Knowing your options in steel, pipe and tube could possibly make or break your next project. Knowing these differences can help you decide if you are using the correct material or if something else is better suited for your application.
DOM Tube - Drawn Over Mandrel
Steel tube with the joint weld removed, then drawn over a mandrel close to room temperature. Although it does technically still have a seam, it's practically invisible to the naked eye while still maintaining one of the strongest weld strengths out there. Commonly used in automotive, motorcycle and race car frames due to its more exact dimensions.
ERW - Electric Resistance Welded
Referring to both spot and seam welding. Manufactured from strip coil then passed through multiple rollers, giving the tube it's shape. Joints are then pressed, electrically charged and butt welded together at temperatures over 2000 F., welds are then removed and the steel is shaped, straightened and cut to size. This option is suitable for water works, oil lines, etc. at low to medium pressures.
Unlike DOM and ERW tube, seamless tube is not cut and formed from sheets or coils of steel. A process called extrusion is used where a die pierces through the center of a solid steel bar creating a tube or square without any seams at all. Seamless tube is often used for high pressure applications such as automobiles, oil lines, gas lines, etc.
Steel rolled and pressed typically at temperatures of over 1700 F., making it easier to work with and form. Due to this process, expansion and contraction is a given, making hot rolled steel more suitable for applications where preciseness isn't required such as structural, railroad tracks, handrails, trailer frames, etc.
Hot rolled steel that is continually rolled and formed as it cools, eliminating expansion and contraction to give it a more precise shape, measurement and greater strength than hot rolled steel. Cold rolled steel is also more expensive than hot rolled due to it being processed more extensively. Applications consist of bar stock, round stock, shafts, heavy load construction, etc.
Pipe that has been hydrostaticly tested for strength, leaks and pressure tolerance. This pipe is often used for gas lines, water and other applications where it's contents need to stay confined and/or contained.
AKA - Structural Pipe. Untested pipe is simply that; welded, seamed pipe that has not been tested for leaks, pressure or tolerance. Untested pipe is a suitable choice (and less expensive) for handrails, braces, forms and any other application where its contents do not need to stay confined and/or contained.