Method for Measuring Scale Thickness

Abstract

To provide a scale thickness measuring method that can perform a measurement more precisely.SOLUTION: A scale thickness measuring method measures a thickness of scale adhered in an outer peripheral surface of a heat transfer tube forming a cylindrical shape centering around an axial line by an eddy current probe. The eddy current probe comprises: an exciting coil that generates an eddy current; and a pair of detection coils that detects an axial line direction component and peripheral direction component of a magnetic field based on the eddy current. The scale thickness measuring method includes the steps of: obtaining a reference point by calculating a differential between the axial line direction component and the peripheral direction component of the magnetic field detected by the pair of detection coils in an area having scale not adhered; moving the eddy current probe within the inside of the heat transfer tube; calculating the differential between the axial line direction component and the peripheral direction component of the magnetic field; obtaining an amount of drift by comparing the differential and the reference point; and calculating a thickness of the scale from a preliminarily acquired calibration curve on the basis of the amount of drift.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a method for measuring scale thickness.

Background Art

[0002] A steam generator of a nuclear power facility houses a large number of heat transfer tubes. It is known that deposits called scale are generated on the outer peripheral surface of these heat transfer tubes over years of operation. If the thickness of such scale becomes excessive, there is a risk of affecting the heat transfer performance of the heat transfer tubes. Therefore, there has been an increasing demand for a technology capable of remotely measuring and evaluating the scale thickness.

[0003] For example, Patent Document 1 below discloses a technique for measuring the scale thickness using a probe that generates eddy currents. In this technique, while inserting and moving the probe through the heat transfer tube, the coil is excited. Then, a magnetic field is generated in the scale, and this magnetic field conversely generates an induced voltage in the coil of the sensor. Since the impedance of the coil at that time is a function of the scale thickness, it is said that the scale thickness can be obtained by measuring the impedance. That is, in this technique, a self-induction standard comparison method is used.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the probe of the self-induction standard comparison method as described above has problems in that it is vulnerable to bending, stretching, rattling, and temperature changes, and it is difficult to accurately measure the scale thickness.

[0006] The present disclosure has been made to solve the above problems, and an object thereof is to provide a method for measuring the scale thickness that enables more accurate measurement.

Means for Solving the Problems

[0007] In order to solve the above problems, a method for measuring the scale thickness according to the present disclosure is a method for measuring the thickness of scale attached to the outer peripheral surface of a heat transfer tube that extends in the axial direction and has a cylindrical shape centered on the axis by an eddy current probe. The eddy current probe includes an excitation coil that generates eddy currents, and a pair of detection coils that are provided integrally with the excitation coil and detect the axial component and the circumferential component of the magnetic field based on the eddy currents. The method for measuring the scale thickness includes a step of obtaining a reference point by calculating the difference between the axial component and the circumferential component of the magnetic field detected by the pair of detection coils in a region of the heat transfer tube where the scale is not attached, a step of inserting the eddy current probe into the heat transfer tube and moving it in the axial direction, a step of calculating the difference between the axial component and the circumferential component of the magnetic field detected by the pair of detection coils, a step of obtaining a drift amount by comparing the difference with the reference point, and a step of calculating the thickness of the scale from a calibration curve acquired in advance based on the drift amount.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to provide a method for measuring the scale thickness that enables more accurate measurement.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0010] Hereinafter, an eddy current probe 1 according to an embodiment of the present disclosure and a method for measuring scale thickness using the same will be described with reference to FIGS. 1 to 5.

[0011] (Configuration of Eddy Current Probe) With reference to FIGS. 1 to 3, the configuration of the eddy current probe 1 will be described. As shown in FIG. 1, the eddy current probe 1 is inserted and used inside a heat transfer tube 90. A plurality of heat transfer tubes 90 are provided, for example, inside a steam generator. The heat transfer tube 90 extends along the axis O and has a cylindrical shape centered on the axis O. An attachment called scale is generated on the outer peripheral surface of the heat transfer tube 90 due to long-term operation. The eddy current probe 1 is used to measure the thickness of this scale.

[0012] The eddy current probe 1 includes a probe body 10 and a plurality of coil assemblies 11. Various wirings are accommodated inside the probe body 10. The probe body 10 has a cylindrical shape extending along the axis O. A plurality of coil assemblies 11 are provided at intervals in the circumferential direction of the axis O at the tip of the probe body 10.

[0013] As shown in FIGS. 2 and 3, the coil assembly 11 has one exciting coil 11a and a pair of detection coils 11b. The exciting coil 11a is in a ring shape. The exciting coil 11a is disposed inside the probe body 10 such that its diameter direction is orthogonal to the inner peripheral surface of the heat transfer tube 90. Further, the exciting coil 11a is disposed in a posture inclined about 45° with respect to the axis O. The exciting coil 11a is excited by a voltage supplied from the outside to generate eddy currents in the vicinity of the inner peripheral surface of the heat transfer tube 90.

[0014] The detection coils 11b are integrally provided on the outer peripheral side (that is, the heat transfer tube 90 side) of the above-described exciting coil 11a. Each detection coil 11b is, for example, in a rectangular ring shape and extends along the inner peripheral surface of the heat transfer tube 90. The detection coils 11b are disposed in a posture inclined about 45° with respect to the axis O, similar to the exciting coil 11a, and a pair of them are provided at intervals in the inclined direction.

[0015] Each detection coil 11b is used to capture a change in the magnetic field based on the eddy currents generated by the exciting coil 11a. For example, changes in the circumferential magnetic field and the axial magnetic field are detected based on the difference in detection voltages between one detection coil 11b and the other detection coil 11b.

[0016] (Method for Measuring Scale Thickness) Next, a method for measuring the scale thickness using the above-described eddy current probe 1 will be described. As shown in FIG. 4, this measurement method includes a reference point determination step S1, a probe movement step S2, a difference calculation step S3, a drift amount calculation step S4, and a scale thickness calculation step S5.

[0017] In the reference point determination step S1, the magnetic field detected by the pair of detection coils 11b is measured on an area of the heat transfer tube 90 where no scale is attached, or on a sample (calibration test piece) having the same material and dimensions as the heat transfer tube 90. Specifically, the difference between the axial O-direction component and the circumferential-direction component of the magnetic field is calculated, and a point where the difference becomes zero is set as the reference point. That is, the reference point determination step S1 is performed to correct the detection result of the eddy current probe 1 in a state without scale.

[0018] Next, the probe movement step S2 is executed. In the probe movement step S2, the eddy current probe 1 is inserted into the heat transfer tube 90 and moved in the axial O direction. At this time, eddy currents are generated in the vicinity of the inner peripheral surface of the heat transfer tube 90 by the excitation coil 11a.

[0019] During the movement of the eddy current probe 1, the scale attached to the outer peripheral surface of the heat transfer tube 90 causes a change in the magnetic field detected by the detection coil 11b. In the subsequent difference calculation step S3, the difference between the axial O-direction component and the circumferential-direction component of the magnetic field detected by the pair of detection coils 11b is calculated. In a state where scale is attached, the value of this difference transitions (drifts) from the above reference point. In the drift amount calculation step S4, the amount of change (drift amount) from this reference point is calculated.

[0020] Subsequently, the scale thickness calculation step S5 is executed. In this step S5, the above drift amount is compared with a calibration curve acquired in advance, and the scale thickness is calculated. As shown by an example in FIG. 5, the drift amount and the scale thickness are in a proportional relationship. That is, as the drift amount increases, the scale thickness also tends to increase. In step S5, the scale thickness is obtained based on this calibration curve. Thus, all the steps of the scale thickness measurement method are completed.

[0021] (Function and effect) When measuring the scale thickness, it has been common to use a probe of a method called the self-induction standard comparison method. In this method, one coil is applied to the test piece and the other coil is applied to the reference piece to detect the difference. It is used when it is necessary to detect the absolute amount such as the amount of material removed in the test piece. However, since the influence of lift-off noise is large, there has been a problem that it is difficult to perform accurate measurement.

[0022] Therefore, the eddy current probe 1 and the method for measuring the scale thickness according to the present embodiment have the above-described configuration. According to the above configuration and method, the difference between the axial direction component and the circumferential direction component of the magnetic field detected by the pair of detection coils 11b is calculated, and the drift amount is obtained by comparing this difference with the reference point. Further, based on the drift amount, the thickness of the scale is calculated from a calibration curve acquired in advance. Since the so-called differential method is used in this way, it is possible to accurately measure the scale thickness in a robust state against disturbances such as bending and stretching of the probe. As a result, it becomes possible to evaluate the scale thickness more precisely and accurately.

[0023] Further, according to the above configuration, since the exciting coil 11a and the pair of detection coils 11b are arranged in a direction inclined with respect to the axis O, eddy currents can be generated in a wider range in the axial direction O and the circumferential direction, and changes in the magnetic field based on the eddy currents can be stably detected in a wider range.

[0024] Furthermore, according to the above configuration, a plurality of coil assemblies 11 are arranged at intervals in the circumferential direction. Thereby, it is possible to stably and accurately measure the scale thickness over the entire circumferential direction of the heat transfer tube 90.

[0025] (Other Embodiments) As described above in detail with reference to the drawings regarding the embodiments of the present disclosure, the specific configuration is not limited to this embodiment, and design changes and the like within the scope not departing from the gist of the present disclosure are also included. For example, in the above embodiment, the configuration in which the coil assembly 11 is inclined at 45° with respect to the axis O was described. However, the posture of the coil assembly 11 is not limited to this, and as long as it is inclined even slightly with respect to the axis O, the inclination angle may be less than 45°.

[0026] Also, in the above embodiment, an example in which the detection coil 11b is provided on the outer peripheral side of the excitation coil 11a was described. However, it is also possible to adopt a configuration in which the detection coil 11b is arranged so as to surround the excitation coil 11a. Further, it is also possible to adopt a configuration in which a pair of coils for performing excitation and detection are provided and arranged along the axis O direction and the circumferential direction, respectively. By any of these methods, the same operational effects as those of the above embodiment can be obtained.

[0027] <Supplementary Note> The method for measuring the scale thickness described in each embodiment is understood, for example, as follows.

[0028] (1) The method for measuring the scale thickness according to the first aspect is a method for measuring the thickness of the scale adhering to the outer peripheral surface of the heat transfer tube 90 that extends in the direction of the axis O and has a cylindrical shape centered on the axis O, using the eddy current probe 1. The eddy current probe 1 includes an excitation coil 11a that generates eddy currents, and a pair of detection coils 11b that are provided integrally with the excitation coil 11a and detect the axial O-direction component and the circumferential-direction component of the magnetic field based on the eddy currents. The method for measuring the scale thickness includes a step S1 of obtaining a reference point by calculating the difference between the axial O-direction component and the circumferential-direction component of the magnetic field detected by the pair of detection coils 11b in a region of the heat transfer tube 90 where the scale is not adhered; a step S2 of inserting the eddy current probe 1 into the heat transfer tube 90 and moving it in the direction of the axis O; a step S3 of calculating the difference between the axial O-direction component and the circumferential-direction component of the magnetic field detected by the pair of detection coils 11b; a step S4 of obtaining a drift amount by comparing the difference with the reference point; and a step S5 of calculating the thickness of the scale from a calibration curve obtained in advance based on the drift amount.

[0029] According to the above configuration, the difference between the axial O-direction component and the circumferential-direction component of the magnetic field detected by the pair of detection coils 11b is calculated, and the drift amount is obtained by comparing this difference with the reference point. Further, based on the drift amount, the thickness of the scale is calculated from a calibration curve obtained in advance. Since the so-called differential method is used in this way, the scale thickness can be accurately measured in a robust state against disturbances such as bending and stretching of the probe.

[0030] (2) In the method for measuring the scale thickness according to the second aspect, the excitation coil 11a and the pair of detection coils 11b are arranged in a direction inclined with respect to the axis O.

[0031] According to the above configuration, since the excitation coil 11a and the pair of detection coils 11b are arranged in a direction inclined with respect to the axis O, eddy currents can be generated in a wider range in the direction of the axis O and in the circumferential direction, and changes in the magnetic field based on these eddy currents can be stably detected in a wider range.

[0032] (3) In the method for measuring the scale thickness according to the third aspect, a plurality of the excitation coils 11a and the pair of detection coils 11b are arranged at intervals in the circumferential direction of the eddy current probe 1.

[0033] According to the above configuration, the scale thickness can be measured stably and accurately over the entire circumferential direction of the heat transfer tube 90.

Explanation of Reference Numerals

[0034] 90 Heat transfer tube 1 Eddy current probe 10 Probe body 11 Coil assembly 11a Excitation coil 11b Detection coil O Axis

Claims

1. A method for measuring the scale thickness that measures the thickness of the scale adhering to the outer peripheral surface of a heat transfer tube that extends in the axial direction and has a cylindrical shape centered on the axis by an eddy current probe, comprising: The eddy current probe includes: An excitation coil that generates eddy currents; A pair of detection coils provided integrally with the excitation coil for detecting the axial direction component and the circumferential direction component of the magnetic field based on the eddy currents; And is provided with; The method for measuring the scale thickness includes: A step of obtaining a reference point by calculating the difference between the axial direction component and the circumferential direction component of the magnetic field detected by the pair of detection coils in a region of the heat transfer tube where the scale is not adhered; A step of inserting the eddy current probe into the heat transfer tube and moving it in the axial direction; A step of calculating the difference between the axial direction component and the circumferential direction component of the magnetic field detected by the pair of detection coils; A step of obtaining a drift amount by comparing the difference with the reference point; A step of calculating the thickness of the scale from a calibration curve acquired in advance based on the drift amount; A method for measuring the scale thickness including.

2. The method for measuring the scale thickness according to claim 1, wherein the excitation coil and the pair of detection coils are arranged in a direction inclined with respect to the axis.

3. The method for measuring the scale thickness according to claim 1 or 2, wherein a plurality of the excitation coils and the pair of detection coils are arranged at intervals in the circumferential direction of the eddy current probe.

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