Abstract: An arrangement for assembling a metal storage tank which includes a framework having a stationary end frame portion and a carriage selectively movable toward and away from the end frame portion on rails disposed on the framework. Cylindrical tank sections, positioned on roller members mounted between the rails, are urged into a successive abutting arrangement by movement of the carriage toward the stationary end frame portion and, subsequently, rotated for on-site seam welding, i.e. one cylindrical tank section to another. The end frame portion and the carriage both include freely rotatable roller members disposed normally with respect to each other, in a vertical plane, to reduce drag upon cylindrical tank section rotation.