| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a method for locally sealing a shielding gas for welding into a tube near a butt welding zone of piping, in a system structure in which sealing of a shielding gas is difficult at the time of welding piping or in which no water soluble film can be used. <P>SOLUTION: In butt welding of a pair of pipes in piping 12, columnar dry ice 11 having an outer diameter equal to the inner diameter of the piping is inserted into the piping, forming a wall inside the piping 12 for the purpose of a purge dam of the shielding gas for welding, thereby suppressing air flow in the air space 13 on the non-welding side inside the piping as well as in the air space 14 inside the piping near the welding back bead. A nozzle 16 for infusing the shielding gas is inserted into the piping 12 from a hole drilled in the groove abutting part in the butt welding zone of the piping 12, with the shielding gas 18 infused into space 14 inside the piping to lower the oxygen concentration, to prevent oxidation in the welding back bead on the piping inner face at the time of the welding. In addition, the outer periphery of the piping in which the dry ice is installed is wrapped with a freezing jacket 10 utilizing liquefied carbon dioxide, suppressing vaporization of the dry ice. <P>COPYRIGHT: (C)2004,JPO</p> |
