Super Austenitic Stainless Steel 904L & 254 SMO
Super Austenitic Stainless Steel Grades at a Glance
| Grade | UNS | EN | Main Alloying Feature | Typical Applications |
|---|---|---|---|---|
| 904L | N08904 | 1.4539 | High Ni, Mo and Cu austenitic stainless steel | Chemical processing, sulphuric-acid service, pharmaceuticals, pulp and paper, heat exchangers |
| 254 SMO | S31254 | 1.4547 | Approx. 6% Mo with nitrogen alloying | Seawater handling, desalination, FGD, offshore, pulp bleaching and chloride-containing environments |
Grade references are provided for material-selection guidance. Final requirements should be confirmed according to the applicable ASTM, EN, ASME or customer specification and material test certificate.
904L vs 254 SMO Stainless Steel
| Selection Factor | 904L | 254 SMO |
|---|---|---|
| Material Type | High-alloy austenitic stainless steel | 6% Mo super austenitic stainless steel |
| Molybdenum Level | Approx. 4–5% | Approx. 6% |
| Nickel Level | High | High |
| Nitrogen Alloying | Lower / grade-dependent | Significant nitrogen alloying |
| PRE / PREN Reference | Approx. mid-30s depending on composition | Approx. 43 depending on composition and calculation method |
| Typical Selection | Sulphuric-acid and aggressive chemical environments | Severe chloride, seawater and localized-corrosion environments |
| Typical Applications | Chemical processing, pharmaceuticals, pulp and paper, heat exchangers | Desalination, FGD, offshore, seawater handling and pulp bleaching |
PRE/PREN is a comparative indicator rather than a complete corrosion-design criterion. Actual corrosion performance depends on temperature, concentration, chloride level, pH, fabrication condition and service environment.
Common Standards for 904L and 254 SMO
| Grade | UNS | EN | Common Flat-Product Standard |
|---|---|---|---|
| 904L | N08904 | 1.4539 | ASTM A240/A240M |
| 254 SMO | S31254 | 1.4547 | ASTM A240/A240M |
The applicable standard depends on product form and project requirements. Buyers should specify the required standard and revision in the purchase order.
Super austenitic stainless steels are highly alloyed austenitic grades designed for severe corrosive environments.
Grades such as 904L and 254 SMO generally provide higher corrosion resistance than conventional 304 and 316L stainless steels in many aggressive chemical and chloride-containing environments. Actual performance depends on temperature, concentration, chloride level, fabrication condition and service environment.
904L is widely used for chemical, pharmaceutical, paper making and sewage treatment industries due to its excellent corrosion resistance. 254SMO is a type of super austenitic stainless steel contains 6% Mo, the PREN value is higher than 43, which is widely used for high concentration of chloride and seawater environment such as seawater desalination, flue gas desulfurization, pulp bleaching equipment and seawater heat exchanger industry.
| Grade | Chemical (%) | Processability | ||||||||
| C | Cr | Ni | Mo | Cu | N | Yield strength /MPa | Tensile strength /MPa | Elongation /% | HRBW | |
| 904L | ≤0.020 | 19.0-23.0 | 23.0-28.0 | 4.0-5.0 | 1.0-2.0 | ≤0.1 | ≥220 | ≥490 | ≥35 | ≤90 |
| 254SMO | ≤0.020 | 19.5-20.5 | 17.5-18.5 | 6.0-6.5 | 0.50-1.00 | 0.18-0.25 | ≥310 | ≥690（sheet/strip) ≥655（plate) | ≥35 | ≤96 |
Mechanical-property requirements vary by product form, thickness and applicable specification. Final acceptance should be based on the purchase specification and MTC.
How to Choose Between 904L and 254 SMO
Choose 904L for Selected Aggressive Chemical Environments
904L is a high-alloy austenitic stainless steel containing relatively high nickel, molybdenum and copper. It is commonly considered for chemical-processing equipment and selected sulfuric-acid-containing environments where conventional 304L or 316L may not provide sufficient corrosion resistance.
Typical applications can include chemical vessels, process piping, heat exchangers, pharmaceutical equipment and pulp-and-paper processing equipment, depending on temperature, concentration and service conditions.
Choose 254 SMO for More Severe Chloride Environments
254 SMO is a 6% molybdenum super austenitic stainless steel with nitrogen alloying and a relatively high PRE/PREN. It is commonly considered for applications where resistance to pitting and crevice corrosion in chloride-containing environments is especially important.
Typical applications include seawater handling, desalination equipment, flue-gas desulfurization systems, offshore equipment, pulp bleaching and selected heat-exchanger applications.
Do Not Select by PREN Alone
PRE/PREN is useful for comparing resistance to localized corrosion, but it does not by itself determine material suitability. Temperature, chloride concentration, acidity, oxidizing conditions, crevice geometry, welding condition and fabrication quality should also be considered.
Corrosion-Environment Selection Guide
| Service Environment | 904L | 254 SMO | Selection Note |
|---|---|---|---|
| General Chemical Processing | Often considered | Consider for more severe conditions | Confirm chemical concentration, temperature and contaminants. |
| Sulfuric-Acid Service | Commonly considered for selected concentration and temperature ranges | May also be evaluated depending on the complete environment | Copper and high nickel content make 904L important for selected sulfuric-acid applications, but corrosion data should be checked for the actual process. |
| High-Chloride Process Water | Application-dependent | Often preferred for more demanding localized-corrosion conditions | Temperature, chloride content and crevice conditions are critical. |
| Seawater / Desalination | Requires careful engineering review | Commonly considered | 254 SMO is widely used in severe chloride applications, but operating conditions and component design still matter. |
| FGD Systems | Application-dependent | Commonly considered for aggressive chloride-containing service | Confirm chloride concentration, acidity, temperature and cleaning conditions. |
| Pulp & Paper / Bleaching | Used in selected chemical environments | Often considered for severe bleaching and chloride exposure | Final grade depends on the chemical process and operating temperature. |
This table is intended for preliminary material selection only. Final grade selection should be based on corrosion data, process chemistry, operating temperature, component design and the applicable engineering specification.
Available Product Forms
Depending on grade, specification, dimensions and quantity, super austenitic stainless steel requirements can be reviewed for product forms such as sheet, coil, plate and other mill products.
Availability should be confirmed according to the required grade, ASTM or EN specification, thickness, width, length, surface condition and quantity.
What to Specify for a 904L or 254 SMO RFQ
To review material availability and prepare an accurate quotation, please provide the following information:
- Grade: 904L / UNS N08904 or 254 SMO / UNS S31254
- Standard: ASTM A240/A240M, EN or other required specification
- Product form: sheet, coil, plate or other required form
- Dimensions: thickness, width and length or coil dimensions
- Quantity: sheets, coils or total tonnage
- Surface condition: where applicable
- Application: chemical processing, seawater, FGD, heat exchanger or other service
- Corrosion environment: chemical type, concentration, chloride level and operating temperature where available
- Inspection: MTC, PMI, dimensional inspection or other required testing
- Destination: country, port or project location
Need 904L or 254 SMO Stainless Steel?
Send your grade, standard, product form, dimensions, quantity, service environment and delivery destination. JISCO JUDE can review material availability and quotation options for your project.
904L & 254 SMO Stainless Steel FAQ
What is super austenitic stainless steel?
Super austenitic stainless steels are highly alloyed austenitic grades developed for demanding corrosion environments. They generally contain higher levels of nickel, molybdenum and, in some grades, nitrogen or copper compared with conventional 304 or 316L stainless steel.
What is the difference between 904L and 316L?
904L contains higher nickel and molybdenum levels and also contains copper. It can provide improved corrosion resistance in selected aggressive chemical environments compared with conventional 316L. Actual performance depends on the service environment.
What is the difference between 904L and 254 SMO?
904L is a high-nickel, molybdenum- and copper-alloyed austenitic stainless steel, while 254 SMO contains approximately 6% molybdenum together with nitrogen alloying. 254 SMO generally has greater localized-corrosion resistance in severe chloride-containing environments.
What is the PREN of 254 SMO?
254 SMO typically has a PRE/PREN of approximately 43, depending on the actual chemical composition and calculation method. PREN should be used as a comparative indicator rather than the sole basis for material selection.
Is 254 SMO suitable for seawater?
254 SMO is widely considered for seawater, desalination and other demanding chloride-containing applications. Final suitability depends on temperature, chloride level, flow conditions, crevice design and the complete service environment.
Which standard covers 904L and 254 SMO plate or sheet?
ASTM A240/A240M is a common flat-product specification for 904L / UNS N08904 and 254 SMO / UNS S31254. Other standards may apply depending on product form and project requirements.
What information is required for a quotation?
Please provide the grade, standard, product form, thickness, width, length or coil dimensions, quantity, service environment, inspection requirements and delivery destination.
