What Is a Seamless Monel 400 Tube?
Seamless Monel 400 Tube — UNS N04400 — is a nickel–copper solid-solution alloy (63% minimum Ni with 28.0–34.0% Cu) produced to ASTM B163 from a solid billet with no weld seam. B163 is the dedicated specification for seamless nickel and nickel-alloy condenser and heat-exchanger tubing.
Monel 400 keeps the corrosion character of unalloyed nickel in reducing media and of copper in oxidizing media, which makes it one of the few alloys suitable for hydrofluoric acid and one of the most proven materials for seawater duty. It is essentially immune to chloride stress-corrosion cracking and stays ductile from sub-zero temperatures to well above 400 °C — the reason it remains the reference alloy for condenser and heat-exchanger tube in marine and refinery service.
Key Features and Advantages
Seamless UNS N04400 tube pairs proven seawater performance with immunity to chloride stress-corrosion cracking:
Exceptional Seawater Performance: almost undetectable corrosion rates in moving seawater, with good performance under high velocities and in tidal zones.
Immune to Chloride Stress-Corrosion Cracking: the nickel–copper matrix is essentially free of chloride SCC, a persistent risk for austenitic stainless steels.
One of the Few Alloys for Hydrofluoric Acid: Monel 400 resists anhydrous HF and all concentrations of hydrofluoric acid up to boiling point when aerated.
Strong in Reducing Media: excellent in hydrochloric and sulfuric acids under reducing conditions and in most organic acids and alkalis.
Ductile from Sub-Zero to High Temperature: 35% minimum elongation in the annealed condition, retained from cryogenic temperatures to well above 400 °C.
Product Specifications and Data
To provide a comprehensive overview of this high-performance material, here are the detailed technical specifications and performance data for UNS N04400 seamless tube.
Equivalent Grade
| UNS | Common grade name | EN material number | EN steel name | JIS grade | GB/T grade |
|---|---|---|---|---|---|
| N04400 | Monel 400 | 2.4360 | NiCu30Fe | NW4400 | NS6400 / Ni68Cu28Fe (legacy) |
Grade correspondence does not make ASTM, ASME, EN, JIS and GB delivery requirements interchangeable. Confirm chemistry, heat treatment, mechanical properties, dimensions, testing and certification against the purchase specification. Approximate or unconfirmed correspondences retain their qualification. See the grade designation index.
Chemical Composition
UNS N04400 seamless tube chemistry is tightly controlled so the corrosion and mechanical performance below is repeatable:
| Grade | Ni | Cu | Fe | Mn | C | Si | S |
|---|---|---|---|---|---|---|---|
| UNS N04400 | 63.0 min | 28.0–34.0 | ≤2.5 | ≤2.0 | ≤0.30 | ≤0.50 | ≤0.024 |
Chemical requirements per ASTM B163-22, Table 1. Single values are maximum content unless a range or minimum is indicated. Monel 400 is the original nickel–copper solid-solution alloy: a 63% minimum nickel base carrying 28.0–34.0% copper, with iron, manganese, carbon, silicon and sulfur held to tight residual limits.
Typical Mechanical Properties
Values below are specification minimums for the delivery condition; they define the acceptance basis for UNS N04400 seamless tube.
| Condition | Tensile Strength, min, ksi (MPa) | Yield Strength (0.2% Offset), min, ksi (MPa) | Elongation in 2 in. or 50 mm, min, % | Rockwell Hardness (or equivalent) for annealed ends |
|---|---|---|---|---|
| Annealed | 70 (483) | 28 (193) | 35 | … |
| Stress-relieved | 85 (586) | 55 (379) | 15 | B75 max |
Mechanical properties per ASTM B163-22, Table 3. Seamless tube is normally supplied in the annealed condition; the stress-relieved condition is available on request and carries a B75 maximum hardness requirement applicable to the annealed ends of the tube. Each tube is hydrostatically or nondestructive electrically tested per the general requirements of ASTM B829.
Typical Physical Properties
These physical properties highlight the material’s ability to perform reliably across a range of environments.
| Density | Melting Range | Thermal Expansion | Thermal Conductivity | Modulus of Elasticity | Electrical Resistivity |
|---|---|---|---|---|---|
| 8.80 g/cm3 | 1300 – 1350 °C | 13.9 μm/m·°C (20–100°C) | 21.8 W/m·K (20–100°C) | 179 GPa | 0.52 μΩ·m (20°C) |
Size Tolerance Chart (mm)
Permissible variations for seamless nickel alloy tube in accordance with ASTM B163-22, Table 4:
| Nominal Outside Diameter, in. (mm) | Permissible Variation in OD, mm | Average Wall, % | Minimum Wall |
|---|---|---|---|
| 1/2 to 5/8 (12.7 to 15.9), excl | +0.13 / −0 | ±12.5 | +25% / −0 |
| 5/8 to 1-1/2 (15.9 to 38.1), incl | ±0.13 | ±10 | +20% / −0 |
| over 1-1/2 to 3 (38.1 to 76.2), incl | ±0.25 | ±10 | +22% / −0 |
Notes (dimensions per ASTM B163-22, Table 4, UNS N04400 group): tolerances apply to individual measurements and include out-of-roundness (ovality). For thin-wall tubes with a nominal wall of 3% or less of the outside diameter, the mean OD shall comply with the table and individual measurements are increased by 0.5% of the nominal OD. Note the asymmetric OD variation for the smallest size group (+0.13 mm / −0). Eccentricity: wall variation in any one cross section shall not exceed ±10% of the actual average wall of that section. For small-diameter and light-wall converter sizes, see Appendix X2 (Table X2.2).
Length Tolerance
- When tube is ordered cut-to-length, the length shall not be less than that specified; a variation of +3.2 mm (1/8 in.) is permitted, and for lengths over 30 ft (9.1 m) a variation of +6.4 mm (1/4 in.) is permitted (ASTM B163-22, 7.2).
- Tube is normally supplied in mill lengths or specific cut lengths as agreed in the order.
Disclaimer: Data above are summarized from ASTM B163-22 (Standard Specification for Seamless Nickel and Nickel-Alloy Condenser and Heat-Exchanger Tubes), Tables 1, 3 and 4. The full and most current specification documents must always be consulted for official design and procurement purposes.
Common Industrial Applications
The combination of corrosion resistance, mechanical strength and manufacturing quality makes UNS N04400 seamless tube a preferred choice for:
Marine and Offshore Engineering
Seawater-cooled condensers, pump shafts, valve trim and propeller shaft lines.
Heat Exchangers and Condensers
Power-station and desalination tubing per ASTM B163 condenser and heat-exchanger duty.
Oil Refinery Overhead Systems
Crude-distillation overhead condenser tubing where HCl-bearing sour water condenses.
Chemical Processing with HF and Reducing Acids
HF alkylating units, acid coolers and transfer lines in reducing duty.
Ordering Guide
When specifying UNS N04400 seamless tube, please include: quantity, outside diameter and wall (nominal or minimum), delivery condition, length, and any third-party inspection or supplementary requirements — our sales team will confirm the production schedule and send a formal quotation.
Frequently Asked Questions
What sizes are available for Monel 400 seamless tube?
The overall range is OD 6–257 mm; WT 0.5–35 mm. Requirements outside this range are reviewed against mill capability on request.
Which specification governs Monel 400 seamless tube?
ASTM B163 / ASME SB163 is the governing specification for Monel 400 seamless tube. The edition in force at order time is stated on the quotation and purchase order; chemistry, mechanical properties, heat treatment, dimensions and testing are reported against the ordered standard and material heat.
What inspection documents are provided?
Each order is documented with a mill test certificate stating heat chemistry and mechanical test results. EN 10204 3.1 certification, hydrostatic testing, eddy-current or ultrasonic inspection and PMI are performed when specified in the purchase order.
Ready to Request a Quotation?
Send the NPS and schedule (or actual OD and wall), quantity, length, end finish and the inspection items you need as acceptance criteria — you will get a written quotation stating the specification and edition, delivery condition, documents included and lead time.
