Project Description
UNS S31254, also designated EN 1.4547 and commercially known as 254 SMO (a trademark of Outokumpu / Alleima), is a 6% molybdenum super-austenitic stainless steel purpose-designed for seawater and halide-rich environments. With a PREN of 43–45 — achieved through synergistic additions of Cr 19.5–20.5%, Mo 6.0–6.5%, and N 0.18–0.25% — 254 SMO was the first commercial 6Mo grade and remains the benchmark CRA for chloride service up to 55 °C. It delivers approximately 50% higher yield strength than 316L through nitrogen solid-solution strengthening, permitting reduced wall thickness at equivalent pressure ratings. At SHUNFU METAL, every heat of 254 SMO is produced via VIM + ESR dual refining and undergoes 100% PMI, ultrasonic testing (UT), eddy current inspection (ET), and hydrostatic pressure verification before shipment.
Equivalent Grades — 254 SMO / S31254
| Grade | UNS | EN / W.Nr. | DIN | GB | ASTM Pipe | PREN |
|---|---|---|---|---|---|---|
| 254 SMO | S31254 | 1.4547 / X1CrNiMoCuN20-18-7 | 1.4547 | 015Cr20Ni18Mo6CuN | A312 | ~43 |
| Alloy 926 | N08926 | 1.4529 / X1NiCrMoCuN25-20-7 | 1.4529 | 015Cr21Ni26Mo6Cu2N | B677 | ~46 |
| 904L | N08904 | 1.4539 | 1.4539 | 015Cr21Ni26Mo5Cu2 | B677 | ~36 |
| 316L | S31603 | 1.4404 / X2CrNiMo17-12-2 | 1.4404 | 022Cr17Ni12Mo2 | A312 | ~25 |
| Alloy 31 | N08031 | 1.4562 | 1.4562 | NS1404 | B622 | ~48 |
| Alloy 625 | N06625 | 2.4856 | 2.4856 | NS3306 | B444 | ~50 |
Oil & Gas Applications — 254 SMO / S31254 CRA Pipe
Vertical lift risers, firewater ring mains, and deluge piping on offshore platforms and FPSO units carrying untreated, oxygenated seawater.
Tube bundles in shell-and-tube exchangers using direct seawater as the cooling medium in refinery and LNG plant utility systems.
Absorber spray nozzles, recirculation pump casings, and slurry piping in coal and fuel-oil power plant FGD systems handling hot, acidic halide condensate.
Brine heater tubes, high-pressure RO feed lines, and multi-stage flash (MSF) evaporator internals in thermal and membrane desalination plants.
Sea chest inlet screens, overboard discharge lines, and produced water treatment pipework on FPSOs and fixed offshore platforms.
Intermediate-pressure AGR amine contactor and regenerator piping under NACE MR0175 Level I–IV where 316L is insufficient.
Methanol, corrosion inhibitor, and oxygen scavenger injection quills and distribution piping in subsea and topside chemical delivery systems.
Chlorine dioxide (ClO₂) bleaching stage piping and washer filtrate lines in kraft pulp mills handling high-chloride bleach liquors at elevated temperatures.
Small-bore control line and umbilical conduits in subsea production systems where continuous seawater immersion and high external pressure demand PREN ≥ 43.
Pipe Supply Range — 254 SMO / S31254
| Product Form | Seamless Pipe, Welded Pipe (ERW / EFW), Capillary Tube |
| OD Range (Seamless) | 6 mm – 610 mm (1/4″ – 24″) |
| OD Range (Welded) | 16 mm – 2540 mm (3/8″ – 100″) |
| Wall Thickness | 0.5 mm – 60 mm (SCH 5S – SCH XXS) |
| Length | Single Random (5–7 m), Double Random (10–12 m), Cut-to-Length |
| End Finish | Plain End (PE), Bevel End (BE), Threaded |
| Surface | Pickled & Passivated, Bright Annealed, Polished |
| Standards | ASTM A312 / ASME SA312, ASTM A213, ASTM A269, ASTM A249, EN 10216-5, EN 10217-7 |
| Certification | EN 10204 3.1 / 3.2, PED 2014/68/EU, NACE MR0175 / ISO 15156 |
SHUNFU METAL maintains 254 SMO pipe inventory in standard diameters and schedules. Non-standard sizes, heavy wall (up to SCH XXS), and custom lengths are produced to order with short lead times. All welds on fabricated pipe receive 100% radiography (RT) or UT per ASME B31.3.
Chemical Composition — 254 SMO / S31254
| Element | Cr | Ni | Mo | N | Cu | Fe | C | Mn | Si | P | S |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Wt % | 19.5–20.5 | 17.5–18.5 | 6.0–6.5 | 0.18–0.25 | 0.50–1.00 | Bal. | ≤0.020 | ≤1.00 | ≤0.80 | ≤0.030 | ≤0.010 |
Composition per ASTM A312 / ASME SA312, UNS S31254. The tightly controlled Mo window (6.0–6.5%) ensures a consistent PREN of 43–45, enabling seawater service up to 55 °C without pitting initiation. Nitrogen (0.18–0.25%) plays a dual role: it provides solid-solution strengthening that elevates yield strength ~50% above 316L, and it stabilizes the austenitic phase, suppressing sigma-phase precipitation during fabrication and elevated-temperature exposure. Copper (0.5–1.0%) improves general corrosion resistance in sulphuric and phosphoric acid streams. At SHUNFU METAL, every melt is verified by optical emission spectroscopy (OES) and inert gas fusion analysis to confirm nitrogen content within specification.
Mechanical Properties — 254 SMO / S31254
Solution-annealed at 1150–1200 °C followed by rapid water quenching. Data per ASTM A312 at room temperature unless noted.
| Tensile Strength, Rm | 650–850 MPa (94–123 ksi) |
| Yield Strength, Rp0.2 | ≥ 300 MPa (≥ 44 ksi) |
| Elongation (50 mm) | ≥ 35% |
| Hardness (Max) | ≤ 260 HBW / ≤ 50 HRB |
| Modulus of Elasticity | 195 GPa (28.3×10⁶ psi) |
| Density | 8.10 g/cm³ (0.293 lb/in³) |
| Melting Range | 1320–1400 °C (2408–2552 °F) |
| Thermal Conductivity | ~14 W/m·K at 20 °C |
| PREN (Calc.) | ~43–45 |
The solution-annealed + water-quenched condition yields a fully austenitic microstructure with exceptional cryogenic toughness — Charpy V-notch impact energy exceeds 60 J at −196 °C per EN 13445-2. SHUNFU METAL performs furnace-chart-controlled annealing on every batch: soak temperature and duration are continuously logged across the furnace zone, and hardness testing on each heat-treated lot confirms uniform grain structure per ASTM E112.
For sour-service qualification, SHUNFU verifies NACE MR0175 / ISO 15156 compliance via ASTM A262 Practice C (Huey intergranular corrosion) and ASTM G48 Method C & D (critical pitting / crevice temperature). PMI is performed on every pipe before dispatch.
Service temperature range: −196 °C to +400 °C in chloride-bearing environments. Welding is performed with overmatched nickel-base fillers (AWS ERNiCrMo-3 / ENiCrMo-3) to preserve full corrosion resistance in the as-welded condition. Post-weld heat treatment is not required due to the ultra-low carbon content (≤0.020%).