What ASTM B338 says about dimensions
ASTM B338 sets specific tolerances for outside diameter, wall thickness, and length. These are not suggestions. Tubes that do not meet these tolerances do not comply with the standard.
For ASTM B338 GR1 titanium tube, the following tolerances apply unless otherwise agreed in writing.
For full technical specifications of ASTM B338 GR1 titanium tube, including complete mechanical properties and test requirements, see the product page here.
Outside diameter tolerances
OD tolerance depends on tube type (seamless or welded) and specified OD range.
| OD range (mm) | Seamless tolerance (±mm) | Welded tolerance (±mm) |
|---|---|---|
| 6 to 25 | 0.10 | 0.08 |
| 25 to 50 | 0.13 | 0.10 |
| 50 to 75 | 0.15 | 0.13 |
| 75 to 100 | 0.20 | 0.15 |
| 100 to 150 | 0.25 | 0.20 |
| 150 to 200 | 0.30 | 0.25 |
For heat exchanger tube sheet rolling, specify tighter OD tolerance. Many buyers require ±0.05 mm instead of the standard tolerance. This ensures consistent expansion across all tubes.
Wall thickness tolerances
Wall thickness tolerance is ±10% of specified wall thickness for both seamless and welded tubes.
Example: For a 1.65 mm wall tube, acceptable range is 1.49 mm to 1.81 mm.
For thin wall tubes (under 1.2 mm), the 10% tolerance can cause problems. A 0.9 mm wall tube with -10% tolerance is 0.81 mm. That difference affects collapse pressure and rolling behavior. Specify tighter tolerance (±5% or ±0.05 mm) for thin wall applications.
Length tolerances
Length tolerance depends on whether tubes are cut to exact length or supplied in random lengths.
| Length type | Tolerance |
|---|---|
| Exact length (cut to order) | +0 mm / -1.5 mm |
| Random length (mill run) | Minimum length specified, no maximum |
| Multiple lengths per order | Each length within ±1.5 mm |
For U-bend tubes, leg length tolerance is typically ±1.5 mm per leg. The bend radius itself has no tolerance specified - the actual radius must match the drawing.
Straightness tolerance
ASTM B338 does not specify a straightness tolerance for straight tubes. This is a common gap in specifications.
For automatic tube insertion into tube sheets, straightness matters. A bent tube will not feed through baffles.
Recommended straightness tolerance for heat exchanger tubes: 1.5 mm per meter of length (0.060 inches per foot).
Write this on the PO if straightness is critical.
Surface finish requirements
ASTM B338 requires the tube surface to be free of:
Laps
Cracks
Scabs
Visible oxide flakes
Embedded iron particles
The standard does not specify a surface roughness value. For most heat exchanger service, pickled finish (Ra 1.5–2.5 µm) is standard. For special applications, specify roughness directly.
| Application | Recommended surface roughness (Ra) |
|---|---|
| Standard heat exchanger | 1.5–2.5 µm (pickled) |
| Food or pharmaceutical | 0.4–0.8 µm (polished) |
| Tube sheet rolling (emery rolled) | 1.0–1.5 µm |
| High-fouling service | 0.8–1.2 µm (polished) |
Flattening test requirements
The flattening test confirms ductility. A tube sample is flattened between parallel plates.
Requirement: No cracks appear on the inside or outside surface when the distance between plates is 3x wall thickness.
For welded tubes, the weld seam must be placed at 90 degrees to the flattening direction. Cracking at the weld seam during flattening is cause for rejection.
Flaring test requirements
The flaring test confirms ability to expand without cracking. A tube end is expanded with a tapered tool.
Requirement: No cracks appear when the tube end is flared to 1.5x original OD.
For welded tubes, the weld seam must survive flaring without cracking. This test is critical for tubes that will be rolled into tube sheets.
Hydrostatic test requirements
ASTM B338 requires each tube to pass a hydrostatic test.
Standard pressure: Calculated to produce a hoop stress of 70% of specified minimum yield strength (138 MPa for GR1). Holding time is 5 seconds minimum.
No leakage is permitted.
For high-pressure service, buyers can specify higher test pressure. Common practice: test at 1.5x design pressure, up to the pressure that produces 90% of yield strength.
Eddy current test requirements (for welded tubes)
Welded tubes require 100% eddy current testing of the weld seam.
The test detects:
Weld seam defects (lack of fusion, porosity)
Longitudinal defects in the weld zone
Wall thickness variations
Acceptance criteria: No signal greater than the reference notch. The reference notch is typically 5% of wall depth.
Eddy current test results are included with the mill certificate.
Receiving inspection checklist
When ASTM B338 GR1 titanium tube arrives, the following checks are recommended.
1. OD measurement
Measure at least 5 tubes per bundle using a micrometer at three points along the tube length.
2. Wall thickness measurement
Cut a short piece from one tube per heat. Measure at 4 points around the circumference.
3. Length check
Measure a sample of tubes.
4. Surface inspection
Check for rust stains, blue or straw discoloration, and visible weld seam.
5. End condition
Check that tube ends are square cut and deburred.
6. Heat number verification
Heat number stamped on the tube should match the mill certificate.
FAQ
1. What is the standard OD tolerance for GR1 heat exchanger tubes?
For 25.4 mm OD, standard tolerance is ±0.10 mm for welded tubes, ±0.13 mm for seamless. Tighter tolerance (±0.05 mm) is available.
2. Can wall thickness vary along the length of one tube?
Yes, some variation is normal. ASTM B338 allows ±10% from specified wall at any point.
3. How to measure wall thickness of installed tubes?
Ultrasonic thickness gauging is the standard non-destructive method.
4. What is the acceptable surface roughness for pickled GR1 tubes?
Pickled finish typically achieves Ra 1.5–2.5 µm. ASTM B338 does not specify a number.
5. Are minor surface scratches acceptable?
Minor scratches that do not reduce wall thickness below minimum are acceptable per ASTM B338.
6. How to check straightness on long tubes?
Roll the tube on a flat surface. A straight tube rolls evenly. A bent tube wobbles.
7. What does a failed flattening test indicate?
The tube material is too brittle. Possible causes: high oxygen content, hydrogen embrittlement, or improper annealing.
8. Is third-party inspection available?
Yes. Third-party inspection (SGS, BV, TÜV) can be arranged at buyer's request.
9. How many samples are tested for flattening and flaring?
ASTM B338 requires two tubes per heat lot for flattening test and two for flaring test. Larger sample sizes are available upon request.
10. Can dimensional tolerances be negotiated?
Yes. Special tolerances can be agreed between buyer and supplier. Expect a price adjustment for tighter tolerances.
Our Factory & Equipment
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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