JP3130115B2 - Tube Magnetostrictive Stress Measurement Method and Apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the magnetostrictive stress of a large-diameter tube.

[0002]

2. Description of the Related Art In a magnetostrictive stress measurement method, when a load acts on a ferromagnetic material, anisotropy occurs in the magnetic permeability, and the magnetic permeability in the load direction increases, and conversely, the magnetic permeability in the direction perpendicular to the load direction decreases. Therefore, this method measures the direction and magnitude of the main stress by detecting the difference between the two magnetic permeability with a magnetostrictive sensor. In the prior art, the stress acting on the tube is measured while moving the magnetostrictive sensor in the circumferential direction of the tube. Such measurements indicate that the pipe is of small diameter, and therefore usually has a predominant bending deformation, the circumferential stress of the pipe is zero or negligible, so the output of the magnetostrictive sensor is the axial stress of the pipe. It corresponds to. However, when the pipe has a large diameter, for example, when the outer diameter is 400 mmφ or more,
The stress in the circumferential direction of the pipe cannot be neglected. This is also the case when the tube has a small diameter but the tube is deformed flat.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and an apparatus for measuring magnetostriction stress in a pipe, which can accurately measure the stress in the circumferential direction of the pipe and in the axial direction of the pipe. is there.

[0004]

According to the present invention, an exciting coil is wound around a first core having a pair of magnetic poles at intervals in a direction intersecting at an angle other than 90 degrees with a tube axis direction of a tube to be measured. The excitation coil is excited by AC power, and a detection coil is provided on a second core having a pair of magnetic poles at intervals in a direction perpendicular to a straight line connecting the pair of magnetic poles of the first core. Using a wound magnetostrictive sensor, the electromotive force V from the detection coil is detected while moving the magnetostrictive sensor in the circumferential direction of the tube, and the induced electromotive force V in the circumferential direction of the tube detected by the detection coil is detected. Is a function approximated by cos2θ when an angle around the tube axis is θ, a circumferential stress σ2 corresponding to the amplitude B of the function is obtained, and thereafter, the induced electromotive force V and the circumferential From the stress σ2 and the magnetostriction sensitivity M of the tube, V = M Based on the relationship between the σ1-σ2),
This is a method for measuring the magnetostrictive stress of a pipe, which is obtained by calculating a stress σ1 in the pipe axis direction.

[0005] The present invention also provides (a) a magnetostrictive sensor, comprising: (a1) a first core having a pair of magnetic poles at intervals in a direction intersecting at an angle other than 90 degrees in the tube axis direction; (A2) a first exciting coil wound around the first core and excited by AC power; and (a3) a pair of magnetic poles spaced apart in a direction perpendicular to a straight line connecting the pair of magnetic poles of the first core. (A4) a magnetostrictive sensor having a detection coil wound around the second core; and (b) moving means for moving the magnetostrictive sensor in the circumferential direction along the outer peripheral surface of the tube. c) a memory for storing the output from the detection coil at an angle θ around the tube axis; (d) a function creating means for reading out the contents of the memory and approximating it with cos 2θ; and (e) an output of the function creating means. In response to the circumferential stress σ2 corresponding to the amplitude B of the function of cos2θ Calculating means for calculating the stress σ1 in the tube axis direction from the output of the memory, the stress σ2 in the circumferential direction, and the magnetostriction sensitivity M of the tube based on the relationship of V = M (σ1−σ2). And a magnetostrictive stress measuring device for a tube.

[0006]

According to the present invention, the direction of the pipe to be measured is 9 mm.
An excitation coil that is excited by AC power is wound around a first core having a pair of magnetic poles spaced apart from each other at an angle other than 0 degrees, for example, 45 degrees. A second core having a pair of magnetic poles is provided at an interval in a direction perpendicular to a straight line connecting the magnetic poles, and a detection coil is wound around the second core. Therefore, an induced electromotive force from the detection coil is Corresponds to the difference between the stress in the pipe axis direction and the stress in the pipe circumferential direction, and when the induced electromotive force V in the pipe circumferential direction detected by the detection coil in this way is defined as an angle θ around the pipe axis, A function is obtained by approximation with cos2θ, a circumferential stress σ2 corresponding to the amplitude B is obtained, and thereafter, the induced electromotive force V, the circumferential stress σ2,
Since the stress σ1 in the tube axis direction is calculated and obtained from the magnetostriction sensitivity M of the tube based on the relationship of V = M (σ1−σ2), even if the tube has a large diameter or a small diameter, It is possible to accurately determine the stress in the pipe axial direction and the circumferential direction of the pipe in a state where is deformed flat.

[0007]

FIG. 1 is a simplified view of a section perpendicular to an axis when a tube 1 according to an embodiment of the present invention is bent. Tube 1
In a state where no stress acts on the pipe 1 and the pipe 1 is not bent, the pipe 1 has a right cylindrical shape, and the center line 2 of the ring is a perfect circle. When an external force acts on the tube 1 to cause the tube 1 to bend, the center line 2 becomes flat as indicated by reference numeral 3 in FIG. The line of symmetry 6 of this center line 3 is perpendicular to another line of symmetry 7 and is offset by an angle C in the direction of angle θ with respect to a vertical line 5 passing through the horizontal axis 4 of the tube 1. Around the center line 3, the circumferential stress σ2 acting on the tube 1 becomes zero at positions 33 to 35 where the pair intersects a pair of straight lines 31 and 32 symmetrical with respect to the symmetry axis 6.

FIG. 2 is an overall perspective view of an apparatus for measuring the stress σ of the tube 1. An annular rail 10 is mounted on the outer periphery of the tube 1, and the magnetostrictive sensor 8 moves along the outer surface of the tube 1 along the rail 10 by driving means 11 including a motor and the like. The rail 10 and the driving unit 11 constitute a moving unit that moves the magnetostrictive sensor 8 along the outer peripheral surface of the tube 1.

FIG. 3 is a perspective view of the magnetostrictive sensor 8, and FIG.
FIG. 2 is a simplified plan view of the magnetostrictive sensor 8. The magnetostrictive sensor 8 has an inverted U-shaped first core 13.
, The exciting coil 14 is wound. The pair of magnetic poles 15 and 16 of the first core 13 have an angle α other than 90 degrees in the tube axis 4 direction.
(In this example, α = 45 degrees). The excitation coil 14 has an AC power source 1 of 50 Hz or 60 Hz, 100 V, for example.
8 is connected, and the exciting coil 14 is excited. Furthermore, a second core 19 is provided, and the core 19 is formed in an inverted U shape. The second core 19 has a detection coil 20
Is wound. A pair of magnetic poles 21 and 22 of the second core 19
Is a straight line 1 connecting the pair of magnetic poles 15 and 16 of the first core 13.
A pair of magnetic poles 21 and 22 are provided at intervals on a straight line 23 perpendicular to 7. The centroids of the magnetic poles 15, 16; 21 and 22 are located at the vertices of an imaginary square.
7, 23 correspond to the diagonal line of the virtual square.
The exciting coil 14 is excited by an AC power supply 18 and the induced electromotive force of the detecting coil 20 is measured by a voltage measuring means 24 such as a voltmeter.
Is detected by Induced electromotive force V of detection coil 20
Is represented by Expression 1 depending on the stress σ1 in the tube axis 4 direction and the stress σ2 in the circumferential direction.

[0010]

V = M (σ1−σ2) where M is the magnetostriction sensitivity, and is a constant that depends on the material of the welded tube 1 and the like. When the pipe 1 has a small diameter, σ2 =
0. The cores 13 and 19 are integrally fixed to each other.

In the magnetostrictive sensor 8, the magnetic pole 1 of the first core 13
5 and 16 are equidistant from the magnetic pole 21 of the second core 19,
Therefore, when no magnetostrictive stress σ1 is generated in the tube axis 4 direction of the tube 1, the magnetic permeability μ of the tube 1 in the tube axis direction and the circumferential direction is equal, and thus the exciting coil 14 is excited by the AC power supply 18. When the magnetic pole 15 moves to the magnetic pole 2
The magnetic flux entering 1 and the magnetic flux exiting from the magnetic pole 21 to the magnetic pole 17 are equal, and the same holds true for the magnetic pole 22, and thus the induction detected by the voltage measuring means 24 connected to the detecting coil 20. The electromotive force V is zero or a very small value. When the magnetostrictive stress σ1 in the pipe axis direction and / or the magnetostrictive stress σ2 in the circumferential direction acts on the pipe 1, the pipe 1
Are different from each other in the tube axis direction and the circumferential direction, and thus the induced electromotive force V of the detection coil 20 has a value corresponding to the magnetostrictive sensitivity M and the magnetostrictive stresses σ1 and σ2. Here, the stress σ1 in the pipe axis direction and the stress σ2 in the circumferential direction may be collectively referred to as stress σ.

FIG. 5 is a block diagram showing an electrical configuration of the embodiment shown in FIGS. The output of the voltage measuring means 24 is provided to a processing circuit 25 realized by a microcomputer or the like. The processing circuit 25 includes the driving unit 1
1 and the measurement result of the voltage measuring means 24 is
Around, it is connected to a memory 27 that stores each angle θ from the vertical line 5. The stored contents of the memory 27 can be displayed by visual display means 28 such as a cathode ray tube or liquid crystal.

FIG. 5 is a flowchart for explaining the operation of the processing circuit 25. The process moves from step n1 to step n2.
While rotating in the circumferential direction, the induced electromotive force V of the detection coil 20 is measured for each angular displacement of the fixed angle, and stored in the memory 27 in step n3. Thus, the magnetostrictive sensor 8
Moves the pipe 1 all around. Such a memory 2
The induced electromotive force T of the detection coil 20 stored in 7 and therefore the corresponding stress σ can be displayed by the display means 28 in step n4.

The relationship between the angle θ displayed by the display means 28 and the induced electromotive force of the detection coil 20 is obtained as shown in FIG. 7 according to the experimental results of the present inventor. From such experimental results, in step n5, a function is obtained by approximating the cosine waveform represented by Equation 2 by the least square method using the least square method.

[0015]

V = A + B cos (2θ−C) Here, θ represents an angle from a vertical line 5 passing through the axis 4 of the tube 1 as shown in FIG. According to the experimental results of the present inventors shown in FIG. 7, A = 0, B = 93.9, and C = 0.56.
rad, ie 32 degrees. The amplitude B corresponds to the stress .sigma.2 in the circumferential direction of the pipe 1. Thus, in step n6, the stress .sigma.2 in the circumferential direction can be calculated and obtained. Number 2
Are as indicated by reference numeral L1 in FIG.

Next, in step n7, based on equation 1,
The induced electromotive force V of the detection coil 20 and the aforementioned step n6
The stress σ1 in the pipe axis direction is calculated from Equation 1 based on the circumferential stress σ2 found in the above.

In this manner, the detection coil 20 obtained when the magnetostrictive sensor 8 is rotated once along the outer peripheral surface of the tube 1
When the induced electromotive force V can approximate the function of cos2θ well, it can be determined that the stress σ2 in the circumferential direction of the pipe is significantly larger than the stress σ1 in the pipe axis direction. Therefore, as described above, the circumferential stress σ2 can be calculated and obtained from the amplitude B.

The magnetostrictive sensor 8 may have a configuration different from the configuration described with reference to FIGS.

[0019]

As described above, according to the present invention, the induced electromotive force V of the detection coil caused by the magnetic anisotropy of the magnetic permeability in the axial direction of the tube and the circumferential direction of the tube is measured by using the magnetostrictive sensor. When the angle around the axis is θ, it is approximated by cos2θ to obtain a function,
The stress σ2 in the circumferential direction corresponding to the amplitude B is obtained, and the stress σ1 in the tube axis direction is calculated from the induced electromotive force V and the stress σ2 in the circumferential direction. Each stress in the circumferential direction can be accurately obtained.
Thus, the present invention is advantageously implemented when the pipe has a large diameter and when the pipe is deformed flat even when the pipe has a small diameter. Moreover, according to the present invention, the induced electromotive force V is cos2θ corresponding to the angle θ as described above.
Since the approximation process is performed only once, it is possible to increase the accuracy of estimating the stress value, and to achieve an excellent effect that the calculation time can be reduced by simplifying the algorithm.

[Brief description of the drawings]

FIG. 1 is a view for explaining a state when a pipe 1 according to an embodiment of the present invention is deformed.

FIG. 2 is a perspective view showing a state in which a stress is measured while moving in the circumferential direction of the tube 1 using a magnetostrictive sensor 8;

FIG. 3 is a perspective view showing a configuration of a magnetostrictive sensor 8;

FIG. 4 is a simplified plan view showing the configuration of the magnetostrictive sensor 8;

FIG. 5 is a block diagram showing an electrical configuration of the embodiment shown in FIGS.

FIG. 6 is a flowchart for explaining the operation of the processing circuit 25;

FIG. 7 is a view showing an experimental result of the inventor of the present invention for an induced electromotive force V obtained from the detection coil 20 of the magnetostrictive sensor 8;

[Explanation of symbols]

 Reference Signs List 1 tube 4 tube shaft 8 magnetostrictive sensor 10 rail 11 driving means 12 moving means 13 first core 14 excitation coil 15, 16, 21, 22 magnetic pole 19 second core 20 detection coil 24 voltage measuring means 25 processing circuit 27 memory 28 display means

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoshiaki Sakai 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Masao Shiokawa 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan (56) References JP-A-3-176627 (JP, A) JP-A-1-308933 (JP, A) JP-A-3-91942 (JP, U) (58) Fields surveyed (Int. Cl. ^7, DB name) G01L 1/00 G01L 1/12

Claims (2)

(57) [Claims] An exciting coil is wound around a first core having a pair of magnetic poles at intervals in a direction intersecting at an angle other than 90 degrees with a tube axis direction of a tube to be measured. Magnetostrictive sensor comprising a second core having a pair of magnetic poles spaced apart in a direction perpendicular to a straight line connecting the pair of magnetic poles of the first core and a detection coil wound therearound. While moving the magnetostrictive sensor in the circumferential direction of the tube, the induced electromotive force V from the detecting coil is detected, and the induced electromotive force V in the circumferential direction of the tube detected by the detecting coil is converted to an angle around the tube axis. Assuming θ, a circumferential stress σ2 corresponding to the amplitude B of the function is obtained as a function approximated by cos2θ, and then the induced electromotive force V, the circumferential stress σ2, and the magnetostriction sensitivity of the tube are obtained. From M, V = M
A method for measuring magnetostriction stress in a pipe, wherein a stress σ1 in a pipe axis direction is calculated and obtained based on a relationship of (σ1−σ2). (A1) a magnetostrictive sensor, comprising: (a1) a first core having a pair of magnetic poles at intervals in a direction intersecting at an angle other than 90 degrees in a tube axis direction of a tube; (A3) a first excitation coil wound around the first core and excited by AC power, and (a3) a first excitation coil having a pair of magnetic poles spaced apart in a direction perpendicular to a straight line connecting the pair of magnetic poles of the first core. (A4) a magnetostrictive sensor having a detection coil wound around the second core; (b) moving means for moving the magnetostrictive sensor in a circumferential direction along the outer peripheral surface of the tube; and (c) a tube. A memory for storing the output from the detection coil at the position of the angle θ about the axis; (d) a function creating means for reading out the contents of the memory and approximating it with cos 2θ; and (e) responding to the output of the function creating means. The circumferential stress σ2 corresponding to the amplitude B of the function of cos2θ is obtained, and And calculating means for calculating the stress σ1 in the tube axis direction from the output of the memory, the stress σ2 in the circumferential direction, and the magnetostriction sensitivity M of the tube based on the relationship of V = M (σ1−σ2). An apparatus for measuring magnetostriction and stress of a tube.