JPH10281915A - How to identify the leak location from the inner pipe in a double pipe - Google Patents

Abstract

(57) [Summary] [Purpose] In double piping, the position of leakage from the inner pipe is
With a simple device, it can be specified in a short range in a short time. SOLUTION: A space 5 formed by an inner tube 2 and an outer tube 3.
Is closed in the measurement section, and after the test gas is injected into the space 5, the air for flowing the test gas into the inner pipe 2 in a certain direction is sucked into the inner pipe 2. Insert the suction nozzle 15 (or sensor) and insert the inner tube 2
Is moved in the tube axis direction to obtain the concentration distribution of the test gas in the tube axis direction. Then, the position at which the concentration has changed is specified as a leak location. Further, the position is specified from the amount (length) of the inserted suction nozzle 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for specifying the location of a leak in a double pipe consisting of an inner pipe and an outer pipe when a leak occurs in a part or a plurality of parts of the inner pipe.

[0002]

2. Description of the Related Art The most basic method for determining the location of a leak from a gas pipe buried underground is to drill a portion that seems to be leaking and insert an odor stick into it. And a method of moving a gas detector along a pipe and estimating a position having the highest gas concentration as a leak position.

[0003] Further, a gas is sucked from the inside of the pipe until oxygen is detected, and the position of the sucked oxygen is calculated by dividing the amount of gas sucked until the oxygen is detected by the cross section (inner diameter) of the pipe. However, there is also a method of estimating this as a leakage position.

[0004] However, any of the above-mentioned methods is a case where the pipe is a single pipe. For example, in the case of a pipe buried underground that requires heat retention or cooling, fluid is passed through the inner pipe, A double pipe is used in which the outside of the inner pipe is covered with a heat insulating material, and the outside is further covered with an outer pipe. In such a double tube, if the outside of the inner tube is sealed with the outer tube, even if a leak occurs in the inner tube, not only this leak itself may not be known, but even if there is a leak. Since the leaked material is only leaking into the outer tube, its position cannot be specified.

[0005] For this reason, if it is considered that a leak has occurred, it is necessary to excavate the section and replace the pipe, which requires enormous costs. Also, if left as it is, the leaked material will fill the space between the inner tube and the outer tube, will flow through the outer tube and flow out from the end, and will accelerate the deterioration of the heat insulating material and reduce the heat insulation performance. Problems occur.

As described above, it is very difficult to detect a leak from the inner pipe of a double pipe, but the following leak detection method is currently known. 1. Leakage is detected by sealing a gas higher in pressure than the fluid pressure in the inner tube between the outer tube and the inner tube and measuring the differential pressure (Japanese Patent Laid-Open No. 52-33583). But,
In this method, even if the presence or absence of leakage can be detected, the leakage position cannot be specified.

[0007] 2. By injecting helium gas between the inner tube and the outer tube, putting two inflators in the inner tube, and detecting the helium gas leaking between the inflators with the nozzle,
Method for detecting leak and its position (Japanese Patent Laid-Open No. 61-1844)
No. 37). However, this method has the disadvantages that it takes time and effort to insert and recover the inflatable body into the inner tube, and requires a device for operating the inflatable body, which requires a large inspection work. is there.

[0008] 3. A method in which the inner pipe and the outer pipe of a double pipe are divided into multiple sections, and a leak and its location are specified based on a pressure change in each section (Japanese Patent Application Laid-Open No. 64-59030).
However, in this method, it takes time and effort to divide a large number between the inner pipe and the outer pipe, and since the pressure change is detected in each of these sections, this detection also takes time and time.

4. A slider attached to the linear body to be fed is inserted into the inner pipe of the heat-insulated double pipe buried underground, and this is advanced by pressurized air. When the slider has passed the leak location, the air flowing into the air space from that location is used to activate the detection means such as an inflatable bag attached to the exhaust plug of the outer tube, and the linear line drawn out at that time The position of the leak is detected based on the length of the body.
306965). However, according to this method, since the slider is moved by the compressed air, the size of the apparatus is increased, and the slider may not move well depending on the inner surface of the inner pipe, and the detection operation takes time. Also, it is difficult to find a small amount of leakage.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for easily detecting a leak from an inner pipe and its position in a double pipe.

[0011]

According to the present invention, there is provided a method for specifying a position of leakage from a double pipe according to the present invention. 1. In a double pipe comprising an inner pipe and an outer pipe, a space formed by the inner pipe and the outer pipe is cut off in a measurement section, and a test gas is injected into the cut-off space. In this state, the inspection gas detection unit is inserted into the inner pipe and moved, and a change position of the gas concentration detected by the gas detection unit is specified as a leak point.
A method for specifying a leak position from an inner pipe in a double pipe.

2. 2. The method according to claim 1, wherein the gas detection unit is a gas suction nozzle, and the leakage position from the inner pipe in the double pipe is specified. 3. 2. The method for identifying a leak position from an inner pipe in a double pipe according to the above item 1, wherein the gas detector is a gas sensor. 4. 4. The method for identifying a leak position from an inner pipe in a double pipe according to the above 1, 2 or 3, wherein helium gas is used as a test gas. 5. 5. The method for specifying a leak position from an inner pipe in a double pipe according to the above 1 or 2 or 3 or 4 used for detecting a plurality of leak locations.

[0013]

[Working] When performing work, in the case of a pit, if there is an underground pipe without a pit, first excavate both ends of the inspection section to dig a working groove. Then, the pipe is cut in the working groove. Next, in the cut section, a space formed between the inner tube and the outer tube is closed and air is purged from this space, and then a test gas such as helium gas is injected into the space.
At the same time, air is blown into the inner tube by a blower or the like to create a flow of air. Then, the suction nozzle or the sensor of the test gas detector is inserted into the inner tube and moved in the test section, thereby detecting the test gas. If there is a pinhole or the like in the inner tube, the test gas leaks from the inner tube into the inner tube, and this can be immediately detected by the test gas detector. Then, the position at which the concentration of the test gas has changed is specified as a leakage point, and the position is specified by obtaining the insertion distance of the suction nozzle or sensor at this time. Further, when there are a plurality of leak locations in the inspection section, the gas concentration changes at the leak locations each time, so that the plurality of leak locations can be specified.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention is based on the premise that a test gas is press-fitted into a space between an inner pipe and an outer pipe of a double pipe. For this purpose, the examination section is limited, both ends of this section are cut off, and the space between the inner tube and the outer tube is closed at both ends.

Then, a test gas is injected into the space from one cut side. At this time, at the other end, air in the space is purged, and the space is replaced with a test gas.
At the same time, a flow of air is created in the inner tube using a blower.
This is for clearly measuring the position where the concentration on the upstream side and the downstream side changes from 0 to a certain value or changes from a certain value to 0 with respect to the position leaking into the inner pipe. In this state, the suction nozzle or sensor of the inspection gas detector is inserted from one end of the inner tube, the concentration of the inspection gas in the inner tube is measured, and if the concentration changes, the location can be estimated as the leak position. . Therefore, the leakage position can be specified by measuring the distance from the end to the tip of the inserted suction nozzle or sensor. The suction nozzle or the sensor may be inserted from either the upstream side (blower side) or the downstream side in the inner pipe. The suction nozzle or sensor may be attached to the end of a graduated pipe or cable.However, while measuring the insertion distance by mechanical means, measure the concentration of the test gas at the same time, and immediately locate the leak position on the display screen. May be displayed or printed out.

[0016]

Embodiment 1 This embodiment will be described with reference to FIGS. 1 is a hot water pipe having a double pipe structure, 2 is an inner pipe, 3 is an outer pipe, 4 is a heat insulating material coated on the outside of the inner pipe 2, 5 is a space formed between the heat insulating material 4 and the outer pipe 3. It is.

6, 6a are working grooves (or pits), 7, 7
a is a shielding plate that closes both ends of the space 5 at the groove of the cut pipe 1 in the working grooves 6 and 6a, 8 is a helium gas cylinder, 9 is a helium gas supply hose. , 10 is an air purge hole, 11 is a blower, 12
Is an air pressure feeding duct, 13 is a wind speed measuring device, 14 is a helium gas measuring device, 15 is a helium gas suction nozzle, and 16 is a helium gas suction hose connecting the suction nozzle 15 and the measuring device 14.

In the case of the above embodiment, helium gas is injected into the space 5 via the helium gas supply hose 9 from the helium gas cylinder 8 into the space 5 closed by the shielding plates 7 and 7a. Is purged from above, and when the space 5 is replaced with 100% helium gas, the purge hole 1
0 is closed. At this time, the pressure of the helium gas in the space 5 is 0.1 to 0.2 kg / cm ² .

Next, the blower 11 is driven to feed air from the air pressure duct 12 into the inner pipe 2 to create an air flow in the inner pipe 2. At this time, the wind speed measured by the wind speed measuring device 13 is 1.3 m / s.

After setting the conditions as described above, the suction nozzle 15 is inserted into the inner pipe 2 from the downstream side, and this suction nozzle 1
5, the helium gas flow 8 ′ leaking from the leak point P in FIG. 1 is sucked, and its concentration is measured by the helium gas measuring device 14. Then, in FIG. 3, the location of the arrow where the helium gas concentration distribution has significantly changed is specified as the leakage position. At this time, the insertion distance of the suction nozzle 15 is 17.2 m from the insertion end. In the above embodiment, the suction nozzle 1
Although the helium gas is sucked in at 5, it is also possible to detect a leaked portion by a method of detecting a helium gas with a helium gas sensor. In addition, the present inspection can be performed using an inert gas such as a nitrogen gas in addition to the helium gas.

[0021]

As described above, according to the present invention, in a double pipe, a leak point from the inner pipe can be specified in a very narrow range, so that repair work on the pipe can be performed in a narrow range, and the construction period and Significant reduction of construction cost is possible. Further, in the present invention, since the test gas is detected while creating an air flow in the inner pipe, the concentration distribution changes dramatically at the leak location. As a result, it is easy to specify the leak location, and there is almost no error. In addition, it is possible to specify a plurality of leak locations and positions. Further, in the present invention, since the suction nozzle or the sensor is only taken in and out of the inner tube, the device is simplified and the working time is reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an explanatory view of a cross section of a pipe.

FIG. 3 is an explanatory diagram of an example in which an average value of a helium gas concentration is plotted to specify a leak location and its location.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hot water piping 2 Inner pipe 3 Outer pipe 4 Heat insulation material 5 Space 6, 6a Working groove 7, 7a Shield plate 8 Helium gas cylinder 8 'Helium gas flow 9 Helium gas supply hose 10 Air purge hole 11 Blower 12 Air pressure duct 13 Wind velocity measuring device 14 Helium gas measuring device 15 Helium gas suction nozzle 16 Helium gas suction hose P Leak point

Claims (5)

[Claims] In a double pipe comprising an inner pipe and an outer pipe, a space formed by the inner pipe and the outer pipe is cut off in a measurement section, and a test gas is injected into the cut off space. Creating an air flow in the inner tube, inserting and moving the inspection gas detector in the inner tube in this state, and identifying a change position of the gas concentration detected by the gas detector as a leak location. A method for specifying the leakage position from the inner pipe in a double pipe. 2. The method according to claim 1, wherein the gas detector is a gas suction nozzle. 3. The method according to claim 1, wherein the gas detector is a gas sensor. 4. The method according to claim 1, wherein helium gas is used as the inspection gas. 5. The method according to claim 1, wherein said method is used for detecting a plurality of leak locations.