JP2014071102A - Board thickness inspection device and board thickness inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a board thickness inspection device and board thickness inspection method capable of efficiently inspecting the soundness of the board thickness of the whole surface of a tank.SOLUTION: The board thickness inspection device includes: a neutron source 2 for emitting fast neutrons: a neutron detector 4 for detecting thermal neutrons; counting means 9 that counts the thermal neutrons detected by the neutron detector 4 and calculates the counting rate per unit time; and determining means 10 for determining whether an inspecting object 20 is in a thin state on the basis of the counting rate of the counting means 9. The board thickness inspection method includes a step of emitting fast neutrons from the neutron source 2, detecting thermal neutrons with the neutron detector 4, counting the thermal neutrons detected by the neutron detector 4, and calculating the counting rate per unit time, and a step of determining the thin state of the inspecting object 20 on the basis of the counting rate.

Description

  The present invention relates to a plate thickness inspection device and a plate thickness inspection method, and more particularly to a plate thickness inspection device and a plate thickness inspection method that are inspected by irradiating neutrons.

  Tanks, towers, large-diameter pipes, etc. (hereinafter collectively referred to as “tanks”) installed in petrochemical plants and power plants, etc., are affected by the environment in use and over time. Deterioration progresses with corrosion and erosion, and the thickness of the tank may be reduced. For this reason, it is an important concern to assess the soundness of the tank by grasping the thickness of the tank in the maintenance management of the tank.

  Conventionally, as a tank inspection widely used, an ultrasonic testing (hereinafter referred to as “UT”) and an eddy current testing (hereinafter referred to as “ECT”) are known. ing. For example, in a state where the equipment in the plant is stopped and the tank is emptied, visual inspection and plate thickness inspection by UT are performed from the inside of the tank. In addition, when the contents are present in the tank and the internal inspection cannot be performed because the plant is in operation or the like, the inspection is performed from the outside by UT or ECT.

  By the way, Patent Documents 1 to 3 disclose a moisture measuring device (moisture detecting device) that detects the presence position of moisture in the heat insulating material arranged on the outer periphery of the tank.

Japanese Patent No. 4763632 JP 2011-27559 A JP 2008-180700 A

  When the contents exist in the tank and inspection is performed from the outside, the conventional UT and ECT have a narrow inspection area (spot), and it takes a long time to inspect a tank with a large surface area, resulting in an increase in inspection cost. To do. In addition, since the inspection area is set with a predetermined interval, it is difficult to inspect the soundness of the plate thickness over the entire surface of the tank. Although it is conceivable to increase the inspection area by using a scan type UT, it is necessary to secure a medium (in many cases, water) area every time an apparatus becomes large, and an unspecified number of inspection objects. It cannot be applied efficiently to conditions such as inspection location and inspection posture.

  Then, this invention makes it a subject to provide the plate | board thickness inspection apparatus and plate | board thickness inspection method which can test | inspect the soundness of plate | board thickness efficiently over the whole surface of a tank.

  In order to solve such a problem, the present invention counts the neutron source that emits fast neutrons, the neutron detector that detects thermal neutrons, and the thermal neutrons detected by the neutron detector, per unit time. A plate thickness inspection apparatus comprising: a counting unit that calculates a count rate of: and a determination unit that determines whether the inspection target is in a thinned state based on the count rate of the counting unit. is there.

  Also, the present invention radiates fast neutrons from a neutron source, detects thermal neutrons with a neutron detector, counts thermal neutrons detected with the neutron detector, and calculates a count rate per unit time And a step of determining a thinning state of the inspection object based on the counting rate.

  ADVANTAGE OF THE INVENTION According to this invention, the plate | board thickness inspection apparatus and plate | board thickness inspection method which can test | inspect the soundness of plate | board thickness efficiently over the whole surface of a tank can be provided.

It is a structure schematic diagram explaining the plate | board thickness test | inspection apparatus which concerns on this embodiment, the tank wall surface which is a test object, and the tank contents. It is a graph which shows the relationship between the plate | board thickness of a tank wall surface, and the count rate in a neutron detector. It is a schematic diagram explaining the management thinning area ratio and the minimum management plate thickness, (a) is a diagram of the tank wall surface viewed in the normal direction, and (b) is a diagram of the tank wall surface viewed in the cross-sectional direction. . It is a graph explaining derivation | leading-out of the reference value of a count rate, a horizontal axis is the plate | board thickness of a tank wall surface, and a vertical axis | shaft is the count rate in a neutron detector. (A) is a conceptual diagram of the test | inspection using the conventional ultrasonic thickness meter, (b) is a conceptual diagram of the test | inspection using the plate | board thickness inspection apparatus which concerns on this embodiment, (c) is this implementation. It is a conceptual diagram of the test | inspection using the plate | board thickness inspection apparatus and ultrasonic thickness meter which concern on a form.

  Hereinafter, modes for carrying out the present invention (hereinafter referred to as “embodiments”) will be described in detail with reference to the drawings as appropriate. In each figure, common portions are denoted by the same reference numerals, and redundant description is omitted.

≪Thickness inspection device≫
A plate thickness inspection apparatus 1 according to the present embodiment will be described with reference to FIG. FIG. 1 is a schematic configuration diagram illustrating a plate thickness inspection apparatus 1, a tank wall surface 20 and a tank content 30 that are inspection targets according to the present embodiment.

  As shown in FIG. 1, the thickness inspection apparatus 1 includes a measuring unit 6 containing a neutron source 2, a moderator 3, neutron detectors 4A and 4B, and shielding bodies 5A, 5B and 5C, amplifiers 7A and 7B, A high-voltage power supply 8, a counter 9, a thickness determination unit 10, a storage unit 11, an input unit 12, and an output unit 13 are provided. And the plate | board thickness test | inspection apparatus 1 arrange | positions the measurement part 6 in the tank wall surface 20 which is a test object from the outer side of a tank in the state which has the tank contents 30 inside a tank, and plate | board thickness in the plate | board thickness measurement range 21 The thinned state (thinned portion 22) can be inspected.

The neutron source 2 is a radiation source that emits fast neutrons. For example, a ²⁵² Cf neutron standard sealed radiation source can be used. Incidentally, as the neutron source 2, it is desirable to use a sealed neutron radiation source having a predetermined quantity or less (for example, 3.7 MBq or less) determined by laws and regulations. As a result, for the plate thickness inspection apparatus 1, for example, the inspection operator can use the plate thickness inspection apparatus 1 by receiving design certification as an authentication device with a display (see the Law Concerning Prevention of Radiation Hazards due to Radioisotopes, etc.). When inspecting, it is not necessary to obtain approval every time it is used.

  The moderator 3 is disposed so as to cover the neutron source 2, and attenuates the energy of fast neutrons emitted from the neutron source 2. Here, the neutron source 2 radiates fast neutrons in all directions, but the shield 5C shields the radiation backward (in the direction opposite to the direction of the tank wall surface 20 as viewed from the neutron source 2). It has become so. That is, the neutron source 2, the moderator 3 and the shielding body 5C irradiate the attenuated neutrons toward the tank wall surface 20.

The neutron detectors 4A and 4B are detectors that detect thermal neutrons. For example, a BF ₃ proportional counter that measures α rays and lithium generated in a ¹⁰ B (n, α) ⁷ Li reaction, ³ He A ³ He proportional counter that measures protons and tritium generated in the (n, p) ³ H reaction can be used. Here, the neutron detectors 4 </ b> A and 4 </ b> B detect thermal neutrons scattered from the plate thickness measurement range 21 of the tank wall surface 20. For this reason, as shown in FIG. 1, shields 5 </ b> A, 5 </ b> B are arranged to reduce neutrons (noise) from other than the plate thickness measurement range 21. In particular, the shielding bodies 5A, 5B, and 5C are arranged so as to sufficiently reduce neutrons (noise) that reach the neutron detectors 4A and 4B directly from the neutron source 2.

  The measurement unit 6 includes a neutron source 2, a moderator 3, neutron detectors 4A and 4B, and shielding bodies 5A, 5B, and 5C, and is arranged in a plate thickness measurement range 21 of the tank wall surface 20 at the time of inspection. Yes.

In the example of FIG. 1, the measurement unit 6 has been described as having one neutron source 2 and two neutron detectors 4A and 4B, but is not limited thereto.
For example, the number of neutron sources included in the measurement unit 6 may be two or more. Thereby, the plate | board thickness measurement range 21 which can be measured by one test | inspection can be expanded, and the frequency | count of a test | inspection required in order to test | inspect the whole range of the tank wall surface 20 can be reduced.
Further, the number of neutron detectors included in the measurement unit 6 may be one, or may be three or more. By setting the number of neutron detectors to one, the plate thickness inspection apparatus 1 can be simply configured and made inexpensive. In addition, by setting the number of neutron detectors to three or more, the plate thickness measurement range 21 that can be measured in one inspection is widened, and the number of inspections required to inspect the entire range of the tank wall surface 20 is reduced. can do.

  Moreover, the measurement part 6 may have a neutron detector position moving mechanism (not shown) that adjusts the interval between the neutron detectors 4A and 4B. By widening the distance between the neutron detectors 4A and 4B, the plate thickness measurement range 21 that can be measured in one inspection is widened, and the number of inspections required to inspect the entire range of the tank wall surface 20 is reduced. Can do.

  The amplifier 7A can boost the voltage of the high-voltage power supply 8 to the voltage applied to the neutron detector 4A and apply the boosted voltage to the neutron detector 4A so that the neutron detector 4A can function. Further, the detection signal detected by the neutron detector 4A is amplified and output to the counter 9. Similarly, the amplifier 7B can boost the voltage of the high-voltage power supply 8 to the voltage applied to the neutron detector 4B and apply the boosted voltage to the neutron detector 4B so that the neutron detector 4B can function. ing. In addition, the detection signal detected by the neutron detector 4B is amplified and output to the counter 9.

  The counter 9 is, for example, a multi-channel analyzer (hereinafter referred to as “MCA”), which detects neutron detection signals detected by the neutron detectors 4A and 4B and amplified by the amplifiers 7A and 7B. , It can be counted for each channel (peak value). Although the counter 9 has been described as using the MCA, it is not limited to this, and may be a simple scaler that does not require a spectrum (wave height distribution), for example.

  The thickness determination unit 10 reduces the plate thickness in the plate thickness measurement range 21 based on the measurement result of the counter 9, the information stored in the storage unit 11, the measurement conditions input via the input unit 12, and the like. The state can be determined. In addition, the detail of the determination method of the thickness reduction state of the plate thickness by the thickness determination part 10 is mentioned later.

The storage unit 11 stores information used when the thickness determination unit 10 determines the thickness reduction state of the plate thickness. Details of the information stored in the storage unit 11 will be described later.
The input unit 12 is operated by an inspection operator to set measurement conditions (for example, an original thickness t ₀ of a tank wall surface 20, which will be described later with reference to FIG. 3, a management thinning area ratio Sr, and a management minimum plate thickness t ₁ ). The thickness can be input to the thickness determination unit 10.

  The output unit 13 can output the determination result of the thickness determination unit 10. For example, when the output unit 13 is a display screen, the determination result of the thickness determination unit 10 can be displayed on the display screen to notify the inspection operator. Further, the output unit 13 may be configured to output the measurement result of the counter 9 together with the determination result of the thickness determination unit 10.

≪Detection principle≫
Next, the detection principle of the thickness reduction state of the plate thickness by the plate thickness inspection apparatus 1 will be described.

  Fast neutrons are irradiated from the neutron source 2 of the measurement unit 6 arranged outside the tank (indicated by solid arrows in FIG. 1). Since neutrons lose energy rapidly due to elastic scattering with light elements, particularly hydrogen element (H), the irradiated fast neutrons pass through the metal tank wall surface 20 and the tank contents 30 (for example, Energy is lost due to elastic scattering with water, hydrogen oil and other hydrogen atoms), and thermal neutronization occurs. Among the thermal neutrons that have lost their energy due to this elastic scattering, neutrons (backscattered rays) scattered backward (opposite to the irradiation direction of fast neutrons) are detected by the measuring unit 6 arranged outside the tank. This is detected by the devices 4A and 4B (indicated by broken line arrows in FIG. 1).

  Here, by covering the neutron source 2 with the moderator 3, the energy of the fast neutrons emitted from the neutron source 2 is attenuated in advance to an energy that can be efficiently converted into thermal neutrons by elastic scattering, whereby the neutron detector 4A. , 4B, the signal detected is increased.

The detection signals of neutrons detected by the neutron detectors 4A and 4B are amplified by the amplifiers 7A and 7B and input to the counter 9. When the neutron detectors 4A and 4B are BF ₃ proportional counters, the counter 9 composed of MCA or the like has a channel range indicating a nuclear reaction between ¹⁰ B and thermal neutrons, and the neutron detectors 4A and 4B are ³ He proportional. In the case of a counter tube, the channel range indicating the nuclear reaction between ³ He and thermal neutrons is defined as a region of interest (hereinafter referred to as “ROI”). A count rate (cps: count per second) is output to the thickness determination unit 10.

  Here, the relationship between the plate | board thickness of the tank wall surface 20 and the count rate of neutron detector 4A, 4B (counter 9) is demonstrated using FIG. FIG. 2 is a graph showing the relationship between the thickness (mm) of the tank wall surface 20 and the counting rate (cps) in the neutron detectors 4A and 4B.

  As shown in the graph of FIG. 2, the counting rate of the neutron detectors 4A and 4B (counter 9) increases as the plate thickness of the tank wall surface 20 (in other words, the distance between the measurement unit 6 and the tank contents 30) increases. A smaller relationship is obtained. That is, when the thickness of the tank wall surface 20 is reduced and the thickness of the tank wall surface 20 is reduced, the relationship between the counting rates of the neutron detectors 4A and 4B (counter 9) is obtained.

  The thickness determination unit 10 can determine the thickness reduction state of the plate thickness in the plate thickness measurement range 21 using this relationship. That is, when the count rate of the neutron detectors 4A and 4B (counter 9) is equal to or greater than a predetermined reference value C, the thickness determination unit 10 determines that the thinning of the plate thickness measurement range 21 is equal to or greater than the reference, and performs counting. When the rate is less than the predetermined reference value C, it is determined that the thickness reduction in the plate thickness measurement range 21 is less than the reference.

<Standard value of count rate>
Here, the management thinning area ratio Sr and the management minimum plate thickness t ₁ used when obtaining the reference value C of the count rate will be described with reference to FIG. FIG. 3 is a schematic diagram for explaining the management thinning area ratio Sr and the management minimum plate thickness t ₁ , (a) is a view of the tank wall surface 20 viewed in the normal direction, and (b) is the tank wall surface 20. It is the figure which looked at the cross-sectional direction.

As shown in FIG. 3A, the area of the measurement region is S ₀ , the area of the thinning region is S _1, and as shown in FIG. 3B, all the thinnings are reduced in the thinning region (S ₁ ). The measurement region (S ₀ ) other than the thinning region (S ₁ ) is simulated as not thinning at all. The thinning area ratio (management thinning area ratio) Sr is defined by the following formula (1).
Sr = S ₁ / S ₀ (1)

Further, as shown in FIG. 3 (b), the thickness of the tank wall 20 thickness reduction does not occur as Motoatsu t _0, the thickness of the plate thickness of the tank wall 20 is minimized, i.e., reduced thickness area The thickness of the tank wall surface 20 is defined as the minimum thickness (minimum management thickness) t ₁ .

The management thinning area ratio Sr and manage the minimum thickness t ₁ is the value set by the management standards set in advance.

  Next, derivation of the reference value C of the count rate will be described with reference to FIG. FIG. 4 is a graph for explaining the derivation of the reference value C of the count rate, the horizontal axis is the thickness (mm) of the tank wall surface 20, and the vertical axis is the count rate (cps) in the neutron detectors 4A and 4B. is there.

The thickness determination unit 10 includes the relationship between the plate thickness and the counting rate (see FIG. 2), the original thickness t ₀ of the tank wall surface 20 (see FIG. 3), the management thinning area rate Sr (see FIG. 3), and the minimum management plate. Based on the thickness t ₁ (see FIG. 3), a reference value C of the count rate is derived. Note that the relationship between the plate thickness and the counting rate (see FIG. 2) is obtained by experiments or the like, and is stored in the storage unit 11 (see FIG. 1) in advance. In addition, the original thickness t ₀ (see FIG. 3), the management thinning area ratio Sr (see FIG. 3), and the minimum management plate thickness t ₁ (see FIG. 3) of the tank wall surface 20 are input from the input unit 12 (see FIG. 1). The inspection operator inputs the information. Further, the combination of the original thickness t ₀ , the management thinning area ratio Sr, and the minimum management plate thickness t ₁ and the tank type are associated with each other and stored in advance in the storage unit 11 (see FIG. 1). By selecting the type of tank, the original thickness t ₀ , the management thinning area ratio Sr, and the management minimum plate thickness t ₁ may be read from the storage unit 11 (see FIG. 1).

  First, the thickness determination unit 10 reads a graph indicating the relationship between the plate thickness and the count rate (see FIG. 2) stored in the storage unit 11 (see FIG. 1). The graph showing the relationship between the plate thickness and the counting rate (see FIG. 2) corresponds to the graph (Sr = 1.00) shown by the thick solid line in FIG.

Next, the thickness determination unit 10 sets a point A in FIG. 4 based on the original thickness t ₀ of the tank wall surface 20 (t ₀ = 10 [mm] in the example of FIG. 4).

  Next, the thickness determination unit 10 determines the relationship between the plate thickness and the count rate in consideration of the management thinning area ratio Sr from the point A (in FIG. 4, Sr = 0.50, 0.20, 0.10, 0.05 and 0.02 are shown as an alternate long and short dash line.) Is read from the storage unit 11 (see FIG. 1). Here, the formula of the count rate in consideration of the management thinning area ratio Sr from the point A indicated by the alternate long and short dash line is obtained in advance by an experiment or the like and stored in the storage unit 11 (see FIG. 1) as an experimental formula.

Next, the thickness determination unit 10 determines the management thinning area ratio Sr (Sr = 0.02 in the example of FIG. 4) and the minimum management plate thickness t ₁ (t ₁ = 2 [mm] in the example of FIG. 4). 4), the point B in FIG. 4 is set. Then, the count rate C at point B is derived as a reference value C for the count rate.

In this way, the thickness determination unit 10 sets the reference value C of the count rate based on the original thickness t ₀ , the management thinning area rate Sr, and the management minimum plate thickness t ₁ , and the neutron detectors 4A and 4B (counter When the counting rate of 9) is equal to or greater than the predetermined reference value C, it is determined that the thinning of the plate thickness measurement range 21 is equal to or greater than the reference, and when the count rate is less than the predetermined reference value C, It is determined that the thinning is less than the standard.

≪Action ・ Effect≫
Next, operations and effects of the plate thickness inspection apparatus 1 according to the present embodiment will be described with reference to FIG. 5A is a conceptual diagram of an inspection using a conventional ultrasonic thickness meter, FIG. 5B is a conceptual diagram of an inspection using a plate thickness inspection apparatus 1 according to the present embodiment, c) is a conceptual diagram of the inspection using the plate thickness inspection apparatus 1 and the ultrasonic thickness meter according to the present embodiment. It should be noted that the inspection objects include a thinning part CW1 and a thinning part CW2.

As shown in FIG. 5A, in the inspection using the conventional ultrasonic thickness gauge (UT), the inspection region P is narrow and the inspection is performed at a predetermined interval. For this reason, as shown in the example of FIG. 5A, the thinning portion CW1 overlapping the inspection region P can be detected, whereas the thinning portion CW2 between the inspection regions P can be detected. could not.
Therefore, in order to improve the reliability of the inspection, it is necessary to narrow the interval between the inspection regions P, and it takes a long time to inspect a tank having a large surface area, resulting in an increase in inspection cost.

On the other hand, as shown in FIG. 5B, in the inspection using the plate thickness inspection apparatus 1 according to the present embodiment, the inspection is performed in the inspection region F having a large width (the plate thickness measurement range 21 in FIG. 1). It is supposed to be. For this reason, as shown in the example of FIG. 5B, it is possible to continuously inspect without a gap between the inspection regions, and to detect the thinning portion CW1 and the thinning portion CW2 without overlooking.
Therefore, compared with the conventional inspection method (see FIG. 5 (a)), the oversight of the thinned portion is reduced, and the reliability of the inspection is improved. The time can be shortened and the inspection cost can be reduced.

Further, as shown in FIG. 5C, for example, the inspection regions P1 and C2 in which the thinned portions CW1 and CW2 are detected by the inspection using the plate thickness inspection apparatus 1 according to the present embodiment are indicated by the inspection region P. A detailed inspection using an ultrasonic thickness meter (UT) may be performed.
As described above, since the inspection using the ultrasonic thickness meter (UT) is performed on the limited inspection regions F1 and F2, the inspection time is shortened as compared with the conventional inspection method (see FIG. 5A). The inspection cost can also be reduced. Moreover, since the inspection can be performed in more detail as compared with the inspection using only the plate thickness inspection apparatus 1 according to the present embodiment (see FIG. 5B), the reliability of the inspection is improved.

  In the inspection using the plate thickness inspection apparatus 1 and the ultrasonic thickness meter (UT) according to the present embodiment shown in FIG. 5C, the inspection regions F1 and F2 are limited, so that a conventional inspection method is used. You may narrow the space | interval of the test | inspection area | region P rather than (refer Fig.5 (a)). This improves the reliability of the inspection.

≪Modification≫
In addition, the inspection method using the plate thickness inspection apparatus 1 and the plate thickness inspection apparatus 1 according to the present embodiment is not limited to the configuration of the above embodiment, and various modifications can be made without departing from the spirit of the invention. Is possible.

The reference value C of the count rate has been described as being obtained based on the original thickness t ₀ , the management thinning area rate Sr, and the minimum management plate thickness t ₁ , but is not limited to this, and is, for example, a constant value. Also good.

  Moreover, in the example shown in FIG.5 (c), the ultrasonic thickness meter (UT) was used about the test | inspection area | regions F1 and F2 with which it was determined with the thickness inspection apparatus 1 which concerns on this embodiment that there exists a thinning part. Although described as performing inspection, the present invention is not limited to this. For example, an inspection by ECT may be performed.

  Moreover, in the structure which combines the inspection using the plate | board thickness inspection apparatus 1 and ultrasonic thickness meter which concern on this embodiment shown in FIG.5 (c), the plate | board thickness inspection apparatus 1 used the ultrasonic thickness meter. An inspection interval calculation unit (not shown) for calculating an inspection interval at the time of inspection is provided, and the output unit 13 has an inspection interval obtained by the inspection interval calculation unit (not shown) together with the determination result of the thickness determination unit 10. May be configured to output.

The inspection interval calculation unit (not shown), for example, increases the count rate of the neutron detectors 4A and 4B (counter 9) (or the count rate and count rate of the neutron detectors 4A and 4B (counter 9)). The larger the difference from the value C), the larger the inspection interval. When the count rate (or the difference between the count rate and the reference value C) is large, it is considered that the area S ₁ of the thinning region (see FIG. 3) is also large. For this reason, even if the inspection interval is increased, the positions of the thinned portions CW1 and CW2 (see FIG. 5) can be suitably specified, so that the inspection time can be shortened and the inspection cost can be reduced.

DESCRIPTION OF SYMBOLS 1 Plate | board thickness inspection apparatus 2 Neutron source 3 Moderator 4A, 4B Neutron detector 5A, 5B, 5C Shielding body 6 Measuring part 7A, 7B Amplifier 8 High voltage power supply 9 Counter (counting means)
DESCRIPTION OF SYMBOLS 10 Thickness determination part 11 Memory | storage part 12 Input part 13 Output part 20 Tank wall surface (inspection object)
21 Thickness measurement range 22 Thinning part 30 Tank contents C Reference value t ₀ Original thickness t ₁ Control minimum thickness Sr Control thinning area ratio P, F, F1, F2 Inspection area CW1, CW2 Thinning part S ₀ measurement the area of the area S ₁ thinning area of the region

Claims (10)

A neutron source emitting fast neutrons;
A neutron detector for detecting thermal neutrons;
Counting means for counting thermal neutrons detected by the neutron detector, and calculating a count rate per unit time;
A plate thickness inspection apparatus comprising: a determination unit that determines whether or not the inspection target is in a thinned state based on a count rate of the counting unit. The determination means includes
The plate thickness inspection apparatus according to claim 1, wherein when the counting rate of the counting unit is equal to or greater than a reference value, it is determined that the thickness is reduced. The reference value is
Control minimum plate thickness that is the minimum plate thickness of the inspection object set by the management standard,
The plate thickness inspection apparatus according to claim 2, wherein the plate thickness inspection apparatus is set based on a management thinning area ratio that is a ratio of the area of the thinning area to the area of the measurement area set according to the management standard. The inspection interval calculating means for calculating the inspection interval of the ultrasonic flaw detection inspection or the eddy current flaw inspection based on the count rate of the counting means is further provided. Plate thickness inspection equipment. The inspection interval calculation means includes
The plate thickness inspection apparatus according to claim 4, wherein the inspection interval increases as the counting rate of the counting unit increases. The plate thickness inspection apparatus according to claim 1, wherein a plurality of the neutron sources are arranged. The plate thickness inspection apparatus according to claim 1, wherein a plurality of the neutron detectors are arranged. The plate | board thickness inspection apparatus of Claim 7 provided with the moving means to change the space | interval of the said several neutron detector arrange | positioned. Radiating fast neutrons from a neutron source, detecting thermal neutrons with a neutron detector, counting the thermal neutrons detected with the neutron detector, and calculating a count rate per unit time;
And a step of determining a thinning state of an inspection object based on the counting rate. The step of determining the thinning state further comprises the step of performing an ultrasonic inspection or an eddy current inspection for the inspection region to be inspected determined to be a thinning state. The plate thickness inspection method described.

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