JP5238578B2 - Surface temperature distribution detection device and pipe thinning detection method using the same - Google Patents

Description

  The present invention relates to a surface temperature distribution detection device for detecting a surface temperature distribution of a structure affected by heat, particularly a pipe in which a high-temperature fluid flows inside, and a pipe thickness reduction detection method using the same.

  Thermal power plants, nuclear power plants, and the like are provided with metal pipes through which high-temperature fluid flows. The pipe may have a thinned portion that is locally thinned by part of the peripheral wall being eroded from the inner surface due to corrosion or wear by the internal fluid. When the pipe is thinned, an opening is finally formed in a part of the pipe, and the internal high-temperature fluid leaks therefrom, which is extremely dangerous. Therefore, a technique capable of diagnosing the pipe thinning situation has been conventionally demanded.

  Conventionally, temperature distribution measurement using optical time domain reflectometry (OTDR) using an optical fiber as a technique capable of diagnosing the thinning situation of pipes, for example, as in Patent Document 1 and Patent Document 2 below. A method of detecting the temperature distribution on the pipe surface by an apparatus has been proposed. A temperature distribution measuring apparatus using the optical fiber is one in which pulsed laser light is incident on the optical fiber, and Raman scattered light intensity generated at each point in the optical fiber is detected by the incident pulsed laser light. Here, when a part of the pipe is thinned, the surface temperature of the thinned part is preferentially increased as compared with other parts. Therefore, this temperature distribution measuring device calculates the temperature of the scattered light generation location from the detection result of the Raman scattered light intensity by utilizing the fact that the Raman scattered light is sensitively dependent on the temperature of the scattered light generation location. It is something to detect. The scattered light generation location can be determined as the scattered light generated at which position in the fiber from the propagation time of the light in the optical fiber. Thereby, it can be specified in which part of the piping the thinned portion is generated.

JP 2003-156315 A Japanese Patent Laid-Open No. 10-207534

  However, the temperature distribution measurement method using OTDR using an optical fiber can detect a temperature change only at intervals of several tens of cm even if it is fine, and the distance resolution is low. In this case, the thinned portion cannot be accurately identified, and a problem remains in detection accuracy. In addition, the temperature distribution measurement method using the OTDR method using an optical fiber has a problem that it takes about one hour to obtain a measurement result and a long time is required for the measurement. When a long time is required for the measurement, even if the temperature change of the fluid appears as the temperature change of the thinned portion, the time change may be averaged and the temperature distribution may not be accurately detected. Therefore, when detecting the thinned portion from the temperature change, it is essential to capture a short-time temperature change such that the temperature change of the fluid appears as the temperature change of the thinned portion.

  Therefore, the present inventors have intensively studied whether or not the occurrence of thinning can be detected by more accurately detecting the temperature distribution of the pipe than the temperature distribution measuring method using OTDR using an optical fiber. Is indirectly detected as an impedance distribution using the electrical time domain reflection method, and it has been found that a high distance resolution with respect to a temperature change and an excellent response speed can be achieved, and the present invention has been completed. High distance resolution and excellent response speed with respect to temperature changes are required not only for piping through which high-temperature fluid flows, but also for general structures affected by heat. Therefore, an object of the present invention is to provide a surface temperature distribution detection device capable of accurately detecting the surface temperature distribution of a structure that is affected by heat, including piping, and a method for detecting pipe thinning using the same. .

  The above problems can be roughly solved by two forms (methods). First, in the first form of the surface temperature distribution detection device for detecting the surface temperature distribution of a structure affected by heat, such as a metal pipe through which a high-temperature fluid flows, the surface temperature distribution detection device is provided on the surface of the structure, A sensor unit that uses a structure as one electrode, and an electrical time domain reflector (hereinafter abbreviated as ETDR) that receives an electric pulse wave from one end of the sensor unit and detects the reflected wave. And an impedance measuring device that measures the impedance of the sensor unit from the detection signal detected by the electrical time domain reflection device. The sensor unit includes a dielectric layer bonded to the surface of the structure, a thermistor layer that is stacked on the dielectric layer, and has a resistivity that varies with temperature, and is stacked on the thermistor layer. The metal electrode is formed in a line shape narrower than the thermistor layer and constitutes the other electrode. And the surface temperature distribution of the structure resulting from the said thermal influence can be detected as an impedance distribution of the said sensor part based on the resistivity change of the thermistor layer, It is characterized by the above-mentioned. The thermistor layer may be an NTC (Negative Temperature Coefficient) thermistor whose resistivity decreases as the temperature rises, or a PTC (Positive Temperature Coefficient) thermistor whose resistivity increases as the temperature rises.

  The ETDR is a device that propagates micropulse waves intermittently transmitted by an electronic circuit through a transmission line, for example, a microstrip line, and receives the reflected micropulse waves. (Relation between impedance and position) is measured. This is called a time domain because only a small time domain is received for one transmission of a pulse wave. The microstrip line refers to a structure in which a dielectric layer is sandwiched between two electrodes that are arranged facing each other vertically or horizontally. The microstrip line constitutes a distributed constant circuit similar to a coaxial cable or the like and has a certain impedance distribution. In the present invention including the second embodiment described later, the impedance of the sensor unit is measured by the impedance measuring device while using the structure to be measured as one electrode in the microstrip line. That is, the sensor unit using the structure as one electrode constitutes a part of the microstrip line, and the metal electrode of the sensor part constitutes the other electrode in the microstrip line. If there are singular points (discontinuous points) with different impedances on the distributed constant circuit (microstrip line), when the incident pulse wave reaches that position, a part of it reflects and returns to the incident end. Is used.

  As described above, in the present invention, a dielectric layer exists between the structure as one electrode in the microstrip line and the metal electrode as the other electrode. In addition, the first embodiment is characterized in that a thermistor layer is provided between the dielectric layer constituting the sensor unit and the metal electrode. When the surface temperature of the structure increases, the resistivity of the thermistor layer also changes accordingly. If the surface temperature of the structure rises uniformly, the resistivity of the thermistor layer also changes uniformly as a whole. On the other hand, if the surface temperature of the structure has a difference (distribution) depending on the location, a difference (distribution) depending on the location also occurs in the resistivity of the thermistor layer according to the temperature distribution. For example, if a part of piping as a structure is thinned and the surface temperature of the thinned part is preferentially raised compared to other parts, a part of the thermistor layer on the thinned part is also The resistivity changes in preference to other parts. In this sense, the thermistor layer can also be called a temperature sensitive layer, and can constitute the other electrode in the microstrip line together with the metal electrode.

  For example, if the thermistor layer is an NTC thermistor layer, when the resistivity of the thermistor layer decreases as the surface temperature of the structure decreases, the thermistor layer can also function as the other electrode in the microstrip line. The apparent electrode area extends not only to the metal electrode but also to the thermistor layer. Thereby, since the electrostatic capacitance of a sensor part increases, the impedance of a sensor part falls. On the other hand, if the thermistor layer is a PTC thermistor layer, the resistivity of the thermistor layer increases as the surface temperature of the structure increases, so the apparent electrode area of the sensor section decreases from the initial thermistor layer to only the metal electrode. Will do. Thereby, since the electrostatic capacitance of a sensor part reduces, the impedance of a sensor part rises. The thermistor layer may be a bulk material (sintered body) of a material having the thermistor characteristics, but the resistivity changes according to the temperature (having thermistor characteristics) in the resin. A composite layer (composite) dispersed in is preferably used.

  The surface temperature distribution detection device according to the first embodiment having such an action can be used for a pipe thinning detection method. Specifically, a pipe thinning detection method for detecting pipe thinning in which a high-temperature fluid flows inside, wherein the pipe is used as one electrode on the surface of the pipe, and a dielectric layer is formed from the pipe side. A sensor portion in which a thermistor layer whose resistivity changes according to temperature and a metal electrode constituting the other electrode are laminated in this order is provided, and the surface of the thinned portion generated in a part of the pipe is When the temperature of the thermistor layer is preferentially higher than that of the other part due to the high-temperature fluid, the resistivity of a part of the thermistor layer at the high-temperature part also changes preferentially over the other part, and the apparent electrode area of the sensor unit changes. By utilizing this, an electric pulse wave is incident from one end of the sensor unit by an electrical time domain reflection device, and the impedance of the sensor unit is measured from the reflected wave by an impedance measurement device, so that it is superior to other parts. To impedance can detect wall thinning of the pipe due to the presence of the portion changes.

  Further, the second form of the surface temperature distribution detection device is provided on the surface of the structure, the sensor unit using the structure as one electrode, and an electric pulse wave is incident from one end of the sensor unit, An electrical time domain reflection device (ETDR) that detects a reflected wave, and an impedance measurement device that measures the impedance of the sensor unit from a detection signal detected by the electrical time domain reflection device. Here, the sensor unit includes a dielectric layer bonded to the surface of the structure, and a metal electrode that is laminated on the dielectric layer and serves as the other electrode. For the dielectric layer, a dielectric material whose relative dielectric constant varies with temperature is used. And the surface temperature distribution of the structure resulting from the said heat influence can be detected as an impedance distribution of the said sensor part based on the dielectric constant change of the said dielectric layer, It is characterized by the above-mentioned.

  In the surface temperature distribution detection device of the second embodiment, if the relative dielectric constant of the dielectric layer changes in accordance with the surface temperature rise of a structure such as a pipe, the capacitance of the sensor unit also changes proportionally. It can be detected as an impedance change. In this sense, the dielectric layer in the second embodiment can also be called a temperature sensitive layer. The dielectric layer here may also be a bulk plate made of a dielectric material, but is preferably a composite layer (composite) in which a large number of dielectric material particles are dispersed in a resin.

  The surface temperature distribution detection device of the second embodiment having such an action can also be used for the pipe thinning detection method. Specifically, a pipe thinning detection method for detecting thinning of a pipe through which a high-temperature fluid flows inside, wherein the pipe is used as one electrode on the surface of the pipe, and a relative permittivity is determined according to temperature. A sensor part comprising a dielectric layer containing a dielectric material that changes and a metal electrode laminated on the dielectric layer and serving as the other electrode, and the surface of the thinned part generated in a part of the pipe is the high temperature When the temperature is preferentially higher than that of the other part due to the fluid, the relative permittivity of a part of the dielectric layer at the high temperature part also changes preferentially over the other part, so that the electric power is supplied from one end of the sensor unit. An electrical pulse wave is incident by a dynamic time domain reflector, and the impedance of the sensor unit is measured from the reflected wave by an impedance measuring device, and the pipe thickness is reduced due to the presence of a part where the impedance changes preferentially over other parts. Inspect It can be.

  According to the surface temperature distribution detection device of the present invention, the surface temperature distribution of a structure that is affected by heat, such as piping, is detected as an impedance distribution. It can be detected more quickly and accurately than the temperature distribution measurement used. Specifically, the surface temperature distribution of the structure is sensed by a thermistor layer or a dielectric layer functioning as a temperature sensing layer of the sensor unit, and impedance based on this is measured. Since the impedance of the sensor unit can be measured almost in real time, the measurement (detection) time can be greatly shortened. Moreover, since the impedance distribution can be measured on the order of millimeters, the distance resolution is also high.

  Therefore, according to the thinning detection method for pipes using such a surface temperature distribution detection device, the thinning state can be detected and diagnosed more quickly and accurately than the thinning detection method using OTDR. If the thermistor layer or dielectric layer as a temperature sensitive layer is a composite layer in which ceramic particles are dispersed in a resin, it is more flexible than, for example, a bulk plate, and can be easily installed on the structure surface. At the same time, it is easy to follow the shape of the structure.

It is a partial fracture perspective view of piping which installed a surface temperature distribution detector. It is a principal part expanded sectional view of piping which installed the surface temperature distribution detection apparatus of the 1st form. It is a schematic diagram of piping and the thickness reduction part temperature distribution which installed the surface temperature distribution detection apparatus of the 1st form. It is a graph which shows the change of the impedance distribution accompanying a temperature rise in the surface temperature distribution detection apparatus of a 1st form. It is a graph which shows the relationship between the temperature change in the specific site | part on a sensor part, and an impedance change rate in the surface temperature distribution detection apparatus of a 1st form. It is a principal part expanded sectional view of piping which installed the surface temperature distribution detection apparatus of the 2nd form. It is a graph which shows the change of the impedance distribution accompanying a temperature rise in the surface temperature distribution detection apparatus of a 2nd form. It is a graph which shows the relationship between the temperature change in the specific site | part on a sensor part, and an impedance change rate in the surface temperature distribution detection apparatus of a 2nd form. It is a graph which shows the change of the impedance distribution accompanying the temperature rise in piping which has a thinning part.

  Hereinafter, embodiments of a surface temperature distribution detection device and a pipe thinning detection method using the surface temperature distribution detection device according to the present invention will be described with reference to the drawings. Various modifications can be made without departing from the scope. In particular, the embodiment in which the surface temperature distribution detection device is provided in the pipe will be described as a representative example. However, the surface temperature distribution detection device of the present invention can be applied to various structures as long as the temperature rises due to the influence of heat. Applicable.

[First embodiment]
First, the configuration of a surface temperature distribution detection device (hereinafter abbreviated as a temperature distribution detection device) will be described. The temperature distribution detector is installed in a pipe through which a high-temperature fluid of about 100 to 250 ° C. flows in a thermal power plant or a nuclear power plant. The pipe is made of a metal such as carbon steel and is formed in a long cylindrical shape. In addition, as shown in FIG. 1, the temperature distribution detection device is configured to detect an electric pulse wave incident from one end of the sensor unit 10 provided on the surface of the pipe 1 and the sensor unit 10 and detecting the reflected wave. A time domain reflection device (ETDR) 11, an impedance measurement device 12 that measures the impedance of the sensor unit 10 from a detection signal detected by the ETDR 11, and a display device 13 that displays a measurement result by the impedance measurement device 12. Have. The sensor unit 10 is provided in a line shape along the longitudinal direction of the pipe 1, and an electric pulse wave is incident from the ETDR 11 through a connector 14 fixed to one end of the sensor unit 10 in the longitudinal direction. As the impedance measuring device 12, for example, a digitizing oscilloscope can be used. A typical example of the display device 13 is a monitor, and is generally provided integrally with the impedance measuring device 12. Although FIG. 1 shows a state in which one sensor unit 10 is provided on the surface of the pipe 1, a plurality of sensor units 10 arranged along the longitudinal direction of the pipe 1 may be arranged side by side. Good. In this case, it is preferable to arrange the sensor units 10 at equal intervals in the circumferential direction. Each sensor unit 10 can be connected to one ETDR 11.

  As shown in FIG. 2, the sensor unit 10 includes a dielectric layer 15 bonded to the surface of the pipe 1, a thermistor layer 16 laminated on the dielectric layer 15, and a metal laminated on the thermistor layer 16. And electrode 17. The sensor unit 10 uses the pipe 1 as one electrode. That is, the sensor unit 10 is configured as a part of a microstrip line having a structure in which a dielectric layer is sandwiched between two electrodes arranged opposite to each other. The microstrip line includes a pipe 1 as one electrode in the microstrip line (hereinafter referred to as a lower electrode with reference to FIG. 2) and the other electrode in the microstrip line (hereinafter referred to as an upper electrode with reference to FIG. 2). And the dielectric layer 15 disposed between the electrodes 1 and 17. The thermistor layer 16 functions as a temperature-sensitive electrode that increases or decreases the apparent area of the sensor unit 10 according to the surface temperature distribution of the pipe 1.

  As the dielectric layer 15, a known resin or ceramic used as an interelectrode insertion material of a capacitor can be used. Among them, a material having excellent thermal stability, low dielectric loss, and low temperature dependence of dielectric loss. Is preferred. Examples of such materials include fluorine resins such as polytetrafluoroethylene (PTFE), polyimide resins, silicone resins, and the like. Since this temperature distribution detection device is a device that detects the distribution of the surface temperature of the pipe 1 through which a high-temperature fluid of about 100 to 250 ° C. flows, the dielectric layer 15 also requires a certain thermal stability (heat resistance). However, if a fluororesin such as polytetrafluoroethylene, a polyimide resin, a silicone resin, or the like, the physical properties are stable even in the temperature range. If the dielectric loss is low and the temperature dependence of the dielectric loss is small, the microstrip line can be lengthened, and a wide range of temperature distribution along the longitudinal direction of the long pipe 1 can be detected. When the dielectric layer 15 and the thermistor layer 16 are laminated, even if the thermistor layer 16 has a low resistance due to the surface temperature of the pipe 1, the DC component is blocked by the dielectric layer 15, so the dielectric loss does not increase. . The dielectric layer 15 has a long thin plate shape and is bonded to the surface of the pipe 1 along the longitudinal direction thereof. The surface temperature of the pipe 1 is transmitted to the thermistor layer 16 through the dielectric layer 15. Therefore, the thickness of the dielectric layer 15 is preferably as small as possible. A standard for the thickness of the dielectric layer 15 is about 0.01 to 0.5 mm. At least the thickness of the thermistor layer 16 is preferably not more than the thickness. Further, reducing the thickness of the dielectric layer 15 is also effective in suppressing radiation loss, which is a kind of transmission loss of the microstrip line in the sensor unit 10.

The thermistor layer 16 is a composite layer in which a large number of ceramic particles whose resistivity changes with temperature (having temperature dependency of resistivity) are dispersed in a resin base material. If the thermistor layer 16 is a composite layer, since it has a certain flexibility, the shape of the pipe 1 can be accurately followed. Therefore, the sensor unit 10 can be easily installed and the temperature distribution sensitivity is improved because the joining state with the pipe 1 is good. The ceramic having the thermistor characteristic may be a ceramic having an NTC characteristic (NTC ceramic) in which the resistivity decreases as the temperature rises, or a ceramic (PTC ceramic) having a PTC characteristic in which the resistivity increases as the temperature rises. Good. As the NTC ceramic, a material obtained by mixing and sintering oxides such as manganese (Mn), nickel (Ni), cobalt (Co), and iron (Fe) can be used. Among these, a MnNiCo-based oxide having a high resistivity temperature dependency and a low resistivity is preferable. Examples of the MnNiCo-based oxide include Mn _1.5 Ni _0.75 Co _0.75 O ₄ with Mn: Ni: Co = 2: 1: 1 and Mn _1.0 Ni _1.5 Co _0.5 O _{4 with} Mn: Ni: Co = 2: 3: 1. Etc. can be illustrated. As the PTC ceramic, one obtained by adding an additive to barium titanate (BaTiO ₃ ) can be used. This utilizes the property that barium titanate rapidly increases in electrical resistance near the Curie temperature. Note that PTC materials include polymer PTCs in which conductive particles such as carbon black and nickel are dispersed in a low melting point polymer, but they are not suitable for the present invention where heat resistance is required. In comparison between the NTC thermistor and the PTC thermistor, an NTC thermistor in which the change in resistivity with respect to temperature is proportional (linear) is preferable.

  As the resin (polymer) that becomes the base material (ceramic particle dispersion medium) of the thermistor layer 16, a material having a certain degree of flexibility when molded and having good heat resistance is used. Preferably, the resin has a heat resistance of 250 ° C. or higher. Examples of such heat-resistant resins include aramid (aromatic polyamide), polyimide, polyamideimide, polyphenylene sulfide, polyetherimide, polyethylene terephthalate, polyether nitrile, polyether ether ketone, polybenzimidazole, and polyarylate. . The particle size of the ceramic particles is not particularly limited, but may be about 0.01 to 500 μm in consideration of ease of production and dispersibility in the resin base material. Preferably it is about 0.1-250 micrometers. Since the ceramic particles are the main material exhibiting the function of the thermistor layer 16, it is preferable to disperse them as much as possible in the resin base material. Specifically, the ratio of the ceramic particles in the thermistor layer 16 is 50 to 95 vol%, preferably 60 to 90 vol%. When the ratio of the ceramic particles in the thermistor layer 16 is low, the sensitivity of the surface temperature of the pipe 1 is lowered, and consequently the detection accuracy of the temperature distribution detector is lowered. On the other hand, when the ratio of the ceramic particles in the thermistor layer 16 is too large, the mechanical strength and flexibility are lowered.

  The thermistor layer 16 has the same length as the dielectric layer 15. This is because the thermistor layer 16 functions as a temperature sensing layer in the sensor unit 10, and if the thermistor layer 16 is shorter than the dielectric layer 15 or the metal electrode 17, the temperature distribution detection range by the sensor unit 10 is substantially shortened. . The width of the thermistor layer 16 is not particularly limited as long as it is larger than the metal electrode 17 as will be described later, but may be the same width as the dielectric layer 15. This is because if the thermistor layer 16 exceeds the width of the dielectric layer 15, the surface of the pipe 1 and the metal electrode 17 are short-circuited when the thermistor layer 16 has a low resistance at a high temperature. On the other hand, when the thermistor layer 16 is narrower than the dielectric layer 15, the region of the thermistor layer 16 functions as a transmission line. That is, it is preferable that the thermistor layer 16 and the dielectric layer 15 have the same area. The thickness of the thermistor layer 16 may be about 0.1 to 1.0 mm.

The metal electrode 17 is made of a metal such as Cu (resistivity 1.72 × 10 ⁻⁸ Ωm) or Ag (resistivity 1.62 × 10 ⁻⁸ Ωm) having good conductivity, and both ends of the sensor unit 10 in the longitudinal direction. It is formed in a line shape. As the conductivity of the metal electrode 17 is higher, the transmission loss (especially conductor loss) of the microstrip line in the sensor unit 10 can be reduced. The metal electrode 17 can be laminated on the thermistor layer 16 by adhesion, printing, coating, spraying, or the like. The metal electrode 17 is provided in the center of the thermistor layer 16 in the width direction. If the metal electrode 17 is shifted in any direction in the width direction on the thermistor layer 16, the apparent increase or decrease in the area of the upper electrode by the thermistor layer 16 will vary, making it impossible to detect an accurate temperature distribution. Further, the width of the metal electrode 17 is made smaller than the width of the thermistor layer 16. This is to ensure the effect of increasing or decreasing the area of the upper electrode by the thermistor layer 16. Therefore, the difference between the width of the metal electrode 17 and the width of the thermistor layer 16 is preferably made as large as possible. Specifically, the width of the metal electrode 17 is set to at least ½ or less of the width of the thermistor layer 16. Preferably, the width of the metal electrode 17 is 1/10 or less of the width of the thermistor layer 16, more preferably 1/20 or less. The greater the difference between the width of the metal electrode 17 and the width of the thermistor layer 16 (the narrower the width of the metal electrode 17), the more significant the amount of impedance change with respect to temperature change. The relationship between the metal electrode 17 and the dielectric layer 15 is not particularly limited. However, if the thickness of the metal electrode 17 is about 1.5 to 2.5 times the thickness of the dielectric layer 15, the conductor loss can be reduced. It is advantageous.

  Next, a mechanism (action) for detecting the surface temperature distribution of the pipe 1 using the temperature distribution detection device will be described. In the unheated state in which the high-temperature fluid is not flowing in the pipe 1 and the surface temperature of the pipe 1 is not increased, the temperature of the thermistor layer 16 that is the temperature sensing layer of the sensor unit 10 is not increased. In this unheated state, if the thermistor layer 16 is an NTC thermistor layer, the initial resistivity is high, and the substantial electrode area of the sensor unit 10 is equal to the area of the metal electrode 17. On the other hand, if the thermistor layer 16 is a PTC thermistor layer, the initial resistivity is low, and the substantial electrode area of the sensor unit 10 is equal to the area of the thermistor layer 16. At this time, an electric pulse wave is incident on the sensor unit 10 from the ETDR 11 via the connector 14, and the reflected pulse wave is detected by the ETDR 11. Then, based on the detection signal from the ETDR 11, the impedance measuring device 12 measures the impedance of the sensor unit 10 according to a predetermined program, and the result is displayed on the display device 13. The impedance distribution at this time is uniform (room temperature) because the surface temperature of the pipe 1 is uniform, the resistivity distribution of the thermistor layer 16 is uniform, and there is no region showing unique reflection in the propagation of the incident pulse wave. Observed.

  On the other hand, when a high-temperature fluid flows in the pipe 1 and the surface temperature of the pipe 1 rises and the temperature is transmitted to the thermistor layer 16 and the thermistor layer 16 also rises in temperature, the resistivity is the NTC thermistor layer. The conductivity is reduced and the substantial electrode area of the sensor unit 10 becomes equal to the area of the thermistor layer 16. That is, as the apparent electrode area of the sensor unit 10 increases, the capacitance increases, and the impedance of the sensor unit 10 decreases. On the other hand, in the case of the PCT thermistor layer, the apparent electrode area of the sensor unit 10 is reduced to the area of the metal electrode 17 by increasing the resistivity as the temperature rises. Thereby, since the electrostatic capacitance of the sensor part 10 falls, the impedance of the said sensor part 10 increases. In addition, if the pipe 1 has no thinned portion and the surface temperature of the pipe 1 is increased substantially uniformly, the impedance distribution of the sensor unit 10 associated therewith also increases or decreases substantially uniformly over the entire longitudinal direction. .

  On the other hand, if the thinned portion 1E occurs in a part of the pipe 1 (see FIG. 1), a difference (distribution) occurs in the surface temperature change between the normal portion and the thinned portion of the pipe 1. Although a detailed mechanism will be described later, when a singular point (discontinuous point) exists in the impedance distribution of the sensor unit 10, a part of the incident pulse wave is reflected at the singular point and returns to the incident end. The greater the amount of change in impedance at this singular point, the greater the amplitude of the reflected pulse wave. In addition, since the electric pulse wave has a constant propagation speed, there is a time delay between the incident of the electric pulse wave and the return of the reflected pulse wave. By measuring this delay time, the position where the electric pulse wave is reflected can be identified from a simple relationship of speed × time. That is, the distribution of the surface temperature change amount can be diagnosed as a function of position from the amplitude and delay time of the reflected pulse wave obtained from one measurement result, and the thinned portion 1E can be detected from the distribution of the surface temperature change.

  Based on this premise, a method for detecting the thinning of the pipe 1 will be described. When the high-temperature fluid flows in the pipe 1, the pipe 1 is corroded or worn by the internal fluid while being heated. When this state is repeated or continued, the peripheral wall of the pipe 1 is eroded from the inner surface, and as shown in FIG. When the high-temperature fluid is caused to flow again in the pipe 1 in the state where the thinned portion 1E exists, the surface temperature of the thinned portion 1E precedes other parts as shown by the oblique lines in FIG. ) Easy to heat up. Along with this, the resistivity of a part of the thermistor layer 16 at the high temperature part also changes preferentially over other parts, and the apparent electrode area of the sensor unit 10 changes. Specifically, if the thermistor layer 16 is an NTC thermistor, the resistivity decreases in the range of the hatched portion in FIG. 3, and the apparent electrode area of the sensor unit 10 becomes an area as indicated by the shaded portion, and the thickness is reduced. Only the impedance of the part corresponding to the part 1E is greatly reduced as compared with other parts. On the other hand, if the thermistor layer 16 is a PTC thermistor layer, the resistivity in the shaded area in FIG. 3 rises preferentially over other parts, and the apparent electrode area of the sensor unit 10 in this part is the metal electrode 17. It becomes the area. As a result, only the impedance of the portion corresponding to the thinned portion 1E is greatly increased compared to other portions. Then, by monitoring the impedance distribution of the peculiar sensor unit 10 with the display device 13 in this way, or when the arithmetic processing unit detects that the impedance distribution has changed in comparison with the reference impedance distribution in the steady state, a warning is given. Is displayed on the display device 13 or an alarm sounds, so that the position and progress of the thinned portion can be detected and diagnosed.

Next, a detection test using the temperature distribution detection device of the first embodiment will be described. In this detection test, an NTC thermistor suitable as the thermistor layer was used as an example. A test piece made of a SUS430 metal plate having a length of 80 mm, a width of 10 mm, and a thickness of 1 mm was used as a simulated pipe. As the dielectric layer, a commercially available PTFE film (manufactured by Nitto Denko Corporation, Nitoflon, 902UL, thickness 0.1 mm) was used and cut into the same area as the test piece. For the thermistor layer, Mn ₃ O ₄ (99.9%), NiO (99.9%), and Co ₃ O ₄ (99.9%) powders manufactured by Kojundo Kagaku Co., Ltd. were used. The MnNiCo-based oxide obtained by mixing and firing so as to be 2: 1: 1 is pulverized, and the powder is a polyimide resin having a glass transition temperature Tg of 295 ° C. and excellent heat resistance (Rika Coat SN, manufactured by Shin Nippon Rika Co., Ltd.). A composite was prepared by dispersing it at a ratio of 80 vol% to -20). The composite as the thermistor layer was formed to a thickness of 0.3 mm with the same area as the PTFE film. Finally, a 1 mm wide Cu line as a metal electrode is laminated at the center in the width direction on the composite to form a sensor part comprising a dielectric layer, an NTC thermistor composite layer, and a Cu electrode. Bonded with a resin (E-209, manufactured by Konishi Bond Co., Ltd.). An SMA connector was installed at one end of the test piece and the sensor unit to provide an incident end for incident pulse waves. The end located on the opposite side of the incident end is open.

A section of about 3 cm from the end of the test piece to which the sensor unit was joined was placed on a hot plate to enable heating. The remaining section was brought into contact with the metal plate held near the freezing point by the cooling unit. A coaxial cable is fixed to one end of the sensor via an SMA connector, and connected to a digitizing oscilloscope (Agilent Technology, 54750A) incorporating an ETDR unit (Agilent Technology, 54754A), and the measured impedance distribution Was taken in by a measurement program (VEE Pro, manufactured by HP). In order to evaluate the temperature dependence of this impedance distribution, the temperature of the hot plate was raised stepwise from 40 ° C. to 240 ° C. at 20 ° C. intervals. FIG. 4 shows the impedance change rate distribution at this time. The impedance change rate is a value obtained by dividing the impedance change amount ΔZ at the time of temperature change by the impedance Z ₀ in the initial state. The horizontal axis in the graph of FIG. 4 is the distance position from the electric pulse wave incident end in the sensor unit. In this graph, a section of 5 to 8 cm is a heating section. FIG. 5 shows the relationship between the temperature change and the impedance change rate at a position 7.5 mm from the incident end of the sensor unit.

  From the result of FIG. 4, when only a part of the test piece (section of 5 to 8 cm on the horizontal axis in the graph) is preferentially heated compared to other parts, the impedance corresponding to the part is also changed accordingly. It can be seen that the distribution changes preferentially as compared with the region. This is due to the fact that the resistivity of the NTC thermistor layer decreases as the temperature rises, and the apparent electrode area of the sensor section (apparent upper electrode area in the microstrip line) increases. As a result, a thinned part occurs in a part of the pipe, and when the surface temperature of the thinned part is preferentially raised over other parts, the impedance distribution of the part is also greatly varied in preference to other parts. Thus, it was confirmed that the thinning condition of the pipe can be detected and diagnosed depending on the presence or absence and degree of the singularity. Note that the measurement of each impedance distribution is completed within 10 seconds, and high-speed measurement is possible. Further, when the result of FIG. 5 is seen, if the sensor unit configured as described above has an impedance change rate of about 8% with respect to a temperature change of 100 ° C., and the impedance is linear with respect to the temperature. Since it has changed, it has also confirmed that it was suitable as a temperature distribution sensor and by extension as a temperature distribution detection apparatus.

[Second form]
In the first embodiment, the resistivity of the sensor unit 10 is changed in accordance with the temperature change. However, the relative permittivity may be changed. Below, the temperature distribution detection apparatus of the structure (2nd form) which changes the relative dielectric constant of a sensor part and the thinning detection method of piping using this are demonstrated.

  The temperature distribution detection device of the second embodiment also has a sensor unit 20 provided in a line shape along the longitudinal direction of the pipe 1 and an electric pulse wave from one end of the sensor unit 20 via the connector 14. An electrical time domain reflection device (ETDR) 11 that enters and detects the reflected wave, an impedance measurement device 12 that measures the impedance of the sensor unit 20 from the detection signal detected by the ETDR 11, and the impedance measurement device 12 The point having the display device 13 for displaying the measurement result is similar to the first embodiment (see FIG. 1). The sensor unit 20 also uses the pipe 1 as a lower electrode in the microstrip line. However, in the second embodiment, as shown in FIG. 6, the sensor unit 20 includes a dielectric layer 25 joined to the surface of the pipe 1 and a metal electrode 27 laminated on the dielectric layer 25. ing. That is, in the second form, there is no thermistor layer as in the first form. Therefore, the metal electrode 27 of the sensor unit 20 becomes the upper electrode in the microstrip line as it is.

  The dielectric layer 25 is a composite layer (composite) in which dielectric material particles whose relative dielectric constant changes according to temperature are dispersed in a resin base material. Thereby, the dielectric layer 25 has a certain flexibility and can be made to correspond exactly to the shape of the pipe 1. The detailed effect of using the dielectric layer 25 as a composite layer is the same as that of the thermistor layer 16 of the first embodiment.

  As the resin serving as a dispersion medium for the dielectric material, a fluororesin such as polytetrafluoroethylene (PTFE) or tetrafluoroethylene-ethylene copolymer resin (ETFE), or a silicone resin can be used. Fluorine resins such as PTFE and ETFE have stable dielectric characteristics even in a high temperature region. ETFE is preferred in that it has higher moldability than PTFE. Silicone resin has low dielectric loss and good stability in a high temperature region such as relative permittivity. A silicone resin is preferable to a fluororesin in terms of high flexibility when formed into a resin molded product. Strictly speaking, the silicone resin has a tendency that the relative dielectric constant decreases as the temperature rises. However, since this tendency is consistent with the essence of the invention, this point is also preferable. As the silicone resin, methyl silicone resin (KR-242A manufactured by Shin-Etsu Silicone) or methylphenyl silicone resin (KR-271 manufactured by Shin-Etsu Silicone) can be used. Methyl silicone resin has a relatively low viscosity and is suitable as a dispersion medium. Since the polyimide used in the first embodiment has a high dielectric loss at a high temperature, it cannot be used in the second embodiment utilizing the temperature dependence of the relative permittivity.

The dielectric material may be paraelectric or ferroelectric. Examples of the dielectric material include BaTiO ₃ , SrTiO ₃ , CaTiO ₃ , Ba (Ti, Zr) O ₃ , Ba (Ti, Sn) O ₃ , (Ba, Ca) TiO ₃ , (Sr, Ca) TiO ₃ , ( Na, Cd) NbO ₃ , (Na, Sr) NbO ₃ , (Sr, Ba) Nb ₂ O ₆ , Ba (In, Nb) O ₃ , (Ba, Na) ₃ (Nb, Ti) ₅ O ₁₅ , PdTiO ₃ , PdZrO ₃ , PdHfO ₃ , Pd (Sc, Nb) O ₃ , Pd (Zn, Nb) O ₃ , (Sr, Pd) TiO ₃ , (Ba, Pd) TiO ₃ , KNbO ₃ , K (Ta, Nb ) O ₃ . Among these, BaTiO ₃ that exhibits a large change in relative dielectric constant around the Curie temperature of 125 ° C., and SrTiO ₃ whose relative dielectric constant is close to the relative dielectric constant of a resin substrate described later are preferable. Furthermore, SrTiO ₃ having a low relative dielectric constant and a high temperature-dependent linearity is more preferable. If the relative dielectric constant of the dielectric material is low, the decrease in the dielectric constant change with respect to temperature is small even when the dielectric material is combined with the resin, and the dielectric loss of the sensor unit 20 can be reduced. The particle size of the ceramic particles is not particularly limited. The standard of the particle size is the same as in the first embodiment. The volume ratio of the dielectric material in the composite (dielectric layer 25) is 80 vol% or less, preferably 60 vol% or less. Regarding the dispersion ratio, a volume ratio at which the temperature sensitivity of the dielectric layer 25 is the highest can be selected, but if the volume ratio exceeds a certain volume ratio, the flexibility of the composite is lost. On the other hand, when the ratio of the dielectric material in the dielectric layer 25 is too low, the impedance change rate with respect to the temperature change is deteriorated.

  The metal electrode 27 is the same as the metal electrode 17 of the first embodiment. The shapes and dimensions of the dielectric layer 25 and the metal electrode 27 are the same as in the first embodiment.

  Next, a mechanism (action) for detecting the surface temperature distribution of the pipe 1 using the temperature distribution detection device of the second embodiment will be described. The functions of the ETDR 11 and the impedance measuring device 12, the electric pulse wave reflection mechanism in the sensor unit 10, and the like are the same as in the first embodiment. When the temperature of the dielectric layer 25 rises as the surface temperature of the pipe 1 rises, the dielectric constant of the dielectric layer 25 changes depending on the characteristics of the dielectric material, and the capacitance also changes. Thereby, the impedance of the sensor unit 10 changes. Similar to the first embodiment, if the surface temperature of the pipe 1 has a distribution (singular point) depending on the location, the impedance distribution becomes non-uniform accordingly. Based on this premise, a method for detecting the thinning of the pipe 1 will be described. When the high-temperature fluid is caused to flow in a state where the thinned portion 1E is present in a part of the pipe 1 and the surface temperature of the thinned portion 1E is preferentially raised over other parts, the dielectric layer 25 in the high temperature part Some relative dielectric constants also change preferentially over other parts, and only the impedance of the part corresponding to the thinned portion 1E greatly changes compared with other parts. Other conditions, effects, and detection / diagnosis operations are the same as those in the first embodiment, and thus description thereof is omitted.

Next, a detection test using the temperature distribution detection device of the second embodiment will be described. A test piece made of a SUS430 metal plate having a length of 80 mm, a width of 10 mm, and a thickness of 1 mm was used as a simulated pipe. The dielectric layer was a composite in which SrTiO ₃ powder was dispersed in a methyl silicone resin (manufactured by Shin-Etsu Silicone, KR-242A) at a rate of 30 vol%. Since this SrTiO ₃ brings about a decrease in relative permittivity with increasing temperature, this dielectric layer also shows the same temperature dependence and is expected to bring about a decrease in capacitance and an increase in impedance with increasing temperature. . This dielectric layer had the same outer dimensions as the test piece and a thickness of 0.2 mm. As a metal electrode, an Ag line having a width of 1 mm was laminated at the center in the width direction on the dielectric layer. Such a sensor part was adhere | attached on the upper surface of the test piece with the epoxy resin (the Konishi bond company make, E-209). An SMA connector was installed at one end of the test piece and the sensor unit to provide an incident end for incident pulse waves. The end located on the opposite side of the incident end is open. In order to evaluate the temperature dependence of the impedance distribution, the temperature of the hot plate is gradually increased from 20 ° C. to 240 ° C. at intervals of 20 ° C. The temperature was raised. The impedance change rate distribution at this time is shown in FIG. The horizontal axis in the graph of FIG. 7 is also the distance position from the electric pulse wave incident end (SMA connector side) in the sensor unit. In this graph, a section of 5 to 8 cm is a heating section. Further, FIG. 8 shows the relationship between the temperature change and the impedance change rate at a position of 7.5 mm from the incident side end of the sensor unit.

  From the result of FIG. 7, when only a part of the test piece (5-8 cm section on the horizontal axis in the graph) is preferentially heated compared to the other parts, the impedance corresponding to the part is also changed accordingly. It can be seen that the distribution is preferentially increased as compared with the region. This is due to the fact that the dielectric constant of the dielectric layer has decreased with increasing temperature. As a result, a thinned part occurs in a part of the pipe, and when the surface temperature of the thinned part is preferentially raised over other parts, the impedance distribution of the part is also greatly varied in preference to other parts. Thus, it was confirmed that the thinning condition of the pipe can be detected and diagnosed depending on the presence or absence and degree of the singularity. Note that the measurement of each impedance distribution is completed within 10 seconds, and high-speed measurement is possible. Further, when looking at the result of FIG. 8, in the case of the sensor unit configured as described above, the impedance changes by about 6% with respect to a temperature change of 100 ° C., and the impedance is linear with respect to the temperature. Since it has changed, it has also confirmed that it was suitable as a temperature distribution sensor and by extension as a temperature distribution detection apparatus.

  Next, the detection test which assumed the case where a thinning part actually exists in a part of piping was done. A SUS square tube having a length of 300 mm, an outer diameter of 20 mm, and an inner diameter of 10 mm (thickness of 5 mm) is used as a test pipe. It was. On the surface of the pipe, a sensor part having a length of 280 mm and the same configuration as that of the sensor part used in the test of the first embodiment was installed at substantially the center in the pipe longitudinal direction. First, the initial condition is the condition in which 20 ° C silicon oil is circulated in the test pipe, and the silicon oil is switched to 150 ° C and the impedance distribution is measured every 20 seconds as the temperature changes over time. did. After switching the fluid in the piping to high temperature oil, the temperature of the piping surface rose to about 110 ° C.

  The thinned portion exists at a position half the length of the sensor portion (about 140 mm). The temperature difference between the thinned part and the other normal thickened part gradually spreads after switching to high temperature oil, reaches a maximum temperature difference of about 20 ° C. after about 120 seconds, and then the passage of time As the temperature difference decreased. Since the difference in temperature distribution was only 20 ° C., it was difficult to distinguish from the variation range depending on the temperature sensitivity position of the sensor with the simple impedance change rate as shown in FIG. Therefore, the impedance distribution (sensor variation) in the soaking state of the sensor was measured, and the impedance change rate was normalized by dividing the impedance change rate by the distribution. In addition, the impedance distribution in the soaking state is an impedance distribution in a state in which the soaking is maintained for about 1800 seconds after switching to a high-temperature fluid. The result is shown in FIG.

  In FIG. 9, when the thinned portion is preferentially heated with respect to other portions as time passes, the impedance of the portion corresponding to the thinned portion (position of 140 mm) is also more preferential than the other portions. It can be seen that it has risen significantly. In addition, the increase in the impedance distribution at the thinned portion is the largest at the point of 120 seconds when the temperature difference becomes maximum, and then the temperature rise becomes saturated and the temperature of the normal portion becomes the temperature of the thinned portion. It can be seen that the impedance distribution becomes uniform as the surface temperature of the entire pipe becomes uniform. Thus, by obtaining the responsiveness of the impedance distribution corresponding to the temperature change in the thinned portion, this ETDR is used to indirectly detect the temperature distribution change in the thinned portion as the impedance distribution change, It was confirmed that the occurrence of thinning can be reliably detected and diagnosed.

1 Pipe 1E Thinning part 10/20 Sensor part 11 Electrical time domain reflector (ETDR)
12 Impedance measuring device 13 Display device 15/25 Dielectric layer 16 Thermistor layer 17/27 Metal electrode

Claims (7)

A surface temperature distribution detection device for detecting the surface temperature distribution of a structure affected by heat,
A sensor unit that is provided on the surface of the structure and uses the structure as one electrode; an electric time domain reflection device that receives an electric pulse wave from one end of the sensor unit and detects the reflected wave; From the detection signal detected by the electrical time domain reflection device, having an impedance measurement device that measures the impedance of the sensor unit,
The sensor unit includes a dielectric layer bonded to the surface of the structure, a thermistor layer that is stacked on the dielectric layer and changes in resistivity according to temperature, and a metal electrode that is stacked on the thermistor layer. Consists of
The metal electrode is formed in a line shape narrower than the thermistor layer and constitutes the other electrode,
A surface temperature distribution detecting device, wherein the surface temperature distribution of a structure caused by the thermal effect can be detected as an impedance distribution of the sensor unit based on a change in resistivity of the thermistor layer.   The surface temperature distribution detection device according to claim 1, wherein the thermistor layer is a composite layer in which ceramic particles whose resistivity changes according to temperature are dispersed in a resin. A pipe thinning detection method for detecting thinning of a metal pipe through which a high-temperature fluid flows.
On the surface of the pipe, the pipe is used as one electrode, and a dielectric layer from the pipe side, a thermistor layer whose resistivity is changed according to temperature, and a metal electrode constituting the other electrode are laminated in this order. Provided sensor part,
When the surface of the thinned portion generated in a part of the pipe is preferentially heated to a higher temperature than the other part by the high-temperature fluid, the resistivity of a part of the thermistor layer in the high-temperature part is also higher than the other part. Utilizing the change in the apparent electrode area in the sensor unit, an electric pulse wave is incident from one end of the sensor unit by an electric time domain reflection device, and the sensor measures the impedance from the reflected wave by the impedance measurement device. A pipe thinning detection method that measures the impedance of a pipe and detects pipe thinning due to the presence of a part where the impedance changes preferentially over other parts. A surface temperature distribution detection device for detecting the surface temperature distribution of a structure affected by heat,
A sensor unit that is provided on the surface of the structure and uses the structure as one electrode; an electric time domain reflection device that receives an electric pulse wave from one end of the sensor unit and detects the reflected wave; From the detection signal detected by the electrical time domain reflection device, having an impedance measurement device that measures the impedance of the sensor unit,
The sensor unit includes a dielectric layer bonded to the surface of the structure, and a metal electrode stacked on the dielectric layer and serving as the other electrode,
The dielectric layer uses a dielectric material whose relative dielectric constant changes according to temperature,
A surface temperature distribution detection device capable of detecting a surface temperature distribution of a structure caused by the thermal effect as an impedance distribution of the sensor unit based on a change in relative dielectric constant of the dielectric layer.   The surface temperature distribution detection device according to claim 4, wherein the dielectric layer is a composite layer in which dielectric material particles are dispersed in a resin. A pipe thinning detection method for detecting thinning of a metal pipe through which a high-temperature fluid flows.
On the surface of the pipe, the pipe is used as one electrode, and includes a dielectric layer containing a dielectric material whose relative dielectric constant changes according to temperature, and a metal electrode stacked on the dielectric layer and serving as the other electrode. Provide a sensor unit,
When the surface of the thinned portion generated in a part of the piping is preferentially heated to a higher temperature than the other part by the high-temperature fluid, the relative dielectric constant of a part of the dielectric layer in the high-temperature part is also higher than the other part. The electric pulse wave is incident from one end of the sensor unit by an electrical time domain reflection device, and the impedance of the sensor unit is measured from the reflected wave by the impedance measurement device. A pipe thinning detection method for detecting pipe thinning due to the presence of a portion where impedance changes more preferentially. The surface temperature distribution detection apparatus according to any one of claims 1, 2, 4, and 5, wherein the structure is a metal pipe through which a high-temperature fluid flows.

Images