JP2007160382A - Method for manufacturing electric resistance welded tube having excellent weld characteristic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric resistance welded tube manufacturing method in which a shape of a width end immediately before the electric welding is forme into an adequate shape, thereby sufficiently discharging a molten steel during the electric welding, reliably removing any penetrator, and obtaining the electric welded tube having the excellent weld characteristic. <P>SOLUTION: A grinding means 11 for giving the taper shape to an upper surface side and a lower surface side of right and left width ends of a strip 20 is provided on an outlet side of a first break-down stand 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an electric resistance welded tube having good welded portion characteristics, and particularly, a welded portion strength such as a pipe required for welded portion toughness for oil well line pipes or a casing pipe for oil well is required. Related to the method of manufacturing the tube.

  Usually, pipes are roughly classified into welded pipes and seamless pipes. Welded pipes are manufactured by rounding plates by roll forming etc. and welding by welding the width ends, as in the case of ERW steel pipes. Seamless pipes are made by drilling a lump of material at a high temperature, etc. Rolled to produce. 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., low temperature toughness is important because pipes are often laid in cold regions, and casing pipes that protect mining pipes are used in oil wells for crude oil mining. Needed, tube strength is valued.

  Usually, a hot-rolled sheet that is a base material of a pipe is subjected to component design, heat treatment, and the like in consideration of the base material characteristics after the pipe is manufactured, and characteristics such as toughness and strength of the base material are ensured.

  However, since the characteristics of the welded part are greatly influenced by the welding method more than the component design and heat treatment of the base metal, it is particularly important to develop a welding technique in the case of ERW welding.

  As a cause of the failure of ERW welding, the oxide generated at the width end of the welded strip called penetrator remains without being discharged from the end face together with the molten steel during ERW welding, and the toughness is caused by this remaining penetrator. There were many cases where the strength decreased and the strength was insufficient.

Therefore, in the past, in order to remove the penetrator, which is the main cause of poor ERW welding, from the welded portion, techniques for actively discharging molten steel from the width end face of the welded strip have been intensively studied. For example, Patent Literature 1 and Patent Literature 2 describe examples in which the shape of the width end face of the welded band material is examined. That is, normally, the left and right width end surfaces of the welded strip material are substantially rectangular due to slits and end grinding, but the upper and lower surface sides of the left and right width end surfaces are respectively tapered before roll forming. It aims at making molten steel discharge | emission favorable at the time of ERW welding with the width | variety edge part shape which processed and tapered.
Japanese Patent Laid-Open No. 2001-170779 JP 2003-164909 A

  When manufacturing an electric resistance welded tube, the belt material is roll-formed and then subjected to electric resistance welding. In this roll forming, in order to maintain a good butt accuracy between the width ends in the process of adding a circumferential bend in the vicinity of the width end in order to make the strip into a pipe, or in the electric resistance welding, A fin pass forming step is required to constrain the end of the plate to make it a shape close to a perfect circle.

  Therefore, as described in Patent Documents 1 and 2, even if a taper shape is given to the width end surface of the strip before roll forming, for example, when bending is applied in the vicinity of the width end portion during roll forming, The taper shape given before roll forming may be distorted, resulting in an irregular shape. As a result, sufficient molten steel cannot be discharged at the time of ERW welding, and the penetrator cannot be reliably removed.

  The present invention has been made in view of the above circumstances, and can make the shape of the width end portion immediately before ERW welding to be an appropriate shape, thereby sufficiently discharging molten steel during ERW welding. Thus, it is an object of the present invention to provide a method of manufacturing an electric resistance welded tube that can reliably remove the penetrator and obtain an electric resistance welded tube with good welded portion characteristics.

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

  [1] In a method of manufacturing an ERW pipe which roll-forms a band and affixes the width end to make an electric resistance welded pipe, the upper surface side of the width end of the band in the middle of roll forming or immediately before ERW welding When the tapered shape is applied to each of the lower surface and the lower surface, the tapered shape has an inclination angle from the width end surface of the strip to the upper surface or the lower surface of 25 ° to 50 °. A method for producing an electric resistance welded tube having good welded portion characteristics, wherein a distance in the thickness direction of the strip material between the taper start position and the upper surface or the lower surface is 20% to 40% of the thickness of the strip material.

  [2] The method for producing an electric resistance welded tube with good welded portion characteristics according to [1], wherein a tapered shape is provided by cutting or grinding.

  In the present invention, an appropriate taper shape is given to the width end portion of the band material in the middle of roll forming or immediately before the electric resistance welding, so the width end shape immediately before the electric resistance welding is an appropriate taper shape. Retained. As a result, sufficient molten steel is discharged during electric resistance welding, and the penetrator is surely removed, so that an electric resistance welded tube with good welded portion characteristics can be obtained.

  The techniques described in Patent Documents 1 and 2 both give a taper shape to the width end portion of the band material before roll forming. This is because the width end surface of the band material before roll forming is flat, and the width end portion is easy to taper, but on the other hand, as described above, the width end portion is bent by bending during roll forming, etc. Is deformed, and it is very difficult to make the shape of the width end portion immediately before the ERW welding into a desired shape. Therefore, the inventors of the present invention performed the taper processing of the width end portion in a process without these problems so that the shape of the width end portion immediately before the ERW welding is maintained in a desired taper shape.

  That is, the bending process in the vicinity of the width end portion of the strip is performed at the initial stage of roll forming. Therefore, if the strip end is bent at the initial stage of roll forming and then the width end of the strip is tapered, there is almost no distortion of the taper shape due to bending, and an appropriate taper is obtained until immediately before ERW welding. The shape can be maintained.

  Alternatively, a desired taper shape can be obtained with certainty if taper processing is applied to the width end portion of the strip immediately before electro-welding welding after roll forming.

  In addition, it is preferable to use cutting or grinding as means for applying a taper process to the width end portion of the strip at that time. In order to give the taper shape as desired, unnecessary portions are removed by cutting or grinding, or plastic deformation is performed by a perforated rolling roll or the like. However, in the method of plastic deformation, the generated surplus portion is removed. Since this is not possible, a surging portion of the surplus occurs in the periphery, and it is not easy to obtain a desired tapered shape in consideration of the surplus portion. On the other hand, if it is the method of removing an unnecessary part, it is not necessary to consider the influence of a surplus part and can obtain a desired taper shape easily.

(First embodiment)
FIG. 1 shows an ERW pipe production line used in the first embodiment of the present invention. In this electric sewing tube manufacturing line, the band material 20 is discharged from the uncoiler 1, straightened by the leveler 2, and gradually rolled up by the roll forming machine 5. The end portion is electro-welded with an electric seam welding machine including an induction heating unit 6 and a squeeze roll (electro-sealed welding portion) 7 to form a pipe 30, and the weld bead part of the pipe 30 is cut with a bead part cutting machine 8. The tube 30 after cutting is adjusted in outer diameter by the sizer 9 and then cut to a predetermined length by the tube cutting machine 10. The roll forming machine 5 includes a first break-down stand 3 that performs bending near the width end portion of the band member 20 in the preceding stage, and constrains the plate end portion rounded to the last stage to have a shape close to a perfect circle. The fin path forming stand 4 is provided.

  In this embodiment, in addition to the basic configuration described above, on the downstream side (exit side) of the first breakdown stand 3, taper shapes are formed on the upper surface side and the lower surface side of the left and right width ends of the band member 20. Grinding means 11 is provided for imparting. The grinding means 11 is a device in which a roll-shaped grinding wheel (grinding roll) 11a is rotated by a motor 11b as shown in FIG. It is. A total of four units are installed at the left and right width end portions of the band member 20 and the roll shaft is inclined at a predetermined angle α, so that the left and right width end portions of the band member 20 are placed on the upper surface side and the lower surface side. Each is provided with a predetermined taper shape (inclination angle α from the width end surface toward the upper surface, plate thickness direction distance β from the upper surface of the starting position at the width end surface).

  And about the taper shape provided to the both right and left width edge part of the strip | belt material 20, the inclination angle (alpha) from the width | variety end surface of the strip | belt material 20 to an upper surface or a lower surface is 25 degrees-50 degrees, and the taper in a width | variety end surface. The distance β between the starting position and the upper surface or the lower surface in the thickness direction of the strip material is 20% to 40% of the strip material plate thickness.

  This is because if the inclination angle α is less than 25 °, the molten steel is not sufficiently discharged from the central portion of the strip thickness, the penetrator remains and becomes defective, and the toughness and strength after ERW welding are reduced. If the angle α exceeds 50 degrees, the taper shape remains as a wrinkle of the pipe of the product even after the electric resistance welding, which is a problem. Further, when the distance β is less than 20% with respect to the plate thickness, the molten steel discharge at the center portion of the plate thickness becomes insufficient and the penetrator tends to remain, and when the distance β exceeds 40% with respect to the plate thickness. Even after ERW welding, the taper shape remains as a flaw in the tube of the product.

  In the ERW pipe manufacturing line configured as described above, after the breakdown is performed in the vicinity of the width end portion of the band member 20 in the first stand 3, a predetermined taper shape is formed at the width end portion of the band member 20. Therefore, there is almost no distortion of the taper shape due to bending, and an appropriate taper shape is maintained until just before ERW welding. As a result, a sufficient amount of molten steel is discharged at the time of electric resistance welding, and the penetrator is surely removed, so that an electric resistance welded tube having good welded portion characteristics such as toughness and strength of the welded portion can be obtained.

  In this embodiment, the grinding means 11 is used to give a predetermined taper shape to the width end portion of the band member 20, but a cutting means may be used instead. That is, FIG. 4 shows a cross-sectional view (corresponding to FIG. 2), and FIG. 5 shows a view taken along the line B-B of FIG. A total of four units are installed, whereby a predetermined taper shape on each of the upper surface side and the lower surface side of the left and right width ends of the band member 20 (inclination angle α from the width end surface toward the upper surface, starting position at the width end surface) A plate thickness direction distance β) from the upper surface may be provided.

  When it is desired to obtain a taper shape with very high accuracy, it is preferable to perform cutting or grinding while directly observing the shape online.

(Second Embodiment)
FIG. 6 shows an ERW pipe production line used in the second embodiment of the present invention. This ERW pipe production line is substantially the same as the ERW pipe production line used in the first embodiment described above, but in the first embodiment, on the downstream side of the breakdown first stand 3, In this embodiment, instead of the grinding means 11 for giving a taper shape to the width end portion of 20, in this embodiment, between the roll forming machine 5 and the induction heating unit 6 (that is, of the electric resistance welding machine). On the entry side, a cutting means 12 for providing a taper shape to the width end of the strip 20 is provided.

  As shown in FIGS. 4 and 5, the cutting means 12 is provided with a total of four cutting tools 12 a at the left and right width ends of the band material 20, and a pair of upper and lower widths. A predetermined taper shape (inclination angle α from the width end surface toward the upper surface, plate thickness direction distance β from the upper surface of the start position at the width end surface) is imparted to the upper surface side and the lower surface side of the end portion, respectively. It is a thing.

  And also in this embodiment, about the taper shape provided to the left and right width end portions of the band member 20, the inclination angle α from the width end surface of the band member 20 toward the upper surface or the lower surface is 25 ° to 50 °. Thus, the distance β in the strip thickness direction between the taper start position on the width end face and the upper surface or the lower surface is set to be 20% to 40% of the strip thickness.

  This is because if the inclination angle α is less than 25 °, the molten steel is not sufficiently discharged from the central portion of the strip thickness, the penetrator remains and becomes defective, and the toughness and strength after ERW welding are reduced. If the angle α exceeds 50 degrees, the taper shape remains as a wrinkle of the pipe of the product even after the electric resistance welding, which is a problem. Further, if the taper start distance β is less than 20% with respect to the plate thickness, the molten steel discharge at the center portion of the plate thickness becomes insufficient and the penetrator tends to remain, and the taper start distance β is 40% of the plate thickness. If it exceeds 50%, the taper shape remains as a flaw of the pipe of the product even after ERW welding, which is a problem.

  In addition, since the band material is almost circular immediately before the electric-welding welding, and the left and right width end portions are extremely close to each other, a taper shape is imparted using a cutting bit 12a that can be processed even in a narrow space. However, it is also possible to reduce the size of the grinding roll and use it to provide a tapered shape. Further, when it is difficult to arrange four cutting tools and grinding rolls on the same cross section, their positions may be shifted in the traveling direction of the strip 20 and arranged in a staggered manner.

  In this manner, in this embodiment, since the predetermined taper shape is applied to the left and right width end portions of the band member 20 immediately before the electric seam welding, the applied predetermined taper shape remains as it is. Since it is used for welding, the molten steel is sufficiently discharged from the width end portion, and the penetrator can be reliably removed. As a result, an electric resistance welded tube having good welded part properties such as toughness and strength of the welded part can be obtained.

  Incidentally, in the above-described first and second embodiments, the upper surface side and the lower surface side of the strip are provided with a taber shape that is symmetric with respect to the plate thickness center plane. Further, a taper shape in which the upper surface side and the lower surface side of the strip are asymmetric with respect to the plate thickness center plane may be provided.

  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 Invention Example 1, the above-mentioned electric resistance welded tube was manufactured based on the first embodiment described above. At that time, as a taper shape to be applied to the upper surface side and the lower surface side of the left and right width end portions of the band member, the inclination angle α was 30 ° and the taper start distance β was 5 mm.

  (Invention Example 2) As Invention Example 2, the above-mentioned electric resistance welded tube was manufactured based on the second embodiment described above. At that time, as a taper shape applied to the upper surface side and the lower surface side of the left and right width end portions of the band member, the inclination angle α was 40 ° and the taper start distance β was 6 mm.

  (Comparative Example 1) As Comparative Example 1, the taper shape to be applied to the upper surface side and the lower surface side of the left and right width ends of the band material, the inclination angle α is 20 °, the taper start distance β is 2.8 mm, Others were the same as Example 1 of the present invention.

  (Comparative Example 2) As Comparative Example 2, the taper shape to be applied to the upper surface side and the lower surface side of the left and right width ends of the band material, the inclination angle α is 55 °, the taper start distance β is 8.6 mm, Others were the same as Example 2 of the present invention.

  (Conventional example) As a conventional example, the grinding means 11 provided on the downstream side of the first breakdown stand 3 is removed in the production line shown in FIG. The above-mentioned ERW tube was manufactured.

  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 pipe according to the example of the present invention has high impact strength at the welded portion, small brittle fracture surface ratio, good toughness, and high product reliability. On the other hand, the electric resistance welded pipes according to the conventional example and the comparative example have a low impact strength at the welded portion, a high brittle fracture surface ratio, a reduced toughness, and poor product reliability.

  Therefore, it was confirmed that an electric resistance welded tube with good welded portion characteristics can be manufactured by the present invention.

It is explanatory drawing of the ERW pipe manufacturing line in the 1st Embodiment of this invention. It is an AA arrow line view of FIG. FIG. 3 is a partial detail view of FIG. 2. It is explanatory drawing of the other taper provision means in the 1st Embodiment of this invention. It is a BB arrow line view of FIG. It is explanatory drawing of the ERW pipe manufacturing line in the 2nd Embodiment of this invention.

Explanation of symbols

1 Uncoiler 2 Leveler
3 Breakdown 1st roll 4 Fin pass forming stand 5 Roll forming machine 6 Induction heating device 7 Squeeze roll (Electro welded part)
8 Bead cutting tool 9 Sizer 10 Pipe cutting machine 11 Grinding means 11a Grinding roll 11b Motor 12 Cutting means 12a Cutting tool 20 Band material 30 Pipe

Claims (2)

  In the method of manufacturing an ERW pipe which roll-forms the strip and butt welds the width end to make a pipe, and the upper surface side and the lower surface of the width end of the strip in the middle of roll forming or immediately before ERW welding When the taper shape is given to each side, the taper shape has an inclination angle of 25 ° to 50 ° from the width end surface of the strip toward the upper surface or the lower surface, and the taper start position on the width end surface of the strip A method for producing an electric resistance welded tube having good welded portion characteristics, wherein a distance in a thickness direction of the strip material between the upper surface and the lower surface is 20% to 40% of the thickness of the strip material.   [2] The method for producing an electric resistance welded tube with good weld characteristics according to claim 1, wherein the taper shape is imparted by cutting or grinding.

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