JPH06288842A - Method and device for measuring magnetostriction stress - Google Patents

Abstract

PURPOSE:To accurately measure each stress in the circumferential and axial directions of a pipe by obtaining the maximum stress in axial direction based on the maximum stress in circumferential direction corresponding to the flatness of the pipe and the output of a magnetostriction sensor. CONSTITUTION:An annular rail 10 is fitted to the outer periphery of a pipe 1 and a magnetostriction sensor 8 is moved on the outer-periphery surface of the pipe 1 along the rail 10. An excitation coil 14 of the sensor 8 is excited by an AC power supply 18 and the induced power of a detection coil 20 is detected by a voltage measuring means 24. An output V of the coil 20 depends on the stress in the direction of a pipe shaft 4 and that in the circumferential direction. A first flatness is obtained by the minimum outer diameter and the maximum outer diameter measured, for example, by slide calipers. Then, the maximum stress in the circumferential direction of the pipe 1 corresponding to the flatness is obtained. The maximum stress in the direction of the pipe shaft 4 is obtained based on it and an output V, thus accurately obtaining the maximum stress in the direction of the pipe shaft 4 in the state where the pipe 1 is deformed flatly.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In the magnetostrictive stress measuring method, when a load is applied to a ferromagnetic material, anisotropy in magnetic permeability occurs, the magnetic permeability in the load direction increases, and the magnetic permeability in the direction perpendicular to the load direction decreases. Therefore, this is a method of measuring the direction and magnitude of the principal stress by detecting the difference between the two magnetic permeabilities 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 has a small diameter, and therefore the bending deformation is usually predominant, and the stress in the circumferential direction of the pipe is zero or very small, and therefore the output of the magnetostrictive sensor is the stress in the axial direction 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 circumferential stress of the pipe cannot be ignored. This is also true when the tube has a small diameter and is deformed flat.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a tube magnetostrictive stress measuring method and apparatus capable of accurately measuring each stress in the tube circumferential direction and tube axial direction. is there.

[0004]

According to the present invention, a magnetostrictive sensor is used to detect an output V corresponding to the permeability of a tube, a flatness S of the tube is obtained, and a circumference of the tube corresponding to the flatness S is detected. The magnetostrictive stress measuring method is characterized in that the maximum stress σ20 in the direction is obtained, and the 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.

Further, according to the present invention, in obtaining the flatness S of the tube, the magnetostrictive sensor is moved in the circumferential direction of the tube to detect the first position where the maximum value of the output V corresponding to the magnetic permeability of the tube is obtained. Then, a second position which is deviated from the first position by 90 degrees in the circumferential direction is obtained, and the outer diameters of the first and second positions are measured to obtain the flatness of the pipe.

Further, according to the present invention, the maximum stress σ1 in the axial direction of the pipe is
In obtaining 0, the magnetostrictive sensor output ΔV corresponding to the circumferential maximum stress σ20 of the pipe is calculated, and the magnetostrictive sensor output V and the circumferential maximum stress σ20 corresponding to the output Δ
The magnetostrictive stress measuring method is characterized by obtaining the sum of V and the maximum stress σ10 in the axial direction of the tube corresponding to the sum.

The present invention further comprises a magnetostrictive sensor for deriving an output V corresponding to the permeability of the tube, a means for moving the magnetostrictive sensor along the outer peripheral surface of the tube, and a means for calculating the flatness S of the tube. In response to the output of the flatness calculating means, a means for calculating and obtaining the maximum stress σ20 in the circumferential direction of the pipe corresponding to the flatness S, and in response to the outputs of the magnetostrictive sensor and the circumferential stress calculating means, A magnetostrictive stress measuring device comprising means for calculating and obtaining the maximum stress σ10 in the axial direction of the pipe.

[0008]

According to the present invention, the magnetostrictive sensor is used to detect the output V corresponding to the magnetic permeability of the tube, 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
The maximum stress σ20 in the circumferential direction of the pipe depends on the flatness S of the pipe in the elastic region of the pipe. By calculating the maximum stress σ20, the maximum stress σ10 in the axial direction of the pipe can be calculated based on the output V.

In order to accurately obtain the flatness S of the pipe, it is necessary to obtain the maximum value DH and the minimum value HV of the outer diameter of the pipe.
Therefore, when the magnetostrictive sensor is moved in the circumferential direction of the tube to obtain the output V corresponding to the magnetic permeability of the tube, the amplitude B of the output V is calculated.
The minimum value of the outer diameter of the pipe is obtained at the first position where the maximum value of is obtained, and the maximum value of the outer diameter of the pipe is obtained at the second position which is deviated by 90 degrees in the circumferential direction from the first position. In this way, the flatness S of the pipe can be accurately obtained.

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 set as the output V of the magnetostrictive sensor. By adding, the maximum stress σ10 in the axial direction of the pipe can be obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a simplified view of a cross section perpendicular to the axis of a pipe 1 according to an embodiment of the present invention when it is bent. Tube 1
Is a steel pipe or the like and is made of a ferromagnetic material. When no stress is applied to 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 circular ring is a perfect circle. When an external force acts on the tube 1 and the tube 1 bends, the center line 2 becomes flat as indicated by reference numeral 3 in FIG. The line of symmetry 6 of this centerline 3 is perpendicular to the other line of symmetry 7 and is offset by an angle C in the angle θ direction with respect to a vertical line 5 passing through the horizontal axis 4 of the tube 1. Axial stress σ1 acting on the tube 1 around the center line 3 is at positions 37 and 39 where the axis of symmetry 6 intersects.
The maximum absolute value is σ10, and the straight line 7 perpendicular to the axis of symmetry 6
It becomes zero at the positions 38 and 40 where it intersects, and thus σ1 in the axial direction is cos θ, where θ is the angle in the circumferential direction.
Change. The circumferential stress σ2 acting on the pipe 1 is at a position 3 where it intersects with a pair of straight lines 31 and 32 that are symmetric with respect to the symmetry axis 6.
It becomes zero at 3 to 36, and in this way the circumferential stress σ2
Changes with cos2θ where θ is the angle in the circumferential direction.

FIG. 2 is a perspective view of the entire apparatus for measuring the stress σ of the tube 1. An annular rail 10 is attached to the outer circumference of the tube 1, and the magnetostrictive sensor 8 moves along the outer peripheral surface of the tube 1 along the rail 10 by a driving means 11 including a motor. The rail 10 and the driving means 11 constitute a moving means for moving 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.
3 is a simplified plan view of the magnetostrictive sensor 8. FIG. The magnetostrictive sensor 8 has an inverted U-shaped first core 13, and the core 13
The exciting coil 14 is wound around. 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.
They are provided at intervals in the direction of the straight line 17 intersecting at (α = 45 degrees in this embodiment). The exciting coil 14 has, for example, an AC power source 1 of 50 Hz or 60 Hz and 100 V.
8 is connected and the exciting coil 14 is excited. Furthermore, a second core 19 is provided, and this core 19 is formed in an inverted U shape. The detection coil 20 is provided in the second core 19.
Is wound. A pair of magnetic poles 21, 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.
It has a pair of magnetic poles 21 and 22 spaced apart on a straight line 23 perpendicular to 7. The centroids of the magnetic poles 15, 16; 21, 22 are located at the respective vertex positions of the imaginary square, and the straight line 1
7 and 23 coincide with the diagonal line of the virtual square.
The exciting coil 14 is excited by an AC power source 18, and the induced electromotive force of the detecting coil 20 is measured by a voltage measuring means 24 such as a voltmeter.
Detected by. Induced electromotive force V of the detection coil 20
Is expressed by Equation 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) where M is the magnetostriction sensitivity, which is a constant depending on the material of the welded pipe 1 and the like. When the tube 1 has a small diameter, σ2 =
It is 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, in the state where the stress σ1 is not generated in the tube axis 4 direction of the tube 1, the tube 1 has the same magnetic permeability μ in the tube axis direction and the circumferential direction, and therefore the exciting coil 14 is connected to the AC power source 18
When excited by, 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 σ1 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 the magnetostriction. Sensitivity M
And the magnetostrictive stresses σ1 and σ2. Here, the stress σ1 in the tube 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 the electrical construction of the embodiment shown in FIGS. The output of the voltage measuring means 24 is given to a processing circuit 25 realized by a microcomputer or the like. The processing circuit 25 is the driving means 1
1 and controls the measurement result of the voltage measuring means 24 to the tube axis 4
Around it, it is connected to a memory 27 that stores at every 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 liquid crystal.

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

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

[0019]

[Equation 1]

When the flatness ratio S is determined, from FIG.
The maximum value σ20 of the bending stress σ2 in the circumferential direction of the tube 1 corresponding to the flatness S is determined. The relationship between the flatness ratio S and the maximum stress in the circumferential direction σ20 in the graph indicated by the reference numeral 42 shown in FIG. 7 is prepared in advance by calculation or 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 thus the outer diameters DV and DH of the pipe 1 are input from the input means 41. Thus, the flatness S is calculated and obtained, and the circumferential stress σ2 corresponding to the flatness S is obtained.

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 the line L3 in FIG. 8, and the output V is a voltage component L1 that changes with cos (θ + C) corresponding to the axial stress σ1 of the tube 1.
And the component L2 that changes with cos (2θ + C) of the stress σ2 in the circumferential direction of the pipe 1 are the values synthesized according to the above-described Expression 1. The first position θ1 at which the maximum value of the output V shown by the line L3 is obtained is the intersection position 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 the position 39 which is offset by 180 degrees around 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 which is deviated from the position 37 by 90 degrees in the circumferential direction. In this way, the line L3 obtained by moving the magnetostrictive sensor 8 in the circumferential direction of the tube 1.
Position 37 where the short axis outer diameter DV is obtained based on the voltage V of
Based on this, it is possible to know the position 38 at which the outer diameter DH of the major axis deviated by 90 degrees is obtained. The line L1 is a value corresponding to the stress σ1 in the circumferential direction as described above, and FIG. 8 shows the output V (σ10) corresponding to the maximum value σ10 of the stress σ1. Also, 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 shown in FIG. From step n1 to step n2, 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 moved in the circumferential direction at a constant interval. The output from the detection coil 20 of the magnetostrictive sensor 8 is detected by the voltage measuring means 24, and its output V is read by the processing circuit 25. In this way, the output V of the magnetostrictive sensor 8 is stored in the memory 27 at every angular displacement of a constant angle in the circumferential direction of the tube 1. In this way, 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 line L3 in FIG. 8 described above.

At step n4, the flatness ratio S is calculated in accordance with the above-mentioned equation 2.

At step n5, the stress σ2 in the circumferential direction corresponding to the flattening ratio S is calculated and obtained based on the memory 27 in which the contents shown in FIG. 7 are stored. In the next step n6, the stress σ1 in the axial direction of the tube 1 is calculated and obtained based on the following expression 3 derived from the above-mentioned expression 1. Thus, in step n7, a series of operations is ended.

[0025]

[Equation 2]

As another embodiment of the present invention, the magnetostrictive sensor 8 corresponding to the circumferential stress σ2 in step n5 of FIG.
Of the output of the magnetostrictive sensor 8 (= V + ΔV), and the stress σ1 (= (in the axial direction of the tube 1 corresponding to the sum of the output ΔV and the output V of the magnetostrictive sensor 8). V + Δ
V) / M) may be obtained. It is also possible to simplify the calculation in this way.

[0027]

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

Further, according to the present invention, in determining the flatness of the tube, the magnetostrictive sensor is moved in the circumferential direction of the tube, and the first position where the maximum value of the output V corresponding to the magnetic permeability of the tube is obtained. The minimum value DV of the outer diameter of the pipe 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 pipe at the second position which is 90 degrees away from the first position are detected. 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.

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 added to the output V of the magnetostrictive sensor. , It becomes possible to obtain the stress Δ1 in the axial direction of the pipe.

[Brief description of drawings]

FIG. 1 is a simplified cross-sectional 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 when the magnetostrictive stress is measured while moving in the circumferential direction of the tube 1 using the magnetostrictive sensor 8.

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

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

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

FIG. 6 is a cross-sectional view showing a state when the pipe 1 is bent and deformed.

FIG. 7 is a graph showing the relationship between the flatness ratio S and the stress σ2 in the circumferential direction.

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

9 is a flow chart for explaining the operation of the processing circuit 25. FIG.

[Explanation of symbols]

 1 Tube 8 Magnetostrictive Sensor 24 Voltage Measuring Circuit 25 Processing Circuit 27 Memory 28 Display Means 41 Input Means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sadaaki Sakai 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Takashi Kuroda 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Main Steel Pipe Co., Ltd.

Claims (4)

[Claims] 1. A magnetostrictive sensor is used to detect an output V corresponding to the magnetic permeability of a pipe, a flatness S of the pipe is obtained, and a maximum stress σ20 in the circumferential direction of the pipe corresponding to the flatness S is obtained. A magnetostrictive stress measuring method, wherein the maximum stress σ10 in the axial direction of the tube is obtained based on the maximum stress σ20 in the circumferential direction and the output V. 2. In obtaining the flatness S of the tube, the magnetostrictive sensor is moved in the circumferential direction of the tube to detect the first position where the maximum value of the output V corresponding to the magnetic permeability of the tube is obtained. 2. The flatness of the pipe is obtained by obtaining a second position, which is deviated from the position 1 by 90 degrees in the circumferential direction, and measuring the outer diameters of the first and second positions. Magnetostrictive stress measurement method. 3. When obtaining the maximum stress σ10 in the axial direction of the pipe, the output ΔV of the magnetostrictive sensor corresponding to the maximum stress σ20 in the circumferential direction of the pipe is obtained, and the output V of the magnetostrictive sensor and the maximum stress σ20 in the circumferential direction are obtained. Is calculated and the maximum stress σ10 in the axial direction of the tube corresponding to the sum is calculated, and the magnetostrictive stress measuring method is characterized. 4. A magnetostrictive sensor for deriving an output V corresponding to the permeability of the tube, a means for moving the magnetostrictive sensor along the outer peripheral surface of the tube, a means for calculating the flatness S of the tube, and a flatness calculation. In response to the output of the means, means for calculating the maximum stress σ20 in the circumferential direction of the tube corresponding to the flatness S, and in response to the outputs of the magnetostrictive sensor and the circumferential stress calculating means, the axis of the tube And a means for calculating and obtaining the maximum stress σ10 in the direction.