ASTM A106 (formally ASTM A106/A106M-22) is the ASTM standard for seamless carbon steel pipe for high-temperature service in refineries, power plants, and process industries. It specifies three grades — A, B, and C — where Grade A is low-tensile (minimum 330 MPa), Grade B is moderate (minimum 415 MPa), and Grade C is higher-temperature (minimum 450 MPa). All grades are seamless (no weld seam), IBR-approved in India under the Indian Boiler Regulations, and the default choice for boiler feedwater, superheater, and instrument piping above the IBR threshold. The difference between grades is primarily carbon content and tensile-strength minimums.
Grade A vs Grade B vs Grade C — how to pick
Grade A is the lowest strength tier — carbon max 0.25%, tensile min 330 MPa. Rarely specified today because Grade B offers better mechanicals at comparable cost.
Grade B is the workhorse — carbon max 0.30%, tensile min 415 MPa. Covers the majority of refinery and power-plant high-temp piping. ASTM A106 Grade B is the most common grade in Indian industrial procurement.
Grade C is the highest strength — carbon max 0.35%, tensile min 450 MPa. Used for higher design temperatures and pressures where Grade B is marginal. Note: Grade C may require preheat and post-weld heat treatment for welding.
Chemical composition (as per ASTM A106)
- Grade A: Carbon 0.25% max, Manganese 0.27–0.93%, Phosphorus 0.035% max, Sulphur 0.035% max
- Grade B: Carbon 0.30% max, Manganese 0.29–1.06%, Phosphorus 0.035% max, Sulphur 0.035% max
- Grade C: Carbon 0.35% max, Manganese 0.29–1.06%, Phosphorus 0.035% max, Sulphur 0.035% max
- Copper, Nickel, Chromium, Molybdenum, and Vanadium are restricted to 0.40% total maximum.
Mechanical properties (as per ASTM A106)
- Yield strength: Grade A = 205 MPa min, Grade B = 240 MPa min, Grade C = 275 MPa min
- Tensile strength: Grade A = 330 MPa min, Grade B = 415 MPa min, Grade C = 450 MPa min
- Elongation: 30% min in 50 mm (straight specimen), 20% min (strip specimen)
- All tubes undergo hydrotest at calculated pressure per ASTM A106 Section 5.
ASTM A106 vs ASME SA-106 — is there a difference?
SA-106 carries the ASME certification mark required for ASME-coded vessels; ASTM A106 does not. For IBR documentation, always specify SA-106 so Form III-C references the correct ASME code.
ASTM A106 is the material specification published by ASTM International. ASME SA-106 is the same specification cross-referenced in the ASME Boiler and Pressure Vessel Code. The chemistry and mechanical requirements are virtually identical — the only distinction is that SA-106 carries the ASME certification mark, required for ASME-coded vessels.
In Indian practice, ASTM A106 and ASME SA-106 are used interchangeably, but specify "SA-106" explicitly for IBR documentation so the Form III-C references the correct ASME code.