Difference between A204 Grade B and A204 Grade C

A204 Grade B and A204 Grade C are molybdenum-alloy steel plates manufactured to ASTM A204/A204M standard, designed specifically for fusion-welded pressure vessels and boilers operating at elevated temperatures. These grades are characterized by the addition of molybdenum (Mo) , which significantly enhances creep resistance and high-temperature strength. They are widely used in the fabrication of heavy-wall pressure vessels, heat exchangers, and steam boilers in power generation and petrochemical industries where sustained service at high temperatures is required.

Key Differences:

The primary distinction is their strength level, which is directly tied to carbon content. A204 Grade B has a carbon content range of 0.20–0.26% and provides a minimum yield strength of 275 MPa (40 ksi) and tensile strength of 485–620 MPa (70–90 ksi). A204 Grade C contains a higher carbon range of 0.23–0.29%, resulting in increased minimum yield strength of 295 MPa (43 ksi) and tensile strength of 515–655 MPa (75–95 ksi).

This higher carbon content in Grade C directly leads to a higher carbon equivalent (Ceq) compared to Grade B. Consequently, A204 Grade C requires more stringent welding procedures, particularly regarding preheating and post-weld heat treatment (PWHT) , to prevent hydrogen-induced cracking in the heat-affected zone. Both grades mandate mandatory PWHT for most thicknesses per ASME Boiler and Pressure Vessel Code requirements.

Chemical Composition

Mechanical Property