A flange is where a piping system admits it will need maintenance, and in duplex service the admission has to match the pipe exactly. Metinox Overseas supplies duplex and super duplex flanges forged to ASTM A182, grades F51, F60, F53 and F55, dimensioned to ASME B16.5 from ½" to 24" in Class 150 through 2500, with export lanes to the USA, the Middle East and Africa and 3.1 certification on every forging. Mixed-grade joints in chloride service are quiet failures waiting for commissioning, so the flange order should trail the pipe order by nothing. The pipe side of the set lives at Duplex Steel Pipes.
Two neighbours complete the picture. Exchanger circuits in the same water take Super Duplex Steel Tubes, and where the service is austenitic rather than duplex, the flange sibling is SS 304 Flanges. One enquiry covering pipe, tube and flanges comes back as one consolidated quote.
Duplex & Super Duplex Steel Flanges by Grade
Table of content
- The F-Grades: F51, F60, F53, F55
- Duplex Flange Types We Forge
- Dimensions, Classes & the Derating Truth
- Match the Flange to the Pipe: The Set Table
- Sour Service & NACE MR0175
- Duplex Flange Testing & Certification
- Flange Export to USA, Middle East & Africa
- Explore Related Ranges
- Duplex & Super Duplex Flanges: Frequently Asked Questions
The F-Grades: F51, F60, F53, F55
| A182 Grade | UNS | Family | Order it when |
|---|---|---|---|
| F51 | S31803 | Duplex 2205 | The standard duplex flange, matching S31803/S32205 pipe |
| F60 | S32205 | Duplex 2205 (tightened) | When the spec names S32205; sits inside F51 chemistry at the strong end |
| F53 | S32750 | Super duplex 2507 | Seawater and desalination circuits matching 2507 pipe and tube |
| F55 | S32760 | Super duplex | When the project spec names S32760; equivalence arguments lose |
Forgings per A182 carry the same phase-balance logic as the pipe: the anneal is the product, and the certificate should prove it.
Types of Duplex & Super Duplex Steel Flanges
Metinox Overseas produces an entire category of Duplex and Super duplex steel flange products that support a wide variety of piping and connecting needs in challenging industrial applications. We have the following product portfolio:
Slip-On Flanges
Low to medium pressure applications Sliding, easy to install flanges that are welded both internally and externally.
Weld Neck Flanges
The flanges are high-strength with long tapered hub which are good in offering good stress distribution, great in high pressure and high temperature services.
Blind Flanges
Plug flanges that are solid and used to seal end of pipelines or valve openings to make sure that it is completely isolated and sealed.
Socket Weld Flanges
Equipped with a socket where the pipe is fitted and welded, providing very solid joints on the small diameter high-pressure piping systems.
Threaded Flanges
They consist of internally threaded flanges designed to be connected to the pipes without any welding, therefore being suitable in those areas where welding cannot be done.
Lap Joint Flanges
Utilized in stub ends to make it easier to align, assemble and disassemble the design, fit well in systems that needed maintenance.
Orifice Flanges
Flanges with a special design are applied in flow measurement processes that require accurate monitoring and control.
Long Weld Neck Flanges
Long neck flanges are intended to be used in special piping systems, high-pressure systems, and in critical process systems.
Dimensions, Classes & the Derating Truth
Dimensions follow ASME B16.5 for ½" through 24" in Class 150 to 2500, with B16.47 covering 26" and above against order, raised face standard and RTJ where the class and spec call for it. Now the honesty: a flange class is a pressure-temperature curve, not a single number, and duplex curves stop early because the material's ~300°C ceiling caps the table regardless of class. Select the class against the B16.5 rating at your actual design temperature, not the cold rating, and remember that above the duplex ceiling no class rescues the material.
Sour Service & NACE MR0175
Duplex families are regulars in sour and offshore service, and there the flange must comply as an individual component: NACE MR0175 / ISO 15156 supply, with the hardness and condition requirements it implies, is arranged at order stage. Say sour in the enquiry and the compliance rides the quote from the first line rather than arriving as a change order.
Duplex Flange Testing & Certification
Forgings are supplied solution annealed with chemistry and mechanicals certified per heat, PMI verification standard practice on duplex grades, and ASTM A923 or intergranular testing available where the specification demands proof of phase condition. Every flange ships marked per A182 and B16.5 with an EN 10204 3.1 certificate, 3.2 via BV, SGS or TUV at order stage. Metinox Overseas is ISO 9001 and PED certified; the program is on our Quality Policy page.
Flange Export to USA, Middle East & Africa
Flanges travel differently from pipe: faces matter more than lengths. Export packing runs face-protected, boxed or palletized with desiccant for the sea leg, per Packing and Dispatch, and consolidations from Mumbai serve the USA, the Middle East and Africa on regular schedules, sharing containers with the matching pipe and tube when ordered as a set. Ex-stock items dispatch in 7 to 14 working days; forged-to-order sizes and F53/F55 items take 4 to 6 weeks.
Explore Related Ranges
- Duplex Steel Pipes – the lines these flanges bolt into
- Super Duplex Steel Tubes – the exchanger side of the same circuits
- SS 304 Flanges – the austenitic flange sibling
- Pipes & Tubes – the full catalogue
Duplex & Super Duplex Flanges: Frequently Asked Questions
Family and grade. F51 is duplex 2205 (S31803), with F60 as its tightened S32205 twin. F53 is super duplex 2507 (S32750) and F55 is super duplex S32760, the copper-and-tungsten variant many offshore specs name explicitly. Match the flange grade to the line material and, where a spec names a grade, order exactly that grade.
Against the B16.5 pressure-temperature table at your actual design temperature, not the cold rating, and with the duplex ceiling near 300 degrees C in mind, since no class rescues the material above it. Pick the class whose rating clears the design pressure at temperature with the margin your criticality demands.
Yes. NACE MR0175 / ISO 15156 compliant supply, with the hardness and condition control it requires, is arranged at order stage for F51 through F55. State sour service in the enquiry so compliance is engineered into the quote rather than retrofitted.
Because a mixed joint puts two different corrosion behaviours and two different strengths in the one place the system already planned to be opened. In chloride service that mismatch becomes the preferential attack site. Matching F-grade to line grade keeps the joint as boring as a joint should be.
Yes, face-protected and palletized from Mumbai on the same consolidations as the matching pipe and tube when ordered as a set, with 3.1 documentation and any NACE or A923 records travelling with the cargo to all three regions.
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