SU1569693A1 - Method of magnetic flaw detection - Google Patents

Abstract

This invention relates to the field of non-destructive testing. The purpose of the invention is to improve the accuracy and reliability of the control. For this, the readout of the magnetic field of the scattering is carried out twice at each point of the test surface at a time interval T = T / 4 + KT / 2, where T is the period of change of the magnetizing field

K = 0, 1, 2 ..., and the presence of a defect is judged by the magnitude of the product of the sum of the signals read at one point by the value of the largest of them. This makes it possible to eliminate the omission of defects in connection with the periodic equality to zero of the strength of the field of dispersion of defects. 1 il.

Description

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The invention relates to the field of non-destructive testing and can be used in various industries, in particular, in power engineering, for example, for inspection of the welded joints of boiler units.

The purpose of the invention is to improve the accuracy and reliability of control by equalizing the sensitivity during the period of changing the magnetizing field and eliminating the omission of defects.

The drawing shows a block diagram of a flaw detector that implements the method of magnetic flaw detection.

The flaw detector contains an electromagnet 1, a generator 2, two magnetically sensitive elements, for example, a Ferrox converter 3 and 4,

two identical measuring channels 5 and 6, each of which consists of series-connected selective amplifiers 7 and 8, detectors 9 and 10, threshold blocks 11 and 12, peak detector 13, pulse shaper 14, adder 15, signal multiplier J6, defect recorder 17 , the comparator 18 and the switch 19. The input of the imaging unit 14 pulses and the measuring input of the peak detector 13 are connected to the output of the measuring channel 8. To the output of the imaging generator 14

connected to the control input of the peak detector 13, the output of which is connected simultaneously to one of the inputs of the adder 15, the switch J9 and the comparator 18, the second inputs of which are connected to the output of the additional measuring channel. Compael output

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connected to the control of the controller 19. The multiplier with 16 strokes is connected to the output 15 and the switch 19, and 17 to the recorder 17 defects. The amplifiers 7 and 8 pick out the second harmonic of the waiting frequency of the flux-gate transduce 3 and 4, the Shaper 14 "d can be performed, for example, p v to a C in d (p n w sh 1 p 1 p p s | p

measures in the form of a one-shot. It is triggered from the front edge of the incoming signal and produces a short reset pulse for the peak detector 13 Over a time slightly longer than t T / 4 + k T / 2. The distance S between converters 3 and 4 is specified from the condition: S V-t, where V is the speed of movement of the converters. 20

The converter 3 is located first in the direction of movement in the control, which is performed at a constant speed in one direction. Registrar ZoMo, ls. 25, for example, in the form of a series-connected threshold block, a defect signal generator and a signaling device. Switch 19 is dual channel. If its control input is not on the direct current, one of its channels is open and the other is locked. If the control input is energized, the channel state is reversed.

At the output of the comparator 18, the presence or (. Absence of voltage is determined by the ratio of the amplitudes of the signals at its inputs. Electromagnet 1 o produces a low-frequency alternating magnetic field, for example, with a frequency of 50 Gi. The flaw detector is used for speed control.

The method is carried out as follows.

The electromagnet 1 with the flux-gate transducers 3 and 4 placed between its poles moves along the surface of the tested product (not shown). In the absence of defects from the outputs of flux-gate transducers 3 and 4, signals are not received, the recorder does not work.

If there is a defect in the monitored product, transducers 3 and 4 are alternately passed over it. Three options are possible for the signals to the inputs of the measuring channels 5, depending on the magnetization of the contact

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rolling area during the passage of converters 3 and 4 above the defect. Let the transducer 3 (first in the direction of scanning) pass through, the intensity of the magnetizing field is not zero. Then, a voltage appears at the ends of its measuring winding, which is fed to the input of measuring channel 5. The second harmonic of the excitation current frequency of fluxgate transducers (excitation is carried out by generator 2) is highlighted by a selective amplifier 7. The detected signal goes far to the input of the threshold unit 11. If the amplitude of the signal exceeds a predetermined threshold of the block 1 1 ,, it arrives at the inputs of the peak detector 13 and the driver 14 pulses. The voltage from the output of the peak detector 13, equal to the amplitude of the signal received from the output of the measuring karala 5, is applied to one of the inputs of the adder 15, the switch 19 and the comparator 18. The voltage is maintained until the control input of the peak the detector 13 will not receive a reset pulse from the imaging unit 14. After time t, the second transducer 4 passes over the defect. If, when it passes over a defect, the field strength is not zero, a signal is also input to the measuring channel 6, which is processed in the same way as the measuring channel 5. The signal goes to the second input of the adder 15, the switch 19 and the comparator 18. From the output the adder 15, a signal equal to the sum of the amplitudes of the signals, is fed to one of the inputs of the multiplier 16. At its second input, the output of the switch 19 simultaneously sends a signal whose amplitude is equal to the amplitude of the largest of the signals received from the outputs of the measuring channel 5 and 6. This is accomplished by the comparator 18 which controls the switch operation depending on the ratio of signal amplitudes at its input.

From the output of the multiplier 16, the signal, whose amplitude is equal to the product of the sum of the amplitudes of the signals received from the outputs of both measurement channels 5 and 6 and the amplitude of the largest of these signals, goes to the recorder 17. If the signal from the output of the multiplier 16 is

the recorder 17, exceeds the rejection level specified in its threshold block, the alarm goes off. Defect will be registered.

Another option is possible when, when the first in the direction of the converter 3 passes over the defect, the intensity of the magnetizing field is zero, then during the passage

of the second transducer 4 over the defect, the field strength is maximal (since the scanning speed is constant, and the distance between the transducers is chosen in a certain manner). The signal comes only from the output of the measuring channel 6, then through the adder 1 5 and the switch 1 9 goes to the two inputs of the multiplier 16. To the output of the multiplier 16, the signal amplitude is equal to the square of the amplitude of the signals to its inputs (since they are equal in amplitude). If the amplitude exceeds the threshold of the recorder 17. the defect is registered.

A third option is also possible, when the field strength when passing the first converter 3 is maximum, and when passing the second one is equal to zero, then the signal comes only from the input of measuring channel 5, and is fed to one of the inputs of the adder 15, switch 19, comparator 18. Amplitude The signal at the output of the multiplier 16 is also equal to the square of the amplitude of the signals at its inputs.

Summing the amplitudes of the signals from two transducers 3 and 4, successively passing over the defect after a certain time, and multiplying the sum by the amplitude of the largest of these signals makes it possible to equalize the sensitivity during the period of change of the magnetizing field, which improves the accuracy and reliability of control.

Improving the accuracy and reliability of the control with the help of the proposed method can be seen in the following example. In known flaw detectors, when magnetising a controlled product with a variable field, the amplitude of the signal from a ferro probe converter from the same defect can vary from zero to, since the converter can pass over the defect at any time during the period of magnetizing change.

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gender (Umax - maximum value of the signal amplitude from this defect). Sensitivity varies, it is possible to skip defects.

In the proposed flaw detector, the sum of the amplitudes of the signals at the output of the sweeper 15 is never zero, since the fluxgate transducers 3 and 4 are located at a certain distance from each other. The amplitude of the signal at the output of the multiplier 16 for the same

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1.21 U fr.qx, which is much less than in known flaw detectors. Indeed, if the first of the transducers 3 crosses the defect at the moment when the intensity of the magnetizing field is maximum, then the signal

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the output of the multiplier J 6 is II tstx. When the first transducer intersects a defect 3 through time, for example, 1G / 4 after the moment when the magnetizing field is zero, the amplitude of the signals of both transducers 3 and 4 is 0.71 UmaK. At the output of the multiplier 16, the signal is equal to Um x, and if the first converter 3 crosses the defect through time fr / b, then the signal amplitude at the output of the multiplier 16 is equal to

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Claims (1)

Invention Formula The method of magnetic flaw detection, in which the magnetizing and magnetically sensitive elements are moved relative to the product under test, is magnetized by an alternating magnetic field, the magnetic fields of the magnetosensitive element are read and an amplitude analysis of its output signals is performed, characterized in that to increase the accuracy and reliability of the control, the reading of the magnetic fields of the scattering is performed twice at each point of the test surface with a time interval chosen from ratios t T / 4 + QD / 2, where T is the period of change of the magnetizing field; K is an integer equal to O ,, 2, ..., and the presence of a defect is determined by the magnitude of the product of the sum. the signals of the magnetosensitive element read at the same point by the magnitude of the larger of these signals. "about