JPH04272593A - Structure for connecting piping - Google Patents

Abstract

PURPOSE:To permit a pressure sealing portion to maintain its soundness even in use for a long time by preventing leakage due to crevice corrosion. CONSTITUTION:A liner 3 is inserted into a pipe joint 1 made of a shape-memory alloy. Connection pipes 2, 2' are inserted from both ends of the liner 3. The space between a pressure sealing portion 4 formed in the liner 3 and each connection pipe 2, 2' is completely filled with a sealant 6.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite type pipe connection structure using a shape memory alloy pipe joint.

0002

2. Description of the Related Art Several pipe connection structures using pipe joints made of shape memory alloys have been disclosed, for example, in Japanese Patent Application Laid-open No. 112884/1984. In other words, a pair of opposing pipes (hereinafter referred to as connection pipes) to be connected are inserted into a shape memory alloy pipe joint (hereinafter referred to as pipe joints) from both sides, and the pipes are heat-treated by heating or cooling. A structure is known in which the inner diameter of a joint is reduced to connect connecting pipes. Further, as shown in FIG. 3, a composite type structure is known in which a liner 3 is inserted between the pipe joint 1 and the connecting pipes 2, 2'. A cross section of the composite type structure shown in FIG. 3 is shown in FIG. This composite type structure covers the outer surface of the connecting pipes 2, 2' with a liner 3 on which a protrusion is formed as a pressure seal part 4.
A pipe joint 1 whose shape changes through heat treatment is placed on the outside of a liner 3. Normally, the liner 3 is made of the same type of metal material as the connecting pipes 2, 2' in order to avoid contact corrosion caused by dissimilar metals. When the pipe fitting 1 is heated or cooled, the pipe diameter is reduced and it comes into close contact with the connecting pipes 2, 2', so that the connecting pipes 2, 2' can be connected. This pipe joint 1 is often made of a Ni-Ti alloy or a Cu-Zn-Al alloy.

Furthermore, many shape memory alloys used in the pipe joint 1 are of a type that connects pipes by reducing the pipe diameter by increasing the temperature rather than lowering the temperature. FIG. 5 shows the relationship between temperature and strain for this type of shape memory alloy. Shape memory alloys commonly used include heat-shrinkable types (dashed line in the figure), which reduce strain (reduced tube diameter) at temperatures higher than room temperature (RT), and low-temperature alloys, which reduce strain at temperatures lower than room temperature (RT). There is a contracted type (solid line in the figure). In either case, when the temperature rises from a low temperature (upper left of the figure, As for the heat-shrinkable type) to a high temperature, the large strain applied at a low temperature decreases from a certain temperature (Ap for the heat-shrinkable type). ) This method takes advantage of the fact that although the tube diameter decreases, the strain does not increase even if the temperature is lowered somewhat (heat-shrinkable types do not increase temperature strain up to Af, and have temperature hysteresis).

[0004] Pipes are connected by utilizing the strain characteristics of shape memory alloys. Piping connections using this shape memory alloy can be constructed in a short time, so for example,
It is suitable for use in places such as nuclear power plants where working hours are severely restricted, or in places where piping is difficult to weld due to close proximity to each other.Furthermore, due to its excellent sealing properties, It is said that the scope of its use will expand in the future.

[0005]

[Problems to be Solved by the Invention] However, in the conventional pipe connection structure, between the connection pipes 2, 2' and the pipe fitting 1,
Alternatively, a gap 5 is formed between the connecting pipes 2, 2' and the liner 3, or between both end faces of the connecting pipes 2, 2'. Especially in the composite type, connecting pipes 2, 2' and liner 3
There is a long gap of about 0.1mm to 0.2mm between the
often occurs. In this case, depending on the type of liquid transferred within the connecting pipes 2, 2', crevice corrosion may occur in the gap 5, and if the pressure seal portion 4 corrodes, leakage may occur. Such leaks may occur depending on the usage environment,
For example, this is an important problem in nuclear power generation facilities. As a countermeasure to this problem, it is strongly desired to develop a pipe connection structure using shape memory alloy pipe fittings that maintains the integrity of the pressure seal even during long-term use. The present invention has been made in order to solve the above problems, and an object of the present invention is to provide a piping connection structure that can maintain the integrity of a pressure seal part even when used for a long time. [Structure of the invention]

[0006]

[Means for Solving the Problems] The present invention provides a cylindrical shape memory alloy pipe joint, a cylindrical metal liner inserted into the pipe joint, and a pair of opposing connections inserted into the liner. It is characterized by comprising a pipe and a sealing material that fills a gap created from a pressure seal portion formed in the liner to the tip of the connecting pipe.

[0007]

[Operation] The main cause of crevice corrosion is that a corrosive liquid enters the crevice and the amount of oxygen dissolved in the solution in the crevice, that is, the dissolved oxygen, decreases, resulting in a decrease in the corrosion resistance of the metal. There are certain conditions that make this crevice corrosion more likely to occur, especially due to the shape of pipe joints that use shape memory alloys. .

[0008] Normally, when the gap is 0.03 mm or less,
The occurrence of crevice corrosion is extremely reduced. Therefore, crevice corrosion can be prevented by filling the gap between the pipe joints with a sealing material and narrowing the gap. In addition, by using a water-repellent sealant for the sealing material, it is possible to prevent water from entering the gap and into the pressure seals formed near both ends of the sealing material, thereby preventing leakage due to crevice corrosion. can do.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a pipe connection structure according to the present invention will be described with reference to FIGS. 1 and 2. Note that Figure 2 is similar to Figure 1.
In order to clearly explain the state before the piping connection structure is assembled, some parts are exaggerated.

In FIGS. 1 and 2, reference numeral 1 denotes a shape memory alloy pipe joint, into which a cylindrical metal liner 3 is inserted. Connecting piping 2, 2 inside this liner 3
' are inserted from both ends of the liner 3, and a sealing material 6 is inserted between the liner 3 and the connecting pipes 2, 2'. Protruding pressure seal portions 4 are formed on the inner surface of the liner 3 near both ends thereof. The thickness of the sealing material 6 is approximately 0.15
mm water-repellent silicone rubber. By heating the pipe fitting 1 and tightening the connecting pipes 2, 2', not only the gap 5 formed from the pressure seal part 4 to the tip of the connecting pipes 2, 2' is filled with the sealing material 6, but also the sealing material 6 is filled with the sealing material 6. 2,2'
It penetrates into the gap and fills it up, forming a protruding portion 7 and completely sealing the gap 5.

That is, before assembling the pipe connection structure shown in FIG.
There is. The pipe joint 1 arranged as shown in Fig. 2 is 100
When heated above ℃, the diameter of the pipe fitting 1 decreases to the state shown in Fig. 1 after the connecting pipes 2 and 2' are tightened, and a sealing material is formed between the liner 3 and the connecting pipes 2 and 2'. 6, the sealing material 6 is completely filled with liner 3 and connecting pipes 2, 2.
′ in close contact. Further, since the excess sealing material 6 enters the gap between the piping on both sides, the sealing performance will not be incomplete. Therefore, according to the pipe connection structure of this embodiment, it is possible to prevent the corrosive solution from leaking from both ends of the connecting pipes and infiltrating into the gap 5 as in the conventional example.

Next, the present invention and the conventional piping connection structure were tested for corrosion when a corrosive solution was flowed into the piping, and the test results are shown in Table 1. The test was performed on three pipe fittings each. As is clear from Table 1, in the conventional example, one leaked due to crevice corrosion 120 hours after the start of the test, and the remaining two leaked about 300 hours after the start of the test. In contrast, in the present invention, no leakage occurred even after 3000 hours, proving the superiority of the present invention.

[0013]

[Table 1]

Although the above examples are test results in a highly corrosive environment, a similar phenomenon has also been observed in the reactor water environment, which is high-temperature pure water. In some conventional examples, leakage occurred after about 1000 hours. In contrast, in the present invention, 300
No leakage was observed even at 0 hours. In addition,
In this test, fluorocarbon rubber was used as the seal material for the pipe joints for high-temperature pure water. Water-repellent materials are suitable as the sealing material in the present invention, but thermosetting resins can also be used as long as they do not undergo volumetric contraction during curing.

[0015]

According to the present invention, leakage due to crevice corrosion can be prevented and the integrity of the pressure seal portion can be maintained. As a result, long-term use is possible even for corrosive liquid piping. Further, when the present invention is applied to the connection of piping used in plants such as nuclear power plants, the reliability is significantly improved compared to the conventional example, and the effect is very large.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of a pipe connection structure according to the present invention.

FIG. 2 is a longitudinal sectional view for explaining the procedure before assembling the piping connection structure in FIG. 1;

FIG. 3 is a perspective view showing a conventional piping connection structure.

FIG. 4 is a vertical cross-sectional view showing a conventional composite type piping connection structure.

FIG. 5 is a curve diagram showing the relationship between temperature and strain of a shape memory alloy.

[Explanation of symbols]

1... Shape memory alloy pipe joint, 2, 2'... Connection piping, 3...
Liner, 4...Pressure seal part, 5...Gap, 6...Seal material,
7...Protruding part.

Claims (1)

[Claims] Claim 1: A pipe joint made of a shape memory alloy, a cylindrical metal liner inserted into the pipe joint, a pair of opposing connecting pipes inserted into the liner, and a pressure formed in the liner. A pipe connection structure characterized by comprising a sealing material filling a gap generated from a seal portion to a tip end of the connection pipe.