Duplex Steel Flanges
Giriraj Impex is a manufacturer, stockist, supplier and exporter of duplex flanges to ASTM A182 grade F51 (UNS S31803) and F60 (UNS S32205). We manufacture duplex flanges to ASME B16.5 from ½" to 24" NB in Class 150 to 2500, ASME B16.47 Series A and B large-diameter flanges and EN 1092-1 flanges, in weld neck, slip-on, blind, socket weld, threaded, lap joint and orifice types.
Duplex flanges are used to join duplex 2205 pipe and fittings in chloride-bearing service – offshore process and water systems, seawater cooling, desalination, chemical plants and pulp and paper mills – where they combine high strength with resistance to pitting and chloride stress corrosion cracking.
Specifications
| Item | Details |
|---|---|
| Material standard | ASTM A182 / ASME SA182 |
| Grades | F51 (UNS S31803), F60 (UNS S32205); dual certified F51/F60 |
| Dimensional standards | ASME B16.5, B16.47 Series A and B, B16.36, B16.48, EN 1092-1, MSS SP-44 |
| Sizes | ½" to 24" NB (B16.5); 26" to 60" NB (B16.47) |
| Classes | 150, 300, 600, 900, 1500, 2500; PN ratings to EN 1092-1 |
| Facings | Raised face, flat face, ring type joint |
| Condition | Solution annealed and rapidly cooled |
| Documents | Mill test certificate (MTC) with PREN; third-party inspection on request |
F51 and F60
F51 and F60 are the ASTM A182 forging grades for duplex 2205. F51 corresponds to UNS S31803 and F60 to UNS S32205, which has tighter, higher minimums for chromium, molybdenum and nitrogen. Flanges are often dual certified F51/F60 so that one item satisfies piping specifications written around either UNS number. The composition limits are the same as for duplex pipe and plate:
| UNS | Grade | C | Mn | P | S | Si | Cr | Ni | Mo | N | Other elements |
|---|---|---|---|---|---|---|---|---|---|---|---|
| S31803 | 2205 | 0.030 | 2.00 | 0.030 | 0.020 | 1.00 | 21.0–23.0 | 4.5–6.5 | 2.5–3.5 | 0.08–0.20 | – |
| S32205 | 2205 | 0.030 | 2.00 | 0.030 | 0.020 | 1.00 | 22.0–23.0 | 4.5–6.5 | 3.0–3.5 | 0.14–0.20 | – |
| S32750 | 2507 | 0.030 | 1.20 | 0.035 | 0.020 | 0.80 | 24.0–26.0 | 6.0–8.0 | 3.0–5.0 | 0.24–0.32 | Cu 0.50 |
| S32760 | Zeron 100 type | 0.030 | 1.00 | 0.030 | 0.010 | 1.00 | 24.0–26.0 | 6.0–8.0 | 3.0–4.0 | 0.20–0.30 | Cu 0.50–1.00, W 0.50–1.00 |
S32760 also requires a minimum PREN of 40. Footnotes as given in the standards.
Flanges for seawater and more severe chloride service are made in super duplex grades F53 and F55.
Flange types
- Weld neck flanges – the common choice for duplex process lines.
- Blind flanges – for line ends, pig receivers and nozzles.
- Slip-on flanges – for lower-pressure water lines where permitted.
- Socket weld flanges – for small-bore lines.
- Lap joint flanges with duplex stub ends, orifice flanges, and spectacle blinds.
Manufacturing and testing
Duplex flanges are forged from A182 F51 or F60 material, solution annealed and rapidly cooled to keep a balanced ferrite–austenite structure, then machined to the dimensional standard. Because a slowly cooled or overheated forging can form brittle phases, many oil and gas specifications call for extra checks: ferrite measurement, Charpy impact tests at low temperature, ASTM A923 testing for detrimental intermetallic phases and ASTM G48 pitting tests. Each flange is dimensionally inspected and marked with the manufacturer's identification, grade, size, class, bore schedule and heat number. Flanges can be supplied to NACE MR0175 / ISO 15156 on request.
Bolting and gaskets
Duplex flanges are usually bolted with duplex or super duplex studs and nuts, or with coated B7 bolting where the specification allows, so that the bolting does not corrode faster than the flange. Insulating gasket kits are used where duplex flanges meet carbon steel to prevent galvanic corrosion. See duplex and super duplex fasteners.
Ordering
Please state the flange type, standard, size, class, facing, bore schedule, grade (F51, F60 or dual), quantity, and any supplementary tests, NACE MR0175 / ISO 15156 or inspection requirement.
Pressure ratings for duplex flanges
ASME B16.5 lists duplex 2205 forgings in their own material group, with pressure-temperature ratings for each class. Because duplex is stronger than austenitic stainless steel, its ratings in the same class are higher at moderate temperatures; the standard also sets an upper temperature limit for the material group, reflecting the risk of embrittlement at sustained high temperatures. Designers should use the B16.5 tables for the actual material group rather than assuming the ratings of carbon or stainless steel flanges. For non-standard designs such as compact flanges, the rating comes from the manufacturer's design calculations to the applicable code.
Applications and related products
Duplex flanges are used offshore for process, produced-water and seawater systems, in onshore chemical and petrochemical plants, desalination and seawater cooling, pulp and paper bleaching, and fertiliser and mining plants with chloride-bearing liquors. They connect duplex pipes and tubes and duplex pipe fittings. Flanges and blinds can also be made from duplex plates and duplex round bars where the specification allows. See all flange materials on the flanges page and grade guidance on the duplex and super duplex steel page.
Frequently Asked Questions
F51 is the ASTM A182 grade for forged duplex 2205 stainless steel, UNS S31803. F51 flanges are used with duplex 2205 pipe and fittings in chloride service.
F51 is UNS S31803 and F60 is UNS S32205. Both are duplex 2205; F60 has tighter, higher minimum levels of chromium, molybdenum and nitrogen. Flanges are often dual certified F51/F60.
Oil and gas projects commonly add ferrite measurement, Charpy impact tests, ASTM A923 for intermetallic phases and ASTM G48 pitting tests. They are agreed with the order.
Duplex or super duplex studs and nuts are used where full corrosion resistance is needed. Coated B7 bolting is sometimes used where the specification allows.
Yes, but an insulating gasket kit is normally used to prevent galvanic corrosion between the duplex and carbon steel flanges.
Yes. Flanges above 24" NB are supplied to ASME B16.47 Series A or B, or to customer drawings.
Request a Quote for Duplex Steel Flanges
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