Eddy current flaw detection device and method

Abstract

To provide an eddy current flaw detection device and method capable of maintaining defect detection accuracy even when probe lift-off occurs on the surface of a test object.SOLUTION: An eddy current flaw detection device includes a probe 11 brought close to an inner surface of a pipe 1 and having an excitation coil and a detection coil, an eddy current measuring device 14 for energizing the excitation coil to induce an eddy current in the pipe 1, acquiring a change in the impedance of the detection coil caused by the change in the eddy current as a detection signal, and acquiring an X component and a Y component of the detection signal, and a computer 15. The computer 15 calculates the amount of lift-off of the probe 11 relative to the inner surface of the pipe 1 on the basis of the X component of the detection signal, corrects the Y component of the detection signal by multiplying it by a correction coefficient corresponding to the calculated amount of lift-off, and determines whether there is a defect in the pipe 1 on the basis of the corrected Y component of the detection signal.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to an eddy current flaw detection device and method for detecting defects in a test object using a probe having at least one coil. [Background technology]

[0002] Patent Document 1 discloses an eddy current flaw detector that uses a probe having multiple coils to detect defects in a test object. The eddy current flaw detector selects and switches between a combination of an excitation coil and a detection coil from among the multiple coils. The excitation coil is then excited to generate a magnetic field, inducing an eddy current in the test object. If a defect exists in the test object, the eddy current changes, which causes a change in the impedance of the detection coil. The eddy current flaw detector acquires and displays the change in impedance of the detection coil as a detection signal. An inspector can determine the presence or absence of a defect in the test object based on the level of the displayed detection signal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-194661 A Summary of the Invention [Problem to be solved by the invention]

[0004] For example, consider a case where a probe is moved along the inner surface of a pipe to detect defects in the pipe. The pipe may be locally deformed due to residual effects of thermal deformation caused by welding to other components. In non-deformed parts of the pipe, if the probe is pressed against the inner surface of the pipe, lift-off of the probe from the inner surface of the pipe will not occur. However, in deformed parts of the pipe, even if the probe is pressed against the inner surface of the pipe, lift-off of the probe from the inner surface of the pipe may occur. If probe lift-off occurs, the level of the detection signal changes according to the amount of lift-off. This reduces the accuracy of defect detection.

[0005] The present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide an eddy current flaw detection device and method that can maintain defect detection accuracy even if lift-off of the probe from the surface of the specimen occurs. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the present invention provides an eddy current flaw detection apparatus comprising: a probe having at least one coil and brought into close proximity with a surface of an object to be inspected; an eddy current measurement device that excites the coil to induce an eddy current in the object to be inspected, obtains a change in impedance of the coil caused by the change in the eddy current as a detection signal, and obtains X-component and Y-component of the detection signal; and a computer that judges the presence or absence of a defect in the object to be inspected based on the X-component and Y-component of the detection signal obtained by the eddy current measurement device, wherein the computer calculates an amount of lift-off of the probe with respect to the surface of the object to be inspected based on the X-component of the detection signal, corrects the Y-component of the detection signal by multiplying the Y-component by a correction coefficient corresponding to the calculated lift-off amount, and judges the presence or absence of a defect in the object to be inspected based on the corrected Y-component of the detection signal. Effect of the Invention

[0007] According to the present invention, even if lift-off of the probe from the surface of the object occurs, the defect detection accuracy can be maintained. [Brief description of the drawings]

[0008] [Figure 1] 1 is a block diagram showing a configuration of an eddy current flaw detector according to an embodiment of the present invention. [Diagram 2] 3A and 3B are axial and radial cross-sectional views of a pipe illustrating an example of a probe arrangement in one embodiment of the present invention. [Diagram 3] 5A and 5B are axial and radial cross-sectional views of a pipe illustrating another example of the arrangement of probes in one embodiment of the present invention. [Figure 4]3A and 3B are diagrams showing the structure of a probe in one embodiment of the present invention as viewed in the radial and circumferential directions of a pipe. [Diagram 5] 1 is a block diagram showing a configuration of an eddy current measurement device according to an embodiment of the present invention. [Figure 6] FIG. 11 is a diagram showing an increase in the Y component of a detection signal due to a defect in a pipe in one embodiment of the present invention. [Figure 7] FIG. 11 is a diagram showing a decrease in the X component of a detection signal due to lift-off of a probe in an embodiment of the present invention. [Figure 8] 4 is a flowchart showing a processing procedure of a computer in one embodiment of the present invention. [Figure 9] FIG. 4 is a diagram showing lift-off characteristics in one embodiment of the present invention. [Figure 10] FIG. 4 is a diagram illustrating a correction characteristic according to an embodiment of the present invention. [Figure 11] FIG. 13 is a view showing the structure of a probe in a modified example of the present invention as viewed from a radial direction of a pipe. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An embodiment of the present invention will be described with reference to the drawings.

[0010] FIG. 1 is a block diagram showing the configuration of an eddy current flaw detector in this embodiment. FIG. 2(a) is an axial cross-sectional view of a pipe showing an example of the arrangement of a probe in this embodiment, and FIG. 2(b) is a radial cross-sectional view of the pipe taken along the arrow AA in FIG. 2(a). FIG. 3(a) is an axial cross-sectional view of a pipe showing another example of the arrangement of a probe in this embodiment, and FIG. 3(b) is a radial cross-sectional view of the pipe taken along the arrow BB in FIG. 3(a). FIG. 4(a) is a view showing the structure of a probe in this embodiment as seen from the radial direction of the pipe, and FIG. 4(b) is a view seen from the direction of the arrow C in FIG. 4(a) (i.e., the circumferential direction of the pipe). FIG. 5 is a block diagram showing the configuration of an eddy current measurement device in this embodiment.

[0011] The eddy current flaw detection apparatus of this embodiment comprises a probe 11 brought close to the inner surface (surface) of a pipe 1 (test object), a moving mechanism 12 that moves the probe 11 along the inner surface of the pipe 1, a pressing mechanism 13 that presses the probe 11 against the inner surface of the pipe 1, an eddy current measuring device 14 that measures eddy currents in the pipe 1 using the probe 11, a computer 15 connected to the moving mechanism 12, the pressing mechanism 13, and the eddy current measuring device 14, and a monitor 16 connected to the computer 15.

[0012] The moving mechanism 12 broadly comprises an axial moving mechanism that moves the probe 11 in the axial direction of the piping 1 (the up and down direction in Figures 2(a) and 3(a)), and a circumferential moving mechanism that moves the probe 11 in the circumferential direction of the piping 1.

[0013] The axial movement mechanism includes a cylindrical holder 17 disposed in the pipe 1 and holding the probe 11, a ball screw 18 disposed at the radial center of the pipe 1, extending in the axial direction of the pipe 1, and screwed into a screw hole of the holder 17, a guide (not shown) extending parallel to the ball screw 18 (i.e., in the axial direction of the pipe 1) and inserted into a through hole (not shown) of the holder 17, a first motor (not shown) for rotating the ball screw 18, and a first drive circuit (not shown) for driving the first motor in response to a command from the computer 15. The rotation of the ball screw 18 moves the holder 17 in the axial direction of the pipe 1, and thus the probe 11 moves in the axial direction of the pipe 1.

[0014] The circumferential movement mechanism has a second motor (not shown) that rotates the guide around ball screw 18, and a second drive circuit (not shown) that drives the second motor in response to a command from computer 15. The rotational movement of the guide rotates holder 17, and thus probe 11 moves in the circumferential direction of pipe 1.

[0015] The pressing mechanism 13 has an electric cylinder 19 arranged between the bottom surface of the probe 11 and the groove bottom of the holder 17, or has a hydraulic cylinder 19 arranged between the bottom surface of the probe 11 and the groove bottom of the holder 17 and a control valve (not shown) that controls the flow of pressure oil from a hydraulic pump (not shown) to the hydraulic cylinder 19. The pressing mechanism 13 further has a third drive circuit (not shown) that extends or retracts the electric cylinder 19 or drives the control valve to extend or retract the hydraulic cylinder 19 in response to a command from the computer 15. The extension or retraction of the cylinder 19 presses the probe 11 against the inner surface of the pipe 1.

[0016] Probe 11 has a housing 20, an excitation coil 21, and detection coils 22A and 22B. Housing 20 has a shape consisting of, for example, a rectangular parallelepiped and a truncated quadrangular pyramid, and has a top surface 23 that contacts the inner surface of pipe 1 and a bottom surface 24 that faces the groove bottom of holder 17. In order to reduce the contact area with probe 11, top surface 23 of housing 20 is smaller than bottom surface 24. Housing 20 is formed from a resin material having high wear resistance (for example, an engineering plastic material or a PEEK material).

[0017] The excitation coil 21 and the detection coils 22A, 22B are arranged so that their end faces are approximately aligned with the top surface 23 of the housing 20, and are housed in the housing 20. The detection coil 22A is arranged in the circumferential direction of the pipe 1 (to the right in FIG. 4(a)) relative to the excitation coil 21, and has high detection sensitivity for defects extending in the circumferential direction of the pipe 1. The detection coil 22B is arranged in a diagonal direction between the axial direction of the pipe 1 (downward in FIG. 4(a)) and the circumferential direction of the pipe 1 relative to the excitation coil 21, and has high detection sensitivity for defects extending in the axial direction of the pipe 1.

[0018] The eddy current measuring device 14 has an oscillator 25, a bridge circuit 26, a phase shifter 27, a 90-degree phase shifter 28, and synchronous detectors 29A and 29B (see FIG. 5). In response to a command from the computer 15, the oscillator 25 applies an excitation signal (AC current) to the excitation coil 21 to generate a magnetic field and induce an eddy current in the pipe 1. If a defect exists in the pipe 1, this causes a change in the impedance of the detection coils 22A and 22B. The bridge circuit 26 is connected to the detection coil 22A or 22B via a multiplexer (not shown), and acquires and outputs the change in impedance of the detection coil 22A or 22B as a detection signal.

[0019] The phase shifter 27 adjusts the phase of the control signal based on the excitation signal of the oscillator 25, and outputs the adjusted control signal. The synchronous detector 29A acquires and outputs an X component (resistance component) synchronized with the phase of the control signal of the phase shifter 27 from the detection signal of the bridge circuit 26.

[0020] The 90-degree phase shifter 28 adjusts the phase of the control signal of the phase shifter 27 to be shifted by 90 degrees, and outputs the adjusted control signal. The synchronous detector 29B acquires and outputs a Y component (reactance component) that is synchronized with the phase of the control signal of the 90-degree phase shifter 28 with respect to the detection signal of the bridge circuit 26.

[0021] The computer 15 has a processor that executes processing according to a program, and a memory that stores programs and data. The computer 15 controls the moving mechanism 12 and the pressing mechanism 13 to control the position of the probe 11. The computer 15 controls the eddy current measuring device 14 to acquire the X component and the Y component of the detection signal. If a defect exists in the pipe 1, the level of the Y component of the detection signal increases significantly, as shown by the arrow D in Fig. 6. Therefore, the computer 15 determines the presence or absence of a defect in the pipe 1 based on the Y component of the detection signal.

[0022] Incidentally, the pipe 1 penetrates, for example, a reactor pressure vessel (not shown) and is welded to the reactor pressure vessel at the penetration position. If the pipe 1 is thin, such as being only a few mm thick, the influence of the thermal deformation caused by the welding described above may remain and the pipe 1 may be locally deformed. As shown in Figs. 2(a) and 2(b), in the non-deformed portion of the pipe 1, if the probe 11 is pressed against the inner surface of the pipe 1, the probe 11 does not lift off from the inner surface of the pipe 1. However, as shown in Figs. 3(a) and 3(b), in the deformed portion of the pipe 1, even if the probe 11 is pressed against the inner surface of the pipe 1, the probe 11 may lift off from the inner surface of the pipe 1. If the probe 11 lifts off, the level of the X component of the detection signal is greatly reduced as shown by the arrow E in Fig. 7, and the level of the Y component of the detection signal is also reduced. This reduces the accuracy of defect detection.

[0023] Therefore, the computer 15 of this embodiment calculates the lift-off amount of the probe 11 from the inner surface of the pipe 1 based on the X component of the detection signal. Then, the computer 15 corrects the Y component of the detection signal by multiplying the Y component by a correction coefficient corresponding to the calculated lift-off amount. Then, the computer 15 judges the presence or absence of a defect in the pipe 1 based on the Y component of the corrected detection signal.

[0024] Next, the eddy current flaw detection method of this embodiment, in particular, the processing procedure of the computer 15 will be described with reference to Fig. 8. Fig. 8 is a flowchart showing the processing procedure of the computer in this embodiment.

[0025] First, in step S1, the computer 15 controls the moving mechanism 12 and the pressing mechanism 13 to move the probe 11 to an initial inspection position. Then, in step S2, the computer 15 controls the eddy current measuring device 14 to obtain the X component and the Y component of the detection signal.

[0026] The computer 15 previously acquires and stores lift-off characteristics (see FIG. 9) that are the relationship between the X component of the detection signal and the lift-off amount of the probe 11. In step S3, the computer 15 calculates the lift-off amount L of the probe 11 that corresponds to the X component of the detection signal acquired in step S2, using the lift-off characteristics described above. Proceeding to step S4, the computer 15 determines whether the lift-off amount L calculated in step S3 exceeds a predetermined value L0 (for example, L0=0.7 mm).

[0027] If the lift-off amount L calculated in step S3 exceeds the predetermined value L0, the process proceeds to step S5. In step S5, the computer 15 controls the amount of extension and contraction of the cylinder 19 of the pressing mechanism 13 based on the lift-off amount L calculated in step S3 (specifically, so that the lift-off amount L becomes smaller). After that, the process returns to the above-mentioned step S2 to reacquire the X-component and the Y-component of the detection signal. Then, the same procedure as above is repeated.

[0028] If the lift-off amount L calculated in step S3 is equal to or smaller than the predetermined value L0, the process proceeds to step S6. The computer 15 acquires and stores in advance a correction characteristic (see FIG. 10) that is a relationship between the lift-off amount of the probe 11 and a correction coefficient. In step S6, the computer 15 calculates a correction coefficient corresponding to the lift-off amount L calculated in step S3 using the aforementioned correction characteristic, and multiplies the Y component of the detection signal acquired in step S2 by the correction coefficient to correct the Y component of the detection signal. The reciprocal of the correction coefficient corresponds to a reduction rate of the Y component of the detection signal due to the lift-off amount of the probe 11.

[0029] Proceeding to step S7, computer 15 determines whether or not level Y of the Y component of the detection signal corrected in step S6 exceeds a predetermined value Y0. If level Y of the Y component of the detection signal corrected in step S6 exceeds predetermined value Y0, proceeding to step S8, computer 15 determines that there is a defect and stores the determination result in association with the position of probe 11. On the other hand, if level Y of the Y component of the detection signal corrected in step S6 is equal to or less than predetermined value Y0, proceeding to step S9, computer 15 determines that there is no defect and stores the determination result in association with the position of probe 11.

[0030] Proceeding to step S10, computer 15 judges whether or not all inspection ranges have been inspected. If not all inspection ranges have been inspected, the process returns to step S1 described above. In step S1, computer 15 controls movement mechanism 12 and pressing mechanism 13 to move probe 11 to the next inspection position. Thereafter, the same procedure as above is repeated. If all inspection ranges have been inspected in step S10, the inspection ends.

[0031] As described above, in this embodiment, even if lift-off of the probe 11 from the inner surface of the pipe 1 occurs, the level of the Y component of the detection signal is corrected by multiplying the correction coefficient corresponding to the amount of lift-off, so that it is possible to prevent a decrease in the level of the Y component of the detection signal, and therefore it is possible to maintain the accuracy of defect detection.

[0032] In the above embodiment, the pressing mechanism 13 has been described as having the cylinder 19, but the present invention is not limited to this. The pressing mechanism 13 may have, for example, a spring.

[0033] In the above embodiment, the probe 11 has three coils (specifically, the excitation coil 21 and the detection coils 22A and 22B), but the present invention is not limited to this. For example, as in a modified example shown in FIG. 11, the probe 11 may have five coils 30A to 30E, and a combination of the excitation coil and the detection coil may be selected and switched. To explain in detail, the coil 30A or 30B is selected and switched as the excitation coil. When the coil 30A is selected as the excitation coil, the coil 30B or 30D is selected and switched as the detection coil. When the coil 30B is selected as the excitation coil, the coil 30C or 30E is selected and switched as the detection coil. Even in such a modified example, the same effect as that of the above embodiment can be obtained.

[0034] In the above embodiment, the probe 11 is of a mutual induction type and has an exciting coil and a detecting coil as separate bodies, but the present invention is not limited to this. The probe 11 may be of a self-induction type and have an exciting coil and a detecting coil as a single body. Therefore, the probe 11 only needs to have at least one coil.

[0035] In the above embodiment, the test object is described as the pipe 1, but it goes without saying that the test object is not limited to this. [Explanation of symbols]

[0036] 1 Pipe (subject) 11 Probe 14 Eddy current measuring device 15. Computers 19 Cylinders 21 Excitation coil 22A, 22B Detection coil 30A~30E coil

Claims

1. a probe having at least one coil and being brought into close proximity to a surface of the subject; an eddy current measuring device that excites the coil to induce an eddy current in the subject, obtains a change in impedance of the coil caused by the change in the eddy current as a detection signal, and obtains an X component and a Y component of the detection signal; and a computer that determines whether or not there is a defect in the test object based on an X component and a Y component of the detection signal acquired by the eddy current measuring device, The computer includes: calculating a lift-off amount of the probe with respect to the surface of the object based on an X component of the detection signal; correcting the Y component of the detection signal by multiplying the Y component by a correction coefficient corresponding to the calculated lift-off amount; The eddy current flaw detector is characterized in that the presence or absence of a defect in the test object is determined based on the Y component of the corrected detection signal.

2. The eddy current flaw detector according to claim 1, a cylinder that expands and contracts to press the probe against the subject; The eddy current flaw detection device is characterized in that the computer controls the amount of extension and contraction of the cylinder based on the calculated lift-off amount.

3. 1. An eddy current inspection method comprising: bringing a probe having at least one coil close to a surface of a test object; exciting the coil to induce an eddy current in the test object; acquiring a change in impedance of the coil caused by the change in the eddy current as a detection signal; and acquiring an X component and a Y component of the detection signal, calculating a lift-off amount of the probe with respect to the surface of the object based on an X component of the detection signal; correcting a Y component of the detection signal by multiplying the Y component by a correction coefficient corresponding to a lift-off amount of the probe; The eddy current inspection method further comprises determining whether or not the test piece has a defect based on the Y component of the corrected detection signal.

4. The eddy current inspection method according to claim 3, An eddy current flaw detection method, comprising controlling an amount of expansion and contraction of a cylinder that presses the probe against the test object based on the calculated amount of lift-off.

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