JPS63252679A - Welding method for double pipe - Google Patents

Abstract

PURPOSE:To obtain a double pipe with the high reliability by performing the butt welding of inner tubes and afterward, using high-melting point material for the outside periphery of the inner pipe to charge it in a cavity and afterward, performing the butt welding of outer pipe. CONSTITUTION:After the butt welding 3 is performed on the inner pipe 1, the external surface of the inner pipe 1 is finished on a grinder and a ceramics sheet 4 is wound round the inner pipe 1 a as the high melting-point material. Next, sleeves 5 which are divided into two in the longitudinal direction are charged therein and the longitudinal welding 7 is performed on two places and then, the girth welding 6 is performed on two places. Even if penetration beads are produced on the longitudinal and girth welding of the outer pipe 2, the ceramics sheet 4 is not molten and the space is maintained between the outer pipe 2 and the inner pipe 1. Accordingly, even if the heat input at the time of welding is not strictly controlled, the penetration required for maintaining the weld strength is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for welding a double-structured pipe for a steam generator used in a fast breeder reactor.

(Prior Art) One type of steam generator used in fast breeder reactors is an integrated once-through steam generator shown in FIG. This is pressure vessel 10
The water supplied from the inlet nozzle 13 at one end passes through a large number of heat transfer tubes 8 and is discharged from the outlet nozzle I4 at the other end. Heat is received from the outside of the heat transfer tube 8 by the liquid Na, and the heat is exchanged to become steam. As shown in FIGS. 9(a) and 9(b), this heat transfer tube 8 consists of an inner tube 1 and an outer tube 2, and has a double tube structure in which the outer surface of the inner tube 1 and the inner surface of the outer tube 2 are in contact with each other. This is to prevent accidents caused by leakage of water from the inner tube 1 and leakage of liquid Na from the outer tube 2, and even if a crack occurs in the inner tube 1 or the outer tube 2, the Leakage can be detected by using the detection groove 23 provided at the boundary between the inner and outer tubes before penetrating the heavy structure tube 8. That is, He is introduced into the detection groove 23, and H
By detecting leakage from changes in pressure and humidity,
Explosion accidents can be prevented. Double structure pipe 8
The inner tube 1 alone has a wall thickness that can withstand the pressure of high-pressure steam, but the outer tube 2 has a wall thickness equal to the detection groove 23 so that it can withstand the internal pressure if a crack occurs in the inner tube 1. It is designed to add strength. When performing butt welding to connect such double structure pipes 8 in the longitudinal direction,
A technique for not impairing the function of the detection groove 23 described above has been disclosed. Figure 10 is JP-A-60-248.
Showing the double +q pipe making 8 disclosed in Publication No. 901,
A sleeve 5 having an inner diameter that allows the outer tube 2 to be easily inserted is inserted in advance, and after butt welding 3 of the inner tube 1 is performed, a predetermined detection groove 23 is secured, and the sleeve 5 is slid. After this, fillet welding 24 is performed between the outer tube 2 and the sleeve 5. In addition, the fruit bark (the prior art devised in No. 62-6072 is shown in Figure 11.12,
In the figure, a sleeve 5 is prepared using a tube material with the same dimensions as the outer tube 2 and machined to have an inner diameter larger than the outer diameter of the inner tube 1.
After butt welding 3 of the inner tube 1 is performed, a sleeve 5 is placed over the outer tube 2 and circumferential welding 6 is performed to secure the detection groove 23. For this reason, it is necessary to divide the sleeve 5 into elongated parts in the longitudinal direction, insert them between the outer tubes 2, and perform longitudinal welding 7 on the divided parts. Also, what is shown in Figure 12 is
The inner diameter of the butt ends of the outer tube 2 is machined in advance to form the detection groove 2.
3, and the inner tube 1 and outer tube 2 are simultaneously welded by electron beam welding.

(Problems to be Solved by the Invention) The above-mentioned conventional techniques and prior art have the following problems.

The prior art shown in FIG. 1O requires homogeneous materials with different diameters for the sleeve 5, and the external dimensions of the welded portion are larger than other heat exchanger tube portions. There have been problems in that the heat exchanger tubes 8 may not match the positions of the heat exchanger tubes 8, and that it becomes difficult to bend the heat exchanger tubes 8 into a helical shape.

In the prior art shown in FIG. 11, the gap between the inner tube 1 and the outer tube 2 at the welded portion is approximately IIm+inside and outside, making it difficult to secure dimensions when welding the outer tube 2. In other words, since the sleeve 5 only has the minimum required wall thickness, uranami welding is required, but the detection groove 23 has a small gap between the inner tube 1 and the outer tube 2, so the inner tube 1 and the outer tube 2 are There was a problem in that there was a risk that the pipe 2 would come into contact with the pipe 2 due to welding. Further, the prior art shown in FIG. 12 has similar problems, and electron beam welding, which is performed while holding a long tube in a vacuum, also has problems in terms of processing equipment.

It is an object of the present invention to solve the above-mentioned problems and provide a method for butt welding double-groove pipes, which can reliably and easily secure the above-mentioned voids.

(Means for solving problems) After the above purpose carries out butt welding of the inner pipe.

A material with a high melting point is used on the outer periphery of the inner tube to fill the above gap,
This is then achieved by butt welding the outer tube.

(Function) Since the high melting point material filled in the void does not melt during welding of the outer tube, at least the space occupied by the high melting point material is maintained, so welding can be performed without losing the function of the leak detection groove. is possible.

(Example) A method for welding a double-structured pipe according to the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the welding procedure of the present invention.

FIG. 1(a) shows a welded inner tube 1 and a grooved outer tube 2. After butt welding 3 is performed on the inner tube 1, the outer surface of the inner tube 1 is finished with a grinder. When the wall thickness of the inner tube 1 is 2 to 3 nn, the width A of the groove may be as long as the width required for the TIG welding torch.

The cut is approximately 20mm inside and outside, the depth B is 1+m inside and outside, and the cut C is 3m inside and outside. Next, as shown in FIG. 4(b), a ceramic sheet 4 as a high melting point material is wrapped around the inner tube 1. In this example, the ceramic sheet 4 used was an AQ, O, +Sio2 ceramic sheet. Since this material is porous, there is no problem in filling it with an inert gas such as He, but in order to ensure leak detection, it is preferable to double it as shown in the figure, and the thickness should be approximately 1 mm. to fit within the groove. The width of the ceramic sheet 4 is preferably wider than the groove width A (23 mm + inside and outside, leaving a space in the installed state. Next, in the same figure (
As shown in c), the sleeve 5 divided into two in the longitudinal direction is inserted, and as shown in FIG. 3, longitudinal welding 7 is first performed at two locations, and then circumferential welding 6 is performed at two locations. Since the wall thickness was thin, TIG welding was used.

Even if a back wave is produced in the longitudinal and circumferential welds of the outer tube 2, the ceramic sheet 4 does not melt, and a space is secured between the outer tube 2 and the inner tube 1. Therefore, the penetration required to ensure weld strength can be obtained without strict heat input control during welding work. Further, the space facilitates the flow of an inert gas such as He. FIG. 4 shows another embodiment of the present invention, which differs from the embodiment in FIG. That's the point. As a result, the circumferential welded portion 3 is not covered with the ceramic sheet 4, which facilitates non-destructive inspection using radiation and improves the reliability of the welded portion.

FIG. 5 shows still another embodiment, in which a ceramic tube 9 is placed in the groove in place of the ceramic sheet 4 in FIG. 4 so that its longitudinal axis is parallel to the axis of the tube 8. The double structure tube 8 containing the ceramic tube 9 is shown in FIG.
FIG. 6 is a longitudinal cross-sectional view of the part that does not include the ceramic tube 9, and FIG.
1? ! FIG.

In this embodiment, even if the weld metal comes into contact with the inner tube 1 due to excessive weld penetration as shown in FIG. 5(b), no problem will occur. Further, the cross-sectional shape of the ceramic tube 9 may be not only circular but also semicircular as shown in FIG.

As described above, the heat exchanger tube having the detection groove can be reliably and easily welded using a tube material of the same quality and size as the outer tube of the double-structured tube 8.

(9. Bright effect) By implementing the present invention, a double-structured tube with high welding reliability can be provided at a low cost, and the design of a heat exchanger tube for a steam generator in a fast breeder reactor has become easier.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the procedure of the welding method for a double-structured pipe according to the present invention in a longitudinal cross-sectional view, FIG. 2 is a cross-sectional view of FIG. 1 (Q), and FIG. FIG. 4 is a longitudinal sectional view showing another embodiment of the present invention; FIG. 5 is a longitudinal sectional view showing still another embodiment of the invention; FIG. The figure is a cross-sectional view of Figure 5, Figure 7 is another example of the ceramic tube shown in Figure 6, Figure 8 is a longitudinal cross-sectional view of an integral once-through steam generator, and Figure 9 is a general double structure. FIG. 10 is a front view and a longitudinal sectional view of a prior art double-walled pipe, and FIGS. 11 and 12 are longitudinal sectional views of a prior art double-walled pipe. 1... Inner tube 2... Outer tube 3... Inner tube welded part 4... Ceramic sheet 5... Sleeve 6... Outer tube circumferential welded part 7... Outer pipe longitudinal welded part 8 ...Double structure tube 9...Ceramics tube

Claims (1)

[Claims] 1. Consisting of an outer tube and an inner tube fitted into the inner diameter of the outer tube, the annular gap facing the welded portion of the outer tube and the inner tube and the inner tube is defined as the outer tube. In the method for welding a double-structured pipe between the inner pipe and the inner pipe, after butt welding the inner pipe and the inner pipe, at least a portion of the annular gap is filled with a porous high melting point material, and then the outer pipe is welded with a porous high melting point material. A method for welding a double-structured pipe, the method comprising butt welding the outer pipe through a sleeve having the same outer diameter as the outer pipe. 2. The method of welding a double-structured pipe according to claim 1, characterized in that the high melting point material is a ceramic sheet, and the ceramic sheet is wrapped around the outer circumference of the inner pipe facing the annular gap. 3. The double structure pipe according to claim 1, characterized in that the high melting point material is a ceramic sheet, which is wrapped around the outer periphery of the inner pipe facing the annular gap, avoiding the weld bead part. Welding method. 4. Ceramic tubes are used as the high melting point material, and these are distributed in multiple locations within the annular gap in a direction in which the longitudinal axis of the tube and the axis of the double-walled tube are parallel to each other. A method of welding a double structure pipe according to claim 1, characterized in that: