Abstract: A fluted tube, defined by a multiplicity of parallel flutes extending over the length of the tube, is constructed by providing a flat portion of sheet metal, forming a series of undulations in one portion to form a corrugated section which is allowed to adjoin and be continuous with a flat section at a transition line or point. The sheet is engaged with tynes at the transition point and simultaneously welded as it is rolled into a spiral to form a multiplicity of flutes each bound by an undulation and a portion of the flat sheet metal. The flat sheet section can have a sufficient length so that it defines the last exterior layer of the spirally wound fluted structure to form a smooth walled, tubular envelope.