SU938123A1 - Electromagnetic method of measuring depth of lengthy electroconductive object flaws - Google Patents

Description

(5) ELECTROMAGNETIC METHOD OF MEASUREMENT OF DEEPER DEFECTS OF EXTENDED ELECTROCONDUCTING

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The invention relates to a control breakdown and can be used to monitor extended electrically conductive objects.

The known method of electromagnetic defectometry, which means that a controlled object is affected by alternating magnetic fields of several frequencies, a change in the magnetic field in a defect-free and controlled area is measured using an inductance coil, eddy currents are produced, the harmonic components of the resulting signal, convert the multidimensional signal by multiplying it by a matrix of coefficients and determine the depth of the defect lj by the result obtained.

The disadvantage of this method lies in the low accuracy of measuring the depth of defects, which is associated with poor accuracy of the OBJECTS

| conversion of a multidimensional signal when the parameters of the object being monitored are varied over a wide range.

The closest to the technical essence is the electromagnetic method for measuring the depth of defects of extended electrically conducting objects, which is due to the fact that an alternating electric current is passed through the test object and the signal of the magnetic field measuring transducer 2j is analyzed due to the interaction of the defect with this current

However, the known method does not provide the necessary accuracy for determining the depth of defects.

The purpose of the invention is to increase the accuracy of measuring the depth of defects. .

The goal is achieved by the fact that, according to the method of measuring the depth of defects of extended electrically conducting objects, a current of another frequency is passed through the product, the amplitude of both received signals, due to the interaction of the defect with the current of this frequency, is measured. according to the corresponding conversion factors of magnetic fields, depending on the frequency of change, the magnetic fields compare the normalized amplitudes of both signals with j, adjust the amplitudes The volume of at least one of the currents passed through the object to the equality of the compared amplitudes of signals, the amplitudes of the currents passed through the object being monitored are measured, and the depth of the defect is determined from them. At the same time, the depth of the defect is determined by the ratio of the amplitudes of the currents passed through the monitored object, or by the difference of the ampli tudes of the currents passed through the monitored object, normalized by the amplitude of one of these currents. FIG. 1 shows the distribution of current densities of two frequencies in the thickness of the monitored object in FIG. 2 is a plot of the ratio of the currents transmitted by the object to the depth of the defect. Curve 1 corresponds to the distribution of current density 3 over the thickness of the object being monitored in a given pipe with an internal radius R and external radius at a higher frequency, curves 2 and 3 to the distribution of current density 3 at a lower frequency at two different values of this frequency flowing through the cross section. The pipe, curve k (Fig. 2), shows the relationship between the depth h of the defect in the pipe and the measured ratio of the low and high frequency currents. The method is carried out as follows. Across the controlled object (pipes pass an alternating electric current of higher frequency, distribute the thickness over the pipe thickness in accordance with curve 1. With the help of a primary measuring instrument, a magnetic field transducer installed permanently or a controlled object moving on the surface of the object being monitored. For this For the purpose, it is advisable to use a differential converter that measures the component of the magnetic field that occurs when the current flows around the alternating current 3, for example The signal is normal to the surface of the object being monitored and, therefore, generates a signal only under the action of a defect of continuity. Then a low frequency current is passed, distributed over the pipe thickness in accordance with curve 2, and the signal due to the interaction of the defect with the lower frequency is passed. and the higher frequencies are normalized by the conversion factors of the primary transducer, depending on the frequency of the measured signal. In particular, when using an induction converter, it is necessary to normalize the amplitudes of the signals over the frequency f of the change in the corresponding signal. Then, the difference between the normalized amplitudes of the signals is obtained, which is determined by the difference between the high and low frequency currents flowing in the annular layer of the monitored pipe enclosed between the radii R 2 and h. According to the principle of equivalence of the effect of a defect, it can be represented by the same distribution current density, as in the whole pipe, but the opposite phase in the defect volume. Thus, we have Hf (R) -r3 d, where H is the magnetic field due to the defect; f {lO is a function depending on the distance between the measuring transducer and the defect, V is the volume of the defect; 3 - current density in a solid object. Since the function f (R) does not depend on frequency, the magnitudes of the magnetic fields acting on the measuring transducer are determined only by the difference in the total current flowing through the defect. However, the latter is completely determined by the difference in the high and low frequency currents flowing in the specified layer. Consequently, if these currents are equal, the magnitudes of the magnetic fields, due to the defect of the normalized amplitudes of the higher and lower frequencies, should be equal to each other. By adjusting the amplitude of at least one current flowing through the pipe, for example, the lowest hour 59m, the currents flowing through the annular layer are equal (2 2. ° to the first approximation corresponds to the equality of the areas AffCp and AEFD (Fig. O. However, if the specified condition is met the ratio of the high and low frequencies flowing through the pipe is uniquely related to the depth of the defect. Consequently, measuring the ratio of the amplitudes of these currents can determine the depth of the defect. The calibration curve is calculated analytically from the known function current density distribution in a tube and has the form shown in Fig. 2. When measuring the depth of small defects, it is advisable to measure the difference in the amplitudes of the currents of the higher and lower frequencies, also uniquely related to the depth of the defect, and to be able to use one calibration curve for different values x currents, the resulting difference is normalized by the amplitude of the current of one of the frequencies, for example, the eaves. The proposed method makes it possible to measure the depth of defects regardless of its opening and transverse dimensions, the ability to measure the depth of the defect regardless of the relative position of the measuring transducer and the defect, which is especially important for continuous monitoring with stationary mounted transducers. The combination of these advantages allows to increase the reliability of the control and simplify the circuit of the primary transducers by reducing the number of stationary transducers. invention 1. Electromagnetic method of measuring the depth of defects of 3 extensive electrically conductive objects, which consists in passing an alternating electric current through the test object and analyzing the magnetic field transducer caused by the interaction of the defect with this current, different from that To increase the measurement accuracy, a current of a different frequency is passed through the product, measured due to the interaction of the defect with the current C (frequency signal of the measuring transducer magnetic field, normalize the amplitudes of the received signals according to the respective conversion factors of magnetic fields depending on the frequency of changes of magnetic fields, compare the normalized amplitudes of both signals, regulate the amplitude of at least one of the currents transmitted through the object to equal the compared amplitudes of the signals, measure the amplitudes currents passed through the controlled object, and the depth of the defect is determined from them. 2. Method pop. 1, characterized in that the depth of the defect is determined by the ratio of the amplitudes of the currents passing through the monitored object. 3. Method pop.1, which is also distinguished by the fact that the depth of the defect is determined by the difference in the amplitudes of the currents transmitted through the counter-object, normalized by the amplitude of these tones. Sources of information are taken during examination t. USSR author's certificate V 7v973b kl. 6 01 N 27/90, 1978.. 2. USSR author's certificate in application 2bO 87b / 25-28, k. G 01 H 27/90, 978 (prototype).

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Claims (3)

Claim 1. The electromagnetic method for measuring the depth of defects extended 938123 ⁴ electrically conductive objects, which consists in the fact that an alternating electric current is passed through the control object and the signal of the measuring magnetic field transducer due to the interaction of the defect with this current is analyzed, which is different in order to increase the measurement accuracy, another current is passed through the product frequency, measure the signal of the measuring transducer of the magnetic field due to the interaction of the defect with the current of this frequency, normalize the amplitudes of both received signals according to the corresponding The conversion factors of magnetic field values, depending on the frequency of change of magnetic fields, compare the normalized amplitudes of both signals, adjust the amplitude of at least one of the currents passed through the object to the equality of the compared signal amplitudes, measure the amplitudes of the currents passed through the controlled object, and determine the depth from them defect. 2. The method of pop. ^ characterized in that the defect depth is determined by the ratio of the amplitudes of the currents passed through the controlled object. 3. The method of pop. 1, the difference between real and th is that the defect depth is determined by the difference in the amplitudes of the currents passed through the controlled object, normalized by the amplitude of one of these TOMS, Sources of information taken into account during the examination 1. USSR copyright certificate V 7 "9731, cl. G 01 N 27/90, 1978.. 2. USSR author's certificate on application 2604876 / 25-28, cl. G 01 And 27/90, 1978 (prototype).