JP2766929B2 - Non-destructive inspection equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nondestructive inspection device for measuring internal stress existing on a surface of a metal material, and more particularly, to a machine without being affected by stress inside the metal material. The present invention relates to a nondestructive inspection device capable of measuring physical properties.

[Conventional technology]

Boiler pipes and turbine rotors used in high-temperature environments have a long operating time because the mechanical properties such as the tensile strength of the metallic material that composes them gradually change depending on the usage conditions. Material tests are performed on the objects. This material test cannot be performed by collecting a test piece as usual, because the test object is an actual machine member such as an operating pipe or rotor. Under these circumstances, generally, only a hardness measurement that can be performed with the actual machine installed without sampling the test piece is performed as a material test, and the tensile strength etc. should be estimated from the obtained hardness data. Has been done.
A hardness measuring device described in Japanese Patent Publication No. 57-84336 has been proposed as a hardness measuring device for the inner wall of a pipe or the inner surface of a rotor center hole. The hardness of a material is a measure of the magnitude of resistance exhibited when the material is deformed by another object, and various test methods and test machines have been devised for quantitatively measuring these. (For example, Machine Research Vol. 37, No. 10
On the other hand, Japanese Patent Application Laid-Open No. 62-240851 discloses means for applying plastic deformation to an object using an indenter having a pressurizer and detecting a change in magnetic permeability of the object using a double coil. A material testing apparatus provided is described. It measures the initial permeability mu ₁ of the subject,
A material testing method of initial permeability mu ₂ of該塑deformation portion after giving plastic deformation to the analyte is measured to determine the mechanical properties of the object based on the difference between these initial permeability mu ₁ and mu ₂ is there. In this method, the initial permeability of the subject is affected by the internal stress due to the magnetostriction effect.

A non-destructive inspection, Vol. 37, No. 9 (1988), PP 730-736, describes a stress measuring device utilizing the magnetostriction effect.

[Problems to be solved by the invention]

In the above prior art, no consideration is given to the effect of plastic deformation on the subject at the time of measurement, and the material cannot be inspected nondestructively (without plastic deformation). Therefore, it is not suitable for measuring mechanical properties of a subject for which nondestructive inspection is desired, as in actual equipment of a nuclear power plant.

Further, in the technique described in Japanese Patent Application Laid-Open No. 62-240851, the initial magnetic permeability is affected by the residual stress existing inside the actual machine member, so that the influence of the residual stress on the initial magnetic permeability cannot be measured. From the change in the magnetic permeability, the mechanical properties of the actual machine members could not be measured.

An object of the present invention is to non-destructively measure an internal stress localized in a subject, and to non-destructively and highly accurately measure a change in mechanical properties of the subject.

[Means for solving the problem]

The above-described problem has data in which the influence of the internal stress on the magnetic properties of the subject is determined in advance, and a closed magnetic circuit passing through the subject and the measurement probe, and a magnetic circuit passing through the reference sample and the compensation probe. Means for detecting the internal stress of the subject based on the difference between the magnetic resistances of the two magnetic circuits, and sequentially giving different magnetomotive forces to the subject, and the lines of magnetic force induced from the subject by the magnetomotive force A magnetic hysteresis curve is detected to detect the magnetic characteristic of the subject based on the magnetic hysteresis curve, and the magnetic characteristic is corrected using the internal stress obtained by the previous detecting means.
Means for determining the mechanical properties of the subject based on the corrected magnetic properties.

[Action]

When a measurement probe is applied to the surface of the subject, a closed magnetic circuit is formed. When an electric current is applied to a coil wound around the measuring probe, a magnetic flux is generated in the magnetic circuit. If there is an internal stress in the subject, the magnetic permeability of the subject changes according to the magnitude of the internal stress due to the magnetostriction phenomenon,
Accordingly, the magnitude of the magnetic flux changes. There is a difference between the magnitude of the magnetic flux generated in the compensating probe that forms a magnetic circuit in contact with the reference sample having no internal stress and the magnitude of the magnetic flux generated in the measuring probe, including the measuring probe and the compensating probe. An unbalanced current occurs in the formed bridge circuit. Since the unbalanced current corresponds to the magnitude of the internal stress of the subject, the unbalanced current is measured to obtain the internal stress.

A magnetometer having an excitation coil and a pickup coil is provided at the center between the magnetic poles of the measurement probe, and different magnetomotive forces are sequentially applied to the subject, so that the magnetic hysteresis curve (in the region where the internal stress is measured) is obtained. BH curve). The magnetic characteristics of the subject obtained from the magnetic hysteresis curve are corrected for the magnetostriction effect due to the previously measured internal stress, and the magnetic characteristics excluding the effect of the internal stress are obtained. Since the magnetic properties are associated with the mechanical properties of the subject, the mechanical properties of the subject are obtained based on the corrected magnetic properties.

Methods for obtaining the magnetic characteristics of the subject include a method using eddy current and a method using Barkhausen noise, and similar effects can be obtained.

The measurement probe as the stress measuring means and the magnetometers for measuring the magnetic properties (eddy current detection coil, Barkhausen noise detection coil) are arranged concentrically, so that the internal stress detection position and the magnetic characteristic detection position Are consistent and the positional accuracy is high.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. First
FIG. 1 shows a state in which a turbine rotor 1 as an object is inspected by a nondestructive inspection apparatus according to one embodiment of the present invention. The device to be destroyed shown in FIG. 1 includes a stress measurement device 3 attached to a center hole 2 provided in a turbine rotor 1, and a stress measurement device 3 connected to the stress measurement device 3 and passed through the inner peripheral surface of the center hole 2. An operation rod 5 to be moved, and a feed device 4 for moving the operation rod 5 in the axial direction and rotating around the axis
And a cable 6 connected to the stress measuring device 3 and a data conversion device 7 and an arithmetic controller 8 connected to the other end of the cable.

FIG. 2 shows an example in which the nondestructive inspection apparatus according to the present invention is applied to inspection of a reactor pressure vessel. The non-destructive inspection device according to the embodiment shown in the figure includes a stress measurement device 3 mounted on the inner wall of a reactor pressure vessel 11, a crane 17 supporting the stress measurement device 3, and a connection to the stress measurement device 3. And a controller 18 that is provided. The subject may be various thick-walled containers used in a chemical plant.

FIG. 3 is a sectional view of a principal part of the stress measuring device shown in FIGS. 1 and 2. The stress measuring device shown in the figure is a high-sensitivity magnetometer 21 for measuring the magnetic properties of the subject 23, and a high-permeability material provided around the magnetometer 21 so as to be able to contact the subject 23. A U-shaped probe 22 and the probe 22
A coil 25 wound around, a pickup coil 26 provided on the surface of the magnetometer 21 facing the subject 23 and connected to the magnetometer, and an excitation coil 28 attached to the magnetometer. , Is provided. The magnetometer 21 is arranged at the center of the U-shaped probe 22. Probe 22 and the probe
A coil 25 wound around 22 constitutes a measurement probe for measuring the internal stress of the subject by bringing the U-shaped end into contact with the subject, and the same configuration is used as a compensation probe. It is provided as. The measuring probe and the compensating probe form a bridge circuit together with the constant voltage circuit 46, the slidac 47, the galvanometer 45 for measuring the bridge current, and the galvanometer 44 for measuring the unbalanced current to form the stress measuring means. ing.

In order to perform measurement by the stress measuring device having the above-described configuration, first, the probe 22 is arranged with its U-shaped end 22A in contact with the surface of the subject 23, and the compensation probe has its end inside. It is arranged in contact with the surface of the reference specimen having no stress. Closed magnetic circuit between subject 23 and probe 22
24 are formed, as well as the compensating probe and the reference analyte forming a closed magnetic circuit. A current flows through the coil 25 and the coil of the compensation probe, and a magnetic flux is generated in both magnetic circuits.However, if the internal stress 27 exists in the stress measurement area 26 of the subject 23, the internal stress 27 The magnetic permeability in the stress measurement area 26 changes according to the size. For this reason, a difference is generated between the magnetic resistance of the magnetic circuit 24 and the magnetic resistance of the magnetic circuit of the compensating probe in contact with the reference sample having no internal stress. The difference in magnetic flux density based on the difference in magnetic resistance is converted into an electric signal by a measurement circuit using a bridge circuit shown in FIG. 5, and based on the relationship between internal stress and magnetic permeability that has been converted into data in advance, Stress measurement area
The internal stress in 26 is calculated and output. Probe 22
By moving along the surface of 23 and measuring the stress at a plurality of locations, the stress distribution of the subject 23 can be obtained.

Next, the excitation coil 28 is energized to apply a magnetomotive force to the stress measurement area 26 of the subject 23. The test object 23 in the stress measurement area 26 generates a magnetic field line 30 based on the electromotive force. However, the magnetic characteristics of the test object 23, such as the initial susceptibility and the maximum susceptibility, are affected by the magnetostriction effect due to the residual stress, The density and the coercive force are not only affected by the magnetostriction effect, but also change due to precipitates and foreign phases inside the subject. Since the mechanical properties of the material of the subject change due to the precipitates and the different phases, the intensity of the magnetic field lines generated based on the given magnetomotive force is:
It changes with changes in the internal stress and mechanical properties of the subject. The line of magnetic force 30 is captured by the pickup coil 29, and its value is measured by the magnetometer 21. Based on the value, a value indicating the magnetic characteristics of the subject is obtained. The effect of the magnetostriction effect due to the residual stress (internal stress), which has been converted into data, was corrected based on the value of the internal stress measured immediately, and the effect of the internal stress was excluded. And the amount of change in magnetic properties. Since the magnetic properties are related to the mechanical properties of the subject, the relationship between the magnetic properties and the mechanical properties is converted into data in advance, so that the subject 23 is measured based on the measured magnetic properties. Is determined.

FIG. 4 shows another embodiment of the stress measuring device according to the present invention. In the embodiment shown in the figure, a magnetometer 32 having a pickup coil 31 and an exciting coil 24 for measuring the magnetic characteristics of a member of an actual machine is arranged outside a probe 33. A coil 36 for generating a magnetic flux in the probe 33 is wound around the leg of the U-shaped probe 33, and has a center line at the center of the probe 33, which is perpendicular to the surface of the probe 33 that is in contact with the subject. A center hole 34 is provided. The magnetometer 32
Is provided concentrically with the center hole 34 with the pickup coil 31 positioned outside the center hole 34, and the magnetic field lines 35 generated by the stress measurement area 26 are
The probe 33 can be taken in by the pickup coil 31 outside the above, so that the size of the probe 33 can be reduced.

In the present embodiment, the lines of magnetic force 35 from the stress measurement region 26 of the subject 21 are introduced into the pickup coil 31 through the center hole 34. Further, the probe 33 is formed so as to be rotatable around the center line of the center hole 34, and by measuring the stress at a plurality of positions and comparing the values while rotating around the center line, Stress measurement area
The direction of action of the stress in 26 is also detected.

In the embodiment shown in FIG. 3 and FIG.
Although a pickup coil is provided for detecting the magnetic field lines from 26, a Hall element may be used instead.

FIG. 5 shows an example of a circuit configuration for stress measurement. The circuit shown in the figure includes a measuring probe (magnetostrictive tube) 41 and a compensating probe 42, a rectifying circuit 48 using a diode connected to the measuring probe 41 and the compensating probe 42, and a measuring circuit provided in the rectifying circuit 48. The unbalanced current measuring galvanometer 44 connected at 43, the resistors γ ₁ , γ ₂ , and the variable resistor γ ₃ connected to the rectifier circuit 48, and connected to the measuring probe 41 and the compensating probe 42 Galvanometer 45 for bridge current measurement,
該検flow meter 45 and the variable resistor gamma ₃ constant voltage device connected via a variable transformer 47 to 46, comprising a, the constant-voltage device
46 is supplied with 50 Hz, 100 V power. The measurement probe 41 here includes the probe 22 (including the coil 25) shown in FIG. 3 and the probe 33 (the coil 36) shown in FIG.
And also referred to as a stress tester.

The measuring probe 41 forms a bridge circuit together with the compensating probe 42, and in this bridge circuit, an unbalanced current based on a difference in magnetism detected by the compensating probe and the measuring probe, that is, an inherent stress difference is detected. And this
It is measured by the unbalanced current measuring galvanometer 44, and the difference in stress is determined.

The magnetic flux distribution generated by the stress tester 52 whose surface 52A facing the subject has a rectangular shape as a whole has a shape as shown in FIG. FIG. 6 shows the distribution of magnetic flux generated on the surface of the subject at the time of stress measurement, in which the distance between magnetic poles of the used stress tester 52 is 5 cm. In the figure, 5 cm from the midpoint of the stress tester pole (the origin of the figure)
The magnetic flux density at the distant position is reduced to 1/5 to 1/6 compared with the surroundings of the magnetic pole. FIG. 6 shows a case where the subject is stress-free. When the subject is under stress, the magnetic field is distorted, but the ratio of the strength depending on the location of the magnetic flux distribution is not much different from that without stress. Therefore, the stress measured by the stress tester 52 has a radius of 5c around the origin in FIG. 6, that is, the point where the magnetometer 51 is installed and the magnetic pole of the stress tester 52 is located at the center.
The average of the stress of the subject within a circle within m (distance between magnetic poles) is shown. As described above, according to the present invention, the stress measurement range can be limited.

FIG. 7 is an example of the magnetic characteristics of the inner wall of the turbine rotor measured by the magnetometer 21. A magnetomotive force H is applied to the inner wall of the turbine rotor by the excitation coil shown in FIG. 3, and the magnetic flux density B is measured by the pickup coil. When the value of the applied magnetomotive force is sequentially changed, the measured value draws a magnetic hysteresis loop 62 via an initial magnetization curve 61. If there is residual stress on the inner wall of the rotor, the magnetic field will be distorted,
Due to the so-called magnetostriction effect, the initial susceptibility 63 and the maximum susceptibility 64 change as compared with the case where there is no stress. Also,
Precipitates inside the rotor and the residual magnetic flux density 65 and coercive force 66 that change due to the different phases are also affected by the magnetostrictive effect.

FIG. 8 shows the stress and magnetic properties obtained by the stress measurement device 3 at a plurality of axial positions on the inner wall of the center hole of the turbine rotor 1, and the horizontal axis represents the axial measurement position, and the vertical axis represents the output value. , Stress distribution 71, coercive force distribution 72 and residual magnetic flux density distribution 7
FIG. If the amount of change in the magnetic property value due to the change in internal stress is determined using an unused material of the same material as the turbine rotor, the coercive force changed according to the material change inside the rotor excluding the magnetostriction effect The distribution and the residual magnetic flux density distribution are required.

FIG. 9 shows a stress distribution 81 localized on the inner wall of the reactor pressure vessel 11 obtained by mounting a no-load sample on a compensation probe using the apparatus shown in FIG. The position of the furnace pressure vessel 11 in the axial direction is illustrated by taking the measured value on the vertical axis. In addition, a coercive force distribution 83 and a residual magnetic flux density distribution 84 are obtained by performing excitation and measurement at a plurality of locations using a magnetometer provided in the stress measurement device 3. In addition, the tenth
As shown in the figure, when the reactor is operating, the reactor pressure vessel lid 91 is
Since it is mounted on the upper part of the reactor pressure vessel 11, in the vector sum of the increase of the axial stress τ _e , the radial stress τ _r and the circumferential stress τ _θ before and after the reactor pressure vessel lid 91 is mounted,
The components in the measurement direction of the stress tester were measured using the stress distribution shown in Fig. 9.
By adding to 81, a correction value 85 of the stress distribution is obtained, and it is possible to estimate the stress distribution when the reactor is in operation (low temperature).

FIG. 11 is an example of a method of displaying the measured values shown in FIGS. 8 and 9. The data conversion device 7 and the arithmetic and control unit 8 shown in FIG. 1 are connected to a computer 100, and the computer 100 has a display 101 as display means. A cross-sectional view 102 representing the measurement position of the subject is displayed at the lower part of the display screen of the display 101, and an X axis representing the position of the subject in the axial direction of the measurement location is displayed above the display 102 in parallel with the axis of the cross-sectional view. I have. A Y-axis representing an output value measured perpendicular to the X-axis is set, and the measured stress distribution 71 and coercive force distribution are plotted on the X-axis corresponding to the display position of the cross-sectional view.
72 is drawn. Further, an XY plotter 105 is connected to the computer 100, and the figure drawn on the display screen of the display 101 is output as a hard copy by the XY plotter 105. As described above, in the present embodiment, there is an effect that the stress distribution and the magnetic characteristic distribution measured by the stress measuring device are visualized while corresponding to the part of the subject.

FIG. 12 shows an embodiment in which a detection coil for measuring Barkhausen noise is mounted on the stress measuring means. Barkhausen noise has a close relationship between the stress (load stress + residual stress) and the microstructure of the material. If the stress is known, a change in the microstructure can be detected by the Barkhausen noise.

The device of the present embodiment has a sensor 100 disposed at the center of the magnetic pole of the stress tester 120, and includes a measuring device main body 104 connected to the sensor 100 outside the stress tester 120. Since the stress tester 120 and the attached bridge circuit, arithmetic device, and the like are the same as those in the embodiment of FIGS. 3 to 5, illustration and description are omitted. The sensor 100 includes an excitation unit having an excitation coil 102 wound around a yoke 101, and a detection coil 103 wound around a high magnetic permeability material. The sensor 100 is connected to the measuring device main body 104 by a signal cable 105, and the measuring device main body 104 is connected to an oscillator 106 connected to the input side of the sensor 100.
And a bandpass filter 107 connected to the output side of the sensor 100
And a display 109 connected to the bandpass filter 107 via a rectifier 108.

The oscillator 106 has a low frequency (several Hz to
(Several tens of Hz), which is amplified in power and supplied to the exciting coil 102 of the sensor 100. The Barkhausen noise of the subject 110 received by the detection coil 103 is applied to the bandpass filter 107.
And is rectified and displayed on the display 109. From the received original waveform of Barkhausen noise, parameters such as its maximum amplitude, average amplitude, pulse height analysis, and frequency spectrum are extracted. FIG. 13 shows the relationship between the hardness of a subject and Barkhausen noise as a typical example of the microstructure parameter.

FIG. 14 shows an embodiment in which an eddy current measuring detection coil is provided in the stress measuring means. Also in this embodiment, since the stress tester is the same as that described in FIGS. 3 to 5,
Description and illustration are omitted. In the figure, at the center between the magnetic poles of the stress tester, a magnetizing coil 111 is arranged with its center line in a direction perpendicular to the surface of the subject, and a detection coil 112 is arranged concentrically with the magnetizing coil 111. I have.
A subject 1 is applied by applying an alternating voltage of constant oscillation to the magnetizing coil 111.
When a magnetic field 114 is applied to the object 13, an eddy current 115 is applied to the subject 113.
Occurs. The voltage induced in the detection coil 112 by the eddy current 115 is detected by the detection coil 112. Since this voltage is proportional to the initial magnetic permeability of the subject 113 as shown in FIG. 15, the initial magnetic permeability is obtained from the voltage command value detected by the detection coil 112. The obtained initial magnetic permeability is corrected by the internal stress measured by the stress tester, and using the reference sample of the same material as the test object, the data of the initial magnetic permeability and the mechanical properties are used to obtain the mechanical properties of the test object. Characteristic is determined.

Further, when it is permissible to apply a small amount of plastic deformation to the subject 113, the indenter 11 that can move up and down through the two coils above the center line of the magnetizing coil 111 and the detection coil is described.
After the initial permeability of the subject is measured, the indenter 116 is pressed by, for example, hydraulic pressure to form an indentation on the surface of the subject. Then, after raising the indenter 116 again, the initial permeability of the subject is measured in the same procedure. Between the amount of change in initial permeability and hardness measured in this way,
The relationship is shown in FIG. That is, the hardness of the measured object 113 can be known by obtaining the amount of change in the initial magnetic permeability by the above method. The graph shown in FIG. 16 may be obtained in advance for components having the same composition and processing as the subject. Since the internal stress measurement and the eddy current measurement are performed at the same location on the subject, the relationship between the tensile strength of the subject and the internal stress can be similarly examined.

In the embodiment shown in FIG. 3, even if a superconducting coil is used as an exciting coil and a superconducting quantum interference element magnetic sensor in which a superconducting pickup coil is arranged is provided instead of the magnetometer (including the pickup coil), FIG. The same effect as the embodiment shown in FIG.

〔The invention's effect〕

According to the present invention, the stress measurement region of the measured object is limited,
Since other magnetic and electrical characteristic values can be detected from the same area, it is possible to detect the stress measurement position in equipment where internal stress is localized, such as the inner surface of the hole of the turbine rotor of the generator or the inner wall of the nuclear pressure vessel. The other characteristic values mentioned above were changed to In-Si
It has the effect of being able to measure with tu.

In addition, the above stress and other characteristics have an effect of increasing reliability of defect inspection and strength evaluation of the measured object by the in-situ calculation.

[Brief description of the drawings]

FIG. 1 is a side view showing a state in which an embodiment of the non-destructive inspection device according to the present invention is applied to a turbine rotor, and FIG. 2 is a diagram showing an embodiment of the non-destructive inspection device according to the present invention in a reactor pressure vessel. FIG. 3 is a cross-sectional view showing a main configuration of the stress measuring device shown in FIGS. 1 and 2, and FIG.
FIG. 5 is a sectional view showing another example of the stress measuring device shown in FIG. 5, FIG. 5 is a circuit diagram showing an example of a circuit configuration of the stress measuring device according to the present invention,
FIG. 7 is a plan view showing an example of a magnetic flux distribution when stress is measured by the stress measuring device shown in FIG. 3 or FIG. 4, FIG. 7 is a conceptual diagram showing magnetic characteristics of a subject, and FIG. Is a conceptual diagram showing an example of the distribution of the magnetic properties and the stress of the subject measured by the stress measuring device of FIG. 3 or 4, FIG. 10 is a front view showing a change in the stress of the subject, FIG. Is a perspective view showing a display example of measured values, FIG. 12 is a cross-sectional view showing an embodiment in which a detection coil and an excitation coil for Barkhausen noise are mounted on a stress measuring device, and FIG. 13 shows a display example of Barkhausen noise. FIG. 14 is a perspective view for explaining the configuration of the eddy current detection coil, FIG. 15 is a graph showing an example of the relationship between the initial magnetic permeability and the voltage induced in the eddy current detection coil, and FIG. 5 is a graph showing an example of a relationship between the hardness of a sample and the amount of change in initial magnetic permeability. 3 ... stress measuring means (stress measuring device) equipped with a magnetometer, 21, 32 ... magnetometer, 22, 33 ... probe, 23 ... subject, 24 ... magnetic circuit, 25 ... coil, 27 ... internal stress, 28, 36 ... excitation coil, 29, 31 ... pickup coil, 30, 35 ... magnetic field lines, 41 ... measurement probe, 42 ...
Compensation probe, 44: Unbalanced current measuring means, 62: Magnetic hysteresis loop, 71: Stress distribution, 72: Coercive force distribution, 73: Residual magnetic flux density distribution, 85: Correction value of stress distribution, 100 ... computer, 101 ... display means, 102 ...
Excitation coil, 103 ... Detection coil, 106 ... Oscillator, 111
... magnetic coil, 112 ... detection coil.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tsubasa Shimizu 502 Kandate-cho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratory, Hitachi, Ltd. In-house (72) Inventor Yuko Oguchi 502 Kandate-cho, Tsuchiura-shi, Ibaraki Pref.Hitachi, Ltd.Mechanical Research Laboratory Co., Ltd. JP-A-63-279185 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 27/72-27/90

Claims (1)

(57) [Claims] 1. A closed magnetic circuit passing through an object and a measurement probe, a magnetic circuit passing through a reference sample and a compensating probe, and having data in which the influence of an internal stress on the magnetic properties of the object is determined in advance. Means for detecting the internal stress of the subject based on the difference between the magnetic resistances of the two magnetic circuits, and sequentially giving different magnetomotive forces to the subject, and the lines of magnetic force induced from the subject by the magnetomotive force To obtain a magnetic hysteresis curve, and a means for obtaining the magnetic characteristics of the subject based on the magnetic hysteresis curve, and correcting the magnetic characteristics using the internal stress obtained by the previous detecting means, and Means for determining the mechanical properties of the subject based on the magnetic properties.