Tesco Steel & Engineering forges ASTM A182 F53 blind flanges — super duplex 2507, UNS S32750, the duplex idea pushed to its practical limit — to ASME B16.5 Class 150–2500 from ½″ to 24″ NB and to ASME B16.47 up to 60″. With 25% chromium, 4% molybdenum and triple-strength nitrogen, F53 clears the PREN ≥40 seawater threshold and delivers yield ≥550 MPa — the closure of hot seawater, chlorinated firewater, produced water and aggressive brines, where even F51 duplex runs out of margin. The richer chemistry demands stricter discipline: documented solution anneal + water quench, with ASTM A923 and NACE MR0175 to order. Sister grade F55 (S32760) serves the same tier. Facings: BLRF, BLFF or BLRTJ. Every lot with EN 10204 3.1/3.2 MTC. ISO 9001:2015, made in Mumbai, India — exported to 50+ countries.
ASTM A182 F53 · UNS S32750 · 2507Super Duplex 25Cr-7Ni-4Mo-N · EN 1.4410PREN ≥40 · Seawater QualifiedYield ≥550 MPa · Tensile ≥800 MPaASME B16.5 ½″–24″ · Class 150–2500RF · FF · RTJ FacingsEN 10204 3.1 / 3.2 · ISO 9001:2015
ASTM A182 F53 Blind Flange — Specifications at a Glance
What is an ASTM A182 F53 Blind Flange?
The severe-service chloride closure. A solid forged disc of super duplex 2507 (UNS S32750) with no bore, closing pipes, valves and nozzles where chlorides are at their worst: hot seawater, firewater, produced water, aggressive brines. The upgraded duplex chemistry — 24–26% Cr, 3–5% Mo, 0.24–0.32% N — clears PREN ≥40, the industry's seawater threshold, with yield ≥550 MPa and tensile ≥800 MPa. Solution annealed + water quenched, hardness ≤310 HB, band roughly -50 °C to +300 °C. Dimensions per ASME B16.5 / B16.47 in RF, FF and RTJ facings; EN 10204 3.1 certified.
Also searched as: super duplex blind flange, 2507 blind flange, S32750 blind, SA-182 F53 blind (the ASME boiler-code twin), 1.4410 / X2CrNiMoN25-7-4 blind (the EN equivalent) — all refer to the product on this page. See also the duplex steel hub, the F53 slip on flanges, siblings F55 / F51 / F60 blind flanges, and the facing pages BLRF / BLFF / BLRTJ.
Pushing Duplex to the Limit
Standard duplex 2205 already beats austenitic stainless in chlorides. Super duplex asks: how far can the recipe go before it stops being manufacturable — and answers with 2507:
More of Everything That Matters
Chromium up to 24–26%, molybdenum to 3–5%, nitrogen tripled to 0.24–0.32% — each feeding the PREN formula directly, together clearing the seawater bar at 41-plus.
The PREN 40 Club
Offshore and marine specifications define super duplex by that number: qualified for warm seawater, crevice conditions and chlorinated firewater, where standard duplex's 34–38 runs out of margin.
Strength Rises With It
Yield ≥550 MPa and tensile ≥800 MPa — a fifth stronger than 2205 and triple ordinary austenitic stainless, in the same solution-annealed condition.
The Price Is Discipline
The richer the chemistry, the faster sigma phase forms if heat treatment wanders — super duplex is only as good as its documented anneal-and-quench, which is exactly what our certificates record.
Super austenitic alternative — no ferrite, lower strength
F53 Chemical Composition (UNS S32750)
Element
C
Si
Mn
P
S
Cr
Ni
Mo
N
Weight %
≤0.030
≤0.80
≤1.20
≤0.035
≤0.020
24.0–26.0
6.0–8.0
3.0–5.0
0.24–0.32
Every step up from F51's window feeds the pitting index: PREN = %Cr + 3.3×%Mo + 16×%N ≥ 40. The high nitrogen is the signature — a required, defining element that strengthens the austenite and sharpens corrosion resistance simultaneously.
Mechanical Properties & The Temperature Band
Property
ASTM A182 F53 Requirement
Tensile Strength
≥ 800 MPa (116 ksi)
Yield Strength (0.2%)
≥ 550 MPa (80 ksi)
Elongation
≥ 15%
Hardness
≤ 310 HB (NACE sour service: ≤32 HRC)
Condition
Solution annealed + water quenched — mandatory, documented
Service Band
~ -50 °C to +300 °C — offshore specifications often cap nearer 250 °C
Richer chemistry, faster sigma. The chromium and molybdenum that buy PREN 40 also accelerate intermetallic precipitation — super duplex can begin forming sigma phase within minutes in the 600–1000 °C window. The documented solution anneal above ~1050 °C + immediate water quench is the only acceptable route; no field heating, flame-cutting or casual welding, ever. ASTM A923 testing verifies the structure where specified.
ASTM A182 F53 Blind Flanges are available in the following specifications:
Material Grade
ASTM A182 F53 (UNS S32750, alloy 2507); ASME SA-182; EN 1.4410 to order
Heat Treatment
Solution annealed + water quenched — mandatory, furnace-documented; ASTM A923 testing to order
Size
1/2"NB to 24"NB per ASME B16.5; 26"–60" per ASME B16.47; EN 1092-1 to order
Class
150#, 300#, 400#, 600#, 900#, 1500#, 2500#
Facings
Raised Face (BLRF), Flat Face (BLFF), Ring Type Joint (BLRTJ) with groove per B16.20
Corrosion Duty
PREN ≥40 — hot seawater, crevice, chloride SCC; sour service per NACE MR0175 / ISO 15156 (≤32 HRC)
Surface Finish
Pickled & passivated or natural machined — no paint; segregated stainless handling throughout
Modifications
NPT-tapped centre (hydrotest / vent / drain / gauge), lifting provisions — machined & certified at the works
Testing
Tension, chemistry incl. nitrogen & hardness per heat; PMI routine; A923 / corrosion tests where specified
Certification
EN 10204 3.1 (standard) / 3.2 witnessed
Why F53 Blind Flanges Are Specified
Clears the Seawater Bar
PREN ≥40 is the offshore qualification line for warm seawater, crevice conditions and chlorinated firewater — F53 crosses it with margin, and the closure inherits the qualification whole.
Strength at the Severe End
Yield 550 MPa — a fifth beyond standard duplex, triple ordinary austenitic — bringing robustness and stronger ratings to lines where everything is already at its limit.
Built for the Offshore Intersection
Sour, chloride-laden and high-pressure arrive together on produced-water and injection systems — F53 with NACE compliance serves exactly that intersection.
Discipline You Can Audit
Documented anneal-and-quench, A923 on demand, PMI on every piece, nitrogen on every certificate — super duplex is a process as much as a chemistry, and the paperwork proves both.
Know the Ladder
Standard tier: F51 / F60. Same tier, W+Cu route: F55. Austenitic alternative: 254 SMO. Facings: BLRF / BLFF / BLRTJ.
Specification Notes — Getting Super Duplex Right
Three details buyers miss.F53 or F55 — name it: both clear PREN 40 but the UNS numbers, chemistries and certification lineages differ; order the one your line class names, not "super duplex" generically. The quench is the qualification: insist on the furnace-documented anneal-and-quench and, on critical lines, A923 results — a slow-cooled super duplex flange passes tension tests and fails in seawater. Sour caps hardness at 32 HRC: NACE MR0175 sits tighter than A182's 310 HB — state the NACE requirement up front so testing and certification align.
How Our F53 Blind Flanges Are Manufactured
1
Forging — cut billet of the spectro-verified S32750 heat — nitrogen included in the analysis — is hot-forged into the solid disc blank with full heat traceability and segregated stainless handling.
2
Solution anneal + water quench — above ~1050 °C and immediately into water, racing the richer chemistry through the sigma window; furnace charts retained against the heat number.
3
Machining & facing — faces, OD and drilling to ASME B16.5 / B16.47; RF serrations, flat face or RTJ groove gauged per B16.20; NPT taps machined where ordered.
4
Testing — tension test, full chemistry and hardness against the heat; PMI on every piece; ASTM A923 and corrosion testing where specified.
5
Pickling & passivation — the restored chromium-oxide skin, with marking of standard, grade, size, class and heat number.
6
Certification & packing — EN 10204 3.1 MTC (3.2 witnessed on request); faces protected, palletised or crated sea-worthy — no carbon-steel contact in transit.
Where F53 Blind Flanges Are Used
The severe end of chloride service: hot seawater cooling and chlorinated firewater/deluge rings offshore, produced-water and injection lines, high-recovery desalination stages, FGD scrubbers, and aggressive brine systems. Production below:
Machined Alloy Blind Flanges — On the Shop FloorStainless Blind Flanges — Crated for Export
F53 Blind Flange Dimensions
Blind dimensions are class-governed — identical across material grades. Full charts:
An ASTM A182 F53 blind flange is a solid forged disc of super duplex stainless steel — alloy 2507, UNS S32750 — drilled to the standard bolt pattern with no bore, used to close pipes, valves and vessel nozzles in the most severe chloride service piping sees: hot seawater, produced water and aggressive brines. Super duplex raises the duplex recipe to roughly 25% chromium, 4% molybdenum and 0.28% nitrogen, clearing the PREN 40 threshold that seawater specifications demand, with yield strength of 550 MPa. Dimensions follow ASME B16.5 from ½ inch to 24 inch and ASME B16.47 beyond, in raised face, flat face and ring joint facings.
What is super duplex stainless steel?
The duplex idea — a balanced half-austenite, half-ferrite structure — pushed to its practical limit. Against standard 2205, super duplex 2507 carries more chromium (24-26%), more molybdenum (3-5%) and roughly triple the nitrogen (0.24-0.32%), lifting both corrosion resistance and strength: PREN clears 40 and yield reaches 550 MPa. The price is discipline — the richer chemistry precipitates damaging phases faster if heat treatment wanders — which is why super duplex is bought from works that document every furnace cycle. F53 is its ASTM forged-flange designation.
Why does PREN 40 matter?
PREN (%Cr + 3.3×%Mo + 16×%N) ranks chloride pitting resistance, and 40 is the line the industry drew for seawater: offshore and marine specifications routinely define 'super duplex' as PREN ≥40 and qualify materials for warm seawater, crevice conditions and chlorinated firewater against it. F51/2205 at 34-38 serves cooler, milder chlorides; F53's 41-plus clears the seawater bar with margin. When a datasheet says PREN ≥40, it is naming this tier — and the blind that closes the line must clear the same number.
When should F53 be used instead of F51?
When the chloride duty outruns 2205: seawater running warm (crevice and pitting margins collapse as temperature climbs), high-chloride produced water, chlorinated firewater and deluge systems, aggressive brines and high-recovery desalination stages. F51 remains the economical duplex for the broad middle; F53 buys roughly six points of PREN and 100 MPa of yield for the severe end. Project specifications usually decide by PREN floor and design temperature — and our F51 blind flange page covers the standard tier.
What is the difference between F53 and F55?
Two routes to the same tier. F53 is UNS S32750 (2507): 25Cr-7Ni-4Mo-N, the plain super duplex. F55 is UNS S32760 (Zeron 100 heritage): a similar base with deliberate tungsten and copper additions and its own certification lineage. Both clear PREN 40, share the 550 MPa yield class and serve the same duties; specifications typically name one, and North Sea paperwork often runs on S32760 while much of the rest of the world runs S32750. Order the designation your line class names — we forge both, and our F55 blind flange page covers its side.
What are the mechanical properties of F53 blind flanges?
Tensile strength 800 MPa (116 ksi) minimum, yield strength 550 MPa (80 ksi) minimum, elongation 15% minimum, hardness 310 HB maximum — in the mandatory solution-annealed and water-quenched condition. That is roughly triple the yield of 316L and 100 MPa beyond standard duplex, with hardness still controlled for sour duty (NACE MR0175 caps super duplex at 32 HRC). Every heat is tension-tested and chemistry-verified including nitrogen, with results on the EN 10204 3.1 certificate.
What temperature range does an F53 blind flange cover?
The same band as all duplex, applied more conservatively: roughly -50°C to +300°C, with many offshore specifications capping super duplex nearer 250°C for long-term service. The 475°C embrittlement of the ferrite sets the metallurgical ceiling; the richer chemistry makes intermediate-temperature excursions even less forgivable than in 2205. Inside the band, nothing in the stainless family matches its combination of strength and chloride resistance.
Why is heat treatment even more critical on super duplex?
The extra chromium and molybdenum that buy PREN 40 also accelerate sigma-phase precipitation — super duplex can begin forming damaging intermetallics within minutes in the 600-1000°C window. Solution annealing above roughly 1050°C followed by an immediate water quench is the only acceptable route, and ASTM A923 testing verifies the structure where specified. A super duplex flange without a documented quench is a liability wearing a certificate; ours ship annealed, quenched, tested and documented.
What facings are F53 blind flanges made with?
All three: raised face (BLRF) — the offshore default — flat face (BLFF) for mating GRP and lined systems, common on seawater and firewater headers, and ring type joint (BLRTJ) for high-pressure injection and wellstream duty, the ring chosen softer than the groove. Each facing has its own page on this site. The forging is common to all three; the mating flange governs the choice, and for RTJ the ring number follows from size and class.
Is F53 suitable for sour service?
Yes, within NACE MR0175 / ISO 15156 limits — super duplex is widely used in sour produced-water and injection service, with hardness capped at 32 HRC and environmental limits on H2S partial pressure set by the standard. State the NACE requirement on the enquiry so testing and certification align; sour, chloride-laden and high-pressure typically arrive together offshore, and that intersection is exactly what F53 was built for.
Can F53 blind flanges be tapped for testing or instruments?
Yes — fill, vent, drain, gauge and injection taps are machined into the centre of the blind at the works and certified with the flange. Super duplex machines harder and work-hardens faster than any grade below it, so field-drilling is firmly off the table; the works tap arrives ready to plug with the heat treatment undisturbed. State the NPT size on the enquiry.
Where are F53 blind flanges used?
The severe end of chloride service: hot seawater cooling and chlorinated firewater and deluge rings offshore, produced-water and injection lines, high-recovery desalination stages, flue-gas desulphurisation scrubbers, and aggressive brine systems. F53 blinds close those lines as isolations, future connections and tapped test blinds — in the line's own super duplex, keeping PREN, strength and certificates uniform across the joint.
Which standards cover F53 blind flanges?
The material standard is ASTM A182 grade F53 (UNS S32750), with ASME SA-182 as its boiler-code twin and EN 1.4410 / X2CrNiMoN25-7-4 as the European equivalent; dimensions follow ASME B16.5 for ½"-24" and ASME B16.47 for 26"-60". ASTM A923 covers intermetallic-phase testing where specified, and NACE MR0175 / ISO 15156 governs sour service. A complete specification reads: 'Blind Flange, RF, 6", ASME B16.5 Class 300, ASTM A182 F53' — and our EN 10204 certificates state dimension standard, grade, heat treatment and test results together.
Is a 6Mo super austenitic an alternative to F53?
Sometimes — the super austenitics (6Mo grades such as 254 SMO) also clear PREN 40 while staying fully austenitic: no 475°C embrittlement concern and generous toughness, at the cost of much higher nickel content and price, with yield strength back near ordinary austenitic levels. Offshore hardware that wants strength with its corrosion resistance picks super duplex; certain heat-exchanger and chemical duties pick the austenitic route. Our 254 SMO page covers that alternative — the specification's strength and temperature demands decide.
Who manufactures ASTM A182 F53 blind flanges in India?
Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer based in Mumbai, India, forging ASTM A182 F53 / UNS S32750 super duplex blind flanges from ½" to 24" NB per ASME B16.5 in Classes 150-2500 and to 60" per ASME B16.47 — solution annealed and water quenched under documented furnace control, PMI-verified, with ASTM A923 testing and NACE MR0175 compliance to order, certified to EN 10204 3.1/3.2 on every lot — in raised face, flat face and ring joint facings, alongside F55 super duplex, F51/F60 duplex, stainless, carbon and nickel-alloy blinds. Exported to more than 50 countries.
