JPH0943204A - Coil for detecting defect in circumferential direction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a defect of a pipe-shaped object to be tested in a circumferential direction with high accuracy by a constitution wherein a coil formed in disk shape is disposed in an inner circumferential portion of the object to be tested such that a central face between both of edge faces includes a central axis of the object to be tested. SOLUTION: Eight pancake type coils 5 held by a cylindrical body 6 are disposed on two planes crossing perpendicularly by four pieces such that the centers of the coils are away from the central axis of the body 6 at the same distance. A central face between both of edge faces of each of the coils includes the central axis of the body 6. The coils 5 are connected from one in one plane to one in another plane to form two series circuits to be used as operation coils. When AC currents 3 are applied to the coils 5, eddy currents 3 which are parallel to the central axle of the body 6 are generated. The eddy currents 3 are varied by being affected by the defect 4 in the circumferential direction, thereby causing the variation of an impedance of the coil 5. As a result, it is possible to readily detect a defect in the circumferential direction with high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a heat exchanger tube, etc.
The present invention relates to a detection coil for an eddy current flaw detection tester that detects defects in a tubular test object, and in particular, can detect defects such as circumferential cracks with high precision using a small disk-shaped coil. For coils.

[0002]

2. Description of the Related Art Many heat exchangers are used for heating or cooling fluids such as raw materials and products in power plants, oil refineries, and other chemical plants. Naturally, these isothermal heat exchangers need to be inspected for maintenance at the time of installation or after being used for a certain period. In the shell-and-tube type, which is the mainstream of heat exchangers, it is almost impossible to bring the measuring end of the nondestructive testing device close to the outer surface of the tube because many tubes are densely assembled. For that purpose, an eddy current flaw detector is used which can inspect the tube only by inserting the measuring end into the inner surface of the tube.

As is well known, the eddy current flaw detection test is an inspection method for detecting a defect (discontinuous portion) by capturing a change in eddy current induced in a test object, and is also called an electromagnetic induction test. In the case of this test, a detection coil in which an alternating current is flowing is used as the measuring end. Conventionally, this detection coil has been used in a method as shown in FIG. That is, the detection coil 2 is inserted inside the tubular test object 1. The axis of the coil 2 wound in a cylindrical shape is the same as or parallel to the axis of the test object 1 as shown in the figure. In this case, the eddy current 3 is generated in the circumferential direction as shown by the current flowing through the coil.

The measurement principle of the eddy current flaw detection test is that the flow of eddy current generated in a tubular test object is changed by being blocked by a defect, which changes the impedance of the coil and is detected and measured by the eddy current flaw detector. It is in. If the tubular test object has a defect 4 such as a circumferential crack as shown in the figure, the defect is caused because the defect 4 and the flow direction of the eddy current 3 coincide with each other in the conventional method described above. Defects cannot be detected because they do not interrupt the current flow and there is almost no change in the impedance of the coil.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and an eddy current flaw detection test capable of accurately detecting a circumferential defect of a tubular test object. An object of the present invention is to provide a coil for detecting a circumferential defect of a device.

[0006]

[Means for Solving the Problem and Its Action] The applicant of the present invention is trying the experiment shown in the following FIGS. 6 and 7 in order to solve this problem. That is, it is smaller than the conventional coil and has a disk shape.
(Hereinafter, this coil will be referred to as “pancake coil” due to its shape). The pancake coil 5 is arranged on the inner circumference of the test object so that the center planes of both end surfaces thereof include the central axis of the test object 1, and if an alternating current is applied, the test object is shown in FIG. At the same time, an eddy current 3 parallel to the central axis is generated. This eddy current is blocked by the circumferential defect 4 and changes, which changes the impedance of the coil, so that the circumferential defect can be detected easily and accurately. The pancake type coil 5 is provided on the end surface of the test object 1
When the perpendicular is drawn from the center axis of the test object, the test object is arranged so that it becomes radial with respect to the center axis, and if an alternating current is applied, the test object will have a spiral shape as shown in FIG. Eddy current 3 is generated. This eddy current is blocked by the circumferential defect 4 and changes, which changes the impedance of the coil, so that the circumferential defect can be easily and accurately detected.

The present invention has been made on the basis of the above-mentioned experiments, and the detection coil of the eddy current flaw detection test apparatus has a pancake shape as described above, and the test object is tested as described above or By arranging it inside, the above-mentioned object is achieved. By doing so, defects in the circumferential direction that could not be detected conventionally can be easily and accurately formed.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing a first embodiment of a circumferential defect detecting coil according to the present invention, in which (a) is a front view,
(B) is a left side view, (C) is its connection diagram, and (D) is another connection diagram ((D) will be described later). In the figure, eight pancake type coils 5 are held in a substantially columnar main body 6. The centers of the eight pancake-type coils 5 are orthogonal to the central axis of the main body with a certain space 2
Four of them are arranged on each plane, and the center plane between both end surfaces of each pancake coil 5 is arranged so as to include the center axis of the main body 6. The eight pancake type coils are sequentially connected from one located on one plane to another located on the other plane, forming two series circuits as shown in (c). These two circuits are used as actuating coils.

FIG. 2 is a diagram showing a second embodiment of the present invention. (A) is a front view, (b) is a left side view, (c) is its connection diagram, (d) is another connection diagram. It is a figure ((d) will be described later). In the same figure, as in the previous example, the centers of the eight pancake type coils 5 are arranged on two planes,
In the case of this example, the perpendiculars drawn from the central axis of the main body 6 to the end faces of the respective coils 5 are arranged radially with respect to the central axis of the main body. The wiring method is the same as in the previous example, as shown in (c).
Similar to the previous example, two series circuits are used as the operating circuits.

Next, the applicant is conducting an experiment to confirm the detection performance of the circumferential defect detecting coil according to the present invention, which will be described below. FIG. 3 is a diagram showing a test piece. As shown, the test piece is a seamless brass tube having an outer diameter of 25.4 mm and a wall thickness of 1.245 mm.
Defects of are processed in this. The shape, dimensional position, etc. of this artificial defect are as described. The width of the slit is about 0.3 mm. The test charts showing the results of experiments using the test pieces under the following conditions are shown in FIGS. 6 to 8, which are collectively shown in FIG. 4. Two test frequencies are used. Sensitivity: The signal of a 3 mmφ drill hole (standard flaw) was set to an amplitude of about 20 mm (135 °) at the recorder output. The following is used as a coil. a) Conventional coil (see FIG. 8) b) Coil shown in the first embodiment (see FIG. 1) c) Coil shown in the second embodiment (see FIG. 2)

The evaluation of the experiment is as shown in FIG. 5 ((a) shows the comparison of the detection performance of each coil, and (b) shows the phase angle of the detected signal). From this result, the following is revealed. The coil of Example 2 is the best in detecting the slits (cracks) in the circumferential direction. The conventional coil has a long through slit (l = 1
There is no detectability except for 0 mm). Although the coil of Example 1 can secure a certain degree of detectability, the detection efficiency is lower than that of the coil of Example 2, and the flaw detector sensitivity is close to the maximum (53.5 db), so the S / N is lowered. In both coils, the slits that do not penetrate have considerably lower peak values than the through slits. It is considered that the coil of Example 2 can evaluate the phase of the defect signal.

In each of the embodiments described above, the number of pancake coils is eight, but this number does not necessarily have to be eight and can be any number of two or more. In the above embodiment, the number of coils required is 2n because the coils are arranged on the two surfaces. However, such an arrangement is not always necessary. Further, in the above-mentioned embodiment, when the series wiring is performed, the coil arranged on one surface is sequentially wired to the coil arranged on the other surface. It is for the pipe end to offset the effect of. Therefore, when used in a place other than the pipe end, the coils arranged on one surface are wired (see FIGS. 1 (d) and 2 (d)). It is needless to say that the present invention can be effectively implemented even in the case of application examples other than the above-mentioned embodiment.

[0013]

As described above, according to the present invention, as a detection coil used in an eddy current flaw detector, a pancake type coil, which is smaller than a conventional coil, is appropriately arranged in an appropriate number on the inner surface of the test object. Thus, it has an excellent effect that a defect in the circumferential direction, which has been difficult in the past, can be accurately detected.

[Brief description of drawings]

FIG. 1 is a first coil for circumferential direction defect detection according to the present invention.
FIG. 4A is a diagram showing an embodiment of the present invention, (A) is a front view, (B) is a left side view, and (C) is a connection diagram thereof.

FIG. 2 is a view showing a second embodiment of the present invention, (a) is a front view, (b) is a left side view, and (c) is a connection diagram thereof.

FIG. 3 is a diagram showing an experimental test piece for confirming detection performance.

FIG. 4 shows the experimental results.

5A and 5B are graphs showing evaluation results of experiments, in which FIG. 5A shows a comparison display of detection performance of each coil, and FIG. 5B shows a phase angle of a detected signal.

FIG. 6 is a diagram showing an arrangement example of pancake coils.

FIG. 7 is a view showing an arrangement example of pancake type coils.

FIG. 8 is a diagram showing a conventional coil.

[Explanation of symbols]

1 Test object 2 Detection coil 3 Eddy current
4 Defect 5 Pancake type coil 6 Main body

Claims (4)

[Claims] 1. A detection coil used in an eddy current flaw detection test apparatus for detecting a defect in a tubular test object, wherein the coil is formed into a disk shape, and the center planes of both end surfaces of the coil are the test object. A coil for circumferential defect detection, which is arranged on the inner circumference of a test object so as to include the central axis of the object and is capable of accurately detecting defects such as cracks in the circumferential direction of the test object. 2. A detection coil used in an eddy current flaw detection test apparatus for detecting defects in a tubular test object, wherein the coil is formed in a disc shape, and the circle is formed from a central axis of the test object. The vertical line drawn to the end face of the plate is arranged on the inner circumference of the test object so as to be radial from the central axis, and it is possible to accurately detect defects such as circumferential cracks of the test object. Coil for circumferential defect detection. 3. The 2n number of disk-shaped coils are arranged such that the centers thereof are located on each of two planes orthogonal to the central axis with a certain distance therebetween, and one of the two planes is disposed on one plane. 3. The circumferential defect detecting coil according to claim 1 or 2, comprising two series circuits connected in sequence from the above coil to the coil on the other plane. 4. The 2n number of disk-shaped coils are arranged such that the centers thereof are located on each of two planes orthogonal to the central axis, the centers of which are spaced apart from each other by n, and the respective planes are arranged. 3. The circumferential defect detecting coil according to claim 1 or 2, comprising two series circuits in which the coils are sequentially connected.