Abstract: Apparatus for making a polyolefin tank within a metallic tank wherein fixtures are attached to the flanges of the fittings of the metallic tank to allow the polyolefin to flow through the tank fittings, while the metallic tank is mounted in a rotational molding apparatus, whereby the outer surfaces of the tank flanges are coated with polyolefin.

Abstract: A polyolefin lined tank consisting of a rigid polyolefin tank within a metallic tank wherein there is no adherence or bonding between the walls of the inner polyolefin tank and the outer metallic tank, but wherein a maximum of 0.04 inch clearance is obtained between the said walls. The polyolefin tank is formed in the metallic tank by a rotational molding technique wherein a high temperature paint or other suitable release agent is first applied to the inner walls of the metallic tank; the tank is heated; and polyolefin powder is placed in the heated tank. The polyolefin powder melts during rotation of the heated tank to thereby coat the inner walls of the tank; the tank is cooled, resulting in shrinkage of the polyolefin away from the metallic walls; during the cooling cycle, the interior of the lined tank is pressurized to control the shrinkage, resulting in minimum clearance between the outer and inner tanks, and stress relief of the inner polyolefin tank.