If you are manufacturing Shell & Tube Heat Exchangers or Condensers for marine applications, you are almost certainly looking at the Copper-Nickel family.
Both CuNi 90/10 (C70600) and CuNi 70/30 (C71500) are the "Gold Standards" for seawater tubing. They both offer exceptional resistance to general corrosion and biofouling.
However, selecting the wrong grade can be a costly mistake:
- Over-specifying (Choosing 70/30 unnecessarily): You waste budget on expensive Nickel.
- Under-specifying (Choosing 90/10 incorrectly): You risk tube failure due to erosion-corrosion in high-velocity flows.
So, how do you decide? Let's break down the critical differences from a Procurement and Engineering perspective.
1. The Core Difference: Chemical Composition
(What you need to check on the Mill Test Certificate)
For a procurement manager, the difference starts with the raw material cost and the chemical analysis on the MTC. Nickel is the expensive ingredient here.
Comparison of Chemical Requirements (ASTM B111 Standard):
| Element | CuNi 90/10 (C70600) | CuNi 70/30 (C71500) | Why it matters? |
| Copper (Cu) | Remainder (~88.6%) | Remainder (~69.5%) | Base metal for thermal conductivity. |
| Nickel (Ni) | 9.0% - 11.0% | 29.0% - 33.0% | Nickel provides strength and corrosion resistance. 70/30 has 3x the Nickel, making it significantly more expensive. |
| Iron (Fe) | 1.0% - 1.8% | 0.40% - 1.0% | Critical for 90/10. Iron is essential to stabilize the protective film. Without this Fe content, 90/10 would corrode quickly. |
| Manganese (Mn) | 1.0% max | 1.0% max | Deoxidizer and strengthens the alloy. |
Procurement Tip: When checking the MTC for CuNi 90/10, always double-check the Iron (Fe) content. It must be above 1.0%. If it's below 1.0%, the tube will fail prematurely in seawater.
2. Physical & Mechanical Properties
(How they perform inside the Heat Exchanger)
| Feature | CuNi 90/10 (C70600) | CuNi 70/30 (C71500) | The Winner? |
| Thermal Conductivity | ~45 W/m·K | ~29 W/m·K | 90/10 Wins. It transfers heat 50% better than 70/30. |
| Tensile Strength | ~275 MPa (Min) | ~360 MPa (Min) | 70/30 Wins. It handles higher internal pressures. |
| Flow Velocity Limit | Max ~3.5 m/s | Max ~4.5 m/s + | 70/30 Wins. It resists erosion from fast-moving water better. |
| Biofouling Resistance | Excellent | Very Good | 90/10 Wins. It releases more Cu ions, preventing barnacle growth better. |
3. Application Scenarios: When to choose which?
✅ Choose CuNi 90/10 (C70600) If:
This is the "Industry Workhorse." It is the most cost-effective choice for 80-90% of marine applications.
You prioritize Heat Transfer Efficiency: Because 90/10 conducts heat better, you might be able to use a smaller heat exchanger (less surface area) to achieve the same cooling effect.
Water Velocity is Moderate: Suitable for standard cooling loops where seawater flow is steady and below 3-3.5 m/s.
Biofouling is a Risk: If the ship or platform is stationary for long periods, 90/10's superior anti-biofouling property saves maintenance costs.
Budget Constraints: It is significantly cheaper than 70/30.
Typical Use: Commercial ship condensers, seawater cooling pipes, evaporator tubes.
✅ Choose CuNi 70/30 (C71500) If:
This is the "Heavy Duty Tank." You choose this when the environment is too harsh for 90/10.
High Water Velocity / Turbulence: If the heat exchanger design requires fast flow rates (above 3.5 m/s) or has turbulent inlet zones, 70/30 is harder and resists "impingement attack" (erosion) much better.
High Pressure / Deep Sea: Used in submarine hulls or deep-sea heat exchangers where external or internal pressure is immense.
Polluted Water / Sand: If the seawater contains sand, silt, or sulfides (pollution), 70/30's harder surface resists abrasion better than the softer 90/10.
Typical Use: Naval vessels (Submarines), Desalination brine heaters, High-velocity inlet zones.
Typical applications
| Application | Preferred Alloy |
|---|---|
| Seawater piping systems | CuNi 90/10 |
| Heat exchangers and condensers | CuNi 90/10 |
| Offshore oil and gas platforms | CuNi 70/30 |
| Desalination plants | CuNi 70/30 |
| Shipbuilding (hull cladding, seawater systems) | CuNi 70/30 |
| Power plant cooling systems | CuNi 90/10 |
The selection between the two alloys depends on the specific requirements of the application, including environmental conditions, mechanical stresses, and budget constraints.
Fabrication and Weldability
Both alloys are known for their excellent fabrication properties:
Formability: CuNi 90/10 is more malleable, allowing for easier bending and forming, which is advantageous in complex installations.
Weldability: Both alloys can be welded using standard techniques. However, it's recommended to use 70/30 filler material when welding either alloy to ensure optimal joint strength and corrosion resistance.
Work Hardening: Neither alloy can be strengthened by heat treatment, but their strength can be increased through cold working processes.
Supply Forms: Straight vs. U-Bend Tubes
(Manufacturing Capabilities)
Beyond choosing the right alloy (90/10 or 70/30), the form of the tube is critical for your heat exchanger assembly. We supply both grades in the following configurations to match your tube sheet design:
Straight Length Tubes:
Available in lengths up to 15 meters (or your specific limit).
Precision cut to length with deburred ends, ready for expanding or welding into the tube sheet.
Ideal for fixed tube sheet heat exchangers.
U-Bend Tubes (U-Tubes):
The Problem Solver: In many heat exchangers, the shell and the tubes expand at different rates due to heat. U-Tubes allow the tubes to expand and contract freely, preventing stress fractures.
Our Service: We provide customized bending services for both C70600 and C71500.
Technical Assurance: The bend area is stress-relief annealed after bending to ensure the mechanical properties remain stable and corrosion resistance is not compromised at the curve.
Why buy U-Tubes directly from us? Buying pre-bent U-tubes reduces your logistics costs and fabrication time. You receive a "ready-to-install" tube bundle kit.
| Trade Name | UNS | Copper Nickel Industry Specifications | Chemical Composition | Min.Tensile (KSI) |
Min.Yield (KSI) |
Elongation % |
| CuNi 90/10 | UNS C70600 UNS C70620 |
ASME SB111, SB171, SB359, SB395, SB466, SB467, SB543 ASTM B111, B122, B151, B171, B359, B395, B432, B466, B467, B543, B608 DIN 2.0872 MIL C-15726, T-15005, T-16420, T-22214 SAE J461, J463 |
Cu 88.6 min Pb .05 max* Fe 1.8 max Zn 1 max* Ni 9-11 max Mn 1.0 max |
38 | 15 | 30 |
| CuNi 90/10 | UNS C7060X | EEMUA 144 90/10, 145 90/10, 14 90/1 | Cu rem. Pb .01 max Fe 1.5-2.0 Zn 0.2 max P 0.2 max S 0.2 max Ni 10-11 Mn 0.5-1.0 |
40 | 15 | 30 |
| CuNi 70/30 | UNS C71500 UNS C71520 |
ASME SB111, SB171, SB359, SB395, SB466, SB467, SB543 ASTM B111, B122, B151, B171, B359, B395, B432, B467, B543, B552, B608, F467, F468 DIN 2.0882 MIL C-15726, T-15005, T-16420, T-22214 SAE J461, J463 |
Cu rem (65.0 min) Pb .05 max* Fe 0.4-1.0 Zn 1 max* Ni 29-33 Mn 1 max |
52 | 18 | 45 |
| CuNi 70/30 | UNS C71640 | ASTM B111, B543, B552 | Cu rem Pb .05 max* Fe 1.7-2.3 Zn 1 max* Ni 29-32 Mn 1.5-2.5 |
63 | 25 | – |
4. Key Takeaways
To summarize your purchasing decision:
CuNi 90/10 is cost-effective and offers good corrosion resistance and thermal conductivity - ideal for standard marine piping and heat exchangers.
CuNi 70/30 provides higher strength and superior resistance in aggressive or high-velocity seawater environments - preferred for offshore and desalination systems.
Decision Factor: Choosing the right alloy depends on the operating environment (flow speed, pollution), mechanical demands (pressure), and budget considerations.
💡 Need help with your Copper Nickel Tube order?
Whether you need the high thermal efficiency of C70600 or the robust strength of C71500, we supply both grades with full EN 10204 3.1 Certification.
