Welding management device for electric resistance welded steel pipe, welding management system, welding management method for electric resistance welded steel pipe, and manufacturing method for electric resistance welded steel pipe

Abstract

To provide a welding management device for electric resistance welded (ERW) steel pipes, a welding management system, a welding management method for ERW steel pipes, and a method for manufacturing ERW steel pipes, which are configured to suppress occurrence of welding defects.SOLUTION: A welding management device for ERW steel pipes comprises: an edge temperature detection unit; an edge temperature difference calculation unit; a V convergence angle calculation unit; a post-weld discharge molten steel area calculation unit; and welding state determination unit that determines whether electric resistance welding conditions are good or bad.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electric-welded steel pipe welding management device, a welding management system, a welding management method for electric-welded steel pipe, and a manufacturing method for electric-welded steel pipe, which quantify the temperature distribution in the open pipe edge portion immediately before electric-welding of the electric-welded steel pipe and combine it with the constituent factors of the electric-welding welding phenomenon to suppress welding defects. [Background technology]

[0002] Electric resistance welded steel pipes are manufactured by continuously bending a steel plate or steel strip in the circumferential direction using roll forming, butting both ends together to form a roughly tubular open pipe with a circular cross-section, and then continuously electric resistance welding both edges of the butted open pipe.

[0003] During electric resistance welding, both edges are heated above their melting point by direct current flow using a contact tip or by induced current from an induction coil, and immediately thereafter the joints of both edges are butted (upset) with a welding roll (squeeze roll). During this process, oxides (penetrators) that are generated during the melting and heating process of the steel plate or steel strip are made to flow onto the inner and outer surfaces of the pipe by the upset and are expelled into unnecessary areas called excess welds (beads), preventing the occurrence of welding defects. After electric resistance welding, the excess welds are cut and removed from the pipe using a cutting tool or the like.

[0004] In order to suppress welding defects, it is important to suppress the generation of penetrators and the aggregation of penetrators until welding as much as possible. To achieve this, it is necessary to adjust the welding conditions so that the time from the melting and heating process to the start of joining of both edges is not excessively long. It is also important to smoothly discharge the penetrators into the bead during the upset process. To achieve this, it is necessary to reduce the deviation of the temperature distribution in the thickness direction of the edge part until the start of joining, and to suppress poor discharge of the penetrators due to solidification of the molten edge part during upset.

[0005] As a method for solving the above problems, various techniques have been disclosed for preventing welding defects in the manufacture of electric resistance welded steel pipes. For example, a welding management system for the welding process has been proposed in which the electric resistance welding phenomenon is visualized and the temperature of the edge portion during the melting and heating process is measured.

[0006] Patent Document 1 proposes a welding temperature measurement method in which the coordinates of the corner positions on the outer and inner surfaces of both edges of an open pipe before they are butted are detected from photographed images, the temperature distribution of the corners on the outer and inner surfaces of both edges is calculated, and the detected coordinates are compared with the calculated temperature distribution to determine the temperature of the edges at the detected coordinates, thereby controlling the heating conditions of both edges.

[0007] Patent Document 2 proposes an operational monitoring device for electric resistance welding that acquires an image of electric resistance welding, acquires an image of a region including a V-convergence portion where both edges of an open pipe before they meet, and converts the temperature of the region in the image where the molten part inside the wall thickness begins to discharge to the surface, either at the meeting point of both edges or at the geometric convergence point formed by both edges, into a temperature using a brightness level, and determines whether the temperature is above a threshold value. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 11-33621 [Patent Document 2] Patent No. 5549963 Summary of the Invention [Problem to be solved by the invention]

[0009] In Patent Document 1, the temperature of the corners on the inner and outer surfaces of the joining end faces is measured, so it is possible to monitor the effect of the lapping state of both end faces before they are butted together. However, there is no temperature data for the center of the wall thickness, which is the most difficult to heat during high-frequency heating in electric resistance welding, so there is a problem that sufficient weld characteristics cannot be obtained due to insufficient heating of the center of the wall thickness.

[0010] In Patent Document 2, a lower limit is set for the temperature of the outer or inner surface at either the abutment point of both edges or the geometric convergence point of both edges to determine the quality of the welding conditions. However, like Patent Document 1, there is no temperature data for the center of the wall thickness, which causes the problem that sufficient weld characteristics cannot be obtained.

[0011] The present invention has been made in consideration of the above circumstances, and aims to provide an electric-welded steel pipe welding management device, a welding management system, an electric-welded steel pipe welding management method, and an electric-welded steel pipe manufacturing method for preventing welding defects. [Means for solving the problem]

[0012] In order to achieve the above-mentioned object, the inventors have conducted extensive research into the effects of the temperature distribution in the thickness direction of the end faces of both edges in electric resistance welding and the geometric angle (V-convergence angle) formed by the straight lines of both edges at that time on the shape of the penetrator remaining in the weld after upsetting with a squeeze roll and the characteristics of the weld. As a result, the following became clear.

[0013] Here, the flow of electric resistance welding will be described using an example of the process from heating to welding in electric resistance welding shown in FIG.

[0014] Conventionally, electric resistance welding is performed by heating using high-frequency current by direct current heating or induction heating. At this time, a heating phenomenon unique to high-frequency heating occurs in the early stage of heating, where the skin effect occurs. Therefore, the temperature of the outer surface and inner surface of the edge part becomes higher than that of the center part of the wall thickness. Heat transfer to the center part of the wall thickness occurs due to thermal conduction of this edge part. Next, as the heating process progresses, the distance between the end faces becomes closer, so the proximity effect occurs and the temperature rise rate of the center part of the wall thickness increases. Then, while the extreme surface layer of the entire edge part is heated to the melting point, it is upset by a squeeze roll and electric resistance welding is performed at the abutment part 202. At this time, the molten metal of the edge part is discharged to the outside of the pipe together with the penetrators distributed on the surface to form a weld bead 207.

[0015] As described above, in electric resistance welding, the temperature of the center of the wall thickness is delayed compared to the inner and outer surfaces of the edge, so the temperature tends to be lower. If the center of the wall thickness of the edge is not heated sufficiently, there is a problem that a sufficient amount of weld metal cannot be obtained during the heating process to eject the penetrator generated in the center of the wall thickness into the weld bead 207. Therefore, during the heating process, it is necessary to make the proximity effect of the center of the wall thickness appear early and reduce the temperature deviation in the wall thickness direction, and for this purpose, measures such as controlling the roll position of the forming roll to adjust the butting state of the joint end faces of both edges, such as the V convergence angle, are required.

[0016] The present invention is based on the above findings, and the gist of the present invention is as follows. [1] A welding management device for electric resistance welded steel pipes, which is manufactured by bending a steel plate or steel strip in the circumferential direction, butting both edges together to form an open pipe, and then using a stand to upset both edges of the butted open pipe, Before electric resistance welding, based on an image of a temperature distribution on at least one open pipe edge surface and spatial coordinates converted from pixel information of the image of the temperature distribution, The outer surface temperature T of the open pipe edge surface 0 , inner surface temperature T i a temperature detection unit for detecting the temperature Tc of the center of the wall thickness and the coordinates of the position where the temperature is measured; An edge temperature difference calculation unit that calculates a temperature difference ΔT between an outer surface and an inner surface of the open pipe edge surface; a V convergence angle calculation unit that calculates a V convergence angle θ formed by straight lines that converge along the open pipe edge portions based on image information of a region including a junction formed by straight lines that converge along both edge portions of the open pipe; a post-welding discharged molten steel area calculation unit that calculates an area A of molten steel discharged onto the outer surface of the pipe downstream of a position directly below the roll center of the welding stand in the welding direction based on image information including molten steel discharged onto the outer surface of the pipe downstream of a position directly below the roll center of the welding stand after electric resistance welding in the welding direction; a welding condition determination unit that determines whether the electric resistance welding conditions are good or bad based on information on a temperature difference ΔT between the outer surface and the inner surface of the open pipe edge surface, a temperature Tc of the wall thickness center portion, the V convergence angle θ, and an area A of the discharged molten steel; The welding management device for electric welded steel pipes is provided with: [2] In determining whether the electric resistance welding conditions are good or bad based on the amount of molten steel discharged onto the outer surface of the pipe downstream of the position directly below the roll center of the welding stand after electric resistance welding in the welding direction, a predetermined outer surface temperature T 0 , the predetermined inner surface temperature T i The welding control device for electric-resistance welded steel pipes described in [1] adjusts the welding power so as to obtain a predetermined temperature Tc at the center of the wall thickness. [3] A welding management device for electric resistance welded steel pipes according to [1] or [2], an edge temperature distribution photographing device for photographing the temperature distribution on both edge surfaces of the open pipe before electric resistance welding; A joint formed by straight lines converging along both edges of the open pipe before electric resistance welding; and a welded portion photographing device for photographing the molten steel discharged onto the outer surface of the pipe downstream of a position directly below the roll center of the welding stand in the welding direction after electric resistance welding; A welding management system for electric welded steel pipes. [4] A welding management method for electric-resistance welded steel pipes, which is manufactured by bending a steel plate or steel strip in the circumferential direction, butting both edges together to form an open pipe, and then using a stand to upset both edges of the butted open pipe, Before electric resistance welding, an outer surface temperature T of the open pipe edge surface is calculated based on an image of the temperature distribution on at least one open pipe edge surface and spatial coordinates converted from pixel information of the image of the temperature distribution. 0 , inner surface temperature T i a temperature detection step of detecting the temperature Tc of the center of the wall thickness and the coordinates of the position where the temperature is measured; An edge temperature difference calculation step of calculating a temperature difference ΔT between an outer surface and an inner surface of the open pipe edge surface; a V convergence angle calculation step of calculating a V convergence angle θ formed by straight lines converging along the open pipe edge portions based on image information of a region including a junction formed by straight lines converging along both edge portions of the open pipe; a post-welding discharged molten steel area calculation process for calculating an area A of molten steel discharged onto the outer surface of the pipe downstream of a position directly below the roll center of the welding stand in the welding direction based on image information including molten steel discharged onto the outer surface of the pipe downstream of a position directly below the roll center of the welding stand after electric resistance welding in the welding direction; a welding condition determination process for determining whether the electric resistance welding conditions are good or bad based on information on a temperature difference ΔT between the outer surface and the inner surface of the open pipe edge surface, a temperature Tc of the wall thickness center portion, the V convergence angle θ, and an area A of the discharged molten steel; The welding management method for electric resistance welded steel pipes includes: [5] A method for manufacturing an electric-resistance welded steel pipe using the welding control method for an electric-resistance welded steel pipe described in [4] above. Effect of the Invention

[0017] According to the present invention, electric resistance welded steel pipe having excellent quality can be obtained by performing welding while measuring the temperature distribution in the wall thickness direction and the welding conditions during electric resistance welding. [Brief description of the drawings]

[0018] [Figure 1] 1 is a diagram for explaining a welding management device and a welding management system including the same, showing one example of an embodiment of the present invention; [Diagram 2] 4 is a flowchart showing a processing procedure of the welding management system according to the present embodiment. [Diagram 3] FIG. 2 is a diagram showing an example of an electric resistance welding mode. [Figure 4] 1 is an explanatory diagram of each part of an image of a welded portion produced by electric resistance welding; [Diagram 5]FIG. 1 is a diagram for explaining an example of a method for determining the quality of a weld from the results of a flattening test under each condition of the temperature Tc at the center of thickness and the discharged molten steel area A in electric resistance welding, setting upper and lower limits Amax and Amin of the discharged molten steel area at each temperature Tc at the center of thickness, and deriving a function passing through each upper and lower limit point. [Figure 6] This figure explains an example of a method for determining the quality of a weld based on the results of a flattening test under each condition of the temperature Tc at the center of wall thickness and the discharged molten steel area A in electric resistance welding, setting upper and lower limits Amax and Amin of the discharged molten steel area at each temperature Tc at the center of wall thickness, deriving a function passing through each upper and lower limit point, and then deriving the upper and lower limits ΔTmax and ΔTmin of the temperature difference between the outer and inner surfaces of the pipe edge surface at a specified position in order to eliminate weld defects. [Figure 7] FIG. 1 is a diagram for explaining an example of a method for deriving an allowable range for any welding condition by deriving a distribution of the allowable range for welding from the relationship between the temperature Tc at the center of the wall thickness and the discharged molten steel area A from the results of a flattening test under each condition of the temperature Tc at the center of the wall thickness and the discharged molten steel area A for each V convergence angle θ in electric resistance welding, and interpolating the distribution of the allowable range for the welding at each V convergence angle θ. [Figure 8] FIG. 13 is a diagram showing the results of deriving the allowable ranges of the temperature Tc at the center of the wall thickness at a specified position and the area A of the discharged molten steel when the V convergence angle θ is 5°. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, a welding management device according to an embodiment of the present invention, a welding management system including the same, and a welding management method for electric resistance welded steel pipes will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, in the description of the drawings, the same parts are indicated by the same reference numerals.

[0020] First, referring to FIG. 1, a process flow of the present embodiment and a schematic configuration of a welding management device including a welding management system will be described. FIG. 1 is a diagram for explaining a welding management device and a welding management system including the same, showing an example of an embodiment for carrying out the present invention. A steel plate (or a steel strip) is continuously formed into a cylindrical shape by roll forming, and then, while proceeding in a welding direction 4 in the figure, the stability of the cylindrical shape is ensured by a fin pass roll 2, and the butt position of both edges is centered and the open tube 1 is formed. After that, both edges of the open tube 1 are heated until melted by supplying a high-frequency current from a high-frequency oscillator 3 through a pair of contact tips 31a, 31b. It is also possible to use an induction heating work coil instead of the contact tips 31a, 31b.

[0021] Next, the open tube 1 is pressed against both edges as it passes through a welding stand 40 surrounded by a group of rolls consisting of squeeze rolls 41a, 41b and top rolls 42a, 42b, and is welded (electric current welding) while molten steel is discharged onto the outer surface (the outer peripheral surface of the tubular steel plate).

[0022] The edge temperature distribution imaging device 10 is a thermometer capable of measuring temperature distribution in a two-dimensional image, such as a thermograph, and is installed so as to be able to image the entire wall thickness of the edge portion of the open pipe 1 located between the contact tips 31a, 31b and the welding stand 40, and images the heated surface from the outer surface to the inner surface at least at one of the opposing edges. In this case, the thermometer may be any thermometer capable of measuring temperature distribution, such as a radiation thermometer or a two-color thermometer. The edge temperature distribution imaging device 10 also includes an adjuster such as a zoom lens for adjusting the optical system and an exposure adjuster. It is preferable to ensure a resolution of 500 μm / pixel or less with an imaging field of view of 100 mm×40 mm. More preferably, it is 100 μm / pixel or less, and in this case, the number of pixels of the camera is preferably 1920×1080 or more. If the resolution is large, such as more than 500 μm / pixel, the detection accuracy of the edge temperature may be significantly deteriorated.

[0023] The welded portion photographing device 11 is installed, for example, using a camera, so as to be able to photograph the downstream side and the upstream side with respect to the squeeze roll center of the welding stand 40 with respect to the welding direction 4, and photographs the state in which both edge portions (welded portions) of the open pipe 1 are heated, melted, and pressure-welded. The position of the welded portion photographing device 11 is adjusted so that the photographed image taken by the welded portion photographing device 11 includes a joint point (V convergence point) described later and the roll center of the squeeze roll. At this time, the camera may be either for color image photographing or for monochrome image photographing. The welded portion photographing device 11 also includes adjusters such as a zoom lens and an exposure adjuster for adjusting the optical system. It is preferable to ensure a resolution of 100 μm / pixel or less with a photographing field of view of 100 mm×40 mm. More preferably, it is 50 μm / pixel or less, and in this case, the number of pixels of the camera is preferably 1920×1080 or more. If the resolution is greater than 100 μm / pixel, the detection accuracy of the molten steel may be significantly deteriorated. Furthermore, electric resistance welding may be performed at a welding speed exceeding 100 m / min, and in order to capture any shooting point within a 100 mm field of view at least once, it is preferable to set the frame rate to 20 fps or higher. If the frame rate is less than 20 fps, there will be areas in the welded part of the electric resistance welded pipe where image analysis of the weld cannot be performed, and there is a possibility that welding defects will be overlooked.

[0024] The welding management device 1000 acquires images of the welded part captured by the edge temperature distribution imaging device 10 and the welded part imaging device 11, respectively, using the edge temperature distribution imaging data input unit 100 and the welded part imaging data input unit 110. The welding management device 1000 is composed of a general-purpose computer such as a workstation or a personal computer, and has a calculation processing function such as a CPU, an image processing function such as a GPU, and various memory functions such as ROM and RAM as an example of a storage unit 1403 described below, as well as a recording medium such as a hard disk connected by a data communication terminal, and outputs such as a display device for graphics and an alarm device. In the welding management device 1000, a series of processes are performed using a memory that stores processing programs, etc., and a CPU that executes the processing programs, such as a temperature distribution processing unit 121 that detects the temperature distribution in the thickness direction from the outer surface to the inner surface of at least one edge portion heated by high-frequency current in an electric resistance welding edge temperature detection unit 122, a coordinate space calculation unit 123 that converts the coordinates (position) of the space where the temperature distribution is imaged, a data processing unit 124 that extracts the temperature distribution at a specified position in the pipe longitudinal direction in the temperature distribution from the outer surface to the inner surface of the heated edge, and an edge temperature difference calculation unit 125 that calculates the temperature difference ΔT between the outer surface and the inner surface of the open pipe edge surface at the specified position. In parallel, a series of processes are performed in the welding image processing unit 131, such as detection of red-hot edges of both ends around the V convergence point by the pipe edge image detection unit 132, calculation of the V convergence angle θ and the V convergence point by the V convergence angle calculation unit 133, detection of the actual joint position of both pipe edges by the joint point detection unit 134, and calculation of the discharged molten steel area A of the post-welding discharged molten steel discharged onto the outer surface of the pipe downstream from the welding stand by the post-welding discharged molten steel area calculation unit 135. Furthermore, welding judgment is performed by the welding state judgment unit 1401, and the judgment result is output by the output unit 1402, and welding management processing is performed.

[0025] Here, the welding management processing procedure by the welding management apparatus 1000 will be described with reference to the flowchart in Fig. 2. Fig. 2 is a flowchart showing the processing procedure of the welding management apparatus of this embodiment. In the flowchart in Fig. 2, for example, the process starts when an operator inputs an instruction to start the welding management process to the edge temperature distribution photography data input unit 100 and the welded part photography data input unit 110, and the processes of steps S1 and S6 proceed simultaneously in parallel.

[0026] In the process of step S1, the edge temperature detection unit 122 before electric resistance welding acquires two-dimensional temperature distribution data over the entire thickness of the edge portion before welding, for at least one of the two edges of the open pipe 1 heated by high-frequency heating, from the edge temperature distribution imaging device 10. Here, two-dimensional temperature distribution data on the joining surface of the edge portion, that is, in the pipe longitudinal direction and wall thickness direction, is extracted from the captured temperature distribution data. This completes the process of step S1, and the welding management process proceeds to the process of step S2.

[0027] In the process of step S2, a plurality of coordinate standard points are detected from the two-dimensional temperature distribution data captured in the process of step S1 or an image captured by a CCD camera attached to the edge temperature distribution imaging device 10, and the coordinate space calculation unit 123 performs spatial coordinate conversion from pixels to units of length. The coordinate standard points referred to here are preferably markers whose coordinate positions or distances between the respective standard points are self-evident in advance, but are not limited to this. By detecting the distance between any two standard points and inputting the real spatial distance of the distance between the standard points, the coordinate space calculation unit 123 performs spatial coordinate conversion in the image of the temperature distribution data. At the same time, the origin of the two-dimensional coordinates is set at an arbitrary position in the image of the temperature distribution data. Also, an arithmetic formula required for coordinate conversion from pixels to units of length may be derived in advance. This completes the process of step S2, and the welding management process proceeds to the process of step S3.

[0028] In the process of step S3, the data processing unit 124 extracts the temperature distribution in the thickness direction of the tube edge part at any longitudinal position of the tube from the temperature distribution data after the spatial coordinate conversion process described above, together with the coordinate values. The data processing unit 124 extracts the range of the tube edge part in the thickness direction, including a region of ±0.5 mm from the longitudinal position of the specified tube, and extracts the entire thickness region of the tube edge part. The corners corresponding to the outer and inner surfaces of the tube edge part are significantly heated due to the skin effect specific to high-frequency heating. Therefore, in the temperature distribution in the thickness direction, the temperature is high around the corner positions of the outer and inner surfaces of the tube edge part. To determine the entire thickness region, the distance between the peaks of the temperature distribution in the thickness direction at the outer and inner surfaces of the tube edge part is set as the tube thickness detected from the temperature distribution, and if the error from the previously inputted tube thickness is 3% or less, the peak apex of the temperature distribution around the outer surface of the tube edge part is set as the origin, and the temperature distribution in the thickness direction up to the peak apex of the temperature distribution around the tube edge part is extracted. If the error exceeds 3%, it is determined that the temperature distribution is not appropriate, and the field of view of the edge temperature distribution imaging device 10 is adjusted (a plurality of coordinate standard points are detected from the image captured by the CCD camera attached to the edge temperature distribution imaging device 10, and the coordinate space calculation unit 123 performs spatial coordinate conversion from pixels to units of length), and the process from step S1 is repeated again until the error is 3% or less. This completes the process of step S3, and the welding management process proceeds to the process of step S4.

[0029] In the process of step S4, the data processing unit 124 uses the extracted temperature distribution data in the thickness direction to extract the temperature at the center between the peaks of the temperatures at the outer and inner surfaces of the pipe edge, and defines this as the temperature Tc at the center of the thickness. At the same time, the temperatures at the peak apex positions of the temperature distribution around the outer and inner surfaces of the pipe edge are respectively defined as the outer surface temperature T o , inner surface temperature T i Extract as. This completes the process of step S4, and the welding management process proceeds to step S5.

[0030] In the process of step S5, the edge temperature difference calculation unit 125 calculates the outer surface temperature T o , inner surface temperature T i Here, the temperature difference ΔT is calculated by using the inner surface temperature T i from the outer surface temperature T o Then, the difference value is stored with a positive or negative sign attached. This completes the process of step S5, and the welding management process proceeds to step S9.

[0031] In the process of step S6, which is performed in parallel with the above steps S1 to S5, the pipe edge image detection unit 132 of the welding image processing unit 131 detects edges of the pipe edge portion that is heated to red heat by high-frequency heating, based on the image captured by the welded portion photographing device 11. Here, a differential method is used as the edge detection method, but the method is not limited to this. A specific description will be given with reference to Figs. 3 and 4. Fig. 3 is a diagram showing an example of the form of electric resistance welding, and Fig. 4 is an explanatory diagram of each part of the welded portion image of electric resistance welding. First, an edge detection image 20 of the welded part is obtained from the change in brightness around the heated part 201 using the captured image. Specifically, a gradient method using first-order differentiation is used to determine the boundary between the molten steel part with high brightness and the non-molten steel part with low brightness as the position showing the extreme value of the brightness change. In the edge detection image 20 of the welded portion, image processing is performed in the vertical direction from the opening 205 in a state where both edges are not joined to each other, and the position where the edge is first detected is set as a point on each edge. This processing is performed similarly on several points in the entire length of the opening 205 in the longitudinal direction, and straight lines La and Lb that approximate both edge end faces of the open pipe are approximated by the least squares method from the multiple points detected on each edge. Here, the opening 205 is an area sandwiched between the heated parts 201 of both edges, and the positions included in the opening 205 may be manually specified in advance before detecting the points on each edge, but this is not limited to this. With this, the processing of step S6 is completed, and the welding management processing proceeds to the processing of step S7.

[0032] In the process of step S7, V convergence angle calculation unit 133 calculates and extracts the V convergence angle θ using the straight lines La and Lb calculated by detecting both edges of the open pipe. The V convergence angle θ in the edge detection image of the weld is the angle formed by the two straight lines La and Lb, and is the acute angle on the opening 205 side. This completes the process of step S7, and the welding management process proceeds to the process of step S8.

[0033] In the process of step S8, the post-weld discharged molten steel area calculation unit 135 calculates the area A of the molten steel discharged on the outer surface of the pipe after the welding stand (SQ stand) 40. Here, the position after the SQ stand 40 refers to the downstream side of the position 204 directly below the roll center of the SQ stand in the welding direction, and this position is specified in advance. The method of specification may be, but is not limited to, a method of directly specifying the coordinate position or a method of detecting the coordinate position of a marker indicating the position 204 directly below the roll center of the SQ stand. Using an image captured by the welding part photographing device 11, the discharged molten steel downstream of the position 204 directly below the roll center of the SQ stand is set as the discharged molten steel 203 after the SQ stand. The area of ​​pixels occupied by this discharged molten steel 203 after the SQ stand is detected as the area of ​​molten steel discharged on the outer surface of the pipe, and a group of pixels having a brightness greater than a predetermined threshold value is determined as the molten steel area. The detected area of ​​molten steel discharged onto the outer surface of the pipe is processed using 50 images in the same field of view, the average value of the detected areas of molten steel is calculated, and this value is set as the area of ​​molten steel discharged onto the outer surface of the pipe, A. It is preferable that the image group on which the averaging process is performed is one or more rotation periods of the SQ roll. This completes the process of step S8, and the welding management process proceeds to the process of step S9.

[0034] In the process of step S9, the welding condition determination unit 1401 determines whether the welding conditions are good or bad based on the temperature Tc of the wall thickness center at the specified position, the temperature difference ΔT between the outer and inner surfaces of the pipe edge surface at the specified position, the V convergence angle θ, and the discharged molten steel area A after the welding stand, which are calculated or detected after the processes of steps 5 and 8 are completed. Specifically, an evaluation test of the weld is performed offline using steel pipes obtained under various welding conditions, and the relationship between the obtained weld characteristics and the temperature Tc of the wall thickness center at the specified position, the temperature difference ΔT between the outer and inner surfaces of the pipe edge surface at the specified position, the V convergence angle θ, and the discharged molten steel area A after the welding stand, which are calculated or detected by the welding management device 1000, is clarified in advance, and the upper and lower limits of the allowable range of the temperature difference ΔT between the wall thickness center Tc at the specified position and the outer and inner surfaces of the pipe edge surface at the specified position, which allows the desired quality of the weld to be obtained, are set.

[0035] The above allowable range is set for each V convergence angle θ, and the method is as follows. The boundaries of the allowable range, which treats the wall thickness center Tc at the specified position when welding is performed at a certain V convergence angle θ and the area A of the molten steel discharged after passing through the welding stand as parameters, are determined by the upper and lower limits of the allowable range using the area A of the molten steel discharged after passing through the welding stand and the temperature difference ΔT between the outer and inner surfaces of the pipe edge surface at the specified position. Offline evaluation tests for welds include flattening tests, ultrasonic testing to detect oxides in welds, and Charpy impact tests using test pieces cut from welds, and the test method is selected according to the desired properties.

[0036] Examples of methods for setting the upper and lower limits of the allowable range of the above-mentioned discharged molten steel area A and the temperature difference ΔT between the outer surface and the inner surface of the pipe edge surface at the specified position will be described below with reference to Figs. 5, 6 and 7, but the present invention is not limited to these. Fig. 5 is a diagram for explaining an example of a method for determining the quality of a welded portion based on the results of a flattening test under each condition of the temperature Tc of the wall thickness center in electric resistance welding and the discharged molten steel area A, setting the upper and lower limits Amax and Amin of the discharged molten steel area at each wall thickness center temperature Tc, and deriving a function passing through each upper and lower limit point. First, the discharged molten steel area A after passing through the welding stand detected under various welding conditions is matched with the characteristics desired for the steel pipe welded portion that was being welded at the time of detection. Here, the flattening ratio of the welded portion measured in the flattening test is used as the characteristic desired for the steel pipe welded portion. Here, the flattening ratio can be calculated based on the flattening test method described in JIS G3478:2015, and is calculated as H / D (outer diameter of the pipe D, distance between flat plates H when cracks start to occur in the weld in the flattening test). The smaller the flattening ratio H / D, the stronger the weld, and it is an index showing the characteristics of an excellent weld. In addition, the flattening ratio has an upper limit that is allowed depending on the type of steel pipe.

[0037] First, the relationship between the discharged molten steel area A, the wall thickness central portion Tc at the specified position, and the flattening ratio H / D at an arbitrary V convergence angle θ is clarified. In order to perform electric resistance welding with the arbitrary V convergence angle θ constant, electric resistance welding is performed without changing the fin width of the fin pass roll used for forming or the roll position of the squeeze roll. When performing electric resistance welding, the edge temperature distribution photographing device 10 measures the temperature difference ΔT between the wall thickness central portion Tc at the specified position and the outer and inner surfaces of the pipe edge surface at the specified position, and the welded portion photographing device 11 calculates the V convergence angle θ and the discharged molten steel area A. Then, electric resistance welding is performed with the welding power adjusted, and the flattening test is performed on the obtained pipe to measure the flattening ratio H / D.

[0038] Next, the roll position of the forming roll located upstream of the squeeze roll is changed to change the outer diameter curvature around the end of the open pipe, thereby adjusting the butt angle of both edges in the electric resistance welding. The butt angle here refers to the angle between the opposing end faces of both edges when the open pipe is viewed from the front. Rolls used for forming with changing roll position include, but are not limited to, edge forming and fin pass rolls. When the butt angle of both edges is changed, electric resistance welding is performed with the welding power adjusted as above, and the above flattening test is performed on the obtained pipe to measure the flattening ratio H / D. When the butt angle of both edges in electric resistance welding is changed, when the cross section is viewed from the front of the open pipe and the width of the opening of the open pipe is wider on the outer surface side (V-shaped butt), the outer surface temperature T 0 is the inner surface temperature T i The temperature difference ΔT between the outer and inner surfaces of the tube edge surface at the specified position is positive. Conversely, when the width of the open tube opening is narrower on the outer side (inverted V-shaped butt), the difference in the proximity effect causes the outer surface temperature T 0 is the inner surface temperature T i and the temperature difference ΔT between the outer surface and the inner surface of the tube edge surface at the specified position becomes negative. In the electric resistance welding repeatedly performed as described above, the flattening ratios H / D measured in the electric resistance welded steel pipe having the combination of the wall thickness center part Tc at the specified position and the discharged molten steel area A are plotted as shown in Fig. 5. Here, the weld property ◯ is equal to or less than the target flattening ratio H / D, i.e., the target weld strength is satisfied, and × is greater than the target flattening ratio H / D, i.e., the target weld strength is not satisfied. For each coordinate data, the upper and lower boundaries of the discharged molten steel area A at the wall thickness center part Tc at each specified position under the condition that the desired flattening ratio can be satisfied are obtained. The upper and lower boundaries of the discharged molten steel area A at each Tc are, under certain conditions for Tc, the maximum discharged molten steel area where the weld characteristic is ◯ adjacent to the data group area where the above-mentioned x is displayed for three or more consecutive plots in the increasing and decreasing directions of the discharged molten steel area A, if the upper limit, and the minimum discharged molten steel area where the weld characteristic is ◯ adjacent to the data group area where the above-mentioned x is displayed for the lower limit. Then, the upper limit Amax and the lower limit Amin of the discharged molten steel area A at each specified position in the wall thickness center Tc are calculated by a calculation method such as the least squares method to obtain the allowable range of the discharged molten steel area A. Although there is no specification on how to give the boundary here, in order to reduce calculation costs, a calculation method of the boundary by linear approximation is also possible. If the discharged molten steel area is less than Amin, the molten steel of the edge part discharged to the outside by the pressure of the squeeze roll during welding is insufficient, oxides remain in the welded part, and the flattening ratio deteriorates. On the other hand, if the discharged molten steel area exceeds Amax, the edge part is overheated during welding, and the generation and growth of oxides on the surface of the edge part becomes significant, and the flattening ratio deteriorates. Therefore, the allowable range of the discharged molten steel area A is Amin to Amax.

[0039] Next, for the coordinate data in which the upper and lower boundaries of the discharged molten steel area A are determined as described above, the upper and lower boundaries of the wall thickness center Tc at the designated position for each discharged molten steel area A are determined from the combinations of the discharged molten steel area A at the wall thickness center Tc at each designated position that exist within the allowable range. FIG. 6 is a diagram for explaining an example of a method for determining the quality of a weld based on the temperature Tc of the wall thickness center in electric resistance welding and the results of a flattening test under each condition of the discharged molten steel area A, setting the upper and lower limits Amax and Amin of the discharged molten steel area at each wall thickness center temperature Tc, and deriving a function passing through each upper and lower limit point, and then deriving the upper and lower limits ΔTmax and ΔTmin of the temperature difference between the outer surface and the inner surface of the pipe edge surface at the designated position to eliminate weld defects. In determining the upper and lower boundaries of the wall thickness center Tc, the boundaries are derived based on the temperature difference ΔT between the outer surface and the inner surface of the pipe edge surface at the designated position calculated at each point as shown in FIG. 6. Here, the temperature difference ΔT between the outer surface and the inner surface of the pipe edge surface at the specified position at each point is divided into data groups at regular intervals, such as 0°C or more and less than 10°C, and -10°C or more and less than 0°C. For example, ΔT1 in FIG. 6 is -200°C or more and less than -150°C, ΔT2 is -150°C or more and less than -100°C, and ΔT4 is 250°C or more and less than 300°C. A data group of maximum value ΔTmax and minimum value ΔTmin of the temperature difference ΔT that satisfies the desired welded joint characteristics within the range of Amin to Amax is extracted from the data group divided as described above, and a boundary that satisfies the range of the maximum value ΔTmax and minimum value ΔTmin of the temperature difference is obtained from the graph of the wall thickness center Tc at the specified position and the discharged molten steel area A. The boundary line is obtained using a calculation method such as the least squares method. Although there is no specification on how to give the boundary here, it is also possible to calculate the boundary by linear approximation in order to reduce calculation costs. As described above, by applying the temperature difference ΔT between the outer and inner surfaces of the pipe edge surface to the boundary of the discharged molten steel area A obtained in Fig. 5, it is possible to remove the levels of × mixed in the plot group where the welded part characteristics are ○, and to eliminate the conditions where the welded part characteristics are ×. Also, from a technical point of view, if the wall thickness center Tc at the above specified position is less than the lower limit ΔTmin, overheating on the outer surface side of the pipe becomes significant, and the area of ​​molten steel discharged to the outer surface of the pipe is overestimated.Therefore, even though the center of the thickness is not heated sufficiently, the image analysis using the welded part photographing device 11 erroneously determines that the area of ​​the molten steel discharged to the outer surface is acceptable, resulting in failure to achieve the desired flattening ratio of the welded part. Also, if the center of the thickness Tc at the specified position exceeds the upper limit ΔTmax, the outer surface of the edge part is not heated sufficiently, and in the upset by the squeeze rolls, the molten part near the outer surface of the edge part solidifies early and blocks the path for discharging the molten steel to the outside of the outer surface, so that the molten steel containing oxides is not discharged sufficiently, and the desired flattening ratio cannot be achieved.

[0040] FIG. 7 is a diagram for explaining an example of a method for deriving an allowable range under any welding condition by deriving a distribution of the allowable range of welding from the relationship between the temperature Tc of the center of thickness and the discharged molten steel area A from the results of a flattening test under each condition of the temperature Tc of the center of thickness and the discharged molten steel area A at each V convergence angle θ in electric resistance welding, and interpolating the distribution of the allowable range of welding with each V convergence angle θ. The allowable range 2000 shown in FIG. 7 is determined by changing the V convergence angle θ and repeating the same process for deriving the allowable range of the combination of the discharged molten steel area A and the center of thickness Tc at the specified position based on the above flattening ratio H / D. Here, the pitch of the V convergence angle θ is not particularly specified, but it is preferable to derive the allowable range by dividing it into 5 or more between the maximum and minimum values ​​of the preset V convergence angle θ under normal operating conditions. In addition, for the conditions of the V convergence angle θ for which the allowable range is not directly obtained as described above, a process such as interpolating and approximating the allowable range of the V convergence angle θ obtained before and after the condition is performed. The results obtained in this process can be recorded in the storage unit 1403. This completes the process of step S9, and the welding management process proceeds to the process of step S10.

[0041] In the process of step S10, output unit 1402 outputs to the outside the pass / fail judgment of the welding conditions obtained in step S9. Since the output to the outside requires an operator to recognize the judgment result, it is preferable to output to a graphic device, an alarm device, or the like provided in welding management device 1000. This completes the process of step S10, and ends a series of welding management processes.

[0042] The welding management device for electric resistance welded steel pipes has been described above as an embodiment of the present invention. The present invention also provides a welding management system having the above-mentioned welding management device. Furthermore, a welding management system having the above-mentioned welding management device can be used when manufacturing electric-resistance welded steel pipes. Specifically, the manufacturing method of electric-resistance welded steel pipes involves continuously bending a steel plate or steel strip in the circumferential direction, butting both edge portions together to form an open pipe, and then electric-resistance welding in which both edge portions of the butted open pipe are continuously upset using a welding stand, and during electric-resistance welding, welding management is performed by the process performed by the above-mentioned welding system. The welding management method for electric-resistance welded steel pipes is also carried out in the manner described above. Furthermore, electric-resistance welded steel pipes can be manufactured using the above-mentioned welding management method for electric-resistance welded steel pipes.

[0043] As described above, according to the present invention, the heating distribution and butt state of the end faces during electric resistance welding are measured with high accuracy, and the amount of molten steel discharged after welding is also taken into consideration, thereby making it possible to suppress welding defects.

[0044] In addition, the above-described embodiments of the present invention are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiments, 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 deviate from the spirit of the present invention. EXAMPLES

[0045] First, to derive the allowable range of welding conditions for various electric resistance welded pipes with a pipe thickness of 5 mm and a steel pipe outer diameter of φ90 mm, the V convergence angle θ was set to 3 to 7°, the position for measuring the temperature Tc at the center of the edge thickness was set to a position 6 mm upstream from directly below the axis of the squeeze roll of the welding stand, and the edge bend forming during forming was adjusted to set the difference value ΔT of the pipe inner and outer surface temperatures at the same position to -300°C to +300°C and the welding speed to 40 m / min, and electric resistance welding was performed. The V convergence angle θ was adjusted by changing the fin roll width of the fin pass roll. In addition, in order to adjust the temperature difference ΔT of the pipe inner and outer surface temperatures, the roll position of the fin pass roll was changed, and the bending deformation around the edge portion in particular was adjusted.

[0046] In various electric resistance welding, two-dimensional images of the temperature distribution before welding were obtained using a two-color thermometer camera while changing the welding power, with a frame rate of 20 fps, the number of pixels in the pipe longitudinal direction being 1920 pixels, the number of pixels in the pipe thickness direction being 1080 pixels, and the field of view in the pipe longitudinal direction being 50 mm. In addition, in various electric resistance welding, images before and after the welding part during welding were obtained using a CCD camera, with a frame rate of 20 fps, the number of pixels in the pipe longitudinal direction being 1920 pixels, and the field of view in the pipe longitudinal direction being 60 mm. From these obtained images, the temperature Tc of the wall thickness center at the specified position of each frame, the temperature difference ΔT between the outer surface and the inner surface of the pipe edge surface at the specified position, the V convergence angle θ, and the discharged molten steel area A after passing through the welding stand were extracted, and the average values ​​of Tc, ΔT, and A for one rotation of the squeeze roll when the V convergence angle θ was fixed to a predetermined value were calculated. The obtained steel pipe was cut to a length of 100 mm and a flattening test of the welded part was carried out based on JIS G3478:2015. The steel pipe was sandwiched between two flat plates, and the distance H between the two flat plates was measured when a crack occurred in the welded part. The flattening ratio H / D was calculated by dividing the distance H between the flat plates by the initial outer diameter D of the steel pipe. If the flattening ratio H / D was 2 / 3 or less, it was considered to have passed. For this series of operations, the allowable range of welding conditions was derived for the V convergence angle from 3° to 7° in 1° increments.

[0047] As a representative example, the results of deriving the allowable range of the temperature Tc at the center of the wall thickness at the specified position and the above-mentioned discharged molten steel area A when the V convergence angle θ is 5° are shown in Figure 8. Regarding the upper and lower limits of the allowable range of the temperature Tc at the center of the wall thickness at each of the above-mentioned specified positions and the above-mentioned discharged molten steel area A, the upper and lower limit values ​​of the temperature Tc at the center of the wall thickness at the specified position for each constant discharged molten steel area A were linearly approximated by the least squares method. Similarly, the upper and lower limit values ​​of the discharged molten steel area A for the temperature Tc at the center of the wall thickness at each constant specified position were linearly approximated by the least squares method. Here, the upper limit (ΔTmax) of the temperature difference ΔT between the outer surface and the inner surface of the pipe edge surface at the specified position was 250°C, and the lower limit (ΔTmin) was -80°C.

[0048] Table 1 shows the temperature Tc at the center of wall thickness, the temperature difference value ΔT between the inner and outer surfaces, the V convergence angle θ, the discharged molten steel area A, and the pass rate of the flattening ratio of the steel pipe for the invention example and the comparative example. For the invention example, the roll position was set up so that the temperature difference ΔT between the outer and inner surfaces of the pipe edge surface was about +100°C and the V convergence angle was about 5°. The temperature Tc at the center of the edge wall thickness was 1400°C±10°C, the discharged molten steel area was 3.2±0.2 mm 2 In contrast, in the comparative example, no welding control was performed during electric resistance welding, the welding power was adjusted, and the state of the discharged molten steel was confirmed only visually.

[0049] A flattening test of the welded part was carried out on 100 samples of 100 mm length cut out from the obtained electric resistance welded steel pipes based on JIS G3478:2015, and the flattening ratio H / D was measured. The pass rate of the flattening ratio H / D is the percentage of the number of steel pipes that satisfied the condition of 2 / 3 or less, and a pass rate of 95% or more is judged to have been properly electric resistance welded. The pass rate of steel pipe No. 1, which is an example of the invention, was 100%, indicating that electric resistance welded was properly performed, whereas the pass rate of steel pipe No. 2, which is a comparative example, was 92%, indicating that the required electric resistance welded was not performed.

[0050] [Table 1] [Explanation of symbols]

[0051] 1 Open Tube 2 Finpass Roll 3. High-frequency oscillator 4 Welding direction 10. Edge temperature distribution imaging device 11 Welding Part Photography Device 20 Edge detection image of welded part 31a, 31b Contact tips 40 Welding Stand 41a, 41b Squeeze roll 42a, 42b top roll 100 Edge temperature distribution photographing data input section 110 Welding part photography data input section 121 Temperature distribution processing section 122 Edge temperature detection part before electric resistance welding 123 Coordinate space calculation unit 124 Data Processing Unit 125 Edge temperature difference calculation section 131 Welding image processing unit 132 Tube edge image detection unit 133 V convergence angle calculation unit 134 Junction detection unit 135 Calculation of area of ​​molten steel discharged after welding 201 Heating section 202 Abutment part 202a, 202b Open tube both edge end faces 203 Molten steel discharged after welding stand 204 Directly below the roll center of the welding stand 205 Opening θ V convergence angle 207 Weld Bead 1000 Welding Management Equipment 1001 Welding Management System 1401 Welding condition judgment part 1402 Output section 1403 Storage section La, Lb Straight line approximating both edge faces of open tube 2000 Tolerance

Claims

1. A welding management device for electric resistance welded steel pipes, which is manufactured by electric resistance welding in which a steel plate or a steel strip is bent in the circumferential direction, both edge portions are butted together to form an open pipe, and then both butted edge portions of the open pipe are upset using a stand, Before electric resistance welding, based on an image of a temperature distribution on at least one open pipe edge surface and spatial coordinates converted from pixel information of the image of the temperature distribution, The outer surface temperature T of the open pipe edge surface ０ , inner surface temperature T ｉ a temperature detection unit for detecting a temperature Tc of the center of the wall thickness and a coordinate of a position where the temperature is measured; an edge temperature difference calculation unit that calculates a temperature difference ΔT between an outer surface and an inner surface of the open pipe edge surface; a V-convergence angle calculation unit that calculates a V-convergence angle θ formed by straight lines converging along the open pipe edge portions based on image information of a region including a junction formed by straight lines converging along both edge portions of the open pipe; a post-welding discharged molten steel area calculation unit that calculates an area A of molten steel discharged onto the outer surface of the pipe downstream of a position immediately below a roll center of a welding stand in the welding direction based on image information including molten steel discharged onto the outer surface of the pipe downstream of a position immediately below a roll center of the welding stand after electric resistance welding in the welding direction; a welding condition determination unit that determines whether the electric resistance welding conditions are good or bad based on information on a temperature difference ΔT between an outer surface and an inner surface of the open pipe edge surface, a temperature Tc of the wall thickness central portion, the V convergence angle θ, and an area A of the discharged molten steel; The welding management device for electric welded steel pipes is provided with:

2. In determining whether the electric resistance welding conditions are good or bad based on the amount of molten steel discharged onto the outer surface of the pipe downstream of the position directly below the roll center of the welding stand after electric resistance welding in the welding direction, a predetermined outer surface temperature T ０ , the predetermined inner surface temperature T ｉ 2. The welding management device for electric-resistance welded steel pipe according to claim 1, further comprising: a welding power adjustment unit that adjusts the welding power so as to obtain a predetermined temperature Tc at the center of the wall thickness.

3. The welding management device for electric resistance welded steel pipes according to claim 1 or 2, an edge temperature distribution photographing device for photographing the temperature distribution on both edge surfaces of the open pipe before electric resistance welding in order to extract the outer surface temperature T0, the inner surface temperature Ti, the temperature Tc of the wall thickness center portion of the open pipe edge surface, and the coordinates of the positions where the temperatures are measured, which are detected by the edge temperature detection unit before electric resistance welding; A joint formed by straight lines converging along both edges of the open pipe before electric resistance welding; and a welded portion photographing device for photographing the molten steel discharged onto the outer surface of the pipe downstream of a position directly below the roll center of the welding stand in the welding direction after electric resistance welding; A welding management system for electric welded steel pipes.

4. A method for managing welding of electric resistance welded steel pipes, which is manufactured by bending a steel plate or a steel strip in a circumferential direction, butting both edge portions together to form an open pipe, and then using a stand to upset both edge portions of the butted open pipe by electric resistance welding, Before electric resistance welding, an outer surface temperature T of the open pipe edge surface is calculated based on an image of the temperature distribution on at least one open pipe edge surface and spatial coordinates converted from pixel information of the image of the temperature distribution. ０ , inner surface temperature T ｉ a temperature detection step of detecting a temperature Tc of the wall thickness center portion and a coordinate of a position where the temperature is measured; an edge temperature difference calculation step of calculating a temperature difference ΔT between an outer surface and an inner surface of the open pipe edge; a V-shaped convergence angle calculation step of calculating a V-shaped convergence angle θ formed by straight lines converging along the open pipe edge portions based on image information of a region including a junction formed by straight lines converging along both edge portions of the open pipe; a post-welding discharged molten steel area calculation process for calculating an area A of molten steel discharged onto the outer surface of the pipe downstream of a position immediately below the roll center of the welding stand in the welding direction based on image information including molten steel discharged onto the outer surface of the pipe downstream of a position immediately below the roll center of the welding stand after electric resistance welding in the welding direction; a welding condition determination process for determining whether the electric resistance welding conditions are good or bad based on information on a temperature difference ΔT between an outer surface and an inner surface of the open pipe edge surface, a temperature Tc of the wall thickness central portion, the V convergence angle θ, and an area A of the discharged molten steel; The welding management method for electric resistance welded steel pipes includes:

5. A method for producing an electric resistance welded steel pipe, using the welding management method for an electric resistance welded steel pipe according to claim 4.

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