Welded vs. Seamless Stainless Steel Tubing

Stainless steel tubing is one of the most versatile metal alloy materials used in manufacturing and fabrication. The two common types of tubing are seamless and welded. Deciding between welded vs. seamless tubing primarily depends on the application requirements of the product. In choosing between the two keep in mind that first, the tubing must be compliant with your project specifications and that secondly, it must meet the conditions for which the tubing will ultimately be used.

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Tubing vs Piping

Though both the words tube and pipe are often used interchangeably, largely because both are hollow-shaped, there are important distinctions between the two when determining welded vs. seamless tubing needs. Tubes are measured by the outside diameter (OD) and wall thickness. A pipe, on the other hand, is measured by its inside diameter (ID). In terms of functionality, tubing is generally used in structural and aesthetic applications whereas piping is used for transporting fluids, liquids, and gases.

Seamless Tubing Manufacturing

Knowing that distinction can also help in determining which tubing is best for a given application, welded or seamless. The method of manufacturing welded and seamless tubing is evident in their names alone. Seamless tubes are as defined &#; they do not have a welded seam. The tubing is manufactured through an extrusion process where the tube is drawn from a solid stainless steel billet and extruded into a hollow form. The billets are first heated and then formed into oblong circular molds that are hollowed in a piercing mill. While hot, the molds are drawn through a mandrel rod and elongated. The mandrel milling process increases the mold&#;s length by twenty times to form a seamless tube shape. Tubing is further shaped through pilfering, a cold rolling process, or cold drawing.

Welded Tubing Manufacturing

A welded stainless steel tube is produced through roll-forming strips or sheets of stainless steel into a tube shape and then welding the seam longitudinally. Welded tubing can be accomplished either by hot-forming and cold-forming processes. Of the two, cold forming results in smoother finishes and tighter tolerances. However, each method creates a durable, strong, steel tube that resists corrosion. The seam can be left beaded or it can be further worked by cold rolling and forging methods. The welded tube can also be drawn similarly to seamless tubing to produce a finer weld seam with better surface finishes and tighter tolerances.

Choosing Between Welded & Seamless

There are benefits and drawbacks in choosing welded vs. seamless tubing.

Seamless Tubing

By definition, seamless tubes are completely homogenous tubes, the properties of which give seamless tubing more strength, superior corrosion resistance, and the ability to withstand higher pressure than welded tubes. This makes them more suitable in critical applications in harsh environments, but it comes with a price.

Benefits

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• Stronger
• Superior corrosion resistance
• Higher pressure resistance

Applications

• Oil and gas control lines
• Chemical injection lines
• Below sea safety valves
• Chemical processing plant steam and heat trace bundles
• Fluid and gas transfer

Welded Tubing

Welded tubing is generally less expensive than seamless tubing due to the simpler manufacturing process in creating welded tubing. It is also readily available, like seamless tubing, in long continuous lengths. Standard sizes can be produced with similar lead times for both welded and seamless tubing. Seamless tubing costs can be offset in smaller manufacturing runs if less quantity is required. Otherwise, though custom-sized seamless tubing can be produced and delivered more quickly, it is more costly.

Benefits

• Cost-efficient
• Readily available in long lengths
• Fast lead times

Applications

• Architectural applications
• Hypodermic needles
• Automotive industry
• Food and beverage industry
• Marine industry
• Pharmaceutical industry

Costs of Welded vs Seamless

Costs of seamless and welded tubing are also related to such properties as strength and durability. Welded tubing&#;s easier manufacturing process can produce larger diameter tubing with thinner wall sizes for less. Such properties are more difficult to produce in seamless tubing. On the other hand, heavy walls can be achieved more easily with seamless tubing. Seamless tubing is often preferred for heavy wall tubing applications that require or can withstand high pressure or perform in extreme environments.

Contact the Experts at Eagle Stainless

Several factors combine to make stainless steel tubing an excellent choice for structural applications in industries ranging from automotive and aerospace to medical and marine. If you&#;re still unsure which tubing is best for your application, as a point of reference, though seamless tubing can be substituted for welded tubing, welded tubing can never be substituted for seamless tubing.

What design code?

How corrosive?
With what?
Size and wt affect availability. Above about 16 to 20" seamless gets hard to find

This is more of a material selection issue and I don't know if any pipeline code which will tell you this. B31.3 doesn't like welded pipe for some reason and applies a factor on wall thickness

There is a lot of preferential engineering here and different companies have different views.

There should be little difference but you may need to look at the impact of the seam weld on corrosion issues.

If you have sour service (H2S) then seamless is definitely preferred, which is a material selection issue under the NACE standards.

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