JP3170382B2 - 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. In such a case, the conventional magnetostrictive stress measurement method can only obtain the stress of two axes in the tube axis direction and the tube circumferential direction, so that the stress of each axis cannot be obtained independently. In addition, when there is no location where the stress is known as in the case of a pipe, a conventionally known shear stress difference integration method cannot be applied as a technique for obtaining the biaxial stress. This is because this method repeats rank integration from a point where the stress is known, such as a free end, and obtains a biaxial stress at a point where the stress is to be measured.

[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]

The present invention provides a Poisson's ratio ν
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 the tube axis direction of the tube to be measured, and the exciting coil is connected to an AC power source. Magnetostrictive sensor configured by winding a detection coil around 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 , While detecting the induced electromotive force V from the detection coil while moving the magnetostrictive sensor in the circumferential direction of the tube,
With respect to the induced electromotive force V in the circumferential direction of the tube detected by the detection coil, a distribution waveform with respect to the angle θ around the tube axis is obtained, and the distribution waveform with respect to the angle θ is subjected to Fourier transform.
Assuming that the amplitude for sθ is (1−ν) σ1, the stress σ1 in the tube axis direction is calculated and obtained, and the amplitude for cos2θ is (1).
-Ν) A method of measuring magnetostrictive stress in a pipe, characterized by calculating and calculating a stress σ2 in a pipe circumferential direction as σ2.

Further, the present invention relates to (a) a magnetostrictive sensor, wherein (a1) a tube having a Poisson's ratio ν in the axial direction of the tube.
A first core having a pair of magnetic poles spaced apart in a direction intersecting at an angle other than degrees, (a2) an exciting coil wound around the first core and excited by AC power, and (a3) a first coil.
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 core;
(B) a moving means for moving the magnetostrictive sensor in the circumferential direction along the outer peripheral surface of the tube; and (c) detecting a position at an angle θ around the tube axis. A memory that stores the induced electromotive force V from the coil; (d) a conversion unit that reads the contents of the memory and performs a Fourier transform of a distribution waveform of the induced electromotive force V with respect to the angle θ; and (e) responds to an output of the conversion unit. Calculating means for obtaining stress σ1 in the tube axis direction from the amplitude (1-ν) σ1 of the component of cos θ, and calculating stress σ2 in the circumferential direction of the tube from the amplitude (1-ν) σ2 of the component of cos2θ. A magnetostrictive stress measuring device for a tube.

[0006]

According to the present invention, a first pole having a pair of magnetic poles spaced apart from each other at an angle other than 90 degrees, for example, 45 degrees, in the direction of the tube axis of the tube to be measured having a Poisson's ratio ν.
An exciting coil excited by AC power is wound around the core, and a second core having a pair of magnetic poles is provided at intervals in a direction perpendicular to a straight line connecting the pair of magnetic poles of the first core. A detection coil is wound around the second core. Therefore, the induced electromotive force from the detection coil is
It corresponds to the difference between the stress in the pipe axial direction and the stress in the circumferential direction of the pipe. Thus, for the induced electromotive force V in the circumferential direction of the tube detected by the detection coil, the distribution waveform with respect to the angle θ around the tube axis is obtained, the distribution waveform with respect to the angle θ is subjected to Fourier transform, and the amplitude with respect to cos θ is calculated as (1-ν ) Σ1 is calculated by calculating the stress σ1 in the pipe axis direction, and the amplitude with respect to cos2θ is calculated by calculating the stress σ2 in the circumferential direction of the pipe as (1−ν) σ2. Even if there is, the stress in the pipe axial direction and the circumferential direction of the pipe in a state where the pipe is deformed flat can be accurately obtained.

[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, and an exciting coil 14 is wound around the first core 13. First core 13
Of the pair of magnetic poles 15 and 16 intersect with each other at an angle α (α = 45 degrees in this embodiment) other than 90 degrees in the direction of the tube axis 4.
Are provided at intervals. For example, a 50 Hz or 60 Hz, 100 V AC power supply 18 is connected to the excitation coil 14 to excite the excitation coil 14.
Further, a second core 19 is provided.
Are formed in an inverted U-shape. A detection coil 20 is wound around the second core 19. A pair of magnetic poles 2 of the second core 19
The reference numerals 1 and 22 are provided at intervals on a straight line 23 perpendicular to a straight line 17 connecting the pair of magnetic poles 15 and 16 of the first core 13. Each centroid of each magnetic pole 15, 16;
Lines 17 and 23 at the vertices of the virtual square
Matches the diagonal of the virtual square. The exciting coil 14 is excited by an AC power supply 18 and the detecting coil 20 is excited.
Is detected by voltage measuring means 24 such as a voltmeter. The induced electromotive force V of the detection coil 20 is
Expression (1) depends on the stress σ1 in the directional direction and the stress σ2 in the pipe circumferential direction.

V = M (σ1−σ2) (1) Here, M is a magnetostriction sensitivity, and is a constant that depends on the material of the welded pipe 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. Equation (1) will be described in more detail. Assuming that the pipe to be measured has a Poisson's ratio ν, the bending in the longitudinal direction of the pipe causes (1) the stress in the pipe axis direction to be Acos θ (2) The pipe circumferential stress for the Poisson's ratio ν is νAco
(3) The stress in the circumferential direction of the pipe is Bcos2θ (4) The stress in the pipe axial direction corresponding to the Poisson's ratio ν is νBco
It is considered that these stresses are generated in a synthesized form. Therefore, the axial stress σ of the equation (1)
The induced electromotive force V represented by the difference between 1 and the pipe circumferential stress σ2 is
Equation (2) is obtained.

V = M {(Acosθ + νBcos2θ) − (Bcos2θ + νAcosθ)} = M {A (1-ν) cosθ + B (ν-1) cos2θ} (2) where A and B represent amplitudes.

In the magnetostrictive sensor 8, the magnetic pole 1 of the first core 13 is
5 and 16 are equidistant from the magnetic pole 21 of the second core 19,
Therefore, in a state where magnetostrictive stress σ1 is not generated in the pipe axis 4 direction of the pipe 1 and magnetostrictive stress σ2 is not generated in the pipe circumferential direction, the magnetic permeability μ of the pipe 1 in the pipe axis direction and the pipe circumferential direction is equal, and therefore the exciting coil When the AC power supply 18 is energized, the magnetic flux entering the magnetic pole 21 from the magnetic pole 15 is equal to the magnetic flux exiting from the magnetic pole 21 to the magnetic pole 17, and the same holds true for the magnetic pole 22. The induced electromotive force V detected by the voltage measuring means 24 connected to the coil 20 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 pipe circumferential direction acts on the pipe 1, the respective magnetic permeability in the pipe axis direction and the pipe circumferential direction of the pipe 1 are different, so that the detection coil 2
The induced electromotive force V of 0 is the magnetostrictive sensitivity M and the magnetostrictive stress σ1, σ2
And the value corresponding to. Here, the stress σ1 in the pipe axis direction and the stress σ2 in the pipe 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 a visual display means 28 such as a cathode ray tube or a liquid crystal.

FIG. 6 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 around the entire circumference of the tube 1. The induced electromotive force V of the detection coil 20 stored in the memory 27, and thus the corresponding stress σ, can be displayed by the display means 28 to step n4.

According to the experimental results of the inventor of the present invention, the relationship between the angle θ displayed by the display means 28 and the stress σ corresponding to the induced electromotive force V of the detection coil 20 is shown in FIGS.
A distribution waveform shown in FIG.

For reference, a stress σ1 in a pipe axial direction having a curve close to cos θ measured using another measuring method.
Is shown in the distribution waveform, and the pipe circumferential stress σ2 having a curve close to cos2θ is shown in the distribution waveform.

Σ1 measured by a magnetostrictive stress measuring device
In order to determine the pipe axial stress σ1 and the pipe circumferential stress σ2 from the distribution waveform representing the difference between σ2 and σ2, the amplitudes A and B expressed by the equation (2) may be obtained. Therefore, step n
In step 5, the distribution waveforms of FIGS. 7 and 8 are subjected to Fourier transform. That is, the angle θ from the vertical line 5 around the pipe axis 4
For each time, the distribution waveform of the induced electromotive force V obtained as a measurement result of the voltage measurement means 24 stored in the memory 27 is Fourier-transformed, and the coefficients of cos θ and cos 2θ are obtained as Fourier amplitudes. The formula of the Fourier transform is incorporated in the processing circuit 25 in advance. C obtained as Fourier amplitude
The coefficient A (1-ν) of osθ is such that the value of cosθ is the maximum value 1
, The stress σ1 in the tube axis direction as σ1 (1-ν)
Is obtained, and the coefficient B (ν−1) of cos 2θ is expressed as cos
When the value of 2θ takes the maximum value 1, the stress σ2 in the pipe circumferential direction is obtained as σ2 (ν-1).

FIG. 9 is a graph showing the Fourier amplitudes of cos θ and cos 2θ with respect to the angle θ obtained by Fourier transforming the distribution waveforms of FIGS. 7 and 8. Here, from the peak value A (1-ν) at the angle θ, σ1
Σ1 is obtained as (1-ν), and σ2 is obtained as σ2 (ν-1) from the peak value B (ν-1) at the angle 2θ.

Theoretically, the Fourier amplitude with respect to the angles θ and 2θ can be obtained from Expression (2) as in Expressions (3) and (4).

[0020]

(Equation 3)

Therefore, the value of the Fourier amplitude for angles other than the angles θ and 2θ should be zero.

On the other hand, in the experimental results shown in FIGS. 7 and 8, the distribution waveform is approximately represented by the difference between cos θ and cos 2θ, but it is considered that the distribution waveform actually includes other angle components. Therefore, if the distribution waveforms obtained from the experimental results of FIGS. 7 and 8 are subjected to Fourier transform, the value of the Fourier amplitude is not zero even at angles other than the angles θ and 2θ as shown in FIG. However, the angles θ and 2
Fourier amplitude value A (1-
If ν) and B (ν-1) are obtained, the pipe axial stress σ1 and the pipe circumferential stress σ2 are obtained independently from the respective values.

[0023]

As described above, according to the present invention, the induced electromotive force V of the detection coil caused by the magnetostrictive stress distribution in the tube axis direction and the tube circumferential direction is measured using the magnetostrictive sensor. A distribution waveform for the angle θ is obtained. The distribution waveform with respect to the angle θ is subjected to Fourier transform, the amplitude with respect to cos θ is set to (1−ν) σ1, and the stress σ1 in the tube axis direction is calculated and obtained. Since σ2 was calculated and found,
Each stress in the pipe axis direction and the pipe circumferential direction can be easily and accurately obtained. Thus, the present invention is advantageously implemented when the pipe has a large diameter or a small diameter even when the pipe is deformed flat.

[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 diagram showing experimental results of the present inventor of a stress σ corresponding to an induced electromotive force V obtained from a detection coil 20 of the magnetostrictive sensor 8;

FIG. 8 is a diagram showing experimental results by the present inventor of a stress σ corresponding to an induced electromotive force V obtained from the detection coil 20 of the magnetostrictive sensor 8;

9 is a graph showing a Fourier amplitude with respect to an angle θ obtained by performing a Fourier transform on the distribution waveforms of FIGS. 7 and 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

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-176627 (JP, A) JP-A-63-261123 (JP, A) JP-A-2-157611 (JP, A) JP-A-5-157 281057 (JP, A) JP-A-1-308933 (JP, A) JP-A-3-91942 (JP, U) JP-A-4-29848 (JP, U) JP-A-3-109140 (JP, U) (58) Field 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 of a tube to be measured having a Poisson's ratio ν. Then, the exciting coil is excited by AC power, and the detection coil is wound around 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 magnetostrictive sensor arranged and arranged, detecting the induced electromotive force V from the detection coil while moving the magnetostrictive sensor in the circumferential direction of the tube, and detecting the induced electromotive force V in the circumferential direction of the tube detected by the detection coil. , A distribution waveform with respect to the angle θ around the pipe axis is obtained, and the distribution waveform with respect to the angle θ is Fourier-transformed to obtain co.
Assuming that the amplitude for sθ is (1−ν) σ1, the stress σ1 in the tube axis direction is calculated and obtained, and the amplitude for cos2θ is (1).
-Ν) A method for measuring magnetostrictive stress in a pipe, characterized by calculating a stress σ2 in a pipe circumferential direction as σ2. 2. A first core comprising: (a) a magnetostrictive sensor having: (a1) a pair of magnetic poles spaced apart in a direction intersecting at an angle other than 90 degrees with a tube axis direction of a tube having a Poisson's ratio ν. (A2) an 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; (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 induced electromotive force V from the detection coil at an angle θ around the tube axis; and (d) a conversion for reading the contents of the memory and performing a Fourier transform on the distribution waveform of the induced electromotive force V with respect to the angle θ. And (e) responding to the output of the conversion means, From the component amplitude (1−ν) σ1, stress σ1 in the tube axis direction is further calculated as co
and a calculating means for calculating the stress σ2 in the pipe circumferential direction from the amplitude (1-ν) σ2 of the component of s2θ.