What Is Zirconium?
| Property | Zr 702 (R60702) | Zr 705 (R60705) |
|---|---|---|
| UNS | R60702 | R60705 |
| Zirconium + Hafnium | 99.2% min | 95.5% min |
| Niobium | - | 2.0-3.0% |
| Iron + Chromium | 0.20% max | 0.20% max |
| Oxygen | 0.16% max | 0.18% max |
| Tensile strength (min) | 379 MPa (55 ksi) | 552 MPa (80 ksi) |
| Yield strength (min) | 207 MPa (30 ksi) | 379 MPa (55 ksi) |
| Elongation (min) | 16% | 16% |
| Density | 6.51 g/cm3 | 6.64 g/cm3 |
| Melting point | 1855°C (3371°F) | ~1855°C |
| Heat treatment | Annealed or stress-relieved | Annealed or stress-relieved |
Corrosion Resistance
Zirconium forms a highly stable zirconium oxide (ZrO2) film that resists attack by most acids:
| Environment | Zirconium Performance | Comparison to Alternatives |
|---|---|---|
| H2SO4 (all conc., to boiling) | Excellent (<0.13 mm/yr) | Outperforms Alloy 20, C-276 |
| HCl (up to 37%, to boiling) | Excellent | Outperforms all nickel alloys |
| HNO3 (all concentrations) | Excellent | Comparable to titanium |
| Phosphoric acid | Excellent | Comparable to Alloy 20 |
| Acetic/formic acid | Excellent | Comparable to C-276 |
| Alkali solutions (NaOH >40%) | Poor; rapid attack | Use nickel or Monel |
| Hydrofluoric acid | Poor; very rapid attack | Use Monel 400 |
| Ferric chloride | Poor | Use C-276 |
Zirconium is attacked by strong alkalis (above 40% NaOH), hydrofluoric acid, oxidizing chloride solutions, and fluorine gas.
ASTM Specifications
| Product Form | ASTM Specification |
|---|---|
| Seamless pipe and tube | B658 |
| Welded pipe and tube | B658 |
| Forgings | B493 |
| Plate, sheet, strip | B551 |
| Bar and rod | B550 |
Applications
- Chemical processing: sulfuric acid piping, HCl handling, acetic acid production, urea synthesis reactors
- Nuclear industry: fuel rod cladding (Zircaloy grades), reactor structural components
- Pharmaceutical: high-purity acid handling systems
- Explosive manufacturing: nitric acid concentrating equipment
Cost and Procurement
Zirconium is 10-20x the cost of stainless steel per kilogram and 3-5x the cost of Inconel 625. Lead times for zirconium piping components range from 20 to 40 weeks. The material is typically specified only after comprehensive corrosion testing confirms that nickel alloys and titanium cannot meet the required corrosion allowance.
Testing
Mill test certificates per EN 10204 3.1 must document chemistry, mechanical properties, and heat treatment. NDT includes radiographic and ultrasonic examination. Hydrostatic testing follows the applicable standard. Welding zirconium requires full inert gas (argon) shielding similar to titanium, with even stricter contamination control.
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