ASTM A790 UNS S32750 Super Duplex Steel Pipe for Oil and Gas Applications

1. Standard and Grade

ASTM A790 covers seamless and welded ferritic/austenitic duplex stainless steel pipe for general corrosive service. Duplex stainless steels have a two-phase microstructure of austenite and ferrite, which gives them higher strength than austenitic grades and better toughness than ferritic grades. They are commonly grouped into lean duplex, standard duplex and super duplex families. UNS S32750 belongs to the super duplex group, is listed as material 1.4410 in EN standards, and is widely known by the commercial designation F53. Pipes of this grade are designed for high-strength, highly corrosive applications such as subsea pipelines, process piping and seawater systems.

2. Chemical Composition (ASTM A790)

The table below lists the specified limits for UNS S32750 per ASTM A790. Iron makes up the balance.

Element	Limit (wt %)
Carbon (C)	0.030 max
Manganese (Mn)	1.20 max
Phosphorus (P)	0.035 max
Sulfur (S)	0.020 max
Silicon (Si)	0.80 max
Chromium (Cr)	24.00-26.00
Nickel (Ni)	6.00-8.00
Molybdenum (Mo)	3.00-4.00
Nitrogen (N)	0.24-0.32
Copper (Cu)	0.50 max
Tungsten (W)	0.50 max

3. Mechanical and Physical Properties

In the solution-annealed condition, ASTM A790 requires the following minimum mechanical properties for UNS S32750 pipe. Typical values are shown where noted.

Property	Value
Tensile strength	800-1000 MPa
Yield strength (0.2 % offset, min)	550 MPa
Elongation in 50 mm (min)	15 %
Hardness (max)	290 HBW (per EN 10028-7 for 1.4410)
Density (typical)	about 7.8 g/cm3
Modulus of elasticity (typical)	about 200 GPa

The yield strength of S32750 is roughly double that of 316L pipe, which allows thinner wall sections for the same design pressure and reduces material weight and welding cost.

4. Corrosion Resistance

The high chromium, molybdenum and nitrogen contents of S32750 give it a pitting resistance equivalent number above 40, calculated with the formula PREN = Cr + 3.3 x Mo + 16 x N. It offers excellent resistance to pitting, crevice corrosion and stress corrosion cracking in seawater, brines and chloride-containing process media, outperforming both conventional austenitic stainless steels and 22% chromium duplex grades. Pipes of this grade also comply with the requirements of NACE MR0175 / ISO 15156 for use in sour oil and gas service containing hydrogen sulfide.

5. Product Forms, Sizes and Applications

ASTM A790 UNS S32750 pipe is produced as seamless pipe, welded pipe and welded tube. Commercially common size ranges include seamless pipe from about 6 mm up to 250 mm outside diameter, welded pipe up to about 1200 mm outside diameter, and wall thicknesses from about 0.3 mm upward, with standard schedules such as 5S, 10S, 40S, 80S and others. Typical applications include:

Oil and gas: subsea flowlines, process systems and equipment handling salty water and sour gas

Chemical processing: piping and heat exchangers for highly corrosive acids, salts and chemicals

Seawater systems: cooling water piping, firefighting systems and desalination plants

Power generation: flue gas desulfurization scrubber systems in power plants

Frequently Asked Questions

What does UNS S32750 mean? UNS S32750 is the Unified Numbering System designation for a super duplex stainless steel containing about 25% chromium, 7% nickel and 3.5% molybdenum. It corresponds to EN material 1.4410 and is commonly called F53.

Is S32750 the same as 2507? Yes. 2507 is the common trade name for UNS S32750 super duplex stainless steel. The standard designation is UNS S32750.

Why is super duplex pipe stronger than 316L pipe? Because of its two-phase austenite-ferrite microstructure and high nitrogen content, which provide a minimum yield strength of 550 MPa, about twice that of annealed 316L.

Can S32750 pipe be used in seawater? Yes. It is one of the best-performing stainless steels in seawater, with high resistance to pitting and crevice corrosion, and is widely used in seawater cooling and offshore systems.

Is S32750 suitable for sour gas service? Yes, within the limits of NACE MR0175 / ISO 15156, which defines acceptable conditions for sulfide stress cracking resistance in oil and gas environments.

What is the difference between seamless and welded S32750 pipe? Seamless pipe is formed from a solid billet and has no longitudinal weld; welded pipe is formed from plate or strip and welded, then solution annealed. Both are covered by ASTM A790 and can meet the same mechanical and corrosion requirements when properly manufactured and tested.