This guide supports procurement discussion and does not replace the approved design code, materials-engineering review or project specification. Verify the current edition of every referenced standard.
Two-phase stainless-steel families
Duplex stainless steels are designed with a mixed austenitic-ferritic microstructure. They combine relatively high strength with useful corrosion resistance. Super duplex grades use higher alloying to address more demanding chloride-bearing environments.
The family name is not a complete specification. Grade, UNS designation, product standard, heat treatment, manufacturing route and test requirements must all be defined.
- Common project references include 2205 within duplex and 2507-type grades within super duplex.
- Higher alloy content does not remove the need for service-specific corrosion assessment.
- Heat treatment and welding control are important to the intended microstructure.
Fabrication and purchasing control
Duplex fabrication requires qualified procedures and appropriate control of heat input, interpass temperature, filler selection and post-fabrication cleaning. Procurement should preserve traceability and clearly state supplementary test requirements.
For package supply, mating pipe, fittings and flanges should be coordinated by grade, wall, bore, pressure class and approved specification.
Family-level comparison
| Consideration | Duplex | Super duplex |
|---|---|---|
| Typical family example | 2205-type grades | 2507-type grades |
| Relative alloying | High-alloy stainless family | Higher Cr/Mo/N-bearing family |
| Chloride service | Useful resistance in suitable conditions | Often considered for more severe conditions |
| Fabrication | Procedure control required | Tighter procedure and cleanliness control commonly required |
| Selection | Engineering review | Engineering review |
Common buyer questions.
Is super duplex a direct upgrade from duplex?+
No. It changes material, fabrication, availability and cost considerations. Substitution requires engineering approval.
What tests may be specified?+
Depending on the product and project, PMI, mechanical, corrosion, NDT, ferrite or other supplementary tests may be required.
Why is heat treatment important?+
The specified solution treatment and cooling help develop the intended phase balance and corrosion performance.
Standards and technical sources.
Links are provided for source context. Always use the edition required by the contract and approved project documents.
International Molybdenum Association — duplex stainless steel