What Is ASTM A790?

ASTM A790 is the standard specification for seamless and welded ferritic/austenitic (duplex) stainless steel pipe. It covers both standard duplex (22% Cr, such as S31803 and S32205) and super duplex (25% Cr, such as S32750 and S32760) grades, making it the primary pipe specification for duplex stainless steel in the oil and gas, chemical, and marine industries.

All ASTM A790 pipes must be solution-annealed and quenched to achieve the target austenite-ferrite balance (typically 40-60% ferrite).

Property	Detail
Scope	Seamless and welded duplex/super duplex pipe
Manufacturing	Seamless (hot/cold finished) or automatic welded
Solution annealing	Mandatory (min. 1020°C for S32205; min. 1025°C for S32750)
Quenching	Water quench required after annealing
Size range	NPS 1/4 to NPS 30+ (OD 13.7 to 762+ mm)
Schedules	Per ASME B36.19 (5S, 10S, 40S, 80S) and B36.10
NDT	Hydrostatic test or eddy current; UT for welded seam
Corrosion test	ASTM A923 (Method A, B, or C); intermetallic detection

Common ASTM A790 Grades

UNS	Common Name	Cr (%)	Ni (%)	Mo (%)	N (%)	PREN	Yield (min)
S31803	2205 (original)	21-23	4.5-6.5	2.5-3.5	0.08-0.20	~34	450 MPa
S32205	2205 (improved)	22-23	4.5-6.5	3.0-3.5	0.14-0.20	~36	450 MPa
S32750	2507	24-26	6-8	3-5	0.24-0.32	~42	550 MPa
S32760	Zeron 100	24-26	6-8	3-4	0.20-0.30	~41	550 MPa
S32304	2304 (lean duplex)	21.5-24.5	3-5.5	0.05-0.60	0.05-0.20	~26	400 MPa
S32101	LDX 2101 (lean)	21-22	1.35-1.7	0.10-0.80	0.20-0.25	~26	450 MPa

Quick Answer

S32205 has replaced S31803 as the preferred 2205 designation. S32205 has tighter nitrogen and molybdenum minimums, ensuring a consistently higher PREN. Most current production meets both designations simultaneously.

Key Testing Requirements

ASTM A790 mandates the following tests:

• Tensile test: One per lot (transverse or longitudinal)
• Flattening test (welded pipe) or hardness test
• Hydrostatic test: At pressure per formula in the standard (may be replaced by NDE)
• ASTM A923 intermetallic test: Method A (sodium hydroxide etch), B (Charpy impact), or C (ferric chloride corrosion) to detect detrimental intermetallic phases (sigma, chi)

The ASTM A923 test is critical. Intermetallic phases form during improper heat treatment or slow cooling and severely degrade toughness and corrosion resistance. Many EPC project specifications require Method C (the most stringent) for all duplex pipe.

Applications

• Offshore topside and subsea piping
• Chemical process piping (organic acids, chloride media)
• Desalination plants
• Pulp and paper industry
• Oil and gas production facilities
• Heat exchangers (tube and shell-side piping)

For welded pipe made with filler metal from plate, ASTM A928 applies instead of A790. For duplex fittings, the corresponding specification is ASTM A815.

Read the full guide to pipe types