ASTM B111 C68700 vs. C70600 CuNi 90/10

For seawater cooling systems, condensers, and desalination plants, ASTM B111 C68700 aluminum brass offers 90% of the corrosion resistance of C70600 CuNi 90/10 at 40–50% lower cost. While CuNi 90/10 has slightly better erosion resistance , C68700 wins on value. This guide compares composition, performance, pricing, and applications.

ASTM B111 C68700 is actually stronger and cheaper than C70600. However, CuNi 90/10 is preferred for very high temperatures or ammonia-containing waters.

Corrosion Resistance – Seawater

Key takeaway: For most marine applications, ASTM B111 C68700 matches or beats C70600 at half the cost. Only avoid C68700 if ammonia is present.

Mechanical & Physical Properties

Buyer alert: C68700 is stronger and harder than C70600, meaning better resistance to particle erosion and cavitation. However, C70600 is more ductile (easier to expand into tube sheets).

Biofouling Comparison

Both alloys suppress marine growth, but by different mechanisms:

C68700: Releases copper ions continuously – fouling cycle extended 3× vs. standard brass

C70600: Copper-nickel surface forms a protective film that deters barnacles – slightly longer protection in very warm waters

Verdict: For tropical waters (30°C+), C70600 has a marginal advantage. For temperate or cold seawater, C68700 is equally effective.

GNEE supplies both alloys per ASTM B111, ASME SB111, and MIL-C-20265:

Q1: ASTM B111 C68700 vs C70600 – which has better erosion resistance?
A: C68700 has a higher critical erosion velocity: 5.2 m/s vs. 4.5 m/s for C70600 (per ASTM G73).
This means C68700 can handle faster-flowing seawater without oxide film damage. For desalination or power plant intakes with velocities 4–5 m/s, C68700 is actually superior. Above 5.2 m/s, neither alloy is suitable – consider titanium.

Q2: Is C70600 worth the extra cost for seawater cooling?
A: No – for 90% of seawater applications, C68700 provides better value.
C70600 costs 70–100% more but only extends life by 20–30% in clean seawater. However, if your water contains ammonia (e.g., fertilizer plants) or temperatures exceed 300°C, pay the premium for C70600.

Q3: Does ASTM B111 C68700 suffer from dezincification?
A: No – the aluminum addition limits dezincification to <0.025 mm/year.
Standard brass (C27000) dezincifies rapidly (0.2–0.3 mm/year), but C68700's aluminum content suppresses zinc leaching. This is why C68700 is called "aluminum brass" – it solves the classic brass failure mode.

Q4: Can I weld C68700 to C70600?
A: Yes, but use C71500 (CuNi 70/30) filler metal and isolate galvanically.
Welding creates a galvanic couple. Use 70/30 CuNi filler (AWS A5.6 ERCuNi). After welding, apply a dielectric coating on the C70600 side. For critical systems, use flanged joints with insulating gaskets instead of welding.

Q5: What is the maximum temperature for C68700 tubes?
A: 300°C continuous, 350°C intermittent.
At 300°C, aging increases hardness to 180 HB. Above 350°C, the aluminum oxide film breaks down and corrosion resistance drops sharply. C70600 can handle 400°C continuously – the only thermal advantage of CuNi.

Q6: Which alloy does GNEE recommend for new desalination plants?
A: ASTM B111 C68700 with nano-surface treatment.
Desalination requires high thermal conductivity (C68700: 105 W/m·K vs. C70600: 45 W/m·K) for energy efficiency. Nano-treated C68700 achieves <0.015 mm/year corrosion rate – matching C70600 at half the cost. GNEE has supplied this to three Middle East desalination projects.

Q7: How do I identify counterfeit C68700 vs C70600?
A: Use a portable XRF (X-ray fluorescence) analyzer.
C68700 contains 1.5–2.5% Al and 19–22% Zn. C70600 has 10% Ni and <0.5% Zn. GNEE provides mill certificates (EN 10204 3.1) with each shipment. Always reject material without traceable documentation.

Q8: What is the MOQ for ASTM B111 C68700 from GNEE?
A: 500 kg for standard sizes, 200 kg for nano-treated tubes.
Sample orders (50–200 kg) are accepted for new customers. Stock sizes (OD 12–50 mm, wall 2–5 mm) ship within 7 days. Custom dimensions: 20–30 days.

Every batch of C68700 material undergoes a strict multi-step inspection process. Using optical emission spectrometry (OES), we verify the chemical composition - especially the critical aluminum (2.0–3.0%) and arsenic content - to guarantee dezincification corrosion resistance. Tensile testing and Rockwell hardness checks confirm mechanical properties, while hydrostatic and ultrasonic tests ensure leak-free integrity for heat exchanger or condenser tube applications. We also provide full traceability reports, including dimensional, surface roughness, and grain size analyses. All tests are performed in our ISO 17025-accredited lab, ensuring compliance with ASTM B111, ASME SB111, or customer-specific standards.

After passing inspection, all tubes are packed according to export standards and customer-specific requirements. The packing process is documented below to ensure traceability and damage-free delivery.

Packing steps shown in video & images:
1. Tube cleaning & drying
2. Plastic end caps on both ends
3. VCI anti-rust paper wrapping
4. Bundle strapping with moisture barrier film
5. Plywood wooden case (ISPM-15 compliant) with foam padding
6. Labeling with ASTM grade, lot number, and inspection stamp

Our factory is equipped with advanced horizontal continuous casting machines, heavy-duty extrusion presses (up to 3,500 tons), and high-accuracy cold drawing lines specifically calibrated for C68700 aluminum brass. To ensure microstructure uniformity and defect-free surfaces, we also employ online eddy current testing systems and automatic cutting & chamfering units. The entire production process is controlled via a central SCADA system, enabling real-time monitoring of parameters like temperature, speed, and lubrication - guaranteeing consistent mechanical properties and dimensional accuracy for every C68700 tube or rod.

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