JP5909874B2 - Welding defect detection system for ERW pipe and method for manufacturing ERW pipe - Google Patents

Description

  The present invention relates to a weld defect detection system for an ERW steel pipe and an ERW steel pipe.

ERW steel pipes are manufactured by forming a strip (steel pipe material) into a cylindrical shape with a molding machine, heating and melting both edges of the V-shaped gap by high-frequency current energization, and press-bonding with a squeeze roll Is done.
Welding conditions are reflected in a moderate temperature, a suitable forming condition, a suitable material and an operating level. Here, by capturing changes in measurable elements, it is possible to determine whether welding is appropriate, to determine the cause of improperness, and to control input power in a feed-forward manner. The basic idea of welding monitoring and heat input control is to capture and set feedback.

In the above-described electric resistance welded pipe welding, the following method has been known as a conventional method for monitoring the welding heat input state among the welding states.
(1) A judgment method with the naked eye of the operator. (2) A method of measuring the temperature of a weld using a radiation thermometer, which is a method of converting total radiant energy into temperature, and using a ratio of energy levels of two specific wavelengths among the total radiant energy. How to convert to (3) A method of electrically detecting a change in resonance frequency and determining an excessive amount of heat input. (4) A method of grasping the shape of the protrusion of the bead after welding.

  Furthermore, even if the heat input is appropriate, if the edge is twisted, the edge shakes, or the squeeze roll pressure (upset) changes, welding failure may occur. As a monitoring method that can be grasped including changes in conditions, (5) the welded part and the heat generating metal part on the welding entry side are scanned by the imaging means and divided into a plurality of images, and the feature quantities of these images are There is a method that enables proper discrimination of the welding state and heat input control by determining the suitability of the welding state based on the analysis signal obtained by the processing unit and determining the suitability of the welding state (for example, Patent Document 1). .

  On the other hand, with regard to the defect detection technique, on-line flaw detection is generally performed on welds by ultrasonic oblique flaw detection. In this method, ultrasonic waves are incident obliquely on the inspection surface of the test material, and internal and external surface defects and internal defects of the test material are detected from reflected waves reflected by the defects. For example, a reflection method using an ultrasonic beam having a refraction angle of 45 ° at 5 MHz is usually applied to an electric resistance tube, and defects of the order of mm, for example, defects such as poor penetration, melt-down, and cracks due to inclusions are detected. ing. In the inspection by this ultrasonic flaw detection method, it is difficult to detect a minute welding defect of about several hundred μm or less. On the other hand, for example, according to the ultrasonic flaw detection method using an array probe as disclosed in Patent Document 2, it is possible to detect minute welding defects of about several tens of μm to several hundreds of μm. .

JP-A-5-318142 JP 2008-286640 A

The prior arts (1) to (5) described above are methods devised so that the welding state is optimized.
However, even with the best welding conditions within the scope of the prior art, very fine weld defects may still occur. This is a case where fine foreign matter is mixed in the electric-welded welded portion and a case where a paddle or the like is present at the end portion (edge portion) of the band material (tube material). In other words, iron oxide or iron on the surface of the tube material is peeled off during the electric seam forming welding process and exists as a small amount of dust in the atmosphere. In the electric seam welding process, the molten steel generated during welding is sputtered. Although present, when these dusts and spatter particles rarely jump into the weld, welding defects may occur. Furthermore, even when a portion where a slight wrinkle is generated at the end portion of the strip is electro-welded, the wrinkle may cause a welding defect. All of these weld defects are as small as several tens of μm to several hundreds of μm, and the occurrence positions may be distributed in a range from the inner surface to the outer surface of the tube along the weld line. there were.

In principle, the ultrasonic flaw detection method using the array probe has a low defect detection capability in the vicinity of the surface of the tube body. Therefore, when a minute defect of about 50 μm exists in the vicinity of the tube surface, the detection sensitivity is high. It may drop and be undetectable.
That is, in the prior art, a technique for detecting a minute welding defect of around 50 μm near the surface of the pipe rarely generated in the welded portion of the ERW steel pipe has not been established, and an ERW steel pipe having such a minute welding defect has not been established. There has been a problem that it is difficult to prevent rarely mixed products.

The present invention has been made to solve the above-mentioned problems, and the gist thereof is as follows.
(1) An electric wire for detecting a welding defect that occurs during the welding of an ERW steel pipe manufactured by continuously welding edges of a V-shaped gap formed by forming a strip into a tubular shape. A detection system for weld defects in a sewn steel pipe, wherein the brightness of a welded portion is monitored by a brightness sensor before welding and before bead cutting, and an image signal of a brightness distribution photographed by the brightness sensor is processed and calculated. From the transition curve for the sum of instantaneous luminance and / or the half-width pipe length, the pipe length part where the dark spot was generated was detected, and then the welded portion was used downstream of the bead cutting using an array probe. A welding defect detection system for ERW pipes, which is inspected with an ultrasonic flaw detector.
(2) An ultrasonic flaw detection apparatus using the array probe includes a wave transmitting unit that applies ultrasonic waves to a welding surface of a welded portion in a tube axis direction of a tubular body, and one of reflected waves reflected by the welded portion. Different transducer groups on one or two or more flaw detection array probes in which the transmitting part and the receiving part are arranged in the circumferential direction of the tube The system for detecting a weld defect in an ERW steel pipe according to (1) above, wherein the system is an ultrasonic flaw detector provided with a transmission / reception unit comprising:
(3) A method of manufacturing an ERW steel pipe to which the weld defect detection system for an ERW steel pipe according to (1) or (2) above is applied, wherein the thickness of the pipe body from the position of the outer surface of the pipe body An electric resistance welded steel pipe having a weld defect size of less than 50 μm in a portion up to a position inside by 1/4 of that and a weld defect size of less than 100 μm in the remaining portion. Manufacturing method .

  According to the present invention, it is possible to accurately detect a minute welding defect of around 50 μm near the surface of a tubular body that rarely occurs in an ERW steel pipe welded portion, and several tens of μm to several 100 μm inside the tubular body. Since welding defects are also detected, the reliability of the quality of the ERW steel pipe is improved.

Schematic diagram of an ERW steel pipe production line showing an example of an embodiment of the present invention Schematic diagram showing an example of the monitoring status of the welded part by the brightness sensor Schematic diagram showing the transition of luminance distribution monitoring data Diagram showing an example of the transition curve of the sum of instantaneous luminance with respect to pipe length Diagram showing one example of transition curve of half-value width of instantaneous luminance with respect to pipe length Explanatory drawing showing the principle of array UT in comparison with conventional UT

  FIG. 1 is a schematic view of an ERW steel pipe production line showing an example of an embodiment of the present invention. In this line, the strip 1 having a coil shape in the initial form is discharged with an uncoiler 2 and formed into a tubular shape with a roll forming machine 3, and the edges of the formed V-shaped gap are brought to the melting point or higher with a high-frequency heating device 4. After being heated and welded by pressing with a squeeze roll 5 to form a pipe 8, the outer surface bead of the welded part is cut with a bead cutting machine 6, and then the pipe 8 is cut into a predetermined length with a cutting machine 7. As the strip 1, a steel strip (hot rolled steel strip or cold rolled steel strip) or a material obtained by cutting the steel strip is used. In the example of FIG. 1, a direct current heating type device is shown as the high-frequency heating device 4, but the present invention is not limited to this, and an induction heating type device may be used (for example, see FIG. 2). Note that there may be a case where electric resistance welding is performed by inserting an impeller (not shown) on the inner side of the pipe material or the pipe in the passing direction range including the energized portion of the high-frequency current.

  In the present invention, the brightness sensor 10 monitors the brightness of the welded portion in the above-described line before welding bead cutting after welding (anywhere between the squeeze roll and the bead cutting machine). Furthermore, after that, the welded portion is inspected by an ultrasonic flaw detector 11 (hereinafter also referred to as array UT) using an array probe on the downstream side of the bead cutting machine. In the example of FIG. 1, the form in which the inspection by the array UT11 is performed on the cut tube 8 (offline inspection form) is shown, but not limited thereto, the inspection by the array UT11 is performed after bead cutting and before cutting. It is good also as a form (form to test | inspect on-line) with respect to this pipe | tube 8. FIG.

The inventors conducted a weld monitoring experiment using a luminance sensor, and as a result, dust and spatter rarely jumped into the welded part, resulting in welding defects, or minute flaws at the end of the band material. It was found that when the welded part is electro-welded and a welding defect occurs, the luminance distribution state on the welding point output side instantaneously changes to the dark side.
An example of the monitoring status of the welded portion by the luminance sensor is shown in FIG. The luminance sensor 10 is also called a luminance camera, and images a monitoring region 12 provided so as to cross the longitudinal direction on the outer surface side of the welded portion 14 between the welding point 13 and the bead cutting machine 6, and the luminance in the captured screen It has a function to derive the distribution. An example of such a brightness sensor is a commercially available line scan camera. The luminance information (instantaneous luminance) for each photographing frame of the luminance sensor 10 is captured and processed by a PC (personal computer) or the like, so that an image signal corresponding to the instantaneous luminance distribution curve is schematically shown in FIG. It can be monitored as aging data. The DS (dark spot) corresponding to the occurrence of welding defects due to rare jumps in dust or spatter or minute flaws at the end of the strip can be detected from the time-dependent data monitored. The information can be converted into the corresponding pipe length position information by the normally used tracking function, and the pipe length position where the welding defect has occurred can be specified, and the position information is notified to the refining process downstream of the pipe forming process. Thus, the pipe length portion including the weld defect can be surely excluded from the product pipe. In FIG. 2, 1b and 1c are edges of the V-shaped gap, and i is a high-frequency current.

In order to detect the change in luminance of the weld defect more reliably, the monitoring region 12 is preferably provided at a position 20 to 200 mm away from the welding point 13 on the downstream side.
Even when the speed of ERW welding exceeds 100 m / min, the luminance distribution monitored by the luminance sensor is less than 1 ms for the imaging speed so that the welding defect can be reliably identified and the welding defect is not overlooked. It is preferable to capture the image signal as a result of shooting at a shooting count of 1000 times / s or more.

  In reality, the luminance distribution captured as an image signal obtained by photographing with a luminance sensor does not necessarily indicate a simple and smooth mountain-shaped curve as shown in the schematic diagram of FIG. In many cases, the curve shape is shown, and it is difficult to immediately detect the DS from the instantaneous luminance data of such a complicated distribution curve shape (that is, to determine whether the welding state is instantaneous or not). Therefore, the inventors examined a method for overcoming this difficulty, and as a result, DS detection was reliably and reliably performed by processing the image signal and using the result of calculating the sum of instantaneous luminance and / or the half-value width. I found it easier. FIG. 4 shows an example of a transition curve of the sum of instantaneous luminance obtained by processing and calculating the image signal with respect to the tube forming length, and FIG. 5 shows processing and calculation of the same image signal as in FIG. An example of the transition curve with respect to the tube forming length of the half-value width of the instantaneous luminance is shown. These transition curves in FIGS. 4 and 5 show a shape having a clear recess in a substantially flat shape, and it can be understood that the tube-forming length portion where DS is generated can be detected reliably and easily.

  On the other hand, on the downstream side of the monitoring region 12, the welded portion is inspected offline or online using the array UT11 as described above. As described above, according to the array UT, it is possible to detect a minute welding defect of about several tens of μm to several hundreds of μm. FIG. 6 is an explanatory view showing the principle of the array UT11 in comparison with the conventional UT, and by using such an array UT, it is much finer than the conventional UT of about φ0.5 mm to 1.0 mm. For example, a welding defect of φ250 μm or less can be detected.

  The array UT illustrated in FIG. 6 has, as a suitable form, a wave transmission unit that inputs ultrasonic waves to the welding surface of the tube axis direction welded portion 14 of the tube body (tube 8), and a reflected wave reflected by the welded portion. Receiving part for receiving a part or all of the above, and the transmitting part and the receiving part are different vibrations on one or more array probes for flaw detection arranged in the circumferential direction of the tube It is an ultrasonic flaw detector provided with a transmission / reception unit comprising a group of children.

  Note that the array UT having a more preferable form is configured to receive a ultrasonic wave incident on the welding surface of the welded portion in the tube axis direction of the tubular body and a part or all of the reflected wave reflected by the welded portion. A transmitting / receiving unit comprising a group of different transducers on one or more array probes for flaw detection, wherein the transmitting unit and the receiving unit are arranged in the circumferential direction of the tube. A thickness measuring probe for measuring the thickness distribution of the tube, and based on the thickness distribution measured by the thickness measuring probe, using the flaw detection array probe, Propagation path calculation means for calculating an ultrasonic propagation path for scanning in the thickness direction of the tubular body, and based on the calculated propagation path, the transmitting unit and receiving wave on the flaw detection array probe The thickness of the tube by controlling the transducer group corresponding to the part or changing the angle of the flaw detection array probe Those in a form and a control unit for controlling the scanning (the invention described in Patent Document 2) are mentioned.

  According to this further preferred embodiment of the array UT, a minute defect of about several hundreds μm or less located inside the thickness of a welded portion such as an electric resistance welded steel pipe having a thickened portion on the inner surface leaks from the inner surface to the outer surface. Because it becomes possible to detect without defects, it becomes possible to improve the welding process so that micro defects that affect the mechanical properties of the welded part of the welded steel pipe do not occur, or to select in the manufacturing process so that defects do not flow out, The quality of the welded steel pipe can be drastically improved, and it can be used under conditions that are severer than before (see the effect column of the invention described in Patent Document 2).

  Even more preferably, the number of transducers of the transducer group for transmission and the transducer group for reception is set to be smaller as it is closer to the welded portion and larger as it is farther from the welded portion. In this way, the opening width at the time of simultaneous excitation becomes narrower toward the side closer to the welded portion, so that the beam width does not become too narrow even if the focal length is short, and the side farther from the welded portion becomes closer to the time of simultaneous excitation. Since the aperture width is wide, the focusing coefficient can be increased even when the focal length is long, and the detection ability does not deteriorate. Accordingly, since the focusing characteristics from each transducer group can be made uniform, flaw detection can be performed with uniform detection sensitivity from the inner surface side to the outer surface side inside the welded portion.

In the present invention, the reason why it is necessary to use both of the luminance sensor and the array UT instead of either is as follows.
In general, when a tube is used, stress tends to concentrate on the surface rather than the central portion in the thickness direction of the tube (strain is easily applied to the surface of the tube). Therefore, if there is a defect on the surface of the tube, the susceptibility to cracking is high, and even if it is a minute flaw, the mechanical characteristics are likely to deteriorate, which is likely to be a problem in use. That is, when there is a defect in the welded part, even if it is a defect of the same size compared to the central part in the thickness direction of the pipe, if the flaw is present in the central part in the thickness direction of the pipe, Although it does not become a problem, when a ridge exists in the vicinity of the surface of the pipe, problems such as cracking are likely to occur during use.

  The inventors have investigated in detail the influence of the presence form of defects, that is, the position and size of the defects, on the mechanical properties of the weld. As a result, if a defect having a size of 100 μm or more exists inside the welded portion of the pipe, the mechanical properties deteriorate, and even if a defect of less than 100 μm exists inside the welded portion of the tube, the mechanical properties are reduced. It has no effect, and when a defect of 50 μm or more exists near the surface of the welded part of the pipe, the mechanical properties deteriorate, and even if a defect of less than 50 μm exists near the surface of the welded part of the pipe It was discovered that it does not affect the mechanical properties.

By the way, the brightness sensor has a high defect detection capability in the vicinity of the surface of the welded part of the pipe, especially in principle for measuring the brightness of the surface of the object to be measured, and sufficiently detects a defect of about 30 μm near the surface of the welded part of the pipe. can do.
On the other hand, the array UT, in principle, has a low defect detection capability near the surface of the tube. Even if this is used, the detection sensitivity decreases when a minute defect of around 50 μm exists near the tube surface. Defects may not be detected.

For these reasons, in order to detect a minute defect of about 50 μm existing on the tube surface, monitoring with a luminance sensor is necessary.
By the way, in the array UT, flaw detection is possible with uniform detection sensitivity from the inner surface side to the outer surface side inside the tube. Therefore, it is possible to detect a minute defect of about 100 μm existing in the welded portion of the ERW steel pipe. For this purpose, it is preferable to set the number of transducers of the transmitting transducer group and the receiving transducer group to be smaller as it is closer to the welded portion and larger as it is farther from the welded portion. In this way, the closer to the welded portion, the narrower the opening width at the time of simultaneous excitation, so the beam width does not become too narrow even if the focal length is short. Since the aperture width is wide, the focusing coefficient can be increased even when the focal length is long, and the detection ability does not deteriorate. Accordingly, since the focusing characteristics from each transducer group can be made uniform, flaw detection can be performed with uniform detection sensitivity from the inner surface side to the outer surface side (see Patent Document 2 [0070] column).

On the other hand, the luminance sensor has a low defect detection capability inside the pipe in principle based on the principle of measuring the luminance of the surface of the object to be measured. Particularly, for a thick pipe having a thickness exceeding 6 mm, it is about 100 μm existing in the pipe weld. In some cases, a minute internal defect cannot be detected.
For these reasons, an array UT is required to detect minute defects of about 100 μm existing inside the pipe welded part without leaking from the inner surface side to the outer surface side.

  In the present invention, by combining the brightness sensor and the array UT, in the vicinity of the outer surface of the pipe welded portion, for example, the portion from the outer surface position of the pipe welded portion to the position inside the pipe wall thickness by 1/4. ERW steel pipes with a weld defect size of 50 μm or more can be eliminated, and the inside of the pipe welded part, for example, from the pipe outer surface position to the position inside the pipe wall thickness by 1/4 of the pipe wall thickness. Since the electric resistance welded steel pipe having a weld defect size of 100 μm or more in the remaining portion excluding the portion can be excluded, the position of the outer surface of the welded steel pipe according to the item (3) of the present invention, that is, the pipe welded portion. Only the ERW steel pipe with a weld defect size of less than 50 μm in the part from the inner wall to a position inside the pipe wall by a quarter of the wall thickness and less than 100 μm in the remaining part is reliably provided. You can The reliability of the quality is significantly improved.

  In the embodiment, a band material in which various artificial ridges such as fine ridges and spatters are provided at the end of the strip width obtained by slicing a hot-rolled steel strip, the ERW steel pipe production line shown in FIG. However, the high-frequency heating device 4 uses the induction heating type device of FIG. 2) and performs an electric resistance welding experiment. At that time, the welded portion including the artificial scissors is monitored by the luminance sensor 10 and inspected by the array UT11. did. The obtained ERW steel pipe is a test conforming to a 90 ° flattening test (for example, a flattening test (in the case of an annular test piece) specified in JIS G3445) of the welded portion, and the pipe diameter line passing through the welded portion is in the flattening direction. The tube is placed at 90 ° with respect to the test, and the flat characteristics of the welded portion are investigated, and the welded portion (the welded portion of the welded portion is the joint interface, almost perpendicular to the pipe circumferential direction) And welding defects existing there were observed by SEM (scanning electron microscope) to investigate the size of the welding defects. The results are shown in Table 1. In Table 1, at each level, the defect detection result of each of the luminance sensor and the array UT is indicated as “◯” when there is a defect, and “X” when there is no defect.

  From Table 1, the flat part of the welded part (the pipe outer diameter in the flattening direction when flattened and cracked in the welded part / the pipe outer diameter before flattening), that is, the defective part, It can be seen that the detection is completely possible by combining the arrays UT.

DESCRIPTION OF SYMBOLS 1 Strip 2 Uncoiler 3 Roll forming machine 4 High frequency heating device 5 Squeeze roll 6 Bead cutting machine 7 Cutting machine 8
DESCRIPTION OF SYMBOLS 10 Brightness sensor 11 Ultrasonic flaw detector (array UT) using array probe
12 Monitoring area 13 Welding point (Point where welded part is welded)
14 Welded part 15 Array probe

Claims (3)

  An electric resistance welded steel pipe for detecting a welding defect that occurs during the welding of an electric resistance welded pipe manufactured by continuously welding the edges of a V-shaped gap formed by forming a strip into a tubular shape. A welding defect detection system that monitors the brightness of a welded part by a brightness sensor before welding and after bead cutting, and processes and calculates an image signal of the brightness distribution photographed by the brightness sensor. From the transition curve for the total and / or half width of the tube length, the tube length portion where the dark spot is generated is detected, and then the ultrasonic inspection using the array probe is performed on the welded portion downstream of the bead cutting. A welding defect detection system for an ERW steel pipe characterized by inspecting with an apparatus.   The ultrasonic flaw detection apparatus using the array probe includes a wave transmitting portion that makes ultrasonic waves incident on a welding surface of a tube axial direction weld portion of a tubular body, and a part or all of a reflected wave reflected by the weld portion. Receiving and receiving, wherein the transmitting and receiving portions are composed of different transducer groups on one or more array detectors for flaw detection arranged in the circumferential direction of the tube It is an ultrasonic flaw detector provided with the part, The detection system of the weld defect of the electric resistance welded steel pipe according to claim 1 characterized by things. A method of manufacturing an ERW steel pipe to which the weld defect detection system for an ERW steel pipe according to claim 1 or 2 is applied, wherein the welded portion is inside by 1/4 of a pipe wall thickness from a pipe outer surface position. A method for producing an ERW steel pipe , characterized in that the size of the weld defect in the portion up to the position where it enters is less than 50 μm and the size of the weld defect in the remaining portion is less than 100 μm.

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