ASTM B338 GR1 Titanium Seamless vs Welded Tube

Seamless tubes start as a solid titanium bar. The bar is pierced and rotated over a mandrel to form a hollow tube. No weld seam exists anywhere in the wall.

Welded tubes start as a flat titanium strip. The strip is roll-formed into a cylindrical shape and welded along the longitudinal seam. Most welded tubes for heat exchanger service then go through a drawing die. This process compresses the weld seam, smooths the surface, and tightens the dimensional tolerances. The correct specification for heat exchanger service is "welded and drawn" (W &D), not "as-welded."

As-welded tubes have a raised weld seam. They are suitable for conduit, fencing, or structural applications. For heat exchangers, the raised seam creates crevices that can trap debris and initiate corrosion. It also makes tube sheet rolling difficult because the seam creates a high spot.

For heat exchanger tubes, welded and drawn is the standard offering. As-welded tubes are not supplied for this service.

For the full technical specifications of ASTM B338 GR1 titanium tube, check the product page here. 

Pressure rating is a common concern. Both types meet the same pressure requirements per ASTM B338 when properly manufactured.

However, engineering practice distinguishes between the two.

Above 500 psi (3.4 MPa), seamless is the standard choice. The weld seam on a welded tube is not weak when properly made. But at high pressure, eliminating the weld seam removes one variable from the safety calculation. Many engineering specifications for high-pressure service explicitly require seamless.

Below 500 psi, welded is fully acceptable. Most shell and tube heat exchangers operate at 150–300 psi. Thousands of welded titanium tubes are in service at these pressures with no issues related to the weld seam.

One nuance: some engineers apply a weld joint efficiency factor to welded tubes, typically 0.85 or 0.90, while seamless tubes get 1.0. This is a conservative practice derived from carbon steel codes. For titanium, the actual weld seam strength is equivalent to the base metal. But if the project specification requires a joint efficiency factor, seamless becomes the only way to achieve the required wall thickness.

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In seawater and most chemical environments, welded GR1 tubes corrode at the same rate as seamless.

The titanium weld seam, when welded correctly, develops the same passive titanium oxide layer as the rest of the tube. This oxide layer is what gives titanium its corrosion resistance. No preferential corrosion occurs at the weld seam.

The key variable is weld quality.

A correctly welded tube uses pure argon shielding on both the inside and outside of the weld zone. The resulting weld appears silver or light gray. This weld will perform identically to the base metal.

A poorly welded tube lacks adequate argon shielding. Oxygen from the air contaminates the hot weld metal. The weld turns blue, straw-colored, or gray. Contaminated welds will corrode preferentially. Our production uses 100% argon shielding on both sides of the weld, and every lot is visually inspected for weld color.

U-bending puts stress on the tube wall. The weld seam, being a change in microstructure, is a potential failure point under high bending stress.

For bend radii above 3x OD, welded tubes work reliably. The bending stress at the weld seam is low enough that no cracking occurs. Most heat exchanger U-bends fall into this category.

For bend radii under 2.5x OD, seamless is the safer choice. Tight bends put high tensile stress on the outer wall of the bend. If the weld seam lies on the outer radius, cracking becomes a risk. Many engineering specifications require seamless for bend radii under 3x OD.

For radii between 2.5x and 3x OD, either can work. Some fabricators accept welded tubes with the weld seam placed on the neutral axis of the bend (the side that sees neither tension nor compression). This requires careful orientation during bending.

For welded U-bends, we can orient the weld seam to the neutral axis upon request. This minimizes stress on the seam during bending.

Rolling (expanding) a tube into a tube sheet requires uniform deformation of the tube wall. The weld seam, being slightly different in hardness and microstructure, can affect how the tube expands.

For standard wall thickness (1.5 mm and above), both seamless and welded roll equally well. The difference in stiffness at the weld seam is too small to matter.

For thin wall tubes (under 1.2 mm), seamless rolls more evenly. The weld seam creates a slightly stiffer longitudinal strip. With thin walls, this stiffness difference can cause the tube to expand oval or create uneven contact with the tube sheet hole. Seamless tubes have no such variation.

For very thin walls (under 0.9 mm), some fabricators prefer seamless. Our welded and drawn tubes are drawn with minimum 25% reduction, which minimizes weld seam stiffness. For thin wall applications, we recommend testing a sample before full production.

Seamless costs significantly more. The exact premium depends on size, quantity, and mill.

On a 500-tube bundle (typical for a medium heat exchanger), the difference ranges from $10,000 to $20,000.

Seamless production requires piercing solid billet, which is slower and generates more scrap. Welded production starts with strip, which is faster and has lower material waste. Most buyers choose welded for standard applications and reserve seamless for high-pressure or critical service.

Not every project needs seamless. Not every project is a good fit for welded. Here is the decision path based on actual operating conditions.

Choose seamless when:

Design pressure exceeds 500 psi

U-bend radius is less than 2.5x OD

Wall thickness is under 1.2 mm and tubes will be rolled

Hydrogen service (weld seams can be preferential sites for hydride formation)

Project specification explicitly requires seamless

Nuclear or safety-critical application

Choose welded when:

Design pressure is below 500 psi

U-bend radius is greater than 3x OD

Wall thickness is 1.5 mm or above

Seawater, cooling water, or standard chemical service

Budget is limited

Lead time is tight (need tubes within 6 weeks)

Not sure?

For applications in the gray area - pressure between 400–600 psi, or bend radius between 2.5x and 3x OD - either option can work. In these cases, here is the decision order:

Check the project specification first. Follow what it says.

If no specification, ask the fabricator about their preference for rolling or bending.

If the fabricator has no preference, welded will save cost.

For most heat exchanger applications, welded and drawn tubes are the right choice. Seamless is reserved for high-pressure, critical, or very thin-wall service where the extra cost is justified.

Discuss Your Project Requirements

For welded tubes:

"ASTM B338 GR1 titanium tube, welded and drawn, pickled finish. Eddy current test per ASTM B338. Mill certificate EN 10204 Type 3.1 required."

For seamless tubes:

"ASTM B338 GR1 titanium tube, seamless, pickled finish. Hydrostatic test per ASTM B338. Mill certificate EN 10204 Type 3.1 required."

Add for either type:

"Heat number stamped on each tube. Traceability required from tube to certificate."

For welded tubes: Run a fingernail across the weld seam. A properly drawn tube has a seam that cannot be felt. Weld color should be silver or light gray. Blue or straw indicates poor argon shielding during welding.

For seamless tubes: Check for wall eccentricity. Cut a short piece from one end. Measure wall thickness at four points around the circumference (0°, 90°, 180°, 270°). Thick and thin measurements should not differ by more than 10%.

For both types: Confirm the heat number on the tube matches the mill certificate.

1. Is there a pressure rating difference between seamless and welded?
No. Both are rated the same per ASTM B338. The weld seam is not a weak point when properly made. Some engineering codes apply a weld efficiency factor to welded tubes (typically 0.85), which effectively derates them. That is a code requirement, not a material limitation.

2. Can welded tubes be used for U-bends?
Yes, for bend radii above 3x OD. For tighter bends, seamless is safer. For welded U-bends, we can orient the weld seam to the neutral axis upon request.

3. How to identify a good quality welded tube?
Two checks. First, run a fingernail across the weld seam. A good tube has a seam that cannot be felt. Second, look at the weld color. Silver or light gray is good. Blue or straw indicates contamination.

4. Do seamless tubes have hidden defects?
Yes. Seamless tubes can have wall eccentricity (thick on one side, thin on the other). They can also have internal surface cracks from the piercing process. Hydrostatic testing and ultrasonic testing catch most of these.

5. Which type is more common in power plants?
Welded. Most power plants switched from seamless to welded for condenser tubes in the 1990s. Performance is identical and cost is lower. Some nuclear plants still specify seamless for conservatism.

6. Can seamless and welded be mixed in the same heat exchanger?
Technically yes, but not recommended. Different expansion behavior can cause tube sheet joint problems. One type should be used for the entire bundle.

7. Does welding change the GR1 grade?
No. The weld metal is the same GR1 material. No filler metal is used. The weld zone may have slightly different grain structure, but mechanical properties still meet ASTM B338.

8. Why do some specifications still call for seamless?
Legacy specifications. Many were written decades ago when welded titanium tubes were less reliable. Modern welded tubes are excellent. If a specification calls for seamless, a deviation request may save significant cost.

9. What is the minimum wall thickness for welded GR1 tubes?
0.5 mm is the practical minimum. Below that, welded tubes are difficult to produce reliably. For thinner walls, seamless is the only option.

10. Which type is recommended for a seawater-cooled condenser?
Welded. Hundreds of power plants and desalination plants use welded GR1 tubes in seawater. It is a proven, cost-effective application.

ASTM B338 titanium tubes are packed in export-grade wooden cases or steel-framed bundles, with each tube end capped to prevent moisture ingress and debris contamination. Tubes are separated by foam or cardboard dividers to avoid surface scratching during transit. For U-bend tubes, individual plastic wrapping and layer separation are provided to maintain bend geometry. All packaging complies with ISPM-15 for international shipping, and heat numbers are clearly marked on each bundle or case for full traceability upon receipt.

Our facility is equipped with dedicated titanium tube production lines, including cold pilger mills, draw benches, and argon-filled annealing furnaces specifically calibrated for commercially pure titanium. For welded tubes, we use automatic TIG welding stations with online eddy current monitoring to detect weld seam defects in real time. Inspection equipment includes a full-spectrum spectrometer for chemical verification, an ultrasonic flaw detector for seamless tubes, and a hydrostatic pressure tester rated to 10,000 psi. All finished tubes pass through a laser micrometer for OD and wall thickness measurement. Our quality lab maintains independent cross-checks on every heat lot, and all inspection equipment is calibrated annually to NIST-traceable standards. This setup allows us to produce ASTM B338 tubes that consistently meet or exceed the required mechanical and corrosion performance.

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