JP4986066B2 - Eddy current flaw detection method and apparatus - Google Patents

Description

  The present invention relates to an eddy current flaw detection method and apparatus for detecting a thinning of the outer surface of a heat transfer tube by volume inspection in an in-service period of a steam generator heat transfer tube in a sodium-cooled fast reactor.

  The eddy current flaw detection for volume inspection of the outer wall thinning of the heat transfer tube during the service period of the steam generator heat transfer tube in the sodium-cooled fast reactor is performed in the state in which sodium is extracted from the container of the steam generator subject to the flaw detection test The ECT probe is inserted into the inspection position inside the tube, the eddy current that changes according to the change in the thickness of the heat transfer tube is measured, and the measurement signal is analyzed. In such an inspection, it is known that if sodium, which is a conductive substance, adheres to the outer surface of the heat transfer tube 41, the eddy current is affected, and the support plate that supports the heat transfer tube is also affected. Yes.

JP 2002-181793 A JP 2007-263946 A

  In the eddy current flaw inspection for volume inspection of the outer wall thinning of the heat transfer tube during the service period of the steam generator heat transfer tube in a sodium-cooled fast reactor, sodium or a heat transfer tube attached to the heat transfer tube An object of the present invention is to realize an eddy current flaw detection method and apparatus capable of reducing the influence of a support plate to be supported and realizing an accurate flaw detection (thinning determination).

The eddy current flaw detection method of the present invention is
An ECT probe of an eddy current flaw detector is inserted into an inspection position inside a heat transfer tube that is supported by a support plate in the vessel with sodium removed from the vessel of the steam generator, and the thickness of the heat transfer tube In the eddy current flaw detection method for measuring the eddy current that changes in accordance with the change of the flaw, and flaw detection of the thinning generated on the outer periphery of the heat transfer tube by analyzing the measurement signal,
Prepare a test body simulating a heat transfer tube supported by the support plate to be inspected,
A measurement similar to that of thinning flaw detection is performed on the inspection position of the specimen using the frequencies ν ₁ and ν ₂ to obtain a reference measurement signal SP ⁰ and store it in a memory and hold it,
Said reference measurement signal SP ⁰ data _{N 1, N} 2 _(N 1 is the reference measurement signal SP ⁰ data in the frequency ν _{1, N 2} is the reference measurement signal SP ⁰ data in the frequency [nu ₂₎ from said memory numerical simulation by reading the And
Wherein the simulation and calibration error, calibrated using the data of experimental measurement signal SP ¹ obtained by measuring in a form deposited sodium with various structures in the specimen,
The signal of the support plate is simulated under each sodium structure (i) by the numerical simulation, and the noise signal N (i) is calculated by performing the subtraction process of the SP signal at _two frequencies ν ₁ and ν ₂ . And store it in memory
The rotation angle at which the noise signal N (i) _jk from the support plate and the sodium structure (i) is minimized (the signal rotation angle for matching the Lissajous waveform) α ⁱ and the amplification degree β ⁱ are N (i) _jk = N ₁ (I)-β _j · α _k (N ₂ (i)) is obtained by a relational expression (where β _j is an amplification factor, j is a variable that varies in the range of 0.1 to 10, α _k is Rotation angle, k is a variable that varies in the range of 0 degrees to 360 degrees) ,
Simulating the thinning signal under the sodium structure (i) present near the support plate, calculating the thinning signal (S ⁱ (j)) and the noise signal (N ⁱ (j)),
For all the sodium structures (i), the rotation angle α and the amplification factor β that maximize the (S ⁱ (j)) / (N ⁱ (j)) ratio are determined and stored in the memory, and retained.
The maximum noise value N from the support plate and the sodium structure (i) is obtained and stored in the memory, and held.
With respect to the inspection position of the actual flaw detection inspection machine, the thinning flaw detection measurement is performed using the frequencies ν ₁ and ν ₂ , the actual machine measurement signal SP ² is acquired, stored in the memory, and held.
The actual machine measurement signal SP ² having the frequency ν ₂ is rotated at the rotation angle α and amplified at the amplification degree β.
Subtracting the actual machine measurement signal SP ² of the frequency ν ₂ after the phase rotation and amplification processing from the actual machine measurement signal SP ² of the frequency ν ₁ to calculate the actual machine thinning signal S;
The presence / absence of a thinning defect is determined by a determination process of ‖S‖ / ‖N‖ ≧ judgment reference value.

The eddy current flaw detector is
The ECT probe of the eddy current flaw detector is provided at the inspection position inside the heat transfer tube provided with an ECT probe and a control processing device, with sodium removed from the vessel of the steam generator and supported by a support plate in the vessel. In the eddy current flaw detector for measuring the eddy current that is inserted and changing according to the change in the thickness of the heat transfer tube, and detecting the thinning generated on the outer periphery of the heat transfer tube by analyzing the measurement signal ,
The control processing device includes:
For a test body that simulates a heat transfer tube supported by the support plate to be subjected to flaw detection inspection,
A measurement similar to that of thinning flaw detection is performed on the inspection position of the specimen using the frequencies ν ₁ and ν ₂ to obtain a reference measurement signal SP ⁰ and store it in a memory and hold it,
Said reference measurement signal SP ⁰ data _{N 1, N} 2 _(N 1 is the reference measurement signal SP ⁰ data in the frequency ν _{1, N 2} is the reference measurement signal SP ⁰ data in the frequency [nu ₂₎ from said memory numerical simulation by reading the And
Wherein the simulation and calibration error, calibrated using the data of experimental measurement signal SP ¹ obtained by measuring in a form deposited sodium with various structures in the specimen,
The signal of the support plate is simulated under each sodium structure (i) by the numerical simulation, and the noise signal N (i) is calculated by performing the subtraction process of the SP signal at _two frequencies ν ₁ and ν ₂ . And store it in memory
The rotation angle at which the noise signal N (i) _jk from the support plate and the sodium structure (i) is minimized (the signal rotation angle for matching the Lissajous waveform) α ⁱ and the amplification degree β ⁱ are N (i) _jk = N ₁ (I)-β _j · α _k (N ₂ (i)) is obtained by a relational expression (where β _j is an amplification factor, j is a variable that varies in the range of 0.1 to 10, α _k is Rotation angle, k is a variable that varies in the range of 0 degrees to 360 degrees) ,
Simulating the thinning signal under the sodium structure (i) present near the support plate, calculating the thinning signal (S ⁱ (j)) and the noise signal (N ⁱ (j)),
For all the sodium structures (i), the rotation angle α and the amplification factor β that maximize the (S ⁱ (j)) / (N ⁱ (j)) ratio are determined and stored in the memory, and retained.
The maximum noise value N from the support plate and the sodium structure (i) is obtained and stored in the memory, and held.
With respect to the inspection position of the actual flaw detection inspection machine, the thinning flaw detection measurement is performed using the frequencies ν ₁ and ν ₂ , the actual machine measurement signal SP ² is acquired, stored in the memory, and held.
The actual machine measurement signal SP ² having the frequency ν ₂ is rotated at the rotation angle α and amplified at the amplification degree β.
Subtracting the actual machine measurement signal SP ² of the frequency ν ₂ after the phase rotation and amplification processing from the actual machine measurement signal SP ² of the frequency ν ₁ to calculate the actual machine thinning signal S;
A control process for determining the presence or absence of a thinning defect by the determination process of ‖S‖ / ‖N‖ ≧ judgment reference value is performed.

The judgment reference value is obtained by visually observing a Lissajous figure of the thinning signal (S ⁱ (j)) and the noise signal (N ⁱ (j)) obtained by simulating the thinning signal. S / N ratio of the thinning signal (S ⁱ (j)) and the noise signal (N ⁱ (j)) in the Lissajous figure specified by determining that it is the minimum Lissajous figure that can be clearly identified It is characterized by the value of.

  In the eddy current flaw inspection for volume inspection of the outer wall thinning of the heat transfer tube during the service period of the steam generator heat transfer tube in a sodium-cooled fast reactor, sodium or a heat transfer tube attached to the heat transfer tube The influence of the supporting plate to support can be reduced, and accurate flaw detection (thinning determination) can be realized.

In the present invention, an ECT probe of an eddy current flaw detector is inserted into an inspection position inside a heat transfer tube installed in a state where sodium is extracted from a container of a steam generator and supported by a support plate in the container. In the eddy current flaw detection method or apparatus for measuring the eddy current that changes in accordance with the change in the thickness of the heat tube and flaw detection on the outer periphery of the heat transfer tube by analyzing the measurement signal,
Prepare a test body simulating a heat transfer tube supported by the support plate to be inspected,
A measurement similar to that of thinning flaw detection is performed on the inspection position of the specimen using the frequencies ν ₁ and ν ₂ to obtain a reference measurement signal SP ⁰ and store it in a memory and hold it,
Said reference measurement signal SP ⁰ data _{N 1, N} 2 _(N 1 is the reference measurement signal SP ⁰ data in the frequency ν _{1, N 2} is the reference measurement signal SP ⁰ data in the frequency [nu ₂₎ from said memory numerical simulation by reading the And
Wherein the simulation and calibration error, calibrated using the data of experimental measurement signal SP ¹ obtained by measuring in a form deposited sodium with various structures in the specimen,
The signal of the support plate is simulated under each sodium structure (i) by the numerical simulation, and the noise signal N (i) is calculated by performing the subtraction process of the SP signal at _two frequencies ν ₁ and ν ₂ . And store it in memory
The rotation angle at which the noise signal N (i) _jk from the support plate and the sodium structure (i) is minimized (the signal rotation angle for matching the Lissajous waveform) α ⁱ and the amplification degree β ⁱ are N (i) _jk = N ₁ (I)-β _j · α _k (N ₂ (i)) is obtained by a relational expression (where β _j is an amplification factor, j is a variable that varies in the range of 0.1 to 10, α _k is Rotation angle, k is a variable that varies in the range of 0 degrees to 360 degrees) ,
Simulating the thinning signal under the sodium structure (i) present near the support plate, calculating the thinning signal (S ⁱ (j)) and the noise signal (N ⁱ (j)),
For all the sodium structures (i), the rotation angle α and the amplification factor β that maximize the (S ⁱ (j)) / (N ⁱ (j)) ratio are determined and stored in the memory, and retained.
The maximum noise value N from the support plate and the sodium structure (i) is obtained and stored in the memory, and held.
With respect to the inspection position of the actual flaw detection inspection machine, the thinning flaw detection measurement is performed using the frequencies ν ₁ and ν ₂ , the actual machine measurement signal SP ² is acquired, stored in the memory, and held.
The actual machine measurement signal SP ² having the frequency ν ₂ is rotated at the rotation angle α and amplified at the amplification degree β.
Subtracting the actual machine measurement signal SP ² of the frequency ν ₂ after the phase rotation and amplification processing from the actual machine measurement signal SP ² of the frequency ν ₁ to calculate the actual machine thinning signal S;
The presence / absence of a thinning defect is determined by the determination process of ‖S‖ / ‖N‖ ≧ judgment reference value.
The judgment reference value is obtained by visually observing the Lissajous figure of the thinning signal (S ⁱ (j)) and the noise signal (N ⁱ (j)) obtained by simulating the thinning signal, and clarifying the thinning signal waveform Value of the S / N ratio of the thinning signal (S ⁱ (j)) and the noise signal (N ⁱ (j)) in the Lissajous figure specified by determining that it is the minimum Lissajous figure that can be identified And

  FIG. 1 is a block diagram of an eddy current flaw detector.

  The eddy current flaw detector according to the first embodiment is used to detect the outer circumferential thinning of the outer surface of the heat transfer tube by volume inspection in the inspection during the service period of the steam generator heat transfer tube in the sodium-cooled fast reactor. This is a suitable device.

  In FIG. 1, an ECT (Eddy Current Testing) probe 1 that is inserted into a heat transfer tube to be inspected and obtains a measurement signal has a known ECT probe configuration as used conventionally.

  The control processing device 2 is configured using a computer, and although not shown in the drawings, a measurement signal output from the detection coil by controlling the excitation current supplied to the excitation coil of the ECT probe 1 via the conductor 3. ECT probe control processing function section that captures the data, a measurement signal processing function section that processes the captured measurement signal to determine whether there is a thinning defect in the heat transfer tube, an input section such as a keyboard or a mouse, a CRT, an LCD, etc. The display part is provided. The processing function unit is configured to be realized by a control processing program installed in a computer.

  The steam generator 4 in the sodium-cooled fast reactor to be inspected is installed in a sodium flow container 43 with a heat generation tube 41 for steam generation supported by a conductive support plate 42.

  The thinning inspection of the heat transfer tube 41 is performed by inserting the ECT probe 1 into the inspection position inside the heat transfer tube 41 with the sodium 44 extracted from the container 43 of the steam generator 4 and changing the thickness of the heat transfer tube 41. This is done by measuring the eddy current that changes according to the frequency and analyzing the measurement signal. In this inspection, it is known that if the conductive substance sodium 44 adheres to the outer surface of the heat transfer tube 41, the eddy current is affected, and the support plate 42 that supports the heat transfer tube 41 is also affected. ing.

  Therefore, in this inspection, signal processing for determining the thinned state of the heat transfer tube 41 is performed in consideration of the influence of the attached sodium 44 and the support plate 42 on the heat transfer tube 41.

  The signal processing for that purpose is executed by the signal processing program built in the computer in the control processing device 2 as described above.

  In the inspection using this eddy current flaw detector, first, as a preparation stage, the configuration of the steam generation heat transfer tube 41 and the support plate 42 in the steam generator 4 of the sodium-cooled fast reactor to be inspected was simulated. A test body is prepared and prepared, and the following measurement and signal processing are executed on the test body using an eddy current flaw detector.

  FIG. 2 is a flowchart of signal processing executed by the control processing device 2 for flaw detection in the eddy current flaw detection device.

  The measurement and signal processing performed using the specimen as a preparation stage are as follows.

Step S1
For each inspection position in the specimen (without thinning and sodium adhesion), the frequency ν ₁ and ν ₂ are used to perform the same measurement as the thinning flaw detection, and the reference measurement signal SP ⁰ is obtained and stored in the memory. Let hold. Here, the reference measurement signal SP ⁰ data in the frequency [nu ₁ and _{N 1,} the reference measurement signal SP ⁰ data in the frequency [nu ₂ and _{N 2.}

  The preparatory process for the test performed without sodium is as follows.

Step S02
The reference measurement signal SP ⁰ data N ₁ and N ₂ are read from the memory, and the reference angle is changed by changing the rotation angle α so that the read reference measurement signal SP ⁰ data N ₁ and N ₂ have the same phase (matching the Lissajous waveform). Processing to rotate (phase shift) the measurement signal SP ⁰ data N ₂ is performed. A rotation angle (phase shift) α having the same phase is created, stored in a memory, and held.

Step S03
The reference measurement signal SP ⁰ data N ₂ is amplified so that the reference measurement signal SP ⁰ data N ₁ and N ₂ have the same magnitude.

  An amplification factor β having the same size is created, stored in the memory, and held.

Step S04
The reference measurement signal SP ⁰ data N ₁ , N ₂ , the rotation angle α and the amplification degree β stored in the memory are read, the noise level N is calculated using the following equation (Equation 1), and the calculation result is Store in memory.
N = N ₁ −β · α (N ₂ ) (Equation 1)
Next, processing in a preparatory stage for inspection performed in a state where various types of sodium are attached to each inspection position of the test body is as follows.

Step S2
The reference measurement signal SP ⁰ data N ₁ and N ₂ are read from the memory and numerical simulation (simulation) is performed, and this simulation and calibration error are obtained by measuring the test specimen and data of the test measurement signal SP ¹ acquired. Use to calibrate. Data of the experimental measurement signal SP ¹ is obtained by measuring by attaching sodium in various configurations with respect to the specimen. The structure of sodium attached to the specimen for measurement to obtain the test measurement signal SP ¹ includes various layer thicknesses of sodium, various different distances from the support plate of the sodium deposit droplet, combinations thereof, support Define the sodium filling the void below the plate, and various other different sodium structures (i). The sodium structure “i” is 1, 2, 3,.

Step S3
The signal (SP signal) of the support plate is simulated (simulated) under the sodium structure (i) defined in step S2.

Under each sodium structure (i), parameters α (signal rotation angle for matching the Lissajous waveform) and β (signal amplification degree for matching the magnitudes) from the analysis signal N ₁ (i) at the frequency ν ₁ The noise N (i) is calculated by subtracting the analysis signal N ₂ (i) at the frequency ν ₂ adjusted using an arbitrary value to reduce the SP signal, and the calculation result is stored in the memory. Here, the noise at the frequency ν ₁ is N ₁ (i), the noise at the frequency ν ₂ is N ₂ (i), and “i” is 1, 2, 3,... N.

The equation (Equation 2) for obtaining the noise N (i) by reducing the SP signal is as follows.
N (i) _jk = N ₁ (i) −β _j · α _k (N ₂ (i)) (Equation 2)
here,
β _j is an amplification coefficient, j is changed in a range of 0.1 to 10 in increments of 0.01,
α _k is a rotation angle, k is a value in increments of 1 degree, and is changed in a range of 0 degrees to 360 degrees,
Calculate for all combinations of i, j, k.

The step values of j and k are considered so as not to depend on each other.
Step S4
The optimum values α ⁱ (optimum rotation angle) and β ⁱ (optimum amplification degree) at which the magnitude of the noise N (i) _jk from the support plate and the sodium structure (i) is minimized are found and stored in the memory. To do.
Step S5
Simulated parameters that define the presence of thinning in the heat transfer tube near the support plate at frequencies ν ₁ and ν ₂ (eg, 20% thinning with a tube thickness of 5 mm across the entire circumference of the heat transfer tube) And a simulation (simulation) analysis of the thinning signal in the presence of the sodium structure (i) (identified in step S2). Here, it is assumed that the simulated thinning signal at frequency ν1 is S ₁ (i), the simulated thinning signal at frequency ν2 is S2 (i), and “i” is 1, 2, 3,.

Then, using the following equations (Equation 3) and (Equation 4), the simulated thinning signal in the sodium structure (j) using the parameters of the optimum rotation angle α ⁱ and the optimum amplification factor β ⁱ that have been found and held in advance. (S ⁱ (j)) and the noise signal (N ⁱ (j)) are calculated, and the calculation result is stored in the memory and held.
S ⁱ (j) = S ₁ (j) −β ⁱ · α ⁱ (S ₂ (j)) (Equation 3)
N ⁱ (j) = N ₁ (j) −β ⁱ · α ⁱ (N ₂ (j)) (Equation 4)
Further, in this simulated thinning simulation, the Lissajous figure of the minimum level that allows the operator to visually observe the Lissajous figure of the simulated thinning simulation signal and clearly identify the thinning signal waveform from the noise signal waveform. Determination to use the value of the S / N ratio between the thinning signal (S ⁱ (j)) and the noise signal (N ⁱ (j)) in the Lissajous figure determined and specified to determine the presence or absence of an actual thinning defect described later Use the reference value.
Step S6
Using the parameters of the optimum rotation angle αi and optimum amplification degree βi from step S4, the ratio of (S ⁱ (j)) / (N ⁱ (j)) is the maximum for all sodium structures (j). The α and β to be converted are found and determined, stored in the memory and held.
Step S7
The maximum value N of noise from the support plate and the sodium structure (i) is calculated using the parameters α and β found and held in step S6, and the calculation result is stored in the memory and held.

Next, measurement and signal processing for inspection performed using an actual machine as an inspection target are as follows.
Step S8
Get the actual measurement signal SP ² at frequency [nu ₁ and [nu ₂ by inserting the ECT probe 1 at the examination position of the heat transfer tubes 41 of the container 43 which was withdrawn sodium 44, held and stored in the memory. Here, the data of the actual measurement signal SP ² at frequency [nu ₁ and _{S 1,} the data of the actual measurement signal SP ² at frequency [nu ₂ and _{S 2.}
Step S9
The actual machine measurement signal SP ² data S ₁ and S ₂ are read from the memory, the actual machine measurement signal SP ² data S ₂ is rotated (phase-shifted) at the rotation angle α, and amplified with the amplification degree β. Then, the actual machine thinning signal S is calculated using the following equation (Equation 5), and the calculation result is stored in the memory and held.
S = S ₁ −β · α (S ₂ ) (Equation 5)
Here, as for the rotation angle α and the amplification degree β, when sodium is not attached to the actual machine to be inspected, the values found and held in steps S02 and S03 are used, and when sodium is attached. Uses the value found and held in step S6.
Step S10
The presence / absence of an actual machine thinning defect is determined using the following equation (Equation 6). When the S / N ratio is 2 or more set as the determination reference value, it is determined that there is a thinning defect, and when it is less than 2, it is determined that there is no thinning defect.
‖S‖ / ‖N‖ ≧ 2 (= judgment reference value) (Equation 6)
Here, the noise N is found in step S04 when sodium is not attached to the actual machine to be inspected, and is found in step S7 when sodium is attached. Use the retained value.

Here, the judgment reference value (“2” in this embodiment) is determined by the operator visually observing the Lissajous figure of the simulated thinning simulation signal in the simulation of simulated thinning in the processing step S5 described above, The thinning signal (S ⁱ (j)) and the noise signal (N ⁱ (j)) of the Lissajous figure specified by judging that it is the minimum Lissajous figure that can clearly identify the thinning signal waveform This is the value of the S / N ratio.

  In the flaw detection technology field, generally, if the S / N ratio is 2 or more, the presence of a thinning defect can be detected. Even in the multi-frequency calculation in this embodiment, if the S / N is 2 or more, it can be confirmed by actual measurement and simulation experiments that the thinning defect can be reliably detected. Was set to “2”.

  In step S5, the determination reference value is automatically calculated by the control processing device 2 in accordance with the Lissajous figure specifying instruction input from the operator and set in the equation (Equation 6), or calculated by the operator and used in the equation (Equation 6). Configure to input to.

It is a schematic diagram of an eddy current flaw detector and a flaw detection inspection object in Embodiment 1 of the present invention. It is a flowchart of the signal processing in the flaw detection test | inspection performed using the eddy current flaw detector in Example 1 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... ECT probe, 2 ... Control processing apparatus, 4 ... Steam generator, 41 ... Heat transfer tube, 42 ... Support plate, 43 ... Container, 44 ... Sodium.

Claims (4)

An ECT probe of an eddy current flaw detector is inserted into an inspection position inside a heat transfer tube that is supported by a support plate in the vessel with sodium removed from the vessel of the steam generator, and the thickness of the heat transfer tube In the eddy current flaw detection method for measuring the eddy current that changes in accordance with the change of the flaw, and flaw detection of the thinning generated on the outer periphery of the heat transfer tube by analyzing the measurement signal,
Prepare a test body simulating a heat transfer tube supported by the support plate to be inspected,
A measurement similar to that of thinning flaw detection is performed on the inspection position of the specimen using the frequencies ν ₁ and ν ₂ to obtain a reference measurement signal SP ⁰ and store it in a memory and hold it,
Said reference measurement signal SP ⁰ data _{N 1, N} 2 _(N 1 is the reference measurement signal SP ⁰ data in the frequency ν _{1, N 2} is the reference measurement signal SP ⁰ data in the frequency [nu ₂₎ from said memory numerical simulation by reading the And
Wherein the simulation and calibration error, calibrated using the data of experimental measurement signal SP ¹ obtained by measuring in a form deposited sodium with various structures in the specimen,
The signal of the support plate is simulated under each sodium structure (i) by the numerical simulation, and the noise signal N (i) is calculated by performing the subtraction process of the SP signal at _two frequencies ν ₁ and ν ₂ . And store it in memory
The rotation angle at which the noise signal N (i) _jk from the support plate and the sodium structure (i) is minimized (the signal rotation angle for matching the Lissajous waveform) α ⁱ and the amplification degree β ⁱ are N (i) _jk = N ₁ (I)-β _j · α _k (N ₂ (i)) is obtained by a relational expression (where β _j is an amplification factor, j is a variable that varies in the range of 0.1 to 10, α _k is Rotation angle, k is a variable that varies in the range of 0 degrees to 360 degrees) ,
Simulating the thinning signal under the sodium structure (i) present near the support plate, calculating the thinning signal (S ⁱ (j)) and the noise signal (N ⁱ (j)),
For all the sodium structures (i), the rotation angle α and the amplification factor β that maximize the (S ⁱ (j)) / (N ⁱ (j)) ratio are determined and stored in the memory, and retained.
The maximum noise value N from the support plate and the sodium structure (i) is obtained and stored in the memory, and held.
With respect to the inspection position of the actual flaw detection inspection machine, the thinning flaw detection measurement is performed using the frequencies ν ₁ and ν ₂ , the actual machine measurement signal SP ² is acquired, stored in the memory, and held.
The actual machine measurement signal SP ² having the frequency ν ₂ is rotated at the rotation angle α and amplified at the amplification degree β.
Subtracting the actual machine measurement signal SP ² of the frequency ν ₂ after the phase rotation and amplification processing from the actual machine measurement signal SP ² of the frequency ν ₁ to calculate the actual machine thinning signal S;
An eddy current flaw detection method characterized by determining the presence or absence of a thinning defect by a determination process of ‖S‖ / ‖N‖ ≧ judgment reference value. 2. The determination reference value according to claim 1, wherein the determination reference value is reduced by visually observing a Lissajous figure of the thinning signal (S ⁱ (j)) and the noise signal (N ⁱ (j)) obtained by simulating the thinning signal. S of the thinning signal (S ⁱ (j)) and noise signal (N ⁱ (j)) in the specified Lissajous figure determined to be the minimum Lissajous figure that can clearly identify the meat signal waveform An eddy current flaw detection method characterized by having a value of / N ratio. The ECT probe of the eddy current flaw detector is provided at the inspection position inside the heat transfer tube provided with an ECT probe and a control processing device, with sodium removed from the vessel of the steam generator and supported by a support plate in the vessel. In the eddy current flaw detector for measuring the eddy current that is inserted and changing according to the change in the thickness of the heat transfer tube, and detecting the thinning generated on the outer periphery of the heat transfer tube by analyzing the measurement signal ,
The control processing device includes:
For a test body that simulates a heat transfer tube supported by the support plate to be subjected to flaw detection inspection,
A measurement similar to that of thinning flaw detection is performed on the inspection position of the specimen using the frequencies ν ₁ and ν ₂ to obtain a reference measurement signal SP ⁰ and store it in a memory and hold it,
Said reference measurement signal SP ⁰ data _{N 1, N} 2 _(N 1 is the reference measurement signal SP ⁰ data in the frequency ν _{1, N 2} is the reference measurement signal SP ⁰ data in the frequency [nu ₂₎ from said memory numerical simulation by reading the And
Wherein the simulation and calibration error, calibrated using the data of experimental measurement signal SP ¹ obtained by measuring in a form deposited sodium with various structures in the specimen,
The signal of the support plate is simulated under each sodium structure (i) by the numerical simulation, and the noise signal N (i) is calculated by performing the subtraction process of the SP signal at _two frequencies ν ₁ and ν ₂ . And store it in memory
The rotation angle at which the noise signal N (i) _jk from the support plate and the sodium structure (i) is minimized (the signal rotation angle for matching the Lissajous waveform) α ⁱ and the amplification degree β ⁱ are N (i) _jk = N ₁ (I)-β _j · α _k (N ₂ (i)) is obtained by a relational expression (where β _j is an amplification factor, j is a variable that varies in the range of 0.1 to 10, α _k is Rotation angle, k is a variable that varies in the range of 0 degrees to 360 degrees) ,
Simulating the thinning signal under the sodium structure (i) present near the support plate, calculating the thinning signal (S ⁱ (j)) and the noise signal (N ⁱ (j)),
For all the sodium structures (i), the rotation angle α and the amplification factor β that maximize the (S ⁱ (j)) / (N ⁱ (j)) ratio are determined and stored in the memory, and retained.
The maximum noise value N from the support plate and the sodium structure (i) is obtained and stored in the memory, and held.
With respect to the inspection position of the actual flaw detection inspection machine, the thinning flaw detection measurement is performed using the frequencies ν ₁ and ν ₂ , the actual machine measurement signal SP ² is acquired, stored in the memory, and held.
The actual machine measurement signal SP ² having the frequency ν ₂ is rotated at the rotation angle α and amplified at the amplification degree β.
Subtracting the actual machine measurement signal SP ² of the frequency ν ₂ after the phase rotation and amplification processing from the actual machine measurement signal SP ² of the frequency ν ₁ to calculate the actual machine thinning signal S;
An eddy current flaw detector characterized by performing a control process for determining the presence or absence of a thinning defect by a determination process of ‖S‖ / ‖N‖ ≧ determination reference value. 4. The determination reference value according to claim 3, wherein the determination reference value is reduced by visually observing a Lissajous figure of the thinning signal (S ⁱ (j)) and the noise signal (N ⁱ (j)) obtained by simulating the thinning signal. S of the thinning signal (S ⁱ (j)) and noise signal (N ⁱ (j)) in the specified Lissajous figure determined to be the minimum Lissajous figure that can clearly identify the meat signal waveform Eddy current flaw detector characterized by having a value of / N ratio.

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