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ASTM A350 LF2 Low Temperature Flanges

LF2 Class 1 and Class 2 forged flanges, impact tested, from stock in Mumbai, India.

A350 LF2 Class 1 Flanges, Impact Tested at −46 °C

ASTM A350 LF2 low temperature carbon steel flanges

Dinesh Tube India supplies ASTM A350 LF2 flanges from Mumbai to LPG, ammonia, gas processing and refinery projects in India and abroad. LF2 is the standard low temperature carbon steel (LTCS) flange grade. Our LF2 Class 1 flanges are normalised and Charpy impact tested at −46 °C, and supplied with an EN 10204 3.1 certificate showing the impact results.

We supply weld neck, slip-on, blind, socket weld, threaded and RTJ flanges from 1/2" to 48", Class 150 to 2500, in LF2 Class 1, Class 2 and dual-certified A105 / LF2.

This page covers LF2 in detail. To compare LF2 with LF1, LF3, LF6 and other grades, see our ASTM A350 flanges page.

Table of Contents


What Is A350 LF2?

LF2 is a carbon–manganese steel grade in ASTM A350, the specification for forgings that need notch toughness testing. "LF" stands for low-temperature forging. LF2 has almost the same chemistry and strength as ASTM A105, but it must be heat treated (normalised, normalised and tempered, or quenched and tempered) and pass a Charpy V-notch impact test, so it stays tough in cold service.

LF2 is a carbon steel, chosen for low-temperature toughness, not for corrosion resistance. In ASME B16.5 it is in Material Group 1.1, the same group as A105, so the flange dimensions and pressure ratings are identical. ASME adopts it as SA350 LF2.

A350 LF2 Flange Specification

Material

ASTM A350 / ASME SA350 Gr LF2 Class 1 & 2

Dual Certification

A105 / A350 LF2 on request

Size

1/2" – 24" (B16.5); 26" – 48" (B16.47 Series A / B)

Pressure Class

Class 150, 300, 600, 900, 1500, 2500; PN 6 – PN 64

Dimensions

ASME B16.5, B16.47, B16.48, EN 1092-1, BS 4504

Types

WN, SO, blind, SW, threaded, lap joint, long weld neck, spectacle blind

Face

Raised face (RF), flat face (FF), ring type joint (RTJ)

Heat Treatment

Normalised; normalised and tempered or Q&T where required

Testing

Charpy impact, tensile, hardness; UT, MPI, PMI on request

Certification

EN 10204 3.1 with impact results; 3.2 / TPI; NACE MR0175 on request
A350 LF2 flange specification

A350 LF2 Class 1 vs Class 2

LF2 Class 1LF2 Class 2
Impact test temperature−46 °C (−50 °F)−18 °C (0 °F)
Charpy energy, average of 3, min20 J (15 ft·lbf)27 J (20 ft·lbf)
Charpy energy, single specimen, min16 J (12 ft·lbf)20 J (15 ft·lbf)
Chemistry and strengthSameSame
Typical useLTCS piping down to −46 °CModerately cold service needing higher toughness

Full-size specimens. The purchaser may specify a lower test temperature. Class 1 is the usual choice for LTCS piping; always state the class on the order.

A350 LF2 Chemical Composition

ElementLimit, %
Carbon (C)0.30 max
Manganese (Mn)0.60 – 1.35
Phosphorus (P)0.035 max
Sulphur (S)0.040 max
Silicon (Si)0.15 – 0.30
Nickel (Ni)0.40 max
Chromium (Cr)0.30 max
Molybdenum (Mo)0.12 max
Copper (Cu)0.40 max
Niobium (Nb)0.02 max
Vanadium (V)0.08 max

Cu + Ni + Cr + Mo + V is limited to 1.00% and Cr + Mo to 0.32%. Check the current edition of A350 for complete limits and any carbon equivalent requirement.

A350 LF2 Mechanical Properties

PropertyRequirement
Tensile strength485 – 655 MPa (70 – 95 ksi)
Yield strength, min250 MPa (36 ksi)
Elongation in 2 in. (50 mm), min22%
Reduction of area, min30%
Hardness, max197 HBW

A350 LF2 vs ASTM A105 Flanges

A350 LF2 Class 1ASTM A105
ServiceLow temperature, down to −46 °CAmbient and high temperature
Heat treatmentAlways requiredRequired only in some cases
Impact testCharpy at −46 °C, mandatoryNot required
Carbon, max0.30%0.35%
Tensile / yield, min485 / 250 MPa485 / 250 MPa
Hardness, max197 HBW187 HBW
B16.5 material group1.11.1

Because the two overlap, flanges are often dual certified A105 / A350 LF2: the forging meets the chemistry and hardness limits of both and is impact tested, so one stock item can serve both ambient and cold lines.

LF2 Flange Pressure Ratings (ASME B16.5)

Class15030060090015002500
Max working pressure, −29 to 38 °C (bar)19.651.1102.1153.2255.3425.5

Material Group 1.1. Below −29 °C, the −29 to 38 °C rating applies down to the impact-tested temperature of the flange, per the design code.

Matching LTCS Materials for LF2 Flanges

ComponentUsual LTCS Grade
Seamless pipeASTM A333 Grade 6
Butt-weld fittingsASTM A420 WPL6
Flanges and forged fittingsASTM A350 LF2 Class 1
Stud bolts / nutsASTM A320 L7 / A194 Gr 7 (impact tested)
Heat exchanger tubesASTM A334 Gr 1 / Gr 6

See our LTCS pipe guide for an overview of low-temperature piping materials.

Need A350 LF2 flanges? Send your class (1 or 2), flange type, size, pressure class, face, bore schedule and any NACE requirement to kamlesh@dineshtube-india.com or call +91 83559 10913. You can also send an enquiry.

Types of A350 LF2 Flanges

A350 LF2 weld neck flange

LF2 Weld Neck Flange

Butt welded to A333 Gr 6 pipe; preferred for cold, high-pressure lines.
A350 LF2 slip-on flange

LF2 Slip-On Flange

Fillet welded; for lower-pressure LTCS lines where the code allows.
A350 LF2 blind flange

LF2 Blind Flange

Closes line ends and nozzles in low-temperature service.
A350 LF2 socket weld flange

LF2 Socket Weld Flange

For small-bore LTCS lines, usually 2" and below.
A350 LF2 threaded flange

LF2 Threaded Flange

NPT threaded, for small non-critical lines without welding.
A350 LF2 RTJ flange

LF2 RTJ Flange

Ring joint face for high-pressure gas and LPG service.

A350 LF2 Flange Applications

  •   LPG, propane and butane storage and loading
  •   Ammonia and urea plants
  •   Gas processing and compressor stations
  •   Pressure let-down and flare lines (auto-refrigeration)
  •   Refrigeration and cold-storage plants
  •   Sour service lines with NACE MR0175 (22 HRC max)
Industries using A350 LF2 flanges

Packing: wooden cases or pallets with face protectors. See all carbon steel flanges.

A350 LF2 Flanges: FAQs

What is A350 LF2 flange material?

A350 LF2 is a forged carbon-manganese steel grade under ASTM A350, made for low-temperature service. It is heat treated and Charpy impact tested, at −46 °C for Class 1. It has a tensile strength of 485–655 MPa, minimum yield of 250 MPa and maximum hardness of 197 HBW.

What is the difference between LF2 Class 1 and Class 2?

The chemistry and strength are the same. Class 1 is impact tested at −46 °C (−50 °F) with a 20 J average minimum; Class 2 is tested at −18 °C (0 °F) with a higher 27 J average minimum. Class 1 is the usual choice for low-temperature carbon steel piping.

What is the difference between A105 and A350 LF2?

Both are forged carbon steel with the same minimum strength and the same ASME B16.5 pressure ratings. LF2 must be heat treated and impact tested at low temperature, so it can be used down to −46 °C; A105 is not impact tested and is for ambient and high-temperature service. Flanges can be dual certified to both.

What is the minimum temperature for A350 LF2 flanges?

LF2 Class 1 is impact tested at −46 °C (−50 °F), so it is normally used for design temperatures down to −46 °C. For colder service, A350 LF3 (to −101 °C) or stainless steel flanges are used.

What pipe and fittings are used with LF2 flanges?

LF2 flanges are used with ASTM A333 Grade 6 seamless pipe and ASTM A420 WPL6 butt-weld fittings, with A320 L7 stud bolts, to make a complete low-temperature carbon steel piping system.

Can A350 LF2 flanges be used for sour service?

Yes, when ordered to NACE MR0175 / ISO 15156, which limits hardness to 22 HRC maximum and may add other requirements. State the NACE requirement on the order so it is covered by testing and the certificate.

Export Destinations for LF2 Flanges

We export A350 LF2 flanges to the Middle East (UAE, Saudi Arabia, Qatar, Kuwait, Oman, Bahrain, Iraq), Africa (Nigeria, Egypt, South Africa, Kenya, Ghana, Tanzania), Asia (Bangladesh, Sri Lanka, Nepal, Indonesia, Malaysia, Thailand, Vietnam, Philippines), Europe and the Americas on request.