Life Before the Square Wave Welder
For a full appreciation of the square wave welder, it is necessary to review the history of ERW starting in the early 1920's. Prior to that time, welded steel tubing was made by heating the edge areas of a formed tube by one means or another and subsequently forcing the edges together to create a forged weld.
The advent of the modern electrical resistance welder began with Johnston, who was granted a patent in the early twenties for a system which simultaneously applied heat and pressure to the tube. His method involved keeping the seam open prior to the welding throat which included a pair of copper electrodes to provide the welding current.