Abstract: The present invention relates to a method of upgrading a tank or a method which involves the assembly of an inner tank within an existing outer tank. In the method of the present invention, rolled panel sections are inserted through a hole of an existing outer tank. The rolled panel sections are adjacently positioned within the existing outer tank and expanded so as to conform to the shape of the existing outer tank. End cap sections either flat or domed depending on the shape of the outer tank are also installed through the hole. All of the seams (axial and transverse) are sealed so as to provide for an inner tank within the outer tank that can rate as a stand-alone tank. Circumferential ribs are installed and attached along a length of the inner tank so as to provide for a structural rigidity of the inner tank.