JP2008030114A - Method of manufacturing electric resistance welded tube with excellent weld characteristic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electric resistance welded tube with excellent weld part characteristic capable of maintaining excellent weld quality by providing a proper taper shape to the end part of a plate (a band material) before the electric resistance welding when manufacturing the electric resistance welded tube. <P>SOLUTION: The electric resistance welding is performed while a V-shape angle formed by lateral end parts of plates immediately before the electric resistance welding is 2-8° after a predetermined taper shape is given to the end parts of the plate by a finpass forming. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a pipe that requires toughness of a welded portion such as for oil well line pipes or a pipe that requires welded portion strength such as a casing pipe of oil well.

  Usually, pipes are roughly classified into welded pipes and seamless pipes. Welded pipes are manufactured by rolling a plate by roll forming or the like and welding by welding the end, as in the case of ERW steel pipes, and seamless pipes are made by drilling a lump of material at high temperature and using a mandrel mill, etc. Rolled and manufactured. In the case of a welded pipe, it is generally said that the properties of the welded part are inferior to that of the base metal, and in the application of the pipe, guarantees of toughness and strength of the welded part have always been discussed for each application.

  For example, in line pipes that transport crude oil, natural gas, etc., pipes are often laid in cold regions, so low temperature toughness is important, and in oil wells for crude oil mining, casing pipes are required to protect the mining pipes. The strength of the tube is regarded as important.

  In general, hot strips (strips), which are the base material of pipes, are subjected to component design and heat treatment in consideration of the base material characteristics after pipe manufacture, ensuring characteristics such as toughness and strength of the base material. The

  However, since the characteristics of the welded part are greatly influenced by the electric resistance welding method more than the component design and heat treatment of the base metal, the development of the welding technique has been important.

  The reason for the failure of ERW welding is that the oxide generated on the end face of the welded plate material called penetrator remains without being discharged from the end face together with the molten steel during ERW welding, and the toughness decreases due to this residual penetrator and the strength. There were many cases where there was a shortage.

Therefore, conventionally, in order to remove the penetrator, which is the main cause of poor ERW welding, from the welded portion, a technique for actively discharging molten steel from the plate end surface of the welded portion has been intensively studied. For example, Patent Documents 1 to 5 describe examples of examining the shape of the plate end surface. In other words, the end face of the plate is generally rectangular due to slits and end face grinding, but this is tapered before roll forming to improve the discharge of molten steel during welding with the processed end shape. It is aimed.
JP 57-31485 A Japanese Patent Laid-Open No. Sho 63-317212 JP 2001-17079A JP 2001-259733 A JP 2003-1649095 A

  However, in Patent Documents 1 to 5, since the taper processing means is merely listed and introduced, the effect may not be sufficient even if it is applied to the ERW tube manufacturing process. Was necessary.

  The present invention has been made in view of the above circumstances, and when producing an electric resistance welded tube, by appropriately giving a tapered shape to the end of the plate (band material) before the electric resistance welding, It is an object of the present invention to provide a method for manufacturing an electric resistance welded tube having good welded portion characteristics that can maintain good welding quality.

  In order to solve the above problems, the present invention has the following features.

  [1] In a method of manufacturing an electric resistance welded tube which forms a plate, abuts the end portions, and is welded by electro-welding to form a tube, after giving a taper shape to the plate end portion by fin pass molding, the V shape angle is set to 2 ° to A method of manufacturing an electric resistance welded tube having good welded portion characteristics, characterized by performing electric resistance welding at 8 °.

  [2] In a method of manufacturing an electric resistance welded tube which forms a plate, butts the end portions and is electro-welded to form a tube, after giving a tapered shape to the plate end portion by rolling a perforated roll, the V shape angle is set. A method of manufacturing an electric resistance welded tube having good welded portion characteristics, characterized by performing electric resistance welding at 2 ° to 8 °.

  [3] The taper shape to be applied to the plate end portion is characterized in that the angle of the taper with respect to the plate thickness direction is 25 ° to 50 °, and the length of the taper in the plate thickness direction is 20% to 40% of the plate thickness. The method for producing an electric resistance welded tube having good weld joint characteristics according to [1] or [2].

  The present invention can obtain an electric resistance welded tube having remarkably good toughness and weld strength.

  As described above, in Patent Documents 1 to 5, since only taper processing means are introduced, there may be cases where the effect is not sufficient even when actually applied to the ERW tube manufacturing process. Detailed examination was necessary.

  Therefore, the present inventors have intensively studied a method for appropriately imparting a desired taper shape to the plate end portion before ERW welding. As a result, the desired taper shape is applied to the end portion of the plate before ERW welding. In order to give it properly, we decided to utilize fin pass molding. In fin pass molding, even if the fin pass roll does not fill the entire circumference of the plate in the circumferential direction, when the plate is inserted into the roll, the plate end is strongly pressed by the fin, and the plate end is sufficiently in the fin. This is because it is understood that they are in close contact. That is, when the plate is inserted into the fin pass roll, the plate end portion in contact with the fin and the plate bottom portion (plate center portion) located on the opposite side of 180 ° are in a state of beam bending, The reaction force of the plate that tries to bend the cross-section into an arc shape acts greatly, and even if the strip does not fill the fin pass roll, a large compressive force acts on the plate end in the circumferential direction. It was grasped that the end portion was strongly pressed by the fin and the shape of the fin was transferred to the end portion of the plate as it was.

  Then, the present inventors pay attention to the fact that the plate end is strongly pressed by the fin, and examine means for actively utilizing this phenomenon. As a result, the fin is provided with two or more stages of taper. did. In this way, even if the amount of upset in the fin pass molding is small, a taper shape can be appropriately given to the plate end portion, and a desired taper shape can be sufficiently given to the plate end portion.

  At that time, when a tapered shape is given to either one of the plate end on the inner surface side of the tube or the plate end on the outer surface side of the tube, the fin shape may be made in two stages.

  In addition, when a tapered shape is simultaneously given to both the plate end on the inner surface side of the tube and the plate end on the outer surface side of the tube, the fin shape having three stages of angles may be used. However, if the angle of any of these fins is larger than the vertical direction of the fin pass roll, the end of the plate may be scraped off by the fins, and a surplus material called a “whisker” may be generated. Since it sometimes causes scratches and causes sparks in ERW welding, it is preferable to keep the angle of the fins below the vertical direction.

  If possible, if a taper shape is applied to one or both sides of the plate edge at the final stand of the fin pass molding, since electric welding is performed immediately after that, the electric tape is maintained while maintaining a good taper shape. Sewing welding is possible. However, even if a taper shape is given at the start stand or a halfway stand of fin pass molding, the taper shape is relatively hard to be crushed in subsequent fin pass molding because the plate end surface once provided with the taper shape is significantly hardened by strong pressure. The taper shape can be maintained even after the fin pass molding.

  In addition, when fin path molding of two or more stands is possible, a two-step taper is given to the fin of one stand, and a taper shape is given to one plate end (for example, the outer surface side of the pipe). It is preferable that a two-step taper having a shape different from the above is given to the fin of the stand and a taper shape is given to the other plate end (for example, the outer surface side of the tube). When a taper shape is given to one side of the plate end portion with one stand, the portion is remarkably processed and hardened by strong pressure. Therefore, even if a taper shape is given to the other plate end portion with another stand, the front stand The taper shape imparted in (1) is relatively difficult to be crushed, and a desired taper shape can be imparted to the plate end after fin pass molding on both the tube inner surface side and the tube outer surface side.

  However, even when a taper shape is imparted to the plate end portion before ERW welding as described above, it may be difficult to sufficiently improve the toughness or strength of the welded portion after ERW welding.

  Detailed investigation of this cause revealed the following.

  That is, in the process in which the plate end portion before the electric seam welding is heated, an oxide that causes a penetrator which is a welding defect is formed on the plate end surface. Thereafter, the oxide on the end face of the plate floats on the surface of the molten steel during ERW welding, and a part is discharged together with the molten steel. At this time, if the end face of the plate is tapered, the molten steel is easily discharged, and at the same time, the penetrator can be effectively discharged. However, since the oxide on the plate end face that is the basis of the penetrator is generated sequentially with the heating of ERW welding, depending on the welding conditions, it is only necessary to give a taper shape to the plate end toughness or strength after welding. In some cases, it was not possible to sufficiently improve.

  Therefore, in order to cope with the above-mentioned problem, the present inventors have re-observed the electric seam welding phenomenon in detail, and as a result, a V-shaped shape in which both end faces in the width direction of the plate are formed in the longitudinal direction immediately before the electric seam welding. Attention was paid to the vertex angle (V-shape angle). That is, in order to effectively discharge the penetrator together with the molten steel, it has been found that not only the taper shape of the plate end but also the V shape angle has a great influence.

  In ERW welding, when the V shape angle of the plate end surface changes, the state of generation and discharge of molten steel differs. That is, when the V shape angle is reduced, the plate end surface starts to be heated far from the welded portion, and gradually increases in temperature as it approaches the welded portion. The heating spreads. With these phenomena, molten steel is gradually generated, but solidification starts before the molten steel generated from the plate thickness upper part (pipe outer surface side) and plate thickness lower part (pipe inner surface side) of the plate end surface reaches the weld, The molten steel at the center of the plate thickness is less likely to be discharged to the outside. As a result, the penetrator generated together with the molten steel tends to stay inside the plate, and the toughness or strength of the ERW weld is greatly reduced.

  Therefore, as a result of intensive studies on the V shape angle, it has been found that if the V shape angle is 2 ° or more, the discharge of molten steel is good and the toughness or strength of the welded portion is improved.

  However, if the V shape angle becomes too large, the heating of the welded portion is insufficient and the temperature of the plate end face is difficult to rise, and molten steel is not generated, and the entire end face called cold welding is covered with an oxide film. As a result, the toughness or strength of the weld is significantly reduced. On the other hand, it was grasped that cold welding can be prevented if the V shape angle is 8 ° or less.

  At that time, if the taper shape is given to the plate end portion, the melting amount of one end portion that is melted first by the volume decrease is reduced, and the melt is performed along the taper shape, Furthermore, since the molten steel is reduced and solidification before the welded portion due to the molten steel is less likely to occur, the penetrator of the ERW welded portion can be discharged sufficiently by the effects of both the V-shape angle and the taper shape, and the toughness and strength Is significantly improved.

  In addition, as a result of optimization of the taper shape to be applied to the plate end, the angle from the perpendicular (angle with respect to the thickness direction of the taper) is set to 25 ° to 50 °, and from the taper start position to the end position It was understood that the length of the vertical line (the length of the taper in the thickness direction) should be 20% to 40% of the thickness.

  That is, if the angle from the perpendicular (taper angle) is less than 25 °, the molten steel discharge from the central portion of the plate thickness becomes insufficient, the penetrator remains and becomes defective, and the toughness and strength after ERW welding decrease. When the angle from the perpendicular (taper angle) exceeds 50 °, the taper shape remains as a flaw on the tube of the product even after the electric resistance welding. Furthermore, if the length of the perpendicular (taper height) from the taper start position to the end position is less than 20% of the plate thickness, the molten steel discharge at the center portion of the plate thickness becomes insufficient and the penetrator tends to remain, If it exceeds 40% of the plate thickness, the taper shape remains as a flaw on the tube of the product even after the electric resistance welding.

  The first embodiment of the present invention as described above will be described below.

  FIG. 1 is a diagram showing an electric resistance welded tube production line used in the first embodiment of the present invention. In this electric sewing tube manufacturing line, the plate (band material) 10 is discharged from the uncoiler 1 and straightened by the leveler 2, and the band material 10 is gradually rounded by the roll forming machine 4 and rounded into a tubular shape. The left and right width ends of the strip 20 are electro-welded with an electric-welding welder including an induction heating unit 5 and a squeeze roll (electro-sealed welding unit) 6 to form a pipe 30, and the weld bead part of the pipe 30 is beaded. After cutting with the partial cutting machine 7, the outer diameter of the cut pipe 30 is adjusted with the sizer 8, and then the pipe cutting machine 9 cuts it to a predetermined length.

  In this embodiment, the roll forming machine 4 is provided with the fin path forming stand 3 including a plurality of stands (for example, 3 stands) at the last stage, and as described above, the fins of each stand have an appropriate shape. Thus, a predetermined taper shape can be given to the upper surface side (the inner surface side of the tube) of the plate end portion and / or the lower surface side (the outer surface side of the tube) of the plate end portion.

  For example, as shown in a sectional view in FIG. 2 (a) and a partial detailed view in FIG. 2 (b), an arbitrary stand of the fin-pass molding stand 3 has a predetermined two-step taper (second-step taper inclination). A fin shape having an angle α and a second inclined portion vertical length β) is provided. By transferring the fin shape to the width end of the strip 10, a taper shape with a taper angle of α and a taper height of β is imparted to the left and right ends of the lower surface of the strip 10 (the outer surface of the tube). To do.

  Then, as described above, a tubular strip 20 having a taper shape with a taper angle β at a taper angle α on the outer surface side and a taper shape with a taper height δ at a taper angle γ on the inner surface side is provided. As shown in FIG. 3, the electric resistance welding is performed such that the V shape angle ψ is 2 ° to 8 °.

  As a result, the penetrator of the electric resistance welded portion can be sufficiently discharged, and an electric resistance welded tube having remarkably good toughness and welding strength can be obtained.

  Furthermore, the present inventors also examined other methods for appropriately imparting a desired taper shape to the plate end portion before ERW welding, and as a result, have come up with the use of a perforated roll.

  This is because when a perforated roll is used, the shape of the end portion of the plate is easily obtained with high accuracy according to the perforated shape. In other words, it is necessary to constrain the moving plate in order to give the taper shape with high accuracy. However, the fluttering of the plate end portion is particularly large before or before roll forming, and the taper shape can be given as it is. difficult. However, by using a perforated roll, it is possible to provide a tapered shape with high accuracy while restraining the plate end portion by the perforated roll itself. In addition, since the perforated roll may be relatively small in equipment, it can be easily installed before roll forming or in the middle of roll forming before electro-welding welding.

  Even when a desired taper shape is given to the end of the plate before electro-welding using a hole-type roll, as described above, the V-shape angle ψ is set to 2 ° to 8 ° so that electro-sewing is performed. It is necessary to perform welding.

  In addition, as described above, the taper shape to be applied to the end of the plate is set so that the angle from the perpendicular (angle with respect to the thickness direction of the taper) is 25 ° to 50 °, and the length of the perpendicular from the taper start position to the end position. The length (the length of the taper in the plate thickness direction) is preferably 20% to 40% of the plate thickness.

  A second embodiment of the present invention based on the above will be described below.

  FIG. 5 is a view showing an electric resistance weld tube production line used in the second embodiment of the present invention. In this electric sewing tube manufacturing line, the plate (band material) 10 is discharged from the uncoiler 1 and straightened by the leveler 2, and the band material 10 is gradually rounded by the roll forming machine 4 and rounded into a tubular shape. The left and right width ends of the strip 20 are electro-welded with an electric-welding welder including an induction heating unit 5 and a squeeze roll (electro-sealed welding unit) 6 to form a pipe 30, and the weld bead part of the pipe 30 is beaded. After cutting with the partial cutting machine 7, the outer diameter of the cut pipe 30 is adjusted with the sizer 8, and then the pipe cutting machine 9 cuts it to a predetermined length.

  In this embodiment, the roll forming machine 4 is provided with a perforated roll 42 after the first breakdown stand 41 of the roll forming machine 4, and the upper end side (the inner surface side of the tube) of the plate end by rolling with the perforated roll 42. ) Or / and a predetermined taper shape can be provided on the lower surface side (the outer surface side of the tube) of the plate end.

  3, for example, a taper shape with a taper angle α and a taper height β is provided on the outer surface side, and a taper shape with a taper angle γ and a taper height δ is provided on the inner surface side. The tubular band member 20 is subjected to electro-welding welding so that the V-shape angle ψ is 2 ° to 8 °.

  As a result, the penetrator of the electric resistance welded portion can be sufficiently discharged, and an electric resistance welded tube having remarkably good toughness and welding strength can be obtained.

  The hole-type roll 42 is preferably installed at a position where the plate (band material) 10 is relatively flat. Except after the above-mentioned first breakdown stand 41, for example, it may be installed in front of the roll forming machine 4.

  Hereinafter, a description will be given based on the first embodiment.

  Here, an electric resistance welded tube of φ600 was manufactured using a strip (steel strip) having a plate width of 1920 mm × 19.1 tmm.

  And the test piece was cut out from the weld part of the manufactured ERW pipe, the Charpy test was done, and the performance was evaluated. Each Charpy test piece is taken from 10 points with different pipe longitudinal directions, the specimen length direction is parallel to the pipe circumferential direction, the notch length center is taken as the weld thickness center position, and 2 mmV of JIS5 An impact test at −46 ° C. was performed as a notch impact test piece, and the absorbed energy and the brittle fracture surface ratio were measured. In addition, the absorbed energy was 125 J or more and the brittle fracture surface ratio was 35% or less as the allowable performance range.

  (Invention Example 1) As Invention Example 1, the above-mentioned electric resistance welded tube was manufactured based on the first embodiment described above. At that time, in the third stand of the fin-pass molding stand comprising three stands, the taper angle α is 25 ° and the taper height β is 4 mm (21% of the plate thickness) on the lower surface side (the outer surface side of the tube 20) of the band member 10. ) Was formed, and roll forming was adjusted so that the V shape angle ψ formed by the plate end surfaces immediately before the ERW welding was 2.5 °, and the ERW welding was performed.

  (Invention Example 2) As Invention Example 2, in the first stand of the fin pass molding stand comprising two stands, the taper angle γ is 45 ° on the upper surface side (the inner surface side of the tube 20) of the band member 10 and the taper height. A substantially linear taper shape with δ of 7 mm (37% of the plate thickness) is provided, and in the second stand of the fin pass forming stand, the taper angle α is 45 on the lower surface side of the strip 10 (the outer surface side of the tube 20). A roll with a taper height β of 7 mm (37% of the plate thickness) and a substantially linear taper shape, and a V-shape angle ψ formed by the plate end surfaces immediately before ERW welding is 7.5 °. The molding was adjusted and electro-resistance welding was performed.

  (Comparative example 1) As a comparative example 1, in a fin stand molding first stand comprising three stands, the taper angle α is 20 ° and the taper height β is 3 mm on the lower surface side (the outer surface side of the tube 20) of the band member 10. (16% of the plate thickness) is provided with a substantially linear taper shape, and the taper angle γ is 20 ° and the taper height δ is 3 mm (the plate thickness) on the upper surface side (the inner surface side of the tube 20) of the band member 10. 16%), a taper shape on a substantially straight line was given, and roll forming was adjusted so that the V-shape angle ψ formed by the plate end faces immediately before the ERW welding was 1.5 °, and ERW welding was performed. .

  (Conventional Example 1) As Conventional Example 1, the plate end surface is substantially rectangular, and the roll forming is adjusted so that the V shape angle ψ formed by the plate end surfaces immediately before ERW welding shown in FIG. 4 is 1.8 °. Electro-sewing welding was performed.

  Table 1 shows the results of measuring the Charpy impact value and the brittle fracture surface ratio at the welded portion of the electric resistance welded tube manufactured as described above.

  From Table 1, the ERW pipes according to Examples 1 and 2 of the present invention have high impact strength at the welded portion, small brittle fracture surface ratio, good toughness, and high product reliability. On the other hand, the ERW pipes according to Comparative Example 1 and Conventional Example 1 have poor impact strength at the welded portion, high brittle fracture surface ratio, reduced toughness, and poor product reliability.

  Thereby, it was confirmed that the electric resistance welded tube with a favorable welded part characteristic can be manufactured by the present invention.

  Hereinafter, a description will be given based on the second embodiment.

  Here, a φ600 electric resistance welded tube was manufactured using a strip (steel strip) having a plate width of 1920 mm × 19.1 tmm.

  And the test piece was cut out from the weld part of the manufactured ERW pipe, the Charpy test was done, and the performance was evaluated. Each Charpy test piece is taken from 10 points with different pipe longitudinal directions, the specimen length direction is parallel to the pipe circumferential direction, the notch length center is taken as the weld thickness center position, and 2 mmV of JIS5 An impact test at −46 ° C. was performed as a notch impact test piece, and the absorbed energy and the brittle fracture surface ratio were measured. In addition, the absorbed energy was 125 J or more and the brittle fracture surface ratio was 35% or less as the allowable performance range.

  (Invention Example 3) As Invention Example 3, the above-described electric resistance welded tube was manufactured based on the second embodiment described above. At that time, the hole-shaped roll 42 is formed on the lower surface side (the outer surface side of the tube 20) of the band member 10 so that the taper angle α is 25 ° and the taper height β is 4 mm (21% of the plate thickness). A shape is imparted, and a substantially linear taper shape with a taper angle γ of 25 ° and a taper height δ of 4 mm (21% of the plate thickness) is imparted to the upper surface side (inner surface side of the tube 20) of the band member 10. The roll forming was adjusted so that the V shape angle ψ formed between the plate end faces immediately before the electric resistance welding was 2.5 °, and the electric resistance welding was performed.

  (Invention Example 4) As Invention Example 4, in the above-described second embodiment, the hole-shaped roll 42 was moved in front of the roll forming machine 4 to manufacture the above-mentioned electric sewing tube. At that time, the hole-shaped roll 42 causes the taper on the lower surface side (the outer surface side of the tube 20) of the strip 10 to be a substantially linear taper having a taper angle α of 45 ° and a taper height β of 7 mm (37% of the plate thickness). A shape is applied, and a substantially linear taper shape with a taper angle γ of 45 ° and a taper height δ of 7 mm (37% of the plate thickness) is provided on the upper surface side (the inner surface side of the tube 20) of the band member 10. The roll forming was adjusted so that the V shape angle ψ formed between the plate end faces immediately before the electric resistance welding was 2.5 °, and the electric resistance welding was performed.

  (Comparative Example 2) As Comparative Example 2, a cutting tool is arranged in front of the roll forming machine 4, and the taper angle α is 20 ° on the lower surface side (the outer surface side of the tube 20) of the strip 10 by the cutting tool. A substantially linear taper shape having a taper height β of 3 mm (16% of the plate thickness) is provided, and a taper angle γ is 20 ° on the upper surface side (the inner surface side of the tube 20) of the band member 10 and the taper height δ. Is adjusted to roll forming so that the V shape angle ψ formed by the plate end faces immediately before ERW welding is 1.5 °. ERW welding was performed.

  (Conventional Example 2) Similar to Conventional Example 1 described above, as Conventional Example 2, the plate end surface is substantially rectangular, and the V shape angle ψ formed by the plate end surfaces immediately before ERW welding shown in FIG. 4 is 1.8 °. The roll forming was adjusted so as to achieve ERW welding.

  Table 2 shows the results of measuring the Charpy impact value and the brittle fracture surface ratio at the welded part of the electric resistance welded tube manufactured as described above.

  From Table 2, the ERW pipes according to Examples 3 and 4 of the present invention have high impact strength at the welded portion, low brittle fracture surface ratio, good toughness, and high product reliability. On the other hand, the ERW pipes according to Comparative Example 2 and Conventional Example 2 have low impact strength at the welded portion, a high brittle fracture surface ratio, reduced toughness, and poor product reliability.

  Thereby, it was confirmed that the electric resistance welded tube with a favorable welded part characteristic can be manufactured by the present invention.

It is a figure which shows the ERW pipe manufacturing line in the 1st Embodiment of this invention. It is a figure which shows the fin-shaped fin pass rolling stand provided with the 2 step | paragraph taper. It is a figure which shows the V shape angle just before the electric-welding welding of the board | substrate which provided the taper shape. It is a figure which shows the V shape angle just before the electric resistance welding of the board of the conventional rectangular end surface. It is a figure which shows the ERW pipe manufacturing line in the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Uncoiler 2 Leveler 3 Fin pass forming stand 4 Roll forming machine 5 Induction heating device (contact chip)
6 squeeze roll
7 Bead cutting machine 8 Sizer 9 Pipe cutting machine 10 Band material (plate)
20 Plate formed into a tube 30 Tube 41 Breakdown first stand 42 Hole type roll

Claims (3)

  In a method of manufacturing an electric resistance welded tube which forms a plate, abuts the end portions, and is welded by electro-welding to form a tube. A method of manufacturing an electric resistance welded tube having good weld-part characteristics, characterized by performing electric resistance welding.   In a method of manufacturing an electric resistance welded tube, which is formed by forming a plate, butting ends and then performing electro-welding welding to form a tube, a taper shape is imparted to the plate end by rolling a perforated roll, and then the V shape angle is set to 2 ° to A method of manufacturing an electric resistance welded tube having good welded portion characteristics, characterized by performing electric resistance welding at 8 °.   The taper shape imparted to the plate end portion is characterized in that the angle of the taper with respect to the plate thickness direction is 25 ° to 50 °, and the length of the taper in the plate thickness direction is 20% to 40% of the plate thickness. Item 3. A method for producing an electric resistance welded tube having good weld joint characteristics according to Item 1 or 2.

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