JPS6324152A - Probe for eddy current flaw detection - Google Patents

Abstract

PURPOSE:To perform flaw detection as to whether a tube has a flaw as well as the operation of an inspection coil by inserting a probe for eddy current flaw detection into the tube and forming a magnetic circuit between the probe for eddy current flaw detection and the tube. CONSTITUTION:When the probe 10 for eddy current flaw detection is inserted into the tube (t), a magnetic circuit is formed between the probe 10 for eddy current flaw detection and a tube (t) and a flaw detection signal which indicates the electromagnetic variation of the tube due to the flaw is detected in this state through the inspection coil 2. Thus, a space where the large-sized, large- capacity coil 2 can be arranged is secured almost at the center part of a columnar yoke (k). The detection sensitivity to the flaw of the tube (t) is therefore increased by using the large-sized inspection coil 2.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a 7I! which is used by being inserted into a tube. Regarding the Jl-style deep wound probe.

[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 interpolated eddy current probe. In this case, if the tube is made of a non-magnetic material, no particular inconvenience will occur, but if the tube is made of a ferromagnetic material, high-sensitivity flaw detection cannot be performed as is. That's tube i! This is because the 611 ratio is large and the eddy current concentrates only near the inner surface of the tube and does not reach the outer surface of the tube, reducing the flaw detection sensitivity of the outer surface of the tube. Therefore, an interpolation type probe having a magnetic circuit as shown below is used for the purpose of reducing the permeability of the tube by air saturation.

8 and 9 show a conventional eddy current flaw detection probe 50, and FIG. 9 is a cross-sectional view taken along the line ■-■ in FIG. L 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, 1986-9
No. 1155) When this interpolation eddy current flaw detection probe 50 is inserted into a pipe for flaw detection, a magnetic circuit shown by a dashed line is formed. That is, a yoke 54 having a cross-sectional area in a direction perpendicular to the axis that is slightly smaller than a cross-sectional area in a direction perpendicular to the axis of the eddy-current flaw detection professional bar 50 is used as part of the magnetic path, and a pair of permanent magnets 51a,
The magnetic flux emitted from 51b enters the tube t, distributes the tube on a cross section perpendicular to the inner axis, magnetically saturates the tube in the axial direction, and thereby secures the magnetic flux density inside the tube. There is. 10th
The figure and FIG. 11 show the state in which eddy current is generated by the conventional eddy current flaw detection probe 50. In the above magnetic saturation state, 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 the 10th circle. 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. In FIG. 12, in the circumferential direction of the tube t,
This indicates that a plurality of defects da and db exist on the same circumference.

[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 Since it is difficult to increase the ratio of magnetic flux density in the tube, it is difficult to increase the magnetic flux density in the tube.
There is a limit to the detection sensitivity for scratches. Since the flow of the 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 is uniformly detected. Therefore, if there are multiple defects da=db on the same circumference in the circumferential direction of the tube t as shown in FIG. The problem was that it was difficult to identify. 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 resolving problems]

In order to achieve the above object, the present invention provides a first invention comprising a cylindrical yoke inserted into a pipe and provided at the center, and a fan-shaped cross section, the direction of magnetization being perpendicular to the central axis, and the outer periphery of the fan-shaped yoke. The second invention consists of a permanent magnet with both magnetic poles magnetized and symmetrically joined to both sides of the yoke, and an inspection coil disposed in the center of the yoke to which the permanent magnet is not joined. In addition to the configuration according to the first invention, a rotary drive IIJ, a mechanism, and an axial movement mechanism are connected to the axial direction of the eddy current flaw detection probe, and furthermore, the third valve invention has the configuration according to the first invention. In addition to using multiple eddy current probes,
The probes are connected in the axial direction, and the direction of each probe magnetic pole is sequentially changed at a certain angle, and is connected to an axial movement mechanism.

[Effect]

The present invention has the following effects due to the above configuration. That is, in the first invention, 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 is increased, and it is a ferromagnetic material.
In addition, when detecting flaws in small-diameter, thick-walled pipes, it is possible to detect flaws with high sensitivity. A space for arranging a large-sized test coil can be secured, and by using the large-sized test coil, detection sensitivity for flaws in the tube can be increased.

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 testing the entire circumference of the tube, it is possible to detect multiple defects on the same circumference. In this case, the increased circumferential resolution also makes it possible to separate and identify these defects.

In addition, the second invention makes it possible to automatically operate the probe by connecting a rotational drive mechanism 81 and an axial movement mechanism to the axial direction of the eddy current flaw detection probe.
Since it can be transported freely, it is possible to perform flaw detection on a large number of comparatively long tubes all over the circumference of the tube efficiently.

Furthermore, the third invention is capable of omitting the rotational drive mechanism of the eddy current flaw detection probes by sequentially changing the angle of each probe of the plurality of eddy current flaw detection probes and connecting the axial movement mechanism. Furthermore, since flaw detection can be performed over the entire surface of the tube, 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 configuration of an embodiment of the first invention, and FIG.
The figure shows a cross-sectional circle taken along line I-1 in FIG.

In FIGS. 1 and 2, t represents a tube, 10 represents an eddy current flaw detection probe, and 40 represents a cable that also serves as an axial movement mechanism. The eddy current flaw detection probe 10 includes a cylindrical yoke k provided at the center, permanent magnets l and la, a test coil 2, and an insulating material 3.
Flaw detection is performed by inserting it into the tube T. As shown in FIG. 2, the permanent magnet 1.1a has a fan-shaped cross section and is symmetrically bonded to both cylindrical sides of the yoke using an adhesive or the like.

Almost in the center of the yoke! i! ! An inspection coil 2 is arranged on the edge material 3.

When the eddy current flaw detection probe 10 is inserted into the tube 1, a magnetic circuit is formed between the eddy current flaw detection probe 10 and the tube, and in this state, a flaw detection signal indicating electromagnetic changes in the tube due to defects is transmitted through the inspection coil 2. To detect. In this way, 61 spaces for arranging a large-sized, large-capacity test coil 2 can be maintained at approximately the center of the cylindrical yoke to which the permanent magnet 1.1a is not connected.
The detection sensitivity for flaws in the tube can be increased by using

Figure 3 shows the vortex Ji shown in Figures 1 and 2, the permanent magnet 1.1a used in the flaw detection probe 10, the yoke and the tube t, and the permanent magnet 1.
．． Each magnetization direction of 1a is perpendicular to the central axis and 1
, both fiB11. s
, and each of them is fixed with 6Nh in the opposite direction, and the magnetic flux flows as shown by the dashed line through the yoke k, magnetizing the cross-sectional direction of the tube. .

In FIG. 3, if the magnetic flux density at part B of the eddy current flaw detection probe 10 is Bp, and the magnetic flux density inside the heat transfer tube is Bt, then B t = (123/ (x++i'z)l HB
It becomes p.

On the other hand, in the 8th article, in the conventional eddy current flaw detection probe 50, the cross-sectional area of the yoke 54A section is Sp, the magnetic flux density of the magnetic flux passing through the A section is Bp', and the section perpendicular to the axis of the heat exchanger tube t. If the area is St, then the magnetic flux density Bt' inside the heat transfer tube is Bt' = (SA/St) ·Bp'.

However, 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 tube bypass path to the cross-sectional area of the magnetic path in the eddy current probe becomes xz/(7
! ++zz) can be made larger than that of conventional SA/St, improving the magnetic flux density in the tube.

The magnetic flux density inside the tube according to an analysis example based on the embodiment of the first invention described above and the magnetic flux density inside the tube using a conventional eddy current flaw detection probe are shown in FIG. 13 and the following table.

In addition, in the above table, the material of the test tube is 21/4Cr1M.
It is made of o steel and has an outer diameter of 25.41 m.

The inner diameter is 18.4 and the thickness is 1.

As can be seen from the analysis examples in FIG. 13 and the table above, the method according to the present invention can improve the magnetic flux density in the tube, and is effective in improving the magnetic flux density in the tube, which is made of ferromagnetic material and has a small diameter and thick wall. Even in flaw detection, defects can be detected with high sensitivity.

In addition, FIG. 4 shows that when a tube is tested using the eddy current flaw detection probe 10 shown in FIGS. 1 and 2, a local eddy current is generated in the tube t by the inspection coil 2. It shows. Therefore, the eddy current flaw detection probe 10
As the tube moves, if a defect exists in the eddy current, the test coil can produce a detailed impedance change of 1* due to the change in the electromagnetic properties of the tube due to the defect. Therefore, based on the detected impedance change value, the recording device (not shown) increases the circumferential resolution for defects.
Even when a plurality of defects exist on the same circumference in the circumferential direction of the tube, it is possible to separate and identify these defects.

FIG. 5 shows an embodiment of the second invention.

In FIG. 5, 10 indicates an eddy current flaw detection probe,
42 is a reducer, 41 is a motor, 5 is a slip ring,
Furthermore, 40 indicates a cable that also serves as an axial movement mechanism.

These are connected to an eddy current flaw detection probe 10, and the eddy current flaw detection probe 10 performs rotational movement via a reducer 42 by the rotational driving force of a motor 41, and is moved in the axial direction by a cable 40 that also serves as an axial movement n groove. do.

The slip ring 5 transmits a flaw detection signal from the test coil 2 of the eddy current flaw detection probe 10 rotating around its axis to a test device (not shown).

In this way, by connecting the rotation drive mechanism to the eddy current flaw detection probe 10 and connecting this to the axial movement mechanism 10, even if the eddy current generated by the eddy current flaw detection probe 10 is localized, As shown in the figure, even for the defect d, which is a hatched area with a wider area than the range in which the eddy current flows, flaw detection is carried out sequentially as shown by the dashed-dotted line in the same figure. You can know the distribution in the circumferential direction, and /l! ! It is possible to operate the 1I style professional flaw detection 10 for deep flaws automatically, and the transportation can be made independent, so it is possible to efficiently perform flaw detection on a large number of comparatively long pipes, covering the entire surface of the pipe. Can be done.

FIG. 6 shows an embodiment of the third invention.

In FIG. 6, a plurality of eddy current deep wound probes are connected to each other in the axial direction so as to be able to respond to the deflection state using a spring 44 (the probes are integrally connected in the axial direction, and the ends thereof are connected to a cable 40 which also serves as an axial movement mechanism). In addition, the mounting directions of the eddy current flaw detection probes 10, 10a, 10b, and 10e are arranged such that the magnetic pole direction is sequentially advanced with a certain angular deviation θ.In the embodiment shown in FIG. 6, the angular deviation θ is It is 45″.

In this way, each eddy current flaw detection probe 10.10a, 10
b. By sequentially changing the angle of the IOC and connecting the cable 40 which also serves as an axial movement mechanism, it is possible to omit the rotational drive mechanism of the eddy current flaw detection probe and to achieve flaw detection over the entire surface of the tube. Therefore, the configuration of the eddy current flaw detection probe can be simplified.

[Effects of the Invention] As is clear from the above embodiments, according to the first invention, defects can be detected with high sensitivity when applied to the detection of small-diameter, thick-walled pipes made of ferromagnetic material. In addition, even if a plurality of defects exist on the same circumference in the circumferential direction of the tube, the increased resolution of defects in the circumferential direction makes it possible to separate and identify these defects.

In particular, by using a large, high-capacity test coil, the detection sensitivity for flaws in the tube can be significantly increased.

According to the second invention, it is possible to know the distribution of defects in the axial direction and the circumferential direction even for defects having a wider area than the range in which the eddy current flows, and the operation of the eddy current flaw detection probe can be controlled. Since it can be done automatically and can be transported freely, flaw detection can be performed efficiently on a large number of relatively long pipes.

According to the third invention, the rotational drive mechanism of the eddy current flaw detection probe can be omitted, and flaw detection can be performed over the entire surface of the tube, so the configuration of the eddy current flaw detection probe can be simplified. .

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an eddy current flaw detection probe according to an embodiment of the first invention, Fig. 2 is a cross-sectional view thereof, Fig. 3 is a magnetic circuit diagram thereof, and Fig. 4 is a detailed explanation of the eddy current. Figure 5 is a schematic diagram of an eddy current flaw detection probe according to an embodiment of the second invention, Part 6 is a schematic diagram of an eddy current flaw detection probe according to an embodiment of the third invention, and Fig. 7 is shown in FIGS. 5 and 6I211. 8 is a schematic diagram of an eddy current flaw detection probe according to the prior art, FIG. 9 is a cross-sectional view of the same, FIG. 10 is an explanatory diagram without showing the eddy current, and FIG. Fig. 12 is an explanatory diagram showing the change in eddy current distribution due to the magnetic flux density in the tube, Fig. 12 is an explanatory diagram without showing defects that are difficult to identify, and Fig. 130 is the magnetic flux in the tube according to the present invention and the prior art. It is an explanatory diagram showing a comparison of densities. 1.1a -------One permanent magnet 2 ------One inspection coil 10 ------One eddy current flaw detection probe 40 ---
−−−−Cable 1 −−−−−−One pipe R−−−−−−One yoke

Claims (1)

[Claims] 1. A cylindrical yoke inserted into a tube and provided at the center, consisting of a cylindrical yoke and a sector-shaped cross section, the direction of magnetization being perpendicular to the central axis, and both magnetic poles attached to the outer periphery of the sector. An eddy current flaw detection probe consisting of a permanent magnet symmetrically connected to both sides of a magnetized yoke, and an inspection coil placed in the center of the yoke where the permanent magnets are not connected. 2. It is inserted into the pipe and consists of a cylindrical yoke provided at the center and a fan-shaped cross section, the direction of magnetization is perpendicular to the central axis, and both magnetic poles are magnetized on the outer periphery of the sector, on both sides of the yoke. In an eddy current flaw detection probe consisting of a permanent magnet symmetrically bonded to a surface and a test coil disposed in the center of the yoke to which the permanent magnet is not bonded, the eddy current flaw detection probe has a rotary drive mechanism and a rotary drive mechanism in the axial direction. An eddy current flaw detection probe characterized by being connected to an axial movement mechanism. 3. It is inserted into the pipe and consists of a cylindrical yoke provided at the center and a fan-shaped cross section, the direction of magnetization is perpendicular to the central axis, and both magnetic poles are magnetized on the outer periphery of the fan, on both sides of the yoke. In an eddy current flaw detection probe consisting of a permanent magnet symmetrically bonded to a surface and an inspection coil disposed in the center of the yoke to which the permanent magnet is not bonded, the eddy current flaw detection probe is provided in a plurality and An eddy current flaw detection probe characterized by being connected to an axial movement mechanism that sequentially changes the magnetic pole direction of each probe at a certain angle.