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Copper-nickel flanges are widely used in marine engineering, chemical industry, shipbuilding, and seawater treatment. Their product advantages primarily lie in corrosion resistance, mechanical properties, processability, and overall cost-effectiveness, as detailed below:
1. Excellent resistance to seawater and chloride corrosion
Resistance to comprehensive seawater corrosion: Copper-nickel alloys (such as Cu-Ni 90/10, 70/30) form a dense layer of cupric oxide (Cu₂O) passivation film on their surfaces when exposed to seawater, effectively preventing chloride ion penetration. with an annual corrosion rate typically <0.05 mm, far lower than carbon steel (0.1–0.5 mm/year) and ordinary stainless steel (0.05–0.2 mm/year). For example, in ship seawater piping systems, copper-nickel flanges can operate in direct contact with seawater for over 20 years without replacement, while carbon steel flanges, even with corrosion-resistant coatings, may develop perforations within five years.
Resistance to pitting corrosion and stress corrosion: Copper-nickel alloys exhibit virtually no pitting corrosion in chloride-ion environments (pitting potential > +0.2 V vs. SCE) and are immune to chloride-induced stress corrosion cracking (SCC). Compared to 316L stainless steel, which may still fail due to crevice corrosion in seawater environments, the corrosion of copper-nickel flange sealing surfaces is negligible.
Resistance to sulfide and biofouling: Copper ions have natural antibacterial properties, inhibiting the attachment of microorganisms (such as barnacles and algae) in seawater and reducing biofouling. Additionally, in oil and gas environments containing H₂S, copper-nickel alloys are unlikely to undergo sulfide stress cracking (SSC), whereas carbon steel and low-alloy steel require additional corrosion inhibition treatment in such environments.
II. Excellent mechanical properties and temperature resistance
Balance of strength and toughness: Copper-nickel alloys have tensile strengths of 300–450 MPa and elongation rates exceeding 30%, combining high strength with impact toughness. For example, Cu-Ni 70/30 flanges maintain good toughness at -196°C, making them suitable for low-temperature seawater systems in liquefied natural gas (LNG) receiving terminals; in contrast, carbon steel tends to become brittle at low temperatures and requires normalizing treatment.
Stability in Medium-Temperature Environments: Copper-nickel alloys can be used long-term at temperatures of 200–300°C with a strength reduction of less than 10%, making them suitable for applications such as heat exchangers and seawater heating pipes. In contrast, austenitic stainless steel may experience intergranular corrosion due to carbide precipitation at temperatures above 300°C, whereas copper-nickel alloys do not pose this risk.
3. Excellent Machining and Welding Performance
Forming and machining properties: Copper-nickel alloys exhibit good plasticity and can be formed via cold bending, hot forging, and other processes. During machining, they do not easily undergo work hardening (work hardening index < 0.3), and their machining efficiency exceeds that of duplex steel and nickel-based alloys. For example, marine copper-nickel flanges can be directly manufactured into complex fittings via cold pressing, whereas duplex steel requires deformation control to prevent cracking.
Wide Welding Adaptability: Copper-nickel alloys can be welded using TIG, MIG, and manual arc welding processes. No special preheating or post-welding heat treatment is required, and the heat-affected zone does not exhibit embrittlement or intergranular corrosion. Compared to nickel-based alloys (such as Inconel 625), which require strict control of interpass temperature during welding, the process difficulty is significantly reduced.
4. Thermal Conductivity and Economic Advantages
High thermal conductivity efficiency: The thermal conductivity of copper-nickel alloys reaches 16–26 W/(m·K), approximately 1.5 times that of 316L stainless steel (16 W/(m·K)), making them suitable for applications requiring rapid heat dissipation or heat exchange (e.g., seawater cooler flanges), thereby reducing thermal stress concentration.
Cost-effectiveness and lifespan: Copper-nickel alloys are more expensive than carbon steel and ordinary stainless steel but cheaper than nickel-based alloys (e.g., Inconel 625 is 3-5 times more expensive). In marine engineering, the lifecycle cost (LCC) advantage of copper-nickel flanges is significant — for example, a certain offshore platform using Cu-Ni 90/10 flanges had an initial cost 30% higher than 316L, but the operational and maintenance costs over 20 years were reduced by 60%, resulting in lower overall costs.
5. Environmental and Weather Resistance Value-Added Features
No risk of heavy metal release: The copper ion release rate in copper-nickel alloys is extremely low (<0.01 mg/L), meeting seawater discharge standards and suitable for marine engineering projects with strict environmental requirements; however, certain stainless steel flanges may release nickel ions under prolonged seawater exposure, posing ecological risks.
Resistance to atmospheric corrosion and fouling: Copper-nickel alloys form a blue-green copper patina (basic copper chloride) on their surfaces in marine atmospheres, further preventing corrosion, making them suitable for coastal exposed pipelines; their smooth surfaces also have antibacterial properties, reducing fouling-induced flow resistance and lowering maintenance frequency.
Summary
Copper-nickel flanges, with their core advantages of “seawater corrosion resistance + balanced mechanical properties + ease of processing,” have become the preferred material for marine engineering, ships, and coastal chemical plants. Compared to stainless steel and carbon steel, their long-term durability in chloride-ion environments and overall cost-effectiveness are particularly notable. Compared to nickel-based alloys, they offer greater economic advantages in moderate-temperature, non-extreme corrosion scenarios. When selecting materials, factors such as medium corrosion resistance, temperature, pressure, and environmental requirements should be considered to fully leverage their balanced advantages in corrosion resistance and mechanical properties.