Why Duplex Sits in the a Series
Duplex, super duplex and 6Mo steels are iron-based, so ASTM covers them with the steel specifications. They often run next to nickel alloys in seawater, offshore and chemical service and turn up in the same scrap lots, but they are priced and classified as alloyed stainless steel. See duplex and 254 SMO scrap.
Specification Reference
| Specification | ASME | Product form | Grades on this site |
|---|---|---|---|
| ASTM A182Forged or rolled alloy and stainless steel flanges, fittings and valves; duplex and 6Mo grades carry F-numbers (F44, F51, F53, F55, F60). | ASME SA-182 | Forgings | Duplex 2205, Super duplex 2507, Super duplex S32760, 254 SMO |
| ASTM A240Chromium and chromium-nickel stainless steel flat products for pressure vessels, including duplex and 6Mo grades. | ASME SA-240 | Plate, sheet and strip | Duplex 2205, Super duplex 2507, Super duplex S32760, 254 SMO |
| ASTM A249Welded austenitic steel boiler, superheater, heat-exchanger and condenser tube. | ASME SA-249 | Welded tube | 254 SMO |
| ASTM A269Seamless and welded austenitic stainless steel tube for general service. | – | Tube | 254 SMO |
| ASTM A312Seamless, welded and cold-worked austenitic stainless steel pipe, including 254 SMO. | ASME SA-312 | Pipe | 254 SMO |
| ASTM A358Electric-fusion-welded austenitic stainless steel pipe for high-temperature service. | ASME SA-358 | Welded pipe | 254 SMO |
| ASTM A479Stainless steel bars and shapes for boilers and pressure vessels. | ASME SA-479 | Bar | Duplex 2205, Super duplex 2507, Super duplex S32760, 254 SMO |
| ASTM A789Seamless and welded ferritic/austenitic (duplex) stainless steel tube. | ASME SA-789 | Tube | Duplex 2205, Super duplex 2507, Super duplex S32760 |
| ASTM A790Seamless and welded ferritic/austenitic (duplex) stainless steel pipe. | ASME SA-790 | Pipe | Duplex 2205, Super duplex 2507, Super duplex S32760 |
| ASTM A815Wrought ferritic, ferritic/austenitic and martensitic stainless steel fittings. | ASME SA-815 | Fittings | Duplex 2205, Super duplex 2507, Super duplex S32760 |
| ASTM A928Duplex stainless steel pipe, electric-fusion welded with filler metal. | ASME SA-928 | Welded pipe | Duplex 2205, Super duplex 2507, Super duplex S32760 |
Forging F-Numbers
Flanges, fittings and valve bodies to ASTM A182 are stamped with an F-number instead of a UNS number. It is the quickest way to identify a duplex forging:
| F-number | UNS | Grade |
|---|---|---|
| F44 | S31254 | 254 SMO |
| F51 | S31803 | Duplex 2205 (original) |
| F60 | S32205 | Duplex 2205 (higher N, Mo) |
| F53 | S32750 | Super duplex 2507 |
| F55 | S32760 | Super duplex S32760 |
A magnet helps as a first check: duplex grades are magnetic, 254 SMO is not. See the magnet test.
FAQ
What is ASTM A182 F53?
A super duplex stainless steel forging, UNS S32750, commonly known as 2507.
What is the difference between F51 and F60?
Both are Duplex 2205. F51 is UNS S31803 and F60 is S32205, which has tighter minimums for nitrogen, chromium and molybdenum. Most modern material is dual-certified.
Which ASTM specification covers duplex pipe?
ASTM A790 for seamless and welded pipe, and A928 for electric-fusion-welded pipe with filler metal.