JP2003185075A - Leakage detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a leakage detecting method capable of surely detecting leakage at the time of a leakage test by positively discharging to the outside a leak due to a nailing mistake. <P>SOLUTION: In the leakage detecting method, a joint for a metal flexible pipe comprising a joint body 1 and a nut 3 to detect gas leaked from the metal flexible pipe in which the outer surface of a metal corrugated pipe 70 passing gas is coated with a synthetic resin layer 71. Gas leaking from the metal corrugated pipe reaches the joint for the metal flexible pipe through the clearance between the metal corrugated pipe and the synthetic resin layer, and passes through a selective permeation member 5 which allows gas to pass through and does not allow liquid to pass through. Thus, the leakage of gas can be detected by positively discharging the gas to the outside. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a joint for connecting a metal flexible pipe for gas, which is laid in the wall surface of a house or under the floor. The present invention also relates to a leak detection method capable of surely detecting a leak.

[0002]

2. Description of the Related Art In recent years, metal flexible pipes are often used as gas pipes for houses and the like. This metal flexible tube is made by corrugating a stainless hoop material of about 0.2 to 0.3 mm, and coating the outer surface of the corrugated tube thus finished with a soft vinyl chloride resin of about 0.5 to 1.0 mm (synthetic resin coating). Layers are commonly used.

As a joint for this metal flexible pipe, for example, there is one disclosed in Japanese Utility Model Publication No. 6-47193 shown in FIG. This joint has a corrugated inner surface that engages with the outer surface of the metal flexible tube F, and has a sleeve B with slits in the axial direction, and a screw on the front part (right side in the drawing), and this end surface is behind the sleeve B. A joint body having a nut C which is pressed against the end surface and a female screw which is screwed to the male screw of the nut C on the inlet side (left side in the drawing), and the sleeve B is mounted on the inner side so that the nut C is screwed in. It consists of A.

In order to connect the metal flexible pipe F, the sleeve B is first opened to open the metal flexible pipe F.
After mounting them in a position where a few ridges are left and fitting them into the joint body A, the nut C is screwed into the joint body A and tightened to move the sleeve B to the back side, and the flexible pipe F The projecting end is crushed to the back wall and connected with a sealing property. Further, in this joint, in order to prevent the intrusion of water and dust from the outside, the T-type watertight packing D disclosed in Japanese Utility Model Publication No. 4-35667 is mounted in the groove formed in the nut C. ing.

By the way, in the method using the metal flexible pipe, the wall flexible panel may be nailed and fixed after the metal flexible pipe is piped in the wall surface or under the floor. At this time, a nail may be accidentally driven into the metal flexible pipe, and therefore, it is obligatory to attach a metal protective plate to the nailing site, but it is not perfect.

Therefore, as disclosed in JP-A-62-31789,
There is also a proposal that a sealing material is filled in advance between the metal corrugated tube and the synthetic resin coating layer on the outer surface so that even if the nail is accidentally nailed, the nail hole is closed by this and the leak is stopped. However, this was unrealistic because of long-term safety concerns. After all, a normal metal flexible pipe is used, and the safety is confirmed by performing a gas leak test before mounting the gas plug, and after mounting and before moving in.

[0007]

However, since the resin coating layer on the outer surface of the above-mentioned metal flexible tube has flexibility and hermeticity by itself, the resin adheres around the driven nail, and even if the inner side Even if gas leaks from the metal corrugated tube, the resin layer on the outside and the joint portion (T-type watertight packing, etc.) may stop the leak and may be sealed. Alternatively, only subtle leaks may occur. On the other hand, the gas leak test is required to be simple and can be performed in a short time. Therefore, for example, about 700 mmAq of air is enclosed in the pipe, and this is a predetermined amount (for example, several 10 mmAq) within a predetermined time (for example, 2 minutes) The leak judgment standard is whether or not it decreases. That is, this inspection only detects a relatively large leak, and the nailing leak as described above may not be found even by the actual leak inspection. Alternatively, there is a problem that it cannot be detected within a predetermined inspection time.

The present invention solves the above problems, and provides a leak detection method which positively discharges a leak due to a nailing mistake and can surely detect the leak during a leak inspection. The purpose is to do.

[0009]

According to a first aspect of the present invention, a joint for a metal flexible pipe composed of a joint body and a nut is connected to one end, and a synthetic resin layer is coated on the outer surface of a metal corrugated pipe through which gas flows. In a leak detection method for detecting gas leaking from a metal flexible pipe, the gas leaked from the metal corrugated pipe is connected to the metal flexible pipe joint through a gap between the metal corrugated pipe and the synthetic resin layer. Reach the joint body and /
Alternatively, it is a leak detection method of detecting a leak of gas by passing the gas through a selective permeable member that allows gas but not liquid to be positively discharged to the outside through the nut. In this case, for example, as defined in claim 2, the permselective member has a continuous porous structure.

If a nail is mistakenly driven into the metal flexible pipe, the metal corrugate pipe does not have a sealing property, and therefore the gas in the pipe leaks out from here. On the other hand, since the outer synthetic resin layer has a hermeticity, the periphery of the nail is sealed and the leakage from here may be stopped. However, since there is a slight gap between the metal corrugated pipe and the synthetic resin layer, the leaked gas (filled air at the time of leak inspection) moves through this gap in the pipe axial direction of the flexible pipe, and Reach the joint. On the other hand, the joint body or the nut side is provided with, for example, an air passage communicating with the outside of the joint, so that the gas is eventually exhausted to the outside through the air passage. At this time, the ventilation passage is used as a through hole, and the through hole is further closed with a selectively permeable member. This also positively permeates and discharges gas from the inside of the joint to the outside, while at the same time from the outside to the inside of the joint. It can prevent the permeation of solids (such as dust) and liquids (such as water and dew). As described above, at the time of the leak inspection, the leak can be surely detected and the nailing error or the like can be known. As the metal flexible pipe used at this time, it is preferable that the metal corrugated pipe and the synthetic resin layer are not in close contact with each other so that a continuous gap is maintained between them in the axial direction. It is desirable that the metal flexible pipe has a ventilation groove formed continuously in the pipe axis direction.

The selective permeation member is made of a sheet material containing a continuous porous membrane formed by pressing and solidifying tetrafluoroethylene resin powder, and then forming continuous fine pores of 0.1 to 5 μm. However, it is possible to pass a gas such as air or water vapor, but repel a liquid such as water. Alternatively, it is a porous body having continuous pores formed from thermoplastic resin powder such as polyethylene, polypropylene, polymethyl acrylate, polystyrene, ethylene vinyl acetate copolymer, and tetrafluoroethylene polymer, or polyvinyl alcohol and formaldehyde. You may use the porous sheet material etc. which have continuous pores shape | molded by making it react with an acid catalyst. These selectively permeable members have gas permeability such as air and water vapor, and moisture permeability, while also having waterproofness that does not allow liquids such as water and chemicals to pass therethrough. Excellent chemical resistance, heat resistance, and weather resistance. Therefore, solids (dust, etc.) and liquids (water, dew, etc.) can be prevented from permeating and entering the fitting from the outside, preventing moisture and dirt from entering from the outside and corroding the inside for a long period after pipe construction. Problem does not occur.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method of the present invention will be described below with reference to the drawings. First, as shown in FIG. 1, the metal flexible tube 7 is composed of a stainless (SUS304) corrugated tube 70 and a vinyl chloride synthetic resin layer 71 covering the outer surface of the corrugated tube 70. The corrugated tube 70 is a continuous 0.2 mm stainless hoop material. The flexible pipe is formed by corrugation, and then the resin coating step is performed to continuously coat the outer surface with a synthetic resin layer 71 of about 0.75 mm to form the outer resin coating layer. . The degree of adhesion between the corrugated tube 70 and the synthetic resin layer 71 can be changed by appropriately changing the resin extrusion molding die shape and molding conditions and operating the size of the interval, etc. As shown in FIGS. 7 and 8, between the metal corrugated pipe 70 and the synthetic resin layer 71, a plurality of ventilation grooves 72 continuous in the pipe axial direction are formed. As shown in FIGS. 7 and 8, the ventilation grooves 72 are recessed grooves extending in the tube axis direction and provided at substantially equal intervals on the circumference. The number, width and height of the ventilation grooves 72 can be set appropriately. To do. For example, in a tube having a diameter of 10 mm, it is possible to exemplify that about 40 concave grooves having a height of 0.5 mm are continuously provided over the entire circumference.

As shown in FIG. 1, the metal flexible pipe joint of the following embodiment has a joint body 1, a retainer 2, a nut 3, a T-type watertight packing 4, a selective permeable member 5, a fireproof gasket 61 and a fireproof expansion packing 62. ， Watertight O-ring 63
It consists of The joint body 1 is on the inlet side (left side in the drawing)
A female thread 11 that is screwed into the nut 3 toward the inner side, an annular recess 12 having a diameter slightly larger than the female thread root diameter, and a reduced diameter hole portion 13 having a tapered inner surface that is reduced toward the inner side. A back wall 14 is formed between the through hole 15 and the stepped surface. Back wall 14
A refractory gasket 61 and a refractory expansion packing 62 are mounted next to it, but these are not always necessary and the flexible pipe may be crushed directly to the back wall. Further, the reduced-diameter hole portion 13 may not be a tapered surface but may be parallel inner surfaces.

The nut 3 is a male screw from the front (right side in the drawing).
31, an engagement groove 32 for locking the retainer 2 rotatably and axially movable on the inner surface side thereof, an O-ring 63 at the rear end of the male screw 31, and a concave groove 33 on the rear inner surface. The formed T-type watertight packing 4 is attached. The engagement groove 32 that locks the retainer 2 may be provided at the front end of the nut 3 or on the outer surface side, and may be a concave groove shape that is not long concave and cannot move in the axial direction. .

The retainer 2 is a metal (copper alloy) tightening body.
21 and a resin (polyacetal) guide body 22 are integrally molded, and are a composite of metal and resin. At the tip end, axial slitting grooves are provided at 4 to 6 places on the circumference, and elastically. The diameter can be expanded and reduced. The tightening body 21 has a projection 20 at the tip thereof that fits into the first valley of the tip of the corrugated tube and crushes one peak, and a pressing surface 34 that contacts the tip of the nut 3 is formed on the rear side. There is. Further, a claw 23 is provided at the rear end of the guide body 22, and the engaging groove 32 of the nut described above is provided.
This claw is fitted inside and locked, and the projection 20 has an annular recess 12
Holds in place. As a result, the front projection 20 is expanded and contracted around the rear locking portion as a fulcrum so that the so-called pivot movement is possible.

Next, a procedure for connecting the metal flexible pipe joint will be described. First, the joint body 1 and the nut 3 are preliminarily screwed and temporarily assembled while leaving a tightening amount of about one ridge of the metal flexible tube 7 to be connected. In this state, the position of the protrusion 20 of the retainer 2 coincides with the position of the recess 12 of the joint body, and the diameter can be expanded. This position is held by fitting a spacer (not shown) between the joint body 1 and the nut 3. Next, when the metal flexible pipe 7 is inserted and pushed in, the protrusion 20 of the retainer 2 is pushed by this pipe and pivots about one end in the engaging groove 32 as a fulcrum, and is pushed open to expand the diameter to make the metal flexible. The insertion of one tip of the pipe is permitted, and the pipe abuts the refractory gasket 61 to prevent the advance. Along with this, the projection 20 is reduced in diameter and fitted into the first valley. At this time, even if the user tries to pull out the tube, it does not come off, so that it can be known that one mountain has passed normally. After that, when the nut is completely tightened, the tip 1 ridge ahead of the protrusion 20 is crushed by the fire-resistant gasket surface and connected with a sealing property. As described above, in this joint, it is intended to crush one peak of the metal flexible tube, and the distance from the protrusion 20 to the gasket and the tightening amount are set to be approximately one peak. Therefore, one tip of the metal flexible pipe is always crushed with a normal sealing property, and at the same time, it has a function of confirming whether or not the pipe is properly inserted. Incidentally, the joint used in the present invention is not limited to the above structure,
For example, the conventional joint shown in FIG. 9 may be used.

[Embodiment 1] In this embodiment, as shown in FIG. 1, the nut 3 is provided with a through hole 17 having a diameter of about 1 mm, and the selective permeable member 5 is provided on the outer surface side of the through hole 17. The holes are closed by sticking and adhering, and the leaked gas is discharged to the outside through the selective permeable member 5. The selectively permeable member 5 has a function of permitting gas permeation from the inside of the joint to the outside, but preventing entry and permeation of solids (dust and the like) and liquid (water and dew etc.) from the outside into the joint. Here, the sheet material has a multilayer structure as shown in FIG. For example, this is composed of a base material layer 51 of polyester, a porous film 52, an adhesive layer 53 and a detaching separator 54, and the total thickness is about 1 mm. The porous membrane 52 is formed by pressing powder of tetrafluoroethylene resin and then rapidly stretching it under appropriate conditions to form 0.1 to 5 μm.
It has a continuous porous structure in which some small pores are continuously connected. The pore diameter and porosity can be changed depending on the stretching method under specific conditions. As described above, the selectively permeable member 5 has gas permeability such as air and water vapor and water repellency that repels liquid, and also has dust resistance, chemical resistance, heat resistance, weather resistance, etc. Are better.

Therefore, if a nail is mistakenly driven into the metal flexible pipe 7 during construction, the airtightness of the metal corrugated pipe 70 is lost, but the airtightness of the synthetic resin coating layer 71 may be maintained. . However, during the leak inspection, the gas (air) leaked from the metal corrugated pipe 70 reaches the main joint at the end through the ventilation groove 72 and the like, and the synthetic resin layer 71 and the nut 3
Can leak out through the through hole 17 through the space between the inner surface and the inner surface. Therefore, it is possible to reliably detect the presence of leakage, and it is possible to take safety measures such as re-installing the pipe. The through holes 17 may be provided on the joint body 1 side, or on both sides of the joint body and the nut, or the selectively permeable member 5 may be attached to the inner surface side of the nut 3. If the selectively permeable member 5 has a porous film 52, it is an adhesive layer.
The 53, the separator 54 and the like are not particularly necessary, and may be fixed by pressing on one surface of the nut 3 by using a pressing member.

[Embodiment 2] In this embodiment, a through hole 18 is provided on the joint body 1 side as shown in FIG. 2, and the through hole 18 is closed by a selectively permeable member 5 or 5a (in the figure, 5a), the leaked gas is the selectively permeable member 5 or 5
It is discharged to the outside via a. That is, as the selective permeable member, the sheet-like selective permeable member 5 used in the above-mentioned embodiment may be attached, but in the present example, the selective permeable member 5a made of a porous body having continuous pores. Was carried out by filling the inside of the hole. Examples of the raw material of this porous body include thermoplastic resin powders such as polyethylene, polypropylene, polymethyl acrylate, polystyrene, ethylene vinyl acetate copolymer, and tetrafluoroethylene polymer. Pore size 1 to 50μ
A three-dimensional continuous network structure having fine pores of about m, here a porous body having continuous pores. This product is suitable for a structure in which it can be formed into a thick wall, and the thickness can be adjusted relatively easily, so that it can be packed in the through hole as in this example. In the case of this example, the gas reaches the through hole 18 through the gap of the axial slit of the retainer 2 and leaks to the outside of the joint through these ventilation passages.
The other parts are the same as those in the above-described embodiment as indicated by the same reference numerals, and the description thereof will be omitted.

[Embodiment 3] In this embodiment, as shown in FIG. 3, a through hole 10 is provided on the nut 3 side, and the through hole 10 is closed by the selectively permeable member 5b. Is discharged to the outside through the selectively permeable member 5b. The selectively permeable member 5b of this example is a small cylindrical body having an average pore diameter of 30 μm, a porosity of about 36 ± 6%, and a size of φ4.0 × height 2.2 mm. In this manufacturing method, first, a polyethylene resin powder is heated to a temperature equal to or lower than a melting point, compressed and pressed to form a porous cylindrical body having continuous pores.
Then, after firing this cylindrical body in an inert gas, the skin is peeled off to obtain a band having a desired thickness. Here, the height of the small cylinder is adjusted. Next, this strip is subjected to water and oil treatment, cut into an appropriate length, and then press punched to form a small cylinder having the above dimensions.

The through hole 10 formed on the nut side has two steps, and the upper end has a tapered surface for easy insertion.
A large diameter hole 10 of mm and a small diameter hole 10 ′ of φ3.0 mm are formed.
Then, the selectively permeable member 5b, which is the small cylindrical body, is press-fitted into the through hole 10 and received by a small-diameter step, and then a punch (not shown) is driven into the through hole to caulk the taper surface at several places to prevent it from coming off. ing. Here, the selectively permeable member 5b
Since the material is pressed in and compressed in the radial direction, the air permeability can be adjusted by changing the compression rate.
It is desirable to apply a water repellent agent to the through holes in advance. As described above, also in the present embodiment, if a leak test is performed, the gas that has passed through the gap between the corrugated tube 70 and the synthetic resin coating layer 71 or the ventilation groove 74 enters the joint, and the synthetic resin layer 71 and the nut 3 It reaches the through hole 10 through the space between the inner surface and the inner surface and is positively discharged to the outside through the selectively permeable member 5b. As a result, the enclosed pressure drops and the leakage is surely detected.

[Embodiment 4] In the present embodiment, as shown in FIG. 4, a through hole 19 is provided in an annular groove 33 for mounting the T-type watertight packing of the nut 3, and the inner surface of the through hole 19 is selectively permeated. A flexible member 5c to close the hole, and further a T-type packing 4a
A through hole 40 that communicates with the inside of the joint is also provided in a part of the above, so that the inside and outside of the joint are communicated with each other through the one-directional selective permeable member 5c. Then, the leaked gas is discharged to the outside through the selectively permeable member 5c. As the selective permeable member, in addition to the above examples, a sheet material made of a porous body having continuous pores formed by reacting polyvinyl alcohol and formaldehyde together with an acid catalyst may be used. As described above, during the leak inspection, the gas leaked from the nailing portion reaches the inside of the joint from the end of the flexible pipe 7 as shown by the arrow in the drawing, and the gas between the synthetic resin layer 71 and the inner surface of the nut 3 is released. Passing through the space, this penetrates to the T-type packing 4a, passes through the through-hole 40, and leaks to the outside through the selectively permeable member 5c. Therefore, as in the previous example, it is surely detected that there is a leak, and subsequent safety measures are taken. Can be taken. Other configurations are the same as those in the above embodiment. Incidentally, in the above-mentioned embodiment, the selectively permeable member is capable of preventing solids and liquids from invading and permeating from the outside in terms of performance, but the permeation and permeation within a functionally unproblematic range are permissible, Such a selectively permeable member is also within the scope of the present invention. For example, a porous metal sintered body having continuous pores or the same porous ceramic body can be used.

[Test Example] The following test was conducted on the embodiment shown in FIG. 3 to confirm long-term performance. The criterion for pass / fail is to maintain the internal sealing pressure of 700 mmAq for 2 minutes, and the pressure drop at this time should be 30 mmAq or more. At the same time, even if it was submerged in various solutions, there was no permeation into the joint. The above air permeability and waterproofness were evaluated, and the number of co-test products was 10 in each test. (1) Heat aging test The sample was left in a constant temperature bath at 70 ° C for 200 days. At this time, the air permeability was 140 mmAq on average, and the waterproof property was 100% acceptable. (2) Cold / heat cycle test 60 ° C. × 2 Hr → Transition time 1 Hr → −10 ° C. × 2 Hr → Transition time 1 Hr → 60 ° C. × 2 Hr → ...
Cycled. The air permeability at this time is 130 m on average.
There was mAq and the watertightness was 100% acceptable. (3) Weather resistance test The sample was left in a sunshine weather tester for 2000 hours. At this time, the air permeability was 130 mmAq on average, and the waterproof property was 100% acceptable. As described above, it was confirmed that there was no problem in the long-term performance test.

In each of the embodiments described above, the air passage is
Through holes 10, 17, 18, 19 in part of fitting body or nut
Was provided, and each of the through holes was closed with a selectively permeable member. According to these examples, it is desirable that solids and liquids can be prevented from penetrating and permeating from the outside into the joint, and that long-term performance stability and aesthetics are achieved. However, for example, if the through holes 10, 17, 18, 19 provided in FIGS. 1 to 4 are left open,
Even if the through holes are closed with a resin cap or the like after passing the leak inspection, it is possible to confirm the presence or absence of a nailing error and take safety measures.

[Embodiment 5] As another embodiment of the ventilation passage, a ventilation passage is used in which the minute gap between the internal thread 11 of the joint body and the external thread 31 of the nut is replaced with the through hole of the above-mentioned example. . In this case, for example, a slight gap between the internal threads 11 and the external threads 31 at the time of the original accuracy may be used, or the accuracy of the internal threads 11 and the external threads 31 may be reduced to allow a slight gap between the internal threads. A gap may be provided and this may be used. Further, at least one notch groove that is axially connected to a part of both screws, that is, continuous from the recess 12 to the mounting portion of the watertight O-ring 63, is formed, and the gas easily travels through this groove and is discharged to the outside. It can also be a ventilated passage. In this case, the watertight O-ring 63 may be removed, and a selective permeable member may be attached to this portion as needed.

[Embodiment 6] As still another example, as shown in FIG. 5, the outer surface of the T-type watertight packing 4b or the groove 33 is formed.
It is also possible to provide at least one concave groove-shaped ventilation passage 41 for communicating the inside and outside of the joint on the inner surface of the.

[0027]

As described above, according to the leak detecting method of the present invention, even if a nail is accidentally driven into the metal flexible pipe, the gas is selectively permeated from the joint portion. A gas leak inspection will always detect that there is a leak, and safety measures can be taken without overlooking a nailing accident. This made it a highly reliable metal flexible pipe joint.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a metal flexible pipe joint for carrying out a first embodiment of the method of the present invention.

FIG. 2 is a cross-sectional view showing a metal flexible pipe joint for carrying out a second embodiment of the method of the present invention.

FIG. 3 is a cross-sectional view showing a metal flexible pipe joint for carrying out a third embodiment of the method of the present invention.

FIG. 4 is an enlarged sectional view of an essential part showing a metal flexible pipe joint for carrying out a fourth embodiment of the method of the present invention.

FIG. 5 is an enlarged sectional view of an essential part showing a metal flexible pipe joint for performing another embodiment of the method of the present invention.

FIG. 6 is a cross-sectional view showing an example of the structure of a selectively permeable member.

FIG. 7 is a half sectional view showing an example of a metal flexible tube suitable for a joint for carrying out the method of the present invention.

8 is a cross-sectional view of FIG.

FIG. 9 is a half sectional view showing an example of a conventional metal flexible pipe joint.

[Explanation of symbols]

1 ... Fitting body 2 ... Retainer
3 ... Nut 4 ... T-type watertight packing 5, 5a, 5b, 5c ... Selective permeable member 7 ... Metal flexible tube 11 ... Female thread of joint body
12 ... Annular recess 13 ... Reduced-diameter hole 14 ... Back wall 10, 17, 18,
19 ... Through hole 20 ... Projection 21 ... Tightening body
22 ... Guide body 23 ... Claw 31 ... Nut external thread
32 ... Engagement groove 33 ... T packing concave groove 34 ... Pushing surface
40 ... Packing through-hole 41 ... Packing ventilation path 51 ... Base material layer
52 ... Porous film 53 ... Adhesive layer 70 ... Metal corrugated tube
71 ... Resin coating layer

Continued front page    (72) Inventor Minoru Fujiyoshi             2nd Daifuku, Kuwana City, Mie Prefecture Hitachi Metals Stock Association             Company Kuwana factory (72) Inventor Takashi Anamizu             1-5-20 Kaigan, Minato-ku, Tokyo Tokyo Gas             Within the corporation (72) Inventor Fumitaka Sato             1-5-20 Kaigan, Minato-ku, Tokyo Tokyo Gas             Within the corporation (72) Inventor Katsuhiro Oki             1-5-20 Kaigan, Minato-ku, Tokyo Tokyo Gas             Within the corporation (72) Inventor Toshiyuki Ueno             Sanco 1-17-14 Sakaemachi, Kawaguchi City, Saitama Prefecture             -Within Gas Seiki Co., Ltd. F term (reference) 2G067 AA16 AA17 CC04 DD18 EE08

Claims (2)

[Claims] 1. A leak detection for detecting gas leaking from a metal flexible pipe having a joint body and a nut, which is connected to one end, and a synthetic resin layer is coated on the outer surface of a metal corrugated pipe through which gas flows. In the method, the gas leaked from the metal corrugated pipe is made to reach the metal flexible pipe joint through a gap between the metal corrugated pipe and the synthetic resin layer, and the gas is passed through the joint body and / or the nut. A leak detecting method for detecting a leak of gas by passing the gas through a selectively permeable member that allows gas but not liquid to be actively discharged to the outside. 2. The leak detection method according to claim 1, wherein the selectively permeable member has a continuous porous structure.