ASTM B165 Seamless Pipe in UNS N04400
ASTM B165 is the specification for seamless pipe in UNS N04400, the nickel-copper alloy that has been the reference material for seawater and hydrofluoric acid service for decades. The grade is a single phase solid solution alloy, which is why it keeps its toughness from cryogenic temperatures up to about 538 degC (1000 degF), hardens only by cold working, and welds readily. The ASME equivalent, SB-165, is used where pressure vessel acceptance is required.
Pipe is delivered in the annealed condition, with a soft matte finish, or in the stress relieved condition where dimensional stability or a specific hardness window is needed. Seawater cooling systems, offshore process piping and chemical plant lines that handle reducing media are the classic applications.
Chemical Composition and Metallurgy
| Element | Requirement, % |
|---|---|
| Nickel | 63.00 min |
| Copper | 28.0-34.0 |
| Iron | 2.50 max |
| Manganese | 2.00 max |
| Carbon | 0.30 max |
| Silicon | 0.50 max |
| Sulfur | 0.024 max |
The nickel-copper balance keeps the alloy austenitic and non magnetic under normal conditions, so it can be used where magnetic interference must be avoided. A sulfur ceiling of 0.024 % matters for hot workability: higher sulfur levels embrittle the alloy during hot piercing and forging, which is one reason the chemistry is checked before every heat is released to the piercing mill.
Mechanical Properties
| Property | Requirement |
|---|---|
| Tensile strength | 480 MPa (70 ksi) min |
| Yield strength | 170 MPa (25 ksi) min |
| Elongation | 35 % min in 2 in |
| Hardness, Rockwell B | typically 65-80 |
| Service temperature range | cryogenic to about 538 degC (1000 degF) |
Those minimums apply to the annealed condition. Cold drawing or cold rolling lifts strength and hardness, but the annealed figures are the ones normally used for wall thickness design in marine and chemical piping.
Seawater and Chemical Resistance
UNS N04400 combines a very low corrosion rate in fast moving seawater with resistance to chloride induced stress corrosion cracking in most fresh and industrial waters, which is the combination offshore engineers need for pumps, valves, heat exchanger tubing and seawater intake lines. The alloy also performs in both oxidising and reducing environments, giving it unusual versatility in chemical service.
Its most distinctive characteristic is compatibility with fluorine chemistry. The alloy resists fluorine, hydrofluoric acid, hydrogen fluoride and its derivatives, and holds its resistance in all concentrations of hydrofluoric acid up to the boiling point. It is also used with sulphuric acid and other reducing agents, and handles hydrocarbons reliably in petrochemical and refining units.
Fabrication, Manufacturing Route and Quality Control
Seamless pipe is produced from high purity billets or ingots that meet the specification, hot pierced into a hollow shell, then cold drawn or cold rolled to final dimensions and surface finish. After cold reduction the pipe is annealed to restore ductility and relieve internal stresses, straightened, cut to length, and tested.
Material control: chemistry verified against the specification before hot working.
Forming: hot piercing followed by cold drawing or cold rolling for dimensional accuracy.
Heat treatment: annealing for ductility and stress relief.
Finishing: straightening, cutting to specified lengths, end preparation.
Testing: hydrostatic and non destructive examination plus chemical testing on each lot.
Fabrication: the alloy is readily welded, machined and cold formed, which keeps shop fabrication straightforward.
Frequently Asked Questions
Q: What is UNS N04400?
It is a nickel-copper solid solution alloy supplied as seamless pipe under ASTM B165, with ASME SB-165 as the pressure vessel equivalent.
Q: Why is it used in marine service?
It has a low corrosion rate in fast moving seawater and resists chloride stress corrosion cracking in most waters.
Q: Does it resist hydrofluoric acid?
Yes. It resists fluorine, hydrofluoric acid and hydrogen fluoride in all concentrations up to the boiling point, which few alloys can match.
Q: Is the pipe magnetic?
No. The nickel-copper austenitic structure is non magnetic under normal conditions.
Q: What surface conditions are available?
Annealed with a soft matte finish or stress relieved, depending on the dimensional and hardness requirements of the order.
Q: Can the pipe be hardened?
Only by cold working. Heat treatment is used for annealing and stress relief rather than for strengthening.
