JPH0769227B2 - Stress estimation method by fixing bending stress direction of pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an initial magnetic anisotropy of a pipe when a stress distribution of the pipe, such as a pipeline mounted on an abutment, is measured by a magnetostrictive sensor. The present invention relates to a stress estimation method by fixing the bending stress direction of a pipe which can estimate a small bending stress by removing this effect even if there is a distribution.

[Prior Art] In places such as the abutment pipe section of a pipeline, since the abutment section of the tube is a fixed and immovable section, when stress occurs due to ground subsidence, etc. In, a large bending stress is generated, and the bending stress gradually attenuates as the distance from the penetrating portion increases. In order to obtain the bending stress distribution for all locations of the entire pipe, it is necessary to measure all areas from large bending stress to small bending stress.

As a conventional method for measuring the stress and residual stress of a steel material or a steel structure, there is a method using a magnetostriction sensor in addition to X-rays and ultrasonic waves. A round bar that can be magnetized using this magnetostrictive sensor,
As a method for measuring the stress of a cylindrical material such as a pipe, there is a magnetostrictive stress measuring method disclosed in Japanese Patent Application No. 63-153622 filed previously.

In the magnetostrictive stress measurement method, when a load acts on a magnetic material, anisotropy occurs in the magnetic permeability, the magnetic permeability in the load direction increases, and on the contrary, the magnetic permeability in the direction perpendicular to the load direction decreases. This is a method of measuring the direction and magnitude of the principal stress by detecting the difference by a magnetostrictive sensor (also called a magnetic anisotropy sensor) having an exciting coil and a detecting coil. According to this measuring method, the measuring time for one point is 10 to 100 m.
Only sec, and handling is extremely convenient.

However, since the conventional magnetostrictive stress measuring method is generally performed by bringing the magnetostrictive sensor into contact with the surface to be measured, the magnetic resistance at the contact surface greatly differs depending on the state of the surface to be measured. Therefore, there is a drawback that the measurement error becomes large.

Therefore, the idea is to measure in a non-contact state, that is, in the state where the magnetostrictive sensor is separated from the measured surface by a certain distance, but in this case, the magnetostrictive sensitivity decreases, so the setting of the magnetostrictive sensor There was another problem that required very subtle adjustments.

In the invention of the above-mentioned prior application, a problem was solved in the non-contact measurement, and a device capable of performing a magnetostrictive stress measurement method for a cylindrical material such as a magnetizable round bar or pipe in a non-contact method was developed. We have provided a method to measure the stress distribution in the circumferential direction of a cylindrical material with higher accuracy than before.

FIG. 1 is a diagram for explaining the magnetostrictive stress measuring method according to the previous application. In FIG. 1 (a), a bending load is applied to the columnar material 1 so that the upper side of the columnar material 1 has a tensile stress + σ and the lower side thereof has a compression stress. Stress-σ
Indicates that is working. Further, FIG. 2B shows the columnar material 1
The magnetostrictive sensor 2 is rotated clockwise from the uppermost point of the cylindrical material 1, that is, the angular position of 0 °, while maintaining a lift-off (gap) at a constant distance h from the central axis of the cylindrical material 1 and its outer peripheral surface. In the figure, a method is shown in which the magnetostrictive signal detected by the magnetostrictive sensor 2 at each angular position between 0 ° and 360 ° is continuously measured by making one rotation along the circumferential direction.

FIG. 2 is a diagram for explaining the SIN approximation method based on the magnetostrictive stress measurement method of FIG. 1, and FIG. 2A shows the angle indicating the orientation of the magnetostrictive sensor 2 on the outer circumference of the cylindrical material 1 and its stress distribution. Since the maximum tensile stress occurs at an angle of 0 ° (that is, directly above the columnar material 1) and the maximum compressive stress occurs at an angle of 180 ° (that is, immediately below the columnar material 1,) the stress distribution is similar to the SINθ curve. To do.

FIG. 2 (b) shows the measured value of the stress by the strain gauge and the SINθ approximate value when a load of −20 kg / mm ² was applied to the cylindrical material. From this figure, it can be seen that the actual stress distribution and the SINθ curve are very similar.

[Problems to be Solved by the Invention] When the pipe bending stress in the vicinity of the bridge abutment is measured by the SINθ approximation method based on the magnetostrictive stress measurement method disclosed in Japanese Patent Application No. 63-153622, the bending stress SIN θ when small
When obtaining the amplitude value of the approximated curve, the amplitude value due to the residual stress when no stress is applied and the amplitude value due to the bending stress are combined, and the bending direction shown in the SINθ curve approximated from the magnetostrictive sensor output and the actual pipe However, there is a problem in that the measurement accuracy of the stress measurement value deteriorates because the bending axis is different.

The present invention has been made to solve the above problems,
Even if there is an initial magnetic anisotropy distribution in the pipe circumferential direction, the direction of the bending stress indicated by the SIN approximation curve is fixed so that it is not affected by this and matches the actual bending stress direction of the pipe. The purpose is to obtain a stress estimation method by fixing the bending stress direction of the pipe.

[Means for Solving the Problems] A stress estimation method by fixing a bending stress direction of a pipe according to the present invention provides a measuring device in which a magnetostrictive sensor relatively moves on an outer peripheral surface or an inner peripheral surface of a pipe material in a non-contact state. Using the method of estimating the bending stress distribution in the pipe circumferential direction of the pipe material by approximating with a SIN curve, when the pipe material has an initial magnetic anisotropy distribution in the pipe circumferential direction, the actual bending stress of the pipe material The direction of the bending stress indicated by the SIN approximate curve is fixed so as to match the direction of, and the SIN approximate curve that approximates the measurement value obtained from the magnetostrictive sensor is calculated, and the signal amplitude of the calculated SIN approximate curve is calculated. The stress estimating means is provided by fixing the bending stress direction of the pipe for estimating the corresponding bending stress value from the value.

[Operation] In the present invention, the bending stress distribution in the pipe circumferential direction of the pipe material is approximated by the SIN curve by using the measuring device in which the magnetostrictive sensor relatively moves in the non-contact state on the outer peripheral surface or the inner peripheral surface of the pipe material. In the method of estimating the bending stress of the pipe by the stress estimating means by fixing the bending stress direction of the pipe, when the pipe has an initial magnetic anisotropy distribution in the circumferential direction of the pipe, the direction of the actual bending stress of the pipe matches. As such, by fixing the direction of the bending stress indicated by the SIN approximate curve, a SIN approximate curve that approximates the measurement value obtained from the magnetostrictive sensor is calculated, and the corresponding bending is calculated from the signal amplitude value of the calculated SIN approximate curve. Estimate the stress value.

[Embodiment] FIG. 3 is a block diagram of a pipe stress measuring apparatus to which the stress estimating method by fixing the bending stress direction of the pipe of the present invention is applied. In the figure, reference numeral 10 denotes a traveling device section, which incorporates a magnetic anisotropy sensor 11 and a traveling carriage 12. The magnetic anisotropy sensor 11 is a sensor for detecting the magnetic anisotropy in the circumferential direction of the pipe material in a non-contact manner, and includes, for example, an exciting coil and a detecting coil that are orthogonal to each other, and a constant exciting current is applied to the exciting coil. hand,
The magnetic anisotropy caused by the action of stress is detected as a voltage signal obtained from the detection coil. Traveling trolley
Reference numeral 12 denotes a traveling mechanism for traveling on rails and / or gears provided on the outer circumference of the pipe to move the magnetic anisotropy sensor 11 in the circumferential direction of the pipe to perform measurement. Reference numeral 13 is a magnetostriction measuring unit, which supplies a constant current to the exciting coil of the magnetic anisotropy sensor 11, and at the same time amplifies the detection signal obtained from the detection coil of the sensor 11 to obtain a voltage signal proportional to the magnetic anisotropy. It is a magnetostriction measuring unit for outputting. Reference numeral 14 denotes a motor driver, which supplies a traveling drive signal to the traveling vehicle 12 to cause the traveling vehicle 12 to travel, and an encoder signal is returned as position information of the traveling result. Reference numeral 15 is an A / D converter, 16 is an interface such as RS232C, 17 is a personal computer (hereinafter referred to as a personal computer), and 18 is a data display unit using a CRT or liquid crystal.

The operation of FIG. 3 will be described. In order to measure the stress in the circumferential direction of the pipe material, for example, a rail or / and a gear (not shown) is attached to the outer peripheral surface of the pipe material on a plane perpendicular to the central axis of the pipe material, and via a holder on the rail or / and gear, Mount the traveling device unit 10 so that it can travel. Next, the personal computer 17 gives a running command for one rotation to the motor driver 14 via the interface 16, and the motor driver 14 sends the running command to the rail or / or
Also, the traveling device 10 on the gear is caused to travel once along the circumference of the pipe. During this running, the magnetic anisotropy sensor 11 (magnetostriction sensor 2
The same as the above) is detected by the magnetostriction measuring unit 13 at each angular position between 0 ° and 360 ° on the outer peripheral surface of the pipe material shown in FIG. 1 (b). The amplified signal is output, and the output is quantized by the A / D converter 15 and supplied to the personal computer 17. The personal computer 17 displays the sensor output value for each angle indicating the azimuth on the outer circumference of the magnetic anisotropy sensor 11 on the data display unit 18, and outputs a hard copy by a printer (not shown) if necessary. The stress estimation process by fixing the bending stress direction of the pipe according to the present invention can be performed based on the data displayed on the data display unit 18 of the measuring device or the hard copy data output by the printer.

The stress estimation method by fixing the bending stress direction of the pipe of the present invention will be described below.

FIGS. 4 (a) to 4 (c) are views showing the initial magnetic anisotropy distribution of the tube and the approximation results when a large bending stress or a small bending stress is applied to the distribution, and the horizontal axis represents magnetostriction. The angle indicating the azimuth on the tube circumference of the sensor and the vertical axis indicate the magnetostrictive sensor output (unit: volt). The + symbol in the figure is the measured value, and the solid line is the SINθ approximation curve that approximates the measured value.

It is assumed that there is a tube having an initial magnetic anisotropy distribution as shown in FIG. 4 (a). When a large bending stress is applied to this tube, the magnetostrictive sensor output becomes as shown in FIG. 4 (b), and the measured value is close to the SINθ approximate curve. This is because the initial magnetic anisotropy distribution is relatively smaller than the stress applied later, so the SIN calculated from the measured values
The bending stress direction of the θ approximation curve (the direction in which the maximum tensile stress is 0 ° and the direction in which the maximum compressive stress is 180 °) coincides with the actual bending stress direction. However, when a small bending stress is applied, the magnetostrictive sensor output becomes as shown in Fig. 4 (c), and the bending stress direction of the SINθ approximate curve calculated from the measured values (the maximum tensile stress is about 67 ° Direction, maximum compressive stress is 247 °) is the actual bending stress direction (maximum tensile stress is 0 °, maximum compressive stress is 180 °)
Does not match. The width variation of the SINθ approximation curve, which indicates the magnitude of stress, is also greatly affected by the initial magnetic anisotropy distribution.

In the present invention, when the tube has an initial magnetic anisotropy distribution, the direction of the bending stress displayed on the SINθ approximate curve is set in the same manner as when the bending stress is largely acting even when the bending stress is small. It is fixed so as to match the actual bending stress direction.

FIG. 5 (a) is a diagram showing the initial magnetic anisotropy distribution of the pipe and its SINθ approximate curve, and FIG. 5 (b) is a diagram showing the sensor output change due to the addition of a small bending stress and its SINθ approximate curve. Is. The horizontal axis in each figure shows the same angle as in FIG. 4, the + mark in FIG. 4 (a) shows the measurement value of the magnetostrictive sensor, and the + in FIG. 4 (b).
The mark indicates the sensor output change (the output change is the value obtained by subtracting the initial value when no stress is applied from the output value of the magnetostrictive sensor when a small stress is applied.), And the solid line indicates the SINθ approximate curve. ing.

FIG. 6 (a) is a diagram showing the initial magnetic anisotropy of the tube of FIG. 5 (a) and the measured value of the magnetostrictive sensor output added with the change due to the addition of a small bending stress in FIG. 5 (b). .

FIG. 6 (b) is a diagram showing the result of approximating the measured values of FIG. 6 (a) by a normal method. Here, the normal method is, for example, a method of obtaining a SINθ approximate curve from the measured value by using the least squares method, and is a method that does not consider the actual bending stress direction of the pipe. The solid line in FIG. 7B shows this normal SINθ approximate curve.

FIG. 6 (c) is a diagram showing the result of approximating the measured values of FIG. 6 (a) by the method of the present invention. Here, the method according to the present invention is to determine the actual bending stress direction of a pipe because the bending direction is the same between two supports of the pipe at any place when calculating the SINθ approximate curve from the measured values. The direction of the bending stress is fixed in this direction and is approximated. Sixth
In the example of Figure (c), the maximum amplitude value of the SINθ approximate curve is fixed in the direction of 0 ° where the maximum tensile stress is generated, and the minimum amplitude value is fixed in the direction of 180 ° where the maximum compressive force is generated. , SINθ approximate curve is calculated from the measured values. The solid line in FIG. 7C shows the SINθ approximate curve of the present invention. According to the method of the present invention, the bending stress direction of the SIN θ curve approximated to the measured value matches the actual bending stress direction, and measurement can be performed from a small bending stress to a large bending stress. In the actual stress measurement, a calibration curve is prepared in advance from the stress value actually measured by a strain gauge or the like and the SINθ approximate value approximated by the magnetostrictive sensor measured value by the method of the present invention. Then, using this calibration curve, the corresponding bending stress is estimated from the signal amplitude value of the SINθ approximate curve calculated by fixing the bending stress direction of the pipe from the magnetostrictive sensor output.

Further, in the above-described embodiment, the example in which the magnetostrictive sensor is made to travel on the outer peripheral surface of the pipe material in a non-contact manner has been shown, but the magnetostrictive sensor may be made to travel on the inner peripheral surface of the pipe material in a non-contact manner as well. Further, in this case, the magnetostrictive sensor may be fixed by rotating the pipe material with respect to the central axis thereof without running the magnetostrictive sensor. In either case, the magnetostrictive sensor and the pipe member may be moved relative to each other, and the same effect can be obtained by fixing one and moving the other.

[Advantages of the Invention] As described above, according to the present invention, the magnetostrictive sensor is bent in the pipe circumferential direction by using a measuring device in which the magnetostrictive sensor relatively moves on the outer peripheral surface or the inner peripheral surface of the pipe material in a noncontact state. SIN the stress distribution
In the method of approximating with a curve, when the pipe material has an initial magnetic anisotropy distribution in the pipe circumferential direction, the bending stress indicated by the SIN approximation curve so as to match the actual bending stress direction of the pipe material. Fixing the direction of, to calculate the SIN approximation curve that approximates the measurement value obtained from the magnetostrictive sensor,
Since the corresponding bending stress value can be accurately estimated from the calculated signal amplitude value of the SIN approximate curve, the effect of improving the measuring accuracy of the bending stress measuring method of the pipe using the magnetostrictive sensor can be obtained. .

[Brief description of drawings]

1 (a) and 1 (b) are diagrams for explaining the magnetostrictive stress measuring method according to the prior application, and FIGS. 2 (a) and 2 (b) are for explaining the SIN approximation method by the magnetostrictive stress measuring method of FIG. FIG. 3 is a block diagram of a pipe stress estimating device to which the stress estimating method by fixing the bending stress direction of the pipe of the present invention is applied, and FIG. 4 (a) to FIG.
FIG. 5 (c) is a diagram showing the initial magnetic anisotropy distribution of the tube and an approximation result when a large bending stress or a small bending stress is applied thereto, and FIG. 5 (a) is an initial magnetic anisotropy of the tube. FIG. 5 (b) is a diagram showing the distribution and its SINθ approximate curve, FIG. 5 (b) is a diagram showing the sensor output change due to the addition of a small bending stress and its SINθ approximate curve, and FIG. 6 (a) is FIG. 5 (a) and FIG. 5 shows the measured value of the magnetostrictive sensor output to which the signal of FIG. 5 (b) is added. FIG. 6 (b) shows the result of approximation of the measured value of FIG. (C) is a figure which shows the result which the measured value of the same figure (a) was approximated by the method of this invention. In the figure, 1 is a cylindrical material, 2 is a magnetostrictive sensor, 10 is a traveling device section, 11 is a magnetic anisotropy sensor, 12 is a traveling carriage, 13 is a magnetostrictive measuring section, 14 is a motor driver, and 15 is an A / D conversion. Bowl, 16
Is an interface, 17 is a personal computer, and 18 is a data display unit.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Sadaaki Sakai 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (56) Reference JP-A-1-308933 (JP, A)

Claims (1)

[Claims] 1. A bending stress distribution in the pipe circumferential direction of the pipe material is estimated by approximation with a SIN curve using a measuring device in which a magnetostrictive sensor relatively moves on the outer peripheral surface or the inner peripheral surface of the pipe material in a non-contact state. In the method described above, when the pipe material has an initial magnetic anisotropy distribution in the pipe circumferential direction, SI is adjusted so as to match the actual bending stress direction of the pipe material.
Fix the direction of bending stress indicated by the N approximation curve,
Calculating a SIN approximation curve that approximates the measurement value obtained from the magnetostrictive sensor, and fixing the bending stress direction of the pipe characterized by estimating the corresponding bending stress value from the signal amplitude value of the calculated SIN approximation curve Stress estimation method.