Description

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254 SMO stainless steel pipe is a high-alloy, low-carbon super-austenitic (6Mo) stainless steel supplied to UNS S31254 (ASTM) and EN 1.4547 (European). It is engineered for aggressive chloride-containing and acidic environments where standard 316L fails by pitting, crevice corrosion or stress-corrosion cracking.

With roughly 20% chromium, 18% nickel, 6% molybdenum and 0.2% nitrogen plus copper, 254 SMO delivers a Pitting Resistance Equivalent Number (PREN) of ≥ 42 - placing it firmly in the "super stainless" category alongside super duplex 2507 and well above conventional austenitic grades. It is a proven, cost-effective substitute for more expensive nickel alloys and titanium in seawater, desalination, chemical and offshore service.

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Chemical Composition ＆Mechanical Properties ＆Physical Properties

Chemical Composition

Element	UNS S31254 (ASTM A312/A213)	EN 1.4547
Carbon (C)	≤ 0.020%	≤ 0.020%
Manganese (Mn)	≤ 1.00%	≤ 1.00%
Silicon (Si)	≤ 0.80%	≤ 0.80%
Phosphorus (P)	≤ 0.030%	≤ 0.030%
Sulfur (S)	≤ 0.010%	≤ 0.015%
Chromium (Cr)	19.5 – 20.5%	19.5 – 20.5%
Nickel (Ni)	17.5 – 18.5%	17.5 – 18.5%
Molybdenum (Mo)	6.0 – 6.5%	6.0 – 6.5%
Nitrogen (N)	0.18 – 0.22%	0.18 – 0.22%
Copper (Cu)	0.50 – 1.00%	0.50 – 1.00%

Mechanical Properties

Property	UNS S31254 (ASTM A312)	Typical Value
Tensile Strength	≥ 650 MPa	650 – 850 MPa
Yield Strength (0.2% offset)	≥ 300 MPa	300 – 430 MPa
Elongation (in 50 mm)	≥ 35%	≥ 35%
Hardness	≤ 100 HRB (typical)	≤ 100 HRB

Physical Properties

Property	Value
Density	8.0 g/cm³
Melting Point	1320 – 1390 °C

Applicable Standards & Specifications

254 SMO is supplied to the product form and service condition required by the project. The principal specifications are:

ASTM A312 / ASME SA312 - Seamless and welded austenitic stainless steel pipe (primary pipe standard).

ASTM A213 / ASME SA213 - Seamless ferritic & austenitic alloy-steel boiler, superheater and heat-exchanger tubes.

ASTM A269 - Seamless and welded austenitic stainless steel tubing for general service (verify latest A269 grade list; S31254 is explicitly covered by A312 and A213).

ASTM A403 - Wrought austenitic stainless steel piping fittings (254 SMO / F44 fittings).

ASTM A182 - Forged fittings, flanges and valves (grade F44 = UNS S31254).

ASTM A240 - Chromium and chromium-nickel stainless steel plate, sheet and strip.

EN 10216-5 - Seamless stainless steel tubes for pressure purposes (European, for 1.4547).

EN 10204 3.1 / 3.2 - Material test / inspection certificates.

NACE MR0175 / ISO 15156 - Sulfide stress cracking resistance for oil & gas (H2S) service.

NORSOK MDS D57 - Material data sheet for 6Mo austenitic stainless steel in offshore/marine service.

Equivalent Grades

Designation	Code	Standard / Region
UNS	S31254	USA (ASTM/UNS)
EN / Werkstoff	1.4547	Europe
EN steel name	X1CrNiMoCuN20-18-7	Europe
AFNOR	Z1 CNDU 20.18.06Az	France
SIS	2378	Sweden
Forging grade	F44	ASTM A182 (UNS S31254)
Common trade name	254 SMO / 6Mo	Industry
China (approx.)	00Cr20Ni18Mo6CuN	GB (reference)
JIS	- (referenced as SUS 312L, non-equivalent)	Japan

Dimensions, Surface Finish & Ends

Parameter	Specification
Outer Diameter	Seamless 1/2″ – 24″ (up to 36″ custom); Welded up to 48″
Wall Thickness	SCH 5S – SCH XXS, or specified wall per application
Length	Single random, double random, or cut length
Surface Finish	Pickled & passivated, bright annealed, polished (Ra ≤ 0.8 µm for hygienic/pharma)
End Type	Plain end (PE), beveled end (BE), threaded where applicable
Heat Treatment	Solution annealed (~1050–1150 °C) and rapidly quenched
Tolerances	Per applicable ASTM/ASME standard or customer drawing

Corrosion Resistance & PREN

Excellent resistance to pitting and crevice corrosion in chloride media (seawater up to ~100,000 ppm Cl⁻).

Resists chloride stress-corrosion cracking (SCC) far better than 316L/317L.

Good performance in diluted hydrochloric, phosphoric and sulphuric acid containing chlorides; outperforms 316L and is comparable to 904L in many acids (not for concentrated hot sulphuric or stagnant seawater above ~30 °C).

Passes ASTM G48 (FeCl₃) pitting test and ASTM B117 salt-spray without red rust for extended periods.

NACE MR0175 / ISO 15156 qualified for sour (H2S) oil & gas service within specified limits.

Key Advantages of 254 SMO Pipe

Superior pitting & crevice resistance (PREN ≥ 42) - survives seawater and high-chloride process streams where 316L fails.

Cost-effective vs nickel alloys - delivers most of Alloy 625 / titanium performance at a fraction of the material cost; a smart 6Mo upgrade.

High strength from nitrogen - higher allowable design stress than 316L for thinner, lighter pipe walls.

Excellent weldability - low carbon avoids intergranular corrosion; weldable without post-weld heat treatment for most services (use NiCrMo-3 filler).

High ductility & impact toughness - fully austenitic, reliable down to cryogenic temperatures.

Versatile product range - pipe, tube, fittings (F44) and flanges available from one source, simplifying procurement.

Proven in demanding industries - desalination, offshore, FGD, pulp & paper and chemical processing worldwide.

Typical Applications

Seawater & marine: seawater cooling, offshore topsides, shipbuilding, thin-walled condenser tubes.

Desalination: intake, brine and high-chloride water-treatment piping.

Chemical processing: reactors, heat exchangers, piping for chloride/acid media.

Oil & gas: offshore, sour-service and subsea components (per NACE MR0175).

Pulp & paper: bleach plant washers, digesters, filter drums.

Power generation: flue-gas desulfurization (FGD) absorber towers, ducts, spray systems.

Food & high-purity: salt making, brewing, hygienic/pharma process lines.

FAQ

Is 254 SMO the same as duplex stainless steel?

No. 254 SMO (UNS S31254) is a super-austenitic stainless steel. Duplex grades (e.g. 2205, 2507) are ferritic-austenitic. They are specified to different ASTM standards - 254 SMO to A312/A213, duplex to A790. Mixing them up is a frequent supplier error.

What does PREN ≥ 42 mean for my project?

PREN estimates pitting resistance from Cr, Mo and N content. PREN ≥ 42 is the accepted minimum for reliable seawater service; 254 SMO typically measures ~43–44, comfortably above the threshold.

Can 254 SMO replace 316L?

In chloride-rich or acidic service, yes - and it should. 316L pits and suffers SCC in seawater; 254 SMO is designed exactly for those conditions. In mild, indoor atmospheres 316L remains the economical choice.

Which ASTM grade covers the forged fittings?

Forged 254 SMO fittings and flanges are supplied as ASTM A182 F44 (UNS S31254); wrought fittings as ASTM A403 WP-S31254.

Is it weldable?

Yes. Low carbon avoids sensitization; use matching NiCrMo-3 (ERNiCrMo-3) filler. Post-weld heat treatment is generally not required for most services.