JPH07301374A - Connecting method of multilayer pipe - Google Patents

Abstract

PURPOSE:To improve connection by connecting a pipe after correcting an external or internal diameter or internal/external diameters in a pipe end part to the prescribed dimension by cutting internal/external surfaces of the pipe end part with the annular space dimension between inner/outer cylinder parts of a pipe joint serving as the reference. CONSTITUTION:First, internal/external diameters in a pipe end part (b) (length part a little larger than depth of annular space between inner/outer cylinder parts) are corrected to the prescribed dimension by cutting internal/external surfaces of the pipe end part (b) with the dimension of annular space (a) serving as the reference. By sticking 8 rapid cure bond between the inner/outer cylinder parts of a pipe joint, after applying this bonding agent to internal/ external peripheral surfaces of the pipe end part, the pipe end part (b) of a multilayer pipe 2 is press fitted to the annular space (a) between the inner/outer cylinder parts. Facing up is performed between an internal peripheral surface of the outer cylinder part 11 swollen by a solvent in the bonding agent and an external peripheral surface of a synthetic resin external layer 21 of the multilayer pipe end part (b) and between an external peripheral surface of the inner cylinder part 12 and an internal peripheral surface of a synthetic resin internal layer 22. By this facing up, a surplus bonding agent and swollen resin are extended to an interior side and inlet side, and connection is ended by waiting for solidification due to volatilizing the solvent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of connecting a multi-layer pipe having an inner layer and an outer layer of a synthetic resin on the inner and outer peripheral surfaces of an intermediate layer with a pipe joint.

[0002]

2. Description of the Related Art A pipe material used for transporting a fluid is required to have various performances depending on the transport conditions of the fluid.
For example, in a pipe material used for transporting a chemical solution in a chemical factory or the like, in addition to internal pressure, external load, mechanical strength such as tensile strength, corrosion resistance to the surrounding environment, and the like, chemical resistance to a transport chemical solution is also required.

However, it is not easy to satisfy these various performances with a single material, and therefore, metal pipes having excellent mechanical strength, for example, steel pipe inner and outer peripheral surfaces have chemical resistance and corrosion resistance. It is known that a multi-layer tube structure coated with an excellent synthetic resin layer satisfies these performances.

In transporting a fluid, it is indispensable to connect pipes with pipe joints, and at the connecting portion, predetermined pull-out strength, internal pressure resistance, external pressure resistance, etc. according to fluid transport conditions. Must be given.

Conventionally, as a method for connecting a single-layer synthetic resin pipe, the TS method [for the inner surface of the receiving end of a synthetic resin pipe joint 1 / A taper of about 30 to 1/45 is attached, and a quick-drying adhesive is applied to the inner peripheral surface of the receiving port and the outer peripheral surface of the pipe end (insertion), and the coated surface is swollen with the solvent in the adhesive, This is a method in which the pipe end is pressed into the pipe joint while spreading the adhesive and the swelling layer, and the TS pipe joint is specified in JIS K 6743]. Fusing method for adhesive resin pipes (the inner surface of the pipe joint receiving end and the outer surface of the pipe end are heated and melted by inserting a heating jig, and after the heating jig is removed, the pipe is quickly attached to the pipe joint receiving pipe. A method of press-fitting an end portion and fusing the interface thereof is known.

The pipe joints used for these connections are usually manufactured by injection molding and have sufficient dimensional accuracy. On the other hand, synthetic resin pipes are manufactured by an extrusion method under outer diameter regulation or inner diameter regulation.For example, in the case of outer diameter regulation, even if the resin discharge amount changes, the outer diameter regulation by the sizing die The thickness is adjusted by adjusting the take-up speed with, but since the inner diameter fluctuation cannot be avoided,
It is impossible to regulate both inside and outside diameters.

In connection with the above-mentioned single layer synthetic resin pipe, however, if the synthetic resin pipe is manufactured under the regulation of the outer diameter,
It is possible to achieve dimensional matching between the inner surface of the receiving end of the pipe joint and the outer surface of the pipe end, and it is possible to join the interface between them with a proper contact pressure that is sufficient.

[0008]

By the way, in the above-mentioned multi-layer pipe, the purpose is to protect the inner peripheral surface of the metal pipe by blocking the transport fluid with the synthetic resin inner layer, so that even in the pipe connecting portion, It is necessary to shield the metal tube from the transport fluid. However, the requirements cannot be satisfied by the TS method and the like for connecting the above-mentioned single-layer synthetic resin pipes.

[0009] Therefore, the inventors of the present invention used a three-layer pipe in which the inner and outer layers are synthetic resin layers and the intermediate layer is a metal pipe, and the metal pipe end surface at the pipe end is shielded from the transport fluid by an adhesive method. In order to make it possible to connect with each other, as shown in FIG. , An outer peripheral surface 120 ′ with a taper is injection-molded into a synthetic resin pipe joint having an inner cylindrical portion 12 ′ that is a joint surface to the synthetic resin inner layer of the three-layer pipe end, and the inside and outside of the pipe joint A quick-drying adhesive is applied between the tubular parts, and the adhesive is applied to the inner and outer peripheral surfaces of the pipe ends, and then the pipe ends are placed in the annular space between the inner and outer tubular parts.
Similar to the method, an attempt was made to connect the three-layer pipe by press-fitting while spreading the adhesive and the swelling layer.

However, it is possible to make dimensional matching of both interfaces between the outer surface of the outer layer of the three-layer pipe and the inner surface of the outer cylindrical portion of the pipe joint, and between the inner surface of the inner layer of the three-layer pipe and the outer surface of the inner cylindrical portion of the pipe joint. Since it is extremely difficult, the contact pressure at these interfaces becomes excessive, and severe stress easily acts on the root of the inner cylinder part and the root of the outer cylinder part. As the inside of the annular space is pressurized,
The effect of hoop stress based on this internal pressure cannot be denied. On the other hand, the adhesive accumulates in the inner part of the annular space, and the space in which the adhesive accumulates is a closed space and the solvent in the adhesive remains without being scattered. Therefore, under the synergistic effect of the stress and the solvent, the resin crack due to the stress is promoted by the melting action of the resin due to the solvent, and so-called solvent crack is likely to occur.

However, when the inner and outer synthetic resin layers of the three-layer tube are made of a difficult-to-adhesive resin such as polyethylene, the method of heat-sealing the joint surfaces must be used instead of the TS method. Also in this case, the resin crack due to the stress is promoted by the melting action of the resin due to the heating, and the crack breakage similar to the solvent crack is likely to occur.

An object of the present invention is to provide a method for connecting a multi-layered pipe, which enables excellent connection of a multi-layered pipe having a synthetic resin outer layer and a synthetic resin inner layer on an outer peripheral surface and an inner peripheral surface of an intermediate layer by an adhesive method or a fusion method. To provide.

An object of the present invention is to provide a pipe end portion of a multi-layer pipe having a synthetic resin outer layer and a synthetic resin inner layer on an outer peripheral surface and an inner peripheral surface of an intermediate layer, respectively, with respect to a synthetic resin outer layer having an inner peripheral surface having a multi-layer pipe end portion. By press-fitting between the inner and outer cylinder parts of a pipe joint having an outer cylinder part to be a joint surface and an outer peripheral surface to an inner cylinder part to be a joint surface to the synthetic resin inner layer of the multilayer pipe end part, by an adhesive or fusion bonding. An object of the present invention is to provide a method for connecting multi-layer pipes which can sufficiently eliminate solvent cracks and the like by reducing the stress acting on the pipe joint when connecting.

An object of the present invention is to provide a pipe end portion of a multi-layer pipe having a synthetic resin outer layer and a synthetic resin inner layer on an outer peripheral surface and an inner peripheral surface of an intermediate layer, respectively, with respect to a synthetic resin outer layer having an inner peripheral surface having a multilayer pipe end portion. By press-fitting between the inner and outer cylinder parts of a pipe joint having an outer cylinder part to be a joint surface and an outer peripheral surface to an inner cylinder part to be a joint surface to the synthetic resin inner layer of the multilayer pipe end part, by an adhesive or fusion bonding. When connecting, it is an object of the present invention to provide a method for connecting multi-layer pipes, which can prevent solvent from remaining in the space between the inner and outer cylindrical portions of the pipe joint and sufficiently eliminate solvent cracks.

[0015]

A method for connecting a multi-layer pipe according to the present invention comprises a pipe end portion of a multi-layer pipe having a synthetic resin outer layer and a synthetic resin inner layer on an outer peripheral surface and an inner peripheral surface of an intermediate layer, respectively. An inner and outer cylinder part of a pipe joint having an outer cylinder part whose surface is a joint surface to the synthetic resin outer layer of the multilayer pipe end and an inner cylinder part whose outer peripheral surface is a joint surface to the synthetic resin inner layer of the multilayer pipe end part. In the method of press-fitting in between and connecting by an adhesive or fusion, the outer diameter or inner diameter or inner / outer diameter of the pipe end is
After correcting the inner and outer surface of the pipe end to a predetermined size based on the annular space between the inner and outer tubular parts of the pipe joint,
The configuration is characterized by performing the above connection.

Another method of connecting a multi-layer pipe according to the present invention is the same method as described above, wherein the inner and outer cylindrical portions of the pipe joint are connected to each other while the inner space of the annular space between the inner and outer cylindrical portions is in communication with the outside. The configuration is characterized in that the pipe end is press-fitted into the annular space.

The structure of the present invention will be described below in detail with reference to the drawings. In (a) of FIG. 1, reference numeral 1 denotes a pipe joint, and an outer cylinder portion 11 and an inner cylinder portion 12 are integrated at a stopper portion 13 at the center of the pipe joint, and an inner peripheral surface 110 of the outer cylinder portion 11 is formed.
In addition, the outer peripheral surface 120 of the inner cylindrical portion 12 is formed into a taper surface so that the mutual interval becomes narrower toward the base of the cylindrical portion, and the inclination thereof is usually 1/30 to 1/45. The pipe joint 1 is manufactured by injection molding of synthetic resin and has sufficient dimensional accuracy.

In FIG. 1 (a), reference numeral 2 denotes a multi-layer pipe to be connected by the method of the present invention, wherein a synthetic resin outer layer 21 is formed on the outer peripheral surface and the inner peripheral surface of an intermediate layer 20, for example, a metal pipe such as a steel pipe.
In addition, each has a synthetic resin inner layer 22.

According to the first aspect of the present invention, in order to connect the multi-layer pipe 2, the pipe end portion is connected to the inner and outer cylindrical portions 11 of the pipe joint 1.
When press-fitted into the annular space a between the cylinders 12, the cylindrical portions 11, 1
First, as shown in (b) of FIG. 1, in order not to apply severe stress to the root of the pipe 2, first, a pipe end b (a portion slightly longer than the depth of the annular space between the inner and outer tubular portions) The inner and outer diameters of) are corrected to a predetermined dimension with reference to the dimension of the annular space a by cutting the inner and outer surfaces of the tube end portion b. For example, in the case of adhesive connection, swelling of each surface in contact with the adhesive (the outer peripheral surface of the outer cylinder of the pipe joint and the outer peripheral surface of the pipe end, and the outer peripheral surface of the inner cylinder of the pipe joint and the inner peripheral surface of the pipe end) In the case of thickness or fusion connection, if the melted thickness of each surface is Δt, the outer diameter of the inner end of the pipe joint between the inner and outer tubular parts is D ₂ , and the inner diameter of the inner end is d ₂ , then the pipe end b
The modified outer diameter D ₀ of D is D ₀ = D ₂ + 4Δt, and the modified inner diameter d is
₀ is set to d ₀ = d ₂ −4Δt, respectively.

In this case, from the length of the cylindrical portion [indicated by c in FIG. 1 (a), usually about 40 mm] and the taper surface gradient (1/30 to 1/45) do it,
The inner diameter of the pipe joint at the inlet of the outer tubular portion 11 is D ₁ ,
Assuming that the outer diameter at the inlet of the inner tubular portion 12 is d ₁ , D ₁ > D
The relationship of ₀ > D ₂ and d ₁ <d ₀ <d ₂ is established.

When the inner and outer synthetic resin layers of the multi-layer pipe are synthetic resins that can be bonded with an adhesive (for example, strong polar synthetic resins such as hard vinyl chloride and soft vinyl chloride), synthetic resins that can also bond pipe joints Injection molding, usually, a quick-drying adhesive is attached between the inner and outer cylinders of the pipe joint, and the adhesive is applied to the inner and outer peripheral surfaces of the pipe end, and then as shown in (c) of FIG. , The pipe end portion b of the multilayer pipe 2 is press-fitted into the annular space a between the inner and outer cylindrical portions (until the tip of the multilayer pipe comes into contact with the stopper portion,
Or press-fitting so as to leave a slight gap between the tip of the multi-layer tube and the stopper portion), the inner peripheral surface of the outer tube portion 11 swollen with the solvent in the adhesive and the multi-layer tube end portion b. The outer peripheral surface of the synthetic resin outer layer 21 and the outer peripheral surface of the inner cylindrical portion 12 are rubbed with the inner peripheral surface of the synthetic resin inner layer 22 of the multi-layer pipe end portion b, and by this rubbing, an extra adhesive is applied to the inner side and the inlet side. The swelling resin is spread, and the outer tube portion 11 of the pipe joint is expanded.
Between the inner peripheral surface of the pipe and the outer peripheral surface of the synthetic resin outer layer 21 of the multilayer pipe end b, and the outer peripheral surface of the inner tubular portion 12 of the pipe joint and the multilayer pipe end b.
The space between the inner peripheral surface of the synthetic resin inner layer 22 and the swelling resin is filled, and the filling is solidified by the solvent volatilization to complete the connection.

In the above description, the resin swells by the thickness Δt on the outer diameter side and the inner diameter side of the inner end between the inner and outer cylindrical portions of the pipe joint, and the resin thickness increases on the outer diameter side and the inner diameter side of the pipe end portion, respectively. Swell by Δt. Street Thus, in the outer diameter side of the rear end of the inner and outer tubular portion of the pipe joint, the solid phase radius of the rear end (D _2/2) + Δt, and the tube end outer peripheral [before swelling diameter described above , solid phase radius D ₂ + 4Δt] becomes a [(D _2/2) + 2Δt] -.DELTA.t, numbers match, therefore, avoiding the effects of excessive stress in the base of the outer cylindrical portion 11 of the pipe joint 1 can, also, in the inner diameter side of the inner end of the inner and outer tubular portion of the pipe joint, the inner end solid radius (d _2/2)
-Δt, and the tube end inner peripheral [diameter before swelling, as described above, d ₂ -4Δt] solid radius of [(d _2/2) -2Δ
t] + Δt, and both are the same, and therefore the pipe joint 1
It is possible to avoid the effect of excessive stress at the base of the inner cylindrical portion 12 of the.

When the inner and outer synthetic resin layers of the multi-layer tube are made of a synthetic resin which is difficult to bond with an adhesive (for example, a synthetic resin having a weak polarity such as polyethylene), a fusion bonding method is used. In the case of this fusion bonding method, for example, as shown in FIG. 2A, a grooved heater ace which receives the protruding heater ace 41 and the multi-layer pipe end b inserted between the inner and outer cylindrical portions of the pipe joint 1. The heating jig 4 having 42 melts the inner peripheral surface of the outer cylinder part and the outer peripheral surface of the inner cylinder part at one end of the pipe joint, and the outer peripheral surface of the synthetic resin outer peripheral surface and the inner peripheral surface of the inner layer of one multilayer pipe end, and then heats Immediately after removing the jig, as shown in FIG. 2B, one pipe end portion b was press-fitted into the annular space a between the inner and outer cylindrical portions 11 and 12 on one end side of the pipe joint 1 to The inner surface of the tubular portion and the outer surface of the outer surface of the multilayer pipe end, and the outer surface of the outer tubular portion and the inner surface of the inner layer of the multi-layer pipe end are fused together, and the other end side of the pipe joint and the other end of the multi-layer pipe are the same. And fuse them together.

In this fusion splicing, the resin is melted by the thickness Δt on the outer diameter side and the inner diameter side of the inner end between the inner and outer cylindrical portions of the pipe joint, and the resin is melted on the outer diameter side and the inner diameter side of the pipe end portion, respectively. It is assumed that the resin melts by the thickness Δt. And Thus, in the outer diameter side of the rear end of the inner and outer tubular portion of the pipe joint, the inner end solid radius (D _2/2) + Δt, and the solid phase the outer diameter of the tube end [(D ₂ / 2) + 2Δt] −Δt, both of which coincide with each other, and therefore, the action of excessive stress at the base of the outer tubular portion of the pipe joint can be avoided, and at the inner diameter side of the inner end of the inner and outer tubular portion of the pipe joint. is the inner end solid radius (d _2/2)
-Δt, and the solid phase the outer diameter of the tube end [(d _2/2) -2
[Delta] t] + [Delta] t, and the two coincide with each other. Therefore, it is possible to avoid the action of excessive stress at the base of the inner tubular portion of the pipe joint.

In the case of the above fusion method, the energization type heating wire can be embedded in the synthetic resin pipe joint to be fusion-bonded,
FIG. 3 shows a structural example of a pipe joint when this system is used. In FIG. 3, 111 is an energization type heating wire embedded in the joint surface of the outer tubular portion 11, 112 is its energizing terminal, 121 is an energization type heating wire embedded in the joining surface of the inner tubular portion 12, 122 Indicates the respective energizing terminals.

In the case of connection by the above-mentioned bonding method, in order to easily attach the adhesive to the outer surface of the inner tubular portion [the inner surface of the outer tubular portion] of the pipe joint, (a) in FIG. )], The inner cylinder portion 12 is shortened, and the outer cylinder portion 11 is lengthened by the shortened length (the outer cylinder portion 11 is shortened, and the inner cylinder portion 12 is lengthened by the shortened length). You can These pipe joints can also be used in the fusion bonding method described above. In these cases, the length of the portion that modifies the outer diameter of the pipe end of the multi-layer pipe is slightly longer than the length of the outer cylinder of the pipe joint, and the length of the portion that modifies the inner diameter of the pipe end. The length is made slightly longer than the length of the inner tubular portion of the pipe joint, and the lengths of the two are different.

When connecting multi-layer pipes according to the invention of claim 1, the multi-layer pipe has an outer diameter of the above-mentioned dimension D ₀ (D ₀ = D ₂ +).
4Δt), and the inner diameter is the above dimension d.
Manufactured a little smaller than ₀ (d ₀ = d ₂ −4Δt),
It is possible to roughly regulate the inner diameter or the outer diameter.

In the description of the invention according to claim 1, both the inner and outer diameters of the pipe end portion of the multilayer pipe are modified, but the invention is only modified by adjusting either the inner diameter or the outer diameter. It is also possible to carry out.

In order to connect the multi-layer pipes according to the second aspect of the present invention, as shown by the dotted line in each of FIGS. 1, 2, 3, and 4, the annular space between the inner and outer tubular portions of the pipe joint is formed. When the inner side of the pipe is opened to the outer surface of the pipe fitting by the communication hole 15 and the adhesive method is used, the solvent of the adhesive is passed through the communication hole,
It is released into the open air, and the solvent is not retained in the annular space between the inner and outer tubular parts of the pipe joint, and the pipe end of the multi-layer pipe is pressed into the annular space. ,
With the press-fitting of the pipe end, the air in the annular space is pushed out from the communication hole, and the pipe end of the multi-layer pipe is pressed into the annular space without pressurizing the interior of the annular space. Although the number of the communication holes 15 may be one, it is preferable that the number of the communication holes 15 is two or more and the communication holes 15 are provided at equal intervals in the outer peripheral direction of the pipe joint.

According to the second aspect of the present invention, it is desirable to correct the inner and outer diameters of the pipe ends of the multi-layer pipe even when connecting the multi-layer pipe. In the present invention, the resin of the pipe joint and the inner and outer resin layers of the multi-layer pipe are preferably the same type of resin, but may be different types of resins. Examples of the resin include hard vinyl chloride, soft vinyl chloride, polyethylene, polypropylene, polyvinylidene fluoride, polyphenylene sulfide, and the like.

In the above description of the present invention, as the multi-layer pipe, the one in which the intermediate layer is a steel pipe is exemplified, but the compressive strength,
Other configurations that can satisfy various performances such as tensile strength, for example,
The fiber layer can also be the intermediate layer. In addition, the multi-layer tube
Any synthetic resin layer may be provided on the inner and outer peripheral surfaces of the intermediate layer directly or via an intervening layer, and may be an adiabatic transport tube having the intermediate layer as a foam layer.

[0032]

According to the first aspect of the invention, since the inner and outer diameters of the pipe ends of the multi-layer pipe are adjusted so as to match the gap size between the inner and outer cylindrical portions of the pipe joint, the inner and outer cylindrical portions of the pipe joint are It is possible to prevent excessive stress from acting on the base of the inner cylinder and the base of the outer cylinder by press-fitting the end of the multilayer pipe into the base. Therefore, even if the solvent of the adhesive remains between the inner and outer cylinders of the pipe joint and is heated, or in an environment in which the growth of resin cracks is promoted, the stress that causes the initial cracks is sufficiently Since it can be suppressed and the occurrence of initial cracks can be well prevented, environmental stress fracture such as solvent cracks can be sufficiently prevented.

According to the second aspect of the invention, in the case of adhesive connection, the adhesive adhered to the annular space between the inner and outer cylinders of the pipe joint is press-fitted into the annular space between the inner and outer cylinders of the pipe joint by press fitting the multi-layer pipe end. When the amount of adhesive is large, the solvent in the adhesive may evaporate and scatter through the communication hole and accumulate in the inner part of the annular space as the amount of adhesive increases. Absent. Therefore, even if stress is applied to the root of the inner tubular portion and the root of the outer tubular portion of the pipe joint due to the press-fitting of the pipe end portion, the residual solvent can be eliminated, so that the solvent crack can be well eliminated. Further, even in the case of fusion splicing, the pressure in the annular space between the inner and outer tubular parts of the pipe joint can be made normal pressure, the action of hoop stress due to the internal pressure can be eliminated, and the stress can be reduced accordingly, so that the resin Even in a heating environment in which the growth of cracks is promoted, the initial cracks can be well prevented from occurring and stress fracture can be sufficiently prevented.

Therefore, by either the adhesive method or the fusion method, a multi-layer tube having an outer layer and an inner layer of synthetic resin respectively on the outer peripheral surface and the inner peripheral surface of the intermediate layer and the end surface of the intermediate layer (metal tube) at the tip of the multi-layer tube are formed. Good connection with guaranteed disconnection from transport liquid.

[0035]

【Example】

 Embodiment 1 It is an embodiment of the invention described in claim 1.

The structure of the pipe joint used is an injection molded product of vinyl chloride resin, and in FIG. 1 (a), the inner diameter D ₁ at the inlet of the outer cylinder is 60.5 mm, and at the back end as well. Has an inner diameter D ₂ of 59.7 mm, an outer diameter d ₁ at the inlet portion of the inner tubular portion of 43.5 mm, and an outer diameter d ₂ at the rear end portion of 44.2.
mm, and the tube portion length c is 40 mm.

The multi-layer pipe used was a steel pipe as an intermediate layer, synthetic resin layers inside and outside as vinyl chloride resin layers, and an outer diameter of 60.
It has a diameter of 5 mm and an inner diameter of 43.5 mm. At the pipe end of this multi-layer pipe, a length of about 45 mm, the outer diameter is 6
The inside diameter was corrected to 0.1 mm and the inside diameter was changed to 43.8 mm by cutting, and an adhesive was used for connection.

Comparative Example 1 Compared to Example 1, the inner and outer diameters of the pipe end of the multilayer pipe were not modified, the outer diameter was kept at 60.5 mm and the inner diameter was kept at 43.8 mm. Similarly, they were connected by an adhesive.

With respect to these Example 1 and Comparative Example 1 (the number of samples is 10 in each case), after the completion of the connection, the connection was disassembled, the connection was disassembled, and the presence or absence of solvent cracks was investigated. While no cracks were observed in the example products, remarkable solvent cracks were observed in 7 out of 10 samples in the comparative example products.

Example 2 For the pipe joint, except that the material was made of polyethylene,
Same as Example 1. The three-layer tube was the same as that used in Example 1 except that the inner and outer synthetic resin layers were polyethylene layers.

A fusion method is used for the connection method, an aluminum alloy product of tetrafluoroethylene resin coating is used for the heating jig, and the heating temperature of this jig is about 220.degree.
(The heating is performed by an electric heating type hand heater).

Comparative Example 2 In contrast to Example 2, the inner and outer diameters of the pipe end of the multilayer pipe were not modified, the outer diameter was kept at 60.5 mm and the inner diameter was kept at 43.5 mm. Same as

Regarding Example 2 and Comparative Example 2 (the number of samples is 10 in each case), after the completion of connection, the connection part was disassembled and the fusion interface was examined after leaving for 3 days.
No abnormality was observed in the example product, whereas cracks were observed in 6 out of 10 samples in the comparative example.

Embodiment 3 It is an embodiment of the invention described in claim 2. As the multilayer pipe, the one used in Example 1 having a vinyl chloride resin layer on the inner and outer circumferences of the steel pipe is used, and unlike Example 1, the inner and outer diameters of the pipe end portion of the multilayer pipe are not corrected, The outer diameter was 60.5 mm and the inner diameter was 43.5 mm. As the pipe joint, the one used in Example 1 and having the inner and outer cylindrical portions communicated to the outside through communication holes was used.

For connection, a method of adhering with an adhesive was used as in Example 1. Comparative Example 3 In contrast to Example 3, a communication hole was not provided, and other than that, Example 3 was used.
Same as.

With respect to these Example 3 and Comparative Example 3 (the number of samples is 10 in each case), after the completion of the connection, the connection was disassembled and the connection was disassembled, and the presence or absence of solvent cracks was investigated. In Example 3, no generation of cracks was observed, whereas in Comparative Example, remarkable solvent cracks were observed in 6 out of 10 cracks.

Example 4 The same as Example 1 except that the pipe joint was provided with a communication hole for communicating the inner portion of the inner and outer cylindrical portions with the outside.

About this Example 4 (the number of samples is 10
After the completion of the connection, the connection was disassembled for 5 days, the connection was disassembled, and the presence or absence of cracks was investigated. No cracks were found.

Example 5 For the pipe joint, except that the material was made of polyethylene,
Same as Example 3. The three-layer pipe was the same as that used in Example 3 except that the inner and outer synthetic resin layers were polyethylene layers.

A fusion method is used for the connection method, an aluminum alloy product of tetrafluoroethylene resin coating is used for the heating jig, and the heating temperature of this jig is about 220.degree.
(The heating is performed by an electric heating type hand heater).

Comparative Example 5 In contrast to Example 5, the same pipe joint as in Example 5 was used except that the pipe joint was not provided with a communication hole, and the same three-layer pipe as in Example 4 was used. The connection was made by the fusion method as in Example 5.

Regarding Example 5 and Comparative Example 5 (the number of samples is 10 in each case), the connection was disassembled and left for 3 days after the connection was completed, and the fusion interface was examined.
No abnormalities were observed in the example product, whereas cracks were observed in 4 out of 10 parts in the comparative example product.

[0053]

According to the multilayer tube of the present invention, the intermediate layer,
For example, a multilayer pipe having an outer layer and an inner layer of synthetic resin on the outer peripheral surface and the inner peripheral surface of the metal pipe is adhered or fused to ensure that the metal pipe end face at the tip of the pipe is shielded from the transport fluid in the pipe, and the solvent. Good connection can be achieved by sufficiently eliminating cracks. Particularly, in the invention described in claim 1, strict dimensional regulation is not required for manufacturing the multilayer pipe, and the manufacturing is facilitated.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of the invention described in claim 1, in which (a) of FIG. 1 shows a pipe joint and a multi-layer pipe, (b) of FIG. 1 (c) indicates the end of connection.

FIG. 2 is an explanatory view showing another example of the invention described in claim 1, (a) of FIG. 1 shows a time of heating and melting the pipe joint and the end portion of the multi-layer pipe, and (b) of FIG. 1 shows a connection end. Each time is shown.

FIG. 3 is an explanatory view showing another example of the pipe joint used in the present invention.

FIG. 4 is an explanatory diagram showing another example of the pipe joint used in the present invention.

FIG. 5 is an explanatory view showing a conventional pipe joint for a three-layer pipe.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pipe joint 11 Outer cylinder part 110 Inner peripheral surface of outer cylinder part 12 Inner cylinder part 120 Outer peripheral surface of inner cylinder part a Annular space between inner and outer cylinder parts 15 Communication hole 2 Multilayer pipe 20 Intermediate layer of multilayer pipe 21 Multilayer pipe Synthetic resin outer layer 22 Synthetic resin inner layer of multi-layer tube b Tube end

Claims (2)

[Claims] 1. A pipe end portion of a multi-layer pipe having a synthetic resin outer layer and a synthetic resin inner layer on an outer peripheral surface and an inner peripheral surface of an intermediate layer, respectively, the inner peripheral surface being a joint surface of the multi-layer pipe end portion to the synthetic resin outer layer. In the method of press-fitting between the inner and outer cylinder parts of the pipe joint having the outer cylinder part and the outer peripheral surface, and the inner cylinder part that is the joining surface to the synthetic resin inner layer of the multilayer pipe end part, and bonding or fusing. The outer diameter or inner diameter or inner / outer diameter of the pipe end is corrected by cutting the inner and outer surfaces of the pipe end to a predetermined dimension with reference to the annular space between the inner and outer cylindrical portions of the pipe joint, and then the connection is made. A method of connecting multi-layer pipes, characterized in that 2. A pipe end portion of a multi-layer pipe having a synthetic resin outer layer and a synthetic resin inner layer on an outer peripheral surface and an inner peripheral surface of an intermediate layer, respectively, wherein an inner peripheral surface is a joining surface of the multi-layer pipe end portion to the synthetic resin outer layer. In the method of press-fitting between the inner and outer cylinder parts of the pipe joint having the outer cylinder part and the outer peripheral surface, and the inner cylinder part that is the joining surface to the synthetic resin inner layer of the multilayer pipe end part, and bonding or fusing. Connection of a multi-layer pipe characterized by press-fitting a pipe end into the annular space between the inner and outer tubular parts under a communication state between the inner part of the annular space between the inner and outer tubular parts of the pipe joint and the outside. Method.