JPH045323B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for measuring the thickness of a liner layer, total wall thickness, etc. of a lined pipe using an eddy current method, and particularly relates to a method for measuring the thickness of a liner layer, total wall thickness, etc. of a lined pipe using an eddy current method, and particularly for measuring the thickness of a zirconium alloy (hereinafter referred to as Zircaloy).
The present invention relates to a measurement method that can be suitably applied to the measurement of liner thickness and total wall thickness in cladding tubes for reactor nuclear fuel in which a pure zirconium liner layer is formed on the inner surface of the tube.

[Prior art]

Rapid increases and decreases in power are essential for efficient nuclear reactor operation, but with conventional Zircaloy nuclear fuel cladding, there are concerns about stress corrosion cracking if there are sudden changes in power. Therefore, a cladding tube in which an extremely thin pure zirconium liner layer is formed on the inner surface of a Zircaloy tube has been developed. In such a cladding tube, it is necessary that the liner layer and the total wall thickness have a predetermined thickness due to strength issues, and therefore, it is necessary to accurately measure these thicknesses.

In general, there are two methods for measuring the thickness of each layer and the entire thickness of pipes made of two or more metals, such as lining pipes: destructive measurement methods and non-destructive measurement methods. This method can only measure both ends of the tube, and cannot be applied to the above-mentioned cladding tube, where measurement of the entire inner surface of the tube is essential. Nondestructive measurement methods include the ultrasonic method and the eddy current method, but the ultrasonic method cannot be applied to the above-mentioned clad tube because it is extremely difficult to identify echoes at the interface between the liner layer and the Zircaloy tube. On the other hand, the eddy current method uses the difference between the conductivity of the zirconium liner layer (1/ρ, ρ = 50 μΩ・cm) and the conductivity of the Zircaloy part (1/ρ, ρ = 70 μΩ・cm). Thickness and total wall thickness can be measured. In other words, the principle of the eddy current method is that when a coil carrying an alternating current is brought close to a metal surface, an eddy current flows on the metal surface, and the eddy current induces an induced magnetic field, changing the impedance of the coil. This means that information about the metal surface can be obtained from the amount of change in impedance.The impedance changes as a result of changes in the liner thickness of the lining tube, and also changes in the total wall thickness. It is also well known that the liner thickness and the total wall thickness of the pipe can be measured in principle.

An example of a specific method for measuring liner thickness using such an eddy current method is disclosed in Japanese Patent Application Laid-Open No. 1987-67405. This is done by determining the impedance component Vy in the direction of coil impedance change due to fluctuations in the air gap between the coil and the inner surface of the tube (hereinafter referred to as lift-off) and the impedance component Vx in the direction orthogonal to it.
The liner thickness is calculated from the value corrected by Vy.

By the way, a reference point is necessary when converting the measured impedance component into liner thickness, so in the above publication, a reference specimen with a known liner layer is used, and one point of this reference specimen that is stationary is used. The impedance component in is the standard. However, as is clear from Figure 6, which shows the change in impedance in the pipe on the normalized impedance plane, the reference point changes greatly when the liftoff is different, but the above method allows for reproducibility of the liftoff when setting the reference point. It is very difficult to
There was a problem in that it was impossible to set a reference (zero) point or sensitivity with good reproducibility, making accurate measurements impossible.

[Purpose of the invention]

The present invention has been made in order to solve the above-mentioned conventional problems, and is a lining tube that improves the reproducibility of reference points and sensitivity when measuring each thickness of a lining tube by the eddy current method. The purpose is to provide a method for measuring the thickness of

[Structure of the invention]

The method for measuring the thickness of a lined pipe of the present invention is to measure the thickness of a lined pipe by inserting a coil for electromagnetic induction testing inside the pipe and using the eddy current method. The average value of one of the outputs of the eddy current measuring device obtained by rotating two types of standard lining tubes with known values and different thicknesses is used as a reference point, and the sensitivity is set by comparing it with the other average value. Calculate the thickness of the lining pipe using
By rotating the standard lining tube and averaging the lift-off amount, the reproducibility of the reference point is improved, and the reproducibility of the sensitivity is also improved.

〔Example〕

Next, an example in which the present invention is applied to the measurement of the liner thickness and total wall thickness of a liner cladding tube is shown in FIGS. 1 to 5.
This will be explained based on the diagram. In FIG. 1a, as shown in FIG. 1b, a liner cladding tube 1 in which a liner layer 1b of pure zirconium is formed on the inner surface of a Zircaloy tube 1a, which is a base material tube, is rotated around its axis by a rotating machine 2. This liner cladding tube 1
A probe 3 that can be inserted into the container is supported by a charging device 4. An absolute value type coil is embedded within the probe 3, and the coil diameter is approximately 1 mm. The signal from this coil, that is, the change in impedance, is detected by an eddy current measuring device 5 and converted into, for example, a voltage. The Zircaloy thickness is calculated and the result is displayed on the display 7.

The test frequencies applied to the coil are 500KHz, which mainly measures the total wall thickness, and a dual frequency of 2MHz and 4MHz, which mainly measures the liner thickness.
Multiple frequencies are used. In measuring liner thickness, when a coil is excited at dual frequencies, the direction of impedance change changes depending on the frequency. Impedance components in a direction perpendicular to this are detected, and the liner thickness can be determined from these impedance components without the effects of variations in lift-off amount, variations in conductivity between the liner layer and the Zircaloy portion, etc.

At one end of the liner cladding tube 1, there is a hole having the same diameter as the liner cladding tube 1 and on the inner surface of the Zircaloy tube 8a.
A first standard liner cladding tube 8 in which a 50 μm thick liner layer 8b of pure zirconium is formed, and a second standard liner cladding tube 9 in which a 130 μm thick pure zirconium liner layer 9b is formed on the inner surface of the Zircaloy tube 9a. are fixed concentrically. Note that the liner layer 1b of the liner cladding tube 1 is within the range of 50 μm to 130 μm.

The measurement procedure in the above structure is to first move the probe 3 into the first standard liner cladding tube 8, rotate the first standard liner cladding tube 8, and measure the output of the eddy current measuring device 5 during one rotation. Each frequency is averaged and this is used as a reference point (zero point).
Further, the probe 3 is moved into the second standard liner cladding tube 9, this second standard liner cladding tube 9 is rotated, and the output of the eddy current measuring device 5 during one rotation is averaged for each frequency. liner thickness
Set the sensitivity by setting the output when the liner thickness is 130 μm and comparing it with the reference point when the liner thickness is 50 μm.Next, move the probe 3 into the liner clad tube 1, which is the tube to be measured, and set the sensitivity. The probe 3 is moved while the cladding tube 1 is rotated. At this time, each of the reference points is subtracted from the output of the eddy current measuring device 5 for each frequency, and based on that value, the calculation device 6 calculates the liner thickness and the total wall thickness based on the sensitivity. The Zircaloy thickness is calculated by subtracting the liner thickness from the wall thickness, and these are displayed on the display 7.
to be displayed.

The results measured by the above method are shown in FIG. 2 together with the results of the conventional method. This shows an example of the output of an eddy current measuring device when a liner-clad tube with a 90 μm liner layer was measured several times using the conventional method using the Zircaloy tube as the reference point (zero point), and the results measured using the method of the present invention. Although it is impossible to accurately measure the thickness using the conventional method, the method of the present invention allows highly accurate measurement.

Furthermore, examples of the results of measuring the liner thickness, total wall thickness, and Zircaloy thickness of the liner cladding tube 1 using the above method are shown in FIGS. 3 to 5. From these results, it is recognized that the method of the present invention corresponds to the actual measured values with high precision and that accurate measurements are possible.

〔Effect of the invention〕

According to the lining pipe thickness measurement method of the present invention,
As described above, when measuring the thickness of a lined pipe using the eddy current method by inserting a coil for electromagnetic induction testing inside the pipe, it is necessary to use a liner with the same diameter as the lined pipe to be measured and a known liner thickness. Using the average value of the output of the eddy current measuring device obtained by rotating two different types of standard lining tubes as a reference point, the thickness of the lining tube is calculated by setting the sensitivity by comparing it with the other average value. Therefore, the lift-off amount can be averaged by rotating the standard lining pipe,
As a result, the reproducibility of the reference point is improved, and
Similarly, the reproducibility of sensitivity can be improved. Therefore, according to the method of the present invention, it is possible to measure the thickness of a lining tube with extremely high accuracy using the eddy current method.

[Brief explanation of drawings]

1 to 5 show an embodiment of the present invention, and FIG. 1a is a schematic configuration diagram of an apparatus for carrying out the method of the present invention,
Figure b is a cross-sectional view taken along the - line in figure a, figure c is a cross-sectional view taken along line - in figure a, figure d is a cross-sectional view taken in figure a along line -, and Figure 2 shows the results of the present invention and the conventional method. Graph showing variation in liner thickness measurement results, Figure 3~
Figure 5 is a graph showing the relationship between measured values and actual values of liner thickness, total wall thickness, and Zircaloy thickness, respectively.
The figure shows changes in coil impedance in a reference test tube on a normalized impedance plane. 1 is a liner cladding tube, 2 is a rotating machine, 3 is a probe, 5 is an eddy current measuring device, 6 is a calculation device, 8 is a first standard liner cladding tube, and 9 is a second standard liner cladding tube.

Claims (1)

[Claims] 1. When measuring the thickness of a lined pipe using the eddy current method by inserting a coil for electromagnetic induction testing inside the pipe, two types of liners with the same diameter as the lined pipe to be measured, known liner thicknesses, and different thicknesses are used. The thickness of the lining pipe is calculated by setting the average value of one of the outputs of the eddy current measuring device obtained by rotating the standard lining pipe as a reference point, and setting the sensitivity by comparing it with the other average value. Features a method for measuring the thickness of lining pipes.