Seawater Piping: The Material Challenge
Seawater is one of the most aggressive environments for metallic piping systems. The combination of high chloride content (approximately 35,000 ppm), dissolved oxygen, marine organisms, suspended solids, and varying temperatures creates multiple corrosion mechanisms that can rapidly degrade unsuitable materials. The two most widely specified materials for seawater piping are copper-nickel alloys (CuNi 90/10 and CuNi 70/30) and titanium (Grade 2 and Grade 12). Each offers exceptional seawater corrosion resistance but with distinct performance characteristics, cost profiles, and application suitability.
This guide provides a comprehensive comparison to help engineers, procurement teams, and project managers select the optimal material for their seawater piping application.
Material Overview
Copper Nickel 90/10 (CuNi 90/10, CW352H, UNS C70600)
| Property | Value |
|---|---|
| Composition | 90% Cu, 10% Ni, 1.5% Fe, 0.5% Mn |
| Density | 8.94 g/cm³ |
| Tensile Strength | 345–450 MPa |
| Yield Strength (0.2%) | 170–275 MPa |
| Elongation | 30–35% |
| Thermal Conductivity | 40–50 W/m·K |
| Maximum Service Temp | ~200°C (continuous seawater: ~80°C) |
Copper Nickel 70/30 (CuNi 70/30, CW354H, UNS C71500)
| Property | Value |
|---|---|
| Composition | 70% Cu, 30% Ni, 0.8% Fe, 0.5% Mn |
| Density | 8.94 g/cm³ |
| Tensile Strength | 450–550 MPa |
| Yield Strength (0.2%) | 220–345 MPa |
| Elongation | 25–30% |
| Thermal Conductivity | 29–37 W/m·K |
| Maximum Service Temp | ~250°C (continuous seawater: ~110°C) |
Titanium Grade 2 (UNS R50400)
| Property | Value |
|---|---|
| Composition | >99.2% Ti, 0.08% max O, 0.03% max N |
| Density | 4.51 g/cm³ |
| Tensile Strength | 345–450 MPa |
| Yield Strength (0.2%) | 275–345 MPa |
| Elongation | 20–25% |
| Thermal Conductivity | 16–17 W/m·K |
| Maximum Service Temp | ~315°C (continuous seawater: >130°C) |
Corrosion Resistance in Seawater
Copper Nickel Alloys
- Forms a protective cuprite (Cu₂O) film enriched with nickel, iron, and chloride ions
- Film forms within days of seawater exposure and self-repairs if damaged
- Excellent resistance to flowing seawater up to 2.5 m/s; higher velocities may cause erosion-corrosion
- CuNi 70/30 offers better resistance to high-velocity seawater and higher temperatures than 90/10
- Resistant to biofouling through copper ion release (biocidal effect)
- Susceptible to sulfide pollution: if seawater contains dissolved sulfides (>2 ppb), the protective film is disrupted
- Ammonia and ammonium compounds can cause stress corrosion cracking
Titanium Grade 2
- Forms an extremely stable TiO₂ passive film that is virtually impervious to chloride attack
- No measurable corrosion rate in natural seawater (<0.001 mm/year)
- Resistant to all seawater velocities up to the design limit of the piping system
- Immune to chloride pitting, crevice corrosion, and stress corrosion cracking in seawater
- Not susceptible to sulfide pollution effects
- No biofouling resistance; titanium is biologically inert and biofilms can develop
- Resistant to chlorinated seawater up to 3 ppm residual chlorine at ambient temperature
Comparative Performance Analysis
| Performance Factor | CuNi 90/10 | CuNi 70/30 | Titanium Gr.2 |
|---|---|---|---|
| General corrosion rate (seawater) | 0.025 mm/year | 0.020 mm/year | <0.001 mm/year |
| Pitting resistance | Good | Very Good | Exceptional |
| Crevice corrosion resistance | Moderate (risk in stagnant conditions) | Good | Exceptional |
| Velocity limit | 2.5 m/s (90/10); 3.0 m/s (70/30) | 3.0 m/s | No practical limit |
| Biofouling resistance | Excellent (biocidal Cu ion release) | Excellent | None (biologically inert) |
| Sulfide pollution resistance | Poor (film breaks down) | Moderate | Exceptional |
| Erosion-corrosion resistance | Moderate | Good | Exceptional |
| Design life (typical) | 20–25 years | 25–30 years | 40+ years |
Cost Comparison
Material Cost (Indicative 2026 Pricing)
| Material | Approximate Cost ($/kg) | Relative Cost vs CuNi 90/10 |
|---|---|---|
| CuNi 90/10 Pipe | $25–35 | 1.0× |
| CuNi 70/30 Pipe | $35–50 | 1.3–1.5× |
| Titanium Grade 2 Pipe | $60–90 | 2.5–3.5× |
Life Cycle Cost Considerations
- Initial cost: CuNi is significantly cheaper in material cost
- Installation cost: Similar for both; both materials can be welded, bent, and joined using conventional techniques
- Maintenance cost: Titanium requires less maintenance due to superior corrosion resistance
- Replacement cost: Ti pipe may outlast CuNi by 15–20 years, avoiding replacement costs
- Biofouling cost: CuNi systems may not require chlorination for biofouling control; titanium systems typically require periodic chlorination
- Weight cost: Titanium is 50% lighter than CuNi, reducing support structure and installation costs for elevated piping
Application Selection Guide
Choose Copper Nickel When:
- Budget constraints favor lower initial material cost
- Biofouling resistance is critical (once-through cooling water, fire water systems)
- Water velocity can be controlled below 2.5–3.0 m/s
- Service temperature is below 80–110°C
- Seawater is clean (no sulfide pollution)
- Design life requirement is 20–25 years
Choose Titanium When:
- Zero corrosion allowance is required (critical systems)
- High seawater velocities (>3 m/s) are expected
- Service temperature exceeds 110°C
- Seawater may contain sulfide pollution
- Extended design life (>30 years) is required
- Weight reduction is important (offshore platforms, floating structures)
- Chlorinated seawater (high residual chlorine) is used
- Long-term life cycle cost analysis justifies the premium
Common Applications Comparison
| Application | Typical Material | Rationale |
|---|---|---|
| Ship seawater cooling | CuNi 90/10 | Cost-effective, biofouling resistance, adequate life |
| Power plant condenser tubes | CuNi 70/30 or Ti Gr.2 | Depends on steam temperature and water chemistry |
| Offshore platform fire water | CuNi 90/10 | Low initial cost, standby service (low flow hours) |
| Desalination plant intake/outfall | Titanium Gr.2 | Long life, high temperature, chlorinated water |
| Subsea seawater injection | Titanium Gr.2 | Zero corrosion, high pressure, inaccessible for replacement |
| Coastal HVAC systems | CuNi 90/10 | Budget-driven, moderate conditions |
Summary
Copper-nickel alloys and titanium both offer proven seawater service performance, but with distinct characteristics. CuNi provides excellent biofouling resistance at a lower cost for moderate-duty applications, while titanium delivers virtually immune corrosion resistance and extended service life for demanding environments. The optimal selection depends on operating conditions, design life expectations, water chemistry, and total cost of ownership analysis.
CoreMetal Steel supplies copper nickel pipe (CuNi 90/10, CuNi 70/30) and titanium pipe (Grade 2, Grade 12) in seamless and welded configurations to ASTM, ASME, and EN standards. Contact our technical team for material selection guidance and project quotation.