JPH0769225B2 - Bending stress estimation method for pipes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a bending which works on a pipeline or the like having a fixed end when a large bending stress occurs due to ground subsidence or the like. The present invention relates to a method for estimating bending stress of a pipe, which estimates the magnitude of stress from a measurement value of a magnetostrictive sensor.

[Prior Art] As a method of 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. As a method for measuring the stress of a cylindrical material such as a magnetizable round bar or pipe using this magnetostrictive sensor, 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 prior application, a device for solving the problems in the non-contact measurement and developing a magneto-striction stress measuring method for a columnar material such as a magnetizable round bar or a pipe by a non-contact method, and measuring device therefor have been 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] In the SINθ approximation method based on the magnetostrictive stress measurement method for a cylindrical material, which is disclosed in Japanese Patent Application No. 63-153622, the bending stress becomes large and the permeability due to the stress of the material causes When the change is small, the output change of the magnetostrictive sensor in the vicinity of the bending axis is small, and the change in the signal amplitude approximated by the SINθ approximation method is also small.

FIG. 3 is a diagram showing the characteristics of the signal amplitude and the bending stress by the SINθ approximation method. The bending stress and the signal amplitude are almost linear characteristics in the bending stress range of about 0 to 12 kg / mm ^2. However, in the range beyond that, the increase of the signal amplitude gradually becomes smaller than the increase of the bending stress, and the signal amplitude comes to have a saturation characteristic.

Further, FIG. 4 shows the angle indicating the azimuth on the tube circumference of the magnetostrictive sensor when the bending stress is large and the sensor output (unit is bolt).
And FIG. 5 is a diagram showing the characteristics of the angle indicating the azimuth on the tube circumference of the magnetostrictive sensor and the sensor output when the bending stress is small. In each case, the + sign in the figure indicates each measured value by the magnetostrictive sensor.

As is clear from the comparison between FIGS. 4 and 5, the magnetostrictive sensor output when the bending stress is large (FIG. 4) is SINθ compared to the magnetostrictive sensor output when the bending stress is small (FIG. 5).
The deviation from the curve becomes larger.

Therefore, in such an area where the bending stress is large, there is a problem that the accuracy of the bending stress measurement by the SINθ approximation method using the magnetostrictive sensor is significantly lowered, or the measurement becomes impossible.

The present invention has been made to solve such a problem, and even in a region where the magnetostrictive sensor output and the bending stress have non-linear characteristics, the value of the bending stress can be estimated more accurately than the magnetostrictive sensor output. The purpose is to obtain a bending stress estimation method.

[Means for Solving the Problem] A method for estimating stress in bending of a pipe according to the present invention uses 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, In the method of estimating the bending stress distribution in the pipe circumferential direction of the pipe material by approximating it with a SIN curve, in the vicinity of the bending stress neutral part of the pipe material, the magnetostrictive sensor output is in a linear region, and the sensor output change has the largest angle. Two ranges are selected, an average value of the inclinations of two straight lines that respectively approximate the outputs of the magnetostrictive sensors within the selected two angular ranges is calculated, and the average value of the calculated inclinations of the two straight lines is used. The pipe bending stress estimating means for estimating the bending stress value is provided.

[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 this method, the bending stress estimating means selects two angular ranges in which the magnetostrictive sensor output is in the linear region and the largest sensor output change is in the vicinity of the bending stress neutral portion of the pipe material, and the selection is performed. The average value of the inclinations of the two straight lines that respectively approximate the magnetostrictive sensor outputs within the two calculated angular ranges is calculated, and the value of the corresponding bending stress is estimated from the calculated average value of the inclinations of the two straight lines.

[Embodiment] FIG. 6 is a block diagram of a pipe stress measuring apparatus to which the pipe bending stress estimating method 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. Then, the magnetic anisotropy caused by the action of stress is detected as a voltage signal obtained from the detection coil. The traveling carriage 12 is, for example, a traveling mechanism that travels on rails and / or gears provided on the outer circumference of the pipe and moves the magnetic anisotropy sensor 11 in the circumferential direction of the pipe to perform measurement. A magnetostriction measuring unit 13 supplies a constant current to the exciting coil of the magnetic anisotropy sensor 11, and at the same time, the sensor
This is a magnetostriction measuring unit that amplifies the detection signal obtained from the 11 detection coils and outputs it as a voltage signal proportional to the magnetic anisotropy. 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. 6 will be described. 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 a holder is mounted on this 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 pipe bending stress estimation process according to the present invention can be performed based on the data displayed on the data display unit 18 of the present measurement device or the hard copy data output by the printer.

Fig. 7 shows the SIN of the magnetostrictive sensor output when the bending stress is large.
It is a figure which shows the result approximated by (theta). In the figure, the horizontal axis is an angle indicating the azimuth of the magnetostrictive sensor on the tube circumference when the magnetostrictive sensor is rotated once on the outer peripheral surface of the tube along the circumferential direction,
The vertical axis represents the output voltage of the magnetostrictive sensor, and its unit is volt (V). Also, the + mark in the figure shows each measurement value by the magnetostrictive sensor, and the solid line shows the curve approximated by SINθ.

In FIG. 7, when the bending stress is large, due to the non-linearity between the magnetostrictive sensor output and the stress, in a region where the bending stress is large, for example, in an angle range of about 135 ° to 225 ° and 315 ° to 45 °. It can be seen that the magnetostrictive sensor output seems to be crushed at the part corresponding to the axis of bending. When the curve connecting these measured values is approximated by the curve of SINθ (curve shown by the solid line in the figure), it is shown that the measurement error increases in the region of large bending stress as shown in FIG. 7. The present invention, for the bending stress of this pipe, near the neutral portion between the tensile stress and the compressive stress (the tensile stress gradually decreases to zero,
Next, in the region where the compressive stress gradually increases from zero), the sensor output of the region where the magnetostrictive sensor has a linear characteristic (the region where the bending stress is small, the magnetostrictive sensor output has a linear characteristic with respect to the bending stress) Based on the data, the bending stress value of the corresponding pipe is estimated.

FIG. 8 is a diagram for explaining the linear approximation method based on the magnetostrictive sensor output data near the stress neutral portion according to the present invention. In the figure, the horizontal axis is the angle indicating the azimuth around the circumference of the tube of the magnetostrictive sensor, and the vertical axis is the output voltage of the magnetostrictive sensor in volts (V), as in FIG. Further, the + mark in the figure indicates each measured value obtained by the magnetostrictive sensor.

In FIG. 8, in the vicinity of the stress-neutral portion, two angular ranges are selected in which the change (ΔV) in the magnetostrictive sensor output is the largest with respect to the change (Δθ) in the angle indicating the azimuth of the magnetostrictive sensor. In this example, the first and second neutral axes are 87 ° and
The angle was set to 270 °, and the angle settings before and after that were ± 10 °. Therefore, the two selected angle ranges are 77 ° -97.
It becomes an area of ゜ and 260 〜 280 ゜.

Next, the inclinations of the _two straight lines L ₁ and L ₂ approximating the magnetostrictive sensor outputs within the two angular ranges thus selected (the change ΔV in the sensor output with respect to a simple unit angle change without considering the sign) / Δθ.) ΔV ₁ / Δθ and ΔV ₂ /
Δθ is obtained, and the average value of the inclinations ΔV ₁ / Δθ and ΔV ₂ / Δθ of these two straight lines is calculated. In the present invention, the bending stress is estimated from the average value of the inclinations of these two approximate straight lines.

FIG. 9 is a diagram showing the characteristics of the inclination and bending stress of a straight line that is linearly approximated by the data in the vicinity of the stress neutral portion according to the present invention. In the figure, the horizontal axis shows bending stress, the unit is kg / mm ²
Is. The vertical axis represents the average slope value of the two approximate straight lines, and the unit is mV / deg. The circles in the figure are the average slope values of the approximate straight line calculated corresponding to the stress actually measured by a strain gauge or the like, and the solid lines are the calibration straight lines that approximate the average slope values of the circles by a straight line.

By using the calibration line or curve shown in Fig. 9, it is possible to accurately measure up to a large range of bending stress, which was too large or could not be measured by the conventional SINθ approximation method in the magnetostrictive stress measurement method. Became.

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.

[Effects of the Invention] As described above, according to the present invention, the magnetostrictive sensor is bent in the circumferential direction of the pipe material by using the measuring device that relatively moves on the outer peripheral surface or the inner peripheral surface of the pipe material in a non-contact state. SIN the stress distribution
In the method of approximating with a curve, in the vicinity of the bending stress neutral portion of the pipe material, the magnetostrictive sensor output is in a linear region, and two angular ranges having the largest sensor output change are selected and selected. The average value of the inclinations of two straight lines that respectively approximate the outputs of the magnetostrictive sensors in the two angle ranges is calculated, and the corresponding bending stress value can be estimated with high accuracy from the calculated average value of the inclinations of the two straight lines. As a result, the effect of improving the measurement accuracy of the bending stress measuring method for a pipe using a 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. Figures and 3 show SINθ
FIG. 5 is a diagram showing characteristics of a signal amplitude and bending stress by an approximation method. FIG. 4 is a diagram showing characteristics of an angle indicating an azimuth on a pipe circumference of the magnetostrictive sensor and a sensor output thereof when the bending stress is large.
FIG. 6 is a diagram showing the characteristics of the angle indicating the azimuth on the pipe circumference of the magnetostrictive sensor and the sensor output when the bending stress is small, and FIG. 6 is the stress measurement of the pipe to which the bending stress estimation method of the present invention is applied. FIG. 8 is a block diagram of the device, FIG. 7 is a diagram showing the result of approximating the magnetostrictive sensor output by SINθ when the bending stress is large,
FIG. 9 is a diagram for explaining the linear approximation method based on the magnetostrictive sensor output data in the vicinity of the stress neutral portion according to the present invention, and FIG. 9 is the characteristic of the slope and bending stress of the straight line approximated by the data in the vicinity of the stress neutral portion according to the present invention FIG. 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, in the vicinity of the bending stress neutral portion of the pipe material, the magnetostrictive sensor output is in a linear region, and two angle ranges having the largest sensor output change are selected, and the selected two angle ranges are included. The bending stress of the pipe is characterized by calculating an average value of inclinations of two straight lines approximating respective magnetostrictive sensor outputs and estimating a corresponding bending stress value from the calculated average value of inclinations of the two straight lines. Estimation method.