To provide the method spatially isolating the necessary section within a tube with a welded place sandwiched from the inspecting hole or the like opened in the vicinity of the welded place or one side opening of the tube, inserting isolating devices for replacing the air with an inert gas poured between them and expanding expansion bags installed to isolating devices within the tube and the method protecting expansion bags from the spark of welding, spatters, the temperature rising of the tube or the like at the time of repairing the welded place of the tube by TIG welding.

Expansion bags 10-5 are sucked to contract and inserted after making the outer diameter dimension smaller than the inspecting hole at the time of inserting breakers 10, 20 from the inspecting hole 3 or the like. Expansion bags 10-5 of two isolating device 10, 20 are expanded within the tube 1 to come into close contact with the tube wall, and the gas is poured between them. Expansion bags 10-5 are protected from the temperature rising of the tube body, spatters or the like by implanting hairs 10-6 into expansion bags 10-5 and immersing water into them. Although expansion bags 10-5 of breakers 10, 20 inserted from the tube opening are directly implanted, expansion bags 10-5 are also protected with the implanted protecting cover.