Tesco Steel & Engineering forges ASTM A182 F11 blind flanges — 1¼Cr-½Mo chrome-moly, the workhorse of steam and power piping — to ASME B16.5 Class 150–2500 from ½″ to 24″ NB and to ASME B16.47 up to 60″. Above A105's 425 °C ceiling carbon steel creeps — stretches permanently under load — and F11's molybdenum slows that mechanism while its chromium holds oxidation in check: the grade that keeps boiler circuits, superheaters and steam headers closed for decades. Supplied as Class 2 by default (Classes 1 and 3 to order); hotter and hydrogen-heavy duty steps to F22, hot sulphur belongs to F5/F9. 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 F11 Cl.1/2/3 · ASME SA-1821¼Cr-½Mo Chrome-MolySteam & Power Creep ServiceASME B16.5 ½″–24″ · Class 150–2500ASME B16.47 to 60″RF · FF · RTJ FacingsEN 10204 3.1 / 3.2 · ISO 9001:2015
ASTM A182 F11 Blind Flange — Specifications at a Glance
What is an ASTM A182 F11 Blind Flange?
The steam-plant closure. A solid forged disc of 1¼Cr-½Mo alloy steel with no bore, closing pipes, valves and nozzles where the metal runs hot for decades. The ½% molybdenum resists creep — the slow permanent stretch that retires carbon steel above ~450 °C — and the 1¼% chromium adds oxidation resistance: useful allowable stresses to roughly 560–590 °C. Standard flange grade Class 2 (tensile ≥485 MPa, hardness 143–207 HB). Dimensions per ASME B16.5 / B16.47 in RF, FF and RTJ facings; EN 10204 3.1 certified.
Also searched as: F11 blind flange, A182-F11 blind, SA-182 F11 blind (the ASME boiler-code twin), F11 Class 2 blind, 1.25Cr blind flange — all refer to the product on this page. See also the alloy steel hub, the F11 slip on flanges, siblings F5 / F9 / F22 / F91 blind flanges, and the facing pages BLRF / BLFF / BLRTJ.
The Creep Story — Why Molybdenum
Above roughly 450 °C, carbon steel under load stretches permanently — slowly, silently, for years — until a pressure part designed without creep in mind fails by it. Steam plant runs exactly there, around the clock, for decades. The answer the industry settled on a century ago still stands:
Molybdenum Slows the Stretch
½% Mo in solid solution dramatically slows creep — the single alloying decision that made long-life steam piping possible, and the backbone of every chrome-moly grade.
Chromium Keeps It Stable
1¼% Cr resists oxidation and long-term microstructural degradation, so the strength bought by the molybdenum survives decades at temperature.
The Blind Inherits the Duty
A closure on a steam header carries the same decades-long load as the pipe — specifying the blind in the line's own F11 keeps creep life and certificates uniform across the joint.
F11 Class 1, 2 & 3 — Chemistry and Strength
Property
Class 1
Class 2 (flange default)
Class 3
Carbon
0.05–0.15%
0.10–0.20%
0.10–0.20%
Manganese
0.30–0.60%
0.30–0.80%
0.30–0.80%
Silicon
0.50–1.00%
0.10–0.60%
0.10–0.60%
Chromium
1.00–1.50%
1.00–1.50%
1.00–1.50%
Molybdenum
0.44–0.65%
0.44–0.65%
0.44–0.65%
Tensile Strength
≥415 MPa (60 ksi)
≥485 MPa (70 ksi)
≥515 MPa (75 ksi)
Yield Strength
≥205 MPa (30 ksi)
≥275 MPa (40 ksi)
≥310 MPa (45 ksi)
Hardness
121–174 HB
143–207 HB
156–207 HB
An unqualified "F11" order receives Class 2 — the flange standard. No F11 class carries a vanadium or niobium requirement; those micro-alloys belong to F91. Elongation is ≥20% across all classes, heat treatment is mandatory, and the certificate states the class explicitly.
Rule of thumb: F11 and F22 are molybdenum-led — strength at temperature for steam and hydrogen. F5 and F9 are chromium-led — hot sulphur corrosion in refinery streams. The families overlap in temperature but not in purpose.
ASTM A182 F11 Blind Flanges are available in the following specifications:
Material Grade
ASTM A182 F11 Class 2 (default); Classes 1 & 3 to order; ASME SA-182 dual-certifiable
Heat Treatment
Annealed or normalized & tempered per A182 — mandatory; condition stated on certificate
Size
1/2"NB to 24"NB per ASME B16.5; 26"–60" per ASME B16.47; EN 1092-1 equivalents 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
Service
Steam & power creep duty; useful allowable stresses to ~560–590 °C per ASME tables
Modifications
NPT-tapped centre (hydrotest / vent / drain / gauge), lifting provisions — machined & certified at the works
Testing
Tension, chemistry & hardness per heat; PMI routine; UT / MPI where specified
Certification
EN 10204 3.1 (standard) / 3.2 witnessed
Why F11 Blind Flanges Are Specified
Creep-Rated Where Carbon Steel Isn't
The blind stays code-rated on steam lines that left A105's allowable-stress table a hundred degrees ago — and holds them shut for the decades power plant expects.
The Economical Chrome-Moly
The lightest alloying that buys real creep strength — F11 owns the volume middle of hot piping precisely because it costs the least of the family.
Bolted, So Fabrication Stays Simple
1¼Cr wants preheat and PWHT when welded — a bolted blind sidesteps all of it, arriving correctly heat treated from the works.
The Matching-Metal Principle
Blind in the line's own grade keeps creep behaviour, inspection intervals and certificates uniform across the joint.
Know the Siblings
Hotter or hydrogen-heavy: F22. Hot sulphur: F5 / F9. Maximum creep: F91. General duty: A105. Facings: BLRF / BLFF / BLRTJ.
Specification Notes — Getting F11 Right
Three details buyers miss.State the class: "F11" alone gets Class 2, the flange default — but if your specification means Class 1 or 3, the strength and hardness windows differ, and the certificate must match. No field modifications: chrome-moly wants its heat treatment left alone; taps and machining belong at the works, certified with the flange. Not a cold-service grade: below about -29 °C ferritic steels need impact testing — cold closures belong to LF2 or stainless, however hot the line runs in normal operation.
How Our F11 Blind Flanges Are Manufactured
1
Forging — cut billet of the spectro-verified F11 heat is hot-forged into the solid disc blank, keeping full heat traceability from melt to marking.
2
Heat treatment — annealed or normalized and tempered per A182; hardness verified into the class 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, chemistry and hardness against the heat; PMI routine on every alloy lot; UT and MPI where specified.
5
Marking — permanent marking of standard, grade (F11 and class), 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.
Where F11 Blind Flanges Are Used
The steam side of industry: power stations — boiler, superheater and reheater circuits — HRSGs behind gas turbines, refinery and petrochemical steam systems, moderate hot-oil duty and mild hot-hydrogen service. Production below:
Black-Coated Blind Flanges — On the Finishing LineLarge Machined Blind with Auxiliary Nozzle Connection
F11 Blind Flange Dimensions
Blind dimensions are class-governed — identical across material grades. Full charts:
An ASTM A182 F11 blind flange is a solid forged disc of 1¼Cr-½Mo alloy steel, drilled to the standard bolt pattern with no bore, used to close pipes, valves and vessel nozzles in hot steam and power-plant service. F11 is the entry grade of the chrome-moly family: the ½% molybdenum carries strength into the creep range where carbon steel quietly stretches, and the 1¼% chromium adds oxidation resistance and stability. 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 kind of steel is A182 F11?
A forged 1¼Cr-½Mo low-alloy steel. In the standard flange grade — F11 Class 2 — the chemistry runs carbon 0.10-0.20%, manganese 0.30-0.80%, silicon 0.10-0.60%, chromium 1.00-1.50% and molybdenum 0.44-0.65%, supplied heat treated (annealed or normalized and tempered). No vanadium or niobium is required in any F11 class. It handles like carbon steel, prices modestly above it, and owns the enormous middle ground of hot steam piping between A105's ceiling and the heavier chrome-molys.
What is creep, and why does F11 resist it?
Creep is slow, permanent stretch under load at high temperature — above roughly 450°C carbon steel deforms measurably over years even at stresses it holds easily when cold, and a pressure part designed without creep in mind eventually fails by it. Molybdenum in solid solution dramatically slows the mechanism, which is why ½Mo steels became the backbone of steam plant. F11 pairs that with enough chromium to keep oxidation and long-term microstructural degradation in check — the combination that lets a blind hold a steam header shut for decades.
F11 Class 1, Class 2 or Class 3 — which one?
Three strength classes share the F11 designation. Class 2 is the standard for flanges — tensile 485 MPa and yield 275 MPa minimum, hardness 143-207 HB — and is what an unqualified 'F11' order receives. Class 1 is a lower-carbon, lower-strength variant (415/205 MPa) with higher silicon, occasionally specified for its weldability; Class 3 is stronger again (515/310 MPa). The certificate states the class explicitly. If your piping class just says F11, Class 2 is almost certainly what it means — we confirm at enquiry when in doubt.
When should F22 be used instead of F11?
F22 carries roughly double the chromium and molybdenum (2¼Cr-1Mo) — more creep strength at the hottest end, better hydrogen-attack resistance per the Nelson curves, and the grade of choice for heavy-wall hydroprocessing and hotter steam. F11 is lighter, cheaper and entirely adequate for the great majority of superheated-steam and moderate hot-hydrogen duty. Specifications draw the line by temperature and hydrogen partial pressure; where your line class draws it decides the blind. Our F22 blind flange page covers the heavier grade.
How do F11 and F22 differ from F5 and F9?
By enemy. F11 and F22 are molybdenum-led: their job is strength at temperature — steam headers, boiler circuits, power piping — where the fluid is not especially corrosive but the metal runs hot for decades. F5 and F9 are chromium-led: their job is hot sulphur corrosion in refinery hydrocarbon circuits. The families overlap in temperature but not in purpose, and specifications rarely swap them. Our F5 and F9 blind flange pages tell the sulphur story.
What are the mechanical properties of F11 blind flanges?
For F11 Class 2 — the flange standard: tensile strength 485 MPa (70 ksi) minimum, yield 275 MPa (40 ksi) minimum, elongation 20% minimum, hardness 143-207 HB, in the mandatory heat-treated condition. Class 1 delivers 415/205 MPa and Class 3 515/310 MPa where specified. Every heat is tension-tested and chemistry-verified, with results and the heat-treatment condition on the EN 10204 3.1 certificate.
What temperature range does an F11 blind flange cover?
Hot service is its home: F11 holds useful allowable stresses to roughly 560-590°C in the ASME tables, and everyday steam practice works it below about 540-565°C, stepping to F22 or F91 beyond. It is not a cold-service grade — below about -29°C ferritic steels need impact testing, and cold closures belong to LTCS or stainless. The band between — from warm to seriously hot — is where most of the world's F11 lives.
What facings are F11 blind flanges made with?
All three: raised face (BLRF) — with the graphite-filled spiral-wound gaskets typical of steam practice — flat face (BLFF) for utility interfaces, and ring type joint (BLRTJ) for high-class hot circuits, 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.
What sizes and classes are F11 blind flanges available in?
From ½" to 24" NB per ASME B16.5 in Classes 150 through 2500, and to 60" per ASME B16.47 where large hot headers need closing. Chrome-moly blinds are generally forged against the order rather than stocked — power and refinery projects specify them by line class, and each lot carries its own heat-treatment record and certification. EN 1092-1 PN-series blinds in equivalent chrome-moly grades are produced to order as well.
Does welding or air-hardening affect F11 blind flanges?
Mildly, and far less than the higher-chromium grades. 1¼Cr steel needs preheat and often post-weld heat treatment when welded — but a blind flange is bolted, never welded, so the closure sidesteps the issue entirely: it arrives from the works correctly heat treated and stays that way. The remaining discipline is ours — controlled forging, heat treatment and hardness verification — and the certificate records it. Field modifications are still best avoided; taps belong at the works.
Can F11 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. Tapped F11 blinds are common in power practice: hydrotesting boiler circuits and steam headers calls for closures that match the line's creep rating, and an NPT-tapped F11 blind is the engineered answer. State the NPT size on the enquiry and the tap arrives ready to plug.
Where are F11 blind flanges used?
The steam side of industry: power stations and their boiler, superheater and reheater circuits, HRSGs behind gas turbines, refinery and petrochemical steam systems, hot-oil duties at moderate severity, and process units running mild hot-hydrogen service. On those lines F11 blinds serve the usual closure duties — isolations, future connections, hydrotest blinds — in the same metal as the pipe, keeping creep behaviour and certificates uniform across the joint.
Which standards cover F11 blind flanges?
The material standard is ASTM A182 grade F11 (Class 1, 2 or 3), with ASME SA-182 as its boiler-code twin; dimensions follow ASME B16.5 for ½"-24" and ASME B16.47 for 26"-60". Pressure-temperature ratings come from the B16.5 tables for the 1¼Cr material group. A complete specification reads: 'Blind Flange, RF, 8", ASME B16.5 Class 600, ASTM A182 F11 Cl.2' — and our EN 10204 certificates state dimension standard, grade, class, heat treatment and test results together.
Who manufactures ASTM A182 F11 blind flanges in India?
Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer based in Mumbai, India, forging ASTM A182 F11 blind flanges in Classes 1, 2 and 3 from ½" to 24" NB per ASME B16.5 in Classes 150-2500 and to 60" per ASME B16.47 — heat treated, hardness-controlled, PMI-verified and certified to EN 10204 3.1/3.2 on every lot — in raised face, flat face and ring joint facings, with NPT-tapped test blinds to order, alongside F5, F9, F22 and F91 chrome-moly, carbon steel, LTCS, stainless and nickel-alloy blinds. Exported to more than 50 countries.
