JPS62225903A - Apparatus for measuring thickness of liner coated pipe - Google Patents

Abstract

PURPOSE:To prevent the generation of abnormal abrasion when a probe is inserted and detached, by constituting a pipe rotating device for supporting a liner pipe to impart axial rotation thereto so that the pipe end part of a pipe to be inspected and that of an adjusting pipe faced thereto are mounted on a position setting roller. CONSTITUTION:A turning roller shaft 36 are supported at both ends thereof so as to be suppressed in its strain and a turning roller 31 is fixed on the said shaft 36 at a required position by a setting screw 58 and the pipe end parts of an adjusting pipe 29 and a pipe 30 to be inspected faced to each other are supported on said roller 31 without generating difference in level. A pinch roller 32 is also positionally adjusted to the corresponding position to restrain the pipe end parts faced to each other. At the time of measurement, the turning roller 31 rotates at a speed equal to that of other turning rollers 35, 46, 47 and, by this constitution, the fluctuation in the pipe radial direction at the pipe end parts faced to each other of the adjusting pipe 29 and the pipe 30 to be inspected is sufficiently suppressed and an insert type eddy current probe can be smoothly inserted and taken out.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a liner cladding thickness measuring device used for measuring the liner layer thickness and other pipe thicknesses of liner cladding used for nuclear fuel cladding. Regarding.

(Prior Art and its Problems) For example, in a nuclear power plant, in order to achieve high efficiency by operating a nuclear reactor to follow a load, it is necessary to be able to perform a sudden increase or decrease in output. However, if conventional silica tubes were used as cladding tubes to enclose nuclear fuel, they would not be able to withstand the sudden fluctuations in output as described above, and there is a risk of stress corrosion cracking occurring in the cladding tubes. be.

In recent years, in order to prevent such stress corrosion cracking, a cladding tube has been developed in which an ultra-thin pure zirconium liner layer 2 is formed on the inner peripheral surface of a Zircaloy tube 1, as shown in FIG. It is expected that cladding tubes will be used extensively in the next few years, replacing conventional cladding tubes.

The liner layer of the liner cladding mentioned above needs to be thick to a certain extent in order to alleviate the local stress strain that occurs on the inner surface of the cladding when the reactor output suddenly increases, and to increase resistance to stress corrosion cracking. There are also restrictions due to the need to maintain a certain level of strength by ensuring the thickness of the zircaloy layer, which is the liner layer, so controlling the liner layer thickness to a constant level is an important issue.

There are two possible methods for measuring the thickness of a pipe made of two types of metal: destructive testing and non-destructive testing. This destructive inspection method is not effective for the above-mentioned liner clad tubes, for which only the inner part of the liner is guaranteed and measurement inside the tube is essential. On the other hand, for non-destructive testing, the ultrasonic method and the eddy current method are considered, but even if the ultrasonic method is used to measure the thickness of the liner cladding, there will be echoes on the surface of the liner layer and It is impossible to identify echoes at the interface between the layer and the liner layer, making it unapplicable. In contrast, a coil carrying an alternating current is placed close to the surface of a metal object, and an eddy current is applied to the surface of the object.The coil changes depending on the situation of the object due to the induced magnetic field induced by the drawn current. In the case of the eddy current method, which obtains information about the surface of the specimen from the amount of change in impedance, the eddy current is affected by the thickness of the specimen, the specific resistance ρ, the magnetic permeability μm, etc. ,−
1. ρ-40μΩ・cm S base material layer has μr-1. ρ−
Since it is 70μΩ・cm, the conductivity of both σ(σ=1
/ρ), and by using this difference, it is possible to measure the liner layer thickness. At the same time, it is also possible to measure the total wall thickness, and by subtracting the liner layer thickness from this total wall thickness, the Zircaloy thickness can be determined.

It is well known that in the case of a pipe made of two types of metal layers, such as a liner-clad pipe, the amount of impedance change changes depending on the thickness of the upper layer. It is also well known that the amount of change in impedance changes.

Therefore, as a method for measuring the thickness of the liner cladding using this eddy current method, as shown in FIG.
is inserted into the pipe, and the coil 4 of the probe 3 is magnetized at a frequency related to the standard liner layer thickness and the eddy current penetration depth, resulting in lift-off fluctuations (air gap fluctuations between the coil and the inner surface of the pipe). Impedance component in the direction of coil impedance change ■8 and impedance component V perpendicular to it
.

JP-A-59-67405) has been proposed in which the liner layer thickness is determined by correcting (■) or (8) by (■).

However, the above method has a problem in that it is necessary to mechanically change liftoff by a certain amount when determining the direction of change in coil impedance due to liftoff fluctuation.

That is, Fig. 14 shows the direction of impedance change due to lift-off fluctuation on a normalized impedance plane when the lift-off fluctuation amount is 100 μm and 200 μm, but when the lift-off fluctuation amount is 100 μm and the AB force direction is 200 μm The AC direction is the impedance change direction due to lift-off fluctuation, and the coil impedance change direction changes depending on the amount of lift-off fluctuation. This makes it difficult to determine the direction of V, , Vx. In Fig. 9, A is the reference liftoff, B is the reference liftoff +100μm, and C is the reference liftoff +200μm.
m, Ro are the specific resistance of the coil at an infinite distance from the object, Lo is the coil inductance at an infinite distance from the object, R is the pure resistance of the coil on the object, L is the inductance of the coil on the object, ω represents the angular frequency. Also the first
FIG. 5 shows that the amount of change in impedance changes non-linearly depending on the amount of variation in lift-off, and it can be seen from this that the direction of change in impedance changes depending on the amount of variation in lift-off. In other words, in the above method, when determining the direction of impedance change due to lift-off fluctuation,
The liner layer thickness cannot be determined accurately unless the off-state fluctuation is kept strictly constant. However, as a practical problem, it is extremely difficult to mechanically strictly change the lift-off variation amount by a constant amount.

In addition, in the above method, the impedance component V8 corresponding to the liner layer thickness is corrected by the impedance component V obtained as the amount corresponding to the lift-off fluctuation amount to improve the measurement accuracy of the liner layer thickness. When trying to measure not only the layer thickness but also the base material layer thickness and total wall thickness, lift-off fluctuations have an impact on the measurement, as well as fluctuations in the conductivity of the liner layer and base material layer that naturally occur in liner cladding. Accurate measurement results cannot be expected unless the effects of these factors on measurements are sufficiently removed. However, in the above direction, fluctuations in conductivity are not taken into consideration, and from this point of view as well, it is difficult to obtain accurate measurement results.

Therefore, in order to solve the problems caused by such conventional methods, the applicant has developed a method of measuring the thickness of the liner cladding tube using an eddy current method using multiple frequencies as described later in an embodiment of the present invention. did.

However, even if we try to improve the accuracy of liner tube thickness measurement by applying this new measurement method to a conventional measurement device, the measurement accuracy obtained by the above-mentioned new measurement method is not enough when viewed from the perspective of the measurement device as a whole. This level of accuracy has not been established in each mechanical part, and it is not necessarily possible to expect an improvement in measurement accuracy if this continues. In addition, in order to ensure sufficient accuracy over a long period of time, various improvements such as support methods and calibration methods are required.

For example, as a device used for such pipe thickness measurement, the applicant of the present application has proposed the device shown in Figs. 16 and 1 separately from the present application.
The apparatus shown in FIG. 7 as a front view and a plan view, respectively, has a liner pipe 5, which is a pipe to be inspected, carried in from a carry-in preparation position A, and is placed on a turning groove 6, 6... from above. While being pressed and restrained by the pinch rollers 7.7..., the turning rollers 6.6... are rotationally driven to give axial rotation to the liner tube 5, while one tube end of the liner tube 5 is rotated. The liner layer thickness is measured by inserting a probe 9 into the liner tube 5 through the adjustment tube 8 using an adjustment tube 8 disposed coaxially with the liner tube 5 on the side as a guide. . Insertion and removal of the probe 9 is performed using a measuring device 11 connected to the probe 9 by a probe support rod 10.
The measurement device 11 is placed on a rail 13 via wheels 12, 12, and is controlled to advance and retreat in the axial direction of the liner tube 5 using the controller 14. After the probe 9 is removed from the turning roller 6.6, the liner tube 5 is transported to the transport position B from above. However, while the tubes to be inspected, such as the above-mentioned liner tubes for nuclear fuel cladding, are thin-walled and small-diameter tubes,
In the tube thickness measuring device shown in FIGS. 16 and 17 proposed by the applicant mentioned above, the tube end of the tube to be inspected 5 is in a state of cantilever support, so the tube end tends to be bent. The tube axes do not easily match at the tube end facing section between the tube 5 to be inspected and the adjustment tube 8, and an abnormally large force is applied to the guide section of the probe 9 when inserting and extracting the probe 9, causing the probe to be distorted by the tube end. 9
The problem is that the guide portion of the device is worn out, and in some cases, the guide portion is scraped.

In addition, in order to maintain a constant lift-off amount (distance 11t between the detection coil and the inner peripheral surface of the pipe to be inspected) required for eddy current measurement as an interpolation type probe, the
9. As shown in FIG.
Expanded diameter sliding portions 17a, 17a... in sliding contact with the inner circumferential surface of 6.
A probe 17 having a guide formed of the following has been developed in the past. This guide is made of plastic such as nylon, and there are a plurality of guides (generally four
~8) slits 17b, 17b... are formed. Due to the elastic deformation of this guide part, the coil 1
5 is kept at a constant distance from the inner circumferential surface of the tube body 16, and is structured to suppress fluctuations in lift-off.

By the way, when applying the above-mentioned eddy current method to the measurement of the liner layer thickness of a liner clad tube with a liner layer formed on the inner circumferential surface, minute changes in the liner layer thickness of several micrometers are considered as changes in coil impedance. Therefore, it is necessary to suppress lift-off fluctuations even more strictly.

In addition, in the case of measuring the liner layer thickness mentioned above, the average thickness of the area corresponding to the spread of the eddy current induced in the test object is measured, so the thickness distribution can be measured over the entire circumference of the tube. In order to make detailed measurements over a wide area, it is necessary to minimize the spread of eddy currents, and for this reason, a coil with a small diameter of about 1#III+φ is generally selected. However, when the coil diameter becomes smaller, the above-mentioned and 71~
The change in impedance of the coil due to the off-state change becomes relatively large, and a problem arises in that measurement accuracy cannot be improved unless lift-off fluctuations during measurement are sufficiently reduced.

When the probe 17 shown in FIGS. 18 and 19 is used for such precision measurement, lift-off fluctuations due to a drop in support pressure due to wear of the enlarged sliding portion 17a, and the use of soft plastic as a material may occur. Lift-off fluctuations associated with plastic deformation cannot be ignored, and sufficient measurement accuracy cannot be obtained.

Furthermore, as shown in FIG. 20, the conventional probe has a built-in active coil L1 that is close to the object 18 and exerts an electromagnetic effect directly on it, and a reference coil L2 that picks up output fluctuations due to disturbance factors. As shown in the figure, the active coil L1 and the reference coil L2
There is a structure in which a bridge circuit is formed with DC resistors R and R2, and the S/N ratio is improved by null mesorad measurement. However, when the liner layer thickness of the liner cladding tube is measured by the multi-frequency measurement method proposed by the applicant using such a probe 19, the impedance of the active coil L1 and the reference coil L2 becomes
Not only does it change due to various disturbance factors, but it also changes significantly with the frequency as a parameter, and the latter change in particular causes a large change in the impedance ratio of both coils, destroying the bridge balance. Highly accurate measurements cannot be expected even if method measurements are used.

(Purpose of the Invention) This invention was made to solve the above problem, and can also be applied when applying the method of measuring the thickness of liner cladding by the eddy current method using multiple frequencies developed by the applicant. The purpose of the present invention is to provide a liner cladding thickness measuring device that can increase accuracy commensurate with the measurement accuracy achieved by the above-mentioned new measurement method in each component, and can ensure sufficient measurement accuracy over a long period of time. shall be.

(Means for Achieving the Object) The thickness measuring device for liner cladding of the present invention includes a tube rotating means that supports the tube to be inspected and gives it axial rotation, and a tube rotation means that is inserted into the tube to be inspected and uses an eddy current method. A probe that obtains a detection signal corresponding to the thickness of the tube to be inspected, a probe drive means for driving the probe forward and backward in the axial direction of the tube to be inspected, a detection signal from the probe, the tube rotation means, and a probe drive means 12. and a signal processing means for outputting thickness data at each position of the tube to be inspected based on these signals, and in order to achieve the above object, the above-mentioned The tube rotation means includes a position regulating roller on which both the tube end of the tube to be inspected and the tube end of the probe guide adjusting tube opposing thereon are placed, and the tube end facing portion on the position regulating roller is pressed and restrained. A pinch roller is provided on the probe body, and the probe body is provided with a pipe pressure welding member provided on its outer circumference and capable of expanding and contracting in the axial radial direction of the probe body, and a pipe pressure member that can be moved forward and backward in the axial direction of the probe body. The probe is equipped with an actuator that expands and deforms the pipe pressure contact body, and a biasing means that adjustably applies a biasing force to the actuator toward its advancing operation side. It has a built-in coil and a reference coil that forms a bridge circuit together with this active coil to obtain a detection signal due to disturbance factors, and a material equivalent to the pipe to be inspected is located at a distance from the active coil by the lift-off amount of the active coil. It is characterized by the arrangement of.

(Embodiment) FIG. 1 shows a block diagram of a liner tube thickness measuring device which is an embodiment of the present invention. In the same figure, tube rotation device 2
0 is used to rotate the liner tube carried in by the pipe carrying device 1W21 and give axial rotation to this liner tube when measuring the tube thickness.After the measurement, the liner tube is transferred to the tube carrying device @22. It is configured to be carried out from the rotating device 20. A probe 23 that directly detects information on the thickness of the liner tube is connected to a probe drive device 24, which inserts the probe 23 into the liner tube on the tube rotation device 20, and also rotates the tube when measuring the tube thickness. Device 2
The probe driving device 24 advances or retreats the probe 23 in parallel with the axial rotation of the liner tube by the rotation of the axis of the liner tube, so that the probe 23 spirally scans the entire inner circumferential surface of the liner tube. The mechanism control device 25 receives a signal a regarding the rotational position J, that is, the circumferential position, of the liner tube from the tube rotation device 20, as well as information on the approximate dimensions and other materials of the liner tube, and also receives the liner tube from the probe drive device 24. While receiving a signal C regarding the axial position of the probe 23 relative to the tube, the tube rotation device 20 and the probe drive device @24
Various commands d regarding starting, stopping, one rotation speed, advance/retreat speed, etc.

e respectively. Measuring device 26
As shown in FIG. 2, a bridge circuit is provided which includes the active coil L1 and the reference coil L2 built into the probe 23 as components, and this converts the impedance change of the active coil L into the liner tube. It is configured to extract it as a measurement signal f. The signal processing device 27 performs signal processing to be described later using the measurement signal f given from the measuring device 26 and the position signal q given from the mechanism control device 25 to obtain thickness information at each position of the liner tube. and record this on recording device 2.
8, and is configured to give commands i regarding the operation to the mechanism control device 25.

FIGS. 3 and 4 respectively show the tube rotation device 20 described above.
FIG. 5 shows a front view and a side view of the main parts of the engine, and FIG. 5 shows an enlarged view of a part thereof. This tube rotation device 20 is
a pair of left and right turning rollers 31 on which the tube end of the adjustment tube 29 and the tube end of the tube to be inspected 30 facing thereon are placed;
31 (FIG. 3 shows only the turning roller 31 disposed on the right side when viewed from the left end side of the device), and a pair of turning rollers 31 and 31 are pressed and restrained from above the two tube ends. One pinch roller 32 is provided. In FIG. 3, another pair of left and right turning rollers 35 and 35 are provided on a pedestal 34 erected to the left of the base 33, on which a slightly rear portion of the tube 30 to be inspected is placed. The turning rollers 35.35 are each connected by the same shaft 36.36 to the turning rollers 31, 31 on which the tube ends rest.

Further, above the pair of turning rollers 35, 35, the turning rollers 35 and 35 hold the pipe 30 to be inspected.
．． Another pinch roller 37 is provided which restrains 351;
This pinch roller 37 and the pinch roller 3 on the pipe end side
2 through the same shaft 38. The right one of the turning rollers 35.35 is a gear 39.4.
It is linked to the rotating shaft 43 of the drive source 42 via a transmission mechanism of 0.41 mm.

A set screw 5 is attached to the boss portion of the turning roller 31.
8 is provided, and by loosening the set screw 58 and sliding the turning roller 31 along the shaft 36, the turning roller 31 can be positioned at a desired position. Also, the pinch roller 32
is a free roller with a built-in bearing that is rotatable around the axis of the shaft 38, and is movable as the turning roller 31 moves.

On the other hand, a pair of left and right turning rollers 46, 46, 47, 47 on which the adjustment tube 29 is placed are placed on each mount 44.45 erected in the middle and left side of the base 33 (in FIG. 3, from the left end side of the device Turning roller 46 located on the right side as viewed.
Turning rollers 46-47 and 46- corresponding to the front and rear positions are provided respectively (only 47 is shown).
47 are also connected by the same shaft 48 and 48, respectively.

Also, turning rollers 46° 47 for the adjustment pipe 29
．． The left and right shafts 48, 48 of 46, 47 are respectively connected to the left and right shafts 36, 36 of the turning roller 31, 31 of the tube 30 to be inspected, forming one shaft. The right one of the turning rollers 46, 46 is linked to the rotating shaft 43 of the drive source 42 through a transmission mechanism consisting of gears 49, 50, 51.

That is, one driving source 42 drives the left and right turning rollers 31, 35, 31, 35, 31, 35, 35, 42 for the tube to be inspected 30 and for the adjustment tube 29, respectively.
46 and 47 are configured to rotate synchronously.

Pulleys 52 and 53 are provided at the front and rear of the adjustment pipe 290, respectively.
are provided, and pulleys 54,55 corresponding to these are also provided on the frame 44,45, and by passing a rubber belt 56,57 between the pulleys 52,54 and pulleys 53,55, the adjusting pipe 29 It is configured to press and restrain the turning rollers 46 and 47 while allowing the rotation of the turning rollers 46 and 47.

Note that since the tube to be inspected 30 is carried from the carry-in preparation position onto the turning rollers 31.31°35.35 in a direction perpendicular to the tube axis, the end of the tube to be inspected 30 does not touch the adjustment tube 29 at this time. As shown in FIG. 5, the gap d between both ends of the tube is set to about 31III (minimum diameter, maximum 6 mm). Therefore, the width dimension of the turning l cola 310 on which both ends of the pipes are placed is set to be sufficiently larger than the above-mentioned gap d.

In the above configuration, the turning roller shaft 36 is supported at both ends to suppress distortion, and the turning roller 31 is fixed at a predetermined position on the shaft by a set screw 58, and the adjusting pipe 29 and the pipe to be inspected 30 are fixed thereon. The facing tube ends are supported without any difference in level. Pinch rollers 32 are also adjusted to corresponding positions to restrain the facing tube ends. During measurement, the turning roller 31 rotates at the same speed as the other turning rollers 35, 46 and 47, and as a result, the deflection in the pipe radial direction at the facing ends of the adjusting pipe 29 and the pipe to be inspected 30 is sufficiently suppressed. , it is possible to smoothly insert and extract the interpolated eddy current prologue. When the length of the tube 30 to be inspected changes, it is easy to handle the change by simply changing the length of the adjusting tube 29 and positioning the turning roller 31 and the pinch roller 32 at the required positions.

In addition, as the turning roller 31 and the pinch roller 32 that presses both pipe ends, separate rollers may be provided for each pipe end, and each pipe end may be restrained and rotated separately. . Moreover, instead of the turning roller 31, a free roller (that is, the same structure as the pinch roller 32) with a built-in bearing that can freely rotate around the axis of the turning roller shaft 36 is provided, and the adjusting tube 29 and the tube to be inspected 30 are mounted on this free roller. The facing tube end of the tube may be received. In this case, the -b-facing tube end is supported without a step difference, and vibration in the tube radial direction is sufficiently suppressed during rotation. In short, any position regulating roller that supports the tube end facing portion without any level difference can be used in place of the turning roller 31 described above.

FIG. 6 shows a front view with half of the probe 23 described above cut away.

This probe 23 has a rod-shaped probe body 5.
Pipe pressure welding bodies 60, 60 are screwed onto the front and rear shafts of the probe body 59, respectively, and opposing pipe pressure welding bodies 60, 60 are respectively screwed onto the shaft portions of the probe body 59 at positions corresponding to the tip side of each pipe pressure welding body 60.
A ring-shaped actuator 61.61 is fitted into the probe body 59 so as to be movable in the axial direction.

Furthermore, spring bearing nuts 62 and 62 are screwed onto the shaft portion of the probe body 59 at positions corresponding to the rear end side of each of the actuators 61 and 61, respectively, and between the actuator 61 and the spring bearing nuts 62, Compression coil springs 63 and 63 are respectively interposed to bias the actuator 61 toward the pipe pressure contact body 60.

Further, a recessed portion 64 for mounting a coil is formed in the intermediate portion of the probe body 59, and a pedestal 66 to which a coil 65 is attached is removably screwed into the recessed portion 64.

The pipe pressure welding body 60 is made of high-density polyethylene resin with a small coefficient of friction and low hardness, and has an enlarged diameter sliding portion 60a having a slightly larger outer diameter than the other portions of the probe body 59, including the portion where the coil 65 is attached. On the inner periphery of the ring-shaped tip facing the actuator 61, a tapered surface 60b whose diameter increases toward the tip side is formed. A plurality of slits 60c are formed in the axial direction, so that elastic expansion/contraction deformation is possible.

Further, the actuator 6 facing the pipe pressure contact body 60
The tapered surface 60 of the pipe pressure welding body 60 is provided on the outer periphery of the tip end of
A tapered surface 61a that comes into contact with b is formed, and due to the mutual sliding action of these tapered surfaces 601) and 61a, as the actuator 61 is pushed toward the pipe pressure contact body 60, the pipe pressure contact body 6
0 is configured to be deformed to expand its diameter.

On the other hand, 62 and the compression coil spring 6 are connected to the spring receiving nut 1.
3 constitutes a biasing means for biasing the actuator 61 toward the pipe pressure welding body 60, and the biasing force is applied by turning the spring receiving nut 62 to avoid displacing the screwed position back and forth. It is configured so that it can be adjusted accordingly.

The rear shaft portion of the probe body 59 is formed into a tubular shape, and a lead wire 67 connecting the coil 65 described above and the bridge circuit shown in FIG. 2 is wired in the hollow portion 59a. When measuring the tube, the rear shaft portion of the probe body 59 is connected to a probe support rod extending from the measuring instrument side.

Next, the operation of this probe will be explained. As shown in FIG.
The probe 23 is deformed to expand its diameter, so the probe 23
During measurement when inserted into the pipe to be inspected 30 which is being rotated by
0a.

60a is pressed against the inner circumferential surface of the tube 30 to be inspected. therefore,
It is possible to measure the eddy current in the inner circumference by moving the probe 23 back and forth while maintaining a constant distance between the inner circumferential surface of the tube 30 to be inspected and the coil 65, thereby greatly suppressing lift-off fluctuations. It is something.

When the support pressure of the tube pressure welding body 60 against the pipe 30 to be inspected decreases due to wear, the spring receiver is rotated by the compression coil spring 63 against the actuator 61 by turning the spring support nut 62.
By increasing the biasing force, it is possible to adjust the support pressure to an appropriate level.

Note that the actuator 61 of the shaft portion of the probe body 59
A stopper 59b for restricting the advancement is provided on the advancing movement side of the
, 59b are formed to prevent the tube press-fitting body 60 from being forced to expand its diameter excessively and becoming an obstacle to insertion into the tube 30 to be inspected, for example.

In order to adjust the compression coil spring 63 to an appropriate biasing force, prepare a standard tubular body for setting the spring pressure, and move the tubular body back and forth, for example, with the probe inserted into the standard tubular body. can be adjusted by measuring the frictional resistance force at this time.

When measuring the thickness of a tube body by connecting the probe 23 to the probe support rod, we measured the amount of change in lift-off when the probe support rod was moved back and forth, and a very good value of only a few μm was obtained. ing. On the other hand, the pipe pressure welding body 60
When the probe support rod was changed in the same manner with the probe 23 removed, the amount of change in lift-off was approximately 500 μm, confirming that the probe 23 has a large effect of suppressing lift-off fluctuations.

In addition, since the pipe pressure welding body 60 is made of high-density polyethylene resin with a small coefficient of friction and low hardness, it can also be used in measurements where there is concern about the occurrence of flaws in the liner layer on the inner peripheral surface, such as in litchi-coated pipes. , which can reliably prevent the occurrence of defects.

FIG. 7 is a schematic diagram showing the arrangement of the coils in the probe 23 described above. In the figure, the active coil L1 is set so that the distance from the surface of the liner layer 30b, that is, the lift-off fR1, is constant when the active coil L1 is inserted into the tube 30 to be inspected and set at the time of measurement.

On the other hand, for the reference coil L2, a plate 69 (Zircaloy plate) made of the same material as the base material layer 30a of the tube to be inspected 30 is arranged via a spacer 68 having a thickness equal to the lift-off amount 1, and the spacer 68 A material whose electrical characteristics are close to those of the air interposed between the active coil L1 and the tube 30 to be inspected is selected. That is, from the reference coil L2 to the above-mentioned riff I-off m
A material equivalent to the tube to be inspected 30 is placed at a distance (A). In order to ensure accurate measurements, it is desirable to use a plate 69 having the same layer structure as the tube to be inspected 30 (liner clad tube), in which a liner layer of pure zirconium is formed on a base material layer of Zircaloy.

When the liner layer thickness of the liner cladding tube is measured by the eddy current method using dual frequency under the following conditions using the probe 33 with the above configuration, the impedance of the active coil L1 and the reference coil L2 is determined. Table 1 shows a comparison with the conventional probe for each frequency.

(1) Inner diameter of liner cladding tube base material layer (Zircaloy): 10.55 mφ Base material layer thickness: 0.87 mφ Liner layer (pure zirconium) thickness: Approximately 90 μm (2)
Probe active coil: A thin copper wire of 0.07 #φ is wound 85 times around a ferrite core with a diameter of 0.85 sφ and a length of 3 #III.

Reference coil: Equivalent to active coil.

Zircaloy plate: Area 3.5m square, thickness 0.87a*.

Lift-off amount j! : approx. 250 μm (3) Frequency Low frequency (f1=1/ω1): 2MH2 High frequency (f2
-1/ω2): 4MHz (blank below) As is clear from this measurement result, in the probe of the example, the absolute values of the impedance of the active coil and the reference coil are almost the same regardless of the frequency, and the difference is the same at a frequency of 2MHz. In case 10.4 M l-
In the case of lz, it is only 30. Therefore, the impedance ratio of both coils hardly changes depending on the frequency, and continues to maintain a value close to 1. In contrast, the conventional probe has a frequency of 150.4 at 2 MHz.
It is recognized that there is an impedance difference of 180 at MHz, and that the impedance ratio also changes greatly depending on the frequency. This means that although it is impossible to maintain bridge balance over a wide frequency range in the conventional example, this is fully possible in this embodiment. Specifically, by using this plow 123, it became possible to suppress the shift in balance of the bridge circuit to within 3%, thereby achieving a significant improvement in S/N.

With conventional probes, it is difficult to suppress the shift in bridge balance to within 5.

It is also known that the maximum sensitivity is achieved when (L impedance)/(L2 impedance) - R/R2 = 1, and according to the present invention, as described above, regardless of the frequency, the The maximum sensitivity can be obtained. For these reasons, high measurement accuracy can be achieved according to the present invention. Incidentally, it was also confirmed that the measurement accuracy of the liner layer thickness in the above case was ±2.8 μm for the probe of the example, which was much improved compared to ±10.5 μm for the conventional probe.

On the other hand, signal processing in the measuring device 26 and signal processing device 27 described above is performed as follows.

The bridge circuit shown in FIG. 2 provided in the measuring device 26 is an active coil L built in the probe 23 side.
The active coil 1 is configured with four impedance elements: a reference coil L2 for maintaining balance with this coil L1, and a pair of pure resistors R1 and R2 that are paired with these coils, and the impedance of the active coil 1 changes. is detected as an unbalanced voltage between contacts a and b due to bridge imbalance. Further, a first dummy circuit 72 is constituted by a combination of an impedance element Z1 which is switched to the active coil L1 by a switch 70, and an impedance element Z2 which is switched to the reference coil L2 by a switch 71, and furthermore, a first dummy circuit 72 is constructed by a combination of an impedance element Z1 which is switched to the active coil L1 by a switch 70, and an impedance element Z2 which is switched to the reference coil L2 by a switch 71. A second dummy circuit 74 is configured by adding an impedance element Z3 connectable in parallel to element Z2 to the first dummy circuit 72. Each of the impedance elements 71 to Z3 is configured by a combination of elements such as a resistor and a capacitor, and the impedance elements Z1 and Z2 are selected to be equivalent to the active coil L1 and the reference coil L2, respectively. Further, the impedance element Z3 is selected to have a value approximately 100 times that of the impedance element Z1. In other words, the second dummy circuit 74 is
The impedance value IZ2+ of the first dummy circuit 72 is set to 1%.
It has been changed.

On the other hand, three types of frequencies are given as the frequency of the alternating current flowing through the active coil [1]. This frequency selection is determined as follows.

■ As the frequency f1, which is mainly used to measure the total wall thickness of the liner cladding tube 8, the penetration depth of the eddy current is δ, where ω: angular frequency (-2πf1) μ: μ ×μO μ,: relative magnetic permeability μ0 = vacuum The magnetic permeability (= 4 yc

■ Frequency f, which is mainly used to measure liner layer thickness,
f is determined so that the penetration depth δ of the eddy current is a value near the liner section.

In such a configuration, the thickness of the liner cladding tube is measured as follows. First, prior to actual measurement, a reference direction is determined as follows.

That is, the active coil L of the bridge circuit in FIG.
1 and reference coil L2 with switch 70.71
and the impedance element Z1 of the first dummy circuit 72. Z2
Switch and connect to measure the output of the bridge circuit.

Next, the impedance element Z3 is connected to the first dummy circuit 72 by the switch 73, that is, the second dummy circuit 74 is connected, and the output of the bridge circuit is measured. Then, the direction of change in the bridge circuit output due to the above two operations is determined for each of the three types of frequencies f1 to f3 described above, and these are determined as reference directions corresponding to each of the frequencies f1 to f3.

Next, the phase angle is adjusted for each frequency so that one direction of the reference -32 corresponding to each frequency f-f3 coincides with the horizontal direction of the impedance plane of the display section of the measuring device 26 described above. The horizontal and vertical components of the impedance measured under these conditions are expressed as 1-11, respectively. V
1, R2, V2, R3, and V3, the liner layer thickness, total wall thickness, and Zircaloy thickness are calculated as described below. Note that the subscripts of the horizontal and vertical components represent the difference in frequency in the triple frequency group.

For calculation, the following operations are required in advance.

(1) The assumed liner layer thickness in the liner layer thickness calculation formula is the frequency f2. Assume that the calculation is performed using f3. where:, 1jkl is a coefficient.

(2) The assumed total thickness of the total thickness calculation formula is the frequency f, f2. Calculate using f3. For example, the calculation formula is: The entire wall thickness is t. Assume as tal. However, C1 is a coefficient.

+jkln+n (3) Assumptions for Zircaloy thickness calculation formula The Zircaloy thickness can be calculated in the same way as the total wall thickness, but simply let the Zircaloy thickness be T and ry and calculate """total"zr ・
...(3)ry can also be calculated.

(4) Determination of coefficients The liner layer thickness, total wall thickness, and Zircaloy thickness are actually measured by standard destructive testing of liner cladding tubes.
) is used to select the optimal term by multiple regression analysis, and the coefficient of each term is determined by the method of least squares. From this, the actual formulas for calculating the reliner layer thickness, total wall thickness, and Zircaloy thickness are obtained.

The calculation program for the actual formula obtained in this way is
The signal is input to the signal processing device 27 shown in the figure, and the active coil L1 and reference coil L2 of the bridge circuit are returned to their original connection state, and eddy current measurement using triple frequencies is performed. As a result, the horizontal and vertical components 1-11 . V
l, R2.

V2. R3 and V3 are sequentially input to the signal processing device 27,
Based on this input data, the above three practical formulas are calculated, and the liner layer thickness, total wall thickness, and Zircaloy thickness are calculated. These calculation results are input to the recording device 28 shown in FIG. 1, and each calculated value is recorded and displayed.

The above method was carried out at a test frequency of 500 kHz when the coil diameter of the active coil L1 in the probe 23 was approximately 1 mm.
The applied pitch measurement (calculation) results in the case of 2MHz, 4M1-(z) are shown in FIGS. 8, 9, and 10.

Figure 8 shows the relationship between the liner layer thickness calculated using this method (vertical axis) and the actual value obtained through destructive testing (horizontal axis). It is confirmed that the values match well. FIGS. 9 and 10 show similar relationships for the total wall thickness and base material B (Zircaloy) thickness, respectively, and it is confirmed that highly accurate measurement results are obtained in both cases.

In the above example, the base metal layer thickness is calculated from the difference between the measured total wall thickness and the liner layer thickness, but the base metal layer thickness can also be calculated in the same way as when calculating the total wall thickness. I can do it. When only the liner layer thickness is measured by the above method, three types of frequencies are not necessary, and two types of frequencies are sufficient because the unknown quantity of the total thickness can be reduced.

Further, the second dummy circuit 7 in the bridge circuit described above
4, the impedance element R2 of the first dummy circuit 72
Although the configuration is such that the impedance element Z3 is connected to the side of the impedance element R1, the impedance element Z3 may be connected to the other side of the impedance element R1.
Impedance element Z1 on the dummy circuit 72 side. Any one of Z2 may be changed by about 1% by adding the impedance element Z3. Note that the procedure for adjusting the impedance elements Z 1 and Z 2 to be equivalent to the active coil L1 and the reference coil L2 is preferably performed as follows.

First, prepare a sample tube with standard liner layer thickness and total wall thickness.
The probe 23 is inserted into this sample tube, and the output of the bridge circuit is measured with the active coil L1 and reference coil L2 connected. Next, as the impedance elements Z and R2 of the first dummy circuit 72, first, pure resistors R3 and R4 equivalent to the pure resistors R1 and R2 in FIG.
2 side and measure the output of the bridge circuit.

After this, additional resistors are added to the pure resistors R3 and R4,
The values of the impedance elements Z and R2 are determined by sequentially connecting capacitors and adjusting the output of the bridge circuit to be equal to that when the coil system is connected. Impedance element Z (approximately 100 times Z or R2) added to one of impedance elements 2.22 is:
Adjust and determine a value such that the change in the output of the bridge circuit when this impedance element Z3 is connected is approximately equivalent to the change in the output of the bridge circuit that occurs when the probe 23 is inserted into the sample tube and the lift-off is changed. .

The first step described above determines the reference direction of the change in coil impedance. Each of the impedance elements 71 to Z3 of the second dummy circuit 72, 74 can meet the above standards without being affected by disturbance factors such as temperature and moisture by appropriately selecting electric elements such as the above-mentioned resistors and capacitors. Able to determine direction correctly. By the above procedure, each impedance element 71
By determining ~Z3, the reference direction can be set under the same sensitivity conditions of the measuring instrument as when actually measuring the liner cladding, and the dynamic range of the measuring instrument can be widened.

Further, the absolute value of the output difference (referred to as reference voltage) of the bridge circuit when switching from the first dummy circuit 72 to the second dummy circuit 74, which determines the reference direction, is an index of the sensitivity of the measuring instrument system. That is, when the sensitivity of the measuring instrument system changes over time, the reference voltage changes accordingly. Therefore, by regularly checking the reference voltage mentioned above and correcting the measured value of the liner cladding by the method described above by the amount corresponding to the change, the measurement deviation due to the change in sensitivity of the measuring instrument system can be calibrated. It is possible to improve measurement accuracy.

FIG. 11 shows the measurement results of the liner layer thickness of the liner cladding tube after 4 months under the same conditions as in the previous example in which the measurement results shown in FIGS. 8, 9, and 10 were obtained. . The vertical axis shows calculated values measured by this eddy current method, and the horizontal axis shows actual measured values obtained by destructive testing.

On the other hand, the changes in the reference voltage between the previous example and the example 4 months later are as shown in Table 1.

Table 1 As is clear from the measurement results shown in Figure 11, if the above reference voltage change is not corrected, there will be some deviation between the actual measured value (horizontal axis) by the destructive test and the measured value by the eddy current method. An increase in the variation is observed. Figure 12 shows the results of calculating the liner layer thickness by correcting the measured values of each component H, Vl, H2, and V2 of the coil impedance change obtained by the eddy current method by the rate of change in the reference voltage.
The vertical axis is the calculated value after correction by the eddy current method, and the horizontal axis is the actual value measured by destructive testing). As is clear from comparing this figure with the previous figure 8, the above correction is extremely effective.
be done.

(Effects of the Invention) As described above, the liner tube thickness measuring device of the present invention has the following effects on the tube rotation device and probe that support the liner tube and give it axial rotation. Therefore, even when implementing the method of measuring the thickness of liner cladding by the eddy current method using the multiple frequencies developed by the applicant, the measurement accuracy of the new measurement method described above can be improved in each component. A commensurate improvement in accuracy is achieved, and the effect of being able to measure the liner layer thickness of a lychee clad tube with high accuracy is obtained.

(1) The tube rotation device supports the tube end of the tube to be inspected and the tube end of the adjustment tube facing it by placing it on position regulating rollers, so it is possible to reduce the level difference in the tube end facing section. The core runout caused by manufacturing errors can be kept within a practically negligible range, and therefore, abnormal wear of the probe sliding portion due to the step difference when inserting and removing the probe can be reliably prevented.

(2) The probe can eliminate lift-off fluctuations due to wear and plastic deformation with simple adjustments, so it can be used to measure the liner layer thickness of liner cladding tubes, which requires significant suppression of lift-off fluctuations.

(3) Regarding the coil inside the probe, the impedance ratio between the active coil and the reference coil does not vary depending on the frequency, so when applied to measuring the liner layer thickness of liner cladding, etc., high measurement accuracy is achieved. can get.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the outline of a liner tube thickness measuring device which is an embodiment of the present invention, Fig. 2 is a wiring diagram of a bridge circuit in the measuring device, Figs. 5
The figures are a front view, a side view, and a partially enlarged view showing the main parts of the tube rotation device, Fig. 6 is a front view with half of the tube cut away, and Fig. 7 shows the coil arrangement of the probe. The schematic diagrams shown in Figures 8, 9, and 10 are the values of the liner layer thickness, total wall thickness, and base material layer thickness of the liner cladding tube measured by the apparatus of the example and the values determined by destructive testing. Figure 11 is a diagram showing the relationship between the measured value of the liner layer thickness measured four months after the above example and the actual value measured by destructive inspection. A diagram showing the relationship between the measured value of layer thickness corrected by the reference voltage change and the actual value measured by destructive inspection. Figure 13 shows the case where the thickness of liner cladding is measured by the eddy current method using an interpolated probe. Fig. 14 is a diagram showing the direction of impedance change due to lift-off fluctuation, Fig. 15 is a diagram showing the relationship between lift-off fluctuation amount and impedance change amount, and Figs. A schematic front view and a schematic plan view, FIGS. 18 and 19 are respectively a front view and a side view of a conventional probe, FIG. 20 is a schematic diagram of another conventional probe, and FIG. 21 is used for null method measurement. It is a bridge circuit connection diagram. 20... tube rotation device, 23... probe, 24...
- Probe drive device, 26... Measuring device, 27... Signal processing device, 29... Adjustment tube, 31... Turning roller, 27... Pinch roller, 59... Probe body, 60... ... Pipe pressure welding body, 60a... Expanded diameter sliding part,
60b...Taber surface, 60C...slit, 61.
... Acquicoator, 61a... Taber surface, 62...
・The spring holder is a nut, 63...compression coil spring, Ll
...Active coil, L2...Reference coil

Claims (1)

[Claims] (1) A tube rotation means that supports the tube to be inspected and gives it axial rotation, a probe that is inserted into the tube to be inspected and obtains a detection signal corresponding to the thickness of the tube to be inspected by the eddy current method, and this probe. A probe driving means for driving the tube to be inspected forward and backward in the axial direction, receives a detection signal from the probe and a position signal obtained from the tube rotation means and the probe driving means, and determines each position of the tube to be inspected based on these signals. In the liner tube thickness measuring apparatus, the tube rotation means rotates the tube end of the tube to be inspected and the tube end of the probe guide adjustment tube opposing thereto. It has a position regulating roller that is placed together with the probe, and a pinch roller that presses and restrains the tube end facing part on the position regulating roller, and the main body of the probe is provided on the outer periphery and can be expanded and contracted in the axial and radial direction of the probe body. an actuator which is provided so as to be movable in the axial direction of the probe body and expands and deforms the tube pressure contact body to expand its diameter, and an adjustable biasing force applied to the actuator in the direction of its advancing motion. The probe has a built-in active coil that exerts an electromagnetic effect on the tube to be inspected, and a reference coil that forms a bridge circuit together with the active coil to obtain a detection signal due to a disturbance factor, A liner tube thickness measuring device characterized in that a material equivalent to the tube to be inspected is placed at a position separated from a reference coil by a lift-off amount.