JPH10239282A - Eddy current flaw-detecting probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evaluate the shape and dimension of a crack quantitatively and at the same time, perform an inverse analysis easily by generating an eddy current in parallel straight line shape with a same strength by a coil exclusive for excitation. SOLUTION: A probe has a cylindrical flaw-detection part body 1 that is inserted into a metal pipe. In this case, a coil winding 3 is wound around the peripheral surface of the flaw-detection part body 1 in peripheral direction nearly equally and in parallel for forming a solenoid coil part 4 with a specific width and at the same time a plurality of magnetic sensors 5 are arranged in peripheral direction on a center part in width direction of the solenoid coil part 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current flaw detection probe used for maintenance inspection of metal tubes and the like of a heat exchanger in a nuclear power plant or the like.

[0002]

2. Description of the Related Art When it is difficult to access from the outside of a metal tube such as a thin tube of a heat exchanger, a probe is inserted into the metal tube to detect flaws. A typical probe is a bobbin type probe that can perform high-speed flaw detection and has good insertability into a curved tube portion. In this bobbin coil type probe, the coil is formed by winding the winding in the circumferential direction of the cylindrical probe, so that the eddy current flows in the circumferential direction of the metal tube. That is, in eddy current testing, eddy current in a metal tube excited by a coil in a probe is disturbed by a defect in the tube, and the defect is detected using a changing magnetic field. In the above probe, when defects such as cracks in the metal tube exist in the circumferential direction of the tube,
Since the direction of the crack is parallel to the direction of the flow of the eddy current, the eddy current is hardly disturbed, and there is a problem that the flaw detection sensitivity is low.

On the other hand, a plurality (often 8
There is also a multi-coil type probe having a single pancake coil (also referred to as a surface coil). The eddy current caused by the pancake coil of this probe is in a relatively narrow range of the metal tube, but there is a portion that flows crosswise to the circumferential crack. There is an advantage that the sensitivity is high.

However, the eddy current generated by the pancake coil of the multi-coil type probe is strong immediately below the winding portion of the coil and becomes weaker as the distance from the center increases, so that the sensitivity decreases near the middle portion between the coils. However, there is a problem that it is not suitable for flaw detection of a crack having a short length existing in the intermediate portion.

[0005] There is also a rotating coil type probe in which about 1 to 3 pancake coils are brought into close contact with the tube wall and scanning is performed in a helical manner while rotating the probe. , There is a problem that the flaw detection time becomes very long.

Further, in each of the above three types of eddy current flaw detection probes, the eddy current caused by the coil is maximum immediately below the winding portion of the coil, and becomes weaker as the distance from the coil increases. Therefore, for the same defect crack, if the relative relationship between the coil and the defect crack changes, the way in which the eddy current is interrupted will differ, and the magnitude and phase of the output signal will also change. Therefore, there is also a problem that it is difficult to accurately perform quantitative evaluation of the shape and size of the defect crack.

[0007]

SUMMARY OF THE INVENTION The present invention addresses the above-mentioned situation, and is provided with a dedicated excitation coil for generating a uniform eddy current in the flaw detection portion main body of the probe, so that a crack generated in the pipe can be reduced. It is intended to facilitate quantitative evaluation of shape and dimensions.

[0008]

That is, an eddy current flaw detection probe according to the present invention which meets the above-mentioned object is an eddy current flaw detection probe provided with a substantially cylindrical or columnar flaw detection body inserted into a metal tube or the like. On the peripheral surface of the flaw detection unit main body, a winding is wound substantially evenly and parallel in the circumferential direction to form a solenoid coil portion having a predetermined width, and a pancake coil or the like is placed on a center portion of the solenoid coil portion in the width direction. The magnetic sensor of the above is provided.

In the eddy current inspection probe according to the present invention, a plurality of the magnetic sensors are disposed in the main body of the inspection part in a circumferential direction without a dead zone between the sensors. It is also possible to perform high-speed flaw detection at substantially the same speed as the probe. further,
It is also possible to bury a core made of a magnetic material below the solenoid coil portion to shorten the width of the solenoid coil portion.

[0010]

In the probe according to the present invention, the solenoid coil forms an eddy current flow in the circumferential direction of the tube, and the eddy current flows at substantially the same intensity at the center in the width direction of the solenoid coil portion. Because of the parallel linear shape, quantitative evaluation of the shape and size of the crack in the tube can be easily performed by the magnetic sensor disposed in this portion. The probe of the present invention is suitable for detecting an axial crack in a pipe.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described.

FIG. 1 is a perspective view showing an eddy current inspection probe according to an embodiment of the present invention, FIG. 2 is a sectional view taken along line AA of FIG. 1, FIG. 3 is a sectional view taken along line BB of FIG. It is sectional drawing which shows the flow of the eddy current of a thin metal tube by a probe.

The probe of the above embodiment includes a column-shaped flaw detection unit main body 1 inserted into a thin metal tube P such as a reactor heat exchanger, and a cable 2 extending from a lower portion of the main body 1. . Then, as shown in FIGS. 1 to 3, the winding 3 is wound around the circumferential surface of the flaw detection unit main body 1 uniformly and substantially in parallel in the circumferential direction, and the width W is equal to the length of the defect crack to be flawed. A solenoid coil portion 4 having a size of at least twice is formed, and a plurality of magnetic sensors 5 each composed of a pancake coil having a diameter of about 3 mm are arranged on the center (in the outer peripheral side) in the width direction of the solenoid coil portion 4 in the circumferential direction. They are arranged as if they were. In addition,
The defect to be detected by the probe is about 3 to 5 mm in length and about 0.1 mm in width.

The magnetic sensors 5 are arranged at equal intervals over the entire circumference of the flaw detection unit 1 so that there is no dead zone between the sensors 5. When the sensor 5 is a wound coil, the width W of the solenoid coil section 4 is determined by a magnetic field provided on the coil section 4 so that a uniform eddy current E is detected by the magnetic sensor 5. It is appropriate to set the diameter of the sensor 5 to at least 5 times or more, preferably 10 to 20 times. In addition, the width W
As described above, it is appropriate that the defect crack to be inspected is twice or more, preferably 20 mm or more, provided that a magnetic core 6 is provided inside the solenoid coil portion 4 as shown in FIG. It is possible to reduce the width W of the solenoid coil part 4 somewhat. In this case, the upper and lower cores 6
Can be connected, or they can be solid cylinders. Although the core 6 is shown in the drawing, there may be cases where the core 6 is not provided.

Thus, in the eddy current flaw detection probe according to the embodiment of the present invention, as shown in FIG. 4, the solenoid coil portion 4 forms a flow of the eddy current E in the circumferential direction of the pipe P,
Further, at the center portion C in the width direction of the solenoid coil portion 4, since the flow of the eddy current E becomes a substantially parallel straight line having the same strength as shown in the figure, the plurality of magnetic sensors 5 disposed in this portion provide It is possible to easily perform a quantitative evaluation of the shape and size of the crack in the pipe P. Further, since the eddy current E is uniform as described above, input parameters are reduced, and it becomes easy to perform an inverse analysis for predicting a shape and a size of a crack from an obtained signal, which is useful for developing an inverse problem analysis code. It becomes possible. And since the flaw detection probe of the above-mentioned embodiment is provided with the magnetic sensor 5 all around, it is not necessary to scan spirally and it is possible to perform high-speed flaw detection, especially for flaw detection of a crack generated in the axial direction of the pipe P. Are suitable. In addition, it is possible to scan spirally by reducing the number of magnetic sensors 5 in the probe.

As described above, in the eddy current flaw detection probe according to the embodiment of the present invention, a pancake coil is taken as an example of the magnetic sensor 5, but another magnetic sensor such as a Hall element or a flux gate may be used instead. Although a magnetic sensor having a diameter of 3 mm was used as the magnetic sensor 5, the size of the sensor 5 can be changed according to the size of a defect crack to be detected.
And it goes without saying that the probe of the present invention can be used for other than a nuclear power plant.

[0017]

As described above, the eddy current flaw detection probe of the present invention is an eddy current flaw detection probe provided with a substantially cylindrical or columnar flaw detection part main body inserted into a metal tube or the like.
A winding is wound around the circumferential surface of the flaw detector body in a substantially uniform and parallel manner in the circumferential direction to form a solenoid coil portion having a predetermined width, and a magnetic sensor is disposed on a central portion in the width direction of the solenoid coil portion. The solenoid coil forms an eddy current flow in the circumferential direction of the tube, and the eddy current flow has a substantially parallel linear shape at the center in the width direction of the solenoid coil portion. Therefore, it is possible to easily perform the quantitative evaluation of the shape and size of the crack in the axial direction of the pipe by the magnetic sensor disposed in this portion, and furthermore, it is said that the eddy current is uniform. Therefore, the parameters at the time of the inverse analysis can be reduced, and this has a remarkable effect that the defect shape can be easily estimated. And, in this probe, by connecting the magnetic sensors in the circumferential direction,
High-speed flaw detection at almost the same speed as that of a conventional bobbin type probe or multi-coil type probe is also possible.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an eddy current inspection probe according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view taken along line BB of FIG. 1;

FIG. 4 is a cross-sectional view showing a flow of an eddy current in a thin metal tube by the probe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flaw detection part main body 2 Cable 3 Winding 4 Solenoid coil part 5 Magnetic sensor 6 Core P Metal tube W Width E Eddy current C Part where eddy current is uniform

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Kotaro Maeda 1-3-7 Tosabori, Nishi-ku, Osaka City Nuclear Engineering Co., Ltd.

Claims (3)

[Claims] 1. An eddy current flaw detection probe provided with a substantially cylindrical or substantially cylindrical flaw detection portion main body inserted into a metal tube or the like, wherein windings are substantially uniformly and substantially circumferentially formed on the peripheral surface of the flaw detection portion main body. An eddy current flaw detection probe characterized by forming a solenoid coil portion having a predetermined width by being wound in parallel, and having a magnetic sensor such as a pancake coil disposed on a central portion in the width direction of the solenoid coil portion. 2. An eddy current flaw detection probe according to claim 1, wherein a plurality of said magnetic sensors are arranged circumferentially on said flaw detection portion main body without a dead zone between said sensors. 3. The eddy current inspection probe according to claim 1, wherein a core made of a magnetic material is buried under the solenoid coil portion.