How Are Welded Tubes Made?

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, 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 alloy that can be welded, such as carbon steel, stainless steel, low-alloy steel, and aluminum. Welded metal tube is typically available in the following shapes:

• Round metal tubing: Round metal tubing offers excellent structural strength with even stress distribution, making it ideal for applications requiring resistance to torsional forces. It’s commonly used in handrails, furniture frames, automotive roll cages, and fluid transportation systems. Flexible metal tubing in round profiles is particularly valuable in plumbing, hydraulic systems, and industrial machinery, where routing around obstacles is necessary.
• Square metal tubing: Square metal tubing provides flat surfaces that make it easier to connect to other components and structures. 2×2 metal tubing is a popular square size used in construction framing, industrial equipment, sign posts, and furniture manufacturing. The flat surfaces facilitate welding and bolting, while the 90-degree corners create a strong load-bearing capacity.
• Rectangular metal tubing: Rectangular metal tubing combines the strength of square tubing with different dimensions on adjacent sides, offering greater design flexibility. Rectangular tubing is frequently used in structural frameworks, vehicle chassis, equipment frames, and agricultural implements. Thin-walled metal tubing in rectangular shapes provides weight savings while maintaining structural integrity, making it popular in modern construction and transportation applications. 16 metal tubing sections in rectangular profiles are commonly stocked in standard lengths for construction projects.

How Are Welded Tubes Made?

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

• A metal coil is first selected using a thickness that will later match the thickness of the finished tube wall (thin-wall metal tubing requires especially precise coil selection). The coil must also be wide enough to achieve the desired circumference and diameter.
• The coil is fed through a series of dies and formed into This brings the two edges of the coil width towards each other until a tube is formed, with one edge touching the other. Metal tubing clamps are often used during this process to maintain proper alignment.
• A welding process is used to join these two edges together.
• 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.
• The tube is then cut to the desired length. Standard lengths, such as 16″ metal tubing, are common.

What Type of Welds Are Used to Make Welded Tube?

• Electric Resistance Welding (ERW): This process joins metal by generating heat through electrical resistance as current flows through the metal pieces being welded together, creating a consistent seam ideal for high-volume production.
• High Frequency Welding: High frequency welding uses electromagnetic induction to generate intense heat precisely along the tube’s seam, producing rapid, clean welds with minimal heat-affected zones.
• Laser Beam Welding: This welding method uses a highly concentrated beam of light to create deep, narrow welds with minimal heat input, resulting in high-quality joints with excellent aesthetic appearance.
• Gas Tungsten Arc Welding (TIG welding): TIG welding uses a non-consumable tungsten electrode to produce exceptionally clean, high-quality welds.
• Plasma Arc Welding: Using a constricted arc of ionized gas, plasma arc welding delivers high energy concentration for deep penetration with faster travel speeds than traditional TIG welding.
• Submerged Arc Welding: This high-deposition welding process uses a continuous wire electrode covered by a layer of granular flux to create strong, deep welds in a single pass for thick-walled applications.

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 a welded tube, a high frequency welding power source is 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 is reached at which they can be joined. At this point, the two heated edges of the unwelded tubing are forced together through another die, and a weld is made.

High-frequency welding is popular because it is an established, repeatable technology, it is cost-effective, and it can handle poor fit-up better than 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 as alternatives to laser welding due to their lower equipment costs and complexity; however, they typically offer 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. Specialized methods are also employed when manufacturing flexible metal tubing for applications requiring bendability.

Seamless Tube vs. Welded Tubes

Seamless tubes are manufactured through a process that creates a hollow tube without any welding seams. These tubes are extruded from a solid billet of metal and pierced to form the hollow section. In contrast, welded tubes are formed from flat metal strips that are shaped and joined along a seam using various welding techniques.

The primary difference between seamless tubes and welded tubes lies in their structural composition. Welded tubes feature a seam where the edges of the metal strip have been joined together, while seamless tubes maintain uniform strength throughout their entire circumference. This distinction affects several performance characteristics:

• Seamless tubes generally offer higher pressure ratings than welded tubes of the same material and dimensions.
• Welded tubes are typically more economical to produce.
• Welded tubes are more widely available in various sizes and can be produced more quickly than seamless varieties.
• Cold-drawn welded tubes undergo additional processing to improve dimensional accuracy and surface finish, narrowing some of the performance gaps between welded and seamless options.

While seamless tubes excel in applications demanding maximum integrity and pressure resistance, modern welding technologies have significantly improved the quality of welded tubes, making them suitable for most industrial applications.