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Corrosion resistance data for copper-nickel flanges must be considered in conjunction with specific alloy grades (e.g., Cu-Ni 90/10, 70/30), corrosion medium type, concentration, temperature, and stress conditions. The following are measured data and industry standard references based on typical operating conditions:
1. Corrosion resistance data in seawater and salt spray environments
1. Static seawater immersion corrosion rate
Cu-Ni 90/10 alloy: In 3.5% sodium chloride (simulated seawater), the corrosion rate at 25°C is <0.005 mm/year; in seawater containing 200 ppm sulfides, the corrosion rate increases to 0.01–0.02 mm/year (data source: ASTM G48 standard test).
Cu-Ni 70/30 alloy: Under the same conditions, the corrosion rate is lower, with a static seawater corrosion rate of <0.003 mm/year at 25°C, and superior pitting resistance compared to the 90/10 alloy (due to higher nickel content).
For comparison, 316L stainless steel has a corrosion rate of approximately 0.01–0.03 mm/year in static seawater, but is prone to erosion corrosion in flowing seawater (flow rate >3 m/s), while the copper-nickel alloy maintains a corrosion rate of <0.05 mm/year even at a flow rate of 5 m/s.
2. Marine atmospheric salt spray corrosion
In a 5% NaCl salt spray test (GB/T 10125 standard, 35°C, continuous spray), after 1,000 hours of testing, the surface oxide film thickness of the Cu-Ni 70/30 alloy was <5 μm, and the weight loss rate was <0.1 g/m², which outperforms carbon steel (weight loss rate 10–20 g/m²) and ordinary brass (weight loss rate 5–10 g/m²).
II. Corrosion Resistance in Acidic Media
1. Dilute Sulfuric Acid Environment
Cu-Ni 90/10 alloy: In a 10% sulfuric acid solution, the corrosion rate at 25°C is approximately 0.1–0.2 mm/year; when the temperature rises to 60°C, the corrosion rate sharply increases to 0.5–1.0 mm/year; when the sulfuric acid concentration exceeds 20%, the corrosion rate exceeds 1.5 mm/year (data source: NACE TM0187 Corrosion Test).
For comparison: Hastelloy C-276 exhibits a corrosion rate of <0.05 mm/year in 10% sulfuric acid at 60°C, significantly outperforming the Cu-Ni alloy.
2. Hydrochloric Acid Environment
Copper-nickel alloys exhibit poor corrosion resistance in hydrochloric acid: at 5% hydrochloric acid and 25°C, the corrosion rate of Cu-Ni 70/30 is approximately 0.5–1.0 mm/year, and the risk of pitting corrosion increases with rising chloride ion concentration; when the temperature exceeds 50°C, the corrosion rate can exceed 2.0 mm/year, so it is strictly prohibited for use in hydrochloric acid medium pipelines.
III. Alkaline Media and Special Environments
1. Sodium Hydroxide (NaOH) Solution
In a 10% NaOH solution at 25°C, the corrosion rate of Cu-Ni 90/10 is <0.01 mm/year, demonstrating excellent alkali resistance; however, when the concentration exceeds 30% or the temperature exceeds 80°C, the corrosion rate increases to 0.1–0.2 mm/year, and stress corrosion cracking (SCC) may occur.
For comparison: Titanium alloys show no corrosion in any concentration of NaOH solution and are more suitable for strongly alkaline conditions.
2. Ammonia (NH₃) medium
Copper-nickel alloys exhibit extremely poor corrosion resistance in ammonia-containing environments: when ammonia concentration exceeds 50 ppm and temperature exceeds 20°C, SCC may occur even without stress. A typical example is the cracking of copper-nickel flanges in ammonia synthesis plants within months (data source: ASME BPVC Section VIII-3 Stress Corrosion Guidelines).
4. Localized Corrosion Resistance Data
1. Pitting Potential (E_b)
Through dynamic potential polarization testing, the pitting potential of Cu-Ni 70/30 in a 3.5% NaCl solution is approximately +0.2V (vs. SCE), higher than 304 stainless steel (-0.1V), but lower than 316L stainless steel (+0.3V), indicating that its resistance to pitting corrosion is superior to that of ordinary stainless steel. However, in chloride-containing environments, surface finish must still be controlled (roughness Ra < 1.6 μm can reduce the risk of pitting corrosion).
2. Crevice Corrosion Critical Temperature (CCT)
The CCT of Cu-Ni 90/10 in a 3.5% NaCl solution is approximately 40°C, meaning that when the temperature exceeds 40°C and gaps are present (such as in flange gasket contact areas), crevice corrosion may occur, with corrosion rates exceeding 0.5 mm/year; in contrast, the CCT of duplex steel 2205 is >70°C, demonstrating superior resistance to crevice corrosion.
5. High-Temperature Oxidation and Long-Term Corrosion Resistance Data
At 300°C in dry air, the oxidation rate of Cu-Ni 70/30 is approximately 0.02 mm/year, with a dense CuO-NiO composite oxide layer forming on the surface; when the temperature rises to 400°C, the oxidation rate increases to 0.1 mm/year, and the oxide layer begins to peel off; compared to 310S stainless steel (oxidation rate at 800°C is 0.05 mm/year), the high-temperature oxidation resistance of the copper-nickel alloy is significantly insufficient.
Data Application Notes
Data Deviation Factors: Actual corrosion rates are influenced by factors such as medium flow rate, dissolved oxygen content, microorganisms (e.g., SRB bacteria), and surface contamination. For example, in seawater containing sulfate-reducing bacteria, the corrosion rate of the copper-nickel alloy may increase by 2–3 times.
Standard References: The above data is based on laboratory static testing. For engineering applications, dynamic operating condition assessments should be conducted in accordance with standards such as NACE MR0175 (oil and gas industry) and ASTM B151 (copper-nickel alloy standard).
Safety margin recommendations: In seawater and slightly acidic media, the design corrosion allowance for copper-nickel flanges is typically 0.5-1.0 mm (calculated for a 20-year service life). In environments where ammonia or high temperatures may be present, copper-nickel materials should be avoided.

As shown by specific data, copper-nickel flanges perform excellently in seawater, neutral salt solutions, and weakly alkaline environments. However, they exhibit significant shortcomings in corrosion resistance in strong acid, ammonia, and high-temperature scenarios. When selecting materials, it is essential to precisely match process parameters with material corrosion data.