JPH0228760B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for joining internally lined metal pipes, and in particular, to prevent corrosion of metal pipes that is likely to occur at the joints of the lined metal pipes, and to prevent corrosion at the joints of the lined metal pipes. To provide a joining method that reliably prevents leakage of internal fluid and allows easy joining work.

Note that the inner-lined metal pipe as used in the present invention is a general term for various types of metal pipes such as steel pipes and lead pipes whose inner surfaces are lined with thermoplastic resin. do.

[Prior Art] Internally lined steel pipes have begun to be widely put to practical use in cooling and heating piping, water supply pipes, etc., for the purpose of preventing internal corrosion of steel pipes and further preventing generation of red water and elution of iron ions, etc. However, when putting this type of inner-lined steel pipe into practical use, the most important problem is the joining method. In other words, internally lined steel pipes are designed to extend the life of the pipe by lining the entire inner peripheral surface of the pipe with a synthetic resin material to prevent the fluid within the pipe from coming into direct contact with the steel pipe. In conventional joining methods, the steel pipe layer is exposed at the joint end face, so water and the like enter the boundary between the steel pipe layer and the lining layer at the joint, causing rapid corrosion. For example, Figures 1 and 2 are longitudinal cross-sectional views of the upper half of a known method of joining lined steel pipes. Figure 1 shows an example of joining using a threaded socket, and Figure 2 shows an example of mechanical joining. , M in the figure
1 is a steel pipe layer, R is a lining layer, 1 is a double-receiving socket with a screw, 2 is a double flange joint, 3 is a push ring, and 4 is a sealing packing. That is, in FIG. 1, a male thread is cut on the outer periphery of the joint end of the lining steel pipe MR, and the pipes are connected to each other via a threaded double-receiving socket 1. In addition, in FIG. 2, the lining steel pipe MR is inserted through the large diameter portions on both sides of both flanged joints 2, and a sealing gasket 4 attached to the inner surface of the opening side of the flanged joints 2 is tightened with a push ring 3 to make watertight. is ensured. However, as is clear from the figure, the distal end surface of the lining steel pipe MR is exposed inside the pipe, so when fluid such as water is flowed through this, the exposed end surface of the steel pipe layer M, and even the steel pipe layer from the end surface side. M
The interface between the lining layer and the lining layer R is rapidly corroded within a short period of time. In particular, once the interface between the steel pipe layer M and the lining layer R is corroded, water will gradually infiltrate from the corroded portion to the depths and the corrosion will propagate, resulting in a serious accident.

In order to solve this problem, a joining method as shown in FIG. 3, for example, has been proposed. That is, in this joining example, a flange R' made of the same or different synthetic resin is welded to the joint end side of the lining layer R, and the flange R' is brought into contact with the butt end side of the steel pipe layer M.
The end faces are fixed to each other by pressure contact with flanges 5 and bolts and nuts 6. In this example, the end face of the lining steel pipe MR is not exposed in the pipe line, so corrosion of the steel pipe M as shown in FIGS. 1 and 2 is suppressed.

[Problems to be Solved by the Invention] However, in this method, the heat generated when welding the synthetic resin flange R' to the lining layer R deforms the lining layer R, and the gap between it and the steel pipe layer M may expand. Furthermore, even if the welding conditions were strictly adjusted, pinhole defects etc. in the welded part W could not be prevented, and as a result, fluid inside the pipe entered through the pinhole defects and accelerated corrosion of the steel pipe layer M. has been done.

On the other hand, there is a method in which the lining layer R is made to protrude from the end face of the steel pipe MR, and this protruding part is flared to integrally form the flange R'. This required precise machining work, making it unsuitable for on-site construction.

Also, flanges formed by any of the above methods
As for R', if the flanges R' and R' are brought into contact as shown in Figure 3, and the metal pipe layers are mechanically joined on the outside, the connection part will be subject to temperature fluctuations, etc. When expansion or contraction occurs, for example, in cold weather, only the synthetic resin flange R′, which has a high coefficient of thermal expansion, contracts, causing the contact surfaces of flanges R′ and R′ to separate, which may cause leakage of internal fluid. It was hot. Furthermore, in order to prevent fluid leakage,
As shown in Japanese Patent Application Laid-open No. 126082 and Japanese Patent Application Laid-open No. 146984/1984, there are some devices in which mechanical fitting means are added, but they have not been able to completely prevent fluid leakage.

As described above, conventional joining methods have serious problems such as corrosion deterioration and leakage of internal fluid starting from the joint, and in order to make maximum use of the characteristics of internally lined steel pipes, it is necessary to prevent corrosion, leakage, etc. It is essential to establish a bonding technology that prevents this from occurring.

In view of these circumstances, the present invention was developed as a result of intensive research to provide a method that prevents corrosion of the lining metal pipes at joints and leakage of internal fluid, and also allows connections to be made in the field with simple work. be.

[Means for Solving the Problems] The present invention, which has achieved the above object, targets metal tubes whose inner surfaces are lined with thermoplastic resin, and the lining layer on the joint end side is bonded from the end surface of the metal tube. The protruding portions of each of the lining layers are made to protrude slightly, and the protruding portions of each of the lining layers are brought into contact with a heating heater to heat them, and the heated lining layers are brought together and fused together, and the metal pipe layers are mechanically bonded to each other. The main point is that the connecting portion is formed by

[Function] In the present invention, each of the lining layers of the lining metal pipe is made to protrude from the end face of the metal pipe layer, the protruding portions are brought into contact with a heater to be heated, and the protruding portions are brought together to melt. wear. As a result, the lining layers are integrated with each other, so that there is no part of the metal pipe layer that comes into direct contact with the internal fluid, and corrosion of the metal layer can be prevented as much as possible. Furthermore, since the lining layers are fused and integrated, they will not be separated due to temperature fluctuations in the internal fluid, and the problem of leakage of the internal fluid at the connection portion has been solved.

On the other hand, since the metal tube layers are joined by mechanical means (bolt/nut fastening means, screw type fitting means, etc.), there is no problem in connection strength itself.

Furthermore, this joining method does not require any special components, requires only a small number of parts, and does not require complicated processes, leading to the proposal of a connection method suitable for on-site construction.

[Example] The configuration and effects of the present invention will be specifically explained below with reference to the drawings of the example, but the drawings are representative examples and do not limit the present invention. It is within the technical scope of the present invention to appropriately change and carry out the specific means of mechanically joining the metal tubes and fusion-bonding the lining layers to each other as long as it is compatible with the spirit of the invention.

4A to 4D are schematic process explanatory diagrams showing an embodiment of the present invention. In this embodiment, a flange 5 is welded and fixed to the outer periphery of the tip of the steel pipe layer M in preparation for mechanical joining of the steel pipe layer M. The tip of the lining layer R is made to protrude slightly from the tip of the steel pipe M in preparation for fusion bonding. Then, as shown in FIG. 4B, the joint portion sides of the inner lining steel pipes MR are butted against each other via the heater 8, and the protruding portion of the lining layer R is heated and pressed in the direction of the white arrow to remove the protruding portion. The steel pipe layer M is heated to a temperature equal to or higher than the fusion temperature while being folded back toward the end face of the steel pipe layer M in the manner of flange processing. Next, after removing the heater 8, the tips are immediately brought closer to each other to fuse the protruding parts [FIG. 4C]. The joining operation is then completed by fastening the facing flanges 5, 5 with bolts and nuts 6 [Fig. 4D]. With this method, the lining layers R and R are completely fused and integrated at the joint,
Since the end face of the steel pipe layer M is isolated from the fluid within the pipe, corrosion of the steel pipe layer does not occur starting at the joint, as in the conventional example. Moreover, the steel pipe layers M and M each have flanges 5
Since they are firmly joined by the bolts and nuts 6, the mechanical strength of the joint can also be maintained at a high level.

FIG. 5 is a vertical sectional view of the upper half of a bonded structure obtained in another embodiment of the present invention, and the fusion bonding of the lining layer R is performed in the same manner as in the example of FIGS. 4A to 4D. However, the joining of the steel pipe layer M is done by omitting the flange portion and using a nut type joint with both receiving bags. That is, the joining and fixing of the steel pipe layer M is achieved by compressing the wedge rings 10 attached to the openings at both ends of the joint body 9 in the direction of the joint body 9 by tightening the cap nuts 11, thereby hugging the steel pipe layer M from the outer peripheral surface side. It is firmly fixed by. The material for the wedge ring 10 is most preferably a flexible alloy such as brass, but it is of course possible to use hard plastic, hard rubber, or the like.

In the above embodiment, a thick lining layer is formed at the joint boundary between the steel pipe layers M, M, in order to prevent defects such as poor fusion.
Of course, it is also possible to bring both end surfaces of the steel pipe layers M, M into direct contact, and in this case, there is no problem at all as long as the joints of the lining layers R, R are sufficiently fused. In addition to the illustrated example, all known mechanical joining methods can be used to mechanically join the steel pipe layers M, M, and welding may also be used in some cases. However, in this case, if the welding heat reaches the lining layer R, it may melt it and reduce the thickness of the lining layer.To avoid this problem, for example, as shown in Fig. 4, the steel pipe layer M
A recommended method is to join a flange ring to the joint end of the flange ring and weld the butt part from the outer periphery.

[Effects of the Invention] The present invention is configured as described above, and since the end face of the steel pipe layer M is no longer exposed inside the pipe at the joint, there is no occurrence of corrosion starting from the joint. As a result, the corrosion resistance of the entire pipe line can be greatly improved, and leakage of internal fluid can also be prevented. Moreover, the joining of the steel pipe layers, which must ensure the mechanical strength of the pipe, is mechanically strong.
It also has extremely strong resistance to internal stress and other external stress caused by expansion and contraction of the pipe, making it possible to utilize the characteristics of the internally lined steel pipe to the maximum extent possible. Furthermore, the joining method itself is simple and can be easily performed on-site.

[Brief explanation of drawings]

Figures 1 to 3 are upper half longitudinal sectional views showing conventional joining examples of internally lined steel pipes, Figures 4A to D are upper half longitudinal sectional views showing embodiments of the present invention in order of process, and Figure 5 is FIG. 7 is a vertical cross-sectional view of the upper half of another embodiment. MR...inner lining steel pipe, M...steel pipe layer,
R... Lining layer, 5... Flange portion, 6...
Bolt/nut, 8... Heater, 9... Joint body, 10... Wedge ring, 11... Cap nut.

Claims (1)

[Claims] 1 A method of butting and joining metal tubes whose inner surfaces are lined with thermoplastic resin, in which the lining layers on the joint end side are made to protrude slightly from the end surfaces of the metal tube layers, and the protruding portions of each of the lining layers are exposed to a heater. are brought into contact and heated, and the heated lining layers are brought together and fused together,
A method for joining inner-lined metal pipes, characterized in that metal pipe layers are mechanically joined to each other to form a joint.