This is an invention relating to the local nitrogen replacement method "L Braze," which simplifies the oxidation prevention process for brazing connection of piping and enables labor saving in on-site work.

When pipe joining is performed by brazing, the formation of an oxide film on the inner surface of the pipe is prevented by introducing a non-oxidizing gas such as nitrogen into the pipe. In this case, although nitrogen gas was flowed throughout the entire piping system in the past, since this consumes a large amount of nitrogen gas, it is not economical and a large nitrogen cylinder is necessary, which required a large amount of labor to transport.

Therefore, the present invention has the following steps in a joining method in which the end portion 2a of pipe 2 is inserted and brazed to the enlarged diameter portion 10 provided at the end portion 1a of pipe 1.

1. 1.An opening portion 11 is provided at the end portion 2a of pipe 2 (insertion side).
2. 2.The end portion 2a of pipe 2 is inserted into the enlarged diameter portion 10 to the position before the opening portion 11 is inserted into the enlarged diameter portion 10.
3. 3.Inject non-oxidizing gas (nitrogen or the like) from the opening 11 into the piping.
4. 4.Insert the end portion 2a of pipe 2 to the position where the opening 11 is inserted into the enlarged diameter portion 10.
5. 5. Braze and join the ends of the two pipes to each other.

With the present invention, since the non-oxidizing gas may be injected only in the vicinity of the end portions of the two pipes, injection of the non-oxidizing gas can be done with a small quantity and in a short time. In addition, since no large nitrogen gas cylinder is required, transportation of the cylinder can be made easier. Furthermore, since the opening for injecting the non-oxidizing gas into the pipe is not exposed to the outside after brazing, there is no problem in terms of strength.

[Legend]
1 Pipe 1, 2 Pipe 2, 10 Enlarged diameter portion, 11 Opening portion, 20 Nozzle, 25 Brazing material