Product Overview
Monel 400 is the most widely used nickel-copper alloy, known for its exceptional performance in seawater and marine environments. The alloy exhibits outstanding resistance to pitting and stress corrosion cracking in marine applications and is extensively used for pump shafts, valve components, and seawater piping systems. Monel 400 maintains good mechanical properties from sub-zero to elevated temperatures and is readily fabricated by standard welding techniques. With decades of proven performance in marine and chemical processing, Monel 400 remains a preferred material for seawater handling equipment and hydrofluoric acid service.
Key characteristics include:
- Outstanding corrosion resistance in seawater and marine environments
- Excellent resistance to hydrofluoric acid and reducing acids
- Good resistance to pitting and stress corrosion cracking
- High strength and ductility from cryogenic to elevated temperatures
- Excellent weldability and fabricability
- Non-magnetic properties
- NACE MR0175 / ISO 15156 compliance for sour service
Chemical Composition
| Element | Content (%) | Role |
| Nickel + Cobalt (Ni+Co) | 63.0 – 70.0 | Base element, provides corrosion resistance, SCC resistance |
| Copper (Cu) | 28.0 – 34.0 | Provides resistance to reducing acids and seawater corrosion |
| Iron (Fe) | ≤ 2.5 | Structural element, cost control |
| Manganese (Mn) | ≤ 2.0 | Deoxidizer, improves hot workability |
| Carbon (C) | ≤ 0.30 | Controlled for strength and hot workability |
| Silicon (Si) | ≤ 0.50 | Deoxidizer |
| Sulfur (S) | ≤ 0.024 | Tightly controlled for hot workability |
Mechanical Properties
Room Temperature Properties (Annealed)
| Property | ASTM Requirement | Typical Achieved |
| Tensile Strength | ≥ 480 – 655 MPa | 70 – 95 ksi (480 – 655 MPa) |
| Yield Strength (0.2% Offset) | ≥ 170 MPa | 25 ksi (170 MPa) |
| Elongation | ≥ 30% | 45 – 55% |
| Hardness | 135 – 165 HRB | 140 – 160 HRB |
| Density | 8.80 g/cm³ | |
| Melting Range | 1300 – 1350°C | |
| Thermal Conductivity at 20°C | 21.8 W/m·K | |
| Coefficient of Thermal Expansion (20-100°C) | 13.9 × 10⁻⁶/°C | |
| Elastic Modulus | 173 – 180 GPa | |
| Magnetic Permeability | Non-magnetic |
Spring Temper Properties
| Property | Value |
| Tensile Strength | 145 – 180 ksi (1000 – 1240 MPa) |
| Operating Temperature | -300°F to 500°F (-184°C to 260°C) |
Key Advantages of Monel 400
Outstanding Seawater Corrosion Resistance – Monel 400 is renowned for its exceptional resistance to seawater and marine environments. The alloy exhibits excellent resistance to pitting and crevice corrosion, making it the material of choice for seawater piping, pump shafts, propeller shafts, and marine platform equipment. Unlike many stainless steels, Monel 400 is resistant to chloride-induced stress corrosion cracking in seawater service.
Excellent Hydrofluoric Acid Resistance – Monel 400 is one of the few materials that can handle hydrofluoric acid across a wide concentration range. Its nickel content provides resistance to HF acid, making it the standard material for HF acid handling equipment in chemical processing and alkylation units.
Good Reducing Acid Resistance – The alloy exhibits excellent corrosion resistance in reducing acids such as hydrochloric acid, sulfuric acid, and phosphoric acid, provided oxidizing species are not present. Its copper content contributes to resistance in these environments where many stainless steels would fail.
Excellent Weldability – Monel 400 can be readily welded using TIG, MIG, resistance welding, and other standard processes. Matching filler metal (AWS A5.14 ERNiCu-7) is recommended. No preheating is generally required, and post-weld heat treatment is not necessary for most applications.
Good Mechanical Properties – The alloy maintains good mechanical properties from cryogenic temperatures down to -184°C up to 260°C (500°F) for spring temper applications. Cold working significantly increases strength while maintaining adequate ductility.
NACE MR0175 / ISO 15156 Compliance – Monel 400 is qualified for sour service applications in the oil and gas industry, resisting sulfide stress cracking (SSC) and hydrogen induced cracking (HIC) in H₂S-containing environments.
Non-Magnetic – The alloy is non-magnetic, making it suitable for applications where magnetic interference must be avoided, such as marine instrumentation.
Monel 400 vs Monel K-500: Comparison
| Property | Monel 400 | Monel K-500 |
| Aluminum Content | None | 2.30 – 3.15% |
| Titanium Content | None | 0.35 – 0.85% |
| Strengthening | Solid-solution | Precipitation hardening |
| Tensile Strength (annealed) | 480 – 655 MPa | — |
| Tensile Strength (aged) | — | ≥ 1000 MPa |
| Yield Strength (aged) | — | ≥ 760 MPa |
| Density | 8.80 g/cm³ | 8.44 g/cm³ |
| Hardness | Lower | Higher |
| Preferred For | Corrosion resistance | High strength + corrosion resistance |
When to choose Monel 400: Applications requiring maximum corrosion resistance in seawater, hydrofluoric acid, and reducing acids where high strength is not required. The alloy is more economical and easier to fabricate than K-500.
When to choose Monel K-500: Applications requiring high strength (equivalent to hardened steel) combined with Monel corrosion resistance. Typical: pump shafts, fasteners, springs, marine propellers.
Available Product Forms from Womic Steel
Seamless Pipe & Seamless Tube
- Outside Diameter: 6mm – 200mm
- Wall Thickness: 1mm – 20mm
- Length: Up to 12m
- Standards: ASTM B165, ASTM B829, ASME SB-165
- Applications: Heat exchanger tubes, seawater piping, chemical process piping, marine systems
- Keywords: Monel 400 seamless pipe, UNS N04400 tube, 2.4360 pipe, nickel-copper alloy tube
Welded Pipe
- Outside Diameter: 50mm – 1000mm
- Wall Thickness: 1.0mm – 20mm
- Standards: ASTM B725, ASTM B730
- Applications: Large-diameter seawater piping, marine platform systems
- Keywords: Monel 400 welded pipe, alloy 400 ERW pipe
Steel Bar (Round, Square, Flat, Hex)
- Diameter: 3mm – 150mm
- Surface: Hot rolled, Bright (cold drawn), Ground, Turned
- Standards: ASTM B164, AMS 4675, ASME SB-164
- Applications: Valve stems, fasteners, shafts, pumps, machining stock, propellers
- Keywords: Monel 400 round bar, UNS N04400 bar stock, nickel-copper bar
Steel Plate & Sheet
- Thickness: 1mm – 50mm
- Width: Up to 2500mm
- Standards: ASTM B127, ASME SB-127
- Applications: Vessel shells, heat exchanger plates, structural components, flange blanks
- Keywords: Monel 400 plate, alloy 400 sheet, N04400 plate
Steel Coil & Strip
- Thickness: 0.5mm – 6.0mm
- Width: 10mm – 1500mm
- Standards: ASTM B127
- Applications: Formed components, bellows, expansion joints, stampings
- Keywords: Monel 400 coil, nickel-copper strip
Flanges & Pipe Fittings
- Types: Weld Neck, Slip-On, Blind, Socket Weld, Threaded, Lap Joint
- Sizes: 1/2" – 24"
- Pressure Rating: Class 150 – Class 2500
- Standards: ASTM B564, ASME SB-564, ASME B16.5, ASME B16.47
- Fittings: Elbows, Tees, Reducers, Caps, Stub Ends, Couplings
- Keywords: Monel 400 flanges, alloy 400 pipe fittings, UNS N04400 weld neck flange
Forgings
- Types: Rings, disks, shafts, valve bodies, pump parts, propeller shafts
- Weight: Up to 3,000kg per piece
- Standards: ASTM B564, AMS 4675
- Keywords: Monel 400 forging, alloy 400 ring, forged block
Monel 400 Valves
- Types: Ball valves, Gate valves, Globe valves, Check valves, Plug valves
- Sizes: 1/2" – 24"
- Pressure Rating: Class 150 – Class 2500
- Temperature Range: -184°C to +260°C
- Design Standards: API 608, API 6D, BS 6364, ASME B16.34
- Seating: Stellite hardfaced, PCTFE (cryogenic), RPTFE, PEEK
- Actuation: Manual, Pneumatic, Electric
- Applications: Marine seawater systems, HF acid service, chemical plants, oil and gas sour service
- Keywords: Monel 400 ball valve, alloy 400 gate valve, nickel-copper valve
Wire & Springs
- Wire Diameter: 0.5mm – 12mm
- Springs: Custom spring manufacturing
- Standards: ASTM B164, AMS 4730
- Keywords: Monel 400 wire, alloy 400 springs, nickel-copper wire
Applications of Monel 400
Marine Engineering – Monel 400 is widely used in seawater piping, pump shafts, propeller shafts, valve components, marine platform equipment, and offshore structures. Its outstanding resistance to seawater corrosion and biofouling makes it the material of choice for critical marine components.
Chemical Processing – The alloy is extensively used in hydrofluoric acid handling equipment (alkylation units), sulfuric acid and hydrochloric acid service, heat exchangers, distillation columns, and piping systems. Its resistance to HF acid is unmatched by most other materials.
Oil and Gas – Monel 400 is specified for sour service equipment, wellhead components, and subsea flowlines requiring resistance to H₂S, CO₂, and chloride environments. Its NACE MR0175 / ISO 15156 compliance ensures reliable performance in sour service.
Aerospace – The alloy is used in aircraft fuel systems, engine components, and hydraulic systems where corrosion resistance and non-magnetic properties are required.
Pulp and Paper – Monel 400 is used in pulp digesters, bleaching equipment, and chemical recovery systems where exposure to aggressive chemicals is common.
Heat Exchangers – The alloy is used in heat exchanger tubing, condenser tubes, and evaporator tubes for marine and chemical applications.
Valves and Pumps – Monel 400 is the standard material for valves, pumps, and fittings handling seawater, HF acid, and other corrosive media.
Standards & Specifications
| Product Form | ASTM Standard | ASME Standard | AMS Standard |
| Seamless Pipe/Tube | ASTM B165 | ASME SB-165 | — |
| Welded Pipe | ASTM B725, ASTM B730 | ASME SB-725, SB-730 | — |
| Bar/Rod | ASTM B164 | ASME SB-164 | AMS 4675 |
| Plate/Sheet/Strip | ASTM B127 | ASME SB-127 | — |
| Forgings | ASTM B564 | ASME SB-564 | AMS 4675 |
| Fittings | ASTM B366 | ASME SB-366 | — |
| Wire | ASTM B164 | ASME SB-164 | AMS 4730 |
| UNS Designation | N04400 | ||
| Werkstoff Number | 2.4360 / 2.4361 | ||
| DIN Designation | NiCu30Fe | ||
| Chinese Equivalent | NS111 | ||
Frequently Asked Questions
Q: Why is Monel 400 the preferred material for seawater applications?
A: Monel 400's outstanding resistance to pitting, crevice corrosion, and stress corrosion cracking in seawater makes it the material of choice for marine piping, pump shafts, propeller shafts, and offshore platform equipment. Unlike 316L or other stainless steels, Monel 400 maintains its corrosion resistance over decades of seawater exposure without degradation.
Q: What is the difference between Monel 400 and Inconel 625?
A: Monel 400 is a nickel-copper alloy optimized for seawater and HF acid resistance. Inconel 625 is a nickel-chromium-molybdenum alloy with superior pitting resistance and high-temperature strength. Choose Monel 400 for seawater and reducing acid service; choose Inconel 625 for oxidizing environments and high-temperature applications.
Q: Is Monel 400 readily weldable?
A: Yes. Monel 400 can be welded using TIG, MIG, resistance welding, and other standard processes. Matching filler metal AWS A5.14 ERNiCu-7 is recommended. No preheating is generally required, and post-weld heat treatment is not necessary for most applications.
Q: What is the maximum service temperature for Monel 400?
A: For spring applications: up to 260°C (500°F). For general service: up to 500°F with oxidation resistance. Monel 400 maintains good mechanical properties from cryogenic temperatures (-184°C) to 260°C.
Q: What is the Chinese equivalent of Monel 400?
A: The Chinese equivalent grade is NS111 (耐蚀合金). It is also commonly referenced by its UNS designation N04400 and Werkstoff number 2.4360.
Q: What product forms are available for Monel 400?
A: Womic Steel supplies Monel 400 in seamless pipe, welded pipe, steel bar, steel plate, steel coil, strip, flanges, pipe fittings, forgings, wire, springs, and valves. Complete product specifications and size ranges are listed in the product availability section.
Q: Is Monel 400 suitable for sour service?
A: Yes. Monel 400 is qualified to NACE MR0175 / ISO 15156 for sour service applications in the oil and gas industry, resisting sulfide stress cracking and hydrogen induced cracking in H₂S-containing environments.
Contact Womic Steel
Website: www.womicsteel.com
E-mail: sales@womicsteel.com
Tel / WhatsApp / WeChat:
Victor: +86 15575100681
Jack: +86 18390957568
Womic Steel – Your reliable partner for Monel 400 (UNS N04400) seamless pipe, welded pipe, steel bar, steel plate, steel coil, flanges, fittings, forgings, springs, and valves for marine engineering, chemical processing, oil and gas sour service, and aerospace applications worldwide. Full traceability, classification society certification, NACE MR0175 compliance, and EN 10204 Type 3.1/3.2 documentation available.
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