Calibration device and calibration method

Abstract

To calibrate an electrostatic capacitance type strain sensor with higher accuracy.SOLUTION: A strain sensor calibration device for measuring a strain of a metal pipe from the change in an electrostatic capacitance of a capacitor formed so that first and second electrodes are arranged in a metal pipe includes a rod-like metal piece, a first fixture that is fixed to a first position of the metal piece and is mounted with the first electrode, a second fixture that is fixed to a second position separated from the first position by a gauge distance, and is mounted with the second electrode, a traction machine of the metal piece, a length measuring device for measuring the gauge distance, an electrostatic capacitance measuring device for measuring an electrostatic capacitance, a high temperature furnace capable heating the metal piece, and the first and second fixtures, a first rod whose one end side is fixed to the first fixture and the other end side extends to the outside of the high temperature furnace, and a second rod whose one end side is fixed to the second fixture and the other end side extends to the outside of the high temperature furnace, wherein the length measuring device measures an interval between the first and second measurement positions regulated on the first and second rods in the outside of the high temperature furnace, and thereby measures the gauge length.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a calibration device and a calibration method. [Background technology]

[0002] Metal pipes that are exposed to high temperatures for long periods of time, such as large-diameter high-temperature steam pipes used in boilers and turbines, develop a type of distortion called creep strain due to the effects of heat and stress from years of use.

[0003] For this reason, technology has been developed to measure the amount of strain by attaching a strain sensor to the surface of a metal pipe.

[0004] For example, a capacitance-type strain sensor has been developed that places two electrode plates facing each other across a weld and measures the amount of strain in the weld from the change in capacitance between the electrode plates (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6573051 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the creep strain that occurs in metals in a high-temperature environment is an extremely small value, on the order of micrometers, and extremely high accuracy is required for a capacitive strain sensor that performs measurements in such a high-temperature environment.

[0007] Therefore, there is a demand for a calibration device and a calibration method that are capable of calibrating such a capacitive strain sensor with higher accuracy in a high-temperature environment.

[0008] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a calibration device and a calibration method that are capable of calibrating a capacitive strain sensor with higher accuracy in a high-temperature environment. [Means for solving the problem]

[0009] The calibration device for solving the above problem is a strain sensor calibration device that forms a capacitor by arranging a first electrode and a second electrode facing each other in the longitudinal direction of a metal tube, and measures the strain of the metal tube from a change in the capacitance of the capacitor, and includes a rod-shaped metal piece corresponding to the metal tube, a first fixture that is fixed to a first position of the metal piece and has the first electrode attached thereto so as to face the second electrode, a second fixture that is fixed to a second position spaced apart from the first position of the metal piece by a gauge length and has the second electrode attached thereto so as to face the first electrode, a towing machine that tows the metal piece in the longitudinal direction, and a calibration device that measures the gauge length at multiple measurement timings while towing the metal piece. the measurement apparatus comprises a length measuring device for measuring the distance between the first measurement position and the second measurement position, a capacitance measuring device for measuring the capacitance of the capacitor at each measurement timing, a high-temperature furnace capable of housing and heating the metal piece, the first fixing device, and the second fixing device, a first rod having one end fixed to the first fixing device and the other end extending outside the high-temperature furnace along the longitudinal direction of the metal piece, and a second rod having one end fixed to the second fixing device and the other end extending outside the high-temperature furnace along the longitudinal direction of the metal piece, and the length measuring device measures the gauge length by measuring the distance between a first measurement position defined on the first rod outside the high-temperature furnace and a second measurement position defined on the second rod outside the high-temperature furnace.

[0010] In addition, the problems and solutions disclosed in this application will be made clear by the description in the section of the preferred embodiment of the invention and the descriptions in the drawings. Effect of the Invention

[0011] It becomes possible to calibrate the capacitive strain sensor with higher accuracy. [Brief description of the drawings]

[0012] [Figure 1] FIG. [Diagram 2] FIG. 4 is a diagram showing a characteristic curve of the capacitive strain sensor. [Diagram 3] FIG. [Figure 4A] FIG. [Figure 4B] FIG. [Figure 5A] FIG. [Figure 5B] FIG. [Figure 6A] FIG. [Figure 6B] FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] At least the following matters will become apparent from the description of this specification and the accompanying drawings. Hereinafter, the present invention will be described in detail based on an embodiment thereof with reference to the accompanying drawings.

[0014] ==First embodiment== FIG. 1 shows the overall configuration of a calibration device 100 according to a first embodiment of the present invention.

[0015] The calibration device 100 is a device for calibrating a strain sensor 300 that measures the amount of strain occurring at a welded portion of a metal pipe (not shown) such as a piping or a large-diameter high-temperature steam pipe used in a boiler or turbine.

[0016] The strain sensor 300 is attached to the surface of a large-diameter high-temperature steam pipe in a thermal power plant, for example, and measures strain occurring in a welded portion of high-chromium steel used in the large-diameter high-temperature steam pipe.

[0017] The strain sensor 300 is configured to have a first electrode 310 and a second electrode 320 that are attached in the longitudinal direction of the metal tube so as to straddle the welded portion of the metal tube, and the first electrode 310 and the second electrode 320 are arranged facing each other to form a capacitor.

[0018] The strain sensor 300 detects the amount of strain occurring in the metal tube as a change in the capacitance C of this capacitor.

[0019] The amount of strain generated in the metal tube appears as a change in the distance d shown in Figure 1. However, since the amount of strain in the metal tube is an extremely small value in the order of micrometers, it is necessary to precisely reproduce the distance d when calibrating the strain sensor 300.

[0020] Therefore, the calibration device 100 of this embodiment comprises a rod-shaped metal piece 110 corresponding to the metal tube, a first fixture 121 fixed to a first position of the metal piece 110, a second fixture 122 fixed to a second position of the metal piece 110, a towing machine 130 that tows the metal piece 110 in the longitudinal direction while calibration is being performed, a length measuring device 140 such as a linear gauge that measures the gauge length L between the first position and the second position while towing the metal piece 110, and a capacitance measuring device 150 that measures the capacitance C of a capacitor formed by a first electrode 310 attached to the first fixture 121 and a second electrode 320 attached to the second fixture 122 while calibration is being performed.

[0021] The first electrode 310 is configured to have a first support 311 and a first electrode plate 312, and the first support 311 is fixed to the first fixture 121. The second electrode 320 is configured to have a second support 321 and a second electrode plate 322, and the second support 321 is fixed to the second fixture 122.

[0022] The first electrode 310 and the second electrode 320 are mounted such that the first electrode plate 312 and the second electrode plate 322 that store electric charge face each other, thereby forming a capacitor.

[0023] In this embodiment, the metal piece 110, which is likened to a metal pipe, is pulled by the pulling machine 130 to generate creep strain, thereby reproducing minute changes in the distance d similar to those in the case where the strain sensor 300 is attached to the metal pipe, and the distance d and the capacitance C can be measured very accurately. This makes it possible to calibrate the strain sensor 300 more accurately.

[0024] In addition, the strain sensor 300 of this embodiment forms a capacitor by arranging the first electrode 310 and the second electrode 320 facing each other in the longitudinal direction of the metal tube, and measures the strain of the metal tube from the change in the capacitance C of this capacitor.

[0025] When calibrating this strain sensor 300, first, the first electrode 310 is attached to the first fixture 121, which is fixed to a first position of the rod-shaped metal piece 110 corresponding to the metal pipe, so as to face the second electrode 320.

[0026] Then, a second electrode 320 facing the first electrode 310 is attached to a second fixture 122 fixed to a second position spaced apart by the gauge length L from the first position of the metal piece 110 .

[0027] Thereafter, the metal piece 110 is pulled in the length direction, and the gauge length L and the capacitance C of the capacitor are measured at multiple measurement timings during the pulling.

[0028] Of course, when the strain sensor 300 is attached to the calibration device 100, the difference between the gauge length L and the distance d, which is necessary for conversion from the gauge length L to the distance d, is precisely measured in advance.

[0029] The calibration device 100 measures the gauge length L and the capacitance C at a plurality of measurement timings while the metal piece 110 is being pulled, thereby measuring an accurate characteristic curve of the strain sensor 300 as shown in FIG.

[0030] If the characteristic curve is outside the specified range, the strain sensor 300 needs to be adjusted.

[0031] In the example shown in FIG. 1, the first position and the second position for specifying the gauge length L are merely examples, and other positions may be used.

[0032] ==Second embodiment== Next, a calibration device 100 according to a second embodiment will be described with reference to FIGS. 3, 4A, 4B, 5A, 5B, 6A, and 6B.

[0033] As shown in FIG. 3, the calibration apparatus 100 according to the second embodiment further includes an electric furnace 161 or a high-temperature furnace 160 capable of accommodating and heating the metal piece 110, the first fixture 121, and the second fixture 122, in comparison with the calibration apparatus 100 according to the first embodiment.

[0034] With this embodiment, creep strain can be induced in the metal piece 110 under the same temperature conditions as a metal pipe exposed to high temperatures, and minute changes in the distance d can be reproduced more accurately, similar to those observed when the strain sensor 300 is attached to a metal pipe at high temperatures, allowing extremely accurate measurement of the distance d and the capacitance C. This allows the strain sensor 300 to be calibrated more accurately.

[0035] Although the electric furnace 161 is an electric type that uses electricity to heat the inside of the furnace, any general high-temperature furnace 160 may be used, such as a gas type that heats the inside of the furnace by burning gas or a fuel oil type that heats the inside of the furnace by burning fuel oil, as long as it can heat the inside of the furnace and maintain it at a predetermined temperature. However, using the electric furnace 161 makes it possible to eliminate the need for equipment such as a supply path for fuel such as gas or fuel oil and an exhaust path for exhaust gas, and therefore allows the calibration device 100 to be configured more simply.

[0036] Moreover, the calibration device 100 according to the second embodiment further includes a first rod 171 and a second rod 172, as shown in FIGS. 4A, 4B, 5A, 5B, 6A, and 6B.

[0037] The first rod 171 is disposed along the length of the metal piece 110 such that one end is fixed to the first fixture 121 and the other end extends outside the high-temperature furnace 160. The second rod 172 is disposed along the length of the metal piece 110 such that one end is fixed to the second fixture 122 and the other end extends outside the high-temperature furnace 160.

[0038] The length measuring device 140 of the second embodiment measures the gauge length L by measuring the distance between a first measurement position defined on the first rod 171 outside the high-temperature furnace 160 and a second measurement position defined on the second rod 172 outside the high-temperature furnace 160.

[0039] In this case, when the strain sensor 300 is attached to the calibration device 100, the difference between the distance between the first measurement position and the second measurement position and the gauge length L, which is necessary to convert the distance between the first measurement position and the second measurement position to the gauge length L, is precisely measured.

[0040] According to this embodiment, it becomes possible to measure the gauge length L outside the high-temperature furnace 160, so that the gauge length L can be measured using a general length measuring device 140 used in a room temperature environment.

[0041] The first rod 171 and the second rod 172 may be one each, or may be two each as shown in FIGS. 4A, 4B, 5A, 5B, 6A, and 6B.

[0042] At this time, two first rods 171 are fixed to the first fixing device 121 on both sides thereof sandwiching the first electrode 310, and similarly, two second rods 172 are fixed to the second fixing device 122 on both sides thereof sandwiching the second electrode 320.

[0043] A first cross member 181 is provided outside the high-temperature furnace 160 so as to suspend two first rods 171 horizontally, thereby defining a first measurement position, and similarly, a second cross member 182 is provided outside the high-temperature furnace 160 so as to suspend two second rods 172 horizontally, thereby defining a second measurement position.

[0044] In this manner, the length measuring device 140 can measure the distance between the first cross member 181 and the second cross member 182, thereby enabling the gauge length L to be measured accurately.

[0045] In this case, it is preferable that the length measuring device 140 is made up of a first length measuring device 141 and a second length measuring device 142, as shown in FIGS. 4A, 4B, 6A, and 6B.

[0046] The first length measuring device 141 measures the distance between the first measurement position and the second measurement position near one end of the first cross member 181 and the second cross member 182. The second length measuring device 142 measures the distance between the first measurement position and the second measurement position near the other end of the first cross member 181 and the second cross member 182.

[0047] In this manner, it is possible to perform measurement with smaller error by adopting the average value of the measurement value by the first length measuring device 141 and the measurement value by the second length measuring device 142. Therefore, it is possible to measure the gauge length L more accurately.

[0048] 5B, the metal piece 110 may be formed in a constricted shape so that the cross-sectional area of ​​the specific portion 111 sandwiched between both ends of the metal piece 110 is smaller than the cross-sectional area of ​​other portions sandwiching the specific portion 111. In other words, the metal piece 110 may be formed so that the diameter of the specific portion 111 is reduced. In this manner, when the metal piece 110 is pulled by the towing machine 130, the reduced diameter specific portion 111 can be elongated.

[0049] A first position where the first fastener 121 is fixed to the other portion (non-reduced portion) between one end of the metal piece 110 and the specified portion 111 may be provided, and a second position where the second fastener 122 is fixed to the other portion (non-reduced portion) between the other end of the metal piece 110 and the specified portion 111 may be provided. In this manner, when the metal piece 110 is pulled by the pulling machine 130, the specified portion 111 of the metal piece 110 is stretched, and the amount of strain of the specified portion 111 appears as the gauge length L, i.e., the amount of change in the distance d between the first electrode 310 and the second electrode 320, so that the strain sensor 300 can be calibrated more accurately.

[0050] The calibration device 100 and the calibration method according to this embodiment have been described above. According to this embodiment, it is possible to calibrate the capacitive strain sensor 300 with higher accuracy.

[0051] Furthermore, since the amount of distortion in the welded portion of high chromium steel can be measured with high accuracy, it is possible to improve the accuracy of remaining life assessment of high chromium steel.

[0052] This will enable monitoring of the progression of damage to pipe welds in thermal power plants during operation, contributing to improved equipment reliability. It will also enable optimization of repair plans and cost reduction for piping systems that use high chromium steel.

[0053] The above-described embodiment is for the purpose of facilitating understanding of the present invention, and is not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit of the present invention, and equivalents thereof are also included in the present invention. [Explanation of symbols]

[0054] 100 Calibration equipment 110 Metal piece 111 Predetermined part 120 Fixtures 121 1st fixture 122 Second fixture 130 Traction machine 140 Length measuring device 141 First Length Measuring Instrument 142 Second Length Measuring Instrument 150 Capacitance Meter 160 High Temperature Furnace 161 Electric furnace 170 Rod 171 First Rod 172 Second Rod 180 Cross member 181 First cross member 182 Second cross member 300 Strain Sensor 310 1st electrode 311 First support 312 1st electrode plate 320 2nd electrode 321 Second support 322 Second electrode plate

Claims

1. A calibration device for a strain sensor that forms a capacitor by arranging a first electrode and a second electrode facing each other in a longitudinal direction of a metal tube, and measures a strain of the metal tube from a change in capacitance of the capacitor, A rod-shaped metal piece corresponding to the metal tube; a first fixture that is fixed to a first position of the metal piece and to which the first electrode is attached so as to face the second electrode; a second fixture that is fixed to a second position of the metal piece that is spaced apart from the first position by a gauge length and to which the second electrode is attached so as to face the first electrode; A traction machine that traction the metal piece in a length direction; a length measuring device that measures the gauge length at a plurality of measurement timings while the metal piece is being towed; a capacitance measuring device that measures the capacitance of the capacitor at each of the measurement timings; a high-temperature furnace capable of accommodating and heating the metal piece, the first fixture, and the second fixture; a first rod having one end fixed to the first fixture and the other end extending outside the high-temperature furnace along the length of the metal piece; a second rod having one end fixed to the second fixture and the other end extending outside the high-temperature furnace along the length of the metal piece; Equipped with A calibration device in which the length measuring device measures the gauge length by measuring the distance between a first measurement position defined on the first rod outside the high-temperature furnace and a second measurement position defined on the second rod outside the high-temperature furnace.

2. 2. The calibration device according to claim 1, The first rods are fixed to the first fixture on both sides of the first electrode, The second rods are fixed to the second fixture on both sides of the second electrode, a first cross member that crosses the two first rods outside the high-temperature furnace to define the first measurement position; a second cross member that crosses the two second rods outside the high-temperature furnace to define the second measurement position; A calibration device comprising:

3. 3. The calibration device according to claim 2, The calibration device includes a first length measuring device that measures the distance between the first measurement position and the second measurement position near one end of the first cross member and the second cross member, and a second length measuring device that measures the distance near the other end.

4. A calibration device according to any one of claims 1 to 3, The calibration apparatus, wherein the high-temperature furnace is an electric furnace.

5. A calibration device according to any one of claims 1 to 4, The metal piece is formed so that a cross-sectional area of ​​a predetermined portion sandwiched between both ends is smaller than a cross-sectional area of ​​other portions sandwiching the predetermined portion, the first position to which the first fastener is fixed is provided in the other portion between one end of the metal piece and the predetermined portion, A calibration device, wherein the second position to which the second fixture is fixed is provided in the other portion between the other end of the metal piece and the specified portion.

6. A method for calibrating a strain sensor in which a capacitor is formed by arranging a first electrode and a second electrode facing each other in a longitudinal direction of a metal tube, and a strain of the metal tube is measured from a change in capacitance of the capacitor, comprising: The first electrode is attached to a first fixture that is fixed to a first position of a rod-shaped metal piece corresponding to the metal tube, the first electrode being opposed to the second electrode; The second electrode is attached to a second fixture that is fixed to a second position spaced apart from the first position of the metal piece by a gauge length, and the second electrode is opposed to the first electrode; placing the metal piece, the first fixture, and the second fixture in a high-temperature furnace; One end of a first rod is fixed to the first fixture along the length of the metal piece, and the other end of the first rod is extended outside the high-temperature furnace; One end of a second rod is fixed to the second fixture along the length of the metal piece, and the other end of the second rod is extended outside the high-temperature furnace; The metal strip is pulled in a longitudinal direction while the high-temperature furnace is heated; measuring the gauge length by measuring an interval between a first measurement position defined on the first rod outside the high-temperature furnace and a second measurement position defined on the second rod outside the high-temperature furnace at a plurality of measurement timings while the metal piece is being towed; measuring the capacitance of the capacitor at each of the measurement timings; Calibration method.

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