JP2018066400A - Double pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pipe capable of being manufactured simply at low cost, having chemical resistance, durability and scale adhesion suppression equivalent to those of a lining pipe.SOLUTION: A pipe includes an outer pipe having a lumen part whose both end parts in a longitudinal direction are opened, and an inner pipe installed in the lumen part and fixed to one end part. A resin raw material constituting the inner pipe is non-adhesion resin. The inner pipe can be inserted along the lumen part of the outer pipe, and has rigidity. The pipe is suitable to, for example, hot spring.SELECTED DRAWING: None

Description

  The present invention relates to a double pipe.

  2. Description of the Related Art Pipes in which a lining material made of a thermoplastic resin such as a fluororesin is in close contact with the inner surface of a metal or general-purpose synthetic resin pipe body (hereinafter sometimes referred to as a lining pipe) are known. (Patent Documents 1 to 4). By using such a lining material, for example, the durability of a steel pipe used for piping for industrial water or domestic water is improved, the chemical resistance of the piping is improved, or scale adhesion is suppressed. It is possible.

  In Patent Document 1, a predetermined tubular lining material is inserted into the inside of a long bent tube with a flange to be lined, and pressurized from the inside of the lining material with a heating fluid to line the inner surface of the long bent tube. The piping obtained by sticking the materials is described. Further, it is described that the lining material is preferably made of vinyl chloride.

  Patent Document 2 describes a synthetic resin tube in which a fluororesin film is bonded to the inner surface of a synthetic resin tube via an adhesive. In the embodiment, a fluorine resin film with an adhesive is pressed and stuck to the inner surface of the pipe with a top roll in a vinyl chloride pipe, and then the roll 5 is rolled in the left-right direction to stick the film to the entire inner surface of the pipe. It is described.

  Patent Document 3 describes a composite pipe in which a polymer layer and a metal layer are alternately stacked, and a connection between the metal layer and the polymer layer is formed by ionic displacement bonding. Moreover, it is described that the polymer layer used as an innermost layer is a fluororesin. Moreover, as a manufacturing method of such a composite pipe, the first polymer resin was extruded to form a first polymer layer, and the reaction derivative was extruded onto the surface of the first polymer layer, and the reaction derivative was extruded. A metal plate film is supplied to the surface of the first polymer layer to form a metal layer, a reaction derivative is extruded to the surface of the metal layer, and a second polymer resin is applied to the outer surface of the metal layer from which the reaction derivative has been extruded. It is described that a second polymer resin is extruded through an extruder to form a second polymer layer.

  In Patent Document 4, for example, a fluororesin lining tube in which a thin stainless steel mesh is wound around an outer peripheral surface is brought into close contact with an inner peripheral surface of a steel pipe having no vent hole, or polytetrafluoroethylene (hereinafter referred to as PTFE) is bonded to the outer peripheral surface. And a fluororesin lining tube in which a seal tape made in a spiral shape is wound is described.

  Such lining pipes, particularly those using fluororesin as a lining material, may be used to deliver mineral spring water such as hot spring water and cold spring water from a source to a facility such as a hot spring inn. For example, in the case of hot spring water, when it is delivered from a hot spring source, its components are altered by cooling or contact with oxygen, so the components in the hot spring water precipitate and adhere to the inner surface of the piping. . By using the lining pipe, it can be expected that the adhesion of the components in the hot spring water to the pipe is suppressed or that the peeling can be facilitated even if it adheres. However, in order to manufacture such a lining pipe, special mechanical equipment is required, and therefore the cost is higher than a pipe that does not use a lining material. Many hot spring operators are unable to use such lining piping because it is difficult to make large capital investments. Moreover, it is the same in the point that not only a hot spring business operator but a conventional lining piping will use an expensive equipment cost.

Japanese Patent Publication No. 56-37889 Japanese Patent Laid-Open No. 10-61833 Special table 2015-520042 gazette Japanese Patent Laid-Open No. 3-149497

  As described above, in view of the current situation that the conventional lining piping is expensive, the object of the present invention is that it can be easily manufactured at low cost, and has chemical resistance, durability, and scale adhesion suppression, The object is to provide a pipe having performance equivalent to that of a lining pipe.

  As a result of diligent investigations by the present inventors, the pipe has a double tube structure of an outer tube and an inner tube, and the inner tube is not fixed to the inner peripheral surface of the outer tube, and both are fixed to at least one end. The non-adhesive resin is used as the resin material constituting the inner tube, and it is found that the above-mentioned object can be achieved by giving the inner tube a predetermined rigidity. It came to complete. The gist of the present invention is as follows.

  A first aspect of the present invention includes an outer tube having a lumen that opens at both ends in the longitudinal direction, and an inner tube that is installed in the lumen and is fixed only to one end. The resin material which comprises is non-adhesive resin, and an inner pipe | tube is related to piping which has the rigidity which can be inserted along the lumen | bore part of an outer pipe | tube. In the embodiment of the piping, it can be suitably used for hot springs.

  In the embodiment, the non-adhesive resin is polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), tetrafluoroethylene-hexa. At least one fluororesin selected from the group consisting of a fluoropropylene copolymer (FEP) and polyvinylidene fluoride (PVDF) can be suitably used.

  In the embodiment, the inner surface roughness Ra of the inner tube may be 0.01 μm or more and 2.0 μm or less.

  In the embodiment, the inner tube has a lumen portion that opens at both ends in the longitudinal direction, and a locking portion that protrudes radially outward is provided at one end thereof, and the locking portion is the outer tube. It can comprise so that it may be latched by at least one edge part. In this case, the latching | locking part may be formed in the one end of the inner tube over the perimeter. Further, two or more inner pipes and outer pipes may be connected to each other, and the locking portions of the adjacent inner pipes may be press-contacted by the end portions of the adjacent outer pipes.

  In the embodiment, a space may be formed between the outer peripheral portion of the inner tube and the inner peripheral surface of the outer tube.

  In the embodiment, a convex portion toward the outer tube may be formed on the outer periphery of the inner tube.

  A second aspect of the present invention relates to a method for manufacturing the first pipe of the present invention described above, and relates to a pipe manufacturing method including a step of forming an inner pipe by extrusion molding.

  According to a third aspect of the present invention, the first pipe of the present invention described above has a lumen portion in which the inner tube opens at both ends in the longitudinal direction, and protrudes radially outward at one end portion thereof. In the case where the locking portion is provided and the locking portion is configured to be locked to one end portion of the outer tube, after inserting the inner tube into the lumen portion of the outer tube, The present invention relates to a method for manufacturing a pipe, including a step of forming an engaging portion by bending an end portion.

  According to the present invention, it is possible to provide a pipe that can be easily manufactured at low cost, and has chemical resistance, durability, and scale adhesion suppression performance equivalent to those of a lining pipe.

In Test Example 1, the material levels are fluorine-based, PPS-based, PEEK, iron, and SUS304, and the relationship between surface roughness Ra, material, and total score is shown.

  The pipe according to the present invention is a double pipe including an outer tube having a lumen portion that opens at both ends in the longitudinal direction, and an inner tube that is installed in the lumen portion and fixed to one end portion. The resin material constituting the inner tube is a non-adhesive resin. Further, the inner tube has a rigidity capable of being inserted along a lumen portion of the outer tube.

  In this way, by using non-adhesive resin as the resin material that constitutes the inner pipe, the chemical resistance, durability, and scale adhesion suppression of the inner surface of the pipe have the same performance as the conventional lining pipe. Can be configured. Further, by configuring the inner tube so that it can be inserted along the lumen of the outer tube, the inner tube can be easily inserted into the outer tube, and the inner tube is at least at one end of the outer tube. It is possible to reduce the manufacturing cost in combination with being fixed and installed without being fixed except at the end. Furthermore, by having such rigidity, it is possible to improve the durability of the inner tube. In addition, the existing pipe can be improved by providing the inner pipe in the lumen portion of the existing pipe. By replacing the inner pipe, the pipe can be easily repaired.

  The outer tube has a lumen that opens at both ends in the longitudinal direction and communicates between both ends. The material constituting the outer tube may be made of metal or synthetic resin. It can be determined appropriately according to the application. Examples of the metal include iron and stainless steel. Examples of the iron include a carbon steel pipe for piping (SGP). Examples of stainless steel include SUS304. Examples of the synthetic resin include vinyl chloride resin and polyester resin. Of these, metals are preferable and stainless steel is more preferable from the viewpoint of heat resistance, strength, and corrosion resistance.

  The magnitude | size of an outer tube | pipe does not have limitation in particular, According to a use etc., it can determine suitably. For example, the outer diameter is 25 to 5000 mm, and the thickness is 2.0 to 20.0 mm. The outer diameter is preferably 25 to 500 mm from the viewpoint of productivity and workability. The thickness is preferably 2.0 to 10.0 mm from the viewpoint of productivity and workability. The length can be arbitrarily set as long as it does not hinder transportation, but is generally 100 to 6000 mm.

  The inner tube is inserted along the lumen of the outer tube and installed without being fixed thereto. It has a lumen that opens at both ends in the longitudinal direction and communicates between both ends. The material constituting the inner tube includes a resin material, and may include an additive as necessary.

  The resin material is a non-adhesive resin. The non-adhesive resin is a resin that can suppress the adhesion of scales and the like and can be removed even when it adheres. Examples of such resins include fluororesins, polyphenylene sulfide (PPS), polyether ether ketone (PEEK), alloys of PPS and other resins, polyamide (PA), and the like. Among these, a fluororesin and PPS are preferable, and a fluororesin is more preferable. As will be described later, in the case of hot springs, the temperature of the hot spring water may exceed 100 ° C., and therefore, from the viewpoint of heat resistance, fluororesin and PPS are preferable, and fluororesin is more preferable.

  Examples of the fluororesin include PTFE, PFA, ETFE, FEP, PVDF, polyvinylidene fluoride (PVF), polychlorotrifluoroethylene (PCTFE), and vinylidene fluoride-hexafluoropropylene copolymer. Of these, PTFE, PFA, ETFE, FEP and PVDF are preferred. These may be used alone or in combination of two or more.

  The fluororesin includes a copolymer obtained by reacting a monomer that is a constituent unit of each fluororesin and another monomer copolymerizable therewith when the fluororesin is synthesized. Examples of other monomers include hydrocarbon compounds having a fluorine atom substituent having a reactive double bond. The structural unit derived from another monomer can be 0.1-10 mol% in a fluororesin, for example.

  A commercial item can be used for a fluororesin. Examples thereof include polyflon and neoflon manufactured by Daikin Industries, Ltd., full-on manufactured by Asahi Glass Co., Ltd., and dyneons manufactured by 3M Japan Co., Ltd.

  The polyphenylene sulfide (PPS) may be a linear type or a crosslinked type.

  Examples of the additive include a filler, a pigment material, and an antioxidant. Examples of the filler include glass fiber, carbon fiber, and graphite. The content of the additive is, for example, 0.1 to 30 parts by mass with respect to 100 parts by mass of the resin material.

  The inner tube may preferably have an inner surface roughness Ra of 0.01 μm or more and 2.0 μm or less from the viewpoint of further suppressing the adhesion of the scale and the viewpoint of further facilitating the removal of the scale. . In particular, the effect can be expected when the resin material constituting the inner pipe is a fluororesin, polyolefin, or PPS, and the effect can be expected when the resin material is a fluororesin. Such surface roughness can be realized by, for example, transferring the unevenness of the mold surface during molding, adjusting the temperature during molding, and post-processing using a lathe.

  The size of the inner tube only needs to be set in the lumen of the outer tube. For example, the outer diameter can be 25 to 5000 mm. The thickness can be 0.1 to 10.0 mm. The length can be arbitrarily set as long as there is no problem in transportation, but is generally 100 to 6000 mm, and preferably the same length as the outer tube.

  A space may be formed between the outer peripheral portion of the inner tube and the inner peripheral surface of the outer tube. When such a space is formed, an air layer is formed, so that a heat insulating effect can be expected.

  Moreover, the convex part which goes to the outer tube | pipe side may be formed in the outer peripheral part of an inner tube | pipe. When such a convex part is formed, it can be expected to suppress the vibration of the inner tube that is caused by the movement of the conveyed product to the lumen part of the inner tube. The configuration of the convex portion is not particularly limited, but is preferably a convex strip that is continuous between both end portions in the longitudinal direction. Further, instead of the outer peripheral portion of the inner tube, a convex portion directed toward the inner tube may be provided on the inner peripheral portion of the outer tube.

  The inner tube has a rigidity capable of being inserted along the lumen of the outer tube. Such rigidity can be adjusted by the composition of the resin material and additive constituting the inner tube, the diameter of the inner tube, the wall thickness, and the like. When the inner tube having such rigidity is inserted into the outer tube along the longitudinal direction thereof, it is easy even if an external force such as a direction intersecting the inner tube and pushing the inner tube is applied. Will not bend. Therefore, the inner pipe can be easily installed on the outer pipe.

  The inner tube is fixed to the outer tube at least at one end. The method of fixing is not particularly limited, but a locking portion that protrudes radially outward is provided at one end of the inner tube so that the locking portion is locked to one end of the outer tube. It is preferable to configure. By comprising in this way, since it is not fixing to an outer pipe | tube except an edge part of an inner pipe | tube, an inner pipe | tube can be installed in an outer pipe | tube more easily or can be replaced | exchanged. In addition, such a locking portion may be physically and / or chemically connected to the end portion of the inner tube, but from the viewpoint of durability of the inner tube, manufacturing cost, etc. It is preferable to be provided integrally with the tube. Such a structure can be realized, for example, as described later.

  The structure of the locking portion of the inner tube is not particularly limited as long as it can be locked to the end of the outer tube, but from the viewpoint of securing the inner tube to the outer tube more securely, It is preferable that it is formed over the circumference. For example, a structure in which the end of the inner tube protrudes in an annular shape in a direction perpendicular to the longitudinal direction is preferable. It is preferable that an annular convex portion for engaging the annular structure engaging portion of the inner tube is formed at the end of the outer tube. The annular convex portion of the outer tube preferably protrudes radially outward in a direction perpendicular to the longitudinal direction of the outer tube and has a locking surface having a structure corresponding to the locking portion of the inner tube. In other words, flange portions are provided at the end portions of the inner tube and the outer tube, respectively. And the surface facing the other end side of the one end portion of the inner tube becomes the locking surface of the inner tube, and the surface opposite to the side facing the other end of the one end portion of the outer tube is the locking surface of the outer tube. The inner tube and the outer tube can be fixed at one end by engaging the locking surfaces with each other. Moreover, you may provide the fixing | fixed part for fixing the flange part of an inner tube between the flange parts of an outer tube on the surface on the opposite side to the above-mentioned latching surface of an inner tube. In addition, according to the structure of piping, a latching | locking part can be provided in the both ends of an inner tube and an outer tube, and both can be fixed by both ends.

  The piping according to the embodiment as described above can be used with only one pipe, or two or more pipes can be used in connection with each other depending on the application. There are no particular limitations on the joint structure when two or more are connected. For example, (a) a flange is provided at the end of the outer tube, and a seal ring or gasket is installed between adjacent inner and outer tubes. And a structure in which the flanges of the outer pipes are fixed with bolts and nuts, and (b) a structure in which the engaging parts of the adjacent inner pipes are pressed against each other by the end portions of the adjacent outer pipes.

  More specifically, the structure of (b) is as follows, for example. Regarding the inner tube, an annular flange portion as a locking portion is provided at the end of the inner tube, and the side facing the inner tube side becomes the locking surface. For the outer tube, an annular flange is provided at the end of the outer tube, and the opposite side of the flange facing the outer tube is in contact with the locking surface of the locking portion of the inner tube. A locking surface of the outer tube to be stopped is formed. Then, two or more double pipes having the same structure are continuously provided in the longitudinal direction, the surfaces opposite to the engaging surfaces of the flange portions of the adjacent inner pipes are brought into contact with each other, and the flanges of the adjacent outer pipes are contacted. By screwing with bolts and nuts or the like through a through hole provided in the part, or by caulking with another structure, the flange parts of the inner pipe can be pressed together, and the sealed state of the pipes can be maintained. As described above, in the case of the structure (b), the sealability between the pipes is ensured by a very simple structure in which the double pipes are screwed together, and long-distance pipes can be easily performed. Such a structure is particularly effective when the resin material constituting the inner tube is a fluororesin. This is because the fluororesin is easily deformed by pressure contact and easily secures sealing properties.

  The piping according to the embodiment as described above can be manufactured as follows, for example.

  First, an outer tube and an inner tube are prepared. As the outer tube, an existing metal tube or a synthetic resin tube can be used. If necessary, a flange or the like is provided at the end of the outer tube by an existing method. The inner tube can be manufactured by injection molding, extrusion molding or the like according to the characteristics, size, etc. of the resin material. From the viewpoint of easily forming a cylindrical body, extrusion molding is advantageous. As extrusion molding, melt extrusion molding, ram extrusion molding, paste extrusion molding, or the like can be employed depending on the resin type and dimensions. As described above, when the inner surface roughness of the inner tube is adjusted to a predetermined range, the inner surface roughness of the inner tube can be easily adjusted by transferring the surface roughness of the mold to the molded product. Therefore, ram extrusion is preferred. Moreover, when the size of the inner tube is small, the surface roughness of the inner tube can be adjusted by adjusting the surface roughness of the outer surface of the core bar used for paste extrusion molding. Generally, the above-described flange portion is not formed in the tube obtained by extrusion molding.

  Next, the inner tube is inserted along the longitudinal direction from the opening at one end of the outer tube into the lumen. Press fit as necessary. After disposing the inner tube over the entire length of the lumen of the outer tube, one end and / or the other end of the outer tube and the inner tube are fixed.

  When the inner tube is fixed to the outer tube by forming a flange portion as a locking portion on the inner tube as described above, after inserting the inner tube into the lumen of the outer tube, the flange portion separately molded is directly A flange portion is formed as a locking portion by connecting to the end portion of the tube or by bending one end portion of the inner tube protruding from the lumen portion of the outer tube. Examples of the method for bending one end portion of the inner tube include a method in which the inner tube is heated above a deformable temperature and mechanically bent.

  The process of bending one end of the inner tube is performed in advance only on one end, and then the other end of the inner tube is inserted from one end of the outer tube into the lumen and protrudes from the other end of the outer tube. A similar bending process may be performed on the other end of the inner tube.

  The double pipes as described above can be easily manufactured at low cost, and have the same performance as lining pipes in terms of chemical resistance, durability, and scale adhesion suppression. It is suitable for various uses for which is required. Examples include hot springs, household wastewater, beverages, adhesive substance manufacturing factories, seawater, food factories, chemical factories, and circulating water piping. In particular, it is suitable as piping for hot springs.

  Hereinafter, based on an Example, embodiment of this invention is described more concretely.

(Test Example 1)
A test piece formed of the material shown in Table 1 and having a surface roughness Ra of a predetermined value is immersed in a hot water bath (storage / cooling tank) in a hot spring area (Nagasaki Prefecture, Obama Hot Spring, source temperature 105 ° C.), 30 After the passage of days, the ease of peeling when the attached scale was boiled with a finger was confirmed by a sensory test with three panelists. Evaluation criteria are very easy: 5 points, easy to take: 4 points, can be taken: 3 points, not completely taken: 2 points, difficult to take: 1 point, the total score of 3 people Those with 9 points or more were usable. Table 1 shows the material, the surface roughness of the test piece, and the total score. Table 1 and FIG. 1 show the relationship between the surface roughness Ra, the material, and the total score, where the material levels are fluorine, PPS, PEEK, iron, and SUS304. It should be noted that in Table 1, the “surface transfer” item of “mold transfer” is “surface roughness (Ra [μm])”, assuming that the surface roughness of the molding surface of the mold is transferred. This indicates that the value of is specified. The “(commercially available)” indicates that the value obtained by directly measuring the surface of a commercially available test piece is defined as the value of “surface roughness (Ra [μm])”. The “# 100 polished surface” is a value obtained by directly measuring a polished surface obtained by performing mold transfer or post-processing of a commercially available test piece with a lathe using a # 100 abrasive, “surface roughness (Ra [μm ]) ”As a value.

The materials used are as follows.
PFA: manufactured by 3M Japan, product name “Dionion PFA”
ETFE (black): Daikin Industries, Ltd., product name “Polyflon PTFE”
ETFE (white): manufactured by Daikin Industries, Ltd., product name “Polyflon PTFE”
PTFE: manufactured by Daikin Industries, Ltd., product name “Polyflon PTFE”
PPS (Crosslinking): Polyplastics Co., Ltd., product name “Durafied PPS”
PPS (Linear): Polyplastics Co., Ltd., product name “Durafied PPS”
PEEK + filler: Product name "VICTREX PEEK" manufactured by Vitrex
Iron (SGP): JFE Steel Corporation, “Carbon Steel Pipe 100A for Piping”
SUS304: Nippon Steel & Sumikin Stainless Steel Pipe Co., Ltd., “welded stainless steel pipe”

  The surface roughness Ra was measured by SURFCOM 1500DX3 (measurement length: 10 mm, measurement speed: 0.3 mm / sec, cut-off wavelength: 0.8 mm) manufactured by Tokyo Seimitsu Co., Ltd.

  As shown in Table 1 and FIG. 1, when iron (SGP) and SUS304 test pieces were used, the total score was less than 9 points. On the other hand, when a fluorine-based, PPS-based, or PEEK non-adhesive resin was used as the resin material, the total score was 9 points or more, which was usable. Among these, it can be seen that the fluorine-based resin is better than the other non-adhesive resin and the surface roughness Ra is better than 0.01 μm to 0.2 μm. In particular, fluorine-based and PPS-based showed effective results in the above surface roughness range.

Example 1
<Manufacture of double piping>
An inner tube having an outer diameter of 130.8 mm, a wall thickness of 3.0 mm, and an inner surface roughness Ra of 1.5 μm was obtained by ram extrusion using the PTFE used in Test Example 1. This inner tube is formed in the lumen of an outer tube (JFE Steel Corporation, “Carbon Steel Pipe 125A for Piping”, outer diameter 139.8 mm, wall thickness 4.5 mm, and flanges are formed at both ends). Double pipe that press-fits, heats both ends of the inner tube, mechanically bends both ends of the inner tube so that flanges are formed at both ends, and fixes the inner tube and outer tube at both ends Got.

<Field test>
The obtained double pipe was used for 2 weeks as a part of the pipe laid in the same hot spring area as in Test Example 1. The double pipe was fixed with a fixture so that the flange part of the inner pipe was sandwiched between the flange part of the outer pipe and the flange part of the existing pipe. No leakage of hot spring water was confirmed during the test period. Moreover, it removed after 2 weeks and confirmed the ease of peeling of the scale for 400 mm in length direction among double piping. Peeling of the scale was performed by striking the outside of the double pipe with a blunt device and applying impact and vibration to the inner pipe. As a result, the conventional piping of Comparative Example 1 described later required about 10 minutes of working time, whereas the double piping of Example 1 can peel off the scale in about 3 minutes of working time. done.

(Comparative Example 1)
It replaced with the double piping of Example 1, and it carried out similarly to Example 1 except having used "Black pipe SGP pipe 125A" (outside diameter 139.8mm, thickness 4.5mm) by JFE Steel Corporation. After being used as part of the hot spring area piping, the ease of scale peeling was confirmed. The comparison with Example 1 is as described above.

Claims (11)

  An outer tube having a lumen that opens at both ends in the longitudinal direction, and an inner tube that is installed in the lumen and fixed to one end, and the resin material constituting the inner tube is non-adhesive A pipe that is resin and has a rigidity that allows the inner tube to be inserted along the lumen of the outer tube.   The piping according to claim 1, which is for hot springs.   Non-adhesive resin is polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer The pipe according to claim 1 or 2, which is at least one fluororesin selected from the group consisting of a coalescence (FEP) and polyvinylidene fluoride (PVDF).   The piping according to any one of claims 1 to 3, wherein the inner surface roughness Ra of the inner tube is 0.01 µm or more and 2.0 µm or less.   The inner tube has a lumen that opens at both ends in the longitudinal direction, and one end thereof is provided with a locking portion that protrudes radially outward, and the locking portion is one end of the outer tube. The pipe according to any one of claims 1 to 4, which is locked to the pipe.   The piping according to claim 5, wherein the locking portion is formed at one end of the inner tube over the entire circumference.   The pipe according to claim 6, wherein two or more inner pipes and outer pipes are connected to each other, and the engaging portions of the adjacent inner pipes are press-contacted by the ends of the adjacent outer pipes.   The piping according to any one of claims 1 to 7, wherein a space is formed between the outer peripheral portion of the inner tube and the inner peripheral surface of the outer tube.   The piping according to any one of claims 1 to 8, wherein a convex portion toward the outer tube side is formed on an outer peripheral portion of the inner tube. A method for manufacturing the pipe according to any one of claims 1 to 9,
A manufacturing method of piping including a step of forming an inner pipe by extrusion molding. A method for producing the pipe according to any one of claims 5 to 9,
A method for manufacturing a pipe, comprising: inserting an inner tube into a lumen portion of an outer tube and then bending at least one end of the inner tube to form a locking portion.

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