ASTM B338 Titanium Tubing Standard Explained
Executive summary: ASTM B338 covers seamless and welded titanium and titanium alloy tubing intended for surface condensers, evaporators, heat exchangers, and similar heat-transfer equipment. The standard addresses unalloyed grades 1, 2, 3, 7, 9, and 12, as well as alloy Grade 5. It defines outside diameter, wall thickness, length tolerances, mechanical properties, flattening and flaring tests, and certification requirements. Procurement teams frequently encounter problems when they specify ASTM B338 tubing without stating whether seamless or welded construction is required, what corrosion environment the tube must survive, and whether supplemental testing such as eddy-current or hydrostatic inspection is needed.
What ASTM B338 actually covers
ASTM B338 applies to titanium tubing used primarily in heat-transfer equipment. The tubing is supplied in straight lengths or coils. The standard covers both seamless tubes produced by extrusion or piercing and welded tubes produced from strip or sheet with a longitudinal weld seam. The choice between seamless and welded construction affects cost, availability, pressure capability, and corrosion behavior at the weld.
The standard does not cover pipe, which is governed by ASTM B861 for seamless pipe and ASTM B862 for welded pipe. Tubing is distinguished from pipe by its use in heat-transfer applications and by tighter dimensional tolerances. For a comparison of titanium pipe standards, see the ASTM B861 explained guide.
Grade selection for tubing applications
Grade selection depends on the balance between corrosion resistance, strength, and cost. Grade 2 is the most common choice for chemical processing and power-plant condensers because it offers excellent resistance to chloride-bearing cooling waters at moderate cost. Grade 7 and Grade 12 offer enhanced corrosion resistance in more aggressive environments through palladium and molybdenum additions. Grade 5 is used when higher strength is required and the heat-transfer duty is less aggressive.
| Grade | Key alloying addition | Corrosion environment | Typical tubing use |
|---|---|---|---|
| Grade 1 | None (CP Ti) | Mildly reducing to oxidizing | Maximum formability, thin-wall tubing |
| Grade 2 | None (CP Ti) | Seawater, brackish water, chlorides | Condensers, heat exchangers |
| Grade 7 | Pd addition | Reducing acids, chlorides | Chemical process tubing |
| Grade 12 | Mo, Ni addition | Moderate reducing environments | Power plant, industrial heat exchangers |
| Grade 5 | Al, V alloy | Less aggressive, strength-critical | High-pressure tubing, aerospace |
A common engineering mistake is selecting Grade 5 tubing for a corrosion-dominated application simply because it is a familiar high-performance alloy. In chloride-rich cooling water, a correctly specified Grade 2 or Grade 7 tube will outlast Grade 5 at lower cost and with better availability.
Dimensional and mechanical requirements
ASTM B338 defines outside diameter, wall thickness, and length tolerances. The standard covers tubes from small instrumentation sizes up to larger condenser tubes. Wall thickness is specified by nominal wall and must meet minimum wall requirements. Outside diameter tolerances vary by tube size and whether the tube is seamless or welded.
Mechanical property requirements depend on grade and condition. Grade 2 tubing in the annealed condition must meet a minimum tensile strength of 345 MPa and a minimum yield strength of 275 MPa. Grade 5 tubing requires minimum tensile strength of 895 MPa and minimum yield strength of 828 MPa.
| Grade | UTS (MPa, min) | YS (MPa, min) | Elongation (%) |
|---|---|---|---|
| Grade 2 | 345 | 275 | 20 |
| Grade 7 | 345 | 275 | 20 |
| Grade 9 | 620 | 485 | 15 |
| Grade 12 | 483 | 345 | 18 |
| Grade 5 | 895 | 828 | 10 |
Testing requirements and common failure modes
ASTM B338 requires tension testing, flattening tests, and flaring or flange tests to demonstrate ductility. The flattening test verifies that the tube wall can deform without cracking. The flaring test evaluates the ability to form a tube end for jointing. These tests are particularly important for welded tubing because they reveal weld-quality issues that might not be visible during visual inspection.
Common failure modes in titanium tubing systems include crevice corrosion under tube supports, galvanic corrosion at joints with dissimilar metals, and erosion-corrosion at high coolant velocities. These failures are rarely caused by the base material specification alone. More often, they result from inadequate attention to tube-to-tubesheet joint design, cooling-water chemistry control, or galvanic isolation.
Hydrostatic testing and nondestructive inspection such as eddy-current testing are frequently added as supplementary requirements. These tests are not automatically included in ASTM B338. If the tubing will operate in a critical pressure boundary, specify hydrostatic or eddy-current testing in the purchase order.
Seamless vs welded tubing: a procurement trade-off
Seamless tubing generally offers more uniform wall thickness and no weld-related corrosion sensitivity. Welded tubing is less expensive, more widely available in long coils, and sufficient for many condenser and heat-exchanger applications. The decision between seamless and welded should be based on the service environment, pressure requirements, and jointing method.
One procurement reality is that welded tubing lead times can be shorter because the starting strip material is more readily available. However, if the specification requires seamless construction, suppliers cannot simply substitute welded tube without customer approval. Ambiguous purchase orders often create last-minute material substitution issues.
Three practical procurement rules for ASTM B338 tubing
Rule 1: State seamless or welded construction explicitly. ASTM B338 covers both. A quotation for welded tubing may not meet a requirement that assumed seamless construction. Specify the construction type, outside diameter, wall thickness, and length or coil requirements clearly.
Rule 2: Match the grade to the corrosion environment, not just the strength requirement. Grade 5 is strong but not always the best corrosion choice. For chloride-bearing cooling water, Grade 2, Grade 7, or Grade 12 often provides better service life and lower total cost.
Rule 3: Specify supplemental testing when the duty is critical. Hydrostatic testing, eddy-current inspection, and more stringent dimensional tolerances are not base requirements. If the tubing is part of a pressure boundary or long-life heat exchanger, add these tests to the purchase order and define acceptance criteria.
Supply chain and fabrication considerations
ASTM B338 tubing is frequently bent, expanded, and welded into tube bundles. Tube bending requires careful control of bend radius, wall thinning, and ovality to avoid collapse or cracking. Expansion into tubesheets must be controlled to prevent over-stressing the tube wall. For tube-to-tubesheet welding, qualified welding procedures and filler metal selection are critical.
Lead times for titanium tubing can vary significantly with diameter, wall thickness, and grade. Thin-wall Grade 2 condenser tubes in common sizes are often stocked by distributors. Large-diameter or heavy-wall Grade 5 tubing may require mill lead times of twelve weeks or more. Programs with tight schedules should confirm availability before finalizing heat-exchanger designs.
For assistance specifying ASTM B338 tubing for heat exchangers, condensers, or process systems, submit your requirements through the RFQ portal. A titanium fabrication partner can support tube bending, welding, and final assembly in addition to material supply.