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Monel alloys typically contain approximately 67% nickel and 30% copper, with small additions of iron, manganese, carbon, and silicon. The following environments are where Monel pipes truly perform:
• Hydrofluoric acid (HF): Monel 400 is the industry-standard material for HF alkylation units in petroleum refineries. It resists HF at all concentrations up to 300°F (149°C)—an environment that rapidly attacks stainless steels, carbon steels, and most other alloys.
• Seawater and brackish water: Monel 400 exhibits outstanding resistance to fast-flowing seawater, with corrosion rates typically below 0.025 mm/year. It is widely used for seawater heat exchangers, desalination plant tubing, and offshore piping systems.
• Sulfuric acid (dilute): At concentrations below 20% and at moderate temperatures, Monel 400 offers excellent resistance, outperforming many stainless steels in dilute H₂SO₄ service.
• Alkaline solutions: Monel alloys resist caustic alkalis (NaOH, KOH) at concentrations and temperatures where carbon steel and even some stainless grades suffer caustic cracking or general corrosion.
• Chloride-free reducing acids: In reducing environments (pure HCl, H₂SO₄ without oxidizers), Monel performs well.
Type | Seamless/Welded/SAW/ERW/EFW Pipe | |
End | BE (Beveled End) | |
Size | OD: 1/2"-48" | |
Manufacturing Technique | Hot rolling / Hot work / Cold rolling / Cold-drawn | |
Producing Standard | ASME B36.10 and ASME B36.19 | |
Monel Steel Grades | ASTM B474 | UNS N04400/ Monel 400 |
ASTM B163 | UNS N04400/Monel400 | |
ASTM B165 | UNS N04400/Monel400 | |
Two Monel alloy grades are commonly produced as pipe and tube products.
Grade | UNS Number | Nominal Composition | Key Characteristics | Primary Applications |
Monel 400 | N04400 | 66% Ni, 31% Cu, 1.4% Fe, 0.15% C max | Original Ni-Cu alloy; excellent general corrosion resistance; good ductility and weldability; immune to Cl⁻ SCC | HF alkylation, seawater HX, chemical processing, marine engineering |
Monel K500 | N05500 | 66% Ni, 29% Cu, 2.8% Al, 0.6% Ti, 0.1% C max | Precipitation-hardenable; Al+Ti form γ′ (Ni₃(Al,Ti)) precipitate; 2–3× yield strength of Monel 400; maintains toughness to −253°C | Pump shafts, marine propellers, oil well tools, springs, valve stems |
Product Form | Standard | Grade Coverage | Typical Size Range | Wall Thickness |
Seamless pipe | ASTM B165 / ASME SB-165 | Monel 400 (UNS N04400) | 1/8″ – 12″ NPS | Sch. 5S through Sch. 80S |
Seamless tube (condenser/HX) | ASTM B163 / ASME SB-163 | Monel 400 (UNS N04400) | 6–25 mm OD, 0.5–2.5 mm WT | BWG 18–26 typical |
Welded pipe | ASTM B705 / ASME SB-705 | Monel 400 (UNS N04400) | 2″ – 24″ NPS | Sch. 5S through Sch. 40S |
Welded tube | ASTM B622/B626 | Monel 400 (UNS N04400) | 6–50 mm OD | 0.5–3 mm WT |
Seamless pipe (K-500) | ASTM B865 | Monel K-500 (UNS N05500) | 1/2″ – 6″ NPS | Sch. 10S through Sch. 80S |
Flanges | ASTM B564 / ASME SB-564 | Monel 400, K-500 | 1/2″ – 24″ Class 150–1500 | Forged ring / forged block |
Fittings (elbows, tees, reducers) | ASTM B366 / ASME SB-366 | Monel 400, K-500 | 1/2″ – 12″ | WP-N (welded) / CR-N (centrifugal cast) |
Bars & billets (for machining) | ASTM B164 | Monel 400, R-405, K-500 | 6–250 mm diameter | Round, hex, square |
The following ASTM specifications govern the manufacture, testing, and acceptance of Monel pipe and tube products. The corresponding ASME specifications (SB- prefix) are identical in technical content and are required for ASME Boiler and Pressure Vessel Code (BPVC) applications.
ASTM Spec | ASME Equivalent | Title | Scope | Key Requirements |
B163 | SB-163 | Seamless Nickel and Nickel-Copper Condenser and Heat-Exchanger Tubes | Seamless tubes for HX/condenser service in Monel 400 | Tensile, yield, elongation; hydrostatic or eddy-current test; grain size; IGC test optional |
B165 | SB-165 | Nickel-Copper Alloy (UNS N04400) Seamless Pipe and Tube | Seamless pipe and tube in Monel 400 only | OD tolerance ±0.5%; wall thickness ±10%; tensile ≥70 ksi; yield ≥28 ksi; hydro or NDE |
B705 | SB-705 | Nickel-Alloy Welded Pipe | Welded pipe in Monel 400 and other Ni alloys | Longitudinal or spiral weld; radiography of weld; tensile (including weld); flattening test |
B865 | SB-865 | Precipitation-Hardening Nickel-Copper-Aluminum Alloy (UNS N05500) Bar, Rod, Wire, and Forging Stock | Monel K-500 semi-finished products (used as feedstock for pipe extrusion) | Solution-annealed or precipitation-hardened condition; tensile ≥140 ksi (aged); hardness 275–375 HB |
B366 | SB-366 | Factory-Made Wrought Nickel and Nickel Alloy Fittings | Welded and seamless fittings in Monel 400 and K-500 | WP-N (welded) and CR-N (cast) class fittings; pressure ratings per MSS SP-43/SP-75 |
B564 | SB-564 | Nickel Alloy Forgings | Forged flanges, fittings, and valve bodies in Monel 400 and K-500 | Forged from billet; solution-annealed or aged; tensile, yield, hardness; ultrasonic testing per ASTM E2375 |
Monel pipe dimensions follow the same NPS (Nominal Pipe Size) system and schedule numbers as stainless steel and carbon steel pipes. The governing dimensional standards are:
• ASME B36.19M: Stainless Steel Pipe — covers dimensions and tolerances for austenitic and nickel-alloy pipe, including Monel. Wall thickness is designated by Schedule numbers (5S, 10S, 40S, 80S).
• ASME B36.10M: Welded and Seamless Wrought Steel Pipe — used as a dimensional reference for standard wall thicknesses; some Monel pipe may be specified to B36.10 schedules where B36.19 does not cover the size.
• ASME B16.5: Pipe Flanges and Flanged Fittings — pressure-temperature ratings for Monel flanges by class (150, 300, 600, 900, 1500, 2500). Monel 400 is listed as Material Group 2.4.
• ASME B16.9: Factory-Made Wrought Buttwelding Fittings — dimensions and tolerances for elbows, tees, reducers, and caps in Monel.
• ASME B16.11: Forged Fittings, Socket-Welding and Threaded — for Monel 400 and K-500 socket-weld and threaded fittings (elbows, tees, couplings, half-couplings, caps, unions).
Monel pipe systems must be designed in accordance with the applicable piping code. The most common design codes and their treatment of Monel alloys are:
Design Code | Monel Treatment | Maximum Allowable Stress (Monel 400, 100°F) | Notes |
ASME B31.3 (Process Piping) | Monel 400 listed in Table A-1 as UNS N04400 | 20.0 ksi (annealed) | Most widely used code for chemical/petrochemical Monel piping |
ASME B31.1 (Power Piping) | Monel 400 listed | 18.3 ksi (annealed) | For power plant seawater cooling systems |
ASME BPVC Section VIII Div.1 | Monel 400 listed in Section II Part D | 20.0 ksi (annealed) | For pressure vessels using Monel pipe as nozzles/shells |
ASME B31.12 (Hydrogen Piping) | Monel 400 listed; VERY LOW HE susceptibility | 15.3 ksi (adjusted for H₂ service) | Monel is highly resistant to hydrogen embrittlement |
API 560/660 | Not specifically listed for fired HX | N/A | Carbon steel or Cr-Mo typically specified; Monel for tubes only |
TEMA (Tubular Exchanger Manufacturers Assoc.) | Monel 400 tube material (Material Group D) | Per ASME II-D | Standard for shell-and-tube HX design |
Monel alloys are recognized under multiple international standards. The following table provides cross-reference equivalents for the most common Monel 400 pipe specification:
Specification Type | ASTM (US) | EN/DIN (Europe) | JIS (Japan) | GB (China) |
Seamless Pipe | B165 (N04400) | DIN 17751 / EN 10216-4 (NiCu30Fe) | JIS H 4600 (NW 4400) | GB/T 2882 (NCu30) |
Welded Pipe | B705 (N04400) | EN 10217-7 (nickel alloy welded) | JIS H 4620 | GB/T 2882 |
Condenser Tube | B163 (N04400) | DIN 17751 | JIS H 4600 | GB/T 2882 |
Bar/Billet | B164 (N04400/N04405) | DIN 17752 / EN 10095 | JIS H 4600 | GB/T 2882 |
Flanges | B564 (N04400) | EN 10269 / EN 1092-1 (flange dims) | JIS B 2220 | GB/T 2882 |
Fittings | B366 (WP-NCR) | EN 10253-4 (nickel alloy buttwt fittings) | JIS B 2313/2316 | GB/T 2882 |
Element | Monel 400 | Monel K-500 |
Nickel (Ni) | 63.0–70.0% | 63.0–70.0% |
Copper (Cu) | Remainder (28–34%) | Remainder (27–33%) |
Iron (Fe) | ≤2.5% | ≤2.0% |
Manganese (Mn) | ≤2.0% | ≤1.5% |
Carbon (C) | ≤0.30% | ≤0.25% |
Silicon (Si) | ≤0.50% | ≤0.50% |
Sulfur (S) | ≤0.024% | ≤0.010% |
Aluminum (Al) | — | 2.30–3.15% |
Titanium (Ti) | — | 0.35–0.85% |
Property | Monel 400 | Monel K-500 |
Tensile Strength | 70 ksi (483 MPa) min | 140 ksi (965 MPa) min |
Yield Strength (0.2%) | 28 ksi (193 MPa) min | 100 ksi (690 MPa) min |
Elongation (in 2″) | 35% min | 20% min |
Hardness | 110–150 HB | 275–375 HB (aged) |
Modulus of Elasticity | 26.0 × 10⁶ psi (179 GPa) | 26.0 × 10⁶ psi (179 GPa) |
Density | 0.319 lb/in³ (8.83 g/cm³) | 0.306 lb/in³ (8.47 g/cm³) |
Melting Range | 2370–2460°F (1300–1350°C) | 2400–2500°F (1315–1370°C) |
Min. Service Temp (cryogenic)","−53°C (LH₂) | −253°C | −253°C |
Property | Monel 400 | 316L SS | Significance for Piping |
Thermal conductivity (20°C) | 21.8 W/m·K | 14.6 W/m·K | Monel conducts heat ~50% better — advantageous for HX tubing |
Coefficient of thermal expansion (20–100°C) | 13.9 × 10⁻⁶/°C | 16.5 × 10⁻⁶/°C | Lower expansion — less thermal stress in constrained piping |
Electrical resistivity (20°C) | 51.0 μΩ·cm | 74.0 μΩ·cm | Lower resistivity — relevant for cathodic protection and stray currents |
Magnetic permeability | 1.0 (slightly magnetic at RT) | 1.02 (non-magnetic austenite) | Both essentially non-magnetic; Monel can become slightly ferromagnetic below 0°C |
Poisson's ratio | 0.32 | 0.30 | Comparable; both standard for piping stress analysis |
Industry | Application | Grade | Pipe Type |
Petroleum Refining | HF alkylation unit piping, heat exchangers, separators | 400 | Seamless (B165) |
Marine / Offshore | Seawater cooling piping, firewater systems, desalination tubing | 400 | Seamless (B165) / Condenser tube (B163) |
Chemical Processing | HF handling, chlorinated solvents, organic acid piping | 400 | Seamless (B165) |
Power Generation | Steam turbine condenser tubing, feedwater heater tubing | 400 | Condenser tube (B163) |
Oil & Gas Production | Downhole tubing, sour service piping (with H₂S) | K-500 | Seamless (B865) |
Aerospace | Fuel and hydraulic lines (limited/specialty) | K-500 | Seamless, small bore |
Nuclear | Heat exchanger tubing in certain reactor designs | 400 | Seamless (B163) |
Pharmaceutical / Food | Pure water and clean-in-place (CIP) piping | 400 | Seamless, polished |
Monel 400 has good weldability and can be joined by all conventional arc welding processes (GTAW/TIG, GMAW/MIG, SMAW, SAW). However, several important considerations distinguish Monel welding from stainless steel welding:
• No preheat required: Monel 400 is a single-phase solid solution alloy with no martensite transformation. Preheat is not required and should be avoided as it can promote carbide precipitation.
• Interpass temperature control: Limit interpass temperature to 350°F (175°C) maximum. Excessive heat input can cause carbide precipitation at grain boundaries and reduce corrosion resistance.
• Matching filler metal: Use ENiCu-7 (SMAW) or ERNiCu-7 (GTAW/GMAW) filler metals per AWS A5.11/A5.14. Do NOT use stainless steel filler metal—galvanic corrosion will occur at the dissimilar metal interface.
• Dissimilar welding to steel: When welding Monel to carbon steel or stainless steel, use ENiCrFe-3 (Inconel 182) or ERNiCr-3 (Inconel 82) filler metal. These Ni-Cr-Fe fillers bridge the composition gap and prevent galvanic corrosion.
• Post-weld heat treatment (PWHT): Generally NOT required for Monel 400. PWHT may be specified for stress relief in thick-wall applications, but solution annealing (1600°F / 870°C) is the preferred treatment if any heat treatment is needed.
Welding Process | Filler Metal (AWS Classification) | Composition | Application |
GTAW (TIG) | ERNiCu-7 (Monel 60) | 65Ni-30Cu-3Mn-2Ti | Matching filler for Monel 400 pipe; Ti acts as deoxidizer |
GMAW (MIG) | ERNiCu-7 (Monel 60) | 65Ni-30Cu-3Mn-2Ti | Matching filler; spray or pulsed transfer |
SMAW (Stick) | ENiCu-7 (Monel 190) | 65Ni-30Cu-3Mn-2Ti coated electrode | Matching filler; most common field welding process |
GTAW (dissimilar to CS/SS) | ERNiCr-3 (Inconel 82) | 72Ni-20Cr-3Mn-3Fe | Dissimilar joints Monel-to-carbon steel or stainless |
SMAW (dissimilar to CS/SS) | ENiCrFe-3 (Inconel 182) | 72Ni-15Cr-8Fe-2Mn | Dissimilar joints; high Cr prevents galvanic corrosion |
Monel 400 pipe can be cold-bent using conventional pipe bending equipment. Work hardening occurs during cold deformation, so the following limits apply:
Minimum bend radius: 3× pipe OD for seamless pipe in the annealed condition.
Cold work limit: ≤15% outer fiber elongation without intermediate annealing.
Post-forming annealing: If cold work exceeds 15%, solution anneal at 1600°F (870°C) for 1 hour per inch of wall thickness, followed by water quenching.
Springback: Expect 10–20% more springback than 316L stainless steel due to higher work hardening rate.
Jinie Technology (Jiangsu) Co., Ltd. (JN Alloys) has been a trusted supplier of specialty alloy products for over 15 years, serving customers across Southeast Asia, the Middle East, Europe, and the Americas. Our Monel pipe offering is backed by:
• Full traceability: Every pipe spool is traceable from raw material to finished product via heat number, with EN 10204 3.1 or 3.2 certification.
• PMI verification: 100% positive material identification on all Monel products before shipment, ensuring no mislabeled or substituted material reaches your project.
• Comprehensive size range: Seamless pipe from 1/8″ to 12″ NPS, condenser tubes from 6 mm to 25 mm OD, and welded pipe up to 24″ NPS.
• Global logistics: Export packing, documentation, and shipping to any international destination. Incoterms FOB, CIF, and DDP available.
• Technical support: Our metallurgists can advise on grade selection, welding procedures, and corrosion evaluation for your specific service conditions.
• Competitive pricing: Long-standing relationships with Monel melt shops
