WELDING COMBINATION METHOD FOR DOUBLE TUBE

PURPOSE:To pack a heat insulating material completely and perform the radiograph test for the welded part, by using approximately cross-shaped joints for inside tubes and outside tubes for the welding combination of double tubes consisting of inside tubes and outside tubes having heat insulating liners. CONSTITUTION:Liners 1 and 2, inside tubes 3 and 4, and outside tubes 5 and 6 from directions X and Y are assembled together with heat insulating materials 7 and 8. Next, upper and lower members 15' and 15' are welded to produce an inside tube joint which has a cross shape in the side view, and this joint is attached to inside tubes 3 and 4 by welding in positions 16 and 18, and a heat insulating material 22 is pressed in after lines 11 and 12 having different diameters are attached to liners 1 and 2 by welding. After a cover 23 for the heat insulating material is welded, inside end plates 24 and 24 of an inside tube joint A are welded. Outside tube joint members 25' and 25' are set so as to surround the combined inside tube joint A and are welded to outside tubes 5 and 6 in positions 26 and 27, and outside end plates 30 and 30 are attached to projecting nozzles 29 and 29 by welding after outside tube joint members 25' and 25' are welded in a position 28. Welding and radiograph tests are executed in each stage of welding.