JP2007040443A - Joint construction of plastic pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a joint construction of a plastic pipe having excellent durability even when used for high-pressure fluid transportation. <P>SOLUTION: In the joint construction of the plastic pipe, a fiber-reinforced layer 3 is cut away from pipe ends of two plastic pipes 1, 1 wound with the fiber-reinforced layer 3 on the outer periphery of a pipe main body 2 respectively. The exposed pipe main bodies 2, 2 are butted with each other. The outer periphery of the butted portion of the pipe main body is sheathed with a plastic joint pipe 5, and the joint pipe 5 and the pipe main body 2 are electrically fused. Lock rings 8, 8 are fitted on the fiber-reinforced layer outside both ends of the joint pipe 5 respectively. The lock rings are energized to the joint pipe 5 side, and the fiber-reinforced layer 3 is sandwiched. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a plastic pipe joint structure, and more particularly to a plastic pipe joint structure exhibiting excellent durability even when used for transporting high-pressure fluid.

  Plastic pipes are lighter than iron pipes, so they have excellent workability, and because they are flexible, they have many advantages such as excellent earthquake resistance and corrosion resistance. Widely used as fluid transport pipes for gases and liquids. However, if the plastic tube is made of only plastic, the tensile strength and pressure resistance equivalent to those of an iron tube cannot be obtained. Therefore, as illustrated in FIG. 6, the outer periphery of the plastic tube main body 2 is reinforced with aramid fibers or glass fibers. In general, fibers are spirally wound as a fiber reinforcement layer 3 and a plastic coating layer 4 is provided on the outside of the fiber reinforcement layer 3 for protection.

  When such a plastic pipe is used for a long-distance fluid transport pipe, since the plastic pipe has a finite length, it is necessary to connect the pipe ends with a joint. As a joint of this plastic pipe, an electric fusion joint (electrofusion joint) is widely used.

  FIG. 7 shows an example of a joint structure using a conventional electric fusion joint (see Patent Document 1).

  When two plastic pipes 1 and 1 are connected by an electric fusion joint, first, as shown in FIG. 6, the covering layer 4 and the fiber reinforcing layer 3 are cut out from the pipe end of the plastic pipe 1 by a predetermined length. The inner tube body 2 is exposed. Next, the exposed ends of the pipe main bodies 2 and 2 are butted against each other, and a plastic joint pipe 5 is put over the pipe ends. A heating wire 6 is embedded in the joint pipe 5, and a part of the plastic is melted by energizing the heating wire 6 to generate heat, and the space between the inner wall of the joint pipe 5 and the outer wall of the pipe body 2 is melted. The two plastic tubes 1 and 1 are connected to each other. In this case, if the reinforcing layer 7 is provided on the outer periphery of the joint pipe 5, the connection strength can be further enhanced.

  The above joint structure has no problem in terms of durability as long as it is used for transporting a 1.0 MPa specification fluid which is generally used at present. However, when it is used for high pressure fluid transportation of 1.5 to 2.0 MPa, which has a higher pressure than this, there is a problem that the joint structure as described below is broken.

  That is, in order to connect the plastic pipes 1 and 1 with an electric fusion joint, it is necessary to cut the coating layer 4 and the fiber reinforcing layer 3 from the pipe ends so that the pipe body 2 is exposed. If the cut length of the fiber reinforcing layer 3 is insufficient and the end thereof extends to the inside of the joint pipe 5, the close contact between the joint pipe 5 and the pipe body 2 becomes incomplete, which is good. This is because the connection strength cannot be obtained. Therefore, after connection, it is inevitable that a gap g in which the pipe body 2 is exposed is formed between the end of the joint pipe 5 and the cut end of the fiber reinforcing layer 3.

However, when a high-pressure fluid of 1.5 to 2.0 MPa is transported by the plastic pipe 1 having the joint structure having the exposed gap g as described above, stress concentrates on the gap g where the pipe body 2 is exposed. In the region, the tube main body 2 extends in the axial direction, and the cross section expands and deforms, and eventually the portion is broken.
Japanese Patent Laid-Open No. 2002-29579

  It is an object of the present invention to provide a plastic pipe joint structure that exhibits excellent durability even when used for high-pressure fluid transportation.

  The plastic pipe joint structure of the present invention that achieves the above object is a pipe body in which the fiber reinforcement layer is cut out and exposed from the pipe ends of two plastic pipes each having a fiber reinforcement layer wound around the outer circumference of the pipe body. In the joint structure of the plastic pipe in which the joint pipe made of plastic is coated on the outer periphery of the joint portion of the pipe main bodies and the joint pipe and the pipe main body are electrically fused. A lock ring is fitted on each of the fiber reinforcement layers on the outer sides of both ends, and the lock ring is urged toward the joint pipe side, and the fiber reinforcement layer is clamped. .

  According to the present invention, the lock rings are arranged on both outer sides of the electrofused joint pipe, and the lock ring is urged toward the joint pipe side, and the end portion of the fiber reinforcement layer is clamped. The exposed portion of the tube body can be completely covered, thereby suppressing the axial extension of the tube body in this region and suppressing cross-sectional deformation due to internal pressure. Even if it is used for the purpose, it is possible to prevent the plastic tube from being broken due to the concentration of stress on the exposed portion of the tube body.

  FIG. 1 illustrates a plastic pipe joint structure according to the present invention.

  In the plastic pipes 1 and 1 to be connected, a reinforcing fiber of a multifilament bundle is spirally wound around the outer circumference of a plastic pipe body 2 to form a fiber reinforcing layer 3, and a plastic covering layer 4 is formed on the outside thereof. It is comprised so that it may provide. The plastic used as the material of the plastic tube 1 is not particularly limited as long as it is a thermoplastic resin, and any of polyethylene, polyamide, polyester, and the like can be used. Preferably, high density polyethylene is used for the tube body 2 and low density polyethylene is used for the covering layer 4.

  The number of fiber reinforcing layers 3 is not limited to one, and two or more layers may be arranged. As the winding direction of the reinforcing fiber in the case of two or more layers, each layer may be the same direction, or may be crossed with each other between the layers. The fiber reinforcing layer is preferably one in which a tape-like sheet in which a plurality of reinforcing fibers made of a multifilament bundle are arranged is spirally wound. The spiral angle as the winding direction of the reinforcing fiber is 45 ° or more and less than 90 °, preferably 50 ° or more and 80 ° or less with respect to the axial direction. The reinforcing fiber is not particularly limited as long as it has high strength and high elastic modulus. Aramid fibers and poly-p-phenylenebenzbisoxazole fibers are preferably used, and aramid fibers are particularly preferable.

  In the joint structure of the present invention, the fiber reinforced layer 3 and the covering layer 4 are cut out from the two plastic pipes 1 and 1 having the above-mentioned configuration in a step shape from the pipe ends, so that the inner pipe body 2 is exposed. Next, the exposed ends of the tube main bodies 2 and 2 are butted against each other, and the plastic joint tube 5 is extrapolated outside the butted portion. A heating wire 6 is embedded on the inner peripheral side of the joint pipe 5. When the heating wire 6 is energized, the surrounding plastic is melted, and the space between the inner wall of the joint pipe 5 and the outer walls of both pipe bodies 2, 2 is between. It is in a fused state.

  The plastic used for the joint pipe 5 is not particularly limited, but the same plastic as the pipe body 2 is preferably used. For example, polyethylene, polyamide, polyester and the like are used, and polyethylene is particularly preferable, and high density polyethylene is particularly preferable. Further, a reinforcing layer 7 is provided on the outer periphery of the joint pipe 5. The reinforcing layer 7 is preferably the same as the fiber reinforcing layer 3, but a metal or ceramic reinforcing tube may be used.

  In the joint structure of the present invention, lock rings 8 and 8 are fitted on the fiber reinforcing layers 3 and 3 on both outer sides of the joint pipe 5, respectively. As shown in FIG. 4, the lock ring 8 has a notch 9 at one place in the circumferential direction, and the diameter is reduced when an external force is applied from the outer circumference toward the inside in the radial direction. Further, a tapered surface 8 a is formed on the outer periphery of the lock ring 8, and the tapered surface 8 a is formed so that the outer diameter gradually decreases as the distance from the joint pipe 5 increases. A large number of protrusions 8 b are formed on the inner periphery of the lock ring 8 so as to be arranged in parallel in the circumferential direction.

  An annular flange 10 is fitted on the outer peripheral side of the lock ring 8 provided in this way. As shown in FIG. 5, the annular flange 10 is provided with a plurality of bolt holes 10 b on the side surface at equal intervals in the circumferential direction and a tapered surface 10 a on the inner periphery. The taper surface 10 a on the inner periphery is formed at the same taper angle as the taper surface 8 a of the lock ring 8, and the inner diameter is formed so as to gradually decrease as the distance from the joint pipe 5 increases.

  A plurality of bolts 11 are spanned between the annular flanges 10 and 10 fitted respectively to the lock rings 8 and 8 on both outer sides of the joint pipe 5 through a plurality of bolt holes 10b. Nuts 12 and 12 are screwed to both ends of the. These nuts 12 and 12 are each tightened so as to be screwed toward the joint pipe 5, and by this tightening, the annular flanges 10 and 10 are locked against the lock rings 8 and 8 as indicated by arrows in FIG. A component force biased toward the joint pipe 5 side and a component force directed radially inward are generated. As described above, due to the two component forces generated in the lock ring 8, the lock ring 8 is reduced in diameter via the notch portion 9, and the cut end portion of the fiber reinforcement layer 3 is clamped and the fiber reinforcement layer 3 is cut. A tensile force toward the joint pipe 5 side is given to the end. Such an effect can be further increased by providing the protrusion 8 b on the inner periphery of the lock ring 8.

  The width of the fiber reinforcement layer 3 clamped by the lock ring 8 is preferably 50% or more of the width of the lock ring 8 as shown in FIG. In this case, the lock ring 8 can pinch the fiber reinforcement layer 3 and at the same time cause the protrusion 8b to bite into the surface of the tube body 2 in the region of the exposed gap g. Of course, as shown in FIG. 3, the fiber reinforcing layer 3 may be sandwiched with substantially the entire width of the lock ring 8. When the end portion of the fiber reinforcing layer 3 is clamped by the lock ring 8 in this way, a protective layer 3a around which a filamentous reinforcing fiber or a resin film is wound is provided on the outer periphery of the end portion of the fiber reinforcing layer 3 as necessary. (See FIGS. 2 and 3). By disposing the protective layer 3a, it is possible to reduce damage due to pinching of the lock ring 8 of the fiber reinforcing layer 3.

  In the joint structure described above, that is, in the joint structure in which the fiber reinforcing layer 3 is cut from the end of the plastic pipe 1, the cut pipe main bodies 2 are butted together, and the joint pipe 5 is covered on the outer periphery thereof, As described in the section, a gap g is generated between the outer end faces of the joint pipe 5 and the cut end of the fiber reinforcing layer 3 based on the expansion and contraction of the pipe body 2. Therefore, particularly when a high-pressure fluid such as 1.5 to 2.0 MPa is transported, breakage is likely to occur at the gap g.

  However, in the joint structure of the present invention, since the end portion of the fiber reinforcement layer 3 is clamped by the lock ring 8, the fiber reinforcement layer 3 is not displaced, and in addition, the outer surface of the lock ring 8 has a tapered surface. Since the bolt 11 and the nut 12 are spanned between the annular flanges 10 and 10 fitted via 8a and 10a and tightened, axial load generated between the pipe bodies 2 and 2 due to internal pressure, thermal expansion, etc. Therefore, the joint pipe 5 is prevented from being broken and the durability can be improved.

  In the present invention, the lock ring is preferably made of a material having a large rigidity and hardness. As the material, gunmetal, stainless steel, aluminum alloy, or other metals can be used.

  The width of the lock ring (the axial width) is preferably at least twice the exposure gap g. Specifically, although it depends on the diameter of the plastic tube, a range of 10 to 60 mm is preferable. The width of the lock ring sandwiching the fiber reinforcement layer is preferably 50% or more of the width of the lock ring.

  The taper angle formed by the taper surface of the lock ring (and the taper surface of the annular flange) with respect to the axial direction is not particularly limited, but is preferably in the range of 10 ° to 20 °. When the taper angle is larger than 20 °, the sandwiching pressure to the fiber reinforcing layer is insufficient, and when the taper angle is smaller than 10 °, the urging force to the joint pipe side is insufficient.

  Moreover, it is preferable to provide a protrusion on the inner peripheral surface of the lock ring as in the illustrated example. By providing the protrusions, it is possible to increase the clamping force of the pinching pressure on the fiber reinforcement layer. As the shape of the protrusion, as shown in the illustrated example, the protrusions arranged in parallel in the circumferential direction are most preferable, but may be independent protrusions formed in a number of points. The height of the protrusion is preferably in the range of 0.5 to 1.5 mm. If it is too low, the effect is small, but if it is too high, the surface pressure decreases, which is not preferable.

  As for the number of bolts to be spanned between the annular flanges on both sides of the joint pipe, three or more bolts may be provided at equal intervals in the circumferential direction. More preferably, it is good to make it into the range of 4-12.

  The pipe body is made of high-density polyethylene, and 3 plies of fiber reinforcement layers with aramid fibers wound at an angle of 85 ° with respect to the axial direction are arranged on the outer periphery, and a coating layer of low-density polyethylene is formed on the outer periphery. A plastic pipe having a diameter of 250 mm and a length of 2000 mm was used, and the pipe ends of the two plastic pipes were connected with two different joint structures of the following examples and comparative examples.

(Example)
It consists of the joint structure of FIG. The lock ring had an axial width of 40 mm and the annular flange had an axial width of 40 mm, both of which were made of stainless steel. Further, six connecting bolts having a screw diameter of 20 mm were arranged at equal intervals. The joint pipe of the electric fusion joint was made of high-density polyethylene, and a reinforcing layer in which an aramid fiber was wound around the outer periphery thereof was disposed.

(Comparative example)
In the joint structure of the above embodiment, the joint structure is the same as that of the embodiment except that the locking mechanism for the lock ring and the annular flange is not provided.

  For the plastic pipes connected by the above two types of joint structures, when high-pressure water with an internal pressure of 2.5 MPa is continuously transported for 30 days in an environment of 40 ° C., respectively, and high-pressure water with an internal pressure of 3.0 MPa is continuously transported for 30 days. Durability was tested with the test.

  As a result, in the plastic pipe connected with the joint structure of the comparative example, in the former test in which the high-pressure water having an internal pressure of 2.5 MPa was continuously transported, it corresponds to the fiber-reinforced layer cut end of the joint structure on the 20th day from the start of water flow. In the test in which the fracture occurred in the gap portion and the latter high-pressure water having an internal pressure of 3.0 MPa was transported continuously, the gap portion corresponding to the cut end portion of the fiber reinforced layer of the joint structure was similarly formed on the 14th day from the start of water flow. Destruction occurred. However, the plastic pipes connected by the joint structure of the example did not break up in any test until the 30-day test was completed.

It is a half sectional view showing an example of the joint structure of the plastic pipe by the present invention. It is an enlarged view of the principal part in FIG. It is an enlarged view of the principal part in FIG. 1 which consists of another example. It is a lock ring used for the joint structure of FIG. 1, (A) is a front view, (B) is XX arrow sectional drawing in (A). It is a cyclic | annular flange used for the joint structure of FIG. 1, (A) is a front view, (B) is a YY arrow sectional drawing in (A). An example of a plastic pipe is shown, (A) is a side view showing a part in cross section, and (B) is a cross-sectional view. It is a half sectional view showing a joint structure of a conventional plastic pipe.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Plastic pipe 2 (Plastic pipe) pipe body 3 Fiber reinforcement layer 4 Coating layer 5 Joint pipe 6 Heating wire 7 Reinforcement layer 8 Lock ring 8a Tapered surface 8b Protrusion 9 Notch 10 Annular flange 10a Tapered surface 10b Bolt hole 11 Bolt 12 Nut g Clearance

Claims (6)

  The tube main bodies exposed by excising the fiber reinforcing layer from the ends of two plastic pipes each having a fiber reinforcing layer wound around the outer periphery of the pipe main body are brought into contact with each other, and the outer periphery of the contact portion between the pipe main bodies In a plastic pipe joint structure in which a plastic joint pipe is covered and the joint pipe and the pipe main body are electrofused, lock rings are respectively fitted on the fiber reinforcement layers outside both ends of the joint pipe. And a plastic pipe joint structure in which the lock ring is urged toward the joint pipe side and the fiber reinforcing layer is sandwiched between them.   The plastic pipe joint structure according to claim 1, wherein a reinforcing layer is provided on an outer periphery of the joint pipe.   The outer periphery of the lock ring disposed on both sides of the joint pipe is formed into a tapered surface whose outer diameter decreases toward the direction away from the joint pipe, and an annular flange is formed on the outer periphery of the lock ring. 3. The plastic pipe joint structure according to claim 1, wherein an external force is applied so as to engage with each other and a bolt is stretched between the annular flanges on both sides of the joint pipe to attract each other.   4. The plastic pipe joint structure according to claim 1, wherein a plurality of protrusions are provided on an inner periphery of the lock ring.   The joint structure of a plastic pipe according to any one of claims 1 to 4, wherein a cut end portion of the fiber reinforcement layer is clamped by the lock ring through a protective layer. The plastic pipe joint structure according to any one of claims 1 to 5, wherein the pipe body and the joint pipe are made of a polyethylene resin, and the fiber reinforcing layer is made of an aramid fiber.

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