What is ASTM B338?
ASTM B338 is the standard specification for seamless and welded titanium tube for condensers and heat exchangers. It covers commercially pure titanium grades (Grade 1, Grade 2, Grade 3) and some alloys (Grade 7, Grade 9, Grade 12). Grade 1 is the softest and most formable. Most heat exchanger tubes are ordered to this standard.
What grades does ASTM B338 cover?
| Grade | Tensile strength (min) | Key characteristic | Typical use |
|---|---|---|---|
| Grade 1 | 240 MPa | Softest, most formable | Bending, flaring, thin wall tube |
| Grade 2 | 345 MPa | Most common general purpose | Heat exchangers, piping |
| Grade 3 | 450 MPa | Higher strength | Pressure applications |
| Grade 7 | 345 MPa | Same as GR2 + palladium | Acidic environments |
| Grade 9 | 620 MPa | Medium strength (3-2.5-3) | Aerospace, hydraulic tubing |
| Grade 12 | 483 MPa | Creep resistant | High temperature service |
For most seawater heat exchangers, Grade 1 or Grade 2 are the choices. Grade 1 bends easier. Grade 2 is stronger.
What sizes does ASTM B338 Grade 1 titanium tube come in?
ASTM B338 covers tube from 1/4 inch (6.35mm) up to 3 inches (76.2mm) outside diameter. Wall thickness ranges from 0.5mm to 5.0mm.
| OD (inch) | OD (mm) | Common wall (mm) | Typical use |
|---|---|---|---|
| 1/4" | 6.35 | 0.5, 0.7, 1.0 | Instrument lines, small coolers |
| 3/8" | 9.53 | 0.5, 0.7, 1.0 | Small heat exchangers |
| 1/2" | 12.70 | 0.7, 0.9, 1.2 | Marine coolers |
| 5/8" | 15.88 | 0.7, 0.9, 1.2 | Heat exchangers |
| 3/4" | 19.05 | 0.9, 1.2, 1.6 | Condensers |
| 7/8" | 22.23 | 0.9, 1.2, 1.6 | Power plant condensers |
| 1" | 25.40 | 1.0, 1.2, 1.6, 2.0 | Industrial heat exchangers |
Dimensional tolerances per ASTM B338：
| Parameter | Tolerance |
|---|---|
| OD (under 1") | ±0.10mm |
| OD (1" to 2") | ±0.15mm |
| OD (over 2") | ±0.20mm |
| Wall thickness | ±10% |
| Length (cut) | +3mm / -0mm |
What are the chemical requirements for Grade 1 under ASTM B338?
ASTM B338 sets strict limits on impurities for Grade 1 titanium. Oxygen and iron are the most important.
| Element | Maximum (%) | Why it matters |
|---|---|---|
| Titanium (Ti) | 99.5% min | Base metal |
| Oxygen (O) | 0.18 | Low oxygen = soft and ductile |
| Iron (Fe) | 0.20 | Too much iron reduces corrosion resistance |
| Carbon (C) | 0.10 | Impurity |
| Nitrogen (N) | 0.03 | Impurity |
| Hydrogen (H) | 0.015 | Can cause hydrogen embrittlement |
What are the mechanical requirements for Grade 1 under ASTM B338?
ASTM B338 requires minimum tensile strength of 240 MPa and yield strength of 170 MPa for Grade 1. Elongation is 24% minimum.
| Property | Requirement | Typical value |
|---|---|---|
| Tensile strength | 240 MPa min | 250-300 MPa |
| Yield strength | 170 MPa min | 180-220 MPa |
| Elongation | 24% min | 25-35% |
| Hardness | Not specified | ~70-80 HRB |
Test methods：
Tensile test per ASTM E8
Flattening test per ASTM B338 (for tube)
Flaring test per ASTM B338 (for tube)
What tests are required for ASTM B338 Grade 1 titanium tube?
| Test | Seamless | Welded | Notes |
|---|---|---|---|
| Chemical analysis | Required | Required | Per heat |
| Tensile test | Required | Required | Per heat |
| Flattening test | Required | Required | Per heat (seam at 90°) |
| Flaring test | Required | Required | Per heat |
| Ultrasonic or eddy current | Required | Required | 100% of tubes |
| Hydrostatic test | Optional | Optional | Upon request |
| Weld radiography | Not required | Upon request | For welded tube only |
Acceptance criteria：
Tensile： must meet minimum values
Flatten： no cracks when flattened to specified distance
Flare： no cracks when flared to specified diameter
Ultrasonic/eddy current： no detectable flaws above reference level
Seamless vs welded under ASTM B338
ASTM B338 covers both seamless and welded titanium tube. But seamless is more common for heat exchangers.
| Factor | Seamless | Welded |
|---|---|---|
| Availability | Widely available | Less common |
| Cost | Higher | Lower (10-20% less) |
| Weld seam | No | Yes |
| Corrosion risk | No weld to worry about | Seam can corrode in some conditions |
| Typical use | Heat exchangers, condensers | Less critical service |
When to choose seamless：
Critical heat exchanger tubes
High pressure or high temperature
Seawater service
Long life requirement
When welded might be acceptable：
Low pressure, non‑critical service
Fresh water or clean environments
Temporary or short‑life equipment
FAQ
Q1： What is the difference between ASTM B338 and ASTM B861?
ASTM B338 covers tube for heat exchangers and condensers. ASTM B861 covers pipe for general piping systems. B338 has tighter dimensional tolerances and different testing requirements. For heat exchanger bundles, use B338. For seawater piping, B861 may be more appropriate.
Q2： Is Grade 1 titanium tube seamless or welded under ASTM B338?
Both are allowed. Seamless is more common for heat exchanger tubes. The standard covers both forms. Most mills produce seamless Grade 1 tube as their standard product. Welded tube is usually made to order.
Q3： What is the maximum OD for ASTM B338 Grade 1 tube?
3 inches (76.2mm) is the maximum OD covered by the standard. Larger sizes are available but fall under ASTM B861 (pipe) rather than B338 (tube). For heat exchanger applications, sizes over 3 inches are rare.
Q4：Do both seamless and welded need flattening and flare tests?
Yes, both seamless and welded tubes must pass flattening and flare tests per ASTM B338. For welded tube, the weld seam must be placed 90° from the flattening direction. This tests the weld in tension rather than compression.
Q5：If a tube passes flattening and flare tests, is the weld good?
Generally yes. But flattening and flare tests are sample tests, not 100% inspection. They catch gross weld defects. For 100% weld quality, specify radiography or eddy current testing on the weld seam. Most seamless tube users avoid this issue by buying seamless.
Q6：What material is not allowed for titanium tube?
Titanium is not allowed to contact carbon steel or copper directly. It causes galvanic corrosion of the less noble metal. In a heat exchanger, titanium tubes in a stainless steel or carbon steel tube sheet need isolation. Use ferrules or coatings at the tube sheet. ASTM B338 does not cover this, but good design practice requires it.
Q7： Can ASTM B338 Grade 1 tube be used for ASME code stamping?
Yes, but specify ASME SB338 instead of ASTM B338. ASME SB338 is identical in content but is recognized by the ASME Boiler and Pressure Vessel Code. For non‑code work, ASTM B338 is fine. For stamped vessels, use SB338.
Q8： What is the most common wall thickness for Grade 1 heat exchanger tubes?
0.9mm and 1.2mm are the most common. BWG 18 (1.24mm) is a typical specification. Thinner walls (0.5-0.7mm) are used for low pressure. Thicker walls (1.6-2.0mm) for higher pressure or extra corrosion allowance.
Q9： Does ASTM B338 require hydrostatic testing?
No, hydrostatic testing is optional under ASTM B338. Ultrasonic or eddy current testing is required for 100% of tubes. Hydrostatic testing can be added upon request. Some customers require both.
Q10： How do I specify ASTM B338 Grade 1 tube correctly?
Write： ASTM B338 Grade 1 titanium tube – 3/4" OD x 1.24mm wall – Seamless – 6.0m cut length – Ultrasonic tested – MTR required. Include standard, grade, dimensions, wall thickness, seamless or welded, length, testing, and documentation.
Q11： What is the difference between Grade 1 and Grade 2 under ASTM B338?
Grade 1 has lower oxygen (0.18% max) and lower strength (240 MPa tensile). Grade 2 has higher oxygen (0.25% max) and higher strength (345 MPa tensile). Grade 1 is softer and bends easier. Grade 2 is stronger and more common. For most heat exchangers, Grade 2 is standard. Grade 1 is used when formability is critical.
Q12： Does ASTM B338 cover titanium alloy tubes like Ti-6Al-4V (Grade 5)?
No, ASTM B338 does not cover Grade 5 (Ti-6Al-4V). Grade 5 is covered under other standards like ASTM B861. ASTM B338 covers Grades 1, 2, 3, 7, 9, and 12 only. If you need Ti-6Al-4V tube, specify a different standard.
Our Testing
We start with chemistry. A spectrometer checks titanium (99.5% min), iron (0.20% max), oxygen (0.18% max). If it fails, the whole melt is scrapped.
Next, mechanical. We pull a tube until it breaks. Must hit 240 MPa tensile and 170 MPa yield. We also flatten a ring and flare a sample. No cracks. No splits.
Then ultrasonic testing. Every tube goes through the tank. Any flaw shows on screen. Reject if signal is above reference level.
You get a Mill Test Report with every order. Heat number on every tube. Third party inspection available if you want it.
Our Packaging
Plastic caps on both ends. Chloride‑free VCI paper between layers. Shrink wrap around each bundle.
Plastic straps or stainless steel straps only. No carbon steel. Carbon steel rusts and rust particles stain titanium.
Wooden case for small diameters or cut lengths. Wooden pallet with steel bundle for standard 6m tubes.
No stamping or marking on the tube itself. Waterproof label on the bundle shows grade (GR1), size, heat number, quantity.
Our Factory Equipment
Vacuum arc remelting (VAR) furnaces melt the billet. No open air melting. Titanium reacts with oxygen.
Rotary forge or extrusion press shapes the hollow shell.
Pilger mills reduce diameter. Dedicated to titanium only. No copper on these lines.
Drawing benches hit final size. Annealing furnaces use vacuum or argon. Oxygen turns titanium blue and brittle.
Ultrasonic tank tests every tube. Clean water only. Dried immediately after.
Straightening and cutting lines use dedicated rollers and saws. No carbon steel dust.
