JPS6232355A - Eddy current flaw inspector - Google Patents

Abstract

PURPOSE:To execute an eddy current flaw inspection by a high detecting capacity, by using a long through-coil for an excitation, and placing plural pieces of air-core detecting coils so as to be opposed in the outside periphery of a body to be inspected. CONSTITUTION:A sine wave voltage generated by an oscillator 10 is supplied to the exciting coil 5 of a detecting part. The coil 5 is a solenoid coil being long enough, therefore, a roughly uniform alternating magnetic field is formed in its inside. Also, to the surface and the surface layer of a body to be inspected 1, the eddy current of the opposite direction flows in the same direction as a current flowing in the coil 5 so as to negate its alternating magnetic field. Moreover, if a defect exists on the surface of the body to be inspected 1, the eddy current goes round the defect and flows, therefore, the magnetic field comes to have a vertical component. As a result, a magnetic field by this defect and a pancake coil 6 are interlinked, and a voltage is induced in the coil 6. This induced voltage is brought to a synchronous detection by a synchronous detector 14 through an amplifying circuit 12 by referring to a phase which has phase-shifted a phase of the oscillator 10 by a phase shifter 13. Also, a high frequency noise component is cut by a band-pass filter 15, and a defect is detected by a pulse height discriminating circuit 16.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an eddy current flaw detection testing device used for detecting surface flaws in metal rods, metal wires, metal tubes, etc.

[Conventional technology]

Eddy current testing using penetrating coils is widely used to detect defects on the surface or surface layer of metal conductors such as rods, wires, and tubes. However, this method has the disadvantage that the defect detection ability decreases as the size of the object increases. The reason for this is that when the average diameter of the detection coil is D and the length of the defect in the circumferential direction on the surface of the object to be inspected is Q, if the filling rate is approximately constant, the defect detection ability is equal to the length of the detection coil L π・This is because it is proportional to D (see Figure 2), that is, as the outer diameter d of the object 1 increases, 1/πD becomes smaller.
As a result, the defect detection ability also decreases. A countermeasure for this is to increase the ratio Q/L between the circumferential length of the detection coil and the circumferential length Q of the defect. Specifically, the probe coil is detected. . In other words, there are two methods: rotating the probe coil around the object (rotating probe method) or arranging many probe coils around the object (multi-probe method).In fact, the rotating probe method is widely used. There is. However, the probe coil has the disadvantage that it is more susceptible to relative lift-off (gap) fluctuations than the through-type coil. In the rotary boolobe method, as a method to reduce this problem, for example, as shown in Japanese Patent Application Laid-Open No. 179354/1982, it has been proposed to maintain a constant distance between the surface of the subject and the probe using a mechanical tracing mechanism. There is. However, this method has a problem in that the tracing mechanism becomes complicated. Furthermore, in the case of the object 1 to be inspected that does not have a circular cross-sectional shape, such as a rectangular steel pipe, it is difficult to detect flaws using the one-rotation probe method. There are 1 methods that can be adopted for the multi-probe method.
For example, as shown in Japanese Patent Application Laid-Open No. 59-9552,
A signal suppression method due to lift-off variation is presented that combines a standard comparison type probe and multi-frequency eddy current testing technology. However, this method has the problem that the electronic circuit becomes complicated.

[Problem that the invention seeks to solve]

As described above, in the through-coil method, as the diameter of the object increases, the defect detection ability decreases.

In principle, the probe coil method can provide a constant detection sensitivity regardless of the diameter of the object to be inspected, but it is susceptible to lift-off, and it is practically impossible to obtain sufficient detection sensitivity in on-site flaw detection where lift-off fluctuations are unavoidable. Ta. When the diameter of the specimen is large, methods that reduce the effects of lift-off fluctuations and have high defect detection ability require complicated mechanical or electronic circuits, whether using a rotating probe method or a multi-probe method. cost and operation and maintenance.

There was a problem.

[Means for solving problems]

This invention was made by focusing on such conventional problems, and uses a sufficiently long through coil for excitation, and a plurality of air-core detection coils are placed at intervals with their surfaces facing the outer circumferential surface of the test object. , are arranged around the subject so as to face each other.

The present invention will be explained in detail below based on the drawings.

FIG. 1 is a diagram showing a detection section of an eddy current flaw detection apparatus according to the present invention. This invention employs a so-called mutual induction method. 1 is an object to be tested such as a metal tube, 2 and 3 are bobbins made of nylon, Bakelite, etc., 4 is a stepped portion of the bobbin 3, 5 is an excitation coil wound around the bobbin 2, and 6 is fixed to the stepped portion. This is a detection coil.

The detection coil 6 is an air-centered flat circular coil (hereinafter referred to as a "pancake coil") using an ultra-fine magnet wire. This pancake coil 6 is installed parallel to the cylindrical surface. This detection coil bobbin 3 is structured to be inserted into the excitation bobbin 2.

In FIG. 1, the excitation coil 5 and its bobbin 2 are not shown in the center in order to show the arrangement of the detection coil 6, but it goes without saying that in reality, these exist continuously. The conducting wire of the pancake coil 6 is taken out to the outside through grooves 7 provided in two places in the detection coil bobbin 3, and guided to the eddy current flaw detection apparatus control section.

FIG. 3 shows an electronic circuit of an eddy current flaw detection device according to the present invention. 10 is an oscillator, 11 is a power amplifier, 12 is an amplifier for the detected signal, 13 is a phase shifter, 14 is a synchronous detection circuit,
15 is a bandpass filter, and 16 is a pulse height discrimination circuit. In this figure, the output of the detection coil 6 is directly connected to the amplifier 12, but it is also possible to configure two coils to form two sides of a bridge circuit, or connect multiple detection coils in series. You can do it like this.

[Effect]

The operation of this invention will be explained below. The sine wave voltage generated by the oscillator 10 is amplified by the power amplifier 11 and supplied to the excitation coil 5 of the detection section.

Since this excitation coil 5 is a sufficiently long solenoid coil, a substantially uniform alternating magnetic field is formed inside it. Eddy currents flow in the same (circumferential) direction as the current flowing through the excitation coil 5 but opposite in direction to the surface and surface layer of the subject so as to cancel out the alternating magnetic field. When there is no defect in the object to be inspected, the generated magnetic field is parallel to the bobbin surface and the magnetic field does not interlink with the pancake coil 6, so no voltage is generated in the pancake coil 6. However, if there is a defect on the surface of the object, the eddy current flows around the defect, and the resulting magnetic field has a perpendicular component. As a result, the magnetic field due to this defect and the pancake coil 6 become interlinked, and a voltage is induced in the pancake coil 6. This induced voltage is amplified by an amplifier 12, and synchronously detected by a synchronous detector 14 with reference to the phase obtained by shifting the phase of the oscillator 10 by a phase shifter 13. At this time, the amount of phase shift is selected so that the influence of lift-off of the subject is minimized. Thereafter, a bandpass filter 15 further cuts out high frequency noise components, and a pulse height discrimination circuit 16 detects defects.

[Embodiments of the invention]

Examples and experimental results will be described below.

FIGS. 4 and 5 show the dimensions of the exciting coil bobbin 2 and the detection coil bobbin 3 used in the experiment, respectively. The unit is l11m. The excitation coil bobbin 2 has a wire diameter of 0.
A 6 nm magnetor wire was wound 108 times. The detection coil is a brass rod with an outer diameter of 4III11 and a wire diameter of 0.05.
It was manufactured by winding +om ultra-fine magnet wire 200 times. Then, two detection coils were attached to the stepped portion of the detection coil bobbin 3, and this bobbin 3 was inserted into the excitation coil bobbin 2 to form a detection section. Since the effective detection range of the circular pancake coil 6 is approximately 0.75 times the diameter, in this embodiment, the effective range is 4X0.75X2=6++n out of the entire circumference. Therefore, we conducted an experiment in which artificial defects were placed within this range.

A commercially available eddy current flaw detection bag opening was used. Outer diameter 1 as a sample
0m, depth of 0.3nm as an artificial defect in a steel pipe with a wall thickness of 1m
, a groove with a width of 0.51111 mm and a length of 10 mm was used. FIG. 6 shows the results of an experiment at the operating frequency of RkHz. From FIG. 6, it can be seen that detection is achieved with a sufficiently high S/N ratio. Further, in the above, when an experiment was conducted using a self-induction method using only the pancake coil 6, the influence of the backlash signal was so large that it could not be detected at all.

In the above description, the detection coil 6 is an air-centered flat circular coil, but it may of course be rectangular.

It is preferable that the shape of the detection coil 6 is selected appropriately depending on the form of the defect to be detected.

〔Effect of the invention〕

As explained above, according to the present invention, the lift-off effect associated with the probe coil can be significantly reduced with an extremely simple configuration, resulting in high detection in eddy current flaw detection in actual sites where some vibration of the sample is unavoidable. ability can be obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a detection section of an eddy current flaw detection testing device according to the present invention, with the central portion of the bobbin 2 cut away. FIG. 2 is a cross-sectional view of a conventional penetrating detection coil and a subject passing through it. FIG. 3 is a block diagram showing the configuration of the electronic circuit section of the eddy current flaw detection apparatus according to the present invention. 4 and 5 are cross-sectional views showing the dimensions of an example of the excitation coil bobbin and the detection coil bobbin of the eddy current flaw detection apparatus of the present invention, and FIG. 6 shows defect detection in eddy current flaw detection using these bobbins. A graph showing an example of a signal, FIG. 7 is a graph showing a defect detection signal according to a conventional method. 1...Object to be inspected 2...Bobbin for exciting coil 3...Bobbin for detection coil 4...Step-cut portion of bobbin for detection coil 5...
...Excitation coil (through-hole coil for excitation) 6 ...
・Detection coil (air-centered flat coil for detection) 7...
Groove 8...Artificial defect lO...
・Oscillator 11...Power amplifier 12...
...Amplifier 13... Phase shifter 14.
... Synchronous detector 15 ... Bandpass filter 16 ... Wave height discrimination circuit 17 ... Penetrating detection coil 18 ... Surface defect 48 Zushima 58 Zukin 4b Zuke 5b Zushima 6 Voice 7 Figure 4 Yaguan procedural amendment (voluntary) Displayed on September 9, 1985 Patent application No. 172149 1985 J, 9e Ming name Eddy current Flaw Detection Testing Device 3, Relationship with the Amendment Case Patent Applicant Address 2-6-3 Otemachi, Chiyoda-ku, Tokyo
- Name 4, object of representation Detailed description of the invention in the specification and drawing 6
, Contents of amendment (1) 2nd line of specification letter (3rd line rl/πD") to rQ/π
D” and correct it. (2) Correct Figure 2 as shown in the attached sheet. 7. Attached document drawing of eyelids... 1. Foliage 2.

Claims (1)

[Claims] A vortex current comprising an excitation penetrating coil arranged to penetrate the test object in the axial direction thereof, and a plurality of air-core flat flat detection coils arranged so that the flat plane faces the outer circumferential surface of the test object passing through the excitation penetrating coil. Flaw detection testing equipment.