High Frequency Welding is the dominant, state-of-the-art technology for manufacturing longitudinal seam pipes.
The Science: It uses high-frequency alternating current (typically 200 kHz to 400 kHz). Thanks to electromagnetic principles known as the "skin effect" and "proximity effect," the electrical current concentrates intensely on the very edges of the formed steel tube.
The Weld: The edges melt instantly. Heavy "squeeze rolls" then forge the molten edges together. Because it uses no filler wire, the resulting weld is incredibly strong and homogenous.