JP2003279305A - Method and apparatus for measuring wall thickness of steel pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly accurately measure wall thickness distribution in a circumferential direction of a steel pipe even if an inspecting probe is displaced or inclined. <P>SOLUTION: When an exciting coil 23 is displaced in a steel pipe pile 21, or the inspecting probe 25 is inclined, the distance between the exciting coil 23 and an inner wall 22 of the steel pipe pile 21 changes in the circumferential direction. Since the displacement or inclination of the inspecting probe 25 is the displacement of the exciting coil 23, by arranging a plurality of distance sensors 24 in the circumferential direction in the vicinity of the exciting coil 23, it is possible to detect its displacement, correct measured values of thickness, measure more accurate wall thickness distribution, and evaluate the state of corrosion. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel pipe wall thickness measuring method and apparatus for measuring the wall thickness of a steel pipe, a steel pipe pile or the like in order to estimate a corrosion state.

[0002]

2. Description of the Related Art Conventionally, in order to improve the earthquake resistance of a ground structure, a steel pipe pile is sometimes driven into the ground. Since there is moisture in the soil, corrosion may occur on the outer surface of the steel pipe pile, and the wall thickness of the steel pipe may decrease, resulting in a decrease in strength. As a method for diagnosing a corrosion state by measuring the wall thickness of a steel pipe pile, the applicant of the present application has disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2001-289824 (Japanese Patent Application No. 2000-104691), which uses a separated eddy current flaw detection method (RF
A method for diagnosing corrosion of steel pipes using the EC method) is disclosed.
Remote field Eddy CurrentTechniq
It may also be abbreviated as RFECT or RFEC method from ue.

FIG. 6, FIG. 7 and FIG.
FIG. 1, FIG. 5 and FIG. 8 of Japanese Patent No. 289824 are shown, respectively. FIG. 6 shows an RFEC flaw detection device 2 for diagnosing corrosion by measuring partial wall thinning of a steel pipe pile 1 in the ground by a separated eddy current flaw detection method.
2 shows a schematic configuration of. 7 and 8 respectively show a side section and a section perpendicular to the axis of the test probe of FIG.

The underground steel pipe pile 1 is driven into the ground as a foundation pile for a ground structure. However, the foundation pile that directly supports the aboveground structure may interfere with the diagnosis, so the steel pipe pile 1 equivalent to the foundation pile is driven into the ground near the foundation pile and the steel pipe pile 1 In some cases, the corrosion diagnosis results may be used to estimate the corrosion of foundation piles.

The exciting coil 3 is inserted inside the steel pipe pile 1,
If a magnetic field is generated by an alternating current, an eddy current that cancels this magnetic field flows in the steel pipe, and a secondary magnetic field is generated thereby. At this time, if the surface of the tube is corroded, the flow of the eddy current is disturbed, and the secondary magnetic field is also disturbed. RFECT is a diagnostic method of detecting the disturbance of the magnetic field by the receiving coil 4 and estimating the wall thickness and corrosion state of the steel pipe.

In FIG. 6, a water immersion ultrasonic probe is also incorporated into an inspection probe 5 as a flaw detection jig on which an exciting coil 3 and a receiving coil 4 of the RFEC method are mounted. Inspection probe 5
Can be moved up and down inside the steel pipe pile 1 by the traveling device 7. The RFEC flaw detection device 2 includes an ultrasonic thickness gauge 8 and is mounted on the instrument storage rack 9 for inspection.
0, and a signal processing personal computer 11 as a data recording device.

A signal from the water immersion ultrasonic probe is transmitted to an ultrasonic thickness gauge 8 on the ground by a high frequency cable 12. On the CRT monitor 13 of the ultrasonic thickness gauge 8, an echo is displayed as a reflection for a pulse signal incident from the inside of the steel pipe pile 1 from the water immersion ultrasonic probe into the pipe wall.

A plurality of receiving coils 4 are arranged at regular intervals in the circumferential direction. The signal received by each receiving coil 4 is
After being amplified by an amplifier and A / D converted from an analog signal to a digital signal, the high frequency cable 12 is used to
It is sent to the FEC flaw detector. The RFEC flaw detection device is realized by, for example, the signal processing personal computer 11 or the like, and according to the program as the data recording device, the RFEC analysis and R
The FEC analysis graph is calibrated and analysis data is output. The analysis data is displayed on the screen of the display monitor 14, for example, as illustrated.

In the RFEC method, when the signal amplitude of the electromotive force in the receiving coil 4 is A and the phase of the electromotive force is Φ, a Lissajous waveform drawn as AcosΦ on the X-axis and AsinΦ on the Y-axis forms the X-axis. Find the Lissajous plane phase angle θ. By obtaining the correlation formula between the Lissajous plane phase angle θ and the wall thickness reduction rate of the wall thickness of the steel pipe in advance with the test piece, the wall thickness reduction rate of the steel pipe pile 1 can be calculated for each position of each receiving coil 4. You can ask.

As shown in FIG. 7, the exciting coil 3 is arranged at the tip of the inspection probe 5 and is close to the receiving coil 4 which is arranged at a distance of at least twice the diameter, and the ultrasonic probe is used. The sound wave probe 6 is arranged. The inspection probe 5 can be moved in the steel pipe in the axial direction while being held by the plurality of holding wheels 15 near the central axis in the steel pipe such as the steel pipe pile 1. A central axis 16 is provided at the center of the inspection probe 5 and maintains a gap between the exciting coil 3 and the receiving coil 4 in the axial direction.

FIG. 8 is a section line VIII-V shown in FIG.
The cross section seen from III is shown. A plurality of receiving coils 4, for example, 12 receiving coils 4 are arranged at regular intervals in the circumferential direction so that the positions thereof are displaced in the front and rear. Display monitor 14 of FIG.
In the display screen of (3), three reception coils 4 arranged adjacent to each other in the circumferential direction are combined, and the metal thinning rate in the circumferential direction is evaluated for a total of 8 channels.

[0012]

In the RFEC method, the steel pipe pile 1 and the like are diagnosed on the assumption that the inspection probe 5 is in the normal posture shown in FIG. 9 (a). Under such a premise, the output from each receiving coil 4 is amplified by the signal amplification / A / D converter.
It is sent to the inspection device 10 through the converter 17 to evaluate the circumferential wall thinning. In the ground, corrosion does not always progress uniformly, but it may progress in a certain direction.

However, even if the steel pipe pile 1 is driven in the vertical direction, there is a possibility that the steel pipe pile 1 may be driven at an inclination due to non-uniformity of the resistance of the ground, or may be inclined due to the fluctuation of the ground with the passage of time. Further, even if the steel pipe pile 1 is driven in the vertical direction, the inspection probe 5 itself may not be able to take a complete vertical posture. Therefore, the central axis 16 is inclined as shown in FIG. 9B, or the central axis 16 is displaced from the axis of the steel pipe pile 1 as shown in FIG. When the inclination or the deviation occurs, a difference occurs between the inner surface of the steel pipe pile 1 and the exciting coil 3 in the same direction in all the normal times. Also, when the traveling device 7 that pulls up the inspection probe 5 is not installed at the center of the steel pipe pile 1, tilting or deviation occurs.

If the inspection probe 5 and the steel pipe pile 1 are biased or tilted, the distance between the exciting coil 3 and the inner wall of the steel pipe pile 1 will be different depending on the direction, and the eddy current generated in the steel pipe pile 1 will be in the circumferential direction. Will be different. This makes RFEC
An error occurs in the measured value by the method, and it becomes impossible to accurately evaluate the change in the wall thickness reduction rate in the circumferential direction.

As shown in FIG. 7, if a water immersion ultrasonic probe 6 is mounted on the inspection probe 5, it is possible to directly measure the wall thickness of the steel pipe pile 1 by ultrasonic waves. However, since the water immersion method ultrasonic probe 6 needs to measure the wall thickness with water interposed in the state of being almost in contact with the inner wall of the steel pipe pile 1, the wall thickness of the entire wall in the circumferential direction can be quickly measured. It is not possible to make measurements.

It is an object of the present invention to provide a steel pipe wall thickness measuring method and apparatus capable of accurately measuring even if the inspection probe is biased or tilted.

[0017]

DISCLOSURE OF THE INVENTION The present invention uses a separated eddy current flaw detection method in which an exciting coil and a receiving coil are axially spaced in a steel pipe and a magnetic flux generated from the exciting coil is received. In the wall thickness measurement method for steel pipes, the deviation of the exciting coil with respect to the center of the steel pipe is detected, and the wall thickness obtained by the separated eddy current flaw detection method is based on the correction table for the deviation obtained in advance with the test piece. Is a steel pipe wall thickness measuring method characterized by correcting the measured value of.

According to the present invention, the wall thickness of the steel pipe is measured by using the separated eddy current flaw detection method in which the exciting coil and the receiving coil are axially spaced from each other and the magnetic flux generated from the exciting coil is received. In doing so, the bias of the exciting coil with respect to the center of the steel pipe is detected. A correction table for the bias of the excitation coil is obtained in advance with a test piece, and the measured value of the wall thickness obtained by the isolated eddy current flaw detection method is corrected based on the correction table, so the error due to the bias of the excitation coil is removed,
It is possible to accurately measure the wall thickness in the circumferential direction.

Further, the present invention is characterized in that the inclination of the receiving coil with respect to the inner wall of the steel pipe is detected, and the measured value of the wall thickness is corrected based on the inclination correction table obtained in advance by a test piece. To do.

According to the present invention, when it is detected that the receiving coil is inclined with respect to the inner wall of the steel pipe, based on the inclination correction table previously obtained by the test piece,
Since the measured value of the wall thickness obtained by the separated eddy current flaw detection method is corrected, it is possible to more accurately measure the wall thickness in the circumferential direction together with the correction due to the deviation.

Further, according to the present invention, the magnetic flux generated from the exciting coil is arranged in the steel pipe at a distance from the exciting coil in the axial direction while moving the sensor having the exciting coil and the receiving coil in the axial direction. In a steel pipe wall thickness measuring device that receives the signal with a receiving coil and measures the wall thickness by the isolated eddy current flaw detection method, a plurality of steel pipe wall thickness measuring devices are placed close to the exciting coil and spaced in the circumferential direction around the axis of the steel pipe. Bias detection means for detecting the bias of the excitation coil with respect to the, the table storage means for storing the correction table for the bias of the excitation coil obtained in advance in the test piece, based on the output from the receiving coil, by the isolated eddy current flaw detection method A wall thickness measuring means for obtaining a wall thickness measurement value of the steel pipe, and a table storing means based on the bias of the exciting coil detected by the bias detecting means. And which refers to the correction table, a steel pipe wall thickness measuring device which comprises a wall thickness correction means for correcting the measured value of the wall thickness as determined by the thickness measuring means.

According to the present invention, the steel pipe wall thickness measuring device moves the magnetic flux generated from the exciting coil from the exciting coil to the axial line while moving the sensor including the exciting coil and the receiving coil in the axial direction in the steel pipe. A bias detecting means, a table storing means, a wall thickness measuring means, and a wall thickness correcting means for receiving the wall thickness with a receiving coil arranged at intervals in the direction and measuring the wall thickness by the separated eddy current flaw detection method. including. A plurality of bias detecting means are arranged in the vicinity of the exciting coil at intervals in the circumferential direction around the axis of the steel pipe, and detect the bias of the exciting coil with respect to the center of the steel pipe. The table storage means stores in advance a correction table for the bias of the exciting coil obtained by the test piece, and the wall thickness measurement means uses the output from the receiving coil to measure the wall thickness of the steel pipe by the separated eddy current flaw detection method. Then, the wall thickness correction unit refers to the correction table stored in the table storage unit based on the bias of the exciting coil detected by the bias detection unit, and obtains the measured value of the wall thickness obtained by the wall thickness measurement unit. to correct. Even if the exciting coil is deviated from the center of the steel pipe and is deviated, the deviation is detected by the deviation detecting means and the measured value of the wall thickness measuring means is corrected by the wall thickness correcting means based on the correction table. It is possible to accurately measure the wall thickness in the circumferential direction by removing.

Further, the present invention further comprises inclination detecting means for detecting the inclination of the receiving coil with respect to the inner wall of the steel pipe, and the table storage means also stores a correction table for the inclination previously obtained by a test piece. Every
The wall thickness correction means corrects the measured value of the wall thickness by referring to a correction table stored in the table storage means based on the inclination of the receiving coil detected by the inclination detection means.

According to the present invention, the inclination detecting means detects the inclination of the receiving coil with respect to the inner wall of the steel pipe, and the wall thickness correcting means comprises:
Since the measured value of the wall thickness is corrected by referring to the correction table for the inclination stored in the table storage means in advance obtained by the test piece, the wall thickness in the circumferential direction can be more accurately combined with the correction by the deviation. A measurement can be made.

Further, in the present invention, the deviation detecting means and the inclination detecting means are characterized in that the distance between the steel pipe and the inner wall of the steel pipe is ultrasonically measured to detect the deviation and the inclination, respectively. .

According to the present invention, the bias of the exciting coil and the inclination of the receiving coil with respect to the inner wall of the steel pipe are detected by ultrasonically measuring the distance with respect to the inner wall of the steel pipe. Bias and inclination can be detected.

[0027]

1 shows a partial construction of a steel pipe wall thickness measuring apparatus used in a steel pipe wall thickness measuring method according to an embodiment of the present invention. FIG. 1A shows a partial side cross section, and FIG. 1B shows a partial plan cross section. The steel pipe pile 21 that is the target of wall thickness measurement is substantially the same as the steel pipe pile 1 of FIG. The configuration of the steel pipe wall thickness measuring device is also the same as that shown in FIG. The exciting coil 23 is inserted inside the inner wall 22 of the steel pipe pile 21 to generate an eddy current in the steel pipe pile 21.
In the present embodiment, when the inclination and the deviation shown in FIG. 9B and FIG. 9C occur, the largest cause of the error is between the exciting coil 23 and the inner wall 22 of the steel pipe pile 21 in either case. Since the distance is different in the circumferential direction, attention is paid to the bias of the exciting coil 23. In order to detect the bias of the exciting coil 23, distance sensors 24 for measuring the distance to the inner wall 22 are installed immediately above the exciting coil 23 at four locations at equal intervals in the circumferential direction, that is, every 90 °, and the distance is measured. By doing so, the bias of the exciting coil 23 is detected as the direction and the distance.

Three or more distance sensors 24 may be provided.
As the distance sensor 24, for example, an ultrasonic sensor can be used. Further, an optical sensor or a sensor that makes direct mechanical contact can be used. However, the optical sensor or direct contact is easily affected by the surface state of the inner wall 22. With the ultrasonic sensor 24, the distance is calculated based on the time when the ultrasonic wave is reflected by the surface of the inner wall 22 and returned, so that an accurate distance can be easily calculated even when the ultrasonic wave is wet.

The structure of the inspection probe 25 including the exciting coil 23 is basically the same as that of the inspection probe 5 shown in FIG. 6, and a plurality of receiving coils are arranged via the central axis 26.
The distribution of the wall thickness of the steel pipe pile 21 can be measured in the circumferential direction.

FIG. 2 shows a schematic electrical configuration for performing wall thickness measurement by the RFEC method in this embodiment. An exciting current is supplied to the exciting coil 23 of the inspection probe 25 from an exciting current output device 32 connected to a personal computer data processing 31 of the inspection device 30 to generate a magnetic field for isolated eddy current flaw detection. The output from the distance sensor 24 is input to the personal computer data processing 31, and the deviation is detected. The measured value of the wall thickness by the RFEC method is given from the detector 33 of the inspection device 30 to the personal computer data processing 31. The output from the receiving coil 34 of the inspection probe 25 is supplied to the detector 33.
The signal is amplified by the signal amplification / A / D converter 35, converted into a digital value, and given.

FIG. 3 shows a schematic procedure in which the personal computer data processing 31 of FIG. 2 in this embodiment obtains the wall thickness of the steel pipe pile 21 as the remaining wall thickness and corrects it by the deviation. In step a1,
An exciting current is supplied from the exciting current output device 32 to the exciting coil 23 of the inspection probe 25, and a sensor output signal given from the receiving coil 34 to the detector 33 via the signal amplification / A / D converter 35 is input. In step a2, based on the sensor output signal, the Lissajous plane phase angle .theta.
To calculate. In step a3, the remaining wall ratio is calculated according to the phase angle-remaining wall ratio correlation formula 40 previously obtained by measurement on the test piece. In step a4, the remaining wall amount is calculated by multiplying the reference wall thickness value 41 by the remaining wall ratio calculated in step a3. As the reference wall thickness value 41, a measurement value is used for a steel pipe of the same pipe type as the steel pipe pile 21 in a state in which there is no thinning due to corrosion. Steel pipe pile with a diameter of 300 mm 2
No. 1 has a thickness of about 7 mm.

In step a5, the residual wall thickness correction is performed using the ultrasonic wall thickness measurement value 42 measured by using, for example, the water immersion ultrasonic contactor 6 shown in FIG. This correction of the amount of remaining wall is correction of the electromagnetic characteristics of the actual steel pipe pile 21. The water immersion method ultrasonic contactor 6 is easily affected by the roughness of the inner wall 22, and continuous measurement along the circumferential direction is also difficult.
However, if good conditions are obtained, pinpoint accurate measurement can be performed. Therefore, in places where ultrasonic thickness measurements can be obtained, RFEC at the same location
Compared with the values measured by the method, it is possible to correct differences in electromagnetic characteristics such as magnetic permeability and electric resistance between individual steel pipes. Further, in step a6, the exciting coil bias correction table 43 is used to correct the remaining amount. This correction is the bias correction of the exciting coil. The excitation coil bias correction table 43 is stored in a table storage means such as a memory or a storage device in the personal computer that performs the personal computer data processing 31. Table 1 below shows an example of the excitation coil bias correction table 43.

[0033]

[Table 1]

Excitation coil bias correction table 4 shown in Table 1
In No. 3, a test piece used in the same manner as the steel pipe pile 21 is prepared, and the exciting coil 23 is intentionally biased to be measured and prepared. As the test piece, a steel pipe having the same diameter, thickness, and JIS standard material as the steel pipe pile 21 is used. The correction value is determined by comparing the data obtained by measurement with the true value obtained by the water immersion type ultrasonic thickness measurement method or the like. Bias amount 5m
If you repeat the measurement by changing m, 10 mm, ...
Table 1 can be obtained. The angle is set such that the biased direction in which the exciting coil 23 comes closest to the inner wall of the test piece is 0 °, and the clockwise direction is + 45 °, + 90 ° ,. If the distance sensor 24 of FIG. 1 is used, the bias direction and bias amount at the time of measurement can be known. Therefore, using the excitation coil bias correction table 43, correction for reducing the influence of the tilt or bias of the inspection probe 25 can be performed. You can When the deviation direction and deviation amount at the time of measurement are not directly described in Table 1, interpolation may be performed.

FIG. 4 shows the concept of correcting the inclination of the receiving coil 34 in another embodiment of the present invention. Figure 4 (a)
Shows a normal state, and FIG. 4B shows a state when the device is tilted. The receiving coil 34 is used in a state of being in contact with the inner wall 22 of the steel pipe pile 21 in a normal state. In a normal state, the ultrasonic distance sensor as the inclination sensor 50 is
The distance from the tilt sensor 50 to the inner wall 22 can be detected based on the time until the inner wall 22 is irradiated with and the reflected wave is received. When the inspection probe 25 tilts as shown in FIG. 4B, the distance from the tilt sensor 50 to the inner wall 22 changes, and it is possible to detect that tilting has occurred. When the receiving coil 34 is tilted, the distance between the coil winding 52 and the inner wall 22 changes, causing an error in the wall thickness measurement value. In this embodiment, it is possible to correct the error due to the inclination as well as the error due to the bias as in the embodiment of FIG.

In this embodiment, four inclination sensors 50 as shown in FIG. 4 are installed at 90 ° intervals in the circumferential direction, signals from the four inclination sensors 50 are processed, and the inspection probe 25 is used.
The inclination amount of can be calculated by converting the distance into an angle. The correction for the inclination can also be performed using the reception coil correction table 53 shown in Table 2. Also in this embodiment, the basic configuration of the device is the same as that in FIG.

[0037]

[Table 2]

FIG. 5 shows a schematic procedure in which the personal computer data processing 31 of FIG. 2 obtains the wall thickness of the steel pipe pile 21 as the residual wall thickness and corrects it by the deviation. Steps b1 to b6 are the same as steps a1 to a6 in FIG.
It is equivalent to each step up to. In step b7, the remaining amount correction for the inclination correction of the receiving coil 34 is performed based on the receiving coil inclination correction table 53 as shown in Table 2. This makes it possible to correct an error caused by the receiving coil 34 obliquely contacting the inner wall 22.

In the above description, the wall thickness is measured in order to diagnose the corrosion state of the steel pipe pile 21 driven into the ground, but the meat such as a conduit for fluid transportation laid in a substantially horizontal posture is measured. The present invention can also be applied to thickness measurement. When the steel pipe is not in a vertical posture, the inspection probe 25
It becomes difficult to keep the center of the steel pipe accurately. By applying the present invention, it is possible to eliminate the influence of the deviation and the inclination, and thus it is possible to accurately measure the wall thickness.

[0040]

As described above, according to the present invention, when the wall thickness of the steel pipe is measured by the separated eddy current flaw detection method, the bias of the exciting coil with respect to the center of the steel pipe is detected and preliminarily obtained by the test piece. Since the measured value of the wall thickness is corrected based on the corrected table, the error due to the bias of the exciting coil can be removed, and the wall thickness can be accurately measured in the circumferential direction.

Further, according to the present invention, when the receiving coil is tilted with respect to the inner wall of the steel pipe, the measured value of the wall thickness is corrected on the basis of the correction table for the tilt previously obtained by the test piece. Together with the correction by
It is possible to more accurately measure the wall thickness in the circumferential direction.

Further, according to the present invention, a plurality of bias detecting means are arranged close to the exciting coil and spaced apart in the circumferential direction around the axis of the steel pipe to detect the bias of the exciting coil with respect to the center of the steel pipe. Then, the measured value of the wall thickness is corrected by referring to the correction table for the bias of the exciting coil obtained in advance on the test piece. Even if the exciting coil is deviated from the center of the steel pipe and the deviation occurs, the measured value is corrected based on the correction table, so the error due to the deviation of the exciting coil can be removed and the thickness measurement in the circumferential direction can be performed accurately. it can.

Further, according to the present invention, the inclination of the receiving coil with respect to the inner wall of the steel pipe is detected, and the measured value of the wall thickness is corrected by referring to the correction table for the inclination obtained in advance with the test piece. Together with the correction, it is possible to more accurately measure the wall thickness in the circumferential direction.

Further, according to the present invention, it is possible to simply and accurately measure the distance using ultrasonic waves and detect the deviation and the inclination.

[Brief description of drawings]

FIG. 1 is a partial side cross-sectional view and a horizontal cross-sectional view showing a simplified configuration for detecting a bias of an exciting coil 23 when measuring a wall thickness by a separated eddy current flaw detection method according to an embodiment of the present invention. It is a figure.

FIG. 2 is a block diagram showing a schematic electrical configuration of an apparatus used in the embodiment of FIG.

3 is a flowchart showing a schematic procedure for measuring the wall thickness of the steel pipe pile 21 in the embodiment of FIG.

FIG. 4 is a partial side sectional view showing a simplified configuration for detecting the inclination of the receiving coil when performing wall thickness measurement by the separated eddy current flaw detection method according to another embodiment of the present invention. .

5 is a flowchart showing a schematic procedure for measuring the wall thickness of the steel pipe pile 21 in the embodiment of FIG.

FIG. 6 is a block diagram showing a schematic configuration of an RFEC flaw detector 2 for performing corrosion diagnosis by measuring partial wall thinning of a steel pipe pile 1 in the ground by a separated eddy current flaw detection method.

7 is a side sectional view showing the configuration of the inspection probe 5 of FIG.

8 is a cross-sectional view taken along the section line VIII-VIII in FIG. 7.

FIG. 9 is a diagram showing a cause of an error in wall thickness measurement of the steel pipe pile 1 as shown in FIG.

[Explanation of symbols]

21 steel pipe pile 22 Inner wall 23 Excitation coil 24 distance sensor 25 Inspection probe 26 central axis 30 inspection equipment 31 PC data processing 34 receiver coil 40 Phase angle-remaining wall ratio correlation formula 43 Excitation coil bias correction table 53 Receiver coil tilt correction table

Continued front page    F term (reference) 2F063 AA16 BA30 BB05 BC02 CB10                       CC10 DA02 DA05 DC08 DD10                       GA08 KA01 LA19                 2F069 AA02 AA71 BB40 GG07 GG09                       GG65

Claims (5)

[Claims] 1. A steel pipe meat in which an exciting coil and a receiving coil are axially spaced in a steel pipe and a wall thickness is measured by a separated eddy current flaw detection method for receiving a magnetic flux generated from the exciting coil. In the thickness measurement method, it is necessary to detect the deviation of the exciting coil with respect to the center of the steel pipe and correct the measured wall thickness obtained by the separated eddy current flaw detection method based on the correction table for the deviation obtained in advance with the test piece. Characteristic steel pipe wall thickness measurement method. 2. The measurement value of the wall thickness is corrected based on a correction table for the inclination, which is obtained in advance by a test piece, by detecting the inclination of the receiving coil with respect to the inner wall of the steel pipe. 1. The method for measuring the wall thickness of a steel pipe according to 1. 3. A receiving coil in which a magnetic flux generated from the exciting coil is axially spaced from the exciting coil while moving a sensor including the exciting coil and the receiving coil in the steel pipe in the axial direction. In a steel pipe wall thickness measuring device that receives the signal by the remote eddy current flaw detection method, a plurality of magnets are placed close to the exciting coil and spaced in the circumferential direction around the axis of the steel pipe. Deviation detecting means for detecting the deviation of the magnetic field, table storage means for storing the correction table for the deviation of the exciting coil previously obtained by the test piece, and the meat of the steel pipe by the separated eddy current flaw detection method based on the output from the receiving coil. A thickness measurement means for obtaining a thickness measurement value and a correction stored in the table storage means based on the bias of the exciting coil detected by the bias detection means. Referring to Buru, steel pipe wall thickness measuring device which comprises a wall thickness correction means for correcting the measured value of the wall thickness as determined by the thickness measuring means. 4. A tilt detecting means for detecting a tilt of the receiving coil with respect to the inner wall of the steel pipe is further included, and the table storing means also stores a correction table for the tilt previously obtained by a test piece, The thickness correction means corrects the measured value of the thickness by referring to a correction table stored in the table storage means based on the inclination of the receiving coil detected by the inclination detection means. 3. The steel pipe wall thickness measuring device according to 3. 5. The bias detecting means and the inclination detecting means measure the distance between the steel pipe and the inner wall of the steel pipe by ultrasonic waves to detect the bias and the inclination, respectively. The described steel pipe wall thickness measuring device.