JPS6093954A - Eddy current flaw detection apparatus - Google Patents

Abstract

PURPOSE:To make it possible to detect the presence and absence of surface flaw in the center hole of a body to be inspected with good efficiency, by radially embedding inspection coils for eddy current flaw detection in the outer peripheral surface of a flaw detection head and measuring impedances of adjacent two coils. CONSTITUTION:A large number of inspection coils 2(1)-2(n) each formed into a cylindrical form are radially embedded in a disc shaped flaw detection head main body 1 along the outer peripheral surface thereof. This flaw detection main body 1 is set to the inlet part of the center hole provided to a rotor being a body to be inspected and a drive shaft 4 is moved into the center hole at every one step by a driver mechanism 5 every when flaw detection is performed to the surface of the center hole from said set position. The inspection coils 2(1)-2(n) are successively changed over by an electronic change-over device and adjacent two coils 2(i), 2(i+1) are selectively excited. The impedances of said coils are measured and compared and the presence or absence of the surface flaw in the center hole is discriminated from the difference thereof to perform flaw detection. By this constitution, the presence or absence of the entire surface flaw in the center hole can be detected in a real time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an eddy current flaw detection device for detecting defects on the inner surface of a center hole of a rotor of a turbine, a turbine generator, or the like.

[Technical background of the invention and its problems]

Non-destructive inspection of the inner surface of the center hole in the rotor of turbines and turbine generators generally involves visually inspecting the inner surface using a borescope to inspect for rust, forgeries, etc., and inspecting for surface cracks or defects near the surface using magnetic particle testing. Ultrasonic flaw detection is also used to detect defects inside the rotor center hole that cannot be detected by magnetic particle flaw detection. Among these flaw detection methods, the magnetic particle flaw detection method often uses wet magnetic particles to inspect for defects opened on the surface or defects below the surface. However, in this magnetic flaw detection method, actually inspecting the rotor center hole requires the steps of magnetizing the rotor, which is the object to be inspected, dispersing wet magnetic particles, and observing the magnetic particle pattern with a borescope. However, it requires a lot of effort - it takes two hours, and cleaning work such as removing magnetic particles is also required after the inspection is completed. In addition, in this magnetic particle flaw detection method, not only the surface inspection inside the rotor center hole but also the uniform distribution of magnetic particles on the object to be inspected is an important element in obtaining appropriate inspection results. In order to determine the presence or absence of defects in the inspected object by properly dispersing the magnetic particles and visually observing the resulting magnetic particle pattern using a borescope, the work must be carried out by a skilled person. As a requirement for high reliability, it is important to record the flaw detection results, but in the magnetic particle flaw detection method described above, no good method has been found other than photographic recording of the magnetic particle pattern.

In order to improve the reliability of turbines and rotors of turbine generators, electric generators, etc., there are 11 flaw detection devices that are easy to operate, have high flaw detection efficiency, and are easy to judge the flaw detection results. 'I present is requested.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and its purpose is to efficiently detect the presence or absence of defects on the inner surface of the center hole of a specimen having a center hole, such as a rotor of a turbine or a turbine generator. It is an object of the present invention to provide an eddy current flaw detection apparatus that can perform a flaw detection process, has a high defect detection ability, and has good recording performance of flaw detection results.

[Summary of the invention]

The eddy current flaw detection apparatus according to the present invention has a plurality of eddy current flaw detection devices in a disc-shaped flaw detection head main body having an outer diameter close to the center hole of the object to be inspected. A flaw detection head having test coils buried radially along the outer circumferential surface and a driving r 11+ with a connecting cable of each of the eddy current flaw detection test coils inserted approximately at the center of the disc-shaped part; , a drive mechanism for moving the drive shaft of the flaw detection head in the direction of the center hole axis of the object to be inspected, and two adjacent coils selected as a pair from among the respective eddy current test coils. switching rγ
An electronic switching device, two impedance measuring devices that measure the impedance of two adjacent coils that change due to eddy currents generated in the test object when the two adjacent coils are switched by the electronic switching device, and these impedance measuring devices. means for comparing the values measured by and determining the difference between them, and determining from the result whether or not there is a defect on the inner surface of the center hole of the object to be inspected; It is characterized by comprising a device for displaying or recording in correspondence with the position of the inner surface.

[Embodiments of the invention]

Below is an example of the present invention! This will be explained with reference to page 71.

FIG. 1 is a perspective view showing an example of the configuration of a flaw detection head used in the eddy current flaw detection apparatus of the present invention.

In FIG. 1, 1 is a disk-shaped flaw detection head body, and inside this flaw detection head body 1 (d: a plurality of cylindrical test coils 2(I) to 2(n) for eddy current flaw detection). are embedded densely in a radial manner along the outer circumferential surface. Each of these test coils 2(1) to 2(n) is inserted into a flaw detection head drive shaft 4 mounted approximately at the center of the flaw detection head body 1. Connecting cable 3 (J(1) e 3(1) v ~ 3(n) *
3'(n)) are connected to their corresponding ends. These flaw detection head body l and flaw detection head u town h
ll+ consists of a 4-piece flaw detection head. Figure 2(a)
*(b)! This figure shows an example of the overall configuration of an eddy current flaw detection apparatus for inspecting an object to be inspected having a leaf center hole, here the inner surface of the center hole of a rotor. Figure 2 (a)? (b
), 5 is a drive mechanism installed on the pedestal soil, and this drive mechanism s5 advances and retreats the flaw detection head drive shaft 4 in its longitudinal direction, and moves the flaw detection head main body l in the center hole of the rotor 6 in the axial direction. Move Z). On the other hand, 7 is a coil selection circuit to which the other end of the connection cable 3 in the flaw detection head 4 is connected, and this coil selection circuit 7 selects a plurality of inspection coils 2 (1) to 2(n), two adjacent coils are selected as a pair and switched sequentially. 8a, /ib Two test coils 2 (1) selected by the coil selection circuit 7.

2 (1+J), an impedance measuring circuit that measures signals due to eddy currents generated in the inspected object as signals corresponding to the impedance of the coil; 9 excites the coils for these impedance measuring circuits 8a and 8b; This is an oscillator that provides an output with a variable oscillation frequency as a power source for the oscillator. 0 is a signal processor into which a voltage signal corresponding to the impedance of the test coil measured by the impedance measuring circuits aa and 8b is input;
No. 1 is a CRT display into which the signal signal processed by the signal processor necessary for image display is input;
The R7 display 11 displays a defect value on a developed view of the inner surface of the center hole, that is, displays it as a C scope image. Further, J2 sends a coil selection command to the coil selection circuit 7, an oscillation operation command to the oscillator 9, signal processing data to the signal processor IO, and synchronization to the CRT display 1. A controller that gives each signal etc.
This controller J2 compares the signals according to the impedance of the two test coils output from the signal processor 10, determines the difference, and determines the presence or absence of a defect on the inner surface of the center hole of the rotor from the result. 013 is a storage medium such as a floppy disk that stores the flaw detection results determined by the controller 12.

Next, to describe the operation of the eddy current flaw detection device configured as described above, as shown in Figs. Every time the center hole surface corresponding to the outer peripheral surface of the flaw detection head body 1 is flawed from that position, the flaw detection head is driven #
The explanation will be given assuming that I4 is moved into the center hole one step at a time by the drive mechanism 5. Now, when the controller 12 issues a selection command to the coil selection circuit 7 and an oscillation start command to the oscillator 9, the coil selection circuit 7 selects two test coils z(f)t2(i+1) at predetermined positions. ), the main oscillator 9 starts oscillation operation at a preset oscillation frequency, and the output for one period is the selected oscillator 9.
It is supplied to the two test coils 2(1)t 2 (1+1> through the impedance measurement circuits 111a and 8bf. Then, these two test coils 2(i) 嘗2(1-B)
is excited, and the test carp/l/2 (
1) The coil 'jMHc1> is the test coil 2 (i+7
) A magnetic field H(1+J) is formed, and an eddy current flows on the inner surface of the center hole of the rotor 6. Therefore, the coil impedance of the test coil 2(1)s 2 (i+7) changes visually due to this eddy current. In this case, is the stacking coil j? (i) The influence on v 2 (i+7) differs depending on the material near the inner surface of the center hole, the presence or absence of defects, etc. Here, if it is assumed that defect J4 exists near the surface of center hole P3 corresponding to inspection coil 2(i), the impedance change of inspection coil 2(1) is equal to that of inspection coil 2(1+c). The size also becomes smaller.

A signal corresponding to the change in impedance of the test coil 2<i)*2 (1+7) is sent to the coil selection circuit 7.
The signals are input to impedance measurement circuits 8a and 8b through the impedance measurement circuits 8a and 8b, where their impedances are measured respectively.

The six impedances measured by the impedance measurement circuits 8a and 8b are applied as voltage signals to the signal processor 10, where the signals are processed and then applied to the controller 12. The controller J2 compares the two impedances, determines the difference, and records the result in the storage medium 13.The signal processing unit 10 then outputs the signal to the CRT display 1, where the signal processing necessary for image display has been performed. Display as a C-scope image.

The above is two adjacent coils 2(1')*2(i+J
), the impedance of the coil 2 (1-H) e 2 (1+;?) is measured and compared, and the difference is determined to determine whether there is a defect.
) are measured in exactly the same way as above, and compared, and the difference is determined to determine whether there is a defect.Then, the two test coils are made into a pair and transferred one by one to the adjacent test coils. It is repeated as it goes. In this case, the test coil is switched by the coil selection circuit 7, and the coil is excited by the oscillation output of the oscillator 9 at the same timing. Then, when the switching of the inspection coils has completed one cycle, the flaw detection head drive shaft 4 is advanced one step at a time into the center hole of the rotor 6 by the drive mechanism 5, and flaw detection is performed in exactly the same manner as described above.

As described above, in this embodiment, a plurality of eddy current test coils 2(I) to 2(n) embedded radially within the disc-shaped flaw detection head main body 1 along its outer peripheral surface are connected to the coil selection circuit 7.
Two adjacent test coils z (1
) v 2 (1+J) is selected, and the impedance measurement circuit 8a measures the change in impedance of the coil due to the vortex flow generated on the inner surface of the center hole of the rotor by excitation of the coil.
Measure L2 at 8b and compare these, and from the difference center 7
The presence or absence of defects on the inner surface of 'L is determined. t
7. Therefore, if a defect 14 exists near the inner surface of the center hole, as shown in FIG. Although the value is extremely small and difficult to detect, the test coil 2 that is in contact with the two rs
N),! Since the impedance difference is detected as the impedance difference of -2(l+J), it is possible to reliably detect the impedance change. Also, since the outer diameter of the flaw detection head body 1 is smaller than the inner diameter of the rotor center hole,
This flaw detection head main body J may deviate from the center position of the center hole due to its own weight or the like.

Therefore, in such a case, the absolute value of the impedance of each test coil will change due to the change in the distance between the horizontal coil and the test object.As a foot-off effect, the dotted line ( As shown in a), there is a large change in the position in the circumferential direction, but as described above, the influence of the lift-off effect is small for two adjacent test coils.

Accordingly, the difference in impedance between two adjacent test coils shows a change (c) only depending on the presence or absence of a defect, as shown by the solid line (b) in FIG. It becomes possible to eliminate the influence of eccentricity.

On the other hand, in this embodiment, two adjacent test coils 2(i)
Since the eddy current flaw detection is performed using the oscillator 9 with a variable oscillation frequency as a power source for exciting the s2 (1"7), the following effects can be obtained.

In other words, in general, when an alternating magnetic field is applied to an object from the surface of the object, the magnetic field's? It is well known that the following equation (1) holds between 1tfR δ and the frequency of the alternating magnetic field.

However, σ is electrical conductivity.

12- Therefore, if the excitation frequency is changed by the oscillator 9 when measuring the impedance of the inspection coil, the difference in impedance between two adjacent inspection coils 2(i)*2(i+1) corresponds to the defect depth. In this way, the presence or absence of defects on the inner surface of the rotor center hole corresponding to the outer circumferential surface of the flaw detection head main body l and its shrinkage can be determined. Tsukitsu flaw detection head body I that can be used for flaw detection in a short time
ff By moving in the axial direction of the center hole, the entire inner surface of the center hole can be inspected for flaws.

Next, another embodiment according to the present invention will be described with reference to FIG.

In general, when the object to be inspected is a ferromagnetic material, the defect detection sensitivity in eddy current testing cannot be as high as when it is a non-magnetic material due to the influence of the magnetic properties of the object. However, the embodiment shown in FIG. 5 improves this point. That is, as shown in FIG. 5, approximately U is sandwiched between inspection coils 2(+) to 2(n) for eddy current flaw detection, which are embedded radially within a disc-shaped flaw detection head l along its outer circumferential surface.
Letter-shaped permanent magnets 15(+) to 15(n) are respectively arranged to apply a DC magnetic field to the inner surface 1 of the rotor center hole.

As shown in Figure 6, the relative magnetic permeability μ in a ferromagnetic material is expressed by the gradient of the magnetic field strength H and the magnetic flux density 1 in the relationship I), and where JIn ``U'' and Wi degree B are It is well known that the size decreases as saturation approaches.In this embodiment, this principle is applied, and as described above, the test coils 2(1) to 2(n) are attached to the main body of the flaw detection head.
) and the permanent magnets 15(+) to 15(n) arranged to sandwich these coils respectively, cause the vicinity of the surface of the center hole of the rotor, which is a ferromagnetic material, to appear to be in a state of magnetic saturation or near saturation. This lowers the relative magnetic permeability of this portion. Therefore, with such a configuration, the magnetic flux density of the ferromagnetic object to be inspected becomes smaller and the relative permeability is apparently lowered. , by improving the detection sensitivity for defects on the inner surface of the rotor center hole.

〔Effect of the invention〕

As described above, the present invention has the following features: A plurality of eddy current test coils are embedded radially along the outer circumferential surface inside a disc-shaped flaw detection head body, and these test coils are connected by an electronic switching device. h 111r Primary switching selects and energizes two adjacent coils as a pair, measures the impedance of the coils, compares them, and determines the presence of defects on the inner surface of the center hole of the object to be inspected from the difference. (Since the structure is such that the inner surface of the center hole is detected by making all judgments, the inner surface of the center hole corresponding to the outer peripheral surface of the flaw detection head body can be detected in a short time. By simply moving in the direction, it is possible to detect defects on the entire inner surface of the center hole in real time.
Impedance of two adjacent coils? 'A? In addition to the function of detecting flaws by comparing the magnet to the inner surface of the center hole, the magnet has the function of forming a DC magnetic field near the inner surface of the center hole and reducing the relative magnetic permeability of the lever part.
It is possible to prevent a decrease in defect detection ability due to the influence of eccentricity with respect to the center hole of the flaw detection head body and the fact that the object to be inspected is a ferromagnetic material, and to improve the reliability of flaw detection results. Furthermore, the #S flaw results are displayed in correspondence with each position on the inner surface of the center hole and are recorded in a timely manner, making it easy to judge the flaw detection results and providing an eddy current flaw detection device with good recording performance. can.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the configuration of a flaw detection head in an embodiment of an eddy current flaw detection apparatus according to the present invention, and FIG.
b) is a clear view of the configuration H() showing the entire structure of the same embodiment; FIGS. 3 and 4 are diagrams for explaining the action when detecting defects on the inner surface of the rotor center hole in the same embodiment; FIG. 5 is a perspective view showing a part of the flaw detection head main body in another embodiment of the present invention, and FIG. 6 is a hysteresis characteristic diagram for explaining the effect in FIG. 5. 1...Flaw detection head body, 2(1) to 2(n)...Inspection coil 16-le, 3...Connection cable, 4...Flaw detection head drive!
11+, 5... Drive mechanism, 6... Rotor, 7...
Coil selection circuit, 8a, sb... Impedance measurement circuit, 9... Oscillator, 10... Signal processor, 1 No.
...CRT display, 12...controller, 13...storage medium, 15(1) to 15(n)...permanent magnet. Applicant's agent Patent attorney Takehiko Suzue 18- Fig. 3 Fig. 4 Center hole inner surface

Claims (2)

[Claims] (1) A plurality of test coils for eddy current flaw detection are embedded radially along the inner and outer circumferential surfaces of the main body of a disc-shaped flaw detection head having an outer diameter close to the center hole of the test object having a center hole, and the flaw detection A flaw detection head is provided with a flaw detection head drive shaft, which is formed by inserting a connection cable of the test coil into the approximate center of the head body, and the drive shaft of this flaw detection head is moved in an axial direction within the center hole of the object to be inspected. a drive mechanism; an electronic switching device that sequentially switches two adjacent coils from among the inspection coils while selecting them as a pair; and when the two adjacent coils selected by the electronic switching device are energized, the object to be inspected; Two impedance measuring devices measure the impedance of the coil, which changes due to eddy currents generated around the coil, and the values measured by these impedance measuring devices are compared to determine the difference, and from the results, the above-mentioned means for determining the presence or absence of defects on the inner surface of the center hole of the object to be inspected;
An eddy current flaw detection device comprising a device for displaying or recording the results determined by this means in correspondence with the position of the inner surface of the center hole. (2) The flaw detection head has magnets arranged to locally magnetically saturate the area around the coils on the inner surface of the center hole so as to sandwich each eddy current flaw detection inspection coil embedded in the main body of the flaw detection head from both sides in the axial direction of the center hole. Claim No. 1 (1)
Eddy current flaw detection device described in ).