JP4946812B2 - Manufacturing method of electric resistance welded tube with good buckling resistance - Google Patents

Description

  The present invention relates to a method for manufacturing an electric resistance welded tube having good buckling resistance. An ERW pipe with good buckling resistance is an ERW pipe that is less susceptible to buckling due to earthquakes or frozen soil after being laid as a line pipe.

In many cases, UOE steel pipes are applied to line pipes for pipelines for transporting oil, natural gas, etc., and JCO, spiral steel pipes, seamless steel pipes, and partly electric sewing pipes are also applied.
The electric resistance welded tube is manufactured by roll-forming a hot-rolled strip (band material, material), butting the end portions of the width of the strip, and performing electric resistance welding. An example of this electric sewing tube manufacturing process is shown in FIG.

  In this process, the material (strip) 10 is dispensed from the uncoiler 1 and straightened by the leveler 2, and then the material width is continuously bent by the roll forming 4. By forming (fin pass molding) used, a substantially arc shape is formed, and both ends of the substantially arc-shaped material are abutted by a squeeze stand 6 while being heated by a power feeding means such as a contact tip 5 to be electro-welded to obtain a tube 10. . The electric power welding means 18 such as the contact tip 5 and the squeeze stand 6 constitute an electric sewing machine 18.

After the electric seam welding, first, a bead part cutting 7 is performed to cut and remove a bead (surplus) from the welded part of the pipe 10, and then the weld distortion is removed by heat treatment around the welded part with a seam annealer 17, and then the pipe 10 is removed. The outside diameter is corrected through the sizer 8, and finally the tube 10 is cut into a predetermined length by the tube cutting machine 9.
In the above roll forming, the width of the strip is generally bent continuously, but since it cannot follow the true arc shape on the way, the mechanical characteristics of the ERW pipe are circumferential compared to other steel pipes. It tends to be uneven. For this reason, after electric welding and forming a tube, the outer diameter was further corrected by 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 being easily buckled and causing damage to the pipes in the event of an earthquake, and if buried in frozen land, soft ground in summer and frozen ground in winter Since the compression force acts in the longitudinal direction of the pipe by alternately repeating the above, the pipe is locally buckled and easily bent, and further has a problem of being damaged.

Therefore, when an electric resistance welded tube is used as a line pipe, the installation rate of the electric resistance welded tube is greatly restricted. Therefore, the penetration rate of the electric resistance welded tube has to be lower than that of a UOE steel pipe or the like.
Therefore, in order to popularize ERW pipes conventionally, focusing on the material, for example, as shown in Patent Document 1 and Patent Document 2, the ratio of the yield stress YS and the maximum tensile stress TS is improved by improving the material. A method has been proposed in which the steel pipe is made larger and particularly YS is reduced to make it difficult to buckle.
JP 58-034133 A Japanese Patent No. 3903747

  However, when examining the circumferential mechanical characteristics of the electric resistance welded line pipe, in the above-mentioned roll forming, in particular, the material outer circumference bottom, which is the center portion of the material width, that is, the portion opposite to the welded portion after becoming a pipe Distortion concentrates in the vicinity of the position (position at approximately 180 degrees in the circumferential angle from the weld) and mechanical characteristics deteriorate, resulting in non-uniform mechanical characteristics in the circumferential direction. There was a problem that an electric resistance welded tube with poor buckling performance would be manufactured. In addition, approximately θ degrees refers to an angle within a range of θ degrees ± 10 degrees.

  The conventional methods all change the average material properties of the strip or the entire steel pipe, and do not show the above-mentioned problems and solutions.

The inventors diligently studied the means for solving the above-mentioned problems and made the present invention having the following gist configuration.
1. In a method for manufacturing an electric resistance welded tube, the belt material is roll-formed into an arc shape, the end of the material is heated on the outlet side of the fin-pass stand after the roll forming, and the squeeze stand is brought into contact with the squeeze stand. The top position of the bottom roll groove bottom of the stand is set higher than the extension line extending downstream of the material bottom position downhill immediately before the first stand of the fin path and further away from the extension line in the later stage , and the fin path A method of manufacturing an electric resistance welded tube having good buckling resistance, characterized in that finpass molding is performed such that the positions are arranged on a descending inclined plane that is substantially the same as the material outer peripheral bottom position on the entrance side of each stand .
2. In the preceding paragraph 1, the outer peripheral position of the material in the squeeze stand is electro-welded as an extension line extending down the material bottom position downhill immediately after the final stand of the fin path or a position above the extension line. A method for producing an electric resistance welded tube having good buckling resistance.

  ADVANTAGE OF THE INVENTION According to this invention, when it lays as a line pipe, the electric resistance welded tube which is hard to receive the influence of the buckling by an earthquake or frozen soil can be manufactured.

The inventors have promoted the circumferential non-uniformity of the mechanical characteristics of the ERW pipe as a result of the above investigation, because the mechanical characteristics in the vicinity of the material outer peripheral bottom position deteriorate, particularly in the vicinity of the position. I thought it was because YS was increasing due to concentration of distortion.
And in order to investigate the cause of the increase in YS in the vicinity of the material outer peripheral bottom position, attention was paid to the fin pass stand at the latter stage of roll forming. In other words, the fin pass stand has the role of making the material width almost arc-shaped so that the subsequent squeeze stand can stably carry out ERW welding, so that the fin pass roll hole mold is almost filled with material. It is necessary to mold. As a result, the butt end of the material is strongly pressed by the fins of the fin path upper roll, and as a reaction force, a large compressive force acts on the portion in the vicinity of the material outer bottom on the side opposite to the butt end of the material. As a result, it was grasped that this part is easy to work harden.

Then, when the molding process in the fin pass stand was observed in detail, it was understood that the height at which the material enters the fin pass stand affects the work hardening degree in the vicinity of the material outer peripheral bottom position after the fin pass.
That is, in any conventional fin pass molding, as shown in FIG. 3, for example, as shown in FIG. 3, a locus 16 formed by moving the center point of the approximate arc shape (shape close to the arc shape) of the material 10 in the material passing direction 20 is formed. The material was processed so as to be substantially coincident with the center point of the roll hole shape formed by the fin pass upper roll 19 and the fin pass lower roll 11, while the material was reduced in diameter so as to obtain an arc approximate shape closer to the arc shape. .

  Accordingly, the material 10 on the fin path entry side has an approximate circular arc shape having a larger diameter than the fin pass roll hole shape and opened on the upper side. Therefore, the height of the material outer peripheral bottom 13 position on the fin pass entry side (this height and Is a height from a reference horizontal plane common to the processes from roll forming to ERW welding, and the same applies hereinafter) is lower than the height of the top point 12 of the bottom roll groove bottom of the fin path. Further, the material 10 reduced in diameter by the fin path tends to return to a large diameter on the exit side of the fin path by elastic recovery. Therefore, the height of the material outer peripheral bottom 13 position on the fin path exit side is lower than the height of the fin roll lowermost groove groove uppermost point 12 position.

As a result, the material outer periphery bottom 13 is processed so as to get over the fin roll lower roll groove bottom uppermost point 12. As a result, the tension 14 in the longitudinal direction of the band material acts on the material outer periphery bottom 13 so that it is easy to work harden. This is because uneven strain accumulated in the pipe circumferential direction, YS in the vicinity of the position 13 of the material outer peripheral bottom increased, and the mechanical characteristics were lowered to easily buckle the pipe.
In addition, in conventional roll forming, a uniform distortion in the circumferential direction is applied as close as possible to a state close to a perfect circle. In many cases, a downhill (more specifically, a material bottom position downhill) is formed to lower the height of the material outer peripheral bottom position) toward the downstream side in the material direction.

Accordingly, the inventors, for example, as shown in FIG. 2, paying attention to the position 12 of the bottom of the bottom roll groove of each stand of the fin path, this position is set to the material bottom position downhill 15 immediately before the first stand of the fin path. The position is higher than the extension line 15A extending downstream and further away from the extension line 15A in the later stage.
As a result, as shown in the figure, the position 12 of the bottom of the roll groove bottom of each stand of the fin path and the position 13 of the material outer peripheral bottom on the side of each stand are substantially on the same plane (this plane is the material passing direction 20). Therefore, the material outer circumferential bottom 13 does not get over the fin roll lower roll groove bottom uppermost point 12, and the tension concentrated on the material outer circumferential bottom 13 is reduced. As a result, the degree of work hardening is reduced and it becomes possible to reduce the uneven distortion in the circumferential direction.

  In addition, after fin pass molding, electric sew welding is performed as a tube shape by the squeeze stand 6, but the material outer peripheral bottom position in the squeeze stand (between the squeeze roll axis) is downstream of the material bottom position downhill immediately after the fin pass final stand. If it is lower than the extended extension line (indicated by reference numeral 15B in FIG. 2), the material outer periphery bottom is processed so as to get over the fin path final stand lower roll groove bottom uppermost point.

Therefore, if the material outer peripheral bottom position in the squeeze stand is set on the extension line 15B extending the downstream side of the material bottom position downhill immediately after the fin pass final stand or the position above the extension line 15B, the material outer peripheral bottom 13 is located at the fin pass final position. It is preferable that the uppermost point 12 at the bottom of the roll groove under the stand is not exceeded, and the uneven distortion in the circumferential direction described above can be further reduced.
In addition, although the work hardening distortion of the vicinity of the welded portion (position of about 0 degree in the circumferential direction from the welded portion) is increased by the above measures, a seam heat treatment (for example, an improvement in welded portion characteristics after the electric resistance welding) (for example, 1 is used), the distortion in the vicinity of the welded portion is alleviated and is unlikely to cause uneven circumferential distortion.

  Manufacturing conditions other than the above (for example, preventing the center position in the width direction of the material from swinging to the left and right in the material passing direction) are the same as in the past, and there is no particular limitation.

An electric resistance welded tube having an outer diameter of 600 mm and a wall thickness of 19.1 mm was manufactured from a steel strip (width: 1900 mm) containing 0.05% C, 0.2% Si and 1.2% Mn by mass%. . In manufacturing, the electric resistance welded tube manufacturing process shown in FIG. 1 was used. There are 3 fin paths in all.
(Conventional example 1)
In Conventional Example 1, the roll position of each fin pass stand and the roll position of the squeeze stand were set as shown in the same column of Table 1. In addition, “substantially the same height” in the same column means that the positional deviation in the height direction is within 5 mm.
(Invention Example 1)
In Example 1 of the present invention, the roll position of each fin pass stand and the roll position of the squeeze stand were set as shown in the same column of Table 1. Other manufacturing conditions were the same as in the conventional example.

  About the electric resistance welded tube manufactured under the conditions of each of the above examples, from the vicinity of the welded portion and from the seam portion to the circumferential direction of approximately 90 degrees and approximately 180 degrees (referred to as the 90-degree position vicinity and the 180-degree position vicinity), Ten JIS No. 13 tensile test pieces were cut out in the longitudinal direction of the pipe and subjected to a tensile test to measure mechanical properties. Of these measurement results, YS (yield stress), TS (maximum tensile stress) near the 90-degree position, and TS near the 180-degree position are shown in Table 1. In addition, the values of YS and TS in Table 1 are average values for the remaining 8 points, excluding the maximum and minimum values, among the total 10 measured values.

  From Table 1, in the example of the present invention, the YS in the vicinity of the 180 degree position is lower than the conventional example and shows a value close to YS at the other angular positions, which is excellent in buckling resistance. In the conventional example, YS near the 180 degree position was higher than YS at other angular positions, and the buckling resistance performance was poor.

It is a schematic diagram which shows an example of the electric sewing tube manufacturing process to which this invention is applied. It is a schematic diagram which shows an example of embodiment of the fin pass shaping | molding in this invention. It is a schematic diagram which shows an example of embodiment of the fin pass shaping | molding in a prior art.

Explanation of symbols

1 Uncoiler 2 Leveler 3 Fin pass stand (Fin pass for short)
4 Roll forming 5 Contact tip 6 Squeeze stand (squeeze for short)
7 Bead cutting 8 Sizer 9 Pipe cutting machine
10 Material (band, pipe after ERW welding)
11 Finpass bottom roll
12 Bottom roll groove bottom uppermost point
13 Material outer bottom
14 Tension acting when the outer periphery of the material rides on the bottom of the lower roll groove
15 Material bottom position downhill just before the first fin pass stand
15A Material bottom position downhill just before the 1st stand of the Finpass extended to the downstream side
15B Extension line that extends downhill from the material bottom position just after the final stand of the Fin Pass
16 Trajectory formed by moving the center point of the approximate circular arc shape of the material in the threading direction
17 Seam Anilla
18 ERW welding machine
19 Fin pass roll
20 Direction of threading

Claims (2)

In a method for manufacturing an electric resistance welded tube, the belt material is roll-formed into an arc shape, the end of the material is heated on the outlet side of the fin-pass stand after the roll forming, and the squeeze stand is brought into contact with the squeeze stand. The top position of the bottom roll groove bottom of the stand is set higher than the extension line extending downstream of the material bottom position downhill immediately before the first stand of the fin path and further away from the extension line in the later stage , and the fin path A method of manufacturing an electric resistance welded tube having good buckling resistance, characterized in that finpass molding is performed such that the positions are arranged on a descending inclined plane that is substantially the same as the material outer peripheral bottom position on the entrance side of each stand .   The material outer peripheral position in the squeeze stand is electro-welded as an extension line obtained by extending a material bottom position downhill immediately after the final stand of the fin path to a downstream side or a position above the extension line. A method for producing an electric resistance welded tube having good buckling resistance described in 1.

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