JPH0348152A - Eddy current flaw inspection and manufacture of reference sample therefor - Google Patents

Abstract

PURPOSE:To accurately decide the internal flaw of an object to be inspected by comparing the reference flaw detection signal related to a reference sample having a know flaw and the actual flaw detection signal of the object to be inspected. CONSTITUTION:Two kinds of eddy current flaw detections are performed with respect to a reference sample 1A having a known flaw. At first, an inspection device 10 is adjusted to pass, for example, a current with frequency of 400kHz through a coil 12 and the coil is sent into a reference pipe 1A and the first flaw detection signal 21 outputted from the inspection apparatus 10 is obtained. Next, for example, a current with frequency of 200kHz is mixed with the current with frequency of 400kHz and both currents are allowed to pass through the coil 12 to obtain the second flaw detection signal 22. By mixing the flaw detection signals 21, 22 in a reverse phase, the third flaw detection signal 23 is synthesized to be set to an actual flaw detection signal 26. Next, the same operation is applied to a pipe 1 being an actual object to be inspected to obtain an actual flaw detection signal 36. By comparing the actual flaw detection signals 26, 36, the internal flaw of the pipe 1 can be decided accurately.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an eddy current flaw detection method for inspecting surface defects, etc. of an object to be inspected using eddy current, and a method for manufacturing a reference sample for eddy current flaw detection, and is applicable to magnetic materials. It can be used for non-destructive inspection of the inner and outer surfaces of non-magnetic plated materials during manufacturing, as well as for non-destructive inspection of the inner and outer surfaces of existing structures and piping while they are in use.

[Background technology]

Eddy current testing has conventionally been used as a non-destructive testing method for structures and piping. In particular, since the inspection work is simpler and cheaper than other non-destructive inspection methods, it is ideal for whole-product inspection, and is often used for inspection during manufacturing of parts that require reliability, or for maintenance inspections during use. has been done.

The second eddy current inspection method utilizes the phenomenon that eddy currents are generated in a conductor placed in a fluctuating magnetic field, and that these eddy currents cause unique disturbances depending on discontinuities such as defects and cracks inside the conductor. It is something to do. For specific inspections, for example, an excitation coil is placed close to a predetermined part of the object to be inspected and an alternating current is passed through it, an alternating magnetic field is applied to the part to generate eddy currents, and excitation is performed in response to the magnetic field caused by the eddy current. A flaw detection signal corresponding to eddy current is detected by changing the impedance of the coil. The flaw detection signal obtained here is generally graphed using X4 orthogonal coordinates, and the disturbance in the signal corresponding to the defect appears as a substantially figure-8-shaped locus.

Therefore, the form, size, etc. of the internal defect to be inspected can be determined based on the form and size of this trajectory.

By the way, when performing eddy current testing on steel, which is a ferromagnetic material, disturbances in the magnetic field due to magnetic non-uniformity in the test object may be picked up as noise, making it impossible to accurately detect the desired eddy current. . A direct current magnetic saturation method is employed as a means to remove such magnetic noise. In this method, by applying a bias by adding an appropriate DC component to the AC magnetic field applied from the excitation coil, it is possible to correct magnetic non-uniformity in the object to be inspected and reduce noise during detection of eddy currents. For this reason, when performing the eddy current flaw detection method on an inspection object with large magnetic noise, DC magnetic saturation is also used.

(Problem to be solved by the invention) Pipes that are subject to the above-mentioned eddy current inspection method are generally made of steel, but in recent years, molten aluminum or the like has been coated on the surface to improve corrosion resistance. Metals such as plated aluminized steel are now being used.

However, in such aluminized steel, the aluminum coating formed on the surface is a non-magnetic material and blocks the DC component of the magnetic field, resulting in the problem that the noise removal by DC magnetic saturation described above does not work effectively. was there. On the other hand, steel coated with aluminum is a ferromagnetic material, and 6N air noise due to magnetic inhomogeneity is noticeable, so it is difficult to perform non-destructive testing using eddy current testing without using direct current R air saturation. was difficult.

For this reason, during manufacturing inspections of aluminized copper products after the aluminum molten bath and maintenance inspections of parts using aluminized steel, other methods such as internal inspections by sampling and radiographic image inspections are used to inspect the products in use. non-destructive testing,
Alternatively, the current situation is that all products are regularly replaced without inspection.

However, because internal inspections do not involve inspecting all parts due to sampling, there is a risk that parts that fail inspection and have defects may continue to be used, and this is a problem in parts where reliability is important, such as piping in plants that handle hazardous materials and high-temperature fluids. It cannot be applied to. In addition, other non-destructive inspections such as radiographic inspection are complicated and inevitably increase inspection costs.Furthermore, replacing all products inevitably increases the economic burden, and even non-defective products cannot be unconditionally inspected. There was a problem that I had to replace it. Therefore, there has been a demand for the development of a technology that enables the application of an economical eddy current flaw detection method with high inspection efficiency and reliability to aluminized steel products and the like.

The purpose of the present invention is to reduce the influence of magnetic noise during inspection.
The object of the present invention is to provide an eddy current flaw detection inspection method that always provides accurate and reliable inspection results, and a method for manufacturing a reference sample used in this inspection.

[Means to solve the problem]

The eddy current flaw detection inspection method of the present invention applies a first magnetic field of a predetermined frequency to a target object, detects an eddy current caused by the magnetic field, and generates a first flaw detection signal, and the frequency is approximately an integer with the first magnetic field. Either a second magnetic field having a ratio or a mixed magnetic field of the second magnetic field and the first magnetic field is applied to the object, and an eddy current caused by the magnetic field is detected to generate a second flaw detection signal. Using an inspection procedure in which a third flaw detection signal is generated by combining the first and second flaw detection signals so that their noise components cancel each other out, Applying the inspection procedure, using the obtained third flaw detection signal as a reference flaw detection signal, and applying the above inspection procedure using the actual inspection target as the object,
The obtained third flaw detection signal is used as an actual flaw detection signal, and by comparing this actual flaw detection signal with the reference flaw detection signal, etc., an internal defect in the object to be inspected is determined.

Here, in embodying the eddy current flaw detection inspection method of the present invention, the same equipment configuration as the normal eddy current flaw detection method can be used as is when executing the above inspection procedure.

In addition, in the above inspection procedure, when the second magnetic field is used as it is for obtaining the second flaw detection signal, when the first and second flaw detection signals are combined, their components cancel each other out. It is preferable that the fundamental vibration components of one of the flaw detection signals be left as the third flaw detection signal.

Therefore, the frequency of the second magnetic field is about twice, three times, or an integral multiple of the frequency of the first magnetic field, or 1/2.
It is preferable to set it so that it is about 1/3 or a fraction of an integer, that is, one becomes a harmonic component of the other.

Furthermore, in the above inspection procedure, when a mixed magnetic field of the first magnetic field and the second magnetic field is used as the magnetic field for obtaining the second flaw detection signal, when the first and second flaw detection signals are combined, The components of each signal corresponding to the first magnetic field may cancel each other out, and the component corresponding to the second magnetic field may be left as is as the third flaw detection signal.

Therefore, the frequency of the second magnetic field is about twice, three times, or an integral multiple of the frequency of the first magnetic field, or l/, 2
．． Any one can be used, including one that is approximately 1/3 to one fraction of an integer. Here, if the first and second magnetic fields have a common overtone series, the component of the second magnetic field may be affected when canceling the component of the first magnetic field.

In such a case, the waves of the first and second magnetic fields may be made into a sine wave or the like with few harmonics. Furthermore, if the frequencies are in an irregular relationship, modulation distortion or the like may occur during synthesis of the third flaw detection signal. Therefore, the frequency of the second magnetic field is 2:3 with respect to the frequency of the first magnetic field.
．． It may be set to an integer ratio such as 3:4.

In addition, when comparing the reference flaw detection signal and the actual flaw detection signal, it should be noted that the direction of the trajectory of the flaw detection signal in the reference flaw detection signal is, for example, Y
Set a reference phase angle for rotation to match the coordinate axis direction, adjust the phase of the trajectory in the actual flaw detection signal according to this reference phase angle, and determine the shape and size of the defect based on the final trajectory. Methods such as determining the following can be used.

On the other hand, as the reference sample, one may be used that has a clear defect shape, depth, width, etc., and is similar to the actual inspection target except for the known defect. For example, if a material with the same shape and shape as the actual inspection target is used, and an artificial defect of a predetermined shape and size is formed on a part of the material, and various types are manufactured with particular regard to the shape and size of the defect, inspection can be carried out. Accuracy can be improved.

By the way, in manufacturing a reference sample, it is necessary to accurately form a predetermined artificial defect in a metal material. However, electric discharge machining, which performs minute electric discharge melting, is expensive to manufacture and is not suitable for actual use. On the other hand, machining using a lathe or milling machine, which is often used in ordinary metal processing, is difficult to process with high precision, and in particular, in the case of thin-walled materials, the base material tends to deform and processing is difficult.

Therefore, the method for manufacturing a reference sample for eddy current testing of the present invention involves immersing a metal material whose surface is coated with a predetermined coating material in an electrolyte solution, and applying an electrolytic voltage between the metal material and the electrolyte solution. However, the coating material is electrolytically corroded to form predetermined artificial defects.

Here, metal materials that can form artificial defects include plate-shaped or tubular materials whose surfaces are coated by plating, such as the aluminized steel pipes mentioned above, and materials with a thickness of 1.0 mm or less that are difficult to machine. It is also applicable to thin walls.

Further, when electrolytically corroding a metal material, only the part where an artificial defect is to be formed is exposed in accordance with the defect, and the other parts are masked to set the shape and dimensions. Adhesive tape or paint can be used for masking, and a tape with holes corresponding to the desired artificial defect shape is pasted on the formation site, and other surfaces around this tape are coated with enamel, etc., as appropriate. May be used together.

Further, the depth of the defect and the like are set by setting the concentration of the electrolytic solution, the electrolytic voltage and current, the reaction time, and the like.

As the electrolyte, use reducing electrolyte water such as boronic acid (IIBF) aqueous solution. 8 liquids can be used, and the electrolytic voltage may be such that a potential difference can be confirmed in the boundary layer between the plating material and the base material.

Here, when applying the electrolysis voltage, the metal material is used as an anode, and the counter electrode placed in the electrolytic solution is used as a cathode. As the counter electrode, an aluminum rod or the like having a diameter of about 211,111 mm can be used, and by arranging the tip near the artificial defect formation site of the metal material, efficient machining is possible by intensively electrolytically corroding the machining site.

In addition, by making the tip of the counter electrode into a spiral circular or rectangular shape that corresponds to the shape of the artificial defect, it is possible to uniformly apply voltage to the defect forming area and form artificial defects with various depths. It is.

Furthermore, in electrolytic processing, it is desirable to perform voltage control based on the so-called constant potential electrolysis method, using known devices such as using a constant potential electrolysis power source such as a potentiostat and using a silver-silver chloride electrode as a reference electrode. You can use .

Further, during electrolytic corrosion, it is preferable to stir gas by passing gas into the electrolytic solution and use bubbles to circulate the electrolytic solution in the vicinity of the processing area as appropriate to prevent performance deterioration due to retention of electrolytic products.

In particular, when forming artificial defects on the inner surface of a tube-shaped material, if the defect formation site is placed at the bottom and air bubbles are sent into the tube, the bubbles will flow along the top of the tube, resulting in sufficient agitation. , and it is possible to prevent the current flow between the defect forming site and the counter electrode from being unnecessarily blocked by air bubbles.

[Effect]

In the present invention, the magnetic noise of the flaw detection signal is reduced by employing an inspection procedure that utilizes a plurality of frequencies.

In other words, the first and second flaw detection signals detected from the target object include noise components due to the magnetic non-uniformity of the target object, but each noise component is mixed in the same way during the inspection, and the second flaw detection signal are canceled out when combined as a flaw detection signal.

Therefore, if such an inspection procedure is applied to an actual inspection object, an actual flaw detection signal that is free from magnetic noise and corresponds to the internal defects of the inspection object will be obtained.

On the other hand, when evaluating the actual flaw detection signal, by applying the same inspection procedure to a reference sample with known defects and comparing the reference flaw detection signal obtained here with the actual flaw detection signal, it is possible to evaluate the internal defects of the inspection target. can be determined relative to known defects, and noise in the inspection procedure is also canceled out.

Therefore, for example, if the actual flaw detection signal is compared with the standard flaw detection No. 13 and expressed in a phase angle schematic diagram similar to the normal eddy current flaw detection method, the loci corresponding to the internal defects to be inspected will be accurately drawn. Become.

As described above, according to the eddy current flaw detection inspection method of the present invention, accurate defect inspection can be performed by comparison with a reference sample, and since it is not affected by magnetic noise during inspection, noise prevention measures such as DC magnetic saturation can be used. There is no need to use it in conjunction with this method, and even aluminized steel can be inspected accurately and reliably.

Furthermore, by using the method of manufacturing a reference sample for eddy current flaw detection of the present invention, it is possible to easily and inexpensively form highly accurate artificial defects on the reference sample by electrolytic corrosion, thereby making it possible to generate a reference flaw detection signal in the reference sample. Since it is possible to improve the accuracy of , and also to easily prepare various reference signals, it is also possible to improve the accuracy in comparison and judgment, thereby achieving the above object.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

In Fig. 1, the object to be inspected in this example is an outer diameter of 2
5.4+w+s, wall thickness 2.77mm, length 6000m
This is a pipe l formed in 5TB3.
This is an aluminized steel pipe made of No. 5 steel with an aluminum coating applied to the surface (outer and inner periphery).

On the other hand, the inspection device 10 used for eddy current flaw detection in this embodiment is as follows:
It includes an excitation coil 12 connected via a cable 11, and this coil 12 is inserted inside the pipe 1 to be inspected. This inspection device 10 generates an alternating current magnetic field of a specified frequency around the coil 12, and
By generating an eddy current on the wall surface of the surrounding pipe 1 and detecting a change in the impedance of the coil 12, a flaw detection signal 1 representing a change in the eddy current generated in the pipe 1 is generated.
4 can be output. Further, a feeding mechanism 13 is connected to the inspection device 10, and this feeding mechanism 13 allows the cable 11 to
The structure is such that eddy current flaw detection can be performed over the entire length of the pipe 1 by sequentially sending the coil 12 in the pipe 1. Note that the coil 1 is moved by the feeding mechanism 13.
The speed at which 2 is moved is set to be a constant speed within the range of 500 to 750 mo+/s.

When inspecting the pipe 1 using such an inspection apparatus IO, this embodiment employs an eddy current flaw detection inspection method based on the present invention. For this purpose, a reference sample corresponding to the pipe 1 to be inspected and having known defects is prepared in advance.

As a reference sample, we created an artificial defect on the inner surface of a pipe basically similar to Pipe 1 to a depth of 10 to 1 mm to simulate actual corrosion.
A reference pipe 1^ in which a recess of 50 μm and a through hole with a diameter of 3 to 5 II is accurately formed is used.

In manufacturing this reference pipe IA, this embodiment employs the method of manufacturing a reference sample for eddy current flaw detection according to the present invention. Hereinafter, with reference to FIGS. 4 to 6, a detailed procedure for forming a circular concave-shaped artificial defect with a diameter of 10III on the inner surface of the pipe LA using this manufacturing method will be explained.

4 and 5, at the bottom of the electrolytic cell 50,
A pipe IA made of aluminized steel and having the same material and shape as the pipe I is arranged substantially horizontally.

Here, as shown in FIG. 6, an adhesive tape 62 having a circular hole 61 corresponding to the defect is pasted around a region 60 on the inside of the pipe IA where an artificial defect is formed. 1. Paint 63 such as enamel is applied to the other surfaces of A, and these make the pipe 1^
is completely masked except for the processed region 60 of the artificial defect.

The inside of the electrolytic bath 50 is filled with an electrolytic solution 51 so as to immerse the pipe IA. This electrolytic solution 51 contains 2
(ld borofluoric acid (HBF,) 54% in a 47% aqueous solution
0d of water is added.

On the other hand, a potentiostat 52 for constant potential electrolysis (NP-IR100O type manufactured by Nichia Scientific Instruments, etc.) is arranged near the electrolytic cell 50. The potentiostat 52 has an anode terminal (-) connected to the pipe IA, and a reference electrode terminal (r-
) is connected to the reference electrode 53, and the scratch terminal (+
) is connected to the counter electrode 54.

The reference electrode 53 is commonly used as a silver-silver chloride electrode, and is made by immersing a silver rod in a saturated potassium chloride (KCI) aqueous solution to form a silver chloride coating on the surface. , is immersed in the electrolytic solution 51 at a position away from the pipe IA in the electrolytic cell 50.

The counter electrode 54 is made of an aluminum bar with a diameter of 21111, and its proximal end is supported through the wall of the tank 50 with a rubber stopper 55, and its distal end is inserted into the pipe IA. The tip portion 56 of the counter electrode 54 has a spiral shape that has a circular shape as a whole corresponding to the artificial defect to be formed, and is arranged to face the processing region 60 .

Further, inside the electrolytic cell 50, a tube 57 to which air is pumped and supplied by a pump or the like (not shown) is arranged, and the tip thereof is inserted into one end side of the pipe IA. Here, the one end of the pipe IA is supported slightly lower than the other end, and the air sent out from the tube 57 forms bubbles 58 in the pipe 1^ and moves to the other end, thereby causing electrolysis in the pipe IA. The liquid 51 is stirred while flowing from one end to the other end.

The amount of air supplied from the tube 57 is preferably set appropriately after conducting preliminary experiments;
Suitable stirring can be obtained by setting the speed to about 00 ad/sec.

Moreover, the electrolytic voltage set to the potentiostat 52 is
The value may be selected by detecting in advance a value at which a voltage change is detected between the steel portion and the aluminum plating layer when a voltage is applied to the pipe IA, and in this embodiment, it is set to -0.350 mV.

After the above settings, by energizing the potentiostat 52 and applying a constant electrolytic voltage between the pipe IA and the pair 111s4, the processing area 60 is electrolyzed. &52
It is electrolytically corroded and gradually becomes concave.

At this time, other portions of the pipe IA are masked with adhesive tape 62 and paint 53 and are not corroded, and only the processed portion 60 exposed from the hole 61 is processed. In addition, since the tip 56 of the counter electrode 54 is formed into a circular spiral shape and is opposed to the processing area 60, the processing area 60 is electrolytically corroded to a uniform depth, and the electrolytic action is concentrated on the area. is done efficiently. Therefore, if the pipe IA is taken out after a certain period of time has elapsed, an artificial defect in the shape of a circular depression with a predetermined depth corresponding to the hole 61 is formed in the processed region 60. This depth is 1 degree of electrolyte 51,
It can be adjusted to a desired value in advance by setting the voltage etc. in the potentiostat 52, the material of the pipe IA, the processing time, etc., and can be treated as a known defect. Therefore, the processed pipe IA is the reference pipe 1 for eddy current testing of pipe 1.
It will be available as ^.

After such preparation of the reference pipe IA, the reference pipe IA
Then, the operation based on the eddy current flaw detection method of the present invention is performed on the pipe l, which is the original inspection target.

The specific operation of this testing method will be explained below with reference to FIG.

First, in order to obtain a reference flaw detection signal using the reference pipe IA, which is a reference sample, two types of eddy current flaw detection are performed on the reference pipe IA.

In the first eddy current flaw detection, the inspection device 10 is adjusted to pass a current with a frequency of 400 Hz through the coil 12 to generate a first magnetic field, and the coil 12 is sequentially sent into the reference pipe IA, and the inspection device The flaw detection signal output from 10 is recorded. Through this operation, the first flaw detection signal 21 is obtained.

In the second eddy current flaw detection, the same operations as in the first eddy current flaw detection are performed. At this time, the coil 12 has a frequency of 400 KH.
A current obtained by mixing a current with a frequency of 200 K II z with a current of z is passed through, and a mixed magnetic field of a first magnetic field and a second magnetic field based on each current that is an integer ratio to each other is outputted from the inspection device 10. Record the flaw detection signal. A second flaw detection signal 22 is obtained by this operation.

In addition, in each eddy current flaw detection, each noise component is in the X-axis direction, and the first and second flaw detection signals 21.2
The phase angle is set so that 2 is in the Y-axis direction.

After setting these phase angles, the third flaw detection signal 23 is synthesized by mixing the first and second flaw detection signals 21 and 22 in opposite phases.

Here, each of the original flaw detection signals 21 and 22 has a noise component 2.
4.25 is included, but the mixing ratio of each signal is 21.22 in addition to being in reverse phase. By adjusting
Each noise component 24.25 is canceled out.

In addition, by anti-phase mixing, the components corresponding to the current at frequency 400 Hz of each of the flaw detection signals 21 and 22 are canceled out, but the frequency 200 that was included in the second deep flaw signal 22 as the third flaw detection signal 23 is canceled out. A component corresponding to a current of Hz remains.

The third flaw detection signal 23 obtained in this way is converted into the actual flaw detection signal 26.
shall be. This actual flaw detection signal 26 shows changes corresponding to the through holes formed in the reference pipe 1^, and noise components have been removed.

Next, an actual flaw detection signal is obtained using the pipe 1 that is the actual inspection target.

Here, the procedure for obtaining the actual flaw detection signal is as follows:
The procedure is the same as that for obtaining the reference flaw detection signal for A, and the reference pipe 1^ is simply replaced with pipe l. That is, the first and second flaw detection signals 31 and 32 are detected by the first and second eddy current flaw detection, and the third flaw detection signal 33 is detected by reverse phase mixing of these flaw detection signals 31 and 32.
Synthesize.

The third flaw detection signal 33 obtained in this way is converted into the actual flaw detection signal 36.
shall be. This actual flaw detection signal 36 shows changes in accordance with internal defects that have occurred in the pipe 1, and noise components have been removed.

Next, the actual flaw detection signal 36 and the reference flaw detection signal 26 are compared, that is, for example, the reference flaw detection signal 2;6 and the actual flaw detection signal 36 are displayed on the same comparison screen 40, and each signal 26 is compared.
．． By comparing the differences in the 36 trajectories, the internal defects that caused each change were compared, and the reference pipe IA
Internal defects in the pipe 1 are determined based on known defects formed in the pipe 1.

According to this embodiment, the following effects can be obtained.

That is, by using a reference pipe IA having an artificial defect that has been accurately processed as a known defect, and comparing the reference flaw detection signal 26 regarding this reference pipe IA with the actual flaw detection signal 36 regarding the pipe 1 to be inspected, pipe l
internal defects can be accurately determined.

FIG. 3 shows a specific example of a trajectory obtained by performing the inspection according to this embodiment on a pipe 1 in which various internal defects were discovered. The trajectories 41° 4243 expressed by the phase angle up to the axis are the depths of 150 t m and 1 formed on the inner circumferential surface of the pipe 1, respectively.
00 u va, 50 pm. Also, among the trajectories extending in the Y-axis direction, the locus 44 is the pipe l.
It is a hole with a diameter of 211IIl passing through the inside and outside of the locus 4.
5゜46 is the depth created on the outer peripheral surface of pipe 1 100~1
The defects are 50 μm and 50 to 60 μm. Furthermore, Y
A locus 47 in the clockwise direction from the axis is a hole with a diameter of 3 sm passing through the inside and outside of the pipe 1.

As described above, in this example, by using the eddy current flaw detection method of the present invention, accurate defect inspection can be performed by comparison with the reference sample.

In particular, in detecting the actual flaw detection signal 36 for the pipe 1 and the reference flaw detection signal 26 for the reference pipe IA, eddy current flaw detection is performed twice, and the first and second flaw detection signals obtained in each are mixed in reverse phase. Therefore, it is possible to cancel out the noise components during inspection that are similarly included in each flaw detection signal.

In addition, in the first eddy current flaw detection, a first magnetic field of 100 Hz was used at a frequency of 400, and in the second eddy current flaw detection, a first magnetic field of 200 Hz was used at a frequency of 400.
Since a mixed magnetic field in which a second magnetic field with a frequency of 200 KHz was added to the first magnetic field according to the method was used, a 200 KHz component of the second magnetic field was left due to the reverse phase mixing and was taken out as a third flaw detection signal.

For this reason, the second flaw detection signal related to pipe 1 or reference pipe IA is used to eliminate noise and detect pipe 1! Or actual flaw detection signal 3 reflecting internal defects of reference pipe IA
6 and a reference flaw detection signal 26 can be obtained.

Furthermore, according to this embodiment, even if magnetic noise occurs due to magnetic non-uniformity in the steel pipe portion of pipe l as described above,
The influence of noise can be avoided during synthesis of the third flaw detection signal, and there is no need to use noise prevention means such as direct current magnetic saturation.

Therefore, it is possible to apply the eddy current inspection method to aluminized steel pipes l without any problems, for which it has been difficult to use the eddy current inspection method in the past. This makes it possible to improve reliability at the time of product shipment or maintenance inspection by taking advantage of the ability to perform accurate and reliable inspections efficiently, which is a feature of the eddy current flaw detection inspection method, and by inspecting all inspection targets without omission. can.

On the other hand, as the reference pipe IA, which is the reference sample, we used a material with the same shape as the pipe I, which is the actual inspection target.
Since an artificial defect with a predetermined shape and size is accurately formed in a part of the sample, the accuracy in comparison and judgment can be improved.

Here, in this example, since the method for manufacturing a reference sample for eddy current testing of the present invention is adopted for manufacturing the reference pipe IA, accurate processing is possible by adjusting the electrolytic corrosion condition settings.

Table 1 shows the correspondence between the amount of electricity and the depth of the artificial defect in the manufacturing procedure shown in this example. Here, the quantity of electricity (coulombs) is determined by the product of the current flowing between the counter electrode 54 and the pipe IA and the energization time, and can be appropriately measured by the potentiostat 52.

Table 1 When the values in this table are graphed, a straight line 71 in FIG. 7 is obtained.

In other words, it can be seen that the depth of the artificial defect has a precise proportional relationship with the amount of electricity supplied during electrolytic corrosion, and that by precisely controlling the amount of electricity, the depth of the artificial defect can be adjusted on the μm order. Here, to adjust the amount of electricity, in addition to adjusting the it value,
Adjustment of the energization time can be used, and the function of the potentiostat 52 can be used as appropriate.

In addition, by performing constant potential electrolysis using the potentiostat 52, and by making the tip 56 of the counter electrode 54 corresponding to the shape of the artificial defect and arranging it opposite to the processing area 60, concentration of electrolytic corrosion can be reduced. Processing efficiency can be improved, and the electrolytic corrosion at the processed portion 60 can be made uniform to form artificial defects to a depth similar to that of the present invention.

Furthermore, during electrolytic corrosion, the tube 57 is placed in the electrolytic solution 51.
Since the electrolytic solution 51 in the pipe IA is circulated appropriately by stirring the electrolytic solution 51 by sending air through the pipe IA to generate bubbles 5B, deterioration in performance due to retention of electrolyzed products can be prevented.

Here, for comparison, the electrolytic solution 5 was prepared under the same conditions as in this example.
When measuring the amount of electricity and defect depth in the same manner as in Table 1 above for an example in which an ultrasonic diaphragm was used as the stirring means in No. 1, it was found that:
The result was as shown by the straight line 72 in FIG. In other words,
Although there is a proportional relationship, it can be seen that the efficiency of electrolytic corrosion decreases. Furthermore, the resulting artificial defects had noticeable irregularities, which is thought to be because the ultrasonic vibration did not provide a sufficient stirring effect. Therefore, when realizing precision machining by electrolytic corrosion as in this example, it is desirable to use air supply and stirring together.

In this way, in this example, the manufacturing method of the reference sample for eddy current testing of the present invention was adopted to manufacture the reference pipe IA, so the manufacturing cost was reduced compared to the electric discharge machining etc. that were conventionally used to obtain high accuracy. It can be done at low cost, and it is possible to manufacture and prepare a large number of various defect shapes and sizes, and it is possible to perform more detailed comparative judgments during inspection work, and improve inspection accuracy.

In addition, since processing is performed using non-mechanical force using electrolytic corrosion, it can be applied to thin-walled objects compared to machining using lathes or milling machines, and the eddy current inspection method of the present invention can be used in a wide range of applications. .

Note that the present invention is not limited to the above embodiments,
It also includes the following modifications.

In other words, the object to be inspected is not limited to the pipe 1, but may be in other shapes such as a plate or box shape, or is not limited to aluminized steel, but can be made of ordinary steel or other magnetic materials, as well as aluminum and other non-magnetic materials. It may be plated with a magnetic material.The present invention can be widely applied to eddy current inspection methods for various inspection targets.

In addition, the coil that applies a magnetic field to the inspection target is not limited to an insertion type that is inserted into the inner surface of a tube like pipe 1 in the above embodiment, but also a rotating probe type coil that inspects the surface of a plate material, a coil that applies a magnetic field to a tube, a wire rod, and a wire rod. Any coil used in normal eddy current testing methods, such as a through-type coil for inspecting the outer surface, may be used, and may be selected as appropriate depending on the object to be inspected.

Furthermore, in detecting the actual flaw detection signal and the reference flaw detection signal from the inspection target and reference sample, the eddy current flaw detection is not limited to the first and second eddy current flaw detection, but may be performed three or more times, and multiple flaw detection signals are used. A third flaw detection signal may be combined.

Further, in the above embodiment, a first magnetic field with a frequency of 400 KHz is used during the first eddy current flaw detection, and a second magnetic field with a frequency of 200 Hz is applied to the first magnetic field during the second four-current flaw detection. Although an applied mixed magnetic field was used, other settings for these first and second magnetic fields may be utilized.

Furthermore, the second magnetic field may be used alone during the second eddy current flaw detection, for example, a fundamental frequency of 400 is used for the first eddy current flaw detection.
If a first magnetic field containing many harmonics at Hz is used for the second eddy current flaw detection, and a similar second magnetic field with a fundamental frequency of 200 kllz is used for the second eddy current flaw detection, mixing will cause harmonic components higher than the second order of the first magnetic field. The components of the second magnetic field can be made to correspond to each other, and a component of the fundamental frequency 400 Hz of the first magnetic field can be obtained as a third flaw detection signal.

In this way, various settings are possible for the frequency settings of the first and second magnetic fields in the first and second eddy current flaw detection.In short, when combining the third flaw detection signal, the first and second The settings may be such that some components of the flaw detection signal remain.

On the other hand, it is preferable to use the material and shape between the inspection target and the path as the reference sample, but known defects formed on this reference sample are not limited to artificial defects such as dents and through holes, but also grooves, etc. , cracks, and other defects that may occur in the inspection target.You can also prepare reference samples with various artificial defects in advance! # If the comparison is made with the following information in hand, the inspection accuracy can be further improved.

In addition, other suitable methods may be adopted for producing the reference sample, but as mentioned above, by adopting the method for producing the reference sample for eddy current testing of the present invention, it is possible to easily obtain a high-precision sample. Moreover, it can be obtained at low cost, and can be said to be suitable for the eddy current flaw detection method of the present invention.

Here, the method for manufacturing the reference sample for eddy current testing is not limited to the device configuration and settings of the above embodiments,
Type and concentration of electrolyte 51, potentiostat 52
The type and electrolysis voltage setting, etc., the material of the verification bridge 53,
It is desirable to change the shape, arrangement, etc. as appropriate for implementation.

Further, the material and arrangement of the counter electrode 54 are arbitrary, and the shape of the tip 56 may be a rectangular frame shape or a simply cut tip, and its arrangement is not limited to facing the artificial defect formation site 60. , or simply those that are close together, etc. However, by doing as in the above embodiment, efficiency and processing results can be improved.

Furthermore, the manner in which air is sent out for stirring may be changed as appropriate, and it is desirable to determine the optimum value through preliminary experiments or the like. In addition, the tube 57 or gas supply devices may be appropriately selected, and the supply is not limited to air. Note that the stirring means is not limited to one that utilizes the movement of bubbles due to gas supply, and may be other machines. It may also be a device that performs regular stirring.

[Effects of the Invention] As explained above, according to the eddy current flaw detection inspection method of the present invention, accurate defect inspection can be performed by comparison with a reference sample, and it is not affected by magnetic noise during inspection. , aluminized steel, etc. can be accurately and reliably inspected.

In addition, according to the method for producing a reference sample for eddy current flaw detection of the present invention, a wide range of reference samples having accurate artificial defects can be prepared easily and inexpensively, so that comparative judgment can be made when adopting the above-mentioned eddy current flaw detection inspection method. accuracy can be improved.

No., 23.33...Third flaw detection signal, 24.25.3
4.35...Noise component, 26...Reference flaw detection signal, 3
6...Actual flaw detection signal, 51...Electrolytic solution, 54...Anti-electro scraping, 57.58...Tube and air bubbles for air supply and stirring, 60...Processed part.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the configuration of an apparatus used in an embodiment of the present invention, Fig. 2 is a schematic diagram showing the operating procedure and signal flow of the embodiment, and Fig. 3 is an evaluation of flaw detection signals in the embodiment. 4 and 5 are cross-sectional views in different directions showing the configuration of the apparatus for manufacturing the reference sample in the above example, and FIG. 6 shows the main parts during the manufacture. The perspective view shown in FIG. 7 is a graph showing the results of comparative experiments of the reference samples produced in the above embodiments.

Claims (5)

[Claims] (1) A first magnetic field with a predetermined frequency is applied to the object, an eddy current due to the magnetic field is detected to generate a first flaw detection signal, and a second magnetic field whose frequency is in a substantially integer ratio with the first magnetic field is applied. Either a magnetic field or a mixed magnetic field of the second magnetic field and the first magnetic field is applied to the object, and an eddy current caused by the magnetic field is detected to generate a second flaw detection signal. Using an inspection procedure in which a third flaw detection signal is generated by combining two flaw detection signals such that their noise components cancel each other out, applying the above inspection procedure to a reference sample having a known defect as a target, The obtained third flaw detection signal is used as the reference flaw detection signal, and the above inspection procedure is applied using the actual inspection object as the object.
An eddy current flaw detection inspection method characterized in that the obtained third flaw detection signal is used as an actual flaw detection signal, and an internal defect in the inspection target is determined by comparing this actual flaw detection signal with the reference flaw detection signal. (2) A metal material whose surface is coated with a predetermined coating material is immersed in an electrolyte solution, an electrolytic voltage is applied between the metal material and the electrolyte solution, and the coating material is electrolytically corroded to form a predetermined artificial defect. A method for producing a reference sample for eddy current flaw detection, characterized by forming a . (3) In claim 2, when applying the electrolytic voltage, a counter electrode is placed in an electrolyte solution near the artificial defect formation site of the metal material, and a counter electrode is disposed between the counter electrode and the metal material. A method for producing a reference sample for eddy current flaw detection, the method comprising: applying the electrolytic voltage to the eddy current test. (4) A method for producing a reference sample for eddy current testing according to claim 2 or 3, characterized in that during the electrolytic corrosion, gas is passed through the electrolytic solution and stirring is performed using bubbles. (5) A method for manufacturing a reference sample for eddy current testing according to any one of claims 2 to 4, wherein the metal material is a plated material or a thin material.