A36 Preheat for FCAW — 1-1/2" to 2-1/2"
Per AWS D1.1:2025 Table 5.11, the minimum preheat for A36 welded with FCAW at 1-1/2" to 2-1/2" is 150°F (65°C), Category B. Preheat below this raises hydrogen-cracking risk in the heat-affected zone; the same temperature is the minimum interpass limit maintained through the weld.
Built on AWS D1.1:2025 Table 5.11 — every value traced to the clause.
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FCAW (Flux Cored Arc Welding)
FCAW uses tubular flux-cored wire, available gas-shielded (E71T-1) or self-shielded (E71T-8) for field work. Category B in Table 5.11.
E71T-1 gas-shielded wire is the workhorse for structural steel erection fillet welds. Self-shielded E71T-8 is preferred for field welding where wind makes gas shielding unreliable. Deposition rates run 8-12 lb/hr depending on wire diameter and position. The flux core provides a protective slag that supports the puddle in vertical-up and overhead positions.
FCAW Tips for Common Structural Steels
For A36 structural steel (36 ksi yield), FCAW with E71T-1M at 220–260 A and 0.045" wire is the dominant field erection process for column connections, shear tabs, and braced frame gusset welds. The flux slag supports the puddle in vertical-up and overhead positions on clip angle and seat connection fillet welds. Category A and B both apply to A36; FCAW.
Typical values for reference — always verify against your approved WPS and electrode manufacturer data.
Filler Metal for FCAW
Gas-shielded: E71T-1C (AWS A5.20, requires 100% CO2) or E71T-1M (requires 75/25 Ar/CO2 mixed gas) — the C/M suffix designates the required shielding gas. Self-shielded: E71T-8 (no external gas, field-ready). Diameter: 0.045" standard, 1/16" for high-deposition. Stick-out: 3/4" to 1-1/4" (longer than GMAW due to resistive heating of flux core).
Typical values for reference — always verify against your approved WPS and electrode manufacturer data.
A36
ASTM A36 is the most commonly specified structural steel in North America, with a minimum yield strength of 36 ksi and 58-80 ksi tensile range. It appears in both Category A (non-low-hydrogen SMAW) and Category B (low-hydrogen processes) of Table 5.11. A36 is available as plate (up to 8" thick), W-shapes, channels, angles, and bars from virtually every domestic mill. Its moderate carbon content (0.26% max for shapes, 0.25% max for plate up to 3/4") and typical carbon equivalent of 0.35-0.42 give it good weldability across all prequalified processes. A36 plate thicker than 1-1/2" carries a slightly higher carbon limit of 0.29%, while plate from 3/4" to 1-1/2" stays at 0.25% max.
Why This Preheat for A36 with FCAW
Widely used structural carbon steel with 36 ksi yield and 0.26% max carbon. With low-hydrogen FCAW, this combination falls under Category B rather than Category A — flux-cored wire in FCAW provides a combination of deoxidizers and low-moisture flux formulations that control hydrogen. The 150°F minimum preheat is lower than what non-low-hydrogen SMAW would require at the same thickness because FCAW significantly reduces the driving force for hydrogen-induced cracking in the heat-affected zone.
Typical Applications for A36
Common in angle-to-gusset fillet welds, beam web clip angles, stiffener plates, base plate bearing connections, light bracing members, stair stringers, handrail posts, and miscellaneous steel fabrication. A36 plate is the default choice for connection elements such as shear tabs, moment end plates under 36 ksi demand, and simple beam-to-column seated connections. In retrofit and renovation, A36 angles and channels are standard for reinforcement brackets and framing infill. Typical shop drawing callouts include 3/8" and 1/2" A36 plate for gussets, 5/16" fillet welds on clip angles, and partial joint penetration groove welds on base plate stiffeners. A36 is so ubiquitous that most structural steel shops maintain permanent inventory in multiple thicknesses from 1/4" through 2" plate. Fillet weld sizes on A36 connections typically range from 3/16" minimum to 5/8" for heavy gusset-to-column welds, with E70XX electrodes providing significant overmatching strength.
Why Preheat Matters at 1-1/2" to 2-1/2"
Heavy plate with significant restraint and thermal mass — preheat is critical to maintain slow cooling for hydrogen escape.
Other Steels with FCAW at 1-1/2" to 2-1/2"
| Steel | Category | Preheat |
|---|---|---|
| A53 Gr.B | B | 150°F (65°C) |
| A633 Gr.E | C | 225°F (110°C) |
| A709 HPS70W | C | 225°F (110°C) |
| A710 Gr.A | C | 225°F (110°C) |
A36 with FCAW
Try Different Combinations
Use the interactive preheat calculator to look up any steel, process, and thickness combination from D1.1:2025 Table 5.11.
A36 Welding Guides
Primary sources
D1.1:2025 reference data. Not affiliated with AWS.
Application context
A36 plate in the 1-1/2 to 2-1/2 inch range with FCAW is the heavy-section production combination — primary fillet runs on heavy A36 transfer-girder splices, transmission-tower base plates, walkway-bracket structural fabrication on heavy plate, and field-erection welds where the higher deposition rate of cored wire moves more steel per shift than SMAW or GMAW under outdoor conditions.
Pre-weld notes
Crossing the 1-1/2 inch threshold changes the preheat-extent rule per Clause 7.6 — for base metal 1-1/2 inch and greater, the heated zone shall extend at least equal to the base-metal thickness, but not less than 3 inches. Real preheat infrastructure is required: induction blankets, electric resistance pads, or oxy-fuel rosebud burners. Through-thickness preheat verification is the binding inspection effort. FCAW-specific concerns at heavy section: the increased pass count of multi-pass deposition makes inter-pass slag removal more critical, and the FCAW classification on the spool must match the WPS-cited variant per Table 6.6 essential variables.
What a CWI verifies
A CWI on A36 FCAW heavy-section work verifies (1) preheat through-thickness, not just surface — sampling 3-6 inches from the arc on the back side catches the through-thickness lag during heat-up, (2) the heated-zone extent against Clause 7.6 (at least equal to base-metal thickness, not less than 3 inches), (3) interpass temperature held above 150°F with a contact pyrometer between pass groups, (4) the FCAW classification on the spool against the WPS-cited variant, and (5) inter-pass slag removal across the joint sequence.