RU2622459C1 - Method of ultrasonic inspection of articles - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: pulses of ultrasonic vibrations are radiated from one side of the controlled object, the first through and the twice reflected pulses are received from the opposite side of the products, and the echo pulses of the ultrasonic oscillations reflected from the defect scan the product over the entire area, ensuring alignment of the emitting and receiving ultrasonic transducers, the envelopes of the amplitudes of the ultrasonic vibrations of the first of the last (through) pulse and echo signals from defects in the time interval between the first and the second through pulses are analyzed, additionally, the coordinates of the reduction product are read that passed the through pulses, the sensitivity of the signal reception is increased in the time interval between the first and the second through pulses, the time interval between the first through pulse and the first echo signal from the defect are measured, according to the measured values the location and depth of the defect are determined.

EFFECT: increasing the reliability of ultrasonic inspection of products.

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Description

The invention relates to non-destructive testing by ultrasonic (US) method and can be used for flaw detection of sheets, plates and other products in the metallurgical and engineering industries.

The method allows to detect and evaluate the size, depth of the location of defects in products that have the ability to install emitting and receiving electro-acoustic transducers (EAP) from opposite sides of the product.

Due to the technological features of the production of sheet metal and plates, most of the internal discontinuities have a pronounced flat shape. In the vast majority of cases, their plane is parallel to the plane of hire. Therefore, defects with the right approach are successfully detected using elastic waves excited along the normal to the sheet surface [1-4].

The object of search and subsequent analysis during flaw detection are, as a rule, defects in the form of planar extended discontinuities, the area of which is from several units to several tens or even hundreds of square centimeters. The flat form of most of the extended discontinuities of various origins has generated in practice their generalized conditional name - “bundles” (“laminations” - in terms of international standards and norms) [1, 4]. The reflection coefficient of elastic waves from “delaminations” in practice can take values from 0.3 to 1.0.

The known shadow method of ultrasonic detection and defect size determination [5], which consists in the fact that on the opposite surfaces of the product set a pair of EAP with sensing lines directed towards each other. The product is probed, for which ultrasound sounding signals are emitted by one and received by another EAP. The product is scanned, for which a pair of EAPs are moved together, repeating soundings. The boundaries and sizes of defects are detected at the moments of disappearance and (or) the appearance in the second EAP of ultrasound signals emitted by the first EAP, due to inhomogeneities (defects) in the product.

The disadvantage of this method [5] is the low accuracy and limited capabilities that allow to detect and evaluate the size of the projection of the defect only in the plane of movement of the EAA.

A known method of ultrasonic flaw detection [6] for flaw detection of metal at metallurgical and engineering enterprises. The presence of a defect in the product in the known method is judged jointly by the amplitude of the echo pulse in the time interval between the probe and bottom pulses in the contact version or the echo pulses from the front face and the bottom of the product — in the immersion version, by the amplitude of the first echo pulse from the bottom of the product and the magnitude of the ratio of the amplitude of the echo pulses in the time interval between the first and second bottom pulses to the amplitude of the first bottom pulse. The disadvantage of the echo-through method is the inability to determine the depth of defects, which is especially important when controlling thick-walled sheets and plates and the dependence of the control results on signal amplitudes. All this reduces the reliability of the control.

A known method for detecting and evaluating the size of a defect [7], which consists in the fact that in the vicinity of the alleged defect on the opposite surfaces of the product install EAP, with sensing lines directed at each other and located in the same plane of sounding, probe the product, which emit ultrasonic signals on the one hand, and they are received on the other side of the product, together they move all EAP along the product, they detect and determine the position of the defect border line using the shadow method, determine the size of the defect in the plane speed sensing. The position of the upper and lower lines of the boundaries of the defect allows us to estimate the size of the projection of the defect. In this case, the radiating EAP has a wide radiation pattern, and the resolution determines the number of receiving EAP.

The disadvantage of this method is the low accuracy determined by the number of receiving EA.

A known method for detecting and determining the size of a defect [8], which consists in the fact that pairs of EAF are installed on the perpendicular surfaces of the product and the shadow method determines the boundaries of the defect. The method allows to determine the spatial dimensions of the defect.

The disadvantages of this method are the low accuracy and the need for access to the product from two perpendicular directions.

There is a known [9] method for detecting and determining the size of a defect, which consists in scanning the product with one EAA in two mutually perpendicular directions: reciprocating across the sheet and discretely rectilinearly along it. This method involves the use of the mirror method of ultrasonic testing and allows scanning to determine the projection of the defect on a plane perpendicular to the direction of sounding.

The disadvantages of this method are the low accuracy and functionality associated with the fact that it does not allow to detect defects collinear to sensing lines. In addition, the mirror method involves the use of ultrasound signals reflected from the plane of the defect, the amplitude of which is small.

The shadow method of ultrasonic flaw detection [5] involves the use of EAPs directed at each other and allows emitting EAPs to operate with large amplitudes of the probing signals and, accordingly, to have a sufficiently high level of through signals at the receiving EAP. At the same time, the traditional problem of ultrasonic flaw detection - providing acoustic contact with the product becomes less relevant. With the shadow ultrasound scanning method, the lines of the defect boundaries are detected by the moments of disappearance (and appearance) of the received ultrasound sounding signals.

In contrast to the known methods used by the echo control method, the shadow method has the following advantages:

- the practical absence of a dead zone;

- minimal dependence on the unstable reflective properties of the defect;

- due to the extremely achievable short path of the beam, the minimum attenuation and scattering of ultrasonic vibrations;

- low level of reverberation noise.

The known method [10] ultrasonic inspection of products with two-way access, which consists in the fact that they emit pulses of ultrasonic vibrations from one side of the controlled product, take the first through (transmitted) and twice reflected through pulses from the opposite side of the product, as well as echo pulses of ultrasonic vibrations reflected from the defect, measure and find the ratio of the amplitudes of the first and second through pulses and the ratio of the amplitudes of the echo signals from the defect to the amplitude of the first through (transmitted) signal and determine their values lyayut defective products. The disadvantage of this method, adopted as a prototype, is the low reliability of control associated with the limited ability to localize the defect in plan and the inability to determine the depth of the defect.

The aim of the invention is to increase the reliability of detection of defects.

To achieve the goal in the method of ultrasonic testing of products, which consists in the fact that pulses of ultrasonic vibrations are emitted from one side of the controlled product, the first through and double reflected through pulses are received from the opposite side of the product, as well as echo pulses of ultrasonic vibrations reflected from the defect, scan the product over the entire area, ensuring the alignment of the emitting and receiving electro-acoustic transducers, analyze the envelopes of the amplitudes of ultrasonic vibrations of the first transmitted (pass-through) pulse and echo signals from a defect in the time interval between the first and second transmitted (pass-through) pulses, additionally read the coordinates of decreasing transmitted through the product pulses, increase the sensitivity of signal reception in the time interval between the first and second transmitted pulses, measure the time interval between the first transmitted pulse and the first echo signal from the defect, from the measured values determine the location and depth of the defect.

The significant differences of the proposed method

In the inventive method, scanning of the controlled product is carried out over the entire surface area on which the emitting EAP is located, and provide synchronous and coaxial movement of the emitting and receiving EAP relative to the product. It doesn’t matter if the EAT system or the controlled product moves. The prototype implies the movement of the controlled product (sheet metal) relative to the stationary emitting and receiving EAP.

In the proposed method, the envelopes of the amplitudes of the ultrasonic vibrations of the first (through) pulses passing through the product are analyzed, taking into account the coordinates of the reduction of through pulses transmitted through the product. In the prototype, the coordinates of the disappearance of past pulses are not stated on the sheet.

The key point of the proposed method is to measure the time interval between the first end-to-end signal and the echo signal from the edge of the defect during the collision of the ultrasound beam to the defect. The measured value determines the coordinate of the occurrence of the edge of the defect.

The shadow method, as noted above, has several advantages over the echo method. However, the main drawback of the shadow method, as was believed to date, is the inability to determine the depth of the defect [5]. Thanks to computer modeling and experimental studies, it was possible to notice a specific feature of the formation of signals at the edges of defects. At the time of entry / exit of the ultrasonic beam and the beginning / end of the formation of an acoustic shadow over the defect, part of the ultrasonic vibrations incident on the defect surface has time to bounce off the defect plane, reach the product surface (scanning surface emitting EAP), reflect from the upper plane of the product and reach through the entire thickness of the product receiving EAP.

Naturally, the travel time of ultrasound rays along the described trajectory differs from the travel time of the through pulse that forms the first through pulse and the more, the deeper the edge of the desired defect lies. By measuring the delay time of these signals relative to the temporary position of the first pass-through signal, you can determine the coordinates of the edges, and hence the approximate orientation of the detected defect. Moreover, if the defect lies near the upper plane of the product (the scanning surface of the radiating EAP), then the signal from the edge of the defect at the receiving EAP is closer to the first through signal. If the defect lies near the bottom surface of the controlled product, the reflected signal from the defect is located near the second through signal. In any case, the signals reflected from the defect plane and the upper plane of the product) from potential defects are within the time interval between the first and second through signals.

Due to the fact that the signal propagation path from the defect is larger than the first through signal (up to a maximum of 3 times when the defect is located near the bottom surface) and ultrasound vibrations undergo double reflection on this path (from the extreme part of the defect plane and from the inner surface of the upper plane products), the amplitude of the signal from the defect is less than the amplitude of the first through signal in the defect-free section of the product. In practice, depending on the thickness H of the product, the depth and reflectivity of the defect, this difference can reach up to 30 dB. Therefore, in practical implementation in the expected time zone (between the first and second through pulses), it is proposed to receive signals at a higher sensitivity than receiving through signals.

In the prototype, the analysis of signals between the first and second through pulses is performed at normal sensitivity. As a result, due to the small amplitudes of the signals reflected from the edges of the defect at the moment the ultrasound hits the beam on the plane, the defect may not be noticeable. And thus, the determination of the depth of defects in a known manner becomes impossible.

In the claimed method, in the process of relative movement (scanning) of the EAE system and the controlled product by determining the position and depth of the edges, the location and depth of the defect (the defect is outlined) in the product are determined.

The prototype only determines the location of the defect in terms of a controlled sheet product and the depth of the defect is not determined.

The inventive method is illustrated by the following graphic materials.

FIG. 1 - sensing and scanning schemes of a controlled product and the formation of an envelope of through signals over a defect: FIG. 1a is a scanning circuit; FIG. 1b - the formation of the envelope of the through signals,

where 1 is a controlled product;

2 - plane scan emitted EAP;

3 - scanning plane of the receiving EAP;

4 - scanning path of the EAA;

5 - a possible local defect (delamination) in the product;

6 - radiating EAP;

7 - EAP displacement sensor (encoder);

8 - receiving EAP;

9 - path of propagation of the ultrasound beam;

10 - amplitude envelopes of through pulses;

11 - zone for reducing the amplitude level of through pulses;

12 - pore level of fixation of reduction of amplitudes of through signals over the defect.

FIG. 2 - display of control signals on a scan of type A on a defect-free section of the monitored product 1: FIG. 2a - display of the emitted (probing) signal; FIG. 2b - display of end-to-end signals,

where 13 is a probe (radiated) pulse on the EAP 6;

14 and 15 - the first and second through signals, respectively, on the EAP 8;

16 - gating zone of the 1st pass-through signal.

FIG. 3a and FIG. 3b - the formation of signals reflected from the bundle located in the upper part of the product, and the display of signals on a scan of type A, respectively,

where 17 are the signals on the EAA 8, reflected from the edge of the plane of the bundle 5, located in the upper part of the product at a depth of h ₁ and re-reflected from the upper plane 2 of the product 1;

17a and 17b - two and three times reflected signals from the edge of the bundle 5.

FIG. 4a and FIG. 4b - the formation of the signal reflected from the bundle located in the lower part of the product, and the display of signals on a scan of type A, respectively,

where 17 is the signal from bundle 5 in FIG. 4a located at a depth of h ₂ from the surface 2 of the product 1.

FIG. 5a and FIG. 5b - simulation results of the passage of ultrasonic waves through the product using a special program of mathematical modeling of the propagation of acoustic waves f. PZFlex.

Consider the possibility of implementing the proposed method.

As an object of measurement, we will consider a metal product 1 (Fig. 1) with good ultrasonic permeability, which has two-sided access for installing an EAA, for example, steel sheet, pipes of large diameter, and also products of a more complex shape.

On the surface 2 of the product 1 of thickness H with a potential defect 5 at a depth h, a radiating EAP 6 is installed (Fig. 1a). On the opposite surface 3 of the product 1 coaxially with the EAP 6, a receiving EAP 8 is installed. Scan the controlled product 1 along the path 4, providing synchronous and coaxial movement of the EAP 6 and 8 (Fig. 1a).

Ultrasound sounding is carried out periodically with the selected frequency of the packages (in practice, 1000-2000 Hz) and the scanning step, which determine the minimum detectable size of the defect 5 (Fig. 1A). The coordinates of the EAP movement on the product 1 is determined using the displacement sensor 7.

Radiated by the EAP 6 ultrasonic vibrations, propagating along the trajectory 9 through the thickness of the product 1, reach the receiving EAP 8 (Fig. 1a). On the defect-free section of the product 1, the amplitudes of the through pulses are almost constant. An almost horizontal line of the envelopes of the through signals 10 is formed (Fig. 1b). When the trajectory of the ultrasound beam 9 hits the defect 5 (Fig. 1a), the amplitudes of the through pulses are weakened until they disappear completely due to the shadowing of the ultrasound path of the defect 5 by the plane of the defect 5 — section 11 in the defectogram (Fig. 1b). As a result, on the defectogram (type C scan), taking into account the data of the path sensor 7, a decrease in the envelopes of the amplitudes of the through pulses is observed, which makes it possible to uniquely identify areas with the projection of defect 5 in the product 1 on the scanning surface (Fig. 1). To unambiguously fix the moment of reduction of the end-to-end signal on the defectogram, a threshold level of 12 is set (Fig. 1b), which makes it possible to automate the process of detecting a defect in a controlled product.

When observing control signals on a Type A sweep on a radiating EAP 6, one can observe a probe pulse 13, and on a receiving EAP 8 a through (transmitted) pulse 14 (Fig. 2). The travel time of ultrasonic vibrations in this case is

where H is the thickness of the controlled product;

with ₁ - the propagation velocity of longitudinal waves in the product (for steel products is 5900 m / s).

In the defect-free section of the product 1, in the A scan, as a rule, one can also observe the second through pulse 15, the amplitude of which is significantly less due to twofold re-reflection of ultrasonic vibrations from the bottom of the product (inner surface of plane 3 of the product) and from the upper surface (inner surface of plane 2 ) Obviously, the time interval between the first and second through pulses (pulses 14 and 15 in Fig. 2b) is two times longer than the interval t _sk between the probe and the first through pulse, and is 2t _ck .

To select the first through pulse 14 and the formation of the amplitude envelope 10 of these pulses as the scan progresses, a gating pulse (temporal selection pulse) 16 can be used (Fig. 2b). In the general case, the use of the latter in the implementation of the method is not necessary, since in digital flaw detectors it is possible in the processing algorithm to set the extraction of the first pulse with the maximum amplitude to form the amplitude envelope.

Performing the described procedures of the method allows you to localize the defect 5 in the product 1 on the scanning plane, but does not allow to determine the depth of the defect. The latter can be important, especially when monitoring plate constructions both in their production and in their operation. In particular, to assess the degree of danger of the identified defect and make informed decisions on the repair of the product.

To solve this problem, the claimed method proposes to analyze signals from potential defects in the time interval between the first 14 and second 15 through pulses (Figs. 2, 3 and 4) at the moments of entry / exit of the ultrasound beam from the projection of the defect. Moreover, unlike the prototype, where the ratios of the amplitudes of the through (past) pulses and signals from the defect are estimated, the analysis is performed in the claimed method.

It is known that the temporal parameters of the signals, in comparison with the amplitude parameters, are more stable and do not depend on the reflective properties of the defect.

The formation of signals reflected from the bundle 5 located in the upper part of the product 1 is as follows.

At the moment of entry / exit of the ultrasound beam 9 and the beginning / end of the formation of an acoustic shadow over the defect, part of the ultrasonic vibrations falling on the defect surface has time to reflect from the plane of the defect 5, reach the surface of the product 2 (scanning surface emitting EAP 6), and reflect from the upper plane 2 of the product 1 and through the entire thickness of the product to reach the receiving EAP 8. Moreover, the formation of the re-reflected echo signal 17 from the plane of the defect 5 and the reception of this signal EAP 8 occurs in a very limited time - only during the collision / removal ultrasound beam to the edge of the defect.

For example, in manual control with a scanning speed of 100 mm / s and with identical diameters of the emitting and receiving EAP equal to 12 mm, the time from the moment the first pass-through signal decreases 14 from the maximum value to complete disappearance (the duration of the edges of the decrease / increase of the envelope of the pass-through signal by Fig. 1b - the edge of zone 11) is only 0.12 s. With automated control at a speed of 1 m / s, this time is even shorter and, all other things being equal, is only 12 ms. But even in such a short time, at a frequency of sending probe pulses of 2 kHz, more than 20 pulses 17 manage to arrive at the receiving EAP 8, which is quite sufficient for the automated measurement of the time interval t _D between the first through signal 14 and the echo signal 17 (Fig. 3 and 4). Subsequently, the ultrasound beam 9 is completely shielded by the plane of the defect 5 and the reflected echo signals 17 from the other edge of the defect 5 appear only after a certain time at the time of completion of scanning by the EAP system 6 and 8 of the entire projection of the defect 5.

The formation of the reflected echo at the edge of the defect 5 is well demonstrated by the simulation program (Fig. 5). At the initial moment of time, part of the ultrasound beam 9 excited by the EAP 6 passes by the edge of the defect 5 in the direction of the EAP 8, and part is reflected from the defect in the direction of the emitted surface 2 (Fig. 1a) of the product 1 (see Fig. 5a) - a kind of splitting of the ultrasonic wave emitted at the edge of the defect occurs. After a time equal to t _ck = H / c ₁ , ultrasonic vibrations through the thickness of the product 1 reach EAP 8 and an impulse 14 is formed (Figs. 2, 3 and 4). Following the pulse 14, as can be seen from FIG. 5b, the receiving EAP 8 receives the echo signal 17 reflected from the surface 2 from the defect 5. The time delay t _{Д of} this pulse relative to the first through signal 14 depends on the depth h of the occurrence of defect 5 in the product 1:

Thus, by measuring the time interval t _D between the first through signal 14 and the first echo pulse 17 reflected again (Figs. 3 and 4), it is possible to determine the depth of the defect 5:

From the expression obtained from (1) and (2), it is seen that with a known size H of the controlled product 1, knowledge of the speed c _{1 of the} propagation of ultrasonic vibrations in the material of the product is not even required. By restricting ourselves to measuring time intervals t _ck and t _D , with accuracy sufficient for practice, it is possible to determine the depth of defect 5 from expression (3) (Fig. 1a).

In FIG. 5b is visible, and in FIG. 3b shows that in addition to the first re-reflected signal 17, when the defect is located closer to the emitted surface, several more reflected echo signals 17a, 17b from the defect are observed (in Fig. 3b). Naturally, their amplitude is even smaller than the amplitude of the first echo signal 17 and in this method it is proposed not to consider them as information signals. To determine the coordinate h of the edge of the defect 5, it is sufficient to measure the time interval t _D between the first through 14 and the first 17 echo signals. Essentially, this boils down to measuring the time interval between the pulse 14 and the first signal with a maximum amplitude of 17 in the time interval 2t _ck (see Fig. 3b and 4b).

In FIG. 3 and 4 show the temporary positions of the signals from the defect for two cases: FIG. 3 - for a defect located in the upper part of the product; FIG. 4 - located at the bottom of the product. As an example, consider a plane-parallel product 1 with a thickness of H = 80 mm, in which layering occurs at a depth of h ₁ = 20 mm (Fig. 3) and h ₂ = 60 mm (Fig. 4). By the expression (2), it is possible to calculate the values of the delay time for both cases: t _D1 = 6.78 μs; t _D2 = 20.34 μs, which is confirmed by the obtained experimental studies on an 80 mm thick plate made of St20 steel and bundle models (cuts) at depths of 20 and 40 mm (t _ck = 13.6 μs; t _D1 = 6.8 μs; t _D2 = 20.3 μs). In experimental studies, ultrasound transducers (EAP 6 and 8 in Figs. 1-3-5) with a diameter of 12 mm piezoelectric plates at a frequency of 5.0 MHz were used.

In turn, the statement of the experimental data in expression (3) gives adequate values for the depths of defects: h ₁ = t _D1 N / 2 t _ck = 6.8 * 80/2 * 13, 6 = 20.0 mm; h ₂ = 59.7 mm.

It is obvious that by measuring the values of t _D along the edges of the defect according to the difference in the depths of the edges in the plan, it is possible to determine not only the depth, but also the orientation of the defect inside the product.

Implementation of the proposed method can be carried out by a modern digital ultrasonic flaw detector, having an additional input for the path sensor 7 and a built-in computer that implements the main procedures of the method according to a given algorithm:

- selection of the first through pulse;

- formation and tracking of the envelope of through pulses;

- determination of the coordinates of reduction (on the defect) and return to the initial state (on the defect-free section) of the envelope of the through signals;

- measuring the travel time of the through pulse through the product;

- increasing the reception sensitivity by a predetermined amount in the time interval between the first and second through pulses;

- measurement of time between the first through and the first echo signal from the defect;

- calculation of the coordinates of the defect: the depth (according to expression (3)) and the location of the defect in the plan (according to the path sensor 7).

The general principle of achieving high accuracy of ultrasonic inspection is that the more scanning lines are used for sensing, the more accurate is the solution to the problem of detecting and evaluating the size of defects. Therefore, the steps in the trajectory 4 (Fig. 1) of the relative displacement of the product 1 and the EAT system 6 and 8 should be chosen optimal based on the need to detect defects of the minimum allowable size. The size of EAP blocks 6 and 8 is usually small, so that scanning can be carried out by moving them relative to product 1. Such movements can be performed by manipulators, scanners, etc. devices located on opposite surfaces of the product 1, and providing not only a coordinated movement of the EAA blocks, but also an accurate determination of the current coordinates of the EAA 6 and 8. However, in some applications, including the claimed method, the movement of the product 1 relative to the EAA can be used or joint movement of both EAF and products. Consideration of the methods of relative movement of the EAA and the product is beyond the scope of the proposed method.

Depending on the state of the scanned surfaces, contact piezoelectric transducers [5], contactless electromagnetic-acoustic transducers (EMAT) [11] and wheeled ultrasonic transducers [12] can be used as EAPs. In the latter case, due to a more stable acoustic contact, the most clear and repeatable defectograms are formed. Rolling the "ultrasonic wheel" along the scanning path takes the minimum time. For example, with a scan path length of about 10 m, it will take less than two minutes to obtain a defectogram in the form of a type C scan (see Fig. 2b) at a scan speed not exceeding 150 mm / s. To further increase the control performance, you can use a matrix of several EAFs, covering the entire control zone with the generated beams.

Thus, the inventive method is implemented, allows you to detect defects, measure their size, determine the depth and, finally, their orientation in the product with two-way access. These tasks are solved using the minimum number of EAP with simple mathematical support and increase the reliability of product control.

Information sources

1. Non-destructive testing methods / Specification of differences in national standards of different countries. T. 2. - M .: Center "Science and Technology", 1994. - 160 p.

2. GOST 22727-88 (77). Sheet hire. Methods of ultrasonic testing.

3. RD5.9332-80. Non-destructive testing. Sheet hire. Ultrasonic methods of continuity control.

4. Standard Specification for Ultrasonic Testing of Steel Sheet by Direct Transducer / US Standard SA-435 / SA-435M.

5. Non-destructive testing: Reference: In 8 vol. / Under the general ed. V.V. Klyueva. T. 3. I.N. Ermolov, Yu.V. Lange. Ultrasonic inspection - 2nd ed., Rev. - M.: Mechanical Engineering, 2008 .-- 864 p.

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Claims (1)

The method of ultrasonic testing of products, which consists in the fact that pulses of ultrasonic vibrations are emitted from one side of the controlled product, the first pass-through and doubly reflected pass-through pulses are received from the opposite side of the product, as well as echo pulses of ultrasonic vibrations reflected from the defect, the product is scanned over the entire area providing coaxiality of the emitting and receiving electro-acoustic transducers, analyze the envelopes of the amplitudes of the ultrasonic vibrations of the first transmitted (through) pulses and echo signals from a defect in the time interval between the first and second pass-through pulses, characterized in that, as the product is scanned, the coordinates of the reduction of pass-through pulses transmitted through the product are read, the sensitivity of signal reception in the time interval between the first and second pass-through pulses is measured, the delay time is measured between the first through pulse and the first echo signal from the defect, the location and depth of the defect are determined from the measured values.

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