JP2011107050A - Device and method for monitoring pipe leakage - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for monitoring pipe leakage that certainly and quickly identifies and monitors a location of leakage of a measuring object, which includes piping and a valve of a plant during operation. <P>SOLUTION: The device for monitoring pipe leakage has: an optical fiber 3 which is continuously laid near an outer surface of an insulating material covering the measuring object, which includes piping and the valve; a pulse light incident means 11 which is provided at the end of the fiber 3 and makes pulse light incident into the optical fiber 3; and a measuring means 15 for back scattering light intensity for continuously measuring back scattering light intensity of the pulse light incident into the optical fiber 3. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a pipe leak monitoring apparatus and method for identifying a steam leak position of a heat insulating material covering a measurement object including a pipe and a valve based on condensed droplets from the heat insulating material and a sudden temperature change.

  In general, when coolant leaks from piping and valves of nuclear power plants and thermal power plants, in the case of minor leakage, the plant operator discovers a puddle on the floor and tracks overhead piping to locate the leakage location. From the fact that the coolant leaks until the water pool is formed on the floor, the time elapsed until the discovery, the leak location specific work time, until the coolant leaks and is discovered If the elapsed time is long and a water pool is not formed on the floor surface or the like depending on the leakage location, it is impossible to detect the leakage of the coolant. In nuclear power generation, where a lot of time and expense is required for restarting the plant due to unplanned shutdown of the plant and recovery of the leak location due to the leak location and size of the coolant, drastic improvement to the early detection of pipe leak is possible. It is desired.

  In recent years, aging of social infrastructure such as power generation facilities and energy transmission lines (abbreviation: infrastructure) has become a major problem, and economic and social losses due to aging damage accidents are large, especially from the 1960s to 1970. It is assumed that many of the main pipes of plants constructed during the period of high growth in the 1990s have been deteriorated by corrosion and fatigue for more than 30 years.

  For this reason, the main piping is subjected to a thinning inspection by an ultrasonic flaw detection method at each periodic inspection, while the valves and flanges are periodically subjected to leakage avoidance work by exchanging gran packing. In these cases, there are many on-site inspection man-hours for periodic inspection and replacement work, and it is becoming indispensable to monitor leaks during operation with the aim of improving future long-term cycle operation and aging plant availability. .

  The conventional pipe leakage monitoring device has a temperature monitoring means for the outer surface of the pipe heat insulating material using an infrared camera, a temperature monitoring means for the valve flange, and a means for detecting a steam leak AE (Acoustic Emission) using FBG (Fiber Bragg Grating) or a piezoelectric ceramic element. is there. The method of monitoring the temperature change by the infrared camera from the heat insulating material of the equipment pipe already implemented is not a leak detection method that is reliable and satisfactory because there are many temperature changes other than the leak.

  In addition, pipe leak vibration and steam leak AE detection means using acceleration sensors using FBG or piezoelectric ceramic elements can detect a remarkable peak spectrum with an AE excited by a leak phenomenon of about 40 kHz. The S / N ratio greatly depends on the background noise level of 30 to 40 kHz, and in reality, the AE attenuation by the pipe heat insulating material and the sound pressure of the harmonics of the vibration in the pipe are equivalent to the AE signal level. In many cases, the necessary S / N ratio cannot be obtained, which is not a definitive technique. In light of these circumstances, there is an urgent need to realize a definitive leak detection method that directly detects leaks in the main piping system including valves and identifies the position.

  Techniques for detecting leaks from plant piping and valve seals after 1990 using optical fibers are described in Patent Documents 1, 2, 3, and 4. In particular, the technique described in Patent Document 1 is an apparatus that detects ultrasonic attenuation quantitatively by FBG by propagating ultrasonic waves to an optical fiber and causing the optical fiber to get wet by leaked water. Due to the monitoring feature, the inside of the optical fiber cannot be continuously monitored.

  The technique described in Patent Document 2 is a technique for detecting high-frequency vibration due to leakage AE using an optical fiber sensor, and has already been partially implemented in the industry as a leakage AE detection method using FBG or interference method. In many cases, the background noise in the local plant interferes with the peak of the leakage AE vibration spectrum of about 40 kHz, and the required S / N ratio cannot be ensured.

  Furthermore, the technique described in Patent Document 3 is a liquid leak detection in which an optical fiber having a clad that swells with a special liquid is immersed in the clad, and the propagation light scattering is quantitatively detected by interferometry or the like due to core compression bending due to expansion. Laws and similar technologies have been filed several times in the 1990s with different inspection targets.

  And the technique described in patent document 4 winds an optical fiber helically on a heat insulating material, an optical fiber deform | transforms with the distortion | strain by liquid leakage, and measures the deformation | transformation by measuring fiber scattered light, such as FBG. This is a leak detection device for identifying a leak position.

JP 2007-24798 A JP 2003-28979 A JP 2001-50855 A JP-A-11-344390

  However, in any of the above-mentioned patent documents, before 2000, when a diode laser becomes widespread, a pulse width and a pulse peak value capable of obtaining a practical S / N ratio and leakage position identification accuracy should be secured. It is assumed that it was difficult to apply a compact and inexpensive high-performance pulse laser capable of

  Further, the leak detection means for detecting the scattered light of the fiber by the clad swelling deformation of the optical fiber clad with the swellable resin has the S / N ratio and the adaptability between the swellable resin and the leaked liquid and the magnitude of the deformation caused thereby. The reliability of the leak detection data depends, and it is assumed that it is difficult to ensure the reliability and certainty required in the power plant.

  For this reason, the leak detection devices described in Patent Documents 1, 2, 3, and 4 are not detection devices that have sufficient reliability and usefulness as a piping leak detection diagnosis technique. As a result, there is a need for a reliable on-site leak detection device for piping systems including valves.

  By the way, reliable leak detection requires reliable leak detection and position identification by directly detecting droplets condensed in the gap between the coolant and the heat retaining material in the piping system including the valve. However, the technology for detecting droplets while continuously identifying the entire leakage position of the entire piping system is not present, and it is currently difficult to reliably detect leaks other than finding a water pool on the floor.

  The present invention has been made in order to solve the above-described problems, and a pipe leakage monitoring device capable of reliably and promptly identifying and monitoring leakage of a measurement object including piping and valves of a plant during operation and It aims to provide a method.

  In order to achieve the above object, a pipe leakage monitoring apparatus according to the present invention includes an optical fiber continuously laid in the vicinity of an outer surface of a heat insulating material covering a measurement object including pipes and valves, and an end of the optical fiber. A pulsed light incident unit that is provided in the optical fiber and makes the pulsed light enter the optical fiber; and a backscattered light intensity measuring unit that continuously measures the intensity of the backscattered light of the pulsed light incident in the optical fiber; It is characterized by having.

  In order to achieve the above-mentioned object, the pipe leakage monitoring method according to the present invention is configured to emit pulsed light from the end of an optical fiber continuously laid in the vicinity of the outer surface of a heat insulating material covering a measurement object including pipes and valves. An incident pulse light incident step; and a back scattered light intensity measurement step for continuously measuring the intensity of the back scattered light of the pulse light incident in the optical fiber after the pulse light incident step. And

  According to the present invention, it is possible to improve the reliability of leakage detection by double-confirming continuous temperature changes and droplets along the optical fiber at the same position on the optical fiber.

It is a partially expanded block diagram which shows the state which laid the optical fiber under the piping which coat | covered the heat insulating material in 1st Embodiment of the piping leak monitoring apparatus which concerns on this invention. It is explanatory drawing which shows the basic composition and operation | movement principle of the optical fiber which identifies a position by attenuation | damping by temperature distribution and droplet adhesion by the Raman scattering of the pulsed light of a diode laser in 1st Embodiment. It is a wave form diagram which shows an example of the spectrum (wavelength distribution) of the backscattered light detected with the photodiode. It is a partially expanded perspective view which shows the internal structure of the optical fiber in 2nd Embodiment of the piping leak monitoring apparatus which concerns on this invention.

  Hereinafter, an embodiment of a pipe leakage monitoring apparatus according to the present invention will be described with reference to the drawings. In the following embodiments, examples in which the present invention is applied to a measurement object including piping and valves of a nuclear power plant will be described.

(First embodiment)
A pipe leakage monitoring apparatus according to this embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a partially enlarged configuration diagram showing a state in which an optical fiber is laid below a pipe covered with a heat insulating material in the first embodiment of the pipe leakage monitoring apparatus according to the present invention. In FIG. 1, the main steam pipe, the water supply pipe, and the recirculation pipe are collectively described as a pipe 1 that is a measurement object. Moreover, in FIG. 1, although the optical fiber is laid under the heat insulating material which coat | covered piping, in 1st Embodiment, the optical fiber is closely laid in the lower part of the heat insulating material outer surface.

  As shown in FIG. 1, the entire circumference of the pipe 1 is covered with a heat insulating material 2 for the purpose of improving thermal efficiency. The optical fiber 3 is laid in the lower part of the outer surface of the heat insulating material 2 so that the optical fiber 3 is continuously adhered along the length direction of the pipe 1.

  FIG. 2 is an explanatory diagram showing the basic configuration and operation principle of an optical fiber that is identified by temperature distribution and attenuation due to droplet adhesion by Raman scattering of pulsed light from a diode laser in the first embodiment. As shown in FIG. 2, a diode laser 11 for exciting pulsed light as a pulsed light incident means is attached to the end of the optical fiber 3, and the light beam has the same optical axis as the pulsed light 12 emitted from the diode laser 11. A coupler 16 is installed. This optical coupler 16 bends the optical axis of the backscattered light 14 and leads it to a photodiode 15 as a backscattered light intensity measuring means, and continuously measures and monitors the backscattered light intensity. Here, the diode laser 11 having a pulse width of 5 nsec to 50 μsec and a wavelength of 400 to 1030 nm and 1200 to 1600 nm is used from the end of the optical fiber 3.

  The optical fiber 3 includes a fiber core that propagates an optical signal in the length direction and a fiber cladding that covers the periphery of the fiber core. In general, the optical fiber is made of optical glass, quartz glass, or optical plastic, and is coated with a fiber cladding that reflects at the interface to reduce the attenuation of propagating light. Propagates by repeated reflection on the fiber cladding surface. Therefore, the backscattered light 14 due to Raman scattering generated in the fiber core can propagate through the optical fiber 3 and transmit the temperature distribution information of the optical fiber 3 to the end.

  The optical fiber 3 has an outer diameter of 100 to several hundreds of μm, and the fiber core 20 has a diameter of several μm to several tens of μm. The optical fiber 3 as a whole has flexible rigidity.

  Next, the effect | action of the piping leak monitoring apparatus of this embodiment is demonstrated.

  As described above, the heat insulating material 2 is coated on the entire circumference of the pipe 1 for the purpose of improving the thermal efficiency. Here, as shown in FIG. 1, when steam leaks from a crack or valve packing of the pipe 1 and this steam condenses in the gap between the pipe 1 and the heat insulating material 2, a liquid that condenses the inner surface of the heat insulating material 2. The droplets 4 are transmitted, and the droplets 4 gather at the lower part of the outer surface of the heat insulating material 2 by gravity.

  The fiber clad of the optical fiber 3 laid so that the droplet 4 is in close contact with the lower part of the outer surface of the heat insulating material 2 is wetted. As shown in FIG. 2, the pulsed light 12 propagating through the optical fiber 3 propagates through the optical fiber 3 several tens of meters while gradually attenuating the pulse intensity while repeating backscattering (Raman scattering). At the position where the fiber 3 is wetted by the droplet 4 (scattering attenuation portion 13), the reflection of the pulsed light is lost at the interface between the fiber cladding and the droplet 4, and the light pulse 12 is scattered to the outer surface of the fiber cladding. The light is rapidly attenuated, and the backscattered (Raman scattered) light from the scattering attenuation unit 13 does not attenuate. By continuously detecting the attenuation of the backscattered light with the photodiode 15 and obtaining the time from when the pulsed light 12 is incident until the backscattered light 14 whose intensity is rapidly attenuated reaches the photodiode 15, The position where the optical fiber 3 is wetted by the droplet 4 and scattered can be identified with an accuracy of 1 to 2 m.

  FIG. 3 is a waveform diagram showing an example of a spectrum (wavelength distribution) of backscattered light detected by a photodiode.

  As shown in FIG. 3, the distribution of the wavelength and the backscattering spectrum intensity gradually attenuates in proportion to the propagation distance after the pulsed light 12 is incident on the optical fiber 3 from the diode laser 11. The intensity ratio of the Raman scattering spectrum (hereinafter referred to as Stokes light) 18 and the Raman scattering spectrum (hereinafter referred to as anti-Stokes light) 19 changes. While the Stokes light 18 is hardly affected by the temperature distribution of the optical fiber 3, the anti-Stokes light 19 changes greatly in proportion to the temperature of the optical fiber 3. Therefore, by taking the ratio of the peak values of both spectra, It becomes possible to obtain the temperature of the optical fiber 3 at each Raman scattering point.

  In the present embodiment, pulsed light incident from the end of the optical fiber 3 by the diode laser 11 repeats Raman scattering and measures a continuous temperature distribution along the optical fiber 3 with backscattered light. The measurement principle can be obtained with an accuracy of ± 1 to 3 ° C. from the attenuation ratio of Stokes light and anti-Stokes light having a continuous spectral distribution.

  Therefore, when the optical fiber 3 is partially damaged due to mechanical external factors such as striking or sudden bending, it is assumed that the backscattered light from the damaged part is rapidly reduced, and the attenuation position is set as the leakage position. However, since the intensity ratio of the Stokes light 18 and the anti-Stokes light 19 at this portion does not change, it is not determined that the liquid droplet 4 is leaking, and an accurate leak diagnosis with redundancy is possible. Is possible.

  As described above, according to this embodiment, in a piping system including a valve having a high coolant leakage potential, a continuous temperature along the optical fiber 3 laid on the lower surface of the heat insulating material 2 without removing the heat insulating material 2. And the droplet 4 can be detected along the longitudinal direction of the optical fiber 3 with a sufficient S / N ratio, and the position of the droplet 4 can be identified. By double checking at the same position on the top, the reliability of leak detection can be improved.

  As a result, the leakage of the piping 1 and the valve of the nuclear power plant and the thermal power plant can be detected at the initial stage, so that the plant stop due to the leakage can be avoided.

  In the present embodiment, the temperature change can be detected by the photodiode 15 as described above. In the prior art, it is necessary to install a plurality of thermocouples directly on the pipe and measure the temperature, and to lay a measurement line for each pair of thermocouples. Therefore, since the temperature can be measured, the apparatus can be simplified.

  Furthermore, in this embodiment, the pulse light incident from the end of the optical fiber 3 by the diode laser 11 improves the position identification accuracy as the pulse width is shorter, but the S / N ratio is determined by the pulse width and the pulse peak value. Is almost proportional to Thereby, the specifications of the pulse width and the laser output are determined from the required position detection accuracy and the required S / N ratio, and the pulse width is 5 nsec to 50 μsec.

  As described above, according to the present embodiment, leakage of the pipe 1 including the valve is caused by continuously wetting the surface of the heat insulating material 2 by the condensed droplets and the surface temperature change by the single optical fiber 3. It is possible to realize a pipe leakage monitoring device that is installed and removed without being removed.

  In this embodiment, the optical fiber 3 is continuously laid along the length direction of the pipe 1 below the outer surface of the heat insulating material. However, the length of the pipe 1 is not limited to this. The optical fiber 3 may be laid in the vicinity of the pipe 1 along the vertical direction.

(Second Embodiment)
FIG. 4 is a partially enlarged perspective view showing the internal structure of the optical fiber in the second embodiment of the pipe leakage monitoring apparatus according to the present invention. The same parts as those in the first embodiment will be described with the same reference numerals.

  As shown in FIG. 4, the optical fiber 3 of the present embodiment includes a fiber core 20 that propagates an optical signal in the length direction and a fiber cladding 21 that covers the periphery of the fiber core 20. A steel material 22 as a protective material is spirally wound along the direction.

  By the way, although the optical fiber 3 allows bending with a radius of curvature of about 100 mm, it is easily damaged by compressive stress. In the present embodiment, the steel material 22 is spirally wound around the outer circumference of the optical fiber 3 along the length (axis) direction in order to protect it from bending, compression, or blow exceeding the allowable value in the laying operation at the site. ing. Protecting the optical fiber 3 prevents excessive bending or mechanical external force applied to the optical fiber 3 and induces light scattering in the fiber clad 21 due to wetting of the optical fiber 3 by the droplet 4.

  That is, when it is assumed that the optical fiber 3 is laid on the pipe 1 at the site, it is practical and convenient that the installation method is installed from above the heat insulating material 2 in consideration of the work man-hour and the curing of the optical fiber. Excellent. Because of the characteristics of the optical fiber 3, it is not suitable for bending or compression, so it is optimal to lay it under the heat insulating material 2 installed on the pipe 1 or equipment, not on the inner surface of the heat insulating material 2 in consideration of workability. .

  Conventional leak detection means based on temperature measurement using a thermocouple, etc. are installed in the gap between the pipes on the inner surface of the heat insulating material and try to detect temperature rise due to leaked steam only at the measurement point. There was a big problem with the reliability of change. Further, the sensor installed inside the heat insulating material has a problem in inspection work because it cannot be confirmed from the outer surface, but the optical fiber 3 according to the present embodiment is protected against a bending load by the steel material 22. In addition to being subjected to direct bending and compression from the sheath structure to the breakage of the optical fiber 3, it can be laid under the outer surface of the heat insulating material of the pipe 1 to improve workability. The optical fiber 3 itself is also easily confirmed.

(Third embodiment)
Next, a third embodiment of the present invention will be described.

  In the present embodiment, although not shown, the fiber clad 21 shown in FIG. 4 forms a clad peeling portion that is thinner than the others at a constant pitch or at a constant pitch.

  As described above, according to this embodiment, at least a part of the fiber clad 21 in the axial direction is made thinner than the other parts, so that the pulsed light scattering due to the adhesion of the droplet 4 is increased and the droplet 4 is prevented from being wet. Sensitivity can be improved.

  The present invention can be variously modified without being limited to the above embodiments. For example, in each of the above-described embodiments, the example in which the diode laser 11 is used as the pulsed light incident unit has been described. However, the present invention is not limited to this, and a pulsed laser light source (oscillator) may be used. When this pulse laser light source is used, the scattered light becomes stronger, and the spatial resolution of the leakage position and the temperature change position can be improved by improving the conventional Raman scattering to Brillouin scattering.

  In each of the above embodiments, the example in which the photodiode 15 is used as the backscattered light intensity measuring means has been described. However, the present invention is not limited to this, and any optical measuring element may be used.

DESCRIPTION OF SYMBOLS 1 ... Pipe 2 ... Thermal insulation material 3 ... Optical fiber 4 ... Droplet 11 ... Diode laser (pulse light incident means)
12 ... Pulse light 13 ... Scattering attenuation part 14 ... Backscattered light 15 ... Photodiode (backscattered light intensity measuring means)
16 ... Optical coupler 17 ... Rayleigh scattering spectrum 18 ... Raman scattering spectrum (Stokes light)
19 ... Raman scattering spectrum (anti-Stokes light)
20 ... Fiber core 21 ... Fiber clad 22 ... Steel (protective material)

Claims (6)

An optical fiber continuously laid in the vicinity of the outer surface of the heat insulating material covering the measurement object including piping and valves;
A pulsed light incident means that is provided at an end of the optical fiber and that makes pulsed light enter the optical fiber;
Backscattered light intensity measuring means for continuously measuring the intensity of the backscattered light of the pulsed light incident on the optical fiber;
A pipe leakage monitoring device characterized by comprising: The backscattered light intensity measuring means takes a ratio of peak values of Stokes light and anti-Stokes light,
The pipe leakage monitoring device according to claim 1. The optical fiber has a fiber core that propagates the pulsed light in the axial direction, and a fiber cladding that covers the periphery of the fiber core,
Making at least a part of the axial direction of the fiber cladding thinner than other parts;
The pipe leakage monitoring device according to claim 1. A spirally wound protective material along the axial direction on the outer periphery of the optical fiber,
The piping leakage monitoring device according to any one of claims 1 to 3, wherein The backscattered light intensity measuring means propagates the pulsed light incident in the optical fiber while repeating backscattering, and identifies the leak position by attenuation of the backscattered light intensity,
The pipe leakage monitoring device according to any one of claims 1 to 4, wherein: A pulsed light incident step in which pulsed light is incident from the end of the optical fiber continuously laid below the outer surface of the heat insulating material covering the measurement object including the pipe and the valve;
After the pulsed light incident step, a backscattered light intensity measuring step for continuously measuring the intensity of the backscattered light of the pulsed light incident in the optical fiber;
A pipe leakage monitoring method characterized by comprising:

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