JPH05281062A - Presuming method for stress or strain in bent pipe - Google Patents

Abstract

PURPOSE:To provide a new method to nondestructively presume stress or strain in the bent pipe part of a hollow cylindrical pipe such as a gas conduit, a water service conduit and plant piping in a factory. CONSTITUTION:In the state where the bent pipe part of a gas conduit or the like is buriedly provided under the ground, and its straight pipe part is supported by an abutment 3 and exposed out of the ground, stress acting on bent pipe parts 5, 7 buriedly provided under the ground or their strain caused by the stress can be presumed by measuring stress in the circumferential directions of the straight pipe parts 4, 6, 8 or strain caused by the stress. Thus, the possibility of the occurrence of a crack in the bent pipe parts 5, 7 can be presumed without digging out the bent pipe parts 5, 7 from the ground for exposing them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for non-destructively estimating stress or strain in a curved pipe portion of a hollow cylindrical pipe such as a gas pipe, a water pipe, a plant pipe in a factory.

[0002]

2. Description of the Related Art A pipe whose straight pipe portion is fixed to an abutment is
When the road surface of the road sinks in a state where it is connected to the elbow that is a curved pipe section buried in the road, stress acts on the elbow, and as a result, distortion occurs in the elbow,
Finally, cracks may occur.

In the prior art, it is necessary to excavate a road to expose the elbow in order to inspect whether the elbow is cracked or not.

[0004]

In such a prior art, as described above, unless the elbow is exposed by excavating the soil, it is impossible to inspect whether or not the elbow is cracked. , Workability is poor.

The object of the present invention is to estimate the stress acting on the curved pipe portion provided in the concealed portion such as soil or the strain caused by the stress without excavating the concealed portion. Another object of the present invention is to provide a method for estimating the stress or strain of a curved pipe section that is made possible.

[0006]

According to the present invention, the curved pipe portion is provided in the concealed portion, and the straight pipe portion connected to the curved pipe portion is exposed. A method for estimating stress or strain in a curved pipe portion, which comprises measuring a strain due to stress and estimating the stress in the curved pipe portion or the strain due to the stress from the measurement result.

[0007]

According to the present invention, the straight pipe portion connected to the curved pipe portion is exposed from the concealed portion, and the circumferential stress of the straight pipe portion or the strain due to the stress is measured, It is possible to estimate the stress in the curved pipe section or the strain due to the stress. Therefore, it is not necessary to expose the curved pipe part from the concealed part and excavate, and workability is good,
For example, the stress or strain acting on the curved pipe portion can be easily estimated at all times as described above.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view for explaining one embodiment of the present invention. A road 2 is connected to the bridge 1, a straight pipe portion 4 which is a steel pipe such as a gas pipe is supported on an abutment 3 of the bridge 1, and a curved pipe portion 5 which is an elbow is buried in the soil of the road 2. The curved pipe portion 5 also includes a straight pipe portion 6 and a curved pipe portion 7.
And the straight pipe part 8 etc. are connected. According to the present invention, the stress acting on the curved pipe portion 5 buried in the soil or the strain due to the stress is measured by measuring the stress in the circumferential direction of the exposed straight pipe portion 4 or the straight pipe portion thereof. By measuring the strain caused by the stress acting on the part 4,
Can be estimated. As a result, it becomes possible to inspect whether or not there is a possibility that cracks will occur in the bent tube portion 5, and maintenance will be facilitated.

FIG. 2 is a simplified view of the straight pipe portions 4 and 6 and the curved pipe portion 5 shown in FIG. The maximum value of the stress in the circumferential direction σ1m at the position 4a which is separated from the connecting portion 9 between the straight pipe portion 4 and the curved pipe portion 5 by the distance L1 in the axial direction of the straight pipe portion 4.
ax is measured, and corresponding to this stress maximum value σ1max,
Maximum strain value ε1max at the position 4a of the curved tube portion 4
Can be obtained from FIG. The position where L2 and L3 are separated from the connecting portion 9 in the axial direction of the straight pipe portion 4 is the reference numeral 4
b, 4c. Strain maximum value ε1ma corresponding to the maximum stress value σ1max at the position 4a of the straight pipe portion 4.
The relationship between x and the maximum strain value ε2max at the desired predetermined position 5a of the curved tube portion 5 is obtained in advance by experiments and is, for example, as shown in FIG. In FIG. 4, lines 11, 12, and 13 are obtained corresponding to the positions 4a, 4b, and 4c of the straight pipe portion 4 individually. In order to obtain the characteristics shown in FIG. 4, as shown in FIG. 2, the end portion 14 of the straight pipe portion 4 is fixed at a fixed position, and the straight pipe portion 4 and the curved pipe portion 5 are soiled. And the force is applied to the part 15 in the middle of the straight pipe portion 6 as indicated by the arrow 16. At each position 4a, 4b, 4c of the straight pipe part 4 and at the position 5a of the curved pipe part 5, a plurality of strain gauges are attached at intervals in the circumferential direction, whereby each position 4a, 4b, 4c;
5a can be measured in the circumferential direction, so that for example the maximum strain ε1max at position 4a can be determined, and in the same way the maximum strain ε2max at position 5a can be determined. The same applies to the positions 4b and 4c. In this way, the lines 11, 12, and 13 described above are obtained. Therefore, it is possible to measure the stress in the circumferential direction at a predetermined position 4a of the straight pipe portion 4 exposed from the soil of the road 2 of FIG. 1 and measure the maximum value as, for example, σ1 as shown in FIG. If it is possible, corresponding to the stress σ1,
The maximum value ε11 of the strain at the position 4a can be obtained from the graph of FIG. 3 created in advance. From the maximum strain ε11 at the position 4a thus obtained, based on the line 11 shown in FIG.
The maximum value ε21 of the strain at the position 5a can be estimated and obtained. The maximum value ε21 of this distortion is the curved tube portion 5
Corresponds to the maximum value of stress at the position 5a. Although the above-mentioned embodiments have been described with reference to the maximum values of stress and strain, even if the circumferential positions of the straight pipe portion 4 and the curved pipe portion 5 are stress or strain at the same position along the pipe axis. The stress or strain in the curved pipe portion 5 buried in the soil can be estimated in the same manner as described above.

FIG. 5 is a graph showing the relationship between the distance in the pipe axis direction from the connecting portion 9 in the straight pipe portion 4 of another embodiment of the present invention and the maximum value σ1max of the circumferential stress at each position. .. According to the same experiment as in FIG. 2 described above, the straight pipe portion 6
When a constant force is applied to the position 15 in the middle of the direction in the direction of the arrow 16, the maximum stress σ1max in the circumferential direction at each position 4a, 4b, 4c of the straight pipe portion 4 is measured, and the line 17 is drawn. obtain. Thereby, the angle α1 of the line 17 is obtained. Similarly, the force of the arrow 16 is greatly changed to obtain the line 18, and the angle α2 at this time is obtained. Maximum stress σ1max at each position 4a, 4b, 4c
Corresponds to the strain amount ε1 for each position. Slope α1,
α2 is generally denoted by α.

Based on the experimental results obtained in FIG. 5, the maximum value ε2max of the circumferential strain at the position 5a of the curved pipe portion 5 can be obtained as shown by the line 19 in FIG. Maximum strain ε2m at this position 5a
ax corresponds to the maximum value of the stress at the position 5a. Therefore, at least two or more positions 4a, 4b, 4 along the pipe axis direction of the straight pipe portion 4 exposed from the soil 2
The circumferential stress is measured for each c and the maximum value σ1max
Then, the inclination, for example, α1, is obtained, and then the maximum value ε2max of the strain generated at the position 5a of the curved pipe portion 5 is obtained and estimated from the line 19 of FIG. 6 corresponding to the obtained inclination α1. You can

Next, one method for measuring the stress in the circumferential direction at each position 4a, 4b or 4c of the straight pipe portion 4 and therefore the maximum value σ1max of the stress will be described.
FIG. 7 is a diagram for explaining the magnetostrictive stress measuring method which is the basis of the stress measurement, and FIG. 7A shows a case where a bending load is applied to the columnar material 21 which may be the straight pipe portion 4 or the like, and the columnar material 21. The tensile stress + σ is shown on the upper side and the compressive stress −σ is shown on the lower side. Further, FIG. 7B shows the magnetostrictive sensor 2 while being perpendicular to the central axis of the columnar material 21 and maintaining lift-off (gap) at a constant distance h from the outer peripheral surface thereof.
The magnetostrictive signal detected by the magnetostrictive sensor 22 at each angular position between 0 ° and 360 ° by rotating 2 from the uppermost point of the cylindrical material 21, that is, the angular position of 0 ° in the clockwise direction along the circumferential direction. It shows a method of continuously measuring.

FIG. 8 shows the SIN according to the magnetostrictive stress measurement method of FIG.
It is a figure explaining an approximation method, and Drawing 8 (a) shows magnetostrictive sensor 2
2 indicates an angle indicating the orientation on the outer circumference of the cylindrical material 21 and its stress distribution, and the angle is 0 ° (that is, directly above the cylindrical material 21).
Since the maximum tensile stress occurs at the angle of 180 ° (that is, immediately below the columnar material 1), the stress distribution is distributed close to the SINθ curve.

FIG. 8 (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 is applied to the cylindrical material. From this figure, it can be seen that the actual stress distribution and the SINθ curve are quite similar.

In the magnetostrictive stress measuring method shown in FIGS. 7 and 8, the straight pipe portion in the vicinity of the curved pipe portion is affected by the flattening of the curved pipe portion, and even the straight pipe portion has a stress distribution. The SIN curve is not clean with respect to the angle θ in the pipe circumferential direction.

A method for solving this problem will be further described below.

FIG. 9 (a) is a diagram showing a stress state when the pipe is flat. In FIG. 9 (a), the compressive stress −σ is at the positions of 0 ° and 180 ° in the circumferential direction of the pipe. It is shown that the tensile stress + σ works at the positions of 90 ° and 270 °.

FIG. 9 (b) is a diagram showing the magnetostrictive sensor output in the flat stress state of the pipe of FIG. 9 (a). The horizontal axis indicates the magnetostrictive sensor on the outer peripheral surface of the pipe perpendicular to the central axis of the pipe material. It is an angle indicating the azimuth on the pipe circumference of the sensor when it is rotated once clockwise. The vertical axis represents the magnetostrictive sensor output (unit: volt), and the measured value of the sensor is indicated by + mark in the figure. As shown in FIG. 9B, in the vicinity of the curved pipe portion of the pipe, the above-mentioned SINθ approximation method cannot be applied even to the straight pipe portion.

FIG. 10 is a block diagram of a pipe stress measuring apparatus to which the pipe flat stress estimating method is applied. 3 in the figure
Reference numeral 0 denotes a traveling device section, which incorporates a magnetic anisotropy sensor 31 and a traveling carriage 32. The magnetic anisotropy sensor 31 is a sensor for detecting the magnetic anisotropy in the circumferential direction of the tube in a non-contact manner. Then, the magnetic anisotropy caused by the action of stress is detected as a voltage signal obtained from the detection coil. The traveling carriage 32 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 31 in the circumferential direction of the pipe to perform measurement. A magnetostriction measuring unit 33 supplies a constant current to the exciting coil of the magnetic anisotropy sensor 31 and at the same time amplifies a detection signal obtained from the detection coil of the sensor 31 to obtain a voltage signal proportional to the magnetic anisotropy. It is a magnetostriction measuring unit for outputting. A motor driver 34 supplies a traveling drive signal to the traveling vehicle 32 to cause the traveling vehicle 32 to travel, and an encoder signal is fed back as position information of the traveling result. Reference numeral 35 is an A / D converter, 36 is an interface such as RS232C, 37 is a personal computer (hereinafter referred to as personal computer), and 38 is C.
It is a data display unit using RT or liquid crystal.

The operation of FIG. 10 will be described. To measure the stress in the circumferential direction of the pipe, for example, a rail or / and a gear (not shown) is attached to the outer peripheral surface of the pipe on a plane perpendicular to the central axis of the pipe, and a holder is mounted on the rail or / and the gear. The traveling device unit 30 is mounted so that it can travel. Next, the personal computer 37 gives a traveling command for one rotation to the motor driver 34 via the interface 36, and the motor driver 34 causes the traveling device 3 on the rail or / and the gear.
0 is run once around the circumference of the pipe. During this traveling, the magnetic anisotropy sensor 31 (the same as the magnetostrictive sensor 22) is moved from the sensor 31 at each angular position between 0 ° and 360 ° on the outer peripheral surface of the pipe shown in FIG. 7B. The detected detection signals are amplified by the magnetostriction measuring unit 33 and output, and the output is quantized by the A / D converter 35 and supplied to the personal computer 37. The personal computer 37 displays the sensor output value for each angle indicating the azimuth on the tube outer circumference of the magnetic anisotropy sensor 31 on the data display unit 38, and outputs a hard copy by a printer not shown if necessary. The flat stress estimation processing of the pipe according to the present invention can be performed based on the data displayed on the data display unit 38 of the measuring device or the hard copy data output by the printer.

FIGS. 11A to 11C are views for explaining a method of approximating the flat stress of the pipe according to the present invention by the SIN2θ curve. FIG. 11A is a diagram showing the magnetostrictive sensor output in the flat stress state of the pipe, and each magnetostrictive sensor output (unit is bolt) with respect to the angle indicating the azimuth on the pipe circumference of the magnetostrictive sensor is shown by + marks. There is.

FIG. 11 (b) is a diagram showing deviation values obtained by subtracting the SINθ approximate value from the magnetostrictive sensor output of FIG. 11 (a). Each deviation value for the same angle as in FIG. 11 (a) ( The unit is volt) and each is shown by + mark.

FIG. 11 (c) is a diagram showing the deviation value shown in FIG. 11 (b) and the SIN2θ approximation curve that approximates the deviation value, and the + sign indicates the same angle as in FIG. 11 (b). The deviation value (unit is volt), and the solid line shows the SIN2θ approximate curve. The deviation value obtained by subtracting the SINθ approximate value from the stress measurement value in the flat state of the pipe according to FIG. 11C is 1/2 of that of the magnetostrictive sensor when the magnetostrictive sensor makes one rotation along the pipe circumferential direction. It can be seen that it can be approximated by the SIN2θ curve that periodically changes with each rotation.

FIG. 12 shows positions 4a, 4b and 4c in the straight pipe portion 4 of FIG. 2 obtained in the same manner as in FIG. 11 (c) described above.
Voltage V corresponding to the maximum stress value σ1max at each position of
It is a figure which shows a, Vb, and Vc. Thus the amplitudes Va, V
By obtaining b and Vc, the maximum value σ1 of the stress in the circumferential direction at the corresponding positions 4a, 4b and 4c is obtained.
max can be easily obtained.

Instead of the above-mentioned magnetostrictive stress measuring method, it is also possible to measure the circumferential stress at each position 4a, 4b, 4c of the straight pipe portion 4 by another method. For example, it is possible to irradiate each position 4a, 4b, 4c of the straight pipe portion 4 with X-rays to measure the crystal lattice, and thereby to find the stress in the circumferential direction. Furthermore, each position 4a, 4b, 4c of the straight pipe part 4
It is also possible to measure the stress in the circumferential direction at each of the positions 4a, 4b, 4c by applying a sound wave to, and from the correspondence between the acoustic elasticity and the stress. INDUSTRIAL APPLICABILITY The present invention can be implemented not only in the context of underground steel pipes, but also in a wide range of applications in relation to pipes buried in concealed parts such as in concrete and in water.

[0026]

As described above, according to the present invention, the concealed portion is provided with the curved pipe portion, and the straight pipe portion connected to the curved pipe portion is exposed from the concealed portion. The stress or strain of the curved pipe can be estimated by measuring the stress in the circumferential direction of the pipe or the strain caused by the stress. Therefore, the stress acting on the bend or its strain can be easily and easily performed. Can be estimated.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining an embodiment of the present invention.

2 is a diagram showing a straight pipe portion 4, a curved pipe portion 5, and a straight pipe portion 6 having the configuration shown in FIG.

FIG. 3 is a graph showing a relationship between a maximum stress σ1max in the circumferential direction of the straight pipe portion 4 and a maximum strain ε1max due to the stress.

FIG. 4 shows the maximum strain ε1 at the position 4a of the straight pipe portion 4.
max and the maximum strain ε2 at the position 5a of the curved tube portion 5
It is a graph which shows the relationship with max.

FIG. 5 is a maximum value σ1ma of stress in the circumferential direction at each position in the pipe axis direction along the pipe axis direction of the straight pipe portion 4 according to another embodiment of the present invention.
It is a graph which shows the relationship with x.

6 is a maximum value ε2ma of circumferential strain at a position 5a of the curved pipe portion 5 corresponding to the inclinations α1 and α2 shown in FIG.
It is a graph which shows the relationship with x.

7 (a) and 7 (b) are diagrams explaining a magnetostrictive stress measuring method.

8A and 8B are diagrams illustrating the SIN approximation method based on the magnetostrictive stress measurement method of FIG. 7.

FIG. 9 (a) is a diagram showing a stress state when the pipe is flat.

9 (b) is a diagram showing a magnetostrictive sensor output in the state of FIG. 9 (a).

FIG. 10 is a block diagram of a pipe stress measuring device to which the pipe flat stress estimation method of the present invention is applied.

11 (a) to 11 (c) are diagrams illustrating a method of approximating the flat stress of a pipe according to the present invention by a SIN2θ curve.

12] Positions 4a, 4 of the straight pipe portion 4 in FIG. 2 described above.
It is a figure which respectively shows output voltage Va, Vb, Vc respectively corresponding to stress (sigma) 1max in the circumferential direction in b, 4c.

[Explanation of symbols]

 1 Bridge 2 Soil 3 Abutment 4, 6, 8 Straight pipe section 5, 7 Curved pipe section

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akifumi Kamiura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Nobuhisa Suzuki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Date Inside the Steel Pipe Co., Ltd. (72) Inventor Sadaaki Sakai 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside the Nippon Steel Pipe Co., Ltd.

Claims (1)

[Claims] 1. A curved pipe portion is provided in a concealed portion, a straight pipe portion connected to the curved pipe portion is exposed, and stress in the circumferential direction of the straight pipe portion or strain due to the stress is measured, and A method for estimating stress or strain in a curved pipe portion, comprising estimating stress in the curved pipe portion or strain due to the stress from the measurement result.