JP2005069883A - Corrosion detecting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a corrosion detecting apparatus capable of being applied to even piping made of a magnetic material and efficiently detecting corrosion of the piping over a wide range. <P>SOLUTION: The corrosion detecting apparatus 10 is provided with a solenoid coil 12 which revolves around a pipe 32, and an AC current is passed through the solenoid coil 12 by a variable frequency oscillator 14. An AC secondary current is passed through the pipe 32 by electromagnetic induction, and the intensity of a magnetic field generated thereby is detected by a magnetometer 16. A drive device 18 drives the magnetometer 16 in such a way as to move in an axial direction of the pipe 32 as moving over the circumferential surface of the pipe 32. A data recorder 20 records magnetic data outputted from the magnetometer 16. An FFT analyzer 22 performs FFT processing on the magnetic data recorded in the data recorder 20 to output frequency characteristics data. An operation part 24 computes the amount of corrosion etc. and outputs them to an output part 26 on the basis of the frequency characteristics data outputted from the FFT analyzer 22. The output part 26 outputs the results of computation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a corrosion detection device, and more particularly to a corrosion detection device capable of detecting corrosion of building piping and the like.

  Conventionally, as a method for detecting corrosion of building piping or the like, a radiographic inspection method, an ultrasonic thickness measurement method, an eddy current flaw detection method, or the like is known.

  Among these, the radiographic inspection method uses radiation and may adversely affect the human body. Moreover, although there is a method that can quantitatively determine, the accuracy is rough and it is difficult to determine the corrosion position.

  In addition, the ultrasonic wall thickness measurement method sends ultrasonic waves by bringing a probe into contact with the pipe, measures the ultrasonic wave reflected from the back surface of the pipe, and measures the round-trip time of the ultrasonic wave. It detects the corrosion position from time.

  However, in this method, since the probe must be brought into direct contact with the pipe, the pipe must be removed, which is not preferable in terms of deterioration of the pipe and workability. Moreover, although it can measure quantitatively, since it becomes a pinpoint measurement, in order to measure over a wide range, a huge number of measurements and analysis are required, and working efficiency deteriorates remarkably.

On the other hand, for example, the eddy current flaw detection method described in Patent Documents 1 to 3 generates a eddy current in a pipe by winding a coil around the pipe and passing an alternating current through the coil. By measuring the strength of the magnetic field, the corrosion position of the pipe is detected, which is harmless to the human body and can be measured without contact with the pipe.
JP 2001-183346 A JP-A-6-148142 JP 2000-81419 A

  However, in the eddy current flaw detection method, when the pipe is made of a magnetic material, the hysteresis loss is large and the current is easily distorted, so that it is difficult to measure accurately and the measurement is performed only in the vicinity of the coil wound around the pipe. There was a problem that it was not possible.

  The present invention has been made in view of the above-described facts, and is applicable to a magnetic material pipe, and also provides a corrosion detection device capable of efficiently detecting the corrosion of a pipe over a wide range. With the goal.

  In order to achieve the above object, the invention according to claim 1 is caused by current supply means for supplying an alternating current to a pipe, resonance means for resonating an alternating current flowing through the pipe, and an alternating current flowing through the pipe. Magnetic field detection means for detecting the strength of the magnetic field, and corrosion detection means for detecting at least the corrosion position of the pipe based on the strength of the magnetic field.

  According to this invention, the current supply means supplies an alternating current to the pipe. For this reason, the piping applied to this invention should just be comprised with the member which can flow an electric current at least. The current supply means includes, for example, a coil disposed so that a center circulates the pipe, and an alternating current supply means for supplying an alternating current to the coil. Can do.

  A coil is arrange | positioned so that the center may circulate around piping. An alternating current having a predetermined frequency is supplied to the coil by an alternating current supply means. As a result, a magnetic field is generated in the pipe by electromagnetic induction, an electromotive force is generated, and an AC secondary current is supplied to the pipe. A solenoid coil having an iron core at the center of the coil may be used.

  The resonance means is connected to the pipe and resonates an alternating current flowing through the pipe. The resonance unit includes, for example, an inductance, a capacitor, a resistor, and the like. In this way, by constructing a circuit with the piping and the resonance means and causing the alternating current to resonate and flow, the alternating current flowing through the piping can be maximized as much as possible, and corrosion can be detected accurately. It becomes possible.

  The magnetic field detection means detects the strength of the magnetic field generated by the alternating current flowing through the pipe. The magnetic field detection means detects, for example, the strength of the magnetic field in the direction perpendicular to the surface of the pipe.

  The corrosion detection means detects at least the corrosion position of the pipe based on the strength of the magnetic field detected by the magnetic field detection means. When corrosion does not occur, the strength of the magnetic field is considered to change compared to when corrosion does not occur. Accordingly, the corrosion detection means determines, for example, whether or not the amount of change in the magnetic field strength is equal to or greater than a predetermined threshold value. can do.

  In this way, since an AC current is passed through the pipe and the corrosion is detected based on the strength of the magnetic field generated thereby, it is not necessary to remove the coating even when the pipe is covered. Since a magnetic field is not directly applied to the pipe, it can be applied to a pipe made of a magnetic material, and pipe corrosion can be accurately detected over a wide range.

  In addition, as described in claim 3, the corrosion detection means includes frequency conversion means for outputting frequency characteristic data obtained by frequency-converting the strength of the magnetic field, and corrosion has occurred based on the frequency characteristic data. And calculating means for determining whether or not there is.

  The frequency conversion means converts the intensity of the magnetic field to frequency characteristic data, that is, data representing the relationship between the frequency and the strength level of the magnetic field, for example, by Fourier transform processing or the like. In this case, the frequency characteristic represented by the frequency characteristic data is such that there is a peak at the position of the frequency of the alternating current flowing in the pipe, but if corrosion has occurred, the peak will decrease. It is thought that.

  For this reason, for example, the calculation means can determine whether or not the level of the peak position has decreased by a predetermined threshold or more, and can determine that corrosion has occurred when the level has decreased by a predetermined threshold or more.

  Further, as described in claim 4, the calculation means may calculate a corrosion amount based on the frequency characteristic data.

  The degree of change in the peak position level is considered to correspond to the degree of corrosion. For this reason, the calculation means obtains the corrosion amount corresponding to the change amount based on the change amount of the peak position level. Thus, by calculating | requiring the amount of corrosion, it becomes possible to estimate how much corrosion is progressing and the lifetime of piping.

  Further, as described in claim 5, the magnetic field detection unit may further include a driving unit that moves the magnetic field detection unit in the axial direction of the pipe while moving the magnetic field detection unit in the circumferential direction of the pipe. Thereby, even when investigating the corrosion of piping over a wide range, it can be performed efficiently and promptly.

  Furthermore, as described in claim 6, a plurality of the magnetic field detection means may be provided along the circumferential direction of the pipe. Thereby, investigation of corrosion of piping can be performed more efficiently.

  As described above, according to the present invention, there is an excellent effect that the corrosion position and the corrosion amount can be efficiently detected over a wide range.

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

  As shown in FIG. 1, the corrosion detection device 10 according to the present invention includes a solenoid coil 12, a variable frequency oscillator 14, a magnetometer 16, a drive device 18, a data recorder 20, an FFT analyzer 22, a calculation unit 24, an output unit 26, A resonance circuit 28 and an oscilloscope 30 are included.

  The solenoid coil 12 includes a donut-shaped iron core 34 that circulates around a cylindrical pipe 32, and a coil 36 that is wound around the iron core 34. In the present embodiment, the solenoid coil 12 is configured such that the iron core 34 is provided at the center of the coil 36, but only the coil 36 may be caused to circulate around the pipe 32 without providing the iron core 34. However, in this case, it is necessary to increase the number of windings compared to the case where the iron core 34 is provided at the center of the coil 36.

  As shown in FIG. 2, the iron core 34 is detachable on the opposite side of the fulcrum P, and rotates in the direction of the arrow in the figure around the fulcrum P like a so-called hinge. For this reason, it can be easily attached and detached even in the middle of the pipe 32.

  The coil 36 is connected to the variable frequency oscillator 14. The variable frequency oscillator 14 allows an alternating current having a set frequency to flow through the coil 36, and the frequency and output level can be made variable.

  As an example, the magnetometer 16 is a triaxial fluxgate magnetometer capable of measuring from several tens of pT (picotesla). As an example, the X axis of the magnetometer 16 matches the axial direction of the pipe 32, the Y axis of the magnetometer 16 matches the circumferential direction of the pipe 32, and the Z axis matches the direction orthogonal to the surface of the pipe 32. Be placed. The magnetometer 16 detects the strength of the magnetic field in each of the X, Y, and Z axes orthogonal to each other and outputs it as magnetic force data.

  As shown in FIG. 1, the driving device 18 moves the magnetometer 16 on the peripheral surface of the pipe 32 at a predetermined speed in the direction of arrow A in the figure, while moving at a predetermined speed in the direction of arrow B in the figure, which is the axial direction of the pipe 32. Control to move with.

  The data recorder 20 records the magnetic force data of each axis output from the magnetometer 16. The FFT analyzer 22 performs FFT (Fast Fourier Transform) processing on the magnetic force data of each axis recorded in the data recorder 20 and outputs frequency characteristic data.

  The calculation unit 24 calculates whether or not corrosion has occurred based on the frequency characteristic data of each axis output from the FFT analyzer 22, the corrosion amount, the corrosion position, and the like, and outputs them to the output unit 26. The output unit 26 includes, for example, a recording device, a display, a printer, and the like for recording the calculation result on a recording medium. Whether or not the pipe 32 specified by the calculation unit 24 is corroded and the amount of corrosion. The corrosion position is output to a recording medium such as a screen or paper. Thereby, it is possible to easily confirm whether or not corrosion has occurred in the pipe 32, the corrosion amount, the corrosion position, and the like.

  One ends of conductive wires 38 and 40 are connected to both ends of the pipe 32 to be measured. Since the pipe 32 is normally covered with a heat insulating material or the like, the pipe 32 is connected to a portion not covered with a heat insulating material such as a valve handle.

  The other end of the wiring 38 is connected to one end of the resistor 42, and the other end of the resistor 42 is connected to one end of the resonance circuit 28. The other end of the resonance circuit 28 is connected to the other end of the wiring 40. Thereby, a loop circuit is formed by the pipe 32, the wiring 38, the resistor 42, the resonance circuit 28, and the wiring 40. An oscilloscope 30 is connected to both ends of the resistor 42.

The corrosion amount W (g) of the pipe 32 can be expressed by the following equation according to the Faraday law, where I ₁ (A) is the current that flows when the pipe is corroded and t (s) is the time.

W = kI ₁ t (1)
Here, k is an electrochemical equivalent. When the corrosion is viewed as an electrophysical phenomenon, the energy is consumed, so that the pipe 32 is rusted and the electric resistance changes. Rather than measuring the electrical resistance as a result of rusting as in the past, it is more reliable to measure the strength of the magnetic field generated by the current I ₂ flowing through the pipe 32 that directly consumes energy. Can be detected.

  For this reason, in the present embodiment, whether or not corrosion has occurred based on the frequency characteristic data obtained by passing a current through the pipe 32 and measuring the strength of the magnetic field generated by this current with the magnetometer 16 and frequency-converting this. No, the amount of corrosion, the corrosion position, etc. are detected.

When an AC current having a predetermined frequency as a primary current is passed through the coil 36 by the variable frequency oscillator 14, an AC magnetic field is formed in the circumferential direction of the pipe 32. For this reason, similarly to the transformer circuit, an electromotive force is generated in the pipe 32 on the secondary side by electromagnetic induction, and an AC secondary current I ₂ flows. When the secondary current I ₂ flows, a current I ₁ according to the Faraday rule flows at the corrosion position, and therefore, a current of i = I ₁ + I ₂ flows through the pipe 32. The ratio between the electromotive force generated in the coil 36 on the primary side and the electromotive force generated in the pipe 32 on the secondary side is constant, and each electromotive force is generated by the same mutual magnetic flux, so the phases are equal. .

Thus, the secondary current I ₂ flows through the pipe 32 by flowing an alternating current as the primary current through the coil 36 according to the theory equivalent to the transformer circuit.

Here, in order to accurately measure the strength of the magnetic field generated by the secondary current I ₂ flowing through the pipe 32 over a wide range, it is preferable to maximize the secondary current I ₂ as much as possible. . For this reason, the corrosion detection apparatus 10 includes a resonance circuit 28.

  The resonance circuit 28 includes a variable inductance 44, a variable capacitor 46, and a resistor 48. For example, the inductance value of the variable inductance 44 and the capacitance value of the variable capacitor 46 can be arbitrarily adjusted.

Accordingly, at least one of the frequency of the variable frequency oscillator 14, the variable inductance 44, and the variable capacitor 46 is adjusted while confirming with the oscilloscope 30 so that the secondary current I ₂ is maximized in a range where the secondary current I ₂ is not distorted. As a result, the secondary current I ₂ can be maximized within a range that is not distorted, and the intensity of the magnetic field generated by the secondary current I ₂ can be accurately measured. It may be provided adjusting means for adjusting the secondary current frequency of automatically variable frequency oscillator 14 as I ₂ becomes maximum within a range that does not distort, variable inductance 44, variable capacitor 46.

  Assuming that the current i flows through the pipe 32, the magnetic field strength H (A / m) at the position of the magnetometer 16 is expressed by the following equation according to Biosavart's law.

H = i / 2R (2)
Here, R is the distance from the center position C of the pipe 32 to the magnetometer 16 as shown in FIG.

  If the distance R from the center position C of the pipe 32 to the magnetometer 16 is constant, the current i changes at a position where the pipe 32 is corroded as compared to a position where there is no corrosion. The strength H changes. Therefore, it can be determined that corrosion has occurred when the change in the magnetic field strength H is greater than or equal to a predetermined value, and the amount of change in the magnetic field strength can be regarded as the amount of corrosion.

Here, assuming that a current of 0.1 (A) flows through the pipe 32 having a diameter of 100φ and a coating of 50 mm, R = 0.1 (m), i = 0.1 (A), and permeability μ ₀ = 4π. As ^{x10 −7} , the magnetic flux density B (= μ ₀ H) is about 628 (nT) from the above equation (2), which is sufficiently larger than the strength of the magnetic field recognized as noise, and is erroneously recognized as noise. Absent.

  The driving device 18 starts with a position in the vicinity of the solenoid coil 12, for example, and the magnetometer 16 moves on the circumferential surface of the pipe 32 at a predetermined speed in the direction A in the figure. Drive to move in the direction at a predetermined speed.

By moving the magnetometer 16 as described above with the primary current I ₁ flowing through the coil 36, the strength of the magnetic field on the surface of the pipe 32 is measured for each of the X to Y axes, and the data recorder 20 sequentially Is output. The data recorder 20 records the magnetic force data of each axis output from the magnetometer 16 at a predetermined sampling interval. Thereby, the strength of the magnetic field at each position on the surface of the pipe 32 is sequentially recorded for each axis.

  The FFT analyzer 22 performs FFT processing on the magnetic force data on each axis at each position recorded in the data recorder 20 and outputs frequency characteristic data.

  Based on the frequency characteristic data for each axis at each position output from the FFT analyzer 22, the calculation unit 24 detects whether or not corrosion has occurred at that position and calculates the amount of corrosion. Calculation of the amount The most notable is the frequency characteristic of the Z axis. In this embodiment, whether or not corrosion has occurred and the amount of corrosion are obtained based on the frequency characteristic data on the Z axis. Of course, the amount of corrosion and the like may be calculated comprehensively in consideration of the frequency characteristic data on the X axis and the Y axis.

  For example, as shown by the solid line in FIG. 4, the frequency characteristic at the position where there is no corrosion has a peak in the frequency of the alternating current passed through the coil 36, and when there is corrosion, as shown by the dotted line in FIG. 4, It is considered that the peak becomes small, that is, the output level becomes small.

  Therefore, the calculation unit 24 obtains a level difference between the output level when there is no predetermined corrosion and the output level determined from the frequency characteristic data of the Z axis output from the FFT analyzer 22, and this value is equal to or greater than a predetermined threshold value. If it is determined that corrosion has occurred. The predetermined threshold value is set to a value at which corrosion can be determined when the level difference is equal to or greater than this value.

  Further, since the obtained level difference is considered to indicate the degree of corrosion, the calculation unit 24 can also calculate the corrosion amount based on the level difference. For example, if the correspondence between the level difference and the corrosion amount is obtained in advance and a lookup table storing the correspondence is stored in a storage unit (not shown), the corrosion corresponding to the obtained level difference is obtained. The quantity can be easily determined from the lookup table.

  When it is determined that corrosion has occurred, the drive unit 18 is instructed to stop the movement of the magnetometer 16, and if the movement of the magnetometer 16 is stopped, the position of the corrosion occurs. It can be specified as the position. Further, in the calculation unit 24, the elapsed time from the start of measurement until it is determined that corrosion has occurred, the sampling interval for sampling the output of the magnetometer 16, the moving speed of the magnetometer 16, the circumference of the pipe 32 The position where corrosion has occurred may be obtained from the relationship of the length of the material. Furthermore, in the calculating part 24, you may make it predict the lifetime of the piping 32 based on the amount of corrosion. The service life of the pipe 32 is obtained by, for example, obtaining the current pipe 32 thickness based on the obtained amount of corrosion, and obtaining a decreasing tendency of the pipe 32 thickness by comparison with the pipe 32 thickness measured in the same manner in the past. Can be predicted.

  The output unit 26 records, for example, the amount of corrosion at the position where the corrosion occurs in the calculation unit 24 on a recording medium or outputs it to a display. At this time, when the calculation unit 24 determines the corrosion position, an image indicating the corrosion position may be output together with the display image of the pipe 32. Thereby, it is possible to easily visually recognize at which position the corrosion has occurred.

  As described above, in the present embodiment, the resonance circuit 28 is connected to the pipe 32 via the wirings 38 and 40 to form a loop circuit, and a current is passed through the solenoid coil 12 wound around the pipe 32 so that the pipe is electromagnetically induced. An induced current is passed through 32 and the intensity of the magnetic field generated thereby is measured to detect the occurrence of corrosion, the amount of corrosion, and the position of corrosion.

  As described above, since the induction current is made to flow through the pipe 32, even when the pipe 32 is coated, it is not necessary to remove the coating, and since the magnetic field is not directly applied to the pipe 32, the magnetism is not affected. It can also be applied to material piping, and corrosion of piping can be accurately detected over a wide range. The detectable range depends on the value of the current that can be passed through the pipe 32. For example, if a current of 0.1 (A) can be passed through the pipe 32 as described above, the range of 20 to 30 m. Corrosion can be measured over a wide range.

  In addition, although the structure provided with one magnetometer 16 was demonstrated in this Embodiment, it is good not only as this but as a structure provided with the several magnetometer 16 as shown in FIG. Thereby, corrosion of piping can be detected more efficiently.

  In addition, a current may be directly supplied to the pipe 32 instead of a secondary current to the pipe 32 by passing a current through the solenoid coil 12.

  Moreover, although this Embodiment demonstrated the case where this invention was applied to the cylindrical piping of a building, the shape of piping is not restricted to a cylindrical shape.

It is a figure which shows schematic structure of a corrosion detection apparatus. It is a figure which shows the state which opened the solenoid coil. It is a figure for demonstrating the strength of the magnetic field in the position of a magnetometer. It is a figure for demonstrating a frequency characteristic. It is a figure which shows schematic structure of the corrosion detection apparatus which concerns on a modification.

Explanation of symbols

10 Corrosion detection device 12 Solenoid coil (AC current supply means)
14 Variable frequency oscillator (AC current supply means)
16 Magnetometer (Magnetic field detection means)
18 Driving device (driving means)
20 Data recorder 22 FFT analyzer (frequency conversion means)
24 Calculation unit (calculation means)
26 Output unit 28 Resonant circuit (resonance means)
30 Oscilloscope 32 Piping 34 Iron core 36 Coils 38 and 40 Wiring 42 Resistance 44 Variable inductance 46 Variable capacitor 48 Resistance

Claims (6)

Current supply means for supplying alternating current to the piping;
Resonance means connected to the pipe and resonating an alternating current flowing through the pipe;
Magnetic field detection means for detecting the strength of the magnetic field generated by the alternating current flowing through the pipe;
Corrosion detection means for detecting at least the corrosion position of the pipe based on the strength of the magnetic field;
Corrosion detection device equipped with.   2. The corrosion detection apparatus according to claim 1, wherein the current supply means includes a coil arranged so that a center circulates the pipe and an alternating current supply means for supplying an alternating current to the coil. .   The corrosion detection means includes frequency conversion means for outputting frequency characteristic data obtained by frequency-converting the strength of the magnetic field, and calculation means for determining whether corrosion has occurred based on the frequency characteristic data. The corrosion detection apparatus according to claim 1 or 2, characterized by the above.   4. The corrosion detection apparatus according to claim 3, wherein the calculation means calculates a corrosion amount based on the frequency characteristic data.   5. The corrosion according to claim 1, further comprising a drive unit that moves the magnetic field detection unit in the axial direction of the pipe while moving the magnetic field detection unit in the circumferential direction of the pipe. Detection device.   The corrosion detection apparatus according to any one of claims 1 to 5, wherein a plurality of the magnetic field detection means are provided along a circumferential direction of the pipe.

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