JPH0639331Y2 - Eddy current flaw detection coil - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention is a detection for eddy current flaw detection for highly accurate flaw detection on the outer surface of an elongated inspected material such as a metal strip, pipe, and rod. Regarding coils.

[Conventional technology]

Conventionally, when a probe coil is used as a detection coil for mutual induction type eddy current flaw detection using a through-type excitation coil, a detection coil having a cylindrical shape, a rectangular shape, or a pancake shape is used. It was installed vertically and used. However, when installed in parallel, it is necessary to make a large gap between the exciting coil and the material to be inspected due to the size of the coil in the radial direction, and when installed vertically, the above gap can be small. Since the flaw detection sensitivity varies depending on the radial position of the detection coil, a plurality of detection coils are arranged alternately in the longitudinal direction of the inspection material so that some of the detection coils overlap each other in the circumferential direction of the inspection material. Had to do.

FIG. 5 is a diagram showing an example in which the detection coil axis is parallel to the flaw detection surface in the conventional method, and FIG. 6 is a diagram showing an example in which the detection coil axis is perpendicular to the flaw detection surface in the conventional method.
In this, 1 is a material to be inspected, 2 is a detection coil, and 3 is an exciting coil.

[Problems to be solved by the device]

When the coil axis was installed parallel to the flaw detection surface by the conventional method, it was necessary to make a large gap between the exciting coil and the material to be inspected due to the size of the coil in the radial direction, resulting in a decrease in sensitivity. . When installed vertically, the detection coils need to be staggered alternately, which causes a detection time difference between defects at the same position in the circumferential direction of the inspection material, and the area of the detection coil in the longitudinal direction of the inspection material. As a result, the problem that the end dead zone becomes long occurs.

The present invention has been made to solve the problems of the prior art. For the eddy current flaw detection, the gap between the material to be inspected and the longitudinal direction of the detection coil is made small to improve the detection accuracy. It is intended to provide a detection coil.

[Means for solving problems]

The detection coil for eddy current flaw detection according to the present invention is a detection coil used for mutual induction type eddy current flaw detection using a through-type excitation coil. Prepare a plurality of coils in which the corresponding parts are respectively bent on the side opposite to the surface facing the material to be inspected, and make the line of the part where each coil is not bent follow the circumferential direction of the material to be inspected. It is characterized in that the bent portions of the coil are arranged next to each other and continuously along the flaw detection surface of the material to be inspected.

[Action]

It goes without saying that when using a combination of a through-type excitation coil and a rectangular flat detection coil, the gap between the flaw detection surface and the inner wall of the excitation coil can be minimized, but the defect position can be moved from the center of the detection coil to the left and right. The relationship between the circumferential position of the defect and the degree of detection when displaced is broader than when a circular coil is used as the detection coil, and both ends are bent so that only the circumferential winding part faces the flaw detection surface in the circumferential direction. If they are arranged consecutively and the defect signals detected by the respective detection coils are added, the sensitivity decrease when the defects are deviated from the center of the individual detection coils is the same as the defects detected by the adjacent detection coils. Since it is compensated by the signal, the sensitivity change in the circumferential direction is almost eliminated. Further, since the flat coil has a weak directivity, it has an advantage that it is effective against various defects.

〔Example〕

FIG. 1 is an exploded view of a detection coil according to the present invention. The winding is bent flat into a rectangular shape. Second
The figure shows an example in which the present invention is applied to flaw detection of a steel pipe.
A steel pipe of mm is used as the material to be inspected 1, and six flat coils whose both ends are bent are continuously arranged in the circumferential direction to form the detection coil 2. In this case, the gap between the detection coil 2 and the flaw detection surface is 4 mm, and the gap between the flaw detection surface and the inner wall of the exciting coil 3 is 7 mm, both of which are small values.

Using this detection coil 2, magnetic saturation was carried out by a magnetic saturation coil (not shown), and the steel pipe was flaw-detected in a state in which noise due to variations in magnetic permeability was eliminated. As a result, φ0.8 mm
An S / N ratio of 15 was obtained for the through drill hole. By the way, the SN ratio is 8 when the same drill hole is detected using the coil shown in FIG.

FIG. 3 is a graph showing the change in the degree of detection when the through-drilling hole of φ0.8 mm is displaced left and right from the coil center for the one detection coil in FIG. It can be seen from this graph that the sensitivity decrease at the end of the detection coil is -2 dB, which is small.

FIG. 4 shows a structure in which six detection coils are combined as shown in FIG. 2 and the detection signals from the respective coils are added.
The relationship between the circumferential position of the 0.8 mm through-drill hole and the detectability is shown, and it can be seen that the sensitivity in the circumferential direction is the same. Thus, by using the detection coil according to the present invention, it is possible to perform flaw detection with extremely high accuracy.

[Effect of device]

If this device is used, the gap between the flaw detection surface and the exciting coil can be minimized as described above, which is advantageous in terms of detection accuracy.However, even if a cooling mechanism is incorporated in a hot flaw detection that requires cooling of the detection coil, the above gap can be reduced. Is advantageous because it can be taken within a range that does not interfere with flaw detection. Further, the detection coils can be continuously arranged in the circumferential direction, and it becomes possible to suppress the sensitivity unevenness in the circumferential direction.

[Brief description of drawings]

FIG. 1 is a developed surface of a detection coil according to the present invention, and FIG.
The figure is a sectional view showing an example in which the present invention is applied to flaw detection of a steel pipe. FIG. 3 is a graph showing a circumferential direction detection characteristic of a detection coil according to the present invention, and FIG. 4 is a graph showing a circumferential direction detection characteristic when six detection coils according to the present invention are continuously arranged in the circumferential direction. . FIG. 5 is a sectional view of a conventional detection coil whose detection coil axis is parallel to the flaw detection surface, and FIG. 6 is a partial sectional view of a conventional detection coil whose detection coil axis is perpendicular to the flaw detection surface. 1: Inspected material, 2: Detection coil 3: Excitation coil

Claims (1)

[Scope of utility model registration request] 1. In a detection coil used for mutual induction type eddy current flaw detection using a through-type excitation coil, a line is bent into a rectangular shape and wound flat, and portions corresponding to opposite sides of the rectangle are respectively covered. Prepare a plurality of coils that are bent on the side opposite to the surface facing the inspection material, bend the lines of the parts of each coil that are not bent in the circumferential direction of the inspection material, and bend each coil. The detection coil for eddy current flaw detection is characterized in that the above-mentioned parts are arranged next to each other and continuously along the flaw detection surface of the material to be inspected.