ASTM A500 Grade B and Grade C are the two most common specifications for cold-formed structural tubing in building frames. This guide compares the two grades on strength, weldability and cost, with selection guidance for columns, beams, trusses and other structural members.
ASTM A500 covers cold-formed welded and seamless carbon steel structural tubing in round, square and rectangular shapes. Grade B and Grade C are both widely specified, with Grade C being the higher-strength option for designs where reduced wall thickness or longer spans matter. Picking between the two affects both the section sizing and the cost per tonne, so the call should be made from the actual structural requirement rather than habit.
Grade B vs Grade C: Strength Numbers
A500 Grade B has minimum yield strength of 46,000 psi (315 MPa) and minimum tensile of 58,000 psi (400 MPa) for walls up to 1/2 inch, and slightly lower for thicker walls. A500 Grade C has minimum yield strength of 50,000 psi (345 MPa) and minimum tensile of 62,000 psi (425 MPa). The roughly 9% yield strength advantage of Grade C allows a designer to reduce wall thickness slightly for the same design load, which reduces weight and often saves cost even though the per-tonne price of Grade C is slightly higher.
When Grade B Is the Right Call
A500 Grade B is the right specification for most routine building framing: residential and light commercial columns, beams, girts, purlins, and bracing. It is also the standard for many fence post and sign post applications. Grade B has a long history of successful use, is widely available from every domestic and offshore mill, and is the most economical option for projects where the design is governed by serviceability rather than strength.
When Grade C Is the Right Upgrade
A500 Grade C is the right specification for long-span trusses, columns in multi-story buildings, and any structural member where the higher yield strength allows a thinner wall or smaller section. It is also the conservative choice for dynamic or cyclic loading, and for cold-climate projects where Charpy impact at low temperature matters. For projects designed to AISC 360 and using Load and Resistance Factor Design (LRFD), Grade C often comes out as the cost-optimal choice because the higher strength reduces tonnage more than the per-tonne price increase.
Welding, Galvanizing and Connection Detail
Both Grade B and Grade C are weldable using standard SMAW, GMAW and FCAW procedures with E70 or E71 electrodes. The cold-formed process gives the corners higher hardness than the flat sides, which can affect the bend radius during fabrication. For hot-dip galvanizing, both grades are suitable, but the customer should be aware that the cold-formed corners may show slightly different appearance after galvanizing due to the localized strain hardening. For exposed architectural applications, consider A1085 (the newer HSS standard with tighter tolerances and a single strength grade).
What to Specify on the Structural Tubing RFQ
State the standard (ASTM A500 Grade B or C), the shape (round, square, rectangular), the outside dimensions and wall thickness, the length (typically 20, 24, 32 or 40 ft), and any supplementary requirements (Charpy at low temperature, hot-dip galvanizing per ASTM A123, painted finish). For long-span and multi-story structures, default to Grade C; for routine framing, Grade B is acceptable. Confirm the mill supplies test reports per EN 10204 3.1 showing the actual yield and tensile strength.
Related Resources from Baobin Steel
- Carbon steel pipe and tube catalog – A500 and A53 structural tube
- Mild steel overview – grades and standards
- Request a quote – send your framing spec for structural tube pricing