When you need steel tubing for a project, the project's blueprints will specify the size of the tubes you need. But the exterior size is only one feature that you have to choose when you're buying steel tubes. You also need the interior diameter, the wall thickness, the construction style, and more. Rather than puzzling over these numbers separately, figure out what wall thickness works for you and then go from there.

Thin Walls Need Welds

Steel tubes are constructed by welding, so you have a seam running down the side of the tube, or by creating a seamless tube. Seamless tubes tend to need thicker walls; welds are great for thin-walled tubes. If you choose to buy a thin-walled tube, then, getting welded tubes will ensure those tubes provide a little more strength.

The issue has to do with pressure on the tube. The weld is strong and can withstand pressure better than seamless tubing, which can have tiny surface defects resulting from the cutting process that created the tube.

Interior vs. Exterior Diameter and Interior Pressure

Interior pressure is an issue, too. The narrower the interior of the tube, the higher the pressure will be inside the tube (think of the grade-school experiment of putting your thumb over a running garden hose nozzle). The thicker the wall of the tube, the narrower the interior of the tube when comparing tubes with identical outer diameters. If you don't want too much pressure inside the tube and you need a tube with a specific exterior diameter, then you have to adjust the wall thickness to make sure the interior diameter keeps the pressure under control.

Corrosion Allowance

The diameter of the tube will contain a few extra millimeters for a corrosion allowance, which is essentially extra material that can be eaten away by corrosion without affecting the overall performance of the tube. But that corrosion allowance layer does affect wall thickness, so keep that in mind when choosing features like seamless or welded.

The alloy you choose also affects tube performance and corrosion resistance, of course, so thickness isn't the only thing you need to look at. There are also the humidity levels of the environment that the tube will be in, as well as machine vibration and temperature. If you're unable to find the tubing you need, contact the sellers you've been working with and ask about customized tubes.