To relatively improve the strength of an electrically welded part by exposing an iron type metal layer at an inner circumferential surface of a metal pipe of the electrically welded part while penetrating a copper type metal layer.
A metal pipe 1 is of a double layer structure of an outer layer of iron type metal layer 2 and an inner layer of copper type metal layer 4 and is formed with an electrically welded part 6 across the whole length generated when the pipe 1 is electrically welded, in parallel with the axis of a pipe. A protrusion 2a is formed on the pipe inner peripheral side of the layer 2 at the pipe inner periperal surface side of the part 6, and the part 2A is exposed while it passes through the layer 4 so that an exposed surface of iron type metal with a constant width is formed. Accordingly, the strength of the part 6 can be relatively enhanced, and even in the case that the wall thickness T of the pipe 1 is samll, it is possible to prevent generation of an insufficient strength resulting from the part 6.
OZAKI KAZUNORI
TAKAHASHI MASAMI
ARAKAWA RYUICHI
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