JP2009285711A - Manufacturing method of electric resistance welded tube excellent in buckling resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that a conventional technique has difficulty to obtain an electric resistance welded tube excellent both in out-of-roundness and buckling resistance. <P>SOLUTION: In the manufacturing method of an electric resistance welded tube, roll-forming is applied while a band steel is passed through, with the abutted both ends in the width direction resistance-welded to form a tube 10 and, after heat treatment on a resistance welded zone, the tube is straightened. In straightening the tube, rotary straightening machines 8 are used, wherein a distance between the stands of the machines is set not less than the outer diameter of the tube 10 and not more than eight times the outer diameter of the tube. Further, the rotary straightening machines are three strands or more in total, wherein the front stage is an entrance stand, the rear stage is an exit stand, and the stand in-between is the center stand. The roll height in the entrance and exit stands are made nearly equal, and the roll height of the center stand is elevated or lowered in the range of 1-40 mm with respect to the roll height of the entrance and exit stands. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an ERW pipe excellent in roundness and buckling resistance, and in particular, when laid as a line pipe, is less susceptible to buckling due to earthquakes and ground changes of frozen soil, roundness. The present invention also relates to a method for manufacturing an electric resistance welded tube having excellent buckling resistance.

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 pipe is rolled into a workpiece (work object) made of hot-rolled strip while continuously passing through it to form an open tubular shape. Manufactured by 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, particularly when the ERW pipe was laid as a line pipe, there was a problem that the pipe was likely to buckle and break easily when an earthquake occurred. In addition, when an ERW pipe is buried as a line pipe in a frozen land zone, the compressive force due to ground changes that softens in the summer and freezes in the winter acts in the longitudinal direction of the pipe, leading to damage to the line pipe. I always had a problem. 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 mechanical characteristics of the line pipe using the ERW pipe, at the time of roll forming of the material, the strain is concentrated in the central portion of the plate width of the material, and the plate width where the strain is concentrated. It has been found that the yield stress in the central portion is higher than the yield stress in the other portions, which is a major cause of non-uniform mechanical properties in the circumferential direction of the ERW pipe.

  In addition, a sizer is frequently used to correct the electric sewing tube for the purpose of improving the roundness of the tube. Since this sizer corrects only by a small amount of diameter reduction by a hole-type roll without rotating the tube, there is a drawback that the strain concentrated on a specific portion in the circumferential direction of the tube cannot be dispersed at all. That is, the conventional technique has a problem that it is difficult to obtain an electric resistance welded tube excellent in both roundness and buckling resistance.

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 order to straighten the tube, a rotation straightening machine is used, and the distance between the stands of the rotation straightening machine is set to be not less than the outer diameter of the pipe and not more than eight times the outer diameter of the pipe. A method of manufacturing an electric resistance welded tube with excellent buckling resistance.
(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, by using a rotation straightening machine and correcting the rotation of the tube, it is possible to obtain an ERW tube having relatively uniform mechanical characteristics in the circumferential direction of the ERW tube. It is possible to manufacture ERW pipes with excellent buckling resistance.

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 material W 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 material W in the plate width direction.
At the final stage of this roll forming, both end portions in the plate width direction are further roll formed by the fin pass stand 3, and the seam before welding is induction heated by the induction heating means 5 made of contact tips or the like, and then pressed by a squeeze roll. It is butt-welded by means. This induction heating and butt welding 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 electro-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 being cut is rotated and corrected by the rotation corrector 8 in order to improve the roundness of the tube and correct the bending of the tube. Reference numeral 20 denotes a material passing direction of the pipe 10 after cutting.

On the other hand, the conventional frequently used ERW pipe forming line illustrated in FIG. 2 is formed by roll forming the material W discharged by the uncoiler 1 and then performing bead cutting and ERW welding on the pipe 10 obtained by ERW welding. The process is the same as that shown in FIG. 1 until the partial heat treatment is performed, but the subsequent processes are different.
That is, in the conventional manufacturing process, the tube 10 connected to the uncoiler 1 is adjusted in outer diameter by the sizer 11 without being rotated, and then cut to a predetermined length by the tube cutter 9.

  In the present invention, a rotation correcting machine 8 is used in which a pair of upper and lower hourglass rolls whose surface shape is a rotational hyperboloid shape is incorporated in each stand. This rotation straightening machine has a total of three or more stands arranged in series so as to form a predetermined roll inclination angle with the material passing direction (pipe longitudinal direction). While rotating the pipe with a pair of hourglass rolls, the pipe is rotated and corrected while feeding in the material passing direction (pipe longitudinal direction).

  The present inventors diligently investigated the behavior of the material (tube) during rotation correction. As a result, compression strain accumulated in the longitudinal direction of the tube between the stands of the rotation correction machine, or compression in the longitudinal direction of the tube. We found that strain and tensile strain were alternately applied. 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 of the tube and plastic deformation has occurred, the yield stress obtained under tensile load when a tensile load is applied in the subsequent material test does not cause plastic deformation due to compressive strain. If the compressive / tensile strain acts alternately in the longitudinal direction of the tube and the number of movable dislocations inside the material increases, the yield stress is lower in the subsequent material test than when there are few movable dislocations. To reduce. In addition, 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 the strain. Tended to equalize in the circumferential direction.

On the other hand, in conventional ERW pipe manufacturing, the sizer corrects only a small amount of diameter reduction with a hole-type roll without rotating the pipe, so that the strain concentrated on a specific part in the pipe circumferential direction is dispersed. Was not made at all.
Therefore, if the pipes after pipe making are rotated and corrected by utilizing the above-mentioned useful action in the rotation straightening machine, the yield stress due to non-uniform strain generated during roll forming is made uniform in the pipe circumferential direction. It is possible to manufacture an electric resistance welded tube having excellent roundness and buckling resistance.

Also, in order to work the bausinger effect as evenly as possible in the circumferential direction and longitudinal direction of the tube by rotating the tube using a rotation straightener, just increase the number of contact between the tube and the roll. Instead, it is necessary to effectively use the longitudinal bending strain of the tube. This is because if the longitudinal bending strain of the tube is too small, the Bauschinger effect becomes insufficient.
For this reason, in the present invention, when straightening the tube, the distance L between the stands of the rotation straightening machine is set to the outer diameter of the tube and not less than 8 times the outer diameter of the tube. Since the distance L between the stands of the rotation straightening machine corresponds to the bending arm length of the pipe when the pipe is rotated and corrected, in order to increase the longitudinal bending strain applied to the pipe, the bending arm length of the pipe should be shortened. It's good.

  However, if the bending arm length of the tube is excessively shortened, the tube is deformed flat, and the roundness of the rotation-corrected tube is deteriorated. Suppose that it is set to be larger than the outer diameter. On the other hand, if the bending arm length of the tube is excessively long, the bending strain in the longitudinal direction of the tube becomes small and the Bausinger effect becomes insufficient. Therefore, the distance L between the stands of the rotation straightening machine is 8 of the outer diameter of the tube. It was set to less than double.

  In addition, the rotation correction machine is usually composed of 3 or more stands, and 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. The roll height of both the entrance side and exit side stands is almost the same (the same when the error is less than 1 mm), and the roll height of the central stand is raised or lowered with respect to these roll heights to cause bending strain in the longitudinal direction of the pipe. Add

  At that time, if the rise or fall amount of the central roll height with respect to both the entry side and exit side roll heights 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. No or significantly lower. On the other hand, if the amount of increase or decrease in the height of the central roll exceeds +40 mm, the flat deformation of the tube becomes remarkably large, and the roundness of the tube decreases. Therefore, it is preferable that the amount of rise or fall of the central roll height (abbreviated as the amount of rise of the center roll or the amount of fall of the center roll) with respect to both the entry side and exit side roll heights is +1 mm or more and +40 mm or less.

A hot-rolled steel strip having a steel composition containing 0.05% C, 0.2% Si and 1.2% Mn in mass% is used as a raw material, and the raw material is applied to the pipe making line shown in FIG. 1 or FIG. An electric resistance welded tube having an outer diameter of 600 mm and a wall thickness of 19.1 mm was manufactured.
At a position of approximately 90 degrees in the circumferential direction from the ERW welded part of the manufactured ERW pipe and a position of approximately 180 degrees (a position opposite to the ERW welded part), a JIS No. 13 tensile test specimen is placed in the longitudinal direction of the pipe. Ten pieces were cut out and subjected to a tensile test to obtain mechanical properties, and the effects were evaluated. The obtained mechanical properties are shown in Table 1.

(No. 1) As an example of the present invention, the tube was formed on the tube forming line of FIG. The values shown in the first column were set.
(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.
(No. 3) As a comparative example, the pipe was formed on the pipe making line of FIG. The values shown in column 3 were set.
(No. 4) As a conventional example, the pipe was made by the pipe making line of FIG.

From the results shown in Table 1, no. In the electric resistance welded tube of the present invention example 1, the yield stress YS in the vicinity of the 180 ° position is No. 1. 2 comparative example, no. 4, and the difference in yield stress in the circumferential direction ΔYS is no. 2 comparative example, no. 4 is smaller than the conventional example.
In contrast, no. 2 comparative example, no. In the conventional example of No. 4, the yield stress YS in the vicinity of the 180 degree position is not lowered, and the circumferential yield stress difference ΔYS is larger than in the example of the present invention. Further, in the case of the comparative example (No. 3), since the distance L between the stands of the rotation correction machine does not satisfy the conditions of the present invention, a large flat deformation occurs during the rotation correction of the tube, and the roundness is rejected. It was.

  Therefore, no. The electric resistance welded tube of Example 1 of the present invention is an electric resistance welded tube excellent in roundness and buckling resistance.

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.

Explanation of symbols

W material (hot rolled strip)
DESCRIPTION OF SYMBOLS 1 Uncoiler 2 Leveler 3 Fin pass stand 4 Roll forming machine 5 Induction heating means (contact chip)
6 Pressure welding means (squeeze roll)
7 Bead cutting machine 8 Rotation straightening machine 9 Pipe cutting machine
10 tubes
11 Sizer
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 order to straighten the tube, a rotation straightening machine is used, and the distance between the stands of the rotation straightening machine is set to be not less than the outer diameter of the pipe and not more than eight times the outer diameter of the pipe. A method of manufacturing an electric resistance welded tube with excellent buckling resistance.   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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