Why Zirconium for Corrosive Service?
Zirconium is a high-performance reactive metal that offers exceptional corrosion resistance in some of the most aggressive chemical environments known to industry. Its corrosion resistance rivals that of tantalum — widely considered the most corrosion-resistant metal — at a fraction of the cost and weight. Zirconium pipe is specified for applications where conventional materials (stainless steel, nickel alloys, titanium) fail, particularly in hot concentrated acids, strong alkalis, and aggressive halogen environments.
This guide covers zirconium pipe materials, corrosion resistance data, mechanical properties, fabrication requirements, and industrial applications in corrosive service conditions.
Zirconium Pipe Grades
Grade 702 (R60702) — Unalloyed Zirconium
| Property | Value |
|---|---|
| Composition | >98.85% Zr + Hf, 0.10% max H, 0.05% max N |
| Density | 6.51 g/cm³ |
| Tensile Strength | 380–505 MPa |
| Yield Strength (0.2%) | 230–345 MPa |
| Elongation | 16–24% |
| Melting Point | 1855°C |
| Crystal Structure | HCP (alpha) at room temp; BCC (beta) above 863°C |
Grade 705 (R60705) — Zirconium-Niobium Alloy
| Property | Value |
|---|---|
| Composition | Zr + 2.5% Nb, 0.05% max H |
| Density | 6.50 g/cm³ |
| Tensile Strength | 440–620 MPa |
| Yield Strength (0.2%) | 310–450 MPa |
| Elongation | 14–20% |
| Advantage over Grade 702 | Higher strength, similar corrosion resistance |
Corrosion Resistance
Zirconium vs Other Materials in Aggressive Media
| Medium | Conditions | Zirconium | Titanium Gr.2 | Hastelloy C-276 | 316L SS |
|---|---|---|---|---|---|
| Hydrochloric acid (HCl) | 10%, 80°C | Excellent (0.0025 mm/yr) | Unacceptable | Good | Unacceptable |
| Sulfuric acid (H₂SO₄) | 50%, 100°C | Excellent | Good | Excellent | Unacceptable |
| Hydrofluoric acid (HF) | All concentrations | Excellent | Unacceptable | Unacceptable | Unacceptable |
| Phosphoric acid (H₃PO₄) | 85%, 100°C | Excellent | Good | Excellent | Moderate |
| Nitric acid (HNO₃) | 65%, boiling | Good | Unacceptable (SCC risk) | Excellent | Unacceptable |
| Sodium hydroxide (NaOH) | 50%, 100°C | Excellent | Excellent | Good | Good |
| Wet chlorine gas | All conditions | Excellent | Excellent | Good | Unacceptable |
| Organic acids (acetic) | Glacial, 120°C | Excellent | Excellent | Excellent | Good |
Unique Advantages
- HF resistance: Zirconium is one of only two metals (with Monel) that resist hydrofluoric acid at all concentrations and temperatures — a critical advantage in petroleum refining and chemical processing
- Alkali resistance: Resistant to all concentrations of NaOH and KOH up to 200°C
- Oxidizing-ferric ion resistance: Zirconium performs exceptionally well in oxidizing media containing ferric and cupric ions that severely attack stainless steels
- Steam resistance: Resistant to high-pressure steam up to 350°C
Industrial Applications
Chemical Processing
- Heat exchangers and condensers in HCl service
- Reactor vessels and agitation systems for sulfuric acid production
- Piping systems for HF alkylation units in petroleum refining
- Evaporators for caustic soda concentration
- Pickling tank linings and heating coils for acid pickling operations
Pharmaceutical and Fine Chemicals
- Reactor internals and piping for aggressive catalyst recovery
- Process equipment for organic synthesis involving halogenated compounds
- Crystallization equipment in aggressive solvent environments
Nuclear Industry
- Cladding for nuclear fuel elements (zirconium’s low neutron absorption cross-section)
- Spent fuel reprocessing equipment
- Waste treatment systems handling highly radioactive acidic solutions
Petrochemical
- HF alkylation unit piping and valves
- PTA (purified terephthalic acid) plant equipment
- Desulfurization systems in refineries
- Process condensate systems handling acidic condensates
Fabrication and Welding
Welding Requirements
- Process: GTAW (TIG) preferred; GMAW for thicker sections
- Shielding: Ultra-high purity argon (99.999%); trailing shield mandatory; back purge required
- Cleanliness: All surfaces must be free of oil, grease, and moisture; dedicated stainless steel wire brushes for cleaning
- Atmosphere control: Weld zone must maintain bright silver appearance; blue or straw color indicates oxygen contamination
- Filler metal: Grade 702 → ERZr2 filler; Grade 705 → ERZr5 filler
Forming and Machining
- Similar formability to stainless steel in annealed condition
- Springback is higher than titanium (approximately 2× that of carbon steel)
- Machining can be performed with carbide tooling at moderate speeds
- Zirconium is galling-prone; use generous lubrication during forming
- CRITICAL SAFETY NOTE: Fine zirconium chips and dust are pyrophoric (can ignite spontaneously). Machining must use generous coolant flow and chips must be kept wet at all times
Specifications and Standards
| Product Form | Specification | Grade Coverage |
|---|---|---|
| Seamless Pipe and Tube | ASTM B653 / ASME SB653 | 702, 705 |
| Welded Pipe | ASTM B653 (with additional requirements) | 702, 705 |
| Plate, Sheet, and Strip | ASTM B550 / ASME SB550 | 702, 705 |
| Bar and Wire | ASTM B550 / ASME SB550 | 702, 705 |
| Fittings | ASTM B653 (per ASME B16.9 dimensions) | 702, 705 |
| Flanges | ASTM B653 (per ASME B16.5 dimensions) | 702, 705 |
| Forgings | ASTM B550 / ASME SB550 | 702, 705 |
Economic Considerations
| Material | Approximate Pipe Cost ($/kg) | Relative Cost |
|---|---|---|
| 316L Stainless Steel | $8–12 | 1.0× |
| Titanium Grade 2 | $60–90 | 6–8× |
| Zirconium Grade 702 | $80–120 | 8–12× |
| Hastelloy C-276 | $50–75 | 5–7× |
| Tantalum | $400–600 | 40–50× |
While zirconium’s initial material cost is higher than most alternatives, its unmatched corrosion resistance in specific aggressive media can result in significantly lower life cycle costs by eliminating replacement, downtime, and maintenance expenses associated with lesser materials.
Summary
Zirconium pipe is the material of choice for corrosive service applications where conventional metals fail, particularly in hydrofluoric acid, hot concentrated hydrochloric acid, and aggressive halogen environments. Its corrosion resistance rivals tantalum at a fraction of the cost, making it an economically attractive option for the most demanding chemical processing applications.
CoreMetal Steel supplies zirconium pipe, tube, fittings, and flanges in Grade 702 and Grade 705 per ASTM B653 and ASME SB653. Contact our technical team for material selection guidance, corrosion data, and project quotation for your most demanding corrosive service applications.