JPS6196401A - Method for measuring thickness of liner on the basis of two frequency - Google Patents

Abstract

PURPOSE:To attain precise measurement by erasing the superposition of a noise signal due to the variation of lift-off or the like to a film thickness signal and its sensitivity change by a specific phase detecting output. CONSTITUTION:A probe 3 is set up so as to be moved in a liner coating tube 1 to be rotated by a rotor 2 in the axial direction of the tube 1 by a driving device 4. At the execution of measurement, two kinds of frequency are used and the impedance change of the coil of the probe 3 is converted into a voltage by an eddy current flaw detector body 5, the voltage is converted into liner thickness by an arithmetic unit 6 and the liner thickness is displayed on a display device together with its measuring position. In this case, the phase detecting output of the body 5 at the change of lift-off is measured by the tube 1 having liner layer conductivity and zircaloy part conductivity which are different values each other to calculate an impedance component of the lift-off changing direction and table based upon the change of the liner thickness. On the basis of the table, the superposition of a noise signal to a film thickness signal and the sensitivity change of the signals are erased by the four kinds of phase detecting outputs of the body 5.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a cladding tube for filling pelleted fuel that forms fuel rods in nuclear reactors by using ultra-thin pure zirconium mt- When combining liner cladding tubes,
The present invention relates to a method for measuring the liner thickness by an eddy current method, and in particular a method that enables measurement of the inner layer on the positive side by eliminating the effects of error factors such as lift-off fluctuations and conductivity fluctuations that can become noise signals during measurement.

(Prior art) In order to slow down the Jul rate of a nuclear power reactor in response to changes in electric power demand, a sudden rise and fall in Ik output is essential. Sudden output fluctuations due to overturning of conventional MI bonds only for Zircaloy
There is a concern that f5 may cause eclipse fL. In order to prevent stress corrosion cracking, liner WI (I pipe), which is made of ultra-thin pure zirconium liner TS on the inner surface of the Zircaro base material pipe, was developed and related technology was established. It is expected that it will be fully used.

The above-mentioned liner clad pipe requires that the liner layer has a specified thickness due to the above problems. Side measurements include destructive inspection and non-destructive inspection, but destructive inspection can only measure the length of the pipe at both ends.

It is unsuitable for liner sand-covered pipes that require guarantee of liner layer throughout the station. Among various methods for non-destructive inspection, the ultrasonic method and the eddy current method are considered, but the If wave method cannot identify echoes at the boundary between the liner layer and the Zircaloy base material tube, so The magnetic permeabilities are both 1 and there is no difference, but the specific resistance ρ is μg-1: * The former is 40 and the latter is 70.
Deluri.

It is also possible to measure the liner layer thickness by using the difference in the reciprocal conductivity (tlc=1/p). #fhtIi flow method is based on the principle that an eddy current is caused to flow on a metal surface by bringing a coil through which a certain frequency of AC type tlIt-flow is brought close to the metal surface.
The impedance of the coil changes due to the eddy current, and the amount of change in impedance is used to obtain detailed information about the metal surface. In the case of a liner sand-covered pipe, if the eddy current method is applied from the inner surface of the pipe, the impedance change 1 will change with each movement of the liner layer, and this can be used to measure the liner layer.

The conventional eddy current method for measuring the liner thickness of liner sand-covered pipes is 'f? IFM 1986-67405, Japanese Patent Application Publication No. 1983
9-67406 etc. Extract the impedance change component due to these beams 7 to 7 (distance between the coil and the pipe Pj blood) and lift off i! The purpose is to correct the liner layer by calculating t. However, the electrical conductivity σAFi of the liner layer of the liner sand-covered pipe changes depending on the degree of heat treatment MA, and the electrical conductivity σB of the Zircaloy part changes depending on the amount of 8n of the hardening component contained in the Zircaloy. These differences in conductivity depending on the product loft naturally occur in liner sand-covered pipes. Therefore, in order to accurately measure the liner layer, it is necessary to take into account changes in the conductivity of the liner layer and the Zircaloy portion, but the prior art disclosed in the above-mentioned Japanese Patent Publication does not take these changes into account.

Another reference technique is JP-A-59-9552.

(Problems to be Solved by the Invention) The present invention eliminates the influence of an error device due to vibrations and fluctuations in the conductivity of the pipe material in the measurement of the liner layer of a liner sand-covered pipe by the % eddy current method. The purpose is to provide seven methods that enable accurate measurements.

(Means, effects and embodiments for solving the problems) The standard or official value of this kind of Kuina WgI tube is that the thickness of the liner layer is 80 μm and the total thickness is about 860 μm. The thickness of this ultra-thin liner layer is measured by the change in impedance of the prologue coil using the eddy current C method from inside the tube.

In this @Akira, during this measurement, changes in lift-off (gap distance M between the coil and tube inner surface) caused by vibrations of the plow 1, etc., and changes in conductivity caused by changes in the material of the liner temporary casing, etc. The superposition of the noise signal on the film thickness signal and the sensitivity change of the film thickness signal are eliminated and corrected. Measurement station I of the ninth type! This is done using the four types of phase detection outputs of the eddy current flaw detector obtained by simultaneously measuring .

FIG. 1 normalizes the change in impedance of the output of the coil and shows it as an impedance average. Inductance Lυ of the coil alone.

The resistance Ro and the frequency kfsm=2trf, the vertical axis is the inductance at the time of measurement "'toLo", and the horizontal axis is the resistance at the time of measurement Rt"(R-Ro)/ωLO, which is normalized.

In diagram Wc1, the components in the impedance change direction at low frequency fa and high frequency fb are shown as i, respectively.
Subscripts a and b are added to distinguish between i, s, and %.

i indicates the variation in the conductivity σA of the liner layer, i indicates the variation in the electrical conductivity σB of the Zircaloy base material, and the child indicates the component due to the variation in the liner layer. In this way, the frequency fa,
It is known that since the impedance change directions of each of the bacmeters i, A, and n% are different during fb, it is possible to identify them by distinguishing them in principle.

Since only two types of phase detection outputs can be obtained with a single frequency, it is impossible to specifically identify them, but with the present invention, i
By using two types of power fILIi, a 4N phase M-wave output is obtained, so that 1fU can be identified by these relationships.

In other words, the liner thickness variation for each parameter IIL, R, and 8 for this 4N phase detection output is created in advance using the known Kuina'wIat pipe standard, and is obtained when measuring the pipe to be inspected. The liner thickness 'fr' is determined from the value of the phase M-wave output by calculation using the above table.When performing this liner RC calculation, the W-opening method is used to calculate it.

An example of an apparatus for carrying out the present invention will now be described.

FIG. 2 shows an outline of its configuration. Kuina Li Dong Tube (1λ
is rotated in the circumferential direction of the tube by a rotary machine (2).The probe (3) is an interpolation type, absolute M value type filter holder, and is moved in the tube in the thin wire direction by a drive device (47). The measurement position is determined.The rounding coil that can obtain high resolution of liner thickness fluctuations is of small diameter, for example, one cylinder.

2 types of #Seshikinri according to book 0, such as fa li 2M
IIZ and fb are set to 4MHz. In this way, we performed the measurement and performed the coil's innovative dance.
Converts to voltage by voltage. This IIt8E is calculated by the Honwaaki method: f: is converted into the liner thickness by the traveling calculation device t, and is displayed on the display (7) together with the measurement position.

The calculations performed by the method of the present invention in the calculation device (0) are as follows:
11 [operation is performed.

Nanowa 101 Quina layer conductivity σA, Zircaloy part conductivity σB known, stepwise known liner! l! , ti liner 11
1 Using the test specimen of cladding or its temple, the above 85!
Using a 6IIt flaw detector, the frequency is set to a low frequency ra, and the phase detection outputs of the eddy protection flaw detector Hta, V IJL
Measure 1st and make the same measurement - 9'r = 7 to 7 /1
The output H-% v6t-
Measure. From these measured values, the direction of change in toe-off is calculated. Let the impedance component in the 7-off fork direction be Vya, and let the impedance component in the direction perpendicular to this 5t be Vxa. The current origin is Hla and V.

Tables 1 and 2 below show the impedance components (dimensionless i1) for fL7j Vxa and Vya obtained by performing measurements in this manner, and also show the coefficients of impedance components (dimensionless i1) for
Figure 6 shows a diagram of changes in Ixa-Vya due to changes in liner thickness at 71, with ixh k on the ordinate and Vya on the abscissa (arbitrary scale).

Table 1 vxa change cheagle (dimensionless It) is ts
>ta>tm>ta>ta>ti>tt>
ta > to, lift or amount xi Fiz dish < 1
g < / s (/ a (l m). Frequency f
a is 2 l[Hg, O is the coil diameter Fi1 ma+
t nine high #llit (measured at 4 MHz of fb, set the coordinate system Vxb - Vyb by the same procedure as above, and
Create a change diagram similar to the table, happy 2 table, and ceramic 1 wheel, and figure 3.

Furthermore, for example, 10
aA f 115Q at σ-41st position,? /40, 11
50ttB f 1/5O 11/70. Vxa -Vya, Vxb -Vyb diagram〈9, 1st
Create a table similar to Table 2.

After making the calculation preparation settings in this way, the liner cladding tube to be inspected is measured at specified points with a flaw detector, and the measured phase detection outputs H6JL, V5a and H5b,'
i5b is converted to the value of the above Vx-Vy coordinate system, calculated using a four-dimensional Kuina thickness calculation table created in advance, and the liner thickness at each measurement point is calculated using the interpolation method.

That is, for example, as one calculation method, fa and f
Total of 11 in b! From the I value, the “Ixa” of the σA1σB value
-Vya and vxb -Vyb - Attack the liner j@ by calculation using the table or table. If the liner I$ values at both frequencies match, the accurate liner thickness at that measurement position can be found, σm, σB and li are known. If there is no match, use the table of σA1cBm combinations with the smallest difference or σB with 1σAft as the center and the center.
By changing σA and keeping the %dB value constant, or by changing gA
, σB are changed to bring the liner thicknesses from the measured values of fa and fb closer to matching.

The sequence of operations may be in a different order than described above.

Although lift-off, σA, and σB can be restored at the same time, these are used as calculation parameters and do not necessarily need to be determined.

The lift-off value caused by vibration can be understood as the lift-off of the average value of either mechanical or electromagnetic vibration. The σA@ and σB values known can be compared with values obtained at different measurement points and used for calibration.

Also, since the changes in conductivity σA and σB are small in a single tube, the effect is only at one point at the end of the tube. can be measured by the above method, and the liner thickness over the entire circumference and length of the pipe to be inspected can be measured using the opening constant σA1 σB. Even with this partially simplified calculation, high Accuracy measurement results are obtained.

(Effects of the Invention) According to the method of the present invention, it is possible to measure the consistent liner thickness by removing the effects of error factors caused by variations in the conductivity of the liner layer, variations in the conductivity of the Zircaloy part, and variations in the conductivity of the Zircaloy part. effective.

[Brief explanation of the drawing]

Figure 1g1 shows the change in the Tagata impedance of the coil t-2.
Normalized impedance plan view shown at frequency loss %2
The figure is a perspective view and a Gronk diagram showing one example of the configuration of the device t implementing the present invention, and FIG.
It is a coordinate system diagram. (1)...2 Ina sand covered pipes (2)--Rotating machine, (3)
... Progue, (4) ... Movement device, (5) ... Eddy current flaw detector main body, (6) ... Arithmetic device, (7) ... φ indicator *
(ti)... liner thickness, (11)... 7 to 7 zero k
(IA)...Quina layer UG electrical conductivity, (σB)--Zircaloy part III electrical conductivity, (fa)...Low frequency &% (fb
)...High frequency & %(a)...Impedance R change due to lift-off fluctuation - dance change component, ψ)...Impedance change component due to Zircaloy sNI electrical efficiency actual intuition, (η
...Impedance change component due to liner thickness variation, (V
y)...impedance component s in the direction of change
('')...Impedance component in the right angle direction (F1a) -
6 Frequency 1k b (Rmean) e *Coil radius.

Claims (1)

[Claims] When measuring the liner thickness of a liner cladding tube using the eddy current method, a film of noise signals is generated due to variations in lift-off caused by vibration of the probe, etc., and fluctuations in conductivity caused by changes in the material of the liner cladding tube. The superimposition on the thickness signal and the sensitivity change of the film thickness signal are canceled and corrected by four types of phase detection outputs of the eddy current flaw detector obtained by simultaneous measurement at two types of measurement frequencies. Frequency-based liner thickness measurement method.