These machines can be used for welding H-beam and T-beam structural components as well as seam welding on large diameter pipe. The gantry travels on a track system and the welding arm assembly can move vertically to accommodate different welding operations and workpiece sizes. This welder is composed of a gantry carriage with welding arm, mechanical tracking unit, control system and welding system. The gantry consists of a bottom travel unit and an upper equipment platform. The operating panel and control box for the welding system are situated in the middle of the equipment for better control of the welding process and ease of operation. The machine is outfitted with a tandem welding system with control systems, ensuring superior welding efficiency and quality.