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 perform a quality assessment of welding conditions from fin pass forming to electric resistance welded welding, thereby suppressing welding defects caused by the surface properties of the end face of the edge portion. [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, the inner surface temperature Ti, and the highest temperature Tp among the maximum values ​​of the edge portion; a molten metal outflow start position detection unit 133 that detects the molten metal outflow start positions d1 and d2 based on image information 20; a molten metal outflow start position difference calculation unit 134 that calculates the position difference Δd between the molten metal outflow start positions d1 and d2; and a welding state determination unit 141 that determines whether the electric resistance weld conditions are good or bad based on the first temperature ratio Tp / To, the second temperature ratio Tp / Ti and the position difference Δd.

Description

Technical Field

[0001] The present invention relates to a welding management device for an electric welded pipe, a welding management method for an electric welded pipe, a manufacturing method for an electric welded pipe, and a welding management system for an electric welded pipe, which can suppress welding defects caused by steps, scratches, etc. occurring at the edge portion of an open pipe immediately before electric welding of the electric welded pipe by performing image analysis on the edge portion of the open pipe.

Background Art

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

[0003] During electric welding, both edge portions described above are heated above the melting point by direct energization using a contact tip or induction current using an induction coil, and immediately thereafter, the end faces of both edge portions are upset by a welding roll (squeeze roll). At this time, oxides (penetrators) generated during the heating process of the edge portion of the steel plate or steel strip are caused to flow out to the inner and outer surfaces of the pipe by upsetting, that is, discharged to an unnecessary portion called the excess portion (bead) to suppress the occurrence of welding defects. After electric welding, the excess portion is cut off 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 the smooth discharge of the penetrator to the outside of the pipe. This requires not only precise welding conditions, such as the high-frequency current used in ERW, but also ensuring smooth surface texture at both edges being joined. If the surface texture of the edges is significantly poor, the skin effect (sometimes called the edge effect), a characteristic of high-frequency heating where heat concentrates at the corners of the heated object, results in an uneven temperature distribution at the edge surface. Therefore, conventionally, slitting or milling is performed on both edges of the steel plate or strip used in ERW pipes to smooth the edges. Subsequently, during fin pass forming, the edges are pressed against fin rolls to adjust the surface texture of the edge surfaces. If this adjustment of the edge surface texture by the fin rolls is insufficient, uneven shapes remain on the edge surface before ERW welding. In particular, if uneven lines remain along the length of the pipe on the edge surface, the discharge of the penetrator to the outside of the pipe is significantly hindered. These uneven grooves along the length of the pipe are caused by defects in slitting or sagging due to contact between the corners of the edge and the forming roll during roll forming. To prevent welding defects, it is necessary to manage the welding process while detecting the surface condition of these edges.

[0005] In the method for manufacturing electric resistance welded pipes disclosed in Patent Document 1, surface defects occurring on the edges of a slit steel strip are detected by an optical defect detector, and information on the presence or absence of surface defects is transmitted to the controller of the electric resistance welding apparatus. The controller performs electric resistance welding while controlling the heat input of the electric resistance welder and the upset force of the squeeze roll based on the information on the presence or absence of surface defects. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 3-18486 [Overview of the project] [Problems that the invention aims to solve]

[0007] The method for manufacturing electric resistance welded pipes disclosed in Patent Document 1 detects surface defects on the edge caused by slitting. Therefore, deterioration of the weld quality caused by these surface defects can be suppressed. However, in electric resistance welding, during fin pass forming, the edge of the slitted steel strip is pressed against a fin roll to adjust the surface properties of the end face of the edge. As a result, surface defects on the edge caused by slitting may be rendered harmless, and the method for manufacturing electric resistance welded pipes disclosed in Patent Document 1 had the problem of over-detecting surface defects on the edge.

[0008] 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 determine the quality of welding conditions from fin pass forming to electric resistance welded welding, thereby suppressing welding defects caused by the surface properties of the end face of the edge portion. [Means for solving the problem]

[0009] 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, joining the two edges to form an open pipe, and performing electric resistance welding on both edges of the joined 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 two edges of the open pipe A welding management device for electric resistance welded pipes, comprising: a molten metal outflow start position detection unit that detects the longitudinal molten metal outflow start position of the open pipe where molten metal begins to flow out from each of the two edges to the pipe surface, based on image information of a region including the edge portion and the welding point where welding of both edges of the open pipe begins; a molten metal outflow start position difference calculation unit that calculates the longitudinal position difference of the molten metal outflow start position detected by the molten metal outflow start position detection unit; and a welding state determination unit that determines the quality of the electric resistance welded welding conditions 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 position difference. [2] The welding condition determination unit determines that the electric resistance welding conditions are good when the position difference is less than or equal to a predetermined upper limit and the second temperature ratio of the outer surface temperature to the maximum temperature is within a predetermined allowable range, as described in [1]. [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, in which, based on information on 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; and before electric resistance welding, the outer surface side of the open pipe A welding management method for an electric resistance welded pipe, comprising: a molten metal outflow start position detection step before electric resistance welding, which detects the molten metal outflow start position in the longitudinal direction of the open pipe where molten metal begins to flow out from each of the two edges to the pipe surface, based on image information of a region including both edges of the open pipe and the welding point where welding of both edges of the open pipe is started, photographed from the inner side; a molten metal outflow start position difference calculation step, which calculates the position difference of the molten metal outflow start position detected in the molten metal outflow start position detection step; and a welding state determination step, which determines whether the electric resistance welding conditions are good or bad 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 position difference. [4] The welding condition determination step is to determine that the electric resistance welding conditions are good when the position difference is less than or equal to a predetermined upper limit and the second temperature ratio of the outer surface temperature to the maximum temperature is within a predetermined allowable range. This is the welding control method for electric resistance welded pipes according to [3]. [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 electric resistance welded pipes, comprising: a welding management device for electric resistance welded pipes as described in [6][1] or [2]; an edge temperature information acquisition device for acquiring information on the temperature distribution of one of the two edges of the open pipe; and a welding area imaging device for imaging an area including both edges of the open pipe and the welding point where welding of both edges of the open pipe is started. [Effects of the Invention]

[0010] According to the present invention, the quality of the welding conditions can be judged between the fin pass forming and the electric resistance welding, thereby suppressing welding defects caused by the surface properties of the end face of the edge portion. [Brief explanation of the drawing]

[0011] [Figure 1] This is a diagram showing an image of a welded joint. [Figure 2] This diagram illustrates the surface characteristics of the end face of the edge portion before electric resistance welding. [Figure 3] This diagram illustrates the surface characteristics of the end face of the edge portion before electric resistance welding. [Figure 4] This is an explanatory diagram illustrating the welding control device and the welding control system including it according to this embodiment. [Figure 5] This flowchart shows the welding management process procedure using the welding management device of this embodiment. [Figure 6] This figure shows the temperature distribution when there is a step on the end face before electric resistance welding. [Figure 7] This figure shows the results of the quality of electric resistance welds according to the second temperature ratio and the difference in the molten metal outflow start position. [Figure 8] This figure shows the pre-determined tolerance ranges for welding conditions, along with the welding conditions for the inventive example and comparative example. [Modes for carrying out the invention]

[0012] The inventors focused on using the skin effect unique to high-frequency heating to detect the surface irregularities of the end faces of both edges of an open pipe before electric resistance welding, and thereby manage the surface properties. Specifically, during the heating process of the edge portion before electric resistance welding, the temperature distribution in the thickness direction on the end face of the edge portion is measured to detect areas where abnormal heating is occurring due to the skin effect. Furthermore, the inventors diligently researched how to capture the welding phenomenon with a camera, visualize the welding phenomenon as an image, and quantify the surface properties of the end face of the edge portion. As a result, the following became clear.

[0013] Here, the flow of electric resistance welding will be explained with reference to Figures 1, 2, and 3. Figure 1 is a diagram showing the welded area image 20. Figure 2 is a diagram to explain the surface properties of the end face of the edge before electric resistance welding. Figure 3 is a diagram to explain the surface properties of the end face of the edge before electric resistance welding. Conventionally, in electric resistance welding, the edges 202a and 202b are heated using a heating device that uses high-frequency current by a direct current heating method or an induction heating method. When the end faces of the edges 202a and 202b are smooth, as shown in Figures 1, 2(i), and 3(i), when high-frequency heating is applied to the edges 202a and 202b, a skin effect occurs in the initial stage of heating due to a heating phenomenon unique to high-frequency heating. As a result, heating is concentrated on the outer and inner surfaces of the corners of the edges 202a and 202b. The central portion of the edge portions 202a and 202b in the thickness direction (hereinafter referred to as the thickness center portion) is heated by heat transfer from the outer and inner surfaces of the edge portions 202a and 202b. In Figures 1 to 3, the heated portion that is heated by high-frequency heating and glows red is denoted with the symbol "201". In Figure 1, the opening between the edge portions 202a and 202b of the open tube is denoted with the symbol "202". Also in Figure 1, the intersection of the straight lines La and Lb along each edge portion 202a and 202b is the V convergence point (sometimes referred to as the joint point), and the V convergence point is denoted with the symbol "204". The welded portion image 20 is an image taken by the welded portion imaging device 12, which will be described later.

[0014] 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, via upsetting by the squeeze rolls. At this time, the molten metal of the edges 202a and 202b flows out to the outside of the pipe along with the penetrator distributed on the end faces, forming a weld bead 203. Also, in the weld image 20 of Figure 1, the indicators "d1" and "d2" are added to show the start positions of the molten metal outflow.

[0015] In electric seam welding, as described above, by melting the entire end faces of the edge portions 202a and 202b and causing the molten metal of the edge portions 202a and 202b to flow out to the outside of the pipe together with the penetrator distributed on the pipe surface, a sound welded portion can be obtained. However, if the surface properties of the end face are not smooth and uneven shapes are manifested on the end face, the skin effect also appears in the uneven portions. As a result, not only does the temperature distribution on the end face become non-uniform, but the discharge of the penetrator is inhibited by the uneven shape. Therefore, the uneven shape of the end faces of the edge portions 202a and 202 causes deterioration of the welding quality. Examples of the uneven shape of the end face include burrs and sags on the end faces of the edge portions 202a and 202 due to slit processing, and streak-like steps generated on the end faces when the end faces of the edge portions 202a and 202b of the steel strip come into contact with guide rolls (not shown). FIGS. 2(ii) and FIGS. 3(ii) show a state in which steps are formed on the end faces of the edge portions 202a and 202b. In the stepped portions shown in FIGS. 2(ii) and FIGS. 3(ii), the skin effect appears and the temperature distribution on the end face becomes non-uniform, and the outflow of the penetrator is inhibited by the steps. Further, such uneven shapes, which are defects on the end face, occur continuously in the longitudinal direction of the pipe. Therefore, before electric seam welding, a state in which the temperature of the portions where the above-described uneven shapes occur and the peripheral portions thereof is extremely high occurs continuously in the longitudinal direction of the pipe.

[0016] Therefore, in order to maintain good surface properties of the end face before electric seam welding, it is necessary not to roughen the surface properties of the end face when performing end face processing such as slit processing or edge milling on the steel strip. Alternatively, measures such as strongly pressing the end face against the fin in fin pass forming to smooth the surface are necessary.

[0017] The present invention is based on the above-described findings. Hereinafter, embodiments of the present invention (hereinafter referred to as "the present embodiments") will be described with reference to the drawings. Note that the present invention is not limited to the following present embodiments.

[0018] Figure 4 is a diagram illustrating the welding control device 100 and the welding control 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 moves in the direction indicated by the arrow in Figure 4 as the direction of travel (welding direction). At the same time, while the stability of the cylindrical shape is ensured by the fin pass roll 2, the butt joint position of both edges 202a and 202b is centered in the center of the welding stand 40 as it is formed into an open tube 1. After that, high-frequency current is supplied to both edges 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 edges 202a and 202b are heated until they melt. It is also possible to use induction heating work coils instead of contact tips.

[0019] 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, the molten steel is discharged to the outside, i.e., to the outer and inner surfaces of the tubular steel plate, while both edges 202a, 202b are welded (referred to as electric resistance welding).

[0020] 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 direction of travel (welding direction) and the edges 202a and 202b are sufficiently close. The position where welding begins is called the welding point 205. When the high-frequency current is sufficiently large, upstream of the welding point 205 in the direction of travel (welding direction), a portion of the end face melts due to high-frequency heating, and the molten metal flows out of the pipe due to electromagnetic force.

[0021] 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.

[0022] 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.

[0023] 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 direction of travel (welding direction). 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.

[0024] 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.

[0025] The welding imaging device 12 includes, for example, a camera. This camera photographs both edges (welded areas) 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 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 process of the edges (welded areas) 202a and 202b of the open pipe 1 being heated and melted, and then pressed together by the squeeze rolls 41a and 41b. The position of the welding imaging device 12 is adjusted so that the images captured by the welding imaging device 12 include the welding point 205, the V convergence point (joining point) 204 (described later), and the roll centers of the squeeze rolls 41a and 41b. In this case, it is preferable that the region between the welding point 205 and the contact tips 31a and 31b in the welding direction (longitudinal direction) includes at least four-fifths of the region upstream from the welding point 205. This is to capture the position furthest upstream in the longitudinal direction of the open pipe 1, that is, in the direction in which the molten metal begins to flow out of the pipe from each of the heated edges 202a and 202b. The camera can be either a color camera or a monochrome camera.

[0026] 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.

[0027] The welding management device 100 is a welding management 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 management 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 start position detection unit 133, a molten metal outflow start position difference calculation unit 134, and a welding state determination unit 141. The edge temperature detection unit 122 before electric resistance welding detects the outer surface temperature To, the inner surface temperature Ti, and the maximum temperature Tp of the edge 202a (202b) based on information on the temperature distribution in the thickness direction of at least one of the two edges 202a and 202b. The maximum temperature Tp is the maximum value in the temperature distribution obtained by subtracting the outer surface temperature and inner surface temperature from the temperature distribution in the thickness direction, and is also 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. The highest temperature among those maximum values ​​is then set as the maximum temperature Tp, or this is not limited to such methods. The edge temperature ratio calculation unit 125 calculates the temperature ratios Tp / To and Tp / Ti, which are the ratios of the outer surface temperature To or inner surface temperature Ti to the maximum temperature Tp. The molten metal outflow start position detection unit 133 extracts two straight lines La and Lb that converge along the edge portions 202a and 202b, which include the heated and red-hot portion (hereinafter referred to as the heated portion) 201, based on the image information 20. Furthermore, the system detects the longitudinal positions d1 and d2 of each edge portion 202a and 202b where molten metal begins to flow out to the outside of the pipe, crossing the heated portion 201 of the edge portions 202a and 202b. The image information 20 includes both edge portions 202a and 202b of the open pipe 1 heated by the high-frequency current, and the welding point 205 where both edge portions 202a and 202b of the open pipe 1 join and welding begins. The molten metal outflow start position difference calculation unit 134 calculates the longitudinal position difference Δd (hereinafter sometimes referred to as position difference Δd) of the molten metal outflow start positions d1 and d2 detected at each edge portion 202a and 202b.The welding condition determination unit 141 determines the quality of the electric resistance weld conditions based on the information of the outer surface temperature To, inner surface temperature Ti, maximum temperature Tp, and position difference Δd of the edge portion 202a. In the following explanation, the temperature ratio Tp / To will be referred to as the first temperature ratio, and the temperature ratio Tp / Ti will be referred to as the second temperature ratio Tp / Ti.

[0028] Furthermore, the welding management device 100 may also have an output unit 142 that outputs the determination result from the welding state determination unit 141.

[0029] 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 image information 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.

[0030] The welding management device 100 is composed of a general-purpose computer such as a workstation or personal computer, and has calculation processing functions such as a CPU, image processing functions such as 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.

[0031] 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. The larger of the two values, the first temperature ratio Tp / To and the second temperature ratio Tp / Ti, is extracted. The first temperature ratio Tp / To is the ratio of the outer surface temperature To of the edge portions 202a and 202b to the maximum temperature Tp. The second temperature ratio Tp / Ti is the ratio of the inner surface temperature Ti of the edge portions 202a and 202b to the maximum temperature Tp. In addition, the welding management device 100 calculates the positions d1 and d2 in the longitudinal direction of the pipe where molten metal begins to flow from each edge portion 202a and 202b to the pipe surface, and the position difference Δd between them, in the welding image processing unit 131. Based on this information, including the first temperature ratio Tp / To, or the second temperature ratio Tp / Ti and the position difference Δd, the welding state determination unit 141 determines whether the electric resistance welding conditions are good or bad.

[0032] The configuration and functions of the welding control device 100 will be described in more detail.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The edge temperature ratio calculation unit 125 calculates the first temperature ratio Tp / To and the second temperature ratio Tp / Ti of each edge portion 202a and 202b of the open tube 1 at a preset position, i.e., a specified position.

[0038] The welding control device 100 performs the series of processes described above in the edge temperature distribution processing unit 121.

[0039] The welding image processing unit 131 includes a pipe edge image detection unit 132, a molten metal outflow start position detection unit 133, and a molten metal outflow start position difference calculation unit 134.

[0040] In parallel with the processing in the edge temperature distribution processing unit 121 described above, the pipe edge image detection unit 132 generates two straight lines La and Lb that converge along the edges 202a and 202b based on the image information 20. The image information 20 includes both edges 202a and 202b of the open pipe 1, and the welding point 205 where both edges 202a and 202b of the open pipe 1 are joined 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. The image information 20 described above is obtained by the welding area imaging device 12 taking an image.

[0041] The molten metal outflow start position detection unit 133 extracts the upstream positions d1 and d2 in the longitudinal direction of the open pipe 1, respectively, in the direction in which the molten metal begins to flow out of the pipe from each edge portion 202a and 202b. Here, the method for extracting the longitudinal position of the molten metal is not limited. For example, since the leading edge of the molten metal that has flowed out of the pipe from each edge portion 202a and 202b in the circumferential direction of the open pipe 1 is convex, one method is to extract the position of the largest leading edge of the molten metal in the circumferential direction.

[0042] The molten metal outflow start position difference calculation unit 134 calculates the position difference Δd between position d1 and position d2, where the molten metal begins to flow out of the pipe.

[0043] The welding management device 100 performs the series of processes described above in the welding image processing unit 131.

[0044] Furthermore, the welding management device 100 performs welding management processing by performing welding determination by the welding state determination unit 141 based on information of the first temperature ratio Tp / To, or the second temperature ratio Tp / Ti and the position difference Δd, and outputting the determination result by the output unit 142.

[0045] 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.

[0046] 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.

[0047] The edge temperature distribution processing unit 121 detects information on the two-dimensional temperature distribution on the joint surface of the edge portions 202a and 202b, that is, information on the two-dimensional temperature distribution in the longitudinal direction and the wall thickness direction of the pipe, from the temperature distribution information including the captured image information.

[0048] This completes the process in step S1, and the welding control process proceeds to the process in step S2.

[0049] 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 two-dimensional temperature distribution information and image information obtained 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.

[0050] 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.

[0051] 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 of the pipe, along with the coordinate values, based on the temperature distribution information after the spatial coordinate transformation process.

[0052] The position in the longitudinal direction of the pipe 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.

[0053] 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.

[0054] The corners, corresponding to the outer and inner surfaces of the 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.

[0055] Therefore, the temperature distribution in the wall thickness direction will have peaks at the corners of the outer and inner surfaces of the edge portions 202a and 202b. Based on this characteristic, the distance between the peak detected at the outer surface of the edge portions 202a and 202b and the peak detected at the inner surface of the edge portions 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 preset pipe wall thickness (actual wall thickness) is within ±3%, 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 process of steps S1 to S3 is repeated until the above error is within ±3%.

[0056] This completes the process in step S3, and the welding control process proceeds to the process in step S4.

[0057] In step S4, the pre-electric resistance welding edge temperature detection unit 122 detects the outer surface temperature To and the inner surface temperature Ti based on information about the temperature distribution of at least one of the two edge portions 202a and 202b of the open pipe 1.

[0058] Specifically, the pre-electric resistance welding edge temperature detection unit 122 (thickness direction temperature distribution detection unit 124) detects the temperature at the center of the peak of the temperature information at the outer surface and inner surface positions of the edge portions 202a and 202b as the outer surface temperature To and inner surface temperature Ti, respectively. The temperature at the center of the peak refers to the temperature at the peak of the peak.

[0059] Furthermore, the pre-electric welding edge temperature detection unit 122 (thickness direction temperature distribution detection unit 124) detects the maximum value excluding the outer surface temperature To and the inner surface temperature Ti, and extracts the highest temperature among these maximum values ​​as the maximum temperature Tp. In detecting the maximum temperature Tp, time averaging is performed on the detected thickness direction temperature distribution, and only the maximum values ​​that exceed a predetermined allowable temperature range for the averaged thickness direction temperature distribution are detected. The highest temperature among these is then set as the maximum temperature Tp, although this is not limited to this method. The allowable temperature range can be determined, for example, by comparing 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, although 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 the positions can be specified by manual input, although this is not limited to this method. Methods for calculating local maxima include the second derivative method, but are not limited to this. If no local maxima exists, the highest temperature Tp is set to 0.

[0060] 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.

[0061] 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 detected 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 lower temperature end of the inner and outer surface temperatures To and Ti of the edge portions 202a and 202b and the maximum temperature Tp becomes larger. As a result, the temperature distribution on the end surface becomes non-uniform, making it easier for the outflow of molten metal to be hindered.

[0062] 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.

[0063] For example, first, the pipe edge image detection unit 132 uses the welded area image 20 shown in Figure 1, captured by the camera, to detect the edges 202a, 202b, the heated area 201, and the edges of the molten metal flowing out of the pipe from the change in brightness around the heated area 201. At the same time, it performs a conversion process from the number of pixels in the welded area image 20 to units of length. Here, a two-axis XY coordinate system is used with the lower left corner of the welded area 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.

[0064] In step S7, a V-convergence point extraction unit (not shown) generates two straight lines La and Lb that converge along the edges 202a and 202b based on the information from the welded area image 20 described above, and extracts the V-convergence point 204, which is the intersection of the two straight lines La and Lb. The welded area image 20 is an image of the region that includes both edges 202a and 202b of the open pipe 1 and the welding point 205 where both edges 202a and 202b of the open pipe 1 are joined and welding begins.

[0065] Specifically, for example, the V-convergence point extraction unit first performs image processing in the vertical direction from the opening 202 in the welded area image 20, where the two edges 202a and 202b are not joined together. The position where the edge is first detected is set as a point on each edge 202a and 202b. The vertical direction means the direction perpendicular to the welding direction (left-right direction in Figure 1) (circumferential direction of the pipe; up-down direction in Figure 1). The V-convergence point extraction unit performs this process at several points along the entire length of the opening 202, for example, 3 to 10 points. Then, the V-convergence point extraction unit generates straight lines La and Lb along each edge 202a and 202b, approximating the end faces of both edges 202a and 202b of the open pipe 1, using the least squares method from the multiple points detected on each edge 202a and 202b. In Figure 1, the opening 202 is the region sandwiched between the heated portions 201 of both edges 202a and 202b. One method for manually specifying the opening 202 is to input the positions included in the opening 202 into the position coordinates on the welded portion image 20 before detecting points on each edge portion 202a and 202b, but this is not the only method.

[0066] The V-convergence point extraction unit extracts the intersection of lines La and Lb as V-convergence point 204 and digitizes the coordinate data.

[0067] This completes the process in step S7, and the welding control process proceeds to step S8.

[0068] In step S8, upstream of the V convergence point 204 extracted in step S7, positions d1 and d2 are detected where molten metal begins to flow out from both heated, red-hot edges 202a and 202b in the circumferential direction outside the pipe. Here, with respect to the flowed-out molten metal, similar to the process in step S6, the molten metal outflow start position detection unit 133 of the welding image processing unit 131 detects the edge of the molten metal based on the weld image 20 captured by the weld imaging device 12.

[0069] Here, the differential method is used for edge detection, but it is not limited to this method. The molten metal outflow start position detection unit 133 uses the captured weld image 20 to detect the edge of the molten metal that has flowed out from the heating unit 201 from the change in brightness around the heating unit 201. There is no particular specification for extracting the position of the molten metal, but here, since the tip of the molten metal is convex, the position of the convex tip is extracted as the molten metal position. The profile of the molten metal extracted by edge detection is output as coordinate data in the longitudinal direction of the pipe and the circumferential direction of the pipe. Then, in the obtained coordinate data, the longitudinal position of the pipe at the position where the coordinate data in the circumferential direction of the pipe is maximum and local maximum is defined as the molten metal outflow start positions d1 and d2.

[0070] Among the extracted molten metal outflow start positions d1 and d2, the molten metal position d1(d2) furthest from the V convergence point 204 is designated as the molten metal outflow start position for one edge section 202a(202b). The same process is performed for the molten metal flowing out to the outside of the pipe at the other edge section 202b(202a). When extracting the molten metal outflow start position from the coordinate data of the molten metal profile, the longitudinal position of the pipe at the position where the data is minimum and local minimum in the circumferential coordinates of the pipe is designated as the molten metal outflow start position d2 for the other edge section 202b(202a). This completes the process in step S8, and the welding management process proceeds to step S9. Note that the process in step S8 for detecting the molten metal outflow start positions d1 and d2 corresponds to the molten metal outflow start position detection process.

[0071] In step S9, the molten metal outflow start position difference calculation unit 134 of the welding image processing unit 131 calculates the molten metal outflow start position difference Δd, which is the difference between the molten metal outflow start positions d1 and d2 at both edge portions 202a and 202b extracted in step S8. The molten metal outflow start position difference Δd is an absolute value. With this, the processing of step S9 is completed, and the welding management process proceeds to step S10. Note that the processing in step S9 in which the molten metal outflow start position difference Δd is calculated corresponds to the molten metal outflow start position difference calculation process.

[0072] In step S10, after the processing in steps S5 and S9 is completed, the welding state determination unit 141 determines whether the electric resistance weld conditions are good or bad. The welding state determination unit 141 determines whether the electric resistance weld conditions are good or bad based on the outer surface temperature To of the edge portions 202a and 202b at the specified position, the first temperature ratio Tp / To of the inner surface temperature Ti and the maximum temperature Tp, or the second temperature ratio Tp / Ti, and the difference Δd in the position where the molten metal outflow started. Extraction of the first temperature ratio Tp / To, the second temperature ratio Tp / Ti, and the position difference Δd is performed by extracting these values ​​within a predetermined time range and calculating the average value of each value. There is no particular specification 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.

[0073] The welding condition determination unit 141 determines that the electric resistance welding conditions are good if the difference in the starting position Δd of the molten metal outflow is within a predetermined range, 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.

[0074] As a specific example of a method for determining the quality of electric resistance welding conditions, an offline evaluation test of the welded joint is performed using steel pipes obtained under various welding conditions. The relationship between the characteristics of the obtained welded joint, the first temperature ratio Tp / To or second temperature ratio Tp / Ti between the outer surface temperature To or inner surface temperature Ti of the edge portions 202a and 202b at a specified position and the maximum temperature Tp, and the difference in the molten metal outflow start position Δd is clarified in advance. Specifically, upper and lower limits are set for the first temperature ratio Tp / To or 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, within the allowable range of the molten metal outflow start position difference Δd.

[0075] In setting the allowable range for the first temperature ratio Tp / To or the second temperature ratio Tp / Ti, the difference in the starting position of molten metal outflow Δd is treated as a parameter. Offline evaluation tests for welds include flattening tests and ultrasonic testing to detect oxides in the weld (according to JIS G 0583:2021 "Automatic Eddy Current Testing Method for Steel Pipes"). Additionally, Charpy impact tests (according to JIS Z 2242:2023 "Charpy Impact Testing Method for Metallic Materials") are performed by cutting a test piece from the weld. The test method is selected according to the desired characteristics.

[0076] An example of how to set the upper and lower limits of the allowable range for the first temperature ratio Tp / To or 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 position and the maximum temperature Tp is described below, but this is not an exhaustive example.

[0077] The temperature measurement position is arbitrary, but the edge temperature information acquisition device 11 measures the temperature of the edge portions 202a and 202b under various welding conditions at a position on the molding machine side, i.e., upstream (opposite direction to the welding direction) of the squeeze rolls 41a and 41b shown in Figure 4. 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 and 202b are below a predetermined value.

[0078] 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.

[0079] 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 point is less than 50°C, the outer and inner surfaces of both edges 202a and 202b may be temporarily heated to their melting point due to disturbances during operation. In that case, the temperature rise will saturate, and the relationship between the difference in the starting position of molten metal outflow Δd and the temperature distribution of the end faces of both edges 202a and 202b will become difficult to observe.

[0080] In the temperature measurement described above, the temperature difference ΔT (°C) is preferably 200°C or less, and more preferably 100°C or less.

[0081] Next, grooves are made on the edges 202a and 202b of the steel strip, and electric resistance welding is performed while changing the stepped shape of the end face. The stepped shape of the end face is not limited to groove processing; it can also be achieved by slitting the edges 202a and 202b and adjusting the amount of fin formation on the edges 202a and 202b during fin pass formation. At this time, the welding management device 100 measures the outer surface temperature To and inner surface temperature Ti of the edges 202a and 202b at specified positions, the first temperature ratio Tp / To or second temperature ratio Tp / Ti, and the difference in molten metal outflow start position Δd. It also calculates the average values ​​of these values. These are performed based on information obtained from the edge temperature information acquisition device 11 and the weld area imaging device 12. Averaging is preferably calculated from five or more image data points.

[0082] For each electric resistance welded pipe obtained from the above-mentioned electric resistance welds, a Charpy impact test using a V-notch test specimen as described in JIS Z 2242:2023 is performed. Figure 6 shows the temperature distribution when there is a step on the end face before electric resistance welding. In the example shown in Figure 6, the inner surface temperature Ti is greater than the outer surface temperature To of the edge portions 202a and 202b, and the temperature of the stepped portion is the highest temperature Tp. Figure 7 shows the results of the quality of the electric resistance weld according to the second temperature ratio Tp / Ti and the difference in the molten metal outflow start position Δd.

[0083] In Figure 7, five full-size Charpy impact test specimens cut from the weld at a test temperature of 0°C are marked with "○" if the average absorbed energy is 27 J or more, and marked with "×" if it is less than 27 J, indicating failure. The welding condition determination unit 141 determines the boundary for this pass / fail determination and sets the upper and lower limits of the second temperature ratio Tp / Ti. One method for determining the pass / fail boundary for weld quality is to set a boundary line that is a linear function of the difference in molten metal outflow start positions Δd between adjacent welds and record it in the memory unit 143. Another method is to pre-set the upper and lower limits of the second temperature ratio Tp / Ti with respect to the difference in molten metal outflow start positions Δd and record them in the memory unit 143, but this is not limited to this method. In Figure 7, the linear function of the difference in molten metal outflow start positions Δd between adjacent welds is shown as a dotted line as the boundary line.

[0084] Using these boundary conditions, the welding condition determination unit 141 determines that the electric resistance weld (ERW) welding conditions are good when the second temperature ratio Tp / Ti is within the acceptable range for the weld at a molten metal outflow initiation position difference Δd for any given welding conditions. Conversely, when the first temperature ratio Tp / To is not within the acceptable range for the weld at a molten metal outflow initiation position difference Δd for any given welding conditions, the ERW welding conditions are determined to be poor. The acceptable range described above will now be explained. For example, multiple ERW welding experiments are performed with different molten metal outflow initiation position differences Δd. For each molten metal outflow initiation position difference Δd, the maximum value of the second temperature ratio Tp / Ti that can be judged as good for the ERW welding conditions is determined. The quality of the ERW welding conditions is determined by performing a Charpy impact test on the weld, and if the absorbed energy is above a predetermined threshold, the ERW welding conditions are judged to be good. Therefore, a Charpy impact test is performed on each weld to determine the maximum value of the second temperature ratio Tp / Ti that results in an absorbed energy above a predetermined threshold. Then, the maximum value of each second temperature ratio Tp / Ti obtained in this way is linearly approximated and used as the boundary of the acceptable range.

[0085] The results obtained in this process 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 the electric resistance welding conditions are good or bad, corresponds to the welding state determination process.

[0086] In step S11, the output unit 142 outputs the pass / fail judgment of the welding conditions obtained in step S10 to an external source. Since the operator needs to recognize the judgment result for the external output, it is preferable to output it to a graphic display or alarm device 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.

[0087] According to this embodiment, welding defects due to steps on the end faces are detected by analyzing the temperature distribution on the end faces of each edge portion 202a, 202b and the welded area image 20 during electric resistance welding. Therefore, over-detection of surface defects can be suppressed. Furthermore, the electric resistance welding conditions are determined to be good when the second temperature ratio Tp / Ti at the molten metal outflow start position difference Δd under any welding conditions is within the above-mentioned acceptable range. Therefore, the occurrence of welding defects can be suppressed.

[0088] 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 within the scope of the present invention, as long as they do not depart from the spirit of the invention. For example, the quality of electric resistance welding conditions may be determined based on the first temperature ratio Tp / To and the position difference Δd instead of the second temperature ratio Tp / Ti. In this case, the same effects and advantages as those of the embodiments described above can be obtained.

[0089] 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]

[0090] For various electric resistance welded pipes with a pipe thickness of 9 mm and an outer diameter of φ370 mm, the upper and lower limits of the second temperature ratio Tp / Ti at the molten metal outflow start position difference Δd were first derived to determine the allowable range of welding conditions. Under these welding conditions, the outer surface temperature To of the edge portion was smaller than the inner surface temperature Ti. In this study, the temperature distribution on the joint surface was measured at a position 20 mm upstream (opposite to the welding direction) from directly below the axis of the squeeze roll of the welding stand, and electric resistance welding was performed at a welding speed of 20 m / min by adjusting the edge bending during forming. The edge portion was pre-processed using an edger roller, and the height of the convex shape was adjusted by the amount of pressure applied by the edger roller.

[0091] In various electric resistance welded (ERW) welding processes, a two-color thermometer camera was used to acquire a 2D image of the temperature distribution of the joint surface at the edge of the pipe before welding, with a frame rate of 20 fps, 1920 pixels in the longitudinal direction of the pipe, 1080 pixels in the thickness direction of the pipe, and a field of view of 50 mm in the longitudinal direction of the pipe. 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, with a frame rate of 20 fps, 1920 pixels in the longitudinal direction of the pipe, and a field of view of 60 mm in the longitudinal direction of the pipe. From these acquired images, the inner surface temperature Ti of the edge at a specified position in each frame, the second temperature ratio Tp / Ti (the highest temperature Tp in the thickness direction excluding the outer and inner surfaces), and the difference in the position of molten metal outflow start Δd were calculated. Of these calculated data, 100 data points were averaged to obtain the operational data for each welding condition.

[0092] Furthermore, Charpy impact tests were performed on the electric resistance welded pipes obtained from each individual electric resistance weld using V-notch specimens as described in JIS Z 2242:2023. The absorbed energy of full-size Charpy impact specimens cut from the weld at a test temperature of 0°C was measured, and the average of five measurements 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 on a map showing the relationship between the molten metal outflow initiation position difference Δd and the second temperature ratio Tp / Ti. A pass / fail boundary was then set for each welding condition, with conditions that yielded steel pipes with an absorbed energy of 27 J or more being considered pass, and conditions that yielded steel pipes with an absorbed energy of less than 27 J being considered fail. In this way, an upper limit for the second temperature ratio Tp / Ti was set according to each value of the molten metal outflow initiation position difference Δd.

[0093] In this embodiment, the upper and lower limits of the second temperature ratio Tp / Ti at the molten metal outflow initiation position difference Δd, which could not be measured in advance, were determined using the upper and lower limits of the second temperature ratio Tp / Ti at the molten metal outflow initiation position difference Δd that were known before and after that point. Using the above-mentioned known linear function equation as a function of the molten metal outflow initiation position difference Δd, interpolation calculations were performed to obtain the upper and lower limits of the second temperature ratio Tp / Ti at the narrow gap length L, which could not be measured.

[0094] Based on the above, the acceptable range for welding conditions was derived.

[0095] Next, in the manufacture of an electric resistance welded pipe with a pipe thickness of 9 mm and an outer diameter of φ370 mm, electric resistance welding was performed at a welding speed of 20 m / min. The edges of the steel strip were slit before forming. Here, the method for measuring 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 difference in the starting position of molten metal outflow Δd is the same as the conditions for deriving the tolerance range described above. Figure 8 is a diagram that summarizes the tolerance range of the welding conditions derived in advance under the above conditions, i.e., the boundary line for acceptance or rejection of the weld quality, and the welding conditions of the inventive example and comparative example. Note that in Figure 8, an example of a linear function of the difference in the starting position of molten metal outflow Δd of adjacent molten metal outflow points is indicated by a dotted line as a boundary line. The boundary line when the difference in the starting position of molten metal outflow Δd is 18 or more and 23 or less is expressed by the following formula. Second temperature ratio Tp / Ti=-0.02×Δd+1.29

[0096] Table 1 shows the pass / fail criteria for the molten metal outflow start position difference Δd, the second temperature ratio Tp / Ti, and the absorbed energy of the Charpy test of the steel pipe for the successful and unsuccessful examples of the invention.

[0097] [Table 1]

[0098] Ten full-size Charpy impact test specimens cut from each of the electric resistance welded pipes of Invention Examples 1 to 3 and Comparative Examples 1 and 2 were subjected to Charpy impact testing of the welded joints according to JIS Z 2242:2023, and the absorbed energy at a test temperature of 0°C was measured. The acceptance criterion for absorbed energy was that 90% or more of the steel pipes met the requirement of 27 J or higher. As shown in Figure 8 and Table 1, Invention Examples 1 to 3 all met the acceptance rate of 90% or higher, while Comparative Examples 1 and 2 fell below this level.

[0099] In Invention Example 1, under constant molding conditions, the clearance conditions for slitting were adjusted to satisfy the relationship between the molten metal outflow start position difference Δd and the second temperature ratio Tp / Ti within an acceptable range.

[0100] In Invention Example 2, the amount of fins formed during fin pass molding was adjusted to satisfy the relationship between the molten metal outflow start position difference Δd and the second temperature ratio Tp / Ti within an acceptable range, while the input power was constant.

[0101] In Comparative Examples 1 and 2, welding control was not performed during electric resistance welding; instead, the welding power was adjusted, and the state of the discharged molten steel was confirmed only visually. [Industrial applicability]

[0102] 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]

[0103] 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 start position detection unit 134 Molten metal outflow start position difference calculation unit 141 Welding condition determination unit 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 d1, d2: Starting point of molten metal outflow Δd Difference in the starting position of molten metal outflow

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 start position detection unit detects the molten metal outflow start position in the longitudinal direction of the open pipe where molten metal begins to flow out from each of the edges to the pipe surface, based on image information 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 start position difference calculation unit calculates the position difference in the longitudinal direction of the molten metal outflow start position detected by the molten metal outflow start position detection unit, A welding management device for electric resistance welded pipes, comprising a welding condition determination unit that determines the quality of electric resistance welded conditions 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 position difference.

2. The welding condition determination unit determines that the electric resistance welding conditions are good when the position difference is less than or equal to a predetermined upper limit and the second temperature ratio of the outer surface temperature to the maximum temperature is within a predetermined allowable range, as described in claim 1, for use as a welding management device for electric resistance welded pipes.

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 weld edge temperature detection step, which, before electric resistance welding, detects the maximum value among the temperature distribution obtained by subtracting the outer surface temperature and inner surface temperature of the one edge, and the highest temperature among the maximum values, based on information of the temperature distribution in the thickness direction of at least one edge of both edges of the open pipe, the outer surface temperature and inner surface temperature of the one edge, and the highest temperature among the maximum values, A step to detect the start position of molten metal outflow in the longitudinal direction of the open pipe, where molten metal begins to flow from each of the edges to the pipe surface, based on image information of a region including both edges of the open pipe and the welding point where welding of both edges of the open pipe begins, before electric resistance welding, A molten metal outflow start position difference calculation step calculates the position difference of the molten metal outflow start position detected in the molten metal outflow start position detection step, A welding management method for electric resistance welded pipes, comprising a welding condition determination step of determining the quality of electric resistance welded conditions 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 position difference.

4. The welding management method for electric resistance welded pipes according to claim 3, wherein the welding condition determination step determines that the electric resistance welding conditions are good when the position difference is less than or equal to a predetermined upper limit and the second temperature ratio of the outer surface temperature to the maximum temperature is within a predetermined allowable range.

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