Abstract: A submerged arc welding machine in which the edges of plates to be butt welded are supported on a channel fixed on a long rigid foundation beam. The plates are otherwise held on inverted caster wheel assemblies. A long rigid bridge spaced above the beam carries a track on which the arc welding apparatus carriage rides. The plate edge portions are held by vertically movable electromagnets, and the channel forms a magnetic shield so that the magnets do not affect the welding arc. Vertically movable rollers allow the plates to be positioned without interference from the channel. A copper backup bar in the channel has a groove that is filled with flux, and the bar is raised to hold the flux under the weld line. A shoe on the carriage lays flux in the groove when the carriage returns after a welding pass, and a vacuum pickup head cleans the groove for the shoe flux delivery. During the welding pass, the pickup head removes flux on opposite sides of the weld.