JPH0734991B2 - Welding method for outer tube of thin wall double tube - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for welding an outer pipe of a thin-walled thick double pipe.

(Prior Art) In heat exchange of a corrosive fluid, it is necessary to consider both the corrosiveness of the fluid on the inner surface of the pipe and the fluid on the outer surface of the tube as the material of the heat exchange tube. Or
A double tube as shown in FIG. 2 in which the materials capable of withstanding each is duplicated is used. For example, in FIG. 2, SUS304 is used for the inner tube 1 for the fluid inside the tube, and Cr-Mo steel is used for the outer tube 2 when the outer fluid contains chlorinated ions Cl ⁻ . At this time, SUS304 is used for the outer tube 3 in the vicinity of the joint between the tube and the tube plate so that the tube and the tube sheet will not become dissimilar materials.

Here, when joining the outer pipes 2 and 3, generally, TIG welding is performed as thin-walled pipe joining, but in welding with constant heat input, as shown in FIG. Is increased, and burn-through is likely to occur on the inner surface of the pipe. So the fourth
As shown in the figure, there is a method of welding by changing the heat input continuously (in the case of (a)) or intermittently (in the case of (b)), but it is difficult to control the heat input and stable welding I couldn't get it.

(Problems to be Solved by the Invention) An object of the present invention is to solve the above-mentioned drawbacks of the conventional method and to perform a normal welding process (constant heat input) in circumferential welding of thin-walled double pipes.
To provide a more stable penetration.

(Means for Solving the Problems) The present invention relates to a method for welding a butt joint of an outer pipe of a thin-walled double pipe, in which two wall plates are connected by sandwiching an inner pipe surface corresponding to a welded portion. , A cooling chamber is configured by slidingly contacting the inner surface of the inner pipe at the peripheral edge of the wall plate, a cooling water supply pipe and a discharge pipe are connected to the wall plate, and cooling water is caused to flow at a predetermined flow rate between the wall plates. Is a method of welding an outer pipe of a thin-walled double-walled pipe, wherein the outer pipe is welded while maintaining a predetermined pressure.

That is, as described above, in the method of FIG. 3, the welding heat is not sufficiently diffused as welding progresses, so-called heat sticks and the penetration increases, and the method of FIG.
I tried to predict that and try to control heat input,
The present invention is characterized in that the heat of welding is positively absorbed by cooling the inner surface of the pipe with water, and stable penetration can be obtained even with a constant heat input.

(Operation) The present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram of a welding method according to the present invention.

In the figure, 1 is an inner pipe, 2 is an outer pipe, 3 is an outer pipe made of the same material as the inner pipe provided at the end of the double pipe, 4 is a water-cooling jig body in which a front wall and a rear wall are connected, 5 Is an O-ring, 6 is a space, 7 is a water inlet pipe,
8 is a water outlet pipe, 9 is a welding torch, 10 is a tungsten electrode, 11 is an arc, and 12 is a shield gas.

The outer diameter of the front and rear walls of the water cooling jig body 4 is made smaller than the inner diameter of the inner pipe 1, and the inner pipe 1 is inserted through an O-ring 5 provided on the outer diameter portion of the front and rear walls.
It adheres to the inner surface. As a result, when water is introduced from the water inlet pipe 7, the space 6 is filled with water, and the water exits from the water outlet pipe 8 to circulate the water. At this time, at first, the water outlet pipe 8 should be as high as possible in order to completely eliminate the air that has entered the space 6, but if the water injection is done vigorously, as shown in the figure, the inner pipe 1 and water Even if the outlet pipe 8 has a space of 2 to 3 mm, the air is completely excluded.

(Effect of the invention) In this way, the inner surface of the inner pipe 1 immediately below the welded portion is in direct contact with water, and since water is circulating, the heat generated by welding is absorbed more and more, and the outer pipes 2, 3 are joined together. Even if the circumference of the part is continuously welded, so-called heat is not accumulated and welding is always performed under constant conditions, and the penetration is stable (constant).

Examples will be shown below.

Example In FIG. 1, the inner tube 1 is made of SUS30 having an inner diameter of 25 mm and a wall thickness of 1.5 mm.
4. The outer tube 2 is a double tube of 2 1 / 4Cr-1Mo steel with an outer diameter of 31 mm and a wall thickness of 1.5 mm, and the outer tube 3 is SUS304 steel with an outer diameter of 31 mm and a wall thickness of 1.5 mm. Was welded using SUS309 series wire 1.2φ. The results are shown in Table 1.

In the case of Nos. 1, 2, and 3 which are not water-cooled, burn-through or penetration depth changes during welding. On the other hand, in the case of the numbers 4, 5, 6, 7, 8 and 9 for cooling the inner pipe of the present invention with water, the penetration is constant and stable welding can be performed.

[Brief description of drawings]

FIG. 1 is an explanatory view of a welding method according to the present invention. Second
The figure is a schematic diagram of the structure of a thin-walled double tube. 3 and 4 show the relationship between heat input and penetration or burn-through in the conventional welding method.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-58-154487 (JP, A) Actually opened 55-154696 (JP, U) Actually opened 54-73318 (JP, U)

Claims (1)

[Claims] Claim: What is claimed is: 1. In a method for welding a butt joint of an outer pipe of a thin double-walled pipe, the inner pipe surface corresponding to the welded portion is sandwiched between 2
A cooling chamber is formed by connecting a plurality of wall plates and slidingly contacting the inner surface of the inner pipe at the peripheral edge of the wall plates, connecting a cooling water supply pipe and a discharge pipe to the wall plates, and cooling water at a predetermined flow rate. A method for welding an outer pipe of a thin-walled double pipe, characterized in that the outer pipe is welded while maintaining a predetermined pressure between the wall plates.