 |
Key Takeaways
254SMO (UNS S31254 / 1.4547 / F44) is a super-austenitic stainless steel with 6% molybdenum, designed specifically for severe chloride environments.
PRE value of approximately 42.5—significantly above 316L (PRE 23) and 904L (PRE 32).
Yield strength of 310 MPa minimum—nearly twice that of 316L (170 MPa).
Critical Pitting Temperature (CPT) ≥ 50°C per ASTM G48, suitable for seawater immersion
Available in pipes ASTM A312, plates ASTM A240, flanges ASTM A182 F44, and fittings ASTM A403.
Cost-effective alternative to nickel alloys and titanium in many high-chloride applications
254SMO is an austenitic stainless steel. Due to its high molybdenum content, it has extremely high resistance to pitting and crevice corrosion. This grade of stainless steel was created for containing halides environments such as seawater.
Stainless steel 254SMO also has high ductility and impact strength，with strength nearly twice than 300 series stainless steel.
International Equivalent Name
254 SMO, UNS S31254, 1.4547, F44, NAS185N, 6Mo, 00Cr20Ni18Mo6CuN
Implementation Standard
ASTM A240/ASME SA-240, ASTM A276, ASTM A182/ASME SA-182, ASTM A312/ASMES A312
Material Standard
Conforms to BS EN 10088-3 standard, material number 1.4547.
Grade | C≤ | Mn≤ | P≤ | S≤ | Si≤ | Cr | Mo | Ni | Cu | N |
254SMO | 0.02 | 1 | 0.03 | 0.01 | 0.8 | 19.5-20.5 | 6.0-6.5 | 17.5-18.5 | 0.5-1.0 | 0.18-0.25 |
Mechanical properties | Tensile, min, ksi[MPa] | Yield, min, ksi[MPa] | Elongation, %(min) | Hardness, HB（max） |
S31254 | 100【690】 | 45【310】 | 35 | 223 |
Grade | Alloy 254 smo |
Density | 8.0 kg/dm^3 |
Modulus of Elasticity | 195 GPa |
Linear Expansion at 68 to 212oF (20 to 100oC) | 16.5 X10^-6/oC |
Thermal Conductivity | 14 w/moC |
Thermal Capacity | 500 J/kgoC |
Electrical Resitivity | 0.85 μΩm |
254SMO achieves a PREN of approximately 42–43, placing it in the "excellent" category for pitting resistance.
| Material Grade | UNS Number | Typical PREN Value | Corrosion Resistance Level |
|---|---|---|---|
| 316 / 316L | S31603 | 23 – 24 | Low |
| Alloy 825 | N08825 | ~30 | Moderate |
| Duplex 2205 | S32205 | ~35 | High |
| 904L | N08904 | ~35 | High |
| Super Duplex 2507 | S32750 | ~40 | Very High |
| 254SMO (6Mo) | S31254 | ~42 – 43 | Excellent |
| AL-6XN | N08367 | ~45 | Excellent |
| Alloy 625 | N06625 | ~50 | Superior |
| Hastelloy C276 | N10276 | ~69 | Extreme |
High ductility: The alloy has high ductility, which is easy to process and form.
High resistance to pitting corrosion: It has high resistance to pitting and crevice corrosion.
Excellent corrosion resistance: It has excellent corrosion resistance in a variety of industrial environments, including salt spray environments.
Higher mechanical strength: Compared with other grades of stainless steel, UNS S31254 provides greater mechanical strength and enhanced pitting resistance.
Good processability and weldability: TIG welding is usually used, with high arc energy and concentrated heat; and there is a cooling effect of argon gas flow, and the heat-affected zone is small, which is conducive to improving the intergranular corrosion resistance of the welded joint. At the same time, the welding quality is stable, the weld is well formed, and there is no spatter and slag.
STANDARD | WERKSTOFF NR. | UNS | AFNOR | EN |
SMO 254 | 1.4547 | S31254 | Z1 CNDU20.18.06AZ | X1CrNiMoCuN20-18-7 |
Product | Standard | Show |
Pipe SMLS& Welded | ASTM A312 |  |
Tube SMLS& Welded | ASTM A269/A213 |  |
Sheet / Plate | ASTM A240 |  |
Bar / Rod | ASTM A276/A479 |  |
Forging / Flange | ASTM A182 |  |
BW Fittings | ASTM A403 |  |
| Property / Alloy | 254SMO | 316L | 904L | AL-6XN |
|---|---|---|---|---|
| Type | Super austenitic stainless steel | Austenitic stainless steel | Super austenitic stainless steel | Super austenitic stainless steel |
| Typical Composition | 20% Cr, 18% Ni, 6% Mo, 0.2% N | 16–18% Cr, 10–14% Ni, 2–3% Mo | 19–23% Cr, 24–26% Ni, 4–5% Mo, Cu | 20–22% Cr, 24–25% Ni, 6–7% Mo, 0.2% N |
| Corrosion Resistance | Excellent pitting and crevice corrosion resistance; strong against chlorides | Moderate; can corrode in strong chloride environments | Excellent resistance to oxidizing and reducing acids; good in chlorides | Superior resistance to pitting, crevice corrosion, and stress corrosion cracking |
| Resistance to Chlorides | Very high | Moderate | High | Very high |
| Maximum Service Temperature | ~1000°F (540°C) | ~1600°F (870°C) intermittent | ~1200°F (650°C) | ~1000°F (540°C) |
| Mechanical Strength | High; good yield and tensile strength | Moderate | Moderate to high | High; better than 316L, comparable to 254SMO |
| Typical Applications | Chemical processing, seawater, acid equipment | Food, pharmaceutical, general chemical | Chemical processing, petrochemical, acid-resistant equipment | Desalination, chemical processing, chloride-heavy environments |
| Cost Level | High | Low to moderate | High | High |
Tanks and pipelines for chemicals with high halide contents
Flue gas desulfurization
Equipment in pulp bleaching plants
Components in gas cleaning systems
Hydraulic and instrumentation tubing
Equipment for handling of seawater, such as seawater cooling, cooling water pipes, ballast water systems, firefighting systems etc.
| Nominal Pipe Size (NPS) | Outside Diameter (mm) | Outside Diameter (in) | Wall Thickness Schedule | Thickness Range (mm) |
|---|---|---|---|---|
| 1/2" | 21.3 mm | 0.840" | SCH 5S to SCH 80S | 1.65 - 3.73 mm |
| 3/4" | 26.7 mm | 1.050" | SCH 5S to SCH 80S | 1.65 - 3.91 mm |
| 1" | 33.4 mm | 1.315" | SCH 5S to SCH 80S | 1.65 - 4.55 mm |
| 1-1/2" | 48.3 mm | 1.900" | SCH 5S to SCH 80S | 1.65 - 5.08 mm |
| 2" | 60.3 mm | 2.375" | SCH 5S to SCH 80S | 1.65 - 5.54 mm |
| 3" | 88.9 mm | 3.500" | SCH 5S to SCH 80S | 2.11 - 7.62 mm |
| 4" | 114.3 mm | 4.500" | SCH 5S to SCH 80S | 2.11 - 8.56 mm |
| 6" | 168.3 mm | 6.625" | SCH 5S to SCH 80S | 2.77 - 10.97 mm |
| 8" | 219.1 mm | 8.625" | SCH 5S to SCH 40S | 3.76 - 12.70 mm |
| 10" | 273.1 mm | 10.750" | SCH 5S to SCH 40S | 3.76 - 12.70 mm |
| 12" | 323.9 mm | 12.750" | SCH 5S to SCH 40S | 4.57 - 12.70 mm |
ASTM A312 / ASME SA312: Seamless and welded austenitic stainless steel pipes
ASTM A358 / ASME SA358: Electric-fusion-welded pipe for high-temperature service
ASTM A943 / ASME SA943: Spray-formed seamless pipe (specialty applications)
| Type | Standard Length | Custom Options |
|---|---|---|
| Random | 4.5 - 7.0 m (15-23 ft) | Upon request |
| Fixed | 6.0 m (20 ft) or 12.0 m (40 ft) | Up to 18 m available |
| Thickness (mm) | Thickness (in) | Standard Width (mm) | Standard Length (mm) | Weight per m² (kg) |
|---|---|---|---|---|
| 3.0 mm | 0.118" | 1000-2000 mm | 2000-6000 mm | 24.0 kg |
| 5.0 mm | 0.197" | 1000-2000 mm | 2000-6000 mm | 40.0 kg |
| 6.0 mm | 0.236" | 1000-2000 mm | 2000-6000 mm | 48.0 kg |
| 8.0 mm | 0.315" | 1000-2000 mm | 2000-6000 mm | 64.0 kg |
| 10.0 mm | 0.394" | 1000-2000 mm | 2000-6000 mm | 80.0 kg |
| 12.0 mm | 0.472" | 1000-2000 mm | 2000-6000 mm | 96.0 kg |
| 15.0 mm | 0.591" | 1000-2000 mm | 2000-6000 mm | 120.0 kg |
| 20.0 mm | 0.787" | 1000-2000 mm | 2000-6000 mm | 160.0 kg |
| 25.0 mm | 0.984" | 1000-2000 mm | 2000-6000 mm | 200.0 kg |
| 30.0 mm | 1.181" | 1000-2000 mm | 2000-4000 mm | 240.0 kg |
| 40.0 mm | 1.575" | 1000-1500 mm | 2000-4000 mm | 320.0 kg |
| 50.0 mm | 1.969" | 1000-1500 mm | 2000-3000 mm | 400.0 kg |
ASTM A240 / ASME SA240: Chromium and chromium-nickel stainless steel plate, sheet, and strip
EN 10028-7: European standard for flat stainless steel products
| Finish | Description | Typical Application |
|---|---|---|
| 2B | Cold-rolled, annealed, pickled, skin-passed | General industrial use |
| No. 4 | Brushed/polished finish | Architectural, food processing |
| BA | Bright annealed, reflective surface | Decorative, high-purity applications |
| Hot-Rolled | As-rolled, pickled | Heavy industrial, structural |
| Descaled | Mechanically descaled + pickled | Welding preparation, critical service |
| Product Type | Size Range (mm) | Size Range (in) | Standard Length |
|---|---|---|---|
| Round Bar | 5 - 200 mm | 0.20" - 8.0" | 3.0 - 6.0 m |
| Square Bar | 10 - 100 mm | 0.40" - 4.0" | 3.0 - 6.0 m |
| Hex Bar | 10 - 80 mm (across flats) | 0.40" - 3.15" | 3.0 - 6.0 m |
| Flat Bar | Width: 20-200 mm; Thickness: 3-50 mm | W: 0.8"-8"; T: 0.12"-2" | 3.0 - 6.0 m |
ASTM A479 / ASME SA479: Stainless steel bars and shapes for pressure vessels and piping
ASTM A276: Stainless steel bars and shapes (general purpose)
| Diameter Range | Diameter Tolerance | Straightness Tolerance |
|---|---|---|
| 5-25 mm | ±0.10 mm | 1.5 mm/m max |
| 25-50 mm | ±0.15 mm | 1.5 mm/m max |
| 50-100 mm | ±0.20 mm | 2.0 mm/m max |
| 100-200 mm | ±0.30 mm | 2.5 mm/m max |
| Fitting Type | Size Range (NPS) | Size Range (DN) | Pressure Class |
|---|---|---|---|
| Elbows (90°/45°) | 1/2" - 24" | DN15 - DN600 | SCH 5S to SCH 80S |
| Tees (Straight/Reducing) | 1/2" - 24" | DN15 - DN600 | SCH 5S to SCH 80S |
| Reducers (Concentric/Eccentric) | 1/2" - 24" | DN15 - DN600 | SCH 5S to SCH 80S |
| Caps | 1/2" - 24" | DN15 - DN600 | SCH 5S to SCH 80S |
| Stub Ends | 1/2" - 24" | DN15 - DN600 | SCH 5S to SCH 80S |
| Socket-Weld Fittings | 1/2" - 4" | DN15 - DN100 | 3000/6000 psi |
| Threaded Fittings | 1/8" - 4" | DN6 - DN100 | 2000/3000 psi |
ASTM A403 / ASME SA403: Wrought austenitic stainless steel piping fittings
ASME B16.9: Factory-made wrought butt-welding fittings
ASME B16.11: Forged fittings, socket-weld and threaded
MSS SP-43: Standard practice for lightweight stainless steel fittings
| Connection Type | Size Range | Typical Application |
|---|---|---|
| Butt-Weld | 1/2" - 24" | Permanent piping systems, high pressure |
| Socket-Weld | 1/2" - 4" | Small-bore instrumentation, moderate pressure |
| Threaded (NPT) | 1/8" - 4" | Low-pressure utility lines, maintenance access |
| Flanged | 1/2" - 24" | Equipment connections, frequent disassembly |
| Flange Type | Size Range (NPS) | Size Range (DN) | Pressure Classes Available |
|---|---|---|---|
| Weld Neck | 1/2" - 48" | DN15 - DN1200 | 150# to 2500# |
| Slip-On | 1/2" - 24" | DN15 - DN600 | 150# to 900# |
| Socket Weld | 1/2" - 4" | DN15 - DN100 | 150# to 900# |
| Threaded | 1/2" - 24" | DN15 - DN600 | 150# to 900# |
| Blind | 1/2" - 48" | DN15 - DN1200 | 150# to 2500# |
| Lap Joint | 1/2" - 24" | DN15 - DN600 | 150# to 900# |
| Orifice | 1/2" - 24" | DN15 - DN600 | 150# to 900# |
ASME B16.5: Pipe flanges and flanged fittings (NPS 1/2" to 24")
ASME B16.47: Large-diameter steel flanges (NPS 26" to 60")
EN 1092-1: European standard for steel flanges
MSS SP-44: Steel pipeline flanges
| Facing Type | Symbol | Typical Application |
|---|---|---|
| Raised Face | RF | Most common; general service |
| Flat Face | FF | Low-pressure, cast iron equipment |
| Ring Joint | RTJ | High-pressure, high-temperature service |
| Tongue & Groove | T&G | Sealing critical fluids, gasket retention |
| Male & Female | M&F | Moderate pressure, easy alignment |
While standard sizes cover most applications, our facility offers comprehensive custom manufacturing:
| Product | Custom Capability | Typical Lead Time |
|---|---|---|
| Pipe | OD up to 1200 mm; wall thickness to 50 mm | 6-10 weeks |
| Plate | Width to 3000 mm; length to 12000 mm; thickness to 100 mm | 4-8 weeks |
| Rod/Bar | Diameter to 300 mm; special profiles | 3-6 weeks |
| Fittings | Non-standard sizes, special end prep | 4-8 weeks |
| Flanges | Large diameter (60"+), special facing, custom drilling | 6-12 weeks |
CPT is typically ~60–70°C in 6% ferric chloride solution, which is significantly higher than standard austenitic stainless steels like 316L.
| Alloy | CPT (6% FeCl₃) | Notes |
|---|---|---|
| 254SMO | 60–70°C | Very high pitting resistance |
| 316L | ~20°C | Susceptible in high-chloride environments |
| AL-6XN | 55–65°C | Comparable to 254SMO |
| 904L | ~50°C | Good pitting resistance |
Q1: What is the PRE (Pitting Resistance Equivalent) of 254SMO?
The PRE of 254SMO (UNS S31254) is approximately 42.5, calculated as: %Cr + 3.3×%Mo + 16×%N = 20 + 3.3×6.1 + 16×0.21.
This places it significantly above 316L (PRE ≈ 23) and 904L (PRE ≈ 32), making it one of the most pitting-resistant austenitic stainless steels commercially available. A PRE above 40 is generally the minimum recommended for continuous seawater immersion service.
Q2: What is the maximum service temperature for 254SMO in chloride environments?
The critical pitting temperature (CPT) for 254SMO per ASTM G48 Method C (10% FeCl₃) is ≥50°C (122°F). In seawater, the alloy performs reliably up to approximately 75°C for non-crevice conditions. Above this temperature, or in stagnant seawater with crevice geometries, super duplex grades (S32750/S32760) or nickel alloys may be more appropriate.
Q3: How does 254SMO compare to 316L stainless steel?
254SMO significantly outperforms 316L in chloride-rich environments. Key differences: PRE of 42.5 vs. 23 for 316L; yield strength of 310 MPa vs. 170 MPa for 316L; molybdenum content of 6.1% vs. 2.1% for 316L. In seawater and FGD applications where 316L fails within 1–2 years, 254SMO typically achieves 10+ years of service life. The trade-off is cost: 254SMO is approximately 2.5–3× more expensive per kilogram than 316L.
Q4: What filler metal should be used for welding 254SMO?
The recommended filler metal for GTAW/TIG welding of 254SMO is AWS ER385 (matching composition, also known as 904L filler) or a higher-alloyed filler such as AWS ERNiCrMo-3 (Inconel 625 composition). Using a slightly over-alloyed filler compensates for dilution at the weld zone and helps maintain corrosion resistance comparable to the base metal. Post-weld solution annealing at 1150–1200°C followed by rapid quench is recommended for critical service applications.
Q5: What is the difference between 254SMO and AL6XN?
Both are 6% molybdenum super-austenitic stainless steels with similar PRE values (~42–46). AL6XN (UNS N08367) has slightly higher nitrogen content (0.18–0.25%) and is produced primarily in North America under ASTM A312. 254SMO (UNS S31254) is more widely available globally and produced under both ASTM and EN standards.
In terms of corrosion performance, they are functionally equivalent in most seawater and chloride applications. AL6XN is often preferred in North American markets due to domestic availability; 254SMO is more commonly specified in European and Asian projects.
Q6: Is 254SMO suitable for seawater desalination equipment?
Yes. 254SMO is one of the primary materials used in multi-stage flash (MSF) and reverse osmosis (RO) desalination plants, specifically for heat exchanger tubes, water boxes, and piping exposed to concentrated brine. Its PRE of 42.5 and high nitrogen content give it superior resistance to the concentrated chloride conditions in desalination processes compared to 316L or 904L.
Q7: What ASTM standards apply to 254SMO pipe and tube?
Seamless and welded pipe: ASTM A312 (UNS S31254)
Heat exchanger and condenser tubes: ASTM A213 (seamless) and ASTM A249 (welded)
General service tubing: ASTM A269
Plate and sheet: ASTM A240
Bar and rod: ASTM A276 and A479
Forgings and flanges: ASTM A182 (F44 designation)
Butt-weld fittings: ASTM A403
All products should be accompanied by a mill test report (MTR) referencing the applicable standard and heat number.
Q8: What is the weight per meter of 254SMO seamless pipe?
Weight per meter is calculated as: W (kg/m) = 0.02466 × (OD – WT) × WT, where OD and WT are in mm.
For example, a 2-inch (60.3mm OD) Schedule 10S pipe with 2.77mm wall: W = 0.02466 × (60.3 – 2.77) × 2.77 ≈ 3.93 kg/m. The density of 254SMO is 8.0 g/cm³.
