Super duplex is a family of high-performance stainless steels with around 25% chromium and a pitting resistance equivalent number (PREN) above 40. Its dual austenitic-ferritic microstructure combines high strength with strong resistance to acids, acid chlorides and caustic solutions, which makes it well suited to demanding oil and gas, chemical, petrochemical and pulp and paper applications.
What makes a stainless steel super duplex?
Super duplex steels take their name from a dual-phase microstructure of both austenitic and ferritic grains, which gives them their combination of high strength and corrosion resistance. The "super" prefix, first used in the 1980s, marks the most highly alloyed grades - those with a pitting resistance equivalent number (PREN) above 40, built around roughly 25% chromium.
The original super duplex stainless steel, Ferralium® 255, was developed by Langley Alloys in the 1960s, and several further grades have followed. For how the two families differ, see the difference between duplex and super duplex stainless steels; for how the PREN figure is calculated, see Understanding PREN.
What is super duplex used for?
Its high chromium content gives superb resistance to acids, acid chlorides, caustic solutions and other aggressive media across the chemical, petrochemical, and pulp and paper industries. Typical components include:
- Pumps
- Valves
- Fasteners
- Pipework
- Connectors
- Oil and gas equipment
Which super duplex grades does Langley Alloys stock?
We hold the most complete range of super duplex material, in these grades:
| Grade | UNS | Also known as |
|---|---|---|
| Ferralium® 255 | S32550 | F61 |
| Alloy 32750 | S32750 | F53 |
| Alloy 32760 | S32760 | F55, Zeron 100® |
Stock forms include:
- Solid bar up to 16" (406.4mm) diameter
- Plate up to 3" thickness
- Pipes, flanges and fittings, through our supply chain