JP5414559B2 - Ultrasonic inspection method - Google Patents

Description

  The present invention relates to an ultrasonic inspection method capable of quantitatively evaluating the thinning state of an inspection object such as a bar or a flat plate caused by corrosion or the like by non-destructive ultrasonic waves.

  Anchor bolts used in plants such as nuclear power plants are used by embedding them in concrete. However, since these buried objects cannot be visually confirmed on the appearance, , Hammering sound, ultrasonic flaw detection and the like are used.

  The former is intended to detect, for example, breakage or looseness of the anchor bolt. On the other hand, the latter is intended to detect a crack generated in a threaded portion or a stem portion of an anchor bolt by observing a wound echo from the crack.

  However, these techniques are difficult to detect because, in many cases, a marked flaw echo does not return from a thinned portion (diameter-decreasing portion) caused by corrosion or the like. Furthermore, it is difficult to quantify the progress of corrosion.

  Therefore, for example, ultrasonic waves are incident from the top end face of the anchor bolt exposed on the concrete surface, and the bottom echo reflected at the other end and the subsequent delayed echo after mode conversion are measured at the top end face, and the amplitude of the delayed echo is measured. It has been proposed to obtain the amount of thinning from the attenuation state of the sound and the relative attenuation state of the amplitude with respect to the bottom echo (Patent Document 1).

  In addition, an ultrasonic wave is incident from one end of a plate-shaped inspection object, and a direct reflected wave that is a longitudinal wave and a delayed echo that is reflected by a thinned portion and mode-converted to a transverse wave are measured, and the difference in beam path is measured. There has also been a proposal for reducing the thickness of the plate (Patent Document 2).

JP 2001-305112 A JP 2002-202116 A

  However, in recent years, evaluation of aging deterioration of buried objects at nuclear power plants and the like has become more important, and it is strongly desired to improve the accuracy and reliability of inspection more than before.

As a result of earnest research to solve the above-mentioned problems, the present inventors have found that the waveform of delayed echo changes depending on the position and length of the thinned portion and other corrosion conditions, and to complete the present invention. It came. Hereinafter, first to fourth techniques related to the present invention will be described.

The first technique related to the present invention is:
Ultrasound that injects ultrasonic waves into the inspection object from the exposed end surface of the inspection object that is partly exposed and embedded, and inspects the thinned part by delayed echo from the thinned part of the inspection object An inspection method,
Injecting ultrasonic waves into the test sample having the thinned portion to obtain a delayed echo,
An index relating to the thinning situation created by a predetermined procedure from the characteristics of the delayed echo, and a database together with the actual thinning situation of the thinning portion of the test sample,
An ultrasonic wave characterized by estimating a thinning state of the inspection object by acquiring a delayed echo from the inspection object and comparing the database with an index obtained by the same procedure as the predetermined procedure Inspection method.

This 1st technique is a technique which estimates the thinning condition of a thinning part using the delay echo in which the thinning condition of the said test target object is reflected.

  Specifically, for many test samples for which the actual thinning situation is known, an index using delayed echo is obtained in a predetermined procedure, and the relationship between the index and the actual thinning situation of the test sample is obtained. When a database is prepared in advance and an inspection object is inspected, an index of the inspection object is obtained by a predetermined procedure, and the thinning state of the inspection object is estimated by collating with the database. is there.

Here, “delayed echo” includes an echo that appears accompanying the delayed echo. In addition, as an element indicating the thinning state of the thinned portion, there are a cross-sectional dimension, a position, a length, a shape, a surface state, etc. of the thinned portion, and an index is basically created for each of these elements. And in this 1st technique , all the data are made into a database in consideration of mutual influence between each index about the relation between these indices and the actual thinning situation, and inspection object The index obtained from the above is comprehensively determined using a database in consideration of the mutual influence described above. For this reason, highly accurate inspection accuracy can be obtained.

The second technique related to the present invention is:
The ultrasonic wave is incident on the inspection sample having the thinned portion to acquire the waveform of the time delay and the delayed echo,
A first index relating to a cross-sectional dimension of the thinned portion obtained by the time delay;
A second index relating to the length of the thinned portion obtained by quantifying the characteristic of the waveform of the delayed echo;
A third index relating to the position of the thinned portion obtained by quantifying the waveform characteristics of the delayed echo,
Create a database with the actual cross-sectional dimensions, lengths and positions of the thinned portions of the test sample,
By comparing the database with the first to third indexes obtained by acquiring time delay and delayed echo waveforms from the inspection object, the thickness reduction state of the inspection object is estimated. The ultrasonic inspection method according to the first technique .

The second technique is a technique for estimating the cross-sectional dimension, length, and position of the thinned portion using the time delay and waveform of the delayed echo that reflects the thinning state of the inspection object. Among the elements indicating the thinning situation, the cross-sectional dimensions, position, and length of the thinning part are important elements for judging the thinning situation, and these appear clearly in the delayed echo. In the second technique , the thinning state of the inspection object is estimated by focusing on these.

  Specifically, for many test samples for which the actual thinning situation is known, the first to third indicators using delayed echoes are acquired in a predetermined procedure, and these indicators and the actual thinning situation When the inspection object is inspected, the first to third indices of the inspection object are obtained in a predetermined procedure and checked against the above database when the inspection object is inspected. This is to estimate the thickness reduction of the object.

And also in this 2nd technique , about each 1st-3rd parameter | index as above-mentioned, and the cross-sectional dimension, length, and position of an actual thinning part mutually influence between each parameter | index. In consideration of this, all the data is made into a database, and the first to third indexes obtained from the inspection object are considered comprehensively using the database in consideration of the mutual influence described above. Judgment is made. For this reason, a highly accurate inspection result can be obtained.

The third technique related to the present invention is:
In addition to the database, a fourth index indicating whether or not the thinned portion is uniformly formed, the ultrasonic wave is incident from a plurality of places on the incident surface, and obtained by the sound pressure difference of each bottom wave,
The ultrasonic wave according to the second technique , wherein the thinning state of the inspection object is estimated by comparing the database with a fourth index obtained by obtaining sound pressure from the inspection object. Inspection method.

In the third technique , since the fourth index indicating whether or not the thinned portion is uniformly formed is added and comprehensively determined, the sectional dimension, length, and position of the thinned portion are determined. It can be estimated more accurately.

ここで、Δｔは時間遅れ、Ｖ_Ｌ、Ｖ_Ｓはそれぞれ縦波と横波の速度、ｄは減肉後の断面寸法である。 The fourth technique related to the present invention is:
The first index is an ultrasonic inspection method according to the second technique or the third technique , which is obtained from the following equation.

Here, Δt is a time delay, V _L and V _S are longitudinal and transverse wave velocities, respectively, and d is a cross-sectional dimension after thinning.

In the above formula, d indicates the cross-sectional dimension after the thinning, but there is a possibility that it does not become an accurate value depending on the situation of the thinned portion. In the fourth technique , the obtained d is used as a first index, taking into account the influence of other indices, and the database is created in consideration of d obtained from the inspection object and the influence of other indices. The situation of the thinned portion with high accuracy can be estimated by using and comprehensively judging.

  The “cross-sectional dimension after thinning” includes the diameter of a cylinder and the cross-sectional dimension of a square or plate.

The fifth technique related to the present invention is:
The second and third indicators are ratios of the wave height of the delayed echo from the thinned portion to the wave height of the delayed echo from the healthy portion without thinning, wherein the second technique to the fourth technique are characterized in that technology is an ultrasonic inspection method according to any one.

In the fifth technique , as a means for digitizing the characteristics of the delayed echo waveform, the ratio of the wave height of the delayed echo that can be easily digitized and can accurately capture the waveform characteristics is adopted. It becomes easy and the thinning situation can be estimated accurately.

The present invention has been made based on the above-described technology, and the invention according to claim 1
  Ultrasound that injects ultrasonic waves into the inspection object from the exposed end surface of the inspection object that is partly exposed and embedded, and inspects the thinned part by delayed echo from the thinned part of the inspection object An inspection method,
  Injecting ultrasonic waves into the test sample having the thinned portion to obtain a delayed echo,
  An index relating to the thinning situation created by a predetermined procedure from the characteristics of the delayed echo, and a database together with the actual thinning situation of the thinning portion of the test sample,
  It is an ultrasonic inspection method for estimating a thinning state of the inspection object by obtaining a delayed echo from the inspection object and comparing the database with an index obtained by the same procedure as the predetermined procedure,
  The ultrasonic wave is incident on the inspection sample having the thinned portion to acquire the waveform of the time delay and the delayed echo,
  A first index relating to a cross-sectional dimension of the thinned portion obtained by the time delay;
  A second index relating to the length of the thinned portion obtained by quantifying the characteristic of the waveform of the delayed echo;
  A third index relating to the position of the thinned portion obtained by quantifying the waveform characteristics of the delayed echo,
  Create a database with the actual cross-sectional dimensions, lengths and positions of the thinned portions of the test sample,
  By comparing the database with the first to third indexes obtained by acquiring time delay and delayed echo waveforms from the inspection object, the thickness reduction state of the inspection object is estimated. This is an ultrasonic inspection method.

The invention according to claim 2
In addition to the database, a fourth index indicating whether or not the thinned portion is uniformly formed, the ultrasonic wave is incident from a plurality of places on the incident surface, and obtained by the sound pressure difference of each bottom wave,
The ultrasonic inspection according to claim 1, wherein the thinning state of the inspection object is estimated by comparing the database with a fourth index obtained by obtaining sound pressure from the inspection object. Is the method.

ここで、Δｔは時間遅れ、Ｖ _Ｌ 、Ｖ _Ｓ はそれぞれ縦波と横波の速度、ｄは減肉後の断面寸法である。 The invention according to claim 3
The ultrasonic inspection method according to claim 1, wherein the first index is obtained from the following equation.

Here, Δt is a time delay, V _L and V _S are longitudinal and transverse wave velocities, respectively, and d is a cross-sectional dimension after thinning.

The invention according to claim 4
The second and third indicators are ratios of the wave height of the delayed echo from the thinned part to the wave height of the delayed echo from the healthy part without thinning. It is an ultrasonic inspection method given in any 1 paragraph.

  ADVANTAGE OF THE INVENTION According to this invention, the ultrasonic inspection method which can improve the precision and reliability of a test | inspection more than before, and can estimate the thinning condition of a test target object simply and accurately can be provided.

It is a figure which shows typically the mode of generation | occurrence | production and propagation of a delayed echo. It is a figure which shows the anchor bolt for various evaluation tests produced in order to investigate the characteristic of an echo. It is a figure which shows the relationship between the amplitude of a reflected wave, and the time to return when the area | region where the reduction | decrease of a diameter produced is close to an upper end surface. It is a figure which shows the relationship between the amplitude of a reflected wave, and the time to return when the area | region where the reduction | decrease of a diameter produced is near a bottom face. It is a figure which shows the relationship between the amplitude of a reflected wave when a thinning part is short, and the time to return. It is a figure which shows the relationship between the amplitude of a reflected wave in case a thinning part is long, and the time to return. It is a figure which shows the relationship between the 2nd parameter | index obtained by using the diameter of the corrosion part as a parameter, and the length of a thinning area | region. It is a figure which shows the relationship between the 3rd parameter | index obtained by using the length of the thinning area | region as a parameter, and the generation | occurrence | production position of a thinning part. It is a figure which shows a mode that the position in the upper end surface of the anchor bolt in which only a part of side surface corrodes is changed with a fixed rule, and the corrosion location is detected by applying an ultrasonic probe. It is a figure in which a thinning part shows the echo of the anchor bolt of one side. It is a figure in which a thinning part shows the echo of the anchor bolt of one side.

  Hereinafter, description will be given based on the embodiment of the present invention.

  In this embodiment, ultrasonic waves are incident on the inspection object from the exposed end face of the anchor bolt that is partially exposed and embedded, and the thinned portion is inspected by a delayed echo from the thinned portion of the anchor bolt. This is an ultrasonic inspection method.

  The delayed echo will be described with reference to FIG. FIG. 1 is a diagram schematically showing how delayed echoes are generated and propagated using anchor bolts. In FIG. 1, 10 is an ultrasonic probe, 20 is an anchor bolt, 21 is the upper end surface (left end surface in FIG. 1), and 22 is the bottom surface (right end surface in FIG. 1). is there.

  The ultrasonic waves incident from the upper end surface 21 of the anchor bolt 20 are not reflected by the inner surface but directly reach the bottom surface 22 and return to the ultrasonic probe 10 to receive echoes (a and b in FIG. 1). , 41, and the like, passing through a path as shown in FIGS. 1 to 3 while being reflected on the inner surface of the anchor bolt 20 and reaching the bottom surface 22 and then received as an echo. be called. On the other hand, when reflecting on the inner surface, mode conversion from longitudinal to transverse waves occurs under certain conditions (4 in FIG. 1), and the velocity of the ultrasonic wave changes. Causes a time lag at regular intervals.

  Next, an inspection sample, an index, and a database used in the ultrasonic inspection method of the present embodiment will be described, and subsequently, an estimation work of the thickness reduction state of the anchor bolt will be described.

(1) Inspection sample In order to accurately detect the diameter reduction and position or degree of corrosion due to corrosion occurring in anchor bolts by inspection using ultrasonic waves, the amount of thickness reduction due to corrosion, the position of the thickness reduction location, etc. It is necessary to prepare various anchor bolts for evaluation tests and perform ultrasonic inspections on the anchor bolts to confirm various characteristics indicated by the echo according to the aspect such as corrosion. For this reason, anchor bolts for evaluation tests (No1) to (No6) shown in FIG. 2 were produced.

  In FIG. 2, the thickness reduction part 23 which is the external shape and diameter reduction part of the anchor bolt 20 from (No1) to (No6) produced is shown. (No1) is a healthy anchor bolt with a diameter of 60 mm and an axial length of 500 mm. (No 2) is a semi-elliptical shape with a thinned portion 23 having a maximum depth of 20 mm formed on one side of the same anchor bolt as (No 1), and (No 3) is a semi-elliptical shape with a maximum depth of 15 mm. The thinned portion 23 is formed on one side of the same anchor bolt as (No1). Note that the axial length of the region of the thinned portion 23 is 50 mm, and the distance from the upper end surface (ultrasonic incident surface) to the upper end of the thinned portion 23 (position of the thinned portion 23) is 140 mm. It is.

  The anchor bolts (No. 4) to (No. 6) are obtained by forming the thinned portion 23 having a trapezoidal cross section over the entire circumference. Table 1 shows the position, length, and diameter of the thinned portion 23.

(2) Index (a) 1st parameter | index A 1st parameter | index is an parameter | index regarding the cross-sectional dimension of the thinning part 23 obtained by time delay.

ここで、Δｔは時間遅れ、Ｖ_Ｌ、Ｖ_Ｓはそれぞれ縦波と横波の速度、ｄはアンカーボルトの直径である。 It is known that the diameter of the anchor bolt is obtained by the following equation using time delay data.

Here, Δt is a time delay, V _L and V _S are the velocity of the longitudinal wave and the transverse wave, respectively, and d is the diameter of the anchor bolt.

  From the above equation, it can be seen that there is a certain relationship between the diameter d of the anchor bolt and the time delay Δt, and if d decreases due to thinning, Δt also decreases. Therefore, d after thinning can be obtained by capturing Δt.

  However, d obtained here is generally not necessarily the same as the actual diameter, and is used as an index. This is the first indicator. The ultrasonic probe is a vertical probe manufactured by Kraut Kramer. Use frequency is 5MHz

(B) 2nd parameter | index A 2nd parameter | index quantifies the characteristic of the waveform of the said delayed echo which appears by the difference in the length of the bolt axis direction of a thinning part area | region. Hereinafter, a description will be given with reference to FIGS. 3 and 4.

  FIG. 3 is a diagram illustrating the relationship between the amplitude (wave height) of the reflected wave and the time (μs) for returning when the thinned portion is close to the incident surface. FIG. 4 is a diagram illustrating the relationship between the amplitude of the reflected wave and the time (μs) for returning when the thinned portion is far from the incident surface.

  Reference numeral 60 in the drawing is an echo (bottom echo) reflected and returned from the bottom surface 22 of the anchor bolt, 70 is a delayed echo generated by mode conversion, and 71 is mode-converted on a healthy side of the echo. Is a delayed echo (delayed echo from a healthy part), and 72 is a delayed echo caused by mode conversion on the side surface whose diameter is reduced due to corrosion. 73 is a delayed echo appearing accompanying the thinning.

  70 is observed later than the bottom wave because part of the path is a transverse wave, but is a longitudinal wave during observation. 71 is a delayed echo from the healthy part, 72 is a delayed echo from the thinned part, and the rest is a delayed echo appearing accompanyingly. Delayed echoes appear in the path as seen in FIG. 1, in addition to easy-to-understand echoes that appear as a result of mode conversion in the healthy and thinned parts, as well as the side, bottom, Reflected by the edge of the bottom, etc., and a complex echo is returned. Therefore, various samples are manufactured and measured, and the pattern of delayed echo obtained is made into a database to estimate the corrosion state.

  The second index is used for estimating the length of the thinning region by quantifying the characteristic of the delayed echo waveform that appears due to the difference in the length of the thinning region.

  Comparing FIG. 3 and FIG. 4, if the thinned portion is close to the incident surface, the delayed echo 71 due to the healthy portion has a peak shape (FIG. 3), but if it is far away, the tendency is weakened (FIG. 4). I understand that. For this reason, the position of the thinned portion is determined using the numerical value obtained by dividing the delayed echo 73 accompanying the thinning by the echo 71 from the healthy portion as the second index.

(C) Third index The third index is obtained by quantifying the characteristics of the delayed echo waveform that appears due to the difference in the occurrence position of the thinned portion.

  FIG. 5 and FIG. 6 are diagrams showing the relationship between the amplitude of the reflected wave of the ultrasonic wave and the return time (μs). Among these, FIG. 5 shows a case where the thinning region of the thinning portion is short, and FIG. 6 shows a case where the thinning region of the thinning portion is long. In addition, the distance from the entrance plane of the center of the thinning region of the thinning portion is the same for any anchor bolt. Further, reference numeral 60 in the figure is an echo reflected and returned by the bottom surface 22 of the anchor bolt, 70 is a delayed echo generated by mode conversion, and 71 is due to mode conversion on a sound side of the echo. A delayed echo (delayed echo from a healthy part), and 72 is a delayed echo caused by mode conversion on the side surface whose diameter is reduced due to corrosion. 73 is a delayed echo appearing accompanying the thinning.

  Comparing FIG. 5 and FIG. 6, it is the same that the echo 71 from the healthy portion shows a peak in any case, but if the thinning region is short, the echo 71 from the healthy portion is low, but the thinning region is It can be seen that the echo 71 from the thinned portion is larger if the length is longer. For this reason, it is possible to use the numerical value obtained by dividing the delayed echo 72 from the thinned portion by the echo 71 from the healthy portion as a third index for determining the position of the thinned portion from the incident surface. .

(D) Fourth index The fourth index is an index indicating whether or not the thinned portion is uniformly formed around the axis of the anchor bolt.

  Compared to the case where the thinning of the outer peripheral surface of the anchor bolt occurs uniformly in the circumferential direction, the detection accuracy can be deteriorated in the case of so-called one-side thinning where only a part of the circumferential direction is thinned. There is sex. Therefore, the case of thinning on one side will be described with reference to FIGS.

  10 and 11 are views showing a state in which an ultrasonic probe is applied to the upper end surface of the anchor bolt 20 with one side thinning (No. 2). FIG. FIG. 11 shows a case where it is applied to the upper part, and FIG. FIG. 9 is a diagram showing a state where the ultrasonic probe 10 is applied by changing the position on the upper end surface of the anchor bolt to detect a corrosion site.

  10 and 11, the vertical axis represents the amplitude, the horizontal axis represents the time (μs) required for the echo to return, 76 represents the echo from the bottom surface, and 77 represents the delayed echo from the healthy part. 78 is an echo from the thinned portion 23.

  Comparing FIG. 10 and FIG. 11, when the acoustic probe 10 is applied directly above the thinned portion 23 (FIG. 10), two bottom echoes 76 of the transverse wave are compared to the case where the acoustic probe 10 is not applied (FIG. 11). 77 is significantly smaller. This makes it possible to detect the position of the side surface where corrosion has occurred.

  In both FIG. 11 and FIG. 12, a small echo 78 from the thinned portion 23 can be seen, whereby an approximate distance from the incident surface of the anchor bolt can be estimated.

  Then, by utilizing the difference in sound pressure of the bottom echo, for example, as shown in FIG. 9, ultrasonic waves are incident from a plurality of points on the upper end surface of the anchor bolt, and the ultrasonic waves are returned even if symmetry is considered. If there is a large difference, it can be estimated that there is unilateral corrosion there.

(3) Database Prior to the inspection, the database obtains the first to fourth indexes for many samples whose conditions of the thinned portion are known in advance, such as (No1) to (No6), and reduces each reduction. It is created by storing together with the actual data of the meat part.

(4) Evaluation Table 1 shows the difference between the evaluation value (first index) of the diameter of the corroded portion and the actual size obtained in the anchor bolts for evaluation tests (No4) to (No6).

  From Table 1, it can be seen that the evaluation value, which is the calculation result, does not match the actual size, but is contained in a small error of 5.4% at the maximum, and the result is obtained with sufficient accuracy. Further, it can be seen that when the diameter reduction region is close to the ultrasonic source, the diameter of the portion tends to be evaluated larger than the actual size.

  Next, in the anchor bolts for evaluation tests (No4) to (No6), the relationship between the second index obtained using the diameter of the corroded portion as a parameter and the length (actual size) of the thinned region is shown in FIG.

  As shown in FIG. 7, even when the length of the corroded portion is the same, it can be seen that the value of the second index tends to increase when the diameter of the thinned portion is small. When the second index exceeds 0.3, it is easy to measure the time delay of the mode conversion echo that appears due to reflection from the thinning region, so that it is possible to more accurately determine the length of the thinning region. it can.

  Next, in the anchor bolts for evaluation tests of (No4) to (No6), the relationship between the third index obtained using the length of the thinned region as a parameter and the occurrence position (actual size) of the thinned portion is shown in FIG. Shown in

  As shown in FIG. 8, even when the diameter of the corroded portion is the same, it can be seen that the value of the third index tends to increase when the length of the thinned region decreases. In addition, since the echo which carries out mode conversion increases in a thinning area | region, when the 3rd parameter | index exceeds 0.2, the length of a thinning area | region can be judged more correctly.

  Thus, since the 1st-3rd parameter | index is mutually related, it turns out that the determination based on these parameter | indexes needs to be comprehensively performed in addition to the collation with a database.

  In Table 2, the 1st-4th parameter | index obtained in the anchor bolt for evaluation tests of (No2)-(No6), and the comprehensive evaluation are shown. This comprehensive evaluation is based on the comprehensive evaluation described above based on the comparison with the database.

  When the comprehensive evaluation of Table 2 is seen, it is understood that the sufficiently accurate evaluation is performed on the actually measured values, and the inspection method of the present invention is useful.

  As described above, the embodiments for the anchor bolt have been described. However, the processing according to the present invention can be applied to an object in which a delayed echo can be observed. For this reason, the present invention is not limited to anchor bolts, and can also be applied to anchor bolts having similar shapes, square bars or plate members having parallel side surfaces facing each other.

  In addition, this invention is not limited to the above embodiment. Various modifications can be made within the same and equivalent scope as the present invention.

1-4 Ultrasonic path 10 Ultrasonic probe 20 Anchor bolt 21 Upper end surface 22 of anchor bolt Bottom surface 23 of anchor bolt Thinning portion 41 Ultrasonic wave 60 Bottom echo 70 Delayed echo 71 Delayed echo 72 from healthy portion Thinning Delayed echo 73 from the part Accompanying delayed echo 76 Bottom echo 77 Delayed echo 78 from the healthy part Echo from the thinned part Δt Time delay V _L , V _S velocity of longitudinal and transverse waves d Diameter of anchor bolt

Claims (4)

Ultrasound that injects ultrasonic waves into the inspection object from the exposed end surface of the inspection object that is partly exposed and embedded, and inspects the thinned part by delayed echo from the thinned part of the inspection object An inspection method,
Injecting ultrasonic waves into the test sample having the thinned portion to obtain a delayed echo,
An index relating to the thinning situation created by a predetermined procedure from the characteristics of the delayed echo, and a database together with the actual thinning situation of the thinning portion of the test sample,
It is an ultrasonic inspection method for estimating a thinning state of the inspection object by obtaining a delayed echo from the inspection object and comparing the database with an index obtained by the same procedure as the predetermined procedure,
The ultrasonic wave is incident on the inspection sample having the thinned portion to acquire the waveform of the time delay and the delayed echo,
A first index relating to a cross-sectional dimension of the thinned portion obtained by the time delay;
A second index relating to the length of the thinned portion obtained by quantifying the characteristic of the waveform of the delayed echo;
A third index relating to the position of the thinned portion obtained by quantifying the waveform characteristics of the delayed echo,
Create a database with the actual cross-sectional dimensions, lengths and positions of the thinned portions of the test sample,
It is characterized in that the thinning state of the inspection object is estimated by comparing the database with the first to third indexes obtained by acquiring time delay and delayed echo waveforms from the inspection object. ultrasonic inspection method that. In addition to the database, a fourth index indicating whether or not the thinned portion is uniformly formed, the ultrasonic wave is incident from a plurality of places on the incident surface, and obtained by the sound pressure difference of each bottom wave,
By matching the fourth index and the database obtained by acquiring the sound pressure from the test object, ultrasonic testing according to claim 1, characterized in that estimating the thinning condition of the test object Method. The first index is an ultrasonic testing method according to claim 1 or claim 2 characterized in that it is obtained from the following equation.

Here, Δt is a time delay, V _L and V _S are longitudinal and transverse wave velocities, respectively, and d is a cross-sectional dimension after thinning. The second and third indicators of claims 1 to 3, characterized in that the ratio of the peak delay echoes from the thinning section for crest delay echoes from healthy portion without thinning The ultrasonic inspection method according to any one of the above.

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