Abstract: A welding apparatus and method is provided for automatically welding a stack of two or more metal tubes together. The tubes are stacked such that there is a pair of opposed longitudinal interfaces (or seams) between each tube in the stack. The welding apparatus broadly comprises: a stationary welding means for forming welds along the seams between each tube; a drive means for linearly advancing the stack of tubes relative to the welding means and for preventing separation of the tubes as the welds are being formed; and an alignment means for continuously and accurately keeping the stack of tubes in proper alignment as the drive means advances the tubes. The welding method broadly comprises: aligning the tubes in accurate stacked relation; holding the tubes together in stacked relation; advancing the tubes relative to a stationary welding means while maintaining the tubes in stacked relation; and welding the opposed longitudinal interfaces between each tube as the tubes are moved relative to the welding means.