Patent ID: 8146620

Claim:
A double walled pipe comprising an inner pipe wall and an outer pipe wall, said outer pipe wall comprising a series of spaced annular corrugations about and extending outwardly of said inner pipe wall, said inner pipe wall having an interior passage of a non circular cross section with at least one generally elongate wall segment forming at least 20% of the circumference of the non circular cross section; and wherein each annular corrugation includes a truss type structure adjacent each generally elongate wall segment; said truss type structure of the corrugation being of a variable height that progressively increases in height from adjacent opposed ends of the elongate wall segment to a center portion of the elongate wall segment; said spanning truss type structure extending outwardly from said inner pipe section and opposing inward deflection of a central portion of the elongate wall segment; said spanning truss type structure merging with remaining portions of said corrugation that extend outwardly of said inner pipe section adjacent said opposed ends of said elongate wall segment.