ERW is a process where strip edges are mechanically pressed together and welded. The heat for welding is generated by resistance of the steel to the flow of electric current. High frequency current (in the range of 400 to 500 kilohertz) which enters the tubing through shoes which act as sliding contacts. An induction coil can also be used with the high frequency current to induce current in the edges of the strip. No direct contact jk

Welded linepipe is not commonly manufactured by the Electric Resistance Weld (ERW) process. The manufacture of welded linepipe by the ERW process begins with coils of  hot rolled sheet steel, which are cut by a slitting machine into strips of precise width needed to produce a desired diameter of  pipe. The slit coils are fed into the pipe/tube mills which cold-form the flat ribbon of steel into a tubular cylinder by a series of tapered forming rolls. The product is then welded along the joint axis. The welded tube then passes under a tool that removes the outside flash resulting from the pressure during welding. Inside flash is likewise removed by cutting tools. The pipe is then subjected to such post-weld heat treatment of the welded seam only or treatment of the full cross-section of the pipe to accurate diameter tolerances. The product is cooled and then cut at the and of the pipe mill by a flying shear or saw.