Duplex Steel S31803 Flanges

Duplex Steel S31803 Flanges are produced from UNS S31803, a dual-phase austenitic-ferritic alloy that has been widely used in industrial piping since the 1980s. Referenced under SA 240 UNS S31803, which is suitable for pressure vessel applications, and ASTM A182 for flanges, this grade shares significant composition overlap with UNS S32205. Many suppliers deliver dual-certified material meeting both designations. S31803 flanges are used in oil and gas, offshore, chemical, and water treatment applications and provide a good balance of mechanical strength and corrosion resistance.

Price of Duplex Steel S31803 Flanges

Pricing for Duplex Steel S31803 flanges varies with size, pressure class, and machining scope, typically aligning closely with Duplex 2205 market rates.

Approx Price Range

Duplex Steel S31803 Flanges are typically priced between ₹900 and ₹4,000 per piece. Since the alloy composition is close to Duplex 2205, pricing is comparable. Larger sizes and higher pressure ratings push cost toward the upper end of that range.

Price Per Unit / Kg

Per-kg pricing for UNS S31803 flanges generally sits between ₹950 and ₹1,450. Heavy wall flanges in larger NPS sizes will cost more per unit due to material volume and additional machining.

Factors Affecting Price

UNS S31803 flanges are produced from ½" NPS to 60" NPS. Most Duplex Steel S31803 Flanges suppliers stock sizes up to 24" NPS as standard. Sizes from 26" to 60" are manufactured to order and carry longer lead times. Wall thickness and bore dimensions are not fixed across the range since both vary by pipe schedule and pressure class assigned during design.

Types of Duplex Steel S31803 Flanges

UNS S31803 flanges are available in the following types:

Weld Neck Flanges
Slip-On Flanges
Blind Flanges
Socket Weld Flanges
Lap Joint Flanges
Threaded Flanges
Orifice Flanges
Ring Type Joint (RTJ) Flanges
Long Weld Neck Flanges
Spectacle Blind Flanges

Specifications of Duplex Steel S31803 Flanges

Duplex Steel S31803 Flanges are manufactured to multiple standards. The table below covers grade designation, dimensional references, pressure classes, and production methods.

Parameter	Details
Grade	Duplex S31803 / UNS S31803 / SA 240 UNS S31803
Standard	ASTM A182, ASME B16.5, ASME B16.47, MSS SP-44, EN 1092-1
Pressure Class	150# to 2500#
Size Range	½" to 60"
Facing Type	Raised Face (RF), Flat Face (FF), Ring Type Joint (RTJ)
Manufacturing Process	Forged, Plate Cut

Chemical Properties of Duplex Steel S31803 Flanges

UNS S31803 has slightly wider composition tolerances compared to S32205, particularly for chromium and nitrogen. The complete elemental breakdown is listed below.

Parameter	Duplex Steel S31803
Grade	Duplex Steel S31803
C	0.030 max
Mn	2.00 max
Si	1.00 max
P	0.030 max
S	0.020 max
Cr	22 – 23
Mo	3 – 3.5
Ni	4.50 – 6.50
N	0.14 – 0.20

Chromium minimum for S31803 starts at 21%, versus 22% for S32205. Nitrogen can be as low as 0.08%, compared to 0.14% minimum for S32205. These differences explain why many end users prefer dual-certified plates and forgings.

Mechanical Properties of Duplex Steel S31803 Flanges

The figures below are the minimum accepted mechanical values for S31803 flanges per ASTM A182, applicable in the solution-annealed and quenched condition.

Parameter	Value
Density	7.8 g/cm³
Melting Point (°C)	1350 °C (2460 °F)
Tensile Strength	Psi – 80000, MPa – 550
Yield Strength (0.2% Offset)	Psi – 116000, MPa – 800
Elongation	15 %

When dual-certified material is used, the mechanical values for S31803 and S32205 are effectively the same since the actual composition typically satisfies both.

Physical Properties of Duplex Steel S31803 Flanges

Reference physical data for UNS S31803 flanges applicable in structural, thermal, and piping design.

Property	Value
Density	7.82 g/cm³
Melting Point	1350 – 1465°C
Thermal Conductivity	19 W/m·K
Electrical Resistivity	0.85 µΩ·m
Magnetic Permeability	Slightly magnetic
Modulus of Elasticity	200 GPa

Dimension Chart of Duplex Steel S31803 Flanges

Dimensional reference for S31803 flanges per ASME B16.5 for NPS ½" to 24". Larger sizes above 24" follow ASME B16.47 Series A or B.

Nominal Size (in)	Outside Diameter (OD) (in)	Min. Thickness (T) (in)	Raised Face Dia. (R) (in)	Bolt Circle (BC) (in)	No. of Bolt Holes	Bolt Hole Dia. (in)	Hub Top Dia. (HT) (in)	Length Thru Hub (WL) (in)
1/2	3.50	0.38	1.38	2.38	4	0.62	0.84	1.81
3/4	3.88	0.44	1.69	2.75	4	0.62	1.05	2.00
1	4.25	0.50	2.00	3.12	4	0.62	1.32	2.12
1¼	4.62	0.56	2.50	3.50	4	0.62	1.66	2.19
1½	5.00	0.62	2.88	3.88	4	0.62	1.90	2.38
2	6.00	0.69	3.62	4.75	4	0.75	2.38	2.44
2½	7.00	0.81	4.12	5.50	4	0.75	2.88	2.69
3	7.50	0.88	5.00	6.00	4	0.75	3.50	2.69
3½	8.50	0.88	5.50	7.00	8	0.75	4.00	2.75
4	9.00	0.88	6.19	7.50	8	0.75	4.50	2.94
5	10.00	0.88	7.31	8.50	8	0.88	5.56	3.44
6	11.00	0.94	8.50	9.50	8	0.88	6.63	3.44
8	13.50	1.06	10.62	11.75	8	0.88	8.63	3.94
10	16.00	1.12	12.75	14.25	12	1.00	10.75	3.94
12	19.00	1.19	15.00	17.00	12	1.00	12.75	4.44
14	21.00	1.31	16.25	18.75	12	1.12	14.00	4.94
16	23.50	1.38	18.50	21.25	16	1.12	16.00	4.94
18	25.00	1.50	21.00	22.75	16	1.25	18.00	5.44
20	27.50	1.62	23.00	25.00	20	1.25	20.00	5.62
22	29.50	1.75	25.25	27.25	20	1.38	22.00	5.82
24	32.00	1.81	27.25	29.50	20	1.38	24.00	5.94

Class 150 values per ASME B16.5.

Size Chart of Duplex Steel S31803 Flanges

The table below outlines the size range for Duplex Steel S31803 Flanges, with stock availability and supply type across the full NPS range.

Size Range (NPS)	Availability	Supply Type	Notes
½" to 2"	Readily available	From stock	Standard bore and wall thickness
2½" to 12"	Readily available	From stock	Bore varies by pipe schedule
14" to 24"	Generally available	From stock	Confirm with the supplier
26" to 48"	Limited	Made to order	Longer lead times apply
50" to 60"	On request	Made to order	Extended lead times

Wall thickness and bore dimensions across all sizes are determined by pipe schedule and pressure class during the design stage.

Pressure Rating Chart of Duplex Steel S31803 Flanges

Pressure ratings for S31803 flanges at 38°C per ASME B16.5. Ratings are reduced at elevated temperatures. See ASME tables for derated values at service temperature.

Class	Pressure Rating at 38°C
150	19.6 bar (285 psi)
300	51.1 bar (740 psi)
600	102.1 bar (1480 psi)
900	153.2 bar (2220 psi)
1500	255.3 bar (3705 psi)
2500	425.5 bar (6170 psi)

Key Features of Duplex Steel S31803 Flanges

Duplex Steel S31803 Flanges offer exceptional strength and corrosion resistance via dual-phase structure, ideal for harsh chloride environments.

Dual austenitic-ferritic structure
High yield strength
PREN value between 30 and 36
Resistance to chloride stress corrosion cracking
SA 240 UNS S31803 compatibility
Dual certification with UNS S32205
Availability in custom sizes and facings

Applications of Duplex Steel S31803 Flanges

UNS S31803 flanges are specified across a range of industries where corrosion resistance and mechanical strength are both required.

Oil and gas production headers, wellhead connections, and processing lines
Offshore platforms for seawater cooling and ballast systems
Chemical plants handling mildly corrosive media
Desalination and water treatment facilities
Pulp and paper mills
Heat exchanger systems
Pressure vessel connections requiring SA 240 UNS S31803 and ASME code compliance

How to Choose the Right Duplex Steel S31803 Flanges Supplier?

Selecting a reliable Duplex Steel S31803 flanges supplier depends on metallurgical consistency, certification depth, and proven supply capability, not just quoted pricing or availability.

Supplier Selection Criteria

Look for suppliers who deal routinely in duplex grades rather than carry S31803 as a secondary line. Dual-certified S31803/S32205 inventory makes it easier to procure both grades when they are in a specification. Consistent mill relationships and reliable heat-to-heat composition data matter more than price alone.

Technical Considerations

Verify heat treatment records with MTC, as solution annealing conditions directly contribute to the ferrite-to-austenite ratio. SA 240 UNS S31803 certification should be available with ASTM and ASME references. Sour service lines require explicit NACE MR0175/ISO 15156 documentation.

Quality & Certification Check

Minimum MTC requirement is EN 10204 3.1. 3.2 Safety-critical lines require third-party witness testing. Indian industries looking for Duplex Steel S31803 Flanges suppliers need to ensure they have IBR approval as per the Boiler and Pressure Vessel regulations.

Procurement Tips for Bulk Orders

Order with a confirmed flange schedule, not estimated quantities. S31803 Flanges sizes above 24” NPS are seldom stocked. Clearly state phased delivery requirements and lock in pricing early, as alloy costs can vary over a multi-month procurement cycle.