ASTM A106 — Seamless Carbon Steel Pipe for High-Temperature Service

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.