Duplex stainless steels (DSS) are widely used in industries such as oil & gas, chemical processing, desalination, and marine engineering due to their unique combination of high strength and excellent corrosion resistance.
To ensure consistency and clarity in global trade, multiple numbering systems are used to classify duplex stainless steels. The most important ones are the UNS (Unified Numbering System), EN/DIN/ISO designations, trade names, and ASTM/ASME standards.
UNS Numbering System
The Unified Numbering System (UNS) provides a universal code, usually starting with S, for duplex stainless steels. This code reflects the chemical composition of the alloy.
For example:
- S31803 → the original 2205 duplex
- S32205 → refined 2205 duplex with better corrosion resistance
- S32750 → super duplex 2507
- S32760 → super duplex Zeron 100
Rule of Thumb:
- S31xxx / S32xxx = Standard duplex grades
- S32xxx / S33xxx / S392xx = Super duplex or lean duplex grades
EN / ISO / DIN Numbering
In Europe, duplex stainless steels are standardized by EN numbers (1.XXXX system). These designations are widely used in engineering drawings and material certificates.
- 1.4462 → Duplex 2205 (UNS S32205)
- 1.4410 → Super duplex 2507 (UNS S32750)
- 1.4501 → Super duplex Zeron 100 (UNS S32760)
This provides a bridge between international standards, making it easier to identify equivalents across regions.
Trade Names and ASTM/ASME Designations
Unlike 304 or 316, duplex stainless steels generally do not have AISI numbers. Instead, they are identified by trade names or ASTM/ASME grades depending on product form:
- 2205 → UNS S32205 / S31803
- 2507 → UNS S32750
- Zeron 100 → UNS S32760
Duplex stainless steels are covered by various ASTM/ASME standards:
- ASTM A240 – Plate, sheet, and strip
- ASTM A276 – Bars
- ASTM A182 – Forged flanges, fittings, valves, parts
- ASTM A789 – Seamless & welded tubes
- ASTM A790 – Pipes
- ASME B16.5 – Pipe flanges & flanged fittings
Example:
- ASTM A240 UNS S31803 → Duplex 2205 plate
- ASTM A182 F51 → Duplex 2205 forged flange
- ASTM A240 UNS S32750 → Super duplex 2507 plate
Summary of Numbering Logic
- UNS Code → Defines chemical composition (e.g., S32205)
- ASTM/ASME Grade → Defines product form & mechanical properties (e.g., F51 for forgings)
- Common/Trade Name → Commercial identification (e.g., 2205, 2507, Zeron 100)
Example:
- ASTM A182 F51 / UNS S31803
- ASTM A182 → Forged components standard
- F51 → Duplex 2205 grade (mechanical & corrosion properties)
- S31803 → Chemical composition designation
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