It depends on the weight of the steel beam and how the tank is constructed. Steel beams are designated by their shape, height and then pounds of steel per foot, i.e. W4x16. The W stands for wide flange (standard I beam) that is +/- 4" high and weighs 16#s per foot. The weight per foot is directly proportional to the strength of the beam.Be careful though with steel because at a certain size the beams have a camber manufactued into them so they are not perfectly flat.