Monel 400 is a binary nickel-copper alloy - simple, proven, and in production for over a century. Incoloy 825 is a more complex nickel-iron-chromium alloy with molybdenum, copper, and titanium additions that give it a broader corrosion resistance profile.
Product Forms
Bar & Rod
Plate & Sheet
Coil & Strip
Pipe & Tube
Fitting: Flange, Tee, Elbow, Reducer etc.
Forging: Ring, Shaft, Circle, Block etc.
| Element | Monel 400 (UNS N04400) | Incoloy 825 (UNS N08825) |
|---|---|---|
| Nickel (Ni) | 63.0% min | 38.0 – 46.0% |
| Copper (Cu) | 28.0 – 34.0% | 1.5 – 3.0% |
| Iron (Fe) | 2.5% max | 22.0% min |
| Chromium (Cr) | - | 19.5 – 23.5% |
| Molybdenum (Mo) | - | 2.5 – 3.5% |
| Titanium (Ti) | - | 0.6 – 1.2% |
| Manganese (Mn) | 2.0% max | 1.0% max |
| Carbon (C) | 0.30% max | 0.05% max |
| Silicon (Si) | 0.50% max | 0.5% max |
| Sulfur (S) | 0.024% max | 0.015% max |
The key takeaway: Monel 400's high copper content (28-34%) is what gives it exceptional resistance to hydrofluoric acid and seawater. Incoloy 825's chromium and molybdenum content is what gives it superior resistance to oxidizing acids, chloride pitting, and stress corrosion cracking. The titanium in 825 acts as a stabilizer, preventing carbide precipitation at grain boundaries during welding - a critical advantage for fabricated piping systems.
Standards & Specifications
Both alloys are covered by well-established ASTM/ASME specifications, which means they can be specified with confidence in coded pressure systems. Here's how the product standards map:
| Specification | Monel 400 | Incoloy 825 |
|---|---|---|
| Seamless Pipe | ASTM B165 / ASME SB165 | ASTM B423 / ASME SB423 |
| Welded Pipe | ASTM B725 / ASME SB725 | ASTM B705 / ASME SB705 |
| Condenser / Heat Exchanger Tube | ASTM B163 | ASTM B163 |
| Werkstoff Number | 2.4360 | 2.4858 |
| UNS Designation | N04400 | N08825 |
| Seamless OD Range | 6.35 – 168.3 mm (1/4" – 6") | 4.0 – 219 mm |
| Welded OD Range | 15.88 – 457.2 mm | 5.0 – 1219.2 mm |
| Wall Thickness | 0.89 – 12.7 mm (Sch 5S – 160) | 0.5 – 20 mm |
| Common Schedules | Sch 10S, 40S, 80S, 160 | Sch 5, 10, 40, 80, 160, XXS |
Mechanical Properties: How They Handle Stress
The mechanical profiles are similar but not identical. Monel 400 is a solid-solution alloy that gains strength through cold work - it cannot be precipitation hardened. Incoloy 825 is also a solid-solution alloy but its stabilizing elements give it slightly better high-temperature performance.
| Property | Monel 400 | Incoloy 825 |
|---|---|---|
| Tensile Strength (min) | 485 MPa (70 ksi) | 586 MPa (85 ksi) |
| Yield Strength, 0.2% offset (min) | 170 MPa (25 ksi) | 241 MPa (35 ksi) |
| Elongation (min) | 35% | 30% |
| Hardness (Brinell, max) | 241 HBW | ~85 HRB |
| Density | 8.80 g/cm³ | 8.14 g/cm³ |
| Melting Range | 1350 – 1390°C | ~1370°C |
| Max Service Temperature | 427°C (482°C in sulfur-free oxidizing env.) | 540°C |
| Cryogenic Performance | Excellent (retains toughness to -196°C) | Good |
Corrosion Resistance: Where Each Alloy Wins
This is where the selection decision really gets made. The two alloys were developed for different corrosion challenges:
| Corrosion Environment | Monel 400 | Incoloy 825 |
|---|---|---|
| Seawater / Marine Splash Zone | Excellent - first choice | Good - acceptable with design care |
| Hydrofluoric Acid (HF) | Excellent - industry standard | Fair - not recommended for HF service |
| Sulfuric Acid (dilute-moderate) | Good | Excellent - preferred for H₂SO₄ |
| Phosphoric Acid | Fair | Excellent - preferred for H₃PO₄ |
| Hydrochloric Acid | Fair to Good (depends on conc./temp.) | Good (reducing mixes) |
| Chloride Stress Corrosion Cracking | Resistant | Highly resistant (Mo + Ti effect) |
| Pitting & Crevice Corrosion | Good | Excellent (Cr + Mo effect) |
| Caustic Alkalis / Caustic Soda | Excellent - top performer | Good |
| Flue Gas Desulfurization (FGD) | Not recommended | Good for FGD environments |
| Oxidizing Acids (HNO₃) | Poor - not recommended | Good |
The HF Acid Factor
Monel 400's resistance to hydrofluoric acid is nearly unique among commercial alloys. In oil refinery alkylation units that use HF as a catalyst - and there are many such units across Saudi Aramco's refineries in Yanbu and Jubail, as well as ADNOC's Ruwais complex - Monel 400 pipe is the default specification for HF handling systems. No other commonly available nickel alloy matches its HF performance at a comparable cost. If your project involves HF acid service, Monel 400 is not a choice - it's the specification.
The Sulfuric Acid Factor
Incoloy 825 was specifically developed for sulfuric and phosphoric acid environments. Its molybdenum and copper additions give it broad resistance across acid concentrations and temperatures that Monel 400 cannot match. For chemical plants in Germany's Ludwigshafen cluster (BASF), the Netherlands' Rotterdam port industrial zone, or Italy's Lombardy chemical belt, where sulfuric acid handling is a daily operation, Incoloy 825 is often the specified grade for acid piping, heat exchanger tubes, and pickling equipment.
Welding & Fabrication Considerations
Monel 400: Readily welded using GTAW (TIG) or SMAW (stick) with matching Monel 60 filler wire (ERNiCu-7). Preheat is not required. The alloy does not undergo precipitation hardening, so post-weld heat treatment is generally unnecessary unless stress relief is specified. One caution: Monel 400 can be susceptible to hot cracking in highly constrained welds, so joint design should avoid high restraint.
Incoloy 825: Weldable with matching Incoloy 825 filler wire (ERNiFeCr-1) or with Inconel 625 filler for dissimilar joints. The titanium content provides natural stabilization against sensitization, but a post-weld stabilizing anneal (at 940°C for 1 hour, air cool) is recommended for service in aggressive environments to ensure full corrosion resistance at the heat-affected zone. For European PED-compliant fabrication, this anneal may be a code requirement.
Sourcing from HUITONG: What We Supply
HUITONG Pipeline Equipment manufactures and exports both Monel 400 and Incoloy 825 pipe to ASTM/ASME standards, with full material traceability.
Monel 400 pipe: ASTM B165 seamless (OD 6.35-168.3mm, Sch 5S-160) and ASTM B725 welded (OD up to 457.2mm). Full EN 10204 Type 3.1/3.2 MTCs. NACE MR0175 compliance available for sour service.
Incoloy 825 pipe: ASTM B423 seamless (OD 4-219mm, Sch 5-160/XXS) and ASTM B705 welded (OD up to 1219.2mm). PED 2014/68/EU compliance with CE marking for European buyers.
Value-added services: Cut-to-length, beveling, threading, custom spool pre-fabrication, PMI verification, third-party inspection (SGS, BV, TÜV).
Documentation: Full heat traceability, chemical and mechanical test reports, non-destructive testing certificates (UT/ET/HT), and country of origin certificates for customs clearance.
FAQ
Q: Which is better for seawater piping, Monel 400 or Incoloy 825?
Monel 400 is generally preferred for seawater piping and marine splash zones due to its proven long-term performance in chloride-rich environments. It forms a stable protective film in seawater that resists biofouling and pitting. Incoloy 825 can also handle seawater but is more commonly chosen when the service also involves sulfuric or phosphoric acid exposure, where its broader acid resistance gives it an edge.
Q: What is the price difference between Monel 400 pipe and Incoloy 825 pipe?
In 2025, Monel 400 seamless pipe typically trades at USD 40-65 per kg, while Incoloy 825 seamless pipe ranges from USD 45-70 per kg. Monel 400 is usually 10-15% cheaper because its simpler nickel-copper composition has lower raw material costs than Incoloy 825's more complex Ni-Cr-Fe-Mo-Cu-Ti chemistry. For large project lots (5+ metric tons), expect volume discounts of 5-10% from most suppliers.
Q: Can Monel 400 and Incoloy 825 pipes be welded?
Yes, both alloys are weldable. Monel 400 is typically welded with Monel 60 filler metal (ERNiCu-7) using GTAW or SMAW - straightforward, no preheat needed. Incoloy 825 is welded with Incoloy 825 filler wire (ERNiFeCr-1) using GTAW, and a post-weld stabilizing anneal at 940°C is recommended for maximum corrosion resistance at the heat-affected zone. For PED-compliant European fabrication, this anneal may be a code requirement.
Q: What ASTM standards apply to Monel 400 and Incoloy 825 pipes?
Monel 400 seamless pipe is covered by ASTM B165 (ASME SB165), with welded pipe under ASTM B725 (ASME SB725). Incoloy 825 seamless pipe falls under ASTM B423 (ASME SB423), with welded pipe under ASTM B705 (ASME SB705). Both also appear in ASTM B163 for condenser and heat-exchanger tube applications. Full material certification to these standards is available from HUITONG on every shipment.
Q: Are these alloys compliant with NACE MR0175 for sour service?
Monel 400 in the annealed condition meets NACE MR0175 / ISO 15156 requirements for sour service in the cold-worked condition (hardness limited to 35 HRC max). Incoloy 825 also meets NACE requirements in the solution-annealed condition. Always confirm the specific heat treatment condition and hardness limits with your supplier when specifying for H₂S-containing service, especially for Saudi Aramco and ADNOC projects where sour service compliance is strictly audited.
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