Grade dossier
254 SMO Stainless Steel for Aggressive Chloride Service
A 6% molybdenum, nitrogen-alloyed superaustenitic grade developed for severe chloride-bearing and process environments where standard 316L lacks margin.
Identity before substitution
Define the grade, product and condition together
A familiar grade name is not a complete purchase specification. Product form, controlling standard, dimensions, condition, finish, certification and service environment determine whether the delivered material is suitable.
Composition control
ASTM A240/A240M flat-product chemistry
Limits are not heat analysis targets
The table summarizes grade limits commonly used for plate, sheet and strip. Pipe, tube, bar, forgings and cast products can be governed by different specifications. Always place the product standard and edition on the purchase order.
| C | 0.020 max |
|---|---|
| Mn | 1.00 max |
| Si | 0.80 max |
| P | 0.030 max |
| S | 0.010 max |
| Cr | 19.50-20.50 |
| Ni | 17.50-18.50 |
| Mo | 6.00-6.50 |
| N | 0.18-0.22 |
| Cu | 0.50-1.00 |
Properties with context
Minimums, typical indicators and delivered condition
Specified annealed flat-product values
| Tensile strength | 650 MPa min |
|---|---|
| 0.2% yield strength | 300 MPa min |
| Elongation | 35% min |
| Hardness | 223 HBW max reference |
Selection indicators
| Density | about 8.0 g/cm3 |
|---|---|
| PRE guidance | typically at least about 42.5 |
| Strength | Higher than conventional austenitic grades |
| Heat treatment | Solution anneal and rapid cooling are critical |
Values depend on product form, thickness, test orientation, condition and governing edition. Use the mill test certificate and the purchase specification for acceptance, not a web table alone.
Selection boundary
Where 254 SMO belongs and where to escalate
Grade selection is an environmental decision, not a popularity contest. Review the complete medium, temperature, geometry, fabrication, cleaning and inspection requirements.
Good reasons to evaluate it
Chlorinated seawater and desalination equipment after design review
Flue-gas and marine exhaust cleaning
Pulp-bleaching equipment
Offshore valves, flanges and piping
Reasons to stop and review
Calling the grade immune to seawater crevice corrosion
Using matching filler without segregation review
Slow cooling after hot work or solution treatment
Ordering by trade name without UNS and standard
Fabrication route
Protect properties through cutting, forming and welding
Use over-alloyed nickel-base filler where the procedure requires it.
Control heat input and interpass temperature.
Remove heat tint and restore the surface.
Use service-specific corrosion tests for critical duties.
Supply definition
Product form changes the applicable requirements
Do not send an RFQ that names only the grade. State form, governing standard, dimensions, tolerances, finish, edge or end condition, quantity, certification and inspection.
Plate, sheet and strip to ASTM A240/A240M
Seamless and welded tube and pipe
Bar, forgings, fittings and flanges
Quarto plate and fabricated process equipment
Certificate checkpoint
Request heat identity, chemical analysis, mechanical results and compliance to the exact product specification. Add PMI, corrosion testing or supplementary examination only when the application requires it.
Interactive selection check
Test 254 SMO against the controlling question
Procurement FAQ
Questions to close before placing the order
Is 254 SMO stainless steel magnetic?
Magnetic response depends on microstructure and delivered condition.
Can 254 SMO replace another grade?
Only after checking the governing standard, composition, mechanical properties, corrosion exposure, fabrication route and certification. A commercial name is not a substitution approval.
Does the table apply to every product form?
Not automatically. The values shown use flat-product requirements as a reference. Other forms can use different product standards, dimensions and tests.
What should a 254 SMO RFQ include?
Product form, standard and edition, UNS or EN designation, dimensions, tolerances, finish, quantity, service, fabrication, certificate and inspection requirements.
Sources, scope and RFQ
Use traceable grade data, then specify the actual product
ASTM A240/A240M requirements for UNS S31254 flat product
Outokumpu Ultra 254 SMO official datasheet
Alleima 254 SMO official tube and pipe datasheet
Applicable NORSOK/IOGP or pressure-code requirements