What Is Titanium Grade 2?
Titanium Grade 2 (UNS R50400) is the most widely used commercially pure (CP) titanium grade for process piping, heat exchangers, and vessels. It combines excellent corrosion resistance in oxidizing acids, seawater, and chloride environments with moderate strength, low density (4.51 g/cm3; roughly 57% of steel), and complete immunity to chloride stress corrosion cracking.
Chemical Composition and Properties
| Property | Value |
|---|---|
| UNS designation | R50400 |
| ASTM grade | Grade 2 (CP titanium) |
| Titanium | Balance (99%+) |
| Carbon | 0.08% max |
| Nitrogen | 0.03% max |
| Oxygen | 0.25% max |
| Iron | 0.30% max |
| Hydrogen | 0.015% max |
| Tensile strength (min) | 345 MPa (50 ksi) |
| Yield strength (min) | 275 MPa (40 ksi) |
| Elongation (min) | 20% |
| Density | 4.51 g/cm3 |
| Melting point | 1668°C (3034°F) |
| Max service temp | 315°C (600°F); in air |
| Heat treatment | Annealed (540-595°C, air cool) |
Corrosion Resistance
Titanium forms a tenacious, self-healing titanium dioxide (TiO2) film that resists most oxidizing media. Grade 2 performance:
| Environment | Resistance |
|---|---|
| Seawater (all temperatures) | Immune to pitting, crevice, and SCC |
| Wet chlorine gas | Excellent |
| Chlorine dioxide | Excellent |
| Nitric acid (all concentrations) | Excellent |
| Organic acids | Excellent |
| Sulfuric acid (dilute, aerated) | Moderate |
| Hydrochloric acid | Poor; rapid attack |
| Reducing acids (unaerated) | Poor |
Titanium is vulnerable to reducing acids, particularly HCl and unaerated H2SO4. For reducing acid environments, palladium-alloyed grades (Grade 7/11) or nickel alloys are required.
Titanium Grades Comparison
| Grade | UNS | Oxygen | Yield (min) | Key Feature |
|---|---|---|---|---|
| Grade 1 | R50250 | 0.18% max | 170 MPa | Highest ductility, lowest strength |
| Grade 2 | R50400 | 0.25% max | 275 MPa | Standard CP grade |
| Grade 7 | R52400 | 0.25% max | 275 MPa | +0.15% Pd, better reducing acids |
| Grade 12 | R53400 | 0.25% max | 345 MPa | +0.3Mo +0.8Ni, crevice resistance |
| Grade 5 | R56400 | 0.20% max | 828 MPa | Ti-6Al-4V, high strength |
ASTM Specifications for Piping
| Product Form | ASTM Specification |
|---|---|
| Seamless pipe | B861 |
| Welded pipe | B862 |
| Forgings | B381 |
| Plate, sheet, strip | B265 |
| Bar and billet | B348 |
| Fittings | B363 |
Applications
- Desalination: MSF and MED evaporator tubes, RO HP piping
- Chemical processing: chlor-alkali, bleaching, chlorine dioxide production
- Offshore oil and gas: seawater cooling systems, fire water piping, heat exchanger tubes
- Power generation: condenser tubes, cooling water piping
- Pulp and paper: bleach plant piping and washers
Testing
Mill test certificates per EN 10204 3.1 must report chemistry (O, N, and Fe are critical), mechanical properties, and heat treatment condition. NDT includes UT for pipe and hydrostatic testing per the applicable standard. Welding titanium requires inert gas shielding (argon) on front, back, and trailing torch to prevent oxygen and nitrogen contamination.
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