What Is ASTM A105? Forged Carbon Steel
ASTM A105 is the default specification for forged carbon steel piping components: flanges, forged fittings, valve bodies, and other pressure-containing parts used in ambient to high-temperature service. It is the forged counterpart of ASTM A216 WCB cast steel.
| Property | Value |
|---|---|
| Specification | ASTM A105 / ASME SA-105 |
| Material type | Forged carbon steel |
| Carbon | 0.35% max |
| Manganese | 0.60-1.05% |
| Silicon | 0.10-0.35% |
| Sulfur | 0.040% max |
| Phosphorus | 0.035% max |
| Chromium | 0.30% max |
| Molybdenum | 0.12% max |
| Nickel | 0.40% max |
| Tensile strength (min) | 485 MPa (70 ksi) |
| Yield strength (min) | 250 MPa (36 ksi) |
| Elongation (min) | 22% |
| Reduction of area (min) | 30% |
| Hardness | 187 HBW max (per NACE: 187 HBW / 22 HRC) |
| Service temp range | -29°C to 425°C (-20°F to 800°F) |
How ASTM A105 Forgings Are Made
A105 forgings start as killed steel billets or ingots. The forging process applies compressive force to the heated steel (typically 1100-1250°C), shaping it into flanges, elbows, tees, couplings, or valve bodies. The mechanical working refines the grain structure, producing a denser, more homogeneous product than castings.
Heat treatment is not mandatory for A105 forgings under NPS 4, but most project specifications require normalizing (heating to 900°C and air cooling) or normalizing and tempering for all sizes. Forgings over NPS 4 must be heat-treated per the standard.
Primary Applications
A105 is specified for virtually every forged carbon steel component in standard piping systems:
- Flanges: weld neck, slip-on, blind, threaded, socket weld per ASME B16.5 and B16.47
- Forged fittings: elbows, tees, couplings, unions per ASME B16.11
- Small-bore valve bodies: gate, globe, and check valves per API 602 and BS 5352
- Branch connections: weldolets, sockolets, threadolets
Temperature and Service Limits
A105 covers service from -29°C to 425°C. Below -29°C, impact toughness is insufficient; switch to ASTM A350 LF2 (impact tested at -46°C). Above 425°C, carbon steel loses creep strength; switch to ASTM A182 F11 or F22 chrome-moly grades.
For sour service containing H2S, A105 must comply with NACE MR0175/ISO 15156. Maximum hardness is 22 HRC (187 HBW). Normalizing or normalizing and tempering is typically required to meet NACE hardness limits; quench-and-temper is also acceptable.
Testing and Certification
ASTM A105 requires chemical analysis and tensile testing. Mill test certificates per EN 10204 3.1 document the heat chemistry, mechanical properties, and heat treatment condition. Supplementary requirements include impact testing (S5), additional NDT (magnetic particle, ultrasonic), and hydrostatic testing when specified by the purchaser or the applicable valve/flange standard.
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