Abstract: Multi-walled panel-like structure having an upper and lower wall integrally bonded to support ribs located therein between with closed cell foam being placed in the interstitial spaces between the walls and ribs. Improved strength is provided by this apparatus and method of construction. The invention is particularly suited for retrofitting single wall tanks and tank bottoms to be double walled tanks and tank bottoms.

Abstract: Improved multi-wall containers and pipes for transporting fluids which have to be protected against leakage and mechanical forces, have an inner and outer wall separated by a continuous foam layer integrated into the containers. Improved strength and resistance to axial inertial pressure is provided by the method of manufacture using chopped glass fibers, continuous windings of glass fibers and suitable polyester resins and circumferential ribs spaced at stress points and integrally incorporated into the containment walls. Vessels produced according to the methods of the invention have a moment of inertia strength of about 4.67 in.sup.4 substantially eliminating torquing, buckling and rupture.