JPH044386A - composite pipe - Google Patents

Abstract

PURPOSE:To know the condition of generating invisible blisters and corrosion in metal pipe by giving a conductivity to make the electric resistance converted by permeating a liquid in the pipe to a synthetic resin layer, in a complex tube made by covering the inner surface of a metal pipe with a synthetic resin layer. CONSTITUTION:There are formed a metal pipe 10 of aluminum or the like, an insulating layer 40 to cover the inner surface, a synthetic resin layer 20 to cover the inner surface, and a synthetic resin layer 30 to cover the peripherial surface of the metal pipe 10. The synthetic resin layer 20 at the innermost surface of the metal pipe 10 has an electric conductivity, and copper, iron, aluminum, or the like, or a conductive powder such as carbon black is kneaded in to give this conductivity. As a result, the electric resistance is converted by permeating a liquid in the tube to the synthetic layer, and the generating condition of blisters in the insulating layer, and the corrosive condition of the metal pipe can be inspected easily.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a composite material which is used for water supply, hot water supply, drainage, etc., and which has a synthetic resin layer provided at least on the inner peripheral surface side of a cylindrical metal layer. Regarding pipes.

(Prior Art) Recently, composite pipes in which the inner and outer peripheral surfaces of metal pipes are coated with synthetic resin layers have been used as piping materials for water supply, hot water supply, drainage, etc. In such a composite pipe, there is no fear that the liquid flowing inside the pipe will come into contact with the metal pipe, and there is no fear that the outer circumferential surface of the metal pipe will be corroded. Therefore, it has excellent corrosion resistance and can be used for a long period of time. However, as the period of use becomes longer, the liquid flowing through the tube penetrates into the synthetic resin layer covering the inner peripheral surface of the metal tube, causing blisters to form on the inner surface of the synthetic resin layer. Furthermore, there is a risk that the metal tube will corrode due to the liquid that has permeated the synthetic resin layer coming into contact with the metal tube.

Blisters that occur on the inner peripheral surface of the synthetic resin layer in the composite pipe and corrosion of the metal pipe cannot be visually observed from the outside. For this reason, the occurrence of blisters in the synthetic resin layer and the corrosion state of the metal pipe have traditionally been determined by cutting out a test piece from the composite pipe in which it is installed, and then checking the synthetic resin layer coated on the inner circumferential surface of the metal pipe of the cut test piece. The state of blistering can be determined by measuring the area ratio of blisters on the surface. Similarly, the synthetic resin layer coated on the inner surface of the metal layer of the cut specimen was peeled off from the metal layer and the area ratio of the corroded part of the metal surface was measured to determine the corrosion status of the metal pipe. or is being captured. Another method has been adopted in which a hole is drilled into the composite pipe, and an endoscope is inserted into the pipe through the hole to observe blisters forming on the inner surface of the synthetic resin layer. There is.

(Problems to be Solved by the Invention) With such an inspection method, it is possible to accurately determine the occurrence of blisters and corrosion in a composite pipe that cannot be directly observed from outside the pipe.

However, in either case, it is necessary to cut out a test piece or drill a hole in a portion of the existing piping, and repairing the cut or holed portion requires time and expense.

The present invention solves the above-mentioned conventional problems, and its purpose is to provide a composite pipe that allows the occurrence of corrosion of blisters and metal pipes, which cannot be directly observed, to be accurately grasped from outside the pipe.

(Means for Solving the Problems) The composite tube of the present invention is a composite tube in which at least the inner circumferential surface of a metal tube is coated with a synthetic resin layer, and the synthetic resin layer prevents liquid flowing through the tube. It is characterized by having conductivity whose electrical resistance changes with penetration, thereby achieving the above object.

(Example) The present invention will be described below with reference to Examples.

As shown in FIG. 1, the composite tube of the present invention includes a metal tube 10 made of aluminum or the like, an insulating layer 40 coated on the inner circumferential surface of the metal tube 10, and an insulating layer 40 coated on the inner circumferential surface of the insulating layer 4o. and a synthetic resin layer 30 coated on the outer peripheral surface of the metal tube 10. The synthetic resin layer 20 provided on the innermost surface side of the metal tube 1o has electrical conductivity, for example,
Electric conductivity is imparted by kneading pure metals such as copper, iron, aluminum, alloys thereof, or conductive powders such as carbon black into synthetic resins. The synthetic resin layer 20 has a property that its electrical resistance decreases when liquid such as water permeates into it. The insulating layer 40 between the inner circumferential surface of the metal tube 10 and the synthetic resin layer 20 is composed of a synthetic resin layer that is not imparted with electrical conductivity.
The conductive synthetic resin layer 20 is electrically insulated from the conductive synthetic resin layer 20.

The synthetic resin constituting the insulating layer 40 is, for example, a thermoplastic resin, and adhesive crosslinked polyethylene, which has excellent water resistance, adhesiveness, heat resistance, etc., is particularly preferable.

The synthetic resin used for the synthetic resin layer 20 located on the innermost side of the metal tube 10 and the synthetic resin layer 30 covering the outer circumferential surface of the metal tube 10 is, for example, a thermoplastic resin, and in particular has good water resistance, Crosslinked polyethylene, which has excellent adhesiveness, heat resistance, etc., is preferred.

In the composite tube of the present invention having such a configuration, the inner peripheral surface of the metal tube 10 is coated with the synthetic resin layer 20 via the insulating layer 40, so that liquid such as water flowing inside the metal tube 10 is coated with the synthetic resin layer 20. There is no direct contact with. Furthermore, since the outer peripheral surface of the metal tube 10 is also coated with the synthetic resin layer 30, the outer peripheral surface of the metal tube 10 is also protected by the synthetic resin layer 30. However, due to long-term use, the liquid flowing inside gradually penetrates into the synthetic resin layer 20 located on the innermost surface side of the metal tube 10 from the inner peripheral surface of the synthetic resin layer 20, and the insulating layer 40 The liquid reaches the interface between the metal plate 10 and the metal plate 10. As a result, the insulating layer 40
Blisters may begin to form on the outer peripheral surface of the metal tube 10, and furthermore, the metal tube 10 may be corroded by the liquid that has permeated the insulating layer 4o.

In the composite tube of the present invention, the occurrence of blisters on the outer circumferential surface of the insulating layer 40 and the corrosion condition of the metal tube 10 can be determined as follows.

First, two holes are drilled in the outer peripheral surface of the composite tube at a predetermined interval in the axial direction. Each type is formed so as to reach the outer periphery of the conductive synthetic resin layer 20 near the insulating layer 40 . Therefore, according to each formula, there is no possibility that the liquid flowing inside the pipe will leak out of the pipe. Then, as shown in FIG. 2, each of the detection parts 51 and 51 of the resistance meter 50 is inserted into each equation, and electricity is generated over a predetermined length in the axial direction at the outer circumference of the conductive synthetic resin layer 20. Measure the resistance value.

Even if the liquid flowing through the pipe has penetrated into the conductive synthetic resin layer 20, if it has not reached the outermost periphery, the measured electrical resistance value will be large. When the liquid flowing through the pipe reaches the outermost periphery of the conductive synthetic resin layer 20, the measured electrical resistance value decreases. Further, if the liquid flows through the synthetic resin layer 20 and permeates into the insulating layer 40 to the extent that the metal tube 10 corrodes, the measured electrical resistance value further decreases.

If the corrosion in the blisters in the insulating layer 40 and the metal tube 10 progresses further, the measured electrical resistance value also decreases depending on the degree of the progress. Therefore, by measuring the electrical resistance value at a predetermined distance in the axial direction at the outer circumference of the conductive synthetic resin layer 20 close to the metal tube 10 using the resistance meter 50, it is possible to determine the occurrence of blisters in the insulating layer 40. The occurrence of corrosion in the metal tube 10 can be accurately grasped.

Further, as shown in FIG. 2, if the resistance of the metal tube 10 is measured using a resistance meter 60, the state of occurrence of corrosion in the metal tube 10 can be grasped more accurately.

The material of the conductive synthetic resin layer 20 is not limited to a mixture of synthetic resin and metal, and may be a conductive polymer resin or the like.

(Effects of the Invention) As described above, the composite pipe of the present invention covers a metal pipe via an insulating layer with a conductive synthetic resin layer whose electrical resistance changes when the liquid flowing inside the pipe permeates. Therefore, the occurrence of blisters in the insulating layer and the occurrence of corrosion in the metal pipe can be accurately determined without cutting out a part of the piped composite pipe or making a through hole in the pipe wall. I can do it. Therefore, it is extremely easy to inspect the occurrence of blisters in the insulating layer and the corrosion status of metal pipes, and repair after inspection is also greatly simplified, resulting in a marked improvement in inspection efficiency.

4. Pa side. Figure 1 is a sectional view showing an example of the composite pipe of the present invention, and Figure 2 is a perspective view showing the state of its inspection.

10... Metal tube, 20... Conductive synthetic resin layer, 30
...Synthetic resin layer, 40...Insulating layer.

that's all

Claims (1)

[Scope of Claims] 1. A composite pipe in which at least the inner circumferential surface of a metal pipe is coated with a synthetic resin layer, the synthetic resin layer being a conductive material whose electrical resistance changes with the penetration of a liquid flowing through the pipe. A composite pipe characterized by having a