The manufacturing process for as-welded mechanical tubing begins with coils of steel, which are slit to the proper width for the desired tube size. The cut strip, or skelp, passes through a series of rolls that progressively cold-form it into a tubular shape. It then passes through an electric resistance welder which joins the edges together, under pressure, to complete the tubular shape. In-line equipment then tests the tube’s weld for integrity.
No filler is added in the welding process, so the composition of the weld is the same as the parent material. Welding leaves a small amount of flash on the tube’s outer and inner surfaces. The outer flash is removed to provide a smooth contour and maintain OD tolerance. Depending upon customer specifications, the inner flash can be controlled to varying degrees.
Following flash removal, the tube is cooled and sized to specified dimensions by a series of finishing rolls. Or, if it has been ordered in square or rectangular shape, it passes through shaping rolls to give it the desired shape and dimensions. Then it is cut to the length ordered. For particularly demanding applications, the tubing may also be annealed for optimum hardness and ductility.