Patent Publication Number: US-2015075663-A1

Title: Pipe and method for manufacturing pipe

Description:
TECHNICAL FIELD 
     The present invention relates to a pipe and a method for manufacturing a pipe. 
     BACKGROUND ART 
     Conventionally, when one pipe is connected to another pipe, a joint structure has been used in which a tapered male screw portion that is formed on an external surface of the pipes and a tapered female screw portion that is formed on an internal surface of a substantially tubular-shaped coupling are screwed together (see JP S37-9634B, for example). A pipe that is made from fiber reinforced plastic has also been used conventionally. In the case of such a pipe, an end portion of a pipe main body that is made from fiber reinforced plastic is inserted into a substantially tubular-shaped connection portion having a tapered male screw portion on its external surface so that the connection portion is fixed to the end portion. 
     Meanwhile, when the external surface of the end portion of the pipe main body is provided with a main body inclined surface whose diameter is gradually reduced toward its end face, and the main body inclined surface is bonded to an opposing inclined surface that is formed on the internal surface of the connection portion, part of reinforced fiber of the fiber reinforced plastic that constitutes the pipe main body is exposed on the main body inclined surface so as to be bonded to the opposing inclined surface of the connection portion. Accordingly, when many pipes are connected to one another via couplings in the vertical direction and a very large tensile load is exerted on each pipe, a shear failure in which part of the reinforced fiber is pulled together with the connection portion and comes out from the pipe main body is likely to occur on the main body inclined surface depending on the structure of the reinforced fiber. 
     SUMMARY OF INVENTION 
     The present invention is directed to a pipe, and it is an object thereof to improve shear strength of a main body inclined surface. 
     The pipe according to the present invention includes: a reinforced fiber structure that has a tubular shape; and a matrix resin that covers an internal side, which is a central axis side of the reinforced fiber structure, and an external side of the reinforced fiber structure, thereby constituting, together with the reinforced fiber structure, a pipe main body that has a tubular shape centered on the central axis, wherein an external surface of an end portion of the pipe main body has a main body inclined surface whose diameter is gradually reduced toward an end face, when the pipe main body is connected to another pipe main body, the main body inclined surface is coupled to a coupling that has a substantially tubular shape, and the reinforced fiber structure includes: a first portion that is constituted by a plurality of fiber bundles extending in parallel with the central axis or by a woven structure of a plurality of fiber bundles, and that is arranged near the main body inclined surface; and a second portion that has a structure different from the structure of the first portion, and is arranged apart from the main body inclined surface. 
     According to the present invention, it is possible to improve shear strength of the main body inclined surface. 
     In a preferable embodiment of the present invention, the reinforced fiber structure includes: an internal layer that is arranged on the central axis side and has a predetermined structure; and an external layer that is arranged on an external side of the internal layer and has a predetermined structure that is different from the predetermined structure of the internal layer, and the first portion is part of the external layer, and the second portion is the internal layer. 
     In this case, the internal layer has a laminated structure of a plurality of fiber bundles that extend in parallel with the central axis and a plurality of fiber bundles that extend in a circumferential direction centered on the central axis, so that it is possible to improve strength against hoop stress. 
     In another preferable embodiment of the present invention, the pipe further includes a connection portion that is a member having a substantially tubular shape centered on the central axis, and includes an opposing inclined surface that is to be bonded to the main body inclined surface of the pipe main body on an internal surface of the connection portion, and a tapered male screw portion on an external surface of the connection portion, wherein when the pipe main body is connected to the other pipe main body, the tapered male screw portion is screwed with a tapered female screw portion that is provided on an internal surface of the coupling, and the main body inclined surface is coupled to the coupling via the connection portion. This allows the pipe to be coupled to the coupling in a removable manner. 
     The pipe is preferably used for pumping crude oil from an oil well. 
     The present invention is also directed to a method for manufacturing a pipe. The method includes: a) arranging a first reinforced fiber sheet along an internal surface of a mold that has a cylindrical shape, the first reinforced fiber sheet including a plurality of fiber bundles that extend in parallel with a central axis of the mold or being constituted by a woven structure of a plurality of fiber bundles; b) arranging a second reinforced fiber sheet on the central axis side of the first reinforced fiber sheet, the second reinforced fiber sheet having a structure that is different from the structure of the first reinforced fiber sheet; c) supplying a resin into the mold and rotating the mold around the central axis, thereby molding a pipe main body; and d) forming a main body inclined surface whose diameter is gradually reduced toward an end face on an external surface of an end portion of the pipe main body. Accordingly, it is possible to improve shear strength of the main body inclined surface. 
     The above-described object and other objects, features, embodiments, and advantages are apparent from the following detailed description of the present invention with reference to the accompanied drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates pipes and a coupling. 
         FIG. 2  is a cross-sectional view illustrating a pipe and the coupling. 
         FIG. 3  is a diagram illustrating a structure of reinforced fiber of the pipe. 
         FIG. 4  illustrates a flow of processing for manufacturing a pipe. 
         FIG. 5  is a diagram illustrating the processing for manufacturing a pipe. 
         FIG. 6  is a diagram illustrating the processing for manufacturing a pipe. 
         FIG. 7  is a diagram illustrating the processing for manufacturing a pipe. 
         FIG. 8  is a diagram illustrating a structure of reinforced fiber of a pipe in a comparative example. 
         FIG. 9  is a cross-sectional view illustrating the vicinity of a main body inclined surface of the pipe in the comparative example. 
         FIG. 10  is a diagram illustrating a structure of reinforced fiber of a pipe in another comparative example. 
         FIG. 11  is a diagram illustrating a structure of reinforced fiber of a pipe in another embodiment. 
         FIG. 12  is a diagram illustrating a structure of reinforced fiber of a pipe in another embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  illustrates pipes  1  according to an embodiment of the present invention, and  FIG. 1  specifically illustrates two pipes  1  that are connected to each other by a coupling  5 . The pipe  1  and the coupling  5  have tubular shapes with their centers on a central axis J 1 . The pipes  1  are used for, for example, pumping crude oil from an oil well and, in this case, a number of pipes  1  are connected to each other via the couplings  5  in a vertical direction. The pipes  1  may be used for underground carbon dioxide storage, seawater desalination plants, geothermal electric power plants, and the like. 
       FIG. 2  is a cross-sectional view of the pipe  1  and the coupling  5 , and specifically illustrates part of a cross-section that includes the central axis J 1  of the pipe  1  and the coupling  5  (the portion that corresponds to the upper side of  FIG. 1 ). The pipe  1  includes a pipe main body  2  that is made from fiber reinforced plastic, and two connection portions  3  that are provided respectively on both end portions of the pipe main body  2  (in  FIG. 2 , only one connection portion  3  is shown). Since the two connection portions  3  have the same shape, in the following description, attention will be given only to the connection portion  3  that is provided on one end portion  21  of the pipe main body  2 . For example, the pipe main body  2  has an internal diameter of 60 millimeters (mm) and an external diameter (excluding the end portion  21 ) of 77 mm. 
     The connection portion  3  is a member that is mainly made from a resin, and has a substantially tubular shape centered on the central axis J 1  (see  FIG. 1 ). The pipe main body  2  has a tubular shape centered on the central axis J 1 , and the end portion  21  of the pipe main body  2  is inserted into the connection portion  3  so that the connection portion  3  is fixed to the end portion  21 . Reinforced fiber or a matrix resin of the fiber reinforced plastic of the pipe main body  2  may be any of various known materials. Also, a resin from which the connection portion  3  is made may be any of various known materials. 
     The connection portion  3  includes: a connection portion main body  31  that has a substantially tubular shape; an annular cover portion  32  that covers an end face  211  of the pipe main body  2  at an edge of the connection portion main body  31 ; and a tapered male screw portion  33  that is formed on an external surface of the connection portion main body  31 . An internal surface of the connection portion main body  31  has an inclined surface  312  whose diameter is gradually reduced toward the cover portion  32  (that is, toward the end face  211  of the pipe main body  2 ). An external surface of the end portion  21  of the pipe main body  2  also has an inclined surface  212  (hereinafter referred to as “main body inclined surface  212 ”) whose diameter is gradually reduced toward the end face  211 , and the inclined surface  312  of the connection portion main body  31  opposes the main body inclined surface  212  of the pipe main body  2  and is bonded to the main body inclined surface  212  (for example, they are bonded together with the matrix resin of the pipe main body  2  or the resin from which the connection portion  3  is made). Hereinafter, the inclined surface  312  of the connection portion main body  31  is referred to as “opposing inclined surface  312 ”. The external surface of the connection portion main body  31  is also an inclined surface (circular conical surface) whose diameter is gradually reduced toward the cover portion  32 , and screw threads are formed along the inclined surface, and thus the tapered male screw portion  33  is formed. 
     The main body inclined surface  212  of the pipe main body  2  in  FIG. 2  is formed by grinding an external surface of an end portion of a tubular-shaped member that is intended to serve as the pipe main body  2 , for example. Although reinforced fiber of the fiber reinforced plastic that constitutes the pipe main body  2  is exposed at the end face  211  and the main body inclined surface  212  of the pipe main body  2 , in the pipe  1  as has already been described, the end face  211  and the main body inclined surface  212  are respectively covered with the cover portion  32  and the opposing inclined surface  312  of the connection portion  3 , thus preventing degradation of the reinforced fiber due to fluid flowing through the pipe  1 , exfoliation of the reinforced fiber and the matrix resin, and the like. Note that in a region on an internal surface side of the pipe main body  2 , the matrix resin is present with a certain thickness so as to form a corrosion-resistant layer. 
       FIG. 3  is a diagram illustrating a structure of reinforced fiber of the pipe main body  2 . The pipe main body  2  having a tubular shape is provided with a reinforced fiber structure  22  that has a tubular shape. As will be described later, in the present embodiment, the reinforced fiber structure  22  is produced by winding a sheet of reinforced fiber (such as glass fibers) into a tubular shape, and therefore it is conceivable that the reinforced fiber structure  22  is in the state of being wound into a tubular shape. An internal side of the reinforced fiber structure  22  that is on the central axis side J 1  and an external side of the reinforced fiber structure  22  (in  FIG. 3 , the lower side and upper sides, respectively) are covered with matrix resins  29 . In other words, the matrix resins  29  constitute the pipe main body  2 , together with the reinforced fiber structure  22 . 
     The reinforced fiber structure  22  includes: internal layers  23  that are arranged on the central axis J 1  side, and external layers  24  that are arranged on the external side of the internal layers  23 . The internal layers  23  have a laminated structure of a plurality of fiber bundles  231 , which extend in parallel with the central axis J 1  (in the lateral direction in  FIG. 3 ), and a plurality of fiber bundles  232 , which extend in a circumferential direction centered on the central axis J 1 . Specifically, the plurality of fiber bundles  231 , each of which extends along the central axis J 1 , are closely arranged on a plurality of circumferences (on a plurality of virtually substantially tubular surfaces) that have their centers on the central axis J 1  and have different radii, so as to form the layers of the fiber bundles  231 . Also, the plurality of fiber bundles  232  that have each a substantially ring-shape centered on the central axis J 1  and have the same radius along the central axis J 1  are closely arranged, so as to form each layer of the fiber bundles  232 . In the internal layers  23 , the layers of the fiber bundles  231  and the layers of the fiber bundles  232  are alternately laminated in a radial direction that is perpendicular to the central axis J 1 , and thus the internal layers  23  have a predetermined structure along the central axis J 1 . 
     The external layers  24  are constituted only by a plurality of fiber bundles  241 , which extend in parallel with the central axis J 1 . Specifically, the plurality of fiber bundles  241 , each of which extends along the central axis J 1 , are closely arranged on a plurality of circumferences that have their centers on the central axis J 1  and have different radii, and the layers of the fiber bundle  241  are laminated in the radial direction. In this manner, the external layers  24  have, along the central axis J 1 , a predetermined structure that is different from that of the internal layers  23 . 
     In the pipe main body  2 , the above-described main body inclined surface  212  is formed on the outer side in the radial direction of the external layers  24 , and the internal layers  23  are arranged only at the location in the radial direction where the end face  211  is present. Thus, on the main body inclined surface  212 , only the external layers  24  of the reinforced fiber structure  22  are exposed and the internal layers  23  located apart from the main body inclined surface  212  in the radial direction are not exposed on the main body inclined surface  212 . 
     The coupling  5  in  FIG. 2  includes a coupling main body  6  made from fiber reinforced plastic, and a connection portion  7  that is a member made from a resin and has a substantially tubular shape centered on the central axis J 1  (see  FIG. 1 ). The connection portion  7  is provided on an internal surface of the coupling main body  6  that has a substantially tubular shape centered on the central axis J 1 . The connection portion  7  includes a connection portion main body  71  that has a substantially tubular shape, and a tapered female screw portion  73  is formed on an internal surface of each end portion of the connection portion main body  71  in the direction of the central axis J 1  (in the lateral direction in  FIG. 2 ). Reinforced fiber and a matrix resin of fiber reinforced plastic of the coupling main body  6  may be any of various known materials. Also, the resin from which the connection portion  7  is made may also be any of various known materials. 
     When connecting one pipe  1  to another pipe  1 , that is, when connecting one pipe main body  2  to another pipe main body  2 , a tapered male screw portion  33  at one end portion  21  of one pipe main body  2  is screwed with one tapered female screw portion  73  that is provided on the internal surface of the coupling  5 , and a tapered male screw portion  33  at one end portion  21  of the other pipe main body  2  is screwed with the other tapered female screw portion  73  of the coupling  5 . In other words, at each end portion  21  of the pipe main bodies  2 , the main body inclined surface  212  is coupled to the substantially tubular-shaped coupling  5  via the connection portions  3  and  7 . Note that the tapered male screw portion  33  is tightened with respect to the tapered female screw portion  73  in a relative manner, and either one of the pipe  1  and the coupling  5  may be rotated. 
     Next, processing for manufacturing the pipe  1  will be described with reference to  FIG. 4 . In the processing for manufacturing the pipe  1 , first, as illustrated in  FIG. 5 , a mold  81  that has a cylindrical shape is prepared, and a first reinforced fiber sheet  821  is arranged along an internal surface  811  of the mold  81  (step S 11 ). The first reinforced fiber sheet  821  is a sheet that includes, as main reinforced fiber, a plurality of fiber bundles that extend in parallel with a central axis J 2  of the mold  81  (see the external layers  24  in  FIG. 3 ). Note that the first reinforced fiber sheet  821  may partially be provided with other fiber bundles, an adhesive, or the like for maintaining the plurality of fiber bundles in a sheet-shape. In  FIG. 5 , although the first reinforced fiber sheet  821  is indicated by one solid line, the first reinforced fiber sheet  821  may be wound twice or threefold or more. Note, however, that the first reinforced fiber sheet  821  may preferably be arranged with substantially the same thickness on the entire circumference having its center at the central axis J 2 . Such a modification applies also to a second reinforced fiber sheet  822  that will be described below. 
     Next, as illustrated in  FIG. 6 , the second reinforced fiber sheet  822  is arranged on the central axis J 2  side of the first reinforced fiber sheet  821 , the second reinforced fiber sheet  822  including reinforced fiber having a structure that is different from that of the first reinforced fiber sheet  821  (step S 12 ). Specifically, the second reinforced fiber sheet  822  has a laminated structure in which the plurality of fiber bundles  231 , which extend in parallel with the central axis J 2 , and the plurality of fiber bundles  232 , which extend in the circumferential direction centered on the central axis J 2 , are alternately laminated in a radial direction that is perpendicular to the central axis J 2  (see the internal layers  23  in  FIG. 3 ). 
     When the first reinforced fiber sheet  821  and the second reinforced fiber sheet  822  have been arranged in the mold  81 , closing members  813  are mounted in openings  812  at both end portions of the mold  81  in the direction of the central axis J 2 , and the openings  812  are closed, as illustrated in  FIG. 7 . The mold  81  is installed in a centrifugal molding device, and a liquid resin is supplied into the mold  81  from a material supplying portion. At this time, the resin is supplied into the mold  81  through a supply port (not shown) that is provided in the closing member  813 . Centrifugal molding is performed by rotating the mold  81  around the central axis J 2 . In the above-described manner, by supplying a resin into the mold  81 , and rotating the mold  81  around the central axis J 2 , the pipe main body  2  (indicated by chain double-dashed lines in  FIG. 7 ) is molded (step S 13 ). Note that when a thermo-setting resin is used, the mold  81  is heated in the centrifugal molding device. 
     When the centrifugal molding has been completed, the closing member  813  is removed from one opening  812  of the mold  81 , and the pipe main body  2  is pulled out from this opening  812 . Then, on each external surface at both end portions  21  of the pipe main body  2 , the main body inclined surface  212  (see  FIG. 2 ) whose diameter is gradually reduced toward the end face  211  of the end portion  21  is formed by a tapering process such as grinding (step S 14 ). Note that the main body inclined surfaces  212  may be formed on both end portions after the pipe main body  2  formed by the processing in step S 13  has been cut into a piece with a desired length. 
     Meanwhile, the connection portion  3  (see  FIG. 2 ), which includes the opposing inclined surface  312  on its internal surface and the tapered male screw portion  33  on its external surface, has been prepared in advance, and end portions  21  of the pipe main body  2  are inserted into the connection portion  3 , with the main body inclined surfaces  212  at both end portions  21  coated with a liquid resin. The main body inclined surface  212  and the opposing inclined surface  312  of the connection portion  3  are bonded together by hardening (for example, thermally hardening) the resin, and the connection portion  3  is fixed to the end portion  21  of the pipe main body  2  (step S 15 ). With these procedures, the pipe  1  in  FIG. 2  is completed. 
       FIG. 8  is a diagram illustrating a structure of reinforced fiber of a pipe main body  91  of a pipe  9  of a comparative example. In the pipe  9  of the comparative example, an entire reinforced fiber structure  92  has a laminated structure in which a plurality of fiber bundles  921 , which extend in parallel with a central axis J 1  (in the lateral direction in  FIG. 8 ), and a plurality of fiber bundles  922 , which extend in a circumferential direction, are alternately laminated in a radial direction. As illustrated in  FIG. 9 , thus, near a main body inclined surface  911 , both types of the plurality of fiber bundles  921 , which extend in parallel with the central axis J 1 , and the plurality of fiber bundles  922 , which extend in the circumferential direction, are exposed and fixed to an opposing inclined surface  931  of a connection portion  93 . 
     When pipes are used in oil wells or the like, many pipes are connected to each other via couplings in the vertical direction, and therefore a very large tensile load is exerted on each pipe. At this time, a shear failure in which the fiber bundles  922  (that is, the fiber bundles  922 , which extend in a circumferential direction) that are fixed to the opposing inclined surface  931  of the connection portion  93  are pulled together with the connection portion  93  and come out from the pipe main body  91  (that is, a shear failure causing offset between layers in the radial direction of the reinforced fiber structure  92 ) may occur on the main body inclined surface  911 . 
     In contrast, in the pipe main body  2  in  FIG. 3 , the portion of the reinforced fiber structure  22  that is arranged near the main body inclined surface  212  is constituted by the plurality of fiber bundles  241 , which extend in parallel with the central axis J 1 . This prevents such a shear failure, in which the fiber bundles of the reinforced fiber structure  22  are pulled together with the connection portion  3  and come out from the pipe main body  2 , from occurring on the main body inclined surface  212 , achieving an improvement in the shear strength (that is, the limit strength that withstands shear) of the main body inclined surface  212 . 
       FIG. 10  is a diagram illustrating a structure of reinforced fiber of a pipe main body  91   a  of a pipe  9   a  of another comparative example. In the pipe  9   a  of this comparative example, an entire reinforced fiber structure  92   a  has a plain woven structure (a plain woven glass cross is used here) in which a plurality of fiber bundles  921   a , which extend along the direction of the central axis J 1  (in the lateral direction in  FIG. 10 ), and a plurality of fiber bundles  922   a , which extend along a circumferential direction, are plain woven. In the pipe  9   a  of the comparative example shown in  FIG. 10 , even if the fiber bundles  922   a , which extend along the circumferential direction, are pulled together with the connection portion  93  on the main body inclined surface  911  (see  FIG. 9 ), the fiber bundles  922   a  are prevented from coming out from the pipe main body  91   a  since the fiber bundles  922   a  are woven with the plurality of fiber bundles  921   a , which extend along the central axis J 1 . 
     On the other hand, when a tensile load is being exerted, there may be the case where screw threads of a tapered male screw portion that is provided on one end of the pipe are pressed toward an end face side of the pipe main body by screw threads of a tapered female screw portion of the coupling, so that a force that is directed toward the central axis side of the pipe acts at the edge of the pipe. As a result, the entire circumference of the edge of the pipe is bent toward the central axis side and compression stress (that is, hoop stress) occurs in the circumferential direction of the pipe, causing deformation (buckling in the circumferential direction) or breakage at the edge of the pipe. In the pipe  9   a  of the comparative example shown in  FIG. 10 , waves (they are in a wave-shape, and may be referred to as “crimps”) have occurred in the plurality of fiber bundles  922   a , which extend along the circumferential direction, resulting in a reduction in the compressive strength against hoop stress. Waves also have occurred in the fiber bundles  921   a , which extend along the central axis J 1 , resulting in a reduction in the tensile strength of the pipe main body  91   a . Note that in a common filament winding method, in which reinforced fiber is wound around a mandrel and molded, the fiber bundles cannot be arranged in parallel with the circumferential direction, so that the compressive strength against the hoop stress is lowered, similarly to the pipe  9   a  of the comparative example. 
     In contrast, in the pipe  1  in  FIG. 3 , since the internal layers  23  have layers of the plurality of fiber bundles  232 , which extend (without waving) in a circumferential direction centered on the central axis J 1 , the strength against hoop stress can be improved, relative to that of the pipe  9   a  in the comparative example. As described above, in the reinforced fiber structure  22 , the external layers  24  are made from a reinforced base material that has a structure with a high shear strength, and the internal layers  23  are made from a reinforced base material that has a structure with a high compressive strength, so that an improvement in the tensile strength of the pipe  1  is achieved. 
     Actually, when tensile tests were performed on two pipes connected via a coupling (see  FIG. 1 ), the results show that a tensile breaking force (tensile strength) was 170 kilonewton (kN) in the case where the pipes  9  of the comparative example in  FIG. 8  were used as the two pipes, and a tensile breaking force was 150 kilonewton in the case where the pipes  9   a  of the comparative example in  FIG. 10  were used as the two pipes. In contrast, a tensile breaking force was 210 kilonewton in the case where the pipes  1  of  FIG. 3  were used, and it is ascertained that the tensile strength of the pipes  1  is higher than the pipes  9  and  9   a  of the comparative examples. Note that in the pipe  9   a  of the comparative example shown in  FIG. 10 , buckling breakage occurred at the edge of the pipe, but no buckling breakage occurred in the pipe  9  of the comparative example in  FIG. 8  and in the pipes  1  in  FIG. 2 . 
     Note that in a sheet winding method, in which a prepreg sheet (that is, a sheet formed by impregnating reinforced fiber with a resin) is wound around a mandrel and molded, it is possible to align the fiber bundles in a desired direction but molding of an elongated pipe main body is not easy. Also, since a relatively expensive prepreg sheet is used, the manufacturing cost of the pipes is also increased. In contrast, as described above, in molding of a pipe main body using centrifugal molding, it is possible to produce an elongated pipe main body easily and at a lower cost. 
       FIG. 11  is a diagram illustrating a structure of reinforced fiber of a pipe main body  2   a  of a pipe  1   a  according to another embodiment of the present invention. Similarly to the internal layers  23  in  FIG. 3 , internal layers  23  of a reinforced fiber structure  22   a  in  FIG. 11  have a laminated structure in which a plurality of fiber bundles  231 , which extend in parallel with a central axis J 1  (in the lateral direction in  FIG. 11 ), and a plurality of fiber bundles  232 , which extend in a circumferential direction centered on the central axis J 1 , are alternately laminated in a radial direction that is perpendicular to the central axis J 1 . On the other hand, external layers  24   a  have a plain woven structure (a plain woven glass cross is used here) in which a plurality of fiber bundles  241   a , which extend along the direction of the central axis J 1 , and a plurality of fiber bundles  242   a , which extend along the circumferential direction, are plain woven. In the manufacturing of the pipe  1   a  in  FIG. 11 , similar procedures as those in the manufacturing of the pipe  1  in  FIG. 2  are performed, except that a sheet that is constituted by the woven structure of the plurality of fiber bundles, as with the external layer  24   a , is used as a first reinforced fiber sheet. 
     In the pipe  1   a  in  FIG. 11 , the portion of the reinforced fiber structure  22   a  that is arranged near the main body inclined surface  212  (see  FIG. 2 ) is constituted by the woven structure of the plurality of fiber bundles  241   a  and the plurality of  242   a . This prevents a shear failure, in which the fiber bundles  242   a , which extend along the circumferential direction, of the reinforced fiber structure  22   a  are pulled together with the connection portion  3  and come out from the pipe main body  2   a , from occurring on the main body inclined surface  212 , achieving an improvement in the shear strength against the tensile load. Also, by the internal layers  23  including the plurality of fiber bundles  232 , which extend the circumferential direction, an improvement in the strength against the hoop stress can be achieved. 
     When a tensile test was performed on the pipes  1   a  in  FIG. 11 , similar to those on the respective pipes  1 ,  9 , and  9   a  in  FIGS. 3 ,  8 , and  10 , the results show that a tensile breaking force was 195 kilonewton, and it is ascertained that the tensile strength is higher than those of the pipes  9  and  9   a  in the comparative examples. No buckling breakage occurred. Note that, in view of preventing the fiber bundles from coming out from the main body inclined surface  212 , the plurality of fiber bundles  241   a , which constitute the plain woven structure, of the external layers  24   a  may extend in a direction that is inclined with respect to the central axis J 1 , and also the plurality of fiber bundles  242   a  may extend in a direction that is inclined with respect to the circumferential direction on the cylindrical surface centered on the central axis J 1 . Also, woven structures other than the plain woven structure may be applied to the external layer  24   a.    
     Although the embodiments of the present invention have been described, the present invention is not limited to the above-described embodiments, and various modifications are possible. 
     In the above-described embodiments, the reinforced fiber structures  22  and  22   a  are respectively provided with the internal layers  23  and the external layers  24  and  24   a  whose structures differ from each other but it is also possible, as illustrated in, for example,  FIG. 12 , that a portion of the reinforced fiber structure  22   b  of the pipe main body  2   b  that is arranged near the main body inclined surface  212  is constituted by the plurality of fiber bundles  231   b , which extend in parallel with a central axis J 1  (in the lateral direction in  FIG. 12 ), and a portion of the reinforced fiber structure  22   b  that is located apart from the main body inclined surface  212  in the direction of the central axis J 1  has a laminated structure in which the plurality of fiber bundles  231   b , which extend in parallel with the central axis J 1 , and the plurality of fiber bundles  232   b , which extend in the circumferential direction, are alternately laminated in the radial direction. Also in the case of a pipe  1   b  in  FIG. 12 , it is possible to improve the shear strength of the main body inclined surface  212 . Note that in  FIG. 12 , illustration of the connection portion  3  is omitted. It is also possible that the structure illustrated in  FIG. 12  is applied only to the external layers of the reinforced fiber structure  22 , and another structure (for example, a laminated structure in which a plurality of fiber bundles that extend in parallel with the central axis J 1  and a plurality of fiber bundles that extend in the circumferential direction are alternately laminated in the radial direction) is applied to the internal layers. 
     As has been described above, the reinforced fiber structure includes: a first portion that is constituted by a plurality of fiber bundles that extend in parallel with the central axis J 1  or by a woven structure of a plurality of fiber bundles, and that is arranged near the main body inclined surface  212 ; and a second portion that has a structure that is different from that of the first portion, and is arranged at a position that is located apart from the main body inclined surface  212  in the direction of the central axis J 1  or the radial direction, so that it is possible to ensure the performance that is desired for the pipe main body  2  using the second portion, while improving the shear strength of the main body inclined surface  212 . In the examples in  FIGS. 3 and 11 , the first portion is part of the external layers  24 ,  24   a  and the second portion is the internal layers  23 . 
     In view of the improvement in the strength against hoop stress, the internal layers  23  of the reinforced fiber structure  22  may be constituted only by a plurality of fiber bundles, which extend in the circumferential direction. 
     Although in the above-describe embodiments, by the pipes  1 ,  1   a , and  1   b  including the connection portion  3 , the pipes  1 ,  1   a , and  1   b  can be connected to the coupling  5  in a removable manner, the connection portion  3  may be omitted in the pipe depending on design of the pipe, and the main body inclined surface  212  of the pipe main body and the internal surface of the coupling  5  may be bonded together (that is, they can be directly connected to each other). Even in this case, it is possible to improve the shear strength of the main body inclined surface  212  by constituting the first portion that is arranged near the main body inclined surface  212  by a plurality of fiber bundles that extend in parallel with the central axis J 1  or providing a reinforced fiber structure that has a woven structure of a plurality of fiber bundles. 
     Although the pipes  1 ,  1   a , and  1   b  are particularly suitable for use in a circumstance at elevated pressure and temperature in which a high corrosion resistance property is required, as in the case of use for pumping crude oil from an oil well, the pipes  1 ,  1   a , and  1   b  may, of course, be used in other circumstances than the above-described circumstance. 
     The configurations of the above-described embodiments and the various modifications may suitably be combined with each other, as long as they are mutually consistent. 
     Although the present invention has been described in detail, the descriptions having already been made are illustrative and not limiting. Therefore, it can be said that many modifications and modes are possible without departing from the scope of the present invention. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 ,  1   a ,  1   b  Pipe 
               2 ,  2   a ,  2   b  Pipe main body 
               3  Connection portion 
               5  Coupling 
               21  End portion 
               22 ,  22   a ,  22   b  Reinforced fiber structure 
               23  Internal layer 
               24 ,  24   a  External layer 
               29  Matrix resin 
               33  Tapered male screw portion 
               73  Tapered female screw portion 
               81  Mold 
               211  End face 
               212  Main body inclined surface 
               231 ,  232 ,  241 ,  231   b ,  232   b ,  241   a ,  242   a  Fiber bundle 
               312  Opposing inclined surface 
               811  Internal surface 
               821  First reinforced fiber sheet 
               822  Second reinforced fiber sheet 
             J 1  Central axis (of pipe) 
             J 2  Central axis (of mold) 
             S 11  to S 15  Step