JP2009285708A - Manufacturing method of electric resistance welded tube excellent in buckling resistance property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem of not sufficiently improving buckling resistance property of an electric resistance welded tube by conventional technology. <P>SOLUTION: In the manufacturing method of the electric resistance welded tube, a steel strip is roll formed while it is being passed, both abutted ends of the strip in a width direction are electric-resistance-welded to form a tube 10, heat treatment is applied to an electric resistance welded area, and then the tube is straightened. When straightening the tube, a rotary straightening machine 8 is used wherein distance between the stands of the rotary straightening machine is set to satisfy the range defined by a formula: L≠D×π×tanα×A, wherein L is the distance between the strands of the rotary straightening machine, D is the outer diameter of the tube, π is a circular ratio, α is the roll inclination angle of the rotary straightening machine, and A is a number within a range of (N/2)±0.025. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an electric resistance tube having excellent buckling resistance, and in particular, manufacturing an electric resistance tube having excellent buckling resistance, which is less susceptible to buckling due to earthquakes and frozen soil even after laying as a line pipe. Regarding the method.

In many cases, UOE steel pipes are applied to pipelines for transporting oil, natural gas, and the like, and JCO, spiral steel pipes, seamless steel pipes, and partly electric-welded pipes are also applied.
The ERW tube is a workpiece (work object) made of hot-rolled strip made of an open tube by continuously rounding the plate width by roll forming, and both ends of the rounded plate width converge to a V shape. The seam is manufactured by electro-welding. However, since the work cross-sectional shape cannot be made to be a perfect circle during the roll forming, the ERW pipe has mechanical characteristics that are not uniform in the circumferential direction compared to other steel pipes. Therefore, after making the pipe by electro-welding, it was further corrected with a sizer to bring it closer to the target roundness, but the non-uniform distortion in the circumferential direction remained.

  As a result, laying ERW pipes as line pipes has the problem of local buckling and damage to the pipes when an earthquake occurs. Due to the ground change, the compressive force acts in the longitudinal direction of the pipe, and the pipe tends to buckle and bend easily, and also has a problem that leads to breakage. Therefore, when an electric resistance welded pipe is applied to a line pipe, the installation condition of the electric resistance welded pipe is greatly restricted. Therefore, the penetration rate of the electric resistance welded pipe has to be lower than that of a UOE steel pipe.

Conventionally, in order to popularize ERW pipes, for example, as shown in Patent Documents 1 and 2, etc., API standard X80 steel pipes with excellent low-temperature toughness due to improved materials and steel materials for line pipes having mechanical composite characteristics Technology development is underway.
JP 58-34133 A Japanese Patent No. 3903747

However, all of the above conventional techniques change the average mechanical properties of the material or the steel pipe, and do not equalize the mechanical characteristics due to non-uniform strain generated during the forming in the pipe circumferential direction. Absent.
When the present inventors examined the circumferential direction mechanical characteristics of the ERW pipe line pipe, when the work was roll-formed, in particular, the center part of the plate width, that is, approximately 180 on the opposite side of the welded part after becoming a pipe. The strain is concentrated near the bottom of the plate and the mechanical characteristics are lowered, which is a major cause of non-uniform characteristics in the pipe circumferential direction. Moreover, since the sizer that corrects only by a small amount of diameter reduction by a hole-type roll without rotating the tube is often used to correct the tube after pipe making, distortion concentrated on a specific part in the circumferential direction of the tube is used. It cannot be dispersed at all. That is, the conventional technique cannot sufficiently improve the buckling resistance performance of the ERW pipe, and this is a problem.

This invention is for solving the said subject, The summary structure is as follows.
(Claim 1)
By roll forming while passing the strip, and welding the both ends of the plate width together to form a pipe, heat-treating the ERW welded part, and then correcting the pipe In this correction, an electric resistance welded tube excellent in buckling resistance, characterized in that a rotation straightening machine is used and the distance between the stands of the rotation straightening machine is set within the range defined by the following expression (1). Manufacturing method.

L ≠ D × π × tanα × A (1)
Here, L is the distance between the stands of the rotation corrector [mm], D is the outer diameter of the tube [mm], π is the circumference [−], α is the roll inclination angle of the rotation corrector, that is, the roll axis direction. The angle [degrees or radians] formed by the pipe material passing direction, A is a number [−] in the range of (N / 2) ± 0.025, where N is a natural number.
(Claim 2)
The rotation straightening machine has a total of 3 or more stands. The front stage is the entrance stand, the last stage is the exit stand, and the stand between them is the central stand. 2. The electric resistance-welded tube with excellent buckling resistance according to claim 1, wherein the roll height of the central stand is raised or lowered within a range of +1 mm or more and +40 mm or less with respect to both of the entrance and exit stands. Manufacturing method.

  According to the present invention, it is possible to obtain relatively uniform mechanical characteristics in the circumferential direction of the ERW pipe, and the ERW pipe is less susceptible to buckling due to earthquakes and frozen soil even after laying as a line pipe. Can be manufactured.

  FIG. 1 is a schematic view showing an example of an electric sewing tube forming line suitable for the implementation of the present invention. In the pipe making line of FIG. 1, the strip is discharged by the uncoiler 1, corrected by the leveler 2, and then roll-formed by the roll forming machine 4 so as to round the plate width. Both ends of the plate width are butted and both the abutted ends (seams before welding) are induction-heated by induction heating means 5 made of contact tips or the like, and then joined by pressure-welding means made of squeeze rolls. This induction heating and joining is called electric resistance welding. The strip is formed into a tube 10 by electro-welding. The pipe 10 is subjected to bead cutting by a bead cutting machine 7 on the exit side of the squeeze roll 6, and after heat-treating an electric-welded welded portion (a seam after welding and its surrounding heat-affected zone) with a seam annealer (not shown), It is cut into a predetermined length by a tube cutter 9. The tube 10 after cutting is rotated and corrected by the rotation corrector 8. Reference numeral 20 denotes a material passing direction of the pipe 10 (taken in the pipe longitudinal direction). On the other hand, in the conventional frequently used ERW pipe forming line illustrated in FIG. 2, the strip 10 is the same as that in FIG. 1 until the bead part cutting and the ERW weld part heat treatment are performed. Is different from FIG. That is, in FIG. 2, the tube 10 is not rotationally corrected after cutting, but is adjusted to the outer diameter by the sizer 11 and then cut to a predetermined length by the tube cutting machine 9.

The rotation corrector used in the present invention may be used to correct the roundness or bending of a pipe. This rotation straightening machine consists of a series of three or more stands with a total of 3 rolls of hourglass rolls whose surface shape is a rotational hyperboloid shape, and the material passing direction while rotating the pipe with the drum rolls. It has a mechanism for feeding in the (longitudinal direction of the tube).
The present inventors have intensively studied the behavior of the material (work that has become a tube) in rotation correction, and as a result, in rotation correction using a plurality of stands, compression strain accumulates in the longitudinal direction of the tube between the stands, Alternatively, it has been found that compressive strain and tensile strain are alternately applied in the longitudinal direction. These suggest that the effect of reducing the yield stress of the material, called the Bauschinger effect in the longitudinal direction of the tube, works effectively. If compressive strain is applied in the longitudinal direction, the yield stress can be easily reduced in subsequent material tests in which tensile strain is applied. If compressive / tensile strain acts alternately in the longitudinal direction, movable dislocations increase within the material, yielding. Stress is easily reduced. Moreover, the strain tends to be uniform in the circumferential direction of the tube due to the rotation of the tube.Furthermore, when examining the circumferential distribution of the yield stress, not only the yield stress of the entire tube is reduced, but also It was understood that the strain tends to equalize in the circumferential direction.

  On the other hand, in conventional ERW pipe manufacturing, roll forming is performed so that the width of a workpiece made of a strip is continuously bent along an arc shape, and the workpiece cross section is shaped along a perfect circle during the roll forming. Therefore, the uneven strain in the circumferential direction remained. According to the investigation results of the present inventors, the cause was that the sizer was frequently used. Since the sizer corrects only by a small amount of diameter reduction by the hole-type roll without rotating the tube, the strain concentrated at a specific portion in the circumferential direction of the tube could not be dispersed at all.

  Therefore, by utilizing the above-mentioned useful action in rotation correction and applying rotation correction to the ERW pipe after pipe making, the yield stress of the ERW pipe that is not uniform in the circumferential direction can be made uniform, The buckling resistance can be greatly improved. As a result, when this ERW pipe is laid as a line pipe, it will be difficult to buckle locally even in the event of an earthquake, and the pipe will not be damaged. Withstands the compressive force applied in the longitudinal direction of the pipe due to the ground change that freezes, the pipe is less likely to buckle and bend.

  In addition, in order to make the Bausinger effect as uniform as possible in the circumferential direction and longitudinal direction of the tube with rotation correction, not only increase the number of contact between the tube and the roll, but also different parts of the tube contact the roll sequentially. It is necessary to do so. This is because if the same part of the tube is always in contact with the roll of each stand of a multi-stand rotation corrector, the strain concentrates only on the local part of the tube, and the strain is uniform in the circumferential and longitudinal directions of the tube. This is because it cannot be dispersed.

  Therefore, the present inventors examined means for sequentially bringing different portions of the pipe into contact with the roll, and as a result, the distance between the stands in relation to the outer diameter D of the pipe and the roll inclination angle α. I came up with the idea that it should be excluded from a specific range. In the rotation corrector, as shown in FIG. 3, the hourglass roll 12 is inclined and the tube 10 is moved forward by the feed speed in the material passing direction 20 generated with the rotation of the roll. Further, the minimum diameter portion a at the central portion in the roll axis direction of the hourglass roll 12 is substantially synchronized to rotate the tube 10 in the tube circumferential direction. Therefore, if the number of rotations of the tube while the tube is advanced by the distance between the stands is substantially equal to a natural number multiple of a half rotation, the tube is locally divided into a portion that always contacts the roll and a portion that does not always contact the roll. That is why.

  Therefore, if the number of rotations of the tube during the advancement of the tube by the distance between the stands does not become a value substantially equal to a natural number multiple of a half rotation, different positions in the outer surface of the tube will be in the roll of any one of the stands. It is possible to make contact with and to distribute the strain in the circumferential direction of the tube. In order to realize this, it is necessary to set the distance between the stands of the rotation corrector within the range in which the formula (1) (the inequality shown below) is established.

L ≠ D × π × tan α × A (1)
Here, L is the distance between the stands of the rotation corrector [mm], D is the outer diameter of the tube [mm], π is the circumference [−], α is the roll inclination angle of the rotation corrector, that is, the roll axis direction. An angle [degree or radian] formed by the direction in which the pipe passes through, and A is a number [−] within a range of (N / 2) ± 0.025, where N is a natural number, and this “(N / 2) ± 0.025 "Range" corresponds to the value range of "a value approximately equal to a natural number multiple of half rotation".

  In addition, the rotation correction machine is usually composed of 3 or more total stands, each stand has 2 rolls of upper and lower totals, the front stage is the entrance stand, the last stage is the exit stand, and the stand between them is the central stand, Make the roll height of both the entrance and exit stands almost the same (the same when the error is less than 1 mm), and raise or lower the roll height of the central stand with respect to these roll heights to cause bending strain in the longitudinal direction of the tube. Add.

  Therefore, the present inventors diligently studied means for further effectively reducing the yield point of the material due to the Bauschinger effect using a rotation corrector. As a result, the roll height of the central stand is higher than the roll height of the entry stand of the rotation straightening machine (abbreviated entry roll height) and the roll height of the exit stand (abbreviated exit roll height). It has been found that the height (abbreviated as the center roll height) may be raised or lowered within a range of +1 mm or more and +40 mm or less.

  That is, if the amount of increase or decrease in the central roll height relative to the heights of both the entry side and the exit side is less than +1 mm, the compressive strain in the longitudinal direction of the pipe is insufficient and is within the elastic deformation of the material. Remarkably low. Further, when the amount of increase or decrease in the height of the central roll exceeds +40 mm, the amount of flatness due to the bending of the tube becomes remarkably large, and the roundness of the tube is impaired. Therefore, it is preferable that the amount of increase or decrease in the center roll height (abbreviated as the center roll increase amount or the center roll decrease amount) with respect to both the entry side and exit side roll heights is +1 mm or more and +40 mm or less.

Using a strip having a steel composition containing 0.05% C, 0.2% Si and 1.2% Mn in mass% as a raw material, the raw material is passed through the pipe making line shown in FIG. 1 or FIG. The straightening conditions after forming the tube are shown in Table 1. An electric resistance welded tube having an outer diameter D of 600 mm and a wall thickness of 19.1 mm was manufactured under the conditions shown in columns 1 to 4. Ten JIS No. 13 tensile test pieces in the longitudinal direction of the pipe from the position of approximately 90 degrees in the circumferential direction and approximately 180 degrees (corresponding to the arc-shaped plate bottom) from the welded part of the manufactured ERW pipe Cut out and conducted a tensile test to determine and evaluate the mechanical properties.
(No. 1) As an example of the present invention, the tube was formed on the tube forming line of FIG. No. The values shown in the first column were set. The roll inclination angle α was 30 degrees. The establishment range of the formula (1) here is L ≠ 600 × π × tan30 ° × {(N / 2) ± 0.025} = 1088.279 × {(N / 2) ± 0.025}. When 517 to 571 [mm], N = 2, L ≠ 1061 to 1115 [mm], when N = 3, L ≠ 1605 to 1660 [mm], when N = 4, L ≠ 2149 to 2203 [mm], and so on. Therefore, within this range, L = 1800 mm.
(No. 2) As a comparative example, the pipe was formed on the pipe making line of FIG. . The values shown in column 2 were set. The roll inclination angle α was 50 degrees. Here, the establishment range of the equation (1) is L ≠ 600 × π × tan50 ° × {(N / 2) ± 0.025} = 2246.402 × {(N / 2) ± 0.025}. From 1067 to 1179 [mm], when N = 2, L ≠ 2190 to 2303 [mm], and so on. Therefore, L = 1100 mm outside this range.
(No. 3) As a comparative example, the tube was formed on the tube forming line of FIG. . The values shown in column 3 were set. The roll inclination angle α was 2 degrees. Here, the range of establishment of equation (1) is L ≠ 600 × π × tan2 ° × {(N / 2) ± 0.025} = 65.824 × {(N / 2) ± 0.025}. From 1644 to 1647 [mm], when N = 51, L ≠ 1677 to 1680 [mm], and so on. Therefore, L = 1645 mm outside this range.
(No. 4) As a conventional example, the pipe was made by the pipe making line of FIG.

  No. above. Table 1 shows the results of determining the mechanical properties of the electric resistance welded tube manufactured under each correction condition of 1-4. From Table 1, in the electric resistance welded tube according to the present invention, the yield stress YS in the vicinity of the 180 ° position is lower than that in the conventional example, showing a value close to that in the vicinity of the 90 ° position, and excellent in buckling resistance. On the other hand, in the ERW pipe according to the comparative example (No. 2) and the ERW pipe according to the conventional example, the yield stress YS near the 180 ° position is higher than that near the 90 ° position, and the buckling resistance performance is poor. Yes. Further, in the correction condition of Comparative Example (No. 3), a large flatness occurred during the rotation correction of the tube, and the material passing speed was remarkably reduced, so that the ERW tube as an acceptable product could not be manufactured.

It is the schematic which shows an example of the electric sewing pipe | tube pipe forming line suitable for implementation of this invention. It is the schematic which shows an example of the electric sewing pipe tube forming line used conventionally conventionally. (A) is a top view which shows roll arrangement | positioning of the rotation correction machine used for this invention, (b) is a definition explanatory drawing of a roll inclination angle.

Explanation of symbols

D tube outer diameter α roll inclination angle 1 decoiler 2 leveler 3 fin pass stand 4 roll forming machine 5 induction heating means (contact tip)
6 Pressure welding means (squeeze roll)
7 Bead cutting machine 8 Rotation straightening machine 9 Pipe cutting machine
10 tubes
11 Sizer
12 Hourglass roll
12a, 12b Roll axis
13 Pass line
20 Feeding direction

Claims (2)

By roll forming while passing the strip, and welding the both ends of the plate width together to form a pipe, heat-treating the ERW welded part, and then correcting the pipe In this correction, an electric resistance welded tube excellent in buckling resistance, characterized in that a rotation straightening machine is used and the distance between the stands of the rotation straightening machine is set within the range defined by the following expression (1). Manufacturing method.
L ≠ D × π × tanα × A (1)
Here, L is the distance between the stands of the rotation corrector [mm], D is the outer diameter of the tube [mm], π is the circumference [−], α is the roll inclination angle of the rotation corrector, that is, the roll axis direction. The angle [degrees or radians] formed by the pipe material passing direction, A is a number [−] in the range of (N / 2) ± 0.025, where N is a natural number.   The rotation straightening machine has a total of 3 or more stands. The front stage is the entrance stand, the last stage is the exit stand, and the stand between them is the central stand. 2. The electric resistance welded tube having excellent buckling resistance according to claim 1, wherein the roll height of the central stand is raised or lowered within a range of +1 mm or more and +40 mm or less with respect to both of the entrance and exit side stands. Manufacturing method.

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