Choosing between these two types of hollow section aluminum extrusion comes down to the application. Structural tubes are preferred in some and seamless work better in others. Here’s a summary of the strengths and weaknesses of each.

Structural Aluminum Tubing Pros:

Very consistent wall thickness around the cross-sections

Can be extruded faster than seamless (which brings down the price)

When extruding small cross-sections it’s sometimes possible to fit multiple opening in a single die, increasing efficiency and lowering the cost per foot

Structural Aluminum Tubing Cons:

Welded seams create a region of weakness where the tube could rupture if subjected to high internal pressure or significant bending

Seams may be visible on the surface and will be highlighted by anodizing

The seam is where corrosion is most likely to start, (although most grades of aluminum don’t corrode to any significant extent.)

Seamless Aluminum Tubing Pros:

Higher-strength/resistance to deformation and internal pressure

Uniform appearance when anodized

Seamless Aluminum Tubing Cons:

Slower extrusion process (which can increase the price)

Inferior concentricity of internal to the outer diameter

We can summarize the arguments this way: If the application involves internal pressure or the extrusion will be subjected to significant deformation, choose seamless. If neither of those apply, ask how concerned you are about appearance. If the answer is, a lot, seamless is probably the correct route. However, if the highest priority is keeping the cost down, pick structural.

Applications for Seamless and Structural Aluminum Extrusion

Seamless extruded tubes are used in applications that involve internal pressure. Hydraulic cylinders, pipes, and fittings are good examples. They are also used when the extrusion will be put through significant deformation. A good example of this bending electrical conduit or bus bars.

Another group of applications are those involving high loads that will deform the tubing or extrusion if it isn’t strong enough. Examples of this type include aircraft seat frames, baseball bats, and driveshafts.

You might also choose seamless when appearance is important. This is especially true if the extrusion will be anodized as that tends to highlight the seam.

Structural tubing is appropriate for all those applications that don’t apply high forces. Railings and window frames are examples, along with wall framing and other architectural and decorative uses. Frames for enclosures, material handling carts, and machine guards are more industrial examples. Many applications in trailers and RVs are well-served by structural tubing too.

An Important Decision

As structural tubing is less expensive it tends to be the default choice. Before specifying structural tubing though, remember to consider the application. It will work most of the time, but in some situations, it could be an expensive mistake. If you’re unsure which direction to go in, we’ll be happy to discuss your application with you.