Monel 400 Buttweld Pipe Fittings
Monel 400 / UNS N04400 / EN 2.4360 (NiCu30Fe) — a 67Ni-30Cu alloy for reducing environments where stainless steels fail. The standard material for seawater and marine systems, hydrofluoric (HF) acid alkylation, brine and caustic service. Near-immune to chloride stress corrosion cracking. Service from cryogenic to ~480°C. ASME B16.9 and EN 10253-2 Type B. EN 10204 3.1/3.2.
½″–24″
Size Range
~30% Cu
Ni-Cu alloy
480 MPa
Min UTS (Annealed)
EN 10204
3.1 Std / 3.2 On Req.
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Monel 400 Grade Equivalents
| Trade Name | UNS | EN W.Nr. | EN Name | ASTM (fittings) | ASME P-No. |
|---|---|---|---|---|---|
| Monel 400 | N04400 | 2.4360 | NiCu30Fe | ASTM B366 WPNC / B564 | 42 |
| Alloy 400 (generic) | N04400 | 2.4360 | NiCu30Fe | ASTM B366 UNS N04400 | 42 |
"Monel" is a registered trademark of Special Metals Corporation. EN designation 2.4360 / NiCu30Fe. Covered by ASTM B366 (WPNC) for welded fittings and ASTM B564 for forgings.
Chemical Composition — UNS N04400 / EN 2.4360
| Element | Specification |
|---|---|
| Ni | ≥63.0% (balance) |
| Cu | 28.0–34.0% |
| Fe | ≤2.5% |
| Mn | ≤2.0% |
| C | ≤0.30% |
| Si | ≤0.50% |
| S | ≤0.024% |
Nickel-copper — Monel 400 is a single-phase solid-solution alloy with no chromium. It relies on its high nickel content for corrosion resistance in reducing media, and is not hardenable by heat treatment. No PWHT required.
Mechanical Properties — Monel 400 (Annealed)
| Min. UTS | Min. YS | Elongation | Hardness | Max Continuous Service |
|---|---|---|---|---|
| 480 MPa | 170 MPa | ≥35% | ≤ 75 HRB | ~480°C |
Annealed condition is standard for buttweld fittings. Monel 400 retains strength and ductility from cryogenic temperatures up to about 480°C, and is not susceptible to the ductile-to-brittle transition of ferritic steels.
Welding & Post-Weld Heat Treatment
No PWHT Required
Monel 400 is a single-phase Ni-Cu solid solution and is not hardened by welding, so post-weld heat treatment is not required. Where residual stresses must be relieved (e.g. before HF acid service), a stress-relief anneal may be specified by the engineering authority.
Recommended Filler
ERNiCu-7 (AWS A5.14) — Monel 60 matching filler for GTAW and GMAW. This is the designated matching filler for N04400 base metal.
Preheat
No preheat required. Clean joint surfaces thoroughly — sulphur, lead and other low-melting-point contaminants must be removed to avoid hot cracking.
Inter-pass Temperature
≤150°C maximum. Use low heat input and stringer beads. Nickel alloys have lower thermal conductivity than carbon steel, so heat concentrates at the joint.
ASME P-Number
P-No. 42 (Ni-Cu alloys). Separate WPS required — cannot be qualified under austenitic SS or other nickel-alloy procedures.
Alloy Selection Guide — Monel 400 vs Alternatives
| Grade | Base | Key Advantage | Typical Use |
|---|---|---|---|
| Monel 400 / N04400 | Ni-Cu | HF acid + seawater | Alkylation, marine |
| 90/10 Cu-Ni / C70600 | Cu-Ni | Seawater (biofouling) | Seawater cooling |
| Inconel 625 / N06625 | Ni-Cr-Mo | Oxidising + sour gas | Subsea, sour gas |
| Alloy 20 / N08020 | Ni-Fe-Cr | Sulphuric acid | Chemical process |
Key Application Areas
Seawater & Marine Systems
Excellent resistance to flowing seawater and near-immunity to chloride SCC — used for seawater piping, pumps, valves and heat exchangers in marine and offshore service.
HF Acid Alkylation
The standard material of construction for refinery hydrofluoric (HF) acid alkylation units — piping, fittings and vessel internals in HF acid service.
Brine & Caustic Service
Resists chloride brines and hot caustic soda (NaOH) where austenitic stainless steels risk stress corrosion cracking.
Reducing Acids
Good resistance to dilute, air-free (de-aerated) sulphuric and hydrochloric acids under reducing conditions.
Cryogenic Service
Retains toughness and ductility to cryogenic temperatures with no ductile-to-brittle transition.
⚠ Avoid Oxidising Media
Not for nitric acid or strongly oxidising conditions — Monel lacks chromium. For oxidising acids use Inconel 625 or Alloy 20.
Available Fitting Types — Monel 400 / UNS N04400
Sizes typically ½″–24″ for nickel alloys due to material cost and availability. Larger sizes available on enquiry with extended lead time.
Elbows — 90° & 45°
Long Radius (1.5D) and Short Radius (1D). ASME B16.9 / EN 10253-2 Type B. ½″–24″.
180° Return Bends
Long Radius. ASME B16.9. ½″–12″.
Equal & Reducing Tees
ASME B16.9 / EN 10253-2 Type B. ½″–24″.
Concentric & Eccentric Reducers
ASME B16.9 / EN 10253-2 Type B. ½″–24″.
Pipe Caps
ASME B16.9 / EN 10253-2 Type B. ½″–24″.
Lap Joint Stub Ends
ASME B16.9 Type A & B. ½″–16″. Paired with backing flanges to reduce cost.
Crosses (4-Way)
ASME B16.9. ½″–8″.
Laterals (45° Y)
ASME B16.9. ½″–8″.
Flanges — All Types
Weld Neck, Slip-On, Blind, Socket Weld, RTJ. ASME B16.5. ASTM B564 UNS N04400. ½″–24″.
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Specify size, schedule, fitting type, standard (ASME B16.9 or EN 10253-2 Type B), and required MTR level (EN 10204 3.1 or 3.2 TPI). We respond within 1 business day.
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