JPH0894457A - In-pipe pressure calculation method based on magnetstrictive measurement - Google Patents

Abstract

PURPOSE: To easily determine that a pipe is stationary from the outside of the pipe by turning the detecting direction of a magnetostrictive sensor mounted on the outer circumferential surface of the pipe. CONSTITUTION: A magnetostrictive sensor 2 is mounted on the outer surface of a pipe 6 to be measured. The sensor 2 can be displaced by 180 deg. or more through a drive means 3. Output signal from the sensor 2 is delivered to a processing circuit 4a in a control means 4. The control means 4 processes the received signal and presents the results on a display means and controls the drive means 3 on the other hand. In such apparatus 1, the detecting direction of the sensor 2 is turned by 180 deg. or more around a normal to the outer circumferential surface of the pipe 6 and an amplitude B is determined based on the output from the sensor 2. Subsequently, the pressure P of fluid flowing through the pipe is calculated according to a formula; P=2tB/MD, where B represents the amplitude, D represents the inner diameter of the pipe, (t) represents the thickness of plate and M represents magnetostrictive sensitivity. Pressure in the pipe can be measured and calculated easily at any point of the pipe 6, and the stationary state of the pipe and the magnitude of inner pressure can be determined easily in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pipe pressure calculation method suitably used for confirming the life and death of a pipe made of a magnetic material such as a steel pipe for transporting a fluid having a pipe pressure.

[0002]

2. Description of the Related Art When repairing a transportation pipe for transporting a fluid such as a gas pipe or a water pipe, it is determined whether or not the pipe to be worked is certainly a pipe used for transporting the fluid. Confirmation work is done.

For example, when repairing a transportation pipe buried in the ground, the above-mentioned life-and-death confirmation work is performed by excavating a wide area around the intended transportation pipe before the work and another transportation pipe. This is done by using the confirmation method such as the method of confirming the positional relationship with the transportation pipe or the two-point locator method. Furthermore, if the life or death of the transport tube is unknown using the above method,
Sometimes it is necessary to perforate and confirm.

[0004]

In the above-mentioned pipe life-and-death confirmation work, for example, in the case of a buried pipe, it is necessary to excavate the periphery of the target pipe wider than the range necessary for the original work such as repair work. However, the work load is heavy and the work time is long.

Fluids such as gas or tap water are each given a specific pipe pressure for transportation. If the pressure can be measured, it is possible to determine the life or death of the tube. However, in a buried pipe or the like, it is difficult to measure the pressure of the fluid passing through any part of the pipe from outside the pipe.

[0006] An object of the present invention is to provide a method for calculating the pressure inside a pipe which enables easy confirmation of the life or death of the pipe from the outside of the pipe.

[0007]

According to the present invention, a magnetostrictive sensor is arranged on the outer peripheral surface of a tube, and the magnetostrictive detection direction of the magnetostrictive sensor is
By rotating the outer peripheral surface by 180 ° or more about the normal direction, the amplitude value B of the output from the magnetostrictive sensor is obtained, and the pressure P of the fluid in the pipe is calculated by using the inner diameter D of the pipe, the plate thickness t and the magnetostriction sensitivity M.

[0008]

[Equation 2]

A method for calculating the pressure inside the tube by magnetostriction measurement, characterized in that

[0010]

According to the present invention, the magnetostrictive sensor is arranged on the outer peripheral surface of the tube, and the magnetostrictive detection direction of the magnetostrictive sensor is rotated by 180 ° or more about the normal line direction of the outer peripheral surface to output from the magnetostrictive sensor. The amplitude value B of is calculated. Further, using the amplitude value B, the inner diameter D of the tube, the plate thickness t, and the magnetostriction sensitivity M, the pressure P of the fluid in the tube is

[0011]

[Equation 3]

Since it is calculated as, it is possible to easily measure and calculate the pressure inside the pipe at an arbitrary position of the pipe.

[0013]

EXAMPLES Generally, when an internal pressure P is applied to a cylinder such as a tube having an inner diameter D and a plate thickness t, a stress σ is applied to the tube wall in the circumferential direction.
Occurs. The distribution of the stress σ is considered to be a uniaxial stress field in only the circumferential direction unless deformation such as bending occurs in the pipe, and its magnitude is proportional to the internal pressure P and is represented by PD / 2t.

There is a magnetostrictive stress measuring method as a method for measuring the direction and magnitude of the stress σ acting on a pipe made of a magnetic material such as a steel pipe. The magnetostrictive stress measurement method is such that when a force such as a stress or a force due to a load acts on a magnetic material, anisotropy occurs in magnetic permeability of the magnetic material. The magnetic permeability in the acting direction changes to either one of the large and small, and the magnetic permeability in the direction in which the compressive stress acts changes to the other in the large or small to the difference between the magnetic permeability in the direction in which the force acts and the magnetic permeability in the direction in which the force does not act. Is a method of measuring the direction and magnitude of stress by utilizing the phenomenon that occurs.

FIG. 1 is a perspective view showing a state in which a pipe pressure is measured by a pipe pressure calculating device 1 according to an embodiment of the present invention. The in-pipe pressure calculation device 1 includes a magnetostrictive sensor 2, a driving unit 3, a control unit 4, and a display unit 5.

The magnetostrictive sensor 2 is installed on the outer surface of the pipe to be measured. The magnetostrictive sensor 2 can be angularly displaced by at least 180 ° or more at one point installed by the driving means 3. The signal from the magnetostrictive sensor 2 is input to the processing circuit 4a in the control means 4. Further, the control means 4 is provided with a memory 4b. The control means 4 processes the input signal, displays it on the display means 5, and controls the drive means 3.

FIG. 2 is a simplified perspective view and plan view of the magnetostrictive sensor 2 of FIG. The magnetostrictive sensor 2 includes a first core 7, an exciting coil 8, an AC power supply 9, a second core 10, a detecting coil 11 and a voltage measuring means 12. First core 7
Is formed in an inverted U shape and the exciting coil 8 is wound. An alternating current power supply 9 is connected to the exciting coil 8, and the exciting coil 8 is excited by the voltage output from the alternating current power supply 9.
The second core 10 is formed in an inverted U shape, and the detection coil 11 is wound around it. The detection coil 11 is connected to voltage detection means 12 realized by a voltmeter or the like. The pair of magnetic poles 7a and 7b of the first core 7 and the pair of magnetic poles 10 of the second core 10.
The centers of a and 10b are located at the vertices of a virtual square, and the straight line 7c connecting the magnetic poles 7a and 7b and the straight line 10c connecting the magnetic poles 10a and 10b are orthogonal to each other and coincide with the diagonal line of the square. To do.

In the magnetostrictive sensor 2, the magnetic pole 7 of the first core 7 is
a and 7b are equidistant from the magnetic poles 10a and 10b of the second core 10. For example, in the state where no stress σ is generated in the tube circumferential direction of the tube 6, the magnetic permeability in the tube circumferential direction is equal to that in the tube axial direction. Therefore, when the exciting coil 8 is excited by the voltage output from the AC power supply 9, the magnetic poles 7a to 10
The magnetic flux entering a is equal to the magnetic flux entering from the magnetic pole 7a to the magnetic pole 10b. Therefore, the currents induced in the detection coil 11 cancel each other out, and no induced electromotive force is generated. Also,
When the stress σ acts in the tube circumferential direction of the tube 6, the magnetic permeability in the tube axial direction of the tube 6 is different from that in the tube circumferential direction, so that a difference occurs in the magnetic resistance in both directions. Therefore, a difference occurs between the amount of magnetic flux entering the magnetic pole 10a and the amount of magnetic flux entering the magnetic pole 10b, and a current flows through the detection coil 11 to generate an induced electromotive force. This induced electromotive force is detected by the voltage detection means 12 and output as the output voltage V of the magnetostrictive sensor 2. The output voltage V is proportional to the difference between the stress σ2 in the tube circumferential direction and the stress σ1 in the tube axis direction, and the magnetostriction sensitivity M, and is represented by M (σ2-σ1). If the stress is acting only in the pipe circumferential direction, the magnetostrictive sensor 2 at one point on the pipe outer peripheral surface with the pipe axial direction as a reference.
Is angularly displaced, the magnetic resistances in the magnetic pole 10a direction and the magnetic pole 10b direction change according to the angle θ between the reference 6a in the tube axis direction and the magnetostrictive sensor 2, and the output voltage V changes according to cos 2θ.

FIG. 3 is a flow chart showing the operation of calculating the pipe internal pressure according to the present invention. In step n1, the reference of the angular displacement amount of the magnetostrictive sensor 2 is set so that the tube axis direction is 0 °, and the magnetostrictive sensitivity M, the tube inner diameter D and the plate thickness t are set.
Enter the initial settings. The magnetostriction sensitivity M is measured in advance using a test piece made of the same material as the tube. The inner diameter D and the plate thickness t may be stored in the memory 4b in advance and read from the memory as needed.
At step n2, the angular displacement amount θ is reset to zero. In step n3, the exciting coil 8 of the magnetostrictive sensor 2 is excited by the current output from the AC power supply 9, and the output voltage V _θ detected by the voltage detecting means 12 connected to the detecting coil 11 is input to the processing circuit 4a. . At step n4, the magnetostrictive sensor 2 is angularly displaced by a preset minute angular displacement amount Δθ. At step n5, the small angular displacement amount Δθ is added to the angular displacement amount θ to update the value. In step n6, it is determined whether or not the amount of angular displacement θ is equal to or greater than a predetermined constant value θc, and if so, the process proceeds to step n7, and if not, the process returns to step n3. The constant value θc is set to at least 180 ° or more with 0 ° being the pipe axis direction as a reference. As a result, the output voltage V _θ can be detected for each minute angular displacement amount Δθ.

[0020] At step n7, based on the output voltage V of the magnetostrictive sensor 2 shown in × in FIG. 4 θ _(θ = 1~θc),
A function approximated by the cosine waveform shown by the following equation is obtained by using the least square method or the like. Accordingly, the output voltage V _θ
The errors at the respective points are averaged, and the amplitude value B can be obtained as a more correct value.

V _θ = A + B cos2θ (1) The function shown by the above equation is shown by the solid line in FIG. At step n8, the internal pressure P is obtained from the amplitude value B of the above-mentioned function. As described above, the output voltage V of the magnetostrictive sensor 2, which is the induced electromotive force of the detection coil 11, is proportional to the stress σ. Assuming that no deformation such as bending has occurred in the pipe and no stress is applied in the pipe axial direction, when the angular displacement amount of the sensor 2 is θ, the output voltage V _θ is expressed by the following equation. be able to.

V _θ = M (0−σ cos 2 _θ ) (2) The second term in the parentheses is the component due to the stress in the pipe circumferential direction in the total stress acting on the pipe, and the stress σ is as described above. Since it is expressed as PD / 2t, the above equation can be expressed as follows.

[0023]

[Equation 4]

From the above equation and equation (1), the relationship between the amplitude value B and the internal pressure P can be obtained. Therefore, the internal pressure P is P = 2tB
/ MD, which can be obtained from the amplitude value B of the equation (1). In step n9, the calculated internal pressure P is displayed on the display screen, and the process ends.

[0025]

As described above, according to the present invention, the magnetostrictive sensor is arranged on the outer peripheral surface of the tube, and the magnetostrictive detection direction of the magnetostrictive sensor is rotated by 180 ° or more about the normal line direction of the outer peripheral surface as an axis. The amplitude value B of the output from the magnetostrictive sensor is obtained. Since the pressure P of the fluid in the pipe is calculated as P = 2tB / MD by using the amplitude value B, the inner diameter D of the pipe, the plate thickness t, and the magnetostriction sensitivity M, it is possible to easily calculate the pressure inside the pipe at any position of the pipe. Can be measured. As a result, it is possible to easily check whether the pipe to be worked is alive or dead or to check the magnitude of the pressure inside the pipe during pipe repair work, etc., easily and in a short time, thus reducing work time and work cost. You can

[Brief description of drawings]

FIG. 1 is a perspective view of a pipe pressure calculation device 1 according to an embodiment of the present invention.

FIG. 2 is a perspective view and a plan view of the magnetostrictive sensor 2 of FIG.

FIG. 3 is a flowchart showing an operation of calculating a pipe internal pressure according to the present invention.

FIG. 4 is a graph showing the relationship between the output voltage of the magnetostrictive sensor 2 and the sensor angle.

[Explanation of symbols]

 1 Pipe Pressure Calculation Device 2 Magnetostrictive Sensor 3 Drive Means 4 Control Means 4a Processing Circuit 4b Memory 5 Display Means 6 Pipes 7 1st Core 8 Excitation Coil 9 AC Power Supply 10 2nd Core 11 Detection Coil 12 Voltage Detection Means

Claims (1)

[Claims] 1. A magnetostrictive sensor is arranged on an outer peripheral surface of a tube, and a magnetostrictive detection direction of the magnetostrictive sensor is rotated by 180 ° or more about a normal direction of the outer peripheral surface, and an amplitude value B of an output from the magnetostrictive sensor is changed. The pressure P of the fluid in the pipe is calculated by using the inner diameter D of the pipe, the plate thickness t, and the magnetostriction sensitivity M. A method for calculating the pressure inside the tube by magnetostriction measurement, which is characterized by