JPH0552816A - Internally inserted probe for pulse-type eddy current examination - Google Patents

Abstract

PURPOSE:To obtain an internally inserted probe for pulse-type eddy current examination which detects a defect such as a crack or thinning of an inner or outer surface of a small diameter tube or the like. CONSTITUTION:Two detecting coils 1,2 are assembled side by side in a case 4. A single excitation coil 3 is placed a small distance away from the detecting coils 1,2. The two detecting coils 1,2 are differentially connected to apply pulse current to the single excitation coil 3. When pulse current is applied to the excitation coil 3, eddy current occurring on an object to be inspected largely changes at a defect. Outputs of the detecting coils 1,2 also increase at the defect. Since the detecting coils 1,2 are differentially connected, a single output is provided, resulting in easy data processing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulse type eddy current flaw detection used in nondestructive inspection for detecting defects such as cracks and thinning of inner and outer surfaces of small-diameter pipes and heat transfer tubes for heat exchangers during manufacturing and during use. The present invention relates to an interpolating probe.

[0002]

2. Description of the Related Art As a method for detecting defects such as cracks and thinning existing on the surface of a material, when a detection coil wound around a ferrite core and an alternating current is passed through it is brought close to the surface of a conductor such as metal. The eddy current flaw detection method is widely known in which the eddy current generated in a conductor changes due to a defect such as a crack on the surface of the conductor, and the impedance and voltage of a detection coil change to detect the defect.

Based on the above-mentioned eddy current flaw detection method, it is possible to detect defects such as cracks and thinning of inner and outer surfaces of small-diameter pipes made of stainless steel or heat transfer tubes for heat exchangers. Mold probes have also been adopted.

In the conventional insertion type probe, as shown in FIG. 4, two detection coils a and b each having a small diameter and wound on the same axis to allow an alternating current to flow are differentially connected (that is, (When one detection coil a has a positive waveform, the other detection coil b has a negative waveform), and it is arranged at the tip of the connection cable c, and the detection coil is placed inside the inspected object having a small diameter. When the inner surface or the outer surface of the object to be inspected has a defect by inserting a and b, impedance and voltage change of the detection coils a and b are processed by a computer to determine the size of the defect and the like.

However, in the case of the conventional insertion type probe consisting of such detection coils a and b, since an alternating current is passed, the metal penetration depth of the eddy current becomes smaller as the alternating frequency increases, Defects in deep areas cannot be detected. That is, the metal penetration depth δ of the eddy current is

[0006]

[Equation 1] Given in. Where f is frequency, σ is electrical conductivity, μ
Is the magnetic permeability. Therefore, as the AC frequency f increases, the penetration depth δ rapidly decreases, so it is difficult to measure the crack depth in the case of a deep crack, and when the probe is lifted up (lift-off), its effect is large. hand,
Deep cracks cannot be detected, and the waveform in the case of the conventional probe is a continuous sine wave.

As described above, in the case of the conventional insertion type probe based on the eddy current flaw detection method, when the frequency of the exciting current of the detection coils a and b is high, the eddy current concentrates on the surface of the metal and reaches the inside of the metal material. Since it does not penetrate, there is a problem that only defects existing on the surface of a small-diameter pipe or the like can be detected.

On the other hand, in recent years, a pulse type eddy current flaw detection method, which is said to be capable of detecting defects existing inside the material, has been adopted.

This pulse type eddy current flaw detection method uses an exciting coil g in which a secondary coil e is wound on the surface of a ferrite core d and a primary coil f is wound on the outer side thereof as shown in the principle of FIG. When a primary current (pulse current) shown in FIG. 6A is applied to the secondary coil e, the primary coil f is applied to the secondary coil e.
The pulse voltage in which the direct electromotive force due to the current fluctuation of 1 and the electromotive force generated by the eddy current are superposed is generated as shown in FIG. When approached, the width of the secondary pulse changes, and if a crack is generated on the metal surface, the flow of the eddy current on the surface changes significantly, and the induced secondary electromotive force also changes significantly, so the secondary pulse ( The width of the pulse voltage) also greatly changes, but the rate of change is larger than that by the usual AC eddy current method, and it can be used as a highly sensitive sensor.

In the above pulse type eddy current flaw detection method, since the exciting coil g is excited by a rectangular pulse current, the amount of heat generated by the coil is significantly larger than that in the conventional method of exciting with a continuous sine wave as in the case of passing an alternating current. It can decrease and instantaneously pass a large current, not only it has high sensitivity especially to aluminum material, but also has a small effect of lift-off, and since pulse current is used, the penetration depth of eddy current is larger than that of alternating current, It is possible to quantitatively measure the depth of a fairly deep crack and obtain the same depth information as in the case of alternating current with a frequency that is one digit lower even if the frequency is large, and that it has high sensitivity in non-magnetic materials. , Etc. (Piping technology November 1988 issue, pages 111 to 114).

An interpolating probe utilizing the principle of the pulsed eddy current flaw detection method, which has many advantages over the one in which an alternating current is flown as described above, has not been proposed so far.

The pulse type eddy current flaw detectors that have been proposed so far are applied to flaw detection of flat plate-shaped materials.
As shown in FIG. 2, two detection coils a and b and one exciting coil g are provided on both sides with the exciting coil g interposed therebetween.
Is placed between the exciting coil g and the detection coils a and b so as to strictly shield the exciting coil g in order to prevent the exciting pulse from the exciting coil g from being directly transmitted in the air. Is provided with a shield h.

When detecting defects such as cracks existing on the surface or inside of the flat plate material, when a pulse current is passed through the exciting coil g, the eddy current on the surface of the material largely changes at the defect. Since the outputs of the detection coils a and b on both sides also largely change due to the change of the eddy current at the defect, there is a device that measures the size and depth of the defect by the output of this detection coil (British Journal of NDT). July 1
988, pages 249-256).

[0014]

However, the above-mentioned pulse type eddy current flaw detector is applied to flaw detection on a material surface or inside while moving along the surface of a flat plate-like material. In the case of being applied as an interpolating type in which the above-mentioned conventional pulse type eddy current flaw detector is inserted into the inside of a pipe or the like, it is necessary to rotate the above-mentioned conventional pulse type eddy current flaw detector in the circumferential direction. Since it is rotated along the inner surface, it is difficult to apply it as an insertion type for small-diameter pipes. Moreover, since the detection coils a and b are separated, the detection coils a and b pass through the defect position. As a result, waveforms are individually generated, and one defect results in two outputs. In data processing, two outputs of the detection coils a and b and an excitation coil g are used.
However, it is difficult to determine the defect because the voltages are separately processed.

Therefore, the present invention is intended to provide an interpolating probe based on the pulse type eddy current flaw detection method which has not been realized up to now and which is suitable for a small diameter pipe or the like.

[0016]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides one exciting coil in which two detection coils wound on the same axis are arranged side by side and differentially connected to each other so that a pulse current flows. Is arranged at a required distance from the two detection coils, and a cable is connected to the side of the detection coil farther from the exciting coil.

[0017]

When a pulse current is passed through the exciting coil and the exciting coil is inserted into the inside of a small diameter pipe or the like with the leading end side, an eddy current is generated on the inner surface of the pipe or the like near the exciting coil. If there is a defect such as a crack on the inner surface of the pipe or the like, the eddy current changes greatly. The output of the detection coil, which is inserted following the exciting coil, also changes significantly at the defective portion. Furthermore,
If the two detection coils are differentially connected, the output of the detection coil will be a single output, so that the data processing can be facilitated.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show an embodiment of an intercalating probe for pulsed eddy current flaw detection of the present invention, in which two detection coils 1 and 2 wound on the same axis are arranged side by side, and One exciting coil 3 for passing a pulse current is arranged on the side of either one of the two detection coils 1 and 2 described above (1 in the figure) with a required space between them. One detection coil 1, 2 and one excitation coil 3,
It is assembled to the elongated case 4 and integrated, and a cable 5 is connected to the side of the detection coil 2 farther from the exciting coil 3 so that a pulse current can be passed through the exciting coil 3 and the detecting coils 1 and 2 are connected. The output generated in 1. is sent to the data processing unit by the cable 5, and the exciting coil 3 and the detection coils 1 and 2 together with the case 4 have a small diameter pipe such as a small diameter pipe made of stainless steel or a heat transfer pipe for a heat exchanger. 6
To be able to insert inside. In addition, of the detection coils 1 and 2 of the insertion type probe I having the above-described configuration, the detection coil 1 closer to the exciting coil 3 has a winding number of half that of the adjacent detection coil 2 or the detection coil 1 of the detection coil 1. The output of the detection coil 1 is adjusted by providing a circuit with a resistor or the like so that the outputs of the detection coils 1 and 2 are as different as possible when there is no defect.

In the case of implementing the interpolating probe I of the present invention, as shown in FIG. 2, a differential amplifier 7 is connected to the two detection coils 1 and 2 to connect the two detection coils 1 to each other. ，
2 and the exciting coil 3
A pulse current generator 8 is connected to this to supply a pulse current, and the differential amplifier 7 and the pulse current generator 8 are connected.
Is connected to the waveform data processing system 9 and the differential amplifier 7
Data processing is performed between the difference between the outputs of the two detection coils 1 and 2 and the pulse voltage from the pulse current generator 8, and the data processed by the waveform data processing system 9 is The data is analyzed by the computer (personal computer) 10 and displayed on the plotter 11.

A half-wave sine wave as shown in FIG. 3A is applied as a pulse current to the exciting coil 3 of the insertion type probe of the present invention, and is inserted into the pipe 6 as an object to be inspected as shown in FIG. Then, an eddy current is generated on the inner surface of the pipe 6 where the exciting coil 3 first approaches. When the inner surface of the pipe 6 is cracked as a defect, the eddy current generated near the exciting coil 3 changes greatly due to the crack. When the two detection coils 1 and 2 positioned behind the exciting coil 3 in the traveling direction sequentially come to the crack, the greatly changed eddy current is detected, and at the crack, FIG.
An output B having a large reception waveform as shown in (B) is generated. Two
The outputs from the two detection coils 1 and 2 are sent to the differential amplifier 7, where the difference between the output of the detection coil 1 and the output of the detection coil 2 is obtained and sent to the waveform data processing system 9.
Since the outputs of the two detection coils become a single output at the output terminals of the differential amplifier, the waveform data processing system 9 facilitates data processing with the pulse voltage sent from the pulse current generator 8. ..

[0022]

As described above, according to the insertion type probe for pulse type eddy current flaw detection of the present invention, it is possible to use two probes in an elongated case.
The two detection coils are arranged side by side, and one exciting coil is arranged with a slight distance from the above two detecting coils to give a pulse current to the exciting coils. Therefore, the advantage of the pulse type eddy current flaw detector is obtained. At the same time, it is possible to obtain the excellent effect that the two detection coils are differentially connected to provide a single output and data processing can be easily performed.

[Brief description of drawings]

FIG. 1 is a side view showing an outline of a pulse type eddy current flaw detection probe of the present invention.

FIG. 2 is a block diagram showing a pulse type eddy current flaw detection probe and a measurement system of the present invention.

FIG. 3 shows changes in output when there is a defect,
(A) is a pulse voltage of the exciting coil, (B) is a diagram showing the output of the detection coil.

FIG. 4 is a schematic view of a conventional insertion type probe.

FIG. 5 is a diagram showing a principle of a pulse type eddy current flaw detection method.

6A and 6B show a pulse current applied to the coil of FIG. 5 and a pulse voltage generated in the coil, where FIG. 6A is a pulse current and FIG. 6B is a pulse voltage.

FIG. 7 is a schematic view of a conventional pulse type eddy current flaw detector.

[Explanation of symbols]

 1, 2 Detection coil 3 Excitation coil 4 Case 5 Cable 6 Piping

Claims (1)

[Claims] 1. An elongated case, in which two detection coils are arranged in the longitudinal direction of the case and differentially connected to each other, and one exciting coil for passing a pulse current is provided at a required distance from the two detection coils. An intercalating probe for pulse type eddy current flaw detection, characterized in that the cable is connected to the side of the detection coil that is located inside the case and that is far from the excitation coil.