PIPE AND METHOD FOR MANUFACTURING PIPE

A pipe includes a tubular reinforced fiber structure, and a tubular matrix resin pipe main body centered on the central axis, together with a reinforced fiber structure, covering an internal side of the reinforced fiber structure on the central axis side, and an external side. An external end surface of the pipe main body has an inclined surface whose diameter is gradually reduced toward the end face, which connects the pipe main body to another pipe main body, with the main body inclined surface coupled to a substantially tubular-shaped coupling. A portion of the reinforced fiber structure near the main body inclined surface has a plurality of fiber bundles extending in parallel to the central axis. This prevents a shear failure of the fiber bundles of the reinforced fiber structure of the main body inclined surface.

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.

DESCRIPTION OF EMBODIMENTS

FIG. 1illustrates pipes1according to an embodiment of the present invention, andFIG. 1specifically illustrates two pipes1that are connected to each other by a coupling5. The pipe1and the coupling5have tubular shapes with their centers on a central axis J1. The pipes1are used for, for example, pumping crude oil from an oil well and, in this case, a number of pipes1are connected to each other via the couplings5in a vertical direction. The pipes1may be used for underground carbon dioxide storage, seawater desalination plants, geothermal electric power plants, and the like.

FIG. 2is a cross-sectional view of the pipe1and the coupling5, and specifically illustrates part of a cross-section that includes the central axis J1of the pipe1and the coupling5(the portion that corresponds to the upper side ofFIG. 1). The pipe1includes a pipe main body2that is made from fiber reinforced plastic, and two connection portions3that are provided respectively on both end portions of the pipe main body2(inFIG. 2, only one connection portion3is shown). Since the two connection portions3have the same shape, in the following description, attention will be given only to the connection portion3that is provided on one end portion21of the pipe main body2. For example, the pipe main body2has an internal diameter of 60 millimeters (mm) and an external diameter (excluding the end portion21) of 77 mm.

The connection portion3is a member that is mainly made from a resin, and has a substantially tubular shape centered on the central axis J1(seeFIG. 1). The pipe main body2has a tubular shape centered on the central axis J1, and the end portion21of the pipe main body2is inserted into the connection portion3so that the connection portion3is fixed to the end portion21. Reinforced fiber or a matrix resin of the fiber reinforced plastic of the pipe main body2may be any of various known materials. Also, a resin from which the connection portion3is made may be any of various known materials.

The connection portion3includes: a connection portion main body31that has a substantially tubular shape; an annular cover portion32that covers an end face211of the pipe main body2at an edge of the connection portion main body31; and a tapered male screw portion33that is formed on an external surface of the connection portion main body31. An internal surface of the connection portion main body31has an inclined surface312whose diameter is gradually reduced toward the cover portion32(that is, toward the end face211of the pipe main body2). An external surface of the end portion21of the pipe main body2also has an inclined surface212(hereinafter referred to as “main body inclined surface212”) whose diameter is gradually reduced toward the end face211, and the inclined surface312of the connection portion main body31opposes the main body inclined surface212of the pipe main body2and is bonded to the main body inclined surface212(for example, they are bonded together with the matrix resin of the pipe main body2or the resin from which the connection portion3is made). Hereinafter, the inclined surface312of the connection portion main body31is referred to as “opposing inclined surface312”. The external surface of the connection portion main body31is also an inclined surface (circular conical surface) whose diameter is gradually reduced toward the cover portion32, and screw threads are formed along the inclined surface, and thus the tapered male screw portion33is formed.

The main body inclined surface212of the pipe main body2inFIG. 2is formed by grinding an external surface of an end portion of a tubular-shaped member that is intended to serve as the pipe main body2, for example. Although reinforced fiber of the fiber reinforced plastic that constitutes the pipe main body2is exposed at the end face211and the main body inclined surface212of the pipe main body2, in the pipe1as has already been described, the end face211and the main body inclined surface212are respectively covered with the cover portion32and the opposing inclined surface312of the connection portion3, thus preventing degradation of the reinforced fiber due to fluid flowing through the pipe1, 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 body2, the matrix resin is present with a certain thickness so as to form a corrosion-resistant layer.

FIG. 3is a diagram illustrating a structure of reinforced fiber of the pipe main body2. The pipe main body2having a tubular shape is provided with a reinforced fiber structure22that has a tubular shape. As will be described later, in the present embodiment, the reinforced fiber structure22is 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 structure22is in the state of being wound into a tubular shape. An internal side of the reinforced fiber structure22that is on the central axis side J1and an external side of the reinforced fiber structure22(inFIG. 3, the lower side and upper sides, respectively) are covered with matrix resins29. In other words, the matrix resins29constitute the pipe main body2, together with the reinforced fiber structure22.

The reinforced fiber structure22includes: internal layers23that are arranged on the central axis J1side, and external layers24that are arranged on the external side of the internal layers23. The internal layers23have a laminated structure of a plurality of fiber bundles231, which extend in parallel with the central axis J1(in the lateral direction inFIG. 3), and a plurality of fiber bundles232, which extend in a circumferential direction centered on the central axis J1. Specifically, the plurality of fiber bundles231, each of which extends along the central axis J1, are closely arranged on a plurality of circumferences (on a plurality of virtually substantially tubular surfaces) that have their centers on the central axis J1and have different radii, so as to form the layers of the fiber bundles231. Also, the plurality of fiber bundles232that have each a substantially ring-shape centered on the central axis J1and have the same radius along the central axis J1are closely arranged, so as to form each layer of the fiber bundles232. In the internal layers23, the layers of the fiber bundles231and the layers of the fiber bundles232are alternately laminated in a radial direction that is perpendicular to the central axis J1, and thus the internal layers23have a predetermined structure along the central axis J1.

The external layers24are constituted only by a plurality of fiber bundles241, which extend in parallel with the central axis J1. Specifically, the plurality of fiber bundles241, each of which extends along the central axis J1, are closely arranged on a plurality of circumferences that have their centers on the central axis J1and have different radii, and the layers of the fiber bundle241are laminated in the radial direction. In this manner, the external layers24have, along the central axis J1, a predetermined structure that is different from that of the internal layers23.

In the pipe main body2, the above-described main body inclined surface212is formed on the outer side in the radial direction of the external layers24, and the internal layers23are arranged only at the location in the radial direction where the end face211is present. Thus, on the main body inclined surface212, only the external layers24of the reinforced fiber structure22are exposed and the internal layers23located apart from the main body inclined surface212in the radial direction are not exposed on the main body inclined surface212.

The coupling5inFIG. 2includes a coupling main body6made from fiber reinforced plastic, and a connection portion7that is a member made from a resin and has a substantially tubular shape centered on the central axis J1(seeFIG. 1). The connection portion7is provided on an internal surface of the coupling main body6that has a substantially tubular shape centered on the central axis J1. The connection portion7includes a connection portion main body71that has a substantially tubular shape, and a tapered female screw portion73is formed on an internal surface of each end portion of the connection portion main body71in the direction of the central axis J1(in the lateral direction inFIG. 2). Reinforced fiber and a matrix resin of fiber reinforced plastic of the coupling main body6may be any of various known materials. Also, the resin from which the connection portion7is made may also be any of various known materials.

When connecting one pipe1to another pipe1, that is, when connecting one pipe main body2to another pipe main body2, a tapered male screw portion33at one end portion21of one pipe main body2is screwed with one tapered female screw portion73that is provided on the internal surface of the coupling5, and a tapered male screw portion33at one end portion21of the other pipe main body2is screwed with the other tapered female screw portion73of the coupling5. In other words, at each end portion21of the pipe main bodies2, the main body inclined surface212is coupled to the substantially tubular-shaped coupling5via the connection portions3and7. Note that the tapered male screw portion33is tightened with respect to the tapered female screw portion73in a relative manner, and either one of the pipe1and the coupling5may be rotated.

Next, processing for manufacturing the pipe1will be described with reference toFIG. 4. In the processing for manufacturing the pipe1, first, as illustrated inFIG. 5, a mold81that has a cylindrical shape is prepared, and a first reinforced fiber sheet821is arranged along an internal surface811of the mold81(step S11). The first reinforced fiber sheet821is a sheet that includes, as main reinforced fiber, a plurality of fiber bundles that extend in parallel with a central axis J2of the mold81(see the external layers24inFIG. 3). Note that the first reinforced fiber sheet821may partially be provided with other fiber bundles, an adhesive, or the like for maintaining the plurality of fiber bundles in a sheet-shape. InFIG. 5, although the first reinforced fiber sheet821is indicated by one solid line, the first reinforced fiber sheet821may be wound twice or threefold or more. Note, however, that the first reinforced fiber sheet821may preferably be arranged with substantially the same thickness on the entire circumference having its center at the central axis J2. Such a modification applies also to a second reinforced fiber sheet822that will be described below.

Next, as illustrated inFIG. 6, the second reinforced fiber sheet822is arranged on the central axis J2side of the first reinforced fiber sheet821, the second reinforced fiber sheet822including reinforced fiber having a structure that is different from that of the first reinforced fiber sheet821(step S12). Specifically, the second reinforced fiber sheet822has a laminated structure in which the plurality of fiber bundles231, which extend in parallel with the central axis J2, and the plurality of fiber bundles232, which extend in the circumferential direction centered on the central axis J2, are alternately laminated in a radial direction that is perpendicular to the central axis J2(see the internal layers23inFIG. 3).

When the first reinforced fiber sheet821and the second reinforced fiber sheet822have been arranged in the mold81, closing members813are mounted in openings812at both end portions of the mold81in the direction of the central axis J2, and the openings812are closed, as illustrated inFIG. 7. The mold81is installed in a centrifugal molding device, and a liquid resin is supplied into the mold81from a material supplying portion. At this time, the resin is supplied into the mold81through a supply port (not shown) that is provided in the closing member813. Centrifugal molding is performed by rotating the mold81around the central axis J2. In the above-described manner, by supplying a resin into the mold81, and rotating the mold81around the central axis J2, the pipe main body2(indicated by chain double-dashed lines inFIG. 7) is molded (step S13). Note that when a thermo-setting resin is used, the mold81is heated in the centrifugal molding device.

When the centrifugal molding has been completed, the closing member813is removed from one opening812of the mold81, and the pipe main body2is pulled out from this opening812. Then, on each external surface at both end portions21of the pipe main body2, the main body inclined surface212(seeFIG. 2) whose diameter is gradually reduced toward the end face211of the end portion21is formed by a tapering process such as grinding (step S14). Note that the main body inclined surfaces212may be formed on both end portions after the pipe main body2formed by the processing in step S13has been cut into a piece with a desired length.

Meanwhile, the connection portion3(seeFIG. 2), which includes the opposing inclined surface312on its internal surface and the tapered male screw portion33on its external surface, has been prepared in advance, and end portions21of the pipe main body2are inserted into the connection portion3, with the main body inclined surfaces212at both end portions21coated with a liquid resin. The main body inclined surface212and the opposing inclined surface312of the connection portion3are bonded together by hardening (for example, thermally hardening) the resin, and the connection portion3is fixed to the end portion21of the pipe main body2(step S15). With these procedures, the pipe1inFIG. 2is completed.

FIG. 8is a diagram illustrating a structure of reinforced fiber of a pipe main body91of a pipe9of a comparative example. In the pipe9of the comparative example, an entire reinforced fiber structure92has a laminated structure in which a plurality of fiber bundles921, which extend in parallel with a central axis J1(in the lateral direction inFIG. 8), and a plurality of fiber bundles922, which extend in a circumferential direction, are alternately laminated in a radial direction. As illustrated inFIG. 9, thus, near a main body inclined surface911, both types of the plurality of fiber bundles921, which extend in parallel with the central axis J1, and the plurality of fiber bundles922, which extend in the circumferential direction, are exposed and fixed to an opposing inclined surface931of a connection portion93.

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 bundles922(that is, the fiber bundles922, which extend in a circumferential direction) that are fixed to the opposing inclined surface931of the connection portion93are pulled together with the connection portion93and come out from the pipe main body91(that is, a shear failure causing offset between layers in the radial direction of the reinforced fiber structure92) may occur on the main body inclined surface911.

In contrast, in the pipe main body2inFIG. 3, the portion of the reinforced fiber structure22that is arranged near the main body inclined surface212is constituted by the plurality of fiber bundles241, which extend in parallel with the central axis J1. This prevents such a shear failure, in which the fiber bundles of the reinforced fiber structure22are pulled together with the connection portion3and come out from the pipe main body2, from occurring on the main body inclined surface212, achieving an improvement in the shear strength (that is, the limit strength that withstands shear) of the main body inclined surface212.

FIG. 10is a diagram illustrating a structure of reinforced fiber of a pipe main body91aof a pipe9aof another comparative example. In the pipe9aof this comparative example, an entire reinforced fiber structure92ahas a plain woven structure (a plain woven glass cross is used here) in which a plurality of fiber bundles921a, which extend along the direction of the central axis J1(in the lateral direction inFIG. 10), and a plurality of fiber bundles922a, which extend along a circumferential direction, are plain woven. In the pipe9aof the comparative example shown inFIG. 10, even if the fiber bundles922a, which extend along the circumferential direction, are pulled together with the connection portion93on the main body inclined surface911(seeFIG. 9), the fiber bundles922aare prevented from coming out from the pipe main body91asince the fiber bundles922aare woven with the plurality of fiber bundles921a, which extend along the central axis J1.

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 pipe9aof the comparative example shown inFIG. 10, waves (they are in a wave-shape, and may be referred to as “crimps”) have occurred in the plurality of fiber bundles922a, which extend along the circumferential direction, resulting in a reduction in the compressive strength against hoop stress. Waves also have occurred in the fiber bundles921a, which extend along the central axis J1, resulting in a reduction in the tensile strength of the pipe main body91a. 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 pipe9aof the comparative example.

In contrast, in the pipe1inFIG. 3, since the internal layers23have layers of the plurality of fiber bundles232, which extend (without waving) in a circumferential direction centered on the central axis J1, the strength against hoop stress can be improved, relative to that of the pipe9ain the comparative example. As described above, in the reinforced fiber structure22, the external layers24are made from a reinforced base material that has a structure with a high shear strength, and the internal layers23are 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 pipe1is achieved.

Actually, when tensile tests were performed on two pipes connected via a coupling (seeFIG. 1), the results show that a tensile breaking force (tensile strength) was 170 kilonewton (kN) in the case where the pipes9of the comparative example inFIG. 8were used as the two pipes, and a tensile breaking force was 150 kilonewton in the case where the pipes9aof the comparative example inFIG. 10were used as the two pipes. In contrast, a tensile breaking force was 210 kilonewton in the case where the pipes1ofFIG. 3were used, and it is ascertained that the tensile strength of the pipes1is higher than the pipes9and9aof the comparative examples. Note that in the pipe9aof the comparative example shown inFIG. 10, buckling breakage occurred at the edge of the pipe, but no buckling breakage occurred in the pipe9of the comparative example inFIG. 8and in the pipes1inFIG. 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. 11is a diagram illustrating a structure of reinforced fiber of a pipe main body2aof a pipe1aaccording to another embodiment of the present invention. Similarly to the internal layers23inFIG. 3, internal layers23of a reinforced fiber structure22ainFIG. 11have a laminated structure in which a plurality of fiber bundles231, which extend in parallel with a central axis J1(in the lateral direction inFIG. 11), and a plurality of fiber bundles232, which extend in a circumferential direction centered on the central axis J1, are alternately laminated in a radial direction that is perpendicular to the central axis J1. On the other hand, external layers24ahave a plain woven structure (a plain woven glass cross is used here) in which a plurality of fiber bundles241a, which extend along the direction of the central axis J1, and a plurality of fiber bundles242a, which extend along the circumferential direction, are plain woven. In the manufacturing of the pipe1ainFIG. 11, similar procedures as those in the manufacturing of the pipe1inFIG. 2are performed, except that a sheet that is constituted by the woven structure of the plurality of fiber bundles, as with the external layer24a, is used as a first reinforced fiber sheet.

In the pipe1ainFIG. 11, the portion of the reinforced fiber structure22athat is arranged near the main body inclined surface212(seeFIG. 2) is constituted by the woven structure of the plurality of fiber bundles241aand the plurality of242a. This prevents a shear failure, in which the fiber bundles242a, which extend along the circumferential direction, of the reinforced fiber structure22aare pulled together with the connection portion3and come out from the pipe main body2a, from occurring on the main body inclined surface212, achieving an improvement in the shear strength against the tensile load. Also, by the internal layers23including the plurality of fiber bundles232, 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 pipes1ainFIG. 11, similar to those on the respective pipes1,9, and9ainFIGS. 3,8, and10, 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 pipes9and9ain the comparative examples. No buckling breakage occurred. Note that, in view of preventing the fiber bundles from coming out from the main body inclined surface212, the plurality of fiber bundles241a, which constitute the plain woven structure, of the external layers24amay extend in a direction that is inclined with respect to the central axis J1, and also the plurality of fiber bundles242amay extend in a direction that is inclined with respect to the circumferential direction on the cylindrical surface centered on the central axis J1. Also, woven structures other than the plain woven structure may be applied to the external layer24a.

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 structures22and22aare respectively provided with the internal layers23and the external layers24and24awhose structures differ from each other but it is also possible, as illustrated in, for example,FIG. 12, that a portion of the reinforced fiber structure22bof the pipe main body2bthat is arranged near the main body inclined surface212is constituted by the plurality of fiber bundles231b, which extend in parallel with a central axis J1(in the lateral direction inFIG. 12), and a portion of the reinforced fiber structure22bthat is located apart from the main body inclined surface212in the direction of the central axis J1has a laminated structure in which the plurality of fiber bundles231b, which extend in parallel with the central axis J1, and the plurality of fiber bundles232b, which extend in the circumferential direction, are alternately laminated in the radial direction. Also in the case of a pipe1binFIG. 12, it is possible to improve the shear strength of the main body inclined surface212. Note that inFIG. 12, illustration of the connection portion3is omitted. It is also possible that the structure illustrated inFIG. 12is applied only to the external layers of the reinforced fiber structure22, and another structure (for example, a laminated structure in which a plurality of fiber bundles that extend in parallel with the central axis J1and 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 J1or by a woven structure of a plurality of fiber bundles, and that is arranged near the main body inclined surface212; 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 surface212in the direction of the central axis J1or the radial direction, so that it is possible to ensure the performance that is desired for the pipe main body2using the second portion, while improving the shear strength of the main body inclined surface212. In the examples inFIGS. 3 and 11, the first portion is part of the external layers24,24aand the second portion is the internal layers23.

In view of the improvement in the strength against hoop stress, the internal layers23of the reinforced fiber structure22may be constituted only by a plurality of fiber bundles, which extend in the circumferential direction.

Although in the above-describe embodiments, by the pipes1,1a, and1bincluding the connection portion3, the pipes1,1a, and1bcan be connected to the coupling5in a removable manner, the connection portion3may be omitted in the pipe depending on design of the pipe, and the main body inclined surface212of the pipe main body and the internal surface of the coupling5may 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 surface212by constituting the first portion that is arranged near the main body inclined surface212by a plurality of fiber bundles that extend in parallel with the central axis J1or providing a reinforced fiber structure that has a woven structure of a plurality of fiber bundles.

Although the pipes1,1a, and1bare 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 pipes1,1a, and1bmay, 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