UNS S32205 | 2205 Controlled Composition | DIN 1.4462 | PREN ~36 | YS 450 MPa | Offshore & Chemical Service
ASTM A182 F60 is a forged duplex stainless steel flange grade with UNS designation S32205, commercially known as controlled-composition 2205 duplex. It shares the same austenite–ferrite two-phase microstructure as F51 (S31803) and the same commercial name "2205," but F60/S32205 carries tighter composition limits on molybdenum and nitrogen — the two elements that most directly govern pitting resistance.
The result is a grade whose pitting resistance equivalent number (PREN) is more consistently above the critical 35 threshold for offshore and chloride-containing service. Modern engineering standards including NORSOK M-630 (MDS D47), Shell DEP, and ExxonMobil GP specifications designate S32205 rather than S31803 for this reason. In practice, Tesco Steel manufactures F60 flanges to the full suite of ASME B16.5, B16.47, DIN EN 1092-1, and GOST 33259 dimensional standards for all pressure classes from 150# to 2500#.
Both F51 (S31803) and F60 (S32205) are sold as "2205 duplex" commercially. The difference is in the specification floor. S31803 permits Mo as low as 2.5% and N as low as 0.08% — at these minimums, PREN can drop to ~30.5, well below the 35 threshold. S32205 (F60) sets minimum Mo at 3.0% and minimum N at 0.14%, so even at worst-case composition the PREN is ~34.1, and at nominal composition it reaches ~36. Specifying F60 eliminates the risk of receiving specification-compliant but lower-performing material.
| Element | F51 / S31803 (%) | F60 / S32205 (%) | Significance |
|---|---|---|---|
| Chromium (Cr) | 21.0–23.0 | 22.0–23.0 | Higher minimum in F60 → better passive film stability |
| Nickel (Ni) | 4.5–6.5 | 4.5–6.5 | Same — phase balance control |
| Molybdenum (Mo) | 2.5–3.5 | 3.0–3.5 ↑ | Tighter min → reliable chloride/reducing acid resistance |
| Nitrogen (N) | 0.08–0.20 | 0.14–0.20 ↑ | Tighter min → consistent strength & pitting resistance |
| Carbon (C) | ≤0.030 | ≤0.030 | Low C prevents sensitisation on welding |
| Manganese (Mn) | ≤2.00 | ≤2.00 | Austenite stabiliser |
| Silicon (Si) | ≤1.00 | ≤1.00 | Deoxidiser |
| Phosphorus (P) | ≤0.030 | ≤0.030 | Grain-boundary embrittler — low limit required |
| Sulphur (S) | ≤0.020 | ≤0.020 | Inclusions reduce pitting initiation resistance |
PREN = %Cr + 3.3 × %Mo + 16 × %N
F60 minimum: 22.0 + (3.3 × 3.0) + (16 × 0.14) = 22.0 + 9.9 + 2.2 = 34.1
F60 nominal: 22.5 + (3.3 × 3.25) + (16 × 0.17) = 22.5 + 10.7 + 2.7 = 35.9
F60 maximum: 23.0 + (3.3 × 3.5) + (16 × 0.20) = 23.0 + 11.6 + 3.2 = 37.8
F51 minimum: 21.0 + (3.3 × 2.5) + (16 × 0.08) = 21.0 + 8.3 + 1.3 = 30.5 ← risk zone
Critical threshold: PREN ≥35 is the accepted minimum for offshore splash zone / moderate chloride service. F60 nominal (35.9) reliably crosses this threshold. F51 at minimum composition (30.5) falls well short — a risk eliminated by specifying F60.
UNS S31500 — Lean Duplex
PREN ~29
Si-alloyed; pulp & paper organic-acid specialist; not chloride-rated
UNS S32205 — Controlled 2205
PREN ~36
YS: 450 MPa | Mo min 3.0%
Offshore splash zone; chemical; guaranteed PREN ≥34 at all compositions
UNS S32750 — Super Duplex
PREN ~43
Seawater immersion; FGD; subsea; max Mo (4%); PREN ≥40 threshold
| Property | F60 / S32205 (min) | 316L / S31603 (min) | Advantage of F60 |
|---|---|---|---|
| Yield Strength (0.2% offset) | ≥450 MPa (65 ksi) | ≥170 MPa | 2.6× higher — thinner walls possible |
| Ultimate Tensile Strength | ≥620 MPa (90 ksi) | ≥485 MPa | 28% higher UTS |
| Elongation | ≥25% | ≥40% | Adequate ductility for flanges; less than austenitic |
| Hardness (max) | ≤290 HBW / ≤31 HRC | ≤217 HBW | Higher as-forged hardness — still within NACE limits |
| NACE MR0175 hardness limit | ≤36 HRC | ≤22 HRC (carbon steel) | Duplex permitted higher hardness than CS in H₂S service |
| ASME B16.5 Pressure Group | 2.3 | 2.2 | Slightly higher pressure-temperature ratings |
The yield strength of F60 (450 MPa minimum) is 2.6× that of 316L stainless (170 MPa). In pressure vessel and piping design to ASME VIII or B31.3, this directly enables thinner-walled forgings. A F60 flange in NPS 6 Class 300 requires approximately 35–40% less wall thickness than the equivalent 316L flange, translating directly to lower weight and material cost per joint — partially offsetting the higher alloy cost per kilogram.
Duplex stainless steel (including F60/S32205) is sensitive to precipitation of harmful phases at elevated temperatures. Both 475°C embrittlement and sigma phase formation are irreversible in service — affected material cannot be returned to compliant condition without a full solution anneal at 1020–1100°C + water quench.
| Phase / Phenomenon | Temperature Range | Time to Form | Effect |
|---|---|---|---|
| 475°C Embrittlement (alpha-prime) | 300–500°C | Hours to weeks at 475°C | Severe toughness loss; brittle fracture at ambient |
| Sigma Phase (Fe-Cr intermetallic) | 600–1000°C | ~5–10 min at 850°C for 2205 | Toughness + corrosion resistance loss |
| Chi Phase | 700–900°C | Slower than sigma | Toughness loss; minor in S32205 vs W-alloyed grades |
| Solution Anneal (only permissible HT) | 1020–1100°C + WQ | Full soak + immediate water quench | Restores correct microstructure and properties |
| PWHT | Any 300–1050°C | N/A | PROHIBITED — promotes all harmful phases |
| Parameter | Requirement for F60 / S32205 | Reason |
|---|---|---|
| Filler metal (GTAW/GMAW) | AWS ER2209 | Overalloyed in N to compensate weld pool N loss; ensures correct phase balance |
| Filler metal (SMAW) | AWS E2209 | Matching consumable for manual arc welding |
| Preheat | Not required (ambient, min 10°C) | Duplex does not require preheat; avoid welding on frozen substrate |
| Maximum interpass temperature | 150°C | Higher temperatures extend time in sigma phase formation range (600–1000°C) |
| Ferrite Number target | FN 30–65 (40–60% ferrite) | Correct phase balance; below FN 25 = too austenitic; above FN 65 = too ferritic |
| Heat input | 0.5–2.5 kJ/mm | Low heat input → excessive ferrite; high heat input → sigma formation in HAZ |
| Shielding gas (GTAW) | Argon + 2–3% N₂ | Nitrogen addition prevents N depletion at weld surface |
| PWHT | PROHIBITED | Any 300–1050°C HT promotes embrittling phases |
| Solution anneal | 1020–1100°C + WQ only | Only permissible heat treatment — full component immersion in water immediately after |
| Category | Standard | Description |
|---|---|---|
| Flanges (forgings) | ASTM A182 / ASME SA182 F60 | Primary procurement standard for F60 duplex flanges |
| Seamless/welded pipe | ASTM A790 S32205 | Companion piping standard — matching S32205 composition |
| Wrought fittings | ASTM A815 WPS32205 | Elbows, tees, reducers — same UNS designation |
| Plate, sheet, strip | ASTM A240 S32205 | Vessel construction companion |
| Dimensions (NPS ½–24) | ASME B16.5 | 150# to 2500# pressure classes |
| Dimensions (NPS 26–60) | ASME B16.47 Series A/B | Large-bore flanges |
| European flanges | EN 1092-1 (1.4462) | PN 6 to PN 400 pressure ratings |
| Sour service | NACE MR0175 / ISO 15156-3 | H₂S-containing environments; ≤36 HRC hardness limit for S32205 |
| Offshore | NORSOK M-630 MDS D47 | Norwegian offshore qualification standard for S32205 |
| Russian/CIS | GOST 33259 | Flange dimensions and materials |
Production headers, separators, wellheads, gas manifolds, subsea tie-back connections. NACE MR0175 / NORSOK M-630 D47 compliance. PREN ~36 qualifies for splash zone and topside seawater-wetted service. For fully submerged seawater piping, specify F53 or F55.
Chloride-containing process streams, acetic acid service, phosphoric acid plants, mixed organic-acid systems where both chloride pitting resistance (PREN ≥35) and high strength are required. F60 outperforms 316L in all chloride-containing chemical environments.
Kraft and sulfite digesters, brown stock washing, moderate-chloride bleach plant piping. F60 (S32205) is the industry-standard duplex grade for pulp and paper process piping where chloride levels are moderate (up to ~1,000 ppm). For high-chloride bleach stages, consider F55/Zeron 100.
Multi-stage flash (MSF) and reverse osmosis (RO) pre-treatment stages, brine heaters, pump casings, distribution headers. F60 provides the cost-effective balance of chloride resistance and strength for the intermediate-pressure sections of large-scale desalination plants.
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ASTM A182 F60 is a forged duplex stainless steel flange with UNS designation S32205, commercially known as controlled-composition 2205. Both F60 (S32205) and F51 (S31803) are sold as "2205 duplex," but F60 enforces tighter minimum limits: Mo ≥3.0% (vs 2.5% for F51) and N ≥0.14% (vs 0.08%). This raises the minimum PREN from ~30.5 (F51) to ~34.1 (F60). Nearly all commercial 2205 production meets S32205 chemistry, but only specifying F60 guarantees it contractually. Modern offshore and process-industry standards (NORSOK, Shell DEP) specify S32205 over S31803.
ASTM A182 F60 corresponds to UNS S32205. The European DIN/EN equivalent is 1.4462, grade X2CrNiMoN22-5-3. Note that EN 1.4462 technically covers both S31803 and S32205 — for guaranteed S32205 composition under EN standards, specify compliance with the tighter composition limits defined in ASTM A182 F60 or ASTM A240 S32205. The commercial name is 2205 Duplex (controlled composition).
The PREN of F60/S32205 is ~34.1 minimum, ~35.9 at nominal composition, and up to ~37.8 at maximum composition. This places F60 above the PREN 35 threshold for offshore splash zone and moderate chloride service. However, PREN 35–38 is below the 40 threshold required for full seawater immersion service. For submerged seawater applications, specify F53 (S32750, PREN ~43) or F55 (S32760, PRE(N+W) ~42). F60 is appropriate for topside seawater-wetted systems, process piping with up to ~1,000 ppm Cl⁻, and splash zone structures.
Minimum mechanical properties per ASTM A182 for F60/S32205: Yield Strength ≥450 MPa (65 ksi); UTS ≥620 MPa (90 ksi); Elongation ≥25%; Hardness ≤290 HBW (Brinell) or ≤31 HRC. These values represent approximately 2.6× the yield strength of 316L austenitic stainless (≥170 MPa). The higher yield strength allows F60 flanges to be designed with thinner walls for equivalent pressure ratings, reducing overall material weight by up to 35–40% compared to 316L for the same service.
Modern standards including NORSOK M-630 MDS D47, Shell DEP, and major EPC specifications require S32205 because it provides a contractual guarantee of consistent composition. S31803 at its minimum composition (Mo 2.5%, N 0.08%) yields a PREN of only ~30.5 — far below the 35 threshold. Since nearly all commercial 2205 production already meets S32205 chemistry, there is typically no price premium for specifying F60 over F51. The specification upgrade costs nothing but eliminates material performance uncertainty. Engineering best practice: always specify S32205 (F60) rather than S31803 (F51) for new projects.
The practical maximum continuous service temperature for F60/S32205 is approximately 300°C (572°F). Above 300°C, the risk of 475°C embrittlement (alpha-prime formation through spinodal decomposition of the ferrite phase) begins to increase. This causes irreversible loss of toughness at ambient temperature. Above 600°C, sigma phase (Fe-Cr intermetallic) forms rapidly — even brief excursions at 850°C in 2205 can form sigma within 5–10 minutes. For services requiring continuous operation above 300°C, austenitic grades (310S, 321H) or nickel-based alloys are more suitable. Minimum service temperature is approximately −50°C; below −46°C, Charpy testing is typically specified.
The standard filler for welding F60/S32205 is AWS ER2209 (GTAW/GMAW) or E2209 (SMAW). ER2209 is intentionally overalloyed in nitrogen to compensate for nitrogen loss from the weld pool and ensure correct weld metal phase balance (FN 30–65, targeting 40–60% ferrite). Maximum interpass temperature is 150°C. Heat input should be in the range 0.5–2.5 kJ/mm. PWHT is strictly prohibited. Shielding gas for GTAW: Argon + 2–3% N₂ to prevent surface nitrogen depletion. For dissimilar joints to carbon steel or 316L, ER2209 remains the standard choice for F60 side welding.
Post-weld heat treatment is strictly prohibited for ASTM A182 F60/S32205 duplex steel. Any heat treatment in the range 300–1050°C promotes 475°C embrittlement (300–500°C), sigma phase (600–1000°C), or chi phase — all irreversible in service. The only permissible heat treatment for duplex stainless steel is a full solution anneal at 1020–1100°C followed immediately by water quenching. This applies to the entire forged component. Stress-relief at subcritical temperatures (as commonly applied to carbon steel) cannot be used for duplex grades.
F60 flange standard: ASTM A182 / ASME SA182 Grade F60. Companion materials: pipe (ASTM A790 S32205), fittings (ASTM A815 WPS32205), plate (ASTM A240 S32205). Dimensions: ASME B16.5 (NPS ½–24), B16.47 Series A/B (NPS 26–60). European: EN 1092-1 (1.4462). Russian: GOST 33259. Offshore: NORSOK M-630 MDS D47. Sour service: NACE MR0175 / ISO 15156-3 (hardness limit ≤36 HRC for S32205). Note: ASME B16.5 Pressure-Temperature Group for S32205 is Group 2.3.
Primary industries: Oil & gas (offshore topside piping, gas processing, production separators, NACE MR0175 sour service); Chemical processing (chloride-containing process streams, phosphoric acid, acetic acid); Pulp & paper (Kraft digesters, moderate-chloride bleach plant piping); Desalination (MSF and RO pre-treatment, brine heaters); Food & beverage (hygienic high-strength piping); Marine (seawater cooling, ballast systems); Power (FGD inlet systems, cooling water headers). In all these industries, F60/S32205 replaces 316L where higher strength and guaranteed PREN ≥34 are required.
Verify whether the engineering spec, purchase order, or code (NORSOK, Shell DEP, ExxonMobil GP) explicitly calls for S31803 or S32205. If it says "2205 duplex" without a UNS number, request clarification — modern best practice and most current standards specify S32205. Identifying this early prevents costly material substitution disputes during fabrication.
Calculate PREN thresholds for your environment. If guaranteed PREN ≥35 is required (offshore splash zone, moderate chloride process streams), specify F60/S32205 — minimum PREN 34.1 vs F51 minimum of 30.5. If PREN ≥40 is required (full seawater immersion, FGD), upgrade to F53 (S32750, PREN ~43) or F55 (S32760, PRE(N+W) ~42).
F60/S32205 is appropriate for process streams with up to approximately 1,000 ppm Cl⁻ at temperatures below 60°C. Above these limits — or in direct seawater service (20,000 ppm+ Cl⁻) — select F53/S32750 (PREN ~43) or F55/S32760 (PRE(N+W) ~42). For low-chloride organic-acid environments (formic, acetic, sulfurous), consider F52/S31500 for its silicon-enhanced acid resistance.
All piping components in the system should carry matching UNS S32205 designations: pipe to ASTM A790 S32205, fittings to ASTM A815 WPS32205, plate to ASTM A240 S32205. Mixing S31803 pipe with S32205 flanges is metallurgically compatible but undermines the composition guarantee across the system — obtain project engineer approval before mixing.
For H₂S-containing environments (sour service) per NACE MR0175 / ISO 15156-3, the hardness limit for S32205 is ≤36 HRC (compared to ≤22 HRC for carbon steel). Request a hardness test certificate with the material test report. The A182 F60 hardness maximum of ≤290 HBW / ≤31 HRC is within the NACE limit, but verify each heat individually for sour-critical applications.
Available in all ASME B16.5 and B16.47 sizes from NPS ½" to 60" | 150# to 2500# pressure classes | All face types | Ready stock of standard items | Export to 96 countries
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| Grade | A182 F60 |
| UNS | S32205 |
| Commercial Name | 2205 Controlled |
| DIN / EN | 1.4462 |
| Type | Standard Duplex SS |
| Cr content | 22.0–23.0% |
| Ni content | 4.5–6.5% |
| Mo content | 3.0–3.5% ↑ |
| N content | 0.14–0.20% ↑ |
| C content | ≤0.030% |
| PREN (nominal) | ~36 |
| PREN (minimum) | ~34.1 |
| UTS (min) | 620 MPa |
| YS (min) | 450 MPa |
| Elongation | ≥25% |
| Hardness (max) | 290 HBW / 31 HRC |
| B16.5 Group | 2.3 |
| Service Temp | −50°C to 300°C |
| NACE hardness | ≤36 HRC |
S32205 tighter limits:
Result:
| F51 / 2205 (S31803) | PREN min 30.5 |
| F60 / 2205 (S32205) ★ | PREN ~36 |
| F53 / 2507 (S32750) | PREN ~43 |
| F55 / Zeron 100 (S32760) | PRE(N+W) ~42 |
PREN ≥35 = offshore splash zone / moderate Cl⁻
PREN ≥40 = seawater immersion
| Preheat | Not required |
| Max interpass | 150°C |
| Filler (GTAW) | ER2209 |
| Filler (SMAW) | E2209 |
| FN target | 30–65 |
| Heat input | 0.5–2.5 kJ/mm |
| Shielding gas | Ar + 2–3% N₂ |
| PWHT | PROHIBITED |
| 475°C embrittlement | 300–500°C |
| Sigma phase | 600–1000°C |
| Solution anneal only | 1020–1100°C + WQ |
PWHT at any intermediate temperature is prohibited — it causes irreversible embrittlement.
