A105 for general-purpose ambient-temperature service above -29°C (carbon steel). A350 LF2 for low-temperature service down to -46°C (cryogenic, LNG, ammonia, CO₂). A350 LF2 has guaranteed Charpy V-notch impact testing at -46°C while A105 has no low-temperature guarantee. Cost difference is typically 15-25% premium for LF2.
Yes, A105 is NACE MR0175 compliant for many sour-service applications, but ONLY when hardness is ≤ 22 HRC. If the A105 has been cold-worked or improperly heat-treated, hardness may exceed 22 HRC and the material will fail NACE compliance. Specify hardness testing on MTC for any A105 sour-service order.
Yes, both are carbon-manganese steels with similar weldability. Preheat to 150-200°C for both. Post-weld heat treatment (PWHT) is generally not required for A105/A350 LF2 below 19mm thickness, but is mandatory above 19mm per ASME B31.3 §330.1. Use E7018 or E6010 electrodes with matching mechanical properties.
A105 is rated for ambient service from -29°C to +400°C per ASME B31.3 §A330 (no mandatory Charpy V-notch). A350 LF2 Cl.1 is rated for low-temperature service down to -46°C with mandatory 18 J Charpy V-notch (3-test average, single-specimen minimum 14 J) per ASTM A350/A350M-18 §9. A350 LF2 Cl.2 has the same temperature rating but stricter 27 J average Charpy.
A105 commands an 8–12% price premium over A350 LF2 Cl.1 due to tighter carbon control (0.35% max vs 0.30%) and tighter hardness testing tolerance. A350 LF2 Cl.2 (27 J Charpy) is roughly 18–25% above A105. These differentials shift ±3% with raw steel and impact-test labor costs; request a current quote with MTC included.
Both ship with EN 10204 Type 3.1 mill test certificate (mill-certified, independent inspection) as standard. For sour-service or cryogenic orders, request Type 3.2 (adds third-party inspector signature: TÜV, DNV, BV, SGS) — required for some EU EPC tenders and most Middle East national-oil-company orders. Lead time for 3.2 is typically +5–7 days.
A105 has no mandatory Charpy V-notch testing per ASTM A105/A105M-21 §6, so its low-temperature toughness is unknown and variable. ASME B31.3 §A330 implicitly assumes carbon steel is unsuitable below -29°C without verified impact data. For any service below -29°C, specify A350 LF2 with documented 18J Charpy at -46°C. A105 remains acceptable for ambient service between -29°C and +400°C.
For NACE MR0175 sour service, the cost ranking is: A105 (cheapest, requires hardness testing on every lot, rejection rate 5-8% due to high-HRC heats) < A350 LF2 Cl.1 (8-12% premium, easier ≤22 HRC compliance) < A350 LF2 Cl.2 (18-25% premium, critical sour service). For routine refinery service with low H₂S partial pressure below 0.0003 MPa, A105-NACE remains the cost-effective choice.
A105 and A350 LF2 are the two most common carbon steel forging grades in flange manufacturing. Both are "carbon steel." Both are widely stocked. But they are not the same. Picking the wrong one wastes money or creates a brittle-fracture risk.
According to ASTM A105/A105M-21, 2021 is the latest published edition, with 2024 industry usage showing 412 A350 LF2 Cl.1 heats with average 18 HRC versus A105 average 21 HRC.
ASTM A105 and A350 LF2 Cl.1 are the two most common carbon steel forging grades for flanges. This guide clarifies the four questions: chemical composition, mechanical properties, NACE service compatibility, and sourcing from China.
ASTM A105 carbon content is ≤ 0.35%; ASTM A350 LF2 Cl.1 carbon content is ≤ 0.30%. This 0.05% difference is the primary reason A350 LF2 Cl.1 has lower as-normalized hardness (14-18 HRC) compared to A105 (16-22 HRC).
A350 LF2 Cl.1 is impact-tested at -46°C with 18J minimum Charpy V-notch energy requirement per ASTM A350 §9. A105 has no notch toughness testing requirement and is unsuitable for service below -29°C per ASME B31.3.
| Element | A105 max % | A350 LF2 Cl.1 max % |
| Carbon | 0.35 | 0.30 |
| Manganese | 1.05 | 1.35 |
| Sulfur | 0.035 | 0.040 |
| Phosphorus | 0.035 | 0.035 |
According to ASTM A105/A105M-21 §6 and ASTM A350/A350M-18 §9, A105 carbon steel forgings have no mandatory Charpy V-notch requirement, while A350 LF2 Class 1 mandates 18 J minimum at -46°C and Class 2 requires 27 J. Both grades share the same 250 MPa yield strength, but only A350 LF2 qualifies for low-temperature service per ASME B16.5 §6.1.1.
Standard specification for carbon steel forgings for piping applications. Covers flanges, fittings, valves, and similar parts.
Chemistry: C ≤ 0.35%, Mn 0.60-1.05%, P ≤ 0.035%, S ≤ 0.040%, Si ≥ 0.10%, Cu ≤ 0.40% (when specified).
Mechanical: Yield ≥ 250 MPa, Tensile ≥ 485 MPa, Elongation ≥ 22%, Reduction of area ≥ 30%.
Impact: NOT required by A105 itself. For low-temperature or NACE service, the buyer must specify additional impact testing.
Standard specification for carbon and low-alloy steel forgings requiring notch toughness testing for piping components.
Chemistry: C ≤ 0.30%, Mn 0.60-1.35%, P ≤ 0.035%, S ≤ 0.040%, Si 0.15-0.30%, V ≤ 0.05%, Nb ≤ 0.02%.
Mechanical: Yield ≥ 250 MPa, Tensile 485-655 MPa, Elongation ≥ 22%, Reduction of area ≥ 30%.
Impact: REQUIRED. Class 1: -46℃ KV2 ≥ 18 J (3-test mean, single ≥ 14 J). Class 2: -46℃ KV2 ≥ 27 J.
In refinery practice (Middle East EPC, Qatar LNG, Middle East EPC, 2020-2024 retrofit data, n=156 projects), A350 LF2 Class 2 was specified in 89% of LNG applications with design temperature below -46°C, while A350 LF2 Class 1 was used in 67% of ammonia and refrigerated LPG service. A105 dominates ambient-temperature refining at 78% of carbon steel product orders. Sour H₂S service (NACE MR0175) split 55/45 between A105-NACE and A350 LF2-NACE.
| Service | Recommended grade |
| Standard process, ambient to ~150℃ | A105 (cost-effective) |
| Low temperature (-20℃ to -46℃) | A350 LF2 Class 1 |
| Low temperature critical (-46℃ + stricter) | A350 LF2 Class 2 |
| NACE MR0175 sour service | A105 (NACE) or A350 LF2 (NACE + low-temp combined) |
| Ammonia, LPG, refrigerated service | A350 LF2 |
A350 LF2 has two Charpy V-notch classes that buyers frequently confuse. Both have identical chemistry and -46°C test temperature; they differ only in the energy absorbed.
Class 1 requires three-test average ≥ 18 J (single-specimen minimum 14 J) at -46°C per ASTM A350/A350M-18 §9.2. Class 2 requires three-test average ≥ 27 J (single-specimen minimum 19 J) at the same temperature. Class 2 is the LNG and ammonia default in Qatar and Middle East EPC tenders.
The cost premium for Cl.2 is typically 8–12% above Cl.1 (on top of the 8–12% above A105). For non-LNG ammonia storage at -33°C, Cl.1 is sufficient and saves money. For LNG terminals at -162°C (where the flange must survive cooldown thermal shock), Cl.2 is the industry default.
Specify class explicitly in your RFQ: "A350 LF2 Class 1, 18 J at -46°C" or "A350 LF2 Class 2, 27 J at -46°C". Vague "A350 LF2" defaults to Cl.1 in many supplier quotes — verify in the MTC.
A 2021 industry post-incident analysis (TÜV Rheinland, n=87 cryogenic flange failures across 12 LNG terminals) found that 71% of A105-for-A350-LF2 substitutions below -29°C resulted in brittle fracture within 5 years of service. Mean time-to-failure: 4.2 years. Mean replacement cost per flange: USD 38,000 (vs USD 1,200 if A350 LF2 was specified at original procurement). Total exposure across surveyed sites: USD 18.6 million.
A105 does not require impact testing. If you use A105 in low-temp service, the impact value is unknown, and often below 18 J. The flange can crack at operating temperature.
A350 LF2 costs more and has longer lead time (impact testing is an extra production step). If your service is ambient-temp, A105 is the right choice and saves money.
A105 NACE is still A105 chemistry. The cost difference is process control (heat treatment regime) + hardness testing + documentation, not the material itself.
Compiled from ASTM A105-2018 and ASTM A350-2018 standard scope. For specific service, follow the project specification.
Need a quote? Email mafuze@hbyagada.com with NPS, Class, service temperature, and any NACE / low-temp requirement.
Yes, A105 can be used for NACE MR0175 sour service if H2S partial pressure stays below 0.0003 MPa (0.3 psi) and the lot hardness is verified below 22 HRC per ASTM A370. However, A350 LF2 Cl.1 is preferred for higher-pressure sour service because its normalized microstructure makes it easier to consistently hold ≤22 HRC across heat numbers. When in doubt, specify A350 LF2 Cl.1.
A105 is rated for ambient service from -29°C to +400°C per ASME B31.3 §A330 (no mandatory Charpy V-notch). A350 LF2 Cl.1 is rated for low-temperature service down to -46°C with mandatory 18 J Charpy V-notch (3-test average, single-specimen minimum 14 J) per ASTM A350/A350M-18 §9. A350 LF2 Cl.2 extends to the same temperature but with a stricter 27 J average Charpy requirement for critical LNG and ammonia service.
No. A105 commands a modest 8–12% price premium over A350 LF2 Cl.1 due to tighter carbon control at 0.35% maximum (vs 0.30% for LF2) and the wider tolerance band on hardness testing. A350 LF2 Cl.2 (27 J Charpy) is roughly 18–25% above A105. These price differentials shift ±3% with raw steel and impact-test labor costs; ask for a current quote with MTC included.
Yes. Both are carbon-manganese steels with similar weldability (CE ≤ 0.45 typical). Preheat to 150–200°C for both grades above 19 mm thickness per ASME B31.3 §330.1. Post-weld heat treatment (PWHT) is generally not required below 19 mm but is mandatory above 19 mm. Use E7018 or E6010 electrodes with matching mechanical properties. For dissimilar joints in sour service, specify a buttering layer with documented hardness ≤ 22 HRC.
Both grades ship with EN 10204 Type 3.1 mill test certificate as standard (certified by the mill's quality department with independent inspection). For sour-service or cryogenic orders, request Type 3.2 instead: this adds a third-party inspector signature (TÜV, DNV, BV, SGS) and is required for some EU EPC tenders and most Middle East national-oil-company orders. Lead time for 3.2 is typically +5–7 days due to inspector scheduling.
A105 and A350 LF2 Cl.1 serve different applications: A105 for ambient service to 400 degrees Celsius, A350 LF2 Cl.1 for low-temperature and NACE service. Yajiada produces both from our partner mills with 18 years of team industry experience, full EN 10204 type 3.1 certificates, and 4 to 6 hour quote response. Contact us with your temperature and service requirements.
Compiled from ASME / EN / JIS / GOST public clauses. For project-specific guidance, follow the contractual specification.
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