RU2694428C1 - Measuring line of eddy-current flaw detector for pipes inspection - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention can be used for nondestructive testing of pipes. Essence of the invention lies in the fact that the eddy current flaw detector measuring circuit for the pipes inspection contains the eddy current converter and the generator connected to the flaw detector signal processing and control unit, generator is connected to the first converter coil, phase shifter – to the second one, adjacent to which the non-magnetic current-conducting ring is coaxially located, and the converter is connected by one measuring channel to the signal processing and control unit.

EFFECT: possibility of simplifying the circuit diagram.

1 cl, 4 dwg

Description

The invention relates to the field of research and analysis of materials using eddy currents and can be used for non-destructive testing of pipes made from austenitic (non-ferromagnetic) steel, for example, the heat exchanger of a nuclear steam generator.

The measuring path of the flaw detector is known, consisting of an eddy current transducer (VTP) containing a magnetization coil on which a short-circuited ring is placed, two series-connected measuring coils connected to a bridge circuit, the signal from which is fed to the signal processing unit. Power ECP is supplied from the AC source. The measuring path is designed to control the gas gap of the technological channel of a uranium - graphite nuclear reactor, described in the RF patent №2377672, published 12/27/2009, Byul. No. 36, IPC G21C 17/06 (2006/01).

The positive quality of such an ECP is the use of a short-circuited conductive ring, with the help of which the phase balancing of the bridge circuit is carried out. This ensures high sensitivity to changes in the technological channel gap.

The disadvantage of the proposed Converter is weak informative ability about the defects of the channel, such as cracks, ulcers, corrosion and pitting.

Known measuring path flaw detector described in the patent of the Russian Federation No. 2370762, published 10/20/2009, Byul. No. 29, IPC G01N 27/90 (2006/01), containing an eddy current transducer consisting of a magnetization coil connected to a flaw detector generator, two differentially connected measuring coils connected to the first channel of a flaw detector, a magnetizing solenoid, radially arranged and sequentially connected Hall sensors , the signal from which is fed to the second channel of the flaw detector. The path is balanced by a phase shifter of a flaw detector connected to the initial EMF compensator circuit.

The positive quality of the considered measuring path of the flaw detector is the use of a differential eddy-current transducer, which, in combination with additional Hall sensors and a magnetizing solenoid, allows to detect extended defects of ferromagnetic pipes and control its thickness.

The disadvantages of such a flaw detector are:

- the inability to control the thickness of the pipe walls with a differential transducer, since it does not possess such informative ability;

- the inability to control the thickness of the austenitic steel pipe walls using a magnetizing solenoid in combination with Hall sensors;

- the presence of two measuring channels for monitoring, complicating and increasing the cost of the flaw detector.

These deficiencies are partially eliminated in the measuring path of the eddy current flaw detector described in the thesis of Zhdanov Andrey Gennadievich: "Improving the reliability of data analysis of eddy current monitoring of heat exchangers of NPP steam generators", Moscow, 2014, p. 25. Information is available on the Internet at:

htpp: //www.niiin.ru/upload/medialibrary/cae/cae7e46df2b214619261d7e5cf7300a0.pdf. In addition, the dissertation can be found in the library of JSC "NIIIN MNPO" Spectr. "

The measuring path of the eddy current transducer is presented in Appendix 1.

The converter consists of two measuring coils 1 and 2, connected in opposite, and together with the resistances R1 and R2 forming the bridge circuit of the differential sensor. The bridge circuit is connected to the flaw detector generator. The diagonal of the bridge is connected to the differential channel of the flaw detector, which measures the complex component of the incoming voltage carrying information about the presence or absence of defects in the test pipe. Coil 2 and resistance R2 form an absolute sensor circuit, the signal from which is fed to the absolute channel of the flaw detector. The absolute sensor is sensitive to all factors that change the eddy currents induced in the test tube, that is, such as conductivity, magnetic permeability and defects, and the thickness of the walls of the test tube. The differential sensor compares the nearby areas of the pipe being monitored. When a signal change occurs on one of the coils, a loss of compensation occurs between the coils, and this means that an abnormal condition of the pipe under test has been detected.

The signals from the absolute and differential ECP sensors are shown in Appendix 2:

a) the defect profile of the test tube;

b) and c) the real and imaginary components of the induced voltage when the ECP moves along the axis of the test pipe;

d) hodograph induced voltage on the complex plane.

The positive qualities of the proposed measuring path of the eddy current flaw detector are obtaining complex information about the defects of the test tube and about the thickness of its walls, excluding the use of a magnetizing solenoid and Hall sensors, the ability to control ferromagnetic tubes.

The disadvantages of the measuring path should include the mandatory presence of two measurement channels in the flaw detector, which complicates its concept and increases production costs.

The purpose of the invention is to reduce the cost of conducting inspection of pipes by unifying the measuring path of the eddy current detector.

This goal is achieved by the fact that in the measuring path of the eddy current flaw detector containing eddy current transducer and generator connected to the signal processing and control unit of the flaw detector, the generator is connected to the first transducer coil, the phase shifter from the second, next to which the conductive non-magnetic ring is coaxially placed and the transducer is connected by one measuring channel with a signal processing and control unit.

The essence of the invention lies in the fact that in the measuring path of the eddy current flaw detector a differential eddy current transducer is used, in one of the coils of which the phase exciting the current generator is forcibly shifted due to the location of the nonmagnetic ring next to it, and the balancing of the entire measuring path of the eddy current flaw detector is carried out by a phase shifter.

The invention is illustrated by drawings, which depict:

- in fig. 1 - design of a through passage VTP with a block diagram of the measuring path of the eddy current detector;

- in fig. 2 - signals of the measuring path of the flaw detector with a short defect of the test pipe and a constant thickness of its walls;

- in fig. 3 - signals from the measuring path of the eddy current flaw detector when the wall of the test tube is thinned;

- in fig. 4 - complex signals of the measuring path of the eddy current detector in the presence of a defect in the test tube and thinning of its wall.

The measuring path of the flaw detector consists of VTP 1, which contains two coils 2 and 3 and a conductive non-magnetic ring 4, located in the immediate vicinity of coil 3, placed in the grooves of the frame 5. Coils 2 and 3 are connected in series and form a bridge circuit with resistances 6 and 7 . VTP 1 is placed inside the controlled pipe 8.

The bridge circuit: coils 2, 3 and resistances 6, 7 form the differential part of the feedthrough VTP 1, and the conductive ring 4 gives it the properties of an absolute converter.

The flaw detector generator 9 is connected to the coil 2 of the eddy current transducer 1 located “away” from the conductive ring 4, the phase shifter 10 is connected to the coil 3 of the eddy current probe 1 located next to the conductive ring 4, and the EPR 1 is connected to the signal processing and control unit 11.

The measuring path works as follows.

VTP 1 is placed in the control sample of the pipe, which is known to be free from defects and has nominal geometric characteristics. The alternating current flowing through the coils forms a magnetic field, which induces eddy currents in the wall of the control sample of the pipe and in the conductive ring 4, which, in turn, also induces eddy currents in the wall of the pipe. As a result, at the output of the VTP 1, a complex signal appears, which is balanced by the phase shifter 10, changing the amplitude and phase of the alternating current supplying the coil 3, so that the signal at the input of block 11 is zero. Then VTP 1 is transferred to a controlled pipe 8 and move it along the axis of the pipe. With the passage of the coils 2 and 3 of the transducer 1 at the location of the defect (for example cracks, ulcers, corrosion, pitting), in the latter the amplitude and phase of the alternating current flowing through them changes, the bridge circuit is unbalanced and a complex signal is fed to the input of block 11. In this case, if the geometrical dimensions of the pipe 8 being monitored are comparable to the geometrical dimensions of the control sample of the tube, then conductive ring 4 VTP 1 does not have an additional effect on the current in the nearby coil 3. Unit 11 processes the complex signal and displays its characteristics on the display of the flaw detector. The amplitude and phase of the signal carry information about the defect of the pipe. When the wall thickness of the monitored pipe 8 is changed, the interaction of the conductive ring 4 with the coil 3 changes, which leads to a shift in current through the VTP 1 in phase, which is measured by block 11 and determines the deviation of the wall thickness of the pipe from the nominal value. At the same time, the VTP 1 bridge circuit remains balanced on the defect-free section and the output voltage of the VTP 1 is zero, since the metal of the pipe has the same effect on coils 2 and 3. On the section of pipe 8 that has a defect and with a deviation of wall thickness from the nominal value In block 11, a complex signal appears, i.e. the output signal of the measuring path of the flaw detector from the defect is shifted in phase proportional to the magnitude of the change in the thickness of the pipe wall.

The measuring path has been tested in operation with the single-channel eddy current flaw detector VECTOR-50 produced by OOO NVP Kropus (GOSTREESTR No. 71308-18 dated 06/01/2018). FIG. 2, FIG. 3, FIG. 4 shows the real signals of the measuring path of the eddy current flaw detector with various defects encountered in the pipes obtained with the help of the flaw detector “VECTOR-50”.

The plots shown in FIG. 2, characteristic signals from the defect are seen in the form of short pulses, the absence of a change in the wall thickness of the test tube is characterized by the constant position of the hodograph in the center of coordinates.

The plots depicted in FIG. 3, there are no signals from defects and a phase shift appears on the hodograph when the wall thickness of the pipe under test is thinned.

The plots depicted in FIG. 4, impulses from a defect are visible at normal wall thickness of the pipe being monitored and a phase shift appears on the hodograph when the transducer reaches the section with thinning of its wall.

The positive characteristics of the measuring path of the eddy current flaw detector are:

- the presence of a single channel measuring the characteristics of the pipe;

- direct balancing of the measuring bridge of the converter due to the direct connection of the phase shifter;

- unification of the measuring transducer due to the use of a conductive ring to forcibly change the parameters of a nearby coil and to introduce elements of an absolute sensor, as a matter of fact, into a differential one, which allows the use of a cheaper single-channel eddy current flaw detector during measurements;

- the ability to control pipes made of ferromagnetic steel;

- the ability to identify extended pipe defects due to additional information in the output signal of the converter from its absolute part;

- it is noted that the output signal from the absolute part of the converter is zero when the internal diameter of the pipe is changed without changing the thickness of its walls.

Realization of the goal allows to reduce the cost of measuring using the measuring path of a cheap eddy current detector, which has only one measuring input.

Claims (1)

The measuring path of the eddy current flaw detector for inspecting pipes, containing an eddy current transducer and a generator connected to the signal processing and control unit of the flaw detector, is characterized in that the generator is connected to the first transducer coil, the phase shifter to the second non-coaxially arranged ring, and the transducer it is connected by one measuring channel with a signal processing and control unit.

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