ASTM B467 UNS C70600 copper-nickel pipe coupons, commonly referred to as 90/10 (90% copper, 10% nickel), provide superior resistance to seawater corrosion and biofouling while offering excellent fabricability and thermal conductivity. This alloy has served as the standard material for shipboard and offshore marine piping systems for over 60 years.
The 90Cu-10Ni composition includes small additions of iron (1.0-1.8%) and manganese (1.0% max) that enhance corrosion resistance and strength. The alloy resists both general corrosion and localized attack in seawater across a wide velocity range, making it ideal for piping systems handling untreated seawater in marine vessels, offshore platforms, and coastal power plants.
Copper-nickel 90/10 dominates shipboard fire main systems, engine cooling circuits, ballast and bilge piping, potable water systems on marine vessels, offshore platform seawater intake and cooling systems, coastal power plant condenser tubes and cooling water piping, and desalination plant seawater feed piping. The material’s resistance to macrofouling (barnacles, mussels) and microfouling (slime) reduces maintenance requirements and maintains flow efficiency.
The copper content provides inherent biocidal properties that inhibit marine organism attachment and growth on interior pipe surfaces. This characteristic reduces pressure drop over time, maintains heat transfer efficiency in heat exchangers, and minimizes maintenance compared to steel or stainless steel systems that require regular mechanical or chemical cleaning to remove fouling.
C70600 maintains corrosion rates typically below 0.5 mils per year in flowing seawater with velocities up to 10 feet per second. The alloy resists erosion-corrosion and impingement attack that can damage other materials. A protective surface film forms naturally in seawater service, providing long-term protection. However, the alloy is susceptible to stress corrosion cracking in ammonia-containing environments and should not be used in such service.
GTAW is the preferred welding process for copper-nickel piping using ERCuNi filler metal. The filler metal is slightly overalloyed with nickel to compensate for copper loss during welding. No preheat is required for thin sections, but sections over 1/2″ may benefit from 200-400°F preheat to reduce thermal stresses. Back purging with nitrogen or argon protects the root pass from oxidation. Welding can be performed in all positions. Post-weld heat treatment is not required. Avoid excessive heat input to prevent grain growth and porosity.
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