Duplex 2205 (UNS S31803 / S32205) — Materials Engineering Reference | RR Hydraulic

Materials Engineering Reference

Duplex 2205
(UNS S31803 /
S32205)

A world-class technical reference for EPC contractors, offshore and chemical process engineers, procurement heads, and TPI inspection agencies specifying Duplex 2205 stainless steel — covering the duplex microstructure, the S31803-to-S32205 chemistry refinement, PREN-based selection logic, intermetallic phase precipitation risk, and the QC and documentation discipline required for critical offshore and chemical process equipment supply.

UNS S31803 / S32205 / F51 / 1.4462 ~50/50 Austenite-Ferrite Duplex ASTM A182 / A240 / A789 / A790 PREN ≈ 33–38 ~2.5× Yield Strength of 316L EN 10204 3.1/3.2 · NACE MR0175

Part 01 / Industry Context & Technical Definition

Duplex Microstructure,
PREN & the S31803-to-S32205
Chemistry Refinement

Duplex 2205 (UNS S31803 /S32205) is the most widely used and best-established duplex stainless steel grade worldwide — combining a balanced austenite-ferrite microstructure to deliver substantially higher strength than standard austenitic stainless steel alongside markedly improved chloride pitting, crevice, and stress corrosion cracking resistance, at a moderate cost premium.

Duplex 2205 (UNS S31803 /S32205) — RR Hydraulic Engineering Reference

1.1 — What “2205” Means and Its Position in the Duplex Family

Duplex 2205 gets its common designation from its nominal composition — approximately 22% chromium and 5% nickel — and shares the same fundamental two-phase (approximately 50% austenite, 50% ferrite) microstructure discussed in detail in RR Hydraulic’s dedicated Super Duplex 2507 reference. 2205 sits in the “standard duplex” tier of the duplex family, with meaningfully lower chromium, molybdenum, and nitrogen content than super duplex grades like 2507 — this gives 2205 somewhat lower pitting/crevice resistance and yield strength than 2507, but at correspondingly lower cost and with somewhat less demanding (though still important) heat treatment and welding process control requirements, making 2205 the more commonly specified duplex grade for the large majority of offshore, chemical process, and general industrial applications where 2507’s higher performance and cost are not specifically required.

1.2 — Duplex 2205 (UNS S31803 /S32205): A Critical Chemistry Refinement

Important distinction — two UNS numbers for “2205”: UNS S31803 was the original duplex 2205 UNS designation, with a permitted nitrogen content range as low as 0.08% at the bottom end of its specification window. Industry experience showed that material produced at the lower end of this nitrogen range exhibited measurably reduced pitting resistance and a greater tendency toward unwanted intermetallic phase precipitation compared to material produced with higher, more consistent nitrogen content. This led to the introduction of UNS S32205 — a tightened chemistry specification with a narrower composition window and, critically, a higher minimum nitrogen content (typically 0.14% minimum, compared to S31803’s 0.08% minimum) — effectively representing the “clean,” consistently high-performance version of 2205 chemistry. In current EPC procurement practice, S32205 has become the de facto standard specification for new project duplex 2205 supply, with S31803 now primarily encountered on older project documentation or as a broader, less restrictive specification envelope that S32205 material happens to also satisfy. When ordering, always specify S32205 explicitly (or verify that S31803-ordered material meets the tighter S32205 nitrogen minimum) to ensure consistent, optimal corrosion performance.

1.3 — Key Engineering Properties

Substantially Higher Strength Than Austenitic Stainless Steel

Duplex 2205’s minimum yield strength (typically 450 MPa in the solution-annealed condition) is roughly 2.5 times that of standard austenitic stainless steel (316L, typically 170–205 MPa) — supporting thinner-walled, lighter-weight components for a given pressure rating, a meaningful benefit for offshore weight-sensitive structures and high-pressure piping.

Good Chloride Pitting and Crevice Corrosion Resistance

2205’s PREN of approximately 33–38 (using the same PREN formula discussed in RR Hydraulic’s Super Duplex 2507 reference: PREN = %Cr + 3.3×%Mo + 16×%N) provides substantially better chloride pitting and crevice corrosion resistance than 316L stainless steel (PREN ~24), suitable for moderate-to-severe chloride environments including many offshore, seawater-adjacent, and chemical process applications, though below super duplex 2507’s PREN of ~42–43 for the very highest chloride severity service.

Good Chloride Stress Corrosion Cracking Resistance

The duplex microstructure’s ferrite phase content provides substantially better resistance to chloride stress corrosion cracking than fully austenitic stainless steel — relevant for hot chloride-bearing process and offshore service where austenitic stainless steel would carry meaningful SCC risk, though 2205’s SCC resistance is somewhat lower than super duplex 2507’s at the highest temperature/chloride combinations.

Good General Corrosion and Erosion-Corrosion Resistance

Good resistance to general corrosion across a range of environments, and notably good resistance to erosion-corrosion in high-velocity flow conditions compared to austenitic stainless steel — a relevant property for piping systems with variable or high flow rates.

1.4 — When to Specify 2205 vs. Super Duplex 2507

Table 1.A — Duplex 2205 vs. Super Duplex 2507 Selection Comparison

Consideration	Duplex 2205	Super Duplex 2507
PREN	~33–38	~42–43
Min. Yield Strength	450 MPa	550 MPa
Cost	Moderate	Higher
Sigma phase precipitation risk during welding/heat treatment	Present, but slower kinetics — somewhat more forgiving process control	Faster kinetics — requires stricter heat input and quench control
Typical service envelope	General offshore/chemical process piping, moderate-to-high chloride severity	Highest chloride severity, subsea, seawater-critical, highest strength requirement

Selection principle: Specify Duplex 2205 as the default higher-strength, chloride-resistant stainless alloy choice for the large majority of offshore, chemical process, and general industrial applications requiring performance above standard austenitic stainless steel — reserving Super Duplex 2507 (RR Hydraulic’s dedicated reference) specifically for the highest chloride severity, subsea, or maximum-strength applications where 2205’s performance margin is judged insufficient.

Part 02 / Standards, Product Forms & Mechanical Properties

Governing Standards,
Product Forms
& Composition Reference

Duplex 2205 is manufactured across forged fitting/flange, bar, plate, and tube/pipe product forms, each governed by a specific ASTM/ASME standard. Full detail on the super duplex tier is available in RR Hydraulic’s dedicated reference.

Duplex 2205 Standards and Product Forms — RR Hydraulic

Formal R.F.Q. — Duplex 2205 Flanges, Fittings, Bar and Tube for EPC / Offshore / Chemical Process Projects
Submit form, size, and quantity to sales@rrhydraulics.com for a certified offer.

2.1 — Governing Standards

ASTM A182 (Grade F51) — Forged Flanges and Fittings

Governs forged duplex flanges, fittings, and valve bodies — Grade F51 corresponds to UNS S31803/S32205, the standard specification for forged pressure-boundary components in this alloy, referenced alongside RR Hydraulic’s ANSI B16 flange dimensional reference.

ASTM A240 — Plate, Sheet, and Strip

Governs flat-rolled duplex 2205 product — plate for pressure vessel fabrication, sheet and strip for general fabrication requiring the alloy’s strength and corrosion performance.

ASTM A789 / A790 — Tube and Pipe

A789 governs welded and seamless duplex tube; A790 governs welded and seamless duplex pipe — the primary specifications for tubular products in process piping, offshore, and instrumentation applications.

ASTM A276 / A479 — Bar

Governs stainless and duplex bar stock for machined components, forging billet, and fastener manufacture in duplex 2205.

ASTM A995 — Duplex Castings

Governs cast duplex components (Grade CD3MN and related grades) for valve bodies and pump casings where cast, rather than forged or bar-machined, construction is specified.

NACE MR0175 / ISO 15156

Provides the material qualification framework for sour service use of duplex 2205, including hardness limits (typically 28–32 HRC maximum depending on the specific service category) — a mandatory reference for offshore and onshore oil & gas applications with H₂S exposure.

2.2 — Chemical Composition and Mechanical Properties

Table 2.A — Duplex 2205 (S32205) Nominal Composition and Mechanical Properties (Solution Annealed)

Element / Property	Value / Range
Chromium	22.0–23.0%
Nickel	4.5–6.5%
Molybdenum	3.0–3.5%
Nitrogen	0.14–0.20% (S32205; S31803 permits down to 0.08%)
Tensile Strength	620–800 MPa (min. 620 MPa per spec)
Yield Strength	450–550 MPa (min. 450 MPa per spec)
Elongation	20–30%
Hardness	≤ 28–32 HRC (per applicable NACE service category)

2.3 — PREN Calculation for 2205

PREN — Pitting Resistance Equivalent Number (Same Formula as Super Duplex)

PREN = %Cr + 3.3 × %Mo + 16 × %N

Example — S32205 nominal composition (22.5% Cr, 3.2% Mo, 0.17% N):
PREN = 22.5 + (3.3 × 3.2) + (16 × 0.17) = 22.5 + 10.56 + 2.72 = ≈ 35.8
Compare against 316L stainless steel (PREN ~24) and super duplex 2507 (PREN ~42–43, per RR Hydraulic’s dedicated reference) — 2205 sits meaningfully above standard austenitic stainless in chloride resistance while remaining below the super duplex tier.

Part 03 / Intermetallic Phase Risk, Heat Treatment & Welding

Solution Annealing,
Sigma Phase Management
& Welding Discipline

Duplex 2205 shares the same fundamental intermetallic phase precipitation risk mechanism discussed in detail in RR Hydraulic’s Super Duplex 2507 reference, though with somewhat more forgiving (slower) precipitation kinetics due to its lower chromium and molybdenum content.

Duplex 2205 Heat Treatment and Welding — RR Hydraulic

3.1 — Intermetallic Phase Precipitation: Present but Slower Than Super Duplex

Important — 2205 Requires the Same Fundamental Heat Treatment Discipline as Super Duplex, Though With More Margin: Like super duplex 2507, standard duplex 2205 is susceptible to embrittling sigma and chi intermetallic phase precipitation when held within, or cooled too slowly through, the approximately 650–980°C temperature range — the same fundamental mechanism discussed in detail in RR Hydraulic’s Super Duplex 2507 reference. However, 2205’s lower chromium and molybdenum content means this precipitation reaction proceeds meaningfully more slowly than in 2507, giving 2205 somewhat greater practical tolerance for welding heat input and cooling rate variation before intermetallic phases become a significant concern. This should not be misread as “2205 doesn’t need careful heat treatment or welding control” — solution annealing at the correct temperature (typically 1020–1100°C) followed by adequate rapid quenching, and welding procedures with controlled heat input and interpass temperature, remain essential quality requirements for 2205 — the difference from 2507 is one of process margin, not of principle.

3.2 — Solution Annealing Requirements

Duplex 2205 is solution annealed at approximately 1020–1100°C (somewhat lower than super duplex 2507’s typical 1025–1125°C range, reflecting the alloy’s different phase balance requirements) followed by rapid quenching (water quench for most product forms and section thicknesses) to achieve the correct approximately 50/50 austenite-ferrite phase balance and avoid intermetallic phase formation during cooling. As with 2507, quench rate adequacy for the specific component section thickness must be verified — thicker sections require correspondingly more aggressive quenching to avoid slow cooling through the critical precipitation temperature range at the component’s core.

3.3 — Welding Practice

Heat Input and Interpass Temperature Control

Welding procedures for 2205 require controlled heat input and interpass temperature, following the same fundamental principles as super duplex 2507 welding (RR Hydraulic’s dedicated reference) though with somewhat greater practical tolerance given 2205’s slower precipitation kinetics — welding procedure qualification specific to 2205 remains standard good practice rather than assuming parameters directly from austenitic stainless steel welding experience.

Matching or Overalloyed Filler Metal

Welding consumables for 2205 (typically ER2209/E2209-type filler) are frequently slightly overalloyed in nickel content relative to the base metal to promote adequate austenite reformation in the weld metal during rapid post-weld cooling, following the same principle discussed for super duplex filler metal selection.

Ferrite Content Verification

Post-weld ferrite content measurement (per ASTM E562 or magnetic ferrite measurement, typically targeting 35–65% ferrite in the weld metal and heat-affected zone) remains a standard, mandatory QC checkpoint for duplex 2205 welds, verifying correct phase balance and confirming the welding procedure has been correctly executed.

Part 04 / QC, Applications & Export

Inspection Protocol,
Industry Applications
& Documentation

RR Hydraulic maintains full traceability from certified duplex heat to finished, tested, and packed 2205 component shipment, with ferrite content, impact testing, and corrosion resistance verification standard on all project-grade supply.

Duplex 2205 Inspection and QC — RR Hydraulic

4.1 — Inspection & QC Protocol

CHEM

Chemical Composition

Verification of Cr, Ni, Mo, and N content against ASTM A182 (F51)/A240/A789/A790 composition limits — critically confirming the nitrogen content meets S32205’s tighter 0.14% minimum rather than S31803’s broader 0.08% minimum where the improved chemistry is specified.

FERRITE

Ferrite Content Measurement

Ferrite content verification per ASTM E562 (point count) or magnetic ferrite measurement on 100% of production, confirming the target 35–65% ferrite balance is achieved.

IMPACT

Charpy Impact Testing

Charpy V-notch impact testing at the specified minimum design temperature on production test coupons per heat/lot — the primary practical indicator of sigma phase or other intermetallic precipitation.

CORR

Corrosion Testing (ASTM G48)

Critical pitting temperature (CPT) and critical crevice temperature (CCT) testing per ASTM G48 Methods A/B/C/D on sampled production lots, verifying the alloy achieves its designed pitting/crevice corrosion resistance.

MECH

Mechanical Testing

Tensile, yield, and elongation testing per ASTM E8/A370 on production test coupons per heat/lot, confirming minimum mechanical property requirements are met.

HARD

Hardness Testing

Rockwell C hardness testing confirming compliance with NACE MR0175 sour-service hardness limits where applicable.

PMI

Positive Material Identification

XRF verification of alloy content on 100% of production lots, confirming the declared duplex 2205 composition versus super duplex 2507 or other stainless grades of similar appearance.

FAI

First Article Inspection

Complete chemical, ferrite content, impact, corrosion, mechanical, and dimensional verification on the first production run of each unique configuration per project order, released before batch production.

4.2 — EN 10204 / Documentation Requirements

Table 4.A — Material Certification for Duplex 2205 Component Supply

Certificate	Content	EPC Requirement	When Mandatory
2.1 / 2.2	Declaration / non-specific	Not acceptable for critical offshore/process supply	Never for critical offshore or chemical process equipment supply
3.1 (EN 10204)	Heat-traceable chemical + mechanical test report	Mandatory — all EPC supply	All offshore, chemical process, and general industrial component supply
3.2 (EN 10204)	3.1 + TPI countersign	Critical / owner-specified critical items	Offshore and high-consequence pressure equipment

4.3 — Applications by Industry

Offshore Platform Process Piping Onshore Oil & Gas Process Equipment Chemical Process Vessels and Piping Pulp and Paper Digester Equipment Desalination Plant Equipment Heat Exchanger and Condenser Tubing Storage Tank Construction Flue Gas Desulphurisation Components Marine and Shipbuilding Structural Components Wellhead and Valve Components Water and Wastewater Treatment Structural Applications Requiring Weight Reduction

Offshore and Onshore Oil & Gas Process Piping

Duplex 2205 flanges, fittings, and piping for offshore platform and onshore process systems handling produced water, moderate-chloride process fluids, and general oil & gas production service — the default, most widely specified duplex grade across the oil & gas industry, balancing strength, corrosion resistance, and cost for the large majority of applications not requiring super duplex’s higher performance tier.

Chemical Process and Pulp & Paper Equipment

2205 vessels, piping, and digester equipment for chemical process and pulp/paper manufacturing where chloride-bearing process fluids and general corrosion resistance requirements exceed standard austenitic stainless steel’s reliable service envelope, without demanding super duplex’s higher-cost, higher-performance tier.

Storage Tanks and Structural Applications

Duplex 2205 plate for storage tank construction and structural applications where the combination of higher strength (supporting thinner wall/lighter structure) and good general corrosion resistance provides a favourable lifecycle cost compared to carbon steel with coating systems or standard austenitic stainless steel.

4.4 — Export Packaging Specification

Flanges, fittings, and bar stock individually protected (bore caps, face protectors) to prevent contamination and mechanical damage during transit
Heat/lot number stamped or tagged on each item, cross-referenced to the accompanying material test certificate including ferrite content, impact test, and corrosion test results, with clear UNS designation (S31803 vs. S32205) marking
Components segregated from carbon steel and other dissimilar materials during packing to avoid surface contamination affecting the alloy’s corrosion performance
Documentation in a waterproof pocket: EN 10204 3.1/3.2 MTC, chemical composition report, ferrite content report, Charpy impact test report, ASTM G48 corrosion test report, mechanical properties report, hardness report, PMI report, and packing list with form/size breakdown per item
ISPM-15 timber or export cartons for international shipment, with country of origin and HS tariff code documentation matched to the duplex product category

Ready to source Duplex 2205 flanges, fittings, bar, or tube for your project?
Submit your form, size, and quantity to RR Hydraulic for a complete, certified commercial offer.

Duplex 2205(UNS S31803 /S32205)