Pipeline inside investigation device

Abstract

To provide a pipeline inside investigation device which allows investigation of inner surface corrosion sites, etc. in a sewage force-feed pipeline, etc. while having a structure for avoiding an irrecoverable state.SOLUTION: A investigation body 29 of the pipeline inside investigation device includes a casing 33, an inside chassis 35 fitted into the casing 33, electronic components 37 having an electronic board and a battery arranged in the inside chassis 35, and a cover member 41 for closing a rear end opening part 31 of the casing 33 in a sealing manner. In the casing 33, water fillers 63, 65 are formed. The water fillers 63, 65 are blocked in a sealed manner with resin taps 67, 69 having water solubility or formed of water soluble resin.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a technique for detecting corrosion on the inner surface of a pipeline such as a sewer pressure pipeline. [Background technology]

[0002] Sewerage pipeline systems include pressure pipeline systems that utilize pump pressure and gravity-flow systems that utilize the difference in ground elevation, but when investigating the corrosion condition of the inner surface of a pressure pipeline system, the pipeline has peaks and valleys and the system must pass through sections of the pipeline that are full, so it is generally difficult to use survey equipment with wheels or surface vehicles that are used to investigate the corrosion condition of the inner surface of gravity-flow pipelines.In addition, devices with drive mechanisms such as motors are too large to be inserted into pressure pipelines and cannot be easily used.

[0003] Therefore, as shown in Patent Document 1, based on the understanding that corrosion of the inner surface of a pressure pipeline due to hydrogen sulfide occurs where there is an air pocket in the pressure pipeline, a small, capsule-shaped investigation device is used that has a capacitance sensor for detecting air pockets but no driving mechanism. Such a small, capsule-shaped investigation device can be introduced into the pressure pipeline from an air valve or repair valve connected to the pressure pipeline. Once introduced into the pressure pipeline, it moves downstream with the flow of sewage in the pressure pipeline, detecting air pockets or air pocket locations using the capacitance sensor during the movement. After detecting an air pocket or air pocket location, the investigation device is retrieved from a downstream manhole or treatment facility, and the air pocket or air pocket location in the pressure pipeline can be identified by, for example, checking the contents of its memory.

[0004] Once the air pocket location is identified, there is a high possibility that corrosion due to hydrogen sulfide has occurred on the inner surface of the pressure pipe at the identified location, so the identified location of the pressure pipe is inspected in more detail to confirm the state of corrosion on the inner surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-52521 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the investigation of air pockets in Patent Document 1, an investigation device without a driving mechanism is carried downstream unmanned by the sewage flow in the sewer pressure pipe. Therefore, if there is a step in the sewer pressure pipe, the investigation device may get caught on the step and may not be able to easily escape from the step by simply being subjected to the sewage flow. Furthermore, if the investigation device gets stuck in a groove in the sewer pressure pipe, it may not be able to easily escape from the groove. Furthermore, the investigation device must have a specific gravity of 1 or less so that it can float in the water in the sewer pressure pipe. However, such lightweight investigation device is subject to buoyancy in the direction of movement (the direction it should move) in the down-flow pipe of the sewer pressure pipe, which can cause it to essentially come to a standstill or to rise in the opposite direction.

[0007] In this way, if the survey equipment gets caught on a step or gets stuck in a trench and can no longer move, remaining inside the sewer pressure pipe, it will have a negative impact on the check valves and air valves, etc. The same is true when it becomes unable to move in the downward piping, and it can also lead to blockage of the sewer pressure pipe, requiring extensive work to retrieve the survey equipment.

[0008] Therefore, the present invention aims to provide an internal pipeline inspection device that can inspect internal corrosion areas of sewer pressure pipelines, etc., and that is equipped with a structure to prevent the device from becoming unrecoverable. [Means for solving the problem]

[0009] To achieve this objective, the present invention provides a pipeline inspection device that inspects the interior of a pipeline while riding downstream on the flow of water. The device includes a casing, a sensor disposed within the casing for detecting or predicting corroded areas on the inner surface of the pipeline, a tank portion provided in the casing with a water inlet, and a plug member for closing the water inlet. The plug member dissolves and opens the water inlet when immersed in water within the pipeline for a predetermined period of time (e.g., a long period of time or a period longer than the predicted time from the introduction of the pipeline inspection device into the pipeline to its removal). The casing may be formed, for example, in the shape of a capsule, a small capsule, a small container, or a small cylinder. The pipeline inspection device of the present invention does not, for example, have a drive mechanism. The tank portion may be part of the casing. Alternatively, the casing may be configured as the tank portion. Alternatively, the tank portion may be configured as a combination of the casing and another component. The tank portion may have one or more water inlets. If the water inlet is large, even a single inlet can allow water such as sewage to flow into the tank while exhausting air from the tank.

[0010] The plug member may be made of PVA (polyvinyl alcohol).

[0011] The sensor is a capacitance sensor that detects the free water surface or air pockets in the pipeline. This capacitance sensor can be configured to have a pair of electrodes that extend along the entire circumference or almost the entire circumference of the inner circumferential surface of the casing. The capacitance sensor detects the free water surface or air pockets by detecting changes in the capacitance between the electrodes due to changes in the dielectric constant of the surroundings. In this case, the free water surface or air pockets in the pipeline can be effectively detected even when the casing rotates in the circumferential direction. [Effects of the Invention]

[0012] By using the pipe line inspection device of the present invention, it is possible to effectively prevent the pipe line inspection device from remaining inside a pipe line such as a sewer pressure pipe line. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram illustrating the configuration of a sewer pressure pipeline as an object to be inspected by the pipeline inspection device according to the present invention. FIG. [Figure 2] 1 is a conceptual diagram showing an inspection state of a pipe line inspection device according to the present invention. [Figure 3] 1 is a perspective view of a pipe line inspection device according to the present invention. [Figure 4] FIG. 1 is a cross-sectional view of the main body of the surveyor. [Figure 5] FIG. 2 is an exploded perspective view of the survey machine body. [Figure 6] 10A and 10B are diagrams illustrating the traction function of the sponge body in the downward piping section. [Figure 7] 10A and 10B are diagrams illustrating a manner in which an air pocket is detected. [Figure 8] 10 is a diagram illustrating the case where the main body of the surveying device is pulled by a sponge body and passes through a step. FIG. [Figure 9] FIG. 10 is a diagram illustrating the case where the main body of the investigation device sinks and descends from a recess in the sewer pressure pipeline into the main pipe. [Figure 10] FIG. 10 is a diagram illustrating the case where the investigation device main body sinks and descends into the main pipe from the air valve side. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0015] First, with reference to Figs. 1 and 2, the configuration of a sewer pressure pipeline as an object to be inspected for internal corrosion using the pipeline inspection device according to the present invention will be described.

[0016] As shown in Figure 1, the sewage pressure pipeline 1 has an upstream piping section 3 and a downstream piping section 5, and extends from a pumping station (not shown) to a manhole 7 at the discharge destination, repeatedly flowing upstream and downstream. Sewage 11 is pressure-fed from a pressure pump 9 at the pumping station as shown by the arrow and discharged into the manhole 7 at the discharge destination.

[0017] A gate valve 13 and an air valve 15 are connected in appropriate positions to the sewer pressure pipeline 1, and a repair valve 17 is provided on the air valve 15. The air valve 15 provided on the starting end of the sewer pressure pipeline 1 is connected via the repair valve 17 to a branch pipe 23 connected to a branch section 21 of a T-pipe 19 of the sewer pressure pipeline 1, and by removing the air valve 15 from the repair valve 17 (see imaginary line), an in-pipe investigation device 25 can be introduced into the main body of the T-pipe 19 (inside the sewer pressure pipeline 1) through the repair valve 17 and the branch pipe 23.

[0018] As shown in Figure 2, the pipe investigation device 25 introduced into the sewer pressure pipeline 1 moves along the flow of sewage 11 (see arrow) within the sewer pressure pipeline 1, using a sponge body or sponge 27 as the towing part of the investigation device body 29. The sponge body 27 sinks within the sewage 11 and moves through the sewage 11. Once the pipe investigation device 25 reaches the manhole 7, it is retrieved using a net 30 installed at the discharge outlet of the sewer pressure pipeline 1.

[0019] Next, the configuration of the pipe line inspection device 25 according to the present invention will be described with reference to FIGS.

[0020] The pipeline investigation device 25 is configured as a corrosion location detection or corrosion location prediction device by connecting a towing sponge body 27 to the investigation device main body 29, and the investigation device main body 29 is composed of a thick-walled capsule-shaped casing 33 made of resin (here made of polycarbonate) and having a rear end opening 31, a thin-walled inner chassis 35 made of resin (here made of polycarbonate) fitted into this casing 33, electronic components 37 including an electronic board and battery arranged inside the inner chassis 35, a cover member 41 that is removably attached to the rear end opening 31 of the casing 33 with bolts or screws 39 and hermetically closes the rear end opening 31, a wire 43 connected to the tip of the casing 33, and an elastic resin avoidance member 45 that is formed so as to cover the rear end of the wire 43 from the tip of the casing 33. The resin avoidance member 45 is formed to have elasticity by attaching resin clay from the tip of the casing 33 to cover the rear end of the wire 43 and drying it, and has a taper angle or inclination angle smaller than the taper angle or inclination angle of the conical portion 47 of the casing 33. In other words, the tip side of the casing 33 has a two-stage tapered structure. The sponge body 27 is attached to the tip of the wire 43. The inside of the casing 33 is sealed by attaching the lid member 41.

[0021] The casing 33 is integrally formed from, for example, a conical portion 47 at the front end side having a conical outer surface with a pointed tip, and a cylindrical portion 49 at the rear end side having a rear end opening 31, and has a length of, for example, about 140 mm, and the outer diameter of the cylindrical portion 49 of the casing 33 is, for example, about 60 mm. The rear end side of the conical portion 47 of the casing 33 is hollow, and the front end side is solid to form a solid portion 51, and the wire 43 is attached to the front side of this solid portion 51. A step 53 is formed between the inner circumferential rear end of the conical portion 47 and the inner circumferential front end of the cylindrical portion 49.

[0022] The wire 43 is attached by forming a radial through-hole 55 on the tip side of the solid portion 51, providing grooves 57 so that the wire 43 can fit from both sides of the through-hole 55 toward the tip, winding the rear end of the wire 43 around the solid portion 51 so that it passes from inside the groove 57 on one side through the through-hole 55 and into the groove 57 on the other side, and connecting the rear end of the wire 43 to the rear end of the wire 43 using a wire sleeve 59. The wire sleeve 59 is covered with the resin avoidance member 45.

[0023] A ring-shaped sensor detection recess 61 is provided around the entire circumference in the middle of the longitudinal direction of the outer surface of the casing 33 or the cylindrical portion 49, and this sensor detection recess 61 is formed in a trapezoidal shape with a low cross-sectional height, and the thickness at the sensor detection recess 61 is thinner than other parts of the casing 33 or the cylindrical portion 49.

[0024] Circular or cylindrical water inlets 63, 65 are formed through the casing 33 or the cylindrical portion 49 at two locations, one at the front and one at the back. Four water inlets 63 on the front side are formed at equal circumferential intervals on the top, bottom, left, and right, and four water inlets 65 on the rear side are also formed at equal circumferential intervals on the top, bottom, left, and right. Each water inlet 63, 65 is hermetically sealed with a resin plug (plug member) 67, 69 made of a water-soluble or water-soluble resin (here, PVA) that dissolves when immersed in water for a predetermined time (for example, a long time, such as 1 hour, 2 hours, 3 hours, or 4 hours). Water inlets 63, 65 are formed to have a diameter of, for example, 7 mm, but the diameter can be 2.5 mm to 10 mm and the height can be 1 mm to 20 mm.

[0025] The inner chassis 35 is configured as a cylindrical body, and is formed so that its outer peripheral surface has the same or nearly the same diameter as the inner peripheral surface of the cylindrical portion 49 of the casing 33, and is fitted into the cylindrical portion 49 of the casing 33 so as to be in close contact, or in overall contact with the inner peripheral surface of the cylindrical portion 49. The inner chassis 35 is positioned in the longitudinal direction by being sandwiched between the cover member 41 and a step portion 53 between the conical portion 47 and the cylindrical portion 49.

[0026] Four notched recesses 71 are formed at equal circumferential intervals at the tip of the inner chassis 35, corresponding to the water inlet ports 63 of the casing 33, and each water inlet port 63 is located inside these notched recesses 71. In addition, four circular holes 73 are formed at equal circumferential intervals at the rear end of the inner chassis 35, corresponding to the water inlet ports 65 of the casing 33, and each water inlet 65 is located inside these circular holes 73.

[0027] A cutout or gap 75 for diameter reduction is formed in the inner chassis 35. This gap 75 has a portion 77 that extends from the bottom of one or the upper cutout recess 71 to the front end of the circular hole 73 at the same circumferential position or the upper one, and a portion 79 that extends from the rear end of the circular hole 73 to the rear end of the inner chassis 35. When the inner chassis 35 is removed from the casing 33 and when it is fitted into the casing 33, the gap 75 allows the inner chassis 35 to elastically reduce its diameter, so that the inner chassis 35 can be removed and fitted smoothly.

[0028] A pair of wide (approximately 10 mm) copper tapes 80 are attached to the outer periphery of the inner chassis 35 at the longitudinal center, corresponding to the sensor detection recesses 61, at intervals along the entire circumference or nearly the entire circumference, excluding the gaps 77. These copper tapes 80 form a capacitance sensor or a detection electrode for the capacitance sensor. By providing the copper tapes 80 nearly the entire circumference, the free water surface or air pockets can be effectively detected even when the casing 33 rotates in the circumferential direction. The sensor detection recesses 61 are formed on the outer periphery of the copper tapes 80 in the casing 33, and this configuration allows the copper tapes 80 to accurately detect the free water surface or air pockets outside the casing 33. Furthermore, the sensor detection recesses 61 are not in contact with the ceiling of the sewer pressure pipeline 1, so they are not easily damaged, even when the casing 33 rubs against the ceiling as it moves. Therefore, when the sewage 11 changes from a full pipe state to one in which there is a free water surface and the upper side of the submerged sensor detection recess 61 is positioned above the free water surface, the detection accuracy of the capacitance sensor is improved because water is less likely to remain above the sensor detection recess 61. Furthermore, even if there is a small air pocket, the outer part of the copper tape 80 of the casing 33 comes into contact with the ceiling of the sewer pressure pipeline 1, which causes a large capacitance to be detected, preventing a situation in which the air pocket cannot be detected.

[0029] The electronic board of the electronic components 37 is provided with a microcomputer, memory, a six-axis acceleration / angular velocity sensor, a three-axis magnetic sensor, etc., and a battery supplies power to the electronic board and applies a constant voltage to a pair of copper tapes 80. The electronic components 37 are fixed to the bottom of the inner chassis 35 and function as a balance weight. The electronic components 37 are also removably attached to the inner chassis 35 with screws 82.

[0030] The microcomputer records the detected capacitance between the pair of copper tapes 80, the detected values ​​of the 6-axis acceleration / angular velocity sensor, the detected values ​​of the 3-axis magnetic sensor, etc., along with the elapsed time in memory. By referring to the as-built drawing of the sewer pressure pipeline 1, the microcomputer estimates which point in the sewer pressure pipeline 1 the investigation device main body 29 passed through at a specific elapsed time (specific elapsed time) based on the detected values ​​of the 6-axis acceleration / angular velocity sensor and the 3-axis magnetic sensor. The microcomputer then estimates the location of the air pocket by referring to the as-built drawing based on the difference between the elapsed time (target elapsed time) when the detected capacitance indicates the presence of an air pocket and the specific elapsed time. For example, it is estimated that the investigation device main body 29 passed the first ascending start point of the sewer pressure pipeline 1 at the specific elapsed time. If an air pocket is detected at the target elapsed time, one minute after the specific elapsed time, it can be estimated that the air pocket is located at a distance equal to 60 seconds multiplied by the estimated speed of the investigation device main body 29 from the first ascending start point.

[0031] Therefore, the location of the air pocket can be identified by recovering the inside-pipe inspection device 25, removing the inner chassis 35 from the casing 33, removing the electronic components 37, and checking the contents recorded in the memory.

[0032] The lid member 41 is integrally formed of a disk-shaped lid main body 81 and a cylindrical sealing portion 85 that protrudes a short distance from the back surface of the lid main body 81 and has an O-ring 83 on its outer peripheral surface. The sealing portion 85 is formed with a smaller diameter than the lid main body 81, and a portion of the lid main body 81 located outer than the sealing portion 85 is formed with bolt-through holes 89 that correspond to the bolt holes 87 in the rear-end opening 31 of the casing 33. The lid member 41 is fixed to the casing 33 by pressing the sealing portion 85 into the rear end of the casing 33, abutting the outer peripheral portion of the lid main body 81 against the rear-end opening 31 of the casing 33 so that the bolt holes 87 and the bolt-through holes 89 are aligned, and passing bolts or screws 39 through the bolt-through holes 89 and screwing them into the bolt holes 87. The casing 33 is sealed by the O-ring 83 of the sealing portion 85 of the lid member 41.

[0033] A sponge body 27 is attached to the tip of the wire 43 extending from the tip of the casing 33 as a conductor. The sponge body 27 is formed in the shape of a short cylinder or thick disk, 100 mm thick and 150 mm in diameter. The tip of the wire 43 is inserted into the sponge body 27 from the rear surface and penetrated to the front surface, and then inserted from the front surface at a position away from the penetration point and penetrated to the rear surface. The tip of the wire 43 is attached to the wire 43 by connecting the tip of the wire 43 to the tip of the wire 43 with a wire sleeve 93. The sponge body or sponge 27 is an open-cell type and is formed to absorb water so that its specific gravity becomes 1 or approximately 1. For example, it functions to float in water. When it is dropped into the sewer pressure pipeline 1, it is placed in the sewage 11 (see Figure 1) and is carried downstream by the sewage 11. The sponge body 27 may be a single piece or may be made up of three layers of sponge body 27, each approximately 30 mm thick and 150 mm in diameter. Here, the inner diameter of the sewer pressure pipeline 1 is, for example, 200 to 300 mm, but the sponge body 27 can have a diameter of about half the inner diameter of the sewer pressure pipeline 1 so that it can move smoothly within the sewer pressure pipeline 1 and generate a large traction force. Alternatively, the sponge body 27 is formed to have an area sufficiently larger than the rear end of the survey machine main body 29. Also, the wire 43 may be provided with a swivel to prevent twisting.

[0034] The investigation device main body 29 can have a specific gravity of less than 1, for example, 0.6 to 0.75, so that it floats on the water or water surface. The sponge body 27 pulls the investigation device main body 29, and for example, in the downward piping section 5, as shown in Figure 6, if the floating speed A exceeds the flow speed B and the sponge body 27 is not connected, the investigation device main body 29 may move upward (Figure 6a), but the pulling force of the sponge body 27 moves the investigation device main body 29 at a traveling speed C that is, for example, slightly lower than the flow speed B (Figure 6b).

[0035] The manner in which the pipeline inspection device 25 detects an air pocket in the sewer pressure pipeline 1 will be described with reference to FIG.

[0036] The flow velocity of the pressure-fed sewage 11 is constant or nearly constant, for example, at 0.6 m / sec to 3.0 m / sec. When the pipe investigation device 25 is inserted or introduced into the pressure-fed sewer pipeline 1, the pipe investigation device 25 rides on the flow of the sewage 11 and moves downstream through the pressure-fed sewer pipeline 1 (see FIG. 2). In a location where the pressure-fed sewer pipeline 1 is filled with sewage 11 and there is neither a free water surface nor an air pocket, as shown in FIG. 7a, the pipe investigation device 25 moves so that the outer surface of the cylindrical portion 49 of the casing 33 rubs against or approaches the ceiling of the pressure-fed sewer pipeline 1. As a result, the sewage 11 in the sensor detection recess 61 is also present outside the upper end of the copper tape 80 attached to the inner chassis 35, and the sewage 11 surrounds the entire outside of the copper tape 80, so the detected capacitance between the copper tapes 80 is large. However, at a location where the sewage 11 flows with a free water surface 95 and an air pocket 97 occurs within the sewer pressure pipeline 1, as shown in Figure 7b, the upper side of the casing 33 of the pipeline investigation device 25 rises above the free water surface 95, and since there is no sewage 11 outside the upper end of the copper tape 80 attached to the inner chassis 35, the detected capacitance between the copper tapes 80 becomes smaller, thereby making it possible to identify the location where the air pocket 97 occurs.

[0037] Here, as shown in Figure 8, there is a case where the inside-pipe investigation device 25 (investigation device main body 29 or casing 33) enters a recess 99 in the sewer pressure pipeline 1 and gets caught on a step 101 (Figure 8a). The recess 99 into which the inside-pipe investigation device 25 enters may be a gate valve 13 or a joint (not shown). In this case, the sponge body 27 pulls the investigation device main body 29 via the wire 43, so that the tip of the avoidance member 45 of the investigation device main body 29 moves to the corner of the step 101 (Figure 8b). If the sponge body 27 further pulls the investigation device main body 29 from here, the tip of the avoidance member 11 bends slightly in the direction of travel and goes over the corner of the step 101 (Figure 8c). Furthermore, when the sponge body 27 pulls the investigation device main body 29, the investigation device main body 29 rotates horizontally with the contact point with the corner of the avoidance member 45 as a fulcrum (see the arrow with the black tip in Figure 8d), and becomes horizontal and escapes from the step 101 (Figure 8e).

[0038] Next, as shown in Figure 9, after the wire 43 is cut for some reason, the pipe investigation device 25 (investigation device main body 29 or casing 33) may enter a recess 99 in the sewer pressure pipeline 1 and get caught on a step 101 (Figure 9a). In this case, the traction force of the sponge body 27 as shown in Figure 8 does not work, so the investigation device main body 29 or casing 33 remains in the recess 99. However, after a certain period of time or if it remains there for a long time, the resin plugs 67, 69 of the water inlets 63, 65 dissolve, opening the water inlets 63, 65. Then, sewage 11 flows into the tank of the investigation device main body 29 from the water inlets 63, 65. Since the specific gravity of the investigation device main body 29 slightly exceeds 1, the investigation device main body 29 sinks from the recess 99 into the main pipe and descends (Figure 9b). Then, it moves downstream with the flow of sewage 11 (see arrow). Here, the tank section into which the sewage 11 flows is the entire inside of the casing 33 or the entire inside of the combination of the casing 33 and the inner chassis 35, but it is also possible to configure a part of the casing 3 as the tank section, with one or more water inlet ports formed in this tank section and closed with a resin plug. Here, when the resin plug dissolves after a predetermined time (for example, a long time) and the water inlet port opens, the sewage flows into the tank section, which is part of the casing 3, and the specific gravity of the investigation device main body 29 becomes slightly more than 1.

[0039] It is also conceivable that at the air valve 15, the pipe investigation device 25 (investigation device main body 29 or casing 33) with its wire 43 cut may enter, for example, the repair valve 17 side in a vertical position (Fig. 10a), but even in this case, the resin plugs 67, 69 of the water inlets 63, 65 will dissolve after a certain period of time, opening the water inlets 63, 65. When this happens, sewage 11 will flow into the investigation device main body 29 from the water inlets 63, 65, and the specific gravity of the investigation device main body 29 will slightly exceed 1, so the investigation device main body 29 will sink and descend into the main pipe from the repair valve 17 side (Fig. 10b).

[0040] Furthermore, the inside-pipe investigation device according to the present invention can be configured from a thick-walled capsule-shaped casing 33 made of resin (here, made of polycarbonate) having a rear-end opening 31, a thin-walled inner chassis 35 made of resin (here, made of polycarbonate) fitted into this casing 33, electronic components 37 including an electronic board and a battery arranged inside the inner chassis 35, and a lid member 41 removably attached to the rear-end opening 31 of the casing 33 with bolts or screws 39 and hermetically closing the rear-end opening 31. In other words, the inside-pipe investigation device 25 can be configured without the wire 43, the resin avoidance member 45, and the sponge body 27. [Explanation of symbols]

[0041] 1 Sewerage pressure pipeline 11 Sewer 25 Pipeline inspection device 33 Casing 63, 65 Water inlet 67, 69 Resin stopper 80 Copper Tape

Claims

1. A pipeline investigation device that investigates the inside of a pipeline while riding the flow of water and moving downstream, A casing; a sensor disposed within the casing for detecting a corroded portion on the inner surface of the pipeline or for predicting a corroded portion on the inner surface of the pipeline; a tank portion provided in the casing and having a water inlet; a plug member that closes the water inlet, The pipe line inspection device is characterized in that the plug member dissolves when immersed in water inside the pipe line for a predetermined period of time, thereby opening the water inlet.

2. 2. The pipe line inspection device according to claim 1, wherein the plug member is made of PVA.

3. the sensor is a capacitance sensor that detects a free water surface or an air pocket in the pipeline; 3. The pipe line inspection device according to claim 1, wherein the capacitance sensor has a pair of electrodes extending along the entire circumference or nearly the entire circumference of the inner circumferential surface of the casing.

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