Tesco Steel & Engineering manufactures ASTM A350 LF3 Class 1 LTCS flanges — the 3.5% nickel low-temperature carbon steel forging grade. The deliberate nickel addition lowers the ductile-to-brittle transition, giving notch toughness verified by a mandatory Charpy V-notch impact test at -150°F (-101°C) — far below the plain-carbon LF1 and LF2 grades. Class 1 is the standard normalized condition. It is used for deep low-temperature and cryogenic-adjacent piping such as ethylene, refrigeration and cold processing. Available in weld neck, slip-on, blind, socket-weld, threaded, lap-joint, spectacle and orifice types to ASTM A350 / ASME B16.5. Class 150 to 2500, NPS 1/2″ to 24″, PN6 to PN400. ISO 9001:2015 certified. Made in India.
ASTM A350 LF3 Class 1 LTCS Flanges
A350 LF3 Weld Neck & RTJ Flanges
Tesco Steel & Engineering manufactures A350 LF3 Class 1 flanges in all types from weld neck to orifice, Class 150 to 2500 — supplied normalized with EN 10204 3.1 / 3.2 certification, the impact-test record, and third-party inspection on request. Explore the wider LTCS flange range, the plain-carbon A350 LF2 flanges and A350 LF1 flanges, the higher-requirement A350 LF3 Class 2 flanges, and the flange dimension charts.
| ASTM A350 LF3 Class 1 flanges are available in the following specifications: | |
|---|---|
| Material Grade | ASTM A350 / A350M Grade LF3, Class 1 (3.5% nickel low-temperature carbon steel) |
| Alloy Type | 3.5% nickel low-temperature carbon steel (LTCS) |
| Impact Test | Charpy V-notch at -150°F (-101°C) |
| Heat Condition | Normalized (or normalized and tempered) — Class 1 |
| Size | 1/2″ NB to 24″ NB (DN 15 to DN 600); larger to ASME B16.47 |
| Class / Rating | 150#, 300#, 600#, 900#, 1500#, 2500# · 3000#, 6000#, 9000# (socket-weld / threaded) |
| Pressure Ratings | PN 6 – PN 400 (PN6, 10, 16, 25, 40, 64, 100, 160, 250, 320, 400) |
| Dimensional Standards | ASME B16.5, ASME B16.47 (Series A & B), MSS SP-44, DIN EN 1092-1 |
| Flange Types | Weld Neck (WNRF), Slip-On (SORF), Blind, Socket Weld (SWRF), Lap Joint, Threaded / Screwed, Spectacle Blind, Long Weld Neck, Orifice, Plate |
| Flange Faces | Raised Face (RF), Flat Face (FF), Ring Type Joint (RTJ), Tongue & Groove (T&G) |
| Testing | Charpy impact, hydrostatic, UT, MT/PT per spec; EN 10204 3.1 / 3.2 |
A350 LF3 is a 3.5% nickel low-temperature carbon steel. The nickel addition is the defining element — it lowers the ductile-to-brittle transition temperature so the steel keeps toughness to -101°C, verified by the mandatory Charpy impact test.
| Element | ASTM A350 LF3 |
|---|---|
| Carbon (C) | 0.20% max |
| Manganese (Mn) | 0.90% max |
| Silicon (Si) | 0.20 – 0.35% |
| Nickel (Ni) | 3.30 – 3.70% (low-temperature toughness) |
| Phosphorus (P) | 0.035% max |
| Sulphur (S) | 0.040% max |
| Cr / Mo / Cu / V | Residual, limited per A350 |
| Mechanical Property | ASTM A350 LF3 |
|---|---|
| Tensile Strength | 70 – 95 ksi (485 – 655 MPa) |
| Yield Strength (min) | 37.5 ksi (260 MPa) |
| Elongation | ~22 – 24% |
| Impact Toughness | Charpy V-notch verified at -150°F (-101°C) |
| Min. Design Temperature | ~ -101°C (-150°F) |
| Condition | Normalized / normalized & tempered (Class 1) |
LF3 Weld Neck Flange (WNRF)
LF3 Slip-On Flange (SORF)
LF3 Blind Flange
| Flange Type | Description & LF3-Specific Use |
|---|---|
| Weld Neck (WNRF) | Tapered hub butt-welded to pipe for high-integrity deep-cold piping; weld with impact-rated nickel-bearing low-hydrogen consumables. |
| Slip-On (SORF) | Fillet-welded over the pipe; used in low-temperature piping at moderate pressure. |
| Blind | Seals pipe ends and vessel nozzles in deep low-temperature systems. |
| Socket Weld (SWRF) | Small-bore (1/2″–2″) instrument and branch connections in cold service. |
| Lap Joint (LJRF) | Used with an LF3 stub end where frequent dismantling is required. |
| Threaded (TRFF) | Internal NPT/BSP threads for non-welded low-pressure connections. |
| Spectacle Blind / Long Weld Neck / Orifice | Isolation spades, nozzle/long-neck and flow-metering flanges in A350 LF3 for deep-cold duty. |
| Property | LF3 | LF2 | LF1 |
|---|---|---|---|
| Type | 3.5% Nickel steel | C-Mn steel | C-Mn steel |
| Impact-test temp | -101°C (-150°F) | -46°C (-50°F) | -29°C (-20°F) |
| Nickel | ~3.5% | None (residual) | None (residual) |
| Yield (min) | 37.5 ksi | 36 ksi | 30 ksi |
| Relative cost | Higher (Ni) | Low | Lowest |
| Typical role | Deep-cold / cryogenic-adjacent | Default LTCS grade | Mild low-temperature |
3.5% nickel gives verified Charpy toughness to -150°F (-101°C) — the coldest of the common A350 grades.
Reaches deep-cold service without resorting to stainless or special alloys where -101°C suffices.
Welded with impact-rated nickel-bearing low-hydrogen consumables and qualified low-temperature procedures.
Meets ASME B31.3 / B16.5 low-temperature requirements with full impact documentation.
| Industry | Typical Application |
|---|---|
| Petrochemical (Ethylene) | Cold-train and low-temperature process flanged connections |
| Gas Liquefaction & Refrigeration | Deep low-temperature gas and refrigerant piping flanges |
| LNG-Adjacent Piping | Low-temperature carbon-steel-family flanges within the design range |
| Air Separation / Cold Boxes | Cold-box and cryogenic-adjacent flanged connections |
| Low-Temperature Storage | Cold storage and loading flanged systems |
| Oil & Gas Cold Service | Deep-cold processing and depressurisation flanges |
Made from certified 3.5% nickel A350 LF3 with chemistry and Charpy impact results documented on the MTC.
Supplied in the normalized condition with verified impact toughness at -150°F.
WNRF, SORF, blind, socket-weld, threaded, lap-joint, spectacle, LWN, orifice and plate — in RF, FF, RTJ and T&G.
EN 10204 3.1 / 3.2 MTC with impact results, heat/lot traceability, hydrostatic and third-party inspection on request.
A350 LF3 Class 1 flange prices reflect the 3.5% nickel content plus forging, normalizing and low-temperature impact testing — it is the premium A350 grade for deep-cold service. Tesco Steel & Engineering offers competitive ex-works pricing from Mumbai with full export documentation and material traceability. Click Ask for Quote or message us on WhatsApp at +91 92233 66922 with flange type, size (NB), pressure class, quantity and documentation requirements.
Q1. What is an ASTM A350 LF3 Class 1 flange?
An ASTM A350 LF3 Class 1 flange is a forged low-temperature carbon steel (LTCS) flange in the 3.5% nickel grade of the A350 specification. The deliberate nickel addition gives notch toughness verified by a mandatory Charpy V-notch impact test at -150 degrees F (-101 degrees C), well below the plain-carbon LF1 and LF2 grades. Class 1 is the standard normalized condition. It is used for deep low-temperature and cryogenic-adjacent piping. Flanges are made to ASTM A350 and machined to ASME B16.5 / B16.47 dimensions.
Q2. Why does A350 LF3 contain 3.5% nickel?
The ~3.5% nickel in A350 LF3 lowers the steel's ductile-to-brittle transition temperature, giving good notch toughness down to -150 degrees F (-101 degrees C). Plain carbon-manganese grades like LF1 and LF2 cannot reach that low without becoming brittle, so nickel is added specifically to extend the safe low-temperature range for deep-cold service.
Q3. What is the impact test temperature for A350 LF3?
ASTM A350 LF3 requires a Charpy V-notch impact test at -150 degrees F (-101 degrees C), with minimum average absorbed energy per the specification. This is the lowest standard impact-test temperature of the common A350 grades and is what qualifies LF3 for deep low-temperature service.
Q4. What is the difference between A350 LF1, LF2 and LF3?
All are forged LTCS grades of ASTM A350, differing in chemistry and minimum impact-test temperature. LF1 is a carbon-manganese steel impact tested at -20 degrees F (-29 degrees C); LF2 is the common C-Mn grade tested at -50 degrees F (-46 degrees C); LF3 contains about 3.5% nickel for service to -150 degrees F (-101 degrees C). Choose the grade by the minimum design temperature; LF3 is for the coldest carbon-steel-family service.
Q5. What is the difference between A350 LF3 Class 1 and Class 2?
A350 LF3 Class 1 and Class 2 share the same 3.5% nickel chemistry and the same -150 degrees F (-101 degrees C) impact requirement. The class denotes the heat-treatment/property variant: Class 1 is the standard condition, while Class 2 is supplied to the tighter (higher strength) requirements some applications call for. The project specification states which class is required.
Q6. What is the chemical composition of A350 LF3?
ASTM A350 LF3 nominal composition: carbon 0.20% max, manganese 0.90% max, silicon 0.20–0.35%, nickel 3.3–3.7%, phosphorus 0.035% max, sulphur 0.040% max, with limits on residual chromium, molybdenum, copper and vanadium. The 3.5% nickel is the defining element for its deep low-temperature toughness.
Q7. What standards apply to A350 LF3 Class 1 flanges?
A350 LF3 Class 1 flanges are forged to ASTM A350/A350M (Grade LF3, Class 1) and machined to ASME B16.5 (1/2 inch to 24 inch) or ASME B16.47 / MSS SP-44 for larger sizes, with EN 1092-1 for PN-rated flanges. Material is supplied normalized (or normalized and tempered) with EN 10204 3.1 / 3.2 certification including the impact-test record. It is broadly comparable to EN 1.5662 (12Ni14) for low-temperature service.
Q8. Can A350 LF3 flanges be welded?
Yes. A350 LF3 is welded with low-hydrogen processes and matching nickel-bearing low-temperature consumables that are themselves impact-tested at the design temperature. Preheat, controlled interpass temperature and, for thicker sections, post-weld heat treatment may be specified; the welding procedure must be impact-tested to confirm the joint's low-temperature toughness.
Q9. What are the mechanical properties of A350 LF3?
Typical ASTM A350 LF3 properties: tensile strength 70–95 ksi (485–655 MPa), yield strength 37.5 ksi (260 MPa) minimum, elongation about 22–24%, with Charpy V-notch impact toughness verified at -150 degrees F (-101 degrees C). It is supplied in the normalized or normalized-and-tempered condition.
Q10. Are A350 LF3 Class 1 flanges supplied with material test certificates?
Yes. Every A350 LF3 Class 1 flange is supplied with EN 10204 3.1 (or 3.2) mill test certificates confirming chemistry, mechanical properties, the Charpy impact-test result and heat/lot traceability, with hydrostatic testing and third-party inspection on request. Tesco Steel & Engineering is an ISO 9001:2015 certified manufacturer and exporter from Mumbai, India.