Why UNS N04400 Fits Petrochemical Duty
UNS N04400 is a nickel-copper alloy in which the copper addition, normally 28-34%, creates a material that resists both oxidising and reducing acids. Petrochemical plants regularly combine chlorides, sulphur compounds, caustic solutions and intermittent high temperature in one process train, a mix that attacks ordinary austenitic stainless steels by pitting and chloride stress corrosion cracking. ASTM B165 pipe made from this grade holds its shape and strength across that combination, which is why it appears in reactors, heat exchangers, tanks, pumps and interconnecting piping.
The grade is also practically non-magnetic, so it is used near instrumentation and analyser loops where a magnetic material would disturb the reading. Working temperature in continuous service is generally limited to 538°C (1000°F).
Grade Identification and Equivalent Designations
Product form: seamless pipe and tube under ASTM B165 / ASME SB165.
Welded pipe is covered by ASTM B725 / ASME SB725 for the same UNS N04400 composition.
Werkstoff designation: 2.4360.
Common trade naming uses the alloy family name together with the UNS number, and the UNS number is the only unambiguous reference for procurement.
Because several neighbouring grades share similar nickel-copper chemistry, orders for petrochemical projects should always state the UNS number and the ASTM product specification rather than a commercial nickname alone.
Chemical Composition Requirements
| Element (%) | C | Mn | Si | S | Cu | Fe | Ni |
|---|---|---|---|---|---|---|---|
| UNS N04400 | 0.30 max | 2.00 max | 0.50 max | 0.024 max | 28.0-34.0 | 2.50 max | 63.00 min |
Copper is the corrosion-controlling element and must sit inside the 28-34% window; below that the alloy loses its resistance to reducing acids, above it ductility and hot workability suffer. Carbon, manganese, silicon, iron and sulphur are all capped to keep the microstructure single phase and to protect weldability.
Mechanical Properties by Condition
| Condition | Tensile strength, min | Yield strength 0.2% offset, min | Elongation in 2 in., min |
|---|---|---|---|
| Annealed, OD 5 in. (127 mm) and under | 70 ksi (480 MPa) | 28 ksi (195 MPa) | 35% |
| Annealed, OD over 5 in. (127 mm) | 70 ksi (480 MPa) | 25 ksi (170 MPa) | 35% |
| Stress relieved, all sizes | 85 ksi (585 MPa) | 55 ksi (380 MPa) | 15% |
Physical constants used in thermal and mechanical design are a density of 8.8 g/cm³ and a melting range beginning near 1350°C (2460°F). Cold-drawn and stress-relieved pipe is normally selected when higher design stress or a better surface finish is required.
Size, Schedule and Form Availability
| Parameter | Seamless pipe | Welded pipe |
|---|---|---|
| Outside diameter | 4 mm to 219 mm | 5.0 mm to 1219.2 mm |
| Wall thickness | 0.5 mm to 20 mm | As ordered to schedule |
| Schedules | SCH 5, 10, 20, 40, 60, 80, 120, 140, 160, STD, XS, XXS | As ordered to schedule |
| Lengths | Single random, double random, cut length | Single random, double random, cut length |
| Ends | Plain, bevelled, threaded or screwed | Plain, bevelled or flanged |
| Finish | AP, BA, polished, 2B, HL, No.1, No.4 | AP, BA, pickled |
| Forms | Round, square, rectangular, hollow, coiled, U-shape, pancake coil | Round, rectangular |
Manufacturing routes offered for this grade include seamless, ERW, EFW, fabricated, cold drawn welded (CDW), DOM and CEW pipe, each of which is selected according to pressure class, diameter and the applicable code. Marking on every length records standard, grade, outside diameter, wall thickness, length and heat number, or the customer's own marking scheme.
Applications Across Chemical Processing
Corrosive process streams: lines carrying acids, salts and mixed chloride media.
Chemical equipment: reactors, heat exchangers, storage tanks, transfer piping and pump bodies.
Crude oil processing: internals and linings for distillation service where chlorides concentrate.
Chlorinated hydrocarbon production: pumps and valves exposed to wet chlorine-bearing streams.
Pollution control and waste treatment: scrubber circuits and industrial effluent systems.
Ancillary duties: dairy, food-grade and fluid transfer lines where hygiene plus corrosion resistance is needed.
The combination of corrosion resistance and moderate strength lets designers use thinner walls than carbon steel with internal linings or coatings, which reduces weight and eliminates a lining maintenance schedule.
Fabrication and Field Notes
The alloy is readily welded by GTAW, GMAW and SMAW using matching nickel-copper filler metal, and it is machined with conventional tooling at lower surface speeds than carbon steel. Cold working is the only practical strengthening route, so bending and forming operations are carried out in the annealed condition and followed by annealing where the code requires it. Stress relief is applied when the pipe will operate in a chloride environment under load and the higher strength condition is acceptable.
Frequently Asked Questions
Q: What is the difference between UNS N04400 and the trade name for this alloy?
They refer to the same nickel-copper composition. The UNS number is the unambiguous reference, and ASTM B165 or ASME SB165 should be quoted alongside it on the order.
Q: Is seamless or welded pipe preferred for petrochemical plants?
Seamless pipe is standard for high-pressure and cyclic service. Welded pipe under ASTM B725 is accepted for larger diameters and lower pressure classes where the weld seam can be fully examined.
Q: What maximum temperature can be used?
Continuous service is normally limited to 538°C (1000°F). Above that, strength and oxidation resistance decline and a nickel-iron-chromium grade is selected instead.
Q: Which schedules are commonly stocked?
Schedules 10, 40, 80, 160 and XXS are the most frequently requested, with schedule 5 and 20 available to order in the smaller diameters.
Q: Can the pipe be heat treated after welding?
Post-weld heat treatment is usually unnecessary for thin-wall piping; when required by the applicable code, annealing is carried out and the pipe is cooled in air.
Q: How is quality verified for petrochemical orders?
Heat chemistry, product tensile testing, hydrostatic testing and non-destructive examination are performed as specified, with heat-number traceability retained through marking and documentation.
