JP2015167973A - Manufacturing method for thi-walled electric-resistance weld pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide manufacturing method for a thick-walled and high-intensity steel pipe which has been incapable of being manufactured by existing equipment without substantially modifying existing steel-pipe manufacturing equipment.SOLUTION: In a manufacturing method for an electric-resistance weld pipe by which a metal strip material is intermediately molded with a cage roll group, finish-molded into a tubular form with a fin pass roll group, and then shaped into a circular pipe by welding width end parts by electric resistance, the intermediate molding is carried out so that a cross-sectional shape of an open pipe immediately before fin pass roll molding may satisfy the following expression. 1.04≤V/H≤1.20, where V is the vertical diameter (mm) of an open pipe outer periphery, and H is the lateral diameter (mm) of the open pipe outer periphery.

Description

  The present invention relates to a method for manufacturing an electric resistance welded steel pipe, and in particular, an electric resistance welded steel pipe suitable for manufacturing a thick-walled and high-strength steel pipe having a large load during roll forming, such as for oil wells, automobiles, and buildings. It relates to the manufacturing method.

  ERW steel pipes have excellent features such as good dimensional accuracy, beautiful surface skin, and high productivity. Steel pipes for line pipes such as oil and natural gas, steel pipes for automobiles, and construction It is used for a wide range of applications such as steel pipes. In recent years, higher strength and thicker ERW steel pipes have been required compared to conventional steel pipes. In the field of manufacturing hot-rolled steel sheets used as ERW steel pipe materials, higher strength steel sheets and thicker steel sheets are used. Is being developed and manufactured. Here, the thick wall means 12 to 26 mm, and the high strength means a steel plate having a tensile strength of 490 MPa or more.

  As shown in FIG. 1, the ERW steel pipe is manufactured by continuously rolling a steel plate (steel strip) into a tube shape and then welding the width end of the steel plate (steel strip). ERW steel pipe manufacturing equipment is usually capable of manufacturing steel pipes with various outer diameters and wall thicknesses by adjusting the position of forming rolls and exchanging rolls in one forming line. The production range of steel pipes in one forming line is limited by the forming force and driving force of the roll on the thick wall side, and buckling of the end of the steel strip, generally called edge wave, occurs during roll forming on the thin wall side. Is limited by

  Therefore, various techniques have been developed to expand the manufacturable range of tubes in one molding line. For example, in Patent Document 1, the inner surface of a strip-shaped metal material (semi-molded product) in a rough and intermediate molding process is moved in the direction of travel of the strip-shaped metal material by an inner surface roll that is rotatable at one or more positions in the circumferential direction. It is disclosed that edge waves are prevented by performing molding by regulating the position of a material in a vertical plane.

  Further, Patent Documents 2 and 3 disclose that a drive bottom roll, a top roll provided to be vertically adjustable and positioned on both sides of the top roll are provided in front of the fin pass stand group of the ERW steel pipe forming line. A plurality of inside rolls that can be adjusted and an outside roll that can be adjusted in the vertical and horizontal directions acting near the coil edge portion are provided in a plurality of stages in the longitudinal direction, and the drive bottom roll and the top roll To obtain sufficient driving force, prevent the thin-walled material from being folded by the combination of the inside roll and the outside roll, and prevent the edge elongation by arranging multiple outside rolls in the longitudinal direction. The open pipe shape in front of the fin pass stand is close to the fin pass roll caliber. Molding apparatus ERW steel pipe can takes it is disclosed.

  Furthermore, in Patent Document 4, in the method for manufacturing a welded steel pipe using the CBR forming method, both sides are pushed by a cage roll between the final center bend exit side and the first fin pass roll exit side. By pressing both sides close to the bottom of the tube in the thickness direction from the inner surface with a presser roller, the concentration of bending stress on the bottom of the tube is reduced, and an ultra-thin, ultra-high strength strip is formed. A method and apparatus for manufacturing a welded steel pipe is disclosed that does not cause hip breakage and does not generate edge waves in the fin pass roll forming stage even when pipes are made to have a small diameter.

JP 56-66323 A Japanese Patent Laid-Open No. 04-178221 Japanese Patent Laid-Open No. 04-178222 Japanese Patent Laid-Open No. 2005-66679

  However, the methods disclosed in Patent Documents 1 to 4 described above are effective in preventing edge waves generated in thin-walled materials, but rolls that cause problems when manufacturing thick-walled and high-strength steel pipes. It was insufficient to solve the shortage of molding force and driving force. In particular, the conventional production equipment often lacks the forming force of the fin pass roll, and it is necessary to reinforce the fin pass stand when trying to produce a thick and / or high strength steel pipe that exceeds the manufacturable range. For this purpose, a huge investment was required because the entire layout of the steel pipe manufacturing facility would be remodeled.

  Also, by adopting a method of pressing the vicinity of the tube bottom on the inner surface side of the tube with a roll during the forming process of the open tube, the shape of the open tube on the finned roll entry side changes, so the molding load of the fin pass roll changes. Although it was theoretically anticipated, the relationship between the shape of the open pipe on the fin pass roll entering side and the forming load of the fin pass roll was not clarified quantitatively at all. Therefore, in the prior art, there is a problem that the entire mill layout needs to be remodeled when attempting to manufacture a steel tube having a thickness and high strength outside the manufacturable range.

  An object of the present invention is to provide a method of manufacturing a thick-walled and high-strength steel pipe that could not be manufactured with the existing equipment without significantly remodeling the existing steel pipe manufacturing equipment.

  The present inventors diligently studied to solve the above problems. As a result, there is a correlation between the cross-sectional shape of the semi-molded product (open tube) on the fin-pass roll entry side and the forming load of the fin-pass roll, and the optimal cross-section of the open tube that can reduce the forming load of the fin-pass roll The present invention has been completed by finding that the open tube can be formed into an optimal cross-sectional shape by the presence of the shape and the method of pressing the vicinity of the tube bottom on the inner surface side of the open tube with a roll.

That is, this invention consists of the following summaries.
(1) After the metal strip is formed intermediately by a cage roll group and finished into a tubular shape by a fin pass roll group, the width end of the metal strip is electro-welded and manufactured as a circular pipe A method for producing a thick-walled electro-welded pipe, characterized in that the intermediate molding is performed so that the cross-sectional shape of the open pipe immediately before the fin pass roll molding satisfies the following formula.
Record
1.04 ≦ V / H ≦ 1.20
Where V: vertical diameter of outer circumference of open tube (mm)
H: Horizontal diameter of outer circumference of open tube (mm)

(2) In the intermediate forming process by the cage roll group, two or more points in the circumferential direction from a roll that presses both side edges of the metal strip from the outer surface side and from an inner wall surface of the semi-molded product of the metal strip The intermediate forming is performed by constraining the position in a plane perpendicular to the material traveling direction of the metal strip using a roll that presses the position of A method for manufacturing a sewing tube.
(3) The electric resistance welded pipe is an electric resistance welded steel pipe having a wall thickness of 12 to 26 mm and a ratio of the wall thickness to the outer diameter of 2 to 20%. (1) or (2) Manufacturing method for thick-walled electro-resistance tube.
(4) The thickness is 12 to 26 mm, the ratio of the thickness to the outer diameter is 2 to 20%, and manufactured by the manufacturing method according to (1) or (2) Steel pipe.

According to the present invention, it is possible to reduce the forming load of the fin pass roll at the time of forming a steel pipe by about 20% as compared with the conventional method, and to manufacture a thick and / or high strength steel pipe that has been impossible to manufacture conventionally. Can do.
Further, since the strain that the steel plate (steel strip) of the material receives during roll forming is reduced, the forming is stabilized and the workability of the product is improved.

It is a schematic diagram which shows one example of an electric resistance steel pipe manufacturing line. It is a schematic diagram which shows the cross-sectional shape of the open pipe before a fin pass roll shaping | molding. It is a figure which shows the relationship between a fin pass roll shaping | molding load and V / H. It is a mimetic diagram showing one embodiment of the present invention. It is an example of a measurement result which shows the time fluctuation of typical forming load.

Embodiments of the present invention will be described below with reference to the drawings.
In the intermediate forming by the cage roll group of the conventional method, the cross section of the open tube immediately before the fin pass roll forming has a shape as shown in FIG. In FIG. 2, it is assumed that the cross-sectional shape of the open tube is bilaterally symmetric, V (mm) is the vertical diameter of the outer periphery of the open tube, and H (mm) is the horizontal diameter of the outer periphery of the open tube.

First, as a result of pipe making experiments, it was found that the forming load of the fin pass roll increases when the cross-sectional shape of the open pipe is extremely long or long.
Therefore, when manufacturing an ERW steel pipe having a strength level of API standard X56, an outer diameter of 600 mm, and a wall thickness of 25.4 mm, using a steel strip of low carbon low alloy steel as a raw material, the longitudinal diameter of the outer circumference of the open pipe is The effect of the cross-sectional shape of the open tube on the forming load of the fin pass roll was examined by using the ratio V / H of the lateral diameter as a variable. The result is shown in FIG. FIG. 3 shows that the forming load of the fin pass roll is reduced when V / H is in the range of 1.04 ≦ V / H ≦ 1.20. When V / H is less than 1.04, the cross-sectional shape of the open tube is a horizontally long shape, so that the molding load of the fin pass roll increases and molding cannot be performed normally. On the other hand, if V / H exceeds 1.20, the shape becomes too long and the forming load of the fin pass roll increases.

  In order to form the open pipe so as to satisfy the above-mentioned relational expression, as shown in FIG. 4, a metal strip is formed between a pair of cage rolls in the most downstream zone (# 3 zone) of the cage roll group. Using a roll (inner roll) that presses two or more positions in the circumferential direction from the inner wall surface side of the semi-molded product, the pair of cage rolls and the inner roll perpendicular to the material travel direction of the metal strip It is preferable to constrain the position in a plane.

  Furthermore, in order to make the effect of reducing the forming load of the fin pass roll remarkable, the electric sewing tube to be formed has a thickness of 12 to 26 mm and a ratio of the thickness to the outer diameter of 2 to 20%. An electric resistance steel pipe is preferable. When the wall thickness is less than 12 mm, the forming load of the fin pass roll is low even in the conventional method, and the effect of reducing the forming load is small. In addition, when the ratio of the wall thickness to the outer diameter is less than 2%, in addition to the low forming load of the fin pass roll even in the conventional method, the metal strip is folded due to the pressing of the inner roll. There is concern about deformation. In addition, when the thickness exceeds 26 mm and the ratio of the outer diameter of the thickness exceeds 20%, it is impossible to form the equipment, so the upper limit is set.

  In addition, when the strength of the material to be molded is low, the molding load of the fin pass roll is low even in the conventional method, and the inner surface of the tube may be dented due to the pressure of the inner roll. Therefore, a material having a tensile strength of 490 MPa or more It is preferable that

  Using a steel strip of low-carbon, low-alloy steel as the raw material, the strength level of API standard X56-X80 class, outer diameter 600mm, wall thickness 25.4mm of electric resistance welded steel pipe, V / H representing the cross-sectional shape was changed as shown in Table 1 to perform intermediate molding, and the molding load of the first fin pass roll was measured. The results are shown in Table 1, and an example of measuring the time variation of the molding load is shown in FIG.

  As shown in Table 1 and FIG. 5, in the example of the present invention, the molding load of the first fin pass roll was significantly reduced as compared with the comparative example, and the molding load was suppressed and the molding was stabilized.

1 Uncoiler 2 Leveler 3 Edge forming machine 4 Intermediate forming machine (cage roll group)
5 Finishing machine (Finpass roll group)
6 Heating device 7 Squeeze roll 8 Bead cutting machine 9 Sizer 20 Steel strip 30 ERW steel pipe

Claims (4)

In the method for producing an electric resistance welded tube, a metal strip is intermediately formed by a cage roll group, and after being formed into a tubular shape by a fin pass roll group, the width end portion of the metal strip is electroformed and welded into a circular pipe. A method for producing a thick-walled electro-welded pipe, characterized in that the intermediate molding is performed so that the cross-sectional shape of the open pipe immediately before the fin pass roll molding satisfies the following formula.
Record
1.04 ≦ V / H ≦ 1.20
Where V: vertical diameter of outer circumference of open tube (mm)
H: Horizontal diameter of outer circumference of open tube (mm)   In the intermediate forming process by the cage roll group, a roll that presses both side edges of the metal strip from the outer surface side, and two or more positions in the circumferential direction from the inner wall surface of the semi-molded product of the metal strip. 2. The thick ERW tube according to claim 1, wherein the intermediate molding is performed by constraining a position in a plane perpendicular to a material traveling direction of the metal strip using a pressing roll. Production method.   The thick-walled electric sewing according to claim 1 or 2, wherein the electric-welded pipe is an electric-welded steel pipe having a wall thickness of 12 to 26 mm and a ratio of the wall thickness to the outer diameter of 2 to 20%. A method of manufacturing a tube.   An electric-welded steel pipe having a thickness of 12 to 26 mm and a ratio of the thickness to the outer diameter of 2 to 20% and manufactured by the manufacturing method according to claim 1 or 2.

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