Eddy current testing equipment and method for electrically welded steel pipes

Abstract

To provide an eddy current flaw detecting device and the like that can provide stable defect detection performance even when a pipe-making speed changes in a pipe-making step of an electroseamed steel pipe.SOLUTION: An eddy current flaw detecting device 100 includes: a differential type detection coil 1 that outputs a flaw detection signal obtained by detecting an eddy current induced in an electroseamed steel pipe P; and a flaw detector 2 to which the flaw detection signal is input. The flaw detector includes: a cut-off frequency variable type high-pass filter to which the flaw detection signal is input; and cut-off frequency setting means 26 to which a pipe-making speed of the electroseamed steel pipe is input and which sets the cut-off frequency of the high-pass filter according to the pipe-making speed. The cut-off frequency setting means sets a cut-off frequency F on the basis of the following formula (1) when the cut-off frequency of the high-pass filter is F, the pipe-making speed of the electroseamed steel pipe is V, a length of the detection coil is L, and a prescribed coefficient of 0.1≤K≤0.4 is K. F=K×V / L...(1).SELECTED DRAWING: Figure 2

Description

Technical Field

[0004] , law , , , law , , ,

[0003] ,

[0002] , , ,

[0001] The present invention relates to an eddy current flaw detector for detecting defects existing in welded parts of electric welded steel pipes and the like. and Eddy current flaw detection method law In particular, the present invention relates to an eddy current flaw detector that can obtain stable defect detection ability even when the pipe manufacturing speed changes and is not constant in the pipe manufacturing process of electric welded steel pipes. and Eddy current flaw detection method law relates to.

Background Art

[0002] As is well known, an electric welded steel pipe (also referred to as an electric resistance welded steel pipe, ERW steel pipe) is manufactured by forming a steel plate (referred to as a hoop material) unwound from a coil into a tubular shape with a roll in the pipe manufacturing process of manufacturing an electric welded steel pipe, and butt-welding the ends of the formed tubular steel plates by applying electric resistance welding. This electric resistance welding is a method of generating eddy currents at the ends of the steel plates using an induction coil to which high-frequency power is applied, and pressing the ends of the steel plates heated (induction heating) by these eddy currents with a roll. The molten steel extruded onto the inner and outer surfaces of the steel pipe by electric resistance welding remains on the steel pipe as beads after cooling, and these beads are cut with a cutting tool immediately after welding.

[0003] In general, a cold drawing process is generally performed as a secondary processing process on the electric welded steel pipe obtained in the above pipe manufacturing process. The cold drawing process is a process of performing cold drawing by passing the steel pipe through a die with a plug or mandrel inserted into the steel pipe. This cold drawing process is suitable for manufacturing electric welded steel pipes having various dimensions using the steel pipe after the pipe manufacturing process as a raw material, and the electric welded steel pipe after the cold drawing process has the advantages that the outer diameter and wall thickness dimensions are uniform and the surface roughness is improved compared to the steel pipe after the pipe manufacturing process with cutting marks of beads remaining on the inner and outer surfaces.

[0004] In the pipe manufacturing process, if scale enters the gap between the butted ends of plate materials, defects (welding defects) may occur in the weld. The scale that enters may be contained in the cooling water used in the pipe manufacturing process or may be floating in the atmosphere during the shaping of the plate materials. If welding defects that occur in the pipe manufacturing process remain in the next secondary processing process, such as the cold drawing process, stress concentration may occur at this welding defect in the secondary processing process, potentially causing cracks in the steel pipe. If cracks occur in the steel pipe, the yield of the steel pipe will decrease, and problems may occur in the secondary processing process, potentially requiring a great deal of manpower to repair. For this reason, it is desirable to be able to accurately detect welding defects in the pipe manufacturing process.

[0005] Conventionally, in the pipe manufacturing process, eddy current testing of electric resistance welded steel pipes is generally performed using through-type and differential detection coils. However, the pipe manufacturing speed in the pipe manufacturing process (corresponding to the longitudinal feed rate of the electric resistance welded steel pipe immediately after welding) is generally not constant but changes during eddy current testing. Figure 1 schematically illustrates an example of a change in pipe manufacturing speed. As shown in Figure 1, when adjusting welding conditions, changing bead cutting tools, or making fine adjustments to their position, the pipe manufacturing speed is 0 or low. When checking the quality of the pipe after manufacturing, the pipe manufacturing speed is medium, and after quality confirmation, pipe manufacturing is performed at high speed. In addition, when the manufacturing of one electric resistance welded steel pipe is completed, or when it is lunchtime or outside of working hours, pipe manufacturing stops and the pipe manufacturing speed becomes 0. In this way, when eddy current testing is performed in situations where the pipe manufacturing speed changes from low speed to high speed, or from high speed to low speed, the magnitude of the flaw detection signal corresponding to the defect among the flaw detection signals output from the detection coil changes in accordance with the change in pipe manufacturing speed, which may result in an inability to obtain stable defect detection performance.

[0006] For example, Patent Document 1 proposes an eddy current testing device (eddy current flaw detection device) that uses a frequency filter to which a flaw detection signal is input, but this does not solve the above problem. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Utility Model Publication No. 58-83253 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] This invention was made to solve the problems of the prior art described above, and provides an eddy current flaw detection device that can obtain stable defect detection even when the pipe manufacturing speed is not constant but changes during the pipe manufacturing process of electric resistance welded steel pipes. and Eddy current flaw detection method law The objective is to provide this. [Means for solving the problem]

[0009] To solve the aforementioned problems, the inventors conducted diligent research. First, the inventors focused on the fact that in the case of eddy current testing using a differential detection coil, the center frequency f0 [Hz] of the inspection signal corresponding to the defect can be easily calculated based on the following equation (A). f0 = V / L ···(A) In equation (A) above, V [mm / sec] is the pipe-making speed of the electric resistance welded steel pipe, and L [mm] is the length of the detection coil. The length of the detection coil is the dimension expressed as L = L1 + L2 + L3, where L1 and L2 are the lengths of the pair of detection coil elements that make up the detection coil, and L3 is the length of the gap between the pair of detection coil elements. When a defect approaches the detection coil, the change in eddy current due to the defect affects the detection coil, so a low-frequency signal component appears in the flaw detection signal output from the detection coil. On the other hand, among the pair of detection coil elements constituting the detection coil, from the time when the defect reaches the center of the leading detection coil element (the defect reaches first) to the time when the defect reaches the center of the subsequent detection coil element, the magnitude of the flaw detection signal output from the detection coil changes linearly from the maximum value to the minimum value (or from the minimum value to the maximum value), so a high-frequency signal component appears. Therefore, the center frequency f0 of the flaw detection signal corresponding to the defect can be simply calculated based on the above formula (A), but the frequency band of the flaw detection signal corresponding to the defect has a wide band, not just the center frequency f0. Therefore, the cut-off frequency of the high-pass filter needs to be set to a value smaller than the center frequency f0.

[0010] Then, the inventors used a variable cut-off frequency high-pass filter as the high-pass filter to which the flaw detection signal is input, and set the cut-off frequency F [Hz] of this high-pass filter to K·f0, which is a value obtained by multiplying the above center frequency f0 by a predetermined coefficient K where 0<K<1. It was found that even if the pipe manufacturing speed V changes, the fluctuation in the magnitude of the flaw detection signal corresponding to the defect passing through the high-pass filter is within a predetermined range, and stable defect detection ability can be obtained. That is, it was found that the cut-off frequency F [Hz] of the high-pass filter may be set based on the following formula (B). F = K·f0 ···(B) From the above formulas (A) and (B), the following formula (1) holds. F = K·V / L ···(1)

[0011] The present invention has been completed based on the above findings of the inventors. In other words, to solve the above problem, the present invention, as a first means, provides an eddy current testing apparatus for testing electric resistance welded (ERW) steel pipes in a pipe manufacturing process where the pipe manufacturing speed changes, comprising: a differential detection coil that outputs a flaw detection signal obtained by detecting eddy currents induced in the ERW steel pipe; and a flaw detector connected to the detection coil and to which the flaw detection signal is input, wherein the flaw detector comprises a high-pass filter with a variable cutoff frequency to which the flaw detection signal is input, and a cutoff frequency setting means that receives the pipe manufacturing speed of the ERW steel pipe and sets the cutoff frequency of the high-pass filter according to the pipe manufacturing speed, wherein the cutoff frequency setting means sets the cutoff frequency F based on the following formula (1), when the cutoff frequency of the high-pass filter is F [Hz], the pipe manufacturing speed of the ERW steel pipe is V [mm / sec], the length of the detection coil is L [mm], and a predetermined coefficient K is greater than 0 and less than 1, and the value of the coefficient K is determined by the performance evaluation apparatus The performance evaluation device comprises a rotating body rotatable around a predetermined axis and provided with an artificial defect, a performance evaluation detection coil having the same coil design as the detection coil and capable of detecting changes in eddy currents due to the artificial defect, a rotation control means for controlling the rotation speed of the rotating body, and a peripheral speed detection means for detecting the peripheral speed of the artificial defect. The performance evaluation detection coil is connected to the flaw detector in place of the detection coil, and the peripheral speed of the artificial defect detected by the peripheral speed detection means is input to the cutoff frequency setting means of the flaw detector. The rotation control means controls the rotation speed of the rotating body so that the change pattern of the peripheral speed of the artificial defect matches the change pattern of the pipe manufacturing speed of the electric resistance welded steel pipe, and the value of the coefficient K is determined so that the fluctuation in the magnitude of the flaw detection signal corresponding to the artificial defect that has passed through the high-pass filter is within a predetermined range. F = K·V / L ···(1)

[0012] In the first means according to the present invention, "length of the detection coil" means the sum of the lengths of each detection coil element in a pair constituting a differential type detection coil and the length of the gap between the pair of detection coil elements. The length of the detection coil elements constituting the detection coil means the dimensions of the detection coil elements in the feeding direction of the electric resistance welded steel pipe that is the target of eddy current detection. "Coil design" refers to the length of each detection coil element in a pair of differential detection coils, and the length of the gap between the pair of detection coil elements. "A performance evaluation detection coil with the same coil design as the detection coil" means that the lengths of each detection coil element (corresponding to L1' and L2' shown in Figure 3(b) below) and the gap length (corresponding to L3' shown in Figure 3(b) below) that constitute the pair of detection coil elements constituting the performance evaluation detection coil are the same as the lengths of each detection coil element (corresponding to L1 and L2 shown in Figure 2 below) and the gap length (corresponding to L3 shown in Figure 2 below) that constitute the pair of detection coil elements that constitute the detection coil of the eddy current testing device. The lengths of the detection coil elements constituting the performance evaluation detection coil refer to the dimensions of the detection coil elements in the direction of feed (direction of rotation) of the rotating body that is the target of eddy current detection. "Velocity change pattern" refers to the progression of changes in velocity (peripheral velocity of artificial defects, pipe formation speed), expressed as acceleration rate, maximum velocity, duration of maximum velocity maintenance, deceleration rate, etc.

[0013] The first eddy current testing apparatus according to the present invention comprises a differential detection coil that outputs a flaw detection signal, and a flaw detector connected to the detection coil and to which the flaw detection signal is input. The flaw detector comprises a high-pass filter with a variable cutoff frequency to which the flaw detection signal is input, and a cutoff frequency setting means that receives the pipe manufacturing speed of the electric resistance welded steel pipe and sets the cutoff frequency F [Hz] of the high-pass filter according to the pipe manufacturing speed based on equation (1). The value of the coefficient K in equation (1) is predetermined using a performance evaluation device. The eddy current testing apparatus needs to be placed on the pipe manufacturing line when the pipe manufacturing process is executed, but the performance evaluation device can be placed offline, away from the pipe manufacturing line, when the pipe manufacturing process is executed. The performance evaluation device comprises a rotating body with artificial defects, a performance evaluation detection coil capable of detecting changes in eddy currents due to the artificial defects, a rotation control means for controlling the rotation speed of the rotating body, and a peripheral speed detection means for detecting the peripheral speed of the artificial defects. The performance evaluation detection coil has the same coil design as the detection coil (a differential type detection coil provided in an eddy current testing device). The rotation control means controls the rotation speed of the rotating body so that the pattern of change in the peripheral speed of the artificial defects matches the pattern of change in the pipe manufacturing speed of the electric resistance welded steel pipe. Therefore, the inspection signal output from the performance evaluation detection coil simulates the inspection signal output from the detection coil of the eddy current testing device in the pipe manufacturing process. Furthermore, the peripheral speed of the artificial defects detected by the peripheral speed detection means simulates the pipe manufacturing speed of the electric resistance welded steel pipe input to the cutoff frequency setting means provided in the inspection device of the eddy current testing device in the pipe manufacturing process.

[0014] Furthermore, in the first means according to the present invention, a performance evaluation detection coil is connected to the flaw detector of the eddy current testing device in place of the detection coil, and the peripheral speed of the artificial defect detected by the peripheral speed detection means is input to the cutoff frequency setting means of the flaw detector. When the rotation speed of the rotating body is controlled by the rotation control means so that the change pattern of the peripheral speed of the artificial defect matches the change pattern of the pipe manufacturing speed of the electric resistance welded steel pipe, the value of the coefficient K is determined so that the fluctuation in the magnitude of the flaw detection signal corresponding to the artificial defect that has passed through the high-pass filter is within a predetermined range. In other words, when a simulated flaw detection signal output from the detection coil of the eddy current testing device (flaw detection signal output from the performance evaluation detection coil) is input to the flaw detector, and a simulated pipe manufacturing speed of the electric resistance welded steel pipe (peripheral speed of the artificial defect detected by the peripheral speed detection means) is input to the cutoff frequency setting means, the value of the coefficient K is determined so that the fluctuation in the magnitude of the flaw detection signal corresponding to the artificial defect that has passed through the high-pass filter is within a predetermined range. Therefore, if the cutoff frequency setting means sets the cutoff frequency F based on equation (1) using the coefficient K of the value determined as described above, it can be expected that even when eddy current testing is performed on electric resistance welded steel pipes in an actual pipe manufacturing process where the pipe manufacturing speed changes, the fluctuation in the magnitude of the flaw detection signal corresponding to the actual defect that has passed through the high-pass filter will be within a predetermined range, and stable defect detection performance can be obtained.

[0015] Furthermore, the inventors used the above-described performance evaluation apparatus to evaluate the variation in the magnitude of the flaw detection signal corresponding to artificial defects that passed through the high-pass filter for multiple performance evaluation detection coils with different coil designs, multiple artificial defects with different change patterns and multiple different coefficient K values. Specifically, they evaluated the variation in the magnitude of the flaw detection signal corresponding to artificial defects that passed through the high-pass filter when using multiple performance evaluation detection coils with different coil designs within the range of coil designs of detection coils normally used in the pipe manufacturing process of electric resistance welded steel pipes, using multiple artificial defects with different change patterns within the range of pipe manufacturing speed change patterns normally set in the pipe manufacturing process of electric resistance welded steel pipes, and using multiple different coefficient K values. As a result, they found that by setting the value of coefficient K to 0.1 ≤ K ≤ 0.4, the variation in the magnitude of the flaw detection signal can be sufficiently reduced regardless of the coil design of the performance evaluation detection coil or the peripheral speed of the artificial defect (in other words, regardless of the coil design of the detection coil equipped in the eddy current testing apparatus or the pipe manufacturing speed of electric resistance welded steel pipes). In other words, to solve the above problems, the present invention, as a second means, provides an eddy current testing apparatus for electric resistance welded steel pipes that performs eddy current testing on electric resistance welded steel pipes in a pipe manufacturing process where the pipe manufacturing speed changes, comprising: a differential detection coil that outputs a flaw detection signal obtained by detecting eddy currents induced in the electric resistance welded steel pipe; and a flaw detector connected to the detection coil and to which the flaw detection signal is input, wherein the flaw detector comprises a high-pass filter with a variable cutoff frequency to which the flaw detection signal is input, and a cutoff frequency setting means that receives the pipe manufacturing speed of the electric resistance welded steel pipe and sets the cutoff frequency of the high-pass filter according to the pipe manufacturing speed, wherein the cutoff frequency setting means sets the cutoff frequency F based on the following formula (1), when the cutoff frequency of the high-pass filter is F [Hz], the pipe manufacturing speed of the electric resistance welded steel pipe is V [mm / sec], the length of the detection coil is L [mm], and a predetermined coefficient K is 0.1 or more and 0.4 or less. F = K·V / L ···(1)

[0016] According to the second means of the present invention, when eddy current testing is performed on electric resistance welded steel pipes in an actual pipe manufacturing process where the pipe manufacturing speed changes, the fluctuation in the magnitude of the flaw detection signal corresponding to the actual defect that has passed through the high-pass filter will be within a predetermined range, and it is expected that stable defect detection capability will be obtained.

[0017] Also, to solve the above problems, the present invention provides an eddy current flaw detection method for an electric welded steel pipe in a pipe manufacturing process where the pipe manufacturing speed changes, using an eddy current flaw detection device to perform eddy current flaw detection on the electric welded steel pipe. The eddy current flaw detection device includes a differential detection coil that outputs a flaw detection signal obtained by detecting an eddy current induced in the electric welded steel pipe, and a flaw detector connected to the detection coil and into which the flaw detection signal is input. The flaw detector includes a cut-off frequency variable type high-pass filter into which the flaw detection signal is input, and a cut-off frequency setting means for inputting the pipe manufacturing speed of the electric welded steel pipe and setting the cut-off frequency of the high-pass filter according to the pipe manufacturing speed. By the cut-off frequency setting means, when the cut-off frequency of the high-pass filter is F [Hz], the pipe manufacturing speed of the electric welded steel pipe is V [mm / sec], the length of the detection coil is L [mm], and a predetermined coefficient greater than 0 and less than 1 is K, a cut-off frequency setting step of setting the cut-off frequency F based on the following formula (1), a rotating body provided with an artificial defect and rotatable around a predetermined axis, a differential detection coil for performance evaluation having the same coil design as the detection coil and capable of detecting a change in eddy current due to the artificial defect, a rotation control means for controlling the rotation speed of the rotating body, and a peripheral speed detection means for detecting the peripheral speed of the artificial defect. A coefficient determination step of preliminarily determining the value of the coefficient K is provided using a performance evaluation device. In the coefficient determination step, the detection coil for performance evaluation is connected to the flaw detector instead of the detection coil, and the peripheral speed of the artificial defect detected by the peripheral speed detection means is input to the cut-off frequency setting means of the flaw detector. When the rotation speed of the rotating body is controlled by the rotation control means so that the change pattern of the peripheral speed of the artificial defect matches the change pattern of the pipe manufacturing speed of the electric welded steel pipe, the value of the coefficient K is determined so that the fluctuation in the magnitude of the flaw detection signal corresponding to the artificial defect passing through the high-pass filter is within a predetermined range. The present invention is also provided as an eddy current flaw detection method for an electric welded steel pipe, characterized by the above. F = K·V / L ···(1)

[0018] Also, to solve the above problems, the present invention provides an eddy current flaw detection method for an electric resistance welded steel pipe in a pipe manufacturing process where the pipe manufacturing speed changes, which uses an eddy current flaw detection device to perform eddy current flaw detection on the electric resistance welded steel pipe. The eddy current flaw detection device includes a differential detection coil that outputs a flaw detection signal obtained by detecting an eddy current induced in the electric resistance welded steel pipe, and a flaw detector connected to the detection coil and to which the flaw detection signal is input. The flaw detector includes a cut-off frequency variable type high-pass filter to which the flaw detection signal is input, and a cut-off frequency setting means to which the pipe manufacturing speed of the electric resistance welded steel pipe is input and that sets the cut-off frequency of the high-pass filter according to the pipe manufacturing speed. The cut-off frequency setting means has a cut-off frequency setting step of setting the cut-off frequency F of the high-pass filter based on the following formula (1), where the cut-off frequency of the high-pass filter is F [Hz], the pipe manufacturing speed of the electric resistance welded steel pipe is V [mm / sec], the length of the detection coil is L [mm], and a predetermined coefficient of 0.1 or more and 0.4 or less is K. This also provides an eddy current flaw detection method for an electric resistance welded steel pipe, characterized by the above. F = K·V / L ···(1)

[0019] Furthermore, to solve the above problems, the present invention also provides an electric resistance welded steel pipe that has been subjected to eddy current flaw detection by any of the above eddy current flaw detection methods.

Effects of the Invention

[0020] ​​​​​​​​​​​​​​​​​Figure 3 shows an example of the results of testing the effect of the coefficient K value on the magnitude of the flaw detection signal corresponding to the artificial defect AD using the performance evaluation device 200. [Figure 5] Figure 3 shows an example of the results of testing the effect of coil design on fluctuations in the magnitude of the flaw detection signal corresponding to artificial defects AD, using the performance evaluation device 200. [Figure 6] Assuming that eddy current testing is performed on an electric resistance welded steel pipe P using an eddy current testing apparatus of a comparative example with a different cutoff frequency setting means 26 shown in Figure 2, an example of the test results is shown in which the variation in the magnitude of the flaw detection signal corresponding to the artificial defect AD was evaluated using the performance evaluation apparatus 200 shown in Figure 3. [Modes for carrying out the invention]

[0022] The following describes an eddy current testing apparatus for electric resistance welded steel pipes according to one embodiment of the present invention, with reference to the attached drawings as appropriate. Figure 2 is a schematic diagram showing the general configuration of an eddy current testing apparatus 100 according to one embodiment of the present invention. In Figure 2, the electric resistance welded steel pipe P and the detection coil 1 are shown in a side view cross-section. The eddy current testing apparatus 100 according to this embodiment is a device for eddy current testing of electric resistance welded (ERW) steel pipes P in a pipe manufacturing process in which the ends of tubularly formed plate materials are butted together and welded. The eddy current testing apparatus 100 is, for example, positioned (fixed) on the exit side of a welding device (not shown) installed on a pipe manufacturing line that performs the pipe manufacturing process. As described above with reference to Figure 1, the pipe manufacturing speed of the ERW steel pipe P (corresponding to the longitudinal feed speed of the ERW steel pipe P immediately after welding, as shown by the thick arrow in Figure 2) is generally not constant but changes when eddy current testing is performed by the eddy current testing apparatus 100.

[0023] As shown in Figure 2, the eddy current testing apparatus 100 comprises a through-type detection coil 1 into which an electric resistance welded steel pipe P is inserted, and a flaw detector 2 connected to the detection coil 1. The detection coil 1 shown in Figure 2 is a self-inductive coil that also functions as an excitation coil, but it is not limited to this, and it is also possible to employ a mutual induction type coil in which the excitation coil is provided separately from the detection coil 1. Furthermore, the detection coil 1 is a differential type (self-comparison type) coil composed of a pair of detection coil elements 1a and 1b, and the differential signals of each detection coil element 1a and 1b are output as flaw detection signals. In other words, the detection coil 1 in this embodiment is a self-inductive self-comparison type coil.

[0024] The basic configuration of flaw detector 2 is similar to that of known flaw detectors commonly used in eddy current testing. However, flaw detector 2 of this embodiment differs from known flaw detectors in that it is characterized by the way in which the cutoff frequency of the frequency filter 25 is set by the cutoff frequency setting means 26. Specifically, the flaw detector 2 comprises an excitation circuit 21, a receiving circuit 22, a synchronous detection circuit 23, an amplifier 24, a frequency filter 25, a cutoff frequency setting means 26, and a determination unit 27. The excitation circuit 21 supplies an AC excitation current to the detection coil 1, which also functions as an excitation coil. This causes an AC magnetic field to act on the electric resistance welded steel pipe P, inducing eddy currents in the electric resistance welded steel pipe P. The detection coil 1 outputs a flaw detection signal (differential signal) obtained by detecting eddy currents induced in the electric resistance welded steel pipe P to the receiving circuit 22. The receiving circuit 22 adjusts the received flaw detection signal to the magnitude required for subsequent processing and outputs it to the synchronous detection circuit 23. The synchronous detection circuit 23 synchronously detects the flaw detection signal output from the receiving circuit 22 based on a reference signal output from the excitation circuit 21 (a reference signal having the same frequency as the excitation current supplied to the detection coil 1), and outputs the synchronously detected flaw detection signal to the amplifier 24. The synchronous detection circuit 23 has a phase adjustment function and adjusts the flaw detection signal corresponding to the defect to a predetermined phase. The amplifier 24 has a set flaw detection sensitivity (amplification degree of the flaw detection signal). The amplifier 24 amplifies the flaw detection signal output from the synchronous detection circuit 23 according to the set flaw detection sensitivity and outputs it to the frequency filter 25. The frequency filter 25 removes unwanted frequency components from the flaw detection signal output from the amplifier 24, extracts only specific frequency components, and outputs them to the determination unit 27. In this embodiment, the frequency filter 25 consists of a high-pass filter and a low-pass filter, and both filters are of the variable cutoff frequency type. The flaw detection signal output from the amplifier 24 to the frequency filter 25 passes through the high-pass filter, then through the low-pass filter, and is output from the frequency filter 25.

[0025] The cutoff frequency setting means 26 receives the pipe-making speed of the electric resistance welded steel pipe P from an external source. The input pipe-making speed may be in the form of a pulse signal (e.g., 1 pulse / mm) or a voltage signal having a voltage value corresponding to the speed. The pipe-making speed is measured, for example, using a touch roller that rotates in contact with the electric resistance welded steel pipe P. Specifically, a rotary encoder that outputs a predetermined number of pulse signals per rotation is attached to the rotation axis of the touch roller. For example, if a touch roller with a circumference of 1000 mm (outer diameter 318.5 mm) is used and a rotary encoder that outputs 1000 pulses / revolution is attached to its rotation axis, a pulse signal will be obtained in which 1 pulse is generated for every 1 mm of longitudinal movement of the electric resistance welded steel pipe P. It is known that pipe-making speeds measured using such a touch roller are used for output control of welding equipment and for short pipe cutting length control when cutting electric resistance welded steel pipe P to product length, so the same pipe-making speed can be input to the cutoff frequency setting means 26. If it is necessary to input the pipe-making speed to the cutoff frequency setting means 26 in the form of a voltage signal corresponding to the speed, the output of the rotary encoder can be input to the F / V conversion circuit, and the output of the F / V conversion circuit can be input to the cutoff frequency setting means 26. Then, the cutoff frequency setting means 26 sets the cutoff frequency corresponding to the input pipe manufacturing speed to the frequency filter 25. Specifically, the cutoff frequency setting means 26 calculates an appropriate cutoff frequency corresponding to the pipe manufacturing speed, and transmits the calculated cutoff frequency to the frequency filter 25 as a command value. Thereby, the cutoff frequency of the frequency filter 25 is changed to the same value as the command value. The specific content of the cutoff frequency setting by the cutoff frequency setting means 26 will be described later. A defect detection threshold value is set in the determination unit 27. The determination unit 27 performs A / D conversion on the flaw detection signal output from the frequency filter 25, then compares the A / D converted flaw detection signal with the defect detection threshold value, and detects a flaw detection signal exceeding the defect detection threshold value as a flaw detection signal corresponding to a defect.

[0026] Hereinafter, the specific content of the cutoff frequency setting by the cutoff frequency setting means 26 will be described. When the cutoff frequency of the high-pass filter constituting the frequency filter 25 is F [Hz], the pipe manufacturing speed of the electric welded steel pipe P is V [mm / sec], the length of the detection coil 1 is L [mm], and a predetermined coefficient greater than 0 and less than 1 is K, the cutoff frequency setting means 26 sets the cutoff frequency F of the high-pass filter based on the following formula (1). F = K·V / L ···(1) In other words, the cutoff frequency setting means 26 simply calculates the center frequency f0 [Hz] of the flaw detection signal corresponding to a defect based on the following formula (A), and as shown in the following formula (B), sets a value obtained by multiplying this center frequency f0 by a predetermined coefficient K where 0 <K <1 as the cutoff frequency F. f0 = V / L ···(A) F = K·f0···(B) As shown in FIG. 2, the length L of the detection coil 1 is a dimension represented by L = L1 + L2 + L3 when the lengths of a pair of detection coil elements 1a and 1b constituting the detection coil 1 are L1 and L2, and the length of the gap between the pair of detection coil elements 1a and 1b is L3.

[0027] In this embodiment, the value of the coefficient K for determining the cutoff frequency F of the high-pass filter is predetermined using a performance evaluation device and stored in the cutoff frequency setting means 26. The cutoff frequency F of the low-pass filter that constitutes the frequency filter 25 is also set based on equation (1) above, but the value of the coefficient K is different from that of the high-pass filter. For example, the value of K used to determine the cutoff frequency F of the low-pass filter is set to 1.5 ≤ K ≤ 2.0.

[0028] Figure 3 is a schematic diagram showing the general configuration of the performance evaluation device 200 used in this embodiment. Figure 3(a) is a perspective view showing the overall configuration of the performance evaluation device 200 when connected to the flaw detector 2 of the eddy current flaw detector 100. Figure 3(b) is a side cross-sectional view showing the configuration of the performance evaluation detection coil 33 provided in the performance evaluation device 200. The performance evaluation device 200 is configured to be movable. When executing the pipe manufacturing process, the performance evaluation device 200 can be placed offline, away from the pipe manufacturing line where the eddy current flaw detector 100 is located. Then, when evaluating the performance of the eddy current flaw detector 100 (determining the value of the coefficient K), the performance evaluation device 200 is moved to the pipe manufacturing line and connected to the eddy current flaw detector 100, specifically as described later, to determine the value of the coefficient K. As shown in Figure 3(a), the performance evaluation device 200 includes a rotating body 31 that is rotatable around a shaft member 32 and has an artificial defect (for example, a drill hole penetrating the rotating body 31 in the thickness direction) AD provided on it. Specifically, the rotating body 31 is fixed to the shaft member 32, and a rotary motor 36 is attached to one end of the shaft member 32 (the upper end in the example shown in Figure 3(a)). As the shaft member 32 rotates due to the rotary motor 36, the rotating body 31 fixed to the shaft member 32 also rotates integrally with the shaft member 32. Although the rotating body 31 shown in Figure 3(a) has a disc shape, it is not limited to this, and various shapes of rotating bodies 31 can be used, such as cylindrical or cylindrical shapes with greater thickness, as long as they can rotate around a predetermined axis.

[0029] Furthermore, the performance evaluation device 200 includes a performance evaluation detection coil 33, which has the same coil design as the detection coil 1 shown in Figure 2, and is capable of detecting changes in eddy currents caused by the artificial defect AD. Specifically, the performance evaluation detection coil 33 in this embodiment is a superimposed coil positioned directly above the artificial defect AD when the rotating body 31 rotates and the artificial defect AD moves, so as to be able to detect changes in eddy currents caused by the artificial defect AD. The performance evaluation detection coil 33 shown in Figure 3 is a self-inducting coil that also functions as an excitation coil, similar to the detection coil 1. However, it is not limited to this, and it is also possible to use a mutually inductive coil in which the excitation coil is provided separately from the performance evaluation detection coil 33. Furthermore, the performance evaluation detection coil 33 is a differential (self-comparison) coil composed of a pair of detection coil elements 33a and 33b, and outputs differential signals from each detection coil element 33a and 33b as a flaw detection signal. In other words, the performance evaluation detection coil 33 in this embodiment is a self-inducting self-comparison coil, the same as the detection coil 1. In order to facilitate the connection between the performance evaluation device 200 and the flaw detector 2 of the eddy current flaw detection device 100, it is preferable that the performance evaluation detection coil 33 of the performance evaluation device 200 be a self-inducting type when the detection coil 1 of the eddy current flaw detection device 100 is a self-inducting type, and that the performance evaluation detection coil 33 be a mutually inductive type when the detection coil 1 is a mutually inductive type. As mentioned above, the performance evaluation detection coil 33 has the same coil design as the detection coil 1 shown in Figure 2. That is, as shown in Figure 3(b), the lengths L1', L2', and gap length L3' of the pair of detection coil elements 33a and 33b that constitute the performance evaluation detection coil 33 are the same as the lengths L1, L2, and gap length L3 of the pair of detection coil elements 1a and 1b that constitute the detection coil 1 of the eddy current testing device 100. Therefore, the length L' (L'=L1'+L2'+L3') of the performance evaluation detection coil 33 is also the same as the length L of the detection coil 1.

[0030] Furthermore, the performance evaluation device 200 includes a rotation control means 34 for controlling the rotation speed of the rotating body 31, and a peripheral speed detection means 35 for detecting the peripheral speed of the artificial defect AD. The rotation control means 34 transmits a control signal indicating a pattern of change in rotational speed to the rotating motor 36, and the rotating motor 36 rotates at a rotational speed that changes according to the change pattern indicated by the transmitted control signal. As a result, the shaft member 32 to which the rotating motor 36 is attached, and consequently the rotating body 31 and the artificial defect AD, also rotate at a rotational speed that changes according to the change pattern indicated by the control signal transmitted from the rotation control means 34. The peripheral speed detection means 35 is attached to the other end of the shaft member 32 (the lower end in the example shown in Figure 3(a)) and consists of, for example, a rotary encoder that outputs a predetermined number of pulse signals per revolution. For example, if the circumference of the part of the rotating body 31 where the artificial defect AD is provided (the length the artificial defect AD moves during one revolution) is 100 mm, and the output of the rotary encoder is 100 pulses / revolution, then the peripheral speed detection means 35 will output a pulse signal of 1 pulse / mm as the peripheral speed of the artificial defect AD. Note that if a voltage signal having a voltage value corresponding to the speed is input to the cutoff frequency setting means 26 of the eddy current flaw detection device 100, the peripheral speed detection means 35 may be configured, for example, with a rotary encoder and an F / V conversion circuit, so that the output of the rotary encoder is converted to a voltage signal and output.

[0031] When determining the value of the coefficient K (the coefficient K for determining the cutoff frequency F of the high-pass filter) using the performance evaluation device 200 having the above configuration, the performance evaluation device 200 is moved to the pipe manufacturing line, and as shown in Figure 3(a), the performance evaluation detection coil 33 is connected to the flaw detector 2 in place of the detection coil 1 of the eddy current testing device 100. Specifically, the detection coil 1 of the eddy current testing device 100 and the signal cable for the detection coil connecting the detection coil 1 and the flaw detector 2 are removed from the flaw detector 2. Although not shown in Figure 3(a), the performance evaluation detection coil 33 is connected to the excitation circuit 21 and the receiving circuit 22 of the flaw detector 2 via the signal cable for the performance evaluation detection coil provided by the performance evaluation device 200. Furthermore, the signal cable for pipe formation speed, which receives the pipe formation speed of the eddy current testing device 100, is removed from the flaw detector 2. As shown in Figure 3(a), the peripheral speed of the artificial defect AD detected by the peripheral speed detection means 35 is input to the cutoff frequency setting means 26 of the flaw detector 2 (not shown in Figure 3(a)) via the peripheral speed signal cable provided by the performance evaluation device 200. On the other hand, the rotation control means 34 has a rotation speed change pattern pre-stored, which is determined so that the change pattern of the peripheral speed of the artificial defect AD matches the change pattern of the pipe-making speed of the electric resistance welded steel pipe P. Then, in the above connection state, the rotation control means 34 controls the rotation speed of the rotating body 31 (by a control signal indicating the pre-stored rotation speed change pattern) so that the change pattern of the peripheral speed of the artificial defect AD matches the change pattern of the pipe-making speed of the electric resistance welded steel pipe P. In this case, the value of the coefficient K is determined so that the fluctuation in the magnitude of the flaw detection signal corresponding to the artificial defect AD that has passed through the high-pass filter constituting the frequency filter 25 of the flaw detector 2 falls within a predetermined range.

[0032] Figure 4 shows an example of the results of a test (Test 1) using the performance evaluation device 200 to examine the effect of the coefficient K (a coefficient K used to determine the cutoff frequency F of the high-pass filter) on the magnitude of the flaw detection signal corresponding to the artificial defect AD. In Test 1, the rotation speed of the rotating body 31 was controlled by the rotation control means 34 so that the maximum peripheral speed of the artificial defect AD was 60 m / min, reaching the maximum speed from a stopped state (peripheral speed = 0 m / min) with an acceleration rate of 3.5 seconds, maintaining the maximum speed for 7 seconds, and then reducing the peripheral speed from the maximum speed to a stopped state with a deceleration rate of 1.0 seconds. In this state, the value of K set in the cutoff frequency setting means 26 was changed to 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0, and the magnitude of the flaw detection signal corresponding to the artificial defect AD (the magnitude of the flaw detection signal that passed through the high-pass filter constituting the frequency filter 25) for each K value was evaluated multiple times. As the detection coil 33 for performance evaluation, an upper coil with L1'=L2'=L3'=2 mm was used. The artificial defect AD was a drill hole with an outer diameter of 1.5 mm. Figure 4 shows an example of the results of a test conducted in Test 1 to examine the effect of the coefficient K value on the variation in the magnitude of the flaw detection signal corresponding to artificial defects AD during acceleration. In Figure 4, the horizontal axis represents the coefficient K, and the vertical axis represents the value obtained by dividing the variation in the magnitude of the flaw detection signal (3σ, where σ is the standard deviation) by the average value of the magnitude of the flaw detection signal, ave. As shown in Figure 4, if 0.1 ≤ K ≤ 0.4, the value of 3σ / ave is 10% or less. Therefore, by setting the coefficient K to 0.1 ≤ K ≤ 0.4, the fluctuation in the magnitude of the flaw detection signal corresponding to the artificial defect AD is small, and stable defect detection performance can be obtained. Consequently, even when eddy current testing is performed on electric resistance welded steel pipes P using the eddy current testing device 100 in the actual pipe manufacturing process, it can be expected that the fluctuation in the magnitude of the flaw detection signal corresponding to the actual defect that has passed through the high-pass filter will be small, and stable defect detection performance can be obtained.

[0033] Figure 5 shows an example of the results of a test (Test 2) conducted using the performance evaluation device 200 to examine the effect of coil design on fluctuations in the magnitude of the flaw detection signal corresponding to artificial defects AD. Figure 5(a) is a table showing the test conditions and results, including the coil design used in Test 2, and Figure 5(b) shows the results of Test 2. The notation "〇-□-△" in the "Coil Design" column in Figure 5(a) means that L1'=〇mm, L2'=△mm, and L3'=□mm for the performance evaluation detection coil 33. For example, "2-1-2" means that L1'=L2'=2mm and L3'=1mm for the performance evaluation detection coil 33. The horizontal axis in Figure 5(b) is the maximum peripheral speed of the artificial defect AD, and the vertical axis is 3σ / ave, as in Figure 4. In Test 2, the rotation speed of the rotating body 31 was controlled by the rotation control means 34 so that the peripheral speed of the artificial defect AD reached each of the maximum speeds shown in Figure 5(a) with an acceleration rate of 4.0 sec from a stopped state (peripheral speed = 0 m / min), maintained the maximum speed for 5 sec, and then decelerated from each maximum speed to a stopped state with a deceleration rate of 4.0 sec, resulting in a change in peripheral speed pattern. In this state, the value of the coefficient K (a coefficient for determining the cutoff frequency F of the high-pass filter) set in the cutoff frequency setting means 26 was set to 0.3 or 0.4 as shown in Figure 5(a), and the magnitude of the flaw detection signal corresponding to the artificial defect AD (the magnitude of the flaw detection signal that has passed through the high-pass filter constituting the frequency filter 25) was evaluated multiple times. The artificial defect AD was a drill hole with an outer diameter of 1.5 mm. As shown in Figure 5, when K = 0.3 or 0.4, the 3σ / ave value is 5% or less for both coil designs, indicating that the fluctuation in the magnitude of the flaw detection signal corresponding to the artificial defect AD is small, and stable defect detection performance can be obtained. Therefore, even when eddy current testing is performed on electric resistance welded steel pipes P using the eddy current testing device 100 in the actual pipe manufacturing process, regardless of which coil design of detection coil 1 is used, it can be expected that the fluctuation in the magnitude of the flaw detection signal corresponding to the actual defect that has passed through the high-pass filter will be small, and stable defect detection performance can be obtained.

[0034] Figure 6 shows an example of the results of a test (Test 3) in which the variation in the magnitude of the flaw detection signal corresponding to the artificial defect AD was evaluated using the performance evaluation device 200 shown in Figure 3, assuming that an eddy current testing device of a comparative example with a different cutoff frequency setting means 26 was used to test the electric resistance welded steel pipe P using eddy current testing. In Figure 6, the horizontal axis represents elapsed time, and the vertical axis represents the magnitude of the flaw detection signal corresponding to the artificial defect AD. In Test 3, the rotational speed of the rotating body 31 was controlled by the rotational control means 34 so that the maximum peripheral speed of the artificial defect AD was 60 m / min, reaching the maximum speed from a stopped state (peripheral speed = 0 m / min) with an acceleration rate of 3.5 seconds, maintaining the maximum speed for 7 seconds, and then reducing the peripheral speed from the maximum speed to a stopped state with a deceleration rate of 3.5 seconds. Unlike the cutoff frequency setting means 26 in Test 1 and 2, the cutoff frequency setting means 26 in Test 3 does not use a coefficient K when determining the cutoff frequency. The cutoff frequency setting means 26 in Test 3 has in advance investigated the cutoff frequency of the high-pass filter (the high-pass filter constituting the frequency filter 25) that maximizes the defect detection ability of the artificial defect AD when the peripheral speed of the artificial defect AD is at its maximum value, and this investigated cutoff frequency is stored in advance as a reference. The cutoff frequency setting means 26 in Test 3 is configured to linearly change the stored reference cutoff frequency according to the peripheral speed of the input artificial defect AD. For example, if the cutoff frequency of the high-pass filter that maximizes the defect detection ability of the artificial defect AD is F' when the maximum peripheral speed of the artificial defect AD is V' (and therefore the reference cutoff frequency is stored as F'), then when the peripheral speed of the artificial defect AD input to the cutoff frequency setting means 26 decreases to 0.5V', the cutoff frequency will also decrease to 0.5F'. As shown in Figure 6, when using the comparative example eddy current testing device, the magnitude of the detection signal corresponding to the artificial defect AD fluctuated significantly, and when evaluated at 3σ / ave, as in Tests 1 and 2, the result was 65.4%. Therefore, even when using the comparative example eddy current testing device to perform eddy current testing on electric resistance welded steel pipe P in an actual pipe manufacturing process, the magnitude of the detection signal corresponding to the actual defect that passed through the high-pass filter fluctuated significantly, and it is considered that stable defect detection performance cannot be obtained. [Explanation of Symbols]

[0035] 1. Detection coil 1a, 1b... Detection coil elements 2...Flaw detector 25... Frequency filter 26. Cutoff frequency setting means 100...Eddy current flaw detection equipment 200... Performance evaluation device P...ERW steel pipe

Claims

1. In the tube manufacturing process of electric resistance welded steel pipes where the tube manufacturing speed changes, an eddy current testing apparatus is used to perform eddy current testing on the electric resistance welded steel pipes, A differential detection coil that outputs a flaw detection signal obtained by detecting eddy currents induced in the aforementioned electric resistance welded steel pipe, The device comprises a flaw detector connected to the detection coil and to which the flaw detection signal is input, The flaw detector comprises a high-pass filter with a variable cutoff frequency to which the flaw detection signal is input, and a cutoff frequency setting means to which the pipe-making speed of the electric resistance welded steel pipe is input and to set the cutoff frequency of the high-pass filter according to the pipe-making speed. The cutoff frequency setting means sets the cutoff frequency F based on the following equation (1), where F [Hz] is the cutoff frequency of the high-pass filter, V [mm / sec] is the pipe-making speed of the electric resistance welded steel pipe, L [mm] is the length of the detection coil, and K is a predetermined coefficient greater than 0 and less than 1. The value of the coefficient K is predetermined using a performance evaluation device. The performance evaluation device is, A rotating body that can rotate around a predetermined axis and has an artificial defect, A differential type performance evaluation detection coil, having the same coil design as the detection coil, is capable of detecting changes in eddy currents due to the aforementioned artificial defect. Rotation control means for controlling the rotational speed of the rotating body, The system includes peripheral speed detection means for detecting the peripheral speed of the artificial defect, When the performance evaluation detection coil is connected to the flaw detector in place of the detection coil, and the peripheral speed of the artificial defect detected by the peripheral speed detection means is input to the cutoff frequency setting means of the flaw detector, the value of the coefficient K is determined such that when the rotation speed of the rotating body is controlled so that the change pattern of the peripheral speed of the artificial defect matches the change pattern of the pipe-making speed of the electric resistance welded steel pipe, the variation in the magnitude of the flaw detection signal corresponding to the artificial defect that has passed through the high-pass filter falls within a predetermined range. An eddy current testing device for electric resistance welded steel pipes, characterized by the following features. F=K・V / L...(1)

2. In the tube manufacturing process of electric resistance welded steel pipes where the tube manufacturing speed changes, an eddy current testing apparatus is used to perform eddy current testing on the electric resistance welded steel pipes, A differential detection coil that outputs a flaw detection signal obtained by detecting eddy currents induced in the aforementioned electric resistance welded steel pipe, The device comprises a flaw detector connected to the detection coil and to which the flaw detection signal is input, The flaw detector comprises a high-pass filter with a variable cutoff frequency to which the flaw detection signal is input, and a cutoff frequency setting means to which the pipe-making speed of the electric resistance welded steel pipe is input and to set the cutoff frequency of the high-pass filter according to the pipe-making speed. The cutoff frequency setting means sets the cutoff frequency F based on the following formula (1), where F [Hz] is the cutoff frequency of the high-pass filter, V [mm / sec] is the pipe-making speed of the electric resistance welded steel pipe, L [mm] is the length of the detection coil, and K is a predetermined coefficient of 0.1 or more and 0.4 or less. An eddy current testing device for electric resistance welded steel pipes, characterized by the following features. F=K・V / L...(1)

3. An eddy current testing method for electric resistance welded steel pipes, in a pipe manufacturing process where the pipe manufacturing speed changes, using an eddy current testing device to perform eddy current testing on the electric resistance welded steel pipe, The eddy current testing apparatus comprises a differential detection coil that outputs a flaw detection signal obtained by detecting eddy currents induced in the electric resistance welded steel pipe, and a flaw detector connected to the detection coil and to which the flaw detection signal is input. The flaw detector comprises a high-pass filter with a variable cutoff frequency to which the flaw detection signal is input, and a cutoff frequency setting means to which the pipe-making speed of the electric resistance welded steel pipe is input and to set the cutoff frequency of the high-pass filter according to the pipe-making speed. The cutoff frequency setting step involves setting the cutoff frequency F based on the following equation (1), where F [Hz] is the cutoff frequency of the high-pass filter, V [mm / sec] is the pipe-making speed of the electric resistance welded steel pipe, L [mm] is the length of the detection coil, and K is a predetermined coefficient greater than 0 and less than 1, using the cutoff frequency setting means. The performance evaluation apparatus comprises a rotating body rotatable around a predetermined axis and having an artificial defect, a differential type performance evaluation detection coil having the same coil design as the detection coil and capable of detecting changes in eddy currents due to the artificial defect, a rotation control means for controlling the rotation speed of the rotating body, and a peripheral speed detection means for detecting the peripheral speed of the artificial defect, and includes a coefficient determination step for predetermining the value of the coefficient K. In the coefficient determination step, the performance evaluation detection coil is connected to the flaw detector in place of the detection coil, and the peripheral speed of the artificial defect detected by the peripheral speed detection means is input to the cutoff frequency setting means of the flaw detector. The rotation speed of the rotating body is then controlled by the rotation control means so that the pattern of change in the peripheral speed of the artificial defect matches the pattern of change in the pipe-making speed of the electric resistance welded steel pipe. The value of the coefficient K is determined so that the variation in the magnitude of the flaw detection signal corresponding to the artificial defect that has passed through the high-pass filter falls within a predetermined range. A method for eddy current testing of electric resistance welded steel pipes, characterized by the features described herein. F=K・V / L...(1)

4. An eddy current testing method for electric resistance welded steel pipes, in a pipe manufacturing process where the pipe manufacturing speed changes, using an eddy current testing device to perform eddy current testing on the electric resistance welded steel pipe, The eddy current testing apparatus comprises a differential detection coil that outputs a flaw detection signal obtained by detecting eddy currents induced in the electric resistance welded steel pipe, and a flaw detector connected to the detection coil and to which the flaw detection signal is input. The flaw detector comprises a high-pass filter with a variable cutoff frequency to which the flaw detection signal is input, and a cutoff frequency setting means to which the pipe-making speed of the electric resistance welded steel pipe is input and to set the cutoff frequency of the high-pass filter according to the pipe-making speed. The cutoff frequency setting means includes a cutoff frequency setting step in which, when the cutoff frequency of the high-pass filter is F [Hz], the pipe-making speed of the electric resistance welded steel pipe is V [mm / sec], the length of the detection coil is L [mm], and a predetermined coefficient K is 0.1 or more and 0.4 or less, the cutoff frequency F is set based on the following formula (1). A method for eddy current testing of electric resistance welded steel pipes, characterized by the features described herein. F=K・V / L...(1)

Images