Notícia

1. Performance limitations in high-temperature environments
Strength decreases significantly with increasing temperature: Copper-nickel alloys (such as Cu-Ni 70/30) experience a reduction in tensile strength from 450 MPa to below 300 MPa when temperatures exceed 300°C, and exhibit increased creep tendency. In contrast, nickel-based alloys (such as Inconel 625) can be used long-term at 650°C, limiting the applicability of copper-nickel flanges in high-temperature steam pipelines, refinery heaters, and similar scenarios.
High-temperature oxidation and zinc leaching risks: Copper-nickel alloys tend to form a loose layer of copper oxide (CuO) in atmospheric conditions above 400°C, leading to surface corrosion. Copper-nickel alloys containing zinc (such as certain modified Cu-Ni-Zn alloys) may undergo zinc leaching corrosion at high temperatures, compromising material uniformity. In contrast, 310S stainless steel (with a high-temperature resistance of 1150°C) offers significant advantages in such environments.
II. Initial Costs and Resource Constraints
Material costs are significantly higher than those of ordinary metals: Copper-nickel alloys (such as Cu-Ni 90/10) cost approximately 5–8 times that of carbon steel and 3–4 times that of 304 stainless steel. Taking a DN100 PN16 flange as an example, the unit price of a copper-nickel flange is approximately 2,000 yuan, while that of a carbon steel flange is only 300 yuan, posing pressure on initial procurement costs for budget-sensitive projects.
Scarcity of copper resources and price volatility: As a strategic resource, copper is subject to significant price fluctuations due to global supply and demand dynamics (over the past five years, copper prices on the London Metal Exchange have fluctuated between 25,000 and 100,000 yuan per ton), which may lead to uncontrollable project costs; in contrast, materials like carbon steel and stainless steel have more stable supply chains and exhibit smaller price fluctuations.
III. Corrosion Resistance Shortcomings in Specific Media
Insufficient corrosion resistance in strong acid and strong alkali environments: Copper-nickel alloys undergo rapid corrosion in dilute sulfuric acid (>5%), nitric acid (>10%), or caustic alkali (pH >12). For example, in acid-base neutralization units in the chemical industry, 316L stainless steel (nitric acid-resistant) or Hastelloy (sulfuric acid-resistant) are more suitable, while copper-nickel flanges may develop perforations within months.
Poor resistance to ammonia corrosion: Copper-nickel alloys undergo stress corrosion cracking (SCC) when exposed to ammonia gas (NH₃) or ammonium salts, and are prohibited in ammonia synthesis plants and refrigeration systems in cold storage facilities. In contrast, carbon steel and aluminum bronze flanges can be safely used in ammonia-containing environments.
4. Insufficient mechanical properties under extreme conditions
Strength limitations under high-pressure conditions: The yield strength of copper-nickel alloys (approximately 150–250 MPa) is lower than that of duplex steel (over 450 MPa) and nickel-based alloys (over 500 MPa). In high-pressure pipelines (e.g., natural gas transmission at 10 MPa or higher), copper-nickel flanges require increased wall thickness to meet strength requirements, leading to further increases in weight and cost, while duplex steel flanges can reduce dimensions due to material strength advantages.
Low-temperature toughness limitations: Although copper-nickel alloys retain toughness at -196°C (LNG temperature), their impact toughness decreases at lower temperatures (e.g., -269°C in liquid helium environments). Nickel-based alloys (e.g., Inconel 625) maintain performance at -270°C and are more suitable for extreme low-temperature research facilities.
5. Special requirements for processing and maintenance
Welding process requires high compatibility with welding materials: When welding copper-nickel alloys, specialized copper-nickel welding wire (such as ERCuNi) must be used. If stainless steel welding materials are mistakenly used, brittle phases may precipitate in the weld, resulting in a strength reduction of over 50%. In contrast, carbon steel flanges can be welded using standard E43 electrodes, which have lower process requirements.
Surface treatment and cleaning costs: Copper-nickel flanges require passivation treatment after processing to enhance corrosion resistance, while stainless steel flanges can be used directly. In sulfur-containing oil and gas environments, copper-nickel surfaces may form black copper sulfide (CuS), which does not affect the base material but requires regular mechanical cleaning, increasing maintenance workload.
6. Weight and Installation Limitations
High density leads to installation load pressure: The density of copper-nickel alloy is approximately 8.9 g/cm³, which is 1.14 times that of carbon steel (7.8 g/cm³) and 3.3 times that of aluminum alloy (2.7 g/cm³). In large-scale offshore pipelines or elevated pipe racks, the use of copper-nickel flanges may require additional reinforcement of support structures, increasing engineering costs.
Risk of galvanic corrosion when connecting dissimilar metals: When copper-nickel alloys come into direct contact with metals such as carbon steel or aluminum, the presence of an electrolyte (e.g., seawater) can form a galvanic couple, causing the copper-nickel flange to act as a cathode and accelerate corrosion of the dissimilar metal. For example, when connecting a copper-nickel flange to a carbon steel pipeline, insulating gaskets must be installed or sacrificial anode protection must be used, increasing installation complexity.
7. Environmental and Special Scenario Restrictions
Ecological Sensitivity Issues Related to Copper Ion Release: In scenarios with strict requirements for copper ion concentration (e.g., EU drinking water standards require Cu < 2 mg/L), such as freshwater aquaculture and drinking water treatment, the copper ion release rate of copper-nickel flanges (approximately 0.05–0.1 mg/L after long-term immersion) meets the standards. However, some projects still prefer to use copper-free materials (e.g., PVDF plastic flanges) to avoid potential risks.
Magnetic permeability affects the operation of special equipment: Copper-nickel alloys have a magnetic permeability close to 1 (weak magnetic properties), but in scenarios requiring non-magnetic materials, such as precision magnetic fluid seals and superconducting magnets, austenitic stainless steel (magnetic permeability ≈ 1) or titanium alloys (non-magnetic) must be used, and copper-nickel flanges cannot meet these requirements.
Summary
The inherent disadvantage of copper-nickel flanges lies in their limited suitability for scenarios beyond the “balance between corrosion resistance and mechanical properties”: in harsh conditions such as high temperatures, strong acids, high pressures, or extreme low temperatures, their performance is surpassed by nickel-based alloys, duplex steels, and other materials. Conversely, in cost-sensitive, lightweight applications, or environments involving special media (such as ammonia, strong acids, or alkalis), carbon steel, stainless steel, or non-metallic materials offer greater advantages. When selecting materials, it is essential to consider the corrosiveness of the operating conditions, temperature and pressure parameters, budget and timeline, as well as environmental requirements. A balance must be struck between the “corrosion resistance advantages” and the “application limitations” of copper-nickel flanges. If necessary, composite solutions (such as copper-nickel flanges combined with corrosion-resistant coatings) can be employed to address any shortcomings.