A method for manufacturing a circular metal tank, from an elongated sheet of metal. The upper and lower longitudinal edges of the metal sheet are bent to produce a first “L” bend and a second “chair” bend, respectively. The sheet of metal is moved in a helical trajectory such that the second bend comes into proximity above the first bend. The second bend and the first bend are welded together such that the wall of the cylindrical tank is formed. Welding of the bends serves to stress relieve or anneal the bent metal, thereby preventing cracks in the metal which may result in leaks and/or compromise the structural integrity of the tank. The first and second bends additionally cooperate to form a helical roller track on the outside of the tank. The tank is supported and rotated about its longitudinal axis on a plurality of rollers that engage the roller track.