Monel 400 (UNS N04400): Nickel-Copper Alloy for Instrumentation Fittings, Valves & Tubing
Monel 400 (UNS N04400) is a wrought nickel-copper alloy of roughly 67% nickel and 30% copper that resists hydrofluoric acid, seawater, brine, and reducing acids better than stainless steel, making it a core material for corrosive-service instrumentation. Because it is a solid-solution alloy rather than an age-hardenable one, it keeps its corrosion resistance across a wide range of temperatures without heat-treatment.
On this page, Monel 400 refers to the wrought nickel-copper process alloy used for instrumentation fittings, valves, and tubing, not marine fasteners, propeller shafting, or musical-instrument wire. Crestflo supplies UNS N04400 as compression tube fittings, instrumentation valves, and instrument tubing, engineered for US drop-in replacement with ready stock for standard items, made-to-order for specials, and 6–8 week delivery. Monel® is a registered trademark of Special Metals Corporation; Crestflo supplies UNS N04400 to standard chemistry and is not affiliated with or endorsed by Special Metals Corporation.
Monel 400 Designations & Equivalents: UNS N04400, Werkstoff 2.4360 & Alloy 400
The same nickel-copper alloy is specified under several systems, so a drawing may call for any of these interchangeably. It is commonly written as Monel® 400, Alloy 400, or Nickel-Copper Alloy 400, and appears in spacing and ordering variants such as Monel-400, Monel400, 400 Monel, and N04400 Monel. Its formal designations are as follows.
| System | Designation |
|---|---|
| UNS | N04400 |
| Werkstoff (EN) | 2.4360 |
| DIN | NiCu30Fe |
| BS | NA13 |
| Trade / common | Monel® 400, Alloy 400, Nickel-Copper Alloy 400 |
For the higher-strength, age-hardenable version of the same nickel-copper base, see Monel K500.
Chemical Composition of Monel 400 (UNS N04400): ~67% Nickel, ~30% Copper
Monel 400 is a binary nickel-copper solid solution with minor iron and manganese. Nickel and copper are mutually soluble across the full range, which gives the alloy its single-phase structure and its resistance to chloride stress-corrosion cracking. Nominal wrought chemistry per the standard specifications is shown below; values are per applicable standard and confirmed against the mill certificate at order.
| Element | Content (wt %) |
|---|---|
| Nickel (Ni) | ≥ 63.0 |
| Copper (Cu) | 28.0–34.0 |
| Iron (Fe) | ≤ 2.5 |
| Manganese (Mn) | ≤ 2.0 |
| Carbon (C) | ≤ 0.3 |
| Silicon (Si) | ≤ 0.5 |
| Sulfur (S) | ≤ 0.024 |
Because the alloy contains no chromium or molybdenum, a PREN (Pitting Resistance Equivalent Number) does not apply, PREN is a Cr/Mo/N index used to compare stainless and duplex grades. Monel 400 corrosion performance is judged by service medium rather than by PREN.
Monel 400 Mechanical Properties: Tensile Strength, Yield, Elongation & Hardness
In the annealed condition Monel 400 combines moderate strength with high ductility and toughness, and it retains that toughness down to cryogenic temperatures. Typical annealed values per the published specifications are listed below; delivered properties depend on product form and temper and are certified per heat.
| Property (annealed) | Value (SI) | Value (imperial) |
|---|---|---|
| Tensile strength | 480–550 MPa | 70–80 ksi |
| Yield strength (0.2% offset) | 170–240 MPa | 25–35 ksi |
| Elongation | ≥ 35% | ≥ 35% |
| Hardness | ≈ 110–150 HB | ≈ 65–80 HRB |
Monel 400 work-hardens as it is cold-worked, so cold-drawn tubing and fittings can reach higher strength than the annealed base values above.
Monel 400 Physical Properties: Density (8.80 g/cm³), Melting Point & Magnetic Behavior
Monel 400 is denser than stainless steel and has a melting range typical of nickel alloys. It is one of the few common corrosion-resistant alloys that is weakly ferromagnetic near room temperature, with a Curie point close to ambient that shifts with exact composition. Its magnetic permeability is low and highly sensitive to temperature and composition around that Curie point, so lots read as only faintly magnetic.
| Property | Value |
|---|---|
| Density | 8.80 g/cm³ (0.318 lb/in³) |
| Melting range | 1300–1350 °C (2370–2460 °F) |
| Elastic modulus | ≈ 179 GPa (26 × 10⁶ psi) |
| Thermal conductivity (20 °C) | ≈ 21.8 W/m·K |
| Coefficient of thermal expansion (20–100 °C) | ≈ 13.9 µm/m·°C |
| Magnetic behavior | Weakly ferromagnetic near room temperature; low magnetic permeability; Curie point ≈ 20–50 °C (composition-dependent) |
Corrosion Resistance of Monel 400: Hydrofluoric Acid, Seawater & Sour Service
Corrosion resistance is why engineers specify UNS N04400. It is the benchmark alloy for hydrofluoric acid service and performs strongly in seawater, brine, neutral and alkaline salts, caustics, and dilute reducing acids such as sulfuric and hydrochloric. Its main limitation is strongly oxidizing media, nitric acid, oxidizing salts, wet chlorine, and ferric or cupric chlorides will attack it, and for those services 316/316L or a Hastelloy grade is usually the better choice.
| Medium | Resistance | Note |
|---|---|---|
| Hydrofluoric acid (HF) | Excellent | Industry benchmark alloy for HF service |
| Seawater / brine | Excellent | Low general corrosion; resists chloride pitting well |
| Reducing acids (dilute H₂SO₄, HCl) | Good | Depends on concentration, temperature, aeration |
| Caustics / alkalis | Excellent | Strong resistance across concentrations |
| Chloride stress-corrosion cracking | Excellent | Key advantage over austenitic stainless |
| Nitric / oxidizing acids | Poor | Choose stainless or Hastelloy instead |
| Wet chlorine, ferric/cupric chloride | Poor | Oxidizing chlorides attack the alloy |
For sour (H₂S) service, nickel-copper alloy N04400 in the annealed condition is accepted under NACE MR0175 / ISO 15156; confirm the applicable environmental limits and hardness levels for your service against ISO 15156. Crestflo instrumentation products are supplied NACE MR0175 / ISO 15156 compliant where the application requires it.
Temperature & Pressure Suitability of Monel 400
Monel 400 retains useful mechanical strength to roughly 480–540 °C and stays tough and ductile down to sub-zero and cryogenic temperatures, so it suits both hot reducing-acid service and cold seawater or LNG-adjacent duty. Pressure rating is a function of product form, size, and wall thickness rather than a property of the alloy itself, so working pressures are established on the fitting, valve, or tubing page and on the mill certificate. For high-pressure instrumentation assemblies, route the requirement through Crestflo engineering with the service conditions.
Fabrication of Monel 400: Weldability, Machining & Forming
Monel 400 is readily welded by gas tungsten arc (GTAW/TIG) and gas metal arc processes using matching nickel-copper filler, and it needs no post-weld heat treatment to restore corrosion resistance. It is tough and gummy to machine, it work-hardens quickly, so it is cut with sharp tooling, positive rake, slow speeds, and heavy feeds to stay under the hardened layer. It forms and cold-works well, which is how cold-drawn N04400 tubing gains strength above the annealed baseline.
When to Choose Monel 400 vs Monel K500, 316/316L, Inconel & Hastelloy
Choose Monel 400 when the service is hydrofluoric acid, seawater, brine, caustics, or reducing acids, or where chloride stress-corrosion cracking must be avoided. Weigh it against the alternatives when strength, oxidizing resistance, or cost drive the decision.
- vs Monel K500: K500 is the age-hardenable version of the same nickel-copper base, offering higher strength and galling resistance; choose it when mechanical loading matters more than the annealed ductility of 400.
- vs 316/316L stainless: 316L costs less and resists oxidizing acids better, but Monel 400 outperforms it in HF, seawater, and chloride SCC resistance.
- vs Inconel: for oxidizing environments and high-temperature strength, a nickel-chromium grade is preferred, see the Inconel vs Monel selection guide.
- vs Hastelloy C-276: C-276 covers mixed oxidizing/reducing and wet-chlorine service where Monel 400 is attacked.
Honest limitations to weigh: Monel 400 is attacked by strongly oxidizing media, costs more than stainless, is not age-hardenable, and can gall against itself.
Applications & Industries for Monel 400
Monel 400 is specified wherever nickel-copper corrosion resistance is essential: hydrofluoric-acid alkylation units, seawater and brine handling, offshore and marine systems, chlor-alkali and reducing-acid process lines, sour oil-and-gas instrumentation, and heat exchangers. Crestflo supplies N04400 instrumentation components into oil and gas, offshore, petrochemical and chemical, and marine and shipbuilding applications.
Monel 400 Standards, Certifications & Traceability
Wrought UNS N04400 is covered by a family of ASTM/ASME product-form specifications, and Crestflo instrumentation parts ship with full material traceability. Crestflo is ISO 9001, ISO 14001, ISO 45001, and PED certified; certificates are held on file and available through the quality team.
| Item | Detail |
|---|---|
| ASTM product-form specs | B165 (seamless pipe/tube), B164 (rod/bar/wire), B564 (forgings), B366 (fittings), B127 (plate/sheet/strip), B725 (welded pipe) |
| Quality system | ISO 9001 / 14001 / 45001 & PED certified |
| Fitting interchange | Compression tube fittings performance-qualified per ASTM F1387 |
| Valve qualification | Instrumentation valves qualified to ASME B16.34 and the applicable API standards |
| Sour service | NACE MR0175 / ISO 15156 compliant where applicable |
| Material certificate | EN 10204 MTC 3.1 standard, 3.2 on request |
| Traceability | Heat / lot number on every part |
| Verification | Positive Material Identification (PMI); in-house NDT; destructive testing at ISO/IEC 17025-accredited labs |
Values are per applicable standard and customizable to requirement; datasheets and CAD are available to customers on request.
Monel 400 Instrumentation Products from Crestflo: Fittings, Valves & Tubing
Crestflo builds instrumentation components in Monel 400, not mill products such as pipe, pipe fittings, elbows, flanges, bar, plate, or forgings. The alloy is offered across three product forms, each with imperial and metric sizes and heat-number traceability:
- Monel 400 compression tube fittings, single and double ferrule, tube OD up to 2" (50 mm), performance-qualified per ASTM F1387, including spare ferrules and nuts.
- Monel 400 instrumentation valves, needle, ball, check, and manifold valves qualified to ASME B16.34 / API, sizes 1/16" to 1".
- Monel 400 seamless instrument tubing, to the ASTM B165 basis, imperial and metric OD/wall.
Ordering-code and part-number details live on each product-form page. For interchange with brands such as Swagelok® or Parker®, request your Monel 400 cross-reference from our engineering team rather than relying on a generic chart. To price a specific form, size, and quantity, request a Monel 400 quote.
Why Source Monel 400 from Crestflo
Crestflo is the instrumentation division of a four-decade-old, Government-of-India-recognized export house with a long Middle-East delivery track record, now serving the US market with drop-in instrumentation components. As your US-serving Monel 400 supplier and stockist, that means:
- Fast, honest delivery: ready stock for standard items, made-to-order for specials, 6–8 week delivery.
- Drop-in interchange: compression fittings performance-qualified per ASTM F1387 for engineered interchange.
- Transparent origin: Indian origin, with US or European melt available on request and full material traceability.
- Verified material: EN 10204 MTC 3.1 (3.2 on request), heat/lot number on every part, and PMI confirmation of N04400 chemistry.
- Flexible supply: small minimum order quantities and a private-label Monel 400 program.
We Engineer Confidence. Reviewed by the Crestflo Engineering Team.
Monel 400 FAQ
What is Monel 400 used for?
Monel 400 (UNS N04400) is used where nickel-copper corrosion resistance is essential, hydrofluoric-acid alkylation, seawater and brine handling, offshore and marine systems, sulfuric and hydrochloric reducing-acid service, and sour (H₂S) oil-and-gas instrumentation. Crestflo supplies it as fittings, valves, and tubing for these services.
Are Alloy 400 and Monel the same?
"Alloy 400" and "UNS N04400" are the generic designations for the alloy commonly called Monel® 400; Monel® is a registered trademark of Special Metals Corporation. Crestflo supplies UNS N04400 to standard chemistry and is not affiliated with Special Metals Corporation.
What are the downsides of Monel 400?
Monel 400 is attacked by strongly oxidizing media such as nitric acid, wet chlorine, and ferric or cupric chlorides; it costs more than stainless steel, is not age-hardenable (use Monel K500 for higher strength), and can gall. Weigh it against 316/316L or Hastelloy C-276 in oxidizing service.
Is Monel 400 better than stainless steel?
For hydrofluoric acid, seawater, and chloride stress-corrosion-cracking resistance, Monel 400 outperforms 316/316L; for oxidizing acids and cost, stainless is usually the better choice. Compare the grades on the 316/316L material page.
What is the chemical composition of Monel 400?
Monel 400 is nominally at least 63% nickel, 28–34% copper, up to 2.5% iron, up to 2.0% manganese, and up to 0.3% carbon, per the standard specification, see the composition table above.
Is Monel 400 magnetic?
Monel 400 is weakly ferromagnetic near room temperature with a Curie point around 20–50 °C, so whether a given lot behaves magnetically depends on its exact composition and the temperature.
Is Monel 400 suitable for sour (H₂S) service?
In the annealed condition, Monel 400 is accepted under NACE MR0175 / ISO 15156; confirm the alloy against the applicable environmental and hardness limits for your service. See the NACE MR0175 standard page.
What is the PREN of Monel 400?
PREN does not apply to Monel 400. PREN is a chromium/molybdenum/nitrogen index for stainless and duplex alloys, and Monel 400 contains no chromium or molybdenum, so its corrosion is assessed by service medium instead.
Does Crestflo make Monel 400 tube fittings and valves?
Yes, Crestflo supplies Monel 400 compression tube fittings, instrumentation valves, and seamless tubing in imperial and metric sizes, with EN 10204 MTC 3.1 (3.2 on request). Start with the Monel 400 tube fittings page.
What is the lead time and minimum order for Monel 400 parts?
Standard items ship from ready stock and specials are made to order, with 6–8 week delivery and a small minimum order quantity; private label is available. See the lead-time page for details.
How much does Monel 400 cost?
Monel 400 pricing is quote-based and depends on product form, size, and quantity. Request a quote for current pricing on fittings, valves, or tubing.