What is The Difference among ERW, DOM and Seamless Steel Pipe?
Electric Resistance Welded (ERW)
ERW is a specific type of welding process that is used to produce welded steel pipe, such as ERW steel pipe. Seam welding is commonly used during the manufacturing of round, square and rectangular steel tubing. The steel strip is unwound from coils and side-trimmed to control width and condition the edges for welding. The strip then passes through a series of contoured rollers which cold-form the material into a circular (square or rectangular) shape. The edges are forced together under pressure as a butt joint and then welded by heating the material to temperatures above 2000° F. The flash weld that has formed is now removed from the outside diameter of the tube. Once the weld has been tested the tube then passes through a series of sizing rolls to attain its precise finished size, after which the tube is then straightened and cut to length.
Drawn Over Mandrel (DOM)
Technically, DOM is not a type of steel tube, but rather the process in which the tube is finished. It is considered a high quality tube, and is normally constructed from SAE 1020 or 1026 steel. The first stages of manufacturing are identical to ones used to make electric resistance welded tube, but in the finishing stages the entire flash weld is removed and the tube is cold drawn over a mandrel. The cold drawn process provides the tube with better dimensional tolerances, improved surface finish and the strongest weld strength achievable. DOM is often incorrectly referenced as “seamless tube” when it actually does have a seam (although it is almost invisible).
Seamless Mechanical Steel Pipe
The seamless steel pipe is manufactured using a process called “extrusion”. During this process a solid steel bar is pierced though the centre using a die, turning the solid round into a round tube. Basically there are two types of seamless steel pipe. Cold Drawn Seamless (CDS) normally made from SAE 1018, having precise tolerances and good surface finish. Hot Finished Seamless (HFS) normally made from SAE 1026, having less critical tolerances and a scaly finish. It is not as strong as CDS. Cold Drawn Seamless (CDS) has some benefits, such as good surface finish, superior machinability, increased dimensional tolerances and high strength to weight ratio. Hot Finish Seamless (HFS) also has some advantages, including cost effective material, good machinability and wide range of sizes.