Scope of SB338
ASME SB338, matching ASTM B338, covers seamless and welded titanium tubes for condensers and heat exchangers. The specification defines the composition, tensile properties, dimensions and pressure tests for each grade. Buyers commonly specify the GR1 to GR7 range, which includes the commercially pure family, the Ti-6Al-4V alloy, the cryogenic alpha alloy and the palladium-stabilized grades.
Commercially Pure Grades GR1 GR2 GR3 GR4
The CP grades differ in oxygen content and therefore in strength. GR1 is the softest and most formable, GR2 is the general-purpose grade for condenser service, GR3 adds strength for pressure duty and GR4 is the strongest CP grade for tube support and structural parts. All four resist seawater and chloride media and weld with the same argon-shielded practice.
Alloy Grades GR5 GR6 GR7
GR5, Ti-6Al-4V, is the high-strength alloy used where tubes must carry high pressure or vibration, and it is supplied in welded and drawn form for special exchangers. GR6, Ti-5Al-2.5Sn, is an alpha alloy known for toughness at cryogenic temperatures. GR7, Ti-0.2Pd, adds palladium to the GR2 base and gives the highest crevice corrosion resistance for aggressive chloride service.
Mechanical Property Comparison
GR1 and GR2 with minimum tensile strength of 240 and 345 MPa.
GR3 with a minimum of 445 MPa for pressure service.
GR4 with a minimum of 550 MPa, the strongest CP grade.
GR5 with a minimum of 895 MPa for high-load tubing.
GR7 matching GR2 strength with palladium-stabilized corrosion resistance.
Selecting a Tube Grade
The selection starts with the process media and the design pressure. For seawater and chloride coolers, GR2 is the economic default, and GR7 is chosen where crevice corrosion is a known risk. High-pressure hydraulic and structural duty moves to GR5, while cryogenic systems use GR6. GR1 and GR3 fill the formability and pressure niches between them.
Supply Forms and Testing
SB338 tubes are supplied seamless or welded, in straight lengths or coils, with pickled, polished or cleaned surfaces. Each tube is dimensionally verified and pressure tested by hydrostatic or pneumatic methods, and the lot is shipped with a certificate reporting composition and mechanical results. This documentation supports quality programs in power, chemical and marine construction.
Frequently Asked Questions
Q: What does SB338 cover?
A: ASME SB338 covers seamless and welded titanium tubes for condensers and heat exchangers, matching ASTM B338.
Q: Which grade is the default for seawater coolers?
A: GR2 is the economic default, with GR7 used where crevice corrosion is a known risk.
Q: What is the strongest CP grade in the range?
A: GR4, with a minimum tensile strength of 550 MPa.
Q: Which grade handles cryogenic service?
A: GR6, Ti-5Al-2.5Sn, is known for toughness at cryogenic temperatures.
Q: What is GR7 used for?
A: GR7, Ti-0.2Pd, is used for the most aggressive chloride and reducing-acid exchanger service.
Q: How are SB338 tubes tested?
A: Each tube is dimensionally verified and pressure tested by hydrostatic or pneumatic methods.
