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Product Overview
UNS S31254 (also known as 254SMo, W.Nr 1.4547) is a premium super austenitic stainless steel purpose‑engineered for extreme chloride and aggressive mixed‑chemical environments.
Its balanced composition—approximately 20% chromium, 18% nickel, 6% molybdenum, plus nitrogen strengthening—yields a Pitting Resistance Equivalent Number (PREN of 42–46). This places it among the most corrosion‑resistant wrought stainless steels available for industrial engineering.
Compared to conventional 300 series stainless steels, UNS S31254 provides over three times greater chloride pitting resistance. It remains stable in complex acid‑chloride media where standard grades suffer rapid localized attack. It is the material of choice for critical assets requiring long, failure‑free service lives:
- Seawater desalination facilities
- Offshore marine structures
- Industrial FGD scrubber systems
Core Engineering Value
UNS S31254 is a dedicated anti‑corrosion alloy, not a general‑purpose stainless steel. It is specified where downtime and maintenance costs are unacceptable, delivering reliable performance under:
- Continuous exposure to high‑chloride seawater and brine
- Mixed acidic & chloride flue gas and process streams
- High‑humidity offshore platform structural parts
- Long‑cycle heat exchanger equipment
Its primary competitive advantage is outstanding resistance to pitting and crevice corrosion—the dominant failure modes of standard stainless steels in seawater service.
Alloy 254 Chemical Composition
Note: All figures represent standard ranges and nominal values. Final acceptance is based on applicable ASTM specifications and official Mill Test Certificates.
| Element | Range (%) | Nominal (%) |
|---|---|---|
| Cr | 19.5 – 20.5 | 20.0 |
| Ni | 17.5 – 18.5 | 18.0 |
| Mo | 6.0 – 6.5 | 6.2 |
| N | 0.18 – 0.25 | 0.20 |
| Cu | 0.5 – 1.0 | 0.7 |
| C | ≤0.02 | 0.01 |
| Mn | ≤1.0 | 0.8 |
| Si | ≤0.8 | 0.5 |
| P | ≤0.03 | 0.02 |
| S | ≤0.01 | 0.005 |
UNS S31254 Applicable Standards
| Product Form | Standard | Description |
|---|---|---|
| Plate / Sheet | ASTM A240 | UNS S31254 plate material specification |
| Seamless Tube | ASTM A312 | Heat exchanger & process seamless pipe |
| Bar / Rod | ASTM A276 | Machining & structural solid bar |
| Forged Fittings | ASTM A182 | Equivalent to Grade F44 |
254SMo Key Physical Properties
| Property | Metric | Imperial |
|---|---|---|
| Density | 8.0 g/cm³ | 0.289 lb/in³ |
| Melting Range | 1320–1390 °C | 2408–2534 °F |
| Elastic Modulus | 195 GPa | 28.3 Mpsi |
| Magnetism | Non‑magnetic | Non‑magnetic |
Thermal Properties
CTE = Coefficient of Thermal Expansion
| Property | Metric | Imperial |
|---|---|---|
| Thermal Conductivity (20°C) | 12 W/m·K | 6.9 BTU·in/hr·ft²·°F |
| CTE (20–100°C) | 15.5 µm/m·K | 8.6 µin/in·°F |
| CTE (20–300°C) | 16.5 µm/m·K | 9.2 µin/in·°F |
| CTE (20–500°C) | 17.0 µm/m·K | 9.4 µin/in·°F |
Room Temperature Mechanical Properties
Solution annealed condition – minimum guaranteed values
| Property | Metric | Imperial |
|---|---|---|
| Tensile Strength | ≥650 MPa | ≥94 ksi |
| Yield Strength (0.2% offset) | ≥300 MPa | ≥43.5 ksi |
| Elongation | ≥35% | ≥35% |
| Brinell Hardness | ≤220 HB | ≤220 HB |
| Charpy V‑Notch Impact Energy | ≥100 J | ≥74 ft·lbf |
W.Nr 1.4547 Core Performance Advantages
| Key Feature | Engineering Value |
|---|---|
| PREN 42–46 | Excellent barrier against chloride pitting failure |
| 6% Mo alloy design | Stable long‑term corrosion resistance in seawater & brine |
| FGD flue gas resistance | Reliable service under mixed acid flue gas erosion |
| Superior crevice corrosion resistance | Safe operation in stagnant seawater dead zones |
| Optimized weldability | No mandatory post‑weld heat treatment required |
| Fully austenitic matrix | Permanently non‑magnetic |
| Wide fabrication flexibility | Compatible with cold forming, hot forging & CNC machining |
Alloy 254 UNS S31254 Industrial Applications
| Industry | Typical Components |
|---|---|
| Seawater Desalination | RO housings, evaporators, heat exchange tube bundles |
| Offshore Engineering | Seawater delivery piping, platform structural parts |
| FGD Flue Gas Desulfurization | Scrubber internals, anti‑corrosion spray pipelines |
| Hydrometallurgy | Acid leaching tanks, reactor agitator shafts |
| Pulp & Paper | Chlorine bleaching production equipment |
| Nuclear Cooling Systems | Seawater circulation heat exchange loops |
Material Selection Guidance
| Service Environment | Recommended Material | Selection Reason |
|---|---|---|
| High‑chloride continuous seawater | UNS S31254 | Maximum anti‑pitting & crevice corrosion capacity |
| FGD mixed acid flue gas | UNS S31254 | Balanced acid and chloride resistance |
| General mild industrial corrosion | 316L Stainless Steel | Cost‑effective conventional choice |
| High mechanical load structural parts | 2205 / 2507 Duplex | Higher tensile and yield strength |
| Strong pure reducing acid medium | Alloy 825 Nickel Alloy | Stable nickel matrix for severe reducing corrosion |
Supply Condition & Quality Assurance
Product Forms
Plate, sheet, seamless tube, welded pipe, solid bar, and all series forged fittings.
Surface Finish
Solution annealed + pickled.
Custom Processing
Precision cutting, bending, and CNC machining available upon request.
Packaging & Export Standard
- Waterproof PE inner wrapping
- Seaworthy plywood crates & heavy steel pallets
- Permanent laser marking: “C&N Hongcheng” + UNS S31254 + heat lot + dimension
Supplied Inspection Documents
- EN10204 3.1 / 3.2 MTC
- PMI composition verification
- Ultrasonic inspection (UT)
- Hydrostatic test records
- Hardness & mechanical test reports
When your project demands the exceptional chloride pitting and crevice corrosion resistance of UNS S31254 (254SMo), partner with C&N / HONGCHENG PIPE FITTINGS LIMITED for full‑lifecycle supply. We provide ASTM‑compliant plates, seamless tubes, forged fittings and custom components — all delivered with full‑batch PMI traceability, EN 10204 3.1 certification, permanent laser marking and fast, tailored processing. From seawater desalination to aggressive FGD systems, rely on our one‑stop inventory and engineering support to keep your critical assets running failure‑free. Contact us
