A Look At Seamless Vs. Welded Tubing

Among the many aluminum products used in a variety of industries, tubing has a significant place in the aerospace industry. 

There are essentially two basic types of tubing produced: seamless tubing and welded tubing.

Metal Tubing Production

The production processes are somewhat indicated by their name. 

For example, welded tubes are made from long, thin sheets of metal that are rolled into a tube shape and then machine welded at the seam. 

On the other hand, seamless tubing is produced from solid metal bars. The bars are hollowed out through either a piercing or extrusion process. This was the original form of aluminum tubing as, at one time, all functional metal tubing was seamless.

At one time, when welded tubing became more common, the quality and strength of the weld seam was typically weak, which meant that the welded tubing was inherently weaker, less attractive, and less durable. However, as the manufacturing processes and machinery for welding tubing improved, welded metal tubing was becoming a viable alternative to seamless tubing.

Making Welded Tubing

Producing welded tubing starts with rolling metal coil down to the desired gauge thickness, which results in a coil of a flat strip. The next step involves cutting the strip according to the width needed for the size of the tube to be produced.

The tube itself is formed by moving the cut coil through a series of rollers and then the seam of the tube is welded, typically in a chemically neutral environment. The welded seem is forged with a rolling application, and heat treating is applied to finish the welded tube.

If the welded seam needs to be smoothed or even hard to see with the naked eye, the tubes can be drawn over mandrels and ground. 

Making Seamless Tubing

Today, the most common methods for producing seamless tubing is done with rotary piercing and rolling. The process starts with a conditioned metal round bar, which is heated, pierced, and then worked.

The bar is moved around what is known as a piercer point in order to create a hollowed out bar, or tube. The interior of the tube is typically supported with a mandrel or a plug while the billet roller is then elongated. 

Both seamless and welded tubing is typically drawn to produce the final dimensional tolerances. Drawing is a process which “pulls” a tube through a die and the different methods for doing this can be described as “sunk drawn” and “plug drawn.” The difference shows up in the inside diameter surface roughness.

According to a PDF from OBCorp.com,

“Rod or plug drawing breaks up the weld bead on welded tubing and removes any dimensional indication. Final annealing further promotes a homogeneous tube. The term “full finished” refers to welded tubes that have been rod or plug drawn and annealed sufficiently to both remove any dimensional indication of the weld area and also break up the dendritic structure of the weld bead and expedite homogenization. Often it is very difficult to see the difference between welded and seamless tubing.”

Today, both welded and seamless metal tubing offer:

• High corrosion resistance
• A long life span
• Reliability

 Seamless Metal Tube Attributes

Unlike welded tubing, the seamless variety has no longitudinal weld seam because of the manufacturing of forcing a hole into a billet. The welded and drawn tubing does have a visible seam that may be a concern for some end users.

The ASME (American Society of Mechanical Engineers) working pressure of a welded tube is about 20 percent less than that of a seamless tube of the same material and size because of the welded seam. However, working pressure is not the primary determining factor for choosing seamless tube over welded tube. 

One aspect of seamless tubing is that, because there is no weld and therefore, low potential for impurities, it can provide superior corrosion resistance. In addition, seamless tubing has diminished potential for defects and differences in malleability that can occur at the welded area in welded tubes.

Also, seamless tubes do not require testing for weld integrity, unlike welded tubes, which can make them more suitable for critical applications.

Welded Tubing Advantages

The most significant advantage of welded tubing over seamless tubing is the higher cost of seamless tubes. In fact, many industries tend to use welded tubing primarily due to its cost efficiency.

The cost of welded and drawn tubing can be less expensive than seamless tubing largely because less drawing and annealing are needed for manufacturing welded and drawn tube. In addition, welded tubing can usually be procured faster than seamless tubing.

Applications of Tubing

Seamless extruded tubing is used primarily in industries that require hydraulic pressures, severe forming, high uniform strength, and more uniform cosmetic appearance after anodizing.

Products produced are softball and baseball bats, truck and SUV drive shafts, aircraft hydraulic lines and seat frames, and CNG cylinders, for example.

Welded tubing can be found in outdoor recreation products like tent poles, camp chair frames, and outdoor tables. In the medical industry, various types of aluminum tubing are used in wheelchair frames, crutches, collapsible stretchers, and bed frames.

Aerospace manufactures use aluminum tubing in fuselage, hydraulic systems, and fuel lines, while automobile and rail transportation manufacturers also apply aluminum tubing for hydraulic systems and fuel lines, as well. The high heat-conductive capabilities make aluminum it a good alternative to steel or other heavier metals in products such refrigerators and HVAC systems.

Aluminum tubing can also be found in a wide range of disparate products from chain-link fence supports  lining tables to electric equipment housing in desktop monitors.

No matter whether you need 100 feet of an aluminum extrusion product, or just a few feet of stainless-steel tubing, AAA Air Support promises to always ship out your part orders quickly and efficiently. Our goal always is to provide your company with the means to complete that project or get that airplane back in the air as quickly as possible.