A500 Gr.B/C Preheat for SMAW (low-hydrogen) — up to 3/4"

SMAW (Low-Hydrogen)

Low-hydrogen SMAW (E7018/E7016) uses basic-coated electrodes requiring rod oven storage, assigned to Category B in Table 5.11.

E7018 is the default electrode for structural fillet and groove welds on common building steels. Rod ovens should hold at a minimum of 250°F per D1.1 Clause 7.3.2.1; exposure time out of the oven is limited to 4 hours maximum per Table 7.1. For overhead position, use 3/32" diameter rods to control puddle size. Vertical-up stringer beads provide the best fusion on thicker members.

A500 Gr.B/C

ASTM A500 Grade B (46 ksi yield for round, 42 ksi for rectangular) and Grade C (50 ksi round, 46 ksi rectangular) cover cold-formed welded and seamless structural tubing — round, square, and rectangular HSS sections. These are the standard tubular members in building frames, trusses, and signage structures, produced in wall thicknesses from 16 gauge (0.065") up to 5/8" for rectangular and 1/2" for round. Table 5.11 assigns both Category A and B preheat requirements. The cold-forming process work-hardens the corners, producing corner radii with higher hardness (up to 20% increase) and reduced ductility compared to the flat faces. This affects welding behavior at corner locations, particularly on heavily loaded connection details where weld starts or stops near corner radii can create initiation points for fatigue cracks.

Why This Preheat for A500 Gr.B/C with SMAW-LH

Cold-formed structural tubing for HSS sections in frames and trusses. With low-hydrogen SMAW-LH, this combination falls under Category B rather than Category A, reflecting the lower hydrogen potential of the consumable. The 32°F minimum preheat is lower than what non-low-hydrogen SMAW would require at the same thickness. Low-hydrogen electrodes and inherently low-hydrogen wire processes reduce the driving force for hydrogen-induced cracking in the heat-affected zone.

Typical Applications for A500 Gr.B/C

Standard for HSS columns in office buildings, hollow section trusses in warehouse roofs, exposed architectural tube steel, sign structures, solar panel racking frames, greenhouse frames, and guard rail posts. A500 tube-to-tube moment connections require through-plate or diaphragm detailing to transfer forces across the closed section. Slotted gusset connections into HSS bracing members are a signature fabrication detail requiring careful fit-up and beveling of the gusset plate. Common sizes include HSS 6x6x3/8 and HSS 8x8x1/2 for columns, HSS 4x4x1/4 for bracing, and HSS 10x6x3/8 for rectangular beam applications. The cold-formed corner radius creates a heat-affected zone consideration that differs from hot-rolled shapes when planning multi-pass weld sequences. Round HSS pipe columns are also common, typically HSS 6.625x0.280 through HSS 12.750x0.500 for mezzanine posts and canopy supports. Fillet welds connecting HSS to cap plates and base plates are the most frequent weld joint detail.

Why Preheat Matters at up to 3/4"

Thin material sheds heat quickly, allowing hydrogen to escape the HAZ readily — lowest preheat tier in Table 5.11.

Other Steels with SMAW (low-hydrogen) at up to 3/4"

A500 Gr.B/C with SMAW (low-hydrogen)

Try Different Combinations

Use the interactive preheat calculator to look up any steel, process, and thickness combination from D1.1:2025 Table 5.11.

A500 Gr.B/C Welding Guides