Aluminum Extrusion: Portholes or Seamless Extruded Tubes from Sandra Brown's blog

There are numerous decisions to be made in life.  Sometimes the answer isn't all that important after all.  Other times, it makes a significant difference.  Take, for example, aluminum tube that has been extruded.  In general, seamless extruded tubes are a little more expensive than seamless extruded tubes, which may lead you to specify structural tubes.  However, this is one of those instances in which saving a few dollars could end up costing a lot more in the long run.  There are times when you want that extruded material to have a hole running through it.  The most basic type of tube or pipe is a circular tube or pipe.  The terms porthole and seamless refer to two different methods of forming the hollow internal section of a building.  In porthole extrusion, metal is pressed into a shape that corresponds to the hollow section you want to extrude.  Because of the laws of physics, the tooling requires ribs in order to hold the shape in place, and the metal must flow around these ribs.  As the metal is extruded, this separates it into sections, which are then forced back together by a second die.  This results in a longitudinal seam that runs the entire length of the extrusion.

Extruded tubes with no seams, as the name implies, avoid this problem.  This procedure entails inserting a forming mandrel into a billet of material from the back and forcing it through until it is very close to the opening in the die.  The material flows through the gap between the mandrel and the die, emerging with both the internal and external dimensions fixed and with no seams on either side of the gap.

When examined under a microscope, the seam frequently reveals a different crystal structure from the aluminum found elsewhere in the extrusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A result of grain distortion caused by the deformation and subsequent pressure that is applied to weld the separate pieces together, this occurs.  This difference is determined by the amount of deformation and pressure that the metal undergoes, which is in turn determined by extruded aluminium pipe speed, temperature, pressure, and alloy series used in the process.

The net result of this distortion is the creation of a weaker region along the seam line in the fabric.  The size and impact of this weakness, on the other hand, are dependent on the profile shape and alloy.  The choice between these two types of hollow section aluminum extruded aluminium pipe is based on the application's specifications.  In some cases, structural tubes are preferred, while in others, seamless tubes perform better.  Here's a quick rundown of the advantages and disadvantages of each.

The Advantages of Structural Aluminum Tubing:

The wall thicknesses are very consistent throughout the cross-sections.

Because it can be extruded more quickly than seamless, it is less expensive.

The ability to fit multiple openings in a single die when extruding small cross sections can increase efficiency while simultaneously lowering the cost per foot.

Aluminum structural tubing has a few disadvantages.  Welded seams create a region of weakness where the tube could rupture if subjected to excessive internal pressure or significant bending.

Anodizing will draw attention to any seams that are visible on the surface of the metal.

The seam is the most likely location for corrosion to begin, although most grades of aluminum are resistant to corrosion to any significant extent.