Tesco Steel & Engineering manufactures ASTM A182 F11 socketweld flanges — 1¼Cr-½Mo alloy steel, Class 2, UNS K11572, W.Nr. 1.7335 — to ASME B16.5 from ½″ to 3″ NB in Classes 150–1500 (2500 and 4″ to order). This is the steam workhorse of the chrome-moly ladder — the first real creep rung, holding strength through decades at 450–550 °C where carbon steel graphitizes — and the default alloy of boiler auxiliaries, steam headers, trap stations, soot blowers and drains. Its chemistry tells its mission: carbon with a deliberate minimum (0.10–0.20%), because creep strength is carbide strength. Socket seated, one external fillet weld, the mildest preheat/PWHT discipline on the ladder — stated honestly below. Facings: SWRF, SWFF, SWRTJ. Hotter steam? F22. Sour and hot? F5. Every lot with EN 10204 3.1/3.2 MTC. ISO 9001:2015, made in Mumbai, India — exported to 50+ countries.
A182 F11 Cl.2 · UNS K11572 · W.Nr. 1.73351¼Cr-½Mo — The Steam WorkhorseFirst Creep Rung of the LadderC 0.10–0.20% — Carbide Strength485 / 275 MPa · 143–207 HBASME B16.5 ½″–3″ · Class 150–1500SWRF · SWFF · SWRTJEN 10204 3.1 / 3.2 · ISO 9001:2015
ASTM A182 F11 Socketweld Flanges — Specifications at a Glance
What is an ASTM A182 F11 Socketweld Flange?
The steam plant's small-bore flange. A forged 1¼Cr-½Mo alloy steel flange (ASTM A182 F11 Class 2 / UNS K11572) with a machined socket: pipe seated square by geometry, one external fillet weld, through-bore matched to the pipe schedule. The first real creep rung of the chrome-moly ladder — Cr-Mo carbides hold strength through decades at 450–550 °C, with carbon specified above a floor (0.10–0.20%) because creep strength is carbide strength. Tensile ≥485 MPa, yield ≥275 MPa, 143–207 HB, normalized & tempered. Sized by ASME B16.5 at ½″–3″ NB, Classes 150–1500; EN 10204 3.1 on every lot.
Also searched as: A182 F11 socket weld flange, F11 Class 2 flange, F11 SWRF flange, 1.25Cr socket weld flange, K11572 flange — all the same product family. Related pages: the facings — SWRF / SWFF / SWRTJ — the socketweld hub, the other F11 types — blind, weld neck, slip-on, F11 grade hub — the ladder neighbours F22 / F5 / F9, and the alloy steel hub.
F11 is where most steam plants start and many finish: creep-rated where carbon steel is not, economical where F22 is unnecessary.
What 1¼Cr-½Mo Buys
Decades at Steam Temperature
Cr-Mo carbides pin the microstructure against creep — the ASME allowable-stress tables carry F11 confidently through the 450–550 °C band where A105 has already left the room.
Carbon With a Floor
C 0.10–0.20% — a minimum, not just a cap: no carbon, no carbides, no creep strength. The mirror image of the corrosion grades' low-C logic, and the one-line summary of what F11 is for.
The Ladder's Easiest Welding
Low chromium means modest hardenability: preheat ~120–180 °C, PWHT by the code's thickness rules — not the near-universal PWHT of the 5Cr/9Cr rungs. Fabricators price that difference.
Graphitization, Solved
Above ~425 °C carbon steel's carbides slowly decompose to graphite and strength collapses over years — the classic old-boiler failure. Chromium stabilises the carbides; F11 exists because of exactly this.
ASTM A182 F11 Class 2 Chemical Composition (UNS K11572)
Element
C
Mn
Si
Cr
Mo
P
S
Weight %
0.10–0.20
0.30–0.80
0.50–1.00
1.00–1.50
0.44–0.65
≤0.040
≤0.040
Identity marks: carbon with a deliberate floor (creep carbides), 1–1.5% Cr stabilising them without air-hardening drama, and P/S at 0.040 — looser than F5/F9's 0.030, a detail estimators trip over in the other direction. PMI reads the Cr-Mo signature on every piece.
Mechanical Properties (Class 2, N&T)
Property
ASTM A182 F11 Class 2 Requirement
Tensile Strength
≥ 485 MPa (70 ksi)
Yield Strength (0.2%)
≥ 275 MPa (40 ksi)
Elongation
≥ 20%
Hardness
143–207 HB — tempering proof and PWHT baseline
Other Classes
Class 1: 415/205 MPa (low-C, max weldability); Class 3: 515/310 MPa — both to order
Why It's Bought
Not ambient numbers — the creep-rupture ratings at 450–550 °C that A105 cannot offer
ASTM A182 F11 Socketweld Flanges are available in the following specifications:
Material Grade
ASTM A182 F11 Class 2 (default — an unqualified 'F11' order is supplied as Class 2); Classes 1 and 3 to order; UNS K11572, W.Nr. 1.7335
Heat Treatment
Normalized and tempered; hardness verified 143–207 HB; furnace records certified
Size
1/2"NB to 3"NB per ASME B16.5; 4″ and larger to order
Class
150#, 300#, 600#, 900#, 1500# (900# shares 1500# dimensions in most sizes); 2500# on request — steam duty spreads across 300–1500
Facings
Raised Face (SWRF), Flat Face (SWFF), Ring Type Joint (SWRTJ) with groove per B16.20
Bore
Socket bore to pipe OD; through-bore matched to pipe schedule (Sch 40/80/160 — 80/160 dominate steam small bore)
Welding
Single external fillet per B16.5/B31.1/B31.3 with 1/16″ expansion gap; preheat ~120–180 °C, PWHT per the governing code's rules
Service Span
Creep-rated steam and hot non-sour process duty, 450–550 °C band; hotter steam → F22, sour heat → F5/F9
Testing
Tension, chemistry and hardness per heat; PMI on every piece; socket depth and bore gauged
Certification
EN 10204 3.1 with heat-treatment records (standard) / 3.2 witnessed
Specification Notes — Getting F11 Sockets Right
Four honest notes.State the class: an unqualified 'F11' order is quoted and certified Class 2; Classes 1 and 3 exist for weldability- and strength-led specifications — if a spec names one, name it. Check the governing code for PWHT: steam-plant work under B31.1 has its own preheat and PWHT tables, and they are not B31.3's — the mildest rung still has rules. The 1/16″ gap stands — expansion against a bottomed socket cracks weld roots, and steam services cycle. And thermal-fatigue drains are the known killer: attemperator and cycling drain-pot services hammer fillet roots — utilities butt-weld those lines as policy, and where your line class says so, the F11 weld neck is the right escalation.
How Our A182 F11 Socketweld Flanges Are Manufactured
1
Forging — cut billet of the spectro-verified F11 heat — the Cr-Mo windows and the carbon floor confirmed — is hot-forged into the flange blank with full heat traceability.
2
Heat treatment — normalized and tempered to the Class 2 requirement; furnace charts retained against the heat number.
3
Hardness & testing — hardness verified in the 143–207 HB band; tension and chemistry per heat; PMI reads the Cr-Mo signature on every piece.
4
Machining — faces, OD and drilling to ASME B16.5; socket counterbore and depth gauged piece by piece, through-bore matched to the ordered schedule; RF serrations, flat face or RTJ groove per B16.20.
5
Marking — laser-marked with grade, class, size, schedule and heat number.
6
Certification & packing — EN 10204 3.1 MTC with heat-treatment records (3.2 witnessed on request); packed sea-worthy.
Where ASTM A182 F11 Socketweld Flanges Are Used
The steam plant's small bore: boiler instrument and gauge connections, steam header drains and vents, soot blower supply lines, steam trap stations, attemperator and feedwater auxiliaries, turbine gland and drain systems — across power stations, sugar and cement captive plants, and the hot non-sour process services that sit above carbon steel's ceiling. Production below:
A182 Alloy Steel Flanges — Export CratedThe Socket Weld Joint — Note the Expansion Gap (X)Steel Flanges — Black-Coated, Crated at Our Works
A182 F11 Socketweld Flange Dimensions
Socket weld flange dimensions are class-governed per ASME B16.5 — identical across material grades (pressure-temperature ratings follow the 1¼Cr material group). Full charts:
An ASTM A182 F11 socketweld flange is a forged 1¼Cr-½Mo alloy steel flange — UNS K11572, supplied as Class 2 unless another class is named — whose back carries a machined socket: the pipe end seats inside, self-aligned square to the face, and is secured with a single external fillet weld. F11 is the steam workhorse of the chrome-moly ladder: the first real creep rung, holding strength through decades at 450-550°C where carbon steel graphitizes and fades, and the default alloy of boiler auxiliaries, steam headers, trap stations and drains. Dimensioned to ASME B16.5 for ½" to 3" NB in Classes 150 to 1500, in raised face, flat face and ring joint facings.
Where does F11 sit on the chrome-moly ladder?
At the creep end — the ladder's original mission. The rungs climb F1 (½Mo) → F11 (1¼Cr-½Mo) → F22 (2¼Cr-1Mo) → F5 (5Cr) → F9 (9Cr), and the reasons for climbing change along the way: F11 and F22 are bought for strength at steam temperatures, while from F5 upward the chromium becomes corrosion armour for sour refinery streams. F11 is where most steam plants start and many finish — economical, weldable with moderate discipline, creep-rated where carbon steel is not. When steam conditions rise beyond its window, F22 is the next rung; when the stream turns sour and hot, the ladder's corrosion half takes over. Every rung has its own pages on this site; this page is the F11 socket weld.
What do F11 Class 1, Class 2 and Class 3 mean?
Three strength levels of the same 1¼Cr-½Mo chemistry, set by carbon and heat treatment. Class 2 — the flange default, and what an unqualified 'F11' order means — carries C 0.10-0.20% and delivers 485 MPa tensile / 275 MPa yield. Class 1 trims carbon (0.05-0.15%) for maximum weldability at 415/205 MPa — it appears mainly in welded fittings practice. Class 3 holds Class 2 chemistry but is heat treated to 515/310 MPa where a designer wants more margin. Almost all stock and almost all piping specifications run Class 2; our certificates state the class explicitly, and if your enquiry just says F11, we quote and certify Class 2.
Why does F11's carbon have a minimum?
Because creep strength is carbide strength. F11's job is to resist slow deformation over years at steam temperatures, and the mechanism is a dispersion of chromium-molybdenum carbides pinning the microstructure — no carbon, no carbides, no creep resistance. So Class 2 specifies carbon as a range with a floor, 0.10-0.20%: the mill must prove there is enough carbon to form the strengthening phase, not just little enough to weld. It is the mirror image of the corrosion-driven grades' logic (LF2 and the stainless L-grades trim carbon toward zero), and a neat one-line summary of what F11 is for. A datasheet printing F11 carbon as '≤0.20' has lost the point — and the floor.
What is the chemical composition of ASTM A182 F11 Class 2?
Carbon 0.10-0.20% (a deliberate range with a minimum — see the carbon FAQ), manganese 0.30-0.80%, silicon 0.50-1.00%, chromium 1.00-1.50%, molybdenum 0.44-0.65%, phosphorus ≤0.040%, sulphur ≤0.040%. The 1¼% chromium is enough to stabilise carbides and confer modest oxidation resistance at steam temperatures without the air-hardening drama of the high-chrome rungs; the silicon range assists scale resistance. Note the P and S ceilings sit at 0.040 — looser than F5/F9's 0.030, a detail estimators occasionally trip over in the other direction. Chemistry is verified per heat and travels on the EN 10204 3.1 MTC.
What are the mechanical properties of A182 F11 socketweld flanges?
In the Class 2 normalized-and-tempered condition A182 requires tensile strength 485 MPa (70 ksi) minimum, yield strength 275 MPa (40 ksi) minimum, elongation 20% minimum, with hardness controlled at 143-207 HB. The room-temperature numbers match carbon steel's — deliberately: F11 is not bought for ambient strength but for its creep-rupture ratings at 450-550°C, where the ASME allowable-stress tables leave A105 behind. The hardness band is the mill's evidence of proper tempering and the baseline your site PWHT should return the weld zone to after joint welding.
How is an F11 socketweld flange welded — preheat and PWHT?
With the mildest discipline on the chrome-moly ladder — but discipline nonetheless. Joint geometry is standard socket weld practice: pipe bottomed, withdrawn 1/16" (1.6 mm) per the code so thermal expansion cannot crack the weld root, single external fillet sized to B16.5/B31.1/B31.3 rules. F11's low chromium means modest hardenability: typical preheat runs around 120-180°C, and PWHT follows the code's thickness and service rules rather than being effectively universal as it is for 5Cr and 9Cr. Steam-plant work under B31.1 has its own PWHT tables — check the governing code, not habit. Our flanges arrive normalized and tempered with records; the joint's pedigree is the fabricator's half of the contract.
F11 or F22 — how do I choose?
By the steam conditions, via the allowable-stress tables. F11 carries the classic subcritical boiler and steam-line window economically; F22 (2¼Cr-1Mo) extends it — higher creep-rupture strength at the hot end, the standard grade for high-energy steam headers and hydrogen-unit auxiliaries, at a modest price and welding-discipline premium. The practical crossover sits where your design code's stress tables and the line's design temperature put it — commonly in the 540-565°C region for long-life duty — not at a number a flange catalogue should pretend is universal. Both grades ship as socket welds from our works; when an enquiry names the design temperature, the quotation names the economical rung.
F11 or F5 — creep or corrosion?
They answer different questions from the same family. F11 is a creep purchase: clean steam or hydrogen-free hydrocarbon at temperature, where strength-over-decades sets the grade and 1¼% chromium exists mainly to stabilise the carbides. F5 is a corrosion purchase: its 5% chromium is armour against the hot sulphidation of crude fractions, and its strength ratings matter less than its survival rates. A steam plant almost never needs F5; a hot sour refinery circuit is wasted on F11. Where a stream is both hot and mildly sour, the corrosion engineer's curves decide — and our F5 page carries that half of the ladder's story.
What facings are A182 F11 socketweld flanges made with?
All three, each with its own page on this site: raised face (SWRF) — the default, with graphite-filled spiral wound gaskets for steam duty — flat face (SWFF) for the rare lined or brittle mate, and ring type joint (SWRTJ) for high-pressure steam and feedwater circuits in Classes 900-1500. The socket, the welding practice and the schedule-matched bore are identical across the three; only the gasket face changes, and the piping class decides which you order.
What sizes and pressure classes do F11 socketweld flanges come in?
ASME B16.5 standardises socket weld flanges from ½" to 3" NB in Classes 150, 300, 600, 900 and 1500 — Class 900 sharing Class 1500 dimensions in most small-bore sizes — with 4" and Class 2500 made to order. Steam-plant duty spreads F11 sockets across Classes 300-1500, with boiler-proximate connections at the high end. As with every socket flange, put the pipe schedule on the enquiry — Sch 80 and 160 dominate high-pressure steam small bore — so the through-bore matches the pipe ID. B16.5 pressure-temperature ratings for the 1¼Cr material group govern the limits; our quotations state them per class.
When should I not use a socket weld flange?
The standard socket weld limits apply, with steam's own emphasis. As always: the socket gap is a crevice (corrosion-sensitive stagnant duty prefers butt welds), fillet welds cannot be radiographed (mandatory-RT and lethal-service classes escalate to weld necks), and hygienic duty excludes sockets. The steam-specific caution: thermal-fatigue duty — spray-water attemperator drains, cycling drain pots, anything that alternates between steam and condensate — hammers the fillet root, and cracked socket welds in drain lines are a documented power-plant failure mode; many utilities butt-weld those specific services as policy. Where your line class says so, our F11 weld neck page has the matching flange.
Where are F11 socketweld flanges used?
Across the steam plant's small bore: boiler instrument and gauge connections, steam header drains and vents, soot blower supply lines, steam trap stations, attemperator and feedwater auxiliaries, turbine gland and drain systems — plus the hot, non-sour process services of refineries and chemical plants that sit above carbon steel's 425°C ceiling but below the sulphidation regime. Power stations, sugar and cement captive plants, and process utilities are the volume homes. Wherever the line itself is F11 or equivalent 1¼Cr pipe, the small-bore closures should match the alloy — same certificate, same thermal expansion, same PWHT behaviour.
What details are needed to get an accurate F11 socketweld flange quotation?
Six elements plus commercial terms: (1) size — ½" to 3" NB; (2) pressure class — 150 to 1500; (3) facing — SWRF, SWFF or SWRTJ with ring number; (4) the pipe schedule — Sch 40, 80 or 160, so the through-bore matches the pipe ID; (5) grade detail — F11 Class 2 (the default) or Classes 1/3 where the specification names them, with any hardness requirements; (6) certification — EN 10204 3.1 with heat-treatment records (our standard) or 3.2 witnessed, PMI as applicable. Add quantity and destination and we return price, weight and delivery — normally within 24 hours.
Who manufactures ASTM A182 F11 socketweld flanges in India?
Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer based in Mumbai, India, producing ASTM A182 F11 Class 2 socket weld flanges from ½" to 3" NB (larger to order) in Classes 150-1500 — each forged from certified heats, normalized and tempered with furnace records, hardness-verified in the 143-207 HB band, machined with gauged socket depth and schedule-matched bore, PMI-checked and laser-marked with grade, class, size, schedule and heat number. Supplied with EN 10204 3.1/3.2 certification, alongside the full chrome-moly ladder — F1, F22, F5, F9 and F91 — and the complete socket weld range in carbon, stainless and nickel alloys. Exported to more than 50 countries.
