welded metal square tube

Structural metal tubing is a key component in many metal fabrication projects and applications. Metal tubing is commonly used because it provides a great combination of strength with low weight, and affordability when compared to solid metal stock. There are two main types available: welded tubing and seamless tubing. This article will take a deeper look at how welded tubes are made.

What are Welded Tubes?

Welded tubes are a type of structural metal tubing that has a weld seam along its longitudinal axis. It can be made from essentially any type of metal or metal engineering that can be welded such as carbon steel, stainless steel, low-engineering steel, and aluminium. Welded metal tube is typically available in the following shapes:

  • Round
  • Square
  • Rectangular

How are Welded Tubes Made?

Manufacturing welded tubing on a large scale is a complex process that involves several steps.

  1. Metal coil is first selected using a thickness that will later match the thickness of the finished tube wall. The coil must also be wide enough so that the desired circumference and diameter can be achieved.
  2. The coil is fed through a series of dies and formed to shape. This brings two edges of the coil width towards each other until a tube is formed with one edge touching the other.
  3. A welding process is used to join these two edges together.
  4. Depending on the welded tube manufacturing process, the excess weld reinforcement may be removed at this time. The newly formed tubing may also undergo a heat-treatment process depending on the desired specifications.
  5. The tube is then cut to the desired length.

What Type of Welds are Used to Make Welded Tube?

  • Electric Resistance Welding (ERW)
  • High Frequency Welding
  • Laser Beam Welding
  • Gas Tungsten Arc Welding (TIG welding)
  • Plasma Arc Welding
  • Submerged Arc Welding

Why are Different Welding Processes Used to Manufacture Welded Tubes?

There are many reasons why one welding process may be chosen over another to manufacture welded tubing. Perhaps the most common method is high frequency welding. To use high frequency welding to make welded tube, a high frequency welding power source activated. Once the power source is activated, leads from the power source which are placed in close proximity to the formed but unwelded tube begin to emit high frequency energy. This energy excites the molecules in the tube until a temperature level at which they can be joined is reached. At this point the two heated edges of the unwelded tubing are forced together through another die and a weld is made.

One of the reasons high frequency welding is so popular is because it is an established repeatable technology, it is cost-effective, and it can handle poor fit-up better, relative to the other tube welding processes. Also, like nearly all large-scale welded tube manufacturing processes, it is performed in a continuous fashion allowing for high degrees of productivity.

Other welding methods are used in place of high frequency welding for different reasons. Laser beam welding may be used for metals that are more difficult to weld than mild steel. Examples include titanium, stainless steel, and other non-ferrous alloys. Gas tungsten arc welding and plasma arc welding are sometimes used in place of laser welding because of their reduced equipment cost and complexity; however, they typically provide slower travel speeds and larger heat affected zones. Resistance welding is occasionally used instead of high frequency welding for medium diameter carbon steel tubing. For welded steel tubing with thick walls, submerged arc welding is used.

References:
Exploring the welded tube making process: The basics for fabricators (thefabricator.com)

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