RU2039979C1 - Method of ultrasonic testing of products made of coarse-grained materials and ultrasonic testing unit for inspection of products made of coarse-grained materials - Google Patents

Abstract

FIELD: nondestructive test of materials quality. SUBSTANCE: product receives pulses at three definite frequencies, whose values are selected in the extreme points of standard envelope spectra, and the class of defect is judged from the relation of amplitudes. The testing unit is provided with a defect class indicator, solver and additional amplitude meter. EFFECT: determination of the true class of defect and its view on the background of noise caused by material structure. 3 cl, 4 dwg

Description

 The invention relates to the field of non-destructive quality control of materials and products and can be used for ultrasonic inspection of welded joints and the base metal of products from medium- and high-alloy steels having a coarse-grained structure, as well as austenitic steels in various industries.

A known method of ultrasonic quality control of products and materials, which consists in the fact that ultrasonic vibrations are emitted into the controlled product, signals are reflected from the discontinuity, their amplitudes are analyzed, and the quality of the product is judged by the results [1]
The disadvantage of this method is the low sensitivity when detecting defects with low reflectivity, such as the accumulation of small pores and adhesion, and the inability to control coarse-grained materials.

 In this method, the presence and magnitude of the defect is judged by the magnitude of the amplitude of the received signal reflected from the discontinuity, which is affected by the quality of the acoustic contact of the transducer with the product. In addition, this method does not allow to identify the type of defect.

A known method of controlling the quality of products and materials, which allows to determine the nature and orientation of defects. This method consists in the fact that ultrasonic pulses with a wide range of frequencies or pulses with a changing frequency in the range of 0.5-10 MHz are emitted into the controlled product, receive reflected pulses at these frequencies, process them, highlighting the envelope of the spectrum of the received signals, compare the envelope of the spectrum with the reference and the result of the comparison judge the nature and type of defect [2]
The disadvantage of the method based on the spectral method is that it cannot be applied in the case of monitoring products from coarse-grained materials, since in the presence of a large number of interference exceeding the amplitude of the defect signal, the spectrum of the analyzed signals will be determined by more than 90% interference from the structure of the material itself. With such a ratio of interference energies and useful information, it is almost impossible to isolate the latter.

A known ultrasonic flaw detector containing a multi-frequency transducer, probing pulse generators connected to the synchronizer via delay blocks that provide alternate operation of the generators, receiving amplifiers, the number of which is equal to the number of generators of the frequencies used, delay blocks of the received signals, coincidence circuits, and an oscillographic indicator. Moreover, they are connected so that the signal from the output of the first receiving amplifier through the delay blocks enters the first input of the first matching circuit; the second input of the first matching circuit receives a signal from the output of the second receiving amplifier. The output of the first match circuit through the second delay unit is connected to the first input of the second match circuit, and the second input of the match circuit with the output of the third receiving amplifier. The output of the last matching circuit is connected to the indicator [3]
The disadvantage of such a flaw detector is the low reliability of the control results due to the passage of structural interference pulses through the matching circuit due to the possible mutual overlap of the interference pulses. In addition, this device only determines the presence or absence of a defect in the product.

A flaw detector is also known, which contains a synchronizer, excitation pulse generators, a sweep generator and a backlight pulse generator, delay and coincidence circuits, piezoelectric transducers, an amplitude meter, a signal indicator and signal reception and processing channels connected to inputs to piezoelectric transducers, and outputs to the inputs of the matching circuit and consisting from series-connected amplifiers, delay circuits, except the last, and normalized pulse shapers [4]
The disadvantage of this flaw detector is the inability to determine the nature and orientation of the defect and, therefore, the true value of the defect, leading to a significant decrease in reliability. The amplitude of the signal from the defect depends not only on the magnitude of the defect, but is the result of several factors. It depends on the shape of the defect whether it is plane or volumetric, on the inclination of the defect plane with respect to the acoustic axis, on the deviation of the defect surface form from the plane and other factors.

 Therefore, in some cases, a very dangerous defect such as a flat crack, oriented unfavorably to the acoustic axis of the piezoelectric transducer, can be skipped. In addition, the presence of several receiving-amplifying channels, as in the known flaw detector, reduces the accuracy of the device, since it is almost impossible to ensure their identity and stability in terms of gain.

 The technical problem consisting in the development of the method and device is to increase the reliability of control of materials and products made of high strength metals with a coarse-grained structure. This is due to the fact that the most acute issue of detecting a defect and determining its size, shape and orientation is in the control of especially responsible objects, which, if destroyed, pose the greatest danger to humans and the environment.

 The technical result achieved by using the method is that it becomes possible to isolate the signal from the defect against the background of interference from the structure of the material in a real scale of amplitudes and, without analyzing the entire frequency spectrum, as is the case with the spectral method, to restore the envelope of the signal spectrum, reflected from the defect.

 In the spectral method for determining the nature of the defect, ultrasonic pulses with a wide uniform spectrum are emitted into the controlled product. The envelopes of the spectra in it are given by a solid line. Reflecting from the defect, the spectrum of the ultrasonic pulse undergoes changes determined by the type of defect and its orientation, therefore, the envelope of the spectrum of the reflected pulse can have a different form depending on the type of defect it is plane or volumetric, and on the slope of the defect with respect to the direction of propagation of the emitted pulse. Knowing the dependence of the shape of the envelope of the spectra on characteristic defects, it is possible, by comparing the resulting envelope with the standard known ones, to accurately determine the nature of the defect.

 From experimental and theoretical studies it is known that the envelopes of the spectra of reflected signals have two main types: one-humped and two-humped, each of which in turn has three subspecies with a maximum in the low-frequency region (Fig. 1d, e); with a maximum in the high frequency region (Fig. 1c, e) and a maximum in the middle frequency region (Fig. 1b) for one-humped and equal peaks for two-humped curves.

It can be seen from the foregoing that to transfer the envelope shape, it suffices to have three samples from the spectrum of signals at frequencies f ₁ , f ₂ , f ₃ . The same conclusion can be obtained in a more rigorous way, using Kotelnikov's theorem for calculations.

The necessary samples can be obtained by radiating instead of one pulse with a wide spectrum, three pulses at different frequencies having a much narrower spectrum (dashed line in Fig. 1a). These pulses with a relatively narrow spectrum of 0.5 MHz are almost ordinary pulses used in ultrasonic inspection, having a duration of 2-6 ISS depending on the frequency of ultrasonic vibrations. If the ratio of frequencies f ₁ , f ₂ , f _{3 is} correctly selected, a comparison of the pulse amplitudes gives an unambiguous answer to the question of the form of the spectrum and, therefore, the shape and orientation of the defect, as in the case of using the spectral method.

 However, in the case of coarse-grained material, the above method does not give a reliable result, since a spectrum of interference pulses is superimposed on the spectrum of useful pulses, and since their energy fraction is at least 10 times greater, the useful component will be indistinguishable. To highlight this useful component, it is necessary to use a multi-frequency method for selecting signals from defects against interference.

 The essence of the proposed method is as follows. First, using radiation at three frequencies, a signal from the defect is extracted in the real amplitude scale in all those channels, which allows one to have pulses reflected from the defect at three frequencies, i.e. Obtain the necessary data to analyze the shape of the envelope of the spectrum, and therefore the nature of the defect. The analysis is carried out by comparing the amplitudes of the pulses with the reference envelopes, which are obtained from known static data that reflect a particular defect. In principle, it is possible to emit pulses and at a larger number of frequencies three is the necessary minimum.

 The proposed device allows to solve the specified technical problem and to obtain a technical result due to the fact that a flaw detector containing a synchronizer, excitation pulse generators, a sweep generator and a backlight pulse generator, delay and coincidence circuits, piezoelectric transducers, an amplitude meter, a signal indicator and signal reception and processing channels connected to piezoelectric transducers, and outputs to the inputs of the matching circuit and consisting of series-connected amplifiers, delay circuits, except the last and normalized pulse shapers, it is equipped with a resolver, a defect type indicator and additional amplitude meters, the inputs of additional amplitude meters, the number of which is equal to the number of reception and processing channels, connected to the outputs of the reception and processing channel meters, and the outputs of the amplitude meters with inputs of the resolving device connected by an output to a defect type indicator.

 The flaw detector is equipped with one broadband amplifier instead of several selective receiving-amplifying channels at the output of the piezoelectric transducers and three switches, while one of the switches is connected by an input through a shaper to the output of a wide-band amplifier, and by outputs, the number of which is equal to the number of channels with the corresponding inputs of the amplitude meters, and the control inputs both switches are connected to the corresponding inputs of the excitation pulse generators.

 In FIG. 1 shows the envelopes of the spectra of the emitted and reflected signals from typical typical defects, and the corresponding temporal waveforms; in FIG. 2 is a block diagram of a device that implements the developed method; in FIG. 3 voltage plots (waveforms) at the characteristic points of the flaw detector; in FIG. 4 signals on the flaw detector indicator.

 An ultrasonic flaw detector contains a synchronizer 1, connected with generators of 2,3,4 exciting pulses, elements of 5,6 delays, piezoelectric transducers 7,8,9, combined in block 10, a broadband amplifier 11 connected through a former 12 of normalized pulses with a switch 13, elements 14, 15 delays, coincidence element 16, connected through the delay elements 17, 18, 19 to the strobe generator 20, a switch 21 connected via amplitude meters 22, 23, 24 to a resolving device 25, the output of which is connected to an indicator 26 of the type of defects, except besides The chambers of the amplitude meters 22, 23, 24 are connected with the amplitude magnitude indicator 27. The output of the backlight pulse generator 28 and the output of the sweep generator 29 are connected to the corresponding inputs of the signal indicator 30.

Flaw detector works as follows. The synchronizer 1 starts the excitation pulse generators 2, 3 and 4 with a repetition period T _p and a time shift of t ₃ 1/4 T _p (figa, b, c, d), provided by delays 5 and 6. Piezoelectric transducers 7, 8 , 9, placed in block 10, radiate into the product and receive the reflected interference pulses and a signal (Fig. 3d, f, g), which are input to the broadband amplifier 11 and in the form of a sequence of bursts of pulses in real-scale amplitudes (Fig. 3z) arrive simultaneously at the switch 21, the indicator 30 and the shaper 12.

The process of isolating a normalized signal from a defect and suppressing interference occurs as in a known flaw detector, with the only difference being that the real pulses are first converted to normalized ones (Fig. 3 and), then in the switch 13 there is a separation of normalized pulses into three channels corresponding to frequencies f ₁ , f ₂ , f ₃ , and the pulses of the first and second signal, pass through the delay elements 14, 15, receive a delay of 2t ₃ and t _3, respectively, as a result of which all packs of normalized pulses are time-aligned (Fig. 3 k, l, m )

 It should be noted that the delay of normalized pulses is carried out without fundamental complications, while in a known flaw detector, the delay of real pulses requires very complex and expensive circuits, without providing the necessary accuracy. Getting on the coincidence element 16, the pulse packets are compared in time for individual pulses and since the probability of coincidence of the normalized interference pulses is extremely small, only the impulse from the defect will appear at the output of the coincidence element 16 (Fig. 3 n).

The resulting normalized impulse from the defect, passing sequentially through delays 17, 18, 19, the outputs of which are combined, is supplied to the backlight pulse generator 23 and the strobe generator 20 in the form of a triple of pulses. The delay value 17 is equal to 2 t ₃ -t _o and is selected so that the illumination pulses (Fig. 3 o) and strobes (Fig. 3 p) fall into the next period of operation of the channels not at the moment of the coincidence pulse when real impulses from defects have already reached a certain value, and immediately before the moment of arrival of a real pulse, which is achieved by reducing the delay by a value of t _about . Moreover, the value of t _about can be adjusted.

 The sweep generator 29 generates a sawtooth voltage (Fig. 3 p), deploying the indicator beam for the entire period, so that all three bursts of pulses are visible. The illumination pulses (Fig.3 o) emit only signals from defects with increased brightness, which allows the operator to immediately assess the type of defect. Packs of real pulses (Fig. 3 h) after the switch 21 are divided into channels (Fig. 3 s, t, y) and fed to meters 22, 23, 24, which measure only those pulses that fall into their strobe (Fig. 3 o p).

From the outputs of the voltage meters, corresponding to the amplitudes of the real pulses from the defects of all channels, they are sent to a resolver that determines the type of defect according to the algorithm laid down in it (for example, A ₁ > A ₂ > A _{3 a} flat inclined defect; or more complex, when angle of inclination), and indicates it on the indicator 26 of the type of defect. At the same time, it remains possible to determine with the help of the amplitude indicator 27 the equivalent defect value for any of the channels.

 The switches 13 and 21 are controlled by the same pulses as the generators 2, 3, 4 of the exciting pulses.

Claims (2)

 1. The method of ultrasonic inspection of products from coarse-grained materials, which consists in the fact that ultrasonic pulses with an oscillation frequency in the range of 0.5 to 10.0 MHz are emitted into the controlled product, receive reflected pulses at the same frequencies and form the resulting envelope of the spectrum of the received signals, compare it with the standard envelopes of the spectra of typical defects and the result of the comparison judge the type of defect, characterized in that the ultrasonic pulses emit at several vibration frequencies, the values of which you irayut extreme points of reference envelopes of spectra of typical defects, is separated from the received useful signal pulses from noise by Equation travel times of the echo signals at different frequencies, and spectral envelope shape for dominating the selected signals relative to the reference which is judged on the type of defects.  2. An ultrasonic flaw detector for monitoring products from coarse-grained materials, containing a synchronizer, 2N -1 delay elements, N channels from serially connected exciting pulse generator and piezoelectric transducer, normalized pulse shaper, coincidence element and indicator, input of the nth exciting pulse generator is connected to the output synchronizer through n -1 series-connected delay elements, where n- 0,1,2, N, characterized in that it is equipped with a broadband amplifier connected between the outputs all x piezoelectric transducers and the input of the normalized pulse generator, the first switch, N outputs of which are connected to the N inputs of the coincidence element, except the last, through the corresponding delay elements, and the output to the output of the normalized pulse generator, the second switch, N amplitude meters connected to the outputs of the second switch, the third switch, the amplitude magnitude indicator, the decisive unit, the defect indicator connected to it, the strobe generator connected to the gate inputs amplitude amplifiers, the outputs of which are connected to the inputs of the decisive unit and through a third switch with an amplitude value indicator, a sweep generator connected between the synchronizer output and the indicator input, and a backlight pulse generator, the output of which is connected to the indicator input connected to the signal input with the output of the broadband amplifier, the remaining N delay elements are connected in series, the input of the first of them is connected to the output of the coincidence element, and their outputs to the corresponding inputs of the strobe generator and generator illumination pulses.

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