JPS62130350A - Probe for eddy current flaw detection - Google Patents

Abstract

PURPOSE:To detect a defect with high sensitivity by providing a permanent magnet which has magnetic poles at both column flank parts and an inspection coil arranged at the center part of a plane. CONSTITUTION:A probe 10 for eddy current flaw detection consists of permanent magnets 1, inspection coils 2, insulating materials 3, etc., and is inserted into a pipe (t) to perform flaw detection. The sectional shape of the permanent magnet 1 consists of column flank parts (a) and symmetrical planes (b) obtained by cutting the column flanks, and an inspection coil 2 is provided on an insulating material 3 almost at the center part of each plane (b). Then when the probe 10 is inserted into the pipe (t), a magnetic circuit is formed between the probe 10 and pipe (t) and a detection signal indicating electromagnetic variation of the pipe due to a defect is detected in this state through the inspection coils 2. Thus, the defect of the pipe (t) is detected with high sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an eddy current flaw detection probe that is used by being inserted into a pipe.

[Conventional technology]

Conventionally, it is difficult to inspect heat transfer tubes built into heat exchangers and underground tubes from the outside.
Normally, periodic inspections are performed from the inside of the tube using an insertion type eddy current probe. In this case, if the tube is made of a non-magnetic material, there will be no particular inconvenience, but if the tube is made of a ferromagnetic material, high-sensitivity flaw detection cannot be performed as it is because the tube has a large magnetic permeability and eddy currents are generated. This is because the flaws concentrate only near the inner surface of the tube and do not reach the outer surface of the tube, reducing the sensitivity of flaw detection on the outer surface of the tube. Therefore, in order to reduce the permeability of the tube by magnetic saturation, an interpolated probe having a magnetic circuit as shown below is used.

8 and 9 show a conventional eddy current flaw detection probe 50, and FIG. 9 is a cross-sectional view taken along the line -n in FIG. t indicates a pipe, 54 is a cylindrical yoke,
Cylindrical permanent magnets 51a and 51b are fitted to both ends thereof, and an inspection coil 52 is attached to the center of the yoke 54 via an insulating material 53.

(For example, Japanese Utility Model Application Publication No. 58-91155) This probe 50 for internal eddy current flaw detection can be used for flaw detection by inserting a tube into the interior.
A magnetic circuit shown by a dashed line is formed. That is, the yoke 54, which has a cross-sectional area perpendicular to the axis slightly smaller than the cross-sectional area perpendicular to the axis of the eddy current flaw detection probe 50, is used as part of the magnetic path, and the magnetic flux emitted from the pair of permanent magnets 51a and 51b is used as a part of the magnetic path. Magnetic flux enters the tube t and is distributed on a cross section perpendicular to the axis inside the tube, magnetically saturating the tube in the axial direction, thereby ensuring a magnetic flux density inside the tube. FIGS. 10 and 11 show how eddy currents are generated by the conventional eddy current flaw detection probe 50. FIG. In the magnetic saturation state described above, when a high frequency signal is passed through the test coil 52, a concentric eddy current is generated inside the tube, forming a vortex in the circumferential direction of the tube t, as shown in FIG. When the magnetic flux density for magnetic saturation is high, the distribution of eddy currents near the outer surface of the tube increases as shown in FIG. 11, thereby ensuring detection sensitivity for flaws. As the eddy current flaw detection probe 50 moves, if there is a change in the electromagnetic characteristics of the tube t due to a defect such as a flaw in the eddy current flow path, a change in the eddy current occurs, which is reflected by the impedance of the test coil 52. The presence or absence of a defect is detected by recognizing it as a change.

FIG. 12 shows that a plurality of defects da and db exist on the same circumference in the circumferential direction of the tube t.

[Problem that the invention seeks to solve]

However, the above-mentioned conventional interpolation eddy current probe 50
However, there are restrictions on the strength of the permanent magnets that are commonly used and the saturation magnetic flux density of the iron core, and there is also the difficulty of making the dimensions smaller, so the cross-sectional area of the magnetic path inside the probe and the cross-sectional area of the magnetic path inside the tube are It is difficult to increase the magnetic flux density in the tube because it is difficult to increase the ratio of There are limits to this. Since the flow of eddy current flowing through the tube t by the inspection coil 52 is directed in the circumferential direction of the tube t as shown in FIG. 1O, the entire circumference of the tube t is uniformly detected. Therefore, when multiple defects da and db exist on the same circumference in the circumferential direction of the tube t as shown in FIG. 12, the resolution in the circumferential direction is insufficient and it is difficult to separate and identify these defects. The problem was that it was difficult to Note that insufficient resolution in the circumferential direction also occurs when flaw detection is performed on non-magnetic tubes.

The present invention solves these conventional problems,
Even if the tube is made of ferromagnetic material and has a small diameter and thick wall, it is possible to detect defects with high sensitivity. The object of the present invention is to provide an excellent eddy current flaw detection probe having a resolution that enables separation and identification of these defects.

[Means for solving problems]

In order to achieve the above object, the present invention has a permanent magnet that is inserted into a tube, has a columnar shape having a cylindrical side surface and a symmetrical plane cut on both side surfaces of the cylinder, and has magnetic poles on both cylindrical side surfaces. The eddy current flaw detection probe is equipped with an inspection coil placed in the center, and is connected to the rotational drive mechanism and axial movement mechanism to the eddy current flaw detection probe. The direction of the magnetic poles is changed sequentially at a constant angle and connected to an axial movement mechanism.

[Effect]

The present invention has the following effects due to the above configuration. That is, when the eddy current flaw detection probe is inserted into the tube, a magnetic circuit is formed between the eddy current flaw detection probe and the tube, and the presence or absence of flaws in the tube can be detected along with the action of the test coil.

In addition, by increasing the ratio of the cross-sectional area of the magnetic path in the probe to the cross-sectional area of the magnetic path in the tube, the magnetic flux density in the tube can be increased. Even in flaw detection, flaws can be detected with high sensitivity. Furthermore, since the direction of magnetization in the tube is the cross-sectional direction, local eddy currents are generated in the tube, and by uniformly detecting flaws around the entire circumference of the tube, it is possible to detect multiple defects on one circumference. Also, since the circumferential resolution increases,
These defects can be separated and identified.

In addition, by connecting a rotational drive mechanism and an axial movement mechanism to the axial direction of the eddy current flaw detection probe, it is possible to automatically operate the probe, and it is possible to transport it freely, so it can be used in large numbers and relatively long. It is possible to efficiently perform multiple flaw detections on a large number of pipes, covering the entire circumference of the pipe.

Furthermore, by sequentially changing the angle of each probe of a plurality of eddy current flaw detection probes and connecting the axial movement mechanism, it is possible to omit the rotational drive mechanism of the eddy current flaw detection probes, and moreover, it is possible to eliminate leakage over the entire surface of the tube. Since flaw detection can be achieved, the structure of the eddy current flaw detection probe can be simplified.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the structure of an embodiment of the present invention, and FIG. 2 shows a sectional view taken along the line 1--1 in FIG.

In FIGS. 1 and 2, t is a tube, 10 is an eddy current flaw detection probe, and 40 is a cable that also serves as an axial movement mechanism. The probe 10 consists of a permanent magnet 1, a test coil 2, an insulating material 3, etc. The shape of the permanent magnet 1, which is inserted into the tube t for flaw detection, is as shown in Fig. 2 (its cross section is a symmetrical plane cutting the cylindrical side surface a, a).
A test coil 2 is disposed on an insulating material 3 approximately in the center of the plane surface b. When the eddy current flaw detection probe 10 is inserted into the tube, the eddy current flaw detection probe 1
A magnetic circuit is formed between 0 and the tube t, and in this state, a flaw detection signal indicating an electromagnetic change in the tube due to a defect is detected through the inspection coil 2.

Fig. 3 shows a magnetic circuit consisting of a permanent magnet 1 and a tube t used in the eddy current flaw detection probe 10 shown in Figs. The magnetic flux flows as shown by the dashed line, magnetizing the cross-sectional direction. In FIG. 3, the magnetic flux density Bp of the magnetic flux in the B section of the eddy current flaw detection probe 10
, if the magnetic flux density inside the heat transfer tube is Bt, then Bt=
(ffi, / (1, + 1.)l · Bp.

On the other hand, in the conventional eddy current flaw detection probe 50 shown in FIG. If the cross-sectional area is St, then the magnetic flux density Bt' in the heat transfer tube is Bt' = (SA/St) · Bp'.

Therefore, by changing the magnetization direction in the tube t from the conventional axial direction to the cross-sectional direction, the ratio of the cross-sectional area of the magnetic path in the tube t to the cross-sectional area of the magnetic path in the eddy current probe is /
'(z+ +1z) can be made larger than in the conventional SA/St, improving the magnetic flux density in the tube.

The magnetic flux density inside the pipe using the conventional eddy current probe was calculated using the analysis example based on the above example.
This is shown in Figure 3 and the table below.

In addition, in the above table, the material of the test tube is 21/4 Cr
- It is made of IMO steel and has an outer diameter of 25.4 mm and an inner diameter of 18.4 mm. As can be seen from the analysis example shown in FIG. 13 and the table above, according to the method of the present invention, the magnetic flux density in the tube can be improved. Even for flaw detection,
Defects can be detected with high sensitivity. In addition, Figure 4 shows the eddy current flaw detection probe 1 shown in Figures 1 and 2.
This shows that when the tube t is flaw-detected using 0, a local eddy current is generated in the tube t by the inspection coil 2. Therefore, if a defect exists in the eddy current as the eddy current flaw detection probe 10 moves, the test coil can detect the impedance change in detail due to the change in the electromagnetic characteristics of the tube due to the defect. Therefore, a recording device (not shown) based on this detected impedance change value can increase the resolution of defects in the circumferential direction, and even if there are multiple defects on the same circumference in the circumferential direction of the tube, , it is possible to separate and identify these defects.

Embodiments of the present invention are shown in FIGS. 5 and 6, respectively.

In FIG. 5, 10 indicates an eddy current flaw detection probe,
42 is a reducer, 41 is a motor, 5 is a slip ring, and 40 is a cable, which are connected in the axial direction of the eddy current flaw detection probe 10.
is connected to a rotational drive mechanism that performs rotational movement via a speed reducer 42 by the rotational driving force of a motor 41, and is connected to a cable 40 that also serves as a hanging rod for the eddy current flaw detection probe 10. Moving.

The slip ring 5 transmits a flaw detection signal from the test coil 2 of the eddy current flaw detection probe IO rotating around its axis to a test device (not shown).

In FIG. 6, a plurality of eddy current flaw detection probes l0110
a, 10b, and 10c are integrally connected in the axial direction with a spring 44 so as to be able to respond to a deflected state, and are connected to a cable 40 at the end. Moreover, the mounting direction of each eddy current flaw detection probe is arranged such that the magnetic pole direction is sequentially advanced with a certain angle deviation θ.

In the embodiment in FIG. 6, the angular deviation θ is 45''.

In addition, in the 7Li example shown in FIG. 5, by connecting a rotational drive mechanism to the eddy current probe 10 and connecting this to an axial movement mechanism, the eddy current generated by the eddy current probe 10 can be localized. Even if there is a defect d as shown in Fig. 7, which is the shaded area that is wider than the range in which the eddy current flows, it can be detected by sequential flaw detection as shown by the dashed-dotted line in the same figure. , it is possible to know the distribution of defects in the axial and circumferential directions, and it is also possible to automatically operate the eddy current flaw detection probe 10, making it possible to transport it freely. Multiple flaws can be detected efficiently over the entire surface of the pipe.

Furthermore, in the embodiment shown in FIG. 6, by sequentially changing the angle of each eddy current flaw detection probe of the plurality of eddy current flaw detection probes l0110a, 10b, and lOC and connecting the axial movement mechanism, the eddy current flaw detection Since the rotational drive mechanism of the probe can be omitted and flaw detection can be carried out over the entire surface of the tube, the structure of the eddy current flaw detection probe can be simplified.

〔Effect of the invention〕

As is clear from the above embodiments, when the present invention is applied to the flaw detection of small-diameter thick-walled tubes made of ferromagnetic material, it is possible to detect defects with high sensitivity, and the same circumference in the circumferential direction of the tube can be detected. The increased circumferential resolution of defects not only makes it possible to separate and identify them, even when multiple defects are present on the surface, but also makes it possible to Even for defects in a wide area, it is possible to know the distribution of defects in the axial and circumferential directions, and the operation of the eddy current flaw detection probe can be automated, making it possible to transport it freely. Its effects are significant, such as being able to efficiently perform flaw detection on relatively long pipes.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an eddy current deep wound probe according to an embodiment of the present invention, Fig. 2 is a sectional view thereof, Fig. 3 is a magnetic circuit diagram thereof, and Fig. 4 is an explanatory diagram of the eddy current without showing it. , FIG. 5 is a schematic diagram of an i-rope for eddy current flaw detection according to another embodiment of the present invention, FIG. 6 is a schematic diagram of an eddy current deep flaw probe according to still another embodiment of the present invention, and FIG. Figures 5 and 6 are explanatory diagrams of the Shimezu embodiment, Figure 8 is a schematic diagram of a conventional eddy current probe for deep wounds, Figure 9 is a cross-sectional view of the same, and Figure 1O shows the eddy current. Figure 11 is an explanatory diagram showing the changes in eddy current distribution due to the magnetic flux density inside the tube, Figure 12 is an explanatory diagram of defects that are difficult to separate and identify according to the prior art, and Figure 13 is an explanatory diagram showing the changes in eddy current distribution due to the magnetic flux density inside the tube. FIG. 3 is an explanatory diagram showing a comparison of the magnetic flux density in the tube according to the present invention and the conventional technology. 1 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - (- - - - One cylindrical side part b - One plane Applicant Kawasaki Heavy Industries Ltd. M8 Figure 9 Figure 1o Figure

Claims (1)

[Claims] 1. A permanent magnet that is inserted into a tube and has a columnar shape having a cylindrical side surface and a symmetrical plane cutting both side surfaces of the cylinder, and has magnetic poles on both cylindrical side surfaces, and a central portion of the plane. An eddy current flaw detection probe consisting of a test coil installed in the . 2. A permanent magnet that is inserted into the tube and has a symmetrical plane with a cylindrical side surface and a symmetrical plane cutting both side surfaces of the cylinder, and a permanent magnet that has magnetic poles on both cylindrical side surfaces and an inspection coil that is placed in the center of the plane. An eddy current flaw detection probe comprising: a rotary drive mechanism and an axial movement mechanism connected to the eddy current flaw detection probe. 3. A permanent magnet that is inserted into the tube and has a symmetrical plane with a cylindrical side surface and a symmetrical plane cut on both side surfaces of the cylinder, and a permanent magnet that has magnetic poles on both cylindrical side surfaces and an inspection coil arranged in the center of the plane. The eddy current flaw detection probe is characterized in that a plurality of the eddy current flaw detection probes are connected in the axial direction, the magnetic pole direction of each probe is sequentially changed at a constant angle, and is connected to an axial movement mechanism. Eddy current flaw detection probe.