ASTM A350 LF2 Weld Neck Flanges — LTCS, Impact Tested at −46 °C
Tesco Steel & Engineering forges ASTM A350 LF2 weld neck flanges in low temperature carbon steel (LTCS) — normalized and Charpy impact tested at −46 °C — from 1/2″ NB to 56″ NB, in ASME B16.5 Class 150–2500, ASME B16.47 Series A & B, EN 1092-1 Type 11, DIN and BS 4504. The strength twin of A105 with certified sub-zero toughness, LF2 is the flange of LNG facilities, flare and blowdown systems, gas processing and cold-climate pipelines, mating A333 Gr 6 pipe. Class 1 standard, Class 2 on request; NACE MR0175 and EN 10204 3.1/3.2 available. ISO 9001:2015, made in Mumbai, India — exported worldwide.
ASTM A350 LF2 LTCS Weld Neck Flange — Black Coated, Raised Face
What is an ASTM A350 LF2 Weld Neck Flange?
ASTM A350 LF2 is the low temperature carbon steel (LTCS) forging grade — normalized and Charpy V-notch impact tested at −46 °C — the material piping codes reach for when a carbon steel line can see below A105's −29 °C limit. An LF2 weld neck flange pairs that certified toughness with the strongest flange design: a long tapered hub butt-welded to the pipe, bore matched to the pipe schedule, joint fully radiographable.
Mechanically, LF2 is A105's twin — same 250 MPa yield minimum, same welding consumables, same dimensions — so it drops into carbon steel piping classes without re-rating. What the extra processing buys is guaranteed behaviour in the cold: normalizing refines the grain, the 655 MPa tensile ceiling caps hardness, and every heat's impact energies at −46 °C are printed on the certificate. Its system partner is A333 Grade 6 pipe, impact tested to the same temperature.
Why cold matters even in hot climates: when high-pressure gas depressurises through a valve into a flare or blowdown header, auto-refrigeration (the Joule-Thomson effect) can chill the steel far below −29 °C in seconds — exactly when the line carries its emergency load. That is why depressurisation systems specify LTCS flanges regardless of the plant's location.
Also searched as: A350 LF2 WNRF flange, SA350 LF2 weld neck flange, LTCS weld neck flange, low temp carbon steel flange, LF2 Class 1 flange — all refer to the product on this page.
Chemical Composition of ASTM A350 LF2
C
Mn
P
S
Si
Ni
Cr
Mo
Cu
Nb
V
0.30 max
0.60-1.35
0.035 max
0.040 max
0.15-0.30
0.40 max
0.30 max
0.12 max
0.40 max
0.02 max
0.08 max
Specification notes: (1) The sum of copper, nickel, chromium, molybdenum and vanadium shall not exceed 1.00%. (2) The sum of chromium and molybdenum shall not exceed 0.32%. Note the 0.30% carbon ceiling — lower than A105's 0.35% — part of what buys the low-temperature toughness.
Mechanical Properties of ASTM A350 LF2
Tensile Strength, MPa [ksi]
Yield Strength, Min, MPa [ksi]
Elongation % min.
Reduction of Area % min.
Hardness HB max
485-655 [70-95]
250 [36]
22
30
197
Note the tensile ceiling — unusual among flange grades — which guards toughness by capping strength and hardness. On top of these values, every heat passes Charpy V-notch testing at −46 °C (Class 1; Class 2 is tested at −18 °C with higher energy), with results reported on the mill test certificate.
ASTM A350 LF2 Weld Neck Flange Specifications
ASTM A350 LF2 Weld Neck Flanges are available in the following specifications:
Size
1/2"NB to 56"NB
Class
150#, 300#, 400#, 600#, 900#, 1500#, 2500#
Sch (Schedule)
XS, XXS, STD & Schedule 20, 40, 80, 160
Pressure Ratings
PN 2.5 - PN 400
Standards
ASME B16.5, ASME B16.47 Series A & B, EN 1092-1 Type 11, DIN 2631–2635, BS 4504
Grade / Impact Class
A350 LF2 Class 1 (Charpy at −46 °C) standard; Class 2 (−18 °C) on request
Other Services
Hot Dip Galvanized (GI) ASTM A350 LF2 Weld Neck Flanges Sand Blasting on ASTM A350 LF2 Weld Neck Flanges Shot Peening on ASTM A350 LF2 Weld Neck Flanges Epoxy Coating on ASTM A350 LF2 Weld Neck Flanges FBE Coating on ASTM A350 LF2 Weld Neck Flanges
Why LF2 for Low-Temperature Flanged Joints
Certified Toughness at −46 °C
Every heat is Charpy tested and the energies printed on the certificate — guaranteed ductile behaviour where plain carbon steel turns glass-brittle.
A105's Strength, Cold-Proofed
Same 250 MPa yield, same dimensions, same consumables — LF2 drops into carbon steel piping classes without re-rating anything but the paperwork.
Built for Blowdown
Auto-refrigeration during depressurisation is LF2's defining duty: flare, vent and blowdown headers keep guaranteed toughness through every cold excursion.
Sour-Service Ready
The 197 HB ceiling sits under the NACE MR0175 hardness limit — and low-temperature sour gas processing is precisely where LF2 lives.
A Weld You Can Prove
Full-penetration butt weld, radiographable, welded with impact-tested E7018-1 consumables to A333 Gr 6 pipe — the joint keeps the −46 °C rating end to end.
Production, Stock & Packing
LF2 runs alongside A105 as our core carbon steel production: certified forged blanks are normalized, CNC-turned with the bore matched to your pipe schedule and the weld end bevelled to 37.5°, impact test coupons go to the laboratory, and finished flanges are marked with grade, class, size, rating and heat number. Stock and packing are shown below:
LNG facilities use LF2 across their warmer circuits — send-out, utilities, boil-off gas handling — wherever the design temperature sits between −46 °C and ambient. Flare, vent and blowdown systems are the signature duty: auto-refrigeration during depressurisation demands certified toughness in every joint. Gas processing and NGL plants, cold-climate pipelines and wellsites, refrigeration and cold storage, and low-temperature sour service round out the range. Below −46 °C the ladder continues to A350 LF3 (3.5% Ni, tested at −101 °C) and then to austenitic stainless; above ambient temperature limits, back to A105.
ASTM A350 LF2 Weld Neck Flange Dimensions
LF2 weld neck flanges share their dimensions with every other material in the same class — OD, thickness, hub, bore, bolt circle and bolting per the standard tables. Full ASME B16.5 charts:
LF2 pricing follows the steel market plus the impact-testing premium, and moves with size, class and quantity — so we quote live rather than publish a static list. Common sizes ship from ready stock alongside our A105 range. To get a firm quotation, usually within 24 hours:
1
List your requirement — size (NB), class or PN, standard (ASME B16.5 / B16.47 / EN / DIN / BS), grade and impact class (LF2 Class 1 or Class 2), pipe schedule or bore, and quantity.
2
Add any extras — NACE MR0175, HIC testing, 3.2 certification, coatings or special face finish.
3
Send it across — via the inquiry form, WhatsApp, or email to sales@tescosteel.com — and we reply with price, delivery and stock position.
It is a weld neck flange forged from ASTM A350 LF2 — the low temperature carbon steel (LTCS) forging grade, normalized and Charpy V-notch impact tested at -46 °C. Mechanically it is the twin of A105, but with certified toughness where ordinary carbon steel turns brittle. The long tapered hub is butt-welded to the pipe with the bore matched to the pipe schedule, making it the standard flange of LNG facilities, flare systems and cold-climate piping.
What temperature is A350 LF2 rated for?
LF2 is impact tested at -46 °C (-50 °F), which qualifies it for design temperatures down to -46 °C under the ASME codes — precisely where A105's -29 °C exemption runs out. The upper end matches ordinary carbon steel, around 425 °C. For deeper cold — down to about -101 °C — step to the 3.5% nickel grade A350 LF3; below that, austenitic stainless takes over. We forge all three.
What is the difference between A350 LF2 Class 1 and Class 2?
The Charpy acceptance criteria. Class 1 — the default supplied unless you specify otherwise — is impact tested at -46 °C with 20 J average absorbed energy; Class 2 is tested at the warmer -18 °C but must absorb 27 J. Class 1 covers the vast majority of low-temperature specifications. State the class in your enquiry and the certificate documents the test temperature and values actually achieved.
What is the difference between A350 LF2 and A105 flanges?
Strength-wise they are twins — both 250 MPa minimum yield, 485 MPa minimum tensile — so LF2 drops into A105 piping classes without re-rating. The differences: LF2 is always normalized, always impact tested at -46 °C, carries a tensile ceiling of 655 MPa to guarantee toughness, and costs a little more for the extra processing. If any part of the line can see below -29 °C — even briefly, during blowdown — LF2 is the correct call.
When should I choose LF3 instead of LF2?
When the design temperature falls below -46 °C. A350 LF3 is the 3.5% nickel version, impact tested at -101 °C, covering ethylene, LPG and other deep-refrigeration services. Between -46 °C and ambient, LF2 is the economical choice; below -101 °C, move to austenitic stainless such as 304L/316L, which has no transition temperature at all. Our LF3 Class 1 and Class 2 flanges have their own pages on this site.
What is the chemical composition of ASTM A350 LF2?
Carbon 0.30% max, manganese 0.60 to 1.35%, phosphorus 0.035% max, sulphur 0.040% max, silicon 0.15 to 0.30%, with residuals capped at nickel 0.40%, chromium 0.30%, molybdenum 0.12%, copper 0.40%, niobium 0.02% and vanadium 0.08%. Two spec rules apply: copper, nickel, chromium, molybdenum and vanadium together must not exceed 1.00%, and chromium plus molybdenum must not exceed 0.32%. The lower carbon ceiling versus A105 is part of what buys the low-temperature toughness.
What are the mechanical properties of A350 LF2 flanges?
Tensile strength 485 to 655 MPa (70 to 95 ksi) — note the deliberate ceiling, which guards toughness — minimum yield strength 250 MPa (36 ksi), minimum elongation 22%, minimum reduction of area 30%, and hardness capped at 197 HB. On top of those, every heat must pass Charpy V-notch impact testing at -46 °C, with the absorbed energy values reported on the mill test certificate.
Which pipe grade do LF2 weld neck flanges mate with?
ASTM A333 Grade 6 — the impact-tested low-temperature seamless pipe that is LF2's system partner, sharing the -46 °C rating and the carbon steel welding procedures. API 5L pipe with supplementary low-temperature testing also appears in cold-climate pipeline work. The weld neck bore is machined to the pipe schedule you state, so the joint is flush inside.
What sizes and standards do you manufacture LF2 weld neck flanges in?
From 1/2 inch NB to 56 inch NB: ASME B16.5 Class 150 to 2500 up to 24 inch, ASME B16.47 Series A and B for 26 inch and above, and European PN 2.5 to PN 400 patterns to EN 1092-1 Type 11, DIN 2631 to 2635 and BS 4504. Raised face is standard, flat face and ring joint on request, and every bore is machined to the mating pipe schedule from Sch 20 through XXS.
How are LF2 flanges welded to pipe?
With low-temperature-qualified carbon steel consumables — E7018-1 is the classic electrode, its -1 suffix denoting impact-tested weld metal — under procedures qualified with Charpy testing when the line class demands it. Preheat follows ordinary carbon steel rules. The 37.5 degree bevel comes machined ready for a full-penetration, radiographable butt weld, and the joint keeps the -46 °C rating when welded to A333 Gr 6 pipe with matching consumables.
Where are ASTM A350 LF2 weld neck flanges used?
LNG liquefaction, storage and regasification terminals on their warmer circuits and utility systems; flare, vent and blowdown lines, where expanding gas auto-refrigerates well below ambient; gas processing and NGL plants; cold-climate pipelines and wellsites in arctic regions; refrigeration and cold storage plants; and any hydrocarbon service whose minimum design temperature dips below -29 °C. Wherever a process safety review finds a cold excursion, LF2 replaces A105.
Why does blowdown service need LF2 flanges?
Because of auto-refrigeration: when high-pressure gas expands across a valve or orifice into a flare or blowdown header, the Joule-Thomson effect can chill the metal far below ambient — often below -29 °C even in a warm climate. Ordinary A105 turns brittle exactly when the line is carrying its emergency load. Impact-tested LF2 keeps guaranteed toughness through the excursion, which is why depressurisation systems are specified LTCS almost universally.
Are LF2 flanges available for sour service (NACE)?
Yes. LF2's 197 HB hardness ceiling sits under the NACE MR0175 / ISO 15156 limit of 22 HRC for carbon steel in H2S service, and low-temperature sour gas processing is one of the grade's natural habitats. We certify NACE compliance on request, supply HIC-resistant material where the specification demands it, and document everything on the EN 10204 3.1 or 3.2 certificate.
Can LF2 flanges be galvanized or coated?
Yes — LF2 is carbon steel and takes the full coating menu: hot-dip galvanizing for outdoor and utility service, epoxy and FBE for buried duty, sand blasting, shot peening, phosphating and anti-rust oil for stock protection. Machined faces and weld bevels are masked or protected so coating never interferes with sealing or welding.
What testing and certification do you supply with LF2 flanges?
Every lot ships with EN 10204 3.1 mill test certificates covering chemical analysis, mechanical properties and the mandatory Charpy V-notch results at -46 °C, with 3.2 certification witnessed by Lloyd's, DNV, BV or TÜV on request. We also offer PMI, ultrasonic and magnetic particle examination, hardness surveys for NACE work, and normalizing documentation — with full heat-number traceability from billet to finished flange.
Do you keep A350 LF2 weld neck flanges in stock? What is the lead time?
Common sizes in Class 150, 300 and 600 — typically 1/2 to 24 inch — are held as ready stock alongside our A105 range and generally ship within days. Large B16.47 diameters, Class 900 to 2500, Class 2 impact testing and NACE or HIC material are produced to order, typically in 2 to 4 weeks. Send your list for a firm delivery commitment.
What information should I include in an LF2 flange enquiry?
Six things: size (NB), pressure class or PN rating, dimensional standard (ASME B16.5, B16.47 or EN/DIN/BS), grade and class (LF2 Class 1 or Class 2), pipe schedule or bore, and quantity. Add any extras — NACE compliance, HIC testing, 3.2 certification, coatings. With these details we return a firm quotation, usually within 24 hours.
Do you export ASTM A350 LF2 flanges outside India?
Yes. Tesco Steel & Engineering is an ISO 9001:2015 certified manufacturer based in Mumbai, and LF2 weld neck flanges ship regularly to LNG projects, gas plants and EPC contractors across the Middle East, Europe, Central Asia, Southeast Asia and the Americas. Flanges travel face-protected in lined crates with full heat-number and impact-test traceability.
