Electric Resistance Welded

Abbreviated ERW, this is a format that signals a specific welding process – actually two processes, spot and seam welding. This process involves several specific steps where the steel is unwound and trimmed, then passed through rollers to cold-form the steel into the proper shape (circular, square or rectangular).

From here, the edges are forced together into a butt joint, then welded at a very high temperature to form a flash weld. Once the weld is tested, the tube passes through various sizing rolls to achieve the proper size, and then the length is cut. The materials used here will generally be available in both hot-rolled and cold-rolled formats.

API 5L Line Pipe Seamless Steel Pipe

Seamless Mechanical Tube

When dealing with seamless mechanical tubing – the type that, as the name suggests, comes with no welded seams – the term to remember is “extrusion.” This is a process where steel bar is pierced in the middle using a die, turning what was previously a solid round bar into a round tube instead. There are two types of seamless tube to consider:

• Hot-finished seamless (HFS): Comes with lower critical tolerances and not as much strength as its alternative, HFS formats are best when cost is an issue and a wide size range is needed.
• Cold drawn seamless (CDS): With extremely precise tolerances and a good finish, this is generally the preferred method for dimensional tolerances and machinability.

Drawn Over Mandrel

Abbreviated DOM, this isn’t actually a steel tube type or manufacturing format – it describes the finishing process often used. Many of the early parts of the process are identical to ERW format, with differences showing up in the finishing stages when the flash weld is removed. In these cases, the tube will be cold drawn over a mandrel, bringing excellent dimensional tolerance and surface finish. Another major benefit of DOM materials is that they boast the strongest weld strength you can find. DOM products do have a seam, despite them sometimes mistakenly being labeled as seamless tube.

For more on the various processes and finishing formats used on steel tube, or to learn about our steel pipe, bar or any of our other steel services, contact the pros at Wasatch Steel today.