Methods of Manufacturing used in the Metal Pipe and Tubing Industries
There are three main processes used in the manufacturing of metal tubing and pipe.
Electric Welded Tubing
Also referred to as Electric Resistance Welded or ERW tubing, is produced when a strip of steel is passed through rollers to form the desired shape. The seam is then welded, forming a flash along the length on the inside and outside of the tube. The weld is then tested to ensure it meets the standard. Once the weld passes the testing process the tubing is formed to the exact size, straightened, and cut to length. ERW tube and pipe is available with the Weld flash in, flash removed or controlled (typically to .010”).
D.O.M. or Drawn over Mandrel tubing
D.O.M. refers to cold rolled electric welded tubing that goes through an additional process. Just as it sounds, the tubing is electrically welded, then it is drawn over a mandrel on the inside diameter of the tube and a die on the outside diameter. The drawing process ensures tighter tolerances and a smoother finish, requiring less machining. Although DOM is often referred to as “seamless” and appears to be seamless, it is not a true seamless product.
Seamless Tubing Process
Seamless tubing is produced when a solid bar is forced over a mandrel. This piercing process eliminates the need for a seam on the tube of pipe. Tolerance and finishes for seamless tubing vary, depending on the finish process. Cold finished tube is produced by drawing a seamless bar over a mandrel on the inside diameter of the tube and a die on the outside diameter. The drawing process ensures tighter tolerances and a smoother finish, requiring less machining and offers a smoother finish and tighter tolerances. Hot finished tube and pipe starts with a seamless shell that is forced through a series of rollers on the outside diameter as a mandrel passes through the inside diameter. Hot rolled tube and pipe sacrifice precise dimensional tolerances for better machinability and reduced cost.