Titanium Grade 7 (UNS R52404) and Grade 12 (UNS R53400) represent the two most important alloy modifications designed to enhance commercially pure titanium’s corrosion resistance through small but strategic additions of precious metals. While Grade 2 titanium offers excellent general corrosion resistance, certain aggressive environments require the enhanced performance these palladium- and ruthenium-modified grades provide.
Chemical Composition
Titanium Grade 7 (UNS R52404 / 3.7124)
- Titanium: Balance
- Palladium: 0.12-0.25%
- Iron: ≤0.30%
- Oxygen: ≤0.25%
- Carbon: ≤0.08%
- Nitrogen: ≤0.03%
- Hydrogen: ≤0.015%
Titanium Grade 12 (UNS R53400 / 3.7225)
- Titanium: Balance
- Palladium: 0.12-0.25% (some specifications also include Ru additions)
- Molybdenum: 0.3-0.8%
- Nickel: 0.6-0.9%
- Iron: ≤0.30%
- Oxygen: ≤0.25%
- Carbon: ≤0.08%
- Nitrogen: ≤0.03%
- Hydrogen: ≤0.015%
Grade 7 adds palladium to pure titanium, while Grade 12 adds palladium plus molybdenum and nickel, creating a more complex alloy system that offers enhanced resistance in specific environments.
Enhanced Corrosion Resistance Mechanisms
Palladium Addition Effect
Palladium enhances titanium’s corrosion resistance through cathodic modification. In reducing acid environments where titanium’s protective TiO₂ film is unstable, the noble palladium particles act as cathodic sites that promote controlled formation and maintenance of the passive oxide film. Even at concentrations as low as 0.12-0.25%, palladium dramatically improves resistance to:
- Reducing acids (HCl, H₂SO₄ at moderate concentrations)
- Crevice corrosion in hot chloride solutions
- Organic acid corrosion
Molybdenum and Nickel Addition Effect (Grade 12)
The additional Mo and Ni in Grade 12 provide solid solution strengthening and further enhance resistance to:
- Crevice corrosion at temperatures above 100°C
- Reducing acid environments with chloride contamination
- Sour (H₂S-containing) environments in oil and gas production
Crevice Corrosion Resistance
This is the most significant practical difference between the grades:
Critical Crevice Corrosion Temperature (CCCT)
Testing in saturated NaCl solution at pH 2:
- Grade 2 (unmodified CP Ti): CCCT ≈ 70°C
- Grade 7 (Pd-modified): CCCT ≈ 105°C
- Grade 12 (Pd+Mo+Ni modified): CCCT ≈ 120°C or higher
Grade 12’s higher CCCT makes it the preferred choice for high-temperature chloride environments where crevice corrosion is a risk, such as hot seawater systems and concentrated brine service.
Performance in Specific Environments
Hydrochloric Acid (HCl)
| Concentration | Temperature | Grade 2 | Grade 7 | Grade 12 |
|---|---|---|---|---|
| 5% HCl | Boiling | Attack | Resistant | Resistant |
| 10% HCl | 60°C | Severe | Resistant | Resistant |
| 1% HCl | Boiling | Attack | Acceptable | Resistant |
Sulfuric Acid (H₂SO₄)
| Concentration | Temperature | Grade 2 | Grade 7 | Grade 12 |
|---|---|---|---|---|
| 5% H₂SO₄ | Boiling | Moderate | Good | Good |
| 10% H₂SO₄ | 80°C | Attack | Acceptable | Resistant |
| 20% H₂SO₄ | 60°C | Severe | Moderate | Acceptable |
Organic Acids
For formic acid and acetic acid service (common in chemical and petrochemical processing):
- Grade 7: Excellent resistance to hot organic acids, widely specified in chemical plant heat exchangers
- Grade 12: Comparable or slightly better resistance, with additional margin in contaminated (chloride-containing) organic acid streams
Mechanical Properties
| Property | Grade 7 | Grade 12 |
|---|---|---|
| Yield Strength (MPa) | ≥345 (min, annealed) | ≥483 (min, annealed) |
| Tensile Strength (MPa) | ≥483 | ≥620 |
| Elongation (%) | ≥20 | ≥18 |
| Hardness (HRC) | ~20 | ~28 |
Grade 12 offers significantly higher strength (approximately 30-40% higher yield strength) due to Mo and Ni solid solution strengthening. This allows thinner-wall designs that can offset the higher material cost in pressure equipment applications.
Application Comparison
Where Grade 7 Is Preferred
- Chemical process heat exchangers in organic acid service
- Flue gas desulfurization (FGD) system components
- Chlor-alkali plant components
- General upgrading from Grade 2 where crevice corrosion is a marginal concern
- Pharmaceutical and food processing equipment
- Automotive exhaust systems (high-temperature oxidation resistance)
Where Grade 12 Is Preferred
- Oil and gas production in sour (H₂S) environments – subsea equipment, Christmas trees
- High-temperature seawater and brine systems (desalination, power plant cooling)
- Geothermal processing equipment
- Chemical process equipment in chloride-contaminated reducing acid service
- Pressure vessels where higher strength allows wall thickness reduction
Welding and Fabrication
Both grades are readily weldable using standard CP titanium procedures:
- Filler metal for Grade 7: AWS A5.16 ERTi-7 (matching) or ERTi-1 for lower cost
- Filler metal for Grade 12: AWS A5.16 ERTi-12 (matching) or ERTi-7 as alternative
- Shielding: 100% argon with trailing shield and back purging mandatory
- Interpass temperature: Maximum 260°C (500°F)
- Post-weld: Generally not required for corrosion resistance
Cost Comparison
- Grade 7: Approximately 15-25% more expensive than Grade 2, due to palladium addition
- Grade 12: Approximately 25-40% more expensive than Grade 2, due to Pd + Mo + Ni additions
- Grade 12 vs Grade 7: Grade 12 is typically 10-15% more expensive than Grade 7
The cost premium must be evaluated against lifecycle benefits in the specific service environment.
CoreMetal Supply for Titanium Products
CoreMetal Steel supplies Titanium Grade 7 and Grade 12 in plate, sheet, pipe, tube, and round bar form. All products comply with ASTM specifications (B265 for plate/sheet, B338 for seamless tube, B861/B862 for pipe) and carry full EN 10204 3.1 mill test certificates.
Contact CoreMetal Steel for quotations on Titanium Grade 7 and Grade 12 products with expert material selection guidance for your corrosive service application.