When it comes to carbon steel forged fittings, ASTM A105 and ASTM A350 LF2 are two of the most widely used material standards. Both are essential in high-pressure piping systems but serve slightly different purposes due to their mechanical and chemical characteristics. Understanding the differences between A105 and A350 LF2 is critical for engineers, procurement teams, and fabricators who demand precision, durability, and safety in their piping systems.
This blog provides a detailed technical comparison of A105 vs A350 LF2 carbon steel forged fittings, covering everything from chemical composition and mechanical properties to temperature ratings and applications.
Overview of ASTM A105 Carbon Steel Forged Fittings
ASTM A105 is a specification that covers forged carbon steel piping components suitable for ambient and high-temperature service in pressure systems. These fittings are primarily used in industries such as oil & gas, petrochemical, power generation, and marine.
- Common Forms: Elbows, tees, couplings, unions, plugs, and caps
- Pressure Classes: 2000, 3000, 6000, and 9000 lbs
- Connection Types: Socket weld and threaded
Overview of ASTM A350 LF2 Carbon Steel Forged Fittings
ASTM A350 LF2 refers to low-temperature carbon steel forged components. The “LF” stands for “low temperature forgings,” and this grade is specifically designed to maintain impact toughness at sub-zero temperatures. These fittings are widely used in cryogenic and low-temperature services in industries like LNG, refrigeration, and offshore drilling.
- Common Forms: Flanges, valves, and fittings for low-temperature pipelines
- Pressure Classes: Similar to A105—up to 9000 lbs
- Connection Types: Socket weld and threaded
Key Chemical Composition Differences
| Element | A105 (%) | A350 LF2 (%) |
|---|---|---|
| Carbon | 0.35 max | 0.30 max |
| Manganese | 0.60–1.05 | 0.60–1.35 |
| Phosphorus | 0.035 max | 0.035 max |
| Sulphur | 0.040 max | 0.040 max |
| Silicon | 0.10–0.35 | 0.15–0.30 |
- Observation: A350 LF2 has a slightly lower carbon content, allowing for better impact resistance at low temperatures. It also has higher manganese content to support strength and ductility at cryogenic service conditions.
Mechanical Properties Comparison
| Property | A105 | A350 LF2 |
|---|---|---|
| Tensile Strength (MPa) | ≥485 | ≥485 |
| Yield Strength (MPa) | ≥250 | ≥250 |
| Elongation (%) | ≥22 | ≥22 |
| Impact Test | Not mandatory | Mandatory at -46°C |
- Observation: Both grades show comparable tensile and yield strength. However, the Charpy V-Notch impact test is mandatory for A350 LF2, ensuring it performs reliably in sub-zero temperatures.
Temperature Rating and Toughness
- A105: Suitable for ambient and high-temperature services, typically from -20°C to 593°C.
- A350 LF2: Suitable for low-temperature services down to -46°C, often required in LNG terminals, cryogenic plants, and cold climate oil fields.
Why this matters: The temperature range determines the ductility and performance of the fitting under extreme conditions. Using A105 in a low-temperature environment may result in brittle failure, while A350 LF2 ensures impact resistance even at sub-zero conditions.
Heat Treatment
- A105: Generally supplied in a normalized or normalized and tempered condition.
- A350 LF2: Always supplied in a normalized, normalized and tempered, or quenched and tempered condition to meet the low-temperature toughness requirement.
Marking and Traceability
- A105 fittings are marked with the manufacturer’s identification, material grade, heat number, and pressure class.
- A350 LF2 fittings include additional markings for impact test compliance and low-temperature service designation.
This traceability is crucial in critical applications where materials must meet strict safety codes and standards such as ASME B16.11 or ANSI B16.5.
Applications
ASTM A105
- Oil refineries
- Power plants
- Petrochemical pipelines
- Steam and gas systems
ASTM A350 LF2
- Cryogenic LNG facilities
- Cold-weather oil extraction
- Refrigeration systems
- Offshore drilling and arctic environments
Pricing and Availability
- A105 fittings are more readily available and generally cost-effective due to wider industrial use.
- A350 LF2 fittings are slightly more expensive due to the additional testing, certification, and heat treatment required.
However, the cost difference is justified in applications where failure at low temperature could lead to catastrophic consequences.
Standards and Compliance
| Standard | A105 | A350 LF2 |
|---|---|---|
| ASME B16.11 | Yes | Yes |
| ASTM A105 | Yes | No |
| ASTM A350 | No | Yes |
| NACE MR0175 | On request | On request |
Ensure that material test certificates (MTCs) are obtained for both grades for regulatory and QA purposes, especially in critical environments.
Conclusion
While ASTM A105 and ASTM A350 LF2 carbon steel forged fittings may appear similar at a glance, they are engineered for different performance conditions. A105 is ideal for general-purpose, ambient-to-high temperature applications, whereas A350 LF2 is tailored for low-temperature, impact-critical environments.
Choosing the wrong material could result in material failure, system leaks, or safety hazards. Therefore, it is vital to consult with industry experts or refer to ASME and ASTM standards before finalising material grades for forged fittings.
For projects requiring certified and tested carbon steel forged fittings—whether A105 or A350 LF2 Surya Fittings offers an extensive range with full compliance to global standards. Reach out to our team for technical datasheets, MTCs, or large-scale procurement.