JPS596751B2 - How to join dissimilar metals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for joining a pressure tube and a metal tube, and in particular, in a pressure tube type nuclear reactor, when a pressure tube made of a zirconium alloy and an extension tube made of a different alloy thereof are joined, the pressure tube The present invention relates to a bonding method that can prevent hydrogenation from occurring.

The joining of dissimilar metals will be described below, taking as an example the joining of a pressure tube and an extension tube used in a pressure tube nuclear reactor.

A typical pressure tube reactor has a candorian tube that passes through a power randria tank filled with heavy water as a moderator, and a pressure tube loaded with nuclear fuel is installed inside the candorian tube. . Light water, which is cooling water, flows inside the pressure pipe. Carbon dioxide gas, which is a heat insulating material, flows between the power landlier pipe and the pressure pipe. This carbon dioxide gas is also used to detect damage to pressure pipes. An upper extension pipe and a lower extension pipe are connected to both ends of the pressure pipe. The material of pressure pipes is generally zirconium.
Niobium alloy is used and SU is used for the upper and lower extension tubes.
S403 is used. Since such dissimilar metals are difficult to weld together, they are joined by pressure bonding. The pressure pipe and the extension pipe are joined by a rolled joint. Joining by this rolled joint will be explained below based on FIG. 1. The lower part of the pressure tube 1 made of zirconium-niobium alloy is inserted into the upper part of the lower extension tube 2 made of SUS403.

At least the inner surface of the pressure tube 1 is subjected to autoclave treatment to form a dense oxide film. A stepped portion 3 is formed at the upper part of the lower extension tube 2, and an annular recess 4 is formed in the stepped portion 3. The lower part of the pressure pipe 1 inserted into the lower extension pipe 2 is not deformed as shown in FIG. 1, but has a straight pipe shape. An inner sleeve 5 is disposed inside the pressure pipe 1, and a convex portion 6 is formed on the outside of the inner sleeve 5 so as to correspond to the recess 4. The diameter of the convex portion 6 of the inner sleeve 5 is slightly smaller than the inner diameter of the pressure tube 1. A protrusion □ is provided at the lower part of the inner sleeve 5, and the protrusion 1 is inserted into a groove 8 provided inside the lower extension tube 2. After assembling the pressure pipe 1, lower extension pipe 2 and inner sleeve 5 as described above, a roll joint consisting of a roller 9, a mandrail 10, a frame 11, etc. for performing a roll joint is placed inside the inner sleeve 5. Insert the insert tool 23. By pushing the mandrail 10, the force of the roller 9 that presses the inner surface of the inner sleeve 5 is adjusted.
When the roller 9 is rotated while being pressed against the inner wall of the inner sleeve 5, the inner sleeve 5 is pushed out and the lower part of the pressure tube 1 is deformed as shown in FIG. In this way, the pressure pipe 1 and the lower extension pipe 2 are joined by pressure bonding. Although not shown, the upper extension pipe is also joined to the pressure pipe 1 in the same manner. The pressure pipe 1 is installed in the force landlier pipe with the upper and lower extension pipes joined together as described above.

When the nuclear reactor is operated, local hydrogenation occurs in the vicinity of point A in FIG. 1, that is, in the portion of the pressure tube 1 near the top of the inner sleeve 5, and there is a risk that the pressure tube 1 will be damaged. There is a similar risk of falling at the joint between the pressure pipe 1 and the upper extension pipe. SUMMARY OF THE INVENTION An object of the present invention is to overcome the drawbacks of the prior art described above and to provide a method for joining a pressure pipe and a metal pipe, which can prevent damage caused by local hydrogenation of the pressure pipe.

A feature of the present invention is that a pressure tube made of a zirconium niobium alloy containing a small amount of niobium and the remainder being substantially zirconium and a metal tube having a different main component are integrated by pressure bonding, Meanwhile, each integrated metal tube is
The purpose is to anneal the pressure pipe in a temperature range of 00°C or higher and at which the pressure pipe does not age harden, and then apply a corrosion-resistant oxide coating treatment to the pressure pipe.

The present invention was made based on the investigation of the cause of pressure pipe breakage described below.

There are two causes for pressure pipe breakage. Firstly, a large tensile residual stress is generated in a portion of the pressure pipe near point A in FIG. The second problem is that the corrosion-resistant oxide film formed on the pressure pipe surface is locally peeled off during pressure bonding (rolled joint). When the pressure pipe 1 is inserted into the lower extension pipe 2 and joined by a rolled joint, the upper part of the inner sleeve 5, that is, A in FIG.
The portion of the pressure tube 1 near the point is subjected to an elbow-sized compression process, and therefore a large tensile residual stress is generated in the portion of the pressure tube 1 near the point A.

When a rolled joint as shown in Figure 1 is performed, approximately 0.3
A residual stress of ~42Kv4J results. In zirconium and its alloys, hydrogen is concentrated in parts that have been subjected to large compression processes and in parts where tensile residual stress exists inside. FIG. 2 shows the results of an experiment using a test piece of Zircaloy-2, which is a type of zirconium alloy, rolled into a tubular shape.

Referring to Fig. 2 and Fig. 5 described below, the normalized hydrogen amount is determined by measuring the hydrogen concentration (unit: Ppn) at each part in the thickness direction of a test piece that has been hydrogenated in an experiment, and the measurement result ( Unit P
pm) to the hydrogen concentration originally present in the test piece (unit: P
pm) is divided by the reference hydrogen concentration (unit: Ppm) arbitrarily determined for each of FIGS. 2 and 5. For this reason, there is no unit for the normalized hydrogen amount. A solid line 12 shows the residual stress distribution in the radial cross section of the tube wall of the above-mentioned rolled test piece. Also, 13
shows the hydrogen concentration distribution in the radial direction h plane of the tube wall of the tubular test piece when the above tubular test piece is hydrogenated by heating in saturated water containing lithium hydroxide. solid line 1
In No. 2, positive residual stress indicates tensile residual stress, and negative residual stress indicates compressive residual stress. From a comparison between the solid line 12 and the broken line 13, it can be seen that there is a lot of hydrogen in the tube wall portion where the tensile residual stress is large, and there is less hydrogen in the tube wall portion where the compressive residual stress is large. Hydrogenation is progressing in areas with a lot of hydrogen.
FIG. 3 shows the results of scratching the outer surface of a tubular test piece to a depth of about 0.2 rrrm and then heating it in an aqueous hydrofluoric acid solution to hydrogenate it. The black parts that look like cracks in the cross section of the tube wall are the parts that are hydrogenated. It can be seen that hydrogenation in the scratched area is more advanced than in other areas. FIG. 4 shows the results of compressing the inner surface of a tubular test piece by forcefully pressing a steel ball therein, and then hydrogenating it using a hydrofluoric acid aqueous solution in the same manner as shown in FIG. Even in this case, hydrogenation is significant in the areas that have undergone compression processing. In the part of the pressure pipe 1 near point A shown in FIG. 1, the upper end of the inner sleeve 5 is strongly pressed during the rolled joint, and is subjected to a compressive load similar to that described above, resulting in a tensile residual core. Because of the force generated, localized significant hydrogenation occurs.
By the way, a tubular test piece that had been rolled and had properties similar to those shown in Figure 2 was annealed in a vacuum at a temperature of about 450°C for about 2 hours to remove stress within the tubular test piece. I did it.

The residual stress distribution and hydrogen concentration distribution in the radial cross section of the tube wall of the tubular specimen subjected to such treatment are
As shown in the figure. The solid line 14 shows the residual force distribution, and the broken line 15 shows
Similarly to the broken line 13 shown in FIG. 2, it shows the hydrogen concentration distribution after hydrogenation using saturated water containing lithium hydroxide. As is clear from the solid line 14, when the above-described annealing is performed, the residual stress in the tube wall of the tubular test piece is reduced and its distribution is also flattened. Furthermore, as shown in Fig. 5, the hydrogen concentration distribution also shows a tendency to become flat with a smaller difference between the maximum and minimum compared to Fig. 2. The amount of hydrogen in the portion where a large amount of hydrogen was present is reduced as shown in the left side portion of FIG. 5, which corresponds to the left side portion of FIG. 21.
Also, the reference hydrogen concentration shown in Fig. 5 is set to a lower value than the reference hydrogen concentration shown in Fig. 2, so when comparing Figs. It is known that even when subtracting , the ratio shown in Figure 5 is smaller. Similar results can be obtained with zirconium-niobium alloys. From these experimental results, in order to prevent local hydrogenation near the ^ point, it is desirable to anneal the pressure tube and the lower extension tube after rolling them. Zirconium alloys are widely used as nuclear reactor materials because they have better corrosion resistance than other metals.

However, in order to further improve the corrosion resistance against hydrogen and the like, a dense corrosion-resistant oxide film is formed on the surface of the cladding tube made of Zircaloy-12 alloy and the pressure tube made of zirconium-niobium alloy. This corrosion-resistant oxide film is obtained by heating a zirconium alloy in superheated steam at about 400° C., and usually forms a dense layer several microns thick.
This treatment is generally referred to as autoclave treatment. Zirconium alloys that have been autoclaved and have a uniform corrosion-resistant oxide film on the surface have excellent corrosion resistance, but if the corrosion-resistant oxide film peels off locally, the corrosion resistance becomes uneven and the zirconium alloy Local hydrogenation may occur. This will be explained using FIG. 6th
In the figure, the vertical axis shows the hydrogen concentration, the upper horizontal axis shows the degree of width (unit: °C), and the lower horizontal axis shows the reciprocal of the absolute temperature T (unit: 0 K.).The vertical axis shows the hydrogen concentration and temperature. It is commonly used to show the relationship between Furthermore, the 6th
The upper horizontal axis and lower horizontal axis of the figure are shown in correspondence. 6th
The figure shows the relationship between the temperature of the above-mentioned Zircaloy-12 tubular test piece and the hydrogen concentration within the test piece, which has a hydrogenation rate. In Fig. 6, the solid line 16 represents the hydrogenation rate when a corrosion-resistant oxide film was formed on the surface of the tubular specimen through autoclave treatment, and the dashed line 17 represents the hydrogenation rate when a corrosion-resistant oxide film was not formed on the surface of the tubular specimen. Hydrogenation rate is shown. This result shows that a tubular test piece with a corrosion-resistant oxide film formed on its surface and a corrosion-resistant oxide film were placed in a cylindrical electric furnace with a temperature distribution in the axial direction and a hydrogen gas atmosphere of about 1 atm inside. Insert an unformed tubular specimen and hold approximately 2
The results were obtained by heating for 0 hours and measuring the hydrogen concentration within these tubular specimens. Death, dashed line 18 in Figure 6
indicates the initial hydrogen concentration originally contained in the tubular specimen. In the width range of 300℃ or higher, the tip of the corrosion-resistant oxide film! The hydrogen velocity of the tubular test piece is extremely high, approximately 70 times that of the tubular test piece with a corrosion-resistant oxide film formed thereon.

Therefore, when a zirconium alloy with a corrosion-resistant oxide film formed thereon is used in a corrosive environment, such as in a nuclear reactor, if the corrosion-resistant oxide film on the surface peels off locally, local hydrogenation occurs in the peeled area. progresses significantly. The above phenomenon is also observed in zirconium-niobium alloys. In the conventional connection method, the pressure pipe 1 having a corrosion-resistant oxide film and the extension pipe 2 are rolled jointed, so that the inner sleeve 5
Since it is pressed against the inner surface of the pressure pipe 1, there is a risk that the corrosion-resistant oxide film will peel off. When a zirconium alloy is hydrogenated due to the above reasons, zirconium hydride precipitates at room temperature.

For this reason, the zirconium alloy becomes extremely brittle. Also,
The hydride itself is brittle and has a different crystal shape and density from zirconium alloys. Therefore, under usage conditions that involve thermal cycles such as starting and stopping a nuclear reactor, there is a high risk that the material will crack due to hydrogenation. The present invention has been made based on the above study results, and according to the present invention, even when Group I V titanium group or its alloy is used in a corrosive environment, hydrogenation of the material can be prevented, A method for joining a group IV titanium group or its alloy with a dissimilar metal made of a different material without causing damage can be obtained. A preferred embodiment of the present invention will be described below with reference to FIG. 19 is a rolled joint process.

The pressure tube 1 used in the pressure tube nuclear reactor sent to the rolled joint step 19 is made of rolled zirconium-2.5% niobium alloy, and is subjected to solution treatment at about 870° C. for about 15 minutes. After that, perform the Yakijinre, and then about 5
It is heat-treated at 00°C for about 24 hours to give it properties suitable for use as a pressure tube in a nuclear reactor. This pressure pipe 1 has an inner diameter of about 1187 m, a wall thickness of about 4.3 wrm, and a length of about 4 m. A lower extension tube 2 and an upper extension tube are respectively joined to both ends of the pressure tube 1 in a rolled joint process.

, Rolled joint is a kind of crimp joint. The roll joint method is the same as the conventional method described above. The pressure tube 1 has extension tubes connected to both ends,
It is sent to an annealing process 20. This annealing is performed in a vacuum atmosphere, and the time required for annealing is approximately 2 hours. The residual stress is considerably removed when the annealing temperature is about 400°C or higher, and is completely removed at about 450°C. However, in the case of zirconium-niobium alloys, when the annealing temperature is about 500°C or higher, age hardening occurs, which changes and deteriorates the characteristics of the pressure tube, which has already been given good characteristics for use in nuclear reactors. Not suitable for pressure pipe applications. It is preferable to set the temperature to 400° C. or higher and within a temperature range in which age hardening does not occur. In other words, niobium is 2
．． In a pressure tube made of a zirconium-niobium alloy in which the balance is substantially zirconium, the annealing temperature is 5%.
When the temperature exceeds 00°C, minute precipitates appear in the zirconium-niobium alloy after solution treatment due to age hardening. Therefore, a potential difference occurs between the solution-treated alloy and the three precipitates, making the pressure tube susceptible to corrosion. Hydrogen generated by corrosion of the pressure pipe further promotes hydrogenation of the pressure pipe. Therefore, the annealing temperature of the pressure tube should be within a temperature range that does not cause age hardening. When the annealing step 20 is completed, the pressure tube is sent to an autoclave treatment step 21. The autoclave treatment is carried out by heating the pressure tube with superheated steam at about 450° C., as described above. As a result, a corrosion-resistant oxide film is formed only on the surface of the pressure pipe. Since the extension tube 4 is made of stainless steel, no corrosion-resistant oxide film is formed on its surface. In this example, a zirconium-niobium alloy pressure tube and a SUS4O
After rolling joint with the extension tube of 3, annealing process 2
Since the material passes through the autoclave treatment step 21, the thermal expansion differs depending on the material, which may cause loosening of the load joint and loss of airtightness. For this reason, after attaching a tightening sleeve made of zirconium-niobium alloy to the outside of the extension tube 2 near the joint between the pressure tube 1 and the extension tube 2 shown in FIG. 1, annealing and autoclaving are performed. It's good to do it. A corrosion-resistant oxide film can be formed on the surface of the pressure pipe without heating as in autoclaving. An example of this is anodic oxidation. This can form a corrosion-resistant oxide film on pressure pipes in a normal temperature atmosphere. In addition, a corrosion-resistant oxide film can also be formed chemically. Finally, the pressure tube is sent to an inspection process 22 to check for leakage from the joint between the pressure tube and the extension tube, and those that have passed this inspection process 22 are installed in a pressure tube reactor. . By joining the pressure pipe and the extension pipe as described above, the two causes of local hydrogenation occurring in the pressure pipe can be eliminated. In other words, the tensile residual stress inside the pressure pipe caused by the rolled joint can be removed by annealing, and a corrosion-resistant oxide film is formed on the pressure pipe surface after the rolled joint. The risk of peeling off is eliminated. Therefore, even if the pressure pipe made by the process of this example is installed in a nuclear reactor and the reactor is operated, local hydrogenation will not occur in the pressure pipe, and there is no risk of damage to the pressure pipe. Gender disappears. After rolling joint the pressure pipe and extension pipe,
Annealing may also be carried out in air.

In this case, an oxide film is formed on the pressure tube surface by annealing. This oxide film is not dense and has little effect on corrosion resistance. Therefore, after removing the oxide film from the pressure pipe surface, it is necessary to form a dense corrosion-resistant oxide film on the pressure pipe surface by autoclave treatment and anodic oxidation. According to the present invention, a pressure tube made of a zirconium-niobium alloy containing a small amount of niobium and the remainder being substantially zirconium absorbs hydrogen to form a hydride and becomes brittle. The phenomenon can be made into a flower market.

[Brief explanation of the drawing]

Fig. 1 is a half-longitudinal cross-sectional view illustrating the rolled joint between the pressure pipe and the lower extension pipe, and Fig. 2 shows the residual residue in the radial cross section of the pipe wall of a tubular specimen that has only been subjected to rolling processing. Characteristic diagram showing the stress distribution and hydrogen concentration distribution. Figure 3 is a local cross-sectional view of the tubular specimen showing the hydrogenation situation when the outer surface of the tubular specimen is scratched. Figure 4 is the characteristic diagram of the tubular specimen. Local F of a tubular specimen showing the hydrogenation status of the part where a steel ball was pressed against the inner surface of the F! FIG. 5 is a characteristic diagram showing the residual stress distribution and hydrogen concentration distribution in the radial cross section of the tube wall of a tube test piece that was annealed after rolling, and FIG. A characteristic diagram showing the difference in hydrogenation rate between when the piece has a corrosion-resistant oxide film and when it does not. FIG. 7 is a process diagram showing a method for joining dissimilar metals according to a preferred embodiment of the present invention. Explanation of symbols: 1...Pressure pipe, 2...Lower extension tube, 5...Inner sleeve, 19...
- Rolled joint process, 20... annealing process, 21... autoclave treatment process.

Claims (1)

[Claims] 1 The ends of a pressure tube made of a zirconium-niobium alloy installed in a pressure tube nuclear reactor and a metal tube whose composition is different from that of the pressure tube are crimped and joined together, and then the integrated A method for joining a pressure tube and a metal tube, characterized in that each tube is annealed at 400° C. or higher in a temperature range at which the pressure tube does not age harden, and then a corrosion-resistant oxide coating treatment is applied to the pressure tube.