Super Duplex Steel Flanges | ASTM A182 F53, F55

Q: Which grade is most commonly used for duplex flanges?

ASTM A182 Grade F51 (UNS S31803/S32205) is the most commonly specified duplex stainless steel grade for flanges. Grade F53 (UNS S32750) and F55 (UNS S32760) are specified for more demanding environments.

Q: What is the typical lead time for Super Duplex flanges?

Standard sizes (1/2 inch to 8 inch) can ship immediately from stock. Custom specifications or large diameters typically require 4 to 6 weeks for manufacturing.

Q: What welding procedures are recommended for Super Duplex flanges?

Use matching or over-alloyed filler metals (ER2594 for GTAW/TIG, E2594 for SMAW). Key controls: interpass temperature below 100 degrees C, heat input 0.5 to 2.5 kJ/mm, and no PWHT required in most cases.

What Are Super Duplex Steel Flanges? Grades, Properties and Standards Explained

Super Duplex Steel Flanges (ASTM A182 F53 and F55) are high performance, forged pipe flanges designed to operate in chloride heavy and high pressure conditions where the austenitic grades fail. These flanges have a PREN of 40 or higher and offer resistance to pitting, crevice corrosion and stress corrosion cracking operating temperatures between -50 degrees C and +300 degrees C. These flanges consist of three parts that are required, namely, the pipe flange, bolting parts, and gasket. The joints are built with a gasket between two flanges joining the two to provide a good seal.

Super Duplex Steel Flanges need to be solution annealed at temperatures of 1040 to 1120 degrees C with a direct water quench to prevent the formation of sigma-phase and ensure the required 40 to 60 percent ferrite ratio. ASTM A182 Super Duplex Flanges are available in both welded or threaded design, which provides flexibility to piping systems and allows easy dismantling and gaining access to piping system parts.

Super Duplex Stainless Steel Flanges are good at high temperature oxidation. But, just like other duplex stainless steels, they become embrittle even on short-term exposure at temperatures above 300 degrees C. Because the hot strength of super duplex alloys is relatively low, fixturing or support is needed during forging and heat treatment to eliminate distortion. Solution treatment is performed after hot forging in order to regain maximum mechanical properties and corrosion resistance.

Super Duplex Pipe Flanges are offered in a vast array of designs that can be used in a broad application in industry such as Super Duplex Socket Weld Flanges, Super Duplex Lap Joint Flanges, Super Duplex Slip-On Flanges, Super Duplex Blind Flanges, Super Duplex Weld Neck Flanges, Super Duplex Threaded Flanges, and Super Duplex Orifice Flanges. Each of them is developed to meet a bunch of installation and performance requirements.

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Understanding Super Duplex Steel Grades: Which One Fits Your Project?
Super Duplex Flanges: Standard Specifications
Chemical Composition Overview
Mechanical Properties of Super Duplex Steel Flanges
Complete Range of Super Duplex Flange Types
Why Super Duplex Outperforms Standard Stainless Steel
UNS S32750 vs UNS S32760: Technical Comparison
How Are Super Duplex Flanges Manufactured?
Critical Applications for Super Duplex Flanges
Certified Super Duplex Materials: Third-Party Verified
Super Duplex Flanges: Expert Answers (FAQ)

Understanding Super Duplex Steel Grades: Which One Fits Your Project?

Super Duplex stainless steel flanges are not a single material but a group of ultra-high-performance alloys whose Pitting Resistance Equivalent Number (PREN) values exceed 40. The choice of UNS S32750 or UNS S32760 depends on your environment, corrosion exposure, and mechanical requirements.

UNS S32750 (F53 / 2507)

PREN: 40 to 43

Best For: General offshore, moderate chloride environments, and high-strength applications.

Key Advantage: Cost-effective high performance standard for most marine uses.

Explore S32750 Flanges →

UNS S32760 (F55 / Zeron 100)

PREN: 43 or above (typically 43 to 47)

Best For: Extreme chlorides, acidic media, and sour service applications requiring W and Cu enhancement.

Key Advantage: Maximum corrosion resistance provided by tungsten and copper additions.

Explore S32760 Flanges →

Not sure which grade? Contact our metallurgical team with your application details. We will recommend the optimal super duplex specification for your operating conditions. Contact Engineering Team

Super Duplex Flanges: Standard Specifications

Parameter	Specification
Standards	ASTM A182/A182M, ASME B16.5, ASME B16.47 Series A and B, MSS SP-44, EN 1092-1
Additional Standards	DIN 2527/2631 to 2638 (PN6 to PN400), JIS B2220 (5K to 20K), BS 4504 PN6 to PN250 available on request
Grades Covered	F53 (UNS S32750), F55 (UNS S32760)
Size Range	DN15 (1/2 inch) to DN1200 (48 inch)
Pressure Classes	ASME: 150 to 2500 \| DIN: PN6 to PN400 \| JIS: 5K to 20K
Face Types	RF (Raised Face), FF (Flat Face), RTJ (Ring Type Joint)
Temperature Range	-50 degrees C to +300 degrees C (-58 degrees F to +572 degrees F)
PREN Value	40 or above (superior pitting resistance)
Surface Finish	Pickled and Passivated (standard). Electropolished available on request.

Chemical Composition of Super Duplex Flanges

Element	S32750 (F53) Typical Range	S32760 (F55) Typical Range	Role
Chromium	24 to 26%	24 to 26%	Base corrosion resistance
Nickel	6 to 8%	6 to 8%	Austenite stabiliser
Molybdenum	3 to 5%	3 to 4%	Pitting resistance
Nitrogen	0.2 to 0.3%	0.2 to 0.3%	Strength and pitting resistance
Tungsten	Not present	0.5 to 1.0% (added)	Specific to F55/S32760 only
Copper	Not present	0.5 to 1.0% (added)	Specific to F55/S32760 only
Carbon	0.030% max	0.030% max	Low carbon prevents sensitisation
Manganese	1.20% max	1.00% max	Austenite stability

Note: Composition ranges are typical values. Refer to grade-specific datasheets for exact ASTM A182 minimum and maximum limits.

Mechanical Properties of Super Duplex Steel Flanges

Property	UNS S32750 (F53)	UNS S32760 (F55)	Test Standard
Tensile Strength (min)	795 MPa (115 ksi)	750 MPa (109 ksi)	ASTM A370
Yield Strength 0.2% (min)	550 MPa (80 ksi)	550 MPa (80 ksi)	ASTM A370
Elongation (min)	15%	25%	ASTM A370
Hardness (max)	32 HRC / 310 HB	32 HRC / 310 HB	ASTM E18
Impact Toughness	45J at -46 degrees C	45J at -46 degrees C	ASTM A370
Density	7.8 g/cm3	7.8 g/cm3	Reference value

The minimum yield strength of 550 MPa is approximately twice that of 316L stainless steel (minimum 170 MPa), enabling lighter wall construction in piping systems without sacrificing pressure integrity.

Complete Range of Super Duplex Flange Types

Weld Neck (WNRF) Best stress distribution for high-pressure systems and critical applications. The tapered hub transfers stress from the flange to the pipe, reducing stress concentration at the base of the connection. Ideal for sub-zero temperatures, high pressure, and thermal cycling conditions.

Slip-On (SORF) Cost-effective solution for lower-pressure lines with easier alignment during installation. The pipe slips through the bore and is welded both inside and outside. Suitable for applications where ease of assembly is a priority.

Blind Flanges (BLRF) Heavy-duty end-sealing for pipelines and pressure vessels. Available with high pressure ratings up to Class 2500. Used to blank off the end of a pipeline or nozzle for maintenance or future expansion.

Socket Weld (SWRF) Designed for small-bore high-pressure piping with compact installation. The pipe is inserted into the socket and fillet welded externally. Pressure classes from 150 to 2500 available.

Lap Joint Flanges Used with stub ends for easy alignment of bolt holes, facilitating maintenance and frequent disassembly. A two-piece design that is cost-effective for systems requiring regular inspection or piping adjustments.

Threaded and Screwed Flanges Non-welding connection for specific hazardous areas where welding is not permitted. NPT threaded and screwed configurations are both available. Suitable for low-pressure pilot processes and systems requiring frequent reconfiguration.

Orifice Flanges Used in flow measurement systems with orifice plates for accurate differential pressure measurement. Supplied in pairs complete with jack screws and pressure tapping connections. Available in all pressure classes.

Reducing Flanges Connect pipes of different bore sizes within the same system without a separate reducer fitting. Available in concentric and eccentric configurations to maintain pipeline alignment.

Long Weld Neck (LWN) Flanges Used in pressure vessels and heat exchangers where the extended neck acts as a nozzle connection. The long neck eliminates the need for a separate nozzle piece in vessel fabrication.

Ring Type Joint (RTJ) Flanges Designed for high-pressure and high-temperature service. The metal ring gasket seated in a precision-machined groove provides a leak-proof seal suitable for Class 600 to 2500 applications in oil and gas and sour service environments.

Request Custom Manufacturing — Non-standard sizes, special face configurations, and project-specific certifications available. Send drawings for a prompt quotation.

Why Super Duplex Outperforms Standard Stainless Steel

Corrosion Mastery

These flanges resist pitting in harsh seawater and chloride environments with a PREN above 40. They provide outstanding resistance against stress corrosion cracking (SCC) and crevice corrosion in environments where standard 316L stainless steel fails. The combination of 24 to 26% chromium, 3 to 5% molybdenum, and 0.2 to 0.3% nitrogen creates a multi-mechanism barrier against the most aggressive corrosive media encountered in offshore, chemical, and marine applications.

Mechanical Superiority

Super Duplex Steel Flanges offer a minimum yield strength of 550 MPa, approximately twice that of 316L stainless steel (minimum 170 MPa). This allows thinner wall construction, making piping systems significantly lighter without sacrificing pressure integrity. Reduced weight also lowers installation time and structural support costs on offshore platforms and large-diameter pipework.

Lifecycle Economics

Although material cost is higher at the outset, Super Duplex delivers lower lifecycle costs through extended service life, reduced maintenance intervals, and minimal unplanned downtime. The ability to specify thinner wall sections further reduces total material volume and fabrication cost, often closing the price gap with austenitic alternatives within the first maintenance cycle.

Environmental Versatility

Super Duplex Steel Flanges operate reliably across the full pH range from acidic to alkaline and maintain structural integrity from -50 degrees C (suitable for many cryogenic applications) to +300 degrees C service temperature. This broad operating envelope makes them suitable for everything from Arctic subsea pipelines to tropical desalination plants in a single standardised material selection.

UNS S32750 vs UNS S32760: Technical Comparison

Property	UNS S32750 (2507 / F53)	UNS S32760 (Zeron 100 / F55)
Chromium (%)	24 to 26	24 to 26
Nickel (%)	6 to 8	6 to 8
Molybdenum (%)	3 to 5	3 to 4
Tungsten (%)	Not present	0.5 to 1.0 (added)
Copper (%)	Not present	0.5 to 1.0 (added)
PREN	40 to 43	43 or above (typically 43 to 47)
Tensile Strength	750 to 950 MPa	750 to 1000 MPa
Yield Strength (min)	550 MPa	550 MPa
Impact Toughness	45J at -46 degrees C	45J at -46 degrees C
Density	7.8 g/cm3	7.8 g/cm3
Max Service Temp	300 degrees C	300 degrees C
Best Applications	Offshore platforms, heat exchangers, general marine service	Acidic chloride media, desalination, sour service, reducing acid environments

Key Insight: The addition of Tungsten and Copper in S32760 provides enhanced resistance to reducing acids such as sulfuric and phosphoric acid compared to S32750, making it the preferred choice for specific chemical processing applications.

View S32750 Specifications | View S32760 Specifications

How Are Super Duplex Flanges Manufactured at Solitaire Overseas?

Super Duplex Steel Flanges are produced through a controlled multi-stage forging and heat treatment process designed to consistently achieve PREN 40 or above and the required 40 to 60 percent ferrite balance.

Step 1: Steelmaking

High-grade scrap and master alloy are melted in an Electric Arc Furnace (EAF), then refined in an Argon Oxygen Decarburization (AOD) converter to fix the precise Cr, Mo, and N chemistry required for PREN 40 or above. Dissolved gases are removed and final alloy composition is set at this stage.

Step 2: Casting and Forging

The conditioned melt is cast and forged to shape under controlled temperature to ensure a uniform dual-phase (ferrite and austenite) microstructure throughout the flange cross-section.

Step 3: Solution Annealing

Flanges are solution annealed at 1040 to 1120 degrees C and immediately water quenched to lock in the 40 to 60 percent ferrite balance and prevent sigma-phase formation. This step is mandatory and cannot be substituted with air cooling.

Step 4: Machining and Testing

Each flange is precision-machined to ASME B16.5 and B16.47 dimensional tolerances and subjected to ferrite content testing (ASTM E562), corrosion testing (ASTM G48 Method A), and impact testing at -46 degrees C (ASTM A370).

Step 5: Documentation

EN 10204 3.1 Mill Test Certificates, PMI (Positive Material Identification) reports, and dimensional inspection reports are issued with every order. EN 10204 3.2 and third-party inspection are available on request.

Critical Applications for Super Duplex Stainless Steel Flanges

Offshore Oil and Gas: Subsea manifolds, risers, and topside process equipment exposed to seawater and sour gas service.
Desalination and Water Treatment: High-pressure brine handling systems and Seawater Reverse Osmosis (SWRO) plants requiring sustained chloride resistance.
Chemical Processing: Chlor-alkali production, fertiliser manufacturing, and acid transport lines including sulfuric and phosphoric acid service.
Marine Engineering: Ballast water systems, fire-fighting systems, and exhaust gas cleaning equipment exposed to seawater.
Power Generation: Flue Gas Desulfurization (FGD) units and geothermal plant piping subject to wet acidic media.
Pulp and Paper: Bleaching plant piping and wash filtrate systems where chlorine compounds demand pitting resistance beyond 316L stainless steel.
Pharmaceutical and Food Processing: Sanitary piping and reactor nozzles in CIP and SIP environments requiring corrosion resistance combined with smooth passivated surfaces.

Related Products from Solitaire Overseas: Super Duplex Steel Pipe Fittings (ASTM A815) | Super Duplex Steel Pipes and Tubes (ASTM A790) | UNS S32615 Products

Certified Super Duplex Materials: Third-Party Verified

Testing Standards

Ferrite content: 40 to 60% (ASTM E562)
Impact testing: -46 degrees C (ASTM A370)
Corrosion testing: ASTM G48 Method A

Certifications

EN 10204 3.1 and 3.2 MTCs
NACE MR0175 / ISO 15156
ISO 9001 Certified
NORSOK M-650 Compliant (available on request for project-specific qualification)

Documentation

Heat traceability records
PMI (Positive Material Identification) reports
Dimensional inspection reports
Hydrostatic test certificates available on request

Frequently Asked Questions - Super Duplex Flanges

Q1: What is the difference between Duplex and Super Duplex flanges?

Super Duplex has higher chromium, molybdenum, and nitrogen content, resulting in a PREN above 40 (compared to 30 to 40 for standard Duplex 2205). This provides approximately 30 to 40 percent better corrosion resistance and higher mechanical strength. Duplex steel flanges (e.g. UNS S31803 and S32205) contain approximately 22% chromium and 3% molybdenum and are suitable for most industrial applications. Super Duplex flanges (e.g. UNS S32750, S32760) are specified for more aggressive environments such as deep-sea applications and high-chloride process streams.

Q2: Which grade is most commonly used for duplex flanges?

ASTM A182 Grade F51 (UNS S31803 and S32205) is the most commonly specified duplex stainless steel grade for flanges, offering an excellent balance of strength, corrosion resistance, and weldability at competitive cost. Grade F53 (UNS S32750) and F55 (UNS S32760) are specified for more demanding environments.

Q3: Can Super Duplex flanges be used in cryogenic applications?

Yes. Super Duplex maintains sufficient toughness down to -50 degrees C, making it suitable for many LNG and cryogenic service applications. Impact testing at -46 degrees C per ASTM A370 is mandatory to verify suitability for these temperatures.

Q4: How do I choose between UNS S32750 and S32760?

S32750 is the standard choice for most offshore and marine applications. Choose S32760 primarily when facing highly acidic chloride environments or when tungsten-enhanced resistance to reducing acids (sulfuric, phosphoric) is required for specific chemical processing applications.

Q5: What is the typical lead time for Super Duplex flanges?

We maintain stock of standard sizes (1/2 inch to 8 inch) which can ship immediately. Custom specifications or large diameters typically require 4 to 6 weeks for manufacturing, though express options are available for urgent projects.

Q6: Are Super Duplex flanges compatible with 316L stainless steel piping?

Direct connection is generally not recommended due to galvanic corrosion risks (Super Duplex is more noble) and different thermal expansion rates. Use compatible Super Duplex piping or proper isolation kits and transition spools.

Q7: Are Duplex Steel Flanges compatible with carbon steel piping?

Duplex Steel Flanges can be connected to carbon steel piping using appropriate transition fittings or isolation gaskets to prevent galvanic corrosion. The flange bolt holes, facing dimensions, and pressure-temperature ratings must be matched according to the applicable standard (e.g. ANSI B16.5 Class 150 or 300).

Q8: What documents are provided with the supply of Super Duplex flanges?

Solitaire Overseas provides Material Test Certificates (MTC) per EN 10204 3.1 as standard with all shipments. EN 10204 3.2 certificates, NACE compliance certificates, third-party inspection reports, heat treatment certificates, hydrostatic test certificates, and dimensional inspection reports are available on request.

Q9: Can Solitaire Overseas supply Super Duplex flanges to custom specifications?

Yes. Solitaire Overseas manufactures Super Duplex Steel Flanges to custom specifications including non-standard sizes, special face configurations, custom bore dimensions, and project-specific material certifications. Please share your drawings or technical datasheet with our team for a prompt quotation.

Q10: What welding procedures are recommended for Super Duplex flanges?

Super Duplex flanges should be welded using matching or over-alloyed filler metals. For GTAW/TIG use ER2594 wire; for SMAW use E2594 electrodes. Key procedure controls: interpass temperature below 100 degrees C, heat input 0.5 to 2.5 kJ/mm, and no PWHT required in most cases. If PWHT is specified for stress relief, full solution annealing at 1040 to 1120 degrees C with immediate water quench is mandatory. Solitaire Overseas provides WPS and PQR documentation on request for project qualification.

Q11: What is the price of Super Duplex Steel Flanges?

Pricing depends on size, pressure class, grade (S32750 vs S32760), quantity, and certification requirements. Contact us for a project-specific quotation. Standard sizes (1/2 inch to 8 inch) are available from stock and can be quoted same-day.

Ready to specify Super Duplex Steel Flanges for your project?

Solitaire Overseas maintains ready stock of ASTM A182 F53 and F55 flanges from 1/2 inch to 8 inch for immediate dispatch, with larger sizes available to order in 4 to 6 weeks. Send us your size schedule and we will respond within 24 hours with pricing and availability.

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