PURPOSE: To make planing or construction in situ easier by arranging a fluid process pipe and an outer pipe surrounding the process pipe, fixing two pieces of lugs on the process pipe and arranging a pin in the space of the lugs.

CONSTITUTION: In respect to a double layer pipe composed of a inner fluid process pipe 1 in which a fluid flows and an outer pipe 3 surrounding the process pipe, each of two pairs of lug 2a, 2b fitting to the inner diameter of the outer pipe 3 is welded at the position opposite with each other in both left and right in horizontal direction to the center axle of the process pipe 1 and in its peripheral direction. Further, while arranging a pin 6 between the two pieces of lug 2a, 2b from the hole of the pipe 3, a cylindrical plate 4 of the pin 6 is welded in the outer pipe 3. As a result, the pipe construction becomes easier and construction time is shortened to a great extent.