Abstract: Orbital welding apparatus in which wire is fed to the welding zone by wire feed mechanism operable by differential rotation of two drive members operable at different speeds, one member carrying a welding electrode and the wire feed mechanism. Both drive members have openings allowing entry of tube to be welded. The drive members cooperate with auxiliary drive members which fit into the respective openings in the main drive members. The auxiliary drive members are guided across an opening in a housing enclosing the drive members by means of a bridge piece securable to the housing across the opening. The apparatus permits orbital welding of very closely spaced tubes without using a wire feed drive motor mounted on the rotatable assembly. Both TIG or MIG arc welding methods may be performed by the invention, or any method involving the feeding of wire into the weld zone.