ASTM B338 Titanium Pipe

ASTM B338 is a standard specification developed by the American Society for Testing and Materials (ASTM) for seamless and welded titanium and titanium alloy tubes used in condensers and heat exchangers. It covers 28 grades of titanium tubing (such as Grade 1 commercially pure titanium, Grade 2 industrial pure titanium, Grade 7 titanium‑palladium alloy, Grade 9 Ti‑3Al‑2.5V, etc.) and specifies strict requirements for chemical composition, room‑temperature tensile properties, dimensional tolerances, and nondestructive testing (eddy current and ultrasonic). This standard is specifically intended for surface condensers, evaporators, and heat exchangers, serving as the core basis for the procurement and quality acceptance of titanium heat exchanger tubes in the chemical, power, marine engineering, and refrigeration industries. Its domestic Chinese counterpart is generally GB/T 3625.

 

The standard covers tubes manufactured by three processes: seamless tubes, welded tubes, and welded and cold‑worked tubes. Seamless tubes are produced from hollow billet through a cold reducing or cold drawing process to ensure a homogeneous microstructure. Welded tubes are manufactured from annealed flat‑rolled products using an automatic arc‑welding process. Welded and cold‑worked tubes combine the economy of the welding process with the performance advantages of seamless tubes.

 

 

ASTM B338 specifies the allowable deviations for dimensions, appearance, and mechanical properties of titanium and titanium alloy tubes. Detailed dimensional control requirements-such as wall thickness, outside diameter, and length-are provided in the full text of ASTM B338. Titanium and titanium alloy tubes shall also meet the following mechanical property requirements:

• The mechanical properties of seamless and welded titanium and titanium alloy tubes shall be determined in accordance with ASTM standard requirements based on their composition.
• Mechanical properties are tested using the following standards: ASTM B861 (for welded titanium and titanium alloy tubes) or ASTM B338 (for seamless titanium and titanium alloy tubes).

 

 

Item	N	C	H	Fe	O	Al	V	Pa	Mo	Ni	Ti
GR1	0.03	0.08	0.015	0.2	0.18	/	/	/	/	/	Bal.
GR2	0.03	0.08	0.015	0.3	0.25	/	/	/	/	/	Bal.
GR3	0.05	0.08	0.015	0.3	0.35	/	/	/	/	/	Bal.
GR4	0.05	0.08	0.015	0.5	0.4	/	/	/	/	/	Bal.
GR5	0.05	0.08	0.015	0.4	0.2	5.5-6.75	3.5-4.5	/	/	/	Bal.
GR7	0.03	0.08	0.015	0.3	0.25	/	/	0.12-0.25	/	/	Bal.
GR9	0.03	0.08	0.015	0.25	0.15	2.5-3.5	2.0-3.0	/	/	/	Bal.
GR12	0.03	0.08	0.015	0.3	0.25	/	/	/	0.2-0.4	0.6-0.9	Bal.

 

 

Grade	Tensile Strength min		Yield Strength min		Elongation
	MPa	kis	Mpa	ksi	%
Gr 1	240	35	138	20	24
Gr 2	345	50	275	40	20
Gr 3	450	65	380	55	18
Gr4	550	80	483	70	24
Gr5	895	130	828	120	20
Gr 7	345	50	275	40	20
Gr 9	620	90	483	70	15
Gr12	483	70	50	50	18

 

 

• Seamless Tube Manufacturing

Seamless tubes shall be manufactured from hollow billet by any cold reducing or cold drawing process, maintaining a continuous periphery at all stages of manufacturing. This process ensures microstructural uniformity and consistency of mechanical properties throughout the tube.

• Welded Tube Manufacturing

Welded tubes are manufactured from annealed flat-rolled products by automatic arc welding or other welding methods. At a minimum, stress-relief heat treatment shall be performed after welding. The use of filler material is not permitted, ensuring that the weld metal composition remains consistent with the base metal.

• Welded and Cold-Worked Tube Manufacturing

This process combines the economy of welded tube production with the performance advantages of seamless tubes. The welded tube is subjected to sufficient cold working to final size, allowing the cast weld microstructure to transform into a typical equiaxed microstructure during subsequent heat treatment. The finished product meets the requirements for seamless tubes.

 

 

Dimensional Tolerances

• The standard specifies the permissible deviations for tube outside diameter and wall thickness, as well as specifies straightness requirements. Outside diameter tolerances range from ±0.004 in. (±0.102 mm) to ±0.010 in. (±0.254 mm), depending on the tube size, and the wall thickness tolerance is ±10%.
• For welded tubes, outside diameter inspection is performed using "go/no‑go" ring gauges. The dimensions of the ring gauges are calculated according to strict formulas:

"Go" ring gauge inside diameter = nominal pipe diameter + positive tolerance + 0.002 in.

"No‑go" ring gauge inside diameter = nominal pipe diameter − negative tolerance

 

Testing Requirements

ASTM B338 imposes very stringent testing requirements for titanium and titanium alloy tubes. These include the following:

• Quality defects in titanium and titanium alloy tubes-such as hot cracks, surface imperfections, porosity, and inclusions-shall conform to the requirements of relevant standards including ASTM E570, E426, E539, and E186.
• Mechanical property testing of titanium and titanium alloy tubes shall be performed in accordance with ASTM B338, including tensile properties, yield strength, and elongation.
• The chemical composition of titanium and titanium alloy tubes shall be analyzed according to ASTM E1447 and shall meet the requirements of the relevant standards.

 

The standard specifies strict nondestructive testing requirements, including eddy current testing, ultrasonic testing, hydrostatic testing, and pneumatic testing:

• Eddy Current Testing: Performed in accordance with Practice E426. The calibration tube is required to have three or more through‑holes with a diameter of Φ0.787 mm (0.031 in.), evenly spaced circumferentially. This rigorous calibration ensures the sensitivity for defect detection.
• Ultrasonic Testing: For welded tubes, the depth of longitudinal notches shall not exceed 10% of the wall thickness or 0.102 mm (0.004 in.), whichever is smaller. For seamless tubes, both longitudinal and transverse notches shall have a depth not exceeding 10% of the wall thickness or 0.102 mm (0.004 in.). This multi‑directional inspection ensures comprehensive quality control.
• Pressure Testing: The hydrostatic test requires a stress level equivalent to 50% of the minimum specified yield strength, with a hold time of not less than 5 seconds. The pneumatic test requires a minimum pressure of 100 kPa (about 15 psi), with a hold time of 5 seconds and no leakage allowed.

 

 

 

• Selection of Grade 2 / Grade 2H

Grade 2 is the most commonly used commercially pure titanium, offering a good balance of strength, formability, and corrosion resistance. Grade 2H provides higher guaranteed strength and is particularly suitable for pressure vessel applications. In practice, over 99% of commercial Grade 2 material already meets the 58 ksi strength requirement.

• Selection of Corrosion‑Resistant Alloys

For highly aggressive environments, palladium‑ or ruthenium‑containing grades should be selected. Grade 7 and Grade 11 contain 0.12–0.25% palladium; Grade 16 and Grade 17 contain 0.04–0.08% palladium; and Grade 26 and Grade 27 contain 0.08–0.14% ruthenium. Ruthenium‑alloyed grades offer a more economical option while providing excellent performance in many corrosive environments.

• High‑Strength Applications

Grade 9 (Ti‑3Al‑2.5V) and Grade 28 (Ti‑3Al‑2.5V‑0.08–0.14Ru) provide higher strength levels while maintaining good workability and corrosion resistance. They are suitable for high‑performance heat exchange equipment where weight reduction is required.

 

 

Q1: What is ASTM B338 and what does it cover?

A:ASTM B338 is the standard specification for seamless and welded titanium and titanium alloy tubes intended for use in surface condensers, evaporators, and heat exchangers. It covers 28 grades of titanium tubing, ranging from commercially pure titanium (Grade 1, Grade 2, Grade 3) to various alloys (Grade 5, Grade 7, Grade 9, Grade 12, etc.). The standard specifies requirements for dimensions, mechanical properties, chemical composition, and non‑destructive testing.

 

Q2: What is the difference between ASTM B338 and ASTM B861?

B:ASTM B338 is specifically designed for tubing used in heat exchangers and condensers, whereas ASTM B861 covers seamless titanium tubes for general piping systems. The two standards differ in their scope, applicable industries, and certain testing requirements.

 

Q3: What are the key mechanical properties of ASTM B338 Grade 5 (Ti‑6Al‑4V)?

A:Grade 5 titanium alloy (Ti‑6Al‑4V) offers exceptional strength: yield strength ≥ 880 MPa, tensile strength ≥ 960 MPa. Ductility is approximately 8%‑10% elongation, with reduction of area exceeding 20%. It maintains good toughness in cryogenic environments and exhibits excellent fatigue resistance-several times that of ordinary steel-along with outstanding creep resistance in working environments below 500°C.

 

Q4: What is the difference between seamless and welded titanium pipes under ASTM B338?

A:Seamless tubes are manufactured from a solid titanium billet that is heated and pierced to create a hollow tube without any seams, resulting in a homogeneous structure with uniform grain flow. Welded tubes are made from flat titanium strip cold‑formed into a cylindrical shape, with edges fused using TIG or plasma arc welding. Seamless tubes offer higher strength and uniform corrosion resistance but are more expensive. Welded tubes are more economical and offer better dimensional consistency, though the weld zone requires careful control to ensure equivalent performance.

 

Q5: What is the typical manufacturing process for ASTM B338 seamless titanium tubes?

A:Seamless titanium tubes are manufactured from hollow billet using either cold reducing or cold drawing processes. The billet is heated, then pierced through the center using a mandrel to create a hollow tube without any seams, followed by extrusion and pilgering (cold rolling) to achieve final dimensions. The manufacturing process maintains a continuous periphery in all stages, ensuring structural integrity with uniform grain flow.

 

Q6: Why is Grade 2 the most commonly used grade for heat exchanger applications?

A:Grade 2 commercially pure titanium offers the optimal balance of mechanical properties and corrosion resistance for most seawater and industrial cooling applications. It provides sufficient strength (480 MPa tensile) for pressure containment, excellent corrosion resistance to chlorides and seawater, good formability for tube bending and expansion, and cost‑effectiveness compared to higher‑alloyed grades. For most seawater heat exchangers, Grade 2 is the standard choice.

 

Q7: What quality control tests should be performed on each batch?

A:Each batch should undergo 100% nondestructive testing (eddy current and/or ultrasonic), dimensional inspection, flattening test (for welded tubes, reverse flattening also), pressure testing (hydrostatic or pneumatic), and surface inspection for defects such as hot cracks, surface imperfections, porosity, and inclusions.

 

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