the technologies adopted for constructing the reversed-field pinch experiment (rfx) vacuum vessel are described. the vessel is of all-welded inconel 625 construction, with very tight dimensional tolerances' 1 mm on the 4-m major diameter, and 0.5 mm on the 1-m minor diameter. welding the thin inconel sheets to create the sandwich structure of the wall has been one of the most significant aspects of the construction. much machining was necessary to obtain the exact dimensions on the single welded components of the vessel special attention was given to the flange fabrication: most of them are equipped with helicoflex seals to house optical windows of various materials and different shapes, operating under thermocycling conditions. the procedures for leak testing and for surface cleaning are reported, along with the assembly operations and controls. the material selection and preparation, welding procedures, and machining is described. port design and fabrication is also discussed