Abstract: A heat sink welding and purging apparatus for use in the welding of pipe joints for piping to be used with nuclear power systems and the like wherein the weld area must be kept below a temperature at which the dangers of carbide precipitation occur. The various embodiments include expandable heat sink and sealing bladders which are expanded in use to respectively seal the adjacent interiors of the ends of the two pipes to be welded at the adjacent joints. After expanding and sealing the pipe openings, coolant is fed into the interior of the apparatus to cool the joint being welded. Also purging gases may be used to eliminate undesirable atmospheric gases adjacent the weld joint.