JP2001289825A - Thickness measuring device of tube by isolated vortex flowing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To delicately measure a thickness or a thickness decreasing rate in an overall periphery of a tube by using many receiving coils and to suppress an increase in a cost. SOLUTION: A plurality of the receiving coils 14 are loaded in an RFEC method measuring probe 11, and divided into two rows. An RFEC method device 10 alternatively switches the coils 14 of the two rows in receiving circuits 21, 22 by a changeover switch 31. A distribution measuring circuit 20 obtains a distribution of the thickness decreasing rate of the overall periphery of the a steel tube pipe 15 based on analytical data obtained from a signal processor 32. Since the coils 14 are switched by the switch 31, a number of the receiving circuits 21, 22 can be reduced even when the number of the coils 14 is increased and a delicate measurement is conducted. Thus, the increase in the cost can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the wall thickness of a metal tube by the separated eddy current method, which measures the thickness of a metal tube by the separated eddy current method and diagnoses flaws and corrosion.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 9, LNG for storing liquefied natural gas (hereinafter abbreviated as "LPG") is known.
In the tank 1 and the like, a plurality of foundation steel pipe piles 3 are used as a foundation in the ground 2. Around the LNG tank 1, a steel pipe pile 4 for anticorrosion for burying the steel pipe pile 3 for foundation for electric protection is embedded. However, when it is considered that the steel pipe pile for foundation 3 of the foundation part is not corroded so much, the steel pipe pile for anticorrosion 4 is left buried without being energized. If the corrosion protection of the steel pipe pile 3 for foundation is performed using the steel pipe pile 4 for corrosion protection, the cost such as the electricity rate increases.
Until the corrosion of the foundation steel pipe pile 3 progresses, the electric corrosion protection using the anticorrosion steel pipe pile 4 is not performed.

[0003] In recent years, there has been a need for checking the degree of corrosion of the steel pipe pile 3 for foundation at the foundation to determine the necessity of cathodic protection or the like. However, the LNG tank 1 exists above the steel pipe pile 3 for foundation, and it is impossible to insert a measurement probe or the like into the steel pipe pile 3 for foundation. Therefore, by examining the degree of corrosion of the anticorrosion steel pipe pile 4 buried around the foundation steel pipe pile 3, it is expected that the degree of corrosion of the steel pipe pile 3 can be estimated to some extent.

[0004] For corrosion diagnosis of steel pipes such as the steel pipe pile 3 for foundation and the steel pipe pile 4 for corrosion protection, particularly the steel pipe buried underground, the separated eddy current method, that is, the remote field eddy current method (hereinafter, referred to as the remote field eddy method).
"RFEC method" is used. RFE
According to the method C, the relative change in the thickness of the steel pipe can be determined relatively easily and at high speed from the inside, and the degree of corrosion thinning can be determined from the change in thickness depending on the position. R
When diagnosing the corrosion state of a steel pipe by the FEC method, a thinning rate as a relative decrease in thickness is obtained and compared with a preset reference value. If it is determined that the thinning rate is greater than the reference value, it is determined that, for example, stronger anticorrosion measures need to be taken.

FIG. 10 shows the relationship between the measured wall thinning rate of various 300A steel pipes and the Lissajous plane phase angle obtained from the signal of the wall thinned portion measured by the RFEC method. As shown in FIG. 11, the Lissajous plane phase angle is represented as AcosΦ on the X axis and AsinΦ on the Y axis when the signal amplitude of the electromotive force in the receiving coil is A and the phase of the electromotive force is Φ. The angle between the Lissajous waveform and the X axis is referred to as θ. FIG. 12A shows an example of the test tube 5 for obtaining the relationship between the phase angle and the wall thinning rate as shown in FIG. 11 when the test tube 5 is measured by the RFEC method. The information is shown in (b).

[0006]

In the corrosion diagnosis of a steel pipe or the like by the RFEC method, it is conceivable to measure the wall thinning rate over the entire circumference of the pipe using a plurality of receiving coils. However, the receiving coil used in the RFEC method has a range in which the thinning rate can be detected is only about the width of the receiving coil. Therefore, in order to measure the wall thinning rate of the entire circumference of a steel pipe pile or the like, it is necessary to arrange the receiving coils circumferentially without leaving a gap between the receiving coil pipes. However, since the steel pipe pile has a ring that is welded to the inner peripheral side for corrosion and the connection between the pile and the pile, the receiving coil is positioned at the center of the pipe so that the step can be overcome. A movable structure using a spring or the like in the radial direction toward the axis has been considered. In order to have a movable structure, a gap is required in the receiving coil tube,
If there is a gap, it becomes impossible to collect the thinning rate data of the gap. For this reason, the receiving coils are prepared in a plurality of rows in the tube axis direction, and the arrangement of the receiving coils is arranged in a staggered manner. ing.

However, the size of the receiving coil is generally small, and a large number of receiving coils are required to measure the wall thinning rate of the entire circumference. Therefore, it is necessary to prepare as many receiving circuits as the number of receiving coils. There is. Since the receiving circuit and the like are more expensive than the receiving coil, if an attempt is made to measure the wall thickness or the wall thinning rate over the entire circumference using many receiving coils, many expensive receiving circuits and the like are required, Within a limited cost, it is difficult to secure a sufficient number of circuits.

SUMMARY OF THE INVENTION It is an object of the present invention to measure the wall thickness and the wall thinning rate over the entire circumference of a pipe using the separated eddy current method by using a large number of receiving coils, and to suppress an increase in cost. An object of the present invention is to provide an apparatus for measuring a wall thickness of a pipe by a separated vortex flow method.

[0009]

According to the present invention, a signal corresponding to a change in magnetic flux generated from an excitation coil arranged so that a central axis thereof coincides with an axis of a metal tube is transmitted from the excitation coil to the central axis. In a tube thickness measuring apparatus based on a vortex separation method in which the thickness of the metal tube is electromagnetically measured based on a signal received by a receiving coil arranged at an interval, the receiving coil is an exciting coil. Are arranged so that a plurality of predetermined coils belong to a plurality of rows arranged at intervals in the direction of the central axis, and in each row, the plurality of receiving coils are arranged at equal intervals along the inner circumference of the metal tube. It is arranged, between adjacent rows, so that the position of the receiving coil is arranged so as not to overlap the position of the same angle around the center axis of the exciting coil, and is shifted at an angle around the center axis. Minutes to a range of numbers A plurality of ranges of changeover switches provided to switch signals from different columns of reception coils belonging to the respective angle ranges; and a signal from the reception coil provided for each changeover switch and switched by the changeover switch. The plurality of ranges of signal processing circuits for analyzing the thickness of the metal tube and measuring the thickness of the metal tube in the circumferential direction based on the thickness measurement results from the plurality of ranges of signal processing circuits. And a distribution measuring circuit for obtaining a thickness distribution.

According to the present invention, the excitation coil is arranged so that the central axis thereof coincides with the axis of the metal tube, and generates a magnetic flux to measure the thickness of the metal tube by the separated vortex method. A plurality of receiving coils are arranged at intervals in the direction of the central axis, and each receiving coil receives a signal based on the magnetic flux generated by the exciting coil. Since the influence of the thickness of the metal tube is electromagnetically reflected on the reception signal, the reception signal can be analyzed to measure the thickness at the portion where the reception coil exists. The receiving coils are arranged so that a plurality of predetermined coils belong to a plurality of rows arranged at intervals in the center axis direction of the exciting coil, and in each row, the plurality of receiving coils are arranged on the inner periphery of the metal tube. Are arranged at equal intervals along, and between adjacent rows, so that the position of the receiving coil does not overlap the position of the same angle around the center axis of the exciting coil, since it is arranged at an angle shifted around the center axis, As a whole, many receiving coils are arranged along the inner periphery of the metal tube, so that the measurement can be performed finely. By switching the receiving coils belonging to different rows and having an angle with respect to the central axis within a predetermined range with a changeover switch, signal analysis and thickness measurement are performed by a signal processing circuit, so the number of signal processing circuits is determined by the number of receiving coils. And the cost increase can be suppressed.

Further, according to the present invention, a signal is received by each of the receiving coils while moving the exciting coil and the receiving coil in the metal tube in the axial direction, and the signals from the receiving coils in different columns are received by the changeover switch. It is characterized by further including a control circuit for switching at a timing so as to be at the same position with respect to the axis of the metal tube.

According to the present invention, the signals from the receiving coils which are divided into a plurality of rows and whose angles around the center of gravity axis are shifted are switched by the changeover switch so as to be at the same position with respect to the axis of the metal tube. Therefore, it is possible to measure the entire circumference at the same position with respect to the axis of the metal pipe, and to accurately obtain the thickness, the wall thickness reduction distribution, and the like.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an RFE as an apparatus for measuring the wall thickness of a pipe by a separated eddy current method according to an embodiment of the present invention.
1 shows a schematic configuration of a C method apparatus 10. An RFEC measurement probe 11 shown in FIG. 1A includes an excitation coil 12, a central shaft 13, and a plurality of reception coils 14, and a steel pipe pile 1
The thickness of the steel pipe pile 15 is measured while moving the inside of the steel pipe 5 in the axial direction with the central axis 13 coincident with the axis thereof. The steel pipe pile 15 has a case where the inside diameter is about 300 mm and is called 300A, for example. The exciting coil 12 and the receiving coil 14 are arranged at a distance of at least twice the outer diameter of the steel pipe pile 15.

The receiving coils 14 are arranged in two rows, for example, in groups of twelve. The two columns are center axis 1
3 and are spaced apart by an interval ΔL. ΔL is, for example, 7.8 cm. FIG. 1B shows an arrangement position of the receiving coils in each column. The receiving coil 14 has a total of 24
Therefore, the positions of S1 to S24 are set at equal intervals, that is, at an angle of 360 ° ÷ 24 = 15 °, and odd-numbered positions are assigned to the first row closer to the exciting coil 12, and even-numbered positions are set. The position is assigned to a second row remote from the excitation coil 12. That is, the receiving coils 14 arranged in the first row and the second row are in a staggered arrangement.

FIG. 1C shows a schematic electrical configuration of the RFEC method apparatus 10. The distribution measuring circuit 20 is based on the analysis data from the twelve receiving circuits 21, 22,.
The wall thickness distribution and the like over the entire circumference of the steel pipe pile 15 are created. One receiving circuit 21 includes one receiving coil belonging to each of the first column and the second column shown in FIG.
For example, a combination such as S1 and S2,
Is configured to be switchable. The signal switched by the changeover switch 31 is input to the signal processing circuit 32. The signal processing circuit 32 includes a lock-in amplifier that amplifies a minute analog signal from the receiving coil 14, an A / D converter that converts the analog signal into a digital signal, and a Lissajous plane phase as shown in FIG. An arithmetic circuit and the like for measuring the thinning rate of the steel pipe pile 15 according to the relationship between the angle and the thinning rate are included.

The RFEC measuring probe 11 is a steel pipe pile 1
The thickness is measured while moving in the inside 5 at a speed of, for example, 1 m per minute. The signals from the receiving coils 14 in the first row and the second row are alternately switched by a changeover switch 31 so that the signal processing circuit 3
2 is input. 4.68 / n where n is a natural number
If the changeover switch 31 is switched every (second),
The measurement pitch is 7.8 / n (cm). This measurement pitch is 1 / n of the distance ΔL between the first and second rows. Therefore, if n = 1, the first row and the second row of the receiving coils 14 are arranged with respect to the axis of the steel
The measurement can be performed at the same position at the pitch of L. n
Is set to 2 or more, measurement can be performed at a finer pitch.

FIG. 2, FIG. 3, FIG. 4 and FIG.
An example of the RFEC measurement probe 11 shown in FIG. FIG. 2 shows the configuration viewed from the right side, mainly in a cross-sectional view above the center line. FIG. 3 shows a state viewed from the front. FIGS. 4 and 5 show the section line IV in FIG.
-IV and the structure seen from the cutting surface line VV are shown, respectively.

As shown in FIG. 4, the center axis 13 of the RFEC measurement probe 11 is held so as to coincide with the axis of the steel pipe pile 15 so that a plurality of holdings can be made. Wheels 35 are provided. FIG.
As shown in FIG. 3, a water immersion ultrasonic probe 36 capable of measuring the wall thickness of the steel pipe pile 15 using ultrasonic waves is also provided. Electrical connection of signals and the like to the receiving coil 14 and the water immersion ultrasonic probe 36 is performed via a cable 37.
If the wall thickness measurement by the water immersion ultrasonic probe 36 is also used,
The wall thickness measurement accuracy along the entire circumference of the steel pipe pile 15 can be improved. As shown in FIG.
Is urged radially outward by a spring device 38. Thereby, even if a step or the like is generated on the inner peripheral surface of the steel pipe pile 15, if the pressing force from the step or the like becomes larger than the biasing force of the spring device 38, the receiving coil 14 is retracted inward in the radial direction, Once the step is over, it can be restored.

FIG. 6 shows a measurement state of the wall thinning rate of the steel pipe pile 15 using the RFEC apparatus 10 of FIG. The RFEC measurement probe 11 includes an excitation coil 12 and a reception coil 14.
At the same time, a water immersion ultrasonic probe 36 is incorporated. The cable 37 is connected to the inspection device 40, and a signal from the water immersion ultrasonic probe 36 is input to the ultrasonic thickness meter 41. The ultrasonic thickness gauge 41 includes a CRT monitor 42 and displays an echo signal. When the echo signal waveform is good,
High-precision wall thickness measurement by ultrasonic waves is possible, and if the RFEC data is calibrated at the measurement position, the accuracy of the RFEC data can be increased.

The inspection apparatus 40 includes a changeover switch 31, a signal processing circuit 32, and an oscillation circuit 30 of the receiving circuits 21, 22,... Shown in FIG. This is realized by the signal processing personal computer 43. The processing result as the distribution measuring circuit 20 is displayed on the display monitor 44. The inspection device 40, the ultrasonic thickness gauge 41, the signal processing personal computer 43, the display monitor 44, and the like are housed in an instrument housing rack 45 and are integrated.

The RFEC measurement probe 11 can be reciprocated in the axial direction in the steel pipe pile 15 embedded in the ground by changing the length suspended by the cable 37 by the traveling device 46. As shown in FIG. 5, the receiving coil 14 can be displaced in the radial direction by the spring mechanism 38, so that even if a step occurs at the steel pipe joint 47 or the like inside the steel pipe pile 15, the receiving coil 14 can move over. .

FIG. 7 shows an example of the evaluation of thinning over the entire circumference displayed on the display monitor 44 of FIG. The 24 receiving coils form one channel by three adjacent coils as shown in S1, S2, and S3 shown in FIG. 1B, and the thinning rate is evaluated as a total of eight channels. In each channel, the signals from the three receiving coils 14 are not analyzed individually but are analyzed in a comprehensive manner, so that the analysis over the entire circumference can be performed quickly.

FIG. 8 shows a schematic configuration of an RFEC method apparatus 50 as an apparatus for measuring the wall thickness of a pipe by the separated eddy current method according to another embodiment of the present invention. In the present embodiment, portions corresponding to the embodiment of FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted. In the RFEC method measurement probe 51 shown in FIG. 8A, the reception coils 14 are arranged in three rows, for example, eight pairs each. FIG. 8B shows the arrangement positions of the receiving coils in each column. Since there are 24 receiving coils 14 in total, the positions of S1 to S24 are set at equal intervals over the entire circumference, and the first row near the exciting coil 12 is further moved to the second row away from the exciting coil 12, and the exciting coil 12 Are sequentially assigned to the third column away from. That is, the positions of the receiving coils 14 arranged in the first row, the second row, and the third row are shifted by a fixed angle of 360 ° ÷ 24 = 15 °.

FIG. 8C shows a schematic electrical configuration of the RFEC apparatus 50. The eight receiving circuits 51, 52,...
Process the signals by switching the signals from the three receiving coils 14 respectively. The distribution measuring circuit 60 includes eight receiving circuits 5
Based on the analysis data from 1, 52,.
Create a distribution of wall thinning over the entire circumference of. One receiving circuit 51 combines the receiving coils 14 belonging to the first, second, and third columns shown in FIG. 8B one by one, for example, S1, S2, and S3, and sets a changeover switch. It is configured to be switchable at 61. The signal switched by the changeover switch 61 is input to the signal processing circuit 32. The distribution measuring circuit 60 can be realized by the signal processing personal computer 43 shown in FIG. 6, as in the embodiment shown in FIG. In the present embodiment, the number of receiving circuits 51, 52,... Can be reduced as compared with the embodiment of FIG. Also,
When displaying the entire circumference of a channel not shown in FIG. 7,
Since data processing may be performed for each of the receiving circuits 51, 52,..., The processing can be simplified.

In each of the embodiments described above, 24 receiving coils 14 are used, but the number can be changed as necessary. In order to measure with the same accuracy, the number should be increased as the diameter increases and decreased as the diameter decreases. Further, the present invention can be applied not only to the measurement of the thinning of the steel pipe pile 15 but also to the flaw detection. The present invention can be applied not only to the steel pipe pile 15 embedded in the vertical direction but also to the measurement of wall thickness reduction and flaw detection of a horizontal underground pipe.

[0026]

As described above, according to the present invention, the receiving coils for measuring the thickness of the metal tube by the separated eddy current method are arranged in a plurality of rows arranged at intervals in the center axis direction of the exciting coil. In each row, the plurality of receiving coils are arranged at equal intervals along the inner circumference of the metal tube so that a plurality of predetermined coils belong to each other, and between adjacent rows, the position of the receiving coil is determined by the center axis of the exciting coil. Since the receiving coils are arranged at different angles so that they do not overlap at the same angular position, a large number of receiving coils can be arranged along the inner circumference of the metal tube as a whole, and measurement can be performed finely. Since the reception coil is switched by the changeover switch and the signal analysis and the thickness measurement are performed in the signal processing circuit, the number of the signal processing circuits can be made smaller than the number of the reception coils, thereby suppressing an increase in cost.

Further, according to the present invention, the excitation coil and the reception coil are divided into a plurality of rows while moving in the metal tube in the axial direction, and the signal from the reception coil whose angle around the center of gravity axis is shifted is also transmitted to the metal pipe. Since it is switched by the changeover switch so that it is at the same position with respect to the axis of the pipe, it is necessary to measure the entire circumference at the same position with respect to the axis of the metal pipe, and to accurately obtain the wall thickness and wall loss rate distribution etc. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing an RFEC method measurement probe 11 and a block diagram showing an electrical configuration of an RFEC method apparatus 10 according to an embodiment of the present invention.

FIG. 2 is a side sectional view of the RFEC measurement probe 11 of FIG.

FIG. 3 is a front view of the RFEC measurement probe 11 of FIG. 2;

FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. 2;

FIG. 5 is a cross-sectional view taken along the line VV of FIG. 2;

FIG. 6 shows a steel pipe pile 15 using the RFEC method apparatus 10 of FIG.
FIG. 3 is a block diagram showing a configuration for performing a thinning measurement.

FIG. 7 is a diagram showing an example of a wall-thinning evaluation result over the entire circumference of the steel pipe pile 15 displayed on the display monitor 44 of FIG. 6;

FIG. 8 is an RFEC method apparatus 50 according to another embodiment of the present invention.
FIG. 1 is a schematic cross-sectional view of an RFEC measurement probe 51 and a block diagram showing an electrical configuration.

FIG. 9 is a simplified sectional view showing a basic portion of the LNG tank 1.

FIG. 10 is a graph showing the relationship between the phase angle obtained by the RFEC method and the wall thinning rate.

FIG. 11 is a diagram showing a definition of a Lissajous plane phase angle in the RFEC method.

FIG. 12 is a cross-sectional view showing the shape of the test tube 5 in which the wall thickness has been changed, and a graph showing information obtained by the RFEC method for the test tube 5;

[Explanation of symbols]

 10,50 RFEC method apparatus 11,51 RFEC method measurement probe 12 excitation coil 13 center axis 14 reception coil 15 steel pipe pile 20,60 distribution measurement circuit 21,22,51,52 reception circuit 30 oscillation circuit 31,61 changeover switch 32 signal Processing circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F063 AA16 AA50 BA30 BB05 BC02 CA40 DA01 DB04 DD07 GA08 GA33 GA38 JA01 LA09 LA11 MA05 NA02 PA10 ZA01 2G053 AA12 AB21 BA12 BA26 BC02 BC14 CA03 CB19 CB29 DA01 DB04 DB05 DB27

Claims (2)

[Claims] 1. A signal corresponding to a change in magnetic flux generated from an exciting coil arranged so that a central axis thereof coincides with an axis of a metal tube. A signal arranged at a distance from the exciting coil in the direction of the central axis. In a tube thickness measuring device based on a separated eddy current method in which a thickness of the metal tube is electromagnetically measured based on a signal received by a coil and received, the receiving coils are spaced apart in a central axis direction of the exciting coil. The plurality of receiving coils are arranged at equal intervals along the inner circumference of the metal tube in each row, and the plurality of receiving coils are arranged at equal intervals in each row. The position of the receiving coil is arranged at an angle around the central axis so as not to overlap the position of the same angle around the central axis of the exciting coil, and is divided into a plurality of angular ranges around the central axis. For each angle range A plurality of range switches provided to switch signals from the receiving coils of different columns to which the switches belong, and a signal from the receiving coil, which is provided for each switch and is switched by the switch, is analyzed and processed. A plurality of signal processing circuits for measuring the thickness of the metal pipe; and a distribution measurement for obtaining a circumferential wall thickness distribution of the metal pipe based on the thickness measurement results from the plurality of signal processing circuits. An apparatus for measuring a wall thickness of a pipe by a separated vortex flow method, comprising: a circuit; 2. A signal is received by each of the receiving coils while moving the exciting coil and the receiving coil in the metal tube in the axial direction. 2. The apparatus according to claim 1, further comprising a control circuit for switching at the same position with respect to the axis.