Incoloy 25-6Mo Plate
Superior pitting resistance austenitic stainless steel for demanding chloride environments
Incoloy 25-6Mo combines the workability of austenitic stainless steel with exceptional resistance to localized corrosion in aggressive seawater and brine applications. The elevated molybdenum and chromium content provides unparalleled PREN (Pitting Resistance Equivalent Number), making it the material of choice for offshore heat exchangers, desalination plants, and chemical processing equipment.
Quick Specifications
- Density
- 8.0 g/cm³ (0.289 lb/in³)
- Melting Point
- 2420-2520°F (1327-1382°C)
- Yield Strength (0.2% offset)
- 50-60 ksi (345-415 MPa) at room temperature
- Tensile Strength
- 85-105 ksi (585-725 MPa) at room temperature
- Elongation
- 35-40% in 2 inches
- Modulus of Elasticity
- 28.5 × 10⁶ psi (196 GPa) at 70°F
Standards & Certifications
Product Description
Incoloy 25-6Mo is an advanced austenitic stainless steel engineered to deliver the highest pitting and crevice corrosion resistance among iron-based alloys. The alloy designation derives from its nominal composition of 25% chromium and 6% molybdenum, combined with optimized nickel content and careful nitrogen additions that collectively produce a PREN exceeding 50. This extraordinary pitting resistance is achieved through balanced synergies between chromium, molybdenum, and nitrogen that work cooperatively to prevent localized corrosion initiation and propagation in the most severe environments.
The microstructure of Incoloy 25-6Mo maintains full austenitic character across the composition range, ensuring superior toughness and ductility even at cryogenic temperatures. The elevated molybdenum content strengthens the passive oxide film on the metal surface, preventing breakdown in high-chloride environments where traditional stainless steels rapidly develop pitting attack. Nitrogen additions further enhance passivity while providing solid-solution strengthening that permits thinner, lighter wall structures compared to conventional stainless steels, yielding significant economic benefits in large-scale applications such as heat exchangers and piping systems.
Incoloy 25-6Mo exhibits outstanding resistance to both pitting corrosion and crevice corrosion under gasket surfaces, fastener heads, and other occluded areas where oxygen depletion would normally initiate attack. Critical pitting temperatures (CPT) measured in ASTM G48 methods C and D are exceptionally high, often exceeding 95°C in natural seawater. This exceptional performance translates to service life measured in decades rather than years, making the initial material cost premium easily justified through reduced maintenance, equipment replacement, and operational downtime.
The combination of superior corrosion resistance, excellent fabricability, and proven long-term performance makes Incoloy 25-6Mo the preferred material for mission-critical applications where reliability is non-negotiable. Extensive service history in deepwater oil platforms, LNG facilities, nuclear desalination plants, and major industrial heat exchangers confirms the alloy's ability to maintain integrity through the complete asset lifecycle. The material's superior strength compared to conventional austenitic stainless steels enables optimized designs with reduced wall thickness, contributing to both economic and operational advantages.
Specifications
| Density | 8.0 g/cm³ (0.289 lb/in³) |
| Melting Point | 2420-2520°F (1327-1382°C) |
| Yield Strength (0.2% offset) | 50-60 ksi (345-415 MPa) at room temperature |
| Tensile Strength | 85-105 ksi (585-725 MPa) at room temperature |
| Elongation | 35-40% in 2 inches |
| Modulus of Elasticity | 28.5 × 10⁶ psi (196 GPa) at 70°F |
| Thermal Conductivity | 7.0 BTU/hr·ft·°F at 212°F (12.1 W/m·K) |
| Coefficient of Thermal Expansion | 8.0 × 10⁻⁶ in/in·°F (14.4 × 10⁻⁶ m/m·°C) 68-212°F |
| Pitting Resistance Equivalent (PREN) | >50 [%Cr + 3.3×(%Mo) + 16×(%N)] |
| Hardness (Annealed) | ≤ 217 HB |
Chemical Composition
| Element | Content (%) |
|---|---|
| Iron (Fe) | Balance |
| Chromium (Cr) | 24.0-26.0 |
| Nickel (Ni) | 6.0-8.0 |
| Molybdenum (Mo) | 5.8-7.0 |
| Nitrogen (N) | 0.18-0.25 |
| Manganese (Mn) | 2.0-3.0 |
| Silicon (Si) | 1.0-2.0 |
| Carbon (C) | ≤ 0.020 |
| Phosphorus (P) | ≤ 0.025 |
| Sulfur (S) | ≤ 0.015 |
| Copper (Cu) | 0.0-0.5 |
Mechanical Properties
| Property | Value |
|---|---|
| Yield Strength @ 70°F | 50-60 ksi (345-415 MPa) |
| Tensile Strength @ 70°F | 85-105 ksi (585-725 MPa) |
| Elongation (2 inch gauge) | 35-40% |
| Reduction of Area | 60-70% |
| Impact Strength (Charpy V-notch @ 32°F) | ≥ 100 ft·lbf (135 J) |
| Yield Strength @ 300°F | 55 ksi (379 MPa) |
| Tensile Strength @ 300°F | 90 ksi (621 MPa) |
| Critical Pitting Temperature (CPT) in 6% FeCl₃ | ≥ 95°C (203°F) per ASTM G48 Method C |
Key Features & Advantages
Applications
Offshore Condensers and Heat Exchangers
Tube bundles, tube sheets, and headers in seawater-cooled condensers on floating production platforms. Incoloy 25-6Mo's superior pitting resistance eliminates the risk of tube perforation and leakage that would compromise platform integrity and operational safety. The alloy maintains performance through extended service intervals, reducing maintenance costs and platform downtime.
Desalination Plant Components
Heat exchanger tubes, piping, and pressure vessels in reverse osmosis and thermal desalination facilities processing high-salinity brines. The combination of superior chloride corrosion resistance and strength permits economical plant designs with extended service intervals measured in 20-30 years rather than requiring periodic replacement of traditional stainless steel components.
LNG Regasification Equipment
Cryogenic heat exchangers, marine risers, and process piping in LNG receiving terminals. Incoloy 25-6Mo maintains exceptional toughness at cryogenic temperatures while resisting corrosion from seawater cooling systems and any potential brine contamination during the regasification process.
Chemical Processing and Pulp & Paper Mills
Reactor vessels, heat exchangers, and piping in chemical bleaching processes and paper mill cooling systems where chloride-containing process streams create severe corrosion challenges. The superior corrosion resistance eliminates the need for protective coatings while enabling longer equipment life and improved product quality.
Subsea Pipeline Components and Wellhead Equipment
Valve bodies, flanges, and nozzles in subsea equipment exposed to both high pressures and seawater with hydrogen sulfide. The combination of corrosion resistance and strength makes Incoloy 25-6Mo ideal for critical components where failure could cause environmental damage and operational catastrophe.
Nuclear Desalination and Power Plants
Condenser tubes, feedwater piping, and cooling system components in nuclear facilities requiring maximum reliability and minimal maintenance. The alloy's proven long-term stability and resistance to water-side corrosion in both fresh and saline cooling systems ensures operational continuity and regulatory compliance.
Frequently Asked Questions
What is PREN and why is it important for Incoloy 25-6Mo?
How does Incoloy 25-6Mo compare to super duplex stainless steels?
Is Incoloy 25-6Mo susceptible to embrittlement or sensitization issues?
What welding procedures and precautions are recommended for Incoloy 25-6Mo?
What is the expected service life of Incoloy 25-6Mo heat exchangers in seawater cooling applications?
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