LTCS Flanges Manufacturer & Exporter — ASTM A350 LF1, LF2, LF3 Low Temperature Carbon Steel
ISO 9001:2015 Certified · Mumbai, India · Exporting to 96 Countries · Charpy Impact Tested
LTCS (Low Temperature Carbon Steel) flanges are forged piping components manufactured from ASTM A350 / ASME SA350 carbon steel specifically engineered for sub-zero temperature service. The defining characteristic of LTCS flanges — and what separates them from standard ASTM A105 carbon steel flanges — is mandatory Charpy V-Notch (CVN) impact testing at sub-zero temperatures. This testing verifies that the material retains sufficient toughness at its minimum design temperature and will not undergo brittle fracture under impact loading. All LTCS grades also require heat treatment (normalise, normalise+temper, or quench+temper) to achieve the required low-temperature toughness.
Tesco Steel & Engineering manufactures ASTM A350 / ASME SA350 LTCS flanges in all grades — LF1, LF2 Class 1, LF2 Class 2, LF3 Class 1, and LF3 Class 2 — in NPS ½″ through 60″, Class 150 through 2500, in all facing types (RF, FF, RTJ, BW, TG) and flange types per ASME B16.5, B16.47, and EN 1092-1. All flanges are supplied with full mill test reports, Charpy impact test certificates, heat treatment records, PMI, and third-party inspection documentation.
LTCS Grade Classification — ASTM A350
ASTM A350 LTCS grades are classified by impact test temperature and nickel content. As the minimum design temperature drops, the required grade increases in alloy content and testing severity.
LF1
−46°C impact
C-Mn Steel · P1
- UNS K03011
- Min YS: 250 MPa
- Normalised / N+T
- Standard cold service
LF2 CLASS 1
−46°C impact
C-Mn Steel · P1 · HB ≤197
- Most common LTCS grade
- Min YS: 250 MPa
- Normalised / N+T
- Gas processing, offshore
LF2 CLASS 2
−46°C impact
C-Mn Steel · P1 · HB ≤235
- High-strength variant
- Min YS: 360 MPa
- Quench + Tempered
- High-pressure cold service
LF3 — CRYOGENIC
−101°C impact
3.5% Ni Steel · P9A
- UNS K32025 (3.3–3.7% Ni)
- Min YS: 260 MPa (Cl.1)
- LNG adjacent service
- Separate WPS required
⚠ Critical: Charpy V-Notch Impact Testing is Mandatory for All LTCS Grades
Every LTCS flange must be supplied with a Charpy V-Notch (CVN) impact test certificate showing the absorbed energy at the grade's test temperature. The minimum required energy is 20 ft-lb (27 J) average per ASTM A350, with no individual specimen below 15 ft-lb (20 J). Impact testing on standard carbon steel (A105) cannot substitute for LTCS impact certification — the heat number, heat treatment condition, and test temperature must all be documented on the Material Test Report (MTR).
Additionally, all LTCS grades require mandatory heat treatment — normalise (N), normalise+temper (N+T), or quench+temper (Q+T). As-forged or as-rolled material does not qualify as LTCS regardless of chemical composition.
Chemical Composition — ASTM A350 LTCS Grades
| Grade | UNS | C (max %) | Mn (%) | Si (%) | Ni (%) | P (max) | S (max) |
| LF1 | K03011 | 0.30 | 0.60–1.35 | 0.15–0.30 | ≤0.40 | 0.035 | 0.040 |
| LF2 Cl.1 & Cl.2 | K03011 | 0.30 | 0.60–1.35 | 0.15–0.30 | ≤0.40 | 0.035 | 0.040 |
| LF3 Cl.1 & Cl.2 | K32025 | 0.20 | ≤0.90 | 0.20–0.35 | 3.30–3.70 | 0.035 | 0.040 |
LF1 and LF2 share the same chemical composition — the distinction is the strength class and heat treatment. LF3's 3.3–3.7% nickel addition is the defining feature that enables impact resistance at −101°C.
Mechanical Properties — ASTM A350 LTCS Grades
| Grade | Class | Min YS (MPa) | Min UTS (MPa) | Elong. (%) | Max Hardness | CVN Test Temp. | Min CVN (avg) |
| LF1 | — | 250 (36 ksi) | 485–655 | ≥22 | HB 197 | −46°C (−50°F) | 27 J (20 ft-lb) |
| LF2 | Class 1 | 250 (36 ksi) | 485–655 | ≥22 | HB 197 | −46°C (−50°F) | 27 J (20 ft-lb) |
| LF2 | Class 2 | 360 (52 ksi) | 515–690 | ≥20 | HB 235 | −46°C (−50°F) | 27 J (20 ft-lb) |
| LF3 | Class 1 | 260 (37.5 ksi) | 485–655 | ≥22 | HB 197 | −101°C (−150°F) | 27 J (20 ft-lb) |
| LF3 | Class 2 | 360 (52 ksi) | 515–690 | ≥20 | HB 235 | −101°C (−150°F) | 27 J (20 ft-lb) |
Minimum Design Temperature — Grade Comparison
Impact test temperature vs minimum design temperature limit per ASME B16.5 and design codes. Longer bar = colder service capability.
ASTM A105 (Carbon Steel — reference)−29°C
A350 LF2 Cl.1 & Cl.2−46°C (most common LTCS)
A350 LF3 Cl.1 & Cl.2 (3.5% Ni)−101°C — LNG adjacent
LF3 — deepest cold capability
For service below −101°C (e.g., LNG at −162°C), austenitic stainless steel (ASTM A182 F304L/F316L) or 9% Ni steel is required.
Dimensional Standards & Specifications
| Standard | Scope |
|---|
| ASTM A350 / ASME SA350 | Material standard for forged LTCS pipe flanges — primary specification for LF1, LF2, LF3 |
| ASME B16.5 | Pipe flanges NPS ½″ to 24″, Class 150–2500 |
| ASME B16.47 | Large diameter flanges NPS 26″ to 60″ (Series A & B) |
| ASME B16.36 | Orifice flanges |
| ASME B31.3 | Process Piping — governs PWHT and impact test requirements for LTCS in process plants |
| ASME B31.8 | Gas Transmission and Distribution Piping — cold climate and LNG-adjacent applications |
| ASME BPVC Sec. IX | Welding qualifications — P1 (LF1/LF2) and P9A (LF3) WPS/PQR requirements |
| EN 1092-1 | European PN-rated flanges for EU cold-service projects |
| BS 1560 / BS 4504 | British standard flanges for UK and Commonwealth offshore projects |
Industry Applications of LTCS Flanges
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Offshore Oil & Gas
LTCS LF2 flanges on topsides process piping, separator trains, and gas export headers in North Sea, Arctic, and sub-Arctic offshore platforms where ambient temperatures drop below −29°C. LF2 is the standard cold-service carbon steel for NORSOK and API offshore specifications.
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LNG & Gas Processing
LF3 (3.5% Ni) flanges on BOG (boil-off gas) lines, LNG vapour return systems, and cold box piping in LNG terminals and FLNG vessels where minimum design temperatures reach −100°C. LF2 for warm-side cold utilities and fuel gas systems.
❄️
Cryogenic Storage
LF3 flanges on secondary piping and utility connections of cryogenic storage tanks for LPG, ethylene, propylene, and liquid nitrogen. LF2 for ambient-temperature connections where auto-refrigeration from depressurisation can drive temperatures below −29°C.
⚗️
Petrochemical Plants
LF2 flanges in ethylene crackers, propylene refrigeration loops, and low-temperature separation columns. Many petrochemical processes operate at sub-zero conditions where LTCS provides the required toughness at lower cost than stainless steel for non-corrosive streams.
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Marine & Shipbuilding
LF2 flanges on LPG carriers, chemical tankers, and Arctic-class vessels. The marine environment combined with cold climate service requires the impact toughness guarantee of LTCS over standard carbon steel for hull-penetrating and cargo piping systems.
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Gas Transmission Pipelines
LF1 and LF2 flanges on gas transmission and distribution pipeline valves, meter stations, and pressure reduction stations in cold climates. Auto-refrigeration during gas expansion (Joule-Thomson effect) can drive local temperatures well below ambient — LTCS provides the required toughness margin.
Frequently Asked Questions — LTCS Flanges
Technical questions about ASTM A350 low temperature carbon steel flanges, Charpy impact testing, LF2 vs LF3, and cryogenic service — answered for engineers and procurement teams.
What is LTCS and how is it different from regular carbon steel?
LTCS (Low Temperature Carbon Steel) refers to ASTM A350 carbon steel grades engineered for sub-zero service. The critical difference from standard ASTM A105 carbon steel is mandatory Charpy V-Notch (CVN) impact testing at sub-zero temperatures. While A105 is limited to −29°C minimum design temperature, LTCS LF1/LF2 grades are impact-tested at −46°C and LF3 at −101°C. All LTCS grades also require mandatory heat treatment — normalise, normalise+temper, or quench+temper — which A105 does not mandate.
What are the ASTM A350 grades and their minimum design temperatures?
ASTM A350 covers: LF1 — impact tested at −46°C, standard C-Mn steel, min YS 250 MPa; LF2 Class 1 — impact tested at −46°C, min YS 250 MPa, HB ≤197, normalised or N+T; LF2 Class 2 — impact tested at −46°C, min YS 360 MPa, HB ≤235, quench+tempered; LF3 Class 1 — impact tested at −101°C, 3.3–3.7% Ni, min YS 260 MPa; LF3 Class 2 — impact tested at −101°C, 3.3–3.7% Ni, min YS 360 MPa. The class designation refers to the strength level and heat treatment condition.
Why is Charpy impact testing required for LTCS flanges?
At sub-zero temperatures, plain carbon steel undergoes a ductile-to-brittle transition — it shifts from ductile fracture (with deformation warning) to sudden brittle fracture. Charpy V-Notch (CVN) impact testing measures the energy absorbed during fracture at the specified sub-zero temperature. ASTM A350 mandates minimum 27 J (20 ft-lb) average absorbed energy to confirm the flange retains toughness at its minimum design temperature. This certification is the fundamental safety requirement distinguishing LTCS from standard A105 carbon steel.
What is the difference between ASTM A350 LF2 and LF3?
The primary difference is the impact test temperature and nickel content. LF2 is a carbon-manganese steel impact tested at −46°C — suitable for most cold climate applications and gas processing. LF3 contains 3.3–3.7% nickel which significantly improves toughness at cryogenic temperatures, and is impact tested at −101°C. LF3 is specified for LNG-adjacent service and cryogenic storage at temperatures around −100°C. The nickel addition also changes the ASME P-Number from P1 (LF2) to P9A (LF3), requiring a separate welding procedure qualification with impact-tested test coupons.
Can LTCS flanges be used in LNG service?
LNG is stored at approximately −162°C. ASTM A350 LF3 is impact tested at only −101°C and is therefore not suitable for direct LNG contact at −162°C. For true cryogenic LNG service, austenitic stainless steel (A182 F304L, F316L) is standard. LF3 is suitable for LNG-adjacent systems — BOG lines, vapour return, and secondary containment piping — where temperatures remain above approximately −100°C. Always confirm the actual minimum design temperature (including auto-refrigeration effects) against the ASME B16.5 P-T rating table.
What is the difference between LF2 Class 1 and Class 2?
Both LF2 classes share the same chemical composition and are impact tested at −46°C. LF2 Cl.1 has min yield strength 250 MPa (36 ksi), max hardness HB 197, achieved by normalising or N+T. LF2 Cl.2 has min yield strength 360 MPa (52 ksi), max hardness HB 235, achieved by quench+tempering. Cl.2 is specified for high-pressure classes (600# and above) or thick-wall flanges where higher strength reduces wall thickness. Both classes are P1 and use the same welding consumables (E7018, ER70S-6).
Is PWHT required for LTCS flanges?
PWHT for LTCS piping is governed by the design code. Under ASME B31.3, PWHT is required for P1 materials (LF1, LF2) when weld joint thickness exceeds 19mm (¾″) in most services. For LF3 (P9A), PWHT is required at lower thicknesses. Critically, the Charpy impact properties of the HAZ must be verified after PWHT — some PWHT cycles reduce HAZ toughness below the required minimum. Specify production weld procedure testing with the actual PWHT cycle and verify CVN results before commencing fabrication.
What ASME P-Number are LTCS flanges?
ASTM A350 LF1 and LF2 (C-Mn grades) are ASME P-Number 1, the same as ASTM A105. Existing P1 WPS qualified for A105 are valid for LF1/LF2, provided impact test requirements of the design code are satisfied. ASTM A350 LF3 (3.3–3.7% Ni) is P9A — nickel alloy steel — requiring a separate WPS qualification with impact-tested test coupons at −101°C. Do not use P1 procedures for LF3.
When should I use LTCS instead of stainless steel for cold service?
LTCS (LF2) costs significantly less than austenitic stainless steel and is preferred when: (1) the fluid is non-corrosive — dry gas, LPG, sweet natural gas, nitrogen; (2) temperature is between −46°C and −29°C; (3) budget is a priority. Stainless steel (304L/316L) is chosen when the process is corrosive, hygiene is required, or temperatures fall below −101°C (LF3's limit). In gas processing and offshore facilities, LTCS (LF2) is the standard for non-corrosive cold utilities while stainless handles corrosive process streams.
What is the chemical composition of ASTM A350 LF3?
ASTM A350 LF3 (UNS K32025): Carbon ≤0.20%, Manganese ≤0.90%, Silicon 0.20–0.35%, Nickel 3.30–3.70%, Phosphorus ≤0.035%, Sulfur ≤0.040%. The 3.3–3.7% nickel addition is the defining feature — nickel lowers the ductile-to-brittle transition temperature, enabling impact energy absorption at −101°C. LF3 has a lower carbon limit (0.20% vs 0.30% for LF2) to maintain weldability despite the nickel addition. The higher nickel content also changes the ASME P-Number from P1 (LF2) to P9A, requiring a separate qualified welding procedure.
How to Select the Right LTCS Flange Grade
A five-step engineering decision process for specifying ASTM A350 low temperature carbon steel flanges.
1
Determine minimum design temperature (MDT)
Identify the coldest temperature in service including upsets and auto-refrigeration. Above −29°C → A105. Between −29°C and −46°C → LF1 or LF2. Down to −101°C → LF3. Below −101°C → austenitic stainless steel or 9% Ni steel.
2
Assess corrosion requirements
LTCS is carbon steel — not corrosion resistant. For non-corrosive fluids (dry gas, LPG, sweet natural gas, nitrogen) LTCS is the cost-effective choice. For corrosive fluids, specify stainless steel or duplex regardless of temperature.
3
Select strength class (Cl.1 vs Cl.2)
Class 1 (normalised, YS 250 MPa) is standard for most 150# and 300# applications. Class 2 (Q+T, YS 360 MPa) is used for 600# and above or thick-wall flanges where the higher strength reduces required wall thickness. Both classes have identical chemical composition and impact test requirements.
4
Confirm Charpy impact test temperature and energy requirements
Verify that the standard test temperature (−46°C for LF2, −101°C for LF3) covers your MDT. If your design code specifies a supplementary impact test at a lower temperature (common for auto-refrigeration scenarios), specify this on the purchase order — the manufacturer must test additional specimens at the required temperature.
5
Verify ASME B16.5 P-T rating and welding procedure
Confirm the required pressure class against the ASME B16.5 P-T table for the material group. Include heat treatment condition (N, N+T, or Q+T) and supplementary CVN requirements in the purchase order. For LF3, ensure a P9A-qualified WPS with impact-tested coupons at −101°C exists before fabrication commences.
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LF1 · LF2 Cl.1 · LF2 Cl.2 · LF3 Cl.1 · LF3 Cl.2 — NPS ½″ to 60″ — Class 150 to 2500 — Charpy CVN certified — Full MTR, heat treatment records
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LTCS Flanges — Export Packaging
Every LTCS flange dispatched by Tesco Steel & Engineering is individually protected — bore plugs, face caps, plastic wrapping — before being loaded into wooden export crates or polybag-lined cases. Charpy impact test certificates, MTRs, heat treatment records, and PMI reports are packed inside each crate.
LTCS blind flanges — various sizes, warehouse stock
LTCS weld neck flanges — plastic-wrapped, export crate
LTCS weld neck flanges — plastic-wrapped, bore detail
LTCS flanges — bulk plastic-wrapped stacks, pre-dispatch
LTCS flanges — polybag-lined wooden export crate
LTCS blind flanges — face-capped, wooden export crate
ASTM A350 LF2 — high-pressure RTJ line blank, LTCS
LTCS large diameter blind flange — raised face, export-ready
LTCS slip-on flanges — mixed sizes, lined export crate
ASTM A350 LF2 — 2″ #150 socket weld RF flange, LTCS
LTCS weld neck RF flange — Class 2500, high-pressure
LTCS weld neck flanges — plastic-wrapped, bulk export load
