Abstract: Briefed in the paper are the straight welding process for small-sized steel welded pipes with O.D.under 10 mm and the installation method for the impedance device for hi-speed welding operation thereof.The problems and limitations related to the conventional processes for small-sized pipe production are analyzed,based on which,the impedance device has been modified,resulting in significantly heightening the productivity of the said small-sized straight welded pipe from 30 m/min.to 60 m/min.and the yield thereof from 70% to 98% or above.