Concentric insulating conduit

A concentric double walled thermal insulating conduit for forming a tubular string in a subterranean well to transport a heated fluid between the surface of the well and a subterranean location while minimizing the heat loss from the heated fluid during transport, comprising:

• an outer tubular member;
• an inner tubular member, the inner and outer tubular member being attached at each end by means of a rigid sealed connection with the inner tubular member being in prestress tension and the outer tubular member being in prestress compression;
• an annular insulating cavity defined between the inner and outer tubular member and extending along substantially the entire length of the concentric walled conduit;
• a fibrous blanket insulating material disposed in said annular insulating cavity;
• and at least one metallic centralizing means for supporting the inner tubular member relative to the outer tubular member and located intermediate the ends thereof;
• the centralizing means comprising a cylindrical section at least partially concentrically overlapping a portion of the inner tubular member and multiple load bearing, rigid support sections affixed to the cylindrical section, each comprising a planar section extending radially between the inner and outer tubular members and axially relative to the inner tubular member, each support section being in contact with the interior of the outer tubular member, and an insulating substrate between the cylindrical section and the inner tubular member whereby the centralizing means prevents radial deflection of the inner tubular member relative to the outer tubular member intermediate the attached ends thereof.