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Monel400 (UNS N04400) is a nickel-copper alloy with a composition ratio of Ni67-Cu23. It is currently the nickel-copper corrosion-resistant alloy with the largest usage, the widest application, and the best overall performance.
Alloy 400 monel has excellent corrosion resistance in hydrofluoric acid and fluorine gas media, and also has excellent corrosion resistance to hot concentrated alkali solution. It is also resistant to corrosion by neutral solutions, water, seawater, atmosphere, organic compounds, etc. An important feature of this alloy is that it generally does not produce stress corrosion cracks and has good cutting performance!
Monel alloy 400 (UNS N04400) is a solid-solution alloy that can be hardened only by cold working. This alloy has excellent corrosion resistance in hydrofluoric acid and fluorine gas medium, and also has excellent corrosion resistance in hot concentrated lye. At the same time, it is also resistant to corrosion by neutral solutions, water, seawater, atmosphere, organic compounds, etc. An important feature of this alloy is that it generally does not produce stress corrosion cracking and has good machinability. It is a corrosion-resistant alloy with the largest amount, the most widely used and excellent comprehensive properties.
Alloy 400 is widely used in many fields, especially marine and chemical processing. Typical applications are pump and propeller shafts; marine fixtures and fasteners; electrical and electronic components; springs; chemical processing equipment; gasoline and fresh water tanks; crude petroleum stills,process vessels and piping; boiler feedwater heaters andother heat exchangers; and deaerating heaters.
Grade | C≤ | Mn≤ | Si | S≤ | Cu | Fe≤ | Ni≤ |
Monel400 | 0.3 | 2 | 0.5 | 0.024 | 28.0-34.0 | 2.5 | 63 |
Product Form | Condition | Tensile(Ksi) | .2% Yield (Ksi) | Elongation(%) | Hardness(HRB) |
Rod&Bar | Annealed | 75-90 | 25-50 | 60-35 | 60-80 |
Rod&Bar | Cold-Drawn Stress Relieved | 84-120 | 55-100 | 40-22 | 85-20HRC |
Plate | Annealed | 70-85 | 28-50 | 50-35 | 60-76 |
Sheet | Annealed | 70-85 | 30-45 | 45-35 | 65-80 |
Tube&Pipe Seamless | Annealed | 70-85 | 25-45 | 50-35 | 75 max* |
Density | 8.80g/cm3 | |
Elastic modulus | 26 000 ksi | |
Heating energy | 0.427 J/g-°C | |
| Coefficient of Thermal Expansion | 70-200F | 7.7 |
70-400F | 8.6 | |
70-800 F | 8.9 | |
70-1000F | 9.1 | |
Monel 400 is the mainstream material for desalination plant critical components — evaporator tube bundles, brine heaters, condenser tubes, and RO brine heat exchangers — because it solves the three core failure modes of seawater service: chloride pitting, stress corrosion cracking, and erosion-corrosion at high flow velocity, while offering thermal conductivity 2.2x that of Inconel 625 for efficient heat transfer.
Desalination plant failure modes: Seawater contains ~35,000 ppm dissolved chlorides. After desalination, brine salinity exceeds 70,000 ppm. These chlorides attack the passive oxide film of stainless steel, causing pitting and crevice corrosion. Thermal cycling between 40°C and 120°C in evaporators adds fatigue stress. High-velocity flow at pump inlets and bends (3–6 m/s) creates erosion-corrosion.
How Monel 400 solves each failure mode:
1) Chloride pitting: The Ni-Cu matrix resists chloride attack through its inherent inertness, not through a passive film that chlorides can rupture. No velocity-limited pitting threshold exists — Monel 400 performs well even above 4 m/s, where 316L begins to pit aggressively.
2) Stress corrosion cracking: Monel 400 generally does not suffer SCC in chloride environments — a fundamental advantage over 304/316L stainless. This is critical for evaporator tubes subject to thermal cycling thousands of times per year.
3) Erosion-corrosion: Monel 400’s protective film regenerates quickly even under turbulent flow exceeding 4 m/s. At desalination pump inlets and elbow bends, this self-healing behavior prevents the wall thinning that plagues carbon steel and copper alloys.
4) Heat transfer efficiency: Monel 400’s thermal conductivity is approximately 2.2x that of Inconel 625. In heat exchanger tube bundles, this translates directly to higher heat transfer efficiency and smaller equipment footprint.
Product | Standard | Show |
Monel 400 Seamless Pipe | ASTM B165 |  |
Monel 400 Welded Pipe | ASTM B474 |  |
Monel 400 Seamless Tube | ASTM B163/B165 |  |
Monel 400 Sheet | ASTM B127 |  |
Monel 400 Bars | ASTM B164 |  |
Monel 400 Forging | ASTM B564 |  |
Monel 400 Fittings | ASTM B366 |  |
JN Monel400 material has excellent hot and cold processing properties. Alloy 400 Monel products are complete. We can provide plates, strips, tubes, wires, rods, forgings, fasteners, flanges, pipe fittings and other products.
STANDARD | WERKSTOFF NR. | UNS | JIS | BS | GOST | AFNOR | EN |
Monel 400 | 2.4360 | N04400 | NW 4400 | NA 13 | МНЖМц 28-2,5-1,5 | NU-30M | NiCu30Fe |
Choose Monel 400 for high-velocity seawater piping, heat exchangers, HF acid service, and desalination — where thermal conductivity, cost efficiency, and antifouling matter.
Choose Inconel 625 for stagnant/polluted seawater, sour gas (H₂S/CO₂) per NACE MR0175, high-temperature (>540°C) service, and subsea wellhead components — where Mo/Cr pitting resistance and strength are critical. They are complementary, not competing.
Dimension | Monel 400 (UNS N04400) | Inconel 625 (UNS N06625) |
Composition | Ni ≥ 63%, Cu 28–34%, Fe ≤ 2.5% | Ni ≥ 58%, Cr 20–23%, Mo 8–10%, Nb 3.15–4.15% |
Tensile Strength (annealed) | ~550 MPa (80 ksi) | ~827 MPa (120 ksi) |
Yield Strength (annealed) | ~240 MPa (35 ksi) | ~414 MPa (60 ksi) |
Max Service Temp | ≤80°C (540°C specific) | ~980°C (1800°F) |
Thermal Conductivity | 21.8 W/m·K (2.2x advantage) | 9.8 W/m·K |
Seawater — Flowing (<3 m/s) | Excellent (<0.025 mm/yr) | Excellent (<0.025 mm/yr) |
Seawater — Stagnant/Warm | Moderate (pitting risk) | Excellent (Mo prevents pitting) |
Seawater — High Velocity (>10 m/s) | Moderate (erosion begins) | Excellent (Mo + Cr protect) |
Crevice Corrosion | Moderate (possible) | Excellent (Mo provides resistance) |
H₂S Sour Gas (NACE MR0175) | Good (limited) | Superior (full compliance) |
HF Acid Resistance | Outstanding (industry-leading) | Moderate |
Pitting Resistance (PREN) | Low (<5, but matrix protects) | Very High (>51) |
Magnetic Property | Non-magnetic | Non-magnetic |
Weldability | Good (ERNiCu-7 filler) | Excellent (ERNiCrMo-3 filler) |
Machinability | Good (work-hardens moderately) | More difficult (higher strength) |
Relative Cost | Economical (Cu-based, no Mo/Cr) | Premium (Mo + Cr + Nb content) |
Key Standards | ASTM B163/B165/B127/B164/B564/B366 | ASTM B444/B446/B443/B564/B366 |
Specify Monel 400 when:
•High-velocity seawater piping, heat exchanger tubes, and condenser tubes (thermal conductivity advantage)
•Desalination plant evaporator tube bundles, brine heaters, and RO concentrate heat exchangers
•HF acid alkylation unit piping in petroleum refining (outstanding HF resistance)
•Marine propeller/pump shafts, fasteners, and instrument housings (non-magnetic requirement)
•Cost-sensitive projects where Mo/Cr premium is not justified by service conditions
Specify Inconel 625 when:
•Stagnant or polluted seawater (e.g., harbor basins, closed-loop cooling tanks) where pitting/crevice risk is high
•Sour gas (H₂S/CO₂) downhole tubing, casing, and subsea umbilicals per NACE MR0175/ISO 15156
•Offshore wellhead, Christmas tree, and manifold components requiring weld overlay (API 6A Annex F)
•High-temperature (>540°C) process environments requiring oxidation resistance
•High-strength requirements (>600 MPa tensile) where Monel 400’s moderate strength is insufficient
Monel 400 alloy has excellent corrosion resistance in fluorine gas, hydrochloric acid, sulfuric acid, hydrofluoric acid and their derivatives, and is one of the few important materials that can resist hydrofluoric acid.
Sulfuric acid environment:
Alloy 400 is corrosion-resistant in sulfuric acid with a concentration of less than 85%.
Aqueous corrosion:
Under most water corrosion conditions, Monel 400 alloy not only has excellent corrosion resistance, but also rarely suffers from pitting corrosion and stress corrosion, with a corrosion rate of less than 0.025mm/a.
High temperature corrosion:
The maximum temperature of alloy 400 in continuous operation in air is generally around 400C, and in high-temperature steam, the corrosion rate is less than 0.026mm/a.
Ammonia:
Due to the high nickel content of Monel 400 alloy, it can resist corrosion under anhydrous ammonia and ammoniated conditions below 585°C.
Monel 400 material annealing temperature is generally between 700 and 900°C, and the best effect is achieved at 825°C. Rapid air cooling after treatment can achieve good corrosion resistance. The purpose of this is to soften the material after forging to keep the material relatively fine particles. The annealing temperature and time are directly related to the final grain size, so the annealing parameters should be carefully considered.
Monel400 can be welded by gas tungsten arc, gas metal arc welding and shielded gas metal arc welding.
Before welding, clean the groove and electrode with acetone, and use GTAW as the welding method. Use ERNiCu-7 as the welding wire and ENICU-7 as the welding electrode.
400 Monel does not require preheating before welding, nor does it require post-weld heat treatment, because the strength of the material is improved after welding, which is beneficial for future use.
The fluidity of the molten metal in 400 material welding is poor, so a large groove angle (60-70°) should be used to allow the welding wire to fill the weld.
Feed water and steam generator tubing
Brine heaters, sea water scrubbers in tanker inert gas systems
Sulfuric acid and hydrofluoric acid alkylation plants
Pickling bat heating coils
Heat exchangers in a variety of industries
Transfer piping from oil refinery crude columns
Plant for the refining of uranium and isotope separation in the production of nuclear fuel
Monoethanolamine (MEA) reboiling tube
Cladding for the upper areas of oil refinery crude columns
Monel 400 has accumulated over 100 years of documented marine service — from WWII-era destroyer propeller shafts to modern LNG carrier seawater systems and offshore platform piping. It dominates four marine application categories: propeller/pump shafts, seawater valves, fasteners, and seawater piping/tubing — where its non-magnetism, antifouling copper content, and zero velocity-limited pitting are unmatched at its price point.
1) Propeller and pump shafts: Monel 400 shafts routinely exceed 20–30 years submerged with only routine inspection. The alloy resists seawater corrosion, cavitation erosion, and marine biofouling simultaneously. For shafts requiring higher yield strength (>100 ksi), Monel K-500 (UNS N05500) is the precipitation-hardened upgrade with nearly identical corrosion resistance.
2) Seawater valves and pumps: Valve bodies, stems, and internals in seawater service face crevice corrosion under gaskets and biofouling in stagnant zones. Monel 400’s copper content provides natural antifouling properties that inhibit barnacle and algae attachment — a practical advantage over stainless steel in tidal zones.
3) Marine fasteners: Non-magnetic, no galling, and resistant to chloride SCC. Monel 400 fasteners per ASTM B164 are the standard for shipbuilding, offshore rigs, and desalination plants where magnetic interference or galling failure is unacceptable.
4) Seawater piping and tubing: ASTM B163/B165 seamless tube for heat exchanger and condenser service; ASTM B127 plate/sheet for tank construction. No velocity-limited pitting means tube wall thickness is designed on mechanical strength, not corrosion allowance — reducing material cost and weight.
5) Offshore oil and gas: Wellhead equipment, valve forgings, drill pipe components, pipeline flanges, pump impellers in brine and sour gas environments. Monel 400 shows good resistance to H₂S-containing drilling fluids and chloride brine, though Inconel 625 is preferred for the most severe sour service per NACE MR0175/ISO 15156.
Is Alloy 400 the Same as Monel?
Yes. "Monel 400" is the original trade name (registered by Special Metals Corporation). "Alloy 400" is the generic industry designation for the identical nickel-copper alloy, standardized as UNS N04400, EN 2.4360 / NiCu30Fe, and covered by ASTM B127/B163/B165/B164/B564/B366. "Monel" alone is ambiguous — it refers to a family of alloys including Monel 400, Monel K-500, Monel R-405, and Monel 450.
Is Monel 400 Magnetic?
No. Monel 400 is essentially non-magnetic at all temperatures. Its primary constituents (nickel and copper) are inherently non-ferromagnetic. The minor iron content (≤ 2.5%) is insufficient to impart significant magnetic permeability. Very slight magnetic response might be detectable with extremely sensitive instruments due to trace impurities or severe cold working, but for all practical engineering purposes — including shipboard compass housings and depth sensor components — Monel 400 is treated as non-magnetic.
Can Monel 400 Be Used in Seawater Desalination?
Yes — it is one of the mainstream materials. Monel 400 is specified for evaporator tube bundles, brine heaters, condenser tubes, and RO concentrate heat exchangers across MED, MSF, and RO desalination technologies. Its seawater corrosion rate (<0.025 mm/yr in flowing conditions) and thermal conductivity (21.8 W/m·K, 2.2x that of Inconel 625) make it the practical choice for heat transfer components. The alloy resists chloride SCC, pitting in high-velocity flow, and erosion-corrosion at pump inlets — all critical desalination failure modes.
How Does Monel 400 Compare to 316L Stainless Steel in Seawater?
Monel 400 outperforms 316L in flowing and high-velocity seawater. 316L relies on a chromium oxide passive film that chlorides can locally rupture, causing pitting (especially above ~1.5 m/s flow velocity) and crevice corrosion under gaskets. Monel 400’s Ni-Cu matrix provides structural corrosion resistance — no velocity-limited pitting threshold, no SCC risk, and natural antifouling from copper content. However, 316L is cheaper and adequate for low-risk, short-life applications. Monel 400’s 25+ year design life justifies the cost premium for critical, maintenance-intensive seawater components.
What Is the Difference Between Monel 400 and Monel K-500?
K-500 is the age-hardenable, high-strength version. Monel K-500 (UNS N05500) adds Al (2.3–3.3%) and Ti (0.35–0.85%) to the Ni-Cu base, enabling precipitation hardening to yield strength ~115 ksi (4x that of annealed Monel 400) while retaining nearly identical seawater corrosion resistance and non-magnetic properties. Choose K-500 for large propeller shafts, high-load marine fasteners, and valve stems requiring both strength and non-magnetism. Choose Monel 400 for piping, tubing, heat exchangers, and general seawater service where moderate strength is sufficient.
Does Monel 400 Require PWHT After Welding?
No — for most applications, post-weld heat treatment is not required. Monel 400 is a solid-solution alloy that does not harden by heat treatment. Welding actually improves local strength. Stress relief may be specified for severe service conditions, but it is not a standard requirement. Use ERNiCu-7 filler wire (GTAW) or ENiCu-7 electrodes (SMAW) for matching chemistry welds. Clean groove and filler with acetone before welding; use wider groove angles (60–70°) to compensate for the molten metal’s poor fluidity.
What Is the Maximum Temperature for Monel 400 in Continuous Service?
Approximately 480°C (900°F) in air, with specific applications extending to 540°C. Above 480°C, mechanical strength declines significantly and oxidation resistance becomes limited compared to Cr-bearing alloys like Inconel 625 (service up to 980°C). In high-temperature steam, corrosion rate remains below 0.026 mm/a. For applications exceeding 540°C, specify Inconel 625 or other Cr/Mo-bearing nickel alloys.
Can Monel 400 Handle Hydrofluoric Acid?
Yes — outstandingly. Monel 400 is one of the few important engineering materials that can resist hydrofluoric acid across a wide range of concentrations and temperatures. This makes it the standard choice for HF alkylation unit piping in petroleum refining. Inconel 625 offers only moderate HF resistance — Monel 400 is clearly superior in this specific environment.
What Are the Galvanic Corrosion Risks with Monel 400?
Monel 400 is a noble alloy and must be insulated from less noble metals. Direct contact with carbon steel, aluminum, or graphite creates galvanic couples where the less noble metal corrodes preferentially. In desalination and marine piping systems, use insulating gaskets, transition fittings, or protective coatings at dissimilar metal junctions. Monel 400-to-stainless steel (316L) junctions are generally acceptable with minor galvanic risk.
Is Monel 400 Compliant with NACE MR0175 / ISO 15156 for Sour Service?
Monel 400 has limited NACE MR0175 sour service coverage. ISO 15156-3 lists Alloy 400 (UNS N04400) as acceptable for specific sour service conditions (non-oxidizing chloride environments), but it does not have the comprehensive sour gas coverage that Inconel 625 enjoys. For critical H₂S/CO₂ sour gas downhole and subsea applications per NACE MR0175, Inconel 625 (UNS N06625) is the standard specification. Monel 400 is used in sour environments where the primary corrosion driver is chloride brine rather than aggressive H₂S.
