Abstract: A tube welding mill is shown through which titanium tube preforms are drawn and closed under a relatively stationary plasma arc welding torch. The tube preforms are drawn through a series of closing capstans, over a knife-edge guide bar and eventually under the plasma arc welding torch. The weld area and some distance down stream of the weld is shielded by inert gas containing box-like trailers including an upper trailer supported on the frame of the mill having resilient side walls which embrace the outer surface of the tube and a lower trailer supported on the mandrel within the tube which is carried by the guide bar. The lower trailer is floated on springs which allow it to move bodily in vertical planes parallel with the tube and otherwise adjust itself to maintain its top edges in sealing engagement with the inside wall of the tube beneath the weld.