Tesco Steel & Engineering manufactures ASTM A182 F5 long weld neck flanges — the hot side of carbon steel's ceiling: 5Cr-1/2Mo alloy steel, UNS K41545 — with ASME B16.5 flange ends in Classes 150–2500 and the barrel made to order. The construction is the LWN's: the flange and the nozzle in one forging, one closing weld at the shell. The chemistry is the mission: nominally 5% chromium against the sulphidation and hydrogen attack of hot refinery hydrocarbon, and molybdenum for creep strength where A105 retires around 425 °C — fired heaters, crude and vacuum units, hydroprocessing-adjacent equipment. The chrome-moly welding discipline is stated plainly below: preheat and PWHT are not optional — 5% chromium air-hardens, and the closing weld at the shell is a chrome-moly weld. Normalized & tempered, hardness certified in the 143–217 HB window; the ladder climbs through F9, F11, F22 and F91. 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 F5 Long Weld Neck Flanges — Specifications at a Glance
What is an ASTM A182 F5 Long Weld Neck Flange?
The refinery's chrome-moly nozzle forging. An ASTM A182 F5 flange (5Cr-1/2Mo, UNS K41545) whose neck continues as a long, heavy-walled straight barrel — the nozzle itself — bevelled for one closing butt weld at the shell or heater header. Cr 4–6% slows hot-sulphur sulphidation by an order of magnitude and resists hydrogen attack; Mo 0.44–0.65% carries creep strength past carbon steel's ~425 °C ceiling. Supplied normalized & tempered, 143–217 HB certified; welded under chrome-moly discipline — preheat and PWHT mandatory. 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: F5 LWN flange, 5 chrome long weld neck flange, chrome-moly nozzle flange, A182 F5 RFLWN, K41545 LWN — all the same product. Related pages: the facings — LWNRF / LWNFF / LWNRTJ — the long weld neck hub, the F5 socketweld on small bore, the ladder — F9 / F11 / F22 / F91 — and the alloy steel hub.
The rule of the two staircases:sulphur severity picks the chromium (F5 → F9); steam creep picks the F11 → F22 → F91 line. Our quotation asks the service before pricing the rung.
What the Chromium and the Molybdenum Buy
Sulphidation Slowed by an Order of Magnitude
Above ~260 °C, sulphur-bearing hydrocarbon steadily wastes bare steel — 5% chromium's film chemistry is the classic refinery answer, from heater tubes to the nozzles that match them.
Hydrogen Attack Resisted
The Nelson curves govern hot hydrogen service — where carbon steel's line is crossed, chromium and molybdenum carbides hold the carbon that hydrogen would strip. Chrome-moly is mandatory there, not optional.
Creep Strength Past the Carbon Ceiling
Molybdenum stiffens the lattice against slow deformation — B16.5's group 5 tables carry F5 ratings deep past A105's ~425 °C practical limit.
Honesty About the Discipline
5% chromium air-hardens: the closing weld demands preheat and PWHT, and schedules that forget the furnace time learn it expensively. The FAQ below states the practice plainly.
Specification Notes — Getting F5 Long Weld Necks Right
Three honest notes.The welding discipline is the price of the chromium: preheat ~200–300 °C, matching B8-class consumables, PWHT at ~675–760 °C — an untreated F5 weld can crack before the fabricator goes home; plan the furnace time with the nozzle count. Below ~425 °C on clean streams, buy carbon steel:A105 serves at a fraction of the cost with none of the overhead — F5's case is sulphur, hydrogen or heat, not habit. And name the staircase: steam-creep duty belongs to F11/F22/F91, hotter sulphur to F9 — state stream, temperature and hydrogen partial pressure and the rung picks itself.
How Our F5 LWN Flanges Are Manufactured
1
Forging — each piece individually forged from the certified F5 heat with the barrel integral — no welded build-ups — in any section up to the heaviest HB patterns.
2
Normalizing & tempering — the full N&T cycle that sets the tough tempered structure; furnace records retained against the heat number.
3
Hardness verification — every lot confirmed inside the 143–217 HB window: the floor proves the heat treatment, the ceiling protects weldability and sour service.
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 confirms the Cr-Mo signature; marked with grade, size, class, schedule and heat number.
6
Certification & packing — EN 10204 3.1 MTC with heat-treatment records (3.2 witnessed on request); chrome-moly WPS guidance included; faces and bevels protected, packed sea-worthy.
Where F5 LWN Flanges Are Used
Chrome-moly country: crude and vacuum unit vessel nozzles, fired-heater and transfer-line adjacent connections, visbreaker and coker services, hydrotreater-adjacent equipment on the sulphur side, hot separator and fractionator bottoms circuits, and the level-bridle and instrument standpipes that ride on all of them. Production and supply below:
Seven elements — the service (stream, temperature, hydrogen) confirms the ladder rung:
1
Size & standard — e.g. 6″ NB ASME B16.5.
2
Pressure class & facing — 150#–2500#; RF (the default), 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 F5 (F5a only if named); stream, temperature and hydrogen partial pressure stated — they confirm F5 against A105 below and F9/F91 above.
6
Certification — EN 10204 3.1 with heat-treatment records (our standard) / 3.2 witnessed; hardness and NACE documentation where applicable.
An ASTM A182 F5 long weld neck flange is a forged 5Cr-1/2Mo alloy steel flange — UNS K41545, the classic refinery chrome-moly — 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 vessel shell or heater header. The chemistry is the mission: nominally 5% chromium resists the sulphidation and hydrogen attack of hot sulphur-bearing hydrocarbon, and the molybdenum carries creep strength where plain carbon steel's ~425°C ceiling ends. Flange ends follow ASME B16.5 in Classes 150 to 2500; the barrel is machined to the ordered length and bore. Fired heaters, crude and vacuum units, and hydroprocessing-adjacent equipment are its home ground — supplied normalized and tempered with the 143-217 HB window certified.
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.
What do the chromium and molybdenum in F5 actually do?
Two elements, two enemies. The chromium — 4.0-6.0%, the grade's name — is corrosion armour for hot hydrocarbon service: it forms the oxide and sulphide-resistant films that slow sulphidation (the steady wastage hot sulphur compounds inflict on bare steel above roughly 260°C) and it resists high-temperature hydrogen attack, the Nelson-curve phenomenon where hydrogen strips carbon out of plain steel from within. The molybdenum — 0.44-0.65% — is the creep element: it stiffens the ferrite lattice against slow deformation, extending useful strength beyond carbon steel's ~425°C practical ceiling. Together they define chrome-moly country: the band of refinery temperature and chemistry where carbon steel wastes away or sags, and where stainless would be overspend. F5 is that country's classic 5-chrome citizen.
Why is F5 the crude-unit and fired-heater grade?
Because crude oil brings sulphur, and heat activates it. From the crude heater onward, refinery streams carry sulphur compounds that above roughly 260°C corrode carbon steel at rates that only rise with temperature — the classic sulphidation curves — while the equipment itself runs hot enough to need creep margin. The industry's long-established answer scales chromium to severity, and 5Cr-1/2Mo became the workhorse rung: enough chromium to slow hot sulphur corrosion by an order of magnitude on heater tubes, transfer lines, and crude and vacuum column bottoms circuits, enough molybdenum for the temperature, and a price that lets whole units be built from it. F5 LWN nozzles put that metallurgy exactly where vessels and heaters need penetrations — matching the shell and tube chemistry so the nozzle is never the corrosion weak point.
What is the chemical composition of ASTM A182 F5 — and what is F5a?
Carbon ≤0.15%, manganese 0.30-0.60%, silicon ≤0.50%, phosphorus ≤0.030%, sulphur ≤0.030%, chromium 4.0-6.0%, molybdenum 0.44-0.65%, nickel ≤0.50% residual. Note the discipline relative to the carbon grades: lower carbon, a low manganese window and tighter P/S — chrome-moly is built for heat, and cleanliness serves its long-life creep duty. F5a is the same 5-chrome chemistry with carbon allowed to 0.25%, buying a higher strength class at the cost of harder welds and lower toughness; it is ordered where a design specifically calls its strength, which is rare in nozzle work — unless your specification names F5a, F5 is the standard supply and what this page describes. Chemistry is verified per heat and travels on the EN 10204 3.1 MTC.
What are the mechanical properties of F5 long weld neck flanges?
Normalized and tempered: tensile strength 485 MPa (70 ksi) minimum, yield strength 275 MPa (40 ksi) minimum, elongation 20% minimum — and a hardness window of 143-217 HB whose both ends mean something. The floor certifies the heat treatment actually happened: soft, under-transformed material fails it. The ceiling protects weldability and service: chrome-moly that arrives too hard cracks in welding and misbehaves in sour and hydrogen duty. The 275 MPa yield outruns A105's 250, and B16.5's group 5 pressure-temperature tables carry F5 ratings deep past carbon steel's — the flange rating extending honestly toward 590°C class territory, with creep governance and the usual two-ceilings reality: the gasket and bolting retire the hot joint before the metal does.
Why do F5 welds demand preheat and PWHT — the chrome-moly discipline?
Because 5% chromium makes the steel air-hardening: cooling from welding temperatures, the heat-affected zone transforms to hard, brittle martensite all by itself — no quench needed — and an untreated joint can crack before the fabricator goes home. The discipline is therefore not optional: preheat around 200-300°C before and during welding slows the cooling and lets hydrogen escape; matching 5Cr-1/2Mo consumables (B8-class electrodes) keep the deposit's chemistry honest; and post-weld heat treatment at roughly 675-760°C tempers the fresh martensite back to tough, stable metal. This is the single biggest practical difference from the A105 world, and it belongs in every plan that touches an F5 nozzle: the closing weld at the shell is a chrome-moly weld, and schedules that forget the PWHT furnace time learn it expensively. Our 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.
What are standard, heavy-barrel and equal-barrel LWN flanges?
Three barrel weights for three duties. The standard LWN carries a barrel a little heavier than the matching pipe — the general-purpose vessel nozzle. The heavy-barrel (HB) pattern thickens the wall substantially — often approaching the hub section for its full length — for high-pressure nozzles, heavy nozzle loads and reinforcement-limited openings, where the extra metal does the area-replacement work the code asks of a vessel opening; hydroprocessing-adjacent equipment uses it freely. The equal-barrel pattern keeps the barrel outside diameter equal to the hub for a clean cylindrical profile — favoured on manway and instrument connections. All three share B16.5 flange ends; the design calculation or the equipment drawing decides which is wanted.
Where does F5 sit on the chrome-moly ladder — F9, F11, F22, F91?
The ladder climbs two staircases at once, and knowing which one you are on picks the grade. The corrosion staircase scales chromium to sulphur severity: F5 (5Cr) is the refinery workhorse; F9 (9Cr-1Mo) doubles the chromium for hotter, more sulphurous streams. The creep staircase serves steam and clean heat: F11 (1¼Cr-½Mo) and F22 (2¼Cr-1Mo) are the power-plant classics, chosen for strength-at-temperature rather than sulphur; and F91 — 9Cr-1Mo modified with vanadium and niobium — is the modern creep-strength-enhanced grade that rules high-energy steam piping, with welding discipline stricter still. All have their own LWN pages here. The honest rule: sulphur severity picks the chromium; steam creep picks the F11/F22/F91 line; and our quotation asks the service before pricing the rung.
When does carbon steel suffice instead of F5?
More often than a chrome-moly page likes to admit, and honesty draws three boundaries. Temperature: clean, low-sulphur duty below roughly 425°C is carbon steel country — A105 nozzles serve at a fraction of the cost, with none of the preheat-and-PWHT overhead. Sulphur: the sulphidation curves that force chromium switch on with hot, sulphur-bearing hydrocarbon; cold sour service is a hardness question, not a chromium one, and carbon steel handles it under NACE rules. Hydrogen: high-temperature hydrogen partial pressure is governed by the Nelson curves — where operating conditions sit above carbon steel's line, chrome-moly is mandatory, not optional. State the stream, temperature and hydrogen partial pressure on the enquiry; the A105 page and this one bracket the decision, and our quotation names the honest side.
What sizes and pressure classes do F5 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 F5 order book reads like a refinery: Class 150/300 heater-adjacent and transfer-line connections, Class 300-600 crude and vacuum unit nozzles, and heavy-barrel patterns where hydroprocessing pressures climb. 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 F5 LWN flange quotation?
Seven elements plus commercial terms: (1) size and dimensional standard — e.g. 6" 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 F5 (F5a only if your specification names it) — with the service stated (stream, temperature, hydrogen) so the ladder rung is confirmed; (7) certification — EN 10204 3.1 with heat-treatment records (our standard) or 3.2 witnessed, hardness and NACE documentation where applicable. Add quantity and destination; quotations normally within 24 hours.
Who manufactures ASTM A182 F5 long weld neck flanges in India?
Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer based in Mumbai, India, producing ASTM A182 F5 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 with furnace records, hardness verified inside the 143-217 HB window, machined with the barrel bored to the ordered schedule or drawing, bevelled for the closing weld, and marked with grade, size, class, schedule and heat number. Supplied with EN 10204 3.1/3.2 certification and chrome-moly WPS guidance — alongside the F9, F11, F22 and F91 ladder, the A105 and LF2 carbon pair, and the complete LWN range. Exported to more than 50 countries.
