Abstract: A traveling carriage is adapted to support and guide a welding head, a propelling apparatus, a wire feed mechanism and a reel for winding a continuous length of welding wire thereon. The welding unit is adapted to travel about an upstanding circumferential workpiece and is further adapted to be hingedly adjustable so as to permit adapting said welding unit to workpieces of varying diameters from a minimum practical dimension to an infinite diameter, that is, the welding machine can be adjusted to travel along a seam of two flat plates being joined. The welding unit has two spaced guide rollers on a side adjacent the work area with a hinge point spaced intermediate therebetween for changing from a working radius of the welder determined by the diameter of the workpiece to straight line configuration for performing a welding operation on a flat workpiece.