What is the main difference between ASTM A500 Grade B and Grade C structural hollow sections?

Question

Accepted Answer

A: The main difference between ASTM A500 Grade B and Grade C structural tubing is their specified minimum mechanical strength. Grade C has higher minimum yield and tensile strength, while Grade B has a higher specified minimum elongation. Both grades are used for cold-formed welded or seamless carbon steel structural tubing, including round, square and rectangular hollow sections.

Property	ASTM A500 Grade B	ASTM A500 Grade C
Minimum yield strength, square/rectangular/special shapes	46 ksi (317 MPa)	50 ksi (345 MPa)
Minimum yield strength, round tubing	42 ksi (290 MPa)	46 ksi (317 MPa)
Minimum tensile strength	58 ksi (400 MPa)	62 ksi (427 MPa)
Minimum elongation in 2 in. / 50 mm	23%	21%
Maximum carbon content	0.26%	0.23%

Grade B may be considered where the project prioritizes general structural service and where a higher specified elongation is useful for secondary fabrication. However, bending, flattening, flaring and end-forming performance should be evaluated based on the actual wall thickness, section geometry, weld location, chemical composition and fabrication procedure—not on grade designation alone.

Grade C is commonly selected where the design requires higher specified material strength. For square, rectangular and other shaped HSS, its minimum yield strength is 50 ksi rather than 46 ksi for Grade B. This can support a more efficient section selection when strength governs the design, but it does not automatically reduce steel weight or increase finished-member capacity because buckling, deflection, connection design and section geometry may control.

Grade B and Grade C are grades under ASTM A500/A500M. They should not be treated as direct equivalents to EN 10219 grades or ASTM A1085 tubing. Confirm the applicable ASTM A500 edition, structural design code, project specification, dimensional requirements and MTC requirements before purchase or substitution.