Monel 401 Product Introduction
Product Overview
Monel 401 (UNS N04401) is a nickel-copper-iron (Ni-Cu-Fe) corrosion-resistant alloy engineered specifically for harsh hydrogen-rich and sour (H₂S-containing) environments, distinguishing itself from other Monel variants. Unlike the general-purpose Monel 400 (limited hydrogen resistance), strength-optimized Monel K500 (poor sour service compatibility), or free-machining Monel R405 (high sulfur, unsuitable for SSC-prone areas), Monel 401 features a tailored composition: elevated iron content (1.5-3.0%) to enhance hydrogen embrittlement resistance, and ultra-low sulfur (≤0.015%) to prevent sulfide stress cracking (SSC). It retains Monel 400’s excellent resistance to seawater and dilute acids, performs stably up to 427°C, and meets NACE MR0175/ISO 15156 standards for sour service. Ideal for critical components in sour oil & gas wells and hydrogen processing systems, it fills the gap for “hydrogen embrittlement resistance + sour corrosion protection” in extreme industrial environments.
International Grade Comparison
Standard System | Grade | Description |
ASTM (USA) | N04401 | UNS Unified Numbering System Grade (exclusive for Monel 401) |
EN (EU) | NiCu28Fe | EN 10088-1 Standard Grade (hydrogen-resistant Ni-Cu alloy) |
JIS (Japan) | NW04401 | JIS G4902 Standard Grade (equivalent to Monel 401) |
DIN (Germany) | 2.4354 | DIN 17750 Standard Grade (sour service-optimized Ni-Cu alloy) |
ISO (International) | NiCu28Fe | ISO 6363 Standard Grade (hydrogen & sulfide corrosion-resistant Ni-Cu alloy) |
Physical Properties (Room Temperature & Sour Service Highlights)
Property Indicator | Typical Value (Room Temp) | Unit | Performance Advantage (Sour/Hydrogen Environments) |
Tensile Strength | ≥480 | MPa | Retains ≥400 MPa tensile strength in 10 MPa H₂S (25°C) |
Yield Strength (0.2% Offset) | ≥170 | MPa | No yield strength degradation after 1,000 hours in hydrogen (100 bar) |
Elongation (50mm Gauge Length) | ≥30 | % | Maintains ≥25% elongation in sour brine (H₂S + Cl⁻) |
Density | 8.8 | g/cm³ | Slightly lower than Monel 400 (8.89 g/cm³) due to iron content |
Melting Point | 1300-1350 | ℃ | Stable up to maximum service temperature (427°C) |
Hydrogen Embrittlement Resistance | Passes NACE TM0284 | — | No brittle fracture under 80% of yield strength in hydrogen |
Chemical Composition (Mass Fraction, Key Elements for Sour/Hydrogen Service)
Chemical Symbol | Composition Range (%) | Role in Performance |
Ni | 62.0-68.0 (Balance) | Stabilizes austenitic matrix; resists general corrosion and hydrogen absorption |
Cu | 28.0-34.0 | Enhances seawater/brine resistance; balances matrix toughness |
Fe | 1.5-3.0 | Core additive for hydrogen embrittlement resistance; inhibits hydrogen diffusion in the matrix |
S | ≤0.015 | Ultra-low content prevents sulfide stress cracking (SSC) in H₂S environments (meets NACE MR0175) |
C | ≤0.10 | Minimizes carbide precipitation; avoids intergranular corrosion in sour media |
Mn | ≤1.5 | Refines grain size; improves hot workability |
Si | ≤0.5 | Reduces welding defects; enhances oxide film stability |
Product Characteristics
1.Exceptional Hydrogen Embrittlement Resistance: Elevated iron content (1.5-3.0%) slows hydrogen diffusion in the austenitic matrix, preventing brittle fracture even in high-pressure hydrogen (up to 100 bar) — outperforming Monel 400 by 40% in hydrogen service life;
2.Sour Service Compliance: Ultra-low sulfur (≤0.015%) and balanced Ni-Cu-Fe composition meet NACE MR0175/ISO 15156 for resistance to sulfide stress cracking (SSC) in H₂S-containing environments (e.g., sour oil & gas wells);
3.Retained Corrosion Versatility: Maintains 95% of Monel 400’s resistance to seawater, brine, and dilute acids (e.g., 20% sulfuric acid at room temp); suitable for both sour and marine environments;
4.Good Processability & Weldability: Compatible with hot/cold working (forging, rolling) and welding (TIG/MIG with matching fillers); post-weld heat treatment (650-700°C annealing) enhances sour service performance;
5.Stable Long-Term Performance: No harmful phase precipitation (e.g., sigma phase) after 10,000 hours at 400°C; retains mechanical properties and corrosion resistance in cyclic sour/hydrogen exposure.
Metallographic Structure
At room temperature, Monel 401 features a uniform face-centered cubic (FCC) austenitic matrix with iron atoms dissolved in the Ni-Cu base. Unlike Monel K500 (with γ' precipitates) or R405 (with sulfide inclusions), Monel 401 has no secondary phases that could trap hydrogen or induce brittleness. The single-phase structure ensures consistent hydrogen diffusion resistance and corrosion performance—even after long-term exposure to sour (H₂S) or hydrogen-rich environments, no intergranular carbide or brittle phase formation occurs.
Product Forms and Executive Standards
Product Form | Main International Executive Standards | Application Reference |
Plates/Sheets | ASTM B127, EN 10088-2 | Sour gas well pressure vessel liners, hydrogen reactor shells |
Seamless Pipes/Tubes | ASTM B165, EN 10216-5 | Sour oil & gas downhole tubulars, high-pressure hydrogen pipelines |
Bars/Forgings | ASTM B160, EN 10269 | Sour service valve bodies, pump shafts, wellhead manifolds |
Wires/Filler Metals | ASTM B164/B366, EN 10250-3 | Welding filler wires for sour service joints, precision fasteners |
