Tesco Steel & Engineering manufactures ASTM A182 F91 long weld neck flanges — the summit of the steam staircase: 9Cr-1Mo-V creep-strength-enhanced ferritic, UNS K91560 — with ASME B16.5 flange ends in Classes 150–2500 and the barrel made to order. The construction is the LWN's: flange and nozzle in one forging, one closing weld at the header or shell — and on Grade 91 that argument peaks, because every weld in a P91 system carries the Type IV question, so the weld this forging deletes is an engineering purchase. The metallurgy is a generation apart: vanadium, niobium and nitrogen build fine carbonitrides in tempered martensite, worth roughly double F22's creep-rupture strength — the grade that carried steam into the 600 °C class and halved the walls doing it. The discipline is equally real, and stated openly below: mandatory N&T window with furnace charts attached, hardness watched at both ends of the band, the famous welding rules. Certificate: 585/415 MPa, ≤248 HBW. The staircase stays honest: F22 below when conditions moderate, plain F9 sideways when the enemy is sulphur. Facings: RF / FF / RTJ. Every lot with EN 10204 3.1/3.2 MTC. ISO 9001:2015, made in Mumbai, India — exported to 50+ countries.
ASTM A182 F91 · UNS K91560 · 1.4903 eq.CSEF — The V-Nb-N GenerationSupercritical & USC Steam — 600 °C Class585 / 415 MPa · ≤248 HBWThe Deleted Weld — Type IV HonestyB16.5 Flange Ends · Class 150–2500Barrel: Length & Bore to OrderEN 10204 3.1 / 3.2 · ISO 9001:2015
ASTM A182 F91 Long Weld Neck Flanges — Specifications at a Glance
What is an ASTM A182 F91 Long Weld Neck Flange?
The summit of the steam staircase, in the nozzle pattern. An ASTM A182 F91 flange (9Cr-1Mo-V CSEF, UNS K91560) whose neck continues as a long, heavy-walled straight barrel — the nozzle itself — bevelled for one closing butt weld at the header, valve chest or shell. Vanadium, niobium and nitrogen build carbonitrides in tempered martensite: roughly double F22's creep-rupture strength, the grade of supercritical and USC steam. And on this grade the LWN peaks: every P91 weld carries the Type IV question, so the weld this forging deletes is bought for engineering, not convenience. C 0.08–0.12%; Cr 8.0–9.5%; Mo 0.85–1.05%; V 0.18–0.25%; Nb 0.06–0.10%; N 0.030–0.070%. Supplied normalized & tempered inside the mandatory window, ≤248 HBW certified, furnace charts attached. Flange ends per ASME B16.5, Classes 150–2500; barrel length and bore stated by you. EN 10204 3.1 on every lot.
Also searched as: F91 LWN flange, P91 long weld neck flange, 9Cr-1Mo-V nozzle flange, CSEF LWN, A182 F91 RFLWN, K91560 LWN — all the same product. Related pages: the facings — LWNRF / LWNFF / LWNRTJ — the long weld neck hub, the F91 socketweld on small bore, the ladder — A105 / F11 / F22 / F5 / F9 — and the alloy steel hub.
Creep-strength-enhanced — the summit: 600 °C-class high-energy steam
This page
The rule of the two staircases: steam creep climbs F11 → F22 → F91; sulphur climbs F5 → F9 — and F91 stands where the steam staircase tops out: same 9-chrome skeleton as F9, a different century of metallurgy inside it.
What the V-Nb-N Trio Buys
Roughly Double F22's Creep-Rupture Strength
Fine vanadium-niobium carbonitrides in tempered martensite pin the structure against creep for decades — the mechanism that carried steam into the 600 °C class and let modern plants halve their pressure-part walls.
The Deleted Weld, Where It Counts Most
Every P91 weld carries the Type IV question — so the LWN's one-forging construction, which removes a whole circumferential weld from the system, is worth more on this grade than anywhere on the ladder.
The Strongest Certificate on the Ladder
585/415 MPa and a 248 HBW ceiling — and behind the room-temperature numbers, the 9Cr-1Mo-V material group's B16.5 ratings that every lower rung has retired from.
Paperwork That Is the Product
Mandatory N&T window, furnace charts attached to the MTC, hardness reported per heat, PMI reading the V-Nb signature — because in a CSEF, the heat-treatment record carries the creep life.
Specification Notes — Getting F91 Long Weld Necks Right
Three honest notes.F91 is not F9: same 9% chromium, never interchangeable — F9 is a sulphidation purchase, F91 a creep purchase with its own welding law; a substitution in either direction is a non-conformance. Demand the records: in this grade a vague heat-treatment certificate is a defect — the creep life lives in the N&T window, so furnace charts belong on the MTC (ours are attached as standard). And descend by arithmetic: inside the 550 °C class F22 serves with easier welding and a friendlier price — F91 bought for moderate duty is discipline paid for nothing.
How Our F91 LWN Flanges Are Manufactured
1
Forging — each piece individually forged from certified heats with the barrel integral — no welded build-ups — in any section up to the heaviest HB patterns.
2
Normalizing & tempering — inside the grade's mandatory window: full martensitic transformation through the section, then the temper that sets the carbonitride dispersion; furnace charts attached to the MTC, not summarised.
3
Hardness verification — every lot checked against the 248 HBW ceiling and watched on the low side too: in Grade 91, soft metal warns of lost creep strength as surely as hard metal warns of cracking risk.
4
Machining — flange end to ASME B16.5; barrel turned to pattern (standard / HB / equal) and bored to the ordered schedule or drawing; RF serrations, flat face or RTJ groove per B16.20; weld end bevelled 37.5°.
5
Testing & marking — chemistry and mechanicals per heat; PMI reads the V-Nb signature on every piece — the audit that separates F91 from plain 9-chrome; marked with grade, type, size, schedule and heat number.
6
Certification & packing — EN 10204 3.1 MTC with N&T furnace charts and hardness results (3.2 witnessed on request); 9Cr WPS guidance included; faces and bevels protected, packed sea-worthy.
Where F91 LWN Flanges Are Used
Around the highest-energy steam in power engineering: main steam and hot reheat headers of supercritical and ultra-supercritical plants, HRSG high-pressure sections of combined-cycle stations, superheater outlet headers and their nozzle stubs, turbine bypass and valve-chest connections, and the instrument standpipes and level bridles that ride on P91 systems — wherever the line is P91 and the owner is counting welds. Production and supply below:
Flange-end dimensions are class-governed per ASME B16.5 (ratings per the 9Cr-1Mo-V material group); barrel length and bore per order. Full class-by-class charts:
Seven elements — temperature confirms the rung, the records confirm the grade:
1
Size & standard — e.g. 4″ NB ASME B16.5.
2
Pressure class & facing — 150#–2500#; RF, FF or RTJ with ring number.
3
Barrel length — overall, face to weld end: 150 / 230 / 300 mm stock or any stated length.
4
Barrel bore & pattern — pipe schedule to match or finished bore in mm; standard, heavy barrel or equal barrel; weld-end prep if non-standard.
5
Grade line & service — ASTM A182 F91, Type 1 (default) or Type 2 where named; design temperature and pressure stated — they confirm F91 against F22 below and plain F9 sideways.
6
Certification — EN 10204 3.1 with N&T furnace charts and hardness results (our standard) / 3.2 witnessed; PMI as applicable.
Example: “LWN Flange RF, 4″ NB, ASME B16.5 Class 1500, barrel 300 mm, Sch 160 bore, heavy barrel, ASTM A182 F91 Type 1, hot-reheat header instrument nozzles — 570 °C steam, EN 10204 3.1 with furnace charts — 6 pcs.” Quotations normally within 24 hours with price, unit weight and delivery.
An ASTM A182 F91 long weld neck flange is a forged 9Cr-1Mo-V creep-strength-enhanced ferritic (CSEF) steel flange — UNS K91560, W.Nr. 1.4903 equivalent, the flange member of the P91 family — whose neck continues as a long, heavy-walled straight barrel that is itself the nozzle, bevelled at its far end for one closing butt weld made out at the header, valve chest or vessel shell. F91 is a different generation from the classic chrome-moly rungs: vanadium, niobium and nitrogen build fine carbonitrides in a tempered-martensite matrix, worth roughly double F22's creep-rupture strength — the grade of supercritical and ultra-supercritical steam, and the summit of the steam staircase. Flange ends follow ASME B16.5 in Classes 150 to 2500; the barrel is machined to the ordered length and bore. Supplied normalized and tempered inside the mandatory window, hardness certified against the 248 HBW ceiling.
How does a long weld neck differ from a standard weld neck flange?
Geometry and mission. A standard weld neck's hub tapers quickly down to the pipe's outside diameter and wall, ending in a weld bevel a few centimetres from the flange face — it is built to butt-weld to pipe and continue as a piping run. A long weld neck keeps a full-section straight barrel for its entire length: no taper to pipe dimensions, wall far heavier than the matching schedule, length made to order. The mission follows the shape — the LWN is not a fitting on a pipe run but a nozzle in its own right, projecting through insulation, vessel walls or exchanger channels, with the butt weld relocated to the shell side where the fabricator wants it. In one certified forging it replaces the weld neck flange, the pipe nipple and one whole circumferential weld.
Why does the LWN's deleted weld matter more on F91 than any other grade?
Because on Grade 91, welds are the counted liability. Every F91 weld carries the Type IV question — the soft heat-affected sub-zone where cross-weld creep strength drops and the fleet's in-service cracking has concentrated — plus a mandatory preheat, a narrow PWHT window and a paperwork trail. Owners of P91 systems respond by designing welds out wherever possible. The long weld neck is exactly that instrument: flange, nozzle neck and reinforcement in one certified forging, with the weld-neck-flange-to-nipple butt weld deleted and the one remaining closing weld relocated out to the header or shell, where access is best and the joint enters the vessel's own PWHT. On A105 the LWN saves fabrication money; on F91 it removes a Type IV site from a creep-designed system — an engineering purchase, not a convenience.
What makes F91 a different generation from the classic chrome-moly grades?
The strengthening mechanism. The classic rungs — F11, F22, F5, F9 — are ferrite-pearlite or bainitic steels strengthened by ordinary chromium-molybdenum carbides. F91 is a martensitic steel: normalized to form martensite through the full section, then tempered, with vanadium and niobium carbonitrides — stabilised by a deliberate nitrogen addition — precipitated as a fine, thermally stable dispersion that pins the structure against creep for decades. The result is roughly double F22's creep-rupture strength, which let modern power plants raise steam conditions into the 600°C class and thin their pressure parts — heavy headers that once strained cranes now hang lighter, and cycling plants shed thermal-fatigue stress with the wall thickness. The price is sensitivity: the entire property set depends on one precise microstructure, which is why F91's heat-treatment and welding rules are the strictest on the ladder.
F91 or F9 — what is the difference?
Same 9% chromium, different centuries — and never interchangeable. F9 is the classic plain 9Cr-1Mo: a corrosion purchase, the top rung of the refinery's sulphidation staircase, heat treated by ordinary routes and welded with standard chrome-moly care. F91 is the vanadium-microalloyed CSEF: a creep purchase for advanced steam, with a mandatory narrow normalize-and-temper window and unforgiving weld rules. Their chemistries diverge in every detail that matters: F91 adds the V-Nb-N trio, narrows carbon to a true 0.08-0.12% band, trims chromium and molybdenum to 8.0-9.5% and 0.85-1.05%, and tightens phosphorus and sulphur to 0.020/0.010. The certificates differ too — F91's 415 MPa yield against F9's 380. A substitution in either direction is a non-conformance: F9 in a creep-designed system lacks the allowables; F91 in a sour stream buys welding discipline the service never uses. Our certificates and PMI — which reads the V-Nb signature — make the distinction auditable.
What are F91 Type 1 and Type 2?
Recent editions of A182 split F91 into two chemistry types. Type 1 is the classic composition described on this page. Type 2 tightens the recipe further — tramp and trace elements are restricted harder, with controls added on elements like arsenic, tin and antimony, and a tighter nitrogen-to-aluminium balance — reflecting a decade of industry research into creep ductility and long-term cracking in 9Cr steels. Advanced projects and some owner specifications now call Type 2 for critical service. Practical guidance: if your specification says simply F91, Type 1 supply satisfies it; if it names Type 2, say so on the enquiry and the quotation and certificate will state Type 2 explicitly. Both types machine to the same LWN patterns and dimensions.
What is the chemical composition of ASTM A182 F91?
Carbon 0.08-0.12%, manganese 0.30-0.60%, silicon 0.20-0.50%, chromium 8.0-9.5%, molybdenum 0.85-1.05%, vanadium 0.18-0.25%, niobium 0.06-0.10%, nitrogen 0.030-0.070%, nickel ≤0.40%, phosphorus ≤0.020%, sulphur ≤0.010%. Everything about it is deliberate: the V-Nb-N trio builds the strengthening carbonitrides, the narrow carbon band balances hardenability against weldability, the nickel cap protects the tempering response, and the tight P/S ceilings — the strictest housekeeping on the ladder — protect long-term creep ductility. Aluminium, titanium and zirconium are additionally restricted because they steal the nitrogen the vanadium needs. Chemistry is verified per heat, PMI-confirmed with the V-Nb signature read, and travels on the EN 10204 3.1 MTC.
What are the mechanical properties of F91 long weld neck flanges?
In the mandatory normalized-and-tempered condition A182 requires tensile strength 585 MPa (85 ksi) minimum, yield strength 415 MPa (60 ksi) minimum, elongation 20% minimum, and hardness not exceeding 248 HBW — the strongest certificate on the chrome-moly ladder, with a yield a full step above F22 Class 3's 310 MPa. As everywhere on the bench, the room-temperature numbers are the entry ticket rather than the mission: what F91 sells is the creep-rupture strength behind B16.5's 9Cr-1Mo-V material-group ratings, which carry its flanges into the 600°C class where every lower rung has retired. Hardness deserves special respect in the F91 world: it is the field's quickest proxy for correct microstructure, with low readings warning of over-tempering (lost creep strength) and high readings of untempered martensite (cracking risk). Our certificates report hardness per heat alongside the furnace records, because in this grade the heat-treatment paperwork is the product.
Why is F91's heat-treatment window so strict?
Because every property F91 is bought for lives in one precise microstructure. Normalizing must fully austenitise and form martensite through the section — and an LWN's heavy barrel is exactly the kind of section that punishes shortcuts; tempering must then precipitate the vanadium-niobium carbonitrides at the right size — high enough in temperature to restore toughness, low enough not to coarsen the dispersion that carries the creep strength. Miss low and hard, brittle zones remain; miss high and the strength quietly evaporates — the flange still looks perfect and passes a tensile test, while its creep life has been halved. This is why F91 components with vague heat-treatment records are rejected by good inspectors, and why our MTCs attach the actual furnace charts, not just a compliance statement.
How demanding is the closing weld on an F91 LWN — the famous rules?
It is made under the strictest discipline in ferritic pressure work — which is precisely why the LWN gives the F91 system only one such weld instead of two. Preheat typically 200-260°C held through welding; controlled interpass; hydrogen-controlled consumables of matching 9Cr-1Mo-V composition, their chemistry managed so the joint tempers properly inside the PWHT band; and PWHT in a narrow window around 745-775°C that must temper the weld without exceeding the base metal's lower transformation temperature. The heat-affected zone carries the grade's known weakness — the soft Type IV zone where cross-weld creep cracks concentrate — so owners qualify procedures carefully and count every joint. Dissimilar connections to austenitic or nickel systems take nickel-based fillers and their own engineering. Field crews treating F91 like ordinary chrome-moly caused the industry's well-documented failures; the rules exist because of them, and WPS guidance travels with every supply.
How are the barrel length and bore of a LWN specified?
Two numbers that belong on every enquiry. Length: measured overall from the flange face to the weld end — 150 mm (6"), 230 mm (9") and 300 mm (12") are the common stock lengths, and any length machines to order; state it explicitly, because 'long' is not a dimension. Bore: the barrel is drilled and bored to order — most commonly to match the inside diameter of the connecting pipe schedule, sometimes cylindrical special bores for level bridles, instrument standpipes or restriction work; state the schedule or the finished bore in millimetres. Add the weld-end preparation (standard 37.5° bevel unless told otherwise) and the nozzle is fully defined.
When does F91 hand off — to F22 below, or beyond the ladder?
Downward by arithmetic: where conditions sit inside the 550°C class, F22 serves with an easier welding regime and a friendlier price, F11 carries the 500°C class below that, and carbon steel takes everything under ~425°C — F91 bought for moderate duty is discipline paid for nothing. Sideways by chemistry: when the enemy is hot sulphur rather than creep, the corrosion staircase answers — plain F9 carries the hottest sour streams on the same 9-chrome skeleton without the CSEF rules. Beyond the ladder: the hottest ultra-supercritical designs push into tungsten-strengthened 9Cr variants, austenitic stainless and nickel-alloy territory — benches this site also stocks. State design temperature, pressure and medium on the enquiry; the staircase and our quotation pick the rung together, and descending honestly is quoted as readily as climbing.
What sizes and pressure classes do F91 LWN flanges come in?
Flange ends follow ASME B16.5 from ½" to 24" NB in Classes 150, 300, 400, 600, 900, 1500 and 2500 — with the full class-by-class LWN dimension charts on this site — and larger diameters forge to order against B16.47 or drawing dimensions, with EN 1092-1 drilling machined on the same barrels. The F91 order book lives where the grade lives: main steam, hot reheat and HRSG high-pressure circuits concentrate in Classes 900-2500, where heavy-barrel patterns and the 9Cr-1Mo-V material group's ratings earn their keep, while instrument and drain connections span the classes below. State size, class, barrel length and bore together — the four numbers define the forging — and our quotation returns price, unit weight and delivery per class.
What details are needed to get an accurate F91 LWN flange quotation?
Seven elements plus commercial terms: (1) size and dimensional standard — e.g. 4" NB ASME B16.5; (2) pressure class — 150 to 2500; (3) facing — RF (the default), FF or RTJ with ring number; (4) barrel length overall, face to weld end — 150/230/300 mm stock or any stated length; (5) barrel bore — pipe schedule to be matched or finished bore in millimetres, with pattern (standard, heavy barrel, equal barrel) and weld-end prep if non-standard; (6) the grade line — ASTM A182 F91, Type 1 (the default) or Type 2 where the specification names it — with the service stated (design temperature and pressure) so the rung is confirmed against F22 below and plain F9 sideways; (7) certification — EN 10204 3.1 with normalize-and-temper furnace charts and hardness results (our standard) or 3.2 witnessed, PMI as applicable. Add quantity and destination; quotations normally within 24 hours.
Who manufactures ASTM A182 F91 long weld neck flanges in India?
Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer based in Mumbai, India, producing ASTM A182 F91 long weld neck flanges with B16.5 flange ends from ½" to 24" NB (larger to order) in Classes 150-2500, in standard, heavy-barrel and equal-barrel patterns — each forged individually from certified heats, normalized and tempered inside the grade's mandatory window with furnace charts attached to the MTC, hardness verified against the 248 HBW ceiling, machined with the barrel bored to the ordered schedule or drawing, bevelled for the closing weld, PMI-checked with the V-Nb signature read on every piece, and marked with grade, type, size, schedule and heat number. Supplied with EN 10204 3.1/3.2 certification and 9Cr WPS guidance — alongside F22 and F11 on the steam staircase, F5 and F9 on the sulphur side, and the complete LWN range. Exported to more than 50 countries.
