PURPOSE: To improve the stress at welded zone efficiently with high workability, by moving a high frequency heating coil made to almost square shape around the welding line as center, along the welding line of pipe in axial direction to heat outer surface thereof, and cooling inner surface.
CONSTITUTION: While cooling inner surface of weld joining zone of the welding line 3 in axial direction of cylindrical pipe or a vessel 2, outer surface of the pipe 2 is heated by moving the high frequency heating coil 1 along said line 3. Therein, said coil 1 is wound to almost square vortex shape around the line 3 as center, and favorably sectional area angle in circumferential direction seeing the center of the pipe 2 is constituted to ≥120°. Said coil 1 can be heated at every discontinuous movement at a fixed interval, or can be moved and heated continuously.
FUJIMOTO KOJI
SHIMIZU NOBUO
SUGAWARA NAOTAKE
SEKI KATSUZO
SHIMIZU TASUKU
