Abstract: A storage tank includes an exterior cover extending over at least a portion of the bottom wall of the tank, but does not cover or enclose the entire tank. The exterior cover is sealed to the tank around the portion of the bottom wall to contain any leakage through the bottom wall portion.

Abstract: A method for welding a first metallic material to a second metallic material where at least one of the first and second metallic materials have at least one surface which has an optical pattern thereon. The method comprises the steps of: arranging the first and second metallic materials into a final position in which they will be welded along a joint; directing focused energy at the joint from a Nd-YAG pulsed laser having an energy output in a range from about 10 Joules to about 30 Joules and a pulse length in a range from about 5 ms to about 9 ms; and traversing the joint at a predetermined welding speed while directing the focused energy such that a weld spot overlap in a range from about 50% to about 90% is maintained, resulting in a welded joint wherein a heat effect zone about the welded joint is minimized further resulting in minimal distortion and damage to an area of the optical pattern proximate to the welded joint.