Tesco Steel & Engineering manufactures ASTM A182 F5 lap joint flanges — the chrome-moly staircase's corrosion rung (UNS K41545, W.Nr. 1.7362) at the lap joint bench: 4–6% chromium bought for sulphidation resistance on hot sour circuits and hydrogen service per the Nelson curves, with molybdenum holding creep strength where plain carbon steel fades. The pattern gives this grade two twists. First, the hot mirror of the LF2 page's ambient argument: the backing flange never gets wet, but clamped against the lap it runs at line metal temperature — so the ring must be F5, not A105. Second, the quiet gift: the flange never welds, so it dodges the chrome-moly preheat/PWHT discipline entirely — the joint's single butt weld belongs to the matched A234 WP5 stub end per B16.9. Per ASME B16.5, ½″–24″ NB, Classes 150–2500, annealed or N&T, hardness held in the 143–217 HB band. Every lot with EN 10204 3.1/3.2 MTC. ISO 9001:2015, made in Mumbai, India — exported to 50+ countries.
ASTM A182 F5 · UNS K41545 · W.Nr. 1.73625Cr-½Mo — The Corrosion RungSulphidation + Hydrogen DutyThe Flange That Dodges the Weld ProcedureStub Ends: A234 WP5 per B16.9½″–24″ NB · Classes 150–2500Pairs Certified TogetherEN 10204 3.1 / 3.2 · ISO 9001:2015
ASTM A182 F5 Lap Joint Flanges — Specifications at a Glance
What is an ASTM A182 F5 Lap Joint Flange?
The chrome-moly backing flange. An ASTM A182 F5 lap joint flange is the loose backing ring of the two-piece system in 5Cr-½Mo alloy steel (UNS K41545) — chromium at 4–6% for sulphidation and hydrogen duty per the Nelson curves, molybdenum for creep strength where carbon steel fades. The point on this pattern: the flange never touches the process, but it runs at line metal temperature — and it never welds, so it escapes the preheat/PWHT discipline that governs every other F5 flange type. Per ASME B16.5, ½″–24″ NB, Classes 150–2500, annealed or N&T, 143–217 HB; stub ends A234 WP5 per B16.9. EN 10204 3.1 on every lot.
Also searched as: F5 backing flange, 5Cr lap joint flange, chrome moly lap joint flange, A182 F5 LJ flange, 5 chrome loose flange — all this page's product. Related pages: the lap joint hub (the pattern's full story), the carbon twins — A105 warm and LF2 cold — the staircase neighbours F9 and F22, the F5 bench — weld neck / blind / long weld neck — and the alloy steel overview.
The Metal-Temperature Argument — Why the Never-Wetted Flange Is Still Chrome-Moly
F5 — the flange runs at line metal temperature through the lap it clamps
The rule, stated as this page's mirror of the cold one: on the LF2 page the cold reaches the never-wetted flange through the site's air; here the heat reaches it through the metal it clamps — and above roughly 425 °C, plain carbon steel's ratings carry the graphitisation caveat and fade fast, while F5's molybdenum holds creep strength and its chromium shrugs off the scale.
The vanadium-modified creep grade — power-plant steam's modern answer
The honest advice runs both ways: sulphur-driven refinery circuits climb from F22 to F5 for the chromium, not the strength — while services that only need creep resistance often stop lower on the staircase and save. Descending honestly is engineering too.
What the Pattern Gives This Grade
The Weld-Procedure Dodge
The backing flange never welds — no preheat, no PWHT, no procedure to qualify or reopen on the ring itself. The chrome-moly discipline concentrates on the joint's single butt weld, which belongs entirely to the stub end.
The Corrosion Rung's Chromium
4–6% chromium is a corrosion purchase — a tenacious scale against sulphidation on hot sour circuits, and a stronger position on the Nelson curves for hydrogen service, where the lower rungs buy mostly strength.
Strength Where Carbon Steel Fades
The 0.44–0.65% molybdenum window is the creep dial — holding usable strength at temperatures where plain carbon steel's rating tables carry caveats and its microstructure starts to drift.
The Turnaround Franchise
Loose flanges align by rotation — on refinery circuits that dismantle at every turnaround, bolt holes line up without pipe-twisting, spools rotate to distribute wear, and re-assembly never reopens a weld procedure.
Specification Notes — Getting F5 Lap Joints Right
Three honest notes.F5a is not F5: the higher-carbon variant (0.25% against 0.15%) is a separately certified grade with its own strength class and stricter welding — enquiries that say '5 chrome' or 'F5/F5a' get a question back before a price. The dodge covers the flange, not the joint: the stub end's butt weld takes the full chrome-moly discipline — qualified procedure, preheat, PWHT — every time. And the pattern's boundaries apply in any grade: heavy external loads, severe vibration and high-moment positions read the weld neck bench — most chrome-moly joints are weld necks, and lap joints earn their place where hot lines dismantle; the hub page states the boundaries fully.
How Our F5 Lap Joint Flanges Are Manufactured
1
Material — certified A182 F5 forgings, annealed or normalised and tempered with the condition stated and furnace records retained; heat-number transfer at the first operation.
2
Machining — B16.5 lap joint dimensions: OD, thickness, bolt circle to class; bore and shoulder turned to suit the stub end's lap.
3
Shoulder dressing — the radius dressed to bear evenly on the back of the lap — spreading bolt load instead of concentrating it.
4
Testing — hardness verified against the 143–217 HB band — floor and ceiling both — the quickest check that the heat treatment went right; chemistry and mechanicals certified per heat.
5
No welding, ever — the ring's whole career is mechanical: no weld, no preheat, no PWHT — the pattern's gift on an air-hardening grade.
6
Pairing & certification — matched to A234 WP5 stub ends where ordered; one EN 10204 3.1 document per pair (3.2 witnessed on request); packed sea-worthy with laps and shoulders protected.
Where F5 Lap Joint Flanges Are Used
Where the heat, the sulphur and the pattern meet: refinery process units — crude and vacuum unit hot circuits, hydrotreater and hydroprocessing loops, sulphur-handling and sour-gas lines — and specifically the positions that earn a lap joint: heater and reactor circuits that dismantle at every turnaround, hot transfer-line spools rotated to distribute erosion, and strainer or exchanger connections opened on schedule, where a never-welded flange means re-assembly without a weld procedure. Production and supply below:
Example: “Lap Joint Flange, 4″ NB, ASME B16.5 Class 300, ASTM A182 F5, with A234 WP5 stub ends Sch 80 (B16.9 Type A, supplied together), pairs on one MTC, EN 10204 3.1 — 12 sets.” Quotations normally within 24 hours with price, unit weights (both parts) and delivery.
F5 Lap Joint Flanges — Frequently Asked Questions
What is an ASTM A182 F5 lap joint flange?
An ASTM A182 F5 lap joint flange is the loose backing flange of the two-piece lap joint system, forged in 5Cr-½Mo alloy steel (UNS K41545) — the chrome-moly grade whose 4-6% chromium buys sulphidation resistance on hot sour hydrocarbon circuits and hydrogen service per the Nelson curves, with molybdenum holding strength where plain carbon steel fades. Like every lap joint flange it slides over the pipe, sits free behind the stub end's flared lap, and carries the entire bolt load without touching the line fluid. The grade's point on this pattern is thermal, not chemical: the backing flange never sees the process, but clamped hard against the lap it runs at essentially the line's metal temperature — and on a chrome-moly circuit that temperature is beyond what plain carbon steel should carry. Manufactured per ASME B16.5 in ½" to 24" NB, Classes 150 to 2500, annealed or normalised and tempered, with EN 10204 3.1/3.2 certification on every lot.
How does the two-piece lap joint system work?
By splitting sealing from bolting. The stub end butt-welds to the pipe: its flared lap provides the gasket face and does all the fluid contact. The backing flange never welds and never wets: it slides on before the stub end is welded — the classic site lesson — spins freely until the bolts enter, and transmits bolt load through its radiused shoulder onto the back of the lap. Two consequences follow on this grade. First, the flange's material follows its own duty — here temperature, which is why the ring is F5 rather than plain carbon steel. Second, and particular to chrome-moly: the flange never welds, so it never enters the weld procedure — no preheat, no PWHT on the ring itself; the joint's single butt weld belongs to the stub end. The full pattern story — stub end types, the alloy economy, the honest boundaries — is on the lap joint hub page.
Why must the never-wetted backing flange still be F5 — the metal-temperature argument?
Because the backing flange gets hot even though it never gets wet. This page is the mirror of the LF2 lap joint page's ambient argument: there, the cold reaches the flange through the site's air; here, the heat reaches it through the metal it clamps. A backing flange bolted hard against the lap of a 450°C chrome-moly line runs at essentially that temperature, and plain A105 is not the steel for it — above roughly 425°C carbon steel's ratings carry the graphitisation caveat and its strength falls away fast, while F5's molybdenum holds creep strength and its chromium shrugs off the scale. So the lap joint economy is narrower on hot circuits than on corrosive cold ones: the flange can still be a simpler grade than a solid exotic alloy, but it cannot drop below the temperature class of the service. F5 backing F5 is the normal answer, and the certificate proves both halves.
What is the chemical composition of ASTM A182 F5?
Carbon ≤0.15%, manganese 0.30-0.60%, silicon ≤0.50%, chromium 4.0-6.0%, molybdenum 0.44-0.65%, nickel ≤0.50%, phosphorus ≤0.030%, sulphur ≤0.030%. The 4-6% chromium band is the identity: enough to form a tenacious chromium-rich scale against sulphidation on hot sour circuits, and enough to blunt hydrogen attack per the Nelson curves — a corrosion purchase, where the lower chrome-moly grades buy mostly strength. The molybdenum, in its oddly precise 0.44-0.65% window, is the creep-strength dial. And note the carbon ceiling of 0.15%: the related grade F5a allows up to 0.25% carbon for higher strength, and the two are not interchangeable on a certificate — an enquiry that says only '5 chrome' gets a question back before it gets a price. Chemistry is verified per heat and travels on the EN 10204 3.1 MTC.
What are the mechanical properties of F5 lap joint flanges?
In the annealed or normalised-and-tempered condition A182 requires tensile strength 485 MPa (70 ksi) minimum, yield strength 275 MPa (40 ksi) minimum and elongation 20% minimum, with hardness controlled in the 143-217 HB band. Two details reward reading. The hardness band has a floor as well as a ceiling — 143 HB guards against an over-soft anneal just as 217 HB guards against a hard, crack-prone one, because in chrome-moly steels hardness is the quickest proxy for whether the heat treatment went right. And for the backing-flange duty the room-temperature numbers are only the entry ticket: the grade is bought for what happens at temperature, where molybdenum holds creep strength long after plain carbon steel has faded — the B16.5 rating tables for the grade's material group carry usable pressures deep into the range where carbon steel's tables carry caveats. Supplied with the heat-treatment condition stated and records retained.
What is the difference between F5 and F5a?
One digit of carbon and a different job. F5 caps carbon at 0.15% and is the standard forging grade for flanges on 5-chrome service — moderate strength, good weldability by chrome-moly standards, the grade this page supplies. F5a raises the carbon window to 0.25% maximum, buying a higher strength class at the cost of harder welds and stricter preheat — it is a deliberate, separately certified choice, not a substitute. The trap is commercial shorthand: enquiries that say '5 chrome', 'Grade 5' or 'F5/F5a' as if the pair were one grade. They are not interchangeable on a certificate, a weld procedure qualified for one does not automatically cover the other, and a backing flange certified F5a against an order that said F5 is a document problem even where the metal would serve. State the grade exactly; where a project genuinely wants F5a, we quote it separately with its own paperwork.
What stub ends pair with F5 lap joint flanges?
The matching stub end is wrought 5Cr-½Mo per ASME B16.9 in ASTM A234 WP5 — the fitting grade that pairs with F5 forgings exactly as A234 WPB pairs with A105 and A420 WPL6 with LF2, sharing the chemistry philosophy and welded to the pipe with the line's qualified chrome-moly procedure, preheat and PWHT included. That butt weld is the joint's only weld, and it belongs entirely to the stub end: the backing flange never enters the procedure. The matching rules are the pattern's usual dimensional ones — lap OD to the flange's shoulder, schedule to the line bore — plus this grade's documentary one: flange and stub end bought as a matched pair and certified together on one EN 10204 document, so the '5 chrome both halves' answer is provable at handover. Where an order needs B16.9 Type A or Type B lap details, state it and the pair is machined to suit.
Does an F5 backing flange need preheat and PWHT?
No — and that is one of the pattern's quiet gifts on chrome-moly duty. Air-hardening 5-chrome steel is demanding to weld: qualified procedures, preheat typically in the 150-260°C region, controlled interpass, and post-weld heat treatment per the code — discipline that every welded F5 flange type inherits. The lap joint backing flange inherits none of it, because it is never welded to anything: it slides over the pipe, floats behind the lap, and does its whole job mechanically. The discipline concentrates instead on the joint's single butt weld — stub end to pipe, A234 WP5 to the line, welded once under full chrome-moly control. On a turnaround this matters twice: fewer alloy welds to make and test in the first place, and a flange that can be swapped, rotated or re-used without any weld procedure being reopened. The dodge covers the flange, not the joint — the stub end's weld takes the full discipline, always.
Where does F5 sit on the chrome-moly staircase?
In the middle, and it is the corrosion rung. The staircase climbs by chromium: F11 at 1¼% and F22 at 2¼% are bought mostly for creep strength in steam and hot hydrogen; F5 jumps to 4-6% chromium, and the jump is a corrosion purchase — sulphidation resistance on hot sour hydrocarbon circuits and a stronger position on the Nelson curves — while its ½ Mo holds respectable creep strength; F9 doubles the chromium to 9% for hotter, sourer duty; and F91, the vanadium-modified 9-chrome, adds the creep strength of a different era for power-plant steam. Every rung has a lap joint page on this site, and the honest advice runs both ways: sulphur-driven refinery circuits climb from F22 to F5 for the chromium, not the strength, while services that only need creep resistance often stop lower and save. State the service and the rung picks itself.
What sizes and pressure classes do F5 lap joint flanges come in?
½" to 24" NB per ASME B16.5 in Classes 150, 300, 400, 600, 900, 1500 and 2500, with larger diameters machined to B16.47 or drawing — the full class-by-class lap joint dimension charts are on this site. The order book mirrors the grade's habitat: refinery process units concentrate in Classes 150 to 600 at mid bore, with Classes 900 and 1500 appearing on hydroprocessing circuits where pressure climbs alongside temperature. Dimensionally an F5 lap joint flange is identical to any other grade's — B16.5 governs by class, not by material — so the charts serve every grade on the bench; what changes is the rating table behind the class, where the grade's material group carries usable pressures at temperatures that retire carbon steel. State size, class and the stub-end question together, and our quotation returns price, unit weight and delivery per class.
How much does an F5 lap joint flange weigh?
Exactly what the same-size lap joint flange weighs in any other steel — B16.5 fixes the dimensions by class, and alloy density differences are negligible. Representative Class 150 figures for the flange alone: 1" roughly 0.8 kg, 2" roughly 2 kg, 4" roughly 5.5 kg, 8" roughly 14 kg, climbing steeply with class; the A234 WP5 stub end adds its schedule-dependent mass. The commercial difference sits in the metallurgy and the paperwork: F5 carries alloy surcharge, controlled heat treatment and per-lot testing in its price, and the matched stub end carries the chrome-moly weld-end preparation in its own. Our quotations state unit and consignment weights per line item, flange and stub end separately, and the site's flange weight chart carries the full reference tables.
How are your F5 lap joint flanges manufactured?
As the pattern's standard sequence with chrome-moly discipline at the heat-treatment step. Certified A182 F5 forgings are supplied annealed or normalised and tempered — the condition stated on the certificate, with furnace records retained — then machined to B16.5's lap joint dimensions: OD, thickness and bolt circle to class, bore and shoulder turned to suit the stub end's lap, and the shoulder radius dressed to bear evenly on the back of the lap. Hardness is verified against the 143-217 HB band — floor and ceiling both — as the quickest check that the heat treatment went right; chemistry and mechanicals are certified per heat; heat-number marking transfers at the first operation. No welding is performed on the flange at any stage — the ring's whole career is mechanical. Where the order includes A234 WP5 stub ends, the pair is dimensionally matched and certified together on one EN 10204 3.1 document (3.2 witnessed on request). Packed sea-worthy with laps and shoulders protected.
What details are needed to get an accurate F5 lap joint 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) the grade stated exactly — F5, not '5 chrome' or 'F5/F5a', per the certificate trap this page describes; (4) the stub end — A234 WP5 matched pair with schedule and B16.9 type, or 'flange only'; (5) the service temperature where it helps — it confirms the rung on the chrome-moly staircase and flags whether F9 or F91 should be quoted instead; (6) certification — EN 10204 3.1 (our standard) or 3.2 witnessed, pairs certified together on one document; (7) quantity as pairs or pieces, and destination. Quotations normally return within 24 hours with price, unit weights for both parts, and delivery.
Who manufactures ASTM A182 F5 lap joint flanges in India?
Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer based in Mumbai, India, producing ASTM A182 F5 lap joint (lapped joint) flanges per ASME B16.5 from ½" to 24" NB (larger to B16.47 or drawing) in Classes 150-2500 — each machined from certified 5Cr-½Mo forgings in the annealed or normalised-and-tempered condition, hardness-verified in the 143-217 HB band, with the shoulder dressed to bear evenly on the lap, heat-number marked, and certified to EN 10204 3.1/3.2. Matched A234 WP5 stub ends per B16.9 are supplied against the same order, pairs certified together on one document. Alongside the complete A182 F5 range — weld neck, slip-on, socket weld, threaded, blind, spectacle blind and long weld neck — the full chrome-moly staircase in every flange type, and the complete lap joint grade bench. Exported to more than 50 countries.
