JP7372804B2 - pipe joint structure - Google Patents

Description

The present invention relates to a pipe-to-pipe joint structure, and more particularly to a pipe joint structure in which flanges at pipe ends are joined by bolts.

Generally, a flange for joining with another pipe is provided at the end of a pipe such as a factory pipe. The flanges of the two pipes are opposed to each other and joined with bolts and nuts. As a type of flange, a loose flange that is loosely fitted onto a pipe is also known (see Patent Document 1, etc.).
Many of these types of tubes are made of metal, and flanges such as loose flanges are also generally made of metal. By making it metal, sufficient strength can be obtained even if the tightening torque is increased. Water-tightness is ensured by increasing the tightening torque.

In recent years, advances in resin synthesis technology have led to improvements in mechanical strength, weather resistance, chemical resistance, earthquake resistance, etc. In response to this, metal pipes are being replaced with resin pipes such as polyvinyl chloride and polyethylene in factory piping and the like. When joining resin pipes, compared to joining metal pipes, even if the bolts and nuts are tightened with a lower torque, the resin pipes themselves can deform and retain watertightness.

Japanese Patent Application Publication No. 5-280674

The inventors considered bolt-joining a metal tube and a resin tube and conducted extensive research. As a result, if the tightening torque when bolting metal pipes and resin pipes is set to a high torque equivalent to that used when joining metal pipes together, resin members such as resin pipes are likely to be damaged; It was discovered that if the torque was set to a low level equivalent to that used when bolts were joined together, the water-stopping properties would be inadequate.
Therefore, it is an object of the present invention to provide a joint structure between a metal pipe and a resin pipe that prevents damage to resin members by lowering the tightening torque and also provides a high water-stopping property even at low torque.

In order to solve the above problem, the inventors conducted further research and found that if at least one flange of the metal tube or the resin tube is a loose flange in which a metal core is coated with resin, the torque can be increased at low torque. It was found that water-stopping properties can be obtained.
The present invention is based on such knowledge, and is a pipe joint structure in which a resin pipe and a metal pipe are joined by bolting the flanges of these pipes,
The flange of at least one of the resin pipe and the metal pipe is a loose flange including an annular core material made of metal and a coating layer covering the core material, and the coating layer is mainly composed of a thermoplastic resin. It is characterized by containing as follows.

In the pipe joint structure, it is preferable that the tightening torque of the bolt connection is set lower than the standard tightening torque for joining metal pipes, for example, about 10% to 50% of the standard tightening torque. It is preferable to set According to the pipe joint structure, high water-stopping performance can be obtained even if the tightening torque is low. Although the mechanism is not necessarily clear, it is thought that the stress applied to the joint surfaces of the tubes can be uniformly distributed by elastically deforming the coating layer by tightening the bolts.
By setting the torque to be low, damage to resin members is particularly prevented.
The metal core ensures the required strength of the loose flange.

The thermoplastic resin is preferably a polyolefin resin. More preferably, the coating layer contains reinforcing fibers in an amount of 10% by mass or more.
The thickness of the coating layer is preferably 1 mm or more.
The thickness of the core material is preferably 3 mm or more.
Preferably, the apparatus further includes an annular packing provided between the resin tube and the metal tube, and two or more annular convex portions are formed on each of both surfaces of the packing.
Preferably, the packing contains ethylene propylene diene (EPDM) rubber.

According to the present invention, in the joint structure of a resin pipe and a metal pipe, high water-stopping properties can be obtained even if the tightening torque is low. By setting the torque to be low, damage to resin members such as resin pipes can be prevented.

FIG. 1 is a sectional view taken along a tube axis, showing a tube joint structure according to an embodiment of the present invention in an assembled state. FIG. 2 is an exploded sectional view of the pipe joint structure. FIG. 3 is a front cross-sectional view showing the loose flange in the pipe joint structure along line III-III in FIG. 4. FIG. 4 is a cross-sectional view of the loose flange taken along line IV-IV in FIG. 3. FIG. 5 is a front view showing the packing in the pipe joint structure along the line VV in FIG. 2.

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 shows a pipe joint structure 1 in, for example, factory piping. The pipe joint structure 1 is constructed by joining a first pipe 10 and a second pipe 20 with bolts. The two tubes 10 and 20 are arranged to face each other on the same tube axis.

The first tube 10 is made of metal. Hereinafter, the first tube 10 will be appropriately referred to as the "metal tube 10." Examples of the metal material of the metal tube 10 include stainless steel, common steel, and iron.
Note that the metal tube 10 only needs to be a tube mainly made of metal, and a member other than metal such as resin may be added thereto.
A flange 13 is welded to the end of the metal tube 10 facing the resin tube 20. The material of the flange 13 is metal such as stainless steel, common steel, or iron. A plurality of bolt holes 13b are formed in the flange 13 at intervals in the circumferential direction.

The second pipe 20 is made of resin. Hereinafter, the second pipe 20 will be appropriately referred to as the "resin pipe 20". Examples of the material for the resin pipe 20 include polyethylene, polyvinyl chloride, polypropylene, and other synthetic resins. Note that the resin pipe 20 may be a pipe mainly made of resin, and may also contain members other than resin, such as metal or reinforcing fibers.
Although the resin pipe 20 has a short tubular shape, the present invention is not limited thereto. The resin pipe 20 may constitute a stub end. The resin pipe 20 may be connected as a stub end to the end of another pipe (not shown) by welding or the like.

As shown in FIG. 2, annular protrusions 21 and 22 are formed in the intermediate portion of the resin tube 20 in the tube axis direction, respectively, to protrude toward the outer circumference and the inner circumference.
A flange portion 23 (flare portion) is integrally formed at the end of the resin tube 20 facing the metal tube 10 . The collar portion 23 has an annular shape and protrudes radially outward from the entire circumference of the opposing end of the resin tube 20 . The end surfaces of the collar portion 23 and the resin tube 20 facing the connection partner tube 10 (the left end surface in FIG. 2) are flush with each other.

As shown in FIG. 2, a loose flange 30 is provided on the outer periphery of the resin pipe 20. As shown in FIG. 3, the loose flange 30 is formed into an annular plate shape having a center hole 31. As shown in FIG. A plurality of bolt holes 32 are formed in the loose flange 30 at intervals in the circumferential direction.
The outer diameter of the loose flange 30 is, for example, approximately 50 mm to 600 mm, but the present invention is not limited thereto.
The inner diameter of the loose flange 30 (the diameter of the center hole 31) is, for example, about 30 mm to 400 m, but the present invention is not limited thereto.

As shown in FIG. 4, the loose flange 30 includes a core material 33 and a covering layer 34. The core material 33 defines the shape of the loose flange 30. The core material 33 is made of metal. Examples of the metal material of the core material 33 include cast iron, stainless steel, and ordinary steel.
The thickness of the core material 33 is preferably 3 mm or more, more preferably about 3 mm to 18 mm, and even more preferably about 6 mm to 12 mm.

The surface of the core material 33 is coated with a coating layer 34 . The coating layer 34 covers all surfaces of the core material 33, that is, the main surfaces on both sides, the outer circumferential end surface, the inner circumferential end surface, and the inner circumferential surfaces of bolt holes and other holes. A core material 33 is buried inside the covering layer 34.
The thickness of the coating layer 34 is preferably 1 mm or more, more preferably about 1 mm to 10 mm, and even more preferably about 3 mm to 6 mm.

The covering layer 34 is made of fiber reinforced resin. Specifically, the covering layer 34 contains a thermoplastic resin as a base material (main component) and reinforcing fibers as a reinforcing material.
The thermoplastic resin is preferably a polyolefin resin such as polypropylene or polyethylene.
The content of the thermoplastic resin in the entire coating layer 34 is preferably 50% by mass or more, more preferably about 70% by mass to 90% by mass.

The reinforcing fibers are preferably glass fibers.
The content of reinforcing fibers in the entire coating layer 34 is preferably 10% by mass or more, more preferably about 10% by mass to 30% by mass.

The loose flange 30 is loosely fitted into the resin pipe 20. As shown in FIG. 2, when the tubes 10 and 20 are not joined, the loose flange 30 is movable in the tube axis direction between the collar portion 23 and the annular projection 21 with respect to the resin tube 20, Moreover, it is rotatable with respect to the resin pipe 20. By rotation, the bolt holes 13b and 32 can be easily aligned.

As shown in FIG. 1, when the tubes 10 and 20 are joined, the loose flange 30 abuts against the collar 23. Moreover, the loose flange 30 faces the flange 13. Bolts 40 are inserted into bolt holes 13b, 32 of these flanges 13, 30. By tightening the bolt 40 and the nut 41 screwed onto the tip thereof, the flanges 13 and 30 and, by extension, the pipes 10 and 20 are bolted together.

As shown in FIGS. 1 and 2, a packing 50 is provided between the resin tube 20 and the metal tube 10. The packing 50 is sandwiched between the flange 13 of the metal tube 10 and the opposite end of the resin tube 20 including the collar 23 . The packing 50 is formed into an annular sheet shape having a center hole 51.
The material of the packing 50 is preferably ethylene propylene diene (EPDM) rubber.

As shown in FIGS. 2 and 5, two (plural) large and small annular protrusions 52 and 53 are formed on both sides of the packing 50, respectively. These annular convex portions 52 and 53 surround the center hole 51 and form a double circle concentric with the center hole 51. The diameter of the annular convex portion 52 on the large diameter side is smaller than the outer diameter of the collar portion 23. The diameter of the annular convex portion 53 on the small diameter side is larger than the inner diameter of the tubes 10 and 20.
A hole 54 through which the bolt 40 passes is formed in a portion of the packing 50 on the outer peripheral side of the annular convex portion 52 on the large diameter side.
Note that the number of annular protrusions of the packing 50 is not limited to two, but may be three or more. Three or more annular convex portions having different diameters may be preferably arranged to form multiple circles concentric with the center circle 51.

As shown in FIG. 1, when the pipes 10 and 20 are joined, the annular protrusions 52 and 53 are crushed by tightening the bolt 40 and nut 41. The sealing pressure at the portion where the annular convex portions 52 and 53 are arranged is higher than the sealing pressure at other portions of the packing 50.

In the pipe joint structure 1, the tightening torque of the bolt 40 and nut 41 is set lower than the standard tightening torque in a joint structure between metal pipes, and preferably set to be equal to the tightening torque in a joint structure between resin pipes. ing. Even with such a low torque, sufficient water-stopping properties (liquid-tightness) can be obtained. Although the mechanism is not necessarily clear, it is thought that the stress applied to the joint between the tubes 10 and 20 can be uniformly distributed by elastically deforming the coating layer 34 by tightening the bolt 40 and nut 41.
This can prevent fluid such as water flowing inside the pipes 10 and 20 from leaking from the joints (specifically between the metal pipe 10 and the packing 50 and between the packing 50 and the resin pipe 20). .
By setting the tightening torque low, it is possible to avoid damage to each member of the pipe joint structure 1 (for example, the packing 50 and the coating layer 34). Furthermore, the metal core material 33 ensures the required strength of the loose flange 30.

The present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit thereof.
For example, the flange of at least one of the metal tube 10 and the resin tube 20 may be a loose flange including a metal core material and a resin-containing coating layer. The flange of the metal tube 10 may be constituted by a loose flange including a metal core material and a resin-containing coating layer. The flange of the metal tube 10 and the flange of the resin tube 20 may both be formed by loose flanges containing a metal core material and a resin-containing coating layer. The flange of the metal tube 10 may be configured by a loose flange including a metal core material and a resin-containing coating layer, and the flange of the resin tube 20 may be configured of resin or metal integral with the resin tube 20.
The reinforcing fibers of the covering layer 34 are not limited to glass fibers, and may be carbon fibers.
The covering layer 34 may be composed only of resin and may not contain reinforcing fibers.

An example will be explained. Note that the present invention is not limited to the following examples.
In Example 1, a pipe joint structure similar to that shown in FIG. 1 was made, and its water-stopping properties were examined.
As the first tube 10, a metal tube (1) made of a flanged stainless steel tube (SUS304) was used. The pipe diameter was a nominal diameter of 75A.
As the second pipe 20, a resin pipe (2) made of a polyethylene pipe made by joining a straight pipe and a short pipe F type of Plant Hyper BK manufactured by Sekisui Chemical Co., Ltd. was used.

A loose flange whose core material was coated with resin was prepared as the flange of the resin pipe.
The material of the core material was SS400. The core material had an outer diameter of 179 mm, an inner diameter of 101 mm, and a thickness of 12 mm. A coating layer having a thickness of 3 mm was applied to the entire surface of the core material. The coating layer was a fiber reinforced resin containing 70% by mass of polypropylene and 30% by mass of glass fiber.
The overall size of the loose flange was 185 mm in outer diameter, 95 mm in inner diameter, and 18 mm in thickness. The center diameter (twice the distance from the center of the loose flange to the center of the bolt hole 32) was 150 mm.
As the packing sandwiched between the metal tube and the resin tube, an EPDM packing having two annular protrusions 52 and 53 was used, as in the embodiment (FIG. 5).

These pipes, loose flanges, and packing were assembled as shown in FIG. 1, and tightened with bolts 40 and nuts 41 to obtain a jointed pipe joint structure. The initial tightening torque was 50 N·m.
After 30 minutes had passed while a hydrostatic pressure (internal pressure) of 1 MPa was applied to the pipe joint structure, the tightening torque of the bolts and nuts was gradually decreased by 5 N·m. Then, by visual observation, the lowest tightening torque (minimum water stop torque) at which no water leaked from the joint between the pipes was measured. The measurement result was 5 N·m.
Since the loose flange includes a resin portion made of a coating layer, it is more easily deformed elastically than a metal flange. It is thought that the elastic deformation uniformly distributed the stress of bolt tightening, resulting in high water-tightness (liquid-tightness) even when the tightening torque was low.
After the measurement, the jointed state of the pipe joint structure was released and the packing was visually observed, and no damage such as breakage or scratches was observed.

[Comparative example 1]
In Comparative Example 1, an uncoated metal (SUS304) loose flange was used in place of the resin-coated loose flange of Example 1.
Moreover, as the first pipe, instead of the metal pipe (1) of Example 1, a polyethylene pipe (based on PE100) with a metal flange and a resin pipe (1) with a nominal diameter of 75A was used.
The other component configurations were the same as in Example 1, and the resin pipe (1) and resin pipe (2) were connected.
The testing and evaluation methods were the same as in Example 1. As a result, the minimum water stop torque was 20 N·m. No damage to the packing was observed.

[Comparative example 2]
In Comparative Example 2, instead of the packing used in Example 1, an EPDM packing having no annular protrusions 52 and 53 and having flat surfaces on its entirety was used.
The other component configurations were the same as in Comparative Example 1, and the resin pipe (1) and resin pipe (2) were connected.
The testing and evaluation methods were the same as in Example 1. As a result, the minimum water stop torque was 50 N·m. No damage to the packing was observed.

[Comparative example 3]
In Comparative Example 3, instead of the resin pipe (2) of Example 1, a metal pipe (2) made of a steel pipe to which a stub end having a flared part (flange part) was welded was used. The material of the stub end and steel pipe was SUS304.
Moreover, in place of the resin-coated loose flange of Example 1, a metal (SUS304) loose flange without coating, similar to Comparative Example 1, was used.
The other components were the same as in Example 1, and the metal tube (1) and metal tube (2) were connected.
The testing and evaluation methods were the same as in Example 1. As a result, the minimum water stop torque was 15 N·m. The packing was damaged and damaged.

[Comparative example 4]
In Comparative Example 4, instead of the packing in Example 1, an EPDM packing similar to Comparative Example 2, which did not have the annular protrusions 52 and 53 and whose entire surfaces were flat, was used.
The other component configurations were the same as in Comparative Example 3, and the metal tube (1) and metal tube (2) were connected.
The testing and evaluation methods were the same as in Example 1. As a result, the minimum water stop torque was 35 N·m. The packing was damaged and damaged.

[Comparative example 5]
In Comparative Example 5, instead of the resin-coated loose flange of Example 1, an uncoated metal (SUS304) loose flange similar to Comparative Example 1 was used.
The other components were the same as in Example 1, and the metal tube (1) and resin tube (2) were connected.
The testing and evaluation methods were the same as in Example 1. As a result, the minimum water stop torque was 30 N·m. No damage to the packing was observed.

[Comparative example 6]
In Comparative Example 6, instead of the packing of Example 1, an EPDM packing without the annular protrusions 52 and 53 and whose entire surfaces were flat was used.
The other component configurations were the same as in Comparative Example 5, and the metal tube (1) and resin tube (2) were connected.
The testing and evaluation methods were the same as in Example 1. As a result, the minimum water stopping torque was 40 N·m. No damage to the packing was observed.

Table 1 below summarizes the contents of Example 1 and Comparative Examples 1 to 6. It was confirmed that by using a loose flange containing a metal core material and a resin coating layer as the flange of one of the pipes, sufficient water-stopping performance could be ensured even with a low tightening torque.

The present invention can be applied to, for example, pipe joints in factory piping.

1 Pipe joint structure 10 Metal pipe (first pipe)
13 Flange 13b Bolt hole 20 Resin pipe (second pipe)
21 Annular projection 23 Flange 30 Loose flange 31 Center hole 32 Bolt hole 33 Core material 34 Covering layer 40 Bolt 41 Nut 50 Packing 51 Center hole 52, 53 Annular protrusion 54 Bolt hole

Claims (4)

A pipe joint structure in which a resin pipe and a metal pipe are joined by bolting the flanges of these pipes,
The flange of at least one of the resin pipe and the metal pipe is a loose flange including an annular core material made of metal and a coating layer covering the core material, and the coating layer is mainly made of thermoplastic resin. A pipe joint structure characterized by containing reinforcing fibers as a component in an amount of 10% by mass or more . The pipe joint structure according to claim 1, further comprising an annular packing provided between the resin pipe and the metal pipe, and two or more annular protrusions are formed on both sides of the packing. The pipe joint structure according to claim 2 , wherein the packing contains ethylene propylene diene rubber. The pipe joint structure according to any one of claims 1 to 3, wherein the thermoplastic resin is a polyolefin resin.

Images