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When should you upgrade from SS 304 to SS 904L?
Short answer
Upgrade from SS 304 to SS 904L when the service involves sulphuric or phosphoric acid, warm chlorides or seawater-cooled equipment where SS 304 and SS 316L pit or crack. SS 904L adds about 25% nickel, 4.5% molybdenum and 1.5% copper, raising PREN to about 34–36, at several times the price of SS 304.
SS 304 vs SS 904L at a glance
| Property | SS 304 | SS 904L |
|---|---|---|
| UNS | S30400 | N08904 |
| EN | 1.4301 | 1.4539 |
| Family | Austenitic stainless steel | Super-austenitic stainless steel |
| C (%) | 0.07 max | 0.020 max |
| Cr (%) | 17.5 – 19.5 | 19.0 – 23.0 |
| Ni (%) | 8.0 – 10.5 | 23.0 – 28.0 |
| Mo (%) | — | 4.0 – 5.0 |
| N (%) | 0.10 max | 0.10 max |
| Cu (%) | — | 1.0 – 2.0 |
| Tensile strength | 515 MPa (75 ksi) | 490 MPa (71 ksi) |
| Yield strength | 205 MPa (30 ksi) | 220 MPa (31 ksi) |
| PREN | 18 – 20 | 32 – 36 |
| Density | 7.93 g/cm³ | 8 g/cm³ |
| Magnetic | Essentially non-magnetic when annealed; cold work can make it slightly magnetic. | Non-magnetic. |
| Typical use | Food, dairy and beverage processing equipment | Sulphuric acid plants and coolers |
Which should you choose?
There's no universal "winner": the right choice depends on service conditions, codes and cost. Share your conditions with us for a recommendation.
Intermediate steps worth checking
Between SS 304 and SS 904L sit SS 316L (PREN about 24) and SS 317L (about 29). Many chloride problems are solved at SS 317L or duplex 2205 for less than SS 904L costs. SS 904L earns its price mainly where sulphuric acid is involved, because its copper content specifically helps in reducing acids.
Fabrication differences
SS 904L is fully austenitic and more prone to hot cracking than SS 304, so welding uses low heat input and matching SS 904L-type filler. It is also more sensitive to intermetallic phases after prolonged heating.
Products in both grades
Related guides, comparisons and articles
Frequently asked questions
Is SS 904L magnetic?
No. Like SS 304, it is non-magnetic in the annealed condition.
Which specification covers SS 904L pipe?
Seamless SS 904L pipe and tube is usually ordered to ASTM B677 and plate to ASTM B625 or A240.
What is the main difference between SS 304 and SS 904L?
SS 904L is a super-austenitic grade with about 25% Ni, 4.5% Mo and 1.5% Cu, many times more resistant to sulphuric acid and chloride pitting than SS 304, at a much higher price.
When should I choose SS 304?
General-purpose stainless applications.
When should I choose SS 904L?
Sulphuric and phosphoric acid, seawater cooling and harsh chemical service.
Can SS 304 replace SS 904L?
Only when the design, code and specification allow it. Strength, corrosion resistance and temperature limits differ, so substitution must be approved by the design authority.
Which has better pitting resistance, SS 304 or SS 904L?
Typical PREN: SS 304 18 – 20, SS 904L 32 – 36. A higher PREN generally means better chloride pitting resistance.