Why not use duplex instead of a super austenitic grade?

Both can reach a comparable PREN, but their strengths differ: duplex offers better mechanical strength, super austenitic better weldability and more predictable high-temperature behaviour. The choice depends as much on fabrication as on the corrosive environment.

Is 904L a super austenitic or an austenitic grade?

It's generally classed as super austenitic due to its higher nickel and molybdenum content than 316L, even though its PREN remains lower than 254 SMO's. It's a transitional grade between the two families.

Do these grades resist crevice corrosion in seawater?

Better than a standard austenitic, but not indefinitely: a high PREN reduces the risk without eliminating it, particularly in stagnant zones or under deposits. Design remains decisive — see the Limits section of the PREN calculator.

My super austenitic grade isn't listed — what should I do?

This table is an extract. Send us your exact designation via a quote request — 926 and other variants exist depending on the mill.

GRADE FAMILY

Super austenitic stainless steels

Super austenitic grades push standard austenitic chemistry further: more nickel, molybdenum and nitrogen for a notably higher PREN, without changing crystal structure. 904L covers sulphuric and phosphoric acid duty; 254 SMO steps up further for seawater and desalination.

What is a super austenitic stainless steel?

A super austenitic steel keeps the same face-centred cubic structure as a standard austenitic, but with substantially higher nickel, molybdenum and nitrogen content. This enhanced chemistry raises the PREN without changing crystallographic family, at the cost of higher material cost and more demanding fabrication.

When to choose this family — and when not to?

Choose it for strong acids or hot seawater and flue gas treatment, where a standard austenitic reaches its limits without justifying a move to duplex. Avoid it by default for routine use: the material cost premium is only justified when the environment genuinely demands it.

Grades in this family

The grades listed are examples, never a closed catalogue — every grade belongs to one of the nine families, which is what makes this claim reliable.

Examples in the super austenitic stainless steels family (familles-nuances.json), EN and PREN filled in from nuances-inox.json when the entry exists — not a closed catalogue
Grade (example)	EN	Indicative PREN
904L	1.4539	34–36 ¹
254 SMO	1.4547	43–45 ¹
926	—	—

¹ inherited value, not yet cross-checked against a product standard.

Typical applications for this family: Acids · Desalination · Flue gas treatment.

My grade isn't listed →

Available forms and dimensions

Welded and seamless tube, heat-exchanger tube, fittings, flanges and bars available in 904L and 254 SMO through our partner mills. Outer diameter from 10 to 273 mm — structured data available for 904L and 254 SMO only. The other grades in this family don't yet have this in our structured reference data: send us your requirement via a quote request.

Applicable standards

EN 10216-5
EN 10217-7
ASTM A312
ASTM A213
ASTM A249
ASTM A269
ASTM A270
EN 10088-1

Frequently asked questions

Why not use duplex instead of a super austenitic grade?: Both can reach a comparable PREN, but their strengths differ: duplex offers better mechanical strength, super austenitic better weldability and more predictable high-temperature behaviour. The choice depends as much on fabrication as on the corrosive environment.
Is 904L a super austenitic or an austenitic grade?: It's generally classed as super austenitic due to its higher nickel and molybdenum content than 316L, even though its PREN remains lower than 254 SMO's. It's a transitional grade between the two families.
Do these grades resist crevice corrosion in seawater?: Better than a standard austenitic, but not indefinitely: a high PREN reduces the risk without eliminating it, particularly in stagnant zones or under deposits. Design remains decisive — see the Limits section of the PREN calculator.
My super austenitic grade isn't listed — what should I do?: This table is an extract. Send us your exact designation via a quote request — 926 and other variants exist depending on the mill.