What Is copper-nickel alloy UNS N04400?
copper-nickel alloy UNS N04400, registered as UNS N04400, is a solid-solution nickel-copper alloy containing about 63% nickel and 28-34% copper with small amounts of iron, manganese, silicon, and carbon. It is not hardenable by heat treatment; its strength comes from cold work and solid-solution hardening. The alloy is essentially non-magnetic in the practical sense, with low magnetic permeability, and it combines excellent resistance to seawater, salt spray, and reducing chemicals with good strength and toughness from cryogenic temperatures up to about 480-540°C in non-oxidizing service. That property envelope explains why it appears across so many industries.
Marine and Offshore Engineering
Seawater is where copper-nickel alloy UNS N04400 proves its worth. It resists pitting, crevice corrosion, and chloride-induced stress corrosion cracking in splash zones, tidal zones, and full immersion, and it retains strength and toughness under low-temperature and dynamic marine loading. Typical components are propeller and pump shafts, valve bodies and stems, fasteners, heat exchangers, condenser tubes, and piping on ships, offshore platforms, and port facilities. Where higher strength is also required, the precipitation-hardened K-500 grade replaces 400 for shafting and valve trim.
Chemical Processing and Oil and Gas
In chemical plants, copper-nickel alloy UNS N04400 handles hydrofluoric acid, non-oxidizing sulfuric and hydrochloric acids, alkaline solutions, salts, and many organic compounds better than most stainless steels in reducing environments. It is especially valued in fluorine chemistry and hydrogen-fluoride systems, appearing in reaction vessels, storage tanks, pipelines, pumps, valves, heat exchangers, agitator shafts, and filtration equipment. In oil and gas, the alloy serves drilling tools, wellhead equipment, subsea valves, flow lines, pumps, and fasteners exposed to crude oil, formation brine, and hydrogen-sulfide-bearing mixtures, where it resists corrosion while maintaining integrity under pressure at moderate temperature.
Aerospace, Electronics, Food, and Nuclear Applications
Aerospace uses copper-nickel alloy UNS N04400 for rocket-engine components, fuel-system piping, valves, fittings, and cryogenic storage and transfer hardware, where its low-temperature toughness and good weldability are decisive. The electrical and electronics industry uses it for contacts, resistance elements, spring contacts, battery parts, and terminals because of its stable electrical behavior, corrosion resistance, and low magnetic permeability in humid and salt-spray environments. Food and pharmaceutical equipment, including heat exchangers, tanks, mixing equipment, and piping, benefits from its corrosion resistance to organic acids, salts, and cleaning agents. In nuclear plants, the alloy appears in non-core auxiliary systems handling light water, deionized water, and non-oxidizing coolants, where low corrosion rates support long-term safe operation.
Specifying copper-nickel alloy UNS N04400 Components
Ordering copper-nickel alloy UNS N04400 starts with the UNS designation N04400. Common governing standards include ASTM B164 for rod, bar, and wire, ASTM B127 for plate, sheet, and strip, ASTM B165 for seamless pipe and tube, and ASTM B366 for wrought fittings; ASME versions of these specifications apply where pressure-vessel codes are involved. The purchase order should state the product form, dimensions, condition, and any supplementary testing such as hydrostatic testing, non-destructive examination, or corrosion testing required by the service. For marine and HF service, specifying the intended application and required certification helps the mill supply the right temper and quality level.
Frequently Asked Questions
What is the composition of copper-nickel alloy UNS N04400? copper-nickel alloy UNS N04400 (UNS N04400) contains about 63% nickel with copper as the principal balance (28-34%), plus small amounts of iron, manganese, silicon, and carbon; it is a solid-solution alloy, not heat treatable.
Is copper-nickel alloy UNS N04400 good in seawater? Yes. It resists pitting, crevice corrosion, and chloride stress corrosion cracking in marine environments and is widely used for shafts, valves, fasteners, and heat exchanger tubes in ships and offshore structures.
What is the difference between copper-nickel alloy UNS N04400 and copper-nickel alloy UNS N05500? K500 (UNS N05500) adds aluminum and titanium and is precipitation hardened, roughly doubling strength and hardness while keeping corrosion resistance similar to 400. Use K500 where mechanical load and wear accompany corrosion.
Which acids does copper-nickel alloy UNS N04400 resist? It resists hydrofluoric acid particularly well, plus non-oxidizing sulfuric and hydrochloric acids, alkalis, and salts. Strong oxidizing media such as hot nitric acid and ferric chloride should be avoided.
What standards cover copper-nickel alloy UNS N04400 products? ASTM B164 covers rod, bar, and wire; B127 covers plate, sheet, and strip; B165 covers seamless pipe and tube; and B366 covers fittings. ASME code editions apply for pressure boundary components.
