| 摘要 |
PROBLEM TO BE SOLVED: To provide a joining method by which a joining work efficiency is improved and a sufficient strength and tenacity is given to a joining part at a local joining of a steel pipe. SOLUTION: Steel pipes 1a, 1b having a vertical end surface are butted each other and the end surfaces are closely adhered by carrying out a pipe enlarging alignment from an inner surface. The end parts of the steel pipes 1a, 1b are induction heated by applying a medium frequency current to a heating coil 4 arranged at outer periphery of the joining part 2, while spraying a shield gas to the joining part 2. When an outer face temperature of the steel pipe end part reaches a range of 1,320-1,420 deg.C, the steel pipe end faces are joined by applying a pressurization of an upsetting volume of 2-8 mm so as to increase thickness of the joined steel pipe end part at a thickness increase ratio of 15-40%. Further, after the joined steel pipe end part is forcefully cooled down to 400 deg.C by spraying a gas or water from a cooling nozzle, a heat treatment is carried out with an intermediate frequency induction heating by applying a current to the heating coil 4 again. |
