Monel 400 Stainless Steel Flanges

Premier Hydrofluoric Acid (HF) Resistance: Monel 400 is the standard material for handling hydrofluoric acid across all concentrations and temperatures up to 150°C (302°F), making it the preferred flange material for HF alkylation units in refineries.

Exceptional Seawater Erosion Resistance: Outstanding resistance to impingement attack and erosion-corrosion in high-velocity seawater and brine service (handles velocities up to 10 m/s or 33 ft/s), significantly outperforming copper-nickel (90/10), 316L, and other stainless steel flanges.

Excellent Chloride Stress Corrosion Cracking Resistance: High nickel content (≥63%) provides outstanding resistance to chloride-induced SCC, outperforming all austenitic stainless steel grades including 304, 316, and duplex.

Superior Biofouling Resistance: Monel 400 naturally resists marine biofouling, reducing maintenance requirements and preserving flow efficiency in seawater cooling systems.

Non-Magnetic Properties: Monel 400 is non-magnetic, making it suitable for sensitive instrumentation and degaussing applications on naval vessels.

Good Resistance to Reducing Acids: Excellent performance in deaerated sulfuric acid, hydrochloric acid, phosphoric acid, and organic acids, particularly in the absence of oxidizing agents.

Good High-Temperature Strength: Maintains excellent mechanical properties up to 400°C (752°F) in non-oxidizing environments.

Excellent Weldability: Nickel-copper alloy offers good weldability with matching filler metals (ERNiCu-7). Weld zones retain corrosion resistance comparable to the base metal.

Full Range of Types: Weld neck (WN), slip-on (SO), blind (BL), socket weld (SW), threaded (TH), lap joint (LJ), plate flanges, and orifice flanges.

Pressure Ratings: Available in Class 150, 300, 600, 900, 1500, and 2500 (PN6 to PN400 in metric equivalents).

Excellent Formability and Fabricability: Good ductility for forming and machining, allowing for custom flange configurations.

International Certifications: Flanges can be certified by ABS, BV, DNV, LR, GL, RINA, CCS, KR, and NK for marine and shipbuilding applications, and comply with NACE MR0175 (limited sour service), ASME, and PED standards.

These standards ensure that our Monel 400 stainless steel flanges meet global requirements for chemical composition, mechanical properties, dimensional tolerances, and pressure-temperature ratings for marine, HF alkylation, and chemical service.

Monel 400 (UNS N04400) is a nickel-copper alloy with high nickel (≥63%) and copper (28-34%) content. The high nickel content provides excellent resistance to chloride stress corrosion cracking and caustic environments, while the copper content provides outstanding resistance to hydrofluoric acid, seawater biofouling, and reducing acids. Unlike precipitation-hardenable nickel alloys, Monel 400 is a solid solution strengthened alloy with no intentional precipitation hardening additions, making it exceptionally stable in marine environments and HF service.

Comparison of Marine and Chemical Performance:

High-Temperature Tensile Properties (Typical Values):

Maximum Recommended Service Temperatures:

Critical Note: Monel 400 is not recommended for service in oxidizing acids (e.g., nitric acid, chromic acid) as it will experience rapid attack. It should also not be used in sulfur-containing environments at high temperatures (above 450°C) due to susceptibility to sulfur attack (sulfidation). For applications requiring higher strength, Monel K-500 (precipitation-hardenable version) should be considered.

Heat Treatment Condition:
Monel 400 flanges are normally supplied in the annealed condition (heat treated at 700–800°C) followed by air cooling. This heat treatment:

l  Relieves internal stresses from forging.

l  Restores optimum ductility and corrosion resistance.

l  Ensures a stable microstructure for marine and HF service.

Delivery Condition: Flanges normally supplied in annealed and pickled condition, providing a clean, smooth surface and excellent corrosion resistance. Upon request, bright annealed (BA) finish can be provided for high-purity applications.

Reference: Based on ASME B16.5 for nickel alloys. For HF service at elevated temperatures, consult project specifications for additional derating.

Standard Dimensions: ASME B16.5 for sizes up to 24″, and ASME B16.47 Series A/B for large diameters up to 60″. EN 1092-1 dimensions available upon request.

Raw Material Selection: High-quality Monel 400 (UNS N04400) nickel-copper alloy billets from certified premium mills (Special Metals, VDM Metals) with certified chemical composition (Ni ≥63%, Cu 28-34% verification) and traceability.

Cutting & Heating: Material is cut to precise weight using band saws, then induction-heated to forging temperature (1100–1200°C). Temperature control is important for nickel-copper alloys.

Forging: Hot forged using hydraulic presses (3000–8000 tons) with controlled reduction rates. Monel 400 has good forgeability at proper temperatures.

Heat Treatment – Annealing: Heat treatment at 700–800°C followed by air cooling to relieve stresses and restore ductility.

Machining: CNC lathes and milling machines produce precise dimensions, bolt holes, and facing surfaces. Monel 400 work hardens moderately; proper tooling recommended.

Surface Finishing: Raised face serration, flat facing, or RTJ groove machining per ASME B16.5 requirements.

Marking: Laser engraving or stamping with grade (Monel 400/N04400), size (NPS), class, heat number, manufacturer identification, and standard.

Inspection & Testing: Dimensional check, PMI, hardness test, and NDT as required.

Surface Treatment: Pickling and passivation using specialized pickling acids optimized for nickel-copper alloys; thorough rinsing required.

Each Monel 400 flange face is inspected for surface roughness, concentricity, and absence of defects.

Chemical Analysis: PMI 100% verification using handheld XRF spectrometer for Ni, Cu, Fe (copper content 28-34% verification critical).

Mechanical Testing: Tensile strength (≥480 MPa), yield strength (≥170 MPa), elongation (≥35%), hardness (≤180 HBW).

Dimensional Inspection: OD, ID, bolt circle, bolt hole alignment, thickness, flatness using calibrated gauges and CMM.

Thread Inspection: NPT thread verification using GO/NO-GO gauges per ANSI B1.20.1.

NDT – Liquid Penetrant Testing (PT): 100% for surface defects.

NDT – Ultrasonic Testing (UT): For internal flaws upon request.

Intergranular Corrosion Test: ASTM G28 – upon request.

Sour Service Qualification (limited, upon request): HIC per NACE TM0284, SSC per NACE TM0177.

Third-Party Inspection: SGS, BV, DNV, ABS, TUV, LR on customer request.

HF Alkylation Units (Petrochemical Refining): Hydrofluoric acid (HF) alkylation reactor flanges, HF acid cooler flanges, regenerator column flanges, HF storage tank manway flanges, alkylate product transfer flanges, acid settling drum flanges (NACE MR0175 limited sour service).

Marine & Shipbuilding: Seawater cooling system flanges, propulsion cooling water line flanges, ballast water treatment system flanges, fire main system flanges, shipboard sanitary system flanges, hydraulic control line flanges, degaussing system flanges (non-magnetic requirement), keel cooler flanges (ABS, BV, DNV, LR, GL, RINA, CCS, KR, NK certified).

Naval Vessels (Military): Non-magnetic flange connections for mine countermeasure vessels, submarine hydraulic system flanges, degaussing system flanges, low-magnetic signature flange connections.

Desalination Plants: Brine heater flanges, brine preheater flanges, multi-stage flash (MSF) evaporator flanges, high-velocity brine handling flanges, chemical injection flanges.

Chemical Processing (Brine & Chlor-Alkali): Brine heater flanges, chlor-alkali plant brine line flanges, salt evaporator flanges, caustic service flanges (deaerated conditions), sodium chloride brine handling flanges.

Offshore Platforms: Seawater intake flanges, firewater system flanges, cooling water flanges, chemical injection flanges (limited sour service, NORSOK M-650 qualified upon request).

Aerospace: Hydraulic system flanges, fuel system flanges for naval aircraft, high-pressure fluid handling flanges.

Power Generation (Coastal): Seawater-cooled condenser flanges, auxiliary cooling water flanges, intake structure flanges.

Oil & Gas (Limited Sour Service): Wellhead flanges for low H₂S environments, produced water flanges (NACE MR0175 limited qualification).

Cryogenic Service: LNG handling flanges maintains good toughness down to -196°C.

Small flanges (≤4″): Heavy-duty cartons with moisture barrier paper on pallets, individual plastic bagging.
Medium flanges (6″–12″): Wooden crates with foam padding dividers, each flange wrapped in VCI paper.
Large flanges (≥14″): Individual wooden crates or steel-framed pallets with foam padding.

All shipments:

VCI paper interleaving between flanges

Plastic end caps for bore protection

Bolt hole protectors for RTJ facings

Individual tagging: Grade (Monel 400/N04400), size, class, heat number, manufacturer identification, standard, PO number

Waterproof shipping marks for export containers

Moisture barrier wrapping for sea freight

Womic Steel's Delivery Strengths:

Ready stock: Class 150 and 300 Monel 400 flanges in sizes 1/2″–12″ – dispatch within 24–48 hours.

Direct cooperation with global shipowners for the most competitive freight rates.

Professional loading by in-house teams using padded slings.

Complete documentation package including EN 10204 3.1 MTR, PMI reports, classification society certificates (ABS, DNV, LR, etc.), and inspection reports.

Continuous cargo tracking and after-sales follow-up.

1. What is Monel 400 best suited for in flange applications?
Monel 400 flanges are primarily used for three key applications: (1) Hydrofluoric acid (HF) alkylation service in refineries (premier material), (2) High-velocity seawater and brine service (excellent erosion resistance), and (3) Non-magnetic naval/marine flange connections where magnetic signature must be minimized.

2. Can Monel 400 flanges be used in seawater?
Yes, excellent resistance. Monel 400 handles high-velocity seawater (up to 10 m/s) without impingement attack – significantly better than 316L or Duplex 2205. It also resists biofouling, reducing maintenance.

3. Is Monel 400 resistant to hydrochloric acid (HCl)?
Limited. Monel 400 has fair resistance to deaerated dilute HCl but is not recommended for concentrated or aerated HCl. For HCl service, Hastelloy C276 is the preferred material.

4. What is the maximum temperature for HF service?
Approximately 150°C (302°F). Above this temperature, other materials may be required. For higher temperature HF service, consult corrosion data.

5. Can Monel 400 flanges be welded directly to carbon steel?
Yes, but use transition piece or proper filler (ERNiCu-7) to avoid galvanic corrosion, especially in seawater service. Direct welding without transition can create galvanic cells.

6. Why is Monel 400 non-magnetic?
Monel 400 has a nickel-copper austenitic structure that is non-magnetic. This property is critical for degaussing systems on naval vessels and for sensitive instrumentation where magnetic fields could interfere.

7. Can you supply Monel 400 flanges with marine classification society certification?
Yes. We can supply Monel 400 flanges certified by ABS, BV, DNV, LR, GL, RINA, CCS, KR, and NK. Please specify your required classification society and class requirements.

8. Are Monel 400 flanges available in EN 1092-1 dimensions?
Yes. We can manufacture Monel 400 flanges to EN 1092-1 Type 01, 02, 05, 11, 12 with PN6 to PN400 pressure ratings. Please specify your standard.

9. What is the typical lead time for Monel 400 flanges?
Stock sizes (1/2″–12″, Class 150/300 WN RF): 2–4 days. Non-stock or special facings (RTJ, T&G): 3–5 weeks. Classification society certification may add 2–5 days for documentation.

10. What is the difference between Monel 400 and Monel K-500?
Monel K-500 is a precipitation-hardenable version of Monel 400 with aluminum and titanium additions, offering higher strength (YS ≥ 550 MPa vs 170 MPa). However, K-500 is more expensive and less weldable. For most flange applications requiring good corrosion resistance, Monel 400 is sufficient. For high-strength rotating components (shafts, bolts), Monel K-500 is preferred.

Complete Product Range: Weld neck, slip-on, blind, socket weld, threaded, lap joint, and plate flanges – one-stop sourcing for marine and HF alkylation projects.

Strict Quality Control: ISO 9001:2015, PED 2014/68/EU, and API Q1 certified facilities.

Premium Mill Sources: Special Metals, VDM Metals certified raw materials – 100% traceable.

Marine Classification Certified: ABS, BV, DNV, LR, GL, RINA, CCS, KR, NK certification available – full documentation package.

Non-Magnetic Verified: Magnetic permeability testing available for naval/military applications.

HF Alkylation Expertise: Proven supply record for HF alkylation units in refineries worldwide.

Advanced Forging & Machining: 3000–8000 ton hydraulic presses and CNC machining centers.

Full Traceability: Heat number stamped on each flange – traceable back to original mill certificate.

Flexible Customization: Special facing types (RTJ, T&G, M&F), custom bolt drilling, and non-standard sizes available.

Seawater Erosion Tested: Proven performance in high-velocity seawater service.

Global Delivery: Exported to major shipyards, naval facilities, refineries, and desalination plants worldwide.

Tel / WhatsApp:
Victor: +86 15575100681
Jack: +86 18390957568

E-mail: info@womicstainless.com

Website: www.womicsteel.com

Contact Womic Steel today for a competitive quote on Monel 400 stainless steel flanges. We offer certified quality, marine classification society certification, HF alkylation expertise, fast production lead times, and reliable global delivery to keep your marine, naval, and refinery projects running smoothly.

Stock Examples (Class 150 WN RF – Monel 400, Annealed):

Stock Examples (Class 300 WN RF – Monel 400, Annealed):

Stock Examples (HF Alkylation Service – Monel 400, Class 300, RF):

Stock Examples (Marine/Shipbuilding – Monel 400, Class 150, FF or RF):

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