Super Duplex UNS S32750 Steel Pipe

1. Standard: ASTM A789, ASME SA789, ASTM A790, ASME SA790
2. Seamless OD: 4 to 219mm
3. Welded OD: 5.0 - 1219.2 mm
4. Thickness: 0.5 - 20mm
5. Grades: Dupplex 2507,UNS S32750, WNR.1.4410

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Product Introduction

Super Duplex UNS S32750 Steel Pipe sits between standard duplex 2205 and the expensive nickel alloys. With 25% chromium, about 7% nickel, 4% molybdenum and a controlled nitrogen content, it gives you chloride pitting resistance and strength that austenitic stainless steels cannot match, at a price well below Inconel or Hastelloy. It is the go-to grade for seawater service, offshore topsides and chloride-laced process piping where 316L or even 2205 would fail by pitting. This page covers what ASTM A790 requires, how the alloy behaves, and where it is the right call.

Product Forms

Bar & Rod

Plate & Sheet

Coil & Strip

Pipe & Tube

Fitting: Flange, Tee, Elbow, Reducer etc.

Forging: Ring, Shaft, Circle, Block etc.

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Chemical Composition of Super Duplex 2507 (UNS S32750)

The composition below follows ASTM A790 for seamless and welded pipe. The high chromium, molybdenum and nitrogen combination is what pushes the pitting resistance into super-duplex territory; the nickel stays low (about 7%) because the duplex structure does not need more.

Element	Content, %	What it contributes
Chromium (Cr)	24.0 - 26.0	Base corrosion resistance and passivity
Nickel (Ni)	6.0 - 8.0	Austenite phase balance and toughness
Molybdenum (Mo)	3.0 - 5.0	Pitting and crevice corrosion resistance
Nitrogen (N)	0.24 - 0.32	Strength and pitting resistance boost
Carbon (C)	0.030 max	Kept low for weldability
Manganese (Mn)	1.20 max	Residual deoxidizer
Silicon (Si)	0.80 max	Residual

Mechanical Properties per ASTM A790

The duplex structure is what gives super duplex its strength: the ferrite and austenite phases act together, and the minimum yield strength is more than double that of 316L. This is one of the few stainless grades where you actually buy it partly for strength, not only for corrosion.

Property	Minimum requirement
Tensile strength	800 MPa (116 ksi)
Yield strength (0.2% offset)	550 MPa (80 ksi)
Elongation	15%
Hardness	Typically below 290 HB

Why the Duplex Structure Matters

Austenitic stainless steels like 316L are roughly 100% austenite. Duplex grades are about half ferrite, half austenite, balanced by controlling the chromium-to-nickel ratio. That mixed structure is what delivers the combination buyers actually want: high strength from the ferrite, toughness and weldability from the austenite, and resistance to chloride stress-corrosion cracking that pure austenitic grades do not have. The trade-off is that super duplex is harder to form and machine than 316L, and it loses toughness above about 300 C - it is not a high-temperature alloy.

Corrosion Performance: PREN and Seawater

The pitting resistance equivalent number (PREN = Cr + 3.3xMo + 16xN) lands around 41 to 43 for 2507, well above 316L (about 24) and even duplex 2205 (about 35). The critical pitting temperature (CPT) in chloride media runs above 50 C, which is why 2507 handles flowing seawater where 316L would pit within months. It also resists chloride stress-corrosion cracking far better than austenitic grades. The limits: it is still a stainless steel, not a nickel alloy, so strongly reducing acids and caustic service are out, and it can suffer hydrogen-induced cracking in sour service if the environment is severe.

Sizes, Supply and Fabrication

2507 pipe is supplied under ASTM A790 in seamless and welded forms, across the standard NPS range. Wall thicknesses follow the duplex schedule series. Two fabrication points matter: super duplex must be solution-annealed and quenched after welding to restore the phase balance, and filler metal must be over-alloyed (typically ER2553) to match the corrosion resistance of the base metal. Forming should stay cold-worked within the alloy limits; hot working is restricted to a narrow temperature window.