Tesco Steel & Engineering manufactures 254 SMO flanges — forged from UNS S31254 (ASTM A182 F44, EN 1.4547), the 6% molybdenum super austenitic stainless steel with a PREN of about 43. The high molybdenum and nitrogen give it outstanding resistance to chloride pitting, crevice corrosion and stress-corrosion cracking — well beyond 316L and 904L — with roughly double the yield strength of 316L. The first-choice stainless for seawater, desalination, FGD and chloride chemical service. Weld neck, slip-on, blind, socket-weld, threaded, lap-joint & spectacle flanges to ASME B16.5 / B16.47, Class 150–2500, ½″–24″. ISO 9001:2015 certified. Made in India.
254 SMO Weld Neck Flanges (UNS S31254 / F44)
254 SMO Slip-On Flanges — Ready Stock
254 SMO is the best known of the 6% molybdenum super austenitic stainless steels. Chemically it sits well above ordinary austenitic grades: around 20% chromium, 18% nickel, 6.1% molybdenum, plus a deliberate nitrogen addition and a touch of copper. That recipe was developed to beat the one weakness of 304 and 316 — chloride attack — and it does so emphatically. Its corrosion number, the PREN, comes out at about 43, putting it in the same league as super duplex while keeping the toughness, formability and non-magnetic behaviour of an austenitic steel. Engineers reach for 254 SMO when 316L has already pitted, or when the alternative would be an expensive nickel alloy or titanium.
| Element | C | Cr | Ni | Mo | N | Cu | Mn | Si | P | S |
|---|---|---|---|---|---|---|---|---|---|---|
| UNS S31254, % | 0.020 max | 19.5–20.5 | 17.5–18.5 | 6.0–6.5 | 0.18–0.22 | 0.50–1.00 | 1.00 max | 0.80 max | 0.030 max | 0.010 max |
The defining features are the ~6.1% molybdenum and the 0.20% nitrogen — both strong pitting-fighters — backed by high nickel for phase stability and a copper addition that helps in sulphuric-acid environments.
| Property | Value (typical, A182 F44) |
|---|---|
| Tensile strength | ≥ 650 MPa (94 ksi) |
| Yield strength (0.2%) | ≥ 300 MPa (44 ksi) |
| Elongation | ≥ 35% |
| Hardness | ≤ 223 HBW (approx. 96 HRB) |
| Density | 8.0 g/cm³ |
| PREN | ≈ 43 (Cr + 3.3×Mo + 16×N) |
| Condition | Solution annealed (~1150–1200°C, rapid quench), essentially non-magnetic |
Note the yield strength — roughly double that of 316L — which often lets designers use thinner, lighter sections for the same pressure rating.
With a PREN of about 43, 254 SMO resists pitting and crevice attack in warm seawater and high-chloride streams where 304/316 fail quickly.
Its high nickel and molybdenum give far better resistance to chloride SCC than standard austenitic stainless, a common failure mode in hot chloride service.
Yield strength around double that of 316L allows thinner walls and lighter flanges for the same duty.
As a fully austenitic grade it stays tough from cryogenic to elevated temperature and is essentially non-magnetic — unlike duplex grades.
In seawater and FGD service it often replaces far costlier nickel alloys and titanium, delivering similar life at lower cost.
Formed and welded with conventional austenitic techniques (with over-alloyed filler), keeping fabrication straightforward.
| Grade | Type | Mo (approx.) | PREN (approx.) | Best Suited To |
|---|---|---|---|---|
| 316L | Austenitic | 2.1% | ~24 | General corrosion, mild chloride service |
| 904L (N08904) | Austenitic | 4.5% | ~35 | Sulphuric acid & moderate chloride |
| Duplex 2205 | Duplex | 3.1% | ~35 | High-strength moderate chloride service |
| 254 SMO (S31254) | Super austenitic (6Mo) | 6.1% | ~43 | Seawater, desalination, FGD, high chloride |
| Super Duplex 2507 | Super duplex | 4.0% | ~43 | High strength + high chloride (magnetic) |
In short: 254 SMO gives super-duplex-class pitting resistance (PREN ~43) while staying austenitic — tougher, non-magnetic and easier to fabricate than duplex, and far more chloride-resistant than 316L or 904L.
| Parameter | Scope |
|---|---|
| Flange types | Weld neck (WNRF), slip-on (SORF), blind, socket-weld, threaded, lap-joint (stub-end), spectacle blind, ring-type-joint (RTJ), orifice, long weld neck |
| Material standard | ASTM A182 / ASME SA182 Grade F44 (UNS S31254); plate ASTM A240, fittings A403 WP-S31254, pipe A312 / A358 TP S31254 |
| Dimensional standards | ASME B16.5 (½″–24″), ASME B16.47 Series A/B, MSS SP-44, EN 1092-1 (type 11/05/01), BS 4504 |
| Pressure classes | Class 150, 300, 600, 900, 1500, 2500 · PN6–PN100 |
| Facings | Raised Face (RF), Flat Face (FF), Ring Type Joint (RTJ), Tongue & Groove |
| Size range | ½″ NB to 24″ NB (DN 15–DN 600); larger to order |
| Certification | EN 10204 3.1 / 3.2, PMI, hydro & third-party inspection on request |
254 SMO Blind Flanges (UNS S31254 / F44)
254 SMO Flanges — Export Crate Packing
| System | Designation |
|---|---|
| UNS | S31254 |
| ASTM / ASME (forged flanges) | A182 / SA182 Grade F44 |
| EN (Werkstoff) | 1.4547 — X1CrNiMoCuN20-18-7 |
| Trade / generic name | 254 SMO · 6Mo · 6% molybdenum super austenitic stainless |
| Plate / sheet | ASTM A240 (S31254) |
| Pipe / tube | ASTM A312 / A358 (TP S31254) |
| Fittings | ASTM A403 WP-S31254 |
| Bar | ASTM A479 (S31254) |
| Industry / Service | Typical 254 SMO Flange Use |
|---|---|
| Seawater systems | Seawater cooling and lift piping, intake and distribution headers on coastal and offshore plant |
| Desalination | SWRO and MSF high-pressure and brine piping, heat-rejection sections, energy-recovery connections |
| Flue-gas desulphurization (FGD) | Scrubber, absorber and outlet duct flanged connections in chloride-laden wet FGD |
| Pulp & paper | Bleach plant (chlorine dioxide) piping, washers and chemical lines |
| Chemical & petrochemical | Halide-bearing process streams, acid service with chlorides, heat-exchanger connections |
| Offshore oil & gas | Topside seawater, firewater and produced-water systems |
254 SMO is welded with conventional processes — GTAW, GMAW, SMAW, SAW — but with one important rule: use an over-alloyed nickel-base filler such as ERNiCrMo-3 (Alloy 625 type, FM 625 / “P12”). A matching-composition filler would under-alloy the weld because molybdenum segregates during solidification, leaving the weld less corrosion-resistant than the base metal. No preheat is required; keep heat input moderate and interpass temperature low, and the finished joint will match the parent metal’s chloride resistance.
Every 254 SMO flange is supplied solution-annealed and verified before despatch. We provide EN 10204 Type 3.1 (or 3.2 third-party witnessed) mill test certificates confirming chemistry, mechanical properties, heat-treatment condition and heat traceability; positive material identification (PMI / XRF) to confirm the ~6% molybdenum that defines the grade; and hydrostatic testing, dimensional inspection to ASME B16.5 and third-party inspection (Bureau Veritas, Lloyd’s, SGS, TÜV, Intertek) on request. Tesco Steel & Engineering is an ISO 9001:2015 certified manufacturer and exporter from Mumbai, India.
What is 254 SMO?
254 SMO is a 6% molybdenum super austenitic stainless steel, designated UNS S31254, ASTM A182 Grade F44 and EN 1.4547. It contains roughly 20% chromium, 18% nickel, 6.1% molybdenum, 0.20% nitrogen and a small copper addition. The high molybdenum and nitrogen give it a PREN of about 43, so it resists chloride pitting, crevice corrosion and stress-corrosion cracking far better than 316L or even 904L. “254 SMO” is a trademark; the generic family name is 6Mo or 6% moly super austenitic stainless.
What is the UNS, ASTM and EN designation for 254 SMO?
254 SMO is UNS S31254. For forged flanges the ASTM grade is A182 F44 (ASME SA182 F44); plate and sheet are ASTM A240 S31254, pipe is ASTM A312 / A358 TP S31254, and fittings are ASTM A403 WP-S31254. The European designation is EN 1.4547, material name X1CrNiMoCuN20-18-7. A flange marked S31254, F44 or 1.4547 is the same material.
What is the chemical composition of 254 SMO (UNS S31254)?
Typical S31254 / F44 composition: carbon 0.020% max, chromium 19.5–20.5%, nickel 17.5–18.5%, molybdenum 6.0–6.5%, nitrogen 0.18–0.22%, copper 0.50–1.00%, manganese 1.00% max, silicon 0.80% max, phosphorus 0.030% max, sulphur 0.010% max, balance iron. The deliberately high molybdenum (~6.1%) and nitrogen set it apart from ordinary austenitic stainless.
What are the mechanical properties of 254 SMO flanges?
In the solution-annealed condition, A182 F44 / S31254 has tensile strength about 650 MPa (94 ksi) minimum, 0.2% yield about 300 MPa (44 ksi) minimum, elongation about 35% minimum, hardness up to ~223 HBW, and density about 8.0 g/cm³. Yield strength is roughly double that of 316L, and the steel is austenitic, tough and essentially non-magnetic.
What is the PREN of 254 SMO and why does it matter?
254 SMO has a PREN (= %Cr + 3.3×%Mo + 16×%N) of about 43. PREN indexes resistance to chloride pitting and crevice corrosion — higher is better. At ~43, 254 SMO comfortably beats 316L (~24) and 904L (~35) and approaches super duplex 2507, which is why it is trusted in warm seawater and high-chloride environments where standard stainless steels pit and fail.
What is the difference between 254 SMO and 316L?
254 SMO has ~6.1% molybdenum and 0.20% nitrogen against ~2% molybdenum and almost no nitrogen in 316L, giving a PREN of ~43 versus ~24. That means far higher resistance to chloride pitting, crevice corrosion and stress-corrosion cracking, plus roughly double the yield strength. Where 316L pits in warm seawater or chloride streams, 254 SMO keeps working.
Is 254 SMO better than 904L?
For chloride pitting and crevice resistance, yes. 904L (N08904) has ~4.5% molybdenum and a PREN of ~35; 254 SMO has ~6.1% molybdenum, a nitrogen addition and a PREN of ~43, with higher strength. 904L remains a good choice for sulphuric acid service, but for seawater and high-chloride environments 254 SMO is stronger and more pitting-resistant.
How does 254 SMO compare with duplex 2205 and super duplex 2507?
254 SMO is austenitic; 2205 and 2507 are duplex (austenitic-ferritic). Its PREN of ~43 sits well above 2205 (~35) and close to 2507 (~43). Duplex grades give higher strength at lower cost, but 254 SMO offers better toughness over a wider temperature range, easier fabrication, non-magnetic behaviour and strong performance in some reducing/acidic chloride media. The choice depends on strength, temperature and the exact environment.
What flange types and sizes do you make in 254 SMO?
All standard types — weld neck (WNRF), slip-on (SORF), blind, socket-weld, threaded, lap-joint (stub-end), spectacle blind, RTJ and orifice — to ASME B16.5 (½″–24″), ASME B16.47 / MSS SP-44 for larger diameters, and EN 1092-1 (1.4547). Classes 150 to 2500 with RF, FF and RTJ facings. Custom sizes are made to drawing.
Where is 254 SMO used?
Wherever chlorides defeat ordinary stainless: seawater cooling and handling, desalination (SWRO and MSF), flue-gas desulphurization (FGD) scrubbers, pulp and paper bleach plants (chlorine dioxide), chemical and petrochemical processing with halides, offshore platforms, and brackish/produced water. It is often the cost-effective alternative to nickel alloys and titanium.
How is 254 SMO welded?
By GTAW, GMAW, SMAW and SAW, but with an over-alloyed nickel-base filler — typically ERNiCrMo-3 (Alloy 625 type, FM 625 / P12) — to compensate for molybdenum segregation and keep the weld's corrosion resistance equal to the base metal. No preheat is needed; interpass temperature is kept low and heat input controlled. Matching-composition fillers are avoided because they under-alloy the weld.
Are 254 SMO flanges supplied with test certificates?
Yes. Every 254 SMO flange ships with EN 10204 Type 3.1 (or 3.2 third-party witnessed) mill test certificates confirming chemistry, mechanical properties, solution-annealed condition and heat traceability, with PMI / XRF confirming the ~6% molybdenum, plus hydrostatic testing and third-party inspection on request. Tesco Steel & Engineering is ISO 9001:2015 certified, based in Mumbai, India.
Is 254 SMO magnetic?
No. 254 SMO is fully austenitic, so it is essentially non-magnetic in the solution-annealed condition (a slight magnetic permeability can develop after heavy cold work). This distinguishes it from duplex grades such as 2205 and 2507, which are magnetic because of their ferrite content.