JP7616155B2 - 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 - Google Patents

Description

The present invention relates to an electric-resistance welded steel pipe welding management device, welding management system, electric-resistance welded steel pipe welding management method, and electric-resistance welded steel pipe manufacturing method, which quantify the temperature distribution in the open pipe edge portion immediately before electric-resistance welding of electric-resistance welded steel pipe and combine it with the constituent factors of the electric-resistance welded welding phenomenon to prevent welding defects.

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.

During electric resistance welding, both edges are heated above their melting point by direct current from 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 caused 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 similar.

To prevent welding defects, it is important to minimize the occurrence of penetrators and the aggregation of penetrators before welding. 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 excessive. 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 in the temperature distribution in the thickness direction of the edge portion until the start of joining, and to prevent poor discharge of the penetrators due to solidification of the molten edge portion during upset.

As a method to solve the above problems, various technologies 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 that visualizes the electric resistance welding phenomenon and measures the temperature of the edge during the melting and heating process.

Patent Document 1 proposes a welding temperature measurement method that detects the coordinates of the corner positions of the outer and inner surfaces of both edges of an open pipe before they are butted from a captured image, calculates the temperature distribution of the corners of the outer and inner surfaces of both edges, compares the detected coordinates with the calculated temperature distribution, determines the edge temperature at the detected coordinates, and controls the heating conditions of both edges.

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-shaped convergence portion where both edges of an open pipe before they meet, converts the temperature of the region where the molten part inside the wall thickness starts to discharge to the surface at either the meeting point of both edges or the geometric convergence point formed by both edges in the image, into a temperature value with a brightness level, and determines whether the temperature is above a threshold value.

Japanese Patent Application Publication No. 11-33621 Patent No. 5549963

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 with the high-frequency heating of 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.

In Patent Document 2, a lower limit is set for the temperature of the outer or inner surface at either the butt point of the two edges or the geometric convergence point of the two edges to determine whether the welding conditions are good or bad. However, like Patent Document 1, there is no temperature data for the center of the wall thickness, so there is a problem in that sufficient weld characteristics cannot be obtained.

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.

In order to achieve the above-mentioned objective, the inventors have conducted extensive research into the effects of the temperature distribution in the thickness direction of the end faces of both edges during 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.

Here, the flow of electric resistance welding will be explained using an example of electric resistance welding from heating to welding shown in Figure 3.

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 stages of heating, where the skin effect occurs. Therefore, the temperature of the outer and inner surfaces 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.

As mentioned 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 expel the penetrators 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. To achieve this, measures such as controlling the roll position of the forming rolls to adjust the butting condition of the joining end faces of both edges, such as the V-convergence angle, are required.

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 a steel strip in the 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,
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,
an edge temperature detection unit before electric resistance welding for detecting an outer surface temperature T ₀ of the open pipe edge surface, an inner surface temperature T _i , a wall thickness central temperature Tc, and coordinates of the positions where the temperatures are 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] A welding management device for electric resistance welded steel pipes as described in [1], in which, when judging the quality of electric resistance welded welding conditions based on the amount of 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 welded welding in the welding direction, the welding power is adjusted so that a predetermined outer surface temperature T ₀ , a predetermined inner surface temperature T _i , and a predetermined central temperature Tc of the wall thickness are obtained for any of the V convergence angles θ.
[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 welded portion photographing device for photographing a joint formed by straight lines converging along both edges of the open pipe before electric resistance welding, and for photographing 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 a steel strip in the 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, comprising the steps of:
an edge temperature detection process before electric resistance welding, for detecting an outer surface temperature _T0 , an inner surface temperature Ti, a wall thickness central temperature _Tc , and coordinates of positions where the temperatures are measured on the open pipe edge surfaces 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;
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 described in [4] above.

According to the present invention, electric resistance welded steel pipes of superior quality can be obtained by measuring the temperature distribution in the wall thickness direction and the welding conditions during electric resistance welding.

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; 4 is a flowchart showing a processing procedure of the welding management system according to the present embodiment. FIG. 2 is a diagram showing an example of an electric resistance welding mode. 1 is an explanatory diagram of each part of an image of a welded portion produced by electric resistance welding; 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 in electric resistance welding and the discharged molten steel area A, 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. 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 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 a specified position in order to eliminate weld defects. FIG. 13 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. 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 discharged molten steel when the V convergence angle θ is 5°.

Below, a detailed description of one embodiment of the present invention, a welding management device and a welding management system including the same, and a welding management method for electric resistance welded steel pipes, will be given with reference to the drawings. Note that the present invention is not limited to this embodiment. Also, in the drawings, the same parts are denoted by the same reference numerals.

First, referring to FIG. 1, the process flow of the present embodiment and the 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 implementing 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 the welding direction 4 in the figure, the stability of the cylindrical shape is ensured by a fin pass roll 2, and the butting positions of both edges are centered and formed into an open tube 1. After that, both edges of the open tube 1 are heated until melted by supplying 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.

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

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 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 on 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 adjusters 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 x 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 x 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.

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.
In addition, electric resistance welding may be performed at a welding speed exceeding 100 m/min, and in order to capture an image of 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 more. 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 welding cannot be performed, and there is a possibility that welding defects will be overlooked.

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, through 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, various memory functions such as ROM and RAM as an example of the storage unit 1403 described below, and also has a recording medium such as a hard disk connected by a data communication terminal, and outputs such as a display device to 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 detecting 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 front edge temperature detection unit 122, converting the coordinates (position) of the space where the temperature distribution is imaged in a coordinate space calculation unit 123, extracting 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 in a data processing unit 124, and calculating the temperature difference ΔT between the outer surface and the inner surface of the open pipe edge surface at the specified position in an edge temperature difference calculation unit 125. In parallel, the welding image processing unit 131 performs a series of processes, such as the detection of the red-hot edges of both ends around the V convergence point by the pipe edge image detection unit 132, the calculation of the V convergence angle θ and the V convergence point by the V convergence angle calculation unit 133, the detection of the actual position where the two pipe edges join by the joint point detection unit 134, and the calculation of the discharged molten steel area A after welding 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, the welding state determination unit 1401 performs welding determination, and the output unit 1402 outputs the determination result, thereby executing welding management processing.

Now, the welding management processing procedure by the welding management device 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 device of this embodiment. In the flowchart in FIG. 2, the process starts when an instruction to start the welding management process is input by an operator to the edge temperature distribution image data input unit 100 and the welded part image data input unit 110, and the processes of steps S1 and S6 proceed simultaneously in parallel.

In the process of step S1, the pre-electric-resistance welding edge temperature detection unit 122 acquires two-dimensional temperature distribution data from the edge temperature distribution imaging device 10 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 in the section up to welding. Here, two-dimensional temperature distribution data on the joining surface of the edge portion, i.e., 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.

In the process of step S2, multiple coordinate standard points are detected from the two-dimensional temperature distribution data captured in the process of step S1 or from 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 here are preferably markers whose coordinate positions or the distance between each standard point is 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 within 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. In addition, the calculation 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.

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 range extracted by the data processing unit 124 includes a region in the longitudinal direction of ±0.5 mm from the longitudinal position of the specified tube, and extracts the region of the entire thickness 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 an appropriate temperature distribution has not been achieved, and the field of view of the edge temperature distribution imaging device 10 is adjusted (a plurality of coordinate reference points are detected from an image captured by a CCD camera attached to the edge temperature distribution imaging device 10, and spatial coordinate conversion is performed from pixels to units of length in the coordinate space calculation section 123), and the process from step S1 is repeated again until the error is reduced to 3% or less. This completes the process of step S3, and the welding management process proceeds to the process of step S4.

In step S4, the data processor 124 extracts the temperature at the center between the temperature peaks at the outer and inner surfaces of the pipe edge using the extracted temperature distribution data in the thickness direction, and sets this temperature as the thickness center temperature Tc. At the same time, the data processor 124 extracts the temperatures at the peak apex positions of the temperature distribution around the outer and inner surfaces of the pipe edge as the outer surface temperature T _o and the inner surface temperature T _{i ,} respectively.
This completes the process of step S4, and the welding management process proceeds to step S5.

In the process of step S5, the edge temperature difference calculation unit 125 calculates the temperature difference ΔT between the outer surface temperature T _o and the inner surface temperature T _i of the extracted pipe edge portion. Here, the temperature difference ΔT is calculated by subtracting the outer surface temperature T _o from the inner surface temperature T _i , and the difference value is stored with a positive or negative sign. This completes the process of step S5, and the welding management process proceeds to the process of step S9.

In step S6, which is performed in parallel with 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 this is not limited to this. A specific description will be given with reference to Figures 3 and 4. Figure 3 is a diagram showing an example of the form of electric resistance welding, and Figure 4 is an explanatory diagram of each part of the electric resistance welding welded portion image.
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 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.

In the process of step S7, the 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.

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 includes, 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 the image captured by the welding part photography 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 the 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 to be the molten steel area. The area of molten steel discharged onto the outer surface of the pipe detected above is processed using 50 images in the same field of view, the average value of the detected molten steel area is calculated, and this value is set as the area A of molten steel discharged onto the outer surface of the pipe. It is preferable that the group of images subjected to the averaging process is equal to or greater than one rotation cycle of the SQ roll. This completes the process of step S8, and the welding management process proceeds to the process of step S9.

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.

The above tolerance range is set for each V convergence angle θ, and the method is shown below. The boundary of the tolerance 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, is determined by 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 the welds, and Charpy impact tests using test pieces cut from the welds, and the test method is selected according to the desired characteristics.

An example of a method 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 above-mentioned specified position will be described below with reference to Figures 5, 6, and 7, but this is not limited to this. Figure 5 is a diagram for explaining 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 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 that passes 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 weld that was being welded at the time of detection. Here, the flattening ratio of the weld measured in the flattening test is used as the characteristic desired for the weld of the steel pipe. 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 the 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 is an indicator of excellent weld characteristics. In addition, the allowable upper limit of the flattening ratio is determined depending on the type of steel pipe.

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 imaging 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 imaging 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.

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.
The rolls used for forming to change the 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 in the same manner as above, and the 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 open pipe is viewed from the front of the open pipe and the cross section is wider on the outer side (V-shaped butt), the outer surface temperature _T0 becomes smaller than the inner surface temperature _T1 due to the difference in the proximity effect, and the temperature difference ΔT between the outer surface and the inner surface of the pipe edge surface at the specified position is positive. Conversely, when the width of the open pipe opening is narrower on the outer side (inverted V-shaped butt), the outer surface temperature _T0 becomes larger than the inner surface temperature _T1 due to the difference in the proximity effect, and the temperature difference ΔT between the outer surface and the inner surface of the pipe edge surface at the specified position is 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 central portion Tc at the specified position and the discharged molten steel area A are plotted as shown in Fig. 5. Here, the welded portion characteristic ◯ is equal to or less than the target flattening ratio H/D, i.e., the target welded portion strength is satisfied, and × is greater than the target flattening ratio H/D, i.e., the target welded portion strength is not satisfied. For each coordinate data, the upper and lower boundaries of the discharged molten steel area A at the wall thickness central portion 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 zone characteristic is ◯ near the data group area where the weld zone characteristic is ◯ 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 zone characteristic is ◯ near the data group area where the weld zone characteristic is ◯, if the lower limit.
Then, the upper limit Amax and the lower limit Amin of the discharged molten steel area A at the wall thickness center Tc of each specified position are calculated using 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 set to Amin to Amax.

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 center of thickness Tc at the designated position for each discharged molten steel area A are determined among the combinations of discharged molten steel area A at the center of thickness Tc at each specified position that exist within the allowable range. Figure 6 is a diagram for explaining 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 of the center of thickness 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 temperature Tc of the center of thickness, deriving a function that passes 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 the designated position to eliminate weld defects. In determining the upper and lower boundaries of the center of thickness Tc, the boundaries are derived based on the temperature difference ΔT between the outer and inner surfaces of the pipe edge surface at the designated position calculated at each point as shown in Figure 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 values ΔTmax and minimum values ΔTmin of the temperature difference ΔT that all satisfy the desired welded joint characteristics within the range of Amin to Amax is extracted from the data groups divided as described above, and a boundary that satisfies the range of the maximum value ΔTmax and the minimum value ΔTmin of the temperature difference is obtained from a 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, a calculation method of the boundary by linear approximation is also possible in order to reduce calculation costs. As described above, by applying the temperature difference ΔT between the outer surface and the inner surface 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 x mixed in the plot group with the welded part characteristic of o, and to eliminate the conditions with the welded part characteristic of x. Also, from a technical point of view, if the wall thickness central part Tc at the above-mentioned specified position is less than the lower limit ΔTmin, the 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 wall thickness central part is not sufficiently heated, the image analysis using the welded part photographing device 11 erroneously determines that the area of molten steel discharged to the outer surface is acceptable, and as a result, the desired flattening ratio of the welded part cannot be satisfied. In addition, if the thickness center Tc at the specified position exceeds the upper limit ΔTmax, the outer surface of the edge will not be heated sufficiently, and when upset by the squeeze rolls, the molten part near the outer surface of the edge will solidify early and block the path for discharging molten steel to the outside of the outer surface, so that molten steel containing oxides will not be discharged sufficiently, and the desired flattening ratio will not be obtained.

7 is a diagram for explaining an example of a method for deriving the allowable range for any welding condition by deriving the 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 parts 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 calculated as described above, a process such as approximation is performed by interpolating the allowable range of the V convergence angle θ calculated before and after the condition. The results obtained by this process can be recorded in the memory unit 1403. This completes the process of step S9, and the welding management process proceeds to the process of step S10.

In the process of step S10, the output unit 1402 outputs the pass/fail judgment of the welding conditions obtained in step S9 to the outside. 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 the welding management device 1000. This completes the process of step S10, and ends the series of welding management processes.

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.

In this way, according to the present invention, it is possible to accurately measure the heating distribution and butt joint condition of the end faces during electric resistance welding, and also take into account the amount of molten steel discharged after welding, thereby suppressing welding defects.

The above-described embodiments of the present invention are merely examples for implementing 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.

First, to derive the allowable range of welding conditions for various electric resistance welded pipes with a pipe thickness of 5 mm and an 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 between the inner and outer surface temperatures of the pipe 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, to adjust the temperature difference ΔT between the inner and outer surface temperatures of the pipe, the roll position of the fin pass roll was changed, and the bending deformation around the edge portion in particular was adjusted.

In various electric resistance welding, a two-color thermometer camera was used to obtain two-dimensional images of the temperature distribution before welding while changing the welding power, with a frame rate of 20 fps, 1920 pixels in the pipe longitudinal direction, 1080 pixels in the pipe thickness direction, and a field of view in the pipe longitudinal direction of 50 mm. In addition, a CCD camera was used to obtain images before and after welding during various electric resistance welding, with a frame rate of 20 fps, 1920 pixels in the pipe longitudinal direction, and a field of view in the pipe longitudinal direction of 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 resulting steel pipe was cut to a length of 100 mm and a flattening test of the welded portion 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 portion. 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, the pipe was deemed 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.

As a representative example, FIG. 8 shows the results of deriving the allowable range of the temperature Tc of the wall thickness center at the specified position and the discharged molten steel area A when the V convergence angle θ is 5°. For the upper and lower limits of the allowable range of the temperature Tc of the wall thickness center at each of the specified positions and the discharged molten steel area A, the upper and lower limits of the temperature Tc of the wall thickness center at the specified position for each constant discharged molten steel area A were linearly approximated using the least squares method. Similarly, the upper and lower limits of the discharged molten steel area A for the temperature Tc of the wall thickness center at each constant specified position were linearly approximated using 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.

Table 1 shows the temperature Tc at the center of wall thickness, the inner and outer surface temperature difference value ΔT, 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. In 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°, and the welding power was adjusted so that the edge wall thickness center temperature Tc was 1400°C±10°C and the discharged molten steel area was 3.2±0.2 ^mm2 . In contrast, in the comparative example, no welding management was performed during electric resistance welding, the welding power was adjusted, and the state of the discharged molten steel was confirmed only visually.

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 pipe 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 considered 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 welding 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 welding was not performed.

REFERENCE SIGNS LIST 1 Open pipe 2 Fin pass roll 3 High frequency oscillator 4 Welding direction 10 Edge temperature distribution imaging device 11 Welded portion imaging device 20 Edge detection image of welded portion 31a, 31b Contact tip 40 Welding stand 41a, 41b Squeeze roll 42a, 42b Top roll 100 Edge temperature distribution imaging data input unit 110 Welded portion imaging data input unit 121 Temperature distribution processing unit 122 Edge temperature detection unit before electric resistance welding 123 Coordinate space calculation unit 124 Data processing unit 125 Edge temperature difference calculation unit 131 Welding image processing unit 132 Pipe edge image detection unit 133 V convergence angle calculation unit 134 Joint detection unit 135 Post-welding discharged molten steel area calculation unit 201 Heating unit 202 Collision unit 202a, 202b Open pipe both edge end faces 203 Molten steel discharged after welding stand 204 Position directly below roll center of welding stand 205 Opening θ V convergence angle 207 Weld bead 1000 Welding management device 1001 Welding management system 1401 Welding state determination unit 1402 Output unit 1403 Memory unit La, Lb Straight line approximating both edge end faces of open pipe 2000 Allowable range

Claims (5)

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,
an edge temperature detection unit before electric resistance welding for detecting an outer surface temperature T ₀ of the open pipe edge surface, an inner surface temperature T _i , a wall thickness central temperature Tc, and coordinates of the positions where the temperatures are 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. The welding management device for electric-resistance welded steel pipes according to claim 1, wherein, when judging the quality of electric-resistance welding conditions based on the amount of 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, the welding power is adjusted so that a predetermined outer surface temperature T ₀ , a predetermined inner surface temperature T _i , and a predetermined central wall temperature Tc are obtained for any of the V-convergence angles θ. 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 welded portion photographing device for photographing a joint formed by straight lines converging along both edges of the open pipe before electric resistance welding, and for photographing 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. 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,
an edge temperature detection process before electric resistance welding, for detecting an outer surface temperature _T0 , an inner surface temperature Ti, a wall thickness central temperature _Tc , and coordinates of positions where the temperatures are measured on the open pipe edge surfaces 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;
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: A method for manufacturing electric-resistance welded steel pipes using the welding management method for electric-resistance welded steel pipes described in claim 4.

Images