What Is UNS N04400 Seamless Pipe?
UNS N04400 seamless pipe is manufactured from copper-nickel alloy UNS N04400, a nickel-copper alloy containing at least 63% nickel and 28%–34% copper. The alloy combines high mechanical strength with excellent resistance to seawater, mineral acids, alkalis, and chloride-induced stress corrosion cracking. Because the pipe is produced without a longitudinal weld seam, it offers uniform wall thickness and pressure integrity, which is why seamless product forms are preferred for critical marine, chemical, and refining applications.
Chemical Composition and Mechanical Properties
copper-nickel alloy UNS N04400 is essentially a two-element alloy: nickel (63.0% minimum) and copper (28.0%–34.0%). Iron (2.5% max), manganese (2.0% max), silicon (0.5% max), carbon (0.3% max), and sulfur (0.024% max) are present in small amounts and influence hot working, weldability, and machinability. The high nickel content provides resistance to reducing acids and caustic environments, while the copper addition is largely responsible for the alloy's outstanding behavior in seawater and other chloride-containing media.
Mechanical requirements are defined in ASTM B165 (identical to ASME SB-165). For annealed pipe with an outside diameter of 5 inches or less, the minimum tensile strength is 70 ksi (480 MPa), the minimum yield strength is 28 ksi (195 MPa), and elongation is 35%. Annealed pipe larger than 5 inches O.D. keeps the 70 ksi (480 MPa) tensile minimum but has a slightly lower yield minimum of 25 ksi (170 MPa). In the stress-relieved condition, all sizes must meet 85 ksi (585 MPa) tensile and 55 ksi (380 MPa) yield, with elongation reduced to 15%.
| Condition | Tensile Strength (min) | Yield Strength (min) | Elongation |
|---|---|---|---|
| Annealed, O.D. ≤ 5 in | 70 ksi (480 MPa) | 28 ksi (195 MPa) | 35% |
| Annealed, O.D. > 5 in | 70 ksi (480 MPa) | 25 ksi (170 MPa) | 35% |
| Stress-relieved, all sizes | 85 ksi (585 MPa) | 55 ksi (380 MPa) | 15% |
Standards and Specifications
UNS N04400 seamless pipe is covered by ASTM B165, which is technically identical to ASME SB-165. The specification establishes dimensional tolerances, tensile requirements, and testing obligations for cold-worked seamless pipe and tube of this nickel-copper alloy. Related copper-nickel alloy UNS N04400 product standards include ASTM B164 for rod, bar, and wire, ASTM B127 for plate, sheet, and strip, and ASTM B366 for welded fittings. For pressure-boundary service, UNS N04400 is also recognized in the ASME Boiler and Pressure Vessel Code.
Applications
UNS N04400 seamless pipe is widely specified where corrosion resistance and strength are both required: seawater desalination plants and marine structures; chemical plants handling sulfuric, hydrofluoric, hydrochloric, and phosphoric acids; heat exchangers and condensers that benefit from the alloy's good thermal conductivity; and petroleum refining systems exposed to corrosive process streams. The alloy also resists caustic alkalis and many salt solutions, and it can serve from cryogenic temperatures up to roughly 1000°F (538°C), depending on the service medium.
Fabrication and Welding Considerations
copper-nickel alloy UNS N04400 is readily hot- and cold-worked and can be welded by conventional arc processes using matching nickel-copper filler metals such as ENiCu-7 covered electrodes or ERNiCu-7 wire. The alloy work-hardens quickly, so machining should be performed with sharp tooling and adequate coolant to avoid work hardening. For pressure piping, completed welds are usually subject to the same hydrostatic or non-destructive examination requirements called out in the purchase specification, ensuring the finished system performs as the base material data predict.
Frequently Asked Questions
What is the UNS number for copper-nickel alloy UNS N04400? UNS N04400 is the Unified Numbering System designation for copper-nickel alloy UNS N04400, the nickel-copper alloy with 63% minimum nickel and 28%–34% copper.
Which ASTM standard covers UNS N04400 seamless pipe? ASTM B165, identical to ASME SB-165, covers cold-worked seamless pipe and tube of UNS N04400 (copper-nickel alloy UNS N04400).
What is the tensile strength of UNS N04400 seamless pipe? annealed pipe has a minimum tensile strength of 70 ksi (480 MPa); stress-relieved pipe has a minimum of 85 ksi (585 MPa), per ASTM B165.
Is UNS N04400 suitable for seawater service? Yes. Its copper content gives copper-nickel alloy UNS N04400 excellent resistance to seawater corrosion, and it is used in desalination plants, marine structures, and marine components.
Can UNS N04400 seamless pipe be welded? Yes. copper-nickel alloy UNS N04400 is weldable by common arc processes using nickel-copper filler metals such as ENiCu-7 or ERNiCu-7.
What temperature limit applies to UNS N04400? copper-nickel alloy UNS N04400 performs well from cryogenic temperatures to about 1000°F (538°C), though the practical limit depends on the service medium and stress level.
