PURPOSE: To sufficiently restrain the oxidation of a back bead by welding in a state that a backup member having a groove for storing inert gas faced to bevel parts is in a bridging.
CONSTITUTION: The bevel parts 2 of a material to be welded (e.g. large pipe-like member, penstock, large diameter pressure vessel) 1 are butted and the cross sectional U-shaped copper-made backup metal 4 having the groove 3 for storing argon gas (as one sample of inert gas) is welded in the bridging state faced to the bevel parts 2 at the back side of the bevel parts 2 of the materials 1 to be welded. At the time of back-bead welding the bevel parts 2 with a welding torch 5 in this state, the argon gas 7 supplied as the shielding from the welding torch 5 side, is stored into the groove 3 in the backup metal 4, and the argon gas 7 in the groove 3 carries out a function of back shield gas to restrain the oxidation of the back bead 6 formed in the bevel parts 2. By this method, it can be unnecessary to specially supply the back shield gas.
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MAEHARA KENJI
OSAWA MORIHIKO
