JPS61264252A - Eddy current flaw inspecting method for metallic tube and its device - Google Patents

Abstract

PURPOSE:To detect even flaws extending in the peripheral direction of a metallic tube to be examined by supplying an exciting current to an exciting coil while holding this coil in such positional relations that the axis of the coil is approxi mately orthogonal to the inside wall of the metallic tube to be examined. CONSTITUTION:Circular holes 16 and 18 whose common axis is on a line orthog onal to the axis of a probe 10 are provided symmetrically on a plane including said axis in the front end in the longitudinal direction of a main body part 15 of the probe 10, and exciting coils 24 and 26 are wound around bobbins 20 and 22 formed into columnar shapes with a ferrite or the like. Circular holes 28 and 30 whose axis is shifted from the axis of circular holes 16 and 18 by about 90 deg. in the circumferential direction of the probe 10, and exciting coils 36 and 38 rae wound around bobbins 32 and 34. Since these coils are so held that their axes are always orthogonal to the inside wall of the metallic tube, namely, in the radial direction, an eddy current E is generated in the metallic tube when exciting AC currents are supplied to these coils. Thus, a flaw P extending in the circumferential direction is detected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an eddy current flaw detection method and device for metal tubes, and particularly to one that can detect defects occurring along the circumferential direction of a metal tube. It can be used to detect flaws in heat exchanger tubes, etc. in chemical plants.

[Background technology and its problems]

In the conventionally widely used eddy current flaw detection method for metal tubes, as shown in FIG. Two excitation cylindrical coils 6 are provided in front and rear in the axial direction so as to be concentric with the central axis of the probe 4, and the probe 4 is moved inside the metal tube 2 to be tested while passing an excitation alternating current to Changes in the eddy current E generated in the metal tube 2 are differentially detected through the two excitation cylindrical coils 6.

However, in such a conventional method, since the eddy electric current iE flows in the circumferential direction of the test metal tube 2 as shown in FIG. 10, defects P such as cracks extending along the circumferential direction exist. However, this has almost no effect on the flow of the eddy current E, and therefore has the disadvantage that such a defect P cannot be detected.

[Purpose of the invention]

An object of the present invention is to provide an eddy current flaw detection method and apparatus for a metal tube that makes it possible to clearly detect defects extending along the circumferential direction of the metal tube.

[Means and effects for solving the problems] The present invention has the following features:
By passing an excitation current through the excitation coil while holding the excitation coil in a positional relationship such that its central axis is approximately orthogonal to the inner wall of the metal tube to be tested, that is, approximately in the radial direction, An eddy current flaw detection method and apparatus for a metal tube generates an eddy current in a direction orthogonal to the metal tube, thereby making it possible to detect defects extending along the circumferential direction of the metal tube.

Specifically, an excitation coil is held in such a positional relationship that its central axis is substantially perpendicular to the inner wall of the metal tube to be tested, and is moved relative to the metal tube, and an excitation alternating current is passed through the coil. A method for detecting defects in a metal tube by measuring changes in eddy currents occurring in the metal tube, and an excitation coil that maintains a positional relationship in which the central axis of the coil is substantially perpendicular to the inner wall of the tube to be metallized. a probe formed to be movable in the axial direction within the metal tube; and circuit means for passing an exciting alternating current through the coil of the probe and measuring changes in eddy currents generated in the metal tube thereby. This device includes a container body.

〔Example〕

FIG. 2 is a diagram showing the overall configuration of an example of an apparatus for carrying out the eddy current flaw detection method for metal tubes according to the present invention.

In FIG. 2, a probe 10 formed in a cylindrical shape so as to be movable inside a metal tube 2 to be tested is connected to two flaw detector bodies 12.
The flaw detector main body 12 applies an exciting alternating current to the flaw detector body 12, and is configured to detect changes in eddy currents caused by this. Note that this flaw detector main body 12 uses a known general circuit means for eddy current flaw detection (for example, Japanese Patent Laid-Open No. 59-7514
(See Publication No. 6).

Further, the output terminal of the flaw detector main body 12 is connected to the input terminal of a 4-pen recorder 14 as a recording means,
The device is configured to record the results of the eddy current flaw detection.

FIG. 1 is an enlarged sectional view showing details of the probe 10.

In FIG. 1, at the tip in the longitudinal direction of the main body 15 of the probe 10, that is, at the left end in the figure, there are two circular holes 16 and 18 whose common central axis is a straight line orthogonal to the central axis. are respectively drilled symmetrically with respect to a plane containing the central axis of the probe 10.

In the circular holes 16 and 18, a cylindrical first excitation coil 24 and a second excitation coil are wound around a bobbin 20 and a bobbin 22, respectively, which are made of a ferrite or other ferromagnetic material. A coil 26 for use is housed and fixed.

Further, as shown by the broken line in FIG. 1, a circular hole similar to the circular hole I6 and the circular hole 18 is provided at the rear end portion in the longitudinal direction of the main body portion 15, that is, at the right end portion in the figure. A circular hole 28 and a circular hole 30 are bored, the central axes of which are offset approximately 90 degrees in the circumferential direction of the probe 10 with respect to the central axes of the circular holes 16 and 18. hole 28
A cylindrical third excitation coil 36 and a fourth excitation coil 38 wound around the bobbin 32 and the bobbin 34, respectively, are housed and fixed in the circular hole 30.

FIG. 3(a) shows the probes of the first excitation coil 24, second excitation coil 26, third excitation coil 36, and fourth excitation coil 38 wound around the bobbin 20. 10 is a diagram showing the positional relationship from the axial direction of FIG. Also,
FIG. 3(b) shows the first to fourth excitation coils 24, 26.
36 and 38 are diagrams showing the positional relationship when viewed from the axial direction of the probe 10. FIG.

As shown in FIG. 1, a terminal block 4o is attached to the rear end of the main body 15, and a cable holder 42 is screwed and fixed thereto. Wiring from the first excitation coil 24, second excitation coil 26, third excitation coil 3G, and fourth excitation coil 38 is connected to the terminal block 40, and these wirings are connected to the terminal. It is configured to be accommodated in a cable 44 from the stand 40 and coupled to the outside.

This cable 44 is led out to the outside through a cable lead-out hole 46 passing through the approximate center of the cable holder 42, and when led out to the outside, a branch cable 48 and a branch cable 5 are formed.
0, each of which is connected to the flaw detector main body 12.

The cable 44 is fixed to the cable holder 42 by screwing setscrews 56 and 58 into the tapped holes 52 and 54.

Figure 4 shows the first to fourth excitation coils 24, 26, 36.
．． 38. In the figure, ■ to ■ are numbers indicating the connection relationships of the wiring of each part, and the corresponding numbers indicate that they are connected.

In the fourth cabinet, the first excitation coil 24, the second excitation coil 26, the third excitation coil 36, and the fourth excitation coil 38 are connected in series, and these are connected to the cable 44, Branch cable 48 and branch cable 5
0 to the flaw detector main body 12.

Next, an example will be described in which the eddy current flaw detection method for metal tubes according to the present invention is carried out using the above-mentioned apparatus.

In this embodiment, a case will be described in which a defect in a heat exchanger tube of a chemical plant is detected.

First, before performing eddy current flaw detection, pretreatment such as cleaning and air blowing of the tube is performed.

Next, the probe 10 is inserted into the tube, which is the metal tube 2 to be tested, as shown in FIG. 2, and is inserted to the innermost part of the tube using compressed air or the like.

Next, the first excitation coil 24 of the probe 10,
The probe 10 is pulled out while passing an excitation alternating current through the second excitation coil 26, the third excitation coil 36, and the fourth excitation coil 38 by the flaw detector main body 12, and an eddy current is generated in the tube at that time. is detected as a change in impedance of the first to fourth excitation coils 24, 26, 36, 38, and recorded on the 4-pen recorder 14.

This result is analyzed using known analysis methods (for example, Japanese Patent Application Laid-Open No. 59-751).
The position, size, etc. of the defect are determined by analyzing the defect using the method (see Japanese Patent Publication No. 46).

5 and 6 show charts in which the eddy current flaw detection was actually performed in this manner and the results were recorded on the four-pen recorder 14. In this example, a crack extending along the circumferential direction that exists in the panful portion of a heat exchanger tube is detected.

In Fig. 5.6, (a) shows the Y-axis signal due to the differential between the third excitation coil 36 and the fourth excitation coil 38, and (b) shows the Y-axis signal due to the differential between the third excitation coil 36 and the fourth excitation coil 38. An X-axis signal due to the differential with the fourth excitation coil 38, (C) a Y-axis signal due to the differential between the first excitation coil 24 and the second excitation coil 26, and (d) the same The X-axis signals due to the differential between the first excitation coil 24 and the second excitation coil 26 are respectively shown.

In both the examples shown in FIGS. 5 and 6, cracks existing in the baffle portion along the circumferential direction are recorded and detected as extremely clear peaks. At this time, the baffle signal is erased.

In this case, the size of the crack can also be estimated from the difference in peak intensity between (a) and (C).

FIG. 7 is a diagram showing the state of the eddy current E generated in the metal tube 2 to be inspected by the method of the present invention, and defects P such as cracks extending along the circumferential direction of the metal tube 2 to be inspected.

The embodiment described above has the following advantages.

First, a first excitation coil 24 which is an excitation coil;
Since the central axes of the second excitation coil 26, the third excitation coil 36, and the fourth excitation coil 38 are always held substantially perpendicular to the inner wall of the metal tube 2, that is, in the substantially radial direction, these When an excitation alternating current is passed through the metal tube, an eddy current E as shown in FIG. 7 is generated in the metal tube. This also makes it possible to detect defects P extending along the circumferential direction.

Second, the first to fourth excitation coils 24.26.3
6 and 38 are arranged in the positional relationship shown in FIG. 3(b), it is possible to detect flaws on substantially the entire surface of the metal tube in one operation.

Thirdly, the first to fourth excitation coils 24.26.3
6.38 are connected differentially, so
Changes in eddy currents due to changes in symmetrical structures are canceled and only randomly existing defect signals are extracted, making it possible to clearly detect defects even in the baffle section as in the previous embodiment. There is. Also,
Defects such as cracks in the tube sheet can also be detected.

Fourth, the first to fourth excitation coils 24.26.3
6 and 38 are wound around bobbins 20, 22, 32 and 34, respectively, made of ferromagnetic material such as ferrite, so the distance between the excitation coil and the inner wall of the metal tube to be tested is the same as above and below the probe 10. More precisely, it varies in the radial direction (
This makes it possible to reduce detection errors due to lift-off (errors due to lift-off signals) to a negligible level, and the detection sensitivity is extremely high.

Further, in the above embodiment, the excitation coils 24, 26, 36 and 38 do not directly contact the inner wall of the metal tube 2 to be tested.
Since they are separated by a fixed distance by the bobbins 20, 22, 32 and 34, this also reduces the influence of errors due to lift-off signals.

In the above embodiment, as shown in FIG. 4, two of each of the first to fourth excitation coils 24, 26, 36 and 38 are connected in series, resulting in a total of four coils. However, as shown in FIG. 8, for example, this is simplified to two coils, each with a different central axis direction in the 90 degree direction of the excitation coil 60 and the excitation coil 62. It is also possible to have such a configuration. In this case, only one eddy current flaw detection unit is required, but the baffle signal and tube plate signal cannot be erased, making it difficult to detect defects in the baffle portion, etc.

Further, in the above embodiment, bobbins 20, 22, 32 and 34
Although an example using a ferromagnetic material such as ferrite has been shown as the material, it is of course possible to use a synthetic resin such as Bakelite. In this case, manufacturing is easy, but the influence of the lift-off signal is large.

Furthermore, the ffjJ oscillation coil 24.26.36.38
may be brought into direct contact with the inner wall of the metal tube 2 to be tested, without going through the bobbin 20, 22, 32, 34. In this case, the detection capability is improved accordingly, but the influence of the foot-off signal becomes greater.

〔Effect of the invention〕

As detailed above, the method and apparatus according to the present invention detect defects while maintaining the excitation coil in a positional relationship such that its central axis is substantially perpendicular to the inner wall of the metal pipe to be tested. This has the effect that defects extending along the circumferential direction of the tube can also be detected.

[Brief explanation of drawings]

FIG. 1 is an enlarged sectional view showing details of the probe in FIG. 2, FIG. ) is a perspective view showing the first excitation coil wound around the bobbin in FIG. 1, and FIG. 3(b) is a perspective view of the first to fourth excitation coils in FIG. FIG. 4 is a diagram showing the connection relationship of the first to fourth excitation coils in FIG. 1, and FIGS. 7 is a diagram showing the flow direction of eddy current when performing eddy current flaw detection by the method and device of the present invention, and FIG. 8 is a diagram showing another implementation of the device of the present invention. The diagrams illustrating examples, FIGS. 9 and 10, are diagrams showing conventional examples. 2...Metal tube to be tested, 10...Probe, 12...
Flaw detector body, 14...4 Ben recorder, 20, 22.
32.34...Bobbin, 24.26.36.38...
- First to fourth excitation coils, 60.62... excitation coils.

Claims (10)

[Claims] (1) While holding an excitation coil in a positional relationship such that its central axis is approximately perpendicular to the inner wall of the metal tube to be tested, move it relative to the metal tube, and apply an excitation alternating current to the metal tube. 1. An eddy current flaw detection method for metal tubes, characterized in that defects existing in the metal tubes are detected by measuring changes in eddy currents generated in the metal tubes. (2) The eddy current flaw detection method for metal tubes according to claim 1, characterized in that a plurality of the excitation coils are used. (3) In claim 2, the excitation coil is a set of two coils that are connected in series to form a pair and are respectively arranged to face different parts of the inner wall of the metal tube. An eddy current flaw detection method for metal tubes characterized by using one or more sets. (4) In claim 3, the two sets of coils are two sets, and the central axes of these two sets of coils are arranged at an angle of 90 degrees to each other. Features of eddy current flaw detection method for metal tubes. (5) The eddy current flaw detection method for metal tubes according to any one of claims 1 to 4, wherein the excitation coil is provided at a position where it does not come into contact with the probe surface. (6) A probe having an excitation coil, the probe being movable in the axial direction within the metal tube while maintaining a positional relationship in which the central axis of the coil is substantially orthogonal to the inner wall of the metal tube; and the coil of the probe. 1. An eddy current flaw detection apparatus for a metal tube, comprising a flaw detector main body having circuit means for passing an excitation alternating current through the tube and measuring changes in eddy current generated in the metal tube thereby. (7) The eddy current flaw detection apparatus for metal tubes according to claim 6, wherein the probe is provided with a plurality of the excitation cylindrical coils. (8) In claim 7, the excitation cylindrical coil is formed into a set in which two coils are connected in series and arranged to face different parts of the inner wall of the metal tube. An eddy current flaw detection device for metal tubes, characterized in that it is formed by installing two or more sets of coils. (9) In claim 8, there are two sets of the two coils, and the centers of the two sets of coils are arranged at an angle of 90 degrees to each other. Eddy current flaw detection equipment for metal tubes. (10) The eddy current flaw detection apparatus for metal tubes according to any one of claims 6 to 9, wherein the excitation coil is provided at a position that does not contact the probe surface.