JPS6221003A - Thickness measurement of lining pipe - Google Patents

Abstract

PURPOSE:To measure the thickness of a lining pipe at a high accuracy, by computing the thickness of the lining pipe with the mean of outputs of an eddy current measuring device as reference point as obtained by rotating a single tube made of a base material with the same diameter as the lining pipe to be measured. CONSTITUTION:In a liner covered pipe 1, a Zircaloy tube 8 with the same diameter as the pipe 1 and a pure Zr tube 9 are fixed concentrically. A probe (PB)3 is moved through the tube 8, the tube 8 is turned and the outputs of an eddy current measuring device 5 during one turn thereof are average in terms of frequency to make respective reference points (zero point). Moreover, while the PB 3 is moved through the tube 9, the tube 9 is rotated, the outputs of the measuring device 5 during one turn thereof are averaged in terms of frequency and the results are compared to the respective reference points to set the sensitivity. Then, the PB 3 is shifted into the pipe 1 to be measured and moved turning the tube 1. The reference points are subtracted from the current output at the measuring point and on the basis of the results and the sensitivity, the liner thickness, overall thickness and the zercaloy thickness are calculated 6 and displayed 7.

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 by 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. 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 technology] 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 is a sudden change in power. Ru. 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 cladding tube because it is extremely difficult to identify echoes at the interface between the liner layer and the Zircaloy portion. On the other hand, in the eddy current method, the conductivity of the zirconium liner layer (1/ρ
, ρ = 50μΩ・am) and the electrical conductivity of the Zircaloy part (1/
By using the difference between ρ and ρ=70 μΩ·cm, it is possible to measure the liner thickness and total wall thickness. 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, which changes the impedance of the coil. This means that information on the metal surface can be obtained from the amount of change in impedance, and it is well known that impedance changes depending on changes in the liner thickness of the lining pipe, and also changes in impedance due to changes in the total wall thickness. This makes it possible in principle to measure the liner thickness and the total wall thickness of the pipe.

An example of a specific method for measuring liner thickness using such an eddy current method is disclosed in Japanese Patent Laid-Open No. 59-67405. 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 corrected value.

By the way, a reference point is required 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 this reference specimen that is stationary is used. The impedance component Vx-Vy at one point is used as a reference. 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 do so, and it is impossible to set a reference (zero) point or sensitivity with good reproducibility, making it impossible to perform accurate measurements.

[Purpose of the invention]

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

[Structure of the invention]

The method for measuring the thickness of a lined pipe according to the present invention is to measure the thickness of a lined pipe by inserting an electromagnetic induction test coil inside the pipe and using an eddy current method. The thickness of the lining pipe is calculated using the average value of the output of the eddy current measuring device obtained by rotating the eddy current measuring device as a reference point, and the zero point is reproduced by rotating the base material pipe with zero liner layer and averaging the lift-off amount. It is characterized by improved sex.

In addition, in the second method of measuring the thickness of a lining pipe according to the present invention, the sensitivity is further set based on the average value of the output of the eddy current measuring device obtained by rotating a single liner pipe having the same diameter as the lining pipe to be measured. The thickness of the lining tube is calculated, and the reproducibility of sensitivity is also improved.

〔Example〕

Next, an embodiment in which the present invention is applied to the measurement of the liner thickness and total wall thickness of a liner cladding tube will be described based on FIGS. 1 to 5. In FIG. 1(a), as shown in FIG. 1(b), a liner cladding tube l having a liner layer 1b of pure zirconium formed on the inner surface of a Zircaloy tube la, which is a base material tube, is attached to a rotator 2.
A probe 3 is supported by a charging device 4 and is held rotatably around its axis by a probe 3 which can be inserted into the liner cladding tube 1 . An absolute value type coil is embedded in the probe 3, and the diameter of the coil is approximately 1. A signal from this coil, that is, a change in impedance, is detected by an eddy current measuring device 5 and converted into, for example, a voltage, and the output is inputted to an arithmetic device 6 programmed with a predetermined calculation formula to determine the liner thickness, total wall thickness, and other values. The Zircaloy thickness is calculated from the above, and the result is displayed on the display 7.

The test frequency applied to the coil was a total of three frequencies: 500 KHz, which was mainly used to measure the total wall thickness, and a dual frequency of 2 MHz and 4 MHz, which was mainly used to measure the liner thickness. There is. In measuring liner thickness, when a coil is excited at dual frequencies, the direction of impedance change changes depending on the frequency. The liner thickness can be determined from these impedance components by eliminating the effects of changes in lift-off amount, changes in conductivity between the liner layer and the Zircaloy portion, etc.

This liner cladding tube 1 is attached to one end of the liner cladding tube work.
A Zircaloy tube 8 and a pure zirconium tube 9 having the same diameter are fixed concentrically.

The measurement procedure in the above structure is to first move the probe 3 into the Zircaloy tube 8, rotate the Zircaloy tube 8,
The output of the eddy current measuring device 5 during one rotation is averaged for each frequency and used as a reference point (zero point). Furthermore, the probe 3 is moved into the pure zirconium tube 9, the pure zirconium tube 9 is rotated, and the output of the eddy current measuring device 5 during one rotation is averaged for each frequency. The sensitivity is set by comparing the output with the reference point in the case of .

Next, move the probe 3 into the liner cladding tube 1 that is the tube to be measured, and rotate the liner cladding tube 1 while rotating the probe 3.
move. At this time, each reference point 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 total thickness based on the sensitivity, and then The Zircaloy thickness is calculated by subtracting the liner thickness from the wall thickness, and these are displayed on the display 7.

The results measured using the above method are combined with the results of the conventional method.
As shown in the figure. This shows an example of the output of the eddy current measuring device when measuring a liner-coated tube with a liner layer of 9.0 μl using the conventional method several times 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 with 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 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 value with high accuracy and that accurate measurement is possible.

〔Effect of the invention〕

According to the method for measuring the thickness of a lining pipe of the present invention, when the thickness of a lining pipe is measured by the eddy current method by inserting a coil for electromagnetic induction testing inside the pipe as described above, it is possible to The thickness of the lining tube is calculated using the average value of the output of the eddy current measuring device obtained by rotating a single base material tube of the same diameter as a reference point, so the lift-off amount is calculated by rotating the base material tube with zero liner layer. can be averaged, resulting in
The reproducibility of the zero point can be improved.Furthermore, the sensitivity can be set from the average value of the output of the eddy current measuring device obtained by rotating a single liner tube with the same diameter as the lined tube to be measured. By calculating the thickness, it is also possible to improve the reproducibility of the sensitivity. Therefore, according to the method of the present invention, it is possible to measure the thickness of the lining tube with extremely high precision using eddy current.

[Brief explanation of drawings]

1 to 5 show an embodiment of the present invention, and FIG.
) is a schematic configuration diagram of an apparatus for carrying out the method of the present invention, and (b) of the same figure
is a cross-sectional view taken along the line I-I of the same figure (a), and the same figure (C) is a cross-sectional view taken along the line I-I of the same figure (a).
), the same figure (d) is m-m of the same figure (a)
Line cross-sectional view, Figure 2 is a graph showing the variation in liner thickness measurement results by the method of the present invention and the conventional method, Figures 3 to 5 are measured values and actual values of liner thickness, total wall thickness, and Zircaloy thickness, respectively. FIG. 6 is a diagram showing the change in coil impedance in a reference test tube on a positive ffl impedance plane. 1 is a liner clad 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 Zircaloy tube, and 9 is a pure zirconium tube. Figure 6 Figure 3 Rainatsu'x difference root L (7am) Figure 4 Figure 5

Claims (1)

[Claims] 1. When measuring the thickness of a lined pipe by the eddy current method by inserting a coil for electromagnetic induction testing inside the pipe, a single base material pipe having the same diameter as the lined pipe to be measured is rotated. A method for measuring the thickness of a lining pipe, characterized in that the thickness of the lining pipe is calculated using the average value of the output of an eddy current measuring device obtained as a reference point. 2. When measuring the thickness of a lined pipe using the eddy current method by inserting a coil for electromagnetic induction testing inside the pipe, the eddy current obtained by rotating a single base material pipe with the same diameter as the lined pipe to be measured Using the average value of the output of the measuring device as a reference point, set the sensitivity from the average value of the output of the eddy current measuring device obtained by rotating a single liner tube with the same diameter as the lined tube to be measured, and calculate the thickness of the lined tube. A method for measuring the thickness of a lining pipe.