °, the effect of suppressing the penetration of the molten steel and heat affected zone of the base material into the weld seam portion of the joining material becomes insufficient, and The tendency to expose to the material side surface increases.

  If the groove depth d is less than 10% of the thickness t of the clad steel strip, the effect of suppressing the penetration of the molten steel and the heat-affected zone of the base material into the weld seam of the joint becomes insufficient, and the weld zone The base metal tends to be exposed on the surface of the joint material of the steel pipe.

  On the other hand, when the groove depth d exceeds 45% of the thickness t of the clad steel strip, the composition of the weld portion becomes a high alloy composition close to the composition of the joint material, so mechanical properties such as toughness and strength of the weld portion Will be inadequate.

  The bevel angle θ is set to 15 ° or more and 35 ° or less, and from the viewpoint of achieving both a high level that the base material is not exposed on the laminated material side surface and not to deteriorate the mechanical characteristics of the welded portion, and the groove depth The thickness d is preferably 20% or more and 45% or less of the thickness t of the clad steel strip.

  In addition, in the present embodiment, it is also very important to set the projected cladding ratio R defined by the following equation (1) to 15% or more and 50% or less. If the projected cladding ratio R is less than 15%, the effect of suppressing the penetration of the molten steel and the heat affected zone of the base material into the weld seam portion of the joining material becomes insufficient, and the joining material of the base material is a steel pipe in the welded portion Exposed to the side surface. When the projected cladding ratio R exceeds 50%, that is, when the position of the cladding interface on the root surface of the Y-shaped groove is closer to the base metal than the thickness center of the clad steel strip 10, the welded seam 14 after electric resistance welding is performed. Most of the weld seams are welded by seam welding of a metal of high alloy composition, which is a joint material, so that mechanical properties such as toughness and strength of the weld are reduced.

As an example showing this tendency, in the case of a clad steel band having a base material thickness of 22.5 mm and a joint material thickness of 2.5 mm, the bevel angle θ is 45 °, the groove depth d is 6 mm, and the projected cladding ratio R is various. As a value, Y-shaped groove processing is performed, electric resistance welding is then performed with an upset amount of 5.0 mm, and the cladding ratio r in the thickness direction of the weld after electric resistance welding is measured. The results are shown in FIG. The cladding ratio r in the thickness direction of the welded portion, which is the vertical axis in FIG. 3, is the thickness (t _w ) of the thickness (t _w ) of the second layer in the welded seam portion shown in FIG. It is a ratio, and when this value is zero, the base material is exposed on the surface of the laminated material side. As apparent from FIG. 3, when the projected cladding ratio R is less than 15%, the base material is exposed at the joint material side surface of the steel pipe at the weld.

  In addition, when using ERW welded clad steel pipe as a line pipe for transporting a corrosive substance, in order to maintain the corrosion resistance of the inner surface of the clad steel pipe over a long period of time, the cladding ratio r of the welded portion after It is desirable to secure 10% or more. Therefore, it is preferable to set the projected cladding ratio R of the Y-shaped groove of the butt portion at the time of electric resistance welding to 30% or more.

  The beveling process in the present embodiment can be performed, for example, using a beveling machine 40 configured as shown in FIG. 4. The beveling machine 40 is a rolling bevel beveling machine capable of continuously processing the traveling clad steel strip 10, and the upper side roll 42 and the lower side roll 44 are respectively disposed in a left-right pair. As shown in FIG. 4, the upper side roll 42 has a rolling portion 42 </ b> A having a large diameter in a tapered shape toward the upper side, whereby both widthwise end portions of the clad steel strip 10 can be made into Y-shaped grooves. it can.

By changing the taper shape of the rolling portion 42A, the groove shape of the width direction end of the clad steel strip can be made into a desired shape. Also, referring to FIG. 2A, the projected cladding ratio R is the ratio of the thickness t _m of the first layer (base material) to the thickness t _{c of} the second layer (joining material) in the clad steel strip 10 , And the groove shape by pressing. Therefore, the projection clad ratio R can be made a desired value by appropriately selecting the above ratio and changing the taper shape of the rolling portion 42A to have an appropriate groove shape.

  After the above-mentioned groove processing, the clad steel strip 10 is formed into a tubular shape, and both widthwise end portions of the clad steel strip are butted and pressurized, and electric resistance welding is performed to obtain an electric-resistance-welded clad steel pipe 20. The upset amount is 0.2 t or more and 1.0 t or less (t: thickness of clad steel strip). When the amount of upset is less than 0.2 t, the insufficient upset causes insufficient discharge of the penetrator from the weld during arc welding, and the toughness and strength of the weld are reduced. On the other hand, when the amount of upset exceeds 1.0 t, the outflow of molten steel due to the pressure of the squeeze roll increases, so that the base material is exposed on the joint material side surface of the steel pipe in the weld area and the corrosion resistance of the relevant part is deteriorated. . The upset amount by the squeeze roll is measured by measuring the outer peripheral length of the pipe after cutting the weld bead portion of the outer surface by welding with the squeeze roll after measuring the outer peripheral length of the pipe in front of the squeeze roll. Calculated by calculating the difference.

  As described above, in the present embodiment, since the amount of upset can be secured without the base material being exposed to the joint material side surface of the steel pipe in the welded portion, the discharge of the penetrator from the welded portion is promoted, and the welded portion The entire temperature distribution is made uniform. Therefore, in the present embodiment, the weld portion has high fracture characteristics in a state in which the weld bead is cut immediately after welding, that is, the weld bead is cut immediately after the welding and no additional welding process such as overlay welding is performed. Have. Specifically, the flat value h / D in a 90 ° flat test in accordance with the specification of JIS G 3445 satisfies less than 0.3. H: Flat crack height (mm), D: Tube outer diameter (mm).

  In the present embodiment, an example is shown in which the welded seam-welded steel pipe is manufactured using the second layer 12 which is a joining material as the inner layer and the first layer 11 which is the base material as the outer layer, but the present invention is not limited thereto The second layer, which is a bonding material, may be an outer layer, and the first layer, which is a base material, may be an inner layer. Also in this case, the same effect can be obtained by pressing from the side of the second layer, which is the joining material, to form a Y-shaped groove.

Example 1
A low carbon low alloy steel which is a base material having a component composition shown in Table 1 and a thickness shown in Table 2 and a stainless steel which is a composite material having a component composition shown in Table 1 and a thickness shown in Table 2 Two layers of various clad hot-rolled steel strips made of steel (SUS316L) were prepared. As shown in FIG. 1, each clad hot-rolled steel strip prepared by ERW welded steel pipe manufacturing equipment in which a rolling-type beveling machine 40 shown in FIG. 4 is disposed between the uncoiler 30 and the roll forming machine 50. The beveling process of the shape shown in Table 2 was performed to the width direction both ends of a clad steel strip by using as a raw material, and as an upset amount shown in Table 2, the electric resistance welded clad steel pipe of 300 mm of outer diameters was manufactured. In addition, the lamination material was made into the inner layer and the base material was made into the outer layer.

The test piece was extract | collected from each manufactured steel pipe, the 90 degree flat test based on the prescription | regulation of JISG3445 was done, and flat value h / D was calculated | required. Further, the corrosion resistance of the welded portion was evaluated by a ferric chloride corrosion test (ASTM G48-A). In this test, the test piece including the welded portion of the forming tube is continuously immersed in a 6 mass% ferric chloride aqueous solution at 50 ° C. for 72 hours, and the mass change before and after the test. It evaluated by the calculated corrosion rate. Here, the thing which satisfy | fills the conditions which satisfy | fill mass variation | change_quantity less than 4.0 g / m < ² > was determined to be pass ((circle)) and the thing which is not satisfy | disqualified as rejection (x). Each evaluation result is shown in Table 2.

  As shown in Table 2, in the present invention example, the flat part h / D of the welded part is smaller by an order of magnitude than the comparative example, and the weld part is excellent in the fracture characteristics and the inner surface maintains the corrosion resistance as stainless steel. It was confirmed to have

(Example 2)
Low carbon low alloy steel which is a base material having a component composition shown in Table 3 and a thickness shown in Table 4 and nickel which is a composite material having a component composition shown in Table 3 and a thickness shown in Table 4 Two layers of various clad hot-rolled steel strips made of the alloy containing (Alloy 625) were prepared. By the method similar to Example 1, the groove processing of the shape shown in Table 4 was performed, and as an upset amount shown in Table 4, a resistance welded welded clad steel pipe having an outer diameter of 300 mm was manufactured. In addition, the lamination material was made into the inner layer and the base material was made into the outer layer.

The test piece was extract | collected from each manufactured steel pipe, the 90 degree flat test based on the prescription | regulation of JISG3445 was done, and flat value h / D was calculated | required. Further, the corrosion resistance of the welded portion was evaluated by a ferric chloride corrosion test (ASTM G48-A). In this test, the test piece including the welded portion of the forming tube is continuously immersed in a 6 mass% ferric chloride aqueous solution at 50 ° C. for 72 hours, and the mass change before and after the test. It evaluated by the calculated corrosion rate. Here, the thing which satisfy | fills the conditions which satisfy | fill mass variation | change_quantity less than 4.0 g / m < ² > was determined to be pass ((circle)) and the thing which is not satisfy | disqualified as rejection (x). Each evaluation result is shown in Table 4.

  As shown in Table 4, in the present invention example, the flat part h / D of the welded part is smaller by an order of magnitude than the comparative example, and the weld part has excellent fracture characteristics and maintains the corrosion resistance of the inner surface as stainless steel. It was confirmed to have

  According to the present invention, welding is performed without any loss of the function as a clad steel pipe as it is in the electric resistance welding, without performing additional welding treatment such as overlay welding after electric resistance welding which is required in the prior art. It is possible to manufacture an electric resistance welded welded clad steel pipe excellent in the mechanical properties of the part.

10 clad steel strip 11 first layer (base material)
12 second layer (joining material)
13 Cladding interface 14 Weld seam part 15 Metal flow 20 ERW welded clad steel pipe 30 Uncoiler 40 Groove forming machine 42 Upper side roll 42A Rolled part 44 Lower side roll 50 Roll forming machine 60 High frequency heating device 70 Squeeze roll 90 Bead cutting machine 96 cutter θ bevel angle d groove depth t clad steel strip thickness t _m first layer (steel) thickness t _c second layer (base material) second in the thickness t _c ^* root face of the (cladding material) a second layer thickness in the thickness t _w weld seam layers (cladding material)

Claims (2)

Preparing a clad steel strip formed by pressure bonding a first layer of carbon steel or low alloy steel as a base material and a second layer of stainless steel or nickel-containing alloy as a joining material;
Wherein the both widthwise end portions of the clad steel strip by pushing processed from the second layer side, the both widthwise end portions perform beveling to Y-groove, the Y-groove, the cladding interface the The clad steel strip is directed from the second layer side toward the thickness center of the clad steel band as it goes to the root surface of the Y-shaped groove , and the bevel angle is 10 ° or more and 50 ° or less, and the groove depth d is the clad steel strip of not more than 45% more than 10% of the thickness t, the following (1) Ri projection clad ratio R der 50% 15% or more as defined in formula,
Thereafter, the clad steel strip is formed into a tubular shape,
Electric seam welding is characterized in that the widthwise end portions of the clad steel strip are butt-pressed and pressure-welded under conditions of upset amount of 0.2 t or more and 1.0 t or less, and electric seam welding is performed to obtain an electric seam welded clad steel pipe. Method of manufacturing clad steel pipe.
Description R = (t _c ^* + d) / t × 100 (%) (1)
Where R: projected cladding ratio
t _c ^* : thickness of the second layer on the root surface (mm)
d: Groove depth (mm)
t: thickness of the clad steel strip (mm) The electric resistance welded stainless steel clad steel pipe according to claim 1, wherein the obtained electric resistance welded stainless steel clad steel pipe satisfies a flatness value h / D of less than 0.3 in a 90 ° flat test in accordance with JIS G 3445. Manufacturing method.
Where h: Flat crack height (mm)
D: Tube outer diameter (mm)

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