Review of ASTM B338 Grade 2 Commercially Pure Titanium Tubes (UNS R50400)
Technical Review of ASTM B338 Grade 2 Commercially Pure Titanium Tubes (UNS R50400)
1. Standard Overview
ASTM B338 Grade 2 titanium tube (equivalent to ASME SB338) is the authoritative standard for seamless and welded titanium and titanium alloy tubes specifically used in heat exchangers, surface condensers, and evaporators. It differs from ASTM B861, the standard for general fluid pressure pipes. This standard mainly controls the outer diameter tolerance, wall thickness accuracy, formability and non-destructive testing requirements of thin-walled heat exchanger tubes.
Grade 2 (UNS R50400) refers to unalloyed commercially pure titanium (CP-Ti) with a single-phase alpha microstructure. It is classified into two main product categories: seamless titanium tubes and welded titanium tubes (Welded & Welded-Cold Worked), which are widely applied in heat exchange equipment serving various corrosive working conditions.
Core Standard Distinction
ASTM B338: Covers Heat Exchanger Tubes — Small bore tubes, dimensioned by outer diameter, dedicated for heat exchange equipment.
ASTM B861: Covers Industrial Pressure Pipes — Sized by NPS nominal size, for general industrial fluid pipelines.
The two specifications are not interchangeable in engineering project material selection.
2. Chemical Composition Standard
Chemical Composition (Maximum Limit, wt.%, per ASTM B338-17 (2021) Finished Tube Standard)
Grade 2 and Grade 2H have identical chemical composition, differing only in mechanical property grades. B338 heat exchanger tubes and B861 pressure pipes share the same chemical composition limits but comply with different manufacturing and inspection standards, and cannot be substituted for each other.
| Element | C | Fe | O | N | H | Single Other Impurity | Total Impurity | Ti |
|---|---|---|---|---|---|---|---|---|
| Max Limit (wt.%) | ≤0.10 | ≤0.30 | ≤0.25 | ≤0.03 | ≤0.0125 | ≤0.10 | ≤0.40 | Balance |
3.1 Mechanical Performance
Tensile Strength: ≥345 MPa (50 ksi)
High ductility for bending, forming and deep processing
3.2 Physical Parameters
Melting Point: 1665 ℃
Low density, lightweight compared with steel & copper alloy
4. Core Material Advantages
Excellent resistance to pitting corrosion, crevice corrosion and chloride-induced stress corrosion cracking, ensuring long-term stable service in seawater environments.
Grade 2 titanium features superior ductility and can be processed into bent tubes and U-bend tubes, serving as the mainstream material for heat exchanger U-tube bundles.
With a much lower density than carbon steel and stainless steel, titanium equipment reduces overall structural weight. Its superior corrosion resistance delivers a far longer service life than 316L stainless steel and copper-nickel alloys, minimizing downtime maintenance and replacement costs and offering prominent life-cycle economic advantages.
5. Two Main Manufacturing Types of ASTM B338 Grade 2 Titanium Tube
5.1 Seamless Titanium Tube
Manufactured via extrusion, cold rolling/cold drawing, vacuum annealing and precision finishing of hollow titanium billets. Suitable for medium and thick-wall tubes under high-pressure working conditions.
5.2 Welded & Cold Worked Tube (WCW)
Low cost, stable dimensional accuracy, specially optimized for thin-wall heat exchanger tubes, the most widely used type for shell & tube heat exchangers.
6. Typical Application Scenarios
Originally designed for heat exchange equipment, ASTM B338 Grade 2 titanium tube are typically applied in the following industrial scenarios:
7. Material Selection & Operation Guidance
Upgrade to Grade 2H (R50400) if higher minimum tensile strength is required by working conditions.
Maintain trace dissolved oxygen in operating media to ensure continuous self-repair of the titanium passive film, which can further extend tube service life.