JPH0574021B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a grid plate inspection device, and is particularly suitable for accurately inspecting stress corrosion cracks occurring in the upper grid plate of a boiling water nuclear reactor. This invention relates to a grid plate inspection device.

[Conventional technology]

Conventional devices of this kind, as described in Japanese Patent Application Laid-Open No. 61-66162, have a ball screw installed in only one direction on a base that can be fixed to a grid plate placed on a grid plate.
A moving block was attached to it, and the moving block was equipped with a sensor holder having a large number of ultrasonic probes.

[Problem to be solved by the invention]

The above conventional technology uses an ultrasonic flaw detection method in which a sensor holder having a large number of ultrasonic probes is pressed against the side surface of a grid plate using an air cylinder, and the sensor holder is moved horizontally by rotating a ball screw with a motor. The structure is such that it detects defects that occur in the grid, but since many ultrasonic probes are fixed vertically, the reach of the ultrasonic waves is limited, so defects may be overlooked. There was a problem with high gender. In addition, there are various methods of ultrasonic flaw detection, such as the edge peak echo method, aperture synthesis method, and holography method, each of which has its own characteristics. In this case, there was a problem that the shape of the crack could not be determined.

The purpose of the present invention is to scan the measurement head of PDM (direct current potential method) in the vertical and horizontal directions of the grid plate to measure the potential difference distribution on the side surface of the grid plate in order to detect cracks generated in the grid plate. The object of the present invention is to provide a grid plate inspection device that can determine the crack occurrence position and crack size by analyzing the measured potential difference distribution using a unique method.

[Means to solve the problem]

The above purpose is to provide a slide base that can be moved horizontally with a ball screw on a casing arranged on a grid plate so that it can be fixed to the grid plate, and a slide base that can be moved vertically with a ball screw on the horizontal slide base. An air cylinder that can be driven in a direction perpendicular to the surface of the grid plate is attached to the vertical slide base, a measuring head is attached to the shaft end of the air cylinder, and a measuring head is attached to the measuring head for detection using PDM (direct current potential method). This is achieved by arranging terminals that serve both as power supply terminals and measurement terminals in the vertical and horizontal directions so that the potential difference distribution in the vertical and horizontal directions on the side surface of the upper grid plate can be measured.

[Effect]

A positioning guide plate and a fixing air cylinder are arranged in two directions in the horizontal plane of the grid plate on the case placed on the grid plate so that the case can be fixed, and a ball screw is installed along with a bearing on the top of the case. The ball screw can be rotated by a drive motor, and a slide base is attached to a bearing that fits into the ball screw so that it can be moved horizontally. A long support plate is attached to the support plate, a ball screw is attached to the support plate along with a bearing, and it is rotated by a drive motor, and a slide base is attached to the bearing that fits on the ball screw to move it in the vertical direction. By attaching an air cylinder that can be driven in a direction perpendicular to the surface of the grid plate to the vertical slide base and attaching a measuring head to the shaft end of the air cylinder, the measuring head is pressed against the side of the grid plate. horizontal direction,
It can be moved freely in the vertical direction, and the upper grid can be moved freely by vertically and horizontally arranging terminals that serve as power supply terminals and measurement terminals for detection using PDM (Direct Current Potential Method). Vertical and horizontal directions of the sides of the board
Since the dimensional potential difference distribution can be measured, the position and shape of cracks generated in the grating plate can be determined with high accuracy.

〔Example〕

An embodiment of the present invention will be described below. Figure 1~
FIG. 3 shows an embodiment of the grid plate inspection device of the present invention, in which FIG. 1 is a plan view, FIG. 2 is a front view, and FIG. 3 is a right side view. In FIGS. 1 to 3, on the upper surface of a grid plate 75, a grid plate inspection apparatus main body 1, which is a frame with slightly larger mesh sizes than the grid, is placed. Also, in the figure, the horizontal direction is
axis, the vertical direction is the Y axis, the direction perpendicular to the plane of the paper, i.e.
The vertical direction of the grid plate is the Z axis. In order to fix the main body 1 to the grid plate 75, the main body 1 includes guide plates 51, 51' for fixing in the X-axis direction, air cylinders 52 for fixing in the X-axis direction, and guide plates 39, 3 for fixing in the Y-axis direction.
9' and an air cylinder 40 for fixing in the Y-axis direction. Although not shown in the figure, the grid plate inspection device is structured so that it is suspended from the tip of the fuel exchange device 83 (see FIG. 13) via a Z-axis rotation motor 81 (see FIG. 13). . Therefore, the approximate position of the grid plate inspection device is controlled by the fuel exchange device 83, but since accurate positioning is difficult, the X-axis fixing guide plates 51, 51' and the Y-axis fixing guide plate 3 , 39' are tapered on the sides that sandwich the lattice plate 75, so that when the lattice plate inspection device main body 1 is lowered into the lattice plate 75, the lattices in two directions are respectively fixed in the X-axis direction by the guide plates 51, 39'. 51'
and the Y-axis direction fixing guide plates 39, 39'. Then, with the main body 1 placed on the upper surface of the lattice plate 75, the X-axis fixing air cylinder 52 and the Y-axis fixing air cylinder 40 are driven to fix the main body 1 to the lattice plate 75. Details of the fixing method will be described later.

X so that it is parallel to the top surface of main body 1 in the X-axis direction.
Shaft guide 36, ball screw bearings 30, 31, and X
An axial ball screw 33 is arranged. An X-axis drive motor 2 is connected to one end of the ball screw via a universal joint 32, and the X-axis drive motor 2 is fixed to a member provided at the end of the main body 1. The X-axis slide stand 34 is attached to the X-axis slide bearing 37 that fits in the X-axis guide 36, and the ball screw bearing 35 that fits in the X-axis direction ball screw 33 is attached to the X-axis slide stand 34, and the X-axis drive By driving the motor 2, the X-axis slide table 34 can be reciprocated in the X-axis direction. An X-axis limit switch actuating member 38 is provided on the side surface of the X-axis slide base 34, and X-axis limit switches 4, 4' are attached to the main body 1, and the X-axis slide base 3 is operated by the X-axis drive motor 2.
4 is driven, the ball screw bearings 30, 31
Avoid collisions.

A Z-axis support plate 57 (FIG. 3) is attached to the X-axis slide table 34, which extends vertically, that is, in the vertical direction of the lattice plate 75 and toward the inside of the lattice plate 75.
A Z-axis guide 58 and a ball screw bearing 5 are mounted on the Z-axis support plate 57 so as to be parallel to the Z-axis.
3, 54 and a Z-axis direction ball screw 56 are arranged.
The Z-axis drive motor 5 is connected to one end of the ball screw 56 via a universal joint 55, and the Z-axis drive motor 5 is fixed to a member provided at the end of the Z-axis support plate 57. A Z-axis slide base 60 is attached to the Z-axis slide bearing 59 that fits into the Z-axis guide 58,
A Z-axis direction ball screw 56 is attached to the Z-axis slide table 60.
A ball screw bearing 61 is fitted to the Z-axis slide base 60, and the Z-axis slide table 60 can be reciprocated in the Z-axis direction by driving the Z-axis drive motor 5.
Z-axis limit switch operating plates 72, 72' are provided on the side surface of the Z-axis slide table 60, and Z-axis limit switches 7, 72' are provided on the Z-axis support plate 57.
7' is attached to prevent it from colliding with the ball screw bearings 53 and 54 when the Z-axis slide base 60 is driven by the Z-axis drive motor 5.

Figure 4 shows the structure around the measurement head. As mentioned above, the Z-axis guide 58 is attached to the Z-axis support plate 57, the Z-axis slide bearing 59 is fitted to the Z-axis guide 58, and the Z-axis slide bearing 59 is further fitted with the Z-axis slide bearing 59. A slide stand 60 is attached. A ball screw bearing 61 that fits into the Z-axis ball screw 56 (see FIG. 3) is attached to the Z-axis slide base 60, and the Z-axis drive motor 5
can be moved in the Z-axis direction by driving. A measuring head driving air cylinder 13 is attached to the surface of the Z-axis slide table 60 facing the grid plate 75, and a measuring head 71 made of a non-conducting material is attached to the shaft end of the air cylinder 13. However, since the measuring head 71 will rotate freely in this state, one measuring head guide rod 73 is provided at each end of the measuring head 71, and it is attached to a linear bearing (not shown) provided inside the Z-axis slide table 60. Let it fit. The measurement head 71 is provided with a number of terminals for measuring potential differences. In FIG. 4, a power supply terminal 16 and a measurement terminal 17 for measuring the horizontal potential difference are shown.

FIG. 5 shows an example of the arrangement of terminals in the measurement head 71. The three holes drilled in the center of the figure are for attaching the measuring head driving cylinder 13 to the shaft and for attaching the measuring head guide rod 73. The other circles indicate the arrangement of the terminals 16 and 17. When detecting a crack using the DC potential method, ideally it is better to supply current perpendicularly to the crack and measure the electrical difference distribution. Therefore, although the measuring head 71 may be rotatable, the rotary type has the disadvantage that it cannot actually measure the upper and lower ends of the grating plate 75 and the corners where the grating plate 75 intersects. Therefore, as shown in FIG. 5, dedicated terminals 16 and 17 are arranged for measuring the potential difference distribution in two directions, horizontal and vertical. That is, those arranged vertically at both left and right ends of the measurement head 71 are for measuring the vertical potential difference distribution, and those arranged horizontally at both the upper and lower ends are for measuring the horizontal potential difference distribution. Since the measuring head 71 can only move within the grid plate 75 in the horizontal direction, the measuring head 71
Terminals 16 and 17 are arranged on the left and right sides of 1. In the vertical direction, the measurement head 71 can be moved outside the grid plate 75 to measure the potential difference distribution around the upper and lower ends of the grid plate 75, but terminals are provided above and below to improve efficiency.

An example of the shape of the terminal is shown in FIG. The terminal has a two-stage cylindrical shape with a cone-shaped tip. A coil spring is placed behind the stepped portion at the tip to allow movement in the direction perpendicular to the surface of the upper grid plate 75, and by pressing a certain amount, the tension between the terminal and the grid plate 75 is increased. This prevents contact resistance from affecting the measured values.

Next, a method for measuring the potential difference distribution will be explained.
When measuring the vertical potential difference distribution, a current is supplied in the vertical direction from the terminals indicated by black circles in FIG. 7, and the potential difference V at four locations is measured using the five terminals in between. Since the terminals are arranged on the left and right,
Potential differences at 8 locations can be measured simultaneously. In this case, two DC power supplies 20 are prepared separately for left and right. When measuring the horizontal potential difference distribution, a current is supplied in the left and right direction from the terminals indicated by the black circles in FIG. 8, and the potential difference V at one location is measured using two terminals in the middle. Since the terminals are arranged on the left and right, and on the top and bottom, it is possible to measure potential differences at four locations at the same time. In this case as well, four DC power supplies 20 are separately prepared.

FIG. 9 shows another method of arranging terminals. Since terminals cannot be placed in the part of the measuring head 71 where the air cylinder 13 for driving the measuring head and the measuring head guide rod 73 (Fig. 4) are located, the terminals are placed at equal intervals both horizontally and vertically in the part other than that part. Arrange them in a matrix. In this case, it is better to provide the terminals at as fine intervals as possible, and at the same intervals in both the horizontal and vertical directions. When measuring the vertical potential difference distribution, a current is supplied in the vertical direction from the terminals indicated by black circles in FIG. 10, and the potential differences V at six locations are measured using the seven terminals in the middle. Since the terminals are arranged in six rows on each side, it is possible to measure potential differences at 36 locations at the same time. Since one DC power supply 20 must be prepared for one pair of power supply terminals, a total of 12 DC power supplies 20 are required with such a terminal arrangement. When measuring the horizontal potential difference distribution, current is supplied in the left and right direction from the terminals indicated by black circles in FIG. 11, and the potential differences V at three locations are measured using the four terminals in between. 9 rows up and down, 2 rows left and right
Since the locations and terminals are arranged, it is possible to measure potential differences at 54 locations simultaneously. In the case of such a terminal arrangement, a total of 18 DC power supplies 20 are required, but only four are shown in FIG. 11 to avoid complication.
FIG. 12 shows another method. By supplying current from the left and right terminals indicated by black circles, the 5 rows of terminals on the left create a potential difference V at 36 locations, the 5 rows of terminals on the right create a potential difference V at 36 locations, and a total of 72 potential differences V. Measure. In this case, nine DC power supplies 20 are required, but only two are shown in FIG. 12.

FIG. 13 shows a system diagram of the control, drive, and measurement system of the grid plate inspection device main body 1. 25 is a computer, 26 is a CRT for displaying measurement results and data processing results, and 27 is an external storage device such as a hard disk for storing data and programs. Computer 25 is interface 2
4 and the GP-IB interface 23, it controls various drive devices, solenoid valves, and computing equipment, takes in measured values, processes them, and outputs the results. The fuel exchange device 83 that moves the entire grid plate inspection device is equipped with a dedicated control device 84, but is also connected to a computer 25 that controls the grid plate inspection device main body 1 so that it functions as one device. As shown in FIG.
Since only one side can be inspected, once the inspection is completed, the grid plate 75 must be lifted upward, rotated 90 degrees at a time, lowered again, and inserted into the grid to inspect the other side. Therefore, the Z-axis rotation motor 81 for rotating the grid plate inspection apparatus main body 1 is supplied with power from the motor drive device 82, and a driving signal is outputted from the computer 25 via the interface 24. The X-axis drive motor 2 and the Z-axis drive motor 5 are supplied with power from motor drive devices 3 and 6, respectively, and driving signals are outputted from a computer 25 via an interface 24. For the X-axis and the Z-axis, limit switches are provided at both ends of the shafts to prevent each slide table from colliding with the bearing and breaking. The Y-direction fixing cylinder 9 and the X-direction fixing cylinder 11 for fixing the grating plate inspection device main body 1 to the grating plate 75 and the measuring head driving cylinder 13 are each provided with a solenoid valve 10,
The solenoid valves 10, 12, 14 are controlled by a computer 25 via an interface 24. The DC power from the plurality of DC power supplies 20 is connected to the computer 25.
A current polarity converter 19 controlled by the current polarity converter 19 switches the polarity of the current at regular intervals and supplies the current to the multiplexer 18, and further the current is distributed to the current supply destinations and the current is supplied to the power supply terminals 16, 16'. The potential difference between the plurality of measurement terminals 17, 17' is measured by switching the measurement terminal to be measured by a multiplexer 21 and connecting it to a minute potentiometer 22. The measured potential difference is transferred to the computer 25 via the GP-IB interface 23. The computer 25 determines the size of the crack from the potential difference distribution in the horizontal and vertical directions of the grid plate 75 using a method described later. Here, the multiplexers 18 and 21 and the minute potentiometer 22 are controlled by a computer 25 via a GP-IB interface 23 or 24.

Next, a method for inspecting the grid plate will be described. 1st
Figure 4 shows the flowchart of the inspection. When the inspection starts, in step (1), the fuel exchange device 83 is driven to position the grid plate inspection device main body 1;
In step (2), the grid plate inspection device main body 1 is lowered, and in step (3) it is inserted into the grid. At this time, the cylinder 9 for fixing in the Y direction and the cylinder 11 for fixing in the X direction are kept in a retracted state, and are lowered until the lower end surface of the grid plate inspection device main body 1 hits the upper end surface of the grid plate 75. Next, the inspection device main body 1 is fixed to the grid plate 75 by driving the Y-direction fixing cylinder 9 and the X-direction fixing cylinder 11. However, if this is done all at once, accurate positioning cannot be achieved.
Therefore, first, in step (4), the Y-direction fixing cylinder 9 is driven to temporarily place the lattice plate 75 between the shaft end of the Y-direction fixing cylinder 9 and the Y-axis fixing guide plate 39 (FIG. 1). Fix it. Next step (5)
to retract the Y-direction fixing cylinder 9. In step (6), the X-direction fixing cylinder 11 is driven to temporarily fix the lattice plate 75 between the shaft end of the X-direction fixing cylinder 11 and the X-axis fixing guide plate 51 (FIG. 2). Next, in step (7), the X-direction fixing cylinder 11 is retracted. Repeat steps (4) to (7) to move the grid plate 75 in the X direction.
Make sure to properly contact the guide plate 51 for fixing in the X-axis direction and the guide plate 39 for fixing in the Y-axis direction in both the Y direction. In step (8), the number of repetitions is counted. In step (9) and step (10), the Y-direction fixing cylinder 9 and the X-direction fixing cylinder 11 are finally driven to fix the inspection device body 1 to the grid plate 75. Measure the potential difference distribution in step (11). The details will be described later. In step (12), it is determined whether the measurement is complete. If the measurement has not been completed, in step (13), the Y-direction fixing cylinder 9 and the X-direction fixing cylinder 11 are retracted, and the fuel exchange device 83 is driven to raise the inspection device main body 1. . In step (14), it is determined whether or not the measurement of one grid has been completed, and if it has been completed, the fuel exchange device 83 moves to the next grid in step (15). If it has not been completed, it is rotated by 90 degrees by the Z-axis rotary motor 81 with the switch 16, and moved by the fuel exchange device 83 in step (17) to the next surface of the grid. This procedure is repeated until all the grid plates 75 have been inspected.

FIG. 15 shows an overall flowchart of defect shape detection by potential difference distribution measurement. Step (21)
Measurement range (x ₁ ~ x ₂ , z ₁ ~ z ₂ ) and measurement pitch △
Set x, △z. In step (22), move to the measurement start point (x ₁ , z ₁ ), and in step (23) measure the potential difference distribution. First, the potential difference distribution over the entire measurement range is measured at coarse pitches. The distribution of the potential difference ratio V/V ₀ is determined from the measured potential difference distribution by setting the potential difference near the measurement start point where there is no crack as the reference potential difference V ₀ . In step (24), the defect position is determined from the measured potential difference distribution. In step (25), the detailed potential difference distribution around the defect is measured. Detailed potential difference distribution means making the potential difference measurement pitch finer. Therefore, in the potential difference distribution measurement in step (23), the measurement pitch is made equal to the interval between the measurement terminals.
Next, in step (26), the potential difference distribution along the defect is determined from the potential difference distribution around the defect, and in step (27), the defect shape is determined by a simple surface crack shape determination method to be described later. Then, the shape of the defect determined in step (28) is output.

Next, the flowchart for measuring the potential difference distribution is shown in the first section.
It is shown in Figure 6. Here, a case will be described in which a vertical potential difference distribution is set. In step (31), the measurement range (x ₁ to x ₂ , z ₁ to z ₂ ) and measurement pitches △x, △z are set. At step (32), the measurement start point (x ₁ ,
Move to z ₁ ). In step (33), by controlling the multiplexer 18, a DC current is supplied to the vertical feed terminal 16 of the grid plate 75, and the grid plate 7
An electric field is created in the vertical direction of 5. Step (34)
Measure the potential difference distribution. Here, the potential difference between a large number of measurement terminals is measured, and the potential difference between vertically adjacent terminals is measured by switching the measurement terminals using the multiplexer 21. The measured potential difference is transferred to the computer 25 through the GP-IB interface 23 and processed as data.
The potential difference shall be evaluated by the amplitude of two measurements, one when the polarity of the current is switched and a positive current is caused to flow, and another when a negative current is caused to flow. Therefore, the number of measurements J is counted in step (35). When the potential difference distribution is measured by passing a + current, 1 is added to the number of measurements J in step (36), and the polarity of the DC current is changed to the current polarity converter 19 in step (37).
Switch by. And step again (34)
Measure the potential difference distribution when a negative current is passed through, calculate the potential difference amplitude, and assign coordinates to the potential difference measurement value in step (38). In step (39), it is determined whether the measurement range is exceeded.
In step (40), it is determined whether the coordinate in the vertical direction, that is, in the Z-axis direction, exceeds the measurement range. If not, in step (41), the Z-axis drive motor 5 is driven to move the inspection device main body. 1 in the Z-axis direction. This step (34) to step (40) are repeated, and when it is determined in step (40) that the coordinate in the Z-axis direction exceeds the measurement range, the X-axis drive motor 2 is driven in step (42) to The inspection device main body 1 is moved in the axial direction. Step (43)
Repeat step (49) from step (49).
When it is determined that the coordinate in the Z-axis direction exceeds the measurement range, in step (51), the X-axis drive motor 2 is driven to move the inspection apparatus main body 1 in the X-axis direction. After repeating this step (34) to step (51) to measure the potential difference distribution over the entire range, in step (52) the inspection device main body 1 is set at the measurement starting point (x ₁ , z ₁ ).
Then, in step (53), move to the origin (x ₀ , z ₀ ) and complete the measurement.

In the potential difference measurement described above, the reason for evaluating by the amplitude of two measurements, one when the polarity of the current is switched and a positive current is passed, and another when a negative current is passed, is as follows.
If there is some temperature distribution in the sample to be measured, a thermoelectromotive force will be generated between the measurement terminal and the sample to be measured, and this will be included as an average potential difference in the measured potential difference. Therefore, in order to measure the potential difference of the sample to be measured itself, the thermoelectromotive force must be removed by some method. One method is to subtract the potential difference measured when the current is turned off from the potential difference measured when the current is applied. Another method is to measure the amplitude of the potential difference by indirectly switching the polarity of the direct current. In the latter case, the insulation value of the potential difference to be measured is larger, so the measurement accuracy is improved accordingly. In addition, the method of cutting off the current has the disadvantage that it takes time for the current to stabilize after flowing, but the method of switching the polarity of the current has the advantage that the current stabilizes instantly. A device for switching the polarity of this current is a current polarity converter 19.

The horizontal potential difference distribution measurement is exactly the same as that shown in FIG. 16. The reason why current is passed in two directions, vertical and horizontal, is as follows. Now, if the crack is parallel to the vertical direction of the grid plate, even if a current is passed in the vertical direction, the electric field is in the vertical direction, so the electric field will not be disturbed by the crack, so it will not be measured. The potential difference distribution is exactly the same as when there is no crack,
It will be determined that there is no crack. However, when a current is passed horizontally through such vertical cracks in the grid plate 75, the horizontal electric field is greatly disturbed by the cracks, resulting in a potential difference distribution. The size of the crack can be determined from this. If the crack is in the lattice plate 75
In the case where the polarization occurs at an angle with respect to both the vertical and horizontal directions, it is possible to determine the shape including the inclination from the potential difference distribution measured by passing current from both directions.

FIG. 17 shows a schematic diagram of the distribution of the potential difference ratio V/V ₀ obtained by flowing a current in the horizontal direction and measuring the horizontal potential difference in the potential difference distribution measurement in step (23) of FIG. 15. In Figure 17, the side is the grid plate 7.
5, the horizontal direction and the vertical direction are taken as the vertical direction. Because the electric field is disturbed around the crack, the potential difference ratio increases. Areas where the potential difference ratio V/V ₀ is large extend long in the vertical direction. Therefore, by detecting the point where the potential difference ratio is the largest, for example, the potential difference ratio V/V ₀ is
It is determined that there is a crack where the value is greater than 1.02. Next, the potential difference distribution is measured at narrow pitches in both the axial and circumferential directions only around the crack. For example, the first
In Figure 5, the range of 〓〓〓〓〓 is all potential difference ratio V/
Since V ₀ is greater than 1.02, measure to include this area. However, since a reference potential difference V ₀ is required, a somewhat wider area than the range of 〓〓〓〓〓 is measured. FIG. 18 shows a schematic diagram of the potential difference distribution around the crack obtained by measuring the potential difference distribution in step (25) of FIG. 15. For vertical cracks,
It is determined that a crack exists where the maximum potential difference is found in the horizontal direction distribution of the measured potential difference distribution, and at the same time, the circumferential distribution of these maximum potential differences is determined to be the potential difference distribution along the crack. .
Using the potential difference distribution, the crack shape is determined by a simple surface crack shape determination method described later.

The method for determining the crack shape from the potential difference distribution along the crack is shown below. A flowchart of the surface crack shape determination method is shown in FIG. Various aspect ratios, e.g. a/c=1.0, are determined in advance by a general-purpose large-scale computer.
The electric field is analyzed for cracks of 0.5, 0.25, and 0.1, and the potential difference distribution on the surface in the direction perpendicular to the crack surface is stored in the storage device of the computer 25 or the external storage device 27. As an example of the potential difference distribution to be stored, the potential difference distribution for each crack depth with an aspect ratio a/c=0.5 is shown in FIG. Figure 19 is obtained by analyzing the electric field using FEM (effective element method) in the case where there is a crack in the center of a flat plate with a thickness of t = 20 mm. The depth a/t of the crack standardized by the plate thickness t is 0, 0.125, 0.25 at the deepest point at the center of the crack.
0.375, 0.5, 0.625 and 0.75. When there is no crack (a/t=0), the potential difference is proportional to the distance z from the crack. On the other hand, if there is a crack, the potential difference increases near the crack. These potential difference distributions are approximated to the nth order and stored in the computer 25. When determining the crack shape, the surface crack length is first determined from the measured potential difference distribution around the crack.
Find 2c* and the maximum potential difference ratio V/V _0nax . As an example, FIG. 21 shows the potential difference distribution around a crack introduced into the inner surface of a stainless steel 12B pipe due to fatigue. Where there are no cracks, the potential difference is almost constant, and when the average is calculated, the reference potential difference is V ₀
= 37.25μV is obtained. The potential difference is large where there is a crack, and the potential difference distribution in this area is approximated to the nth order. FIG. 21 shows a curve obtained as a result of fourth-order approximation. When the crack length 2c on the surface is determined from the intersection of this fourth-order approximate curve and the reference potential difference V ₀ , 2c = 22.5 mm is obtained. The maximum potential difference ratio V/V _0nax corresponding to the deepest point of the crack is determined from the approximate curve. In the case of Figure 21, V _nax
=38.0μV, so V/V _0nax =38.0/24.75=
1.535 was obtained. Next, in order to create the relationship between the potential difference ratio V/V ₀ and _the crack depth a/t for cracks with various aspect ratios a/c from the potential difference distribution shown in FIG. ratio a/
Create the relationship c. In this case, in the electric field analysis using FEM, a flat plate with a thickness t = 20 mm is analyzed, so the relationship between the potential difference ratio V/V ₀ and the aspect ratio a/c at the measurement position d* corresponding to the distance d between the measurement terminals is must be created. Therefore, d* = d corrected by the plate thickness t* of the member to be measured
The potential difference for each crack depth at the position x20/t* is determined, and the relationship between the potential difference ratio V/V ₀ and the aspect ratio a/c is created as shown in FIG. Potential difference ratio V/
The relationship between V ₀ and aspect ratio a/c is approximated to the nth order for each crack depth a/t and stored in the storage device 27 of the computer 25. Next, the potential difference ratio V/V ₀
Using the relationship between the aspect ratio a/c and the aspect ratio a/c, a master curve of the relationship between the potential difference ratio V/V ₀ and the crack depth a/t for the aspect ratio a/c=0.5 is created as shown in FIG. In this case as well, the relationship between the potential difference ratio V/V ₀ and the crack depth a/t is approximated to the nth order, for example, to the fifth order. The crack depth a* is determined by substituting the maximum potential difference ratio V/V _0nax obtained by fourth-order approximation of the potential difference distribution into this master curve. Next, the aspect ratio a*/c* of the crack is determined from the surface crack length 2c* (=2c×20/t) corrected for the plate thickness, and compared with the aspect ratio a/c of the master curve. If the two do not match, use the relationship between the potential difference ratio V/V ₀ and the aspect ratio a/c to determine the aspect ratio a/c.
A master curve of the relationship between the potential difference ratio V/V ₀ and the crack depth a/t for c=a*/c* is created, and the maximum potential difference ratio V/V _0nax is substituted to determine the crack depth a*. This operation is repeated until the two match, for example, until the difference between a/c and a*/c* is 0.01 or less. The shape of the entire crack is determined by substituting the potential difference ratio at each measurement position into a master curve of the relationship between the aspect ratio, the potential difference ratio V/V ₀ and the crack depth a/t when they match. In this case, the potential difference ratio at each measurement position may be substituted for the potential difference ratio, or an nth-order approximated potential difference ratio distribution may be substituted.

The results of specific calculations regarding the potential difference distribution around the fatigue crack shown in FIG. 21 will be shown. The plate thickness of the stainless steel pipe is t* = 15.8 mm, and the distance between the measurement terminals is d = 5 mm, so d* = d x 20/
Find the potential difference for each crack depth for each aspect ratio at the position of t*=5×20/15.8=6.3 mm. However, since the potential difference is measured with the crack located at the center of the measurement terminal, z=d*/2=
The potential difference at the position of 3.15 mm is determined, and the relationship between the potential difference ratio V/V ₀ and the aspect ratio a/c as shown in FIG. 22 is created. Using these relationships, a master curve of the relationship between the potential difference ratio V/V ₀ and the crack depth a/t for the aspect ratio a/c=0.5 is created as shown in FIG. This curve shows the maximum potential difference ratio V/
Substituting V _0nax =1.535 gives a*/t=0.2665, giving a*=5.31 mm. Surface crack length 2c
=22.5mm with plate thickness correction 2c*=22.5×20/15.8
= 28.48mm, and the aspect ratio of the crack is a*/
c*=5.31/14.28=0.37. Therefore, when we next created a master curve for a/c = 0.37 and determined the crack depth, a * = 4.97 mm was obtained, and a
*/c*=0.348. Once again, by creating a master curve for a/c=0.34 and finding the crack depth, a*=4.92mm is obtained, and a*/c*=
The aspect ratio was 0.344, and the aspect ratios were almost the same. These are the results of manual calculations, but when calculated using the computer 25, a master curve for a/c = 0.348 was created and a* = 4.94mm, a/
c=0.345 was obtained, and the aspect ratios were almost the same. FIG. 24 shows the correspondence between the surface crack shape determined in this way and the beach mark on the fracture surface after fracture. As can be seen in FIG. 21, because the potential difference measurement interval was coarse, the cracks were a little shallow near the crack tips on the surface, but apart from that, the results were in very good agreement. Therefore, if the potential difference distribution can be measured at a finer pitch, the accuracy will be even better.

However, the above-mentioned method can be applied when the crack is perpendicular to the electric field, and cannot be applied directly to a crack that is inclined. Second
Figure 5 shows a schematic diagram of the potential difference distribution measured around the tilted crack. In the figure, the position where the potential difference in the horizontal direction reaches the maximum value is shown in the potential difference distribution obtained when a current is passed in the horizontal direction.
In such a case, the angle with respect to the horizontal direction is determined by linearly approximating the coordinate point of the measurement position where the potential difference is maximum using the method of least squares, and the crack length 2c* is determined from the coordinates at both ends. At this time, if the angle between the normal direction of the crack and the direction of the electric field is Θ, the potential difference ratio V/V ₀ ' is smaller than the potential difference ratio V/V ₀ when the crack is perpendicular to the electric field. Therefore, in the first approximation, V/V ₀ '=V/V ₀ ° _cps 〓. Therefore,
When determining the crack shape using the above method, the measured potential difference ratio V/V ₀ ' is corrected by Θ and V/V ₀ = V/
V ₀ ′

Claims (1)

[Claims] 1. Direct current is applied to the surface of the member through at least one pair of power supply terminals spaced apart from each other, and at least one pair of potential difference measurement terminals is provided between the pair of power supply terminals to measure the potential difference. , in a grid plate inspection device for a nuclear reactor upper grid plate that detects defects from the potential difference,
A positioning plate and a fixing air cylinder are provided on the main body disposed on the upper surface of the lattice plate for fixing the main body in the X direction and the Y direction perpendicular to the lattice plate,
An X-axis linear slide guide and a ball screw bearing are attached to the top surface of the main body, a ball screw is fitted to the hall screw bearing, and an X-axis drive motor is connected to one end of the ball screw via a universal joint. an X-axis direction drive section is attached to the upper part of the bearing that fits into the X-axis direction linear slide guide, a support member extending in the Z-axis direction is provided on the drive section, and a support member extending in the Z-axis direction is provided on the support member. A linear slide guide and a ball screw bearing are attached, a ball screw is fitted to the ball screw shaft, a Z-axis driving motor is provided at one end of the ball screw via a universal joint, and the linear slide in the Z-axis direction is installed. There is a Z mark on the top of the bearing that fits into the guide.
An axial drive unit is attached, an air cylinder that can be driven in a direction perpendicular to the side surface of the grid plate is attached to the drive unit, and a number of electrodes are installed at the shaft end of the air cylinder for both supplying direct current and measuring potential difference. A measuring head made of a non-conductor is attached to the main body, a hanging member is provided on the upper part of the main body, and a Z-axis is connected to a member whose shaft end can be attached to the tip of the fuel exchange device. A grid plate inspection device characterized by having a configuration in which a rotation motor is attached. 2. Two X-axis direction limit switches are provided on the upper surface of the main body, a limit switch actuating member is provided on the side surface of the X-axis direction driving section, and two Z-axis direction limit switches are provided on the support member extending in the Z-axis direction. 2. The grid plate inspection device according to claim 1, further comprising a limit switch actuating member provided on a side surface of the Z-axis direction drive section. 3 A computer for control, a CRT for displaying measurement results and data processing results, an external storage device for recording data and programs, a drive device for driving the motor, a solenoid valve for driving the air cylinder, and a power supply. A DC power source for supplying current to the terminals, a current polarity converter, an interface for connecting to the computer, a micropotentiometer for measuring the potential difference distribution on the grid plate, a multiplexer, and a GP-IB. A grid plate inspection device according to claim 1 or 2, which is provided with an interface. 4. Claims 1, 2, or 3, wherein terminals for both current supply and potential difference measurement are arranged in two directions in the measurement head so that the potential difference distribution in the X-axis direction and the Y-axis direction can be measured. The grid plate inspection device described. 5. The grid plate inspection device according to claim 4, wherein the terminals arranged in the X-axis direction and the Y-axis direction are arranged on the outer periphery of the measurement head. 6. Direct the terminals placed on the measurement head in the X-axis direction,
The lattice plate inspection device according to claim 4, wherein the lattice plate inspection device is arranged in a matrix at equal intervals in both the Y-axis directions.