Patent Publication Number: US-2023151927-A1

Title: High-pressure tank and method for manufacturing high-pressure tank

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2020-130016 filed on Jul. 31, 2020, incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a high-pressure tank and a method for manufacturing the high-pressure tank. 
     2. Description of Related Art 
     There is known a technology related to a tank that stores fuel gas. In this technology, a tubular molded portion is formed by winding a sheet-shaped fiber-reinforced resin layer, and a tank body is formed by arranging the formed tubular molded portion around the peripheral surface of a liner (for example, Japanese Unexamined Patent Application Publication No. 2017-94491 (JP 2017-94491 A)). 
     SUMMARY 
     Required dimensions of tanks that store gas may vary depending on, for example, purposes of use and installation places of the tanks. To manufacture tanks having different dimensions in the related art, a plurality of manufacturing lines is necessary to form bodies having different dimensions. Therefore, there is a demand for a technology capable of changing the dimensions of tanks by a simple method. 
     The present disclosure provides a high-pressure tank and a method for manufacturing the high-pressure tank. 
     A first aspect of the present disclosure relates to a high-pressure tank. The high-pressure tank includes a reinforcing layer and a liner having a gas-barrier property and disposed on an inner surface of the reinforcing layer. The reinforcing layer includes a cylindrical reinforcing pipe having a plurality of cylindrical pipe forming portions coupled together, and a pair of semispherical reinforcing domes, one of the pair of semispherical reinforcing domes being disposed at a first end of the reinforcing pipe, and the other one of the pair of semispherical reinforcing domes being disposed at a second end of the reinforcing pipe. 
     According to the first aspect, the reinforcing layer includes the cylindrical reinforcing pipe having the cylindrical pipe forming portions coupled together. The dimension of the reinforcing pipe can arbitrarily be adjusted by combining and joining an arbitrary number of pipe forming portions having arbitrary lengths. Thus, the dimension of the high-pressure tank can be changed by a simple method. 
     In the first aspect, the high-pressure tank may further include a junction arranged in a recess provided between the adjacent pipe forming portions abutting against or approaching each other, the junction joining the adjacent pipe forming portions. 
     According to the structure described above, a decrease in the joining strength of the reinforcing pipe can be suppressed or prevented by joining the pipe forming portions by the junction at the joining position where the strength is likely to decrease. 
     In the aspect described above, an outer diameter of the junction may be larger than an outer diameter of the reinforcing pipe. According to the structure described above, a decrease in the strength at the joining position of the pipe forming portions can be suppressed or prevented more securely by arranging the junction to cover the outer surfaces at the joining position of the pipe forming portions where the strength is likely to decrease. 
     In the aspect described above, an inner diameter of the junction may be smaller than an inner diameter of the reinforcing pipe. According to the structure described above, the decrease in the strength at the joining position of the pipe forming portions can be suppressed or prevented more securely by arranging the thick junction at the joining position of the pipe forming portions where the strength is likely to decrease. 
     In the aspect described above, a material for the junction may contain a reinforcing fiber and a thermoplastic resin. According to the structure described above, the pipe forming portions can easily be joined by thermocompression bonding. By containing the fiber bundle, the strength at the joining position of the pipe forming portions can be improved. 
     In the first aspect, at least one pipe forming portion out of the pipe forming portions may include, at an axial end of the one pipe forming portion, a fitting portion having a shape in which the fitting portion protrudes toward another pipe forming portion adjacent to the at least one pipe forming portion. The other pipe forming portion adjacent to the at least one pipe forming portion may include, at an axial end of the other pipe forming portion, a fitted portion having a recessed shape conforming to the shape of the fitting portion. 
     According to the structure described above, axial displacement is reduced or prevented at the joining position while improving the joining strength of the pipe forming portions. Thus, variation in the axial dimension of the reinforcing pipe can be reduced. 
     In the aspect described above, the junction may protrude from an outer surface of the reinforcing pipe toward an outer side of the reinforcing pipe. 
     In the aspect described above, the junction may protrude from art inner surface of the reinforcing pipe toward an axis center of the reinforcing pipe. 
     In the aspect described above, at least one pipe forming portion out of the pipe forming portions may have a first abutment surface at art axial end of the one pipe forming portion. Another pipe forming portion adjacent to the at least one pipe forming portion may have a second abutment surface. The first abutment surface and the second abutment surface may abut against each other. 
     A second aspect of the present disclosure relates to a method for manufacturing a high-pressure tank. The method includes causing adjacent cylindrical pipe forming portions to abut against each other, arranging a junction made of a material containing a reinforcing fiber and a thermoplastic resin on an outer surface at an abutment position of the adjacent pipe forming portions, forming a cylindrical reinforcing pipe by heating and thermocompressively bonding the junction to join the pipe forming portions, and forming a liner made of a resin and having a gas-barrier property on an inner surface of the formed reinforcing pipe. 
     According to the second aspect, the liner is formed after joining the pipe forming portions. Thus, it is possible to reduce or prevent such a trouble that the liner enters the abutment position of the pipe forming portions when the high-pressure tank is charged with gas. 
     A third aspect of the present disclosure relates to a method for manufacturing a high-pressure tank. The method includes preparing a plurality of cylindrical pipe forming portions, forming, at an end of at least one pipe forming portion out of the pipe forming portions, a fitting portion having a shape in which the fitting portion protrudes toward another pipe forming portion adjacent to the at least one pipe forming portion, forming, at an end of the other pipe forming portion adjacent to the at least one pipe forming portion, a fitted portion having a recessed shape conforming to the shape of the fitting portion, forming liners each made of a resin and having a gas-barrier property on inner surfaces of the pipe forming portions, and forming a cylindrical reinforcing pipe by heating and thermocompressively bonding the liners on the pipe forming portions having the fitting portion and the fitted portion fitted together to join the pipe forming portions. 
     According to the third aspect, at least one pipe forming portion and other pipe forming portion adjacent to the at least one pipe forming portion can be joined without using an adhesive or junction, and therefore the number of components can be reduced. 
     The present disclosure may be implemented in various forms other than the high-pressure tank and the method for manufacturing the high-pressure tank. For example, the present disclosure may be implemented in various forms such as a reinforcing pipe, a method for manufacturing the reinforcing pipe, and an apparatus for manufacturing the high-pressure tank. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like signs denote like elements, and wherein: 
         FIG.  1    is a sectional view illustrating the structure of a high-pressure tank of a first embodiment; 
         FIG.  2    is an explanatory drawing schematically illustrating the structure of pipe forming portions; 
         FIG.  3    is a process drawing illustrating a method for manufacturing the high-pressure tank; 
         FIG.  4    is a process drawing illustrating a method for manufacturing a reinforcing pipe; 
         FIG.  5    is an explanatory drawing illustrating an example of a method for forming the pipe forming portions; 
         FIG.  6    is an explanatory drawing schematically illustrating a method for joining a first pipe forming portion and a second pipe forming portion; 
         FIG.  7    is an explanatory drawing illustrating an example of a method for forming reinforcing domes; 
         FIG.  8    is an explanatory drawing illustrating a method for forming an outer helical layer; 
         FIG.  9    is an explanatory drawing schematically illustrating the structure of pipe forming portions as Other Aspect 1 of the first embodiment; 
         FIG.  10    is an explanatory drawing schematically illustrating a method for joining the pipe forming portions as Other Aspect 1 of the first embodiment; 
         FIG.  11    is an explanatory drawing schematically illustrating the structure of pipe forming portions as Other Aspect 2 of the first embodiment; 
         FIG.  12    is an explanatory drawing schematically illustrating a method for joining the pipe forming portions as Other Aspect 2 of the first embodiment; 
         FIG.  13    is an explanatory drawing schematically illustrating the structure of pipe forming portions according to a second embodiment; 
         FIG.  14    is a process drawing illustrating a method for manufacturing a reinforcing pipe according to the second embodiment; 
         FIG.  15    is an explanatory drawing schematically illustrating the structure of pipe forming portions as another aspect of the second embodiment; 
         FIG.  16    is an explanatory drawing illustrating the end of a first pipe forming portion and the end of a second pipe forming portion; 
         FIG.  17    is an explanatory drawing schematically illustrating the structure of pipe forming portions according to a third embodiment; 
         FIG.  18    is a process drawing illustrating a method for manufacturing a high-pressure tank of the third embodiment; 
         FIG.  19    is a process drawing illustrating a step of forming a reinforcing pipe; 
         FIG.  20    is an explanatory drawing illustrating a first pipe forming portion and a second pipe forming portion; 
         FIG.  21    is an explanatory drawing illustrating the first pipe forming portion and the second pipe forming portion on which liners are formed; 
         FIG.  22    is an explanatory drawing illustrating a method for joining the reinforcing pipe to a reinforcing dome having a dome-side liner; and 
         FIG.  23    is an explanatory drawing schematically illustrating an example of sectional shapes of pipe forming portions according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIG.  1    is a sectional view illustrating the structure of a high-pressure tank  100  of a first embodiment.  FIG.  1    illustrates a central axis AX of the high-pressure tank  100 . The high-pressure tank  100  of this embodiment is a storage container that stores gas such as hydrogen gas. For example, the high-pressure tank  100  is used for storing hydrogen to be supplied to a fuel cell for a vehicle or a stationary fuel cell. For example, the high-pressure tank  100  stores a fluid having a high pressure of 10 to 70 MPa. The high-pressure tank  100  may store not only the hydrogen gas but also oxygen, natural gas, or the like. 
     The high-pressure tank  100  includes a reinforcing layer  30 , a liner  20 , a first cap  81 , and a second cap  82 . The liner  20  has a gas-barrier property, and is arranged on the inner surface of the reinforcing layer  30 . The first cap  81  and the second cap  82  are arranged at opposite ends of the high-pressure tank  100 . Axial directions of the individual portions agree with the central axis AX of the high-pressure tank  100 . The first cap  81  has a communication hole  81   h  that communicates a space in the liner  20  with an external space. A connection device including a valve is arranged in the communication hole  81   h . The second cap  82  has no communication hole that communicates with the external space, but may have the communication hole. The second cap  82  may be omitted. 
     The liner  20  is made of a resin having a gas-barrier property to suppress permeation of gas to the outside. Examples of the resin of the liner  20  include a mixed resin of high-density polyethylene and an ethylene-vinyl alcohol copolymer resin, and various resins having a gas-barrier property, such as nylon, polyamide, polypropylene, epoxy, and polyester. 
     The reinforcing layer  30  is a fiber-reinforced resin layer for reinforcing the liner  20 , and includes a coupled body  40  and an outer helical layer  70 . The coupled body  40  includes two reinforcing domes  50  and one reinforcing pipe  60 . The resin of the reinforcing layer  30  may be a thermosetting resin such as a phenol resin, a melamine resin, a urea resin, or an epoxy resin, and is particularly preferably an epoxy resin from the viewpoint of mechanical strength or the like. For example, the fiber in the reinforcing layer  30  may be a glass fiber, an aramid fiber, a boron fiber, a carbon fiber, or a combination of the plurality of types of fiber. The fiber in the reinforcing layer  30  is preferably a carbon fiber from the viewpoint of lighter weight, mechanical strength, or the like. 
     The reinforcing dome  50  has a so-called semispherical shape with an outer diameter gradually increasing from a first end to a second end. The second end of the reinforcing dome  50  means an end closer to the center of the high-pressure tank  100  out of both ends of the reinforcing dome  50  along an axial direction of the high-pressure tank  100 . The first cap  81  is arranged at the first end of the reinforcing dome  50 .  FIG.  1    illustrates the semispherical reinforcing dome  50 , but the reinforcing dome  50  may have various shapes other than the semispherical shape, such as a flat-plate shape and a rectangular shape. 
     The reinforcing pipe  60  has a substantially cylindrical appearance shape. The reinforcing pipe  60  is formed by coupling a plurality of cylindrical pipe forming portions. In this embodiment, the reinforcing pipe  60  includes three pipe forming portions and junctions P 1 . The pipe forming portions are a first pipe forming portion  61 , a second pipe forming portion  62 , and a third pipe forming portion  63 . In this embodiment, the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63  are coupled by joining adjacent pipe forming portions by using the junctions P 1 . 
     The junction P 1  is made of a resin-impregnated fiber, and has an appearance shape of a ring. For example, the fiber in the junction P 1  may be a glass fiber, an aramid fiber, a boron fiber, or a carbon fiber, and is particularly preferably a carbon fiber from the viewpoint of lighter weight, mechanical strength, or the like. The resin of the junction P 1  may be a thermoplastic resin such as polyamide, polypropylene, polyphenylene sulfide, polycarbonate, or thermoplastic polyurethane. The shape of the junction P 1  may be not only the ring shape but also, for example, an arc shape or a flat-plate shape conforming to the outer peripheral shape of the reinforcing pipe  60 . In a case where the junction P 1  has the arc shape or the flat-plate shape, a plurality of junctions P 1  is preferably arranged on outer peripheries of joining positions of the pipe forming portions  61 ,  62 , and  63 . The junction P 1  can be formed by winding a fiber bundle around a substantially cylindrical mandrel similarly to a method for forming the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forcniny portion  63  as described later. 
     For example, the second pipe forming portion  62  and the third pipe forming portion  63  are used for extending the axial length of the reinforcing pipe  60 . The lengths of the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63  may be set arbitrarily. For example, the lengths of the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63  may be equal to or different from each other. For example, in a case of manufacturing high-pressure tanks having a plurality of lengths, the length of the first pipe forming portion  61  is preferably set to a length corresponding to the length of a reinforcing pipe of a high-pressure tank having the shortest dimension among the high-pressure tanks having the plurality of lengths from the viewpoint of increasing manufacturing efficiency. The second pipe forming portion  62  and the third pipe forming portion  63  are preferably set to have lengths that compensate for a difference between the length of the first pipe forming portion  61  and the length of a reinforcing pipe of each of the high-pressure tanks having the plurality of lengths, that is, set to have lengths that extend the first pipe forming portion  61 . As in the case of the second pipe forming portion  62  and the third pipe forming portion  63 , the lengths of the pipe forming portions to be used for extending the first pipe forming portion  61  are preferably set equal to each other from the viewpoint of improving productivity. 
     The reinforcing dome  50  is arranged at each of both ends of the reinforcing pipe  60  so that the inner surfaces of the reinforcing domes  50  come into contact with the outer surface of the reinforcing pipe  60 . The outer helical layer  70  is formed by helically winding a resin-impregnated fiber around the outer surface of the coupled body  40  including the reinforcing domes  50  and the reinforcing pipe  60 . The outer helical layer  70  mainly functions to prevent detachment of the reinforcing dome  50  from the reinforcing pipe  60  when the internal pressure of the high-pressure tank  100  increases. For convenience of illustration in  FIG.  1   , hatching is omitted for the outer helical layer  70 , the liner  20 , and the junctions P 1 . 
       FIG.  2    is an explanatory drawing schematically illustrating the structure of the pipe forming portions.  FIG.  2    illustrates an end  61 R of the first pipe forming portion  61 , a first end  62 L and a second end  62 R of the second pipe forming portion  62 , and a first end  63 L and a second  63 R of the third pipe forming portion  63 . The first pipe forming portion  61  is joined to the second pipe forming portion  62  by the junction P 1  in a state in which the end  61 R abuts against the first end  62 L of the second pipe forming portion  62 . The second pipe forming portion  62  is joined to the third pipe forming portion  63  by the junction P 1  in a state in which the second end  62 R of the second pipe forming portion  62  abuts against the first end  63 L of the third pipe forming portion  63 . The other end (not illustrated) of the first pipe forming portion  61  and the second end  63 R of the third pipe forming portion  63  correspond to both the ends of the reinforcing pipe  60 . 
     A diameter-decreasing portion  61 HR is formed on an outer surface near the end  61 R of the first pipe forming portion  61 . The diameter-decreasing portion  61 HR is a portion where the outer diameter of the reinforcing pipe  60  gradually decreases toward the end  61 R by gradually reducing the thickness of the fiber-reinforced resin layer toward the end  61 R. The inner diameters of the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63  are substantially constant. The first end  62 L of the second pipe forming portion  62  has a diameter-decreasing portion  62 HL where the diameter decreases toward the first end  62 L. The diameter-decreasing portion  61 HR and the diameter-decreasing portion  62 HL form a groove-shaped recess H 1  on the outer surface of the reinforcing pipe  60  by causing the end  61 R and the first end  62 L to abut against each other. Similarly, a diameter-decreasing portion  62 HR of the second end  62 R of the second pipe forming portion  62  and a diameter-decreasing portion  63 HL of the first end  63 L of the third pipe forming portion  63  form a recess H 1  on the outer surface of the reinforcing pipe  60 . The junction P 1  is arranged in each recess H 1 . 
       FIG.  2    illustrates an outer diameter Dn and a thickness Tn of the reinforcing pipe  60 . The outer diameter Dn is equal to maximum diameters of the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63 . The thickness Tn means a maximum value of the thickness of the reinforcing pipe  60 . As illustrated in  FIG.  2   , an outer diameter D 1  of the junction P 1  is larger than the outer diameter Dn of the reinforcing pipe  60 . The junction P 1  protrudes from the outer surface of the reinforcing pipe  60  toward an outer side of the reinforcing pipe  60  by an amount corresponding to a thickness U 1 . The maximum thickness of the junction P 1  is larger than the thickness Tn. 
     Next, a method for manufacturing the high-pressure tank  100  is described with reference to  FIG.  3    to  FIG.  8   .  FIG.  3    is a process drawing illustrating the method for manufacturing the high-pressure tank  100 .  FIG.  4    is a process drawing illustrating a method for manufacturing the reinforcing pipe  60 . In Step S 10 , the reinforcing pipe  60  is formed. In Step S 12  of  FIG.  4   , a plurality of pipe forming portions is prepared. That is, the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63  are prepared. 
       FIG.  5    is an explanatory drawing illustrating an example of a method for forming the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63 . The first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63  can be formed by winding a fiber bundle FB around a substantially cylindrical mandrel  58  by a filament winding method. In the filament winding method, the fiber bundle FB is wound around the mandrel  58  by moving a fiber bundle guide  210  while rotating the mandrel  58 .  FIG.  5    illustrates an axial width Ln and a thickness Tn of the fiber bundle FB wound around the mandrel  58 . The width Ln corresponds to the axial length of each of the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63 , and can arbitrarily be adjusted based on a movement amount of the fiber bundle guide  210 . For example, the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63  having different lengths can be formed by setting the width Ln to the length of each of the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63 . The thickness Tn can be set to an arbitrary thickness by, for example, adjusting a rotation speed of the mandrel  58 , that is, the number of turns of the fiber bundle FB. For example, the diameter-decreasing portions  61 HR,  62 HL,  62 HR, and  63 HL can be formed by gradually reducing the number of turns in a moving direction of the fiber bundle guide  210 . Pipe forming portions having different inner diameters and internal shapes can be formed by changing the shape of the outer surface of the mandrel  58 , for example, by providing a projection or recess in the outer surface of the mandrel  58 . One pipe forming portion may be formed by using one mandrel  58 . Alternatively, a plurality of pipe forming portions may simultaneously be formed around one mandrel  58 . For example, the second pipe forming portion  62  and the third pipe forming portion  63  may simultaneously be formed by using one mandrel  58 . In the example of  FIG.  5   , the fiber bundle FB is wound by hooping the fiber bundle FB, but the fiber bundle FB may be wound helically. The filament winding (FW) method may be any one of the following wet FW and dry FW. 
     In general, the following methods exist as typical methods for forming an object from a fiber-reinforced resin. 
     Wet FW 
     Wet FW is a method that involves impregnating, immediately before winding the fiber bundle FB, a liquid resin having a low viscosity into the fiber bundle FB, and winding the resin-impregnated fiber bundle around the mandrel. 
     Dry FW 
     Dry FW is a method that involves preparing a tow-prepreg by drying a fiber bundle pre-impregnated with a resin, and winding the tow-prepreg around the mandrel. 
     Resin Transfer Molding (RTM) 
     RTM is a method that involves molding fibers by placing the fibers in a pair of male and female molds and injecting a resin through a resin inlet after fastening the molds to impregnate the resin into the fibers. 
     Centrifugal Winding (CW) 
     CW is a method that involves forming a tubular member by attaching a fiber sheet to the inner surface of a rotating cylindrical mold. The fiber sheet may be a fiber sheet pre-impregnated with a resin, or a fiber sheet that is not impregnated with the resin. In the latter case, the fiber sheet is wound into a tubular shape, and then the resin is injected into the mold and impregnated into the fiber sheet. 
     In the example of  FIG.  5   , the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63  are formed by the filament winding method, but may be formed by another method such as RTM. The resin of each of the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63  or the reinforcing pipe  60  may be cured in Step S 10  or Step S 60 . 
     In Step S 14  of  FIG.  4   , the junctions P 1  are prepared. The junctions P 1  may be prepared simultaneously with Step S 12  or before or after Step S 12 . In this embodiment, two junctions P 1  are prepared in Step S 14 . The number of junctions P 1  to be prepared is at least equal to the number of joining points of the pipe forming portions. In Step S 16 , the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63  are joined by using the prepared junctions P 1 . 
       FIG.  6    is an explanatory drawing schematically illustrating a method for joining the first pipe forming portion  61  and the second pipe forming portion  62 . A method for joining the second pipe forming portion  62  and the third pipe forming portion  63  is similar to the method for joining the first pipe forming portion  61  and the second pipe forming portion  62 , and its description is therefore omitted. As illustrated in  FIG.  6   , the junction P 1  has a thickness T 1  larger than the thickness Tn of the reinforcing pipe  60 , and has the outer diameter D 1  larger than the outer diameter Dn of the reinforcing pipe  60 . The inner diameter of the junction P 1  is larger than the inner diameters of the first pipe forming portion  61  and the second pipe forming portion  62 . The junction P 1  is arranged between the end  61 R of the first pipe forming portion  61  and the first end  62 L of the second pipe forming portion  62 . 
     When the first pipe forming portion  61  and the second pipe forming portion  62  are moved toward the junction P 1 , the recess H 1  is formed by causing the end  61 R and the first end  62 L to abut against each other on the inner surface of the junction P 1 . The junction P 1  is arranged in the formed recess H 1 . The junction P 1  may be fitted into the recess H 1  by inserting the end of any one of the first pipe forming portion  61  and the second pipe forming portion  62  abutting against each other into the junction P 1 . The junction P 1  is thermocompressively bonded to the recess H 1  by heating the junction P 1  arranged in the recess H 1  to a temperature equal to or higher than a melting point of the thermoplastic resin of the junction P 1 , such as 150° C. or 200° C. Thus, the first pipe forming portion  61  and the second pipe forming portion  62  are joined together. The reinforcing pipe  60  formed by joining the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63  is heated to cure the resin. The thermocompression bonding of the junction P 1  may be performed simultaneously with the curing of the resin of the reinforcing pipe  60 . 
     In a case where the resin of the reinforcing pipe  60  is cured in Step S 10 , complete curing or precuring falling short of the complete curing may be performed. In the complete curing, the resin is completely cured until the viscosity of the resin is stable at a value equal to or larger than its target value. In general, when an uncured thermosetting resin is heated, the viscosity first decreases. When the resin is heated continuously, the viscosity increases. When the resin is heated continuously for a sufficient time, the viscosity of the resin is stable at a value equal to or larger than its target value. On the premise of this transition, “precuring” is a process in which curing is continued after the viscosity having decreased first and then increased again reaches the original viscosity and the curing is terminated at any time point before the end of the complete curing. When the precuring is performed in Step S 10  and the complete curing is performed in Step S 60  described later, the reinforcing pipe  60  can be joined more firmly to the reinforcing domes  50  and the outer helical layer  70 . 
     In Step S 20  of  FIG.  3   , the reinforcing domes  50  are formed.  FIG.  7    is an explanatory drawing illustrating an example of a method for forming the reinforcing domes  50  in Step S 20 . The reinforcing domes  50  can be formed by winding the fiber bundle FB around a mandrel  56  by a filament winding method. The mandrel  56  preferably has an outer shape corresponding to a combination of two reinforcing domes  50 . In the filament winding method, the fiber bundle FB is wound around the mandrel  56  by moving the fiber bundle guide  210  while rotating the mandrel  56 . In the example of FIG,  7 , the fiber bundle FB is wound helically. The filament winding method may be the wet FW or the dry FW described above. Two reinforcing domes  50  can be obtained by cutting the wound fiber bundle FB along a cutting line CL. The reinforcing domes  50  may be formed by another method such as RTM. 
     In Step S 30  of  FIG.  3   , the first cap  81  or the second cap  82  is joined to each reinforcing dome  50 . In Step S 40 , the coupled body  40  is formed by joining the reinforcing domes  50  to both the ends of the reinforcing pipe  60 . For example, the joining in Step S 30  and Step S 40  can be performed by using an adhesive or a pressure-sensitive adhesive. 
     In Step S 50  of  FIG.  3   , the outer helical layer  70  is formed around the outer surface of the coupled body  40 .  FIG.  8    is an explanatory drawing illustrating a method for forming the outer helical layer  70  in Step S 50 . The outer helical layer  70  can be formed by winding the fiber bundle FB around the outer surface of the coupled body  40  by a filament winding method. In the filament winding method, the fiber bundle FB is wound around the coupled body  40  by moving the fiber bundle guide  210  while rotating the coupled body  40  about the central axis AX. The filament winding method may be the wet FW or the dry FW. The outer helical layer  70  mainly functions to prevent detachment of the reinforcing dome  50  from the reinforcing pipe  60  when the internal pressure of the high-pressure tank  100  increases. To achieve this function, a winding angle α of the fiber bundle FB is preferably equal to or smaller than 45°. The winding angle α is an angle of the fiber bundle FB with respect to the central axis AX of the coupled body  40 . 
     In Step S 60  of  FIG.  3   , the uncured resin of the reinforcing layer  30  is cured. The curing corresponds to the complete curing described above. in Step S 70 , the liner  20  is formed on the inner surface of the cured reinforcing layer  30 . In Step S 70 , the liner can be formed by, for example, injecting a liquid liner material into the reinforcing layer  30  with caps and curing the liner material while rotating the reinforcing layer  30 . When the formation of the liner  20  is finished, the high-pressure tank  100  illustrated in  FIG.  1    is completed. The liner  20  may be formed in a step other than Step S 70  of  FIG.  3   . For example, the liner  20  may be formed separately from the reinforcing domes  50  and the reinforcing pipe  60 , and then the liner  20 , the two reinforcing domes  50 , the first cap  81 , and the second cap  82  may be joined in Step S 30 . The liner  20  can be formed in this manner by, for example, injection molding. In this case, the liner  20  may be formed in such a manner that two segments of the liner  20  to be obtained by splitting the entire liner  20  substantially at the center are separately subjected to injection molding and are joined after being ejected from an injection mold. 
     According to the high-pressure tank  100  of this embodiment described above, the reinforcing layer  30  includes the cylindrical reinforcing pipe  60  formed by coupling the cylindrical pipe forming portions  61 ,  62 , and  63 . The axial dimension of the reinforcing pipe  60  can arbitrarily be adjusted by combining and joining an arbitrary number of pipe forming portions  61 ,  62 , and  63  having arbitrary lengths. Thus, the dimension of the high-pressure tank  100  can be changed by a simple method without providing a plurality of manufacturing lines for manufacturing reinforcing pipes  60  having different lengths. 
     The high-pressure tank  100  of this embodiment includes the junction P 1  for joining the adjacent pipe forming portions  61  and  62 . The junction P 1  is arranged in the recess H 1  thrilled by causing the diameter-decreasing portions  61 HR and  62 HL of the adjacent first and second pipe forming portions  61  and  62  to abut against each other. By joining the outer surfaces by the junction P 1  at the abutment position of the pipe forming portions  61  and  62  where the strength is likely to decrease, a decrease in the strength of the reinforcing pipe  60  can be suppressed or prevented. By providing the recess at the arrangement position of the junction P 1 , the arrangement position of the junction P 1  can easily be recognized from the appearance. Thus, the junction P 1  can easily be arranged at the abutment position of the pipe forming portions  61  and  62 . 
     According to the high-pressure tank  100  of this embodiment, the outer diameter D 1  of the junction P 1  is larger than the outer diameter Dn of the reinforcing pipe  60 . By arranging the junction P 1  to cover the outer surfaces at the joining position of the first pipe forming portion  61  and the second pipe forming portion  62  where the strength is likely to decrease, the decrease in the strength of the reinforcing pipe  60  can be suppressed or prevented more securely. The junction P 1  protrudes from the outer surface of the reinforcing pipe  60  toward the outer side of the reinforcing pipe  60  by the amount corresponding to the thickness U 1 . By setting the thickness of the junction P 1  to be larger than the thickness of the reinforcing pipe  60 , the strength at the joining position of the first pipe forming portion  61  and the second pipe forming portion  62  can be improved. 
     According to the high-pressure tank  100  of this embodiment, the material containing the reinforcing fiber and the thermoplastic resin is used for the junction P 1 . Thus, the first pipe forming portion  61  and the second pipe forming portion  62  can easily be joined by thermocompression bonding. By containing the fiber bundle, the strength at the joining position of the first pipe forming portion  61  and the second pipe forming portion  62  can be improved. 
     According to the method for manufacturing the high-pressure tank  100  of this embodiment, the reinforcing pipe  60  is formed by joining the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63  by the junctions P 1 , and then the liner  20  is formed on the inner surface of the formed reinforcing pipe  60 . By forming the liner  20  after joining the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63 , it is possible to reduce or prevent such a trouble that the liner  20  enters the abutment positions of the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63  when the high-pressure tank  100  is charged with gas, as compared to a case where the liners  20  are individually formed on the first pipe forming portion  61 , the second pipe forming portion  62 , and the third pipe forming portion  63  are then joined together. 
     Other Aspect 1 of First Embodiment 
       FIG.  9    is an explanatory drawing schematically illustrating the structure of pipe forming portions as Other Aspect 1 of the first embodiment. This embodiment differs from the first embodiment in that the end  61 R of the first pipe forming portion  61  and the first end  62 L of the second pipe forming portion  62  are joined while being spaced away from each other by a distance S 1 , and a junction P 12  having a different shape is provided in place of the junction P 1 . This embodiment is similar to the first embodiment in terms of the other structure. As illustrated in  FIG.  9   , the junction P 12  is arranged in a recess H 12  formed by the diameter-decreasing portion  61 HR and the diameter-decreasing portion  62 HL, protrudes from the outer surface of the reinforcing pipe  60  toward the outer side of the reinforcing pipe  60  by an amount corresponding to a thickness U 12 , and further protrudes from the inner surface of the reinforcing pipe  60  toward an axis center of the reinforcing pipe  60  by an amount corresponding to a thickness B 12 . 
       FIG.  10    is an explanatory drawing schematically illustrating a method for joining the first pipe forming portion  61  and the second pipe forming portion  62 . The junction P 12  has a thickness T 12  larger than the thickness Tn of the reinforcing pipe  60 , and has an outer diameter D 121  larger than the outer diameter Dn of the reinforcing pipe  60 . The thickness T 12  is larger than the thickness T 1  of the junction P 1  of the first embodiment. An inner diameter D 122  of the junction P 12  means a minimum value of the inner diameter of the junction P 12 . The inner diameter D 122  is smaller than the inner diameters of the first pipe forming portion  61  and the second pipe forming portion  62 . The width of the junction P 12  is larger than the distance S 1 . The distance S 1  may be set to an arbitrary distance, but is preferably small to the extent that the strength of the reinforcing pipe  60  does not decrease. 
     When the first pipe forming portion  61  and the second pipe forming portion  62  are moved toward the junction P 12 , the recess H 12  is formed by causing the end  61 R of the first pipe forming portion and the first end  62 L, of the second pipe forming portion to approach each other on the inner surface of the junction P 12  to positions where the distance S 1  is secured. Ihe junction P 12  is arranged in the recess H 12 . The inner diameter D 122  of the junction P 12  is smaller than the inner diameters of the first pipe forming portion  61  and the second pipe forming portion  62 . The inner surface of the junction P 12  is pushed inward from a space between the end  61 R of the first pipe forming portion and the first end  62 L of the second pipe forming portion, and protrudes toward axis centers of the first pipe forming portion  61  and the second pipe forming portion  62  as illustrated in  FIG.  9   . The junction P 12  is thermocompressively bonded to the recess H 12  by heating. Thus, the first pipe forming portion  61  and the second pipe forming portion  62  are joined together. 
     According to the high-pressure tank  100  of this embodiment, the junction P 12  is arranged in the recess H 12  formed in a state in which the diameter-decreasing portions  61 HR and  62 HL of the adjacent first and second pipe forming portions  61  and  62  approach each other. The outer diameter D 121  of the junction P 12  is larger than the outer diameter Dn of the reinforcing pipe  60 . The inner diameter D 122  of the junction P 12  is smaller than the inner diameter of the reinforcing pipe  60 . By forming the junction P 12  to cover the outer surface of the reinforcing pipe  60  and protrude from the inner surface of the reinforcing pipe  60  toward the axis center of the reinforcing pipe  60 , the junction P 12  having a larger thickness than the thicknesses Tn of the first pipe forming portion  61  and the second pipe forming portion  62  can be arranged at the joining position of the first pipe forming portion  61  and the second pipe forming portion  62  where the strength is likely to decrease. Thus, the decrease in the strength at the joining position of the first pipe forming portion  61  and the second pipe forming portion  62  can be suppressed or prevented more securely. 
     Other Aspect 2 of First Embodiment 
       FIG.  11    is an explanatory drawing schematically illustrating the structure of pipe forming portions as Other Aspect 2 of the first embodiment. This embodiment differs from the first embodiment in that the shape of the diameter-decreasing portion  61 HR of the first pipe forming portion  61  and the shape of the diameter-decreasing portion  62 HL of the second pipe forming portion  62  are different, and a junction P 13  having a different shape is provided in place of the junction P 1 . This embodiment is similar to the first embodiment in terms of the other structure. As illustrated in  FIG.  11   , the junction P 13  is arranged in a substantially rectangular recess H 13  formed by the diameter-decreasing portion  61 HR and the diameter-decreasing portion  62 HL, and protrudes from the outer surface of the reinforcing pipe  60  toward the outer side of the reinforcing pipe  60  by an amount corresponding to a thickness U 13 . 
       FIG.  12    is an explanatory drawing schematically illustrating a method for joining the first pipe forming portion  61  and the second pipe forming portion  62 . The junction P 13  has a substantially rectangular sectional shape, has a thickness T 13  equal to the thickness Tn of the reinforcing pipe  60 , and has an outer diameter D 131  larger than the outer diameter Dn of the reinforcing pipe  60 . An inner diameter D 132  of the junction P 13  corresponds to the outer diameter of the recess H 13 , that is, the outer diameters of the diameter-decreasing portion  61 HR and the diameter-decreasing portion  62 HL. The width of the junction P 13  corresponds to the width of the recess H 13 . 
     The diameter-decreasing portion  61 HR is formed into a rectangular shape by trimming an outer peripheral surface near the end  61 R of the first pipe forming portion  61  having the thickness Tn so that the outer peripheral surface has, for example, a thickness Tn 2  that is substantially a half of the thickness Tn of the first pipe forming portion  61 . By forming the diameter-decreasing portion  61 HR, an abutment surface  61 S having the thickness Tn 2  is formed near the end  61 R. The thickness Tn 2  is not limited to the substantial half of the thickness Tn of the first pipe forming portion  61 , and may arbitrarily be adjusted depending on the thickness of the junction P 13  or the required strength of the reinforcing pipe  60 . The diameter-decreasing portion  62 HL is provided near the first end  62 L of the second pipe forming portion  62  so that the second pipe forming portion  62  is substantially line-symmetric to the first pipe forming portion  61  across the junction P 13 . The second pipe forming portion  62  has an abutment surface  62 S that faces the abutment surface  61 S. The abutment surface  61 S and the abutment surface  62 S are perpendicular to an axial direction of the reinforcing pipe  60 . The abutment surface  61 S and the abutment surface  62 S may be formed by machining such as trimming, grinding, or cutting together with or independently of the diameter-decreasing portion  61 HR and the diameter-decreasing portion  62 HL. When the first pipe forming portion  61  and the second pipe forming portion  62  are moved toward the junction P 13 , the abutment surface  61 S and the abutment surface  62 S abut against each other on the inner surface of the junction P 13 . The junction P 13  is arranged on the outer surface of the recess H 13  formed by causing the diameter-decreasing portion  61 HR and the diameter-decreasing portion  62 HL to abut against each other. 
     According to the high-pressure tank  100  of this embodiment, the end  61 R of the first pipe forming portion  61  has the abutment surface  61 S, and the first end  62 L of the second pipe forming portion  62  has the abutment surface  62 S that abuts against the abutment surface  61 S. By bringing the first pipe forming portion  61  and the second pipe forming portion  62  into surface contact with each other at their joining position, axial displacement is reduced or prevented. Thus, variation in the axial dimension of the reinforcing pipe  60  can be reduced. 
     Second Embodiment 
     The structure of a high-pressure tank  100  of a second embodiment is described with reference to  FIG.  13    and  FIG.  14   .  FIG.  13    is an explanatory drawing schematically illustrating the structure of pipe forming portions according to the second embodiment. The high-pressure tank  100  of the second embodiment differs from the high-pressure tank  100  of the first embodiment in that a reinforcing pipe  60   b  is provided in place of the reinforcing pipe  60  and the junctions P 1  are not provided. The reinforcing pipe  60   b  differs from the reinforcing pipe  60  of the first embodiment in that the recesses are not provided. The other structure of the high-pressure tank  100  of the second embodiment is similar to that of the first embodiment. 
     The reinforcing pipe  60   b  includes a first pipe forming portion  61   b , a second pipe forming portion  62   b , and a third pipe forming portion  63   b . An end  61 R of the first pipe forming portion  61   b  has an abutment surface  61   b S (first abutment surface). A first end  62 L of the second pipe forming portion  62   b  has an abutment surface  62   b S (second abutment surface), A second end  62 R of the second pipe forming portion  62   b  and a first end  63 L of the third pipe forming portion  63   b  also have similar abutment surfaces. The abutment surfaces  61   b S and  62   b S are perpendicular to an axial direction of the reinforcing pipe  60   b . The thicknesses of the abutment surfaces  61   b S and  62   b S are equal to thicknesses Tn of the first pipe forming portion  61   b  and the second pipe forming portion  62   b , and are larger than, for example, the thickness Tn 2  of the abutment surface  61 S illustrated in  FIG.  12   . In a state in which the reinforcing pipe  60   b  is formed as illustrated in  FIG.  13   , the abutment surface  61   b S of the first pipe forming portion  61   b  and the abutment surface  62   b S of the second pipe forming portion  62   b  abut against each other. 
     In this embodiment, the first pipe forming portion  61   b , the second pipe forming portion  62   b , and the third pipe forming portion  63   b  are joined by using adhesives Q 1 . A pressure-sensitive adhesive may be used in place of the adhesive Q 1 . The adhesives Q 1  are applied to cover inner peripheral surfaces at the joining positions of the first pipe forming portion  61   b , the second pipe forming portion  62   b , and the third pipe forming portion  63   b . The adhesive Q 1  may be a thermosetting resin such as a phenol resin, a melamine resin, a urea resin, or an epoxy resin, and is particularly preferably an epoxy resin from the viewpoint of mechanical strength or the like. The adhesive Q 1  may further contain a reinforcing fiber such as a glass fiber, an aramid fiber, a boron fiber, or a carbon fiber from the viewpoint of improving the strength of the reinforcing pipe  60   b.    
       FIG.  14    is a process drawing illustrating a method for manufacturing the reinforcing pipe  60   b  according to the second embodiment. In Step S 12 , the first pipe forming portion  61   b , the second pipe forming portion  62   b , and the third pipe forming portion  63   b  are formed by winding the fiber bundle FB around the substantially cylindrical mandrel  58  by the filament winding method similarly to the first embodiment, In Step S 13 , the first pipe forming portion  61   b , the second pipe forming portion  62   b , and the third pipe forming portion  63   b  having the abutment surfaces  61   b S and  62   b S are formed by a method such as grinding, trimming, or cutting of the ends of the formed first pipe forming portion  61   b , the formed second pipe forming portion  62   b , and the formed third pipe forming portion  63   b  along planes perpendicular to the axial direction. In a case where the abutment surfaces  61   b S and  62   b S can be formed in Step S 12 , Step S 13  may be omitted. In Step S 15 , the abutment surfaces of adjacent pipe forming portions, such as the abutment surface  61   b S and the abutment surface  62   b S, are fixed while abutting against each other, and the adhesives Q 1  are applied to the abutment positions from an inner side of the first pipe forming portion  61   b , the second pipe forming portion  62   b , and the third pipe forming portion  63   b . To improve the strength of the reinforcing pipe  60   b , the adhesives Q 1  may be applied to the abutment surfaces of the first pipe forming portion  61   b , the second pipe forming portion  62   b , and the third pipe forming portion  63   b  or the outer peripheral surfaces of the first pipe forming portion  61   b , the second pipe forming portion  62   b , and the third pipe forming portion  63   b  together with or in place of the inner peripheral surfaces of the first pipe forming portion  61   b , the second pipe forming portion  62   b , and the third pipe forming portion  63   b . In Step S 17 , the adhesives Q 1  are thermally cured. Step S 17  may be omitted and the adhesives Q 1  may thermally be cured simultaneously with the complete curing or precuring of the reinforcing pipe  60   b . In a case where precuring is performed in Step S 17 , the adhesives Q 1  may be cured simultaneously with the complete curing of the reinforcing layer  30  in Step S 60 . 
     According to the high-pressure tank  100  of this embodiment, the end  61 R of the first pipe forming portion  61   b  and the first end  62 L of the second pipe forming portion  62   b  have the abutment surfaces  61   b S and  62   b S that are substantially perpendicular to the axial direction and have thicknesses equal to the thicknesses Tn of the first pipe forming portion  61   b  and the second pipe forming portion  62   b . By increasing the contact area between the pipe forming portions  61   b  and  62   b  at their joining position, axial displacement is reduced or prevented at the joining position. Thus, variation in the axial dimension of the reinforcing pipe  60   b  can be reduced. 
     According to the high-pressure tank  100  of this embodiment, the abutment surfaces  61   b S and  62   b S are formed by cutting the ends  61 R and  62 L of the pipe forming portions  61   b  and  62   b  along the planes perpendicular to the axial direction. As compared to a case where the abutment surfaces  61   b S and  62   b S are formed by the filament winding method alone, the surface roughnesses of the abutment surfaces  61   b S and  62   b S can be reduced, and the axial displacement can be reduced or prevented at the joining position, Thus, the variation in the axial dimension of the reinforcing pipe  606  can be reduced. 
     Other Aspect of Second Embodiment 
       FIG.  15    is an explanatory drawing schematically illustrating the structure of pipe forming portions as another aspect of the second embodiment. A high-pressure tank  100  of this embodiment differs from the high-pressure tank  100  of the first embodiment in that a reinforcing pipe  60   b   2  is provided and the junctions P 1  are not provided. The reinforcing pipe  60   b   2  differs from the reinforcing pipe  60  of the first embodiment in that a fitting portion  61 E and a fitted portion  62 F are provided in place of the recess H 1 . The other structure of the high-pressure tank  100  is similar to that of the first embodiment. 
       FIG.  16    is an explanatory drawing illustrating an end  61 R of a first pipe forming portion  61   b   2  and a first end  62 L of a second pipe forming portion  62   b   2 . In the reinforcing pipe  60   b   2 , the end  61 R of the first pipe forming portion  61   b   2  and the first end  62 L of the second pipe forming portion  62   b   2  have abutment surfaces  61 E and  62 F having sectional shapes different from those of the abutment surface  61   b S and the abutment surface  62   b S of the second embodiment. The abutment surface  61 E is shaped to protrude toward the second pipe forming portion  62   b   2 , and is formed by, for example, cutting, trimming, or grinding the end  61 R of the first pipe forming portion  61   b   2  in Step S 13  of  FIG.  14   . The abutment surface  61 E includes an outer peripheral surface  61 Ea and an inner peripheral surface  61 Eb, and is shaped to protrude toward the second pipe forming portion  62   b   2  by forming an inferior angle as an angle θ1 between the outer peripheral surface  61 Ea and the inner peripheral surface  61 Eb. The abutment surface  61 E functions as the fitting portion  61 E to be fitted to the fitted portion of the adjacent second pipe forming portion  62   b   2 . 
     The abutment surface  62 F has a recessed shape conforming to the projecting shape of the abutment surface  61 E, and is formed by cutting or trimming the first end  62 L of the second pipe forming portion  62   b   2 . The abutment surface  62 F includes a first surface  62 Fa and a second surface  62 Fb. The first surface  62 Fa abuts against the outer peripheral surface  61 Ea of the first pipe forming portion  61   b   2 . The second surface  62 Fb abuts against the inner peripheral surface  61 Eb of the first pipe forming portion  61   b   2 . The abutment surface  62 F functions as the fitted portion  62 F to which the fitting portion  61 E of the first pipe forming portion  61   b   2  is fitted. In this embodiment, the areas of the outer peripheral surface  61 Ea and the first surface  62 Fa are set larger than the areas of the inner peripheral surface  61 Eb and the second surface  62 Fb. This structure improves the strength on an outer side of the fitting position between the first pipe forming portion  61   b   2  and the second pipe forming portion  62   b   2 . The first end  62 L of the second pipe forming portion  62   b   2  may have the projecting fitting portion that protrudes toward the first pipe forming portion  61   b   2 , and the end  61 R of the first pipe forming portion  61   b   2  may have the fitted portion. 
     The fitting portion  61 E is fitted to the fitted portion  62 F by moving the first pipe forming portion  61   b   2  toward the second pipe forming portion  62   b   2  while their central axes AX agree with each other. The first pipe forming portion  61   b   2  and the second pipe forming portion  62   b   2  that are fitted together may be bonded thermocompressively by the complete curing or precuring of the reinforcing pipe  60   b , or may be bonded by the thermal curing in Step S 17  of  FIG.  14    by applying the adhesive Q 1  similar to that of the second embodiment or a pressure-sensitive adhesive to the fitting position. In a case where the adhesive Q 1  is applied, the adhesive Q 1  may be applied not only to the inner peripheral surface or the outer peripheral surface at the fitting position, but also to the abutment surface  62 F or the abutment surface  61 E. 
     According to the high-pressure tank  100  of this embodiment, the first pipe forming portion  61   b   2  has the fitting portion  61 E to be fitted to the fitted portion  62 F of the second pipe forming portion  62   b   2 . Therefore, axial displacement is reduced or prevented at the joining position while improving the strength of the reinforcing pipe  60   b   2 . Thus, variation in the axial dimension of the reinforcing pipe  60   b   2  can be reduced. 
     Third Embodiment 
     The structure of a high-pressure tank  100  of a third embodiment is described with reference to  FIG.  17    to  FIG.  22   .  FIG.  17    is an explanatory drawing schematically illustrating the structure of pipe forming portions according to the third embodiment. The high-pressure tank  100  of the third embodiment differs from the high-pressure tank  100  of the first embodiment in that a reinforcing pipe  60   c  is provided in place of the reinforcing pipe  60  and the junctions P 1  are not provided. The reinforcing pipe  60   c  is formed by joining a first pipe forming portion  61   c , a second pipe forming portion  62   c , and a third pipe forming portion  63   c  by thermocompression bonding of the liners  20 . The other structure of the high-pressure tank  100  of the third embodiment is similar to that of the first embodiment. 
     As illustrated in  FIG.  17   , the reinforcing pipe  60   c  includes the first pipe forming portion  61   c , the second pipe forming portion  62   c , and the third pipe forming portion  63   c .  FIG.  17    schematically illustrates the sectional structure of a part of the reinforcing pipe  60   c  to facilitate understanding of the technology. As illustrated in  FIG.  17   , the first pipe forming portion  61   c  includes a fitting portion  61 E to be fitted to a fitted portion  62 F of the adjacent second pipe forming portion  62   c . The second pipe forming portion  62   c  includes a fitting portion  62 E to be fitted to a fitted portion  63 F of the adjacent third pipe forming portion  63   c . The first pipe forming portion  61   c , the second pipe forming portion  62   c , and the third pipe forming portion  63   c  are coupled by fitting the fitting portions  61 E and  62 E to the fitted portions  62 F and  63 F, respectively. The first pipe forming portion  61   c , the second pipe forming portion  62   c , and the third pipe forming portion  63   c  that are coupled together are joined by thermocompression bonding of abutment surfaces of the liners  20 . 
       FIG.  18    is a process drawing illustrating a method for manufacturing the high-pressure tank  100  of the third embodiment. The method for manufacturing the high-pressure tank  100  of this embodiment differs from the method for manufacturing the high-pressure tank  100  of the first embodiment in that. Step S 10   c  for forming the reinforcing pipe  60   c  is provided in place of Step S 10 , Step S 32  is provided, and Step S 70  is not provided. 
       FIG.  19    is a process drawing illustrating the step of forming the reinforcing pipe  60   c  in Step S 10   c . In Step S 12 , the first pipe forming portion  61   c , the second pipe forming portion  62   c , and the third pipe forming portion  63   c  are formed by the filament winding method similarly to the first embodiment. In the following description, the method for manufacturing the third pipe forming portion  63   c  is similar to the method for manufacturing the second pipe forming portion  62   c , and its description is therefore omitted. 
       FIG.  20    is an explanatory drawing illustrating the first pipe forming portion  61   c  and the second pipe forming portion  62   c  manufactured in Step S 12 . In Step S 13 , the first pipe forming portion  61   c  having the projecting fitting portion  61 E that protrudes toward the second pipe forming portion  62   c  and the second pipe forming portion  62   c  having the recessed fitted portion  62 F conforming to the shape of the fitting portion  61 E and the fitting portion  62 E that protrudes toward the third pipe forming portion  63   c  are formed by trimming or grinding an end  61 R of the first pipe forming portion  61   c  prepared in Step S 12  and a first end  62 L of the second pipe forming portion  62   c  prepared in Step S 12 . The inner surface of the second pipe forming portion  62   c  includes an inner surface  62 FB near the first end  62 L and an inner surface  62 EB near a second end  62 R. The inner diameter of the inner surface  62 FB is set smaller than the inner diameter of the inner surface  62 EB. With this structure, the inner surface of the second pipe forming portion  62   c  has a step between the inner surface  62 FB and the inner surface  62 EB. The step to be formed by the difference between the inner diameter of the inner surface  62 FB at the first end  62 L of the second pipe forming portion  62   c  and the inner diameter of the inner surface  62 EB at the second end  62 R of the second pipe forming portion  62   c  can be formed by using a mandrel  58  having a stepped shape conforming to the shapes of the inner surface  62 FB and the inner surface  62 EB when forming the second pipe forming portion  62   c  in Step S 12 . 
     The fitted portion  62 F of the second pipe forming portion  62   c  has a bottom face  62 FS and side walls  62 FW. The bottom face  62 FS abuts against the fitting portion  61 E of the first pipe forming portion  61   c . The side walls  62 FW surround the bottom face  62 FS. The side wall  62 FW on the inner side of the reinforcing pipe  60   c  includes a first side wall  62 FW 1  and a second side wail  62 FW 2  to have a step. The first side wall  62 FW 1  abuts against an inner surface  61 EB of the fitting portion  61 E. The second side wall  62 FW 2  is located at a position closer to the inner surface of the reinforcing pipe  60   c  than is the first side wall  62 FW 1 . With this structure, the side wall  62 FW of the fitted portion  62 F has the step between the first side wall  62 FW 1  and the second side wall  62 FW 2 . The height of the step between the first side wall  62 FW 1  and the second side wall  62 FW 2  corresponds to the height of a step between the inner surface  61 EB of the fitting portion  61 E and an inner surface  21 B of a first liner  21 . 
       FIG.  21    is an explanatory drawing illustrating the first pipe forming portion  61   c  and the second pipe forming portion  62   c  on which the liners  20  are formed. In Step S 18  of  FIG.  19   , the liners  20  are individually formed on the inner peripheral surfaces of the first pipe forming portion  61   c  and the second pipe forming portion  62   c . More specifically, the first liner  21  is formed by applying a liquid liner material to the inner peripheral surface of the formed first pipe forming portion  61   c , and a second liner  22  is formed by applying the liquid liner material to the inner peripheral surface of the second pipe forming portion  62   c.    
     In regions where the liners  20  are formed on the inner peripheral surfaces of the first pipe forming portion  61   c  and the second pipe forming portion  62   c , non-coated regions can be formed by covering, for example, regions other than coated regions with masking tapes when applying the liner material. As illustrated in  FIG.  21   , in this embodiment, a non-coated region of the first liner  21  is formed near the fitting portion  61 E of the first pipe forming portion  61   c  by covering the inner surface  61 EB near the fitting portion  61 E. Thus, the shape near the fitting portion  61 E of the first pipe forming portion  61   c  having the first liner  21  is a sectional shape having the step conforming to the first side tail  62 FW 1  and the second side wall  62 FW 2  of the fitted portion  62 F. This structure increases the abutment area between the first liner  21  and the second pipe forming portion  62   c  to improve the joining strength of the first pipe forming portion  61   c  and the second pipe forming portion  62   c . Thus, the strength of the reinforcing pipe  60   c  can be improved. For example, when applying the liner, an extension member (not illustrated) is temporarily attached to the pipe forming portion  62   c  to form a liner protrusion  22 E of  FIG.  21   . As in this example, the regions where the liners  20  are formed can be extended from outer edges of the first pipe forming portion  61   c  and the second pipe forming portion  62   c . An outer surface  22 T of the liner protrusion  22 E abuts against the inner surface  21 B of the first liner  21 . With the liner protrusion  22 E of the second pipe forming portion  62   c , the contact area between the first liner  21  and the second liner  22  increases to improve the joining strength of the first pipe forming portion  61   c  and the second pipe forming portion  62   c . Thus, the strength of the reinforcing pipe  60   c  can be improved. 
     In Step S 19  of  FIG.  19   , the first pipe forming portion  61   c  and the second pipe forming portion  62   c  are joined together. More specifically, the first pipe forming portion  61   c  and the second pipe forming portion  62   c  are coupled by fitting together the fitting portion  61 E of the first pipe forming portion  61   c  having the first liner  21  and the fitted portion  62 F of the second pipe forming portion  62   c  having the second liner  22 , and are joined by thermocompressively bonding the first liner  21  and the second liner  22  by heating. 
     In Step S 20  and Step S 30  of  FIG.  18   , the reinforcing domes  50  are formed, and the first cap  81  is joined to one of the formed reinforcing domes  50 . In Step S 32  of this embodiment, dome-side liners  24  are formed on the inner surfaces of the reinforcing domes  50 . More specifically, the dome-side liners  24  are formed by applying a liquid liner material to the inner surfaces of the formed reinforcing domes  50 . 
       FIG.  22    is an explanatory drawing illustrating a method for joining the reinforcing pipe  60   c  to the reinforcing dome  50  having the dome-side liner  24 . In this embodiment, as illustrated in  FIG.  22   , a recess  50 S conforming to the shape of the end of the first pipe forming portion  61   c  is formed by providing a non-forming region with a masking tape or the like near the other end of the reinforcing dome  50  when forming the dome-side liner  24  in Step S 32 . When forming the coupled body  40  by joining the reinforcing dome  50  and the reinforcing pipe  60   c , the end of the first pipe forming portion  61   c  of the reinforcing pipe  60   c  is joined to the recess  50 S. In Step S 50  of  FIG.  18   , the outer helical layer  70  is formed around the outer surface of the coupled body  40  similarly to the first embodiment. In Step S 60 , the uncured resin of the reinforcing layer  30  is cured completely. When the complete curing of the reinforcing layer  30  is finished, the high-pressure tank  100  of this embodiment is completed. 
     According to the method for manufacturing the high-pressure tank  100  of this embodiment, the first liner  21  and the second liner  22  are formed on the inner surface of the first pipe forming portion  61   c  and the inner surface of the second pipe forming portion  62   c , respectively. The first pipe forming portion  61   c  and the second pipe forming portion  62   c  are joined by thermocompressiyely bonding the first liner  21  and the second liner  22  by heating in a state in which the fitting portion  61 E of the first pipe forming portion  61   c  and the fitted portion  62 F of the second pipe forming portion  62   c  are fitted together. Thus, the reinforcing pipe  60   c  is formed. The first pipe forming portion  61   c  and the second pipe forming portion  62   c  can be joined without using the adhesive or junction, and therefore the number of components can be reduced. By omitting the step of applying the adhesive or junction, the productivity of the reinforcing pipe  60   c  can be increased. 
     Other Embodiments 
       FIG.  23    is an explanatory drawing schematically illustrating an example of sectional shapes of pipe forming portions according to another embodiment. As demonstrated by pipe forming portions  64  to  69  of  FIG.  23   , various shapes may be employed as the sectional shapes of the pipe forming portions. To obtain the strength of the high-pressure tank  100 , the ends of the pipe forming portions are preferably shaped to increase the area of the abutment surfaces of the pipe forming portions. 
     The embodiments described above are directed to the example in which the reinforcing pipe has three pipe forming portions. The number of pipe forming portions is not limited to three, and may be an arbitrary number such as two, four, or more. 
     The embodiments described above are directed to the example in which the recess H 1 , H 12 , or H 13  is formed on the outer surface of the reinforcing pipe by causing adjacent pipe forming portions to abut against or approach each other. The recess may be formed on the inner surface of the reinforcing pipe. In this case, the junction may be arranged in the recess on the inner surface of the reinforcing pipe to join the adjacent pipe forming portions. 
     The present disclosure is not limited to the embodiments described above, but may be implemented by various structures without departing from the spirit of the present disclosure. For example, the technical features of the embodiments corresponding to the technical features of the individual aspects described in the “SUMMARY” section may be replaced or combined as appropriate to solve a part or all of the problems described above or attain a part or all of the effects described above. Any technical feature may be omitted as appropriate unless otherwise described as being essential herein.