JPH10160710A - Division-type flaw-detecting sensor and flaw detecting method for conductive tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a division-type flaw-detecting sensor in which the influence of a tube sheet is eliminated and in which a flaw generated in the circumferential direction of a tube near the mounting part of the tube sheet can be detected with good accuracy by a method wherein gaps are formed between cross sections of a plurality of magnetic-substance cores arranged in a circular shape and a primary coil and a secondary coil are wound so as to be piled up on the respective cores. SOLUTION: A primary coil 4 and a secondary coil 5 are wound so as to be piled up on two semicircular magnetic-substance cores 3, sensor divided bodies 2 are formed, the sensor divided bodies 2 are arranged so as to form a nearly circular shape by keeping respective gaps at prescribed distances G (1mm or higher) between both opposite edges of the cores 3, and a division-type flaw-detecting sensor 1 is constituted. Then, a sensor assembly provided with the flaw detecting sensor 1 is inserted into a tube 200 to be inspected, a square-wave current, e.g. at a frequency of 100Hz to 10kHz and a current of 0.1 to 0.5A is supplied to the primary coil 4, the pulse width of pulse waveform voltage which is output from the secondary coil 5 is measured, and a flaw such as a crack, a thickness reduction or the like which is generated in the circumferential direction of the tube 200 is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive tube,
For example, a split-type flaw detection sensor capable of effectively detecting circumferential cracks or thinning of non-magnetic tubes such as copper-based tubes and austenitic stainless steel tubes, and a conductive tube using this sensor. It relates to a flaw detection method.

[0002]

2. Description of the Related Art Conventionally, in a heat exchanger using a non-magnetic tube such as a copper tube or an austenitic stainless steel tube,
Due to the effect of the tube plate (baffle), a simple and excellent method of inspecting using electromagnetic induction for cracks and thinning occurring near the tube plate portion where these tubes are attached, particularly in the circumferential direction. There is no present.

[0003]

SUMMARY OF THE INVENTION The present inventors have made it possible to detect cracks and thinning of the above-mentioned non-magnetic tube, particularly in the circumferential direction, using a pulse eddy current flaw detection method having a relatively large penetration depth. Various experimental studies were carried out with an eye on the possibility. One of the features of the pulse eddy current flaw detection method is that the penetration depth is large unlike the alternating current method based on the usual eddy current flaw detection test. When this pulse eddy current flaw detection method is used, a thickness of 4
mm or more of stainless steel, copper alloy or aluminum alloy, it is possible to extract information on the back side
By passing a low-frequency alternating current of about z or less to increase the penetration depth, it is possible to detect a flaw on the back side of a thick member, which was considered impossible with the conventional eddy current method.

First, the principle of measurement of the pulse eddy current flaw detection method will be briefly described. As shown in FIG. 3, a primary coil 102 and a secondary coil 103 are wound around a ferrite core 101 so as to constitute a flaw detection sensor 100. This sensor 10
0 moves the end of the sensor and the surface of the conductive test object 104 close to a distance of about 1 mm on the metal surface, and at the same time, the primary coil 102 of the sensor 100
A square-wave ON-OFF current as shown in FIG.
An eddy current is generated on the surface of the test object. This eddy current sequentially permeates inside with a delay. When the induced magnetic field induced by the eddy current is detected by the secondary coil 103, a pulse-shaped secondary voltage as shown in FIG. 4B is generated in the secondary coil. The pulse width of the pulse waveform voltage detected by the secondary coil 103 is measured, and
Flaws such as cracks 105 can be detected. This pulse normally causes an oscillation phenomenon as shown in FIG. 4C, but in order to prevent this, a resistor is actually inserted in parallel with the primary and secondary coils.

[0005] The detection principle of such a pulse eddy current flaw detection method is that the decay time of the eddy current induced on the surface of the object to be inspected 104, that is, the pulse width is such that the object to be inspected 104 is damaged, such as cracks and thinning, This is based on the fact that different materials are used.

That is, FIG. 5 shows that this sensor 10
7 shows an attenuation curve of an output pulse (secondary voltage) from the secondary coil 103 when 0 is set. The decay curves are V ₀ in the case of air, V _Fe when approaching the test object 104 made of a magnetic material (steel), and the test object 1 made of a non-magnetic material (copper).
Assuming that V _Cu approaches V 04, the attenuation curve changes as shown in FIG. When viewed in the same material, as shown in FIG. 6, the attenuation curve C _0, the attenuation curve by a lift-off C
₁ and C ₂ , but there is a point P where the influence of the lift-off is small. In the flaw detection sensor 100 used in this example, it is around 60 μs.

If there is a flaw such as a crack or a thinning, the attenuation curves C ₀ , C ₁ , C _2, etc. move in parallel by the movement amount (Δt), and change to, for example, an attenuation curve C ₃ . Therefore, by detecting and outputting the movement amount (Δt), the presence or absence of a flaw can be detected.

However, as a result of conducting many research experiments, the present inventors have found that the sensor and the detection method shown in FIG.
It has been found that, due to the effect of the wall thickness of the tube sheet to which the tube is attached, cracks and wall thinning particularly occurring in the circumferential direction cannot be accurately detected.

Therefore, the object of the present invention can be suitably used in carrying out the above-mentioned pulse eddy current flaw detection method, and in the flaw detection of a magnetic tube in a heat exchanger, the thickness of a tube plate to which the tube is attached is considered. An object of the present invention is to provide a split-type flaw detection sensor capable of accurately detecting cracks, wall thinning, and the like that occur in the circumferential direction of a pipe in the vicinity of a pipe sheet mounting portion without affecting the effect.

Another object of the present invention is to provide a pulse eddy current flaw detection method capable of accurately detecting cracks, thinning, and the like of a tube when inspecting a conductive tube for damage using the split type flaw detection sensor. To provide a method for detecting flaws in a conductive tube using the method described above.

Still another object of the present invention is to use the above-mentioned split-type flaw detection sensor, particularly in the case of flaw detection in a heat exchanger using a non-magnetic tube, to reduce the influence of the wall thickness effect of the tube sheet on which the pipe is mounted. It is an object of the present invention to provide a non-magnetic tube flaw detection method using a pulse eddy current flaw detection method that can accurately detect cracks, wall thinning, and the like that occur in the circumferential direction of a tube near a tube plate mounting portion.

[0012]

The above object is achieved by the split type flaw detection sensor and the flaw detection method for a conductive tube according to the present invention. In summary, the present invention provides a method in which a plurality of magnetic cores are arranged in a substantially circular shape, and a gap is provided between end faces of the magnetic cores facing each other. Is a split-type flaw detection sensor characterized in that a primary coil and a secondary coil are overlapped and wound. Preferably, each of the magnetic cores is made of ferrite, silicon steel, permalloy, magnetic amorphous metal, or the like, and has substantially the same shape.

According to another aspect of the present invention, a split-type flaw detection sensor having the above-described configuration is used, the flaw detection sensor is inserted into a conductive tube, a pulse-like current is applied to the primary coil, and a secondary coil is used. A method for detecting a flaw in a conductive tube based on a detected change in voltage is provided. According to the method of the present invention, circumferential flaws of the non-magnetic tube can be effectively inspected.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A split type flaw detection sensor according to the present invention and a flaw detection method for a non-magnetic tube using the flaw detection sensor will be described in more detail with reference to the drawings.

Embodiment 1 FIGS. 1 and 2 show a split-type flaw detection sensor 1 according to an embodiment of the present invention. Generally, the split type flaw detection sensor 1 of the present invention
A plurality of magnetic cores 3 are arranged in a substantially circular shape so that a gap (G) is provided at a portion facing each other.
Is configured by winding a primary coil 4 and a secondary coil 5 in an overlapping manner. In this embodiment, the flaw detection sensor 1 forms a sensor divided body 2 by winding a primary coil 4 and a secondary coil 5 on a semicircular magnetic core 3 and forming the sensor divided body 2.
The magnetic cores 3 are arranged so as to form a substantially circular shape. At this time, each of the sensor divided bodies 2 is arranged so that a gap of a predetermined distance (G) of 1 mm or more is formed between the opposite end faces of each of the magnetic cores 3. It is preferable that the magnetic cores 3 of the respective sensor divided bodies 2 have substantially the same shape, but they may be formed in different shapes if necessary. In this embodiment, ferrite is used as each magnetic core 3, but a silicon steel plate, permalloy, magnetic amorphous metal, or the like can also be suitably used.

In this embodiment, the inner diameter of the inspected pipe 200 is 1
The inner diameter (D _IN ) defined by the two magnetic material (ferrite) cores 3 used in the present embodiment is 5.7 mm.
mm, outer diameter (D _OUT ) is 12 mm, and width (W ₀ ) is 4 mm
The gap (G) formed between both end faces of both ferrite cores 3 was about 2 mm.

In this embodiment, the primary coil 4 of the split-type flaw detection sensor 1 is formed by winding a copper wire having a wire diameter of 0.12 60 times, and the secondary coil 5 has a wire diameter of 0.07 mm. It was formed by winding a copper wire 120 times. Thus, the outer diameter (D) of the flaw detection sensor 1 is approximately 14 mm, and the width (W) is approximately 6 mm.
It became. The ends of these split-type flaw detection sensors were arranged so as to have the same polarity.

In this embodiment, as shown in FIG. 2, the sensor divided body 2 constituting the split-type flaw detection sensor 1 is bonded to the outer periphery of the rod-shaped support 10 with an appropriate adhesive or the like. Further, plastics such as Teflon (trade name of polytetrafluoroethylene manufactured by DuPont) or the like is used on both sides of the support 10 in the axial direction to guide the sensor 1 in the tube 200 to be inspected. The formed guide bars 11 and 12 were integrally arranged to form the sensor assembly 20.

That is, in this embodiment, the guide bar 1
The diameter of 1 and 12 was 15 mm. Also, a plastic hard tube (not shown) is connected to the guide bar on the hand side, in this embodiment, the guide bar 11 on the left side in FIG. 2, and the primary coil 4 and the secondary coil are internally provided. The electrical leads for 5 were housed. The defect detection of the tube 200 is performed by inserting and withdrawing the flaw detection sensor assembly 20 configured as above into the tube 200 to be inspected. At this time, by making the guide bar 12 on the right side, that is, the distal end side longer in FIG. 2, the influence on the lift-off fluctuation of the distal end portion can be reduced. In the present embodiment, the length of the guide bar 11 on the hand side is 75 mm, and the length of the guide bar 12 on the distal end side is 200 mm.
mm, a good result could be obtained.

Using the split type flaw detection sensor 1 having the above configuration,
According to the above-described pulse eddy current flaw detection method, a flaw in the conductive tube was detected, and good results were obtained.

More specifically, in this embodiment, as shown in FIG. 7B, the inner diameter of the tube 200 to be inspected is a tube plate (baffle) 201 made of aluminum bronze which is attached by expansion. d _in ) 15.7 mm, outer diameter (d _out )
A 20 mm non-magnetic brass tube was used. As shown in FIG. 7B, a pseudo crack (tube end) having a width of 0.2 mm and a thickness of 60% or 30% on one side (tube end) and inside (tube center) of the tube sheet 201 is formed. (Thickness reduction at the center of the tube) is formed in the circumferential direction on the outer surface, and the sensor assembly 20 including the split type flaw detection sensor 1 having the above-described configuration is inserted into the tube 200 to be inspected. Directional flaws (cracking and thinning) were measured.

FIGS. 7 (C) and 7 (D) show the shapes of 60% and 30% circumferential thickness reduction. The 60% thickness reduction has a crescent shape with a depth of 1.2 mm. Formed, 3
The 0% thickness reduction was formed at the same width as the 60% thickness reduction in the circumferential direction at a depth of 0.6 mm. Also, in this embodiment,
As shown in FIG. 2, the flaw detection sensor assembly 20 is
When inserting and withdrawing from the inside of the tube 200, the adapter 13 is arranged at the hand side of the tube 200 to be inspected, and the sensor 1
To reduce fluctuations in lift-off.

According to the pulse eddy current flaw detection method of the present invention, the primary coil 4 of the sensor 1 has a frequency of 100 Hz to 100 Hz, for example.
A rectangular wave current having a frequency of 10 kHz and a current of 0.1 to 0.5 A is supplied.
V, a rectangular current of 200 mA was supplied, and the pulse width of the pulse waveform voltage output from the secondary coil 5 was measured.
FIG. 7 (A) shows the waveform of the thinning near the tube sheet at that time.

According to the pulse eddy current flaw detection method, the tube sheet 201 affects the output of the secondary coil as a change in the sheet thickness.
If the split-type flaw detection sensor 1 of the present invention is used, as described above, this problem can be solved by adjusting the two sensor split bodies 2 so as to cancel each other because they are similarly affected. is there. That is, by using the split type flaw detection sensor 1 of the present invention, it is possible to cancel the noise signal from the tube sheet portion without the influence of the tube sheet 201, and in the present embodiment, it is possible to identify the inspection of 30% thinning. there were.

At the time of inspection, as described above, the tube sheet 20
After the balance was made so that the noise was small inside and outside of No. 1, the scanning was performed by combining scanning and rotation of about ± 20 mm around the flaws. FIG. 5 shows that the split flaw detection sensor 1 of the present invention can effectively detect circumferential flaws generated before and after the tube sheet. As a result of further experiments, the use of the split-type flaw detection sensor 1 of the present invention eliminates the effect of the wall thickness effect of the tube sheet 201 and can also detect the circumferential flaw of the tube inside the tube sheet satisfactorily. I understood that.

Inspection using the split type flaw detection sensor 1 of the present invention requires a slight balance adjustment because the inspection is performed while rotating the flaw detection sensor. It takes less than a minute, and it can be seen that it is significantly superior to UT (ultrasonic angle flaw detection).

Embodiment 2 The split-type flaw detection sensor 1 described in Embodiment 1 is composed of two sensor divided bodies 2, but the split-type flaw detection sensor 1 of the present invention is not limited to this. For example, as shown in FIG. 8, it is also possible to configure with four sensor divided bodies 2. Also in this case, the adjacent poles are arranged so as to be the same.

The other configuration of the split-type flaw detection sensor 1 of this embodiment is the same as that of the first embodiment. Members having the same configuration and function are denoted by the same reference numerals, and detailed description is omitted.

[0029]

As described above, in the split-type flaw detection sensor according to the present invention, a plurality of magnetic cores are arranged so as to form a substantially circular shape, and the magnetic cores are provided at the portions between the end faces facing each other. Since a gap is provided and a primary coil and a secondary coil are wound on each magnetic core in an overlapping manner, the magnetic core is preferably used when performing the pulse eddy current flaw detection method. Even when inspecting for scratches on non-magnetic tubes, eliminate the effects of the wall thickness effect of the tube sheet to which the tube is attached, and avoid cracks and wall thinning that occur in the circumferential direction of the tube near the tube plate attachment part. It can be detected with high accuracy.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic configuration of a split-type flaw detection sensor according to a first embodiment of the present invention.

FIG. 2 is a perspective view of the split flaw detection sensor of the present invention shown in FIG. 1, and is a view showing an entire configuration of a sensor assembly in which this sensor is integrated.

FIG. 3 is a diagram illustrating a conventional pulse eddy current flaw detection method.

FIG. 4A shows a rectangular wave current supplied to a primary coil in the pulse eddy current flaw detection method.
(C) shows a pulse voltage waveform generated in the secondary coil.

FIG. 5 shows a pulse voltage waveform generated in a secondary coil due to a difference in a material of a test object.

FIG. 6 is a diagram illustrating a difference in an attenuation curve of an output pulse voltage generated in a secondary coil for explaining the principle of the pulse eddy current flaw detection method.

FIG. 7A shows an output pulse voltage waveform generated in a secondary coil obtained by the pulse eddy current flaw detection method of the present invention, and FIGS. 7B, 7C, and 7D show usage waveforms; It is a figure explaining the shape of a to-be-inspected pipe | tube and a wound.

FIG. 8 is a sectional view of a split-type flaw detection sensor according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Split-type flaw detection sensor 2 Sensor divided body 3 Magnetic core 4 Primary coil 5 Secondary coil 200 Tube to be inspected 201 Tube sheet

Claims (5)

[Claims] A plurality of magnetic cores are arranged so as to form a substantially circular shape, a gap is provided in a portion between end faces of each magnetic core facing each other, and a primary is provided in each magnetic core. A split-type flaw detection sensor characterized in that a coil and a secondary coil are wound in an overlapping manner. 2. The split-type flaw detection sensor according to claim 1, wherein each magnetic core is made of ferrite, silicon steel, permalloy, or magnetic amorphous metal. 3. The split-type flaw detection sensor according to claim 1, wherein the respective magnetic cores have the same shape. 4. A flaw detection sensor according to claim 1, 2 or 3, wherein said flaw detection sensor is inserted into a conductive tube.
A method for detecting flaws in a conductive tube, wherein a pulsed current is applied to the primary coil and a flaw in the conductive tube is detected based on a change in voltage detected by the secondary coil. 5. The method according to claim 4, wherein the conductive tube is a non-magnetic tube.