Tesco Steel & Engineering manufactures ASTM A350 LF2 lap joint flanges — the impact-tested cousin for the cold sites, defined by one line: Charpy 20 J average at −46 °C, Class 1, tested per heat-treatment lot. The lap joint twist on the grade is the page's whole argument: the backing flange never touches the process — but it lives at ambient, and on an LNG jetty or arctic station, ambient is exactly what the Charpy test proves. So the pattern's famous economy still works on cold sites — a stainless or LTCS line still takes a carbon-steel backing flange — but the cheap half must be LF2, not A105. The chemistry is A105's family with the toughness dials turned: carbon trimmed, manganese raised, and the tensile capped in a 485–655 MPa window because over-strong is over-brittle. Matched stub ends follow the same philosophy: A420 WPL6 per B16.9 for LTCS lines, pairs certified together with the impact results on the document. Per ASME B16.5, ½″–24″ NB, Classes 150–2500; plain, primed or galvanised for the cold marine deck. Every lot with EN 10204 3.1/3.2 MTC. ISO 9001:2015, made in Mumbai, India — exported to 50+ countries.
ASTM A350 LF2 Class 1 · NormalisedCharpy 20 J @ −46 °C — Per LotThe Backing Flange That Lives in the ColdTensile 485–655 MPa — A Window, Not a FloorStub Ends: A420 WPL6 per B16.9½″–24″ NB · Classes 150–2500Pairs Certified TogetherEN 10204 3.1 / 3.2 · ISO 9001:2015
ASTM A350 LF2 Lap Joint Flanges — Specifications at a Glance
What is an ASTM A350 LF2 Lap Joint Flange?
The impact-tested backing flange. An ASTM A350 LF2 lap joint flange is the loose backing ring of the two-piece system in impact-tested low-temperature carbon steel: Charpy 20 J at −46 °C, Class 1, per heat-treatment lot. The point on this pattern: the flange never touches the process, but it lives at ambient — and on cold sites, ambient is the test temperature. So cold lines keep the alloy economy, with LF2 as the cheap half instead of A105. Per ASME B16.5, ½″–24″ NB, Classes 150–2500, normalised; stub ends A420 WPL6 per B16.9. EN 10204 3.1 with impact results.
Also searched as: LF2 backing flange, LTCS lap joint flange, low-temp loose flange, A350 LF2 LJ flange, impact-tested backing ring — all this page's product. Related pages: the warm-site twin — A105 lap joint — the lap joint hub (the pattern's full story), the LF2 bench — weld neck / blind / long weld neck / spectacle blind — and the LTCS overview.
The Ambient Argument — Why the Never-Wetted Flange Still Needs Charpy
LF2 (this page) — the flange itself sits at −46 °C ambient and chill
The rule cold-service specifications write explicitly: temperature is not chemistry — the backing flange gets cold even though it never gets wet, and a brittle ring under full bolt load is exactly the failure the impact test exists to prevent.
What the Charpy Line Buys
Toughness, Proven Per Lot
20 J average at −46 °C on every heat-treatment lot — not trusted on chemistry, tested on specimens: the certificate matters as much as the grade name.
The Tuned Chemistry
Carbon trimmed to 0.30, manganese raised to 1.35 — the two dials that lower the brittle transition, on the same honest carbon-steel family as A105.
The Tensile Window
485–655 MPa with a deliberate ceiling — over-strong carbon steel is over-brittle carbon steel, and the cap protects the toughness the grade is bought for.
The Cold Economy
The alloy economy survives the cold — stainless and LTCS lines still take carbon-steel backing at a fraction of solid-alloy cost, with LF2 keeping the cheap half honest.
Specification Notes — Getting LF2 Lap Joints Right
Three honest notes.Normalised is part of the grade: the toughness depends on the heat treatment — un-normalised LF2 is not LF2, and our furnace records travel with the certificate. −46 °C is Class 1's floor: colder duties read the higher A350 grades (LF3 and beyond) — state the design minimum temperature and the grade conversation is short. And the pattern's boundaries apply in any grade: heavy external loads, severe vibration and high-moment positions read the weld neck bench — the hub page states them fully.
How Our LF2 Lap Joint Flanges Are Manufactured
1
Material — certified A350 LF2 forgings, normalised with 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
Impact testing — Charpy specimens per heat-treatment lot, broken at −46 °C, results recorded on the certificate; hardness checked against the 197 HB cap.
5
Finish — plain (oiled), primed, or hot-dip galvanised with bores cleared — the cold marine deck's standard.
6
Pairing & certification — matched to A420 WPL6 or stainless stub ends where ordered; one EN 10204 3.1 document per pair, impact values included (3.2 witnessed on request); packed sea-worthy.
Where LF2 Lap Joint Flanges Are Used
Where the cold and the pattern meet: LNG terminals and jetties — backing flanges behind stainless and LTCS stub ends on loading systems that dismantle — arctic and cold-climate gas processing, refrigerated storage and process systems, cold-country outdoor pipe racks where even utility lines face the ambient argument, and the marine cold where the galvanised LF2 backing ring is the collar tradition's winter dress. Production and supply below:
Backing Flanges — Production Batch at Our WorksThe Two-Piece System — Flange, Stub End, Butt Weld, PipeCarbon Steel Lap Joint Flanges — The Certificate Tells LF2 From A105
LF2 Lap Joint Flange Dimensions
Flange dimensions are class-governed per ASME B16.5 — identical to A105's; stub ends per B16.9. Full class-by-class charts:
Example: “Lap Joint Flange, 4″ NB, ASME B16.5 Class 150, ASTM A350 LF2 Class 1 hot-dip galvanised, to back 316L Sch 40S stub ends (B16.9 Type A long, supplied together), design min. temp −42 °C, pairs on one MTC with Charpy values, EN 10204 3.1 — 16 sets.” Quotations normally within 24 hours with price, unit weights (both parts) and delivery.
LF2 Lap Joint Flanges — Frequently Asked Questions
What is an ASTM A350 LF2 lap joint flange?
An ASTM A350 LF2 lap joint flange is the loose backing flange of the two-piece lap joint system, machined in impact-tested low-temperature carbon steel — the grade whose defining line is a Charpy V-notch requirement of 20 J average at −46°C (Class 1). 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 subtle and real: the backing flange never sees the process, but it lives at ambient temperature — and on arctic, LNG and cold-climate sites, ambient is exactly what the Charpy test proves. Manufactured per ASME B16.5 in ½" to 24" NB, Classes 150 to 2500, normalised, supplied plain, primed or galvanised, with EN 10204 3.1/3.2 certification carrying the impact results 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. The two virtues follow: bolt holes always align, and the flange's material follows its own duty rather than the line's chemistry. On this page that duty is temperature: the LF2 flange backs LTCS and cold-service stainless lines where the steel that carries the bolts must stay tough at the site's own ambient, exactly as the next FAQ argues. The full pattern story — stub end types, the alloy economy, the honest boundaries — is on the lap joint hub page.
Why LF2 and not A105 behind a cold line — the ambient argument?
Because the backing flange gets cold even though it never gets wet. The lap joint pattern's famous economy says the flange can be cheaper than the line — and on a warm site that cheaper grade is plain A105. But temperature is not chemistry: a backing flange on an LNG jetty, an arctic pipeline station or a cold-climate gas plant sits at the site's ambient and at the line's chill through the metal it clamps, and plain A105 carries no toughness guarantee below its transition — a brittle flange under full bolt load is exactly the failure the impact test exists to prevent. So the cold-service rule is simple: the alloy economy still works — a stainless or LTCS line still takes a carbon-steel backing flange — but the cheap half must be LF2, Charpy-proven at −46°C, not A105. Piping specifications for cold service write this rule explicitly; this page exists because of it.
What is the chemical composition of ASTM A350 LF2?
Carbon ≤0.30%, manganese 0.60-1.35%, silicon 0.15-0.30%, phosphorus ≤0.035% and sulphur ≤0.040%, with residual caps of copper ≤0.40%, nickel ≤0.40%, chromium ≤0.30%, molybdenum ≤0.12% and vanadium ≤0.08%. Read it against A105 and the toughness tuning shows: carbon trimmed from 0.35 to 0.30 (carbon raises the brittle transition), manganese allowed up to 1.35 against A105's 1.05 (manganese lowers it), silicon in a tighter killed-steel window. Nothing here is exotic — it is the same honest carbon steel family, tuned by two dials toward low-temperature toughness and then proven by the Charpy test rather than trusted on chemistry alone. Chemistry is verified per heat and travels on the EN 10204 3.1 MTC beside the impact results.
What are the mechanical properties of LF2 lap joint flanges?
Tensile strength 485-655 MPa (70-95 ksi) — a window, not just a floor: the ceiling exists because over-strong carbon steel is over-brittle carbon steel, and capping the tensile protects the toughness the grade is bought for. Yield strength 250 MPa (36 ksi) minimum, elongation 22% minimum, hardness capped at 197 HB. For the backing-flange duty the numbers are generous exactly as A105's are — the flange works in bolting and bending, and the B16.5 class tables govern the joint's rating (LF2 shares A105's material group, so the pressure-temperature curves are identical on the warm side). What LF2 adds is the cold side: where A105's curves simply stop being trusted below −29°C, LF2 carries the joint to −46°C with the impact certificate to prove it. Supplied normalised — the heat treatment the toughness depends on — with records retained.
What does the Charpy requirement actually say?
Charpy V-notch impact energy of 20 joules average (three specimens, with the specification's minimum-single-value rule) at −46°C, for LF2 Class 1 — the grade's defining line and the whole reason it exists. The test takes notched bars from material representing the heat and heat-treatment lot, chills them to the test temperature, and breaks them in a pendulum machine: the energy absorbed measures the steel's resistance to brittle fracture at exactly the temperature where carbon steels turn treacherous. The practical consequences for purchasers: the impact test is per heat-treatment lot, so the certificate matters as much as the grade name; the normalised condition is part of the deal — un-normalised LF2 is not LF2; and the −46°C figure sets the grade's service floor in the piping codes' impact-exemption logic. Our certificates carry the Charpy values alongside chemistry and mechanicals on every lot.
What stub ends pair with LF2 lap joint flanges?
For LTCS lines, the matching stub end is wrought low-temperature carbon steel per ASME B16.9 in ASTM A420 WPL6 — the fitting grade that pairs with LF2 forgings exactly as A234 WPB pairs with A105, sharing the impact-tested, normalised philosophy and welded with the line's qualified LTCS procedure. For cold-service stainless lines, the stub end follows the fluid — 304L and 316L are cryogenically tough by nature — with this page's LF2 flange as the backing whose toughness matches the site, per the ambient argument. The matching rules are the pattern's usual dimensional ones: lap OD to flange shoulder, schedule to line bore, and flange and stub end bought as a matched pair, certified together on one document — with the LF2 side's Charpy results and the stub end's own certification both on the record.
What is the difference between LF2 and A105 lap joint flanges?
One test and two tuned dials. The chemistry is the same honest carbon-steel family with carbon trimmed and manganese raised; the flange dimensions, classes and warm-side ratings are identical (the two grades share a B16.5 material group); the finishes and the pattern's mechanics are the same. What separates them is the Charpy line: LF2 proves 20 J at −46°C on every heat-treatment lot, and A105 proves nothing below ambient. The decision rule follows service temperature, not process contact: on warm sites A105 backs everything and costs less; on cold sites — LNG, arctic, refrigerated systems, cold-climate outdoor racks — the backing flange itself needs the toughness, and LF2 is the specification's answer. Both pages of the pair link each other, and where a project runs both climates, the two grades are quoted side by side with the certificates telling them apart.
What finishes are available on LF2 backing flanges?
The same three as the A105 page, chosen by the atmosphere the flange lives in — which on this grade's sites is usually harsh. Plain (oiled) for indoor and painted systems; primed for the site's coating system; and hot-dip galvanised for the marine and offshore cold — the LNG jetty and northern platform habitat where LF2 backing flanges most often serve, frequently behind stainless or cupronickel stub ends in the collar tradition. The cold-service note on galvanising: the zinc coating itself is unaffected by low temperature, and the practice is standard on cold marine sites; bores are cleared of excess zinc after dipping, and where a specification restricts zinc near stainless welding, the primed finish substitutes. State the finish on every enquiry alongside the stub-end question — the two lines together define the order.
What sizes and pressure classes do LF2 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: cold-climate gas processing, LNG terminals and refrigerated systems concentrate in Classes 150 and 300 at small and mid bore, with Class 600 appearing on higher-rated cold gas duty. The B16.5 ratings are A105's on the warm side — the shared material group — with the cold-side service floor at −46°C carried by the impact certificate rather than the rating tables. State size, class, finish and the stub-end question together, and our quotation returns price, unit weight and delivery per class with the Charpy documentation noted.
How much does an LF2 lap joint flange weigh?
Exactly what the same-size A105 lap joint flange weighs — the two grades share dimensions, and density does not change with toughness. 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 A420 WPL6 stub end adds its schedule-dependent mass. The commercial difference sits in the certificate, not the kilograms: LF2 carries the normalising heat treatment and the per-lot Charpy testing in its price, a modest premium that buys the −46°C service floor. 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 LF2 lap joint flanges manufactured?
As the A105 pattern with the cold-service discipline added. Certified LF2 forgings are normalised — the heat treatment the toughness depends on, with furnace records retained — then machined to B16.5's lap joint dimensions: OD, thickness, bolt circle to class, bore and shoulder turned to suit the lap, and the shoulder radius dressed to bear evenly on the back of the lap. Charpy specimens representing each heat-treatment lot are tested at −46°C and the results recorded; hardness is checked against the 197 HB cap; heat-number marking transfers at the first operation. The finish — plain, primed or hot-dip galvanised — is applied to order, and where the order includes A420 WPL6 or stainless stub ends, the pair is dimensionally matched and certified together on one EN 10204 3.1 document (3.2 witnessed on request), impact values included. Packed sea-worthy with faces and laps protected.
What details are needed to get an accurate LF2 lap joint flange quotation?
Seven elements plus commercial terms: (1) size and dimensional standard — e.g. 3" NB ASME B16.5; (2) pressure class — 150 to 2500; (3) finish — plain, primed or hot-dip galvanised, per the site's atmosphere; (4) the stub end — A420 WPL6 matched pair for LTCS lines, a stainless stub end for cold alloy-economy work (state grade and schedule), or 'flange only'; (5) the design minimum temperature where it helps — it confirms LF2 Class 1 against the alternatives, and colder duties steer the conversation to the higher A350 grades; (6) certification — EN 10204 3.1 (our standard) or 3.2 witnessed, Charpy results included, pairs certified together; (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 A350 LF2 lap joint flanges in India?
Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer based in Mumbai, India, producing ASTM A350 LF2 Class 1 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, normalised LF2 forgings with the shoulder dressed to bear evenly on the lap, Charpy-tested at −46°C per heat-treatment lot with results on the certificate, hardness-checked, supplied plain, primed or hot-dip galvanised, heat-number marked, and certified to EN 10204 3.1/3.2. Matched LTCS stub ends (A420 WPL6 per B16.9) and cold-service stainless stub ends are supplied against the same order, pairs certified together on one document. Alongside the complete A350 LF2 range — weld neck, slip-on, socket weld, threaded, blind and long weld neck — and the full lap joint grade bench. Exported to more than 50 countries.
