Method and device for manufacturing electric resistance welded pipe, and monitoring device

Abstract

A method for manufacturing an electric resistance welded pipe (20) comprises: a molding step for molding a metal sheet (10) into a pipe shape while the metal sheet is conveyed; a welding step for abutting and welding both end parts (11L, 11R) of the metal sheet (10) to form the metal sheet (10) into an electric resistance welded pipe (20); a cutting step for cutting a weld bead (22); and a heat treatment step for applying heat treatment on a welded part (21). In this manufacturing method, the convergence point (12) of the end parts (11L, 11R) is set as the position of a welding surface (211) in the welding step, and a first deviation amount of the convergence point (12) with respect to a reference position (R) in the circumferential direction is detected. A second deviation amount is calculated by multiplying the first deviation amount by a coefficient (C), and the relative relationship between the circumferential position of a cutting portion (23) and the circumferential position of the welding surface (211) is acquired on the basis of the second deviation amount. Further, on the basis of the relative relationship, a determination is made as to whether or not the electric resistance welded pipe (20) is successfully manufactured.

Description

Electric resistance welded pipe manufacturing method and manufacturing device, and monitoring device

[0001] The present disclosure relates to a method and apparatus for manufacturing electric resistance welded pipes, and more particularly to a monitoring device used in the manufacture of electric resistance welded pipes.

[0002] Electric resistance welded pipes, also known as electric resistance welded pipes, are manufactured through processes such as forming, welding, cutting, and heat treatment. In the forming process, a metal plate unwound from a coil is formed into an open pipe. In the welding process, both ends of the open pipe-shaped metal plate are welded to form the electric resistance welded pipe. In the welding process, both ends of the metal plate are heated and melted, and then upset, so that weld beads are formed on the inner and outer surfaces of the electric resistance welded pipe. In the cutting process, the weld beads are cut by a cutting device, and cutting marks of the weld beads are left on the surface of the electric resistance welded pipe. In the heat treatment process, a heat treatment device performs heat treatment such as normalizing, annealing, or quenching on the welded portion of the electric resistance welded pipe.

[0003] In conventional heat treatment processes, the cutting marks (cut portions) of the weld bead are considered to be the weld seam, and the heater of the heat treatment device is moved along the cut portions to perform heat treatment along the weld seam. The cut portions of the weld bead are nearly flat and have a metallic luster immediately after cutting, so they can be detected using optical techniques.

[0004] In response to this, Patent Document 1 discloses a technique for detecting a true weld seam in an electric resistance welded pipe. In Patent Document 1, a thermal imaging camera captures an image of the weld seam after cutting the weld bead and before heat treatment, and a two-dimensional thermal image including the weld seam before heat treatment is acquired. Based on this two-dimensional thermal image, the position of the weld seam before heat treatment and the position of the cut portion of the weld bead before heat treatment are calculated. In Patent Document 1, a thermal imaging camera captures an image of the weld seam after heat treatment, and a two-dimensional thermal image including the weld seam after heat treatment is acquired. Based on this two-dimensional thermal image, the position of the cut portion of the weld bead after heat treatment and the position of the heater (inductor) after heat treatment are calculated. From the positions of the cut portion of the weld bead before and after heat treatment, a deviation amount relative to the position of the weld seam before heat treatment is detected, and the position of the true weld seam after heat treatment is calculated. Then, based on the position of the heater after heat treatment and the position of the true weld seam, the deviation amount between the position of the heater and the position of the weld seam is calculated. Based on this amount of deviation, the heater element moves in the circumferential direction of the electric resistance welded pipe so as to approach the position of the true weld seam. Patent Document 1 describes that since the position of the heater element can be corrected using the amount of deviation of the cut portion of the weld bead before and after heat treatment and the amount of deviation of the weld seam before and after heat treatment, the accuracy of tracking the heater element to the weld seam is improved compared to conventional techniques in which the center of the cut portion is not necessarily the center of the weld line, causing errors.

[0005] Japanese Patent Application Laid-Open No. 2018-30173

[0006] In Patent Document 1, a thermal imaging camera is used to capture an image of a weld seam of an electric-resistance welded pipe. However, in actual electric-resistance welded pipe manufacturing, thermal diffusion occurs in and around the weld seam of the electric-resistance welded pipe, making it difficult to obtain a clear thermal image of the weld seam. Therefore, it is difficult to accurately detect the true weld seam, i.e., the position of the weld surface in the circumferential direction of the electric-resistance welded pipe, using a thermal image.

[0007] An object of the present disclosure is to accurately detect the position of a welded surface in the circumferential direction of an electric resistance welded pipe when heat treating a welded portion of the electric resistance welded pipe.

[0008] A method for manufacturing an electric-resistance welded pipe according to the present disclosure includes a forming step in which a metal plate is conveyed while being shaped into a tubular shape so that both ends of the metal plate face each other; a welding step in which the metal plate is butt-welded to form an electric-resistance welded pipe; a cutting step in which the weld bead formed on the surface of the electric-resistance welded pipe during the welding step; and a heat treatment step in which the welded portion of the electric-resistance welded pipe formed during the welding step is heat-treated after the cutting step. In this manufacturing method, a convergence point, where the both ends converge as they approach each other as they move downstream in the conveyance direction of the metal plate, is defined as the position of the welded surface of the electric-resistance welded pipe during the welding step. A first deviation of the convergence point in the circumferential direction of the electric-resistance welded pipe relative to a predetermined reference position is detected. Furthermore, a second deviation is calculated by multiplying the first deviation by a predetermined coefficient corresponding to the amount of twist of the electric-resistance welded pipe. Based on the second deviation, a relative position between the circumferential position of the cut portion formed by cutting the weld bead during the cutting step and the circumferential position of the welded surface is obtained. Furthermore, a pass / fail judgment is made on the manufacturing quality of the electric-resistance welded pipe based on the relative position.

[0009] Another method for manufacturing an electric-resistance welded pipe according to the present disclosure includes a forming step in which a metal plate is shaped into a tubular shape while being conveyed, a welding step in which the metal plate is butt-welded to form an electric-resistance welded pipe, a cutting step in which the weld bead formed on the surface of the electric-resistance welded pipe in the welding step, and a heat treatment step in which the welded portion of the electric-resistance welded pipe formed in the welding step is heat-treated after the cutting step. In this manufacturing method, a convergence point where the two ends approach and converge as they move downstream in the conveyance direction of the metal plate is defined as the position of the welded surface of the electric-resistance welded pipe in the welding step, and a first deviation of the convergence point in the circumferential direction of the electric-resistance welded pipe relative to a predetermined reference position is detected. Furthermore, a second deviation is calculated by multiplying the first deviation by a predetermined coefficient corresponding to the amount of twist of the electric-resistance welded pipe, and the relative position of the cut portion formed by cutting the weld bead in the cutting step and the circumferential position of the welded surface are obtained based on the second deviation. In the heat treatment step, based on this relative relationship, a heater included in a heat treatment device for applying heat treatment to the welded portion is moved so that the welding surface is positioned at the center in the circumferential direction of the heat treatment area of ​​the heater.

[0010] According to the present disclosure, when heat treating a welded portion of an electric resistance welded pipe, the position of the welded surface in the circumferential direction of the electric resistance welded pipe can be detected with high accuracy.

[0011] FIG. 1 is a schematic diagram showing the configuration of an electric-resistance-welded pipe manufacturing apparatus according to each embodiment. FIG. 2 is a view of a heat treatment apparatus included in the manufacturing apparatus shown in FIG. 1, viewed along the transport direction of the electric-resistance-welded pipe. FIG. 3 is a side view of the manufacturing apparatus shown in FIG. 1, showing a portion of the manufacturing apparatus. FIG. 4 is a plan view of the manufacturing apparatus shown in FIG. 1, showing a portion of the manufacturing apparatus. FIG. 5 is a diagram illustrating the hardware configuration of a monitoring device included in the manufacturing apparatus shown in FIG. 1. FIG. 6 is a flowchart showing the processing of the monitoring device according to the first embodiment. FIG. 7A is a schematic diagram for explaining the processing of the monitoring device according to the first embodiment. FIG. 7B is a schematic diagram for explaining the processing of the monitoring device according to the first embodiment. FIG. 7C is a schematic diagram for explaining the processing of the monitoring device according to the first embodiment. FIG. 7D is a schematic diagram for explaining the processing of the monitoring device according to the first embodiment. FIG. 7E is a schematic diagram for explaining the processing of the monitoring device according to the first embodiment. FIG. 8 is a flowchart showing the processing of the monitoring device according to the second embodiment. FIG. 9 is a schematic diagram for explaining the processing of the monitoring device according to the second embodiment. FIG. 10 is a schematic diagram for explaining the processing of the monitoring device according to the second embodiment. Fig. 11 is a schematic diagram for explaining the processing of the monitoring device according to the second embodiment. Fig. 12 is a diagram partially showing a cross section of an electric resistance welded pipe. Fig. 13 is a diagram for explaining the verification content by the present inventors. Fig. 14A is a diagram for explaining the verification content by the present inventors. Fig. 14B is a diagram for explaining the verification content by the present inventors.

[0012] In the manufacture of electric resistance welded pipes, the weld beads formed on the inner and outer surfaces of the electric resistance welded pipe are cut in a cutting process, and the welded portion of the electric resistance welded pipe is heat treated in a heat treatment process. As described above, in conventional heat treatment processes, the cutting marks (cut portions) of the weld beads are considered to be the weld seam portion, and the heater elements of a heat treatment device that performs, for example, normalizing, annealing, or quenching, are made to follow the cut portions of the weld beads.

[0013] However, in the manufacture of electric resistance welded pipes, twisting (rolling) can occur in the electric resistance welded pipe due to various factors, such as the occurrence of camber (bending) in the base material coil, or unevenness in the coil edge strength or thickness. Meanwhile, in the cutting process, the position of the cutting device (cutting tip) in the circumferential direction of the electric resistance welded pipe is fixed. Therefore, if twisting occurs in the electric resistance welded pipe, a misalignment occurs between the center of the cut portion of the weld bead and the weld surface in the circumferential direction of the electric resistance welded pipe, as shown in Figure 12.

[0014] In the heat treatment process following the cutting process, due to mechanical constraints, the heater element of the heat treatment device is only installed on the outer surface of the electric-resistance welded pipe. Therefore, the heat treatment of the welded portion of the electric-resistance welded pipe is performed by heat conduction from the outer surface to the inner surface. During this process, the heat transmitted through the electric-resistance welded pipe diffuses, narrowing the area heat-treated by the heater element (heat treatment area) in the circumferential direction from the outer surface to the inner surface of the electric-resistance welded pipe, as shown by the dashed line in Figure 12 . Therefore, if the position of the weld surface is shifted circumferentially from the center of the cut portion of the weld bead, it may be impossible to heat-treat the weld surface or the heat-affected zone around it at a sufficient temperature, particularly on the inner surface of the electric-resistance welded pipe.

[0015] To solve this problem, it is conceivable to heat treat the weld at a higher temperature. However, in this case, the temperature on the outer surface of the electric resistance welded pipe near the heater may become higher than necessary, which may promote grain growth. Therefore, in the heat treatment process, it is necessary to heat the entire weld surface and heat-affected zone to an appropriate temperature, such as just above the Ac3 point.

[0016] The inventors monitored the circumferential deviation of the electric resistance welded pipe at the point where both ends of the metal plate converge, relative to the line center, during the welding process. The line center is an imaginary line through which the central axis of the electric resistance welded pipe passes when the electric resistance welded pipe formed from the metal plate is transported in an electric resistance welded pipe manufacturing device without swinging up and down or left and right. The position of the point where both ends of the metal plate converge corresponds to the position of the weld surface of the electric resistance welded pipe during the welding process. Furthermore, the inventors discovered that by multiplying this deviation by a certain coefficient, the circumferential deviation of the weld surface of the electric resistance welded pipe at the cutting position of the weld bead can be obtained relative to the line center. The details of the verification conducted by the inventors are described in detail below.

[0017] The inventors cut samples from the electric resistance welded pipe immediately after cutting the weld bead, etched the cross section of each sample, and measured the circumferential deviation of the weld surface from the line center. As shown in Figure 13 , there is a positive correlation between the circumferential deviation of the weld surface from the line center monitored during the welding process and the circumferential deviation of the weld surface from the line center measured immediately after cutting the weld bead. The inventors conducted the verification with the center of the cutting device aligned with the line center in the circumferential direction of the electric resistance welded pipe. Therefore, Figure 13 can be said to indicate a positive correlation between the circumferential deviation of the weld surface from the line center during the welding process and the circumferential deviation of the weld surface from the center of the cut portion of the weld bead.

[0018] The inventors also cut a sample from the electric resistance welded pipe immediately before cutting the weld bead and confirmed that the weld surface was located directly below the apex of the weld bead. Then, the circumferential deviation of the weld surface from the line center monitored during the welding process and the circumferential deviation of the weld bead apex from the line center were obtained for one coil. As shown in Figures 14A and 14B , the deviation of the weld surface during the welding process and the deviation of the weld bead apex exhibit similar behavior throughout the entire length of the coil. Near the end point of the coil, the coil is no longer located upstream in the transport direction, so the deviation of the weld surface during the welding process is larger, but the deviation of the weld bead apex also exhibits similar behavior. Therefore, it was found that there is a good correlation between the circumferential deviation of the weld surface from the line center monitored during the welding process and the circumferential deviation of the weld surface from the line center measured immediately before cutting the weld bead.

[0019] The above verification results revealed that by detecting the amount of circumferential misalignment of the electric resistance welded pipe between a predetermined reference position and the weld surface during the welding process and multiplying this misalignment by a predetermined coefficient representing the amount of twist of the electric resistance welded pipe from the welding process, it is possible to calculate the amount of circumferential misalignment of the weld surface from the reference position during the cutting process and subsequent processes. During the cutting process, the cut portion of the weld bead is formed at a fixed position in the circumferential direction of the electric resistance welded pipe, and the circumferential position of the cut portion can be identified. Therefore, if the amount of circumferential misalignment of the weld surface from the reference position can be calculated during the cutting process and subsequent processes, it is possible to obtain the relative relationship between the circumferential position of the cut portion of the weld bead and the circumferential position of the weld surface. Based on these findings, the inventors have completed a method for manufacturing an electric resistance welded pipe according to an embodiment.

[0020] A method for manufacturing an electric-resistance welded pipe according to an embodiment includes a forming step in which a metal plate is conveyed while being shaped into a tubular shape so that both ends of the metal plate face each other; a welding step in which the metal plate is butt-welded to form an electric-resistance welded pipe; a cutting step in which the weld bead formed on the surface of the electric-resistance welded pipe during the welding step; and a heat treatment step in which the welded portion of the electric-resistance welded pipe formed during the welding step is heat-treated after the cutting step. In this manufacturing method, a convergence point, where the both ends converge as they approach each other as they move downstream in the conveyance direction of the metal plate, is defined as the position of the welded surface of the electric-resistance welded pipe during the welding step. A first deviation of the convergence point in the circumferential direction of the electric-resistance welded pipe relative to a predetermined reference position is detected. Furthermore, a second deviation is calculated by multiplying the first deviation by a predetermined coefficient corresponding to the amount of twist of the electric-resistance welded pipe. Based on the second deviation, a relative position of the circumferential position of the cut portion formed by cutting the weld bead during the cutting step and the circumferential position of the welded surface is obtained. Furthermore, a pass / fail judgment is made on the manufacturing quality of the electric-resistance welded pipe based on this relative position (first configuration).

[0021] Another embodiment of a method for manufacturing an electric-resistance welded pipe includes a forming step in which a metal plate is conveyed while being shaped into a tubular shape so that both ends of the metal plate face each other; a welding step in which the metal plate is butt-welded to form an electric-resistance welded pipe; a cutting step in which the weld bead formed on the surface of the electric-resistance welded pipe during the welding step; and a heat treatment step in which the welded portion of the electric-resistance welded pipe formed during the welding step is heat-treated after the cutting step. In this manufacturing method, a convergence point, where the both ends approach and converge as they move downstream in the conveyance direction of the metal plate, is defined as the position of the welded surface of the electric-resistance welded pipe during the welding step. A first deviation of the convergence point in the circumferential direction of the electric-resistance welded pipe relative to a predetermined reference position is detected. Furthermore, a second deviation is calculated by multiplying the first deviation by a predetermined coefficient corresponding to the amount of twist of the electric-resistance welded pipe. Based on the second deviation, a relative position of the circumferential position of the cut portion formed by cutting the weld bead during the cutting step and the circumferential position of the welded surface are obtained. In the heat treatment process, based on the relative relationship, the heater included in the heat treatment device for applying heat treatment to the welded portion is moved so that the welding surface is positioned in the circumferential center of the heat treatment area of ​​the heater (second configuration).

[0022] In the methods for manufacturing electric-resistance welded pipe according to the first and second configurations, the first deviation is detected as the circumferential deviation of the convergence points of both ends of the metal plate relative to a predetermined reference position. The second deviation can be calculated by multiplying the first deviation by a coefficient corresponding to the amount of twist of the electric-resistance welded pipe. The second deviation corresponds to the circumferential deviation of the welding surface from the reference position after the cutting process. As described above, if the second deviation can be calculated, the relative relationship between the circumferential position of the cut portion of the weld bead and the circumferential position of the welding surface can be obtained. Therefore, the position of the welding surface after the cutting process, more specifically, the circumferential position of the welding surface relative to the cut portion of the weld bead, can be accurately detected.

[0023] In the first and second configurations, the first deviation amount in the circumferential direction of the electric resistance welded pipe between the convergence points at both ends of the metal plate during the welding process is detected, and the second deviation amount can be calculated from the first deviation amount. Because the convergence points at both ends of the metal plate are geometric features, the first deviation amount can be detected optically. Therefore, there is no need to use a thermal imaging camera as in Patent Document 1, and there is no decrease in detection accuracy due to unclear thermal images.

[0024] Therefore, according to the methods for manufacturing electric resistance welded pipes of the first and second configurations, the position of the welded surface in the circumferential direction of the electric resistance welded pipe can be detected with high accuracy when heat treating the welded portion of the electric resistance welded pipe.

[0025] If the weld surface is significantly misaligned circumferentially with respect to the cut portion of the weld bead, the weld portion of the electric-resistance welded pipe, specifically the weld surface and heat-affected zone, will likely deviate from the heat treatment area of ​​the heater when the heater element of the heat treatment device follows the cut portion of the weld bead. In this case, it is difficult to perform sufficient heat treatment on the entire weld surface and heat-affected zone of the electric-resistance welded pipe. In contrast, with the first configuration, the acceptance or rejection of the manufacturing of the electric-resistance welded pipe is determined based on the circumferential position of the weld surface rather than the cut portion of the weld bead. More specifically, the acceptance or rejection of the heat treatment can be determined based on the relative position of the circumferential position of the cut portion of the weld bead and the circumferential position of the weld surface. This allows for accurate judgment of the acceptance or rejection of the manufacturing of the electric-resistance welded pipe and prevents the production of electric-resistance welded pipes with insufficient heat treatment of the weld portion.

[0026] In the second configuration, the heater element of the heat treatment device is moved so that the weld surface is positioned in the circumferential center of the heat treatment area based on the relative relationship between the circumferential position of the cut portion of the weld bead and the circumferential position of the weld surface. That is, the heater element follows the weld surface of the electric-resistance welded pipe during the heat treatment process. In this case, even if the weld surface is circumferentially misaligned with respect to the cut portion of the weld bead, the weld surface and heat-affected zone of the electric-resistance welded pipe tend to fit within the heat treatment area of ​​the heater element. Therefore, it is possible to perform overall good heat treatment on the weld surface and heat-affected zone.

[0027] In the method for manufacturing an electric resistance welded pipe according to the first or second configuration, the electric resistance welded pipe may have a thickness of 5.0 mm or more (third configuration).

[0028] As the wall thickness of an electric resistance welded pipe increases, the heat treatment area of ​​the heater element of the heat treatment device narrows circumferentially on the inner surface side of the electric resistance welded pipe. Therefore, if the welding surface is circumferentially misaligned with respect to the cut portion of the weld bead, the thicker the electric resistance welded pipe, the more likely the weld (welding surface and heat-affected zone) will be outside the heat treatment area of ​​the heater element on the inner surface side of the electric resistance welded pipe. However, in the electric resistance welded pipe manufacturing method according to the above embodiment, the relative relationship between the circumferential position of the cut portion of the weld bead and the circumferential position of the weld surface can be determined based on the second misalignment amount. Therefore, even if the electric resistance welded pipe has a thickness of 5.0 mm or more, as in the third configuration, the manufacturing pass / fail of the electric resistance welded pipe can be accurately determined, or the heater element can be made to follow the welding surface, thereby providing an overall good heat treatment to the welding surface and heat-affected zone.

[0029] The monitoring device according to the embodiment is used in the manufacture of electric-resistance welded pipe, which involves a forming process in which a metal plate is conveyed while being shaped into a tubular shape with both ends of the metal plate facing each other, a welding process in which the both ends are butt-welded to form the metal plate into an electric-resistance welded pipe, a cutting process in which the weld bead formed on the surface of the electric-resistance welded pipe in the welding process is cut, and a heat treatment process in which the welded portion of the electric-resistance welded pipe formed in the welding process is heat-treated after the cutting process. The monitoring device is configured to perform the following processes: acquire image data captured by the imaging device, including a convergence point where both ends approach and converge as they move downstream in the conveying direction of the metal plate; detect a first deviation amount of the convergence point in the circumferential direction of the electric-welded pipe relative to a predetermined reference position based on the image data, with the convergence point being the position of the welding surface of the electric-welded pipe in the welding process; calculate a second deviation amount by multiplying the first deviation amount by a predetermined coefficient corresponding to the twist amount of the electric-welded pipe, and acquire, based on the second deviation amount, the relative relationship between the circumferential position of the cutting portion formed by cutting the weld bead in the cutting process and the circumferential position of the welding surface; and determine whether the electric-welded pipe is acceptable for manufacture based on this relative relationship (fourth configuration).

[0030] An electric-resistance welded pipe manufacturing apparatus according to an embodiment includes a welding apparatus, a cutting apparatus, a heat treatment apparatus, and a monitoring apparatus. The welding apparatus is configured to butt-weld both ends of a metal plate being formed into a tubular shape while being transported, thereby forming the metal plate into an electric-resistance welded pipe. The cutting apparatus is disposed downstream of the welding apparatus in the transport direction of the metal plate. The cutting apparatus is configured to cut a weld bead formed on the surface of the electric-resistance welded pipe. The heat treatment apparatus is disposed downstream of the cutting apparatus in the transport direction. The heat treatment apparatus includes a heater for applying heat treatment to the welded portion of the electric-resistance welded pipe. The monitoring apparatus is configured to control the movement of the heater. The monitoring device is configured to perform the following processes: acquire image data captured by the imaging device, including a convergence point where both ends approach and converge as they move downstream in the conveying direction; detect a first amount of deviation of the convergence point in the circumferential direction of the electric-welded pipe relative to a predetermined reference position, based on the image data, with the convergence point being the position of the welding surface of the electric-welded pipe in the welding device; calculate a second amount of deviation by multiplying the first amount of deviation by a predetermined coefficient corresponding to the amount of twist of the electric-welded pipe, and acquire, based on the second amount of deviation, the relative relationship between the circumferential position of the cutting portion formed by cutting the weld bead with the cutting device and the circumferential position of the welding surface; and move the heater based on this relative relationship so that the welding surface is positioned in the circumferential center of the heat treatment area of ​​the heater (fifth configuration).

[0031] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In these drawings, the same or equivalent components are designated by the same reference numerals, and the same description will not be repeated.

[0032] 1 is a schematic diagram showing the configuration of an electric resistance welded pipe manufacturing apparatus 100. Referring to Fig. 1, the manufacturing apparatus 100 manufactures an electric resistance welded pipe 20 from a strip-shaped metal plate 10 while transporting the metal plate 10 along its longitudinal direction.

[0033] The metal plate 10 serving as the base material is typically a steel plate (steel strip). However, the metal plate 10 may be a metal plate other than a steel plate, such as an aluminum alloy plate. Although not particularly limited, the manufactured electric resistance welded pipe 20 may have a thickness (wall thickness) of, for example, 5.0 mm or more. The electric resistance welded pipe 20 may be a so-called thick-walled pipe. That is, the electric resistance welded pipe 20 may have a thickness of 10.0 mm or more. The electric resistance welded pipe 20 may have a thickness of 12.7 mm or more, or may have a thickness of 15.0 mm or more. The electric resistance welded pipe 20 may have a thickness of 20.0 mm or less.

[0034] 1, the manufacturing apparatus 100 includes a forming device 30, a welding device 40, a cutting device 50, and a heat treatment device 60. The forming device 30, the welding device 40, the cutting device 50, and the heat treatment device 60 are arranged in this order from upstream to downstream in the conveying direction of the metal plate 10.

[0035] The metal sheet 10 unwound from a coil is continuously supplied to the forming device 30. Both widthwise ends 11L, 11R of the metal sheet 10 may be trimmed, for example, by an edge mirror (not shown), before being fed into the forming device 30. The forming device 30 includes, for example, a breakdown roll group 31, a fin pass roll group 32, and a seam guide 33. The breakdown roll group 31, the fin pass roll group 32, and the seam guide 33 are arranged in this order from upstream to downstream in the conveyance direction of the metal sheet 10.

[0036] The forming device 30 forms the metal sheet 10 being conveyed into a tubular shape (open pipe shape). The breakdown roll group 31 performs bending processing on both end portions 11L, 11R of the metal sheet 10. The breakdown roll group 31 bends both end portions 11L, 11R of the metal sheet 10 upward on the plane of FIG. 1 , so that the entire metal sheet 10 is curved into an arc shape. The fin pass roll group 32 performs finish forming on the metal sheet 10 so that the metal sheet 10 has a substantially circular cross section. The seam guide 33 is disposed between both end portions 11L, 11R of the metal sheet 10, which has now become roughly tubular, and adjusts the distance between the opposing end portions 11L, 11R.

[0037] The welding device 40 welds both ends 11L, 11R of the metal plate 10. More specifically, the welding device 40 is configured to butt-weld both ends 11L, 11R of the metal plate 10, which is being formed into a tubular shape while being transported, to form the metal plate 10 into an electric resistance welded pipe 20. The welding device 40 includes a heating device 41 and a squeeze roll 42.

[0038] The heating device 41 is configured to heat and melt both end portions 11L, 11R of the metal plate 10. The heating device 41 is typically an electric resistance heating device. The heating device 41 may also be a high-frequency heating device. In this case, the heating device 41 supplies a high-frequency current to the metal plate 10, melting both end portions 11L, 11R of the metal plate 10 by Joule heat. The heating device 41 can supply the high-frequency current to the tubular metal plate 10 by induction or directly using electrodes such as a work coil or contact tips.

[0039] The squeeze roll 42 is disposed downstream of the heating device 41 in the conveying direction of the metal sheet 10. The squeeze roll 42 is configured to apply pressure to the metal sheet 10 to press both end portions 11L, 11R against each other.

[0040] The cutting device 50 is disposed downstream of the welding device 40 in the conveyance direction of the metal plate 10 (electric-resistance welded pipe 20). The cutting device 50 is configured to cut the weld bead formed on the surface of the electric-resistance welded pipe 20. The cutting devices 50 are disposed on both the outer surface side and the inner surface side of the electric-resistance welded pipe 20.

[0041] The manufacturing apparatus 100 includes at least one heat treatment apparatus 60. This heat treatment apparatus 60 is disposed downstream of the welding apparatus 40 in the conveying direction of the metal sheet 10. In this embodiment, the manufacturing apparatus 100 includes a plurality of heat treatment apparatuses 60. These heat treatment apparatuses 60 are arranged along the conveying direction of the metal sheet 10.

[0042] FIG. 2 is a view of one of the heat treatment devices 60 as viewed along the transport direction of the electric-resistance welded pipe 20. The heat treatment device 60 is disposed, for example, above the electric-resistance welded pipe 20. The heat treatment device 60 includes a heater 61 and a drive mechanism 62. The heater 61 is typically an induction coil (heating coil). The heater 61 applies heat treatment to the weld 21 of the electric-resistance welded pipe 20. The weld 21 includes a weld surface 211 and a heat-affected zone surrounding the weld surface 211. The drive mechanism 62 is configured to move the heater 61 within the heat treatment device 60. A known heat treatment device can be used as the heat treatment device 60. The heat treatment device 60 is a device for performing normalizing, annealing, quenching, or the like on the weld 21.

[0043] Although not shown, a shaping device (sizer) may be disposed downstream of the heat treatment device 60 in the conveyance direction of the electric resistance welded pipe 20. The shaping device can adjust the shape of the electric resistance welded pipe 20.

[0044] [Method for Manufacturing Electric Resistance Welded Pipe] Next, a method for manufacturing the electric resistance welded pipe 20 using the manufacturing apparatus 100 will be described. The method for manufacturing the electric resistance welded pipe 20 according to this embodiment includes a forming step, a welding step, a cutting step, and a heat treatment step.

[0045] 1 , in the forming process, the metal sheet 10 is formed into a tubular shape so that both end portions 11L, 11R face each other while being conveyed. More specifically, the metal sheet 10 is unwound from a coil and then continuously supplied to a forming device 30, where it is formed into a tubular shape by the forming device 30. As the metal sheet 10 passes through the forming device 30, it is formed into an open pipe shape in which both end portions 11L, 11R face each other and are spaced apart from each other in the circumferential direction.

[0046] (Welding Process) In the welding process, the two end portions 11L, 11R of the metal plate 10 are butt-welded to form the metal plate 10 into an electric-resistance welded pipe 20. More specifically, the metal plate 10 formed into a tubular shape in the forming process is continuously supplied to a welding device 40. The metal plate 10 is first supplied to a heating device 41, which heats the two end portions 11L, 11R. This melts the two end portions 11L, 11R of the metal plate 10. The metal plate 10, with the two end portions 11L, 11R molten, is supplied to a squeeze roll 42. The two end portions 11L, 11R of the metal plate 10 approach each other and come into contact as they move downstream in the conveying direction. The squeeze roll 42 presses the metal plate 10, with the two end portions 11L, 11R in contact, from the outer surface side. This presses the two end portions 11L, 11R of the metal plate 10 against each other.

[0047] After passing through the squeeze rolls 42, the metal plate 10 is conveyed downstream and solidified by natural cooling, whereby the metal plate 10 is joined to the electric resistance welded pipe 20.

[0048] (Cutting process) In the welding process, weld beads are formed on the surface of the electric resistance welded pipe 20. Molten metal is extruded from both end portions 11L, 11R of the metal plate 10 by the squeeze rolls 42, thereby forming weld beads on each of the outer and inner surfaces of the electric resistance welded pipe 20. In the cutting process, the weld beads formed on the surface of the electric resistance welded pipe 20 are cut. Specifically, each weld bead on the outer and inner surfaces of the electric resistance welded pipe 20 is cut by a cutting device 50.

[0049] (Heat Treatment Step) The heat treatment step is performed after the cutting step. In the heat treatment step, the welded portion 21 ( FIG. 2 ) of the electric resistance welded pipe 20 formed in the welding step is heat treated. In this embodiment, when the electric resistance welded pipe 20 passes through the heat treatment devices 60, the heaters 61 ( FIG. 2 ) of the heat treatment devices 60 apply heat treatment such as normalizing, annealing, or quenching to the welded portion 21 of the electric resistance welded pipe 20.

[0050] [Configuration and Processing of Monitoring Device] Fig. 3 is a diagram (side view) of the manufacturing apparatus 100 as viewed from the side with respect to the conveyance direction of the metal plate 10 and the electric-resistance-welded pipe 20. Fig. 4 is a diagram (plan view) of the manufacturing apparatus 100 as viewed from above with respect to the conveyance direction. Figs. 3 and 4 show enlarged views of the welding device 40, cutting device 50, and heat treatment device 60 of the manufacturing apparatus 100. As shown in Figs. 3 and 4, the manufacturing apparatus 100 according to this embodiment further includes a monitoring device 70. The configuration and processing of the monitoring device 70 will be described in detail below.

[0051] 3 and 4 , the monitoring device 70 is communicably connected to the imaging device 81. The monitoring device 70 is connected to the imaging device 81, for example, via a network. The imaging device 81 is disposed in a position where it can capture an image of the convergence point 12 of both end portions 11L, 11R of the metal sheet 10. The convergence point 12 is a point where both end portions 11L, 11R of the metal sheet 10 approach each other and converge as they move downstream in the conveyance direction during the welding process. The imaging device 81 is disposed, for example, near the squeeze roll 42 of the welding device 40.

[0052] The imaging device 81 captures the self-luminous pattern (radiation pattern) of an area including the V-shaped convergence point 12 at both ends 11L, 11R of the metal plate 10. Although not particularly limited, the imaging device 81 may be, for example, a 3CCD color camera having 1920 × 512 pixels. The imaging device 81 captures the area including the convergence point 12 under the following conditions: a field of view of 50 mm × 190 mm, a resolution of 100 μm / pixel, a frame rate of 500 fps, and an exposure time of 1 / 10,000 sec. The imaging device 81 may capture images of the metal plate 10 being transported continuously or intermittently at predetermined time intervals.

[0053] The monitoring device 70 may also be communicably connected to another imaging device 82. The monitoring device 70 is connected to the imaging device 82, for example, via a network. In the example of Fig. 3, the imaging device 82 is provided near the heat treatment device 60. The imaging device 82 may be a 3CCD color camera similar to the imaging device 81.

[0054] The monitoring device 70 performs processing using data of images captured by the imaging devices 81 and 82. The monitoring device 70 is, for example, a computer. Fig. 5 is a diagram illustrating an example of the hardware configuration of the monitoring device 70. As shown in Fig. 5, the monitoring device 70 may include a central processing unit (CPU) 71, a main memory device 72, an auxiliary memory device 73, an input device 74, an output device 75, etc.

[0055] The CPU 71 executes various programs loaded from the auxiliary storage device 73 to the main storage device 72 and performs information calculations. The main storage device 72 is, for example, a RAM, and is used as a work area for temporarily storing various programs executed by the CPU 71, information used by the CPU 71, calculation results by the CPU 71, etc. The auxiliary storage device 73 is, for example, a HDD or ROM. The functions (processing) of the monitoring device 70 are realized, for example, by loading a control program stored in the auxiliary storage device 73 into the main storage device 72 and having the CPU 71 execute the control program. The input device 74 is a device for an operator to perform input operations, and includes, for example, a pointing device such as a mouse or touch panel, a keyboard, etc. The output device 75 is a device for outputting processing results, etc., of the CPU 71. The output device 75 may include a display.

[0056] Fig. 6 is a flowchart showing the processing of the monitoring device 70. Figs. 7A to 7E are schematic diagrams for explaining the processing of the monitoring device 70. Below, the method for manufacturing the electric resistance welded pipe 20 according to this embodiment and the processing of the monitoring device 70 will be described in detail with reference to Fig. 6 and Figs. 7A to 7E.

[0057] 6, the method for manufacturing the electric resistance welded pipe 20 according to this embodiment includes steps S1 to S4. Steps S1 to S4 are executed by the CPU 71 of the monitoring device 70 (FIG. 5).

[0058] In step S1, a process is executed to acquire image data captured by the imaging device 81. The image data includes the convergence points 12 of both end portions 11L, 11R of the metal plate 10. The image data is input from the imaging device 81 to the monitoring device 70 via a network, for example.

[0059] After step S1, step S2 is performed. In step S2, a procedure is performed to detect a first deviation amount based on the image data. The first deviation amount is the amount of positional deviation of the convergence point 12 of both end portions 11L, 11R of the metal plate 10 in the circumferential direction of the electric resistance welded pipe 20 from a predetermined reference position. The first deviation amount can be detected, for example, as follows.

[0060] In step S2, the position of the convergence point 12 of both end portions 11L, 11R of the metal plate 10 is derived from the image data captured by the imaging device 81. FIG. 7A is a diagram schematically illustrating an example of image data 90 captured by the imaging device 81. Referring to FIG. 7A , for example, the conveyance direction of the metal plate 10 is defined as the x direction, and the direction perpendicular to the conveyance direction (circumferential direction) is defined as the y direction, and the x and y coordinates of the convergence point 12 in the image data 90 are derived. The monitoring device 70 performs necessary processes, such as red component extraction, binarization, and labeling, on the image data 90, and then can detect the tip of a region (convergence region) 91 where both end portions 11L, 11R of the metal plate 10 converge in a V-shape as the convergence point 12. The position of the tip of the convergence region 91 can be derived, for example, by the method described in International Publication No. WO 2011 / 118560 or WO 2013 / 157422.

[0061] In this embodiment, the y coordinate of the tip of the V-shaped convergence region 91 is derived as the position of the convergence point 12 in the circumferential direction. The monitoring device 70 may acquire the position of the convergence point 12 for each of two or more temporally consecutive image data and use the average value of these as the position of the convergence point 12, or may derive the position of the convergence point 12 based on a single image data.

[0062] In step S2, the difference in the circumferential direction (y direction) between the position of the convergence point 12 of both end portions 11L, 11R of the metal plate 10 and a predetermined reference position R is further derived. In the example of FIG. 7A , the reference position R is the position of the line center in the circumferential direction of the electric resistance welded pipe 20. However, the reference position R does not necessarily have to be set at the line center. The reference position R can be any fixed position that can serve as a reference in the circumferential direction of the electric resistance welded pipe 20, and can be selected arbitrarily.

[0063] The reference position R may be, for example, a fixed y coordinate stored in advance in the monitoring device 70, or may be identified by detecting a reference piece that has been installed in advance in the manufacturing apparatus 100. If a reference piece is installed in the manufacturing apparatus 100, the imaging device 81 can image this reference piece together with the convergence points 12 at both end portions 11L, 11R of the metal plate 10. The monitoring device 70 can identify the y coordinate of the reference piece from the image data captured by the imaging device 81 and use this as the reference position R in the circumferential direction of the electric resistance welded pipe 20.

[0064] The monitoring device 70 can calculate the first deviation amount by calculating the difference between the circumferential position of the convergence point 12 at both end portions 11L, 11R of the metal plate 10 and the reference position R. The first deviation amount is a value that represents the degree to which the convergence point 12 is deviated in the circumferential direction (y direction) of the electric resistance welded pipe 20 with respect to the reference position R. The monitoring device 70 can determine to which side in the circumferential direction the convergence point 12 is deviated with respect to the reference position R based on whether the difference between the circumferential position of the convergence point 12 at both end portions 11L, 11R of the metal plate 10 and the reference position R is positive or negative.

[0065] After step S2, step S3 is performed. In step S3, a second deviation amount is calculated by multiplying the first deviation amount calculated in step S2 by a predetermined coefficient C. The coefficient C and the second deviation amount will be described below with reference to FIGS. 7B to 7E.

[0066] 7B partially shows a cross section of the electric resistance welded pipe 20 (metal plate 10) at the position of the welding device 40. Referring to FIG. 7B, the convergence point 12 formed in the metal plate 10 during the welding process is the portion where both end portions 11L, 11R (FIG. 7A) abut. The convergence point 12 corresponds to the position of the welding surface (abutment surface) 211 of the electric resistance welded pipe 20 during the welding process. In other words, the first deviation amount of the convergence point 12 from the reference position R in the circumferential direction of the electric resistance welded pipe 20 is the deviation amount of the welding surface 211 in the circumferential direction from the reference position R during the welding process.

[0067] Figure 7C partially shows a cross section of the electric resistance welded pipe 20 at a position just before the cutting device 50. Figure 7D partially shows a cross section of the electric resistance welded pipe 20 at a position just after the cutting device 50. Figure 7E partially shows a cross section of the electric resistance welded pipe 20 at a position between the cutting device 50 and the heat treatment device 60. With reference to Figures 7B and 7C to 7E, the welding surface 211 may have moved in the circumferential direction of the electric resistance welded pipe 20 from its position at the time of the welding process downstream of the welding device 40 due to, for example, twisting of the electric resistance welded pipe 20.

[0068] The amount of twist of the electric-resistance welded pipe 20 after the welding process corresponds to the coefficient C used in step S3. The coefficient C can be obtained in advance, for example, by conducting a preliminary test under the same conditions as the manufacturing conditions of the electric-resistance welded pipe 20. That is, the predetermined coefficient C is a value obtained in advance in the preliminary test. In the preliminary test, the monitoring device 70 acquires the position (coordinates) of the convergence point 12 of both end portions 11L, 11R of the metal plate 10, and a sample of the electric-resistance welded pipe 20 is obtained at a measurement position after (downstream from) the welding process, and the position of the welding surface 211 in the circumferential direction of the electric-resistance welded pipe 20 is measured. The measurement position is a position where the relative positional relationship between the cutting area (processing area) of the cutting device 50 and the welding surface 211 in the circumferential direction can be confirmed. Specifically, a measurement position immediately before or after the cutting device 50 can be used to acquire a sample of the electric-resistance welded pipe 20. Alternatively, a measurement position can be set to a position between the cutting device 50 and the heat treatment device 60, or if multiple heat treatment devices 60 are present, a position after the cutting device 50 and before the most upstream (first stage) heat treatment device 60, and a sample of the electric resistance welded pipe 20 can be obtained. The amount of twist of the electric resistance welded pipe 20 corresponding to coefficient C is the amount of twist that occurs in the electric resistance welded pipe 20 from the welding position to the cutting position or the heat treatment position, and more specifically, it is the amount of twist that occurs in the electric resistance welded pipe 20 from the convergence point 12 to the measurement position of the welding surface 211 in the preliminary test.

[0069] As shown in FIG. 7C , when a sample of the electric-resistance welded pipe 20 is obtained at a position immediately before (on the entry side of) the cutting device 50, a weld bead 22 is present on the inner and outer surfaces of the electric-resistance welded pipe 20 before the cutting process by the cutting device 50. In a cross-section of the electric-resistance welded pipe 20, the weld surface 211 is located directly below the apex of the weld bead 22. By observing the cross-section of the electric-resistance welded pipe 20, the amount of circumferential positional deviation of the weld surface 211 from the reference position R can be confirmed. Because the cutting device 50 is fixedly positioned in the circumferential direction of the electric-resistance welded pipe 20, the cutting area of ​​the cutting device 50 is fixed in the circumferential direction of the electric-resistance welded pipe 20 with respect to the reference position R. When the reference position R is the line center as in this embodiment, the center of the cutting area of ​​the cutting device 50 in the circumferential direction of the electric-resistance welded pipe 20 coincides with the reference position R. The position immediately before the cutting device 50 refers to, for example, a position 200 mm or less upstream of the cutting device 50.

[0070] As shown in FIG. 7D , when a sample of the electric resistance welded pipe 20 is obtained at a position immediately after (on the outlet side of) the cutting device 50, the cutting process by the cutting device 50 has been performed, and therefore a cut portion (cutting mark) 23 of the weld bead 22 ( FIG. 7C ) is present on the electric resistance welded pipe 20. By observing the cross section of the electric resistance welded pipe 20, the amount of circumferential displacement of the weld surface 211 from the reference position R can be confirmed. In the circumferential direction of the electric resistance welded pipe 20, the center position of the cut portion 23 coincides with the line center. When the reference position R is the line center as in this embodiment, the center position of the cut portion 23 coincides with the reference position R in the circumferential direction of the electric resistance welded pipe 20. Immediately after the cutting device 50, the center position of the cut portion 23 coincides with the center position of the cutting area of ​​the cutting device 50 in the circumferential direction of the electric resistance welded pipe 20. A position immediately after the cutting device 50 refers to, for example, a position 200 mm or less downstream of the cutting device 50.

[0071] As shown in Figure 7E, when a sample of the electric resistance welded pipe 20 is obtained at a position between the cutting device 50 and the heat treatment device 60, compared to immediately before or immediately after the cutting device 50 (Figures 7C and 7D), twisting of the electric resistance welded pipe 20 downstream of the cutting device 50 may cause the welding surface 211 and the cutting portion 23 to move in the circumferential direction of the electric resistance welded pipe 20. However, even in this case, the amount of circumferential displacement of the welding surface 211 from the reference position R can be confirmed by observing the cross section of the electric resistance welded pipe 20. The amount of circumferential displacement of the center of the cutting portion 23 from the reference position R can also be measured.

[0072] Through a preliminary test, it is possible to obtain in advance a correlation between the circumferential positional deviation amount (first deviation amount) of the welding surface 211 from the reference position R at the time of the welding process and the circumferential positional deviation amount (second deviation amount) from the reference position R at a measurement position after (downstream of) the welding process. The first deviation amount and the second deviation amount have a positive correlation (proportional relationship) as shown in Fig. 13 . Therefore, in the manufacturing method according to this embodiment, the first deviation amount is detected in step S2, and then the second deviation amount is calculated in step S3 by multiplying the first deviation amount by a coefficient C as a proportionality constant.

[0073] In step S3, the relative relationship between the circumferential position of cut portion 23 of weld bead 22 formed in the cutting step and the circumferential position of weld surface 211 is detected based on the second deviation amount.

[0074] When the reference position R is the line center as in this embodiment, the position of the center of the cut portion 23 in the circumferential direction of the electric resistance welded pipe 20 coincides with the reference position R at the time of the cutting process. Therefore, when the coefficient C corresponds to the amount of twist of the electric resistance welded pipe 20 from the welding process to the cutting process, the second deviation amount itself becomes the amount of circumferential positional deviation of the welding surface 211 from the center of the cut portion 23. On the other hand, even when the reference position R is the line center, the position of the center of the cut portion 23 may deviate from the reference position R in the circumferential direction of the electric resistance welded pipe 20 at a time after the cutting process. Therefore, when the coefficient C corresponds to the amount of twist of the electric resistance welded pipe 20 from the welding process to after the cutting process but before the heat treatment process, the sum or difference of the second deviation amount and the amount of circumferential positional deviation of the center of the cut portion 23 from the reference position R becomes the amount of circumferential positional deviation of the welding surface 211 from the center of the cut portion 23.

[0075] If the reference position R is not the line center, the position of the circumferential center of the cut portion 23 at the time of the cutting process does not coincide with the reference position R. In this case, regardless of whether the coefficient C corresponds to the amount of twist of the electric resistance welded pipe 20 from the welding process to the cutting process, or to the amount of twist of the electric resistance welded pipe 20 from the welding process to after the cutting process but before the heat treatment process, the sum or difference of the second deviation amount and the amount of circumferential positional deviation of the center of the cut portion 23 from the reference position R is the amount of circumferential positional deviation of the welding surface 211 from the center of the cut portion 23.

[0076] The coefficient C corresponds to the amount of twist of the electric-resistance welded pipe 20 from the welding process to the cutting process when the coefficient C is obtained at the time of the cutting process, that is, immediately before or immediately after the cutting device 50. The coefficient C corresponds to the amount of twist of the electric-resistance welded pipe 20 from the welding process to after the cutting process but before the heat treatment process when the coefficient C is obtained after the cutting process, that is, between the cutting device 50 and the heat treatment device 60.

[0077] After step S3, step S4 is performed. In step S3, as described above, the relative relationship between the circumferential position of the cut portion 23 of the weld bead 22 formed in the cutting process and the circumferential position of the welding surface 211 is obtained. More specifically, in step S3, the amount of circumferential positional deviation of the welding surface 211 from the center of the cut portion 23 is determined. In step S4, a process is performed to determine whether the electric resistance welded pipe 20 is acceptable for manufacture based on the relative relationship obtained in step S3.

[0078] For example, if the amount of circumferential positional deviation of the welding surface 211 from the center of the cut portion 23 is large, even if the cut portion 23 before the heat treatment step is detected by an optical method using, for example, an imaging device 82 and the heater 61 is caused to follow the cut portion 23, as in the conventional method, the welding surface 211 is likely to fall outside the range of heat treatment performed by the heater 61. Therefore, the monitoring device 70 may determine that the electric resistance welded pipe 20 is unacceptable for production if the absolute value of the amount of circumferential positional deviation of the welding surface 211 from the center of the cut portion 23 exceeds a predetermined threshold. On the other hand, the monitoring device 70 can determine that the electric resistance welded pipe 20 is acceptable for production if the absolute value is equal to or less than the predetermined threshold.

[0079] The threshold value used in step S4 can be obtained in advance, for example, by conducting a preliminary test under the same conditions as the manufacturing conditions of the electric resistance welded pipe 20. For example, the range (circumferential direction) of the inner surface of the electric resistance welded pipe 20 that has been heat treated can be measured, and a threshold value for determining whether the manufacturing is acceptable, specifically whether the heat treatment is acceptable, can be set based on this.

[0080] The processing of steps S1 to S4 may be performed in real time during the manufacture of the electric resistance welded pipe 20. Alternatively, data during the manufacture of the electric resistance welded pipe 20 may be accumulated, and the processing of steps S1 to S4 may be performed, for example, after all of the strip-shaped (coil-shaped) metal plate 10 has been manufactured into the electric resistance welded pipe 20.

[0081] [Effect] In the present embodiment, during the manufacture of the electric-resistance welded pipe 20, the amount of positional deviation in the circumferential direction of the electric-resistance welded pipe 20 of the convergence point 12 of both end portions 11L, 11R of the metal plate 10 relative to a predetermined reference position R is detected as a first deviation amount. Furthermore, a second deviation amount can be calculated by multiplying the first deviation amount by a predetermined coefficient C corresponding to the amount of twist of the electric-resistance welded pipe 20. Based on this second deviation amount, the relative relationship between the circumferential position of the welding surface 211 and the circumferential position of the cut portion 23 after the cutting process can be obtained. Therefore, during heat treatment of the welded portion 21 of the electric-resistance welded pipe 20, the position of the welding surface 211 in the circumferential direction of the electric-resistance welded pipe 20 can be accurately detected.

[0082] For example, due to twisting of the electric resistance welded pipe 20, the welding surface 211 may be circumferentially misaligned from the center of the cut portion 23 of the weld bead 22 immediately before the heat treatment device 60. Therefore, even if the position of the cut portion 23 is detected and heat treatment is performed along the cut portion 23, it is difficult to determine whether the heat treatment has been properly performed on the welding surface 211 and the heat-affected zone surrounding it, making it difficult to accurately determine whether the electric resistance welded pipe 20 is manufactured. In contrast, in this embodiment, the manufacturing acceptance / rejection of the electric resistance welded pipe 20 is determined based on the position of the welding surface 211, rather than the position of the cut portion 23. More specifically, the manufacturing acceptance / rejection of the electric resistance welded pipe 20 is determined based on the relative relationship between the circumferential position of the welding surface 211 and the circumferential position of the cut portion 23 at the time of or after the cutting process. Therefore, the manufacturing acceptance / rejection of the electric resistance welded pipe 20 can be determined with higher accuracy. As a result, it is possible to prevent the outflow of electric resistance welded pipes 20 with insufficient heat treatment of the weld portion 21.

[0083] In this embodiment, the electric resistance welded pipe 20 has a thickness of, for example, 5.0 mm or more. The electric resistance welded pipe 20 may have a thickness of 10.0 mm or more. The electric resistance welded pipe 20 may have a thickness of 12.7 mm or more, or may have a thickness of 15.0 mm or more. In this embodiment, even if the difference in the heat treatment area of ​​the heater 61 between the outer surface side and the inner surface side of the electric resistance welded pipe 20 becomes large depending on the thickness of the electric resistance welded pipe 20, the second deviation amount related to the position of the welding surface 211 can be used to accurately determine whether the electric resistance welded pipe 20 is acceptable for manufacturing.

[0084] Second Embodiment Fig. 8 is a flowchart showing the processing of the monitoring device 70 according to this embodiment. In this embodiment, the basic configuration of the manufacturing apparatus 100 for electric resistance welded pipe 20 is the same as in the first embodiment (Figs. 1 to 5), but the manufacturing method for electric resistance welded pipe 20 is slightly different from that in the first embodiment. More specifically, in this embodiment, the processing executed by the monitoring device 70 differs from that in the first embodiment.

[0085] 8, the manufacturing method according to this embodiment includes steps S1 to S3 similar to those of the first embodiment. However, the manufacturing method according to this embodiment includes step S5 instead of step S4 in the first embodiment. Steps S1 to S3 and S5 are executed by the CPU 71 (FIG. 5) of the monitoring device 70. The processing of steps S1 to S3 and S5 may be executed in real time during the manufacturing of the electric resistance welded pipe 20.

[0086] As in the first embodiment, the monitoring device 70 acquires the relative relationship between the circumferential position of the weld surface 211 after the cutting process but before the heat treatment process and the circumferential position of the cut portion 23 of the weld bead 22 through steps S1 to S3 (FIGS. 7B to 7E). Referring to FIGS. 9 and 10, in step S5, a process of moving the heater 61 included in the heat treatment device 60 is executed based on this relative relationship. The monitoring device 70 is configured to control the movement of the heater 61 within the heat treatment device 60. When the manufacturing apparatus 100 includes multiple heat treatment devices 60, the monitoring device 70 may be configured to control the movement of the heater 61 for each heat treatment device 60 independently of the other heat treatment devices 60.

[0087] More specifically, as shown in FIG. 9 , in step S5, the cutting portion 23 formed in the cutting process is imaged by the imaging device 82, and the cutting portion 23 is detected based on the obtained image data. The imaging device 82 images the cutting portion 23 before heat treatment. The monitoring device 70 detects the center position (coordinates) of the cutting portion 23 in the circumferential direction of the electric resistance welded pipe 20 from the image data acquired from the imaging device 82. The method of detecting the cutting portion 23 by an optical technique using the imaging device 82 is the same as conventional, so a description thereof will be omitted. The monitoring device 70 may detect the position of the cutting portion 23 in the circumferential direction of the electric resistance welded pipe 20 using a known optical technique. The monitoring device 70 can, for example, detect the amount of circumferential positional deviation of the center of the cutting portion 23 from a reference position R.

[0088] Because the processing of steps S1 to S3 has obtained the relative circumferential position of welding surface 211 with respect to cut portion 23, once the circumferential position of cut portion 23 is detected, it is possible to derive the circumferential position of welding surface 211 immediately before the heat treatment process. That is, by taking into consideration the amount of circumferential positional deviation of the center of cut portion 23 with respect to reference position R detected in step S5 and the amount of circumferential positional deviation between the center of cut portion 23 and welding surface 211 obtained in steps S1 to S3, it is possible to obtain the amount of circumferential positional deviation of welding surface 211 with respect to reference position R immediately before the heat treatment process.

[0089] 10 , the monitoring device 70 moves the heater 61 based on the circumferential position of the welding surface 211 immediately before the heat treatment process so that the welding surface 211 is located in the circumferential center of the heat treatment area of ​​the heater 61. More specifically, the monitoring device 70 sends a signal to the drive mechanism 62 of the heat treatment device 60, causing the drive mechanism 62 to move the heater 61. The heater 61 may move in the circumferential direction of the electric resistance welded pipe 20 or in the width direction (left-right direction) of the electric resistance welded pipe 20. When the manufacturing apparatus 100 includes multiple heat treatment devices 60, the monitoring device 70 moves the heater 61 of at least the most upstream heat treatment device 60 based on the circumferential position of the welding surface 211 immediately before the heat treatment process so that the welding surface 211 is located in the circumferential center of the heat treatment area of ​​the heater 61. The monitoring device 70 may move the heater 61 of the other heat treatment devices 60 in the same manner as the most upstream heat treatment device 60.

[0090] However, for heat treatment devices 60 other than the most upstream device, movement control of the heater 61 may be performed using a marking device 63 and a detection device 64 shown in Fig. 11. The marking device 63 is disposed near the cutting device 50. The marking device 63 may be disposed at a position that substantially coincides with the cutting device 50 in the conveying direction, or may be disposed immediately before or after the cutting device 50. The marking device 63 applies a marking at a predetermined position on the outer surface of the electric resistance welded pipe 20. The marking device 63 may apply a marking at a position that is a predetermined angle (e.g., 90°) away from the upper end of the electric resistance welded pipe 20 around the line center when viewed along the conveying direction.

[0091] The detection device 64 is provided corresponding to each of the heat treatment devices 60 other than the heat treatment device 60 located most upstream among the multiple heat treatment devices 60. In the example of FIG. 11 , the detection device 64 is provided corresponding to the second heat treatment device 60 from the upstream side among the multiple heat treatment devices 60. The detection device 64 is located on the inlet side (upstream side) of this heat treatment device 60. The detection device 64 can capture an image including markings applied to the outer surface of the electric resistance welded pipe 20. The marking device 63 and the detection device 64 may have the same configuration as the marking device and detection device described in JP 2019-217507 A, for example.

[0092] The circumferential position of the marking on the electric resistance welded pipe 20 can be identified based on the image data captured by the detection device 64. At the time the marking is applied by the marking device 63, that is, during the cutting process, the circumferential position of the marking is fixed, and the amount of circumferential positional deviation of the welding surface 211 from the reference position R immediately before the heat treatment process is determined by steps S1 to S3 and S5. Therefore, the amount of circumferential positional deviation of the welding surface 211 from the reference position R at the time the marking is detected by the detection device 64 can be derived. Therefore, based on the amount of circumferential positional deviation of the welding surface 211 from the reference position R determined using the marking, the monitoring device 70 can move the heater 61 so that the welding surface 211 is positioned in the circumferential center of the heat treatment area of ​​the heater 61, even for heat treatment devices 60 other than the most upstream one.

[0093] The detector 64 may be provided for all heat treatment devices 60 except for the most upstream one, but it is not necessarily required to be provided for all heat treatment devices 60. When the detector 64 is provided for only some of the heat treatment devices 60, for the heat treatment devices 60 not provided with the detector 64, a linear approximation of the circumferential positional deviation of the welding surface 211 from the reference position R obtained for the other heat treatment devices 60 may be performed to determine the circumferential positional deviation of the welding surface 211 from the reference position R. In this case, the monitoring device 70 can move the heater 61 for each heat treatment device 60 based on the circumferential positional deviation of the welding surface 211 from the reference position R so that the welding surface 211 is positioned in the circumferential center of the heat treatment area of ​​the heater 61.

[0094] In this embodiment, as in the first embodiment, the position of the welding surface 211 in the circumferential direction of the electric-resistance welded pipe 20 can be accurately detected during heat treatment of the welded portion 21 of the electric-resistance welded pipe 20. Furthermore, in this embodiment, the heater 61 is moved so that the welding surface 211 is positioned in the circumferential center of the heat treatment area of ​​the heater 61 of the heat treatment device 60, based on the relative relationship between the circumferential position of the welding surface 211 after the cutting process and the circumferential position of the cut portion 23 of the weld bead 22. That is, in the heat treatment process, the heater 61 follows the welding surface 211, not the cut portion 23. For example, by tracking the transported metal plate 10, the heater 61 can be made to follow the welding surface 211 at the timing when the convergence point 12 detected in the welding process arrives at the heat treatment device 60. In this case, even if the welding surface 211 is circumferentially misaligned with respect to the cut portion 23, the welding surface 211 of the electric-resistance welded pipe 20 and the surrounding heat-affected zone are likely to be contained within the heat treatment area of ​​the heater 61. Therefore, it is possible to perform a satisfactory heat treatment on the entire welded portion 21, including the weld surface 211 and the heat-affected zone. As a result, it is possible to improve the toughness of the welded portion 21, and it is possible to manufacture a high-quality electric resistance welded pipe 20.

[0095] In this embodiment, as in the first embodiment, the electric resistance welded pipe 20 can have a thickness of, for example, 5.0 mm or more. The electric resistance welded pipe 20 may have a thickness of 10.0 mm or more. The electric resistance welded pipe 20 may have a thickness of 12.7 mm or more, or may have a thickness of 15.0 mm or more. In this embodiment, even if the difference in the heat treatment area of ​​the heater 61 between the outer surface side and the inner surface side of the electric resistance welded pipe 20 becomes large depending on the thickness of the electric resistance welded pipe 20, the heater 61 is made to follow the welding surface 211, so that the weld 21 can be subjected to good heat treatment overall.

[0096] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0097] 100: Manufacturing device 10: Metal plate 11L, 11R: End 12: Convergence point 20: Electric resistance welded pipe 21: Welded portion 211: Welded surface 22: Weld bead 23: Cutting portion 40: Welding device 50: Cutting device 60: Heat treatment device 61: Heating element 70: Monitoring device 81, 82: Imaging device 90: Image data

Claims

1. A method for manufacturing electric resistance welded pipe, comprising: a forming step of forming a metal plate into a tubular shape while conveying the metal plate so that both ends of the metal plate face each other; a welding step of butt-welding the both ends together to form the metal plate into an electric resistance welded pipe; a cutting step of cutting the weld bead formed on the surface of the electric resistance welded pipe in the welding step; and a heat treatment step of heat treating the weld of the electric resistance welded pipe formed in the welding step after the cutting step, wherein the convergence point where the both ends approach and converge as they move downstream in the conveyance direction of the metal plate is defined as the position of the weld surface of the electric resistance welded pipe in the welding step, and a first deviation amount of the convergence point in the circumferential direction of the electric resistance welded pipe relative to a predetermined reference position is detected; a second deviation amount is calculated by multiplying the first deviation amount by a predetermined coefficient corresponding to the amount of twist of the electric resistance welded pipe; and a relative relationship between the circumferential position of the cut portion formed by cutting the weld bead in the cutting step and the circumferential position of the weld surface is obtained based on the second deviation amount. The manufacturing method further comprises determining whether the electric resistance welded pipe is acceptable for manufacturing based on the relative relationship.

2. A method for manufacturing electric resistance welded pipe, comprising: a forming step of shaping a metal plate into a tubular shape while conveying the metal plate so that both ends of the metal plate face each other; a welding step of butt-welding the both ends together to form the metal plate into an electric resistance welded pipe; a cutting step of cutting the weld bead formed on the surface of the electric resistance welded pipe in the welding step; and a heat treatment step of heat treating the welded portion of the electric resistance welded pipe formed in the welding step after the cutting step, wherein the convergence point where the both ends approach and converge as they move downstream in the conveyance direction of the metal plate is taken as the position of the welded surface of the electric resistance welded pipe in the welding step, and a first deviation amount of the convergence point in the circumferential direction of the electric resistance welded pipe relative to a predetermined reference position is detected; a second deviation amount is calculated by multiplying the first deviation amount by a predetermined coefficient corresponding to the amount of twist of the electric resistance welded pipe; and a relative relationship between the circumferential position of the cut portion formed by cutting the weld bead in the cutting step and the circumferential position of the welded surface is obtained based on the second deviation amount. In the heat treatment step, a heater included in a heat treatment device for applying heat treatment to the welded portion is moved based on the relative relationship so that the welding surface is positioned in the circumferential center of a heat treatment area of ​​the heater.

3. A manufacturing method according to claim 1 or 2, wherein the electric resistance welded pipe has a thickness of 5.0 mm or more.

4. A monitoring device used in the manufacture of electric-resistance welded pipes, which performs the following steps: a forming step in which a metal plate is shaped into a tube while being conveyed, with both ends of the metal plate facing each other; a welding step in which the both ends are butt-welded to form the metal plate into an electric-resistance welded pipe; a cutting step in which a weld bead formed on the surface of the electric-resistance welded pipe in the welding step is cut; and a heat treatment step in which a weld of the electric-resistance welded pipe formed in the welding step is heat-treated after the cutting step, the monitoring device comprising: a process of acquiring image data captured by an imaging device, the image data including a convergence point at which the both ends approach and converge as they move downstream in the conveyance direction of the metal plate; and a process of detecting a first deviation amount of the convergence point in the circumferential direction of the electric-resistance welded pipe from a predetermined reference position, based on the image data, with the convergence point being the position of the weld surface of the electric-resistance welded pipe in the welding step. a process of calculating a second deviation amount by multiplying the first deviation amount by a predetermined coefficient corresponding to the amount of twist of the electric-resistance welded pipe, and obtaining, based on the second deviation amount, a relative relationship between the circumferential position of the cut portion formed by cutting the weld bead in the cutting process and the circumferential position of the weld surface; and a process of determining whether the electric-resistance welded pipe is acceptable for manufacture based on the relative relationship.

5. An electric-resistance welded pipe manufacturing apparatus comprising: a welding device configured to butt-weld both ends of a metal plate being formed into a tubular shape while being transported, thereby forming the metal plate into an electric-resistance welded pipe; a cutting device arranged downstream of the welding device in the transport direction of the metal plate and configured to cut a weld bead formed on the surface of the electric-resistance welded pipe; a heat treatment device arranged downstream of the cutting device in the transport direction and including a heater for heat treating the welded portion of the electric-resistance welded pipe; and a monitoring device configured to control the movement of the heater, wherein the monitoring device performs the following processes: a process of acquiring image data captured by an imaging device and including a convergence point at which the both ends approach and converge as they move downstream in the transport direction; and a process of detecting a first deviation amount of the convergence point in the circumferential direction of the electric-resistance welded pipe from a predetermined reference position, based on the image data, with the convergence point being the position of the weld surface of the electric-resistance welded pipe in the welding device. a process of multiplying the first deviation amount by a predetermined coefficient corresponding to the amount of twist of the electric-resistance-welded pipe to calculate a second deviation amount, and obtaining, based on the second deviation amount, a relative relationship between the circumferential position of the cutting portion formed by cutting the weld bead with the cutting device and the circumferential position of the welding surface; and a process of moving the heater based on the relative relationship so that the welding surface is positioned in the circumferential center of a heat treatment area of ​​the heater.

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