Super Austenitic SS 904L & 254 SMO Flanges & Fittings
Super austenitic stainless steels combine high nickel, molybdenum and copper (904L) or 6 % molybdenum with nitrogen (254 SMO) to resist sulphuric and phosphoric acid, chloride pitting and stress corrosion cracking.
Teshi Group manufactures 904L and 254 SMO weld neck, slip-on, blind and socket weld flanges, forged fittings and butt weld fittings for acid plants, zinc and copper smelters and flue-gas desulphurisation, with EN 10204 3.1 certification and PMI on every piece.
904L & 254 SMO — grades, chemistry and properties
Grades and ASTM / ASME specifications
| Grade | Forged flanges & fittings | Butt weld fittings | Plate | Pipe |
|---|---|---|---|---|
| 904LUNS N08904 · W.Nr. 1.4539 | ASTM A182 F904L | ASTM A403 WP904L | ASTM A240 / B625 | ASTM A312 / B677 |
| 254 SMO (6Mo)UNS S31254 · W.Nr. 1.4547 | ASTM A182 F44 | ASTM A403 WPS31254 | ASTM A240 S31254 | ASTM A312 S31254 |
Chemical composition (weight %, maximum unless a range is given)
| Grade | C | Mn | Si | Cr | Ni | Mo | Cu | N |
|---|---|---|---|---|---|---|---|---|
| 904L | 0.020 | 2.00 | 1.00 | 19.0–23.0 | 23.0–28.0 | 4.0–5.0 | 1.00–2.00 | 0.10 |
| 254 SMO (6Mo) | 0.020 | 1.00 | 0.80 | 19.5–20.5 | 17.5–18.5 | 6.0–6.5 | 0.50–1.00 | 0.18–0.25 |
Mechanical properties (minimum, room temperature)
| Grade | Tensile strength | Yield strength (0.2 %) | Elongation | Note |
|---|---|---|---|---|
| 904L | 490 MPa (71 ksi) | 215 MPa (31 ksi) | 35 % | PREN ≈ 34 |
| 254 SMO (6Mo) | 650 MPa (94 ksi) | 300 MPa (44 ksi) | 35 % | PREN ≥ 42 |
Values are minimums and limits from the governing ASTM / ASME specifications, summarised for convenience. The current edition of the specification takes precedence; confirm requirements against your project specification.
Where it is used
- Sulphuric acid dilution, cooling and storage
- Zinc and copper smelter roaster gas cleaning and leaching circuits
- Phosphoric acid evaporators
- Flue-gas desulphurisation scrubbers
- Seawater and brackish cooling water
Testing & certification
- Solution annealed and water quenched
- PMI on every piece for Ni, Mo and Cu
- Intergranular corrosion test to ASTM A262 when specified
- EN 10204 3.1 certificate; 3.2 with third-party inspection on request
904L & 254 SMO products we manufacture
All products
01OEM manufacturerWeld Neck Flanges
ASME B16.5 · ASME B16.47
02OEM manufacturerBlind Flanges
ASME B16.5 · ASME B16.47
03OEM manufacturerSlip-On Flanges
ASME B16.5 · EN 1092-1 Type 12
04OEM manufacturerButt Weld Elbows
ASME B16.9 · ASME B16.25
05OEM manufacturerButt Weld Tees
ASME B16.9 · ASME B16.25
06OEM manufacturerWeldolets & Sockolets
MSS SP-97 · ASME B16.11
Industries and projects
Mining & Smelters
Where 904L & 254 SMO is specified
ViewIndustryChemical & Petrochemical
Where 904L & 254 SMO is specified
ViewIndustrySteel & Metals
Where 904L & 254 SMO is specified
ViewProjectsMega-projects & EPC supply
Project BOQs, shutdowns and annual rate contracts
ViewGrade data sheets
Other materials
904L & 254 SMO by product
FAQ
904L & 254 SMO: common questions
Why is SS 904L used in sulphuric acid plants?
904L (UNS N08904) has 23–28 % nickel, 4–5 % molybdenum and 1–2 % copper, which give good resistance to dilute and moderately concentrated sulphuric acid at temperatures where 316L corrodes quickly.
What is the difference between 904L and 254 SMO?
904L relies on nickel and copper for acid resistance. 254 SMO (UNS S31254, ASTM A182 F44) has 6 % molybdenum and 0.18–0.25 % nitrogen, giving a PREN above 42 and much better resistance to chloride pitting and crevice corrosion.
Which ASTM specification covers 904L flanges?
Forged 904L flanges are made to ASTM A182 / ASME SA182 grade F904L, with dimensions to ASME B16.5 or B16.47. Butt weld fittings are made to ASTM A403 WP904L.
Can Teshi Group supply 904L with third-party inspection?
Yes. 904L and 254 SMO flanges and fittings are supplied with EN 10204 3.1 certificates as standard, and with 3.2 certification witnessed by the inspection agency your order specifies.
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