A105 vs A350 LF2

ASTM A105 and ASTM A350 LF2 are both carbon steel forging specifications for flanges, fittings, and valve components. The critical difference is low-temperature performance. A350 LF2 is impact-tested at -46degC (-50degF) and guaranteed to resist brittle fracture at cryogenic temperatures. A105 is limited to -29degC (-20degF) minimum design temperature without supplementary impact testing.

Property Comparison

Property	ASTM A105	ASTM A350 LF2
Min. design temperature	-29degC (-20degF)	-46degC (-50degF)
Impact test required?	No (unless supplementary)	Yes—mandatory
Impact test temperature	N/A (or per S5 supplement)	-46degC (-50degF)
Impact energy (min.)	N/A	20 J (15 ft-lb) per Charpy V-notch
Yield strength (min.)	250 MPa (36 ksi)	250 MPa (36 ksi)
Tensile strength (min.)	485 MPa (70 ksi)	485-655 MPa (70-95 ksi)
Carbon (max.)	0.35%	0.30%
Heat treatment	Normalized	Normalized and tempered (mandatory)
ASME B16.5 group	1.1	1.2
Cost	Baseline	15-30% premium

When to Use Each

Application	Recommended Material
Ambient temperature process piping (0 to 425degC)	A105
Cold climate outdoor piping (above -29degC)	A105
Cryogenic or low-temp service (-29 to -46degC)	A350 LF2
LNG regasification piping	A350 LF2 (or LF3 for lower temps)
Cold climate outdoor piping (below -29degC)	A350 LF2
Autorefrigeration risk (depressurization)	A350 LF2
General utility piping	A105

Common Mistake

Specifying A105 for piping systems that may experience autorefrigeration. When high-pressure gas is rapidly depressurized (e.g., blowdown, emergency depressuring), Joule-Thomson cooling can drop metal temperatures well below -29degC. These systems require A350 LF2 or LF3, even if the normal operating temperature is ambient.

Key Metallurgical Differences

A350 LF2 has a lower maximum carbon content (0.30% vs. 0.35%) and mandatory normalize-and-temper heat treatment. The lower carbon and controlled heat treatment produce a finer grain structure that resists brittle fracture at low temperatures. The mandatory Charpy V-notch impact test at -46degC verifies this toughness.

A105 may be normalized, normalized and tempered, or quenched and tempered—but impact testing is not required unless supplementary requirement S5 is invoked.

Pro Tip

Some suppliers offer dual-certified A105/A350 LF2 flanges. These forgings meet both specifications simultaneously, including impact testing. Dual-certified stock simplifies procurement for projects that mix ambient and low-temperature service, but verify that the mill test certificate shows actual impact test results at -46degC.

Pressure-Temperature Ratings

Both materials share similar pressure-temperature ratings per ASME B16.5, but they fall into different material groups:

Class	A105 (Grp 1.1) @ 100degF	A350 LF2 (Grp 1.2) @ 100degF
150	285 psig	290 psig
300	740 psig	750 psig
600	1480 psig	1500 psig

The difference in rated pressure is minimal. The real reason to choose A350 LF2 is low-temperature toughness, not higher pressure capacity.

Read the full guide to flanges