Welding control device for electric resistance welded pipes, welding control method for electric resistance welded pipes, method for manufacturing electric resistance welded pipes, and welding control system for electric resistance welded pipes.

Abstract

The present invention provides a welding management device for electric resistance welded pipes, a welding management method for electric resistance welded pipes, a method for manufacturing electric resistance welded pipes, and a welding management system for electric resistance welded pipes, which can detect misalignment by distinguishing between misalignment and wall thickness differences during electric resistance welded welding when continuously welding both edges of an open pipe. [Solution] The electric resistance welded pipe welding management device 100 includes an electric resistance welded edge temperature detection unit 122 that detects the outer surface temperature To, inner surface temperature Ti, and maximum temperature Tp of one edge; a molten metal outflow area calculation unit 133 that calculates the molten metal outflow area S based on a weld image 20 of the region including the welding point 205; a molten metal outflow area difference calculation unit 134 that calculates the area difference ΔS of the molten metal outflow area S; and a misalignment determination unit 141 that determines misalignment of electric resistance welds based on a first temperature ratio Tp / To, a second temperature ratio Tp / Ti, and the area difference ΔS.

Description

Technical Field

[0001] The present invention relates to a welding management device for an electric resistance welded pipe, a welding management method for an electric resistance welded pipe, a manufacturing method for an electric resistance welded pipe, and a welding management system for an electric resistance welded pipe.

Background Art

[0002] An electric resistance welded pipe is formed by continuously bending a steel plate or a steel strip in the circumferential direction using roll forming, and abutting both edge portions to form an open pipe with a circular cross-section. Thereafter, both edge portions of the abutted open pipe are continuously subjected to electric resistance welding to manufacture the pipe.

[0003] During electric resistance welding, both edge portions described above are heated above the melting point by direct energization using a contact tip or induced current using an induction coil, and immediately thereafter, the end faces of both edge portions are abutted (upset) by welding rolls (squeeze rolls). At that time, oxides (penetrators) generated during the heating process of the edge portions of the steel plate or steel strip are allowed to flow out to the inner and outer surfaces of the pipe by upsetting, that is, they are discharged to an unnecessary portion called a surplus portion (bead) to suppress the occurrence of welding defects. After electric resistance welding, the surplus portion is cut and removed from the pipe using a cutting tool or the like.

[0004] To suppress welding defects, it is crucial in electric resistance welded (ERW) welding to ensure that the penetrator is smoothly discharged from the pipe. This requires not only precise welding conditions, such as the high-frequency current used in ERW, but also adjustment of the radial position of both edges of the open pipe so that they are aligned and upset correctly. If welding is performed with the edges not aligned, i.e., with a misalignment of the radial edges, the discharge of the penetrator may be impaired. Furthermore, after ERW welding, the weld bead is cut from both the inner and outer surfaces of the ERW pipe. If welding is performed with the aforementioned misalignment, cutting the bead will reveal the resulting step (sometimes called a "step"). While such steps are removed along with the bead, some steps that could not be removed during bead cutting may remain on the inner and outer surfaces of the ERW pipe. Processing the ERW pipe with steps present can cause stress to concentrate in the stepped areas, leading to weld failure. While some degree of misalignment is unavoidable in electric resistance welding, the misalignment addressed in this invention refers to misalignment that impairs the quality of the welded joint.

[0005] Conventionally, in edge forming and fin pass forming within roll forming, the roll position is adjusted so that the bending deformation of both edges is symmetrical. This suppresses the occurrence of misalignment. However, if this adjustment is insufficient, misalignment will occur, so welding control to detect misalignment is necessary even during electric resistance welding.

[0006] A device for monitoring such misalignments is disclosed in Patent Document 1. In the device disclosed in Patent Document 1, a region including the V-convergence area and the metal portion that has flowed out onto the surface of the metal plate due to electromagnetic force, which is below the V-convergence area in the direction of welding, is photographed by an imaging device. The bias of the light-emitting region of the metal portion is captured from the image captured by the imaging device, and the misalignment is detected based on the light-emitting region thus captured. This is because if a misalignment occurs, a bias will occur in the light-emitting region due to melting or red-hotness. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 6361840 [Overview of the project] [Problems that the invention aims to solve]

[0008] As described above, the apparatus described in Patent Document 1 detects misalignment by detecting the bias in the luminescence area of ​​the metal portion that has flowed onto the surface of the metal plate. However, even when there is a difference in thickness between the two edges that abut each other, bias occurs in the luminescence area of ​​the metal portion that has flowed onto the surface of the metal plate. This is because the difference in thickness between each edge causes a difference in the degree of concentration of the high-frequency current that heats each edge. The apparatus described in Patent Document 1 cannot detect such bias in the luminescence area caused by the difference in thickness between the two edges. Therefore, for example, it may determine that misalignment has occurred even though a difference in thickness has occurred, and adjust the roll position of the forming roll to correct the misalignment. As a result, even if the roll position of the forming roll is adjusted, it may not be possible to control the electric resistance weld as intended. Thus, the apparatus described in Patent Document 1 over-detects misalignment, and as a result, it is not possible to control the electric resistance weld according to the misalignment or thickness difference, which may impair the quality of the welded joint, and there was room for improvement in these respects.

[0009] The present invention has been made to solve the above-mentioned problems, and aims to provide a welding management device for electric resistance welded pipes, a welding management method for electric resistance welded pipes, a method for manufacturing electric resistance welded pipes, and a welding management system for electric resistance welded pipes that can distinguish between misalignment and wall thickness differences during electric resistance welding and detect misalignment when electric resistance welding both edges of an open pipe. [Means for solving the problem]

[0010] The means to solve the above-mentioned problems are as follows: [1] A welding management device for electric resistance welded pipes manufactured by bending a steel plate or steel strip in the circumferential direction, butting the two edges together to form an open pipe, and performing electric resistance welding on both edges of the butted open pipe, comprising: an edge temperature detection unit before electric resistance welding that detects the outer surface temperature, inner surface temperature, and the maximum value of the temperature distribution obtained by subtracting the outer surface temperature and inner surface temperature of the one edge from the temperature distribution in the thickness direction of the one edge, based on information on the temperature distribution of at least one edge of the two edges of the open pipe, and the highest temperature among the maximum values, and the A welding management device for electric resistance welded pipes, comprising: a molten metal outflow area calculation unit that calculates the outflow area of ​​molten metal flowing out from each of the edges of the open pipe to the pipe surface based on a weld image of the region including both edges of the open pipe and the welding point where welding of the edges of the open pipe begins; a molten metal outflow area difference calculation unit that calculates the area difference of the outflow area of ​​molten metal flowing out from each of the edges to the pipe surface detected by the molten metal outflow area calculation unit; and a misalignment determination unit that determines misalignment of electric resistance welds based on a first temperature ratio of the outer surface temperature and the maximum temperature, or a second temperature ratio of the inner surface temperature and the maximum temperature, and the area difference. [2] The electric resistance welded pipe welding control device according to [1], wherein the misalignment determination unit determines that misalignment has occurred in electric resistance welded pipes when the area difference is less than or equal to a predetermined upper limit, and the first temperature ratio or second temperature ratio when the area difference occurs is less than or equal to a threshold value for the first temperature ratio or second temperature ratio corresponding to the area difference. [3] A welding control method for electric resistance welded pipes manufactured by bending a steel plate or steel strip in the circumferential direction, butting the two edges together to form an open pipe, and then performing electric resistance welding on both edges of the butted open pipe, comprising: an edge temperature detection step before electric resistance welding, which detects the maximum value among the outer surface temperature, inner surface temperature, and temperature distribution obtained by subtracting the outer surface temperature and inner surface temperature of the one edge from the temperature distribution in the thickness direction of the one edge, based on information on the temperature distribution of at least one of the edges of the open pipe in the thickness direction, and the highest temperature among the maximum values; and the outer or inner side of the open pipe. A welding management method for electric resistance welded pipes, comprising: a molten metal outflow area calculation step of calculating the outflow area of ​​molten metal flowing out from each of the two edges of the open pipe to the pipe surface based on a weld image of the region including both edges of the open pipe photographed from the face side and the welding point where welding of both edges of the open pipe is started; a molten metal outflow area difference calculation step of calculating the area difference of the outflow areas of molten metal flowing out from each of the two edges to the pipe surface calculated in the molten metal outflow area calculation step; and a misalignment determination step of determining misalignment of electric resistance welds based on a first temperature ratio of the outer surface temperature and the maximum temperature, or a second temperature ratio of the inner surface temperature and the maximum temperature, and the area difference. [4] The difference determination step is that the area difference is less than or equal to a predetermined upper limit, A welding control method for electric resistance welded pipes according to [3], wherein it is determined that misalignment of electric resistance welds has occurred when the first temperature ratio or the second temperature ratio when the aforementioned area difference occurs is below a threshold value of the first temperature ratio or the second temperature ratio corresponding to the area difference. [5] A method for manufacturing an electric resistance welded pipe, comprising bending a steel plate or steel strip in the circumferential direction, butting the two edges together to form the open pipe, and performing electric resistance welding on both edges of the open pipe, wherein the welding is controlled during the electric resistance welding by the welding control method for electric resistance welded pipes described in [3] or [4]. A welding management system for an electric welded pipe, comprising the welding management device according to [6][1] or [2], an edge temperature information acquisition device that acquires information on the temperature distribution of one of the two edge portions of the open pipe, the two edge portions of the open pipe, and a welding part imaging device that images a region including the welding points where welding of the two edge portions of the open pipe is started.

Advantages of the Invention

[0011] According to the present invention, it is possible to distinguish between the difference in appearance of the two edge portions of the open pipe and the difference in wall thickness of the two edge portions and detect the difference in appearance.

Brief Description of the Drawings

[0012] [Figure 1] It is a diagram showing an image of the welding part. [Figure 2] It is a diagram for explaining the surface state of the end face of the edge portion before electric welding. [Figure 3] It is a diagram for explaining the state of the welding part before and after removing the welding bead. [Figure 4] It is a diagram for explaining the welding management device of the present embodiment and the welding management system including the same. [Figure 5] It is a flowchart showing the welding management processing procedure by the welding management device of the present embodiment. [Figure 6] It is a diagram showing the temperature distribution from which the outer surface temperature, the inner surface temperature, and the maximum temperature are extracted. [Figure 7] It is a diagram showing a cross section of the welding part where the segregation line appears. [Figure 8] It is a diagram showing the results of the quality of the electric welded product according to the second temperature ratio and the area difference. [Figure 9] It is a diagram showing the results of the quality of the electric welded products of Invention Examples 1 to 3 and Comparative Examples 1 and 2.

Embodiments for Carrying Out the Invention

[0013] The inventors of this invention have diligently researched the electric resistance welding phenomenon to distinguish and detect misalignment in electric resistance welding and the difference in wall thickness between the two edges of an open pipe. Here, misalignment means that the end faces of the two edges of an open pipe do not face each other directly, but rather their positions are offset in the radial direction of the open pipe. One cause of such misalignment is that the bending deformation of the two edges of the open pipe before electric resistance welding is different. The difference in wall thickness between the two edges means the difference in wall thickness of the end faces of each edge in the radial direction of the open pipe.

[0014] In electric resistance welding (ERW), a current is generated along the longitudinal direction of the open pipe on the surface of each edge. This current generates an electromagnetic force, which causes the molten metal at each edge to flow out to the outer or inner surface of the open pipe. Furthermore, when the two edges of the open pipe come close together just before ERW welding is performed, the proximity effect, which is unique to high-frequency heating, increases the current density on the surface of each edge, accelerating heating. When the two edges face each other directly, the proximity effect heats the entire end face of both edges almost uniformly just before ERW welding. However, if there is a misalignment, the heating of each end face will be uneven due to the proximity effect, resulting in non-uniform heating. In other words, if there is a misalignment, the entire end face of both edges will not be heated uniformly. To capture this phenomenon, it is necessary not only to photograph the welding phenomenon with a camera and visualize the welding phenomenon as an image with the camera, but also to acquire temperature distribution data of the end face just before welding. Therefore, we conducted intensive research by analyzing the image data acquired by the camera and the temperature distribution data acquired by the thermometer, and the following was revealed.

[0015] First, the process of electric seam welding will be described with reference to FIGS. 1, FIGS. 2, and FIGS. 3. FIG. 1 is a diagram showing a welded part image 20. FIG. 2 is a diagram for explaining the surface condition of the end face of the edge part before electric seam welding. FIG. 3 is a diagram for explaining the state of the welded part before and after removing the weld bead. Conventionally, in electric seam welding, heating of the edge parts 202a and 202b is performed by a high-frequency oscillation device 3, which is a heating device using a high-frequency current by a direct current heating method or an induction heating method. When the end faces of the edge parts 202a and 202b are smooth, as shown in FIGS. 1, FIGS. 2(i), and FIGS. 3(i), when high-frequency heating is performed on the edge parts 202a and 202b, a skin effect appears in the initial stage of heating, which is a heating phenomenon peculiar to high-frequency heating. As a result, heating is concentrated on the outer surface and the inner surface of the edge parts 202a and 202b having corners. The central part in the thickness direction of the edge parts 202a and 202b (hereinafter referred to as the thickness central part) is heated by the heat transfer from the outer surface and the inner surface of the edge parts 202a and 202b. In FIGS. 1 to 3, the portion heated by high-frequency heating and made red-hot (referred to as the heated part) is marked with the symbol "201". In FIG. 1, the opening between the edge parts 202a and 202b of the open tube is marked with the symbol "202". Also, in FIG. 1, the intersection of the straight lines La and Lb along each edge part 202a and 202b is a V-convergence point (sometimes referred to as a joining point), and the V-convergence point (sometimes referred to as a joining point) is marked with the symbol "204". The welded part image 20 is an image taken by a welded part photographing device 12 described later.

[0016] As the heating process progresses, the squeeze rolls described later bring the end faces of each edge 202a and 202b closer together, shortening the distance between them. As a result, the proximity effect occurs, increasing the current density at the end faces of each edge 202a and 202b, and increasing the heating rate in the center of the wall thickness. Then, while heating the outermost layer of the entire pipe thickness of the edges 202a and 202b to the melting point, electric resistance welding is performed at the welding point (sometimes called the abutment point) 205 shown in Figure 1, after upsetting by the squeeze rolls. At this time, the molten metal generated at the edges 202a and 202b flows out to the outside of the pipe along with the penetrator distributed on the end faces of the edges 202a and 202b, forming a weld bead 203. Also, in the weld image 20 of Figure 1, the indicators "d1" and "d2" are added to show the starting positions of the molten metal outflow. In Figure 1, the labels "Sa" and "Sb" in the weld image 20 indicate the area of ​​molten metal per unit weld length that flowed out from each edge 202a and 202b. The respective areas Sa and Sb are collectively denoted as "S".

[0017] In electric resistance welding, as described above, the entire end face of edge portions 202a and 202b is melted. A sound weld is then obtained by allowing the molten metal from edge portions 202a and 202b, along with the penetrator, to flow out of the pipe. However, if the temperature distribution at the end face is uneven, the molten portion near the outer or inner surface of the end face may solidify before the entire amount of penetrator can be discharged outside the pipe. When this happens, the discharge of molten metal by upsetting is hindered by the solidified molten portion near the outer or inner surface. As a result, penetrator remains inside the weld, and the quality of the weld deteriorates. Such uneven temperature distribution at the end face can occur, for example, when there is misalignment between the two edges, which causes heating due to the proximity effect to concentrate on a part of the end face. That is, as shown in Figure 2(ii), when misalignment occurs, the proximity effect is most pronounced in the part where both end faces are closest to each other in the circumferential direction of the open pipe. As a result, the temperature distribution at each end face becomes uneven, hindering the outflow of the penetrator.

[0018] Furthermore, after electric resistance welding, the weld bead 203 on the inner surface and the weld bead 203 on the outer surface of the electric resistance welded pipe are removed using bead cutting blades (not shown). Now, let's explain how the weld bead 203 is cut. On the outer surface of the electric resistance welded pipe, the weld bead 203 on the outer surface is cut using a concave bead cutting blade. Also, there are no restrictions on the space in which the bead cutting blade can be moved when cutting the weld bead 203. Therefore, the weld bead 203 can be removed along the curved surface of the outer surface of the electric resistance welded pipe. At the same time, stepped areas caused by misalignment can be removed. Stepped areas refer to stepped areas that occur when electric resistance welding is performed while misalignment is present.

[0019] On the inner surface of the electric resistance welded pipe, a convex-shaped bead cutting blade is inserted into the inside of the electric resistance welded pipe to cut the inner weld bead 203. On the inner surface of the electric resistance welded pipe, there are constraints on the space available to move the bead cutting blade when cutting the weld bead 203. Therefore, it becomes difficult to remove the weld bead 203 and the stepped portion. As a result, there is a possibility that the stepped portion, in particular, may remain. Figure 3(ii) shows this condition. Furthermore, when cutting the stepped portion on the inner surface of the electric resistance welded pipe, the surrounding area of ​​the stepped portion must also be cut, which may result in the wall thickness of the weld becoming extremely thin. In addition, if electric resistance welding of an open pipe is performed with misalignment, the stepped portion will occur continuously along the longitudinal direction of the electric resistance welded pipe.

[0020] Furthermore, in electric resistance welding (ERW), high-frequency heating of each edge portion 202a and 202b generates an electromagnetic force at each edge portion 202a and 202b. This electromagnetic force causes the molten metal on the end faces of the edges 202a and 202b to flow out to the outer or inner surface of the ERW pipe. Also, if there is a misalignment, the electromagnetic force is not uniformly applied to the opposing edge surfaces of each edge portion 202a and 202b, and the force causing the molten metal to flow out is weaker on the surfaces that do not overlap with the opposing edge portions. As a result, the positions d1 and d2 where the molten metal begins to flow out of the pipe differ between one edge portion 202a (202b) and the other edge portion 202b (202a) before ERW welding, along the longitudinal direction of the open pipe. In addition, the difference in the electromagnetic force generated at each edge portion 202a and 202b results in a difference in the area of ​​molten metal flowing out to the outer or inner surface of the ERW pipe. These can be observed visually. Furthermore, this phenomenon also occurs when there is a difference in thickness between one edge portion 202a (202b) and the other edge portion 202b (202a).

[0021] Furthermore, if misalignment occurs, the area S of molten metal flowing out of the pipe, and the amount of molten metal flowing out, will be asymmetrical between the outer and inner surfaces of the electric resistance welded pipe. Figure 2(ii) shows an example of this. Specifically, one edge portion 202b (right side in Figure 2(ii)) is located radially inward from the other edge portion 202a. In this case, at the edge portion 202b on one side, the area of ​​molten metal flowing out to the outer surface is larger than the area of ​​molten metal flowing out to the inner surface. Similarly, at the edge portion 202a on the other side, the area of ​​molten metal flowing out to the inner surface is larger than the area of ​​molten metal flowing out to the outer surface. This asymmetry increases as the degree of misalignment increases, and the area difference ΔS between the molten metal flow areas Sa and Sb on the outer or inner surfaces of each edge portion 202a and 202b also increases.

[0022] Figure 2(iii) shows the case where there is a difference in wall thickness between the edges 202a and 202b. In this case, the area S of molten metal flowing out of the pipe from the edge 202b on the thinner side (right side in Figure 2(iii)) is larger than the area S of molten metal flowing out of the pipe from the other edge 202a. When observed from the outside of the pipe, the molten metal flowing out is asymmetrical between the edges 202a and 202b, but there is no localized abnormal heating at each end face that was observed when misalignment occurred. Therefore, misalignment and wall thickness difference can be distinguished based on the temperature distribution at the end faces of the edges 202a and 202b and the area difference ΔS of molten metal flowing out of the pipe from the edges 202a and 202b.

[0023] The present invention is based on the findings described above. Hereinafter, embodiments of the present invention (hereinafter referred to as "these embodiments") will be described with reference to the drawings. However, the present invention is not limited to these embodiments.

[0024] Figure 4 is a diagram illustrating the welding control device 100 and the welding management system 10 including it according to this embodiment. After the steel plate or steel strip is continuously formed into a cylindrical shape by roll forming, it proceeds in the direction indicated by the arrow in Figure 4 as the welding direction (direction of progress). At the same time, the fin pass roll 2 ensures the stability of the cylindrical shape and the surface condition of the end face, and the butt joint position of both edge portions 202a and 202b is centered in the center of the welding stand 40 as it is formed into an open tube 1. Subsequently, high-frequency current is supplied to both edge portions 202a and 202b of the open tube 1 from the high-frequency oscillator 3 via a pair of contact tips 31a and 31b, and both edge portions 202a and 202b are heated until they melt. It is also possible to use induction heating work coils instead of contact tips 31a and 31b.

[0025] Next, the open pipe 1 passes through a welding stand 40 surrounded by a group of rolls consisting of squeeze rolls 41a, 41b and top rolls 42a, 42b, and both edges 202a, 202b are pressed together. At the same time, molten metal is discharged to the outer and inner sides of the open pipe 1 as both edges 202a, 202b are welded (referred to as electric resistance welding).

[0026] In electric resistance welding, welding begins when the two edges 202a and 202b of the open pipe 1 are close together upstream of the squeeze rolls 41a and 41b in the welding direction (direction of travel) (opposite to the welding direction). The position where welding begins is called the welding point 205. The welded portion is called the welded area. When the high-frequency current is sufficiently large, a phenomenon can be observed where a portion of the end face melts due to high-frequency heating upstream of the welding point 205 in the welding direction (direction of travel), and the molten metal flows out of the pipe due to electromagnetic force.

[0027] The welding management system 10 includes an edge temperature information acquisition device 11, a weld imaging device 12, and a welding management device 100. The edge temperature information acquisition device 11, the weld imaging device 12, and the welding management device 100 will be described in order below.

[0028] The edge temperature information acquisition device 11 acquires information on the temperature distribution of at least one of the two edge portions 202a and 202b of the open pipe 1 before electric resistance welding. The edge temperature information acquisition device 11 has a thermometer capable of measuring the temperature distribution based on a two-dimensional image, such as a thermograph. The edge temperature information acquisition device 11 also has an imaging device that photographs the edge portions 202a and 202b in order to acquire the temperature distribution of the edge portions 202a and 202b. A CCD camera can be used as the imaging device.

[0029] The edge temperature information acquisition device 11, which has the imaging device, is installed above the open tube 1 and its position is adjusted so that the entire thickness of the edges 202a and 202b of the open tube 1 can be photographed in the thickness direction. The imaging area of ​​the imaging device described above is a predetermined area of ​​the edges 202a and 202b of the open tube 1 located between the contact tips 31a and 31b and the welding stand 40 in the welding direction (direction of travel). The imaging device also photographs the heated surface from the outer surface to the inner surface of the tube at least one of the opposing edges 202a (202b). Examples of thermometers mentioned above include radiation thermometers and two-color thermometers. Any thermometer can be used as long as it can acquire the temperature distribution. The edge temperature information acquisition device 11 also has adjusters such as a zoom lens and an exposure adjuster for adjusting the optical system. The adjustment device preferably has a field of view of 100 mm × 40 mm and a resolution of 500 μm / pixel or higher. A resolution of 100 μm / pixel or higher is more preferable.

[0030] The resolution of the imaging device (camera) should preferably be 1920 x 1080 or higher. If the resolution is lower than 500 μm / pixel, the accuracy of temperature detection for the edges 202a and 202b may deteriorate. The frame rate should preferably be set to 1 fps (frames per second) or higher. If the frame rate is less than 1 fps, in the welding phenomenon, the starting point at which the surface properties affect the end face temperature distribution may be missed.

[0031] The welding imaging device 12 has, for example, at least one camera. This camera photographs both edges 202a and 202b of the open pipe 1 from either the outer or inner side. In the example shown in Figure 4, the camera is positioned on the outer side of the open pipe 1, between the contact tips 31a and 31b and the welding stand 40, so as to be able to photograph the downstream side of the welding stand 40 in the welding direction. This camera is used to photograph the heating and melting of both edges 202a and 202b of the open pipe 1 and their subsequent pressing and welding by the squeeze rolls 41a and 41b. The position of the welding imaging device 12 is adjusted so that the welding point 205, the V convergence point 204 (described later), and the roll centers of the squeeze rolls 41a and 41b are included in the welding image 20 captured by the welding imaging device 12. The camera may be either a color image camera or a monochrome image camera. In addition to the camera described above that takes images from the outer surface of the open pipe 1, the welding imaging device 12 may also have another camera positioned on the inner surface of the open pipe that takes images from the inner surface of the open pipe, capturing the welding point 205, the V convergence point 204, and the area including the roll center.

[0032] The welding imaging device 12 also includes adjusters such as a zoom lens and an exposure adjuster for adjusting the optical system. The adjusters should have a field of view of 100 mm × 40 mm and a resolution of 100 μm / pixel or higher. A resolution of 50 μm / pixel or higher is more preferable. The camera should preferably have 1920 × 1080 pixels or more. If the resolution is lower than 100 μm / pixel, the detection accuracy of the V convergence point 204 and the welding point 205 may deteriorate. Furthermore, electric resistance welded pipes may be welded at speeds exceeding 100 m / min. In such cases, it is preferable to set the frame rate to 20 fps or higher in order to capture any desired point at least once within the 100 mm field of view. If the frame rate is less than 20 fps, areas of the welded section of the electric resistance welded pipe may not be subject to image analysis, potentially leading to missed welding defects.

[0033] The welding control device 100 is a welding control device for electric resistance welded pipes manufactured by bending a steel plate or steel strip in the circumferential direction and joining the two edges 202a and 202b to form an open pipe 1. Subsequently, electric resistance welded pipes are manufactured by upset electric resistance welding on both edges 202a and 202b of the joined open pipe 1. The welding control device 100 also includes an edge temperature detection unit 122 before electric resistance welding, an edge temperature ratio calculation unit 125, a molten metal outflow area calculation unit 133, a molten metal outflow area difference calculation unit 134, and a misalignment determination unit 141.

[0034] The pre-weld edge temperature detection unit 122 detects the outer surface temperature To, inner surface temperature Ti, and maximum temperature Tp of one of the two edge portions 202a and 202b based on information about the temperature distribution in the thickness direction of at least one of the edge portions 202a (202b). The maximum temperature Tp is the maximum value of the temperature distribution obtained by subtracting the outer surface temperature To and the inner surface temperature Ti from the temperature distribution in the thickness direction, and is the highest temperature among those maximum values. In detecting the maximum temperature Tp, time averaging is performed on the detected temperature distribution in the thickness direction, and only the maximum values ​​that exceed a predetermined allowable temperature range for the averaged temperature distribution in the thickness direction are detected. There are methods, but are not limited to, such as setting the highest temperature among the maximum values ​​as the maximum temperature Tp. The maximum temperature Tp is affected by the welding power and the misalignment amount of both edge portions 202a and 202b, and becomes larger as the welding power or misalignment amount increases. The misalignment amount refers to the degree of misalignment, that is, the magnitude of the displacement between the centers of both edge portions 202a and 202b in the wall thickness direction of the open tube 1. Furthermore, even when no misalignment occurs between the two edge portions 202a and 202b, the maximum temperature Tp may be observed in the end face temperature distribution. This is due to the influence of the surface properties of the end face. In other words, it is due to the slitting process at both ends in the width direction of the steel plate or strip, or the edge damage received from the roll during the forming of the steel plate or strip into a cylindrical shape. Thus, during the forming of the steel plate or strip into a cylindrical shape, the maximum temperature Tp is generated when high-frequency heating is concentrated on minute protrusions on the end face. If such a protrusion on the end face is minute, it does not hinder the discharge of molten metal during welding, but if the protrusion becomes large, abnormal areas occur in the temperature distribution of the end face, hindering the discharge of molten metal. The edge temperature ratio calculation unit 125 calculates the first temperature ratio Tp / To, which is the ratio of the outer surface temperature To to the maximum temperature Tp. Furthermore, the second temperature ratio Tp / Ti, which is the ratio of the inner surface temperature Ti to the maximum temperature Tp, is calculated.

[0035] The molten metal outflow area calculation unit 133 calculates the areas Sa and Sb of molten metal flowing out of each edge portion 202a and 202b to the outside of the pipe, respectively, based on the welded area image 20. The welded area image 20 includes both edge portions 202a and 202b of the open pipe 1 heated by high-frequency current, and the welding point 205 where welding begins by bringing the two edge portions 202a and 202b of the open pipe 1 together. Preferably, the welded area image 20 includes at least three-quarters of the length upstream from the welding point 205 to the contact tips 31a and 31b in the welding direction (longitudinal direction). This is because, even if molten metal is identified from the welded area image 20 downstream of the welding point 205 in the welding direction and its area is calculated, it is not possible to distinguish which of the two edge portions 202a and 202b the molten metal flowed out from. In other words, in this embodiment, the area S of molten metal flowing out from each edge portion 202a, 202b refers to the area S of molten metal flowing out from each edge portion 202a, 202b to the pipe surface upstream of the welding point 205, including the welding point 205. The molten metal flow area calculation unit 133 extracts two straight lines La and Lb that converge along each edge portion 202a, 202b based on the weld image 20. Furthermore, the molten metal flow area calculation unit 133 detects the longitudinal positions d1 and d2 of the open pipe 1 where molten metal begins to flow out from each edge portion 202a, 202b to the outside of the pipe, based on the weld image 20.

[0036] The molten metal outflow area difference calculation unit 134 calculates the area difference ΔS of the respective areas Sa and Sb of molten metal flowing out of each edge portion 202a and 202b to the outside of the pipe.

[0037] The misalignment determination unit 141 determines the quality of the electric resistance weld conditions based on information such as the outer surface temperature To, inner surface temperature Ti, maximum temperature Tp, and area difference ΔS of the edge portion 202a.

[0038] Furthermore, the welding control device 100 may also have an output unit 142 that outputs the judgment result from the misalignment determination unit 141.

[0039] The welding management device 100 includes, for example, an input unit 110, which includes an edge temperature distribution data input unit 111 and a weld area imaging data input unit 112. The welding management device 100 acquires edge temperature distribution information obtained by the edge temperature information acquisition device 11 through an input operation using the edge temperature distribution data input unit 111. The welding management device 100 also acquires a weld area image 20 of the weld area captured by the weld area imaging device 12 through an input operation using the weld area imaging data input unit 112.

[0040] The welding management device 100 is composed of a general-purpose computer such as a workstation or personal computer, and has calculation processing functions by a CPU, image processing functions by a GPU, and various memory functions such as ROM and RAM as an example of the storage unit 143 described later. In addition, the welding management device 100 is equipped with a recording medium such as a hard disk connected by a data communication terminal, and output units such as a graphic display device and an alarm device.

[0041] In the welding management device 100, the edge temperature distribution processing unit 121 calculates the first temperature ratio Tp / To and the second temperature ratio Tp / Ti using a memory that stores processing programs and a CPU that executes the processing programs. It also extracts the larger of the two values, the first temperature ratio Tp / To and the second temperature ratio Tp / Ti. Furthermore, the welding management device 100 calculates the respective areas Sa and Sb of molten metal flowing from each edge portion 202a and 202b to the pipe surface, and the area difference ΔS, in the welding image processing unit 131. Then, based on this information of the first temperature ratio Tp / To or the second temperature ratio Tp / Ti and the area difference ΔS, the misalignment determination unit 141 determines whether the electric resistance weld conditions are good or bad.

[0042] The configuration and functions of the welding control device 100 will be described in more detail.

[0043] The edge temperature distribution processing unit 121 includes an edge temperature detection unit 122 before electric resistance welding and an edge temperature ratio calculation unit 125.

[0044] The pre-electric resistance weld edge temperature detection unit 122 detects the temperature distribution in the thickness direction from the outer surface to the inner surface of the pipe of at least one edge portion 202a (202b) heated by the high-frequency current. The pre-electric resistance weld edge temperature detection unit 122 may include a spatial coordinate calculation unit 123 and a thickness direction temperature distribution detection unit 124.

[0045] The spatial coordinate calculation unit 123 calculates coordinates in three-dimensional space based on the pixel information of edge portions 202a and 202b, which contain temperature distribution information for a predetermined area, i.e., the temperature detection range, for obtaining temperature distribution information. Although not particularly limited, the spatial coordinate calculation unit 123 can calculate spatial coordinates based on image data that can be displayed as two-dimensional coordinates. The spatial coordinate calculation unit 123 sets X and Y coordinates for the image itself within the two-dimensional image data, and further sets a Z coordinate in the depth direction of the image, thereby treating the image data as three-dimensional data.

[0046] Furthermore, the thickness-direction temperature distribution detection unit 124 detects the temperature distribution at a preset position along the length of the pipe. The thickness-direction temperature distribution detection unit 124 detects at least the outer surface temperature To, the inner surface temperature Ti, and the highest temperature Tp in the temperature distribution in the thickness-direction excluding the outer and inner surfaces of the edge portions 202a and 202b.

[0047] The edge temperature ratio calculation unit 125 calculates the first temperature ratio Tp / To and the second temperature ratio Tp / Ti for each edge portion 202a, 202b of the open pipe 1 at a preset position, i.e., a specified position. The specified position is preferably, for example, one of the locations in the region between the welding point 205 and the contact tips 31a, 31b in the welding direction (longitudinal direction), at least up to three-quarters of the region upstream from the welding point 205.

[0048] The welding control device 100 performs the series of processes described above in the edge temperature distribution processing unit 121.

[0049] The welding image processing unit 131 includes a pipe edge image detection unit 132, a molten metal outflow area calculation unit 133, and a molten metal outflow area difference calculation unit 134.

[0050] In parallel with the processing in the edge temperature distribution processing unit 121 described above, the pipe edge image detection unit 132 extracts two straight lines La and Lb that converge along the edges 202a and 202b from the welded area image 20. The welded area image 20 includes both edges 202a and 202b of the open pipe 1 and the welding point 205 where the two edges 202a and 202b of the open pipe 1 meet and welding begins. It also extracts the boundary line of the heated portion 201 of the edges 202a and 202b that have been heated by high-frequency heating. Here, the boundary line of the heated portion 201 means the boundary between the red-hot heated portion 201 and the base material that has not been heated. This boundary is identified by edge detection that performs a differential calculation on the brightness of the heated portion 201, but is not limited to this. The welded area image 20 described above is obtained by the welded area imaging device 12.

[0051] The molten metal outflow area calculation unit 133 calculates the areas Sa and Sb of molten metal outflowing from each edge portion 202a and 202b to the outside of the pipe. Here, the method for calculating the area S of the molten metal is not limited. For example, one method is to calculate the total number of pixels occupied by the heating portion 201, which is shown in red in a color image, or in white in a monochrome image. In this case, the area S is calculated for at least three-quarters of the region upstream from the welding point 205 in the region between the welding point 205 and the contact tips 31a and 31b in the welding direction (longitudinal direction). Alternatively, one method is to draw a straight line perpendicular to the welding direction passing through an arbitrary point, for example, the welding point 205, and detect the distance between the outflowing molten metal 206 at the edge portions 202a and 202b and the welding point 205 along that line. Then, the area S of the outflowing molten metal 206 crossing the line per unit time is calculated using the method of area approximation. Here, if the distance between the molten metal 206 flowing out at the edges 202a and 202b and the welding point 205 is shorter than the boundary of the red-hot heated portion 201, and the boundary of the molten metal 206 flowing out cannot be detected, then the area S may be set to 0.

[0052] The molten metal outflow area difference calculation unit 134 calculates the area difference ΔS of the respective areas Sa and Sb of molten metal flowing out of the pipe from each edge portion 202a and 202b.

[0053] The welding management device 100 performs the series of processes described above in the welding image processing unit 131.

[0054] Furthermore, the welding management device 100 performs welding management processing such as determining misalignment based on information of the first temperature ratio Tp / To or the second temperature ratio Tp / Ti and the area difference ΔS using the misalignment determination unit 141, and outputting the determination result using the output unit 142.

[0055] Here, the welding management processing procedure by the welding management device 100 will be described. Figure 5 is a flowchart of the welding management processing procedure by the welding management device 100 of this embodiment. In the flowchart of Figure 5, for example, when the operator gives an instruction to start the welding management processing to the edge temperature distribution data input unit 111, the process proceeds to step S1. Steps S1 to S5 are referred to as the edge temperature distribution processing steps. Also, when the operator gives an instruction to start the welding management processing to the weld area imaging data input unit 112, the process proceeds to step S6. Steps S6 to S9 are referred to as the weld area image processing steps. The processes of steps S1 to S5 and steps S6 to S9 may be performed simultaneously.

[0056] In step S1, the edge temperature distribution processing unit 121 acquires information from the edge temperature information acquisition device 11 about the two-dimensional temperature distribution over the entire thickness of at least one of the edge portions 202a and 202b at a predetermined longitudinal position before welding.

[0057] The edge temperature distribution processing unit 121 detects the two-dimensional temperature distribution information on the joint surface of the edge portions 202a and 202b, that is, the two-dimensional temperature distribution information in the longitudinal direction and the wall thickness direction of the pipe, from the temperature distribution information including the captured image information. With this, the processing of step S1 is completed, and the welding management process proceeds to the processing of step S2.

[0058] In step S2, the spatial coordinate calculation unit 123 (spatial coordinate calculation unit for temperature detection range 123) detects multiple coordinate standard points from the image information of the two-dimensional temperature distribution acquired in step S1. It also performs spatial coordinate transformation from pixels to units of length. The image information is image information captured by a camera, such as a CCD camera, attached to the edge temperature information acquisition device 11.

[0059] The coordinate standard points referred to here are preferably markers whose coordinate positions or the distance between each standard point are self-evident, but this is not required. The spatial coordinate calculation unit 123 detects the distance between any two standard points and performs a spatial coordinate transformation within the image information of the temperature distribution information by inputting the actual spatial distance between the standard points. At the same time, the spatial coordinate calculation unit 123 sets the origin of the 2D coordinate system at an arbitrary position in the image information of the temperature distribution information. The spatial coordinate calculation unit 123 may also derive in advance the calculation formulas necessary to transform coordinates from pixels to units of length. With this, the processing in step S2 is completed, and the welding management process proceeds to the processing in step S3.

[0060] In step S3, the thickness-direction temperature distribution detection unit 124 (the thickness-direction temperature distribution detection unit 124 at the specified position) detects the temperature distribution in the thickness direction of the edge portions 202a and 202b at any position in the longitudinal direction, along with their coordinate values, based on the temperature distribution information after the spatial coordinate transformation process.

[0061] The position in the longitudinal direction is not particularly limited. For example, it may be any position from 3 mm in the opposite direction to the welding direction relative to the center of the squeeze rolls 41a and 41b to an intermediate position between the center of the squeeze rolls 41a and 41b and the contact tip 31 or work coil (not shown). Note that the position 3 mm in the opposite direction to the welding direction relative to the center of the squeeze rolls 41a and 41b mentioned above means a position 3 mm downstream from the center of the squeeze rolls 41a and 41b in the welding direction.

[0062] The temperature distribution detection unit 124 detects the temperature distribution within a range of ±0.5 mm in the longitudinal direction relative to a preset position in the longitudinal direction of the pipe, and the temperature distribution detection unit 124 detects the entire thickness of the edge portion.

[0063] The outer and inner surface corners of edge portions 202a and 202b tend to heat up more easily than flat areas other than the corners due to the skin effect unique to high-frequency heating.

[0064] Therefore, the temperature distribution in the wall thickness direction will have peaks at the corners of the outer and inner surfaces of the edges 202a and 202b. Due to this characteristic, the distance between the peak detected at the outer surface position of the edges 202a and 202b and the peak detected at the inner surface position of the edges 202a and 202b is determined to be the wall thickness of the pipe. If the error between the determined pipe wall thickness (determined pipe wall thickness value) and the previously measured pipe wall thickness (actual wall thickness) is within ±3%, then omissions in the wall thickness temperature distribution and the acquisition of temperature distributions other than the wall thickness can be excluded, and it is determined that the temperature distribution measurement result has obtained sufficient accuracy. If the above error is not within ±3%, the field of view of the edge temperature information acquisition device 11 is adjusted, and the processing of steps S1 to S3 is performed again, and repeated until the above error is within ±3%. With this, the processing of step S3 is completed, and the welding management process proceeds to the processing of step S4.

[0065] In step S4, the pre-electric welding edge temperature detection unit 122 extracts the outer surface temperature To and inner surface temperature Ti based on the temperature distribution information of at least one of the two edge portions 202a (202b) of the open pipe 1.

[0066] Specifically, the pre-electric welding edge temperature detection unit 122 (thickness direction temperature distribution detection unit 124) extracts the temperature at the center of the peak of the temperature information detected at the outer surface position of the edge portions 202a and 202b in step S3 as the outer surface temperature To. Similarly, in step S3, the temperature at the center of the peak of the temperature information detected at the inner surface position of the edge portions 202a and 202b in step S3 is extracted as the inner surface temperature Ti. The temperature at the center of the peak refers to the temperature at the apex of each peak detected in step S3.

[0067] Furthermore, the pre-electric resistance welding edge temperature detection unit 122 (thickness direction temperature distribution detection unit 124) extracts the maximum temperature values ​​excluding the outer surface temperature To and the inner surface temperature Ti. The pre-electric resistance welding edge temperature detection unit 122 extracts the highest temperature among these maximum values ​​as the maximum temperature Tp. Figure 6 shows the temperature distribution from which the outer surface temperature To, inner surface temperature Ti, and maximum temperature Tp have been extracted. In extracting the maximum temperature Tp, time averaging is performed on the temperature distribution in the thickness direction, and only the maximum values ​​that exceed a predetermined allowable temperature range for the averaged temperature distribution in the thickness direction are extracted. Then, the highest temperature among these is set as the maximum temperature Tp, although this is not limited to this method. The allowable temperature range can be determined, for example, by determining the temperature difference between the average value of temperatures T1 and T2 at the rising ends of the convex temperature distribution showing the maximum value and the maximum value, in the thickness direction temperature distribution, but this is not limited to this method. Furthermore, the positions of temperatures T1 and T2 at the rising ends of the convex temperature distribution showing the maximum value can be determined from the temperature gradient before and after the convex temperature distribution showing the maximum value, or by manually specifying the position, but are not limited to these methods. The calculation of the maximum value can be done using methods such as the second derivative method, but are not limited to this method. If no maximum value exists, the highest temperature Tp is set to 0.

[0068] This completes the process in step S4, and the welding control process proceeds to step S5. Note that the process in step S4, which extracts the outer surface temperature To, the inner surface temperature Ti, and the highest temperature Tp, corresponds to the pre-electric resistance welding edge temperature detection process.

[0069] In step S5, the edge temperature ratio calculation unit 125 calculates the first temperature ratio Tp / To and the second temperature ratio Tp / Ti between the outer surface temperature To and inner surface temperature Ti of the edges 202a and 202b extracted as described above, and the maximum temperature Tp. The edge temperature ratio calculation unit 125 then extracts the larger of the first temperature ratio Tp / To and the second temperature ratio Tp / Ti and stores it in the storage unit 143. With this, the process of step S5 is completed, and the welding management process proceeds to step S10. Note that the relative magnitudes of the outer surface temperature To and the inner surface temperature Ti change depending on the butt joint conditions of both edges 202a and 202b immediately before electric resistance welding is performed. A large first temperature ratio Tp / To or second temperature ratio Tp / Ti indicates the presence of a convex portion on the end face of the edges 202a and 202b, and that heating is concentrated on this convex portion due to the skin effect. Furthermore, this significantly increases the maximum temperature Tp, and the temperature difference between the temperature at the end with the lower temperature (To, Ti) of the inner and outer surface temperatures of the edge portions 202a and 202b, and the maximum temperature Tp, becomes larger. In particular, burrs and burrs from slitting at both ends in the width direction of the steel plate or strip, and edge damage received from the roll during cylindrical shaping, can usually be reduced by adjusting the end face characteristics during fin formation of the fin pass roll, thereby minimizing the convex shape of the end face. Therefore, the effect of the convex shape of the end face on the outflow of weld metal in electric resistance welding can be neutralized. However, if fin formation at both ends is insufficient, the convex shape of the end face cannot be reduced, resulting in an uneven temperature distribution on the end face. In addition, an increase in misalignment also increases the first temperature ratio Tp / To or the second temperature ratio Tp / Ti. For these reasons, a large first temperature ratio Tp / To or the second temperature ratio Tp / Ti indicates an uneven temperature distribution on the end face, making it easier for the outflow of molten metal to be inhibited.

[0070] In step S6, the pipe edge image detection unit 132 of the welding image processing unit 131 detects the edges 202a and 202b that are heated by high-frequency heating, based on the weld image 20 captured by the welding imaging device 12. Here, the differential method is used for edge detection, but it is not limited to this method.

[0071] For example, first, the pipe edge image detection unit 132 uses the weld image 20 shown in Figure 1, captured by the camera, to detect the edges 202a, 202b, the heated section 201, and the edges of the molten metal flowing out of the pipe from the change in brightness around the heated section 201. At the same time, it performs a conversion process from the number of pixels in the weld image 20 to units of length. Here, a two-axis XY coordinate system is used with the lower left corner of the weld image 20 in Figure 1 as the origin, and the length is treated as millimeters, but this is not limited to this. In the conversion process from the number of pixels to units of length, the number of pixels per 100 mm is detected by first photographing a standard sample such as a gauge in the same field of view, and the conversion process from the number of pixels to length is performed. With this, the processing in step S6 is completed, and the welding management process proceeds to the processing in step S7.

[0072] In step S7, a welding point extraction unit (not shown) extracts welding points 205 where edges 202a and 202b meet from the welding image 20 described above. For example, first, approximate lines La and Lb are calculated from edges 202a and 202, and a V-convergence point 204 is extracted from the intersection of these two lines. Specifically, lines La and Lb that approximate the end faces of both edges 202a and 202b of the open pipe 1 are generated by the least squares method from multiple points detected on each edge 202a and 202b. It is preferable that five or more points are required to generate the lines La and Lb. Then, welding points 205 located downstream in the welding direction are extracted based on this V-convergence point 204. For example, the heated area 201 downstream from the V-convergence point 204 in the welding direction is detected based on the change in brightness. In other words, areas with low brightness are determined to be openings 202, and areas with high brightness continuously downstream in the welding direction are determined to be weld beads 203 where welding has been performed. The brightness threshold and the number of consecutive pixels considered to be weld beads 203 are arbitrary. Here, the position furthest downstream of the openings 202 in the welding direction is extracted as the welding point 205. The time required to determine the welding point 205 is preferably one cycle or more of the squeeze roll (SQ roll). With this, the processing of step S7 is completed, and the welding management process proceeds to the processing of step S8.

[0073] In step S8, the area S of molten metal flowing out of the pipe in the circumferential direction from both heated, red-hot edges 202a and 202b upstream of the welding point 205 extracted in step S7 is calculated. Here, similar to the process in step S6, the molten metal flow area calculation unit 133 of the welding image processing unit 131 calculates the area S of the flowing molten metal based on the welding image 20 captured by the welding imaging device 12. The area S is calculated for at least three-quarters of the region upstream of the welding point 205 in the welding direction (longitudinal direction) between the welding point 205 and the contact tips 31a and 31b.

[0074] The molten metal outflow area calculation unit 133, for example, uses the captured weld image 20 to detect molten metal outflow from both edge portions 202a and 202b based on changes in brightness around the heated portion 201. The number of pixels of the detected molten metal is converted into an area to calculate the molten metal outflow areas Sa and Sb from each edge portion 202a and 202b, respectively. This completes the process in step S8, and the welding management process proceeds to step S9. Note that the process in step S8, which calculates the molten metal outflow area S, corresponds to the molten metal outflow area calculation process.

[0075] In step S9, the molten metal outflow area difference calculation unit 134 of the welding image processing unit 131 calculates the difference (area difference ΔS) between the outflow areas Sa and Sb calculated in step S8. The area difference ΔS is an absolute value. With this, the process of step S9 is completed, and the welding management process proceeds to step S10. Note that the process in step S9 in which the area difference ΔS is calculated corresponds to the molten metal outflow area difference calculation process.

[0076] In step S10, the misalignment detection unit 141 performs misalignment detection. This is done after the completion of the processes in step S5 and step S9. The misalignment detection unit 141 performs misalignment detection based on the outer surface temperature To or inner surface temperature Ti of the edge portions 202a and 202b at the specified position, the first temperature ratio Tp / To or second temperature ratio Tp / Ti between the inner surface temperature and the maximum temperature Tp, and the area difference ΔS. The calculation of the first temperature ratio Tp / To, the second temperature ratio Tp / Ti, and the area difference ΔS is performed within a predetermined time range, and the average value of each value is calculated. There is no particular requirement for the number of data points required to calculate the average value, but it is preferable to have three or more data points. The time for performing the above processing is preferably 0.15 seconds or more, and more preferably one squeeze roll cycle or more.

[0077] The misalignment determination unit 141 determines that no misalignment has occurred in the electric resistance weld if the area difference ΔS is less than or equal to a predetermined threshold for area difference ΔS, and the larger of the first temperature ratio Tp / To and the second temperature ratio Tp / Ti is less than or equal to a predetermined upper limit. The threshold for the area difference ΔS and the upper limits for each temperature ratio Tp / To and Tp / Ti can be determined in advance through experimentation. Furthermore, the determination that no misalignment has occurred means that the edges 202a and 202b are facing each other directly. Therefore, the determination that no misalignment has occurred can be interpreted as meaning that there are no welding defects, or that there are no welding defects.

[0078] As a specific example of a method for determining misalignment in electric resistance welding, an offline evaluation test of the weld is performed using steel pipes obtained under various welding conditions. The relationship between the characteristics of the obtained weld, the outer surface temperature To or inner surface temperature Ti of the edge portions 202a and 202b at a specified location, the first temperature ratio Tp / To or the second temperature ratio Tp / Ti between the maximum temperature Tp and the area difference ΔS is clarified in advance. More specifically, within the allowable range of the area difference ΔS, the upper limit of the first temperature ratio Tp / To or the second temperature ratio Tp / Ti between the outer surface temperature To or inner surface temperature Ti of the edge portions 202a and 202b and the maximum temperature Tp is determined experimentally in advance. Similarly, in order to distinguish the effect of misalignment and thickness difference, the threshold (upper limit) of the area difference ΔS is also determined experimentally in advance.

[0079] An offline evaluation test of welded joints can be performed by observing the C-section of the electric resistance welded portion (referred to as the weld) using an optical microscope. For example, the C-section of the weld is polished, and the polished C-section of the weld is etched with a picric acid etchant. This makes metal segregation lines 209 appear in the C-section of the weld, as shown in Figure 7. At the weld (i.e., the weld point 205), when each edge portion 202a and 202b is upset by a squeeze roll, the molten metal is pushed out toward the outer surface and inner surface of the pipe, causing it to bulge. When the molten metal pushed toward the inner and outer surfaces of the pipe solidifies, segregation lines 209 are formed along the solidified metal. Therefore, as shown in Figure 7, the segregation lines 209 in the weld extend in an arc shape from approximately the center of the pipe in the thickness direction toward the outer surface of the pipe, and also extend in an arc shape from approximately the center of the pipe in the thickness direction toward the inner surface of the pipe. Therefore, the portion between the segregation line 209 extending from the central part to the outer surface of the pipe in the thickness direction and the segregation line 209 extending from the central part to the inner surface of the pipe in the thickness direction can be considered as the central parts c1 and c2 of each edge portion 202a and 202b of the open pipe 1 in the thickness direction. The distance between the central parts c1 and c2 in the thickness direction is the misalignment amount Δh described above. Here, the allowable amount of misalignment amount Δh may be predetermined according to the desired characteristics of the weld. The larger the misalignment amount Δh, the worse the characteristics of the weld. For this reason, upper and lower limits of the misalignment amount Δh that satisfy the target characteristics of the weld are predetermined, and the range between these upper and lower limits is the allowable amount described above. Note that the characteristics of the weld refer to the joint strength of the weld. As a test method for measuring joint strength, one example is ultrasonic testing, also known as flattening testing, which detects oxides in the weld (in accordance with JIS G 0583:2021 "Automatic Eddy Current Testing Method for Steel Pipes"). Another example of a test method is clarifying the fatigue characteristics of the weld (JIS Z 2273:2023 "General Rules for Fatigue Testing Methods for Metallic Materials"). Furthermore, another example of a test method is Charpy impact testing, in which a test piece is cut from the weld and tested (in accordance with JIS Z 2242:2023 "Charpy Impact Testing Method for Metallic Materials").The boundary line between the welded edges 202a and 202b is referred to as the weld line, and in Figure 7, the weld line is labeled with the symbol "210".

[0080] An example of how to set the upper limit of the first temperature ratio Tp / To or the second temperature ratio Tp / Ti between the outer surface temperature To or inner surface temperature Ti of the edge portions 202a and 202b at the specified location and the maximum temperature Tp is described below, but this is not an exhaustive example.

[0081] The temperature measurement location is on each edge portion 202a, 202b, in the welding direction (longitudinal direction), within the region between the welding point 205 and the contact tips 31a, 31b, at least up to three-quarters of the way upstream from the welding point 205. The edge temperature information acquisition device 11 measures the temperature of the edge portions 202a, 202b at a position on the molding machine side of the welding point 205, i.e., on the upstream side (opposite side of the welding direction), under various welding conditions. The edge temperature information acquisition device 11 measures the temperature at a position where the outer surface temperature To and inner surface temperature Ti of the edge portions 202a, 202b are below a predetermined value.

[0082] For example, temperature measurements are taken at a position where the temperature difference ΔT (melting point (°C) - To, Ti (°C)) between the outer surface temperature To and inner surface temperature Ti of the edge portions 202a and 202b is 50°C or more.

[0083] If the temperature difference ΔT between the outer surface temperature To or inner surface temperature Ti of the edges 202a and 202b and their melting points is less than 50°C, the outer and inner surfaces of both edges 202a and 202b may be temporarily heated to their melting points due to disturbances during operation. In that case, the temperature rise will saturate, and the relationship between the area difference ΔS and the temperature distribution of the end faces of both edges 202a and 202b will become difficult to observe. In the temperature measurement described above, the temperature difference ΔT (°C) is preferably 200°C or less, and more preferably 100°C or less.

[0084] Next, electric resistance welded (ERW) welding is performed while varying the misalignment amount Δh of each edge portion 202a and 202b of the steel strip. One method for adjusting the misalignment amount Δh is to move the roll position of the edge forming roll in the width direction of the steel strip in the edge forming process upstream of the forming machine to adjust the asymmetry of the bending deformation amount of the steel strip. While adjusting the misalignment amount Δh in this way, the welding control device 100 calculates the outer surface temperature To and inner surface temperature Ti of the edges 202a and 202b at the specified positions, the first temperature ratio Tp / To and the second temperature ratio Tp / Ti, and the area difference ΔS. It also calculates the average value of these values. These are performed based on information obtained from the edge temperature information acquisition device 11 and the weld part imaging device 12. It is preferable to calculate the average from five or more image data points. A Charpy impact test of a V-notch test specimen as described in JIS Z 2242:2023 is performed on the ERW pipes obtained from each of the above ERW welds.

[0085] Figure 8 shows the pass / fail results for electric resistance welded joints according to the second temperature ratio Tp / Ti and the area difference ΔS. The threshold (upper limit) of the area difference ΔS is indicated by a dotted line extending vertically in Figure 8. In Figure 8, welds with an average absorbed energy of 27 J or more from five full-size Charpy impact test pieces cut from the weld at a test temperature of 0°C are marked as pass ("○"), and those with an average absorbed energy of less than 27 J are marked as fail ("×"). The misalignment judgment unit 141 determines the pass / fail boundary in this way and determines the upper limit of the second temperature ratio Tp / Ti corresponding to each area difference ΔS. Then, the maximum value of each second temperature ratio Tp / Ti obtained in this way is linearly approximated and set as the boundary of the pass range. As for the pass / fail boundary of weld joint quality, one method is to set a boundary line which is an arbitrary function of adjacent area differences ΔS and record it in the storage unit 143. Another method is to pre-set an upper limit for the second temperature ratio Tp / Ti according to the area difference ΔS and record it in the memory unit 143, but this is not limited to this method. In Figure 8, the upper limit for the second temperature ratio Tp / Ti is shown as a dotted line as a linear function of adjacent area differences ΔS.

[0086] Using these boundary conditions, if the area difference ΔS of any welding condition is less than or equal to the threshold (upper limit) of the area difference ΔS, and the second temperature ratio Tp / Ti is within the acceptable range of the weld, the misalignment determination unit 141 determines that there is no misalignment in the electric resistance weld. On the other hand, even if the area difference ΔS of any welding condition is less than or equal to the threshold (upper limit) of the area difference ΔS, if the second temperature ratio Tp / Ti is not within the acceptable range of the weld, it is determined that misalignment has occurred in the electric resistance weld. The acceptable range mentioned above refers to the range in the vertical direction of Figure 8 that is less than or equal to the upper limit of the second temperature ratio Tp / Ti shown by the dotted line in Figure 8.

[0087] Here, we will explain how to calculate the threshold (upper limit) of the area difference ΔS. Electric resistance welding is performed while varying the thickness difference of each edge portion 202a and 202b of the steel strip. One method for adjusting the thickness difference of each edge portion 202a and 202b is to adjust the thickness difference by tapering one of the edges 202a (202b) by grinding or other means. Electric resistance welding is then performed on the steel strip with the adjusted thickness difference in the same manner as described above. At that time, various measurement data are collected and analyzed. Specifically, the temperature distribution of each edge portion 202a and 202b is measured to calculate the first temperature ratio Tp / To and the second temperature ratio Tp / Ti, and the molten metal outflow areas Sa and Sb at each edge portion 202a and 202b are calculated to calculate the area difference ΔS. Furthermore, a Charpy impact test is performed on the electric resistance welded pipe obtained in this way to determine the quality of the electric resistance welded joint. The misalignment detection unit 141 identifies the area difference ΔS that causes deterioration in the quality of the electric resistance welded joint due to the difference in wall thickness, and sets this as the threshold (upper limit) of the area difference ΔS.

[0088] The results obtained from these processes can be recorded in the storage unit 143. With this, the process in step S10 is completed, and the welding management process proceeds to the process in step S11. The process in step S10, which determines whether or not there are misalignments based on the quality judgment of the electric resistance welding conditions, corresponds to the misalignment determination process.

[0089] In step S11, the output unit 142 outputs the determination of whether or not there is misalignment in the electric resistance weld obtained in step S10 to an external source. Preferably, in order to allow the operator to recognize the determination result, the output unit 142 is configured to output the determination result to a graphic device, alarm device, etc., provided in the welding management device 100. With this, the process of step S11 is completed, and the series of welding management processes is finished.

[0090] According to this embodiment, by analyzing the temperature distribution on the end faces of each edge portion 202a, 202b during electric resistance welding and the welded area image 20, misalignment of each edge portion 202a, 202b and thickness difference between each edge portion 202a, 202b are distinguished and misalignment is detected. Therefore, it is possible to suppress false detections where a thickness difference occurs when it is not misalignment, and to suppress over-detection of misalignment as a result. In addition, when the second temperature ratio Tp / Ti at the area difference ΔS under any welding conditions is within the above-mentioned acceptable range, it is determined that there is no harmful misalignment, that is, no misalignment has occurred. Therefore, the occurrence of welding defects can be suppressed.

[0091] It should be noted that the present invention is not limited to the embodiments described above, and other embodiments, examples, and operational techniques made by those skilled in the art are all included in the scope of the present invention, as long as they do not depart from the spirit of the invention. For example, instead of the second temperature ratio Tp / Ti, the quality of the electric resistance welding conditions, i.e., the presence or absence of misalignment, may be determined based on the first temperature ratio Tp / To and the area difference ΔS. In this case, the same effects and advantages as those of the embodiments described above can be obtained.

[0092] The welding control device 100 for electric resistance welded pipes has been described above as an embodiment of this invention. This embodiment also provides a welding control method using the welding control device 100 described above, a method for manufacturing electric resistance welded pipes including this welding control method, and a welding control system having the welding control device. In the method for manufacturing electric resistance welded pipes, a steel plate or steel strip is subjected to continuous bending in the circumferential direction, and both edge portions 202a and 202b are butted together to form an open pipe 1. Then, electric resistance welded pipes are manufactured by continuous upset electric resistance welding on both edge portions 202a and 202b of the butted open pipe 1. Furthermore, during electric resistance welding, welding control is performed by the process (welding control method) performed by the welding system described above. [Examples]

[0093] For various electric resistance welded pipes with a pipe thickness of 16 mm and an outer diameter of φ406 mm, first, in order to derive the allowable range of welding conditions, a threshold (upper limit) of the second temperature ratio Tp / Ti at an area difference ΔS for any given welding condition was derived. In other words, a threshold (upper limit) of the second temperature ratio Tp / Ti corresponding to each area difference ΔS was derived. In the welding conditions of this embodiment, the outer surface temperature To of the edge portion was lower than the inner surface temperature Ti. In this embodiment, the position of the edge temperature information acquisition device 11, which measures the temperature distribution on the end face of each edge portion, was set to a position 30 mm upstream (opposite direction to the welding direction) from directly below the axis of the squeeze roll of the welding stand. Furthermore, the amount of bending deformation of both edges was adjusted by adjusting the edge bending during forming. In this way, the amount of misalignment of both edges was adjusted. To adjust the difference in wall thickness, one of the edges of the steel strip before forming into a cylindrical shape was tapered by grinding, thereby changing the wall thickness of the edge on one side. Electric resistance welding was performed at a welding speed of 15 m / min. In addition, in order to derive the upper limit of the second temperature ratio Tp / Ti, the smoothness of the surface characteristics of the end faces of each edge was adjusted by the amount of fin forming on the fin pass roll.

[0094] In various electric resistance welded (ERW) welding processes, a two-color thermometer camera was used to acquire two-dimensional images of the temperature distribution of the joint surface at the edge before welding. The frame rate was 20 fps, the number of pixels in the longitudinal direction of the pipe was 1920, the number of pixels in the thickness direction of the pipe was 1080, and the field of view in the longitudinal direction of the pipe was 50 mm. In addition, in various ERW welding processes, a CCD camera was used to acquire images of the area before and after the weld during welding. The frame rate was 20 fps, the number of pixels in the longitudinal direction of the pipe was 1920, and the field of view in the longitudinal direction of the pipe was 60 mm. From each of the acquired images, the second temperature ratio Tp / Ti (the inner surface temperature Ti of the edge at a specified position in each frame, and the highest temperature Tp in the thickness direction excluding the outer and inner surfaces) and the area difference ΔS were calculated. Of these calculated data, 100 data points were averaged to obtain the operational data for each welding condition.

[0095] Furthermore, Charpy impact tests using V-notch specimens as described in JIS Z 2242:2023 were performed on electric resistance welded pipes obtained from individual electric resistance welds. The absorbed energy of full-size Charpy impact specimens cut from the weld at a test temperature of 0°C was measured. This was done five times, and the average of the five measurement results was used as the quality data for the weld under each welding condition. The operational data and the quality data for the weld were reflected in maps and tables showing the relationship between the area difference ΔS and the second temperature ratio Tp / Ti. A pass / fail boundary was set for each welding condition, where a steel pipe with an absorbed energy of 27 J or more was considered a pass, and a steel pipe with an absorbed energy of less than 27 J was considered a fail. For example, the absorbed energy value of each Charpy impact specimen is reflected on a graph with the area difference ΔS on the horizontal axis and the second temperature ratio Tp / Ti on the vertical line. For each area difference ΔS, the quality data with the minimum absorbed energy among the quality data that are judged as pass is extracted. Then, a linear function of the second temperature ratio Tp / Ti was calculated, passing through adjacent quality data points (area difference ΔS) along the horizontal axis. This boundary line was defined as the upper limit of the second temperature ratio Tp / Ti. The boundary line is shown as a solid line in Figure 9. An example of the boundary line is expressed by the following equation (1). Second temperature ratio Tp / Ti=-1.2×10 -3 ×ΔS+0.99 ···(1) Furthermore, the area difference ΔS is 130 mm. 2 If it exceeds this value, it is a region where the effect of the thickness difference becomes apparent. Therefore, the threshold (upper limit) for the area difference ΔS is 130 mm. 2 This was done. In Figure 9, the threshold (upper limit) of the area difference ΔS is indicated by a dotted line extending vertically in Figure 9.

[0096] In this embodiment, the upper limit of the second temperature ratio Tp / Ti at an area difference ΔS that could not be measured in advance was determined using the upper limit of the second temperature ratio Tp / Ti at an area difference ΔS that was known before and after that point. Using a linear function equation that takes the known area difference ΔS as a function, interpolation calculations were performed to obtain the upper limit of the second temperature ratio Tp / Ti at an area difference ΔS that could not be measured. From the above, the allowable range of welding conditions was derived.

[0097] Next, an electric resistance welded pipe with a pipe thickness of 16 mm and an outer diameter of φ406 mm was manufactured. The welding speed was 15 m / min. The inner surface temperature Ti of the edge, the highest temperature Tp in the temperature distribution in the wall thickness direction excluding the outer and inner surfaces, and the area difference ΔS were measured and calculated in the same manner as in the embodiment described above.

[0098] Next, the welded section was cut out from the steel pipe after the weld bead had been removed, and the C-section of the welded section was polished. Then, etching with picric acid was performed to reveal the segregation lines. On the weld line of each edge, the portions between the segregation lines that extended in an arc shape from the center in the thickness direction of the steel pipe toward the inner or outer surface were defined as the central points c1 and c2 in the thickness direction of each edge. The distance from the inner surface of the steel pipe to each central point c1 and c2 was calculated by image analysis, and the difference between them was defined as the misalignment amount Δh.

[0099] Ten full-size Charpy impact test specimens were cut from each of the electric resistance welded pipes in Invention Examples 1-3 and Comparative Examples 1 and 2. Charpy impact tests were performed on the welded joints according to JIS Z 2242:2023, and the absorbed energy at a test temperature of 0°C was measured. For each of Invention Examples 1-3 and Comparative Examples 1 and 2, the percentage of steel pipes with an absorbed energy of 27 J or more out of the total number of Charpy impact tests (hereinafter referred to as the pass rate) was calculated, and the quality of the electric resistance welded joint was judged to be acceptable if the pass rate was 90% or higher. Acceptance means that the quality of the electric resistance welded joint is good and no misalignment has occurred.

[0100] Table 1 and Figure 9 show the area difference ΔS, the second temperature ratio Tp / Ti, and the Charpy impact test results for each of the electric resistance welded tubes for Invention Examples 1-3 and Comparative Examples 1-3. A "○" is marked in Table 1 if the Charpy impact test was passed, and a "×" is marked if it was failed.

[0101] [Table 1]

[0102] As shown in Table 1 and Figure 9, misalignment and thickness difference could be distinguished and misalignment detected. Furthermore, it can be seen that the quality of the welded parts in Invention Examples 1 to 3 all passed the test, while Comparative Examples 1 and 2 failed.

[0103] Invention Example 1 is an example of manufacturing an electric resistance welded pipe by adjusting the centering of the edge forming roll to satisfy the relationship between the allowable area difference ΔS and the second temperature ratio Tp / Ti, under constant molding conditions.

[0104] Invention Example 2 is an example of manufacturing an electric resistance welded pipe by adjusting the upper roll position of the squeeze roll to satisfy the relationship between the allowable area difference ΔS and the second temperature ratio Tp / Ti, while keeping the input power constant.

[0105] Invention Example 3 is an example of manufacturing electric resistance welded pipes by adjusting the upper roll position of the fin pass roll to satisfy the relationship between the area difference ΔS and the second temperature ratio Tp / Ti within an allowable range, while preventing rolling of the steel pipe in the circumferential direction during pipe manufacturing, under constant power input.

[0106] Comparative Examples 1-3 involved no welding control during electric resistance welding, only adjusting the welding power and visually inspecting the state of the discharged molten steel. In Comparative Example 1, the slit sag of the steel strip remained large, and no adjustments were made to the centering of the edge forming or the roll position of the fin pass roll, resulting in an area difference ΔS of 100 mm. 2 This is an example of manufacturing electric resistance welded pipes by adjusting the input power to achieve a specific result.

[0107] Comparative Example 2 shows that the slitting of the steel strip remained large, and the roll position of the fin pass roll was not adjusted, resulting in an area difference ΔS of 125 mm. 2 This is an example of manufacturing electric resistance welded pipes by adjusting the input power to achieve a specific result.

[0108] Comparative Example 3 is an example in which an electric resistance welded pipe was manufactured in the same manner as in Invention Example 1, except that the wall thickness of one of the edges to be welded together was approximately 2 mm thinner than the wall thickness of the other edge. [Industrial applicability]

[0109] As described above, by using the welding control device described in the present invention, it is possible to detect the stepping of the edge portion before electric resistance welding and provide electric resistance welded pipes with superior quality in the welded portion. [Explanation of symbols]

[0110] 1 Open tube 2. Fin pass roll 3. High-frequency oscillator 31, 31a, 31b Contact tips 40 Welding Stands 41a, 41b Squeeze Roll 42a, 42b Top Roll 10. Welding Management System 11. Edge temperature information acquisition device 12. Weld imaging device 100 Welding control device 110 Input Section 111 Edge temperature distribution data input section 112 Welding joint image data input section 121 Edge temperature distribution processing unit 122 Pre-weld edge temperature detection unit 123 Spatial Coordinate Calculation Unit 124 Thickness-direction temperature distribution detection unit 125 Edge temperature ratio calculation unit 131 Welding Image Processing Unit 132 Tube edge image detection unit 133 Molten Metal Outflow Area Calculation Unit 134 Molten Metal Outflow Area Difference Calculation Unit 141 Mismatch detection section 142 Output section 143 Storage section 20 Images of welded joints 201 Heating section 202 Opening Both edges of the 202a and 202b open tubes La, Lb straight line 203 Weld Bead 204 V convergence point (junction point) 205 welding points 206 Molten metal spill 209 Segregation lines 210 Welding line d1, d2: Starting point of molten metal outflow S, Sa, Sb Molten metal spill area ΔS: Difference in molten metal outflow area c1, c2 center

Claims

1. A welding control device for electric resistance welded pipes manufactured by bending a steel plate or steel strip in the circumferential direction, butting the two edges together to form an open pipe, and then performing upset welding on both edges of the butted open pipe, An electric resistance welded edge temperature detection unit detects, based on information about the temperature distribution in the thickness direction of at least one of the edges of the open pipe, the outer surface temperature of the one edge, and the maximum value of the temperature distribution obtained by subtracting the outer surface temperature and inner surface temperature of the one edge from the temperature distribution in the thickness direction of the one edge, and the highest temperature among the maximum values, A molten metal outflow area calculation unit calculates the outflow area of ​​molten metal flowing from each of the edges to the pipe surface based on a weld image of the region including both edges of the open pipe and the welding point where welding of both edges of the open pipe begins. A molten metal outflow area difference calculation unit calculates the difference in the area of ​​molten metal outflow from each of the two edge portions detected by the molten metal outflow area calculation unit to the pipe surface, A welding management device for electric resistance welded pipes, comprising a misalignment determination unit that determines misalignment of electric resistance welds based on a first temperature ratio of the outer surface temperature to the maximum temperature, or a second temperature ratio of the inner surface temperature to the maximum temperature, and the area difference.

2. The aforementioned misalignment detection unit determines that the area difference is less than or equal to a predetermined upper limit, and The electric resistance welded pipe welding management device according to claim 1, which determines that misalignment of the electric resistance weld has occurred when the first temperature ratio or the second temperature ratio when the aforementioned area difference occurs is below a threshold value of the first temperature ratio or the second temperature ratio corresponding to the area difference.

3. A welding control method for electric resistance welded pipes manufactured by bending a steel plate or steel strip in the circumferential direction, butting the two edges together to form an open pipe, and then performing upset welding on both edges of the butted open pipe, A pre-electric welding edge temperature detection step that detects the maximum value among the temperature distribution obtained by subtracting the outer surface temperature and inner surface temperature of the one edge from the temperature distribution in the thickness direction of the one edge, based on information of the temperature distribution in the thickness direction of at least one edge of the open pipe, and the highest temperature among the maximum values, A molten metal outflow area calculation step calculates the outflow area of ​​molten metal flowing from each of the edges to the pipe surface, based on a weld image of the region including both edges of the open pipe, taken from the outer or inner side of the open pipe, and the welding point where welding of both edges of the open pipe begins. A molten metal outflow area difference calculation step calculates the difference in the area of ​​molten metal outflow from each of the two edge portions to the pipe surface, which was calculated in the molten metal outflow area calculation step. A welding management method for electric resistance welded pipes, comprising a misalignment determination step for determining misalignment of electric resistance welds based on a first temperature ratio of the outer surface temperature to the maximum temperature, or a second temperature ratio of the inner surface temperature to the maximum temperature, and the area difference.

4. The aforementioned difference determination step is that the area difference is less than or equal to a predetermined upper limit, A welding control method for electric resistance welded pipes according to claim 3, wherein it is determined that misalignment of the electric resistance weld has occurred when the first temperature ratio or the second temperature ratio when the aforementioned area difference occurs is below a threshold value of the first temperature ratio or the second temperature ratio corresponding to the area difference.

5. A method for manufacturing an electric resistance welded pipe, comprising bending a steel plate or steel strip in the circumferential direction, butting the two edges together to form the open pipe, and then performing electric resistance welding on both edges of the open pipe, A method for manufacturing an electric resistance welded pipe, wherein welding control is performed during the electric resistance welded welding process according to the welding control method for electric resistance welded pipes described in claim 3 or 4.

6. A welding control device for electric resistance welded pipes according to claim 1 or 2, An edge temperature information acquisition device that acquires information on the temperature distribution of one of the two edges of the open tube, A welding management system for electric resistance welded pipes, comprising a welding area imaging device that images a region including both edges of the open pipe and the welding point where welding of both edges of the open pipe begins.

Images