Duplex 31803 (UNS S31803 / F51) – Standard Duplex Stainless Steel for General Service

Short Description:

Duplex 31803 (UNS S31803 / F51 / W.Nr. 1.4462) is a standard duplex stainless steel with a balanced ferritic-austenitic microstructure offering excellent corrosion resistance and high strength. Womic Steel supplies Duplex 31803 in multiple product forms including seamless pipe, welded pipe, steel bar, steel plate, steel coil, strip, flanges, fittings, forgings, and valves for chemical processing, marine engineering, oil and gas, and structural applications.

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Product Description

Duplex 31803 is the original duplex stainless steel grade, providing approximately twice the yield strength of standard austenitic stainless steels such as 316L while offering superior resistance to chloride stress corrosion cracking, pitting, and crevice corrosion. The ferritic-austenitic microstructure, with approximately 40-50% ferrite and 50-60% austenite, provides a unique combination of high strength, good toughness, and excellent corrosion resistance . With a PREN value of approximately 34, Duplex 31803 offers reliable performance in moderate chloride environments.

Key characteristics include:

High strength – approximately twice that of 316L stainless steel

Good corrosion resistance – PREN ~34

Resistance to chloride stress corrosion cracking

Good weldability with proper procedures

Cost-effective alternative to nickel alloys

Wide operating temperature range from -50°C to 300°C

Chemical Composition

Element	Content (%)	Role
Chromium (Cr)	21.0 – 23.0	Oxidation resistance, corrosion resistance
Nickel (Ni)	4.5 – 6.5	Austenite stabilizer, corrosion resistance
Molybdenum (Mo)	2.5 – 3.5	Pitting and crevice corrosion resistance
Nitrogen (N)	0.08 – 0.20	Austenite stabilizer, strengthening
Carbon (C)	≤ 0.030	Controlled for weldability
Manganese (Mn)	≤ 2.00	Deoxidizer
Silicon (Si)	≤ 1.00	Deoxidizer
Phosphorus (P)	≤ 0.030	Impurity control
Sulfur (S)	≤ 0.020	Impurity control
Iron (Fe)	Balance	Base element

Room Temperature Properties (Solution Annealed)

Property	Value
Tensile Strength	≥ 620 MPa (90 ksi)
Yield Strength (0.2% Offset)	≥ 450 MPa (65 ksi)
Elongation	≥ 25%
Hardness	≤ 290 HB
Density	7.80 g/cm³
PREN	Cr + 3.3Mo + 16N ≈ 34

Impact Properties

Temperature	Impact Energy (Longitudinal)
Room Temperature	≥ 80 J
-40°C	≥ 45 J
-50°C	≥ 27 J

Key Advantages of Duplex 31803

High Strength – Duplex 31803 offers approximately twice the yield strength of 316L stainless steel, allowing designers to specify thinner wall sections and reduce overall weight. This high strength is achieved through the ferritic-austenitic microstructure, which combines the strength of ferrite with the ductility and toughness of austenite.

Corrosion Resistance – The alloy offers good resistance to pitting and crevice corrosion in chloride-containing environments. The PREN value of approximately 34 provides reliable performance in moderate seawater and chemical applications.

Stress Corrosion Cracking Resistance – Duplex 31803 provides excellent resistance to chloride stress corrosion cracking (SCC), a mode of failure common to austenitic stainless steels in chloride environments. The ferrite phase provides resistance to SCC that is superior to 304 and 316 austenitic grades.

Weldability – The alloy can be welded using standard welding techniques with appropriate filler metals. Proper heat input control and interpass temperature management are required to maintain the correct ferrite-austenite balance in the weld zone.

Cost-Effective – Duplex 31803 offers a cost-effective alternative to nickel alloys and higher-grade duplex steels, providing a favorable balance of performance and price for a wide range of applications.

Available Product Forms from Womic Steel

Seamless Pipe & Seamless Tube

Outside Diameter: 6mm – 350mm

Wall Thickness: 1mm – 40mm

Length: Up to 12m

Standards: ASTM A790, ASME SA-790

Applications: Heat exchanger tubes, process piping, seawater systems

Keywords: Duplex 31803 seamless pipe, UNS S31803 tube, F51 pipe, 1.4462 seamless tube

Welded Pipe

Outside Diameter: 50mm – 1200mm

Wall Thickness: 1.0mm – 25mm

Standards: ASTM A790, ASTM A928

Applications: Large-diameter process piping, structural applications

Keywords: Duplex 31803 welded pipe, F51 ERW pipe

Steel Bar (Round, Square, Flat, Hex)

Diameter: 6mm – 500mm

Surface: Hot rolled, Bright (cold drawn), Ground, Turned

Standards: ASTM A276, ASTM A479

Applications: Valve stems, fasteners, shafts, pumps, machining stock

Keywords: Duplex 31803 round bar, F51 bar stock, S31803 bar

Steel Plate & Sheet

Thickness: 1mm – 100mm

Width: Up to 3000mm

Standards: ASTM A240, ASME SA-240

Applications: Vessel shells, structural components, flange blanks

Keywords: Duplex 31803 plate, F51 sheet, S31803 plate

Steel Coil & Strip

Thickness: 0.5mm – 6.0mm

Width: 10mm – 1500mm

Standards: ASTM A240

Applications: Formed components, stampings

Keywords: Duplex 31803 coil, F51 strip

Flanges & Pipe Fittings

Types: Weld Neck, Slip-On, Blind, Socket Weld, Threaded, Lap Joint

Sizes: 1/2" – 48"

Pressure Rating: Class 150 – Class 2500

Standards: ASTM A182, ASME B16.5, ASME B16.47

Keywords: Duplex 31803 flanges, F51 weld neck flange

Forgings

Types: Rings, disks, shafts, valve bodies, custom geometries

Weight: Up to 5,000kg

Standards: ASTM A182, ASME SA-182

Keywords: Duplex 31803 forging, F51 ring

Duplex 31803 Valves

Types: Ball valves, Gate valves, Globe valves, Check valves

Sizes: 1/2" – 24"

Pressure Rating: Class 150 – Class 2500

Temperature Range: -50°C to +300°C

Design Standards: API 608, API 6D, ASME B16.34

Seating: Stellite hardfaced, RPTFE, PEEK

Keywords: Duplex 31803 ball valve, F51 gate valve

Duplex 31803 vs Duplex 2205 vs Super Duplex

Property	Duplex 31803 (F51)	Duplex 2205 (F60)	Super Duplex 2507 (F53)
PREN	~34	~36	≥ 40
Yield Strength	450 MPa	450 MPa	550 MPa
Mo Content	2.5-3.5%	3.0-3.5%	4.0-5.0%
N Content	0.08-0.20%	0.14-0.20%	0.24-0.32%
Pitting Resistance	Good	Good	Excellent
Seawater Service	Moderate	Good	Excellent
Cost	Lowest	Moderate	Highest
Application	General chemical, moderate chloride	Marine, oil & gas, chemical tankers	Extreme seawater, subsea, offshore

Standards & Specifications

Product Form	ASTM Standard
Seamless Pipe/Tube	ASTM A790
Welded Pipe	ASTM A790, ASTM A928
Bar/Rod	ASTM A276, ASTM A479
Plate/Sheet/Strip	ASTM A240
Forgings	ASTM A182
UNS Designation	S31803
W.Nr.	1.4462
F No.	F51

Applications of Duplex 31803

Chemical Processing – Duplex 31803 is used in heat exchangers, pressure vessels, tanks, piping systems, and pumps in chemical plants where good corrosion resistance and high strength are required.

Marine Engineering – The alloy is used in seawater piping, offshore platform equipment, and ballast water systems where resistance to chloride corrosion is essential.

Oil and Gas – Duplex 31803 is used in pipelines, manifolds, process equipment, and separators in moderate chloride environments.

Structural Applications – The high strength of duplex 31803 makes it suitable for structural applications in marine and offshore environments.

Pulp and Paper – The alloy is used in digesters, bleaching equipment, and chemical recovery systems.

Frequently Asked Questions

Q: What is the difference between Duplex 31803 and Duplex 2205?

A: Duplex 2205 (S32205) has tighter control on molybdenum (3.0-3.5%) and nitrogen (0.14-0.20%), providing slightly better corrosion resistance (PREN 36 vs 34) and is the preferred grade for marine and offshore applications.

Q: Is Duplex 31803 suitable for seawater service?

A: Yes, for moderate seawater service. The PREN of 34 provides good resistance to pitting in seawater, making it suitable for many marine applications. For more severe seawater conditions, Super Duplex 2507 (PREN ≥ 40) may be required.

Q: Is Duplex 31803 readily weldable?

A: Yes, with proper welding procedures. The alloy is readily weldable using GTAW, GMAW, and SMAW processes. Control of heat input and interpass temperature is essential to maintain proper ferrite-austenite balance.

Contact Womic Steel

Website: www.womicsteel.com
E-mail: sales@womicsteel.com

Tel / WhatsApp / WeChat:

Victor: +86 15575100681

Jack: +86 18390957568

Womic Steel – Your reliable partner for Duplex 31803 (UNS S31803 / F51) seamless pipe, welded pipe, steel bar, steel plate, steel coil, flanges, fittings, forgings, and valves for chemical processing, marine, and structural applications worldwide. Full traceability and EN 10204 Type 3.1/3.2 documentation available.

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1.4462 seamless tube