JP2735992B2 - 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 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 a 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 output V corresponding to the permeability of a tube is detected by using a magnetostrictive sensor, a flatness S of the tube is obtained, and a circumference of the tube corresponding to the flatness S is determined. A magnetostrictive stress measuring method characterized in that a maximum stress σ20 in the axial direction is obtained, and a maximum stress σ10 in the axial direction of the pipe is obtained based on the maximum stress σ20 in the circumferential direction and the output V.

According to the present invention, in determining the flatness S of the tube, the magnetostrictive sensor is moved in the circumferential direction of the tube to detect a first position at which the maximum value of the output V corresponding to the permeability of the tube is obtained. Then, a second position, which is shifted by 90 degrees in the circumferential direction from the first position, is obtained, and the outside diameters of the first and second positions are measured to obtain the flatness of the pipe.

[0006] The present invention also provides a maximum stress σ1 in the axial direction of the tube.
In obtaining 0, the output ΔV of the magnetostrictive sensor corresponding to the maximum stress σ20 in the circumferential direction of the tube is obtained, and the output V of the magnetostrictive sensor and the output Δ corresponding to the maximum stress σ20 in the circumferential direction are obtained.
The magnetostrictive stress measuring method is characterized in that a sum with V is obtained, and a maximum stress σ10 in the axial direction of the pipe corresponding to the sum is obtained.

Further, the present invention provides a magnetostrictive sensor for deriving an output V corresponding to the magnetic permeability of a tube, means for moving the magnetostrictive sensor along the outer peripheral surface of the tube, means for calculating the flatness S of the tube, In response to the output of the flatness calculating means, means for calculating and calculating the maximum circumferential stress σ20 of the pipe corresponding to the flatness S, and in response to each output of the magnetostrictive sensor and the circumferential stress calculating means, Means for calculating and calculating a maximum stress σ10 in the axial direction of the tube.

[0008]

According to the present invention, an output V corresponding to the magnetic permeability of a tube is detected by using a magnetostrictive sensor, and this output V is not only the maximum stress σ10 in the axial direction of the tube but also the maximum stress in the circumferential direction of the tube. σ
20, the maximum stress σ20 in the circumferential direction of the pipe is a value that depends on the flatness S of the pipe in the elastic region of the pipe. By determining the maximum stress σ20, the maximum stress σ10 in the axial direction of the pipe can be determined based on the output V.

In order to accurately determine the flatness S of a pipe, it is necessary to determine the maximum value DH and the minimum value HV of the outer diameter of the pipe.
For this purpose, when the magnetostrictive sensor is moved in the circumferential direction of the tube and the output V corresponding to the magnetic permeability of the tube is obtained, the amplitude B of the output V is obtained.
Is obtained at the first position where the maximum value is obtained, and the maximum value of the outer diameter of the tube is obtained at the second position which is 90 degrees circumferentially displaced from the first position. Thus, the flatness S of the pipe can be accurately obtained.

Further, according to the present invention, the output ΔV of the magnetostrictive sensor corresponding to the maximum stress σ20 in the circumferential direction of the pipe obtained from the flatness S of the pipe is obtained, and this output ΔV is used as the output V of the magnetostrictive sensor. By the addition, the maximum stress σ10 in the axial direction of the tube can be obtained.

[0011]

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
Is a steel pipe or the like and is made of a ferromagnetic material. In a state where no stress acts on the tube 1 and the tube 1 is not bent, the tube 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 axial stress σ 1 acting on the tube 1 is at the positions 37, 39 intersecting with the axis of symmetry 6.
, The maximum absolute value σ10, and a straight line 7 perpendicular to the symmetry axis 6
Are zero at the positions 38 and 40 where the angle .sigma.
Change. The circumferential stress σ2 acting on the pipe 1 is at a position 3 where it intersects a pair of straight lines 31 and 32 symmetrical with respect to the axis of symmetry 6.
It becomes zero between 3 and 36, and thus the stress σ2 in the circumferential direction
Changes by cos2θ when the angle in the circumferential direction is θ.

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 expressed by Expression 1 depending on the stress σ1 in the tube axis 4 direction and the stress σ2 in the circumferential direction.

V = M (σ1−σ2) (1) Here, M is the 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.

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, when no stress σ1 is generated in the direction of the tube axis 4 of the tube 1, the magnetic permeability μ of the tube 1 in the tube axis direction and the circumferential direction is equal, so that the exciting coil 14
When excited by the voltage, the induced electromotive force V detected by the voltage measuring means 24 connected to the detection coil 20 is zero or a very small value. When the stress 1 in the tube axis direction and / or the stress σ2 in the circumferential direction acts on the tube 1, the respective magnetic permeability in the tube axis direction and the circumferential direction of the tube 1 are different, so that the induced electromotive force V of the detection coil 20 is 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.

The input means 41 is, for example, a keyboard or the like. In order to calculate the flatness S of the tube 1, for example, the maximum outer diameter DH and the minimum outer diameter DV of the tube 1 measured using calipers are calculated. Entered by the operator.

FIG. 6 is a sectional view of the tube 1 taken at right angles to the axis. Tube 1
Is bent, the section perpendicular to the axis of the tube 1 becomes flat within the range of elasticity, the minimum outer diameter is DV, and the maximum outer diameter is D.
When H is set, the flattening ratio S is as shown in Expression 2.

[0019]

(Equation 1)

When the flatness S is determined, FIG.
The maximum value σ20 of the bending stress σ2 in the circumferential direction of the pipe 1 corresponding to the flatness S is determined. The relationship between the flatness S and the maximum circumferential stress σ20 in the graph indicated by the reference numeral 42 shown in FIG. 7 is prepared in advance by calculation or by experiment. The contents of the graph shown in FIG. 7 are stored in advance in the memory 27 shown in FIG. 5 as a table, for example, and the outer diameters DV and DH of the tube 1 are input from the input means 41 in this way. Thus, the flatness S is calculated and obtained, and the corresponding circumferential stress σ2 is calculated.

The relationship between the angle θ displayed by the display means 28 and the induced electromotive force V of the detection coil 20 is obtained as shown in FIG. The output V is as shown by a line L3 in FIG. 8, and the output V is a voltage component L1 that varies with cos (θ + C) corresponding to the axial stress σ1 of the tube 1.
And a component L2 that varies with the cos (2θ + C) of the stress σ2 in the circumferential direction of the tube 1 are values synthesized according to the above-described equation 1. The first position θ1 at which the maximum value of the output V indicated by the line L3 is obtained is the intersection point 37 between the symmetry axis 6 and the center line 3 shown in FIG.
At 7, it is possible to refine the minimum outer diameter DV of the tube 1 between a position 39 which is offset by 180 degrees about the tube axis 4. Further, it is possible to measure the maximum outer diameter DH which is the major axis between the positions 38 and 40 of the line shifted 90 degrees in the circumferential direction from the position 37. Thus, the line L3 obtained by moving the magnetostrictive sensor 8 in the circumferential direction of the tube 1
37 where the outer diameter DV of the short axis is obtained based on the voltage V
And the position 38 at which the outer diameter DH of the long axis shifted by 90 degrees can be obtained based on this. The line L1 is a value corresponding to the stress σ1 in the circumferential direction as described above, and FIG. 8 shows an output V (σ10) corresponding to the maximum value σ10 of the stress σ1. Also, the line L2
Corresponds to the stress σ2 in the circumferential direction, and the output V (σ20) corresponding to the maximum value σ20 of the stress σ2 is shown in FIG.

The operation will be described with reference to FIG. The flowchart shown in FIG. 9 shows the operation of the processing circuit 25 of FIG. The process moves from step n1 to step n2, and the magnetostrictive sensor 8 is moved in the circumferential direction of the tube 1 by the driving means. The magnetostrictive sensor 8 is moved very close to the outer surface of the tube 1 and is kept at a constant interval in the circumferential direction. The output from the detection coil 20 of the magnetostrictive sensor 8 is detected by the voltage measuring means 24, and the output V is read by the processing circuit 25. Thus, the output V of the magnetostrictive sensor 8 is stored in the memory 27 at every angular displacement of a certain angle in the circumferential direction of the tube 1. Thus, the magnetostrictive sensor 8 is moved over the entire circumference of the tube 1. The detection coil 2 stored in such a memory 27
The induced electromotive force V of 0 can be displayed by the display means 28 as shown by the above-mentioned line L3 in FIG.

In step n4, the flattening ratio S is calculated in accordance with the above-mentioned equation (2).

In step n5, a circumferential stress σ2 corresponding to the flatness S is calculated and obtained based on the memory 27 storing the contents shown in FIG. In the next step n6, the axial stress σ1 of the tube 1 is calculated and obtained based on the following equation 3 derived from the above-described equation 1, and a series of operations is ended in step n7.

[0025]

(Equation 2)

As another embodiment of the present invention, the magnetostrictive sensor 8 corresponding to the circumferential stress .sigma.2 at step n5 in FIG.
Is obtained (= M · σ2), the sum (= V + ΔV) of the output ΔV and the output V of the magnetostrictive sensor 8 is obtained, and the axial stress σ1 (= ( V + Δ
V) / M) may be obtained. In this way it is also possible to simplify the operation.

[0027]

As described above, according to the present invention, the maximum stress .sigma.20 in the circumferential direction of the pipe corresponding to the flatness S can be obtained in the elastic region of the pipe by obtaining the flatness S of the pipe. Therefore, by considering the circumferential maximum stress σ20 based on the output V of the magnetostrictive sensor, it becomes possible to accurately determine the maximum stress σ10 in the axial direction of the pipe. This makes it possible to accurately determine the maximum stress σ10 in the pipe axis direction in a state where the pipe is deformed flat even if the pipe has a large diameter or a small diameter.

According to the present invention, when determining the flatness of the tube, the magnetostrictive sensor is moved in the circumferential direction of the tube, and the first position at which the maximum value of the output V corresponding to the permeability of the tube is obtained. The minimum value DV of the outer diameter of the tube at the first position where the maximum value of the output V is detected and the maximum value DH of the outer diameter of the tube at the second position shifted by 90 degrees from the first position. Based on the above, the flatness S of the pipe can be accurately calculated and obtained. This makes it possible to accurately determine the maximum stress σ10 in the axial direction of the pipe.

According to the present invention, the output ΔV of the magnetostrictive sensor corresponding to the maximum stress σ20 in the circumferential direction of the pipe obtained from the flatness S of the pipe is added to the output V of the magnetostrictive sensor. , It is possible to determine the stress Δ1 in the axial direction of the tube.

[Brief description of the drawings]

FIG. 1 is a simplified cross-sectional view for explaining a state when a tube 1 of one embodiment of the present invention is deformed.

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

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

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

FIG. 5 is a block diagram showing a configuration related to a detection coil 20 of the magnetostrictive sensor 8;

FIG. 6 is a cross-sectional view showing a state where the pipe 1 is deformed by bending.

FIG. 7 is a graph showing a relationship between an oblateness S and a circumferential stress σ2.

FIG. 8 is a diagram showing an output V of the magnetostrictive sensor 8;

FIG. 9 is a flowchart for explaining the operation of the processing circuit 25;

[Explanation of symbols]

 1 tube 8 magnetostrictive sensor 24 voltage measuring circuit 25 processing circuit 27 memory 28 display means 41 input means

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yoshiaki Sakai 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Takashi Kuroda 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan (56) References JP-A-3-176627 (JP, A)

Claims (4)

(57) [Claims] 1. Using a magnetostrictive sensor, an output V corresponding to the permeability of a pipe is detected, a flatness S of the pipe is obtained, and a maximum stress σ20 in a circumferential direction of the pipe corresponding to the flatness S is obtained. A method for measuring a magnetostrictive stress, wherein a maximum stress σ10 in an axial direction of a pipe is obtained based on the maximum stress σ20 in the circumferential direction and the output V. 2. Finding a flatness S of a tube by moving a magnetostrictive sensor in a circumferential direction of the tube to detect a first position at which a maximum value of an output V corresponding to a permeability of the tube is obtained; 2. The flattening rate of the pipe according to claim 1, wherein a second position shifted by 90 degrees in the circumferential direction from the position (1) is obtained, and an outer diameter of the first and second positions is measured to obtain a flatness of the pipe. Magnetostrictive stress measurement method. 3. An output ΔV of the magnetostrictive sensor corresponding to the maximum stress σ20 in the circumferential direction of the pipe is obtained in obtaining the maximum stress σ10 in the axial direction of the pipe, and the output V of the magnetostrictive sensor and the maximum stress σ20 in the circumferential direction are obtained. And a maximum stress .sigma.10 in the axial direction of the pipe corresponding to the sum. 4. A magnetostrictive sensor for deriving an output V corresponding to the magnetic permeability of a pipe, means for moving the magnetostrictive sensor along the outer peripheral surface of the pipe, means for calculating a flatness S of the pipe, Means for calculating and calculating the maximum circumferential stress σ20 of the pipe corresponding to the flatness S in response to the output of the means, and the axis of the pipe in response to the outputs of the magnetostrictive sensor and the circumferential stress calculating means. Means for calculating and calculating the maximum stress σ10 in the direction.