| 摘要 |
PURPOSE:To improve the efficiency of weld heat input and the working efficiency of equipment in the production of an electric welded pipe having a polygonal section and to improve the quality of said electric welded pipe, by disposing the ridge formd in an impeder fitted loosely in an open pipe to the butt parts. CONSTITUTION:An impeder 4 having the sectional shape resembling to the sectional shape of an open pipe 1 having a polygonal section is held inserted freely in said pipe and in this state the pipe is induction-heated from the outside to weld the butt parts 1d of both side edge parts 1a, 1b, whereby a polygonal steel pipe 3 is obtained. The included angle of the adjacent two faces of said ridge 4c in such a high-frequency electric welding method is formed to <=120 deg., and the angle alpha1 to the horizontal plane is inclined to >=10 deg., so that the ridge 4c is disposed in proximity to the lower part of the butt parts 1d. Then, the effective current i1 toward a welding V point 2 is increased to improve the efficiency of weld heat input; at the same time the welding flash is moved downward along the slope of the impeder 4 to prevent the deterioration in the quality in the weld zone and to decrease the times for replacing the impeder 4, whereby the working efficiency of equipment is improved. |
