RU2397485C2 - Electro-magnet defectoscope for detection of corrosion defects of walls of ferro-magnet structures - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: facility consists of: generator, attachable transformer-converter containing exciting, measuring, compensating and additional measuring windings forming two differential measuring pairs, phase metre, first, second and third stages of amplifiers, amplitude detector, four digit-analogue converters, four adders, digit indicator, multiplexer, analogue-digit converter, and microprocessor controller.

EFFECT: increased responsiveness of defectoscope to extended corrosion defects both on external and internal sides of structure wall.

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Description

The present invention relates to the field of non-destructive testing (NDT) of parts, assemblies and structures of ferromagnetic steel grades.

A device for eddy current monitoring of corrosion damage of ferromagnetic products, containing a series-connected generator, a transformer converter of the overhead type, comprising an exciting, measuring and compensation inductance coils and a phase meter connected to its second input through a phase shifter with a generator and an indicator [1].

The disadvantage of this device is the low information content of the control, since the device does not allow to detect extended corrosion damage with smooth entry zones due to the use of a differential converter.

Closest to the proposed invention is a device for eddy current monitoring of corrosion damage to metal products, containing a series-connected generator, transformer overhead transducer, including exciting, measuring, compensating and additional measuring inductors, forming two differential measuring pairs, the first of which is connected to the phase meter, and the second - with a compensator connected by a second input to the generator, an amplifier, a second phase meter m, through the adder outputs phase meters connected to the indicator, and their second inputs via phase shifters with generator [2].

The disadvantages of this device include low sensitivity to subsurface defects due to the use of an overhead eddy current transducer, which has a significant influence on the depth of penetration of an electromagnetic field into a controlled medium by a geometric factor (field weakening with increasing distance from the transducer end face).

The aim of this invention is to increase the sensitivity of the flaw detector to extensive corrosion damage located on both the outer and inner sides of the wall of the structure.

This goal is achieved due to the fact that the flaw detector is additionally equipped with an amplitude detector, a multiplexer, an analog-to-digital converter, two three-stage amplifiers, three adders, four digital-to-analog converters, and a microprocessor-based programmable controller; an additional measuring winding is located outside the field winding at a distance of three diameters, complemented by a second compensation winding located above the measuring and forming a second differential pair with an axis perpendicular to the axis of the exciting winding; measuring channels of differential pairs are parallel, consisting of a series-connected first stage of the amplifier; a phase meter in the first channel or an amplitude detector in the second, the first adder, the second amplifier stage, the second adder, the third amplifier stage, the adders with their second inputs connected to the outputs of the digital-analog converters, the outputs of the amplitude detector, phase meter, second and third amplifier stages through the multiplexer are connected with the input of the analog-to-digital converter, the microprocessor controller is connected via the address bus and data bus to the generator, digital-analog and analog-to-digital converters Browsers, multiplexer, third stages of amplifiers, and the functions of push-pull compensation, automatic gain control and piecewise linear approximation are performed by the controller programmatically.

The drawing shows a structural diagram of a flaw detector. The flaw detector consists of a transformer overhead transducer 1 containing an exciting 2 and two differential pairs of measuring 3.1 and 3.2; 4.1 and 4.2 windings, of which 3.2 and 4.2 are measuring, 3.1; 4.1 - compensation, controlled product 5, generator 6, the first stages of amplifiers 7, 8, amplitude detector 9, phase meter 10, digital-to-analog converters (DAC) 11, 14, 17, 20, adders 12, 13, 18, 19, second 15, 16 and the third 21, 22 stages of amplifiers, a digital indicator 23, a multiplexer 24, an analog-to-digital converter (ADC) 25, a microprocessor controller 26.

Measuring pairs of windings 3.2 and 3.1; 4.2 and 4.1 are included in the counter. The measuring windings 4.2, 4.1 are placed outside the field winding 2 by a distance L equal to the three diameters of the winding 2 (L = 3d). The axis of the coils 2 and 4 are mutually perpendicular. Due to this, the electromagnetic field of the transducer in the area of the measuring pair of windings 4.2 and 4.1 contains mainly a longitudinal component of the tension H _x , the value of which decreases along the wall thickness T of the product under test mainly due to the skin effect (the influence of the geometric factor is largely suppressed). The effect of the skin effect is attenuated by choosing a low frequency electromagnetic field (f = 10-200 Hz). Moreover, this arrangement of the windings 4.2 and 4.1 acts as a compensator for the initial converter EMF due to the orthogonal component H _{z of the} excitation winding 2.

The electromagnetic field in the area of the measuring windings 2.1 and 2.2 contains all three components of the field strength H _x , H _y , H _z , and the vertical component H _z makes a significant contribution. Its value in the Z direction largely depends on the diameter of the field winding and the distance h, and therefore, in this zone the field penetrates into the controlled product to a shallow depth.

An electromagnetic flaw detector operates as follows.

Using the exciting winding 2 in the controlled product 5, a low-frequency electromagnetic field is excited, which propagates through the thickness T of the controlled product 5 in its different zones in different ways. In the zone of location of the measuring pair 3.2 and 3.1, the field penetrates mainly into the surface and subsurface layers of the object under control, and in the zone of the location of the measuring pair 4.2 and 4.1 it penetrates the entire thickness T, weakening only due to the skin effect. Therefore, the signals of the measuring pair 3.2 and 3.1 carry information about the appearance of corrosion damage on the outer (relative to the electromagnetic transducer 1) side of the product wall, and the signals of the windings 4.2 and 4.1 - about corrosion damage to both the outer and inner sides. For this reason, the signal amplitude is measured in the measuring channel of the windings 3.2 and 3.1, and the phase is measured in the measuring channel of the windings 4.2 and 4.1. Informative signals of windings 3.2 and 3.1; 4.2 and 4.1, amplified in the first stages of amplifiers 7 and 8, are respectively supplied to an amplitude detector 9 and a phase meter 10, at the output of which the measured amplitude and phase respectively are converted to constant voltage. In the defect-free section of the monitored product, these voltages are compensated at the adders 12 and 13, the second inputs of which are supplied with compensating voltages generated by the DACs 11,14 after measuring the ADC of 25 compensated voltages. Uncompensated voltages then go to the second stages of the amplifiers 15, 16 and are compensated by the adders 18.19, DACs 17, 20, ADC 25 in the second cycle. The compensated voltage is selected using the multiplier 24. Further, the measured voltages are fed to the third stages of the amplifiers 21, 22 and the ADCs are measured for further processing in the microprocessor controller 26, including linearization of the dependences of the measured voltages on the depth of corrosion damage using piecewise linear approximation, as well as correction iju reading phase channel according to the channel signal amplitude value, whereby the sensitivity of the phase equalized channel to the inner and outer walls of corrosion damage to the product. All operations related to the choice of the frequency of the generator 6, with push-pull compensation of informative signals, the choice of voltage measured using the ADC 25, the automatic gain control of the third stages of the amplifiers 22, 23, the linearization of the functional dependences U _out = f (T), control of the digital indicator 23, are produced in the microprocessor controller programmatically. The implementation of push-pull compensation significantly increases the sensitivity of the flaw detector to the thickness of the product wall, and therefore to the depth of corrosion of the metal product.

Information sources

1. Flaw detection, 1968, No. 5, p.113.

2. Auth. testimonial. No. 838545, G01 No. 27/90. Published on June 15, 81, Bulletin No. 22.

Claims (1)

An electromagnetic flaw detector for detecting corrosion damage to the walls of ferromagnetic structures, containing a series-connected generator, a transformer overhead transducer, including exciting, measuring, compensating and additional measuring windings, forming two differential measuring pairs, the first of which is connected to the phase meter, and the second to the amplifier, output the phase meter through the adder are connected to the indicator, and its second input - to the generator, characterized in that, for the purpose of To increase the sensitivity and information content of the control, the flaw detector is additionally equipped with an amplitude detector, a multiplexer, an analog-to-digital converter, two three-stage amplifiers, three adders, four digital-to-analog converters, and a microprocessor-based programmable controller; an additional measuring winding is located outside the field winding at a distance of three diameters, complemented by a second compensation winding located above the measuring and forming a second differential pair with an axis perpendicular to the axis of the exciting winding; measuring channels of differential pairs are parallel, consisting of a series-connected first stage of the amplifier, a phase meter in the first channel and an amplitude detector in the second, first adder, second stage of the amplifier, second adder, third stage of the amplifier; the adders with their second inputs are connected to the outputs of the digital-to-analog converters, the outputs of the amplitude detector, phase meter, second and third stages of amplifiers are connected through the multiplexer to the input of the analog-to-digital converter; the microprocessor controller is connected through the address bus and the data bus to the generator, digital-to-analog and analog-to-digital converters, a multiplexer, third stages of amplifiers, and the functions of push-pull compensation, automatic gain control and piecewise-linear approximation are performed in the controller by software.