Difference between A204 Grade B and A285 Grade B

ASTM A204 Grade B and ASTM A285 Grade B are both specifications for steel plates used in the fabrication of welded pressure vessels and boilers. However, they are fundamentally different types of steel designed for distinct service conditions. A204 Grade B is a molybdenum-alloy steel intended for higher-temperature applications, while A285 Grade B is a carbon steel for general, moderate-strength service.

ASTM A204 Grade B is a molybdenum-alloy steel plate designed for welded boilers and pressure vessels operating at elevated temperatures . It is the intermediate strength grade within the A204 specification, with a tensile strength range of 70-90 ksi (485-620 MPa) . The addition of molybdenum as the primary alloying element provides enhanced strength and creep resistance at elevated temperatures. The steel must be manufactured using killed steel practices . Plates under this specification can be furnished up to 6 inches (150 mm) in thickness, limited only by the capacity of the composition to meet mechanical property requirements.

ASTM A285 Grade B is a carbon steel plate of low- and intermediate-tensile strength for fusion-welded pressure vessels . It has a tensile strength range of 50-70 ksi (345-485 MPa) and a minimum yield strength of 27 ksi (190 MPa) . This grade may be produced using various steel practices including killed, semi-killed, capped, or rimmed steel at the producer's option . It is limited to a maximum thickness of 2 inches (50 mm) for reasons of internal soundness . This material is commonly used in storage tanks, heat exchangers, and other low-pressure, temperature-controlled vessels where its good weldability is advantageous.

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