ASTM A790 Duplex Stainless Steel Pipe: Grades, Properties and Applications

What ASTM A790 Covers

ASTM A790 (and its ASME counterpart SA790) covers seamless and welded duplex and super duplex stainless steel pipe for general corrosive service, with special emphasis on resistance to chloride pitting, crevice corrosion and stress corrosion cracking. Duplex grades combine the strength of ferritic steel with the corrosion resistance of austenitic steel: the two-phase ferrite-austenite microstructure delivers roughly twice the minimum yield strength of conventional 316L pipe while remaining weldable and tough.

Common Grades and Chemical Composition

Typical grades specified to A790 include UNS S31803 and S32205 (both commonly called 2205 duplex) and UNS S32750 (commonly called 2507 super duplex). Composition ranges per ASTM A790 (wt%):

Element	S31803	S32205 (2205)	S32750 (2507)
Carbon, max	0.030	0.030	0.030
Chromium	21.00-23.00	22.00-23.00	24.00-26.00
Nickel	4.50-6.50	4.50-6.50	6.00-8.00
Molybdenum	2.50-3.50	3.00-3.50	3.00-5.00
Nitrogen	0.08-0.20	0.14-0.20	0.24-0.32
Manganese, max	2.00	2.00	1.20
Silicon, max	1.00	1.00	0.80

Mechanical Properties (ASTM A790)

Property	S31803 / S32205	S32750
Tensile strength, min (MPa)	620	800
Yield strength, min (MPa)	450	550
Elongation, min (%)	25	15

With minimum yield strengths of 450 MPa (S32205) and 550 MPa (S32750), A790 duplex pipe allows thinner walls than 316L for the same design pressure - a common route to weight and cost savings in pressure systems.

Size Range, Wall Thickness and Delivery Condition

Sizes: typically 1/2 in to 24 in nominal pipe size, with other sizes available by agreement.

Wall thickness: schedule 10S to schedule 160S and heavier.

Types: seamless or welded, both covered by the standard.

Delivery condition: solution annealed and quenched, then pickled or polished as required.

Corrosion Resistance: Why Duplex Beats Austenitic in Chlorides

The pitting resistance equivalent number, PREN = Cr + 3.3 x Mo + 16 x N, ranks chloride pitting resistance. S32205 reaches about 34-36 and S32750 about 40-45, far above the roughly 24-26 of 316L. Combined with the duplex microstructure, this gives outstanding resistance to pitting, crevice corrosion and chloride stress corrosion cracking in seawater, brine, and acidic process streams - the environments that most often defeat austenitic pipe.

Typical Applications

Oil and gas flowlines, process piping and subsea hardware.

Heat exchangers and condensers in seawater-cooled plants.

Pressure vessels and chemical processing systems handling chlorides.

Marine equipment, shipbuilding and desalination plants.

Flue gas desulfurization and pulp and paper equipment.

Frequently Asked Questions

What does ASTM A790 cover?

It covers seamless and welded duplex and super duplex stainless steel pipe for corrosive service, including grades S31803, S32205 and S32750 among others, with requirements for composition, mechanical properties, heat treatment and testing.

What is the difference between ASME SA790 and ASTM A790?

They are the same specification. ASME SA790 is the designation adopted for use under the ASME Boiler and Pressure Vessel Code; ASTM A790 is the identical specification issued by ASTM.

Which grades are available to A790?

Common duplex and super duplex grades include UNS S31803, S32205 (2205), S32750 (2507), S32760 and S32550, with S32205 and S32750 being the most widely specified.

What is the advantage of duplex pipe over 316L pipe?

Roughly double the minimum yield strength, much better resistance to chloride pitting, crevice corrosion and stress corrosion cracking, and lower thermal expansion. The main trade-offs are higher material cost and stricter welding control.

How is A790 pipe supplied?

Solution annealed and quenched, then pickled or polished. Sizes typically run from 1/2 in to 24 in NPS with schedules from 10S to 160S and heavier, in seamless or welded form.

Can A790 duplex pipe be welded in the field?

Yes, with qualified welding procedures and matching or over-alloyed filler metal. Heat input and interpass temperature must be controlled to preserve the ferrite-austenite balance and avoid secondary phase precipitation.