SS 904L and 254 SMO flanges, fittings and pipe
Super-austenitic stainless steels for sulphuric and phosphoric acid service and high-chloride water. We manufacture flanges and fittings in both grades and supply matching pipe and bolting.
Product forms and specifications
| Product | Specification and grade |
|---|---|
| Forged flanges | ASTM A182 F904L (UNS N08904), ASTM A182 F44 (UNS S31254) |
| Plate flanges and blinds | ASTM B625 (904L plate), ASTM A240 S31254 |
| Butt-weld fittings | ASTM A403 WP904L, ASTM A403 WPS31254 |
| Forged socket-weld and threaded fittings | ASTM A182 F904L, F44 |
| Pipe (stocked and sourced) | ASTM B677 seamless and B673 welded (904L); ASTM A312 / A358 S31254 |
| Bolting | ASTM B649 bar for 904L and 254 SMO studs and nuts |
We manufacture the flanges, fittings and fabrications listed. Pipe is supplied from stock or sourced from approved mills.
Chemistry and strength
| Grade | UNS / W.Nr. | Nominal chemistry (%) | Min tensile / yield, MPa | PREN |
|---|---|---|---|---|
| 904L | N08904 / 1.4539 | Cr 19–23, Ni 23–28, Mo 4–5, Cu 1–2, C 0.02 max | 490 / 215 | about 34–36 |
| 254 SMO (F44) | S31254 / 1.4547 | Cr 19.5–20.5, Ni 17.5–18.5, Mo 6.0–6.5, N 0.18–0.25, Cu 0.5–1.0 | 650 / 300 | 42 and above |
For design use the values in the current edition of the specification your order calls for.
Where it is used
904L carries copper and high nickel, which hold it passive in dilute and medium-strength sulphuric acid where 316L corrodes. It is the usual choice for acid plant piping in zinc and copper smelters, phosphoric acid and fertiliser plants, and acid coolers.
254 SMO trades copper for 6% molybdenum and nitrogen. Its pitting resistance is far higher, so it is chosen for seawater, brine, flue-gas desulphurisation and bleach plant chloride service.
Questions buyers ask
Is 904L better than 316L for sulphuric acid?
In most dilute and intermediate concentrations, yes. The copper and higher nickel in 904L keep it passive where 316L corrodes actively. Concentration, temperature and impurities all matter, so share your process conditions with the enquiry.
What test certificates come with 904L flanges?
EN 10204 3.1 material test certificates as standard, with PMI. Intergranular corrosion testing to ASTM A262 and third-party witnessed 3.2 certificates are available when your QAP asks for them.
Do you make 254 SMO (F44) flanges?
Yes. We manufacture ASTM A182 F44 flanges in B16.5 and B16.47 patterns and to drawing.
Get a price for 904L and 254 SMO
Tell us the grades, standards, sizes and quantities. Our estimation team replies from info@teshigroup.com, usually within one working day for standard items.
Drawings, BOQ spreadsheets and QAPs are easiest by email. Attach them to a message to info@teshigroup.com and mention your project name.