Patent Number: 060524243
Section: claims

1. A piercing welding method for fabricating a double-wall structure having an inner wall, an outer wall surrounding said inner wall, and reinforcing ribs that connect said outer wall and said inner wall, the method comprising externally applying an electron beam at a right angle to the outer wall such that the applied electron beam penetrates the outer wall to reach an abutting rib, said abutting rib having a rib width, whereupon the outer wall is welded to the rib to form a welded structure having at least two piercing weld beads that are spaced apart by an unwelded area, wherein each of said at least two weld beads has a root and a weld bead width, wherein the sum of the widths of the at least two weld beads is at least 25% of the rib width, and wherein a length of the unwelded area exterior to the root of each bead is no more than 20% of the rib width. 2. The method according to claim 1, wherein the double-wall structure is the hull of ship, the fuselage of an airplane, a car body, a bridge structure, one of various containers in industrial plants, or a vacuum vessel. 3. The method according to claim 2, wherein the vacuum vessel is one for use in a nuclear fusion device. 4. The method according to claim 1, wherein shields are inserted between the outer and inner walls of the double-wall structure. 5. The method according to any one of claims 1-4, wherein wraparound welding is applied to the piercing welded end of each rib. 6. The method according to claim 1 further comprising welding the inner wall to the abutting rib by a welding technique selected from the group consisting of arc welding, electron beam welding, and laser beam welding.