JP2007330983A - Method for manufacturing electric resistance welded tube having excellent weld characteristic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an electric resistance welded tube having excellent weld characteristic capable of maintaining excellent welding quality by adequately giving a tapered shape to an end of a plate (a strip) before the electric resistance welding when manufacturing the electric welded tube. <P>SOLUTION: After giving a taper shape to a plate end by the fin-pass forming, the butt angle of end faces orthogonal to a plate is set to be within ±1° to perform the electric resistance welding. <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 Unexamined Patent Publication No. 63-317212 Japanese Patent Laid-Open No. 2001-170779 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 that forms a plate, abuts the end portions, and is welded by electro-welding to form a tube. After a tapered shape is imparted to the plate end portion by fin pass molding, A method for producing an electric resistance welded tube having good welded portion characteristics, characterized by performing electric resistance welding with a butt angle within ± 1 °.

  [2] The taper shape to be imparted to the end of the plate 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 welded portion characteristics according to [1].

  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.

  Accordingly, 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 taper shape is appropriately applied to the end portion of the plate before ERW welding. In order to obtain the desired tapered shape to be imparted, it was 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 is large, 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 this 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 fin pass molding, electro-welding is performed immediately after that, so 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). A two-step taper having a shape different from the above may be imparted to the fin of the stand and a taper shape may be imparted 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 problem, the present inventors have re-examined the electric seam welding phenomenon in detail, and as a result, the butt angle between the both ends of the width direction of the plate in the electric resistance welding (the both ends of the width direction of the plate). We paid attention to the angle between vertical surfaces. In other words, 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 butt angle between the vertical surfaces to which the taper shape is not given is greatly affected.

  In ERW welding, when the butting angle of the vertical surface (plate vertical end surface) of the plate end changes, the discharge state of the molten steel changes. That is, when the butt angle is set so as to open to the tube outer surface side, the tube end surface with the tapered shape is heated preferentially on the tube inner surface side, and the molten steel is generated first, and the molten steel is being electrowelded. Along with the butting of the end face of the plate, it is pushed out to the tube outer surface side. Also, when the butt angle is set so that it opens to the inner surface of the tube, the outer surface of the plate end surface with a tapered shape is preferentially heated to generate molten steel first, and the molten steel is subjected to electric resistance welding. Along with the end face of the plate, it is pushed out to the inner surface of the tube.

  In this case, for example, if the butt angle that opens to the outer surface side of the tube is positive and the butt angle that opens to the inner surface side of the tube is negative, the plate on one side is larger when the butt angle is larger than ± 1 °. Since the end surface melts preferentially and the amount of molten steel flowing to the opposite plate end surface increases significantly, it cannot be discharged sufficiently during the welding time until the butt is completed, and the molten steel is trapped inside the plate halfway. As a result, ERW welding is completed. As a result, the penetrator that agglomerates in the molten steel or on the surface of the steel stays inside the plate, and the toughness or strength of the ERW welded portion is significantly reduced. From the above, it is necessary to make the butting angle of the vertical surface of the plate end portion at the time of ERW welding within ± 1 ° (−1 ° to + 1 °).

  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, Further, since the molten steel is reduced, the effects of both the butt angle and the taper shape can sufficiently discharge the penetrator of the ERW weld, and the toughness and strength are 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.

  One 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 an 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 seam welding is performed such that the butting angle θ of the vertical surface of the plate end is within ± 1 °.

  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.

  Hereinafter, a description will be given based on examples.

  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, and the center of the notch length is taken as the weld thickness center position. 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 the invention example 1, the above-mentioned ERW pipe was manufactured based on the above-described embodiment. At that time, in the third stand of the fin-pass molding stand composed of three stands, the taper angle γ is 25 ° and the taper height δ is 4 mm (21% of the plate thickness) on the upper surface side (inner surface side of the tube 20) of the band member 10. ) Was applied, and roll forming was adjusted so that the butting angle θ of the plate vertical end face immediately before ERW welding opened 0.3 ° to the pipe outer surface side, and 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 taper height β of 7 mm (37% of the plate thickness) is given a substantially linear taper shape, and the abutment angle θ of the plate vertical end surface immediately before ERW welding is 0.2 ° open to the tube inner surface side. The roll forming was adjusted to ERW welding.

  (Comparative Example) As a comparative example, in the first stand of the fin pass molding composed of three stands, the taper angle α is 20 ° and the taper height β is 3 mm (plate) on the lower surface side (the outer surface side of the tube 20) of the strip 10 16% of the thickness) of a substantially linear taper shape with a taper angle γ of 20 ° and a taper height δ of 3 mm (16% of the plate thickness) on the upper surface side (the inner surface side of the tube 20) of the band member 10. A substantially linear taper shape was provided, and roll forming was adjusted so that the butting angle θ of the plate vertical end surface immediately before ERW welding was opened by 1.1 ° toward the pipe outer surface side, and ERW welding was performed.

  (Conventional example) As a conventional example, the plate end surface is made substantially rectangular, and the roll forming is adjusted so that the butting angle θ of the plate vertical end surface immediately before ERW welding shown in FIG. Then, electric resistance 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 the comparative example and the conventional example have low 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.

It is a figure which shows the ERW pipe manufacturing line in one 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 butt | matching state just before ERW welding of the board which provided the taper shape. It is a figure which shows the butt | matching state just before ERW welding of the board of the conventional rectangular end surface.

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

Claims (2)

  In a method of manufacturing an electric resistance welded tube that forms a plate, butts the end portions, and welds the ends together to form a pipe, after adding a taper shape to the end portion of the plate by fin pass molding, the angle of butt of the vertical surface of the plate end portion is set. A method of manufacturing an electric resistance welded tube with good weld characteristics, wherein the electric resistance welding is performed within ± 1 °.   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 2. A method for producing an electric resistance welded tube having good weld joint characteristics according to Item 1.

Images