PURPOSE: To improve sealing performance by coaxially arranging inner and outer shells by forming an annular part between both, forming a flange by joining both shells in both end parts, and forming a flange surface by bending a plastic liner along an outside surface of the flange by extending the plastic liner for lining the inner shell inside surface side to the outside of an end part.

CONSTITUTION: A pipe segment 10 is constituted by doubly arranging an inner shell 11 and an outer shell 12 so as to form an annular part 14 between both shells 11, 12. Both end parts of both shells 11, 12 are joined so as to form a flange 16. A communicating port 15 is arranged in the outer shell 12 to connect a fluid detecting device. An inner plastic liner 13 lining an inside surface of the inner shell 11 is extended outward from an end part, and the extending part is bent along an outer flange surface 17 of the flange 16 to form a flange surface 18.