RU2834598C1 - Rail ultrasonic inspection method - Google Patents

Abstract

FIELD: measuring.

SUBSTANCE: invention can be used for ultrasonic inspection of rails. An ultrasonic transducer (UST) is placed in a given scanning zone and control operations are carried out, including probing with ultrasonic frequency pulses, recording of reflected signals by means of flaw detector with provision of their visualization in the form of amplitude-time scanning. A time zone corresponding to a given scanning zone is selected on the sweep, the aperture of which is selected from the condition that the probing pulse does not enter it, a signal utility criterion is set, and reflected signals recorded in this time zone are analysed. UST is moved in scanning zone and control operations are repeated. In the allocated time zone, the arithmetic mean value of the amplitudes of the received signals is determined through a step specified by the flaw detector, amplitude N of which is in the range satisfying the condition N ≤ N₁ – N₂, where N₁ is the dynamic range of signals displayed on the flaw detector screen, N₂ is the criterion for qualifying the signal as useful. Signal usefulness criterion is exceeding of its amplitude of this arithmetic mean value by N₂ ≥ 12 dB. Each signal, the amplitude of which exceeds the obtained arithmetic mean value by the value N₂ ≥ 12 dB, in a given scanning area is formed as a result of accumulation due to additional summation of signals taking into account time shift of signals relative to each other, corresponding to movement of UST during scanning, in n scanning cycles, in which the amplitude of the received signals exceeds the level of -6 dB within the boundaries of the main lobe of the beam pattern of the UST. Wherein n = m, where m is the number of maxima of these signals.

EFFECT: providing the possibility of increasing the reliability of ultrasonic testing of rails.

1 cl, 7 dwg

Description

The invention relates to the field of non-destructive ultrasonic testing of rails and can be used in ultrasonic flaw detection of rails of railway infrastructure and subway systems.

One of the pressing issues in the field of continuous ultrasonic testing of rails is the problem of identifying a useful signal on an ultrasonic defectogram against a background of noise and interference.

The known methods of ultrasonic testing of rails are overwhelmingly based on measuring the amplitude of the received signal from a defect or artificial reflector and then measuring the noise level on a defect-free section of the rail. After collecting statistical data, a conclusion is made that upon detection of a reflector (defect or structural element) of certain dimensions, the required signal/noise ratio with a given probability will be ensured. In this case, to set the rejection sensitivity, a received signal is received from the control reflector, and a sign of detection of a defect is the receipt of a received signal with an amplitude exceeding a given level, which is the rejection level (Interstate standard GOST 18576-96. "Non-destructive testing. Railway rails. Ultrasonic methods". Publishing house of standards. Moscow, 2001). However, the range of visible signals below the standard level (half the height of the flaw detector screen) is visually limited, and adding gain (increasing sensitivity) to detect defects at an early stage of development (small sizes) does not produce results, since in addition to useful signals, the amplitude of noise signals also increases, which with a high degree of probability can lead to false rejection.

For example, a method of ultrasonic testing of rails is known, in which an ultrasonic transducer is placed in a given scanning zone and testing operations are carried out, including probing with ultrasonic frequency pulses, recording of received signals by means of a flaw detector with provision of their visualization in the form of an amplitude-time sweep, allocation of a time zone (selection zone) corresponding to the given scanning zone, the aperture of which is selected from the condition of non-inclusion of the probing pulse in it, setting the criterion of the signal usefulness in the form of a strobe pulse, the level of which corresponds to the given sensitivity of testing, and analysis of the received signals recorded in this time zone, moving the ultrasonic transducer in the scanning zone and repeating the testing operations (A.A. Markov, D.A. Shpagin. Ultrasonic flaw detection of rails. Study guide. "Education-culture", St. Petersburg, 2008, pp. 51-53, 88-100). In this method, a strobe pulse is used to set the signal usefulness criterion in accordance with the specified control sensitivity at which a minimal defect can be detected. In this case, the flaw detector identifies the received signal as useful when it falls within the allocated time zone and its level exceeds the strobe pulse level.

However, this method does not provide sufficiently reliable results, which is due to the dependence of the testing results on the quality of the acoustic contact of the ultrasonic transducer with the tested object and the influence of subjective factors, such as incorrect sensitivity settings. This disadvantage of the method is especially evident during continuous testing of rails at high speeds. Loss of acoustic contact is inevitable, and a significant drop in the level of reflected signals leads to the omission of defects in the rail. Another situation is also possible, in which there is a significant increase in signal amplitudes, leading to re-rejection. Therefore, the traditional testing method, which consists of making a decision on rejection "from above", has a low level of reliability of the testing results.

Also known is a method of ultrasonic testing of rails, in which an ultrasonic transducer is placed in a given scanning zone and testing operations are carried out, including probing with ultrasonic frequency pulses, recording the received signals by means of a flaw detector with provision for their visualization in the form of an amplitude-time sweep, selecting a time zone corresponding to the given scanning zone on it, the aperture of which is selected from the condition of non-entry of the probing pulse into it, setting a signal usefulness criterion and analyzing the received signals recorded in this time zone, including determining their amplitudes after a given period of time, moving the ultrasonic transducer in the scanning zone and repeating the testing operations, while in the selected time zone an adaptive threshold is formed on the basis of the rate of rise of the leading edge of the received signal over a given period of time and the offset added to the amplitude of the noise signal, the values of which are selected depending on the type of the ultrasonic transducer used, the criterion for the usefulness of the signal is the excess of the adaptive threshold by the signal amplitude at a given rate of rise of the leading edge of the signal and if the increment of the amplitude over a given the time interval is greater than the specified value, the adaptive threshold is formed from this specified value, and if this increment is less than the specified value or equal to it, the adaptive threshold is considered to completely repeat the signal shape and, accordingly, the signal is considered noise (RU 2662464 C1, 2018).

However, in this method, the selected parameters for calculating the adaptive threshold depend significantly on the nature of the analyzed signals (for example, with a smooth or sharp increase/decrease in the ultrasonic frequency pulse). This also reduces the reliability of ultrasonic testing of rails.

Of the known methods, the closest to the proposed one is the method of ultrasonic testing of rails, in which an ultrasonic transducer is placed in a given scanning zone and testing operations are carried out, including probing with ultrasonic frequency pulses, recording reflected signals using a flaw detector with provision of their visualization in the form of an amplitude-time sweep, selecting a time zone on it corresponding to a given scanning zone, the aperture of which is selected from the condition of not including a probing pulse in it, setting a criterion for the usefulness of the signal and analyzing the reflected signals recorded in this time zone, moving the ultrasonic transducer in the scanning zone and repeating the testing operations, in the selected time zone determining the arithmetic mean value of the amplitudes of the received signals through a step set by the flaw detector, the amplitude N of which is in the range satisfying the condition N ≤ N ₁ - N ₂ , where N ₁ is the dynamic range of the signals displayed on the flaw detector screen, N ₂ is the criterion for qualifying the signal as useful, and the excess of its amplitude over this arithmetic mean value is selected as the criterion for the usefulness of the signal by the value N ₂ ≥ 12 dB (RU 2472143 C1, 2013). The time zone in this method is selected from the time aperture based on the condition that the probing ultrasonic pulse does not enter this zone, since due to its significant amplitude it can introduce a significant error in the calculation of the arithmetic mean value of the signal amplitudes in the selected time zone. To calculate the arithmetic mean value of the signals, a range of amplitudes is used such that the amplitude N of these signals does not exceed the difference between the dynamic range N ₁ of the signals displayed on the flaw detector screen and the criterion N ₂ for qualifying the signal as useful. This approach to determining the arithmetic mean value of reflected signals (echo signals) is the most optimal, it allows, in particular, to eliminate the uncertainty in making a decision on the usefulness of signals when they have a significant amplitude, for example, signals from reflectors in the form of structural elements in rails.

However, this method also does not provide the required reliability of ultrasonic testing of rails. This is due to the following circumstances. Even outside the area of bolted or welded joints, defectograms may contain a large number of noise signals (noise tracks) associated with the diffuse reflection of ultrasonic waves from various areas of the rail head and caused by the quality of reflecting surfaces (e.g., contamination, a network of thermal cracks). Noise signals may have an amplitude commensurate with the amplitude of the received useful (main) signals. Therefore, the arithmetic mean value of the amplitudes of noise signals in each emission-reception cycle may reach significant values, which in turn may lead to only a slight excess of the useful signal over the noise level, and, consequently, to the omission of defects. In addition, the presence of noise tracks and the noise background as a whole significantly complicates the process of visual assessment of defectograms.

The technical problem solved by the invention consists in creating a method of ultrasonic testing, devoid of the disadvantages of the prototype. The technical result of the invention consists in increasing the reliability of ultrasonic testing of rails.

This is achieved by the fact that in the method of ultrasonic testing of rails, in which an ultrasonic transducer is placed in a given scanning zone and testing operations are carried out, including probing with ultrasonic frequency pulses, recording reflected signals by means of a flaw detector with provision of their visualization in the form of an amplitude-time sweep, allocation of a time zone corresponding to a given scanning zone on it, the aperture of which is selected from the condition of non-entry of the probing pulse into it, setting the criterion of signal usefulness and analysis of the reflected signals recorded in this time zone, moving the ultrasonic transducer in the scanning zone and repeating the testing operations, in the allocated time zone the arithmetic mean value of the amplitudes of the received signals is determined through a step set by the flaw detector, the amplitude N of which is in the range satisfying the condition N ≤ N ₁ - N ₂ , where is the dynamic range of the signals displayed on the flaw detector screen, N ₂ is the criterion for qualifying the signal as useful, and the excess of its amplitude of this arithmetic mean value by the value N is selected as the criterion of signal usefulness. ₂ ≥ 12 dB, each signal, the amplitude of which exceeds the obtained arithmetic mean value by the value N ₂ ≥ 12 dB, in a given scanning zone is formed as a result of accumulation due to additional summation of signals taking into account the time shift of the signals relative to one another, corresponding to the movement of the ultrasonic transducer during scanning, in n scanning cycles, in which the amplitude of the received signals exceeds the level of -6 dB within the boundaries of the main lobe of the directional pattern of the ultrasonic transducer, where n = m, where m is the number of maxima of these signals.

The specified technical result is ensured by the entire set of essential features presented in the invention formula, each of which is necessary, and together they are sufficient to solve the specified technical problem and to achieve the specified technical result.

The claimed invention is dependent on the invention protected by Russian patent No. 2472143.

Fig. 1 shows the flaw detection information in the form of a fragment of a type B scan. Fig. 2 shows the sequence of reflected signals from one reflector when moving the ultrasonic transducer along the rail in the form of type A scans. Fig. 3 explains the time shifts of signals when moving the ultrasonic transducer relative to the reflector in the rail. Fig. 4 shows an example of the number of cycles involved in summation and averaging when accumulating signals. Figs. 5 - 7 show the results of implementing the invention.

In accordance with the proposed method, a time zone is allocated in one emission-reception cycle of an ultrasonic, predominantly piezoelectric, transducer installed on a controlled rail for calculating the arithmetic mean value of the amplitudes of the received signals in it. The time zone is selected from the time aperture based on the condition that the probing pulse does not enter this zone, since due to its significant amplitude it can introduce a significant error in calculating the arithmetic mean value of the signal amplitudes in the selected time zone. To calculate the arithmetic mean value of the signals, a range of amplitudes is used such that the amplitude N of these signals does not exceed the difference between the dynamic range N ₁ of the signals displayed on the flaw detector screen and the criterion N ₂ of qualifying the signal as useful. The criterion of usefulness in the form of exceeding the value of 12 dB was established experimentally. This approach to determining the arithmetic mean value of the reflected signals allows, in particular, to eliminate the uncertainty in making a decision on the usefulness of signals when they have a significant amplitude, for example, signals from structural elements in rails. Such signals make a significant contribution to the average signal level, which is fraught with an increase in this level and, accordingly, could lead to the omission of defects.

The peculiarity of the proposed method is accumulation of signals during continuous ultrasonic testing of rails by summing the signals taking into account the time shift of the signals relative to one another. The shift is caused by the difference in the time of arrival of ultrasonic waves from the ultrasonic transducer to the reflector and back when the ultrasonic transducer moves along the rail with a set scanning pitch, for example, 5 mm. Since during ultrasonic testing of rails, for example, by means of a mobile vehicle, the ultrasonic transducer, i.e. the emitter-receiver, moves relative to the reflector, therefore the signals from the reflector are always received by the ultrasonic transducer at certain intervals relative to one another. A three-dimensional image (type B scan) of one of the variants of a set of signals that are displayed on a defectogram when the ultrasonic transducer passes several sections (cross-sections) of the rail with reflectors located in them is shown in Fig. 1. The fragments of the type B scan shown in Fig. 1 can be presented as a set of type A scans of the same signal. Fig. 2 shows several type A scans of signals explaining the physics of the process. As can be seen from Fig. 2, the useful signal 1 from the same reflector changes both in amplitude and in duration when the ultrasonic transducer moves along the rail. The same situation occurs with the noise signal 2. When accumulating signals by summing them when the ultrasonic transducer moves along the rail, it is necessary to take into account their time shift (time shift) Δt relative to one another in each scanning cycle (Fig. 3). In this case, simultaneously with the summation of the useful signal, the summation of noises occurs, which have a random amplitude value. Their summation and averaging reduces their energy weight in the overall ultrasonic picture when testing rails, since noise signals, as a rule, do not have an envelope, and their amplitude is random in nature without pronounced increases and decreases. The main parameters of signal accumulation during ultrasonic testing of rails, in addition to the value of the time shift of signals when changing the mutual arrangement of the ultrasonic transducer-reflector pair during rail scanning, include the number n of scanning (summing) cycles involved in summing and averaging. The number n of scanning cycles is defined as the number m of amplitude maxima of the received signals from the reflectors within the boundaries of the main lobe of the ultrasonic transducer radiation pattern at the level of -6 dB (n=m). In this case, for noise signals, the value n is, as a rule, significantly less than for useful signals. This parameter is graphically illustrated in Fig. 4 for n=13. The choice of the value of the level -6 dB is due to the need to exclude the possibility of missing defects when they are detected by something other than the main lobe of the radiation pattern, which is ensured by setting the search sensitivity to be twice as high as the control sensitivity, i.e. by 6 dB. Such signal processing during ultrasonic flaw detection leads to a significant reduction in the display of interference on the defectogram and an increase in the clarity of selecting useful signals from reflectors in the rail against the background of interference and noise. This improves the quality of display of ultrasonic rail testing data, for example, in the form of a B-type scan, and minimizes the number of extraneous (non-useful) low-amplitude signals, which allows for objectively detecting and identifying defects in rails with sufficient accuracy and, accordingly, increasing the reliability of ultrasonic rail testing.

Examples of implementation. Operations of continuous ultrasonic testing of rails were carried out on the test section of the Moscow Center for Diagnostics and Monitoring of Perovo-4 Devices using the mobile testing facility of the SUPDK SEVER railcar equipped with the ECHO-COMPLEX-2 multichannel flaw detector (manufactured by JSC Firma TVEMA). The testing results were compared without signal accumulation in accordance with the prototype method and with signal accumulation in accordance with the proposed method. The testing results are explained by fragments of defectograms in Fig. 5 - Fig. 7, which display type B scans from a number of reflectors in the rails obtained by the prototype method (images I) and the proposed method (images II). In this case, the signals recorded by the ultrasonic transducers emitting in the direction of the railcar movement (approaching) are indicated on the defectograms in blue, and the signals recorded by the ultrasonic transducers emitting ultrasonic waves in the direction opposite to the direction of the railcar movement (departing) are indicated in yellow. The same reflector on the defectogram is recorded by both the approaching and departing ultrasonic transducer. The defectograms in Fig. 5 and Fig. 6 were obtained using a piezoelectric transducer with an input angle of 42 degrees without rotation as the ultrasonic transducer. The defectograms in Fig. 7 were obtained using a piezoelectric transducer with an input angle of 58 degrees and a rotation relative to the longitudinal axis of the rail of 34 degrees as the ultrasonic transducer. In Fig. 5, defectograms I and II show signals from the bolt holes of the bolted joints and a signal from a defect in the form of a horizontal crack in the fillet transition from the head to the web of the rail with an outlet on the end surface of the rail. In Fig. 6, defectograms I and II show a number of signals from the bolt holes of the bolted joints and one signal from a defect in the form of a crack developing from the cylindrical wall of the bolt hole of the bolted joint. In Fig. 7, defectograms I and II show two signals from two artificial reflectors simulating transverse cracks in the rail head. From the images provided, it follows that the proposed method provides, in comparison with the prototype method, a significantly higher quality of display of ultrasonic rail testing data, a virtually complete elimination of noise signals 2 and an increase in the conventional dimensions of reflectors in the rails. Multiple repetitions of the passes showed the same result, while no cases of missing defects were recorded.

The tests conducted confirm the conclusion about the increased reliability of ultrasonic testing of rails compared to the prototype method.

The method of ultrasonic testing of rails, implemented in accordance with the invention, ensures higher reliability of ultrasonic testing of rails compared to similar known methods.

Claims (1)

A method of ultrasonic testing of rails, in which an ultrasonic transducer is placed in a specified scanning zone and testing operations are carried out, including probing with ultrasonic frequency pulses, recording reflected signals by means of a flaw detector with provision for their visualization in the form of an amplitude-time sweep, selecting a time zone on it corresponding to a specified scanning zone, the aperture of which is selected from the condition of not including a probing pulse in it, setting a criterion for the usefulness of a signal and analyzing the reflected signals recorded in this time zone, moving the ultrasonic transducer in the scanning zone and repeating the testing operations, in the selected time zone determining the arithmetic mean value of the amplitudes of the received signals through a step specified by the flaw detector, the amplitude N of which is in the range satisfying the condition N ≤ N ₁ - N ₂ , where N ₁ is the dynamic range of the signals displayed on the flaw detector screen, N ₂ is the criterion for qualifying a signal as useful, and the excess of its amplitude of this arithmetic mean value by the value of N ₂ is selected as the criterion for the usefulness of a signal ≥ 12 dB, characterized in that each signal, the amplitude of which exceeds the obtained arithmetic mean value by N ₂ ≥ 12 dB, in a given scanning zone is formed as a result of accumulation due to additional summation of signals taking into account the time shift of the signals relative to one another, corresponding to the movement of the ultrasonic transducer during scanning, in n scanning cycles, in which the amplitude of the received signals exceeds the level of -6 dB within the boundaries of the main lobe of the directional pattern of the ultrasonic transducer, where n = m, where m is the number of maxima of these signals.