PURPOSE: To make it possible to insulate two metallic pipes electrically from each other and make needless insulation joints adjacent to the wall penetration area by arranging two metallic pipes at an interval and connecting the interval space with a fiber reinforced plastic layer.

CONSTITUTION: The pipe unit consists of two metallic pipes 1 which face each other at an interval of appropriate length with the central line matched and FRP layer 2 which not only covers the outer plane of the metallic pipes but also connects the two metallic pipes. Outside of the FPR layer 2, there is a ring-like protruded part 3 which is made by increasing partially the number of lamination. The protruded part 3 is formed in the external oblique perimeter against the central line of the metallic pipes 1.